Study On Grain Boundary Doping And Interface Modification Of Garnet-type Solid Electrolyte

Recent years,inorganic solid electrolyte is focused on by many researchers as its naturally good chemical stability and electrochemical stability.Garnet type solid electrolyte is a newly developed Li ion conductor with high conductivity and better stability against lithium anode.And,Garnet type solid electrolyte is supposed to replace liquid electrolyte in Li ion batteries in the near future.In this work,we synthesized Garnet type solid electrolyte by solid state reaction and improved its performance.The research content of this thesis includes mainly two parts:the first part is about research and improvement on grain boundaries of Garnet type solid electrolyte,the second part is about improving interface between Garnet type solid electrolyte and lithium anode.In our research,we use LiAlO₂ and LiBO₂ as doping salts to find out how they affect the performance of Garnet type solid electrolyte.SEM shows lithium salts doped samples has less pores between grains comparing to undoped sample.In addition,LiBO₂ also play a role as flux,which made the grains of Garnet type solid electrolyte bigger.EIS shows at low temperature,lithium salts doping improved the grain boundary conductivity of Garnet solid electrolyte.At-30°C,the grain boundary conductivity of undoped Garnet electrolyte is 7.56 × 10-3 S cm^-1.LiAlO₂ doped Garnet electrolyte showed better grain boundary conductivity while do little effect on grain conductivity.the grain boundary conductivity of 0.1-LiAlO₂?mol ratio?doped Garnet reached 2.17 x 10-5 S cm^-1.LiBO₂ doped Garnet electrolyte also showed better grain boundary conductivity than undoped Garnet electrolyte.The grain boundary conductivity of 0.1-LiB02?mol ratio?doped Garnet electrolyte reached 1.97× 10-5 S cm^-1.As a conclusion,lithium salt doping do improve grain boundary conductivity of Garnet type solid electrolyte.In low temperature interval,Arrhenius curves show that lithium salt doping also affected Ea?activation energy?of grain boundary in Garnet.The Ea of grain boundary in undoped Garnet is 0.958 eV.The Ea of grain boundary in LiAlO₂ and LiBO₂ doped Garnet are 0.888 eV,0.635 eV respectively.In high temperature interval,Arrhenius curves show that lithium salt doping reduced ion trapping effect in solid electrolyte and exhibited better conductivity.Among those,LiAlO₂ doped Garnet electrolyte showed best performance.We did some research on interface between Garnet type solid electrolyte and lithium anode.In argon atmosphere,AILi49 composite anode which contains Al-Li alloy?Al4Li9?was made by 200? heating.The AlLi49 composite anode was used to replace pure lithium anode.This result to an improvement on Garnet interface issue.Garnet solid electrolyte has a poor interface wettability with lithium,but has a good interface wettability with AlLi49 composite anode.Using AlLi49 composite anode,the interface resistance which is 75.0 ?·cm2 reduced a lot comparing to Li anode which is 740.6?·cm2.SEM images on interface also proved Garnet has a better contact with AlLi49 composite anode than Li anode.The symmetric cell prepared with AlLi49 composite anode showed stable cycle performance under current densities of 50uA·cm-2 and 100uA·cm-2 with almost no polarization voltage.It even cycled stably more than 400 hours under a current density of 50uA·cm^-2.