Main performance parameters of the battery–three
Open circuit voltage
Battery terminal voltage under open circuit condition is known as the open circuit voltage. The battery open circuit voltage is equal to the difference of the battery positive electrode potential and the anode electrode potential when the battery is in the circuit (ie when there is no current through the poles).the Open circuit voltage is marked by V, ie V open = Ф +-Ф-, which Ф +, Ф-are positive cells and negative electrode potential. Battery open circuit voltage generally is less than its emf. This is because the two poles of the battery electrolyte solution in the electrode potential is usually not balanced, but the stable electrode potential. Generally ,battery's open circuit voltage is similar to the battery EMF.
Internal resistance
Battery internal resistance is the resistance when the current through the battery internal gets. It includes the ohmic resistance and polarization resistance, polarization resistance also includes internal resistance of electrochemical polarization and concentration polarization resistance. Since the existence of internal resistance, battery voltage is always less than the battery emf <IMG src="http://t12.baidu.com/it/u=2325898283,3451946212&fm=0&gp=10.jpg" name=pn19> or the open circuit voltage. Battery internal resistance is not constant, in the charging and discharging process ,it changes over time (getting larger), because the composition of active material, electrolyte concentration and temperature are constantly changing. Ohm's law Ohm's resistance to comply with the polarization resistance increases with current density, but not linear. It Often increases with the current density .
Resistance is an important indicator to decide the battery performance, which directly affects the battery voltage, operating current, the output of energy and power, for the battery, its internal resistance is smaller, it is better.