Effect Of Calendering Research Articles

Simulating solid-state battery cathode manufacturing via wet-processing with resolved active material geometries

Prior to the development of a solid-state battery cell, researchers have limited knowledge about the microstructure of the electrodes and how they are affected by manufacturing. Therefore, numerical simulations can be considered as a powerful tool to link the fabrication process to the final microstructure of the electrode. In this paper, a numerical simulation of a wet-processed solid-state battery cathode with a formulation of 75 % LiNi9Mn0.5Co0.5O2 (NMC), 17.5 %LPSCl, 5 % Timcal C65 and 2.5 % Polyisobutene (PIB) is presented. From nano-computed tomography images, realistic shapes of active material particles are extracted and used in the simulation, which is well-calibrated to experimental data. In particular, we study the effects of calendering on the microstructure of the simulated cathode and deduce structure-property relations.

Discrete modeling of the calendering process for positive electrodes of Li-ion batteries

The electronic properties of Li-ion batteries crucially depend on the microstructure of their electrodes. One step of the manufacturing process, called ‘calendering’, consists in compressing the electrodes between two counterrotating cylinders to increase their density. Through a new simulation model, we investigate the effect of calendering on microstructural and electronic properties of the electrodes. Our model takes into account the real geometry of the rotating cylinder and a new contact law involving the elastic behavior of the active material and the cohesive-plastic behavior of the binder layer. Our results align well with experimental data for porosity, final thickness, and elongation. We show that the bonding structure induced by calendering involves mostly vertical tensile contacts and horizontal compressive contacts. This unexpected observation highlights the importance of shear deformation induced by rolling and thickness reduction. Using the FFT method, we also investigate the ionic and electronic conductivities of the numerically calendered electrodes.

Effect of calendering on the performance of 100% recycled polyester weft-knitted fabrics

Government policies focus on the textile sector to follow a tendency towards sustainability and circular economy, thus, raising the use of recycled textiles which require further performance improvement to be completely competitive with other textile products while using secondary treatments that are also environmentally friendly. In this study, a 100% recycled polyester weft-knitted fabric, currently used by commercial brands in the apparel and sport textile industry, is calendered and its properties are examined before and after such treatment. This research investigates variations in the physical (appearance and thickness), mechanical (tensile strength and elastic recovery), and physiological (water vapour resistance, spray test, and wettability) characteristics of the samples. The calendering treatment reduces water vapour resistance up to 23%, which is particularly interesting for garments used in sports. Additionally, the contact angle is increased by the calendering process which translates in poorer wettability. Novel findings of this work include that, whereas in the original fabric sweat marks are visible, sweat stains do not appear on the calendered fabric and moisture management improves, while mechanical properties do not undergo significant changes. These results have not been previosly found in the literature, giving a particular interest to a conventional process in this type of recycled fiber that can contribute to the advancement of knowledge in the textile industry and enhance the performance of treated fabrics. All these aspects make the treatment particularly interesting to improve the technical performance of the textile material while using an economic treatment with low effect on the environment.

Pore-scale modeling and investigation on the effect of calendering on lithium-ion battery cathodes

The cathode of lithium-ion batteries (LIBs) is a porous electrode that has a crucial influence on cell performance and durability. In making the electrode, a metal foil is first coated with a cathode slurry and dried. The electrode then undergoes a hard-pressing by rollers, i.e., calendering process. In the present study, the effects of calendering on the cathode's effective transport properties and its impact on the battery's charging performance are investigated using a multiscale approach. Microscopic images of LiNi0.8Co0.1Mn0.1O2 samples are obtained using X-ray computed tomography and SEM. This material's three-dimensional microstructure is generated using a numerical reconstruction algorithm based on the distribution characteristics of active material, additives, and pores observed from the microscopic images. Pore-scale simulations are performed on models of various calendering ratios (CRs) to evaluate the pore distribution, effective lithium-ion diffusivity, and electrical conductivity of the cathode material at different CRs. The computed effective transport properties of the cathode are applied to a macroscopic model to study the charging performance of LIBs at various CRs. It is found that the battery performance increases with CR and reaches optimal electrochemical performance at CR = 20 %. When the cathode is calendered to CR = 35 %, the battery's charging performance deteriorates, and this effect is more pronounced at high charging rates. The present study demonstrates a multiscale approach combining experiment characterization and pore-scale simulation for investigating the effects of calendering on LIB cathode. This approach can be employed for the future optimization of LIB fabrication processes.

