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Advantages of nickel cadmium batteries: high efficiency, light body, long driving range, and low requirements for user use and maintenance. Disadvantages: high price, uneven domestic lithium battery technology, and safety hazards for lithium batteries used in electric vehicles. Advantages of lead-acid batteries: high cost-effectiveness. The battery price is relatively cheap, the capacity is large, and there are many brands of batteries to choose from, with mature technology. Disadvantages: low efficiency. The battery pack is bulky, resulting in a heavy body weight and short driving range, and the battery needs to be maintained on schedule. Overall, lithium batteries are better. I hope my answer can help you.

Nickel cadmium battery is an alkaline battery in which the positive electrode active material is mainly made of nickel and the negative electrode active material is mainly made of cadmium. The positive electrode is nickel hydroxide, the negative electrode is cadmium, and the electrolyte is potassium hydroxide solution. Its advantages are lightweight, earthquake resistant, and long lifespan, commonly used in small electronic devices.

The positive electrode material of nickel cadmium batteries is a mixture of nickel hydroxide and graphite powder, and the negative electrode material is a sponge mesh like cadmium powder and cadmium oxide powder. The electrolyte is usually sodium hydroxide or potassium hydroxide solution. When the ambient temperature is high, use a sodium hydroxide solution with a density of 1.17-1.19 (at 15 ℃). When the ambient temperature is low, use a potassium hydroxide solution with a density of 1.19-1.21 (at 15 ℃). Use potassium hydroxide solution with a density of 1.25~1.27 (at 15 ℃) below -15 ℃. To balance low-temperature performance and charge retention capability, sealed nickel cadmium batteries use potassium hydroxide solution with a density of 1.40 (at 15 ℃). In order to increase the capacity and cycle life of the battery, a small amount of lithium hydroxide is usually added to the electrolyte (approximately 15-20 g per liter of electrolyte).

After charging a nickel cadmium battery, the active material on the positive electrode plate becomes nickel hydroxide [NiOOH], and the active material on the negative electrode plate becomes metallic cadmium; After discharging the nickel cadmium battery, the active material on the positive electrode plate becomes nickel hydroxide, and the active material on the negative electrode plate becomes cadmium hydroxide.

Chemical reactions during discharge process

(1) Negative electrode reaction

The cadmium on the negative electrode loses two electrons and becomes divalent cadmium ion Cd2+, which immediately combines with two hydroxide ions OH - in the solution to form cadmium hydroxide Cd (OH) 2, which is deposited on the negative electrode plate.

(2) Positive electrode reaction

The active material on the positive electrode plate is nickel hydroxide (NiOOH) crystal. Nickel is a trivalent ion (Ni3+), and every two nickel ions in the lattice can obtain two electrons transferred from the negative electrode in the external circuit, generating two divalent ions 2Ni2+. At the same time, every two water molecules in the solution ionize two hydrogen ions, which enter the positive electrode plate and combine with two oxygen negative ions on the lattice to generate two hydroxide ions. Then, together with the original two hydroxide ions on the lattice, they combine with two divalent nickel ions to form two nickel hydroxide crystals.

Chemical reactions during the charging process

When charging, connect the positive and negative poles of the battery to the positive and negative poles of the charger respectively. The electrochemical reaction inside the battery is completely opposite to that during discharge, that is, the negative pole undergoes a reduction reaction and the positive pole undergoes an oxidation reaction.

(1) Negative electrode reaction

During charging, cadmium hydroxide on the negative electrode plate ionizes into cadmium ions and hydroxide ions. The cadmium ions then obtain electrons from the external circuit, generating cadmium atoms that attach to the electrode plate. The hydroxide ions enter the solution and participate in the positive electrode reaction.

(2) Positive electrode reaction

Under the action of an external power source, in the lattice of nickel hydroxide on the positive electrode plate, two divalent nickel ions each lose one electron to generate trivalent nickel ions. At the same time, each of the two hydroxide ions in the lattice releases a hydrogen ion, leaving the oxygen negative ion on the lattice. The released hydrogen ion combines with the hydroxide ion in the solution to form water molecules. Then, two trivalent nickel ions combine with two oxygen anions and the remaining two hydroxide ions to form two nickel hydroxide crystals.

At the end of battery charging, the charging current will cause a water splitting reaction inside the battery, resulting in the release of a large amount of oxygen and hydrogen gas on the positive and negative plates, respectively. From the above electrode reaction, it can be seen that sodium hydroxide or potassium hydroxide does not directly participate in the reaction, but only plays a conductive role. From the perspective of battery reactions, water molecules are generated during the charging process and consumed during the discharging process. Therefore, the electrolyte concentration changes very little during the charging and discharging processes, and the degree of charge and discharge cannot be detected by a density meter.

terminal voltage

After being fully charged, immediately disconnect the charging circuit. The electromotive force of the nickel cadmium battery can reach around 1.5V, but soon drops to 1.31-1.36V. The terminal voltage of nickel cadmium batteries varies with the charging and discharging process, which can be expressed by the following equation:

U Charge=E Charge+I Charge R

U=E=I=R

From the above equation, it can be seen that the terminal voltage of the battery is higher during charging than during discharging, and the higher the charging current, the higher the terminal voltage; The larger the discharge current, the lower the terminal voltage.

