METHOD FOR MANUFACTURING SECONDARY BATTERY, OR SECONDARY BATTERY

Abstract

A method for manufacturing a secondary battery by coating an electrode slurry on an object for a secondary battery. A step of pressurizing and transferring the slurry to the next step; a step of transferring pressurized carbon dioxide gas or liquefied carbon dioxide or supercritical fluid of carbon dioxide gas to the next step; a step of merging and mixing the slurry and the carbon dioxide gas or liquefied carbon dioxide or supercritical fluid of carbon dioxide gas; and a step of coating the mixed mixture or layered coating a plurality of layers thereof on the object with a coating device. As a result, the total length of a drying device is extremely short, and the desired thick film of the positive electrode can be easily formed. In addition, a solid electrolyte layer can be formed in a short time.

Claims

1. A method for manufacturing a secondary battery by coating an electrode slurry on an object for a secondary battery, comprising: a pressurizing step of pressurizing and transferring the slurry to post step, a transferring step of transferring pressurized carbon dioxide gas or liquefied carbon dioxide or supercritical fluid of carbon dioxide gas to the post step, a mixing step of merging and mixing the slurry and the carbon dioxide gas or the liquefied carbon dioxide or the supercritical fluid of carbon dioxide gas to obtain a mixture, and a coating step of coating the mixture on the object or layered coating thereof in form of a plurality of layers with a coating device.

2. The method according to claim 1, wherein the mixing step is a step of making a supercritical fluid.

3. The method according to claim 1, wherein merged fluid is mixed by an in-line mixer installed between before and after the merging.

4. The method according to claim 1, wherein at least one fluid of the slurry and the carbon dioxide gas is transferred to the post step via an automatic opening/closing valve.

5. The method according to claim 3, wherein liquid pressure and temperature of the merged fluid comprising the slurry and the carbon dioxide gas are set to supercritical point or more, the merged fluid is circulated by a circulation device for supercritical fluid to form the supercritical fluid, and the supercritical fluid is coated to the object.

6. The method according to claim 1, wherein the secondary battery is an all-solid-state battery.

7. The method according to claim 6, wherein the electrode slurry is a solid electrolyte slurry.

8. The method according to claim 1, wherein at least one fluid of the slurry and the pressurized carbon dioxide gas or liquefied carbon dioxide is circulated at a temperature and pressure corresponding to the supercritical point or more, and each fluid is transferred to the post step.

9. The method according to claim 3, wherein for the slurry, a plurality of slurries selected from different types of particles or fibers for an all-solid-state battery positive electrode are prepared, each slurry is pumped independently by a pump, and each slurry is merged with the pressurized carbon dioxide gas or liquefied carbon dioxide or supercritical fluid of carbon dioxide gas to form the merged fluid, each merged fluid is mixed to form the supercritical fluid, and the supercritical fluid is laminated or alternately laminated on the object with a respective coating device for supercritical fluid, and is laminated so that at least one coating layer of the mixed supercritical fluid is formed into a plurality of layers.

10. The method according to claim 9, wherein the particles or fibers of the all-solid-state battery positive electrode slurry comprise positive electrode active material particles, solid electrolyte particles, and a conductive assistant.

11. The method according to claim 1, wherein the slurry is a negative electrode slurry.

12. The method according to claim 1, wherein in forming the electrode, a gradient coating is performed so as to increase density of active material particles in a direction closer to a current collector and decrease the density of the active material in a direction away from the current collector.

13. The method according to claim 12, wherein in forming the electrode between the current collector and a solid electrolyte layer which are the objects of the all-solid-state battery, and in changing ratio of the active material particles to the solid electrolyte particles, gradient formation, wherein weight or mass per unit area or unit volume of the active material is increased in a direction closer to the current collector, and the weight or mass per unit area or unit volume of the active material is decreased in a direction closer to the solid electrolyte layer, is performed by forming a plurality of layers with a continuous gradient or a stepwise gradient.

