Probing Electrode-Electrolyte Interfaces in Rechargeable Alkali-Ion Batteries

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Rechargeable batteries have a vital role to play in meeting our future energy needs, helping to decarbonise the economy and meet ambitious net-zero emissions commitments. However widespread deployment requires further increases in energy density and reductions in cost. Current battery lifetimes fall well below expectations due to unwanted side reactions, and we lack the fundamental understanding needed to design solutions to significantly improve capacity retention. The performance of electrode materials is largely defined by reactions occurring at the interfaces between typically solid electrodes and liquid electrolytes. Within a few nanometres of these interfaces, electrons are transferred, ions are solvated/desolvated, and undesired side-reactions proceed. Understanding the structural and chemical evolution of these interfaces is critical to developing improved electrode materials and electrolyte formulations, as well as understanding the electrochemical conditions under which these are stable. However, extracting information from these buried interfaces during operation is extremely challenging, due to the dense solid/liquid phases which scatter most interface-sensitive probes (e.g. electrons, ions).The key aim of this project is to adapt powerful interface-sensitive techniques, so that they can probe buried electrochemical interfaces under realistic operating conditions. This will combine complementary X-ray spectroscopy, and neutron reflectometry to chemically and spatially resolve the evolution of electrode interfaces operating in liquid environments. Specially adapted windows will be developed that are transparent to these probes (electrons, X-rays and neutrons) but which also seal the electrochemical environment and act as the electrodes.These new capabilities will then be used to reveal the interfacial processes occurring at ion insertion electrodes in rechargeable alkali metal (Li, Na, K) ion batteries. The proposed operando approach promises to transform our understanding of how ions and solvent arrange at biased electrodes in these electrolytes, and the effect on the reactions occurring. A particular focus will be on concentrated (>5M) electrolytes where high salt concentrations are thought to expand the electrochemical operating window, and salt decomposition is expected to have a more significant contribution to side reactions. This understanding will inform the selection of electrode materials and electrolyte formulations that offer improved safety and/or lower cost.This project falls within the EPSRC research areas of Energy Storage and Analytical Science, where the aim is to develop and apply novel characterisation tools to reveal the chemical structure of buried electrode-electrolyte interfaces in alkali-ion batteries. This will involve the use of X-rays and Neutron techniques available at Diamond light source and the ISIS muon and neutron source, as well as other international facilities.