Reviving Fatigue Surface for Solid-State Upcycling of Highly Degraded Polycrystalline LiNi 1-x-y Co x Mn y O 2 Cathodes.

The ongoing tide of spent lithium-ion batteries urgently calls for high-value output in efficient recycling. Recently, direct regeneration is emerged as a novel recycling strategy but fails to repair the irreversible morphology and structure damages of the highly degraded polycrystalline layered oxide materials. Here, we carry out a solid-state upcycling study for the severely cracked LiNi 1-x-y Co x Mn y O 2 cathodes. The specific single-crystallization process during calcination is investigated and the surface rock salt phase is recognized as the intrinsic obstacle to the crystal growth of the degraded cathodes due to sluggish diffusion in the heterogeneous grain boundary. Accordingly, we revive the fatigue rock salt phase by restoring a layered surface and successfully reshape severely broken cathodes into the high-performance single-crystalline particles. Benefiting from morphological and structural integrity, the upcycled single-crystalline cathode materials exhibit an enhanced capacity retention rate of 93.5% after 150 cycles at 1C compared with 61.7% of the regenerated polycrystalline materials. The performance is also beyond that of the commercial cathodes even under a high cut-off voltage (4.5 V) or high operating temperature (45 °C). This work provides scientific insights for the upcycling of the highly degraded cathodes in spent LIBs. This article is protected by copyright. All rights reserved.