14. The method according to claim 1, wherein the coating is a spraying method or a pulsed spraying method.

15. The method according to claim 1, wherein electrode binder is polyvinylidene fluoride, and 70% or more of volatile component excluding the carbon dioxide gas or supercritical fluid of carbon dioxide gas is normal methylpyrrolidone.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0095] FIG. 1 is a schematic cross-sectional view of an embodiment of the present invention, in which the slurry is pressurized, transferred downstream, and merged with the liquefied carbon dioxide similarly transferred downstream in a coating device.

[0096] FIG. 2 is a schematic cross-sectional view of an embodiment of the present invention, in which the slurry is pressurized and circulated, and if necessary, the temperature and liquid pressure are set to above the supercritical point of the supercritical fluid of carbon dioxide gas, and the slurry is transferred to a downstream coating device, and the liquefied carbon dioxide is pressurized and circulated, heated if necessary, the carbon dioxide gas SCF (carbon dioxide gas supercritical fluid) is transferred to the coating device, merged and mixed with the slurry in the coating device.

[0097] FIG. 3 is a schematic cross-sectional view of an embodiment of the present invention, in which the slurry is pressurized by a pump and transferred upstream of the pump in the SCF circuit, and the liquefied carbon dioxide is also pressurized and adjusted by the pump and transferred upstream of the pump in the SCF circuit, and they are circulated in the SCF circuit while being heated by a heater downstream of the pump.

[0098] FIG. 4 is a schematic cross-sectional view of an embodiment of the present invention, in which the slurry is pressurized by a pump, heated and circulated, the heated and pressurized slurry is transferred upstream of the pump in the SCF circuit, and the liquefied carbon dioxide is also pressurized and circulated by a pump, and the heated liquefied carbon dioxide is transferred upstream of the pump in the SCF circuit, and a coating head is installed in the SCF circuit.

DESCRIPTION OF EMBODIMENTS

[0099] 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.

[0100] The drawings schematically show preferred embodiments of the present invention.

[0101] In FIG. 1, the slurry 51 in the tank 1 is pressurized by the pump 3, and transferred to the coating device 5 via the pipe (hose) 8, and if necessary, via the automatic opening/closing valve 6. On the other hand, the liquefied carbon dioxide 2 is pressurized by the pump 4 if necessary and sent to the coating device 5 via the automatic opening/closing valve 7 if desired. The coating device 5 may be a mixer or a coating head having an automatic opening/closing valve function for coating. The merged and finely mixed fluid can be made into SCF by setting the liquid pressure of the coating head to a desired liquid pressure abo ve the supercritical point of carbon dioxide gas and by setting the temperature to a desired temperature above the supercritical point if necessary, and it can be sprayed and atomized under suitable spray conditions of low viscosity, for example, 50 mPa.Math.s or less, by using, for example, an airless spray nozzle at the tip of the coating head.

[0102] In FIG. 2, the slurry in the tank 21 is sucked by the pump 23, pressurized to an arbitrary pressure above the supercritical point of carbon dioxide gas, and sent to the commercially available pressure-resistant explosion-proof heater 29 to be heated. The heated slurry passes through the upper part of the automatic opening/closing valve 26, the flow rate is adjusted by the circulation valve 253 via the pipe (pressure-resistant hose) 28, and the slurry is sucked again by the pump 23 to form a circulation circuit. The pump 23 can be selected from a gear pump, a screw pump, a centrifugal pump, a multiple-plunger pump, etc., and the power may be an electric motor such as a servo motor. In order to keep the pressure constant, an air pressure-driven multiple-plunger pump of a balance feed type (instantaneous follow-up when the pressure collapses) with little pulsation can instantly suck the flow amount transferred from the automatic opening/closing valve 26 to the downstream coating device 25 by the pump 23, thereby it exerts its effect with little pulsation. On the other hand, the liquefied carbon dioxide 22 passes through the pressure regulating valve 252, and is directly or via the automatic opening/closing valve 27, or pressurized by the pump 24, heated by the heater 29′, and passes through the upper part of the automatic opening/closing valve 27, and sucked again by the pump 24 via the pipe (hose) 28 and via the circulation valve 254 to form a circulation circuit, and the pump continues to operate. The type of the pump 24 is preferably a bellows pump, and the flow amount transferred downstream from the automatic opening/closing valve flows into the pump 24. In both circuits, it is even better if the pressure and temperature are set at an arbitrary value above the supercritical point.

