The Elements Outside the Cell
Buried 4f orbitals make the magnets, a filled 3d shell makes the windings, and a wide bandgap is the reason 800 V architectures arrived with silicon carbide and not before.
The Periodic Table of the EV · Part 5 — Beyond the Cell · Chapter 10 · 20 min read
Part 5 — Beyond the Cell
The rest of the vehicle
Magnets, windings and semiconductors — three more places where an electron configuration decides an engineering outcome.
A battery is the expensive part of an electric vehicle, but it is not the only part whose design is dictated by an electron configuration. The motor magnets depend on orbitals so deeply buried they barely bond to anything. The windings depend on a filled d shell. And the entire 800 V architecture depends on a bandgap.
~400 kJ/m³
Nd₂Fe₁₄B energy product
312 °C
Its Curie temperature
60–85 kg
Copper in an EV
3.26 eV
SiC bandgap, against silicon’s 1.12
10.1 — Neodymium and dysprosium — the f-block magnets
Rare earths are the lanthanides, filling the 4f subshell. The reason they make superb magnets is geometric: the 4f orbitals are deeply buried beneath the filled 5s and 5p shells.
Because they barely participate in bonding, their electrons retain large unpaired spin and orbital angular momentum. Neodymium at 4f⁴ has a large magnetic moment — and because the 4f orbitals are spatially anisotropic and strongly spin–orbit coupled, they also confer enormous magnetocrystalline anisotropy, the tendency of magnetisation to lock onto a specific crystal axis.
In plain English
Coercivity (H_c) is the reverse magnetic field required to demagnetise a material. High magnetocrystalline anisotropy gives high coercivity, which means the magnet resists being demagnetised by the motor’s own stator field and by heat. That is the property you are actually buying.
Nd₂Fe₁₄B delivers the highest energy product, (BH)_max, of any commercial magnet — around 400 kJ/m³. Iron supplies the raw magnetisation, boron stabilises the tetragonal crystal structure, and neodymium supplies the anisotropy.
10.1.1 — Why dysprosium is added
Nd₂Fe₁₄B has a Curie temperature — the temperature above which ferromagnetism disappears — of only 312 °C, and its coercivity falls steeply well below that. A traction motor rotor can reach 150 to 180 °C.
Substituting a few per cent dysprosium for neodymium raises the anisotropy field and therefore high-temperature coercivity. The costs are real: dysprosium couples antiparallel to iron so remanence falls, and at 5.2 ppm it is one of the scarcest elements in the crust.
Why this matters
Supply is concentrated, prices are volatile, and separating chemically near-identical lanthanides is environmentally intensive. The mitigations are worth knowing: grain-boundary diffusion, which places dysprosium only at grain surfaces where it is actually needed; ferrite-assisted synchronous reluctance motors; and induction motors, which use no permanent magnets at all, at some efficiency cost.
10.2 — Copper — the winding
Copper has the second-highest conductivity of any element at 5.96 × 10⁷ S/m, behind only silver at 6.30 × 10⁷ — which costs about a hundred times more.
The reason is its position: as a group 11 d-block metal, copper’s single 4s electron above a filled 3d¹⁰ shell is highly mobile, and the filled d shell means low electron–phonon scattering.
Important
An EV uses roughly 60 to 85 kg of copper, about four times an internal-combustion vehicle: motor windings, busbars, the high-voltage harness, charging cables and the on-board charger. This is why EV adoption forecasts and copper demand forecasts are the same document.
Aluminium windings appear occasionally — better conductivity per kilogram, and cheaper — but they need about 60 per cent more cross-section for the same resistance, and aluminium-to-copper joints suffer galvanic corrosion and creep.
10.3 — Silicon and silicon carbide — the bandgap argument
Bandgap (E_g) is the energy gap between the filled valence band and the empty conduction band in a semiconductor. It determines how much thermal energy is needed to promote an electron into conduction, and therefore the maximum operating temperature and breakdown field.
| Material | Bandgap (eV) | Breakdown field (MV/cm) | Thermal conductivity (W/m·K) |
|---|---|---|---|
| Si | 1.12 | 0.3 | 150 |
| SiC (4H) | 3.26 | 2.8 | 490 |
| GaN | 3.40 | 3.3 | 130 |
The mechanism matters. Breakdown field scales roughly with the square of the bandgap, so a device that withstands ten times the field can be made ten times thinner for the same blocking voltage. On- resistance scales with thickness, so a SiC MOSFET has dramatically lower conduction loss at high voltage — and it switches far faster, cutting switching losses and shrinking the magnetics.
Technical framing
This is why 800 V EV architectures arrived with SiC and not before. At 400 V, silicon IGBTs are adequate. At 800 V they are not.
And 800 V halves the current for a given power, which quarters I²R loss and allows thinner cable — a mass saving worth tens of kilograms, in a vehicle already carrying 60 to 85 kg of copper.
Gallium in GaN offers an even wider bandgap and faster switching. It currently dominates on-board chargers and DC-DC converters rather than the main inverter, where SiC’s far superior thermal conductivity of 490 against 130 W/m·K wins.
10.4 — Platinum group metals — fuel cells and electrolysers
Platinum catalyses the oxygen reduction reaction in PEM fuel cells because its d-band centre sits at almost exactly the position that binds oxygen intermediates neither too strongly nor too weakly — the Sabatier principle, expressed as a volcano plot with platinum at the peak.
