"Electrochemical Shock" of Intercalation Electrodes: A Fracture Mechanics Analysis

Fracture of electrode particles due to diffusion-induced stress has been implicated as a possible mechanism for capacity fade and impedance growth in lithium-ion batteries. In brittle materials, including many lithium intercalation materials, knowledge of the stress profile is necessary but insufficient to predict fracture events. We derive a fracture mechanics failure criterion for individual electrode particles and demonstrate its utility with a model system, galvanostatic charging of LixMn2O4. Fracture mechanics predicts a critical C-rate above which active particles fracture; this critical C-rate decreases with increasing particle size. We produce an electrochemical shock map, a graphical tool that shows regimes of failure depending on C-rate, particle size, and the material's inherent fracture toughness K-Ic. Fracture dynamics are sensitive to the gradient of diffusion-induced stresses at the crack tip; as a consequence, small initial flaws grow unstably and are therefore potentially more damaging than larger initial flaws, which grow stably. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3464773] All rights reserved.