JP6939760B2 - Positive electrode current collector foil - Google Patents

Description

The present disclosure relates to a positive electrode current collector foil.

Japanese Unexamined Patent Publication No. 2016-07654 (Patent Document 1) discloses an electrode having a titanium foil.

Japanese Unexamined Patent Publication No. 2016-07654

Conventionally, an aluminum (Al) foil has been used for the positive electrode current collector foil. Generally, the electrode manufacturing process includes a roll press. The Al foil has a thickness of a predetermined value or more so that the Al foil does not break during roll pressing.

Titanium (Ti) foil can be considered as an alternative material to Al foil. Ti foil is superior to Al foil in mechanical properties such as elongation. By using the Ti foil for the positive electrode current collector foil, the thickness of the positive electrode current collector foil can be reduced while maintaining the same strength as the conventional Al foil. It is considered that the volumetric energy density of the battery can be improved by reducing the thickness of the positive electrode current collector foil that does not directly contribute to the battery capacity.

However, Ti has a larger electrical resistivity than Al. The use of Ti foil can increase battery resistance to a non-negligible extent.

An object of the present disclosure is to achieve both volumetric energy density and battery resistance.

Hereinafter, the technical configuration and the action and effect of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The scope of claims should not be limited by the correctness of the mechanism of action.

The positive electrode current collector foil of the present disclosure includes a first aluminum layer, a titanium layer and a second aluminum layer. The titanium layer has a first main surface and a second main surface. The second main surface is the opposite surface of the first main surface. The first aluminum layer covers the first main surface. The second aluminum layer covers the second main surface. The thickness of the titanium layer is 2 μm or more and 6 μm or less. The thickness of each of the first aluminum layer and the second aluminum layer is 0.1 μm or more and less than the thickness of the titanium layer.

The base layer of the positive electrode current collector foil is a Ti layer. When the thickness of the Ti layer is 2 μm or more, the positive electrode current collector foil can have the strength to withstand the roll press. It is expected that the volumetric energy density will be improved when the thickness of the Ti layer is 6 μm or less.

A first Al layer and a second Al layer are formed on both the front and back surfaces of the Ti layer. Hereinafter, in the present specification, "each of the first Al layer and the second Al layer" may be collectively referred to as "Al layer". Al has a small electrical resistivity as compared with Ti. It is expected that the increase in battery resistance is suppressed by forming the Al layer on the surface of the Ti layer.

The thickness of the Al layer is 0.1 μm or more. If the thickness of the Al layer is less than 0.1 μm, the battery resistance may increase to a non-negligible degree. The larger the thickness of the Al layer, the lower the battery resistance is expected. However, the thickness of the Al layer is less than the thickness of the Ti layer. If the thickness of the Al layer is greater than or equal to the thickness of the Ti layer, wrinkles and wrinkles may occur during roll pressing.

From the above, according to the positive electrode current collector foil of the present disclosure, it is expected that both the volumetric energy density and the battery resistance are compatible.

FIG. 1 is a schematic cross-sectional view showing the configuration of the positive electrode current collector foil of the present embodiment. FIG. 2 is a schematic cross-sectional view showing the configuration of the electrode group of this embodiment. FIG. 3 is a schematic plan view showing the configuration of the positive electrode of this embodiment. FIG. 4 is a schematic plan view showing the configuration of the negative electrode of this embodiment.

Hereinafter, embodiments of the present disclosure (referred to as “the present embodiment” in the present specification) will be described. However, the following description does not limit the scope of claims.

<Positive current collector foil>
FIG. 1 is a schematic cross-sectional view showing the configuration of the positive electrode current collector foil of the present embodiment.
The positive electrode current collector foil 11 includes a first Al layer 1, a Ti layer 3, and a second Al layer 2. The thickness of the positive electrode current collector foil 11 may be, for example, 2.2 μm or more and 16 μm or less. The thickness of the positive electrode current collector foil 11 may be, for example, 13 μm or less, or 10 μm or less. The thickness of the positive electrode current collector foil 11 may be, for example, 3.2 μm or more, or 4.2 μm or more.

