Highly durable organic electrode for sodium-ion batteries via a stabilized alpha-C radical intermediate

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized alpha-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the alpha-radical demonstrates reversible transformation between three states: C = C; alpha-C . radical; and alpha-C- anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per alpha-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.