The Preparation,modification And Electrochemical Properties Research Of Hard Carbon

Lithium ion battery is the dominant energy storage devices in current energy storage market due to its high capacity,high voltage and better cyclic stability.But the expensive price constrains its wide application because of the low proportion of lithium element on earth.The structure and electrochemical mechanism for sodium ion battery are similar with those of lithium ion battery.With the high storage of Na element on earth,the costs of Na-containing compounds are lower than the cathodes like Li Fe PO₄or Li Co O₂ of lithium ion batteries.Thus,sodium ion batteries are more and more popular in both research fields and practical application fields.Besides cathode material,the selection of anode is also significant for electrochemical performance for sodium ion batteries.Hard carbon derived from carbonization of biomass or polymers is a promising anode of Na⁺battery owing to its larger layer distance,proper specific area,abundant pore structures and lower cost compared with graphite.Heteroatoms doping method used in modification of hard carbon can enlarge the storage capacity and enhance the rate stability.Here we use F₂ as the doping reagent to modify the hard carbon anode and obtain larger interlayer distance and specific area thus prompt its electrochemical properties.The specific capacity increased from 266 to 335 m Ah g^-1and the capacity retention rate was 92.2%for modified hard carbon.It can be concluded that heteroatoms doping method is effective for enhancing electrochemical properties for hard carbon.Hard carbon can be used to prepare fluorinated carbon due to its large tap density.Fluorinated carbon owns highest specific capacity in all sorts of solid cathode materials and lithium/fluorinated carbon primary battery obtains numerous advantages like stable discharge capability,easy bringing and potential in miniaturization.Selection of carbon sources and fluorination craftsmanship are important for their electrochemical properties.Here we successfully prepare hard carbon from phenolic resin and fluorinated at various temperatures.The discharge platform of the sample obtained at condition of 350℃,4h is 2.9 V and the maximum specific capacity is 920 m Ah g^-1.The capacity increased but the potential platform decreased with the increasing fluorination temperatures which caused by high F/C ratio and low electrons’migration capability.This research supplies an important reference for industrial production.