WO2012101693A1

WO2012101693A1 - Negative electrode collector for lithium ion batteries, and lithium ion battery

Info

Publication number: WO2012101693A1
Application number: PCT/JP2011/005768
Authority: WO
Inventors: 一樹遠藤; 藤川　万郷
Original assignee: パナソニック株式会社
Priority date: 2011-01-28
Filing date: 2011-10-14
Publication date: 2012-08-02

Abstract

Provided is a highly safe lithium ion battery which can be suppressed in excessive increase in battery temperature without deteriorating collector characteristics and negative electrode active material density even in cases wherein a short circuit has occurred by a foreign substance stuck therein. A negative electrode collector for lithium ion secondary batteries of the present invention has a three-layer structure that is obtained by forming metal layers (110), each of which is formed of Cu or Ni, on both surfaces of a base layer (100) that is formed of a metal or alloy that has a melting point of 120-800˚C (inclusive). The base layer (100) has an electrical conductivity of 10⁶ S/m or more, and for example, the base layer (100) is formed of Al. The thickness of the base layer (100) is, for example, 1-100 μm.

Description

Negative electrode current collector for lithium ion battery and lithium ion battery

The present invention relates to a lithium ion battery having improved safety against an internal short circuit, and a negative electrode current collector used in the battery.

In recent years, with the reduction in size and weight of electronic devices such as mobile phones and notebook computers, it is required to increase the capacity of secondary batteries as power sources for these devices. From such a demand, lithium ion batteries capable of increasing the energy density are widely used. The lithium ion battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.

Generally, when a short circuit having a relatively low resistance value occurs inside the battery, a large current flows at the short circuit point, so that the heat generation of the battery may be accelerated and lead to overheating. In order to avoid such a phenomenon in a lithium ion battery having a high energy density, various safety measures are taken from the viewpoint of the battery configuration in addition to the viewpoint of manufacturing.

Generally, a separator having a shutdown function for blocking the ionic current by blocking pores due to heat generated when an internal short circuit occurs in the battery is used. The short-circuit current stops flowing due to the shutdown function, and the heat generation stops. However, when the heat generation in the short-circuited portion is large, the separator is melted before the shutdown functions, thereby causing a melt-down that opens a large hole in the separator. When the positive electrode and the negative electrode are short-circuited due to meltdown, further overheating is caused. In some cases, the battery ignites or smokes, which is very dangerous.

Therefore, it has been proposed to form a porous film made of a heat-resistant resin such as aramid on the separator (see Patent Document 1). Since heat-resistant resins such as aramid do not melt even at high temperatures, it is considered that using the technique of Patent Document 1 has a high ability to maintain insulation between positive and negative electrodes even in an overheated environment.

However, although the porous film made of a heat-resistant resin itself exhibits high heat resistance in the prior art disclosed in Patent Document 1, if the film breaks during short-circuiting, it is easily dragged by the melting or shrinking of the underlying separator, and this causes the short-circuit location to expand. May cause further overheating.

Then, the method of suppressing the electric current at the time of a short circuit is proposed by forming the resistor layer (it consists of a mixture of carbon powder and a polyimide resin) which has high resistance on the collector surface (refer patent document 2). . As described above, since overheating accelerates when the resistance value of the short-circuited portion is low, it is considered that if the technique of Patent Document 2 is used, the resistance value increases even if an internal short-circuit occurs, and thus overheating is suppressed. .

However, in the technique of Patent Document 2, the resistance value of the internal short-circuit portion is increased by the resistor layer, so that safety is improved. However, in order to ensure sufficient safety against short-circuit due to a foreign object having a large diameter such as a nail. When the necessary resistor layer is formed, the electronic resistance at the interface between the active material particles and the current collector becomes too high, and the load characteristics of the battery deteriorate.

In Patent Document 3 and Patent Document 4, in order to reduce the weight of the current collector without reducing the strength of the current collector, the conductivity of the metal is deposited by vapor deposition on both surfaces of a resin film such as PET or PP. A method of using a sheet on which a thin film is formed as a current collector has been proposed. According to this current collector, the resin film of the current collector at the short-circuit portion is melted by heat due to the heat generated at the time of the short circuit, and the current is interrupted by the heat-melted resin film.

