47
elements/molecules enabling multivalent ion migration within the crystalline hosts
are promising. To this end, Senguttuvan et al. developed a 0.85 V Zn-full cell based
on Zn metal anode and a hydrated bilayered V 2 O 5 electrodeposited on a carbon
substrate as the cathode and a solution of 0.5 M Zn(TFSI) 2 in acetonitrile as the nonaqueous electrolyte. The schematic illustration of the non-aqueous ZIB is provided
in Fig. 5b. Electrochemical profiles obtained for the 0.3-1.5 V window are provided
in Fig. 5c. The cycle performance studies revealed stable specific capacities
(~170 mAh g
−1
for over 120 cycles at 0.1 °C) with 99% Coulombic efficiency and
suggested the high structrual integrity of the cathode thereby demonstrating the
excellent plating/stripping effectiveness in the corresponding electrolyte. More
importantly, a 130 mAh g
−1
specific capacity at 20 °C rates corresponding to
1500 W kg
−1
power that is almost equivalent to standard Li-ion batteries was realized. The enhanced electrochemical performance was attributed to the layered cathode structure being stabilized by water molecules at the interlayers (with wide
spacing of 11–13 Å) thereby enabling facile reversible Zn-ion (de) insertion.
Importantly, the oxide host structure remained unaffected by the presence of oxygen-bearing TFSI salt in the electrolyte [26].
Han et al. studying the insertion chemistry in a layered-type water stabilized
δ-MnO 2 nanostructured cathode (K 0.11 MnO 2 ·0.7H 2 O) confirmed reversible Zn insertion in a non-aqueous electrolyte media of Zn(TFSI) 2 in acetonitrile solution without macroscopic phase transitions and significant proton intercalation. The
fabricated Zn-δMnO 2 cell delivered a maximum of 123 mAh g
−1
over 125 cycles at
0.1 °C with gradual capacity fade in the potential domain of 0.05–1.9 V. The capacity fade was attributed to the reduced electrolyte performance, the competing reactions for ZnO formation on the electrode surface and Mn dissolution [102].
Cubic PBAs with formula, A x M 1 [M 2 (CN) 6 ] y ·nH 2 O, (M 1 /M 2 —metal ions; cyanide
(CN) ligands; A—mobile alkaline metal ions) belonging to Fm3̅ m space group benefit as cheap, nontoxic, easy-to-prepare, and open-framework cathodes of ZIBs. An
eco-friendly PBA cathode, K 0.05 Fe(III)[Fe(III) (CN) 6 ]·2.6H 2 O, integrated with a
cheap, biodegradable, and biocompatible “ionic liquid in water” electrolyte and a
nontoxic/low-cost Zn anode delivered reversible discharge capacities of 120 mAh g
−1
at 0.1 °C with 99% Columbic efficiency for the initial ten cycles at a current of
10 mA g
−1
(∼0.1 °C) in the potential domain 0.8–2 V. Fourier electron density analysis with powder XRD studies done on another PBA cathode, potassium nickel
hexacyanoferrate K 0.86 Ni[Fe(CN) 6 ] 0.954 (H 2 O) 0.766 in 0.5 M Zn(ClO 4 ) 2 in acetonitrile
electrolyte medium confirmed that the inserted Zn
2+
-ion occupies the center of the
large interstitial cavity, the same location as of the potassium and zeolite water in
the cubic open-framework structure [103, 104].
