Each cell of a battery stores electrical energy as chemical energy in two electrodes, a reductant (anode) and an oxidant (cathode), separated by an electrolyte that transfers the ionic component of the chemical reaction inside the cell and forces the electronic component outside the battery. The output on discharge is an external electronic current I at a voltage V for a time Δt. The chemical reaction of a rechargeable battery must be reversible on the application of a charging I and V. Critical parameters of a rechargeable battery are safety, density of energy that can be stored at a specific power input and retrieved at a specific power output, cycle and shelf life, storage efficiency, and cost of fabrication. Conventional ambient-temperature rechargeable batteries have solid electrodes and a liquid electrolyte. The positive electrode (cathode) consists of a host framework into which the mobile (working) cation is inserted reversibly over a finite solid-solution range. The solid-solution range, which is reduced at higher current by the rate of transfer of the working ion across electrode/electrolyte interfaces and within a host, limits the amount of charge per electrode formula unit that can be transferred over the time Δt = Δt(I). Moreover, the difference between energies of the LUMO and the HOMO of the electrolyte, i.e., electrolyte window, determines the maximum voltage for a long shelf and cycle life. The maximum stable voltage with an aqueous electrolyte is 1.5 V; the Li-ion rechargeable battery uses an organic electrolyte with a larger window, which increase the density of stored energy for a given Δt. Anode or cathode electrochemical potentials outside the electrolyte window can increase V, but they require formation of a passivating surface layer that must be permeable to Li(+) and capable of adapting rapidly to the changing electrode surface area as the electrode changes volume during cycling. A passivating surface layer adds to the impedance of the Li(+) transfer across the electrode/electrolyte interface and lowers the cycle life of a battery cell. Moreover, formation of a passivation layer on the anode robs Li from the cathode irreversibly on an initial charge, further lowering the reversible Δt. These problems plus the cost of quality control of manufacturing plague development of Li-ion rechargeable batteries that can compete with the internal combustion engine for powering electric cars and that can provide the needed low-cost storage of electrical energy generated by renewable wind and/or solar energy. Chemists are contributing to incremental improvements of the conventional strategy by investigating and controlling electrode passivation layers, improving the rate of Li(+) transfer across electrode/electrolyte interfaces, identifying electrolytes with larger windows while retaining a Li(+) conductivity σ(Li) > 10(-3) S cm(-1), synthesizing electrode morphologies that reduce the size of the active particles while pinning them on current collectors of large surface area accessible by the electrolyte, lowering the cost of cell fabrication, designing displacement-reaction anodes of higher capacity that allow a safe, fast charge, and designing alternative cathode hosts. However, new strategies are needed for batteries that go beyond powering hand-held devices, such as using electrode hosts with two-electron redox centers; replacing the cathode hosts by materials that undergo displacement reactions (e.g. sulfur) by liquid cathodes that may contain flow-through redox molecules, or by catalysts for air cathodes; and developing a Li(+) solid electrolyte separator membrane that allows an organic and aqueous liquid electrolyte on the anode and cathode sides, respectively. Opportunities exist for the chemist to bring together oxide and polymer or graphene chemistry in imaginative morphologies.

Electrodes composed of silicon nanoparticles (SiNP) were prepared by slurry casting and then electrochemically tested in a fluoroethylene carbonate (FEC)-based electrolyte. The capacity retention after cycling was significantly improved compared to electrodes cycled in a traditional ethylene carbonate (EC)-based electrolyte.

Li-air batteries are potentially viable ultrahigh energy density chemical power sources, which could potentially offer specific energies up to similar to 3000 Wh kg(-1) being rechargeable. The modern state of art and the challenges in the field of Li-air batteries are considered. Although their implementation holds the greatest promise in a number of applications ranging from portable electronics to electric vehicles, there are also impressive challenges in development of cathode materials and electrolyte systems of these batteries. (C) 2010 Elsevier B.V.

N-Methyl-(n-butyl) pyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI), a kind of ionic liquid, is used as the additive in the electrolyte of Li-S battery. The changing of viscosity and conductivity of the electrolyte with different content of PYR14TFSI addition is tested. And the electrochemical impedance, the cycle performance and the columbic efficiency of the Li-S battery with different content of PYR14TFSI additive in the electrolyte are also tested. The results show that the addition of PYR14TFSI can not only inhibit the dissolution of lithium polysulfides (Li2Sx), but also decrease the migration rate of polysulfides ions in the electrolyte. Therefore, shuttle phenomenon in the lithium-sulfur battery is suppressed effectively with the addition of PYR14TFSI. Consequently, a coulombic efficiency nearing 100% and long cycling stability are achieved. (C) 2013 Elsevier B.V.