Japanese Patent Laid-Open No. 9-208736 JP-A-10-199574 JP-A-9-213338 JP-A-9-283149

However, in the techniques of Patent Document 3 and Patent Document 4, current collection for the negative electrode depends on conductive thin films formed on both surfaces of the resin film, so that current collection at a large current becomes insufficient, and the load characteristics of the battery are low. descend. In addition, since a metal conductive thin film is formed on both sides of the resin film, it is necessary to form a conductive thin film having a certain thickness in order to obtain a predetermined load characteristic. Since it is formed, it takes time to form a thickness with which sufficient electrical conductivity can be obtained, and the productivity is significantly reduced. Furthermore, in order to increase the energy density of the battery, usually, rolling is performed after applying a composite material layer containing an active material on the current collector. However, if a resin is used as the base material of the current collector, a metal is used as the base material. Since the resin has flexibility as compared with the case of using, the resin is deformed during rolling to relieve the stress, and as a result, it is difficult to increase the density of the active material.

The present invention has been made in view of such problems, has excellent load characteristics, is filled with a negative electrode active material at a high density, and even when an internal short circuit occurs, the battery temperature is excessive. An object of the present invention is to provide a highly safe lithium ion battery capable of suppressing the increase.

The negative electrode current collector for a lithium ion battery according to the first aspect of the present invention comprises a base material layer made of a metal or an alloy having a melting point of 120 ° C. or higher and 800 ° C. or lower, and contact or non-contact with both surfaces of the base material layer. And a metal layer containing Cu or Ni.

A lithium ion battery according to a second aspect of the present invention includes a negative electrode plate having a negative electrode active material layer formed on the surface of the negative electrode current collector, and a positive electrode active material layer formed on the surface of the positive electrode current collector. The positive electrode plate has an electrode group wound or laminated via a separator, and the electrode group is housed in a metal outer can, and one of the metal outer can and the two electrode plates Are electrically connected.

According to the present invention, a metal layer having Cu or Ni is formed on both surfaces of a base material layer made of metal or alloy in contact or non-contact, so that the load characteristics of the lithium ion battery are excellent and the negative electrode of the negative electrode plate The active material can be filled with high density. In addition, since the base material layer is made of a metal or alloy having a melting point of 120 ° C. or higher and 800 ° C. or lower, even when an internal short circuit occurs, it melts due to heat generation and interrupts the current. Can be suppressed.

It is sectional drawing of the negative electrode collector for lithium ion batteries which concerns on this embodiment. It is sectional drawing which showed the structure of the lithium ion battery typically. It is a figure explaining the state before a foreign material pierces about the negative electrode produced by apply | coating and drying a slurry-like negative electrode mixture to a negative electrode collector. It is a figure explaining the state which the foreign material pierced about the negative electrode. It is a figure explaining the state which the short circuit part of the negative electrode heat | fever-generated and the base material layer was fuse | melted.

Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. However, the embodiments are for facilitating understanding of the principle of the present invention, and the scope of the present invention is as follows. The present invention is not limited to the embodiments, and other embodiments in which those skilled in the art appropriately replace the configurations of the following embodiments are also included in the scope of the present invention.

FIG. 1 is a cross-sectional view of a negative electrode current collector 800 for a lithium ion battery according to this embodiment. As shown in FIG. 1, the negative electrode current collector 800 for a lithium ion battery includes a base layer 100 and a metal layer 110, and the metal layer 110 is formed on both surfaces of the base layer 100. Has been. A negative electrode active material layer 120 is formed on the surface of the metal layer 110.

The base material layer 100 is made of a metal or alloy having a melting point of 120 to 800 ° C. Since the base material layer 100 is formed of a metal or alloy having a melting point in the above range, even when an internal short circuit of the battery occurs, the current can be interrupted by melting by heat generation. That is, when the melting point of the metal or alloy forming the base material layer 100 is less than 120 ° C., there is a risk of breakage at a location where current is concentrated, such as a lead weld, when a large current such as high output charge / discharge flows. Further, if the melting point of the metal or alloy is higher than 800 ° C., melting due to heat generation when an internal short circuit occurs is unlikely to occur, and the current interruption effect at the time of the short circuit may be diminished. Therefore, the melting point of the metal or alloy used for the base material layer 100 is 120 to 800 ° C. Preferably, it is 200 to 700 ° C.

