From Neutral Zwitterion to Electroactive Disalt: Electrochemical Insights into Double Zwitterionic Viologens for Anion‐Insertion Batteries

In the quest for sustainable and metal‐free energy storage systems, viologen‐based materials offer exciting prospects as they are synthetically well accessible and show two reversible electrochemical processes with anion insertion. This study introduces and compares two π ‐extended viologen–carboxylate materials bearing double zwitterionic backbones as model compounds based on 1,1′‐bis(4‐carboxyphenyl)‐4,4′‐bipyridinium ([bcbp]): the neutral [bcbp] as a double zwitterionic molecule ( 1 ) and its corresponding (Li) 2 [bcbp](ClO 4 ) 2 disalt ( 2 ) . The choice of these two materials for our electrochemical studies is motivated by the literature available on their synthesis routes and solid‐state properties. Electrochemical tests in lithium half‐cells revealed that compound ( 1 ) is initially inactive but gradually converts into the electroactive disalt ( 2 ) via spontaneous chemical insertion of LiClO 4 from the electrolyte. Compound ( 2 ) directly displays the expected reversible two‐electron p ‐type mechanism involving perchlorate anion (de)insertion, while lithium ions act as spectator species. The system delivers stable cycling performance and high coulombic efficiency, supporting the interest of viologen‐based zwitterionic salts as host material for negative electrode application in anionic rocking‐chair organic batteries. The bipyridinium‐bis(carboxylate) radical ((Li)[bcbp] • ( 3 ) ) formed during our synthesis optimizations is likewise electrochemically assessed. This fundamental work highlights the tunability of double zwitterionic viologens as molecular platforms to promote optimized p ‐type negative electrode materials.