METHOD FOR MANUFACTURING SECONDARY BATTERY, OR SECONDARY BATTERY

Abstract

A method for manufacturing secondary batteries, forming a positive electrode for lithium-ion batteries, it was necessary to select polyvinylidene fluoride (PVDF) or the like as a binder due to the problems of heat resistance or chemical resistance when using a liquid electrolyte such as an organic solvent. Solvents which can dissolve such a resin are limited to normal methylpyrrolidone (NMP) and the like, have a high boiling point, and require a long, high-temperature oven.

By mixing a slurry with a low boiling point solvent, and applying the resultant mixture to a heated object, a parent solvent evaporates due to the azeotropic effect of the low boiling point solvent, and spraying, especially pulsed spraying can evaporate at least 90% of the parent solvent on the object within 5 seconds even when the temperature of the object is 100° C. lower, preferably at least 50° C. lower than that of the parent solvent. Therefore, a drying device has a very small total length, thus by lamination in the form of a thin film, the positive electrode can be easily made into a thick film thickness.

Claims

1. A method for manufacturing a secondary battery, which includes an assembly of a positive electrode, a negative electrode, and an electrolyte material of the secondary battery, comprising: preparing a slurry from a plurality of materials selected from positive electrode active material particles, electrolyte materials, negative electrode active material particles or short fibers, conductive assistant particles or short fibers, thickeners, binders, and parent solvents for the thickeners or the binders; moving the slurry from an independent material handling device prepared for the slurry; moving a solvent having a boiling point lower than that of a parent solvent for the slurry by another material handling device; merging the slurry and the low boiling point solvent to form a merged liquid; and applying the merged liquid to the object; and wherein the object is at least one of a current collector for positive electrode, a positive electrode layer, a separator, an electrolyte layer, a current collector for negative electrode, and a negative electrode layer.

2. The method according to claim 1, wherein the low boiling point solvent is mixed with the slurry in advance to form a mixed fluid, the mixed fluid is dispersed in the material handling device to form a dispersed slurry, and the dispersed slurry is circulated at a flow velocity that does not cause separation of the low boiling point solvent and the slurry, or is moved to an application device and applied to the object by the application device.

3. The method according to claim 1, wherein the object is heated at the time of application, evaporation of the parent solvent is accelerated by the evaporation of the low boiling point solvent, and the slurry is applied by the application device.

4. The method according to claim 1, wherein the low boiling point solvent is a poor solvent with respect to the binder.

5. The method according to claim 1, wherein the binder or the thickener for slurry can be selected from a plurality of types, a parent solvent can be selected as the solvent for binder, and particles of the slurry can be selected from a plurality of types of solid particles or short fibers, or a single or multiple independent slurries selected from a plurality of types of particles or short fibers are prepared, they are mixed with the low boiling point solvent to form a mixed fluid which is applied to the object, as method for mixing or applying them, at least one method selected from a rotary stirring method, a centrifugal force dispersion method, a static mixer method, a vibration method, an ultrasonic vibration method, an ultrasonic atomization method, a spraying method, a pulse spraying method, a slot nozzle method, an air assist slot nozzle method, a fine particle spraying slit nozzle method, and a centrifugal atomization method of a bell or a disc is used.

6. A method for manufacturing a secondary battery, wherein the secondary battery is a polymer battery and at least electrolyte material is an electrolyte polymer, at least a positive electrode layer on a current collector formed by the method according to claim 1 is selected as the object, the electrolyte polymer is applied to an electrode layer, and at least a part of the electrolyte polymer is allowed to penetrate into the electrode.

7. The method according to claim 2, wherein the secondary battery is an all-solid-state battery, at least one of a current collector for positive electrode, a positive electrode layer, a separator, an electrolyte layer, a current collector for negative electrode, and a negative electrode layer is used as the object, a plurality of materials are selected from positive electrode active material particles, electrolyte particles or short fibers, negative electrode active material particles or short fibers, conductive assistant particles or short fibers, binders, and parent solvents for binder, thickeners, and solvents, and are made into a slurry, the slurry is moved from the independent material handling device prepared for the slurry to the application device, the solvent having a boiling point lower than that of the parent solvent for slurry is moved to the application device by another material handling device, and is merged with the slurry to form a merged liquid which is applied to the heated object.

