Graphene Based Composites As High Performance Lithium&Sodium Ion Battery Anode

Facing the increasing energy crisis and environmental pollution,find new clean energy sources to replace traditional fossil fuels becomes more and more important.The distribution of this new energy(such as solar energy,wind energy,tidal energy,etc.)is always uneven,the use of this new energy is always difficult.Converted this new energy into electrical energy is an effective way.Thus,the requirements of energy storage batteries are getting higher and higher.The development of electrochemical energy storage batteries has been through several stages,such as Lead-Acid batteries,Nickel-Cadmium batteries(Ni-Cd),Lithium batteries,Nickel-MH batteries(Ni-MH),Sodium-Sulfur batteries(Na-S)and Lithium ion batteries(Li-ion batteries).Among these energy storage batteries,Lithium-ion batteries shows amazing future for its excellent electrochemical performance,including high operating voltage,high mass energy density and volumetric energy density,long cycle life,fast charge and discharge performance,no memory effect,low pollution,low self-discharge rate and so on.Now,lithium-ion batteries have been widely used in mobile phones,laptops and other portable consumer electronics.However,with the gradually used in energy storage power station?smart grid and electric vehicles,the traditional lithium-ion battery can not properly meet the market demand for its relatively low energy density and power density,so looking for new electrode mateirlas with higher energy density and power density is imminent.In addition,the high cost of lithium-ion battery caused by the lack of lithium resources and exploitation difficulties also limited the wide applications of lithium-ion battery.Thus,exploring new electrochemical energy storage system has become imminent.Sodium ion batteries have similar advantages to lithium-ion batteries,such as high voltage,high energy density and no memory effect.More importantly,the sodium resources are rich in reserves,easy mining,low prices,making the sodium ion battery has a wide potential application.As for the above two aspects,this paper mainly investgated the application of graphene and its composite materials in lithium ion battery and sodium ion battery,and prepared a variety of electrode materials with excellent lithium(sodium)storage capacity.In the first chapter,we briefly introduced the working principle,structure and current research progress of lithium-ion battery.We summarized the current research hotspots,we put forward our research ideas and research contents of this paper.In the second chapter,we introduced the reagents and related instruments?the battery preparation procedure?the commonly used material characterization method and the electrochemical characterization method of the electrode materials used in the paper.In the third chapter,we first introduced the research progress of graphene.Currently,graphene materials used in lithium ion battery anode material always shows lower specific capacity and poor rate performance due to agglomeration.We farbricated the nitrogen doped three-dimensional porous graphene by combine nitrogen atom doping and three-dimensional porous structure design.When used as anode materials for lithium ion batteries,it delivers a high specific capacity and good cycle performance(it delivers a high specific capacity of 1094 mAh/g after 100 cycles at a current density of 100 mA/g)and excellent rate performance(it still provides a charge specific capacity of 480 mAh/g,even at a high current density of 2000 mA/g).In the fourth chapter,we have successfully prepared nitrogen-doped titania nanoparticles anchored on nitrogen-doped three-dimensional porous graphene composites by combining facile template process and electrostatic assembling method,followed by high temperature heat treatment in NH3 atomsphere.The three-dimensional graphene framework allows the electrolyte penetrate into the inverse opal structure and possess high electronic conductivity.The intimate contact between the TiO2 and the graphene suppresses the growth and aggregation of TiO2 nanoparticles during heating process,leading to decreased Li+ diffusion length.The nitrogen-doping in both TiO2 and graphene matrix could improve the electronic conductivity on the TiO2 particle surface and between adjacent particles.As expected,when used as anode for Li-ion batteries,the composite delivers an excellent reversible capacity of 165mAhg-1 after 200 cycles at 100mAg-1 and outstanding rate capability of 114mAhg-1 after 1000 cycles at lAg-1.With rational design,this strategy could be extended to other electrode materials that may hold great promise for the development of high energy storage systems.In the fifth chapter,a three-dimensional porous graphene/tin dioxide composite is successfully prepared through electrostatic assembly method using polystyrene nanospheres as template.Through the three-dimensional porous structure design,it can not only fully alleviate the volume expansion of tin dioxide in the lithiation process,but also improve the electrical conductivity of the whole electrode,so the composite shows excellent cycle performance and rate capability.Besides,the lithium storage mechanism of this composite has been investgated.In the sixth chapter,we first modified the surface potential of graphene oxide,and then the stannic chloride was in situ reduction on the surface of graphene oxide.Due to the Kirkendall Effect,the metal tin nanoparticles slowly converted into SnO2 nanoparticles,thus the graphene/SnO2 composite with sandwich-like structure was prepared.Besides,we measured the electrochemical performance of this graphene/SnO2 composite.When used as anode materials for lithium ion batteries,it delivers a high specific capacity and good cycle performance.At a current density of 100mA/g,the composite provides a charge capacity of about 1384 mAh/g after 50 cycles,and it still provides a specific capacity of 665mAh/g even at a high current density of 2000mA/g.Besides,the lithium storage mechanism of this composite has been investgated.In the seventh chapter,we studied the antimony-based anode materials used in sodium ion battery.Graphene/antimony composite was prepared by in situ reduction of antimony trichloride on charge-modified graphene oxide surface,followed by heat treatment.The electrochemical performance of this sandwich-like composite was studied.When used as anode materials for sodium ion batteries,it delivers a high mass specific capacity of about 430mAh/g even after 200 cycles at 100mA/g and excellent rate performance of 330mAh/g at 5000mA/g.In the eighth chapter,we summarized the research work during doctoral period,showing the perspective and outlook of our studies.