Organic Acid‐Based Hydrothermal Leaching of LiFePO₄ Cathode Materials

Abstract

This study conducts hydrothermal leaching of commercial LiFePO4 (LFPO) cathode materials with oxalic acid, citric acid, or glycine without any other oxidants or reductants. Of these acids, glycine exhibits the weakest leaching behavior, with the leaching efficiency of lithium (Li), iron (Fe), or phosphorus (P) less than 15% even at 200 °C and an acid concentration of 0.8 mol L−1 for 10 min. For oxalic acid, at 200 °C for 10 min, with a pulp density of 30 g L−1 and an acid concentration of 0.8 mol L−1, the leaching efficiencies for Li and P are 100% and 97%, respectively, and 98.5% of Fe precipitates as iron oxalate (FeC2O4) that can be used as a precursor for preparing LFPO cathode materials. Citric acid shows the highest leaching efficiency for Li, Fe, and P, reaching 96%, 100%, and 88%, respectively, at 90 °C for 10 min with a pulp density of 10 g L−1 and an acid concentration of 0.8 mol L−1. The continuous hydrothermal leaching of LFPO cathode materials with citric acid is first achieved. These results clarify the superiority of citric acid over oxalic acid and glycine with respect to the leaching efficiency for Li, Fe, and P from LFPO batteries under hydrothermal conditions.

Closed-loop recycling of lithium iron phosphate cathodic powders via citric acid leaching

“…Citric acid was proposed as "green chemical" for LIBs' hydrometallurgical recycling because it is soluble in water and naturally biodegradable (Li et al 2010). However, despite organic acids are becoming increasingly common for metals' leaching from Nickel Manganese Cobalt (NMC) and Lithium Cobalt Oxide (LCO) cathodes (Golmohammadzadeh et al 2018;He et al 2017;Kim et al 2023;Zeng et al 2015), they have been rarely applied to LFP recycling (Li et al 2023;Wang et al 2022b).…”