Preparation Flexible Electrodes With High Performance And Their Electrochemical Performance

Due to their lightweight, flexible and stretchable, major research and development efforts have been devoted to design advanced flexible electronic devices for next-generation, high-performance portable electronic devices. Now, the electrodes were prepared by mixing active materials, acetylene black and binder agent at certain ratio and then coating on mental current collector. Furthermore, the addition of current collector and binders make the lithium ion batteries more heavy, rigid, bulky and poor flexibility. For future flexible electronics, there is a great challenge to fabricate a lightweight, high energy density and flexible electrode without binder and metal current collectors. In this paper, we developed two flexible electrodes with high performance by electrospinning technology.1.The large areas flexible nitrogen-doped carbon nanofibers film（N-CNF） was synthesised by electrospinning and carbonization, which were directly used as working electrodes in the sodium-ion batteries. The N-CNF acted as the anode in the cell has some advantages:1) structure stablility, the N-CNF was composed of intertwined nitrogen-doped carbon nanofibers, so the N-CNF has good flexiblility and mechanical property, which is favourable for maintainning the structure of the electrode during the cycling; 2)high surface area, the flexible N-CNF film with a high surface area of 564.4 m2 g-1, which is in favor of the infiltration of electrolyte and increase reactive sites; 3)High nitrogen content, the mass content of nitrogen in N-CNF is 7.15 wt%, furthermore, nitrogen doping can effectively increase the active sites and electric conductivity of carbon nanofibers. The N-CNF was directly used as electrode in sodium ion batteries, showing excellent cycle stability and superior rate performance. The N-CNF exhibits a reversible capacity of 210 mAh g-1 at the7000 th cycle at a current density of 5 A g-1（corresponding to acapacity retention of 99%） and retained a capacity of 154 mAh g-1even at a very high current density of 15 A g-1.2. The flexible SnO₂/nitrogen doping carbon nanofibers film（SnO₂@N-CNF）: we report a new electrospinning strategy to encapsulate SnO₂ nanoparticles in a flexible nitrogen-dopedcarbon nanofiber film. The flexible electrode showed an excellent rate performance and good cycling performance due to the carbon coating, nanostructure and the nitrogen doping, producing a highly conductive pathway for electrons and fast transport channels for lithium ions. In the resulting SnO₂@N-CNF film, 5–10 nm SnO₂ particles were well dispersedand surrounded by intertwined nitrogen-dopedcarbon nanofibers. This unique nanostructure can effectively accommodate the huge volume change of the SnO₂ particles during lithium ion insertion and extraction. The SnO₂@N-CNF film with a high surface area of 506 m2 g-1 and high nitrogen content of 5.6 wt%, which is favourable for the lithium ions can rapidly diffuse to the surface of electrode and can effectively increase electric conductivity of the carbon nanofibers. The SnO₂@N-CNF was directly used as electrode in lithium ion batteries, showing excellent cycle stability and superiorrate performance.The electrode material exhibited a reversible capacity of 754 mAh g-1 atthe 300 th cycle under a current density of 1 A g-1（corresponding to a capacity retention of 99%）and retained a capacity of 245.9 mAh g-1even at a very high current density of 5 A g-1.