JP2007257863A - Electrolyte layer for lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte layer achieving a lithium ion secondary battery suppressing electrolyte leakage, and enhancing the battery output or the volume output density. <P>SOLUTION: The electrolyte layer 410 for the lithium ion secondary battery contains a frame made of a polymer electrolyte 411 and an electrolyte 415 filled in a space formed with the frame. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrolyte layer for a lithium ion secondary battery, and more particularly to an electrolyte layer for a lithium ion secondary battery that can suppress both a decrease in battery output and leakage of the electrolyte.

  Conventional electrolyte layers used for lithium ion secondary batteries consisted of only “electrolyte” or “polymer electrolyte”.

  When using an “electrolyte”, the lithium ion secondary battery is conventionally filled with the electrolyte, or the electrolyte layer is surrounded by a sealing member made of elastomer or the like so that the electrolyte exists only between the electrodes. It had a sealed structure.

In the case of using “polymer electrolyte”, conventionally, the polymer electrolyte is arranged between the electrodes. Patent Document 1 discloses a lithium ion secondary battery using a gel electrolyte as a polymer electrolyte.
JP 11-354158 A

  However, when only the electrolytic solution is used, there is a problem that the electrolytic solution leaks due to damage to the exterior of the secondary battery. On the other hand, when the seal member is used, the leakage is suppressed, but the battery output is reduced as compared with the case where only the electrolyte is used because the seal member contacts a part of the electrode surface. was there. In order to solve this problem, if the seal member is not in contact with a part of the electrode surface, it becomes necessary to form an extra space in the secondary battery, and the output density per unit volume of the secondary battery (hereinafter referred to as “ There is a problem that the volume output density ”is also reduced.

  In addition, when the polymer electrolyte is used, the leakage is suppressed, but the ionic conductivity of the polymer electrolyte is inferior to that of the electrolytic solution, so that there is a problem that the battery output is reduced as compared with the case of using the electrolytic solution. It was.

  In order to solve the above-described problems, an object of the present invention is to provide an electrolyte layer capable of realizing a lithium ion secondary battery in which leakage is suppressed and volume output density or battery output is excellent.

  The present inventors have found that the above problem can be solved by using a polymer electrolyte instead of a conventional seal member, and have completed the present invention.

  That is, this invention solves the said subject with the electrolyte layer for lithium ion secondary batteries characterized by including the frame which consists of a polymer electrolyte, and the electrolyte solution with which the space formed of the said frame was filled.

  According to the present invention, it is possible to provide an electrolyte layer capable of realizing a lithium ion secondary battery in which leakage is suppressed and the battery output or volume output density is excellent.

  A first aspect of the present invention is an electrolyte layer for a lithium ion secondary battery comprising a frame made of a polymer electrolyte and an electrolytic solution filled in a space formed by the frame.

  According to the first aspect of the present invention, it is possible to use an electrolyte solution that is more excellent in ion conductivity than a polymer electrolyte. Further, since a polymer electrolyte is used instead of a conventional sealing member that does not have a function as an electrolyte, a leakage occurs. The liquid and the decrease in battery output or volume output density can be suppressed.

  The shape of the frame made of the polymer electrolyte is not particularly limited. For example, the polymer electrolyte 111 may be arranged in a frame shape as illustrated in the schematic plan view of the electrolyte layer in FIG. To D, the polymer electrolyte 111 may be arranged in a frame shape, and may be further arranged in a stripe shape, a bun shape, a honeycomb shape, a grid shape, or the like. In FIG. 1, reference numeral 110 denotes an electrolyte layer. FIG. 1 is merely an example, and the shape of each component of the electrolyte layer in the present invention is not limited to FIG.

  The volume ratio of the polymer electrolyte to the electrolytic solution is preferably 1: 0.1 to 1: 2, more preferably 1: 1 to 1: 1.6, and particularly preferably 1: 1.3. If the volume of the electrolyte when the volume of the polymer electrolyte is 1 is 0.1 or more, the battery output is excellent compared to a secondary battery using only the polymer electrolyte, and if it is 2 or less, a frame made of the polymer electrolyte This is preferable because the volume of the electrolyte does not become too large with respect to the volume of the electrolyte, and the leakage of the electrolyte can be suppressed.

  The thickness of the electrolyte portion of the electrolyte layer is preferably 35 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. A thickness of 35 μm or less is preferable because battery output is improved.

