  Silicon is a promising anode material for next-generation lithium-ion
batteries. However, the volume change and the voltage hysteresis during
lithiation and delithiation are two substantial drawbacks to their lifetime and
performance. We investigate the reason for the voltage hysteresis in amorphous
silicon nanoparticles covered by a solid-electrolyte interphase (SEI).
Concentration gradients inside the nanoscale silicon can not produce the
massive stresses necessary to cause the reported voltage hysteresis. Our
chemo-mechanical model shows that plastic deformation of the stiff, inorganic
SEI during lithiation and delithiation reproduces the observed silicon
open-circuit voltage hysteresis. Additionally, the viscous behavior of the SEI
explains the difference between the voltage hysteresis observed at low currents
and after relaxation. We conclude that the visco-elastoplastic behavior of the
SEI is the origin of the voltage hysteresis in silicon nanoparticle anodes.
Thus, consideration of the SEI mechanics is crucial for further improvements.
