Study On The Application And Performance Of Honeycomb Structure Cobalt Compounds In Lithium Sulfur Battery

Traditional lithium-ion batteries（LIBs）cannot meet the growing demand for electric vehicles and mobile power devices due to theoretical capacity density limitations.The theoretical specific capacity of lithium sulfur battery is 1675 m Ah·g^-1and the theoretical energy density is 2800 Wh·kg^-1,which brings a new dawn for the energy storage industry.However,a series of problems remain to be solved,such as the poor conductivity of sulfur materials,the shuttle effect caused by electrolyte dissolution of polysulfide lithium,and the change in the volume of cathode materials caused by structural damage during the charge-discharge cycle,which will lead to huge capacity attenuation,the formation of low coulomb efficiency and poor rate energy of lithium-sulfur batteries.In this paper,the chemical reaction of charge and discharge cycle of lithium sulfur battery was analyzed.Conducting comprehensive analysis of lithium sulfur battery by adding cobalt compounds,sandwich structure electrode and separator modified functional layer were proposed respectively.1.The Co@C and Co F₂@C material with honeycomb carbon hole structure were designed and prepared,and the sandwich structure composite working electrode was designed by introducing the material into lithium sulfur battery.The effects of sulfur content ratio of active material,working electrode load and inter layer of different materials on the electrochemical performance of Li-S battery were investigated by orthogonal experiments.The result shows that the excellent electrochemical performance was achieved under the conditions of 60%sulfur content mass ratio,active substance loading of 1.0 mg·cm^-2and electrolyte to active substance ratio of 20 ul·mg^-1.2.The electrochemical performance of lithium-sulfur batteries under high load and rate conditions was investigated by introducing the honeycomb cobalt fluoride into the cell separator for modification to reduce the volume density of the working electrode.The thickness of the separator,the morphology,size and structure of the material were analyzed by SEM,HRTEM and BET characterization methods.The adsorption of polysulfide by binding materials was detected by UV vis,and a visual U-tube experiment was designed to analyze the XPS of the modified separator,and the SEM graphs,deposition and decomposition data of polysulfide were analyzed.The reason of the modification separator to the high performance of lithium sulfur battery was analyzed by means of experimental method and theoretical calculation,the cell with Co F₂-modified separator presents satisfactory cycle stability with a capacity decay of 0.076%per cycle within 300 cycles at 1 C rate with the sulfur loading of 2.0 mg·cm^-2.A low-capacity decay of 0.088%per cycle for 200 cycles at 0.2 C is also achieved with the sulfur loading of 3.0mg·cm^-2.In addition,a high-capacity retention of 697.5 m A·g^-1is achieved with the sulfur loading of 4.0 mg·cm^-2and the E/S（electrolyte volume/sulfur mass）ratio of 8μL·mg^-1.The results show that the modified separator can effectively improve the battery dynamics of oxidation reduction,adsorb and catalyze polysulfide,improve the diffusion coefficient of lithium ions,reduce the impedance of the battery,lithium metal negative electrode protection,and achieve high performance lithium sulfur batteries.The research of this subject provides a new idea and method for the direction of lithium sulfur battery.The synthesis of cobalt chemicals has simple operation,and the active materials sulfur and graphite materials have wide sources and low prices,and the experimental design process is simple to operate and high repeatability.It provides a new research idea to inhibit the shuttle effect of lithium sulfur battery and improve the battery performance.