Current collector and secondary battery

Abstract

To provide a current collector capable of suppressing heat generation in the event of an internal short circuit in a battery.SOLUTION: A current collector 10 according to the present disclosure includes a metal foil 11 and a conductive resin layer 12 laminated on the metal foil 11. The conductive resin layer 12 in the current collector according to the present disclosure includes a resin 12a and a conductive material 12b, and the melting point of the resin 12a is lower than 120°C. The secondary battery 1 according to 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 10 of the present disclosure.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, so-called resin current collectors have been proposed which are made of resin to which a conductive filler such as metal powder has been added, instead of metal foil.

[0003] For example, Patent Document 1 discloses a current collector for a bipolar secondary battery having a structure including one or more layers containing a resin and a conductive material, in which the resin for at least one layer is a crystalline resin having a melting point of 120° C. or higher. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-170833 A Summary of the Invention [Problem to be solved by the invention]

[0005] Since the surface resistance of such a resin current collector is large, in a battery equipped with the resin current collector, it is considered that the flow of current in the planar direction during an internal short circuit can be effectively suppressed, and as a result, localized heat generation in the battery can be prevented. However, there is room for further improvement in suppressing heat generation during an internal short circuit in a battery.

[0006] An object of the present disclosure is to provide a current collector capable of suppressing heat generation in the event of an internal short circuit in a battery. [Means for solving the problem]

[0007] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> Metal foil, and A conductive resin layer laminated on the metal foil A current collector having the conductive resin layer contains a resin and a conductive material, The melting point of the resin is less than 120°C. Current collector. <Aspect 2> 2. The current collector according to aspect 1, wherein the conductive resin layer has a resin content of 50% by mass or more. <Aspect 3> 3. The current collector according to aspect 1 or 2, wherein the conductive resin layer has a thickness of 1 μm or more and 10 μm or less. <Aspect 4> A positive electrode current collector and a negative electrode current collector are provided, 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. Secondary battery. <Aspect 5> Further comprising a negative electrode active material layer, The negative electrode active material layer has a silicon-based negative electrode active material. 5. The secondary battery according to embodiment 4. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a current collector capable of suppressing heat generation in the event of an internal short circuit in a battery. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is (a) a schematic cross-sectional view showing an example of a current collector according to the present disclosure, and (b) a schematic cross-sectional view of the current collector according to the present disclosure showing a state in which a conductive foreign object is captured in a conductive resin layer that has melted due to heat generated by an internal short circuit. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an example of a secondary battery according to the present disclosure. [Diagram 3] FIG. 3 is a graph showing the amount of heat generated during an internal short circuit in each example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0011] Current collector The current collector of 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°C.

[0012] The present inventors have found that heat generation during an internal short circuit is suppressed in a battery having a current collector in which a conductive resin layer containing a resin with a low melting point is disposed on a metal foil. The reason for this, without intending to be bound by any theory, is believed to be that when an internal short circuit occurs in a battery due to the inclusion of conductive foreign matter, the resin melts early due to the heat generated by the internal short circuit, and covers and captures the inclusion of the conductive foreign matter, thereby cutting off the flow of current and suppressing further temperature rise.

[0013] Hereinafter, the current collector of the present disclosure will be described with reference to Fig. 1. Fig. 1 is (a) a schematic cross-sectional view showing an example of the current collector of the present disclosure, and (b) a schematic cross-sectional view of the current collector of the present disclosure showing a state in which a conductive foreign object is captured in a conductive resin layer that has melted due to heat generated by an internal short circuit. Note that the dimensional relationships in Fig. 1 and other drawings do not reflect the actual dimensional relationships.

[0014] As shown in FIG. 1( a ), a current collector 10 of the present disclosure has a metal foil 11 and a conductive resin layer 12 laminated on the metal foil 11 .

[0015] Metal foil The material used as the metal foil 11 is not particularly limited, and any material that can be used as a battery current collector can be appropriately adopted. Here, the "current collector" may be a positive electrode current collector or a negative electrode current collector. The material of the metal foil that can be used as the positive electrode current collector may be, for example, SUS, nickel, chromium, gold, platinum, aluminum, iron, titanium, zinc, etc., and these metals plated or vapor-deposited with nickel, chromium, carbon, etc., but is not limited thereto. The material of the metal foil that can be used as the negative electrode current collector may be, for example, copper, copper alloy, and copper plated or vapor-deposited with nickel, chromium, carbon, etc., but is not limited thereto.

