Development and characterization of borate-modified Li1.5Al0.3Mg0.1Ge1.6(PO4)3 NASICON-type glass-ceramic electrolytes

As the world transitions to renewable electricity and electrifies more of its energy demand, power generation and use are being transformed, with batteries taking center stage. They are already indispensable in portable electronics and have become the key enabling technology for electric vehicles, where very high energy density is critical. However, conventional lithium-ion batteries are constrained by important drawbacks: the flammability of liquid electrolytes, the limited energy density, and the reliance on scarce raw materials. Solid-state batteries have emerged as suitable alternative for next-generation devices, aiming to overcome these challenges by replacing the liquid electrolyte with a solid-state one, either inorganic, polymeric or composite/hybrid. This architecture promises enhanced safety, compatibility with metallic lithium or sodium anodes, suppression of dendrite growth and, potentially, higher energy density. Yet, solid-state batteries still face major hurdles, including insufficient room-temperature conductivity, unstable electrode-electrolyte interfaces, and reduced electrochemical performance due to poor solid–solid contact. Progress in this field critically depends on the discovery and optimization of advanced solid electrolytes, with NASICON-type glass-ceramics among the most promising candidates. In such scenario, this Master’s Degree Thesis addresses these challenges by investigating the influence of borate modifiers on the Li1.5Al0.3Mg0.1Ge1.6(PO4)3 (LAMGP), a promising NASICON-type glass-ceramic solid electrolyte material. To establish the scientific context, the state of the art of ceramic electrolytes is first reviewed, focusing on the main structural families, discussing their conduction mechanisms, processing strategies, practical limitations and the effect of doping elements. In particular, the addition of B2O3 has been shown to significantly improve the properties of this system. On this foundation, the work proceeds with an experimental study of LAMGP glass-ceramics modified with LiBO2 and Li2B4O7, with the aim of achieving effects comparable to B2O3, analyzing how these additives affect crystallization behavior, microstructure, and electrochemical properties. This approach allows for a systematic correlation between composition, microstructure, and performance, with the goal of identifying how borate additives can be exploited to optimize NASICON-type electrolytes for solid-state battery applications. Results demonstrate that the addition of borate phases significantly affects the crystallization pathway and microstructure of the glass-ceramics. LiBO2 promotes the formation of cohesive crystallites, enhancing densification and leading to improved ionic conductivity. Conversely, Li2B4O7 tends to favor the development of secondary phases, resulting in microstructural heterogeneities and poorer conductivity response. Overall, the study confirms that the careful selection and tuning of glass modifiers in LAMGP systems can tailor the balance between densification, crystallization, and ionic conductivity. The findings contribute to a deeper understanding of structure–property correlations in borate-modified NASICON-type glass-ceramic electrolytes, highlighting their potential and paving the way for safer and more efficient lithium-based solid-state batteries.