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

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

Probing and Interpreting the Porosity and Tortuosity Evolution of Li-O2 Cathodes on Discharge Through a Combined Experimental and Theoretical Approach

Li-O2 batteries offer a high theoretical discharge capacity due to the formation of light discharged species such as Li2O2 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 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.The authors acknowledge the ALISTORE European Research Institute for the funding support of A.T.’s Ph.D. thesis. S.E. acknowledges funding from the EPSRC grant EP/L016087/1. A.A.F. acknowledges the Institut Universitaire de France for funding support. This work has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme through the projects BATNMR, ARTISTIC and SuPERPORES (Grant Nos. 835073, 772873 and 714581, respectively). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357