Regulated Zn Plating and Stripping by a Multifunctional Polymer‐Alloy Interphase Layer for Stable Zn Metal Anode

Abstract Metallic zinc electrode with a high theoretical capacity of 820 mAh g−1 is highly considered as a promising candidate for next‐generation rechargeable batteries. However, the unavoidable hydrogen evolution, uncontrolled dendrite growth, and severe passivation reaction badly hinder its practical implementations. Herein, a robust polymer‐alloy artificial protective layer is designed to realize dendrite‐free Zn metal anode by the integration of zincophilic SnSb nanoparticles with Nafion. In comparison to the bare Zn electrode, the Nafion‐SnSb coated Zn (NFSS@Zn) electrode exhibits lower nucleation energy barrier, more uniform electric field distribution and stronger anti‐corrosion capability, thus availably suppressing the Zn dendrite growth and interfacial side reactions. As a consequence, the NFSS@Zn electrode exhibits a long cycle life over 1500 h at 1 mA cm−2 with an ultra‐low voltage hysteresis (25 mV). Meanwhile, when paired with a MnO2 cathode, the as‐prepared full cell also demonstrates stable performance for 1000 cycles at 3 A g−1. This work provides an inspired approach to boost the performance of Zn anodes.

As shown in Figure S1, the SS@Zn electrode is covered with a large amount of SS particles with an average size of approximately 0.14 μm.Moreover, the linear scanning profiles of SS@Zn electrode demonstrates that the thickness of SnSb alloy coatings is estimated to be ~10 μm.Except for the Zn peaks from Zn substrate, the characteristic peaks of metallic SnSb (JCPDS No. 33-0118) can be clearly observed for the SS@Zn electrode (Figure S3), the intensity of which are however very weak due to poor crystallinity.As shown in Figure S4, the XPS survey spectra of NFSS@Zn electrode give direct evidence for the existence of Zn, Sn, Sb, and F elements, in accordance with the above EDS mapping results.As shown in Figure S5, the contact angle of SS@Zn electrode is 60.5°, which is much smaller than that of NF@Zn electrode (130°).This result reveals that the SS protective layer can significantly improve hydrophilicity.
As shown in Figure S6, at a higher current density of 20 mA cm -2 and a cut-off capacity of 30 mA cm -2 (51% DOD), the NFSS@Zn electrode presents stable plating/stripping over 120 h, much better than 28 h for SS@Zn electrode, 22 h for NF@Zn electrode, and 3 h for bare Zn electrode.These tests obviously demonstrate that the NFSS layer can effectively inhibit the dendrite growth and promote stable Zn plating/striping, thereby extending the operational lifetime of the Zn anode.

S9
The surface morphologies of the cycled bare Zn, NF@Zn, SS@Zn, and NFSS@Zn electrodes were investigated by high-resolution cross-sectional SEM.As shown in Figure S9, a large pile of Zn4SO4(OH)6•5H2O mixed with vertical-growing Zn flakes is formed on cycled bare Zn electrode.After NF modification, the growth of Zn dendrites is effectively inhibited.However, there is still the presence of the flake-like Zn4SO4(OH)6•5H2O.When a SS protective layer is introduced, the cycled SS@Zn electrode exhibits relatively uniform Zn deposition, but some granular-like protrusions are visible.In contrast, the cycled NFSS@Zn electrode shows complete protection against the growth of Zn4SO4(OH)6•5H2O and dendritic Zn flakes, suggesting highly efficient suppression of side reactions and dendrite growth.As shown in Figure S11, the NFSS@Zn electrode possesses a lower nucleation overpotential of 33.3 mV compared to bare Zn (138.3 mV), NF@Zn (99.8 mV), and SS@Zn (44.7 mV) electrodes, revealing the controllable and homogeneous Zn nucleation by the NFSS coating layer during Zn plating.electrode that is sandwiched between two stainless steel spacers, and these green, purple, and blue curves are indexed to the SS@Zn, NF@Zn, and NFSS@Zn electrodes, respectively.The resistivity of the protection film was estimated according to the following equation: [S1]  =  *   =  *   *  L is the thickness of the protection film, I is the applied current, R is the resistance, S is the contact area between the stainless steel and the Zn foil (0.5 cm -2 ), and U is the average voltage.
To calculate the activation energies of the transfer and desolvation of Zn 2+ ions in the asobtained samples, EIS measurements were conducted at different temperatures ranging from 20 to 60 ℃.As shown in Figure S14, the Rct values of NFSS@Zn display higher stability compared to those of bare Zn, NF@Zn, and SS@Zn electrodes as temperature increases.This result indicates that the NFSS layer can maintain interface stability and favor rapid charge transfer.Additionally, the observed reduction in activation energy (33.5 kJ mol -1 ) for NFSS@Zn implies that the NFSS protective layer effectively enhances the desolvation of Zn 2+ S15 ions, leading to efficient ion transfer processes and improved kinetics of Zn plating and stripping during cycling.As shown in Figure S15a, CV curves of NFSS@Zn electrode in initial three cycles are well overlapped, indicating the good reversibility of Zn plating/stripping.However, the enclosed areas of CV curves of bare Zn electrode in the second and third cycles are much larger than that of the first cycle (Figure S15b).In contrast, the cycled NFSS@Zn electrode in full cells remain a dense and smooth morphology.
Therefore, the NFSS protective layer holds great promise in suppressing the side reactions and regulating Zn deposition behavior.

Figure S1 .
Figure S1.(a) SEM image of SS@Zn electrode.(b) Size distribution of SS nanoparticles on

Figure S4 .
Figure S4.XPS survey spectra of the bare Zn and NFSS@Zn electrodes.

Figure S5 .
Figure S5.Contact angle measurement of (a) SS@Zn and (b) NF@Zn electrodes with 3 M ) planes of Zn4SO4(OH)6•5H2O (JCPDS No. 39-0688), respectively, are detected in the cycled bare Zn, NF@Zn, and SS@Zn electrodes.In comparison, the diffraction peaks of Zn4SO4(OH)6•5H2O by-product are obviously reduced after the introduction of NFSS layer, again confirming the inhibition of side reactions by NFSS.

Figure S8 .
Figure S8.(a) SEM and (b-d) corresponding EDS maps of the cycled bare Zn electrode.

Figure S10 .
Figure S10.(a) SEM and (b-h) corresponding EDS maps of the NFSS@Zn electrode after 100

Figure S11 .
Figure S11.Galvanostatic voltage profiles of asymmetric cells using the bare Zn, NF@Zn,

Figure S12 .
Figure S12.Measurements of the conductivity of Zn foil protected by the NF, SS, and NFSS

Figure S13 .
Figure S13.Nyquist plots measured at open circuit voltage (OCV) over the frequency range of

Figure S15 .
Figure S15.CV curves of the symmetric (a) NFSS@Zn and (b) bare Zn cells measured at 0.1

Figure S16 .
Figure S16.The charge density difference for Zn 2+ absorbed on (a) bare Zn and (b) NFSS.

Figure S17 .
Figure S17.(a) Binding energy of Zn atom adsorbed on the top site of SnSb.(b) The charge