The Crucial Role of Foil Production in Manufacturing Lithium-ion Battery Copper Foil
The current production of lithium-ion battery copper foil is primarily done through the ED copper foil method, which involves four main stages: copper dissolution, original foil manufacturing, surface treatment, and slicing inspection. Among these, the key stage lies in the use of a ED copper foil machine to electrolytically prepare the original foil. In this process, the electrolyte undergoes ionization under the influence of direct current and water molecules, causing copper ions to move towards the cathode drum of the ED copper foil machine where they are reduced and deposited as copper foil.
The know-how in the ED copper foil process forms a technological barrier. It involves stages such as additive formulation debugging, cathode drum surface grinding, production current-voltage output efficiency calibration, which also differ among copper foil manufacturers, creating their own technological barriers. Based on the core technology of ED copper foil, it covers five major areas: manufacturing technology for ultra-thin and extremely thin ED copper foil, additive technology, cathode drum grinding technology, copper dissolution technology, and copper powder cleaning technology, among which three are used for the foil-making process.
Key Technical Indicators of Lithium Battery Copper Foil
Key technical indicators of lithium-ion copper foil encompass various parameters, such as thickness and tensile strength, directly affecting the energy density, lifespan, and safety of lithium-ion battery products. Key physical performance indicators of copper foil mainly include thickness, thickness uniformity, surface density, surface roughness, tensile strength, elongation, porosity, etc., while chemical performance indicators include oxidation resistance, corrosion resistance, heat resistance, and other durability indicators. Relatively, thinner copper foil is more prone to breakage, affecting the safety of lithium-ion batteries. Therefore, extremely thin or ultra-thin copper foils need to possess higher tensile strength, posing higher technical requirements for the comprehensive performance of copper foil products.
| Technical Indicator | Impact on Lithium Battery | Indicator Requirements |
| Thickness | Energy Density | Lower thickness leads to higher energy density |
| Thickness Uniformity | Capacity and Performance Consistency | Higher thickness uniformity results in higher battery capacity and consistency |
| Area Density | Mass, Capacity, and Energy Density | Lower area density leads to lighter batteries with higher capacity and energy density |
| Surface Roughness | Internal Resistance and Cycle Life | Lower surface roughness results in lower internal resistance and longer cycle life |
| Tensile Strength | Yield Rate, Capacity, Internal Resistance, and Cycle Life | Higher tensile strength leads to higher yield rate, capacity, lower internal resistance, and longer cycle life |
| Elongation | Yield Rate, Capacity, Internal Resistance, and Cycle Life | Higher elongation leads to higher yield rate, capacity, lower internal resistance, and longer cycle life |
| Porosity | Rate Performance and Cycle Life | Lower porosity leads to better rate performance and longer cycle life |
| Oxidation Resistance, Corrosion Resistance, Heat Resistance | Yield Rate, Safety, and Cycle Life | Stronger resistance leads to higher yield rate, safety, and longer cycle life |
The ‘extreme thinning’ trend of lithium-ion copper foil
The ‘extreme thinning’ trend of lithium-ion copper foil has emerged. The thickness indicator of lithium-ion copper foil is directly linked to the energy density of lithium-ion batteries. As lithium-ion battery products move towards smaller volumes, lighter weight, and higher energy density, higher requirements are placed on the thickness of lithium-ion batteries. Thinner copper foils can reduce the weight of lithium-ion batteries, decrease resistance, and increase the amount of active material contained per unit volume in batteries, thereby increasing battery capacity for the same volume.
Presently, lithium-ion copper foils of 8μm, 6μm, and 4.5μm correspondingly consume copper foil at rates of 830g/kWh, 623g/kWh, 484g/kWh, with corresponding energy densities of 157Wh/kg, 162Wh/kg, 166Wh/kg. A 6μm copper foil has an energy density optimization of 3.36% compared to an 8μm copper foil, while a 4.5μm copper foil has an energy density optimization of 5.73% compared to an 8μm copper foil. On average, every 1μm decrease in copper foil thickness achieves a 2.56Wh/kg increase in battery energy density. Therefore, as the demand for energy density in power batteries rapidly increases, extreme thinning has become the main direction for copper foil technology iteration and evolution, moving from mainstream 8μm ultra-thin copper foil towards 6μm and 4.5μm extreme thin copper foils.
| Indicator | 8μm Copper Foil | 6μm Copper Foil | 4.5μm Copper Foil |
| Unit Area Mass (g/m²) | 71.68 | 53.76 | 40.32 |
| Copper Foil Consumption (g/kWh) | 830 | 622.5 | 484.17 |
| Battery Capacity (kWh) | 50 | 50 | 50 |
| Copper Foil Usage (kg) | 41.5 | 31.13 | 24.21 |
| Battery Mass (kg) | 319.23 | 308.86 | 301.94 |
| Battery Mass Energy Density (Wh/kg) | 156.63 | 161.89 | 165.6 |
| Energy Density Optimization (Compared to 8μm Copper Foil) | / | 3.36% | 5.73% |