Making a lithium-ion battery, of the sort that can power an electric vehicle, is a bit like baking a cake. The ion-rich powder is first mixed into a lump-free batter, then spread evenly on foil. The solvents must be dried in an oven, just as baking removes water, then the results must be carefully stacked. The underlying chemistry is fairly well understood. But the best battery makers, like the best bakers, improve their craft over years in the kitchen.

Many masters of this craft now reside in China. On October 9 its Ministry of Commerce said battery-makers would soon need a licence to export goods, kit or ingredients. Its new rules were part of an overhaul of China’s export controls, which also included limits on rare earths.

The regime has rattled China’s trading partners and enraged P

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