Utilizing Latent Multi‐Redox Activity of p‐Type Organic Cathode Materials toward High Energy Density Lithium‐Organic Batteries

• Published in: Advanced energy materials 2020-08, Vol.10 (32), p.n/a
• Main Authors: Lee, Sechan, Lee, Kyunam, Ku, Kyojin, Hong, Jihyun, Park, Soo Young, Kwon, Ji Eon, Kang, Kisuk
• Format: Article
• Language: English
• Subjects: Batteries; Cathodes; Electric potential; Electrode materials; Electrodes; electrolyte optimization; Electrolytes; Flux density; Lithium; Molecular structure; organic electrode materials; organic rechargeable batteries; p‐type redox reactions; Rechargeable batteries; Redox reactions; Voltage
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202001635

Organic electrode materials hold great potential due to their cost‐efficiency, eco‐friendliness, and possibly high theoretical capacity. Nevertheless, most organic cathode materials exhibit a trade‐off relationship between the specific capacity and the voltage, failing to deliver high energy density. Herein, it is shown that the trade‐off can be mitigated by utilizing the multi‐redox capability of p‐type electrodes, which can significantly increase the specific capacity within a high‐voltage region. The molecular structure of 5,10‐dihydro‐5,10‐dimethylphenazine is modified to yield a series of phenoxazine and phenothiazine derivatives with elevated redox potentials by substitutions. Subsequently, the feasibility of the multi‐redox capability is scrutinized for these high‐voltage p‐type organic cathodes, achieving one of the highest energy densities. It is revealed that the seemingly impractical second redox reaction is indeed dependent on the choice of the electrolyte and can be reversibly realized by tailoring the donor number and the salt concentration of the electrolyte, which places the voltage of the multi‐redox reaction within the electrochemical stability window. The results demonstrate that high‐energy‐density organic cathodes can be practically achieved by rational design of multi‐redox p‐type organic electrode materials and the compatibility consideration of the electrolyte, opening up a new avenue toward advanced organic rechargeable batteries. Multi‐redox capable p‐type organic electrodes, a series of phenoxazine (PXZ) and phenothiazine derivatives, are suggested for modifying the 5,10‐dihydro‐5,10‐dimethylphenazine. The rational design of p‐type organic electrodes and the compatibility considerations relating to the electrolytes give rise to an elevated redox potential and multi‐redox capability for high energy density. This work opens up a new avenue toward advanced organic rechargeable batteries.