41
that gradually proceeds towards the recovery of LiV 3 O 8 . The complete electrochemical reaction through intercalation/de-intercalation is well supported by XRD simulation. Thus, although the layered-type structure of LVO undergoes slight
modification during the electrochemical reaction with Zn
2+
or Li
+
ions, the phase
behavior is different from that observed during lithiation. Therefore, the present
study encourages the utilization of such an approach to understand the phase evolution in layered-type systems but also demonstrates vanadium-based intercalation
hosts as a promising cathode for ZIBs.
A similar anionic [V 3 O 8 ]
−
layered network containing H 2 V 3 O 8 nanowire cathode,
in which hydrogen atoms are linked between the layers, and each layer consists of
VO 6 octahedra and VO 5 trigonal bipyramids, is utilized for ZIBs. This cathode
nanowire of Zn-H 2 V 3 O 8 battery delivers a high capacity of ~424 mAh g
−1
at
0.1 mA g
−1
within the potential window of 0.2–1.6 V using a 3 M Zn(CF 3 SO 3 ) 2
electrolyte [66]. Interestingly, the nanowire cathode retains nearly 94% of the
capacity after 1000 cycles at high current rate of 5 A g
−1
. In general, the metal ions
in [V 3 O 8 ] layers containing M x V n O m , (where M = metal ion) network can stabilize
the structural integrity. A highly durable Na 2 V 6 O 16 ·1.63H 2 O nanowire cathode and
an aqueous Zn(CF 3 SO 3 ) 2 electrolyte have been developed [72]. This aqueous Zn-ion
battery provides a high capacity of 352 mAh g
−1
at 50 mA g
−1
and exhibits a capacity retention of 90% over 6000 cycles at 5 A g
−1
current density within the potential
range of 0.2–1.6 V. A similar [V 3 O 8 ]
−
layered background containing pilotaxitic
Na 1.1 V 3 O 7.9 nanoribbons/graphene cathode shows a reversible capacity of
171 mA h g
−1
after 100 cycles at 300 mA g
−1
current drain [69]. The results indicate
that the micro-structure is stable after long-term cycling for ZIBs. Recently Kundu
et al. reported V 3 O 7 •H 2 O cathode, a similar two-dimensional [V 3 O 8 ] layers show
very high capacity and power (375 mAh g
−1
at 1C rate and 275 mAh g
−1
at 8C rate)
in an aqueous electrolyte of 1 M ZnSO 4 [73]. The structural evolution during electrochemical cycling was monitored through operando in situ analysis. Interestingly,
a formation/dissolution of an additional new phase, Zn 4 (OH) 6 SO 4 •5H 2 O evolved
during discharge/charge processes, respectively. Though the observation is not quite
new, its role on electrochemical reaction is not well defined. According to them, this
observation is a side reaction in which dissolved oxygen from the electrolyte may
interact with available species (Zn
2+
, SO 4
2−
and H 2 O) to precipitate on the surface of
the electrode. However, further systematic studies are necessary to identify the real
contribution in conjunction with redox electrochemical kinetics.
Besides the (V 3 O 8 )
−
layered background, another framework of pyrovanadate,
(V 2 O 7 )
4−
can stabilize a larger structure as Zn-pyrovanadate, α-Zn 2 V 2 O 7 . This structure consists of a layered structure of tetrahedrally coordinated VO 4 and distorted
trigonal bipyramid ZnO 5 polyhedra. Sambandam et al. reported on an α-Zn 2 V 2 O 7
nanowire cathode that delivered high specific reversible specific capacities of 197
and 138 mAh g
−1
at two different current densities of 300 and 4000 mA g
−1
,
respectively, for 200 and 1000 cycles through an insertion mechanism [70].
