LiCoO_2和LiMn_2O_4在水系电解液中的赝电容研究

Investigation on pseudo-capacitive properties of LiCoO_2 and LiMn_2O_4 in aqueous electrolyte

用溶胶-凝胶法合成了LiCoO2和LiMn2O4样品粉末。以LiCoO2和LiMn2O4电极为正极,活性炭(AC)电极为负极,分别组装成模拟非对称超级电容器AC/LiCoO2和AC/LiMn2O4,通过循环伏安、恒流充放电和电化学阻抗研究其电容性能。测试结果表明,这类非对称电容器在Li2SO4溶液中展示了较好的电容性能。在电压范围(0～1.4)V、电流密度为100mA·g-1时,AC/LiCoO2和AC/LiMn2O4电容器的初始比电容分别为45.9和44.6F·g-1。但在大电流密度下,AC/LiMn2O4具有更大的比电容和更好的循环性能。实验结果还表明,在水系电解液中,LiCoO2和LiMn2O4均是通过Li+脱嵌导致过渡元素(Co,Mn)价态变化所产生的赝电容来实现储能。

LiCoO2 and LiMn2O4 powders were synthesized by a sol-gel process.An asymmetric supercapacitor was fabricated with LiCoO2（or LiMn2O4） electrode as a positive electrode and activated carbon （AC） as a negative electrode in aqueous electrolyte.Pseudo-capacitive properties of asymmetric supercapacitors were determined by cyclic voltammetry,charge/discharge test and electrochemical impedance measurement.The AC/LiCoO2 and AC/LiMn2 O4 asymmetric supercapacitor exhibited good capacitive behaviors in Li2SO4 solution in the potential range of （0 ～ 1.4） V,and delivered initial specific capacitance values of 45.9 and 44.6 F·g-1（based on the active mass of the two electrodes） at a current density of 100 mA·g-1,respectively.However,the AC/LiMn2O4 capacitor exhibited greater specific capacitance and better cycling performance than the AC/LiCoO2 cell at 400 mA·g-1.Both LiCoO2 and LiMn2 O4 electrode utilized the charge-transfer pseudo-capacitance arising from the fast and reversible Faradaic reactions caused by insertion/deinsertion of Li-ion.