A surface modification layer with cobalt aluminate inhibits 4.6 V high-voltage phase transition of LiCoO₂

Inhibiting the high-voltage phase transition of lithium cobaltate has been a major challenge. Here, we utilize a simple and feasible strategy by using the surface modification layer with cobalt aluminate to achieve ultra-long cyclicity of LiCoO₂ at high voltage. This strategy can protect the electrode from electrolyte attack without hindering the migration of lithium ions, and reduce the loss of active cobalt. Simultaneously, Co (II) of the modified layer is oxidized Co (III) in the redox reaction, which provides extra electrons to induce the deintercalation/intercalation of lithium ions for the half-cell in process of the initial charge/discharge. Electrochemical in-situ characterization reveals that the compound material presents excellent high-voltage structural stability due to reversible phase transition induced by the surface modification layer. As a result, CoAl₂O₄ coated LiCoO₂ achieves excellent ultra-long cycling with high-capacity retention of 86.3% after 500 cycles at 1 C (1C = 274 mA g⁻¹, 3.0–4.6 V).