Study On Properties Of Inorganic Sulfide Solid Electrolyte And The Lithium Sulfur Battery

At present,with the rapid development of electronic devices and electric vehicles,the performance requirements for energy storage equipments are getting higher and higher.Traditional lithium ion batteries have been widely used because of their high energy density.However,due to the presence of carbonate organic electrolyte,the safety performance of traditional lithium ion batteries is a big problem for their application.The all solid state lithium metal battery is the most promising new energy storage device.Because the introduction of lithium metal anode can greatly improve the energy density of the battery,while the use of solid electrolyte can fundamentally solve the problems of poor safety performance of traditional lithium ion battery.Therefore,the development of solid electrolyte with wide electrochemical window,high room temperature conductivity,excellent chemical stability,low cost and other comprehensive properties is an important prerequisite for the industrialization of all solid state lithium metal batteries.Sulfide solid electrolytes have long been noted for their high room temperature ionic conductivity.For example,solid electrolyte Li₁₀Ge P₂S₁₂ has an ionic conductivity of more than 10^-2 S cm^-1,which is comparable to that of conventional liquid electrolytes.However,there are still many problems in the materials of sulfide solid electrolytes,such as the high preparation cost,poor chemical stability,harsh conditions for synthesis and preparation,prominent interface problems between LGPS and electrode materials,and poor cycle stability of the assembled solid batteries with those solid electrolytes.In order to solve the above problems,the research work of this paper mainly includes the following aspects:Designed a new synthesis route of the sulfide solid electrolytes,For the first time,we propose to use simple materials such as elemental S,P,Si,etc as raw materials which have more stable chemical properties and lower cost.The solid electrolyte is obtained by high energy ball milling method and high temperature sintering process.We have optimized the whole production process.At the same time,we also explored the elemental Si particle size which has a great effect on morphology and properties of those electrolytes.And we found the conductivity of electrolytes can be greatly improved through different halogen doped.Because the doping of halogen can not only abate the bondage of anion to lithium ions,but also expand the ions transport channel.The highest conductivity of the electrolyte prepared by this method can reach 1.35×10^-3 S cm^-1 at room temperature.The electrochemical stability window is above 9 V.The all solid state lithium sulfur battery assembled by"laminating method"using this electrolyte has a higher capacity and a certain cycle performance,which can effectively prove the feasibility of preparing sulfide solid electrolytes by this route of method.Meantime,the poor chemical stability of sulfide solid electrolytes seriously restricts its application.Considering that the main unstable component in the electrolytes is S,and O has a batter chemical stability,we use O to replace part of the S sites in the lattice.It can effectively improve the chemical stability of the electrolyte in the wet environment.The rate of H₂S production after doping is only about 20%of that before doping.At the same time,the electrochemical properties of the electrolyte were not negatively affected.Therefore,this study is beneficial for the large-scale production of the sulfide solid electrolyte.Due to the inadequate solid-solid contact between electrode and electrolyte,the interface of all-solid-state battery is much easy to deteriorate in the cycling process,which seriously restricts the cycling performance of the solid battery.In this article,a kind of organic-inorganic composite solid electrolyte is cleverly designed.The gel solid electrolyte layer prepared by flexible polymer electrolyte and ionic liquid can effectively improve the contact area between the inorganic solid electrolyte and the cathode electrode.Meanwhile,this composite electrolytes can further stabilize the solid-solid interface and effectively reduce the interface impedance.The solid state lithium sulfur battery assembled by the composite electrolyte matched with S and lithium metal has a good cycling stability.The capacity of the battery is maintained at 541 m Ah g^-1 after 150 cycles at 0.1 C at room temperature.At the same rate,the capacity reached 1023 m Ah g^-1 after 50 cycles at 60°C.It shows that the composite electrolyte has good compatibility with anode and cathode.Further,we used the First-principles calculationss to evaluate the effect of Se doping on the electrolyte LSIPSI and optimize the molecular structure of the electrolytes.The electrochemical properties of Se doped sulfide solid electrolyte with were systematically studied in this paper.The effects of doping sites and ratio on the electrolytes structure and lithium ion transport path were also investigated by the first principles calculation.After the calculations,we conducted experiments to successfully obtain the solid electrolyte containing element Se which has high conductivity,excellent chemical stability and wide electrochemical window.The experimental results fully verify the accuracy of the calculation results,which is of great significance for the future design of high performance solid electrolytes using the materials genome engineering method.