JP2018049824A - Collector member for lithium ion secondary battery, collector for lithium ion secondary battery and high-power tab for lithium ion secondary battery using the same, and method of manufacturing collector member for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a collector member for a lithium ion secondary battery, capable of obtaining a lithium ion secondary battery which is excellent in durability without causing a deterioration in battery performance even if a micro-short circuit occurs temporarily at the inside of the lithium ion secondary battery.SOLUTION: A collector member for a lithium ion secondary battery comprises a conductive film containing a conductive material and a polymer compound, and is characterized in that an electric resistance value (R) in a first direction of directions perpendicular to a thickness direction of the conductive film, an electric resistance value being minimum in the first direction, is smaller than an electric resistance value (R) in a second direction perpendicular to the thickness direction and the first direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a current collector for a lithium ion secondary battery, a current collector for a lithium ion secondary battery using the same, a high voltage tab for a lithium ion secondary battery, and a current collector for a lithium ion secondary battery Regarding the method.

In recent years, secondary devices such as lithium ion secondary batteries, electric double layer capacitors, and the like are used as power devices for electronic devices, hybrid vehicles, electric vehicles, and household power supply facilities. In particular, lithium ion secondary batteries are considered suitable for electric vehicles because of their high energy density and high durability against repeated charging and discharging, and various developments have been intensively advanced.

In particular, as a method for improving the battery performance of a bipolar battery, a technique of using a current collector containing a specific polymer material is disclosed (see Patent Document 1).

However, current collectors containing conventional polymer materials cause current to flow from the current collector surface toward the micro short circuit when a short circuit occurs temporarily inside the lithium ion secondary battery. There was a problem in the durability of the battery performance, for example, the battery performance deteriorated even with an extremely small short circuit.

JP 2012-150905 A

The present invention provides a lithium ion secondary battery that is capable of obtaining a lithium ion secondary battery that is excellent in durability without degradation of battery performance even when a short-circuit occurs temporarily inside the lithium ion secondary battery. It aims at providing the current collection member for batteries.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have reached the present invention.
That is, this invention consists of an electroconductive film containing an electroconductive material and a high molecular compound, and among the directions orthogonal to the thickness direction of the said electroconductive film, electric resistance value becomes the 1st which becomes the minimum. An electric resistance value (R ¹ ) in a direction is smaller than an electric resistance value (R ² ) in a second direction orthogonal to the thickness direction and the first direction. Current collector for secondary battery; current collector for lithium ion secondary battery using current collector for lithium ion secondary battery of the present invention; lithium ion secondary using current collector for lithium ion secondary battery of the present invention High-voltage tab for secondary battery; a first mixture orthogonal to the thickness direction of the conductive film by stretching the mixture of the conductive material and the polymer compound into a film and aligning the orientation of the conductive material in the stretching direction. In the direction Kicking electric resistance value (R ¹⁾ is a feature to obtain a small conductive film than the electric resistance value (R ²⁾ in a second direction perpendicular to the above thickness direction and the first direction A method for producing a current collecting member for a lithium ion secondary battery.

When the current collector member for a lithium ion secondary battery according to the present invention is used, even if a micro short circuit is temporarily generated inside the lithium ion secondary battery, the direction in which the current flows is limited. As a result, the current flowing toward the portion is reduced, the battery performance is not deteriorated, and a lithium ion secondary battery excellent in durability can be obtained.

FIG. 1 is a perspective view schematically showing a conductive film constituting a current collecting member for a lithium ion secondary battery of the present invention. FIG. 2 is a perspective view schematically showing an example of a current collecting member for a lithium ion secondary battery that can be used as a high voltage tab for a lithium ion secondary battery. 3 (a) and 3 (b) show that the current collecting member for a lithium ion secondary battery of the present invention is used as a current collector for a lithium ion secondary battery and a high voltage tab for a lithium ion secondary battery in a stacked battery. It is a perspective view showing typically an example of composition at the time of having done. FIG. 4A and FIG. 4B are process diagrams schematically showing a method for producing a conductive film by hot pressing a woven fabric.

The current collecting member for a lithium ion secondary battery of the present invention is composed of a conductive film containing a conductive material and a polymer compound, and has an electric resistance among the directions orthogonal to the thickness direction of the conductive film. The electric resistance value (R ¹ ) in the first direction where the value is minimum is smaller than the electric resistance value (R ² ) in the second direction orthogonal to the thickness direction and the first direction. It is characterized by that.

The conductive material constituting the conductive film is selected from conductive materials, but from the viewpoint of suppressing ion permeation in the current collector, a material that does not have conductivity with respect to lithium ions used as a charge transfer medium Is preferably used.

