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Lithium batteries are rechargeable cells in which lithium ions move between a host negative electrode and a lithium-transition-metal oxide or phosphate positive electrode through a non-aqueous electrolyte, the charge being balanced by electrons in the external circuit. The term covers several chemistries; the lithium-ion version, in which lithium stays in an inserted form at both electrodes, is the one that dominates, and its position rests on a combination of high cell voltage, energy density and long cycle life rather than on any single property ^[1]. Capacity loss over time is not caused by one mechanism but by several acting together: growth of the surface film on the negative electrode, loss of cyclable lithium, mechanical damage to the electrode coating and, at the positive electrode, transition-metal dissolution and structural change ^[2]. Electrode materials are chosen against that background, lithium titanate being a case where a higher operating potential is accepted in exchange for almost no volume change and a very long life ^[3]. Silicon offers roughly ten times the capacity of graphite but expands on lithiation, so it is taken in nanostructured form ^[4]. Mixed transition-metal oxides store charge by conversion and have been examined in fibrous morphologies ^[5]. Safety under abuse and the cost of the electrolyte remain the outstanding concerns.