DCR Breakdown in Pouch Cells: A Teardown Analysis

1. Introduction: The “Hidden Ceiling” of Fast Charging

In the rapidly evolving field of lithium‑ion batteries, direct current resistance (DCR) serves as a fundamental metric that governs charge/discharge rate capability, cycle life, and safety. Pouch cells, prized for their high energy density and lightweight construction, dominate applications ranging from electric vehicles to energy storage systems. However, the overall DCR of a cell is not a single lumped value; it is the sum of contributions from various internal components. Understanding the distribution and origin of these resistances is key to unlocking superior fast‑charging performance and thermal management. According to Joule’s law, heat generated during charging is proportional to the square of the current multiplied by resistance (Q=I²Rt). Achieving ultra‑fast charging therefore demands high currents, which in turn necessitates minimal resistance to control heat and maintain efficiency. Optimizing DCR effectively expands the power envelope of a battery.

This article presents a teardown analysis of a 2 Ah pouch cell, quantifying the contribution of each internal component to the total DCR. By isolating and measuring the resistance of the cathode, anode, separator, current collectors, and welds, we identify the dominant factors limiting performance and suggest directions for improvement.

Figure 1. Factors affecting the fast charging of lithium-ion batteries at different levels^[1]

Figure 2. Schematic illustration of internal impedance and Direct Current Resistance (DCR) components in a battery cell.

2. Experimental Methodology

Our team conducted a comprehensive teardown of a 2Ah pouch cell, alongside its corresponding separator and current collectors. The objective was to isolate and measure the contribution of each component to the total cell DCR. All samples were extracted from a pristine cell to ensure representative conditions.

Figure 3.  Pouch cell sample and components used for Direct Current Resistance (DCR) teardown analysis.

3. Testing Workflow

The workflow for dissecting the cell’s DCR followed a systematic sequence:

• Cell disassembly – carefully opening the pouch under inert atmosphere to avoid contamination.

• Electrode resistance measurement – using a four‑point probe or controlled‑pressure method on both cathode and anode sheets.

• Separator ionic resistance measurement – employing electrochemical impedance spectroscopy (EIS) with blocking electrodes.

• Current collector contact resistance – measuring the resistance of welded tabs and foil‑to‑tab joints.

• Data analysis – combining individual measurements to reconstruct the full DCR budget.

Figure 4. Experimental workflow for quantifying DCR in pouch cell components.

4. Quantifying Direct Current Resistance (DCR) Distribution

We use High-precision instruments, such as the IEST Electrode Tortuosity Tester & Separatorlon Conductivity Tester(EIC Series) and IEST Battery Cycle Tester Electrochemical Property Analyzer(ERT Series), were utilized to ensure 0.01% measurement accuracy. The resulting data reveals a clear hierarchy of impedance contributors:

Figure 5. Pie chart of Direct Current Resistance (DCR) distribution in pouch cells: cathode, anode, and separator.

5. Results and Discussion

5.1 Cathode and Anode Impedance: The Dominant Factor

Together, the cathode and anode account for 77% of the total DCR. This portion largely determines the cell’s rate capability. Within the electrode impedance, three underlying mechanisms can be distinguished:

• Charge‑transfer resistance – the barrier to lithium‑ion transfer across the electrode/electrolyte interface. It is the primary component and directly reflects the kinetics of the electrochemical reaction.

• Diffusion (Warburg) impedance – the resistance associated with lithium‑ion transport inside the active material particles. A high diffusion resistance slows down charge/discharge, especially at high rates.

• SEI layer resistance – for the anode, the solid‑electrolyte interphase contributes an additional impedance. A stable, thin SEI keeps this resistance low and prolongs cycle life.

Figure 6. Nyquist plots for cathode and anode symmetric cells to analyze Direct Current Resistance (DCR) kinetics.

5.2 Current Collector Resistance: The Electronic Highway

The current collectors (copper for anode, aluminium for cathode) together contribute nearly 18% of the total DCR. This resistance arises from the bulk foil resistivity and the contact resistance between the foil and the electrode coating, as well as the welded tab connections. Foil thickness, width, and tab design all influence this contribution. Because the current collectors carry the entire electronic current, any excessive resistance here can lead to localised heating and act as a safety risk under high‑rate operation.

5.3 Separator Ionic Resistance: The Liquid‑Phase Pathway

The separator contributes about 5.2% of the DCR. This is the resistance experienced by lithium ions migrating through the electrolyte‑filled pores of the separator. It depends critically on the separator’s porosity, pore size distribution, thickness, and the degree of electrolyte wetting. A well‑designed separator with high ionic conductivity is essential for achieving high power density.