Fabrication Of Carbon Nanofibers Composited With Transition Metal Mompounds And Its Application In Zinc-Ion Batteries

With the continuous development of large-scale electrochemical energy storage devices,aqueous Zn-ion batteries are considered as ideal next-generation energy storage devices due to their high operational safety,environmental friendliness,and abundant resources.In recent years,with the continuous in-depth research on zinc-ion batteries,it has been found that nickel-based materials with a two-dimensional layered structure have become ideal cathode materials due to the advantages of large interlayer distance and high energy density,however,its ion agglomeration phenomenon and volume expansion effect in the long cycle test lead to poor rate performance and low cycle efficiency of aqueous Zn-ion batteries.In response to the above challenges,this paper starts from the working principle of the battery,introduces strategies such as structural engineering and composite engineering to regulate the structure and shape of the cathode material,and strives to improve the energy storage capacity and cycle stability of zinc-ion batteries.The main research contents are as follows:1)A composite carbon nanofiber membrane（CNF@MnS/CoNi₂S₄）that can be directly used as a cathode material was successfully prepared by combined electrospinning,carbonization,and vulcanization processes.The morphology and structure of coordination polymer particles can be regulated by simply controlling the concentration of metal salts and organic ligands in the solvothermal process.The large interlayer distance of transition metal sulfides is conducive to the diffusion of zinc ions in their lattices.At the same time,the network structure of carbon nanofibers significantly improves the electron transfer ability during the electrochemical reaction,thereby enhancing the cycle stability of the electrode material.Subsequently,the assembled CNF@MnS/CoNi₂S₄//Zn battery exhibited specific capacities of 152.40m Ah g^-1 and 0.29 m Ah cm^-2（based on active material mass）at a current density of 2 A g^-1,respectively,and A high energy density of 258.78 Wh kg^-1 was achieved at a high power density of 3.40 k W kg^-1.Moreover,it can retain up to 87.34%of its initial capacity after 2000 cycles at a current density of 5 A g^-1.2)NiCo₂S₄ nano needle array cathode material（CC@NC-NiCo₂S₄）coated with nitrogen-doped carbon nanocoating was prepared by hydrothermal method,dopamine polymerization effect,heat treatment and vulcanization process.The NiCo₂S₄ nano-array structure has a stable lattice structure and a spacious ion migration channel,which enables it to obtain rapid ion deintercalation capabilities;nitrogen-doped carbon nano-coating can enhance electrical conductivity and stabilize the nano-needle array structure of the material.Subsequently,the assembled CC@NC-NiCo₂S₄//Zn battery exhibited high specific capacities of 0.58 and 0.46 m Ah cm^-2（based on active material mass）at current densities of 2 and 20 m A cm^-2,respectively.And it exhibits a high energy density of 386 Wh kg^-1 at a power density of 1.34 k W kg^-1,while still having an energy density of 293.1 Wh kg^-1 at a high power density of 12.7 k W kg^-1.In addition,it can maintain up to 80%of its initial capacity and 99%of its Coulombic efficiency after1000 cycles at a current density of 4.65 A g^-1.3)The PVA-KOH gel electrolyte was successfully prepared by physical cross-linking method and low-temperature freezing process,and a quasi-solid CC@NC-NiCo₂S₄//Zn battery was assembled,which reached a high energy density of 238 Wh kg^-1 at a power density of 1.27 k W kg^-1.In addition,it has an initial capacity of 89%and a high Coulombic efficiency of 99%after 500 cycles at a current density of 5 m A cm^-2.The excellent electrochemical performance of quasi-solid-state batteries is attributed to their abundant active sites,fast ion deintercalation rates,easily permeable electrolytes,and excellent structural stability.