JP7167113B2 - Manufacturing method of electrode coating material - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a method for manufacturing an electrode coating material.

Conventionally, particles of an electrode active material of a battery and other electrode raw materials are mixed with a solvent to form a coating material for coating the surface of a current collector. The technique disclosed in Patent Document 1 is also an example. In the technique of the document, kneading is performed while controlling the slurry temperature and "strain rate".

JP 2017-073363 A

Manufacture of electrode coating materials according to conventional techniques has the following problems. In the case of batteries for high output applications, raw material particles having a hollow structure or a porous structure (hereinafter collectively referred to as "hollow porous structure") may be used. When raw material particles having a hollow porous structure are kneaded with a solvent, the hollow porous structure of the raw material particles may be destroyed. This is not suitable for high output applications. Even if kneading is carried out while controlling the slurry temperature and "strain rate" as in Patent Document 1, destruction of the hollow porous structure cannot be prevented.

The disclosed technology has been made to solve the problems of the conventional technology described above. That is, the object is to provide a method for producing an electrode coating material that can knead raw material particles with a kneading solvent to form a wet material without destroying the hollow porous structure of the raw material particles.

In the manufacturing method of the electrode coating material according to one aspect of the disclosed technology, the driving torque of the mixer when the hollow or porous electrode raw material particles are kneaded together with the kneading solvent is determined by the hollow structure or the porous structure of the electrode raw material particles. The electrode coating material, which is a wet body in which the electrode raw material particles are mixed with the kneading solvent, is obtained by driving the mixer with a driving torque equal to or lower than the upper limit value determined in the upper limit torque determination step, which determines the upper limit value that does not cause crushing. and a kneading step to obtain Here, in the upper limit torque determination step, the crushing strength based on the measured value of the crushing force when the electrode raw material particles are crushed by pressurization or the friction force F during kneading based on the nominal value of the crushing strength determined by the manufacturer of the electrode raw material particles , the volume V of the region that receives the shear stress during kneading, and the number N of the electrode raw material particles in the region that receives the shear stress during kneading. do.

In the manufacturing method of the electrode coating material in the above embodiment, during the kneading step, the mixer is driven with a drive torque within a range not exceeding the upper limit value determined in the upper limit torque determination step. It is possible to obtain an electrode coating material that is a wet body while maintaining the properties. The electrode plate subjected to the coating process using this electrode coating material and the battery constructed using the electrode plate are also included in those manufactured by the manufacturing method of the electrode coating material according to the technology disclosed herein.

In the kneading step of the manufacturing method of the electrode coating material in the above embodiment, the driving torque of the mixer is further measured, and the kneading speed is adjusted so that the measured driving torque is equal to or lower than the upper limit. is desirable. As a result, even if the kneading resistance fluctuates during kneading, the drive torque can be maintained below its upper limit.

According to the technology disclosed herein, there is provided a method for producing an electrode coating material that can knead raw material particles with a kneading solvent to form a wet material without destroying the hollow porous structure of the raw material particles.

It is a schematic diagram which shows the outline|summary of the manufacturing process of an electrode plate. It is a functional block diagram of a kneading device used in a kneading process. FIG. 3 is a schematic diagram showing the state of electrode raw material particles and kneading blades in a mixer.

Embodiments embodying the disclosed technology will be described in detail below with reference to the accompanying drawings. In this embodiment, the technique of the present disclosure is applied to the "kneading" part of the manufacturing of the electrode plate according to the procedure shown in FIG. In the kneading step, the electrode raw material particles are kneaded together with a kneading solvent to obtain a wet body. This wet body is used as a coating material in the subsequent coating process. In this embodiment, particles of the active material and the additive are used as the electrode raw material particles. Additives include conductive materials, binders, thickeners, and the like. As the active material particles, hollow or porous particles are used. Water or an organic solvent is used as the kneading solvent.

In the kneading step in this embodiment, a kneading device having the functional configuration shown in FIG. 2 is used. It comprises a mixer 1 and a control circuit 2 . The control circuit 2 measures the drive torque of the drive motor 3 of the mixer 1 and controls its rotational speed. Any torque measurement method may be used, such as monitoring power values, current values, etc., or measuring strain in the drive transmission system. The type of the mixer 1 is not particularly limited, and may be a planetary mixer, a twin-screw kneader, a three-roll mill, or the like.

In the kneading process in this embodiment, the control circuit 2 adjusts the rotational speed of the drive motor 3 so that the drive torque of the drive motor 3 is maintained within a certain range. The driving torque is focused on so as not to destroy the hollow structure or porous structure of the electrode raw material particles. Therefore, prior to the kneading process, the upper limit torque determination process is performed.

