In recent years, recycling of numerous spent lithium-ion battery cathode materials has received increasing attention in order to protect the environment as well as to conserve resources, and the recovery of spent LiFePO₄ (LFP) by direct regeneration has been widely studied. A considerable body of literature has delved into the failure mechanism of LFP. The mechanism is characterized by an irreversible phase change, which is primarily attributed to the sluggish diffusion of lithium ions (Li⁺) during cycling. Additionally, the migration of iron (Fe) ions to occupy Li⁺ sites further impedes Li⁺ diffusion. Consequently, the electrochemical performance of directly regenerated LFP is diminished by the phenomenon of Li defects. Here, a method of direct regeneration of LFP based on a doping strategy using environmentally friendly and economically efficient natural biomass amino acids has been developed, which inhibits Fe ion migration and improves the diffusion kinetics of Li⁺ and electrons by constructing a nitrogen-doped carbon coating. The regenerated LFP cathode exhibits excellent cycling stability and rate performance (98.7% capacity retention over 100 cycles at 1C current density and a high capacity retention of 87.9% after 500 cycles at 1C).

中文翻译：

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通过原位涂层和使用氨基酸的杂原子掺杂策略，从废阴极中再生出高性能的 LiFePO4

近年来，为了保护环境和节约资源，众多废旧锂离子电池正极材料的回收利用日益受到关注，通过直接再生回收废旧LiFePO ₄ (LFP)已得到广泛研究。大量文献深入研究了 LFP 的失败机制。该机制的特点是不可逆相变，这主要归因于循环过程中锂离子（Li ⁺）的缓慢扩散。此外，铁（Fe）离子迁移占据Li ⁺位点进一步阻碍Li ⁺扩散。因此，直接再生LFP的电化学性能因Li缺陷现象而降低。这里，开发了一种基于掺杂策略的直接再生LFP的方法，使用环保且经济高效的天然生物质氨基酸，通过构建氮掺杂碳来抑制Fe离子迁移并改善Li ⁺和电子的扩散动力学涂层。再生LFP正极表现出优异的循环稳定性和倍率性能（1C电流密度下100次循环后容量保持率为98.7%，1C电流密度下500次循环后容量保持率为87.9%）。