[0016] <Conductive Resin Layer> The conductive resin layer 12 includes a resin 12a and a conductive material 12b.

[0017] (resin) The melting point of the resin 12a is less than 120° C. The melting point may be 40° C. or more, 45° C. or more, 50° C. or more, 55° C. or more, or 60° C. or more, and may be 110° C. or less, 100° C. or less, 95° C. or less, 90° C. or less, or 85° C. or less.

[0018] If the melting point of resin 12a is low, when an internal short circuit occurs in the battery due to the inclusion of conductive foreign matter 13, as shown in Figure 1(b), the heat generated by the internal short circuit causes resin 12a to melt early and cover and capture the inclusion of conductive foreign matter 13, thereby blocking the flow of current and suppressing further temperature rise.

[0019] The content of the resin 12a in the conductive resin layer 12 may be 50% by mass or more. This 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. If this content is within the above range, the fluidity of the resin 12a when it melts due to heat generation is high, and it is easy to capture the conductive foreign matter 13 that has been mixed in.

[0020] The thickness of the conductive resin layer 12 may be 1 μm or more and 10 μm or less. This 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. When the thickness of the conductive resin layer 12 is within the above range, it is easy to capture the conductive foreign matter 13 that has been mixed in.

[0021] Resin 12a may be a crystalline resin, specifically, resin 12a may be an acrylic resin, a polyvinyl chloride resin, a methacrylic resin, a polyethylene resin, a polystyrene resin, or an AS resin. Note that a crystalline resin refers to a resin whose polymer chains have the property of being regularly arranged at a temperature below the melting point.

[0022] (Conductive materials) The conductive material 12b is not particularly limited, and may be any material commonly used as a conductive assistant for batteries. For example, the conductive material 12b may be, but is not limited to, VGCF (Vapor Grown Carbon Fiber), acetylene black (AB), Ketjen Black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc.

[0023] The content of the conductive material 12b in the conductive resin layer 12 may be greater than 0 mass%, greater than or equal to 5 mass%, or greater than or equal to 10 mass%, and may be less than or equal to 50 mass%, less than or equal to 40 mass%, less than or equal to 30 mass%, or less than or equal to 20 mass%.

[0024] (Other Ingredients) The conductive resin layer may optionally contain components other than the resin and the conductive material. For example, it may contain a metal oxide filler such as aluminum oxide, but from the viewpoint of the fluidity of the resin accompanying heat generation during an internal short circuit, the content of the metal oxide filler in the conductive resin layer is preferably less than 10 mass%, less than 5 mass%, less than 1 mass%, or less than 0.1 mass%, and more preferably does not contain a metal oxide filler.

[0025] <<Manufacturing method of current collector>> The method for producing the current collector of the present disclosure is not particularly limited, and existing techniques for forming thin resin films can be appropriately adopted.

[0026] For example, the current collector 10 can be produced by kneading the resin 12a and the conductive material 12b and rolling the mixture on 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 applied slurry.

[0027] 《Secondary battery》 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. Fig. 2 is a schematic cross-sectional view showing a secondary battery 1 of the present disclosure using a current collector 10 of the present disclosure as a positive electrode current collector. 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.

[0028] The secondary battery of the present disclosure may be a liquid battery or a solid-state battery. In the present disclosure, a "solid-state battery" means a battery that uses at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. The solid-state battery of the present disclosure may also be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as an electrolyte.

[0029] <Positive electrode current collector and negative electrode current collector> For the current collector, reference may be made to the above description of the current collector of the present disclosure.

[0030] <Positive Electrode Active Material Layer and Negative Electrode Active Material Layer> The positive electrode active material layer contains a positive electrode active material, and optionally a solid electrolyte, a conductive additive, and a binder.The negative electrode active material layer contains a negative electrode active material, and optionally a solid electrolyte, a conductive additive, and a binder.

