External-to-internal synergistic strategy to enable multi-scale stabilization of LiCoO2 at high-voltage

Abstract

High-voltage LiCoO2 (LCO) offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries, however, LiCoO2 is subject to serious structural and interfacial degradation above voltages >4.55 V (vs. Li/Li+). Herein, an in-situ Li6.25La3Zr2Al0.25O12 (LLZAO) layer is constructed on the LCO surface to achieve operating voltage at 4.6 V. The detailed characterizations (ex-situ XRD, ex-situ Raman, DFT, etc.) reveal that the LLZAO layer greatly enhances Li+ conductivity attributed to the ion-conducting layer on the surface/interface, and closely combines with LiCoO2 particle to ensure stable cathode/electrolyte interface, thus suppressing the highly reactive Co4+ and O- triggered surface side reactions at high-voltage. Moreover, the introduction of La3+/Zr4+/Al3+ with a larger ionic radius (La3+/Zr4+ are larger than Co3+) and weaker electronegativity (La/Zr/Al are weaker than Co) into Co3+ sites readjusts the electron cloud density between Co–O–Li, which reinforces the Co–O bond and widens the band-center gap of Co 3d and O 2p, thus restraining the detrimental phase transition (from H3 to H1-3 phase) and the formation of Co3O4 spinel phase (attributed to lattice oxygen release), subsequently alleviating the particle cracking and structural collapse during repeated Li+ de/intercalation. Therefore, after 100 cycles at 3.0–4.6 V, LCO@1.0LLZAO exhibits a superior discharge capacity of 188.5 mA h g−1, with a capacity retention of 85.1%. The above research has brought about meaningful guidance for the evolution of cathode materials with high voltage.