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Nano-Micro Lett. (2022) 14:82 obtained lattice parameters were used to construct the solid- state electrolyte structures. All first-principles calculations are performed with the projector augmented wave (PAW) potential [45, 46] and the Vienna Ab initio Simulation Pack- age (VASP) [47]. The structures screened by Supercell Pro- gram were subjected to structural relaxation using VASP software to take the lowest energy structures. Structural relaxation was achieved with a total energy of 10–5 eV and a force of 0.01 eV Å−1 as convergence criteria. The truncation energy is uniformly set to 520 eV during the calculation. 3 Results and Discussion 3.1 Characterization of the Zeolite‐Based Protecting Layers Before coating, the pristine zeolite powder underwent a Zn2+-exchange treatment in 1 M ZnSO4 for 6 h, in order to provide immediate Zn2+ supply for smooth Zn stripping/plat- ing (Fig. S1a-b) [35, 48]. Afterward, the zeolite-based pro- tecting layers were deposited on Zn foils via a simple knife coating method, with a blend slurry of the Zn2+-exchanged zeolite and PVDF binder (weight ratio: 8:2) in NMP solvent. As revealed by SEM observation, the layers are very dense in the vertical direction, without any detectable penetrating holes/cracks (Fig. 1a and S4a-b), even exhibiting a rough top surface (Fig. S4c-d). The large surface roughness [49, 50] and the hydrophobic nature of the PVDF binder [51] endow the zeolite-Zn a much larger contact angle (CA) than the bare Zn foil (113° vs. 76°, Fig. 1b), very favorable to isolate the underneath Zn foil from the corrosive aqueous electrolyte. As a result, the corrosion potential of the Zn foils shifts from − 17 to − 15 mV after zeolite-layer coating, along with a lower corrosion current (from 62 to 49.7 μA, Fig. 1c), indicating a suppressed corrosion rate on the Zeolite-Zn foils [13, 52]. To further confirm the anticorrosive ability of the protect- ing layer, a static self-corrosion experiment was performed by soaking a bare- and Zeolite-Zn foil in 1 M ZnSO4 elec- trolytes for 15 days. Postmortem XRD, Raman and SEM analyses (Figs. 1d–e and S5a-c) clearly show the formation of Zn4(OH)6SO4·5H2O and even ZnO on the surface of the soaked bare-Zn [15, 16, 23]. On the other hand, the gen- eration of corrosion products and the surficial morphology evolution of the underneath Zn are remarkably suppressed Page 5 of 13 82 by the zeolite-based protecting layer (Fig. S5d-f), suggest- ing a slow corrosion rate. Probably, the anticorrosive abil- ity of the layer stems from not only the physical isolation of electrolyte from Zn anodes, but also the desolvation of hydrate Zn2+ by the zeolite cavities. As revealed by first principles calculation (Fig. S6), the lowest migration barri- ers of bare and hydrate Zn2+ in the FAU-/ETR-type zeolites are determined to be 0.0086/0.3821 and 0.5002/1.4648 eV, respectively, indicating the much higher migration difficulty of hydrate Zn2+ than its bare counterparts. Therefore, the pores of FAU and ETR zeolite are helpful to remove the solvation sheath of hydrate Zn2+, due to the very different migration barriers between the bare and hydrate Zn2+. Based on theoretical calculation, we also investigate the transport behaviors of I3− ions within the zeolite lattice. The migration barriers of I3− are 0.59/1.60 eV in FAU-/ETR- type zeolite, respectively (Fig. S7), much higher than those of the bare and hydrate Zn2+. The even harder migration of I3− indicates that the zeolite layer can not only protect Zn from water-induced corrosion, but also suppress the quick self-discharge caused by I3− shuttling. The quite different migration barriers in different zeolites further highlight the significant influence of zeolites’ structure on cation sieving and Zn2+ desolvation. This topic is worthy for additional in-depth study. − To experimentally examine the I3 -blocking ability of the zeolite-based coating, we specifically designed a spectro- photometry test by making good use of the characteristic optical absorption (centered at 288 and 354 nm) and intense brown color of this anion [25]. Firstly, I3−-pregnant ZnSO4 electrolyte (with 0.5 mM KI + 0.5 mM I2) was employed to simulate the electrolyte in real Zn||I2 batteries [23]. Then, identically-sized Zeolite-Zn and bare-Zn foils were sepa- rately immersed into the I3−-pregnant solution. After 36 h, the brown color of the bare-Zn soaking solution, along with the absorption bands of I3−, had thoroughly faded, suggesting the completely reduction of I3− by metallic Zn (Fig. 1f). In contrast, considerable amount of I3− survived in the Zeolite-Zn soaking solution, as revealed by the brown color and the relatively strong residual absorption bands of I3− (Fig. 1g), indicating the remarkable I3−-blocking ability of the zeolite protecting layer. Moreover, the I3−-blocking ability of the zeolite layer can also be confirmed by another visually-monitored shuttling experiment, as shown in Fig. 1h [53]. In the H-shape quartz container, the left and right chambers are filled with brown I3− (0.1 M KI and 0.1 M I2) 13PDF Image | Boosting Zn Battery by Coating a Zeolite‐Based Cation‐Exchange
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