Page 131 - Battery Reference Book

Nickel-zinc secondary batteries 4/15
system. Good capacity retention (up to 6 months) has the highest available in alkaline batteries). wide
made the nickel-zinc battery a more direct competi- temperature tolerances (-39 to $8 1°C operating
tor of the silver-zinc and silver-cadmium systems. temperature, -53 to +73"C storage temperature),
Nickel-zinc batteries are available from only a limited moderate cycle life (150 cycles maximum), and
number of suppliers (e.g. Medicharge, UK). Yardney recycle flexibility. Eagle Picher claim that, with further
have pioneered the development of the nickel-zinc improvements in design, coupled with a lowering of
couple for electric traction, and a number of road unit costs through mass production, the nickel-zinc
vehicles that axe now operating are powered by Yard- battery holds promise of the lowest potential
ney nickel-zinc experimental batteries. If development production cost per unit of energy supplied. The
work is successful. the nickel-zinc battery will be batteries have high-rate low-temperatwe capabilities,
a useful contender for electric vehicle propulsion in a flat discharge voltage for a large portion of the
that it will offer a significant performance improve- discharge, which is maintained over a wide current
ment over Peatl-acid at a modest increase in price. range, and can be left fully discharged for long periods
Of particular importance in the consolidation of the without deterioration. These batteries are claimed to
design of this battery is the effect of charging on have an excellent shelf life even when wet and a charge
cell performance, on frequency of reconditioning and retention of 60% for 30 days. Charging is non-critical
on battery cycle life. Certain techniques have been and is carried out for 4h at constant current until
identified by Yardney that have a favourable effect the voltage rises to 2.1 V, when charging is stopped.
on these parameters. The main characteristics of the The batteries can be fully recharged with 10-15%
nickel-hydrogen battery are listed in Table 4.10. overcharge.
Eagle Picher offer a range of vented nickel-zinc The basic cell reaction is:
batteries in the capacity range 2-35Ah. These 2NiOOH + Zn + 2HzO + Ni(OH), + Zn(OH),
are commerciadly available and are particularly re- (4.1)
commended for field communication power supplies. Until recently one company (Yardney) offered a range
They are recommended for use whenever one or of vented nickel-zinc cells in the capacity range 2 to
more of the following characteristics are required: 3.5 Ah at a working voltage of 1.6 V per cell. Typical
high voltage 1(1.5-1.6 V working voltage per cell, characteristics of a .5 Ah nickel zinc battery are shown

Table 4.10 Characteristics of Yardney nickel-zinc batteries

Theoretical energy density 374 w h/kg
Practical energy density 44-77 W hkg and 79- 134 W h/dm3 depending on cell model and conditions of use
Open-circuit cell voltage 1.75-1.8 V (Le. the highest operating voltage of any of the alkaline batteries)
Nominal voltage under load 1.6V
Voltage regulation 55% at a fixed load and temperature limits within &5"C
Recommended discharge 1.ov
cut-off voltage
Cycle life Dependent on model and conditions of use; typical number of complete
charge/discharge cycles obtainable:
Depth of discharge(%) Approx. cycles
95-75 100-200
75-50 200-400
50-25 over 400
Wet life Up to 3 years when manufacturer's recommended charge and discharge rates are
used and operating and storage temperatures do not exceed 37°C
Dry storage life Up to 5 yeas
Gassing on discharge or stand Slight
Operational temperature +73 to -21°C; down to -53°C with heaters; for optimum cell performance, from
range 156 to -45°C
Storage temperature range Wet, +37 to -47°C; dry +73 to -64°C
Operating attitude In any position although, for optimum service, upright is recommended
Internal resistance Very low; varies with cell model, temperature and rate of discharge
Resistance to mechanical stress Excellent, extremely rugged. leakproof and spillproof. Construction similar to design
of Yardney Silvercel batteries which have met the stringent requirements of Spec.
MIL E-5272A. Can be packaged to meet the most severe requirements
Charging time Can be fully iecharged within 10-20 h, depending on requirements and type of cell
Charge retention Up to 70% of nominal capacity after 6 months charged stand at room temperature