A green recycling process designed for LiFePO ₄ cathode materials for Li-ion batteries

Abstract

A green process route is proposed to recycle LiFePO ₄ cathode materials from FePO ₄·2H ₂O metastrengite I intermediate phase.

Abstract

A green process route to recycle LiFePO ₄/C electrode materials is proposed in this work. First, a robust strategy to synthesize LiFePO ₄/C cathode materials from a precursor of a crystalline FePO ₄·2H ₂O phase (metastrengite I) is presented. In order to prepare crystalline FePO ₄·2H ₂O, 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 FePO ₄·2H ₂O with lithium sources, we find that LiFePO ₄/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 LiFePO ₄ powders and recovered LiFePO ₄ electrode materials from spent batteries are both tested with our developed recycling process, where we decompose LiFePO ₄ powders/electrodes to prepare crystalline FePO ₄·2H ₂O, and then re-synthesize LiFePO ₄/C cathode materials. In both cases, our recycled LiFePO ₄/C exhibits a very comparable discharge capacity of ∼140 mA h g ⁻¹ at 1 C with a capacity retention of ∼99%.