Optimizing Dry Electrode Process with Powder and Electrode Resistivity Analysis

1. Abstract

Dry electrode technology is emerging as a key enabler for next-generation battery formats — including large-format cylindrical cells, semi-solid/solid-state cells, and high-capacity designs — because it eliminates solvent use, reduces capital and energy costs, and enables thicker, crack-free electrodes. This article presents a practical metrology workflow for evaluating dry electrode powder and film quality using IEST Powder Resistivity & Compaction Density Tester (PRCD3100) and IEST Battery Electrode Resistance tester (BER2500). We summarize experimental procedures, key test parameters, and diagnostic readouts that link PTFE fibrillation, feed/processing conditions, and roll-press pressure to powder/electrode resistivity and compactness. The methods help R&D engineers compare materials and processing windows rapidly and quantitatively, accelerating optimization of dry electrode process parameters and formulations.

2. Advantages of Dry Electrode Technology Over Wet Process

Traditional lithium battery manufacturing predominantly uses wet electrode processing. This method involves mixing active materials, conductive agents, and binders in a solvent, coating the slurry onto a current collector ^[1], drying, and calendering. The process, especially for cathodes, requires toxic N-methyl-2-pyrrolidone (NMP) solvent, necessitating extensive and energy-intensive recovery systems. Drying and solvent recovery alone account for a significant portion of equipment, labor, and energy costs. Furthermore, the “binder migration” phenomenon during drying can lead to electrode delamination, poor conductive network formation, and reduced adhesion, issues that are exacerbated in thick electrodes.

In contrast, the dry electrode process offers a compelling alternative. This solvent-free approach directly compresses electrode material powders onto the current collector. The dry electrode technology eliminates the need for solvent recovery, reduces factory footprint and capital expenditure, and is more environmentally friendly. The dry mixing process enables more uniform component distribution without capillary effects, preventing delamination and facilitating the production of crack-free, high-performance thick electrodes ^[3].

3. Main dry electrode routes and their trade-offs

Two dry film-forming methods have matured in industry:

• PTFE fibrillation (binder fibrillation) — Mix active powder, conductive additive and PTFE binder ^[2], then apply high shear to fibrillate PTFE into a network of micro/nanofibers that entangle and bind particles into a self-supporting film. Subsequent roll-pressing consolidates the film and bonds it to the foil.

• Electrostatic powder spraying ^[4] — Charge powder in a spray gun so that particles deposit onto an oppositely charged current collector; the deposited layer is then thermally pressed to coalesce binder and form a film.

PTFE fibrillation is currently the mainstream for dry electrodes because it produces films with superior cohesion, flexibility and process robustness compared with electrostatic spraying. Practical fibrillation is performed using equipment such as high-pressure air classifiers (airflow pulverizers), twin-screw extruders or open mills; airflow mills maximize throughput while screw extruders typically give higher yield. Process parameters — feed rate, shear/pressure, and gas injection pressure (for airflow mills) — strongly influence fibrillation quality and ultimately electrode electrical properties.

4. Experimental Methodology for Dry Process Evaluation

4.1 Test Equipment

This study uses two purpose-built instruments from IEST to quantify electrical and packing properties across powder and film processing steps:

• Powder Resistivity & Compaction Density Tester (PRCD3100) — Measures powder resistivity, electrical conductivity and compaction density while applying controlled compressive loads (up to 5 T). The instrument records resistivity and thickness in real time as pressure is stepped, enabling pressure-dependent powder diagnostics.

• BER2500 Electrode Resistance Tester (BER2500) — Measures resistance, resistivity, conductivity and thickness of electrode disks (Ø14 mm) under applied pressures from 5 to 60 MPa. It supports single-point and variable-pressure scans that simulate calendering and in-service contact conditions.

  

  Figure 1. Schematic diagram of the powder resistivity & compaction density meter (PRCD3100, IEST) and two test principles of powder resistivity

2. Test Conditions

2.1 Testing Equipment:

Figure 1 shows the PRCD3100, an independently developed powder resistivity and compaction density tester by IEST. This equipment allows simultaneous collection of parameters such as resistivity, conductivity, and compacted density of powder samples under different pressures (up to 5T). It assists researchers in studying the effects of varying pressures on the electrical and mechanical properties of powder samples.

Figure 1. Schematic diagram of the powder resistivity & compaction density meter (PRCD3100, IEST) and two test principles of powder resistivity

Figure 2. (a) External view of BER2500; (b) Structural diagram of BER2500.

4.2 Experimental Procedure:

Dry electrode process experimental steps: Active particles, conductive agents, and PTFE binder are mixed in a V-type mixer in a ratio of 95:3:2 by mass. The mixture is thoroughly blended, and then the uniformly mixed powder is fibrillated in an airflow pulverizer. Different feed rates are used to achieve varying degrees of fibrillation in the mixed powder. After fibrillation, the negative electrode mixed powder is roll-pressed under different pressures to form a self-supporting film.

4.2.1 Dry powder resistance testing:

• Prepare two sets each of uniformly mixed positive and negative electrode powders, named Positive-1, Positive-2, Negative-1, and Negative-2. These two sets of powders are fed into the airflow pulverizer at different feed rates to fibrillate them and prepare dry electrode powders. Specifically, the feed rates are Positive-1 > Positive-2 and Negative-1 > Negative-2.
• Within the pressure range of 6 to 350 MPa, with 20 MPa increments, apply pressure in a stepwise manner while maintaining pressure for 10 seconds. Utilize the PRCD3100’s built-in four-probe resistance testing module and thickness testing module to continuously record the changes in resistivity and thickness under different pressures. This allows for the characterization of how resistivity and compacted density of the positive and negative dry electrode powders vary with pressure.

