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The electromotive force and voltage of the battery

by:dcfpower     2021-03-31
(1) The electromotive force (E) of the electromotive force battery is equal to the difference of the equilibrium potential of the two electrodes that make up the battery, that is, Eu003dφe+-φe- under isothermal and isostatic conditions, when the system changes, the system Gibbs free energy The reduction of is equal to the maximum non-expansion work done externally. If the non-expansion work is only electrical work, then ΔGT.Pu003d-nFE where n is the electron measurement coefficient of the electrode in the oxidation or reduction reaction. When the chemical energy in the battery is irreversibly transformed into electrical energy, the potential difference E'between the two poles must be less than the reversible electromotive force E. ΔGT.Pu003d-nFE' formula (1-21) reveals the maximum limit of the conversion of chemical energy into electrical energy, and provides a theoretical basis for improving battery performance. The electromotive force is a theoretical value in an ideal equilibrium state, which is mainly determined by the electrochemical activity of the positive and negative active materials constituting the battery. The electromotive force of the MH/Ni secondary battery is about .50V, and the battery voltage in practical applications is lower than this value. (2) Open circuit voltage and operating voltage Open circuit voltage refers to the potential difference between the two poles of the battery in the open circuit state (almost no current is passed through), generally expressed by Vopen: Vopenu003dφ+ -φ- The open circuit voltage of the battery is equal to The difference between the positive and negative mixed potential of the battery. Its height depends on the nature of the battery's positive and negative electrode materials, electrolyte and temperature conditions, and has nothing to do with the battery's geometric structure and external dimensions. The open circuit voltage of the battery is generally less than the electromotive force. Working voltage refers to the voltage displayed on the two poles during the discharge process of the battery after the load is connected. It is also called the load (load) voltage or the discharge voltage. The initial voltage of the battery discharge is called the initial voltage. Due to the existence of ohmic resistance and overpotential, the working voltage of the battery is lower than the open circuit voltage, and of course it is also lower than the electromotive force: Vu003dE-IR内u003dEI(RΩ+Rf) or Vu003dE- η+- η--IRΩ u003dφ+- φ--IRΩ where η+ and η- represent the overpotential of positive polarization and negative polarization respectively; I is the working current of the battery; RΩ and Rf represent ohmic internal resistance and polarization internal resistance respectively; φ + And φ- are the electrode potentials or polarization potentials of the positive and negative electrodes respectively when current flows. The working voltage of the battery is related to the discharge system, that is, the various conditions specified when the battery is discharged, mainly including whether the discharge method is continuous or intermittent, the size of the external resistance and the discharge current, the length of the discharge time, the determination of the final voltage and the discharge environment temperature The level. (3) Rated voltage Rated voltage, also known as nominal voltage or nominal voltage, refers to the lowest value (guaranteed value) of the open circuit voltage of a battery, or the standard voltage for battery operation under specified conditions, that is, when the battery is discharged at a rate of 0.2C The average voltage of the whole process. The battery system can be distinguished simply by the rated voltage: alkaline manganese battery 1.5V, nickel-cadmium battery 1.2V, lead-acid battery 2.0V, lithium ion battery 3.6V, etc. (4) Discharge termination voltage For all secondary batteries, the discharge termination voltage is an important indicator that must be strictly regulated. The discharge end voltage is also called the discharge cut-off voltage, which refers to the lowest working voltage value at which the battery discharges, the voltage drops to the point where the discharge is no longer suitable. According to the different types of batteries and different discharge conditions, the requirements for the capacity and life of the battery are also different, and the discharge end voltage specified is also different. Generally, when discharging at a low temperature or a large current, the termination voltage is specified to be lower; for a long time or intermittent discharge at a small current, the termination voltage is specified to be higher. (5) Charging voltage The charging voltage refers to the voltage applied to both ends of the battery by the external power source when the secondary battery is being charged. The basic charging methods are constant current charging and constant voltage charging. u003c/pu003e
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