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Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium-excessive layered-oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3 Co1/3 Mn1/3 O2 . The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries.

Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium-excessive layered-oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3 Co1/3 Mn1/3 O2 . The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries.

Activation of oxygen redox during the first cycle has been reported as the main trigger of voltage hysteresis during further cycles in high‐energy‐density Li‐rich 3d‐transition‐metal layered oxides. However, it remains unclear whether hysteresis only occurs due to oxygen redox. Here, it is identified that the voltage hysteresis can highly correlate to cationic reduction during discharge in the Li‐rich layered oxide, Li1.2Ni0.4Mn0.4O2. In this material, the potential region of discharge accompanied by hysteresis is apparently separated from that of discharge unrelated to hysteresis. The quantitative analysis of soft/hard X‐ray absorption spectroscopies discloses that hysteresis is associated with an incomplete cationic reduction of Ni during discharge. The galvanostatic intermittent titration technique shows that the inevitable energy consumption caused by hysteresis corresponds to an overpotential of 0.3 V. The results unveil that hysteresis can also be affected by cationic redox in Li‐rich layered cathodes, implying that oxygen redox cannot be the only reason for the evolution of voltage hysteresis. Therefore, appropriate control of both cationic and anionic redox of Li‐rich layered oxides will allow them to reach their maximum energy density and efficiency. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIB) have received much research attention in the past decades as they are considered to be one alternative to the currently prevalent lithium ion batteries, and carbonaceous and organic compounds present two promising classes of SIB electrode materials advantaged by abundance of their constituent elements and reduced environmental footprints. To accelerate the development of these materials for SIB applications, future research directions must be guided by a thorough understanding of the charge storage mechanism. This review presents recent efforts in mechanism elucidation for these two classes of SIB electrode materials since, compared to their inorganic counterparts, they have unique challenges in material analysis. Topics covered will include characterization techniques and analytical frameworks for mechanism elucidation, emphasizing the advantages and limitations of individual experimental methodologies and providing a commentary on scientific rigor in result interpretation. [ABSTRACT FROM AUTHOR]

Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium‐excessive layered‐oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3Co1/3Mn1/3O2. The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high‐capacity lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

With the increase of device requirements, rechargeable lithium‐ion batteries are facing tremendous challenges in large‐scale applications due to the high price and gradual shortage of lithium sources. In contrast, multivalent ion batteries, such as aluminum, magnesium, and zinc, are promising candidates for the next‐generation energy‐storage systems because of their high volumetric energy density, safe operation, and abundant reserves. The strong intercalation between multivalent ions and the host materials, however, will cause lower ion‐diffusion kinetics and a poor discharge capacity. One of the main challenges is to search for a suitable cathode material with a high capacity and good structural stability to overcome the abovementioned problems. Two‐dimensional layered materials, with characteristic unique structural features, good conductivity, and high electrochemically active surface, have attracted attention from researchers during the past decade. In this review, the design approach and synthetic procedures for the preparation of two‐dimensional materials as cathodes for multivalent ion batteries, including interlayer engineering, two‐dimensional heterostructures, pore/hole engineering, and heteroatom doping, are summarized. Meanwhile, the relationship between the design configuration and optimized electrochemical performance is rationally and systematically presented. Additionally, perspectives for the sustainable synthesis of cathode materials are proposed for multivalent metal‐ion chemistry. [ABSTRACT FROM AUTHOR]

The accelerating development of technologies requires a significant energy consumption, and consequently the demand for advanced energy storage devices is increasing at a high rate. In the last two decades, lithium‐ion batteries have been the most robust technology, supplying high energy and power density. Improving cathode materials is one of the ways to satisfy the need for even better batteries. Therefore developing new types of positive electrode materials by increasing cell voltage and capacity with stability is the best way towards the next‐generation Li rechargeable batteries. To achieve this goal, understanding the principles of the materials and recognizing the problems confronting the state‐of‐the‐art cathode materials are essential prerequisites. This Review presents various high‐energy cathode materials which can be used to build next‐generation lithium‐ion batteries. It includes nickel and lithium‐rich layered oxide materials, high voltage spinel oxides, polyanion, cation disordered rock‐salt oxides and conversion materials. Particular emphasis is given to the general reaction and degradation mechanisms during the operation as well as the main challenges and strategies to overcome the drawbacks of these materials. [ABSTRACT FROM AUTHOR]

