Preparation And Electrochemical Supercapacitor Performance Based On MnO₂

Supercapacitor is an environmental energy storage device. It has high energy density, good reversibility and long cycle life. MnO₂ are very promising candidates as electrode materials in supercapacitors due to their low cost, low toxiclty and environment friendly characteristics.In this paper MnO₂ powder is prepared by molten salt method in three different systems: KCl-LiCl, KCl-LiCl-NaCl, KCl-ZnCl₂.The results show that different systems have great effects on synthesis of the samples. Samples synthesized in KCl-LiCl and KCl-LiCl-NaCl system are compound ofα-MnO₂ andγ-MnO₂ butβ-MnO₂ in KCl-ZnO₂ system. The sample prepared in the KCl-LiCl-NaCl system under the conditions of 2h,450℃,m(KMnO₄+MnCl₂): m(KCl-LiCl-NaCl)=l:3 has the best supercapacitor properties. The discharged specific capacitance reached 227.65F·g^-1 at the current density of 2mA·cm^-2.Its equivalent series resistance (R_S) and electrode reaction resistance (R_r) are 0.84Ωand 0.94Ωseparately.Tested at the current density of 5mA·cm^-2 for 100 cycles its discharge specific capacitance is 191.25F·g^-1 and its charge/discharge efficiency reaches 100%.MnO₂ were synthesized by hydrothermal method with different reaction conditions.The production is compound of a-MnO₂ andγ-MnO₂.Under the prime prepared condition of 2h,125℃,2mL isopropanol the R_S and R_r of MnO₂ are 0.24Ωand 1.96Ω.The discharge specific capacitance reaches 303.55F·g^-1at 2mA·cm^-2.Its discharge specific capacitance is 198.34F·g^-1 at the current density of 5mA·cm^-1 after 100 cycles attenuated by 29.75%. The charge/discharge efficiency after 20 cycles is 100%. The sample prepared by hydrothermal method under the prime condition is doped with carbon nanotubes(CNTs), TiO₂ and La. XRD and electrochemical tests were carried out. The results of XRD show that the structures of the doped samples don't change. Electrochemical test results show that proper adulteration ratio of CNTs, TiO₂ and La all make supercapacitor performances of the samples better and the best ratio are 5%,1% and 1% in order.The sample with 1% TiO₂ doped has the best impedance property, R_Sand R_r of MnO₂ are 0.17Ωand 0.23Ω. The sample with 5% CNTs doped has the best cyclic performance and the highest capacitance, its discharge specific capacitance is 380.98F·g^-1,higher than MnO₂ without CNTs by 25.50%.Its discharge specific capacitance is 310.25F·g^-1 tested at the current density of 5mA·cm^-2 for 100 cycles, compared with the capacitance before cycled (349.12 F·g^-1) only 11.13% of the capacitance is lost.