Conductive materials include 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.) And the like, and mixtures thereof, but are not limited thereto.
These conductive materials may be used alone or in combination of two or more. Moreover, these alloys or metal oxides may be used. From the viewpoint of electrical stability, preferably nickel, aluminum, stainless steel, carbon, silver, copper, titanium and mixtures thereof, more preferably nickel, silver, aluminum, stainless steel and carbon, particularly preferably nickel and Carbon. In addition, these conductive materials may be obtained by coating a conductive material (a metal material among the above-described conductive materials) by plating or the like around a particle ceramic material or a resin material.
The electric conductivity of the conductive material is preferably 1 to 1 × 10 ¹⁰ mS / cm.
The electrical conductivity of the conductive material is as follows: 30 mg of the conductive material is placed in a glass cylinder having an inner diameter of 5 mm, tapped 50 times, and sandwiched between SUS316 cylinders with a diameter of 5 mm, and a pressure of 250 kN is applied. However, it is a value measured by sandwiching SUS316 cylinders at both ends with a measurement terminal clip of an electrochemical measuring device (Solartron 1280C).

The conductive material has a ratio of the length to the diameter (length / diameter; hereinafter referred to as aspect) from the viewpoint of affinity with the polymer compound constituting the conductive film and anisotropy of the electrical resistance value of the conductive film. (Preferably 2 or more) is preferable, and the shape is more preferably tubular or fibrous. Preferable examples include carbon nanotubes or conductive fibers. As conductive fibers, carbon fibers such as PAN-based carbon fibers, pitch-based carbon fibers, and synthetic fibers are uniformly made of highly conductive metal or graphite. Conductive fiber dispersed, metal fiber made of metal such as stainless steel, conductive fiber with organic fiber surface coated with metal, conductive fiber surface coated with resin containing conductive material Examples thereof include fibers. Among these conductive fibers, carbon fibers are preferable. A polypropylene resin in which graphene is kneaded is also preferable.
When the conductive material is a material having an aspect ratio of 2 or more, the average length is preferably 0.2 to 10,000 μm, and the average diameter is preferably 0.1 to 10 μm. Within this range, when the conductive film is produced, the conductive material is easy to line up along the stretching direction of the film and the crystal direction of the polymer compound constituting the conductive film, and the anisotropy clearly defined by the electrical resistance value is present. It is preferable because it is easily expressed.

Examples of the polymer compound constituting the conductive film include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), poly Tetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin and mixtures thereof Etc.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferable, and polyethylene (PE), polypropylene (PP) and polymethylpentene are more preferable. (PMP).

FIG. 1 is a perspective view schematically showing a conductive film constituting a current collecting member for a lithium ion secondary battery of the present invention. Hereinafter, the thickness direction, the first direction, the second direction, and the like of the conductive film will be described with reference to this drawing.
In the conductive film 10 shown in FIG. 1, the thickness direction of the conductive film is the direction indicated by the double arrow T. Of the directions orthogonal to this direction, one direction having the smallest electrical resistance value is defined as a first direction (a direction indicated by a double-headed arrow X in FIG. 1), and the thickness direction and the first direction are A direction orthogonal to the direction (a direction indicated by a double-headed arrow Y in FIG. 1) is defined as a second direction.
The first direction and the second direction are directions parallel to the main surface of the conductive film.

In the conductive film constituting the current collecting member for the lithium ion secondary battery of the present invention, the electrical resistance value (R ¹ ) in the first direction of the conductive film is the electrical resistance value (R ² ) in the second direction. Smaller than. That is, it can be said that the film has anisotropy in conductivity on the main surface of the conductive film.
The fact that the conductive film constituting the current collecting member is an anisotropic film has a direction in which it is difficult for current to flow in the conductive film, and the current flow in the conductive film is free. It means rather limited. Therefore, even if a micro short-circuit occurs temporarily inside the lithium ion secondary battery, it is limited to some extent that current freely flows in the conductive film. The direction in which the current flows is biased in a specific direction according to the anisotropy. As a result, current is prevented from concentrating and flowing on the main surface of the conductive film, so that a lithium ion secondary battery with no deterioration in battery performance and excellent durability can be obtained.
In addition, since the current does not flow on the main surface of the conductive film, when the distribution of the active material in contact with the conductive film is uneven and the voltage distribution varies, the current flows on the main surface of the conductive film. The variation in the voltage distribution can be suppressed by flowing.

In the conductive film 10 shown in FIG. 1, a conductive fiber 12 as a conductive material is included in the matrix of the polymer compound 11, and the conductive fiber 12 is in the direction along the first direction in the conductive film 10. Oriented.
When the conductive fibers are oriented in this way, in the first direction, the conductivity is good and the electric resistance value (R ¹ ) is minimized. On the other hand, in the second direction, the electrical conductivity is poor and the electric resistance value (R ² ) is large. That is, R ¹ is smaller than R ² .

