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Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes
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Original Research Paper
Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes Takumi Kusano ⇑, Masahiko Ishii, Masaaki Tani, Osamu Hiruta, Takuro Matsunaga, Hiroshi Nakamura Toyota Central R&D Labs., Inc., 41-1 Yokomichi, Nagakute, Japan
a r t i c l e
i n f o
Article history: Received 5 June 2020 Received in revised form 4 September 2020 Accepted 27 September 2020 Available online xxxx Keywords: Concentrated slurry Wet granules X-ray CT Viscoelasticity Large amplitude oscillatory shear
a b s t r a c t Dynamic rheological behaviors of concentrated slurry and wet granules made of graphite, carboxymethyl cellulose, and water have been investigated, because there are few studies on wet granules despite the importance of controlling them. The internal structure and the rheological behaviors of the wet granules were compared with those of the concentrated slurry through the X-ray computed tomography (CT) observation and large amplitude oscillatory shear (LAOS) measurement. At small strain (1%), the concentrated slurry showed larger storage modulus G0 than loss modulus G00 , that is, tand (=G00 /G0 ) less than 1.0. In contrast, the wet granules indicated larger G00 than G0 , that is, tand more than 1.0. This rheological behavior of wet granules seems to be attributed to the voids that was suggested to exist in the granular layer. On the other hand, at large strain (100%), the tand values of the wet granules were extremely higher than those of the slurry. It appears that this behavior of wet granules is due to the collapse of the granular layer indicated by the high second-harmonic intensities observed in the LAOS measurement. These results elucidated the change of rheological behavior from slurry to wet granules with increasing solid content. Ó 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction Processes for functional materials such as lithium ion secondary batteries, fuel cells and solar cells consist of the fabrication and coating of slurry [1–5]. Slurry is fabricated by dispersing precursor powder into a medium together with polymers as a binder or dispersant, which is then coated onto a target surface and dried. To lower the energy consumption and cost of the slurry fabrication process, it is important to reduce the amount of dispersion medium to be evaporated during drying, i.e., to increase the soid content concentration of slurry. Therefore, concentrated slurry was often used for the processes. However, if the amount of dispersion medium is greatly reduced (to 30% or less), the material forms wet granules rather than the concentrated slurry. Replacing slurry with concentrated slurry and wet granules has the potential to greatly lower the energy consumption and cost of processing by shortening the drying step. Since wet granules are already used in granulation processes for forming tablets and the like, 3D printing forming processes, and casting [6–10], it is possible to use wet granules in the manufacturing process for lithium ion secondary battery electrodes. In a previous study, for the manufacture of sec⇑ Corresponding author. E-mail address: [email protected] (T. Kusano).
ondary battery electrodes, we have already examined the shear properties of wet granules [11]. The study elucidated that the shear properties of wet granules are strongly dependent on the water distribution. The relationship between shear behavior and water content was also reported in the fields of powder technology and geomechanics [12–14]. However, these studies mainly focused on shear properties under steady shear conditions. If wet granules are used for the electrode manufacturing process, they will be exposed to more complex stress than applied in a steady shear test. Therefore, it is necessary to evaluate dynamic rheological behavior under oscillatory shear conditions. Although previous studies have reported the dynamic compression properties of powder [15] and simulated powder behavior under oscillatory shear [16], to our knowledge, there are few studies that have measured the dynamic rheological behavior of wet granules [17]. This is probably because wet granules show the nonlinear behavior at high-strain-rate in rheological measurement. Generally, the dynamic rheological behaviors of slurry, such as the dynamic viscoelasticity, are measured on a parallel-plate or cone-plate using a rheometer. Although dynamic viscoelasticity can be used to analyze linear behavior, it is difficult to apply to nonlinear systems. In the electrode manufacturing process, the nonlinear behavior of slurry often has a major impact on the
https://doi.org/10.1016/j.apt.2020.09.023 0921-8831/Ó 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Nomenclature G0 G00
c x tand CSC RZ
storage modulus [Pa] loss modulus [Pa] strain [%] angular frequency [rad/s] loss tangent [–] concentration of a solid content [wt%] Maximum roughness [lm]
Ra Rq RZJIS
r
G0 1 G00 1
arithmetic mean roughness [lm] root-mean-square roughness [lm] ten-point average roughness [lm] stress [Pa] storage modulus of first harmonics [Pa] loss modulus of first harmonics [Pa]
2.3. Dynamic viscoelasticity measurement
productivity and performance of electrodes. Therefore, it is necessary to elucidate the nonlinear behavior of concentrated slurry and wet granules. Large amplitude oscillatory shear (LAOS) measurement is capable of quantitatively analyzing nonlinearity under high strain [18]. By applying Fourier transformation to stress responses, the contribution of higher harmonic terms can be elucidated, which cannot be accomplished by normal viscoelastic measurement [19]. In this study, the internal structures of concentrated slurry and wet granules were observed using X-ray computerized tomography (CT), and the differences in rheological properties were identified by dynamic viscoelastic and LAOS measurement. Then, the change of rheological behavior from slurry to wet granules with increasing solid content was investigated by comparing the X-ray CT and LAOS results of model concentrated slurry and model wet granules for lithium ion secondary battery electrodes. Furthermore, the viscoelasticity of wet granules was compared with the shear properties obtained by powder shear test.
The storage modulus G’, loss modulus G‘‘ and tand (=G”/G’) of both concentrated slurry and wet granules were measured by a strain-controlled rheometer. In the case of viscoelastic measurements of wet granules, there has been a problem of slippage between the sample and rheometer plate. This slippage can be reduced by modifying the rheometer plates through the application of surface irregularities [20–23]. In this study, the irregularities that are roughly equivalent to the size of the primary powder particles were formed on the rheometer plate surface (arithmetic average roughness Ra = 3.65 lm, root mean square roughness Rq = 4.59 lm, and maximum height roughness Rz = 26.18 lm) by using electric discharge machining (EDM). The modified parallel-plates (Fig. 1) were attached to a straincontrolled rheometer ARES-G2 (TA Instruments). The gap between the plates was set to 1.0 mm for the concentrated slurry at CSC = 55, 60 and 65 wt%. For the wet granules at CSC = 70 and 75 wt%, the samples were pressed by plates with a force of 10.0 kPa. The G’, G‘‘ and tand were measured at frequency x = 6.28 rad/s and strain c in the range of between 0.01 and 1000%.
