Abstract: In this paper, the analysis method of charge and discharge curve of lithium battery is introduced in detail, including charge efficiency, discharge characteristics, capacity evaluation, internal resistance evaluation and cycle life evaluation. Through the interpretation of the charge and discharge curve, the performance and characteristics of lithium batteries can be deeply understood, which provides an important basis for the selection, use and optimization of batteries.

I. Introduction

The performance of lithium batteries is crucial to the operation of various electronic devices and power tools. Charge and discharge curve is one of the important means to evaluate the performance of lithium batteries, which can directly reflect the voltage and current changes in the process of charging and discharging. By analyzing the charge-discharge curve, the information about the battery capacity, internal resistance, efficiency and other key parameters can be obtained, which can provide guidance for optimizing the battery design and improving the battery performance.

Second, lithium battery charging curve analysis

The charge and discharge curve of the lithium battery is the relationship between the voltage and discharge capacity of the battery, and also the curve of the remaining capacity SOC. In the process of charging the lithium battery, the voltage gradually rises and the current gradually decreases. The slope of the charging curve reflects the speed of the charging speed, and the higher the slope, the faster the charging speed. At the same time, the platform area of the charging curve indicates that the battery is full, at which point the voltage tends to stabilize.
1. Charging efficiency analysis: Charging efficiency is an important indicator to measure battery charging performance. The higher charging efficiency means that the battery can more efficiently convert the incoming electrical energy into chemical energy for storage. By comparing the actual charging capacity with the theoretical charging capacity of the charging curve, the charging efficiency can be evaluated. In addition, the energy loss during charging can be observed to find ways to improve the efficiency of charging.
2. Charging termination voltage: charging termination voltage refers to the voltage value when the battery is full. Setting the charge termination voltage correctly can avoid overcharge and extend battery life. By analyzing the charging curve, the appropriate charging termination voltage is determined to ensure that the battery is charged within the safe range.

Third, lithium battery discharge curve analysis

During the discharge process, the voltage drops gradually and the current also decreases. The shape and slope of the discharge curve can also provide important information about battery performance.

1. Evaluation of discharge characteristics: the slope of the discharge curve can reflect the discharge performance of the battery. A flatter discharge curve usually indicates that the battery has good discharge stability and can provide stable energy output. In addition, by observing the platform area of the discharge curve, the voltage changes of the battery at different discharge depths can be understood and the discharge capacity of the battery can be evaluated.

The voltage varies with different temperature

2. Discharge capacity evaluation: the area of the discharge curve is proportional to the discharge time, so the discharge capacity of the battery can be evaluated by calculating the area under the curve. The size of the discharge capacity directly affects the use time and endurance of the battery.

3. Internal resistance: Internal resistance is the resistance inside the battery, which will affect the discharge characteristics. Higher internal resistance will lead to faster voltage drop and lower discharge power. By analyzing the discharge curve, the internal resistance of the battery can be estimated and its effect on the battery performance can be assessed.

Fourth, capacity evaluation

The capacity of a lithium battery refers to the amount of charge that the battery can store, usually expressed in milliampere-hours (mAh) or ampere-hours (Ah). By integrating the charge and discharge curve, the actual capacity of the battery can be calculated. At the same time, multiple charge and discharge cycle tests can also be carried out to observe the attenuation of capacity to evaluate the cycle life of the battery.
Fifth. Evaluation of internal resistance

Internal resistance is the resistance inside the battery, which affects the charge and discharge performance and efficiency of the battery. The smaller internal resistance helps to improve the discharge efficiency and power output of the battery. The internal resistance of the battery can be estimated by analyzing the relationship between voltage and current in the charge-discharge curve. In addition, the size of the internal resistance is also related to the health state of the battery, so the internal resistance evaluation can also be used for battery fault diagnosis.

Sixth. Cycle life assessment
Cycle life refers to the ability of a battery to maintain certain performance after multiple charge and discharge cycles. The cycle life of the battery can be evaluated by observing the change of the charge and discharge curve of multiple cycles. If the shape and characteristics of the curve remain relatively stable after multiple cycles, it indicates that the battery has a good cycle life. At the same time, the capacity decay during the cycle can also be analyzed to predict the service life of the battery.

Seventh. Summary

The charge and discharge curve of lithium battery is the relationship between the voltage and discharge capacity of the battery, and also the curve of the remaining capacity SOC, which is an important means to better analyze and evaluate the performance of the battery. Through the analysis of charging efficiency, discharge characteristics, capacity, internal resistance and cycle life, the performance of the battery can be fully understood. This analysis method is of great significance for battery design optimization, quality control and application selection. In practical applications, combined with a variety of testing means and data analysis methods, the performance of lithium batteries can be more accurately evaluated, and the reliable operation of all kinds of electronic equipment and power tools can be guaranteed.