4.2.2 Dry electrode resistance testing:

• Prepare negative dry electrode sheets prepared under different roll pressing pressures for single-point testing, named Negative-1 and Negative-2. Prepare a set of stable production process positive and negative electrode sheets for variable pressure testing.
• Single-point testing: Set up testing parameters in the MRMS software, select single-point testing mode with a pressure of 5 MPa and a holding time of 15 seconds. Sample 6 data points per electrode sheet, with the software automatically recording thickness, resistance, resistivity, conductivity, and other data.
• Variable pressure testing: Set up testing parameters in the MRMS software, select variable pressure testing mode with a lower pressure limit of 5 MPa and an upper pressure limit of 60 MPa, with 5 MPa increments and a holding time of 15 seconds. Select 1 point per electrode sheet for testing, with the software automatically recording thickness, resistance, resistivity, conductivity, and other data.

5. Data Analysis

5.1 Analysis of Dry Powder Resistivity

Figure 3. Comparison of resistivity and compacted density test results for positive and negative dry electrode powders.

Figure 3 displays the test results of resistivity and compacted density for cathode and anode dry electrode powders prepared at different feed rates, where Anode-1 > Anode-2 and Cahode-1 > Cahode-2.

The results indicate that:

• Faster feed rates during airflow fibrillation produced powders with lower electronic resistivity and slightly higher compacted density.

• Mechanistic interpretation: increasing feed rate enhances PTFE fibrillation; initially, micron-scale active particles embed in 100–200 µm PTFE granules, and under continuing shear these PTFE granules elongate into primary fibers (micron scale) and then finer secondary fibers. Well-fibrillated PTFE forms nanofiber sheaths around active particles, improving particle-to-particle contact and enabling a continuous percolating conductive network — outcomes that reduce bulk powder resistivity and increase pack density.

5.2 Analysis of Dry Electrode Resistivity

Figure 4. Comparison of resistivity and thickness test results for cathode dry electrode.

Figure 4 illustrates the resistivity and thickness test results of cathode dry electrode sheets under different roll pressing pressures, where roll pressing pressure Cathode-1 > Cathode-2.

The results indicate that:

• Increasing roll-press (calender) pressure reduces electrode thickness and increases compacted density, yielding a clear reduction in overall electrode resistivity.

• Higher calender pressures also improved measurement repeatability — the coefficient of variation (COV) for resistance decreased at higher nip pressures, indicating more uniform contact and lower statistical dispersion across sampled points.

• Variable-pressure scans of both cathode and anode films show monotonic resistivity decline as applied pressure increases, suggesting that the BER2500 variable-pressure test can emulate calendering and quickly identify target compaction ranges for a given formulation.

Figure 5. Comparison of variable pressure test results for cathode and anode dry electrode.

Figure 5 shows the variable pressure test results for positive and negative dry electrode sheets. The test results indicate that the resistivity of the electrode sheets decreases with increasing test pressure, indirectly simulating the changes in resistivity under different roll pressing pressures. This testing method can assist researchers in quickly identifying the optimal compacted density suitable for the material, thereby saving research and development testing time.

6. Practical Recommendations for Dry Electrode Process Optimization

Based on the diagnostic workflow and observed correlations, we recommend the following practical actions for R&D and pilot lines:

1. Control feed rate during fibrillation — Use feed-rate maps to target PTFE fibrillation states that minimize powder resistivity while avoiding over-fibrillation that could reduce film porosity excessively.

2. Use PRCD3100 pressure sweeps to determine the pressure window where powder resistivity exhibits the strongest improvement; choose downstream calender setpoints accordingly.

3. Employ BER2500 variable-pressure scans on pilot films to validate that calendering yields consistent resistivity and thickness at production pressures (5–60 MPa).

4. Track consistency metrics (mean resistance, standard deviation, COV) across multiple sampling points to detect formulation or process drift early.

5. Document process interactions (e.g., fibrillation degree × calender pressure) because both steps jointly determine final electrode impedance and adhesion.

7. Summary

This study demonstrates how systematic resistance measurement using the PRCD3100 and BER2500 instruments provides critical insights for optimizing thedry electrode process.

Key findings include:

• In the fibrillation stage, a higher jet mill feed rate, associated with greater PTFE fibrillation, produces powders with lower resistivity.

• In the calendering stage, higher pressure produces electrode sheets with lower resistivity and better consistency.

• Variable-pressure testing offers an efficient method for screening optimal compaction parameters.

Dry electrode technology represents a significant upgrade over traditional wet processing, offering a shorter, more cost-effective, and environmentally friendly manufacturing route. It enables higher energy density and superior mechanical properties, making it particularly suitable for next-generation batteries like solid-state and 4680 cells. While challenges remain in perfecting the dry electrode process, its potential for performance enhancement makes it a highly promising direction for future battery manufacturing.

8. References

[1] Li Qingying et al., Dry preparation technology of electrodes and related materials [J] CHINESE JOURNAL OF RARE METALS, 2023, Vol.47 No.12 1705~1715.

[2] DUONG H,SHIN J,YUDI Y. Dry electrode coating technology［A］. 48th Power Sources Conference［C］California: Maxwell Technologies,Inc.,2018: 34－37.

[3] Li Yongxing, et al. Progress in solvent-free dry-film echnology for batteries and supercapacitors[J]. Materials Today,2022.

[4] Al-Shroofy M, Zhang Q, Xu J, et al. Solvent-free dry powder coating process for low-cost manufacturing of LiNi 1/3 Mn 1/3 Co 1/3 O 2, cathodes in lithium-ion batteries[J]. Journal of Power Sources, 2017, 352:187-193.