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 systems. However, its poor rate performance and high voltage polarization attributed to innately slow Li⁺ kinetics at room temperature have 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 behavior 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 polarization 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 behavior observed at room temperature can significantly be enhanced upon cycling at elevated temperatures.