Abstract: Since their successful commercialization in 1990s, lithium‐ion batteries (LIBs) have been widely applied in portable digital products. The energy density and power density of LIBs are inadequate, however, to satisfy the continuous growth in demand. Considering the cost distribution in battery system, it is essential to explore cathode/anode materials with excellent rate capability and long cycle life. Nanometer‐sized electrode materials could quickly take up and store numerous Li+ ions, afforded by short diffusion channels and large surface area. Unfortunately, low thermodynamic stability of nanoparticles results in electrochemical agglomeration and raises the risk of side reactions on electrolyte. Thus, micro/nano and hetero/hierarchical structures, characterized by ordered assembly of different sizes, phases, and/or pores, have been developed, which enable us to effectively improve the utilization, reaction kinetics, and structural stability of electrode materials. This review summarizes the recent efforts on electrode materials with hierarchical structures, and discusses the effects of hierarchical structures on electrochemical performance in detail. Multidimensional self‐assembled structures can achieve integration of the advantages of materials with different sizes. Core/yolk–shell structures provide synergistic effects between the shell and the core/yolk. Porous structures with macro‐, meso‐, and micropores can accommodate volume expansion and facilitate electrolyte infiltration. [ABSTRACT FROM AUTHOR]

The non-aqueous lithium oxygen battery has been considered as one of the most promising energy storage systems owing to its potentially high energy density, exceeding that of any other existing storage system for storing sustainable and clean energy. The success of Li-O2 batteries could efficiently reduce greenhouse gas emissions and the consumption of non-renewable fossil fuels. How to achieve high round-trip efficiency, high capacity, and satisfactory cycling performance, however, is still a great challenge for the lithium oxygen battery. Thus, this report will point out what factors will affect the electrochemical performance and will aim to describe how to increase the electrochemical performance by air electrode optimization. Based on recent achievements, several approaches to solving this problem, such as synthesizing electrocatalysts with high catalytic activity and designing appropriate air electrode structures, are described in details. Also, recent progress associated with novel air electrode designs and understanding the reaction process is discussed. [ABSTRACT FROM AUTHOR]

Fast lithium ion and electron transport inside electrode materials are essential to realize its superb electrochemical performances for lithium rechargeable batteries. Herein, a distinctive structure of cathode material is proposed, which can simultaneously satisfy these requirements. Nanosized Li3V2(PO4)3 (LVP) particles can be successfully grown up on the carbon nanofiber via electrospinning method followed by a controlled heat‐treatment. Herein, LVP particles are anchored onto the surface of carbon nanofiber, and with this growing process, the size of LVP particles as well as the thickness of carbon nanofiber can be regulated together. The morphological features of this composite structure enable not only direct contact between electrolytes and LVP particles that can enhance lithium ion diffusivity, but also fast electron transport through 1D carbon network along nanofibers simultaneously. Finally, it is demonstrated that this unique structure is an ideal one to realize high electron transport and ion diffusivity together, which are essential for enhancing the electrochemical performances of electrode materials. [ABSTRACT FROM AUTHOR]

An excellent integrated anode (Sn-AB) is constructed by using epoxy (A)-amine (B) glue binding with ultrafine Sn nanoparticles. The electrode with strong adhesion and tensile strength can effectively tolerate the large volume changes of Sn, thereby guaranteeing excellent Li-storage properties. The development of AB binder, therefore, provides a novel and potential tactics for enhancement of electrode integration and mechanical strength. [ABSTRACT FROM AUTHOR]

