JP2015159089A - Production method of electrode paste by continuous biaxial kneader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of electrode paste by a continuous biaxial kneader, capable of obtaining an electrode paste mixed and stirred uniformly in a short time, without dissolving a binder powder previously into a solvent completely, in the production of the electrode paste of a lithium ion secondary battery.SOLUTION: Pretreatment for adding a small quantity of solvent to the powder of an active material, a conductive aid, a binder and a dispersing aid, composing an electrode paste, and mixing the powder into pendular state or funicular state by means of a mixer is performed. Subsequently, this powder mixture in the pendular state or funicular state is supplied to a continuous biaxial kneader and kneaded. A kneaded product thus obtained is added with a solvent and diluted by means of a mixer, thus obtaining an electrode paste.

Description

  The present invention relates to a method for producing an electrode paste using a continuous biaxial kneader that is preferably used for producing an electrode paste using a continuous biaxial kneader, particularly an electrode paste for a lithium ion secondary battery. is there.

  The manufacturing process of the lithium ion secondary battery is roughly divided into an electrode manufacturing process and a battery assembling process, and the electrode manufacturing process was obtained by dissolving a binder (binder) that is a powder resin. Electrode pasting process to knead liquid binder (dissolving binder) with active material, conductive aid, dispersion aid, solvent, etc. to make electrode paste, coating process of electrode paste to current collector, and press slit of current collector Including processes. The binder (binder) that is dissolved in the dissolution step is, for example, a powder resin such as polyvinylidene fluoride (PVDF), and a solvent such as 1-methyl-2-pyrrolidone (NMP) is added to the binder. The tank is charged and dissolved by rotating the stirring blade. However, since it is a powder resin, a dissolution time of 2 to 3 hours is required to completely dissolve it in a solvent even if it is stirred at a high speed with a mixer. If the binder at this time is insufficiently dissolved and swelled, the binder that has not been sufficiently dissolved during the finishing process will pass through the filter and enter the electrode paste. Causes streaks. When such a streak occurs, the function as a battery deteriorates. Therefore, stirring is performed for a long time with a mixer until the binder is completely dissolved.

  The process of mixing, dissolving, kneading, and dispersing the processing materials not limited to solid / solid and solid / trace liquid oily and aqueous in the electrode pasting process is conventionally batch-type. Many. The equipment used for this processing includes a biaxial mixer (eg, planetary mixer), a triaxial mixer (eg, a mixer having three low-speed blades, a mixer having two low-speed blades and one high-speed blade), four-shaft There are apparatuses such as a mixer (for example, a mixer having two low-speed and high-speed blades) and a kneader.

In the batch processing method as described above, shearing stress (shear stress) is applied to the processing material on the blade rotating in the tank and the inner wall surface of the tank, but the opportunity to apply this shearing stress is , The moment when the blade approaches the inner wall of the tank and is discontinuous. Even in the case of a planetary kneader that rotates and revolves using a frame-type blade, the blade is only operated twice when it rotates once. In addition, there were the following problems.
1 The powder at the time of preparation and the processing material at the time of kneading adhere (fix) to the container (tank) or blade (blade), and the work of scraping off the kneading work is required.
2 Material scattered and adhering to the container (tank) is mixed into the processing material during kneading, causing quality defects.
3 In the diluting process after kneading, if it is not gradually diluted, it will be easy to form lumps and lumps (partial aggregation of powder).
4 The kneading ability depends on the number of times of approaching (displacement) between the blade (blade) and the tank (container), but the number of times of approaching is small, the phenomenon of material lifting is also observed, and the kneading time is long.
5 The only way to deal with the increase in production volume is to increase the size of the machine, necessitating an increase in equipment costs and installation space.

  As described above, since there are various problems in the case of batch processing, a method for continuously producing a positive electrode paint (electrode paste) for a lithium ion battery using a twin-screw kneading extruder has also been proposed (for example, (See Patent Document 1). However, in the method described in Patent Document 1, a powder component such as an active material is added from a powder supply unit to an extruder, and a binder solution (resin solution, solution binder) is added to the binder supply unit during kneading. In addition, after passing through the kneading section in the extruder, the solvent is supplied from the solvent supply unit, and the paint (electrode paste) is obtained from the paint discharge port. In this method, before being put into the extruder, the binder, which is a powder resin, is dissolved by stirring with a solvent with a mixer to create a resin solution, and this resin solution is supplied to the extruder. As described above, it takes a considerable time to completely dissolve the powder resin, and the powder resin cannot be efficiently operated.

