Hierarchical microstructure constructed with graphitic carbon-coated Ni3S2 nanoparticles anchored on N-doped mesoporous carbon nanoflakes for optimized sodium storage

Bimetallic sulfide Fe5Ni4S8 nanoparticles modified N/S co-doped carbon nanofibers as anode materials for high-performance sodium-ion batteries

Transition metal sulfides (TMSs) have garnered significant attention owing to high theoretical capacities, favorable environmental compatibility, abundant natural resources, and suitable discharge/charge voltage platform in the field of anode materials for sodium-ion batteries (SIBs). However, the sluggish reaction rates and significant volume alteration during the process of sodiation/desodiation restrict the practical application of TMSs for SIBs. Herein, a novel bimetallic sulfide Fe5Ni4S8 nanoparticles modified nitrogen/sulfur co-doped carbon nanofibers (NSCFs) composite is successfully synthesized using a straightforward electrostatic spinning and sulfurization treatment. As an anode material for SIBs, Fe5Ni4S8/NSCFs exhibits a high reversible specific capacity of 686.34 mAh g-1 at 0.1 A/g and a capacity of 607.26 mAh g-1 after 120 cycles at 1.0 A/g with a capacity retention rate of 96.9 %. Even at 10.0 A/g, it still maintains a capacity of 481.14 mAh g-1 after 800 cycles, indicating an excellent electrochemical energy storage performance. Density functional theory calculations demonstrate that the Fe5Ni4S8 exhibits enhanced binding with NSCFs, promoted electron transfers, improved Na+ adsorption ability, and decreased Na+ diffusion barrier energy compared to those of monometallic sulfide FeS. Additionally, the three-dimensional network skeleton of NSCFs can effectively enhance the electrical conductivity and relieve the volume change during the discharge and charge process. The innovative multicomponent design and nanostructural configuration provide a promising strategy to develop high-performance anode materials based on bimetallic sulfide for SIBs.

Rationally engineering a hierarchical porous carbon and reduced graphene oxide supported magnetite composite with boosted lithium-ion storage performances

Ferric gallate (Fe-GA), an ancient metal-organic framework (MOF) material, has been recently employed as an eco-friendly and cost-effective precursor sample to synthesize a porous carbon confined nano-iron composite (Fe/RPC), and the Fe element in the Fe/RPC sample could be further oxidized to Fe₃O₄ nanocrystals in a 180 °C hydrothermal condition. On this foundation, this work reports an optimized approach to engineering a hierarchical one-dimensional porous carbon and two-dimensional reduced graphene oxide (RGO) supporting framework with Fe₃O₄ nanoparticles well dispersed. Under mild hydrothermal condition, the redox reaction between metal iron atoms from Fe/RPC and surface functional radicals from few-layered graphene oxide sheets (GO) is triggered. As a result, reinforced microstructure and improved atomic efficiency have been achieved for the Fe₃O₄@RPC/RGO sample. The homogeneously dispersed Fe₃O₄ nanoparticles with controlled size are anchored on the surface of the larger sized RGO coating layers while the smaller sized RPC domains are embedded between the RGO sheets as spacer. Challenges including spontaneous aggregation of RPC, over exposure of Fe₃O₄ nanoparticles and excessive restacking of RGO have been significantly inhibited. Furthermore, micro-sized carbon fiber (CF) is chosen as a structural reinforcement additive during electrode fabrication, and the Fe₃O₄@RPC/RGO sample delivers a good specific capacity of 1170.5 mAh·g^-1 under a current rate of 1000 mA·g^-1 for 500 cycles in the half cell form. The reasons for superior electrochemical behaviors have been revealed and the lithium-ion storage performances of the Fe₃O₄@RPC/RGO sample in the full cell form have been preliminarily investigated.