Preparation And Lithium Storage Properties Of Cross-linked Carbon Nanosheets Based On Semi-coke

Semi-coke is a solid product of coal carbonization at low temperature,which is widely used in building materials,calcium carbide,metallurgy,silicon carbon,chemical fertilizer and other industries.However,as people’s increasing awareness of environmental protection and energy saving,the demand for semi-coke in traditional industries is becoming less and less,which has caused the semi-coke industry to fall into the predicament of oversupply in the market.The sales channels of semi-coke produced by the company is becoming more and more narrow,resulting in a large backlog of semi-coke,which further causes the waste of resources and potential safety hazards.Therefore,it is an urgent problem to find new ways to utilize semi-coke and realize the conversion of high value-added semi-coke resources.Because semi-coke has the characteristics of high fixed carbon,good surface structure and performance,this paper uses physical and chemical methods to convert semi-coke into semi-coke-based carbon nanosheets.The prepared semi-coke-based carbon nanosheets are applied to the anode of lithium-ion batteries,which provides a new idea for the development of semi-coke in the direction of high value.The specific research contents of this paper are as follows:1.Purified semi-coke was obtained by mechanical ball milling and acid treatment,and the effect of acid treatment on the structure and electrochemical performance of the sample was studied.Through the analysis of XRD,it is found that the acid treatment can remove the impurities in the original semi-coke.Therefore,the discharge capacity of 291.9 m Ah g^-1 for the purified semi-coke can be obtained after 100 cycles at 0.2 A g^-1,which is higher than the original semi-coke.2.Semi-coke-based cross-linked carbon nanosheets with lamellar structure and high specific surface area were prepared by molten salt method.The effects of calcination temperature and different molten salt systems on the structure and electrochemical properties of the materials were investigated.The results show that the cross-linked carbon nanosheets with a thickness of 10-30 nm were obtained by calcining at 800 ^oC for 2 h in nitrogen atmosphere with Na Cl/KCl as molten salt system.As the anode material of Li-ion battery,the discharge capacity of the material reaches527.5 m Ah g^-1 after 100 cycles at the current density of 0.2 A g^-1.The reason is that the carbon network formed by the interconnection of the nanosheets is conducive to the better contact between the electrode material and the electrolyte,thus promoting the electrochemical reaction.3.Semi-coke-based cross-linked carbon nanosheets were prepared by calcium carbonate template method.The effects of calcium carbonate content on the structure and lithium storage properties of carbon materials were investigated.The electrochemical performance test showed that when the ratio was 5:1（calcium carbonate:purified char）,the semi-coke-based cross-linked carbon nanosheets with specific surface area of 458 m² g^-1,pore volume of 0.16 cm³ g^-1 and thickness of 10 nm could be obtained.When the current density is 0.2 A g^-1,the discharge capacity of the electrode material reaches 719.6 m Ah g^-1 after 100 cycles,which is obviously superior to the electrochemical performance of the semi-coke-based cross-linked carbon nanosheets prepared by molten salt method.This is because the materials with richer pore structure and thinner nanosheets structure can increase the contact area between the active material and the electrolyte and improve the utilization rate of the active material.