Upcycling End-of-Life LiCoO2 via Coupled Regeneration and Ti-Gradient Interfacial Engineering for High-Voltage Cathodes

High-voltage lithium cobalt oxide (LiCoO 2 , LCO) offers high energy density for advanced electronics, but elevated cut-off voltages accelerate surface Co/O loss and structural degradation. Here, we report a scalable waste-to-value upcycling route that combines process-intensified regeneration with interfacial engineering to convert end-of-life LCO into a high-voltage-stable cathode. Mechanochemical leaching and continuous NH 4 HCO 3 -assisted co-precipitation produce a spherical Al-doped, Li-deficient precursor, which is regenerated by relithiation and calcination. Surface hydrolysis of tetrabutyl titanate followed by mild lithium-assisted annealing forms a conformal Li-Ti-O shell and a shallow Ti-enriched near-surface gradient. Multiscale characterization verifies the nanoscale coating and interfacial transition region, and first-principles calculations show that Ti lowers the surface energy of the LCO (104) facet, explaining the improved near-surface stability. The optimized material delivers 228.8 mAh g –1 at 0.2 C, 183.7 mAh g –1 at 5 C, and 85% capacity retention after 100 cycles at 1 C (3.0–4.6 V). This regeneration-to-interface-conversion strategy provides a practical route for greener, scalable rejuvenation of reclaimed LCO.