Electrode manufacturing method and electrode manufacturing device

Abstract

To provide a method and a device for manufacturing a battery for a secondary battery that can reduce manufacturing costs without using a slurry.SOLUTION: A method for manufacturing an electrode for a secondary battery includes a forming step of forming powder particles 12, in which the surfaces of active material particles 16 are coated with binder 17, into a sheet on the surface of a current collector 11, and a hot pressing step of hot-pressing the powder particles 12 formed into a sheet to form an active material layer 14 on the current collector 11.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrode for a secondary battery and an apparatus for manufacturing an electrode for a secondary battery. [Background technology]

[0002] Electrodes constituting secondary batteries such as lithium-ion secondary batteries are generally produced by applying a slurry in which an active material, a binder, and a conductive additive are dispersed onto a current collector and drying the slurry (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-92622 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional electrode manufacturing methods using slurry require a drying process because a solvent is used. Furthermore, when manufacturing electrodes using the roll-to-roll method, the installation area for the slurry drying section is larger than the area where the slurry is applied. This results in increased energy consumption and higher manufacturing costs. Furthermore, environmentally hazardous solvent vapor recovery and regeneration processes are required, further increasing manufacturing costs.

[0005] The present invention has been made in consideration of the above points, and its main object is to provide a method for manufacturing a battery for a secondary battery, which can reduce manufacturing costs without using a slurry, and an apparatus for manufacturing a battery for a secondary battery. [Means for solving the problem]

[0006] The method for manufacturing an electrode for a secondary battery according to the present invention includes a supplying step of supplying powder particles, the surfaces of which are coated with a binder, onto a current collector; a forming step of forming the powder particles supplied onto the current collector into a sheet; and a hot pressing step of hot pressing the powder particles formed into a sheet to form an active material layer on the current collector.

[0007] The manufacturing apparatus for electrodes for secondary batteries according to the present invention includes a supply unit that supplies powder particles, the surfaces of which are active material particles coated with a binder, onto a current collector, a forming unit that forms the powder particles supplied onto the current collector into a sheet, and a heat-press unit that heat-presses the powder particles formed into a sheet to form an active material layer on the current collector. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for manufacturing a battery for a secondary battery, which does not use a slurry and can reduce manufacturing costs, and an apparatus for manufacturing a battery for a secondary battery. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram schematically illustrating a configuration of a manufacturing apparatus used in a method for manufacturing an electrode for a secondary battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically illustrating the structure of a powder particle. [Figure 3] 1 is a flowchart showing steps of a method for manufacturing an electrode for a secondary battery according to an embodiment of the present invention. [Figure 4] FIG. 3 is a cross-sectional view schematically showing a state in which a powder particle sheet is formed on a current collector by a molding process. [Figure 5] FIG. 3 is a cross-sectional view schematically showing a state in which an active material layer is formed on a current collector by a hot pressing process. [Figure 6] 1 is a cross-sectional SEM photograph of a positive electrode produced in an example. [Figure 7] 1 is a cross-sectional SEM photograph of a positive electrode produced in a comparative example. [Figure 8]FIG. 10 is a diagram schematically illustrating another configuration of a manufacturing apparatus used in a method for manufacturing an electrode for a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] The secondary battery in this embodiment includes a lithium-ion secondary battery, a lithium-sulfur secondary battery, etc. The electrode has a structure in which an active material layer is formed on a current collector, and includes a positive electrode and a negative electrode. The active material layer includes an active material and a binder, and may further include a conductive additive.

[0012] Known materials can be used for the current collector, active material, binder, and conductive additive. For example, in the case of a lithium-ion battery, aluminum foil or the like is used for the positive electrode current collector, and copper foil is used for the negative electrode current collector. Furthermore, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium iron phosphate (LiFePO4), or the like is used for the positive electrode active material, and graphite, silicon, lithium metal, or the like is used for the negative electrode active material. Polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or the like is used for the binder. Carbon materials such as carbon black and acetylene black are used for the conductive additive.

[0013] 1 is a diagram schematically illustrating the configuration of a manufacturing apparatus 10 used in a method for manufacturing an electrode for a secondary battery according to an embodiment of the present invention. In this embodiment, a roll-to-roll manufacturing apparatus is described as an example in which an active material layer is formed on a current collector while the current collector is being transported, but a sheet-by-sheet manufacturing apparatus in which an active material layer is formed on each current collector may also be used.

