Reproducible Production of Lithium-Ion Coin Cells

Abstract

Due to the simple structure and the possibility of manual production, coin cells enable fast and, compared to larger cell formats, an inexpensive examination option in battery research. The comparability and traceability of coin cell structures in literature are only feasible to a limited extent due to the lack of a standard in manual production. Since the findings from the literature are barely building up on each other and have not been repeated, a full factorial Design of Experiments (DoE) was performed to investigate the significance of earlier findings in terms of their influence on the reproducibility of the performance. The parameters studied were the anode-to-cathode ratio, the amount of electrolyte, the spring type and the separator count. To quantify the reproducibility of coin cell assembly, the number of functional cells (here: successful formation followed by 30 cycles) and the empirical coefficient of variation for the performance parameters discharge capacity, internal resistance and coulombic efficiency were compared. The critical parameters found in prior literature have no statistically significant influence on reproducibility when focusing on the number of functional cells. Instead, other uninvestigated parameters seem to influence the system coin cell more. By further examining the parameter settings that produced the most functional cells (≥75% of 8 cells), guidance for constructing coin cells (type R2032) was suggested, and other potential influencing parameters are discussed for further study.