Discussion on anode and cathode of lead acid battery

The anode and cathode in the battery are directly opposite, but they also participate in the chemical reaction. When discharging, the battery is connected to the load of the external circuit, and the electrons flow from the negative plate through the load of the external circuit to the positive plate, so that the potential of the positive plate decreases.

When charging, it is the reverse of the discharge reaction. The positive and negative poles of the battery are connected to the DC power supply when the power supply voltage is higher than the electromotive force (E) of the battery, the current flows into the positive pole of the battery and flows out of the negative pole of the battery, that is, the electrons flow to the negative pole by the positive plate through the external circuit.

Before the negative electrode of the battery is discharged, the electrode surface has a negative charge, and the solution near it has a positive charge, and the two are in equilibrium. When discharging, electrons are immediately released to the external circuit. The negative charge on the electrode surface decreases, while the oxidation reaction of metal dissolution progresses slowly (Me - e →Me+), which cannot timely supplement the reduction of electrons on the electrode surface, and the charged state on the electrode surface changes.

This state of reduced negative charge on the surface promotes the electrons in the metal to leave the electrode and the metal ion Me+ to transfer into the solution, accelerating the Me－e→Me＋ reaction. There is always a moment when a new dynamic equilibrium is reached.

However, compared with before discharge, the number of negative charge on the electrode surface decreases, and the corresponding electrode potential becomes positive. That is, the electrochemical polarization voltage becomes high, which severely impedes the normal charging current. Similarly, when the battery's positive electrode is discharged, the number of positive charges on the electrode surface decreases and the electrode potential becomes negative.

How is the voltage of the positive and negative electrode in the battery generated

A current can flow through a wire because there is a difference between high potential energy and low potential energy in a current. This difference is called potential difference, or voltage. In other words, in a circuit, the potential difference between any two points is called the voltage at those points. Voltage is usually represented by the letter U, and the unit of voltage is volt (V), which is short for volt, and is represented by the symbol V. High voltage can be expressed in kilovolts (kV), low voltage can be expressed in millivolts (mV), or microvolts (μ V). Voltage is the cause of electric current.

Battery voltage also known as electromotive force, the battery has positive and negative electrodes, electromotive force is the difference between the balance electrode potential of two electrodes, with lead-acid battery as an example,E= ф+0-ф-0+RT/F*In(αH2SO4/αH2O).

E-  the electromotive force

ф+0 - Positive standard electrode potential, its value is 1.690

ф-0 - negative standard electrode potential, its value is -0.356

R - General gas constant, with a value of 8.314

T - Temperature, which is related to the temperature of the battery

F - Faraday's constant, with a value of 96500

αH2SO4 - Activity of sulfuric acid, and sulfuric acid concentration

αH2O - The activity of water, dependent on the concentration of sulfuric acid

As can be seen from the above equation, the standard electromotive force of the lead-acid battery is 1.690- (-0.0.356) =2.046V, so the nominal voltage of the battery is 2V. The electromotive force of lead acid battery is also related to temperature and sulfuric acid concentration.

When the battery is discharged, the positive reaction is :PbO2+4H++SO42-+ 2E -=PbSO4+2H2O

Negative reaction :Pb+SO42-- 2E -=PbSO4

Total reaction :PbO2+Pb+2H2SO4===2PbSO4+2H2O(reaction to the right is discharge, reaction to the left is charge)

When you charge it, if it's connected reversely, it burns because in the chemical equation above, the charging reaction doesn't work as it should, so the material in the battery cannot be recycled, then it burns.