《Ti layer》
The Ti layer 3 is a base layer of the positive electrode current collector foil 11. The Ti layer 3 has a first main surface 3a and a second main surface 3b. The second main surface 3b is the opposite surface of the first main surface 3a. The Ti layer 3 may be composed of, for example, substantially only Ti. The Ti layer 3 may be composed of, for example, 1% by mass or less of impurities and the remaining Ti. The impurities may be, for example, 0.2% by mass or less. The impurity may be, for example, oxygen. The Ti layer 3 may be, for example, a pure Ti foil or the like.

The thickness of the Ti layer 3 is 2 μm or more and 6 μm or less. When the thickness of the Ti layer 3 is 2 μm or more, the positive electrode current collector foil 11 can have a strength that can withstand a roll press. When the thickness of the Ti layer 3 is 6 μm or less, it is expected that the volumetric energy density will be improved. The thickness of the Ti layer 3 may be, for example, 2 μm or more and 4 μm or less, or 4 μm or more and 6 μm or less.

《Al layer》
The first Al layer 1 covers the first main surface 3a. The second Al layer 2 covers the second main surface 3b. A positive electrode active material layer (not shown) may be formed in contact with the first Al layer 1 and the second Al layer 2. It is expected that the increase in battery resistance is suppressed by forming the first Al layer 1 and the second Al layer 2 on the surface of the Ti layer 3.

Each of the first Al layer 1 and the second Al layer 2 can be formed by, for example, vacuum deposition. Each of the first Al layer 1 and the second Al layer 2 may be composed of, for example, substantially only Al. Each of the first Al layer 1 and the second Al layer 2 may be composed of, for example, 1% by mass or less of impurities and the remaining Al. The impurity may be, for example, oxygen. The first Al layer 1 and the second Al layer 2 may have substantially the same composition, or may have different compositions from each other, for example.

The thickness of each of the first Al layer 1 and the second Al layer 2 is 0.1 μm or more. If the thickness of the Al layer is less than 0.1 μm, the battery resistance may increase to a non-negligible degree. The larger the thickness of the Al layer, the lower the battery resistance is expected. The thickness of each of the first Al layer 1 and the second Al layer 2 may be, for example, 1 μm or more.

However, the thickness of each of the first Al layer 1 and the second Al layer 2 is less than the thickness of the Ti layer 3. If the thickness of the Al layer is equal to or greater than the thickness of the Ti layer 3, wrinkles and wrinkles may occur during roll pressing. The thickness of each of the first Al layer 1 and the second Al layer 2 may be, for example, 3 μm or less, or 1 μm or less.

The thickness of the first Al layer 1 and the thickness of the second Al layer 2 may be substantially the same or different from each other, for example.

Hereinafter, examples of the present disclosure (referred to as “the present examples” in the present specification) will be described. However, the following description does not limit the scope of claims.

<Manufacturing of positive electrode current collector foil>
<< Comparative Examples 1 to 3 >>
Al foils (1N30 material) having the thicknesses shown in Table 1 below were prepared. In Comparative Examples 1 to 3, the Al foil was used as the positive electrode current collector foil. That is, in Comparative Examples 1 to 3, the positive electrode current collector foil is composed of only a single Al layer. In Table 1 below, the thickness of the Al foil is described in the column of "1st Al layer" for convenience.

<< Comparative Examples 4 to 8 >>
Ti foils having the thicknesses shown in Table 1 below were prepared respectively. The Ti foil is composed of a chemical component corresponding to "Pure Titanium Type 1" of "JIS H 4600". In Comparative Examples 4 to 8, the Ti foil was used as it was as the positive electrode current collector foil. That is, in Comparative Examples 4 to 8, the positive electrode current collector foil is composed of only a single Ti layer.

