42
0.4–1.4 V. In specific, the electrode displays the energy density of 87.3 Wh kg
−1
for
a given power density of 18.9 W kg
−1
at 50 mA g
−1
current density (based on whole
cell). The lowest energy density of 60 Wh kg
−1
is higher than those of commercial
Pb-acid (30 Wh kg
−1
) and Ni–Cd (50 Wh kg
−1
) batteries. Another pyrovanadate,
Zn 3 V 2 O 7 (OH) 2 ·2H 2 O undergoes structural evolution during electrochemical reaction through intercalation/de-intercalation mechanism [65]. The cathode delivers a
long cyclability with reversible capacity of 101 mAh g
−1
after 300 cycles with 68%
retention using 1 M ZnSO 4 electrolyte cycled between 0.2 and1.8 V.
VS 2 is one among the member of transition-metal dichalcogenides (TMDs), with
hexagonal system, which shows similar crystal structure to that of graphite lamellar
with an interlayer spacing of 5.76 Å. The aqueous Zn-VS 2 -nanosheets battery, the
first chalcogenide based first report for ZIB, delivers a reversible capacity of
110.9 mAh g
−1
at 0.5 A g
−1
after 200 cycles with nearly 98% capacity retention in a
1 M ZnSO 4 electrolyte solution [74]. The overall capacity in this study is governed
by the combination of diffusive-controlled reaction and surface controlled capacitive reaction through cyclic voltammetry study by applying different scan rates.
Nearly 62% of the total capacity contribution was confirmed to be from surface
capacitive capacity at 0.2 mV S
−1
scan rate. The NASICON-type phosphate
Na 3 V 2 (PO 4 ) 3 (NVP) is a promising cathode and the Zn//0.5 M Zn(CH 3 COOH) 2 //
Na 3 V 2 (PO 4 ) 3 battery configuration showed a reversible capacity of 97 mAh g
−1
with
74% capacity retention after 100 cycles at 0.5 °C [75]. Before Zn insertion, initially
2 moles of Na were electrochemically de-intercalated from the NVP structure and
reversible Zn-intercalation occurred from the subsequent cycles and the formation
of a new inserted phase, Zn x NaV 2 (PO 4 ) 3 was observed. These interesting studies
clearly open the door towards the development of safe, eco-friendly, and economically viable electrodes for ZIB applications. The number of published reports for
vanadium cathodes based for aqueous ZIBs are quite high, in the last couple of
years, thereby making it tedious to report all these results. Table 2 presents a few of
the selected works with detailed electrochemical properties including rate performance, concentration of the electrolytes, and additives, if any.
Open-Framework Structures
There are some special categories of open-framework structures like Prussian blue
analogues (PBAs) that have garnered significant attention as hosts for multivalent
cations. Zhang et al. reported on an open 3-D framework structure of Zn 3 [Fe(CN) 6 ] 2
(ZnHCF) that was cycled between 0.8 and 2 V and this cathode exhibited good
stability with a capacity retention of 76% after 100 cycles when being fully charged/
discharged in 2 h (1C, where 1C = 60 mA g
−1
) and 81% capacity retention after
100 cycles at a high current drain of 24 min (5C) for a full charge/discharge [92].
The average operation voltage of 1.7 V of this cell, recorded the second highest for
ZIBs through Zn-ions intercalation/de-intercalation mechanism. The same group
reported again on the same material of ZnHCF, prepared under different conditions,
exhibiting a high energy density of 104 Wh kg
−1
, providing an operating voltage of
J. Kim et al.
0.4–1.4 V. In specific, the electrode displays the energy density of 87.3 Wh kg
−1
for
a given power density of 18.9 W kg
−1
at 50 mA g
−1
current density (based on whole
cell). The lowest energy density of 60 Wh kg
−1
is higher than those of commercial
Pb-acid (30 Wh kg
−1
) and Ni–Cd (50 Wh kg
−1
) batteries. Another pyrovanadate,
Zn 3 V 2 O 7 (OH) 2 ·2H 2 O undergoes structural evolution during electrochemical reaction through intercalation/de-intercalation mechanism [65]. The cathode delivers a
long cyclability with reversible capacity of 101 mAh g
−1
after 300 cycles with 68%
retention using 1 M ZnSO 4 electrolyte cycled between 0.2 and1.8 V.
VS 2 is one among the member of transition-metal dichalcogenides (TMDs), with
hexagonal system, which shows similar crystal structure to that of graphite lamellar
with an interlayer spacing of 5.76 Å. The aqueous Zn-VS 2 -nanosheets battery, the
first chalcogenide based first report for ZIB, delivers a reversible capacity of
110.9 mAh g
−1
at 0.5 A g
−1
after 200 cycles with nearly 98% capacity retention in a
1 M ZnSO 4 electrolyte solution [74]. The overall capacity in this study is governed
by the combination of diffusive-controlled reaction and surface controlled capacitive reaction through cyclic voltammetry study by applying different scan rates.
Nearly 62% of the total capacity contribution was confirmed to be from surface
capacitive capacity at 0.2 mV S
−1
scan rate. The NASICON-type phosphate
Na 3 V 2 (PO 4 ) 3 (NVP) is a promising cathode and the Zn//0.5 M Zn(CH 3 COOH) 2 //
Na 3 V 2 (PO 4 ) 3 battery configuration showed a reversible capacity of 97 mAh g
−1
with
74% capacity retention after 100 cycles at 0.5 °C [75]. Before Zn insertion, initially
2 moles of Na were electrochemically de-intercalated from the NVP structure and
reversible Zn-intercalation occurred from the subsequent cycles and the formation
of a new inserted phase, Zn x NaV 2 (PO 4 ) 3 was observed. These interesting studies
clearly open the door towards the development of safe, eco-friendly, and economically viable electrodes for ZIB applications. The number of published reports for
vanadium cathodes based for aqueous ZIBs are quite high, in the last couple of
years, thereby making it tedious to report all these results. Table 2 presents a few of
the selected works with detailed electrochemical properties including rate performance, concentration of the electrolytes, and additives, if any.
Open-Framework Structures
There are some special categories of open-framework structures like Prussian blue
analogues (PBAs) that have garnered significant attention as hosts for multivalent
cations. Zhang et al. reported on an open 3-D framework structure of Zn 3 [Fe(CN) 6 ] 2
(ZnHCF) that was cycled between 0.8 and 2 V and this cathode exhibited good
stability with a capacity retention of 76% after 100 cycles when being fully charged/
discharged in 2 h (1C, where 1C = 60 mA g
−1
) and 81% capacity retention after
100 cycles at a high current drain of 24 min (5C) for a full charge/discharge [92].
The average operation voltage of 1.7 V of this cell, recorded the second highest for
ZIBs through Zn-ions intercalation/de-intercalation mechanism. The same group
reported again on the same material of ZnHCF, prepared under different conditions,
exhibiting a high energy density of 104 Wh kg
−1
, providing an operating voltage of
J. Kim et al.