Hybrid surface coating layers comprising boron and phosphorous compounds on LiNi0.90Co0.05Mn0.05O2 cathode materials to ensure the reliability of lithium-ion batteries

Abstract

High-energy lithium-ion batteries (LIBs) have undergone significant technological advancements in response to the expanding market for electric vehicles (EVs). Ni-rich layered cathode materials (LiNixCo1-x-yMn1-x-yO2, x ≥ 0.8) are a viable option because of their high reversible capacity over 200 mAh/g. However, the inherent challenges of Ni-rich cathodes include the occurrence of residual lithium, side reactions, and structural instability. Herein, we propose a hybrid surface coating of boron and phosphorous on a LiNi0.9Co0.05Mn0.05O2 (NCM955) cathode material to minimise the side reactions and enhance the structural stability. The hybrid surface coating on NCM955 provides an excellent discharge capacity of 180 mAh/g at 5 C-rate compared to the bare NCM955 capacity of 159 mAh/g. After 300 cycles, the coated NCM955 retained 84% of its capacity, while the uncoated retained only 46%. The improvement can be attributed to the enhanced lithium-ion diffusion achieved through hybrid coating, as confirmed by impedance measurements and cyclic voltammetry analysis. TEM and XPS analyses were performed to validate the presence of the coating layer, confirming the presence of the desired material on the surface. This study provides practical guidance for designing highly reliable, high-capacity cathode materials for use in EV applications.