Study On Lithium Storage Properties Of High Capacity Silicon-based And Carbon-based Materials

Lithium-ion batteries(LIBs)have the advantages of high energy density,wide working temperature and environment friendly.They have been widely used in notebook computers,smart phones,light tablets and other products.However,the application fields of LIBs are extending from small energy storage fields(electronic equipment)to large-scale energy storage fields(electric vehicles)with the rapid development of social economy.The theoretical specific capacity of commercial graphite anode is only 372 m Ah/g,which can not content the energy storage needs of society.Research shows that silicon has the advantages of ultra-high theoretical specific capacity(3579 m Ah/g),rich content and suitable working voltage at room temperature.Simultaneously,there is a strong synergistic effect between the micro-component of nano-porous carbon,which makes the composites show high specific capacity and stable cyclic performance.Therefore,silicon and nano-porous carbon materials have attracted extensive attention for researchers of LIBs.Here,the electrochemical properties of three-dimensional network silicon/carbon composites and single atoms Zn microporous carbon anode materials were investigated in this paper.The main researchs are as follows:(1)Aiming at the problems of large volume expansion,easy crushing and poor conductivity of silicon anode materials,we designed a novel silicon-carbon composite structure by using the morphology controllable ZIF-8.Firstly,the surface of nano silicon was modified,and then a layer of small particles ZIF-8 were grown in-situ.After carbonization,a three-dimensional network Si@NC composite structure was finally formed.Results show that the three-dimensional network Si@NC can not only effectively relieves the volume expansion of silicon during the charging and discharging process,but also provides a fast transport channel for lithium-ion.(2)To further improve the cycle stability of Si/C anode,we designed three-dimensional network Si@ZIF-8@ZIF-67 composites.Firstly,the Si@ZIF-8 composite was further wrapped with ZIF-67,and then carbonized to obtain a three-dimensional network Si@Co-NC composites.Double coated Si@Co-NC composites show very stable long cycle properties because there are no nano-silicon particles on the surface.(3)To further improve the lithium storage performance of heteroatom loaded porous carbon materials,we prepared ZIF-8 precursor with specific size by simple wet chemical method,and then obtained SA-Zn/C-800 anode material loaded by single atom after gradient heating carbonization.Uniformly dispersed single-atom Zn microporous carbon materials provide more Li~+binding sites,improve the utilization of active materials and regulate the microenvironment of carbon matrix.The SA-Zn/C-800 anode material exhibits ultra-high specific capacity and cycling stability.