Preparation Of Bimetallic Compounds And Their Electrochemical Properties As Supercapacitor Electrode Materials

Supercapacitors are becoming popular in today's energy storage devices.As a new energy storage device,super capacitor has attracted much attention due to its high power density,short charging time and long cycle life.Especially in electric vehicles,industrial power,aerospace and many other areas.Among the active materials reported at present,the metal compounds have achieved high specific capacity and excellent cyclic stability.It is the most promising type of electrode active material for the realization of high energy density supercapacitors.However,the disadvantage of low energy density has seriously hindered its practical application.Therefore,in order to improve the energy density of supercapacitors,developing new electrode materials and improving the electrochemical capacity of ultracapacitor will undoubtedly become a breakthrough to solve this problem.Among all kinds of electrode materials,metal compounds have achieved high specific capacity and excellent cycling stability.They are the most promising electrode active materials for realizing high energy density supercapacitors.In this paper,a series of nickel cobalt based compounds,such as nickel cobalt molybdate,nickel cobalt phosphates were constructed by changing the proportion of nickel/cobalt metal ion and the type of coordination anions.The electrochemical performance of nickel cobalt based samples have been systematically studied.Nickel phosphate,with high specific capacitance,rich production,low cost and friendly environment,is considered as a very potential pseudo capacitance electrode material.However,the poor conductivity resulted in the relatively poor performance and cyclic stability of nickel phosphate.Cobalt phosphate is well known for its excellent cyclic stability and excellent ratio performance,but it has lower performance.Therefore,it is of great significance to improve the cycling and ratio performance of cobalt phosphate and to improve the specific capacitance of nickel phosphate.Firstly,we adopted a simple and green environmental protection chemical co-precipitation method at room temperature.The synthesis condition is more simple,environment friendly and suitable for mass production.In order to study the influence of Nickel/Cobalt metal ratio on the electrical properties of metal phosphate,the molar ratio of nickel to cobalt ions was controlled in the reaction precursor,and the transition metal phosphates with different morphologies were successfully synthesized by controlling the reaction ratio.After calcining the precursor,the electrochemical properties of the precursor were tested,and the influence of the ratio of nickel and cobalt ions on its structure and electrochemical properties was investigated.The experimental results show that when the ratio of nickel and cobalt is 2:1,the sample obtained by calcining at 300?for 3 hours has the best performance.The nickel cobalt bimetallic phosphate samples showed higher specific capacity,ratio performance and cyclic stability than pure cobalt phosphate and pure nickel phosphate samples.When the current density is 1A g^-1,the specific capacitance is up to 1576 F g^-1,and it has good multiplier and cycle stability.The sample and graphene are assembled into asymmetrical supercapacitors,and the materials also exhibit excellent electrochemical properties.The material shows excellent electrochemical performance as an asymmetrical super capacitor cathode.Under 1 A g^-1 current density,the specific capacitance is 100 F g^-1,and the energy density is 21.7 Wh kg^-1.when the power density is 4.9 kW kg^-1Inspired by the excellent electrochemical performance of phosphate bimetallic salts,we have also made an attempt at bimetallic molybdate.Molybdate is also synthesized by chemical co-precipitation method.Nanorod nickel cobalt molybdates precursor were obtained,followed by calcination of the muffle furnace.In order to study the effect of calcination temperature on molybdate structure and its electrochemical performance,bimetallic molybdate with different phases was obtained by controlling calcination temperature,and the electrical properties of the bimetallic molybdate were tested.The experimental results show that the calcining temperature is 300?as the best reaction condition.When the current density is 1A g^-1,the specific capacitance can be as high as 1000 F g^-1,and the electrode material has good multiplier and cyclic stability.