ABSTRACT
High-capacity LiNi1-x-yCoxMnyO2 (NCM) (x + y ≤ 0.2) is a potential candidate for realizing high-energy-density lithium-ion batteries (LIBs). However, successful application of this cathode requires overcoming the irreversible phase transition (layered-to-spinel/rock-salt), interfacial instability caused by residual lithium compounds, and the electrolyte oxidation promoted by highly oxidized Ni4+. In this study, we investigate the roles of fullerene with malonic acid moieties (MA-C60) as a superoxide dismutase mimetic (SODm) electrolyte additive in LIBs to deactivate reactive radical species (O2•-, LiOCO3•, and Li(CO3)2•) induced by electrochemical oxidation of residual lithium compound, Li2CO3 on the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode surface and to scavenge trace water to avoid undesirable hydrolysis of LiPF6. Further, MA-C60 maintains the structural stability of NCM811 cathodes and mitigates the parasitic reaction of residual lithium compounds with LiPF6 through the formation of a stable cathode–electrolyte interface. Our findings showed that MA-C60 helps overcome the challenges associated with Li2CO3 oxidation at the NCM811 cathode, which produces CO2 gas and O2•- that react with the solvent molecules.

Abstract

Abstract

The advancement of electrolyte systems has enabled the development of high-performance Li metal batteries (LMBs), which have tackled intractable dendritic Li growth and irreversible Li plating/stripping. In particular, the robust electrode–electrolyte interfaces created by electrolyte additives inhibit the deterioration of the cathode and the Li metal anode during repeated cycles. This paper reports the application of electrode–electrolyte interface modifiers, namely lithium nitrate (LiNO₃) and lithium difluoro(bisoxalato) phosphate (LiDFBP) as a N donor and F donor, respectively. LiDFBP and LiNO₃ with different electron-accepting abilities construct a mechanically robust, LiF-rich inner solid electrolyte interphase (SEI) and ion-permeable, Li₃N-containing outer SEI layers on the Li metal anode, respectively. A well-structured dual-layer SEI capable of transporting Li⁺ ions is formed on the Li metal anode, while the cathode–electrolyte interface (CEI) on the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode is strengthened. Ether-based electrolytes containing LiDFBP and LiNO₃ lead to a long cycle life (600 cycles) of Li|NCM811 full cells at C/2 with 80.9% capacity retention and a high Coulombic efficiency (CE) of 99.94%. Structural optimization of the SEI and CEI provides an opportunity for advancing the practical uses of LMBs.

Abstract

The Energy Spotlight in this issue features three articles recently published in ACS Energy Letters. These highlights are presented by Nam-Soon Choi, Javier Vela, Jeffrey DuBose, and Prashant V. Kamat. They have highlighted new electrolytes for lithium-ion batteries, synthesis of CsPbBr₃/mesoporous-SiO₂ composites with high luminescence yield and greater stability, and halide segregation in single-cation and mixed-cation perovskite films.

“Selected as Editor’s Highlights”

Abstract

Abstract

Our Energy Focus is among the most read articles for the past month (July 2020).

Optimized Electrolyte with High Electrochemical Stability and Oxygen Solubility for Lithium–Oxygen and Lithium–Air Batteries (Letter)

• External link of publication

Abstract

Nickel-rich layered oxides are currently considered the most practical candidates for realizing high-energy-density lithium metal batteries (LMBs) because of their relatively high capacities. However, undesired nickel-rich cathode–electrolyte interactions hinder their applicability. Here, we report a satisfactory combination of an antioxidant fluorinated ether solvent and an ionic additive that can form a stable, robust interfacial structure on the nickel-rich cathode in ether-based electrolytes.

The fluorinated ether 1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether (TFOFE) introduced as a cosolvent into ether-based electrolytes stabilizes the electrolytes against oxidation at the LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811) cathode while simultaneously preserving the electrochemical performance of the Li metal anode. Lithium difluoro(bisoxalato)phosphate (LiDFBP) forms a uniform cathode–electrolyte interphase that limits the generation of microcracks inside secondary particles and undesired dissolution of transition metal ions such as nickel, cobalt, and manganese from the cathode into the electrolyte. Using TFOFE and LiDFBP in ether-based electrolytes provides an excellent capacity retention of 94.5% in a Li|NCM811 cell after 100 cycles and enables the delivery of significantly increased capacity at high charge and discharge rates by manipulating the interfaces of both electrodes. This research provides insights into advancing electrolyte technologies to resolve the interfacial instability of nickel-rich cathodes in LMBs.

• External link of publication

https://pubs.acs.org/doi/10.1021/acsami.0c06830

Abstract

Abstract

“Featured on the Front Cover”

Abstract

Optimized Electrolyte with High Electrochemical Stability and Oxygen Solubility for Lithium–Oxygen and Lithium–Air Batteries (Letter)

Energy conversion and storage (ECS) technologies require significant advancements in catalysts and electrode materials with proper electro- and photochemical characteristics. Metal-organic frameworks (MOFs) have compositional and structural benefits because of their highly ordered and tunable metal nodes and organic linkers that affect the efficiency and durability of ECS technology. In this regard, MOFs utilizing metal-containing nodes with organic bridges are regarded as up-and-coming components to modify catalysts, electrodes, and ionic conductors (electrolytes) for ECS.

• <External Link of Publication>

https://pubs.acs.org/doi/10.1021/acsenergylett.0c00459

“Featured on the Inside Back Cover”

Abstract

Abstract

Li metal anodes and Ni-rich layered oxide cathodes with high reversible capacities are promising candidates for the fabrication of high energy density batteries. However, low Coulombic efficiency, safety hazards from likely vertical Li growth, and morphological instability of Ni-rich cathodes hinder the practical applications of these electrodes. Here, we report that fluorinated compounds can be employed as interface modifiers to extend the applicable voltage range of ether-based electrolytes, which have been used specifically so far for lithium metal batteries with charging cut-off voltages lower than 4 V (vs. Li/Li+). A complementary electrolyte design using both 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and fluoroethylene carbonate in concentrated ether-based electrolytes significantly improves the capacity retention (99.1%) in a Li|LiNi0.8Co0.1Mn0.1O2 full cell, with a high Coulombic efficiency of 99.98% after 100 cycles at 25 °C. Thus, the modified electrolyte system is promising for addressing the reductive and oxidative decompositions of labile ether-based electrolytes in high energy density Li metal batteries with Ni-rich cathodes.

Abstract

Fast-charging lithium-ion batteries (LIBs) can be achieved using structurally optimized electrodes and electrolytes. Electrolytes largely affect the interfacial structures of electrodes that are critical to reducing charging time of LIBs without sacrificing battery durability. However, most widely used LiPF6-based electrolytes suffer from reactive species, such as HF and PF5, that seriously damage interfacial structures of electrodes on repeated cycling and form resistive species at the electrode surface that hamper the fast charging of LIBs. To resolve these detrimental effects of LiPF6-based electrolytes, we report an electrolyte additive, (trimethylsilyl)isothiocyanate (TMSNCS) based on aminosilane, with a high electron donating ability that can scavenge HF and PF5. TMSNCS effectively deactivates reactive species and attains long-term stability of interfacial layers formed on anodes and cathodes in LiPF6-based electrolytes. After 300 cycles at a 2C charge rate and a 1C discharge rate, the NCM622/graphite full cell with 0.1% TMSNCS delivers a superior discharge capacity of 144 mAh/g and exhibits an excellent capacity retention of 91.8%. Furthermore, the stabilization of PF5 by the TMSNCS additive drastically alleviates undesired decomposition reactions of fluoroethylene carbonate (FEC) and enhances high-temperature performances of the FEC-containing full cells.

Abstract

Abstract

Abstract

Reactive oxygen species or superoxide (O₂^–), which damages or ages biological cells, is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium–oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C₆₀) was used as a superoxide disproportionation chemocatalyst mimicking the function of SOD. As expected, MA-C₆₀ as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm^–2) with 0.5 mAh cm^–2 cutoff survived up to 50 cycles after MA-C₆₀ was introduced to the electrolyte. Moreover, the SOD-mimetic catalyst increased capacity, e.g., more than a 6-fold increase at 0.2 mA cm^–2. The experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li₂O₂) and density functional theory calculation confirmed that the solution mechanism of Li₂O₂ formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C₆₀.

“Featured on the Outside Back Cover”

ABSTRACT

In conjunction with electrolyte additives used for tuning the interfacial structures of electrodes, functional materials that eliminate or deactivate reactive substances generated by the degradation of LiPF₆‐containing electrolytes in lithium‐ion batteries offer a wide range of electrolyte formulation opportunities. Herein, the recent advancements in the development of: (i) scavengers with high selectivity and affinity toward unwanted species and (ii) promoters of ion‐paired LiPF₆ dissociation are highlighted, showing that the utilization of the above additives can effectively mitigate the problem of electrolyte instability that commonly results in battery performance degradation and lifetime shortening. A deep mechanistic understanding of LiPF₆‐containing electrolyte failure and the action of currently developed additives is demonstrated to enable the rational design of effective scavenging materials and thus allow the fabrication of highly reliable batteries.

“Featured on the Front Cover”

ABSTRACT

Transition metal ion dissolution due to hydrofluoric acid attack is a long‐standing issue in the Mn‐based spinel cathode materials of lithium‐ion batteries (LIBs). Numerous strategies have been proposed to address this issue, but only a fragmentary solution has been established. In this study, reported is a seaweed‐extracted multitalented material, namely, agar, for high‐performance LIBs comprising Mn‐based cathode materials at a practical loading density (23.1 mg cm⁻² for LiMn₂O₄ and 10.9 mg cm⁻² for LiNi_0.5Mn_1.5O₄, respectively). As a surface modifier, 3‐glycidoxypropyl trimethoxysilane (GPTMS) is employed to enable the agar to have different phase separation behaviors during the nonsolvent‐induced phase separation process, thus eventually leading to the fabrication of an outstanding separator membrane that features a well‐defined porous structure, superior mechanical robustness, high ionic conductivity, and good thermal stability. The GPTMS‐modified agar separator membrane coupled with a pure agar binder to the LiNi_0.5Mn_1.5O₄/graphite full cell leads to exceptional improvement in electrochemical performance outperforming binders and separator membrane in current commercial products even at 55 °C; this improvement is due to beneficial features such as Mn²⁺ chelation and PF₅ stabilizing capabilities. This study is believed to provide insights into the potential energy applications of natural seaweeds.

