Fast Capacitive Energy Storage and Long Cycle Life in a Deintercalation–Intercalation Cathode Material

Abstract Ni‐rich Li‐ion cathode materials promise high energy density, but are limited in power density and cycle life, resulting from their poor dynamic characteristics and quick degradation. On the other hand, capacitor electrode materials promise high power density and long cycle life but limited capacities. A joint energy storage mechanism of these two kinds is performed in the material‐compositional level in this paper. A valence coupling between carbon π‐electrons and O²⁻ is identified in the as‐prepared composite material, using a tracking X‐ray photoelectron spectroscopy strategy. Besides delivering capacity simultaneously from its LiNi_0.8Co_0.1Mn_0.1O₂ and capacitive carbon components with impressive amount and speed, this material shows robust cycling stability by preventing oxygen emission and phase transformation via the discovered valence coupling effect. Structural evolution of the composite shows a more flattened path compared to that of the pure LiNi_0.8Co_0.1Mn_0.1O₂, revealed by the in situ X‐ray diffraction strategy. Without obvious phase transformation and losing active contents in this composite material, long cycling can be achieved.