Charging nickel-zinc batteries

Fully charged nickel-zinc batteries lose only about 20% of their original capacity within a month on open-circuit stand at 25°C. The self-discharge rate of nickel-zinc, like that of most batteries, increases with temperature. 

Temperature Dependence of Performance. Temperature has a strong influence on battery performance. As a general rule of thumb, nickel-based batteries achieve optimal performance when charged cold and discharged warm. Unfortunately, in many applications, temperature is ambient and uncontrolled. Figure 31.12 shows the effect of temperature on the discharge capacity of the nickel-zinc battery at four different rates. At lower rates, the discharge capacity is a linear function of temperature. At the 6C rate, the relationship starts to become nonlinear, primarily due to the increased conductivity of the electrolyte above 30°C. 

It should be stressed that the manufacturer s recommendations should be strictly adhered to in charging any battery. Excessive overcharge, current which is too high or too low, or the use of an inappropriate charging algorithm may result in reduced performance, reduced cycle life and potential safety hazards. Use only a charger specifically designed for the nickel-zinc battery. 

FIGURE 31.17 Seven-cell, 30 Ah nickel-zinc battery charge profile at room temperature. C/1.75 charge to... 

FIGURE 31.18 EOC voltage as a function of charging current and temperature for a 30 Ah single-cell nickel-zinc battery. Courtesy of Eve reel Corp.)... 

Batteries may produce potentially explosive gases, particularly near the end of charge or when over-discharged. Any battery which has a safety relief vent has the potential for venting hydrogen or other explosive gases. The nickel-zinc battery presents no special hazard in this respect compared to other batteries which are capable of venting. 

Nickel—2iiic batteries containing a vibrating zinc anode lias been reported (83). In this system zinc oxide active material is added to the electrol 1 e as a slurry. During charge the anode substrates are vibrated and the zinc is electroplated onto the surface in a unifomi mamier. Tlie stationary positive electrodes (nickel) are encased in a thin, open plastic netting which constitutes the entire separator system. 

It must be emphasized that the most appropriate charging regime is very dependent on the cell system under consideration. Some are tolerant to a considerable amount of overcharging (e.g. nickel-cadmium batteries), while for others, such as zinc-silver oxide and most lithium secondary cells, overcharging can result in permanent damage to the cell. Sealed battery systems require special care float charging should not be used and trickle charge rates should be strictly limited to the manufacturer s recommended values, since otherwise excessive cell temperatures or thermal runaway can result. 

The nickel-based systems have traditionally included the following systems -nickel-iron (Ni/Fe), nickel-cadmium (NiCd), nickel metal hydrides (NiMH), nickel hydrogen (Ni/H2), and nickel-zinc (Ni/Zn). Of these, the metal hydride chemistry has been the most successful in the secondary battery market. AU nickel systems are based on the use of a nickel oxide active material (undergoing one valence change from charge to discharge or vice-versa). The electrodes can be pocket type, sintered type, fibrous type, foam type, pasted type, or plastic roll-bonded type. All systems use an alkaline electrolyte, KOH. 

Spanos C, Turney DE, Fthenakis V (2015) Life-cycle analysis of flow-assisted nickel zinc-, manganese dioxide-, and valve-regulated lead-acid batteries designed for demand-charge reduction. Renew Sustain Energy Rev 43 478-494. doi 10.1016/j.rser.2014.10.072... 

For instance, the nickel-iron battery, invented almost at the same time (Edison, 1901) as the nickel-cadmium battery, has a poor charge efficiency, which causes excessive heating and hydrogen release. Another example is nickel-zinc technology, for which further study seems necessary, because it is subject to the formation of dendrites which limit its lifetime. 

Figure 6.14 shows the distribution of current in another example of a zinc/air, nickel-cadmium hybrid battery, this one designed to handle a transmit load for 2 minutes at 900 mA and a receive load of 50 mA for 18 minutes, similar to the application illustrated in Fig. 6.9. During the receive period, the load is carried by the zinc/air battery which, at the same time, charges the nickel-cadmium battery. During the transmit period, the load is carried by both batteries.

---