Neutron Total Scattering as a Tool for Battery Electrolyte Design

The future of battery science promises groundbreaking innovations, from the development of all-solid-state lithium metal batteries, set to revolutionise battery-powered aircrafts, to novel battery chemistries designed to meet growing demands.¹ While transitioning from liquid to solid electrolytes brings unique challenges, in terms of reduced ionic conductivity and interfacial contact, the intrinsic absence of long-range order in amorphous electrolytes further complicates our fundamental understanding of their degradation.<br/><br/>Neutron total scattering (NTS) is a powerful tool for addressing these challenges due to its high sensitivity to light elements, such as lithium, and its atomistic resolution. The varying neutron scattering lengths of isotopes of the same element enable the acquisition of multiple isotopically distinct patterns that will constrain the derivation of the material structure, permitting us to separate key features. Combined with Monte Carlo simulations, NTS allows us to achieve an experimental, atomistic picture of the systems, where a wide range of intermolecular interactions take place.²<br/><br/>Here, we use NTS and Monte Carlo simulations to understand and design next generation battery electrolytes. Starting with known systems, such as lithium phosphorus oxynitrate, we provided new insights into the local atomic structure experimentally with previously unobtainable precision, showing key observed differences from previously established models, such as the presence of a rich glass network in which lithium plays a key stabilising role. With this information in hand, we directly linked material properties (e.g., ionic conductivity) with our measured nanoscale structures to develop a machine learning model that can be predictive in the optimisation of composition, structure, and diffusivity for material discovery.³<br/><br/>Concurrently, total scattering offers a unique opportunity for understanding new chemistries, such as fluoride ion. By shuttling an anion instead of a cation, fluoride ion batteries are a promising alternative to lithium, as they rely on earth abundant materials. However, the commercialization of fluoride ion batteries is hindered by the limited solubility of fluoride salts. By comparing three different promising liquid electrolytes for fluoride ion batteries, we used neutron total scattering on an instrument such as the NIMROD diffractometer at ISIS, the UK neutron and muon source, to understand the molecular mechanisms behind their solubility. The wide <i>Q</i> range of NIMROD, that spans from the molecular to the mesoscopic scale, allowed us to shed a light on the solvation of anions and cations, that directly links to charge diffusion and conductivity, as well as on the formation of the hazardous HF.⁴<br/><br/>In summary, we present new advancements in NTS and its use in battery technologies. Our state-of-the-art NTS techniques reveal how these innovations can be directly applied to both understand and optimize disordered electrolyte materials, paving the way for next-generation battery technologies.<br/><br/>[1] Pasta, M. et al., “2020 roadmap on solid-state batteries” <i>J. Phys. Energy</i> 2020, 2, 032008.<br/>[2] Di Mino, C. et al., “Strong structuring arising from weak cooperative O-H...π and C-H...O hydrogen bonding in benzene-methanol solution” <i>Nat. Commun.</i> 2023, 14, 5900.<br/>[3] Nicholas, T. C. et al., “Geometrically frustrated interactions drive structural complexity in amorphous calcium carbonate” <i>Nat. Chem.</i> 2024, 16, 36.<br/>[4] Galatolo, G. et al., “Advancing Fluoride-Ion Batteries with a Pb-PbF2 Counter Electrode and a Diluted Liquid Electrolyte” ACS <i>Energy Lett</i>. 2024, 9, 1, 85.