Discrete element method and electrochemical modelling of lithium ion cathode structures characterised by X-ray computed tomography

Electrode microstructure can profoundly affect the performance of lithium-ion batteries. In this work, the effect of the calendering process on electrode microstructures is investigated using the Discrete Element Method (DEM) with a bonded particle model. A comprehensive evaluation between realistic electrode structures and idealised DEM structures as characterised using X-ray computed tomography (XCT) is presented. The electrode structural and transport properties of tomography scans and DEM structures, i.e. porosity distribution, specific surface area and tortuosity factors are studied. Following consideration of the carbon binder domain (CBD) phase, electrochemical analysis is further performed. Excellent agreement between tomography and idealised structures from DEM simulations is achieved, taking into account the effect of calendering. With electrode compression battery performance is improved after calendering. This study provides a basis for using DEM and electrochemical analysis to quantitatively evaluate the battery performance in future.

Effect of Calendering on Local Ionic and Electronic Transport of Porus Electrodes

The microstructure determines transport properties in lithium-ion battery electrodes. There is generally a tradeoff between electronic and ionic transport when adjusting the microstructure. One way of adjusting the microstructure is through calendering, where the electrode is compressed following drying. Understanding how calendering affects not only the average but also the local electronic and ionic transport provides additional insight when developing battery electrodes and engineering better batteries. If a correlation exists between the two properties, an optimal porosity that maximizes both ionic and electronic transport could be determined.In order to better understand the influence of microstructure on these transport properties, we tested a series of commercial-grade electrodes including NMC cathodes, graphite anodes, and a graphite-silicon anode. The local electronic conductivity of the electrodes was found using a micro-flexible-surface probe previously developed by our research group [1]. Likewise, the local ionic conductivity was found using an aperture probe previously developed by our research group [2]. All electrodes were obtained from Argonne National Laboratory in calendered and un-calendered states.Through testing various electrodes before and after calendering, we found that not every electrode experienced an increase in electronic conductivity after calendering, and that in general heterogeneity of the electronic conductivity decreased after calendering. The local ionic resistance, as indicated by MacMullin number, was found to increase after calendering, as expected. Figure 1 illustrates the local ionic and electronic transport results for one cathode. Ionic transport was found to be almost solely influenced by porosity. However, electronic transport was found to be influenced by a variety of factors including the nature, distribution, and connectivity of conductive materials.[1] Vogel et al., J. Electrochem. Soc. 168, 100504 (2021).[2] Liu et al., ECS Meeting s 2021, 444. Figure 1

Effect of Calendering on the Properties of Paper Containing Flexible Calcium Carbonate with a Cellulose Nanofibril Core.

Flexible calcium carbonate (FCC) was prepared by attaching a large amount of calcium carbonate to cellulose nanofibrils (CNFs) by an in situ calcium carbonate formation method. FCC normally consists of CNFs and calcium carbonate at a 1:40 ratio by weight. FCC-containing papers resulted in a higher bulk, higher stiffness, and higher tensile strength than a commercialized ground calcium carbonate (GCC)-containing papers at the same ash content. However, there were speculations that calendering on FCC-containing paper might cause a large drop in bulk and no increase in smoothness due to the larger size of the FCC (avg. dia. 20–30 μm) than the GCC (dia. 2 μm). FCC-containing paper was shown to respond to the calendering process very effectively to increase the Bekk smoothness and to maintain high bulk. Furthermore, FCC-containing paper was so effective in increasing smoothness that it might need less calendering pressure to match the smoothness of GCC-containing paper. If so, there could be potential to increase the bulk and stiffness further in FCC-containing papers at the same smoothness as GCC-containing paper by applying reduced calendering pressure.

A Comparative Study on the Wettability of Unstructured and Structured LiFePO4 with Nanosecond Pulsed Fiber Laser.