In this paper we report the electrochemical characteristics of a novel cathode material Li2CoPO4F prepared by solid-state reactions The solid-state reaction mechanism involved in synthesizing the Li2CoPO4F also is analyzed in this paper When cycled between 2 0 V and 5 0 V during cyclic voltammetry measurements the Li2CoPO4F samples present one fully reversible anodic reaction at 481 V When cycled between 2 0 V and 5 5V peaks occurring at 481 V and 51 V in the first anodic scan evolved to one broad oxidative mound-like pattern in subsequent cycles Correspondingly the X-ray diffraction (XRD) pattern of the Li2CoPO4F electrode discharged from 5 5V to 2 0 v is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5 0V to 2 0V This difference may correspond to a structural relaxation that appears above 5V In the constant current cycling measurements the Li2CoPO4F samples exhibited a capacity as high as 109 mAh g(-1) and maintained a good cyclability between 2 0 V and 5 5V vs Li/Li+ XRD measurements confirmed that the discharged state is Li2CoPO4F Combining these XRD results and electrochemical data proved that up to 1 mol l i(+) is extractable when charged to 5 5 V Published by Elsevier B V

Abstract

The Li intercalation potential of LiMPO₄ and LiMSiO₄ compounds with M = Fe, Mn, Co and Ni is computed with the GGA + U method. It is found that this approach is considerably more accurate than standard LDA or GGA methods. The calculated potentials for LiFePO₄, LiMnPO₄ and LiCoPO₄ agree to within 0.1 V with experimental results. The LiNiPO₄ potential is predicted to be above 5 V. The potentials of the silicate materials are all found to be rather high, but LiFeSiO₄ and LiCoSiO₄ have negligible volume change upon Li extraction.

Abstract

This study demonstrates that proper SEI layer on graphite anode is essential in LiNi_0.5Mn_1.5O₄(LNMO)/graphite 5 V lithium-ion batteries. Succinic anhydride (SA) and 1,3-propane sultone (PS) were found to greatly extend cycle life and suppress swelling behavior of LNMO/graphite cells. The benefits of SA and PS were ascribed not only to the stable SEI layer they form on graphite but also to their stability toward the oxidation at high voltage. Using 1 M LiPF₆ EC/EMC (1/2, v/v) solutions with SA and PS, LNMO/graphite Al-laminated pouch cell with nominal capacity of 600 mA h exhibited about 80% capacity retention after 100 cycles. This is the first report on the successful LNMO/graphite 5 V LIB to our best knowledge.

The effect of fluorinated ethylene carbonate (FEC) as a cosolvent in alkyl carbonates/LiPF6 on the cycling performance of high-voltage (5 V) cathodes for Li-ion batteries was investigated using electrochemical tools, X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HRSEM). An excellent cycling stability of LiCoPO4/Li, LiNi0.5Mn1.5O4/Si, and LiCoPO4/Si cells and a reasonable cycling of LiCoPO4/Si cells was achieved by replacing the commonly used cosolvent ethylene carbonate (EC) by FEC in electrolyte solutions for high-voltage Li-ion batteries. The roles of FEC in the improvement of the cycling performance of high-voltage Li-ion cells and of surface chemistry on the cathode are discussed.

1/3Co_1/3Mn_1/3O₂/graphite pouch batteries cycled under high voltage. Mixing 0.5 wt % EDPN into the electrolyte greatly improved the capacity retention, from 32.5% to 83.9%, of cells cycled for 100 times in the range 3.0-4.5 V with a rate of 1C. The high rate performance (3C and 5C) was also improved, while the cycle performance was similar to that of the cell without EDPN when cycled between 3.0 and 4.2 V. Further evidence of a stable protective interphase film can be formed on the LiNi_1/3Co_1/3Mn_1/3O₂ electrode surface due to the presence of EDPN in the electrolyte. This process effectively suppresses the oxidative decomposition of electrolyte and the growth in the charge-transfer resistance of the LiNi_1/3Co_1/3Mn_1/3O₂ electrode and greatly improves the high-voltage electrochemical properties for the cells. In contrast, EDPN has no positive effect on the cyclic performance of the LiNi_0.5Co_0.2Mn_0.3O₂-based cell under high operating voltage.]]>

This paper presents an overview of the various types of lithium salts used to conduct Li(+) ions in electrolyte solutions for lithium rechargeable batteries. More emphasis is paid towards lithium salts and their ionic conductivity in conventional solutions, solid-electrolyte interface (SEI) formation towards carbonaceous anodes and the effect of anions on the aluminium current collector. The physicochemical and functional parameters relevant to electrochemical properties, that is, electrochemical stabilities, are also presented. The new types of lithium salts, such as the bis(oxalato)borate (LiBOB), oxalyldifluoroborate (LiODFB) and fluoroalkylphosphate (LiFAP), are described in detail with their appropriate synthesis procedures, possible decomposition mechanism for SEI formation and prospect of using them in future generation lithium-ion batteries. Finally, the state-of-the-art of the system is given and some interesting strategies for the future developments are illustrated.

