Computational Model for Predicting Particle Fracture During Electrode Calendering

In the context of calling for low carbon emissions, lithium-ion batteries (LIBs) have been widely concerned as a power source for electric vehicles, so the fundamental science behind their manufacturing has attracted much attention in recent years. Calendering is an important step of the LIB electrode manufacturing process, and the changes it brings to the electrode microstructure and mechanical properties are worth studying. In this work, we reported the observed cracking of active material (AM) particles due to calendering pressure under ex situ nano-X-ray tomography experiments. We developed a 3D-resolved discrete element method (DEM) model with bonded connections to physically mimic the calendering process using real AM particle shapes derived from the tomography experiments. The DEM model can well predict the change of the morphology of the dry electrode under pressure, and the changes of the applied pressure and porosity are consistent with the experimental values. At the same time, the model is able to simulate the secondary AM particles cracking by the fracture of the bond under force. Our model is the first of its kind being able to predict the fracture of the secondary particles along the calendering process. This work provides a tool for guidance in the manufacturing of optimized LIB electrodes

Binder-free CNT cathodes for Li-O2_2 batteries with more than one life

Li-O$_2$ batteries (LOB) performance degradation ultimately occurs through the accumulation of discharge products and irreversible clogging of the porous electrode during the cycling. Electrode binder degradation in the presence of reduced oxygen species can result in additional coating of the conductive surface, exacerbating capacity fading. Herein, we establish a facile method to fabricate free-standing, binder-free electrodes for LOBs in which multi-wall carbon nanotubes (MWCNT) form cross-linked networks exhibiting high porosity, conductivity, and flexibility. These electrodes demonstrate high reproducibility upon cycling in LOBs. After cell death, efficient and inexpensive methods to wash away the accumulated discharge products are demonstrated, as reconditioning method. The second life usage of these electrodes is validated, without noticeable loss of performance. These findings aim to assist in the development of greener high energy density batteries while reducing manufacturing and recycling costs.Comment: 24 pages, 6 figures, 10 figures in S

Proximal femoral nail antirotation (PFN-ATM) fixation of extra-capsular proximal femoral fractures in the elderly: Retrospective study in 102 patients

SummaryBackgroundThe best surgical strategy for extra-capsular proximal femoral fractures (PFFs) is controversial in the elderly. Poor bone quality and neck screw instability can adversely affect the results with currently available fixation devices, which predominantly consist in dynamic hip screw-plates and proximal reconstruction nails.HypothesisThe helical blade of the proximal femoral nail antirotation (PFN-A™) achieves better cancellous bone compaction in the femoral neck, thereby decreasing the risk of secondary displacement.Materials and MethodsWe retrospectively reviewed consecutive cases of PFN-A™ fixation performed between 2006 and 2008 in 102 patients (75 females and 27 males) with a mean age of 84.9±9.5 years (range, 70–100 years). Functional outcomes were assessed using the Parker Mobility Score.ResultsMean follow-up in the 102 patients was 21.3±17.5 months (4–51 months). Fracture distribution in the AO classification scheme was A1, n=45; A2, n=41; and A3, n=16. At last follow-up, Parker Mobility Score values in the 65 survivors were 0–3, n=35; 4–6, n=11; and 7–9, n=19. Fracture union was consistently achieved, after a mean of 10.3±3 weeks. Blade back-out allowed by the device design occurred in 16 (15.7%) patients but caused pain due to screw impingement on the fascia lata in only five patients (of whom two underwent reoperation). Cephalic blade cut-out was noted in three (2.9%) patients, of whom one required reoperation because of acetabular penetration. Two hardware-related fractures were recorded.DiscussionThe new PFN-A™ device ensures reliable fixation with low mechanical complication rates. Although our data do not constitute proof that a helical blade is superior over a neck screw, they suggest a decreased rate of construct failure and may serve as a basis for a comparative study.Level of evidenceLevel IV, retrospective study

High Accuracy Battery Modeling : Fully 3D-Resolved Lithium-Ion Battery Mesostructure Including Carbon Binder Domains