In the current collecting member for a lithium ion secondary battery of the present invention, the ratio (R ¹ / R ² ) between the electric resistance value (R ¹ ) in the first direction and the electric resistance value (R ² ) in the second direction is It is preferable that it is 0.5 or less. When the ratio (R ¹ / R ² ) between the electric resistance value (R ¹ ) with respect to the first direction and the electric resistance value (R ² ) with respect to the second direction is 0.5 or less, the inside of the lithium ion secondary battery Even if a short-circuit occurs temporarily in the battery, the current in the conductive film flows preferentially in the first direction having a smaller electrical resistance value, and as a result, the current flow is limited. Performance deterioration is reduced, and a lithium ion secondary battery with more excellent durability can be obtained.
The electrical resistance value (R ¹ ) with respect to the first direction is preferably 1 × 10 ⁻¹⁰ to 1 × 10 ¹ Ω · m, and the electrical resistance value (R ² ) with respect to the second direction is 2 × 10. It is preferably ⁻¹⁰ to 1 × 10 ¹⁰ Ω · m, and more preferably 2 × 10 ^{−4 to} 5 × 10 ⁰ Ω · m. When the electrical resistance value (R ¹ ) is in this range, the contact resistance with the active material that contacts the conductive film can be reduced, cycle characteristics are favorable, and the electrical resistance value (R ² ) is in this range. Therefore, variation in the voltage distribution of the active material in contact with the conductive film can be suppressed, and cycle characteristics are improved, which is preferable.
The electrical resistance value is calculated according to the following method.
A first strip that is 1 cm wide × 23 cm long and cut in the longitudinal direction with respect to the first direction and a second strip that is cut in the longitudinal direction with respect to the second direction are respectively prepared from the conductive film. . For each of the first strip and the second strip, a point 1.5 cm from the end of the strip is used as a starting point (0 cm measurement point), and from there, 5 cm measurement points, 10 cm measurement points, 15 cm measurement points, and 20 cm, respectively. The measurement point. For each of the first strip and the second strip, the film thicknesses at five points including the starting point are measured, and the values are averaged to be t ¹ (μm) and t ² (μm), respectively.
Subsequently, for each of the first strip and the second strip, one of the measurement terminals of the electrochemical measurement device (Solartron 1280C) is kept in contact with the 0 cm measurement point, and the other measurement terminal is moved to the 5 cm measurement point. The resistance value (Ω) at each measurement point is read by contacting the 10 cm measurement point, the 15 cm measurement point, and the 20 cm measurement point. The four measured resistance values are plotted on a graph where the vertical axis is the resistance value and the horizontal axis is the distance between measurement points (distance from the starting point to the measurement point), and the plotted points are linearly approximated by the least square method. Find the slope of the straight line obtained. The inclinations of the first strip and the second strip are defined as a ¹ (Ω / cm) and a ² (Ω / cm), respectively, and the electric resistance values R ¹ and R ² of the first strip and the second strip are expressed as follows. Obtained from the following formula.
^{R 1 = a 1 × (t} 1/10000 × 1)
^{R 2 = a 2 × (t} 2/10000 × 1)

The conductive film preferably has a thickness of 5 to 400 μm. In addition, the electric resistance value (R ³ ) in the thickness direction is not particularly limited, but since it is preferable that the conductivity in the thickness direction is high when a stacked battery is formed, 1 × 10 ⁻³ to 1 It is preferably × 10 ⁻¹ Ω · m.

The content of the conductive material in the conductive film is preferably 5 to 90 parts by weight, more preferably 15 to 80 parts by weight in 100 parts by weight of the conductive film, from the viewpoint of conductivity in the thickness direction. .
From the viewpoint of film strength, the content of the polymer compound in the conductive film is preferably 10 to 95 parts by weight, more preferably 20 to 80 parts by weight, based on 100 parts by weight of the conductive film.

For the conductive film, in addition to the conductive material and the polymer compound, if necessary, other components [dispersing agent, crosslinking accelerator (aldehyde / ammonia-amine skeleton-containing compound, thiourea skeleton-containing compound, guanidine skeleton-containing compound] , Thiazole skeleton-containing compound, sulfenamide skeleton-containing compound, thiuram skeleton-containing compound, dithiocarbamate skeleton-containing compound, xanthate skeleton-containing compound and dithiophosphate skeleton-containing compound), cross-linking agent (sulfur, etc.), colorant , Ultraviolet absorbers, general-purpose plasticizers (phthalic acid skeleton-containing compounds, trimellitic acid skeleton-containing compounds, phosphoric acid group-containing compounds, epoxy skeleton-containing compounds, etc.)] and the like can be appropriately added. From the viewpoint of electrical stability, the total amount of other components added is preferably 0.001 to 5 parts by weight, more preferably 0.001 to 3 parts by weight, based on 100 parts by weight of the conductive film.