  Details of the electrolytic solution and the polymer electrolyte constituting the electrolyte layer of the present invention are described below.

(Electrolyte)
As the electrolytic solution, a conventionally known one such as a solution in which a supporting salt is dissolved in a nonaqueous solvent can be used.

  Non-aqueous solvents include propylene carbonate and cyclic carbonates such as ethylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1, 2-dimethoxyethane, 1,2-dibutoxyethane, and ethers such as 1,3-dioxolane and diethyl ether; lactones such as γ-butyrolactone; nitriles such as acetonitrile; esters such as methyl propionate; dimethyl Amides such as formamide; esters such as methyl acetate and methyl formate; sulfolane; dimethyl sulfoxide; and 3-methyl-1,3-oxazolidine-2-one Such as at least one may be preferably mentioned.

Examples of the supporting salt include inorganic acid ion salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiTaF ₆ , LiAlCl ₄ , and Li ₂ B ₁₀ Cl ₁₀ , and Li (C ₂ F ₅ SO ₂ ) ₂ N At least one lithium salt selected from the group consisting of organic acid anion salts such as Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ , and Li (C ₂ F ₅ SO ₂ ) ₂ N Preferably mentioned. The electrolytic solution may contain other additives depending on the purpose.

(Polymer electrolyte)
The polymer electrolyte can be classified into an intrinsic polymer electrolyte and a gel electrolyte. In the present invention, both are preferable, and a gel electrolyte is more preferable. Further, as illustrated in FIG. 2, an intrinsic polymer electrolyte 212 and a gel electrolyte 213 may be used in combination as the polymer electrolyte 211. In FIG. 2, reference numeral 210 denotes an electrolyte layer, and reference numeral 215 denotes an electrolytic solution. FIG. 2 is merely an example, and the shape of each component of the electrolyte layer in the present invention is not limited to FIG.

(Intrinsic polymer electrolyte)
An intrinsic polymer electrolyte is a solid electrolyte made of a polymer. Intrinsic polymer electrolytes have the advantage that there is no risk of liquid leakage because the electrolyte does not contain an electrolyte and the safety is high. As the polymer constituting the intrinsic polymer electrolyte, conventionally known polymers such as polyethylene oxide, polypropylene oxide, polyester resin, aramid resin, polyolefin resin, copolymers thereof, and alloys thereof are preferably exemplified. Preferred examples of the polyester resin include PET, preferred examples of the aramid resin include para aromatic polyamide and meta aromatic polyamide, and preferred examples of the polyolefin resin include polyethylene and polypropylene.

  In order to improve ion conductivity, an intrinsic polymer electrolyte may be obtained by introducing an ionic dissociation group such as a carboxylic acid group, a phosphoric acid group, a sulfonic acid group, or a siloxylamine group.

  Examples of the method for producing an intrinsic polymer electrolyte include a method in which a polymer electrolyte raw material and a lithium salt are mixed and polymerized by heat or light.

  Examples of the polymer electrolyte raw material include a polymer constituting the above-described intrinsic polymer electrolyte, an oligomer thereof, or a monomer capable of forming the polymer by polymerization. As lithium salt, what was described in the term of the above-mentioned electrolyte solution is mentioned preferably. In the polymerization, a photopolymerization initiator or a thermal polymerization initiator can be appropriately added.

(Gel electrolyte)
The gel electrolyte is a gel electrolyte in which a polymer forms a three-dimensional network structure by interaction between molecular chains such as chemical bonding, crystallization, or molecular entanglement, and an electrolytic solution is held in the voids. Since the gel electrolyte can be deformed like an elastomer, it has an advantage that it has excellent adhesion to the current collector, or the positive electrode active material layer or the negative electrode active material layer, and can easily suppress leakage.

  As gel electrolyte, the polymer itself holds an electrolyte solution with a true polymer electrolyte having ionic conductivity as a skeleton, or the polymer itself has a ionic conductivity polymer or a polymer with low ionic conductivity as a skeleton. Can be used. The details of the electrolytic solution are as described above.

  As the intrinsic polymer electrolyte contained in the gel electrolyte, those described above can be preferably used. As the polymer having no ion conductivity or a polymer having low ion conductivity, a conventionally known polymer such as polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, a copolymer thereof, or an alloy thereof is preferably used. be able to.

