LFP cells
LFP has low electronic conductivity and small particles that are harder to bond, so carbon-coated foil is widely used to reduce interface resistance and improve adhesion, especially in power and fast-charge cells.
Battery materials guide
Modified Aluminium Foil for Batteries
Modified battery foil is aluminium current-collector foil whose surface has been coated, perforated or etched to lower interface resistance, improve electrode adhesion or protect the foil from corrosion. It is used on the cathode side of lithium-ion cells and in supercapacitors. This guide compares the main types, explains which suits LFP, NCM, high-rate and capacitor designs, and lists what to specify when buying.
- Substrate
- 1060 · 1070 · 1235 · 1100
- Thickness
- Typically 10 – 20 µm
- Temper
- H18 (full hard)
- Types
- Coated, perforated, etched
What is modified aluminium foil for batteries?
In a lithium-ion cell, the cathode active material (LFP, NCM, NCA, LCO or LMO) is coated as a slurry onto a thin aluminium foil, the current collector. The foil carries electrons in and out of the electrode and supports the coating mechanically. Plain rolled foil works, but its natural oxide film and smooth surface create contact resistance and limit how well the electrode sticks. "Modified" foil changes that surface.
The most common modification is a thin conductive carbon primer, usually a few hundred nanometres to a few micrometres thick per side, made from carbon black, graphite, carbon nanotubes or graphene in a binder. Other routes perforate the foil to make it lighter and allow ions to pass through, or etch it chemically or electrochemically to increase the real surface area. Each one addresses a different limitation, so the right choice depends on the cell chemistry and the performance target.
Why aluminium on the cathode? It is light, conductive and cheap, and in common carbonate electrolytes with LiPF6 it forms a stable passive film at high cathode potentials. On the anode side of a graphite cell aluminium would alloy with lithium at low potential, so copper foil is used there instead. The exception is cells with lithium titanate (LTO) anodes, which operate at about 1.55 V versus lithium, where aluminium foil can be used on both electrodes.
Types of modified battery foil compared
| Type | How it is made | Main benefit | Typical use |
|---|---|---|---|
| Carbon-coated (conductive primer) | Gravure or slot-die coating of a carbon/binder dispersion on one or both sides, then drying | Lower interface resistance, better adhesion, some corrosion protection | LFP power and storage cells, high-rate cells, supercapacitors |
| Graphene / CNT-coated | As above, with graphene or carbon nanotubes as the conductive phase | Very thin, highly conductive layer at low coat weight | High-power cells and fast-charging designs |
| Polymer or ceramic primer-coated | Thin functional layer, sometimes with ceramic particles or PTC behaviour | Corrosion barrier; some designs limit current under overheating | High-voltage NCM cells, safety-focused designs |
| Perforated / porous foil | Mechanical punching, laser drilling or chemical etching through the foil | Lower weight, allows ion flow through the collector (pre-lithiation) | Lithium-ion capacitors, some high-power cells |
| Etched high-surface foil | Chemical or electrochemical etching of the surface without perforating it | More contact area and mechanical keying for the coating | Supercapacitor electrodes, high-rate cells |
| Dry-electrode compatible foil | Carbon-primed foil designed for laminating solvent-free electrode film | Bonding of dry electrode films without solvent | Supercapacitors, dry-process battery lines |
Coat weights, conductivity and peel strength vary widely between products. Ask for test data on your own electrode formulation rather than comparing headline figures across suppliers.
Choosing the substrate alloy and thickness
The coating is only as good as the foil underneath. Battery foil is rolled from high-purity 1xxx aluminium to the full-hard H18 temper so that it is strong enough to survive coating, calendering and winding at high line speeds.
| Alloy | Aluminium content | Characteristics | Where it fits |
|---|---|---|---|
| 1235 | ≥ 99.35 % | Economical, good conductivity, widely rolled to thin gauges | Consumer and general-purpose cells |
| 1060 | ≥ 99.60 % | Higher conductivity and purity | Power and storage cells |
| 1070 | ≥ 99.70 % | Higher purity still, low resistivity | High-rate and power cells |
| 1100 | ≥ 99.00 % | Small copper addition gives slightly higher strength | Cells where foil strength during processing matters |
| 1085 / higher purity | ≥ 99.85 % | Very high purity for low resistance and clean surfaces | Supercapacitors and specialised cells |
Typical cathode foil thicknesses run from about 10 to 20 µm, with 12 – 15 µm common in electric-vehicle cells; thinner foil saves weight and cost but needs higher strength and cleaner rolling to avoid breaks. Key substrate properties to specify are thickness tolerance, tensile strength and elongation in H18, pinhole count, surface wettability (dyne level), flatness and edge-wave, and freedom from oil residues that would spoil coating adhesion. For general foil grades and gauges see our lithium-ion battery foil guide.
Which modified foil for which battery?
NCM / NCA cells
High cathode voltages make aluminium corrosion and interface stability more important. Carbon or functional primer coatings are used for high-rate and high-voltage designs; plain foil is common in energy-optimised cells.
High-rate and fast-charge cells
The aim is the lowest possible internal resistance and heat, so thin, highly conductive carbon, graphene or CNT primers are the usual choice.
LTO anodes
Aluminium can serve as the anode collector in LTO cells, saving weight and cost compared with copper, often with a carbon primer.
Supercapacitors (EDLC)
Etched or carbon-coated high-purity foil gives good contact with activated-carbon electrodes and low equivalent series resistance.
