Ambient-Pressure Relithiation of Degraded LixNi0.5Co0.2Mn0.3O2 (0 < x < 1) via Eutectic Solutions for Direct Regeneration of Lithium-Ion Battery Cathodes

With the rapid growth of the lithium-ion battery (LIBs) market, recycling and re-use of end-of-life LIBs to reclaim lithium (Li) and transition metal (TM) resources (e.g., Co, Ni), as well as eliminating pollution from disposal of waste batteries, has become an urgent task. Here, for the first time the ambient-pressure relithiation of degraded LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes via eutectic Li+ molten-salt solutions is successfully demonstrated. Combining such a low-temperature relithiation process with a well-designed thermal annealing step, NCM523 cathode particles with significant Li loss (approximate to 40%) and capacity degradation (approximate to 50%) can be successfully regenerated to achieve their original composition and crystal structures, leading to effective recovery of their capacity, cycling stability, and rate capability to the levels of the pristine materials. Advanced characterization tools including atomic resolution electron microscopy imaging and electron energy loss spectroscopy are combined to demonstrate that NCM523's original layered crystal structure is recovered. For the first time, it is shown that layer-to-rock salt phase change on the surfaces and subsurfaces of the cathode materials can be reversed if lithium can be incorporated back to the material. The result suggests the great promise of using eutectic Li+ molten-salt solutions for ambient-pressure relithiation to recycle and remanufacture degraded LIB cathode materials.