The base material layer 100 is not particularly limited, but for example, Al, 72Ag-28Cu (BAg-8), Sn, 58Bi-42Sn, etc. can be used from the above-mentioned conditions, and preferably Al.

The electric conductivity of the base material layer 100 is preferably 10 ⁶ S / m or more. This is because if the electrical conductivity is less than 10 ⁶ S / m, the electrical conductivity may decrease.

The thickness of the base material layer 100 is not particularly limited, but is preferably 1 to 100 μm, and more preferably 5 to 20 μm. When the thickness is less than 5 μm, it becomes difficult to process into a foil shape, and at the same time, the strength tends to be insufficient and the productivity may be lowered. When the thickness is 20 μm or more, the current interruption effect at the time of short circuit may be reduced, and the current occupying ratio in the battery becomes high, so that the energy density tends to decrease.

The metal layer 110 is not particularly limited as long as it does not alloy with Li, react with the electrolytic solution, or dissolve in the anode in the potential region used as the negative electrode, but is made of, for example, Cu or Ni. It can also be formed of a Cu alloy such as Au, a Ni alloy such as Ni—Fe, or an alloy containing Cu and Ni such as Cu—Ni.

The thickness of the metal layer 110 is not particularly limited, but is preferably 0.1 to 2 μm. When the thickness is smaller than 0.1 μm, it becomes difficult to uniformly cover the surface of the base material layer 100, and the surface of the base material layer 100 is partially exposed. Side reactions such as Li alloying may occur. When the thickness is larger than 2 μm, the ratio of the metal layer 110 in the negative electrode current collector becomes high, and the current blocking effect at the time of short circuit may be reduced.

The method for laminating the metal layer 110 on the base material layer 100 is not particularly limited, and for example, electroplating, electroless plating, vapor deposition, or the like can be suitably used.

Next, a lithium ion battery 900 using the above negative electrode current collector 800 for lithium ion battery will be described.

FIG. 2 is a cross-sectional view schematically showing the configuration of the lithium ion battery 900. As the lithium ion battery 900, for example, a cylindrical lithium ion secondary battery as shown in FIG. 2 can be adopted. This lithium ion secondary battery is provided with a safety valve mechanism that releases gas to the outside of the battery when the pressure in the battery increases due to the occurrence of an abnormality such as an internal short circuit.

In the lithium ion battery 900, an electrode group 104 in which a positive electrode 101 and a negative electrode 102 are wound through a separator 103 is housed in a battery case 107 together with a non-aqueous electrolyte. Insulating

plates

109 and 119 are arranged above and below the electrode group 104, the positive electrode 101 is joined to the filter 112 via the positive electrode lead 105, and the negative electrode 102 is also connected to the negative electrode terminal via the negative electrode lead 106. Is joined to the bottom.

The positive electrode 101 includes a positive electrode current collector and a positive electrode active material layer carried thereon. The positive electrode active material layer can contain a binder, a conductive agent, and the like in addition to the positive electrode active material. The positive electrode 101 is prepared, for example, by mixing a positive electrode mixture composed of a positive electrode active material and an optional component with a liquid component to prepare a positive electrode mixture slurry, applying the obtained slurry to a positive electrode current collector, and drying the mixture. .

Similarly, for the negative electrode 102, for example, a negative electrode mixture composed of a negative electrode active material and an optional component is mixed with a liquid component to prepare a negative electrode mixture slurry, and the obtained slurry is applied to the negative electrode current collector 800 and dried. To make. When the negative electrode active material is an element that can be alloyed with lithium, a silicon compound, a tin compound, or the like, the negative electrode active material layer may be formed by a vapor phase method. Examples of the vapor phase method include chemical vapor deposition (CVD), vacuum deposition, and sputtering.

As the positive electrode active material of the lithium ion battery 900, a lithium composite metal oxide can be used. For example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O _z (M = Na, Mg, Sc, Y , Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B). Here, x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3. In addition, x value which shows the molar ratio of lithium is a value immediately after active material preparation, and increases / decreases by charging / discharging. Further, a part of these lithium-containing compounds may be substituted with a different element. Surface treatment may be performed with a metal oxide, lithium oxide, a conductive agent, or the like, or the surface may be subjected to a hydrophobic treatment. A positive electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type. The positive electrode active material layer may be a stack of two or more layers having different compositions.