Over the last 40 years, metallic lithium as an anode material has been of great interest owing to its high energy density. However, dendritic lithium growth causes serious safety issues. Awareness and understanding of the Li deposition and stripping processes have grown rapidly especially in recent years, and consequently, there have been many attempts to suppress the Li dendrites. Recent developments that have modified the electrolytes and the Li anode in order to inhibit the growth of Li dendrite and improve cycling performance are summarized. It has been shown that current density, solid-electrolyte interphase (SEI) film, Li+ transference number, and shear modulus have significant impact on the growth behavior and the Coulombic efficiency. Various methods have been introduced to increase the surface area of the Li anode, enhance Li+ conductivity, form stable SEI film, and improve mechanical strength of electrolytes. These approaches are discussed in details, and the perspectives regarding the future use of Li anode are also outlined. It is hoped that this review will facilitate the future development of Li metal batteries. [ABSTRACT FROM AUTHOR]

Improving the lithium (Li) storage properties of silicon (Si)-based anode materials is of great significance for the realization of advanced Li-ion batteries. The major challenge is to make Si-based anode materials maintain electronic conduction and structural integrity during cycling. Novel carbon-coated Si nanoparticles (NPs)/reduced graphene oxides (rGO) composites are synthesized through simple solution mixing and layer-by-layer assembly between polydopamine-coated Si NPs and graphene oxide nanosheets by filtration, followed by a thermal reduction. The anodic properties of this composite demonstrate the potency of the novel hybrid design based on two dimensional materials for extremely reversible energy conversion and storage. A high capacity and an extremely stable cycle life are simultaneously realized with carbon-coated Si/rGO composite, which has a sandwich structure. The unprecedented electrochemical performance of this composite can be ascribed to the synergistic effect of polydopamine and rGO. The polydopamine layer forms strong hydrogen bonding with rGO through chemical cross-linking, thus firmly anchoring Si NPs on rGO sheets to prevent the aggregation of Si NPs and their electronic contact loss. Finally, its structural feature with stacked rGO clipping carbon-coated Si NPs inside it enables to keep the overall electrode highly conductive and mechanically robust, thus maintaining its initial capacity even with extended cycling. [ABSTRACT FROM AUTHOR]

The surface framework of LiCoO2 is modified through a surface treatment called phosphidation, which suppressed the unwanted phase transition occurring above 4.2 V. The surface instability of LiCoO2 toward organic electrolytes is simultaneously improved by changing its surface structure from an O2-based framework to a PO4-based framework that can protect against HF attack during cycling. Phosphidated LiCoO2 is successfully synthesized that showed greater stability in its bulk and surface structures. The phosphidated form enables faster Li+ diffusion and prevents irreversible phase transitions, especially when charged above 4.2 V, and consequently demonstrates excellent cycling performance and rate capabilities. The improved kinetics and stability resulting from phosphidation make LiCoO2 highly suitable as a high-voltage cathode material for use in lithium ion batteries. [ABSTRACT FROM AUTHOR]

For the purpose of reducing not only the consumption of natural resources, but also the environmental pollution from internal combustion engines, much effort has been dedicated to developing new energy storage systems (ESSs) and electric vehicles (EVs) powered by batteries. There are several stringent requirements, such as high power/energy density, good safety, and high reliability against external environmental abuse. For next-generation batteries to meet these requirements, the development of a new energy conversion system is crucial. Therefore, lithium-oxygen (lithium-O2) batteries have attracted intensive attention, due to their high theoretical energy density, compared with those of gasoline engines. However, present lithium-O2 batteries exhibit low round-trip efficiency and cyclic degradation, thus preventing their commercialization as next-generation power sources. This drawback may be attributed to the high thermodynamic stability of discharge products and their intrinsic insulating character, leading to the surge of polarization in oxygen reduction reactions/oxygen evolution reactions (ORRs/OERs). To alleviate cyclic degradation and improve round-trip efficiency, it has been reported that the polarization can be reduced by adopting adequate cathode catalysts, based on their surface structures regulating oxygen adsorption. Here we provide and discuss several design strategies for tailoring catalytic materials from a structural and morphological viewpoint, as well as their effect on discharge products. [ABSTRACT FROM AUTHOR]

