Material Design Of Separator Interlayer And High-performance Lithium-sulfur Battery

With the development of electric vehicles,it becomes rapidly increasing to require higher energy density of power batteries.At present,due to the limited potential of existing cathode materials,the increase in energy density of commercial lithium-ion batteries is approaching a theoretical limit.The future development direction of power batteries is to develop higher energy density battery systems.Lithium-sulfur batteries,as a new generation of secondary batteries,have an extremely high theoretical energy density.In order to solve the problem of rapid capacity decay caused by shuttle effect,coating functional materials on the separator is a simple and effective method to block the diffusion of polysulfides.From the perspective of interlayer materials of the separator,this paper researched the influence of the interlayer materials and structures of the separator on the performance of lithium-sulfur batteries.It is mainly divided into the following three aspects:(1)In situ template-sacrificing approach to a highly conductive 3D hybrid interlayer material.A highly conductive interlayer,as the dual current collector,is necessary to re-utilize lithium polysulfide for better performance of lithium-sulfur batteries.Slurry coating usually results in the poor conductivity owing to the insulating binders.Herein,a metal coordinated compound(Mn-BDC)is served as the sacrificed template to induce a highly conductive polypyrrole(PPy)skeleton via in situ polymerization.Simultaneously,the decomposition of Mn-BDC produces fine particles that are highly absorptive in the PPy skeleton.The resultant PPy hybrid interlayer,about 5?m in thickness,can remarkably inhibit the shuttle effect and reuse the adsorbed lithium polysulfide.As a result,a high specific capacity of 517.3 mA h·g^-1 is achieved after 500 cycles at 0.5C with a fading rate of 0.093%per cycle.(2)Hydroxylated nanoporous carbon interlayer material and its structure-activity relationship.Hydroxylated nanoporous carbon which is a separator-modified interlayer material,the effects of its pore structure on electrolyte ion transport and the performance of lithium-sulfur batteries were studied in the second part.The results show that the hydroxylated nanoporous carbon materials with a pore diameter of 100 nm has good ionic conductivity,it can not only inhibit the shuttle effect significantly but improve the rate performance as the second current collector with high porosity structure effectively.The assembled lithium-sulfur battery retains a specific capacity of 493 mA h·g^-1 after 500charge-discharge cycles at a current density of 0.5C,with an average attenuation rate of0.102%.Besides,the specific capacity of the first cycle can reach 466 mA h·g^-1 at 2C,and it remains210 mA h·g^-1 after 500 cycles.(3)The effect of Co₃S₄ with rod-shaped microporous skeleton structure on the performance of batteries has been discussed based on the multifunctional intermediate layer material of cobalt-based zeolite imidazolate frameworks(ZIF-67)material sulfurized derivative.The results show that Co₃S₄ prepared by the ZIF-67 precursor method has various properties of catalysis,adsorption and conductivity.It obtained higher rate performance with the modified separator.A high specific capacity of 550 mAh·g^-1 was performed and the average attenuation rate of 0.108%was achieved by 300 cycles at the current density of 1C.