Chemical battery.li ion 18650 battery pack

　　In a chemical battery, the direct conversion of Chemical energy into electrical energy is the result of spontaneous chemical reactions such as oxidation and reduction in the battery, which are carried out on two electrodes respectively. The negative electrode active material is composed of reducing agents with negative potential and stable in the electrolyte, such as active metals such as zinc, cadmium, lead, and hydrogen or hydrocarbons. The positive active material is composed of oxidants with positive potential and stable in electrolyte, such as Manganese dioxide, Lead dioxide, nickel oxide and other metal oxides, oxygen or air, halogen and its salts, Oxyacid and its salts, etc. Electrolytes are materials with good ionic conductivity, such as aqueous solutions of acids, bases, and salts, organic or inorganic non-aqueous solutions, molten salts, or solid electrolytes. 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 electrical energy. When the external circuit is closed, current flows through the external circuit under the action of the potential difference between the two electrodes. At the same time, within the battery, due to the absence of free electrons in the electrolyte, the transfer of charge is inevitably accompanied by the oxidation or reduction reaction between the polar active substance and the electrolyte interface, as well as the migration of reactants and reaction products. The transfer of charge in the electrolyte is also completed by the migration of ions. Therefore, the normal charge transfer and material transfer process inside the battery is a necessary condition to ensure the normal output of electrical energy. When charging, the direction of power and mass transfer inside the battery is exactly opposite to that of discharge; The electrode reaction must be reversible in order to ensure the normal process of mass and electricity transfer in the opposite direction. Therefore, reversible electrode reactions are a necessary condition for forming a battery. G is the increase in Gibbs reaction free energy (joules); F is Faraday constant=96500 ℃=26.8 A · h; N is the equivalent number of battery reactions. This is the basic thermodynamic relationship between the battery electromotive force and the battery reaction, and also 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 will deviate from the electrode potential of Thermodynamic equilibrium. This phenomenon is called polarization. The greater the current density (the current passing through the unit electrode area), the more severe the polarization. Polarization phenomenon is one of the important reasons for energy loss in batteries.

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