Date: 2026-07-07 hits: 104
Copper foil is used as the negative electrode carrier and current collector in lithium-ion batteries. The thickness of the copper foil plays a crucial role in lithium batteries, affecting their performance, safety, and cost.
I. Impact on Battery Energy Density
1. Mass Energy Density: As a negative electrode current collector, copper foil itself does not participate in electrochemical reactions. The thinner the copper foil, the higher the proportion of active materials (such as graphite) in the battery. For example, reducing the copper foil thickness from 10µm to 6µm reduces the overall mass of inactive materials in the battery by about 40%, allowing for more active material to be accommodated in the same volume, theoretically increasing the mass energy density by 5%-8%.
2. Volumetric Energy Density: The thickness advantage of thinner copper foil directly reduces the volume proportion of inactive materials inside the battery. Taking an 18650 battery as an example, using 8µm copper foil compared to 12µm copper foil can improve the internal space utilization of the cell by about 3%, resulting in a corresponding increase in volumetric energy density.
II. Impact on Battery Internal Resistance and Rate Performance
1. DC Internal Resistance (DCR): The DC resistance of copper foil is inversely proportional to its thickness. According to Ohm's law, the resistance of 10µm copper foil is approximately twice that of 5µm copper foil. Actual measurement data shows that a lithium battery with 10µm copper foil has an internal resistance of approximately 60mΩ at 25°C, while the internal resistance of a battery with 5µm copper foil can be reduced to below 45mΩ. Lower internal resistance helps reduce heat loss during charging and discharging.
2. Rate Performance: Due to its lower resistance, thinner copper foil results in a more uniform current distribution during high-current charging and discharging, preventing localized overheating. For example, a battery using 6µm copper foil can retain 85% of its discharge capacity at a 10C rate, while a battery using 10µm copper foil only retains 78%. The improvement in rate performance is particularly significant in high-power batteries.
III. Impact on Battery Cycle Life
1. Mechanical Strength and Cycle Stability
Copper foil thickness is positively correlated with mechanical strength: the tensile strength of 10µm copper foil is approximately 280MPa, while that of 4µm copper foil drops to 220MPa. Thin copper foil is prone to micro-cracks during electrode rolling or cycling, leading to poor contact between the current collector and active material, and increased internal resistance. Experiments show that batteries with 4µm copper foil retain 82% of their capacity after 500 cycles, while batteries with 8µm copper foil achieve 88%.
2. Risk of Lithium Dendrite Penetration
Copper foil with a thickness less than 5µm is more susceptible to dendrite penetration during long-term cycling if lithium dendrites grow on the negative electrode, leading to internal short circuits. Studies show that batteries using copper foil thinner than 5µm have an internal short-circuit failure rate approximately 30% higher in the later stages of cycling compared to batteries with 8µm copper foil.
IV. Impact on Battery Safety
1. Thermal Conductivity and Heat Dissipation
Copper foil thickness affects the internal thermal conduction efficiency of the battery. The thermal conductivity of 10µm copper foil is approximately 2 W/(m·K). Although increasing the thickness has a limited effect on improving thermal conductivity, thinner copper foil results in a shorter heat dissipation path when heat is concentrated under high current. The risk of localized overheating needs to be compensated for through structural design (such as adding thermally conductive adhesive).
2. Needle Penetration Test Performance: Thicker copper foil (e.g., 10µm) can delay the occurrence of internal short circuits in needle penetration tests because copper itself has a certain mechanical barrier effect. Test data shows that the peak thermal runaway temperature of a battery using 10µm copper foil during needle penetration is 210°C, while the peak temperature of a battery using 6µm copper foil reaches 240°C, indicating a higher risk of thermal runaway.
V. Impact on Production Costs and Processes
1. Material Costs
Copper foil thickness has a linear relationship with cost: 8µm copper foil costs approximately 120 RMB/kg, while 4µm copper foil, due to its complex production process, can cost over 200 RMB/kg. For example, using 6µm copper foil for a 1GWh power battery increases material costs by approximately 800,000 RMB compared to 10µm.
2. Production Process Adaptability
(1) Rolling Process: Thin copper foil (<5µm) is prone to uneven thickness during rolling, requiring roll precision of ±0.5µm. Equipment investment is 50% higher than conventional production lines.
(2) Coating Process: When thin copper foil carries active materials, coating tension control is more stringent. Tension fluctuations exceeding 5N can cause electrode wrinkling, reducing yield from 95% to below 85%. VI. Thickness Selection Strategies for Different Application Scenarios
(1) Consumer Electronics Batteries
Recommended thickness: 4-6µm, prioritizing energy density while considering cycle life (300 cycles required)
(2) Power Batteries
Recommended thickness: 6-8µm, balancing energy density, rate performance, and cycle life (1000 cycles)
(3) Energy Storage Batteries
Recommended thickness: 8-10µm, prioritizing long cycle life (over 5000 cycles) and safety
VII. Conclusion
The selection of copper foil thickness is a comprehensive balance of battery energy density, performance, safety, and cost: Consumer electronics tend towards ultra-thin designs to improve portability, power batteries need to optimize overall performance in the 6-8µm range, while the energy storage field focuses more on the long-cycle reliability of thicker copper foil. With the development of coating technology and composite current collectors, the boundaries of copper foil thickness are gradually being broken, but process stability and cost control remain key to industrialization.
