49
tively [62], while Zn 2 V 2 O 7 nanowire displays the specific energies of 166.3 and
114.3 Wh kg
−1
at specific powers of 36 and 3168 W kg
−1
(based on cathode mass),
respectively [70]. This nanowire Zn-ion battery offering an energy density of
87.3/60 Wh kg
−1
for a given power density of 18.9/1663 W kg
−1
at 50/4400 mA g
−1
current density (based on whole cell) is still higher than those of commercial Pb-acid
(~30 Wh kg
−1
) and Ni-Cd (50 Wh kg
−1
) batteries. Thus, the performances of the
electrodes, mainly based on manganese and vanadium materials discussed above,
show potential for clear superiority to the performance parameters of commercially
used alkaline Zn/MnO 2 batteries, the scope for further enhancements on ZIB performance is still wide open. The following are the conclusions that can be derived from
the research developments on ZIBs so far:
1. Tunnel-type and layered-type electrode structures with sufficiently wide geometric dimensions tend to favor reversible Zn insertion; though some of these
electrodes undergo irreversible phase transition that seem to be dependent on the
crystal structure, synthesis, and morphology of the electrode and the type of
electrolyte used.
2. The strategies of conductive inclusions combined with pre-inclusion of additives
in nanostructured manganese-based electrodes and structural water inclusion
and/or metal-ion doping in vanadium-based electrodes have been successful, at
least to a certain extent, to avoid active material dissolution, and hence increase
zinc storage capacities in addition to extending the cycling stability of these
electrodes to a few thousands of cycles from a few hundred cycles under high
current drains.
3. Although major strides on the electrochemical performance of ZIBs have been
made, three major drawbacks including low intrinsic electrical conductivity of
manganese/vanadium materials, active material dissolution, especially, in
manganese- based electrodes and formation of by-products via electrode phase
transition or side reactions hinder the achievement of practical zinc storage
capacities equivalent to theoretical values.
4. Compared to other salts, ZnSO 4 and bulky anion salts including Zn(CF 3 SO 3 ) 2
and Zn (TFSI) 2 show high solubility in aqueous solutions and form mildly acidic
electrolytes that demonstrate good electrochemical stability, minimum dendritic
growth and cause considerably low corrosion in ZIBs. ZnSO 4 is low-cost; however, the formation of byproducts like ZHS during can accumulate on the cathode surface thereby leading to capacity fade during repeated cycling. Whereas
the use of Zn(CF 3 SO 3 ) 2 /Zn (TFSI) 2 salts offers higher electrochemical stability
and performance but at the cost of the economic feature as the salt price is highly
expensive than the low-cost ZnSO 4 to realize large-scale production. For nonaqueous ZIBs, only Zn (TFSI) 2 salt has been used so far to demonstrate reversible Zn insertion.
5. As for anodes, more efforts to analyze the pH of the solution can be a useful
approach to control the hydrogen evolution and avoid the formation of dendrites
thereby offering stability to repeated Zn stripping/plating reactions for the long
term.
Recent Developments of Zinc-Ion Batteries
tively [62], while Zn 2 V 2 O 7 nanowire displays the specific energies of 166.3 and
114.3 Wh kg
−1
at specific powers of 36 and 3168 W kg
−1
(based on cathode mass),
respectively [70]. This nanowire Zn-ion battery offering an energy density of
87.3/60 Wh kg
−1
for a given power density of 18.9/1663 W kg
−1
at 50/4400 mA g
−1
current density (based on whole cell) is still higher than those of commercial Pb-acid
(~30 Wh kg
−1
) and Ni-Cd (50 Wh kg
−1
) batteries. Thus, the performances of the
electrodes, mainly based on manganese and vanadium materials discussed above,
show potential for clear superiority to the performance parameters of commercially
used alkaline Zn/MnO 2 batteries, the scope for further enhancements on ZIB performance is still wide open. The following are the conclusions that can be derived from
the research developments on ZIBs so far:
1. Tunnel-type and layered-type electrode structures with sufficiently wide geometric dimensions tend to favor reversible Zn insertion; though some of these
electrodes undergo irreversible phase transition that seem to be dependent on the
crystal structure, synthesis, and morphology of the electrode and the type of
electrolyte used.
2. The strategies of conductive inclusions combined with pre-inclusion of additives
in nanostructured manganese-based electrodes and structural water inclusion
and/or metal-ion doping in vanadium-based electrodes have been successful, at
least to a certain extent, to avoid active material dissolution, and hence increase
zinc storage capacities in addition to extending the cycling stability of these
electrodes to a few thousands of cycles from a few hundred cycles under high
current drains.
3. Although major strides on the electrochemical performance of ZIBs have been
made, three major drawbacks including low intrinsic electrical conductivity of
manganese/vanadium materials, active material dissolution, especially, in
manganese- based electrodes and formation of by-products via electrode phase
transition or side reactions hinder the achievement of practical zinc storage
capacities equivalent to theoretical values.
4. Compared to other salts, ZnSO 4 and bulky anion salts including Zn(CF 3 SO 3 ) 2
and Zn (TFSI) 2 show high solubility in aqueous solutions and form mildly acidic
electrolytes that demonstrate good electrochemical stability, minimum dendritic
growth and cause considerably low corrosion in ZIBs. ZnSO 4 is low-cost; however, the formation of byproducts like ZHS during can accumulate on the cathode surface thereby leading to capacity fade during repeated cycling. Whereas
the use of Zn(CF 3 SO 3 ) 2 /Zn (TFSI) 2 salts offers higher electrochemical stability
and performance but at the cost of the economic feature as the salt price is highly
expensive than the low-cost ZnSO 4 to realize large-scale production. For nonaqueous ZIBs, only Zn (TFSI) 2 salt has been used so far to demonstrate reversible Zn insertion.
5. As for anodes, more efforts to analyze the pH of the solution can be a useful
approach to control the hydrogen evolution and avoid the formation of dendrites
thereby offering stability to repeated Zn stripping/plating reactions for the long
term.
Recent Developments of Zinc-Ion Batteries