Mixing machine and mixing method

Abstract

The present invention provides a kneader and a kneading method that can simultaneously suppress damage and improve dispersibility when mixing electrode materials. [Solution] The kneader 1 comprises a barrel 2 into which the electrode material for the battery is fed, a pair of rotating shafts 5 rotatably mounted for kneading the electrode material inside the barrel 2, and a pair of paddles 7 integrally rotatably mounted on the pair of rotating shafts 5 to shear the electrode material by rotation. The paddles 7 have a plurality of protrusions 19 projecting toward the inner wall of the barrel 2 at equal intervals in the circumferential direction. At least one of the plurality of protrusions 19 has a top portion 21 formed by hollowing out at least one of the axial sides of the paddle 7.

Description

Technical Field

[0001] The present disclosure relates to a kneader for kneading an electrode material of a battery and a kneading method.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1, an electrode paste manufacturing apparatus for manufacturing a paste-like electrode material used for an electrode plate of a battery is well-known. The paste-like electrode material is manufactured, for example, by kneading a powder and a solvent. Therefore, at the start of kneading the powder and the solvent, the viscosity of the slurry in which the powder and the solvent are mixed is high. Therefore, if a high shearing force is applied to the slurry at the start of kneading, the material may be damaged. Thus, in the case of Patent Document 1, by providing a "coarse kneading zone" in which the diameter of the paddle is reduced and the distance between the inner wall of the barrel and the paddle is made larger than before, an excessive shearing force is not applied to the material at the start of kneading.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of Patent Document 1, by reducing the diameter of the paddle and increasing the clearance between the inner wall of the barrel and the paddle, a large shearing force is not applied to the slurry material of the electrode. However, when the clearance between the inner wall of the barrel and the paddle increases, the flow rate of the slurry material decreases accordingly, making it difficult for the slurry material to disperse. Therefore, since it becomes difficult for the slurry material to mix, the kneading efficiency may decrease.

[0005] An object of the present disclosure is to provide a kneader and a kneading method capable of achieving both damage suppression and dispersibility improvement when kneading an electrode material. [Means for solving the problem]

[0006] A kneader that solves the above problem comprises a barrel into which electrode material for a battery is fed; a pair of rotating shafts rotatably provided for kneading the electrode material inside the barrel; and a pair of paddles integrally rotatably provided on the pair of rotating shafts, which shear the electrode material by rotation, wherein the paddles have a plurality of protrusions projecting toward the inner wall of the barrel at equal intervals in the circumferential direction, and at least one of the plurality of protrusions has a top portion formed by hollowing out at least one of the axial sides of the paddle.

[0007] A kneading method to solve the above problem is a method for shearing an electrode material for a battery by rotating a pair of paddles that are integrally rotatable on the pair of rotating shafts when the electrode material is put into a barrel that houses a pair of rotating shafts that are rotatably provided for kneading the electrode material for a battery, wherein the electrode material is sheared by using a paddle in which a plurality of protrusions projecting toward the inner wall of the barrel are formed at equal intervals in the circumferential direction, and at least one of the plurality of protrusions has a top formed by hollowing out at least one of the sides of the paddle in the axial direction. [Effects of the Invention]

[0008] This disclosure makes it possible to achieve both damage suppression and improved dispersibility when mixing electrode materials. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing the configuration of a kneading machine according to one embodiment. [Figure 2] This is a cross-sectional view taken along line II-II, as shown in Figure 1. [Figure 3] A perspective view of the paddle. [Figure 4] This is a close-up view of the paddle's protrusion. [Figure 5] This is a diagram illustrating the rotation of a conventional paddle. [Figure 6] This is a schematic diagram showing the shape of another conventional paddle 29. [Figure 7] This is a schematic diagram showing the shape of a two-piece comparison paddle. [Figure 8] This graph shows the correlation between the blackness and viscosity of a slurry material. [Figure 9] This is an explanatory diagram illustrating the kneading action that occurs in slurry material when a paddle is used. [Modes for carrying out the invention]

[0010] An embodiment of this disclosure is described below. This disclosure is not limited to these examples and includes all modifications in the sense and scope equivalent to the claims. For illustrative purposes, the drawings may exaggerate or simplify some parts of the configuration, and the dimensional proportions of the parts may differ from those of the actual components.

