Effect Of Preparation Process On Structure And Electrochemical Performance Of Nano-e₂SiO₄/C

As the anode material of lithium-ion battery,olivine ferrous silicate?Fe₂SiO₄?has a theoretical specific capacity of 526 mAh/g,which is much higher than that of graphite.Ball milling solvents and raw materials have a great influence on the structure and properties of materials.The effects of ball milling solvents,carbon sources and iron sources on the structure,microstructure and electrochemical properties of Fe₂SiO₄ were studied,and the technological conditions for the preparation of excellent ferrous silicate anode materials were explored.The crystal structure was analyzed by X-ray diffraction?XRD?and the morphology was observed by scanning electron microscope?SEM?.The electrochemical properties of the materials were determined by the galvanostatic charge-discharge method,cyclic voltammetry and AC impedance method.Fe₂SiO₄/C nanocomposites?FS/C-W,FS/C-E,FS/C-M?were prepared by wet milling of ferrous oxalate,gaseous nano-silica and ammonium citrate under different ball milling solvents?deionized water,ethanol and A mixture of the two at 3:7?.XRD shows that the three materials are olivine Fe₂SiO₄ crystal structure,while SEM shows that FS/C-M has 30mm⁷5nm small particle size nanoparticles with uniform dispersion,shortens the lithium-ion diffusion channel,and makes FS/C-M have low impedance,good reversible lithium storage capacity,rate performance and cycle performance.Using gaseous nano-silica and ferrous oxalate dihydrate as raw materials,three kinds of Fe₂SiO₄/C nanocomposites were prepared by the solid-state method with different carbon sources.The Fe₂SiO₄/C prepared with polyvinylpyrrolidone as a carbon source is named FS/C-PVP,the Fe₂SiO₄/C prepared with ammonium citrate as a carbon source is named FS/C-AC,and the Fe₂SiO₄/C prepared with citric acid as a carbon source is named FS/C-CA.XRD shows that the three materials have on the olivine crystal structure.Fe₂SiO₄,SEM shows that FS/C-CA is composed of uniformly dispersed nanoparticles,while FS/C-PVP and FS/C-AC are formed the agglomeration of nanoparticles and submicron particles.The reversible specific capacity of FS/C-CA at 0.1C rate after high rate charge-discharge is 662.1 mAh/g;The specific discharge capacity is 666.6 mAh/g,100 when the first discharge specific capacity is 537.8 mAh/g after 100 cycles at 1C rate.The small particle size and high specific surface area of FS/C-CA increase its specific capacity.Using ferrous acetate tetrahydrate and ferrous oxalate dihydrate as the iron source and mixing with SBA-15,citric acid respectively,Fe₂SiO₄/C nanocomposites were synthesized by high-temperature solid-state method.The two materials are referred to as FS/C-FA and FS/C-FO respectively.XRD shows that both FS/C-FA and FS/C-FO are composed of olivine Fe₂SiO₄ crystal and Fe₃O₄ crystal.It was observed by SEM that both of them were spherical particles,and the FS/C-FO particles were uniform,and the primary particle size was distributed between28⁷4nm.Due to the smaller particle size,the electrochemical performance of FS/C-FO is better than that of FS/C-FA,and the reversible capacity can reach 700.3mAh/g at 0.1C ratio.