Alkali Metal Ion Energy Storage Properties Of Carbon Materials With Different Pore Structures And Hierarchical Dimension

With the rapid development of new energy technology,rechargeable batteries occupy a large share of power storage markets.Among various types of rechargeable batteries,alkali metal ion batteries have outstanding advantages in energy,power,safety,lifespan and cost,and become one of the most promising rechargeable energy storage devices.The choice of anode materials is considered as an importance investigation aspect for improved performance of since the emergence of alkali metal-ion batteries.However,due to the limited theoretical capacity and low reaction kinetics of anode materials currently studied,the energy and power densities of batteries are still limited.Therefore,advanced anode materials with high capability and high stability are still urgently needed.Among the different anode materials,carbon materials have been used as electrode materials for various batteries because of their abundant resources,low cost,environmental friendliness and stable electrochemical properties.Here,carbon-based materials with different porous structure and morphologies are developed for good performance as anode materials for alkali ion batteries,and high performane can be achieved in both lithium ion and sodium ion batteries.The main content can be divided into the following parts:Firstly,two-dimensional（2D）carbon nanosheets（CNSs）with hierarchical porous structure were successfully prepared by high-resolution pyrolysis of potassium citrate.The templating effect of potassium salts during high temperature annealing enables the product to assemble into two-dimensional nanosheet structures,while the activation effect of potassium salts make the product produce hierarchical porous structure.The unique 2D nanosheet structure of CNSs helps to increase the surface active sites and shorten the diffusion distance of lithium ions,while the hierarchical porous structure further improves the reactivity and reaction kinetics of lithium ions storage.In addition,CNS-950 has a higher reversible capacity than commercial activated carbon.CNS-950 is further applied to a full battery with transition metal oxides as a cross electrode,showing outstanding performance in specific energy and specific power performance.Secondly,CNSs derived from potassium citrate was further used as anode material to study the performance of carbon nanosheets for sodium ion batteries.By using the rich micropores of CNSs and the special nanosheet structure,The obtained carbon nanosheet has a high specific surface area of 2062.7 m² g^-1 and a total pore volume of 1.0 cm³ g^-1.The high specific surface area,nanosheet morphology and porous structure not only provide abundant defects and active sites,but also shorten the diffusion distance of sodium ions.These characteristics enable CNSs to show excellent energy storage performance as electrode material of sodium ion batteries.Lastly,The nitrogen and fluorine co-doped carbon nanosheets/hollow microspheres composites（N,F@NSs）were obtained by using ferric nitrate,polytetrafluoroethylene and melamine as raw materials in a phased pyrolysis reaction,and the excess Fe was removed by pickling.The obtained N,F@NSs not only have abundant porous structures,but also nitrogen and fluorine co-doping makes the surface more defects formed,and the catalytic effect of Fe enables the composite carbon materials to achieve different degrees of graphitization.Due to these characteristics,the sodium ion batteries based on N,F@NSs shows excellent energy storage performance.It is found that the porous structure and special morphology can improve the alkali metal ion storage of carbon-based materials,and further affect the electrochemical performance of electrode materials.The heteroatom doping in carbon material also has a profound influence on the electrochemical performance of electrode active material.