Synthesis And Performance Research Of P2-type Layered Oxide Sodium-ion Solid Electrolyte

All-solid-state sodium-ion batteries?ASS-SIBs?are one of the most promising energy storage devices in the future because of their large energy density,high security and low cost.As the important part of ASS-SIBs,sodium-ion electrolyte has very few types and obvious shortcomings.Sodium layered oxides are used in the electrode of sodium-ion batteries.Layered oxides have large ionic migration pathway,stable crystal structure,high chemical stability.These advantages make the layered oxdies have potential to be solid sodium-ion electrolyte.However,there is very little research on layer oxide sodium ion solid electrolyte,and the performance is poor.In this thesis,two Na₂Zn₂TeO₆?NZTO?and Na₂Mg₂TeO₆?NMTO?electrolytes with excellent performance have been sythensized by traditional solid-state reaction and modified by microelement doped.These investigations supply a new research rote for sodium-ion solid electrolyte.The detail research are as follows:?1?Na₂Zn₂TeO₆?NZTO?was successfully sythensized by traditional solid-state reaction and its crystal structure and electrochemical performance were characterized.From the results,NZTO was a P2-type layerd oxide and its space group was P₆₃22.The Na⁺migration pathway in NZTO crystal lattice was between two honeycomb frameworks.The ionic conductivity of NZTO at RT was 6.9×10^-44 S cm^-11 with high thermostability and high stability with moisture environment,but appered large electrochemical window of 4.02 V and good stability with metallic Na anode.Furthermore,ASS-SIBs constructed by Na₃V₂?PO₄?₃/NZTO/Na was proper functioned,illustrated that NZTO was to be a solid electrolyte which could be used in SS-SIBs.?2?Trace amount Ga was successfully doped in NZTO to replace part of Zn.The crystal structure,electrochemical performance of Ga doped NZTO and Na⁺transport mechanism in NZTO before and after Ga doped were investigated.From the results,the vacancy in Na1position was increased by Ga dopping which led to the decrease of Na⁺migration barrier.When the amount of Ga dopping is 0.1,the ionic conductivity of Na_1.9Zn_1.9Ga_0.1TeO₆ is 1.1×10^-33 S cm^-1.Moreover,the stability with metallic Na anode was promoted after Ga doped.Furthermore,Ga doped also optimized the electrochemical performance of ASS-SIBs which is constructed by Na₃V₂?PO₄?₃/Na_1.9Zn_1.9Ga_0.1TeO₆/Na.?3?Trace amount of Ca was successfully introduced in NZTO.From the result of experimental characterization,Ca²⁺cations promote the performance of NZTO by enlarging layer spacing,increasing density and changing element distribution of grain-bourndary.When the Ca doping amount in NZTO was 0.02,the sodium ionic conductivity was 7.5×10^-44 S cm^-11 at RT.We also demonstrated that the electrochemical window and the stability with metallic Na anode were enhanced and the cycle performance of ASS-SIBs was improved by Ca doped.?4?Na₂Mg₂TeO₆?NMTO?solid electrolyte was successfully sthesized by traditional solid-state reaction.XRD,²³Na NMR,and EIS analyses shown Na₂Mg₂TeO₆?NMTO?solid electrolyte had similar structure but larger migration pathway with NZTO.NMTO exhibited high ionic conductivity of 2.3×10^-4S cm^-1at RT only requires a simple solid-state synthetic route.It also shows excellent chemical stability under ambient conditions,a large electrochemical window of⁴.2 V?vs.Na⁺/Na?,and high stability with metallic Na.The all-solid-state battery NVP/NMTO/Na works properly with a current rate of 0.2 C at 80 ^oC,which revealed that the potential of NMTO to be the solid electrolyte used in ASS-SIBs.