Stable Zn Metal Anodes with Limited Zn-Doping in MgF2 Interphase for Fast and Uniformly Ionic Flux

Abstract

The practical applications of aqueous Zn metal batteries are currently restricted by the inherent drawbacks of Zn such as the hydrogen evolution reaction, sluggish kinetics, and dendrite formation. To address these problems, herein, a limitedly Zn-doped MgF2 interphase comprising an upper region of pure, porous MgF2 and a lower region of gradient Zn-doped MgF2 is achieved via radio frequency sputtering technique. The porous MgF2 region is a polar insulator whose high corrosion resistance facilitates the de-solvation of the solvated Zn ions and suppression of hydrogen evolution, resulting in Zn metal electrodes with a low interfacial resistance. The Zn-doped MgF2 region facilitates fast transfer kinetics and homogeneous deposition of Zn ions owing to the interfacial polarization between the Zn dopant and MgF2 matrix, and the high concentration of the Zn dopant on the surface of the metal substrate as fine nuclei. Consequently, a symmetric cell incorporating the proposed Zn metal exhibits low overpotentials of ~ 27.2 and ~ 99.7 mV without Zn dendrites over 250 to 8000 cycles at current densities of 1.0 and 10.0 mA cm−2, respectively. The developed Zn/MnO2 full cell exhibits superior capacity retentions of 97.5% and 84.0% with average Coulombic efficiencies of 99.96% after 1000 and 3000 cycles, respectively.

Novel Concept of Separator Design: Efficient Ions Transport Modulator Enabled by Dual‐Interface Engineering Toward Ultra‐Stable Zn Metal Anodes

“…Note that the capacity retention beyond 100% might be attributed to gradual activation of MnO 2 cathode and/or the evolution of storage mechanism. [ 40,47,51 ] Moreover, when the current density increases to 1 A g −1 after activation for 10 cycles, the modified battery can still deliver a specific capacity of 108 mAh g −1 after 1800 cycles, which is twice higher than that of the unmodified one (51.4 mAh g −1 ). To investigate the regulation effectiveness of DIE separator for full batteries, another kind of Zn‐MnO 2 batteries was also assembled, in which the MnO 2 cathode was attached to the BTO enriched side of DIE separator.…”

“…Usually, the sluggish and inhomogeneous ions transport would finally lead to the uneven Zn deposition during the plating process. [51,52] In detail, zinc ions would give priority to deposit at the protuberant site of the substrate to form a large curvature radius of dendrite, thus increasing the local electric field and leading to the uneven electric field distribution especially around the Zn dendrite. [53,54] In addition, the uneven electric field distribution aggravates the inhomogeneity of ion concentration gradient and inducing the rampant 2D diffusion of Zn 2+ on the substrate, then Zn 2+ would migrate to the small protrusions with higher specific surface energy.…”

Robust ZnS interphase for stable Zn metal anode of high-performance aqueous secondary batteries

“…As a result, the Zn@ZnS electrode presents a higher capacity and activity during cycling, which is in accordance with charging-discharging performance. Furthermore, the oxidation peak of Zn@ZnS anode shifts to the lower voltage, and the reduction peak shifts to the higher voltage during the charging/discharging process, suggesting that the ZnS layer facilitates the redox of metallic Zn with a lower polarization [41][42]. Moreover, the R ct for Zn@ZnS is only 201 Ω, whereas the R ct for pure Zn is as high as 288 Ω, showcasing that the Zn@ZnS has slightly faster charge-transfer kinetics S2).…”

Guiding Principles for the Design of Artificial Interface Layer for Zinc Metal Anode

“…The interfacial polarization (Maxwell-Wagner effect) between the Zn-doped MgF 2 region and the MgF 2 layer results in rapid Zn transfer kinetics. [27] The introduction of other appropriate elements doped into the Zn lattice to form an interfacial layer can change the charge distribution on the zinc surface, thereby driving faster Zn 2 + diffusion during cycling. Guo's team skillfully prepared the dense ZnS layer in situ through the vapor-solid reaction.…”

“…diffused Zn into the MgF 2 layer to form a gradient MgF 2 interfacial phase. The interfacial polarization (Maxwell‐Wagner effect) between the Zn‐doped MgF 2 region and the MgF 2 layer results in rapid Zn transfer kinetics [27] …”