8. The method according to claim 2, wherein for the slurry, a plurality of different types of slurries are prepared for positive electrodes for all-solid-state batteries, the low boiling point solvent is added to each of them, and the slurries are moved from the respective material handling devices to the application device, and the respective slurries are merged and mixed in the application device, or the plurality of slurry materials and the low boiling point solvent are mixed and moved to the application device by the material handling device, and are applied to the object.

9. The method according to claim 1, wherein porous carbon and silicon particles or SiOx particles having a specific surface area of 2000 m.sup.2/g or more measured by a BET method are selected as active material for the negative electrode, or at least one is selected from these and single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene to form a structure that holds the silicon particles or the SiOx particles, and that is contained in a slurry for negative electrode.

10. The method according to claim 2, wherein when applying the one or more types of slurries with a slot nozzle, the slurry is branched into stripes in multiple rows orthogonal to moving direction of the object by combining the slot nozzle wetted portion and one or more shims to make flow of the slurry in application width direction uniform, and the slurry is branched into one step or multiple steps with respect to the moving direction of the object so that the slurry is applied in a plurality of stripes, or a part of downstream of the shim is cut by the entire application width, and stripe flows are merged and applied by the entire width.

11. The method according to claim 5, wherein slurry flow from the slot nozzle is made into spraying particles with a compressed gas outside the slot nozzle or mixed while being crushed, and applied to the object.

12. The method according to claim 2, wherein a plurality of application devices for the merged liquid or the mixed fluid are prepared, and lamination on the object is achieved by the application device for a single slurry or a plurality of slurries.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0058] FIG. 1 is a schematic cross-sectional view of an embodiment of the present invention, in which a slurry is moved downstream by a material handling device, merged with a low boiling point solvent similarly moved downstream by a material handling device, and sprayed in a pulsed manner by an application device.

[0059] FIG. 2 is a schematic cross-sectional view of an embodiment of the present invention, in which a slurry is guided to the nozzle inside the multi-tube at the tip part of the application device, another type of slurry or a low boiling point solvent or the like is guided to the nozzle outside, and their merged liquid is crushed with a compressed gas to form spraying particles at the tip part of the nozzle and sprayed.

[0060] FIG. 3 is a schematic cross-sectional view of an application device having a stirring means according to an embodiment of the present invention, in which two types of materials (for example, a single or multiple slurries, a low-boiling point solvent, a conductive assistant dispersion liquid, etc.) are merged downstream of the material switching device located in the extension of each material handling device.

DESCRIPTION OF EMBODIMENTS

[0061] In the following, preferred embodiments of the present invention will be described with reference to the drawings. The following embodiments are given only for the illustrative purpose to facilitate the understanding of the invention, and not intended to exclude feasible additions, replacements, modifications made thereto by persons skilled in the art without departing from the technical scope of the present invention.

[0062] The drawings schematically show preferred embodiments of the present invention.

[0063] In FIG. 1, the slurry 3 can be handled by the material handling device 1. Specifically, the slurry 3 in the tank 11 is sucked up by the pump 7, and returned to the tank via upstream of the material opening/closing valve 6 by the pipe 5 which is a slurry flow path to form a slurry circulation circuit.

[0064] The slurry in the tank is generally stirred by a stirring device or the like (not shown).

[0065] When heating the slurry to reduce its viscosity, by installing a heater in the circulation circuit and circulating, temperature management for keeping the temperature of the slurry constant can be performed, so the temperature of the liquid should be constant. At this time, it is important that the slurry is not returned to the tank 11 but is returned to the downstream of the pump 7 to be sucked so that the heating of the slurry 3 in the tank 11 is not promoted by excessive circulating heat. Regardless of whether the slurry is heated with a heater or the like, the faster the circulation speed, the more the particles or the like can be prevented from settling. Circulation amount of the pump is selected from about 0.5 to 30 liters per minute, the circuit passing through the valve is made into a small circulation circuit to adjust the flow rate, and a large-flow-rate circulation circuit (large circulation circuit) that returns from the pump outlet to the tank is formed to generate a jet flow in the tank, or a large flow of slurry is generated in the tank by a stirrer or a circulation flow to prevent precipitation of the slurry. The inner diameter of the pipe or the like of the small circulation circuit may be about 2 to 10 mm, and the larger the inner diameter of the pipe of the large circulation circuit than the inner diameter of the small circulation pipe, the larger the circulation amount can be, so it is good. The pump may be a positive displacement type pump such as a gear pump, a mono pump, a single or double electric plunger pump, or a double electric diaphragm pump, and the drive can be controlled in milliseconds by using a servo motor, so that the accuracy is improved. Other than the positive displacement pump, in particular, it is necessary to keep the pressure of the nozzle or the like attached to the application device and the opening/closing valve constant, so it is necessary to install a hydraulic regulator up to the material opening/closing valve of the material handling device to keep the hydraulic pressure constant. In addition, it is even better to keep the liquid temperature constant. In particular, a hydraulic pressure regulator that follows the millisecond unit is important not only for high-speed line speed of 20 m/min or higher, but also for stability of the application amount.

