Lithium ion battery

Abstract

To provide a lithium ion battery excellent in ion conductivity by ingeniously designing a separator and adopting a gel polymer.SOLUTION: A lithium ion battery 20 is configured to include: a negative electrode active material layer 13 having one surface in contact with a negative electrode current collector 11 and containing negative electrode active material particles 17; a positive electrode active material layer 14 having one surface in contact with a positive electrode current collector 12 and containing positive electrode active material particles 16; a separator 25 whose both surfaces being sandwiched by the negative electrode active material layer 13 and the positive electrode active material layer 14 and provided with a through-hole for holding an electrolytic solution 19; and a gel polymer 18 covering a surface of the separator 25 and swollen with the electrolytic solution 19.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a lithium-ion battery having a separator as a component.

Background Art

[0002] Lithium-ion batteries are used as power sources in various fields, such as power sources for electric vehicles (EVs), hybrid electric vehicles (HEVs), and power sources for small electronic devices such as laptop computers and mobile phones.

[0003] A separator, which is a component of a lithium-ion battery, has both ion conductivity and electrical insulation. This separator is installed so as to be sandwiched between a positive electrode and a negative electrode, electrically insulates both of them to prevent internal short circuits, and allows lithium ions to permeate through an electrolyte. The role played by the separator is becoming increasingly important for the lithium-ion battery to be charged and discharged with high efficiency and to repeat stable operation.

[0004] And, in order to improve the conductivity of this lithium ion, prior art documents that devise the separator or adopt a gel polymer are disclosed (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Patent Document 1, a technique is disclosed in which a gel-like active ingredient is inserted into the pores of a porous polymer forming a separator, and further, one or both surfaces of the separator are coated with the gel-like active ingredient. However, it is technically difficult to insert a sticky gel-like active ingredient into the pores of a porous polymer. Also, when the gel-like active ingredient is interrupted and the insertion interval is opened in the middle of continuous pores, there is a problem that ion conductivity is interrupted.

[0007] In Patent Document 2, a technique is disclosed in which an adhesive resin layer provided with a large number of through-holes is disposed on both surfaces of a separator, and an electrolytic solution is held in the through-holes to ensure ion conductivity. However, with this configuration, there is a problem that it does not contribute to improving the ion conductivity in the separator.

[0008] An object of the present invention is to solve such problems, and by devising a separator and further adopting a gel polymer, an object is to provide a lithium ion battery having excellent ion conductivity.

Means for Solving the Problems

[0009] The lithium ion battery according to the present invention includes a negative electrode active material layer that has one side in contact with a negative electrode current collector and contains negative electrode active material particles, a positive electrode active material layer that has one side in contact with a positive electrode current collector and contains positive electrode active material particles, a separator that is sandwiched between both sides by the negative electrode active material layer and the positive electrode active material layer and is provided with through-holes for holding an electrolytic solution, and a gel polymer that covers the surface of the separator and swells with the electrolytic solution.

Effects of the Invention

[0010] According to the present invention, by devising a separator and further adopting a gel polymer, a lithium ion battery having excellent ion conductivity is provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a lithium-ion battery 20 according to an embodiment of the present invention. As such, the lithium-ion battery 20 is configured by housing a stacked body formed by stacking a plurality of battery cells 10 (101, 102, 103, 104) in an outer casing 27. A negative electrode lead wire 21 is connected to the negative electrode current collector (negative electrode current collector 11 in FIG. 2) of the battery cell 101 located at one end of this stacked body. And a positive electrode lead wire 22 is connected to the positive electrode current collector (positive electrode current collector 12 in FIG. 2) of the battery cell 104 located at the other end of the stacked body.

[0013] FIG. 2 is a cross-sectional view of a battery cell 10 constituting a lithium-ion battery 20. The battery cell 10 has a negative electrode current collector 11, a negative electrode active material layer 13, a separator 25, a positive electrode active material layer 14, and a positive electrode current collector 12 stacked in this order, and a seal member 26 is annularly arranged so as to surround its outer periphery.

