弱结晶二氧化锰超级电容器充放电分析

以等物质的量的高锰酸钾和乙酸锰为原料,采用机械化学法制备出弱结晶型α-MnO₂超级电容器电极材料.在1.2V电压内,200mA·g^-1电流密度下对对称型超级电容器进行恒流充放电测试.采用XRD法、循环伏安及交流阻抗法对充放电前后电极材料的结构以及电化学性能进行表征,首次采用求斜率法对充放电曲线分析.结果表明:超级电容器表现出法拉第电容与双电层电容的双重特征;在循环过程中,电化学惰性物质Mn₃O₄生成,循环伏安图中氧化还原峰逐渐消失;充放电曲线的法拉第电容特征逐渐消失而接近双电层电容理想曲线;超级电容器的比容量、等效串联电阻发生了对应的变化,其最大电极比容量达到416F·g^-1,经过近500次循环后,比容量为220F·g^-1.

Charge-discharge process of a weak-crystalline manganese dioxide supercapacitor

Equivalent moles of KMnO₄ and Mn(CH₃COO)₂ were used to prepare a weak-crystalline α-MnO₂ supercapacitor electrode material via a mechanochemical route. An assembled symmetrical supercapacitor was tested by galvanostatic charging-discharging within 1.2 V at 200 mA·g^-1. The structure and electrochemical performances of the electrode material were identified by XRD, cyclic voltammetry and AC impedance both before and after charging-discharging. The slope of the charge-discharge curve was analyzed for the first time. It suggests that the supercapacitor exhibits both double-layer capability and pseudocapacitance property. Mn₃O₄, an electrochemical inert, has formed in the charging-discharging process. During cycling, redox peaks disappeared gradually in the cyclic voltammetry diagram, and the pseudocapacitance property disappeared in the discharge curve, then the discharge curve was dosed to the ideal line of double-layer capacitance; the specific capacity and equivalent series resistance of the MnO₂ supercapacitor changed accordingly, the maximum specific capacity of the MnO₂ electrode reached as high as 416 F·g^-l, and retained 220 F·g^-1 after nearly 500 cycles.