Understanding Nickel-Cadmium Batteries: Function, Application, and Environmental Impact

what is nicd battery ?

Nickel-cadmium batteries generate direct current through chemical reactions of their internal components. The core of these batteries consists of redox reaction materials, surrounded by nickel plates and separators. A single nickel-cadmium cell provides about 1.2 volts of voltage. By connecting three to four such cells in series, a voltage output of 3.6 to 4.8 volts can be obtained. This configuration makes nickel-cadmium batteries suitable for a variety of electronic devices.

Functioning of Nickel Cadmium Batteries | NiCd Batteries

I.what is nickel cadmium cell ?

DC voltage triggers, a technology based on nickel-cadmium batteries, are gradually replacing traditional lead-acid batteries. These batteries are popular in various fields in recent years due to their lightweight, ease of carrying, and transportation. Toys, calculators, and tiny DC motors frequently use them. 

The working principle of nickel-cadmium batteries is similar to that of lead-acid batteries, generating DC voltage through redox reactions of metals, cadmium, and a separator layer. With technological advancements, to enhance battery efficiency, designers are exploring the possibilities of more chemical elements, making the battery structure more compact and efficient. 

The nickel-cadmium battery has redox reactive substances at its core, surrounded by nickel plates and separators, with a single cell voltage of about 1.2 volts. If three to four cells are connected in series, the output voltage can reach 3.6 to 4.8 volts, meeting broader usage requirements. This configuration not only enhances the battery's applicability but also increases its practicality in various application scenarios.

II. Voltage Composition of Nickel-Cadmium Batteries

The working principle of nickel-cadmium batteries is similar to other batteries, using nickel (Ni) and cadmium (Cd) to enhance their performance. As a source of direct current voltage, the battery requires an anode and a cathode. In nickel-cadmium batteries, the anode is made of a cadmium layer, and the cathode consists of a nickel oxide (NiO2) layer, which is covered over the redox active layer. A separator soaked in KaOH is placed above the nickel oxide layer to provide the necessary OH- ions for the chemical reaction.
The anode collector is the layer of nickel, and the cathode collector is the layer of cadmium. KOH or NaOH is utilized as a separator layer between these layers, primarily to supply OH- ions. A safety valve, sealing pad, insulation ring, insulation spacer, and casing are all included in the battery's packing. The insulation ring and spacer are used to maintain the distance between the anode and cathode and provide necessary insulation to prevent short-circuiting. The design of the casing is intended to protect the internal structure of the battery from external factors such as battery failure or mishandling.
The entire battery structure is similar to that of lead-acid batteries, containing three main layers: the nickel layer, separator layer, and cadmium layer. Once the battery is assembled, it is usually not opened to ensure all layers are visible and safe. When the gadget is not in use, it is advised to remove the battery to maintain safety because of the chemical processes occurring inside the battery. A schematic diagram of the nickel-cadmium battery is provided below.

Nickel-Cadmium Battery Equation

In nickel-cadmium batteries, the electrochemical reaction involves the redox process of nickel and cadmium. The primary processes that occur during charging and discharging are explained by the chemical equations you supplied. Here is a correction and detailed explanation of the equations you listed:

1. Cathode reaction (during discharge, reverse for charging):

2NiOOH + 2H2O + 2e- => 2 Ni(OH)2 + 2 OH-
In this reaction, divalent nickel oxide (NiOOH) is reduced to nickel hydroxide (Ni(OH)2) with the involvement of electrons, while hydroxide ions (OH-) are generated.

2. Anode reaction (during discharge, reverse for charging):

Cd + 2 OH- => Cd(OH)2 + 2e-
Here, cadmium (Cd) reacts with hydroxide ions to form cadmium hydroxide (Cd(OH)2) and releases electrons.

3. Overall reaction:

2NiOOH + Cd + 2H2O <-> 2 Nickel (OH)2 + Cd (OH)2
This equation demonstrates the reaction between nickel and cadmium during the entire discharge process, involving water as a reaction medium.
These reactions form the basis of the operation of nickel-cadmium batteries, transferring electrons between the two electrodes to produce current. During the charging process, these reactions occur in reverse, restoring the initial chemical state.

III. Voltage Characteristics of Nickel-Cadmium Batteries

Nickel-cadmium batteries are a classic type of rechargeable battery, featuring the following characteristics:

1. Temperature Range

- The charging temperature range is between 0 and 45 degrees Celsius. Exceeding this range may prevent the battery from charging normally and even pose an explosion risk.
-20 to 65 degrees Celsius is the temperature range at which discharge occurs. Within this temperature range, the battery can safely discharge.

2. Toxicity

Cadmium is a hazardous heavy metal that is present in nickel-cadmium batteries and is very dangerous for human health. Cadmium concentrations in the human body are usually very low (about 1 microgram per liter), but it can directly damage the digestive and respiratory systems.

3. Voltage and Energy Efficiency

- Single cell voltage: about 1.2V. Depending on the voltage requirements, batteries can be configured in either series or parallel connections.
- Energy density: about 50-60Wh per kilogram of battery, between nickel-iron and nickel-metal hydride batteries.
- Specific power: about 200W, higher than nickel-iron batteries, but lower than nickel-metal hydride and nickel-zinc batteries.

4. Types and Sizes

Nickel-cadmium batteries come in various sizes, such as AAA, AA, A, C, D, F, etc., usually with cylindrical and rectangular casings. Each size of battery has its specific output voltage and capacity.

