Structure Determination from Powder Diffraction Data for Rechargeable Battery Materials

Abstract

Recently, research and development into existing compounds that can be made into cathode components in rechargeable post lithium batteries systems is a major priority today. The reciprocal space theory, heavy atom method, direct methods, geometry optimization, and global optimization, all involve chemical and physical knowledge as well. This dissertation discusses such works from the point of a view of structural features for phase changes of battery compounds. The methods and techniques summarize the peculiarities between single X-ray crystal and Powder XRD. ab-initio method for determining the lattice parameters of an unknown structure, Ba(ClO4)2 that was successfully used to characterize crystal systems despite difficulties; Rietveld refinement should be done final step. Magnesium batteries have received attention as a type of post lithium-ion battery because of their potential advantages in cost and capacity. Among the host candidates for magnesium batteries, orthorhombic -V2O5 is one of the most studied materials, and it shows a reversible magnesium intercalation with a high capacity especially in a wet organic electrolyte. Studies by several groups during the last two decades have demonstrated that water plays some important roles in getting higher capacity. Very recently, proton intercalation was evidenced mainly using nuclear resonance spectroscopy. Nonetheless, the chemical species inserted into the host structure during the reduction reaction are still unclear (i.e., Mg(H2O)n2+, Mg(solvent, H2O)n2+, H+, H3O+, H2O or any combination of these). Additionally, the crystal structure of the reduced phase has not been identified. In this work the crystal structure of the magnesium-inserted phase of -V2O5—electrochemically reduced in 0.5 M Mg(ClO4)2 + 2.0 M H2O in acetonitrile—was solved for the first time using a powder synchrotron X-ray structure determination method. An orthorhombic structure (P21212 space group; a = 11.512 Å, b = 10.5483 Å, and c = 4.3681 Å) was identified; the structure was tripled along the b-axis from that of the pristine V2O5 structure. There were three large cavity sites surrounded by oxygen atoms in the structure. Examination of the interatomic distances around the cavity sites suggested that H2O, H3O+, or solvated magnesium ions are too big for the cavities, leading us to conclude that the intercalated species are single Mg2+ ions or protons. The general formula of magnesium-inserted V2O5 is Mg0.17HyV2O5, (0 < y ≤ 1.16). This work provides an explicit answer to the question about Mg intercalation into -V2O5.Li ion batteries (LIBs) are useful energy storage devices for portable electronics applications and electric vehicles. To date, many positive electrode materials for LIBs have been developed with various crystal structures such as layered, spinel, and olivine types. We report a new structure type of material, LiMo4O6, which is interesting due to its unique structure. LiMo4O6 consists of infinite anion chains of Mo4O6 where Mo6 clusters are edge-shared and all non-shared edges are capped by oxygen. The infinite chains are aligned parallel to one another and linked by bridging oxygen atoms. Such four parallel Mo4O6 chains create open one-dimensional tunnels to accommodate positive guest ions of Li+. In this study, synthesis of LiMo4O6, and its electrochemical intercalation and structural properties have been characterized with non-aqueous electrolyte system: 1.0M LiPF6 in EC/DMC (1:2). Electrochemical experiments of cyclic voltammetry and galvanostatic charge/discharge have been carried out with a voltage range of 2.0 V ~ 3.2 V vs. Li, a rate of 0.02 mV/s and 1/20C, respectively. A [Co(C6H6N2)2(H2O)2](BF4)2, the CoII atom is located on an inversion centre. The transition metal is in a slightly distorted octahedral coordination environment, defined by the cyano N atoms of four hex-3- enedinitrile ligands in equatorial positions and the O atoms of two water molecules in axial positions. The bridging mode of the hex-3-enedinitrile ligands leads to the formation of cationic chains extending parallel to [110]. The BF4 counter-anion is disordered over two sets of sites [occupancy ratio = 0.512 (19):0.489 (19)]. It is located in the voids between the cationic chains and is connected to the aqua ligands of the latter through O—H F hydrogen bonds. One methylene H atom of the hex-3-enedinitrile ligand forms another and weak C—H O hydrogen bond with a water O atom of a neighbouring chain, thus consolidating the three-dimensional network structure. The previously unknown crystal structure of barium perchlorate anhydrate, determined and refined from laboratory X-ray powder diffraction data, represents a new structure type. The title compound was obtained by heating hydrated barium perchlorate [Ba(ClO4)2 xH2O] at 423 K in vacuo for 6 h. It crystallizes in the orthorhombic space group Fddd. The asymmetric unit contains one Ba (site symmetry 222 on special position 8a), one Cl (site symmetry 2 on special position 16f) and two O sites (on general positions 32h). The structure can be described as a three-dimensional polyhedral network resulting from the corner- and edge-sharing of BaO12 polyhedra and ClO4 tetrahedra. Each BaO12 polyhedron shares corners with eight ClO4 tetrahedra, and edges with two ClO4 tetrahedra. Each ClO4 tetrahedron shares corners with four BaO12 polyhedra, and an edge with the other BaO12 polyhedron. ⓒ 2017 DGIST