M. E. Arroyo y de Dompablo

Low-potential sodium insertion in a nasicon-type structure through the Ti(III)/Ti(II) redox couple

We report the direct synthesis of powder Na3Ti2(PO4)3 together with its low-potential electrochemical performance and crystal structure elucidation for the reduced and oxidized phases. First-principles calculations at the density functional theory level have been performed to gain further insight into the electrochemistry of Ti(IV)/Ti(III) and Ti(III)/Ti(II) redox couples in these sodium superionic conductor (NASICON) compounds. Finally, we have validated the concept of full-titanium-based sodium ion cells through the assembly of symmetric cells involving Na3Ti2(PO4)3 as both positive and negative electrode materials operating at an average potential of 1.7 V.

Electrochemical lithium intercalation in Li2Ti3O7-Ramsdellite structure

Electrochemical lithium intercalation has been carried out in the Ramsdellite-type structure of Li2Ti3O7. The intercalation of 2.24 lithium ions at a very low potential in this compound leads to the formation of a new phase Li4.24Ti3O7. From powder X-ray diffraction we deduce that the structure of Li4.24Ti3O7 is closely related to the parent Ramsdellite. Both the large reversibility and the relatively high specific capacity (235 Ah Kg−1) make this compound a promising material as the negative electrode for secondary lithium cells.

Benefits of N for O substitution in polyoxoanionic electrode materials: a first principles investigation of the electrochemical properties of Li2FeSiO4−yNy (y = 0, 0.5, 1)

First principles calculations have been used to investigate the effect of N for O substitution on the electrochemical properties of Li2FeSiO4. Within the Li2FeSiO4 structure, hypothetical models of the N-substituted Li2FeSiO3N and Li2FeSiO3.5N0.5 have been analyzed. The computational results indicate that the lithium deinsertion voltage associated to the Fe3+/Fe4+ redox couple can be decreased by N substitution (4.86 V in Li2FeSiO4, 4.7 V in Li2FeSiO3.5N0.5 and 4.1 V in Li2FeSiO3N). The high theoretical specific capacity of Li2FeSiO4 (330 mA h g−1) could be retained in N-substituted silicates thanks to the oxidation of N3− anions. The redox activity of N ions is observed in a voltage range of ca. 3.5–4.2 V. In the light of the potential benefits of N substitution for O experimental work is encouraged, in particular to investigate the reversibility and overpotential of the N redox reaction.

High-pressure investigation of Li2MnSiO4 and Li2CoSiO4 electrode materials for lithium-ion batteries.

In this work, the high-pressure behavior of Pmn2(1)-Li(2)MnSiO(4) and Pbn2(1)-Li(2)CoSiO(4) is followed by in situ X-ray diffraction at room temperature. Bulk moduli are 81 and 95 GPa for Pmn2(1)-Li(2)MnSiO(4) and Pbn2(1)-Li(2)CoSiO(4), respectively. Regardless of the moderate values of the bulk moduli, there is no evidence of any phase transformation up to a pressure of 15 GPa. Pmn2(1)-Li(2)MnSiO(4) shows an unusual expansion of the a lattice parameter upon compression. A density functional theory investigation yields lattice parameter variations and bulk moduli in good agreement with experiments. The calculated data indicate that expansion of the a lattice parameter is inherent to the crystal structure and independent of the nature of the transition-metal atom (M). The absence of pressure-driven phase transformation is likely associated with the incapability of the Li(2)MSiO(4) composition to adopt denser structures while avoiding large electrostatic repulsions.

New electrode materials for lithium rechargeable batteries

Abstract In this paper, a contribution to the search of new electrode materials for lithium batteries is reported. First, we will present the electrochemical behavior of an Aurivillius-type phase with the composition Bi 4 V 2 O 11 . This oxide may be used as cathode material (390 A h/kg) if the voltage is not so low (average voltage 1.6 V). On the other hand, if Bi 4 V 2 O 11 is reduced down to 0.5 V, it reacts with 28 Li ions per formula unit. Considering only the low voltage region, Li 28 Bi 4 V 2 O 11 could be a candidate to anode material (360 A h/kg at 0.7 V). Our research has also been directed towards the applications of several types of titanium oxides in lithium batteries. Among these compounds, we present the results for K x Ti 8 O 16 and Li 2 Ti 3 O 7 . The best results are those obtained from the ramsdellite Li 2 Ti 3 O 7 : the large reversibility, low polarization and relatively high capacity (235 A h/kg) make this compound a promising material as negative electrode for lithium ion cells. However, the relatively high average potential, close to 1.4 V, would reduce considerably the performance of a rocking-chair battery using this ramsdellite instead of carbon.

