The composite structure of mixed τ-(Ag, Cu)xV2O5 bronzes—Evidence for T dependant guest-species ordering and mobility

The complex structural behavior of τ-[AgCu]∼0.92V4O10 has been elucidated by single crystal X-ray diffraction and thermal analysis. The τ-phase region is apparently composed of several distinct phases and this study identifies at least three: τ1rt, τ2rt and τlt. τ1rt and τ2rt have slightly different compositions and crystal habits. Both phases transform to τlt at low temperature. The room temperature modification τ1rt crystallizes in an incommensurately modulated structure with monoclinic symmetry C2(0β1/2) [equivalent to no 5.4, B2(01/2γ) in the Intnl. Tables for Crystallography, Volume C] and the cell parameters a=11.757(4)Å, b=3.6942(5)Å c=9.463(2)Å β=114.62(2)° and the q-vector (00.921/2), but it is more convenient to transform this to a setting with a non-standard centering X=(1/21/200; 001/21/2; 1/21/21/21/2;) and an axial q vector (00.920). The structure features a vanadate host lattice with Cu and Ag guests forming an incommensurate composite. The structural data indicates perfect Ag/Cu ordering. At low temperature this modification is replaced by a triclinic phase characterized by two independent q-vectors. The τ2rt phase is similar to the low temperature modification τlt but the satellite reflections are generally more diffuse

Important variation in vibrational properties of LiFePO4 and FePO4 induced by magnetism

A new thermodynamically self-consistent (TSC) method, based on the quasi-harmonic approximation (QHA), is used to obtain the Debye temperatures of LiFePO4 (LFP) and FePO4 (FP) from available experimental specific heat capacities for a wide temperature range. The calculated Debye temperatures show an interesting critical and peculiar behavior so that a steep increase in the Debye temperatures is observed by increasing the temperature. This critical behavior is fitted by the critical function and the adjusted critical temperatures are very close to the magnetic phase transition temperatures in LFP and FP. Hence, the critical behavior of the Debye temperatures is correlated with the magnetic phase transitions in these compounds. Our first-principle calculations support our conjecture that the change in electronic structures, i.e. electron density of state and electron localization function, and consequently the change in thermophysical properties due to the magnetic transition may be the reason for the observation of this peculiar behavior of the Debye temperatures

Spark Plasma Sintering: An Easy Way to Make Infrared Transparent Glass-Ceramics

International audienceInfrared transparent glass-ceramics have been prepared in the system GeS2-Sb2S3-CsCl using spark plasma sintering in shorter times in comparison with conventional thermal treatments. The combined effects of pressure, time, and temperature allow the controlled crystallization of Cs-based crystals. The different glass-ceramics have been characterized by scanning electron microscopy and X-ray diffraction. The optical properties were also investigated

A Critical Review for an Accurate Electrochemical Stability Window Measurement of Solid Polymer and Composite Electrolytes

All-solid-state lithium batteries (ASSLB) are very promising for the future development of next generation lithium battery systems due to their increased energy density and improved safety. ASSLB employing Solid Polymer Electrolytes (SPE) and Solid Composite Electrolytes (SCE) in particular have attracted significant attention. Among the several expected requirements for a battery system (high ionic conductivity, safety, mechanical stability), increasing the energy density and the cycle life relies on the electrochemical stability window of the SPE or SCE. Most published works target the importance of ionic conductivity (undoubtedly a crucial parameter) and often identify the Electrochemical Stability Window (ESW) of the electrolyte as a secondary parameter. In this review, we first present a summary of recent publications on SPE and SCE with a particular focus on the analysis of their electrochemical stability. The goal of the second part is to propose a review of optimized and improved electrochemical methods, leading to a better understanding and a better evaluation of the ESW of the SPE and the SCE which is, once again, a critical parameter for high stability and high performance ASSLB applications

Electrochemistry and transport properties of electrolytes modified with ferrocene redox-active ionic liquid additives

Used in their pure, undiluted form, ionic liquids usually result in Li-ion battery electrolytes with inadequate performance due low Li+ transport numbers (tLi+). Alternatively, they can be used as additives dissolved in carbonates to maintain a high tLi+ while providing the electrolyte with additional properties such as resistance to combustion, current collector passivation, and decreased Li dendritic growth. Additional properties can be imparted to the ionic liquid via the modification of their structure. Ionic liquids modified with electroactive moieties such as ferrocene (Fc-IL) can be used as an additive in Li-ion battery (LiB) electrolytes to prevent cathode over-oxidation via the redox shuttle mechanism. The aim of the present work is to evaluate the properties of LiB electrolytes modified with such Fc-IL at different concentrations. At low concentrations (0.3–0.5 mol/L), the redox-active ionic liquid behaves as expected for a redox shuttle. We show that at 1 mol/L, however, the redox ionic liquid yields a different discharge behavior after the overcharging step, providing an increase in discharge capacity. This behavior is linked to the deposition of the ferrocenium-IL at the positive electrode. Such electrolyte is non-flammable and is highly efficient to achieve shuttling of excess charge. Based on this principle, it is expected that novel ionic liquids can be designed for development of other types of additives and contribute to developing safer battery electrolytes. As a part of this commemorative issue, this contribution highlights the type of collaborative research currently being done on energy storage devices at the Department of Chemistry at the Université de Montréal.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Synthesis, structure, and electrochemical properties of LiFeV2O7

