JP2020140793A - Manufacturing method of electrode plate - Google Patents

Abstract

To provide a manufacturing method of electrode plate capable of forming a low resistance active material layer where decentralization of carbon nano particles and carbon black particles is good, while using a clay-like mixture containing active material particles, and the like.SOLUTION: A manufacturing method of an electrode plate 1 includes a step S1 of obtaining a first blend 17 by mixing carbon nano particles 12 and a disperse medium 15, a step S2 of obtaining a second blend 18 by mixing the first mixture 17 and carbon black particles 13, a step S3 of obtaining a third blend 19 by mixing the second blend 18 and active material particles 11, and then thick-kneading with shear stress τ=200 N/m2 or more, a step S4 of forming particle aggregate 22 of wet particles 21, a step S5 of forming an undried active material film 5x on a current collector foil 3, and a step S6 of forming an active material layer 5 by desiccating the undried active material film 5x.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing an electrode plate in which an active material layer is formed on a current collecting foil.

As an electrode plate used for a power storage device such as a battery or a capacitor, an electrode plate in which an active material layer containing active material particles, carbon black particles and the like is formed on a current collecting foil is known. Such an electrode plate is manufactured by, for example, the following method. First, active material particles, carbon black particles, and the like are dispersed in a dispersion medium to prepare a liquid active material paste. Then, this active material paste is applied onto the current collecting foil to form an undried active material film, and then the undried active material film is heated and dried to form an active material layer. In addition, as a related prior art, for example, Patent Document 1 can be mentioned.

JP-A-2018-13188

By the way, the present inventor has described at least one of carbon nanotubes and carbon nanoparticles having good conductivity (hereinafter, also referred to as “carbon nanoparticles”) in order to reduce the resistance of the active material layer of the electrode plate. It was examined to form an active material layer in addition to the active material paste of.

However, since the above-mentioned carbon nanoparticles are small in size and easily aggregate, the dispersion of the carbon nanoparticles in the active material paste is insufficient, and the carbon nanoparticles tend to form large aggregates. In addition, carbon black particles are also likely to aggregate. Therefore, in order to improve the dispersion of carbon nanoparticles and carbon black particles, ultrasonic vibration is applied to the liquid or fluid active material paste having a relatively low solid content NV, and the active material paste is applied. It was considered to add a dispersant to the paste. However, it has been found that the addition of the dispersant is not preferable because the resistance of the active material layer increases and the effect of adding the carbon nanoparticles decreases when the dispersant is added. Further, in a clay-like mixture having a high solid content NV, the dispersibility cannot be improved even if ultrasonic vibration is applied.

The present invention has been made in view of the present situation, and the dispersion of carbon nanoparticles and carbon black particles is good even though a clay-like mixture containing active material particles, carbon nanoparticles and carbon black particles is used. The present invention provides a method for producing an electrode plate capable of forming an active material layer having low resistance.

One aspect of the present invention for solving the above problems is a collection foil, carbon nanoparticles formed on the current collection foil and being at least one of an active material particle, a carbon nanotube and a carbon nanofiber, and a carbon nanoparticle. A method for producing an electrode plate including an active material layer containing carbon black particles, wherein the first mixing step of mixing the carbon nanoparticles and a dispersion medium to obtain a first mixture, the first mixture, and the above. The second mixing step of mixing carbon black particles to obtain a second mixture, the second mixture and the active material particles are mixed and kneaded with a shear stress of τ = 200 N / m ² or more to form a clay-like electrode. The third mixing step of obtaining the three mixtures, the particle aggregate forming step of forming a particle aggregate in which the wet particles composed of the third mixture are aggregated, and the undried active material film obtained by rolling the particle aggregate are collected. It is a method for manufacturing an electrode plate including a step of forming an undried film formed on an electric foil and a step of drying the undried active material film on the current collecting foil to form the active material layer. ..

In the above-described electrode plate manufacturing method, in the first mixing step, carbon nanoparticles are first mixed with the dispersion medium, in the second mixing step, then carbon black particles are mixed, and in the third mixing step, the active material. Mix the particles. It has been found that by mixing in such an order, the carbon nanoparticles and carbon black particles and the dispersion medium can be reliably mixed in the third mixture as compared with the case of mixing in other orders. First, the most agglomerating carbon nanoparticles are mixed with the dispersion medium to help the carbon nanoparticles get wet with the dispersion medium without being hindered by the active material particles or the carbon black particles, and to obtain the first mixture. Then, the carbon black particles that easily aggregate next are mixed with the first mixture to promote the carbon black particles to get wet with the dispersion medium without being hindered by the active material particles, and to obtain a second mixture. Finally, it is considered that the carbon nanoparticles and the carbon black particles and the dispersion medium are surely mixed in the third mixture by mixing the active material particles with the second mixture and kneading them to obtain a third mixture.
Moreover, in the third mixing step, since the third mixture is kneaded with a shear stress of τ = 200 N / m ² or more, the agglomerated carbon nanoparticles or carbon black particles are crushed and the carbon nanoparticles in the third mixture are crushed. It is considered that the particles and carbon black particles can be well dispersed.

