Phosphate glasses and glass-ceramics: materials of the future for advanced batteries and catalysts

Understanding the structure of glass and the interactions between the structural elements of these materials is crucial for the development of new, more efficient, and cheaper sodium-ion batteries and new catalysts.

Zagreb, June 21, 2024 – Glass, which at first glance may seem like an ordinary material, has a long history and an important role in our lives as one of the oldest manufactured materials. It is an indispensable part of everyday life and, due to its unique properties, the subject of intense research by scientists worldwide. By researching phosphate glasses and glass-ceramics, scientists at the Ruđer Bošković Institute (RBI) have discovered how to enhance their potential for advanced technological applications by tailoring their properties to design better materials for next-generation batteries and catalysts.

The potential of phosphate glasses

Phosphate glasses are particularly interesting because of their ability to conduct electricity, making them ideal for use in sensors and batteries. Research by scientists at the RBI has shown that by changing the composition of the glass, they can significantly improve its ability to conduct electricity. This phenomenon allows scientists to prepare new glasses with better properties for use in sodium-ion batteries, which are a cheaper and more accessible alternative to lithium-ion batteries.

Enhanced electrical conductivity for advanced batteries

But how exactly does glass, which is typically considered a non-conductive material, manage to conduct electricity? In laboratories like the Laboratory for Functional Materials at the RBI, researchers delve deep into the world of phosphate glasses and glass-ceramics.

Sara Marijan, a doctoral student of the Croatian Science Foundation (HrZZ) and a scientific assistant at the Laboratory for Functional Materials, under the guidance of Dr. sc. Luka Pavić and Assoc. Prof. Dr. sc. Jana Pisk from the Faculty of Science at the University of Zagreb (PMF), focuses on special multi-component glass systems. This glass consists of four different types of oxides in its basic formulation. Such multi-component systems allow more complex control over the optical, mechanical, and electrical properties of glass, thanks to the combination of different oxides that can form a mixed glass network and thus improve the investigated properties.

Additionally, they are designed for use in sodium-ion batteries and are a combination of sodium oxide and three glass-forming oxides. In this, the classical glass formers, phosphorus and niobium pentoxide, are present in the majority, while vanadium pentoxide is added as a third, minor, conditional glass former. The addition of vanadium pentoxide is particularly interesting because it can have a dual role; besides modifying the structure of the glass, it can also contribute to the overall electrical conductivity.

''What makes these materials so special is their ability to conduct electrical current through a dual mechanism. Glasses like those we research in our laboratory, which contain both sodium oxide and vanadium pentoxide, can conduct electrical current by the movement of sodium ions through the glass network, but also by the hopping of electrons from one vanadium ion to another. Such a dual conduction mechanism can lead to better efficiency in charging and discharging batteries,'' explains Sara Marijan.

In research recently conducted by scientists from the RBI, in collaboration with Assoc. Prof. Dr. sc. Jana Pisk and Assoc. Prof. Dr. sc. Željko Skoko from the PMF, and Prof. Peter Mošner and Prof. Ladislav Koudelka from the Faculty of Chemical Technology at the University of Pardubice, they experimented with adding different amounts of vanadium and niobium pentoxide to these multi-component phosphate glass systems to see how it changes the glass's ability to conduct electricity. They found that the addition of niobium pentoxide promotes faster movement of sodium ions through the glass, significantly increasing the glass's conductivity.

The impact of niobium

As more niobium is incorporated, the structure of the glass transitions into a hybrid of niobates and phosphates. This change is crucial as the glass achieves its optimal conductivity, especially when the niobium content is around 20%. However, if there is too much niobium, niobate clusters are formed that slow the movement of sodium ions through the glass structure. Therefore, it is crucial to understand the delicate relationship of these components' proportions to find the optimal composition.

''Using advanced techniques such as electron paramagnetic resonance and vibrational and impedance spectroscopy, we observed that structural changes led to increased glass performance, especially with around 20% niobium, where conductivity was highest. This detailed examination helped us discover that up to a certain point, the addition of niobium can be beneficial, but beyond that, it can hinder the material's electrical properties,'' explains Sara Marijan.

Catalytic properties of glass

''In addition to the development of glass and glass-ceramics synthesis and the correlation of their thermal and electrical properties with structural features, a new direction we have opened in collaboration with Assoc. Prof. Dr. sc. Jana Pisk from the PMF within Sara's doctoral research is the examination of these materials as catalysts. It is surprising that there is not a large number of studies on this topic, even though phosphate glasses and glass-ceramics have shown potential as catalysts in chemical reactions, such as epoxidation, which opens new directions for their use,'' states mentor Dr. sc. Luka Pavić, one of the research leaders.

''Exploring the possibilities of glass as a catalyst, we discovered that glasses with a high content of vanadium oxide exhibit excellent catalytic activity and selectivity in catalytic reactions,'' explains Sara Marijan.

It is worth noting that the initial material can be regenerated and reused, maintaining its efficiency in the next catalytic cycle. Moreover, these glasses can be prepared by a simple process that ensures reproducibility and simplifies the preparation of these materials on larger scales, which is of particular importance for industrial-scale catalytic applications.

The significance of the research

''Such research is important because understanding how different oxides connect within the glass structure opens possibilities for developing new types of sodium-ion batteries that could be more efficient and cost-effective than current lithium-ion options,'' concluded the scientists.

Moreover, this research has further confirmed the multifunctionality of phosphate glasses and glass-ceramics. Additionally, it has shown that electrical and catalytic properties are closely linked to the structural features of the glass, allowing further adaptation and optimization for specific applications.

In their research, the team used advanced techniques such as Raman and infrared spectroscopy, solid-state impedance spectroscopy, and gas chromatography to closely study the glass structure and its correlation with electrical and catalytic properties. These methods revealed that simple changes in composition can directly affect the glass's ability to conduct electricity and significantly increase its conductivity, as well as achieve high catalytic activity.

The results of the research on phosphate glasses and glass-ceramics by the scientists of the Laboratory for Functional Materials have been published in several scientific journals: Journal of Physics and Chemistry of Solids, International Journal of Minerals, Metallurgy and Materials, Journal of Non-Crystalline Solids, and International Journal of Molecular Sciences. The research was supported by projects of the Croatian Science Foundation and the HAZU Foundation.