Synergistic enhancement of LiNi0.9Co0.05Mn0.05O2 cathode performance through F- doping and Gd2O3 coating: Mechanistic insights into rate capability and cycling stability

High-nickel and low-cobalt layered cathodes possess remarkable advantages of high energy density and low cost, presenting great prospects in promoting high-energy-density batteries. However, they suffer from severe interfacial and structural degradation during the cycling process, resulting in relatively low transport kinetics and cycle life. In this paper, a dual-modification strategy was employed to synthesize the LiNi0.9Co0.05Mn0.05O2 (FNCM955@Gd2O3) cathode with F- bulk doping and Gd2O3 multifunctional rare earth oxide coating on the basis of the LiNi0.9Co0.05Mn0.05O2 cathode (NCM955) through a simple two-step heat treatment process. The F- bulk doping effectively reduces the Li+/Ni2+ cation mixing, enhancing the reversibility of the H2-H3 phase transition and the stability of the material structure. The Gd2O3 multifunctional rare earth oxide coating layer can not only act as a "physical passivation film" to block the direct contact between the electrode and the electrolyte, alleviating the structural degradation and interfacial instability; but also serve as an "electron reservoir" to perform charge compensation for the interfacially unstable Ni4+, suppressing the occurrence of the transformation of harmful phases such as the NiO rock salt phase and enhancing the transport kinetics of the material. Therefore, the NCM955 with F- bulk doping and Gd2O3 multifunctional rare earth oxide coating exhibits excellent cycle stability in the voltage range of 0.2C and 2.7-4.3 V, with a capacity retention rate of 78.5 % after 200 cycles, which is 16.2 % higher than the 62.3 % of the original NCM955. In addition, even at a rate of 5C, FNCM955@Gd2O3 can also provide a superior discharge specific capacity of 159.5 mAh g- 1. This work opens up a new solution idea for simultaneously addressing the problems of interfacial instability and overall structural degradation of high-nickel and low-cobalt cathode materials.