Analysis of Dynamic Response Characteristics of Lithium Battery Packs

The dynamic response characteristics of lithium battery packs refer to the changes in parameters such as voltage, current, and internal resistance over time under different working conditions (such as variations in charging and discharging currents, temperature changes, etc.). Analyzing the dynamic response characteristics of lithium battery packs is of great significance for the design of battery management systems, the optimization of battery performance, and the guarantee of battery safety. The following is an analysis from several key aspects:

First, the dynamic response characteristics during the charging and discharging process

Voltage response

At the initial stage of charging and discharging: During the initial stage of charging and discharging, the voltage response of the lithium battery pack is relatively fast. For instance, at the beginning of charging, the battery voltage will rise rapidly, which is due to the rapid change in the polarization phenomenon inside the battery. Similarly, at the beginning of discharge, the battery voltage will drop rapidly.

Mid-stage of charging and discharging: As the charging and discharging process progresses, the rate of change in battery voltage will gradually slow down and enter a relatively stable stage. At this point, the change in battery voltage is mainly affected by the rate of chemical reactions inside the battery and the internal resistance of the battery.

At the end of charging and discharging: At the end of charging and discharging, the rate of change of battery voltage will accelerate again. For example, at the end of charging, the battery voltage will rapidly approach the charging cut-off voltage; At the end of discharge, the battery voltage will drop rapidly to the discharge cut-off voltage.

Current response

Current sudden change: When a lithium battery pack is subjected to a current sudden change (such as a sudden increase or decrease in load), its current response will change rapidly. The battery pack needs to be capable of adjusting the output current within a short period of time to meet the load requirements.

Current stability: During the steady-state charging and discharging process, the current of the lithium battery pack should remain relatively stable. Fluctuations in current may cause problems such as an increase in the internal temperature of the battery and an intensification of polarization, thereby affecting the performance and lifespan of the battery.

Internal resistance change

The relationship between internal resistance and charging and discharging states: The internal resistance of lithium battery packs varies with changes in charging and discharging states. During the charging process, the internal resistance of the battery may gradually increase. During the discharge process, the internal resistance of the battery may first decrease and then increase.

The relationship between internal resistance and temperature: Temperature also has a significant impact on the internal resistance of lithium battery packs. Generally speaking, as the temperature rises, the internal resistance of the battery will gradually decrease. However, as the temperature rises further, the internal resistance of the battery may increase again. This is due to the accelerated chemical reaction rate and intensified polarization phenomenon inside the battery.

Second, the influence of temperature changes on dynamic response characteristics

Dynamic response at low temperatures

Voltage drop: In low-temperature environments, the voltage response of lithium battery packs will slow down, and the rate of voltage drop will accelerate. This is due to the fact that the chemical reaction rate inside the battery slows down and the polarization phenomenon intensifies at low temperatures.

Increased internal resistance: Low temperatures can also cause a significant increase in the internal resistance of batteries, thereby affecting their charging and discharging performance and efficiency.

Dynamic response at high temperatures

Voltage fluctuation: In high-temperature environments, the voltage response of lithium battery packs may become unstable, resulting in voltage fluctuation phenomena. This is due to the accelerated chemical reaction rate inside the battery at high temperatures, the intensification of polarization phenomena, and the uneven temperature distribution inside the battery.

Internal resistance change: At high temperatures, the internal resistance of a battery may first decrease and then increase. In the early stage, as the temperature rises, the internal resistance of the battery decreases. However, when the temperature is too high, the internal resistance of the battery may increase again, and even lead to thermal runaway of the battery.

Third, the impact of dynamic response characteristics on battery management systems

State estimation: The battery management system needs to accurately estimate the state of the battery (such as SOC, SOH, etc.) based on the dynamic response characteristics of the lithium battery pack. By monitoring parameters such as voltage, current and temperature of the battery in real time and conducting algorithm calculations in combination with the battery model, an accurate estimation of the battery state can be achieved.

Balance control: In lithium battery packs, due to the differences among individual cells, it may lead to an imbalance during the charging and discharging process of the battery pack. The battery management system needs to formulate a balanced control strategy based on the dynamic response characteristics of the lithium battery pack to ensure that the charging and discharging states of each individual battery in the battery pack remain consistent.

Safety protection: The battery management system also needs to formulate safety protection strategies based on the dynamic response characteristics of lithium battery packs. For instance, when the battery voltage is too high or too low, the current is too large or too small, or the temperature is too high or too low, the battery management system should promptly take measures for protection to prevent safety accidents such as thermal runaway and explosion of the battery.