Flow Behavior Of Slurries Research Articles

Particle Dynamics Study on Influencing Factors of Ice Slurry Flow Characteristics in District Cooling Systems

In district cooling systems, substituting the conventional cooling medium with ice slurry represents an ideal approach to achieve economical operation. During pipeline transportation, ice slurry exhibits heterogeneous flow characteristics distinct from those of pure fluids. Consequently, investigating the flow field characteristics of non-homogeneous ice slurry, quantitatively analyzing the rheological variations and flow resistance laws due to the uneven distribution of ice particles, and standardizing the comprehension and depiction of flow patterns within ice slurry pipes hold significant theoretical importance and practical value. This study analyzes the heterogeneous isothermal flow characteristics of ice slurry in a straight pipe by employing particle dynamics and the Euler–Euler dual-fluid model. Taking into account the impact of ice particles’ non-uniform distribution on the rheological properties of ice slurry, a particle concentration diffusion equation is incorporated to develop an isothermal flow resistance model for ice slurry. The flow behavior of ice slurry with initial average ice particle fractions (IPFs) ranging from 0% to 20% in DN20 horizontal straight and elbow pipes is examined. The findings reveal that the degree of heterogeneous flow in ice slurry is inversely proportional to the initial velocity and directly proportional to the initial concentration of ice particles. When the flow velocity is close to 0.5 m/s, the flow resistance of ice particles exhibits a linear positive correlation with changes in flow velocity, whereas the flow resistance of the fluid-carrying phase displays a linear negative correlation. As the flow rate increases to 1 m/s, the contribution of each phase to the total flow resistance becomes independent of the initial velocity parameter. Additionally, the drag fraction of the ice particle phase is positively associated with the initial concentration of ice particles. Furthermore, the phenomenon of “secondary flow” arises when ice slurry flows through an elbow, enhancing the mixing of ice particles with the carrier fluid. The extent of this mixing intensifies with a decrease in the turning radius and an increase in the initial velocity.

Study on effects of anti-freeze protein and polyvinyl alcohol on the production and flow behavior of ice slurry

Ice slurry is a promising functional fluid with high thermal energy density and high heat transfer rate. However, the agglomeration of the ice particles in flowing ice slurry can cause blocking of tubes. In this study, anti-freeze protein (AFP) and polyvinyl alcohol (PVA) were selected as additives to prevent the agglomeration of ice particles in ice slurry. Ice slurry was generated using the release of the supercooled state of 3 mass% NaCl solution containing the additives. The size of the ice particles in the ice slurry was observed, and the average area of the ice particles was evaluated to reveal the effects of the additives on the ice particle size. Furthermore, the flow behavior of the ice slurry in a tube was observed, and the effects of the additives on the flow behavior and prevention of the agglomeration of the ice particles were evaluated experimentally. It was found that the average area decreased with increasing concentration of the additives, and the effect of AFP on the average area was particularly significant. In the case of without the additives, the ice particles flowed in the tube while the ice particles agglomerated. On the other hand, the ice particles in the ice slurry with the additives flowed without agglomeration in the tube, especially in the case of AFP addition. It was found that AFP prevented the agglomeration of the ice particles in the ice slurry flow. Moreover, the ice slurries with AFP show the significant tendency for pseudo-plastic fluid.

Direct observation of carbon slurry flow behavior and its effect on electrochemical performance in a microfluidic electrochemical flow capacitor.

