30
need to be overcome to enhance the electrochemical reactivity and hence, the performance in these electrodes to be considered for commercial applications. As for
the electrolytes of ZIBs, solutions of sulfate (ZnSO 4 and triflate Zn(CF 3 SO 3 ) 2 ) salts,
respectively, are the ones that are most commonly used, mainly due to the low-cost
feature of the former and the ability to facilitate stable electrochemical reaction
under long- term cycling for the latter [22]. However, more studies for electrolyte
optimization are required to ensure smooth reaction under higher electrochemically
stable windows. Further, although the detrimental issues of dendrite formation and
corrosion on the anode side are not expected to be severe as in the case of the alkaline Zn-MnO 2 battery system, the evolution of these reactions need to be understood
completely for the use of ZIBs in real-time applications [23].
2 Electrolytes for Zinc-Ion Battery
Oh and co-workers studied mildly acidic, low pH, and low-cost 2 M ZnSO 4 aqueous
solutions as an alternative to high pH alkaline electrolytes to improve the electrochemical performance in the Zn-MnO 2 battery system as early as the 1990s [17, 18].
Later, in 2009, Kang et al. used an almost neutral/very mildly acidic aqueous 0.1 M
Zn(NO 3 ) 2 electrolyte (pH ~ 6) to describe reversible insertion of Zn-ion in MnO 2
[24]. Aided with the Pourbaix diagram for the Zn/water system and a mild acidic
aqueous electrolyte in 2012, the same group demonstrated the long-term electrochemical reversibility of Zn-intercalation in cathodic MnO 2 and stripping/plating of
Zn at the anode end in an aqueous 1 M ZnSO 4 electrolyte solution [8]. The reactions
occurring above and below 0 V (vs. Zn
2+
/Zn), revealed a low redox potential.
Kashir et al. identified that low salt concentration, despite the different anions
used, in mildly aqueous zinc electrolyte solutions exhibited better electrochemical
properties than the high concentration counterparts [25]. In particular, sulfate
counter- ion-based ZnSO 4 are economical and showed significant performance,
compared with those containing the Zn(NO 3 ) 2 , Zn(CH 3 COO) 2 , ZnCl 2 , Zn(ClO 4 ) 2 ,
and ZnF 2 counterparts [25]. However, the exact role of the anions is yet to be determined. Later, the more expensive salts containing bulky anions including sulfonate,
Zn(CF 3 SO 3 ) 2 , and imidazolate, Zn(C 2 F 6 O 4 N) 2 were investigated for their better
cycling stability and lifetime compared with those containing ZnSO 4 electrolyte
for ZIBs.
The efforts to overcome the problem of active material dissolution and hence
improve the electrochemical performance in cathodes, specially, manganese oxide
materials, were focused on pre-including additives in the electrolyte in ZIBs. This
approach followed the usage of MnSO 4 additive to prevent manganese dissolution
for Zn-MnO 2 system in the 1990s [18]. Thus, the additive added electrolyte solution
of ZnSO 4 , was expected to compensate the Mn
2+
dissolution from the cathode manganese oxide due to the following disproportionate reaction:
J. Kim et al.
need to be overcome to enhance the electrochemical reactivity and hence, the performance in these electrodes to be considered for commercial applications. As for
the electrolytes of ZIBs, solutions of sulfate (ZnSO 4 and triflate Zn(CF 3 SO 3 ) 2 ) salts,
respectively, are the ones that are most commonly used, mainly due to the low-cost
feature of the former and the ability to facilitate stable electrochemical reaction
under long- term cycling for the latter [22]. However, more studies for electrolyte
optimization are required to ensure smooth reaction under higher electrochemically
stable windows. Further, although the detrimental issues of dendrite formation and
corrosion on the anode side are not expected to be severe as in the case of the alkaline Zn-MnO 2 battery system, the evolution of these reactions need to be understood
completely for the use of ZIBs in real-time applications [23].
2 Electrolytes for Zinc-Ion Battery
Oh and co-workers studied mildly acidic, low pH, and low-cost 2 M ZnSO 4 aqueous
solutions as an alternative to high pH alkaline electrolytes to improve the electrochemical performance in the Zn-MnO 2 battery system as early as the 1990s [17, 18].
Later, in 2009, Kang et al. used an almost neutral/very mildly acidic aqueous 0.1 M
Zn(NO 3 ) 2 electrolyte (pH ~ 6) to describe reversible insertion of Zn-ion in MnO 2
[24]. Aided with the Pourbaix diagram for the Zn/water system and a mild acidic
aqueous electrolyte in 2012, the same group demonstrated the long-term electrochemical reversibility of Zn-intercalation in cathodic MnO 2 and stripping/plating of
Zn at the anode end in an aqueous 1 M ZnSO 4 electrolyte solution [8]. The reactions
occurring above and below 0 V (vs. Zn
2+
/Zn), revealed a low redox potential.
Kashir et al. identified that low salt concentration, despite the different anions
used, in mildly aqueous zinc electrolyte solutions exhibited better electrochemical
properties than the high concentration counterparts [25]. In particular, sulfate
counter- ion-based ZnSO 4 are economical and showed significant performance,
compared with those containing the Zn(NO 3 ) 2 , Zn(CH 3 COO) 2 , ZnCl 2 , Zn(ClO 4 ) 2 ,
and ZnF 2 counterparts [25]. However, the exact role of the anions is yet to be determined. Later, the more expensive salts containing bulky anions including sulfonate,
Zn(CF 3 SO 3 ) 2 , and imidazolate, Zn(C 2 F 6 O 4 N) 2 were investigated for their better
cycling stability and lifetime compared with those containing ZnSO 4 electrolyte
for ZIBs.
The efforts to overcome the problem of active material dissolution and hence
improve the electrochemical performance in cathodes, specially, manganese oxide
materials, were focused on pre-including additives in the electrolyte in ZIBs. This
approach followed the usage of MnSO 4 additive to prevent manganese dissolution
for Zn-MnO 2 system in the 1990s [18]. Thus, the additive added electrolyte solution
of ZnSO 4 , was expected to compensate the Mn
2+
dissolution from the cathode manganese oxide due to the following disproportionate reaction:
J. Kim et al.