Design And Construction Of Graphene Regulated High Performance Anode Materials For Sodium/potassium Batteries

At present,lithium-ion batteries have been widely used in many aspects of people’s lives because of their high energy density.However,the high price and uneven distribution of lithium resources limit its application in large-scale energy storage.Compared with lithium-ion batteries,sodium/potassium batteries have attracted much attention because of their low cost.However,the larger ion radius of Na/K(Na:1.02 (?),K:1.38 (?))leads to the delayed reaction kinetics,resulting in lower energy density.In this context,the development of high-performance electrode materials is the key to improve the performance of sodium/potassium batteries.It should be pointed out that the current research has reported the development of high-performance cathode materials,but there is no consensus on the optimization and regulation of anode materials.In order to meet the above challenges,the introduction of graphene to composite materials is an effective strategy,which can improve the conductivity of materials and reduce the volume effect.However,there are still many bottlenecks in graphene based composite anode materials.Firstly,the mass of graphene prepared by conventional methods is uncontrollable,especially for the fast charging negative electrode system,the improvement of conductivity is not obvious.Secondly,the binding force between graphene and anode material is weak,and the electrode is easy to be powdered or peeled off with the cycling of sodium/potassium ions.Thirdly,the proportion of carbon in the composites is usually high,which affects the energy density of the battery.Therefore,it is imperative to develop the controllable preparation of graphene based composite anode materials and explore the effective combination of graphene and anode materials,so as to obtain a new type of sodium/potassium battery anode materials with high stability and high performance.Accordingly,this paper includes the following research contents(1)Developing heteroatom doping strategy to improve the conductivity and structural stability of materials.The stable combination of rGO and materials was achieved by heteroatom doping.One dimensional bismuth sulfide nanorods were anchored in the three-dimensional conductive N-doped graphene framework to be used as anode materials for high performance sodium ion batteries.Nitrogen doping can not only improve the overall conductivity of the material and ensure the rate performance,but also enhance the structural stability of the composite anode material and improve the cycle performance of the battery.(2)Improving the introduction mode of graphene to further enhance the structure stability of graphene composites.N-doped graphene was directly coated on the surface of two-dimensional SnSe/C by plasma enhanced chemical vapor deposition(PECVD).In addition,the quality of carbon introduced by CVD is lower than that of the traditional rGO method,which has less influence on the energy density of the electrode.In the composite,"inner" and "outer" carbon work together to achieve excellent electrochemical sodium storage performance.(3)Exploring the influence of metal composite on graphene based anode materials.Metal particles were introduced into the vertical graphene grown by PECVD to enhance its adsorption on the anode materials,and the dendrite free and long-life three-dimensional sodium metal anode materials were prepared.The compounding metal can improve the overall conductivity and realize the rapid melting load of sodium.The vertical structure of graphene can alleviate the volume effect of sodium,and the uniform growth of cobalt particles/nitrogen can induce the uniform deposition of sodium and inhibit dendrite growth.Finally,long life sodium metal battery is realized.(4)Developing the heteroatom dual-doping technology to promote the electrochemical performance of materials.Nitrogen and sulfur double doped graphene hollow spheres were prepared by CVD method,and the conductivity and structural stability were improved by doping.Nitrogen and sulfur dual-doping can expand the interlayer spacing and reduce the volume change during the process of potassium ion insertion and removal.In addition,doping can also improve the conductivity,enhance the adsorption of potassium and promote the diffusion of potassium ions.Meanwhile,the three-dimensional hollow structure can further alleviate the volume effect and enhance the potassium storage capacity of materials.