Battery is a device that converts chemical energy into electrical energy by holding electrolyte solutions and metal electrodes in part of the space of cups, tanks or other containers or composite containers that generate electric current. It can be divided into positive pole and negative pole. With the progress of science and technology, batteries generally refer to small devices that can generate electricity. Such as solar cells. The main performance parameters of the battery are electromotive force, capacity, specific energy and resistance. Using batteries as energy source, we can get the current with stable voltage, stable current, stable power supply for a long time, little influence from the outside world, and the battery is simple in structure, easy to carry, easy to charge and discharge operation, not affected by the outside climate and temperature, stable and reliable in modern social life. All aspects play a very important role.
In chemical batteries, the direct conversion of chemical energy to electrical energy is the result of spontaneous oxidation and reduction reactions within the batteries, which are carried out on two electrodes respectively. The negative active material is composed of reductants with negative potential and stable in electrolyte, such as active metals such as zinc, cadmium, lead and hydrogen or hydrocarbons. Positive active substances consist of oxidants with positive potential and stable in electrolyte, such as manganese dioxide, lead dioxide, nickel oxide, oxygen or air, halogen and its salts, oxyacid and its salts, etc. Electrolytes are materials with good ionic conductivity, such as acid, alkali, salt aqueous solution, organic or inorganic non-aqueous solution, molten salt or solid electrolyte. When the external circuit is disconnected, although there is a potential difference (open circuit voltage) between the two poles, there is no current, and the chemical energy stored in the battery is not converted into electricity. When the external circuit is closed, the current flows through the external circuit under the action of the potential difference between the two electrodes. At the same time, because there are no free electrons in the electrolyte, the charge transfer is bound to be accompanied by the oxidation or reduction reaction between the active substance and the electrolyte interface, as well as the material transfer of reactants and reaction products. The transfer of charge in electrolyte is also accomplished by ion transfer. Therefore, the normal charge transfer and material transfer process inside the battery is the necessary condition to ensure the normal output of electric energy. When charging, the direction of the transmission and mass transfer process inside the battery is exactly opposite to that of discharge; the electrode reaction must be reversible to ensure the normal operation of the reverse mass transfer and mass transfer process. Therefore, reversible electrode reaction is a necessary condition for battery formation. G is Gibbs reaction free energy increment (focal), F is Faraday constant = 96500 Library = 26.8 an. h, and N is the equivalent of battery reaction. This is the basic thermodynamic relationship between the cell electromotive force and the cell reaction. It is also the basic thermodynamic equation for calculating the energy conversion efficiency of the cell. In fact, when the current flows through the electrode, the potential of the electrode will deviate from the potential of the thermodynamic equilibrium. This phenomenon is called polarization. The greater the current density (the current passing through the area of the unit electrode), the more serious the polarization is. Polarization is one of the important reasons for energy loss of batteries.
There are three reasons for polarization:
①The polarization caused by the resistance of each part of the battery is called ohmic polarization.
②The polarization caused by the retardation of charge transfer process in the electrode-electrolyte interface layer is called activation polarization, and the polarization caused by the retardation of charge transfer process in the electrode-electrolyte interface layer is called activation polarization.
③The polarization caused by the slow mass transfer in the electrode-electrolyte interface layer is called concentration polarization. The methods to reduce polarization are to increase the reaction area, decrease the current density, increase the reaction temperature and improve the catalytic activity of the electrode surface.
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