Working principle of lead-acid battery

Sealed Maintenance Free Battery anode (PbO₂) and cathode (Pb) into the electrolyte (dilute sulphuric acid), between the poles will produce 2V power, this is according to the principle of lead battery, through charging and discharging, the anode and cathode electrolyte will be the following changes:

(anode) (electrolyte) (cathode) PbO ₂ + 2 h ₂ SO ₄ + Pb = PbSO ₄ + 2 h ₂ O + PbSO ₄ (discharge). (lead dioxide) (sulphuric acid) (spongy lead) PbO₂ in Pb valence reduction, negative charge flows; in spongy lead, Pb valence increases and positive charge flows.

(Anode) (Electrolyte) (Cathode) PbSO ₄ + 2 h ₂ O + PbSO ₄ = PbO ₂ + 2 h ₂ SO ₄ + Pb (Charge reaction) (Must) under the condition of electricity (Lead sulphate) (Water) (Lead sulphate).

In the first lead sulphate, the valence of the lead increases, it is oxidised and the positive charge flows to the positive electrode; in the second lead sulphate, the valence of the lead is reduced and the negative charge flows to the negative electrode.

1. Chemical changes in discharge: when the Lead acid battery is connected to the external circuit and discharged, dilute sulfuric acid will react with active substances on the negative and positive plates to generate new compounds of lead sulfate. The sulfuric acid component is released from the electrolyte by discharge. The longer the discharge, the thinner the sulfuric acid concentration. The components consumed are proportional to the discharge, as long as the concentration of sulfuric acid in the electrolyte is measured, that is, the specific gravity, the discharge or residual energy can be known.

2. Chemical changes in charge: due to the discharge in the anode plate, cathode plate produced lead sulfate, will be decomposed and reduced to sulfuric acid, lead and lead dioxide when charging, so the concentration of electrolyte in the Maintenance Free Lead Acid Battery gradually increased, that is, the proportion of electrolyte rose, and gradually returned to the concentration before discharge.

This change shows that the active substance in the battery has been converted to the state of power supply again, when the two poles of lead sulfate is transformed into the original active substance, that is, is equal to the end of the charge, and the cathode plate produces hydrogen, the anode plate produces oxygen, charging to the final stage, the current is almost used in the water electrolysis, so the electrolyte will be reduced, this time should be supplemented with pure water.