Binder Distribution Research Articles

Elemental mapping by micro X-ray fluorescence to assess binder distribution of improved soils

This paper explores micro X-ray fluorescence (µXRF) as a novel technique in geotechnical engineering to investigate the binder distribution in a cement-improved clay. The technique scans a 2D surface of a specimen providing continuous heatmaps of an element of interest such as calcium, a major component in cement. A soft and sensitive natural clay was improved with cement using different mixing times ranging between 30 s and 10 min. The subsequent µXRF tests revealed a poor binder distribution with considerable binder accumulations for short mixing times. Longer mixing times, however, resulted in a well distributed binder. The unconfined compressive strength after around four weeks of curing ranged from 100 to 200 kPa for the shortest mixing times to 400–450 kPa for the longest mixing time as a direct result of the varying binder distributions. The paper demonstrates that the µXRF technique can be a useful technique to characterise the binder distribution in improved soils.

Modeling and Optimizing the Drying Process of Electrode Manufacturing for Lithium‐Ion Batteries

Drying the electrode is a crucial process in the manufacture of lithium‐ion batteries, which significantly affects the mechanical performance and cycle life of electrodes. High drying rate increases the battery production but reduces the uniformity of the binder in the electrode, which causes the detaching of the electrode from the collector. Herein, a physical model that couples solvent evaporation and binder diffusion is established to study the uneven enrichment of binder during the drying process. The results indicate that the drying process at the high solvent partial pressure and in a temperature‐drop situation ensures sufficient time for the diffusion of binder, which breaks the trade‐off between drying efficiency and electrode quality. Based on a comprehensive correlation analysis between process parameters and drying performance, an empirical equation is established to predict binder distribution. This work could offer insights into the formation and evolution of binder enrichment in electrodes and potentially provide guidelines for optimizing the drying processes of electrode.

Multiphysics Simulation of Battery Electrode Drying

Scaling Li-ion battery production to meet the demands of increasingly electrified grids and transportation systems will require higher throughput at all levels of the battery cell production process. One of the more energy intensive battery manufacturing steps is the necessary drying of solvents which persist in the electrodes after the initial slurry coating of their current collectors. It is critical to both optimize this drying process to minimize the time and resources required, as well as to understand the effect that the drying has on the electrode microstructure. As it is both expensive and time-intensive to iteratively test different temperatures on multiple initial electrode microstructures, it is necessary to have reliable, high-fidelity simulations which can model the evaporation process. Furthermore, it is easier to control microstructural features such as porosity, and particle size in a simulated environment, Indeed, by simulating evaporation, the design-of-experiments space can be minimized, and process conditions can be established to accelerate the production of high quality, lower cost electrodes. To that end, we develop a multiphysics model of solvent evaporation using Sandia’s in-house finite element software. By coupling the solvent equations of motion to species conservation equations for the carbon binder material and energy flux driven by evaporative cooling, we demonstrate good agreement between simulation and simple evaporation experiments. This model tackles several difficult aspects of evaporation, namely the evolution of free surfaces and gas-liquid phase-changes. We additionally extend our model to account for mesoscale features (i.e. particle size, porosity, binder distribution) and determine how different temperature profiles and microstructures affect the heating requirements for the electrode. These extensions present a key advantage over conventional 1D models, as these features can have a significant effect on the evaporation process and the final distribution of conductive additive and binder. We leverage this advantage to examine how several design parameters such as porosity, particle size distribution, and heating rate affect the resulting electrode structure and binder distribution. These results demonstrate a pathway to optimizing the electrode drying process and promise to inform the development of improved multiphysics models in the future.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

The Impact of PTFE:PVDF Ratio on the Fabrication of Free-Standing Electrodes for Solvent-Free Dry Electrodes in Libs

