Novel Graphene-based Nanomaterials Prepare For Lithium Ion And Lithium Sulfur Batteries

Lithium ion batteries are the most widely used secondary batteries at the moment,but the anode materials are facing with low energy density,unsatisfactory cycle stability,and poor rate performance.To address these challenges,it is essential to develop novel energy storage materials with high energy density and long-cyclic life for the anode.Lithium sulfur batteries,with theoretical specific capacity up to 1675 mA h g-1,are attracting great attention as the secondary batteries.However,the sulfur cathode of lithium sulfur batteries still sustains many serious obstacles,such as poor electrical conductivities,severe volume variations and dissolution of the polysulfides in electrolyte.Thus,to solve these above problems,it is a key strategy to develop an advanced sulfur-host material,which owns high conductivity,excellent sulfur sealing,volume-variation accommodation and preferable inhibition for polysulfides.In this thesis,two novel graphene-based nanomaterials are fabricated by a one-step catalytic thermolysis with transition metals,using borane-tert-butylamine complex and ion-exchange resins as the precursors.All these make it of effectivity to overcome these existing problems for the anode of lithium ion batteries and the cathode of lithium sulfur batteries.The major research contents are as follows:1.Novel three-dimensional,crumpled nitrogen-and boron-dual-self-doped graphene sheets(NBGs)have been synthesized through a facile one-step catalytic thermolysis by metal cobalt,which using the borane-tert-butylamine complex containing nitrogen and boron atoms as a precursor.Three-dimensional crumpled structures can reduce the restacks of graphene,and atomic introduction greatly increases Li+ adsorption and diffusion through the abundant active defects,which preferably improve the capacity and cyclic stability of LIBs anode.As an anode material,NBGs-1000 reveals a high reversible capacity up to 909 mA h g-1 at a current rate of 50 mA g-1.The capacity decay is only within 0.064%per cycle after 500 cycles at a large current density of 500 mA g-1.It also exhibits remarkable rate performance,including large capacities of 429 mA h g-1 and 318 mA h g-1 at 1 A g-1 and 2 A g-1,respectively.2.Three-dimensional porous graphene networks containing in situ grown carbon nanotube clusters composite(CNTs@3DG)have been fabricated via one-step pyrolysis of exchanged cation resins,using exchanged nickel and cobalt as dual catalysts.Three-dimensional porous graphene networks can provide a unique,multi-dimensionally supported structure for CNTs.Clusters of CNTs are in situ grown at the inner walls of porous graphene networks,and a anchored interaction between graphene layers and CNTs forms a stable 3D architecture of interconnected graphene and CNTs,which offering convenient channels for lithium ion and electron transports.In addition,after the KOH activation,abundant micro-,meso-and macroporous structures are gained,which the specific surface area and electronic conductivity are up to 1673 m2 g-1 and 1055 S m-1,respectively.This promising CNTs@3DG anode material reveals an ultrahigh reversible capacity of 1132 mA h g-1 and an advantageous capacity retention of 93%after 200 cycles at 100 mA g-1.More significantly,capacity decays of 0.017 and 0.025%per cycle after 1000 cycles are obtained at large current densities of 1 and 2 A g-1,respectively.3.3DG-CNTs composed of capillary-like carbon nanotube clusters in situ grown in three-dimensional graphene networks,is a high-efficiency sulfur host material for lithium-sulfur batteries.Clusters of carbon nanotubes anchoring in inner walls of 3D graphene networks act as capillary action,which is beneficial to restrict the agglomeration of large immersed sulfur content.Moreover,abundant pore structures,and the confined space formed by CNT clusters and three dimensional graphene networks can inhibit the dissolved polysulfides,which effectively reduces the shuttling effect and promotes the sulfur utilization during the whole charge/discharge process.With an areal sulfur mass loading of 81.6 wt%,this promising 3DG-CNTs/S cathode exhibits initial specific capacities up to 1229 mA h g-1 and 1190 mA h g-1,with capacity decays of 0.044%and 0.059%per cycle at 0.5 and 1 C during 500 cycles,respectively.