A high-capacity cathode based on silicates material for advanced lithium batteries

Silicate materials have been proposed as alternative cathodes for Li-ion battery applications. A novel mixture of silicates, labelled Li₆MnSi₅, based on the molar ratio among the Li/Mn/Si precursors, with promising electrochemical properties as positive electrode material is synthesized through a solid-state reaction. The results indicate the proposed synthetic method as effective for preparation of nanostructured silicate powders with average particle diameter of 30 nm. Structural morphology of the samples was determined using X-ray powder diffraction (XRPD), XPS and FESEM analysis. A joint analysis by XRPD data and by density functional theory (DFT) identified LiHMn₄Si₅O₁₅, Li₂Mn₄Si₅O₁₅, Li₂Si₂O₅ and Li_0.125Mn_0.875SiO₄ as components of Li₆MnSi₅ mixture. The electrochemical performance of Li₆MnSi₅ was evaluated by charge/discharge testing at constant current mode. Li₆MnSi₅ discharge behaviour is characterized by high capacity value of 480 mA h g^?1, although such capacity fades gradually on cycling. Ex situ XPS studies carried out on the electrode in both full charged and discharged states pointed out that Li₂Si₂O₅ is decisive for achieving such high capacity. The discharge/charge plateau is most probably related to the change in the oxidation state of silicon at the surface of the silica material.