Powder rolling unit

Abstract

A powder rolling unit comprises: a rolling roll (2a) and / or a rolling roll (2b) that forms a rolled sheet (5) by rolling a powder material (4); a hopper (1) that stores the powder material (4) in the upper part of the rolling roll (2a) and / or the rolling roll (2b); and a squeegee (3) that is disposed above the rolling rolls (2a, 2b) and disposed parallel to the axial directions of the rolling rolls (2a, 2b), and that vibrates at a prescribed frequency. When the distances between the squeegee (3) and the rolling rolls (2a, 2b) are divided by the particle diameter (D50) of powder forming the powder material (4) to be rolled, 22 ≤ distances (L1a, L1b) between squeegee (3) and rolling rolls (2a, 2b) / particle diameter (D50) ≤ 58 is satisfied.

Description

Powder Rolling Unit

[0001] The present disclosure relates to a powder rolling unit.

[0002] In recent years, dry coating methods, which directly form powder films, have been attracting attention as a method that can form powder layers with high performance and low environmental impact compared to wet coating methods, which disperse powder in a solvent and then apply the powder.The dry coating method suppresses material damage to the powder caused by the solvent, maintains high performance, does not require drying the solvent, and can produce powder layers with significantly reduced energy consumption.

[0003] In a conventional dry powder film-forming method, for example, a powder-rolling apparatus is used to roll-form powder to produce a rolled sheet such as an electrode sheet from a powder containing an electrode active material.

[0004] For example, Patent Document 1 discloses a powder rolling device that includes a rolling section that rolls powder to form a rolled sheet, a hopper formed above the rolling section that stores the powder, a plurality of feeders that are provided in the width direction of the rolled sheet and supply powder to the hopper, and a control section that controls the level of powder in the width direction within the hopper so that the film thickness in the width direction remains within a certain range.

[0005] Patent No. 5772427

[0006] However, in Patent Document 1, the powder flows naturally into the nip region of the rolling section, so the basis weight in the direction of powder flow is not stable, resulting in variations in the basis weight of the rolled sheet obtained after passing through the rolling section.

[0007] Therefore, an object of the present disclosure is to provide a powder rolling unit that can suppress clogging of the powder material in the nip area and suppress variation in the basis weight of the rolled sheet.

[0008] A powder rolling unit according to one aspect of the present disclosure includes a rolling roll that rolls a powder material to form a rolled sheet, a hopper that stores the powder material above the rolling roll, and a squeegee that is arranged above the rolling roll and parallel to the axial directions of the rolling rolls and vibrates at a predetermined frequency, and when the distance between the squeegee and the rolling roll is divided by the particle diameter (D50) of the powder that constitutes the powder material to be rolled, the following relationship holds: 22≦(distance between the squeegee and the rolling roll) / particle diameter (D50)≦58.

[0009] According to the powder rolling unit of the present disclosure, clogging of the powder material in the nip region can be suppressed, and variation in the basis weight of the rolled sheet can be suppressed.

[0010] FIG. 1 is a schematic diagram showing a powder rolling unit according to an embodiment of the present disclosure as viewed from the side. FIG. 2 is a schematic diagram showing a powder rolling unit according to an embodiment of the present disclosure as viewed from above. FIG. 3A is a schematic diagram showing how particles of powder material are uniformly supplied to a nip region by a squeegee according to an embodiment of the present disclosure. FIG. 3B is a schematic diagram showing the positional relationship between a pair of rolling rolls and a squeegee when viewed from the side of a powder rolling unit according to an embodiment of the present disclosure. FIG. 4 is a diagram showing the presence or absence of a squeegee, the presence or absence of squeegee vibration, particle diameter (D50), the distance between the squeegee and the rolling roll, the distance between the squeegee and the rolling roll / particle diameter (D50), the presence or absence of missing material mixture, the presence or absence of bridges in the hopper, and variations in basis weight.

[0011] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement positions, and connection configurations shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in independent claims are described as optional components.

[0012] In addition, each drawing is a schematic diagram in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present disclosure, and is not necessarily an exact illustration, and may differ from the actual shape, positional relationship, and proportion. In each drawing, the same reference numerals are used to denote substantially the same configurations, and duplicated explanations may be omitted or simplified.

[0013] Furthermore, in the following embodiments, expressions such as thickness direction or cylindrical shape are used. For example, thickness direction or cylindrical shape does not only mean a completely thickness direction or cylindrical shape, but also means a substantially thickness direction or cylindrical shape, i.e., a shape with an error of a few percent. Furthermore, thickness direction or cylindrical shape means a thickness direction or a cylindrical shape within the range in which the effects of the present disclosure can be achieved. The same applies to other expressions using "direction" and "shape."

[0014] (Summary) A powder rolling unit according to the present disclosure will be described below.

[0015] A powder rolling unit according to one aspect of the present disclosure applies vibration to the powder near the rolling rolls to improve the fluidity of the powder in the nip region, thereby preventing clogging of the powder and enabling uniformity of the basis weight of the resulting rolled sheet.

[0016] Such a powder rolling unit includes a hopper as a material supply section, a pair of rolling rolls, and a squeegee. The squeegee is vibrated by ultrasonic waves and transmits the vibrations to the powder to impart fluidity to the powder. The hopper may be provided with one or more squeegees.

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0018] (Embodiment) Hereinafter, the present embodiment will be described with reference to FIGS.

[0019] 1 is a schematic side view of a powder rolling unit according to an embodiment of the present disclosure, showing a hopper 1, rolls 2a and 2b, a squeegee 3, powder material 4, and a resulting rolled sheet 5.

[0020] 2 is a schematic diagram showing a powder rolling unit according to an embodiment of the present disclosure as viewed from above, in which the axial direction of the squeegee 3 is indicated by an arrow and the standing wave caused by the vibration of the squeegee 3 is indicated by a two-dot chain line.

[0021] FIG. 3A is a schematic diagram illustrating particles of powder material 4 being uniformly delivered to a nip region by a squeegee 3 according to an embodiment of the present disclosure.

[0022] FIG. 3B is a schematic diagram showing the positional relationship between the pair of rolls 2 a and 2 b and the squeegee 3 when the powder rolling unit according to the embodiment of the present disclosure is viewed from the side.

[0023] FIG. 4 is a diagram showing the presence or absence of the squeegee 3, the presence or absence of vibration of the squeegee 3, the particle diameter (D50), the distances L1a and L1b between the squeegee 3 and the rolling rolls 2a and 2b, the distances L1a and L1b between the squeegee 3 and the rolling rolls 2a and 2b / particle diameter (D50), the presence or absence of missing material mix, the presence or absence of bridges in the hopper 1, and variations in basis weight.

[0024] [Powder Rolling Unit] (Functional Configuration of Powder Rolling Unit) As shown in Figures 1 and 2, the powder rolling unit is equipped with a hopper 1 that stores powder material 4 made of powder above a pair of rolling rolls 2a, 2b and has the function of supplying the powder material 4 to the pair of rolling rolls 2a, 2b, and a squeegee 3 arranged inside the hopper 1.

[0025] The squeegee 3 is disposed in the hopper 1 and is vibrated at a predetermined frequency by a vibrator 6. The squeegee 3 vibrated by the vibrator 6 is able to impart vibrations to the powder material 4 stored inside the hopper 1. This allows the squeegee 3 to constantly supply the powder material 4 to the pair of mill rolls 2a, 2b without clogging the pair of mill rolls 2a, 2b with the powder material 4. In this embodiment, the pair of mill rolls 2a, 2b may be simply referred to as mill rolls 2a, 2b.

