Research On The Construction And Performance Of All Solid Sodium Ion Batteries

All-solid-state battery is a new secondary batteries,which has solid state positive,negative and electrolytes materials.The use of solid electrolyte material instead of the previous organic liquid electrolyte can effectively solve the safety issues such as leakage in order to increase the safety performance of the battery.However,the electrochemical performance of all-solid-state batteries is quite different from that of traditional batteries.The main factors that affect the electrochemical performance are the electrochemical performance of the positive electrode material(capacity,cycle performance,structural stability,etc.),the ionic conductivity of electrolyte and the solid-solid contact interface resistance between positive electrode material and solid electrolyte.Therefore,how to improve the electrochemical performance of the positive material,improve the ionic conductivity of the solid electrolyte,and reduce the solid-solid interface resistance between the solid electrolyte and the electrode layer become the research priorities of all-solid-state batteries.A new chrysanthemum-structured Na3V2(P4)3/C material has been successfully assembled with multi hierarchical nanosheets via hydrothermal method,which shows excellent electrochemical performance.It rendered a high initial specific capacity of 117.4 mAh g-1 at current density of 0.05 C.Further increase the current density to 10 C,the initial specific capacity still achieves 101.3 mAh g-1 and remains at 87.5 mAh g-1 after 1000 cycles.The as-prepared sample exhibits outstanding electrochemical performance due to its unique structure.The sodium ion transport distance can be shortened due to thinner nanosheets.The chrysanthemum structure can better adjust the volume change during the cycles to ensure the stability of the structure.Na3Zr2Si2PO12(NZSP)has been successfully synthesized by the conventional solid-state reaction at 1150? with adding 5 wt%excess of Na2CO3 and 10 wt%excess of NH4H2PO4.Excessive sodium and phosphorus sources in the precursors were added to compensate the loss of sodium and phosphorus during heat-treatments and effectively inhibited the formation of ZrO2 impurity phase,which reduced the grain boundaries resistance and increased the ion conductivity.The ionic conductivity of Na3Zr2Si2PO12(NZSP)is significantly increased by adding 5 wt%excessive of Na2CO3,10 wt%excessive of NH4H2PO4,resulting in ionic conductivity of 1.935x10-4 S cm-1 at room temperature.Furthermore,NZSP's electrochemical stability over a wide voltage window up to 5 V,which can meet the requirement of most of the sodium-ion positive materials.Based on the synthesis of positive materials and solid electrolytes,an interfacial modification strategy was proposed to prepare a hybrid solid-state sodium-ion battery by coating and co-sintering.A small amount of liquid electrolyte was utilized to improve the ionic contact of NZSP and NVP in the composite electrode.At 25?,the hybrid solid-state sodium-ion batteri demonstrate electrochemical performance with discharge capacity of 81.6 mAh g-1 at 20 mA g-1 and maintain a high and reversible capacity of 62.23 mAh g-1 for 30 cycles.