Nickel-cadmium battery performance characteristics

Each battery system has its own characteristics in terms of high-power performance. Lead-acid and nickel-cadmium batteries show relatively low power outputs. However, lithium-ion batteries and nickel-metal hydride batteries exhibited good power performance even when they appeared at the early stages of their commercialization. 

The characteristics of nickel/metal hydride batteries are very similar to those of sealed nickel/cadmium batteries. The cell voltage differs by only 20 mV, and charging as well as discharging performance are so alike that both battery systems can be replaced by each other in all normal applications. The discharge curves in Fig. 1.38 confirm this. 

The silver-cadmium (cadmium/silver oxide) battery has significantly longer cycle life and better low-temperature performance than the silver-zinc battery but is inferior in these characteristics compared with the nickel-cadmium battery. Its energy density, too, is between that of the nickel-cadmium and the silver-zinc batteries. The battery is also very expensive, using two of the more costly electrode materials. As a result, the silver-cadmium battery was never developed commercially but is used in special applications, such as nonmagnetic batteries and space applications. Other silver battery systems, such as silver-hydrogen and silver-metal hydride couples, have been the subject of development activity but have not reached commercial viability. 

The effect of temperature and discharge rate on the capacity of a sealed nickel-cadmium battery is shown in Fig. 28.12. These data are typical of standard batteries. Manufacturers should be contacted to obtain performance characteristics of specific batteries. 

The service life of a sealed nickel-cadmium battery, normalized to unit weight (kilograms) and size (liters), at various discharge rates and temperatures is summarized in Fig. 28.15. The curves are based on a capacity, at the C/5 discharge rate at 2(fC, of 30 Ah/kg and 85 Ah/L, reflecting the performance of standard-type sealed cylindrical batteries. Manufacturers should be contacted for performance characteristics of specific batteries. 

The discharge characteristics of the nickel-cadmium battery under the constant-power mode, at several different power levels, are shown in Fig. 28.18. These are similar to the data presented in Fig. 28.7 for constant-current discharges, except that the performance is presented in hours of service instead of percent discharge capacity. The power levels are shown based on the -rate. The -rate is calculated in a manner similar to calculating the C-rate, but based on the rated watthour capacity. For example, for the E/5 power level, the power for a battery rated at 780 mWh is 156 mW. 

Special-purpose sealed nickel-cadmium batteries are manufactured with specifically designed characteristics, overcoming some of the limitations of standard batteries, to meet the requirements for certain applications. Manufacturers recommendations should be followed because of the specific performance characteristics of these batteries. 

Figure 2.8 shows the charge characteristics when charging is performed at a constant current In nickel-cadmium batteries, characteristics such as cell voltage, internal gas pressure, and cell temperature vary during charging, depending... 

Performance characteristics of sealed lithium—molybdenum disulphide cells are compared with those sealed cylindrieal sintered plate nickel-cadmium batteries in Table 9.15. 

The wide applicability and range of sealed nickel-cadmium batteries is a result of their remarkable performance characteristics, some features of which are ... 

Since portable computers have unique characteristics as a result of the portability, they have unique accessories as well. First of all, portable computers can use either of two power sources batteries or AC power. There are many different sizes and shapes of batteries, but most of them are either Nickel-Cadmium (NiCad), Lithium Ion, or Nickel Metal Hydride (NiMH). All of these perform equally well as batteries, but NiCad batteries can only be recharged a finite number of times. After a time, they develop a memory and must be recharged on a special deep charging machine. NiMH and Lithium Ion batteries don t normally develop a memory and can be recharged many times, but they re a little more expensive. 

The vented-type battery needs to perform water addition in which water consumed by electrolysis is periodically added. However, in recent years, the vented-type nickel-cadmium secondary battery which has reduced the water addition frequency is produced commercially for trains and the like. The battery controls the electrolysis of the water under float charging by using the pasted-type cadmium electrode which has a high hydrogen overpotential characteristic for the negative electrode. 

A more recent design that has shown significantly improved performance characteristics is the plastic-bonded or pressed-plate electrode. This new development of electrode materials in industrial batteries is a spin-off from the development of electrode materials for use in aircraft and sealed portable consumer batteries. In the plastic-bonded plate, which is mainly used in the cadmium electrode, the active material cadmium oxide is mixed with a plastic powder, normally PTFE, and a solvent to produce a paste. The paste is isotropic and the materials are manufactured at the final density for the active material. As a result, dust problems are eliminated during manufacturing. The paste is extruded, rolled, or pasted onto a center current collector normally made of nickel-plated perforated steel. The plate stmcture is welded to nickel-plated steel tabs. 

Each cf these two nain types of battery has its own advantages and the choice between nickel-cadmium and lead-acid batteries depends veiy much on the particular application and on the performance characteristics required. 

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