[0103] In FIG. 3, the slurry 331 in the tank 31 is sucked by the pump 33, pressurized, and sucked by the pump 333 of the supercritical fluid circuit via the pipe 38 and further via the automatic opening/closing valve 36. In addition, the liquefied carbon dioxide is pressurized to a desired pressure by the pump 34 and also sucked by the pump 333 via the automatic opening/closing valve 37. The pressurized slurry 331 and the liquefied carbon dioxide 32 may be merged and mixed by an in-line mixer or the like, or may be sucked by the pump 333. The in-line mixer 371 is installed downstream of the pump 333, and the slurry and the carbon dioxide gas are finely mixed, and sucked by the pump 333 via the explosion-proof heater 339, the filter 330, the density or flow rate sensor 340, and via the coating head 351, the pipe 338, and further via the circulation valve 332, to form a circulation circuit, and SCF can be formed by setting the liquid pressure and temperature to desired values above the supercritical point. When SCF is formed, the viscosity can be lowered, so it can be coated on the object while being atomized by the airless spray nozzle 352 or the like downstream of the coating head. Needless to say, by relatively moving the coating head and the object, it is possible to be coated in multiple layers in the form of a thin film. In addition, the circulation circuit can be provided with the automatic drain valve 361, the manual drain valve 390, the stop valve 391, the circulation valve 332, the density sensor 340 or the like. In addition, the slurry 331 in the tank 31 can be automatically stirred by the stirring device 350 if necessary.

[0104] In FIG. 4, the slurry 451 and the liquefied carbon dioxide 42 are the same in terms of supply to the coating device, so description thereof will be omitted. The respective automatic opening/closing valves 46 and 47 are mounted on the in-line mixer 471, and can be modified for SCF from, for example, the TD type of Hokuto Corporation, which is capable of simultaneous merging and mixing. In addition, a plate or a filter with countless porous bodies, a laminate thereof, a static mixer, a dynamic mixer, etc., which is a type of in-line mixer, can be applied after the merging. The merged fluid is sucked by the pump 443 and pressurized and pumped, and if necessary, finely mixed by the in-line mixer 471′, heated by the heater 449, the agglomerates and foreign substances are filtered by a filter, the mixing is supported if necessary, and the mixing condition of the fluid is managed by the density sensor 460 if necessary, the circulation flow rate is adjusted by the circulation valve 452 via the coating heads 455 and 456 connected in parallel circuit, and via the pipe 48, and the fluid is sucked again and pumped by the pump 443 to form a circulation circuit. By setting the pressure and temperature of the fluid to desired values above the supercritical point of carbon dioxide gas, the finely mixed fluid of the merged fluid become SCF, which is sprayed on the object by the airless nozzles 455 and 456 attached to the tips of coating heads 453 and 454. The coating head may be a simple airless spray gun improved for SCF and may be manual or automatic, and in any number. In order to pursue an accurate coating weight by moving the coating heads 453 and 454 and the object relative to each other, the coating head 455 can be traversed to accurately spray coat the object. A plurality of coating heads, for example, 10, may be used regardless of traverse, stationary spray, etc. At least one of a plurality of coating heads can be used exclusively for coating weight measurement and can be used as data for quality management and automatic control of the coating amount over time.

