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Nitroaromatics as High‐Energy Organic Cathode Materials for Rechargeable Alkali‐Ion (Li+, Na+, and K+) Batteries

Organic cathode materials with existing redox functionalities are attracting increasing attention for rechargeable alkali‐ion batteries due to their high theoretical gravimetric capacity, molecular diversity, and sustainability. However, they are still restricted in specific capacity and energy density. The discovery of new multielectron redox‐active functionalities that can impart significantly enhanced capacity and energy density is highly desired. Herein, a group of organic nitroaromatic compounds (p‐, o‐, and m‐dinitrobenzene (DNB)) is reported as novel high‐energy cathode materials for alkali‐ion batteries. For the first time, nitro groups in DNBs are found to undergo an electrochemically reversible two‐step two‐phase reaction at a voltage above 2 V, rendering a high theoretical capacity of 638 mAh g−1. A systematic study is undertaken to reveal the reaction mechanism and verify the redox reversibility. By confining the optimum p‐DNB within a microporous carbon nanosphere host, record‐high reversible capacities of 620, 573, and 536 mAh g−1 at 50 mA g−1 are achieved for lithium‐, sodium‐, and potassium‐ion batteries, respectively. Demonstrating nitro as a unique redox‐reversible functionality, this work opens a new direction in the development of novel high‐performance organic nitroaromatic cathode materials for next‐generation alkali‐ion batteries.