The extensive application of LFP battery has led to scrap quantity increasing yearly, resulting in waste of resources, pollution of the environment, harm to human health and other serious problems. Due to the low content of valuable metal lithium in waste LFP batteries and poor economic recovery, low-cost recovery has become a research hotspot. Although achieved some results and applications, there were still problems such as low recovery efficiency and high cost of valuable elements. Therefore, the higher-value all-element recycling and reuse of spent LFP batteries has become the key and difficult point to solve the above problems, as great significance. A low-cost process of recovering Li and FePO4 from simulated spent LFP was investigated through a closed-loop coupling technology of isomorphic substitution leaching and solvent extraction.
The isomorphic-induced substitution method is used to enable Fe³⁺ to efficiently substitute for Fe²⁺ and Li⁺ in LFP. Without the aid of external forces or energy, Fe³⁺ spontaneously and rapidly leaches out more than 99% of Li⁺, yielding two kinds of mixed leaching solutions, namely LiCl-FeCl₃ and Li₂SO₄-Fe₂(SO₄)₃. FePO₄ precipitates form spontaneously without the need to add any precipitating agents.
Based on the solvent extraction method, the TBP (Tri-octyl phosphate)-sulfonated kerosene (SK) extraction system is used to synchronously extract iron and lithium from the FeCl₃ single-leaching LFP leaching solution. The separation of iron and lithium is achieved through stepwise stripping, and the recycling of FeCl₃ for the leaching and extraction processes is realized. Moreover, Li₂CO₃ is successfully prepared from the lithium stripping solution. The N235 (tri-octylamine)-TBP-SK extraction system is employed to extract and remove iron from the Fe₂(SO₄)₃-H₂O₂ co-leaching LFP leaching solution, realizing the purification of the leaching solution. Through stripping, Fe₂(SO₄)₃ is recycled for leaching LFP. The organic phase is regenerated without damage by adopting the acid washing and saponification processes, and Li₂CO₃ is successfully prepared from the raffinate solution.
According to the characteristics of each process stage, the leaching process and the extraction process are ingeniously coupled, and the closed-loop recycling process flow of LFP is verified and realized; thus, Fe3+ is recycled in the leaching process and the extraction process, demonstrating high operability and atomic economy. In addition, the by-products generated are non-toxic and pollution-free, achieving the complete harmless treatment of hazardous substances. The proposal of these two processes contributes to the sustainable development of the lithium-ion battery industry and provides a closed-loop green process idea for waste treatment. The closed-loop recycling LFP process was coupled of the leaching, the oxidation concentration, the extraction and the stripping process. In each cycle, the Li and FePO4 recovery efficiency can reach 99% and 98%, respectively. The purity of lithium carbonate prepared exceeds 99.5%.
In short, the coupling process of isomorphic induced leaching and solvent extraction was carried out higher-value all-element and efficient recycling of spent LFP, which provided new research ideas and technical support for the recycling of spent LFP batteries. And the research direction of the comprehensive recycle-utilization of spent lithium batteries and the application field of solvent extraction were expanded.