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Cui et al. Energy Mater 2023;3:300023 https://dx.doi.org/10.20517/energymater.2022.90 Page 3 of 12

of the ZVNW-CC synthesis process was shown in Supplementary Figure 1. The preparation process of
ZVNW was the same as the above-mentioned steps, except that CC was not used.

Sample characterization
For crystallographic analysis, the as-obtained samples were characterized by the powder X-ray diffraction
(XRD, Cu Kα radiation, λ = 1.5418 Å). Surface elemental oxidation states were identified by X-ray
photoelectron spectroscopy (XPS, Thermo Scientific Escalab 250Xi) using Al Kα as the X-ray source. The
spectrometer was calibrated by the C 1s peak with a binding energy of 284.6 eV. The surface structure was
obtained using field-emission scanning electron microscopy (FE-SEM, S-4700 Hitachi). The lattice fringes
were analyzed using field-emission transmission electron microscopy (FE-TEM, Philips Tecnai F20 at
200 kV). The weight changes of the sample were examined by a thermal gravimetric analyzer (Netzsch STA
449E3) at 800 °C with a heating rate of 5 °C min in N .
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2
Electrode preparation and electrochemical performance
A ZVNW-CC electrode disk (diameter: 12 mm) was used directly as a cathode, zinc foil (diameter: 16 mm)
as an anode, and a Whatman CF/F separator was placed between the electrodes. The electrodes were
assembled using a 2016-type coin cell and tested in 3 M Zn(CF SO ) solution. The active material loading
3 2
3
-2
was approximately 3 mg cm . For comparison, a ZVNW cathode was fabricated by casting a slurry mixture
of 70 wt% active material, 20 wt% acetylene black, and 10 wt% polyvinylidene fluoride (PVDF) binder in N-
methylpyrrolidone (NMP) on Ti foil. The mixture was then dried at 60 °C for 12 h under vacuum. Cyclic
voltammetry (CV) was performed over a potential range of 0.2 to 1.6 V (vs. Zn /Zn) at 0.1 mV s .
-1
2+
Galvanostatic charge/discharge (GCD) cycling was conducted at various current rates. CV tests were
performed on a CHI 600E electrochemical station. All the tests were performed at room temperature.
RESULTS AND DISCUSSION
Structural and phase analysis
The as-obtained sample was characterized by XRD. Figure 1 shows that the diffraction peaks at 12.3°, 16.9°,
20.9°, 24.7°, 30.1°, 32.1°, 34.2°, 36.5°, 38.9°, 42.7°, 51.6°, and 62.6°corresponded to (001), (100), (011), (002),
(102), (111), (200), (201), (112), (202), (203), and (204) planes of hexagonal Zn (OH) V O ·2H O (JCPDS
2
2
3
2
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NO. 87-0417), respectively. In addition, the diffraction peak intensity of (001) is much higher than that of
(102), suggesting the [001] direction (c-axis) crystallographic preferred orientations of ZVNW. The inset
image in Figure 1 shows the crystal structure of Zn V O (OH) ·2H O, which consists of a Zn-O layer formed
2
7
3
2
2
by edge-sharing [ZnO ] octahedra and a V-O layer. The Zn-O layers were separated by V-O-V pillars
6
formed by corner-sharing [VO ] tetrahedra along the c-axis. Water molecules were randomly filled in the
4
[19]
large cavities . Supplementary Figure 2 indicates the XRD pattern of ZVNW-CC. The carbon peaks at 26°
were clearly observed because the content of ZVNW was lower than that of CC.
To further characterize the valence state and composition of ZVNW-CC, the XPS techniques were
performed. Figure 2A shows the overall XPS spectrum of ZVNW-CC, illustrating that it is composed of Zn,
V, O, and C elements. Figure 2B shows the high-resolution XPS spectrum of Zn 2p. The peaks centered at
binding energies of 1045.0 and 1021.9 eV were attributed to Zn 2p and Zn 2p , respectively. And their
1/2
3/2
binding energy difference was about 23.1 eV, proving the existence of Zn 2+[13,20] . Figure 2C is a high-
resolution V 2p XPS spectrum of ZVNW-CC. The binding energies of the fitted peaks corresponding to
V 2p and V 2p were 524.7 eV and 517.4 eV, respectively, indicating the existence of V 5+[20] . The XPS
1/2
3/2
spectrum of O 1s was performed in Figure 2D, and the fitted peaks at 530.1, 530.8, and 532.8 eV
corresponded to O , O-H bond, and H O molecule, respectively.
2-
2