Non-aqueous gel polymer electrolytes (GPE) based on ionic liquids, 1-buthyl- 3methylimidazolium trifluoromethanesulfonate (BMIM triflate), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM TFSI), respectively,
were prepared for use in ZIB applications. The inclusion of the ionic liquid led to
the formation of good GPEs while the retention of NMP molecules in the polymer
was crucial to improve GPE properties. In the Zn-MnO 2 cell with the former GPE
(PVdF-HFP/BMIM triflate/Zn(CF 3 SO 3 ) 2 ), ex situ XPS, SEM, and EDX studies
Recent Developments of Zinc-Ion Batteries
elements/molecules enabling multivalent ion migration within the crystalline hosts
are promising. To this end, Senguttuvan et al. developed a 0.85 V Zn-full cell based
on Zn metal anode and a hydrated bilayered V 2 O 5 electrodeposited on a carbon
substrate as the cathode and a solution of 0.5 M Zn(TFSI) 2 in acetonitrile as the nonaqueous electrolyte. The schematic illustration of the non-aqueous ZIB is provided
in Fig. 5b. Electrochemical profiles obtained for the 0.3-1.5 V window are provided
in Fig. 5c. The cycle performance studies revealed stable specific capacities
(~170 mAh g
−1
for over 120 cycles at 0.1 °C) with 99% Coulombic efficiency and
suggested the high structrual integrity of the cathode thereby demonstrating the
excellent plating/stripping effectiveness in the corresponding electrolyte. More
importantly, a 130 mAh g
−1
specific capacity at 20 °C rates corresponding to
1500 W kg
−1
power that is almost equivalent to standard Li-ion batteries was realized. The enhanced electrochemical performance was attributed to the layered cathode structure being stabilized by water molecules at the interlayers (with wide
spacing of 11–13 Å) thereby enabling facile reversible Zn-ion (de) insertion.
Importantly, the oxide host structure remained unaffected by the presence of oxygen-bearing TFSI salt in the electrolyte [26].
Han et al. studying the insertion chemistry in a layered-type water stabilized
δ-MnO 2 nanostructured cathode (K 0.11 MnO 2 ·0.7H 2 O) confirmed reversible Zn insertion in a non-aqueous electrolyte media of Zn(TFSI) 2 in acetonitrile solution without macroscopic phase transitions and significant proton intercalation. The
fabricated Zn-δMnO 2 cell delivered a maximum of 123 mAh g
−1
over 125 cycles at
0.1 °C with gradual capacity fade in the potential domain of 0.05–1.9 V. The capacity fade was attributed to the reduced electrolyte performance, the competing reactions for ZnO formation on the electrode surface and Mn dissolution [102].
Cubic PBAs with formula, A x M 1 [M 2 (CN) 6 ] y ·nH 2 O, (M 1 /M 2 —metal ions; cyanide
(CN) ligands; A—mobile alkaline metal ions) belonging to Fm3̅ m space group benefit as cheap, nontoxic, easy-to-prepare, and open-framework cathodes of ZIBs. An
eco-friendly PBA cathode, K 0.05 Fe(III)[Fe(III) (CN) 6 ]·2.6H 2 O, integrated with a
cheap, biodegradable, and biocompatible “ionic liquid in water” electrolyte and a
nontoxic/low-cost Zn anode delivered reversible discharge capacities of 120 mAh g
−1
at 0.1 °C with 99% Columbic efficiency for the initial ten cycles at a current of
10 mA g
−1
(∼0.1 °C) in the potential domain 0.8–2 V. Fourier electron density analysis with powder XRD studies done on another PBA cathode, potassium nickel
hexacyanoferrate K 0.86 Ni[Fe(CN) 6 ] 0.954 (H 2 O) 0.766 in 0.5 M Zn(ClO 4 ) 2 in acetonitrile
electrolyte medium confirmed that the inserted Zn
2+
-ion occupies the center of the
large interstitial cavity, the same location as of the potassium and zeolite water in
the cubic open-framework structure [103, 104].
Non-aqueous gel polymer electrolytes (GPE) based on ionic liquids, 1-buthyl- 3methylimidazolium trifluoromethanesulfonate (BMIM triflate), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM TFSI), respectively,
were prepared for use in ZIB applications. The inclusion of the ionic liquid led to
the formation of good GPEs while the retention of NMP molecules in the polymer
was crucial to improve GPE properties. In the Zn-MnO 2 cell with the former GPE
(PVdF-HFP/BMIM triflate/Zn(CF 3 SO 3 ) 2 ), ex situ XPS, SEM, and EDX studies
Recent Developments of Zinc-Ion Batteries