Dual-Redox Sites Guarantee High-Capacity Sodium Storage in Two-Dimension Conjugated Metal-Organic Frameworks

2D pi-d conjugated metal-organic frameworks (c-MOFs) are promising anode candidates for sodium-ion batteries (SIBs) due to their high intrinsic conductivity and stability in organic electrolytes. However, the development of c-MOFs with multi-redox sites to improve the overall performance of SIBs is highly desired but remains a great challenge. Herein, this work reports the electrochemically active hexaazatrinaphthylene-based 2D pi-d c-MOFs (HATN-XCu, X = O or S) as advanced anode materials with dual-redox sites for SIBs. The ordered porous and layer-stacked structure can provide fast transmission and diffusion channels for ions along the stacking directions. Ex situ Fourier transformed infrared spectra together with X-ray photoelectron spectroscopy reveal the dual-redox site storage mechanism of HATN-XCu, namely, the continuous multi-electron reactions occurring on the redox-active C(sic)N group and [CuX4] unit, respectively. Based on the synergistic effect of dual-redox sites, HATN-OCu anode exhibits impressive reversible capacity (500 mAh g(-1) at 0.1 A g(-1)) and high-rate performance (151 mAh g(-1) at 5 A g(-1)). Significantly, a sodium-ion full battery assembled using a HATN-OCu anode and Na3V2(PO4)(2)O2F cathode also displays high-rate performance (117 mAh g(-1) at 5 A g(-1)) and stable long-cycle life (the capacity retention of 80% after 500 cycles at 2 A g(-1)).

Automated summary

This work reports the development of a hexaazatrinaphthylene-based 2D pi-d conjugated metal-organic framework as an advanced anode material for sodium-ion batteries. This material exhibits dual-redox sites, leading to impressive reversible capacity and high-rate performance. Furthermore, when combined with a specific cathode material in a sodium-ion full battery, it also demonstrates stable long-cycle life.