JP7009772B2 - Laminated battery and manufacturing method of laminated battery - Google Patents

Description

The present disclosure relates to laminated batteries.

A laminated battery having a plurality of cells having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order in the thickness direction is known. For example, Patent Document 1 has a plurality of unit cells including a positive electrode layer having a positive electrode current collector and a positive electrode mixture layer, a solid electrolyte layer, and a negative electrode layer having a negative electrode current collector and a negative electrode mixture layer. Lithium ion secondary batteries are disclosed. Further, Patent Document 1 discloses a nail piercing test as a method for evaluating the safety of an all-solid-state battery.

Japanese Unexamined Patent Publication No. 2016-207614

As described above, a nail piercing test is known as a method for evaluating the safety of an all-solid-state battery. The nail piercing test is a test in which a conductive nail is pierced into an all-solid-state battery and changes (for example, temperature changes) when an internal short circuit occurs in the battery are observed.

When the present inventors have examined in detail a nail piercing test on a laminated battery in which a plurality of all-solid-state battery cells are electrically connected in parallel, a cell having a small short-circuit resistance (short-circuit resistance) and a cell having a large short-circuit resistance have a large short-circuit resistance. I got a new finding that cells are mixed. When a cell having a small short-circuit resistance and a cell having a large short-circuit resistance coexist, a current flows from a cell having a large short-circuit resistance to a cell having a small short-circuit resistance. Hereinafter, this may be referred to as "wraparound current". When a wraparound current is generated, the temperature of the cell having a small short-circuit resistance (the cell into which the current has flowed) rises, and as a result, deterioration of the battery material is likely to occur.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a laminated battery having a reduced wraparound current.

In order to solve the above problems, in the present disclosure, a plurality of cells having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order are provided in the thickness direction. The plurality of cells are a laminated battery in which the plurality of cells are electrically connected in parallel, and the plurality of cells are the conditions (i): all the positive electrode current collectors of the plurality of cells are Ti, Ti alloy, Fe and At least one of the conditions of at least one of Fe alloys and condition (ii): that all the negative electrode current collectors of the plurality of cells are at least one of Ti, Ti alloys, Fe and Fe alloys. Provide a laminated battery that meets.

According to the present disclosure, since the plurality of cells satisfy at least one of the condition (i) and the condition (ii), it is possible to obtain a laminated battery having a reduced wraparound current.

Under the above condition (i), the positive electrode current collector at least one of the plurality of cells may be Ti.

In the above disclosure, the Fe alloy may be SUS.

In the above disclosure, the negative electrode current collector at least one of the plurality of cells may be Cu or a Cu alloy.

Further, in the present disclosure, in the method for manufacturing a laminated battery for manufacturing the above-mentioned laminated battery, the plurality of cells are the condition (iii): the positive electrode current collector of at least one of the plurality of cells is a surface. Further, at least one of the conditions (iv): that the negative electrode current collector of at least one of the plurality of cells is a SUS having an oxide layer on the surface thereof. Provided is a method for manufacturing a laminated battery, which comprises a heat treatment step of filling and forming the oxide layer by heat treatment in the range of 200 ° C. to 500 ° C.

According to the present disclosure, by forming an oxide layer on the surface of SUS by heat treatment within the above range and using it as a current collector, a laminated battery with a reduced wraparound current can be obtained.

The laminated battery of the present disclosure has an effect that the wraparound current can be reduced.

It is a schematic sectional drawing which shows an example of the laminated battery of this disclosure. It is schematic cross-sectional view explaining the nail piercing test. It is a graph which shows the relationship between a cell position and a short circuit resistance. It is an equivalent circuit explaining the wraparound current. It is schematic cross-sectional view explaining the nail piercing test. 2 is a schematic cross-sectional view illustrating a method for manufacturing a laminated cell. It is a graph which illustrates the voltage profile in a nail piercing test. It is schematic cross-sectional view explaining the test method of a contact resistance test. It is the result of the contact resistance test in Experimental Example 1 and Comparative Experimental Examples 1 to 3.

Hereinafter, the laminated battery and the method for manufacturing the laminated battery of the present disclosure will be described in detail.

A. Laminated Battery FIG. 1 is a schematic cross-sectional view showing an example of the laminated battery of the present disclosure. The laminated battery 100 shown in FIG. 1 has cells 10 (10A, 10B to 10H to:) having a positive electrode current collector 4, a positive electrode active material layer 1, a solid electrolyte layer 3, a negative electrode active material layer 2, and a negative electrode current collector 5 in this order. It has a plurality of 10N) in the thickness direction. Further, the plurality of cells 10 are electrically connected in parallel. The method of parallel connection is not particularly limited, but for example, the cells 10A and 10B shown in FIG. 1 are connected in parallel so as to share the negative electrode current collector 5. The two adjacent cells may or may not share the positive electrode current collector 4 or the negative electrode current collector 5. In the latter case, for example, by forming the positive electrode current collector 4 or the negative electrode current collector 5 in a two-layer configuration, two adjacent cells have a positive electrode current collector 4 or a negative electrode current collector 5 between them. Will have them individually.

