Theoretical Investigations On Ti_1-xNb_xAlC Solid Solutions Properties And Corresponding Two Dimensional TiNbC Lithium-ion Storage Capability

Over the past decades,MAX phases compounds have huge value for industrial production and practical applications and attracted much attention duo to their favorable properties of ceramics and metals such as high structural stiffness,oxidation resistance,good electrical and thermal conductivity,and so on.Many MAX phases materials have been synthesized and reported by experimental synthesis methods made great progress.Furthermore,MAX phases compounds have been wildly studied on MAX phases solid solution to improve the mechanical properties.Recently years,with the booming increased research on two dimensional?2D?materials,a new family 2D MXenes are experimentally obtained by chemical acid HF etching the"A"element of MAX phases materials.MXenes have unique physical and chemical properties for many applications,and also accelerate the discovery of MAX phases compounds.In this article,we studied the(Ti_1-xNb_x)₂AlC?where x=0,0.5,1.0?solid solutions and its corresponding 2D TiNbC MXene for lithium-ion batteries applications.Based on the first-principles calculations,we systematically investigate the structure,electronic,mechanical and opticals properties of(Ti_1-xNb_x)₂AlC?where x=0,0.5,1?solid solutions.The density of states at the Fermi level are positive value,indicating that the(Ti_1-xNb_x)₂AlC solid solutions exhibit metallic behavior.The(Ti_1-xNb_x)₂AlC solid solutions are stable hexagonal crystal,because of its five independent elastic constants satisfy the Bonn mechanical stability conditions.In addition,the(Ti_1-xNb_x)₂AlC solid solutions display brittle characteristics.As the concentration of Nb atoms increases,(Ti_1-xNb_x)₂AlC solid solution will be formed.The bulk modulus significantly increased with the concentration of Nb atoms increasing,but the shear modulus changed a little,indicating that the mechanical properties strengthened.The calculated results of lattice thermal conductivity indicate that(Ti_1-xNb_x)₂AlC solid solutions have good thermal conductivity at room temperature?300 K?.Moreover,the opticals properties of(Ti_1-xNb_x)₂AlC solid solutions for photon energy at the range of 0 to 25 eV have been discussed competely.Imaginary part of the complex dielectric function are positive value while the photon energy closed to 0 eV,indicating that the solid solutions have metallic with strong absorption properties.The material can be used for reflective coating or shielding material in the ultraviolet spectral duo to the reflectance greater than 90%of reflection spectrums in photon energy of 8 to11.5 eV area.At the same time,benefit from the tremendous progress in experimental researches,2D TiNbC MXenes was synthesized and we discussed the TiNbC as anode materials for lithium-ion storage capacity.MXenes will adsorb functional groups?such as-O,-F,-OH?by form of TiNbCT₂?T=O,F,OH?compounds under experimental synthesis process.Adsorption energy are positive of single lihium-ion adsorbed in TiNbC?OH?₂,the result of shows that-OH group intercalation on Ti NbC surface is harmful for lithium-ions storage.and at high concentration of lithium-ions adsorbed in TiNbCF₂ surface should form LiF polymers and unfavorable for lithium-ions recycling process.The study of single lithium-ions diffusion on TiNbC shows that TiNbC as anode materials with high cycling rate and rapid charge and discharge.lithium-ions storage capacity of TiNbC is up to 350 mAh/g,which is comparable to traditional graphite electrode materials.Therefore,TiNb C can be used as anode material for lithium-ion batteries.