Ohms law diagram

Relationship Between DCIR and Peak Discharge C-Rate in Lithium-Ion Cells

AION Engineering INC

Correct management of performance parameters in lithium-ion cell technology plays a critical role in energy storage and fast discharge processes.

DCIR represents the internal resistance of the cell under DC current. Therefore, how much the cell will heat up during discharge depends on the current drawn and the DCIR value. The heating of the cell is related to the formula below:

Below is a sample DCIR measurement procedure. (This test can be customized according to the conditions in which the cell is used and can be performed at different SOC, current, and ambient temperature values ​​appropriate for the usage scenario.)

  1. Preparation:
    • Cell fully charged (100% SOC).
    • Constant temperature (25°C).
  2. Open Circuit Voltage Measurement (V1):
    • Measure open circuit voltage
  3. Current Application:
    • Apply 1C current suddenly.
    • Duration: 5 seconds.
  4. Voltage Measurement Under Load (V2):
    • Record the voltage as soon as current is applied.
  5. DCIR Calculation:
  1. Result and Analysis:
    • Repeat the measurement several times and take the average value.
    • Compare with different current levels.

Relationship Between DCIR and Peak Discharge C-Rate

There is an inversely proportional relationship between DCIR and peak discharge C-rate. When the internal resistance is high, the Joule heating (I²R) increases as the current drawn from the cell increases, which makes thermal management difficult and limits the current that can be drawn. Therefore, optimizing the thermal management of the cells ensures safe and efficient operation even at high current demands. The relationship between the data obtained from NMC-based cells available on the market is clearly seen in the graph below. This also shows us that the maximum current value that can be drawn from a cell is due to the design of the cell rather than the material.

Basic Design Factors Affecting DCIR

The main parameters affecting DCIR are:

  • Tab Position and Thickness: Directly affects the length of the current path and resistance. Thicker tabs reduce internal resistance.
  • Foil Thickness and Length: Thick foil provides lower resistance, while long current path leads to increased resistance.
  • Foil-to-Tab Weld: More contact area in the weld = lower joint resistance
  • Layer Count: More layers = more parallel elements = lower resistance (1/R1 + 1/R2 + 1/R3 + … = 1/Rtot)
  • Conductive Agent in Anode and Cathode Muds: Conductive additives increase coating conductivity and reduce internal resistance.
  • Separator Thickness: Thin separators increase ionic conductivity while requiring attention for safety.
  • Electrolyte Concentration: High electrolyte concentration increases ionic conductivity and can also affect viscosity.

The Importance of Optimization

Optimizing these parameters is of great importance to maximize the performance of NMC-based batteries. Especially in cells with high current draw capacity, good planning of thermal management strategies increases performance by maintaining safe operating limits.

Stay tuned for more information and analysis on cell design!

Kerem Buğra Batuş, Cell Design & Process Development

At AION Energy, we accelerate lithium-ion battery development using AI-driven design and advanced technologies, delivering innovative, sustainable energy solutions for a better future

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