Quantifying the apparent electron transfer number of electrolyte decomposition reactions in anode-free batteries

Solid electrolyte interphase (SEI) is pivotal in dictating the stability of anodes in non-aqueous batteries. However, electrolyte decomposition mechanism as an indispensable piece of the puzzle to construct a stable SEI is with few quantitative understandings. Herein, as a quantitative descriptor, the apparent electron transfer number (ETN) is acquired by a facile yet precise methodology in working lithium metal batteries with lithium bis(fluorosulfonyl)imide (LiFSI)-dimethyl carbonate (DMC)-based localized high-concentration electrolyte. Through accurate measurements of the electrolyte evolution and concurrently accumulated inactive Li by electrolyte quantitative nuclear magnetic resonance (ely-qNMR) and titration-qNMR, respectively, the decomposition rates of different electrolyte components and ETNs that define the fate of electrolyte can all be acquired in a “one-stop” fashion. The recognition of ETNs (1.0 for DMC and 5.1 for LiFSI) provides pioneering insights into the electrolyte decomposition mechanism and affords new visions for electrolyte design to promote the continuous rise of non-aqueous rechargeable batteries.