[0011] (Mixing machine 1) As shown in Figure 1, the kneader 1 comprises a barrel 2 into which the electrode material for the battery is fed, and a pair of kneading shafts 3 that knead the electrode material fed into the barrel 2. The kneading shafts 3 rotate in the same direction by an actuator 4, such as a motor. By rotating, the kneading shafts 3 transport the electrode material fed into the barrel 2 from upstream to downstream and knead it, turning it into a slurry. The kneader 1 generates a paste to be applied to the current collector of the electrode plate by kneading the electrode material. In this example, the electrode plate is a negative electrode plate. In this example, the paste is a negative electrode composite paste. In this example, the battery is a lithium-ion secondary battery.

[0012] Each of the kneading shafts 3 has a pair of rotating shafts 5 that are rotatably mounted to knead the electrode material inside the barrel 2. Multiple screws 6 and paddles 7 are integrally rotatably mounted on the rotating shafts 5, aligned in the axial direction. Thus, the kneader 1 comprises a pair of screws 6 that convey the electrode material inside the barrel 2 by rotating in the same direction, and a pair of paddles 7 that are integrally rotatably mounted on the pair of rotating shafts 5 and shear the electrode material by rotation.

[0013] (electrode material) The electrode material to be mixed in the mixer 1 shown in Figure 1 includes an active material and additives. When the electrode material is the material for the negative electrode plate, the electrode material for the negative electrode plate includes a negative electrode active material and negative electrode additives. The negative electrode active material is, for example, a powdered carbon material such as graphite. In this example, the negative electrode active material is, for example, natural graphite. The negative electrode additives include, for example, a negative electrode solvent, a negative electrode thickener, and a negative electrode binder. The negative electrode solvent is, for example, water. As described above, the electrode material of a battery includes a solid component and a solvent.

[0014] The negative electrode thickener used is, for example, a polymer system that is insoluble in organic solvents but dissolves in water to exhibit viscosity. Examples of polymer systems used are cellulose derivatives such as carboxymethylcellulose (CMC) and methylcellulose (MC).

[0015] For the negative electrode binder, for example, a polymer material that disperses in water is used. Examples of polymer materials include vinyl acetate copolymer, styrene-butadiene block copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), and rubbers such as gum arabic. Examples of polymer materials include fluorine-based resins such as polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer (ETFE).

[0016] (Barrel 2) As shown in FIGS. 1 and 2, the barrel 2 has a housing chamber 9 that rotatably houses a pair of kneading shafts 3. As shown in FIG. 2, the housing chamber 9 has a first housing chamber 9a that houses the first kneading shaft 3a, which is one of the pair of kneading shafts 3, and a second housing chamber 9b that houses the second kneading shaft 3b, which is the other of the pair of kneading shafts 3. The first housing chamber 9a and the second housing chamber 9b are formed in a shape in which circular holes partially overlap when viewed from the axial direction of the kneading shaft 3.

[0017] As shown in FIG. 1, the barrel 2 has an inlet 10 into which the electrode material is charged and an outlet 11 for discharging the kneaded electrode material. The inlet 10 is arranged at the proximal end in the longitudinal direction of the barrel 2. The outlet 11 is arranged at the distal end in the longitudinal direction of the barrel 2.

[0018] (Screw 6) As shown in FIG. 1, the screw 6 has a stirring screw 6a arranged at a position facing the inlet 10 and a return screw 6b arranged at a position facing the outlet 11. The stirring screw 6a sends the electrode material charged from the inlet 10 downstream while stirring it. The return screw 6b sends the kneaded electrode material to the outlet 11 at the end of the conveyance path of the electrode material. The stirring screw 6a and the return screw 6b have blades 12 formed in a spiral shape around the axis. The pair of screws 6 are arranged such that the blades 12 mesh with each other. The blade 12 of the stirring screw 6a and the blade 12 of the return screw 6b are formed such that the spiral directions are opposite.

