Organic Cathode Materials for Sodium-Ion Batteries: From Fundamental Research to Potential Commercial Application

Organic electroactive compounds hold great potential to act as cathode material for organic sodium-ion batteries (OSIBs) because of their environmental friendliness, sustainability, and high theoretical capacity. Although some organic electrodes have been developed with good performance, their practical application is still obstructed by some inherent drawbacks such as low conductivity and solubility in organic electrolytes. In addition, research on OSIBs has been mainly focused on the performance of electrodes on the material level and neglected the trade-off relationship between the high redox potentials and specific capacities. Almost all organic cathodes used in OSIBs lack the ability to be charged first in half-cells because of the absence of detachable sodium ions, resulting in low attractiveness when assembling full cells with hard carbon as anode. Here, this review presents several existing reaction mechanisms in OSIBs and designs of organic cathode materials. Furthermore, strategies are proposed in order to provide guidelines for improving their performance according to some critical parameters (output voltage, specific capacity, and cycle life) in potential practical OSIBs, and some accounts of organic materials assembled in full cells are summarized. Finally, the challenges and prospects of organic electrodes for OSIBs are also discussed in this review.