Micro-four-line probe to measure electronic conductivity and contact resistance of thin-film battery electrodes

Electronic conductivity of battery electrodes and the interfacial resistance at the current collector are key metrics affecting cell performance. However, in many cases they have not been properly quantified because of the lack of a suitably accurate and convenient non-destructive measurement method. There are also indications that conductivity across deposited films is not uniformly distributed. To characterize these variations, a micro-four-line probe has been developed for local mesoscale measurement of electronic conductivity of thin-film electrodes. The micro-four-line probe, coupled with a previously discussed mathematical model, overcomes key limitations of traditional point probes. This new approach allows pressure-controlled surface measurements to determine electronic conductivity without removal of the current collector. In addition, the probe allows one to measure the local interfacial contact resistance between the electrode film and the current collector. The method was validated by comparing to other conductivity sampling methods for a conductive test film. Three commercial-quality Li-ion battery porous electrodes were also tested and conductivity maps were produced. The results show significant local conductivity variation in such electrodes on a millimeter length scale. This method is of value to battery manufacturers and researchers to better quantify sources of resistance and heterogeneity and to improve electrode quality.