Critical raw materials

In plain words

Raw materials an economy depends on but whose supply could be interrupted – because they come mostly from one country or a few mines, or only as a by-product of mining something else. The EU, the United States and other countries keep official lists. Several rely on such inputs: natural graphite for graphene, tungsten for WS₂ and WSe₂, borates for boron nitride, and gallium, indium or tellurium for others. Supply risk can matter as much as performance in deciding whether a material reaches the market.

Going deeper

Every material reaches a device through a chain from mine to refinery to precursor, and one narrow step is enough to put supply at risk. Natural graphite is mined mostly in China; gallium, tellurium and indium come only as by-products of other metals. Substitution, recycling, new sources and using less reduce the exposure.

What makes a material critical

A raw material is called critical when an economy depends on it and its supply is at risk. Assessments combine the two. Economic importance asks how much industry would lose without it and whether it can be substituted. Supply risk asks how concentrated production is, how stable the producing countries are, how much is imported and how much comes back through recycling. By-products add a twist: gallium is extracted from bauxite refining, tellurium from copper refining and indium from zinc, so their supply depends on demand for the main metal rather than on their own price. The EU revises its list every three years; the United States, Japan and others keep their own.

Where 2D materials are exposed

Natural graphite, the feedstock for graphene powders and for anodes, is mined mostly in China – about three quarters of world production in 2023 – and processed there even more, and China introduced export licensing for graphite at the end of 2023. Tungsten, needed for WS₂ and WSe₂, is on the EU list and mined mostly in China too, where exports of tungsten and molybdenum products have needed a licence since February 2025; borates, for hBN, come largely from Turkey and the United States; and powders, sapphire and silicon carbide come from a handful of suppliers. precursors add their own constraints, since selenium and tellurium are by-products and their hydrides are hazardous.

Reducing the risk

The usual remedies apply: substitute where possible – synthetic graphite from petroleum coke, sodium-ion cells that avoid some critical inputs – recycle scrap, used cells and sputtering targets, open new mines and refineries, and keep stockpiles. Thin films help by their nature: a of MoS₂ weighs a few milligrams per square metre, so electronics use little material, while , coatings and battery electrodes use tonnes. The EU’s Critical Raw Materials Act of 2024 sets targets for how much of its demand should be mined, processed and recycled within the EU and how little may come from any single other country.

For specialists

Materials assessed as both economically important and at high supply risk, using indicators of production concentration, the governance of producing countries, import reliance, substitutability and end-of-life recycling (as in the EU methodology and Graedel’s criticality framework). The EU list, revised every three years, includes graphite, tungsten, boron, gallium and germanium, and the Critical Raw Materials Act of 2024 sets targets for domestic extraction, processing and recycling; the United States keeps its own list, and China introduced export licensing for graphite at the end of 2023 and for tungsten, molybdenum, tellurium, bismuth and indium products in February 2025.

For 2D materials the exposure lies in feedstocks, precursors and – graphite, molybdenum and tungsten compounds, chalcogens, borates, MAX-phase powders, sapphire and SiC – and is reduced by substitution, synthetic routes, recycling and diversified supply; thin-film uses consume little material, bulk uses such as composites and battery anodes a great deal.

Where this comes from

Methodology of metal criticality determination Graedel et al. · Environmental Science and Technology 46, 1063 (2012)
Mineral commodity summaries 2024 U.S. Geological Survey · U.S. Geological Survey (2024)
Regulation (EU) 2024/1252 establishing a framework for ensuring a secure and sustainable supply of critical raw materials European Union · Official Journal of the European Union, L series (2024)

Battery electrode

A battery stores energy by moving ions – in phones and cars, lithium ions – between two electrodes, the anode and the cathode. Charging pushes the ions into the anode, where they slip between the layers of a material such as graphite; using the battery lets them flow back. Layered and 2D materials matter because ions can enter and leave the gaps between layers, and because thin conductive flakes can help electrons reach every grain of an electrode.

A lithium- or sodium-ion cell shuttles ions through an electrolyte between a negative electrode (the anode on discharge) and a positive one (the cathode), while electrons pass through the external circuit. Graphite, the standard anode, intercalates lithium between its layers up to LiC₆, about 372 mAh/g; layered oxides such as LiCoO₂ and NMC dominate cathodes. 2D materials enter as conductive additives (graphene flakes replacing part of the carbon black), as higher-capacity anodes that alloy or convert (phosphorus, antimony, SnS₂, SnO), as hosts for larger ions such as sodium, which graphite takes up poorly, and as MXene electrodes. Their weaknesses are large volume change, irreversible first-cycle loss from the high surface area, low packing density and cost, so gains at cell level are usually far smaller than those claimed for the material.