  In the method described in Patent Document 1, powders such as active materials are first charged into the extruder from the powder supply unit of the extruder, and the binder solution is supplied to the extruder during the kneading. However, in such an operation, it is difficult to obtain an electrode paste that is accurately weighed with the required components. That is, powders such as active materials are powders having a particle size of 100 μm or less, such as powders, fine powders, and ultrafine powders (nanoparticles). When supplying to the hopper, it tends to adhere to the surface and corners of the hopper. In particular, fine particles such as nanoparticles tend to adhere to a hopper, a wall surface inside a machine, or the like as the density becomes lighter, which may further cause a component to be out of order. In addition, in the method of adding a binder solution in the middle of kneading, it can be said that the powders kneaded by the time the binder solution is mixed always have the same particle size, the same density, and the same wet state. In addition, it is mixed in various states, and further, it may cause stagnation due to its light density, so there are ingredients in the early stage paste and the later stage paste discharged from the extruder In some cases, an error may occur and a measurement error (measurement error) may occur, making accurate uniform ejection impossible. That is, there is a strong possibility that differences in the concentration, specific gravity, composition, viscosity, and the like of the paste after discharge are strong, which causes deterioration of the characteristics of a lithium ion secondary battery using such an electrode paste.

Japanese Patent No. 4448704 (paragraphs 0011, 0026, 0051)

  As described above, the problem to be solved by the present invention is that, when producing an electrode paste for a lithium ion secondary battery, the step of dissolving a powdery resinous binder in advance in a solvent is omitted, and production is efficiently performed in a short time. This prevents the occurrence of bumps and lumps, and the kneading device is sealed so that there is no problem in the working environment, eliminating the scraping work of the material adhering to each part, making it difficult to cause measurement errors in the material components, and uniform kneading. It is to provide a method for producing an electrode paste using a continuous biaxial kneader.

  According to the present invention, a pretreatment step of adding a solvent to a powder of an active material, a conductive aid, a binder, and a dispersion aid constituting the electrode paste and mixing the powder into a pendular state or a phenicular state with a mixer, Supplying the powder mixture in the pendular state or the phenicular state to a continuous biaxial kneader and kneading while heating, adding a solvent to the kneaded material discharged from the continuous biaxial kneader and diluting with a mixer The manufacturing method of the electrode paste by the continuous biaxial kneader including a process is provided, and the said subject is solved.

  Further, according to the present invention, the liquid content of the solvent for mixing the powder in the pendular state or the phencular state is 5 to 20% by mass, and heating of the jacket during kneading in the continuous biaxial kneader A method for producing an electrode paste by the continuous biaxial kneader having a temperature of 50 to 70 ° C. is provided, and the above problems are solved.

  As described in the “Attenberg table” indicating the properties of the material in the kneading, the pendular state includes a solvent (liquid) but a small amount, and the surface of the powder. The state is completely uncoated with solvent, and the phencular state is a moist state where the powder surface is coated with a solvent but there is a gas in the gap between the powders. It is. "Bubble" is a condition that hardens when grasping the powder mixture, but breaks when touched. "Moist" is a condition that solidifies when the powder mixture is grasped, and the mass can be easily broken. It is.

  The present invention is configured as described above, and a solvent is added to the powder of the active material, conductive additive, binder, and dispersion aid constituting the electrode paste, and the mixture is mixed in a pendular state or a phenicular state with a mixer. Pretreatment step, supplying the powder mixture in the pendulum state or phencular state to a continuous biaxial kneader and kneading while heating, adding a solvent to the kneaded material discharged from the continuous biaxial kneader Including a step of diluting with a mixer. According to the present invention, a powder mixture in a pendular state or a phenicular state is prepared by adding a small amount of solvent to a powder material such as an active material, a conductive aid, a binder, and a dispersion aid in a pretreatment step. However, this work is not simply a powder resin binder, which is mixed with a solvent by a mixer, and dissolved completely to make a binder solution (liquid binder). Since only a small amount of solvent is added to the material to make it dry and moist as described above, it takes much shorter time than when the binder powder is completely dissolved in the solvent as in the past. The pretreatment process is completed in the work. At this time, since the powder mixture is batch-type, it can be accurately measured, has a predetermined component, and when it is supplied to the kneading machine in the next process, it is in a slightly wet state with a liquid. It is possible to supply the components as measured.

  In the step of kneading with a continuous twin-screw kneader while heating without adding a solvent, the binder powder in the powder mixture is undissolved by heating it through warm water through the jacket of the barrel of the kneader. There is no object, it melts cleanly and the whole is uniformly kneaded, and no kneading or lumps occur, and the kneaded material in a homogeneously kneaded state is discharged from the discharge port. Thereafter, the kneaded product is stirred and diluted with a solvent by a mixer, so that an electrode paste having the desired components as weighed can be obtained without requiring a long time as in the prior art.