ABSTRACT

Dye-sensitized solar cells (DSSCs) have been receiving growing attentions as a potential alternative to order photovoltaic devices due to their high efficiency and low manufacturing cost. DSSCs are composed of a photosensitizing dye adsorbed on a mesoporous film of nanocrystalline TiO2 as a photoelectrode, an electrolyte containing triiodide/iodide redox couple, and a platinized counter electrode. To improve photovoltaic properties of DSSCs, new dicationic salts based on ionic liquids were synthesized. Quite comparable efficiencies were obtained from electrolytes with new dicationic iodide salts. The best cell performance of 7.96% was obtained with dicationic salt of PBDMIDI.

ABSTRACT

Lithium-excess 3d-transition-metal layered oxides (Li_1+xNi_yCo_zMn_{1−x−y−z}O₂, >250 mAh g⁻¹) suffer from severe voltage decay upon cycling, which decreases energy density and hinders further research and development. Nevertheless, the lack of understanding on chemical and structural uniqueness of the material prevents the interpretation of internal degradation chemistry. Here, we discover a fundamental reason of the voltage decay phenomenon by comparing ordered and cation-disordered materials with a combination of X-ray absorption spectroscopy and transmission electron microscopy studies. The cation arrangement determines the transition metal-oxygen covalency and structural reversibility related to voltage decay. The identification of structural arrangement with de-lithiated oxygen-centred octahedron and interactions between octahedrons affecting the oxygen stability and transition metal mobility of layered oxide provides the insight into the degradation chemistry of cathode materials and a way to develop high-energy density electrodes.

ABSTRACT

“Highlighted as the Front Cover” 

ABSTRACT

With the emergence of stretchable electronic devices, there is growing interest in the development of deformable power accessories that can power them. To date, various approaches have been reported for replacing rigid components of typical batteries with elastic materials. Little attention, however, has been paid to stretchable separator membranes that can not only prevent internal short circuit but also provide an ionic conducting pathway between electrodes under extreme physical deformation. Herein, a poly(styrene‐b‐butadiene‐b‐styrene) (SBS) block copolymer–based stretchable separator membrane is fabricated by the nonsolvent‐induced phase separation (NIPS). The diversity of mechanical properties and porous structures can be obtained by using different polymer concentrations and tuning the affinity among major components of NIPS. The stretchable separator membrane exhibits a high stretchability of around 270% strain and porous structure having porosity of 61%. Thus, its potential application as a stretchable separator membrane for deformable energy devices is demonstrated by applying to organic/aqueous electrolyte–based rechargeable lithium‐ion batteries. As a result, these batteries manifest good cycle life and stable capacity retention even under a stretching condition of 100%, without compromising the battery’s performance.

ABSTRACT

An ethyl 4,4,4-trifluorobutyrate (ETFB) additive, with ester and partially fluorinated alkyl moieties, is employed to stabilize the interface structure of Ni-rich layered LiNi_0.7Co_0.15Mn_0.15O₂ (NCM) cathodes and graphite anodes. The analysis of the surface chemistry of the electrodes shows that ETFB serves as a bifunctional additive for constructing protective layers on both electrodes in a full cell. Cycling tests reveal that the addition of 1% ETFB leads to excellent capacity retention (84.8%) for the NCM/graphite full cell, which also delivers a superior discharge capacity of 167 mAh g⁻¹ and a high Coulombic efficiency of over 99.8% after 300 cycles at 45 °C. The ETFB-derived protective layer effectively reduces intergranular cracking in secondary NCM cathode particles upon repeated charge-discharge cycling and limits the dissolution of transition metal ions from the cathode at high temperatures. In addition, after ETFB reduction, the graphite anode develops a thermally stable interface structure, which suppresses the self-discharge of graphite coupled with the NCM cathode at 60 °C.

This paper has been highlighted in Research Interfaces’ June 2018 Battery Science literature review. 

ABSTRACT

Sodium (Na) metal anodes with stable electrochemical cycling have attracted widespread attention due to their highest specific capacity and lowest potential among anode materials for Na batteries. The main challenges associated with Na metal anodes are dendritic formation and the low density of deposited Na during electrochemical plating. Here, we demonstrate a fluoroethylene carbonate (FEC)-based electrolyte with 1 M sodium bis(fluorosulfonyl) imide (NaFSI) salt for the stable and dense deposition of Na metal during electrochemical cycling. The novel electrolyte combination developed here circumvents the dendritic Na deposition that is one of the primary concerns for battery safety and constructs the uniform ionic interlayer achieving highly reversible Na plating/stripping reactions. The FEC-NaFSI constructs the mechanically strong and ion-permeable interlayer containing NaF and ionic compounds such as Na2CO3 and sodium alkylcarbonates.

“Highlighted as the Back Cover“

ABSTACT

High-capacity Si-embedded anodes and Li-rich cathodes are considered key compartments for post lithium-ion batteries with high energy densities. However, the significant volume changes of Si and the irreversible phase transformation of Li-rich cathodes prevent their practical application. Here we report lithium fluoromalonato(difluoro)borate (LiFMDFB) as an unusual dual-function additive to resolve these structural instability issues of the electrodes. This molecularly engineered borate additive protects the Li-rich cathode by generating a stable cathode electrolyte interphase (CEI) while simultaneously tuning the fluoroethylene carbonate (FEC)-oriented solid electrolyte interphase (SEI) on the Si–graphite composite (SGC) anode. The complementary electrolyte design utilizing both LiFMDFB and FEC exhibited an improved capacity retention of 85%, a high Coulombic efficiency of ∼99.5%, and an excellent energy density of ∼400 W h kg⁻¹ in Li-rich/SGC full cells at a practical mass loading after 100 cycles. This dual-function additive approach offers a way to develop electrolyte additives to build a more favorable SEI for high-capacity electrodes.

ABSTRACT

Here, we report the first electrochemical assessment of organophosphonate-based compound as a safe electrode material for lithium-ion batteries, which highlights the reversible redox activity and inherent flame retarding property. Dinickel 1,4-benzenediphosphonate delivers a high reversible capacity of 585 mA h g^–1 with stable cycle performance. It expands the scope of organic batteries, which have been mainly dominated by the organic carbonyl family to date. The redox chemistry is elucidated by X-ray absorption spectroscopy and solid-state ³¹P NMR investigations. Differential scanning calorimetry profiles of the lithiated electrode material exhibit suppressed heat release, delayed onset temperature, and endothermic behavior in the elevated temperature zone.

ABSTRACT

A crumply and highly flexible lithium-ion battery is realized by using microfiber mat electrodes in which the microfibers are wound or webbed with conductive nanowires. This electrode architecture guarantees extraordinary mechanical durability without any increase in resistance after folding 1000 times. Its areal energy density is easily controllable by the number of folded stacks of a piece of the electrode mat. Deformable lithium-ion batteries of lithium iron phosphate as cathode and lithium titanium oxide as anode at high areal capacity (3.2 mAh cm⁻²) are successfully operated without structural failure and performance loss, even after repeated crumpling and folding during charging and discharging.

ABSTRACT

The roles of a partially fluorinated ether (PFE) based on a mixture of 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane and 2-(difluoro(methoxy)methyl)-1,1,1,2,3,3,3-heptafluoropropane on the oxidative durability of an electrolyte under high-voltage conditions, the rate capability of the graphite and 5 V-class LiNi0.4Mn1.6O4 (LNMO) electrodes, and the cycling performance of graphite/LNMO full cells are examined. Our findings indicate that the use of PFE as a cosolvent in the electrolyte yields thermally stable electrolytes with self-extinguishing ability. Electrochemical tests confirm that the PFE combined with fluoroethylene carbonate (FEC) effectively alleviates the oxidative decomposition of the electrolyte at the high-voltage LNMO cathode and enables reversible electrochemical reactions of the graphite anodes and LNMO cathodes at high rates. Moreover, the combination of PFE, which mitigates electrolyte decomposition at high voltages, and FEC, which stabilizes the anode-electrolyte interface, enables the reversible cycling of high-voltage full cells (graphite/LNMO) with a capacity retention of 70.3% and a high Coulombic efficiency of 99.7% after 100 cycles at 1C rate at 30 °C.

ABSTRACT

All-solid-state lithium-ion batteries (ASLBs) employing sulfide solid electrolytes (SEs) have emerged as promising next-generation batteries for large-scale energy storage applications in terms of safety and high energy density. While slurry-based fabrication processes using polymeric binders and solvents are inevitable to produce sheet-type electrodes, these processes for ASLBs have been overlooked until now. In this work, we report the first scalable single-step fabrication of bendable sheet-type composite electrodes for ASLBs using a one-pot slurry prepared from SE precursors (Li₂S and P₂S₅), active materials (LiNi_0.6Co_0.2Mn_0.2O₂ or graphite), and polymeric binders (nitrile-butadiene rubber (NBR) or polyvinyl chloride (PVC)) via a wet-chemical route using tetrahydrofuran. At 30 °C, the LiNi_0.6Co_0.2Mn_0.2O₂ and graphite electrodes wet-tailored from SE precursors and NBR exhibit high capacities of 140 mA h g⁻¹ at 0.1C and 320 mA h g⁻¹ at 0.2C, respectively. Particularly, the rate capability of the graphite electrode in an all-solid-state cell is superior to that of a liquid electrolyte-based cell. Additionally, the effects of the size of the SE precursors and the polymeric binders on the electrochemical performance are investigated. Finally, the excellent electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂/graphite ASLBs assembled using the as-single-step-fabricated electrodes are also demonstrated not only at 30 °C but also at 100 °C.

ABSTRACT

Lithium difluoro(oxalato)borate (LiDFOB) with one oxalate moiety bonded to a central boron core was employed as a salt-type additive to enhance the interfacial stabilities of high-voltage Li-rich cathodes and graphite anodes. Our investigation revealed that the LiDFOB additive modified the surface film on the electrodes and effectively restrained degradation of the cycling performance of the electrodes. Investigation of the surface chemistries of the electrodes confirmed that LiDFOB produces a LiF-less surface film on the Li-rich cathode and a LiF-rich surface film on the graphite anode. Moreover, the use of 1% LiDFOB drastically improved the rate capabilities of Li-rich cathodes and graphite anodes. Within 100 cycles at a rate of C/2 at 25 °C, only 45.8% of the initial discharge capacity of a high-voltage Li-rich/graphite full cell was delivered in the baseline electrolyte, while the LiDFOB-containing electrolyte retained 82.7%.