[0019] (Paddle 7) As shown in Figure 1, the paddle 7 is formed as a group of paddles arranged in the axial direction of the paddle 7, with multiple pairs of paddles positioned opposite each other in a direction perpendicular to the axis of the paddle 7. The paddle 7 includes a kneading paddle 13 that shears and kneads the electrode material during the transport process, and a resistance paddle 14 that compresses the transported electrode material to make its bulk density as uniform as possible. The groups of kneading paddles 13 and resistance paddles 14 are arranged alternately in the axial direction. The electrode material introduced into the barrel 2 from the input port 10 is kneaded by the multiple kneading paddles 13 and resistance paddles 14 as it flows downstream, generating a slurry-like material (slurry material).

[0020] As shown in Figure 2, the pair of paddles 7 (in this example, kneading paddles 13) comprises a first paddle 16 mounted coaxially on the first kneading shaft 3a and a second paddle 17 mounted coaxially on the second kneading shaft 3b. The first paddle 16 is housed in the first housing chamber 9a so as to be rotatable about the axis L1 of the first kneading shaft 3a. The second paddle 17 is housed in the second housing chamber 9b so as to be rotatable about the axis L2 of the second kneading shaft 3b. The first paddle 16 and the second paddle 17 are arranged with a predetermined distance between them and the inner wall of the barrel 2.

[0021] The paddle 7 (in this example, the first paddle 16 and the second paddle 17) has a paddle body 18 that is substantially circular when viewed from the axial direction, and a plurality of protrusions 19 that partially protrude from the paddle body 18. The plurality of protrusions 19 are formed to protrude radially outward from the paddle body 18 and are arranged at equal intervals in the circumferential direction of the paddle 7. For example, the paddle 7 is formed in a substantially triangular shape when viewed from the axial direction of the paddle 7 by arranging three protrusions 19 at equal intervals in the circumferential direction.

[0022] As shown in Figure 1, the multiple paddles 7 arranged in the axial direction are positioned 180 degrees rotated relative to adjacent paddles 7 in the axial direction. That is, adjacent paddles 7 in the axial direction are positioned such that their protrusions 19 are 180 degrees apart in the rotational direction. Thus, adjacent paddles 7 in the axial direction have rotational phases that differ by 180 degrees each. Therefore, the multiple paddles 7 arranged in the axial direction are positioned so that every other paddle has the same rotational phase in the axial direction.

[0023] (Protrusion 19) As shown in Figure 3, one of the multiple protrusions 19 has a top 21 formed by hollowing out at least one side of the paddle 7 (in this example, the kneading paddle 14) in the axial direction (X-axis direction in Figure 3). In this example, the multiple protrusions 19 have hollowed-out portions 22 formed by hollowing out a part of the protrusion 19 on both sides of the top 21 in the axial direction of the paddle 7. Thus, the hollowed-out portions 22 are provided on both sides of the top 21 in the axial direction of the paddle 7.

[0024] The weight-reducing portion 22 is formed in an inclined shape that slopes downward from the top portion 21 toward the paddle body 18 of the paddle 7. In this example, the top portion 21 is formed in a pointed shape, for example. The top portion 21 is located at the axial center of the paddle 7. As a result, the inclined weight-reducing portion 22 is formed to have the same area on both sides of the top portion 21 in the axial direction of the paddle 7. Note that the top portion 21 only needs to be formed on at least one of the multiple protrusions 19.

[0025] (First slope section 23 and second slope section 24) As shown in Figures 2 and 4, the multiple protrusions 19 have a first inclined surface 23 positioned adjacent to the top 21 in the direction of rotation of the paddle 7 (direction of arrow A1 in Figure 4), and a second inclined surface 24 positioned adjacent to the top 21 in the direction of counter-rotation of the paddle 7 (direction of dashed arrow A2 in Figure 4). Note that the first inclined surface 23 and the second inclined surface 24 only need to be formed on at least one of the multiple protrusions 19.

[0026] The first inclined surface 23 is formed such that the slope from the outer circumferential surface of the paddle body 18 toward the top 21 is gentle. The first inclined surface 23 guides the electrode material toward the top 21 when the paddle 7 rotates. The second inclined surface 24 is formed to have a steeper slope than the first inclined surface 23. The second inclined surface 24 allows the electrode material that has reached the top 21 to flow downstream when the paddle 7 rotates.