[0026] The powder material 4 supplied to the rolling rolls 2a and 2b at a constant rate is rolled at the compression point where the distance between the surface of the rolling roll 2a and the surface of the rolling roll 2b is shortest. Therefore, a rolled sheet 5 made of the powder material 4 rolled by the rolling rolls 2a and 2b at the compression point can be obtained.

[0027] The squeegee 3 is disposed above the rolls 2a and 2b and is disposed so as to be parallel to the axial direction of each of the rolls 2a and 2b. If the squeegee 3 is not disposed parallel to the rolls 2a and 2b, the distance from one end of the squeegee 3 to the compression point may differ from the distance from the other end of the squeegee 3 to the compression point. In this case, a difference due to variation occurs between the basis weight at one end of the obtained rolled sheet 5 and the basis weight at the other end of the rolled sheet 5.

[0028] Furthermore, it is desirable that the squeegee 3 be positioned parallel to the rolls 2a, 2b when viewed along the flow direction of the rolled sheet 5. This is because if they are not positioned parallel, the distance from the center of the squeegee 3 to the compression point will differ from the distance from the end of the squeegee 3 to the compression point, resulting in a difference due to variation between the basis weight at the center of the obtained rolled sheet 5 and the basis weight at the end of the rolled sheet 5. Note that in this embodiment, "parallel" does not only mean completely parallel, but also means substantially parallel, i.e., includes an error of about a few percent.

[0029] The squeegee 3 also vibrates at a predetermined frequency. Specifically, the squeegee 3 vibrates at a frequency of 2 kHz to 300 kHz. By using a vibrator 6 that vibrates at a frequency of 2 kHz to 300 kHz, the squeegee 3 can be vibrated efficiently. For example, assuming that powder with a particle diameter of 100 μm to 700 μm is being handled, a high-frequency vibration of 2 kHz to 300 kHz is required to impart fluidity to the powder. This is because low-frequency vibrations below 2 kHz result in an insufficient number of vibrations to the powder, making it impossible to impart sufficient fluidity to the powder. Furthermore, high-frequency vibrations above 300 kHz result in significant vibration attenuation as the vibrations propagate through the powder, making it impossible to impart sufficient fluidity to the powder.

[0030] 1 and 3A, the squeegee 3 vibrating at the above frequency is in contact with the powder material 4, so when the squeegee 3 vibrates, the vibration of the squeegee 3 is transmitted to the powder material 4. The vibration of the powder material 4 reduces the frictional resistance between the powder particles (between the particles) of the powder material 4, improving the fluidity of the powder. In other words, the vibration of the squeegee 3 improves the fluidity of the powder material 4, making it possible to constantly supply the powder material 4 to the compression point.

[0031] For example, the powder material 4 present on the rolling rolls 2a and 2b moves in the rotational direction of the rolling rolls 2a and 2b. At this time, the powder constituting the powder material 4 is not aligned and exists in a disordered manner. The powder material 4, which is composed of disordered powder, passes between the rolling rolls 2a and 2b and the vibrating squeegee 3, which is arranged with a certain gap between them, making it possible to align the powder constituting the powder material 4 before reaching the compression point. By aligning the powder constituting the powder material 4, the filling rate of the powder material 4 supplied to the compression point can be controlled, preventing the material mixture from slipping out and reducing the variation in the basis weight of the resulting rolled sheet 5. For example, if the squeegee 3 does not vibrate, the powder material 4 is not subjected to vibration from the squeegee 3, and the powder simply exists in a disordered manner, making it impossible to align the powder. This does not improve the fluidity of the powder material 4, and may result in clogging of the powder material 4 as it passes through the squeegee 3. As a result, even if clogging of the powder material 4 does not occur, the filling rate of the powder material 4 cannot be controlled, making it difficult to reduce the variation in the basis weight of the resulting rolled sheet 5.

[0032] The squeegee 3 only needs to vibrate in at least one of the thickness direction of the resulting rolled sheet 5, the width direction of the rolled sheet 5, and the flow direction of the rolled sheet 5. When focusing on the movement of each particle constituting the powder material 4, since each particle is surrounded by and in contact with adjacent particles on all sides, vibrating in each direction can reduce the coefficient of friction with the particles in contact in each direction. This makes it possible to improve the fluidity of the powder material 4. When the squeegee 3 vibrates in two or more directions, it is possible to further improve the fluidity of the powder material 4.

[0033] (Distance Between Squeegee 3 and Rollers 2a and 2b) Next, the distance between the squeegee 3 and the rollers 2a and 2b will be described.

[0034] As shown in FIGS. 1 and 3B, the squeegee 3 has the role of improving the fluidity of the powder material 4 in the nip region between the rolls 2a and 2b, and is therefore preferably located as close to the rolls 2a and 2b as possible. In this embodiment, at least a portion of the squeegee 3 may be positioned between the rolls 2a and 2b so as not to contact the rolls 2a and 2b. In other words, at least a portion of the squeegee 3 may be located in the nip region. Furthermore, it is desirable that the squeegee 3 be positioned above the rolls 2a and 2b so as to overlap both the rolls 2a and 2b. This is because if the squeegee 3 is too far from the rolls 2a or 2b, the distance L1a or L1b becomes large, and powder material 4 with poor powder alignment is supplied to the nip region, resulting in variations in the basis weight of the rolled sheet 5. Here, the nip region refers to the region between the rolls 2a and 2b.

[0035] Specifically, the distance L1a between the rolling roll 2a and the squeegee 3 is the shortest distance when a straight line is drawn between the axial center of the rolling roll 2a and the axial center of the squeegee 3; the distance L1b between the rolling roll 2b and the squeegee 3 is the shortest distance when a straight line is drawn between the axial center of the rolling roll 2b and the axial center of the squeegee 3; and the distance between the compression points (distance between compressions) where the distance between the rolling rolls 2a and 2b is shortest, i.e., the shortest distance Lr between the rolling roll 2a and the rolling roll 2b at the compression point, are defined.

[0036] When the distances L1a and L1b between the squeegee 3 and the rolling rolls 2a and 2b are divided by the particle diameter (D50) of the powder constituting the powder material 4 to be rolled, the following relationship holds: 22≦(distances L1a and L1b between the squeegee 3 and the rolling rolls 2a and 2b) / particle diameter (D50)≦58.

[0037] It is desirable that at least one of the distances L1a and L1b be greater than or equal to the distance Lr and less than or equal to Lr + 50 mm. This is because if at least one of the distances L1a and L1b is greater than Lr + 50 mm, it becomes difficult for the powder particles aligned by vibration to maintain their alignment all the way to the nip region, resulting in variations in the basis weight of the resulting rolled sheet 5. Furthermore, if at least one of the distances L1a and L1b is smaller than Lr, the amount of powder material 4 supplied to the nip region becomes small, making it impossible to obtain the desired rolled sheet 5. Note that the distances L1a and L1b do not necessarily have to be the same distance.

