Promoting homogeneous tungsten doping in LiNiO2 through a grain boundary phase induced by excessive lithium

LiNiO 2 (LNO) is one of the most promising cathode materials for lithium-ion batteries. Tungsten element in enhancing the stability of LNO has been researched extensively. However, the understanding of the specific doping process and existing form of W is still not perfect. This study proposes a lithium-induced grain boundary phase W doping mechanism. The results demonstrate that the introduced W atoms first react with the lithium source to generate a Li-W-O phase at the grain boundary of primary particles. With the increase of lithium ratio, W atoms gradually diffuse from the grain boundary phase to the interior layered structure to achieve W doping. The feasibility of grain boundary phase doping is verified by first principles calculation. Furthermore, it is found that the Li 2 WO 4 grain boundary phase is an excellent lithium ion conductor, which can protect the cathode surface and improve the rate performance. The doped W can alleviate the harmful H2↔H3 phase transition, thereby inhibiting the generation of microcracks, and improving the electrochemical performance. Consequently, the 0.3wt% W-doped sample provides a significant improved capacity retention of 88.5% compared with the pristine LNO (80.7%) after 100 cycles at 2.8-4.3 V under 1 C. A novel approach for excessive lithium-induced W grain boundary phase doping is presented. Li 2 WO 4 grain boundary phase exhibits higher stability during thermal diffusion with LiNiO 2 (LNO), resulting in W typically existing in this form, uniform doping of W in LNO can be achieved through this structure, significantly improving the cycling stability of the LNO.