Explanation of common terms related to lithium batteries

Lithium-ion battery - capacity, voltage, internal resistance, multiplier/hour rate, self-discharge, memory effect, cycle life.

Capacity

• The capacity of a lithium-ion battery is given by certain discharge conditions and is called the capacity of a lithium-ion battery and is expressed by the symbol C (capacity). The common unit is Ampere-hour (Ah) or mAh.

Voltage

1.Open Circuit Voltage (OCV)

• The terminal voltage of a lithium-ion battery in the open-circuit state is called the open-circuit voltage. The open circuit voltage of lithium-ion battery is equal to the difference between the positive potential and the negative potential.

2.Operating Voltage

• The operating voltage is the voltage displayed during the discharge of the lithium-ion battery after the load is turned on, also known as the discharge voltage. The operating voltage when the lithium-ion battery is initially discharged is called the initial voltage. Due to the presence of ohmic resistance and polarization overpotential, the operating voltage of lithium-ion battery is lower than the open circuit voltage after the load is turned on.

Internal resistance

• The resistance that occurs when current passes through a lithium-ion battery reduces the voltage of the lithium-ion battery. This resistance is called the internal resistance of the lithium-ion battery.
• The internal resistance of a lithium-ion battery is not constant and changes over time during discharge because the composition of the active material, the concentration of the electrolyte and the temperature are constantly changing.
• The internal resistance of lithium-ion battery includes ohmic internal resistance and polarized internal resistance, and polarized internal resistance includes electrochemical polarization and concentration difference polarization. The presence of internal resistance makes the end voltage of lithium-ion battery lower than the electric potential and open-circuit voltage of lithium-ion battery when discharging and higher than the electric potential and open-circuit voltage when charging.
• Ohmic resistance follows Ohm's law; polarization resistance increases with increasing current density, but not linearly, always linearly with increasing logarithm of current density.

Charge and discharge rate

Multiplier:The value of the current required to release the rated capacity of a lithium-ion battery in a specified time.

If the rated capacity of lithium-ion battery is 600mAh, then 600mA is 1C (1 multiplier), 300mA is 0.5c, 6A (6000mA) is 10C, and so on. Hourly rate:Also known as hourly rate, it refers to the number of hours it takes for a lithium-ion battery to discharge its rated capacity with a certain amount of power. If the rated capacity of lithium-ion battery is 600mAh, it takes 1 hour to discharge 600mA current, so it is said that 600mA current is the rate of 1 hour

Self-discharge

Self-discharge is the loss of chemical energy caused by the spontaneous reaction of a lithium-ion battery when it is not connected to the outside world. The self-discharge rate of lithium-ion battery is the initial capacity of lithium-ion battery after a period of storage minus the stored capacity of lithium-ion battery as a percentage of the initial capacity The ratio of the storage capacity of the lithium-ion battery to the initial capacity. The self-discharge rate of Li-ion Li-ion battery does not exceed 10% per month, which is much lower than 30% of NiMH Li-ion battery and 15% of NiCd Li-ion battery.

Memory effect

The memory effect of lithium-ion battery is that the lithium-ion battery is not discharged when it is charged, and the undischarged power makes the pole plate crystallize, which is called the memory effect. When there is a memory effect, lithium-ion battery capacity will have a significant drop. Lithium-ion battery charging Before no discharge, there is no memory problem for NiCd Li-ion battery.

Cycle life

• The cycle life of a lithium-ion battery is the cycle life of a lithium-ion battery when it is fully discharged after a full charge, and this cycle continues until the capacity decays to 75% of the original capacity.
• The cycle life is related to the charge and discharge conditions of the lithium-ion battery.
• The charge/discharge cycle life of 1C can reach 1000-1500 times at room temperature.

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