Investigation On Graphene Nanoribbons And Theirs Nanocomposites For Lithium Ion Batteries

Lithium-ion batteries(LIBs) are widely used in portable electronic devices such as notebook computers, mobile phones, cameras, miner’s lamp etc. due to low energy consumption, high energy density, high working voltage, low self-discharge, environment friendly and good cycle performance. At present, material has a vital influence on lithium ion battery. There are many good qualities for carbon materials, for example, low price, environment friendly, diverse structure, simple preparation, easy modification and high security. In this paper, we systematically study the utility efficiency and action mechanism of graphene nanoribbons in cathode and anode materials of lithium ion batteries from the preparation of graphene nanobelts, composite metal oxide and lithium transition metal phosphate composite.In this thesis, Graphene nanoribbons were synthesized from multiwalled carbon nanotubes by a solvent oxidization method and were self-assembled to a tridimensional network structure. And a larger specific surface area and more pore structure were obtained relative to the raw carbon nanotubes. This structure not only provides more lithium ion storage sites but also provides more reaction interface for lithium ion. It can shorten transport diffusion paths of the lithium ion and electrolyte, which is benefit to improve the capacity and rate performance of anode materials for lithium ion battery. The cyclic voltammograms and charge/discharge test showed that the storage modes is mainly the electric double layer mechanism accompanied by a small amount of faradaic pseudocapacitance reaction process.The galvanostatic charge-discharge experiments show that the reversible capacity of graphene nanoribbons maintained 716 m Ah g-1 and 519 m Ah g-1 at the current density of 0.6 A g-1 and 1 A g-1 after 200 cycles, which showed excellent rate performance.Graphene nanoribbons wrapped Sn O2 nanoparticles which are anchored on carbon nanotubes(GCSCNTs) were synthesized by a two-step hydrothermal method. Sn O2 nanoparticles in the diameter of about 5 nm are uniformly anchored on the surface of carbon nanotubes, and graphene nanoribbons firmly wrapped on Sn O2 nanoparticles @ CNTs. Electrochemical experiments prove that GCSCNTs exhibit superior lithium storage capacity and cycling performance. The GCSCNTs show a reversible capacity of 1038 m Ah g-1 at a current density of 0.1 A g-1. Over 1000 cycles at the current density of 1 A g-1, GCSCNTs can keep the specific capacity of 502 m Ah g-1. The excellent performance is mainly due to its special structure.The graphene nanoribbon/Li Fe PO4 cathode composite material was obtained by a simple solution diffusion method, which is mainly depended on the electrostatic attraction between Li Fe PO4 and the graphene nanoribbons. Results demonstrate that electrostatic adhesion of GNRs is more effective to improve the electrochemical reaction activity of LFPO than mixing of carbon nanotubes. The comparative investigations on multiwalled carbon nanotubes and GNRs as a conducting additive in LFPO prove that GNRs will be a new superior carbon conducting additives for high-rate lithium-ion batteries.