Low temperature synthesis and electrode properties of Li_4Mn_5O_12 spinel oxides

摘要

The difficulties caused by Jahn-Teller distortion in the Li_4Mn_2O_4 spinel cathodes have motivated the development of alternate manganese oxides in which the problems of lattice distortion can be minimized. In this regard, the 3 V spinel cathode Li_4Mn_5O_12 has become an attractive candidate. But it is difficult to synthesize Li_4Mn_5O_12 without oxygen vacancies by conventional ceramic procedures as Mn~4+ tends to reduce to Mn~3+ at higher temperatures. We present in this paper the synthesis of nearly stoichiometric Li_4Mn_5O_12 by oxidizing Mn~2+ with lithium peroxide in aqueous solutions followed by firing at T<=500 deg C. Li_4Mn_5O_12 is unstable at higher temperatures and it disproportionates irreversibly to Li_1+xMn_2-xO_4 (x<0.33) and Li_2MnO_3 at T >500 deg C. The nearly stoichiometric Li_4Mn_5O_12 obtained by this procedure at T <+500 deg C exhibits capacity over 150 mAh/g in the range 3.3-2.3 V with <2