Study On The Capacitive Performance Of CoNi₂S₄ Prepared By The Hydrothermal Method

In recent years,supercapacitors have been widely used in energy storage due to their high power density and long cycling life.Among them,electrode materials are an important factor determining the electrochemical performance of supercapacitors.Among various electrode materials,cobalt nickel sulfide is considered a pseudocapacitive electrode material with great potential due to its high theoretical specific capacity and excellent electrochemical activity.This article aims to prepare Co Ni₂S₄ electrode materials with excellent electrochemical performance through two-step hydrothermal method and one-step hydrothermal method,respectively.By changing the process conditions,Co Ni₂S₄ series materials with different morphology and electrochemical performance were prepared.Using physical characterization and electrochemical analysis methods to determine appropriate process parameters to prepare Co Ni₂S₄ electrode materials with excellent electrochemical performance.On the basis of the optimal process conditions,Co Ni₂S₄ and EG were composite to obtain O-CNS/EG composite materials with better electrochemical performance.Based on the two-step hydrothermal method,Co Ni₂S₄ material（T-CNS-St10）with a surface resembling chestnut shell was prepared under the conditions of sodium sulfide as a sulfurizer,1.6 g of precipitant added,135 ^oC and 6 h of primary hydrothermal temperature and time,and 10 h of sulfurization time.This material has an excellent specific capacitance of 1940.2 F g^-1 at a current density of 4 A g^-1.After 5000consecutive charges and discharges,the capacitance retention rate is 74%of the initial value.Assemble it with activated carbon as positive and negative electrodes to form a flat plate capacitor.At a power density of 400 W kg^-1,the corresponding energy density is 46.4 Wh kg^-1.At a current density of 1 A g^-1,the specific capacitance of the device reaches 122.2 F g^-1.After 5000 charges and discharges,the device maintains an initial specific electrical capacity of 56%.A one-step hydrothermal method was used to synthesize Co Ni₂S₄ material（O-CNS）with different microstructures and electrochemical properties by changing the type and concentration of sulfurizer,sulfurization temperature and time.Physical characterization and electrochemical analysis were used to determine that the crystalline Co Ni₂S₄ electrode material with excellent electrochemical performance was obtained by sulfurization of 8 mmol sodium sulfide for 10 hours at 165 ^oC.This material has an excellent specific capacitance of 1940.6 F g^-1 at 4 A g^-1.After 5000 charges and discharges,the specific capacitance retention rate reaches 80%.When this material is assembled with AC,the specific capacitance of the device at 1 A g^-1 is 125.9 F g^-1.After5000 charges and discharges,the specific capacitance retention rate of the device is68%,and the corresponding power density at 50.2 Wh kg^-1 is 433.1 W kg^-1.The O-CNS/EG composite material synthesized on the basis of one-step hydrothermal process conditions has a specific capacitiance of 2121.5 F g^-1 at a current density of 4 A g^-1.After 5000 consecutive charges and discharges,the capacitance retention rate is as high as 90%.The specific capacitance of the capacitor assembled with composite material and AC is 150.9 F g^-1 at 1 A g^-1,and the capacitance retention rate is 72%after 5000charges and discharges.The energy density of the device is as high as 59.7 Wh kg^-1 at400 W kg^-1.This thesis has 98 figures,6 tables and 127 references.