45
strongly on the current rate; at 10 C the phenomenon is weakly observed only after
800 cycles, while at 1C the transition is already completed after 250 cycles. Thus,
understanding the aging mechanism will be helpful to achieve electrode stability
under long- term cycle lifespan.
3.2 Anodes
Zn metal is the major anode component used for ZIBs, while other materials like
Mo 6 S 8 and Mo 2.5 + y VO 9 + z were tested as anodes for ZIBs. Chae et al. first demonstrated Zn-ion intercalation into Chevrel phase Mo 6 S 8 using a 0.1 M ZnSO 4 electrolyte in a three-electrode beaker-type cell set-up (Fig. 4a) [97]. During the discharge
process, Zn-intercalation into Mo 6 S 8 occurred via single-phase and two-phase reactions in the composition range of Mo 6 S 8 to Zn 0.24 Mo 6 S 8 and Zn 0.24 Mo 6 S 8 to
Zn 2.2 Mo 6 S 8, respectively (Figs. 4b and c). Within a potential domain of 0.2–1 V, the
electrode delivered an initial discharge capacity of 134 mAh g
−1
at 0.05C and
retained almost 62% of the initial capacity upon returning from cycling at four progressive current densities from 0.05–1 C, the current rate maintained at each rate for
four cycles. Cheng et al. studied Mo 6 S 8 electrode in both aqueous (1 M ZnSO 4 ) and
non-aqueous (1 M Zn(ClO 4 ) 2 in acetonitrile) electrolytes. The electrodes exhibited
good cyclability in aqueous and non-aqueous electrolyte mediums, respectively, as
average stable capacities of ~60 and ~ 65 mAh g
−1
was maintained for 150 discharge/charge cycles at 180 mA g
−1
[98].
Zn x Mo 2.5 + y VO 9 + z with an open tunnel structure demonstrated good rate capability and cyclability in both aqueous (0.5 M Zn(CH 3 COO) 2 electrolyte) and nonaqueous (0.2 M Zn(CF 3 SO 3 ) 2 in 1:4 PC/dimethylsulfoxide (DMSO) solution)
electrolytes [99]. The anode exhibited capacities of 180 and 135 mAh g
−1
in aqueous and non-aqueous electrolytes, respectively, at 20 mA g
−1
. During Zn-ion
intercalation/de-intercalation, the anode was able to retain the parent structure under
electrochemical cycling.
Fig. 4 (a) Illustration of ZnMo 6 S 8 structure. (b) CV curves of the Mo 6 S 8 electrode at 0.05 mV s
−1
.
(c) Initial discharge and charge curves of the Zn-Mo 6 S 8 cell at 0.05 °C (6.4 mA g
−1 ) in the voltage
range of 0.25–1.0 V vs. Zn/Zn
2+
. (reprinted with permission from ref. [97])
Recent Developments of Zinc-Ion Batteries
strongly on the current rate; at 10 C the phenomenon is weakly observed only after
800 cycles, while at 1C the transition is already completed after 250 cycles. Thus,
understanding the aging mechanism will be helpful to achieve electrode stability
under long- term cycle lifespan.
3.2 Anodes
Zn metal is the major anode component used for ZIBs, while other materials like
Mo 6 S 8 and Mo 2.5 + y VO 9 + z were tested as anodes for ZIBs. Chae et al. first demonstrated Zn-ion intercalation into Chevrel phase Mo 6 S 8 using a 0.1 M ZnSO 4 electrolyte in a three-electrode beaker-type cell set-up (Fig. 4a) [97]. During the discharge
process, Zn-intercalation into Mo 6 S 8 occurred via single-phase and two-phase reactions in the composition range of Mo 6 S 8 to Zn 0.24 Mo 6 S 8 and Zn 0.24 Mo 6 S 8 to
Zn 2.2 Mo 6 S 8, respectively (Figs. 4b and c). Within a potential domain of 0.2–1 V, the
electrode delivered an initial discharge capacity of 134 mAh g
−1
at 0.05C and
retained almost 62% of the initial capacity upon returning from cycling at four progressive current densities from 0.05–1 C, the current rate maintained at each rate for
four cycles. Cheng et al. studied Mo 6 S 8 electrode in both aqueous (1 M ZnSO 4 ) and
non-aqueous (1 M Zn(ClO 4 ) 2 in acetonitrile) electrolytes. The electrodes exhibited
good cyclability in aqueous and non-aqueous electrolyte mediums, respectively, as
average stable capacities of ~60 and ~ 65 mAh g
−1
was maintained for 150 discharge/charge cycles at 180 mA g
−1
[98].
Zn x Mo 2.5 + y VO 9 + z with an open tunnel structure demonstrated good rate capability and cyclability in both aqueous (0.5 M Zn(CH 3 COO) 2 electrolyte) and nonaqueous (0.2 M Zn(CF 3 SO 3 ) 2 in 1:4 PC/dimethylsulfoxide (DMSO) solution)
electrolytes [99]. The anode exhibited capacities of 180 and 135 mAh g
−1
in aqueous and non-aqueous electrolytes, respectively, at 20 mA g
−1
. During Zn-ion
intercalation/de-intercalation, the anode was able to retain the parent structure under
electrochemical cycling.
Fig. 4 (a) Illustration of ZnMo 6 S 8 structure. (b) CV curves of the Mo 6 S 8 electrode at 0.05 mV s
−1
.
(c) Initial discharge and charge curves of the Zn-Mo 6 S 8 cell at 0.05 °C (6.4 mA g
−1 ) in the voltage
range of 0.25–1.0 V vs. Zn/Zn
2+
. (reprinted with permission from ref. [97])
Recent Developments of Zinc-Ion Batteries