Lithium-ion capacitors
Perforated foil allows lithium pre-doping through the collector stack; carbon priming improves contact.
Electrolyte salt matters too. LiPF6 forms a protective fluoride-rich layer on aluminium, but imide salts such as LiTFSI and, to a lesser degree, LiFSI can corrode bare aluminium at high potential. Cells that use these salts, or that run above about 4.3 V, are where protective coatings earn their cost.
What to put in a modified foil specification
Specification checklist
- Substrate
- Alloy, temper (H18), thickness and tolerance, tensile strength and elongation, pinholes
- Coating
- Type (carbon black, graphite, graphene, CNT, primer), single or double side, coat weight per side (g/m²) and tolerance
- Coated width
- Coated width and position, uncoated margins for tab welding, and total slit width
- Performance
- Surface or through-thickness resistance, peel strength with your electrode, and electrolyte soak stability
- Surface
- Coverage, absence of streaks, pinholes and agglomerates; wettability of uncoated areas
- Roll format
- Core inner diameter (76 mm is common), outer diameter or roll length, joints allowed per roll
- Packing
- Vacuum or moisture-barrier bags with desiccant, clean-room compatible wrapping, pallet orientation
Agree the test methods along with the values. Resistance results depend strongly on probe type and pressure, and peel strength depends on the electrode used in the test. The most useful acceptance test is a short run on your own coating line followed by cell-level resistance and cycling checks.
Storage and handling of coated foil
- Keep it dry: store sealed rolls in a cool, dry room and open them only in the coating area; many carbon primers absorb moisture.
- Acclimatise before opening: let rolls reach room temperature in their packaging to avoid condensation.
- Avoid dust and contact damage: unpack in a clean environment and lift by the core, never by the foil surface.
- Use first-in, first-out: coated foil has a recommended use-by period; confirm it with the supplier.
- Protect the uncoated margins: the bare strips are later used for tab welding and must stay clean and oxide-free.
Common mistakes when buying modified foil
- Comparing datasheets, not cells: conductivity and peel figures measured by different methods cannot be compared; test candidates on the same electrode and cell format.
- Ignoring the substrate: a good coating on foil with oil residue, pinholes or poor flatness still causes coating defects and breaks.
- Over-specifying coat weight: a heavier carbon layer adds cost and thickness without always lowering resistance further.
- Forgetting the tab margin: coated lanes must leave clean bare aluminium where tabs are welded, or weld quality suffers.
- Poor storage on site: opening rolls in humid air or leaving them unsealed between shifts can degrade adhesion.
Battery foil supply from Metline
Metline supplies high-purity aluminium battery foil and coated current-collector foil to cell makers, electrode producers and research laboratories worldwide. We work from your specification, provide material certificates and coating test results, and pack rolls for moisture-sensitive export shipment.
Alongside current-collector foil we supply aluminium for other cell and pack parts: foil for pouch-cell laminate, strip for tabs and busbars, battery shell and can stock, and extrusions for battery trays and cooling plates.
- Send the specificationSubstrate, coating, widths, roll format, test methods and volumes.
- Sample and validateSample rolls or sheets for trials on your line; agree acceptance values from the results.
- QuotationPrice and delivery terms (EXW, FOB, CIF or DAP), with packing suited to your factory.
- Supply and documentsRolls with certificates of analysis for substrate and coating, shipped by sea or air.
References and standards
- Zhu, P. et al., "A review of current collectors for lithium-ion batteries", Journal of Power Sources 485 (2021) 229321
- IEC 62660-1 – Secondary lithium-ion cells for the propulsion of electric road vehicles: performance testing
- EN 546-2 – Aluminium and aluminium alloys: foil, mechanical properties
- GB/T 3198 – Aluminium and aluminium alloy foil
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
Modified aluminium (aluminum) battery foil: FAQ
Why is carbon-coated aluminium foil used in lithium-ion batteries?
The carbon layer lowers the contact resistance between the cathode coating and the foil, improves adhesion so less binder is needed, and shields the aluminium from electrolyte attack. The result is lower internal resistance, less heat at high current and more consistent cells.
Why is aluminium used for the cathode and copper for the anode?
Aluminium is stable at the high potential of the cathode because it forms a passive film, but at the low potential of a graphite anode it alloys with lithium. Copper does not, so it is used on the anode. With LTO anodes, which work at a higher potential, aluminium can be used on both sides.
Which modified foil suits LFP and which suits NCM?
LFP cells benefit most from carbon-coated foil because LFP has low electronic conductivity and fine particles. NCM and NCA cells use carbon or functional primer coatings mainly for high-rate or high-voltage designs; energy-focused NCM cells often use plain foil.
What thickness is battery current-collector foil?
Cathode foil is typically 10 – 20 µm thick, with 12 – 15 µm common in electric-vehicle cells. The coating adds well under a few micrometres per side.
Can you supply single-side or patterned coatings?
Yes. Coatings can be applied to one or both sides, and coated widths can be arranged in lanes with uncoated margins for tab welding. Specify the pattern on a drawing.
What packing is used for coated foil?
Rolls are sealed in moisture-barrier or vacuum bags with desiccant, supported on their cores in cartons or wooden cases, and labelled with lot data for traceability.
Specifying modified battery foil?
Send the substrate, coating type, widths and volumes. We will reply with suitable options, test data and a delivered price.
