Charge/discharge characteristics of Jahn-Teller distorted nanostructured orthorhombic and monoclinic Li2MnSiO4 cathode materials

Li2MnSiO4 is a promising cathode material for lithium ion rechargeable batteries, however, synthesizing the desired crystallographic phase is challenging. We report the synthesis and electrochemical charge/discharge studies of carbon coated nanostructured Li2MnSiO4 in orthorhombic and monoclinic crystallographic phases. Li2MnSiO4 has been synthesized using solid state and sol-gel processes in bulk and nano-geometries without and with carbon coatings. The electrochemical performance of these Li2MnSiO4 samples was measured at a C/20 charge/discharge rate within 1.5-4.8 V voltage window. The first charge specific capacities are similar to 290 mA h g(-1) and similar to 180 mA h g(-1) for Li2MnSiO4 orthorhombic and monoclinic phase cathode materials. Charging-discharging of cells suggests that the degradation is lower for monoclinic Li2MnSiO4 cathode materials compared to that of orthorhombic Li2MnSiO4 cathode materials. This can be understood in terms of the relatively large electronic band gap and associated Jahn-Teller distortion observed in Li deficient Li2MnSiO4 materials, where Mn3+ intrinsically may lead to irreversible effective lithium insertion in distortion free starting Li2MnSiO4 materials for monoclinic materials.