Mechanism For Synthesizing Nanocarbons And Their Lithium Storage Performance

As a high value-added carbonaceous product,nanocarbons has great applications in divergent fields such as energy storage,conversion equipment,biosensors,electronic nanodevices and water treatment.However,the current methods to prepare nanocarbons are limited by complicated preparation process,serious pollution and high energy consumption,which makes it difficult for the green large-scale preparation of nanocarbons.Therefore,it is significantly important to develop a green and environmentally-friendly method for synthesizing nanocarbons.In this research,LiH is used as the raw material,carbon dioxide?CO₂?and metal carbonate?Na₂CO₃?as carbon source.The mechanism and electrochemical properties of nanocarbons synthesized by LiH-CO₂ and LiH-Na₂CO₃ reactions were studied systematically.We have uncovered the effects of three triggered ways?heating,ball milling and water introducing?and pressure of CO₂ on the nanocarbons microstructure and lithium storage performance.Meanwhile,the pores formation mechanism and electrochemical properties of hierarchical porous nanocarbons were revealed.The main contents and results are as follows:The third chapter proposes a method for efficient and environmentally friendly preparation of nanocarbons.We demonstrate that the conversion of CO₂ into naocarbons can be achieved within less than 13 s by three triggered ways?heating,ball milling and water introducing?.The morphologies and porosity of as-synthesized nanocarbons are strongly related to the pressure CO₂ and synthesis methods.With the CO₂ gaseous increasing,the reaction of LiH-CO₂ becomes intensely,and the porous structure of nanocarbons gradually decreases.Mechanistic investigation shows that the porous structure of nanocarbons is caused by the formation of H₂.The size of the hole is closely related to the rate of H₂ blowing,and the blowing speed of H₂ is mainly caused by the severity of the reaction.Therefore,the microstructure of the product can be regulated by controlling the severity of the gas pressure and synthesis methods.Based on the third chapter,the main influencing factors affecting the synthesis of nanocarbon materials and their lithium storage properties were further analyzed.It is found that the brand and particle size of LiH raw materials have great influence on the reaction process and the microstructure of nanocarbon.The experimental results show that Alfa brand LiH has stronger reactivity,lower reaction trigger temperature and more porous structure than Aladdin brand LiH.By mechanical ball milling,the particle size of LiH becomes smaller.The reaction of LiH-CO₂ is more intense,while the porous structure of synthetic nanocarbon is much mildly.Mechanism studies have shown that the brand and particle size of LiH have a great influence on the reactivity,the microstructure and morphology of the product?C?.The porous structure of nanocarbons is mainly caused by H₂ blowing.Nanocarbons with different morphology and microstructure can be prepared by changing the brand and particle size of LiH.Electrochemical test results show that the performances of nanocarbons synthesized by LiH?Aladdin?and LiH?Alfa?heating with 50 bar CO₂.At a current density of 0.2 A g^-1,the capacities are 710 and 670 mA h g^-1,respectively.The capacity has reached 380and 278 mA h g^-1 at the current density of 0.2 A g^-1,respectively,performing high capacity and rate performance.In the fifth chapter,metal carbonate?Na₂CO₃?was used as the carbon source to prepare nano-scale porous carbon with micropores,mesopores and macropores by high temperature reaction with LiH,which systematically reveals its reaction mechanism,pore formation and types of product.The hierarchical porous carbon synthesized from reacting Na₂CO₃ with LiH exhibits hierarchical porous structure and ultrahigh specific surface area(1227.5 m² g^-1).Mechanistic investigation shows that HPC have rich porous structure due to the mild reaction of LiH and Na₂CO₃.Owing to that,H₂ can be slowly blown.The rich pore structure can not only reduce electron and ion transmission distance,but also provide plenty of storage sites for Li ions.Ultrahigh specific surface area can increase the interface reaction area and improve the amount of lithium ion adsorption.Therefore,the porous nanostructures exhibit excellent electrochemical properties.At a current density of 1 A g^-1,the capacity of the nanocarbons stabilized at672 mA h g^-1 after 100 cycles.And the capacity reached 976 mA h g^-1 after 150 cycles at a current density of 0.2 A g^-1,exhibiting ultrahigh specific capacity and cycle stability.