Organic electrode materials have emerged as promising alternatives to conventional inorganic materials because of their structural diversity and environmental friendliness feature. However, their low energy densities, limited by the single-electron reaction per active group, have plagued the practical applications. Here, we report a nitroaromatic cathode that performs a six-electron reaction per nitro group, drastically improving the specific capacity and energy density compared with the organic electrodes based on single-electron reactions. Based on such a reaction mechanism, the organic cathode of 1,5-dinitronaphthalene demonstrates an ultrahigh specific capacity of 1,338 mAh⋅g−1 and energy density of 3,273 Wh⋅kg−1, which surpass all existing organic cathodes. The reaction path was verified as a conversion from nitro to amino groups. Our findings open up a pathway, in terms of battery chemistry, for ultrahigh-energy-density Li-organic batteries.