[0038] For these reasons, it is sufficient that the squeegee 3 is located relative to the rolling roll 2a in a range where either Lr≦L1a≦Lr+50 mm or Lr≦L1a<Lr+50 mm is satisfied, and it is sufficient that the squeegee 3 is located relative to the rolling roll 2b in a range where either Lr≦L1b≦Lr+50 mm or Lr≦L1b<Lr+50 mm is satisfied.

[0039] Furthermore, the position of the squeegee 3 in the thickness direction of the resulting rolled sheet 5 is preferably such that the distance between the center of the squeegee 3 and the center between the rolls 2a and 2b, i.e., the distance between the center of the squeegee 3 and the compression point, is equal to or less than Lr / 2 + the radius rs of the squeegee 3. In other words, it is preferable that the squeegee 3 is located above the rolls 2a and 2b so as to overlap both of them. If this range is exceeded, the distance L1a or L1b will be large, and powder material 4 with poorly aligned powder will be supplied to the nip region, resulting in variations in the basis weight of the rolled sheet 5.

[0040] If the shortest distance Lr between the rolling rolls 2a and 2b is too long compared to the particle diameter (D50) of the powder, the powder material 4 will slip out from between the rolling rolls 2a and 2b, making it impossible to form the desired rolled sheet 5. If the shortest distance Lr is too narrow, the load on the powder material 4 will be too high, making it impossible to form the desired rolled sheet 5. For this reason, in this embodiment, the shortest distance Lr is set according to the particle diameter (D50) of the powder.

[0041] (Material and Shape of Squeegee 3) Next, the material and shape of the squeegee 3 will be described.

[0042] The squeegee 3 is formed of, for example, a metal material. By using a metal material for the squeegee 3, high-frequency waves propagate through the squeegee 3 without significant attenuation. High-frequency waves with short wavelengths tend to attenuate easily, but metal materials have the property of easily transmitting waves, so a squeegee 3 made of a metal material can suppress the attenuation of high-frequency waves. As a result, the vibration state is uniform throughout the squeegee 3, suppressing variations in the basis weight in the width direction of the rolled sheet 5.

[0043] Examples of metal materials that can be used include stainless steel, titanium, aluminum, copper, iron, and nickel. In particular, stainless steel or titanium is preferred as the metal material because it has high corrosion resistance and is resistant to rust. Titanium is also preferred as the metal material because it is easily vibrated by light ultrasonic waves.

[0044] The squeegee 3 may be made of a material other than a metal material. For example, the squeegee 3 may be made of a resin material or a ceramic material, or may be made of a composite member that selectively uses two or more materials from among a metal material, a resin material, and a ceramic material.

[0045] Furthermore, the shape of the squeegee 3 is desirably cylindrical in order to uniformly vibrate the surrounding powder material 4. For example, the shape of the squeegee 3 is a long cylinder extending along a predetermined direction. In this case, the diameter of the squeegee 3 is desirably 2 mm or more and 30 mm or less. This is because if the diameter of the squeegee 3 is greater than 30 mm, the squeegee 3 will be difficult to vibrate, making it difficult to impart sufficient fluidity to the powder material 4. If the diameter is smaller than 2 mm, the squeegee 3 will become too thin, causing deformation of the squeegee 3 and making it difficult to impart sufficient fluidity to the powder material 4.

[0046] (Amplitude of Squeegee 3) Next, the amplitude of the squeegee 3 will be described.

[0047] It is desirable that the squeegee 3 vibrates in at least one of the width direction, thickness direction, and length direction of the resulting rolled sheet 5. If the squeegee 3 vibrates in two or more of the above three directions, it is possible to further improve the fluidity of the powder material 4. In particular, in the case of a cylindrical squeegee 3, it is desirable that the squeegee 3 vibrates in at least one of the thickness direction or flow direction of the rolled sheet 5 in order to efficiently transmit vibrations to the powder material 4 surrounding the squeegee 3. In this case, it is possible to further improve the fluidity of the powder material 4.

[0048] Furthermore, it is desirable that the amplitude of the squeegee 3 is 0.1 μm or more in at least one of the three directions. This is because if it is less than 0.1 μm, it becomes difficult to impart sufficient fluidity to the powder material 4. From the viewpoint of improving the fluidity of the powder material 4, it is desirable that the amplitude of the squeegee 3 is as large as possible, and therefore the amplitude of the squeegee 3 may be amplified to a practically feasible extent.

[0049] Furthermore, as shown by the two-dot chain line in Figure 2, the squeegee 3 usually vibrates due to a standing wave. In other words, when the squeegee 3 vibrates, there are vibration antinodes in the squeegee 3 where the amplitude increases and vibration nodes where the amplitude decreases. In order to transmit the vibration of the squeegee 3 to the powder material 4 without attenuation, it is desirable to position the wall surface of the hopper 1 in Figure 2 at the vibration node. In other words, it is desirable to control the vibrator 6 so as to adjust the frequency of the squeegee 3 in accordance with the width of the hopper 1 parallel to the axial direction of the squeegee 3.

[0050] (Frequency at which the squeegee 3 is vibrated) Next, the frequency at which the squeegee 3 is vibrated will be described.

[0051] As shown in Figures 1 and 2, the squeegee 3 is vibrated by a vibrator 6 connected to the squeegee 3. At this time, the squeegee 3 vibrates naturally at a frequency of 2 kHz to 300 kHz due to the vibrator 6. That is, the squeegee 3 vibrates at a high frequency near the ultrasonic band. Specifically, when the powder material 4 supplied to the hopper 1 passes between the rolling rolls 2a, 2b and the squeegee 3 (between the rolling roll 2a and the squeegee 3 and between the rolling roll 2b and the squeegee 3), the vibration of the squeegee 3 is transmitted to the powder material 4, thereby increasing the fluidity of the powder material 4. As a result, clogging is suppressed when the powder material 4 passes through the gap between the rolling rolls 2a, 2b and the squeegee 3.

[0052] This is because the squeegee 3 vibrates at a high frequency, so that the powder material 4 in contact with the squeegee 3 is less susceptible to frictional resistance due to powder pressure. This increases the fluidity of the powder material 4 in contact with the squeegee 3, thereby suppressing retention and aggregation of the powder material 4.

[0053] Furthermore, for the powder material 4 located near the squeegee 3, the vibration of the squeegee 3 reduces the frictional force between adjacent powder particles, increasing the fluidity and thereby suppressing aggregation of the powder material 4.

[0054] The fluidity of the powder material 4 tends to increase as the vibration frequency of the squeegee 3 increases. Therefore, if the squeegee 3 is vibrated at a frequency of 2 kHz or higher, which is a high frequency region near the ultrasonic band, the fluidity of the powder material 4 can be sufficiently increased. However, since the vibration tends to attenuate as the frequency increases, it becomes more difficult for the vibration of the squeegee 3 to propagate through the powder material 4. However, if the frequency is 300 kHz or lower, the fluidity of the powder material 4 can be sufficiently increased.

[0055] As a result, even when using powder material 4 with low fluidity and a particle diameter (D50) of 700 μm or less, the vibrating squeegee 3 allows the powder material 4 to pass through the gap between the rolling rolls 2 a, 2 b and the squeegee 3 without stagnation or agglomeration. This makes it possible to adjust the film thickness and filling rate of the powder material 4. As a result, a rolled sheet 5 with little variation in basis weight can be obtained.

[0056] (Vibrator 6) Next, the vibrator 6 will be described.

