Current collector and secondary battery

Abstract

The invention relates to a current collector and a secondary battery. A current collector according to the present disclosure has a metal foil and a conductive resin layer laminated on the metal foil. The conductive resin layer in the current collector of the present disclosure contains a resin and a conductive material, and the melting point of the resin is less than 120 DEG C. The secondary battery of the present disclosure includes a positive electrode current collector and a negative electrode current collector, and at least one of the positive electrode current collector and the negative electrode current collector is the current collector of the present disclosure.

Description

Technical Field

[0001] The present disclosure relates to a current collector and a secondary battery. Background Art

[0002] In recent years, so-called resin current collectors have been proposed as an alternative to metal foils. The resin current collectors are made of a resin to which a conductive filler such as metal powder is added.

[0003] For example, Japanese Patent Application Laid-Open No. 2010-170833 discloses a current collector having a structure including one or more layers of resin and conductive material. The current collector is a current collector for a bipolar secondary battery. In the current collector, a crystalline resin having a melting point of 120° C. or higher is used as at least one layer of resin. Summary of the invention

[0004] Such a resin collector has a large surface resistance, so in a battery having the resin collector, the flow of current in the surface direction during an internal short circuit can be effectively suppressed, and as a result, it is believed that local heating of the battery can be prevented. However, there is still room for further improvement in suppressing heating during an internal short circuit of the battery.

[0005] An object of the present disclosure is to provide a current collector capable of suppressing heat generation during an internal short circuit of a battery.

[0006] The inventors of the present application have found that the above-mentioned problems can be solved by the following means.

[0007] Solution 1

[0008] A current collector comprises a metal foil and a conductive resin layer laminated on the metal foil, wherein the conductive resin layer contains a resin and a conductive material, and the melting point of the resin is lower than 120°C.

[0009] Solution 2

[0010] The current collector according to claim 1, wherein the content of the resin in the conductive resin layer is 50% by mass or more.

[0011] Solution 3

[0012] The current collector according to aspect 1 or 2, wherein the thickness of the conductive resin layer is 1 μm or more and 10 μm or less.

[0013] Solution 4

[0014] A secondary battery comprising a positive electrode current collector and a negative electrode current collector, wherein at least one of the positive electrode current collector and the negative electrode current collector is the current collector according to any one of aspects 1 to 3.

[0015] Solution 5

[0016] The secondary battery according to claim 4 further comprises a negative electrode active material layer, wherein the negative electrode active material layer comprises a silicon-based negative electrode active material.

[0017] According to the present disclosure, a current collector capable of suppressing heat generation during an internal short circuit of a battery can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals represent like elements, and wherein:

[0019] Figure 1A A schematic cross-sectional view showing an example of a current collector disclosed in the present invention;

[0020] Figure 1B A schematic cross-sectional view of the current collector of the present disclosure showing how conductive foreign matter is captured by a conductive resin layer that has melted due to heat generated by an internal short circuit;

[0021] Figure 2 is a schematic cross-sectional view showing an example of a secondary battery of the present disclosure; and

[0022] Figure 3 Graphs showing the amount of heat generated during an internal short circuit in each example. DETAILED DESCRIPTION

[0023] The following is a detailed description of the embodiments of the present disclosure. Note that the present disclosure is not limited to the following embodiments, and can be implemented with various modifications within the scope of the disclosed gist.

[0024] Current Collector

[0025] The current collector of the present disclosure comprises a metal foil and a conductive resin layer laminated on the metal foil. The conductive resin layer in the current collector of the present disclosure comprises a resin and a conductive material, and the melting point of the resin is less than 120°C.

[0026] The inventors of the present application have found that in a battery having a current collector in which a conductive resin layer containing a low melting point resin is arranged on a metal foil, heat generation during an internal short circuit is suppressed. It is believed that in the case of an internal short circuit of a battery caused by the mixing of conductive foreign matter, the resin melts at an early stage due to the heat caused by the internal short circuit, thereby capturing the mixed conductive foreign matter in a manner that covers the mixed conductive foreign matter. As a result, it is believed that the flow of current is blocked, suppressing further temperature rise. In a battery having a current collector in which a conductive resin layer containing a low melting point resin is arranged on a metal foil, as a reason for suppressing heat generation during an internal short circuit, it is believed that the flow of the above-mentioned current is blocked, suppressing further temperature rise. However, this reason is not intended to be bound by any theory.

