What is a nickel cadmium battery used for?
We have described nimH batteries in detail in previous articles. In addition to nickel-metal hydride batteries, some nickel-metal based batteries are also common in electric devices, such as nickel-cadmium batteries, nickel-zinc batteries and nickel-oxygen batteries.
This article will be dedicated to a detailed explanation of nickel cadmium battery, will introduce the principles, advantages and disadvantages, charging and maintenance methods of nickel cadmium battery.
The application scenario of nickel cadmium battery
Nickel cadmium battery is commonly used as mobile power, such as consumer electronics and small mobile power.
In addition, it also widely used in communications, backup uninterruptible power , and stationary power in trains and trams. About 40% of nickel cadmium battery is used to power lighting, air conditioning, or other electrical components in trains. Nickel cadmium battery has low energy density and remarkable memory effect.
Memory effect usually refers to that the battery has been subjected to a specific charge and discharge amplitude and mode for a long time. Even if the battery is charged and discharged extensively in the future, it can only release the energy of the specific charge and discharge amplitude before (less than the changed charge and discharge amplitude), which seems to “remember” the previous energy.
For these reasons, nickel cadmium battery is ideal for relatively constant applications such as consumer electronics and the rail industry, but rarely for automotive electrification.
Principle of nickel cadmium battery
Nickel cadmium rechargeable battery is the first type of battery to be used in mobile phones, notebook computers and other equipment. It has good high-current discharge characteristics, strong charge-discharge resistance and easy maintenance. The general discharge chemical equation of nickel cadmium battery is as following:
Cd+2NiO(OH)+2H2O=2Ni(OH)2+Cd(OH)2
The reaction is opposite when charging.
The active substance of cathode of nickel cadmium battery is composed of nickel oxide powder and graphite powder. Graphite does not participate in chemical reaction, and its main function is to enhance electrical conductivity. The active substance of anode is composed of cadmium oxide powder and iron oxide powder.
The role of iron oxide powder is to make the cadmium oxide powder have high diffusing ability, prevent caking, and increase the capacity of the plate.
The active substances are wrapped in perforated steel strips, which become cathode and anode of the battery after pressure forming.
The plates are separated by alkali resistant hard rubber insulating rods or perforated PVC corrugated boards.
The electrolyte is usually a solution of potassium hydroxide.
The advantages of nickel cadmium battery
- The cycle life of nickel cadmium battery is about 300~700 times, which can be used for a long time;
- Compared with other batteries, it is cheaper and economical;
- Made of metal containers, it is very strong;
- Nickel cadmium batterycan discharge in a wide temperature range, the temperature range between -20℃~60℃;
- Because of the small internal resistance, nickel cadmium battery can be used for high current discharge, and the voltage change is very small during discharge;
- Completely sealed, no need to maintain;
- The performanceof nickel cadmium battery will not be greatly affected under the condition of overcharging or over discharging and it has strong resistanceto over charge and over discharge .
The disadvantages of nickel cadmium battery
The most fatal drawback of nickel cadmium battery is that if they are not handled properly during charging and discharging, serious “memory effect” will occur, which will greatly shorten their service life.
Like we described earlier in this article, the so-called “memory effect”, in short, happens when the power of the battery is not completely discharged before charging, which will cause the reduction of the battery capacity over time.
In the process of the battery charge and discharge(discharge is more obvious), it will produce some small bubbles on the battery plate, over a long period the bubbles that accumulate reduce the surface area of the battery plate and also indirectly affect the capacity of the battery.
If a nickel cadmium battery is not fully discharged and then recharged, it will not be able to discharge its full charge the next time, such as when it is fully charged after discharging 80% of its charge, which is called the memory effect. Of course, we can reduce the “memory effect” by mastering the proper charging and discharging methods.
Another drawback is that during charging and discharging, the cathode grows needle-like crystals of cadmium, sometimes penetrating the separator and causing internal dendritic crystal short circuits. In addition, cadmium is toxic, because nickel cadmium battery contain cadmium, which must be recycled after use.
So nickel cadmium battery is not conducive to the protection of ecological environment.
The use and maintenance method of nickel cadmium battery
The key to improve battery performance and prolong battery life is to avoid memory effect. Therefore, in the process of using nickel cadmium battery, attention should be paid to:
1. After normal use, it is necessary to discharge until completely out of power before charging, so as to ensure the service life.
2. After about 10 charge and discharge cycles, a complete discharge and overcharge can be carried out to prevent the memory effect. The method of overcharging is to prolong the charging time than the normal charging time about twice, to reduce the memory effect.
3, battery charge and discharge should be as far as possible according to the maintenance method of operation, do not overcharge, over discharge or often undercharge. And try not to interrupt in the charging process, wait until the one-time charge is completed and then disconnect the power supply. When the battery is used after a long time, it should be fully charged first.
Do not: incomplete discharge, long-term small current deep discharge or short circuit during battery use are important factors that cause battery capacity reduction and shortened life. For a long time, improper operation will not only affect the use, but also will inevitably affect the capacity and life of the battery.
Other nickel-metal based batteries
Other nickel-metal based batteries, such as nickel-zinc batteries and nickel-oxygen batteries, also have mature applications. Nickel-zinc batteries are used in power tools, lawn and garden machines, light electric vehicles, consumer electronics, and some hybrid electric vehicles.
Compared with other nickel-metal batteries, the self-discharge rate and cost of nickel-zinc batteries are relatively low, and more importantly, the nickel-zinc batteries have less environmental pollution than nickel pot and nickel-metal hydride batteries.
Nickel metal hydride gas battery (NiH2) is widely used in aerospace field, among which low Earth orbit and geosynchronous satellite are typical representatives. Despite their high cost and relatively low energy density, nimH batteries have a long cycle and calendar life.
Low Earth orbit satellites usually need 3500 cycles and 6 years of calendar life. Geostationary satellites require a lower cycle life of about 2000 cycles, but the calendar life is as high as 20 years. Nickel-metal hydride batteries have irreplaceable advantages in this special field.
Although other similar nickel-metal batteries have been developed and applied, their advantages are not superior to the existing nickel-cadmium, nickel-hydrogen, nickel-zinc and nickel-hydrogen batteries on the market.
