An effective gradient coating strategy to improve the structure stability of Ni-rich nickel-cobalt-manganese ternary layer oxide cathode

Abstract

Ni-rich cathode materials with high nickel and low cobalt are currently developing for lithium-ion batteries, aiming to increase energy density of the nickel-cobalt-manganese ternary layer oxide (NCM). However, the practical application of Ni-rich cathode materials is hindered by limited cycle stability, which arises from their inherent structural instability during the cycling process. Through layer-by-layer codeposition followed by high-temperature sintering, we design a concentration gradient core-shell structure consisting of a nickel-rich core with a Ni:Co:Mn mole ratio of 9:0.5:0.5, two interlayers with increasing Mn content gradient, and a high-manganese thin shell (CG-NCM). The structure demonstrates a stabilized lattice configuration and a decreased degree of Li+/Ni2+ mixing during electrochemical cycling. The XRD, XPS, TEM results are consistent with the findings from the first principles calculations, indicating a significant reduction in the mixing of lithium and nickel within the layer structure, thereby improving conductivity and structural stability. Remarkably, CG-NCM exhibits a capacity retention of 96.26 % after 100 cycles at 1C, whereas unmodified Li(Ni0.794Co0.11Mn0.096)O2 (CC-NCM) only retains 80.25 % of its capacity. This study shows that CG-NCM has excellent structural, electrochemical and thermodynamic properties, and its gradient structure design provides a broad prospect for the development of high-stability cathode materials for lithium-ion batteries.