| Sodium ion batteries has become the most potential energy storage device ever since lithium ion battery attributed to advantages of high sodium abundance and low cost.However,the large radius of sodium ion leads to slow kinetics in the sodiated process.Therefore,it is urgent to find suitable anode materials to promote the commercial development of sodium ion batteries.Alloy anode materials have attracted considerable attention benefitted from the high theoretical specific capacity and safe working potential.However,alloy materials are prone to problems such as volume expansion and electrode material pulverization during the charging/discharging process,resulting in irreversible capacity loss.Therefore,in this paper,the bean pod-like tin-based alloy/nitrogen-doped carbon fibers membrane materials were prepared by facile electrostatic spinning technology.The self-supporting flexible membrane materials can be used as anode directly without binder,which improved the energy density and cycle life of the batteries.The electrochemical performances of different alloy compounds were tested by assembling sodium ion batteries,and the sodium storage mechanism was studied and analyzed.The main research contents are as follows:（1）The solution of Sn Cl2·2H2O,Co Cl2·6H2O,hollow carbon spheres（HCSs）and polyacrylonitrile（PAN）was electrospun into membrane with three-dimensional network structure by facile electrospinning technique.After the subsequent heat treatment technology,the Sn Co alloys were filled into the nitrogen-doped carbon fibers containing hollow carbon spheres to obtain bean pod-like Sn Co/nitrogen-doped carbon fibers（B-Sn Co/NCFs）composite.The non-active metal Co forms tight metal bond with Sn,which improved the electrical conductivity and accelerated the reaction kinetics of the electrode.The nitrogen-doped carbon substrate containing hollow carbon spheres not only effectively prevents the agglomeration of Sn Co alloy,but enhances the flexibility of the electrode,reducing the volume and thermal effect.Therefore,when B-Sn Co/NCFs used as the anode of sodium ion battery,it shows good cycling performance(369.5 m Ah g-1 reversible specific capacity after 200 cycles at 0.1 A g-1)and rate performance(243.6 m Ah g-1 specific capacity at high current density of 1.6 A g-1).（2）The solution of Sn Cl2·2H2O,Sb Cl3,hollow carbon spheres（HCSs）and polyacrylonitrile（PAN）was electrospun into membrane with three-dimensional network structure by electrospinning technology.After high temperature calcination,the Sb Sn alloys were encapsulated in the nitrogen-doped carbon fibers containing hollow carbon spheres to obtain bean pod-like Sb Sn alloys/nitrogen-doped carbon fibers（B-Sb Sn/NCFs）composite membrane.Sb,as the active metal,can improve the overall capacity of the electrode.Besides,the different sodiated potentials between Sn and Sb make two metals alternately used as volume buffer in the charging and discharging process.In addition,the unique carbon substrate also contributes to enhance the stability and flexibility of the electrode,which effectively improved the electrochemical performance.Therefore,when B-Sb Sn/NCFs membrane material used as the anode of sodium ion batteries,it shows excellent cycling performance(486.9 m Ah g-1 reversible capacity after 400 cycles at 0.1 A g-1)and rate performance(388.2 m Ah g-1 specific capacity at1.6 A g-1).The B-Sb Sn/NCFs||NVOPF@3Dc full cell also shows good electrochemical performance,the soft-pack cell has the ability of lighting up light-emitting diodes（LEDs）,demonstrating the potential commercial prospect. |