After that, a particle aggregate composed of the wet particles composed of the third mixture is formed, and the undried active material film is formed by using the particle aggregate, so that the carbon nanoparticles and the carbon black particles are well dispersed. An undried active material film can be formed. Further, by drying this, it is possible to form an active material layer in which carbon nanoparticles and carbon black particles are well dispersed. Therefore, in the above-mentioned production method, an active material layer having good dispersion of carbon nanoparticles and carbon black particles and low resistance can be formed.

It is a perspective view of the positive electrode plate which concerns on embodiment. It is a flowchart of the manufacturing method of the electrode plate which concerns on embodiment. It is explanatory drawing which shows the state of kneading a 3rd mixture by using a roll mill. It is explanatory drawing which shows the state of forming the undried active material film on the current collector foil by using a roll press apparatus. It is a graph which shows the relationship between the solid content NV of a wet particle and the ductility of a wet particle. It is explanatory drawing which shows the ductility test performed on the wet particle. It is a graph which shows the relationship between the material color difference (luminance) and the number of pixels on the surface of the active material layer of a positive electrode plate. 6 is a graph showing the relationship between the shear stress τ applied to the third mixture during kneading and the dispersion index of the conductive material in the active material layer. It is a graph which shows the relationship between the compounding ratio of the 1st carbon nanoparticles in the solid content of a wet particle, and the IV resistance ratio of a battery. It is a graph which shows the relationship between the compounding ratio of the 2nd carbon nanoparticles in the solid content of a wet particle, and the IV resistance ratio of a battery. It is a graph which shows the relationship between the compounding ratio of 3rd carbon nanoparticles in the solid content of a wet particle, and the IV resistance ratio of a battery.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a perspective view of the positive electrode plate (electrode plate) 1 according to the present embodiment. In the following description, the longitudinal direction EH, the width direction FH, and the thickness direction GH of the positive electrode plate 1 are defined as the directions shown in FIG. The positive electrode plate 1 is specifically used for manufacturing a square and sealed lithium ion secondary battery mounted on a vehicle such as a hybrid car, a plug-in hybrid car, or an electric vehicle. It is a strip-shaped positive electrode plate used for manufacturing a mold electrode body.

The positive electrode plate 1 has a current collecting foil 3 made of a strip-shaped aluminum foil extending in the longitudinal direction EH. The first active material layer 5 is formed in a band shape on the region extending in the center of the width direction FH and in the longitudinal direction EH of the first main surface 3a of the current collector foil 3. Further, in the second main surface 3b on the opposite side of the current collecting foil 3, the second active material layer 6 is formed in a band shape on the region extending in the center of the width direction FH and in the longitudinal direction EH. Both ends of the positive electrode plate 1 in the width direction FH do not have the first active material layer 5 and the second active material layer 6 in the thickness direction GH, respectively, and the current collector foil 3 is exposed in the thickness direction GH. It is 1 m.

The first active material layer 5 and the second active material layer 6 are formed by using a particle aggregate 22 in which clay-like wet particles 21 are aggregated, as will be described later. The first active material layer 5 and the second active material layer 6 are composed of active material particles 11, carbon nanoparticles 12, carbon black particles 13, and a binder 14. The weight ratio of these is active material particles: carbon nanoparticles: carbon black particles: binder = 90.7: 3.9: 3.9: 1.5.

In the present embodiment, as the active material particles 11, positive electrode active material particles capable of inserting and removing lithium ions, specifically, lithium nickel cobalt manganese oxide particles which are one of lithium transition metal composite oxide particles are used. There is. Further, as the carbon nanoparticles 12, carbon nanotubes (CNTs) having a diameter φ of several nm and a length L of several μm are used. Further, acetylene black (AB) particles are used as the carbon black particles 13, and polyvinylidene fluoride (PVDF) is used as the binder 14.

Next, a method for producing the particle aggregate 22 and a method for producing the positive electrode plate 1 using the particle aggregate 22 will be described (see FIGS. 2 to 4). First, in the "first mixing step S1", the carbon nanoparticles 12 and the dispersion medium 15 are uniformly mixed to obtain the first mixture 17. In this embodiment, as described above, carbon nanotubes having a diameter of φ of several nm and a length of L of several μm are used as the carbon nanoparticles 12. Further, as the dispersion medium 15, a PVDF solution in which the binder 14 (PVDF in this embodiment) was dissolved in N-methylpyrrolidone (NMP) was used. Further, the mixing ratio of the carbon nanoparticles 12 and the dispersion medium 15 is such that the solid content NV is 78.0 wt% (NMP is 22.0 wt%) and the carbon nanoparticles in the solid content are in the third mixture 19 described later. The weight ratio of 12 was adjusted to 3.9 wt%, and the weight ratio of the binder 14 was adjusted to 1.5 wt%. Further, in the present embodiment, the first mixing step S1 was performed using a biaxial kneader (not shown) provided with a pair of kneading screws in the kneading cylinder.