2. Experimental method 2.1. Fabrication of concentrated slurry and wet granules
2.4. Large amplitude oscillatory shear (LAOS) measurement
The concentrated slurry and wet granules were fabricated by adding and mixing distilled water to graphite and carboxymethyl cellulose (CMC). OMAC-R 1.2Z/SS (particle size: 12.4 lm, Osaka Gas Chemicals Co., Ltd.) was used for the graphite and CMC1170 (1% aqueous solution viscosity: 0.8 Pa·s, Daicel Corporation) was used for the CMC. The materials were mixed together using the ARE-310 planetary centrifugal mixer (Thinky Corporation). First, CMC was dispersed into the distilled water to form an aqueous solution with a concentration of 3.5 wt%. Then, graphite was added to the CMC aqueous solution with a graphite/CMC solid content weight ratio of 99:1, and distilled water was added at the specified solid content concentration (CSC) from 55 to 75 wt%. Here, since we want to mainly discuss the viscoelastisity of graphite particles, CMC with the relatively low weight ratio was used. Finally, these materials were mixed using the planetary centrifugal mixer.
The storage modulus G’ and loss modulus G” obtained by dynamic viscoelasticity measurements will refer to the moduli G’ and G” calculated from the first harmonics (G’1 and G”1), which is the typical output of commercial rheometer software [18]. Therefore, the LAOS measurements are fundamental for elucidating the viscoelastic behavior of samples with non-linear viscoelasticity, such as concentrated slurry and wet granules. LAOS measurements were performed by a strain-controlled rheometer ARES-G2 (TA Instruments). In the LAOS test, the time-based changes in stress were measured under five cycles (5 s) of strain applied at a maximum strength (amplitude) of 0.01, 1, and 100%. This strain was applied over time as a sine wave at x = 6.28 rad/s. The timebased changes in stress measured over the five cycles were averaged and the resulting single-cycle time-based stress change was used for the analysis. In addition, the amplitude of each harmonic component was calculated by applying Fourier transformation to the obtained time-based stress changes, and Lissajous figures were plotted from the applied strain and stress. The ARES-G2 software was used for analysis.
2.2. X-Ray CT measurement The BL33XU beamline at SPring-8 was used to perform X-ray CT measurement of the concentrated slurry and wet granules. The concentrated slurry and wet granules were packed into a polyimide tube (inner diameter: 2.0 mm, outer diameter: 2.1 mm) to perform the measurement. The detecting apparatus was an X-ray complementary metal-oxide semiconductor (CMOS) camera (Hamamatsu Photonics K.K.), which was used to obtain images with a pixel size of 0.25 lm. The X-ray energy was set to 20 keV. Images with an exposure time of 100 ms were obtained every 0.1°, resulting in a total of 1801 transmission images up to 180°. In addition, the flowability of the samples was examined by visual observation.
2.5. Shear test of wet granules The shear properties (internal friction angle and cohesion) were analyzed using an NS500 powder shear tester (Nano Seeds Corporation). The shear rate was set to 10 lm/s, and a cell with a diameter of 30 mm was used. The powder shear test was carried out at an initial load of 100 kPa. The powder shear test was performed under 100 kPa because it is easier to observe the difference in the cohesion under larger normal force. 2
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Fig. 1. Viscoelastic measurements of wet granules with the rheometer plates modified to reduce slippage.
3.2. Dynamic viscoelastic behavior of concentrated slurry and wet granules
3. Results and discussion 3.1. Appearance and internal structure of concentrated slurry and wet granules
Fig. 4 shows the relationship between the strain c and G’ and G‘‘ of the slurries at CSC = (a) 55 wt%, (b) 60 wt%, and (c) 65 wt%. The results show almost no linear behavior at any CSC value. In all cases, both G’ and G” decrease as c increases, before increasing again when c slightly exceeds 10%. In the figures, G’ also reaches a local maximum. This behavior which G’ and G‘‘ increase with c, correspond approximately to shear thickening behavior under steady shear flow. The shear thickening is caused by the friction with collisions (contact forces) between particles in a concentrated suspension. A rise in elasticity of slurries as c increases is also caused by the contact forces between particles [24–27]. Fig. 5 shows the relationship between the strain c and viscoelastic modulus (G’ and G‘‘) of the wet granules at CSC = (a) 70 wt% and (b) 75 wt%. These results also show almost no linear behavior. Both G’ and G” decreases as c increases and, at c = 1%, the sample changes from a solid state (G’ > G‘‘) to a liquid state (G’ < G”). However, unlike the samples at CSC = 55–65 wt%, elasticity did not rise as c increased. Therefore, LAOS measurement was carried out to analyze this phenomenon.
Fig. 2 shows the appearance of the samples with a solid content concentration (CSC) of between 55 and 75 wt%. At a range of CSC from 55 to 65 wt%, the samples are in a liquid state that exhibits flowability (i.e., slurry). Compared to the samples at a range of CSC from 55 to 65 wt%, the samples break down more easily and are in a powder state with a higher gaseous phase content (i.e., wet granules) at CSC = 70 and 75 wt%. The X-ray CT results for the samples at CSC = 65, 70, and 75 wt% are shown at the bottom of Fig. 2. Note that the X-ray CT images at CSC = 70 and 75 wt% exhibit the internal structure of one granule. At CSC = 65 wt%, the sample is evidently a slurry, with no voids in the internal structure. In contrast, voids are visible in the samples at CSC = 70 and 75 wt%. Fig. 3 shows 3D images reconstructed from X-ray CT data of wet granules (CSC = (a) 70 and (b) 75 wt%). Fig. 3 indicates that voids in wet granules are relatively more continuous in the sample at CSC = 75 wt%. Then, viscoelastic measurement was carried out for the concentrated slurry and wet granules with these different solid content concentrations.
