A tough Janus-faced CEI film for high voltage layered oxide cathodes beyond 4.6 V

Cathode electrolyte interphase (CEI) film is suffering from electrochemical disintegration and physical disturbance caused by particles' volumetric variation while layered oxide cathodes are operated at high voltage. However, most CEI design strategies only focus on the electrochemical stability of the film. Herein a novel tough Janus-faced CEI film with excellent high-voltage stability and ultrahigh Young's modulus similar to 30 Gpa is in-situ constructed by succinonitrile (SN) and cyclohexylbenzene (CHB) additives. SN is adsorbed on electrode particles due to the coordinative interaction with transition metals, then CHB is electrochemically polymerized generating an outer layer subsequently. This Janus-faced film not only prevents the decomposition of electrolyte and the irreversible phase transition on particles surface, but also suppresses the particles cracking and Co element dissolution. With the multiply protection of this film, the cyclic performances of LiCoO2 and LiNi0.8Co0.1Mn0.1O2 cathodes are remarkably improved, over 500 & 600 cycles at the high voltages of 4.6 & 4.7 V vs. Li+/Li, respectively. This work not only provides a novel design of functional CEI film, but also throws light on other electrochemical protection fields such as metal corrosion.