Upcycling subcritical lithium extraction residue to Ni-rich cathode of LiNi_0.9Co_0.06Mn_0.04O₂: A sustainable short-process recycling strategy

The efficient recovery and recycling of transition metals from the lithium extraction residue of spent lithium-ion batteries (LIBs) is of great significance to the recycling of valuable resources. Herein, the subcritical lithium extraction residue (SLER) is used as the research object, and the research ideas of low acid leaching, solvent extraction purification and co-precipitation regeneration are applied to obtain the regenerated cathode materials of LiNi_0.9Co_0.06Mn_0.04O₂ (Ni90). Attributed to the presence of transition metals in SLER in the form of divalent oxides ((NiO)_x(MnO)_y, CoO) and carbonates (MnCO₃), low acid leaching of SLER can be achieved. The low acid leaching process shows that a 50% reduction in sulfuric acid consumption compared to the extraction of lithium residue obtained by conventional methods. And the leaching kinetics reveal that the transition metals leaching are controlled by chemical reactions. The precursor is directly obtained by one step co-precipitation method with a combination of NH₃·H₂O and NaOH from the purified liquid extracted with di-2-ethylhexyl phos-phoric acid (P204) solvent, which avoids the lengthy step precipitation and multistage extraction. Furthermore, density functional theory (DFT) calculations with density of states and electrochemical tests demonstrate that Al doping significantly improves the conductivity and cycling performance of the regenerated cathode material Ni90. This process provides a referential approach for the efficient recovery and short-process regeneration of lithium extraction residue from spent LIBs.