Novel anode material for Li ion secondary battery by wet deposition process.

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From our studies on the high energy density Ni38-Sn62 alloy anodes for Li ion batteries until March 2004, we have clarified that the solid phase reaction of Ni_3Sn_4 phase in the electrode and Li shows good reversibility, therefore enabling its high energy density which exceeds that of conventional anode materials. This year, we have focused on the evaluation of a long term charge - discharge cycling of the electrode, and the accompanying changes in its electrode property.As a result, we have clarified that the electroplated Ni_<38>Sn_<62> alloy thin film shows good anode property that realizes more than 150 cycles with a high capacity of 500 mA/g. Regarding the changes in the crystal structures of the electrode, it has been indicated that with the repeated cycling of the alloy thin film and Li, the periodicity of the crystal becomes lower. Particularly, we have shown that after repeated cycling, some unreacted low crystalline LiSn alloy phases starts to be detected after discharge. Fr … More om the observations on the surface morphology changes, the occlusions of the pores observed after the initial cycles in our previous studies were confirmed. To investigate the reasons for the good cyclability obtained regardless of such changes in the structure and morphology, we measured the diffusion coefficient of Li in the electrode. No large changes were seen for the first 3 cycles, and the value was indicated to be approximately 6.43 x 10^<-10> cm^2 s^<-1>. Even after 10 cycling, the increase of the value was only to 8.04 x 10^<-10> cm^2 s^<-1>, and it was shown that the appropriate diffiusivity of Li in the solid is maintained with cycling. Studies on the annealing of the electrode have shown that the grain boundary of the electrode may be accounting as the diffusion pathways for Li.We believe that our studies that have been conducted with scope on the use of alloy anode materials in long-term use will make important contributions to the indications for the establishment of design manuals for Sn-based anode materials. Less