Fig. 2. Appearance (CSC = 55, 60, 65, 70 and 75 wt%) and X-ray CT images (CSC = 65, 70 and 75 wt%) of carbon/CMC/water mixtures. 3
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Fig. 3. 3D images reconstructed from X-ray CT data of carbon/CMC/water wet granules (CSC = (a) 70 and (b) 75 wt%) with a unit size of 165 mm 165 mm 165 mm.
Fig. 4. Strain c dependence of storage modulus G’ and loss modulus G” of the wet granules at CSC = (a) 55 wt%, (b) 60 wt% and (c) 65 wt% at x = 6.28 rad/s.
formation when c = 0.01%. When c = 0.01% (Fig. 6), the stress-time curve closely maintains sinusoidal at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt%. There is also little phase difference with respect to c, and the Lissajous figures show long, narrow ellipsoids. The amplitude of each harmonic obtained by Fourier transformation is approximately 1% of the amplitude of the fundamental harmonic, including the amplitude of the third harmonic. This amplitude is at the level of noise. In other words, although the results of
3.3. LAOS measurement of concentrated slurry and wet granules Since the viscoelastic measurement data at c = 10% (the intersection of G’and G‘‘) was unstable, we performed the LAOS measurements in linear region (0.01%), and the regions before and after the intersection (1% and 100%). Fig. 6 shows the time-based changes in stress r and applied strain c, the Lissajous figures, and the power spectrum obtained from the results of Fourier trans4
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Fig. 5. Strain c dependence of storage modulus G0 and loss modulus G00 of the wet granules at CSC = (a) 70 wt% and (b) 75 wt% at x = 6.28 rad/s.
Fig. 6. The stress data, Lissajous patterns and power spectrum of wet granules at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt% at c = 0.01%.
5
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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monic is 37% at CSC = 70 wt% and 35% at CSC = 75 wt%. In addition, the even harmonic components also exhibit clear peaks and the amplitude of the second harmonic exceeds 1% at CSC = (b) 70 wt% and (c) 75 wt%. In polymer melts, it has been reported that even harmonics might be caused by shear bands, wall slip, and disaggregation [29–31]. Since the wet granules used in this system are susceptible to collapse (unlike polymer melts) and the wet granules at CSC = 70 and 75 wt% show different values of tand, this indicates collapse of the powder layer under high strain. Therefore, when c = 100%, it is assumed that slippage occurred with the wet granules (CSC = 70 and 75 wt%) because of the powder layer collapse occurred in the plane parallel to the shear plate inside the sample.
viscoelastic measurements in Figs. 4 and 5 show that G’ begins to decrease, the LAOS measurements show that linearity is maintained. When c = 1%, the stress-time curves no longer show a sinusoidal wave, and the Lissajous figures are no longer ellipsoidal (Fig. 7). From Figs. 4 and 5, every samples showed the decrease of G’ at c > 0.1%. These results indicate that the concentrated slurry and wet granules show a nonlinear regime at c = 1%. According to the power spectrum, the amplitude of the third harmonic exceeds 10% and nonlinearity increases. It has been previously reported that in colloidal suspensions, the rotational velocity of particles is proportional to the shear rate [28]. Therefore, third harmonics of concentrated slurry and wet granules may have increased because of faster rotational velocity. When c = 100%, the amplitude of the third harmonic also exceeds 10% at CSC = 65 wt%, and nonlinearity increases noticeably (Fig. 8(a)). In the same way as the results for c = 1%, it is assumed that the increase in the third harmonic accompanies the rotation of carbon particles. In contrast, at (b) CSC = 70 and (c) 75 wt%, both the waveform for the stress-time curve and the Lissajous figures are almost rectangular. Therefore, the power spectrum shows large nonlinearity (Fig. 8(b) and (c)). The amplitude of the third har-
3.4. Rheological behavior of concentrated slurry and wet granules The results of LAOS measurement demonstrated that nonlinearity becomes stronger in both concentrated slurry and wet granules under high strain. However, since the first harmonics is still dominant, the viscoelasticity of the concentrated slurry and wet granules was discussed using the values for G’, G‘‘, and tand obtained from viscoelastic measurements (Figs. 4 and 5). Here, it
Fig. 7. The stress data, Lissajous patterns and power spectrum of wet granules at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt% at c = 1%. 6
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Fig. 8. The stress data, Lissajous patterns and power spectrum of wet granules at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt% at c = 100%.
