A green recycling process designed for LiFePO4 cathode materials for Li-ion batteries

Abstract

A green process route to recycle LiFePO₄/C electrode materials is proposed in this work. First, a robust strategy to synthesize LiFePO₄/C cathode materials from a precursor of a crystalline FePO₄·2H₂O phase (metastrengite I) is presented. In order to prepare crystalline FePO₄·2H₂O, a solution precipitation route is adapted, where the reaction conditions such as temperature and pH are precisely controlled. Among various heat treatment temperatures to calcine our prepared FePO₄·2H₂O with lithium sources, we find that LiFePO₄/C cathode materials synthesized at 700 °C deliver a maximum discharge capacity of 168.51 mA h g⁻¹ at 0.1 C (1 C rate = 170 mA h g⁻¹) with a capacity retention of 99.36% after the 25^th cycle at 1 C. Furthermore, commercially available LiFePO₄ powders and recovered LiFePO₄ electrode materials from spent batteries are both tested with our developed recycling process, where we decompose LiFePO₄ powders/electrodes to prepare crystalline FePO₄·2H₂O, and then re-synthesize LiFePO₄/C cathode materials. In both cases, our recycled LiFePO₄/C exhibits a very comparable discharge capacity of ∼140 mA h g⁻¹ at 1 C with a capacity retention of ∼99%.