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Page 14 of 31 Miao et al. Energy Mater 2023;3:300014 https://dx.doi.org/10.20517/energymater.2022.89

Briefly, the electrolyte structure on the Zn anode surface has a significant impact on the performance of Zn
anodes. The side reactions on the Zn anode surface, like dendritic formation, corrosion, and H evolution,
2
can be alleviated by modifying the interfacial electrolyte structure. Controlling the Zn nucleation
overpotential, adjusting the Zn surface texture, and introducing “electrostatic shielding” and zincophilic
additives/cosolvents, can all promote the uniform Zn flux and the electric field distribution at the Zn
2+
surface, leading to an even deposition of Zn. By preventing side reactions from directly contacting with
water and Zn metal, the in-situ formed SEI layer at the Zn/electrolyte interface can also help stabilize Zn
anodes.

Analytical methodologies of interfacial structures
A full understanding of the interfacial electrolyte structure, the Zn deposition behavior, and their internal
linkages is essential to guide the rational design of Zn/electrolyte interfaces. In order to qualitatively or
quantitatively assess the effectiveness of interface modification brought on by electrolyte design, various
characterization methods are utilized. These approaches make it possible to observe the surface morphology
evolution of deposited Zn, interfacial compositions and structures, underlying mechanisms, and
electrochemical properties.

Morphology
The electron microscope technology allows for the observation of the surface morphology of Zn anodes
[Figure 6A]. A camera, for example, gives the general profile of Zn plates. By using in-situ optical
microscopy, the processes of Zn deposition and dendrite growth are observed. Optical microscopy with
three-dimensional (3D) imaging can not only view the morphological changes of Zn electrodes in real time
but also quantitatively measure the Zn plating rates at different locations of 3D structures. The morphology
of Zn deposition is effectively examined using scanning electron microscopy (SEM). The SEM images of the
Zn surface can estimate the formation and thickness of an SEI layer. Transmission electron microscopy
(TEM) is another common tool to visualize the Zn deposition morphology at better resolution as well as its
lattice plane spacing. In addition, atomic force microscopy (AFM) has been used to directly monitor the
roughness of Zn surface and the Zn nucleation process.

Structure and composition
As shown in Figure 6B, the composition and structure of Zn/electrolyte interfaces can be characterized by
various spectroscopic techniques. For instance, Raman and FTIR spectroscopy can identify specific
functional groups that are present on Zn surfaces, allowing for inferring interfacial reaction products.
Moreover, the Raman mapping is performed to examine the distribution of these products on the Zn
surface. The apparent components of the SEI layer can be identified using solid-state NMR technology and
X-ray photoelectron spectroscopy (XPS). Especially in the XPS, the internal composition of SEI can be
determined as long as prolonging argon ion (Ar ) sputtering time. The X-ray diffraction (XRD) analysis
+
contributes to understanding the structural modifications and material transformations brought on by the
corrosion response of Zn metal in contact with electrolytes. The suggested corrosion mechanism is
supported by comparing the obtained XRD profile to the powder diffraction files (PDFs) of the Zn
corrosion byproducts (e.g., ZnO, Zn(OH) , and alkaline Zn salt).
2

Theoretical mechanism
The Zn/electrolyte interfacial structure and property can be examined at the atomic level using theoretical
simulations [Figure 6C]. Some physicochemical properties at Zn surfaces can be explored via DFT
2+
calculation. For instance, DFT calculation is performed to simulate the Zn diffusion path at SEI, and the
resulting diffusion energy barrier is used to measure ion conductivity . In addition, the wettability of Zn
[88]
metal in electrolytes can be assessed by DFT calculation. The strong binding energy between the adsorbate