Edouard Boivin

Edouard Boivin
Institut de Chimie de la matière condensée de Bordeaux · Groupe 2: Energie - Matériaux et Batteries

PhD

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12
Publications
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Publications

Publications (12)
Article
Layered oxides for Na‐ion batteries containing Fe have attracted strong interest mainly due to their low cost. However, full oxidation of Fe3+ to Fe4+ is rarely seen before O‐redox sets in and is typically accompanied by voltage and capacity fade on cycling. On charging P2‐Na0.67[Fe0.5Mn0.5]O2, Fe3+ is oxidized to only ≈Fe3.3+ before the onset of O...
Article
O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg²⁺ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magneto...
Article
Full-text available
Vanadium phosphate positive electrode materials attract great interest in the field of Alkali-ion (Li, Na and K-ion) batteries due to their ability to store several electrons per transition metal. These multi-electron reactions (from V2+ to V5+) combined with the high voltage of corresponding redox couples (e.g., 4.0 V vs. for V3+/V4+ in Na3V2(PO4)...
Article
7Li, 31P and 19F solid state NMR spectroscopy was used to investigate the local arrangement of Oxygen and Fluorine in LiVPO4F1‐yOy materials, interesting as positive electrode materials for Li‐ion batteries. From the evolution of the 1D spectra versus y, 2D 7Li RFDR experiments combined and a tentative signal assignment based on DFT calculations, i...
Article
Vanadyl-type defects in vanadium oxy-fluoride phosphates confer interesting properties to these materials as positive electrodes in Li-ion or Na-ion batteries. The influence of defects concentration on the phase diagram and redox mechanisms in LiVPO4F1-yOy Tavorite phases has been investigated by combining operando Synchrotron X-ray powder diffract...
Article
Mixed valence LiVPO4F1-yOy materials were obtained for the first time over a large composition range (here, 0.35 ≤ y ≤ 0.75), through a single step solid state synthesis. Interestingly, the competition between the ionic character of the V3+-F bond and the strong covalency of the V4+=O vanadyl bond originates a complex crystal chemistry at the local...
Article
Tavorite-type compositions offer a rich crystal chemistry for positive electrodes in rechargeable batteries, among which LiVIIIPO4F has the highest theoretical energy density (i.e. 655 Wh.kg-1). In this article, we report for the first time the synthesis of the related Na-based phase crystallizing in the Tavorite-like structure. Its in-depth struct...
Article
A new potentially interesting material as a positive electrode for lithium-ion batteries, Li2V(III)(H0.5PO4)2, was obtained by hydrothermal synthesis. Its crystal structure was solved thanks to single-crystal X-ray diffraction. This material is isostructural to Li2Fe(III)(PO4)(HPO4) and also closely related to Li2Fe(II)(SO4)2. It can be described a...
Article
In a recent study, we showed by solid-state NMR that LiVPO4F, which is a promising material as positive electrode for Li-ion batteries, often exhibits some defects that may affect its electrochemical behavior. In this paper, we use DFT calculations based on the projector augmented-wave (PAW) method in order to model possible defects in this (parama...
Article
Full-text available
Tavorite-type compositions offer a very rich crystal chemistry, among which LiVIIIPO4F has the highest theoretical energy density (i.e. 655 Wh/kg). In this article, an in-depth study of vanadyl-type defects generated by temperature-controlled oxidation of this material under air is proposed and their influence on the electrochemical properties are...
Article
Full-text available
Polyanionic materials attract strong interest in the field of Li-ion battery research thanks to the wide range of compositions, structures and electrochemical properties they offer. Tavorite-type compositions offer a very rich crystal chemistry, among which LiVPO4F has the highest theoretical energy density (i.e. 655 W h kg−1). A new Tavorite-type...

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Project (1)
Project
Develop high voltage materials and/or high capacity electrodes exchanging two electrons per transition metal.