The wettability of electrodes increases the power and energy densities of the cells of lithium-ion batteries, which is vital to improving their electrochemical performance. Numerous studies in the past have attempted to explain the effect of electrolyte and calendering on wettability. In this work, the wettability behavior of structured and unstructured LiFePO4 electrodes was studied. Firstly, the wettability morphology of the structured electrode was analyzed, and the electrode geometry was quantified in terms of ablation top and bottom width, ablation depth, and aspect ratio. From the result of the geometry analysis, the minimum measured values of aspect ratio and ablation depth were used as structured electrodes. Laser structuring with pitch distances of 112 μm, 224 μm, and 448 μm was applied. Secondly, the wettability of the electrodes was measured mainly by total wetting time and electrolyte spreading area. This study demonstrates that the laser-based structuring of the electrode increases the electrochemically active surface area of the electrode. The electrode structured with 112 μm pitch distance exhibited the fastest wetting at a time of 13.5 s. However, the unstructured electrode exhibited full wetting at a time of 84 s.

Investigating electrode calendering and its impact on electrochemical performance by means of a new discrete element method model: Towards a digital twin of Li-Ion battery manufacturing

Lithium-ion battery (LIB) manufacturing optimization is crucial to reduce its CO2 fingerprint and cost, while improving their electrochemical performance. In this article, we present an experimentally validated calendering Discrete Element Method model for LiNi0.33Mn0.33Co0.33O2–based cathodes by considering explicitly both active material (AM) and carbon-binder domain (CBD). This model was coupled to a pre-existing Coarse-Grained Molecular Dynamics model describing the slurry equilibration and its drying and a 4D-resolved Finite Element Method model for predicting electrochemical performance. Our calendering model introduces important novelties versus the state of the art, such as the utilization of un-calendered electrode mesostructures resulting from validated simulations of the slurry and drying combined with the explicit consideration of the spatial distribution and interactions between AM and CBD particles, and its validation with both experimental micro-indentation and porosity vs. calendering pressure curves. The effect of calendering on the electrode mesostructure is analyzed in terms of pore size distribution, tortuosity factor and particles arrangement. In addition, the evolution of the macroscopic electrochemical behavior of the electrodes upon the degree of calendering is discussed, offering added insights into the links between the calendering pressure, the electrode mesostructure and its overall performance.

Effect of calendering on rate performance of Li4Ti5O12 anodes for lithium-ion batteries

Lithium titanate (LTO) anodes despite their low specific capacity of 175 mAhg−1 from a low volume change and intercalation voltage of 1.55 V vs lithium are excellent for automotive applications requiring fast and safe charging at times like regenerative braking. The present study focuses exclusively on the effect of calendering on the charging rate of LTO anodes. Calendering is a process where the current collector coated with the electrode, both anode, and the cathode is passed between two rolls at an elevated temperature to compact and improve the electrode’s energy density and electrochemical performance. The anode, LTO coated on aluminum foil current collector, calendered at about 42% (i.e. reducing the thickness of uncalendered anode from ~175 to ~100 μm) showed exceptional capacity retention even at 10C rate. Rate performance analyses reveal that calendering improves the capacity at high C-rate, whereas it doesn’t impact significantly at low C-rate. Electrochemical impedance spectroscopy measurements show that the resistive losses decrease with calendering.

Mesoscale Effects of Composition and Calendering in Lithium-Ion Battery Composite Electrodes

AbstractMacrohomogeneous battery models are widely used to predict battery performance, necessarily relying on effective electrode properties, such as specific surface area, tortuosity, and electrical conductivity. While these properties are typically estimated using ideal effective medium theories, in practice they exhibit highly non-ideal behaviors arising from their complex mesostructures. In this paper, we computationally reconstruct electrodes from X-ray computed tomography of 16 nickel–manganese–cobalt-oxide electrodes, manufactured using various material recipes and calendering pressures. Due to imaging limitations, a synthetic conductive binder domain (CBD) consisting of binder and conductive carbon is added to the reconstructions using a binder bridge algorithm. Reconstructed particle surface areas are significantly smaller than standard approximations predicted, as the majority of the particle surface area is covered by CBD, affecting electrochemical reaction availability. Finite element effective property simulations are performed on 320 large electrode subdomains to analyze trends and heterogeneity across the electrodes. Significant anisotropy of up to 27% in tortuosity and 47% in effective conductivity is observed. Electrical conductivity increases up to 7.5× with particle lithiation. We compare the results to traditional Bruggeman approximations and offer improved alternatives for use in cell-scale modeling, with Bruggeman exponents ranging from 1.62 to 1.72 rather than the theoretical value of 1.5. We also conclude that the CBD phase alone, rather than the entire solid phase, should be used to estimate effective electronic conductivity. This study provides insight into mesoscale transport phenomena and results in improved effective property approximations founded on realistic, image-based morphologies.

