Impact of laboratory-scale pouch cell design on electrochemical characterization of battery materials

Batteries are widely studied, yet laboratory-scale results are difficult to extrapolate due to prototype-specific characteristics. In this paper, we present a comparative study of three home-made pouch cell formats to unravel the influence of design characteristics on common electrochemical tests. Cells of each format were tested through the formation cycle, discharge-rate capability, cycling and calendar aging tests. We show that electrochemical behavior depends on the amount and placement of extra negative surfaces in the cell. Face-to-face extra surfaces contribute from the beginning of the cell testing due to their easy accessibility, while external extra surfaces, if present, gain relevance over time due to slower diffusion toward the less accessible faces. Accordingly, formation cycles and brief discharge rate tests were mainly influenced by the face-to-face extra surfaces. In contrast, the long-term cycling and calendar tests showed both the face-to-face extra surface influence at early testing times, and the progressive contribution of the external surfaces, which became visible later in testing. Constant voltage steps after calendar storage and cycling pauses at the discharged state confirm these findings. In our study, bi-layer pouch cells with limited extra negative surfaces and convenient cell characteristics were the most representative cells for laboratory long-term testing. • Comparison in electrochemical results across three lab-scale pouch-cell formats. • Face-to-face extra negative surfaces contribute early in cell life due to easy access. • External extra negative surfaces contribute over time due to hindered accesibility. • Lithium recovery times reveal the differing accesibility of extra negative surfaces. • Bi-layer cells best represent long-term behavior due to their limited extra surface.