Carbon slurries have been used as "flowable electrodes" in various electrochemical systems, and the slurry flow characteristics play an important role in the system electrochemical performance. For example, in an electrochemical flow capacitor (EFC), activated carbon particles must pass electrical charge from a stationary electrode to surrounding particles via particle-electrode and particle-particle interactions to store energy in the electric double layer. So far, particle behaviors under a continuous flow condition have not been observed due to the slurry's opacity, and studies of the device's performance thus have been mainly on a bulk level. To understand the relation between the hydrodynamic behavior and the electrochemical performance of carbon slurries, we have constructed a microfluidic EFC (μ-EFC) using transparent materials. The μ-EFC allows for direct observation of particle interactions in flowing carbon slurries using high-speed camera recording, and concurrent measurements of the electrochemical performance via chronoamperometry. The results indicate an interesting dependence of the particle cluster interaction on the flowrate, and its effect on the slurry charging/discharging behavior. It is found that an optimal flowrate could exist for better electrochemical performance.

Numerical investigation of slurry property effect on grouting and blocking of flowing water in rock fractures

AbstractIn order to investigate the slurry flow behavior, our newly proposed numerical method is applied to simulate the fracture grouting with flowing water condition. First, by numerical validation and experiment comparison, the advantages of this method in computation efficiency and accuracy are shown. Second, the initial velocity of water and slurry properties at different levels are selected as the influencing factors, the water reduction effect, grouting pressure, and slurry deposition behavior in different cases are investigated, and the variation characteristics of flow field and slurry outflow are analyzed. The simulation results show that within the range of slurry properties and flow velocity given in this paper, cement slurry cannot seal the water inflow. Instead, quick setting slurry with different material ratios can effectively seal the fracture. The sealing efficiency is more sensitive to the initial flow rate than the slurry property. When the groundwater flow rate is low, the effect of slurry proportion on sealing can be ignored. Meanwhile, slurry properties have more influence on the final grouting pressure. There is an obvious surge in grouting pressure after sealing, which can be used as a criterion for fracture sealing.

Simulation study of micro-proppant carrying capacity of supercritical CO2 (Sc-CO2) in secondary fractures of shale gas reservoirs

Micro-proppants with stronger portability have more potential to migrate to the massive micro-sized secondary fractures (SFs) or natural fractures activated by supercritical CO2 (Sc-CO2) fracturing in shale gas reservoirs. However, the transportation behaviour of micro-proppants in massive SFs has been scarcely studied to date. In this study, we report the simulation of micro-proppant migration across a fracture intersection during Sc-CO2 fracturing based on a combination of computational fluid dynamics and the discrete element method. A straight fracture intersection model was first validated against experimental data from an earlier study. Next, the influential factors, including fluid viscosity, cross angle, proppant diameter, fluid velocity and the ratio of proppant diameter to SF, were examined in the transportation behaviour of micro-proppants in Sc-CO2 fracturing. The results show that the poor proppant distribution in SFs is dominated by the ultralow viscosity of Sc-CO2, but the decrease of proppant diameter to 25 μm presents slurry flow behaviour, resulting in a migration distance around 8 times longer than that of 200 μm and much stronger proppant-carrying capacity into SFs. The transportation behaviour of micro-proppants into SFs depends on the suspended proppants concentration and the rolling proppants from the proppant embankment in the primary fracture (PF), determined by the combined effects of different factors. Fast fluid velocity of 0.2 m/s increases the priority of the proppant embankment formation in SFs. Cross angles greater than 45° limit the suspended proppants in SF, and the proppant embankment in the SF dominantly depends on rolling proppants from PF. Greater SF aperture facilitates proppants transportation into the SF due to the reduced bridging effect, but not into the PF. The key findings are optimized proppant-carrying capacity into SFs and improved stimulated volume during Sc-CO2 fracturing in shale reservoirs.

