| Safety problems of lithium ion battery in the application become increasingly prominent with the expansion of its application field.The successfully research of solid electrolyte will be expected to solve this problem.The perovskite-type Li3xLa(2/3)-xTiO3(LLTO)solid electrolyte is promising to be used in the next generation of solid lithium batteries to replace liquid electrolytes,bescuse of its stable structure,simple preparation process and large variable range of components.It can effectively solve the safety problems caused by flammable and leaking liquid electrolyte in traditional lithium ion batteries.However,the ionic conductivity of solid electrolyte is lower,which limits its application in lithium ion battery.The aim of the project is to improve the ionic conductivity of solid electrolyte through rearech on preparation process of LLTO and using ion doping and composition optimization,and the main research contents are as follows:(1)LLTO solid electrolyte was prepared by solid phase reaction sintering.The effects of calcination temperature and lithium ion content on the structure and ionic conductivity of solid electrolyte were studied.It was found that the density of LLTO solid electrolyte increased with the increase of sintering temperature.Its crystalline phase changed from cubic to tetragonal,and Ionic conductance increased first and then decreased.As lithium content of LLTO increasing,the carrier concentration were increased,and the ionic conductivity increased.However,high lithium content will lead to melting and decrease ionic conductivity.Finally,the LLTO solid electrolyte sintered at 1300℃ with a lithium content of 0.42 exhibited the best lithium ionic conductivity,which reaches up to 1.30×10-3 S·cm-1.(2)Al3+ ions and Zr4+ ions doped at the B site of Li0.42La0.57TiO3 were used to improve the conductivity of solid electrolyte ions.The effect of ionic doping on the structure and ionic conductivity of solid electrolyte was studied.It was found that Zr4+ ions entered the lattice of Li0.42La0.57TiO3 solid electrolyte,resulting to enlarge the cell volume and expand the transport channel of lithium ions.Thus the ionic conductivity of solid electrolyte increased.When the doping amount of Zr4+was 0.02,the ionic conductivity of electrolyte reached to 1.43×10-3 S·cm-1.The doping of Al3+ ions with Li0.42La0.57TiO3 solid electrolyte leaded to the increase of oxygen vacancy in the lattice,thus the ionic conductivity was improved.When the doping amount of Al3+ was 0.03,the ionic conductivity of electrolyte reached to 1.54×10-3 S·cm-1.Comparing ionic conductivity of solid electrolyte,Al3+ doped Li0.42La0.57TiO3 solid electrolyte was higher.(3)The ion conductivity of solid electrolyte was improved by doping Sr2+ions at the A-site of Li0.42La0.57TiAl0.03O3.The effect of Sr2+ ion doping amount on the structure and ionic conductivity of solid electrolyte was studied,and the electrochemical stability of the assembled half-cell was studied.It was found that Sr2+ ion doping resulted in lattice distortion of Li0.42La0.57TiAl0.03O3,which enlarges the transport channel of lithium ions.Meanwhile,Sr2+ substituted for La3+to produce more oxygen vacancies.When the Sr2+ doping amount was 0.03,the ionic conductivity of solid electrolyte reached to the maximum value,namely 1.84×10-3 S·cm-1,under the dual action of expanding the lithium ion transport channel and oxygen vacancy.The solid electrolytes were assembled into symmetrical cells.It was found that the solid electrolyte had a wide electrochemical window,which facilitated the free transfer of lithium ions in the electrolyte.However,its stability with lithium electrode was poor,resulting in increasing interfacial resistance.The solid electrolyte was assembled into a solidstate battery,and the batteries delived high capacity retention of 91.8%after 90 cycles at 1C,showing good cyclic stability... |
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