Charge-discharge properties of LiCoO_2 electrodes modified by olivine-type compounds of LiMgPO_4 for lithium secondary batteries

摘要

Fine particles of Olivine-type LiMgPO_4 were prepared directly from a mixture of Li_2O, MgO, and P_2O_5 as starting materials using a mechanical milling technique at room temperature. LiMgPO_4 fine particles were investigated as surface modification materials of LiCoO_2 cathodes in lithium cells. Electrolytes of these cells were 1 mol dm~(-3) LiPF_6-ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3:7 volume ratio). LiMgPO_4-modified LiCoO_2 cathodes exhibited better charge-discharge performance for high charge cut-off potential of 4.5 V (vs. Li/Li~+) in lithium cells than that of LiCoO_2 cathode. Olivine-type LiMgPO_4 may inhibit oxidative decomposition of the electrolytes on LiCoO_2 particle surface without a crystal structure change of LiCoO_2 for high charge cut-off potentials.