Why Aluminum Foil Is Used as the Cathode Current Collector
In a lithium-ion cell the positive electrode coating is applied to a thin aluminium foil that carries electrons between the active material and the external circuit. Aluminium is chosen for the cathode side because a compact passive oxide film forms spontaneously on its surface and stays stable at the high potentials of a charged cell, roughly 3.0-4.2 V versus Li/Li+. Copper would dissolve rapidly at the same potential, which is why it is reserved for the anode side. The passive film is only a few nanometres thick, so it protects the metal without adding measurable contact resistance.
The positive electrode accounts for the largest share of both cell mass and cell cost, and the mass ratio of positive to negative electrode material is commonly 3:1 to 4:1. That means the foil behind the coating has a direct influence on energy density, coating yield and cycle life. Thickness uniformity, surface texture, tensile strength and residual contamination all affect how evenly the slurry wets the surface and how the finished electrode behaves after thousands of cycles.
Alloy Grades Commonly Used for Battery Foil
Battery cathode foil is produced from high-purity, non-heat-treatable wrought alloys. Chemical composition limits for these alloys are published in EN 573-3, ISO 209 and GB/T 3190, and the same four-digit designations are recognised worldwide.
| Alloy | Aluminium content / main addition | Usual temper | Typical cathode gauge | Typical role |
|---|---|---|---|---|
| 1060 | 99.60% Al minimum | H18, O | 12-20 µm | Standard choice with a good conductivity and cost balance |
| 1070 | 99.70% Al minimum | H18 | 10-16 µm | Higher purity and lower resistivity |
| 1235 | 99.35% Al minimum | H18, O | 12-20 µm | Used where strength matters more than purity |
| 1100 | 99.00% Al with copper addition | H18 | 14-20 µm | Higher strength, slightly lower conductivity |
| 1050 | 99.50% Al minimum | H18, O | 12-20 µm | Alternative to 1060 in several markets |
Most energy cells use a cathode collector between 9 and 20 µm thick, while high-power cells often move to 12-15 µm to reduce internal resistance. For comparison, the anode side uses copper foil of roughly 6-10 µm.
Mechanical, Electrical and Surface Requirements
The requirements below reflect typical commercial product rather than guaranteed contract minima; every cell manufacturer sets its own purchase specification on top of them.
Gauge and profile: 9-20 µm nominal, with local thickness deviation normally held within about ±3% across the web.
Tensile strength: approximately 150-200 MPa for 1060 or 1070 in H18 temper. Soft O temper grades sit far lower and are chosen only where formability dominates.
Elongation: 2-4% or more in H18, enough to survive coating tension without web breaks.
Electrical conductivity: typically 60-62% IACS for 1060, equivalent to a resistivity near 2.8 micro-ohm centimetre. Higher purity 1070 sits at the upper end of that band.
Surface: one matte, adhesion-friendly face and one smoother face is common, and the surface energy must allow uniform wetting by the solvent-based slurry.
Cleanliness: low residual rolling oil, no visible inclusions, a controlled pinhole count and burr-free slit edges.
Flatness: no wrinkles or edge waves, because slack areas distort the coating gap and cause gauge variation.
Tensile testing of finished foil generally follows the room-temperature method described in GB/T 228.1, while dimensional tolerances for rolled sheet and strip are taken from the ASTM B209, EN 485-2 or GB/T 3880 families and then adapted to foil gauges by agreement between supplier and cell maker.
From the Rolling Mill to the Coated Electrode
Cathode foil is produced by continuous or DC casting, hot rolling, cold rolling and finally foil rolling to gauge on cluster mills. The final anneal sets temper and surface state: a full soft anneal produces O temper, while H18 product keeps most of its work hardening. Slitting follows under clean conditions because fine metallic debris is a short-circuit risk in a finished cell.
Electrode fabrication begins once the coil arrives. Active material such as lithium iron phosphate or a layered nickel-cobalt-manganese oxide is mixed with a binder and conductive carbon in a solvent, coated on one or both faces, dried, calendered to a target porosity and slit into electrode strips. The active powders themselves are made by high-temperature calcination, usually in the 600-800 °C range, but that step belongs to powder synthesis and never involves the collector foil. The foil only sees moderate drying temperatures during electrode manufacture, so its temper and flatness must remain stable in that window.
Selection and Quality Control Checklist
Cell designers match the foil to the chemistry and to the cell format. High-nickel layered oxides compacted to a high density call for flatter and stronger foil that resists calendering tension, while lower-cost iron phosphate designs tolerate a slightly wider gauge window. Pouch cells place extra emphasis on a pinhole-free surface, and cylindrical cells are more sensitive to burr height and tab welding quality.
Verify every delivery against the mill certificate for alloy, temper, gauge and mechanical values.
Check the thickness profile across the web, not only along the centre line.
Measure wettability and contact resistance on samples taken from both faces and both ends of the coil.
Inspect for pinholes, oil staining, dents and edge burrs under controlled lighting.
Require splice-free jumbo coils of consistent length so coating lines run to the end of the web.
FAQ
Q: Why is aluminium foil used on the cathode and copper on the anode?
Aluminium passivates and remains stable at the high potentials of the positive electrode, near 3.0-4.2 V versus Li/Li+, where copper would corrode. Copper is used on the negative side because it is stable at low potentials, where aluminium would instead alloy with lithium.
Q: What thickness of aluminium foil is normal for a lithium-ion cathode?
Most energy cells use 12-20 µm, while high-power designs often select 12-15 µm to cut resistance. Foil below 10 µm is available but demands tighter handling and coating control.
Q: Does temper matter for cathode foil?
Yes. H18 supplies the strength needed to resist coating and calendering tension, whereas O temper is softer and easier to form but far weaker. The choice must match the cell format and the tension of the coating line.
Q: Is the aluminium foil itself calcined during battery production?
No. Calcination applies to the synthesis of the active cathode powder. The collector foil is annealed at the rolling mill and then dried at moderate temperature during electrode coating.
Q: How does surface roughness affect cell performance?
A controlled matte surface improves mechanical keying of the coating and lowers contact resistance. Surfaces that are too smooth cause adhesion loss, while excessive roughness or contamination raises local resistance and can create hot spots.
Q: Can 1100 be used instead of 1060?
It can, but the copper addition lowers electrical conductivity and adds cost without benefit for most cells. Grades 1060, 1070 and 1235 remain the mainstream choices for lithium-ion cathode collectors.