Preparation And Research Of Cathode Of Quasi-solid Electrolyte Li-S Battery

Compared with the traditional commercial lithium-ion batteries,lithium-sulfur?Li-S?batteries has a very remarkable energy density and specific capacity which is as high as 1675 mAh·g^-1 and is about 10 times more than the commercial lithium-ion batteries.The battery can fully meet the requirements of the power battery.Furthermore,sulfur,the active material,is abundant in nature,non-toxic,environment-friendly and low cost,which is suitable for the industrial production.Nevertheless,there exist many its own defects in the sulfur of Li-S batteries,such as,the extremely poor conductivity,the shuttle effect caused by the dissolution of polysulfides and the volume expansion during the charging and discharging process.In order to solve the above problems,the cathode composites were prepared and the solid electrolyte were utilized to assemble the battery to make up for the inherent defects of Li-S batteries.The main work was as follows.In this paper,the cathode composites including nano-TiO₂ as a host material were prepared by the grinding and the melt diffusion method and were assembled into solid-state Li-S batteries.The content of sulfur was 41.4 wt.%in the cathode composites with a good electrical conductivity,a low contact resistance and a definite chemical anchor effect.The above battery showed the initial discharge capacities of 1160 mAh·g^-1 at 0.15 C and 270 mAh·g^-1 after 67 cycles.In addition,the effect of the melt diffusion method on the Li⁺diffusion of cathode materials was expounded,and then the Li-S battery with excellent electrochemical properties were obtained.In this paper,polyvinylidene fluoride?PVDF?was used as substrate,polymethyl methacrylate?PMMA?as pore preparation agent,sodium hydroxide solution as pretreatment solution to prepare porous conductive carbon material via high-temperature carbonization.The composite material was fabricated by the melt diffusion method and assembled into a button cell.The content of sulfur was 42.7wt.%in the cathode composites.The above battery showed the initial discharge capacities of 1037 mAh·g^-1 at 0.1 C and 683 mAh·g^-1 after 240 cycles.In addition,this paper expounded the forming mechanism of the porous structure of the material and the relationship between the structure and the performance of the battery.The two composites were characterized accordingly,including scanning electron microscope?SEM?,transmission electron microscope?TEM?,thermo-gravimetric analysis test,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The electrochemical performances of two kinds of button cells assembled by composites were tested,including charge-discharge test,cyclic voltammetry?CV?,galvanostatic intermittent titration technique?GITT?and electrochemical impedance spectra?EIS?analysis.The results indicated that both materials had excellent electrochemical properties.In the first material,the sulfur was uniformly coated on the host material and had a higher Li⁺diffusion performance after heat treatment.The second material had excellent conductive properties and a uniform as well as abundant macroporous and mesoporous structure providing sulfur load space and physical adsorption effect for polysulfides.