The current collecting member for a lithium ion secondary battery of the present invention can be used as a current collector for a lithium ion secondary battery or a high voltage tab for a lithium ion secondary battery.
When the current collector member for a lithium ion secondary battery according to the present invention is used, even if a micro short circuit is temporarily generated inside the lithium ion secondary battery, the direction in which the current flows is limited. The current flowing toward the part can be reduced. Therefore, the current collecting member for a lithium ion secondary battery according to the present invention can be preferably used as a current collector and a high current tab capable of improving the safety of a laminated battery having a particularly large current value.
The stacked battery has a configuration in which single cells are stacked using the positive electrode side current collector, the positive electrode, the separator, the negative electrode, and the negative electrode side current collector as a single cell.
In a stacked battery that is often used, a metal foil such as an aluminum foil or a copper foil is used as a current collector. The current collector for a lithium ion secondary battery of the present invention includes a conductive material and a polymer compound. A resin current collector made of a conductive film.
Further, the high-power tab for a lithium ion secondary battery of the present invention is a member (terminal) used for taking out current from the current collector to the outside of the battery and charging from an external power source, and comprising a conductive material and a polymer compound. A resin current collector made of a conductive film.
That is, in the stacked battery, any or all of the positive electrode side current collector, the negative electrode side current collector, and the high voltage tab may be the conductive film 10 shown in FIG.

Known materials can be used as the positive electrode active material, the negative electrode active material, the separator and the like in the stacked battery. The positive electrode active material and the negative electrode active material may be a coated active material coated with a resin such as an acrylic resin.

FIG. 2 is a perspective view schematically showing an example of a current collecting member for a lithium ion secondary battery that can be used as a high voltage tab for a lithium ion secondary battery.
A high voltage tab 120 for a lithium ion secondary battery shown in FIG. 2 is formed by providing a striped metal thin film 20 extending in a direction along the first direction on the conductive film 10 shown in FIG.
When such a metal thin film 20 is provided, current can flow through the metal thin film 20 provided along the first direction, and the electrical resistance value becomes small. On the other hand, the metal thin film does not contribute to the current flow along the second direction.
Therefore, the anisotropy of the current collecting member for the lithium ion secondary battery can be ensured.
And since an electric current can be taken out of a battery from a metal thin film, the function as a high electric power tab is exhibited preferably.

The metal thin film can be formed on the conductive film by a known metal thin film forming method such as sputtering, vapor deposition, or plating.
As a method of forming a stripe-shaped metal thin film, a part where a metal thin film is not formed is masked and a thin film is formed by sputtering or the like, or after a thin film is formed on the entire conductive film, a part where the metal thin film is formed is formed. A method of removing the metal thin film other than the portion masked by etching and masking by etching is mentioned.

It is preferable that the high voltage tab for the lithium ion secondary battery of the present invention including the current collecting member for the lithium ion secondary battery further includes a current limiting element such as a PTC thermistor and a fuse. As the current limiting element, current suppressing means or current interrupting means described in Japanese Patent No. 5540588 can be used.
Since the high voltage tab is used as a member (terminal) used for taking energy into and out of the battery as a current, it is preferable to provide a connection part in which metal thin films are connected to each other.
By providing the current limiting element, it is possible to prevent a current from flowing into the minute short-circuited portion via the connecting portion when temporarily short-circuited, and as a result, a large current from flowing to the minute short-circuited portion.

When the current collector for a lithium ion secondary battery according to the present invention is used as a current collector for a lithium ion secondary battery and a high voltage tab for a lithium ion secondary battery, the lithium ion secondary as a current collector for the lithium ion secondary battery is used. A secondary battery current collecting member and a lithium ion secondary battery current collecting member as a high voltage tab can be laminated and used. In this case, the current collector for the lithium ion secondary battery and the high voltage tab for the lithium ion secondary battery may be arranged and laminated so that the first direction is the same direction. The first and second high-voltage tabs for the body and the lithium ion secondary battery may be arranged in a direction perpendicular to each other and stacked. From the viewpoint of current collection efficiency and the like, it is preferable to arrange and laminate the current collector for the lithium ion secondary battery and the high voltage tab for the lithium ion secondary battery in the same direction.

3 (a) and 3 (b) show that the current collecting member for a lithium ion secondary battery of the present invention is used as a current collector for a lithium ion secondary battery and a high voltage tab for a lithium ion secondary battery in a stacked battery. It is a perspective view showing typically an example of composition at the time of having done.
In the stacked battery, the positive electrode 31, the separator 32, and the negative electrode 33 are repeatedly stacked via a current collector, and the high-power tab is disposed on the outermost side.
FIG. 3A shows an example in which the first direction of the high voltage tab 120 for the lithium ion secondary battery and the first direction of the current collector 10 for the lithium ion secondary battery are in the same direction.
On the other hand, FIG. 3B shows an example in which the first direction of the high-voltage tab 120 for the lithium ion secondary battery and the first direction of the current collector 10 for the lithium ion secondary battery are perpendicular to each other. Yes.
3A and 3B show only the periphery of the uppermost single cell in the stacked battery, and the structure below the current collector 10 for the lithium ion secondary battery is omitted. doing.

The current collector for a lithium ion secondary battery of the present invention can be produced, for example, by the following method. The following method is a method for producing a current collecting member for a lithium ion secondary battery according to the present invention. A mixture obtained by mixing a conductive material and a polymer compound is stretched into a film and the orientation of the conductive material is set in the stretching direction. By aligning, the electric resistance value (R ¹ ) in the first direction orthogonal to the thickness direction of the conductive film is the second direction orthogonal to the thickness direction and the first direction. characterized in that to obtain a small conductive film than the electric resistance value (R ²⁾ in a method for producing a lithium ion secondary battery current collector member.