Further, the plurality of cells 10 are
Condition (i): All the positive electrode current collectors 4 of the plurality of cells 10 are at least one of Ti, Ti alloy, Fe and Fe alloy, and
Condition (ii): All the negative electrode current collectors 5 of the plurality of cells 10 are at least one of Ti, Ti alloy, Fe and Fe alloy.
One of the features is that at least one of the above conditions is satisfied.

According to the present disclosure, since the plurality of cells satisfy at least one of the condition (i) and the condition (ii), it is possible to obtain a laminated battery having a reduced wraparound current. As described above, when the present inventors have examined in detail a nail piercing test on a laminated battery in which a plurality of cells are electrically connected in parallel, a cell having a small short-circuit resistance and a cell having a large short-circuit resistance are mixed. I got a new finding to do.

This new finding will be described with reference to FIG. As shown in FIG. 2, a nail 110 is pierced into a laminated battery 100 in which a plurality of cells 10 (10A, 10B to 10H to 10N) are electrically connected in parallel. At this time, the short-circuit resistance _R ( _RA , RB to _RH to _RN ) is obtained for each cell 10. As a result of such detailed examination, for example, as shown in FIG. 3, it was found that a cell having a small short-circuit resistance and a cell having a large short-circuit resistance coexist.

When a cell having a small short-circuit resistance and a cell having a large short-circuit resistance coexist, a current flows from a cell having a large short-circuit resistance to a cell having a small short-circuit resistance. For example, as shown in FIG. 4, when cell 10A and cell 10H are electrically connected in parallel and a short circuit occurs in a laminated battery in which the short circuit resistance _RA of the cell 10A is smaller than the short circuit resistance _RH of the cell 10H, Ohm's law occurs. A wraparound current I from the cell 10H to the cell 10A is generated based on the above. When the wraparound current I is generated, the temperature of the cell 10A rises due to Joule heat generation, and as a result, deterioration of the battery material is likely to occur.

The reason why cells with low short-circuit resistance and cells with high short-circuit resistance coexist is not completely clear, but it is presumed as follows. On the surface side of the laminated battery (for example, position P1 in FIG. ₃ ), as shown in FIG. 5, for example, a state in which the positive electrode current collector 4 and the negative electrode current collector 5 are in contact with each other by inserting a nail 110 into the cell 10. In addition, it is presumed that a state in which the positive electrode active material layer 1 and the negative electrode current collector 5 come into contact with each other occurs.

On the other hand, on the center side of the laminated battery (for example, position P ₂ in FIG. 3), the nail enters while entraining the fragments of each member, so that the positive electrode current collector and the negative electrode current collector do not come into contact with each other and the positive electrode. It is presumed that the active material layer and the negative electrode current collector do not come into contact with each other. As the "non-contact state", for example, a state in which debris of the solid electrolyte layer exists between the two, a state in which a void exists between the two, and the like are assumed. As a result, the short-circuit resistance increases on the center side of the laminated battery.

The behavior of the short-circuit resistance on the surface side (for example, the position P3 in FIG. ₃ ) opposite to the nailed surface of the laminated battery may change depending on the configuration of the laminated battery. Then, the short-circuit resistance became smaller in each case. The reason is that the nail enters while entraining more debris of each member, so that the positive electrode current collector and the negative electrode current collector are electrically connected by the debris having high electron conductivity. It is presumed to be.

On the other hand, in the present disclosure, by using a specific material for at least one of the positive electrode current collector and the negative electrode current collector, the contact resistance of the positive electrode current collector and the negative electrode current collector (particularly contact in a high pressure state). Resistance) can be increased. As a result, a laminated battery with a reduced wraparound current can be obtained. In the present disclosure, the positive electrode current collector and the negative electrode current collector may be simply collectively referred to as a current collector.

Further, the problem that a cell having a small short-circuit resistance and a cell having a large short-circuit resistance coexist is a problem that does not occur in a single battery, and can be said to be a problem peculiar to a laminated battery. Further, in a typical all-solid-state laminated battery, all the components are solid, so that the pressure applied to the laminated battery during the nail piercing test is very high. For example, since a high pressure of 100 MPa or more, particularly 400 MPa or more is applied to the tip of the nail in the portion through which the nail passes, it is important to control the short-circuit resistance in a high pressure state. On the other hand, in a liquid battery, since there is a gap in the electrode through which the electrolytic solution permeates, the pressure applied to the battery during the nail piercing test is significantly reduced. That is, it is difficult to conceive of managing short-circuit resistance in a high-voltage state based on the technology of a liquid-based battery.

1. 1. Structure of Laminated Battery The laminated battery of the present disclosure has a plurality of cells having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order in the thickness direction. The total number of cells included in the laminated battery is, for example, 3 or more, may be 10 or more, may be 30 or more, or may be 50 or more. On the other hand, the total number of cells is, for example, 200 or less, may be 150 or less, or may be 100 or less.

Further, the plurality of cells are: Condition (i): All positive current collectors of the plurality of cells are at least one of Ti, Ti alloy, Fe and Fe alloy, Condition (ii): All of the plurality of cells. The negative electrode current collector satisfies at least one of the conditions of at least one of Ti, Ti alloy, Fe and Fe alloy.

Here, Ti and Fe mean a simple substance of Ti and a simple substance of Fe, respectively. On the other hand, the Ti alloy and the Fe alloy mean an alloy containing Ti as a main component and an alloy containing Fe as a main component, respectively. Examples of Fe alloys include stainless steel (SUS), with SUS304 being preferred.

In the condition (i), all the positive electrode current collectors of the plurality of cells may be one kind of Ti, Ti alloy, Fe and Fe alloy, or two or more kinds. Similarly, under the condition (ii), all the negative electrode current collectors of the plurality of cells may be one kind of Ti, Ti alloy, Fe and Fe alloy, or two or more kinds. For example, all current collectors in a plurality of cells may be at least one of Ti and Ti alloys and at least one of Fe and Fe alloys.

Further, in the condition (i), at least one positive electrode current collector of the plurality of cells may be Ti or a Ti alloy. Similarly, under condition (ii), at least one negative electrode current collector in the plurality of cells may be Ti or a Ti alloy. Compared with, for example, SUS, Ti or a Ti alloy has an excellent effect that the resistance can be reduced during normal use (electron conductivity can be increased) and at the same time, the contact resistance can be increased during a short circuit. The ratio of the positive electrode current collector, which is Ti or a Ti alloy, to all the positive electrode current collectors is, for example, 50% or more, 70% or more, or 90% or more. The ratio of the negative electrode current collector, which is Ti or a Ti alloy, to all the negative electrode current collectors is, for example, 50% or more, 70% or more, or 90% or more.

Further, under the condition (i), it is preferable that at least one positive electrode current collector of the plurality of cells is an Fe alloy. Similarly, under condition (ii), at least one negative electrode current collector of the plurality of cells may be an Fe alloy. The Fe alloy is preferably SUS. Further, it is preferable that the SUS has an oxide layer on the surface. Further, the oxide layer is preferably an oxide film of SUS. The thickness of the oxide layer is, for example, 10 nm or more, and may be 20 nm or more. The ratio of the positive electrode current collector, which is SUS having an oxide layer on the surface, to all the positive electrode current collectors is, for example, 50% or more, 70% or more, or 90% or more. .. The ratio of the negative electrode current collector, which is SUS having an oxide layer on the surface, to all the negative electrode current collectors is, for example, 50% or more, 70% or more, or 90% or more. ..

Further, when the plurality of cells satisfy the condition (i), any negative electrode current collector can be used as the negative electrode current collector. Above all, the negative electrode current collector of at least one of the plurality of cells is preferably Cu or a Cu alloy. The ratio of the negative electrode current collector, which is Cu or a Cu alloy, to all the negative electrode current collectors is, for example, 50% or more, 70% or more, or 90% or more.

Further, in the present disclosure, the contact resistance of the positive electrode current collector and the negative electrode current collector under a pressure of 100 MPa may be 0.037 Ω · cm ² or more in all of the plurality of cells, 0.047 Ω · ·. It may be cm ² or more, and may be 0.103 Ω · cm ² or more. On the other hand, the contact resistance of the positive electrode current collector and the negative electrode current collector under a pressure of 100 MPa may be 0.277Ω · cm ² or less in all of the plurality of cells.

Further, in the laminated battery after the nail piercing test, the short-circuit resistance of the cell having the smallest short-circuit resistance is defined as R _Min , and the short-circuit resistance of the cell having the largest short-circuit resistance is defined as R _Max . For example, when a metal active material (particularly Si or Si alloy) is used as the negative electrode active material, the value of R _Max / R _Min is preferably 100 or less, and more preferably 5.0 or less. The conditions for the nail piercing test are the conditions described in Reference Examples 1 and 2 described later.

2. 2. Cell The cell in the present disclosure has a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order. The cell is typically a cell utilizing Li ion conduction (Li ion cell). Further, the cell is preferably a cell (secondary battery) that can be charged and discharged.

(1) Positive Electrode Collector and Negative Electrode Collector The positive electrode collector collects the above-mentioned positive electrode active material layer, and the negative electrode pole collector collects the above-mentioned negative electrode active material layer. The metal elements contained in the positive electrode current collector are as described above. Examples of the shape of the positive electrode current collector include a foil shape and a mesh shape. The thickness of the positive electrode current collector is, for example, 0.1 μm or more, and may be 1 μm or more. If the positive electrode current collector is too thin, the current collector function may be reduced. On the other hand, the thickness of the positive electrode current collector is, for example, 1 mm or less, and may be 100 μm or less. If the positive electrode current collector is too thick, the energy density of the battery may be low.

The metal elements contained in the negative electrode current collector are as described above. Examples of the shape of the negative electrode current collector include a foil shape and a mesh shape. The thickness of the negative electrode current collector is, for example, 0.1 μm or more, and may be 1 μm or more. If the negative electrode current collector is too thin, the current collector function may be reduced. On the other hand, the thickness of the negative electrode current collector is, for example, 1 mm or less, and may be 100 μm or less. If the negative electrode current collector is too thick, the energy density of the battery may be low.

(2) Negative electrode active material layer The negative electrode active material layer contains at least a negative electrode active material, and may contain at least one of a solid electrolyte material, a conductive material, and a binder, if necessary.

The negative electrode active material is not particularly limited, and examples thereof include a metal active material, a carbon active material, and an oxide active material. Examples of the metal active material include simple substances and metal alloys. Examples of the metal element contained in the metal active material include Si, Sn, In, Al and the like. The metal alloy is preferably an alloy containing the above metal element as a main component. Examples of Si alloys include Si—Al alloys, Si—Sn alloys, Si—In alloys, Si—Ag alloys, Si—Pb alloys, Si—Sb alloys, Si—Bi alloys, and Si—. Examples thereof include Mg-based alloys, Si—Ca based alloys, Si—Ge based alloys, and Si—Pb based alloys. For example, the Si—Al alloy means an alloy containing at least Si and Al, and may be an alloy containing only Si and Al, or an alloy containing another metal element. good. The same applies to alloys other than Si—Al alloys. The metal alloy may be a two-component alloy or a three-component or higher multi-component alloy.

On the other hand, examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, soft carbon and the like. Examples of the oxide active material include lithium titanate such as Li ₄ Ti ₅ O ₁₂ .

Examples of the shape of the negative electrode active material include particles. The average particle size (D ₅₀ ) of the negative electrode active material is, for example, in the range of 10 nm to 50 μm, and may be in the range of 100 nm to 20 μm. The ratio of the negative electrode active material in the negative electrode active material layer is, for example, 50% by weight or more, and may be in the range of 60% by weight to 99% by weight.

The solid electrolyte material is not particularly limited, and examples thereof include an inorganic solid electrolyte material such as a sulfide solid electrolyte material and an oxide solid electrolyte material. Examples of the sulfide solid electrolyte material include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -LiI-LiBr, Li ₂ SP ₂ S. ₅ -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S- SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (where m and n are positive numbers. Z is any of Ge, Zn, Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers; M is any of P, Si, Ge, B, Al, Ga and In). The above description of "Li ₂ SP _{2 S 5" means a sulfide solid electrolyte material using a raw material composition containing Li 2 S and P 2 S 5 , and} the same applies to other descriptions. be.

In particular, the sulfide solid electrolyte material preferably comprises an ionic conductor containing Li, A (A is at least one of P, Si, Ge, Al and B), and S. Further, the above-mentioned ionic conductor contains an anion structure (PS ₄ ^3- structure, SiS ₄ ^4- structure, GeS ₄ ^4- structure, AlS ₃ ^3- structure, BS ₃ ^3- structure) having an ortho composition as a main component of the anion. It is preferable to have. This is because it can be used as a sulfide solid electrolyte material with high chemical stability. The ratio of the anion structure of the ortho composition is preferably 70 mol% or more, more preferably 90 mol% or more, with respect to the total anion structure in the ionic conductor. The proportion of anionic structure in the ortho composition can be determined by Raman spectroscopy, NMR, XPS and the like.

The sulfide solid electrolyte material may contain lithium halide in addition to the above-mentioned ionic conductor. Examples of lithium halide include LiF, LiCl, LiBr and LiI, and among them, LiCl, LiBr and LiI are preferable. The ratio of LiX (X = I, Cl, Br) in the sulfide solid electrolyte material is, for example, in the range of 5 mol% to 30 mol%, and may be in the range of 15 mol% to 25 mol%.

The solid electrolyte material may be a crystalline material or an amorphous material. Further, the solid electrolyte material may be glass or crystallized glass (glass ceramics). Examples of the shape of the solid electrolyte material include particles.

Examples of the conductive material include carbon materials such as acetylene black (AB), Ketjen black (KB), carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). Examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF).

The thickness of the negative electrode active material layer is, for example, in the range of 0.1 μm to 300 μm, and may be in the range of 0.1 μm to 100 μm.

(3) Positive Electrode Active Material Layer The positive electrode active material layer contains at least one positive electrode active material, and may contain at least one of a solid electrolyte material, a conductive material, and a binder, if necessary.

The positive electrode active material is not particularly limited, and examples thereof include an oxide active material. Examples of the oxide active material include rock salt layered active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , Li ₄ Examples thereof include spinel-type active materials such as Ti ₅ O ₁₂ and Li (Ni _0.5 Mn _1.5 ) O ₄ , and olivine-type active materials such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , and LiCoPO ₄ . Further, as the oxide active material, Li _{1 + x} Mn _{2- xy My} O ₄ (M is at least one of Al, Mg, Co, Fe, Ni and Zn, 0 <x + y <2). A spinel active material, lithium titanate, or the like may be used.

Further, a coat layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material. This is because the reaction between the positive electrode active material and the solid electrolyte material can be suppressed. Examples of the Li ion conductive oxide include LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , and Li ₃ PO ₄ . The thickness of the coat layer is, for example, in the range of 0.1 nm to 100 nm, and may be in the range of 1 nm to 20 nm. The coverage of the coat layer on the surface of the positive electrode active material is, for example, 50% or more, and may be 80% or more.

The solid electrolyte material, the conductive material, and the binder used for the positive electrode active material layer are the same as those described in the above "(2) Negative electrode active material layer", and thus the description thereof is omitted here. The thickness of the positive electrode active material layer is, for example, in the range of 0.1 μm to 300 μm, and may be in the range of 0.1 μm to 100 μm.

(4) Solid electrolyte layer The solid electrolyte layer is a layer formed between the positive electrode active material layer and the negative electrode current collector. Further, the solid electrolyte layer may contain at least a solid electrolyte material, and may further contain a binder, if necessary. The solid electrolyte material and the binder used for the solid electrolyte layer are the same as those described in "(2) Negative electrode active material layer" above, and thus the description thereof is omitted here.

The content of the solid electrolyte material in the solid electrolyte layer is, for example, in the range of 10% by weight to 100% by weight, and may be in the range of 50% by weight to 100% by weight. The thickness of the solid electrolyte layer may be, for example, in the range of 0.1 μm to 300 μm, or may be in the range of 0.1 μm to 100 μm.

B. Method for Manufacturing a Laminated Battery The method for manufacturing a laminated battery of the present disclosure is the method for manufacturing a laminated battery for manufacturing the laminated battery according to the above "A. Laminated battery", wherein the plurality of cells are the condition (iii) :. The positive electrode current collector of at least one of the plurality of cells is a SUS having an oxide layer on the surface, and the condition (iv): the negative electrode current collector of at least one of the plurality of cells is on the surface. It further satisfies at least one of the conditions of SUS having an oxide layer, and has a heat treatment step of forming the oxide layer by heat treatment in the range of 200 ° C. to 500 ° C.

According to the present disclosure, by forming an oxide layer on the surface of SUS by heat treatment within the above range and using it as a current collector, a laminated battery with a reduced wraparound current can be obtained.

The heat treatment temperature is usually in the range of 200 ° C to 500 ° C. When the heat treatment temperature is within the above range, the contact resistance can be sufficiently increased. The heat treatment time is not particularly limited, but is, for example, 10 minutes or more, and may be 60 minutes or more. On the other hand, the heat treatment time is, for example, 24 hours or less, and may be 6 hours or less. The heat treatment atmosphere is preferably an atmosphere in which oxygen is present, and more preferably an air atmosphere. Moreover, as a heat treatment apparatus, for example, a firing furnace can be mentioned. Further, the assembly process of the laminated battery can be performed in the same manner as the general assembly process, and is not particularly limited.

The present disclosure is not limited to the above embodiment. The above embodiment is an example, and any object having substantially the same structure as the technical idea described in the claims of the present disclosure and having the same effect and effect is the present invention. Included in the technical scope of the disclosure.

The present disclosure will be described in more detail. First, in Reference Examples 1 and 2, it was confirmed that cells having a small short-circuit resistance and cells having a large short-circuit resistance coexist in the conventional laminated battery.

[Reference Example 1]
(Preparation of positive electrode)
LiNbO ₃ was coated on the positive electrode active material (Li _1.15 Ni _1/3 Co _1/3 Mn _1/3 W _0.005 O ₂ ) in the atmospheric environment using a rolling flow coating device (manufactured by Paulec). .. Then, firing was carried out in an atmospheric environment to form a coat layer containing LiNbO ₃ on the surface of the positive electrode active material. As a result, a positive electrode active material having a coat layer on the surface was obtained.

Next, a polypropylene (PP) container contains butyl butyrate, a 5 wt% butyl butyrate solution of a PVDF-based binder (manufactured by Kureha), the obtained positive electrode active material, and a sulfide solid electrolyte material (LiI and LiBr). Li ₂ SP ₂ S ₅ series glass ceramics, average particle size D ₅₀ = 0.8 μm) and a conductive material (gas phase growth carbon fiber, VGCF, manufactured by Showa Denko), positive electrode active material: sulfide solid The electrolyte material: conductive material: binder = 85: 13: 1: 1 was added in a weight ratio. Next, the PP container was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT). Next, the PP container was shaken with a shaker (manufactured by Shibata Scientific Technology, TTM-1) for 3 minutes, and further stirred with an ultrasonic disperser for 30 seconds to obtain a coating liquid.

Next, an Al foil (made in Japan, positive electrode current collector) was prepared. The obtained coating liquid was applied onto the Al foil by the blade method using an applicator. The coated electrode was naturally dried and then dried on a hot plate at 100 ° C. for 30 minutes to form a positive electrode active material layer on one surface of the positive electrode current collector. Next, it was cut according to the battery size to obtain a positive electrode.

(Manufacturing of negative electrode)
In a PP container, butyl butyrate, a 5 wt% butyl butyrate solution of PVDF-based binder (made by Kureha), a negative electrode active material (silicon, high-purity chemical, average particle size D ₅₀ = 5 μm), and a sulfide solid electrolyte. A material (Li ₂ SP ₂ S ₅ series glass ceramics containing LiI and LiBr, average particle size D ₅₀ = 0.8 μm) and a conductive material (gas phase growth carbon fiber, VGCF, manufactured by Showa Denko) are used. Negative electrode active material: sulfide solid electrolyte material: conductive material: binder = 55: 42: 2: 1 was added in a weight ratio. Next, the PP container was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT). Next, the PP container was shaken with a shaker (manufactured by Shibata Scientific Technology, TTM-1) for 30 minutes, and further stirred with an ultrasonic disperser for 30 seconds to obtain a coating liquid.

Next, as shown in FIG. 6A, a Cu foil (negative electrode current collector 5) was prepared. The obtained coating liquid was applied onto the Cu foil by the blade method using an applicator. The coated electrode was air-dried and then dried on a hot plate at 100 ° C. for 30 minutes. As a result, as shown in FIG. 6B, the negative electrode active material layer 2 was formed on one surface of the Cu foil (negative electrode current collector 5). Then, the same treatment was carried out, and as shown in FIG. 6C, the negative electrode active material layer 2 was formed on the other surface of the Cu foil (negative electrode current collector 5). Next, it was cut according to the battery size to obtain a negative electrode.

(Preparation of solid electrolyte layer)
In a PP container, a 5 wt% heptane solution of heptane and a butylene rubber binder (manufactured by JSR), a sulfide solid electrolyte material (Li ₂ SP ₂ S ₅ glass ceramics containing LiI and LiBr), average particle size. D ₅₀ = 2.5 μm) was added. Next, the PP container was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT). Next, the PP container was shaken with a shaker (manufactured by Shibata Scientific Technology, TTM-1) for 30 minutes, and further stirred with an ultrasonic disperser for 30 seconds to obtain a coating liquid.

Next, Al foil (made in Japan) was prepared. The obtained coating liquid was applied onto the Al foil by the blade method using an applicator. The coated electrode was air-dried and then dried on a hot plate at 100 ° C. for 30 minutes. Next, it was cut according to the battery size to obtain a transfer member having an Al foil and a solid electrolyte layer.

(Manufacturing of evaluation battery)
The two obtained transfer members were placed on the negative electrode active material layers formed on both sides of the negative electrode current collector, respectively, and were subjected to a cold isotropic pressure pressurization method (CIP method) at a pressure of 4 ton / cm ² . Pressed. Then, the Al foil of the transfer member was peeled off. As a result, as shown in FIG. 6D, the solid electrolyte layer 3 was formed on the negative electrode active material layer 2. Next, the two positive electrodes obtained above were placed on the solid electrolyte layers formed on both sides of the negative electrode current collector, respectively, and 4ton / cm ² was subjected to the cold isotropic pressure pressurization method (CIP method). Pressed with the pressure of. As a result, as shown in FIG. 6 (e), the positive electrode active material layer 1 and the positive electrode current collector 4 were formed on the solid electrolyte layer 3. In this way, two laminated cells were obtained. Further, 30 of the obtained two laminated cells were laminated and sealed with an aluminum laminated film to obtain an evaluation battery.

[Reference Example 2]
(Manufacturing of negative electrode)
In a PP container, butyl butyrate, a 5 wt% butyl butyrate solution of PVDF-based binder (made by Kureha), a negative electrode active material (natural graphite, made by Nippon Carbon, average particle size D ₅₀ = 10 μm), and a sulfide solid electrolyte. The material (Li ₂ SP ₂ S ₅ series glass ceramics containing LiI and LiBr, average particle size D ₅₀ = 0.8 μm) was used as the negative electrode active material: sulfide solid electrolyte material: binder = 59: 40: 1. Added by weight. Next, the PP container was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT). Next, the PP container was shaken with a shaker (manufactured by Shibata Scientific Technology, TTM-1) for 30 minutes, and further stirred with an ultrasonic disperser for 30 seconds to obtain a coating liquid.

(Manufacturing of evaluation battery)
Two laminated cells were obtained in the same manner as in Reference Example 1 except that the obtained coating liquid was used. Further, an evaluation battery was obtained in the same manner as in Reference Example 1 except that 40 of the obtained two laminated cells were laminated.

[evaluation]
The evaluation batteries obtained in Reference Examples 1 and 2 were subjected to a nail piercing test under the following conditions.
Charge status: Not charged Resistance meter: Hioki RM3542
Nail: SK material (φ8 mm, tip angle 60 °)
Nail speed: 25 mm / sec

The short-circuit resistance of the cell was obtained from the voltage profile at the time of nailing. An example of the voltage profile is shown in FIG. As shown in FIG. 7, the voltage of the cell drops due to the time of nailing. Here, the initial voltage is V ₀ , and the minimum voltage at the time of nailing is V. Further, the internal resistance of the cell is measured in advance, and the internal resistance is defined as r. Further, the short-circuit resistance of the cell is R. Assuming that all the currents generated by the voltage drop at the time of nailing are short-circuit currents, the relationship of V / R = (V ₀ −V) / r holds. From this relationship, the short-circuit resistance R of the cell can be calculated. The voltage profiles of each cell were collected and the change in short-circuit resistance in the thickness direction was confirmed. The results are shown in Tables 1 and 2. The short-circuit resistance values in Tables 1 and 2 are relative values when the short-circuit resistance of the first cell is 1. The cell close to the nail piercing surface was designated as the first cell.

As shown in Tables 1 and 2, in Reference Examples 1 and 2, the short-circuit resistance of the first cell was larger than the short-circuit resistance of the tenth cell. It is presumed that this is because the insulating part of the laminated film was caught in the nail piercing. Further, in Reference Example 1, the short-circuit resistance of the 40th cell is larger than the short-circuit resistance of the 1st cell or the 10th cell, and in Reference Example 2, the short-circuit resistance of the 60th cell is the 1st cell or the 10th cell. It was larger than the short-circuit resistance of. In this way, it was confirmed that cells with low short-circuit resistance and cells with high short-circuit resistance coexist.

[Comparative Experiment Example 1]
An Al foil (thickness 15 μm, manufactured by UACJ 1N30) was prepared as a positive electrode current collector, and a Cu foil (thickness 12 μm, manufactured by Furukawa Electric, electrolytic Cu foil) was prepared as a negative electrode current collector.

[Experimental Example 1]
A SUS foil (SUS304, thickness 15 μm, manufactured by Toyo Seiho) was prepared as a positive electrode current collector, and a Cu foil (thickness 12 μm, thickness 12 μm, manufactured by Furukawa Electric, electrolytic Cu foil) was prepared as a negative electrode current collector.

[Experimental Example 2]
Ti foil (thickness 10 μm, TR207C-H manufactured by Takeuchi Metal Foil Powder Industry) is prepared as a positive electrode current collector, and Cu foil (thickness 12 μm, manufactured by Furukawa Electric, electrolytic Cu foil) is prepared as a negative electrode current collector. did.

[Experimental Example 3]
An Al foil (thickness 15 μm, manufactured by UACJ 1N30) was prepared as a positive electrode current collector, and an Fe foil (thickness 10 μm, manufactured by Takeuchi Metal Foil Powder Industry) was prepared as a negative electrode current collector.

[Experimental Example 4]
Fe foil (thickness 10 μm, manufactured by Takeuchi Metal Foil Powder Industry) was prepared as a positive electrode current collector, and Cu foil (thickness 12 μm, manufactured by Furukawa Electric, electrolytic Cu foil) was prepared as a negative electrode current collector.

[evaluation]
The contact resistances of the positive electrode current collector and the negative electrode current collector prepared in Comparative Experimental Example 1 and Experimental Examples 1 to 4 were measured. Specifically, as shown in FIG. 8, the negative electrode current collector 5 is arranged on the bakelite plate 21, the capton film 22 having a penetration portion is arranged on the negative electrode current collector 5, and the positive electrode is arranged on the capton film 22. The current collector 4 was arranged. Further, the SK material block 23 having a diameter of 11.28 mm was arranged on the positive electrode current collector 4 so as to overlap the penetrating portion of the Kapton film 22 in a plan view. In this state, the resistance value when 100 MPa was applied was measured by an autograph 24 with a resistance meter (RM3542 manufactured by Hioki). The results are shown in Table 3.

As shown in Table 3, it was confirmed that Experimental Examples 1 to 4 had a larger contact resistance at 100 MPa than Comparative Experimental Example 1. In particular, the Ti used in Experimental Example 2 has more than twice the contact resistance at 100 MPa as compared with the SUS used in Experimental Example 1. Here, the specific resistances of the current collectors used in Experimental Examples 1 to 4 and Comparative Experimental Example 1 were examined. Table 4 shows the specific resistance of each current collector.

As shown in Tables 3 and 4, it was confirmed that Ti used in Experimental Example 2 has an excellent effect of having a small specific resistance and a large contact resistance as compared with the SUS used in Experimental Example 1. .. That is, it was confirmed that Ti has an excellent effect that the resistance can be reduced (the electron conductivity can be increased) during normal use and the contact resistance can be increased at the time of short circuit, as compared with SUS.

[Comparative Experiment Example 2]
An Al foil (thickness 15 μm, UACJ 1N30) was prepared as a positive electrode current collector. On the other hand, a conductive material (furness black, average primary particle size 66 nm, manufactured by Tokai Carbon), a filler (alumina, CB-P02 manufactured by Showa Denko) and PVDF (KF polymer L # 9130 manufactured by Kureha) are used. A paste was prepared by mixing with N-methylpyrrolidone (NMP) so that the volume ratio was PVDF = 10: 60: 30. The obtained paste is applied to a Cu foil (thickness 12 μm, manufactured by Furukawa Electric Co., Ltd., electrolytic Cu foil) so that the thickness after drying is 10 μm, and dried in a drying oven to form a coat layer. did. The obtained Cu foil was prepared as a negative electrode current collector.

[Comparative Experiment Example 3]
Conductive material (furness black, average primary particle size 66 nm, manufactured by Tokai Carbon), filler (alumina, CB-P02 manufactured by Showa Denko) and PVDF (KF polymer L # 9130 manufactured by Kureha), conductive material: filler: PVDF = A paste was prepared by mixing with N-methylpyrrolidone (NMP) so as to have a volume ratio of 10:60:30. The obtained paste was applied to an Al foil (thickness 15 μm, 1N30 manufactured by UACJ) so that the thickness after drying was 10 μm, and dried in a drying oven to form a coat layer. The obtained Al foil was prepared as a positive electrode current collector. On the other hand, a Cu foil (thickness 12 μm, manufactured by Furukawa Electric Co., Ltd., electrolytic Cu foil) was prepared as a negative electrode current collector.

[evaluation]
The contact resistance of the positive electrode current collector and the negative electrode current collector prepared in Experimental Example 1 and Comparative Experimental Examples 1 to 3 was measured. The method for measuring the contact resistance is as described above, but the applied pressure was changed from 0.1 MPa to 100 MPa. The results are shown in Table 5 and FIG.

As shown in Table 5 and FIG. 9, it was confirmed that the tendency of contact resistance was completely different between 0.1 MPa (low pressure state) and 100 MPa (high pressure state). Specifically, at 0.1 MPa (low pressure state), the contact resistance is higher in the order of Comparative Experimental Example 2, Comparative Experimental Example 3, Experimental Example 1, and Comparative Experimental Example 1, but at 100 MPa (high pressure state), the contact resistance is high. , Comparative Experimental Example 2 and Experimental Example 1 were almost the same and highest, followed by Comparative Experimental Example 3 and Comparative Experimental Example 1. In order to reduce the wraparound current, it is important that the contact resistance is high in the high voltage state, but this tendency is difficult to assume based on the contact resistance in the low voltage state (for example, the contact resistance assumed from the specific resistance). Further, as shown in FIG. 9, it was confirmed that the SUS used in Experimental Example 1 has an excellent effect that the reduction rate of the contact resistance is small even when the low pressure state is changed to the high pressure state. ..

[Experimental Example 5]
The SUS foil (SUS304, thickness 15 μm, manufactured by Toyo Seiho) was heat-treated at 200 ° C. for 1 hour under the conditions of air atmosphere to form an oxide layer (oxide film of SUS) on the surface. The obtained SUS foil was prepared as a positive electrode current collector, and a Cu foil (thickness 12 μm, manufactured by Furukawa Electric Co., Ltd., electrolytic Cu foil) was prepared as a negative electrode current collector.

[Experimental Example 6]
A SUS foil (SUS304, thickness 15 μm, manufactured by Toyo Seiho) was heat-treated at 500 ° C. for 1 hour under the conditions of air atmosphere to form an oxide layer (SUS oxide film) on the surface. The obtained SUS foil was prepared as a positive electrode current collector, and a Cu foil (thickness 12 μm, manufactured by Furukawa Electric Co., Ltd., electrolytic Cu foil) was prepared as a negative electrode current collector.

[Experimental Example 7]
A SUS foil (SUS304, thickness 15 μm, manufactured by Toyo Seiho) was heat-treated at 700 ° C. for 1 hour under the conditions of air atmosphere to form an oxide layer (SUS oxide film) on the surface. The obtained SUS foil was prepared as a positive electrode current collector, and a Cu foil (thickness 12 μm, manufactured by Furukawa Electric Co., Ltd., electrolytic Cu foil) was prepared as a negative electrode current collector.

[evaluation]
The contact resistances of the positive electrode current collector and the negative electrode current collector prepared in Experimental Examples 1 and 5 to 7 were measured. The method for measuring the contact resistance is as described above. The results are shown in Table 6.

As shown in Table 6, it is suggested that by forming an oxide layer on the surface of SUS, the contact resistance is increased and the wraparound current can be reduced. In particular, Experimental Examples 5 and 6 heat-treated at 200 ° C. and 500 ° C. had higher contact resistance than Experimental Example 7 heat-treated at 700 ° C. In Experimental Example 7, sensitization (a phenomenon in which a Cr-deficient layer is formed by the binding of C and Cr in SUS and the corrosion resistance is lowered) may have occurred.

1 ... Positive electrode active material layer 2 ... Negative electrode active material layer 3 ... Solid electrolyte layer 4 ... Positive electrode current collector 5 ... Negative electrode current collector 10 ... Cell 100 ... Laminated battery 110 ... Nail

Claims (4)

A stack having a plurality of cells having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order in the thickness direction, and the plurality of cells are electrically connected in parallel. It ’s a battery manufacturing method .
The plurality of cells are
Condition (i): All the positive electrode current collectors of the plurality of cells satisfy the condition that they are at least one of Ti, Fe and SUS304.
The negative electrode current collector at least one of the plurality of cells is Cu or a Cu alloy.
The solid electrolyte layer contains an inorganic solid electrolyte material .
The plurality of cells are
Condition (iii): The positive electrode current collector at least one of the plurality of cells is SUS304 having an oxide layer on the surface, further satisfying the condition.
A method for manufacturing a laminated battery, comprising a heat treatment step of forming the oxide layer by heat treatment in the range of 200 ° C. to 500 ° C. The method for manufacturing a laminated battery according to claim 1, wherein in the condition (i), at least one of the positive electrode current collectors of the plurality of cells is Ti. The method for manufacturing a laminated battery according to claim 1 or 2, wherein the number of cells included in the laminated battery is 10 or more. The method for manufacturing a laminated battery according to any one of claims 1 to 3, wherein the negative electrode active material layer contains Si as a negative electrode active material.

Images