Open circuit voltage and resistance of lithium batteries.3.7 volt 18650 lithium battery

　　The terminal voltage of a battery in an open circuit state is called the open circuit voltage. The open circuit voltage of a battery is equal to the difference between the positive electrode potential of the battery and the negative electrode potential when there is no current passing through the two poles. The open circuit voltage of the battery is represented by V on, i.e. V on= Ф+-Ф-， among Ф+、Ф- Respectively represent the positive and negative electrode potentials of the battery. The open circuit voltage of a battery is generally less than its electromotive force. This is because the electrode potential established by the two poles of the battery in the electrolyte solution is usually not an equilibrium electrode potential, but a stable electrode potential. It can generally be approximated that the open circuit voltage of a battery is the electromotive force of the battery.

　　The internal resistance of a battery refers to the resistance experienced when current passes through the interior of the battery. It includes ohmic internal resistance and polarization internal resistance, and polarization internal resistance also includes electrochemical polarization internal resistance and concentration polarization internal resistance. Due to the presence of internal resistance, the working voltage of the battery is always lower than the electromotive force or open circuit voltage of the battery. The internal resistance of a battery is not a constant and constantly changes (gradually increases) over time during the charging and discharging process. This is because the composition of active substances, the concentration and temperature of the electrolyte are constantly changing. Ohm internal resistance obeys Ohm's law, and polarization internal resistance increases with the increase of current density, but it is not linear. It often increases with the increase of current density.

　　Internal resistance is an important indicator that determines the performance of a battery. It directly affects the working voltage, current, output energy, and power of the battery. For batteries, the smaller the internal resistance, the better.

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