| Compared with the traditional lithium ion battery materials,organic electrode materials have the advantages of high theoretical specific capacity?rich raw material?low cost(not involving expensive elements)?simple design and its system is safe.It is a kind of energy storage material with wide application prospects.Among of these,organic carbonyl compounds as a new class of electrochemical energy storage materials have been widely concerned.The typical characteristic of this kind of material is that it has a large conjugate system,and also contains many carbonyl functional groups,so that the material has the advantages of structure diversity and high specific capacity.It has become the research hotspot of the lithium ion battery organic cathode material,and is expected to develop into the next generation of organic electrode materials for the green lithium battery.In this paper,the electrochemical properties of pillar[n]quinones(n=4 or 5)as cathode materials for lithium ion batteries are studied by means of theoretical calculation,and the interaction between them and different types of graphene is explored.The composite materials with excellent lithium storage properties and stable structure have been obtained,this research provide theoretical guidance for people to design and search new macrocyclic compound with multi carbonyl.The work of this paper is divided into the following three aspects:1)The density functional theory(DFT)has been used to systematically study the electrochemical properties of the pillar[5]quinone as a cathode material for LIBs.The optimized structures of P5Q accepting different number of electrons and binding different number of lithium atoms are obtained,respectively.The geometry structure,thermodynamics property,electronic structural property,solvent effect and redox potential are discussed in detail.The uneven-distribution of extra electrons in several P5Qn-anions can minimize the repulsive interactions as far as possible.It is confirmed by theoretical calculation that more than eight intercalated lithium atoms into per P5Q are calculated in this work,indicating a high utilization of carbonyl groups of P5Q as a cathode material.Compared with pillar[4]quinone and pillar[6]quinone,P5Q is predicted to have better cycling performance due to its higher structural stability.2)We introduce heteroatom(O or S atom)into the bridge positions of pillar[4]quinone(P4Q),and then become oxa-and thia-pillar[4]quinones(P4QO and P4QS).The geometry structure,electronic structural property,solvation free energy,physical parameters,and average redox potential are discussed in detail by DFT methode.By the results of theoretical calculation,The theoretical specific capacity(Ctheo)of P4QO and P4QS can reach 659 mAh/g and 582 mAh/g,respectively,which is much higher than that of P4Q(Ctheo = 446 mAh/g).The extent of electron delocalization of P4QO and P4QS will increase compare to P4Q.In addition,P4QO and P4QS possess better structural stability during Li-binding processes.Generally,as organic cathode materials for LIBs,P4QO and P4QS is superior to P4Q.3)We use molecular dynamics simulation(MD)methode to calculate the interactions between the heterapillar[4]quinones(P4QO and P4QS)and different types of graphene(graphene(G),defective graphene(DG),nitrogen doped defective graphene(NDG)).According to the interaction strength and the extent of structural change during binding process,we select the best compound material.Through the theoretical calculation,we found the tiny structural change occur in P4QO during binding process and can maintain the molecular structure well,hence it is more suitable to compounded with carbon materials and then construct the compound materials of pillar[n]quinone/different types of graphene.In these three types of graphene materials,although adsorptivities of NDG and G are very close,however,NDG can effectively improve the reversible capacity of LIBs,Therefore,NDG is a excellent substrate material for adsorbing heterapillar[4]quinones. |
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