[0057] The squeegee 3 is provided with a vibrator 6. When the vibrator 6 vibrates, the vibration is transmitted to the squeegee 3, causing the squeegee 3 to vibrate.

[0058] The vibrator 6 has a plurality of piezoelectric bodies and electrodes provided on the end surfaces of each of the plurality of piezoelectric bodies. In the vibrator 6, each of the plurality of piezoelectric bodies is sandwiched between electrodes. In other words, the vibrator 6 has a sandwich structure of piezoelectric bodies and electrodes. For example, the number of piezoelectric bodies is an even number, such as two, four, or six. The electrodes are thin metal plates made of, for example, copper, phosphor bronze, or the like.

[0059] The piezoelectric material may be, for example, a lead zirconate titanate (PbTiO ３ -PbZrO ３ PZT-based, commonly known as PZT), and barium titanate (BaTiO ３ As the piezoelectric material, for example, quartz crystal and LiNbO ３ Alternatively, a piezoelectric single crystal such as the above may be used.

[0060] When the piezoelectric body is made of piezoelectric ceramics (for example, PZT), each piezoelectric body has a thickness of approximately 2 mm to 5 mm.

[0061] Furthermore, the vibrator 6 has a sandwich structure in which a piezoelectric body is sandwiched between a metal front plate and a metal backing plate, and a Langevin type vibrator whose overall length is half the wavelength is preferred because it has high output and high reliability.

[0062] Specifically, the Langevin vibrator has a structure in which a metal front plate and a metal backing plate are arranged on either side of a piezoelectric body such as PZT and are fastened together with bolts. The metal front plate and the metal backing plate are made of duralumin. The bolts are made of steel, titanium alloy, or the like. A screw hole for connection is formed in the center of the metal front plate, and the squeegee 3 is inserted into the screw hole and fastened, firmly connecting the vibrator 6 and the squeegee 3. This allows the vibration generated by the vibrator 6 to be transmitted to the squeegee 3. At this time, a horn that amplifies the amplitude or a horn that disperses the direction of vibration may be connected between the vibrator 6 and the squeegee 3.

[0063] The vibrator 6 is a vibrator that excites waves. A positive charge and a negative charge are applied to the thin metal plates provided on both end surfaces of the piezoelectric body of the vibrator 6, respectively. This converts electrical energy into mechanical energy. The conversion of the electrical signal into mechanical vibration causes the vibrator 6 to vibrate at a high frequency. This vibration is propagated to the squeegee 3.

[0064] When the vibrator 6 is long, it is preferable that the polarization direction of the piezoelectric material such as PZT coincides with the longitudinal direction of each vibrator 6 so that the vibrator 6 has a structure that expands and contracts in the longitudinal direction of each vibrator 6. In this case, the vibration direction of the vibrator 6 is the longitudinal direction of the vibrator 6, making it easier to control the vibration direction of the generated vibration.

[0065] (Rolling Rolls 2a, 2b) Next, the rolling rolls 2a, 2b will be described.

[0066] The rolls 2a and 2b roll the powder material 4 supplied from the hopper 1 to form a rolled sheet 5. Specifically, the powder material 4, whose fluidity has been improved by the vibration of the squeegee 3, is supplied to the nip region of the rolls 2a and 2b, where it is compressed and stretched. At this time, the shortest distance between the rolls 2a and 2b, which is the compression point, determines the thickness of the rolled sheet 5. The distance between the rolls 2a and 2b is determined by the thickness of the rolled sheet 5, and it is desirable that the shortest distance Lr between the rolls 2a and 2b be 2 mm or less. This is because, when using a powder material 4 with a powder particle diameter of 700 μm or less, if the distance between the rolls 2a and 2b is greater than 2 mm, the compressive force on the powder material 4 is insufficient, the powder material 4 cannot be sufficiently rolled, and the desired rolled sheet 5 may not be obtained.

[0067] The obtained rolled sheet 5 may be passed through the gap between the rolls 2 a and 2 b multiple times. Alternatively, the rolled sheet 5 may be stretched one or more times by using rolls 2 a and 2 b having roll diameters, peripheral speeds, gaps, etc. different from those of the rolls 2 a and 2 b.

[0068] The rolling rolls 2 a and 2 b have a predetermined diameter, for example, 100 mm to 200 mm. In this case, the rolling rolls 2 a and 2 b may be heated to heat-press the powder material 4 with the rolling rolls 2 a and 2 b, or the rolled sheet 5 may be heat-pressed with the rolling rolls 2 a and 2 b.

[0069] (Surface Roughness of the Surfaces of the Rolling Rolls 2a and 2b) Next, the surface roughness of the surfaces of the rolling rolls 2a and 2b will be described.

[0070] The surface roughness (surface roughness) of the roll 2a, one of the rolls 2a and 2b, is higher than the surface roughness of the roll 2b, the other of the rolls 2a and 2b. In other words, the surface roughness of the roll 2a is higher than the surface roughness of the roll 2b.

[0071] By making the surface roughness of the rolling roll 2a rougher than that of the rolling roll 2b, the rolled sheet 5 obtained by supplying the powder material 4 to the nip region and applying pressure and stretching to it is easily discharged from between the rolling rolls 2a and 2b while adhering to the surface of the rolling roll 2a. This allows the rolling rolls 2a and 2b to transport the rolled sheet 5 that has passed between the rolling rolls 2a and 2b to the next roll.

[0072] For example, the surface roughness A1 of the rolling roll 2a is 0.5 μm, and the surface roughness B1 of the rolling roll 2b is 0.2 μm. The surface roughness A1 of the rolling roll 2a is 2.5 times the surface roughness B1 of the rolling roll 2b. This means that if the surface roughness of the rolling roll 2a is slightly higher than that of the rolling roll 2b, a weaker rolled sheet 5 may tear off from the rolling roll 2a. In this case, the rolled sheet 5 that has passed between the rolling rolls 2a and 2b cannot be discharged toward the next roll located at the desired position. For this reason, it is desirable that the surface roughness A1 be higher than the surface roughness B1 so that the rolled sheet 5 can be transported to the next roll while adhering to the rolling roll 2a. The surface roughness A1 and the surface roughness B1 may be appropriately set depending on the particle size of the powder, the material used for the surfaces of the rolling rolls 2a and 2b, the rotation speed of the rolling rolls 2a and 2b, etc. Therefore, the ratio of surface roughness A1 / surface roughness B1 is not limited to 2.5.

[0073] (Rotational Speed ​​of Rollers 2a and 2b) Next, the rotational speed of the rolls 2a and 2b will be described.

[0074] The rotation speed of one of the rolls 2a and 2b, the roll 2a, is faster than the rotation speed of the other roll 2b. Furthermore, since the roll 2a has a higher surface roughness than the roll 2b, the roll 2a is set to rotate faster than the roll 2b so that the roll 2a can easily take up the rolled sheet 5. In other words, by making the rotation speed of the roll 2a faster than the roll 2b, the rolled sheet 5 obtained by supplying the powder material 4 to the nip region and applying pressure and stretching it is easily discharged from between the roll 2a and the roll 2b while adhering to the surface of the roll 2a. This allows the roll 2a and the roll 2b to more easily transport the rolled sheet 5 that has passed between the rolls 2a and 2b to the next roll.