[0027] The following reference Figure 1A , Figure 1B , the collector of the present disclosure is described. Figure 1A This is a schematic cross-sectional view showing an example of the current collector of the present disclosure. Figure 1B This is a schematic cross-sectional view of the collector of the present disclosure showing how conductive foreign matter is captured by the conductive resin layer that is melted due to heat generated by an internal short circuit. Figure 1A , Figure 1B The dimensional relationships in the other drawings do not reflect the actual dimensional relationships.

[0028] like Figure 1A As shown, the current collector 10 of the present disclosure includes a metal foil 11 and a conductive resin layer 12 laminated on the metal foil 11 .

[0029] metal foil

[0030] The material used as the metal foil 11 is not particularly limited, and a material that can be used as a collector of a battery can be appropriately used. Among them, the "collector" can be a positive electrode collector or a negative electrode collector. The material of the metal foil that can be used for the positive electrode collector can be, for example, SUS, nickel, chromium, gold, platinum, aluminum, iron, titanium, zinc, etc., and the product of plating or vapor-depositing nickel, chromium, carbon, etc. on these metals. However, the material of the metal foil that can be used for the positive electrode collector is not limited to these. The material of the metal foil that can be used for the negative electrode collector can be, for example, copper, copper alloys, and the product of plating or vapor-depositing nickel, chromium, carbon, etc. on copper, but is not limited to these.

[0031] Conductive resin layer

[0032] The conductive resin layer 12 includes a resin 12 a and a conductive material 12 b .

[0033] Resin

[0034] The melting point of the resin 12a is less than 120°C. The melting point may be 40°C or higher, 45°C or higher, 50°C or higher, 55°C or higher, or 60°C or higher, and may be 110°C or lower, 100°C or lower, 95°C or lower, 90°C or lower, or 85°C or lower.

[0035] If the melting point of the resin 12a is low, when an internal short circuit of the battery occurs due to the mixing of the conductive foreign matter 13, the following situation is considered to occur. Figure 1B As shown, it is considered that the resin 12a melts early due to the heat generated by the internal short circuit, and can capture the mixed conductive foreign matter 13 by covering the mixed conductive foreign matter 13. As a result, it is considered that the flow of current is blocked, and further temperature rise can be suppressed.

[0036] The content of the resin 12a in the conductive resin layer 12 may be 50% by mass or more. The content may be 60% by mass or more, 70% by mass or more, or 80% by mass or more, and may be less than 100% by mass, 95% by mass or less, or 90% by mass or less. When the content is within the above range, the fluidity of the resin 12a when it is melted due to heat generation increases, and the conductive foreign matter 13 mixed in is easily captured.

[0037] The thickness of the conductive resin layer 12 may be 1 μm or more and 10 μm or less. The thickness may be 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, and may be 9 μm or less, 8 μm or less, 7 μm or less, or 6 μm or less. If the thickness of the conductive resin layer 12 is within the above range, it is easy to capture the conductive foreign matter 13 mixed in.

[0038] The resin 12a may be a crystalline resin, specifically, the resin 12a may be an acrylic resin, a polyvinyl chloride resin, a methacrylic resin, a polyethylene resin, a polystyrene resin, or an AS resin. The so-called crystalline resin refers to a resin having a property that the polymer chains are regularly arranged at a temperature below the melting point.

[0039] Conductive materials

[0040] The conductive material 12b is not particularly limited, and any conductive material commonly used as a conductive aid for a battery can be appropriately used. For example, the conductive material 12b may be VGCF (vapor grown carbon fiber), acetylene black (AB), Ketjen black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc. However, the conductive material 12b is not limited to these.

[0041] The content of the conductive material 12b in the conductive resin layer 12 may be more than 0 mass%, 5 mass% or more, or 10 mass% or more, and may be 50 mass% or less, 40 mass% or less, 30 mass% or less, or 20 mass% or less.

