The Chemical Stability of Nasicon As a Solid Electrolyte for Seawater Batteries

Abstract

Seawater batteries have attracted significant attention for use as grid-scale energy storage systems (ESSs) due to the effective utilization of abundant resources of seawater as a catholyte. Sodium ions in seawater selectively transfer through a solid electrolyte to the anode for saving the chemical energy. For the selective transfer of sodium ions, NASICON (Na3Zr2Si2PO12) electrolytes are one of the suitable candidates for the solid electrolyte to prevent a short circuit between the catholyte and anode. However, NASICON powder is known to be dissolved in water because of the structural instability, leading to catastrophic failure of the system, while NASICON solid electrolytes are stable in seawater during the battery operation.

In this regard, we have carefully compared the stability of NASICON powder and pellets in both DI water and seawater associated with different degradation mechanism. Figure shows the structural stability of NASICON pellets after the immersion tests in DI water and seawater indicative of the chemical stability of NASICON in seawater. In addition, the electrochemical performance shows higher stability of the seawater-immersed electrolyte than the DI water-immersed electrolyte. The corresponding analyses are carried out to confirm the effect of the investigation.

Furthermore, we have employed polymer coating methods to enhance stability and performance as a seawater battery system. The coating layer enables to prevent direct contact with seawater, resulting in longer stability during operation without compromising ionic conductivity. These results reveal that NASICON solid electrolytes can be operated in seawater with high stability and performance.