As the negative electrode active material of the lithium ion battery of the present invention, for example, metals, metal fibers, carbon materials, oxides, nitrides, tin compounds, silicon compounds, various alloy materials, and the like can be used. Examples of the carbon material include carbon materials such as various natural graphites, cokes, graphitized carbon, carbon fibers, spherical carbon, various artificial graphites, and amorphous carbon. As the oxide, for example, lithium titanate having a spinel crystal structure is used. Lithium titanate having a typical spinel crystal structure is represented by the formula: Li ₄ Ti ₅ O ₁₂ . However, the general _{_{_{_{formula: Li x Ti 5-y M}}}} y O 12 + lithium titanate represented by _z may be used as well. Here, M is composed of vanadium, manganese, iron, cobalt, nickel, copper, zinc, aluminum, boron, magnesium, calcium, strontium, barium, zirconium, niobium, molybdenum, tungsten, bismuth, sodium, gallium, and rare earth elements. At least one selected from the group, x is a value of lithium titanate immediately after synthesis or in a completely discharged state, 3 ≦ x ≦ 5, 0.005 ≦ y ≦ 1.5, − 1 ≦ z ≦ 1. In addition, a simple substance such as silicon (Si) or tin (Sn), or a silicon compound or tin compound such as an alloy, a compound, or a solid solution is preferable from the viewpoint of a large capacity density. For example, as a silicon compound, SiO _x (0.05 <x <1.95), or any one of these may be B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, An alloy, a compound, a solid solution, or the like in which a part of Si is substituted with at least one element selected from the group consisting of Ta, V, W, Zn, C, N, and Sn can be used. As the tin compound, Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (0 <x <2), SnO ₂ , SnSiO ₃ or the like can be applied. A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, you may laminate | stack two or more layers from which a negative electrode active material layer differs in a composition.

As the binder for the positive electrode 101 or the negative electrode 102, for example, PVDF, PTFE, polyethylene, polypropylene, and aramid resin can be used. Examples of the conductive agent included in the electrode include natural graphite and artificial graphite graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and other carbon blacks, carbon fibers and metal fibers. Conductive fibers such as carbon powder, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, organic conductive materials such as phenylene derivatives, etc. Is used.

The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 97% by weight of the positive electrode active material, 1 to 20% by weight of the conductive agent, and 1 to 10% by weight of the binder.

Also, the blending ratio of the negative electrode active material and the binder is preferably in the range of 93 to 99% by weight of the negative electrode active material and 1 to 10% by weight of the binder, respectively. Further, when the negative electrode active material layer is formed by a vapor phase method, the binder may not be included.

As the positive electrode current collector, a long porous conductive substrate or a nonporous conductive substrate is used. As the material used for the conductive substrate, for example, stainless steel, Al, Ti or the like is used. It is more preferable to use Al from the viewpoint of imparting a current interruption effect at the time of a short circuit to the positive electrode current collector and reducing the weight. The thickness of the positive electrode current collector is not particularly limited, but is preferably 1 to 100 μm, and more preferably 5 to 20 μm. By setting the thickness of the positive electrode current collector in the above range, it is possible to reduce the weight while maintaining the strength of the electrode plate.

As the separator 103 interposed between the positive electrode 101 and the negative electrode 102, a microporous thin film, a woven fabric, a non-woven fabric or the like having a high ion permeability and having a predetermined mechanical strength and an insulating property is used. As a material of the separator 103, for example, polyolefin such as polypropylene and polyethylene is preferable from the viewpoint of safety of the lithium ion battery because it is excellent in durability and has a shutdown function. The thickness of the separator 103 is generally 10 to 300 μm, but is preferably 40 μm or less. Further, the range of 15 to 30 μm is more preferable, and the more preferable range of the separator thickness is 20 to 25 μm. Furthermore, the microporous film may be a single layer film made of one kind of material, or a composite film or multilayer film made of one kind or two or more kinds of materials. The porosity of the separator 103 is preferably in the range of 30 to 70%. Here, the porosity indicates the volume ratio of the pores to the separator volume. A more preferable range of the porosity of the separator 103 is 35 to 60%.

