- Nickel–zinc battery
Nickel–zinc battery specific energy 100 W·h/kg energy density 280 W·h/L specific power > 900 W/kg Energy/consumer-price 2–3Wh/US$ Cycle durability 400–1000 Nominal cell voltage 1.65 V
The nickel–zinc battery (sometimes abbreviated to the chemical symbols for the elements "NiZn") is a type of rechargeable battery that may be used in cordless power tools, cordless telephones, digital cameras, battery operated lawn and garden tools, professional photography, flashlights, electric bikes, and light electric vehicle sectors.
Larger nickel–zinc battery systems have been known for over 100 years. Since 2000, development of a stabilized zinc electrode system made this technology viable and competitive with other commercially available rechargeable battery systems.
The battery was later developed by an Irish chemist, Dr. James J. Drumm (1897–1974) and installed in four 2-car Drumm railcar sets between 1932 and 1948 for use on the Dublin–Bray line. Although successful they were then withdrawn when the batteries wore out. Early nickel–zinc batteries were plagued by limited number of discharge cycles. In the 1960s, nickel–zinc batteries were investigated as an alternative to silver–zinc batteries for military applications, and in the 1970s were again of interest for electric vehicles. A company called Evercel Inc. formerly developed and patented several improvements in nickel–zinc batteries but withdrew from that area in 2004.
Presently this battery technology has limited consumer availability, with only AA cells offered for the digital camera market in some camera stores, or other outlet stores. Both D-cells and sub-C cells are currently used in commercial applications.
Nickel–zinc batteries perform well in high-drain applications, and may have the potential to replace lead–acid batteries because of their higher energy-to-mass ratio and higher power-to-mass ratio (up to 75% lighter for the same power). NiZn are also lower in cost, compared to nickel-cadmium batteries (expected to be priced somewhere in between NiCd and lead–acids). NiZn may be used as a substitute for nickel-cadmium. The European Parliament has supported bans on cadmium-based batteries; nickel–zinc offers the European power tool industry an alternative.
Charge Reaction: 2Ni(OH)2(s) + Zn(OH)2(s) ↔ 2Ni(OH)3(s) + Zn(s).
Note that the stoichiometry above is different than below, but the reactions are identical. Water is consumed and generated on the charge and discharge cycles.
Discharge Reaction: H2O + Zn + 2NiOOH ↔ ZnO +2Ni(OH)2.
Electrochemical open circuit voltage potential: ~1.73 V.
The tendency of the zinc electrode to dissolve into solution and not fully migrate back to the cathode during recharging has, in the past, presented challenges to the commercial viability of the NiZn battery. The zinc's reluctance to fully return to the same location of the solid electrode adversely manifests itself as shape change and dendrites or whiskers, which may reduce the cell discharging performance or eventually short out the cell, resulting in low cycle life.
Recent advancements have enabled manufacturers to prevent this problem. These advancements include improved electrode separator materials, zinc material stabilizers, and electrolyte improvements (using phosphates). One manufacturer (PowerGenix), which has developed 1.6V batteries, has claimed battery cycle life comparable to NiCd batteries.
Battery cycle life is most commonly specified at a discharge depth of 80 percent of rated capacity and assuming a one-hour discharge current rate. If the discharge current rate is reduced, or if the depth of discharge is reduced, then the number of charge-discharge cycles for a battery increases.
When comparing NiZn to other battery technologies, it is important to note that cycle life specifications may vary with other battery technologies, depending on the discharge rate and depth of discharge that were used.
Nickel–zinc cells have an open circuit voltage of 1.8 volts when fully charged  and a nominal voltage of 1.65 V. This makes NiZn an excellent replacement for electronic products that were designed to use alkaline primary cells (1.5 V). NiCd and NiMH both have nominal cell voltages of 1.2 V, which may cause some electronic equipment to shut off prior to a complete discharge of the battery because the minimal operating voltage is not provided.
Due to their higher voltage, fewer cells are required (compared to NiCd and NiMH) to achieve a given battery-pack voltage, reducing pack weight, size and improving pack reliability. They also have low internal impedance (typically 5 milliohms), which allows for high battery discharge rates.
NiZn batteries do not use mercury, lead or cadmium, or metal hydrides that are difficult to recycle. Both nickel and zinc are commonly occurring elements in nature. Zinc and nickel can be fully recycled.
NiZn cells use no flammable active material or organic electrolyte.
Properly designed NiZn cells can have very high power density and low temperature discharging performance.
Currently, only Sub C, AA and AAA NiZn cells are available. Compared with other secondary systems, nickel–zinc cells have lower volumetric energy density. Nickel is also more costly than the lead used in lead-acid batteries.
Known charging regimes include constant current of C or C/2 to cell voltage = 1.9 V. Maximum charge time is 2½ hours. Trickle charging is not recommended, as recombination is not provided for, and excess hydrogen will eventually vent, adversely affecting battery cycle life. Charge is reinitiated after cell voltage has fallen below 1.6 V.
- ^ a b c "Building A Better Battery", Kerry A. Dolan, Forbes.com, Forbes Magazine, 11 May 2009, accessed 2011-02-12, Forbes-44.
- ^ Famous Irish Chemists: James J. Drumm
- ^ a b c David Linden (ed)., Handbook of Batteries, McGraw Hill, 2002, ISBN 0-07-135978-8, chapter 31.
- ^ Evercel financial statement 2007, Evercel.com, page 9, retrieved 23 November 2010.
- ^ Battery-meter-problem, NiZn discharge curves and camera voltage cutoffs, PentaxForums.com
- ^ "A Brief History of Battery Developments", PowerGenix.com, 2010, retrieved 12 February 2011.
- ^  New NiZn batteries offer lightning-fast recycle
- ^ "PowerGenix NiZn Material Safety Data Sheet", PowerGenix.com, accessed=2011-02-12.
- ^ PowerGenix NiZn Quick Charger
- ^ PowerGenix AA Battery Specifications
- PowerGenix Batteries - homepage of PowerGenix (retrieved 2011-02-12)
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