Battery-active monoclinic Li2MnSiO4 synthesized via temperature programmed reaction

Abstract

Abstract Hitherto, synthesis of a single-phase Li2MnSiO4 has been perceived to be a challenging task owing to the formation energy possessed by different polymorphs is very close. In this context, we report a facile synthesis protocol by optimizing the synthesis conditions such as gas atmosphere, annealing temperature and time to obtain a phase pure crystalline monoclinic phase of Li2MnSiO4 (m-Li2MnSiO4). During the process, to avoid the formation of mixed phases of Li2MnSiO4, the dried precursor substance is subjected to following heat treatment conditions: (1) dried precursor is heated at ambient atmosphere followed by annealing; (2) maintaining a controlled flow of either O2 gas purging adapting a temperature-programmed reaction (TPR). Analysis of X-ray powder patterns reveal that during the process of heat treatment, the controlled purging of O2 is imperative to achieve battery-active monoclinic Li2MnSiO4. Perhaps the formation of m-Li2MnSiO4 occurs during the decomposition of starting material at ∼ 300 °C itself as evident from TGA/DSC analysis further annealing is essential to improve its crystallinity. The controlled flow of O2 purging results in mono dispersion of nanoparticles (TEM analysis) whereas the conventional method of annealing leads to the agglomeration of nanoparticles. Interestingly, m-Li2MnSiO4 product thus obtained exhibit mesoporosity irrespective of synthesis conditions employed. The superior electrochemical performance observed in m-Li2MnSiO4 prepared via temperature-programmed reaction (TPR) is attributed to its higher surface area, high pore volume and mono dispersion of nanoparticles. The degradation of capacity of m-Li2MnSiO4 when the lower voltage is extended to 2.5 V is owing to the formation Mn2O3.