What do a wasps' nest from my loft and lithium-ion batteries share in common? The go-to choice of power supply for electrical vehicles is as often as not banks of those circular cells you'd find in cheaper laptops, although several thousand of them boxed up. Li-ion cells are preferred in road vehicles and the larger eVTOLs for their superior energy-density, which affords them greater endurance if not the same capacity of LiPo cells for discharging that energy more rapidly.
That said, most Lipo battery-packs are supplied as flat cells packaged into blocks, or in other words, into squarer spaces. What is rarely taken into account when quoting the energy density of the one option or the other, however, is that packing method. For circles contain only three-quarters the area of squares so technically you can discount the energy available from a given volume of Li-ion packs by 25%.
I recall from delivering milk in glass bottles (so shaped originally as to be able to be carry several by the neck in one hand) that they were much the same height as the one-litre tetra-paks that would replace them in large part, not least for being square instead of round.
The original tetrahedron that made the packaging famous has largely disappeared too. Which shows how much we depend on processes of manufacture and packaging when it comes to product evolution. It remains to be seen therefore whether the 'jelly-roll' battery cell will go the same way as the glass milk bottle...
