Eight Important Parameters Of Lithium Batteries - Popularization of Lithium Battery Knowledge

Lithium-ion batteries have the advantages of high energy density, high conversion efficiency, long cycle life, no memory effect, no charge and discharge delay, low self-discharge rate, wide operating temperature range and environmental friendliness, making them an ideal carrier of electric energy and widely used in various fields. Generally speaking, when we use lithium-ion batteries, we will pay attention to some technical indicators as the main factors to measure the "good or bad" of their performance. The following are the indicators that we need to pay special attention to when using them.

1. Capacity

The unit of capacity is generally "mAh" (milliampere-hour) or "Ah" (ampere-hour), and there is a difference between rated capacity and actual capacity when using them. Rated capacity refers to the total amount of electricity that a fully charged lithium-ion battery can provide when it is discharged to the cut-off voltage at a certain discharge rate (C-rate) under laboratory conditions (relatively ideal temperature and humidity environment). The actual capacity is generally not equal to the rated capacity, and it is directly related to temperature, humidity, charge and discharge rate, etc. Battery capacity tester is a device specially used for battery capacity testing, which is mainly used in battery production and testing processes. By providing a stable test environment and precise control means, battery capacity testing equipment can efficiently and accurately charge and discharge the battery and accurately measure the actual capacity of the battery.

2. Energy Density

Energy density refers to the amount of electricity that can be stored and released by a battery per unit volume or unit weight. There are two units: Wh/kg and Wh/L, which represent weight specific energy and volume specific energy respectively. The amount of electricity here is the integral of the capacity (Ah) and the operating voltage (V) mentioned above. When applied, the energy density indicator is more instructive than the capacity.

3. Charge and Discharge Rate

This indicator affects the continuous current and peak current of the lithium-ion battery during operation. Its unit is generally C (abbreviation of C-rate), such as 1/10C, ​​1/5C, 1C, 5C, 10C, etc. Take an example to explain the specific meaning of the rate indicator. If the rated capacity of a battery is 10Ah and its rated charge and discharge rate is 1C, it means that this model of battery can be repeatedly charged and discharged at a current of 10A until the cut-off voltage of charging or discharging is reached.

4. Voltage

The voltage of lithium-ion batteries has some parameters such as charging cut-off voltage and discharging cut-off voltage. The charging/discharging cut-off voltage refers to the maximum and minimum operating voltage allowed by the battery. Exceeding this limit will cause some irreversible damage to the battery, resulting in reduced battery performance, and even fire, explosion and other safety accidents in severe cases. There is a certain correspondence between the open circuit voltage and operating voltage of the battery and the capacity of the battery. We can use BMS to monitor, control and protect the battery to ensure the safety, performance and life of the battery. ACEY provides BMS testers. BMS testing equipment is a professional test equipment designed for the research and development and production testing of BMS.

5. Life

The life of lithium-ion batteries will gradually decay with use and storage, and there will be more obvious performance. The life of lithium-ion batteries is divided into two parameters: cycle life and calendar life. Cycle life is generally measured in times, which represents the number of times the battery can be charged and discharged in cycles. Of course, there are conditions here. Generally, it is to perform deep charge and discharge (100% DOD or 80% DOD) at rated charge and discharge current under ideal temperature and humidity, and calculate the number of cycles when the battery capacity decays to 80% of the rated capacity.

6. Internal Resistance

The internal resistance of a lithium-ion battery refers to the resistance encountered by the current flowing through the battery when the battery is working. The unit of internal resistance is generally milliohm (mΩ). Batteries with large internal resistance have large internal power consumption and severe heat generation during charge and discharge, which will cause accelerated aging and life decay of lithium-ion batteries, and will also limit the application of high-rate charge and discharge. Therefore, the smaller the internal resistance, the better the life and rate performance of lithium-ion batteries.

7. Self-Discharge

When the battery is placed, its capacity is constantly decreasing. The rate of capacity decrease is called the self-discharge rate, which is usually expressed as a percentage: %/month. Once the self-discharge of a lithium-ion battery causes the battery to be over-discharged, the impact caused is usually irreversible. Even if it is recharged, the available capacity of the battery will be greatly lost and the life will decay rapidly. Therefore, lithium-ion batteries that have been unused for a long time must be charged regularly to avoid over-discharge due to self-discharge, which will greatly affect the performance.

8. Operating Temperature Range

Due to the characteristics of the chemical materials inside lithium-ion batteries, lithium-ion batteries have a reasonable operating temperature range (common data is between -40℃~60℃). If they are used beyond the reasonable range, the performance of lithium-ion batteries will be greatly affected. Lithium-ion batteries made of different materials have different operating temperature ranges. Some have good high-temperature performance, while others can adapt to low-temperature conditions. The operating voltage, capacity, charge and discharge rate and other parameters of lithium-ion batteries will change significantly with changes in temperature. Long-term use at high or low temperatures will also accelerate the attenuation of the life of lithium-ion batteries. Therefore, efforts to create a suitable operating temperature range can maximize the performance of lithium-ion batteries.

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