Developing a stable and safe electrolyte that works at voltages as high as 5 V is a formidable challenge in present Li-ion-battery research because such high voltages are beyond the electrochemical stability of the conventional carbonate-based solvents available. In the past few years, extensive efforts have been carried out by the research community toward the exploration of high-voltage electrolytes. In this review, recent progress in the study of several promising high-voltage electrolyte systems, as well as their recipes, electrochemical performance, electrode compatibility, and characterization methods, are summarized and reviewed. These new electrolyte systems include high-voltage film-forming additives and new solvents, such as sulfones, ionic liquids, nitriles, and fluorinated carbonates. It appears to be very difficult to find a good high-voltage (∼5 V) electrolyte with a single-component solvent at the present stage. Using mixed fluorinated-carbonate solvents and additives are two realistic solutions for practical applications in the near term, while sulfones, nitriles, ionic liquids and solid-state electrolyte/polymer electrolytes are promising candidates for the next generation of high-voltage electrolyte systems.

The electrochemical oxidative stability of solvent molecules used for lithium ion battery, ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate in the forms of simple molecule and coordination with anion PF(6)(-), is compared by using density functional theory at the level of B3LYP/6-311++G (d, p) in gas phase. EC is found to be the most stable against oxidation in its simple molecule. However, due to its highest dielectric constant among all the solvent molecules, EC coordinates with PF(6)(-) most strongly and reaches cathode most easily, resulting in its preferential oxidation on cathode. Detailed oxidative decomposition mechanism of EC is investigated using the same level. Radical cation EC(*+) is generated after one electron oxidation reaction of EC and there are five possible pathways for the decomposition of EC(*+) forming CO(2), CO, and various radical cations. The formation of CO is more difficult than CO(2) during the initial decomposition of EC(*+) due to the high activation energy. The radical cations are reduced and terminated by gaining one electron from anode or solvent molecules, forming aldehyde and oligomers of alkyl carbonates including 2-methyl-1,3-dioxolane, 1,3,6-trioxocan-2-one, 1,4,6,9-tetraoxaspiro[4.4]nonane, and 1,4,6,8,11-pentaoxaspiro[4.6]undecan-7-one. The calculation in this paper gives a detailed explanation on the experimental findings that have been reported in literatures and clarifies the mechanism on the oxidative decomposition of EC.

xCo_yM_z]O₂（0 < x,y,z < 1,M＝Mn,缩写NMC；M＝Al,缩写NCA）}具有能量密度高、循环性能好、价格适中等优异的综合性能,是目前锂离子电池（LIBs）中最具应用前景的一类正极材料.随着纯电动汽车（EVs）及混合电动汽车（HEVs）的快速发展,人们对LIBs的能量密度、循环寿命以及安全性要求不断提高.然而,在传统电解液体系中,三元正极材料在高电压、高温下会发生剧烈的结构变化和界面副反应,给实际应用带来巨大挑战,尤其是高镍三元材料的循环寿命和安全性.其中,开发适配的电解液添加剂是提高锂离子电池电化学性能最经济有效的方法之一.从物质本征结构出发,综述了近5年来包括碳酸亚乙烯酯（VC）、氟代物、新型锂盐、含P、含B、含S、腈类等及其复合物作为电解液添加剂在NMC及NCA正极材料中的应用及作用机理,并进行总结与展望.]]>

