Study On Assisted Sintering And Electrochemical Properties Of NASICON Solid Electrolyte

Compared with traditional liquid lithium ion batteries,solid-state sodium ion batteries have attracted extensive attention because of their easy availability of raw materials,low cost and high safety.Different from the traditional liquid lithium ion battery using flammable organic electrolyte,the use of non flammable solid electrolyte in solid-state sodium ion battery can greatly improve the safety of the battery in application.Inorganic ceramic electrolyte has high ionic conductivity.Instead of organic electrolyte and diaphragm,it has high mechanical strength and can effectively inhibit dendrite growth.However,there are still some problems,such as low conductivity(unable to meet the application requirements～10^-3 S·cm^-1),large electrolyte/electrode interface resistance,dendrite growth and so on.Therefore,how to improve the ionic conductivity of inorganic ceramic solid electrolyte,reduce the interface resistance of electrolyte/electrode,reduce the electronic conductivity and inhibit the growth of dendrites is the research focus of solid-state sodium battery.Taking NASICON(Na₃Zr₂Si₂PO₁₂)electrolyte with high ionic conductivity and high stability as the main research object,this paper studied the effects of different sintering additives on the structure,density,conductivity and application performance of electrolyte in solid-state sodium battery.The main research contents are as follows:（1）NASICON(Na₃Zr₂Si₂PO₁₂)electrolyte was synthesized by high temperature solid state method with adding Bi₂O₃ assisted sintering,and the battery was assembled for testing.The effects of different Bi₂O₃ additions on the phase composition,ionic conductivity,electronic conductivity and battery performance of NASICON electrolyte were studied in detail.Finally,when the addition amount of Bi₂O₃ is 0.1 mol（NZSP-0.2Bi）,the density of the sample is 95.68%and the ionic conductivity at room temperature is 1.27×10^-3 S·cm^-1.However,after adding bismuth oxide,the interface between electrolyte and electrode is unstable during battery cycle,resulting in side reactions and promoting the growth of dendrite in electrolyte,resulting in the decline of battery cycle performance.（2）NASICON(Na₃Zr₂Si₂PO₁₂)electrolyte was synthesized by high temperature solid state method with adding Sm₂O₃ and Ho₂O₃ assisted sintering,and the battery was assembled for testing.The effects of different additions of Sm₂O₃ and Ho₂O₃ on the phase composition,ionic conductivity,electronic conductivity and battery performance of NASICON electrolyte were studied in detail.Finally,the density of NZSP-0.2Sm and NZSP-0.3Ho samples with the addition of Sm₂O₃ and Ho₂O₃ of 0.1 mol and 0.15mol both reached 95.99%and the ionic conductivity reached 1.36×10^-3 S·cm^-1 and1.07×10^-3 S·cm^-1,respectively.Moreover,the introduction of Sm₂O₃ and Ho₂O₃ will form a grain boundary phase with low electron conductivity at the grain boundary,hinder the electron transfer at the grain boundary and improve the critical current density（CCD value）.The CCD values of NZSP-0.2Sm and NZSP-0.3Ho were 0.85m A·cm^-2 and 0.65 m A·cm^-2(the CCD value of NZSP was 0.35 m A·cm^-2),respectively,which effectively inhibited the growth of sodium dendrite.（3）NASICON(Na₃Zr₂Si₂PO₁₂)electrolyte was synthesized by high temperature solid state method with adding CaF₂ assisted sintering,and the battery was assembled for testing.The optimum addition of CaF₂ was determined to be 0.2 mol.The reasons for increasing the relative density and ionic conductivity of F^-assisted sintered NASICON electrolyte were analyzed in detail.Finally,the best sample NZSP-0.2CaF₂was obtained,the density was 95.37%,and the ionic conductivity at room temperature was 1.13×10^-3 S·cm^-1.