High-Voltage LiCoO2 Material Encapsulated in a Li4Ti5O12Ultrathin Layer by High-Speed Solid-Phase Coating Process

The LiCoO2 (LCO) cathode has been widely used in material markets, especially in conventional lithium ion batteries, due to its stable electrochemical performance. Increasing the working cutoff potential represents an efficient pathway to boost the capacity of LCO batteries; however, high working potentials usually induce severe Co3+ dissolution and extensive growth of solid electrolyte interphase (SEI) layer, leading to rapid degradation of the electrochemical performance. In this work, a high voltage cathode is prepared by the encapsulation of aluminum (Al)-doped LiCoO2 in a continuous Li4Ti5O12 (LTO) layer using a high-speed solid-phase coating method. The chemical composition evolution of the coating layer during the cycling process was characterized and evaluated through in situ XRD, XPS, and XAS analyses. The precipitation of aluminum fluoride (AlF3) at the defective sites of the LTO coating layer in the initial charge–discharge cycles effectively was found to fortify the structural integrity of the coating layer and prevent the etching of the LCO from undesirable side reactions with the liquid electrolyte. The modified LCO demonstrated an excellent capacity retention of 89.9% after 100 cycles at 0.2 C. The high-speed solid-phase coating method established in this study could be scaled up straightforwardly, providing a highly commercializable approach for large-scale production of stable high-voltage LCO cathode materials.