Study On Preparation And Sintering Process Of Na₃Zr₂Si₂PO₁₂-based Solid Electrolyte

The all-solid sodium battery has attracted more and more attention due to its high energy density and safety.The core of the all-solid sodium battery research is the solid electrolyte.Among the NASICON-based solid electrolytes,the NZSP(Na₃Zr₂Si₂PO₁₂)-based solid electrolyte has the highest ion conductivity.The main research content of this subject is to modify NZSP by doping with heterovalent metal ions to prepare NZSP-based solid electrolyte to achieve excellent electrochemical performance.By adding Bi₂O₃ as a sintering aid,both the density of NZSP-based solid electrolyte and its ionic conductivity are increased.Also,the sintering process of NZSP-based solid electrolyte is studied.First,the Na₃Zr₂Si₂PO₁₂ solid electrolyte film is prepared by the tape casting.The dispersant is（5-6 mass%）,that binder is（6-7 mass%）and plasticizer is（4-5 mass%）.According the thermogravimetric test,the temperature of removing organic matter is determined to be 600℃,and the heating rate is 1℃/min.The ion conductivity of the NZSP prepared by the tape casting reaches 2.78×10^-4 S/cm.Assembling the symmetrical battery Na|NZSP|Na,it can circulate stably for about 180 h at a current density of 0.03m A/cm².Secondly,the Na₃Zr₂Si₂PO₁₂-based solid electrolyte doped with heterovalent metal ions is explored.XRD analysis shows that the Mg²⁺doped Na₃Zr₂Si₂PO₁₂ electrolyte has the least phase content,and SEM analysis shows that the heterovalent metal doped Na₃Zr₂Si₂PO₁₂ electrolyte is relatively dense.Among this,the electrochemical impedance spectroscopy test determines that the best electrochemical performance is that of the Mg²⁺doped Na₃Zr₂Si₂PO₁₂ The ionic conductivity of Na_3.6Zr_1.7Mg_0.3Si₂PO₁₂ electrolyte reaches 7.762×10^-4 S/cm,the relative density is 87.2%,with the Arrhenius activation energy for the electrical conductivity of 0.22 e V.Assembling the symmetrical battery Na|NZSP|Na,it can circulate stably for about 1050 h at a current density of 0.03 m A/cm².In order to further improve the sintering density,the sintering mechanism of Na₃Zr₂Si₂PO₁₂-based solid electrolyte doped with Bi₂O₃ sintering aid was studied.When Bi₂O₃ content is 5 mass%,the linear shrinkage rate at 1000℃is 8.26%and the relative density is 86.17%.The maximum shrinkage rate at a heating rate of 5℃/min and10℃/min are 0.0021 min^-1 and 0.0053 min^-1,respectively.It is calculated that the density of Na₃Zr₂Si₂PO₁₂-based solid electrolyte is 91.5%,which the ionic conductivity reaches7.37×10^-4 S/cm.The Arrhenius activation energy is 0.30 e V.The ionic conductivity of Na_3.6Zr_1.7Mg_0.3Si₂PO₁₂ with 5 mass%Bi₂O₃ doping reaches as high as 1.027×10^-3 S/cm.The assembled symmetrical battery Na|NZSP|Na can circulate stably for about 1200 h at a current density of 0.03 m A/cm².After assembling full battery Na|NZSP|NMTP,it cycles for 45 cycles at a current density of 0.2 C,that the specific capacity of the battery decreases from the initial 95.3 m Ah/g to 62.2 m Ah/g,with the capacity retention rate of65.6%.