Structural and Electrochemical Characterization of Li2MnSiO4 Cathode Material

The candidate cathode material Li2MnSiO4 for lithium-ion cells was synthesized by an all-acetate precursor sol/gel method under a reducing atmosphere at 600, 700, and 800 degrees C. The material prepared at 700 degrees C was a pure phase and had the structural order of Li3PO4 orthorhombic (S.G. Pmn2(1)) phase. The temperature dependence of the molar magnetic Susceptibility of Li2MnSiO4 was found to be consistent with an antiferromagnetic material with a Neel temperature of 12 K. The calculated effective moment confirmed that the observed magnetic behavior involves Mn2+ ions in a high spin configuration in tetrahedral sites. Scanning electron microscopy of Li2MnSiO4 showed large aggregates (10 to 50 mu m) composed of nanosized particles (100-200 nm). The as-prepared material was almost electrochemically inactive despite the presence of 15 wt % carbon additive. The material was treated by carbon coating using cellulose carbon source precursor and particle size reduction using high-energy ball milling. In coin-cell tests, the carbon-coated and ball-milled materials yielded charge capacities of 190 and 172 mAh/g, respectively, under a current density of 10 mA/g. At present, the cationic mixing between Li+ and Mn2+ ions in their mutual crystallographic sites is the main impediment to the achievement of the full theoretical capacity of Li2MnSiO4 (333 mAh/g).