Toward understanding the real mechanical robustness of composite electrode impregnated with a liquid electrolyte

Abstract The mechanical robustness of highly loaded composite electrodes is important for ensuring the long-term reliability of high-energy-density secondary batteries. Considering that in real state, the electrodes in batteries are completely impregnated with electrolyte, the swelling of the polymeric binder must be carefully observed and controlled to maintain the electric connectivity within the electrode. However, the decrease in the cohesion/adhesion of electrodes caused by electrolyte impregnation has not been directly measured due to the absence of appropriate tools. Here, the surface and interfacial cutting analysis system and a specifically designed sample holder are well combined to realize this breakthrough measurement. When electrode is impregnated with a liquid electrolyte, not only the 12% increase in electrode thickness but also the greater than 74% decrease in cohesion/adhesion, which is caused by the swelling of the amorphous phase of the polymeric binders, is clearly observed. The large decrease in cohesion/adhesion can be greatly ameliorated by controlling both the degree of crystallinity and crystallite size of the polymeric binder through a simple annealing process. Thus, it believes that the measurement of the real cohesion and adhesion of composite electrodes can provide an innovative and practical way to secure the reliability of high-energy-density batteries.