Research On Preparation,Modification And Electrochemical Performance Of Nasicon-type Solid Electrolyte Li_1.3Al_0.3Ti_1.7（PO₄）₃

NASICON-type solid electrolyte Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）has high ionic conductivity at room temperature,stability to water and oxygen in the air,high safety and low cost,and can be large-scale produced and commercialized.However,there are still problems such as low grain boundary conductivity,complicated preparation process,high energy consumption,and difficulty in assembling batteries.In view of the existing problems,the solvothermal method was used to synthesize LATP,the best calcination and sintering temperature were determined.On this basis,element doping was carried out to further improve the ion conductivity.For the difficulty of LATP solid electrolyte assembly batteries,PEO and PVDF was used as a polymer substrate,and Gd³⁺doped LATP inorganic solid electrolyte was added to it to prepare LATP-PEO-PVDF composite solid electrolytes.The paper got the following results:（1）The NASICON structure LATP solid electrolyte material with good polyhedral morphology and crystallinity was successfully synthesized by solvothermal method.It was determined that the optimal calcination temperature is 700℃,there is no incomplete reaction or amorphous transformation process,and no unreacted intermediates were produced.When the sintering temperature is 900℃,the LATP solid electrolyte has a pure phase,and does not produce non-lithium ionic conductor Al PO₄and Ti O₂ mixed phases.The sintered electrolyte pellet has high crystallinity,uniform particles and dense contact,and there are no holes caused by incomplete sintering and cracks caused by over-sintering crystal grains.It has the highest ionic conductivity of1.38×10^-4S cm^-1 at room temperature,the lowest activation energy of 0.330 eV,and the solid electrolyte is pure ionic conductor.（2）The Gd-doped Li_1.3Al_0.3-xGd_xTi_1.7（PO₄）₃ electrolytes material were prepared by solvothermal method.Al³⁺were replaced by Gd³⁺,increasing the size of the crystal lattice,causing a mismatch between the crystal lattice and grain boundaries,and making the contact between particles closer.Smaller voids increase the effective contact area between particles and reduce the grain boundary resistance,which facilitates the diffusion and transportation of Li⁺.It is determined that the maximum doping amount of Gd³⁺is x=0.075,it is the maximum content of Gd³⁺to replace Al³⁺and can completely enter the lattice of LATP,and does not emerge too much non-lithium ion conductive Gd PO₄ phase.With the Gd doping content of 0.075,the solid electrolyte has the highest ionic conductivity of 4.23×10^-4 S cm^-1 at room temperature,the lowest activation energy of 0.247 eV and the highest relative density of 94.89%.（3）The LATP-PEO-PVDF（LPP）composite solid electrolyte was prepared by the solution casting method.When the amount of LATP added is 10%,the composite electrolyte has the highest ionic conductivity 1.14×10^-5 S cm^-1（25℃）and 9.05×10^-5S cm^-1（60℃）,and changes the ion migration number from 0.14 increased to 0.42.The chemical window can be stabilized at 5.18 V,and the constant current cycle test is carried out at a current density of 0.3 m A cm^-2 for 400 h,and the voltage is always maintained at 0.025 V,which has good interface compatibility with lithium metal.The assembled Li Fe PO₄/LPP-10%/Li solid-state battery has a discharge specific capacity of103.4 m Ah g^-1 in the first cycle at 0.5 C,the discharge specific capacity is still 90.2m Ah g^-1 after 100 cycles and it has a good rate capability.