Functionalities of the LiV3−xNbxO8 surface layer on a Li2NiO2 cathode additive for enhancing the moisture stability and cycling performance of lithium-ion batteries†

Abstract

Incorporating an over-lithiated lithium nickel oxide (Li₂NiO₂) cathode additive is an effective way to compensate for the initial Li⁺ consumption, mainly caused by solid electrolyte interphase formation in high-capacity Si or SiO_x anodes used in advanced lithium-ion batteries (LIBs). Li₂NiO₂ offers a large initial charge capacity (∼320 mA h g⁻¹) and high irreversibility (∼70%), which is beneficial for providing surplus Li⁺ to the anodes. Then, the irreversible Li⁺ consumption can be compensated by the surplus Li⁺ in the first cycle, thereby increasing the practical energy density of LIBs. Unfortunately, the vulnerability of Li₂NiO₂ to moisture, owing to its high Li concentration, facilitates the formation of impurities such as LiOH and Li₂CO₃, leading to a significant increase in the interfacial resistance with a loss of cycling stability. In this study, we coat the surfaces of Li₂NiO₂ particles with a lithium trivanadate (LiV₃O₈) functional layer to enhance moisture stability and mechanical strength through surface stabilization. Furthermore, the structural engineering of LiV₃O₈ through the elemental substitution of Nb effectively reduces the interfacial resistance resulting from a strong enhancement in the ionic conductivity of LiV_3−xNb_xO₈. In practice, a full-cell assembled with a cathode composed of LiNi_0.8Co_0.1Mn_0.1O₂ and LiV_3−xNb_xO₈-coated Li₂NiO₂ exhibits enhanced energy density by compensating for the capacity loss, maintaining a stable cycling performance over 200 cycles. In conclusion, this study offers a practical solution for enhancing lithium-ion battery performance by improving moisture stability, reducing interfacial resistance, and improving energy density and cycling longevity through advanced cathode surface engineering.