Continuous Flow Electrochemical Synthesis of Olivine‐Structured NaFePO₄ Cathode Material for Sodium‐Ion Batteries from Recycle LiFePO₄

Abstract To mitigate the environmental impact of the improper disposal of spent LiFePO₄ batteries and reduce resource waste, the development of LiFePO₄ recycling technologies is of paramount importance. Meanwhile, olivine‐structured NaFePO₄ in sodium‐ion batteries has received great attention, due to its high theoretical specific capacity of 154 mAh g⁻¹ and excellent stability. However, olivine NaFePO₄ only can be synthesized from olivine LiFePO₄. Accordingly, in this proposal, developing the continuous flow electrochemical solid‐liquid reactor‐based metal ion insertion technology is to utilize the olivine FePO₄, recycled from LiFePO₄, and to synthesize NaFePO₄. Additionally, by employing I⁻ as the reducing agent, NaFePO₄ is successfully synthesized with a discharge‐specific capacity of 134 mAh g⁻¹ at 0.1C and a remarkable capacity retention rate of 86.5% after 100 cycles at 0.2C. And the reasons for sodium deficiency in the synthesized NFP are elucidated through first‐principles calculations. Furthermore, the kinetics of the solid‐solution reaction 2 (Na_2/3+βPO₄→ Na_1‐αFePO₄) mechanism improve with cycling and are sensitive to temperature. Utilizing a minimal amount of reducing agent in the electrochemical reactor, NaFePO₄ synthesis is successfully achieved. This innovative approach offers a new, cost‐effective, and environmentally friendly strategy for preparing NaFePO₄ from recycling LiFePO₄.