[0105] In the present invention, in order to improve productivity, for example, a slot nozzle with a coating width of 50 to 1500 mm can be used. Fine particles can be ejected from a slit nozzle consisting of a narrow, long groove with a wide width equivalent to the slot nozzle, and can be coated to the object corresponding to the high-speed line speed. In addition, for each layer of one type of slurry coated, 1 to 200 heads such as spraying heads can be arranged in one row, 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 and coat 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.

[0106] In addition, a plurality of rotary screens or the like may be installed for coating in the moving direction by applying the method of JPH6-86956 also invented by the present inventor. By filling the sprayed amount to innumerous 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 coating width of the object, and blowing out with liquefied gas or compressed gas at the place facing the object, it can be made into fine particles and adhere 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.

[0107] In the above method, 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 and then to perform a thin film layered coating. 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 also be continuously coated on the object without interrupting the coating. In addition, the above method also serves as a positive displacement supply method, and it 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 R to R 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 simply modify and use a part of the conventional lithium battery electrode forming lines.

[0108] In the present invention, a method of making the slurry into particles and transferring them by pressure difference may be used, inkjet and dispenser may be used for atomization. As for inkjet and dispenser, it can be coated 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 such as a disc or a bell used in the general coating field, and may be coated by transferring with carrier gas or the like by using the particle group. Other than that, in the case of low viscosity, atomization with a bubbler or ultrasonic wave, or a method of hitting a spraying flow against a rotating roll or belt, etc., at an extremely close distance for further micronization regardless of viscosity or the like can be used. The particle group atomized as described above may be transferred and adhered to the object by differential pressure of a carrier gas or the like. Adhesion of the particles to the object may be performed by being electrostatically charged or dew condensed with solvent vapor. The synergistic effect of the two is even better.

[0109] This method can be widely applied not only in the field of secondary batteries but also in coatings or the like 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 as described above, the uniformity and coating efficiency can be further improved and a good effect can be exhibited.

[0110] Further, it is even better if the transferring is performed in a pulsed manner because the adhesion efficiency and impact are increased.

INDUSTRIAL APPLICABILITY

[0111] The present invention can contribute to improving the productivity and performance of secondary batteries.

[0112] Even if NMP is used, the mainstream of which evaporates slowly and is the solvent for the slurry especially for forming positive electrodes of secondary batteries, it can be volatilized at a relatively low temperature in a short time according to the present invention, so it leads to resource saving, energy saving and space saving, and can greatly reduce cost and improve productivity. Since a positive electrode having a thick film thickness without defects such as cracks can be formed, which is difficult with conventional methods, a secondary battery with high performance can be manufactured. In addition, the slurry is made into fine particles mainly by a spray method or the like and instantaneously wet and adhere to the object with impact, so not only the electrode layer of the secondary electrode with high adhesion and low interfacial resistance, but also a laminate of electrolyte layer and electrode layer of an all-solid-state battery can also be manufactured with a thick film thickness and high quality from a desired thin film by spray coating simultaneously on the R to R object, such as the electrode layer and the solid electrolyte layer.

DESCRIPTION OF THE REFERENCE NUMERAL

[0113] 1, 21, 31, 41 tank [0114] 2, 22, 32, 42 liquefied carbon dioxide [0115] 51, 251, 331, 451 slurry [0116] 3, 4, 23, 24, 33, 34, 43, 44, 333, 441, 443 pump [0117] 5, 25 coating device [0118] 6, 7, 26, 27, 36, 37, 46, 47 automatic opening/closing valve [0119] 8, 8′, 28, 28′, 38, 38′, 48, 48′, 148, 338 pipe [0120] 29, 29′, 49, 49′, 449, 339 heater [0121] 252, 300, 502 carbon dioxide gas pressure regulating valve [0122] 253, 254, 332, 450, 452 circulation valve [0123] 255, 390, 490, 492 manual drain valve [0124] 256, 391, 491, 493 stop valve [0125] 361, 461 automatic drain valve [0126] 351, 453, 454 coating head [0127] 455, 456 spray nozzle [0128] 471, 471′ in-line mixer