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

Abstract

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 ∼290 mA h g⁻¹ and ∼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.