Lithium ion battery and negative electrode current collector of the same

Abstract

To provide a negative electrode current collector of a lithium ion battery which maintains its quality while adopting an inexpensive conductive filler.SOLUTION: In a negative electrode current collector 11, a conductive filler 15 having a volume expansion ratio when lithium ions are absorbed of 2% or less is dispersed in a continuous phase of a resin 16.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a negative electrode current collector used in the negative electrode of a lithium ion battery. [Background technology]

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

[0003] In conventional lithium-ion batteries, the positive electrode current collector uses conductive carbon such as graphite as a conductive filler mixed with a conductive resin, and the negative electrode current collector uses metal elements such as platinum, gold, silver, copper, nickel, and titanium as a conductive filler mixed with a conductive resin (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6785110 Summary of the Invention [Problem to be solved by the invention]

[0005] The reason why the conductive fillers made of the above-mentioned metal elements are used for the negative electrode current collector is that they do not occlude lithium ions and do not cause volume changes. However, the conductive fillers made of metal elements are expensive, which leads to an increase in the cost of lithium-ion batteries that use them.

[0006] Therefore, it is considered to use conductive carbon such as graphite, which is used as a conductive filler for a positive electrode current collector, as a conductive filler for a negative electrode current collector. However, when conductive carbon such as graphite is used as a conductive filler for a negative electrode current collector, this conductive filler absorbs lithium ions and causes a volume change (expansion). Then, the conductive resin begins to crack, and the electrolyte (containing lithium ions) penetrates into the cracked area. Furthermore, the conductive filler further inside the negative electrode current collector reacts (expands) in the same way, and the negative electrode current collector expands by 7 to 10% due to the lithium ions. As a result, the continuous phase of the conductive resin is cracked, and the electrolyte that has penetrated inside expands the conductive carbon, causing cracks in the negative electrode current collector. This causes a problem of degrading the quality of the lithium ion battery.

[0007] The present invention aims to solve these problems, and has an object to provide a lithium ion battery that maintains its quality while employing an inexpensive conductive filler. [Means for solving the problem]

[0008] The negative electrode current collector according to the present invention has a conductive filler having a volume expansion rate of 2% or less when lithium ions are absorbed dispersed in a continuous phase of a resin. The lithium ion battery according to the present invention includes a negative electrode active material layer having one side in contact with the negative electrode current collector and having negative electrode active material particles dispersed in an electrolyte, a positive electrode active material layer having one side in contact with the positive electrode current collector and having positive electrode active material particles dispersed in an electrolyte, and a separator sandwiched on both sides by the negative electrode active material layer and the positive electrode active material layer. Effect of the Invention

[0009] The present invention provides a lithium ion battery that maintains its quality while employing an inexpensive conductive filler. [Brief description of the drawings]

[0010] [Figure 1]FIG. 2A is a cross-sectional view of a battery cell including a negative electrode current collector according to an embodiment of the present invention, and FIG. 2B is an enlarged cross-sectional view of an interface portion of the negative electrode current collector according to an embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view of a lithium-ion battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1(A) is a cross-sectional view of a battery cell 10 including a negative electrode current collector 11 according to an embodiment of the present invention. Fig. 1(B) is an enlarged cross-sectional view of an interface portion of the negative electrode current collector 11 of the present invention.

[0012] 1(A) and 1(B), a battery cell 10 includes a negative electrode current collector 11, a negative electrode active material layer 13 having one side in contact with the negative electrode current collector 11 and having negative electrode active material particles 17 dispersed in an electrolyte 19, a positive electrode current collector 12, a positive electrode active material layer 14 having one side in contact with the positive electrode current collector 12 and having positive electrode active material particles (not shown) dispersed in an electrolyte (not shown), and a separator 25 sandwiched on both sides by the negative electrode active material layer 13 and the positive electrode active material layer 14. In the battery cell 10, a seal member 26 is annularly arranged to surround the side surfaces of the negative electrode current collector 11, the negative electrode active material layer 13, the separator 25, the positive electrode active material layer 14, and the positive electrode current collector 12 stacked in this order.

[0013] As shown in FIG. 1(B), conductive filler 15 having a volume expansion rate of 2% or less when lithium ions are absorbed is dispersed in resin 16 constituting the continuous phase of negative electrode current collector 11. In other words, in negative electrode current collector 11, a dispersed phase of conductive filler 15 having a volume expansion rate of 2% or less when lithium ions are absorbed is formed using resin 16 as a dispersion medium. Examples of conductive filler 15 having such characteristics include hard carbon or amorphous carbon. By using such a relatively inexpensive material as conductive filler 15 of negative electrode current collector 11, it is possible to prevent resin 16 from cracking and contribute to cost reduction.