[0042] Other Ingredients

[0043] The conductive resin layer may optionally contain components other than the resin and the conductive material. For example, the conductive resin layer may contain a metal oxide filler such as aluminum oxide. However, from the viewpoint of the fluidity of the resin associated with heat generation during an internal short circuit, the content of the metal oxide filler in the conductive resin layer is preferably less than 10% by mass, less than 5% by mass, less than 1% by mass, or less than 0.1% by mass. In terms of the content of the metal oxide filler in the conductive resin layer, it is more preferred that the metal oxide filler is not contained.

[0044] Method for producing current collector

[0045] The method for producing the current collector of the present disclosure is not particularly limited, and a conventional resin thin film forming technique can be appropriately adopted.

[0046] For example, the current collector 10 can be produced by kneading the resin 12a and the conductive material 12b and rolling the kneaded mixture onto the metal foil 11. Alternatively, the current collector 10 can be produced by applying a slurry containing the resin 12a and the conductive material 12b onto the metal foil 11 and then drying the slurry.

[0047] Secondary battery

[0048] The secondary battery of the present disclosure includes a positive electrode current collector and a negative electrode current collector, and at least one of the positive electrode current collector and the negative electrode current collector is the current collector of the present disclosure. Figure 2 The schematic cross-sectional view of the secondary battery 1 of the present invention using the current collector 10 of the present invention as the positive electrode current collector is shown. In this case, the secondary battery 1 may include a metal foil 11 and a conductive resin layer 12 as the positive electrode current collector 10, a positive electrode active material layer 14, an electrolyte layer 15, a negative electrode active material layer 16, and a negative electrode current collector 17 in this order.

[0049] The secondary battery of the present disclosure may be a liquid battery or a solid battery. In addition, with respect to the present disclosure, a "solid battery" refers to a battery that uses at least a solid electrolyte as an electrolyte, and therefore, in a solid battery, a combination of a solid electrolyte and a liquid electrolyte may be used as an electrolyte. In addition, the solid battery of the present disclosure may be an all-solid battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0050] Positive electrode collector and negative electrode collector

[0051] Regarding the current collector, reference can be made to the above description related to the current collector of the present disclosure.

[0052] Positive electrode active material layer and negative electrode active material layer

[0053] The positive electrode active material layer contains a positive electrode active material, and optionally a solid electrolyte, a conductive auxiliary agent, and a binder. The negative electrode active material layer contains a negative electrode active material, and optionally a solid electrolyte, a conductive auxiliary agent, and a binder.

[0054] Positive active material

[0055] As the positive electrode active material, a known active material can be used. For example, in the case of forming a lithium ion battery, various lithium-containing composite oxides can be used as the positive electrode active material. Various lithium-containing composite oxides include lithium cobalt oxide, lithium nickel oxide, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2, lithium manganate, spinel lithium compounds, etc. In addition, as an olivine-type positive electrode active material, lithium iron phosphate (LFP) can be used. The positive electrode active material can be, for example, in the form of particles, and its size is not particularly limited.

[0056] The positive electrode active material may have a coating layer. For example, in the case of a lithium ion battery, the coating layer is a layer containing a material having lithium ion conductivity, low reactivity with the positive electrode active material and the solid electrolyte, and a coating layer that does not flow even when in contact with the active material or the solid electrolyte. Specific examples of materials constituting the coating layer include LiNbO 3 In addition, we can also list Li 4 Ti 5 O 12 , Li 3 PO 4 etc., but not limited to these.

[0057] Negative active material

[0058] As the negative electrode active material, a known active material can be used. For example, in the case of constituting a lithium ion battery, as the negative electrode active material, Si-based negative electrode active materials; carbon-based negative electrode active materials; various oxide-based negative electrode active materials; metallic lithium, lithium alloys, etc. can be used. Examples of Si-based negative electrode active materials are silicon (Si), Si alloys, silicon oxide, etc. Examples of carbon-based negative electrode active materials are graphite, hard carbon, etc. Examples of various oxide-based negative electrode active materials are lithium titanate, etc. The negative electrode active material can be, for example, in the form of particles, and there is no particular limitation on its size.