Fig. 10 shows the relationship between CSC and G’, G‘‘, and tand under high strain (c = 100%). With the slurries (CSC = 55, 60, and 65 wt%), G’ and G” maintained almost the same value. At c = 100%, an increase in elasticity against strain can also be observed (Fig. 4). This increase in elasticity against strain is caused by the contact forces between carbon particles or the hydroclusters of carbon particles [29]. In contrast, with the wet granules (CSC = 70 and 75 wt%), G’ became smaller than G‘‘ (G’ < G”) and tand increased rapidly. The LAOS results (Fig. 8) suggests that collapse of the powder layer occur under high strain in wet granules. Simulations have predicted the occurrence of jamming transition attributed to contact forces between particles under high strain when oscillatory shear is applied to powder layer [16]. Therefore, the powder layer collapse indicated in Fig. 8 may be caused by the jamming transition of powder, which suppresses deformation of the powder layer. Here, the magnitude of tand was larger than unity at c = 100% (Fig. 10), whereas tand for all mixtures at c = 1% was basically less than unity (Fig. 9). At c = 1%, the LAOS results indicate that the wet granular layer did not collapse, and there was a tand difference depending on the presence or absence of voids. Therefore, the magnitude and difference of tand were small. On the other hand, at
is re-emphasized that G’ and G” obtained by oscillatory measurements referred to the first harmonic moduli G0 1 and G00 1. Fig. 9 shows the relationship between CSC and G’, G‘‘, and tand at low strain (c = 1%) and x = 6.28 rad/s. At low strain (c = 1%), the elastic response G’ of the slurries (CSC = 55, 60, and 65 wt%) was larger than the viscous response G”, and tand was lower than 1.0. In contrast, the viscous response G‘‘ of the wet granules (CSC = 70 and 75 wt%) was larger than the elastic response G’, and tand was higher than 1.0. With the wet granules (CSC = 70 and 75 wt %), the LAOS measurement identified almost no even-numbered harmonics, indicating that collapse of powder layer did not occur. This suggests that, with the wet granules the existence of voids inside (Figs. 2 and 3) facilitated movement of the graphite particles, which was expressed in the tand value (higher than 1.0). Furthermore, the tand value of the sample at CSC = 75 wt% is higher than the sample at CSC = 70 wt%. This seems to be caused by the existence of continuous voids in the sample at CSC = 75 wt%, as shown in Fig. 3. In our previous study, the porosity of wet granules depended on the duration or speed of mixing.[11] These results imply that the mobility of wet granules, i.e. tand can be also controlled by the process parameter. 7
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Fig. 9. CSC dependence of storage modulus G0 , loss modulus G00 and tand at c = 1%.
Fig. 11. Shear test of wet granules at CSC = 70 and 75 wt%.
4. Conclusion In this study, the internal structure of slurries and wet granules was observed using X-ray CT, and the differences in the rheological properties of these samples were identified by dynamic viscoelastic and LAOS measurements. Both the viscoelastic and LAOS measurements were performed after modifying the surfaces of the rheometer plates to reduce slippage. At low strain (c = 1%), the elastic response G’ of the concentrated slurry was larger than the viscous response G‘‘, and tand was lower than 1.0. In contrast, the viscous response G” of the wet granules was larger than the elastic response G’, and tand was higher than 1.0. Furthermore, the LAOS measurement indicated that collapse of wet granular layer did not occur. These results seem to be caused by the existence of voids inside the wet granules, which were observed by X-ray CT. These voids probably increase the mobility of the powder compared to concentrated slurry, which contains no voids. Furthermore, the tand value of the sample at CSC = 75 wt% is higher than the sample at CSC = 70 wt%. These results are attributed to the existence of continuous voids in the sample at CSC = 75 wt%. In contrast, under high strain (c = 100%), the G’ and G‘‘ values of the wet granules differed more widely than the G’ and G” values of the concentrated slurry. As a result, the tand value of the wet granules was larger than the tand value of the concentrated slurry. This is due to collapse of the wet granular layer in the wet granules. As is the case with low strain, the tand value of the sample at CSC = 75 wt% is higher than the sample at CSC = 70 wt%. Shear test results of wet granules indicated that the difference of tand between wet granules is caused by cohesion difference. These results elucidated the change of rheological behavior from concentrated slurry to wet granules for lithium ion secondary battery electrodes with increasing solid content.
Fig. 10. CSC dependence of storage modulus G0 , loss modulus G00 and tand at c = 100%.
c = 100%, from the LAOS result, the wet granular layer collapsed. As a result, the magnitude and difference of tand were remarkably large. In Figs. 9 and 10, the minimum G’ value was observed at CSC = 60 wt%. At CSC = 60 wt%, the particles are close to each other and the CMC cannot enter the spaces between the particles. As a result, CMC cannot function as a binder, and the viscoelasticity has decreased. Meanwhile, at CSC = 65 wt%, the viscoelasticity increases again because the friction between the particles becomes stronger, which results in the minimum tand value at CSC = 60 wt%. Furthermore, we performed powder shear test in order to elucidate the reason of higher tand value at CSC = 75 wt%. Fig. 11 shows the results of shear test performed to identify the powder yield locus (PYL) at CSC = 70 and 75 wt%. The cohesion of the sample at CSC = 70 wt% is higher than the sample at CSC = 75 wt% (70 wt%: 1.19 kPa, 75 wt%: 0.18 kPa). This is because the cohesion force between powder particles in the sample at CSC = 70 wt% is stronger due to the higher water content. As a result, tand at CSC = 70 wt% shows low values.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 8
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Acknowledgement The X-ray CT experiments were performed at the BL33XU beamline of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI; Proposal No. 2018B7035, 2019A7035, 2019B7035). References [1] X. Ding, J. Liu, T.A.L. Harris, A review of the operating limits in slot die coating processes, AlChE J. 62 (7) (2016) 2508–2524. [2] M. Schmitt, M. Baunach, L. Wengeler, K. Peters, P. Junges, P. Scharfer, W. Schabel, Slot-die processing of lithium-ion battery electrodes-Coating window characterization, Chem. Eng. Process 68 (2013) 32–37. [3] S. Lim, K.H. Ahn, M. Yamamura, Latex migration in battery slurries during drying, Langmuir 29 (2013) 8233–8244. [4] M. Bodner, H.R. Garcia, T. Steenberg, C. Terkelsen, S.M. Alfaro, G.S. Avcioglu, A. Vassiliev, S. Primdahl, Enabling industrial production of electrodes by use of slot-die coating for HT-PEM fuel cells, Int. J. Hyd. E. 44 (25) (2019) 12793– 12801. [5] H. Li, C. Zuo, A.D. Scully, D. Angmo, J. Yang, M. Gao, Recent progress towards roll-to-roll manufacturing of perovskite solar cells using slot-die processing, Flex. Print. Electrom. 5 (2020) 014006. [6] W. Pietsch, Agglomeration in Industry: Occurrence and Applications, WileyVCH, Weinheim, 2004. [7] N. Mitarai, F. Nori, Wet granular materials, Adv. Phys. 55 (2006) 1–45, https:// doi.org/10.1080/00018730600626065. [8] Y. Tsunazawa, D. Fujihashi, S. Fukui, M. Sakai, C. Tokoro, Contact force model including the liquid-bridge force for wet-particle simulation using the discrete element method, Adv. Pow. Tec. 27 (2) (2016) 652–660. [9] M. Sweeney, L.L. Campbell, J. Hanson, M.L. Pantoya, G.F. Christopher, Characterizing the feasibility of processing wet granular materials to improve rheology for 3D printing, J. Mater. Sci. 52 (2017) 13040–13053. [10] C. Liao, S. Hsiau, Experimental analysis of dynamic properties in wet sheared granular matter, Pow. Tech. 197 (2010) 222–229. [11] T. Kusano, M. Tani, O. Hiruta, H. Nakamura, Relationship between water distribution and shear properties of wet granules, Adv. Pow. Tec. 30 (12) (2019) 3253–3259. [12] F. Gabrieli, P. Lambert, S. Cola, F. Calvetti, Micromechanical modelling of erosion due to evaporation in a partially wet granular slope, Int. J. Num. Anal. Meth. Geomech. 36 (2012) 918–943. [13] H. Lu, X. Guo, Y. Jin, X. Gong, Effect of moisture on flowability of pulverized coal, Chem. Eng. Res. Des. 133 (2018) 326–334. [14] M. Scheel, R. Seemann, M. Brinkmann, M. di Michiel, A. Sheppard, B. Breidenbach, S. Herminghaus, Morphological clues to wet granular pile stability, Nat. Mater. 7 (2008) 189–193.