As the non-aqueous electrolyte, a liquid, gel or solid (polymer solid electrolyte) substance can be used.

A liquid non-aqueous electrolyte (non-aqueous electrolyte) can be obtained by dissolving an electrolyte (for example, a lithium salt) in a non-aqueous solvent. The gel-like non-aqueous electrolyte includes a non-aqueous electrolyte and a polymer material that holds the non-aqueous electrolyte. As this polymer material, for example, PVDF, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, polyvinylidene fluoride hexafluoropropylene and the like are preferably used.

As the non-aqueous solvent for dissolving the electrolyte, a known non-aqueous solvent can be used. Although the kind of this non-aqueous solvent is not specifically limited, For example, cyclic carbonate ester, chain | strand-shaped carbonate ester, cyclic carboxylic acid ester etc. are used. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and the like. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). A non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

For the electrolyte dissolved in the non-aqueous solvent, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , and LiB ₁₀ Cl ₁₀ are used. Can do. One electrolyte may be used alone, or two or more electrolytes may be used in combination.

In addition, the non-aqueous electrolyte may contain a material that can be decomposed on the negative electrode as an additive to form a film having high lithium ion conductivity and increase charge / discharge efficiency. Examples of the additive having such a function include vinylene carbonate (VC), 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, and the like. These may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate is preferable. In the above compound, part of the hydrogen atoms may be substituted with fluorine atoms. The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 2 mol / L.

Furthermore, the non-aqueous electrolyte may contain a known benzene derivative that decomposes during overcharge to form a film on the electrode and inactivate the battery. As the benzene derivative, those having a phenyl group and a cyclic compound group adjacent to the phenyl group are preferable. As the cyclic compound group, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, a phenoxy group and the like are preferable. Specific examples of the benzene derivative include cyclohexylbenzene, biphenyl, diphenyl ether and the like. These may be used alone or in combination of two or more. However, the content of the benzene derivative is preferably 10% by volume or less of the entire non-aqueous solvent.

The filter 112 is connected to the inner cap 113, and the protrusion of the inner cap 113 is joined to the metal valve plate 114. Further, the valve plate 114 is connected to a terminal plate 108 that also serves as a positive electrode terminal. The terminal plate 108, the valve plate 114, the inner cap 113, and the filter 112 are integrated to seal the opening of the battery case 107 via the gasket 111.

When an abnormality such as an internal short circuit occurs in the unit cell 100 and the pressure in the unit cell 100 increases, the valve body 114 swells toward the terminal plate 108, and the inner cap 113 and the valve body 114 are disconnected. The current path is interrupted. When the pressure in the unit cell 100 further increases, the valve body 114 is broken. As a result, the gas generated in the unit cell 100 is discharged to the outside through the through hole 112a of the filter 112, the through hole 113a of the inner cap 113, the tear of the valve body 114, and the opening 108a of the terminal plate 108. Is done.

Next, the operation of the negative electrode current collector 800 for a lithium ion battery used in the above lithium ion battery 900 will be described.

FIG. 3 is a diagram for explaining a state before a foreign object is stuck in the negative electrode 102 produced by applying a slurry-like negative electrode mixture to a negative electrode current collector 800 for a lithium ion battery and drying it. As shown in FIG. 3, the metal layer 110 is formed on both surfaces of the base material layer 100, and the negative electrode active material layer 120 is formed on the surface of the metal layer 110. The negative electrode active material layer 120 schematically describes negative electrode active material particles.

The thickness of the negative electrode active material layer 120 is not particularly limited, but is, for example, 100 μm or less, and preferably 10 to 100 μm.

The average particle diameter of the negative electrode active material particles in the negative electrode active material layer 120 is not particularly limited, but is, for example, 50 μm or less, preferably 30 μm or less, and more preferably 10 μm or less. Further, this is not the case when the negative electrode active material layer is formed by a vapor phase method.

FIG. 4 is a diagram for explaining a state in which the foreign material 200 is stuck in the negative electrode 102 described above. As shown in FIG. 4, when a large foreign object 200 such as a nail is pierced through the negative electrode 102, an internal short circuit occurs between the negative electrode 102 and a positive electrode (not shown), and the short-circuited portion generates heat. To do.

