Anti-site reordering in LiFePO4: Defect annihilation on charge carrier injection

Abstract

Defects critically affect the properties of materials. Thus, controlling the defect concentration often plays a pivotal role in determining performance. In lithium rechargeable batteries, the operating mechanism is based on ion transport, so large numbers of defects in the electrode crystal can significantly impede Li ion diffusion, leading to decreased electrochemical properties. Here, we introduce a new way to heal defects in crystals by a room-temperature electrochemical annealing process. We show that defects in olivine LiFePO4, an important cathode material, are significantly reduced by the electrochemical recombination of Li/Fe anti-sites. The healed LiFePO4 recovers its high-power capabilities. The types of defects in LiFePO4 and recombination mechanisms are discussed with the aid of first-principles calculations.