Study On Electrochemical Performance Of Coated Artificial Graphite And Sucrose-based Carbon At High Current Densities

Recent years, a demand for promoting Li-ion batteries'power density has been called, for they have been used as power sources for Hybrid-Electric Vehicles. The nature of the electrode materials is of course of primary importance to the power properties of Li-ion batteries. In this work, carbon anode materials were studied to improve the electrochemical performance of Li-ion batteries at high current densities. Artificial graphite and sucrose were used as precursors for carbon anode materials, and the electrochemical performances of the electrode were investigated.On the basis of previous studies of our laboratory, aqua-mesophase pitch(AMP) was used to coat artificial graphite by several times, and the amount of AMP was small in every time. Electrochemical tests and SEM analysis showed that when the AMP with a mass ratio of 20% were divided into two times to coat artificial graphite ,the coating layers were the most homogeneous, and the obtained carbon materials'electrochemical properties were the best at the current density of 20mA/g, of which the discharge capacity was 366.4mAh/g and the coulombic efficiency reached 89.6% at the first cycle. While the amorphous coating layers of carbon materials coated by four times were fairly thick, and the reversible discharge capacity of the obtained carbon materials was 268.6mAh/g at the current density of 100mA/g. The capacity retention ratio was up to 76.3%, which was the highest in all kinds of coated samples.In addition, sucrose-based carbon materials were obtained by adding different contents of expanded graphite to sucrose and then being pyrolyzed at the temperatures of 800℃and 1000℃. Analysis methods including SEM, TEM, and XRD were applied to study the surface morphology and internal structures. Electrochemical testing methods including cyclic voltammetry and galvanostatic charge-discharge processes were applied to study the electrochemical performance and analyze the mechanism of lithium storage in the obtained material. The results of electrochemical testing showed that the sucrose-based carbon material obtained by adding 3(wt)% EG and being pyrolyzed at 800℃exhibited the best charge-discharge performance at high current densities. Its reversible discharge capacity was 210mAh/g at the current density of 100mA/g, with a capacity retention ratio of 85.5%. The reversible discharge capacity kept above 178.6mAh/g at the current density of 200mA/g , with a capacity retention ratio of 72.5%.