Analysis of Electrode Conductivity and Compression Properties in Single and Double-Sided Battery Electrodes

1. Abstract

We present a comparative study of electrode conductivity and compressive behavior for single-sided and double-sided electrodes fabricated from NCM, LCO, and graphite (GR) active materials. Using a IEST BER2500 electrode resistance tester, we measured through-thickness resistance and thickness changes across 5–60 MPa to assess how coating configuration and applied pressure influence electrode conductivity and electrode thickness. The dataset highlights process-sensitive effects that are relevant for electrode formulation, coating strategy, and roll-press settings in production.

2. Introduction: Electrode Conductivity and Coating Configuration in Battery Manufacturing

Lithium-ion batteries have become a primary energy storage solution for consumer electronics, electric vehicles, and grid storage due to their long cycle life and high-rate capability. However, challenges remain in reducing production costs while improving performance and durability. A deep understanding of manufacturing processes and their impact on final cell performance is therefore critical. Future advancements depend not only on materials but also on production engineering.

Electrode fabrication processes—including coating and calendering—are crucial for achieving desired electrode compaction density and designed capacity. To increase battery capacity and enhance electronic conductivity and electrochemical performance, cell manufacturers often employ specific coating and calendering strategies. Investigating the microstructural evolution of electrodes during these processes, and understanding how process parameters influence final electrode structure and properties, enables finer control over electrode performance. This is essential for optimized lithium-ion battery design and manufacturing control ^[1].

Electronic conductivity is a key factor determining battery performance. Taking graphite anodes as an example, during charge/discharge, lithium ions intercalate into and deintercalate from the graphite layered structure. Using an advanced two-probe method to measure electrode resistance, and applying pressure to simulate the calendering process, reveals that the resistivity of a fully calendered electrode can drop to about one-third of that of an uncalendered electrode sheet ^[2]. Since cathode active materials typically exhibit low intrinsic conductivity, manufacturers incorporate significant amounts of conductive additives. The conductive network formed by these additives plays the primary role in electron transport. After calendering, active material particles pack more tightly, and the compression of conductive additives at particle boundaries is the main reason for the increase in coating conductivity, whereas the conductivity at the active material surface is less affected. This places higher demands on the uniformity of component distribution during slurry mixing and coating^[3].

3. Experimental Instrument and Test Methods

3.1 Experimental Equipment

The test equipment used was the BER2500 Electrode Resistance Tester (IEST), with an electrode diameter of 14 mm and an applicable pressure range of 5–60 MPa. The equipment is shown in Figures 1(a) and 1(b).

Figure 1. (a) BER2500 appearance; (b) BER2500 structure diagram

3.2 Sample Preparation

Prepare lithium cobalt oxide (LCO) and ternary material (NCM) material slurries with the same formula, at the same time, prepare graphite (GR) slurry, apply LCO and NCM slurry on aluminum foil, apply GR slurry on copper foil, and apply two sheets of each electrode. After the electrode is dry, select one of them and apply it on the reverse side to make a double-sided electrode. Single-sided and double-sided electrodes of three different active materials were thus obtained.

3.3 Testing Procedure

Using IEST’s BER2500 equipment, tests were conducted in Single-Point Mode, Variable-Pressure Mode, and Steady-State Mode to compare sheet resistance and compression properties of the single and double-sided samples.

• Single-Point Mode: A pressure of 25 MPa (cathode) or 5 MPa (anode) was applied at six uniform points on the electrode. Pressure was held for 15 seconds at each point.

• Variable-Pressure & Steady-State Mode: A single point was selected. Pressure was increased in 5 MPa intervals from 5 MPa to 60 MPa, holding for 15 seconds at each step to measure sheet resistance and thickness. This constituted the Variable-Pressure Mode. Subsequently, in Steady-State Mode, pressure was decreased in identical 5 MPa intervals, again holding for 15 seconds at each step until reaching 5 MPa. Software recorded thickness and real-time resistance, outputting a data file.

4. Results: Electrode Conductivity Variations in Single and Double-Sided Electrodes

Resistivity tests under different pressures were performed on the single and double-sided electrodes for the three active materials. Results for NCM are shown in Figure 2 as an example. The data indicate a difference in resistivity between single and double-sided NCM electrodes at low pressure; this difference diminishes as pressure increases. A similar trend was observed for LCO and GR samples.

Comparing resistivity at the same pressure points, double-sided LCO and NCM electrodes showed slightly higher resistivity than their single-sided counterparts at low pressure, converging as pressure increased. This is attributed to differences in contact resistance. The GR samples exhibited relatively consistent resistivity across all pressure points.

Traditional four-probe methods primarily characterize coating resistance, as current flows parallel to the coating layer, ignoring interface resistance with the current collector and coating gradients. Our method aligns the electron conduction path with that in an actual battery cell. Since the Cu foil, Al foil, and probe materials are highly conductive, their bulk resistance is minimal. However, contact resistance between the probe and the coating cannot be ignored. For single-sided electrodes, one probe contacts the current collector directly, while for double-sided electrodes, both probes contact the coating. This contact difference causes the observed resistivity discrepancy. Increasing test pressure improves probe contact, reducing the proportion of contact resistance and minimizing the resistivity difference between single and double-sided electrodes. Consequently, subsequent Single-Point Mode tests used 25 MPa for LCO/NCM and 5 MPa for GR.

