Battery Slurries Research Articles

Structural Analysis of Cathode Slurry Under Flow Using New Probe for Rheo-Impedance Measurements

A battery slurry will experience a variety of shear stresses as it goes through the manufacturing process. The full characterization of a slurry for quality control is challenging due to the complex and changing relationship between active material particles, binder, and the carbon black conductive network as a function of these different shear environments. Rheology is a powerful tool for measuring suspension stability and the viscosity at different shear stresses. However, it cannot characterize the structure of the carbon black conductive network because the rheological properties are dominated by the larger active material particles. Poor distribution or aggregation of the carbon black additive will create an electrode with higher electrical resistance, resulting in more heat generation and a shorter cycle life. Electrochemical impedance spectroscopy is an information dense technique that probes the sample using an alternating current or potential at a range of frequencies. Amongst its many applications, EIS can discriminate between simultaneous events that take place over different time scales, such as the measurement of conductivity within a solid electrode vs the ionic conductivity of the electrolyte. Combining these techniques into a simultaneous measurement will characterize the rheological behavior and the structure of the carbon black conductive network under flow and temperature conditions that are relevant for a manufacturing environment. A novel probe for the simultaneous measurement of rheological properties and electrochemical impedance spectroscopy (Rheo-EIS) is herein presented. A structural analysis of Li-ion battery cathode slurries and carbon paste is used to demonstrate the technique.

Optimization of mixing speed and time to disperse the composite conductive agent composed of carbon black and graphene in lithium-ion battery slurry

This paper proposed an optimal approach to disperse the composite conductive agent which is composed of carbon black (CB) and graphene (Gr) within lithium-ion battery (LIB) slurry with different mixing speeds and mixing times. The internal structures of LIB slurry are characterized by Electrochemical Impedance Spectroscopy, Scanning Electron Microscopy, and Raman experiment. Initially, a composite conductive solution is prepared by mixing the composite conductive agent with NMP solvent under the conditions of five different mixing speeds n1 (n1 = 1000, 1100, 1200, 1300, 1400 rpm) in the case of mixing time t1 = 10 min. Subsequently, LIB slurry is prepared by blending the composite conductive solution, LiCoO2 and PVDF-NMP solution under the conditions of five different mixing speeds n2 (n2 = 1000 ± 280, 1100 ± 280, 1200 ± 280, 1300 ± 280, 1400 ± 280 rpm) in the case of mixing time t2 = 6 min. By analyzing the internal structure of different LIB slurries, it shows that in the case of n1 = n2 = 1200 rpm, a conductive network structure is well formed within LIB slurry. Additionally, in order to determine the optimal time to prepare the composite conductive solution for LIB slurry, nine different t1 (t1 = 0, 10, 20, 30, 40, 50, 60, 70, 80 min) are selected. By analyzing the internal structure of different LIB slurries, a well-formed conductive network structure and a uniformly distributed composite conductive agent are deduced in LIB slurry when t1 = 50 min. Therefore, it can be concluded that the composite conductive agent composed of CB and Gr is able to be uniformly dispersed in LIB slurry by establishing a well-formed conductive network structure under the optimal mixing speed n1 = n2 = 1200 rpm and the optimal mixing time t1 = 50 min, t2 = 6 min. This kind of the internal structure has the potential to be used to further analyze the dispersion characterizations of LIB slurry under different composite conductive agent and CB/Gr ratios with the aim of improving the final performance of LIB.

Continuous Anode Slurry Production in Twin-Screw Extruders: Effects of the Process Setup on the Dispersion

Screw design in the extrusion process has an important effect on the distribution of material through the extruder, resulting in partially filled sections in the processing zone. Accordingly, the local accumulation of material in the extruder leads to variations in material strain conditions and also influences the local residence time of the material in a given screw section. This work evaluates particle dispersion in anode slurry considering three different screw arrangements. The particle size distribution is considered as a quality parameter representing the microstructure of the battery slurry components and their distribution. Numerical simulation of the material flow behavior through a laboratory extruder was performed to investigate the filling ratios and resulting shear rates for different screw designs and process conditions. The importance of process parameters and a suitable screw configuration to achieve specific particle sizes in battery slurry is discussed.

