Voltage Hysteresis of Silicon Nanoparticles: Chemo-Mechanical Particle-SEI Model

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. The reason for the voltage hysteresis in amorphous silicon nanoparticles covered by a solid-electrolyte interphase (SEI) is investigated. Concentration gradients inside the nanoscale silicon cannot produce the massive stresses necessary to cause the reported voltage hysteresis. The 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. It is concluded 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. Silicon nanoparticle anodes show an open-circuit voltage hysteresis that has not been explained so far. This article demonstrates that a chemo-mechanical model of silicon nanoparticles and the covering solid-electrolyte interphase layer explains the observed voltage hysteresis. Viscosity of the solid-electrolyte interphase can in addition reproduce the experimental voltage difference between slow cycling and the relaxed system.image

Automated summary

This study explains the observed voltage hysteresis in silicon nanoparticle anodes through a chemo-mechanical model and identifies the viscosity of the solid-electrolyte interphase as the cause.