[0014] The content of resin 16 in the composition of negative electrode current collector 11 is preferably in the range of 10 to 90 mass %, more preferably 15 to 85 mass %, and even more preferably 20 to 80 mass %, based on the total mass of resin 16 and conductive filler 15. The content of resin 16 is not particularly limited as long as it does not impair the function of negative electrode current collector 11.

[0015] Hard carbon (non-graphitizable carbon) is produced by heating a carbonaceous precursor to approximately 1000°C under anaerobic conditions. Precursors of hard carbon include polyvinylidene chloride (PVDC), lignin, and sucrose. Hard carbon has a lower density and a much higher porosity than soft carbon (easily graphitizable carbon).

[0016] Amorphous carbon is a non-crystalline, glass-like carbon material. It is produced by baking and carbonizing a hardened molded body of a specific resin. It has high rigidity and a dense, pore-free structure.

[0017] On the other hand, the positive electrode current collector 12 has a conductive filler (not shown) such as graphite dispersed in a continuous phase of a resin (not shown). The positive electrode current collector 12 does not occlude lithium ions and expand in volume, unlike the negative electrode current collector 11, so the material of the dispersed conductive filler is not limited. The positive electrode current collector 12 may also be, for example, copper, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, or the like dispersed in a continuous phase of a resin.

[0018] 2 is a cross-sectional view of a lithium-ion battery 20 according to an embodiment of the present invention. Thus, the lithium-ion battery 20 is configured by housing a stack of a plurality of battery cells 10 (101, 102, 103, 104) in an exterior body 27. A negative electrode lead wire 21 is connected to the negative electrode current collector 11 of the battery cell 101 located at one end of the stack in the stacking direction. A positive electrode lead wire 22 is connected to the positive electrode current collector 12 of the battery cell 104 located at the other end of the stack in the stacking direction.

[0019] In addition, the negative electrode current collector 11 and the positive electrode current collector 12 adjacent to each other in the stacked battery cells 10 may be integrated into a bipolar electrode.

[0020] The resin 16 forming the continuous phase with the negative electrode current collector 11 and the resin (not shown) forming the continuous phase with the positive electrode current collector 12 may be a polymer material that is either conductive or non-conductive. Examples of the conductive resin 16 include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylenevinylene, and polyoxadiazole.

[0021] Examples of the non-conductive resin 16 include aliphatic polyolefins [polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyisobutylene, polybutadiene, polymethylpentene (PMP), and copolymers thereof, etc.], alicyclic polyolefins [polycycloolefins (PCO), etc.], polyester resins [polyethylene terephthalate (PET), etc.], polyethernitrile (PEN), synthetic rubbers [styrene butadiene rubber (SBR), etc.], acrylic resins [polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), etc.], crosslinked or non-crosslinked epoxy resins, silicone resins, and mixtures thereof.

[0022] The negative electrode active material layer 13 may contain, in addition to the negative electrode active material particles 17 and the electrolyte solution 19, one or more selected from a conductive assistant, an adhesive resin, and a known solution-drying type binder for electrodes (also called a binder). The positive electrode active material layer 14 may also contain, in addition to the positive electrode active material particles (not shown) and the electrolyte solution 19, one or more selected from a conductive assistant, an adhesive resin, and a known solution-drying type binder for electrodes (also called a binder).

[0023] The negative electrode active material particles 17 are, for example, carbon-based materials [graphite, non-graphitizable carbon, amorphous carbon, resin baked bodies (e.g., phenolic resin, furan resin, etc. baked and carbonized), cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), and carbon fibers, etc.], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites (carbon particles whose surfaces are coated with silicon and / or silicon carbide, silicon particles or silicon oxide particles whose surfaces are coated with carbon and / or silicon carbide, and silicon carbide, etc.), and silicon alloys (silicon-aluminum Examples of the conductive materials include particles of conductive materials (e.g., aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper alloy, silicon-tin alloy, etc.), conductive polymers (e.g., polyacetylene, polypyrrole, etc.), metals (tin, aluminum, zirconium, titanium, etc.), metal oxides (titanium oxide, lithium-titanium oxide, etc.), metal alloys (e.g., lithium-tin alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.), and mixtures of these with carbon-based materials.

