Research

A clean energy economy needs batteries that store more energy, more safely and at lower cost than today’s Li-ion cells, and that are made from abundant elements. Our work spans sodium-ion batteries, all-solid-state batteries and their solid electrolytes, and multivalent batteries, and, across all three, the interphases, interfaces and surfaces where their components meet. We use first-principles calculations, statistical mechanics and machine learning, often together with experimental collaborators, to understand and design electrodes, electrolytes and the interfaces between them.

Organic electroactive materials are built from abundant elements such as carbon, hydrogen, nitrogen, oxygen and sulfur, and offer a sustainable alternative to the transition-metal oxides used in today’s batteries. Their molecules can also be tailored almost at will. In practice, however, most organic electrodes work at low voltages, conduct electrons poorly, and crystallize in structures that are hard to resolve, because the light atoms that matter most, lithium and hydrogen, scatter X-rays only weakly. We combine first-principles calculations with experiments by our collaborators to understand each of these limitations at the molecular level.

Our predictions about materials are only as reliable as the methods behind them. First-principles calculations, chiefly density functional theory, rest on approximations that fail for some materials, and they can follow only a few hundred atoms for tens of picoseconds, while many properties of real materials, such as ion transport, phase behaviour and degradation, emerge over far larger systems and longer times. Alongside our work on specific materials, we therefore develop and test methods that make first-principles simulations more accurate, build realistic models of surfaces and interfaces, and bridge length and time scales by combining first-principles data with cluster expansions, Monte Carlo and kinetic Monte Carlo simulations, and machine-learned interatomic potentials. We test them against experiments, often together with our collaborators, and, where we can, release them as open-source codes, such as kMCpy and SALAMI, listed on our Software page.

Porous frameworks, such as metal–organic frameworks, hold small molecules inside pores only a few ångströms wide. By choosing the size and chemistry of those pores, a framework can be made to store a gas or to take up one gas and reject another, which makes these materials candidates for capturing CO₂, separating air and hydrocarbons, and storing hydrogen at moderate pressures. Our first-principles calculations, working alongside adsorption, diffraction and spectroscopy measurements by our collaborators, show where the molecules bind and why a framework prefers one gas over another.