Tuning surface chemistry to reduce the step-like degradation of LiCoO2 at 4.6 V.

Elevating the cut-off voltage is an effective route to increase the energy density of LiCoO 2 (LCO). However, the highly delithiated LCO faces the issues of poor structural reversibility, O loss, and Co dissolution, etc., especially in the surface region. Herein, the step-like surface degradation (SSD) of pristine LCO (P-LCO) is firstly revealed to be responsible for the rapid capacity decay. To reduce the adverse impact of SSD, a solid electrolyte is coated and annealed to achieve the optimized surface structure chemistry of LCO (SE-LCO), featuring the outermost surface Li 3 PO 4 , surface rock-salt layer, and subsurface spinel-like layer. Benefiting from this surface optimization, the SE-LCO not only shows an enhanced but more reversible phase transition to enhance the structure stability, but also promotes the formation of tough cathode electrolyte interface (CEI) to reduce the O loss and Co dissolution issues. As a result, SE-LCO/graphite cell achieves excellent cycle stability with a remarkable capacity retention of 81.2% after 800 cycles in a potential range of 3–4.55 V, which is among the best reported cell performances. This work broadens the cognition for developing more advanced LCO cathodes. [Display omitted] • The step-like surface degradation (SSD) of P-LCO at 4.6 V is firstly revealed. • The enhanced but more reversible O3/H1–3 phase transition is achieved via tuning surface chemistry. • A tough CEI layer is formed to reduce the O loss and Co dissolution issues upon cycles. [ABSTRACT FROM AUTHOR]