Thank relativity every time your car starts. Lead-acid batteries get about 80 per cent of their voltage from special relativistic effects.
The transfer of electrons between two forms of lead in the batteries yields a potential of more than 2 volts, higher than most other batteries. But why they are so good has been a puzzle. Lighter weight tin, for example, which sits one row above lead in the periodic table, is too feeble to power a battery.
Pekka Pyykkö at the University of Helsinki in Finland and colleagues have calculated that the stronger charges on the heavier lead nuclei attract electrons more powerfully, so they reach 60 per cent the speed of light compared to tin's 35 per cent. According to relativity, this gives the electrons higher effective masses, increasing their binding energy to the electrode that attracts them and thus their voltage.
Without these relativistic effects, Pyykkö and colleagues calculate that lead-acid batteries would generate only 0.39 volts. With them, they predict 2.13 volts, in good agreement with the measured 2.11 volts.
"Batteries involving other heavy elements, such as mercury, will probably have very similar effects," Pyykkö told New Scientist.
Journal reference: Physical Review Letters, vol 106, p 018391
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