Facile Electrochemical Activity of Monoclinic Li2MnSiO4 as Potential Cathode for Li-Ion Batteries

Synthesis of pure single-phase Li2MnSiO4 is challenging because of its rich polymorphism. Here, we demonstrate our success in preparing crystalline pure, battery-grade monoclinic phase Li2MnSiO4 (LMS) employing the temperature-programmed reaction technique. Systematic analysis of the electrochemical behavior of Li2MnSiO4 reveals its excellent battery activity in the monoclinic phase, with an initial discharge capacity of similar to 250 mAh g(-1) associated with the reversible intercalation of more than one Li+. The extraction of Li+ ions from Li2MnSiO4 corresponding to the oxidation of Mn2+ to Mn3+ then to Mn4+ appears as single oxidation/reduction peaks at 4.3/3.9 V in the first charge/discharge sweep of cyclic voltammogram within the potential window of 3.0-4.4 V. However, an extension of cathodic sweep to 2.5 V results in the appearance of an additional redox peak at 2.7/3.1 V vs Li+/Li-o due to the reversible phase transition of monoclinic phase into battery-active orthorhombic phase induced by Jahn-Teller-active Mn3+ as evident from ex situ X-ray diffractograms. Indeed, the reversible intercalation of Li+ into the newly formed phase accounts for the high specific capacity of LMS within the potential window of 2.5-4.4 V. The capacity loss in the repeated cycles of monoclinic Li2MnSiO4 is explained by the formation of Mn2O3 owing to the dissolution of Mn3+.