# Assessing the Efficacy of Seawater Batteries Using NASICON Solid Electrolyte
## 3 Results  
### Analyzing the Structure of NASICON Membranes (2% and 6% Excess Na)  
The properties of particulate matter can be determined with the help of particle size analysis and its distribution. The conductivity of crystalline electrolytes is influenced by particle size, and generally, reducing particle size leads to better ionic conductivity. A rigorous and very energetic ball grinding procedure is used to obtain a significantly finer degree of particles after starting with initial macro precursors (0.0055 mm for ZrO\({}_{2}\) and 0.2 mm to 0.5 mm for SiO\({}_{2}\)). The precursor mixture is preserved after sintering with an average particle size of \(\sim\)1.0 \(\upmu\)m in the small micrometric range after ball milling. Table 1 shows that 10% of particles are below 1000 nm for NASICON powder with an excess of 2% and 6% respectively (523.8 nm and 910.5 nm respectively), while for NASICON membranes sintered at 1150 \({}^{\circ}\)C the particles have a size between 1056.8 (NAS-2%) and 1517.0 nm (NAS-6%). Of NASICON membranes sintered at 1175 \({}^{\circ}\)C the particles have a size between 1161.7 nm (NAS-2%) and 679.5 nm (NAS-6%); in time for sintered NASICON membranes at 1200 \({}^{\circ}\)C the particles have a size between 1010.8 nm (NAS-2%) and 833.6 nm (NAS-6%). From the data obtained, it is noted that during sintering, there is a change in the texture of the composition of NASICON as a direct consequence of the high sintering temperature. The higher the sintering temperature, a decrease in the particle size is observed. The microstructural and elemental investigations were carried out using a field emission scanning electron microscope with auto electronic emission at variable pressure (field emission scanning electron microscope variable pressure--FESEM VP) from the brand Carl Zeiss. The microscope is equipped with an EDX (energy dispersive X-ray spectroscopy) system that allows the quantitative and qualitative analysis of all chemical elements up to B (Z = 5). Figure 2 presents the surface images of the crack in the sample powder of Na\({}_{3.06}\)Zr\({}_{2}\)Si\({}_{2}\)PO\({}_{12}\) and Na\({}_{3.18}\)Zr\({}_{2}\)Si\({}_{2}\)PO\({}_{12}\). As shown in Figure 2, the micrographs show the close arrangement and packaging of NASICON particles with smoothed granules and diameters in the micron range to the submicron, as well as the appearance of network mesopores, through the unoccupied spaces between the particle assemblies. In order to investigate the chemical composition of the NASICON samples, energy spectrum tests were performed on samples of Na\({}_{3.06}\)Zr\({}_{2}\)Si\({}_{2}\)PO\({}_{12}\) and Na\({}_{3.18}\)Zr\({}_{2}\)Si\({}_{2}\)PO\({}_{12}\) that had been calcined at 1100 \({}^{\circ}\)C. For the two NASICON 2% and 6% powders, the chemical composition is composed \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Sample** & **D\({}_{10}\) [nm]** & **D\({}_{50}\) [nm]** & **D\({}_{90}\) [nm]** & **D\({}_{\mathbf{m}}\) [nm]** \\ \hline NAS Ref. & 705.8 & 876.8 & 1109.9 & 861.2 \\ \hline \multicolumn{5}{c}{2\% excess Na} \\ \hline NAS-2\% 1100 (powder) & 523.8 & 656.9 & 812.1 & 646.6 \\ \hline NAS-2\% 1150 & 1056.8 & 1323.9 & 1688.1 & 1299.6 \\ \hline NAS-2\% 1175 & 1161.7 & 1465.6 & 1880.1 & 1438.0 \\ \hline NAS-2\% 1200 & 1010.8 & 1263.2 & 1607.5 & 1240.3 \\ \hline \multicolumn{5}{c}{6\% excess Na} \\ \hline NAS-6\% 1100 (powder) & 680.5 & 853.7 & 1070.2 & 839.3 \\ \hline NAS-6\% 1150 & 1517.0 & 1906.7 & 2438.0 & 1871.3 \\ \hline NAS-6\% 1175 & 679.5 & 1197.1 & 2005.9 & 1035.4 \\ \hline NAS-6\% 1200 & 833.6 & 1036.7 & 1313.8 & 1018.3 \\ \hline \hline \end{tabular}  
* The distributions’ modal diameter is D\({}_{\mathbf{m}}\); the median is D\({}_{50}\).  
\end{table} 
Table 1: Particle size distribution for NASICON powder and membranes with excess of 2% and 6% Na.