A sodium salt-assisted roasting approach followed by leaching for recovering spent LiFePO₄ batteries

Mild-temperature (<1000 °C) carbothermic reduction has been proven as an effective way to recover Li and transition metals by converting lithium transition metal oxides to transition metals/alloys and Li₂CO₃. However, LiFePO₄ cannot be reduced by carbon because of its thermodynamically stable olivine structure. Herein, LiFePO₄ is converted to Fe and lithium salts by carbon with the assistance of Na₂CO₃ that acts as an activating agent to break down the chemical bonds of LiFePO₄ and thereby enable the carbothermic reduction. Using Na₂CO₃ as the activating agent, LiFePO₄ was reduced to Fe, NaLi₂PO₄, and LiNa₅(PO₄)₂ which can be separated by magnetic separation with a Li recovery rate of 99.2%. Using NaOH as the activating agent, LiFePO₄ was oxidized to Fe₃O₄, NaLi₂PO₄ and LiNa₅(PO₄)₂ at 600 °C, and the roasted products can be separated by magnetic separation process with a Li recovery rate of 92.7%. Various sodium salts were tested to screen proper salts for the reduction process, and a 400-g scale roasting-separation process has been demonstrated. Overall, the salt-assisted roasting is a promising way to recycle spent LiFePO₄ batteries without using strong mineral acids and shows great potential for the industrial-scale implementation.