Full explanation

Wafer and wafer-scale growth

A wafer is the thin, round slice of ultra-pure silicon – today 300 millimetres across – on which computer chips are made, hundreds at a time. Wafer-scale growth means making a 2D material evenly over a whole wafer rather than as scattered flakes, which is what any factory needs. For the best 2D materials that is still hard: a sheet one atom thick has to have the same thickness, quality and orientation from one edge of a dinner-plate-sized disc to the other.

The substrate format of the semiconductor industry – 200 and 300 mm silicon wafers, with sapphire, SiC and glass for particular processes – and the scale at which a material must be grown, transferred and processed to enter manufacturing. Wafer-scale growth of 2D materials uses CVD and MOCVD of TMDCs, CVD of graphene and hBN, and MBE, with targets of uniform layer number, low defect and grain-boundary density and, increasingly, a single orientation on vicinal sapphire or Cu(111). The obstacles are the growth temperature against the thermal budget of a finished wafer (growth on the back end of line needs to stay below about 400 to 450 °C), the transfer from growth substrate to device wafer, and metrology that confirms thickness and quality across the wafer at production speed.

Full explanation

Chalcogenide, halide and pnictide

Family names for compounds, taken from the element in them that carries the negative charge. Chalcogenides contain sulfur, selenium or tellurium; halides contain fluorine, chlorine, bromine or iodine; pnictides contain phosphorus, arsenic, antimony or bismuth. Most layered crystals belong to one of these families, and the catalogue groups many of them that way.

Compounds named for their most electronegative constituent: chalcogenides of group 16 (S, Se, Te; oxides are conventionally counted apart), halides of group 17 (F, Cl, Br, I) and pnictides of group 15 (P, As, Sb, Bi; nitrides usually keep their own name). Down each group the anion grows larger and less electronegative, so bonding turns more covalent, gaps shrink and spin–orbit coupling grows. Chalcogenides give the MX₂ semiconductors and metals, halides mostly ionic, often magnetic insulators built from edge-sharing octahedra, and pnictides many metals, semimetals and the parents of the iron-based superconductors; mixed-anion compounds such as oxychalcogenides and chalcohalides combine two.

Full explanation

Composites and coatings

The biggest market for 2D materials so far: flakes of graphene or other layered materials mixed in small amounts into plastics, rubber, concrete, paints or battery electrodes, to make them stiffer, tougher, more conductive or less permeable. Sold by the tonne, these products use cheap flakes made in bulk rather than perfect single layers. Whether a few percent of flakes really helps depends on how well they are spread out, how they line up and how firmly they hold on to the material around them.

Bulk uses in which exfoliated or chemically derived flakes – graphene nanoplatelets, reduced graphene oxide, hBN, MXenes, clays – are dispersed in a matrix or applied as a film. In polymer composites a few weight percent can raise stiffness and toughness, cross the percolation threshold for electrical conduction – as low as about 0.1 percent by volume for thin, wide flakes – and raise thermal conductivity; aligned flakes in barrier coatings lengthen the diffusion path of water, oxygen and ions and slow corrosion; flakes used as conductive additives replace part of the carbon black in battery electrodes; MXene films give strong electromagnetic shielding. Performance depends on flake size and thickness, dispersion without restacking, alignment and bonding to the matrix, and on powders whose properties vary widely between suppliers.

Full explanation

Substrate

The base a thin film or flake sits on – often a polished slice of silicon, glass or sapphire. For a crystal one atom thick, the substrate is not just a table: its bumps, stray charges and vibrations reach right into the sheet and change how it conducts and glows. That is why the same material can behave differently on two substrates, and why the flattest, cleanest one – boron nitride – gives the best results.

The material beneath a 2D layer. It acts on the layer through surface roughness, charged impurities, surface optical phonons, dielectric screening, strain and charge transfer, and during growth it sets orientation through epitaxy. Replacing SiO₂ with hexagonal boron nitride, which is atomically flat and nearly free of dangling bonds and charge traps, improved the mobility and charge homogeneity of graphene by close to an order of magnitude.

Full explanation