[0014] As shown in FIG. 1, a manufacturing apparatus 10 for an electrode for a secondary battery in this embodiment includes a conveying section 20, a supplying section 30, a forming section 40, and a heat pressing section 50.

[0015] The conveying section 20 conveys the current collector 11. Specifically, the current collector 11 wound around the delivery roll 21 is pulled out and conveyed along a predetermined conveying path, and then the electrode 15 formed on the current collector 11 is wound around the take-up roll 22.

[0016] The supply unit 30 is disposed downstream of the delivery roll 21, and supplies powder particles 12 (see FIG. 2) in which the surfaces of active material particles 16 are coated with binder 17 onto the current collector 11. The supply unit 30 is configured, for example, as a hopper, and supplies the powder particles 12 stored in the supply unit 30 onto the current collector 11 being conveyed.

[0017] 2 is a cross-sectional view schematically showing the structure of powder particle 12, and powder particle 12 has a structure in which a binder 17 and a conductive additive 18 are dispersed and coated on the surface of active material particle 16. A method for producing powder particle 12 will be described later.

[0018] The forming unit 40 is disposed downstream of the supply unit 30 and forms the powder particles 12 supplied to the current collector 11 into a sheet. The forming unit 40 is configured, for example, with a squeegee, and adjusts the gap between the squeegee and the conveyed current collector 11 to adjust the thickness of the powder particles 12 formed into a sheet (hereinafter referred to as "powder particle sheet 13"). The forming unit 40 may also be configured with a mechanism that involves compression, such as a pressure roll.

[0019] The heat press unit 50 is disposed downstream of the molding unit 40 and heat-presses the powder particle sheet 13 to form an active material layer 14 on the current collector 11. This forms an electrode 15 in which the active material layer 14 is formed on the current collector 11. In this embodiment, the heat press unit 50 is composed of a planar heating unit 60 that heats the powder particle sheet 13 in a non-contact manner, and a heat roll press unit 70 that is disposed downstream of the planar heating unit 60. The planar heating unit 60 is composed of, for example, an infrared lamp, and the heat roll press unit 70 is composed of, for example, a pair of heat rolls. The planar heating unit 60 may be omitted.

[0020] The electrode 15 formed in the hot press section 50 is taken up by a take-up roll 22 arranged downstream of the hot press section 50 .

[0021] Next, a method for manufacturing an electrode for a secondary battery according to this embodiment will be described.

[0022] FIG. 3 is a flowchart showing a method for manufacturing an electrode for a secondary battery according to this embodiment.

[0023] As shown in Fig. 3, first, powder particles 12 are prepared (step S1). As shown in Fig. 2, the powder particles 12 have a structure in which a binder 17 and a conductive additive 18 are dispersed and coated on the surfaces of active material particles 16. Note that the conductive additive 18 may be omitted. The binder 17 and the conductive additive 18 may be made of the same materials as those used for the binder and the conductive additive contained in the active material layer of the electrode.

[0024] The powder particles 12 can be produced, for example, by dispersing the active material particles 16 in a solvent in which the binder 17 and the conductive additive 18 are dissolved, and then evaporating the solvent. Alternatively, the powder particles 12 may be produced by mixing and heating the active material particles 16 with the binder 17 and the conductive additive 18, each having a particle size smaller than that of the active material particles 16.

[0025] Next, powder particles 12 are supplied onto the surfaces of the active material particles 16 on the current collector 11 (supplying step: step S2). When the surfaces of the powder particles 12 are not coated with the conductive additive 18, a mixture of the powder particles 12 and the conductive additive 18 may be supplied onto the current collector 11.

[0026] Next, the powder particles 12 supplied onto the current collector 11 are formed into a sheet (forming step: step S3). As a result, a powder particle sheet 13 is formed on the current collector 11. The forming step is preferably performed by rolling the powder particles 12 supplied onto the current collector 11 for reasons that will be described later.

[0027] 4 is a cross-sectional view schematically showing a state in which a powder particle sheet 13 is formed on a current collector 11 by a molding process. In this state, the powder particles 12 are simply dispersed in a sheet-like form at a constant density, and there are few locations where the active material particles 16 are in contact with each other or with the current collector 11 via the binder 17. As a result, the contact resistance between the active material particles 16 is large, and the binding force between the active material particles 16 and the current collector 11 is also weak.

