Lithium batteries have transformed power storage—from smartphones to electric cars and submarines. But like every battery their chemical composition changes through every charge cycle.
Lithium ions sitting in layers of graphite move between electrodes and change the oxidation state of, magnesium oxide, for example. The chemical rearrangements cause the graphite and oxide layers to physically expand and contract by up to 15 per cent at every cycle, cracking and detaching from the electrodes.