Surface effects in cylindrical anode particles: Mechanical versus electrochemical performance determined by charging condition in lithium-ion batteries

Abstract

Surface stresses, in nano-sized battery anode particles undergoing chemomechanical interactions, have a compressive effect on diffusion-induced stresses. This, on the one hand, improves the mechanical endurance of the particles and, on the other hand, degrades their electrochemical performance. However, this straightforward prediction of an improved mechanical performance is re-evaluated in this work in light of large axial length-increase during lithiation within Si nanowires. Interestingly, we observed that the influence of surface stress on length-increase of nanowires is dependent on the charging conditions (galvanostatic/potentiostatic). The mathematical model we present to capture the sensitive interplay among these effects is based on the finite deformation formulation, considering two-way coupling of diffusion-induced stresses and stress-enhanced diffusion. Additionally, we consider the influence of a constraining material at the core, whose material and geometrical properties can be suitably tuned. Finally, we present a competitive analysis for the overall performance of the anode particles under the combined effects of surface stresses and constraining material to determine the best possible particle sizes for different charging conditions. Such a comprehensive approach strengthens our understanding of different mechanical and electrochemical factors in general chemomechanical interactions involved in various applications of nanostructures.