Next, in the "second mixing step S2", the above-mentioned first mixture 17 and carbon black particles 13 are uniformly mixed to obtain a second mixture 18. In the present embodiment, acetylene black particles are used as the carbon black particles 13 as described above. Further, the mixing ratio of the first mixture 17 and the carbon black particles 13 is such that the solid content NV is 78.0 wt% (NMP is 22.0 wt%) and the carbon nano is in the solid content in the third mixture 19 described later. The weight ratio of the particles 12 was adjusted to 3.9 wt%, the weight ratio of the carbon black particles 13 was 3.9 wt%, and the weight ratio of the binder 14 was 1.5 wt%. Further, in the present embodiment, the second mixing step S2 was continuously performed following the first mixing step S1 using the twin-screw kneader (not shown) used in the first mixing step S1.

Next, in the "third mixing step S3", the above-mentioned second mixture 18 and the active material particles 11 are mixed and kneaded with a shear stress of τ = 200 N / m ² or more to obtain a clay-like third mixture 19. .. In the present embodiment, lithium nickel cobalt manganese oxide particles are used as the active material particles 11 as described above. Further, the mixing ratio of the second mixture 18 and the active material particles 11 is such that the solid content NV of the third mixture 19 is 78.0 wt% (NMP is 22.0 wt%) and the active material particles 11 in the solid content. The weight ratio of the carbon nanoparticles 12 is 90.7 wt%, the weight ratio of the carbon nanoparticles 12 is 3.9 wt%, the weight ratio of the carbon black particles 13 is 3.9 wt%, and the weight ratio of the binder 14 is 1.5 wt%. It was adjusted.

In the present embodiment, the first half of the third mixing step S3 uses the twin-screw kneader (not shown) used in the first mixing step S1 and the second mixing step S2, and is continuous following the second mixing step S2. I went to. As a result, a third mixture 19 in which the active material particles 11, the carbon nanoparticles 12, the carbon black particles 13 and the dispersion medium 15 are uniformly mixed is obtained.

As a result of the present inventor examining the mixing order of the materials, the following has been found, although not detailed. That is, (1) when the active material particles 11, the carbon nanoparticles 12, and the carbon black particles 13 are simultaneously mixed with the dispersion medium 15, even if they are kneaded, the carbon nanoparticles 12 and carbon in the third mixture 19 The black particles 13 remain agglomerated.
Further, (2) when the active material particles 11 are first mixed with the dispersion medium 15, then the carbon nanoparticles 12 and the carbon black particles 13 are mixed and further kneaded, the carbon nanoparticles 12 in the third mixture 19 are also mixed. And the carbon black particles 13 remain agglomerated.

Further, (3) first, the carbon nanoparticles 12 are mixed with the dispersion medium 15, then the active material particles 11, and then the carbon black particles 13 are mixed and further kneaded, or (4) first, carbon. When the nanoparticles 12 are mixed with the dispersion medium 15, then the active material particles 11 and the carbon black particles 13 are simultaneously mixed and further kneaded, the aggregation of the carbon nanoparticles 12 is suppressed in the third mixture 19. However, the carbon black particles 13 remain agglomerated.

On the other hand, as described above, in the first mixing step S1, the carbon nanoparticles 12 were first mixed with the dispersion medium 15, and in the second mixing step S2, the carbon black particles 13 were mixed with the first mixture 17. In the third mixing step S3, the active material particles 11 are finally mixed with the second mixture 18 and further kneaded to make the third mixture 19 more than any of the above-mentioned cases (1) to (4). It has been found that the aggregation of carbon nanoparticles 12 and carbon black particles 13 can be suppressed.

Next, in the latter half of the third mixing step S3, the above-mentioned third mixture 19 is kneaded with a shear stress of τ = 200 N / m ² or more. In this embodiment, a roll mill 200 having three rolls is used (see FIG. 3). The roll mill 200 is arranged in parallel with the charging roll 210, the intermediate roll 220 arranged in parallel with the charging roll 210 via the first roll gap Ga, and the intermediate roll 220 with the second roll gap Gb in parallel. It is provided with a finishing roll 230. A motor (not shown) for rotationally driving the rolls is connected to each of the charging roll 210, the intermediate roll 220, and the finishing roll 230, and the charging roll 210 (peripheral speed Va) is connected in the rotation direction indicated by the arrow in FIG. ), The intermediate roll 220 (peripheral speed Vb) and the finishing roll 230 (peripheral speed Vc) are rotated (Va <Vb <Vc).

Further, the roll mill 200 includes a mixture supply unit 240 that supplies the third mixture 19 toward the first roll gap Ga above the first roll gap Ga of the charging roll 210 and the intermediate roll 220. Further, the roll mill 200 includes a doctor blade 250 in the vicinity of the finishing roll 230 for scraping and recovering the film-like third mixture 19 transferred to the finishing roll 230.
When the third mixture 19 is charged into the mixture supply unit 240, the third mixture 19 is rolled by the charging roll 210 and the intermediate roll 220 to form a film, and a film is formed on the intermediate roll 220. Subsequently, the film-like third mixture 19 is further rolled on the intermediate roll 220 and the finishing roll 230, and transferred onto the finishing roll 230. The film-like third mixture 19 is then scraped and recovered by the doctor blade 250.

