Bottom-preferred stripping mechanism towards quantified inactive metallic Zn0-dominant zinc loss in rechargeable zinc metal battery

Electrically isolated metallic Zn (Zn0) and electrochemically side reaction (ECSR), causes irreversible anode capacity loss and limited cycle life in zinc metal battery. However, the quantitative distinguishment between inactive metallic Zn0 and ECSR, their formation mechanism and correlation with anode cycling reversibility have never been disclosed, limiting further anode modification design. Here, we develop an acid-assisted continuous titration-collection-gas chromatography technique (AAC-TCGC) that accurately quantify the amount of inactive Zn0 and ECSR in anode, and discover that inactive Zn0 accounts for the majority of Zn loss, rather than the commonly-assumed electrochemically side reaction-derived ECSR-dominant Zn anode capacity loss. Detailed component of SEI (Solid Electrolyte Interface Layer) compound is also characterized, illustrating a solvent-derived zinc oxide/hydroxide-dominant SEI that facilitates vertical/inclined thin-plate Zn deposition, but salt-derived ZnF2-dominant SEI that favors horizontal platelet-shaped Zn(002) deposition. Simulation results reveal a new electric resistance-derived, bottom-preferred Zn stripping mechanism that leads to abundant inactive Zn0 formation in vertical thin-plate Zn deposition structure, but few inactive Zn0 in dumpy platelet-shaped Zn structure. Our study provides new theories and strategies on the distinguishment, formation mechanism and structure-performance relationship of inactive Zn, important for building more efficient Zn metal battery.