40
at 0.1 A g g
−1
using a 3 M Zn(CF 3 SO 3 ) 2 electrolyte and metallic Zn as an anode
within a wide potential range of 0.2–1.6 V [68]. However, the electrolyte is seemingly very expensive (roughly 15 times costlier than ZnSO 4 ). These nanowires display a long term of cycle stability with a capacity retention of nearly 93% for
1000 cycles at 1 A g
−1
current density. The structural evolutions during electrochemical reaction were studied using XRD and Raman and X-ray photoelectron
spectroscopies. It is found that the indigenous ions can act as pillars to stabilize the
layered structure, thereby ensuring an enhanced cycling stability. Surprisingly,
based on Zn 0.25 V 2 O 5 ·nH 2 O [62], yet another pillar-stabilized cathode,
Ca 0.25 V 2 O 5 ·nH 2 O, a double layered calcium vanadium oxide bronze, has been
reported for ZIBs [71]. The V 2 O 5 layers stack along the c-axis and the intercalated
metal ions (Zn
2+
or Ca
2+
) as well as water molecules reside in the interlayer space
and strongly expand the interlayers. The nanobelts cathode delivered a high capacity of 340 mAh g
−1
at 0.2C, good rate capability and prolonged cycling lifespan of
3000 cycles, holding 96% capacity retention at a very high applied current rate of
80C in the potential range of 0.2–1.6 V using Zn(CF 3 SO 3 ) 2 electrolyte.
Further investigations on the crucial role of water molecules facilitating structural stability and superior electrochemical performance in layered-type V 2 O 5 ·nH 2 O
cathodes of ZIBs was also performed [67]. The H 2 O-solvated Zn
2+
possesses largely
reduced (screening) effective charge and thus greatly suppresses the electrostatic
interactions with the V 2 O 5 framework and thereby effectively promotes its diffusion. The influence of the “lubricating” effect of water molecules thus contribute to
the aqueous Zn battery showing an energy density of 90 Wh kg
−1
at a high-power
density of 6.4 kW kg
−1
(based on the active mass of cathode and anode materials).
The resulting performance thus make such “structural water-contained” layered
oxides a promising candidate for high-performance, safe, and environment-friendly
energy storage devices.
Layered LiV 3 O 8 (LVO), a well-known candidate for LIBs, follows the monoclinic system which comprises of the corner sharing of two edge shared octahedral
(VO 6 ) and trigonal bipyramid (VO 5 ) units to form (V 3 O 8 )
−
layers along the (100)
plane, the layers being linked by Li
+
ions in the interstitial octahedral and tetrahedral sites. Hence, it is highly feasible that the Zn-ions can well intercalate into the
host cathode since both Li
+
and Zn
2+
have almost similar ionic radii. Alfaruqi et al.
demonstrated that the flake-type LVO cathode delivers an average discharge capacity of 172 mAh g
−1
at 133 mA g
−1
current density after 65 cycles within the potential
range of 1.2–0.6 V [63]. Apart from that, the electrochemical regulation through the
operando in situ XRD study is a quite interesting and complex phenomenon. The
initial stage of Zn-ions intercalation (during discharge) is inferred to the singlephase reaction of LiV 3 O 8 where the Zn-ions begin to occupy vacant lithium sites
with different energies to form a ZnLiV 3 O 8 phase. In the intermediate stage, the
peak splitting feature of the (100) plane appears to suggest a two-phase reaction of
LVO and ZnLiV 3 O 8 . A complete single-phase reaction to form Zn y LiV 3 O 8 , y > 1 at
the end of the discharge is noted at the final stage, as shown in Figs. 3c–g.
On the other hand, a complete one-step early stage of the electrochemical charging/Zn de-intercalation is represented by the single-phase reaction of Zn y LiV 3 O 8
J. Kim et al.
at 0.1 A g g
−1
using a 3 M Zn(CF 3 SO 3 ) 2 electrolyte and metallic Zn as an anode
within a wide potential range of 0.2–1.6 V [68]. However, the electrolyte is seemingly very expensive (roughly 15 times costlier than ZnSO 4 ). These nanowires display a long term of cycle stability with a capacity retention of nearly 93% for
1000 cycles at 1 A g
−1
current density. The structural evolutions during electrochemical reaction were studied using XRD and Raman and X-ray photoelectron
spectroscopies. It is found that the indigenous ions can act as pillars to stabilize the
layered structure, thereby ensuring an enhanced cycling stability. Surprisingly,
based on Zn 0.25 V 2 O 5 ·nH 2 O [62], yet another pillar-stabilized cathode,
Ca 0.25 V 2 O 5 ·nH 2 O, a double layered calcium vanadium oxide bronze, has been
reported for ZIBs [71]. The V 2 O 5 layers stack along the c-axis and the intercalated
metal ions (Zn
2+
or Ca
2+
) as well as water molecules reside in the interlayer space
and strongly expand the interlayers. The nanobelts cathode delivered a high capacity of 340 mAh g
−1
at 0.2C, good rate capability and prolonged cycling lifespan of
3000 cycles, holding 96% capacity retention at a very high applied current rate of
80C in the potential range of 0.2–1.6 V using Zn(CF 3 SO 3 ) 2 electrolyte.
Further investigations on the crucial role of water molecules facilitating structural stability and superior electrochemical performance in layered-type V 2 O 5 ·nH 2 O
cathodes of ZIBs was also performed [67]. The H 2 O-solvated Zn
2+
possesses largely
reduced (screening) effective charge and thus greatly suppresses the electrostatic
interactions with the V 2 O 5 framework and thereby effectively promotes its diffusion. The influence of the “lubricating” effect of water molecules thus contribute to
the aqueous Zn battery showing an energy density of 90 Wh kg
−1
at a high-power
density of 6.4 kW kg
−1
(based on the active mass of cathode and anode materials).
The resulting performance thus make such “structural water-contained” layered
oxides a promising candidate for high-performance, safe, and environment-friendly
energy storage devices.
Layered LiV 3 O 8 (LVO), a well-known candidate for LIBs, follows the monoclinic system which comprises of the corner sharing of two edge shared octahedral
(VO 6 ) and trigonal bipyramid (VO 5 ) units to form (V 3 O 8 )
−
layers along the (100)
plane, the layers being linked by Li
+
ions in the interstitial octahedral and tetrahedral sites. Hence, it is highly feasible that the Zn-ions can well intercalate into the
host cathode since both Li
+
and Zn
2+
have almost similar ionic radii. Alfaruqi et al.
demonstrated that the flake-type LVO cathode delivers an average discharge capacity of 172 mAh g
−1
at 133 mA g
−1
current density after 65 cycles within the potential
range of 1.2–0.6 V [63]. Apart from that, the electrochemical regulation through the
operando in situ XRD study is a quite interesting and complex phenomenon. The
initial stage of Zn-ions intercalation (during discharge) is inferred to the singlephase reaction of LiV 3 O 8 where the Zn-ions begin to occupy vacant lithium sites
with different energies to form a ZnLiV 3 O 8 phase. In the intermediate stage, the
peak splitting feature of the (100) plane appears to suggest a two-phase reaction of
LVO and ZnLiV 3 O 8 . A complete single-phase reaction to form Zn y LiV 3 O 8 , y > 1 at
the end of the discharge is noted at the final stage, as shown in Figs. 3c–g.
On the other hand, a complete one-step early stage of the electrochemical charging/Zn de-intercalation is represented by the single-phase reaction of Zn y LiV 3 O 8
J. Kim et al.