Common terminology of lithium battery May 31, 2021

In the lithium battery industry, I will often encounter some terms when communicating with friends, such as battery capacity, discharge rate, voltage, internal resistance, cycle life, remaining capacity SOC, etc.

a. Battery capacity (Capacity)

Refers to the amount of electricity that can be obtained from battery lithium under certain discharge conditions.

We know in high school physics that the formula for power is Q=I*t, the unit is coulomb, and the unit of battery capacity is specified as Ah (Ampere hour) or mAh (Milliamp hour). This means that a 1AH battery can be discharged for 1 hour when it is fully charged with a current of 1A.

The battery of Apple's mobile phone is generally about 2000mAh, the lithium battery of electric bicycle is generally about 8~15Ah, and the battery of electric car is generally 20~200Ah. For example, BYD's electric car e6 is a 200Ah battery.

b. Charge-discharge rate (Charge-Rate/Discharge-Rate)

It indicates how much current is used to charge and discharge. It is generally calculated as a multiple of the battery's nominal capacity, which is generally called a few C.

Like a battery with a capacity of 1500mAh, it is stipulated that 1C=1500mAh. If it is discharged at 2C, it will be discharged at a current of 3000mA, and if it is charged and discharged at 0.1C, it will be charged and discharged at a current of 150mA.

c. Open Circuit Voltage (OCV: Open Circuit Voltage)

The voltage of the battery generally refers to the nominal voltage (also called the rated voltage) of the lithium battery. The nominal voltage of an ordinary lithium battery is generally 3.7V, and we also call its voltage platform 3.7V. The voltage we are talking about generally refers to the open circuit voltage of the battery.

When the battery capacity is 20~80%, the voltage is concentrated around 3.7V (about 3.6~3.9V), the capacity is too high or too low, and the voltage changes greatly.

d. Energy/Power

The battery discharges according to a certain standard, the energy (E) that the battery can release, the unit is Wh (watt hour) or KWh (kilowatt hour), and 1KWh = 1 kilowatt hour of electricity.

There is a basic concept in the physics book, E=U*I*t, which is also equal to the battery voltage multiplied by the battery capacity.

The formula for power is P=U*I=E/t, which represents the energy that can be released per unit time. The unit is W (watt) or KW (kilowatt).

Like a battery with a capacity of 1500mAh, the nominal voltage is generally 3.7V, so the corresponding energy is 5.55Wh.

e. Internal resistance (Resistance)

Since it cannot be equivalent to an ideal power supply during charging and discharging, it has a certain internal resistance. Internal resistance consumes energy. Of course, the smaller the internal resistance, the better.

The internal resistance of the battery is in milliohms (mΩ).

Generally, the internal resistance of a battery is composed of ohmic internal resistance and polarized internal resistance. The size of the internal resistance is affected by the material, manufacturing process, and structure of the battery.

f. Cycle Life

A charge and discharge of a battery is called a cycle, and the cycle life is an important indicator of battery life performance.

The IEC standard stipulates that the mobile phone lithium battery should be discharged to 3.0V at 0.2C and charged to 4.2V at 1C. After 500 cycles of repeated cycles, the battery capacity should be maintained at more than 60% of the initial capacity. In other words, the cycle life of a lithium battery is 500 times.

The national standard stipulates that after a cell phone battery has a cycle life of 300 times, the capacity should maintain 70% of the initial capacity.

(Source: iYPOWE)

The mobile phone battery capacity is less than 60% of the initial capacity, generally, it is necessary to consider scrapping.

g. Cut-Off Voltage

The termination voltage is divided into the charge termination voltage and the discharge termination voltage, that is to say the voltage at which the battery cannot continue to be charged or discharged, and the continued charging or discharging under the termination voltage has a great impact on the life of the battery.

The end-of-charge voltage of lithium batteries is generally 4.2V, and the end-of-discharge voltage is 3.0V.

Deep charging or deep discharging of lithium batteries exceeding the termination voltage is strictly prohibited.

h. Remaining capacity SOC (State of Charge)

Refers to the percentage of the remaining power of the battery to the total power that can be discharged, 0~100%. Reflect the remaining battery power.


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