Defect-engineered gradient reconstruction for the upcycling of spent LiFePO4 to generate high-value LiFe1−xMnxPO4/C cathodes

Recycling spent lithium-ion (Li⁺) batteries is critical for achieving environmental conservation and the strategic recovery of essential resources. Compared with conventional methods for recovering cathode materials, which are energy-intensive and prone to secondary pollution, the direct regeneration approach has emerged as a rapid and highly efficient method, gaining widespread attention in recent years. However, this approach faces major challenges, including degraded electrochemical performances and limited economic value. This study, therefore, proposes a high-value direct regeneration strategy to convert degraded spent LiFePO₄ (S-LFP) into a gradient manganese (Mn)-doped regenerated LiFe_0.7Mn_0.3PO₄/C (R-LFMP) composite. This method leverages the inherent microcracks and Li vacancies present in S-LFP, likely acting as diffusion channels for the Mn²⁺/Li⁺ ions. Through a two-step mechanochemical ball-milling and carbothermal reduction process, this approach achieves simultaneous Li replenishment and surface-localised Mn gradient doping with enhanced structural control. Notably, the R-LFMP exhibits an exceptional electrochemical performance. At 0.1 C, it delivers a discharge capacity of 161.4 mA h g⁻¹ and an energy density of 563.5 Wh kg⁻¹ (representing a 60.5 % improvement over S-LFP). Additionally, it maintains 83 % capacity retention after 900 cycles at 0.5C, a considerable enhancement compared to commercial LFMP (62 %). Furthermore, the regenerated cathode material generates a net profit of $7.102 kg⁻¹, surpassing the profitability of conventional recycling methods by 90 %. Overall, this study introduces a transformative and sustainable LFP regeneration technology, achieving breakthroughs in electrochemical restoration and high-value recycling, while paving the way for the closed-loop utilisation of LFP-based energy storage systems.