Study On Synthesis And Performance Of Iron-Based Materials As Anode For Lithium/Potassium-Ion Batteries

In recent years,lithium/potassium-ion batteries（LIBs/PIBs）have received extensive attention and have been reported by researchers.Iron-based anode materials have become promising anode materials for commercial application due to their high theoretical specific capacity,abundant resources,low cost,and low toxicity.However,the disadvantages of iron-based anode materials,such as low electrical conductivity and large volume expansion during cycling,limit their further development.Therefore,it is necessary to take measures to improve the electrical conductivity of iron-based anode materials and suppress the volume change during cycling to improve their electrochemical performance.In this dissertation,FeSe/C,FeS/C and FeP/C nanofiber composites were synthesized by electrospinning technology combined with annealing procedure for the purpose of improving the electrochemical performance of iron-based anode materials.Their lithium/potassium storage properties were investigated through a series of physical characterization and electrochemical performance tests.The main contents of the work are as follows:This dissertation firstly introduces the electrospinning method of FeSe/C nanofibers.Combined with an ingenious annealing process,the selenization of the raw material Fe₄[Fe（CN）₆]₃,the carbonization of PAN,and the N-doping of carbon are realized in one step.FeSe and N-doped C composite nanofibers（FeSe/C NFs）exhibits excellent cycling and rate performance when applied to the anode of LIBs/PIBs.In LIBs,the FeSe/C NFs-650 electrode obtained at 650°C annealing temperature exhibits a specific discharge capacity of 661 m Ah g^-1 after 300 cycles at 1000 m A g^-1,and exhibits a discharge capacity of 335 m Ah g^-1 at 5000 m A g^-1;In PIBs,a capacity of 227m Ah g^-1 is exhibited after 100 cycles at 500 m A g^-1,and the capacity reaches 164 m Ah g^-1 at high rate(5000 m A g^-1).FeS with similar physical and chemical properties to FeSe but with higher specific capacity and has more application prospects.Based on the above studies,N,S double-doped FeS/C nanofibers（N,S-FeS/CN）were prepared by combining electrospinning technology and high-temperature annealing steps,which exhibits excellent electrochemical performance in LIBs/PIBs.In LIBs,the N,S-FeS/CN-600 electrode obtained at 650°C sulfidation annealing temperature exhibits a high specific discharge capacity of 653 m Ah g^-1 after 250 cycles at 1000 m A g^-1 and a high discharge capacity of 301 m Ah g^-1 at 5000 m A g^-1 Discharge specific capacity;the performance in PIBs is consistent with that in LIBs,the capacity after 500 cycles at 500 m A g^-1 is 124 m Ah g^-1,and the capability at 5000 m A g^-1 is 93 m Ah g^-1.Metal phosphide as the negative electrode of PIBs can alleviate the problem of volume change to a certain extent,and the composite with porous carbon material can significantly improve its electrochemical performance.Porous nitrogen-doped FeP/C nanofibers（P-FeP/C-N NFs）were fabricated by electrospinning,which exhibits excellent lithium/potassium storage performance.In LIBs,the P-FeP/CN NFs electrode obtains a capacity of 514 m Ah g^-1 after 300 cycles at 1000 m A g^-1 and a capacity of 305m Ah g^-1 at 5000 m A g^-1;In PIBs,the capacity remains at 274 m Ah g^-1 after 250 cycles at 100 m A g^-1 and 150 m Ah g^-1 at 5000 m A g^-1.