Synthesis And Electrochemical Properties Of Coal Tar Pitch-Based Anode Materials For Sodium-Ion Batteries

Sodium-ion battery has been considered as a promissing candidate to replace lithium-ion battery in the fields of large scale energy storage system and low-speed electric vehicle,alleviating the problem of low lithium reserves.Low-cost preparation of high-performance electrode materials is a challenge for the practical application of sodium-ion battery.Non-graphite carbon materials have been widely studied as sodium-ion battery anodes,including hard carbons derived from biomass or polymers,and soft carbons prepared from aromatic rich raw materials.Among them,soft carbon anode with good electro conductivity,excellent rate performance and initial coulombic efficiency,is suitable for charge/discharge process at large currents.However,soft carbons usually possess small interlayer distance,which is due to the strong ?-? interaction between the aromatics during carbonization.The small interlayer distance results in the unsatisfying sodium storage capacity,which can be enhanced by controlling the microstructure of soft carbon and adding sodium ion storage active sites.Aiming at the low-cost preparation of high-performance soft carbon anode,coal tar pitch with large reserves and low price was choosen as aromatic rich raw material.Sodium-ion battery aondes with high capacity,good rate and cycling peipormance were prepared through rational designing the precursor composition,molecular structure and soft carbon morphology.The detailed study includes:(1)Construction of flexible carbon anode with microscopic phase separation structure.Polyacrylonitrile(PAN)derived integral hard carbon anode has large interlayer distance and abundant sodium ion storage active sites,but the electroconductivity and rate performace are poor.To solve this problem,coal tar pitch was added into the precursor solution,and flexible carbon nanofiber was prepared through electrospinning followed by heat treatment in NH3.The carbon nanofiber has a microscopic phase separation structure,that high graphitization areas are continuously distributed in the amorphous carbon matrix.The amorphous carbon areas remain the abundant sodium storage active sites while the high graphitization areas greatly improve the electroconductivity.High nitrogen doping was achieved during the NH3 treatment,further enhancing the reversible sodium ion storage.The free-standing anode delivers high specific capacity of 345 mAh g-1 at 0.1 A g-1,and cycled 10000 times at 1 and 2 Ag-1 without capacity decrease.The carbon nanofiber also shows good electrochemical performance in flexible sodium-ion full cell.(2)Preparation of iodine treated pitch derived carbon nanosheets.Soft carbon anodes obtained from direct carbonization of coal tar pitch possess small interlayer distance and less sodium storage active sites.To solve this problem,planar aromatics of coal tar pitch was cross-linked by the sp3 carbon on alkyl side chain to form a three dimensional structure after the iodization/deiodization process.The strong ?-? interaction between the aromatics during carbonization was effectively reduced and average interlayer distance of the soft carbon was increased from 0.342 nm to 0.371 nm.High-performance sodium-ion battery anode with two-dimensional nanosheet structure was prepared through salt template method.The sodium storage property of pitch derived soft carbon was significantly enhanced by the change in microstructure and morphology.Reversible capacity of the soft carbon is increased from 209 mAh g-1 to 261 mAh g-1 in sodium-ion half cell.The prepared soft carbon anode also shows good electrochemical performance in potassium-ion battery.(3)Preparation of pitch resin derived carbon nanosheets.Pitch resin was firstly synthesized by reaction of coal tar pitch and cross-linking agent 1,4-benzenedimethanol.High-performance sodium-ion battery anode was prepared through heat treatment the mixture of pitch resin and salt template.The planar aromatics was cross-linked by the sp3 carbon to form large molecules with complex structures,thus the strong ?-? interaction between the aromatics during carbonization was effectively reduced.The average interlayer distance of the soft carbon is increased to 0.381 nm.The prepared carbon anode possesses high capacity of 272 mAh g-1 at 0.1 A g-1.After cycling at 1 and 2 A g-1 for 1000 times,the capacity retention are 94.0%and 93.4%,respectively.Sodium-ion full cell assembled by the soft carbon anode and NVP cathode delivers reversible capacity of 210 mA h g-1 at 0.1 A g-1,showing obvious discharge voltage plateau between 3.3 and 2.5 V.(4)Construction of few-layered MoS2 embeded in pitch resin derived carbon composite.Soft carbon/MoS2 composite with nanobox structure was prepared by carbonization of pitch resin,MoS2 precursor and salt template.Few-layered MoS2 is uniformly distributed in the carbon,thus enhancing the electron conduction and suppressing volume expansion of MoS2 during charge-discharge process.The aonde possesses reversible specific capacity as high as 553 mAh g-1,and good rate and cycling performance.The microstructure of coated soft carbon has an important influence on the electrochemical performance.The anode with pitch resin derived large interlayer distance carbon shows obviously enhanced sodium ion diffusion kinetics.