Direct Regeneration of Spent Lithium Iron Phosphate via a Low-Temperature Molten Salt Process Coupled with a Reductive Environment

A huge number of spent lithium-ion batteries(LIBs) have caused serious problems such as resource waste andenvironmental pollution. Lithium iron phosphate (LFP) is one ofthe major cathode materials in the spent LIBs. It is urgently neededto develop a safe, environmentally friendly, and cost competitiveapproach to regenerate the LFP cathode collected from the spentLIBs. The nitrate molten salt process has been utilized toregenerate layered cathode materials, which are nevertheless non-compatible with the LFP regeneration process. The LFP crystallattice will be destroyed during the molten salt process by theoxidative environment, where Fe(II) is oxidized to Fe(III). A newapproach is proposed in this work to tackle this issue, where a low-temperature molten salt process is coupled with a reductiveenvironment to suppress oxidation of Fe(II). In detail, lithium nitrate is used as a molten salt medium and lithium sourcesimultaneously. Sucrose is used as a carbon source to provide a reductive environment. Through a short molten-salt relithiation stepat 300 degrees C and further annealing process at 650 degrees C, LFP particles with a lithium-deficient and damaged structure can be successfullyrecovered. The rapid lithium replenishment process exposes more (101) crystal planes facilitating lithium-ion transportation. As aresult, the regenerated LFP delivers a specific capacity of 145 mAh g-1at 0.5C, which is more than a 13% increase relative to thespent LFP and has a better rate performance than pristine LFP at 5C. In addition, we also point out that the LFP is converted toLi3PO4with the increase in lithium source and the extension of treatment time. This work provides a new promising way toregenerate spent LFP cathodes.

Automated summary

This study proposes a new method to regenerate spent lithium iron phosphate (LFP) cathode materials, which utilizes a low-temperature molten salt process combined with a reductive environment to suppress oxidation. The recovered LFP particles have a lithium-deficient and damaged structure, leading to higher specific capacity and better rate performance.