[0027] As shown in Figure 4, the length of the first inclined surface 23 in the direction of rotation of the paddle 7 (first circumferential length d1) is formed to be longer than the length of the second inclined surface 24 in the direction of rotation of the paddle 7 (second circumferential length d2). In this example, the top portion 21 is positioned offset from the center (dotted line in Figure 2) in the circumferential direction of the paddle 7 to the opposite side of the direction of rotation in order to provide the first inclined surface 23 and the second inclined surface 24 on the protrusion 19.

[0028] The first inclined surface 23 and the second inclined surface 24 are formed in a curved shape when viewed from the axial direction of the paddle 7. In this case, the curvature of the first inclined surface 23 is gentler than the curvature of the second inclined surface 24. Curvature is an indicator of how much the curved surface is curved in the first inclined surface 23 and the second inclined surface 24. A larger curvature indicates a gentler curve, while a smaller curvature indicates a steeper curve. As described above, the projection 19 is formed in an asymmetrical shape when viewed from the axial direction of the paddle 7.

[0029] (Effect of the embodiment) Next, the operation of the kneader 1 and the kneading method of this embodiment will be described. (A phenomenon in which high shear force is applied to the electrode material) As shown in Figure 2, the first paddle 16 and the second paddle 17 start rotating from the same starting point in the same direction and rotate with the same rotational phase. Figure 2 shows an example where both the first paddle 16 and the second paddle 17 rotate counterclockwise (in the direction of arrow R1) in the direction of the paper. When the first paddle 16 and the second paddle 17 rotate in the direction of arrow R1, most of the slurry material inside the barrel 2 flows in the direction of arrow R1 as it is pushed by the protrusions 19.

[0030] However, of the slurry material inside barrel 2, the slurry material located around the inner wall of barrel 2 and outside the circumference of the rotation trajectory of the protrusion 19 flows in the direction of passing through the gap between the inner wall of barrel 2 and the protrusion 19 (in the direction of the white arrow in Figure 2). In other words, the slurry material located between the inner wall of barrel 2 and the protrusion 19 flows in the opposite direction to the rotation direction of the first paddle 16 and the second paddle 17 so as to pass through the narrow gap between the inner wall of barrel 2 and the protrusion 19. Therefore, a high shear force was applied to the slurry material, which could potentially damage it.

[0031] Figure 5 is an operation diagram of a kneader 1 having conventional paddles 27 (conventional paddle 27a on the right and conventional paddle 27b on the left). The conventional paddle 27a on the right and conventional paddle 27b on the left have symmetrical projections 28 and do not have a top 21, a first slope 23, and a second slope 24 as in this example. Also, in Figure 4, of the three projections 28a, 28b, and 28c formed on the conventional paddle 27a on the right, the projection 28a located at the top of the paper (at the 12 o'clock position on a clock face) is used as the rotation reference "0 degrees", and the conventional paddles 27a on the right and conventional paddle 27b on the left rotate counterclockwise on the paper.

[0032] When the right conventional paddle 27a and the left conventional paddle 27b rotate, the shear rate applied to the slurry material located near the protrusion 28a of the right conventional paddle 27a becomes very high when the protrusion 28a of the right conventional paddle 27a passes near a "90-degree" angle. This is because, as the protrusion 28a of the right conventional paddle 27a passes alongside the left conventional paddle 27b, the flow of slurry material pushed out by the left conventional paddle 27b collides with the protrusion 28a of the right conventional paddle 27a. As a result, relatively speaking, the flow velocity of the slurry material flowing around the protrusion 28a of the right conventional paddle 27a is accelerated, so it is presumed that the shear rate becomes very high. A higher shear rate means that a higher shear force is applied to the slurry material, which can lead to damage to the slurry material.

[0033] (The principle of low shear in this example) Figure 6 shows the shape of another conventional paddle 29 (conventional paddle 29a, conventional paddle 29b). In this example, the conventional paddle 29 has a first conventional paddle 29a which is substantially elliptical in shape, and a second conventional paddle 29b which is substantially elliptical in shape and positioned at a predetermined amount rotated axially with respect to the first conventional paddle 29a. Both the first conventional paddle 29a and the second conventional paddle 29b, which are substantially elliptical in shape, have a pair of protrusions 30. The protrusions 30 of the first conventional paddle 29a and the protrusions 30 of the second conventional paddle 29b are positioned so that their phases differ by 90 degrees when rotated.

