Preparation And Properties Of Cobalt Selenide-based Sodium-ion-battery Anode Materials

Lithium ion batteries(LIBs)have been in the leading position in the application of energy storage devices in electric vehicles and handheld electronic products.However,due to the limited reserves of lithium resources on the earth,the application of LIBs in the future large-scale renewable energy storage is hindered.Sodium is not only widely distributed on the earth,but also easy to obtain.In addition,sodium and lithium are in the same main group,and have similar chemical properties.Therefore,many researchers regard sodium ion batteries as an alternative to LIBs in large-scale renewable energy storage applications.Although graphite is regarded as an ideal anode material for lithium-ion batteries by researchers,due to the fact that the distance between layers of graphite is smaller than that of sodium ion,it can not meet the need of the insertion and removal of sodium ion,so it is necessary to find new anode materials.Cobalt selenide,nickel selenide and other metal selenides stand out in many negative electrode materials due to their good electrochemical performance,so it is of great value to develop new metal selenides and optimize their application in sodium ion batteries.Starting from the nanostructure and material composition,the shuttle like three-dimensional hollow porous cobalt selenide anode material was successfully prepared by self sacrificing template method.The main research contents are as follows:Using cobalt acetate as cobalt source and polyvinylpyrrolidone as a ctivator,solid shuttle precursor was prepared by oil bath method.After that,the precursor was selenized.In the process of selenization,the cation exchange between the anion and the anion resulted in the hollow and porous shuttle like selenide.On the one hand,this unique structure can provide more area to contact with electrolyte,on the other hand,the path of ion transport is shortened,and then the charge and discharge speed is improved.After that,the surface of cobalt selenide was coated with dopamine.After high temperature carbonization,there was a carbon shell on the surface of cobalt selenide.The carbon shell has two functions: one is to improve the conductivity,the other is to make the structure stronger.It is found that the specific capacity of the electrode material reaches 564.99 m A h g-1 in the first cycle,when the current density is maintained at 1 A g-1,and after 100 cycles of charging and discharging,the specific capacity of the electrode material is 268.30 m A h g-1,showing good electrochemical performance.Cobalt(nickel)selenide was successfully prepared by using cobalt acetate as cobalt source and nickel acetate as nickel source.In order to find out the optimal composition ratio of cobalt and nickel in the sample,three propo rtions of nickel cobalt mole ratio of 1:5,1:3 and 1:1 were chosen to prepare the sample.In order to improve the electrochemical performance of cobalt selenide,a carbon shell is also coated on it.The battery test shows that when the ratio of nickel to c obalt is 1:3,the specific capacity of 367.48 m A h g-1 can be achieved after 100 times of constant current charging and discharging at the current density of 1 A g-1,and 245.40 m A h g-1 can be achieved at the high current density of 10 A g-1.