Enhanced Electrochemical Delithiation of LiFePO4 in a Composite Aqueous Electrolyte for High-Performance Olivine FePO4

Development of delithiation methods with cost-efficiency and highly kinetic effectivity is of great importance for the preparation of diversified intercalation materials, mechanistic study, and lithium extraction from spent lithium-ion batteries. Electrochemical delithiation in aqueous electrolytes is low-cost, straightforward, and fast, but has been plagued by incomplete delithiation. To address this issue, we propose to add oxidation reagents, usually applied in chemical delithation, to traditional aqueous delithiation electrolyte. As a demonstration, herein, a Na 2 SO 4 + Na 2 S 2 O 8 composite aqueous electrolyte is used to obtain olivine FePO 4 from the electrochemical delithiation of LiFePO 4 , and compared with the similar delithiation in Na 2 SO 4 aqueous electrolyte. The delithiation goes completion in the composite electrolyte 79% faster than that in traditional electrolyte. The resulting olivine FePO 4 exhibits integrity in terms of structure and electrochemical properties, with discharge specific capacity of 157.1 mAh g −1 at 0.1 C, constant voltage plateau of 3.37 V, and 98.8% capacity retention after 100 cycles, all comparable to the LiFePO 4 starting material. Mechanistic studies show that Na 2 S 2 O 8 promotes the electrochemical delithiation by providing acidic and chemically oxidative conditions.