Preparation And Properties Of Chalcogenide Glass And Glass Ceramic Solid Electrolytes

Lithium-sulfur batteries have the advantages such as high specific capacitance,low cost,environmental friendly etc.and are therefore expected to be one of the next generation dynamic batteries.The conventiona llithium-sulfur batteries using aprotic solvent electrolytes suffer from the problems of lithium dendrite growth and the “shuttle effects” of polysulfides,which lead to safety and durability issues.One promising strategy to eliminate these issues is to replace aprotic solvent electrolytes by solid electrolytes.Developing solid electrolytes with excellent ionic conductivity and stability is crucial for the commercialization of lithium-sulfur batteries.Typical solid electrolytes include polymer electrolytes,oxide electrolytes,sulfide electrolytes,etc.Profiting from the large ionic radius and the strong polaribility of the anions,which facilitates the transport of Li⁺,sulfide solid electrolyte show relatively high ionic conductivity.In this paper,three sulfide solid electrolyte systems,Li₂S-P₂S₅,GeS₂-Ga₂S₃-Li₂S and GeS₂-Ga₂S₃-Li₂S-LiI,were studied.Ball milling,a technique compatible with large scale production,was applied to mechanically synthesize the glassy solid electrolytes;Furthermore,controllable crystallization was applied on the glassy solid electrolytes to create metastable fast-ion-conductor crystals or nano-crystallites within the glassy matrix,so that the ionic conductivity can be improved.The main conclusions are as follow:1、70Li₂S-30P₂S₅（mol%）glass powder was prepared by ball milling,then the glass powder was annealed in high vacuum to form metastable Li₇P₃S₁₁ with high lithium ion conductivity.The process condition of controllable crystallization was systematically studied.The results show that if the annealing temperature is too high,loss of sulfur in Li₇P₃S₁₁ occurs and a low ionic conductive phase Li₄P₂S₆ forms,and if the annealing temperature is too low,the crystallization is not thorough.Both situations result in low iconicconductivity.The highest ionic conductivity of 2.44×10-4 S/cm is achieved by heat treatment at 260 ℃ for 1 h.2、GeS₂-Ga₂S₃-Li₂S glass powder was prepared by ball milling with the compositon of 56GeS₂-14Ga₂S₃-30Li₂S,48GeS₂-12Ga₂S₃-40Li₂S,and 40GeS₂-10Ga₂S₃-50Li₂S.The increase of Li₂S content leads to the break of [S₃（Ga）Ge-Ge（Ga）S₃] homo-bond and to the formation of non-bridging sulfur stucture,which benefit the improvement of ionic conductivity.The highest ionic condutivity of 7.76×10-6 S/cmis achieved in the glass solid electrolyte 40GeS₂-10Ga₂S₃-50Li₂S.3、GeS₂-Ga₂S₃-Li₂S-Li I glass powderwas prepared by replacing part of Li₂S with Li I.The total percentage of Li⁺ waskept at 50 mol%.The addition of halogen I-can destroy [S₃（Ga）Ge-Ge（Ga）S₃] and V1-[GeS₄] bridged sulfur-structure,creat non-bridged sulfurstructure,and partially replace S^2-by I-to form larger ion transport channels.All these structural modifications improve the ionic conductivity.The ionic conductivities of theglasse with the LiI replacement ratio of 40 mol% is 1.31×10-3 S/cm,two order of magnitude higher thanthe glasses without LiI.Cyclic voltammetry test shows thatthe electrochemical performance of the solid electrolyte was very stable at room temperature.The electrochemical window was as high as 6V vs Li⁺/Li,satisfying to the battery charge and discharge conditions.4、Glass-ceramic with different crystallinity were prepared by 10 h annealing of the 32GeS₂-8Ga₂S₃-40Li₂S-20 LiI and 28GeS₂-7Ga₂S₃-20Li₂S-30 Li I glasses.It shows that in the galss-ceramics the transport of lithium ions at the glass/crystal interfaces behaves in a hopping manner,which can siginficantly improve the entire ionic conductivity.For 32GeS₂-8Ga₂S₃-40Li₂S-20 LiI glass,when the crystallinity is 33.56%,which is achived by 10 h annealing at 260℃,the maximumconductivity of 6.6×10-4 S/cm can be reached.The conductivity is 18 times higher than the base glass.For 28GeS₂-7Ga₂S₃-20Li₂S-30 LiI glass,when the crystallinity is 4.24%,which is achived by 10 h annealing at 255 ℃,the maximumconductivity of 4.64×10-4 S/cm can be reached.The conductivity is 1.5 times higher than the base glass.Electrochemical window can reach 6V vs Li⁺/Li.