[0014] FIG. 3 is an enlarged cross-sectional view of a separator 25 (broken line portion in FIG. 2) applied to the battery cell 10. Here, one side of the negative electrode active material layer 13 is in contact with the negative electrode current collector 11 (FIG. 2) and contains negative electrode active material particles 17. One side of the positive electrode active material layer 14 is in contact with the positive electrode current collector 12 (FIG. 2) and contains positive electrode active material particles 16. The separator 25 is sandwiched between the negative electrode active material layer 13 and the positive electrode active material layer 14 on both sides, and a through hole 15 for holding the electrolytic solution 19 is provided. The gel polymer 18 is swollen with the electrolytic solution 19 and covers the surface of the separator 25.

[0015] In this embodiment, the surfaces of the negative electrode active material particles 17 and the positive electrode active material particles 16 are also covered with the gel polymer 18. Whether the same gel polymer 18 as that on the surface of the separator 25 is used or a different one is used is not particularly limited. Since the gel polymer 18 contains a large amount of the electrolytic solution 19, it prevents the drying of the separator 25 and ensures ion conductivity. Further, the surfaces of the negative electrode active material particles 17 and the positive electrode active material particles 16 are joined to the gel polymer 18, so that the ion conductivity is kept good.

[0016] When adjacent ones of the positive electrode active material particles 16 or the negative electrode active material particles 17 are in contact with each other, in addition to the case where the gel polymers 18 covering the surfaces are in close contact with each other, the electrolytic solution 19 is dispersed and interposed therebetween. Note that there may be a case where the swelling of the gel polymer 18 due to the electrolytic solution 19 proceeds and the single dispersed phase of the electrolytic solution 19 disappears. Further, it is not an essential requirement that the surfaces of the negative electrode active material particles 17 and the positive electrode active material particles 16 are covered with the gel polymer 18, and there may be a case where they are directly covered with the electrolytic solution 19.

[0017] The gel polymer 18 is obtained by injecting the electrolytic solution 19 into a matrix polymer (host polymer) made of an ion conductive polymer. Examples of the ion conductive polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride - hexafluoropropylene (PVdF - HEP), polymethyl methacrylate (PMMA), and copolymers thereof.

[0018] The electrolytic solution 19 is a solution in which an electrolyte is dissolved in a non-aqueous solvent. As the non-aqueous solvent, a non-aqueous solvent used in known non-aqueous electrolytic solutions or the like can be used. For example, carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate, lactone compounds, chain carboxylic acid esters, cyclic or chain ethers, phosphate esters, nitrile compounds, amide compounds, sulfones, sulfolane, etc., and mixtures thereof can be mentioned.

[0019] As the electrolyte, an electrolyte used in known non-aqueous electrolytic solutions or the like can be used. For example, lithium salts of inorganic acids such as LiPF6, LiBF4, LiSbF6, LiAsF6, and LiClO4, lithium salts of organic acids such as LiN(CF3SO2)2, LiN(C2F5SO2)2, and LiC(CF3SO2)3, etc. can be mentioned. Among these electrolytes, LiPF6 is preferable from the viewpoints of battery output and charge-discharge cycle characteristics.

[0020] In addition to the electrolytic solution 19, the gel polymer 18 may contain one or more selected from conductive aids, adhesive resins, and known binders (also referred to as binders) for electrodes of the solution-drying type. As the conductive aid, although not particularly limited, for example, metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.), carbon nanofibers, carbon nanotubes, etc.] can be mentioned. Also, one selected from among these conductive aids may be used alone, or two or more thereof may be used in combination. Also, these alloys or metal oxides may be used. By blending these conductive aids, good electron conductivity is imparted to the gel polymer 18.

[0021] As the conductive aid, from the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium, and mixtures thereof are preferable, and more preferably silver, aluminum, ste They are non-metallic and carbon, more preferably carbon. As the conductive assistant, it may be a particulate ceramic material or a material obtained by coating a resin material with a conductive material (a metallic one among the materials of the above-mentioned conductive assistant) such as plating.