The front view which showed one Example of the continuous biaxial kneader used for this invention, and cut | disconnected the barrel etc. FIG. The top view of the twin-screw kneader shown in FIG. The feed blade is shown, (A) is a perspective view, (B) is an explanatory view seen from the side. The return blade is shown, (A) is a perspective view, (B) is an explanatory view seen from the side.

  The production method according to the present invention, in the production of an electrode paste of a lithium ion secondary battery, weighs the active material, conductive additive, binder, and dispersion aid powder constituting the electrode paste and mixes them with a mixer (powder mixing). Machine), a small amount of solvent is added, mixed and stirred, and a pretreatment step is performed to create a powder mixture in a pendulum state or a phenicular state. The processing time at this time is about 10 minutes. The obtained powder mixture is solid or moist enough to be hardened when gripped, broken or broken when touched. A small amount of solvent is added at this time, and the liquid content is preferably about 5 to 20%.

  Next, the powder mixture is supplied from the hopper of the continuous twin-screw kneader into the barrel of the kneader that is sealed, mixed, dissolved, kneaded and dispersed by the action of the blades while moving inside, and kneaded. It is discharged as a kneaded product in a state.

  The continuous biaxial kneader used in the present invention is preferably an apparatus capable of producing a highly viscous paste. The continuous biaxial kneader shown in FIG. 1 and FIG. 2 has two kneading shafts 2 rotatably accommodated in a parallel state in a barrel (tank) 1 that can be opened and closed in the vertical direction. The two kneading shafts rotate in different directions via a motor 3 connected to one of the shafts 2 and a gear mechanism 4 that transmits the rotation to the other kneading shaft. A hopper 5 for feeding a powder mixture (processing material) into the barrel and a supply port 6 leading to the hopper 5 are formed on one end side of the barrel, and a discharge port 7 for the processed material is formed on the other side. Has been.

  The kneading shaft 2 is provided with a supply screw 8 that feeds the powder mixture in the forward direction, a feed blade 9 that moves forward while kneading, and a return blade 10 that moves backward while kneading. The supply screw 8 is formed in a spiral shape so as to advance the powder mixture charged from the supply port 6 toward the discharge port 7, and is disposed in the material supply unit zone 11, when the supply screw 8 rotates. The amount of movement of the powder mixture in the forward direction is adjusted by the feed amount. The biaxial blades may be rotated in a non-overlapping different direction constant velocity rotating blade that rotates at the same speed in different directions without overlapping the biaxial blades, or at different speeds in different directions (for example, 1: A different direction, different speed rotating blade (differential or tangential method) rotating in 2) is preferable.

  The feed blade 9 has a function of feeding the material in the forward direction while kneading the material, and the return blade 10 has a function of feeding the material in the backward direction while kneading the material. It is arranged in the material kneading zone 10 following this. The feed blade 9 and the return blade 10 can be variously configured. The blade members 13 and 14 shown in FIG. 3 and FIG. 4 have twisted fin type blades, and a feed blade portion 9a formed on the outer periphery of a substantially cylindrical boss portion 15 attached to the kneading shaft 2 with a right twist. (FIG. 3) and a return blade portion 10a (FIG. 4) formed in a left twist. The blade portions 9a, 10a have a twist angle (α) of about 30 ° to 90 °, and the cross-sectional shape is substantially hexagonal. The edge angle (θ) of the tip portion of the blade portion is about 30 ° to 60 °, preferably about 45 °. When such an angle is set, in the tangential circular motion, the driving power is low at 30 ° or less and 60 ° or more, and when it is about 30 ° to 60 °, the material is likely to bite.

  Further, the edge width (b) of the tip portions of the blade portions 9a and 10a is preferably about 2 mm to 10 mm, and is preferably about 5% to 20% of the blade diameter (d). If it is smaller than 2 mm, the inner wall of the barrel is close to a line contact state via the processing material, and the shear stress is insufficient. If it is larger than 10 mm, it will be in a surface contact state, and powerful power will be required for operation, and it will be difficult to control the temperature of the material.

  Each of the blade portions has a boss portion with a large diameter so that the height of the blade is reduced. That is, the ratio between the blade diameter (d) and the maximum height (H) of the blade portion is formed to be about H / d = about 0.15 to 0.25. If it is smaller than 0.15, the height of the blade portion is too low, the function of capturing the material and sending the material in the left-right direction (forward, backward direction) is weakened and the flow is reduced. This is because it stays near the boss part and starts to adhere to the blade part in an unstable state. In a preferred embodiment, it is formed to have a thickness of about 0.2.

