Calculation On Crystalline Structure Of Spinel LiMn₂O₄and Al,Ti-displacing Materials And Ion-sieve Properties Of Li⁺/H⁺Exchange

Along with developing of Density Functional Theory, quantum mechanics is becomingmore and more accurate in calculation method, while quantum mechanics based on DFT haveattracted much attention of theory–calculation–scientists in the past decade because of itsapplication in the field of material characteristics and properties. The so–called first principles,namely on the base of quantum mechanics, can get the microscopic crystal structure, finalenergy and a series of physical properties of target compound directly, but no need to use anyexperimental parameters, and that it can explain the fundamental reasons of material stabilityand physical and chemical characteristics through calculation. The spinelLiMn₂O₄macroscopic performance of ionic exchange and screening can be interpreted frommicroscopic crystallography by first principles. The paper employs CASTEPpackage ofmaterial analysis software Materials studio. The main contents are as follows:We explored the electronic structure of spinel LiMn₂O₄and ion–sieve property ofLi⁺/H⁺exchange. It is found that HMn_2O4unit cell contracted after Li⁺was substituted byH⁺, and the XRD is accorded with standard spectrum, as the XRD peaks ofHMn₂O₄obviously shifted toward high angle correspondingly. According to the XRD analyses ofhomologous lattice atoms, we conclude that two elements Mn and O play a decisive role inthe XRD mode and intensity. Among them, Li presents+1valence and is completely ionized,and can be exchanged by H⁺thoroughly; while H displays the mutual connections of electronclouds with ambient O in the isoelectronic density map, and only takes a0.42positive charge.Atomic partial densities of states show that the strong covalent bonding between Mn–O ismainly attributed to the orbital overlap of Mn–d and O–p between–7.3^–1.6eV below theFermi level, and forms the hole tunnels of framework that are beneficial to ion exchange. Thevolumes of lattice point and hole polyhedrons comply with the following sequences:V8a>V48f>V8b, V16c>V16d, V16c>V48f. Li+is most apt to migrate to an adjacent16c position, andalkali metal ion exchanges are subjected to the limitation of ionic radius and the size of actingenergy which illustrated the special selectivity to Li⁺.We have also systemically studied the electronic structure of LiAlMnO₄and theadsorption property of ion–sieve HAlMnO₄when Mn³⁺is fully replaced by Al³⁺. The resultsshow that it improves the intensity of metallic bond and makes the crystal cell shrink, but stillmaintains the host structure, which is beneficial to the improving of crystal stablility andcycle performance when Mn is just substituted by Al. Further analysis discovered the main effect to crystal structure is O–p, Al–p and Mn–d. The electron density figure shows that Liwill not overlap with other atoms, and it displays a group of closed–curved shape. That Li isfully ionization indicated the permission of Li⁺insertion/extraction, while the orbital overlaprevealed certain contravalency between H and O accompanying with–OH formation. And theexchange capability is enlarged because of the raising of H ionicity, which indicates that a partof H atoms are from delocalization to localization by detaching from OH hybrid track. Theadsorption of alkali metal is also calculated in order to compare the specificity of ion–sieve,the discussions similarly display that the adsorption property of alkali metal ion is affected byionic radius and acting energy, the calculation on possible lattice point of Li+shows16c is themost feasible migratory channel.Simultaneously, we have detailedly researched the electronic structure of LiAlMnO₄and the adsorption of ion–sieve HAlTiO₄as Mn is substituded completely. The resultsindicate that the structure stability is increased, the phase analysis of X–ray shows LiAlMnO₄and HAlTiO₄are all spinel–style, in which Al and Ti builds Al–Ti–O skeleton by alternativebonding, it proves they are all p–d hybridization. What’s more, the ND of LiMn₂O₄、LiAlMnO₄and LiAlMnO₄display that it can’t change atoms’ lattice point, meanwhile, thespinel structure will not be deformed by atom replacement. The selectivity to Li⁺is enhancingas the ampliative ionicity of ion–sieve, a further calculation to alkali metal is also found theadsorption to Li⁺is the greatest. According to above researches, we know that it will improvethe adosorption of ion–sieve notablely by means of replacement. Further more, the absolutevalue of their atom binding energy is bigger than HMn₂O₄, and it indicates that theirstabilities are raised with different degrees.