In the literature, reported 3D-resolved models rely on oversimplifications, such as an implicit representation of the carbon-binder domains (CBD) through the use of effective parameters for porosity and tortuosity or by merging CBD with the Active Material (AM) as a single solid phase. This work’s novelty relies on the explicit representation of CBD, leading to a new level of accuracy in terms of electrochemical modeling. This achievement is made possible thanks to an in-house algorithm, called INfinite Number Of phases meshing through Voxelization (INNOV) [1] . INNOV can generate a volumetric mesh from data of different types due to its flexible input format. INNOV takes as input binary stack of images to reconstruct the 3D structure. Such an input can result from tomography imaging, from slicing a 3D object or from Coarse Grained Molecular Dynamics (CGMD) simulations [2] . For the latter a function has been developed to convert its output (coordinates of the centers and radii of the particles) into a binary stack of images. The segmentation method of Nielson and Franke [3] has been translated and optimized for MATLAB language and modified to suit the COMSOL Multiphysics meshing importation process. This algorithm is designed in the scope of the ARTISTIC Project [4] to import a multi-phase volumetric mesh of an electrode (from a CGMD simulation) into COMSOL Multiphysics to simulate the performances of the cell. The core of this work is to increase the current level of precision of the modeling of batteries by separating active and inactive materials. In doing so, one must not sacrifice the integrity of the mesostructure geometry. To ensure this, INNOV provides a number of observables, which can be compared to experimental numbers (e.g. arising from tomography characterizations). Once the integrity of the mesh is ensured, electrochemical simulations can be done to characterize the structure (Figure 1). Such characterizations can capture the role of CBD to further understand the limiting phenomena and predict the optimal LIB structure to achieve the optimization of the fabrication process. Simulations on NMC/Li half-cell have been carried out to demonstrate the versatility of this algorithm. In conclusion, INNOV offers a time-efficient tool to perform meshing without requiring substantial computational resources. Simulations can later be performed to characterize these meshes with the CBD explicitly considered. It is also a powerful tool to couple with tomography imaging. FIGURE TABLE Figure 1. From CGMD simulation to a volumetric mesh (35.1*35.1*42 µm). In yellow is the CBD, in red the AM. At the far right is the discharge curve for this specific mesh with COMSOL. REFERENCES [1] M. Chouchane, A. Rucci, A.A. Franco (submitted 2019) [2] A.C. Ngandjong et al. Multiscale Simulation Platform Linking Lithium Ion Battery Electrode Fabrication Process with Performance at the Cell Level. J. Phys. Chem. Lett. (2017). 5966–5972 doi:10.1021/acs.jpclett.7b02647 [3] G.M. Nielson, R. Franke Computing the separating surface for segmented data. IEEE Vis. (1997). 229–233 doi:10.1097/MOP.0000000000000041 [4] https://www.u-picardie.fr/erc-artistic/ Figure 1 <jats:p /

Self-Standing and Binder Free Cathode: Facile and Scalable Fabrication with MWCNT for Recyclable and Sustainable Application of Li-O₂ Battery

It’s well known that the Li-O2 battery can achieve theoretically1 ten times as much energy density (5200Wh/kg) as Li-ion battery but often limited in reality on the capacity and the cycling. In this system, the carbon cathode provides merely a framework for the lithium peroxide deposition but is not an active material. The dissolved oxygen in the electrolyte is indeed the active material. In other words, the capacity depends on the porosity and the framework architecture. Our previous X-ray tomographic study2 pointed out that a sparse structure is needed to increase the capacity by impeding the pore clogging and oxygen depletion. The conventional fabrication by evaporating the solvent of a slurry can only provide ~20% porosity which is insignificant. Other templating fabrications3,4 are often reported in the literature, but procedures are tedious. To fabricate sparse and self-standing cathode with the multi-wall carbon nanotubes (MWCNTs), we propose a facile and scalable two steps Buchner approach. The MWCNTs are firstly dispersed in a solvent by sonification. A direct filtration with the separator of a battery can omit a stacking step in the battery assembling (Figure 1). Preceded by a drying process, the cathode is then investigated in the overall cell for electrochemical performance and cyclability. The data of X-ray nano-Computed Tomography acquired in APS synchrotron (ID32) shows that the material is highly porous and the pores are fully filled with the discharge product Li2O2 which conducts to a capacity improvement. Impedance is utilized alongside with tomography data for a complementary understanding of the dominance between lithium ion and oxygen depletion during the discharge. The self-standing and flexible properties of such cathode even without polymer binder are beneficial for industrial application. We demonstrate the possibility of loading other particles with our approach. A gain of specific surface area for the deposition of lithium peroxide can be obtained with the loading at a price of the mechanical property detriment. Thereby, several percentages of loading are studied to obtain the best trade-off. Besides, bared carbon-nanotube framework with loaded particle trends to loss the structural stability. A sandwich-like structure is hence investigated for the efficiency of the particle confinement. Finally, our approach is highly eco-friendly. The solvent for nanotube dispersion can be reused after the filtration. And the aged cathode is entirely recyclable by proceeding a low-cost acid retreatment then ultrasonic re-dispersion. The impact of the recycling in terms of electrochemistry and pressure evolution have also been studied. Figure 1. (a) image of the homogeneous laid out cathode in a Buchner (b) SEM image of the intersection separator and cathode and (c) sandwich structure (d) electrochemical curve with pressure evolution Reference: (1) Abraham, K. M. A Polymer Electrolyte-Based Rechargeable Lithium/Oxygen Battery. Journal of The Electrochemical Society 1996, 143 (1), 1. https://doi.org/10.1149/1.1836378. (2) Su, Z.; De Andrade, V.; Cretu, S.; Yin, Y.; Wojcik, Michael. J.; Franco, Alejandro. A.; Demortière, A. X-Ray Nano-Computed Tomography in Zernike Phase Contrast for Study 3D Morphology of Li-O2 Battery Electrode. ACS Applied Energy Materials (submitted) (3) Cho, S. A.; Jang, Y. J.; Lim, H.-D.; Lee, J.-E.; Jang, Y. H.; Nguyen, T.-T. H.; Mota, F. M.; Fenning, D. P.; Kang, K.; Shao-Horn, Y.; et al. Hierarchical Porous Carbonized Co 3 O 4 Inverse Opals via Combined Block Copolymer and Colloid Templating as Bifunctional Electrocatalysts in Li-O 2 Battery. Advanced Energy Materials 2017, 7 (21), 1700391. https://doi.org/10.1002/aenm.201700391. (4) Gaya, C.; Yin, Y.; Torayev, A.; Mammeri, Y.; Franco, A. A. Investigation of Bi-Porous Electrodes for Lithium Oxygen Batteries. Electrochimica Acta 2018, 279, 118–127. https://doi.org/10.1016/j.electacta.2018.05.056. Figure 1 <jats:p /

