Tailoring Co3d and O2p Band Centers to Inhibit Oxygen Escape for Stable 4.6 V LiCoO2 Cathodes. (17th November 2021) - Kong, Weijin
Abstract: High‐voltage LiCoO2 delivers a high capacity but sharp fading is a critical issue, and the capacity decay mechanism is also poorly understood. Herein, we clarify that the escape of surface oxygen and Li‐insulator Co3 O4 formation are the main causes for the capacity fading of 4.6 V LiCoO2 . We propose the inhibition of the oxygen escape for achieving stable 4.6 V LiCoO2 by tailoring the Co3d and O2p band center and enlarging their band gap with MgF2 doping. This enhances the ionicity of the Co−O bond and the redox activity of Co and improves cation migration reversibility. The inhibition of oxygen escape suppresses the formation of Li‐insulator Co3 O4 and maintains the surface structure integrity. Mg acts as a pillar, providing a stable and enlarged channel for fast Li + intercalation/extraction. The modulated LiCoO2 shows almost zero strain and achieves a record capacity retention at 4.6 V: 92 % after 100 cycles at 1C and 86.4 % after 1000 cycles at 5C. Abstract : The escape of surface oxygen and Li‐insulator Co3 O4 formation are the main causes for the capacity fading of 4.6 V LiCoO2 cathode. The oxygen escape is significantly inhibited by tailoring the Co3d and O2p band centers and enlarging their band gap with MgF2 doping, which enables a stable cycling of 4.6 V LiCoO2 cathode.