Carbon-coated Aluminum Foil for Enhanced LiFePO₄ Electrode Conductivity

1. Abstract

This study employs the IEST Battery Electrode Resistance Analyzer (BER2500) to evaluate and compare the electronic conductivity of bare aluminum foil and carbon-coated aluminum foil, as well as the conductivity of LiFePO₄ electrodes coated on each type of current collector. The research aims to elucidate how carbon-coated aluminum foil improves electrode performance in lithium-ion batteries, particularly for LiFePO₄-based systems.

Lithium-ion batteries comprise multiple integrated components, including electrodes, separators, and electrolytes. The electrode, especially the current collector, plays a vital role in electron conduction and active material support. Aluminum foil is widely used as a current collector in positive electrodes. To enhance rate capability, cycle life, and adhesion, conductive coatings—especially carbon coatings—are applied to the foil. This aluminum battery coating reduces interfacial resistance, improves bonding with active materials, and mitigates issues such as particle detachment during cycling.

2. Introduction

Lithium-ion batteries are complex systems composed of cathode and anode electrodes, separators, electrolytes, and current collectors. Among these, the current collector is crucial for electron conduction and structural support. Aluminum foil is the most widely used positive electrode current collector, valued for its high conductivity and stability. However, the conductivity of aluminum foil alone is not always sufficient to meet the performance requirements of advanced electrodes such as LiFePO₄.

To address this, manufacturers increasingly use aluminum battery coatings, most commonly in the form of carbo-coated aluminum foil. This conductive carbon layer reduces contact resistance, strengthens bonding between the active material and the collector, and minimizes issues such as particle detachment during cycling^[1]. In particular, CCAF is widely adopted for LiFePO₄ electrodes, where the material’s inherently low electronic conductivity and weak adhesion to current collectors limit performance.

When applied, the carbon coating improves surface roughness and contact uniformity, lowering charge transfer resistance and internal polarization. This enhances lithium-ion diffusion, leading to better rate capability, cycling stability, and longer service life for LiFePO₄-based batteries.

Figure 1. Schematic diagram of surface morphology for bare aluminum foil and carbon-coated aluminum foil ^[1]

Currently, most of the carbon-coated aluminum foils are utilized LiFePO₄ power batteries. This is mainly due to the inherent low electronic and ionic conductivity of the olivine crystal structure LiFePO₄ material and issues such as weak adhesion to the current collector ^[2]. However, the application of carbon-coated aluminum foil is somewhat limited. Carbon-coated aluminum foil exhibits lower contact impedance and higher adhesion. When applied to the positive electrode current collector of LiFePO₄ , it reduces the charge transfer resistance between them and the internal resistance of the battery. This diminishes internal polarization of the battery, enhances the diffusion rate of lithium-ion within the material, thereby improving the rate capability and cycling performance of the battery ^[3-5].

Figure 2. Schematic Diagram Illustrating the Impact of Carbon-Coated Current Collectors on Cell Performance^[1]

3. Test Conditions

3.1 Test Equipment

Testing was performed using the IEST Battery Electrode Resistance Analyzer (BER2500), designed for precise measurement of electrode resistance, resistivity, conductivity, and compaction density. Samples of bare aluminum foil and carbon-coated aluminum foil, as well as LiFePO₄ electrodes coated on each foil type, were prepared for analysis(Figure 3).

The BER2500 allows testing under pressures from 5–60 MPa, simulating realistic electrode manufacturing conditions. By monitoring resistance and conductivity at different pressures, it provides insights into the mechanical and electrical behavior of coated foils.

Figure 3. (a): External view of BER2500; (b): Structural diagram of BER2500

3.2 Experimental Procedure

Foil Resistance Test

• Samples: bare aluminum foil (KB) and carbon-coated aluminum foil (TCB).

• Parameters: single-point test at 5 MPa for 15s, with 8 measurements per sample.

• Data: thickness, resistance, resistivity, and aluminum foil conductivity were recorded.

Electrode Resistance Test

• Samples: LiFePO₄ coated on bare aluminum foil (K-LFP) and LiFePO₄ coated on carbon-coated aluminum foil (TC-LFP).

• Parameters: single-point test at 25 MPa for 15s, with 8 measurements per electrode.