High-capacity Li-rich layered composite oxide, xLi(2)MnO(3) center dot (1-x)LiMO2 (M = Mn, Ni, Co), is a promising candidate cathode material for high-energy electrochemical energy storage. Enabling the high-performance of high-voltage cathode relies on an electrolyte breakthrough and the solid electrolyte interface (SEI) stabilization. In this study, the 0.6Li(2)MnO(3) center dot 0.4LiNi(0.45)Co(0.25)Mn(0.3)O(2) (Li1.2Mn0.525Ni0.175Co0.1O2, LMNC) cathode is operated at 2.5-4.8 V with 5 wt% fluorinated linear carbonate, di-(2,2,2 trifluoroethyl) carbonate (DFDEC), as a high-voltage electrolyte additive, for the first time and applied to a high-energy lithium-ion battery. The cathode with DFDEC outperforms that in electrolyte only, delivering a high capacity of 250 mAhg(-1) with an excellent charge-discharge cycling stability at the rate of 0.2C. Upon the use of DFDEC, the cathode surface is effectively passivated by a stable SEI composed of DFDEC decomposition products, which inhibit a detrimental metal dissolution and structural cathode degradation. A full-cell based on the SEI-stabilized LMNC cathode and graphite anode successfully demonstrates doubled energy density (similar to 278 Whkg(-1)) compared to similar to 136 Whkg(-1) of a commercialized cell of graphite//LiCoO2 and an excellent cycling stability. (C) 2014 The Electrochemical Society.

Non-flammability of electrolyte and tolerance of cells against thermal abuse should be guaranteed for widespread applications of lithium-ion batteries (LIBs). As a strategy to improve thermal stability of LIBs, here, we report on nitrile-based molecular coverage on surface of cathode active materials to block or suppress thermally accelerated side reactions between electrode and electrolyte. Two different series of aliphatic nitriles were introduced as an additive into a carbonate-based electrolyte: di-nitriles (CN-[CH2]n-CN with n = 2, 5, and 10) and mono-nitriles (CH3-[CH2]m-CN with m = 2, 5, and 10). On the basis of the strong interaction between the electronegativity of nitrile functional groups and the electropositivity of cobalt in LiCoO2 cathode, aliphatic mono- and di-nitrile molecules improved the thermal stability of lithium ion cells by efficiently protecting the surface of LiCoO2. Three factors, the surface coverage θ, the steric hindrance of aliphatic moiety within nitrile molecule, and the chain polarity, mainly affect thermal tolerance as well as cell performances at elevated temperature.

Further development of high-voltage lithium-ion batteries requires electrolytes with electrochemical windows greater than 5 V. Sulfone-based electrolytes are promising for such a purpose. Here we compute the electrochemical windows for experimentally tested sulfone electrolytes by different levels of theory in combination with various solvation models. The MP2 method combined with the polarizable continuum model is shown to be the most accurate method to predict oxidation potentials of sulfone-based electrolytes with mean deviation less than 0.29 V. Mulliken charge analysis shows that the oxidation happens on the sulfone group for ethylmethyl sulfone and tetramethylene sulfone, and on the ether group for ether functionalized sulfones. Large electrochemical windows of sulfone-based electrolytes are mainly contributed by the sulfone group in the molecules which helps lower the HOMO level. This study can help understand the voltage limits imposed by the sulfone-based electrolytes and aid in designing new electrolytes with greater electrochemical windows.

We report, from a theoretical point of view, the first comparative study between the highly water-stable hydroxamate and the widely used carboxylate, in addition to the robust phosphate anchors. Theoretical calculations reveal that hydroxamate would be better for photoabsorption. A quantum dynamics description of the interfacial electron transfer (IET), including the underlying nuclear motion effect, is presented. We find that both hydroxamate and carboxylate would have efficient IET character; for phosphate the injection time is significantly longer (several hundred femtoseconds). We also verified that the symmetry of the geometry of the anchoring group plays important roles in the electronic charge delocalization. We conclude that hydroxamate can be a promising anchoring group, as compared to carboxylate and phosphate, due to its better photoabsorption and comparable IET time scale as well as the experimental advantage of water stability. We expect the implications of these findings to be relevant for the design of more efficient anchoring groups for dye-sensitized solar cell (DSSC) application.

N,N'-4,4'-diphenylmethane-bismaleimide (BMI) is attempted to enhance the high-voltage performance for lithium-ion batteries. When 0.1% (m/v) BMI is added into the control electrolyte, the high-voltage cycling performance of LiCoO2/Li cells is improved evidently while charging the cell up to 4.5V rather than the conventional 4.2V. Analysis of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) demonstrate that an interface film forms on the cathode surface from BMI in electrolyte. AC impedance spectra and charge/discharge test were tested after incubation of the charged cell at 60 degrees C. Linear sweep voltammetry (LSV) is used to test the electrochemical stability window of the electrolyte with BMI addition. The results demonstrate that the improvement of high-voltage performance is attributed to the surface film on cathode. In addition, the BMI addition does not cause damage in conventional performance with 4.2 V electrochemical window. The BMI-containing electrolyte provides high-voltage cycling performance with 4.5V electrochemical window, making LiCoO2 battery a simple and promising system for applications with high energy density. (C) 2014 Elsevier Ltd.