Patrick Rozier

Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide

Toward Titanium Carbide Batteries Many batteries and capacitors make use of lithium intercalation as a means of storing and transporting charge. Lithium is commonly used because it offers the best energy density, but also because there are difficulties in storing larger cations without disrupting the crystal structure of the host. Lukatskaya et al. (p. 1500) developed a series of MX compounds, where M represents a transition metal and X is carbon or nitrogen.The compound Ti3C2 forms a two dimensional layered structure, which is capable of accommodating a wide range of cations, including multivalent ones, either spontaneously or electrochemically The layered material Ti3C2 can intercalate much larger cations than Li+, allowing for energy storage applications. The intercalation of ions into layered compounds has long been exploited in energy storage devices such as batteries and electrochemical capacitors. However, few host materials are known for ions much larger than lithium. We demonstrate the spontaneous intercalation of cations from aqueous salt solutions between two-dimensional (2D) Ti3C2 MXene layers. MXenes combine 2D conductive carbide layers with a hydrophilic, primarily hydroxyl-terminated surface. A variety of cations, including Na+, K+, NH4+, Mg2+, and Al3+, can also be intercalated electrochemically, offering capacitance in excess of 300 farads per cubic centimeter (much higher than that of porous carbons). This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions.

The vanadium oxide bronze Cu2.33−xV4O11. Solid state chemistry, XRD

Abstract Solid state chemistry of the vanadium oxide bronze (VOB) Cu 2.33− x V 4 O 11 shows that at 600°C the synthesis in both Cu 2 O or CuOV 2 O 5 V 2 O 4 systems leads to the conclusion that the homogeneity range is rather narrow (0≤ x 2.33− x V 4 O 11 average structure shows that this phase crystallizes in the monoclinic system, space group Cm with the cell parameters a =15.309(3); b =3.610(1); c =7.335(2) A; β =101.84(1)° with Z =4 unit formula. The detailed description of the structure is reported. The copper ions lie between [V 4 O 11 ] n layers built up of VO 6 octahedra. Cu ions exhibit non usual tetrahedral coordination and CN=3+2 polyhedra making the estimation of the electric balance between the couples Cu + Cu 2+ and V 4+ V 5+ difficult. A superstructure, which also exists at low temperature, is shown at room temperature by Bragg and Weissenberg diagrams. The homogeneity range of this VOB is discussed in light of its structural features.

Enabling Flexible Heterostructures for Li-Ion Battery Anodes Based on Nanotube and Liquid-Phase Exfoliated 2D Gallium Chalcogenide Nanosheet Colloidal Solutions

2D metal chalcogenide (MC) nanosheets (NS) have displayed high capacities as lithium-ion battery (LiB) anodes. Nevertheless, their complicated synthesis routes coupled with low electronic conductivity greatly limit them as promising LiB electrode material. Here, this work reports a facile single-walled carbon nanotube (SWCNT) percolating strategy for efficiently maximizing the electrochemical performances of gallium chalcogenide (GaX, X = S or Se). Multiscaled flexible GaX NS/SWCNT heterostructures with abundant voids for Li+ diffusion are fabricated by embedding the liquid-exfoliated GaX NS matrix within a SWCNT-percolated network; the latter improves the electron transport and ion diffusion kinetics as well as maintains the mechanical flexibility. Consequently, high capacities (i.e., 838 mAh g-1 per gallium (II) sulfide (GaS) NS/SWCNT mass and 1107 mAh g-1 per GaS mass; the latter is close to the theoretical value) and good rate capabilities are achieved, which can be majorly attributed to the alloying processes of disordered Ga formed after the first irreversible GaX conversion reaction, as monitored by in situ X-ray diffraction. The presented approach, colloidal solution processing of SWCNT and liquid-exfoliated MC NS to produce flexible paper-based electrode, could be generalized for wearable energy storage devices with promising performances.

The composite structure of Cu2.33−xV4O11

Abstract The copper vanadium oxide bronze Cu2.33−xV4O11 exhibits a three part composite structure refined on the basis of XRD low-temperature studies. It crystallizes in the triclinic system with the non-centric superspace group X1 and cell parameters a =15.280(3) A ; b 1 =3.616(1) A ; c =14.674(3) A ; α=90.0°; β=101.95(3)°; γ=90.0° with a modulation q-vector equal to (0,0.11,0). The three different parts of this composite structure differ by their b-unit cell repeat defined as b1 ; b 2 =2.964(1) A ( b 2 ∗ =b 1 ∗ +2q ) and b 3 =3.257(1) A ( b 3 ∗ =b 1 ∗ +1q ). These parts are respectively associated to the V4O11 substructure and to each of the two different copper sites. Such refinement allows us to describe the structure using only one and fully occupied crystallographic site for each of the Cu ions. The maximum composition (x=0) is then achieved. Bond valence sum calculations on the basis of such composite structure is in agreement with electronic structure calculation made using the average one and allows us to attribute the proper valence state to each Cu ions. Then, the calculated ratio appears, contrary to the average structure, in prefect agreement with the one deduced from XPS experiment.