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Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes Takumi Kusano ⇑, Masahiko Ishii, Masaaki Tani, Osamu Hiruta, Takuro Matsunaga, Hiroshi Nakamura Toyota Central R&D Labs., Inc., 41-1 Yokomichi, Nagakute, Japan
a r t i c l e
i n f o
Article history: Received 5 June 2020 Received in revised form 4 September 2020 Accepted 27 September 2020 Available online xxxx Keywords: Concentrated slurry Wet granules X-ray CT Viscoelasticity Large amplitude oscillatory shear
a b s t r a c t Dynamic rheological behaviors of concentrated slurry and wet granules made of graphite, carboxymethyl cellulose, and water have been investigated, because there are few studies on wet granules despite the importance of controlling them. The internal structure and the rheological behaviors of the wet granules were compared with those of the concentrated slurry through the X-ray computed tomography (CT) observation and large amplitude oscillatory shear (LAOS) measurement. At small strain (1%), the concentrated slurry showed larger storage modulus G0 than loss modulus G00 , that is, tand (=G00 /G0 ) less than 1.0. In contrast, the wet granules indicated larger G00 than G0 , that is, tand more than 1.0. This rheological behavior of wet granules seems to be attributed to the voids that was suggested to exist in the granular layer. On the other hand, at large strain (100%), the tand values of the wet granules were extremely higher than those of the slurry. It appears that this behavior of wet granules is due to the collapse of the granular layer indicated by the high second-harmonic intensities observed in the LAOS measurement. These results elucidated the change of rheological behavior from slurry to wet granules with increasing solid content. Ó 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction Processes for functional materials such as lithium ion secondary batteries, fuel cells and solar cells consist of the fabrication and coating of slurry [1–5]. Slurry is fabricated by dispersing precursor powder into a medium together with polymers as a binder or dispersant, which is then coated onto a target surface and dried. To lower the energy consumption and cost of the slurry fabrication process, it is important to reduce the amount of dispersion medium to be evaporated during drying, i.e., to increase the soid content concentration of slurry. Therefore, concentrated slurry was often used for the processes. However, if the amount of dispersion medium is greatly reduced (to 30% or less), the material forms wet granules rather than the concentrated slurry. Replacing slurry with concentrated slurry and wet granules has the potential to greatly lower the energy consumption and cost of processing by shortening the drying step. Since wet granules are already used in granulation processes for forming tablets and the like, 3D printing forming processes, and casting [6–10], it is possible to use wet granules in the manufacturing process for lithium ion secondary battery electrodes. In a previous study, for the manufacture of sec⇑ Corresponding author. E-mail address: [email protected] (T. Kusano).
ondary battery electrodes, we have already examined the shear properties of wet granules [11]. The study elucidated that the shear properties of wet granules are strongly dependent on the water distribution. The relationship between shear behavior and water content was also reported in the fields of powder technology and geomechanics [12–14]. However, these studies mainly focused on shear properties under steady shear conditions. If wet granules are used for the electrode manufacturing process, they will be exposed to more complex stress than applied in a steady shear test. Therefore, it is necessary to evaluate dynamic rheological behavior under oscillatory shear conditions. Although previous studies have reported the dynamic compression properties of powder [15] and simulated powder behavior under oscillatory shear [16], to our knowledge, there are few studies that have measured the dynamic rheological behavior of wet granules [17]. This is probably because wet granules show the nonlinear behavior at high-strain-rate in rheological measurement. Generally, the dynamic rheological behaviors of slurry, such as the dynamic viscoelasticity, are measured on a parallel-plate or cone-plate using a rheometer. Although dynamic viscoelasticity can be used to analyze linear behavior, it is difficult to apply to nonlinear systems. In the electrode manufacturing process, the nonlinear behavior of slurry often has a major impact on the
https://doi.org/10.1016/j.apt.2020.09.023 0921-8831/Ó 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Nomenclature G0 G00
c x tand CSC RZ
storage modulus [Pa] loss modulus [Pa] strain [%] angular frequency [rad/s] loss tangent [–] concentration of a solid content [wt%] Maximum roughness [lm]
Ra Rq RZJIS
r
G0 1 G00 1
arithmetic mean roughness [lm] root-mean-square roughness [lm] ten-point average roughness [lm] stress [Pa] storage modulus of first harmonics [Pa] loss modulus of first harmonics [Pa]
2.3. Dynamic viscoelasticity measurement
productivity and performance of electrodes. Therefore, it is necessary to elucidate the nonlinear behavior of concentrated slurry and wet granules. Large amplitude oscillatory shear (LAOS) measurement is capable of quantitatively analyzing nonlinearity under high strain [18]. By applying Fourier transformation to stress responses, the contribution of higher harmonic terms can be elucidated, which cannot be accomplished by normal viscoelastic measurement [19]. In this study, the internal structures of concentrated slurry and wet granules were observed using X-ray computerized tomography (CT), and the differences in rheological properties were identified by dynamic viscoelastic and LAOS measurement. Then, the change of rheological behavior from slurry to wet granules with increasing solid content was investigated by comparing the X-ray CT and LAOS results of model concentrated slurry and model wet granules for lithium ion secondary battery electrodes. Furthermore, the viscoelasticity of wet granules was compared with the shear properties obtained by powder shear test.
