ABSTRACT
Lithium iron phosphate (LiFePO4, LFP)-based lithium-ion batteries are dominating the energy storage market due to their attractive features such as safety and better performance characteristics such as excellent cycle life and high-temperature stability. However, an effective means to recycle or reuse LFP electrodes is yet to be realized as the increased production of LFP batteries increases the backflow of environmentally harmful spent batteries. In this chapter, we emphasize a chemical means to convert this waste (spent LFP) to wealth (fresh battery electrodes). Specifically, the failed LFP-based electrodes are regenerated as NaFePO4 for use in rechargeable sodium-ion battery applications. The regeneration process needs optimization for generating better NaFePO4. This facile, scalable, and low-temperature chemical method involves two stages: First is the rapid chemical delithiation, resulting in completely delithiated FePO4. This is followed by chemical sodiation to prepare NaFePO4 (NFP). The approach of chemical sodiation is accomplished by utilizing reducing agents such as NaI. The as-prepared NFP is utilized as electrodes in sodium-ion batteries, and the improvements in electrochemical performance are utilized as benchmark for process optimization. Specific parameters for optimization are sodiation time, stoichiometry of NaI, solvent, and sodiation temperature. It is realized that 6 min of sodiation, with an excess NaI stoichiometry of 3.8, in acetonitrile solvent at a sodiation temperature of 60°C is ideal for obtaining high performance NaFePO4.
