Design criteria for electrochemical shock resistant battery electrodes

Mechanical degradation of electrode active materials (“electrochemical shock”) contributes to impedance growth of battery electrodes, but relatively few design criteria have been developed to mitigate fracture. Using micromechanical models and in situ acoustic emission experiments, we demonstrate and explain C-rate independent electrochemical shock in polycrystalline electrode materials with anisotropic Vegard coefficients. We conclude that minimizing the principal shear strain, rather than minimizing net volume change as previously suggested, is an important new design criterion for crystal chemical engineering of electrode materials for mechanical reliability. Polycrystalline particles of anisotropic Li-storage materials should be synthesized with primary crystallite sizes smaller than a material-specific critical size to avoid fracture along grain boundaries. Finally, we revise the electrochemical shock map construction to incorporate the material-specific critical microstructure feature sizes for C-rate independent electrochemical shock mechanisms, providing a simple tool for designing long-lived battery electrodes.