The storage modulus G’, loss modulus G‘‘ and tand (=G”/G’) of both concentrated slurry and wet granules were measured by a strain-controlled rheometer. In the case of viscoelastic measurements of wet granules, there has been a problem of slippage between the sample and rheometer plate. This slippage can be reduced by modifying the rheometer plates through the application of surface irregularities [20–23]. In this study, the irregularities that are roughly equivalent to the size of the primary powder particles were formed on the rheometer plate surface (arithmetic average roughness Ra = 3.65 lm, root mean square roughness Rq = 4.59 lm, and maximum height roughness Rz = 26.18 lm) by using electric discharge machining (EDM). The modified parallel-plates (Fig. 1) were attached to a straincontrolled rheometer ARES-G2 (TA Instruments). The gap between the plates was set to 1.0 mm for the concentrated slurry at CSC = 55, 60 and 65 wt%. For the wet granules at CSC = 70 and 75 wt%, the samples were pressed by plates with a force of 10.0 kPa. The G’, G‘‘ and tand were measured at frequency x = 6.28 rad/s and strain c in the range of between 0.01 and 1000%.
2. Experimental method 2.1. Fabrication of concentrated slurry and wet granules
2.4. Large amplitude oscillatory shear (LAOS) measurement
The concentrated slurry and wet granules were fabricated by adding and mixing distilled water to graphite and carboxymethyl cellulose (CMC). OMAC-R 1.2Z/SS (particle size: 12.4 lm, Osaka Gas Chemicals Co., Ltd.) was used for the graphite and CMC1170 (1% aqueous solution viscosity: 0.8 Pa·s, Daicel Corporation) was used for the CMC. The materials were mixed together using the ARE-310 planetary centrifugal mixer (Thinky Corporation). First, CMC was dispersed into the distilled water to form an aqueous solution with a concentration of 3.5 wt%. Then, graphite was added to the CMC aqueous solution with a graphite/CMC solid content weight ratio of 99:1, and distilled water was added at the specified solid content concentration (CSC) from 55 to 75 wt%. Here, since we want to mainly discuss the viscoelastisity of graphite particles, CMC with the relatively low weight ratio was used. Finally, these materials were mixed using the planetary centrifugal mixer.
The storage modulus G’ and loss modulus G” obtained by dynamic viscoelasticity measurements will refer to the moduli G’ and G” calculated from the first harmonics (G’1 and G”1), which is the typical output of commercial rheometer software [18]. Therefore, the LAOS measurements are fundamental for elucidating the viscoelastic behavior of samples with non-linear viscoelasticity, such as concentrated slurry and wet granules. LAOS measurements were performed by a strain-controlled rheometer ARES-G2 (TA Instruments). In the LAOS test, the time-based changes in stress were measured under five cycles (5 s) of strain applied at a maximum strength (amplitude) of 0.01, 1, and 100%. This strain was applied over time as a sine wave at x = 6.28 rad/s. The timebased changes in stress measured over the five cycles were averaged and the resulting single-cycle time-based stress change was used for the analysis. In addition, the amplitude of each harmonic component was calculated by applying Fourier transformation to the obtained time-based stress changes, and Lissajous figures were plotted from the applied strain and stress. The ARES-G2 software was used for analysis.
2.2. X-Ray CT measurement The BL33XU beamline at SPring-8 was used to perform X-ray CT measurement of the concentrated slurry and wet granules. The concentrated slurry and wet granules were packed into a polyimide tube (inner diameter: 2.0 mm, outer diameter: 2.1 mm) to perform the measurement. The detecting apparatus was an X-ray complementary metal-oxide semiconductor (CMOS) camera (Hamamatsu Photonics K.K.), which was used to obtain images with a pixel size of 0.25 lm. The X-ray energy was set to 20 keV. Images with an exposure time of 100 ms were obtained every 0.1°, resulting in a total of 1801 transmission images up to 180°. In addition, the flowability of the samples was examined by visual observation.
2.5. Shear test of wet granules The shear properties (internal friction angle and cohesion) were analyzed using an NS500 powder shear tester (Nano Seeds Corporation). The shear rate was set to 10 lm/s, and a cell with a diameter of 30 mm was used. The powder shear test was carried out at an initial load of 100 kPa. The powder shear test was performed under 100 kPa because it is easier to observe the difference in the cohesion under larger normal force. 2
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Fig. 1. Viscoelastic measurements of wet granules with the rheometer plates modified to reduce slippage.
3.2. Dynamic viscoelastic behavior of concentrated slurry and wet granules
3. Results and discussion 3.1. Appearance and internal structure of concentrated slurry and wet granules
Fig. 4 shows the relationship between the strain c and G’ and G‘‘ of the slurries at CSC = (a) 55 wt%, (b) 60 wt%, and (c) 65 wt%. The results show almost no linear behavior at any CSC value. In all cases, both G’ and G” decrease as c increases, before increasing again when c slightly exceeds 10%. In the figures, G’ also reaches a local maximum. This behavior which G’ and G‘‘ increase with c, correspond approximately to shear thickening behavior under steady shear flow. The shear thickening is caused by the friction with collisions (contact forces) between particles in a concentrated suspension. A rise in elasticity of slurries as c increases is also caused by the contact forces between particles [24–27]. Fig. 5 shows the relationship between the strain c and viscoelastic modulus (G’ and G‘‘) of the wet granules at CSC = (a) 70 wt% and (b) 75 wt%. These results also show almost no linear behavior. Both G’ and G” decreases as c increases and, at c = 1%, the sample changes from a solid state (G’ > G‘‘) to a liquid state (G’ < G”). However, unlike the samples at CSC = 55–65 wt%, elasticity did not rise as c increased. Therefore, LAOS measurement was carried out to analyze this phenomenon.