The current wet process of LIB electrode fabrication presents several challenges, including the use of the environmentally toxic and harmful N-methyl-2-pyrrolidone (NMP) solvent and non-uniform binder distribution due to the capillary force of the drying process. In addition, it is difficult to increase the thickness of the electrode and leads to relatively low-capacity electrodes. To address these issues, solvent-free dry electrode processes are promising. In the dry electrode process, binders play crucial roles in free-standing electrode formation. Fibrillization of Polytetrafluoroethylene(PTFE) occurs at a temperature of about 19 ℃, and the shear force of high temperature and high pressure helps to maintain the shape of the free-standing electrode.In this study, we performed a comparative analysis through the physical blending of PTFE and PVDF polymer binders with different ratios. A variety of characterization tools are used to investigate the optimal ratio that ensures good cycle performance for high-loading cathode electrodes while maintaining free-standing electrodes: 180° peel test, sheet-resistance test, SAICAS, FE-SEM, and electrochemical performance tests Keywords: Solvent-free, Dry electrode; electrode fabrication; PTFE polymer binder, Fibrillization, Lithium ion batteries Figure 1

Revisiting mixing uniformity effect on strength of cement-based stabilized soft clay

Despite the fact that mixing uniformity (i.e. the consistency of binder distribution) significantly influence the quality of ground improvement during in situ soil mixing projects, its quantitative evaluation was rarely concerned due to the difficulty of measurement from an engineering perspective. A methodology was proposed to quantitatively evaluate the mixing uniformity of stabilized soil using handheld X-fluorescence spectrometry (XRF), which is helpful to elucidate the significance of mixing uniformity on strength. In other words, the calcium content was monitored to ascertain the distribution of cement within the matrix, and a quantitative index was subsequently established. It was observed that an increase in mixing uniformity resulted in a transition in the behavior of the stabilized clay from a plastic to a brittle failure mode, and from a localized failure to a global shear failure under unconfined compression. Subsequent observation of the destruction process revealed that cracks were more readily formed in the low cement zones and then bypass the high cement zones. Furthermore, the effect of mixing uniformity on strength is likely to be amplified with prolonged curing periods. The enhancement of uniformity would increase the volume of the high binder zones, thereby enhancing the overall high-strength performance. The proposed methodology is capable of characterizing the discreteness between the tracked element's measured and theoretical contents, thusing avoiding the uncertainty associated with other indirect indicators. The convenience of the portable handheld XRF apparatus was confirmed, as it can be readily deployed in situ or ex situ to track calcium content within the stabilized mass after borehole sampling.

Effects of cutting temperature on the genes and fatigue properties of asphalt during its refining process

Asphalt binders performance is affected by refining process and crude oil. In this work, we investigated the effect of cutting temperature on the genes and fatigue properties of asphalt during asphalt refining. Five cutting temperatures (420 °C to 440 °C, interval of 5 °C) were set during the asphalt preparation, expanded the asphalt samples through ageing method. Fourier Transform Infrared (FTIR), Gel Permeation Chromatography (GPC), Nuclear Magnetic resonance Spectrum (1HNMR), Elemental analyzer, and improved Brown-Ladner method were used to characterize the asphalt genes. The fatigue performance of asphalt through Linear Amplitude Sweep (LAS) combined with the Simplified Viscoelastic Continuum Damage (S-VECD). Finally, the Pearson correlation method was used to analyze the correlation between genes and fatigue parameters of binders. The results showed that the cutting temperature and aging process changed the genes distribution of binders and these influence the fatigue properties of binders. In addition, the fatigue life of asphalt decreased at high strain levels and increased at low strain levels as the cutting temperature and the degree of ageing increased. The Pearson correlation results indicated a significant correlation between the genes and fatigue parameters of asphalt, however, the key genes affecting low-strain (2.5% and 5 %) and high-strain (10% and 20%) level fatigue in asphalt are significantly different. The outcomes of the paper provide insights about the influence of cutting temperature on the variation of asphalt genes and fatigue parameters, to allow more informed to promote of asphalt preparation.

Microanalysis of behavior characteristics for asphalt binders on different mineral surfaces based on MD and SEM

To investigate the influence of different minerals on the behavior characteristics of asphalt binders at micro scale, molecular dynamics (MD) and scanning electron microscopy (SEM) were combined to study the interaction of asphalt binders and different mineral surfaces. Firstly, commonly used aggregates were analyzed by X-ray diffraction (XRD), and the main mineral categories were obtained, including quartz, albite, biotite and calcite. Secondly, the asphalt-mineral micro models were established by combining the reasonable asphalt micro model and mineral micro model, and the interface behavior characteristics were analyzed by MD simulation. Finally, the interface structure of asphalt and minerals was observed through SEM testing, which intuitively revealed the behavior characteristics of asphalt on different mineral surfaces. The results show that the relative concentration distribution of asphalt binders at the asphalt-mineral interface is relatively high, and it can be affected by mineral category, surface structure state and asphalt type. The transition zone of biotite, albite and asphalt interface is relatively wide, which means that the influence of biotite, albite and asphalt diffusion characteristics is relatively obvious, and the interface interaction ability is relatively strong. The study reveals the behavior characteristics of asphalt binders on different mineral surfaces, and provides a research basis for exploring the structural stability of asphalt-aggregate interface.