Impact of Screw Geometry and Solids Content on the Properties of Continuously Produced Si Anodes

Within the realm of lithium‐ion batteries, there is a growing emphasis on achieving high energy density and environmentally friendly production at a low cost. To address these demands, the battery slurries in this study incorporate the high‐energy anode material silicon. They are systematically produced through continuous extrusion, aiming to realize cost reductions by significantly reducing the overall process time. In this study, it is demonstrated that the choice of screw configuration and solids content during kneading influences the specific energy input and the stress intensity during processing significantly. The stress intensity, represented here by the specific torque, has a great influence on the slurry properties as well as the electrochemical performance of the battery. An increased stress intensity leads to an increase in adhesive strength and ionic resistance. In the results, it is indicated that carbon black decomposition increases significantly, but when a critical specific stress intensity in form of the specific torque is reached, delamination and fracture of the graphite particles occur, leading to a loss of lithium‐ion storage capacity, favoring lithium plating and severely degrading both capacity by up to 40% at 1C and long‐term performance by up to 10% after 50 cycles.

Fluid–Solid Mixing Transfer Mechanism and Flow Patterns of the Double-Layered Impeller Stirring Tank by the CFD-DEM Method

The optimization design of the double-layered material tank is essential to improve the material mixing efficiency and quality in chemical engineering and lithium battery production. The draft tube structure and double-layered impellers affect the flow patterns of the fluid–solid transfer process, and its flow pattern recognition faces significant challenges. This paper presents a fluid–solid mixing transfer modeling method using the CFD-DEM coupling solution method to analyze flow pattern evolution regularities. A porous-based interphase coupling technology solved the interphase force and could be used to acquire accurate particle motion trajectories. The effect mechanism of fluid–solid transfer courses in the double-layered mixing tank with a draft tube can be obtained by analyzing key features, including velocity distribution, circulation flows, power, and particle characteristics. The research results illustrate that the draft tube structure creates two major circulations in the mixing transfer process and changes particle and vortex flow patterns. The circulating motion of the double-layered impellers strengthens the overall fluid circulation, enhances the overall mixing efficiency of the fluid medium, and reduces particle deposition. Numerical results can offer technical guidance for the chemical extraction course and lithium battery slurry mixing.

Impact of Mixing Shear on Polymer Binder Molecular Weight and Battery Electrode Reproducibility

The viscosity and microstructure of Li-ion battery slurries and the performance of the resulting electrodes have been shown to depend on the mixing protocol. This work applies rheology to understand the impact of shear during mixing and polymer molecular weight on slurry microstructure and electrode performance. Mixing protocols of different shear intensity are applied to slurries of LiNi0.33Mn0.33Co0.33O2 (NMC), carbon black (CB), and polyvinyldiene difluoride (PVDF) in N-methyl-2-pyrrolidinone (NMP), using both high-molecular-weight (HMW) and low-molecular-weight (LMW) PVDF. Slurries of both polymers are observed to form colloidal gels under high-shear mixing, even though unfavorable interactions between high molecular weight PVDF and CB should prevent this microstructure from forming. Theoretical analysis and experimental results show that increasing shear rate during the polymer and particle mixing steps causes polymer scission to decrease the polymer molecular weight and allow colloidal gelation. In general, electrodes made from high molecular weight PVDF generally show increased rate capability. However, high shear rates lead to increased cell variability, possibly due to the heterogeneities introduced by polymer scission.

