The performance and safety of rechargeable batteries depend strongly on the materials used. Lithium insertion materials suitable for negative and positive insertion electrodes are reviewed. Future trends, such as alternative materials for achieving higher specific charges—the Figure shows a scheme for reversible lithium storage in a high specific charge carbonaceous material—are discussed.

The rate capability of various lithium-ion half-cells was investigated. Our study focuses on the performance of the carbon negative electrode, which is composed of TIMREX SFG synthetic graphite material of varying particle size distribution. All cells showed high discharge and comparatively low charge rate capability. Up to the 20 C rate, discharge capacity retention of more than 96% was found for SFG6. The rate capability of the half-cells is a function of both the particle size distribution of the graphite material and the preparation method of the electrode. A transport limitation model is proposed to explain the restrictions of the high current performance of graphite electrodes. The key parameters found to influence the performance of a graphite negative electrode were the loading, the thickness, and the porosity of the electrode.Lithium-ion batteries have attracted considerable scientific and technological attention for more than a decade. Being already broadly available for small portable electronic devices like mobile phones, laptop computers, video camcorders, and personal digital assistants, the field of commercial applications of lithium-ion batteries is gradually extending to large battery systems. A particular field of growing importance is the transportation sector, where the lithium-ion battery technology is envisaged for traction batteries in overall electric vehicles and for onboard ͑42 V͒ batteries in conventional, hybrid, and fuel cell vehicles. For these purposes, the vehicle battery must deliver sufficient power. At the same time, the automotive industry imposes good cycle and calendar lifetime 1,2 for the systems used with moderate material costs. Therefore, high-ratecapable and comparatively cheap electroactive materials are required for the development of high-power lithium-ion batteries. [3][4][5] Graphite materials with a high degree of graphitization based on synthetic or natural sources are attractive candidates for negative electrodes of lithium-ion batteries due to the relatively high theoretical specific reversible charge of 372 mAh/g. The electrochemical insertion of lithium into graphite leads to an intercalation compound with a chemical composition of LiC 6 . It was generally believed that graphite negative electrodes have only a moderate rate capability. 6,7 Slow kinetics 8,9 and a solid-state diffusion limitation during charge and discharge reactions were suggested as rationalities of why the graphite electrode does not deliver high currents. 10-12 Arora et al. 13 suggested that one of the most important parameters that limits the performance of lithium-ion batteries at high rates is the transport of lithium ions in the electrolyte. The transport of lithium ions in the solid phase takes place mainly within single particles, where diffusion lengths are much shorter than the thickness of the whole electrode. 13,14 However, recently we demonstrated that graphitebased electrodes support a much higher current density than believed before. 15 There are also other studies that could s...

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Lithium nickel manganese oxides, LiNi15Mn5O2÷5, (0 y 0.5) were prepared via a new solution technique. The corresponding mixed nickel manganese hydroxide precursors were synthesized in an oxidative coprecipitation method. Subsequent calcination in the presence of LiOH leads to crystalline products with a partially disordered layered-type cs-NaFeO2 structure. X-ray photoelectron spectroscopic analysis has indicated a strong enrichment of lithium at the surface. The electrochemical performance of these materials as positive electrodes in lithium-ion batteries was evaluated as a function of the calcination temperature and manganese content. A calcination temperature of 700°C leads to the best cycling stability. At this temperature, a sufficiently high degree of crystallinity was achieved, having a strong influence on the cycling stability of these "4 V" materials. The specific charge and cycling stability obtained for the solution-prepared pure lithium nickel oxide, LiNiO2, was low, but was significantly enhanced by replacing some nickel with manganese. With increasing manganese content, the specific charge increased to about 170 mAh g' for materials with a Ni:Mn ratio of about 1:1. Ex situ magnetic susceptibility measurements proved that during lithium deinsertion, the trivalent manganese is preferentially oxidized, and seems to be the more reactive redox center in these oxides. InfroductionCurrently interest is focused on the use of lithium transition metal oxides as positive electrode materials in rechargeable high energy density lithium-ion transfer battery systems.'-3 Elemental lithium has been substituted by some forms of carbon as the negative electrode material for safety reasons. Oxides containing highly mobile lithium function as the lithium source in these types of cells. Attention has focused on lithium metal oxides of the form LiMeO2 (Me = Co, Ni), which have the layered cz-NaFeO2 structure type. This structure is shown in Fig. 1 for LiNiO2. In a distorted cubic-closed-packed oxygen array, the lithium and the transition metal atoms are distributed in the octahedral interstitial sites in such a way that Me02 layers are formed. These layers consist of edge sharing [Me06] octahedra of trigonal symmetry. Between these layers, lithium resides in octahedral coordination sites [Li06], leading to alternating lithium and nickel layers along the [111] direction. In a crystal lattice of the space group R3m, oxy-

unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 139.80.123.44 Downloaded on 2015-01-03 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 139.80.123.44 Downloaded on 2015-01-03 to IP

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