β - MnO2 as a superior insertion cathode for high-energy aqueous Zn-ion storage applications

Abstract

Rechargeable Zn-ion batteries are attractive energy storage devices owing to their high specific capacity, high cell voltage, eco-friendliness, and low cost. It is being used in various applications ranging from bulk to small flexible and wearable applications. In this work, the sphere-like morphology of β-MnO₂ has been synthesized and used as a cathode in Zn-ion cells. The electrochemical half-cell performance of β-MnO₂ has been analyzed using a lab-scale three-electrode setup using 1 M ZnSO₄ electrolyte. Further, the pouch-type full cell having a 2 × 2 cm² area has been fabricated and tested at different C-rates. Zn-ion pouch cell delivers a high specific capacity of 218.42 mAh g⁻¹ at 64 mA g⁻¹. The cycle stability of the cell has been carried out by continuously running the 250 galvanostatic charge-discharge cycles at 483 mA g⁻¹ current density. The pouch cell showed a specific capacity retention of 81.11 % at the 250th cycle at a coulombic efficiency of 99 %. On the other hand, the effect of MnSO₄ on the ZnSO₄ has been studied using a coin cell (CR-2032) where the cell delivers as high as the specific capacity of 245.8 mAh g⁻¹ at the current density of 64 mA g⁻¹. β-MnO₂ micro sphere-based Zinc ion cells delivered good electrochemical performance in both coin and pouch cell configurations. Therefore, β-MnO₂ will be a potential cathode for aqueous rechargeable Zn-ion storage applications due to their good cycle life, good rate capability, and high specific energy.