Synthesis of copolymers of N‐vinylpyrrolidone and 2‐ethylhexyl acrylate by DL‐methionine‐mediated reversible deactivation radical polymerization and their dispersion behavior in preparation of LiFePO4 battery positive slurry with high solid content

AbstractDispersants play a significant role in the formulation of positive battery slurry. Adding a small amount of dispersant can effectively reduce the viscosity of the slurry, which is beneficial for the production of positive batteries. A series of copolymers of N‐vinylpyrrolidone (NVP) and 2‐ethylhexyl acrylate (2‐EHA) with different molar ratios of NVP to 2‐EHA, different polymer molecular weights and different polymer structures are synthesized by dl‐methionine‐mediated reversible deactivation radical polymerization. The ability of these copolymers to disperse LiFePO4 battery positive slurry with a high solid content (57.08%) as dispersants has been evaluated. Research shows that when the ratio of NVP to 2‐EHA is 20 and the polymer molecular weight is 6000, poly(N‐vinylpyrrolidone‐ran‐2‐ethylhexyl acrylate) (NVP‐ran‐2‐EHA) exhibits the strongest dispersing ability to the slurry. This polymer can reduce the viscosity of the slurry by 43.925% and has the longest stabilization time of 3 h, which is better than poly(N‐vinylpyrrolidone) (PVP) and poly(N‐vinylpyrrolidone)‐block‐poly(2‐ethylhexyl acrylate) (PVP‐b‐PEHA) with the same molecular weight.

Flow modeling for conveying sections in a co-rotating twin-screw extruder based on energy dissipation rate for continuous mixing of lithium-ion battery slurries

In the present work, we propose a new modeling scheme for flows of non-Newtonian fluids in the fully filled narrow-pitched conveying section in a co-rotating twin screw extruder, emphasizing the application to viscoplastic lithium-ion battery slurries for electrode manufacturing. A predictive tool for the relationship between flow rate, screw speed, and pressure build-up was presented for flows with a general class of inelastic non-Newtonian fluids. By introducing the effective viscosity and effective shear rate based on the energy dissipation rate, we showed that the conventional relationship between throughput number and pressure number for various non-Newtonian fluids collapse into a single master curve of a Newtonian fluid, from which the predictive relationship between flow rate, screw speed, and pressure build-up was established. The method was validated numerically with power-law fluids, a Carreau fluid, and a Herschel-Bulkley fluid (anode slurries) for a narrow-pitched conveying element module.

Classification of battery slurry by flow signal processing via echo state network model

Classification of battery slurry by flow signal processing via echo state network model

Process and Drying Behavior Toward Higher Drying Rates of Hard Carbon Anodes for Sodium‐Ion Batteries with Different Particle Sizes: An Experimental Study in Comparison to Graphite for Lithium‐Ion‐Batteries

Sodium‐ion batteries are considered to be one of the most promising postlithium batteries on the verge of commercialization. The electrode processing is expected to be similar to lithium‐ion batteries. However, the producibility and material processing challenges of potential electrode materials for anodes and cathodes are poorly understood. For industrial electrode production, a deep understanding of the processing of electrode materials with different particle morphologies is of great importance. In particular, the correlation between the process conditions and the electrode properties needs to be investigated further to understand the complex interactions between the battery slurry materials, the binder system, the drying process, and the microstructure formation. One promising anode material is hard carbon. The water‐based processing of hard carbon slurries presented in this article shows that the drying behavior is strongly interconnected with the particle size and particle interactions in the drying electrode. This study shows that all the hard carbons investigated do not exhibit binder migration at moderate drying rates. Even at very high drying rates (9 g m−2 s−1, 12 s drying time), an increase in adhesion force of up to 39% is observed for comparatively smaller particles compared to the adhesion force at lower drying rate.

Numerical Investigation of the Local Shear Rate in a Twin‐Screw Extruder for the Continuous Processing of Li‐Ion Battery Electrode Slurries

The mixing step for electrode slurry preparation in the manufacture of batteries is highly relevant because it directly affects the downstream production processes and the performance of the battery cells. In this work, a study of the flow behavior and material strain in a twin‐screw extruder is carried out to analyze its efficiency for continuous battery slurry processing. Here, individual elements of the extruder screw are simulated using the smoothed particle hydrodynamics method. Based on the resulting flow profiles, a dimensionless analysis is used to validate the calculations. Hence, the local shear rate and pressure profiles are evaluated for different screw geometries. The effects of the screw design and process setup are discussed, to accordingly improve the mixing process.

