1070 is the highest-purity aluminium grade that is routinely rolled into current-collector foil for lithium-ion cells. Its value is not mechanical but electrochemical: fewer impurity phases at the foil surface mean fewer parasitic reactions against the electrolyte and lower resistive heating during charge and discharge.
Composition and Purity Position
| Grade | Aluminium, min | Fe, max | Si, max | Cu, max |
|---|---|---|---|---|
| 1050 | 99.50% | 0.40% | 0.25% | 0.05% |
| 1060 | 99.60% | 0.35% | 0.25% | 0.05% |
| 1070 | 99.70% | 0.25% | 0.20% | 0.04% |
| 1235 | 99.35% | Si + Fe, 0.65% max (combined limit) | 0.05% | |
Chemistry is controlled to ASTM B479 for annealed foil and to the composition limits of GB/T 3190-2020, with 1050 and 1060 values shown for reference. Iron and silicon are the two elements that determine how the foil behaves during rolling and coating, because both form coarse intermetallic particles when present above the limits above.
Why High Purity Matters in a Cell
On the cathode side the foil acts as a mechanical carrier and as the electron path. Iron-rich particles are cathodic to the aluminium matrix and initiate local dissolution during cycling, so a tighter iron limit raises the number of cycles before capacity fade accelerates. Lower silicon also reduces the number of brittle particles that crack during electrode calendering and winding. High-purity aluminium in the annealed condition reaches roughly 61 to 62% IACS, which lowers ohmic loss in high-rate cells.
Thickness, Temper and Surface Condition
Battery foil is supplied below 0.2 mm and in practice between about 8 and 20 micrometres, most commonly 10 to 16 micrometres for passenger-car cells. It is delivered in the O temper, soft and fully annealed, because the electrode coating line requires the foil to conform without springback. Surface requirements are strict: residual rolling oil below a low threshold for wettability, no slitter burr on the edge that could pierce the separator, uniform surface roughness for coating adhesion, and a flatness that keeps the coating thickness within tolerance across the web.
Process and Quality Control
Foil is rolled on multi-roll mills with closed-loop thickness control, then annealed to a uniform grain structure and finally slit to the width required by the coating line. Inspection typically covers thickness profile across the web, width and burr, tensile strength and elongation, wettability by the water-break test, and chemical analysis by heat number. Rolls are packed on cores with moisture barrier protection because surface hydration degrades coating adhesion.
Frequently Asked Questions
Q: What is 1070 aluminium foil used for in batteries?
A: It is used primarily as the cathode current collector in lithium-ion cells, and also in supercapacitors and in some pouch-cell tab stock, because its high purity limits electrochemical side reactions.
Q: How does 1070 compare with 1235 foil?
A: 1070 has the higher purity at 99.70% minimum aluminium against 99.35% minimum for 1235, so 1070 gives slightly better conductivity, while 1235 costs less and is adequate for many energy-storage and lower-rate cells.
Q: Which tempers are available in 1070 foil?
A: Practically the O temper only for current collector use. Harder tempers such as H18 exist for packaging work but are unsuitable for electrode coating because of low elongation.
Q: Why must the foil edge be burr-free?
A: A burr raised during slitting can penetrate the separator during winding and create an internal short circuit, so edge quality is controlled and inspected as a safety characteristic rather than a cosmetic one.
Q: What thickness tolerance is normal for 1070 battery foil?
A: Tolerances are agreed between mill and coating line, typically a fraction of a micrometre around nominal across the usable web, because thickness variation shifts coating loading and cell impedance.