46
4 Non-aqueous Zinc-Ion Batteries
Although the use of aqueous electrolytes, both acidic and alkaline solutions, appears
promising, challenges of understanding the reaction mechanism, hydrogen evolution, limited operating potential window, passivation layer formations affecting
Zn-ion diffusion and hence cycling ability remain [100]. For example, the role of
proton (de) intercalation and Zn-hydroxide precipitate formation (dissolution) in
aqueous ZIBs has not yet been completely understood [42]. In addition, the knowledge on the structural variations in the cathode especially with various manganese
oxide polymorphs during Zn-ion insertion from aqueous electrolyte medium is limited [36]. Meanwhile, recently, a combination of computational and three electrode
based experimental studies confirmed that non-aqueous electrolytes, viz., acetonitrile- Zn (II) bis(trifluorometylsulfonyl)imide (AN-Zn(TFSI) 2 ), AN-Zn(CF 3 SO 3 ) 2,
and propylene carbonate (PC) − Zn(TFSI) 2 support reversible Zn-deposition/stripping on Zn metal anode with no irreversible reaction or further redox reaction thus
offering anodic stability of electrolyte components of anions and solvents within a
wide electrochemical window (~3.8 V vs Zn/Zn
2+
). Also, the linear sweep voltammetry of the three electrolytes shows highest current density at 0.5 M concentration
(Fig. 5a) [101]. More importantly, this breakthrough report facilitates the access of
cell potentials beyond the usual aqueous electrolyte window (~ 1.5 V). Moreover,
this warrants a critical investigation on non-aqueous ZIBs towards gaining a deeper
understanding on their underlying mechanisms and advancements for practical
applications. Furthermore, the work on non-aqueous ZIBs with intercalation cathodes are only in their infant stages and more strides forward are expected to be taken
in this direction soon.
As reported for aqueous ZIBs, the strategies of utilizing layered-type compounds
with apparently low migration energies (than 3-D spinel or 1D-olivine structures)
and designing the corresponding nanostructures incorporated with “pillar”
Fig. 5 (a) Linear sweep voltammetry curves at a scan rate of 0.025 V s
−1 for 0.5 M AN−Zn(TFSI) 2 ,
AN−Zn(CF 3 SO 3 ) 2 , and PC − Zn(TFSI) 2 electrolytes to evaluate the stability of anions and solvents
with respect to Zn anode through a three electrode based analysis. (reprinted with permission from
ref. [101]) (b) Schematic illustration of a non-aqueous ZIB system, i.e., Zn||0.5 M AN−
Zn(TFSI) 2 ||V 2 O 5 (red: oxygen (O), green: zinc (Zn), blue: vanadium (V)) showing intercalation/
de-intercalation of Zn
2+ ions into the bilayered vanadium oxide. (c) Electrochemical profiles of the
non-aqueous ZIB within the potential window of 0.3-1.5 V at 0.1 °C. (reprinted with permission
from ref. [26])
J. Kim et al.
4 Non-aqueous Zinc-Ion Batteries
Although the use of aqueous electrolytes, both acidic and alkaline solutions, appears
promising, challenges of understanding the reaction mechanism, hydrogen evolution, limited operating potential window, passivation layer formations affecting
Zn-ion diffusion and hence cycling ability remain [100]. For example, the role of
proton (de) intercalation and Zn-hydroxide precipitate formation (dissolution) in
aqueous ZIBs has not yet been completely understood [42]. In addition, the knowledge on the structural variations in the cathode especially with various manganese
oxide polymorphs during Zn-ion insertion from aqueous electrolyte medium is limited [36]. Meanwhile, recently, a combination of computational and three electrode
based experimental studies confirmed that non-aqueous electrolytes, viz., acetonitrile- Zn (II) bis(trifluorometylsulfonyl)imide (AN-Zn(TFSI) 2 ), AN-Zn(CF 3 SO 3 ) 2,
and propylene carbonate (PC) − Zn(TFSI) 2 support reversible Zn-deposition/stripping on Zn metal anode with no irreversible reaction or further redox reaction thus
offering anodic stability of electrolyte components of anions and solvents within a
wide electrochemical window (~3.8 V vs Zn/Zn
2+
). Also, the linear sweep voltammetry of the three electrolytes shows highest current density at 0.5 M concentration
(Fig. 5a) [101]. More importantly, this breakthrough report facilitates the access of
cell potentials beyond the usual aqueous electrolyte window (~ 1.5 V). Moreover,
this warrants a critical investigation on non-aqueous ZIBs towards gaining a deeper
understanding on their underlying mechanisms and advancements for practical
applications. Furthermore, the work on non-aqueous ZIBs with intercalation cathodes are only in their infant stages and more strides forward are expected to be taken
in this direction soon.
As reported for aqueous ZIBs, the strategies of utilizing layered-type compounds
with apparently low migration energies (than 3-D spinel or 1D-olivine structures)
and designing the corresponding nanostructures incorporated with “pillar”
Fig. 5 (a) Linear sweep voltammetry curves at a scan rate of 0.025 V s
−1 for 0.5 M AN−Zn(TFSI) 2 ,
AN−Zn(CF 3 SO 3 ) 2 , and PC − Zn(TFSI) 2 electrolytes to evaluate the stability of anions and solvents
with respect to Zn anode through a three electrode based analysis. (reprinted with permission from
ref. [101]) (b) Schematic illustration of a non-aqueous ZIB system, i.e., Zn||0.5 M AN−
Zn(TFSI) 2 ||V 2 O 5 (red: oxygen (O), green: zinc (Zn), blue: vanadium (V)) showing intercalation/
de-intercalation of Zn
2+ ions into the bilayered vanadium oxide. (c) Electrochemical profiles of the
non-aqueous ZIB within the potential window of 0.3-1.5 V at 0.1 °C. (reprinted with permission
from ref. [26])
J. Kim et al.