The Carbon Black Dispersion Index DICB: A Novel Approach Describing the Dispersion Progress of Carbon Black Containing Battery Slurries

The targeted adjustment of carbon black (CB) particle size in electrode slurries is a key step in battery production. Based on the energy input and dispersion device, the resulting particle structure of CB differs significantly. Most frequently, especially in more recent publications, the median particle size was used to describe changes during dispersion. However, this value does not contain enough information to describe the dispersion progress of bimodally distributed particles sufficiently. In this short communication, a novel approach describing the dispersion progress of CB containing slurries is introduced. This method was developed utilizing the hierarchical structure and fragmentation behavior of CB. The Carbon Black Dispersion Index DICB allows quick and easy assessment of the dispersion progress by isolating the CB aggregates of the bimodal distribution. This value offers major benefits with regards to quality control and production monitoring.

Clarification of the dispersion mechanism of three typical chemical dispersants in lithium-ion battery (LIB) slurry

This paper mainly clarified the dispersion mechanism of three typical chemical dispersants which are polyethylene glycol octylphenyl ether (Triton X-100, T-100), polyethylene pyrrolidone (PVP) and carboxymethyl cellulose (CMC) within lithium-ion battery (LIB) slurry. Initially, the optimum amounts of T-100, PVP and CMC are selected from 0%, 0.5%, 1.5% and 2.5% by evaluating the impedance of LIB slurry in the case of adding each typical chemical dispersant with EIS method. Moreover, the impedance spectrum of three different slurry samples which are PVDF-NMP solution, LiCoO2 slurry and Carbon Black (CB) slurry with the optimum amount of each dispersant are also investigated. After using SEM and C element distribution images of LIB slurry to verify the correctness of the dispersion mechanism of each dispersant, it is concluded that the dispersion CMC with its optimum amount 1.5% is the best one to promote the formation of conductive paths and CB-coated LiCoO2 network structure within LIB slurry, which has the considerably potential to improve the performance of LIB.

Multicomponent Comminution within a Stirred Media Mill and Its Application for Processing a Lithium-Ion Battery Slurry

This study presents an approach for targeted comminution of component mixtures within a wet-operated stirred media mill. In the first step, a general understanding of the interactions between individual components on the grinding result with mixtures could be gained with basic experiments and following our former research work. In particular, a protective effect of the coarser particles on the fines could be elucidated. These findings were used to develop a process for the production of a battery slurry containing fine ground silicon particles as well as dispersed carbon black and graphite particles. By a tailored sample preparation applying a combination of particle dissolution and separation, the particle size distributions of carbon black and graphite particles were analyzed separately within the produced battery slurries. Based on the selective particle size analysis, the slurry preparation could be transferred from a complex multistage batch process using a dissolver to a stirred media mill, which was finally operated in a continuous one-passage mode. The prepared slurries were subsequently further processed to silicon-rich anodes using a pilot scale coating and drying plant. Afterward, the produced anodes were electrochemically characterized in full cells. The cell results prove a comparable electrochemical behavior of anode coatings derived from a dissolver- or mill-based slurry production process. Therefore, we could demonstrate that it is possible to integrate the mixing process for the production of multicomponent slurries into the comminution process for the preparation of individual materials upstream. Even with nearly identical starting sizes of their feed materials, the targeted particle size distributions of the single components can be reached, taking into account the different material-dependent particle strengths and sequential addition of single components to the multicomponent comminution process.

