The Lithium Storage Of New-Type Graphene/Nanosi1Icon Composite As Lithium Ion Battery Anodes

The economy of today’s society solely depends on energy sources; thedevelopment and utilization of New-type energy sources are seriously concerned. Assecond generation rechargeable chemical power source lithium ion battery has it’sown Superior performance, for example: high energy density, low consumption, nomemory effect and low self-discharge, low internal impedance, high cost performance,low pollution and so on. Finding new materials with high charge capacity and cyclingstability is the focus of the study of the lithium ion battery anodes material. Thetheoretical capacity of Li22Si5is up to4212mAh g-1, this is the highest theoreticalcapacity among the alloys studied at present. However, the volume expansion ofsilicon can lead to the pulverization of electrode during lithium insertion andextraction, which leads to bad cycling stability. Graphene, with superior electricalconductivities, high surface areas, excellent thermal property and mechanical property,made it a potential good material for lithium ion battery anodes which may take theplace of graphite in the future. But the relatively low theoretical capacity of graphenelowers its attractiveness. This thesis mainly focuses on the study of new-typeGraphene/Nanosilicon composite as lithium ion battery anodes, the work can bespecified into following four aspects:1. In the first aspect, we have successful synthesized Graphite Oxide (GO) by amodified Hummers method, then reduce the GO at high temperature to Graphene.Thestructure and morphology of the material were characterized using SEM、STM、AFM、XRD、Raman and FTIR.2. In the second aspect, we mechanically mixed the GO and HF treatednanosilicon by sonication, the Graphene/Nanosilicon composite paper electrode wasprepared by filtration of the mixture and subsequent reducing at high temperature. Incomparison to the original graphene and nanosilicon, the cycling stability ofGraphene/Nanosilicon composite is improved significant. After cycling for100cycles,the capacity maintains in325mAh/g.3. In the third aspect, we covalently linked the GO layers by esterificationreaction with1,4-Phenylenediboronic Acid, this can increase the spacing betweenGraphene layers. The Graphene/Nanosilicon/BDBA composite was prepared withsimilar procedure as the Graphene/Nanosilicon composite. We have characterized the structure and morphology of this composite by SEM、STM、AFM、XRD、Raman andFTIR. The cycling stability of the new-type Graphene/Nanosilicon composite is betterthan the Graphene/Nanosilicon composite. After cycling for100cycles, the capacitymaintains in410mAh/g.4. In the fourth aspect, we prepared N-doped Graphene from high temperaturereduction of GO/melamine mixture. After contrasting of the performance of lithiumstorage between the original graphene and new-type Graphene, we found that the firstcycle capacity of new-type Graphene can reach828mAh/g, after cycling for50cycles, the capacity maintains in292mAh/g, the charge retention rate maintains in70%, this is remarkablely better than the original graphene.