Constructing lattice-matched strain buffer layer on LiCoO2 for stable high-voltage cycling

Lithium cobalt oxide (LCO) has received considerable attention due to its high volumetric energy density, particularly at elevated cut-off voltages up to 4.7 V. However, the poor cyclic stability of high-voltage LCO limits its practical application, primarily due to detrimental phase transitions above 4.55 V, oxygen loss upon deep delithiation, and the interfacial side reactions. In this study, we introduce an in-situ formed strain buffer layer on LCO particles by CePO4 coating to improve its high-voltage performance. The coated CePO4 layer reacts with LCO particles spontaneously to generate a lattice-matched Li8CeO6 phase, which can facilitate Li+ transportation and relieve near-surface intrinsic stress. With less lattice strain, the undesirable phase transition and notorious surface degradation are suppressed significantly. Moreover, strong covalence of Ce 4f and O 2p bonds, and delocalized electrons in Ce-O6 octahedral configuration help to suppress oxygen redox at 4.6 V. A high capacity retention of 93.3% after 300 cycles at 4.6 V and 88% after 100 cycles at 4.7 V is harvested. This strategy of constructing a strain buffer layer near the particle surface provides a novel insight for stabilizing the high-voltage LCO and paves the way for further modification of other cathode materials.