AICE Expert Insights | Rolling Ultra-Thin Lithium Battery Aluminum Foil Is 'The Art of Microns'

Industry Trends

The explosive growth of the NEV and ESS industries has driven the development of lithium battery aluminum foil towards ultra-thinness (≤10μm), requiring a balance between lightweight, high energy density, and safety. The mainstream aluminum foil thickness has evolved from 12μm to 8μm, but the stability of mass production processes and yield rates remain industry bottlenecks.

Technical Challenge Positioning

Rolling Limit: When the thickness is reduced to below 10μm, the plastic deformation resistance of aluminum foil increases sharply, leading to issues such as strip breakage and surface pinholes.

Performance Imbalance: The challenge of balancing high tensile strength (≥260MPa) with low elongation (≤3%) to avoid brittle fractures during battery charge and discharge cycles.

Core Difficulties in Rolling Process

1. Micro Precision Control

Thickness tolerance must be stabilized within **±0.1μm**, which is difficult to achieve with traditional rolling mill roll system deflection compensation. Plate shape fluctuations (such as center and edge waves) significantly affect thickness uniformity, requiring dynamic adjustment of rolling force distribution.

2. Material Deformation Resistance Management

In ultra-thin rolling, aluminum grain refinement to sub-micron levels can easily trigger work hardening and residual stress concentration. Asynchronous rolling (controlling the speed difference between upper and lower rolls) is used to reduce deformation resistance, but it requires simultaneous optimization of lubricant viscosity and spray accuracy.

3. Surface Quality Control

Aluminum foil surface roughness must be ≤0.2μm, with no micro-cracks or oxide layers invisible to the naked eye. Dust adhesion and roll surface scratches during rolling are the main sources of defects, necessitating cleanroom-level environments and online defect detection systems.

Performance Challenges and Solutions

1. Mechanical Performance Optimization

Strength-Elongation Balance: Through alloy composition optimization (e.g., adding trace amounts of Fe, Si) and intermediate annealing processes (precise control of annealing time at 300-350℃), grain refinement is achieved while enhancing ductility.

Corrosion Resistance Enhancement: Development of surface passivation coating technologies (e.g., phosphate + silicone composite coatings) to resist electrolyte corrosion.

2. Battery Compatibility Verification

Aluminum foil must pass 500 charge-discharge cycle tests with a thickness expansion rate of ≤5%.

The interfacial bonding strength with cathode materials (e.g., LFP) must be ≥1.5N/cm to avoid pole piece delamination.

Innovative Practices and Achievements

1. Process Breakthroughs

North China Aluminum independently developed a six-roll UC mill + shape meter closed-loop control system, achieving thickness fluctuations of ≤±0.08μm.

Innovative application of nano-lubricant spray technology increased rolling speed to 800m/min and reduced strip breakage rate to below 0.5%.

2. Mass Production Data

The yield rate of 8μm aluminum foil increased from an initial 40% to 78%, with single roll length exceeding 20,000 meters. The product is applied in top-tier battery enterprises such as CATL and BYD, enhancing battery energy density by 10%-15%.