FIG. 5 is a diagram illustrating a state where the short circuit portion of the negative electrode 102 generates heat and the base material layer 100 is melted. As shown in FIG. 5, when the short-circuit portion of the negative electrode 102 generates heat, the heat generation causes the base material layer 100 to melt, and a void 130 is generated in the base material layer 100. Since the gap 130 is generated, the internal short circuit current can be cut off, and an excessive increase in the battery temperature at the time of the short circuit can be suppressed.

In addition, although the part 117 which is not melt | dissolving and contacts the space | gap part 130 among the metal layers 110 may lose | disappear by the heat_generation | fever of a short circuit part, it interrupts | blocks an internal short circuit current more in that case. And an excessive increase in battery temperature can be suppressed.

(Other embodiments)
In the above-described embodiment, the negative electrode current collector 800 for a lithium ion battery is configured as a three-layer structure including the base material layer 100 and the metal layer 110 formed in contact with both surfaces thereof. However, the scope of the present invention is not limited to such an embodiment.

A negative electrode current collector 800 for a lithium ion battery includes a base material layer 100 made of a metal or an alloy having a melting point of 120 to 800 ° C., and a metal layer 110 made of Cu or Ni formed in contact with both surfaces of the base material layer 100. And a conductive resin layer formed in contact with both surfaces of the metal layer 110 is also possible. The conductive resin layer is formed of, for example, a conductive polymer, and polypyrrole, polyaniline, polyacetylene, polythiophene, polyparaphenylene, polyphenylene vinylene, or the like can be used as the conductive polymer.

The softening point of the conductive polymer is preferably 100 to 400 ° C., more preferably 200 to 300 ° C. The thickness of the conductive resin layer is not particularly limited, but is preferably 0.1 to 2 μm.

The negative electrode current collector 800 for a lithium ion battery includes a base material layer 100 made of a metal or an alloy having a melting point of 120 to 800 ° C., a conductive resin layer formed in contact with both surfaces of the base material layer 100, A structure provided with a metal layer 110 made of Cu or Ni formed in contact with both surfaces of the conductive resin layer is also possible.

Even in the negative electrode current collector 800 for a lithium ion battery having these structures described above, the base material layer 100 and the conductive resin layer are melted in the short-circuit portion at the time of short-circuit, so that the internal short-circuit current can be interrupted. And since the current collection of a negative electrode is performed from the base material layer 100, the metal layer 110, and a conductive resin layer, a load characteristic is good. Furthermore, since the base material layer 100 and the metal layer 110 make it difficult to relieve stress during rolling, a decrease in the density of the negative electrode active material hardly occurs.

The present invention is not limited to the above-described three layers and five layers as long as the substrate layer and the metal layer are provided, and the present invention may be applied to a four-layer or six-layer structure. Included in the range.

Next, the present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
(1) Production of Negative Electrode 102 A metal layer 110 made of Cu having a thickness of 1 μm was formed on both surfaces by using an aluminum foil having a thickness of 10 μm as a base material layer 100 to produce a negative electrode current collector 800 for a lithium ion battery.

In addition, 3 kg of artificial graphite, 40 g% aqueous dispersion of styrene-butadiene rubber particles (trade name: BM-400B, manufactured by Nippon Zeon Co., Ltd.), 30 g of carboxymethylcellulose and an appropriate amount of water were used in a double-arm kneader. The mixture was stirred to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied and dried on both surfaces of a negative electrode current collector 800 for a lithium ion battery, and rolled three times at a linear pressure of 110 kg / cm. The thickness after rolling was 160 μm, and the active material density of the negative electrode active material layer 120 was 1.55 g / cm ³ . This was cut into a dimension of 57.5 mm in width and 650 mm in length to produce a negative electrode 102. One end of a nickel lead was connected to the portion of the negative electrode 102 where the negative electrode current collector for a lithium ion battery was exposed.

