Surface modification of over-lithiated layered oxide by low-temperature chemical vapor deposition for high energy lithium-ion batteries

In comparison to traditional lithium-ion battery cathode materials, over-lithiated layered oxides cathodes (OLOs) contain extra lithium ions. Because of this over-lithiation, they are considered a promising candidate for application as the cathode material in high-energy lithium ion batteries. However, to utilize the additional lithium ions, OLOs must be charged beyond 4.4 V vs. Li/Li⁺, i.e., highly oxidizing conditions. Consequently, oxidative side reactions on the surface of OLOs are problematic, hindering the performances of these lithium ion batteries. To overcome this problem, we have developed an artificial homogeneous solid electrolyte interface (a-SEI) comprising an organic surface coating on OLO. The surface coating is deposited by low temperature-chemical vapor deposition using a mix of CO₂ and CH₄ gases. Using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, we determined that the modified a-SEI is composed of alkylcarbonate and lithium carbonate. The surface modified OLO shows improved performance due to its enhanced rate capability, high initial capacity, and long cycle life. We used AC impedance analyses to investigate these improvements and found that they result from fast charge transfer reactions and the stabilization of the surface via surface modification.