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. A common electrode design for secondary batteries is a porous thin film of active material particles, conductive carbon particles, and polymeric binder. The film is coated on a metallic current collector. For commercially produced cells based on lithium-ion intercalation chemistry, the active materials are commonly a transition metal oxide on aluminum for the cathode and graphite on copper for the anode.Among the key properties determining electrode performance are the volume-averaged (effective or bulk) electronic conductivity of the film and the interfacial resistance at the current collector.1-4 These two quantities are surprisingly difficult to measure accurately for common thin-film electrodes because of the relatively large contact resistance between the sample and external probes, mechanical fragility of the sample, and the presence of the attached current collector. Lack of experimental data makes it hard to meet a longstanding need to be able to predict these parameters from knowledge of the composition and structure of the constituent materials.Commercial Li-ion battery electrodes are fabricated by first by making a slurry of the active material, carbon additive, binder, and a carrier solvent. This slurry is spread onto a metal foil current collector in a continuous process using a blade or slit to control deposition thickness, and then is immediately dried. Even in commercial coating processes it is difficult to achieve a uniform distribution of particles and porosity, leading to variability in the electronic conductivity of the electrodes.5 While this variability...

This paper describes research to understand the relationships between materials, microstructure, and performance for primary alkaline battery cathodes composed primarily of electrolytic manganese dioxide (EMD). Specifically, the effect of various carbon additives on electronic transport within cathodes was investigated. Of the various carbon additives investigated, TIMCAL BNB90 was the best performer and graphene nanopowder was the next best. These additives had the lowest Scott density and highest BET surface area of the tested additives, and exhibited well-connected and elongated carbon pathways in SEM/FIB cross sections. Additionally, this work shows a decrease in electronic conductivity for the porous cathode in the presence of KOH electrolyte. The two top-performing cathodes, when wet with concentrated KOH had a conductivity that was about 30% below that of the dry conductivity.

Measurement of the electronic conductivity of porous thin-film battery electrodes poses significant challenges, particularly when the film is attached to a metallic current collector. We have developed a micro-four-line probe and testing procedure that overcomes many of these difficulties while relying on principles similar to commonly used four-point probes. This work describes a mathematical model that enables rapid inversion of the data collected by such experiments to compute two properties: bulk electronic conductivity of the film and contact resistance with the current collector. The model accounts for variable probe and sample geometry and variable resistance between the probe and the sample. Results from 2D and 3D models are presented. The full 3D model combines a Fourier series with the boundary element method to generate a solution that requires significantly less computational cost than a corresponding finite element solution for the same level of accuracy. The model confirms that the ideal probe line spacing is close to the value of the electrode film thickness. Transportation, communication, and mobile electronics are just a few of the many industries that are relying increasingly on battery technology. Lithium-ion batteries that employ particle-based thin-film electrodes are a critical part of this technological advance. However, such electrodes can exhibit conductivity limitations, including significant spatial variations due to particle and composition inhomogeneities, which can cause so-called hot and cold spots, undesired sidereactions, and an overall decrease in cell performance and safety. [1][2][3] One key to resolving such manufacturing and materials problems is accurate measurement of relevant properties. The general approach for conductive properties is to perturb the sample with an imposed current and then measure the electric potential on two or more points on the surface. However, it is surprisingly difficult to accurately measure the electrical conductivity and contact resistance (between electrode and current collector) of these films. [4][5][6][7][8][9] This is because the contact resistance between probe and sample is high relative to the resistance of the sample, the sample is mechanically fragile, and the conductivity of the electrode film is confounded by the presence of a highly conductive adjacent metal layer (the current collector). The electrode film can be delaminated from the current collector in order to eliminate the last problem, 4 though it is more desirable to measure electrodes non-destructively as is proposed in this work.Conductive property measurements.-Multiple methods have been used in the past to measure the conductivity or resistivity of thin films or layered materials. The four-point-probe method has been in use for many decades, and is particularly useful in measuring singlelayer conductive materials. On the other hand, with point probes it is difficult to control the pressure imparted to the electrode material during the measurement, which can change conduc...