Electronic conductivity and structural chemistry in Li–Te–V5+,4+ oxide glasses

The electronic conductivity of the Li2O–Te2V2O9 glass system reveals that, even for high lithium content, electron hopping occurs between V4+ and V5+. The study of the V4+ content versus various syntheses shows that more than lithium content, the nature of the counter ion used in Li+ reagent and its decomposition behavior are responsible for the efficiency of the spontaneous V5+ reduction via a ‘sprouting’ phenomenon. The electron hopping process implies interconnection of VOn polyhedra which are accessible for both V4+ and V5+ species. Such fact gives information about short and medium range ordering in the glasses. On the basis of the LiVTeO5 crystal structure and in agreement with wide angle X-ray scattering experiments, a possible rearrangement bringing together VO5 square pyramids is proposed to explain the electron hopping. Such proposal corresponds to a lithium network forming effect. It could explain why for Li/V>1 the electronic conductivity increases with lithium content while the V4+ amount remains low.

Li-Driven Copper Extrusion/Re-injection in Various Cu-based Oxides and Sulfides

The present paper is in part a continuation of our recent work dealing with the fully reversible Li-driven Cu extrusion/injection of Cu in Cu2.33V4O11. The peculiar electrochemical property of such a compound was mainly ascribed to both structural considerations (presence of anchoring oxygen, giving flexibility to the [V4O11] layers) and electronic considerations, such as the existence of a delicate balance between the two Cu+/Cu2+ and V4+/V5+ redox centers. To support such suggestions, numerous compounds were revisited for their electrochemical–structural interplay. Network dimensionality, lattice flexibility, and cationic mobility parameters were addressed by exploring in depth the richness of the Cu–V–O system, while the importance of the donor/acceptor energy levels was checked via the choice of compounds having the right energy match between the two redox centers. As an extensive trial-and-error approach was not realistic, we relied on simple considerations based on the ionization energy of the various d-metals to narrow down metal pairs having redox levels occurring within the same range of energies. Bearing this in mind, it was logical to consider compounds still containing Cu ions but with Nb instead of V or compounds having V and Ag instead of Cu. Regardless of our effort, it turned out that the number of potential candidates worth considering for practical applications is still very limited, in spite of the elegance of this new Li reactivity mechanism.

KVTeO5 and a redetermination of the Na homologue.

A single crystal of KVTeO(5), potassium vanadium tellurite, has been grown. The present structure determination has been conducted together with the refinement of the NaVTeO(5) homologue, sodium vanadium tellurite, for the sake of precise comparison. The network consists of [VTeO(5)](n) ribbons built up by VO(4) tetrahedra linking centrosymmetric Te(2)O(6) groups and stacked along the [010] direction; the alkali cations are intercalated in between. The Te(IV) atom exhibits a typical one-sided coordination number (CN) of 4, completed by a lone pair, which forms a distorted triangular bipyramid with the four O atoms.

TiC-carbide derived carbon electrolyte adsorption study by ways of X-ray scattering analysis

Understanding ion adsorption in nanoporous carbon electrodes is of great importance for designing the next-generation of high energy density electrical double-layer capacitors. In this work, X-ray scattering is used for investigating the impregnation of nanoporous carbons with electrolytes in the absence of applied potential. We are able to show that interactions between the carbon surface and electrolytes allow adsorption to take place in sub-nanopores, thus confirming experimentally for the first time the results predicted by molecular dynamic simulations.

Structural study of lithium insertion in vanadium oxides used as cathode materials

Combined soft and solid state chemistry followed by precise XRD investigations allow one to determine the Li-V-O system as well as the structural modifications induced by Li insertion in silver vanadates. On the basis of these studies the authors propose an interpretation of both Li//V{sub 2}O{sub 5} and Li//Ag{sub 2}V{sub 4}O{sub 11} batteries electrochemical behavior. In the 1<x<3 domain, disproportionation of V{sup 4+} occurs leading to the formation of different mixtures between lithium vanadates and vanadium oxides. The different domains are related to the different steps observed in the Li//V{sub 2}O{sub 5} discharge curve. It is also demonstrated that the sprouting phenomenon occurring in the Ag{sub 2}V{sub 4}O{sub 11} vanadate induces the formation of a new phase Ag{sub 1+x}V{sub 3}O{sub 8} instead of the oxygen deficient form Ag{sub 2}V{sub 4}O{sub 11{minus}y}. According single crystal XRD structural determination this phase is shown to be isostructural with Li{sub 1+x}V{sub 3}O{sub 8}. Electrochemical Li insertion starts with the reduction of Ag{sup +} leading to the lithiated phase meaning that whatever the starting phase used, the main insertion process occurs in Li{sub 1+x}V{sub 3}O{sub 8}.

A new aquahydroxidocopper(II) oxovanadium(IV) vanadate, Cu(H2O)(OH)VO(VO4).

Single crystals of the title compound have been prepared hydrothermally. Vanadate tetrahedra and distorted oxovanadium octahedra form layers, linked by two independent Cu atoms located on inversion centres. Each Cu atom is surrounded by six O atoms, forming an octahedron distorted by Jahn-Teller elongation. One of the two independent interlayer spaces bridged by the Cu atoms is significantly more compact than the other.