Insight into mechanical robustness of composite electrodes for rechargeable lithium batteries

Abstract

The mechanical robustness of composite electrodes is easily overlooked, because their electrochemical properties are well measured when they are assembled as unit cells. However, considering long service time of secondary batteries especially for electric vehicles or energy storage systems, it should be taken into account that the electrode structure can be collapsed by continuous mechanical stress during charging/discharging processes. In addition, lower binder content and higher loading level for higher-energy-density batteries can further weaken the mechanical robustness of composite electrodes. Thus, reliable cohesion/adhesion measurement methods must be developed for designing composite electrodes. As we have already demonstrated, a surface and interfacial cutting analysis system (SAICAS) is a versatile tool to measure cohesion and adhesion of any kinds of composite electrodes with precision of 1 μm depth. In this presentation, the effect of liquid electrolyte swelling on the mechanical robustness of composite electrodes will be dealt with a newly devised sample holder containing both electrode sample and liquid electrolyte. When the composite electrodes are impregnated with liquid electrolyte, all cohesion and adhesion dramatically drop comparing to those at dry state. It can be ascribed to the swelling of polymeric binder’s amorphous phase. So, when the crystalline structure of polymeric binder are controlled by annealing process, the mechanical robustness can be greatly improved by increasing both crystallinity and crystallite size of binders.