Constructing a Three-Phase Reaction System for Efficiently Recycling Spent LiFePO4

In recent years, a large number of spent lithium iron phosphate (LiFePO4, abbreviated as LFP) batteries have been retired. Selective leaching is the most suitable recycling option for spent LFP (S-LFP). However, the current mainstream oxidants and acids are not economical, safe, and green. Herein, we constructed a HNO3-O2 system to achieve efficient leaching of Li from S-LFP. HNO3 can be recovered by high temperatures after use to achieve the recycling of acid, and O2 is more economical and safer than mainstream oxidants. In the comfortable oxidizing environment provided by HNO3, O2 is used to oxidize Fe2+ in S-LFP into Fe3+, and Li+ is extracted from S-LFP into the solution with a leaching rate of almost 100%. The lithium-rich solution is further used to leach the Li from the spent graphite anode, and then the Li in the solution is captured using CO2 to obtain Li2CO3. The iron phosphate (FePO4) slag from Li extraction is regenerated into LFP based on the above obtained Li2CO3 through carbon thermal reduction. The regenerated LFP displays a high discharge capacity of 163.85 mAh g–1 and a stable cycling performance, which are comparable to those of commercial LFP.