When nickel cadmium batteries are discharged at standard discharge current, the average operating voltage is 1.2V. When discharging at an 8-hour rate, the terminal voltage of the battery drops to 1.1V, and the battery is discharged.

Capacity and influencing factors

After the battery is fully charged, under certain discharge conditions, when it reaches the specified termination voltage, the total capacity discharged by the battery is called the rated capacity of the battery. The capacity Q is expressed as the product of the discharge current and the discharge time, expressed as follows:

Q=I·t(Ah)

The capacity of nickel cadmium batteries is related to the following factors:

① The quantity of active substances;

② Discharge rate;

③ Electrolyte.

The discharge current directly affects the discharge termination voltage. At the specified discharge termination voltage, the larger the discharge current, the smaller the capacity of the battery.

The use of electrolytes with different compositions has a certain impact on the capacity and lifespan of batteries. Usually, in high-temperature environments, a small amount of lithium hydroxide is added to the electrolyte to form a mixed solution in order to increase battery capacity. Experimental results have shown that adding 15-20 g of aqueous lithium hydroxide per liter of electrolyte can increase the capacity by 4% to 5% at room temperature and 20% at 40 ℃. However, excessive lithium ion content in the electrolyte not only increases the resistance of the electrolyte, but also allows lithium ions (Li+) remaining on the positive electrode plate to slowly infiltrate into the lattice, causing harmful effects on the chemical changes of the positive electrode.

The temperature of the electrolyte has a significant impact on the capacity of the battery. This is because as the electrolyte temperature increases, the chemical reaction of the active material on the electrode plate gradually improves. The more harmful impurities in the electrolyte, the smaller the capacity of the battery. The main harmful impurities are carbonates and sulfates. They can increase the resistance of the electrolyte and easily crystallize at low temperatures, blocking the micropores of the electrode plate and significantly reducing the capacity of the battery. In addition, carbonate ions can also interact with the negative electrode plate, generating cadmium carbonate that adheres to the surface of the negative electrode plate, causing poor conductivity and increasing the internal resistance and capacity of the battery.

internal resistance

The internal resistance of nickel cadmium batteries is related to the conductivity of the electrolyte, the structure and area of the electrode plates, while the conductivity of the electrolyte is related to density and temperature. The internal resistance of a battery is mainly determined by the resistance of the electrolyte. The resistivity of potassium hydroxide and sodium hydroxide solutions varies with density. The electrical resistivity of potassium hydroxide solution and sodium hydroxide solution is the smallest at 18 ℃.

Efficiency and lifespan

Under normal usage conditions, the capacity efficiency η Ah of nickel cadmium batteries is 67% -75%, the electrical energy efficiency η Wh is 55% -65%, and the cycle life is about 2000 times.

The calculation formulas for capacity efficiency η Ah and electrical energy efficiency η Wh are as follows:

I release · t release

ηAh=----------X100%

I charge · t charge

U release, I release, t release

ηAh=---------------X100%

U Charge · I Charge · t

(The average voltage should be taken for U charging and U discharging)

memory effect 

During the use of nickel cadmium batteries, if the battery is not fully discharged before charging, the next time it is discharged, it will not be able to fully discharge its battery. For example, nickel cadmium batteries start charging after only releasing 80% of their charge, and when fully charged, the battery can only release 80% of its charge. This phenomenon is called the memory effect.

After the battery is fully discharged, the crystals on the plates are very small. After partial discharge of the battery, nickel hydroxide does not completely transform into nickel hydroxide, and the remaining nickel hydroxide will combine together to form larger crystals. The enlargement of crystals is the main reason for the memory effect in nickel cadmium batteries.

general comparison

Nickel cadmium batteries can be charged quickly and have a longer cycle life, more than twice that of lead-acid batteries, reaching over 2000 cycles, but at a price 4-5 times that of lead-acid batteries. Although its initial purchase cost is high, its long-term actual usage cost is not high due to its advantages in color capacity and service life. But proper recycling is necessary during use, otherwise heavy metal cadmium can pollute the environment.

Nickel hydrogen batteries, like nickel cadmium batteries, are also alkaline batteries with similar characteristics to nickel cadmium batteries. However, nickel hydrogen batteries do not contain cadmium or copper, and there is no problem of heavy metal pollution.

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