Figure 5. (a) Raman spectra of ν-SO42-band of ZnSO4 of different concentrations. (b) zinc ion
association in MOF channel.
As a proof-of-concept demonstration, the MOF-growing zinc anode was
paired with a MnO2 cathode (Figure S3, supporting
information) to assemble full cells. The
Zn@Zn2(bim)4//MnO2 cell
demonstrated improved rate performance in higher discharge capacities
than the cell with bare Zn anode as the current density increased from
0.1 to 2 A g-1 (Figure 6a). Although the discharge
capacities of cells with Zn and
Zn@Zn2(bim)4 were almost the same at 0.1
A g-1, the gap between the two cells gradually
amplified with an increase in current density. The detailed voltage
profiles at 0.5 and 1 A g-1 are shown in Figure 6b.
Additionally, the
Zn@Zn2(bim)4//MnO2 cell
exhibited a slightly smaller discharge capacity (115.5 mAh
g-1) compared to the bare zinc full cell (139.6 mAh
g-1) but a much more stable cycling performance over
1200 cycles at 1 A g-1, retaining 48% of the capacity
for Zn@Zn2(bim)4//MnO2vs 23% for Zn//MnO2 (Figure 6c). A similar trend
is found at a smaller cathode loading (e.g., 1.2 mg
cm-2) (Figure S4, supporting information).
Furthermore, both cells were disassembled after cycling, and the zinc
deposition morphology was viewed from both the cross-section and top
views. For bare zinc, the zinc deposition was highly porous and stuck to
the glass fiber separator, as shown in Figure 6d and f. In contrast, the
surface of the Zn@Zn2(bim)4 after
cycling was smooth, and the zinc was densely deposited underneath the
MOF layer (Figure 6e and g). Therefore, compared to the bare zinc cell,
the repeated stripping and depositing of zinc with
Zn@Zn2(bim)4 are less likely to pierce
the separator, thereby leading to an increased cycle life in symmetric
cells.