Purification–lithiation collaborative regeneration of mixed graphite/LiFePO4: building 2D Li+-diffusion channels towards enhanced energy-storage capabilities

Abstract

Direct regeneration of LiFePO₄ (LFP), as a promising short-process recycling method, has attracted considerable attention. However, spent materials in industry mainly arise from large-scale mechanical dismantling, which is composed of spent graphite, whereas retired graphite constitutes 30% of mixed materials. Owing to the high oxidation temperature of graphite, a relatively high sintering temperature is selected for graphite removal. However, over-calcined LFP pre-oxidized precursors lead to low recovery of the spent phase. Herein, a purification–lithiation collaborative regeneration method is proposed for preparing precursors with high purity. Assisted by a “tailored” reductive carbon, the crystalline phase was recovered. As a Li-storage cathode, the optimized samples displayed an initial capacity of 133.0 mA h g⁻¹ at 1.0C. Even at a current density of 5.0C, optimized samples showed 112.5 mA h g⁻¹ with 100% capacity retention ratio after 500 cycles. Supported by detailed physical–chemical analysis, the rationally introduced Li–Fe anti-sites could induce the construction of two-dimensional Li-diffusion channels, along with enhanced Li-diffusion behaviors. This work is expected to provide guidance of the direct regeneration process of LFP samples with graphite impurities.