Papers by Arnaud Demortière
Microscopy and Microanalysis
npj Computational Materials, 2022
The segmentation of tomographic images of the battery electrode is a crucial processing step, whi... more The segmentation of tomographic images of the battery electrode is a crucial processing step, which will have an additional impact on the results of material characterization and electrochemical simulation. However, manually labeling X-ray CT images (XCT) is time-consuming, and these XCT images are generally difficult to segment with histographical methods. We propose a deep learning approach with an asymmetrical depth encode-decoder convolutional neural network (CNN) for real-world battery material datasets. This network achieves high accuracy while requiring small amounts of labeled data and predicts a volume of billions voxel within few minutes. While applying supervised machine learning for segmenting real-world data, the ground truth is often absent. The results of segmentation are usually qualitatively justified by visual judgement. We try to unravel this fuzzy definition of segmentation quality by identifying the uncertainty due to the human bias diluted in the training data....
Microscopy and Microanalysis, 2021
The actual growth of the global energy demand in the context of the energetic transition calls an... more The actual growth of the global energy demand in the context of the energetic transition calls an augmentation of the energy production based on green sources as low-cost photovoltaics (PVs). In the last few years, the perovskite solar cells (PSCs) technology reached a first plan place among PVs. The unprecedented growth in the power conversion efficiency (PCE) of PSCs from 3.8% in 2009 to 25.5 % highlighted this technology as a promising candidate to replace the conventional Si-based and thin-film solar cell technologies [1]. One of the major challenges in manufacturing low-cost, high-performance tandem devices was the lack of a high-efficiency upper cell with a band gap greater than 1.5V. The recently introduced organic / inorganic hybrid perovskite solar cells allow to overcome these limitations due to their unique advantages. Recently, one of the best performance among mixed organic-inorganic halide perovskite (HPs) came with the triple cations/double halides Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3 (CsMAFA) composition in single junction cell [2], that also appeared as one of a top cell in a monolithic perovskite/silicon tandem architecture reaching above 29 % PCE [3]. Despite promising PCEs, the main obstacle for the future commercialization of perovskite-based solar cells is their lack in stability when exposed moisture for extended periods. Several ex-situ studies have emerged providing clues to determine the weaknesses of the materials [4].Recently, the development of TEM liquid cells [5] provided a large panel of techniques to characterize at micro-and nano-scale the solid-liquid interfaces, allowing dynamical observation of crystallization processes of nanomaterials in solutions with high resolution and fast acquisitions [6]. In this work, for the very first time, we successfully monitored by in situ liquid-cell TEM imaging the moisture-induced phase segregation of CsMAFA (Fig. 1), also characterised by EDX, STEM, SAED and 4D-STEM-ASTAR [7]. The phase and orientation maps acquired in 4D-STEM added to the elementary EDX maps made it possible to determine the species formed after the segregation of the CsMAFA phases in water. The particles were characterized by STEM and TEM imaging, The growth kinetics of these grains were quantified after segmentation of the TEM images (Fig. 2) showing different growth rates according to various morphologies of grains. The particle growth is influenced by several factors described by the LSW as limitation by diffusion, but also by the density of the species present in the liquid which significantly affect the growth of neighboring grains. The different techniques used around the liquid TEM cell have made it possible to follow the different stages of degradation of CsMAFA in water from the pristine state, through phase segregation and finally partial dissolution in water. The results presented here provide answers around the resolution of humidity instability problems of hybrid perovskite devices.References:[1] M.A. Green et al, The emergence of perovskite solar cells, Nature Photon. [2] J.-P. Correa-Baena et al, Promises and challenges of perovskite solar cells, Science. 358 (2017)
This last decade, fundamental studies of electrochemical phenomena have been slowed down by a lac... more This last decade, fundamental studies of electrochemical phenomena have been slowed down by a lack of effective insitu (and operando) experimental setup, which is able to clearly identify structural modifications inside and at the surface of electrode materials. Evolution of microstructures, the appearance of cracks and porosities, the formation of SEI at the electrode/electrolyte interface, and the transformation of crystal phases have to be properly investigated in order to get a better insight into the influence of charge/discharge processes in materials and the reaction mechanisms implied in electrochemical storage. Improving our understanding of the microstructural changes and crack formation in Li-ion electrode materials during electrochemical cycling can provide new insight into battery behavior. In order to monitor microstructural evolution dynamically during electrochemical cycling, we developed a micro-scale battery set-up implemented within a FIB/SEM instrument [1]. The s...
