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Page 12 of 31 Miao et al. Energy Mater 2023;3:300014 https://dx.doi.org/10.20517/energymater.2022.89

increase the Zn nucleation overpotential and promote the uniform deposition of Zn. However, the rules are
unfit for inorganic additives. Because compared with the baseline electrolyte, the Zn nucleation
overpotential is smaller in the electrolyte that contains inorganic additives [72-75] and the reasons are still
unclear.

Adjustion of surface texture
The surface morphology of Zn anodes has been reported to be related to the Zn surface texture [76,77] . The
texture reflects the desired orientation of the Zn anode, which controls the corrosion resistance of the Zn
[78]
electrode and the direction of Zn dendrite growth . The growth of Zn dendrite is favorable when the angle
between the Zn anode surface and the growth direction of Zn crystal is large . The crystalline orientation
[79]
affects the crystal growth direction, which in turn influences the surface morphology and dendrite growth
direction . Figure 5C (left) depicts the Zn growth direction in different crystalline orientations. When the
[77]
Zn orientation index is (100) or (110), the angle between the Zn growth direction and the substrate is
70-90°. Such crystal growth directions are in favor of Zn dendritic growth; While the Zn orientation index is
(101), (102), (112), or (114), the angle between the crystal growth direction and the substrate exhibits 30-70°,
which shows the intermediate state; The angle between the crystal growth direction and the substrate is
0-30° as the Zn orientation index is the (002), (103), or (105), which generally exhibits no dendrite growth.
Both the crystalline structure of the substrate and the surface energy of the crystal plane have a significant
impact on the surface texture. In the former case, the epitaxial growth process plays a major part in
influencing the substrate crystal orientation, which allows the freshly nucleated metals to align with the
[80]
substrate and grow epitaxially parallel to the substrate to reduce the surface energy . For the latter, the
surface energy, which is influenced by the coordination environment and the adsorption layer on the
[64]
surface, limits the thermodynamically favored exposed crystal plane . The introduction of additives/
cosolvents can alter the coordination environment of Zn surfaces, and therefore brings about a change in
-
the surface texture of Zn anodes [right of Figure 5C]. For instance, Yuan et al. proposed that OTf in the
electrolyte induces Zn to deposit along the Zn (002) facet, where the strong coordination ability of Zn
2+
2+
and OTf plays a crucial part .
-
[81]
Restriction of Zn deposition site
2+
During the Zn nucleation stage, in order to reduce the nuclear energy barrier, Zn diffusing along the Zn
2+
anode surface will aggregate together to form Zn nuclei. In the stage of crystal growth, due to the high
electric field density on these nuclei sites, the later Zn is attracted to these nuclei, which leads to the Zn
2+
uneven deposition and dendrite formation . Regulating Zn migration and uniformizing the Zn surface
[82]
2+
electric field prevent the uneven Zn deposition, which can be achieved by adsorbing additives/cosolvents on
[83]
the Zn electrode surface [83-87] . For example, some polymers such as polyacrylamide (PAM) and
polyethylene oxide (PEO) are able to adsorb on the Zn surface. The polar functional groups of these
[84]
polymers have strong attractions to Zn and show zincophilicity, which leads to the homogeneous
2+
dispersion of Zn on the surface and achieves the uniform Zn deposition [left of Figure 5D]. In addition to
2+
zincophilicity, the uneven Zn deposition can be suppressed through the electrostatic shielding mechanism.
The cations (e.g., Na and tetrabutylammonium ions (TBA ) ) which have a lower redox potential than
+ [86]
+[85]
Zn and highly polar organic molecules (e.g., diethyl ether (Et O) ) can act as “electrostatic shielding” to
2+
[87]
2
protect Zn anodes from the growth of dendrites. These materials adhere to the initial Zn nuclei and provide
a positive electrostatic shield around it. As two like electric charges repel each other, the later Zn will be
2+
deposited elsewhere, thereby preventing the Zn growth on the initial tip and inhibiting Zn dendrite
formation [right of Figure 5D].