[0028] Next, the powder particle sheet 13 is hot-pressed (hot-pressing step: step S4), whereby an active material layer 14 is formed on the current collector 11.

[0029] 5 is a cross-sectional view schematically showing the state in which an active material layer 14 is formed on a current collector 11 by a hot pressing process. In this state, the binder 17 coated on the surfaces of the active material particles 16 melts, and the active material particles 16 are compressed, thereby binding the active material particles 16 to each other and to the current collector 11 via the binder 17. This results in an active material layer 14 having low contact resistance between the active material particles 16 and strong adhesive strength between the active material particles 16 and the current collector 11.

[0030] As described above, the molding step of powder particle sheet 13 is preferably performed by rolling powder particles 12 supplied onto current collector 11. Because binder 17 such as PVDF coated on the surfaces of active material particles 16 has good slip properties, rolling powder particles 12 supplied onto current collector 11 can improve the density of powder particles 12. This improves thermal conductivity in the hot pressing step of powder particle sheet 13, allowing binder 17 to melt more quickly.

[0031] In contrast to conventional electrode manufacturing methods using a slurry, the electrode manufacturing method of this embodiment does not use a solvent, and therefore does not require a step of drying the slurry or a step of recovering and regenerating the solvent vapor, thereby significantly reducing the electrode manufacturing cost.

[0032] Furthermore, in the manufacturing method of the electrode according to this embodiment, in the molding step (step S3), the powder particle sheet 13 formed on the current collector 11 has the powder particles 12 uniformly dispersed in a state in which the surfaces of the active material particles 16 are coated with the binder 17, and therefore the binder 17 is also uniformly dispersed. Therefore, in the subsequent hot pressing step (step S4), the active material particles 16 can be uniformly bound together and between the active material particles 16 and the current collector 11 by the molten binder 17. As a result, a secondary battery with excellent cycle characteristics can be realized. [Example]

[0033] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples in any way.

[0034] <Preparation of powder particles for the positive electrode> 0.45 g of active material particles (LFP: lithium iron phosphate) 16 were dissolved in a solvent (NMP: N-methyl-pyrrolidone) with 5 wt % of binder (PVDF) 17 and 5 wt % of conductive additive (CB: carbon black) 18. 0.45 g of the active material particles 16 were dispersed in the solvent, and the solvent was then heated to evaporate. This produced powder particles 12 in which the surfaces of the active material particles 16 were coated with the binder 17 and conductive additive 18.

[0035] <Preparation of positive electrode> The powder particles 12 prepared by the above method were supplied onto a current collector 11 (aluminum foil) having a thickness of 20 μm, and then the powder particles 12 supplied onto the current collector 11 were formed into a sheet having a thickness of 100 μm.

[0036] The powder particles 12 formed into a sheet shape (powder particle sheet 13) were pressed and held at room temperature and a pressure of 50 kN for 15 seconds, and then hot-pressed and held at a temperature of 200°C and a pressure of 50 kN for 15 seconds to produce a positive electrode 15 in which an active material layer 14 was formed on a current collector 11.

[0037] For comparison, a slurry was formed by mixing 0.45 g of active material particles (LFP), 5 wt % of a binder (PVDF) relative to the active material particles, and 5 wt % of a conductive additive (CB) relative to the active material particles in an organic solvent (NMP) using a conventional method. This slurry was then applied to a current collector (aluminum foil), and the resulting mixture was heated and pressed at a temperature of 200°C and a pressure of 50 kN for 15 seconds to produce a positive electrode in which an active material layer was formed on the current collector 11.

[0038] Fig. 6 is a photograph of the cross section of the positive electrode produced in this example taken with a scanning electron microscope (SEM), and Fig. 7 is a photograph of the cross section of the positive electrode produced in the comparative example taken with an SEM. The fluorine component (PVDF) in the positive electrode was photographed by EDS (energy dispersive X-ray spectroscopy) at the same position as the SEM photograph, and the position where fluorine was detected by EDS was dyed and highlighted.

[0039] As shown in Fig. 6, it was confirmed that in the positive electrode produced in this example, the binder 17 was present throughout the positive electrode so as to fill the gaps formed between the active material particles 16. On the other hand, as shown in Fig. 7, it was confirmed that in the positive electrode produced in the comparative example, the binder was unevenly distributed in the gaps formed between the active material particles 16.