In the present embodiment, the second roll gap Gb between the intermediate roll 220 and the finishing roll 230 is adjusted so that the shear stress τ applied to the third mixture 19 between the intermediate roll 220 and the finishing roll 230 is 200 N / m ² . This shear stress τ is determined by (shear stress τ) = (motor torque) / (machining) from the torque of the motor that rotates the finishing roll 230 and the machining volume of the third mixture 19 (second roll gap Gb × machining area). Volume). The processing area of the third mixture 19 is obtained by (processing area) = (processing width in the axial direction of the roll) × (processing length in the rotation direction of the roll). The "machining length in the rotation direction of the roll" was set to the length in the range in which a pressure of 98% or more was applied to the maximum value of the pressure applied to the third mixture 19 between the intermediate roll 220 and the finishing roll 230.

Further, in the present embodiment, kneading was performed by passing the third mixture 19 through the roll mill 200 five times. From the second time onward, the recovered film-like third mixture 19 was folded into a plurality of folded states and charged into the mixture supply unit 240.
By kneading the third mixture 19 with such a high shear stress τ, the agglomerated carbon nanoparticles 12 and carbon black particles 13 are crushed and uniformly dispersed in the third mixture 19. Can be done.

Next, in the "particle assembly forming step S4", the particle aggregate 22 in which the wet particles 21 made of the third mixture 19 are aggregated is formed. In the present embodiment, an extruder (not shown) in which an extrusion screw is arranged in the extrusion cylinder and has a cutting blade for cutting the third mixture 19 extruded from the extrusion cylinder is used. As a result, columnar wet particles 21 having a diameter D = 2.0 mm and a height H = 2.0 mm were granulated to obtain a particle aggregate 22 in which the wet particles 21 were aggregated.

Here, the results of a test investigating the dispersibility of the carbon nanoparticles 12 and the carbon black particles 13 in the wet particles 21 will be described (see FIG. 5). FIG. 5 shows the relationship between the solid content NV of the wet particles 21 and the ductility of the wet particles 21 for Examples and Comparative Examples. Specifically, as an example, the solid content NV of the wet particles 21 is changed from 77.0 wt% to 80.0 wt% in 7 steps, and other than that, as described above, the first mixing step S1 to particle assembly. The body forming step S4 was carried out to obtain particle aggregates 22 of the wet particles 21 respectively.

On the other hand, as a comparative example, instead of the above-mentioned first mixing step S1 to third mixing step S3, active material particles 11, carbon nanoparticles 12, carbon black particles 13 and a dispersion medium 15 are simultaneously mixed to form a third mixture. I got 19. After that, the third mixture 19 is kneaded using a roll mill 200 in the same manner as in the latter half of the third mixing step S3 described above, and further, in the same manner as in the particle aggregate forming step S4 described above, the wet particles 21 A particle aggregate 22 was obtained. In this comparative example as well, the solid content NV of the wet particles 21 is changed in 7 steps from 77.0 wt% to 80.0 wt% to produce the particle aggregates 22 of the wet particles 21, respectively, as in the examples. did.

Next, a "ductility test" was performed on each of the wet particles 21 of Examples and Comparative Examples (see FIG. 6). A ductility test apparatus 300 is used for this malleability test. The spreadability test apparatus 300 includes an upper member 310 having a flat lower surface 310b and a lower portion 320 having a flat upper surface (upper surface of the first slide member 321 described later) 321a, and the upper member 310. Wet particles 21 are arranged between the lower surface 310b and the upper surface 321a of the lower side 320 (see FIG. 6A). A load sensor (not shown) is attached to the upper member 310 so that the load FA in the vertical direction applied from the wet particles 21 to the upper member 310 can be measured. Further, the ductility test device 300 is configured to be capable of measuring the size ta of the gap between the lower surface 310b of the upper member 310 and the upper surface 321a of the lower portion 320.

Further, the lower side portion 320 has a first slide member 321 and a second slide member 323 arranged below the first slide member 321. The lower surface 321b of the first slide member 321 is a slope located upward toward the left side in FIG. Further, the upper surface 323a of the second slide member 323 also faces the lower surface 321b of the first slide member 321 and is a slope located upward toward the left side in FIG. When the first slide member 321 is slid to the left in FIG. 6 with respect to the second slide member 323, the first slide member 321 moves to the left and upward, so that the first slide member 321 Wet particles 21 arranged between the upper surface 321a and the lower surface 310b of the upper member 310 are stretched (see FIG. 6B).

Then, the thickness of the wet particles 21 when the load FA applied from the wet particles 21 to the upper member 310 becomes a predetermined load (the size of the gap between the lower surface 310b of the upper member 310 and the upper surface 321a of the lower portion 320). To measure. The measurement results for each of the wet particles 21 of Examples and Comparative Examples are shown in FIG. In FIG. 5, the measurement result (thickness of wet particles 21 = gap size ta) when the solid content NV is 77.0 wt% in the example is shown as a reference (= ductility 100%). is there.
When the solid content NV is the same, the smaller the ductility of the wet particles 21 (the softer the wet particles 21), the smaller the aggregation of the carbon nanoparticles 12 and the carbon black particles 13 in the wet particles 21 (the better the dispersion). I know there is).

