The relationship between the positive and negative electrodes of the battery

by:Power Kingdom     2021-07-06

   The positive and negative poles in the battery are directly opposite, but they participate in the chemical reaction at the same time. During discharging, the battery is connected to the load of the external circuit, and electrons flow from the negative plate to the positive plate through the load of the external circuit, so that the potential of the positive plate drops.

When    is charging, it is the reverse process of the discharge reaction. When charging, 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, current flows in from the positive electrode of the battery and flows out from the negative electrode of the battery, that is, electrons flow from the positive plate to the negative plate through the external circuit.

   Before the negative electrode of the battery is discharged, the surface of the electrode is negatively charged, and the nearby solution is positively charged, and the two are in equilibrium status. When discharging, electrons are immediately released to the external circuit. The negative charge on the surface of the electrode decreases, and the oxidation reaction of metal dissolution progresses slowly Me-e→Me+, which can not supplement the decrease of electrons on the electrode surface in time, and the charged state of the electrode surface changes.

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

   But compared with before discharge, the number of negative charges on the electrode surface is reduced, and the corresponding electrode potential becomes positive. That is, the electrochemical polarization voltage becomes higher, which seriously hinders the normal charging current. In the same way, when the positive electrode of the battery is discharged, the number of positive charges on the surface of the electrode decreases, and the electrode potential becomes negative.

  How does the voltage of the positive and negative poles in the battery generate

  The reason why the current can flow in the wire is also because of the current There is a difference between high potential energy and low potential energy. This difference is called potential difference, also called voltage. In other words, in the circuit, the potential difference between any two points is called the voltage of these two points. Usually the letter U is used to represent voltage, and the unit of voltage is volts (V), referred to as volts, represented by the symbol V. High voltage can be expressed in kilovolts (kV), low voltage can be expressed in millivolts (mV) or microvolts (μv). Voltage is the cause of current.

  The voltage of a battery is also called electromotive force. There are two positive and negative electrodes in the battery. The electromotive force is the difference between the balanced electrode potentials of the two electrodes. Take a lead-acid battery as an example. Eu003dФ+0-Ф-0+RT/F*In(αH2SO4/αH2O).

  Among them: E—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, its value is 8.314

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  T—temperature, related to the temperature of the battery

  F—Faraday constant, its value is 96500

  αH2SO4—activity of sulfuric acid, related to sulfuric acid concentration

  αH2O—activity of water, related to sulfuric acid concentration

   It can be seen from the above formula that the standard electromotive force of a lead-acid battery is 1.690-(-0.0.356)u003d2.046V, so the nominal voltage of the battery is 2V. The electromotive force of lead-acid batteries is also related to temperature and sulfuric acid concentration.

   When the battery is discharged, the positive reaction is: PbO2+4H++SO42-+2e-u003dPbSO4+2H2O

Negative reaction: Pb+SO42--2e-u003dPbSO4

  Total reaction: PbO2+Pb+2H2SO4u003du003du003d2PbSO4+2H2O (right reaction is discharge, left reaction It is charging)

When charging, if the connection is reversed, the principle of'burning' is that in the above chemical equation, the'charging' reaction cannot proceed according to theory. The materials cannot be recycled, so it will be burnt out.

  


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