(2) Production of Positive Electrode 101 A polypropylene aqueous dispersion was applied and dried on both surfaces of a 15 μm thick aluminum current collector to form an insulating resin. The coating weight was about 0.1 mg / cm. N-methyl-pyrrolidone (hereinafter referred to as NMP) solution (trade name: PVDF # 1320, manufactured by Kureha Co., Ltd.) 1 kg containing lithium carbonate 3 kg, PVDF 12% by weight, 90 g of acetylene black and an appropriate amount of NMP The mixture was stirred with a combination machine to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was applied and dried on both sides of a 15 μm thick aluminum current collector, and rolled three times at a linear pressure of 1000 kg / cm. The thickness after rolling was 175 μm. This was cut into dimensions of 56 mm in width and 600 mm in length to produce the positive electrode 101. One end of the aluminum lead was connected to the portion of the positive electrode 101 where the positive electrode current collector was exposed.

(3) Preparation of Electrolyte Solution A nonaqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent containing EC and EMC at a volume ratio of 1: 3.

(4) Battery assembly The above-described positive and negative electrodes were wound through a separator 103 made of a single layer of polyethylene resin having a thickness of 20 μm to constitute an electrode group 104. The upper insulating plate 109 and the lower insulating plate 119 were attached to both ends in the longitudinal direction of the electrode plate group, and then inserted into a bottomed cylindrical battery case 107 (diameter 18 mm, height 65 mm, inner diameter 17.85 mm). The other ends of the aluminum lead and the nickel lead were connected to the lower part of the positive electrode terminal and the inner bottom surface of the battery case 107, respectively. Thereafter, 5.5 g of the non-aqueous electrolyte described above was injected into the battery case 107. A terminal plate 108 that supports the positive terminal was attached to the opening of the battery case 107, and the end of the opening was caulked toward the terminal plate 108 to seal the battery case 107. Thus, a cylindrical lithium ion battery having a design capacity of 2000 mAh was produced. This is referred to as the battery of Example 1.

(Example 2)
For the battery of Example 1, except that the negative electrode current collector 800 for a lithium ion battery was formed by forming a metal layer 110 made of Cu having a thickness of 3 μm on both surfaces of an aluminum substrate layer 100 having a thickness of 6 μm. A lithium ion battery was produced in the same manner as in Example 1. The negative electrode thickness after rolling was 159 μm, and the negative electrode active material density was 1.57 g / cm ³ . This is referred to as the battery of Example 2.

(Comparative Example 1)
A lithium ion battery was fabricated in the same manner as in Example 1 except that a 10 μm thick copper foil was used for the negative electrode current collector for the lithium ion battery. The negative electrode thickness after rolling was 157 μm, and the negative electrode active material density was 1.57 g / cm ³ . This is referred to as the battery of Comparative Example 1.

(Comparative Example 2)
The battery of Example 1 is the same as Example 1 except that a negative electrode current collector for a lithium ion battery is formed by forming a metal layer made of Cu having a thickness of 1 μm on both surfaces of a PET resin substrate having a thickness of 10 μm. Similarly, a lithium ion battery was produced. When forming Cu on the PET resin substrate, a thickness of about 0.1 μm was formed by vapor deposition, and then the thickness was set to 1 μm by electroplating. The negative electrode thickness after rolling was 176 μm, and the negative electrode active material density was 1.40 g / cm ³ . This is referred to as the battery of Comparative Example 2.

(Comparative Example 3)
For the battery of Comparative Example 2, Comparative Example 2 was used except that a negative electrode current collector for a lithium ion battery was formed by forming a metal layer made of Cu of 3 μm thickness on both sides of a PET resin substrate of 6 μm thickness. Similarly, a lithium ion battery was produced. The negative electrode thickness after rolling was 175 μm, and the negative electrode active material density was 1.41 g / cm ³ . This is referred to as the battery of Comparative Example 3.

Using the lithium ion batteries obtained in Examples 1 and 2 and Comparative Examples 1 to 3, the following nail penetration test and charge / discharge test were performed to evaluate safety and load characteristics.

[Nail penetration test]
Each battery was charged under the following conditions. Then, in a 20 ° C. environment, an iron nail having a diameter of 2.7 mm was pierced from the side surface of the charged battery to a depth of 2 mm at a speed of 5 mm / second to generate an internal short circuit. The temperature reached after 30 seconds of the battery at that time was measured with a thermocouple placed on the side surface of the battery away from the nail penetration position. The results are shown in Table 1.