[0075] For example, the rotational speed A2 of the rolling roll 2a is 26 m / min, and the rotational speed B2 of the rolling roll 2b is 6.5 m / min. The rotational speed A2 of the rolling roll 2a is four times the rotational speed B2 of the rolling roll 2b. The rotational speeds A2 and B2 may be set appropriately depending on the particle size of the powder, the material used for the surfaces of the rolling rolls 2a and 2b, the surface roughnesses A1 and B1, etc. Therefore, the ratio of the rotational speed A2 / the rotational speed B2 is not limited to 4.

[0076] (Relationship between Distances L1a, L1b and Particle Diameter (D50)) Next, with reference to FIG. 4, the reason for determining 22≦(Distances L1a, L1b) / Particle Diameter (D50)≦58 will be described based on the relationship between the distances L1a, L1b between the squeegee 3 and the rolling rolls 2a, 2b and the particle diameter (D50).

[0077] Here, the powder rolling unit was set with the components thereof set as follows, and the presence or absence of missing mix, the presence or absence of bridges in the hopper 1, and variations in basis weight were examined.

[0078] Specifically, in each component of the powder rolling unit, the surface roughness A1 of the surface of the rolling roll 2a was set to 0.5 μm, the surface roughness B1 of the surface of the rolling roll 2b was set to 0.2 μm, the rotational speed A2 of the rolling roll 2a was set to 26 m / min, the rotational speed B2 of the rolling roll 2b was set to 6.5 m / min, the ratio of the rotational speed A2 of the rolling roll 2a to the peripheral speed ratio of the rotational speed B2 of the rolling roll 2a was set to 4, the shortest distance Lr between the rolling rolls 2a and 2b was set to 455 μm, the width of the hopper 1 was set to 240 mm, and the diameter of the squeegee 3 was set to 4 mm.

[0079] In this case, the following are shown: presence or absence of the squeegee 3, presence or absence of ultrasonic vibration of the squeegee 3, particle diameter (D50), distances L1a and L1b, distances L1a and L1b / particle diameter (D50), presence or absence of missing material mixture, presence or absence of bridges in the hopper 1, and variation in basis weight. The variation in basis weight is calculated by subtracting the minimum value from the maximum value and dividing the result by 2, and averaging the values.

[0080] First, in (1), in the case of a powder rolling unit not provided with a squeegee 3, when a powder material 4 having a powder particle diameter of 511 μm was used, the occurrence of missing composite material was suppressed, the occurrence of bridging in the hopper 1 was suppressed, and the variation in basis weight was ±2.88%.

[0081] Next, in (2), in the case of a powder rolling unit provided with a squeegee 3, the squeegee 3 vibrates at a frequency of 2 kHz or more and 300 kHz or less, a powder material 4 having a powder particle diameter of 952 μm is used, and when the distances L1a and L1b are 20,000 μm, the distance L1a and L1b / particle diameter (D50) becomes 21, and a bridge is formed in the hopper 1, so that the rolled sheet 5 is not output from between the rolling rolls 2a and 2b.

[0082] Next, in (3), in the case of a powder rolling unit provided with a squeegee 3, when the squeegee 3 vibrates at a frequency of 2 kHz or more and 300 kHz or less, when a powder material 4 having a powder particle diameter of 511 μm is used, and when the distances L1a and L1b are 10,000 μm, the distance L1a and L1b / particle diameter (D50) becomes 20, and a bridge is formed in the hopper 1, so that a rolled sheet is not output from between the rolling rolls 2a and 2b.

[0083] Next, in (4), in the case of a powder rolling unit provided with a squeegee 3, the squeegee 3 vibrates at a frequency of 2 kHz or more and 300 kHz or less, a powder material 4 having a powder particle diameter of 511 μm is used, and when the distances L1a and L1b are 20,000 μm, the distance L1a and L1b / particle diameter (D50) is 39, the occurrence of missing composite material is suppressed, the occurrence of bridging in the hopper 1 is suppressed, and the variation in basis weight is ±0.79%.

[0084] Next, in (5), in the case of a powder rolling unit provided with a squeegee 3, the squeegee 3 vibrates at a frequency of 2 kHz or more and 300 kHz or less, a powder material 4 having a powder particle diameter of 511 μm is used, and when the distances L1a and L1b are 25,000 μm, the distance L1a and L1b / particle diameter (D50) is 49, the occurrence of missing composite material is suppressed, the occurrence of bridging in the hopper 1 is suppressed, and the variation in basis weight is ±2.51%.

[0085] Next, in (6), in the case of a powder rolling unit provided with a squeegee 3, when the squeegee 3 vibrates at a frequency of 2 kHz or more and 300 kHz or less, when a powder material 4 having a powder particle diameter of 511 μm is used, and when the distances L1a and L1b are 30,000 μm, the distance L1a and L1b / particle diameter (D50) is 59, the occurrence of missing composite material is suppressed, the occurrence of bridging in the hopper 1 is suppressed, and the variation in basis weight is ±3.4%.

[0086] Next, in (7), in the case of a powder rolling unit provided with a squeegee 3, the squeegee 3 vibrates at a frequency of 2 kHz or more and 300 kHz or less, a powder material 4 having a powder particle diameter of 308 μm is used, and when the distances L1a and L1b are 20,000 μm, the distance L1a and L1b / particle diameter (D50) is 65, which causes the mixture to slip out and suppresses the occurrence of bridges in the hopper 1.

[0087] Next, in (8), in the case of a powder rolling unit provided with a squeegee 3, the squeegee 3 vibrates at a frequency of 2 kHz or more and 300 kHz or less, a powder material 4 having a powder particle diameter of 225 μm is used, and when the distances L1a and L1b are 20,000 μm, the distance L1a and L1b / particle diameter (D50) is 89, which causes the mixture to slip out and suppresses the occurrence of bridges in the hopper 1.

[0088] From the above (1) to (8), it was found that bridging occurs in the hopper 1 when the distance L1a, L1b / particle diameter (D50) is 21 or less, and that gaps of the mixture occur when the distance L1a, L1b / particle diameter (D50) is 65 or more. Of (1) to (8), those that suppressed gaps of the mixture and the occurrence of bridging in the hopper 1 were (4) to (6). In (6), the variation in basis weight was ±3.4%, which was higher than the variation in basis weight in (1). Therefore, it was found that (4) and (5), which suppress gaps of the mixture and the occurrence of bridging in the hopper 1 and have small variations in basis weight, are desirable.

[0089] In (3), the distance L1a, L1b / particle diameter (D50) = 20 should be excluded because a bridge is formed in the hopper 1. In addition, in (2), the distance L1a, L1b / particle diameter (D50) = 21 should also be excluded.

[0090] For this reason, the lower limit of the distance L1a, L1b / particle diameter (D50) is set to 22.

[0091] In addition, in order to exclude (6), the distances L1a, L1b / particle diameter (D50)=59 in (6) should also be excluded.

[0092] For this reason, the upper limit of the distance L1a, L1b / particle diameter (D50) is set to 58.

[0093] (Method of Supplying Powder Material 4) Next, a method of supplying powder material 4 to the powder rolling unit will be described.

