钠锰比对NaxMnO2的性能和钠离子脱嵌过程的影响

采用高温固相法合成了Na_xMnO₂,并用X-射线衍射、X-射线光电子能谱、场发射扫描电镜、循环伏安、电化学阻抗谱和恒流充放电技术研究了钠锰比对材料的形态结构、电化学性能和钠离子脱嵌过程的影响. 结果表明,Na_xMnO₂ 主要由Na_0.7MnO₂ 和Na_0.91MnO₂ 组成,且Na_0.91MnO₂ 的量随着钠锰比的增加而增加. 随着钠锰比的增加,SEI 膜扩散、界面电化学反应和固相扩散的活化能先减少后增大,而材料的放电比容量则先增大后减少. 当钠锰比为0.80 时,合成的材料1C 倍率下首次放电比容量为152.8 mAh·g^-1,50 次循环容量保持率为80.6%,5C 大倍率下放电比容量为88.3 mAh·g^-1,表现出了良好的循环性能和倍率性,相应的SEI 膜扩散、界面电化学反应和固相扩散过程的活化能分别为68.23、40.07 和57.62 KJ·mol^-1.

Influences of Na-Mn Ratio on Electrochemical Performances and Intercalation-Deintercalation Processes of Sodium Ion in NaxMnO2

In this work, Na_xMnO₂ was synthesized by a solid-state reaction. The influences of Na:Mn ratio on the structure, morphology and electrochemical performance, and sodium ion intercalation/deintercalation processes were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge test. The preparedNa_xMnO₂ was mainly composed of Na_0.7MnO₂ and Na_0.91MnO₂, and the content of Na_0.91MnO₂ increased with the increase of Na:Mn ratio. However, the activation energy values of surface membrane diffusion, interfacial electrochemical reaction and Na⁺ diffusion in the bulk material first decreased and then increased with the increase of Na:Mn ratio, while the discharge capability first increasedand then decreased with the increase of Na:Mn ratio. The sample synthesized with the Na:Mn ratio of 0.80 delivered a discharge capacity of 152.8 mAh·g^-1 with a capacity retention of 80.6% after 50 cycles at 1C. Even being charged/discharged at 5C, this sample still provided a discharge capacity of 88.3 mAh·g^-1, showing good cycle-stability and rate performance. The activation energy values of surface membrane diffusion, interfacial electrochemical reaction and solid-phase diffusion were found to be 68.23, 40.07 and 57.62 kJ·mol^-1, respectively.