Research On The Construction And Performance Of Electrode Materials Based On Graphether Heterostructure

Lithium-ion batteries have been commercialized because of their low self-discharge,high recyclability,and high capacity.Energy storage systems in various fields such as portable electronic devices,renewable resources,and new energy vehicles require lithium-ion batteries.However,the content of lithium minerals in the earth's crust(0.0065%)is very low,and the problem of lithium dendrite growth affects the safety and stability of lithium-ion batteries.Sodium-ion batteries have received widespread attention due to their rich sodium reserves(2.83%),high charge and discharge rates,and no safety hazards.However,electrode materials for sodium-ion batteries are very scarce.Two-dimensional materials have a special structure and excellent physical properties,and are widely used in the field of energy storage.In addition,different two-dimensional materials can construct two-dimensional heterostructures through weak van der Waals forces and two-dimensional heterostructures can exert the synergistic effect of two-dimensional materials.Based on firstprinciples density functional theory,this thesis designs three two-dimensional heterostructures as electrode materials for sodium-ion batteries,analyzes the geometric structure,electronic properties,sodium ion adsorption,diffusion properties,theoretical specific capacity and other aspects of these three heterostructures.The three tasks are as follows:(1)Based on the graphether/graphene heterostructure,we explored its possibility as an electrode material for sodium-ion batteries.The heterostructure has inherent metallic properties which facilitate the transport of electrons.The average adsorption energy of sodium ions between the layers of the heterostructure is-0.95 e V,which is lower than the average adsorption energy of graphether and graphene,indicating that sodium ions tend to be embedded in the interlayer.The diffusion barriers of sodium ions on the surface of graphether,between the heterostructure layers and the surface of graphene are 0.21 e V,0.32 e V and 0.10 e V,respectively,indicating that sodium ions have ultra-high diffusion mobility in the graphether/graphene heterostructure.In addition,the theoretical specific capacity of the heterostructure can reach 493 m Ah/g,which is higher than graphene/black phosphorus(431 m Ah/g),graphene/phosphorus(485 m Ah/g)and phosphorus/boron nitride(445 m Ah/g).These conclusions indicate that the graphether/graphene heterostructure can be used as a new and highperformance electrode material for sodium-ion batteries.(2)Based on the graphether/boron nitride heterostructure,through our calculations,the graphether/boron nitride heterostructure is a narrow band gap semiconductor with 0.59 e V,but it exhibits metallic characteristics after adsorbing a single sodium atom,which guarantees the necessary electrical conductivity during charge and discharge.The lattice matching degrees of the armchair and zigzag directions are 3.8% and 2.6%,respectively,indicating that the heterostructure has a certain degree of structural stability.Molecular dynamics simulations at room temperature(300 K)show that the heterostructure has good reversibility.The diffusion barrier of sodium ions on the surface of graphether is the lowest(0.17 e V),and the barrier of diffusion on the surface of boron nitride is the highest(0.41 e V),indicating that the heterostructure has a higher charge-discharge rate and sodium ion diffusion rate.The maximum theoretical capacity of graphether/boron nitride heterostructure is460 m Ah/g.The heterostructure can meet the needs of sodium-ion battery electrode materials for low diffusion barrier and high charge and discharge rate.(3)Graphether and silicene are stacked vertically to build a graphether/silicene heterostructure.The small interlayer spacing(2.82 ?)during the cycle of charging and discharging can reduce the dramatic expansion of the graphether/silicene heterostructure volume.Molecular dynamics simulations were carried out at 300 K and 500 K,respectively,to prove that the system structure has good thermodynamic stability,which is beneficial to increase the cycle times of sodium-ion batteries.In addition,the graphether/silicene heterostructure has metal conductive properties.The average adsorption energy of sodium ions in the heterostructure is-3.38 e V,which is lower than the smallest adsorption energy(-2.81 e V)in the boron nitride/black phosphorus heterostructure,which can effectively avoid the clustering of sodium ions during the sodiumization process.In addition,the minimum diffusion barrier of sodium ions on the heterostructure is 0.25 e V,indicating that sodium ions can diffuse and move freely on the heterostructure.The heterostructure can stably hold 38 sodium atoms,and the theoretical specific capacity can reach 324 m Ah/g.These properties indicate that the graphether/silicene heterostructure can be used as an ideal high-performance anode material for future sodium-ion batteries.