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Lithium battery terminology

Time:2019/7/2 15:24:51
Capacity
The amount of electricity that a lithium battery can give under certain discharge conditions is called the capacity of a lithium battery and is expressed by the symbol C (Capacity).

Commonly used units are ampere hours, referred to as Anshi (Ah) or mAh (mA)

Voltage
• Open circuit voltage (OCV)
The terminal voltage of a lithium battery in an open state is called an open circuit voltage. The open circuit voltage of the lithium battery is equal to the difference between the reduction electrode potential of the positive electrode of the lithium battery and the potential of the negative electrode.
• Operating Voltage
The working voltage refers to the voltage displayed during the discharge process after the lithium battery is turned on, which is also called the discharge voltage. The initial operating voltage at the discharge of the lithium battery is called the initial voltage. After the lithium battery is turned on, the operating voltage of the lithium battery is lower than the open circuit voltage due to the presence of ohmic resistance and polarization overpotential.


Internal resistance
• When the current passes through the inside of the lithium battery, the resistance is reduced, and the voltage of the lithium battery is lowered. This resistance is called the internal resistance of the lithium battery.
• The internal resistance of a lithium battery is not constant and changes over time during discharge because the composition of the active material, electrolyte concentration and temperature are constantly changing.
• Lithium battery internal resistance includes ohmic internal resistance and polarization internal resistance, and polarization internal resistance includes electrochemical polarization and concentration polarization. The existence of the internal resistance causes the terminal voltage of the lithium battery to be discharged lower than the electromotive force and the open circuit voltage of the lithium battery, and the terminal voltage during charging is higher than the electromotive force and the open circuit voltage.

• Ohmic resistances follow Ohm's law; polarization resistance increases with increasing current density, but is not linear, and increases linearly with increasing logarithm of current density.


(charge and discharge) rate / time rate
Magnification: refers to the current value required by a lithium battery to discharge its rated capacity within a specified time. It is numerically equal to a multiple of the rated capacity of the lithium battery, usually indicated by the letter C.

If the nominal capacity of a lithium battery is 600 mAh, 600 mA is 1 C (1 rate), 300 mA is 0.5 C, 6 A (6000 mA) is 10 C, and so on.
Time rate: Also known as hourly rate, it refers to the number of hours required for a lithium battery to discharge its rated capacity at a certain current.
For example, the rated capacity of a lithium battery is 600 mAh, and it takes 1 hour to discharge its rated capacity at a current of 600 mA, so the current of 600 mA is said to be 1 hour.


Self-discharge
Self-discharge refers to the loss of chemical energy due to spontaneous reaction in a lithium battery when the lithium battery is not connected to the outside world. The self-discharge rate of a lithium battery is the ratio of the initial capacity of the lithium battery to the initial capacity of the lithium battery after storage for a period of time.
The self-discharge rate of lithium-ion lithium battery is not more than 10% per month, far less than 30% of Ni-MH battery, and 15% of Ni-Cd lithium battery.

Memory effect
Lithium battery memory effect refers to the lithium battery when it is not fully discharged. The undischarged power will cause the plate to "crystallize", which is called "memory effect". When the memory effect is produced, the lithium battery capacity will drop significantly. Lithium-ion lithium battery does not need to be discharged before charging, and there is no memory problem of nickel-cadmium lithium battery.

Cycle life
• The lithium battery is fully discharged after full charge and is cycled until the capacity decays to 75% of the initial capacity. The cycle number is the cycle life of the lithium battery.
• Cycle life is related to lithium battery charge and discharge conditions.
• Lithium-ion lithium battery can have a 1C charge and discharge cycle life of 1000-1500 times at room temperature.
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