Progress in Sodium Silicates for All‐Solid‐State Sodium Batteries—a Review

Abstract

All solid‐state sodium batteries (ASSSBs) are considered a promising alternative to lithium‐ion batteries due to increased safety in employing solid‐state components and the widespread availability and low cost of sodium. As one of the indispensable components in the battery system, organic liquid electrolytes are the currently used electrolytes due to their high‐ionic conductivity (10−2 S cm−1) and good wettability; however, their low‐thermal stability, flammability, and leakage tendency pose safety concerns. The growing sodium‐ion battery technology with solid electrolytes is a viable solution due to their improved safety. However, solid electrolytes suffer from insufficient ionic conductivity at room temperature (10−4–10−3 S cm−1), poor interface stability, high charge‐transfer resistance, and low wettability, yielding inferior battery performance. Sodium rare‐earth silicates are a new class of materials with a 3D structure framework similar to sodium‐superionic conductors (NASICONs). These silicates can be used as a solid electrolyte for solid‐state sodium batteries due to their high‐ionic conduction (10−3 S cm−1) at 25 °C. Herein, the sodium rare‐earth silicate synthesis, crystal structure, ion‐conduction mechanism, doping, and electrochemical properties are discussed. This emerging type of inorganic solid electrolyte can pave the way to building next‐generation ASSSBs.

High ionic conducting rare-earth silicate electrolytes for sodium metal batteries

“…This observed overpotential is due to the oxidation and reduction of Na ion transport through the electrode/electrolyte interfaces. 61 The stable galvanostatic prole further supports the mechanical 38,41,44 stability of NGS15 solid electrolyte, dendrite blocking, and good anode/electrolyte interface.…”

“…33,37 These materials also have the advantage of low sintering temperature (∼1500 °C) comparing Na-b-alumina (>1600 °C). 38 The ionic conductivity was found to be lower, even at higher temperatures. Despite moderate ionic conductivity, obtaining a single phase of silicates has been a signicant concern since its discovery.…”

“…3 (a) and (b) RT-impedance for NGS5-20 prepared via routes 1 and 2, respectively. (c) and (d) Arrhenius plots for NGS5-20 prepared via routes 1 and 2, respectively, and (e) Arrhenius plot of solid electrolytes compared with NGS15 38,41,44.…”

Characterization of Na2Zn2TeO6 ceramic solid electrolyte densified by hot pressing

“…13 In addition, the processing temperature of NZTO is much lower than other Na-ion conducting oxides such as Na-β/β″alumina, NASICONtype Na 3 Zr 2 Si 2 PO 12 , and sodium silicates Na 5 YSi 4 O 12 . [14][15][16][17][18][19][20][21][22][23] Densification temperature and room temperature ionic conductivity for NZTO and other Na-ion and Li-ion conducting oxide-based solid electrolytes [24][25][26][27][28][29] are compared in Table 1.…”

“…Interestingly, first‐principles calculations display both high room temperature conductivity of 9.77 mS cm −1 and wide intrinsic electrochemical stability for NZTO 13 . In addition, the processing temperature of NZTO is much lower than other Na‐ion conducting oxides such as Na‐β/β″alumina, NASICON‐type Na 3 Zr 2 Si 2 PO 12 , and sodium silicates Na 5 YSi 4 O 12 14–23 . Densification temperature and room temperature ionic conductivity for NZTO and other Na‐ion and Li‐ion conducting oxide‐based solid electrolytes 24–29 are compared in Table 1.…”