Preparation and electrochemical characterization of doped spinel LiMn1.88Ge0.1Li0.02O4 cathode material

Abstract

LiMn1.88Ge0.1Li0.02O4 cathode material is investigated with the aim of improving the electrochemical performance of spinel LiMn2O4 by substituting stoichiometric Ge and Li into Mn sites. While the formal oxidation number of Mn ions is still + 3.5 after doping, it is expected that the difference in electronegativity between Mn and Ge induces a local change in the bonding nature of Mn-O that in turn increases the effective oxidation state of Mn ions. The increase in the effective oxidation state results in a reduction of Mn dissolution, thus providing structural stability and cyclability. The bulk-synthesized LiMn1.88Ge0.1Li0.02O4 exhibits capacity retention of 63% of the first cycle capacity (124 mAh/g) after 100 cycles at 1C while LiMn2O4 exhibits only 44% retention.