The Performance And Storage Mechanism Of Li₂FeSiO₄/C As Electrode For Aqueous Capacitor By Electrospinning Method

The intrinsically low electrical conductivity and sluggish Li⁺transport degrade of Li₂FeSiO₄ materials limit its practical applications.At present,Li₂FeSiO₄ electrode materials areprepared by using the high-temperature solid-phase method,which acquires powder materials with larger particle size and serious agglomeration,resulting in longer diffusion paths and slower electrode reactions.The electrochemical properties become poorer.However,the electrospinning process has the advantages of simple operation and low cost.It is a very promising choice for preparing materials with smalle particle size.In this paper,Li₂FeSiO₄/C electrode materials with one-dimensional nanofibers or uniform nanoparticle morphologies are prepared by electrospinning process.Li₂FeSiO₄/C structures,electrochemical properties and charge storage mechanisms were studied.1.Li₂FeSiO₄/C samples are synthesized by the combination of powder and electrospinning method.Li₂FeSiO₄ and PVP with differnent mass ratios are selected and optimized.The results demonstrate that the amount of Li₂FeSiO₄ will have a significant influence on the morphology and properties of the sample.Prior to heating treatment,Li₂FeSiO₄/PVP-0.4 and Li₂FeSiO₄/PVP-1.3 precursors are fibrous.But the adhesion of fibers is sever.The Li₂FeSiO₄/PVP-0.8 precursor fibers have no adhesion.The powder particles are attached to the Li₂FeSiO₄/PVP-0.8 precursor fibers surface.The particles are distributed uniformly with less agglomeration.The fibers thickness is uniform and the surface is rough and nanowires.After heating treatment,Li₂FeSiO₄/PVP-0.4 and Li₂FeSiO₄/PVP-1.3 are irregularly particles and agglomeration.The Li₂FeSiO₄/PVP-0.8 products have a more uniform particle size and less agglomeration,which help to improve the electrode performance.When acted as the aqueous capacitor electrode,Li₂FeSiO₄/PVP-0.8 has first specific capacitance of approximately 150 F/g,at scan rate of 0.5 mV/s.2.By changing the synthesis process,Li₂FeSiO₄/C electrode materials are synthesized by the combination of electrospinning and sol-gel method.Before and after heating treatment,the morphology of the samples shows nanofibers.The diameter of precursor fibers is about twice the diameter of the product Li₂FeSiO₄/C fibers.The diameter of the product fibers becomes finer,mainly due to the partial decomposition of PVP and other raw materials during the heating process to generate CO₂ and other gases dispersed in the air and the remaining raw materials react to produce the target product.The one-dimensional nanofiber Li₂FeSiO₄/C electrode materials help to reduce of the effective transport length for Li⁺and improve the electrochemical performance.The Li₂FeSiO₄/C products have good rate capability.At scan rates of 0.5 mV/s,1 mV/s,5 mV/s,10 mV/s,and 0.5 mV/s,the specific capacitances are 165F/g,133 F/g,98 F/g,86 F/g,and 161.1 F/g,respectively.3.The charge storage mechanism of Li₂FeSiO₄/C samples are synthesized by using the solid-phase method,the combination of powder and electrospinning method and the combination of electrospinning and sol-gel method are analyzed in detail.By calculating the b-values of the three samples,the b-value of the samplesare close to 0.5 at the peak potential,which is the behavior of the battery under diffusion controlling.At the non-peak value,the b-value is close to 1,which is the capacitance behavior that is not controlled by diffusion.Three samples are mixed charge storage mechanisms.Compared with sample a and sample b,sample c contributes the largest specific capacitance to the total capacitance.This is mainly that the morphology of one-dimensional nanofibers help to shorten the lithium migration path,which is beneficial to enhance the material capacity.And the material size is reduced.It is more conducive to the non-diffusion behavior of lithium ions.Therefore,the growth of its capacitive behavior is more dominant.