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How To Evaluate The Excellence of Lithium Batteries

Views: 0     Author: Site Editor     Publish Time: 2024-04-30      Origin: Site


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As an important energy storage device, lithium batteries are very important to evaluate the performance of lithium batteries. To evaluate the performance of lithium batteries, multiple performance indicators need to be considered. This article will explain in detail the main performance indicators of lithium batteries, including rated capacity, battery internal resistance, voltage, discharge plateau time, charge and discharge rate, self-discharge rate, efficiency and cycle life.

1. Battery capacity

(1) Rated capacity

Hardware model: 48VAGV lithium battery, lithium iron phosphate lithium battery, system version: battery system. Rated capacity is one of the important performance indicators of lithium batteries. It indicates the amount of charge the battery can provide under specific temperature and discharge rate conditions. Usually expressed in units of milliamp-hours (mAh) or ampere-hours (Ah). For example, a 1000mAh lithium battery means that under certain conditions, it can provide 1000mA of current for a continuous discharge of 1 hour. Rated capacity is the battery capacity specified by national standards.

The size of the rated capacity is related to the battery's volume, chemical materials, and design. Generally speaking, larger capacity lithium batteries can store more energy and thus provide longer use time. It should be noted that factors such as discharge rate and temperature in actual use will also affect the capacity performance of the battery.

(2) Battery capacity

Battery capacity reflects the actual amount of electricity stored in the battery, expressed in Ah ampere-hours. Similarly, the greater the ampere-hour, the greater the battery capacity and the longer the electric vehicle's driving range. National standards stipulate that the actual capacity of a newly shipped battery is greater than the rated capacity value as a qualified battery. For example, for electric bicycle batteries currently on the market, it takes more than 2 hours (120 minutes) to discharge at a constant current of 5A, which is greater than (2 hours × 5A) 10Ah. It is equivalent to driving an electric vehicle continuously on a flat road for more than 2 hours.

2. Lithium battery performance

(1) Internal resistance of lithium battery

Battery internal resistance refers to the degree of resistance to current flow inside the battery. It includes ohmic internal resistance and polarization internal resistance. The ohmic internal resistance is the resistance of the internal electrodes, electrolytes and connecting components of the battery, while the polarization internal resistance is related to the chemical reaction and ion transport on the electrode surface.

The internal resistance of the battery has an important impact on the discharge performance and efficiency of the battery. Lower internal resistance can reduce energy loss and improve battery discharge efficiency and output power. At the same time, the size of the internal resistance will also affect the temperature rise and charging time of the battery.

(2) Lithium battery voltage

The voltage of lithium battery is divided into open circuit voltage and working voltage. The open circuit voltage is the voltage of the battery when no load is connected, while the operating voltage is the voltage of the battery during the discharge or charging process.

The open circuit voltage usually reaches its highest value when the battery is fully charged, usually around 4.1-4.2V. As the battery discharges, the voltage will gradually decrease, and when the battery is exhausted, the voltage will drop to about 3.0V. The operating voltage will vary based on the load current and battery status.

Voltage is an important parameter for measuring battery power and state of charge. By measuring the battery's voltage, you can get a rough idea of the battery's remaining power and health.

(3) Discharge platform time

The discharge plateau time refers to the time it takes for the battery to discharge from a fully charged state to a specific voltage (such as 3.6V). This indicator reflects the performance of the battery during the stable discharge stage.

A longer discharge plateau time means that the battery can maintain a stable voltage output for a longer period of time and provide stable power support. The discharge plateau time is affected by factors such as the chemical properties of the battery, discharge rate and temperature.

(4) Charge and discharge rate

The charge-discharge rate refers to the current value required by the battery to discharge or charge into the rated capacity within a specified time. Represented by the letter C, such as 1C, which means the battery is fully discharged or charged within 1 hour. A higher charge and discharge rate means that the battery can be charged and discharged quickly, but it will also have a certain impact on the battery's life and performance.

The selection of charge and discharge rates needs to be determined based on specific application scenarios and equipment needs. For example, for devices that require fast charging, you can choose lithium batteries that support higher charging rates.

(5) Self-discharge rate

The self-discharge rate refers to the power loss rate caused by the internal chemical reaction of the battery in the open circuit state. A lower self-discharge rate means the battery is better able to retain its charge during storage.

The self-discharge rate is affected by factors such as the battery's manufacturing process, material quality, and storage conditions. High-quality lithium batteries usually have a low self-discharge rate, which can extend the battery's storage life.

(6) Battery efficiency

The efficiency of lithium batteries includes charging efficiency and discharging efficiency. Charging efficiency refers to the ratio of the input electrical energy converted into chemical energy of the battery during the charging process, while discharge efficiency refers to the ratio of the electrical energy output by the battery to the stored chemical energy during discharge.

The level of efficiency will affect the energy utilization efficiency and charging time of the battery. Higher efficiency means the battery can convert electrical energy more efficiently and reduce energy loss.

(7) Cycle life

Cycle life refers to the service life of a lithium battery when its battery capacity drops to a certain level after multiple charge and discharge cycles. Cycle life is usually evaluated using a specific charge and discharge regime.

Generally speaking, the cycle life of lithium batteries is required to be more than 500 times under GB standards, and the capacity retention rate is more than 60%-70%. Cycle life is affected by many factors, including charge and discharge depth, temperature, charge and discharge rate, etc.

Prolonging the cycle life of lithium batteries can be achieved through reasonable use and charging methods, such as avoiding overcharging and over-discharging, controlling charging temperature, etc. For example, under normal circumstances, it is used for commuting to and from get off work or picking up children to school. If it is driven continuously for about 1 hour (about 25 kilometers) every day within the city, it is equivalent to about 180 battery cycles in a year. If it is qualified The battery can be used for nearly two years. At this time, the battery capacity is still 70% of the rated capacity, which is equivalent to an electric vehicle that can drive continuously for 70 minutes, or about 30 kilometers.

3. Safety performance

4. Environmental adaptability

5. Knowledge points

Attached: Common knowledge about battery cell models 1; Specifications and parameters of large-capacity lithium polymer batteries 2; Specifications and parameters of large-capacity lithium iron phosphate batteries.

6. Summary

To sum up, the performance indicators of lithium batteries cover many aspects, and these indicators are of great significance for evaluating the performance and applicable scenarios of lithium batteries. When selecting and using lithium batteries, it is necessary to comprehensively consider these indicators and make reasonable selection and use according to specific needs. At the same time, continuous technological progress and research are also promoting the improvement of lithium battery performance to meet the growing demand for energy storage.

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