Fig. 2 shows the appearance of the samples with a solid content concentration (CSC) of between 55 and 75 wt%. At a range of CSC from 55 to 65 wt%, the samples are in a liquid state that exhibits flowability (i.e., slurry). Compared to the samples at a range of CSC from 55 to 65 wt%, the samples break down more easily and are in a powder state with a higher gaseous phase content (i.e., wet granules) at CSC = 70 and 75 wt%. The X-ray CT results for the samples at CSC = 65, 70, and 75 wt% are shown at the bottom of Fig. 2. Note that the X-ray CT images at CSC = 70 and 75 wt% exhibit the internal structure of one granule. At CSC = 65 wt%, the sample is evidently a slurry, with no voids in the internal structure. In contrast, voids are visible in the samples at CSC = 70 and 75 wt%. Fig. 3 shows 3D images reconstructed from X-ray CT data of wet granules (CSC = (a) 70 and (b) 75 wt%). Fig. 3 indicates that voids in wet granules are relatively more continuous in the sample at CSC = 75 wt%. Then, viscoelastic measurement was carried out for the concentrated slurry and wet granules with these different solid content concentrations.
Fig. 2. Appearance (CSC = 55, 60, 65, 70 and 75 wt%) and X-ray CT images (CSC = 65, 70 and 75 wt%) of carbon/CMC/water mixtures. 3
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Fig. 3. 3D images reconstructed from X-ray CT data of carbon/CMC/water wet granules (CSC = (a) 70 and (b) 75 wt%) with a unit size of 165 mm 165 mm 165 mm.
Fig. 4. Strain c dependence of storage modulus G’ and loss modulus G” of the wet granules at CSC = (a) 55 wt%, (b) 60 wt% and (c) 65 wt% at x = 6.28 rad/s.
formation when c = 0.01%. When c = 0.01% (Fig. 6), the stress-time curve closely maintains sinusoidal at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt%. There is also little phase difference with respect to c, and the Lissajous figures show long, narrow ellipsoids. The amplitude of each harmonic obtained by Fourier transformation is approximately 1% of the amplitude of the fundamental harmonic, including the amplitude of the third harmonic. This amplitude is at the level of noise. In other words, although the results of
3.3. LAOS measurement of concentrated slurry and wet granules Since the viscoelastic measurement data at c = 10% (the intersection of G’and G‘‘) was unstable, we performed the LAOS measurements in linear region (0.01%), and the regions before and after the intersection (1% and 100%). Fig. 6 shows the time-based changes in stress r and applied strain c, the Lissajous figures, and the power spectrum obtained from the results of Fourier trans4
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Fig. 5. Strain c dependence of storage modulus G0 and loss modulus G00 of the wet granules at CSC = (a) 70 wt% and (b) 75 wt% at x = 6.28 rad/s.
Fig. 6. The stress data, Lissajous patterns and power spectrum of wet granules at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt% at c = 0.01%.
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monic is 37% at CSC = 70 wt% and 35% at CSC = 75 wt%. In addition, the even harmonic components also exhibit clear peaks and the amplitude of the second harmonic exceeds 1% at CSC = (b) 70 wt% and (c) 75 wt%. In polymer melts, it has been reported that even harmonics might be caused by shear bands, wall slip, and disaggregation [29–31]. Since the wet granules used in this system are susceptible to collapse (unlike polymer melts) and the wet granules at CSC = 70 and 75 wt% show different values of tand, this indicates collapse of the powder layer under high strain. Therefore, when c = 100%, it is assumed that slippage occurred with the wet granules (CSC = 70 and 75 wt%) because of the powder layer collapse occurred in the plane parallel to the shear plate inside the sample.
viscoelastic measurements in Figs. 4 and 5 show that G’ begins to decrease, the LAOS measurements show that linearity is maintained. When c = 1%, the stress-time curves no longer show a sinusoidal wave, and the Lissajous figures are no longer ellipsoidal (Fig. 7). From Figs. 4 and 5, every samples showed the decrease of G’ at c > 0.1%. These results indicate that the concentrated slurry and wet granules show a nonlinear regime at c = 1%. According to the power spectrum, the amplitude of the third harmonic exceeds 10% and nonlinearity increases. It has been previously reported that in colloidal suspensions, the rotational velocity of particles is proportional to the shear rate [28]. Therefore, third harmonics of concentrated slurry and wet granules may have increased because of faster rotational velocity. When c = 100%, the amplitude of the third harmonic also exceeds 10% at CSC = 65 wt%, and nonlinearity increases noticeably (Fig. 8(a)). In the same way as the results for c = 1%, it is assumed that the increase in the third harmonic accompanies the rotation of carbon particles. In contrast, at (b) CSC = 70 and (c) 75 wt%, both the waveform for the stress-time curve and the Lissajous figures are almost rectangular. Therefore, the power spectrum shows large nonlinearity (Fig. 8(b) and (c)). The amplitude of the third har-
3.4. Rheological behavior of concentrated slurry and wet granules The results of LAOS measurement demonstrated that nonlinearity becomes stronger in both concentrated slurry and wet granules under high strain. However, since the first harmonics is still dominant, the viscoelasticity of the concentrated slurry and wet granules was discussed using the values for G’, G‘‘, and tand obtained from viscoelastic measurements (Figs. 4 and 5). Here, it
Fig. 7. The stress data, Lissajous patterns and power spectrum of wet granules at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt% at c = 1%. 6
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Fig. 8. The stress data, Lissajous patterns and power spectrum of wet granules at CSC = (a) 65 wt%, (b) 70 wt% and (c) 75 wt% at c = 100%.
