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LiFePO 4 is one of the most important cathode materials for Li-ion batteries studied over the past few years. Impressive work has revealed important structural aspects and the correlations between structure and composition and electrochemical properties. Fewer efforts have been devoted to the surface chemical aspects of this material. We report herein on a study of the stability aspects of LiFePO 4 at two temperatures, 30 and 60°C. Three types of solutions were used based on EC-DMC 1:1 solvent mixtures those involving no acidic contamination ͑using LiClO 4 as the electrolyte͒, those contaminated by HF͑using LiPF 6 as the Li salt͒, and LiPF 6 solutions deliberately contaminated with H 2 O. Iron dissolution from LiFePO 4 in these electrolytes, as well as the electrochemical response as a function of solution composition and aging, were studied at the two temperatures. The effect of additives that neutralize acidic species in solution was also studied. In general, LiFePO 4 develops a unique surface chemistry. Highly stable behavior of LiFePO 4 cathodes, without any substantial iron dissolution at elevated temperatures, was observed and measured when the solution contains no acidic or protic contaminants.LiFePO 4 olivine is one of the most important cathode materials for Li-ion batteries studied in recent years. Olivine compounds are promising candidates for replacing standard LiCoO 2 cathodes that are currently used in commercial Li-ion batteries because of the high reversibility of their lithiation process, their relative low cost as compared to most other relevant cathode materials for Li-ion batteries, and because of their environmental friendliness. 1 LiFePO 4 has a theoretical capacity of 170 mAh/g and a redox potential around 3.5 V vs Li/Li + . 2 This provides an energy density comparable to compounds such as LiCoO 2 , 3 LiNiO 2 , 3 and LiMn 2 O 4 . 3 Although compounds such as LiCoO 2 have higher theoretical capacities, the full intercalation range is not accessible due to limitations imposed by structural changes or detrimental interaction with the electrolyte at high charging potentials. Li x FePO 4 , on the other hand, can undergo complete lithiation-delithiation cycling without any significant changes in the material's structure, which leads to the impressive stability of the capacity of Li x FePO 4 cathodes during prolonged cycling. 4 A major disadvantage of this material is its low intrinsic electrical conductivity. 1,2,4 However many research groups have presented convincing ways to overcome the intrinsic low electrical conductivity of LiFePO 4 , thus demonstrating a fast rate performance of Li x FePO 4 cathodes in Li-ion battery systems. 5-10 While all of the above has shown that Li x FePO 4 -based cathodes demonstrate promising electrochemical characteristics at room temperature, there is evidence that at elevated temperatures the olivine undergoes iron dissolution. 11,12 This is highly important and could be detrimental to its commercialization. Transition metal dissolution under certain conditions ...

V 2 O 3 powder is frequently used in conductive polymer composites and in catalysts. [1][2][3] In addition, a variety of VO x and MVO x (e.g., V 2 O 5 , V 6 O 13 , CaV 3 O 7 ) compounds have been suggested and tested as cathode materials for rechargeable Li batteries. [4][5][6][7][8][9][10] These vanadium oxide-based compounds are still among the most intensively studied cathode materials for rechargeable Li batteries. It should be noted that studies related to Li-battery materials are of high interest in materials science. [11][12][13][14] The synthesis of spherical V 2 O 3 nanoparticles by the reductive pyrolysis of ammonium oxovanadium(IV) carbonato hydroxide has been reported. [15] Nanocrystalline V 2 O 3 was synthesized by the thermal decomposition of divanadium pentoxide by Su and Schlogl. [16] In this report, we present results of the RAPET dissociation (RAPET: reaction under autogenic pressure at elevated temperatures) of VO(OC 2 H 5 ) 3 , which produces carbon-coated vanadium oxide (CCVO). This novel method, using only a metallic alkoxide precursor in the absence of a catalyst or a solvent, is a one-step process yielding a core/shell morphology. Further oxidation of the CCVO produces carbon-coated V 2 O 5 (CCV 2 O 5 ) nanoparticles. In the present study, we explore to what extent the carbon shell enables electrical contact among the CCVO particles, while not interfering with a smooth Li intercalation with the V 2 O 3 particles. It is interesting to discover whether these active materials can be used in composite electrodes for Li batteries, as they would possibly reduce the need for significant addition of carbonaceous materials, in order to maintain electrical contact among the particles and between the active mass and the current collector. Usually, composite cathodes based on Li-intercalating transition-metal oxides or sulfides have to include additional carbon particles (5-15 wt %) [17,18] in order to achieve electrical contact between the active mass and the current collector (and among the particles themselves). As the particles are smaller (which may be very important for achieving high rates), critical problems may arise regarding the electrical properties of the composite electrodes, because the carbon particles may not be in direct contact with all of the very small particles of the active mass. Hence, the use of an active mass where each particle is coated by a thin (conductive) carbon layer that is permeable to Li ions may be very advantageous for Li-battery application. This paper is the first report on the use of CCVO as the active mass in composite cathodes for rechargeable Li batteries. The carbon and hydrogen content in the CCVO samples was determined by elemental analysis measurements. The calculated elemental percentage of carbon in the precursor, VO(OC 2 H 5 ) 3 , was 44.3 %, while the elemental percentage of hydrogen was 9.6 %. The measured percentage of carbon in the carbon-coated V 2 O 3 (CCV 2 O 3 ) product is usually 30 %, while the percentage of hydrogen is only 0.3 %. Hence, it...

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Carbon-coated V 2 O 5 nanoparticles ͑CCV 2 O 5 ͒ are good candidates as cathodic materials for rechargeable Li batteries. These nanoparticles were prepared by burning off carbon-coated V 2 O 3 nanoparticles in air ͑around 400°C͒. The V 2 O 3 nanoparticles were prepared by a simple, single-stage reaction under autogenic pressure. Variations in the conditions of the burning process determine the properties of the carbon coating ͑e.g., thickness, weight % of carbon͒. Several types of electrodes were investigated. These included composite electrodes comprising different batches of CCV 2 O 5 , additional carbon particles and PVdF binder, composite electrodes comprising micrometric size, commercial V 2 O 5 as the active mass, and electrodes in which the CCV 2 O 5 or micronic size V 2 O 5 particles were embedded in aluminum foils without using any carbon additive or binder. The electrochemical response in terms of capacity, cyclability, and rates ͑up to 5C͒ at different potential ranges ͑narrow 3-4 V and wide 2-4 V domains, vs Li/Li + ͒ was investigated in LiClO 4 1 M and in LiPF 6 1 M ethylene carbonate/dimethyl carbonate solutions by standard electrochemical techniques, including chronopotentiometry, cyclic voltammetry, and impedance spectroscopy. The behavior of the CCV 2 O 5 electrodes ͑nanoparticles͒ was compared to that of electrodes comprising micronic size V 2 O 5 particles. In general, CCV 2 O 5 electrodes demonstrated a higher capacity, much better rate capability, and very good stability upon cycling and aging at elevated temperatures compared to electrodes comprising microparticles of V 2 O 5 . In situ and ex situ atomic force microscopy imaging was used for the morphological analysis of these electrodes.