<< Example 1 >>
A positive electrode current collector foil having a three-layer structure was produced by the following procedure.
Ti foil was prepared. The Ti foil is a material that will later become the Ti layer 3. The Ti foil is composed of a chemical component corresponding to "Pure Titanium Type 1" of "JIS H 4600". The thickness of the Ti foil was 4 μm.

The Ti foil was immersed in acetone for 5 minutes. As a result, the Ti foil was degreased. After degreasing, the Ti foil was immersed in the cleaning solution for 5 minutes. The cleaning solution consists of 0.25% by mass of hydrofluoric acid, 4% by mass of nitric acid, and the balance of water. After washing, the Ti foil was thoroughly rinsed with ion-exchanged water. From the above, the surface of the Ti foil was cleaned.

The Ti foil was cut into plane dimensions of 45 mm x 20 mm. A vacuum deposition apparatus was prepared. Ti foil was placed on the holder in the chamber. A resistance heating boat (made of tungsten) was prepared. Al mass was weighed. The Al mass was placed on a resistance heating boat. A resistance heating boat was placed in the chamber. The resistance heating board was located below the Ti foil in the chamber. The distance between the Ti foil and the resistance heating boat was about 40 cm.

The inside of the chamber was depressurized to a degree of vacuum of ^{10 -4 Pa or less.} A rotary pump and a turbo molecular pump were used for the depressurization operation. The Al mass was heated by passing an electric current through the resistance heating boat. As a result, Al steam was generated. Al vapor solidified on the surface of the Ti foil, and Al was deposited on the surface of the Ti foil. As a result, the first Al layer 1 was formed. After the formation of the first Al layer 1, the second Al layer 2 was formed on the opposite surface of the Ti foil (Ti layer 3). The second Al layer 2 was formed in the same manner as the first Al layer 1.

The thickness of each of the first Al layer 1 and the second Al layer 2 was calculated from the mass increment accompanying the deposition of Al and the specific gravity of Al (2.7 g / cm ^3). The thickness of each of the first Al layer 1 and the second Al layer 2 was 3 μm. It was confirmed that the calculated value was in good agreement with the measured value by the thickness gauge. From the above, the positive electrode current collector foil 11 of Example 1 was manufactured.

<< Examples 2 and 3, Comparative Examples 9 and 10 >>
As shown in Table 1 below, a positive electrode current collector foil was produced in the same manner as in Example 1 except that the thicknesses of the first Al layer and the second Al layer were changed.

<Battery manufacturing>
Each positive electrode current collector foil obtained above was used to manufacture a positive electrode. Further, a battery containing the positive electrode was manufactured. The procedure is as follows.

1. 1. Manufacture of positive electrode The following materials were prepared.
Positive electrode active material: Lithium nickel cobalt manganate (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ )
Conductive material: Acetylene black (AB)
Binder: Polyvinylidene fluoride (PVdF)
Dispersion medium: N-methyl-2-pyrrolidone (NMP)

A coating material was prepared by dispersing the positive electrode active material, the conductive material, and the binder in the dispersion medium. The mixing ratio of the solid content was "positive electrode active material / conductive material / binder = 95/2/3 (mass ratio)".

The paint was applied to the surface (both front and back surfaces) of the positive electrode current collector foil by the applicator and dried to form the positive electrode active material layer. The basis weight of the positive electrode active material layer was ^{200 g / m 2 per side.} A hot air dryer was used for the drying operation. The drying temperature was 80 ° C. The drying time was 15 minutes. The positive electrode active material layer and the positive electrode current collector foil were compressed by a roll press machine. The target density of the positive electrode active material layer after roll pressing was 3.5 g / cm ³ .

2. Manufacture of negative electrode The following materials were prepared.
Negative electrode active material: Spherical natural graphite (average particle size = 10 μm, specific surface area = 4.7 m ² / g)
Binder: Carboxymethyl cellulose (CMC) / Styrene butadiene rubber (SBR) = 1/1 (mass ratio)
Dispersion medium: Water Negative electrode current collector foil: Copper (Cu) foil (thickness = 10 μm)

A paint was prepared by dispersing the negative electrode active material and the binder in the dispersion medium. The mixing ratio of the solid content was "negative electrode active material / binder = 97/3".