[0040] <Fabrication of lithium-ion secondary batteries> The positive electrode prepared in this example and a negative electrode using lithium metal as an active material were wound together with a separator interposed therebetween to prepare an electrode assembly, which was then housed in a battery case together with a non-aqueous electrolyte to prepare a lithium ion secondary battery. For comparison, the positive electrode prepared in the comparative example and a negative electrode using lithium metal as an active material were wound together with a separator interposed therebetween to prepare an electrode assembly, which was then housed in a battery case together with a non-aqueous electrolyte to prepare a lithium ion secondary battery.

[0041] For the fabricated lithium ion secondary batteries, the battery capacity and the binding strength between the active material layer of the positive electrode and the current collector were measured by the following methods.

[0042] <Battery capacity measurement> The fabricated lithium-ion secondary battery was charged at a constant current, and the total current (mAh) was measured until the set voltage (4.3 V) was reached. The battery capacity (charge) was calculated (mAh / g) from the battery mass measured beforehand. After waiting for 10 seconds, the battery was discharged at a constant current, and the total current (mAh) was measured until the set voltage (2.8 V) was reached. The battery capacity (discharge) was calculated (mAh / g) from the battery mass measured beforehand. This charge / discharge cycle was repeated three times, and the battery capacity (discharge) calculated after the third cycle was determined as the battery capacity. The current value in each measurement was a value corresponding to the weight of the active material in the electrode, specifically, (theoretical capacity of the active material) × (weight of the active material in the electrode) × 1 / 20.

[0043] <Measurement of the adhesive strength between the positive electrode active material layer and the current collector> The mass A of the current collector was measured in advance, and a positive electrode having an active material layer formed on the current collector was fabricated by the methods of the Examples and Comparative Examples, and the mass B of the fabricated positive electrode was measured. Next, the active material layer was held facing downward relative to the current collector, and the mass C of the positive electrode was measured when the active material layer no longer fell off. The adhesion ratio between the active material layer and the current collector was then calculated using the following formula, and this adhesion ratio was used as an index for evaluating the binding strength between the active material layer of the positive electrode and the current collector.

[0044] Adhesion ratio = (CA) / (BA) Table 1 shows the results of measuring the battery capacity of the fabricated lithium ion secondary batteries and the adhesion ratio between the positive electrode active material and the current collector.

[0045] [Table 1]

[0046] As shown in Table 1, it was confirmed that the lithium ion secondary battery produced using the positive electrode produced by the method of this example had performance equivalent to that of the lithium ion secondary battery produced using the positive electrode produced using the conventional slurry in terms of battery capacity and the degree of adhesion between the active material layer and the current collector.

[0047] Therefore, compared to conventional electrode manufacturing methods using a slurry, the electrode manufacturing method of this embodiment does not use a solvent, and therefore does not require a slurry drying process or a solvent vapor recovery and regeneration process, thereby significantly reducing the electrode manufacturing cost.

[0048] While the present invention has been described above with reference to preferred embodiments, these descriptions are not limiting and various modifications are possible. For example, in the above embodiment, the formation of powder particle sheet 13 on current collector 11 was performed in two steps: a supply step of supplying powder particles 12 onto current collector 11 and a molding step of forming powder particles 12 supplied onto current collector 11 into a sheet. However, the formation may be performed in a single step of forming powder particles 12, in which active material particles 16 have their surfaces coated with binder 17, into a sheet on the surface of current collector 11. Specifically, as shown in FIG. 8 , the powder particles 12 are dropped from a hopper 80 storing the powder particles 12 into a gap between a pair of rollers 81, and the sheet-shaped powder particles 13 are supplied through the gap between the pair of rollers 81 onto current collector 11 and molded with a forming roller 82. In this case, the electrode manufacturing apparatus is composed of a forming section (80, 81, 82) that forms powder particles, the surfaces of which are active material particles coated with a binder, into a sheet on the surface of a current collector, and a heat pressing section that heat-presses the powder particles formed into a sheet to form an active material layer on the current collector. [Explanation of symbols]