FIG. 3 shows the condition of the electrode raw material particles 4 and the kneading blades 5 in the mixer 1 (in the case of the type having the kneading blades 5). In the mixer 1, the material to be kneaded is sandwiched between the kneading blades 5 and the housing 6, and is subjected to shear stress due to the movement of the kneading blades 5. As shown in FIG. This shear stress is a factor that attempts to destroy the hollow structure or porous structure of the electrode raw material particles 4 . The stress applied to the individual electrode raw material particles 4 due to the shear stress is referred to as frictional force.

The frictional force F that the individual electrode raw material particles 4 receive in the mixer 1 is expressed by the following equation.
F = τ/N …………(1)
τ: Shear stress applied to the material to be kneaded in the area sandwiched between the kneading blade 5 and the housing 6 N: Number of electrode raw material particles 4 in the same area

The number of " N " is the number of electrode raw material particles 4 present in the closest region between the kneading blade 5 and the housing 6 (region A in FIG. 3). This is because shear stress during kneading is applied to the material to be kneaded in this region.

The shear stress τ applied to the material to be kneaded in the equation (1) is expressed by the following equation.
τ = T/V (2)
T: Driving torque of driving motor 3 V: Volume of area (area A) receiving shear stress

From the formulas (1) and (2), the rubbing force F can be expressed by the following formula.
F=T/(N×V) …………(3)

The following equation holds for the driving torque T.
T = μ×u×S …………(4)
μ: Viscosity of material to be kneaded u: Relative speed of tip of kneading blade 5 with respect to housing 6 S: Area of region (region A) receiving shear stress viewed from above in FIG.

From the formulas (3) and (4), the rubbing force F can be expressed by the following formula.
F = (μ×u)/(N×h) …………(5)
h: clearance between the tip of the kneading blade 5 and the housing 6 (=V/S)

In equation (5), the frictional force F is determined by the viscosity μ of the material to be kneaded, the relative velocity u of the kneading blades 5, the number N of the electrode raw material particles 4 subjected to shear stress, and the clearance h of the kneading blades 5. is represented. All of these are known values or values that can be measured or calculated. Viscosity μ can be measured with a suitable viscometer. The relative speed u can be calculated from the rotation speed of the drive motor 3 and the maximum diameter of the kneading blades 5 . The number N can be calculated from the ratio of the volume occupied by the electrode raw material particles 4 in the material to be kneaded to the volume of one electrode raw material particle 4 . The particle size of the raw material can be measured by image analysis or a suitable particle size meter, and the nominal value provided by the raw material manufacturer is acceptable. The volume V can be calculated from the clearance h of the mixer 1, the dimension in the depth direction in FIG. The clearance h etc. are known values according to the specifications of the mixer 1 .

The driving torque is kept within a certain range in the kneading process of this embodiment so as not to break the hollow porous structure of the individual electrode raw material particles 4 . This is because if the frictional force F applied to the electrode raw material particles 4 having a hollow porous structure becomes excessive, the hollow porous structure will be destroyed (this is called "crushing"). The crushing strength (the dimension is the same as the pressure) is an index of how difficult it is to destroy a hollow porous structure. The rubbing force F during kneading must be less than the upper limit value based on the crushing strength.

The crushing force when the electrode raw material particles 4 are crushed by pressurization can be measured using a fine particle crushing force measuring device "NS-A100 type" manufactured by Nanoseeds. If the crushing force is measured, the crushing strength can be calculated based thereon. If there is a nominal value for crushing strength provided by the manufacturer of raw material particles, it is acceptable. If the crushing strength is known, the upper limit of the frictional force F can be determined.

If the upper limit of the frictional force F is determined by the crushing strength, the upper limit of the driving torque T can be determined by the following equation based on the above equation (3).
T = F x N x V …………(6)

Therefore, in the present embodiment, the kneading step is carried out so that the drive torque T of the drive motor 3 is equal to or less than the upper limit determined in the upper limit torque determination step. The driving torque T is measured during the kneading process, and if the measured driving torque T exceeds the upper limit, the driving torque T is decreased by decreasing the rotation speed of the driving motor 3 . As a result, the driving torque T is suppressed below the upper limit.

If the kneading is continued, the viscosity μ of the material to be kneaded decreases, and thus the measured drive torque T may decrease. In this case, the rotation speed may be increased in order to prevent the kneading efficiency from being lowered. A lower limit value of the driving torque T may be set. The rotational speed is increased when the measured drive torque T is below the lower limit. However, even if the rotation speed is increased, the drive torque T must be within a range that does not exceed the upper limit. By performing such control, it is possible to continuously apply an appropriate stress without crushing the electrode material particles 4 while applying a kneading force necessary for uniformly dispersing the material to be kneaded.

