Fast ammonium sulfate salt assisted roasting for selectively recycling degraded LiFePO4 cathode

Abstract

Selectively recycling degraded cathode materials from retired lithium-ion battery is an efficient approach which could shorten recovery processes and reduce energy consumption and carbon emissions. Herein, we propose a fast ammonium sulfate ((NH4)2SO4) salt roasting method to extract Li and recycle FePO4 from commerical LiFePO4 cathode materials. Compared with the traditional hydrometallurgy recovery process, (NH4)2SO4 assisted roasting achieved the fast delithiation of LiFePO4 within 5 min at 300 °C, and converted LiFePO4 to FePO4 in air atmosphere. Almost 98% of Li was converted to soluble Li2SO4, and air acted as a clean and cheap oxidant. TG-DSC analysis in different atmospheres indicated that the whole reaction mainly consisted of two steps: (NH4)2SO4 firstly decomposed to NH4HSO4 and (NH4)2S2O7, and then the LiFePO4 reacted with O2, (NH4)2SO4 and (NH4)2S2O7 at ∼300 °C. Thermodynamic analysis also supported the above reaction mechanism. In a word, (NH4)2SO4 salt assisted roasting provides an effective approach to selectively extracting Li from polyanionic cathode materials.