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Battery Principle Brief Editor

Jul 06, 2017

Battery Principle brief editor

Principle brief editor

In the chemical battery, chemical energy can be directly converted into electricity by the battery spontaneous oxidation, reduction and other chemical reactions, the reaction was carried out on two electrodes. Negative active substances from the negative potential and stability in the electrolyte of the reducing agent composition, such as zinc, cadmium, lead and other active metals and hydrogen or hydrocarbons. The positive electrode active material consists of oxidants such as manganese dioxide, lead dioxide, nickel oxide and the like, oxygen or air, halogen and its salts, oxygenic acid and its salts, etc., which are more stable and stable in the electrolyte. The The electrolyte is a material having good ionic conductivity, such as an aqueous solution of an acid, an alkali, a salt, an organic or inorganic nonaqueous solution, a molten salt or a solid electrolyte. When the external circuit is disconnected, there is a potential difference (open circuit voltage) between the poles, but no current, the chemical energy stored in the battery is not converted to electrical energy. When the external circuit is closed, the potential difference between the two electrodes under the current flow through the external circuit. At the same time inside the battery, due to the absence of free electrons in the electrolyte, the charge transfer must be accompanied by bipolar active material and electrolyte interface oxidation or reduction reaction, as well as reactants and reaction products of material migration. The transfer of charge in the electrolyte is also done by the migration of ions. Therefore, the battery inside the normal charge transfer and material transfer process is to ensure the normal output power of the necessary conditions. When charging, the battery inside the transmission and mass transfer process is just the opposite direction of discharge; electrode reaction must be reversible, in order to ensure the opposite direction of mass transfer and transmission process of normal. Therefore, the electrode reaction reversible is necessary to constitute the battery conditions. G is the Gibbs reaction free energy increment (coke); F is Faraday constant = 96500 library = 26.8Ah hours; n is the equivalent number of battery reactions. This is the basic thermodynamic relationship between the battery electromotive force and the battery reaction and the basic thermodynamic equation for calculating the energy conversion efficiency of the battery. In fact, when the current flows through the electrode, the electrode potential must be deviated from the thermodynamic equilibrium of the electrode potential, this phenomenon is called polarization. The greater the current density (the current through the unit electrode area), the more severe the polarization. Polarization is one of the important causes of battery energy loss.

Polarization has three reasons:

① by the battery part of the resistance caused by the polarization known as the ohmic polarization;

② polarization caused by the process of charge transfer in the electrode-electrolyte interface layer is called activation polarization;

③ polarization caused by the slow mass transfer process in the electrode-electrolyte interface layer is called concentration polarization. The method of reducing the polarization is to increase the electrode reaction area, reduce the current density, increase the reaction temperature and improve the catalytic activity of the electrode surface.

Performance parameter editing

Electromotive force

Electromotive force is the difference between the potential electrodes of the two electrodes. In the case of lead-acid batteries, E = Ф + 0-Ф-0 + RT / F * In (αH2SO4 / αH2O).

Among them: E-electromotive force

Ф + 0 - positive standard electrode potential, the value of 1.690V

Ф-0- negative electrode standard electrode potential, its value is -0.356V

The R-universal gas constant has a value of 8.314

T-temperature, and the battery temperature

F-Faraday constant, which is 96485

ΑH2SO4-sulfuric acid activity, and sulfuric acid concentration

ΑH2O-water activity, and sulfuric acid concentration

As can be seen from the above formula, 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 the lead-acid battery is related to the temperature and the concentration of sulfuric acid.