Design,preparation,structural Regulation And Application Of New Graphene Materials

Lithium secondary battery energy storage devices have a good application prospect in portable electronic equipment and electric vehicles because of the high energy density,high power density and long cycle life.However,the excessive consumption of lithium resources promotes the development and exploration of new energy storage systems.Hence,new generation of energy storage devices such as potassium ion battery,aluminum battery and double ion battery are emerging gradually.The electrode material is the key factor to determine the performance of the device.Owing to the abundant resources,low cost and environmentally friendly,various carbonaceous materials have been followed with interest and studied earnestly.Graphite,one of the most commonly used electrode materials,exhibits excellent electrochemical performances for potassium ion battery,aluminum battery and dual ion battery.However,the insufficient specific capacity,serious volume expansion and poor cyclic stability significantly hinder its practical application.Graphene has shown superhigh capacity for new battery systems in terms of the unique flexible structure and physical and chemical properties.However,the synthesis and application of graphene still face the following difficulties:Large scale production of high-quality graphene can not be realized.Volume expansion of graphene electrode during cycle is serious.The research about ion storage mechanism of graphene electrode has not been completed.The initial coulombic efficiency of graphene electrode is low and it is easy to fall off.The cost and the synthesis pathways of graphene need to be improved.Therefore,exploring a new synthesis scheme,optimizing the preparation process,designing new-style graphene materials and constructing stable structure are the key points during the research of graphene electrode.In view of this,this topic starts with the perspective of design,preparation,structural regulation and application of new-type graphene materials.Combining with the methods of catalytic graphitization and high temperature graphitization to design a simple,high-efficiency and environmentally friendly synthesis route,prepare a series of new graphene materials with special structure,investigate the energy storage applications,so that to providing the reference for the research of graphene electrode material.In view of the complex synthesis process and difficulty in large-scale production of high-quality graphene,two novel materials,helical graphene and carbon nanoscroll,were prepared by a simple one-step low temperature catalytic graphitization using carboxymethyl chitosan and ferric chloride hexahydrate as carbon source and catalyst for the first time.By properly controlling the mass ratio of carbon source and catalyst,the structural adjustment and controllable synthesis of helical graphene and carbon nanoscroll can be realized.The structure,morphology and formation mechanism of the new materials have been fully investigated.Helical graphene and carbon nanoscroll own fast electronic and ionic transport channels,superior structural stability and admirable volumetric expansion adaptability,which provides high possibility as cathode materials for aluminum battery and dual ion batteries with superior anion storage property.As results,carbon nanoscroll as cathode for Al Bs displays a superior reversible specific capacity of 101.24 m Ah g^-1 at an ultrafast rate of 50 A g^-1,around 100%of the initial capacity.Assembled with helical graphene cathode and soft carbon anode,the sodium dual ion full battery cycle at 2 A g^-1 current density after 2000 times with few capacity fading,demonstrating a superior electrochemical performance.In order to solve the serious volume expansion of graphene electrode during the cycle process,a nevol material of multilayer and multi-walled graphene tube has been designed and synthesized for the first time.The mixture of molten urea and ferric chloride hexahydrate is used as precursor,the controllable synthesis of multilayer and multiwalled graphene tube was achieved by one-step low temperature catalytic pyrolysis of carbon.Each layer of multilayer multi-walled graphene tube can be used as an independent unit to store ions,thus achieving ultra-high specific capacity.The special multi-layer multi-wall structure provides more active sites at the interface between electrode and electrolyte,which is conducive for the rapid migration of electrons and ions.The in-situ doping of N element can also greatly improve the ion storage ability.The special nanoscale multilayer graphene tube structure can effectively inhibit the severe volume expansion caused by K⁺ions embedded into the graphene lattice.As anode for potassium ion batteries,multilayer and multi-walled graphene tube show a superior the capacity retention rate about 95.9%after 300 cycles at a current density of100 m A g^-1.In addition,the high charge specific capacity of 62.83 m Ah g^-1 is achieved at 500 m A g^-1 ultra-high current density,and it still retains 86.8%of the initial capacity after 4800 cycles.In order to investigate the ion storage mechanism of graphene electrode material,two materials,graphene quantum dots and it derived dendritic graphene,were designed and synthesized with anhydrous citric acid as raw material for the first time.Ultrathin carbon film@graphene quantum dots composites were synthesized by a simple one-step low temperature catalytic graphitization.Dendritic graphene was prepared by high temperature catalytic graphitization with the ultrathin carbon film@graphene quantum dots as precursors.The structure,morphology and formation mechanism of two novel materials are fully explored.A new-type potassium dual ion hybrid capacitor,assembled with ultrathin carbon film@graphene quantum dots as cathode and dendritic graphene as anode,shows excellent electrochemical performances,including high specific capacity,excellent rate performance and stable cycling performance.With the support of XPS and TEM,the anion mixing storage mechanism and structural stability of electrodes are discussed in detail.In the full cell,a reversible specific capacity of 97.46m Ah g^-1 at 200 m A g^-1 was achieved,and it still retains 90.2%of the initial capacity after 30000 cycles at 5000 m A g^-1.In order to solve the low initial coulombic efficiency and active material shedding behaviors of graphene electrode,a special protection architecture should be designed.We put forward wearing a stable armor on the surface of the interconnected and jumbled graphene sheets.Sucrose was treated under the condition of low temperature catalytic graphitization to in situ produce crystal carbon shell armoring the internal interleaved accumulation few-layer graphene sheets.The structure,morphology and physical and chemical properties were fully investigated.The crystal carbon shell that acts as the armor not only maintains the structure stability of the composite but also limits the side reaction between the electrolyte and the graphene sheets.The stable electronic and ionic transport channels is constructed to promote the rapid exchange of ions and electrons.The extremely high specific capacity is achieved by the ions embedded behavior of the crystal carbon shell and the ion adsorption/deembedd behaviors of the internal graphene sheets.As anode for potassium ion battery,it achieves specific charge capacity of 297.89m Ah g^-1 at 100 m A g^-1 with high initial coulombic efficiency,and maintains good cyclic stability at 1000 m A g^-1 for 3200 cycles.As cathode for aluminum battery,it retains the initinal capacity with no fading after 10000 cycles at 4 A g^-1.In order to reduce the cost and improve the synthesis pathways of graphene material,the elastic graphene sphere was successfully synthesized with biomass wastes such as overnight rice,moldy corn and potato as raw material for the first time.Preparation process includes the simple acid leaching,hydrothermal reaction and high temperature graphitization.The designed synthetic scheme utilizes waste resources while without any chemical additives,which is an efficient,environmentally friendly and safe route for preparing graphene.The whole EGS particle is made up of nanoscale few-layer(3-8layers)graphene sheets,which are stacked like curving bricks together with gaps existing between different sheets.This elastic graphene sphere structure can provide the rapid ion migration paths,superior structural stability and excellent volume expansion adaptation ability,which are conducive to the enhancement of charge capacity,rate property and cycling stability compared to commercial graphite and graphene.It delivers a reversible specific capacity of 352.43 m Ah g^-1at 50 m A g^-1 over 290 cycles with the initial Coulombic efficiency of about 61.0%and maintains a high capacity retention of about 90.9%at 200 m A g^-1 after cycling 2100 times.In addition,ultralong cycle-life at 1000 m A g^-1is excavated,which possesses a high charge capacity of 175.34m Ah g^-1 with?82.8%retained capacity after 11000 cycles.