  More preferably, the polymer contained in the gel electrolyte is polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, or polyethylene oxide. The copolymerization ratio of polyvinylidene fluoride and propylene hexafluoride in the vinylidene fluoride-hexafluoropropylene copolymer is not particularly limited and can be appropriately determined according to the purpose. The polyethylene oxide is preferably chemically crosslinked.

  When using gel electrolyte, it is preferable that the ratio of the polymer contained in gel electrolyte is 5-20 mass% with respect to the said gel electrolyte total amount. If it is 5% by mass or more, liquid leakage is further suppressed, and if it is 20% by mass or less, battery output is improved, which is preferable.

  Moreover, when using a polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer as a polymer contained in the gel electrolyte, the ratio of the polymer contained in the gel electrolyte is 10 to 20 mass with respect to the total amount of the gel electrolyte. % Is preferred.

  Moreover, when using the polyethylene oxide chemically crosslinked as a polymer contained in a gel electrolyte, it is preferable that the ratio of the polymer contained in a gel electrolyte is 5-10 mass% with respect to a gel electrolyte total amount.

  A second aspect of the present invention is a lithium ion secondary battery including the above-described electrolyte layer for a lithium ion secondary battery.

  An electrode included in the lithium ion secondary battery includes at least a current collector and an active material layer. In the present invention, the electrode included in the lithium ion secondary battery has a positive electrode active material layer 331 disposed on one surface of a current collector 320 shown in FIG. 3A and a negative electrode active material layer 332 disposed on one surface. A bipolar type including a bipolar type electrode 31 and a current collector 320 having a positive electrode active material layer 331 disposed on both sides thereof shown in FIG. 3B and a current collector 320 having a negative electrode active material layer 332 disposed on both sides thereof. Any non-type electrode 32 is preferable, and the bipolar electrode 31 is more preferable. FIG. 3 is merely an example, and the shape of each component of the electrode included in the lithium ion secondary battery in the present invention is not limited to FIG.

  The lithium ion secondary battery structure other than the electrode is not particularly limited, and a conventionally known structure can be appropriately selected. For example, a structure in which a laminate in which the electrolyte layer of the present invention is disposed between a plurality of the bipolar electrodes may be sealed with an exterior material.

  The shape of the polymer electrolyte constituting the electrolyte layer included in the lithium ion secondary battery of the present invention is not particularly limited, and a polymer is interposed between the positive electrode active material layer 431 and the negative electrode active material layer 432 as shown in FIG. The shape in which the electrolyte 411 is disposed may be employed, or the shape in which the 411 is disposed between the positive electrode active material layer 431 and the negative electrode active material layer 432 and between the current collectors 420 may be employed. In FIG. 4, reference numeral 410 denotes an electrolyte layer, and reference numeral 415 denotes an electrolytic solution. FIG. 4 is merely an example, and the shape of each component of the lithium ion secondary battery in the present invention is not limited to FIG.

  Further, in the present invention, when there is a possibility that the positive electrode active material layer and the negative electrode active material layer are in contact, such as when the volume of the polymer electrolyte is smaller than the volume of the electrolyte, A separator may be disposed between the material layer. For example, the separator is a portion filled with an electrolyte solution between the positive electrode active material layer and the electrolyte layer, between the negative electrode active material layer and the electrolyte layer, or between the positive electrode active material layer and the negative electrode active material layer. Etc. can be arranged.

  A third aspect of the present invention is a vehicle including the above-described electrolyte layer for a lithium ion secondary battery or the above-described lithium ion secondary battery.

  Since the electrolyte layer included in the vehicle of the present invention is excellent in battery output or volume output density, the mass or volume of the secondary battery can be reduced. The fact that the mass or volume occupied by the secondary battery in the vehicle can be reduced is advantageous in terms of vehicle design.

  EXAMPLES Next, although an Example is given and this invention is demonstrated concretely, these Examples do not restrict | limit this invention at all.

Example 1
[Preparation of positive electrode slurry]
A material composed of LiMn ₂ O ₄ [85% by mass] as a positive electrode active material, acetylene black [5% by mass] as a conductive additive, and PVDF [10% by mass] as a binder is weighed in the above ratio, and then applied. NMP was added as a slurry viscosity adjusting solvent until the viscosity became optimum for the process, and mixed to prepare a positive electrode slurry. The NMP is volatilized and removed when the electrode is dried. Therefore, an appropriate amount was added so as to obtain an appropriate slurry viscosity, not an electrode constituent material. Moreover, the said ratio shows the ratio converted with the component except a slurry viscosity adjustment solvent.