As can be seen from the graph of FIG. 5, when the solid content NV of the wet particles 21 is equal, the examples (carbon nanoparticles 12, carbon black particles 13, active material) are compared with the comparative example (all materials are mixed at the same time). The wet particles 21 are less spreadable (the wet particles 21 are softer), and the carbon nanoparticles 12 and the carbon black particles 13 are less agglomerated (good dispersion) in the wet particles 21 when the particles 11 are mixed in this order. ).

The reason why such a result occurs is not clear at present, but in order to make it easier to get wet with the dispersion medium 15, it is considered that it is better to mix with the dispersion medium 15 in order from the material that easily aggregates. That is, as in the embodiment, first, the carbon nanoparticles 12 that are most likely to aggregate are mixed with the dispersion medium 15, and the carbon nanoparticles 12 become the dispersion medium 15 without being hindered by the active material particles 11 and the carbon black particles 13. Along with encouraging wetting, the first mixture 17 is obtained. After that, the carbon black particles 13 that are likely to aggregate next are mixed with the first mixture 17, and the carbon black particles 13 are promoted to get wet with the dispersion medium 15 without being hindered by the active material particles 11, and the second mixture 18 is mixed. obtain. Finally, the active material particles 11 are mixed with the second mixture 18 and kneaded to obtain the third mixture 19, whereby the carbon nanoparticles 12, the carbon black particles 13 and the dispersion medium 15 are surely obtained in the third mixture 19. It is thought that it was mixed with.

After the particle aggregate forming step S4, in the "first undried film forming step S5" (see FIG. 2), the first undried active material film 5x obtained by rolling the particle aggregate 22 is placed on the current collector foil 3. Form. The first undried film forming step S5 is performed using the roll press device 100 (see FIG. 4). The roll press device 100 includes three rolls, specifically, a first roll 110, a second roll 120 arranged in parallel with the first roll 110 via a first roll gap G1, and the first roll 110. The two rolls 120 are provided with a third roll 130 arranged in parallel with the second roll gap G2. Motors (not shown) for rotationally driving the rolls are connected to the first rolls 110 to the third rolls 130, respectively, and the first roll 110 (peripheral speed V1), The second roll 120 (peripheral speed V2) and the third roll 130 (peripheral speed V3) are rotated (V1 <V2 <V3), respectively. Further, the roll press device 100 supplies a particle aggregate 22 composed of wet particles 21 toward the first roll gap G1 above the first roll gap G1 of the first roll 110 and the second roll 120. A supply unit 140 is provided.

When the particle aggregate 22 (wet particle 21) is charged into the aggregate supply unit 140, the particle aggregate 22 is rolled by the first roll 110 and the second roll 120, and the film-like first undried active material film 5x And a film is formed on the second roll 120. Subsequently, the first undried active material film 5x is the first of the current collecting foil 3 passed between the second roll 120 and the third roll 130 and between the second roll 120 and the third roll 130. Transferred onto the main surface 3a. As a result, the "undried one-sided positive electrode plate 1x" having the first undried active material film 5x is continuously formed on the current collector foil 3.

Next, in the "first drying step S6", the first undried active material film 5x on the current collector foil 3 is dried to form the first active material layer 5. Specifically, the above-mentioned undried one-sided positive electrode plate 1x is conveyed into a drying device (not shown), and hot air is blown to the first undried active material film 5x of the undried one-sided positive electrode plates 1x to obtain the first undried one side. The NMP remaining in the active material film 5x is evaporated to form the first active material layer 5. The negative electrode plate having the first active material layer 5 on the current collector foil 3 is also referred to as a single-side positive electrode plate 1y.

Next, in the "second undried film forming step S7", the second undried active material film 6x obtained by rolling the particle aggregate 22 in the same manner as in the first undried film forming step S5 described above is applied to the current collecting foil. Form on top of 3. That is, using the above-mentioned roll press device 100 prepared separately, a second undried active material film 6x is formed on the second roll 120 by using the particle aggregate 22, and then on the second roll 120. The second undried active material film 6x is transferred onto the second main surface 3b of the current collector foil 3 in the one-side positive electrode plate 1y conveyed by the third roll 130. As a result, the dried first active material layer 5 is provided on the first main surface 3a of the current collecting foil 3, and the undried second undried active material film is provided on the second main surface 3b of the current collecting foil 3. A "single-dried double-sided positive electrode plate 1z" having 6x is continuously formed.

Next, in the "second drying step S8", the second undried active material film 6x on the current collector foil 3 is dried in the same manner as in the above-mentioned first drying step S6 to form the second active material layer 6. Form. Specifically, the single-dried double-sided positive electrode plate 1z is transported into a drying device (not shown), and hot air is blown onto the second undried active material film 6x of the single-dried double-sided positive electrode plates 1z to form a second active material layer. 6 is formed. As a result, a positive electrode plate (positive electrode plate 1w before pressing) having a current collecting foil 3, a first active material layer 5, and a second active material layer 6 is formed.

