Green and High-Yield Recovery of Phosphorus from Municipal Wastewater for LiFePO4 Batteries

Abstract

The rapidly growing demand for lithium iron phosphate (LiFePO4) as the cathode material of lithium-ion batteries (LIBs) has aggravated the scarcity of phosphorus (P) reserves on Earth. This study introduces an environmentally friendly and economical method of P recovery from municipal wastewater, providing the P source for LiFePO4 cathodes. The novel approach utilizes the sludge of Fe-coagulant-based chemical P removal (CPR) in wastewater treatment. After a sintering treatment with acid washing, the CPR sludge, enriched with P and Fe, transforms into purified P–Fe oxides (Fe2.1P1.0O5.6). These oxides can substitute up to 35% of the FePO4 reagent as precursor, producing a carbon-coated LiFePO4 (LiFePO4/C) cathode with a specific discharge capacity of 114.9 mA·h·g−1 at current density of 17 mA·g−1), and cycle stability of 99.2% after 100 cycles. The enhanced cycle performance of the as-prepared LiFePO4/C cathode may be attributed to the incorporations of impurities (such as Ca2+ and Na+) from sludge, with improved stability of crystal structure. Unlike conventional P-fertilizers, this P recovery technology converts 100% of P in CPR sludge into the production of value-added LiFePO4/C cathodes. The recovered P from municipal wastewater can meet up to 35% of the P demand in the Chinese LIBs industry, offering a cost-effective solution for addressing the pressing challenges of P scarcity.