| Sodium ion batteries have potential to be a new generation of energy storage systems due to abundant resources of sodium.Therefore,the development of cathode and anode sodium storage materials with good electrochemical performance is of great significance for the large-scale application of sodium ion batteries.Among many electrode materials,conducting polymers have been widely studied as electrode materials because of their conductivity,structural designability and unique redox properties.Polyaniline(PANI)as one kind of conducting polymers has been playing a great role in the sodium ion batteries because of its high theoretically specific capacity(296 mAh g-1),high electrical conductivity,facile preparation and low cost.Meanwhile,carbon anode materials can be prepared by pyrolysis of PANI.Generally,electrode materials with granular irregular morphology have some shortcomings such as agglomeration or structural cracking during charging and discharging,resulting in inferior electrochemical performance of electrode such as weak conductivity and poor cycling stability.One-dimensional(1D)structure design is an effective strategy that can improve the electrochemical properties of materials,which can not only improve the conductivity of materials,increase the contact area between the electrolyte and the electrode material,but also shorten the electrical/ionic transport path,and maintain good structural stability during the cycle process due to its well supporting effect.Furthermore,the 1D hollow structure design of materials can enhance the volume buffering capacity and electrolyte penetration during cycling,and significantly improve the rate and cycle stability of electrode.Therefore,in this thesis,we prepared polyaniline hollow nanofibers via sacrificial template method,and discussed the influence of preparation conditions on the diameter,wall thickness and fiber structure,and then studied the electrochemical performance of polyaniline hollow nanofibers with different structures as the cathode material and the hollow carbon nanofibers by pyrolysis of PANI that as anode material for SIBs.The main research contents and results are as follows:1.We combined template-sacrifice method with electrospinning technology to obtain polyaniline hollow nanofibers(PANI-HNFs).PANI-HNFs with good morphology and controllable tube wall and inner diameter were prepared by in-situ polymerization and subsequent dissolution process.Electrochemical tests showed that PANI-HNFs as a cathode material for sodium ion batteries has a reversible capacity of 153 mAh g-1 at a current density of 0.3C(1C=150 mA g-1),the capacity retention can reach 73.3%after 1000cycles,and the capacity still maintains 70 mAh g-1 at a large rate of 8C,exhibiting high reversible capacity,stable cycle performance and excellent rate performance.The excellent electrochemical performance of PANI-HNFs is mainly due to its unique hollow fiber structure,which not only increases the contact area between the material and the electrolyte,but also forms a good electron and ion transport network.In addition,the 1D hollow structure can effectively alleviate the volume stress and enhance the stability of the electrode.These factors are beneficial to the improvement of electrochemical performance of PANI.2.The hollow carbon nanofibers(HCNFs)were prepared by pyrolysis of PANI-HCNFs.The effects of calcination temperature and inner diameter on the electrochemical performance of HCNFs as anode material for SIBs were investigated.It was found that when the calcination temperature was 1400°C,the hollow carbon nanofibers(the wall thickness was about 130 nm,and the inner diameter was about 800 nm)had the best electrochemical performance.Electrochemical tests showed that HCNFs as anode materials for SIBs exhibited a reversible specific capacity of 276 mAh g-1 at a current density of 100mA g-1,and showed excellent cycle stability that the capacity retention is as high as 96.4%after 450 cycles.It also shows a reversible capacity of 85 mAh g-1 at a high current density of 1600 mA g-1,displaying good rate performance,and the capacity retention remains 70%after 5000 cycles at the same current density,exhibiting excellent cycle stability.The excellent electrochemical performance of HCNFs also benefits from the hollow fiber structure,which facilitates the penetration of the electrolyte and improves the ion/electron transport path.Meanwhile,the hollow structure alleviates the volume change of the material during cycling,and improves the structural stability of the electrode.The above results verify that the hollow 1D structure designed in this work can effectively improve the comprehensive electrochemical performance of the electrode material,and the preparation of the hollow 1D structure by the sacrificial template method can also be extended to other electrochemical reaction systems with large volume changes. |
PDF Full Text Request