Flow behavior of impounded fly ash slurries using flow test

Coal ash is one of the largest industrial waste products generated in the United States. Since 1967, several failures in ash impoundments have been reported, releasing millions of gallons of impounded fly ash slurry and resulting in loss of life and mass environmental destruction. Several studies have been carried out to understand the flow behavior of fly ash slurries. However, several questions remain unanswered regarding the flow behavior of fly ash slurries after containment loss. In this study, a new flow test, a miniature version of a cylindrical slump test, was developed to investigate flow behavior of six different fly ash slurries. The flow behavior of these slurries was evaluated based on the yield stress derived from the flow test results. The results showed that some fly ash slurries flowed at higher solids content (>60 %), while others flowed at lower solids content (<50 %) and stopped flowing at higher solid content. Furthermore, some slurries did not flow at all. It was found that the chemical compositions of fly ash, the state of hydration (hydrated or non-hydrated), original solids content when received, and initial solids content of fly ash slurries at the start of the flow test played a major role in the flow behavior of fly ash slurries. The interactions between these factors were complex, and it was difficult to identify the effect of a single factor. Most of the fly ash slurries showed shear flow, and some slurries at high solids content showed elongational flow. The fly ash slurries with shear flow had larger flow areas after containment loss. The addition of an anionic polyacrylamide significantly increased the yield stress by 2.8 – 3.5 times and decreased the flow of fly ash slurries.

Experimental Investigation on Flow Behavior of Paste Slurry Transported by Gravity in Vertical Pipes

In order to dispose of large quantities of mineral tailings, paste backfill is proposed and widely adopted. Paste backfill, which has high concentration and yield stress and behaves as a non-Newtonian fluid, is prepared at the surface plant and then transported underground. Vertical pipelines are more likely to suffer various failures, such as pipe breaks, wear and plugging, during the transport process. Few present studies focus on the flow behavior of paste slurry flowing in vertical pipes. In this work, two L-shaped pipeline systems with internal diameters (ID) of 40 mm and 65 mm with electrical resistance tomography (ERT) were manufactured to visualize flow regimes and measure the axial velocity and pipe pressure of slurry flowing in the upper and lower zones of vertical pipes. Flow regimes were extracted from ERT-reconstructed images stacked by time-series. Based on this, four typical flow regimes were summarized, and the characteristics of velocity and pressure change with vertical pipe depth were discussed.

Analysis on flow resistance of two-phase ice slurry in pulsating flow

The pulsating flow plays a potential role in improving the heat transfer performance of ice slurry. However, the flow resistance characteristics of ice slurry in pulsating flow have not been fully understood. Therefore, the pulsating flow behavior of ice slurry is numerically investigated using the Eulerian-Eulerian multiphase model in the present study. The results showed that there is a phase lag between face-averaged velocity and pressure drop of ice slurry under pulsating flow, which changes from 0 to π/2. The phase lag increases with the increase of pulsating frequency, inlet ice volume fraction and pipe diameter. The instantaneous frictional resistance coefficient of ice slurry can be divided into two stages including acceleration and deceleration, which is larger than that at steady state in accelerating process and smaller than that at steady state in decelerating process. The cycle-averaged frictional resistance coefficient at low Reynolds number is obviously greater than that at steady state, while it is closer to the steady-state value at high Reynolds number. And the cycle-averaged frictional resistance coefficient increases with increasing the pulsating velocity amplitude, dimensionless frequency and inlet ice volume fraction. The pipe diameter has a significant influence on the cycle-averaged frictional resistance coefficient at low Reynolds number. In addition, the correlation is formed from the numerical results to predict the cycle-averaged frictional resistance coefficient of ice slurry.

Experimental and Mechanistic Characterizations of Oil-Based Cement Slurry Flow Behavior Through Fractures in a Carbonate Reservoir

