In the current era of rapid development in lithium-ion battery technology, Direct Current Resistance (DCR) is a core indicator determining a battery’s charge/discharge rate performance, cycle life, and safety. However, the overall DCR of a battery cell is not a single fixed value, but rather the sum of the resistance contributions of its internal components. Understanding the distribution and sources of these resistances is key to unlocking ultra-fast charging performance and optimizing thermal management.
According to Joule’s law, the heat generated during charging is proportional to the square of the current and the resistance (formula: Q=I²Rt). Therefore, achieving ultra-fast charging requires high current input, which necessitates controlling the internal resistance to an extremely low level to suppress heat generation and maintain efficiency. Optimizing DCR can effectively broaden the battery’s power application range.
This article will quantify the contribution of each internal component to the total DCR through a disassembly and analysis of a 2Ah pouch cell. By separating and measuring the resistance of the positive electrode, negative electrode, separator, current collector, and solder joints, we will identify the main factors limiting performance and propose optimization directions.
1. Experimental Methods
A 2Ah pouch cell and its associated separator and current collector were completely disassembled and analyzed. The goal was to isolate and measure the contribution of each component to the cell’s total damping coefficient (DCR). All samples were taken from a brand-new cell to ensure representative testing conditions.
2. Testing Procedure
To accurately analyze the DCR composition of the battery cell, we followed a systematic testing procedure:
• Cell Disassembly: Carefully unpack the aluminum-plastic film packaging in a glove box under inert gas protection to avoid sample contamination.
• Electrode Resistance Measurement: Measure the resistance of the positive and negative electrodes separately using the four-probe method or voltage-controlled method.
• Separator Ion Resistance Measurement: Perform the test using electrochemical impedance spectroscopy (EIS) with a blocking electrode (using a coin cell or a dedicated fixture).
• Current Collector Contact Resistance Measurement: Measure the resistance at the welded tabs and the connection between the foil and the tabs.
• Data Analysis: Integrate the independent measurement data of each component to reconstruct the complete DCR distribution.
Opinion: The experimental method encompasses the resistance of both the electrode assembly and the structural components. The total resistance of the electrode assembly is derived from the test results of each individual electrode. The structural components are relatively simple and easier to test than square structures, but they are difficult to accurately reflect real-world application scenarios. Electrochemical impedance spectroscopy (EIS) of symmetrical cells can further decompose ohmic impedance, membrane impedance, reaction impedance, and diffusion impedance. The choice of the state of charge (SOC) of the symmetrical resistor also affects the resistance value. The change in the cell’s DC resistance (DCR) with SOC also indicates that the DCR is dynamic; in some cases, the DCR at the ends is even twice as high as the DCR in the middle. The corresponding SOC state must also be matched accordingly.
3. Quantification of DC Internal Resistance (DCR) Distribution
Impedance Components | Percentage of Total DCR | Resistance Value (mΩ)
Positive Impedance | 41.22% | 20.73
Negative Impedance | 35.82% | 18.01
Copper Current Collector Resistance | 9.55% | 4.11
Aluminum Current Collector Resistance | 8.16% | 4.80
Separator Ionization Resistance | 5.23% | 2.63
Welding Impedance | 0.02% | 0.012
5. Results and Discussion
Positive and Negative Electrode Impedance: The positive and negative electrodes together contribute 77% of the total DCR, a proportion that largely determines the rate performance of the battery cell. Within the electrode impedance, the following sources can be further distinguished:
• Charge Transfer Resistance: The resistance to lithium ion transport across the electrode/electrolyte interface, a major component of electrode impedance, directly reflecting the kinetics of the electrochemical reaction.
• Warburg Diffusion Impedance: The resistance associated with lithium ion transport within the active material particles. High diffusion resistance significantly reduces the charge/discharge rate of the battery cell at high rates.
• SEI Film Resistance: Additional impedance contributed by the solid electrolyte interphase (SEI) layer. A stable, dense, thin SEI film can maintain this resistance at a low level and extend battery cycle life.
The current collectors (copper foil for the negative electrode and aluminum foil for the positive electrode) contribute nearly 18% of the total DC internal resistance. This resistance originates from the resistivity of the foil itself, the contact resistance between the foil and the electrode coating, and the resistance of the tab welding connection. The foil thickness, width, and tab design all affect this proportion of resistance. Since the current collector carries all the electron current, excessively high resistance here can lead to localized heating, posing a safety hazard under high-rate operating conditions.
Membrane Ion Resistance: Liquid Phase Transport Path
The membrane contributes approximately 5.2% of the DC internal resistance. This is the resistance encountered by lithium ions migrating through the electrolyte-wetted membrane pores, and it primarily depends on the membrane’s porosity, pore size distribution, thickness, and the degree of electrolyte wetting. A high-performance membrane with excellent ionic conductivity is one of the key conditions for achieving high power density.
6. Summary
By physically disassembling the pouch cell and measuring the contribution of each component to the total DC internal resistance, we identified the distribution location of the main internal resistance components. The electrodes themselves contribute more than three-quarters of the total impedance, making them a core target for performance improvement through materials engineering (such as particle size optimization, conductive additives, and coating design). While the current collector and separator account for a small percentage, their contributions are still significant—especially in high-power applications. Reducing their resistance by thickening the foil, optimizing tab welding, or employing advanced separator coatings can significantly improve the cell’s rate performance and thermal behavior. This disassembly and analysis method provides a clear, data-driven roadmap for optimizing pouch cell performance for next-generation electric vehicles and energy storage systems.
