First-principles quantum simulations complemented with kinetic Monte Carlo calculations were performed to gain insight into the oxygen vacancy diffusion mechanism and to explain the effect of dopant composition on ionic conductivity in yttria-stabilized zirconia ͑YSZ͒. Density-functional theory ͑DFT͒ within the local-density approximation with gradient correction was used to calculate a set of energy barriers that oxygen ions encounter during migration in YSZ by a vacancy mechanism. Kinetic Monte Carlo simulations were then performed using Boltzmann probabilities based on the calculated DFT barriers to determine the dopant concentration dependence of the oxygen self-diffusion coefficient in ͑Y 2 O 3 ͒ x ͑ZrO 2 ͒ ͑1−2x͒ with x increasing from 6% to 15%. The results from the simulations suggest that the maximum conductivity occurs at 7-9 mol % Y 2 O 3 at 600-1500 K and that the effective activation energy increases at higher Y doping concentrations in good agreement with previously reported literature data. The increase in the effective activation energy for migration arises from the higher-energy barrier for oxygen vacancy diffusion across an Y-Y common edge relative to diffusion across one with a Zr-Y common edge of two adjacent tetrahedra. The binding energies between oxygen vacancies and dopants were extracted up to the fourth nearest-neighbor interaction. Our results reveal that the binding energy is the strongest when the vacancy is in the second nearest-neighbor position relative to the Y dopant atom. The methodology was also applied to scandium-doped zirconia ͑SDZ͒. Preliminary results from quantum simulations of SDZ suggest that the effective activation energy for vacancy diffusion in SDZ is lower than that of YSZ, in agreement with experimental observations. The agreement with experimental studies on the two systems analyzed in this paper supports the use of this technique as a predictive tool on electrolyte systems not yet characterized experimentally.

Manganese oxide (MnO 2 ) is one of the most promising intercalation cathode materials for zinc ion batteries (ZIBs). Specifically, a layered type delta manganese dioxide (δ-MnO 2 ) allows reversible insertion/extraction of Zn 2+ ions and exhibits high storage capacity of Zn 2+ ions. However, a poor conductivity of δ-MnO 2 , as well as other crystallographic forms, limits its potential applications. This study focuses on δ-MnO 2 with nanoflower structure supported on graphite flake, namely MNG, for use as an intercalation host material of rechargeable aqueous ZIBs. Pristine δ-MnO 2 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-MnO 2 nanoflowers and MNG cathodes were studied in CR2032 coin cells. MNG exhibits a fast insertion/extraction of Zn 2+ 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-MnO 2 cathode at the same specific current density. MNG demonstrated superior electrical conductivity compared to the pristine δ-MnO 2 . The results obtained pave the way for improving the electrical conductivity of MnO 2 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-MnO 2 ) 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-MnO 2 electrode. Overall, the proposed electrolyte shows good promise for Zn/δ-MnO 2 battery system.

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