Electrolyte-Regulated Epitaxial-Like Gradient Interface for Stable 4.8 V LiCoO ₂

Pushing lithium cobalt oxide (LiCoO 2 ) to its theoretical capacity by raising the cutoff voltage is crucial for higher energy density. The main obstacle, however, is the interfacial instability of the highly delithiated LiCoO 2 at ultrahigh voltages (>4.6 V), which results in rapid structural failure. Here, we propose a strategy of engineering an epitaxial-like grown cathode–electrolyte interphase to stabilize the ultra-high-voltage cathode interface. A fluorine-rich lithium salt with a moderate oxidation potential of 5.50 V is used to preferentially derive LiF for establishing an epitaxial-like grown gradient protective layer. Consequently, the LiCoO 2 exhibits excellent cycling stability at an ultrahigh voltage of 4.8 V, releasing 251 mAh g –1 (i.e., 91.7% of its theoretical capacity) and sustaining 220 cycles. The efficacy of this epitaxial-like gradient interface in stabilizing 4.8 V LiCoO 2 is further validated by a 6.82 Ah Li||LiCoO 2 pouch cell, which delivers a specific energy of 557 Wh kg –1 and operates 60 times with a capacity retention of 85.2%. Moreover, we propose a decomposition mechanism for the salt anion and present the atomic-level structure of the gradient protective interface, offering new insights into designing electrolyte components and engineering interfacial layers for ultra-high-voltage cathode materials.