5. Nickel-Cadmium Battery Benefits and Drawbacks

① Benefits

- Delivering a large amount of current: Nickel-cadmium batteries can provide a high current in a short time, suitable for devices requiring high power output.
- Tolerance to overcharging: Compared to other battery types, nickel-cadmium batteries have a higher tolerance to overcharging, making them practical in some commercial and industrial applications.
- Cycle life: Nickel-cadmium batteries can handle up to 500 charge cycles, providing sufficient life span for many applications.
② Disadvantages
- Environmental issues: Nickel-cadmium batteries contain cadmium, a toxic metal that poses potential hazards to the environment and human health. This has caused its usage to be restricted or outright prohibited in numerous nations and areas.
- Poor temperature resistance: Compared to other types of batteries (such as lithium-ion batteries), nickel-cadmium batteries have lower temperature resistance, limiting their application in extreme temperature environments.

IV. Operating Principle of Nickel-Cadmium Battery Voltage

The operating principle of nickel-cadmium batteries is based on the chemical reactions between layers. The battery, which has anode and cathode connections, is a source of direct current. When manufacturing the battery, the conductive heavy metal cadmium coating is maintained in a redox state. The separator layer is positioned above the cadmium layer, which serves as the cathode terminal. The separator layer's job is to supply the OH- ions required for the chemical reaction by drawing them from the water that the layer is submerged in. The cadmium layer reacts with the OH- ions coming from the anode side of the separator layer, producing cadmium oxide and electrons, while the nickel layer produces nickel oxide.
During the charging process, the battery's anode nickel hydroxide is reduced to a higher valence state of nickel hydroxide, while the cathode's cadmium is oxidized. During discharge, these reactions reverse, with nickel at the anode being oxidized and cadmium at the cathode being reduced, thus releasing electrical energy. These chemical reactions proceed smoothly with the help of the electrolyte, whose main function is to transfer ions, maintaining the internal charge balance of the battery. Through these complex chemical processes, nickel-cadmium batteries can provide stable and reliable power.

V.Appendix

1.Environmental Impact and Recycling

Nickel-cadmium batteries have significant environmental concerns primarily due to the toxicity of cadmium. Cadmium is a heavy metal with serious environmental and health implications if not properly handled or disposed of. These batteries are considered hazardous waste and must be recycled or disposed of correctly to prevent cadmium from leaching into the soil and water systems, which can be detrimental to wildlife and human health.
Method of Recycling:
① Gathering and Delivery: Spent NiCd batteries are gathered and delivered to recycling centers.
②Battery Disassembly: Batteries are mechanically or manually disassembled to separate plastics, metals, and other materials.
③ Metal Recovery: Cadmium and nickel are recovered through processes like pyrometallurgical treatment or hydrometallurgical operations.
④ Purification: Recovered metals are purified for reuse in new batteries or other applications.

2.Comparison with Other Rechargeable Batteries

Comparing NiCd batteries with other types of rechargeable batteries can highlight their relative strengths and weaknesses:
①NiCd vs. NiMH (Nickel-Metal Hydride):
- Energy Density: NiMH batteries frequently have higher energy densities than NiCd batteries.
- Memory Effect: Both types exhibit memory effects, but it is more pronounced in NiCd batteries.
- Environmental Impact: Because poisonous cadmium is absent from NiMH batteries, they have a lower environmental impact than NiCd batteries.
②NiCd vs. Li-ion (Lithium-ion):
- Voltage: Li-ion batteries provide higher voltage per cell (approximately 3.6V) compared to 1.2V for NiCd batteries.
- Energy Density: Li-ion batteries have much higher energy densities than other types of batteries, which enables extended use between charges.
- Maintenance: Li-ion batteries require less maintenance and are more stable at higher temperatures than NiCd batteries.
③NiCd vs. Lead-Acid:
- Weight: NiCd batteries are lighter than lead-acid batteries, making them more suitable for portable applications.
- Cost: Lead-acid batteries are generally cheaper per watt-hour than NiCd batteries.
- Maintenance: Both types require maintenance, but lead-acid batteries are more sensitive to deep discharge cycles.

3.Future Developments

Research is ongoing to improve the efficiency, capacity, and environmental friendliness of NiCd batteries. This includes exploring alternative materials to replace cadmium and innovations in battery design to enhance performance and reduce costs. Additionally, there's an increasing focus on developing more robust recycling technologies to recover more materials and reduce environmental impacts.

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Common Questions

1. How long do Ni-Cd batteries last?
The lifespan of Ni-Cd batteries varies depending on usage and maintenance, but they typically offer many charge/discharge cycles and can last up to 20 years in solar battery applications.
2. What advantages can Ni-Cd batteries provide?
Ni-Cd batteries deliver high current output, are relatively tolerant of overcharging, and can withstand up to 500 charging cycles. They are preferred in applications needing long-term, high-discharge rates and are generally more affordable in certain industrial uses.
3. What are the environmental impacts of Ni-Cd batteries?
Cadmium, a hazardous heavy metal found in Ni-Cd batteries, can harm the environment if it is not disposed of appropriately. However, they can be recycled to mitigate these environmental risks.
4. What applications commonly use Ni-Cd batteries?
Ni-Cd batteries are used in various applications including two-way radios, professional video cameras, power tools, emergency lighting systems, and backup power for telecommunications and solar power systems.
5. How does temperature affect Ni-Cd batteries?
Ni-Cd batteries perform well across a wide range of temperatures, but exposure to high temperatures can lead to premature failure by weakening the battery's internal components.