Novel insights into aqueous Zn–MnO2 batteries: a simple and robust approach to refute the Zn2+ intercalation mechanism

Abstract

Aqueous Zn–MnO₂ batteries, long favored for their abundant and low-cost materials, eco-friendliness, and high safety, have recently prompted a resurgence in academic interest due to advancements in recharging them with slightly acidic electrolytes. Nevertheless, these batteries face significant obstacles that impede their market penetration, particularly in flexible and wearable electronics and stationary energy storage systems, where their inherent advantages could be highly beneficial. To tackle this, comprehending these batteries' reaction mechanisms is imperative, though insufficient. A widely accepted mechanism for aqueous Zn–MnO₂ batteries involves the intercalation/de-intercalation of Zn²⁺ into/from the cathode structure. This mechanism has significantly influenced academic research focused on optimizing battery performance. However, the validity of this mechanism has been debated, as proponents and opponents have employed similar characterization techniques (XRD, XPS, EQCM, etc.), and reached conflicting conclusions, making consensus difficult. A novel approach is introduced in this study to circumvent this controversy by utilizing an anion exchange membrane to exclude Zn²⁺ from the vicinity of the cathode. The findings reveal that despite preventing Zn²⁺ intercalation, the battery's capacity exhibited minimal differences (less than 10%) compared to the scenario where intercalation is possible.