Charging conditions:
Constant current charging; current value 1400mA / end-of-charge voltage 4.3V
Constant voltage charging; voltage value 4.3V / charging end current 100mA
[Charge / discharge test]
Each battery was charged and discharged under the following conditions in a 20 ° C. environment, and the discharge capacities during 0.2 C discharge and 3 C discharge were determined. The percentage (%) of the discharge capacity at the time of 3C discharge with respect to the discharge capacity at the time of 0.2C discharge was determined and used as the initial load characteristics. The results are shown in Table 1.

Charging / discharging conditions:
Constant current charging; current value 1400mA / end-of-charge voltage 4.2V
Constant voltage charge; voltage value 4.2V / charge end current 100mA
Constant current discharge; current value 400 mA (0.2 C) / discharge end voltage 3.0 V
Constant current charging; current value 1400mA / end-of-charge voltage 4.2V
Constant voltage charge; voltage value 4.2V / charge end current 100mA
Constant current discharge; current value 6000 mA (3 C) / discharge end voltage 3.0 V

In the battery of Comparative Example 1 using a negative electrode current collector for a lithium ion battery made of only Cu, the battery surface temperature rose significantly due to overheating accompanying the expansion of the short-circuited portion. Further, Comparative Example 2 and Comparative Example 3 using a base material layer made of PET instead of the Al base material layer had a large decrease in load characteristics, although the battery surface temperature was lower than that of Comparative Example 1 due to the current blocking effect. . This is presumably because current collection at a large current becomes insufficient because current collection at the negative electrode depends only on Cu of the thin metal layer. Moreover, the negative electrode active material density in the same rolling conditions was also low. This is presumably because the base material layer made of PET resin has relaxed the stress during rolling.

On the other hand, in the batteries of Example 1 and Example 2, the battery surface temperature is greatly reduced as compared with Comparative Example 1, and it is clear that the current blocking effect due to Al of the base material layer is exhibited. Furthermore, the active material density during rolling was high, and the load characteristics were hardly deteriorated. This is different from Comparative Example 2 and Comparative Example 3 in which PET resin is used for the base layer in this example, and the base layer is less deformed and less stress-relieved during rolling, and the base layer is also electronically conductive. Is considered to be due to the high contribution to current collection.

However, according to a comparison between Example 1 and Example 2, the battery surface temperature after the nail penetration test of Example 2 where the metal layer is thick is somewhat high, and the thickness of the metal layer is more preferably 2 μm or less.

Since the present invention can provide a lithium ion battery having excellent safety while preventing deterioration of the load characteristics of the battery, it is useful as a technique that can be developed not only for small power sources such as portable electronic devices but also for large power sources such as EVs. is there.

DESCRIPTION OF SYMBOLS 100: Base material layer 101: Positive electrode 102: Negative electrode 103: Separator 104: Electrode group 105: Positive electrode lead 106: Negative electrode lead 107: Battery case 108: Terminal board 109: Insulating plate 110: Metal layer 111: Gasket 112: Filter 113: Inner cap 114: Valve body 119: Insulating plate 120: Negative electrode active material layer 800: Negative electrode current collector for lithium ion battery 900: Lithium ion battery

Claims

A base material layer made of a metal or alloy having a melting point of 120 ° C. or higher and 800 ° C. or lower;
A negative electrode current collector for a lithium ion battery, comprising: a metal layer having Cu or Ni formed on both surfaces of the base material layer in contact or non-contact.
The negative electrode current collector for a lithium ion battery according to claim 1, wherein the base material layer has an electric conductivity of 10 6 S / m or more.
The negative electrode current collector for a lithium ion battery according to claim 1 or 2, wherein the base material layer is made of Al.
The negative electrode plate in which the negative electrode active material layer was formed in the surface of the negative electrode collector for lithium ion batteries of any one of Claim 1 thru | or 3, and the positive electrode active material layer in the surface of a positive electrode collector. The positive electrode plate has an electrode group wound or laminated via a separator, and this electrode group is housed in a metal outer can, and one of the metal outer can and the two electrode plates And a lithium ion battery characterized by being electrically connected to each other.