[Preparation of negative electrode slurry]
A material composed of hard carbon [90% by mass] as a negative electrode active material and PVDF [10% by mass] as a binder is weighed in the above ratio, and then NMP as a slurry viscosity adjusting solvent until the viscosity becomes optimum for the coating process. Were added and mixed to prepare a negative electrode slurry. The NMP is volatilized and removed when the electrode is dried. Therefore, an appropriate amount was added so as to obtain an appropriate slurry viscosity, not an electrode constituent material. Moreover, the said ratio shows the ratio converted with the component except a slurry viscosity adjustment solvent.

[Production of bipolar electrode]
SUS foil was prepared as a current collector. After applying the positive electrode slurry to one side of each current collector, a positive electrode active material layer was formed on one side of the current collector using a vacuum oven. Subsequently, a negative electrode slurry was applied to the remaining surface of the current collector, and then a bipolar electrode was produced using a vacuum oven.

  In the obtained bipolar electrode, the thickness of the current collector is 80 μm, the plane area is 170 × 120 mm, the thickness of the positive electrode active material layer is 30 μm, the plane area is 130 × 80 mm, The thickness of the material layer was 30 μm, and the plane area was 130 × 80 mm.

[Formation of electrolyte layer and formation of laminate]
An electrolyte layer including a frame made of a gel electrolyte and an electrolytic solution filled in a space formed by the frame was formed on the bipolar electrode.

More specifically, a polymer electrolyte frame including a polymer skeleton made of an electrolyte solution: PVDF (volume ratio 1: 1) was formed on a polyethylene terephthalate (PET) separator. As the electrolytic solution, a mixed solution (volume ratio 1: 1) of propylene carbonate and ethylene carbonate containing 1M LiPF ₆ was used. The resulting polymer electrolyte is a gel electrolyte.

Next, a separator in which a polymer electrolyte frame is formed is laminated on the bipolar electrode so as to be in contact with the positive electrode active material layer, and then propylene carbonate and ethylene carbonate containing 1 M LiPF ₆ in the frame made of the polymer electrolyte. An electrolyte solution composed of a mixed solution (volume ratio 1: 1) was poured, the inside of the frame was filled with the electrolyte solution, and an electrolyte layer exemplified by reference numeral 410 in FIG. 4B described above was formed. Next, a negative electrode active material layer of another bipolar electrode was laminated so as to be in contact with the electrolyte layer (the separator is omitted in FIG. 4B, but the separator includes a positive electrode active material layer 431 and a negative electrode active material layer). 430 between them to prevent contact with 432).

  In the obtained electrolyte layer, the volume ratio of the polymer electrolyte to the electrolytic solution was 1: 1.3, the plane area was 130 × 80 mm, and the thickness of the electrolytic solution portion was 30 μm.

  Thereafter, an electrolyte layer was formed in the same manner on the positive electrode active material layer of the laminated bipolar electrode, and the step of laminating the bipolar electrode was repeated to form a laminate.

[Sealing of laminate]
The laminate was sealed using a laminate sheet to obtain a lithium ion secondary battery.

(Example 2)
A lithium ion secondary battery was obtained in the same manner as in Example 1 except for the following items.

On the separator, polyethylene oxide (30% by mass) as a polymer electrolyte raw material, LiMn ₂ O ₄ (16% by mass) as a lithium salt, and a photopolymerization initiator are prepared, and acetonitrile (54% by mass) is used as a solvent. The added electrolyte slurry was applied, arranged in a frame shape, and the solvent was blown off. After the solvent was blown off, ultraviolet rays were irradiated for 20 minutes to form an intrinsic polymer frame. The mass% is a value with respect to the total amount of the polymer electrolyte raw material, the lithium salt, and the solvent. The photopolymerization initiator was added to 0.2% by mass with respect to the polymer electrolyte raw material.

(Comparative Example 1)
A lithium ion secondary battery was obtained in the same manner as in Example 1 except for the following items.

