LFP cells
LFP has low intrinsic conductivity, so reducing contact resistance gives clear gains. Coated foil is widely used in LFP for energy storage, buses and passenger EVs.
Battery materials guide
Carbon Coated Aluminium Foil: How It Works and How to Specify It
Carbon coated aluminium foil is battery-grade aluminium foil, typically 12 – 20 µm thick, with a conductive layer of carbon black, graphite or graphene about 0.5 – 3 µm thick on one or both sides. Used as the cathode current collector in lithium-ion cells and in some capacitors, it lowers the contact resistance between foil and electrode coating, improves adhesion and protects the aluminium from electrolyte attack. This guide explains the benefits, substrate and coating options, test methods and buying checklist; Metline supplies bare and carbon coated battery foil to cell and electrode makers worldwide.
- Substrate
- 1235, 1060, 1070, 1100 H18
- Foil thickness
- About 12 – 20 µm
- Coating
- 0.5 – 3 µm per side
- Main use
- LFP and NCM cathodes, capacitors
What carbon coated foil is and why cells use it
In a lithium-ion cell the cathode active material, such as lithium iron phosphate (LFP) or a nickel-manganese-cobalt oxide (NCM), is mixed with a conductive additive and binder and spread onto aluminium foil. The foil carries electrons in and out of the electrode. Aluminium is used on the cathode side because it is light, cheap, highly conductive and protected by a passive film at the high potentials of the positive electrode.
That same passive film is also a problem. Aluminium oxide is an electrical insulator, and the contact between hard oxide particles and a smooth, oxidised foil is made at relatively few points. The result is a contact resistance at the foil-electrode interface that adds to cell impedance, generates heat at high current and can grow as the cell ages and the electrode loosens.
A thin carbon primer solves much of this. The carbon particles bond to the foil through a binder, penetrate the thin oxide at many points and present a rough, conductive surface that the electrode coating grips firmly. Peer-reviewed studies have shown a clear reduction in contact resistance for LFP cathodes on carbon coated current collectors, which is why the coated foil is now standard in many LFP and high-power cell designs.
The aluminium substrate
The base is a high-purity 1xxx-series foil in full-hard H18 temper. The hard temper gives the tensile strength needed to run the foil through coating, drying, calendering and slitting lines at speed without breaks or wrinkles. Typical alloys are 1235, 1060, 1070 and 1100; 1100 and certain modified 1235 grades give higher strength for very thin gauges.
| Property | Typical range for battery foil | Why it matters |
|---|---|---|
| Alloy | 1235, 1060, 1070, 1100 (≥ 99.0 – 99.7 % Al) | Purity supports conductivity and corrosion behaviour |
| Temper | H18 (full hard) | Strength for high-speed coating and calendering |
| Thickness | About 9 – 25 µm; 12, 13, 15, 16 and 20 µm common | Thinner foil saves mass and volume but is harder to handle |
| Thickness tolerance | Around ± 3 – 4 % | Uniform electrode loading and calendering |
| Tensile strength | Roughly 180 – 280 MPa depending on alloy and gauge | Resists breaks on coating and winding lines |
| Elongation | Roughly 1.5 – 4 % | Survives calendering without cracking |
| Surface tension (dyne) | Typically ≥ 31 – 32 mN/m | Clean, oil-free surface for wetting by the coating slurry |
| Width | About 200 – 1,400 mm, ± 1 mm | Matched to coating line width |
| Pinholes | Very few, with limits on size and count per m² | Pinholes cause coating defects and weak points |
Ranges are typical of published battery-foil specifications; the purchase specification agreed with the cell maker governs. Each lot is supplied with test results.
For a full explanation of bare foil grades, see our lithium-ion battery foil and current collector foil guides.
Carbon black, graphite and graphene coatings
| Coating | Character | Typical use |
|---|---|---|
| Conductive carbon black | Fine particles with high surface area; low cost; forms a uniform, thin layer | General LFP and NCM cathodes, mainstream coated foil |
| Graphite (flake) | Plate-like particles lie flat and give good in-plane conduction and adhesion | High-power cells, thicker coatings |
| Graphene or graphene blends | Very thin sheets; high conductivity at low loading; higher cost | Premium and high-rate cells |
| Carbon nanotube blends | Fibrous conductive network | High-rate and specialty cells |
| Binder | Water-based (for example acrylic or CMC/SBR types) or PVDF-based | Must resist NMP solvent in the cathode slurry and the electrolyte |
Typical coating parameters
- Coating thickness
- About 0.3 – 3 µm per side; 1 – 2 µm is common
- Coating areal density
- Roughly 0.5 – 2.0 g/m² per side
- Sides
- One side or both sides
- Pattern
- Continuous, or intermittent (skip) coating leaving bare tab areas
- Edge margin
- Uncoated edges for tab welding, for example a 230 mm coat on 260 mm foil
- Total thickness
- For example 16 µm foil + 1 µm per side ≈ 18 µm
Thicker carbon layers lower contact resistance further but add mass and volume that store no energy. Most cell makers choose the thinnest coating that reliably covers the foil and passes adhesion tests.
How carbon coated foil is produced
- Casting and rollingHigh-purity aluminium is cast into coil and cold-rolled, with intermediate annealing, then foil-rolled to the final gauge in H18 temper.
- CleaningRolling oil is removed and the surface is treated so the dyne level meets the specification.
- Slurry preparationCarbon, binder and solvent (usually water) are dispersed into a stable, fine slurry.