ABSTRACT

 We present an ultraconcentrated electrolyte composed of 5 M sodium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane for Na metal anodes coupled with high-voltage cathodes. Using this electrolyte, a very high Coulombic efficiency of 99.3% at the 120th cycle for Na plating/stripping is obtained in Na/stainless steel (SS) cells with highly reduced corrosivity toward Na metal and high oxidation durability (over 4.9 V versus Na/Na⁺) without corrosion of the aluminum cathode current collector. Importantly, the use of this ultraconcentrated electrolyte results in substantially improved rate capability in Na/SS cells and excellent cycling performance in Na/Na symmetric cells without the increase of polarization. Moreover, this ultraconcentrated electrolyte exhibits good compatibility with high-voltage Na₄Fe₃(PO₄)₂(P₂O₇) and Na_0.7(Fe_0.5Mn_0.5)O₂ cathodes charged to high voltages (>4.2 V versus Na/Na⁺), resulting in outstanding cycling stability (high reversible capacity of 109 mAh g^–1 over 300 cycles for the Na/Na₄Fe₃(PO₄)₂(P₂O₇) cell) compared with the conventional dilute electrolyte, 1 M NaPF₆ in ethylene carbonate/propylene carbonate (5/5, v/v).

ABSTRACT

Porous structured materials have unique architectures and are promising for lithium-ion batteries to enhance performances. In particular, mesoporous materials have many advantages including a high surface area and large void spaces which can increase reactivity and accessibility of lithium ions. This study reports a synthesis of newly developed mesoporous germanium (Ge) particles prepared by a zincothermic reduction at a mild temperature for high performance lithium-ion batteries which can operate in a wide temperature range. The optimized Ge battery anodes with the mesoporous structure exhibit outstanding electrochemical properties in a wide temperature ranging from −20 to 60 °C. Ge anodes exhibit a stable cycling retention at various temperatures (capacity retention of 99% after 100 cycles at 25 °C, 84% after 300 cycles at 60 °C, and 50% after 50 cycles at −20 °C). Furthermore, full cells consisting of the mesoporous Ge anode and an LiFePO₄ cathode show an excellent cyclability at −20 and 25 °C. Mesoporous Ge materials synthesized by the zincothermic reduction can be potentially applied as high performance anode materials for practical lithium-ion batteries.

ABSTRACT

The cycling and storage performances of LiCoO₂ (LCO)-LiNi_0.5Co_0.2Mn_0.3O₂(NCM)/pitch-coated silicon alloy-graphite (Si-C) full cells with ethylene carbonate (EC)–based and fluoroethylene carbonate (FEC)–based electrolytes are investigated at elevated temperatures. Excess FEC (used as a co-solvent in LiPF₆-based electrolytes), which is not completely consumed during the formation of the solid electrolyte interphase (SEI) layer on the electrodes, is prone to defluorination in the presence of Lewis acids such as PF₅; this reaction can generate unwanted HF and various acids (H₃OPF₆, HPO₂F₂, H₂PO₃F, H₃PO₄) at elevated temperatures. Our investigation reveals that the HF and acid compounds that are formed by FEC decomposition causes significant dissolution of transition metal ions (from the LCO-NCM cathode) into the electrolyte at elevated temperatures; as a result, the reversible capacity of the full cells reduces because of the deposition of the dissolved metal ions onto the anode. Moreover, we demonstrate possible mechanisms that account for the thermal instability of FEC in LiPF₆-based electrolytes at elevated temperatures using model experiments.

“Highlighted as the Back Cover“ 

ABSTRACT

Lithium difluoro(bisoxalato)phosphate (LiDFBP) is introduced as a novel lithium-salt-type electrolyte additive for lithium-rich cathodes in lithium-  ion batteries. The investigation reveals that LiDFBP is oxidized to form a uniform and electrochemically stable solid electrolyte interphase (SEI)   on   the lithium-rich cathode. The LiDFBP-derived SEI layer effectively suppresses severe electrolyte decomposition at high voltages and mitigates   the voltage decay of the lithium-rich cathodes caused by undesirable phase transformation to spinel-like phases during cycling. Furthermore, the cell with electrolyte containing LiDFBP achieves substantially improved cycling performance and delivers a high discharge capacity of 116 mA h g⁻¹ at a high C rate (20 C). The unique function of the LiDFBP additive on the surface chemistry of lithium-rich cathodes is confirmed through X-ray photoelectron spectroscopy, SEM, and TEM analyses.

ABSTRACT

We demonstrate a unique synthetic route for oxygen-deficient mesoporous TiO_x by a redox–transmetalation process by using Zn metal as the reducing agent. The as-obtained materials have significantly enhanced electronic conductivity; 20 times higher than that of as-synthesized TiO₂ material. Moreover, electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements are performed to validate the low charge carrier resistance of the oxygen-deficient TiO_x. The resulting oxygen-deficient TiO_x battery anode exhibits a high reversible capacity (∼180 mA h g⁻¹ at a discharge/charge rate of 1 C/1 C after 400 cycles) and an excellent rate capability (∼90 mA h g⁻¹ even at a rate of 10 C). Also, the full cell, which is coupled with a LiCoO₂ cathode material, exhibits an outstanding rate capability (>75 mA h g⁻¹ at a rate of 3.0 C) and maintains a reversible capacity of over 100 mA h g⁻¹ at a discharge/charge of 1 C/1 C for 300 cycles.

ABSTRACT

ABSTRACT

Employing linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as electrolyte solvents provides an opportunity to design appropriate electrolyte systems for high-performance sodium-ion batteries (SIBs). However, in practice, the use of linear carbonate-containing electrolytes is quite challenging because linear carbonates readily decompose at Na metal electrodes or sodiated anodes. One of the promising approaches is using an electrolyte additive to resolve the critical problems related to linear carbonates. Our investigation reveals that remarkable enhancement in electrochemical performance of Na₄Fe₃(PO₄)₂(P₂O₇) cathodes with linear carbonate-containing electrolytes is achieved by using a fluoroethylene carbonate (FEC) additive. Importantly, the initial Coulombic efficiency of the Na deposition/stripping on a stainless steel (SS) electrode is drastically improved from 16% to 90% by introducing the FEC additive into ethylene carbonate (EC)/propylene carbonate (PC)/DEC (5/3/2, v/v/v)/0.5 M NaClO₄. The underlying mechanism of FEC at the electrode-electrolyte interface is clearly demonstrated by ¹³C nuclear magnetic resonance (NMR). In addition, the Na₄Fe₃(PO₄)₂(P₂O₇) cathode in EC/PC/DEC (5/3/2, v/v/v)/0.5 M sodium perchlorate (NaClO₄) with FEC delivers a discharge capacity of 90.5 mAh g⁻¹ at a current rate of C/2 and exhibits excellent capacity retention of 97.5% with high Coulombic efficiency of 99.6% after 300 cycles at 30 °C.

ABSTRACT

It is known that grafting one polymer onto another polymer backbone is a powerful strategy capable of combining dual benefits from each parent polymer. Thus amphiphilic graft copolymer precursors (poly(vinylidene difluoride)-graft-poly(tert-butylacrylate) (PVDF-g-PtBA)) have been developed via atom transfer radical polymerization, and demonstrated its outstanding properties as a promising binder for high-performance lithium-ion battery (LIB) by using in situ pyrolytic transformation of PtBA to poly(acrylic acid) segments. In addition to its superior mechanical properties and accommodation capability of volume expansion, the Si anode with PVDF-g-PtBA exhibits the excellent charge and discharge capacities of 2672 and 2958 mAh g⁻¹ with the capacity retention of 84% after 50 cycles. More meaningfully, the graft copolymer binder shows good operating characteristics in both LiN_0.5M_1.5O₄ cathode and neural graphite anode, respectively. By containing such diverse features, a graft copolymer-loaded LiN_0.5M_1.5O₄/Si-NG full cell has been successfully achieved, which delivers energy density as high as 546 Wh kg⁻¹ with cycle retention of ≈70% after 50 cycles (1 C). For the first time, this work sheds new light on the unique nature of the graft copolymer binders in LIB application, which will provide a practical solution for volume expansion and low efficiency problems, leading to a high-energy-density lithium-ion chemistry.

“Highlighted as the Inside Cover Picture“ 

ABSTRACT

As high-energy-density lithium-ion batteries (LIBs) are being developed, their thermal stability problems become more apparent. In spite of elaborate precautions, exothermic reactions between electrolytes and electrode materials at elevated temperatures can lead to battery explosion. In this study, we introduce a novel flame-retardant additive with a fluorinated hyperbranched cyclotriphosphazene structure for high-voltage LIBs. Along with the effective reduction of flammability, it enhances the electrochemical performance by generating a thermally and electrochemically stable solid electrolyte interphase on both the cathode and the anode, which is rare for conventional additives. In full cells composed of a 5 V-class spinel cathode and a graphite anode with practical-level mass loading, this new additive demonstrates significant improvements in discharge capacity retention and coulombic efficiency during cycle testing.

ABSTRACT

Thanks to the advantages of low cost and good safety, magnesium metal batteries get the limelight as substituent for lithium ion batteries. However, the energy density of state-of-the-art magnesium batteries is not high enough because of their low operating potential; thus, it is necessary to improve the energy density by developing new high-voltage cathode materials. In this study, nanosized Berlin green Fe₂(CN)₆ and Prussian blue Na_0.69Fe₂(CN)₆ are compared as high-voltage cathode materials for magnesium batteries. Interestingly, while Mg²⁺ ions cannot be intercalated in Fe₂(CN)₆, Na_0.69Fe₂(CN)₆ shows reversible intercalation and deintercalation of Mg²⁺ ions, although they have the same crystal structure except for the presence of Na⁺ ions. This phenomenon is attributed to the fact that Mg²⁺ ions are more stable in Na⁺-containing Na_0.69Fe₂(CN)₆ than in Na⁺-free Fe₂(CN)₆, indicating Na⁺ ions in Na_0.69Fe₂(CN)₆ plays a crucial role in stabilizing Mg²⁺ ions. Na_0.69Fe₂(CN)₆ delivers reversible capacity of approximately 70 mA h g^–1 at 3.0 V vs Mg/Mg²⁺ and shows stable cycle performance over 35 cycles. Therefore, Prussian blue analogues are promising structures for high-voltage cathode materials in Mg batteries. Furthermore, this co-intercalation effect suggests new avenues for the development of cathode materials in hybrid magnesium batteries that use both Mg²⁺ and Na⁺ ions as charge carriers.

