Enhanced grain connection and ionic conductivity of Na3.3La0.3Zr1.7Si2PO12 ceramic electrolyte by adding Na2B4O7

NASICON-type Na 3 Zr 2 Si 2 PO 12 (NZSP) is supposed to be one of the greatest feasible solid electrolytes due to its high electrochemical performance and safety. Herein, Na 2 B 4 O 7 (NBO) additive is proposed to enhance the grain connection and ionic conductivities , and reduce the sintering temperature . The grain boundary microstructure of Na 3.3 La 0.3 Zr 1.7 Si 2 PO 12 (NLZSP) is adjusted via introducing NBO additive to facilitate the densification sintering at 950 °C. NLZSP with 3 wt% NBO (NZSP(NBO3)) demonstrates an optimized total ionic conductivity ( σ t ) of 1.81 mS cm −1 at 25 °C and low activation energy ( E a ) of 0.22 eV. EIS and SEM analysis reveals that NBO additive promotes more intimate contact between NLZSP grains and extensively reduces the grain-boundary resistance ( R gb ) from 135 Ω cm 2 for NLZSP to 8 Ω cm 2 for NLZSP(NBO3). Besides, wide electrochemical stability window of 5 V vs Na + /Na and galvanostatic sodium stripping-plating up to 400 h reconfirms the super stability of NLZSP(NBO3)/Na interface, while small contact angle of 82° will bring better wettability and interface contact of NLZSP(NBO3)/Na. Solid-state sodium metal batteries (SMBs) based reduced graphene oxide wrapped NaTi 2 (PO 4 ) 3 (NTP@rGO) 3D conductive cathode and NLZSP(NBO3) ceramic electrolyte shown excellent rate performance and cycle stability (91.4% of capacity retention after 200 cycles at 1C). Hence, NLZSP(NBO) ceramic electrolyte exhibits a significant advantage in enhancing grain connection, regulating ionic conductivity and reducing sintering temperature, and is anticipated to be used in all solid-state sodium ions batteries (ASSSIBs).