Preparation And Modification Of Graphitized Coke Anode Materials

With the rapid development of energy storage devices such as electric vehicles and portable electronics,the market has put forward requirements for Lithium-ion batteries（LIBs）with higher energy density,better rate performance,and more stable cycles.As the main anode material for the production of LIBs,graphite has gradually been unable to meet people’s demand for energy.Needle coke and sponge coke,as by-products in the petroleum processing process,have the advantages of easy graphitization,wide source,low lithium intercalation potential and high electrical conductivity.However,the disadvantages of poor rate performance and low cycle reversible capacity restrict its application in anode of LIBs.Therefore,the modification of carbon materials is a hot topic of researchers.In this paper,the mildly expanded treatment and the phenolic resin coating treatment were used to modify the petroleum coke materials.The specific research contents are as follows:（1）Using H₂SO₄,H₂O₂,KMn O₄ as the oxidant and intercalation agent,respectively,the graphitized needle coke（GNC）was subjected to mildly expanded treatment to obtain the mildly expanded graphitized needle coke（MEGNC）.The GNC undergoes two gas expansions during the mildly expanded process,and the interlayer spacing expands from0.346 nm to 0.352 nm.The electrochemical performance of MEGNC was studied,and it was founded that the expansion of the interlayer spacing can not only effectively improve the diffusion rate of lithium ions,provide more lithium ion storage sites,but also relieve the expansion and fragmentation to ensure stability during cycling volume by process by reserving space between the graphite layers during the charging and discharging.The specific performance of electrochemical performance improvement is as follows:a.The reversible capacity contributed by the platform below 0.5 V of the MEGNC half-cell is significantly improved;b.The assembled Li Fe PO₄//MEGNC full cell exhibits excellent rate capacity and cycle performance.Density functional theory（DFT）was used to simulate the intercalation and deintercalation process of lithium ions.The results of DFT show that the expansion of the interlayer spacing effectively reduces the migration resistance of lithium ions and improves the diffusion rate of lithium ions.In addition,the DFT results also show that the interlayer spacing can alleviate the volume expansion and the corresponding volumetric stress change,proving the theoretical feasibility of the experiment.（2）Using GNC as raw material,phenolic resin-coated GNC samples were prepared by the method of phenolic formaldehyde resin（PF）impregnation-evaporation-pyrolysis carbonization.SEM images show that 10%PF coating can form a uniform coating on the surface.Moreover,electrochemical performance analysis of the samples under different coating amounts also prove that the 10%PF coating has the best improvement effect.Therefore,the optimal coating amount of the PF is 10%.This is because too little coating will lead to uneven coating,and too much will lead to too thick coating,which is easy to form a thicker passivation film during the charging and discharging process,and increases the transmission resistance of lithium ions.（3）Using graphitized sponge coke（GSC）as raw material,GSC was coated with the optimal coating amount of 10%PF to prepare PF-coated GSC（GSC@10%C）samples.The electrochemical performance of GSC@10%C was investigated,and it was found that GSC@10%C showed a significant increase in capacity at both current densities of 200m A g^-1 and 500 m A g^-1.Moreover,the reversible capacity and stability during cycling are significant improvement.The reason is that the PF hard carbon coating layer can not only increase the storage site of lithium ions,prevent the solvent co-intercalation phenomenon,but also alleviate the volume expansion effect during the charging and discharging process and reduce the exfoliation of the graphite layer.Improve cycle stability.