ABSTRACT

We developed a new type of additive with poly(acrylic acid) (PAA) for stable cycling retention of silicon anodes. Diamino-Polyethylene Glycol (diamino-PEG) is used as a thermally curable additive with PAA polymeric binder for silicon nanoparticle based negative electrodes. Amino groups of the diamino-PEG form amide bonds with carboxylic acid groups of the PAA binder, which gives strong binding force even under high humidity. The highly cross linked amide bonds between diamino-PEG and PAA binder in silicon nanoparticle based negative electrodes leads to reduced electrical contact loss of silicon particles during electrochemical reaction. It also supports stable cycling performance and enhances specific capacity compared to the case of using only a silicon anode PAA binder.

ABSTRACT

Agarose, which is one of the natural polysaccharides that is generally extracted from seaweed, has recently attracted great attention as an environmentally-benign building element for a wide variety of applications. Notably, its disaccharide repeating units bearing ether/hydroxyl groups carry unprecedented performance benefits far beyond those accessible with traditional synthetic polymers. Herein, intrigued by these unusual chemical features of agarose, we explore its potential applicability as an alternative electrode binder and also as a carbon source for high-performance rechargeable lithium-ion batteries. The agarose binder enables silicon (Si) active materials to be tightly adhered to copper foil current collectors, thereby providing significant improvement in the electrochemical performance of the resulting Si anode (specific capacity = 2000 mA h g⁻¹ and capacity retention after 200 cycles = 71%). In addition, agarose can be exploited as a cathode binder. An LiMn₂O₄ cathode containing agarose binder shows an excellent cell performance (initial coulombic efficiency of ∼96.2% and capacity retention after 400 cycles of ∼100%). Through the selective carbonization of Si-dispersed agarose, Si/C (hard carbon) composite active materials are successfully synthesized. Eventually, the Si/C composite anode and the LiMn₂O₄ cathode mentioned above are assembled to produce a full cell featuring the use of agarose as an alternative green material. Benefiting from the exceptional multifunctionality of agarose, the full cell presents a stable cycling performance (capacity retention after 50 cycles of >87%).

ABSTRACT

A family of organophosphorus compounds including triphenyl phosphite (TPP), trimethyl phosphite (TMP), tris(2,2,2-trifluoroethyl) phosphite (TFEP), and tris(trimethylsilyl) phosphite (TMSP) is investigated as additives for the stabilization of high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode-electrolyte interface. Our investigation reveals that the cycling performance of Li/LNMO half cells with the TMP, TFEP or TMSP additive is drastically improved at 60 °C compared to the baseline electrolyte. Among the various phosphite-based additives tested, TMSP additive enables facile Li ion transport at high C rates and significantly enhances the storage performance of the Li/LNMO cells at 60 °C. To understand the effects of the phosphite-based additives on electrolyte oxidative decomposition at high voltages, the surface chemistry of the cathode after precycling is investigated via ex-situ X-ray photoelectron spectroscopy (XPS). Additionally, the roles of phosphite-based additives to suppress LiPF₆ hydrolysis and to remove HF are examined via ¹⁹F and ³¹P NMR spectroscopies.

HIGHLIGHTS

• Phosphite-based additives improves electrochemical performance of LiNi_0.5Mn_1.5O₄.

• Phosphite-based additives modify the surface chemistry of LiNi_0.5Mn_1.5O₄.

• TMSP effectively removes HF and deactivates the reactivity of POF₃.

• The TMSP-derived SEI allows fast lithium ion conduction at high rates.

ABSTRACT

Lithium difluorophosphate (LiDFP) as a reducible additive is employed to overcome the unsatisfactory rate capability and cycling instability of highly pressed graphite electrodes with high mass loading (8.1 mg/cm²) with a vinylene carbonate (VC)-derived surface film that hampers the charge transport at the graphite–electrolyte interface at high rates. Our investigation reveals that LiDFP modifies the surface chemistry induced by VC and makes a more ionically conductive surface film on graphite, ensuring good rate capability.

HIGHLIGHTS

• The combination of VC + LiDFP improves the rate capability of graphite.

• VC reinforces the mechanical property of the LiDFP-derived SEI.

• The nature of the SEI is a key parameter affecting the kinetics of graphite.

ABSTRACT
Nanostructured Si-based materials are key building blocks for next-generation energy storage devices. To meet the requirements of practical energy storage devices, Si-based materials should exhibit high-power, low volume change, and high tap density. So far, there have been no reliable materials reported satisfying all of these requirements. Here, we report a novel Si-based multicomponent design, in which the Si core  is covered with multifunctional shell layers. The synergistic coupling of Si with the multifunctional shell provides vital clues for satisfying all Si anode requirements for practical batteries. The Si-based multicomponent anode delivers a high capacity of B1000 mA h g1, a highly stable cycling retention (B65% after 1000 cycles at 1 C), an excellent rate capability (B800 mA h g1 at 10 C), and a remarkably suppressed volume expansion (12% after 100 cycles). Our synthetic process is simple, low-cost, and safe, facilitating new methods for developing electrode materials for practical energy storage.

ABTRACT
The organophosphorus compounds tris(trimethylsilyl) phosphite (TMSP) and vinylene carbonate (VC) have been considered for use as functional additives to improve the electrochemical performance of Li1.1Mn1.86Mg0.04O4 (LMO)/graphite full cells. Our investigation reveals that the combination of VC and TMSP as additives enhances the cycling properties and storage performance of full cells at 60 C. The
unique functions of the TMSP additive in the VC electrolyte are investigated via ex situ X-ray photoelectron spectroscopy (XPS) and 19F nuclear magnetic resonance (NMR) measurements. The TMSP additive effectively eliminates trace water and hydrogen fluoride (HF) and produces a protective film on the LMO cathode that alleviates manganese dissolution at 60 C. ã2015 Elsevier Ltd. All rights reserved.

Keywords

• Lithium-ion battery
• electrolyte additive
• vinylene carbonate
• tris(trimethylsilyl) phosphite
• solid electrolyte interphase

Abstract
Advanced polymeric binders with unique functions such as improvements in the electronic conduction network, mechanical adhesion, and mechanical durability during cycling have recently gained an increasing amount of attention as a promising means of creating high-performance silicon (Si) anodes in lithium-ion batteries with high energy density levels. In this review, we describe the key challenges of Si anodes, particularly highlighting the recent progress in the area of polymeric binders for Si anodes in cells.

Keywords

• Lithium-ion battery
• silicon anode
• volume expansion
• polymeric binder

ABSTRACT
A thin, uniform, and highly stable protective layer tailored using tris(trimethylsilyl) phosphite (TMSP) with a high tendency to donate electrons is formed on the Li-rich layered cathode, Li1.17Ni0.17Mn0.5Co0.17O2. This approach inhibits severe electrolyte decomposition at high operating voltages during cycling and dramatically improves the interfacial stability of the cathode. The TMSP additive in the LiPF6-based electrolyte is found to preferentially eliminate HF, which promotes the dissolution of metal ions from the cathode. Our investigation revealed that the TMSP-derived surface layer can overcome the significant capacity fading of the Li-rich cathode by structural instability ascribed to an irreversible phase transformation from layered to spinel-like structures. Moreover, the superior rate capability of the Li-rich cathode is achieved because the TMSPoriginated surface layer allows facile charge transport at high C rates for the lithiation process.

KEYWORDS

• electrolyte additive
• tris(trimethylsilyl) phosphite
• solid electrolyte interphase
• lithium-rich layered cathode
• lithium-ion battery

ABSTRACT
We demonstrate the important strategy to design suitable electrolyte systems that make the desirable interfacial structure to allow the reversible sodiation/desodiation of Sn4P3 anodes. Our investigation reveals that the remarkable improvement in the electrochemical performance of Sn4P3 anodes for NIBs is achieved by the combination of fluoroethylene carbonate (FEC) with tris(trimethylsilyl)phosphite (TMSP). We clearly present the unique functions of this binary additive combination to build up a protective surface film on the Sn4P3 anode against unwanted electrolyte decomposition and to prevent the formation of the Na15Sn4 phase, which is accompanied by a large volume expansion during the Na insertion (sodiation) process.

         “Highlighted as the back cover”           

ABSTRACT
Nanostructured germanium is a promising material for high-performance energy storage devices. However, synthesizing it in a cost-effective and simple manner on a large scale remains a significant challenge. Herein, we report a redox-transmetalation reaction-based route for the large-scale synthesis of mesoporous germanium particles from germanium oxide at temperatures of 420600 C. We could confirm that a unique redox-transmetalation reaction occurs between Zn0 and Ge4þ at approximately 420 Cusing temperature-dependent in situ X-ray absorption fine structureanalysis. This reaction has several advantages, which include (i) the successful synthesis of germanium particles at a low temperature (∼450 C), (ii) the accommodation of large volume changes, owing to the mesoporous structure of the germanium particles, and (iii) the ability to synthesize the particles in a cost-effective and scalable manner, as inexpensive metal oxides are used as the starting materials. The optimized mesoporous germanium anode exhibits a reversible capacity of∼1400 mA h g1 after 300 cycles at a rate of 0.5 C (corresponding to the capacity retention of 99.5%), as well as stable cycling in a full cell containing a LiCoO2 cathode with a high energy density (charge capacity = 286.62 mA h cm3).

KEYWORDS

• mesoporous germanium
• redox-transmetalation
• zincothermic reduction
• germanium anode
• energy storage devices

ABSTRACT
Nanostructured micrometer-sized Al–Si particles are synthesized via a facile selective etching process of Al–Si alloy powder. Subsequent thin Al2O3 layers are introduced on the Si foam surface via a selective thermal wet oxidation process of etched Al–Si particles. The resulting Si/Al2O3 foam anodes exhibit outstanding cycling stability (a capacity retention of 78% after 300 cycles at the C/5 rate) and excellent rate capability.

ABSTRACT
The demand for new energy storage systems to be employed in large-scale electrical energy storage systems (EESs) has grown recently, particularly for green energy storage and grid-supporting applications. Rechargeable Mg bat-teries are promising candidates for such applications because of their good safety characteristicsand raw materials’abundance. Recent progress in the field is noticeable, but further efforts are required to support the successful implementation of rechargeable Mg batteries. We address progress in the development of rechargeable Mg batteries and problems to be resolved in future research, briefly summarize the most recent advances in the development of rechargeable Mg batteries, from amaterials perspective, and cover progress on each of the major components of Mg batteries:the electrolyte, the cathode material, and the anode material. We provide apractical guideline for further development of self-sustainable rechargeable Mg batteries as afuture power source.

