Structure-Activity Relationship Between The Pore Structure Of Bagasse-Derived Hard Carbon And Its Sodium Storage Performance

In recent years,Na-ion batteries have been considered as secondary batteries suitable for large-scale energy storage by taking advantage of low cost,high safety and high power characteristics.Research and development of new practical and high-performance electrode materials is the key to promote the development of sodium-ion batteries.Hard carbon is considered to be the most suitable anode material for commercial applications of sodium-ion batteries due to its low charge-discharge potential,large capacity,and stable structure.Biomass materials are popular due to their abundant raw materials,simple synthesis,and low cost.In this paper,the biomass bagasse is used as a high-quality carbon source for the synthesis of hard carbon anode materials.The impact on the sodium storage performance is explored by matching the separator,structure regulation,electrolyte optimization and surface coating of the material.The specific research contents are as follows:(1)First of all,this paper uses biomass bagasse as a precursor to directly carbonize hard carbon materials in one step,and uses X-ray diffraction(XRD),scanning electron microscopy(SEM)and other technical means to analyze the morphology and structure of the samples.Physical property characterization research.For the obtained hard carbon,glass fiber diaphragm(GF/C)and polyolefin diaphragm(Celgard2325,Celgard2400,Celgard2500)were tested respectively.Overall performance,Celgard2400 separator is better than other separators in terms of long cycle and magnification except that the initial reversible capacity is lower than that of glass fiber separator(GF/C).(2)In order to further improve the sodium storage capacity and cycle performance of hard carbon,hard carbon materials with different particle sizes were obtained by sieving hard carbon.The electrochemical test results show that the capacity increases with the decrease of the particle size,and the first reversible capacity of the hard carbon material over 2000 mesh is 245.9m Ah/g at a current density of 50m A/g.Excellent cycle performance and rate capability are obtained by combining ether electrolytes.After 3000cycles at a current density of 1A/g,the capacity is still as high as 171.5m Ah/g,with a retention rate of 93.2%;when the current density increases from 0.025A/g to 2A/g,the capacity retention rate is 75%;the surface density reaches 15mg/cm~2,at a current density of 50m A/g,the reversible capacity is still 203.5m Ah/g after 100 cycles.(3)The capacity of hard carbon benefits from its natural porous structure and wide interlayer spacing,but its low initial Coulombic efficiency due to its more defects.In response to this phenomenon,the first Coulombic efficiency and rate performance are improved by coating the carbon material with pitch and starch,respectively.The results of material structure characterization and electrochemical test show that the specific surface area of carbon materials coated with pitch and starch is 5.7m~2/g and 4.8m~2/g,which is lower than that of uncoated hard carbon materials(39.5m~2/g).At a coating amount of 5%,the rate performance has been greatly improved,and the first-time Coulombic efficiencies have all moved towards more than 90%.