Chemically induced crack instability when electrodes fracture

We show that the resistance to fracture in electrode materials of Li batteries can be altered substantially by varying the chemical potential of Li, or equivalently, the open circuit voltage of a battery (V_cell), due to high Li mobility. Based on a thermodynamic analysis using input from first-principles electronic structure calculations, we determine the dependence of the energy (w_f) and critical stress (σf) of decohesion on the cell voltage of Li intercalation compounds. We demonstrate that w _f can decrease, increase or stay constant, with V_cell, depending on how the local Li concentration changes as new crack surfaces form. We show that chemically induced crack instabilities can occur when V _cell drives phase transitions within the decohering region, resulting in a discontinuous increase in crack separation and a dramatic drop in the maximal stress for decohesion. Copyright © 2012 The Electrochemical Society.