Keywords

• electrochemistry
• energy storage systems
• lithium · magnesium
• structure¢activity relationships

ABSTRACT
Advanced electrolytes with unique functions such as in situ formation of a stable artificial solid electrolyte interphase (SEI) layer on the anode and the cathode, and the improvement in oxidation stability of the electrolyte have recently gained recognition as a promising means for highly reliable lithium-ion batteries with high energy density. In this review, we describe several challenges for the cathode (spinel lithium manganese oxide (LMO), lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide(NCM), spinel lithium manganese nickel oxide (LNMO), and lithium-rich layered oxide (Li-rich cathode))-electrolyte interfaces and highlight the recent progress in the use of oxidative additives and high-voltage solvents in high-performance cells.

ABSTRACT
Despite Si being one of the most promising anode materials in lithium-ion batteries, significant challenges remain, including a large volume change, low electrical conductivity and high temperature operation for practical use. Herein, we demonstrate a facile synthesis of Si particles with double-shell coating layers, in which aluminum trifluoride (AlF3) acts as an artificial defensive matrix, and carbon layers enhance electrical conductivity and compatibility with carbon black. Our study reveals that Si anodes with double shell layers composed of AlF3 exhibit excellent electrochemical properties at 25 C and 60 C, owing to the formation of a stable solid electrolyte interface layer on the Si surface, and the good mechanical strength and chemical nature of AlF3 layers. The Si@AlF3@C anode shows a significantly improved cycling performance (capacity retention of 75.8% after 125 cycles at 25 C and 73.7% at 60 C after 150 cycles, compared to the specific capacity in the first cycle) and excellent rate capability of >1600 mA h g1, even at a 5C rate (at 25 C). Furthermore, the AlF3 assisted Si electrode exhibits remarkably reduced volume expansion (thickness change of 71% after 125 cycles at 25 C and 128% after 150 cycles at 60 C).

ABSTRACT
SnSe alloy is examined for the first time as an anode for Na-ion batteries, and shows excellent electrochemical performance including a high reversible capacity of 707 mA h g1 and stable cycle performance over 50 cycles. Upon sodiation, SnSe is changed into amorphous NaxSn nanodomains dispersed in crystalline Na2Se, and SnSe is reversibly restored after desodiation.

ABSTRACT
A Au nanoparticle-coated Ni nanowire substrate without binder or carbon is used as the electrode (denoted as the Au/Ni electrode) for Li-oxygen (Li-O 2 ) batteries. A minimal amount of Au nanoparticles with sizes of <30 nm on a Ni nanowire substrate are coated using a simple electrodeposition method to the extent that maximum capacity can be utilized. This optimized, one body, Au/Ni electrode shows high capacities of 921 mAh g −1 Au , 591 mAh g −1 Au , and 359 mAh g −1 Au , which are obtained at currents of 300 mAg −1 Au , 500 mAg −1 Au , and 1000 mAg −1 Au respectively. More importantly, the Au/Ni electrode exhibits excellent cycle stability over 200 cycles.

ABSTRACT
Lithium bis(oxalato)borate (LiBOB) is utilized as an oxidative additive to prevent the unwanted electrolyte decomposition on the surface of Li1.17Ni0.17Mn0.5Co0.17O2 cathodes. Our investigation reveals that the LiBOB additive forms a protective layer on the cathode surface and effectively mitigates severe oxidative decomposition of LiPF6–based electrolytes.Noticeable improvements in the cycling stability and rate capability of Li1.17Ni0.17Mn0.5Co0.17O2 cathodes are achieved in the LiBOB-added electrolyte. After 100 cycles at 60◦C, the discharge capacity retention of the Li1.17Ni0.17Mn0.5Co0.17O2 cathode was 28.6% in the reference electrolyte, whereas the LiBOB-containing electrolyte maintained 77.6% of its initial discharge capacity. Moreover, the Li1.17Ni0.17Mn0.5Co0.17O2 cathode with LiBOB additive delivered a superior discharge capacity of 115 mAh g−1 at a high rate of 2 C compared with the reference electrolyte. The OCV of a full cell charged in the reference electrolyte drastically decreased from 4.22 V to 3.52 V during storage at 60◦C, whereas a full cell charged in the LiBOB-added electrolyte exhibited superior retention of the OCV. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0211414jes] All rights reserved.

ABSTRACT
We demonstrate a facile synthesis of micrometer-sized porous Si particles via copper-assisted chemical etching process. Subsequently, metal and/or metal silicide layers are introduced on the surface of porous Si particles using a simple chemical reduction process. Macroporous Si and metal/metal silicide-coated Si electrodes exhibit a high initial Coulombic efficiency of ∼90%. Reversible capacity of carbon-coated porous Si gradually decays after 80 cycles, while metal/metal silicide-coated porous Si electrodes show significantly improved cycling performance even after 100 cycles with a reversible capacity of >1500 mAh g−1. We confirm that a stable solidelectrolyte interface layer is formed on metal/metal silicide-coated porous Si electrodes during cycling, leading to a highly stable cycling performance.

KEYWORDS

• lithium-ion batteries
• porous Si anode
• interfacial coating layer
• solid electrolyte interphase
• surface coating

ABSTRACT
We introduce an effective way to improve the electrochemical properties of graphite anodes by Li4Ti5O12 (LTO) coating for lithium rechargeable batteries. LTO coated graphite is prepared by a sol–gel method coupled with hydrothermal reaction. LTO coating renders the electrochemical performance of graphite to be significantly improved compared to pristine graphite. Moreover, LTO coating layers affect the stability of the solid electrolyte interphase (SEI) by making an even SEI film without further electrolyte decomposition and thus making it more stable. Also, LTO coating layers prevent the electrolyte decomposition species from going into the interior graphite, proving that LTO coating can contribute to not only  the electrochemical properties of graphite but also its thermal stability.

Keywords

• Graphite
• Spinel lithium titanium oxide
• Solid electrolyte interphase
• Surface modification
• Lithium rechargeable batteries

ABSTRACT
A highly promising anode material with an amorphous SiOx nanostructure finely impregnated with carbon nanofibers is presented. The nanostructure material has a unique integral feature in that carbon nanofibers smaller than several nm in diameter are finely dispersed in amorphous SiOx media in an aligned manner. The synthetic route to fabricate the nanostructure is very simple and easy, using natural porous silicate, sepiolite, activated through the process of sintering and acid treatments on carbon source-loaded sepiolite nanocomposites. Upon the treatments, the nanocomposite material is changed in respect of its structure and chemical composition from crystalline Mg silicate to the carbon nanofiber-impregnated amorphous SiOx phase (CNF–SiOx nanostructure), and the electrochemical activity is greatly improved. The CNF–SiOx nanostructure exhibits excellent electrochemical performance with a reasonably high capacity of approximately 720 mA h g1 for a current density of 70 mA g1 (C/10 rate) and outstanding rate capability with a capacity retention of 96.8% for a current density of 700 mA g1 and 87% at 1400 mA g1 relative to that at 35 mA g1, even at a high electrode loading level above 8 mg cm2. The cycling performance is also very stable, with a capacity retention of 94.7% over 50 cycles at a rate of 350 mA g1 and with a Coulombic efficiency above 99%.

ABSTRACT
Lithium difluoro(oxalato)borate (LiFOB) is investigated as an additive for enhancing the electrochemical performance of high-voltage lithium cobalt oxide (LiCoO2, LCO)/lithium nickel manganese cobalt oxide (LiNi0.6Co0.2Mn0.2O2, NMC) cathodes and high-capacity silicon/graphite (Si-C) anodes. LCO-NMC/Si-C full cells with a LiFOB additive have been found to exhibit improved high temperature lectrochemical performance. To confirm the effects of LiFOB on the cathode and the anode, the surface chemistry of the anodes and cathodes cycled in electrolytes with and without the LiFOB additive are examined using exsitu X-ray photoelectron spectroscopy (XPS). The LiFOB additive produces a LiF-based solid electrolyte interphase (SEI) on the Si-C anode and a carboxylate-based SEI on the LCO-NMC cathode.

Keywords

• lithium-ion battery
• electrolyte
• lithium difluoro(oxalato)borate
• solid electrolyte interphase

ABSTRACT
Binary solventmixtures containing NaClO4 salt were investigated as electrolytes for sodium-ion batteries. The electrochemical performance of Na4Fe3(PO4)2(P2O7) cathodes was substantially improved when paired with an ethylene carbonate (EC)/propylene carbonate (PC)-based electrolyte. Our investigation revealed that EC/PC/1MNaClO4 exhibits superior oxidation durability at the cathode and is highly stable toward a Na-metal electrode.

Keywords

• Sodium-ion batteries
• Electrolyte
• Mixed-polyanion cathode
• Solid electrolyte interphase

ABSTRACT
Silicon (Si) has been investigated as promising negative-electrode (anode) materials because its theoretical specific capacity of 4200 mAh/g for Li4.4Si is far higher than that of carbonaceous anodes in current commercial products. However, in practice, the application of Si to
Li-ion batteries is still quite challenging because Si suffers from severe volume expansion and contraction and lead to a continuous solid electrolyte interphase (SEI)-filming process by cracking of Si. This process consumes the limited Li+ source, builds up thick and unstable SEI layer on the Si active materials, and will eventually disable the cell. Since unstable SEI reduces electrochemical performance and thermal stability of the Si anode, the surface chemistry of the anode should be modified by using a functional additive. It is found that lithium bis(oxalato)borate
(LiBOB) as an additive effectively protected the Si anode surface, improved capacity retention when stored at 60oC, and alleviated exothermic thermal reactions of fully lithiated Si anode.

Keywords

• Silicon
• Solid electrolyte interphase
• Electrolyte, Additive
• Thermal reactions

Abstract
Sn4P3 is introduced for the first time as an anode material for Na-ion batteries. Sn4P3 delivers a high reversible capacity of 718 mA h g−1, and shows very stable cycle performance with negligible capa­city fading over 100 cycles, which is attributed to the confinement effect of Sn nanocrystallites in the amorphous phosphorus matrix during cycling.