[0094] As shown in FIGS. 1 and 2 , powder material 4 is supplied to a hopper 1. The hopper 1 temporarily stores the powder material 4 and continuously supplies the powder material 4 to the nip region of the rolling rolls 2a and 2b. The powder material 4 may be supplied to the hopper 1 by intermittently supplying the powder material 4 to the nip region of the rolling rolls 2a and 2b, or by continuously supplying the powder material 4 to the nip region of the rolling rolls 2a and 2b using a known constant-volume supplying device such as a screw feeder or a vibrating feeder. From the viewpoint of maintaining a constant powder pressure generated between the rolling rolls 2a and 2b and the squeegee 3, it is desirable to continuously supply the powder material 4 to the nip region of the rolling rolls 2a and 2b using a constant-volume supplying device such as a screw feeder or a vibrating feeder. This allows the powder pressure generated between the rolling rolls 2a and 2b and the squeegee 3 to be maintained constant, resulting in a rolled sheet 5 with little variation in basis weight.

[0095] (Particle diameter of powder) Next, the particle diameter of the powder material 4 will be described.

[0096] The particle diameter (D50) of the powder in the powder material 4 is preferably, for example, 100 μm or more and 700 μm or less. In this case, the smaller the particle diameter (D50) of the powder, the more likely the fluidity of the powder material 4 is to decrease, but the vibration of the squeegee 3 improves the fluidity of the powder material 4. Therefore, retention and aggregation are suppressed in the powder material 4, and the powder particles are aligned and arranged. Therefore, the powder material 4 is in a high-quality state with little variation in basis weight.

[0097] Here, the particle diameter (D50) is a volume-based median diameter calculated from the particle size distribution measured by a laser diffraction / scattering method, etc. This particle diameter (D50) can be measured using a commercially available laser analysis / scattering particle size distribution measuring device.

[0098] Here, the basis weight is a value expressed as the amount of powder per unit area in weight, and the unit of basis weight is, for example, g / cm２ It is shown as follows.

[0099] Furthermore, the powder may contain only one type of powder, or may contain two or more types of powder. Furthermore, the powder material 4 may be granulated powder obtained by compacting a predetermined amount of powder to enlarge it. The powder material 4 may be any powdery substance. In other words, the raw materials of the powder material 4, the composition of the powder material 4, and the particle shape of the powder material 4 are not particularly limited. In this embodiment, the powder material 4 is a particle group containing a positive electrode active material used in a lithium-ion secondary battery.

[0100] [Manufacturing Method] Next, a method for manufacturing the rolled sheet 5 with less variation in basis weight by using a powder rolling unit will be described.

[0101] The manufacturing method includes supplying powder material 4 to a hopper 1 (powder supplying step), supplying the powder material 4 with the powder aligned to a nip region by passing the powder material 4 between rolling rolls 2a, 2b and a squeegee 3 (powder alignment step), and rolling the powder material 4 by the rolling rolls 2a, 2b to obtain a rolled sheet 5 (powder rolling step).

[0102] First, the powder material 4 is prepared. The raw material of the powder material 4 is not particularly limited, but for example, a particle group containing an active material may be used. When a particle group containing an active material is used, the active material is mixed with appropriate additives (for example, a binder, a conductive material, etc.) to prepare the powder material 4. Examples of the mixing method include a method using a mortar, a ball mill, a mixer, etc. In particular, a method of mixing powders without using a solvent, etc. is preferred because it does not cause material deterioration.

[0103] Next, in the powder supplying step, the powder material 4 is supplied to the hopper 1. The powder material 4 may be supplied to the hopper 1 intermittently, or may be supplied continuously using a known constant volume supplying device such as a screw feeder or a vibrating feeder.

[0104] In the powder alignment process, a squeegee 3 is used to supply the powder material 4 with aligned powder to the nip region. That is, in the powder alignment process, the squeegee 3 controls the amount of powder material 4 supplied to the nip region and the degree of disintegration. At this time, the squeegee 3 vibrates at a frequency of 2 kHz to 300 kHz. The squeegee 3 resonates (natural vibration) with a sinusoidal standing wave. The squeegee 3 vibrates in at least one direction among the thickness direction, width direction, and length direction of the resulting rolled sheet 5. This can enhance the fluidity of the powder material 4. Furthermore, when the squeegee 3 vibrates in multiple directions, the fluidity of the powder material 4 can be further enhanced.

[0105] Next, in the powder rolling process, roll pressing is performed using rolling rolls 2a and 2b. The powder material 4, whose powder has been aligned by the vibration of the squeegee 3, is compressed from the nip region with the supply amount controlled by the vibration of the squeegee 3. As a result, a rolled sheet 5 is formed by compressing the powder material 4, whose powder has been aligned by the squeegee 3.

[0106] As described above, in the method for manufacturing the rolled sheet 5, the powder supplying step, the powder aligning step, and the powder rolling step are performed in this order to form the rolled sheet 5 made of the powder material 4. Such a rolled sheet 5 can be used in an energy device. For example, when a particle group containing an active material is used as the powder material 4, an electrode sheet for an energy device can be manufactured.

[0107] The fabricated energy device can have an electrode sheet with little variation in basis weight, in which the powder material 4 is fluidized and directly coated. Therefore, according to the manufacturing method of the rolled sheet 5, the powder material 4 is directly coated without dispersing the powder material 4 in a solvent or the like, coating it, and drying it. This prevents material degradation due to the solvent and enables high-capacity energy devices. It also prevents the use of solvents and the increased costs associated with drying the solvent. Furthermore, it reduces the large amount of energy consumed in the drying process, resulting in a manufacturing method with a low environmental impact. Meanwhile, when the basis weight of the rolled sheet 5 is highly uniform, the quality of the electrode in the energy device can be improved, and high-capacity energy devices with good quality can be manufactured at low cost.

[0108] (Rolled Sheet 5) Next, the rolled sheet 5 formed using the powder rolling unit will be described.

[0109] The rolled sheet 5 according to this embodiment is used, for example, in an energy device. The formed rolled sheet 5 has a film thickness of 30 μm or more. The rolled sheet 5 contains powder composed of at least one type of particulate material. The concentration of the solvent contained in the powder layer is 50 ppm or less. The powder layer has a small variation in basis weight.

[0110] This allows for the formation of a rolled sheet 5 with little variation in basis weight and suppressed deterioration due to the solvent. Furthermore, since drying of the solvent is not required, the energy consumed for drying the solvent can be reduced, thereby suppressing the environmental impact and preventing an increase in manufacturing costs. Therefore, by using such a powder layer in an energy device, the capacity and quality of the energy device can be increased, the environmental impact can be reduced, and low costs can be achieved.

[0111] The rolled sheet 5 of this embodiment can be used in, for example, a lithium ion secondary battery.

[0112] Hereinafter, the use of the rolled sheet 5 in a lithium ion secondary battery will be described in detail.

[0113] The rolled sheet 5 is used, for example, in combination with a known current collector as an electrode (positive electrode or negative electrode) of a lithium ion secondary battery. Such an electrode includes a current collector and the rolled sheet 5.

[0114] The electrode may further include another layer located between the current collector and the rolled sheet 5. The other layer may be, for example, a connection layer made of a conductive carbon material or the like.

[0115] The thickness of the rolled sheet 5 is 30 μm or more. There is no particular upper limit to the thickness of the rolled sheet 5, but the thickness of the rolled sheet 5 is, for example, 2000 μm or less.

[0116] The rolled sheet 5 also contains a powder material 4 made up of at least one type of particulate material.

