Chemo-mechanical couplings in batteries

With a theoretical capacity ten times larger than that of graphite, silicon as a material for negative electrodes brings promises of increasing the capacity of lithium-ion batteries. However, the use of silicon raises several challenges due to the large volume change, stresses and mechanical disintegration that silicon experiences during lithiation. Mechanics is involved in the lithiation of silicon in two ways: i) insertion of lithium in silicon leads to diffusion-induced stresses, ii) the resulting state of stress of silicon affects the lithiation reaction essentially through a contribution of stress to the chemical potential of lithium. In this work, we develop a combined experimental/theoretical approach to characterize the effect of stress on lithiation. First, we conduct an experimental study of the effect of stress on the lithiation of amorphous silicon by modifying, through an external mechanical loading, the stress state of silicon thin-film electrodes during lithiation/delithiatio. Second, we develop a theoretical model of the effect of stress on lithiation in the setting of large strain elasto-plasticity, for both the monophasic and biphasic lithiation, with the objective to forge a fundamental understanding of the experimental results.