In a lithium-ion cell the cathode coating is spread on a thin aluminium foil that carries electrons between the active material and the cell terminal. That foil, the current collector, is usually 10 – 20 µm thick, 99.3 – 99.7 % pure aluminium in the hard H18 temper, and it can be supplied plain, carbon-coated or perforated. This guide explains why aluminium is used, the foil types available, the properties that matter on a coating line, and how to write a purchase specification.
Battery active materials such as lithium iron phosphate (LFP) or nickel-manganese-cobalt oxide (NMC) are poor electronic conductors on their own. The current collector is the conductive backbone that supports the coated electrode and gathers current from every point of it.
A collector has four jobs. It must conduct electrons with very little resistance; it must give the coating something to adhere to through thousands of charge cycles; it must stay chemically stable at the electrode's working voltage in contact with the electrolyte; and it must be as thin and light as possible, because it stores no energy. Every micron removed from the collector leaves more room and mass for active material, which is why foil thickness has fallen steadily as cell makers chase energy density.
In a conventional lithium-ion cell, the positive electrode (cathode) uses aluminium foil and the negative electrode (anode) uses copper foil, typically around 6 – 8 µm. Getting this the right way round matters, and it is a point some supplier literature gets wrong.
Rolled 1xxx foil, cleaned and degreased so that the slurry wets it evenly. The default for most LFP and NMC cathodes and for supercapacitor electrodes. Low cost and mature; performance depends on surface cleanliness and thickness consistency.
Plain foil with a thin conductive carbon primer (carbon black, graphite or graphene in a binder), usually around a micron or less per side. It lowers contact resistance, improves adhesion of the cathode layer and shields the aluminium from electrolyte attack. Widely used with LFP for high-rate and long-life cells. See our carbon-coated foil guide.
Foil with many fine through-holes, made by mechanical or chemical perforation. It lets ions pass through the collector, which helps in pre-lithiation and in some supercapacitor and hybrid designs, and it reduces collector weight. Strength and handling on the line fall as open area rises.
Foils with small manganese or iron additions (for example 8xxx or 3xxx-type chemistries) for higher tensile strength, so very thin gauges survive high-speed coating and calendering without breaks.
Textured surface that increases the contact area with the coating and improves mechanical keying. Used where adhesion is the limiting factor.
Solvent-free dry electrode processes press a powder film onto the collector, which places more emphasis on surface primers and flatness than on slurry wettability. Carbon-primed foil is often used.
Modified foils, including coated and porous variants, are covered in more depth in the modified aluminium foil for batteries guide, and plain battery foil by alloy in the aluminium foil for lithium-ion battery guide.
Purity is a trade-off. Higher-purity aluminium conducts better and is more resistant to corrosion, but it is softer and more likely to tear when rolled very thin. Slightly less pure grades, with controlled iron and silicon, roll to thinner gauges with higher strength. Almost all collector foil is supplied in the H18 (full hard) temper because it gives the strength needed to run tensioned webs through coaters and calenders.
| Alloy | Minimum aluminium | Character | Typical use |
|---|---|---|---|
| 1070 | 99.70 % | Highest conductivity of the common grades; softer | Cathode and supercapacitor foil where conductivity is the priority |
| 1060 | 99.60 % | Good conductivity, moderate strength | General cathode foil |
| 1235 | 99.35 % | Fe + Si controlled; rolls well to thin gauges | The most widely used cathode foil alloy |
| 1100 | 99.00 % | Small Cu addition; slightly stronger | Cathode foil and tabs where extra strength helps |
| 1085 | 99.85 % | Very high purity | Specialised high-conductivity and capacitor applications |
| 3003 / 8xxx-type | — | Mn or Fe additions for strength | Thin, high-strength foil for fast lines |
Minimum aluminium contents are the Aluminum Association / EN 573-3 registered values. Mechanical values for battery foil are set by the buyer's specification and by standards such as GB/T 33143 (aluminium and aluminium alloy foil for lithium-ion batteries); typical H18 cathode foil is specified at around 160 – 200 MPa minimum tensile strength with 1 – 3 % minimum elongation depending on thickness.