Next, in the "pressing step S9", the above-mentioned pre-press positive electrode plate 1w is roll-pressed with a roll press device (not shown) to increase the densities of the first active material layer 5 and the second active material layer 6, respectively. Thus, the positive electrode plate 1 shown in FIG. 1 is completed.

Here, the results of a test investigating the dispersibility of the conductive materials (carbon nanoparticles 12 and carbon black particles 13) in the active material layers 5 and 6 of the positive electrode plate 1 will be described (see FIGS. 7 and 8). FIG. 7 shows the results (two specific examples) of "luminance analysis" in which the material color difference (luminance) on the surface of the first active material layer 5 of the positive electrode plate 1 is image-analyzed. Specifically, the conductive material (carbon nanoparticles 12 and carbon black particles 13) has extremely low reflectance, while the active material particles 11 contain nickel and cobalt and have high reflectance. Therefore, on the surface of the first active material layer 5 of the positive electrode plate 1, the portion where the conductive material is abundant (the portion where the active material particles 11 are small) has low brightness and the portion where the active material particles 11 are abundant (the portion where the active material particles 11 are abundant). The part with less conductive material) has higher brightness. Therefore, the brightness of each pixel was obtained for an image (total number of pixels: 250,000) showing the surface of the first active material layer 5 of the positive electrode plate 1. FIG. 7 shows the frequency distribution of the luminance of each analyzed pixel.

When the dispersion of the conductive material in the first active material layer 5 is good, the brightness variation (standard deviation of brightness) becomes small as shown in Specific Example 1 shown by the solid line (Standard deviation of brightness = 3.0 in Specific Example 1). ). On the other hand, when the dispersion of the conductive material in the first active material layer 5 is not good, the brightness variation (standard deviation of brightness) becomes large as shown in Specific Example 2 shown by the broken line (in Specific Example 2, the standard deviation of brightness = 5). .4). Therefore, the dispersibility of the conductive material in the first active material layer 5 can be evaluated by using the magnitude of the standard deviation of the brightness as an index. Hereinafter, this standard deviation of brightness is also referred to as “dispersion index”.

FIG. 8 shows the shear stress τ applied to the third mixture 19 during the kneading in the third mixing step S3 and the dispersion index of the conductive materials (carbon nanoparticles 12 and carbon black particles 13) in the active material layers 5 and 6. Shows the relationship with. Specifically, the shear stress τ at the time of kneading was changed to 6 steps, and other than that, the first mixing step S1 to the pressing step S9 were performed as described above to manufacture the positive electrode plates 1, respectively. Then, the above-mentioned "luminance analysis" was performed on each positive electrode plate 1 to obtain the standard deviation (= dispersion index) of the luminance.

As can be seen from the graph of FIG. 8, if the shear stress τ applied to the third mixture 19 during kneading is at least 200 N / m ² or more, the dispersion index can be made a small value of 2.0 or less. On the other hand, when the dispersion index is 2.0 or less from the result of investigating the dispersion state of the conductive material (carbon nanoparticles 12 and carbon black particles 13) in the first active material layer 5 by the SEM image, the first active material layer It is known that the dispersion of the conductive material in No. 5 is particularly good. Therefore, it can be seen that by setting the above-mentioned shear stress τ to 200 N / m ² or more, the dispersion of the conductive material in the first active material layer 5 can be improved.

Next, in the following Examples and Comparative Examples, the relationship between the blending ratio of the carbon nanoparticles 12 in the solid content of the wet particles 21 and the IV resistance of the battery was investigated (see FIGS. 9 to 11).
As Examples 1 to 4 (see FIG. 9), the blending ratio of the carbon nanoparticles 12 in the solid content of the wet particles 21 was changed to 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%. , Other than that, four types of positive electrode plates 1 were manufactured in the same manner as in the embodiment. The blending ratio of the carbon nanoparticles 12 was changed so that the blending ratio of the entire conductive material (the blending ratio of the carbon nanoparticles 12 and the carbon black particles 13 combined) in the wet particles 21 was equal (7.8 wt%). Accordingly, the blending ratio of the carbon black particles 13 was changed. Further, as the carbon nanoparticles 12, as described above, carbon nanotubes (CNTs) having a diameter φ of several nm and a length L of several μm were used (referred to as “first carbon nanoparticles” in FIG. 9). .. Further, these positive electrode plates 1 were used, and a negative electrode plate was separately prepared to manufacture a lithium ion secondary battery (hereinafter, also simply referred to as “battery”).

