Dynamic Structure Discovery and Ion Transport in Liquid Battery Electrolytes

Abstract: The lithium-ion battery (LIB), the realisation of which earned the Nobel Prize in Chemistry 2019, has since its 1991 commercialisation become the dominant energy storage technology first for cell phones and other mobile electronics, then for power tools and other domestic appliances, and currently for electric cars and other vehicles. However, many applications would still benefit from higher power and energy densities, longer life-lengths and safer batteries. Such improvements would for example accelerate the electrification of transport, lower the pollution and the greenhouse gas emissions. Electrolytes are extremely crucial for the operation of the LIBs, yet they have so far changed surprisingly little the last 25 years. Further improvement can be made by novel electrolyte concepts. Highly concentrated electrolytes (HCEs) may enable higher energy and power densities, as well as improved thermal, chemical and electrochemical stabilities as compared to the current state-of-the-art, while also being more flexible in their composition. They also have more complex structures and ion transport mechanisms. I here present a novel method for studying both more standard electrolytes and HCEs by analysing molecular dynamics simulation trajectories. This method automatically detects the time-dependent structures present and characterises them by statistical physics, giving an extraordinarily detailed view of the structure and dynamics. I describe the theory and implementation of this method as well as its application to several HCEs and the ubiquitous LP30 electrolyte. These studies enhance the picture of ion transport conveyed previously and future application should add substantially to the design of battery electrolytes and beyond. The lithium-ion battery (LIB), the realisation of which earned the Nobel Prize in Chemistry 2019, has since its 1991 commercialisation become the dominant energy storage technology first for cell phones and other mobile electronics, then for power tools and other domestic appliances, and currently for electric cars and other vehicles. However, many applications would still benefit from higher power and energy densities, longer life-lengths and safer batteries. Such improvements would for example accelerate the electrification of transport, lower the pollution and the greenhouse gas emissions. Electrolytes are extremely crucial for the operation of the LIBs, yet they have so far changed surprisingly little the last 25 years. Further improvement can be made by novel electrolyte concepts. Highly concentrated electrolytes (HCEs) may enable higher energy and power densities, as well as improved thermal, chemical and electrochemical stabilities as compared to the current state-of-the-art, while also being more flexible in their composition. They also have more complex structures and ion transport mechanisms. I here present a novel method for studying both more standard electrolytes and HCEs by analysing molecular dynamics simulation trajectories. This method automatically detects the time-dependent structures present and characterises them by statistical physics, giving an extraordinarily detailed view of the structure and dynamics. I describe the theory and implementation of this method as well as its application to several HCEs and the ubiquitous LP30 electrolyte. These studies enhance the picture of ion transport conveyed previously and future application should add substantially to the design of battery electrolytes and beyond.

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