[0022] The negative electrode active material particles 17 are, for example, carbon-based materials [graphite, non-graphitizable carbon, amorphous carbon, resin fired bodies (such as those obtained by firing and carbonizing phenolic resins and furan resins, etc.), cokes (such as pitch coke, needle coke, and petroleum coke, etc.), and carbon fibers, etc.], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites (those obtained by coating the surface of carbon particles with silicon and / or silicon carbide, those obtained by coating the surface of silicon particles or silicon oxide particles with carbon and / or silicon carbide, and silicon carbide, etc.), and silicon alloys (such as silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper alloy, and silicon-tin alloy, etc.)], conductive polymers (such as polyacetylene and polypyrrole, etc.), metals (such as tin, aluminum, zirconium, and titanium, etc.), metal oxides (such as titanium oxides and lithium titanium oxides, etc.), and metal alloys (such as lithium-tin alloy, lithium-aluminum alloy, and lithium-aluminum-manganese alloy, etc.), and particles such as mixtures of these with carbon-based materials.

[0023] The positive electrode active material particles 16 are not particularly limited as long as they are those adopted for the use of lithium ion batteries. For example, composite oxides of lithium and transition metals {composite oxides with one kind of transition metal (such as LiCoO2, LiNiO2, LiAlMnO4, LiMnO2, and LiMn2O4, etc.), composite oxides with two kinds of transition metal elements (for example, LiFeMnO4, LiNi 1-x Co x O2, LiMn 1-y Co y O2, LiNi 1 / 3 Co 1 / 3 Al 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05Composite oxides containing three or more types of O2) and metal elements (for example, LiMaM’bM’’cO2 (where M, M’, and M’’ are different transition metal elements respectively, and a + b + c = 1 is satisfied), LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, etc.), lithium-containing transition metal phosphates (for example, LiFePO4, LiCoPO4, LiMnPO4, and LiNiPO4), transition metal oxides (for example, MnO2 and V2O5), transition metal sulfides (for example, MoS2 and TiS2), and conductive polymers (for example, polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polyvinyl carbazole), etc. Examples of the above lithium-containing transition metal phosphates may be those in which a part of the transition metal sites are substituted with other transition metals. Also, one selected from among these compounds may be used alone, or two or more may be used in combination.

[0024] The separator 25 has a function of holding the electrolytic solution 19 and ensuring lithium ion conductivity between the negative electrode current collector 11 and the positive electrode current collector 12, and a function as a partition wall that electrically insulates the negative electrode active material layer 13 and the positive electrode active material layer 14. As the separator 25, for example, known ones such as a porous separator made of a polymer, fiber, etc. that absorbs and holds the electrolytic solution 19, a non-woven fabric separator, etc. can be used.

[0025] The separator 25 is sandwiched on both sides by the negative electrode active material layer 13 and the positive electrode active material layer 14, and is provided with a through hole 15 that holds the electrolytic solution 19. This through hole 15 linearly penetrates the separator 25 in the thickness direction, and each of both ends forms an opening at the interface with the negative electrode active material layer 13 and the positive electrode active material layer 14. This through hole 15 has an inner diameter in the range of 50 μm to 500 μm, and can be formed by adopting laser processing, electrical discharge machining, cutting machining, or any other arbitrary processing method.

[0026] The negative electrode current collector 11 has a conductive filler (not shown) dispersed in a resin (not shown) that constitutes a continuous phase. The conductive filler (not shown) used for the negative electrode current collector 11 is required to have the property of not occluding lithium ions and not causing volume change. Specifically, metal elements such as platinum, gold, silver, copper, nickel, and titanium are exemplified.

[0027] The positive electrode current collector 12 has a conductive filler such as graphite (not shown) dispersed in a resin (not shown) that constitutes a continuous phase. The positive electrode current collector 12 does not occlude lithium ions and expand in volume like the negative electrode current collector 11. Examples of the conductive filler (not shown) used for the positive electrode current collector 12 include copper, aluminum, titanium, stainless steel, nickel, fired carbon, conductive polymer, and conductive glass.

[0028] The resin (not shown) that forms the continuous phase in the negative electrode current collector 11 and the resin (not shown) that forms the continuous phase in the positive electrode current collector 12 may or may not have conductivity as a polymer material. Examples of the resin having conductivity include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, and polyoxadiazole.

