Preparation,Characterization And Supercapacitance Of Nickel And Cobalt Selenide Electrode Materials

Nickel cobalt based metal oxides and sulfides have received much attention.At present,it has excellent electrochemical performance in many fields.However,selenium,which is in the same host family,has not been reported in the field of electrochemistry.In order to develop better electrode active materials,metal selenide gradually into people’s field of vision.Firstly,the conductivity of metal selenide is higher than that of metal sulfide.It is favorable for the charge and transfer in the reaction process;secondly,the Faraday pseudo capacitance provided by the metal selenide is much higher than that of the carbon material.Therefore,it is of great value to apply metal selenide to supercapacitors.Therefore,we can synthesize the nickel cobalt metal selenide with excellent performance by a simple solvothermal method.The detailed research contents of the thesis were described as follows:(1)By changing the experimental conditions,solvothermal method for the preparation of multiphase bimetallic nickel cobalt selenide,obtained when the reactant nickel cobalt salt molar ratio of 2:1,with relatively better performance.Electrochemical test,when the current density from 2 A / g increased to 10 A / g,the capacity retention rate of up to 85 %.The specific capacity was 131.7 F / g at a current density of 0.2 A / g,and the maximum energy density and power density were 38 Wh / kg and 2175 W / kg,respectively,when assembled into a hybrid supercapacitor.Finally,the cycle performance test,at 1 A / g for 5000 times after the charge and discharge,still able to maintain more than 83 % of the capacity,indicating that the electrochemical stability of the material is good.(2)By the solvothermal method,the synthesis of multi phase nickel cobalt selenide is obtained.The results show that the material has better performance when the molar ratio of nickel cobalt salt is 2:1.When the current density increased from 2 A/g to 10 A/g,the capacity retention rate was up to 85 %.At the current density of 0.2 A/g,the specific capacity was F/g,and the maximum energy density and power density were respectively 38 Wh/kg and 2175 W/kg.Finally,the cycle performance is tested,when at the 1 A/g,,it still can maintain more than 83 % capacity after charging and discharging for 5000 times,indicating that the material has good electrochemical stability.(3)By simple two step solvothermal method,the plurality of groups of selenium electrode materials was prepared of by adjusting the amount of selenium source.The energy storage mechanism is analyzed,but we propose a new energy storage mechanism.In the system of three electrodes,at the current density at 2 A/g,the specific capacity is 748 F/g.however,when added to the high current density of 30 A/g,the specific capacity still has about 320 F/g.so it showed a very good rate capability.When it is assembled into an asymmetric capacitor,the charge and discharge performance of the cycle is excellent.After 5000 times,the specific capacity is still up to 82.3 %.After calculating the energy density and power density,the maximum is as high as 33 Wh/kg and 3750 W/kg.Therefore,the NiCoSe2 electrode material is very suitable for supercapacitors.