| With the increasing depletion of traditional energy and the aggravation of environmental pollution,people pay more attention to the research and development of new energy and its storage scheme.As a kind of green and efficient secondary battery,the lithium-ion battery has been widely concerned and researched.With the increasing need for large capacity and high energy density power batteries and energy storage batteries,the safety of lithium-ion batteries has become a major obstacle to its further development.The root of the safety problem is that the organic liquid electrolyte is flammable at high temperature,and it is easy to react with the electrode and cause irreversible damage.In recent years,the rapid development of solid electrolyte has greatly improved the safety of lithium-ion batteries.As one of the garnet solid electrolyte,Li7La3Zr2O12(LLZO)has many advantages,such as:good chemical stability,wide electrochemical window,high mechanical strength,etc,and shows a bright application prospect.The cubic phase structure of LLZO has relatively higher ionic conductivity than tetragonal phase,but its structure is not stable.How to stabilize the cubic phase structure of LLZO and improve the ionic conductivity is a hot topic in this field.In this thesis,solid phase reaction method and sol-gel method were adopted respectively.The pure phase solid electrolyte LLZO was prepared by optimizing the preparation parameter-rs.And on this basis,the effect of element doping on the electrochemical performance of the electrolyte was further studied.The main research contents are as follows:(1)Solid state reaction method:High energy mechanical ball milling was used to fully mix the raw materials.Based on the analysis of TG-DSC results,the pre sintering temperature was determined to be 800?,and the process parameters such as the amount of lithium salt added,sintering temperature and sintering time were optimized.The optimal preparation process conditions is adding lithium salt by excess 20%wt and treating at 1000? for 9h.The ionic conductivity of LLZO electrolyte material is 3.57×10-7 S·cm-1.(2)Sol-gel method:In order to reduce the sintering temperature and sintering time of solid phase method,LLZO electrolyte materials were prepared by sol-gel method using LiNO3,La(NO3)3·6H2O and Zr(NO3)4·5H2O as raw materials.By means of XRD,SEM and EIS,the preparation conditions is treating LLZO at,800? for 3h.The ionic conductivity of LLZO electrolyte material is 9.86×10-1S·cm-1.(3)Element doping:In order to further improve the structural stability and ionic conductivity of the materials,the effects of Mn and Al doping on LLZO were studied.When the Al element is doped,the pure phase LLZO solid electrolyte materials can be prepared by two methods.In the solid-phase reaction method,th.e best doping ratio is 2%wt and the highest ionic conductivity is 1.04× 10-5S·cm-1.When the sol-gel method is used,the best.doping ratio is 1.5%wt.And the highest ionic conductivity of the material is 4.51×10-5S·cm-1.The doping of Al can signific-antly improve the ionic conductivity of the material.When the Mn element was doped by sol-gel method,the doping of elemental Mn could inhibit the volatilization of lithium and increase the ionic conductivity of the material,up to 6.44×10-5S·cm-1.The results show that the doping of Mn is more beneficial to the structural stability and the improvement of ionic conductivity. |
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