Effects of Organic Montmorillonite (OMMT) and Pre-Orientation on Property of Poly(l-lactic acid) (PLLA)/Ethylene Propylene Diene Monomer (EPDM) Blends.

Poly(l-lactic acid)/ethylene propylene diene monomer/organic montmorillonite (PLLA/EPDM/OMMT) samples were melt-compounded and then processed into sheets via two routes, namely, compression-molding and calendering. Tensile performance, morphology, and thermal property of the samples were investigated. Tensile test showed that the incorporation of OMMT resulted in significant enhancement in the tensile ductility of the PLLA/EPDM samples. SEM observation revealed that EPDM domain size decreased largely with increasing OMMT loading, indicating the compatibility of OMMT with PLLA/EPDM blends. Moreover, the elongation at break, tensile yield strength, and modulus of the calendered samples were found to be much higher than those of the compression-molded samples. It can be attributed to the pre-oriented rigid amorphous fraction of PLLA matrix and pre-stretched EPDM phases in the calendered samples produced by the stretching/shearing effect of calendering. Compared to the spherical/ellipsoidal EPDM particles in the compression-molded samples, these stretched EPDM phases with higher aspect ratio in the calendered samples can be more effective to initiate craze, and terminate the craze growing to a crack along transversal direction. Therefore, the calendered samples show a better tensile ductility than the compression-molded ones. Moreover, annealing was carried out to increase the crystallinity of the samples. Tensile performance, morphology, and thermal property of the annealed samples were also systematically investigated.

Effect of calendering and temperature on electrolyte wetting in lithium-ion battery electrodes

Abstract The formation process during which the liquid electrolyte wets into the porous electrode films usually takes several days or weeks at elevated temperatures, which poses a distinct bottleneck in the manufacturing line of lithium-ion batteries, especially for large-size batteries. However, despite the significance of achieving rapid and complete wetting, reliable scientific investigation on the wettability between the porous electrode and the liquid electrolyte has rarely been reported. In this study, a systematic study of the effect of different manufacturing factors on electrolyte wetting rate is conducted. The effect of calendering degree and wetting temperature on the electrodes obtained through both organic solvent-based processing and water-based processing are studied in detail. The results suggest that although increasing calendering degree increases volumetric energy density, it generally reduces electrolyte wetting rate. While switching anode manufacturing from conventional processing to aqueous processing retards the electrolyte wetting process, switching cathode processing from organic system to aqueous system can drastically influence the pore structure of the cathodes, resulting in irregularly shaped wetted regions. The results also show that while the electrolyte wetting rate of all the tested electrolytes increases with increasing temperature, the change is significant only for the electrolytes with relatively high salt concentrations.

The Impact of Calendering on the Electronic Conductivity Heterogeneity of Lithium-Ion Electrode Films