  Instead of the electrolyte layer composed of the gel electrolyte and the electrolyte solution, the same gel electrolyte layer as in Example 1 was used. FIG. 5A shows a partial schematic cross-sectional view of the lithium ion secondary battery used in Comparative Example 1. 5A, reference numeral 511 represents a gel electrolyte, reference numeral 520 represents a current collector, reference numeral 531 represents a positive electrode active material layer, and reference numeral 532 represents a negative electrode active material layer.

(Comparative Example 2)
A lithium ion secondary battery was obtained in the same manner as in Example 1 except for the following items.

  A seal member made of an epoxy resin was used at a location (periphery) where the active material of the bipolar electrode was not formed, and a seal portion 550 was formed as shown in FIG. The length L of the seal portion protruding from the current collector 520 was 5 mm. In FIG. 5B, reference numeral 515 indicates an electrolytic solution.

(Measurement of battery output)
The battery outputs of the lithium ion secondary batteries obtained in Examples 1-2 and Comparative Examples 1-2 were measured.

  Table 1 shows the battery outputs of Example 2 and Comparative Examples 1 and 2 when the battery output of Example 1 is 100. Table 1 also shows the battery volume of Example 2 and Comparative Examples 1 and 2 and the volume output density obtained by dividing the battery output by the battery volume when the battery volume of Example 1 is 100. Show.

  From Examples 1-2, the lithium ion secondary battery including the electrolyte layer of the present invention is superior in battery output and volume output density as compared with the secondary battery of Comparative Example 1 which is a conventional lithium ion secondary battery. I understand that. Moreover, it turns out that it is excellent in the volume output density compared with the secondary battery of the comparative example 2 which is a conventional lithium ion secondary battery. Further, in the case of Example 2, since the intrinsic polymer electrolyte is included, the battery output is lower than that in Example 1, but it is understood that the volume output density is superior to Comparative Examples 1 and 2.

(A)-(D) are the plane top views which showed the example of arrangement | positioning of the polymer electrolyte in the electrolyte layer of this invention. It is the plane schematic which illustrated the electrolyte layer of this invention using the polymer electrolyte which consists of an intrinsic polymer electrolyte and a gel electrolyte. (A) is a schematic sectional view of a bipolar electrode, and (B) is a schematic sectional view of a non-bipolar electrode. (A)-(B) are the fragmentary sectional schematic diagrams of the lithium ion secondary battery which show the example of arrangement | positioning of a polymer electrolyte. (A) is the partial cross-section schematic of the lithium ion secondary battery of the comparative example 1, (B) is the partial cross-section schematic of the lithium ion secondary battery of the comparative example 2. FIG.

Explanation of symbols

31 Bipolar electrode,
32 Electrodes of non-bipolar type,
110 electrolyte layer,
111 polymer electrolyte,
115 electrolyte,
210 electrolyte layer,
211 polymer electrolyte,
212 intrinsic polymer electrolyte,
213 gel electrolyte,
215 electrolyte,
320 current collector,
331 positive electrode active material layer,
332 negative electrode active material layer,
410 electrolyte layer,
411 polymer electrolyte,
415 electrolyte,
420 current collector,
431 positive electrode active material layer,
432 negative electrode active material layer,
511 gel electrolyte,
515 electrolyte,
520 current collector,
531 Positive electrode active material layer,
532 negative electrode active material layer,
550 seal part,
L Length of the seal part that protrudes from the current collector.

Claims (7)

A frame made of a polymer electrolyte;
An electrolyte filled in a space formed by the frame;
The electrolyte layer for lithium ion secondary batteries characterized by including. The polymer electrolyte comprises a gel electrolyte;
2. The electrolyte layer for a lithium ion secondary battery according to claim 1, wherein a ratio of the polymer contained in the gel electrolyte is 5 to 20 mass% with respect to the total amount of the gel electrolyte.   The electrolyte layer for a lithium ion secondary battery according to claim 2, wherein the polymer is polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, or chemically crosslinked polyethylene oxide.   The electrolyte layer for a lithium ion secondary battery according to claim 1, wherein the polymer electrolyte is an intrinsic polymer electrolyte.   A lithium ion secondary battery comprising the electrolyte layer for a lithium ion secondary battery according to claim 1.   The lithium ion secondary battery according to claim 5, comprising a bipolar electrode. The electrolyte layer for a lithium ion secondary battery according to any one of claims 1 to 4, or the lithium ion secondary battery according to claim 5 or 6,
Including a vehicle.

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