[0034] Figure 7 shows a two-piece comparison paddle 31 having a thickness W of "r / 2", which is half the thickness W of a conventional paddle 29 (see Figure 6). In this example, the comparison paddle 31 has a two-piece first comparison paddle 31a and a two-piece second comparison paddle 31b positioned at a predetermined rotation around the axis relative to the first comparison paddle 31a. The first comparison paddle 31a is constructed by overlapping two paddle pieces 33a, each having a projection 32a formed at an opposing position. The two paddle pieces 33a are positioned so that one is rotated a predetermined amount relative to the other. The second comparison paddle 31b is constructed by overlapping two paddle pieces 33b, each having a projection 32b formed at an opposing position. The two paddle pieces 33b are positioned so that one is rotated a predetermined amount relative to the other.

[0035] Figure 8 is a graph showing the correlation between the blackness and viscosity of the negative electrode slurry material. In this graph, the plotted points for the blackness and viscosity of the conventional paddle 29 are shown as "P1," and the plotted points for the blackness and viscosity of the comparative paddle 31 are shown as "P2." Incidentally, blackness shows a high value when the shear force is too high due to damage to the active material, and a low value when the shear force is appropriate because damage to the active material is suppressed.

[0036] Referring to the graph in Figure 8, it can be seen that the comparative paddle 31, which has a two-piece structure with a thickness W of half ("r / 2"), has a lower degree of blackness than the conventional paddle 29, which has a single-piece structure with a thickness W of "r". Therefore, it can be inferred that there is a certain correlation between the thickness W of the paddle 7 and the shear force applied from the paddle 7 to the slurry material. In other words, it is thought that if the tip shape of the paddle 7 is formed to be thin, the shear force applied from the paddle 7 to the slurry material can be kept low.

[0037] As shown in Figure 9, the kneading action generated from the paddle 7 to the slurry material has indicators such as the dispersion mixing component "K", the distribution mixing component "M", and the feeding efficiency component "T". Dispersion mixing is a mixing method that, for example, finely distributes the slurry material and is mainly related to the shear applied to the material. Distribution mixing is a mixing method that, for example, stirs the slurry material to suppress variations in composition and physical properties and is related to the homogenization of the strain applied to the material. Feeding efficiency is, for example, the material transport efficiency during kneading.

[0038] Incidentally, dispersion mixing and distribution mixing influence each other, and it is known that the balance changes depending on the thickness W of the paddle 7, for example. Specifically, as the thickness W of the paddle 7 increases, distribution mixing decreases and dispersion mixing increases. Therefore, it can be seen that if the paddle 7 is made thinner, dispersion mixing decreases, and as a result, the shear force can be kept low. Thus, it can be seen that in order to keep the shear force applied from the paddle 7 to the slurry material low, the tip shape of the paddle 7 should be made thin.

[0039] (Characteristics of this example) As shown in Figures 2 to 4, in this example, the projection 19 of the paddle 7 is formed with a top 21 created by hollowing out at least one (both in this example) of both sides in the axial direction of the paddle 7. As a result, the axial thickness W of the paddle 7 is reduced at the projection 19 of the paddle 7, making it possible to reduce the shear force applied to the slurry material from the projection 19 of the paddle 7. In particular, the flow velocity of the slurry material flowing in the opposite direction of rotation between the inner wall of the barrel 2 and the projection 19, and the flow velocity of the slurry material flowing vigorously around the projection 19 when the projection 19 faces the opposing paddle 7, are kept low. Therefore, from this viewpoint as well, the structure of this example is very effective.

[0040] Furthermore, the projection 19 has a gently sloping first inclined surface 23 adjacent to the rotational direction of the paddle 7. This makes it possible to make the projection 19 have a shape that does not oppose the flow of the slurry material (for example, a streamlined shape). This makes it possible to keep the shear force applied to the slurry material from the projection 19 low. Thus, it contributes even more to suppressing damage to the slurry material.