By performing the kneading step with a driving torque equal to or lower than the upper limit value, a wet body in which the hollow porous structure of the electrode raw material particles 4 is maintained, that is, an electrode coating material can be obtained. By using this coating material, it is possible to obtain an electrode plate and a battery in which the hollow porous structure of the electrode raw material particles 4 is maintained. Such electrode plates and batteries are suitable for high power applications.

Examples are described below. This embodiment deals with the case of manufacturing a positive electrode plate for a lithium ion battery. The materials used in this example are as follows.
Active material: Ternary composite lithium metal oxide Conductive material: Acetylene black, carbon nanotube Binder: Polyvinylidene fluoride Thickener: Not used Kneading Solvent: N-methyl-2-pyrrolidone

The blending ratio of the solid components was as follows in terms of % by weight.
Active material particles: 93.62
Acetylene black: 3.92
Carbon nanotubes: 0.98
Polyvinylidene fluoride: 1.48

The solid component and the kneading solvent were mixed at a solid content ratio of 80% by weight to obtain a material to be kneaded. Kneading was performed with a roll mill.

Table 1 shows the measurement results of the crushing strength of the active material particles. Here, a total of four types, two types each of hollow structure and porous type, were targeted. The measurement was performed by measuring the crushing force at the time of crushing using the microparticle crushing force measurement device described above, and calculating based on this. Table 1 also lists the measured particle size (diameter) and the upper limit torque value based on the crushing strength.

The above crushing force measurement will be described in more detail. The measurement was carried out as follows under a normal laboratory environment using the above measuring apparatus.
- Sprinkle the powder of the sample on the stage by free fall.
・The crushing needle is pressed against the sample spread on the stage.
・Record the pressing force waveform chart.
・On the waveform chart, the difference between the peak value of the pressing force and the baseline (the level before pressing starts) is defined as the crushing force G [N].

The crushing force G measured as described above was applied to the following formula based on JIS Z 8844:2019 to calculate the crushing strength P [Pa].
P = (2.8×G)/(π×D ² ) …………(7)

In formula (7), "D" is the diameter [m] of the crushed particle. The diameter D used in the calculation of formula (7) is obtained as follows.
・Images of particles sandwiched between the crushing needle and the stage were taken.
・The above image was analyzed with the image analysis software "WinROOF", and the particle size was measured for each particle.

Table 2 shows the results of the above measurements on 10 particles of the sample "hollow material 1" in Table 1.

The particle size and crushing strength of "hollow material 1" in Table 1 are the "average" particle size and crushing strength in Table 2. The standard deviation of "crushing strength" in Table 1 was 2.96 [MPa]. The data in the columns of "hollow material 2", "porous material 1", and "porous material 2" in Table 1 are also based on the results of the same measurement of each sample.

The crushing strength obtained as described above is the upper limit of the frictional force F in the above equation (6). Once the number N is determined, the upper limit of the drive torque T is also determined. The number N is calculated by the following formula.
N={V×(π/sqrt(18))}/{(π×D ³ )/6} …………(8)

The numerator on the right side of equation (8) is the volume occupied by the electrode raw material particles 4 in the volume V of the region receiving the shear stress. This is based on a geometrical theoretical formula assuming that spherical particles are closely packed within the region. This is because the area is pressurized by the movement of the kneading blades 5 . Therefore, the value is higher than the value calculated from the blending ratio of the entire material to be kneaded. The volume V is a known value according to the specifications of the mixer 1 as described above.

The denominator of the right side of the equation (8) is the volume of one electrode raw material particle 4 (diameter D). As the diameter D, the "particle size" in Table 1 can be used. (8) can be solved as follows. "Particle size" in Table 1 is obtained from this formula (9).
N = 1.41 x (V/D3) …………( ⁹ )

The four types of active material particles shown in Table 1 were actually kneaded under the above mixing conditions, and it was inspected whether or not crushing occurred. As the type of mixer 1, a roll mill was used. The drive torque during kneading was set at three levels of 30, 60, and 90 [N·m]. The electrode layer after coating was observed with a scanning electron microscope (SEM) to determine whether or not crushing occurred. Table 3 shows the results.

In Table 3, some items in the "driving torque" column are shown in bold italics. This exceeds the "upper limit torque" in Table 1 for the corresponding grade. In other words, it is expected that the electrode raw material particles 4 will be subjected to a frictional force F that exceeds the crushing strength due to the kneading. On the other hand, the "driving torque" of the normal font in Table 3 is less than the "upper limit torque". In other words, it is expected that the frictional force F applied to the electrode raw material particles 4 will not reach the crushing strength even during kneading.

