Oxygen-Powered Sustainable FePO₄ Preparation Routines for Sodium Metal Batteries with Li Acetate Recovery

Triphylite NaFePO₄ emerges as a promising solution for sodium secondary batteries due to its abundant constituent elements and high energy density, making it attractive for sustainable energy storage applications. However, the direct synthesis of triphylite NaFePO₄ is hindered by its thermal metastability. In this study, we propose an oxygen-powered sustainable production method for heterosite FePO₄, the desodiated form of triphylite NaFePO₄, derived from LiFePO₄. Oxygen gas serves as the oxidizing agent for delithiating LiFePO₄, and a closed-loop process has been successfully established to enable lithium recycling, which is essential for achieving cost-effective FePO₄ production. Furthermore, we propose a high energy density metal cell configuration that utilizes the charged state of sodium metal batteries (Na/FePO₄ configuration), aiming to improve the cyclability of Na-metal-free cells while maintaining the high energy density, thereby addressing a significant challenge in sodium metal battery technology.