[0041] Furthermore, if the shear force applied to the slurry material from the protrusion 19 can be kept low, the diameter of the paddle body 18 can be maintained at the same size. In other words, it becomes possible to maintain a small gap between the inner wall of the barrel 2 and the paddle body 18. As a result, it becomes possible to generate a sufficient flow velocity for the slurry material between the inner wall of the barrel 2 and the paddle body 18. Thus, it becomes possible to achieve both suppression of damage to the slurry material and dispersion of the slurry material.

[0042] (Effects of the embodiment) The kneader 1 and kneading method of this embodiment provide the following benefits.

[0043] (1) The kneader 1 comprises a barrel 2 into which the electrode material for the battery is fed, a pair of rotating shafts 5 rotatably mounted for kneading the electrode material inside the barrel 2, and a pair of paddles 7 integrally rotatably mounted on the pair of rotating shafts 5, which shear the electrode material by rotation. The paddles 7 have a plurality of protrusions 19 projecting toward the inner wall of the barrel 2 at equal intervals in the circumferential direction. At least one of the plurality of protrusions 19 has a top portion 21 formed by hollowing out at least one of the axial sides of the paddle 7.

[0044] With this configuration, since the shape of the top 21 of the protrusion 19 is thinned in the axial direction of the paddle 7, it is possible to provide a relief area for the slurry material that will be sheared. Therefore, it is possible to keep the shear force applied to the slurry material from the protrusion 19 of the paddle 7 low. In addition, if the shear force applied to the slurry material from the protrusion 19 of the paddle 7 is kept low, the diameter of the paddle body 18 can be maintained. As a result, the decrease in the flow velocity of the slurry material is suppressed, and sufficient fluidity of the slurry material is ensured. Thus, it is possible to achieve both damage suppression and improved dispersibility when mixing electrode materials.

[0045] (2) The weight-reducing portions 22 of the top portion 21 are provided on both sides of the top portion 21 in the axial direction of the paddle 7. With this configuration, since weight-reducing portions 22 are formed on both sides of the top portion 21 in the axial direction of the paddle 7, it is possible to make the thickness of the protrusion 19 of the paddle 7 thinner. This contributes further to reducing the shear force and, consequently, to further suppressing damage to the electrode material.

[0046] (3) The top portion 21 is formed in a pointed shape. With this configuration, the area of ​​the tip of the projection 19 facing the inner wall of the barrel 2 is minimized, which further contributes to reducing the shear force. Therefore, it further contributes to suppressing damage to the electrode material.

[0047] (4) The cutout portion 22 of the top portion 21 is formed in an inclined shape that slopes downward from the top portion 21 toward the paddle body 18 of the paddle 7. With this configuration, slurry material located near the top portion 21 can be smoothly released to the surrounding area by the inclined cutout portion 22.

[0048] (5) The top portion 21 is positioned at the center of the paddle 7 in the axial direction. The inclined cutout portion 22 is formed to have the same area on both sides of the top portion 21 in the axial direction of the paddle 7. With this configuration, slurry material located near the top portion 21 can be released evenly to both sides by the cutout portion 22, which has the same area on both sides of the paddle 7 in the axial direction. This contributes to suppressing uneven mixing.

[0049] (6) At least one of the multiple protrusions 19 has a first inclined surface 23 which is positioned adjacent to the top 21 in the rotational direction of the paddle 7 and has a gently sloping surface formed from the outer peripheral surface of the paddle body 18 of the paddle 7 toward the top 21, and a second inclined surface 24 which is positioned adjacent to the top 21 in the counter-rotational direction of the paddle 7 and has a steeper slope than the first inclined surface 23. With this configuration, the slope of the first inclined surface 23 adjacent to the top 21 in the rotational direction of the paddle 7 is formed to be gentler than the slope of the second inclined surface 24 adjacent to the top 21 in the counter-rotational direction of the paddle 7. As a result, the side surface of the protrusion 19 which the slurry material collides with during shearing has a shape that does not oppose the flow of the slurry material (for example, a streamlined shape). Thus, it further contributes to reducing the shear force applied to the slurry material during mixing, and in turn, further contributes to suppressing damage to the electrode material.

[0050] (Other embodiments) This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0051] The shape of the projection 19 is not limited to a shape having only one pointed tip 21, but may also be a shape in which the tip 21 is continuous in the axial direction of the paddle 7. In other words, the tip 21 is not limited to a point shape, but may be formed in a linear shape.