Microscopy and Microanalysis, 2021
Microscopy and Microanalysis, 2021
Direct observation of 3D motion of nanoparticles is of critical importance for the study of inter... more Direct observation of 3D motion of nanoparticles is of critical importance for the study of interparticle interactions and for in situ colloidal self-assembly using Liquid Cell (LC). Measuring nanoparticle dynamics with high spatial and temporal resolution opens potential for dynamic studies in LC as well as interaction between particles and substrates. For this study we have used TEM based automated 4D-(precession) STEM crystallographic mapping techniques (ASTAR) [1] to study phase & orientation mapping (down to 1-5 nm scale) of nanoparticles as they dynamically interact in situ at different time scales within the liquid.
This is a critical review of artificial intelligence/machine learning (AI/ML) methods applied to ... more This is a critical review of artificial intelligence/machine learning (AI/ML) methods applied to battery research. It aims at providing a comprehensive, authoritative, and critical, yet easily understandable, review of general interest to the battery community. It addresses the concepts, approaches, tools, outcomes, and challenges of using AI/ML as an accelerator for the design and optimization of the next generation of batteriesa current hot topic. It intends to create both accessibility of these tools to the chemistry and electrochemical energy sciences communities and completeness in terms of the different battery R&D aspects covered.
Advanced Energy Materials, 2021
Despite a significant progress in the field of tomography, capture the carbon binder domain morph... more Despite a significant progress in the field of tomography, capture the carbon binder domain morphology presented in the Li-ion electrode remains challenging, due to its low attenuation coefficient. In this work, quantitative phase contrast X-ray nanoholotomography is used as a straightforward approach that provides a large reconstructed volume, where the carbon binder domain can be resolved along with the active materials and the pore space. As a result, a complete quantitative analysis of the microstructures of three LiNi 0.5 Mn 0.3 Co 0.2 O 2 high energy density electrodes, including the characterization of each phase separately along with the statistical quantification of their inter-connectivity at particle scale, is performed. The microstructural heterogeneities are quantified and comparison between different electrodes is done. The results from this work suggest the negative impacts of the carbon binder domain excess to the electrode performance at high Crates. Those results are true in the case of high energy density electrodes, and are due to the reduction of the electrochemical active surface area. This sheds light to the optimization of the electrode design to improve the power rate of high energy density electrodes.
The Journal of Physical Chemistry C, 2021
Li-O 2 batteries offer a high theoretical discharge capacity due to the formation of light discha... more Li-O 2 batteries offer a high theoretical discharge capacity due to the formation of light discharged species such as Li 2 O 2 , which fill the porous positive electrode. However, in practice, it is challenging to reach the theoretical capacity and completely utilize the full electrode pore volume during discharge. With the formation of discharge products, the porous medium evolves, and the porosity and tortuosity factor of the positive electrode are altered through shrinkage and clogging of pores. A pore shrinks as solid discharge products accumulate, the pore clogging when it is filled (or when access is blocked). In this study, we investigate the structural evolution of the positive electrode through a combination of experimental and computational techniques. Pulsed field gradient nuclear magnetic resonance results show that the electrode tortuosity factor changes much faster than suggested by the Bruggeman relation (an equation that empirically links the tortuosity factor to the porosity) and that the electrolyte solvent affects the tortuosity factor evolution. The latter is ascribed to the different abilities of solvents to dissolve reaction intermediates, which leads to different discharge product particle sizes: on discharging using 0.5 M LiTFSI in dimethoxyethane, the tortuosity factor increases much faster than for discharging in 0.5 M LiTFSI in tetraglyme. The correlation between a discharge product size and tortuosity factor is studied using a pore network model, which shows that larger discharge products generate more pore clogging. The Knudsen diffusion effect, where collisions of diffusing molecules with pore walls reduce the effective diffusion coefficients, is investigated using a kinetic Monte Carlo model and is found to have an insignificant impact on the effective diffusion coefficient for molecules in pores with diameters above 5 nm, i.e., most of the pores present in the materials investigated here. As a consequence, pore clogging is thought to be the main origin of tortuosity factor evolution.
