Preparation And Modification Of Sulfur Based Solid Electrolyte And Its Application In All-solid-state Li-S Batteries

With rapid growing demands in large scale energy storage devices and electric vehicles,the secondary batteries are required to have improved safety and higher energy density.The all-solid-state Li-S battery could eliminate the "shuttle effect" caused by the polysulfide compound with substitution of solid electrolyte for the organic liquid electrolyte.And the solid electrolyte would successfully suppress the growth of lithium dendrites with great mechanical properties.Moreover,the all-solid-state Li-S battery solve the safety hazard caused by liquid electrolyte leakage with use of solid electrolyte.Therefore,all-solid-state Li-S battery has been attracted enormous interest with the possibility and potential of its industrialization in the future.Solid electrolyte is the key for the all-solid-state Li-S battery.And sulfide-based solid electrolyte is considered as one of the most promising solid electrolytes due to its high ionic conductivity at roomtemperature,wide electrochemical window,facile liquid phase synthesis and attractive mechanical properties.Up to now,higher ionic conductivity and superior interfacial stability of solid electrolytes at the electrodes are still two challenging issues for the practical applications of all-solid-state Li-S batteries.This work mainly focus on thesetwo issues and the main research contents are described as follows:(1)Sulfide solid electrolyte was synthesized by a liquid-phase reaction method.Li7P3S11(LPS)was successfully prepared through a optimized experimental condition(such as the ratio of raw materials,reaction time and heat treatment temperature,etc.)with an ionic conductivity up to 1.3*10-3 S/cm at room temperature.(2)A composite solid electrolyte LPS-PEO was prepared by a liquid-phase reaction method.And the ionic conductivity and interfacial compatibility with metallic lithium for the composite solid electrolyte LPS-PEO were investigated.It is found that PEO polymer electrolyte could fill in the space between LPS particles and promote Li+transport,thus effectively improve the ionic conductivity of LPS solid electrolyte.The ionic conductivity of LPS-PEO solid electrolyte with the optimal PEO content can be improved to 2.1*10-3 S/cm at room temperature.Moreover,as PEO polymer coat on the surface of LPS,direct contact between LPS and lithium metal could be avoided,suppressing the reaction between LPS solid electrolyte and lithium electrode.Therefore,the LPS-PEO composite electrolyte has a much better interfacial compatibility with Li meta.(3)Sulfide solid electrolyte LPS is in situ coated on nano-silicon particles(Si@LPS)as the anode material with high energy density.The mechanism of LPS coating for the Si electrochemical performance has been studied.It is found that LPS coating can effectively alleviate the volume expansion of silicon caused by lithiation and delithiation during cycling.Furthermore,with a high ionic conductivity at room temperature,Si@LPS exhibits a great electrochemical performance with improved cycling stability and rate capability.The capacity of the Si@LPS electrode retains 1904 mAh/g after 100 cycles at a rate of 100 mAh/g,and 1332 mAh/g after 500 cycles at a rate of 500 mAh/g.Si nanoparticles are double encapsulated with graphene(G)and LPS(Si@G@LPS)to further improve their electrochemical performance with much improved electron conductivity and ionic conductivity.The Si@G@LPS anode exhibits a further enhanced cycling stability and rate capability.(4)All-solid-state Li-S battery with LPS electrolyte has merits of high electrochemical performance and enhanced safety.To improve the interfacial compatibility between the LPS and metallic lithium anode,two experimental schemes have been proposed.1.All-solid Li-S batteries with LPS-PEO composite electrolyte were assembled.Since the LPS-PEO composite electrolyte has a much better interfacial compatibility with Li metal,the electrochemical performance of the all-solid-state Li-S battery based on LPS-PEO composite electrolyte has been improved compared to that with LPS electrolyte.2.All-solid-state Li2S/Si battery has been assembled with Li2S/graphene cathode.Si@LPS anode and LPS electrolyte.This new battery yields a high theoretical specific energy density up to 1495 Wh kg-1.Moreover,Li2S cathode was used as lithium source instead of using metallic lithium,avoiding interface reaction between lithium metal anode and sulfide electrolyte Li7P3S11.All-solid-state Li2S/Si battery shows a promising electrochemical performance due to great interfacial compatibility between electrode and electrolyte.