[0052] The shape of the top 21 of the protrusion 19 may be a flat surface, provided that it is thinned in the axial direction of the paddle 7. The top portion 21 may be positioned, for example, offset to one side from the axial center of the paddle 7.

[0053] The number of protrusions 19 on the paddle 7 is not limited to three; it may be four or more, or two or fewer. • Of the multiple protrusions 19 that the paddle 7 has, only a specific protrusion 19 may have the top portion 21 of this example.

[0054] The number of screws 6 and paddles 7 on the kneading shaft 3 may be changed to numbers other than those in this example. Multiple input ports 10 may be provided depending on the material to be put into the barrel 2.

[0055] The electrode material to be mixed is not limited to a paste for the negative electrode of a lithium-ion secondary battery, but may also be a paste for the positive electrode of a lithium-ion secondary battery. • The rechargeable battery does not have to be a lithium-ion rechargeable battery; other types of batteries are also acceptable.

[0056] The battery is not limited to a sealed battery with a rectangular prism shape; it may also have a shape other than a rectangular prism, such as a cylindrical shape. Secondary batteries are not limited to being installed in electric vehicles or hybrid vehicles; they may also be installed in vehicles such as gasoline-powered or diesel-powered vehicles. Furthermore, secondary batteries may be used as power sources for mobile vehicles such as trains, ships, aircraft, and robots, as well as for electrical products such as information processing devices.

[0057] • As used in this disclosure, the phrase "at least one" means "one or more" of the desired options. For example, as used in this disclosure, "at least one" means "only one option" or "both of the two options" if there are two options. As another example, as used in this disclosure, "at least one" means "only one option" or "any combination of two or more options" if there are three or more options.

[0058] This disclosure is described in accordance with the embodiments, but is not limited to the structures of these embodiments and includes various modifications and variations within the equivalence range. This disclosure also includes various combinations and forms, as well as combinations and forms of one, more, or fewer of these elements. [Explanation of symbols]

[0059] 1... Mixing machine, 2... Barrel, 5... Rotating shaft, 7... Paddle, 18... Paddle body, 19... Protrusion, 21... Top, 22... Weight reduction section, 23... First slope section, 24... Second slope section.

Claims

1. A kneader comprising: a barrel into which battery electrode material is introduced; a pair of rotating shafts rotatably mounted for kneading the electrode material inside the barrel; and a pair of paddles integrally rotatably mounted on the pair of rotating shafts, which shear the electrode material by rotation, The paddle has a plurality of protrusions that project toward the inner wall of the barrel at equal intervals in the circumferential direction, A kneader in which at least one of the plurality of protrusions has a top formed by hollowing out at least one of the axial sides of the paddle.

2. The kneading machine according to claim 1, wherein the weight-reducing portion of the top is provided on both sides of the top in the axial direction of the paddle.

3. The kneader according to claim 1, wherein the top portion is formed in a pointed shape.

4. The kneading machine according to claim 1, wherein the weight-reducing portion at the top is formed in an inclined shape that slopes downward from the top toward the paddle body of the paddle.

5. The top portion is positioned at the axial center of the paddle. The kneading machine according to claim 4, wherein the inclined weight-reducing portion is formed to have the same area on both sides of the top of the paddle in the axial direction.

6. At least one of the aforementioned multiple protrusions is A first inclined portion is positioned adjacent to the top of the paddle in the direction of rotation of the paddle, and has a gently sloping surface formed from the outer circumferential surface of the paddle body toward the top of the paddle, The kneader according to claim 1, further comprising a second inclined portion that is positioned adjacent to the top of the paddle in the counter-rotation direction and has a steeper incline than the first inclined portion.

7. A kneading method for a battery electrode material, wherein when the electrode material is introduced into a barrel housing a pair of rotating shafts rotatably mounted for kneading the electrode material, the electrode material is sheared by the rotation of a pair of paddles that are integrally rotatably mounted on the pair of rotating shafts, A kneading method for shearing the electrode material, wherein a plurality of protrusions projecting toward the inner wall of the barrel are formed at equal intervals in the circumferential direction, and at least one of the plurality of protrusions has a top formed by hollowing out at least one of the sides of the paddle in the axial direction.

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