Electrochemical Self‐Assembly of Boron‐Based Cathode‐Electrolyte Interphase to Stabilize 4.65 V LiCoO2

Abstract

The cathode‐electrolyte interphase (CEI) is vital for the stability of LiCoO2 (LCO) beyond 4.55 V (vs Li/Li+). Herein, the full coverage of boron‐based CEI is achieved on LCO surface via utilizing the self‐wetting synthesis of boric acid (i.e., B‐LCO), accompanying with the subsequent electrochemical self‐assembly process upon cycles. Initially, the B‐LCO is coated with borate deposits (size of 10–20 nm), then it melts and fully covers the surface upon sintering, leading to the full coverage of boron‐based artificial CEI, which directly reduces the side reactions induced by highly oxidative Co4+/On− (0 < n < 2). Significantly, during cycling, the in situ interfacial reactions between the surface boron‐based species and LiF promote the formation of crystalline LiB6O9F components, showing the mechanically robust and highly Li+ conductive characteristics. Due to the synergism of robust CEI and structurally tough surface rocksalt (RS) phase, not only the more reversible phase transition and uniform Li+ (de)lithiation are achieved, but also the particle cracks and surface deterioration issues are effectively inhibited. As a result, the B‐LCO||Li cells show excellent cycle stability, with a high retention of 84.0% in 500 cycles in 3–4.65 V.