- CoatingGravure, micro-gravure or slot-die coating applies a thin, even film, continuous or patterned.
- Drying and curingThe coated foil passes through an oven so the binder cures and the coating bonds to the foil.
- Inspection and slittingOnline thickness and defect inspection, then slitting to width and rewinding on clean cores.
The main production challenges are keeping the coating uniform across the width, avoiding pinholes and streaks, preventing foil breaks at very thin gauges, and making sure the binder will not swell or dissolve when the cathode slurry (often based on NMP) is applied on top.
Tests and acceptance criteria
| Test | Method | What it shows |
|---|---|---|
| Coating thickness and areal density | Micrometer, weight difference before and after coating | Consistency of the primer layer |
| Surface or through-plane resistance | Four-point probe or electrode resistance tester | Electrical benefit of the coating |
| Adhesion | Tape test (for example ASTM D3359), rub test, peel test with cathode | Coating stays bonded through processing |
| Solvent resistance | Immersion or wipe with NMP | Coating survives cathode slurry |
| Electrolyte resistance | Soak in electrolyte at elevated temperature | No swelling or delamination in the cell |
| Substrate mechanicals | Tensile and elongation to standard foil test methods | Foil runs on coating and winding lines |
| Surface defects | Online camera inspection, visual | No pinholes, streaks, bare spots or foreign particles |
The real proof is in the cell. Ask for, or run, impedance (EIS) and rate-capability comparisons between electrodes on bare and coated foil made from the same slurry. Gains vary with the active material and electrode design, so published laboratory figures should be read as indicative only.
Where carbon coated foil is used
High-power NCM and LMO cells
Power tools, hybrid vehicles and start-stop batteries benefit from lower impedance at high current.
Lithium titanate (LTO) cells
Fast-charging, long-life cells where low resistance is essential.
Energy storage systems
Lower resistance means less heat and higher round-trip efficiency in stationary batteries.
Supercapacitors and solid polymer capacitors
Carbon coated foil can lower equivalent series resistance and improve adhesion of activated-carbon electrodes.
Emerging chemistries
Lithium-sulphur and sodium-ion research cells use coated aluminium collectors to protect the foil and improve contact.
Carbon coated vs bare aluminium foil
| Factor | Bare battery foil | Carbon coated foil |
|---|---|---|
| Contact resistance with cathode | Higher | Lower |
| Electrode adhesion | Depends on binder content | Stronger; binder can be reduced |
| Corrosion protection | Passive oxide only | Additional barrier layer |
| Rate performance | Baseline | Usually improved, especially for LFP |
| Cost | Lower | Higher (coating step) |
| Mass and thickness | Lowest | + about 1 – 4 µm and about 1 – 4 g/m² for two sides |
| Tab welding | Direct | Needs uncoated margins or pattern coating |
For energy-optimised NCM cells at moderate rates, bare foil is often adequate. For LFP, high-power and long-life designs, the coated foil usually pays for itself through lower resistance and better yield.
What to specify when buying
- Substrate alloy, temper and thickness, with tolerance
- Width, coated width and edge margins, or the intermittent coating pattern
- Coating material, thickness or areal density per side, and one- or two-sided
- Resistance target and test method
- Adhesion, solvent and electrolyte resistance tests and acceptance levels
- Roll length, core size, outer diameter and splice rules
- Packing: vacuum-sealed or nitrogen-flushed bags with desiccant, in clean wooden cases
- Documentation: mill certificate for the substrate and coating test report for each lot
- EnquireSend the specification and expected volumes.
- SampleSample rolls for electrode and cell trials.
- QualifyAgree the specification after trials.
- SupplyRegular shipments on EXW, FOB, CIF or DAP terms with lot test reports.
References and standards
- Novel carbon coating on aluminum current collectors for lithium-ion batteries, SN Applied Sciences (2022)
- ASTM D3359 – Standard Test Methods for Rating Adhesion by Tape Test
- EN 546 – Aluminium and aluminium alloys: foil
- EN 573-3 – Chemical composition and form of wrought products
Carbon coated aluminium (aluminum) foil: FAQ
What is carbon coated aluminium foil used for?
Mainly as the cathode current collector in lithium-ion batteries, especially LFP and high-power cells, and in some supercapacitors. The carbon layer lowers contact resistance and improves adhesion of the electrode.
How thick is the carbon coating?
Usually about 0.5 – 3 µm per side, with 1 – 2 µm most common. That corresponds to roughly 0.5 – 2 g/m² per side, depending on the carbon type and binder.
Which aluminium alloy is used as the substrate?
High-purity 1235, 1060, 1070 or 1100 in H18 temper, typically 12 – 20 µm thick. Higher-strength grades are used for the thinnest gauges.
Does the coating reduce energy density?
Slightly, because it adds a few micrometres and grams per square metre that store no energy. In practice the lower resistance and possible reduction in binder often offset this, especially in power-oriented cells.
Can tabs be welded to coated foil?
Tabs are normally welded to uncoated areas. Specify uncoated edge margins or an intermittent coating pattern that leaves bare foil where tabs will be attached.
How should carbon coated foil be stored?
In its sealed packaging, in a dry, clean room at moderate temperature. Moisture and dust can affect the coating and the subsequent electrode coating step, so open rolls only just before use.
Qualifying coated foil for a new cell?
Send your substrate and coating specification. Metline will reply with matching foil, sample rolls and test data.
