Sustainable Recycling Strategies for High-Performance Cathode Material Synthesis from Spent Cathodes:

Abstract

With the rising demand for low-cost and safe electric vehicle batteries, lithium iron phosphate (LiFePO₄, LFP) batteries have surged in market share. This suggests that a large amount of LFP waste batteries will emerge in the foreseeable future. However, traditional recycling methods, such as hydrometallurgy, face difficulties in achieving economic viability due to the low embedded value in LFP. Only the valuable lithium is selectively extracted, and the remaining FePO₄ is discarded, which can lead to serious environmental impacts. Therefore, direct cathode recycling method, which can restore the original performance of spent cathode material without destructing their structure, is considered a promising strategy for LFP recycling, because it allows for cost reduction and the recycling of FePO4. Previously reported direct recycling methods generally consist of a lithium replenishing step and a sintering step for restore the compositional and structural defects, respectively. However, growth of particle size inevitably occurs during sintering, which can decrease the power density of the battery because LFP has low ionic conductivity. Moreover degraded surface conductive carbon layer also should be restored. In this context, we propose a crystal size-tunable direct recycling process for LFP cathode materials, employing oxidative fast delithiation-based pulverization method. By using the pulverized FePO4 powder as reactant, the particle size of recycled LFP could be successfully controlled. Additionally, in an oxidizing atmosphere where carbon burns, LFP also gets oxidized, resulting in a inhomogeneous solid mixture, which is why direct recycling methods have not been widely attempted. In our method, compositional inhomogeneity could be suppressed, so that the recycled LFP with a newly introduced carbon layer were successfully synthesized, and they demonstrated superior performance compared to pristine LFP.