There are many varieties of chemical batteries with different performances. The indicators commonly used to characterize its performance include: electrical properties, mechanical properties, storage properties, etc., and sometimes also include performance and economic costs. We mainly introduce its electrical properties and storage properties. Electrical properties include: electromotive force, rated voltage, open circuit voltage, working voltage, termination voltage, charging voltage, internal resistance, capacity, specific energy and specific power, storage performance and self-discharge, life, etc. The storage performance mainly depends on the self-discharge size of the battery.
EMF
The electromotive force of the battery, also known as the battery standard voltage or theoretical voltage, is the potential difference between the positive and negative poles when the battery is disconnected.
Rated voltage
Rated voltage (or nominal voltage) refers to the recognized standard voltage when the battery of this electrochemical system works.
Open circuit voltage
The open circuit voltage of the battery is the battery voltage under no load conditions. The open circuit voltage is not equal to the electromotive force of the battery. It must be pointed out that the electromotive force of the battery is calculated from the thermodynamic function, while the open circuit voltage of the battery is actually measured.
Operating Voltage
Refers to the actual discharge voltage of the battery under a certain load, usually refers to a voltage range.
⑸ Termination voltage
It refers to the voltage value when the discharge is terminated, which varies according to the load and usage requirements.
Charging voltage
It refers to the voltage at which the DC voltage of the external circuit charges the battery. The general charging voltage is greater than the open circuit voltage of the battery, usually within a certain range
Internal resistance
The internal resistance of the battery includes: the resistance of the positive and negative plates, the resistance of the electrolyte, the resistance of the separator and the resistance of the connector, etc.
Positive and negative resistance
The positive and negative plates of the commonly used lead-acid batteries are paste-coated, and are composed of lead-antimony alloy or lead-calcium alloy grid frame and active material. Therefore, plate resistance is also composed of grid resistance and active material resistance. The grid is in the inner layer of the active material, and there will be no chemical change during charging and discharging, so its resistance is the inherent resistance of the grid. The resistance of the active material varies with the state of charge and discharge of the battery.
When the battery is discharged, the active material of the plate is converted into lead sulfate (PbSO4), and the greater the lead sulfate content, the greater its resistance. When the battery is charged, lead sulfate is reduced to lead (Pb), and the lower the lead sulfate content, the lower its resistance.
Electrolyte resistance
The resistance of the electrolyte varies depending on its concentration. Once a certain concentration is selected within the specified concentration range, the resistance of the electrolyte will change with the degree of charge and discharge. When the battery is charged, the concentration of the electrolyte increases while the active material of the electrode plate is reduced, and its resistance decreases; when the battery is discharged, the concentration of the electrolyte solution decreases while the active material of the electrode plate is sulfated, and its resistance increases.
Spacer resistance
The resistance of the separator varies depending on its porosity. The resistance of the separator in new batteries tends to be a fixed value, but increases as the battery runs longer. Because, during the operation of the battery, some lead slag and other deposits are on the separator, which reduces the porosity of the separator and increases the resistance.
Connector resistance
The connecting body includes the inherent resistance of metals such as connecting bars when the single cells are connected in series, the connecting resistance between the battery plates, and the metal resistance of the connecting body formed by the positive and negative plates. If the welding and connection are in good contact, the connecting body resistance can be regarded as a fixed resistor.
The internal resistance presented by each battery is the sum of the resistances of the above objects. The relationship between the internal resistance R of the battery and the electromotive force, terminal voltage and discharge current: Rs=(E-Uf)÷If
The internal resistance of a battery gradually increases during discharge and decreases during charging. Therefore, during the charging and discharging process of the battery, the terminal voltage will also change due to the change of its internal resistance. Therefore, the terminal voltage is lower than the electromotive force of the battery during discharge and higher than the electromotive force of the battery during charging.
