As the core current collector material for lithium-ion battery anodes, copper foil plays a critical role in determining battery energy density, reliability and safety. This article provides a systematic overview of copper foil selection, covering manufacturing processes, thickness classification and performance standards, while also examining emerging trends such as composite copper foil technologies.
1. Classification of Copper Foil
1) By Manufacturing Process
Electrolytic Copper Foil (ED Copper Foil)
Accounting for over 90% of the market, ED copper foil is characterized by mature technology and cost efficiency.
· Leading Chinese producers: Nuode Copper (ultra-thin copper foil below 6 μm), Jiayuan Technology, Zhongyi Technology, Defu Technology
· International suppliers: Mitsui Mining & Smelting (Japan), producing 3–5 μm ultra-thin copper foil
Rolled Annealed Copper Foil (RA Copper Foil)
RA copper foil offers superior ductility and flexibility but faces higher technical barriers and significantly higher costs.
· Major suppliers: Nippon Mining (Japan), Fukuda Metal Foil & Powder, Olin Brass (US)
· Large-scale domestic production has yet to emerge in China
2) By Thickness (IPC Standard)
· Ultra-thin copper foil: ≤ 6 μm (e.g. 4.5 μm, 6 μm)
· Very thin copper foil: 6–12 μm
· Thin copper foil: 12–18 μm
The mainstream product remains 6 μm copper foil, accounting for approximately 58% of the market, while 4.5 μm foil has seen rising penetration, reaching around 6%.
3) By Performance Grade (IPC Standard)
Copper foil is categorized into six grades, including Standard Electrolytic (STD-E), High Ductility (HD-E) and High-Temperature High-Ductility (THE-E), based on tensile strength, elongation and thermal performance.
2. Why Copper Foil Is Used for Anodes
1) Electrochemical Stability
At anode operating potentials (~0.1 V vs. Li/Li⁺), copper does not undergo lithium intercalation, whereas aluminium can form lithium–aluminium alloys at low potentials, leading to failure.
The oxide layer on copper foil is relatively loose and does not significantly impair conductivity, while aluminium forms a dense oxide film that is prone to corrosion at elevated potential.
2) Electrical Conductivity and Mechanical Strength
Copper exhibits superior electrical conductivity (5.96 × 10⁷ S/m) compared with aluminium (3.5 × 10⁷ S/m), effectively reducing internal resistance.
Its high ductility (elongation ≥ 5%) and tensile strength (≥ 300 MPa) ensure mechanical integrity during coating, slitting and winding processes, minimising the risk of electrode cracking.
3) Process Compatibility
The roughness of ED copper foil (Rz ≤ 2.5 μm) enhances adhesion between the active material and the current collector, reducing coating delamination.
Although composite copper foil solutions (e.g. PET-based copper foil) offer substantial weight reduction—up to 65%—traditional ED copper foil remains dominant in mass production due to higher process maturity and stability.
4) Safety Considerations
Copper foil has a dissolution potential of approximately 3.35–3.40 V. Under severe over-discharge conditions (< 2.5 V), copper dissolution may occur, posing safety risks. This is typically mitigated through battery management systems (BMS) by setting a discharge cut-off voltage of ≥ 2.5 V.
3. Application Trends in Specialized Copper Foils
Composite Copper Foil (e.g. PET-Based Copper Foil)
· Structure: A 4–6 μm polymer substrate (PET or PP) coated with ~1 μm copper layers on both sides
· Advantages:
o Weight reduction of 50–80%
o Energy density improvement of 5–10%
o “Point-disconnection” effect under puncture, enhancing safety
· Challenges:
o High equipment costs
o Yield improvement still required, particularly in electroplating processes (e.g. equipment supplied by Dongwei Technology)
4. Conclusion
Copper foil remains the preferred anode current collector for lithium-ion batteries due to its balanced electrochemical stability, superior conductivity, mechanical robustness and strong process compatibility. The mainstream solution continues to be 6 μm electrolytic copper foil (e.g. Nuode NT6, Jiayuan JY6), while further thickness reduction to 4.5 μm and the adoption of composite copper foil represent key future development directions.
Material selection should ultimately be based on a comprehensive assessment of battery design objectives—such as energy density and safety—alongside cost considerations.
Source：OFweek Lithium Battery Network