【摘要】 采用溶胶-凝胶法并辅以微波热处理合成了Na掺杂改性的Li_2-xNa_xMnSiO₄/C（x=0,0.05,0.09,0.13）复合正极材料.利用X射线衍射（XRD）、扫描电子显微镜（SEM）、恒电流充放电测试、循环伏安（CV）和交流阻抗（EIS）测试等对材料进行了表征.结果表明,经微波辐射后得到的电极材料具有Pmn2₁型空间结构,其碳层分布均匀,粒径细小均匀,约为15～30 nm.在微波辅助原位碳包覆和Na掺杂共同作用下,复合材料的电荷转移电阻明显降低,Li⁺扩散速率增大,展现出优良的电化学性能.在0.1C倍率下Li_1.91Na_0.09MnSiO₄/C样品首次放电比容量为211 m A獉h/g,50次循环后仍保持80 m A獉h/g的可逆容量;0.5C和2.0C倍率下的放电比容量分别为106和53 m A獉h/g,大电流下的可逆容量明显提高.更多还原

【Abstract】 Li_2-xNa_xMnSiO₄/C（x=0,0.05,0.09,0.13）composite cathode materials were synthesized with microwave assisted sol-gel method.The crystal structure,morphology and electrochemical performance were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,galvanostatic charge-discharge test,cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）.The results indicate that the as-prepared materials can be well indexed to Pmn2₁space group.The particles are fine with carbon layer coated uniformity and their size are evenly distributed in the range of 15—30 nm.With the synergistic effects of Na⁺doping and microwave assisted in-situ carbon coating,the charge transfer resistance is reduced while the diffusion of Li⁺is enhanced significantly,leading to excellent electrochemical performance.The Li_1.91Na_0.09MnSiO₄/C exhibits an initial discharge capacity as high as 211 m A·h/g at 0.1C and retained 80 m A·h/g after 50 cycles.The reversible capacities at high rate currents are also improved obviously,with discharge capacities of 106 m A·h/g and 53 m A·h/g at 0.5C and 2.0C separately.更多还原