The structure of a novel compound, LiFeV2O7, has been determined from single-crystal X-ray diffraction data. The phase crystallizes in the non-centrosymmetric monoclinic Cc space group. The structure can be described as a layered type compound alternating (Li,Fe)–O sheets and V–O chains that are perpendicular to the [101] direction. Within the (Li,Fe)–O sheets, “hexagonal” holes are formed and assembled into tunnels running parallel to the [201] direction and hosting the vanadium atoms. Original (V4O14)8– strings are observed within the structure in association with well-known (V2O7)4– pyrovanadate units. Both units alternate parallel to the [−101] direction. LiFeV2O7 displays a reversible insertion–deinsertion mechanism for Li+ ions. The theoretical capacity for the insertion of one Li+ into LiFeV2O7 reaches 97 mAh/g. When the compound is cycled between 3.50 and 2.35 V versus Li+/Li, the electrochemical curve displays an initial capacity of 100 mAh/g, with 85% of this capacity retained after 60 cycles. No evidence of the formation of Fe4+ upon oxidation to a high voltage was observed. LiFeV2O7 represents the first reported phase in the Li2O–Fe2O3–V2O5 ternary diagram with electrochemical activities

Structural evolution of zirconium carbide under ion irradiation

Zirconium carbide is one of the candidate materials to be used for some fuel components of the high temperature nuclear reactors planned in the frame of the Gen-IV project. Few data exist regarding its behaviour under irradiation. We have irradiated ZrC samples at room temperature with slow heavy ions (4 MeV Au, fluence from 10(11) to 5 x 10(15) cm(-2)) in order to simulate neutron irradiations. Grazing incidence X-Ray diffraction (GIXRD) and transmission electron microscopy (TEM) analysis have been performed in order to study the microstructural evolution of the material versus ion fluence. A high sensitivity to oxidation is observed with the formation of zirconia precipitates during the ion irradiations. Three damage stages are observed. At low fluence (10(14) cm(-2)), the micro-strains saturate and the loops coalesce to form a dense dislocation network. No other structural modification is observed. The material shows a moderate cell parameter increase, corresponding to a 0.6 vol.% swelling, which saturates around 10(14) ions/cm(2), i.e., a few Zr dpa. As a result, in spite of a strong covalent bonding component, ZrC seems to have a behaviour under irradiation close to cubic metals. (c) 2007 Elsevier B.V. All rights reserved

Effect of composite electrode thickness on the electrochemical performances of all-solid-state li-ion batteries

International audienc

Assessing the Electrochemical Stability Window of NASICON-Type Solid Electrolytes

All-Solid-State Lithium Batteries (ASSLBs) are promising since they may enable the use of high potential materials as positive electrode and lithium metal as negative electrode. This is only possible through solid electrolytes (SEs) stated large electrochemical stability window (ESW). Nevertheless, reported values for these ESWs are very divergent in the literature. Establishing a robust procedure to accurately determine SEs’ ESWs has therefore become crucial. Our work focuses on bringing together theoretical results and an original experimental set up to assess the electrochemical stability window of the two NASICON-type SEs Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP). Using first principles, we computed thermodynamic ESWs for LATP and LAGP and their decomposition products upon redox potentials. The experimental set-up consists of a sintered stack of a thin SE layer and a SE-Au composite electrode to allow a large contact surface between SE and conductive gold particles, which maximizes the redox currents. Using Potentiostatic Intermittent Titration Technique (PITT) measurements, we were able to accurately determine the ESW of LATP and LAGP solid electrolytes. They are found to be [2.65–4.6 V] and [1.85–4.9 V] for LATP and LAGP respectively. Finally, we attempted to characterize the decomposition products of both materials upon oxidation. The use of an O2 sensor coupled to the electrochemical setup enabled us to observe operando the production of O2 upon LAGP and LATP oxidations, in agreement with first-principles calculations. Transmission Electron Microscopy (TEM) allowed to observe the presence of an amorphous phase at the interface between the gold particles and LAGP after oxidation. Electrochemical Impedance Spectroscopy (EIS) measurements confirmed that the resulting phase increased the total resistance of LAGP. This work aims at providing a method for an accurate determination of ESWs, considered a key parameter to a successful material selection for ASSLBs. © Copyrigh