Abstract
P2-Na0.67Ni0.15Mn0.85O2 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 Na0.67Ni0.15Mn0.85−xTixO2 (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 Mn3+ content to alleviate the Jahn-Teller effect. Notable, the Na0.67Ni0.15Mn0.80Ti0.05O2 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.
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