The electrochemical performance of state-of-the-art Na-ion batteries (NIBs) is still not comparable with that of Li-ion batteries (LIBs) due to a lack of high-performance electrode materials. Organic electrode materials offer several advantages over their inorganic counterparts, yet they suffer from low specific capacity and poor cycling stability in NIBs due to their low electronic conductivity and severe solubility in liquid electrolytes. By exploiting the structural tunability of organic electrode materials (OEMs), valuable insights into the reaction mechanism and relationship between the structure of OEMs and their electrochemical performance can be understood and further serve to establish substitution guidelines for the rational design of high-capacity organic anode materials.<br/> <br/>This research investigates three sodium carboxylates with selective N substitution or extended conjugation structures, thereby exploiting the correlation between molecular structure and electrochemical performance to establish substitution rules for high-capacity OEMs. These results demonstrate that substitution position and type of functional groups used are essential in creating active centers for uptake/removal of Na<sup>+</sup> and thermodynamically stabilizing the organic structures. The utilization of rational host design and electrolyte modulation led to optimization and further investigation of a unique organic electrode material, 2,2’-bipyridine-4,4’-dicarboxylic acid disodium salt (Na-DCA), resulting in an extended cycle life of up to 500 cycles. Furthermore, a full cell based on the optimized 2,2’-bipyridine-4,4’-dicarboxylic acid disodium salt anode and polyaniline cathode was demonstrated to confirm the feasibility of achieving all-organic batteries. This work provides a valuable guideline for the design principle of high-capacity and stable OEMs for sustainable energy storage.

Establishing substitution rules of functional groups for high-capacity organic anode materials in Na-ion batteries.

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