[0066] A low boiling point solvent, a dispersion liquid of the conductive assistant or the like can be handled by the simple material handling device 100. They are filled in the simple pressure pot 12, and the solvent or the like is sent to the material opening/closing valve 16 via the pipe 8 by the gas pressure supply 9, and is sent to the application device by opening the material opening/closing valve 16. The application device 2 can continuously inject the mixture or inject it in a pulsed manner Further, the pattern can be applied to the object of Roll to Roll at a wide range and high speed continuously or in accordance with the cell shape by the slot nozzle. In addition, a commercially available dispersion device manufactured by Primix Corporation or the like, which is capable of micro-dispersion, can be incorporated into the material handling device 1, and the slurry downstream of the dispersion device can be returned to the upstream and circulated while being supplied to the application device. Regardless of whether or not the micro-dispersion device is used, an easily separable slurry at least containing a poor solvent, a parent solvent, and a plurality of particles is circulated in the material handling device 1 so as not to be separated, and the volume of the wetted portion downstream of the material opening/closing valve 16 that is difficult to circulate and the volume of the nozzle flow path is 2 ml or less, preferably 1 ml or less.

[0067] For the present invention, even a slot nozzle having a width of 500 mm can have a wetted portion volume of 2 ml or less.

[0068] In addition, for the dispersion of a mixture of a slurry containing a plurality of particles or the like (for example, a positive electrode slurry using NMP) and a low boiling solvent such as a poor solvent, it is better to add a micro-dispersion device to the material handling device, or select one or more other dispersing devices such as a dynamic mixer, a static mixer, a dispersion device such as a collision dispersion device, a small-diameter multi-stage filter, etc. and install it in the circulation circuit, and increase the flow velocity by making the inner diameter of the pipe as small as possible, and a spraying nozzle, a slot nozzle or the like having a small volume of the wetted portion can be directly set downstream of the material opening/closing valve, and a good slurry in which the low boiling point solvent is dispersed can be applied to the object. In addition, since the problem of separation can be solved if the volume of the wetted portion inside the nozzle is 2 ml or less, preferably 0.5 ml or less, for example, intermittent pattern coating in accordance with the cell structure is possible.

[0069] By incorporating a micro-dispersion device in the material handling device, it is possible to apply a slurry having better dispersion even with a poor solvent.

[0070] FIG. 2 is a nozzle used at the tip part of the application device (not shown). For the nozzle, a double thin tube made of stainless steel can be applied. As for the material, it may be a plastic tube such as PFA, and the material shape is not limited. The first fluid (slurry) 21 flowing through the inner pipe 23 and the second fluid (solvent) or the low boiling point solvent 28 flowing through the outer tube 24 are crushed by the compressed gas 25 to form spraying particles 27. The first fluid may be in the outer tube and the second fluid may be in the inner tube. In addition, the type and viscosity of each fluid are not limited. The shape and number of the tube are not limited, it may be triple or quintuple, and even if the shape is a multi-row dense tube pipe, a three-dimensional flow path may be formed by combining a shim or the like that is thinly processed into a nozzle flow path with a plurality of flow paths. The shape of the flow path is not limited either, it may be circular or □. Regardless of whether it is a tube or a process, the desired fluid in each flow path is not limited, and for example, it may be a combination of, for example, two or three separate slurries and a low boiling point solvent, or a combination of two or three separate slurries and a conductive assistant dispersion liquid.