Battery Materials Characterization Workflow for Effective Battery Electrode Manufacturing Processes

A lithium-ion battery’s performance characteristics demand the highest performing materials in the anode, cathode, electrolyte, and separator. Materials characterization is an essential set of analytical techniques for ensuring optimal battery performance during the stages of material selection, development, and manufacturing. Key material characterization technologies for ensuring that batteries achieve their performance characteristics include thermal analysis, rheology, mechanical analysis and isothermal microcalorimetry. Thermal analysis provides insights into material thermal stability and structure change under different temperature ranges. Rheology provides insights into battery slurry storage, mixing, coating, and drying for more uniform and defect free electrode manufacturing. Mechanical testing provides insights into structure-property relationship such as verifying whether the polymer material in a separator will shut down safely without melting. Isothermal microcalorimetry allows researchers to study the electrochemistry of a working battery cell by enabling direct heat flow measurements that provide insights into battery lifetime. This presentation will focus on the electrode manufacturing with thermal analysis and rheology characterization to highlight how advanced material characterization can help battery researchers, developers, and production specialists develop better analytical material characterization and quality control procedures.

A Review of Dispersion Film Drying Research

Abstract Dispersion drying is an essential step in an enormous number of research and industry fields, including self-assembly, membrane fabrication, printing, battery electrode fabrication, painting, and large-scale solar cell fabrication. The drying process of dispersion directly influences the structure and properties of the resulting dried film. Thus, it is important to investigate the underlying physics of dispersion drying and the effects of different drying parameters. This article reviews modeling studies of coating drying processes, along with corresponding experimental observations. We have divided drying processes into two conceptual stages. In the first drying stage, liquid evaporation, particle sedimentation, and Brownian motion compete and affect the particle distribution during drying and thus in the final film structure. We have included a comprehensive discussion of the influences of drying parameters, such as evaporation rate, particle sizes, and temperature, on the above competition and the resulting film structure. A drying regime map describing where different drying phenomena dominate was formulated based on the literature. We also extended our discussion to the practical applications of battery slurry drying an essential step in conventional battery electrode manufacturing. In the second drying stage, the physics of porous drying and crack formation are reviewed. This review aims to provide a comprehensive understanding of dispersion drying mechanisms and to provide guidance in the design of film products with favorable structures and properties for targeted practical applications.

Mixotrophic denitrification processes in basalt fiber bio-carriers drive effective treatment of low carbon/nitrogen lithium slurry wastewater

Lithium battery slurry wastewater was successfully treatedby using basalt fiber (BF) bio-carriers in a biological contact oxidation reactor. This resulted in a significant reduction of COD (93.3 ± 0.5 %) and total nitrogen (77.4 ± 1.0 %) at 12 h of HRT and dissolved oxygen (DO) of 0–1 mg/L. The modified Stover-Kincannon model indicated that the total nitrogen removal rate was 4.462 kg/m3/d in R-BF while the substrate maximum specific reaction rate (qmax) in the Monod model was 0.323 mg-N/mgVSS/d. A stable internal environment was established within the bio-nest. Metataxonomic analysis revealed the presence of denitrification and decarbonization bacteria, combined heterotrophic nitrification-aerobic denitrification bacteria, nitrite-oxidizing bacteria, and ammonia-oxidizing bacteria. Functional analysis displayed changes related to (aerobic)chemoheterotrophy, nitrogen respiration, nitrate reduction, respiration/denitrification of nitrite, and nitrate in R-BF. The study proposes a novel approach to achieve denitrification for the treatment of lithium slurry wastewater at low C/N conditions.

Modeling Approaches for the Description of the Carbon Black Particle Size in Batch and Continuous Dispersion Processes for Lithium-Ion Battery Slurries

