Analytical Model on Stress-Regulated Lithiation Kinetics and Fracture of Si-C Yolk-Shell Anodes for Lithium-Ion Batteries

Despite various Si-based anode designs proposed by different researchers, the low areal capacity of these anodes remains an obstacle to their utilization as they still fail to meet the requirements for commercial Li-ion batteries. To tackle this challenge, a novel design of pomegranate-inspired Si-C yolk-shell composite anodes was developed recently, where single silicon nanoparticles are encapsulated by conductive carbon shells with void spaces between particles and shells to accommodate expansion. Despite overall excellent cycling performance, lithiation halting and carbon shell pulverization are experimentally observed in some Si-C yolk-shell anode designs, which undermine the structural integrity and limit the battery performance. Quantitative understanding of these failure modes is still lacking despite being critical to improve the yolk-shell anode designs. We present a theoretical study on lithiation-induced stress field in Si-C yolk-shell composite anodes and its influence on lithiation kinetics and mechanical degradation. For the first time, it is demonstrated that the contribution of surface stresses to the lithiation-induced stress field in nano-sized silicon anodes is negligible. We identify promising designs to achieve full anode capacity without carbon shell fracture while reducing consumption of carbon material. Results from the present study may offer insight on improving designs of Si-C yolk-shell composite anodes. (C) 2016 The Electrochemical Society. All rights reserved.