First, a conductive material, a polymer compound, and other components are mixed as necessary. As a mixing method, a known masterbatch production method and a thermoplastic resin composition (a composition comprising a dispersant, a filler and a thermoplastic resin, or a composition comprising a masterbatch and a thermoplastic resin), etc. A known mixing method is used, and the pellet-like or powder-like components can be mixed by heating, melting and mixing using an appropriate mixer such as a kneader, an internal mixer, a Banbury mixer, and a roll.

There is no particular limitation on the order of addition of each component during mixing.
The obtained mixture may be further pelletized or powdered with a pelletizer or the like.

The current collecting member for a lithium ion secondary battery of the present invention can be obtained by applying a physical pressure to the mixture obtained by the above mixing and stretching it in a certain direction to form a film. Examples of the forming method for drawing into a film by stretching include known film forming methods such as a T-die method, an inflation method, and a calendar method. In general, a material for forming a film has a property that a crystal structure of a resin constituting the film and a filler contained in the film are aligned in the stretching direction by stretching in a certain direction before the structure is fixed. When a conductive material is included as a constituent material, the conductive material is oriented in the stretching direction by stretching the film. As a result, the electrical resistance value of the current collector for the lithium ion secondary battery is anisotropic [first It means that the electric resistance value (R ¹ ) in the direction is smaller than the electric resistance value (R ² ) in the second direction].

In the above molding method, the mixture is stretched by applying physical pressure, and then the melted mixture is formed into a film after passing through a step of flowing in a certain direction. When the mixture flows in a certain direction, the conductive material contained in the mixture is oriented in the direction of flow and the orientation of the conductive material can be aligned, so the conductive material is oriented in a specific direction within the conductive film. The conductive film can be manufactured.
Then, because the conductive material is oriented in a specific direction, the electric resistance value (R ¹ ) in the first direction orthogonal to the thickness direction of the conductive film is equal to the thickness direction and the first direction. A conductive film smaller than the electrical resistance value (R ² ) in the second direction orthogonal to the direction of 1 can be obtained.

Further, as a method for producing a current collecting member for a lithium ion secondary battery according to the present invention, a woven fabric having a non-conductive resin fiber as a warp and a conductive fiber as a weft is used together with a polymer compound. There is a method of heat pressing.
FIG. 4A and FIG. 4B are process diagrams schematically showing a method for producing a conductive film by hot pressing a woven fabric.
FIG. 4A shows a woven fabric in which resin fibers having no conductivity are warp yarns and the conductive fibers are weft yarns. For example, the fabric 50 is a fabric using warp yarns made of polypropylene resin fibers 51 and weft yarns made of polypropylene resin fibers kneaded with graphene. Then, the woven fabric 50 is mixed with polypropylene resin pellets, put into a mold, and heated and pressed. Polypropylene resin pellets, polypropylene resin constituting the resin fibers 51 as warp yarns, and polypropylene resin constituting the conductive fibers 52 as weft yarns. Melt to form a film.

FIG.4 (b) has shown typically the electroconductive film obtained by heat-pressing the textile fabric shown to Fig.4 (a).
In the obtained conductive film 60, the melted resin becomes the polymer compound 61, and the graphene contained in the conductive fiber 52 remains linear according to the position where the conductive fiber 52 was present. A conductive material 62 is formed.
FIG. 4B shows a state in which graphene as the conductive material 62 remains in the first direction, and the conductive material remains in this way, so that the first direction of the conductive film is shown. The electric resistance value (R ¹ ) in the first direction is the minimum value, the electric resistance value (R ¹ ) in the first direction is smaller than the electric resistance value (R ² ) in the second direction, It becomes a film having anisotropy in properties.

EXAMPLES Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples without departing from the gist of the present invention. Unless otherwise specified, “part” means “part by weight” and “%” means “% by weight”.

<Production Example 1>
<Preparation of coating resin solution>
A 4-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 407.9 parts of N, N-dimethylformamide (hereinafter referred to as DMF) and heated to 75 ° C. . Next, a monomer compounded solution containing 242.8 parts of methacrylic acid, 97.1 parts of methyl methacrylate, 242.8 parts of 2-ethylhexyl methacrylate and 116.5 parts of DMF, and 2,2′-azobis (2,4-dimethylvalero) Nitrile) 1.7 parts and 2,2′-azobis (2-methylbutyronitrile) 4.7 parts dissolved in 58.3 parts of DMF and an initiator solution were stirred while nitrogen was blown into a four-necked flask. Then, radical polymerization was carried out by continuously dropping with a dropping funnel over 2 hours. After completion of dropping, the reaction was continued at 75 ° C. for 3 hours. Subsequently, the temperature was raised to 80 ° C., and the reaction was continued for 3 hours to obtain a copolymer solution having a resin concentration of 50%. To this, 789.8 parts of DMF was added to obtain a resin solution having a resin solid content concentration of 30% by weight.

