| Lithium-sulfur batteries is considered as the next generation lithium secondary batteries system with high theoretical energy density and abundant sulfur resources.High-sulfur-loading,low electrolyte consumption and thin lithium metal anode are the prerequisites for lithium-sulfur batteries to realize their advantages of high energy density and practical application.However,under the above harsh practical conditions,the lithium-sulfur soft pack batteries has the problems of low double-sided capacity and poor cycle performance,which hinder its industrial application.In this paper,based on the structural design of sulfur carbon composite cathode materials,the method of large-scale melting impregnation and spray drying is used to combine sulfur with commercial carbon materials to produce high load of sulfur carbon composite cathode materials;On this basis,the influence of the structure and morphology of the sulfur-carbon composite cathode material on the electrochemical performance was studied,and the preparation process of the lithium sulfur soft coated batteries was explored,which provided an important scientific basis for the industrial application of the lithium sulfur soft coated batteries.The main research work of this paper is as follows:(1)Preparation of S/KB/CNT composite cathode with high sulfur load and study on the technology of lithium-sulfur soft pack batteries.The S/KB/CNT composite anode material with high sulfur load was obtained by using the KB/CNT composite of KB and CNT as the carrier by melting impregnation method,and was used in lithium-sulfur soft pack batteries.The influence of process parameters on the performance of lithium-sulfur soft pack batteries,such as the load of double-sided sulfur in the cathode,the concentration and dosage of lithium salt in electrolyte and the composition of solvent,was studied.The results show that under the practical conditions of high-sulfur-loading,low electrolyte consumption and thin lithium metal anode,the higher the double sulfur load of the cathode,the lower the mass specific capacity based on sulfur mass,and the unit double capacity of the cathode first increases and then decreases.The lower the concentration of lithium salt Li TFSI,the higher the capacity of lithium-sulfur soft pack batteries;The less the amount of electrolyte,the lower the capacity of lithium-sulfur soft pack batteries.Therefore,when the cathode has a double-sided sulfur load of 9.0 mg/cm~2,Li TFSI concentration of 0.1 M,electrolyte dosage(E/S)of 5μL/mg,and solvent DOL/DME volume ratio of 1,the sulfur cathode of lithium-sulfur soft pack batteries has the best electrochemical performance.The mass specific capacity and double-sided capacity of the first cycle are 992.5 m Ah/g and 9.1 m Ah/cm~2,and the mass specific capacity and double-sided capacity of 806.8 m Ah/g and 7.4 m Ah/cm~2are still maintained after32 cycles.(2)Preparation of S/KB/GO composite microsphere cathode material by spray drying and its electrochemical properties.S/KB/GO composite microsphere cathode material was prepared by spray drying with commercial elemental sulfur,Kochen black and graphene micromaterials.GO is not only beneficial to the formation of microsphere morphology of cathode material,but also can inhibit the flying shuttle of polylithium sulfide.When the ratio of GO/KB was 1/5,the S/KB/GO composite microsphere anode material had the highest reversible capacity and cyclic stability.In the button batteries with a positive single-side sulfur load of up to 4.0 mg/cm~2,the first cycle discharge capacity of S/KB/GO-5 composite microsphere cathode material at 0.1 and 0.2 C is 944.7 and 753.5 m Ah/g,respectively,and maintains 613.7 and 500m Ah/g,respectively,after 100 cycles.In lithium-sulfur soft pack batteries with high sulfur load(9.0 mg/cm~2)and low electrolyte consumption(E/S=5μL/mg),the mass specific capacity and double-sided capacity of S/KB/GO-5 composite microspheres are 1047.2 m Ah/g and 9.4 m Ah/cm~2,respectively,showing excellent electrochemical performance. |
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