Preparation Of Iron Matrix Composites And Its Application In Sodium Ion Batteries

Sodium-ion battery（SIBs）has become a promising alternative for commercial lithium-ion batteries（LIBs）in the large-scale market application due to the rich natural sodium abundance and similar storage principle and cell configuration to LIBs.Because sodium ions have a larger ion radius than lithium ions,the ion diffusion rate is slow and the volume expansion of the electrode material during charge and discharge is greater,resulting in poor rate performance and cycle stability of the electrode.In order to solve the above problems,the nanostructure design of materials and the combination with conductive carbon materials are common and effective modification strategies.In non-oxygen metal compounds.Among the metal non-oxides materials,Iron-based materials have been widely concerned and show better application prospects with the advantages of abundant natural reserves,low price and environmentally friendly.Therefore,the development and preparation of high-performance and low-cost Iron-based materials are of great significance for sodium-ion batteries in the large-scale grid storages and electric vehicles.In this paper,a variety of iron-based nanocomposites were synthesized by sol-gel method or water bath and then high temperature annealing using polypropylene（PS）spheres as templates,and applied to sodium ion anodes,showing excellent electrochemical performance.The main contents of this paper are as follows:（1）the three-dimensional porous Fe₃N@carbon frameworks（Fe₃N@C/3DPCF）composed of Fe₃N nanoparticles and hierarchical porous carbon network were synthesized by the sol-gel and post-annealing method at 500°C with the polystyrene spheres as soft templates.The hierarchical porous carbon structure can protect Fe₃N nanoparticles from the air oxidation,accommodate the volumetric expansion of Fe₃N,and accelerate the diffusion of electrolytes and the transmission of electrons during Na⁺insertion and extraction processes.Meanwhile,the interface coupling effect between Fe₃N nanoparticles and porous carbon further improved the electrochemical performance and structural integrity of the electrode.The Fe₃N@C/3DPCF electrode for sodium-ion battery exhibited a reversible capacity of 494.6 m A h g^-1 at 0.1 A g^-1,and high rate capacity of 310 m A h g^-1at 2 A g^-1.Moreover,the full cell and flexile cell assembled with pre-sodiated Fe₃N@C/3DPCF as anode and Na₃V₂（PO₄）₃@C as cathode respectively delivered the discharge specific capacities of 351.2 and 390.5 m Ah g^-1 at 0.1 A g^-1.（2）the ingeniously designed Fe Se₂ hollow spheres with the dual protection of nitrogen-doped carbon shells and MXene（Ti₃C₂T_x）materials were synthesized and exhibited the excellent rate and cycle performance for SIBs,achieving the specific capacity of 344 m Ah g^-1 in only～26.4 s charging process at 50 A g^-1 and the reversible capacity of 287 m Ah g^-1after 1200 cycles.The hollow structure,nitrogen-doped carbon shell and MXene layer can play a dual protective role and promote mass transfer/electron transfer,alleviate the volume expansion of Fe Se₂ during discharge/charge process,reduce the direct contact between Fe Se₂ and electrolyte,and improve the sodium storage rate performance and cycle stability.Moreover,the full cell assembled with pre-sodiated Fe Se₂@NC@MXene as anode and Na₃V₂（PO₄）₃@C as the cathode delivered a reversible capacitance of 466 m Ah g^-1 after 600 cycles at 1 A g^-1,with a capacitance retention rate of 90.3%.