[0029] Examples of the resin having no conductivity include aliphatic polyolefins [such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyisobutylene, polybutadiene, and polymethylpentene (PMP) and copolymers thereof], alicyclic polyolefins [such as polycycloolefin (PCO)], polyester resins [such as polyethylene terephthalate (PET)], polyether nitrile (PEN), synthetic rubbers [such as styrene butadiene rubber (SBR)], acrylic resins [such as polyacrylonitrile (PAN), polymethyl acrylate (PMA), and polymethyl methacrylate (PMMA)], crosslinked or non-crosslinked epoxy resins, silicone resins, and mixtures thereof.

[0030] In the battery cells 10 to be stacked, it is preferable that the negative electrode current collector 11 and the positive electrode current collector 12 adjacent to each other are integrated bipolar electrodes.

[0031] FIG. 4 is an enlarged cross-sectional view around the separator 25 shown by the broken line in FIG. 3. The electrolytic solution 19 will be filled up to every corner of the through holes 15 by so-called capillary action. Further, by covering both surfaces of the separator 25 with the gel polymer 18, the electrolytic solution 19 can be confined inside the through holes 15.

[0032] Since the gel polymer 18 is swollen with the electrolytic solution 19, smooth ion conduction in the separator 25 is realized through the through holes 15 due to their high affinity. In other words, by sealing both ends of the through holes 15 filled with the electrolytic solution 19 with the gel polymer 18, good ion transmission is realized between the gel polymer 18 - electrolytic solution 19 - gel polymer 18.

[0033] Also, since the openings at both ends of the through holes 15 are blocked by the gel polymer 18, while allowing lithium ions to pass through, the passage of fine particles floating in the electrolytic solution 19 is suppressed. Further, even if gas is generated inside the negative electrode active material layer 13 or the positive electrode active material layer 14, since it is covered with the gel polymer 18, the generation of gas accumulation on the surface of the separator 25 is prevented. If gas accumulation is generated, the separator 25 in contact therewith will be dried, the ion conductivity will deteriorate, and lithium will precipitate. In this embodiment, there is an effect of avoiding such a situation. Also, the through holes 15 filled with the electrolytic solution 19 also serve as a buffer to replenish the electrolytic solution 19 impregnated in the separator 25 when it is depleted.

[0034] Although not shown, at least one of the negative electrode current collector 11 (FIG. 2) and the positive electrode current collector 12 may be covered on the surface with the gel polymer 18. Also in this case, similar to the description of the separator 25, drying of the current collectors 11 and 12 due to the gas 15 is prevented, lithium precipitation is prevented, and good electron transport property is maintained.

[0035] According to the above-mentioned paste-type lithium ion battery 20, by holding the electrolytic solution 19 in the through holes 15 and covering the surfaces with the gel polymer 18 so as to close both ends thereof, the ion conductivity in the separator 25 can be improved.

[0036] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0037] 10... battery cell, 11... negative electrode current collector, 12... positive electrode current collector, 13... negative electrode active material layer, 14... positive electrode active material layer, 15... through hole, 16... positive electrode active material particles, 17... negative electrode active material particles, 18... gel polymer, 19... electrolytic solution, 20... lithium ion battery, 21... negative electrode lead wire, 22... positive electrode lead wire, 25... separator, 26... sealing member, 27... exterior body.

Claims

1. A negative electrode active material layer that is in contact with one side of a negative electrode current collector and contains negative electrode active material particles, A positive electrode active material layer that is in contact with one side of a positive electrode current collector and contains positive electrode active material particles, A separator that is sandwiched on both sides by the negative electrode active material layer and the positive electrode active material layer and is provided with through-holes for holding an electrolytic solution, A lithium ion battery comprising a gel polymer that covers the surface of the separator and swells with the electrolytic solution.

2. The lithium ion battery according to claim 1, wherein the surfaces of the negative electrode active material particles and the positive electrode active material particles are covered with the gel polymer.

3. The lithium ion battery according to claim 1 or claim 2, wherein at least one of the negative electrode current collector and the positive electrode current collector has its surface covered with the gel polymer.

4. The lithium ion battery according to claim 1 or claim 2, wherein a conductive auxiliary agent is contained in the gel polymer.

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