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Cui et al. Energy Mater 2023;3:300023 https://dx.doi.org/10.20517/energymater.2022.90 Page 5 of 12

increasing the contact area between ZVNW and CC, which enhanced the structural stability of the ZVNW-
2+
CC electrode. And 1D nanostructure can shorten the diffusion pathway of Zn during the charging and
discharging process, promoting the electrochemical performance of the ZVNW-CC electrode. SEM images
in Figure 2F and G show a higher-resolution view of the sample. ZVNW, ranging in size from 20-200 nm,
was stacked and interlaced grown on CC, forming a multi-void network structure.

The microstructure of ZVNW, peeled from CC through prolonged sonication, was further characterized by
TEM. Figure 3A shows a TEM image of a single ZVO nanowire. The surface of the ZVNW was rough,
which increased the contact area between the electrode and electrolyte. Figure 3B is its HRTEM image. The
inter-planar distances of 2.01 and 2.31 Å were attributed to (210) and (112) planes of ZVO, respectively.
Figure 3C shows the fast Fourier transform electron diffraction (FFT-ED) pattern of the HRTEM image,
which suggests the single-crystal feature. Figure 3D shows the EDS analysis of a single ZVO nanowire. It
was further confirmed that the ZVNW were composed of Zn, V, and O elements, which were uniformly
distributed in the ZVNW.

Electrochemical performances
The electrochemical properties of ZVNW and ZVNW-CC electrodes were evaluated by CV and GCD.
Figure 4A shows the CV curves of these two electrodes at 0.1 mV s . The surrounding CV curve area of the
-1
ZVNW-CC electrode was much larger than that of the ZVNW electrode, indicating that the ZVNW-CC
electrode exhibited higher specific capacity. Figure 4B presents the first three cycles of the CV plot for the
-1
2+
ZVNW-CC electrode at a scan rate of 0.1 mV s in the voltage range of 0.2-1.6 V (vs. Zn/Zn ). Three pairs
of redox peaks were observed at 0.56/0.76, 0.85/1.07, and 1.35/1.46 V, which were attributed to the three-
[21]
2+
step reaction of Zn insertion and extraction into the ZVO lattice structure . Among the reduction
reactions at 0.56, 0.85, and 1.35 V showed that the vanadium element in ZVNW-CC was gradually reduced
from +5 valence to +α (α < 5), and the oxidation reactions at 0.76, 1.07, and 1.46 V corresponded to the
gradual oxidation of V to V . The cyclic scanning process of the first three loops almost overlapped,
α+
5+
indicating that the storage process of Zn was highly reversible. GCD tests were conducted between 0.2 and
2+
2+
1.6 V (vs. Zn/Zn ). Figure 4C and D indicates the GCD profiles of ZVNW-CC and ZVNW electrodes for
the first five and 50th cycles at 50 mA g . In the discharge curve, there were two distinctive potential
-1
plateaus within the range of 0.69-1.00 and 0.45-0.69 V, which corresponded to the two main oxidation peaks
of CV. Similarly, another two potential plateaus in the charge curve within 0.88-1.15 and 0.6-0.88 V
corresponded to the reduction peaks. The related charge-discharge curve of ZVNW-CC electrodes at
-1
50 mA g exhibited a smaller overpotential (∆V(Q/2)) than that of the ZVNW electrode (0.26 vs. 0.34 V,
Figure 4C and D). In sharp contrast, the specific capacity of the ZVNW-CC electrode was larger than that of
the ZVNW electrode, benefitting from the synergistic effects of morphology regulation and a self-
supporting electrode.

The rate performances are presented in Figure 5A, where the current density increases from 50 to
1,000 mA g and then returns to 50 mA g . The ZVNW-CC cathode displayed specific capacities of 361.8,
-1
-1
328.2, 292.8, 251.1, and 207.6 mAh g at 50, 100, 200, 500, and 800 mA g , respectively. Even at
-1
-1
1,000 mA g , the ZVNW-CC cathode can still deliver a reversible capacity of 145.9 mAh g . And returning
-1
-1
-1
-1
to 50 mA g , the specific capacity of 346.9 mAh g and the capacity recovery of 95.8% can still be obtained.
However, the capacities of the ZVNW electrode were evidently lower than those of ZVNW-CC at every
corresponding current density. This indicated that the structural stability and electrochemical reversibility
of the ZVNW-CC cathode were much superior to those of the ZVNW electrode. In order to assess the
commercial potential of the ZVNW-CC electrode, long-cycle performance testing was necessary. The
cycling performances of the ZVNW and ZVNW-CC electrodes were examined at current densities of 200,
500, and 1,000 mA g , respectively, and were shown in Figure 5B-D. The discharge capacity of the ZVNW-
-1