Internal Resistance of Lithium Ion Battery

Lithium Battery Internal Resistance

The internal resistance of lithium batteries is one of the important parameters for measuring their performance, directly affecting the battery's discharge efficiency, energy density, cycle life, and safety. Here is an analysis of the issues related to the internal resistance of lithium batteries:

1,Definition and Composition of Internal Resistance

The internal resistance of lithium batteries includes ohmic resistance and polarization resistance. Ohmic resistance is mainly composed of the resistance of electrode materials, electrolyte, separator, and the contact resistance of various parts, which is related to the battery's size, structure, and connection method. Polarization resistance refers to the resistance caused by polarization during electrochemical reactions, including electrochemical polarization resistance and concentration polarization resistance.

2, Factors Affecting Internal Resistance

Structural Design: The number, size, and position of battery tabs directly affect the size of the battery's internal resistance. Increasing the number of tabs can effectively reduce the battery's internal resistance.
Raw Material Performance: The performance of positive and negative electrode active materials, conductive agents, coating, and calendaring will affect the internal resistance. For example, the electronic conductivity between particles can be improved by coating and doping the positive electrode materials.
Manufacturing Process: The preparation process of electrodes and separators, the assembly process of the battery, and the injection process of the electrolyte will all affect the battery's internal resistance to some extent.
Operating Conditions: Temperature, charging and discharging status, usage duration, and the size of the load current will also impact the internal resistance.

3, Methods of Measuring Internal Resistance

DC Internal Resistance Measurement Method: Apply a short-time pulse to the battery using a current source, measure the difference between its terminal voltage and open-circuit voltage, and divide this difference by the test current, which is considered the battery's DC internal resistance.
AC Internal Resistance Measurement Method: Apply a small amplitude AC input to the battery as an excitation, monitor its terminal voltage response, and use a specific program to analyze the data to obtain the battery's AC internal resistance.

4, Impact of Internal Resistance on Battery Performance

Discharge Efficiency: A lower internal resistance can reduce energy loss during charging and discharging, improving the battery's output power and efficiency.
Energy Density: There is a trade-off relationship between battery internal resistance and energy density; batteries with high energy density may have higher internal resistance.
Cycle Life: An increase in battery internal resistance is usually related to the battery aging process. Therefore, monitoring changes in battery internal resistance is significant for predicting battery life and maintaining the battery's health status.

5, Internal Resistance and Environmental Factors

Temperature: Temperature is a key environmental parameter affecting battery internal resistance. Under low-temperature conditions, the ion conductivity of the electrolyte decreases, leading to an increase in battery internal resistance.
Charging and Discharging Cycles: After undergoing multiple charging and discharging cycles, the internal structure of the battery may undergo subtle changes, which can lead to an increase in battery internal resistance.

In summary, the internal resistance of lithium batteries is a complex phenomenon affected by various factors and has a direct and profound impact on battery performance. Understanding and optimizing battery internal resistance is crucial for improving the overall performance of the battery.