Toward Practical High‐Areal‐Capacity Aqueous Zinc‐Metal Batteries: Quantifying Hydrogen Evolution and a Solid‐Ion Conductor for Stable Zinc Anodes
Longtao Ma, Qing Li, Yiran Ying, Fei‐Xiang Ma, Shengmei Chen, Yang Yang Li, Haitao Huang, Chunyi Zhi
Abstract
Abstract The hydrogen evolution in Zn metal battery is accurately quantified by in situ battery–gas chromatography–mass analysis. The hydrogen fluxes reach 3.76 mmol h −1 cm −2 in a Zn//Zn symmetric cell in each segment, and 7.70 mmol h −1 cm −2 in a Zn//MnO 2 full cell. Then, a highly electronically insulating (0.11 mS cm −1 ) but highly Zn 2+ ion conductive (80.2 mS cm −1 ) ZnF 2 solid ion conductor with high Zn 2+ transfer number (0.65) is constructed to isolate Zn metal from liquid electrolyte, which not only prohibits over 99.2% parasitic hydrogen evolution but also guides uniform Zn electrodeposition. Precisely quantitated, the Zn@ZnF 2 //Zn@ZnF 2 cell only produces 0.02 mmol h −1 cm −2 of hydrogen (0.53% of the Zn//Zn cell). Encouragingly, a high‐areal‐capacity Zn@ZnF 2 //MnO 2 (≈3.2 mAh cm −2 ) full cell only produces maximum hydrogen flux of 0.06 mmol h −1 cm −2 (0.78% of the Zn//Zn cell) at the fully charging state. Meanwhile, Zn@ZnF 2 //Zn@ZnF 2 symmetric cell exhibits excellent stability under ultrahigh current density and areal capacity (10 mA cm −2 , 10 mAh cm −2 ) over 590 h (285 cycles), which far outperforms all reported Zn metal anodes in aqueous systems. In light of the superior Zn@ZnF 2 anode, the high‐areal‐capacity aqueous Zn@ZnF 2 //MnO 2 batteries (≈3.2 mAh cm −2 ) shows remarkable cycling stability over 1000 cycles with 93.63% capacity retained at ≈100% Coulombic efficiency.