Preparation And Energy Storage Performance Of Hard Carbon Anode Materials For High Energy Density Sodium Ion Batteries

Due to the intensification of environmental pollution and the energy crisis,the advantages of clean energy such as wind,solar and tidal energy are gradually emerging.However,due to the unstable characteristics of this kind of energy,large-scale energy storage devices are needed for energy storage and transportation.So far,Lithium-ion batteries(LIBs)have been playing a leading role in energy storage owing to their high energy density and good cycling stability.However,the large-scale applications of LIBs are still restricted by the limited abundance of lithium resources and its uneven distribution.Because of this,Sodium-ion batteries(SIBs)have drawn extensive attention as a potential and promising alternative to LIBs for large-scale applications due to the huge advantages of sodium in terms of low cost and large resource availability.However,the lack of suitable anode materials has hindered the commercial development of SIB technology.Despite a wide range of materials,including carbons,alloys,oxides,phosphides,and sulfides having been revealed to possess large Nastorage capacities,their cycling efficiencies and stabilities are insufficient for battery application.Among all the reported anode materials,hard carbon(HC)appeared to be the most promising candidate for SIBs because of its appropriate operating potential,high capacity,and considerable cyclability.Nevertheless,the structure-activity relationship between the sodium storage capacity of hard carbon anode material and its structure is unclear,significantly affecting the application of hard carbon anode materials.To further clarify the inherent connection between the material structure and the sodium storage capacity.This paper analyzed deeply the sodium storage mechanism of hard carbon materials by constructing hard carbon materials with different carbon layer spacing,and provided a research basis for further application of hard carbon anode materials.The specific research contents are as follows:(1)Based on this,firstly,a series of hard carbon materials were prepared from polyaniline in the temperature range of 600-1400℃,and the relationship between microstructure and properties of hard carbon materials was systematically discussed.Among them,the material prepared at 1200 ℃ has the best electrochemical performance of a specific capacity of 313 mAh/g at a current density of 50 mA/g and approximately 165.9 mAh/g below 0.1 V due to suitable carbon layer spacing.(2)Furthermore,coal tar soft pitch was taken as the precursor for anode material due to the coal-rich and oil-poor energy structure of China.As a consequence,the sodium capacity of pitch-based carbon by direct carbonization is generally below 100 mAh/g.In order to prepare coal-based hard carbon materials with large layer spacing,the waste plastics(polyethylene terephthalate)with a large number of aromatic hydrocarbons and an ester group were used to break the interactions between aromatic hydrocarbons to interfere with the graphitization of pitch.The effects of the mixing ratio of polyethylene terephthalate and coal tar pitch,and carbonization temperature were investigated.The results show that when the mass ratio of the two materials is 3:1,the hard carbon electrode material prepared at a carbonization temperature of 1100℃has the best electrochemical performance.This electrode shows an initial coulombic efficiency of ～70% with a typical voltage platform of 0.1 V.It still has a specific capacity of 215 mAh/g after 100 cycles at a current density of 50 mA/g with excellent cycling performance.