Synthesis And Electrochemical Performance Of Sb-doped Porous Sno₂coating On Mno₂for Supercapacitor

Manganese dioxide (MnO2) is considered to be one of the most promisingelectrode materials for supercapacitors due to its superior characteristics as largespecific capacitance, environmental friendly, natural abundance and low cost. Despiteall of the superiority, some drawbacks still exist such as low surface area, poorelectronic conductivity and partial dissolution in the electrolyte during cycling,which hinder its practical applications in supercapacitors. Coating inorganic layer onMnO2surface can suppress the dissolution of MnO2and improve the cycling stabilityof MnO2electrode. Meanwhile, when the coating layer possesses excellent electricalconductivity, it also can offset the electrical conductivity of MnO2. However, thecoating layer certainly will adverse to the quickly contact between electrolyte ions andMnO2, and decrease the charge/discharge rate of the electrode, which will lead to thecapacitance of electrode materials declines. Therefore, it is urgently to make theelectrolyte conveniently access to the MnO2with improving the cycling stability andelectrical conductivity of MnO2.In this study, MnCO3precursor was firstly synthesized by a facile route, thencoating MnCO3with SbCl3and SnCl4through sol-gel method, followed by annealingat certain conditions, and Sb doped SnO2coated on MnO2(SS-MnO2) was obtained.Since CO2was produced and diffusion outside during thermal decomposition ofMnCO3, the Sb doped SnO2coating layer is porous and it is beneficial to thepercolation of electrolyte. The influences of preparation conditions including thecoating amount of SnO2, the doping amount of Sb, the coating time and the calcinedtemperature on the discharge performance of SS-MnO2electrode were investigatedand analyzed by orthogonal experiments, and the optimum preparation conditionswere obtained. The morphology and structure of SS-MnO2were characterized bySEM and TEM, and the content of elements in the SS-MnO2surface was analyzed byEDS.The electrochemical performances of SS-MnO2electrode, as well as pure MnO2(P-MnO2) electrode and SnO2coated MnO2(SS-MnO2) electrode were evaluated andcompared by galvanostatic charge-discharge test, cyclic voltammogram (CV) andelectrochemical impedance spectroscopy (EIS). Results of charge-discharge testsdemonstrated that the discharge effect at large current work condition and the cycling stability of SS-MnO2electrode is superior to both P-MnO2electrode and S-MnO2electrode. And results of CV tests showed that when the scanning rate is200mV.s-1,the SS-MnO2electrode still maintained good capacity performance, while the P-MnO2electrode emerged serious electrode polarization. Moreover, analysis of EIS suggestedthat the internal resistance of SS-MnO2electrode is much smaller than that of P-MnO2and S-MnO2electrodes. All these investigations proved that the electrochemicalperformances of MnO2were improved effectively by Sb doped SnO2coating.In addition, the electrochemical behaves of SS-MnO2electrode in differentelectrolyte including neutral electrolyte, acidic electrolyte and alkaline electrolytewere researched systematically in this paper, and the results indicated that theSS-MnO2electrode in neutral electrolyte possesses lower capacitance and bettercycling stability than that of in acidic electrolyte and alkaline electrolyte.