Theoretical Design And Performance Study Of Two-Dimensional Carbon-Based Anode Materials

The development and optimization of high-performance metal ion battery anode materials is crucial for the green energy evolution.However,the development of commercial anode materials is limited by their low storage capacity and poor cycle stability.The atomically-thin two-dimensional materials may offer large surface areas for ion transport and storage.Two-dimensional materials are suitable anode materials with high capacity and long lifespan.By density functional theory simulations,we explore the electrochemical properties of several carbon-based materials as metal ion battery anode.The main contents are as follows:Graphene is inert toward Na-ion storage,we introduce kagome topology into the honeycomb lattice,changing the charge distribution of graphene for improving the Na storage performance.Herein,a form of two-dimensional carbon allotrope is designed,namely,fish-scale-like graphene（FSL-graphene）,consisting of a kagome and a honeycomb sublattice.It has excellent stability,which is confirmed by the cohesive energy,phonon modes,thermal stability,and mechanical stability.FSL-graphene has an indirect band gap（0.33 e V）and high carrier mobility(～7×10³ cm²V^-1s^-1).As a sodium-ion battery anode,FSL-graphene exhibits an ultra-high theoretical Na storage capacity of 3347.1m A h g^-1,superior to most previously reported two-dimensional anode materials.Meanwhile,it possesses low diffusion energy barriers（0.19-0.23 e V）,low open-circuit voltages（0.59-0.61 V）,and small changes in lattice constants（1.3%）.Furthermore,the electrolytes with high dielectric constants（e.g.,ethylene carbonate）could improve the adsorption and migration of Na on FSL-graphene.This study provides an insight for designing high-performance carbon anode materials for sodium-ion batteries by focusing on the topological lattices.A new two-dimensional MoPC monolayer with the Janus structure has been designed.This novel two-dimensional monolayer has superior stability and metallic conductivity.This section investigates the application of two-dimensional MoPC as anode for lithium and sodium ion batteries.The obtained adsorption energy values suggest that the Li/Na atom adsorption over MoPC is a favorable process.According to the Hirshfeld charge and partial density of states analysis,charge transfer takes place from Li/Na atom to MoPC monolayers,implying high electronic conductivity of MoPC during the adsorption process.The calculated theoretical storage capacities of the MoPC for Li and Na are 771.1 and 385.8 m A h g^-1,respectively.Furthermore,the diffusion barriers of single Li/Na ions on MoPC are as low as 0.02/0.06 e V,indicating that MoPC has an ultrahigh diffusion capacity.The open-circuit voltages all fall in the range of 0.1-1 V for Li/Na ion on the MoPC monolayers,which may effectively suppress the formation of Li/Na dendrite on anodes during the charge/discharge process.During the Li/Na ions intercalation process,the structural integrity of MoPC is well preserved,which gives rise to good cycling stability.These results indicate that MoPC can be served as an appealing anode for rechargeable both Li/Na-ion batteries.A new stable two-dimensional Dirac material has been successfully predicted,namely Be₃C₂monolayer.It owns a similar hexagonal honeycomb lattice to graphene and outstanding dynamical and thermal stabilities.In this section,the performance of Be₃C₂ monolayer as potassium ion battery anode material is studied.The metallic character of Be₃C₂ monolayer remains unchanged at different adatom concentrations,which is a good characteristic for anode material.The theoretical K storage capacity of Be₃C₂ monolayer is up to 1049.9 m A h g^-1,which is rather high on the two-dimensional potassium-ions batteries anode materials.A reliable diffusion barrier of 0.59 e V for K-ion on the Be₃C₂ monolayer suggests good diffusivity.The value of open-circuit voltage is lower than conventional anode materials such as Li₄Ti₅O₁₂.Ab initio molecular dynamics simulations confirm the room-temperature stability of the Be₃C₂ monolayers at the maximum concentration of K ions.Our results indicate that Be₃C₂ monolayer can be a good anode material for potassium-ions batteries application.