1235 aluminium foil is the volume grade behind most lithium-ion cathode current collectors. It is not the purest aluminium available, but it delivers the electrochemical cleanliness that cell makers require at a cost structure that supports gigawatt-hour production, which is why it appears in the majority of commercial cell specifications.
Composition and Standard Basis
1235 is registered with a minimum aluminium content of 99.35% under GB/T 3190-2020. Iron and silicon are controlled as a combined impurity limit rather than as separate maxima, because the two elements behave together during rolling and both form second-phase particles. Copper is held very low to limit side reactions against the electrolyte. Foil product requirements, including thickness tolerances and surface condition, are covered by GB/T 3198 for aluminium foil and by ASTM B479 for annealed foil in the American scheme, with EN 573-3 governing the wrought composition designation in Europe.
Thickness and Mechanical Condition
| Parameter | Typical battery foil range | Why it matters |
|---|---|---|
| Thickness | 8-20 micrometres (10-16 common) | Energy density and web handling |
| Thickness tolerance | tight band across the usable web | Uniform coating loading and impedance |
| Tensile strength | approx. 120-180 MPa, O temper | Web tension without stretching |
| Elongation | a few percent at 10 micrometres | Calendering and winding without cracking |
| Conductivity | around 60% IACS | Ohmic loss in high-rate cells |
The foil is supplied fully annealed. Any residual work hardening from the final pass would reduce elongation and lift the risk of micro-cracks during calendering, when the coated electrode is compressed between rolls.
How the Foil Is Rolled
Production uses multi-roll mills with closed-loop gauging because a 0.010 mm exit thickness cannot be held by mechanical screwdown alone. Reduction is taken in many light passes with intermediate annealing to keep the grain structure uniform and avoid the coarse grains that cause orange-peel surfaces after coating. Final passes use fine-ground work rolls and clean rolling oil, since oil residue changes surface wettability and can cause the slurry coating to de-wet.
Surface and Edge Requirements
Three properties decide acceptance on a coating line. First, wettability: the surface must be free of oil and hydrated oxide so that the cathode slurry spreads evenly. Second, roughness: a lightly textured surface anchors the coating, while an over-polished surface allows the coating to flake. Third, edge quality: slitting must leave no burr that could puncture the separator in a wound cell, which makes edge inspection a safety item rather than a cosmetic one.
Frequently Asked Questions
Q: What is 1235 aluminium foil used for?
A: It is used mainly as the cathode current collector in lithium-ion cells for electric vehicles and energy storage, and as tab and pouch material where a conductive, formable thin gauge is needed.
Q: How does 1235 differ from 1070 foil?
A: 1070 has a higher minimum aluminium content at 99.70% and therefore slightly better conductivity, while 1235 at 99.35% minimum offers a lower cost per square metre and is adequate for most cell designs.
Q: Should 1235 foil be supplied in O or H temper?
A: O temper for current collector use. Harder tempers reduce elongation, and electrode calendering will crack a hardened foil that would form cleanly when annealed.
Q: Why is copper kept low in battery foil?
A: Copper is nobler than aluminium and can deposit on the foil surface or dissolve during cycling, creating local galvanic attack and increasing self-discharge, so the limit is held tight.
Q: How is 1235 battery foil tested?
A: Thickness profile scanning across the web, width and burr measurement, tensile and elongation tests, wettability by water-break or contact angle, and chemical analysis per heat, with results recorded on the mill certificate.