High-energy density ultra-thick drying-free Ni-rich cathode electrodes for application in Lithium-ion batteries

Lithium-ion batteries (LIBs) can be considered as one of the pivotal components required to succeed in the drive towards a greener future. However, the current processing methods for the cathode electrode make it harmful and costly due to the toxic solvent drying and recovery stages. Additionally, the reliance on LIBs particularly emphasizes the imperative for increased energy density in both volume and weight, which predominantly relies on the cathode. To surmount these challenges, this research analyses the true requirements of a novel process and introduces a novel solvent-assisted binder (SaB) dry electrode approach to satisfy them. This innovative method incorporates a low-boiling point and relatively non-toxic solvent (ethanol) at less than 3 wt.%, enhancing the processability of the electrode without compromising safety, cost reductions, or environmental impact associated with traditional dry processes. The SaB process allows the calendaring to cause less damage to the electrode thanks to the binder distribution and allows for better fibrillization of the binder, improving the electrode microstructure. Over 100 cycles at 1C, the SaB dry electrode achieves 77.70% capacity retention, surpassing the standard dry electrode's 72.39% at a loading of approximately 30 mg cm−2 and is also capable of performing at ultra-high loadings up to 60 mg cm−2.

Mechanical and Electrochemical Implications of Drying Temperature on Lithium‐Ion Battery Electrodes

AbstractLithium‐ion battery (LIB) electrodes are typically produced with n‐methyl‐2‐pyrrolidone, a toxic solvent that is a known carcinogen and reproductive hazard. Accordingly, aqueous processing has been an expanding area of research interest in the field of LIB manufacturing. Although aqueous processing has been widely successful in anode processing, serious challenges remain in processing the cathode. In this work, the drying mechanics of cathode processed with both solvents is investigated though implementation of a chemical‐engineering‐based model to better understand the utilization of heat provided by experimentally determining the heat and mass transfer coefficients. Electrochemical performance is also evaluated to determine the impact of drying temperature on cycling performance. Binder distribution is determined via various methods to confirm differences in binder homogeneity as a function of both solvent and drying temperature. Identified is the large difference in the efficiency in which the heat is used as well as an ideal drying temperature for both aqueous and non‐aqueous processed cathodes. Also identified is the increased sensitivity to processing temperature for aqueous processed electrodes compared to non‐aqueous processed counterparts, pointing to the possibility of tuned drying regimes which would capitalize on the potential cost savings of aqueous processing for cathodes.

Effect of hydroxy propyl cellulose grade and foam quality on foam granulation of a high drug load formulation

Foam granulation is a relatively newer wet granulation process whereby foamed binder solutions are added to the powders in the mixer to reduce localized over-wetting encountered during the wet granulation. This study is the first to investigate the effect of binder grade and foam quality on foam granulation process and granule properties of a high drug load formulation. Two different HPC grades, HPC LF (two times more viscous) and HPC EXF at an equivalent 7.4%w/w solution concentration, and foam quality of 50%, 90% and binder solution dripped were added to a high drug load (81%w/w) formulation for wet granulation. The granules were evaluated for compactibility and resultant compact strengths. The 50% foam quality of either HPC LF and HPC EXF resulted in lowest impeller power reading and water activity compared to 90% foam quality or dripped HPC solution. Granules prepared with 50% foam quality also exhibited smaller granule size, wider size distribution and higher specific surface area, resulting in higher compactibility. Whilst the granules prepared with different foamed HPC grades were not significantly different in compression behavior, they were higher in compact strengths, suggesting that foam mixing was more efficient in binder distribution compared to binder liquid penetration and distribution.

