Direct Proof of the Reversible Dissolution/Deposition of Mn²⁺/Mn⁴⁺ for Mild-Acid Zn-MnO₂ Batteries with Porous Carbon Interlayers.

ABSTRACT: Mild-acid Zn-MnO₂ batteries have been considered a promising alternative to Li-ion batteries for large scale energy storage systems because of their high safety. There have been remarkable improvements in the electrochemical performance of Zn-MnO₂ batteries, although the reaction mechanism of the MnO₂ cathode is not fully understood and still remains controversial. Herein, the reversible dissolution/deposition (Mn²⁺/Mn⁴⁺) mechanism of the MnO₂ cathode through a 2e^- reaction is directly evidenced using solution-based analyses, including electron spin resonance spectroscopy and the designed electrochemical experiments. Solid MnO₂ (Mn⁴⁺) is reduced into Mn²⁺ (aq) dissolved in the electrolyte during discharge. Mn²⁺ ions are then deposited on the cathode surface in the form of the mixture of the poorly crystalline Zn-containing MnO₂ compounds through two-step reactions during charge. Moreover, the failure mechanism of mild-acid Zn-MnO₂ batteries is elucidated in terms of the loss of electrochemically active Mn²⁺. In this regard, a porous carbon interlayer is introduced to entrap the dissolved Mn²⁺ ions. The carbon interlayer suppresses the loss of Mn²⁺ during cycling, resulting in the excellent electrochemical performance of pouch-type Zn-MnO₂ cells, such as negligible capacity fading over 100 cycles. These findings provide fundamental insights into strategies to improve the electrochemical performance of aqueous Zn-MnO₂ batteries.

SUBMITTER: Moon H 

PROVIDER: S-EPMC7967064 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature