Negative electrode and battery

Abstract

To provide a negative electrode that can suppress deterioration of a negative electrode collector.SOLUTION: A negative electrode for use in a battery has, in that order, a negative electrode current collector being an Al current collector, a protective layer formed on the surface of the Al current collector, and a negative electrode active material layer. The protective layer contains Si and O, Si forms a Si-O-Al bond with Al of the Al current collector via O, and the negative electrode active material layer contains a negative electrode active material having a lower reaction potential than Al.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a negative electrode and a battery.

Background Art

[0002] In recent years, with the rapid spread of electronic devices such as personal computers and mobile phones, the development of batteries used as their power sources has been underway. Also, in the automotive industry, the development of batteries used in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs) has been underway.

[0003] For example, Patent Document 1 discloses a all-solid-state battery having a negative electrode active material layer containing a Si-based active material as a negative electrode active material and a negative electrode current collector made of Ni foil. Also, Patent Document 2 discloses a lithium-ion secondary battery having, in order, a substrate made of an alloy mainly composed of aluminum and a plating layer containing nickel and phosphorus and plated on the surface of the substrate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] From the perspective of reducing the weight of the battery to improve the energy density and enhancing the heat dissipation of the battery to suppress battery degradation, it is assumed that Al (aluminum) is used as the material for the negative electrode current collector. On the other hand, since Al has a relatively high reaction potential, when a material with a lower reaction potential than Al is used as the negative electrode active material, the negative electrode current collector (Al current collector) may react with Li ions prior to the negative electrode active material, and the negative electrode current collector may deteriorate. In addition, when the negative electrode current collector deteriorates, the capacity of the battery may decrease.

[0006] The present disclosure has been made in view of the above circumstances, and the main object is to provide a negative electrode capable of suppressing the deterioration of the negative electrode current collector.

Means for Solving the Problems

[0007] [1] A negative electrode used in a battery, The negative electrode has, in this order, a negative electrode current collector that is an Al current collector, a protective layer formed on the surface of the Al current collector, and a negative electrode active material layer. The protective layer contains Si and O. The Si constitutes a Si-O-Al bond with the Al of the Al current collector via the O. The negative electrode active material layer contains a negative electrode active material having a reaction potential lower than that of Al.

[0008] [2] The reaction potential of the negative electrode active material is 0.3 V (Li + / Li) or less, the negative electrode according to [1].

[0009] [3] The Si is bonded to a functional group having an amino group, the negative electrode according to [1] or [2].

[0010] [4] Between the protective layer and the negative electrode active material layer, there is a resin layer containing a resin and a conductive material, the negative electrode according to any one of [1] to [3].

[0011] [5] A battery having a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode is the negative electrode according to any one of [1] to [4].

Advantages of the Invention

[0012] In the present disclosure, there is an effect that deterioration of the negative electrode current collector can be suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0014] Hereinafter, the negative electrode and the battery in the present disclosure will be described in detail. Each of the drawings shown below is schematically illustrated, and the size and shape of each part are exaggerated as appropriate for easy understanding.

[0015] A. Negative Electrode FIG. 1 is a schematic cross-sectional view illustrating a negative electrode in the present disclosure. The negative electrode AN shown in FIGS. 1(a) and 1(b) has, in this order, a negative electrode current collector 1 which is an Al current collector, a protective layer 2 formed on the surface of the Al current collector 1, and a negative electrode active material layer 3. Further, the protective layer 2 contains Si and O, and the Si forms a Si—O—Al bond with the Al of the Al current collector via the O. The negative electrode active material layer 3 contains a negative electrode active material having a reaction potential lower than that of Al. Although details will be described later, as shown in FIG. 1(b), the negative electrode AN may have a resin layer 4 containing a resin and a conductive material between the protective layer 2 and the negative electrode active material layer 3.

[0016] In the negative electrode in the present disclosure, the protective layer formed on the surface of the Al current collector contains Si and O, and the Si forms a Si—O—Al bond with the Al of the Al current collector via the O. When a negative electrode having such a protective layer is used in a battery, it is presumed that the movement of Li ions to the Al current collector is blocked by the protective layer. As a result, even when a negative electrode active material having a reaction potential lower than that of Al is used, the reaction between the Al current collector and Li ions can be suppressed, and deterioration of the Al current collector can be suppressed.