Fig. 10 shows the relationship between CSC and G’, G‘‘, and tand under high strain (c = 100%). With the slurries (CSC = 55, 60, and 65 wt%), G’ and G” maintained almost the same value. At c = 100%, an increase in elasticity against strain can also be observed (Fig. 4). This increase in elasticity against strain is caused by the contact forces between carbon particles or the hydroclusters of carbon particles [29]. In contrast, with the wet granules (CSC = 70 and 75 wt%), G’ became smaller than G‘‘ (G’ < G”) and tand increased rapidly. The LAOS results (Fig. 8) suggests that collapse of the powder layer occur under high strain in wet granules. Simulations have predicted the occurrence of jamming transition attributed to contact forces between particles under high strain when oscillatory shear is applied to powder layer [16]. Therefore, the powder layer collapse indicated in Fig. 8 may be caused by the jamming transition of powder, which suppresses deformation of the powder layer. Here, the magnitude of tand was larger than unity at c = 100% (Fig. 10), whereas tand for all mixtures at c = 1% was basically less than unity (Fig. 9). At c = 1%, the LAOS results indicate that the wet granular layer did not collapse, and there was a tand difference depending on the presence or absence of voids. Therefore, the magnitude and difference of tand were small. On the other hand, at
is re-emphasized that G’ and G” obtained by oscillatory measurements referred to the first harmonic moduli G0 1 and G00 1. Fig. 9 shows the relationship between CSC and G’, G‘‘, and tand at low strain (c = 1%) and x = 6.28 rad/s. At low strain (c = 1%), the elastic response G’ of the slurries (CSC = 55, 60, and 65 wt%) was larger than the viscous response G”, and tand was lower than 1.0. In contrast, the viscous response G‘‘ of the wet granules (CSC = 70 and 75 wt%) was larger than the elastic response G’, and tand was higher than 1.0. With the wet granules (CSC = 70 and 75 wt %), the LAOS measurement identified almost no even-numbered harmonics, indicating that collapse of powder layer did not occur. This suggests that, with the wet granules the existence of voids inside (Figs. 2 and 3) facilitated movement of the graphite particles, which was expressed in the tand value (higher than 1.0). Furthermore, the tand value of the sample at CSC = 75 wt% is higher than the sample at CSC = 70 wt%. This seems to be caused by the existence of continuous voids in the sample at CSC = 75 wt%, as shown in Fig. 3. In our previous study, the porosity of wet granules depended on the duration or speed of mixing.[11] These results imply that the mobility of wet granules, i.e. tand can be also controlled by the process parameter. 7
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Fig. 9. CSC dependence of storage modulus G0 , loss modulus G00 and tand at c = 1%.
Fig. 11. Shear test of wet granules at CSC = 70 and 75 wt%.
4. Conclusion In this study, the internal structure of slurries and wet granules was observed using X-ray CT, and the differences in the rheological properties of these samples were identified by dynamic viscoelastic and LAOS measurements. Both the viscoelastic and LAOS measurements were performed after modifying the surfaces of the rheometer plates to reduce slippage. At low strain (c = 1%), the elastic response G’ of the concentrated slurry was larger than the viscous response G‘‘, and tand was lower than 1.0. In contrast, the viscous response G” of the wet granules was larger than the elastic response G’, and tand was higher than 1.0. Furthermore, the LAOS measurement indicated that collapse of wet granular layer did not occur. These results seem to be caused by the existence of voids inside the wet granules, which were observed by X-ray CT. These voids probably increase the mobility of the powder compared to concentrated slurry, which contains no voids. Furthermore, the tand value of the sample at CSC = 75 wt% is higher than the sample at CSC = 70 wt%. These results are attributed to the existence of continuous voids in the sample at CSC = 75 wt%. In contrast, under high strain (c = 100%), the G’ and G‘‘ values of the wet granules differed more widely than the G’ and G” values of the concentrated slurry. As a result, the tand value of the wet granules was larger than the tand value of the concentrated slurry. This is due to collapse of the wet granular layer in the wet granules. As is the case with low strain, the tand value of the sample at CSC = 75 wt% is higher than the sample at CSC = 70 wt%. Shear test results of wet granules indicated that the difference of tand between wet granules is caused by cohesion difference. These results elucidated the change of rheological behavior from concentrated slurry to wet granules for lithium ion secondary battery electrodes with increasing solid content.
Fig. 10. CSC dependence of storage modulus G0 , loss modulus G00 and tand at c = 100%.
c = 100%, from the LAOS result, the wet granular layer collapsed. As a result, the magnitude and difference of tand were remarkably large. In Figs. 9 and 10, the minimum G’ value was observed at CSC = 60 wt%. At CSC = 60 wt%, the particles are close to each other and the CMC cannot enter the spaces between the particles. As a result, CMC cannot function as a binder, and the viscoelasticity has decreased. Meanwhile, at CSC = 65 wt%, the viscoelasticity increases again because the friction between the particles becomes stronger, which results in the minimum tand value at CSC = 60 wt%. Furthermore, we performed powder shear test in order to elucidate the reason of higher tand value at CSC = 75 wt%. Fig. 11 shows the results of shear test performed to identify the powder yield locus (PYL) at CSC = 70 and 75 wt%. The cohesion of the sample at CSC = 70 wt% is higher than the sample at CSC = 75 wt% (70 wt%: 1.19 kPa, 75 wt%: 0.18 kPa). This is because the cohesion force between powder particles in the sample at CSC = 70 wt% is stronger due to the higher water content. As a result, tand at CSC = 70 wt% shows low values.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 8
Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023
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Please cite this article as: T. Kusano, M. Ishii, M. Tani et al., Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2020.09.023