Preparation Of Na₃PSe₄-based Solid Electrolyte And Its Interface Stability Against Na

All-solid-state batteries have attracted intensive attention because of their high energy density,high safety and other advantages that solve the flammable and explosive problems of commercial organic liquid lithium-ion batteries.As an important part of all-solid-state batteries,solid-state electrolytes have become one of the research priorities.However,there are still many problems that need to be solved urgently at the beginning of all-solid-state battery research.For example,the ionic conductivity of the electrolyte is low,the growth of lithium/sodium dendrites,the instability of the electrode/electrolyte interface,and the high contact resistance of the electrode/electrolyte solid-state interface.In this paper,the interfacial stability of Na₃PSe₄ sulfide solid electrolyte with sodium metal anode has been studied.The chemical/electrochemical instability at the interface is improved by three means,so that the assembled all-solid-state sodium anode battery performs well good performance.In this paper,fluoride-modified Na₃PSe₄ solid electrolyte was prepared by solid-phase sintering method.Four kinds of fluoride-modified electrolytes Na_3-nxM_xPSe_4-x（M=Ag,Zn,Ca,Al,where n=positive valence number）were designed and synthesized.After XRD characterization and synthesized analysis,the electrolytes of trace added mount of AlF₃ were synthesized,and the electrolyte can show good electrochemical stability.However,the XRD phase characterization results show that AlF₃ cannot be doped into the Na₃PSe₄ solid electrolyte lattice,and cannot change the structure of the electrolyte itself.When the doping amount is 0.1 or more,unknown impurity phases are generated in the electrolyte.Through Mapping,it can be seen that when the designed doping amount is 0.05,AlF₃ is uniformly distributed in the electrolyte.The assembled sodium symmetric battery was subjected to constant current charge-discharge tests,and the results showed that when the doping amount was 0.05,its electrochemical stability was greatly improved compared to the unimproved Na₃PSe₄ solid electrolyte and it can be stably cycled for 400 h without short circuit,which shows that the interface stability has been improved,and the all-solid-state battery assembled with metal sodium anode also shows good cycle performance.By modifying the surface of metal sodium,an artificial SEI layer is constructed to block the chemical and electrochemical reactions between the electrolyte and the electrode.Dissolve In Cl₃ in THF,and then drop the solution evenly on the surface of sodium metal.After THF volatilizes,it can be seen through SEM that a dense and flat interface layer is formed on the surface of sodium metal.The cycle stability of the symmetric battery assembled with the modified sodium metal sheet id well improved,and the capacity retention rate of the assembled all-solid-state battery is also higher than that of the unmodified sodium anode.By preparing the composite solid electrolyte membrane of Na₃PSe₄ electrolyte and different polymers,the purpose is to coat a layer of polymer on the surface of the electrolyte to improve the air and electrochemical stability of the Na₃PSe₄ electrolyte itself.The composite electrolyte prepared by using ACN as solvent,a amount of PEO as polymer,and NaTFSI as sodium salt.The electrolyte membrane is subjected to aging and constant current charge-discharge tests.The results show that when the PEO content is 15%,the electrochemical stability of the composite electrolyte membrane is improved,but its ionic conductivity remains to be improved.