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 °C. The material prepared at 700 °C was a pure phase and had the structural order of Li ₃PO₄ orthorhombic (S.G. Pmn2₁) phase. The temperature dependence of the molar magnetic susceptibility of Li ₂MnSiO₄ was found to be consistent with an antiferromagnetic material with a Néel 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 μm) 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 ballmilled 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 Li ₂MnSiO₄ (333 mAh/g).