Electrical conductivity is a fundamental characteristic determining the performance of lithium-ion batteries. However, methods to measure the conductivity nondestructively have proven difficult. This is due to the presence of a metallic conductive current collector as well as dominating effect of the contact resistance between the film and the probe. In previous research we developed a micro-four-line probe [1] that can measure thin-film electrodes without removing the current collector. We found that the conductivity of even high-quality electrodes is not homogenous, and has variation on length scales much larger than the size of the active material particles.

Even though the micro-four-line probe worked well, we continue to improve the design. The previous design was fabricated in a clean room on a rigid glass substrate. This limited the geometry of the sample and made adaptation to industrial use difficult. To address this problem, we switched to a flexible polymer substrate, as shown in the figure, which allows for increased sample size and potential low-cost manufacturing. In addition, changes were made to the computer-controlled probe holder and stage, again with an aim toward lowering cost and increasing usability. The stage is used to move the probe over the surface of the sample in order to produce a conductivity map.

We will report conductivity results using the new probe for both anodes and cathodes, including the effect of cycling. Results will also be compared to related work on ionic conductivity of the same electrodes. The hope is that this probe technology can be adapted to manufacturing use as well as to assist other researchers in understanding limiting mechanisms in battery performance.