[0059] In particular, the negative electrode active material may be a Si-based negative electrode active material. Si is more likely to generate heat at low temperatures (about 160 to 220°C) than carbon-based negative electrode active materials. Therefore, in a secondary battery using Si as a negative electrode active material, when the temperature of the battery rises due to an internal short circuit, etc., Si may generate heat, making it difficult to suppress the increase in the amount of heat generated by the battery. By making the collector of the secondary battery the collector disclosed in the present invention, even if the negative electrode active material is a Si-based negative electrode active material, the heat generated during an internal short circuit can be effectively suppressed.

[0060] Solid electrolytes, conductive additives and adhesives

[0061] The material of the solid electrolyte is not particularly limited, and any material that can be used as a solid electrolyte for a secondary battery can be used. For example, the solid electrolyte may be a sulfide solid electrolyte.

[0062] Examples of sulfide solid electrolytes include, but are not limited to, sulfide amorphous solid electrolytes, sulfide crystalline solid electrolytes, and argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li 2 SP 2 S 5 Department, Li 2 S-SiS 2 、LiI-Li 2 S-SiS 2 、LiI-Li 2 SP 2 S 5 、LiI-LiBr-Li 2 SP 2 S 5 , Li 2 SP 2 S 5 -GeS 2 、LiI-Li 2 SP 2 O 5 、LiI-Li 3 PO 4 -P 2 S 5 , Li 7-x PS 6-x Cl x etc.; or a combination thereof. However, the specific sulfide solid electrolyte is not limited to these. 2 SP 2 S 5 For example, Li 7 P 3 S 11 , Li 3 PS 4 , Li 8 P 2 S 9 Li et al. 2 SP 2 S 5 -GeS 2 For example, Li 13 G 3 S 16 , Li 10 G 2 S 12 The sulfide solid electrolyte may be glass or crystallized glass (glass ceramic).

[0063] There is no particular limitation on the conductive additive. For example, the conductive additive may be VGCF (vapor grown carbon fiber), acetylene black (AB), Ketjen black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc. However, the conductive additive is not limited to these.

[0064] The binder is not particularly limited, and may be, for example, polyvinylidene fluoride (PVdF), butadiene rubber (BR), styrene butadiene rubber (SBR), or a combination thereof, but is not limited thereto.

[0065] Electrolyte layer

[0066] The electrolyte layer may be a solid electrolyte layer containing at least a solid electrolyte. The solid electrolyte layer may optionally contain a binder, etc. For the solid electrolyte and the binder, reference may be made to the above descriptions related to the positive electrode active material layer and the negative electrode active material layer of the present disclosure.

[0067] The method for producing the secondary battery of the present disclosure is not particularly limited, and a conventionally known method can be applied for production.

[0068] Comparative Manufacturing Example

[0069] Fabrication of current collector

[0070] The mixture contains 60 mass % of polyvinylidene fluoride (PVdF) (melting point: 150° C.), aluminum oxide (Al 2 O 3 A slurry of 30 mass % of aluminum (A), 10 mass % of acetylene black (AB) as a conductive material, and a solvent was applied onto an aluminum (Al) foil using a coating blade of Gap 50. The slurry was dried to prepare a current collector of a comparative manufacturing example.

[0071] Production Example 1

[0072] A slurry containing 80% by mass of a vinyl chloride resin (melting point: 85° C.), 20% by mass of vapor-grown carbon fiber (VGCF) as a conductive material, and a solvent was applied onto an Al foil using a coating blade of Gap 50. The slurry was dried to prepare a current collector of Manufacturing Example 1. The thickness of the conductive resin layer formed was 5 μm.

[0073] Production Example 2

[0074] A current collector of Production Example 2 was prepared in the same manner as in Production Example 1 except that the resin was an acrylic resin (melting point: 60° C.). The thickness of the formed conductive resin layer was 5 μm.

[0075] Comparative Example

[0076] Solid-state battery manufacturing

[0077] Preparation of positive electrode collector

[0078] As the positive electrode current collector, the current collector of Comparative Production Example was used.

