Diffusion-Induced Transient Stresses in Li-Battery Electrodes Imaged by Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring and Environmental Scanning Electron Microscopy

Quick charging of Li-ion batteries is often accompanied by rapid expansion of composite battery electrodes, resulting in the appearance of transient stresses inside the electrodes' bulk. Although predicted theoretically, they have never been tracked by direct in situ measurements. Herein, using multiharmonic electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), acoustic images of strong transient deformations in LiFePO₄ electrodes were obtained in the form of giant resonance frequency and resonance width shifts. The formation of cracks was verified by scanning electron microscopy. The effects of charging rate, stiffness of the polymeric binder, and solution concentration have been identified. The attractive feature of EQCM-D is its high sensitivity for selective probing of average mechanical characteristics of the operated electrodes, especially of the particle-binder interactions, directly linked to the electrode cycling performance. Using EQCM-D, an inexpensive, simple, and fast method of structural health monitoring for battery electrodes can be intelligently designed.