[0017] 1. Negative electrode current collector The negative electrode current collector in the present disclosure is an Al current collector. The Al current collector is a current collector using aluminum (Al) as a material. The Al current collector preferably contains Al as a main material. The Al current collector may be a single Al or an Al alloy. In the Al alloy, the reaction potential of a metal element other than Al is preferably lower than that of Al. The ratio of the Al element to all metal elements is, for example, 50 mol% or more, may be 70 mol% or more, or may be 90 mol% or more. On the other hand, in the Al alloy, the ratio of the Al element to all metal elements is, for example, 99 mol% or less. The shape of the Al current collector is, for example, a foil shape and a mesh shape. The thickness of the Al current collector is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

[0018] 2. Protective layer FIG. 2 is a diagram for explaining the protective layer in the present disclosure. The protective layer is a layer formed on the surface of the Al current collector, contains Si and O, and the Si forms a Si—O—Al bond with the Al of the Al current collector via the O.

[0019] The above Si may be bonded to a functional group having an amino group, may be bonded to a functional group having a vinyl group, may be bonded to a functional group having an epoxy group, or may be bonded to a functional group having a methacrylic group. Among these, as shown in FIG. 2, it is preferable that the above Si is bonded to a functional group having an amino group. For example, when the negative electrode has a resin layer described later, it is assumed that the amino group interacts with the oxygen atom in the resin, and the protective layer functions as an adhesive layer that adheres the Al current collector and the resin layer. As a result, a negative electrode with improved peel characteristics is obtained. The functional group (R in FIG. 2) having an amino group or the like is, for example, a hydrocarbon group having 2 or more and 10 or less carbon atoms.

[0020] Also, as shown in FIG. 2, the above Si may form a Si—O—Si bond with another Si via the above O. That is, a siloxane bond may be present in the protective layer.

[0021] The thickness of the protective layer is not particularly limited, but for example, it is 100 nm or more, and may be 150 nm or more. On the other hand, the thickness of the protective layer may be, for example, 300 nm or less, may be 250 nm or less, or may be 200 nm or less.

[0022] The method for forming the protective layer, that is, the method for manufacturing the Al current collector having the protective layer formed on the surface is not particularly limited, but for example, a method having the following first to third steps can be mentioned. For details of each step, for example, the content described in the examples can be mentioned. First step: A step of immersing the Al current collector in a solution of water, aqueous ammonia, and hydrogen peroxide solution. Second step: A step of immersing the Al current collector after the first step in an alcohol solution containing alkoxysilane and alcohol. Third step: A step of immersing and washing the Al current collector after the second step in alcohol.

[0023] Examples of the alkoxysilane include, in addition to the compounds described in the Examples, for example, (3-aminopropyl)trimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0024] 3. Negative electrode active material layer The negative electrode active material layer contains a negative electrode active material having a reaction potential lower than that of Al.

[0025] The reaction potential of the negative electrode active material is not particularly limited as long as it is lower than the reaction potential of Al. In terms of Li standard, for example, it is 0.3 V (Li + / Li) or less, may be 0.2 V (Li + / Li) or less, and may be 0.1 V (Li + / Li) or less. On the other hand, the reaction potential of the negative electrode active material is, for example, -0.5 V (Li + / Li) or more. The reaction potential of the negative electrode active material can be determined by cyclic voltammetry (CV).

[0026] Examples of the negative electrode active material include Si-based active materials and carbon-based active materials. The Si-based active material is an active material containing Si element. Examples of the Si-based active material include Si single substance, Si alloy, and Si oxide. The Si alloy preferably contains Si element as a main component. The proportion of Si element in the Si alloy is, for example, 50 mol% or more and 99 mol% or less.

[0027] The carbon-based active material is an inorganic active material containing C element, and examples thereof include graphite, hard carbon, and soft carbon.

