context: However, because of the larger sodium ionic radius (rNa+ 1.02 Å vs. rLi+ 0.76 Å), it is necessary to explore suitable cathode materials and modification methods that could accommodate sufficient sodium ions as well as ensure reversible and fast Na+ insertion/extraction. Various types of cathode materials have been proposed, including layered transition-metal oxides (NaxMO2), Prussian blue analogues (PBAs, NaxMy[Fe(CN)6]), polyanion-type compounds, and organic compounds. Due to the strong P–O covalent bond of the PO43− group, combined with the high electronegativity of the fluoride anion (F−), fluorophosphate-based polyanion compounds generally have robust crystal frameworks and tunable high redox potentials, which makes them get more attention.
answer: layered transition-metal oxides (NaxMO2), Prussian blue analogues (PBAs, NaxMy[Fe(CN)6]), polyanion-type compounds, and organic compounds