RESEARCH
NEXT GENERATION OF SOLID-STATEÂ BATTERIES ELECTROLYTES
Rechargeable lithium-ion batteries have revolutionized the portable electronics industry because of their high energy density and efficiency. They may also prove valuable for a variety of other applications, including electrification of the transport system and grid-scale stationary energy storage. However, they still suffer from several significant safety and reliability issues, many of which are related to the use of electrolytes dissolved in organic solvent. Solid-state electrolytes could resolve all of these problems. However, most candidate materials have much lower ionic conductivity compared to that of liquid electrolytes, which reduces the power density of the cell and limits their practical applications. In Pasta group, we are exploring glass, ceramic, and composite solid electrolytes. For the ceramic, we focus on lithium and sodium anti-perovskites. This family of solid electrolytes have received a significant increase in attention in the last decade because of their high ionic conductivity (10-3 S cm-1), a wide electrochemical stability window, easy processability, and chemical stability against Li and Na metals. In addition, the performance, properties, and ion transport mechanisms of anti-perovskites can be tailored through, for example, defect tuning, chemical substitution, and microstructural engineering. The glass versions of anti-perovskite solid electrolytes have been reported to have even higher ionic conductivities than the ceramic versions due to their negligible grain boundaries contribution. Lastly, we are also focusing on producing highly thin and dense solid electrolyte films with scalable processes to manufacture all-solid-state batteries.
LITHIUM METAL ANODES
Lithium metal anodes are known as the 'holy grail' of batteries as Li is the lightest and most electronegative metal, which leads to it having a theoretical energy density an order of magnitude larger than graphite anodes for Li-ion batteries (3860 mAh g-1 vs 372 mAh g-1). However, the high reactivity of Li and its non-uniform plating lead to several issues including the formation of an unstable interfacial layer and filament growth which causes capacity loss and potential safety issues. We are investigating the fundamental science behind the formation of these filaments and how it relates to the electrolyte and interface properties.
TRANSITION METAL FLUORIDE CATHODES
Transition metal fluoride (TMF) cathodes can store multiple Li-ions per metal centre due to a multielectron conversion reaction and hence offer a 200% to 300% increase in theoretical energy density compared to state- of-the-art intercalation cathodes. In a recent publication we were able to prove that the reversibility of the FeF2 conversion reaction is governed by topotactic cation diffusion through an invariant lattice of fluoride anions and the nucleation of metallic particles on semicoherent interfaces. This new understanding is used to showcase the inherently high discharge rate capability of FeF2. [1] We currently study the reaction mechanism of other TMF cathodes by synthesizing nanostructured active material which allows us to extrapolate crystal structures and morphological features of individual particles to the whole electrode. With several collaborators we are optimizing the electrochemical performance of our cathodes and study their applicability for high temperature operation.
[1] Xiao, Albert W., et al. , Nature Materials 19.6 (2020): 644-654.
CLEAN ENERGY THROUGH PRUSSIAN BLUE ANALOGUES
Prussian blue analogues (PBAs) are a diverse and versatile family of open-framework crystals. Careful control of the chemistry allows our team to tune the materials' macroscopic properties for targeted applications in energy storage. Batteries made from PBAs have the potential to improve energy density, decrease charging time, or increase the cell's safety profile. Can we design PBAs with tailored materials properties for targeted application?
FLUORIDE-ION BATTERIES
The climate crisis is driving the search for novel battery chemistries that can power high-energy applications, such as electric vehicles and electric flights. Among the available candidates, fluoride-ion batteries (FIBs) are a promising technology because of their high theoretical energy density and utilization of abundant and widespread materials. However, FIBs present several new challenges that have prevented them from reaching commercialization. At this incipient stage, the discharge/charge mechanism at both electrodes is still poorly understood; furthermore, the design of a liquid electrolyte system for long-term cycling stability has not been realized. We are investigating possible liquid electrolytes as well as studying the comprehensive mechanistic evaluation and stable long-term cycling through the use of monodisperse, nanocrystalline metal fluoride cathodes.
SINGLE-ATOM ELECTROCATALYSTS
At the current rate of CO2 emissions, the world is on track for more than 3 °C warming by the year 2100, with catastrophic consequences to global climate. Hydrogen is among the most promising alternative energy sources to replace traditional fossil fuels. Hydrogen generation from electrochemical water splitting is a viable, carbon neutral alternative to steam reforming. Electrocatalysts make the water-splitting reaction more energy efficient by lowering the activation barrier that must be overcome before the reaction can proceed. Platinum is the most effective and durable electrocatalyst, but it is prohibitively scarce and expensive for mass production of electrolyzers. We are investigating single-atom electrocatalysts in which the monoatomic nature of the active sites not only have maximal atom utilization efficiency (lower cost) but also offer opportunities for tuning reaction rates and selectivities.