[0024] The positive electrode active material particles are not particularly limited as long as they are used in lithium ion batteries. For example, a composite oxide of lithium and a transition metal {composite oxides containing one type of transition metal (LiCoO2, LiNiO2, LiAlMnO4, LiMnO2, LiMn2O4, etc.), composite oxides containing two types 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 0.05 O2) and composite oxides containing three or more metal elements (e.g., LiMaM'bM''cO2 (where M, M', and M'' are different transition metal elements and satisfy a+b+c=1), LiNi 1 / 3 Mn 1 / 3 Co 1 / 3O2, etc.), lithium-containing transition metal phosphates (e.g., LiFePO4, LiCoPO4, LiMnPO4, and LiNiPO4), transition metal oxides (e.g., MnO2 and V2O5), transition metal sulfides (e.g., MoS2 and TiS2), and conductive polymers (e.g., polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polyvinylcarbazole) are examples of particles. The lithium-containing transition metal phosphate may be one in which a part of the transition metal site is replaced with another transition metal. In addition, one type selected from these compounds may be used alone, or two or more types may be used in combination.

[0025] The coating resin 18 coats a part of the surface of at least one of the negative electrode active material particles 17 and the positive electrode active material particles (not shown), preferably the entire surface of the negative electrode active material particles 17 and the positive electrode active material particles (not shown). In this way, the coating resin 18 makes it difficult for the volume of the negative electrode active material layer 13 and / or the positive electrode active material layer 14 to change during charging and discharging.

[0026] Examples of the coating resin 18 that can be used include vinyl resin, urethane resin, polyester resin, polyamide resin, epoxy resin, polyimide resin, silicone resin, phenol resin, melamine resin, urea resin, aniline resin, ionomer resin, and polycarbonate. Among these, vinyl resin, urethane resin, polyester resin, and polyamide resin are preferred, and vinyl resin is more preferred, from the viewpoints of high absorbency for the electrolyte solution 19 and improved electrical properties.

[0027] The electrolytic solution 19 is a nonaqueous solvent in which an electrolyte is dissolved. As the nonaqueous solvent, a nonaqueous solvent used in a known nonaqueous electrolytic solution 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 carboxylate esters, cyclic or chain ethers, phosphate esters, nitrile compounds, amide compounds, sulfones, sulfolane, and mixtures thereof can be mentioned.

[0028] The electrolyte may be any electrolyte used in a known non-aqueous electrolyte. For example, lithium salts of inorganic acids such as LiPF6, LiBF4, LiSbF6, LiAsF6, and LiClO4, and lithium salts of organic acids such as LiN(CF3SO2)2, LiN(C2F5SO2)2, and LiC(CF3SO2)3 are included. Among these electrolytes, LiPF6 is preferred from the viewpoint of battery output and charge / discharge cycle characteristics.

[0029] In this embodiment, a gel polymer electrolyte may be used as the electrolytic solution 19. The gel polymer electrolyte is obtained by injecting an electrolytic solution 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.

[0030] The separator 25 has a function of retaining the electrolyte 19 to ensure lithium ion conductivity between the negative electrode current collector 11 and the positive electrode current collector 12, and a function as a partition between the negative electrode active material layer 13 and the positive electrode active material layer 14. As the separator 25, for example, a known separator such as a porous separator made of a polymer or fiber that absorbs and retains the electrolyte 19, or a nonwoven fabric separator can be used.

[0031] According to the negative electrode current collector 11 of the embodiment described above, the conductive filler 15 dispersed in the continuous phase of the resin 16 has a characteristic that the volume expansion rate when lithium ions are absorbed is 2% or less. This makes it possible to maintain the quality of a lithium ion battery while employing an inexpensive conductive filler (e.g., hard carbon or amorphous carbon).

[0032] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0033] 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...conductive filler, 16...resin, 17...negative electrode active material particles, 18...coating resin, 19...electrolyte, 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 current collector in which a conductive filler having a volume expansion rate of 2% or less when lithium ions are absorbed is dispersed in a continuous phase of a resin.

2. A negative electrode current collector in which a dispersed phase of a conductive filler having a volume expansion rate of 2% or less when lithium ions are absorbed is formed in a resin dispersion medium.

3. 3. The negative electrode current collector according to claim 1, wherein the conductive filler is hard carbon or amorphous carbon.

4. a negative electrode active material layer having one side in contact with the negative electrode current collector according to claim 1 or 2 and having negative electrode active material particles dispersed in an electrolyte; a positive electrode active material layer having one side in contact with a positive electrode current collector and having positive electrode active material particles dispersed in an electrolyte; a separator sandwiched on both sides by the negative electrode active material layer and the positive electrode active material layer.

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