Abstract In this paper, techniques have been developed to experimentally and mechanistically describe the oil-based cement slurry (OBCS) flow through fractures in carbonate reservoirs when it is co-injected with a pad fluid. Experimentally, a three-dimensional (3D) physical model is used to simulate flow behavior within fractures in carbonate rocks by using the ultra-fine cement and class G cement with or without pad fluids. The injection pressures of an OBCS flow are measured and recorded as a function of time during the experiments at a constant flowrate, while effects of fracture width (i.e., 0.5 mm and 1.0 mm) and cement type (i.e., the class G cement and the ultra-fine cement) on injection pressure are examined and analyzed. Theoretically, the Navier–Stokes (NS) equations are modified and integrated to obtain the explicit velocity equations of visco-plastic materials in a planar fracture, and to further quantify the injection pressure of the slurry flow as a function of viscosity, flowing distance of the injected slurry, fracture width, and flowrate. It is found from the experimental measurements that the fracture width imposes a much larger impact on injection pressure along the fracture than other parameters. Once slurry is made in contact with water, its injection pressure not only increases rapidly with one or two orders of magnitude or even larger but also is changed from its linear to exponential relationship with time after a certain time. During the linear stage, the injection pressure of ultra-fine cement is smaller than that of the class G cement, while an opposite pattern is yielded during the exponential stage, i.e., the exponent of the injection pressure formula pertaining to the ultra-fine cement is found to be about 1.5 times larger than that of the class G cement. By incorporating the experimentally measured patterns of the slurry distribution within the fracture model, the newly developed mechanistic model has been validated by reproducing the experimental pressure measurements, allowing us to perform reliable characterization of the OBCS flow behavior in a fracture and then to efficiently and accurately predict and optimize its water-plugging performance.

Experimental analysis of water and slurry flows in gravity-driven helical mineral separators

This paper aims to provide essential information of the water and slurry flow behaviour in a popular full-scale mineral separation spiral. Besides critical measurements of the free surfaces, the wall roughness and wall contact angle, novel measurements and assessment of the commonly encountered ‘bubble line’ are provided herein. The free surface shapes of three flows: water-only, chromite slurry and magnetite slurry are compared for the first time, which highlights operational spiral phenomena. The research provides insight into the mechanics behind the ‘wetting-in’ process by showing that this process affects the wall contact angle more than the surface roughness. The most representative roughness height of the spiral trough was found to be 138.4 μm and the wall contact angle of the spiral surface was 88.14°, measured in the water phase. The experiments showed that the free surface shape and the position and width of the bubble line in a water-only flow reached a steady state after 1.25 spiral turns. The results and findings are applicable to spirals of other makes and models and can validate future spiral fluid flow simulations.

Effect of metal oxide particles on the flow and forced convective heat transfer behaviour of microencapsulated PCM slurry

ZnO, nano ZnO and nano Al2O3 were mixed with microencapsulated phase change material slurry (MPCS) for improving the heat transfer performance of slurries in this paper. The thermal and rheological properties of MPCS were measured using DSC, thermal conductivity meter and rheometer. The results show that the thermal conductivity of 5 wt% MPCS with 1 wt% ZnO, nano ZnO and nano Al2O3 was 17.9 %, 19.4 % and 23.5 % higher than that of 5 wt% MPCS, respectively. The forced convection heat transfer experiment of slurries was carried out in a loop system with various heat flux and flow conditions. The influences of heat flux, flow rate and metal oxide particles on the flow and heat transfer behaviour of slurries were investigated. The results show that the heat transfer was significantly enhanced for all slurries with metal oxide particles under three flow conditions. Compared with water, the local heat transfer coefficient (hx) of MPCSs with 1 wt% ZnO, nano ZnO and nano Al2O3 increased by 6.5 %, 9.1 % and 12.4 % under laminar flow, 6.6 %, 15.5 % and 14.9 % under transition flow, and 15.7 %, 19.0 % and 21.6 % in turbulent condition, respectively.

Fabrication of a Ceramic Foam Catalyst Using Polymer Foam Scrap via the Replica Technique for Dry Reforming.

