Study On The Preparation And Electrochemical Performance Of 3D Networking Nanofiber Membrane Electrodes By Electrospinning Method

Electrodes are the key to the performance of lithium-ion batteries.The electrodes used in traditional lithium-ion batteries are basically prepared by using a coating process.The process flow is long and the mechanical properties of matal collector are poor.During the bending process,the active materials are easily detached from the collector and the cycle life is limited.Especially,in the case of large rate charge/discharge,the active materials are easily detached from the metal current collector due to volume change during charging and discharging,and the cycle life is affected.The three-dimensional?3D?network structure self-supporting electrodes without the metal current collector prepared by electrospinning technology can provide electron transmission channels and ion transmission channels to improve the electronic conductivity and ion conductivity of the active material,and The in-situ composite of the carbon fiber and active materials can avoids the phenomenon of shedding and thus prolongs the cycle life of the battery.Li₃V₂?PO₄?₃ and TiO₂ have high discharge specific capacities and stable structures.They are currently widely studied and considered as the most promising electrodes,but their intrinsic electronic conductivity is very poor,which severely limits their application.Based on the advantages of 3D network structure electrodes,electrospinning technology was used to prepare3D Li₃V₂?PO₄?₃/C and TiO₂ electrodes to improve their cycle performance and rate performance.The main research contents and results are as follows:?1?The Li₃V₂?PO₄?₃/C electrode material with 3D network structure was prepared by electrospinning.the 3D long-range networking structure of fiber membrane was well maintained by adopting a hot-press process,and the combined use of polyacrylonitrile?PAN?and polyvinylpyrrolidone?PVP?promoted the growth of Li3V₂?PO₄?₃ on the surface of the conductive carbon fibers.When the sample was sintered at 800?for 20h,The obtained Li₃V₂?PO₄?₃ fiber electrode has the best crystallinity,high degree of graphitization,and the specific surface area is 186.4 m2/g,which is the most excellent electrode for electrochemical performance.In the range of 3-4.8V,the electrode has an initial discharge specific capacity of146.2mAh/g at 5C,and after 850 cycles,decays to 143.4 mAh/g,the capacity retention was 98%,coulomb efficiency remained at 100%during the test.This high performance is ascribed to the enhanced electronic and ionic conductivities resulting from the 3D long-range conductive networks,high distribution of Li₃V₂?PO₄?₃ on the surface of carbon fibers and the novel binder-free,self-standing electrode structure.?2?The TiO₂/C electrode material with 3D network structure was prepared by electrospinning.The as-prepared nano TiO_2-x/carbon fiber membrane electrode displays a well electrochemical reaction kinetics and a high specific capacity,due to the characteristic of oxygen deficiency,high specific surface area and high porosity,binder-free and self-standing structure.The high reversible capacity could be jointly generated from porous carbon,full-lithiation of TiO₂ and interfacial lithium storage.At a current density of 100 mA/g,the reversible discharge capacity can reach 464 mAh/g.Even at 500mA/g,the discharge capacity still remains 312mAh/g.Compared with pure carbon fiber and bare TiO₂ powder,the TiO_2-x/C fiber membrane electrode exhibits an excellent cycle performance with a discharge capacity of 209mAh/g after 700 cycles at the current density of 300 mA/g,and the Coulomb efficiency always maintains at¹00%.?3?The as-prepared Li₃V₂?PO₄?₃/C and TiO₂ electrodes and the self-prepared gel-electrolyte were assembled into a gel-state battery.Although the impedance of gel-state battery is large,it can exhibits relatively good electrochemical performance,especially for the TiO_2-x gel-state battery,at 300 mA/g current density,after 1500 cycles,the specific discharge capacity remains at180.1 mAh/g,and the Coulomb efficiency remains constant at 100%during the test except the first cycle.