[0031] (Cathode active material) As the positive electrode active material, a known active material may be used. For example, in the case of constructing a lithium ion battery, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Various lithium-containing composite oxides such as O2, lithium manganate, and spinel-based lithium compounds can be used. In addition, lithium iron phosphate (LFP) can be used as an olivine-type positive electrode active material. The positive electrode active material may be, for example, particulate, and the size of the particulate is not particularly limited.

[0032] The positive electrode active material may have a coating layer. For example, in the case of constructing a lithium ion battery, the coating layer is a layer containing a material that has lithium ion conductivity, has low reactivity with the positive electrode active material and the solid electrolyte, and can maintain the shape of the coating layer without flowing even when it comes into contact with the active material and the solid electrolyte. Specific examples of materials that constitute the coating layer include LiNbO3, Li4Ti5O 12 , Li3PO4, etc., but are not limited to these.

[0033] (Negative electrode active material) As the negative electrode active material, a known active material may be used. For example, in the case of constructing a lithium ion battery, the negative electrode active material may be a Si-based negative electrode active material such as silicon (Si), a Si alloy, or silicon oxide; a carbon-based negative electrode active material such as graphite or hard carbon; various oxide-based negative electrode active materials such as lithium titanate; metallic lithium, a lithium alloy, or the like. The negative electrode active material may be, for example, particulate, and the size of the particulate is not particularly limited.

[0034] 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 the negative electrode active material, when the temperature of the battery rises due to an internal short circuit or the like, there is a risk that heat will be generated by Si, making it difficult to suppress an increase in the amount of heat generated by the battery. In contrast, by using the current collector of the secondary battery as the current collector of the present disclosure, heat generation during an internal short circuit can be effectively suppressed even if the negative electrode active material is a Si-based negative electrode active material.

[0035] (Solid electrolyte, conductive agent, and binder) The material of the solid electrolyte is not particularly limited, and any material that can be used as a solid electrolyte for use in secondary batteries can be used. For example, the solid electrolyte may be a sulfide solid electrolyte.

[0036] 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 Li2S-P2S5-based (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2 (Li 13 GeP3S 16 , Li 10 GeP2S 12 ), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x P.S. 6-x Cl x etc.; or combinations thereof. The sulfide solid electrolyte may be a glass or a crystallized glass (glass ceramic).

[0037] The conductive assistant is not particularly limited. For example, the conductive assistant may be VGCF (Vapor Grown Carbon Fiber), acetylene black (AB), Ketjen Black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc., but is not limited thereto.

[0038] The binder is not particularly limited. For example, the binder may be a material such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), or styrene butadiene rubber (SBR), or a combination thereof, but is not limited thereto.

[0039] <Electrolyte layer> 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, the above description of the positive electrode active material layer and the negative electrode active material layer of the present disclosure can be referred to.

[0040] The method for producing the secondary battery of the present disclosure is not particularly limited, and the battery can be produced by applying a conventionally known method. EXAMPLES

[0041] Comparative manufacturing example <Preparation of current collector> A slurry containing 60 mass% polyvinylidene fluoride (PVdF) (melting point: 150°C), 30 mass% aluminum oxide (Al2O3), 10 mass% acetylene black (AB) as a conductive material, and a solvent was applied onto an aluminum (Al) foil using a coating blade of Gap 50. This was dried to produce a current collector of the comparative manufacturing example. Example 1 A slurry containing 80 mass% of vinyl chloride resin (melting point: 85°C), 20 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 Gap50. This was dried to produce a current collector of Production Example 1. The thickness of the formed conductive resin layer was 5 μm.

[0042] Example 2 Except for using an acrylic resin (melting point: 60° C.) as the resin, a current collector of Production Example 2 was produced in the same manner as in Production Example 1. The thickness of the formed conductive resin layer was 5 μm.

[0043] Comparative Example (Fabrication of solid-state batteries) (Preparation of positive electrode current collector) As the positive electrode current collector, the current collector of the comparative production example was used.

