| With the vigorous development and utilization of clean and renewable energy such as wind energy and solar energy,people have higher and higher requirements for energy storage equipment.Traditional lithium-ion batteries cann't meet the needs of large-scale energy storage due to problems such as limited lithium resources.Therefore,sodium-ion batteries with low cost,high energy density,and good safety have begun to gradually replace lithium-ion batteries in various energy storage places.However,the main reason for the delay in commercialization of sodium ion batteries is the lack of suitable anode materials.Hard carbon is considered as the most promising negative electrode material,but it faces problems such as high disorder,poor conductivity,and low first-time Coulomb efficiency.However,soft carbon has a high degree of graphitization,good conductivity but low sodium storage capacity,and generally cannot be directly used for the negative electrode of sodium ion batteries.It is a feasible strategy to prepare soft and hard carbon composite materials to make full use of the advantages of hard carbon high sodium storage capacity and good electrical conductivity of soft carbon.As a by-product of petroleum processing and coal processing,pitch has a wide range of sources and high carbon content.It is a high-quality soft carbon precursor.At the same time,pitch is easy to crosslink and is also a high-quality hard carbon precursor.Therefore,this paper uses low-cost asphalt raw materials,through two methods of co-carbonization of soft and hard carbon precursors and pitch coating of wood chips-derived hard carbon to prepare two soft/hard carbon composites with different structures.The specific work content is as follows.Using pitch as the soft carbon precursor,the amorphous soft/hard carbon composite materials was successfully prepared by co-carbonization with the cross-linked pitch and applied to the negative electrode of sodium ion battery.The results show that the chemically cross-linked hard carbon precursor produces a large number of free radicals during the pyrolysis process,and when co-carbonized with the pitch,it will hinder the graphitization tendency of the pitch and make the pitch solid-phase carbonized to form an amorphous carbon material.The ratio of soft/hard carbon precursors in the material and the carbonization temperature are the key factors affecting its electrochemical performance.The electrochemical results show that the ratio of hard and soft carbon precursor is 1:1,and the material HSC11-1500 with a carbonization temperature of 1500?performs reversible specific capacity of 234.5mAhg-1 at the current density of 0.05 A g-1,and the first coulombic efficiency It reached 82.6%.After the sample HSC11-1500 was cycled for 100 cycles,the specific capacity reached 221.4 mAhg-1,the capacity retention rate was 94.4%,and the cycle stability was good.The HSC11-1100 carbonized at 1100°C exhibits the most excellent rate performance.When the current density is increased to 1 A g-1,it still has a specific capacity of78 mAhg-1.Using pitch with good solubility as the coating source,the wood shavings derived hard carbon is surface-coated with a composite material with a soft/hard carbon heterogeneous structure,and the obtained composite material is used for the negative electrode of a sodium ion battery.The results show that the pitch-derived carbon is a soft carbon with a high degree of order.On the one hand,it reduces the edge defects on the surface of the wood chips,and on the other hand,it provides a channel for the rapid transmission of electrons and sodium ions.The electrochemical results show that compared with the wood chip-derived hard carbon MC-1400,the coated pitch PMC10-1400 has a specific capacity of 324 mAhg-1 at a current density of 0.03 A g-1,and the first coulombic efficiency is increased to 82.7%.After 100cycles of the sample PMC10-1400,it still has a specific capacity of 282.7 mAhg-1and a capacity retention rate of 87.2%. |
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