The paint was applied to the surface (one side) of the negative electrode current collector foil by the applicator and dried to form the negative electrode active material layer. The basis weight of the negative electrode active material layer was 125 g / m ² . A hot air dryer was used for the drying operation. The drying time was 10 minutes. The negative electrode active material layer and the negative electrode current collector foil were compressed by a roll press machine. The target density of the negative electrode active material layer after roll pressing was 1.6 g / cm ³ .

3. 3. Assembly A separator with a three-layer structure was prepared. The separator was formed by laminating a polypropylene layer, a polyethylene layer and a polypropylene layer in this order. The separator had a thickness of 20 μm.

FIG. 2 is a schematic cross-sectional view showing the configuration of the electrode group of this embodiment.
The electrode group 50 was formed by laminating the negative electrode 20, the separator 30, the positive electrode 10, the separator 30, and the negative electrode 20 in this order.

FIG. 3 is a schematic plan view showing the configuration of the positive electrode of this embodiment.
The positive electrode active material layer 12 had a plane dimension of 40 mm × 15 mm (dimension in the xy plane). A lead joint was formed at one end in the x-axis direction. At the lead joint, the positive electrode current collector foil 11 was exposed from the positive electrode active material layer 12. The width dimension (width dimension in the x-axis direction) of the lead joint was 5 mm. The positive electrode lead terminal 13 was bonded to the lead joint portion by ultrasonic bonding. The positive electrode lead terminal 13 was made of Al.

FIG. 4 is a schematic plan view showing the configuration of the negative electrode of this embodiment.
The negative electrode active material layer 22 had a planar dimension of 42 mm × 16 mm. A lead joint was formed at one end in the x-axis direction. At the lead joint, the negative electrode current collector foil 21 was exposed from the negative electrode active material layer 22. The width dimension of the lead joint was 7 mm. The negative electrode lead terminal 23 was bonded to the lead bonding portion by ultrasonic bonding. The negative electrode lead terminal 23 was made of Cu.

A pouch made of aluminum laminated film was prepared. The electrode group 50 was housed in the pouch. The electrolyte was injected into the pouch. The electrolytic solution contained the following solvent and lithium salt.

Solvent: EC / EMC = 1/3 (volume ratio)
Lithium salt: LiFP ₆ (1 mol / L)

Here, "EC" indicates ethylene carbonate. "EMC" indicates ethyl methyl carbonate.

The pouch was sealed with a heat sealer. From the above, the battery was manufactured. The battery of this embodiment is a laminated lithium-ion battery.

4. Initial charge / discharge The initial discharge capacity was measured by a cycle of charging, pausing, and discharging. The initial discharge capacity of each battery was within the range of 43 ± 1 mAh.

Charging: CCCV method, CC current = 5mA, CV voltage = 4.2V, cut current = 1mA
Pause: 30 minutes Discharge: CC method, CC current = 5mA, cut voltage = 2.5V

Here, the "CCCV method" indicates a constant current-constant voltage method. "CC current" indicates the current during constant current charging (or constant current discharging). "CV voltage" indicates the voltage at the time of constant voltage charging.

<Evaluation>
《Roll press》
In the above "1. Manufacture of positive electrode", the state of the positive electrode after roll pressing was confirmed. The results are shown in Table 1 below. In the "Roll press" column of Table 1 below, "OK" indicates that no abnormality was found in the positive electrode. "NG" indicates that an abnormality was found in the positive electrode.

《Battery resistance》
The SOC (state of charge) of the battery was adjusted to 50% by CC-type charging (CC current = 5 mA). After adjusting the SOC, a 30-minute rest was provided. After the rest, the battery was charged for 10 seconds with a current (I) of 50 mA. The amount of increase in voltage between terminals (ΔV) 10 seconds after the start of charging was measured. The battery resistance (R) was calculated by the relational expression of "ΔV / I = R". The results are shown in Table 1 below.

