Title: Energy storage and the compressibility of atoms

Abstract

The development of reversible energy storage in ‘rocking chair’ batteries using Lithium ions usually requires research on special materials for the electrodes. The requirement is essentially that they can act as suitable hosts for the storage of lithium ions. Lithium ions have the electronic configuration of helium and can therefore be categorised as the hardest (i.e. least compressible) of the singly charged ions. Reversible storage therefore requires, in addition to freedom of movement of the ions through the lattice, that the host material should possess the flexibility required to store the ion and subsequently eject it without any recrystalisation, because the latter would imply a change of phase of the host material and hence a loss of energy and reversibility. The storage-recovery cycle often makes use of polaronic distortion of the lattice, which implies the use of ‘soft’ or highly compressible constituent atoms. It will be shown that these ‘soft’ atoms belong to a specific class for which the outer electrons are subject to a double-well quantum-mechanical potential. Such atoms belong to a limited class in the Periodic Table. Thus, specific atoms are singled out as the most favourable. A table involving such atoms will be presented.