Carbon nitride derived nitrogen-doped carbon nanosheets for high-rate lithium-ion storage

Study on Energy Storage of ZnCo2Sx Based on Sulfur Vacancy Modulation of Ion Transport Rate

Nowadays, high-rate, high-cycle anode materials for lithium batteries are a research hotspot, and defect engineering for electronic structure modulation is expected to be an effective strategy to improve electrochemical performance. In this paper, we controlled the concentration of ZnCo2S4 sulfur vacancies by regulating the hydrothermal time and performed density functional theory (DFT) calculations on ZnCo2S3.125 with vacancies. The results showed that ZnCo2S3.125 exhibited metallic properties, and the vacancies helped to accelerate the diffusion of carriers and improve the storage capacity. The discharge capacity of ZCS-6 initially reached 2,503.2 mAhg-1 in the first cycle, then maintained at 1,529.8 mAhg-1 after 200 cycles. The excellent cycling performance was attributed to the vacancies that enhanced the carrier transport and adsorption capacity of ZnCo2Sx. Notably, the sulfur vacancy-based surface defect strategy in this study had a greater impact on the electrochemical performance than the morphology optimization strategy.

Fe Powder Catalytically Synthesized C3N3 toward High-Performance Anode Materials of Lithium-Ion Batteries

Recently, carbon nitrides and their carbon-based derivatives have been widely studied as anode materials of lithium-ion batteries due to their graphite-like structure and abundant nitrogen active sites. In this paper, a layered carbon nitride material C₃N₃ consisting of triazine rings with an ultrahigh theoretical specific capacity was designed and synthesized by an innovative method based on Fe powder-catalyzed carbon-carbon coupling polymerization of cyanuric chloride at 260 °C, with reference to the Ullmann reaction. The structural characterizations indicated that the as-synthesized material had a C/N ratio close to 1:1 and a layered structure and only contained one type of nitrogen, suggesting the successful synthesis of C₃N₃. When used as a lithium-ion battery anode, the C₃N₃ material showed a high reversible specific capacity up to 842.39 mAh g^-1 at 0.1 A g^-1, good rate capability, and excellent cycling stability attributed to abundant pyridine nitrogen active sites, large specific surface area, and good structure stability. Ex situ XPS results indicated that Li⁺ storage relies on the reversible transformation of -C=N- and -C-N- groups as well as the formation of bridge-connected -C=C- bonds. To further optimize the performance, the reaction temperature was further increased to synthesize a series of C₃N₃ derivatives for the enhanced specific surface area and conductivity. The resulting derivative prepared at 550 °C showed the best electrochemical performance, with an initial specific capacity close to 900 mAh g^-1 at 0.1 A g^-1 and good cycling stability (94.3% capacity retention after 500 cycles at 1 A g^-1). This work will undoubtedly inspire the further study of high-capacity carbon nitride-based electrode materials for energy storage.

MOF-derived nitrogen-doped porous carbon nanofibers with interconnected channels for high-stability Li+/Na+ battery anodes

Heteroatom-doped porous carbon materials have been widely used as anode materials for Li-ion and Na-ion batteries, however, improving the specific capacity and long-term cycling stability of ion batteries remains a major challenge. Here, we report a facile based metal-organic framework (MOFs) strategy to synthesize nitrogen-doped porous carbon nanofibers (NCNFs) with a large number of interconnected channels that can increase the contact area between the material and the electrolyte, shorten the diffusion distance between Li+/Na+ and the electrolyte, and relieve the volume expansion of the electrode material during cycling; the doping of nitrogen atoms can improve the conductivity and increase the active sites of the carbon material, can also affect the microstructure and electron distribution of the electrode material, thereby improving the electrochemical performance of the material. As expected, the obtained NCNFs-800 exhibited excellent electrochemical performance with high reversible capacity (for Li+ battery anodes: 1237 mA h g-1 at 100 mA g-1 after 200 cycles, for Na+ battery anodes: 323 mA h g-1 at 100 mA g-1 after 150 cycles) and long-term cycling stability (for Li+ battery anodes: 635 mA h g-1 at 2 A g-1 after 5000 cycles, for Na+ battery anodes: 194 mA h g-1 at 2 A g-1 after 5000 cycles).