ABSTRACT
We report a highly promising organophosphorus compound with an organic substituent, tris(trimethylsilyl) phosphite (TMSP), to improve the electrochemical performance of 5 V-class LiNi0.5Mn1.5O4 cathode materials. Our investigation reveals that TMSP alleviates the decomposition of LiPF6 by hydrolysis, effectively eliminates HF promoting Mn/Ni dissolution from the cathode, and forms a protective layer on the cathode surface against severe electrolyte decomposition at high voltages. Remarkable improvements in the cycling stability and rate capability of high voltage cathodes were achieved in the TMSP-containing electrolyte. After 100 cycles at 60 C, the discharge capacity retention was 73% in the baseline electrolyte, whereas the TMSP-added electrolyte maintained 90% of its initial discharge capacity. In addition, the LiNi0.5Mn1.5O4 cathode with TMSP delivers a superior discharge capacity of 105 mA h g1 at a high rate of 3 C and an excellent capacity retention of 81% with a high coulombic efficiency of over 99.6% is exhibited for a graphite/LiNi0.5Mn1.5O4 full cell after 100 cycles at 30 C.

“Highlighted as the Back Cover“

ABSTRACT
We present a promising electrolyte candidate, Mg(TFSI)2 dissolved in glyme/diglyme, for future design of advanced magnesium (Mg) batteries. This electrolyte shows high anodic stability on an aluminum current collector and allows Mg stripping at the Mg electrode and Mg deposition on the stainless steel or the copper electrode. It is clearly shown that nondendritic and agglomerated Mg secondary particles composed of ca. 50 nm primary particles alleviating safety concern are formed in glyme/diglyme with 0.3 M Mg(TFSI)2 at a high rate of 1C. Moreover, a Mg(TFSI)2-based electrolyte presents the compatibility toward a Chevrel phase Mo6S8, a radical polymer charged up to a high voltage of 3.4 V versus Mg/Mg2+ and a carbon−sulfur composite as cathodes.

KEYWORDS

• electrochemistry
• diglyme, magnesium battery
• magnesium deposition
• magnesium stripping

ABSTRACT
The thermal reactions of lithiated and delithiated sulfur cathodes with 1.3M lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in tetra(ethylene glycol)dimethyl ether (TEGDME) are investigated by differential scanning calorimetry (DSC). To understand the thermal reactions of cycled sulfur cathodes, the products formed during cycling are characterized by ex-situ X-ray photoelectron spectroscopy (XPS).

ABSTRACT
Highly porous electrodes composed of natural polysaccharide act as a microporous binder and a carbon-coating source of micron-sized macroporous Si active materials was achieved. This highly porous Sibased anodes exhibit significantly improved electrochemical properties which show a high specific capacity (2010 mA h g1) after 80 cycles.

ABSTRACT
Since LiMn2O4 spinel materials are inexpensive, environmentally-friendly, and safe, they are considered a promising cathode  candidate for lithium ion batteries in EVs to replace commercialized materials such as LiCoO2, LiNi1/3Mn1/3Co1/3O2 and  LiNi0.5Co0.2Mn0.3O2. However, LiMn2 O4 spinel electrodes severely degrade at high temperature due to Mn dissolution. Also, the dissolved Mn2+ ions causes self-discharge where reduction of Mn2+ ions into Mn metals occurs on a graphite anode surface accompanied by oxidation of lithiated graphite at a charged state, and this results in severe capacity fading at high temperature. In this study, ion-exchangeable binders and a separator having functional groups of sodium carboxylate or sulfonate are, for the first time, examined to solve the Mn dissolution problem of LiMn2O4 spinel materials at high temperature. Ion exchange between Na+ ions of the functional groups of the binders and the separator and dissolved Mn2+ ions of the LiMn2O4 electrodes inhibits self-discharge, resulting in improved cycle performance. This result is supported by the IR spectra of the binders, an ICP analysis of the electrolytes, and ex situ XRD patterns of lithiated graphite electrodes.

ABSTRACT
The nanostructured Si particles are synthesized by a silver-assisted catalytic etching process of commercially available bulk Si particles in a hundred-gram scale. The electrochemical performance of the porous Si anode at 30 C and 60 C is significantly improved when carbon coating layers are formulated with a fluoroethylene carbonate-based electrolyte.

ABSTRACT
To enhance the electrochemical properties of the Sn3.95Fe0.05P3 anode,we focus on reducible additives tomitigate damage to the anode by electrolyte decomposition. It is found that the the electrochemical performance of the anode is significantly improved when formulated with an FEC-added electrolyte. Ex-situ X-ray photoelectron spectroscopy (XPS) reveals that the FEC additive builds an LiF-based solid electrolyte interphase (SEI) with less organic species on the anode upon cycling.

Keywords

• Lithium-ion batteries
• Tin phosphide
• Solid electrolyte interphase
• Electrolyte additive

ABSTRACT
Chemical reduction of micro-assembled CNT@TiO2@SiO2 leads to the formation of titanium silicide-containing Si nanotubular  structures. The Si-based nanotube anodes exhibit a high capacity (>1850 mA h g1) and an excellent cycling performance (capacity retention of >99% after 80 cycles).

ABSTRACT
The impact of phosphorous (P)-doping on the electrochemical performance and surface chemistry of soft carbon is investigated by means of galvanostatic cycling and ex situ X-ray photoelectron spectroscopy (XPS). P-doping plays an important role in storing more Li ions and discernibly improves reversible capacity. However, the discharge capacity retention of P-doped soft carbon electrodes deteriorated at 60 oC compared to non-doped soft carbon. This poor capacity retention could be improved by vinylene carbonate (VC) participating in forming a protective interfacial chemistry on soft carbon. In addition, the effect of P-doping on exothermic thermal reactions of lithiated soft carbon with electrolyte solution is discussed on the basis of differential scanning calorimetry (DSC) results.

Key Words

• Soft carbon
• Phosphorous doping
• Solid electrolyte interphase
• Electrolyte
• Thermal reactions

ABSTRACT
The cycling performance of lithium–sulfur batteries in binary electrolytes based on tetra(ethylene glycol)dimethyl ether (TEGDME) and 1,3-dioxolane(DOL)with lithiumnitrate (LiNO3) additive were investigated. The highest ionic conductivity  was obtained for 1 M LiN(CF3SO2)2 (LiTFSI) in TEGDME/DOL=33:67(volume ratio)-based electrolyte. The cyclic efficiency of lithium–sulfur batteries was dramatically increased with LiNO3 additive as a shuttle inhibitor in electrolytes. The lithium–sulfur cell assembled with 1 M LiTFSI in TEGDME/DOL containing 0.2 M LiNO3 additive for electrolyte, the elemental sulfur for cathode, and the lithium metal for anode demonstrated the initial discharge capacity of about 900 mAh g−1 and an enhanced cycling performance.

Keywords

• Lithium–sulfur battery .
• Tetra(ethylene glycol)dimethyl ether . 1,3-Dioxolane .
• Lithium nitrate

ABSTRACT
We discuss the similarities and dissimilarities of sodium- and lithium-ion batteries in terms of negative and positive electrodes. Compared to the comprehensive body of work on lithium-ion batteries, research on sodium-ion batteries is still at the germination stage. Since both sodium and lithium are alkali metals, they share similar chemical properties including ionicity, electronegativity and electrochemical reactivity. They accordingly have comparable synthetic protocols and electrochemical performances, which indicates that sodium-ion batteries can be successfully developed based on previously applied  approaches or methods in the lithium counterpart. The electrode materials in Li-ion batteries provide the best library for research on Na-ion batteries because many Na-ion insertion hosts have their roots in Li-ion insertion hosts. However, the larger size and different bonding characteristics of sodium ions influence the thermodynamic and/or kinetic properties of sodium-ion batteries, which leads to unexpected behaviour in electrochemical performance and reaction mechanism, compared to lithiumion batteries. This perspective provides a comparative overview of the major developments in the area  of positive and negative electrode materials in both Li-ion and Na-ion batteries in the past decade. Highlighted are concepts in solid state chemistry and electrochemistry that have provided new opportunities for tailored design that can be extended to many different electrode materials for sodium-ion batteries.

ABSTRACT
A new photo-cross-linkable poly(acrylic acid) (PAA) polymer functionalized with a photoreactive benzophenone group (PAABP) was synthesized and examined as a binder for Si-based anodes. Upon UV irradiation, the PAA-BP binders formed an  irreversible cross-linked structure through the formation of a new three-dimensional C–C bond network between the benzophenone moiety and the PAA backbone. The photo-cross-linked PAABP binder demonstrated a marginal volume expansion (38%) after full lithiation, compared to conventional binders and this resulted in an improved cycle performance of the Si anode over 100 cycles with a high reversible capacity of ca. 1600 mA h g21. We attributed this phenomenon to the enhanced mechanical  properties of the photo-cross-linked PAA-BP binder, which were evaluated using nanoindentation and swelling measurements.

ABSTRACT
Lithium bis(oxalato) borate (LiBOB) is investigated as an additive for the stabilization of a high-voltage cathode–electrolyte interface. It is found that the electrochemical performance of Li/LiNi0.5Mn1.5O4 cells with a LiBOB additive is improved at 60 ◦C. To confirm the effects of LiBOB on electrolyte oxidative decomposition, the surface chemistry of separators and high-voltage LiNi0.5Mn1.5O4 cathodes cycled in electrolytes with and without a LiBOB additive are examined using ex situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS).

Keywords

• Li-ion battery
• High-voltage spinel cathode
• Electrolyte
• Lithium bis(oxalato)borate
• Solid electrolyte interphase

ABSTRACT
The positive impact of a fluoroethylene carbonate (FEC) solvent on the interfacial stability of Li metal electrodes and the electrochemical performance of lithium-sulfur (Li-S) cells is investigated. To confirm the effects of FEC on electrolyte ecomposition andcell resistance, the surface chemistry and impedance of an Li electrode cycled in electrolytes with and without a FEC solvent are investigated using attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectrometry (ToF-SIMS), and electrochemical impedance spectroscopy. A protective layer with a FEC solvent for the formation of robust SEI and carbonate-based solvents for the suppression of polysulfide attack against an Li anode was formed on the Li anode by UV-curing polymerization. It is found that the protective layer with FEC effectively suppresses the significant overcharge by the shuttle process of polysulfide species and improves cycling performance of Li-S cells. © 2013 The Electrochemical Society. [DOI: 10.1149/2.101306jes] All rights reserved.

ABSTRACT
We report a simple route for synthesizing titanium silicide-coated Si anodes via the silicothermic reduction process of TiO2-coated Si. The titanium silicide enhances the electrical conductivity of Si nanoparticles and provides a highly stable solid electrolyte interface layer during the cycling, resulting in excellent electrochemical performances and significantly improved high thermal stability.

