Claire Villevieille

Influence of Conversion Material Morphology on Electrochemistry Studied with Operando X-Ray Tomography and Diffraction

X-ray diffraction and X-ray tomography are performed on intermetallic particles undergoing lithiation in a porous electrode. Differences between ensemble phase evolution and that at a single-particle level are explored. It is found that all particles evidence core-shell lithiation; however, particles with internal porosity are more mechanically robust and exhibit less fracture.

Novel electrochemical cell designed for operando techniques and impedance studies

A novel electrochemical cell has been designed for operando experiments at synchrotron facilities and in house. The cell can be adapted to the most common techniques such as X-ray diffraction, X-ray absorption spectroscopy, neutron diffraction as well as electrochemical impedance spectroscopy. It allows the investigation of host materials with insertion and/or conversion reactions under high current densities, high and low temperature and pressure. We are, with this cell, able to study advanced and complex systems with a high precision and quality. The stability and advantage of the cells were demonstrated by in situ synchrotron X-ray diffraction and electrochemical impedance spectroscopy using different systems such as Li(Ni, Co, Mn)O2, LiFePO4 or Li(Ni, Co, Al)O2.

Antimony based negative electrodes for next generation Li-ion batteries

Crystalline TiSb2 and NbSb2 prepared by the ceramic route were examined as negative electrodes for lithium-ion batteries. The crystal structures of both materials are different, as well as their electrochemical responses. TiSb2 has a specific charge of 450 mA h g−1 at an average potential of 0.7 V vs. Li+/Li and is able to maintain this specific charge during 70 cycles while NbSb2 has a specific charge of 400 mA h g−1 for the first few cycles which then fades continuously. The reaction mechanism was revisited in this paper by applying high resolution in situ synchrotron X-ray diffraction characterization combined with electrochemical tests.

A low-temperature benzyl alcohol/benzyl mercaptan synthesis of iron oxysulfide/iron oxide composite materials for electrodes in Li-ion batteries

A low-temperature reaction of benzyl alcohol/benzyl mercaptan with iron(III) acetylacetonate was used to synthetize micron and submicron-sized materials composed of one-pot mixture of iron oxysulfide and iron oxide. The final compound as well as reference materials greigite and magnetite were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. The crystal structure, chemical composition, and morphology of the particles of the iron oxysulfide/iron oxide composite were compared to the ones of the references, iron sulfide and iron oxide. The materials showed clear differences both in reduction and oxidation when they were cycled between 0.1–3.0 V or 1.0–3.0 V vs. Li+/Li. In all cases, electrochemical properties of the iron oxysulfide/iron oxide mixture make out to the ones of two reference materials. The in situ XRD investigation of greigite nanoplatelets confirmed that a topotactic reaction occurs between 3.0 and 1.0 V vs. Li+/Li, followed by a conversion reaction at potentials negative to 1.0 V vs. Li+/Li during the first lithiation.

Crystal structure evolution via operando neutron diffraction during long-term cycling of a customized 5 V full Li-ion cylindrical cell LiNi0.5Mn1.5O4vs. graphite

Disordered spinel LiNi0.5Mn1.5O4 (d-LNMO) is the cathode material of choice for next generation batteries based on 5 V systems. Unfortunately, once cycled under real conditions i.e. in a full-cell configuration (versus graphite), it displays a quite pronounced fading of the electrochemical performance, even under optimized cycling conditions, and about a half of the specific charge is ‘lost’ after 500 cycles. Thus, we intensively investigated the crystal structure evolution of a full-cell d-LNMO vs. graphite by means of operando neutron diffraction. For this purpose, a new cylindrical electrochemical cell was designed, suitable for operando neutron diffraction studies and allowing for precise Rietveld refinement analyses. During the first cycle, lithium content in the electrode materials (graphite and d-LNMO) could be determined, thus, allowing an estimation of the lithium consumption in side reactions. The neutron diffraction data obtained after long-term cycling (100 cycles) show that the fading of the electrochemical performance can be attributed to an insufficient amount of lithium in the system, which presumably is consumed by side reactions since no structural damage was observed in the positive and negative electrodes.