Significant specific energies of 166.3 and 114.3 Wh kg
−1
at specific powers of 36
and 3168 W kg
−1
(based on cathode material mass), respectively, were delivered by
this cathode using 1 M ZnSO 4 aqueous electrolyte within the potential range of
Recent Developments of Zinc-Ion Batteries
that gradually proceeds towards the recovery of LiV 3 O 8 . The complete electrochemical reaction through intercalation/de-intercalation is well supported by XRD simulation. Thus, although the layered-type structure of LVO undergoes slight
modification during the electrochemical reaction with Zn
2+
or Li
+
ions, the phase
behavior is different from that observed during lithiation. Therefore, the present
study encourages the utilization of such an approach to understand the phase evolution in layered-type systems but also demonstrates vanadium-based intercalation
hosts as a promising cathode for ZIBs.
A similar anionic [V 3 O 8 ]
−
layered network containing H 2 V 3 O 8 nanowire cathode,
in which hydrogen atoms are linked between the layers, and each layer consists of
VO 6 octahedra and VO 5 trigonal bipyramids, is utilized for ZIBs. This cathode
nanowire of Zn-H 2 V 3 O 8 battery delivers a high capacity of ~424 mAh g
−1
at
0.1 mA g
−1
within the potential window of 0.2–1.6 V using a 3 M Zn(CF 3 SO 3 ) 2
electrolyte [66]. Interestingly, the nanowire cathode retains nearly 94% of the
capacity after 1000 cycles at high current rate of 5 A g
−1
. In general, the metal ions
in [V 3 O 8 ] layers containing M x V n O m , (where M = metal ion) network can stabilize
the structural integrity. A highly durable Na 2 V 6 O 16 ·1.63H 2 O nanowire cathode and
an aqueous Zn(CF 3 SO 3 ) 2 electrolyte have been developed [72]. This aqueous Zn-ion
battery provides a high capacity of 352 mAh g
−1
at 50 mA g
−1
and exhibits a capacity retention of 90% over 6000 cycles at 5 A g
−1
current density within the potential
range of 0.2–1.6 V. A similar [V 3 O 8 ]
−
layered background containing pilotaxitic
Na 1.1 V 3 O 7.9 nanoribbons/graphene cathode shows a reversible capacity of
171 mA h g
−1
after 100 cycles at 300 mA g
−1
current drain [69]. The results indicate
that the micro-structure is stable after long-term cycling for ZIBs. Recently Kundu
et al. reported V 3 O 7 •H 2 O cathode, a similar two-dimensional [V 3 O 8 ] layers show
very high capacity and power (375 mAh g
−1
at 1C rate and 275 mAh g
−1
at 8C rate)
in an aqueous electrolyte of 1 M ZnSO 4 [73]. The structural evolution during electrochemical cycling was monitored through operando in situ analysis. Interestingly,
a formation/dissolution of an additional new phase, Zn 4 (OH) 6 SO 4 •5H 2 O evolved
during discharge/charge processes, respectively. Though the observation is not quite
new, its role on electrochemical reaction is not well defined. According to them, this
observation is a side reaction in which dissolved oxygen from the electrolyte may
interact with available species (Zn
2+
, SO 4
2−
and H 2 O) to precipitate on the surface of
the electrode. However, further systematic studies are necessary to identify the real
contribution in conjunction with redox electrochemical kinetics.
Besides the (V 3 O 8 )
−
layered background, another framework of pyrovanadate,
(V 2 O 7 )
4−
can stabilize a larger structure as Zn-pyrovanadate, α-Zn 2 V 2 O 7 . This structure consists of a layered structure of tetrahedrally coordinated VO 4 and distorted
trigonal bipyramid ZnO 5 polyhedra. Sambandam et al. reported on an α-Zn 2 V 2 O 7
nanowire cathode that delivered high specific reversible specific capacities of 197
and 138 mAh g
−1
at two different current densities of 300 and 4000 mA g
−1
,
respectively, for 200 and 1000 cycles through an insertion mechanism [70].
Significant specific energies of 166.3 and 114.3 Wh kg
−1
at specific powers of 36
and 3168 W kg
−1
(based on cathode material mass), respectively, were delivered by
this cathode using 1 M ZnSO 4 aqueous electrolyte within the potential range of
Recent Developments of Zinc-Ion Batteries