[0028] Examples of the shape of the negative electrode active material include particulate shape and layered shape. The average particle diameter (D 50 ) of the negative electrode active material is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the average particle diameter (D 50 ) of the negative electrode active material is, for example, 50 μm or less, and may be 20 μm or less. The average particle diameter (D50 ) refers to the cumulative 50% particle diameter in the volume-based particle size distribution measured by a laser diffraction particle size distribution measuring device. The proportion of the negative electrode active material in the negative electrode active material layer is, for example, 50% by weight or more and 80% by weight or less.

[0029] The negative electrode active material layer may contain at least one of a conductive material, a binder, and an electrolyte as required. Examples of the binder include rubber-based binders such as butadiene rubber (BR), acrylate butadiene rubber (ABR), and styrene butadiene rubber (SBR), and fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0030] Examples of the conductive material include carbon materials. Examples of the carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0031] Examples of the electrolyte include solid electrolytes. Examples of the solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. The sulfide solid electrolyte preferably contains sulfur (S) as the main component of the anion element. The oxide solid electrolyte preferably contains oxygen (O) as the main component of the anion element. The halide solid electrolyte preferably contains a halogen as the main component of the anion. Among these, sulfide solid electrolytes are preferred.

[0032] Other examples of the solid electrolyte include organic solid electrolytes such as polymer electrolytes and gel electrolytes. Further, a liquid electrolyte (electrolyte solution) can also be mentioned as the electrolyte.

[0033] The thickness of the negative electrode active material layer is not particularly limited, but is, for example, 0.5 μm or more and 1000 μm or less.

[0034] 4. Resin layer As shown in FIG. 1(b), the negative electrode AN may have a resin layer 4 containing a resin and a conductive material between the protective layer 2 and the negative electrode active material layer 3.

[0035] Examples of the resin include thermoplastic resins, thermosetting resins, and conductive polymers. Among them, the resin layer preferably contains a thermoplastic resin. A thermoplastic resin is a resin that softens by heat. The softening temperature of the thermoplastic resin is, for example, 100°C or higher and 200°C or lower. Examples of the thermoplastic resin include poly(meth)acrylic acid, poly(meth)acrylate methyl, polyethylene, polypropylene, polyethylene terephthalate, polyether nitrile, polyimide, polyamide, polytetrafluoroethylene, polyacrylonitrile, poly(meth)acrylate, and vinyl halide resins. Note that “(meth)acrylic acid” is a concept that includes both acrylic acid and methacrylic acid, and “(meth)acrylate” is a concept that includes both acrylate and methacrylate.

[0036] Examples of the thermosetting resin include epoxy resins and vinyl ester resins. The resin layer usually contains a cured product obtained by curing a thermosetting resin. Examples of the conductive polymer include polyaniline and polypyrrole. Also, the resin contained in the resin layer may be one type or two or more types.

[0037] Regarding the conductive material, it is the same as the content described in “3. Negative electrode active material layer”. The thickness of the resin layer is not particularly limited, but for example, it is 0.5 μm or more and 10 μm or less.

[0038] 5. Negative electrode The negative electrode in the present disclosure is used in a battery. The battery will be described later.

[0039] B. Battery As shown in FIG. 3, the battery in the present disclosure has a positive electrode CA, a negative electrode AN, and an electrolyte layer EL disposed between the positive electrode CA and the negative electrode AN. In particular, in the battery of the present disclosure, the negative electrode is the negative electrode described above.

[0040] According to the present disclosure, since the battery has the negative electrode described above, the battery is such that a decrease in capacity due to deterioration of the Al current collector is suppressed.

[0041] 1. Negative electrode Regarding the negative electrode, since it is the same as the content described in "A. Negative electrode", the description here is omitted.

[0042] 2. Positive electrode As shown in FIG. 3, the positive electrode CA in the present disclosure usually has a positive electrode active material layer 5 and a positive electrode current collector 6 from the electrolyte layer EL side.

[0043] The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may contain at least one of a conductive material, a binder, and an electrolyte as necessary. The conductive material, the binder, and the electrolyte are the same as the content described in "A. Negative electrode".

[0044] Examples of the positive electrode active material include oxide active materials. Examples of the oxide active material include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05 O2 and other rock salt layer-type active materials, spinel-type active materials such as LiMn2O4, olivine-type active materials such as LiFePO4, etc. Also, sulfur (S) may be used as the positive electrode active material. The shape of the positive electrode active material is, for example, particulate.