The CASTEP ab initio calculation was coupled with TEM-EELS analysis to elucidate the nanostructural change of Si during Li+ insertion. Even if the previous research alleged that Si should change into amorphous lithium suicide in the initial stage of Li+ insertion, our observation let us know that during the electrochemical Li+ insertion, Si transforms into LiSi with medium-range ordering, and finally into a well-known crystalline phase, Li15Si4. Because some macroscopic observation (such as the volume expansion and charge-discharge behaviors) is almost in accordance with the microstructural analysis for this clarified phase transition, we can say that the correlation between experimental edge spectra and theoretical calculation based on density functional theory is very meaningful way to clarify the phase transition of materials. [ABSTRACT FROM AUTHOR]

Abstract: LiCo1− x Fe x PO4/C composites with various amounts of Fe (x =0, 0.05 and 0.1) were synthesized by vibrant type ball-milling coupled with microwave heating to investigate the role of doped Fe2+ in LiCo1− x Fe x PO4/C composites. The initial charge–discharge curves and cyclic voltammetry profiles of LiCo1− x Fe x PO4/C composites apparently featured an improved kinetic property compared to LiCoPO4. It was observed that the initial discharge capacity (120mAhg−1) of LiCo0.95Fe0.05PO4 is higher than that (108mAhg−1) of LiCoPO4 and the difference between the oxidation–reduction peaks is getting smaller with the increase of Fe doping. The electrochemical improvement in LiCo1− x Fe x PO4/C composites could be attributed to the enhanced Li+ diffusivity induced by the enlargement of 1D channel in polyanion structure of LiCoPO4. [Copyright &y& Elsevier]

Abstract: The influence of substrate morphology and ageing on the charge–discharge performance of a Sn–Ni alloy anode electrodeposited on a Cu substrate are examined. The Sn–Ni alloy (Sn 82at.%–Ni 18at.% anode) shows a high capacity of around 480mAhg−1 up to 12 cycles, but its capacity rapidly fades with cycling. The initial capacity and the cyclic properties of the alloy electrode are significantly improved when the surface morphology of the Cu substrate is changed from smooth-type to nodule-type. Optimized ageing treatment leads to further enhancement in the charge–discharge performance of the anode. The increase in the capacity and better cyclic properties are attributed to stronger adhesion between the Si–Ni anode and the Cu substrate. This is induced by inter-locking of the nodule-type Cu substrate and a buffering effect of Cu–Sn intermetallic compounds formed during ageing. [Copyright &y& Elsevier]

Abstract: Si–carbon composite prepared by mechanical milling showed good cyclic capacity retention until the utilization of Si was limited below 32%, whereas the retention of a Si–Cu–carbon composite obtained by two-step mechanical milling was maintained up to 55%. A comparison between the first charge curves of a Si–carbon composite and a Si–Cu–carbon composite at 0.1C, indicated that the Si–carbon composite underwent a much higher polarization than the Si–Cu–carbon composite, leading to the difference in utilization of Si. Impedance spectroscopy let us confirm that the electrochemical alloying between Si and Li+ is much easier in the Si–Cu–carbon composite than in the Si–carbon composite. The superiority of the Si–Cu–carbon composite in kinetics enabled its electrode to have a more homogeneous Li+ concentration after Li+ insertion. Because this phenomenon means that the Si–Cu–carbon composite has a more homogeneous volume expansion than the Si–carbon composite, the disparity in electrochemical performance between the Si–carbon composite and the Si–Cu–carbon composite was attributed to enhanced Li+ transfer in the Si–Cu–carbon composite. [Copyright &y& Elsevier]

