Lithium-ion batteries

Batteries are, and will continue to be, important to society as we experience an ever greater imperative to move away from the paradigm of convenient, though scarce, fossil fuels.  Lithium-ion batteries are our current go-to standard for demanding applications because they offer favorable energy density, an attractive combination of high capacity with low mass.  They can also be recharged more times than Nickel-Cadmium and don’t need heavy metals for production.

New Materials Combos

Presently, a major effort is underway to employ silicon as an electrode material in these batteries because it could significantly boost their storage capacity but there is a major challenge.  As the electrodes pass lithium ions back and forth during normal cycling, the silicon can expand and contract by a factor of about three!  This activity disturbs the layer which grows on the electrode to protect it and can break electrical contact with the surrounding housing.  The batteries will eventually fail unless scientists figure out how to modulate or work around the volume expansion.  One attempt to minimize the effect involves adding chemicals to the battery to help form a better layer over the electrodes.  From flame retardation properties to arctic performance needs, optimal combination of materials can boost performance for specific applications.  Battery folks are currently trying to understand what accounts for the better performance of one additive over another, in order to predict which to use when, say, a battery must be flame retardant AND work in the Arctic.

Solid Electrolyte Interphase and HAXPES

In my HAXPES work on these batteries, I analyze the protective surface layers on electrodes of used batteries to see what elements and compounds are present.  The protective layer is generally known as the Solid Electrolyte Interphase (SEI) and it is crucial to performance.  The SEI must insulate the active material in the electrode from the rest of the battery, but it has to be as thin as possible too.  Looking for trends among batteries that had performed well or poorly helps to guide construction of better lithium-ion batteries by revealing which components or additives might generate a good SEI.