The Role of Surface Free Energy in Binder Distribution and Adhesion Strength of Aqueously Processed LiNi0.5Mn1.5O4 Cathodes

This study identifies the critical aspects of binder distribution and mechanical integrity in aqueously processed LNMO cathodes, employing a comprehensive approach involving surface characterization techniques, adhesion strength testing, and electrochemical characterization. The investigation includes the use of the Washburn and Sessile Drop methods for surface free energy analysis, revealing key insights into the interfacial free energy of adhesion between cathode constituents. The results explain the formation of carbon-binder-domains and their impact on adhesion strength, with a particular focus on the conductive additives’ (CA) surface area. The study demonstrates the effectiveness of reducing CA surface area and employing alternative conductive additives, such as vapor-grown carbon fibers (VGCF), in improving adhesion strength and mitigating capacity fade attributed to delamination during cycling. Furthermore, the research emphasizes the role of heat treatment beyond the melting point of the polyvinylidene fluoride (PVDF) latex binder, showcasing its influence on wetting and enhancing mechanical integrity. The presented methodology provides a valuable tool for predicting and optimizing binder distribution, offering insights into improving the overall performance and reliability of aqueously processed cathodes for advanced lithium-ion batteries.

Application of Multistage Drying Profiles for Accelerated Production of Li‐Ion Battery Anodes Using Infrared Radiation: Validation with Electrochemical Performance and Structural Properties

The drying of solvent‐processed electrodes is a critical process step in the manufacturing of lithium‐ion batteries. The technology used to introduce the energy required for drying into the material, combined with the specified process parameters, significantly influences the resulting electrode properties. A major challenge is to counteract binder migration effects that may occur during drying of the porous electrode structure, causing a decrease in adhesion and electrochemical performance, especially for high drying rates. From this motivation, investigations on the influence of process design during near‐infrared drying of aqueous‐processed graphite anodes are carried out. A multistage drying design with varying parameters in specific drying sections with energy input by radiation is applied. The results show that the specific application of a three‐stage drying profile in combination with energy input by radiation enables a significant decrease in drying time by at least 60% while the electrode properties can be preserved. These findings indicate a beneficial development of binder distribution as a consequence of multistage NIR drying, evidenced by adhesion and electrochemical performance. Finally, the application of the multistage drying profile is theoretically transferred to an industrial‐scale roll‐to‐roll dryer, whereby the necessary dryer length can be reduced by 53%.

Direct observation and elemental analysis of material nanoparticles in solution using scanning electron-assisted dielectric microscopy and EDS

High-resolution observation and elemental analysis of various particles in solution are important in the fields of materials, analytical chemistry, and industrial applications. Analysis of slurries of raw materials is essential for the development of highly functional materials. Recently, we have developed an SEM-based scanning electron assisted dielectric microscope (SE-ADM), which can directly observe biological samples and organic materials in aqueous solutions. Here, we have developed an SE-ADM system with the addition of energy-dispersive x-ray spectrometry that enables direct observation and elemental analysis of nanoparticles in solution. Using this system, we were able to directly observe and conduct elemental analysis of ceramic slurries and to clarify the dispersion state of alumina particles in solution, the distribution of binder, and the bonding state of silica and magnesium particles. Furthermore, our system can be applied to diverse liquid samples across a broad range of scientific and industrial fields, for example, nanotubes, organic specimens, batteries, and catalytic materials.

3D printing of potassium sodium niobate by binder jetting: Printing parameters optimisation and correlation to final porosity

Binder Jetting (BJT) is a non-fusion-based Additive Manufacturing (AM) technique. It consists of the selective deposition of a liquid binder to join powder particles, thereby enabling the creation of near-net-shaped parts.In this study, the main printing parameters correlated to the binder distribution and infiltration (binder saturation, binder set time, drying time, and target bed temperature) were optimised to improve the precision of green parts printed with potassium sodium niobate (KNN) powder. The optimisation procedure was conducted using the Taguchi statistical method. An L9 orthogonal array with four factors of control at three levels each was employed. The analysis showed that the drying time had the greatest influence on the precision of green parts, followed by binder saturation and target bed temperature. Binder set time did not seem to affect the results.Dimensional analysis, microstructural and piezoelectric characterisation of parts densified by pressureless sintering were conducted. The highest average relative density exceeded 80% for the specimens printed with the lower binder saturation. Piezoelectric properties exhibit more complex behaviour. The prolonged infiltration of larger binder volumes is correlated to higher g33, thus FOMh and FOM33, and lower values for ε33T. On the other hand, d33 does not display a specific dependence on density or printing parameters.The results of this study indicate that BJT can be used to fabricate high-precision KNN components with good piezoelectric properties. The optimisation of printing parameters is essential to achieve the desired results.