[0049] 10. Electrode manufacturing equipment 11 Current collector 12 Powder particles 13 Powder particle sheet 14 Active material layer 15 Electrode (positive electrode) 16 Active material particles 17 Binder 18 Conductive additives 20 Conveying section 21 Delivery roll 22 Winding roll 30 Supply section 40 Molding section 50 Heat Press Section 60 Planar heating section 70 Heating roll press section 80 Hopper 81 Pair of Rollers 82 Forming roller

Claims

1. A method for manufacturing an electrode for a secondary battery, comprising: a forming step of forming powder particles, in which the surfaces of active material particles are coated with a binder, into a sheet on the surface of a current collector; a heat pressing step of heat pressing the powder particles formed into the sheet shape to form an active material layer on the current collector; A method for manufacturing an electrode, comprising:

2. The forming step includes: a supplying step of supplying the powder particles, the surfaces of which are coated with a binder, onto the current collector; a forming step of forming the powder particles supplied onto the current collector into a sheet shape; The method for manufacturing the electrode of claim 1 , comprising:

3. The method for manufacturing an electrode according to claim 2 , wherein the forming step is performed by rolling the powder particles supplied onto the current collector.

4. The method for manufacturing an electrode according to claim 1 or 2, wherein the powder particles are formed by coating the surfaces of the active material particles with a conductive additive dispersed thereon.

5. The method for manufacturing an electrode according to claim 1 , wherein the forming step is performed by forming the mixture of the powder particles and the conductive additive particles into a sheet shape on the surface of the current collector.

6. The method for manufacturing an electrode according to claim 2 , wherein the supplying step is performed by supplying a mixture of the powder particles and conductive additive particles onto the current collector.

7. The method for producing an electrode according to claim 1 , wherein the forming step and the hot pressing step are performed successively on the current collector being transported.

8. The electrode manufacturing method according to claim 2 , wherein the supplying step, the molding step, and the hot pressing step are successively performed on the current collector being transported.

9. The method for manufacturing an electrode according to claim 1 or 2, wherein the hot pressing step is performed by a non-contact planar heating step and a hot roll pressing step using a pair of rolls on the powder particles formed into the sheet shape.

10. The method for manufacturing an electrode according to claim 1 , wherein the powder particles are obtained by dispersing the active material particles in a solvent in which the binder is dissolved, and then evaporating the solvent.

11. An apparatus for manufacturing electrodes for secondary batteries, comprising: a forming unit that forms powder particles, in which the surfaces of active material particles are coated with a binder, into a sheet on the surface of a current collector; a heat press unit that heat-presses the powder particles formed into a sheet shape to form an active material layer on the current collector; An electrode manufacturing apparatus comprising:

12. The forming portion is a supply unit that supplies powder particles, the surfaces of which are coated with a binder, onto the current collector; a forming unit that forms the powder particles supplied onto the current collector into a sheet shape; The electrode manufacturing apparatus according to claim 11, comprising:

13. The electrode manufacturing apparatus according to claim 12 , wherein the forming section is configured as a rolling section that rolls the powder particles supplied onto the current collector.

14. The electrode manufacturing apparatus according to claim 11 or 12, wherein the powder particles are formed by coating the surfaces of the active material particles with a conductive additive dispersed thereon.

15. The method for manufacturing an electrode according to claim 11 , wherein the forming section forms the mixture of the powder particles and the conductive additive particles into a sheet shape on the surface of the current collector.

16. The electrode manufacturing apparatus according to claim 12 , wherein the supply unit supplies the mixture of the powder particles and the conductive additive particles onto the current collector.

17. a conveying unit that conveys the current collector, The electrode manufacturing apparatus according to claim 11 , wherein the forming unit and the hot pressing unit are disposed downstream in the conveying direction of the current collector conveyed by the conveying unit.

18. a conveying unit that conveys the current collector, The electrode manufacturing apparatus according to claim 12 , wherein the supply unit, the forming unit, and the hot pressing unit are respectively arranged downstream in this order in a transport direction of the current collector transported by the transport unit.

19. 13. The electrode manufacturing apparatus according to claim 11 or 12, wherein the heating press section is composed of a planar heating section that heats the powder particles formed into the sheet shape in a non-contact manner, and a heating roll press section that is arranged downstream of the planar heating section.

20. 12. The electrode manufacturing apparatus according to claim 11, wherein the powder particles are obtained by dispersing the active material particles in a solvent in which the binder is dissolved, and then evaporating the solvent.

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