Bi4V2O11 and related compounds as positive electrode materials for lithium rechargeable batteries

Abstract In the search for new intercalation electrode materials, several phases related to the compound Bi 4 V 2 O 11 have been tested as positive electrodes in room temperature electrochemical lithium cells. Bi 4 V 2 O 11 , Bi 3.6 Pb 0.4 V 2 O 11− y and Bi 4 V 1.8 Cu 0.2 O 11− y are structurally similar compounds differing only from a microstructural point of view. Electrochemical lithium intercalation is not affected by such structural and compositional differences, since the performance of all these phases is equivalent. The surprising amount of 8 lithium ions per vanadium atom inserted in Bi 4 V 2 O 11 during the first discharge at an average potential of 1.7 V implies a theoretical specific energy of 655 W h/Kg. In spite of this promising value, the irreversibility found after the first discharge slightly reduces the possibilities of these materials as positive electrodes in room temperature rechargeable lithium batteries. Even so, the energy density is high enough to consider the materials for future improvements.

A First-Principles Investigation of the Role Played by Oxygen Deficiency in the Electrochemical Properties of LiCu0.5Mn1.5O4 − δ Spinels

The effect of oxygen deficiency in Cu-based spinels Li[Cu 0.5 Mn 1.5 ] oat O 4-δ was examined using first-principles calculation. Two main results were obtained upon oxygen removal: (i) a progressive unit cell expansion owing to the presence of both more reduced transition metal cation and oxygen vacancies, (ii) a progressive decrease in the average lithium deinsertion voltage as the oxygen deficiency increases. Computational results indicate that the oxygen deficiency gives rise to a partial reduction of Mn 4+ to Mn 3+ , whereas upon lithium deinsertion, this reaction is reversed together with the oxidation of Cu 2+ to diamagnetic Cu 3+ . The electrochemical tests in lithium cells of two spinels with 8 values 0.04 and 0.1 were consistent with these calculations. Computational data indicate that the oxidation of Cu +2 to Cu +3 would be favored in highly oxygen deficient spinels; this contradicts the experimental results that show a decrease of the specific capacity in the high-voltage range with the oxygen deficiency. However, in the prepared spinels, there is an important fraction of Cu ions occupying tetrahedral sites. Therefore, computational investigation points to the electrochemical inactivity of tetrahedral Cu rather than to the oxygen content as the origin of the poor charge capacity observed in the high-voltage range.

Electrode characteristics of Li2Ti3O7-ramsdellite processed by mechanical grinding

The effect of mechanical grinding on the electrochemical properties of Li2Ti3O7 regarding lithium insertion is studied. X-ray diffraction experiments of milling compounds showed a progressively amorphization of the crystalline material due to both crystalline size decreasing and internal strain increasing. These structural modifications are reflected in the electrochemical behavior of Li2Ti3O7, when it is used as the positive electrode in lithium cells. As a function of milling time a higher specific capacity is obtained during the first discharge of the cell, but when charging an increasing in the irreversible capacity is observed. The most promising Li2Ti3O7 based electrode has been achieved, under our experimental conditions, for 13 hours milling that produces a compound with crystallite size of approximately 20 nm.

Novel superconductors obtained by electrochemical Zn intercalation of β-ZrNCl and related compounds

Abstract We present results of an electrochemical intercalation study of Zn into β-ZrNCl, β-ZrNBr and β-HfNCl. For β-ZrNCl an intercalation reaction takes place, leading to the final compound Zn0.04ZrNCl with a superconducting transition temperature Tc of 15 K. A similar behaviour is observed for β-ZrNBr where the insertion reaction produces the superconducting compound Zn0.04ZrNBr with a Tc of 14 K, whereas attempts to obtain ZnxHfNCl superconductors applying the same conditions failed. In comparison to β-MNX compounds with monovalent inserted ions, superconductivity in Zn doped β-MNX occurs at much lower levels of electron doping, although the values of Tc are similar.

Structural Evolution of Li3 + x Fe ( MoO4 ) 3 upon Lithium Insertion in the Compositional Range 0 ⩽ x ⩽ 1

Li 3 Fe(MoO 4 ) 3 reversibly inserts I lithium ion per formula down to 2 V vs Li. A preliminary room temperature phase diagram for Li 3 + x Fe(MoO 4 ) 3 (0 < x < 1) is constructed combining electrochemical and in situ X-ray diffraction results. Single-phase regions are detected at x = 0, 0.75, and 1. The crystalline structure of the final compound Li 3 + 1 Fe(MoO 4 ) 3 is derived from that of Li 3 Fe(MoO 4 ) 3 by completely filling the tunnel formed by square pyramidal sites along the a-axis of the structure. The close structural relationship between the host and inserted compounds ensures a good capacity retention of this material over prolonged electrochemical cycling in lithium cells.