Apples to apples: shift from mass ratio to additive molecules per electrode area to optimize Li-ion batteries

Abstract

Electrolyte additives in liquid electrolyte batteries can trigger the formation of a protective solid electrolyte interphase (SEI) at the electrodes e.g. to suppress side reactions at the electrodes. Studies of varying amounts of additives have been done over the last few years, providing a comprehensive understanding of the impact of the electrolyte formulation on the lifetime of the cells. However, these studies mostly focused on the variation of the mass fraction of additive in the electrolyte while disregarding the ratio (r_add) of the additive's amount of substance (n_add) to the electrode area (A_electrode). Herein we utilize our accurate automatic battery assembly system (AUTOBASS) to vary electrode area and amount of substance of the additive. Our data provides evidence that reporting the mass ratios of electrolyte components is insufficient and the amount of substance of additive relative to the electrodes' area should be reported. Herein, the two most utilized additives, namely fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were studied. Each additive was varied from 0.1 wt-%–3.0 wt-% for VC, and 5 wt-%–15 wt-% for FEC for two electrode loadings of 1 mA h cm⁻² and 3 mA h cm⁻². To help the community to find better descriptors, such as the proposed r_add, we publish the dataset alongside this manuscript. The active electrode placement correction reduces the failure rate of our automatically assembled cells to 3%.