Research On The Performance Of Advanced Two-Dimensional Materials In High Energy Density Secondary Batteries

With the rapid growth of the global economy,the energy system with high energy density,environmental friendliness,high safety and long life has attracted wide attention.The rapid development of electronic devices,energy vehicles and other industries has put forward higher requirements for the energy density of secondary batteries.As an important part of the battery,electrode materials play a key role in the performance of the battery,so the preparation of electrode materials with high energy density and high safety will become one of the important directions of developing the battery.However,there are still some problems that hinder the commercialization of high energy density electrode materials:(1)High energy density electrode materials have poor cycling performance and rate capability due to their large volume and low internal ionic and electronic conductivity;(2)In the process of cycling,it is easy to generate larger volume change,which will cause the active material is broken even fall off from the current collector,resulting in the failure of electrochemical performance;(3)High energy density electrode materials with a large volume changes and uneven ion transport in the process of cycling lead to unstable interface problems and uncontrollable dendrite growth bringing security risks.In order to solve the above problems of high energy density electrode materials,two-dimensional(2D)materials were used to modify electrode materials.The unique layered structure and large specific surface area of 2D materials can effectively alleviate volume expansion,reduce the actual current density,provide more deposition sites,improve interface problems,and reduce the dissolution of lithium polysulfide(LiPS).Combined with the above advantages,the 2D material realizes a high energy density and high performance battery system by vacuum filtration,surface coating and in-situ electrodeposition modified electrode materials.The main research content of this paper is as follows:(1)Lithium-sulfur(Li-S)batteries are considered to be one of the most promising energy systems due to their high energy density.However,the shuttle effect and low conductivity seriously hinder the development of commercial Li-S batteries.The flexible and freestanding MXene as current collector composite covalent organic frameworks(COF)derived nitrogendoped carbon is used as the sulfur host material to limit the shuttle of LiPS,improve the electrical conductivity and energy density of the cathode.Meanwhile,PEO solid electrolyte with low solubility of LiPS and high safety was used to replace the traditional flammable electrolyte to construct all-solid Li-S battery.Through the synergistic effect of COF derived carbon,MXene and solid electrolyte,the LiPS dissolution,volume destruction and conductivity problems are improved,providing an all-solid Li-S battery scheme with high safety and high stability.(2)As one of silicon-based materials,two-dimensional siloxene has been widely studied due to its advantages of small volume expansion,high energy density,simple synthesis and low price.However,the low electronic conductivity and interface problems of siloxene have hindered its commercial application.A convenient and easy to scale coating method is used to improve siloxene anode.Ga-based liquid metal with low melting point,high conductivity,environmental protection and self-healing is coated on the surface of the electrode,meanwhile it is penetrated into the inside by heating to form a three-dimensional(3D)conductive network.At the same time,it reacts with current collector to form metal bonds,avoiding the shedding of active substances.The siloxene anode modified by liquid metal coating has high specific capacity,stable cycle performance and excellent rate capability.Thus,a new method of selfhealing liquid metal reinforced electrode material system is provided to achieve high energy density lithium-ion batteries with excellent cycling stability.(3)The development of siloxene material as anode is seriously affected due to the unstable interface which will cause the unstable cycle performance and rate capability.The interface between anode and electrolyte was modified by using a thin COF layer grown in-situ on the siloxene surface.Meanwhile,porous COF layers as bulk buffer layer improve the stability of siloxene anode,resulting in superior electrochemical performance.The modified battery was circulated for 1500 cycles at 8 A g-1 with an excellent capacity retention rate about 96%.(4)Fe metal battery is considered as one of the most promising battery systems because of its low cost,high energy density,abundant resources and environmentally friendly.However,the uncontrolled dendrite growth of Fe anode during the cycling leads to short circuit and many side reactions in the battery.Flexible and free-standing MXene/Fe composite electrodes were prepared by in-situ electrodeposition,and the growth behavior of metal iron on MXene was investigated.The unique structure of MXene reduces the actual current density and provides more Fe deposition sites,inhibiting the growth of Fe dendrites.Polyaniline(PNAI)organic dual ion full battery based on the composite anode showed excellent electrochemical performance.