Low‐Resistance LiFePO4Thick Film Electrode Processed with Dry Electrode Technology for High‐Energy‐Density Lithium‐Ion Batteries

LiFePO4emerges as a viable alternative to cobalt‐containing cathodes, such as Li[Ni1–x–yMnxCoy]O2and Li[Ni1−x−yCoxAly]O2. As Fe is abundant in nature, LiFePO4is a low‐cost material. Moreover, stable structure of LiFePO4imparts long service life and thermal stability. However, the practical implementation of LiFePO4cathode in energy storage devices is impeded by its low energy density and high ionic/electrical resistance. Herein, the LiFePO4electrode with high active material loading and low ionic/electrical resistance through the dry process is reported for the first time. The dry process not only enables the uniform distribution of the polymeric binders and conductive additives within the thick electrode but also inhibits the formation of cracks. Furthermore, the bridge‐like connection of polytetrafluoroethylene facilitates the insertion and extraction of Li ions to the LiFePO4crystal. Hence, the dry‐processed LiFePO4electrode with high areal capacity (7.8 mAh cm−2) exhibits excellent cycle stability over 300 cycles in full‐cell operation. In addition, it is demonstrated that the estimated energy density of prismatic cell with the dry‐processed LiFePO4electrode is competitive with state‐of‐the‐art Li[Ni1–x–yMnxCoy]O2‐based battery.

10 mAh cm−2 Cathode by Roll‐to‐Roll Process for Low Cost and High Energy Density Li‐Ion Batteries

AbstractRoll‐to‐roll dry processing enables the manufacture of high energy density and low cost Li‐ion batteries (LIBs). However, as the thickness of the electrode fabricated by dry processing becomes greater (≥10 mAh cm−2), Li‐ion migration resistance (Rion) and charge‐transfer resistance (Rct) in the electrode dramatically increase due to long diffusion lengths for Li‐ion and electron. Therefore, it is important to reduce diffusion lengths in the electrode to achieve high energy density LIBs. The dry electrode with a high areal capacity of 10 mAh cm−2 and low resistance can be achieved by following three characteristics. First, the fibrillization behavior of polytetrafluoroethylene (PTFE) binder is controlled by adjusting the processing temperature during the fibrillization process, which enables uniform distribution of PTFE binder and carbon black (CB). Second, pore size/distribution and conducting network are engineered by multi‐dimensional conducting agents, enhancing Li‐ions and electrons transport in the electrode. Finally, the structural integrity of LiNi0.80Co0.15Al0.05O2 (NCA) particles is improved without fractures, which enables uniform pore distribution in the electrode by controlling the calendering step. The prepared 10 mAh cm−2 dry electrode with homogeneous microstructure shows reduced Rion and Rct due to short diffusion lengths, which improves electrochemical performances in LIBs with a high volumetric energy density of ≈710 Wh L−1.

Limitations of Polyacrylic Acid Binders When Employed in Thick LNMO Li-ion Battery Electrodes

Polyacrylic acid (PAA) is here studied as a binder material for LiNi0.5Mn1.5O4 (LNMO) cathodes for lithium-ion batteries. When the LNMO electrodes are fabricated with an active mass loading of ∼10 mg cm−2 (∼1.5 mA h cm−2), poor discharge capacity and short cycle life is obtained in full-cells with graphite electrodes. The electrochemical results with PAA are compared with a commonly used water-based binder, sodium carboxymethyl cellulose (CMC), which shows better electrochemical performance. The main cause for these problems in PAA based cells is identified to be the high internal resistance in the initial cycles, caused by factors such as contact resistance, inhomogeneous binder distribution and poor electrolyte wetting of the active material.

