8
conductor but poor electrical conductor. The β-NiOOH material is oxidized sufficiently to react with H 2 O, thus the β-Ni(OH) 2 is thought to coat the β-NiOOH and
prevent it from self-discharging by contact with H 2 O. A few percent Co(OH) 2 and
often Cd(OH) 2 is usually mixed with the NiOOH to improve cycle life and reduce
oxygen evolution reaction [36].
The zinc electrode in a Ni-Zn is usually the first to fail, and a very long list of
additives and methods are researched to solve the problem [35], with the most successful being addition of Ca(OH) 2 [28, 37] and perhaps with developments from
PowerGenix corporation [38]. One recent advance is the development of “flowassist” Ni-Zn wherein the zinc side is flowing electrolyte, which will be discussed
in Sect. 3.2. A demonstration project funded by the US National Energy Technology
Laboratory and ConEdison of New York showed a 30 kWh “flow-assist” Ni-Zn battery to cycle at 1100 healthy cycles at 2 h rates and ~ 75% depth-of-discharge of the
available zinc [13], which demonstrated a cost estimate for manufacturing this technology (including US labor) of $400 per kWh.
An example of a commercial Ni-Zn battery recently produced by Evercel is
shown in Fig. 6. Energy capacity of this Evercel Ni-Zn technology circa 2001 was
110 Wh/L, 65 Wh/kg, with cycle life near 500 when one-hour charge–discharge
times are used and 20% of theoretical capacity is cycled. Sintered nickel plaque
provides the best cycle life, but due to cost concerns the Ni side is often a carbonpaste PTFE-bound NiOOH electrode (US Patent 4,546,058).
2.3 Separators in Use for Alkaline Batteries
Separators command a large fraction of total battery cost, up to 25% in some cases
[39], and play a key role in performance. Extensive work has been performed on
separators for lithium-ion batteries for preventing catastrophic short-circuits and
electrolyte combustion [40]. Aqueous batteries usually have no risk of thermal runFig. 5 Crystal structures are shown for Ni(OH) 2 on the left and NiOOH on the right. Red atoms
are oxygen, gray are nickel, and small spheres are hydrogen
D. E. Turney et al.
conductor but poor electrical conductor. The β-NiOOH material is oxidized sufficiently to react with H 2 O, thus the β-Ni(OH) 2 is thought to coat the β-NiOOH and
prevent it from self-discharging by contact with H 2 O. A few percent Co(OH) 2 and
often Cd(OH) 2 is usually mixed with the NiOOH to improve cycle life and reduce
oxygen evolution reaction [36].
The zinc electrode in a Ni-Zn is usually the first to fail, and a very long list of
additives and methods are researched to solve the problem [35], with the most successful being addition of Ca(OH) 2 [28, 37] and perhaps with developments from
PowerGenix corporation [38]. One recent advance is the development of “flowassist” Ni-Zn wherein the zinc side is flowing electrolyte, which will be discussed
in Sect. 3.2. A demonstration project funded by the US National Energy Technology
Laboratory and ConEdison of New York showed a 30 kWh “flow-assist” Ni-Zn battery to cycle at 1100 healthy cycles at 2 h rates and ~ 75% depth-of-discharge of the
available zinc [13], which demonstrated a cost estimate for manufacturing this technology (including US labor) of $400 per kWh.
An example of a commercial Ni-Zn battery recently produced by Evercel is
shown in Fig. 6. Energy capacity of this Evercel Ni-Zn technology circa 2001 was
110 Wh/L, 65 Wh/kg, with cycle life near 500 when one-hour charge–discharge
times are used and 20% of theoretical capacity is cycled. Sintered nickel plaque
provides the best cycle life, but due to cost concerns the Ni side is often a carbonpaste PTFE-bound NiOOH electrode (US Patent 4,546,058).
2.3 Separators in Use for Alkaline Batteries
Separators command a large fraction of total battery cost, up to 25% in some cases
[39], and play a key role in performance. Extensive work has been performed on
separators for lithium-ion batteries for preventing catastrophic short-circuits and
electrolyte combustion [40]. Aqueous batteries usually have no risk of thermal runFig. 5 Crystal structures are shown for Ni(OH) 2 on the left and NiOOH on the right. Red atoms
are oxygen, gray are nickel, and small spheres are hydrogen
D. E. Turney et al.