| Lithium-ion battery has become an indispensable energy storage device in mobile e-products and its applications in electric vehicles and grid-level energy storage are increasing dramatically in recent years.Considering the power reserve and robust safety,all-solid-state lithium battery with better safety and higher energy density has been extensively studied.Solid electrolyte plays a key role in all-solid-state battery.chloride solid electrolyte has become one of the most promising solid electrolytes because of the combined advantages of sulfide and oxide solid electrolytes,which are excellent chemical and electrochemical stability,good mechanical deformability and high ionic conductivity.However,currently,the ion-transport mechanism and structurerelationship of most of chloride solid electrolytes remain unclear and an effective strategy to guide the material design and property tuning has yet to be developed.Thus,study on the ion-transport mechanism and structure-property relationship is essential.In the first section,we give a brief introduction of the electrochemical fundamentals of all-solid-state battery.Subsequently,we illustrate the classification of lithium-ion solid electrolytes.Finally,we focus on the development and current research of chloride electrolyte and then discuss its application in all-solid-state battery.In the second section,reagents and instruments used in experiments are listed in experiments in chapter 3 and chapter 4.Characterization and analysis methods of materials are given.In the third section,the true crystal structure of Li3YCl6(LYC)and its ionic transport mechanism were explored.There are two issues on current studies of LYC.Issue one is that all of the reported LYC electrolytes contain impurity of LiCl so far,indicating that the reported LYC is not actually stoichiometric.Thus,by decreasing the annealing temperature to 450℃,impurity of LiCl has been avoided and LYC with pure phase has thus been obtained,which means that the first issue has been solved.The second issue is that substantial discrepancy is observed in comparison of theoretical simulation and experiment on ionic conductivity of LYC.Base on Rietveld refinements of diffraction characterization,we conclude that LYC possess an orthorhombic(Pnma space group)structure rather than previously reported trigonal(P3ml)structure.Thus,we demonstrated the true crystal structure of LYC and the Li-ion migration pathway was illustrated.In the fourth section,based on the work of the third section,a series of offstoichiometric LixY(6-x)/3Cl6 has been synthesized.According to the results,when x=2.4,the ionic conductivity of LixY(6-x)/3Cl6 reaches a maximum of 6.12×10-4 S cm-1,which is higher than that of reported LYC.In the case of 2.1≤x ≤ 2.7,the ionic conductivity of LixY(6-x)/3Cl6 will increases with the improvement of crystallinity,which is diametrically different to that of LYC.Subsequently,by utilizing bond-valence site energy method,the lithium pathway of Li2.4Y1.2Cl6 has been simulated,showing that 1D migration pathway of Li2.4Y1.2Cl6 is along b axis in crystal structure.In the fifth section,a series of Li2-xMn1-xGaxCl4(x=0,0.1,0.3,and 0.5)materials were synthesized by the mechanochemical approach.As confirmed by X-ray powder diffraction and Rietveld refinements,Ga3+can be successfully incorporated into the octahedral sites that are partially occupied by Mn2+.The as-milled materials with relatively low crystallinity generally exhibit higher ionic conductivity than the well crystallized ones produced by annealing at 250℃.Among all the materials studied,the as-milled Li 1.9Mn0.9Ga0.1Cl4 shows the highest ionic conductivity(8.3×10-5 S cm-1),which is two orders of magnitude higher than that of the as-milled Li2MnCl4(7.12×107 S cm-1).While the unit cell volume does not vary significantly with the composition,the appropriate Li vacancy content should play an important role in the optimized ionic conductivity of Li1.9Mn0.9Ga0.1Cl4. |
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