Doping Modification Study Of Electrolyte Materials For All-solid-state Batteries

Among the many solid-state lithium-ion electrolytes,the NASICON structure of the solid-state lithium-ion conductor(Li_1.3Al_0.3Ti_1.7（PO₄）₃)has a high total ionic conductivity,and it is promising to be experimentally explored to bring it up to the application standard of battery conductivity(10^-2～10^-3S/cm).Therefore,in this paper,the electrochemical properties of LATP electrolytes were improved by adding a templating agent to the preparation of LATP electrolytes,using high temperature quenching and cooling method to prepare LATP electrolytes,and using montmorillonite to dope and modify the LATP electrolytes.XRD,SEM and AC impedance tests were used to characterize and analyze the microscopic morphology,internal structure and electrochemical properties of each experimental sample.（1）Graphene was used as a template agent to prepare LATP lithium ion conductors by co-precipitation method.The results show that the special physical structure of graphene causes the formation of a uniform porous structure inside LATP,which promotes the grain growth inside LATP,expands the migration channels of lithium ions and enhances the total ionic conductivity of LATP.The optimum doping ratio of 0.5wt%for the preparation of LATP samples with graphene as the template agent achieves the highest total ionic conductivity,2.42×10^-4S/cm.（2）The LATP lithium ion conductor was prepared using high temperature quenching and cooling.The results show that the quenching process causes the phase transition to not take place in time,so that the grain size of LATP remains the same after quenching as before quenching,and that the subsequent heat treatment causes the grains that have stopped growing to grow slowly and bond more tightly between the grains,which in turn expands the lithium ion migration channel,reduces the activation energy of LATP and increases the total ionic conductivity.The highest total ionic conductivity of 1.14×10^-4S/cm was achieved for LATP after quenching and cooling followed by a heat treatment at 950°C for 3hours.（3）Different ratios of montmorillonite doping were used to prepare LATP lithium ion conductors.The results showed that the doping of the appropriate amount of montmorillonite effectively enhanced the densities of LATP,expanded the migration channels of lithium ions at the grain boundaries,reduced the grain boundary impedance as well as the activation energy of LATP,and increased the total ionic conductivity of the LATP samples.The highest total ionic conductivity,4.22×10^-4S/cm,was achieved when the MMT doping was 4wt%.（4）LATP solid electrolytes prepared with and without graphene as a templating agent,montmorillonite-doped and undoped LATP solid electrolytes were tested for air stability,respectively.The effects of graphene and montmorillonite on the air stability of LATP solid electrolytes were investigated separately by electrochemical impedance tests.The results show that the addition of graphene templating agent during the preparation of LATP solid electrolytes can homogenise the internal pores of the LATP solid electrolytes and facilitate the migration of lithium ions,and the LATP solid electrolytes prepared with graphene as the templating agent can still maintain 75%of the initial total conductivity when tested after seven weeks;the doping of montmorillonite helps to enhance the densities of the LATP solid electrolytes,thus facilitating the The montmorillonite-doped LATP solid-state electrolyte maintained 98%of its initial total conductivity after ten weeks.