Green chemical delithiation of lithium iron phosphate for energy storage application

Abstract

• The use of chemical reagents is important to the surface characteristics of FePO 4 . • A simple and environmental friendly route for the chemical delithiation of LiFePO 4 . • Damaged carbon coating can be regenerated through cycling and the formation of CEI. • Chemically delithiated LiFePO 4 as a precursor for NaFePO 4 cathode of sodium battery. • Delithiated sample in a sodium ion battery gave a capacity retention > 85.4% after 70 cycles. Heterosite FePO 4 is usually obtained via the chemical delithiation process. The low toxicity, high thermal stability, and excellent cycle ability of heterosite FePO 4 make it a promising candidate for cation storage such as Li + , Na + , and Mg 2+ . However, during lithium ion extraction, the surface chemistry characteristics are also affected by chemical agents. In this work, heterosite FePO 4 was synthesized via the delithiation of LiFePO 4 by acetonitrile solution with nitronium tetrafluoroborate (NO 2 BF 4 /AN) or by peracetic acid (PAA) to extract lithium ion from the olivine structure. As a host of lithium and sodium ion, heterosite FePO 4 prepared by PAA exhibits better capacity, cycle retention, and high rate capability than that delithiated by the conventional NO 2 BF 4 /AN method. The superior electrochemical performance of using PAA could be attributed to the better integrity of the carbon coating on the pristine LiFePO 4 surface. The delithiated samples were further tested as a cathode in a sodium ion battery with capacity retention > 85.4% after 70 cycles. This work provides a simple and eco-friendly method to synthesize heterosite FePO 4 without organic solvent and demonstrates its viability for lithium and sodium battery applications.