ACS Applied Energy Materials, 2020
We investigated the lithium peroxide (Li 2 O 2) and pore size distribution in 19 lithium-O 2 batt... more We investigated the lithium peroxide (Li 2 O 2) and pore size distribution in 19 lithium-O 2 battery electrodes at different states of charge using transmission X-ray 20 microscopy coupled with Zernike phase contrast to carry out nano-Computed 21 Tomography. We report that such technique enables, at the nanoscale, to distinguish light 22 elements such as carbon and Li 2 O 2 in Li-O 2 battery cathode electrodes. We verified by 23 wave-propagation simulation that this approach efficiently improves the contrast of 24 images in comparison with the pure absorption. The Li 2 O 2 distribution and thickness, 25 interphases, and pore network are visualized and quantified, which give a valuable insight 26 into our cathode architecture. From this 3D analysis, we highlight modifications of the air-27 cathode morphology and the Li 2 O 2 spatial organization as well as their potential 28 implication in terms of carbon surface passivation and pore-clogging. After the full 29 recharge process, this technique can also reveal the spatial distribution of the residual 30 Li 2 O 2 and other byproducts.
European Journal of Mineralogy, 2019
Single-phase marićite, NaFePO4, was synthesized from monosodium phosphate and iron oxalate at 750... more Single-phase marićite, NaFePO4, was synthesized from monosodium phosphate and iron oxalate at 750°C, at atmospheric pressure. Thermal treatment of synthetic marićite in air indicated oxidative decomposition into Na3Fe 3+ 2(PO4)3 nasicon and-Fe2O3 at temperatures above 225°C. Intergrowth of the reaction products is found to occur at the nanoscale without identified crystallographic relationship with the marićite precursor. Electrochemical activity of the reaction product is confirmed with the reversible insertion of one Na at 2.55 V vs Na + /Na 0 .
Microscopy and Microanalysis, 2019
The recent development of liquid cell for TEM [1, 2] enables an exciting opportunity to explore [... more The recent development of liquid cell for TEM [1, 2] enables an exciting opportunity to explore [3, 4] and even quantify [5, 6] complex electrochemical reactions occurring inside batteries during operation. Indeed, the miniaturization of new electrochemistry echips (Protochips) [7] with complex electrode designs (3-electrodes cell) adds the capability to perform true in situ/operando quantitative electrochemical reactions, which can be followed using TEM multi-techniques.
Microscopy and Microanalysis, 2019
Microscopy and Microanalysis, 2019
ACS Omega, 2019
Manipulating the atomic structure of semiconductors is a fine way to tune their properties. The r... more Manipulating the atomic structure of semiconductors is a fine way to tune their properties. The rationalization of their modified properties is, however, particularly challenging as defects locally disrupt the long-range structural ordering, and a deeper effort is required to fully describe their structure. In this work, we investigated the photoelectrochemical properties of an anatase-type structure featuring a high content of titanium vacancies stabilized by dual-oxide substitution by fluoride and hydroxide anions. Such atomic modification induces a slight red-shift band gap energy of 0.08 eV as compared to pure TiO 2 , which was assigned to changes in titanium− anion ionocovalent bonding. Under illumination, electron paramagnetic resonance spectroscopy revealed the formation of Ti III and O 2 − radicals which were not detected in defect-free TiO 2. Consequently, the modified anatase shows higher ability to oxidize water with lower electron−hole recombination rate. To further increase the photoelectrochemical properties, we subsequently modified the compound by a surface functionalization with N-methyl-2-pyrrolidone (NMP). This treatment further modifies the chemical composition, which results in a red shift of the band gap energy to 3.03 eV. Moreover, the interaction of the NMP electron-donating molecules with the surface induces an absorption band in the visible region with an estimated band gap energy of 2.25−2.50 eV. Under illumination, the resulting core−shell structure produces a high concentration of reduced Ti III and O 2 − , suggesting an effective charge carrier separation which is confirmed by high photoelectrochemical properties. This work provides new opportunities to better understand the structural features that affect the photogenerated charge carriers.