Electrical conductivity is a key metric in the performance of lithium-ion batteries. However, accurately measuring the electronic conductivity nondestructively is difficult. We have developed a micro-four-line probe that has been used to make this measurement and to demonstrate the heterogeneity of electrical conductivity of lithium-ion electrodes on a mm scale [1]. Such heterogeneity or non-uniformity can cause the lithium ion battery to degrade unevenly overtime, which is undesirable. The design of the micro-four-line probe has been improved into a flexible-four-line probe. This flexible measurement device is able to conform to the surface of the electrode, which improves the contact and the resulting electronic conductivity measurement. The flexible probe has been used to take accurate measurements of electronic conductivity and the contact resistance between the film and the current collector. The microstructure of lithium-ion electrodes is another important characteristic that determines the performance of lithium-ion cells, including electronic and ionic conductivity of electrodes. Calendering, an important step in the manufacturing process, affects the microstructure as the film is compressed to a uniform thickness. Prior to calendering there are more substantial variations in the thickness of the electrode film, which constitutes surface roughness, as illustrated in the included thickness profile (figure). The effect of calendering on the electronic heterogeneity of electrode films will be reported. The flexible probe will be used to measure the variation in electronic conductivity across the electrodes. A thickness analysis of the electrode films before and after calendering will complement the electrical measurements. This information increases our understanding of electrode manufacturing processes to allow for future optimization of these processes.

The effect of electrode calendering on the performance of fully printed Zn∣MnO2 batteries

Primary zinc–carbon batteries with a coplanar battery architecture were prepared by screen printing. Prior to battery activation by printing of an acidic zinc chloride electrolyte, printed zinc and manganese dioxide electrodes were compacted by calendering. Material densification of the electodes resulted in electrode layer thickness reduction on both sides, modified micropore surface area and volume on the cathode side. Galvanostatic impedance measurements and chronopotentiometry were used to characterise fabricated batteries with the individually prepared electrode configurations. While calendering of both electrodes of the batteries showed adverse effects by an increase of internal resistances and a reduction of discharge capacities, exclusive calendering of the zinc anode increased the active material utilisation by electrochemical cell reaction and thus the discharge efficiency of the battery.

The effect of calendering on the mechanical properties of paper-based, self-reinforcing composites

In this study, self-reinforcing composites (SRCs) were produced via the partial dissolution route with a NaOH/urea solvent from paper made of softwood sulphite dissolving and abaca pulp. Solvent welding leads to increased tensile strength due to gluing the fibres together with the dissolved portion of cellulose but does not densify the material completely. The resulting porosity makes it difficult to compare the obtained materials with other composites and gives the potential for optimizing the SRCs. Calendering, however, is a well-known and easy method to reduce the thickness of paper and therefore reduce the porosity, but the influence of calendering on the mechanical properties has not been widely studied for paper or for SRCs at this stage. The change of morphology and mechanical properties was investigated by calendering the untreated paper and the SRCs with nip pressures from 10 up to 200 kN/m and then comparing scanning electron microscopy (SEM), X-ray diffraction, tensile strength and short-crush resistance. The SEM imaging indicated that calendering indeed densifies the paper and the SRCs by increasing the nip pressures, but tensile strength measurements showed that the strength of paper and SRCs increases for low nip pressures but significantly decreases for high nip pressures despite better densification. Furthermore, it was found that the elastic modulus can be increased by calendering, and short-crush resistance is not influenced by calendering at all.

Paper‐Derived Ferroelectric Ceramics: A Feasibility Study

Preceramic paper may serve as a preform to manufacture single sheet as well as multilayer porous ferroelectric ceramic products. In this article, the authors discuss the formation, microstructure, and properties of preceramic papers highly loaded with BaTiO3 filler ranging from 70 to 80 vol% and their conversion into ceramic materials. In order to increase the density of the single sheets, post calendering is applied. These sheets are used for the fabrication of multilayer ceramics using warm lamination technique. After binder burnout and sintering up to 1300 °C for 2 h in air, porous paper‐derived multilayer BaTiO3 is obtained. The effect of ceramic filler content and calendering on the residual porosity in sintered samples is studied. Furthermore, the influence of porosity on the microstructure, mechanical, dielectric, and piezoelectric properties of the sintered BaTiO3 ceramics is investigated.

Effects of Calendering on Print Densities of Coated Paperboards

In this study, the effect of calendering on print quality was determined. For this purpose, five different pigment-coating formulations were prepared. They were coated on the surface of the base paperboard, previously coated with starch. Half of the coated base paperboards were calendered. Then, the Ugra82 (Ugra82 Plate Control Wedge) was printed on calendered and uncalendered-coated base paperboard surface by offset printing using black inks. All solid density measurements on the printed wedge were performed by a calibrated Gretag Macbeth Spectrolino Spectrophotometer (D50, 2 degree observer, included UV, with white backup). Double coating of the base paperboard surface is important for printability. As a result of measurement, it was found that calendering increased the surface smoothness. The surface smoothness of coated paperboard increased as long as ink absorption reduced. Hence, density value augmented after calendering. Generally, the raise of the kaolin ratio in the coating formulations affected positively printability.

