Zhang Jiansheng, Liang Guisheng, Wang Chao, Lin Chunfu, Chen Jiajia, Zhang Zhongru, Zhao Xiu Song
Institute of Materials for Energy and Environment, College of Materials Science and Engineering, Qingdao University, Qingdao 266071, P.R. China.
State Key Laboratory for Physical Chemistry of Solid Surface, Collaborative Innovation Centre of Chemistry for Energy Materials, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P.R. China.
ACS Appl Mater Interfaces. 2020 Jun 24;12(25):28313-28319. doi: 10.1021/acsami.0c07702. Epub 2020 Jun 11.
In this work, we revisited the stability of the Cr/Cr redox couple in a sodium superionic conductor (NASICON)-type compound, NaTiCr(PO). Experimental results showed that the NaTiCr(PO) compound exhibited a specific capacity of 49.9 mA h g at 20 mA g, about 80% of its theoretical capacity of 62.2 mA h g with one Na insertion/deinsertion per formula NaTiCr(PO). The redox couple was found to be stable against cycling with some 90.3% capacity retention after 300 cycles within the voltage range between 2.5 and 4.7 V. With a wider voltage range between 2.5 and 5.0 V, the capacity retention was about 76.6% after 1000 cycles, indicating the redox couple is stable against overvoltage. In addition, the effect of Ti/Cr ratio on the reversibility of the redox couple was studied by varying in NaTiCr(PO) (where = 0.6, 0.8, 1.0, 1.2, 1.4, 2.0). It was confirmed that = 1 is optimal for balancing the electrode stability and the capacity. The obtained optimal content of Cr in the compound provides useful guidance for designing new Cr-based NASICON-type cathode materials. Furthermore, in situ X-ray diffraction (XRD) analysis of compound NaTiCr(PO) indicated a two-phase sodium-ion storage mechanism, which is different from the previously reported one-phase mechanism. Rietveld refinement XRD analysis showed a small volume change of the compound during cycling (about 2.6%), indicating good structural stability.
在这项工作中，我们重新研究了钠超离子导体（NASICON）型化合物NaTiCr(PO)中Cr/Cr氧化还原对的稳定性。实验结果表明，NaTiCr(PO)化合物在20 mA g下的比容量为49.9 mA h g，相对于每式NaTiCr(PO)有一个Na嵌入/脱嵌时其理论容量62.2 mA h g的约80%。发现该氧化还原对在循环过程中是稳定的，在2.5至4.7 V的电压范围内300次循环后容量保持率约为90.3%。在2.5至5.0 V的更宽电压范围内，1000次循环后容量保持率约为76.6%，表明该氧化还原对对于过电压是稳定的。此外，通过改变NaTiCr(PO)中的 （其中 = 0.6、0.8、1.0、1.2、1.4、2.0）研究了Ti/Cr比对氧化还原对可逆性的影响。证实 = 1对于平衡电极稳定性和容量是最佳的。化合物中获得的Cr的最佳含量为设计新型Cr基NASICON型阴极材料提供了有用的指导。此外，对化合物NaTiCr(PO)的原位X射线衍射（XRD）分析表明存在两相钠离子存储机制，这与先前报道的单相机制不同。Rietveld精修XRD分析表明化合物在循环过程中的体积变化很小（约2.6%），表明具有良好的结构稳定性。
