Interface Enginieering For Stable Lithium/Sodium Metal Anodes

Reducing the use of traditional fossil fuels and developing new sources of energy are effective ways to reduce environmental problems and meet the growing energy needs of human society.However,due to the limitation of material capacity,the current commercial lithium ion battery has not been able to meet the requirements for a long time.Lithium/sodium metal has the advantages of high theoretical specific capacity and low electrode potential when it is used as the anode material of the battery,which can greatly improve the energy density of the battery and the ability to work at higher voltage.However,the commercial application of lithium/sodium metal anode have been hindered by several intractable issues such as uncontrollable dendrite growth and "dead lithium/sodium" accumulation at the interface between lithium/sodium metal and electrolyte.Artificial solid electrolyte interphase(SEI)layers possess good ionic conductivity and high Young’s modulus,which can reduce the side reactions and inhibit the growth of lithium/sodium dendrites.Carbon-based porous materials can provide sufficient space for lithium/sodium metal deposition to reduce the volume expansion of electrode.In this paper,zwitterion polymer was used as the interface protection layer to modify the interface between lithium metal anode and electrolyte.The amorphous carbon material was used as a host to modify the interface between sodium metal anode and electrolyte.The specific research contents are listed as follows:(1)A uniform artificial interface layer containing polymer 3-((2-(Methacryloyloxy)ethyl)(dimethyl)ammonio)-1-propanesulfonate(PDMAPS)and polymer 2-Methacryloyloxyethyl phosphorylcholine(PMPC)was constructed on the surface of electrode by a simple and lowcost spin coating method.Due to the electrostatic adsorption of sulfonate group and phosphate group on lithium ion and the same force of cationic group on anions,the cations and anions can reach the state of uniform diffusion in the(PDMAPS+PMPC)film.Due to the unique zwitterion effect and the assistance of sulfonate and phosphate groups,favorable ionic conductivity and high lithium ion transference number could be achieved simultaneously.High lithium ion transference number will make the lithium ion flux distribution more uniform at the interface between lithium metal and electrolyte,which enables a uniform lithium metal deposition.At the same time,the introduction of phosphate group can greatly improve the stability of the interface between lithium metal and electrolyte,and show excellent cycling stability.(2)A layer of hard carbon was constructed on the electrode by coating method as the host of sodium metal.The interfacial side reaction and the growth of sodium dendrite is inhibited by the process of sodium intercalation and plating at the amorphous hard carbon anode(the process in which sodium ions are intercalation in the hard carbon until saturated and then sodium ions gain electrons on the surface of the hard carbon to generate sodium metal).And the three-dimensional macroporous substrate of hard carbon provides sufficient space for sodium metal deposition,which can reduce the influence of the interface fluctuation between sodium metal anode and electrolyte.Finally,the hybrid sodium anode with high coulombic efficiency and high stability was successfully constructed.