| The portable electronic devices become miniaturization,thinness and flexibility.Lithium-ion batteries became the main object of flexible battery research because of lithium-ion batteries had high specific energy density,which could make the battery lighter.Traditional lithium-ion batteries used metal as collector,and the stability of the electrode structure cannot be guaranteed under bending state,which affected the electrochemical performance of the battery.In this paper,electrospinning was taken and used Polyvinylidene fluoride（PVDF）and Styrene–butadiene–styrene elastomer copolymers（SBS）.SBS/PVDF nanofiber membrane was used as electrode substrate,Li Fe PO4 was used as active material for positive electrode,nano graphite was used as active material for negative electrode.The self-supporting flexible electrode without metal was prepared.The physical structure and morphology of the flexible electrode were characterized by SEM and WCA.The electrochemical performance of the electrode was characterized by cyclic voltammetry test,constant current charge-discharge test and AC impedance test.The subject successfully prepared the SBS/PVDF substrate flexible anode and cathode,which improved the cycle stability and rate performance.The main work given as follows:Firstly,the SBS/PVDF nanofiber membrane was prepared by electrospinning.The mixing of the two polymers could improve the spinnability of the spinning solution,and the fiber fineness and uniformity were improved.The performance of the fiber membrane was characterized by SEM,CFP and mechanical properties tests.When the mass ratio of SBS to PVDF was 3:2,the performance of the fiber membrane is the best.The nanofiber membrane has high porosity,uniform pore size distribution,fiber strength and tensile properties.The chemical structure of membrane was stable in the electrolyte,had good moisture affinity and absorption rate for electrolyte.SBS/PVDF nanofiber membrane was used as electrode substrate to increase the electrode flexibility and internal stress.Therefore,SBS/PVDF nanofiber membranes can be used as self-supporting substrates for flexible electrodes of lithium-ion batteries.Then,made the electrode paste,which was prepared by using Li Fe PO4and acetylene black as conductive agent.The electrode paste was coated on the SBS/PVDF nanofiber membrane to prepare the self-supporting flexible cathode without metal collector.The nanostructure of membrane can strengthen the bonding of the electrode materials and improve the stability of the electrochemical properties when electrode in the bending state.The flexible positive electrode had a discharge specific capacity of 160.3 m Ahg-1at 0.1 C.After 100 cycling had discharge specific capacity of 154.6 m Ahg-1,with capacity retention rate of 96%.At the current density of 1 C,the specific discharge capacity of the battery is 136 m Ahg-1,which shows a stable cycle performance and a good rate performance.Secondly,a self-supporting flexible anode without metal collector was prepared by coating nano-graphite on SBS/PVDF nanofiber membrane.In the process of charge and discharge,the volume expansion of graphite will destroy the structure of the electrode and affect the electrochemical performance.The internal fibers of SBS/PVDF nanofiber membrane are connected with each other,which has stable internal structure and good mechanical properties.The structure of SBS/PVDF membrane can provide internal stress of flexible anode and reduce the damage of structure,thus ensuring the electrochemical stability of the graphite negative electrode.For the flexible anode had a discharge specific capacity of 338.3 m Ahg-1at a current density of 0.1 C.After 100 cycling had discharge specific capacity of 315.4 m Ahg-1,with a retention rate of 93%Finally,a complete flexible lithium-ion battery was assembled with the prepared Li Fe PO4flexible cathode and the graphite flexible anode,which could make the LED glow,but could not glow for a long time. |
