Phthalocyanine-based covalent organic frameworks as novel anode materials for high-performance lithium-ion/sodium-ion batteries

In this work, three kinds of phthalocyanine-based covalent organic frameworks, NA-NiPc (4-nitronickel phthalocyanine + 4-aminonickel phthalocyanine), PPDA-NiPc (4-nitronickel phthalocyanine + p-phenylenediamine) and DAB-NiPc (4-nitronickel phthalocyanine + 4,4'-diaminobiphenyl), with different pore sizes are synthesized by a catalyst-free coupling reaction. The X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and Transmission electron microscopy (TEM) test results indicate that the pore sizes of the NA-NiPc, PPDA-NiPc and DAB-NiPc frameworks are approximately 1.55 nm, 2.11 nm and 2.74 nm, respectively, which is consistent with the simulated results after optimizing the geometric conformation by HyperChem software; additionally, the specific surface areas are 382, 471 and 575 m(2) g(-1) respectively. As the pore size of the frame increases, the surface area of the material increases accordingly, resulting in different electrochemical behaviors. The initial capacities of the NA-NiPc, PPDA-NiPc and DAB-NiPc electrodes in lithium-ion batteries are 422, 469 and 566 mAh/g, respectively, and after 700 cycles, the capacities remain at 557, 670 and 941 mAh/g, demonstrating capacity retention rates of 131.8%, 142.9% and 166%, respectively, at a current density of 100 mA/g. Even at a high current density of 2 A/g, high specific capacities of 385, 512 and 767 mAh/g can still be observed. Moreover, the use of the NA-NiPc, PPDA-NiPc and DAB-NiPc electrodes in sodium-ion batteries also display excellent behaviors, such as high capacities, stable cycling performances and excellent rate capabilities. With increasing framework porosity, the performances of both lithium-ion and sodium-ion batteries gradually improve, fully indicating that the size of the framework is the key factor in determining the performance of a battery.

Automated summary

In this study, three different-phthalocyanine-based covalent organic frameworks with varying pore sizes were synthesized, and electrochemical experiments revealed that increasing the framework porosity led to improved performance in both lithium-ion and sodium-ion batteries.