Lithium Battery Grading Principle and Function
Lithium Battery Grading Principle and Function
Lithium battery grading: Simply understood, it is the selection of capacity and the screening and grading of performance. Battery grading involves determining the capacity of lithium batteries by charging and discharging them, and measuring the discharge capacity when the batteries are fully charged. So, how is lithium battery grading done, and what are the methods of grading? Please read on.
What is lithium battery grading?
The first explanation: Lithium battery grading is simply the selection of capacity and the screening and grading of performance. During lithium battery grading, computer management is used to obtain data from each test point, thereby analyzing the size of the battery capacity and data such as internal resistance, determining the quality grade of the lithium batteries. This process is known as grading. After the first grading of lithium batteries, they need to be left to stand for a period, generally no less than 15 days, during which some inherent quality issues will become apparent.
The second explanation: After a batch of lithium batteries is made, although the size may be the same, the capacity of the batteries will vary. Therefore, it is necessary to charge the batteries on the equipment according to the specifications and then discharge them according to the specified current (to depletion). The time it takes to discharge the power multiplied by the discharge current is the capacity of the battery. Only batteries that meet or exceed the designed capacity are considered qualified, while those with a capacity less than the design capacity are not qualified. This process of selecting qualified batteries through capacity testing is called grading.
The formation of lithium batteries: Generally refers to a series of technological measures implemented on batteries during their initial charging to stabilize their performance, including small current charging and discharging, and constant temperature standing.
Principle of lithium battery grading:
The grading of lithium batteries is completed through a formation and grading cabinet (since the basic principles of formation and grading are the same, the functions of formation and grading are integrated into the same cabinet, known as the formation and grading cabinet). The function of the formation and grading cabinet is essentially like a charger, but it can charge and discharge a large number of batteries simultaneously.
During lithium battery grading, computer management is used to obtain data from each test point, thereby analyzing the size of the battery capacity and data such as internal resistance, determining the quality grade of the battery. This process is known as grading.
What is the function of lithium battery grading?
The lithium battery cells produced cannot be sold immediately and should be stored in the warehouse for at least 15 days. During this period, some inherent defects will become apparent, such as excessive self-discharge. After the cells have reached the storage period, they are taken out for re-testing and re-grading after receiving an order, which means recharging and discharging again, eliminating those that do not meet the grade or have quality issues, and then handing them over to the sales department with about 50% of the power remaining, and finally to the mobile phone battery assembly factory.
The battery cells to be used for lithium battery assembly are graded again through the formation machine, and through this process, some cells that do not meet the requirements can be selected and returned to the cell factory. After the lithium battery is tested by the battery testing machine, it can be seen that the cells have been charged and discharged again and are "charged". Therefore, it is normal to have two bars of power when you get the battery.
Each channel of the battery grading can be started and stopped independently, with a fast response. Each channel has an independent constant current source and constant voltage source, with real-time sampling of current and voltage, and truly non-disturbance continuous switching from constant current to constant voltage. It can be used for cycle life testing.
Classifying and organizing lithium batteries involves selecting single cells with the same internal resistance and capacity for combination. Only those with very close performance can be combined into a lithium battery pack. For example, to meet the energy requirements of electric vehicles, a power battery pack often needs to be composed of tens to thousands of batteries. Due to the complexity of the system, the behavior of the battery pack has its uniqueness, and the performance of the battery pack is not simply obtained by adding or subtracting the performance of single cells.
Accuracy requirements for the formation and grading of lithium batteries:
In order to improve the electrochemical performance of lithium batteries, such as cycle life, stability, self-discharge, and safety, it is necessary to strictly control the consistency of lithium batteries or accurately assess the battery grade. Therefore, there are high requirements for the measurement accuracy of current and voltage in the formation and grading equipment. Limited by the sensor acquisition accuracy, the measurement accuracy of current and voltage in the current market formation and grading equipment is generally about one thousandth. The higher the control accuracy of current and voltage for the formation, the better the quality of the lithium battery products. A current voltage sensor with an accuracy above one ten-thousandth is a more ideal choice.
Batteries are all graded and inspected before leaving the factory. The grading cabinet in the lithium battery factory is for grading. Lithium batteries are widely used in various fields such as electronic products due to their high energy density, high voltage, high cycle life, high safety, and environmental protection. Therefore, it is very important to ensure the consistency and reliability of lithium battery products.
