Research On Carbon Anode Materials For Sodium/Potassium Ion Batteries

With the vigorous development of portable electronic devices and electric vehicles,the demand for lithium-ion batteries continues to grow,and its long-term development is constrained by the scarcity and uneven distribution of lithium resources.Sodium/potassium ion batteries are considered the most promising to expand the scale of grid energy storage due to their rich sodium/potassium resources and low cost.The development of electrode materials with high capacity,long life and good rate performance is the key to realize the application of sodium/potassium ion batteries.Anode materials are widely studied as an important part of energy storage batteries.Carbon-based materials stand out because of their rich resources,simple synthesis process,and excellent electrochemical performance.In this paper,three different carbon sources are selected,and the best electrochemical performance of carbon materials is achieved by designing carbonization process routes at different temperatures,and the sodium/potassium storage mechanism is analyzed in combination with testing and related literature.（1）Using sawdust as a carbon source,systematically study the effect of carbonization temperature on the microstructure of hard carbon,and further analyze the correlation between microstructure and electrochemical performance.The study found that low specific surface area,low defects,and good microporous structure help to improve the first coulombic efficiency of hard carbon anode materials.The first coulombic efficiency of wood chip-derived hard carbon material（SC-1400）obtained by pyrolysis at 1400℃is as high as 83.4%.The slope capacity has a good linear fit with I_D/I_D+I_G,indicating that the slope capacity corresponds to the adsorption of surface defects.With the increase of carbonization temperature,the pseudo-graphite area increases,the closed cell structure is produced,and the platform capacity increases.（2）Polyacrylonitrile-derived hard carbon nanofibers,a good 3D carbon fiber skeleton network,are prepared by electrospinning combined with different temperature pyrolysis processes,which are used as a binder-free,self-supporting potassium ion battery negative electrode material.The carbon fiber（PAN-1200）obtained by pyrolysis at 1200℃has the most excellent electrochemical performance,achieving a reversible capacity of up to 277.5 mAh g^-1,and the first coulombic efficiency of 76.9%.The capacity retention rate was 90.4%for 400cycles at a current density of 0.1 A g^-1.Combining a variety of test methods and electrochemical performance to analyze the hard carbon potassium storage mechanism,mainly including defects and functional groups’adsorption of potassium ions,intercalation reaction and potassium ion deposition in closed pores.The terminal potential is overpotential deposition.（3）Using pitch as the carbon source,the pre-oxidation process is used to transform the structure of soft carbon from order to disorder.As the anode material of potassium ion battery,the electrochemical performance of the two is also different.The first lap reversible specific capacity of the oxidized asphalt is 226.5 and 210.9 mAh g^-1 at a current density of 20 mA g^-1,and the first coulombic efficiency is 70.3%and 71.8%,respectively.The specific discharge capacities of CPP and COPP were 184.2 and 173.1 mAh g^-1 in the first cycle at a current density of 0.1A g^-1,respectively,and the capacity retention rates after 100 cycles were 87.4%and 83.5%,respectively.Comparing the difference of its electrochemical performance and analyzing its potassium storage mechanism,the capacity contribution in the high voltage interval mainly corresponds to the adsorption of surface defects,and the capacity contribution in the low voltage interval mainly corresponds to the intercalation reaction and pore filling.