The Structure Design And Application Of Two-dimensional Phosphorene And Phosphorene-like Materials

Nowadays,with the aggravation of environmental pollution,economic development and the vigorous development of portable electronic equipment,electric vehicle equipment and fixed storage power grid,the demand for energy in the human world is increasing.Two-dimensional materials show a series of extraordinary electronic,optical and mechanical properties different from their bulk materials,and have broad application prospects in the fields of energy storage and conversion.Among them,black phosphorene（α-P）has high carrier mobility and high on-off ratio at the same time,which can combine the advantages of graphene and transition metal sulfide to overcome their shortcomings,and has excellent chemical,physical,optical and mechanical properties widely used in photoelectric and energy devices.Due to the extraordinary characteristics ofα-P,it has also aroused widespread concern and research upsurge for the novel allotropes of phosphorene and phosphorene-like materials.Based on the first-principles calculation,this paper has carried out research works on phosphorene in three aspects:（1）To improve the volume expansion of phosphorus-based anode of lithium/sodium-ion batteries（LIBs/SIBs）,enhance the cyclic reversibility of anode and prolong the service life of battery;（2）It is tested whether various phosphorene can be used as suitable anchoring materials,which can improve the shuttle effect caused by the dissolution of lithium sulfide and realize the long-term cycle stability and excellent performance lithium-sulfur（Li-S）batteries.（3）The structural characteristics of phosphorene and phosphene-like materials are studied in details,and successfully predicted the new phosphorene and graphane,which provides ideas and guidance for predicting new structures.In the first part,based on the analysis of adsorption energies and diffusion barrieriers,the feasibility of using two kinds of phosphorene（β-P andγ-P）with lower in-plane atomic density thanα-P as anode materials of LIBs/SIBs is studied.The results show thatγ-P exhibits the strongest adsorption for Li/Na atoms among the three phosphorene monolayers,whileα-P andβ-P show similar adsorption for Li/Na atoms.This shows that bothβ-P andγ-P can ensure the high capacity of LIBs and SIBs.Moreover,these three phosphorene（α-P,β-P andγ-P）composed of P₆hexagons have lifeboat-shaped or wave-shaped grooves,which provide the convenient paths for the diffusion of Li/Na atoms,make the diffusion barriers lower and ensure the charge/discharge efficiency of the batteries.Futhermore,the calculated electrode potential profiles for Li/Li⁺or Na/Na⁺with respect to specific capacity of the three phosphorene show a similar variation tendency,andγ-P shows a higher overall voltage due to its stronger adsorption to Li/Na atoms.In addition,becauseβ-P has three-fold symmetrical lattice,the adsorption and diffusion of Li/Na atoms onβ-P during charging leads to equivalent in-plane expansion instead of anisotropy,which can improve the serious uniaxial expansion ofα-P along armchair direction during charging,and is beneficial to maintaining the integrity and reversibility of the anode.Therefore,β-P andγ-P with lower in-plane atomic density can be effective substitutes forα-P,which can improve the volume expansion of lithium/sodium-ion batteries anodes.In the second part,based on the adsorption properties of various lithium sulfide intermediates and the diffusion behavior of lithium atoms and lithium sulfides during lithiation/delithiation,and compared withα-P,whether seven novel phosphenesβ-P,γ-P,δ-P,ε-P,ζ-P,θ-P andη-P are suitable for anchoring materials of lithium-sulfur batteries was studied.The results show that the binding energies between Li₂S_nand all phosphorene substrates are larger than those between Li₂S_nand electrolyte solvent molecules（dimethoxyethane and dioxolane）,which indicates that the binding strength between Li₂S_nand phosphorene substrates is proper during the process of lithiation and delithiation.The results of electronic properties show that a new electronic state will appear near the Fermi level of phosphorene adsorbed with Li₂S_n,and its band gap is significantly reduced compared with that of the original phosphorene.With the progress of lithiation reaction,the number of charges transferred from Li₂S_nspecies to phosphorene substrates increases,which ensures the binding strength and increases the conductivity of the system.Among all phosphorene substrates,ε-P shows the strongest chemical interaction with Li₂S_n,but it may lead to the decomposition of Li₂S,whileα-P,β-P,γ-P,δ-P,ζ-P,θ-P andη-P can strike a balance between binding strength and intactness of the Li₂S_nspecies,thus overcoming the shortcomings of strong and weak anchoring materials.Moreover,the layered two-dimensional morphology of phosphorene（weak van der Waals interaction between layers）provides enough space to adapt to the structural changes during charging/discharging,and can be used to modificate the separator of Li-S batteries.In the third part,based on the analysis of point group,space group and Raman active vibration modes,the structural similarities between phosphorene and graphane are summarized,and a"three identical,one divergent"pattern is proposed to describe the structural characteristics of phosphorene and phosphene-like materials.Then,one new crystal structure of phosphorene（αβ-P）and four new crystal structures of graphane（γδ-G,αγ-G,βγ-G andαδ-G）are successfully predicted.The electronic properties show thatγδ-G,αγ-G,βγ-G andαδ-G all exhibit direct band gaps more than 3 e V and the results of the PDOS are in accord with the common characteristics of single-layer honeycomb systems.Among these four new graphane,βγ-G has the lowest binding energy,which is only 0.02 e V/atom higher thanβ-G,the most stable one among all graphane theoretically predicted.This meansβγ-G may co-exist withβ-G during experimental systhesis of graphane,which can be distinguished from the side views with threefold structures forβγ-G and twofold structures forβ-G.Except forαδ-G,the other three graphane show negative Poisson’s ratios when they are subjected to tensile strain in x-and y-directions due to their threefold armchair geometric structures.According to the observation direction and the number of six-membered rings,this work summarized the hydrogenation modes of graphane,and found that hydrogenation modes of these new graphane conformers can be regarded as the combination of basic hydrogenation modes fromα-G,β-G,γ-G andδ-G.Theoretically,this prediction method of new structures and corresponding relationship are not only suitable for phosphorene and graphane,but also can be extended to all materials with phosphorene-like structures,even other materials.In this paper,some achievements have been made in improving the volume expansion of the anode of LIBs/SIBs,finding suitable anchoring materials for Li-S batteries and predicting new structures of phosphorene and phosphorene-like materials,which have made some contributions to the application of phosphorene in the fields of energy storage and the design of new structures.