| Property | Why it matters | How it is usually specified |
|---|---|---|
| Thickness and tolerance | Sets cell energy density; variation causes uneven coating weight and calendering | Nominal µm with a tight band, often ±3 – 4 % or ±0.5 µm for thin gauges |
| Tensile strength | Resists web breaks under line tension | Minimum MPa in the rolling direction, tested on narrow strips |
| Elongation | Prevents cracking during calendering and winding | Minimum % (low values are normal for hard foil) |
| Surface wettability | Slurry must spread evenly; oily foil causes pinholes and poor adhesion | Dyne level, commonly ≥ 30 – 32 mN/m by dyne pen; or a brush water test |
| Pinholes | Holes let slurry bleed through and weaken the web | Maximum count per m² by light-table inspection |
| Flatness and edge quality | Wavy edges or burrs disturb coating and can puncture separators | Visual and slit-edge burr limits, coil set limits |
| Surface cleanliness | Particles and oxides raise resistance and can cause internal shorts | No visible dust, oxidation spots or roll marks; clean-room packing |
| Coil geometry | Must match the coater | Width (often 200 – 1600 mm slit), core ID, OD, joint count |
Areal weight follows directly from thickness and the density of aluminium (2.70 g/cm³). These figures are useful for checking supplier data and for cell design calculations:
| Foil thickness (µm) | Areal weight (g/m²) |
|---|---|
| 8 | 21.6 |
| 10 | 27.0 |
| 12 | 32.4 |
| 13 | 35.1 |
| 15 | 40.5 |
| 16 | 43.2 |
| 18 | 48.6 |
| 20 | 54.0 |
| Factor | Plain foil | Carbon-coated foil | Porous foil |
|---|---|---|---|
| Interface resistance | Baseline | Lower, especially with LFP | Similar to plain, depends on coating |
| Coating adhesion | Depends on surface cleanliness | Improved by the primer | Coating locks through holes |
| Protection against corrosion | Relies on passive film | Primer adds a barrier layer | More edge area exposed |
| Rate capability | Standard | Better at high C-rates | Ion transport through the foil |
| Mechanical strength | Highest for a given thickness | Same base foil | Reduced by open area |
| Cost | Lowest | Higher (extra coating step) | Highest |
| Typical use | Mainstream NMC and LFP cathodes | Power cells, LFP storage, long cycle life | Pre-lithiation, hybrid capacitors, specialised cells |
A practical rule: start with plain 1235 or 1070 H18 foil, then move to carbon-coated foil if cell testing shows high interface resistance, coating delamination after cycling, or poor high-rate performance. Porous foil is a design decision for specific cell architectures rather than a general upgrade.
Pouch cells also use aluminium in the packaging laminate, a different product: see 8021 foil for pouch cell packaging.
For the cathode (positive electrode) in standard lithium-ion cells. Aluminium reacts with lithium at the low anode potential, so graphite and silicon anodes use copper foil. In sodium-ion and LTO-anode cells aluminium can be used on both sides.
Most cathode foil is between 10 and 16 µm, with 12 – 15 µm the most common and thinner 8 – 10 µm foil used where energy density is the priority. Thinner foil needs higher strength to run on the coater without breaking.
1235 H18 is the most widely used because it rolls cleanly to thin gauges. 1070 and 1060 are chosen where conductivity matters more, and stronger alloyed foils are used for very thin gauges on fast lines.
A thin conductive carbon primer reduces the contact resistance between coating and foil, improves adhesion and protects the aluminium from electrolyte attack. The benefit is greatest with LFP cathodes, high charge rates and long-life cells.
Specifications commonly ask for at least 30 – 32 mN/m measured with dyne pens, which shows the surface is clean enough for water- or NMP-based slurries to wet evenly. Agree the test method with the supplier.
Yes. Foil can be supplied slit to the required width on the requested core, with sealed export packing and mill test certificates. Send the full specification and expected volume for a quotation.
Send the alloy, thickness, width, surface requirement and volumes. Our team will reply with availability, test data and delivery terms.