[0045] The thickness of the positive electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0046] The positive electrode current collector is a member that collects electrons from the positive electrode active material layer. The material of the positive electrode current collector is not particularly limited, and examples include SUS, aluminum, nickel, iron, titanium, and carbon. Examples of the shape of the positive electrode current collector include foil shape and mesh shape.

[0047] 3. Electrolyte layer The electrolyte layer is disposed between the positive electrode and the negative electrode. More specifically, it is disposed between the positive electrode active material layer and the negative electrode active material layer.

[0048] The electrolyte layer contains at least an electrolyte. The electrolyte is the same as that described in "A. Negative electrode". In particular, it is preferable that the electrolyte layer contains a solid electrolyte as the electrolyte.

[0049] In the present disclosure, the electrolyte layer containing a solid electrolyte may be referred to as a solid electrolyte layer, and a battery having a solid electrolyte layer may be referred to as an all-solid-state battery. Further, the electrolyte layer may contain a binder as necessary. The binder is the same as that described in "A. Negative electrode". The thickness of the electrolyte layer is, for example, 1 μm or more and 500 μm or less.

[0050] 4. Battery The battery in the present disclosure may include an exterior body that houses the above-described members. Examples of the exterior body include a laminate-type exterior body and a case-type exterior body. Further, the battery in the present disclosure may include a restraining jig that applies a restraining pressure in the thickness direction to the above-described members. A known jig can be used as the restraining jig. The restraining pressure is, for example, 0.1 MPa or more and 50 MPa or less, and may be 1 MPa or more and 20 MPa or less.

[0051] The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion secondary battery. Further, the battery is preferably an all-solid-state battery. The use of the battery is not particularly limited, and examples thereof include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. In particular, it is preferably used as a driving power source for a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or a battery electric vehicle (BEV). Further, the battery in the present disclosure may be used as a power source for a moving body other than a vehicle (for example, a railway, a ship, an aircraft), or may be used as a power source for an electric product such as an information processing device.

[0052] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same operational effects is included in the technical scope of the present disclosure.

Examples

[0053] [Example 1] Water, aqueous ammonia, and aqueous hydrogen peroxide were mixed at a weight ratio of 5:1:1 to prepare a solution, and a negative electrode current collector (Al foil) was immersed in this solution for 15 minutes. Next, the Al foil was immersed in a methanol solution in which APTMS ((3-aminopropyl)trimethoxysilane) was dissolved to a weight ratio of 1% for 30 minutes. Then, the Al foil was immersed in propanol for washing and air-dried. Thereby, a protective layer was formed on the surface of the Al current collector. Thereby, a negative electrode member having an Al current collector and a protective layer was produced.

[0054] Here, the Al current collector having the protective layer formed thereon was subjected to cross-section processing with a cross-section polisher and subjected to SEM-EDX analysis. As a result, it was confirmed that Si element and O element were present on the surface of the Al current collector, and it was confirmed that the thickness of the protective layer was 200 nm.

[0055] 100 mg of a sulfide solid electrolyte (SE: Li2S-P2S5) was placed in a cylindrical container with a φ11.28 hole, and pressed at 100 MPa using a φ11.28 SUS pin to obtain a solid electrolyte layer. On one side of the solid electrolyte layer, the above-mentioned negative electrode member punched out to 1 cm 2 was placed and pressed at 600 MPa. On the other side of the solid electrolyte layer, a Li foil punched out to 1 cm 2 was placed. On both the Al current collector side and the Li foil side, they were arranged in the order of SUS pins and restraining jigs, and restrained at 15 MPa. As a result, a half cell having an Al foil, a protective layer, a solid electrolyte layer, a Li foil, and a SUS foil in this order was obtained.

[0056] [Example 2] A half cell was fabricated in the same manner as in Example 1, except that a negative electrode member having a resin layer on the protective layer was used. The resin layer was formed as follows.

