Modification And Electrochemical Properties Of Separators For Lithium-sulfur Batteries

Environmental issues and energy issues have always been important issues affecting the further development of the earth.With the continuous development and progress of society and the traditional non-renewable resources are gradually exhausted,we need to vigorously develop new energy to achieve sustainable economic development when facing the problem of environmental pollution.We urgently need to develop new energy energy storage devices with high specific capacity and high energy density for the growing demand for electronic equipment and new energy vehicles.Lithium-sulfur batteries are hailed as a new generation of ideal energy storage devices due to their high theoretical specific capacity(1675 m Ah g^-1),but the"shuttle effect"of polysulfides generated during charging and discharging of lithium-sulfur batteries.It has become a major obstacle to the commercial application of lithium-sulfur batteries.The electrochemical performance of the battery can be effectively improved by modifying the separator in the lithium-sulfur battery.Compared with the commonly methods for synthesizing modified separator such as coating method,vacuum filtration method,electrochemical deposition method,etc.,a novel hydrothermal self-assembly method was used to synthesize Ni(OH)₂,Co(OH)₂and Ni-Co double metal hydroxide nanosheet array material are used to modify the separator.This method is simple,time-consuming,and the morphology of the synthesized material is controllable.The specific research contents are as follows:(1)Using nickel nitrate hexahydrate and ammonia water as raw materials,and a commercial separator for lithium-sulfur batteries as the substrate,Ni(OH)₂nanosheet array material modified separator was synthesized by a hydrothermal self-assembly method.The effect of reaction time on the composition,structure and morphology of the product was investigated by XRD,SEM and TEM,and it was confirmed that the product with a reaction time of 15 min had good crystal form and uniform flower-like morphology.The synthesized Ni(OH)₂modified separator was applied to the test of lithium-sulfur battery.According to the test results,when charging and discharging at 1.7-2.8 V,the lithium-sulfur battery containing Ni(OH)₂modified separator can achieve a discharge specific capacity of 816m Ah g^-1at a rate of 2 C.After 400 cycles,the discharge specific capacity can still be maintained at 558 m Ah g^-1at 0.2 C.In addition,the contact angle and adsorption performance of Ni(OH)₂modified separator were tested to further confirm that it has good wetting performance to electrolyte and adsorption performance of lithium polysulfide.(2)Using cobalt nitrate hexahydrate and ammonia water as raw materials and commercial separators for lithium-sulfur batteries as substrates,Co(OH)₂nanosheet array materials modified separators were synthesized by hydrothermal self-assembly method.The effect of reaction time on the composition,structure and morphology of the product was investigated by XRD,SEM and TEM,and it was confirmed that the product with a reaction time of 5 min had good crystal form and uniform flower-like morphology.The synthesized Co(OH)₂modified separator was applied to lithium-sulfur battery test.According to the test results,when charging and discharging at 1.7-2.8 V,the lithium-sulfur battery containing Co(OH)₂modified separator can reach a specific discharge capacity of 709 m Ah g^-1at a rate of 2 C.After 400 cycles,the discharge specific capacity can still be maintained at 391 m Ah g^-1at 0.2 C.In addition,the contact angle and adsorption performance of the Co(OH)₂modified separator were tested to further confirm that it has good wetting performance to the electrolyte and the performance of adsorbing lithium polysulfide.(3)Using nickel nitrate hexahydrate,cobalt nitrate hexahydrate and ammonia water as raw materials,and a commercial separator for lithium-sulfur batteries as the substrate,a Ni-Co double metal hydroxide nanosheet array material modified separator was synthesized by a hydrothermal self-assembly method.The effect of reaction time on the composition,structure and morphology of the product was investigated by XRD,SEM and TEM,and it was confirmed that the product had a good crystal form and a uniform flower-like morphology when the mass ratio of nickel nitrate hexahydrate and cobalt nitrate hexahydrate was 3:2.The synthesized Ni-Co double metal hydroxide modified separator was applied to the lithium-sulfur battery test.According to the test results,when charging and discharging at1.7-2.8 V,the lithium-sulfur battery containing Ni-Co double metal hydroxide modified separator can achieve a specific discharge capacity of 703 m Ah g^-1at a rate of 2 C.After 400cycles,the discharge specific capacity can still be maintained at 396 m Ah g^-1at 0.2 C.In addition,the contact angle and adsorption performance of the Ni-Co double metal hydroxide modified separator were tested,and it was further confirmed that it has good wettability to the electrolyte and adsorption performance of lithium polysulfide.