it's LiFePO4 (aka LFP, Lithium Iron Phosphate), unless there's a new Polonium version I haven't heard of
When most people refer to lithium-ion batteries, they're often thinking of chemistries other than LiFePO4, like NMC (Nickel Manganese Cobalt) or NCA (Nickel Cobalt Aluminum), which have higher energy density.
He was talking about Po vs PO.
Graphene Aluminum Ion is probably going to be the long term here.