Stable Electrochemical Properties of Titanium Doped Layered P2-type Na <sub>0.67</sub> Ni <sub>0.15</sub> Mn <sub>0.85</sub> O <sub>2</sub> Cathode Material for Sodium Ion Batteries
Huawei Han, Shihong Guo, Yimeng Chen, Shuai Guo, Ningyun Hong, Jiangtao Fan, Zhen Long, Xiaoqing Qiu
Abstract
P2-Na 0.67 Ni 0.15 Mn 0.85 O 2 layered sodium transition metal oxides have drawn much attention as a promising candidate cathode due to its high specific capacity and high working voltage. However, undesired cyclability and poor rate performance originated from the serve Jahn-Teller effect and mixed Na + /vacancy ordering during the cycle process. To address this issue, we designed a series P2-type Na 0.67 Ni 0.15 Mn 0.85−x Ti x O 2 (x = 0, 0.05, 0.10, 0.15) cathode by using a modified sol-gel method, and comprehensively investigated the influence of Ti doping Mn sites with the structural and electrochemical properties. It was found that Ti-substitution not only increases the interlayer distance to suppress Na + /vacancy ordering, but also reduces Mn 3+ content to alleviate the Jahn-Teller effect. Notable, the Na 0.67 Ni 0.15 Mn 0.80 Ti 0.05 O 2 electrode exhibited a remarkable cycling stability (85.36% capacity retention after 200 cycles at 1 C). Ti-substitution would greatly increase charge/discharge reversibility and boosts Na + diffusion mobility kinetics, which were clearly elucidated by Ex-situ X-ray Diffraction (XRD), cyclic voltammetry (CV) and Galvanostatic Intermittent Titration Technique (GITT), respectively. This simple and effective work provides a novel strategy for developing high-performance cathode materials for practical SIBs.