Figure 2. Resistivity curves for three types of single and double-sided electrodes

5. Analysis of Electrode Thickness and Compression Properties

Figures 3(a), 3(b), and 3(c) show the resistance, resistivity, and total electrode thickness measured at six different locations on single and double-sided samples under constant pressure. Overall, for the same material, the Coefficient of Variation (COV) for resistivity across different measurement locations was similar for single and double-sided versions. However, comparing the three materials, the resistivity COV trend was GR > LCO > NCM. This relates to active material properties and electrode microstructure. Firstly, the material’s intrinsic resistivity influences the COV; lower resistivity magnifies the impact of contact resistance on results. GR has very low resistivity, leading to a higher COV. Secondly, material hardness may affect results; softer materials may form more consistent interfaces under pressure, yielding better test consistency. LCO, being less deformable (Figure 4), showed a higher COV than NCM. The use of lower pressure for GR testing might also contribute to its higher COV. Finally, slurry dispersion uniformity during preparation plays a role; better dispersion results in lower resistivity COV for both single and double-sided electrodes.

From Figure 3(a), the resistance of double-sided electrodes is approximately double that of their single-sided counterparts. However, the thickness of double-sided samples (Figure 3(c)) is slightly less than double that of single-sided ones. Therefore, the resulting resistivity (Figure 3(b)) shows little difference between single and double-sided configurations, as it is normalized by thickness. Furthermore, testing at higher pressures minimizes the proportional contribution of contact resistance, further reducing the resistivity difference.

Figure 3. Consistency across different measurement locations for three types of single and double-sided electrodes

The steady-state mode was used to conduct loading compression-unloading rebound tests on the electrode under different quantified pressure conditions, and the thickness changes were recorded. The thickness deformation was normalized and calculated based on the initial pressure point of 5MPa, the stress-strain curves of different electrodes are obtained (as shown in Figure 4), and their deformation conditions are summarized (as shown in Table 1).

Figure 4. Stress-strain (compression property) curves for three types of single and double-sided electrodes

Table 1. Summary of deformation for three types of single and double-sided electrodes

The results show consistent trends for maximum deformation, reversible deformation, and irreversible deformation across the single and double-sided electrodes of all three active materials. The thickness change for double-sided coatings was not significantly different from single-sided ones. Since the coating layer undergoes most of the deformation compared to the metallic current collector during compression, the minor differences observed are likely due to the varying proportion of current collector thickness within the total electrode thickness. This indicates that the compression properties are primarily determined by the active material’s characteristics.

6. Comparative Performance of Single-Sided vs Double-Sided Electrodes

The comprehensive testing reveals several key distinctions between single and double-sided electrode configurations. While double-sided electrodes exhibited approximately double the resistance of single-sided versions, their resistivity values—when properly normalized for thickness and measured at appropriate pressures—showed remarkable convergence. This demonstrates that the fundamental conductivity properties remain consistent regardless of coating configuration when measurement conditions are optimized.

Notably, the contact resistance effects proved more pronounced in double-sided electrodes, particularly at lower pressure levels. However, this effect diminished significantly when testing pressures were increased to simulate actual calendering conditions. For LCO and NCM cathodes, the optimal testing pressure was established at 25 MPa, while graphite anodes required only 5 MPa to achieve consistent results across both single and double-sided configurations.

7. Compression, recoverability and irreversible deformation

Stress–strain curves derived from ramp and unload cycles show consistent trends across materials. Maximum, reversible, and irreversible thickness changes follow the same relative ordering for single- and double-sided electrodes, indicating that the coating architecture (single vs. double) does not fundamentally change compressibility; instead, the active material’s mechanical properties dominate. In short, electrode thickness evolution under compressive loading depends primarily on the active-layer mechanical response and the relative fraction of current collector in the stack thickness. This result highlights that optimizing electrode thickness and spring-back behavior requires material-level tuning (binder, conductive-additive distribution, and particle morphology) as much as process control.

8. Conclusion: Optimizing Electrode Conductivity Through Coating Design

This study utilized the IEST BER2500 Electrode Resistance Tester to analyze the conductivity and compression properties of single and double-sided NCM, LCO, and GR electrodes. The method effectively distinguishes performance variations based on coating configuration while demonstrating that intrinsic material properties—rather than coating geometry—primarily determine compression behavior.

The findings provide crucial insights for battery manufacturing optimization. In practical production, the choice between single or double-sided coating should consider the specific process and formulation requirements. While double-sided coating enhances energy density, our results confirm that proper process control can maintain consistent electrode conductivity regardless of configuration. This conductivity testing approach enables rapid investigation of process impacts on electrode resistivity and can potentially be implemented directly within production lines for quality control.

Ultimately, this work demonstrates that understanding the fundamental relationships between electrode conductivity, thickness, and coating configuration enables manufacturers to make informed decisions that enhance both battery capacity and overall electrochemical performance.

9. References

[1] Lu Zhaocai, Wang Yuxi, Wang Zhitao, Sun Xiaohui, Li Jingkang. Influence of heated calendering process on cathode film performance of lithium-ion batteries.[J]. Energy Storage Science and Technology.

[2] Zhang Caixia. Research on correlation of artificial graphite processing performance.[J]. Power Supply Technology, 2022, 46(11): 1256-1260.

[3] Song Lan, Xiong Ruoyu, Song Huaxiong, Tan Penghui, Zhang Yun, Zhou Huamin.Multiscale nonuniformity of lithium-ion batteries.[J]. Energy Storage Science and Technology, 2022, 11(02): 487-502.