Introduce the electromotive force and voltage of the battery

The electromotive force and voltage of the battery (1) The electromotive force of the battery (E) is equal to the difference in the equilibrium potential between the two electrodes constituting the battery, that is, Eu003d+-EE- under isothermal and isothermal conditions, when the system changes, The reduction in Gibbs free energy of the system is equal to the maximum non-expansion work done. If the non-expansion work is only electrical work, then ΔGT,Pu003d-nFE where n is the measurement coefficient of electrode electrons in the oxidation-reduction reaction. When the chemical energy in the battery is irreversibly converted into electrical energy, the potential difference E'between the two poles must be less than the reversible electromotive force E. ΔGT. The formula Pu003dnFE (1-21) gives the maximum limit for the conversion of chemical energy into electrical energy, which provides a theoretical basis for improving battery performance. Electromotive force (Electromotiveforce, emf) is a theoretical value in an ideal equilibrium state, determined by the electrochemical activity of the battery's positive and negative active materials. The electromotive force of the MH/Ni secondary battery is approx. 50V, the actual battery voltage is lower than this value. (2) Open circuit voltage and working voltage Open circuit voltage refers to the potential difference between the two poles when the battery is in an open circuit state (almost no current), generally expressed by V: Vonu003d+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 properties of the battery's positive and negative materials, electrolyte and temperature conditions, but 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. The working voltage refers to the voltage displayed by the two poles after the battery is connected to the load during the discharging process. 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-IRu003dEI(R+Rf) or Vu003dE-η+-η-IRu003d+- The types of phiphi-IReta+ and eta- are anode polarization and cathode overpotential, respectively; I is the working current of the battery; R is respectively the RF ohmic resistance and polarization resistance; when the current passes, + and-are the positive electrode potential and Negative electrode potential or polarization potential. The working voltage and discharge system of the battery, that is to say, the battery discharge under various conditions, the discharge mode mainly includes continuous or intermittent, the size of external resistance and discharge current, the length of discharge time, the final voltage and the discharge environment temperature. (3) Rated voltage Rated voltage, rated voltage or rated voltage, refers to the battery with the lowest open circuit voltage value (guaranteed value), or it is the voltage of the standard battery under specified conditions, that is, the average voltage of the entire process When the battery is discharged by a multiplier of 0.2 degrees Celsius. The rated voltage can easily distinguish the battery system: alkaline manganese battery 1.5v, nickel-cadmium battery 1.2v, lead-acid battery 2.0v, lithium ion battery 3.6v, etc. (4) End-of-discharge voltage Regarding all secondary batteries, the end-of-discharge voltage is an important indicator that must be strictly controlled. Discharge termination voltage, also known as discharge cut-off voltage, means that when the battery is discharged, it is not suitable to continue discharging if the voltage is reduced to the lowest working voltage. According to different types of batteries and different discharge conditions, the battery capacity and life requirements are different, so the prescribed discharge termination voltage is also different. Under normal circumstances, the terminal voltage is lower when discharging at low temperature or high current; when discharging with small current for a long time or discharging intermittently, a higher terminal voltage should be set. (5) Charging pressure Charging voltage means that when the battery is charging, the external power supply adjusts the voltage at both ends of the battery. The basic charging methods are constant current charging and constant voltage charging. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Analysis of the four major advantages of power lithium-ion batteries