| Recently,sodium-ion batteries have attracted much attention due to their aboundance and low cost.However,sodium-ion batteries with organic electrolytes have the safty concerns such as fire and explosion.Using solid electrolyte instead of organic electrolyte is expected to solve the safety risks of batteries.Among current sodium-ion solid electrolytes,NASICON electrolytes have the advantages of wide electrochemical window,high mechanical strength,air stability and high i onic conductivity.However,Na3Zr2Si2PO12（NZSP）solid electrolytes have low ceramic induced density,low ionic conductivity at room temperature,and la rge interfacial impedance.In view of the above problems,this paper conducts a study on the performance optimization of the NZSP,and the main study findings obtained are as follows:（1）Using the high temperature solid phase method,pure phase NZSP powders were synthesized at a sintering temperature of 1150℃ by introducing excess Na and P into the precursor.The spherical granulation of powders by spray drying realized the particle size grading of polyvinyl alcohol binder on NZSP particles and near normal distribution,and the density of NZSP ceramics reached 97.5% at the sintering temperature of 1250℃.The induced density increase can effectively reduce the crystal boundary impedance,and the ionic conductivity reached 6.96?10-4 S·cm-1 at room temperature,which was higher than that of 4.94×10-4 S·cm-1 of ceramic pieces prepared by conventional sintering method.In addition,the ceramics obtained by spray drying have a wide electrochemical window（＞6 V）,which can match high voltage cathode materials and improve the energy density of the battery.（2）Through the addition of Hf4+ doping and La2O3 sintering agent,Na3Hf0.2Zr1.6Si2PO12-Na3La（PO4）2（NZHSP-NLP） ceramic pieces with high density（98.8%） and high ion conductivity (1.66×10–3 S·cm-1) were prepared by conventional sintering temperature at 1200℃.To improve the"solid-solid contact" between the anode and the ceramic sheet,PEO-Na FSI polymer electrolytes were coated on the surface of the ceramic sheets.Symmetric batteries Na/PEO/NZHSP-NLP/PEO/Na were stably circulated for 500 h at a 0.1 mA cm-2 current density.Assembled half batteries NVP@C/IL/NZHSP-NLP/PEO/Na had a first lap discharge capacity of109.9 mAh g-1,the first electric coulombic efficiency of 97.8%,and 101.9 mAh g-1 after 50 cycles,with a capacity retention rate of 92.7%.（3）This work also introduced the concept of "high entropy"into sodium-ion solid electrolyte materials.High-entropy oxide Na3Sc0.1In0.1Hf0.1Nb0.1Ta0.1Zr1.5Si2PO12 ceramic pieces with 98.2%density were combined at a low sintering temperature of 1150℃ by the solid phase method.Furthermore,ionic conductivity of the Na3Sc0.1In0.1Hf0.1Nb0.1Ta0.1Zr1.5Si2PO12 can reach 8.29×10–4 S·cm-1 at room temperature,and up to 5.69×10-3S·cm-1 when the temperature was raised to 100℃.An Arrhenius curve fitting yielded a Na3Sc0.1In0.1Hf0.1Nb0.1Ta0.1Zr1.5Si2PO12 with an activation energy of 0.28 eV lower than the 0.32 eV of Na3Zr2Si2PO12. |
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