Further, as Comparative Examples 1 to 4, the positive electrode plates 1 were manufactured by the following methods using a liquid active material paste. Specifically, the blending ratio of the carbon nanoparticles 12 in the solid content of the active material paste is 0 wt%, 1.0 wt%, 2.0 wt% and 3.0 wt%, and the blending ratio of the entire conductive material is 7.8 wt. The blending ratio of the carbon black particles 13 was changed according to the change in the blending ratio of the carbon nanoparticles 12 so as to be%. Further, in this active material paste, a dispersant (specifically, a naphthyl group-containing acrylic resin) was blended at a ratio of 0.9 wt%, and instead, the blending ratio of the active material particles 11 was reduced. That is, the mixing ratio of the solid content was set to active material particles: conductive materials (carbon nanoparticles and carbon black particles): binder: dispersant = 89.8: 7.8: 1.5: 0.9. The active material paste was prepared by dispersing the active material particles 11, the carbon nanoparticles 12, the carbon black particles 13, and the dispersant in the dispersion medium 15 while applying ultrasonic vibration. The solid content NV of the active material paste was 48.0 wt% (NMP was 52.0 wt%).

Next, the above-mentioned active material paste was applied to the first main surface 3a of the current collector foil 3 and dried by heating to form the first active material layer 5. Since the carbon nanoparticles 12 in the active material paste tend to settle, ultrasonic vibration was continuously applied to the active material paste until just before the coating. Further, the active material paste was also applied to the second main surface 3b of the current collector foil 3 and dried by heating to form the second active material layer 6. Then, the pressing step S9 was performed in the same manner as in the embodiment to manufacture the positive electrode plates 1 respectively. Further, each of these positive electrode plates 1 was used to manufacture a lithium ion secondary battery.

Next, the IV resistance of each of the batteries according to Examples 1 to 4 and Comparative Examples 1 to 4 was measured. Specifically, the battery adjusted to SOC 56% is discharged at an ambient temperature of 25 ° C. at a discharge current value I = 20C for 5 seconds, and the battery voltage V1 at the start of this discharge and the battery voltage V2 after 5 seconds are obtained. Was measured, and the IV resistance R of the battery was calculated by R = (V1-V2) / I. Then, the "IV resistance ratio" of the other batteries was calculated using the IV resistance R of the battery of Comparative Example 1 as a reference (= 100%). The result is shown in FIG.

Further, in Examples 5 and 6 (see FIG. 10), the carbon nanoparticles 12 are larger than the carbon nanotubes used in the embodiments and Examples 1 to 4, specifically, the diameter φ is several nm and the length. Two types of positive electrode plates 1 were manufactured by changing to carbon nanotubes having an L of several tens of μm (referred to as “second carbon nanoparticles” in FIG. 10). The blending ratio of the carbon nanoparticles 12 in the solid content of the wet particles 21 was 1.0 wt% and 2.0 wt%. Further, each of these positive electrode plates 1 was used to manufacture a battery.

Further, as Comparative Examples 5 to 7, the carbon nanoparticles 12 were changed to the same large carbon nanotubes as in Examples 5 and 6, and the blending ratio of the carbon nanoparticles 12 in the solid content of the active material paste was 1.0 wt%. Liquid active material pastes were prepared at 2.0 wt% and 3.0 wt%. Then, using these active material pastes, the positive electrode plates 1 were manufactured in the same manner as in Comparative Examples 1 to 4, and the batteries were further manufactured.
Next, for each of the batteries according to Examples 5 and 6 and Comparative Examples 5 to 7, the IV resistance was measured in the same manner as for the batteries according to Examples 1 to 4 and Comparative Examples 1 to 4, respectively, and the IV was measured. The resistivity ratios were calculated respectively. The result is shown in FIG.

Further, as Examples 7 to 9 (see FIG. 11), the carbon nanoparticles 12 are referred to as carbon nanoparticles having a diameter φ of about 150 nm and a length L of about 6 μm (in FIG. 11, “third carbon nanoparticles”). ), And three types of positive electrode plates 1 were manufactured. The blending ratio of the carbon nanoparticles 12 in the solid content of the wet particles 21 was 1.0 wt%, 2.0 wt%, and 3.0 wt%. Further, each of these positive electrode plates 1 was used to manufacture a battery.

Further, as Comparative Examples 8 to 10, the carbon nanoparticles 12 were changed to the same carbon nanoparticles as in Examples 7 to 9, and the blending ratio of the carbon nanoparticles 12 in the solid content of the active material paste was 1.0 wt%. Liquid active material pastes were prepared at 2.0 wt% and 3.0 wt%. Then, each positive electrode plate 1 was manufactured using these active material pastes, and each battery was manufactured.
Next, for each of the batteries according to Examples 7 to 9 and Comparative Examples 8 to 10, the IV resistance was measured in the same manner as for the batteries according to Examples 1 to 6 and Comparative Examples 1 to 7, respectively, and the IV was measured. The resistivity ratios were calculated respectively. The result is shown in FIG.

