Obscure Variables in Battery Research: Impacts of Spacer Thickness and Slurry Formulation Protocols

Abstract

While much battery research focuses on new materials and full-cell designs, early-stage battery evaluation still relies on small, lab-scale coin cells, where often-overlooked factors can significantly affect test results. This work investigates two critical yet underexamined aspects of electrode performance: cell pressure and slurry formulation. First, the impact of spacer thickness, and thus internal cell pressure, on the electrochemical performance of sodium-ion coin cells is examined using hard carbon anodes. Findings show that insufficient compression leads to unstable contact, reduced capacity, and greater variability, while greater compression promotes higher capacity and greater cycle stability. Theories explaining these findings are discussed. Second, the optimization process of aqueous slurry mixing for hard carbon electrodes is presented. The sources of particle agglomeration and slurry inconsistency are found, ultimately developing a reliable protocol that improves coating uniformity and slurry stability.