Preparation of Cathode Active Materials for High Energy Density Lithium Secondary Battery and Their Characteristics for Batteries.

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As a cathode active materials for lithium secondary batteries, V_2O_5 and LiNiO_2 are the most promising materials among the candidates.1) Electrochemically prepared V_2O_5 (e-V_2O_5) from a VOSO_4 solution showed an intermediate crystal structure and electrochemical behavior between crystalline V_2O_5 (c-V_2O_5) and amorphous V_2O_5-P_2O_5 (a-V_2O_5-P_2O_5). V_2O_5 prepared by the ozone oxidation method (O_3-V_2O_5) showed almost the same characteristics as those of e-V_2O_5. The discharge capacities of e-and O_3-V_2O_5 are both about 250-260 mAh/g for ten cycles, when the cut-off voltage is 2.0 V.These values are higher than those for c-V_2O_5 and a-V_2O_5-P_2O_5. The chemical diffusion coefficient change of Li^+ in the cathode material (D) for four types of V_2O_5 was measured at various discharge stages by galvanostatic intremittent technique and AC technique. In the case of c-V_2O_5, D changed dramatically as discharge progressed. This behavior coincided with the literature and was supported by in situ XRD measurements. D of a -V_2O_5-P_2O_5 did not change so much, which suggests the structure is resistant to its destruction by Li^+ insertion. The change in D for e-and O_3-V_2O_5 is not very large compared to that of c-V_2O_5 till about x=0.8, after which the D values decreased.2) To increase the capacity and cycleability of LiNiO_2, Fe, Mg, and In were added to prepare LiFe_xNi_<1-x>O_2, LiMg_xNi_<1-x>O_2 and LiIn_xNi_<1-x>O_2. In the case of Fe and Mg addition, the capacity decreased, whereas in the case of In, the capacity of LiIn_<0.005>Ni_<0.995>O_2 increased to 168 mAh/g which is larger compared to 164 mAh/g for LiNiO_2 and cycleability was also improved. In seems to act as a structure stabilizer in LiNiO_2.