[0071] The present inventor can alternately apply a plurality of types of slurries in the form of a thin film by using respective application devices, but in the application of the present invention, the liquid containing a plurality of types of slurries can be merged into one application device and applied to the object, so it is possible to use a small booth even with the spraying method, and the software for application can be inexpensive, which is an advantage. For example, when 5 types of slurry materials are included, the 5 types of slurries and the dispersion liquid of the conductive assistant can be independently sent to the application device, but it is possible to divide into groups of three types of liquids and two types of liquids, and merge them with respective application devices for lamination and application. The method of the present invention, in which a plurality of liquids including slurries are merged and applied to the object with one application device, other than secondary batteries, it can also be applied to various applications such as field of batteries (for example, fuel cells, solar cells, especially organic solar cells), semiconductors, FPDs, LEDs, electronics, pharmaceuticals, general coating, etc., and can also be applied to slot nozzle application.

[0072] As described above, in the present invention, not limited to the secondary battery, each desired liquid can be transferred to the application device, and applied to the object using spraying, a slit nozzle, or the like.

[0073] FIG. 3 is a more detailed schematic cross-sectional view of the vicinity of the application device. The first fluid circulates in the pipe 5 via the upstream of the material opening/closing valve 6. The first fluid may be a slurry composed of one or more types of particles. Similarly, the second fluid circulates via the upstream of the material opening/closing valve 36 of the pipe 38. The second fluid may be a slurry. No circulation is required if the second fluid is a non-sedimentable, low viscosity liquid. The first fluid moves from the downstream of the material opening/closing valve 6 to the application device provided with the stirring device 30. Similarly, the second fluid also moves from the downstream of the material opening/closing valve 36 to the application device 32 provided with the mixing device 30 or the stirring means 37, and merges with the first fluid. The two fluids can be mixed and dispersed well by high-speed movement mixing, ultrasonic vibration mixing, collision mixing as shown in the figure, or a combination thereof of the stirring mechanism 37 such as a dynamic mixer, a static mixer. By making the flow path of the head-on collision mixing device (30) of the two materials shown in the figure in the form of a nozzle, collision stirring can be performed close to the outlet of the flow path. A short distance of 1 mm or less is preferable between the flow paths of the left and right nozzles, etc., and it is important to make a head-on collision, and it is also important to increase the flow velocity and increase the head-on collision energy by making the diameter of the nozzle flow path 500 μm or less, more preferably 300 μm or less. In addition, a sufficient collision flow velocity can be obtained by increasing the volume of the merging part as much as possible, for example, by setting the inner diameter to be four times or more the nozzle diameter. The higher the hydraulic pressure, for example, 0.3 MPa or more, or even 10 times or more, the more ideal.

[0074] In the present invention, a method similar to the method of JP2003-300000, of which the present inventor is the representative inventor, can be adopted as a material handling device for experiments and semi-production. It is especially effective when the amount of slurry or the like is small, that is, a uniform mixed state of slurry can be created by installing level sensing by an optical fiber sensor near the lower part of the syringe where the inner diameter of the syringe changes to control the level of the slurry, setting the pressure to push the slurry to 30 kPa or more, preferably 65 kPa or more, and moving the slurry in the left and right syringes left and right at high speed, and switching for example, a 70 cc slurry in 2 seconds with syringes of about 70 cc on the left and right, and switching the syringe pressure left and right while creating a jet at the lower part of the syringe. Therefore, a slurry composed of active material particles of a secondary battery, a conductive assistant, a binder such as PVDF, and NMP as a parent solvent is created in a state where the mixed state is relatively stable by moving the slurry with a normal syringe, when about 10% of normal heptane having a boiling point of 100° C. or lower is added to the slurry, it is instantly separated, and normal heptane floats on the upper part of the left and right syringes. This poor solvent cannot be used when it is separated from the slurry, but it can be solved by being performed under the above-mentioned conditions. That is, a poor solvent is dispersed and mixed well in the slurry by a jet flow at the lower part of the syringe, the high boiling point NMP evaporates due to the azeotropic effect of volatilization of low boiling point normal heptane, which is a poor solvent, and the sprayed slurry can form an ideal electrode on the heated object. That is, by using syringes of about 50 to 70 cc or two containers that are relatively larger, the poor solvent and the slurry are moved in the syringe while causing a jet flow at the lower part of the syringe and dispersing together, it can be used as a small-quantity production in a test device or semi-production system even without using two expensive material handling devices. An upper limit sensor of fiber is provided on the upper parts of the left and right syringes to be used as a level control and an upper limit sensor.

