First-Principles Study Of Novel Two-Dimensional Titanium/Carbon-based Electrode Materials

In recent years,due to the growth of global energy demand,limited fuel reserves and increasingly serious environmental problems,the research of new energy storage system has become an important issue of human sustainable development.Rechargeable metal ion batteries have attracted wide attention in the energy field due to their advantages such as high conversion efficiency,easy maintenance,low cost and little pollution to the environment.Among them,multivalent ion battery has become one of the most potential metal ion batteries because of its super high theoretical capacity and inherent safety.Therefore,it is of great significance for the development of new energy storage systems to find high performance electrode materials suitable for multivalent ion batteries.Since the synthesis of graphene,two-dimensional materials have attracted great interest in the field of electrochemistry.Compared with bulk phase materials,two-dimensional materials have a larger surface area and can provide a shorter diffusion path for metal ions,so they are one of the best candidates for metal ion battery electrode materials.In this paper,three novel Ti/carbon-based 2D materials are predicted systematically using first principles,and their applications in the field of electrode materials for multivalent ion batteries are studied theoretically.The main research contents are as follows:（1）We successfully predict a novel two-dimensional TiClO monolayer derived from a recently synthesized Ti-based compound.Two-dimensional TiClO has good energetical,dynamical,mechanical and thermal stabilities.Due to the small cleavage energy（1.13 J/m²）,it is feasible to obtain monolayer TiClO by its bulk structure.Two-dimensional TiClO exhibits intrinsically metallic,its excellent electrical conductivity makes it promising to be applied in metal ion batteries.We study the performance of 2D TiClO as anode material for magnesium ion batteries.TiClO monolayer has extremely high magnesium ion storage capacity(1079 m A h g^-1),low diffusion barrier（0.41～0.68 e V）,and suitable average open-circuit voltage（0.96 V）.The TiClO monolayer exhibits small lattice change（<4.3%）during magnesium ion insertion,demonstrating excellent cyclic stability.In addition,compared with monolayer TiClO,bilayer TiClO can enhance the adsorption interaction between substrate and magnesium atoms and maintain quasi-one-dimensional diffusion characteristics.These properties indicate that TiClO monolayer can be used as anode material for magnesium ion batteries.（2）Inspired by the structure of Biphenylene,we design a two-dimensional carbon allotrope BP-graphene.By calculating the binding energy,phonon spectra and molecular dynamics simulations,we confirm the stability of BP-graphene.BP-graphene has excellent mechanical properties and 0.259 e V indirect band gap,it is expected to be widely used in the field of flexible electronics technology.Using first principles calculations,we investigate its performance as an anode material for calcium ion batteries.Due to its unique lattice structure,the highest specific capacity of BP-graphene can reach 1682 m A h g^-1,which is better than most reported two-dimensional electrode materials.In addition,BP-graphene has stable ion adsorption sites,good electrical conductivity after adsorption,fast ion diffusion,low open-circuit voltage,it is an excellent candidate for ultra-high capacity of calcium ion battery anode materials.（3）Through the ordered arrangement of carbon atoms,we propose a new two-dimensional carbon material HH-graphene.The stability of two-dimensional HH-graphene was verified by calculating binding energy,phonon dispersion curves,and molecular dynamics simulations.Similar to BP-graphene,two-dimensional HH-graphene is an indirect band-gap semiconductor with a band gap of 1.810 e V.Similarly,we investigate the performance of two-dimensional HH-graphene as a calcium ion battery anode.During the calcium atoms adsorption process,HH-graphene shows metallic property,ensuring its good electrical conductivity as an electrode material.The results show that there are two stable adsorption sites on the HH-graphene surface,and the charge transfer is obvious.HH-graphene’s low open circuit voltage（0.19～0.44V）,ultra-low diffusion barrier（0.15e V）and excellent calcium storage capacity(1871 m A h g^-1)show that two-dimensional HH-graphene can be applied in calcium ion battery electrode materials.