[0117] The concentration of the solvent contained in the rolled sheet 5 is 50 ppm or less. In other words, the powder layer is substantially free of solvent. Here, "substantially free of solvent" means that the powder layer is completely free of solvent, or that the solvent is unavoidably contained at 50 ppm or less as an impurity or the like. The solvent concentration is a concentration based on weight. In any region on the surface of the rolled sheet 5, the variation in the powder layer basis weight is, for example, 8% or less.

[0118] The basis weight can be measured, for example, by the following method.

[0119] First, the rolled sheet 5 is punched into circles or polygons of a given size, and the weight of the punched rolled sheet 5 is measured. The basis weight can be determined by dividing this weight by the area of ​​the punched circle or polygon.

[0120] The variation in basis weight is measured, for example, by the following method.

[0121] First, an arbitrary region on the surface of the powder layer in a planar view is selected. This region may be a central region on the surface of the powder layer, or may be a region including the edge of the powder layer. Then, within this region, for example, five or more circular or polygonal shapes of arbitrary size are punched out, and the basis weight is measured using the above-described method. Nine or more punched out locations may be used to increase the accuracy of the variation measurement. The basis weight variation is calculated by dividing the difference (more specifically, the absolute value of the difference) between the average basis weight of all punched locations and the basis weight of the punched location with the largest difference from the average by the average. In other words, a basis weight variation of 8% or less means that the difference from the average basis weight at any punched location is 8% or less of the average.

[0122] Furthermore, the rolled sheet 5 is produced, for example, through a coating process that is substantially free of solvent. This allows the rolled sheet 5 to be formed without being substantially free of solvent. As a result, the rolled sheet 5 is not damaged by the solvent. This prevents deterioration of the rolled sheet 5 and reduces variation in the basis weight of the powder material 4 in the rolled sheet 5, making it possible to form a powder layer for a large, high-capacity energy device that has high capacity and excellent quality.

[0123] The rolled sheet 5 can also be used for the positive electrode, negative electrode, etc. of an energy device such as a lithium ion secondary battery.

[0124] When the rolled sheet 5 is used for a positive electrode, for example, the rolled sheet 5 containing the powder material 4 is a positive electrode mixture layer. That is, the positive electrode mixture layer is used in combination with a positive electrode current collector. The powder material 4 in the positive electrode mixture layer contains a positive electrode active material as at least one type of particulate material. When the rolled sheet 5 is used for a negative electrode, for example, the rolled sheet 5 containing the powder material 4 is a negative electrode mixture layer. That is, the negative electrode mixture layer is used in combination with a negative electrode current collector. The powder material 4 in the negative electrode mixture layer contains a negative electrode active material as at least one type of particulate material.

[0125] The concentration of the solvent contained in the positive electrode mixture layer and the negative electrode mixture layer is 50 ppm or less. That is, the positive electrode mixture layer and the negative electrode mixture layer are substantially free of solvent. Here, "substantially free of solvent" means that these layers are completely free of solvent and that these layers unavoidably contain 50 ppm or less of solvent as impurities or the like.

[0126] The solvent is, for example, an organic solvent. The method for measuring the solvent is not particularly limited, and can be measured using, for example, gas chromatography, mass variation analysis, etc. Examples of organic solvents include nonpolar organic solvents such as heptane, xylene, and toluene, polar organic solvents such as tertiary amine solvents, ether solvents, thiol solvents, and ester solvents, as well as combinations thereof. Examples of tertiary amine solvents include triethylamine, tributylamine, and triamylamine. Examples of ether solvents include tetrahydrofuran and cyclopentyl methyl ether. Examples of thiol solvents include ethane mercaptan. Examples of ester solvents include butyl butyrate, ethyl acetate, and butyl acetate.

[0127] Next, the materials used in the positive electrode mixture layer and the negative electrode mixture layer will be described in detail.

[0128] The positive electrode active material is a substance in which metal ions such as lithium (Li) are inserted into or extracted from the crystal structure at a potential higher than that of the negative electrode, and oxidation or reduction occurs along with the insertion or extraction of the metal ions such as lithium. The type of the positive electrode active material is appropriately selected, and examples thereof include oxide active materials.

[0129] The positive electrode active material in this embodiment may be, for example, lithium transition metal oxide particles containing a transition metal element such as Co, Mn, or Ni. ｘ CoO ２ , Li ｘ NiO ２ , Li ｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M１－ｙ O ｚ , Li ｘ Ni １－ｙ M ｙ O ｚ , Li ｘ Mn ２ O ４ , Li ｘ Mn ２－ｙ M ｙ O ４ , LiMPO ４ , Li ２ MPO ４ F (M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3). These may be used alone or in combination of two or more. In terms of increasing the capacity of a lithium ion secondary battery, the positive electrode active material particles are preferably Li ｘ NiO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Ni １－ｙ M ｙ O ｚ It is preferable that the lithium-nickel composite oxide particles contain lithium-nickel composite oxide particles such as (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B; 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3).

[0130] Examples of the shape of the positive electrode active material include particulates. When the positive electrode active material is particulate, the particle diameter of the positive electrode active material is, for example, in the range of 0.05 μm to 30 μm, and may be in the range of 1 μm to 15 μm. If the particle diameter of the positive electrode active material is 0.05 μm or more, handling tends to be improved. On the other hand, if the particle diameter is 30 μm or less, using an active material with a small particle size increases the surface area, making it easier to obtain a high-capacity positive electrode. Note that the particle diameter of the material contained in the positive electrode mixture layer or the negative electrode mixture layer in this specification is, for example, the above-mentioned D50.

[0131] The negative electrode active material is a substance in which metal ions such as lithium are inserted into or extracted from the crystal structure at a lower potential than the positive electrode, and which undergoes oxidation or reduction as the metal ions such as lithium are inserted or extracted.

[0132] Examples of the negative electrode active material in this embodiment include lithium alloys such as metallic lithium, lithium-aluminum alloys, lithium-lead alloys, lithium-silicon alloys, and lithium-tin alloys; carbon materials such as graphite, coke, and organic sintered bodies; and SnO ２ , SnO, TiO ２ These may be used alone or in combination of two or more. Furthermore, as the negative electrode active material, a composite in which the above-mentioned negative electrode active materials are appropriately mixed may also be used.

[0133] The particle size of the negative electrode active material is, for example, 30 μm or less. By using an active material with a small particle size, the surface area is increased, and a high capacity can be achieved.

[0134] Next, the positive electrode current collector and the negative electrode current collector will be described in detail.

[0135] The positive electrode in this embodiment includes a positive electrode current collector made of, for example, a metal foil. The positive electrode current collector may be, for example, a foil, plate, or mesh-like material made of aluminum, gold, platinum, zinc, copper, stainless steel (SUS), nickel, tin, titanium, or an alloy of two or more of these metals. The thickness and shape of the positive electrode current collector may be appropriately selected depending on the application of the positive electrode.

[0136] The negative electrode in this embodiment includes a negative electrode current collector made of, for example, a metal foil. The negative electrode current collector may be, for example, a foil, plate, or mesh-like material made of stainless steel, gold, platinum, zinc, copper, nickel, titanium, tin, or an alloy of two or more of these metals. The thickness and shape of the negative electrode current collector may be selected as appropriate depending on the application of the negative electrode.

[0137] (Operation and Effect) Hereinafter, the operation and effect of the powder rolling unit in this embodiment will be described.

