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

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.