  The tip of each of the blade portions is close to the inner wall of the barrel 1, and the gap between them has a constant clearance (c) in the circumferential direction of the blade so as to shorten the kneading time and continuously apply shear stress. ) Are arranged close to each other with a narrow gap. This clearance (c) is formed to be about 1 mm to 10 mm. If it is smaller than 1 mm, the blade and the kneaded material rotate together, resulting in insufficient kneading. On the other hand, if it is larger than 10 mm, even in a large machine, the speed difference between the barrel inner wall and the tip of the blade part becomes loose, the material is easily fixed to the wall part, and the temperature control becomes difficult due to the fixing of the material. This is because uniform kneading cannot be performed. In the preferred embodiment, the clearance is about 2.0 mm.

  In the blade member, the feed blade 9 and the return blade 10 are combined so as to face each other in the axial direction, but may be combined face to face so that the phase of the blade portion is shifted by 90 °. Specifically, a material that is fed out while kneading the material toward the discharge port and a material that is returned to the supply port are arranged in a pair to give the material compression, shear, expansion, collision, and impact. Crushing and kneading.

  The number of blade portions (blades) provided on the blade member can be set as appropriate, but preferably about 2 to 8 are provided. A single blade portion is not preferable because the balance of material distribution is poor when the shaft is rotated, the shaft is loaded by an unbalanced load, and the kneading degree is easily short-circuited. Also, if there are more than 8 blade parts, the opportunity to apply shear stress to the material between the blade part and the inner wall of the barrel is too close, and the frequency of compression and expansion applied to the material is reduced, resulting in sufficient crushing action. It is because it becomes impossible to play.

  As described above, in the material kneading section zone 12, the material fed by the feeding action of the supply screw 8 is continuously sheared (sheared) in a narrow gap between the inner wall of the barrel and the tip of the blade section when passing through this zone. Force) and kneaded by compression / expansion, collision and impact. In a zone close to the material supply section zone 11, the material supplied from the material supply section zone 11 moves back and forth between the blades combined in a face-to-face relationship, giving the material a flow in the left-right direction (forward, backward direction), The powder activated by the powder mixing is inactivated, and the aggregation of the material is crushed. Even between the blades that are provided subsequently, the material is subjected to a shearing action, with a small liquid component, and a strong kneading action due to high shear stress at high viscosity, resulting in kneading in the form of a highly viscous paste that is finally kneaded. It is discharged from the discharge port as an object.

  Further, the material kneading zone 10 is partitioned by a partition plate (separator) 16 with an opening for imparting resistance to the material flowing in the zone. The partition plate 16 is formed in a disc shape having an outer diameter substantially the same as the outer diameter of the blade, and an opening (not shown) is formed in the peripheral portion so that the material can partially pass therethrough. The material is prevented from returning through the partition plate, and when the material passes through the opening, compression / expansion, collision / impact action acts on the material, so that partial aggregation of the powder is eliminated. The generation of lumps is reduced and the wetting of the powder is further promoted, so that it is efficiently dissolved and kneaded.

  A jacket 17 is provided on the outer periphery of the barrel 1 of the material kneading section zone 12. A temperature adjusting medium such as warm water is circulated through the water supply port and the discharge port of the jacket 17 to heat the inside of the barrel so that the binder powder is sufficiently dissolved and melted. The temperature at this time is preferably 50 to 70 ° C., and by passing hot water through the jacket, the powder resin for electrode paste supplied in the powder state by the pretreatment as described above, such as polyvinylidene fluoride (PVDF) The resin can be dissolved and kneaded cleanly and continuously without any undissolved material.

  Next, the kneaded material discharged from the discharge port 7 of the continuous biaxial kneader is diluted with a mixer (dilution mixer) so as to become a paste having a desired viscosity by adding a solvent, and coating the slurry-like electrode paste Become a liquid. At this time, the shape of the kneaded material discharged from the discharge port as described above is a pipe or a cylinder corresponding to the shape of the discharge port. It is preferable that an appropriate dividing net 18 is provided at the discharge port 7 of the machine, and it is divided into pieces and supplied to the mixer. As this divided network, a configuration such as a breaker plate or a screen of an extruder is selected. The dividing net may be fixedly provided at the discharge port, or may be detachably provided so that it can be attached when it is necessary to divide.