Energy storage is a key technology for alternative power trains like electric and hybrid electric vehicles. Lithium-ion batteries (LIB) are widely used for this purpose due to their high energy density and elaborated developmental state. Also, the increasing usage of electrified transportation leads to ever-increasing demands on LIBs in terms of fast charging ability and power density. The fragmentation of carbon black (CB) aggregates and agglomerates, respectively, has high impact on the resulting microstructure and mechanical integrity as well as conductivity of electrodes and furthermore, the electrochemical performance of LIBs [1]. To achieve optimized cell performances and to reduce the process times or increase throughputs while conserving the slurry quality, a method to predict the CB particle sizes based on simulations and experiments has been developed.This work demonstrates how the dispersion process can be modelled, thus laying the foundation for an optimized microstructure of the electrode right at the beginning of the process chain. For this purpose, a high-intensity batch process in a planetary mixer is investigated and modelled for the description of the CB fragmentation, and the approach is then applied to a continuous twin-screw extruder. Through the use of computational fluid dynamics, theoretical equations and considerations, and experimentally obtained data, the models are parametrized and can be used to predict the result of the dispersion process in form of the CB particle size. The critical values here are the shear rate in the laminar flow and the viscosity of the slurry, which determine the transferred energy onto the particles during the process. By appropriately modelling these characteristic values, it is possible to transfer the models to machines of different types and designs.Furthermore, it is shown how the predicted particle size of CB affects the microstructure of the electrodes. For this purpose, an innovative structural parameter is calculated from mercury intrusion measurements of manufactured electrodes, which expresses the internal porosity of the CB particles, or of the conductive microstructure, respectively. Based on the modelled CB particle size, this parameter can already be used to estimate the developing microstructure of the electrodes depending on the selected process parameters during dispersion. Such an approach is the basis for further work in order to holistically depict and digitalize the entire process chain of the LIB production and its counteracting influences.The experimental process data (power uptake of dispersion machines, viscosities, CB particle sizes), electrode structures, electrode properties (adhesive tensile strengths, spec. resistances) and cell performance data are shown to illustrate the approaches and the value of the created models. All LIB cathodes investigated consist of industrially relevant formulations (> 95 wt% active material NMC622, < 2.5 wt% CB). Reference s : [1] Mayer, J. , Almar, L., Asylbekov, E., Haselrieder, W., Kwade, A., Weber, A. and Nirschl, H., Influence of the Carbon Black Dispersing Process on the Microstructure and Performance of Li‐ion Battery Cathodes, Energy Technol. (2019)

Concentration dependence of yield stress, thixotropy, and viscoelasticity rheological behavior of lithium-ion battery slurry

The rheological properties of electrode slurry are mainly influenced by the concentration, which further affects the Lithium-ion batteries (LIBs) quality and manufacturing processes. In this work, various methods including steady-state shear, creep, rheological model fitting, hysteresis loop, and small amplitude oscillatory shear (SAOS) measurement were employed to investigate the concentration-dependent rheological behaviors of slurry, in particular its yield stress, thixotropy, and viscoelasticity. Results show that the difference in yield stress obtained from varying methods is observed, in which the yield stresses measured by the SAOS test are closer to the steady-state value due to its advantage that non-destructive property at small deformations only causes minimum disturbance. The improvement of slurry concentration enhances the bonding strength between particles, thereby resulting in an increase of yield stress and thixotropy, and a decrease of the time scale of transient behavior during the creep process. In oscillatory shear measurement, both storage and loss modulus are concentration-dependent, while yielding and strain stiffening corresponding to critical strains exhibit concentration-independent. In addition, the increase in concentration leads to a more pronounced strain stiffening behavior and a lower characteristic frequency as well as a longer relaxation time. Understanding the relationship between concentration and rheological behaviors will be helpful for material design, preparation, and production in different stages.

Controlling Drying Stress and Mechanical Properties of Battery Electrodes Using a Capillary Force-Induced Suspension System

Capillary suspension processing, which uses a ternary system consisting of solid/fluid/fluid, has recently been proposed as a method for manufacturing Li-ion battery electrodes to enhance the coating performance and the adhesion of the electrodes. In this paper, we apply the concept of capillary suspension to the battery slurry and control the drying characteristics and mechanical stability. The network structure formed inside the slurry using the capillary suspension processing can be confirmed by the rheological properties and cryo-scanning electron microcopy (cryo-SEM) images. It is found that the pendular bridges of the secondary fluid restrict the rearrangement of particles during drying and thus lower the residual stress of the electrodes as evidenced by drying stress and Fourier transform infrared (FT-IR). Due to the reduction in residual stress and porous structural features, the capillary suspension-based electrodes are more sustainable to severe deformation such as repetitive bending. This paper proposes a method that can dramatically enhance the mechanical stability of electrodes that could possibly be applied to next-generation battery technology such as flexible or thick electrodes.