Megapores with spherical-like cells connected through windows and high porosities make up catalyst supports in the form of ceramic foams. These characteristics provide significant benefits for catalytic processes that are limited by mass or heat transport. This study focuses on the manufacture of ceramic foam using a polymeric sponge replica process and polymer foams as a template for catalyst supports, which are industrial waste from the packaging sector. To make ceramic foam catalysts, they were dipped in a catalyst solution, followed by a breakdown stage and a sintering process. Experiments focused on determinants that affect the desired characteristics of ceramic foams, such as the types of polymer foams that affect foam morphology, the rheology of catalyst solution that affects catalyst dispersion, and the polymer decomposition rate that affects catalytic performance during dry reforming of the methane process. The cell architectures of polyurethane and polyvinyl alcohol foams are attractive for catalyst support preparation because they have 98–99% porosity and typical cell sizes of 200 and 50 μm, respectively. The polyurethane performance was superior to the performance of polyvinyl alcohol in terms of higher porosity and better catalytic-solution absorption offering high catalyst active areas. The catalyst prepared from concentrated 10 wt % Ni/Al2O3–MgO (10NAM) slurry had the highest surface area (59.18 m2/g) and the highest metal oxide dispersion (5.65%). These results are relevant to the flow behavior of catalyst slurry which plays a key role in coating the catalyst gel on the polymer template. The thermal decomposition rate used to remove the polymer template from the catalyst structure is proportional to the ceramic foam structure (catalyst support structure). The slow decomposition rate bent and fractured foam-cell struts more than the faster rate. On the other hand, achieving good catalyst dispersion on catalyst supports necessitated a high sintering rate. When sintering was adjusted at a high sintering rate, the metal–particle dispersion was relatively high, around 7.44%, and the surface area of ceramic foam catalysts was 64.61 m2/g. Finally, the catalytic behavior toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions.

Effects of Grain Morphology on Flow Behavior of Semi-Solid Slurries

The flow behavior of semi-solid slurry determines the quality of the castings produced by the semi-solid forming process. Many studies have done to investigate the flow behavior of slurry under different conditions, and results show that the rheological behavior of slurry with dendritic structure is inappropriate for semi-solid forming. In this study, slurries with varying morphologies of grain for the same alloy with the same fraction solid have tested using a partial filling method. The SEED process was employed, and the pouring temperature adjusted to prepare semi-solid slurries with different grain morphologies. The flow pattern, entrapped air during the filling process, and also microstructure of the samples were examined to characterize the macro and micro flow behavior. The results show that a turbulent macro-flow, leading to entrapped air, and severe segregation appeared in the sample using slurry of Tpour ≥ 660 °C . For the slurry of Tpour &lt; 660 °C, none of the three phenomena found in the sample. This investigation further showed that the detriment of dendrite on the semi-solid forming process, and implied that large size dendrite in semi-solid slurry must avoided.

Numerical simulation of hydrate slurry flow and deposit behavior based on openfoam-IATE

With the extension of oil exploitation from offshore to the deep sea, the development and utilization of natural gas hydrate have become one of the hottest energy issues. However, the agglomeration between hydrate particles will lead to severe pipeline hydrate plugging. Therefore, a dynamic model considering phase change about hydrate formation and decomposition as well as aggregation was proposed based on the interface area transportation equation and convection heat transfer equation, and then used to simulate hydrate slurry flow in this study. By integrating with traditional solid-liquid flow models, the aggregation, breakage, nucleation of hydrate particles, and deposits insulation were all considered in CFD software OpenFOAM-4.x. The influences of flow rate and the safe area for hydrate slurry flow were analyzed emphatically. Results show that flushing has a good dissociation effect on hydrate deposits formed by low-concentration slurry. By comparing deposition conditions of different concentrations and flow rates, it can be seen that high-concentration slurry results in a larger slope and thickness of the deposition front, while the flow rate mainly affects the extension of the deposits length. With the increase of the flow rates, the hydrate deposits evolve from belt-like deposits to point-like deposits. In addition, the hydrate deposition morphology function of different working conditions was constructed by the principal component analysis method.

