In-situ investigation and application of cyano-substituted organic electrode for rechargeable aqueous Na-ion batteries

Rechargeable aqueous alkali-ion batteries are of great interest in cost-effective, risk-free and green energy-storage technologies. Although redox-active organic compounds are regarded as a kind of promising electrode materials, the limited capacity and low charge-transfer capability still hinder their applications in aqueous alkali-ion batteries. Herein, we have designed a cyano-substituted diquinoxalinophenazine (3CN-DPZ) organic electrode. For the first time, in-operando monitoring techniques, i.e., in-situ Raman and in-situ FTIR investigations, combined with the theoretical calculations are thoroughly carried out to explore the role of electron-withdrawing cyano substituents in 3CN-DPZ organic electrode for aqueous Na+ storage. It is demonstrated that the introduced cyano groups provide redox-active sites for the 3CN-DPZ organic electrode upon Na+ uptake/removal and have the strong electron absorption ability coordinated with Na+ in aqueous electrolyte. Therefore, the 3CN-DPZ organic electrode delivers a large specific capacity of 305.1 mAh/g at 1 A/g, a high rate capability of 211.3 mAh/g at 64 A/g, and an exceptional cycling retention of ∼ 97.9 % over 5000 cycles. Furthermore, a high-performance aqueous Na-ion battery (ANIB) has been fabricated with considerable energy/power characteristics and long cycling lifespan, revealing its potential scalable applications in satisfying the various requirements of high-safety and low-cost energy storage systems.