[0044] (Forming of positive electrode active material layer) The positive electrode active material, the sulfide solid electrolyte, the conductive additive, and the binder were weighed out and molded in a mass ratio of positive electrode active material:sulfide solid electrolyte:conductive additive:binder=85:13:1.3:0.7 to obtain a positive electrode active material layer (thickness 70 μm). 0.8 Co 0.15 Al 0.05 LiNbO3 coated on O2 (manufactured by Sumitomo Metal Mining Co., Ltd.) was used. 10LiI-90 (0.75Li2S-0.25P2S5) was synthesized as the sulfide solid electrolyte, which was then crystallized and micronized. Vapor grown carbon fiber (VGCF, manufactured by Showa Denko K.K.) was used as the conductive additive. PVdF was used as the binder.

[0045] (Forming of solid electrolyte layer) The same sulfide solid electrolyte as above and a binder were mixed in a mass ratio of 99.6:0.4 to obtain a solid electrolyte mixture, and the obtained solid electrolyte mixture was molded to obtain a solid electrolyte layer (thickness 15 μm).

[0046] (Forming of negative electrode active material layer) The negative electrode active material, the sulfide solid electrolyte, the conductive additive, and the binder were weighed out and molded in a mass ratio of negative electrode active material:sulfide solid electrolyte:conductive additive:binder=53:41:4.5:1.5 to obtain a negative electrode active material layer (thickness 50 μm). Note that Si (manufactured by Mitsui Kinzoku Co., Ltd., average particle diameter D50=2.5 ​​μm) was used as the negative electrode active material. The sulfide solid electrolyte, conductive additive, and binder were the same as those used in the positive electrode active material layer.

[0047] (Preparation of negative electrode current collector) Nickel (Ni) foil (thickness: 30 μm) was used as the negative electrode current collector.

[0048] (Fabrication of solid-state batteries) Using the above layers, a solid-state 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. The conductive resin layer of the collector was laminated so as to be in contact with the positive electrode active material layer. The initial capacity of the obtained solid-state battery was confirmed (2.5-4.05V (CCCV), charge 1 / 3C, discharge 1 / 3C, rest condition 1 / 100C, 5 cycles), and then the voltage was adjusted (4.05V, CCCV, charge 1 / 3C, rest condition 1 / 100C) to obtain a solid-state battery of the comparative example.

[0049] Examples 1 and 2 In the preparation step of the positive electrode current collector, the solid-state batteries of Examples 1 and 2 were obtained in the same manner as in the comparative example, except that the current collector of Comparative Production Example was replaced with the current collector of Production Example 1 or 2. Note that the numbers of Production Examples correspond to the numbers of Examples.

[0050] "evaluation" Evaluation of the amount of heat generated by the battery A nail penetration test was conducted by penetrating the center of the solid-state battery with a nail having a diameter of 3 mm and a tip angle of 45° at a speed of 1 μm / s. The behavior of the current and voltage during the nail penetration test was observed for each of the solid-state batteries according to the examples and comparative examples, and the resistance of the battery was calculated from the amount of change from the initial values ​​of the current and voltage at the time when an internal short circuit occurred. Furthermore, the amount of heat generated by the battery was calculated based on the following formula: Heat output [W] = current [A] 2 ×Resistance [Ω].

[0051] "result" The results are shown in Figure 3. The results of the Examples are shown as relative values ​​with the results of the Comparative Example taken as 100. As shown in Figure 3, the solid-state battery according to the Examples had a smaller amount of heat generated upon internal short circuit than the solid-state battery according to the Comparative Example. In particular, the amount of heat generated upon internal short circuit was the smallest in Example 2, which used an acrylic resin with a lower melting point. [Explanation of symbols]

[0052] 1 Secondary battery 10 Current collector 11 Metal foil 12 Conductive resin layer 12a Resin 12b Conductive material 13 Conductive foreign objects

Claims

1. Metal foil, and A conductive resin layer laminated on the metal foil A current collector having the conductive resin layer contains a resin and a conductive material, The melting point of the resin is less than 120°C. Current collector.

2. The current collector according to claim 1 , wherein the conductive resin layer has a resin content of 50 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 positive electrode current collector and a negative electrode current collector are provided, At least one of the positive electrode current collector and the negative electrode current collector is the current collector according to any one of claims 1 to 3. Secondary battery.

5. Further comprising a negative electrode active material layer, The negative electrode active material layer has a silicon-based negative electrode active material. The secondary battery according to claim 4 .

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