<Result>
<< Comparative Examples 1 to 3 >>
Even if the thickness of the Al foil was increased from 12 μm to 20 μm, the battery resistance did not substantially increase (Comparative Examples 1 and 2). The contribution of the electrical resistance of the Al foil to the battery resistance is considered to be small.

In Comparative Example 3, the thickness of the Al foil was 10 μm. In Comparative Example 3, the Al foil was cut during the roll press. In Comparative Example 3, a positive electrode of a predetermined quality could not be manufactured, so that a battery was not manufactured.

<< Comparative Examples 4 to 8 >>
In Comparative Examples 5 to 7, the thickness of the Ti foil was 2 μm or more and 6 μm or less. In Comparative Examples 5 to 7, roll pressing was possible. However, the battery resistance of Comparative Examples 5 to 7 increased to a non-negligible degree with respect to the battery resistance of Comparative Example 1 (Al foil).

In Comparative Example 8, the thickness of the Ti foil was 1 μm. In Comparative Example 8, the Ti foil was cut during the roll press. In Comparative Example 8, a positive electrode of a predetermined quality could not be manufactured, so that a battery was not manufactured.

In Comparative Example 4, the thickness of the Ti foil was 10 μm. In Comparative Example 4, the positive electrode active material layer was peeled off during the roll press. It is considered that the positive electrode active material layer was peeled off because the difference between the amount of elongation of the Ti foil and the amount of elongation of the positive electrode active material layer was large during the roll press. In Comparative Example 4, a battery was not manufactured because a positive electrode of a predetermined quality could not be manufactured.

<< Examples 1 to 3, Comparative Examples 9 and 10 >>
In Examples 1 to 3, the thickness of the positive electrode current collector foil (total thickness of the three layers) was 10 μm or less. In Examples 1 to 3, roll pressing was possible. Further, the battery resistances of Examples 1 to 3 were within the permissible range.

In Comparative Example 9, the thickness of the Ti layer and the thickness of the Al layer were the same. In Comparative Example 9, wrinkles were generated during the roll press. In Comparative Example 9, a positive electrode of a predetermined quality could not be manufactured, so that a battery was not manufactured.

In Comparative Example 10, the thickness of the Ti layer was less than 0.1 μm. In Comparative Example 10, the battery resistance increased to a non-negligible degree.

The present embodiment and the present embodiment are exemplary in all respects and are not restrictive. The technical scope defined by the description of the claims includes all changes within the meaning and scope equivalent to the claims.

1 1st Al layer (1st aluminum layer), 2 2nd Al layer (2nd aluminum layer), 3 Ti layer (titanium layer), 3a 1st main surface, 3b 2nd main surface, 10 positive electrode, 11 positive electrode current collector foil , 12 Positive electrode active material layer, 13 Positive electrode lead terminal, 20 Negative electrode, 21 Negative electrode current collector foil, 22 Negative electrode active material layer, 23 Negative electrode lead terminal, 30 Separator, 50 Electrode group.

Claims (1)

First aluminum layer,
Includes titanium layer and second aluminum layer
The titanium layer has a first main surface and a second main surface.
The second main surface is the opposite surface of the first main surface.
The first aluminum layer covers the first main surface, and the first aluminum layer covers the first main surface.
The second aluminum layer covers the second main surface, and the second aluminum layer covers the second main surface.
The thickness of the titanium layer is 2 μm or more and 6 μm or less.
The thickness of each of the first aluminum layer and the second aluminum layer is 0.1 μm or more and less than the thickness of the titanium layer.
The titanium layer is a titanium foil.
Each of the first aluminum layer and the second aluminum layer is composed of 1% by mass or less of impurities and the remaining aluminum.
Positive electrode current collector foil.

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