The Research On Synthesis And Performance Of Lithium (Sodium) Solid Electrolyte Materials

In modern society,the demand for energy is rapidly increasing.However,due to the insufficient reserves of traditional fossil energy and the huge environment pollution,new types of clean and renewable energy(wind energy,solar energy,water energy,etc)have attracted more attention.However the storage of renewable energy requires large-scale energy storage equipment.Among them,lithium ion battery is a kind of mature energy storage equipment,which has been widely used in various fields of social life.However,traditional lithium-ion batteries are easy to burn and explode,causing great hazards.In all-solid-state lithium battery,the solid electrolyte replaces the liquid organic electrolyte,which improves the safety and energy density of the battery.Therefore,the research and development of solid electrolyte materials are urgently important.However,the global reserves of lithium resources are insufficient.When lithium-ion batteries are used in large-scale energy storage equipment,huge cost limits their applications.Therefore,due to abundant reserves of sodium resources,sodium ion batteries become an important candidate for future large-scale energy storage equipment.For lithium(sodium)solid-state batteries,the ionic conductivity and interface electrochemical stability of solid electrolyte materials are key factors that affect the electrochemical performance of solid-state batteries.In the dissertation,three kinds of solid lithium(sodium)ion conductors are prepared,and the characterization and performance of them are explored.This provides new ideas for the future development of solid electrolytes.The detailed research contents are as follows:(1)A new type of solid electrolyte Li₅AlH₂O₂Cl₆(denoted as LAHCO)was synthesized by solid-phase melting method,which had a rock salt(A₁B₁)crystal structure,and Li₂OHCl and LiAlCl₄were used as precursors.In pure LAHCO structure,neutron diffraction results revealed that Li,Al,H atoms occupied at A sites and O,Cl atoms occupied at B sites.In a series of products with different compositions,LAHCO compound with excess LiAlCl₄(0.4Li₂OHCl–0.6LiAlCl₄)showed the highest Li⁺ionic conductivity of 10^-4S cm^-1at room temperature,which was higher than pure Li₂OHCl(10^-7S cm^-1)and pure LiAlCl₄(10^-6S cm^-1)?And also it showed good compatibility with lithium metal and good electrochemical stability.The entropy of the mixing effect in the LAHCO-LiAlCl₄system was the reason for the increase in ionic conductivity.The presence of excess LiAlCl₄provided a large amount of Aland Cl sources for the surface of LAHCO,which helped to reduce the ion hopping barrier and promoted the migration of lithium ions.(2)Sodium thioantimonate nonahydrate(Na₃SbS₄·9H₂O)was mechanically ball milled,and the ultrafine powder was heated at 150^oC in a vacuum to remove the bound water to obtain anhydrous Na₃SbS₄.We combined real-time electrochemical impedance measurements with theoretical simulation based on density functional theory(DFT)and in situ quasi-elastic neutron scattering(QENS)to reveal the difference of Na-ion conduction in tetragonal and cubic structures,respectively.The energy barrier for Na-ion diffusion in the tetragonal structure was determined to be much larger(5?10 times)than that in the cubic structure from theoretical simulation and experimental results.The high degree of symmetry in cubic Na₃SbS₄led to less interatomic correlations between Na and S(Sb)atoms,shorter jump distance(2.85(?)),and larger diffusion coefficient(2.07×10^-10m²/s)of Na⁺.This research provided insight into understanding the Na-ion diffusion process in Na-ion conductors with phase transitions and provided fundamental guidance for designing novel solid-state Na-ion conductors.(3)Firstly,Li_1.3Al_0.3Ti_1.7(PO₄)₃powder samples were synthesized by high temperature solid phase method,and then a composite polymer electrolyte membrane PVDF-HFP/LATP/g-C₃N₄was prepared by simple casting method.The preparation conditions of Li_1.3Al_0.3Ti_1.7(PO₄)₃were explored and the characterization test was carried out.The results showed that the LATP calcined at 900^oC had better ionic conductivity(1.41×10^-5S cm^-1).Then,the influence of g-C₃N₄on the composite polymer electrolyte membrane was studied by phase characterization,morphology characterization and electrochemical test.The results showed that the addition of g-C₃N₄improved the ionic conductivity of the composite polymer electrolyte membrane(2.55×10^-5S cm^-1),and the composite polymer electrolyte membrane PVDF-HFP/LATP/g-C₃N₄had a wide electrochemical window(decomposition voltage is 5.0 V)and good electrochemical stability.