Paving the way for electrochemical recycling of spent lithium-ion batteries: Targeting the direct regeneration of de-lithiated materials

The recycling of spent lithium-ion batteries has become an urgent imperative. Electrochemical technology has emerged as an environmentally friendly approach for selectively extracting lithium from discarded cathode materials, garnering significant attention. However, the lack of a clear understanding of the structural evolution during the de-lithiation process and the re-lithiation mechanism of transition-metal oxides after lithium extraction has hindered the direct regeneration of de-lithiated materials into battery-worthy materials. This limitation has impeded the further advancement of this promising technology. Here, for the first time the structural transformation associated with water-molecule intercalation during the electrochemical process of spent layer material (LiNi0.55Co0.15Mn0.3O2) is demonstrated. X-ray diffraction technique monitors the structural evolution upon de-lithiation, revealing an unusual phase transformation from H3 to “H4” driven by water-molecule intercalation. This transformation triggers significant lattice expansion along c-axis and introduces notable lattice distortion in de-lithiated material. These characteristics render direct calcination for material regeneration impractical, due to lattice collapse from dehydration, obstructing lithium intercalation at high temperatures. Interestingly, low-temperature calcination can endow resynthesized materials with a well-ordered layer structure after creating a lithium-water-balance layer structure for de-lithiated materials by hydrothermal process. Consequently, the regenerated material delivers a capacity of 132.5 mAh/g at 5C.