Aqueous synthesis of Li2MnAO4/C (A = Si, Ge) as positive electrode active materials for lithium-ion batteries by acid–base reaction

Abstract

Polyanion-type positive electrode active materials such as LiFePO₄ are promising materials for high-safety lithium-ion batteries because of their highly stable anion structure. However, polyanion-based positive electrode active materials with high energy densities and good safety features are more desirable than LiFePO₄ at present. Among the polyanionic materials, Li₂MAO₄ (M = Mn, Fe; A = Si, Ge) systems have high theoretical capacities owing to their two-electron redox in many cases, and these materials are synthesized using sol–gel or solid-phase methods. This study provides a more simple and environmentally friendly method for the aqueous synthesis of Li₂MAO₄via an acid–base reaction. The material could be simultaneously composited with carbonized carbon. Li₂MnGe_xSi_1−xO₄/C (x = 0, 0.5, 1.0) and metal substituted Li₂Mn_0.8Fe_0.2SiO₄/C and Li₂Mn_0.8Fe_0.2GeO₄/C were successfully prepared, and showed discharge capacities of 195 mA h g⁻¹ and 178 mA h g⁻¹, respectively, at 0.13 mA cm⁻² and 25 °C. Thus, the developed method can be effectively used to fabricate polyanion-type positive electrode active materials.