Theoretical Design And Performance Study Of Anode Materials For Metal-Ion Batteries

Developing metal-ion batteries is an important method to alleviate future energy shortages,and the performance of metal-ion batteries is closely related to anode materials.Since the successful preparation of graphene,two-dimensional（2D）materials have become the preferred anode material for new types of batteries due to their unique structural configuration and excellent properties,replacing traditional bulk materials.2D materials have a large specific surface area,which not only provides abundant ion adsorption sites,but also significantly promotes the rapid diffusion of ions on the surface.In this paper,several widely studied metal-ion batteries and the research progress of their anode materials are introduced in detail.Based on the current research status and the problems encountered in the development of metal-ion batteries,we comprehensively evaluated the performance of Silicether,BC₃N₂and BC₃N₂/Graphene heterostructures as anode materials of metal ion batteries using the first-principles calculations based on density functional theory.The specific research contents are as follows:（1）The performance of the monolayer of Silicether as the electrode material for sodium ion and magnesium ion batteries was studied.The original Silicether monolayer has semiconductor characteristics,but the Silicether system after adsorption by a single sodium ion or magnesium ion presents metal characteristics,which means that Silicether has excellent electronic conductivity.The diffusion potential barrier of Na⁺and Mg²⁺on Silicether monolayer is as low as 0.40 e V and 0.21e V,respectively,indicating an excellent charge-discharge rate.The theoretical storage capacity of Na⁺and Mg²⁺on the Silicether monolayer is 418 m A h g^-1and 744 m A h g^-1,which is higher than that of many previously reported anode materials.Silicether monolayer just shows a small volume expansion from the pristine Silicether to full-load Silicether,indicating that it can effectively reduce the structural changes during the charging and discharging process.Silicether monolayer meets most important characteristics of high-performance battery anode.Then the sodium ion battery performance of the Silicether bilayer is calculated.The Silicether bilayer can increase Na adsorption energy,which means that the adsorption structure is more stable,and can also maintain the fast ion diffusion rate as Silicether monolayer,and can also absorb more sodium ions.However,due to the increase of the weight of the substrate,its Na storage capacity decreases to 244m A h g^-1.（2）The properties of BC₃N₂/Graphene heterostructure and BC₃N₂monolayer as anode materials of sodium ion batteries were studied.The performance of BC₃N₂monolayer as SIBs anode has been excellent.It exhibits single Na adsorption energy of 0.21 e V,Na diffusion barrier of0.15 e V,Na theoretical capacity of 777 m A h g^-1,an open circuit voltage of 0.72 V,and a volume change of 0.36%.Then we construct the BC₃N₂/graphene heterostructure and study its electrochemical properties.The research results indicate that the heterostructure has metal properties,which can ensure high conductivity,and the heterostructure structure has excellent thermodynamic stability at 300 K.The large adsorption energy（0.67 e V）indicates that there is a strong interaction between the Na⁺and the substrate,which can ensure the strong stability of the adsorption system.The diffusion barrier of Na on BC₃N₂/Graphene is lower（0.026 e V）,and Na⁺has a faster diffusion rate and charge-discharge rate on the heterostructure.BC₃N₂/Graphene has higher theoretical capacity(689 m A h g^-1)as anode material of sodium ion battery,and BC₃N₂/Graphene heterostructure has appropriate average open circuit voltage of battery anode.Obviously,the rapid diffusion potential barrier and the ultra-high theoretical storage capacity make the BC₃N₂/Graphene heterostructure a high-performance electrode material for sodium ion batteries.（3）The performance of two-dimensional BC₃N₂monolayer as anode material for LIBs and KIBs was studied.Both Li⁺and K⁺show large adsorption energy on BC₃N₂,indicating that the adsorption of Li and K on BC₃N₂is exothermic and spontaneous.There is a significant charge transfer between Li⁺/K⁺and the substrate,which is essential to enhance the conductivity of the material.Li⁺and K⁺show extremely low diffusion barriers（0.055 e V and 0.093 e V）on the BC₃N₂monolayer,which indicates that Li⁺/K⁺has an excellent diffusion rates on the BC₃N₂monolayer and can improve the charging and discharging speed of the battery.BC₃N₂monolayer also shows high theoretical capacity(both 776m A h g^-1)for Li/K,which is far higher than the capacity of many commercial metal-ion battery anodes.The average electrode potential of Li⁺and K⁺on BC₃N₂monolayer is 1.16 V and 1.53 V,which indicates that BC₃N₂monolayer can be used as high-performance anode material for LIBs and KIBs,and the maximum lattice expansion rate of BC₃N₂monolayer after lithium and sodium are fully adsorbed is less than 1%,which means excellent cycle stability.BC₃N₂monolayer exhibits excellent application potential as an anode material for metal-ion batteries.