[0075] In the present invention, in order to improve productivity, for example, a slit nozzle having a width of 200 to 1500 mm can be used for application to the object corresponding to the high-speed line speed. In addition, for each layer of one type of slurry applied, 1 to 200 spraying heads can be arranged in substantially one row or a plurality of rows orthogonal to the moving direction of the object to form a head group to enable the spraying or spraying with impact in a pulsed manner. If necessary, the head group can be reciprocated (swing) by, for example, 15 mm in the head arrangement direction to sufficiently wrap a pattern of, for example, 15 mm Heads for a required type of slurry and heads for a desired number of times of lamination can be arranged to meet the required speed.

[0076] In addition, a plurality of rotary screens or the like may be installed in the moving direction by applying JPH6-86956 also invented by the present inventor. By filling the slurry and powder to in numerous holes that penetrate through a wide range (for example, holes with a diameter of about 150 to 300 μm) in cylindrical screens or seamless belts or pipes made of stainless steel or the like that are the same as or wider than the application width of the object, and blowing out with liquefied gas or compressed gas at the place facing the object, it is made into fine particles and adheres to the object uniformly over the entire surface. It is cheap to use a commercially available sheet screen for screen printing or a screen for rotary screen. In addition, the same effect can be obtained by making holes having a diameter of, for example, about 0.2 mm to 0.5 mm at a pitch of 0.5 to 2.0 mm, for example, in zigzags, in a cylindrical pipe wider than the object.

[0077] In the above two methods, it is better to set the distance between the position where the atomization and blow-out is performed and the object to be about 1 to 60 mm because the impact effect is improved. It is even better to arrange them in multiple rows in the moving direction of the object for lamination in the form of a thin film Through-holes of screen and cylinder can be formed, for example, in a pattern corresponding to a cell. As a matter needless to say, it can be continuously applied to the object without interrupting the application. In addition, the above method also serves as a positive displacement supply method and can also follow the line by changing the rotation speed, so that an expensive positive displacement pump or controller or the like is not required, and the device design and manufacture can be carried out on the extension line of Roll to Roll of the roll coater and the rotary screen printing method, and it is a positive displacement type different from the above-mentioned method, so it is also possible to modify and use a part of the electrode line of the conventional lithium battery.

[0078] In the present invention, a method of making the slurry into particles and moving them by pressure difference may be used, inkjet and dispenser may be used for atomization. Further, as for inkjet and dispenser, it can be applied in the form of a thin film by further micronizing the particles with a compressed gas or the like. In addition, it may be atomized by a rotary atomizer of a disc or a bell used in the general coating field. Other than that, any method such as atomization with a bubbler or ultrasonic wave, or a method of hitting a spraying flow against a rotating roll at an extremely close distance for further micronization may be used. The atomized particle group may be moved by a carrier gas and adhered to the object by differential pressure.

[0079] The differential pressure can increase the impact by pulling out the particles by the ejector effect at a higher gas pressure just before the adhesion and colliding them at high speed.

[0080] This method can be widely applied not only in the field of secondary batteries but also in coatings in the fields of solar cells, semiconductors, electronics, biotechnology, pharmaceuticals or the like. The carrier gas can be pulsed and the uniform coating is also possible on uneven surfaces. By charging the fine particles, the uniformity and coating efficiency can be further improved and a good effect can be exhibited. The differential pressure can increase the impact by pulling out the particles by the ejector effect at a higher gas pressure just before the adhesion and colliding them at high speed.

[0081] Further, it is even better if the movement is performed in a pulsed manner because the adhesion efficiency and impact are increased.

INDUSTRIAL APPLICABILITY

[0082] According to the present invention, even if NMP is used, a positive electrode having a thick film thickness without defects such as cracks can be formed, so that a secondary battery having high performance can be manufactured. In addition, a laminate composed of an electrolyte layer and electrode layers of an all-solid-state battery having low interfacial resistance and high adhesion can also be manufactured with a thick film thickness and high quality from a desired thin film.

DESCRIPTION OF THE REFERENCE NUMERAL

[0083] 1, 100 material handling device [0084] 2, 32 application device [0085] 3 slurry [0086] 4 solvent [0087] 5, 8, 38 pipe [0088] 6, 16, 36 material opening/closing valve [0089] 7 pump [0090] 9 gas pressure supply [0091] 10 pulse spraying [0092] 11 tank [0093] 12 pressure pot [0094] 21 first fluid (slurry) [0095] 22 second fluid (solvent) [0096] 23 inner nozzle [0097] 24 outer nozzle [0098] 25 compressed gas [0099] 27 spraying particles [0100] 28 low boiling point solvent [0101] 30 mixing device [0102] 37 stirring means