β-Ketoenamine-bond confinement enables near-planar quinone polymer cathodes for high-capacity and ultrastable iron-organic batteries

β-Ketoenamine-bond confinement enables near-planar quinone polymer cathodes that promise 96.8% utilization of carbonyl sites with low energy barrier (0.14 eV), resulting in iron batteries with a high capacity (313 mAh g −1 ) and life (80 000 cycles).