  Core-shell electrode particle designs offer a route to improved lithium-ion
battery performance. However, they are susceptible to mechanical damage such as
fracture and debonding, which can significantly reduce their lifetime. Using a
coupled finite element model, we explore the impacts of diffusion-induced
stresses on the failure mechanisms of an exemplar system with an NMC811 core
and an NMC111 shell. In particular, we systematically compare the implications
of assuming constant material properties against using Li
concentration-dependent diffusion coefficient and partial molar volume. With
constant material properties, our results show that smaller cores with thinner
shells avoid debonding and fracture regimes. When factoring in a
concentration-dependent partial molar volume, the maximum values of tensile
hoop stress in the shell are found to be significantly lower than those
predicted with constant properties, reducing the likelihood of fracture.
Furthermore, with a concentration-dependent diffusion coefficient, significant
barriers to full electrode utilisation are observed due to reduced lithium
mobility at high states of lithiation. This provides a possible explanation for
the reduced accessible capacity observed in experiments. Shell thickness is
found to be the dominant factor in precluding structural integrity once the
concentration dependency is accounted for. These findings shed new light on the
performance and effective design of core-shell electrode particles.