Semi-solid processing of aluminum and magnesium alloys: Status, opportunity, and challenge in China

Owing to its low cost, short process and low energy consumption, semi-solid processing (SSP) of aluminum (Al) and magnesium (Mg) alloys has been considered as a competitive approach to fabricate complicated components with excellent performance. Over the past decade, significant progress has been achieved in deeply understanding the SSP process, the microstructure and performance of the fabricated components in China. This paper starts with a retrospective overview of some common slurry preparation methods, followed by presenting the performance and the underlying mechanisms of SSP fabricated alloys. Then, the mainstream opinions on the microstructure evolution and rheological flow behavior of semi-solid slurry are discussed. Subsequently, the general situation and some recent examples of industrial applications of SSP are presented. Finally, special attention is paid to the unresolved issues and the future directions in SSP of Al and Mg alloys in China.

Rheology of enzyme liquefied corn stover slurries: The effect of solids concentration on yielding and flow behavior.

The measurement of yield stress and shear thinning flow behavior of slurries formed from unpretreated corn stover at solids loadings of 100-300 g/L provides a key metric for the ability to move, pump, and mix this lignocellulosic slurry, particularly since corn stover slurries represent a major potential feedstock for biorefineries. This study compared static yield stress values and flow hysteresis of corn stover slurries of 100, 150, 200, 250, and 300 g/L, after these slurries were formed by adding pellets to a cellulase enzyme solution (Celluclast 1.5L) in a fed-batch manner. A rotational rheometer was used to quantitate relative yield stress and its dependence on processing history at insoluble solids concentrations of 4%-21% (wt/vol). Key findings confirmed previous observations that yield stress increases with solids loadings and reaches ~3000 Pa at 25% (wt/vol) solids concentration compared to ~200 Pa after enzyme liquefaction. While optimization of slurry forming (i.e., liquefaction) conditions remains to be done, metrics for quantifying liquefaction extent are needed. The method for obtaining comparative metrics is demonstrated here and shows that the yield stress, shear thinning and shear thickening flow behaviors of enzyme liquefied corn stover slurries can be analyzed using a wide-gap rheometry setup with relative measuring geometries to mimic the conditions that may exist in a mixing vessel of a bioreactor while applying controlled and precise levels of strain.

Flow correlations and transport behaviour of turbulent slurries in partially filled pipes

Transportation of fluids in partially filled pipes is common to many areas of industry (e.g. sewerage, mining, and nuclear), yet many aspects remain under-developed, particularly for multiphase and non-Newtonian flows. In this paper a simple framework to enable the accurate prediction of the bulk flow behaviour and settling characteristics of slurries in open conduits is developed and validated experimentally. The experiments involve measurements of flow rate, flow depth and the settling regime for two different solids concentrations of two types of non-colloidal suspensions across a broad range of channel slopes, Reynolds numbers, and Froude numbers. A method is presented that can be used to make a priori predictions of critical sedimentation velocities, which can inform future pipeline designs and operations to minimise the environmental and commercial costs of slurry transfers, including reducing the risk of pipe blockages. Only one parameter required for this technique is not related to the measurable physical properties of the pipeline or fluid. However, it is empirically shown to be well represented by a single, dimensionless constant for all fluids and pipelines tested.

Effect of carboxymethyl cellulose on the flow behavior of lithium-ion battery anode slurries and the electrical as well as mechanical properties of corresponding dry layers

