Enhanced Performance Induced by Phase Transition of Li2FeSiO4 upon Cycling at High Temperature

Owing to its low cost, thermal stability and theoretically high capacity, Li2FeSiO4 has been a promising cathode material for high-energy-density Li-ion (Li+) battery system. However, its poor rate performance and high voltage polarisation attributed to innately slow Li+ kinetics at room temperature, has fundamentally curbed its ascent into prominence. Here, the rate performance of Li2FeSiO4 at high temperatures in electrolyte comprising molten salt (ionic liquid) was investigated. Subsequently, a comparison of the phase transition behaviour observed at both high-temperature and room-temperature cycling was elucidated. Our results show that remarkable rate performance with good cyclability in conjunction with low voltage polarisation is attained upon cycling of Li2FeSiO4 at high temperatures, due to the faster phase transformation from unstable monoclinic structures to thermodynamically stable orthorhombic structures triggered by elevated temperature. What this study adds to the burgeoning body of research work relating to the silicates is that the initially slow phase transformation behaviour observed at room temperature can significantly be enhanced upon cycling at elevated temperatures.