Na0.33V2O5‐type metal vanadates generally show better cycling stability than α‐V2O5 as a cathode in Li‐ion batteries, because they contain enough crystallographic voids that allow for lithium intercalation without significant structural deformation, but metal leaching upon cycling deteriorates their capacity retention. Here a new barium vanadate Ba0.16(1)V2O5 is reported that does not undergo Ba leaching during cycling and shows a great promise for fast Li intercalation. Sr0.15(1)V2O5 is isostructural to Na0.33V2O5 (space group C2/m), while Ba0.16(1)V2O5 adopts a new structure (space group P21/c), a derivative of Na0.33V2O5. The framework of Ba0.16(1)V2O5 consists of edge‐shared VO6 octahedral layers and the VO5 pyramidal bridge, generating unidirectional tunnels. Unlike the in‐plane arrangement of atoms in Sr0.15(1)V2O5, the nonplanar arrangement in Ba0.16(1)V2O5 makes the host framework more flexible and creates larger voids for Ba. Compared with the combination of displacement and intercalation mechanisms in the Sr0.15(1)V2O5 cathode, Li intercalation looks dominant in the Ba0.16(1)V2O5 cathode due to its increased flexibility. Hence, Ba0.16(1)V2O5 exhibits improved cycling stability compared to Sr0.15(1)V2O5, suggesting that lower symmetry leads to higher cyclic stability in the V2O5‐related compounds. This study illustrates how guest cations can tune the structural symmetry to modulate the reaction mechanism of electrode materials toward superior performances. [ABSTRACT FROM AUTHOR]

Electrocatalysis An effective method to optimize oxygen electrocatalyst and Li‐O2 electrode performance of nanostructured manganese oxide involves controlling the bonding nature with SeO42− anchoring, as shown by Y.‐M. Kang, S.‐J. Hwang, et al. in their Communication on page 15984 ff. [ABSTRACT FROM AUTHOR]

Controlling the bulk and surface structure of metal oxide nanostructures is crucial to obtain superior electronic and electrochemical properties. However, the synthetic or post-treatment techniques for preparing such structures, especially those with complex configurations, still remains a challenge. Herein, we report a completely novel approach—an amorphous carbon coating on the surface coupled with a controlled metal oxidation state in the bulk—via a simple glucose treatment. The bulk and surface structures of iron oxides are controlled by the carbothermal reaction associated with the decomposition of glucose. These novel configurations of iron oxides possess an amorphous carbon layer and ferrous state with high electronic conductivity, which definitely enhances their electrochemical properties compared to pristine iron oxides. Our findings provide an effective solution for the synthesis of complex metal oxide nanostructures, which can pave the way to further expand the electronic or electrochemical applications of metal oxides. [ABSTRACT FROM AUTHOR]

A hydroxide co-precipitation method is used to synthesize transition metal hydroxide (Ni 1/3 Co 1/3 Mn 1/3 (OH) 2 ), which is the precursor for layer-structured LiNi 1/3 Co 1/3 Mn 1/3 O 2 . The optimum pH range for the preparation of Ni 1/3 Co 1/3 Mn 1/3 (OH) 2 using a continuous stirred-tank reactor is calculated by taking into account the underlying chemical equilibria. The entire growth process of the Ni 1/3 Co 1/3 Mn 1/3 (OH) 2 particles is investigated by monitoring the structure, morphology, particle size distribution, and tap density as a function of the reaction time. The results confirm that the co-precipitation reaction in the presence of ammonia started with the formation of crystal nuclei and (001) plane dominated nanosheets. The reaction ended with spherical and dense hydroxide precursors. The crystal growth mechanism was interpreted during the co-precipitation process, which involved the quick nucleation of primary particles followed by its slow aggregation and crystallization. The electrochemical properties of the final cathode materials with different morphologies are also studied. The results show that the electrochemical performances of the final LiNi 1/3 Co 1/3 Mn 1/3 O 2 are strongly affected by the hierarchical structure of Ni 1/3 Co 1/3 Mn 1/3 (OH) 2 . [ABSTRACT FROM AUTHOR]

