Solvation Structure Design for Aqueous Zn Metal Batteries

A brightener-inspired polymer interphase enables highly reversible aqueous Zn anodes via suppressing side-reactions and manipulating the nucleation process. Aqueous Zn anodes have been revisited for their intrinsic safety, low cost, and high volumetric capacity; however, deep-seated issues of dendrite growth and intricate side-reactions hindered their rejuvenation. Herein, a “brightener-inspired” polyamide coating layer which elevates the nucleation barrier and restricts Zn 2+ 2D diffusion is constructed to effectively regulate the aqueous Zn deposition behavior. Importantly, serving as a buffer layer that isolates active Zn from bulk electrolytes, this interphase also suppresses free water/O 2 -induced corrosion and passivation. With this synergy effect, the polymer-modified Zn anode produces reversible, dendrite-free plating/stripping with a 60-fold enhancement in running lifetime (over 8000 hours) compared to the bare Zn, and even at an ultrahigh areal capacity of 10 mA h cm −2 (10 mA cm −2 for 1 h, 85% depth of discharge). This efficient rechargeability for Zn anodes enables a substantially stable full-cell paired with a MnO 2 cathode. The strategy presented here is straightforward and scalable, representing a stark, but promising approach to solve the anode issues in advanced Zn batteries.

Rechargeable aqueous Zn/MnO2 battery chemistry in a neutral or mildly acidic electrolyte has attracted extensive attention recently because all the components (anode, cathode, and electrolyte) in a Zn/MnO2 battery are safe, abundant, and sustainable. However, the reaction mechanism of the MnO2 cathode remains a topic of discussion. Herein, we design a highly reversible aqueous Zn/MnO2 battery where the binder-free MnO2 cathode was fabricated by in situ electrodeposition of MnO2 on carbon fiber paper in mild acidic ZnSO4+MnSO4 electrolyte. Electrochemical and structural analysis identify that the MnO2 cathode experience a consequent H+ and Zn2+ insertion/extraction process with high reversibility and cycling stability. To our best knowledge, it is the first report on rechargeable aqueous batteries with a consequent ion-insertion reaction mechanism.