That is a d-band electronic-structure argument, and it is why substitution has been so hard. Iridium — at 0.4 ppb crustal abundance, one of the rarest stable elements — plays the same role for oxygen evolution in PEM electrolysers, and is a genuine bottleneck for green-hydrogen scale-up.
Important
This is a materials ceiling that batteries do not face. Lithium at 20 ppm is scarce; iridium at 0.4 ppb is 50,000 times scarcer. The comparison is worth holding whenever hydrogen and batteries are discussed as interchangeable options.
10.5 — The structural elements
- •Aluminium — 82,300 ppm abundance, density 2.70, excellent strength-to-weight after alloying, recyclable at about 5 per cent of primary energy, and self-passivating with a 4 nm Al₂O₃ film. Battery enclosures, crash structures, motor housings.
- •Iron and steel — the cheapest structural material by a wide margin, still dominant in body-in-white and in cell cans.
- •Magnesium alloys — the lightest structural metal at 1.74 g/cm³, used in housings, limited by corrosion and cost.
Quick check: test yourself
1.Why does a motor magnet need dysprosium when neodymium already provides the anisotropy?
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2.Why did 800 V architectures require silicon carbide?
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3.Why is iridium a bigger constraint on hydrogen than lithium is on batteries?
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Chapter summary
- ✓Neodymium magnets work because 4f orbitals are buried beneath filled 5s and 5p shells, so their electrons keep large unpaired spin and confer huge magnetocrystalline anisotropy — hence coercivity.
- ✓Dysprosium buys high-temperature coercivity against a 312 °C Curie point, and costs remanence plus dependence on a 5.2 ppm element. Grain-boundary diffusion and magnet-free motors are the responses.
- ✓Copper’s single mobile 4s electron above a filled 3d¹⁰ shell gives the second-highest conductivity of any element, and an EV carries 60–85 kg of it.
- ✓Breakdown field scales with bandgap squared, so SiC devices are ten times thinner for the same blocking voltage — which is why 800 V systems arrived with SiC rather than before it.
- ✓Platinum and iridium are constrained by d-band position and by 5 ppb and 0.4 ppb abundances respectively — a ceiling batteries do not share.
Frequently asked questions
Why are neodymium magnets used in EV motors?+
Because 4f orbitals are deeply buried beneath the filled 5s and 5p shells, so they barely participate in bonding and their electrons retain large unpaired spin and orbital angular momentum. Neodymium at 4f⁴ has a large magnetic moment, and because the 4f orbitals are spatially anisotropic and strongly spin–orbit coupled they also confer enormous magnetocrystalline anisotropy — the tendency of magnetisation to lock onto a crystal axis. That gives high coercivity, so the magnet resists demagnetisation by the stator field and by heat. Nd₂Fe₁₄B delivers the highest energy product of any commercial magnet, around 400 kJ/m³.
Why is dysprosium added to motor magnets, and why is the industry removing it?+
Nd₂Fe₁₄B has a Curie temperature of only 312 °C and its coercivity falls steeply well below that, while a traction motor rotor can reach 150 to 180 °C. Substituting a few per cent dysprosium for neodymium raises the anisotropy field and therefore high-temperature coercivity. The costs are that dysprosium couples antiparallel to iron so remanence falls, and that at 5.2 ppm it is one of the scarcest elements in the crust with concentrated, volatile supply. Mitigations are grain-boundary diffusion — placing dysprosium only at grain surfaces where it is needed — ferrite-assisted synchronous reluctance motors, and induction motors that use no permanent magnets at all.
Why did 800 V EV architectures arrive with silicon carbide?+
Because breakdown field scales roughly with the square of the bandgap, and SiC’s 3.26 eV against silicon’s 1.12 eV gives 2.8 MV/cm against 0.3. A device that withstands ten times the field can be made ten times thinner for the same blocking voltage, and on-resistance scales with thickness — so a SiC MOSFET has dramatically lower conduction loss at high voltage and switches far faster. At 400 V, silicon IGBTs are adequate; at 800 V they are not. And 800 V halves the current for a given power, which quarters I²R loss and allows thinner cable, worth tens of kilograms.
How much copper does an electric vehicle use and why?+
Roughly 60 to 85 kg, about four times an internal-combustion vehicle, across motor windings, busbars, the high-voltage harness, charging cables and the on-board charger. Copper is used because it has the second-highest electrical conductivity of any element at 5.96 × 10⁷ S/m, behind only silver at a hundred times the price. As a group 11 d-block metal its single 4s electron above a filled 3d¹⁰ shell is highly mobile, and the filled d shell means low electron–phonon scattering. Aluminium windings appear occasionally but need about 60 per cent more cross-section for the same resistance.
Why has platinum been so hard to replace in fuel cells?+
Because the argument for it is electronic-structure deep. Platinum catalyses oxygen reduction because its d-band centre sits at almost exactly the position that binds oxygen intermediates neither too strongly nor too weakly — the Sabatier principle, drawn as a volcano plot with platinum at the peak. Iridium plays the same role for oxygen evolution in PEM electrolysers, and at 0.4 ppb crustal abundance it is a genuine bottleneck for green hydrogen scale-up. This is a materials ceiling that batteries do not face.
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The Periodic Table of the EV is an original educational series on the materials science of electric vehicles. All values are standard-condition literature figures for representative materials, not measured data from a specific product, and sources differ on several of them. Always verify against the specific material datasheet in use before making design, purchasing or certification decisions.