Advanced multilayer model electrode for binder distribution within composite electrodes of lithium batteries

The loading levels of composite electrodes are increasing continuously to satisfy the energy density requirements of lithium-ion batteries (LIBs) in electric vehicles (EVs). Furthermore, a faster coating and drying process in the mass-production line yields a nonuniform binder distribution. Thus, it is necessary to understand its distribution within the composite electrode and control it for a better and more reliable electrochemical performance. Therefore, we propose the utilization of an advanced multilayer electrode model consisting of several electrode layers with different binder contents. Using these controlled electrode models, the adhesive strength within each layer was examined using a surface and interfacial cutting analysis system (SAICAS). This was followed by a composition analysis using EDX on each surface. Subsequently, the electronic conductivities of the model electrodes were measured using an electrode resistance meter to determine the bulk and interfacial electrode resistances. Furthermore, the electrochemical properties of each model electrode were evaluated to correlate their relationships and design the optimum binder distribution. Thus, this multilayer model provides a highly effective platform for determining the optimum binder distribution in highly loaded composite electrodes for high-energy–density and long-lasting LIBs.

Failure Modes of Flexible LiCoO2 Cathodes Incorporating Polyvinylidene Fluoride Binders with Different Molecular Weights.

Understanding the mechanical failure modes of lithium-ion battery [Li-ion batteries (LIBs)] electrodes is exceptionally important for enabling high specific energy and flexible LIB technologies. In this work, the failure modes of lithium cobalt oxide (LCO) cathodes under repeated bending and the role of the polymer binder in improving the mechanical durability of the LCO electrodes for use in flexible LIBs are investigated. Mechanical and electrochemical evaluations of LCO electrodes (areal capacity of ≥2.5 mA h cm-2) employing poly(vinylidene fluoride) (PVDF) binder were carried out, followed by extensive optical and electron microscopies. We find that the molecular weight (MW) of the PVDF significantly influenced the surface and bulk microstructure of the LCO electrodes, particularly the distribution of carbon additive and binder, which plays a crucial role in affecting the mechanical and electrochemical properties of the electrodes. Multiple mechanical failure modes (e.g., surface scratches and microcracks) observed in the LCO electrodes subjected to repeated bending originated from the use of low MW PVDF; these failure modes were successfully mitigated by using a high MW PVDF. Remarkably, the optimized flexible LCO electrode incorporating high MW PVDF showed comparable discharge capacity retention during galvanostatic cycling after repeated bending (7000 cycles at 50 mm bending diameter) to electrodes not subjected to the repeated bending. This study highlights the importance of carrying out a comprehensive investigation of the failure mechanisms in flexible electrodes, which identified the pivotal role of the PVDF MW in the electrode microstructure and its effects on the electrode resilience to failure during repeated bending.

Using multi-threshold non-local means joint distribution method to analysis the spatial distribution patterns of binder and fibers in gas diffusion layers of fuel cells

The gas diffusion layer (GDL) in fuel cell plays a crucial role in mass transfer, electron conduction and structural support. The distribution of binder and hydrophobic agent directly affects the mass transfer and conductivity of the fuel cell. In this study, a multi-threshold segmentation-based image processing method was used to distinguish between pores, fibers, and binder in the GDL. The relationship between binder distribution and fiber density as well as the thickness of the binder layer was investigated. Specifically, the study first utilized a joint distribution map based on grayscale values and non-local means values, with global Rényi entropy as the optimization objective. A bee algorithm was employed to search for the global optimal point, achieving threshold segmentation of micro-scale images. Subsequently, by comparing the results of element segmentation using one-dimensional and multi-dimensional segmentation methods, a three-dimensional convolutional kernel of different sizes was used to obtain the distance from each point in the structure to the edge, effectively separating adherent fibers. Finally, convolutional methods were used to analyze the relationship between the thickness of the binder layer and fiber density. It was found that there is a positive correlation between thickness and spatial density of fibers when the fiber layer is thin. These research findings provide theoretical basis for the content and distribution of binder in the basal layer process of GDL fabrication, and contribute to a more accurate description of the microstructure and properties of actual materials, enhancing the understanding of the preparation process and microstructure properties of GDL in fuel cells. The image processing method utilized in this study enables the computation of crucial parameters within the GDLs' multi-component segmentation algorithm, utilizing a limited sample size. Additionally, it offers valuable insights into the spatial distribution characteristics of fibers and the presence of thin matrix layers. These findings highlight the potential of this method for future applications in the realm of realistic three-dimensional structural reconstructions, thus holding promising prospects for further advancements in this field.