Nano Letters, 2018
We demonstrate that changes in the unit cell structure of lithium battery cathode materials durin... more We demonstrate that changes in the unit cell structure of lithium battery cathode materials during electrochemical cycling in liquid electrolyte can be determined for particles of just a few hundred nanometer in size, using in situ transmission electron microscopy (TEM). The atomic coordinates, site occupancies (including lithium occupancy) and cell parameters of the materials can all be reliably quantified. This was achieved using electron diffraction tomography (EDT) in a sealed electrochemical cell, with conventional liquid electrolyte (LP30) and LiFePO4 crystals, which has a well-documented charged structure to use as reference. The structure refined for the charged LiFePO4, i.e. FePO4, corresponds well to literature data. In situ EDT in a liquid environment cell provides a viable alternative to in situ X-ray and neutron diffraction experiments, due to the more local character of TEM, allowing to obtain single crystal diffraction
Nano letters, Jan 14, 2018
Although in sodium-oxygen (Na-O) batteries show promise as high-energy storage systems, this tech... more Although in sodium-oxygen (Na-O) batteries show promise as high-energy storage systems, this technology is still the subject of intense fundamental research, owing to the complex reaction by which it operates. To understand the formation mechanism of the discharge product, sodium superoxide (NaO), advanced experimental tools must be developed. Here we present for the first time the use of a Na-Omicrobattery using a liquid aprotic electrolyte coupled with fast imaging transmission electron microscopy to visualize, in real time, the mechanism of NaOnucleation/growth. We observe that the formation of NaOcubes during reduction occurs by a solution-mediated nucleation process. Furthermore, we unambiguously demonstrate that the subsequent oxidation of NaOof which little is known also proceeds via a solution mechanism. We also provide insight into the cell electrochemistry via the visualization of an outer shell of parasitic reaction product, formed through chemical reaction at the interfa...
The journal of physical chemistry letters, Jan 17, 2018
While large dispersions in electrochemical performance have been reported for lithium oxygen batt... more While large dispersions in electrochemical performance have been reported for lithium oxygen batteries in the literature, they have not been investigated in any depth. The variability in the results is often assumed to arise from differences in cell design, electrode structure, handling and cell preparation at different times. An accurate theoretical framework turns out to be needed to get a better insight into the mechanisms underneath and to interpreting experimental results. Here, we develop and use a pore network model to simulate the electrochemical performance of three-dimensionally resolved lithium-oxygen cathode mesostructures obtained from TXM nano-computed tomography images. We apply this model to the 3D reconstructed object of a Super P carbon electrode and calculate discharge curves, using identical conditions, for four different zones in the electrode and their reversed configurations. The resulting galvanostatic discharge curves show some dispersion, (both in terms of ...
Advanced Energy Materials, 2016
ALD of the Li3PO4 solid electrolyte In 2010, H. Fjellvag et al have reported the successful depos... more ALD of the Li3PO4 solid electrolyte In 2010, H. Fjellvag et al have reported the successful deposition of lithium lanthanum titanate (Li0.32La0.3TiOz: LLT) thin film as solid electrolyte by ALD. The deposition took place on standard 2D substrates [23]. Unfortunately, the LLT has been known to be unstable in direct contact with many negative electrodes material. To overcome this technological barrier, the authors have proposed [22] in 2011 the deposition by ALD of Li2O/Al2O3 overlayers (annealed at 700 °c) acting as a barrier layer for LLT: the ionic conductivity evaluated at 400 °C close to 10-4 S/cm has been extrapolated to be close to 10-7 S/cm at RT (no real measurement has been proposed at RT). The complex stacking of the solid electrolyte LLT-Li2O-Al2O3 and the high operating temperature of the post deposition annealing (700 °C) seriously hinder its development as the thermal budget used to fabricate a 3D MB is significantly penalized by this post annealing step. Lithium tantalate solid-state electrolyte [21] has been deposited by ALD at 225 °C using subcycle combination of Li2O / Ta2O5 layers by X. Sun et al in 2013. Despite an excellent uniformity and conformality of the thin film in 3D anodic aluminum oxide template, the lithium tantalate solid electrolyte exhibited a low ionic conductivity of 2 × 10 −8 S/cm at RT and the electrochemical window stability was not evaluated. Recently, B. Dunn and JP. Chang et al have reported [38] the synthesis by ALD at 290 °C of LixAlySizO thin film acting as a solid electrolyte for 3D batteries. A step conformal deposition of such electrolyte (between 6 up to
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Papers by Arnaud Demortière