  Silicon anodes promise high energy densities of next-generation lithium-ion
batteries, but suffer from shorter cycle life. The accelerated capacity fade
stems from the repeated fracture and healing of the solid-electrolyte
interphase (SEI) on the silicon surface. This interplay of chemical and
mechanical effects in SEI on silicon electrodes causes a complex aging
behavior. However, so far, no model mechanistically captures the interrelation
between mechanical SEI deterioration and accelerated SEI growth. In this
article, we present a thermodynamically consistent continuum model of an
electrode particle surrounded by an SEI layer. The silicon particle model
consistently couples chemical reactions, physical transport, and elastic
deformation. The SEI model comprises elastic and plastic deformation, fracture,
and growth. Capacity fade measurements on graphite anodesand in-situ mechanical
SEI measurements on lithium thin films provide parametrization for our model.
For the first time, we model the influence of cycling rate on the long-term
mechanical SEI deterioration and regrowth. Our model predicts the
experimentally observed transition in time dependence from square-root-of-time
growth during battery storage to linear-in-time growth during continued
cycling. Thereby our model unravels the mechanistic dependence of battery aging
on operating conditions and supports the efforts to prolong the battery life of
next-generation lithium-ion batteries.