ABSTRACT
Magnesium (Mg) deposition and dissolution behaviors of 0.2 M MgBu2-(AlCl2Et)2, 0.5 M Mg(ClO4)2, and 0.4M (PhMgCl)2-AlCl3-based electrolytes with and without tris(pentafluorophenyl) borane (TPFPB) are investigated by ex situ scanning electron microscopy (SEM) and galvanostatic cycling of Mg/copper (Cu) cells. To ascertain the factors responsible for the anodic stability of the electrolytes, linear sweep voltammogrametry (LSV) experiments for various electrolytes and solvents are conducted. The effects of TPFPB as an additive on the anodic stability of 0.4M (PhMgCl)2-AlCl3/THF electrolyte are also discussed.

Keywords :

• Anodic limit
• Electrolyte
• Magnesium deposition
• Magnesium dissolution
• Scanning electron microscopy

ABSTRACT
Over the past tens of years, the major energy source has been fossil fuels which are non-renewable, fi nite, and environmentally  harmful. As a part of efforts to address these problems, Li ion batteries have been extensively studied to obtain more efficient energy storage systems. [ 1–4 ] However, the commonly used electrode materials in Li ion batteries are inorganic compounds of LiCoO 2 , LiFePO 4 , LiMn 2 O 4 and Li 4 Ti 5 O 12 prepared from limited Li-containing mineral resources. This problem will be exacerbated if the demand for lithium, and hence its price, increases greatly as a result of widespread commercialization of electric vehicles. Accordingly, sodium ion batteries are an attractive alternative to replace lithium ion batteries because Na resources are inexhaustible and of lower cost. [ 5 , 6 ] Although, Na ion batteries have recently received a great deal of attention as a next generation system and have shown promising electrochemical performance including stable cyclability and good rate capability, they face the critical problem of lower energy density than Li ion batteries. Most cathode and anode materials that have been introduced to date for Na ion batteries show similar or slightly lower specifi c capacity and redox potential than those of Li ion batteries. [ 7–9 ] In general, conventional cathode materials having a high redox potential have been developed based on intercalation chemistry, and it is thus diffi cult to highly increase the specifi c capacity of these cathode materials due to limited storage sites and oxidation state. [ 5 , 10–13 ] Therefore, in order to improve the energy density of Na ion batteries, new anode materials having a high specifi c capacity and appropriately low redox potential should be introduced. [ 14 ] Thus far, however, there have been few studies on sodium insertion materials for anodes with high capacity. [ 15–23 ] The general strategy for storing a large number of ions is to use conversion chemistry such as alloying  materials. The representative example is Si-based materials, and Si can store 4.4 Li ions per Si, delivering 4200 mA h g − 1 . However, it is known that Na ions are not electrochemically inserted in Si, despite of the existence of Na-Si alloys. Accordingly, Sibased materials unfortunately cannot be used as anodes in Na ion batteries, although Si is the most promising anode material  for Li ion batteries. Sn and Sb-based materials have meanwhile been introduced as promising anode materials having a high  reversible capacity, but their specifi c capacities do not exceed ca. 1000 mA h g − 1 . [ 24–26 ] In this study, we introduce, for the fi rst time, an amorphous red P/carbon composite as an anode material for Na ion batteries. This composite shows reversible capacity of 1890 mA h g − 1 at a current density of 143 mA g − 1 (ca. 0.05C rate), appropriate redox potential of ca. 0.4 V vs. Na/Na + , good rate capability delivering 1540 mA h g − 1 at a current density of 2.86 A g − 1 (ca. 1C rate) (about 80% of the reversible capacity delivered at 143 mA g − 1 ), and excellent cycle performance with negligible capacity fading over 30 cycles. This specifi capacity of the composite is the highest value among Na-ion  insertion materials reported to date.

ABSTRACT
A new polyanion-based compound, Na 3.12 M 2.44 (P 2 O 7 ) 2 (M = Fe, Fe 0.5 Mn 0.5 , Mn) is synthesized and examined as a cathode for Na ion batteries. Off-stoichiometric synthesis induces the formation of a Na-rich phase, Na 3.32 Fe 2.34 (P 2 O 7 ) 2 – a member of the solid solution series Na 4− α Fe 2+ α /2 (P 2 O 7 ) 2 (2/3 ≤ α ≤ 7/8) – which delivers a reversible capacity of about 85 mA h g − 1 at ca. 3 V vs. Na/Na + and exhibits very stable cycle performance. Above all, it shows fast kinetics for Na ions, delivering an almost constant 72% reversible capacity at rates between C/10 and 10C without the necessity for nanosizing or carbon coating. We attribute this to the spacious channel size along the a -axis, along with a single phase transformation upon de/ sodiation.

ABSTRACT
Tris(pentafluorophenyl) borane (TPFPB) is evaluated as an additive for improving electrochemical performance of lithium peroxide (Li2O2)-based electrodes. It is found that TPFPB significantly reduced the charge potential of Li2O2-based electrodes during the first charge process and improved reversible capacity during cycling without adding air (or O2) to the cell. To confirm the effect of TPFPB on electrolyte decomposition, the surface chemistry of Li2O2-based electrodes cycled in electrolytes with and without TPFPB was investigated.

Keywords

• Lithiumeoxygen battery
• Lithium peroxide
• Electrolyte
• Tris(pentafluorophenyl) borane
• Solid electrolyte interphase

ABSTRACT
The self-discharge of Zn anode material is identified as a main factor that can limit the energy density of alkaline Zneair batteries. Al2O3 has most positive effect on controlling the hydrogen evolution reaction accompanied by corroding Zn anode among various additives. The overpotential for hydrogen evolution is measured by potentio-dynamic polarization analysis. Al-oxide with high overpotential for hydrogen evolution reaction is uniformly coated on the surface of Zn powders via chemical solution process. The morphology and composition of the surface-treated and pristine Zn powders are characterized by SEM, EDS, XRD and XPS analyses. Aluminum is distributed homogeneously over the surface of modified Zn powders, indicating uniform coating of Al-oxide, and O1s and Al2p spectra further identified surface coating layer to be the Al-oxide. The Al-oxide coating layer can prevent Zn from exposing to the KOH electrolyte, resulting in minimizing the side reactions within batteries. The 0.25 wt.% aluminum oxide coated Zn anode material provides discharging time of more than 10 h, while the pristine Zn anode delivers only 7 h at 25 mA cm2. Consequently, a surface-treated Zn electrode can reduce self-discharge which is induced by side reaction such as H2 evolution, resulting in increasing discharge capacity.

Keywords

• Self-discharge
• Overpotential
• Hydrogen evolution
• Surface modification

ABSTRACT
Trigonal Na4Ti5O12 with a tunnel-structured three-dimensional framework was first examined as an anode material for Li ion batteries. The nanosized Na4Ti5O12 was synthesized at 600◦C using the solid state method with carbon-coated nanosized TiO2 anatase. Carbon layers on TiO2 play an important role of inhibiting the growth of Na4Ti5O12 particles. Li ions are reversibly de/intercalated in the Na4Ti5O12 structure, and this shows the reversible capacity of ca. 100 mA h g−1 with no capacity fading over 100 cycles. During the repeated charge and discharge, the ion exchange between Na ion and Li ion happens to form LixNa4−xTi5O12, and this causes an increase of the relative tunnel size due to smaller Li ion, resulting in decreasing polarization of voltage profiles. Also, trigonal Na4Ti5O12 was additionally examined as an anode for Na ion batteries.

ABSTRACT
Energy-storage technologies, including electrical double-layer capacitors and rechargeable batteries, have attracted significant  attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and “load leveling” of  renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double-layer capacitors requires a step  change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased  understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning  lithium batteries and electric double-layer capacitors.

Keywords

• battery safety
• electrical double-layer capacitors
• energy storage
• Li–air battery
• Li–S batteries

ABSTRACT
Electrode designs, which can accommodate severe volume changes (ca. 400%) of silicon anode materials upon lithium insertion, are the main prerequisite for high-performance lithium ion batteries. Among various techniques investigated for this purpose, a robust polymeric binder is a promising means to inhibit mechanical fracture of silicon negative electrodes during cycling. Lithium ion batteries (LIBs) are one of the most promising energy storage devices owing to their high power and energy densities.[1] For LIBs, silicon is a promising candidate anode material owing to its high theoretical specific capacity of 4200 mAhg1 for Li4.4Si, low electrochemical potential between 0 and 0.4 V versus Li/Li+, and small initial irreversible capacity compared with other metal- or alloy-based anode materials.[2] Nevertheless, the practical application of  silicon to LIBs is still quite challenging because silicon suffers from severe volume changes (ca. 400%) during Li+ insertion  and extraction processes, which breaks electrical contact between the silicon particles and results in degradation of  electrodes and rapid capacity loss.[3] To alleviate volume change, silicon nanoparticles and porous silicon materials  have been extensively studied because the smaller particles undergo smaller absolute volume change.[4] The aggregation  of silicon particles upon cycling, however, accelerates the degradation of electrodes. Thus, many efforts have focused on  the synthesis of silicon–carbon composites to prevent the agglomeration of silicon, resulting in a highly improved cycle  performance.[5] Although remarkable improvements in the electrochemical performance of silicon-based anodes have  been achieved, electrode deformation and external cell expansion still occur because of the inherent volume change  of silicon. This large cell volume change is the main factor limiting the commercialization of silicon-based anode materials.

ABSTRACT
Remarkable improvements in the electrochemical performance of Si materials for Li-ion batteries have been recently achieved, but the inherent volume change of Si still induces electrode expansion and external cell deformation. Here, the void structure in Si-encapsulating hollow carbons is optimized in order to minimize the volume expansion of Si-based anodes and improve electrochemical performance. When compared to chemical etching, the hollow structure is achieved via electroless etching is more advanced due to the improved electrical contact between carbon and Si. Despite the very thick electrodes (30 ∼ 40 μ m), this results in better cycle and rate performances including little capacity fading over 50 cycles and 1100 mA h g − 1 at 2C rate. Also, an in situ dilatometer technique is used to perform a comprehensive study of electrode thickness change, and Si-encapsulating hollow carbon mitigates the volume change of electrodes by adoption of void space, resulting in a small volume increase of 18% after full lithiation corresponding with a reversible capacity of about 2000 mA h g − 1 .