<Production Example 2>
<Production of coated positive electrode active material>
As the positive electrode active material, a coated positive electrode active material coated with a resin was used.
Into a universal mixer, 1578 g of LiCoO ₂ powder was stirred at room temperature and 150 rpm, and 146 g of the resin solution (resin solid content concentration 30 wt%) obtained in Production Example 1 was added dropwise over 60 minutes, and further 30 minutes. Stir. Next, 44 g of acetylene black [manufactured by Denki Kagaku Kogyo Co., Ltd.] was mixed in three portions with stirring, the temperature was raised to 70 ° C. while stirring for 30 minutes, the pressure was reduced to 0.01 MPa and held for 30 minutes. . By the above operation, 1666 g of a coated positive electrode active material was obtained.

<Production Example 3>
<Preparation of coated negative electrode active material>
As the negative electrode active material, a coated negative electrode active material coated with a resin was used.
Put 1578 g of graphite powder [manufactured by Nippon Graphite Industry Co., Ltd.] in a universal mixer and stir at 150 rpm at room temperature and apply 292 g of the resin solution (resin solid content concentration 30 wt%) obtained in Production Example 1 over 60 minutes. The mixture was added dropwise and stirred for another 30 minutes. Next, 88 g of acetylene black [manufactured by Denki Kagaku Kogyo Co., Ltd.] was mixed in three portions with stirring, the temperature was raised to 70 ° C. while stirring for 30 minutes, the pressure was reduced to 0.01 MPa and held for 30 minutes. . By the above operation, 1754 g of a coated negative electrode active material was obtained.

<Example 1>
In a twin-screw extruder, 70 parts of polypropylene [trade name “Sun Allomer PL500A”, manufactured by Sun Allomer Co., Ltd.], 25 parts of carbon nanotube [trade name: “FloTube 9000”, manufactured by CNano Inc.] (average length 10 μm, average diameter 15 nm) , An aspect ratio of about 670), and 5 parts of a dispersant [trade name “Yumex 1001”, manufactured by Sanyo Chemical Industries, Ltd.] were melt-kneaded at 200 ° C. and 200 rpm to obtain a resin mixture (Z-1). .
The obtained resin mixture (Z-1) is passed through a T-die extrusion film molding machine and stretched to obtain a current collecting member for a lithium ion secondary battery having a film thickness of 100 μm [resin current collector (X-1)] was obtained. The electrical resistance values and the ratios thereof in two directions orthogonal to the resin current collector (X-1) were measured by the following method and listed in Table 1.

<Measurement of electrical resistance ratio>
In the resin current collector, a first strip which is 1 cm wide × 23 cm long and cut in the longitudinal direction with respect to the film stretching direction (referred to as the first direction), and a direction perpendicular to the first direction (second 2nd strips cut in the longitudinal direction with respect to the first direction). For each of the first strip and the second strip, a point 1.5 cm from the end of the strip is used as a starting point (0 cm measurement point), and from there, 5 cm measurement points, 10 cm measurement points, 15 cm measurement points, and 20 cm, respectively. The measurement point. For each of the first strip and the second strip, the film thicknesses at 5 points including the starting point were measured, and the values were averaged to be t ¹ (μm) and t ² (μm), respectively.
Subsequently, for each of the first strip and the second strip, one of the measurement terminals of the electrochemical measurement device (Solartron 1280C) is kept in contact with the 0 cm measurement point, and the other measurement terminal is moved to the 5 cm measurement point. The 10 cm measurement point, 15 cm measurement point, and 20 cm measurement point were brought into contact with each other, and the resistance value (Ω) at each measurement point was read. The measured and read four resistance values are plotted on a graph where the vertical axis is the resistance value and the horizontal axis is the distance between measurement points (distance from the starting point to the measurement point), and the plotted points are linearly approximated by the least squares method. The slope of the obtained straight line was determined. For each of the first and second strips, the slopes of the straight lines are determined as a ¹ (Ω / cm) and a ² (Ω / cm), and the electric resistance values R ^{1 of the first} and second strips are obtained. and it obtains the R ² from the following equation was calculated the ratio.
^{R 1 = a 1 × (t} 1/10000 × 1)
^{R 2 = a 2 × (t} 2/10000 × 1)

<Example 2>
A warp yarn made of fibers obtained by spinning a kneaded product of polypropylene and graphene obtained in the same manner as in the examples of WO2015 / 125916 and a weft yarn made of polypropylene fibers were heated at 180 ° C. and 50 MPa. By pressing, the current collecting member [resin current collector (X-2)] for a lithium ion secondary battery of the present invention in the form of a film in which fibers were fused and integrated was obtained. At this time, the fibers of the warp yarn are almost in shape and can be confirmed visually. The electrical resistance values and the ratios in two directions orthogonal to the resin current collector (X-2) were measured in the same manner as in Example 1, and are shown in Table 1.

