Surface Growth and Intergranular Separation of Polycrystalline Particles for Regeneration of Stable Single-Crystal Cathode Materials

Abstract

The direct regeneration technology has been developed because of its short-range, high efficiency, and green characteristics. However, the existing direct regeneration method is hardly applied in collaborative reconstruction of the damaged crystal and particle of spent polycrystalline layered materials. The single-crystal regeneration with restructuring the morphology and crystal structure was herein achieved for the first time by low-temperature lithium supplementation followed with high-temperature molten salt conversion, which could effectively solve the structural defects of spent polycrystalline layered materials. We found that the realization of single-crystal regeneration with the molten salt process is attributable to that the original crystal growth of primary particles in the polycrystal transfer to the subsequent division along the grain boundary. At the test conditions of 25 °C and 2.8–4.3 V, the capacity retention capacity of the regenerated single-crystal materials reach 83.3% after 200 cycles at 1 C, which is much higher than 20.0% for conventional direct lithiation regeneration and 61.6% for low-temperature molten salt regeneration. Interestingly, the regenerated single-crystal NCM622 in the graphite full-cell test displays a capacity retention rate of 85.24% after 800 cycles at a rate of 1 C at 2.5–4.35 V. This work opens up a new way for the direct regeneration of spent polycrystalline layered cathode materials.

A Universal Molten Salt Method for Direct Upcycling of Spent Ni‐rich Cathode towards Single‐crystalline Li‐rich Cathode

“…In addition, these treatments mainly focus on the results of the Li supplement and the evolution process of regeneration has not been fully investigated. We note that melting and reconstructing spent cathode particles at the elevated temperature can effectively resolve the above issues, including Li supplement, microcracks healing, grains reconstruction [10b, 16] and formation of Li‐rich structure [14a] . The abbreviated process is schematically illustrated in Figure 1a.…”

Engineering commercial polycrystalline precursors to single crystal Ni-rich cathodes with outstanding long-cycle performance

“…7b, the crystal behaves as an intact structure before charging, and the atomic layers parallel to the (003) crystal plane slide reversibly during charging and then return to their initial state after discharge. 62 The superior crystal structure and regular geometry can reduce the resistance to slip occurrence, and the family of (003) and (012) crystal face distribution will further facilitate the slip occurrence and reversible recovery, thus providing outstanding cycling stability.…”

Stacking Fault Formation in LiNi0.6Co0.2Mn0.2O2 during Cycling: Fundamental Insights into the Direct Recycling of Spent Lithium-Ion Batteries

“…This particle shape is common among NCM-and NCA-based materials, although NCM622 compounds consisting of large, isolated primary particles with diameters of 2−5 μm were recently proposed to improve the cyclability. 27,28 Ex Situ XRD Measurements. As described in the Introduction, changes in the crystal structure of NCM622…”