钠离子电池高电位稳定电极Na $_2$ Ni $_2$ TeO $_6$的解散扩散动力学
Unraveling diffusion kinetics of honeycomb structured Na$_2$Ni$_2$TeO$_6$ as a high-potential and stable electrode for sodium-ion batteries
摘要：
为了寻找有潜力的钠离子电池正极材料并了解其扩散动力学，本文采用循环伏安法（CV）、电化学阻抗谱（EIS）、恒电流充放电（GCD）和恒电流间歇滴定法（GITT）对蜂窝结构Na $_{2}$ Ni $_{2}$ TeO $_{6}$材料进行了详细的电化学研究。在0.05 C和0.1 C电流倍率下，$^{-1}$的放电容量分别为82和77 mAhg，在1 C下的中工作电位为$\approx$ 3.9 V，在0.5 C下循环500次后，容量保持率高达80%，并具有良好的倍率性能。不同扫描速率下的CV数据分析揭示了钠离子存储的赝电容机制。有趣的是，{ \it in-situ} EIS测量显示在不同的充电/放电阶段以及在不同的循环次数之后电荷转移电阻的系统变化。使用CV、EIS和GITT提取的扩散系数主要在10 $^{-10}$至10 $^{-12}$ cm $^{2}$ s $^{-1}$的范围内，并且在电化学循环期间Na $^+$ -离子浓度的脱嵌/插入与通过光电发射研究确定的Ni $^{3+}$ /Ni $^{2+}$价态的比率一致。此外，即使经过各种充放电循环，回收的活性材料的循环后结果也显示出非常稳定的结构和形态。我们详细的电化学研究和扩散动力学研究确立了该材料作为钠离子电池的高工作电位和长寿命电极。
英文摘要：
In search of the potential cathode materials for sodium-ion batteries and to understand the diffusion kinetics, we report the detailed analysis of electrochemical investigation of honeycomb structured Na$_{2}$Ni$_{2}$TeO$_{6}$ material using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge (GCD) and galvanostatic intermittent titration technique (GITT). We found the discharge capacities of 82 and 77 mAhg$^{-1}$ at 0.05~C and 0.1~C current rates, respectively, and the mid-working potential of $\approx$3.9~V at 1~C and high capacity retention of 80\% after 500 cycles at 0.5~C as well as excellent rate capability. The analysis of CV data at different scan rates reveals the pseudo-capacitive mechanism of sodium-ion storage. Interestingly, the {\it in-situ} EIS measurements show a systematic change in the charge-transfer resistance at different charge/discharge stages as well as after different number of cycles. The diffusion coefficient extracted using CV, EIS and GITT lies mainly in the range of 10$^{-10}$ to 10$^{-12}$ cm$^{2}$s$^{-1}$ and the de-insertion/insertion of Na$^+$-ion concentration during electrochemical cycling is consistent with the ratio of Ni$^{3+}$/Ni$^{2+}$ valence state determined by photoemission study. Moreover, the post-cyclic results of retrieved active material show very stable structure and morphology even after various charge-discharge cycles. Our detailed electrochemical investigation and diffusion kinetics studies establish the material as a high working potential and long life electrode for sodium-ion batteries.
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