<Example 3>
<Example 1> In Example 1 except that 25 parts of carbon nanotubes were changed to 71 parts of nickel powder (Type 255 manufactured by Vale), 70 parts of polypropylene were changed to 27 parts, and 5 parts of dispersant were changed to 2 parts. By carrying out similarly, the current collection member [resin current collector (X-3)] for lithium ion secondary batteries of the present invention with a film thickness of 100 μm was obtained. The electrical resistance values and the ratios in two directions orthogonal to the resin current collector (X-3) were measured in the same manner as in Example 1, and are shown in Table 1.

<Example 4>
Using the current collecting member for a lithium ion secondary battery obtained in <Example 1> as a base material, nickel was deposited in a stripe shape with a line width of 5 mm and a line interval of 1 mm along the first direction with a thickness of 1 μm. Thus, a current collecting member for a lithium ion secondary battery of the present invention having a film thickness of 100 μm [high voltage tab (X-4)] was obtained. As in Example 1, the electrical resistance values and the ratios thereof in two directions perpendicular to the high voltage tab (X-4) were measured and listed in Table 1.

<Comparative Example 1>
<Example 1> In Example 1 except that 25 parts of carbon nanotubes were changed to 71 parts of nickel powder (Type 255 manufactured by Vale), 70 parts of polypropylene were changed to 27 parts, and 5 parts of dispersant were changed to 2 parts. Similarly, it melt-kneaded using the biaxial extruder, and obtained the resin mixture (Z-2). Further, the resin mixture (Z-2) was molded by a solution casting method to obtain a comparative current collector for a lithium ion secondary battery [resin current collector (H-1)] having a thickness of 100 μm. The electrical resistance values and the ratios thereof in two directions orthogonal to the resin current collector (H-1) were measured in the same manner as in Example 1, and are shown in Table 1.

<Comparative example 2>
Using the current collecting member for lithium ion secondary battery obtained in <Comparative Example 1> as a base material, nickel was deposited on the entire surface of the base material with a film thickness of 1 μm, and a comparative lithium ion secondary battery with a film thickness of 100 μm was used. A current collecting member [high power tab (H-2)] was obtained. As in Example 1, the electrical resistance values and the ratios in the two directions perpendicular to the high voltage tab (H-2) were measured and listed in Table 1.

<Examples 5 to 10, Comparative Example 3>
<Cycle charge / discharge test>
A laminate cell was prepared by the following method using the prepared current collecting member as a positive electrode side current collector, a negative electrode side current collector and a high voltage tab, and a cycle charge / discharge test was performed by the following method. did.

<Production of evaluation cell>
Prepare two rectangular glass epoxy boards (Nikko Kasei Nicolite NL-EG-23N) with an outer shape of width 105mm x length 205mm, and leave the inner periphery of each 15mm width, and glass epoxy on both sides. A film for heat sealing (Admer QE-060 manufactured by Mitsui Chemicals) having the same shape as the outer periphery of the substrate was fixed. Next, a rectangular PE separator (manufactured by Celgard) with a width of 95 mm and a length of 195 mm is fixed by heat-sealing to one side of the glass epoxy substrate, and a frame-shaped glass epoxy substrate is fixed to one side of the separator. A frame member was produced.
The current collectors for lithium ion secondary batteries produced in Examples 1 and 2 and Comparative Example 1 were cut into rectangles each having an outer shape of width 105 mm × length 205 mm, and the coated positive electrode active material obtained in Production Example 2 was further formed thereon. A positive electrode active material composition (coated positive electrode active material concentration: 95%) obtained by mixing material particles with N-methylpyrrolidone (hereinafter referred to as NMP) in a rectangular shape having a width of 66 mm and a length of 166 mm using a squeegee Was applied, and then NMP was evaporated to form a positive electrode active material layer. At this time, the basis weight corresponding to the positive electrode covering active material is 130 mg / cm ² .
The lithium ion secondary battery current collector produced in Example 3 and Comparative Example 1 was cut into rectangles each having an outer shape of 105 mm in width and 205 mm in length, and the coated negative electrode active material particles obtained in Production Example 3 were formed thereon. A negative electrode active material composition (coated negative electrode active material concentration: 95%) obtained by mixing with NMP was applied in a rectangular shape with a width of 70 mm and a length of 170 mm with a squeegee, leaving the outer periphery, and then NMP was evaporated. Thus, a negative electrode active material layer was formed. The basis weight corresponding to the negative electrode-coated active material at this time is 53 mg / cm ² .
A frame-shaped glass epoxy substrate having the positive electrode active material layer in the single cell frame member so that the positive electrode current collector and the negative electrode current collector are a combination of the current collector members for lithium ion secondary batteries described in Table 2. The separator and the active material layer were placed inside such that the negative electrode active material layer was opposed to each other with the separator interposed therebetween. In addition, inside the frame-shaped glass epoxy substrate of the single-cell frame member before containing the positive electrode active material layer, an electrolyte solution [mixed solution of ethylene carbonate and diethylene carbonate (EC / DEC = 3/7 ( The volume ratio)) LiPF ₆ 1M solution] was poured. Thereafter, a portion where the positive electrode side current collector / glass epoxy substrate / negative electrode side current collector overlap is heat-sealed to produce a single cell, and this single cell is in contact with the positive electrode side current collector and the negative electrode side current collector. A laminated cell was produced by stacking 8 layers in the direction. Furthermore, the high current tabs (X-4 or H-2) produced in Example 4 or Comparative Example 2 were respectively combined with the positive electrode side current collector and the negative electrode side current collector in the outermost layer, as shown in Table 2, respectively. Pasted to be. Further, a strip-shaped nickel foil for current collection is attached to one side perpendicular to the striped Ni layer on the high voltage tab (X-4) with a conductive adhesive, and either one of the high voltage tab (H-2) A strip-shaped nickel foil for current collection was attached to one side with a conductive adhesive. Next, the laminated cell was accommodated in a laminate container and sealed while being arranged so that the adhered nickel foil was exposed to the outside, and an evaluation cell was produced.
Next, the following cycle charge / discharge test was performed.

