# Assessing the Efficacy of Seawater Batteries Using NASICON Solid Electrolyte
## 4 Discussion  
### The NASICON Principles Used in seawater Electrolytic Processes  
Just like Li+ in lithium-ion batteries and Pb2+ in lead-acid batteries, seawater can act as an energy carrier. NASICON is the crucial component of the rechargeable seawater battery (SWB) that selectively transfers Na+ from seawater, and it exemplifies this potential. SWBs are specifically designed for water, particularly saltwater environments, unlike many conventional batteries that are not. The battery structure has three electrodes: one positive electrode (seawater) and one negative electrode (NASICON). When the solid electrolyte is in direct contact with the seawater, Na+ can pass between the electrodes. To transfer Na+, a buffer layer is created with a non-aqueous electrolyte, while the negative electrode's active material is Na metal. In comparison to other aqueous or underwater batteries, this battery has the advantage of heat control and explosion prevention while operating in seawater conditions. NASICON-based seawater electrolytic technologies are based on the selective exclusion of the majority of seawater components, making it possible for only Na+ to pass through. The NASICON solid electrolyte, which acts as a ceramic separator, can help facilitate sustainable redox reactions in seawater, such as sodium ions reacting with water electrolysis and chloride oxidation. Using sodium as a charge carrier, NASICON-based seawater electrolytic technologies aim to store energy. The negative electrode undergoes various redox reactions, including Na deposition/dissolution, while the positive electrode is where oxygen evolution and reduction reactions typically occur. The utilization of abundant seawater and air as open cathodes enhances the economic feasibility of this system (Figure 10) [20]. Ceramic membranes are becoming more and more popular due to their exceptional mechanical stability and high selectivity, but their chemical stability in seawater is limited. NASICON is a ceramic material that conducts sodium ions and has been shown to be stable in seawater while showing high selectivity and conductivity of sodium ions. The most ionic conductivity among the materials of Na1+xZr2 Si2P3-xO12, with a x = 2, was discovered by [PERSON] and [PERSON] in 1976 with Na3 Zr2 Si2 PO12 (NZSP) [21; 22; 23; 24; 25; 26]. The structure of Na1+xSi2P3-xO12 is composed of ZrO6 octahedra that connect at corners with PO4/SiO4 tetrahedra. Na+ ions are present in the interstitial zones of this framework. The ZrO6 octahedral structure has six oxygen molecules, while the oxygen corners of silicate or phosphate tetrahedral structures have oxygen molecules that connect them. Along the axis, repeating structures are formed in this manner. The main way to  
Figure 10: Schematic of NASICON seawater battery. transport sodium ions in the 3D structure, which is located in the interstitial sites between octahedral and tetrahedral structures, is through migration through holes [27; 28; 29; 30]. The ionic conductivity of NASICON at room temperature (RT) is comparable to that of solid organic electrolytes (10\({}^{-6}\)-10\({}^{-3}\) Scm\({}^{-1}\)), with a range of 10\({}^{-4}\)-10\({}^{-3}\) Scm\({}^{-1}\). By controlling the Na\({}^{+}\) sites (Na1, Na2, and Na3) and the barriers that ions traverse, the ion-conducting mechanism of the NASICON is governed. The NASICON formula unit has four locations, but two-thirds of them are currently in use. The interstitial site is filled with three oxygen atoms, which create a triangular barrier with a cross-sectional area of 5.223 A [13]. Seawater batteries require NASICON to be stable in seawater. NASICON membranes have been found to exhibit virtually no increase in ionic conductivity after being immersed in seawater for 150 days, as evidenced by studies. The conductivity values of the blank sample and the sample submerged in seawater were from 3.8 \(\times\) 10\({}^{-4}\) to 3.1 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\)[13].