ABSTRACT
The influence of solvents on the discharge behavior of lithium-sulfur cells was investigated by ex situ Raman spectroscopy and X-ray  diffraction. Lithium polysulfide species formed in a sulfur cathode during cycling are characterized by Raman experiments for the first  time and their structures are examined with regard to three different electrolytes at fully charged and discharged states. Moreover,  ex-situ Raman studies give the evidence for the formation of lithium polysulfide on a Li metal anode by shuttle phenomena  and the coexistence of soluble lithium polysulfide with elemental sulfur even after full charge. It was found that 1,3-dioxolane  (DOX)/1M LiTFSI facilitates the migration of soluble lithium polysulfide toward a lithium anode and initiates a polysulfide shuttle  causing a considerable capacity loss in lithium-sulfur cells. Raman results and cycling tests using an air-tight cell demonstrated that  tetra(ethylene glycol) dimethyl ether (TEGDME)-based electrolytes hindered the significant overcharge and led to the formation of  Li2S2 contributing to high discharge capacity through further electrochemical reduction to Li2S.

ABSTRACT
Over the past several decades, the major energy source globally has been fossil fuels, which are non-renewable, fi nite, and environmentally hazardous. In efforts to address these problems, clean and sustainable energy systems have been studied including solar cells, fuel cells, and rechargeable batteries. Li ion batteries are currently the dominant energy storage systems in the portable electronic device market. However, the commonly used electrode materials in Li ion batteries are inorganic compounds of LiCoO 2 , LiFePO 4 , LiMn 2 O 4 , Si, and Sn prepared from limited mineral resources. Additionally, the synthetic steps of  these materials often include energy demanding ceramic processes.  Therefore, there is demand to prepare future electrode materials from renewable resources with minimum energy consumption. [ 1 , 2 ] One possible approach to this end is to supply electrode materials from biomass or recyclable organic materials, which are mostly synthesized via solution phase routes.

ABSTRACT
We demonstrate a simple process to synthesize silicon-based multicomponents via a high-temperature annealing of bulk silicon  monoxide in the presence of sodium hydroxide. The carbon-coated Si-based anodes exhibit a highly stable cycling performance  (capacity retention of 99.5% after 200 cycles) with a reversible charge capacity of 1280 mA h g1.

ABSTRACT
The manganese dissolution behavior of lithium hexafluorophosphate (LiPF6) dissolved in carbonate-based organic solvents is investigated by ex situ field emission scanning electron microscope (FE-SEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and inductively coupled plasma (ICP). It is found that the LiPF6 salt anions in the electrolytes are prone to oxidize upon contacting delithiated lithium manganese oxide with high oxidizing power and the electrons that evolved from the oxidation of anions are consumed in the reduction of tetravalent manganese ions to trivalent manganese ions at 60 °C. The generated trivalent manganese ions readily undergo a disproportion reaction and thereby release divalent manganese ions into the electrolytes, which leads to a capacity loss in the lithium manganese oxide cathode.

Keywords

• Spinel lithium manganese oxide
• Disproportion reaction
• LiPF6
• Anodic limit
• Manganese dissolution

Commercially available silicon monoxide is an unstable material at high temperatures (> 10008C), at which point it disproportionates to silicon nanocrystals and amorphous silicon suboxides.[1, 2] The nanostructuring of SiO, or its conversion to Si, has been carried out using several approaches, such as mechanical milling,[3] chemical vapor deposition,[4] and reduction by elemental metals at high temperatures (> 900 8C).[5] However, these methods did not retain the original morphology of the SiO. Herein, we demonstrate a process for fabricating three-dimensional nanoporous SiO by metalassisted chemical etching, without changing the chemical and physical properties of the original materials. Subsequent chemical-assisted thermal annealing led to the conversion of porous SiO into shape-preserving Sibased multicomponent systems that consisted of core (Si dispersed in amorphous silicon suboxides) and shell (crystalline silica). Small amounts of alkaline solutions induced the crystallization of amorphous silica into crystalline silica, and simultaneously assisted the disproportionation at a modest temperature (> 700 8C). We used the porous SiO and the Sibased systems as anode materials in lithium-ion batteries. These systems exhibited a high reversible capacity (ca. 1600 mA h g1 ) and a stable retention over 100 cycles. The chemical-assisted thermal disproportionation is simple, low in costs, and mass-productive (high yield of > 99% on a scale of tens of grams per batch), and thus, opens up an effective way to produce high-performance anode materials. In addition, the nanostructuring of SiO by the above-mentioned process may be extended to a wide variety of applications, such as optoelectronics,[6] solar cells,[7] antireflection coatings,[8] and lithium-ion batteries.

Abstract
A series of sulfonated poly(fluorenyl ether nitrile oxynaphthalate) (SPFENO) copolymers with different  degrees of sulfonation were synthesized. Their degree of sulfonation was controlled by adjusting the  molar ratio of the reactants. The polymer electrolytes prepared with a SPFENO membrane exhibited high  ionic conductivities and solution holding capacity, which depended on the degree of sulfonation. The  quasi-solid-state electric double layer capacitors (EDLCs) consisted of activated carbon electrodes and  polymer electrolytes were ssembled, and their electrochemical characteristics were studied by cyclic  voltammetry and charge-discharge cycle tests. A SPFENO membrane with proper degree of sulfonation was effective for maintaining high ionic conductivity and keeping good electrode–electrolyte interfacial  contact during cycling, which resulted in good cycling performance of the EDLC.

Keywords

• Degree of sulfonation
• Electric double layer capacitor
• Polymer electrolyte
• Proton exchange membrane
• Sulfonated aromatic polymer

ABSTRACT
A novel dimeric ionic liquid based on imidazolium cation and bis(trifluoromethanesulfonyl) imide (TFSI) anion has been synthesized through a metathesis reaction. Its chemical shift values and thermal properties are identified via 1H nuclear magnetic resonance (NMR) imaging and differential scanning calorimetry (DSC). The effect of the synthesized dimeric ionic liquid on the interfacial resistance of gel polymer electrolytes is described. Differences in the SEM images of lithium electrodes after lithium deposition with and without the 1,1′-pentyl-bis(2,3-dimethylimidazolium) bis(trifluoromethane-sulfonyl)imide (PDMITFSI) ionic liquid in gel polymer electrolytes are clearly discernible. This occurs because the PDMITFSI ionic liquid with hydrophobic moieties and polar groups modulates lithium deposit pathways onto the lithium metal anode. Moreover, high anodic stability for a gel polymer electrolyte with the PDMITFSI ionic liquid was clearly observed.

Keywords

• Dimeric ionic liquid
• Gel polymer electrolyte
• Ionic conductivity
• Interfacial resistance
• Lithium dendrite

Abstract
A porosity-controllable Si-based composite electrode was fabricated in the present study. Poly(methyl methacrylate) (PMMA), which possesses the unique thermal property of unzipping, was utilized as a pore-forming agent during electrode fabrication. PMMA-treated electrodes presented relatively low volume expansion and little deformation during lithiation. The cyclic dilation behavior of PMMA-treated electrodes was investigated by applying an in situ electrochemical dilatometric method, and enhanced dimensional reversibility during cycling was observed. The dilation behavior was closely related to the electrochemical performance, and PMMA-treated electrodes exhibited improved capacity retention and low impedance change during cycling. The newly generated pores in the PMMA-treated electrode can accommodate the volumetric expansion of Si-based active materials, which suppresses electrode deformation and the breakdown of the electrical network. The porosity plays an important role in Si-based electrodes. Thus, controlling the porosity through PMMA-treatment can be an effective way for the application of Si-based composite electrodes for advanced lithium-ion batteries.

Keywords

• Silicon
• Lithium-ion battery
• Porosity
• Dilatometry
• Volume change

Abstract
There has been tremendous interest in using nanomaterials for advanced Li-ion battery electrodes, particularly to increase the energy density by using high specific capacity materials. Recently, it was demonstrated that one dimensional (1D) Si/Sn nanowires (NWs) and nanotubes (NTs) have great potential to achieve high energy density as well as long cycle life for the next generation of advanced energy storage applications. In this feature article, we review recent progress on Si-based NWs and NTs as high capacity anode materials. Fundamental understanding and future challenges on one dimensional nanostructured anode are also discussed.

ABSTRACT
In the past decade, there have been exciting developments in the fi eld of  lithium ion batteries as energy storage devices, resulting in the application of  lithium ion batteries in areas ranging from small portable electric devices to  large power systems such as hybrid electric vehicles. However, the maximum  energy density of current lithium ion batteries having topatactic chemistry is  not suffi cient to meet the demands of new markets in such areas as electric  vehicles. Therefore, new electrochemical systems with higher energy densities  are being sought, and metal-air batteries with conversion chemistry are  considered a promising candidate. More recently, promising electrochemical  performance has driven much research interest in Li-air and Zn-air batteries.  This review provides an overview of the fundamentals and recent progress  in the area of Li-air and Zn-air batteries, with the aim of providing a better  understanding of the new electrochemical systems.

Abstract
The discharge capacities of spinel-type Formula cells charged in electrolytes with solid electrolyte interphase (SEI)-forming additives are investigated after being stored at Formula . The presence of Mn deposits on the anode surface, which is responsible for the capacity fading of cells, is clearly shown by means of open-circuit voltage, ex situ X-ray diffraction, and energy-dispersive spectrometry measurements. Unlike fluoroethylene carbonate, using vinylene carbonate as an SEI former leads to a noticeable improvement in the discharge capacity retention of cells that were stored for 20 days at Formula .
KeyWords

• electrolytes
• graphite
• lithium compounds
• secondary cells
• X-ray diffraction

ABSTRACT
The electrochemical performance of graphite/lithium cobalt oxide (LiCoO2) cells in N-methoxymethyl- N,N-dimethylethylammonium bis(trifluoromethane-sulfonyl) imide (MMDMEA-TFSI)-containing electrolytes is significantly enhanced by the formation of a fluoroethylene carbonate (FEC)-derived protective film on an anode during the first cycle. The electrochemical intercalation of MMDMEA cations into the graphene layer is readily visualized by ex situ transmission electron microscopy (TEM). Moreover, differences in the X-ray diffraction (XRD) patterns of graphite electrodes in cells charged with and without FEC in dimethyl carbonate (DMC)/MMDMEA-TFSI are clearly discernible. Conclusively, the presence of FEC in MMDMEA-TFSI-containing electrolytes leads to a remarkable enhancement of discharge capacity retention for graphite/LiCoO2 cells as compared with ethylene carbonate (EC) and vinylene carbonate(VC).

Keywords

• Graphite
• Lithium cobalt oxide
• Ionic liquid
• Fluoroethylene carbonate
• Lithium-ion battery