• Data: electrode thickness, resistance, resistivity, conductivity, and compaction density

4. Data Analysis

4.1 Foil Resistance Analysis

Figure 4. Comparison of Thickness, Resistance, and Resistivity Test Results for Two Types of  Foils

As shown in Figure 4, the carbon coated aluminum foil exhibited greater thickness due to the dual-side carbon layer (~2 µm). Although its electrical conductivity was lower than that of bare foil—attributed to additional interfacial contact resistance—the carbon-coated variant demonstrated superior measurement stability and lower coefficient of variation (COV). The carbon layer increases surface roughness, offering more electron pathways and improving test reproducibility.

3.2 Electrode Resistance Analysis

Figure 5. Comparison of Thickness, Resistance, and Resistivity Test Results for Two Types of Electrodes

For LiFePO₄ electrodes, the results were reversed: electrodes on carbon coated aluminum foil exhibited lower resistance and resistivity compared to electrodes on bare foil. The conductive carbon layer increased the contact area between the active material and current collector, reducing interface resistance and enabling more efficient electron transfer.

Additionally, the carbon layer improved adhesion and provided mechanical buffering, reducing particle detachment during cycling. This enhanced the long-term durability of LiFePO₄ electrodes, demonstrating that aluminum battery coatings play a significant role in advancing electrode stability and battery performance.

4. Summary

This study utilized the Battery Electrode Resistance Analyzer (BER2500) developed by IEST to test the electronic conductivity performance of bare aluminum foil and carbon-coated aluminum foil, as well as the electronic conductivity performance of  LiFePO₄ electrodes coated on bare aluminum foil and carbon-coated aluminum foil. The study investigated the impact of adding a carbon coating on the electronic conductivity of foils and LiFePO₄ electrodes.

This study shows that while bare aluminum foil has higher initial conductivity, carbon-coated aluminum foil is superior as a current collector for LiFePO₄ electrodes. By reducing interface resistance, improving adhesion, and stabilizing conductivity, the aluminum battery coating improves rate performance, cycle life, and overall electrochemical stability.

In summary, in addition to improving interface contact resistance, the use of carbon-coated aluminum foil also potentially provides the following synergistic benefits:

(1) The chemically and electrochemically stable conductive layer can serve as an effective diffusion barrier, preventing the diffusion of oxygen generated during electrolyte decomposition and lithium-ion insertion reactions. This effectively prevents the formation of an oxide layer on the surface of the metal current collector, thereby preventing degradation;

(2) The conductive layer with a well-designed formulation exhibits good conductivity, enabling the formation of large contact areas with low interface resistance between the current collector and the active coating. This facilitates rapid charge transfer processes;

(3) The flexibility and mechanical buffering of the conductive layer can enhance the adhesion of the physical interface, thereby minimizing the loss of contact area caused by stress generated at the interface during long-term cycling reactions. Through the design and development of unique conductive coatings, experimental results have demonstrated that the conductive interface layer can significantly improve electrochemical performance, such as reversible capacity, capacity retention, and rate capability.

5. References

[1] Busson, C, Blin, M.A., Guichard, P., Soudan, P., Crosnier, O., Guyomard, D., & Lestriez, B. (2018). A primed current collector for high performance carbon-coated LiFePO4 electrodes with no carbon additive. Journal of Power Sources, 406, 7-17.

[2] Kong Lingyong, Huang Shaozhen, Shang Weili, et al. Preparation of carbon-coated aluminum foil with highly conductivity and the effect on high energy density LiFePO₄ battery[J]. Electronic Components and Materials, 2016, 35(1): 64-67.

[3] DENG Long-Zheng, WU Feng, GAO Xu-Guang, XIE Hai-Ming, YANG Zhi-Wei. Effects of Coating Carbon Aluminum Foil on the Battery Performance[J]. Chinese Journal of Inorganic Chemistry, 2014, 30(4): 770-778.

[4] Ma Shoulong, Yang Maoping, Liu Xingliang, et al. Study on the effect of aluminum-coated carbon on the performance of LiFePO4/C batteries[J]. Battery, 2017, 47(1): 39-42.

[5] Yang Fanming, Jiao Qifang, Wu Wei, et al. Influence of carbon coated aluminum foil on the performance of LiFePO₄ battery.[J]. Chemical Engineering Progress, 2019, 38(10): 4639-4644.