In Table 3, all cases where the drive torque is equal to or less than the upper limit torque have "crush" as "no", and all cases where the drive torque exceeds the upper limit torque are shown as "crush" as "yes". . From this, the relationship between the driving torque and the presence or absence of crushing is clear. In the "evaluation" column, "good" is given to those without crushing, and "fail" to those with crushing.

The "Remarks" column in Table 3 shows the results of evaluation of the presence or absence of agglomerates of the electrode raw material particles 4 in the electrode layer after coating. Those in which aggregates with a size of 20 μm or more were observed by SEM observation are blank, and those in which there were no such aggregates are indicated by “*”. The presence of agglomerates means that the degree of kneading was insufficient. In the case of “Hollow Material 1” and “Hollow Material 2”, among those with “good” “evaluation”, no agglomerates were observed in those with higher “driving torque”, and agglomerates were observed in those with lower “driving torque”. there is

In Table 3, aggregates were observed in both "porous material 1" and "porous material 2". However, this does not mean that the manufacturing method of this embodiment cannot be applied to porous electrode raw material particles 4 . The "upper limit torque" of "porous material 1" and "porous material 2" in Table 1 is considerably higher than 30 [N m], so the torque value that can eliminate agglomerates without causing crushing because it is possible to find

It is also possible to eliminate agglomerates without increasing the driving torque. For example, depending on the type of mixer 1, by extending the kneading time, there are some that can eliminate agglomerates without increasing the driving torque. Before mixing and kneading the electrode raw material particles 4, a separate process for eliminating agglomerates may be performed. In this case, it is not necessary to consider the elimination of agglomerates by kneading. By any one of these means, the manufacturing method of the present embodiment can be applied to the porous electrode raw material particles 4 as well.

In determining the upper limit torque, it is not always necessary to measure the crushing force using the microparticle crushing force measuring device described above. As shown in Table 3, the upper limit torque may be determined only by trying kneading while changing the driving torque and judging the result.

The determined upper torque limit is generally valid for the same raw material within the same production lot. The crushing strength of the electrode raw material particles 4 may differ if the production lots of the raw materials are the same even if the specifications are the same. Therefore, it is desirable to perform the upper limit torque determination step again for each production lot of the electrode raw material particles 4 .

As described in detail above, according to the present embodiment, the upper limit torque that does not crush the hollow porous structure of the electrode raw material particles 4 is determined, and the kneading process is performed while the driving torque of the mixer does not exceed the upper limit torque. ing. As a result, a method for producing an electrode coating material is realized in which the material particles can be kneaded with the kneading solvent to form a wet material without destroying the hollow porous structure of the electrode material particles 4 . The upper limit torque is the crushing strength ([Pa]), which is the upper limit frictional force at which individual electrode raw material particles 4 are not crushed, the number of electrode raw material particles 4 in the region receiving the shear stress of kneading, and the shear stress of kneading. It can be obtained by multiplying it with the volume of the receiving area.

The present embodiments and examples are merely examples, and do not limit the disclosed technology in any way. Therefore, the disclosed technique can naturally be improved and modified in various ways without departing from the gist thereof. For example, the application is not limited to the positive electrode of lithium-ion batteries. It may be the positive electrode of the same battery, or the positive and negative electrodes of a battery other than a lithium ion battery.

Reference Signs List 1 mixer 2 control circuit 3 drive motor 4 electrode material particles 5 kneading blade 6 housing

Claims (2)

an upper limit torque determination step of determining an upper limit value for driving torque of the mixer when the hollow or porous electrode raw material particles are kneaded together with a kneading solvent in the mixer so as not to crush the hollow or porous structure of the electrode raw material particles;
and a kneading step of obtaining an electrode coating material, which is a wet body in which the electrode raw material particles are mixed with the kneading solvent, by driving the mixer with a driving torque equal to or lower than the upper limit value determined in the upper limit torque determining step. ，
In the upper limit torque determination process,
a crushing strength based on a measured value of the crushing force when the electrode raw material particles are crushed by pressurization or a rubbing force F during kneading based on a nominal value of the crushing strength determined by the manufacturer of the electrode raw material particles;
The volume V of the area subjected to shear stress during kneading,
With the number N of the electrode raw material particles in the region that receives shear stress during kneading,
T = F x N x V
A method of manufacturing an electrode coating material in which the upper limit value of the driving torque is T defined by : 2. The method for manufacturing an electrode coating material according to claim 1, wherein in the kneading step,
measuring the drive torque of the mixer;
adjusting the kneading speed so that the measured drive torque value is equal to or less than the upper limit.

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