As can be seen from the graphs of FIGS. 9 to 11, the IV resistance R tends to decrease as the blending ratio of the carbon nanoparticles 12 increases. Further, it can be seen that when the blending ratios of the carbon nanoparticles 12 are equal, the IV resistance R is smaller in the examples than in the comparative examples.
The reason is considered to be as follows. That is, first, in Comparative Example 1, the conductive material contained in the active material layers 5 and 6 of the positive electrode plate 1 is only the carbon black particles 13, and the carbon nanoparticles 12 are not included. Since the carbon nanoparticles 12, which have better conductivity than the carbon black particles 13, are not contained in the active material layers 5 and 6, the IV resistance R is the largest in the battery using the positive electrode plate 1. On the other hand, in each of the other batteries of Comparative Examples 2 to 10 and Examples 1 to 9, the active material layers 5 and 6 of the positive electrode plate 1 contain carbon nanoparticles 12 having good conductivity, so that they are comparative examples. The IV resistance R was smaller than that of the battery of 1. Further, it is considered that as the blending ratio of the carbon nanoparticles 12 increases, the conductivity of the active material layers 5 and 6 becomes better, so that the IV resistance R of the battery tends to decrease.

Further, in Comparative Examples 1 to 10, since the dispersant is added to the active material paste, the dispersant remains in the active material layers 5 and 6. Since the conductivity of the active material layers 5 and 6 is lowered by this dispersant, the IV resistance ratio of the battery is increased. On the other hand, in Examples 1 to 9, since the dispersant is not used, the dispersant does not exist in the active material layers 5 and 6. Therefore, since the conductivity of the active material layers 5 and 6 does not decrease, it is considered that the IV resistance ratio of the battery of the example was smaller than that of the comparative example when the compounding ratio of the carbon nanoparticles 12 was the same.

As described above, in the method for producing the positive electrode plate 1, the carbon nanoparticles 12 are first mixed with the dispersion medium 15 in the first mixing step S1, and then the carbon black particles 13 are mixed in the second mixing step S2. The mixture is mixed, and the active material particles 11 are mixed in the third mixing step S3. By mixing in such an order, the carbon nanoparticles 12, the carbon black particles 13, and the dispersion medium 15 can be reliably mixed in the third mixture 19 as compared with the case of mixing in other orders.
Moreover, in the third mixing step S3, the third mixture 19 is kneaded with a shear stress τ = 200 N / m ² or more, so that the agglomerated carbon nanoparticles 12 or carbon black particles 13 are crushed and the third The carbon nanoparticles 12 and the carbon black particles 13 can be well dispersed in the mixture 19.

After that, the particle aggregate 22 in which the wet particles 21 made of the third mixture 19 are aggregated is formed, and the undried active material films 5x and 6x are formed by using the particle aggregate 22 to form the carbon nanoparticles 12 and the carbon nanoparticles 12. It is possible to form undried active material films 5x and 6x in which the carbon black particles 13 are well dispersed. Further, by drying the carbon nanoparticles 12, the active material layers 5 and 6 in which the carbon nanoparticles 12 and the carbon black particles 13 are well dispersed can be formed. Therefore, in the method for producing the positive electrode plate 1, the active material layers 5 and 6 can be formed in which the carbon nanoparticles 12 and the carbon black particles 13 are well dispersed and the resistance is low.

In the above, the present invention has been described in accordance with the embodiments and examples, but the present invention is not limited to the above-described embodiments and examples, and is appropriately modified and applied without departing from the gist thereof. It goes without saying that you can do it.
For example, in the first half of the first mixing step S1, the second mixing step S2, and the third mixing step S3 of the embodiment, mixing was performed using a twin-screw kneader, but for example, a kneader, a planetary mixer, or the like was used. May be mixed.
Further, in the latter half of the third mixing step S3 of the embodiment, the third mixture 19 was kneaded using a roll mill. For example, a single-screw kneader, a twin-screw kneader, or a multi-screw kneader having three or more shafts. It may be kneaded by using or the like.

1 Positive electrode plate (electrode plate)
3 Current collector foil 5 1st active material layer 5x 1st undried active material film 6 2nd active material layer 6x 2nd undried active material film 11 Active material particles 12 Carbon nanoparticles 13 Carbon black particles 14 Binder 15 Dispersion Medium 17 1st mixture 18 2nd mixture 19 3rd mixture 21 Wet particles 22 Particle aggregate 100 Roll press device 200 Roll mill S1 1st mixing step S2 2nd mixing step S3 3rd mixing step S4 Particle aggregate forming step S5 1st Undried film forming step S6 First drying step S7 Second undried film forming step S8 Second drying step S9 Pressing step

Claims (1)

With the current collector foil
A method for producing an electrode plate, which is formed on the current collecting foil and includes active material particles, carbon nanoparticles which are at least one of carbon nanotubes and carbon nanofibers, and an active material layer containing carbon black particles. hand,
In the first mixing step of mixing the carbon nanoparticles and the dispersion medium to obtain a first mixture,
A second mixing step of mixing the first mixture and the carbon black particles to obtain a second mixture, and
A third mixing step of mixing the second mixture and the active material particles and kneading them with a shear stress of τ = 200 N / m ² or more to obtain a clay-like third mixture.
A particle aggregate forming step of forming a particle aggregate in which wet particles composed of the third mixture are aggregated, and
The undried film forming step of forming the undried active material film obtained by rolling the particle aggregate on the current collecting foil, and
A drying step of drying the undried active material film on the current collecting foil to form the active material layer, and
A method for manufacturing an electrode plate.

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