alkaline battery

Basic structure and working principle of alkaline battery

Alkaline batteries are mainly iron nickel and cadmium nickel batteries. Taking cadmium nickel alkaline batteries as an example, its structure is shown in the figure below.

Structure diagram of cadmium nickel battery

Cadmium nickel series batteries are generally represented by the following symbols

Nickel cadmium battery symbol

Among them, (-) represents the negative pole of the current, and the active material of the charged negative pole is Jin; (10) Indicates the positive pole of the battery, and the active material of the positive pole in the charged state is Jin hydroxide; Koh (H2O) indicates that the electrolyte is an aqueous solution of potassium hydroxide; The vertical line represents the interface between solid cadmium and nickel hydroxide and electrolyte.

The positive grid and negative grid of nickel cadmium battery are punched steel strips, and then sintered onto the punched steel strips with carbonyl nickel powder at high temperature to become punched nickel plated steel strips. Then impregnate nickel hydroxide respectively to make positive and negative plates. The electrolyte is 20% – 30% Koh, and the relative density is 1.28 ± 0.01; The number of positive and negative plates is equal, and the middle cadmium plate is made of rubber liquid or polypropylene Microfiber (0.25mm thick); The shell is stamped from high-quality steel plate and plated with brocade; The battery cover sealing plate adopts hydrogen arc welding (engineering plastic shell is also used now). The voltage of its single battery is 1.25V, and the discharge termination voltage is generally set at 1.1V.

The change of oxidation or reduction and the transfer of electrons of the active substances on the electrode are expressed by chemical symbols, which is the electrochemical reaction formula of the electrode. The combination of the reaction formulas of the two electrodes is the chemical reaction equation occurring in the battery.

The reaction formula of electrode during discharge is:

Electrode reaction formula during discharge

The discharge reaction formula is obtained by adding the above two formulas:

Discharge reaction

The reaction formula of electrode during charging is:

Electrode reaction formula during charging

The discharge reaction formula is obtained by adding the above two formulas:

Discharge reaction

From the charging reaction formula, the function of charging is to restore the discharged active substances cadmium hydroxide and nickel hydroxide to the state before discharge, that is, cadmium and nickel hydroxide. The discharge reaction formula and the charging reaction formula are reversible, which together are:

Discharge reaction and charging reaction are reversible

The above formula is the equation of chemical reaction of cadmium nickel battery. If it is made into a battery, the chemical energy of the reaction will be converted into electrical energy. If it is not made into a battery, the chemical energy of the reaction will become heat.

When the battery is discharged, the negative active material cadmium gives two electrons, which are combined with two hydroxyl ions (2oh-) in the electrolyte to generate a hydrogen oxidation pot (CD (OH) 2). The two electrons flow out of the negative electrode and pass through the load of the external circuit to the positive electrode. On the positive electrode, two nickel hydroxide molecules [2ni (OH) 2] receive two negative charges, and with the participation of water, two nickel hydroxide molecules (2nioh) and two hydroxyl ions (2oh-) are generated. In the electrolyte, two negative charges are carried by two hydroxyl ions and migrate from the positive electrode to the negative electrode, completing the whole discharge process of the battery

During charging, the direction of charge flow is opposite to that during discharge, and the positive discharge active material nickel hydroxide [ni (OH) 2] gradually becomes the charged active material nickel hydroxide (nioh); Cadmium hydroxide, the active substance in the negative discharge state, gradually becomes cadmium (CD), the active substance in the charged state, and the active substance of the battery also changes again and again. If you continue to charge the battery after the battery is fully charged, the active substance will no longer change. Oxygen will be released from the positive electrode, hydrogen will be released from the negative electrode, and electrolytic water reaction will occur, which is called overcharge. After discharge, there is always a small amount of undischarged nickel oxide (nioh) in the positive electrode and a small amount of undischarged cadmium (CD) in the negative electrode, indicating that the utilization rate of active substances is less than 100%.

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