Effect of hot calendering on physical properties and water vapor transfer resistance of bacterial cellulose films

This work investigates the effect of hot calendering on bacterial cellulose (BC) films properties, aiming the achievement of good transparency and barrier property. A comparison was made using vegetal cellulose (VC) films on a similar basis weight of around 40 g.m−2. The optical–structural, mechanical, and barrier properties of BC films were studied and compared with those of highly beaten VC films. The Young’s moduli and tensile index of the BC films are much higher than those obtained for VC (14.5–16.2 vs 10.8–8.7 GPa and 146.7–64.8 vs 82.8–40.3 N.m.g−1), respectively. Calendering increased significantly the transparency of BC films from 53.0 to 73.0 %. The effect of BC ozonation was also studied. Oxidation with ozone somewhat enhanced the brightness and transparency of the BC films, but at the expenses of slightly lower mechanical properties. BC films exhibited a low water vapor transfer rate, when compared to VC films and this property decreased by around 70 % following calendering, for all films tested. These results show that calendering could be used as a process to obtain films suitable for food packaging applications, where transparency, good mechanical performance, and barrier properties are important. The BC films obtained herein are valuable products that could be a good alternative to the highly used plastics in this industry.

Geometric and Electrochemical Characteristics of NMC Electrodes with Different Calendering Conditions

The energy and power capabilities of Li ion batteries (LIBs) have been considered critical factors to determine the commercial values of the LIB powered applications. Many efforts have been done to improve the energy density and rate capability of LIBs. In addition to intrinsic material properties of anode and cathode active materials, the structure of electrode at micro and nano scales also plays a critical role in determining the energy density and rate capability of a LIB (1-3). Calendering is a process in battery manufacturing to lower the porosity of the electrode and increase electrical contact. Increased calendering can increase the packing density of active materials in LIB electrodes, thereby increasing the volumetric energy density. The specific energy density is also increased by calendering via decreasing the percentage of inactive materials, such as current collector and separator. However, higher fraction of active materials in LIB electrodes can change electrodes’ structural properties significantly, such as porosity, specific surface area, pore size distribution and tortuosity (4). To this end, there are few reports on the geometric characteristics and their impact on the electrochemical performance of LIB electrodes with different calendering conditions due to the inhomogeneity, complexity, and three-dimensional (3D) nature of the electrode’s microstructure (5, 6). Recently, porous electrode microstructures have been reconstructed by advanced tomography techniques such as X-ray nano-computed tomography (nano-CT) and focused ion beam scanning electron microscope (FIB-SEM) (7, 8). The reconstructed microstructures have been employed to investigate the geometric characteristics and spatial inhomogeneity of porous electrodes. In this study, we investigated real 3D Li[Ni1/3Mn1/3Co1/3]O2 (NMC) electrode microstructures under different calendering conditions and the effect of calendering on the performance of LIBs (4). To investigate geometric characteristics of porous microstructures, cathode electrodes were fabricated from a 94:3:3 (weight %) mixture of NMC, PVDF, and super-P carbon black. To change the calendering condition, initial thickness of the electrodes was set 50µm, 80um, 90um, 100um. Then all electrodes were pressed down to 50 µm by using a rolling press machine. A synchrotron X-ray nano-CT at the Advanced Photon Source of Argonne National Lab was employed to obtain morphological data of the electrodes, with voxel size of 58.2 × 58.2 × 58.2 nm3. The morphology data sets were quantitatively analyzed to characterize their geometric properties. The geometric analysis showed that high packing density can result in smaller pore size and more uniform pore size distribution. The specific surface area and tortuosity of different electrodes will be reported. The charge/discharge experiments were also conducted for these electrodes. The geometric properties and cell testing results will be analyzed and reported. Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850.