Interface Design Of Long Cycling Graphite Anode And Research On Nitrogen Doped Graphene Anode In Potassium Ion Batteries

The new energy market is developing rapidly.However,in the context of limited and uneven distribution of lithium resources;and the increasing price of lithium ores,potassium ion batteries have great potential as alternatives to lithium ion batteries due to their abundant raw materials;low cost;and relatively high energy density.However,potassium ion batteries still face some problems that need to be solved urgently.Due to the large ion radius of potassium ions,which causes greater damage to the material structure during the cycling process,the reall capacity of potassium ion batteries is not high,the cycle stability and the rate performance is poor.From the perspective of designing a stable graphite interface protective layer,this thesis has designed a potassium ion graphite anode that can achieve a stable long cycle.In addition,this paper prepared stable and high energy density graphene potassium ion battery anode materials by doping graphene with nitrogen..The main research contents are as follows.1.In order to improve the cycle stability of graphite anode in potassium ion batteries,this work designed an interface protective layer to wrap graphite with graphene oxide,through freeze drying and then remove oxygen residues by rapid and efficient microwave reduction,preparing a stable graphite anode.The graphene coating interface can effectively inhibit the continuous peeling of graphite anode during the cycling,the stability of the graphite structure during cycling is ensured,solving the problem of instability of graphite anode during the cycling in potassium ion batteries effectively.Under test conditions of 0.2A g-1,compared to graphite capacity decreasing after 150 cycles,the anode shown stable cycling for more than 3000 cycles,which means the battery can operate for more than one year.By comparing the electrodes after the cycling with X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM),it was found that the layered structure of graphite would be broken during the cycling,resulting in continuous peeling of the graphite layered structure.A stable graphene protective coating can effectively avoid this problem,greatly improving the cyclic stability of graphite.2.In order to obtain potassium ion battery anode materials with higher capacity and good stability,this work uses a hydrothermal method followed by heat treatment to introduce nitrogen doping into graphene,providing more sites for the adsorption of potassium ions,improving the capacity of graphene as a potassium ion battery anode effectively.Through electrochemical testing,the negative electrode material can still provide a reversible capacity of 300 mAh g-1 after 1000 cycles.After 200 cycles at a high current density of 5A g-1,it still has a reversible capacity of 125.1 mAh g-1,XPS proves that hydrothermal method effectively introduces nitrogen doping,and the main types of doped nitrogen are pyridine nitrogen and pyrrole nitrogen,which can effectively improve the reversible cycle capacity of graphene.