Preparation And Study Of NASICON-type Solid Electrolyte Material For Sodium Ion Batteries

At present,lithium-ion batteries most commonly use liquid organic electrolyte,which is prone to heat,explosion and other safety problems.Therefore,it is important to improve the safety of lithium-ion batteries.All-solid-state batteries use solid electrolyte instead of organic liquid electrolyte.In the case,leakage and explosion of liquid electrolyte can be completely avoided.All-solid-state batteries can not only meet the increasingly diverse needs of electronic products,but also produce miniaturized,multi-shaped batteries,which are expected to replace lithium-ion batteries as the next generation of energy storage batteries.Among all types of sodium-ion solid electrolytes,Na3Zr2Si2PO12 has become the most promising inorganic solid electrolyte,because of its high ionic conductivity,high decomposition voltage and stable chemical properties.However,the ionic conductivity of Na3Zr2Si2PO12 is 10^-4 at room temperature,which can not meet the requirements of all-solid-state batteries,and the high preparation temperature make it is not easy to prepare pure phase.The application of this type of electrolyte is also limited.In this paper,Al and Mg elements are doped in Zr site of Na3Zr2Si2PO12 solid electrolyte,and solid electrolysis is prepared by liquid phase sintering method.In order to reduce the sintering temperature of the electrolyte and improve the ionic conductivity and sintering performance.?1?In single doping,the content of impurities ZrO2 and Na3PO4 in materials can be reduced by using electrolytes doped with Al³⁺.The optimum density of electrolyte material is 91.97%,and the ionic conductivity can reach 1.19×10^-3 S·cm^-1 at room temperature.Mg²⁺used as dopant,the impurity mass in electrolyte material is reduced significantly,and the pure phase is obtained.The highest ionic conductivity of electrolyte material is 1.25×10^-3 S·cm^-1 at room temperature,and the density of electrolyte material is 92.6%.The ionic conductivity of electrolyte material is higher and more compact than that of dopant Al³⁺.?2?In Na3.05+2xMgxAl0.05Si1.95-xPO12?x=0,0.05,0.1,0.15,0.2?system,when co-doped with Al³⁺,Mg²⁺,it was found that higher ionic conductivity and density could be obtained when Mg²⁺was introduced at 0.1.The ionic conductivity at room temperature was 1.78×10^-3S·cm^-1 and the density of electrolyte material was 95.6%.The ionic conductivity was higher than that obtained by using Mg²⁺as dopant alone.The higher conductivity proves that joint regulation of Mg²⁺and Al³⁺can obtain more suitable ion transport pipelines for Na⁺passage.The improvement of ionic conductivity lays a good foundation for further development of all solid state batteries.In Na3.1+xAlxMg0.05Si1.95-xPO12 system?x=0,0.05,0.1,0.15,0.2?,the ionic conductivity is the highest at room temperature(1.16×10^-3 S·cm^-1)when the amount of Al³⁺is 0.05.Compared with the two systems,under the condition of Co-doping of Mg²⁺and Al³⁺,Mg²⁺has more obvious regulation on ion channels and obtain more favorable ion channels for Na⁺to through.?3?High ionic conductivity can be obtained at lower sintering temperature and the density of electrolyte material can be significantly increased.When Na2B4O7 is selected as liquid sintering additive,the highest room temperature conductivity of electrolyte material can reach 1.5×10^-3 S·cm^-1,and the density of electrolyte material can reach 95%.Using liquid phase sintering technology on the basis of Al³⁺doping can not only reduce grain boundary impedance,but also improve grain impedance.In the sintering process of NBO,a part of B³⁺ions can enter the lattice and play the role of doping.B³⁺doping can introduce more Na⁺as the transport ion,and reduce the activation energy of Na⁺so as to improve the conductivity of grain ions.