Silicon (Si) has attracted much attention as a promising anode material for Li ion battery because of its high theoretical specific capacity and low working potential. However, Si has shown poor cycling behavior and reversibility, which result from its huge volume change and the following pulverization. In this study, an electrospinning method was adopted to synthesize Pitch-incorporated into Si/Carbon nanofibers (Si/Pitch CNFs), which has high crystalline carbon network compared to other Si/Carbon nanofibers without the carbon matrix obtained from the decomposition of pitch. We demonstrated that this high crystalline carbon network in the form of nanofiber has two kinds of merits: it not only reduced the diffusion length for Li ion transport thanks to its 1D morphology but also helped to tolerate high strain of Si and maintain electron transport throughout the entire electrode. As a result, Si/Pitch CNFs showed a greatly enhanced kinetic performance, even at 10C, thus showing its feasibility as a high-power material for future applications like electric vehicles (EV) and energy storage systems (ESS). [ABSTRACT FROM AUTHOR]

Petroleum asphalt based ultrathin hollow carbon shell (PACS) was prepared via a facile template-assisted method. As the anode material of lithium-ion batteries, PACS exhibits high reversible capacity, excellent cycling stability, and superior rate performance. A high reversible capacity of 334 mA h g −1 and 90% kept of the theoretical capacity can still be maintained in PACS at a current density of 1 A g −1 even after 1000 cycles, which is ascribed to the unique hollow structure, ultrathin porous shells (4.7 nm), the doped nitrogen atoms, and high level of disorder degree. Meanwhile, the present study paves a milestone for the high-valued utilization of petroleum asphalt and other kinds of heavy oil. [ABSTRACT FROM AUTHOR]

Highlights: [•] LiNi0.5Mn1.5O4 (LNMO) coated with layer of Li2O–2B2O3 (LBO)–glass was synthesized. [•] The LBO coating layer effectively suppressed the growth of an organic CEI layer. [•] The LBO coated LNMO had stabilized the cell impedance during cycling. [•] These changes greatly enhance cyclic retention of LNMO at high temperature. [Copyright &y& Elsevier]

Wereport a new discovery for enhancing Li ion transport at thesurface of Li3V2(PO4)3particles through superionic pathways built along an ionic conductor.The Li3V1.95Zr0.05(PO4)3/C composite has much higher initial discharge capacity,superior rate-capability, and excellent cycling performance when comparedwith pristine Li3V2(PO4)3/C. This is partly due to the occupation of vanadium sites by Zr4+ions in the Li3V2(PO4)3host crystals and facile Li ion migration through a LiZr2(PO4)3-like secondary phase that formson the surface of the Li3V1.95Zr0.05(PO4)3particles. Our findings about high Liion transport and structure stabilization induced by Zr incorporationsuggests a breakthrough strategy for achieving high-power Li rechargeablebatteries using NASICON-structured cathode materials in combinationwith nanoarchitecture tailoring. [ABSTRACT FROM AUTHOR]

Abstract: Silicon sub-oxides, SiO x (0 < x < 1) can be regarded as a promising anode material for high performance Li-ion batteries for its unique electrochemical reactions to Li. We designed and synthesized the columnar-shape SiO x nanoconifers (0.9 < x < 1), directly self-organized on metallic NiSi x nanowires (NWs) for its anodic use in Li rechargeable batteries. The half-cell incorporating SiO x nanoconifers/NiSi x NW heterostructures displays good cyclic retention and rate capability, which are attributed to the structural and kinetic stability of the hierarchical SiO x nanoconifers rigidly supported by metallic NiSi x core NWs by providing a reversible electrochemical route with a lower activation energy. [Copyright &y& Elsevier]

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). [Copyright &y& Elsevier]