Modification Studies Of Low-temperature Petroleum Coke As Anode Material For Lithium Ion Batteries

1.First of all,in a protective atmosphere of nitrogen,low-temperature petroleum coke underwent carbonization treatments at different temperatures,the microstructure of the material which is tested by the true density,BET and SEM spectra characterization,and the materials with different temperature treatments are under the charge-discharge characteristics testing,then exploring the relationship between the microstructure and the charge-discharge characteristics of materials to establish its optimal heat treatment temperature of 650?.2.Secondly,petroleum coke with low temperature undergoes coating modification,then the specific discharge capacity and coulombic efficiency have markedly improved.Different cladding materials exhibit different performance,for example,materials coated with nitrogenous polymer show higher discharge capacity characteristics,while materials coated with inorganic salt such as LiF,Li₂CO₃,CaCO₃ behave good recycling properties.Stable discharge capacity of petroleum coke which processed the coating modification of nitrogenous polymer can reach to above 370 mAh·g^-1,while the specific discharge capacity of petroleum coke which processed the coating modification of LiF,Li₂CO₃,and CaCO₃ still maintains above 300 mAh·g^-1 after cycle of two hundred times.It is apparent to see the surface of petroleum coke covers a layer of stable pyrolytic carbon/inorganic materials through SEM characterization.On one hand,pyrolytic carbon/inorganic salts on the surface of the material not only can form a stable SEI?solid electrolyte interface?film,but also provides a number of reversible lithium insertion site,so as to improve the first coulombic efficiency and discharge capacity.On the other hand,due to stable pyrolytic carbon/inorganic materials is difficult to deform and split,so the material can make charge-discharge cycle performance more stable.3.In this thesis,we test the material coated with LiF in different ratio.The specific discharge capacity of petroleum coke processed the coating modification of LiF steadily maintains about 335 mAh·g^-1 at 0.1C,315 mAh·g^-1 at 0.2C,280 mAh·g^-11 at 0.5C,220mAh·g^-1at 1C,which shows excellent performance of ratio.4.According to the different effects of polymers and inorganic salts coating on charge-discharge properties of petroleum coke,through primary coating modification and secondary coating modification,the study researches effects of the secondary coating modification on charge-discharge characteristics of material.The study has shown that the sequence of polymers and inorganic salts coating modification has greatly influence on discharge properties of material.The specific discharge capacity of petroleum coke processed the secondary coating modification of polymer/Li₂CO₃?PL?steadily maintains about 400mAh·g^-1,The specific discharge capacity of petroleum coke processed the secondary coating modification of Li₂CO₃/polymer?LP?steadily maintains about 300 mAh·g^-1.The analysis of SEM characterization shows that the coating layer of polymer on the surface of LP sample completely covers the coating layer of Li₂CO₃,while the coating layer of Li₂CO₃ on the surface of PL sample completely covers the coating layer of polymer,forming a C/polymer/Li₂CO₃ three-dimensional coating structure,and the structure can give full play to characteristics of the both coating materials.