[0079] Forming of positive electrode active material layer

[0080] The positive electrode active material, sulfide solid electrolyte, conductive aid and binder were weighed so that the mass ratio was positive electrode active material: sulfide solid electrolyte: conductive aid: binder = 85:13:1.3:0.7, and the molding was performed to obtain a positive electrode active material layer (thickness 70 μm). 0.8 Co 0.15 Al 0.05 O 2 (Sumitomo Metal Mining Co., Ltd.) coated with LiNbO 3 As a sulfide solid electrolyte, 10LiI-90 (0.75Li 2 S-0.25P 2 S 5 ), which was crystallized and micronized. As a conductive additive, vapor-grown carbon fiber (VGCF, manufactured by Showa Denko K.K.) was used. As a binder, PVdF was used.

[0081] Forming of solid electrolyte layer

[0082] The same sulfide solid electrolyte and binder as described above were mixed so as to have a mass ratio of 99.6:0.4 to prepare a solid electrolyte composite, and the obtained solid electrolyte composite was molded to obtain a solid electrolyte layer (thickness 15 μm).

[0083] Forming of negative electrode active material layer

[0084] The negative electrode active material, sulfide solid electrolyte, conductive aid and binder were weighed so that the mass ratio was negative electrode active material: sulfide solid electrolyte: conductive aid: binder = 53:41:4.5:1.5, and the molding was performed to obtain a negative electrode active material layer (thickness 50 μm). In addition, Si (manufactured by Mitsui Kinzoku Co., Ltd., average particle size D50 = 2.5 μm) was used as the negative electrode active material. The sulfide solid electrolyte, conductive aid and binder were the same as those used in the positive electrode active material layer.

[0085] Preparation of negative electrode current collector

[0086] As the negative electrode current collector, nickel (Ni) foil (30 μm in thickness) was used.

[0087] Solid-state battery manufacturing

[0088] Using the above-mentioned layers, a solid battery having a layer structure of "positive electrode collector (metal foil / conductive resin layer) / positive electrode active material layer / solid electrolyte layer / negative electrode active material layer / negative electrode collector" was obtained. Furthermore, the conductive resin layer of the collector is stacked in contact with the positive electrode active material layer. For the obtained solid battery, the initial capacity was confirmed (2.5-4.05V (CCCV), charging 1 / 3C, discharging 1 / 3C, rest condition 1 / 100C, 5 cycles). Then, for the solid battery, the voltage was adjusted (4.05V, CCCV, charging 1 / 3C, rest condition 1 / 100C), thereby obtaining a solid battery of the comparative example.

[0089] Examples 1 and 2

[0090] Solid batteries of Examples 1 and 2 were obtained in the same manner as in the Comparative Example except that the current collector of the Comparative Example was used instead of the current collector of the Comparative Example in the positive electrode current collector preparation step. The numbers of the Production Examples correspond to the numbers of the Examples.

[0091] evaluate

[0092] Evaluation of the heat generation of batteries

[0093] A nail penetration test was conducted on the central part of the solid battery using a nail with a diameter of 3 mm and a top angle of 45° at a speed of 1 μm / s. For each solid battery involved in the embodiment and the comparative example, the behavior of the current and voltage during the nail penetration test was observed, and the resistance of the battery was calculated based on the change in the current and voltage compared to the initial value at the time of internal short circuit. Furthermore, the heat generation of the battery was calculated based on the following formula:

[0094] Heat generation [W] = current [A] 2 × Resistance [Ω].

[0095] result

[0096] The results are shown in Figure 3 The results of the examples are shown as relative values ​​with the results of the comparative examples being 100. Figure 3 As shown, the solid batteries according to the examples generate less heat during an internal short circuit than the solid batteries according to the comparative examples. In particular, in Example 2 using an acrylic resin having a lower melting point, the heat generated during an internal short circuit is the smallest.

Claims

1. A current collector comprising a metal foil and a conductive resin layer laminated on the metal foil, wherein the conductive resin layer contains a resin and a conductive material, and the melting point of the resin is lower than 120°C.

2. The current collector according to claim 1, wherein The content of the resin in the conductive resin layer is 50% by mass or more.

3. The current collector according to claim 1, wherein The conductive resin layer has a thickness of 1 μm or more and 10 μm or less. 4 . A secondary battery comprising a positive electrode current collector and a negative electrode current collector, wherein at least one of the positive electrode current collector and the negative electrode current collector is the current collector according to claim 1 . 5 . The secondary battery according to claim 4 , further comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises a silicon-based negative electrode active material.

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