[0138] As described above, the powder rolling unit of Technology 1 in this embodiment includes the rolls 2a and / or 2b that roll the powder material 4 to form the rolled sheet 5, the hopper 1 that stores the powder material 4 above the rolls 2a and / or 2b, and the squeegee 3 that is arranged above the rolls 2a and 2b and parallel to the axial directions of the rolls 2a and 2b and vibrates at a predetermined frequency. When the distance between the squeegee 3 and the rolls 2a and 2b is divided by the particle diameter (D50) of the powder that constitutes the powder material 4 to be rolled, the following relationship holds: 22≦(distance L1a, L1b between the squeegee 3 and the rolls 2a and 2b) / particle diameter (D50)≦58.

[0139] This allows the squeegee 3 to vibrate the powder material 4 stored inside the hopper 1. This allows the powder material 4 to be supplied to the mill rolls 2a and / or 2b at a constant rate (uniform powder supply amount) so that the powder material 4 is not blocked by the mill rolls 2a and / or 2b. This improves the fluidity of the powder material 4 near the nip region inside the hopper 1.

[0140] Furthermore, if the relationship 22≦distance L1a, L1b / particle diameter (D50)≦58 is satisfied, it is expected that the occurrence of dropout of the mixture and the occurrence of bridges in the hopper 1 will be suppressed, and the variation in the basis weight of the rolled sheet 5 will be reduced.

[0141] Therefore, according to this embodiment, clogging of the powder material 4 in the nip region can be suppressed, and variations in the basis weight of the rolled sheet 5 can be suppressed. As a result, a rolled sheet 5 with a uniform basis weight can be obtained. In particular, according to this embodiment, it is possible to obtain a desired rolled sheet 5, and therefore a decrease in yield can be suppressed.

[0142] The powder rolling unit of Technology 2 in this embodiment is the powder rolling unit described in Technology 1. In this case, a pair of rolls 2 a, 2 b is provided. The pair of rolls 2 a, 2 b rolls the powder material 4 to form a rolled sheet 5.

[0143] As a result, since the squeegee 3 is positioned parallel to the rolling rolls 2a, 2b, the distance from one end of the squeegee 3 to the compression point is the same as the distance from the other end of the squeegee 3 to the compression point, and differences due to variations are less likely to occur between the basis weight of one end of the resulting rolled sheet 5 and the basis weight of the other end of the rolled sheet 5.

[0144] Furthermore, the powder rolling unit of Technology 3 in this embodiment is the powder rolling unit described in Technology 2. In this case, the surface roughness of one roll 2a of the pair of rolls 2a, 2b is higher than the surface roughness of the other roll 2b of the pair of rolls 2a, 2b.

[0145] This makes it easier for the rolled sheet 5 to be discharged from between the rolls 2a and 2b while adhering to the surface of the roll 2a, thereby enabling the rolled sheet 5 that has passed between the rolls 2a and 2b to be transported to the next roll.

[0146] Furthermore, the powder rolling unit of Technology 4 in this embodiment is the powder rolling unit described in any one of Technologies 1 to 3. In this case, the rotation speed of one roll 2a is faster than the rotation speed of the other roll 2b.

[0147] This makes it easier for the rolled sheet 5 to be discharged from between the rolls 2a and 2b while adhering to the surface of the roll 2a, which allows the rolled sheet 5 that has passed between the rolls 2a and 2b to be more easily transported to the next roll.

[0148] Furthermore, the powder rolling unit of Technology 5 in this embodiment is the powder rolling unit described in any one of Technologies 2 to 4. In this case, at least a part of the squeegee 3 is disposed between the pair of rolls 2 a, 2 b so as not to come into contact with the pair of rolls 2 a, 2 b.

[0149] With this, when the powder material 4 stored inside the hopper 1 is supplied to the nip region between the rolling rolls 2a and 2b, the squeegee 3 can apply vibration to the powder material 4. Therefore, the vibration of the squeegee 3 improves the fluidity of the powder material 4, making it possible to obtain a rolled sheet 5 with little variation in basis weight.

[0150] Furthermore, the powder rolling unit of Technique 6 in this embodiment is the powder rolling unit according to any one of Techniques 1 to 5. In this case, the predetermined frequency at which the squeegee 3 vibrates is 2 kHz or more and 300 kHz or less.

[0151] For example, in the case of low-frequency vibrations of 2 kHz or less, the number of vibrations applied to the powder may be insufficient, making it impossible to impart sufficient fluidity to the powder. Also, in the case of high-frequency vibrations of 300 kHz or more, vibration attenuation increases when the vibrations are transmitted through the powder, making it impossible to impart sufficient fluidity to the powder.

[0152] However, according to this embodiment, when handling powder with a particle diameter of 100 μm or more and 700 μm or less, it is possible to impart fluidity to the powder. Therefore, the fluidity of the powder material 4 is improved by the vibration of the squeegee 3, and a rolled sheet 5 with little variation in basis weight can be obtained.

[0153] (Other Embodiments) Although the powder rolling unit according to the present disclosure has been described above based on the embodiments, the present disclosure is not limited to these embodiments.

[0154] For example, the powder rolling unit according to this embodiment is not limited to one squeegee 3. That is, the powder rolling unit may further include a multi-stage squeegee. Specifically, the multi-stage squeegee may be arranged in the hopper 1 so that the axial direction of the multi-stage squeegee is parallel to the axial direction of the rolls 2a and 2b. The multi-stage squeegee can gently crush the powder material 4 in advance so that the powder material 4 does not clog between the rolls 2a and 2b and the squeegee 3. Furthermore, multiple multi-stage squeegees may be arranged above the squeegee 3. For example, one multi-stage squeegee may be arranged above the squeegee 3 and the roll 2a, and another multi-stage squeegee may be arranged above the squeegee 3 and the roll 2b.

[0155] In addition, as long as they do not deviate from the gist of this disclosure, various modifications that a person skilled in the art may make to the embodiments, and other forms constructed by combining some of the components of the embodiments, are also included in the scope of this disclosure.

[0156] The powder rolling unit of the present disclosure forms a uniform powder layer without using a solvent, and can be applied to applications such as a mixture layer for a high-quality lithium-ion secondary battery.

[0157] REFERENCE SIGNS LIST 1 Hopper 2a, 2b Rolling roll 3 Squeegee 4 Powder material 5 Rolled sheet 6 Vibrator

Claims

1. A powder rolling unit comprising: a rolling roll for rolling a powder material to form a rolled sheet; a hopper for storing the powder material above the rolling roll; and a squeegee arranged above the rolling roll and parallel to the axial directions of the rolling rolls and vibrating at a predetermined frequency, wherein when the distance between the squeegee and the rolling roll is divided by the particle diameter (D50) of the powder constituting the powder material to be rolled, the following relationship holds: 22≦(distance between the squeegee and the rolling roll) / particle diameter (D50)≦58.

2. The powder rolling unit according to claim 1, wherein the rolling rolls are provided as a pair, and the pair of rolling rolls roll the powder material to form a rolled sheet.

3. The powder rolling unit according to claim 2, wherein the surface roughness of one of the pair of rolls is higher than the surface roughness of the other of the pair of rolls.

4. The powder rolling unit according to claim 3, wherein the rotation speed of one of the rolling rolls is faster than the rotation speed of the other of the rolling rolls.

5. The powder rolling unit according to any one of claims 2 to 4, wherein at least a portion of the squeegee is disposed between a pair of the rolling rolls so as not to come into contact with the pair of the rolling rolls.