  Ternary positive electrode active material (particle size: 5-10 μm) Lithium nickel manganese cobaltate (NMC), conductive additive (primary particle size: 48 nm), and binder powder resin: polyvinylidene fluoride (PVDF) with a solid content of 86 13.7% by weight of a solvent 1-methyl-2-pyrrolidone (NMP) was added so as to be 3% by weight, and the mixture was stirred and mixed with a mixer (powder mixer). At this time, the powder mixture in the state of being stirred and mixed is in a wet state such that it is solidified when gripped but broken when touched in a pendulum (moist) state or a phencular (moist) state. At this time, the time required for stirring and mixing was about 30 minutes.

  When this pretreated powder mixture was supplied to the supply port of the continuous twin-screw kneader shown in FIG. 1 having a blade diameter of φ68 mm and a capacity of 1 liter, a 3-pass treatment was performed, and the following results were obtained. It was.

  As can be seen from the above results, according to the present invention, when one pass is performed, the discharge amount is small and the residence time is long. However, when two passes and three passes, the discharge amount is stable and the residence time is short, Almost the same results were obtained, and it was confirmed that they were sufficiently kneaded. As described above, the active material and the binder powder and the like are mixed by powder metering and mixed in a slightly moist state in the pretreatment, and then processed by a continuous twin-screw kneader to have a residence time of about 15 to Complete dissolution in 20 minutes (2 to 3 passes) eliminates the need for conventional melting mixer facilities and equipment installation locations.

  On the other hand, before adding the PVDF powder to the active material as in the past, in order to completely dissolve the PVDF powder in NMP in advance, it was stirred and mixed with a stirrer equipped with a high-speed mixer. did. Therefore, it has been confirmed that the processing time is remarkably shortened by the manufacturing method of the present invention only by considering the dissolution time. In the present invention, the kneaded product discharged from the discharge port of the twin-screw kneader is a high-kneaded state, so that a slurry is then diluted by adding a solvent in another mixer (dilution mixer). However, the processing time by this mixer is about 60 minutes, and the processing time as a whole can be shortened.

  The electrode paste obtained as described above has no undissolved PVDF, is completely dissolved, and can uniformly coat the current collector foil. In addition, the adhesive strength was sufficient, no generation of lumps or lumps, and no destruction of the active material particles. In addition to manufacturing electrode pastes for lithium ion batteries, the present invention requires chemical, pharmaceutical, electronic, and ceramics that require a powder resin as a binder added to a plurality of powders, mixed and stirred to form a paste. It can also be applied to the processing of food, feed and other fields.

DESCRIPTION OF SYMBOLS 1 Barrel 2 Kneading shaft 6 Supply port 7 Discharge port 8 Supply screw 9 Feed blade 10 Return blade 11 Material supply part zone 12 Material kneading part zone 13, 14 Blade member 16 Partition plate 17 Jacket 18 Divided net

Claims (5)

  A pre-treatment process in which a solvent is added to the powder of the active material, conductive auxiliary agent, binder, and dispersion auxiliary agent constituting the electrode paste, and the mixture is mixed into a pendular state or a phencular state by a mixer, this pendular state or phencular Including a step of supplying the powder mixture in a state to a continuous biaxial kneader and kneading while heating, a step of adding a solvent to the kneaded material discharged from the continuous biaxial kneader and diluting with a mixer A method for producing an electrode paste using a shaft kneader.   The method for producing an electrode paste by a continuous biaxial kneader according to claim 1, wherein the liquid content of the solvent for mixing the powder into the pendular state or the phencular state is 5 to 20% by mass.   The method for producing an electrode paste by a continuous biaxial kneader according to claim 1 or 2, wherein a heating temperature of a jacket for heating the continuous biaxial kneader during kneading is 50 to 70 ° C.   The method for producing an electrode paste by a continuous biaxial kneader according to claim 1, wherein the kneaded material discharged from the continuous biaxial kneader is supplied to a dilution mixer in a divided state and diluted.   The continuous biaxial kneader has a material supply zone provided with a supply screw for advancing the powder mixture supplied to the barrel and a material kneading zone to knead the powder mixture. A feed blade that advances while kneading the material and a return blade that moves backward are provided, the tip of the blade portion of each blade is close to the inner wall of the barrel, and a partition plate with an opening that partitions the material kneading zone is provided, The powder mixture is compressed / expanded, impacted and impacted while being advanced and retracted through the opening of the partition plate while being advanced and retracted through the narrow gap between the inner wall of the barrel by the feed blade and the return blade. The manufacturing method of the electrode paste by the continuous biaxial kneader in any one of Claims 1-4 received and kneaded.

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