Manganese oxide (MnO₂) is one of the most promising intercalation cathode materials for zinc ion batteries (ZIBs). Specifically, a layered type delta manganese dioxide (δ-MnO₂) allows reversible insertion/extraction of Zn²⁺ ions and exhibits high storage capacity of Zn²⁺ ions. However, a poor conductivity of δ-MnO₂, as well as other crystallographic forms, limits its potential applications. This study focuses on δ-MnO₂ with nanoflower structure supported on graphite flake, namely MNG, for use as an intercalation host material of rechargeable aqueous ZIBs. Pristine δ-MnO₂ nanoflowers and MNG were synthesized and examined using X-ray diffraction, electron spectroscopy, and electrochemical techniques. Also, performances of the batteries with the pristine δ-MnO₂ nanoflowers and MNG cathodes were studied in CR2032 coin cells. MNG exhibits a fast insertion/extraction of Zn²⁺ ions with diffusion scheme and pseudocapacitive behavior. The battery using MNG cathode exhibited a high initial discharge capacity of 235 mAh/g at 200 mA/g specific current density compared to 130 mAh/g which is displayed by the pristine δ-MnO₂ cathode at the same specific current density. MNG demonstrated superior electrical conductivity compared to the pristine δ-MnO₂. The results obtained pave the way for improving the electrical conductivity of MnO₂ by using graphite flake support. The graphite flake support significantly improved performances of ZIBs and made them attractive for use in a wide variety of energy applications.

Recently, because of their cost effectiveness, high safety and environmental friendliness, zinc-ion batteries (ZIBs) are receiving enormous attention. Until now, aqueous-based ZIBs have been the focus of attention. However, the issues regarding hydrogen evolution, and zinc electrode passivation as well as dendrite formation limit their practical application. In this work, a biocompatible, stable and low-cost choline chloride/ urea (ChCl/urea) deep eutectic solvent is reported as an alternative electrolyte for rechargeable ZIBs based on delta-type manganese oxide (δ-MnO₂) intercalation electrode. The behavior of the zinc electrode on stripping and deposition in ChCl/urea electrolyte was examined. Besides, the charge storage and charge-transfer characteristics of the battery was studied. The results showed that there was no sign of dendrite formation on the zinc electrode during long-term cycling. Consequently, the fabricated battery exhibited good electrochemical performance with the maximum specific capacity of 170 mAh/g and good cyclability. In addition, the system showed reversible plating/stripping of zinc (Zn) without dendrite formation and no passivation layer on the zinc electrode. Hence, the results confirmed the reversible intercalation of Zn from the deep eutectic solvent ChCl/urea into the δ-MnO₂ electrode. Overall, the proposed electrolyte shows good promise for Zn/δ-MnO₂ battery system.

The present work describes the effects of dimethyl sulfoxide (DMSO) in KOH aqueous electrolyte on the performance of a zinc-air flow battery. Aqueous electrolytes containing 7 M KOH and (0 to 20)% v/v DMSO were studied revealing a critical role of DMSO on the dissolution and deposition of zinc. The anodic zinc dissolution process was studied via cyclic voltammetry, Tafel polarization and electrochemical impedance spectroscopy (EIS). The presence of DMSO showed improved zinc dissolution performance with the highest peak of zinc dissolution being the electrolyte containing 5% v/v DMSO. Tafel analysis demonstrated a significant decrease in polarization resistance and an increase in corrosion rate due to the introduction of DMSO to the electrolyte. This suggests that DMSO has the ability to suspend zinc oxide in the electrolyte, thus preventing passivation of the zinc surface. EIS results revealed that by adding DMSO to the electrolyte, charge transfer resistance increased. This is attributed to the formation of passive layers having arisen from DMSO adsorption, the formation of zincate ions in the vicinity of the zinc surface, and the deposition of discharged products. A difference in Nyquist plots was observed for 20% v/v DMSO/KOH and 0% v/v DMSO/KOH electrolytes implying non-Debye relaxation behavior taking place due to the surface effects. The electrolytes were implemented in a zinc-air flow battery. Maximum power densities of 130 mW/cm² (5% v/v DMSO) and 125 mW/cm² (20% v/v DMSO) were obtained and were observed to be about 43% and 28% higher than that of the DMSO-free electrolyte. Results indicated that when 20% v/v DMSO was added to KOH solution, there was 67% zinc utilization efficiency (550 mAh/g) which provided 20% improvement in discharge capacity. Further, the battery with 20% v/v DMSO demonstrated excellent cyclability. Overall, DMSO shows great promise for enhancement of zinc dissolution/deposition in zinc-air batteries.

Zinc-air batteries are a promising technology for large-scale electricity storage. However, their practical deployment has been hindered by some issues related to corrosion and passivation of the zinc anode in an alkaline electrolyte. In this work, anionic surfactant sodium dodecyl sulfate (SDS) and nonionic surfactant Pluronic F-127 (P127) are examined their applicability to enhance the battery performances. Pristine zinc granules in 7 M KOH, pristine zinc granules in 0–8 mM SDS/7 M KOH, pristine zinc granules in 0–1000 ppm P127/7 M KOH, and SDS coated zinc granules in 7 M KOH were examined. Cyclic voltammograms, potentiodynamic polarization, and electrochemical impedance spectroscopy confirmed that using 0.2 mM SDS or 100 ppm P127 effectively suppressed the anode corrosion and passivation. Nevertheless, direct coating SDS on the zinc anode showed adverse effects because the thick layer of SDS coating acted as a passivating film and blocked the removal of the anode oxidation product from the zinc surface. Furthermore, the performances of the zinc-air flow batteries were studied. Galvanostatic discharge results indicated that the improvement of discharge capacity and energy density could be sought by the introduction of the surfactants to the KOH electrolyte. The enhancement of specific discharge capacity for 30% and 24% was observed in the electrolyte containing 100 ppm P127 and 0.2 mM SDS, respectively.