Correlation study between the structure and ionic conductivity in NaSICON glasses and glass-ceramics for energy storage applications

• Grant number: 25/24058-5
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: January 01, 2026
• End date: December 31, 2028
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Inorganic Chemistry
• Principal Investigator: Silvia Helena Santagneli
• Grantee: Gustavo Vieira Freire
• Host Institution: Instituto de Química (IQ). Universidade Estadual Paulista (UNESP). Campus de Araraquara. Araraquara , SP, Brazil
• Associated research grant: 23/07718-6 - Multinuclear solid-state NMR spectroscopy: An approach between the structure and the properties of new material, AP.R

Abstract

Glass-ceramics obtained from phosphate glass have a highlighted as candidates for solid-state electrolytes, particularly those with NaSICON-type (Na+ superionic conductor) structures. The glass-ceramic obtained from phosphate glasses has been studied for application in a solid-state electrolyte, due to the facility of preparation and the decrease of porosity that affects ionic conductivity. The high conductivity these materials have spurred numerous advancements in their compositions, manufacturing processes for obtaining electrolytes with promising electrical properties, with conductivities reaching up to 10-3 S cm-1 a 25 °C. NaSICON-type ceramic predominantly consists of phosphates and follows the general formula A1B2(PO4)3. In this formula, A represents the mobile cation, typically Li+ or Na+, which occupies the structure's interstitial spaces. The B component is a tetravalent cation (like Ti4+, Ge4+, Zr4+, Hf4+) that is coordinated by oxygen anions in an octahedral arrangement. The interplay of cation sizes-both those that are mobile and tetravalent-affects how easily the mobile cations (Na+ or Li+) can move through the structure when an electric field is applied, thereby impacting the overall electrical conductivity. The partial or total replacement of tetravalent cations (B(IV)) by trivalent ones (B(III)) allows the increase in the amount of Li+ or Na+ ions in the structure in the same proportion to maintain charge neutrality. A stoichiometry of the type A1+xB(III)xB(IV)2-x(PO4)3 is then established, which has proven successful in increasing the conductivity of these materials. Our contribution in this project will be the preparation of glasses and glass-ceramics based on the silicate and sodium phosphate system, with the general formula Na1B2(PO4)3, which has potential applications in solid electrolytes. The replacement of tetravalent cations by trivalent ones, such as B(III) = Al, In, and Sc, and B(IV) = Si, Ge, can influence the ease with which the Na ion diffuses into the structure in the presence of an electric field, and consequently, the electrical conductivity. Therefore, structural monitoring and control of these factors are mandatory. The charge balances also allow for systems with increased Na+ amounts in the structure after crystallization, such as the Na1+xZr2SixP3-xO12 system. The structural evolution of these systems will be monitored by solid-state, one-dimensional, and two-dimensional NMR, combined with other spectroscopic and X-ray diffractometry techniques, with a primary focus on investigating the Si/P ratios and their influence on the materials' structure and conductivity (AU)