Seminars

Abstract: Mechanical stress caused by chemically induced strains is currently the largest obstacle to improving the energy density of rechargeable batteries. Stresses regulate material kinetics and structural stability, leading to low capacity retention and charging rate capability. Overcoming these challenges requires knowledge of the mechanical properties and the underlying kinetic processes of the active materials. There is, however, a lack of experimental tools suited for studying chemo-mechanics of energy materials. The active materials have a dynamic composition that evolves during operation, have small characteristic sizes, and are sensitive to the environment. Considering these circumstances, we introduce the first operando nanoindentation platform for locally probing battery materials during chemical reactions in an inert environment. With this powerful new technique, we can track the concurrent evolution of stress and lithium concentration fields, and rigorously model their interplay. We explain the Li kinetics of amorphous silicon electrodes including the asymmetric rate-capability, sharp reaction front, and the violation of the self-similarity of Li propagation profiles due to stress reversal. The framework brings about insights on fundamental mechanisms and advises on battery design and operation.