Operando monitoring of the solution-mediated discharge and charge processes in a Na-O2 battery using liquid-electrochemical TEM

Despite the fact that Na-O2 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, NaO2, advanced experimental tools must be developed. Here we present for the first time the use of a Na-O2 micro-battery using a liquid aprotic electrolyte coupled with fast imaging transmission electron microscopy to visualize, in real time, the mechanism of NaO2 nucleation/growth. We observe that the formation of NaO2 cubes during reduction occurs by a solution-mediated nucleation process. Furthermore, we unambiguously demonstrate that the subsequent oxidation of NaO2, of 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 interface between the growing NaO2 cubes and the electrolyte, and suggest that this process is responsible for the poor cyclability of Na-O2 batteries. The assessment of the discharge- charge mechanistic in Na-O2 batteries through operando electrochemical TEM visualization should facilitate the development of this battery technology

Computational Model for Predicting Particle Fracture During Electrode Calendering

In the context of calling for low carbon emissions, lithium-ion batteries (LIBs) have been widely concerned as a power source for electric vehicles, so the fundamental science behind their manufacturing has attracted much attention in recent years. Calendering is an important step of the LIB electrode manufacturing process, and the changes it brings to the electrode microstructure and mechanical properties are worth studying. In this work, we reported the observed cracking of active material (AM) particles due to calendering pressure under ex situ nano-X-ray tomography experiments. We developed a 3D-resolved discrete element method (DEM) model with bonded connections to physically mimic the calendering process using real AM particle shapes derived from the tomography experiments. The DEM model can well predict the change of the morphology of the dry electrode under pressure, and the changes of the applied pressure and porosity are consistent with the experimental values. At the same time, the model is able to simulate the secondary AM particles cracking by the fracture of the bond under force. Our model is the first of its kind being able to predict the fracture of the secondary particles along the calendering process. This work provides a tool for guidance in the manufacturing of optimized LIB electrodes

Computational Model for Predicting Particle Fracture During Electrode Calendering

In the context of calling for low carbon emissions, lithium-ion batteries (LIBs) have been widely concerned as a power source for electric vehicles, so the fundamental science behind their manufacturing has attracted much attention in recent years. Calendering is an important step of the LIB electrode manufacturing process, and the changes it brings to the electrode microstructure and mechanical properties are worth studying. In this work, we reported the observed cracking of active material (AM) particles due to calendering pressure under ex situ nano-X-ray tomography experiments. We developed a 3D-resolved discrete element method (DEM) model with bonded connections to physically mimic the calendering process using real AM particle shapes derived from the tomography experiments. The DEM model can well predict the change of the morphology of the dry electrode under pressure, and the changes of the applied pressure and porosity are consistent with the experimental values. At the same time, the model is able to simulate the secondary AM particles cracking by the fracture of the bond under force. Our model is the first of its kind being able to predict the fracture of the secondary particles along the calendering process. This work provides a tool for guidance in the manufacturing of optimized LIB electrodes