We present a holistic view on the role of polymeric binders in waterborne LiB anodes, including preparation and processing of wet slurries as well as microstructure, electrical conductivity and mechanical integrity of dry electrode layers. We focus on carboxymethyl cellulose (CMC), with respect to technical application the influence of soft, nano-particulate styrene–butadiene rubber (SBR) as secondary binder is also addressed. We discuss the influence of CMC concentration, molecular weight (Mw) and degree of substitution (DS) on flow behavior of anode slurries. Rheological data are not only relevant for processing, here we use them to characterize the adsorption of CMC on active material particles and dispersion of these particles in the slurry at technically relevant concentrations. The fraction of CMC adsorbed onto graphite particles increases with increasing Mw and decreasing DS. Electrical conductivity increases with Mw, i.e. with decreasing free polymer deteriorating conductive carbon black pathways. CMC does not contribute to the adhesion of electrode layers, irrespective of Mw or DS, technically feasible adhesion is inferred by SBR. Cohesive strength of anode layers, determined here for the first time under well-defined mechanical load, increases with increasing Mw and decreasing DS, i.e. with increasing fraction of adsorbed CMC and corresponding improved particle dispersion. Strong cohesion and high electrical conductivity are correlated to an alignment of graphite particles as revealed by electron microscopy, presumably enabled by higher particle mobility in well-dispersed slurries. Accordingly, targeted choice of CMC is a valuable means to control processing, electrical conductivity and mechanical strength of LiB electrodes.

Numerical simulation and comparative analysis of pressure drop estimation in horizontal and vertical slurry pipeline

Transportation of solids with water as a carrier in the form of slurry through long length pipelines is widely used by many industries and power plants. The transportation of slurry through vertical pipeline is a challenging task and require modification to overcome the pressure loss and power consumption requirements. In this perspective, numerical simulation of three-dimensional horizontal slurry pipeline (HSPL) and vertical slurry pipeline (VSPL) carrying glass beads solid particulates of spherical diameter 440 µm and density 2,470 kg/m3 is carried out. The 3D computational model for horizontal and vertical slurry pipeline is developed for a pipe of 0.0549 m diameter and analyzed in available commercial software ANSYS Fluent 16. The simulation is conducted by using Eulerian multiphase model with RNG k-ɛ turbulence closure at solid concentration range 10 – 20% (by volume) for mean flow velocities ranging from 1-4 ms-1. It is found that the pressure drop rises for both HSPL and VSPL with escalation in mean flow velocity and solid concentration. The predicted pressure drop in VSPL is found to follow the same pattern as with HSPL but higher in magnitude for all chosen velocity and solid concentration range. The obtained results of predicted pressure drop in HSPL are validated with the available experimental data in the literature. A parametric study is conducted with the aim of visualizing and understanding the slurry flow behavior in HSPL and VSPL. Finally, the results of solid concentration contour, velocity contour, solid concentration profiles, velocity profiles and pressure drop are predicted for both the slurry pipelines.

Effect of Polymeric Binders on Dispersion of Active Particles in Aqueous LiFePO4-Based Cathode Slurries as well as on Mechanical and Electrical Properties of Corresponding Dry Layers.

We investigated the effect of carboxymethyl cellulose (CMC) and the particulate fluorine/acrylate hybrid polymer (FAHP) on the flow behavior of LiFePO4-based cathode slurries as well as on electrical and mechanical properties of the corresponding dry layers. CMC dissolves in water and partly adsorbs on the active particles. Thus, it has a strong impact on particle dispersion and a critical CMC concentration distinguished by a minimum in yield stress and high shear viscosity is found, indicating an optimum state of particle dispersion. In contrast, the nanoparticulate FAHP binder has no effect on slurry rheology. The electrical conductivity of the dry layer exhibits a maximum at a CMC concentration corresponding to the minimum in slurry viscosity but monotonically decreases with increasing FAHP concentration. Adhesion to the current collector is provided by FAHP, and the line load in peel tests strongly increases with FAHP concentration, whereas CMC does not contribute to adhesion. The electrical conductivity and adhesion values obtained here excel reported values for similar aqueous LiFePO4-based cathode layers using alternative polymeric binders. Both CMC and FAHP contribute to the cohesive strength of the layers; the contribution of CMC, however, is stronger than that of FAHP despite its lower intrinsic mechanical strength. We attribute this to its impact on the cathode microstructure since high CMC concentrations result in a strong alignment of LiFePO4 particles, which yields superior cohesive strength.