<Cycle charge / discharge test>
The fabricated evaluation cell was charged to 33 V by a constant current constant voltage method (current value: 4 mA / cm ² ) in an environment of 45 ° C., and then discharged to 22 V by a constant current method (current value 4 mA / cm ² ). The above-described charging operation and discharging operation were performed once again, which was designated as charge / discharge at the first cycle, and the above-described operations were repeated until the charge / discharge operation at 50th cycle was completed.
A value (capacity maintenance ratio) obtained by dividing the discharge capacity at the 50th cycle of the evaluation cell by the discharge capacity at the first cycle was calculated. Three evaluation cells having the same configuration were prepared, and the average value of the capacity retention ratio in each combination is shown in Table 2. A higher capacity retention ratio after 50 cycles means that there is no performance degradation due to deterioration.

表１中、ＰＰはポリプロピレン、ＣＮＴはカーボンナノチューブ、Ｎｉはニッケルをそれぞれ表す。

In Table 1, PP represents polypropylene, CNT represents carbon nanotube, and Ni represents nickel.

In Examples 5 to 10, the capacity retention rate after 50 cycles was as high as 80% or more, whereas in Comparative Example 3, the capacity retention rate after 50 cycles was the current collecting member for the lithium ion secondary battery of the present invention. The deterioration of the evaluation cell due to charge / discharge was confirmed.

The current collecting member for a lithium ion secondary battery obtained by the present invention is particularly useful as a current collector for a lithium ion secondary battery used for a mobile phone, a personal computer, a hybrid vehicle, and an electric vehicle.

10, 60 Conductive film (current collector for lithium ion secondary battery)
11, 61 Polymer compound 12, 52 Conductive fiber 20 Metal thin film 31 Positive electrode 32 Separator 33 Negative electrode 50 Fabric 51 Resin fiber 62 Conductive material 120 High-power tab for lithium ion secondary battery

Claims (8)

A conductive film comprising a conductive material and a polymer compound,
Of the directions orthogonal to the thickness direction of the conductive film, the electric resistance value (R ¹ ) in the first direction where the electric resistance value is the smallest is the thickness direction and the first direction. A current collecting member for a lithium ion secondary battery, wherein the current collecting member is smaller than an electric resistance value (R ² ) in a second direction orthogonal thereto. ^2. The ratio (R ¹ / R ² ) between the electric resistance value (R ¹ ) with respect to the first direction and the electric resistance value (R ² ) with respect to the second direction is 0.5 or less. A current collecting member for a lithium ion secondary battery. 3. The current collector for a lithium ion secondary battery according to claim 1, wherein an electric resistance value (R ¹ ) with respect to the first direction is 1 × 10 ⁻¹⁰ to 1 × 10 ¹ Ω · m. The lithium ion secondary battery according to any one of claims 1 to 3, wherein an aspect ratio of the conductive material is 2 or more, and the conductive material is oriented in a direction along the first direction in the conductive film. Current collecting member. The collector for lithium ion secondary batteries using the current collection member for lithium ion secondary batteries in any one of Claims 1-4. A high voltage tab for a lithium ion secondary battery using the current collecting member for a lithium ion secondary battery according to claim 1. The high voltage tab for a lithium ion secondary battery according to claim 6, wherein a stripe-shaped metal thin film extending in a direction along the first direction is provided on the conductive film. An electrical resistance value in a first direction perpendicular to the thickness direction of the conductive film is obtained by stretching a mixture of the conductive material and the polymer compound into a film and aligning the orientation of the conductive material in the stretching direction ( R ¹ ) obtains a conductive film having a smaller electrical resistance value (R ² ) in a second direction perpendicular to the thickness direction and the first direction. The manufacturing method of the current collection member for secondary batteries.

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