[0057] A resin slurry containing a vinyl-based resin (polymethyl methacrylate), a conductive material (carbon), and a dispersion medium was prepared. In the resin slurry, the ratio of the vinyl-based resin and carbon was a weight ratio of 4:1. This resin slurry was applied to the surface of the Al current collector (the surface of the protective layer) prepared in the same manner as in Example 1 by the blade method, and dried on a hot plate at 50 °C for 20 minutes. Then, it was further dried on a hot plate at 150 °C for 30 minutes. A resin layer was formed on the protective layer. As a result, a negative electrode member having an Al current collector, a protective layer, and a resin layer was obtained.

[0058] When the thickness of the resin layer was confirmed with a micrometer, the thickness of the resin layer was 4 μm.

[0059] [Comparative Example 1] A half cell was fabricated in the same manner as in Example 1, except that a negative electrode member without a protective layer was used.

[0060] [Evaluation] (Cyclic Voltammetry Measurement) For the half cells of Example 1, Example 2, and Comparative Example 1, cyclic voltammetry (CV) measurements were performed using an electrochemical measurement device. The CV measurements were carried out under the condition of a sweep rate of 0.5 mV / sec. The voltage was changed in the order of from the initial voltage to 0 V, from 0 V to 2 V, and from 2 V to 0 V. In the second cycle, the maximum current value (the maximum current value on the reduction side) flowing up to 0 V was acquired. The maximum current value of Comparative Example 1 was set to 100 and evaluated relatively. The results are shown in Figure 4. In addition, the current observed in the CV measurement using the above half cell is a current caused by the reaction of Al and Li.

[0061] As shown in Figure 4, the maximum current amounts of Example 1 and Example 2 were significantly lower than those of Comparative Example 1. In particular, in Example 2 provided with a resin layer, the maximum current amount decreased to 1 / 10 or less of that of Comparative Example 1. From this, it was confirmed that by forming a protective layer on the surface of the Al current collector, the reaction between Al and Li ions was suppressed. That is, it was indirectly confirmed that even in a battery provided with a negative electrode active material layer containing a negative electrode active material having a reaction potential lower than that of Al, the reaction and breakage of the Al current collector can be suppressed by using the negative electrode in the present disclosure.

[0062] [Reference Example 1] A resin layer was formed on the surface of the Al current collector in the same manner as in Example 2. Thereby, a test member having an Al current collector and a resin layer was obtained.

[0063] [Reference Example 2] An Al current collector with a protective layer formed thereon was prepared in the same manner as in Example 1. A resin layer was formed on the surface of this Al current collector (the surface of the protective layer) in the same manner as in Example 2. Thereby, a test member having an Al current collector, a protective layer, and a resin layer was obtained.

[0064] [Evaluation] (Peeling Test) The test members prepared in Reference Examples 1 and 2 were punched out to φ11.28 and a load of 600 MPa was applied 3 times in a state sandwiched between SUS pins. Then, it was visually confirmed whether there was peeling of the resin layer. The results are shown in Table 1.

[0065]

Table 1

[0066] As shown in Table 1, peeling was suppressed by the protective layer. It is presumed that this is because the amino groups in the protective layer interacted with the oxygen atoms in the resin, causing the protective layer to function as an adhesive layer that adhered the Al current collector and the resin layer.

Explanation of Reference Numerals

[0067] 1 … Negative current collector (Al current collector) 2 … Protective layer 3 … Negative electrode active material layer 4 … Resin layer 5 … Positive electrode active material layer 6 … Positive current collector CA… Positive electrode AN… Negative electrode EL… Electrolyte layer 10 … Battery

Claims

1. A negative electrode used in a battery, wherein the negative electrode sequentially includes a negative electrode current collector that is an Al current collector, a protective layer formed on the surface of the Al current collector, and a negative electrode active material layer, the protective layer contains Si and O, the Si forms a Si—O—Al bond with Al of the Al current collector via the O, and the negative electrode active material layer contains a negative electrode active material having a reaction potential lower than that of Al.

2. The reaction potential of the negative electrode active material is 0.3 V (Li ＋ / Li) or less. The negative electrode according to claim 1.

3. The negative electrode according to claim 1, wherein the Si is bonded to a functional group having an amino group.

4. The negative electrode according to claim 1, further having a resin layer containing a resin and a conductive material between the protective layer and the negative electrode active material layer.

5. A battery including a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode is the negative electrode according to any one of claims 1 to 4.

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