  Surface stresses, in nano-sized anode particles undergoing chemomechanical
interactions, have a relaxing effect on the diffusion-induced stresses thus
improving the mechanical endurance of the particles, whereas, the compressive
effect of surface stresses degrades the electrochemical performance. However,
this straightforward prediction of an improved mechanical performance is
challenged in this work. Silicon nanowires undergoing huge volumetric changes
during lithiation, may undergo significant axial length-increase, which serves
as an important criterion in determining the mechanical performance of SiNWs.
Interestingly, surface stresses tend to reduce the length-increase under
potentiostatic charging condition, but under galvanostatic charging, the
length-increase gets enhanced, thus degrading the mechanical performance of the
SiNWs. To further make the study more inclusive, the nanowire is modelled with
a constraining material at its core, and a competitive analysis is presented
for the overall performance of the anode particles under the combined effects
of surface stresses and constraining material. The mathematical model is based
on large deformation theory, considering two-way coupling of diffusion-induced
stresses and stress-enhanced diffusion. It is hoped that this study will
provide a fresh perspective in designing next-generation lithium-ion battery
particles.
