# Assessing the Efficacy of Seawater Batteries Using NASICON Solid Electrolyte
## 1 Introduction
Recent research has revealed that solid-state sodium-ion batteries can utilize non-combustible solid-state electrolytes to achieve a higher energy density and enhance safety. The group of inorganic solid electrolytes (ISEs) comprises Na\({}_{3}\)Zr\({}_{2}\)Si\({}_{2}\)PO\({}_{12}\), sulfide Na\({}_{3}\)Sb\({}_{4}\) and halide Na\({}_{2.25}\)Y\({}_{0.25}\)Zr\({}_{0.75}\)Cl\({}_{6}\)[11]. Efforts to improve the performance of electrode materials are essential due to the impact of low temperatures (LT) performance on SIBs [4]. Although liquid electrolytes are widely used because of their low cost, high ionic conductivity, and ease of use, solid electrolytes are often preferred because they are nontoxic, nonflammable, noncorrosive, nonvolatile, and thermally stable over a wide temperature range. One of the most promising candidates for sodium storage electrodes in SIB materials is electrode materials that are based on sodium superionic conductors (NASICON), which have significant structural stability and high ionic conductivity [2; 5; 13]. Among all the inorganic fillers, active NASICON material (such as Na\({}_{3}\)Zr\({}_{2}\)Si\({}_{2}\)PO\({}_{12}\), Na\({}_{3,4}\)Zr\({}_{1,9}\)Zn\({}_{0.1}\) Si\({}_{2}\)P\({}_{0.8}\)O\({}_{12}\)) due to its high ionic conductivity and excellent chemical stability and attention [4]. NASICON-type materials with the general formula A\({}_{\rm x}\)M\({}_{2}\) (XO\({}_{4}\))\({}_{3}\) possess interesting properties such as high thermal and chemical stability, high ionic conductivity, and low thermal expansion. Li-ion and Na-ion batteries can use NASICON-type materials as cathodes, anodes, and electrolytes, depending on their \(A\) cations and \(M\) transition metals. Solid state Na-ion batteries use Na\({}_{1+\rm x}\)Zr\({}_{2}\)P\({}_{3-\rm x}\)Si\({}_{\rm x}\)O\({}_{12}\) (\(0\leq\rm x\leq 3\)), (NZSP), which has a difficult to reduce from its stable oxidation state + 4, as their electrolyte. The R\({}_{3}\)C (Rhombohedral) space group is maintained for all components in NASICON materials, except for those in the range \(1.8\leq\rm x\leq 2.2\) that have monoclinic structures (C\({}_{2}\)/c groups). Monoclinic Na\({}_{1+\rm x}\)Zr\({}_{2}\)P\({}_{3-\rm x}\)Si\({}_{\rm x}\)O\({}_{12}\) (\(1.8\leq\rm x\leq 2.2\)), especially when x = 2, has the largest ionic conductivity, which can reach \(2.0\times 10^{-1}\) S cm\({}^{-1}\) at 300 \({}^{\circ}\)C and 6.7 \(\times\) 10\({}^{-4}\) S cm \({}^{-1}\) at room temperature (RT). Modified Na\({}_{3}\)Zr\({}_{2}\)Si\({}_{2}\)PO\({}_{12}\) with sintering additives has a conductivity of 1.63 \(\times\) 10\({}^{-3}\) S cm\({}^{-1}\) at room temperature. The versatility and robustness of sodium-ion battery systems are due to NASICON ceramics' wide electrochemical stability window, which can be compatible with different electrode materials and operating voltages [1]. Additionally, NASICON materials are resistant to humidity [11]. Advanced battery technologies can take advantage of the rising demand for energy storage solutions, fueled by the increasing adoption of electric vehicles, renewable energy integration, and grid modernization efforts. Solid-state sodium batteries are designed to address critical issues in energy storage technology by taking advantage of the abundant sodium and its potential advantages in cost, safety, and performance as an alternative to lithium. Solid-state sodium batteries can be more recyclable than lithium-ion batteries, resulting in better durability [14]. The use of rechargeable seawater batteries (SWBs) is attracting attention as a potential solution for marine environment batteries. As the cathode material, SWBs utilize Na\({}^{+}\) ions that are dissolved in seawater or saltwater. Seawater is being investigated for its use as a cathode material or electrolyte. Flooding is avoided because these SWBs operate while submerged in seawater. The safety of the operation is maintained by the absence of hazardous components and an explosion risk. The development of SWBs has occurred between coin cells and prismatic cells.