JP2018110050A - Current collector for lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current collector for a lithium ion battery having excellent alkali resistance. In one aspect, the present disclosure includes an electrode foil containing aluminum and an oxide layer coating a surface of the electrode foil, wherein the oxide layer has the general formula M2O.nSiO2 (provided that In the formula, M represents at least one selected from sodium, potassium and tetraalkylammonium, and n represents a number of 0.5 or more and 6.0 or less), which is a layer containing a silicic acid compound, The present invention relates to a current collector for a lithium ion battery, wherein the oxide layer covers the electrode foil in a solid content of 10 μg/cm 2 or more and 35 μg/cm 2 or less. [Selection diagram] None

Description

  The present disclosure relates to a current collector for a lithium ion battery and a lithium ion battery.

  Lithium ion batteries have a higher energy density per weight and volume than lead-acid batteries and nickel metal hydride batteries, which contributes to the reduction in size and weight of on-board electronic devices. In recent years, hybrid vehicles and electric vehicles have become widespread as efforts toward zero emission of automobiles, and improving the performance of lithium-ion batteries is an important key for improving fuel efficiency and extending mileage.

  Lithium ion batteries generally have a structure in which a non-aqueous electrolyte is filled in a three-layer structure of a positive electrode, a separator, and a negative electrode. The positive electrode and the negative electrode are manufactured, for example, by coating a current collector with a mixture paste in which an active material, a conductive material, and a binder are mixed. Currently, the negative electrode manufacturing method is mainly an aqueous process in which an aqueous slurry (mixture paste) is applied and dried on a copper foil serving as a current collector. The positive electrode manufacturing method includes N-methylpyrrolidone as a solvent. A non-aqueous process in which a positive electrode mixture paste is prepared using an organic solvent and applied to an aluminum foil as a current collector is the mainstream.

  In recent years, from the viewpoint of reducing raw material costs and environmental burdens, it has been desired to adopt an aqueous process for the production of a positive electrode. However, when water is used as the solvent, a part of the lithium (Li) ions contained in the positive electrode active material is eluted to make the positive electrode mixture paste alkaline, and when applied to the aluminum foil as a current collector and dried In addition, corrosion of the aluminum foil and generation of hydrogen gas occur. Thereby, there existed a problem that it was difficult to obtain the smooth coating film (positive electrode mixture layer) with high adhesiveness with a collector.

  In order to solve such a problem, for example, Patent Document 1 discloses a method of obtaining an alkali-resistant current collector by controlling the impurity content contained in aluminum, which is a current collector, to high purity. Has been proposed.

  Patent Document 2 discloses a positive electrode using a current collector covered with a protective layer composed of at least one component selected from oxalate, silicon, chromium, and phosphorus in a positive electrode active material. It is disclosed.

JP 2009-9778 A JP 2000-294252 A

  Conventional current collectors are not sufficient for alkali resistance. Moreover, the method proposed in Patent Document 1 is effective only for an aluminum foil having a specific composition, and lacks versatility. And the method proposed in Patent Document 2 does not disclose the coating amount of the protective layer, and its feasibility is not clarified.

  The present disclosure provides a current collector for a lithium ion electrode excellent in alkali resistance.

In one embodiment, the present disclosure includes an electrode foil containing aluminum and an oxide layer covering a surface of the electrode foil, and the oxide layer has the general formula M ₂ O · nSiO ₂ (wherein the formula Wherein M represents at least one selected from sodium, potassium and tetraalkylammonium, and n represents a number of 0.5 or more and 6.0 or less. The present invention relates to a current collector for a lithium ion battery, wherein a coating amount of the physical layer on the electrode foil is 10 μg / cm ² or more and 35 μg / cm ² or less in terms of solid content.

  In one aspect, the present disclosure relates to a lithium ion battery including a current collector according to the present disclosure.

  According to this indication, there can exist an effect that the current collector for lithium ion batteries excellent in alkali resistance can be provided.

  The present disclosure is based on the finding that by forming a predetermined amount of a predetermined oxide layer on the surface of an aluminum foil, the alkali resistance can be improved while maintaining the electrical conductivity of the current collector.

That is, in one embodiment, the present disclosure includes an electrode foil containing aluminum and an oxide layer that covers a surface of the electrode foil, and the oxide layer has the general formula M ₂ O · nSiO ₂ ( In the formula, M is a layer containing a silicic acid compound represented by at least one selected from sodium, potassium and tetraalkylammonium, and n is a number of 0.5 or more and 6.0 or less. The current collector for a lithium ion battery (hereinafter referred to as “the current collector according to the present disclosure”) has a coating amount of the oxide layer on the electrode foil of 10 μg / cm ² or more and 35 μg / cm ² or less in terms of solid content. Also referred to as "body").

The details of the mechanism of the effect of the present disclosure are not clear, but the following is presumed.
In the present disclosure, a predetermined oxide layer is formed on the surface of an electrode foil containing aluminum, and the coating amount on the electrode foil of the oxide layer is a predetermined amount, whereby the mixture applied on the current collector Even if the paste is alkaline, the contact between the mixture paste and the electrode foil is suppressed, and the alkali resistance is considered to be improved. In addition, when the mixture paste is applied to the current collector and dried, corrosion of the current collector and generation of hydrogen gas are suppressed, and a mixture layer excellent in smoothness can be formed. And it is thought that the raise of the surface resistance of a collector can be suppressed because the coating amount to the electrode foil of an oxide layer is a predetermined amount. Furthermore, when the current collector according to the present disclosure is used for the production of a positive electrode for a lithium ion battery, it becomes possible to produce an electrode using an aqueous process of the positive electrode active material, thereby reducing the cost and environmental burden of the production of the lithium ion battery. It is thought that reduction can be achieved.
However, these are estimations, and the present disclosure is not limited to these mechanisms.

<Electrode foil>
The electrode foil used for the current collector according to the present disclosure is an electrode foil containing aluminum. As the electrode foil containing aluminum, a conventionally used aluminum foil can be used. For example, a high-purity aluminum foil can be used. The aluminum purity of the aluminum foil is preferably 99.0% or more, and more preferably 99.3% or more. As aluminum, for example, at least one selected from Japanese Industrial Standards JIS aluminum alloy 1N30, 1085, 1080, 1070, and 1050 can be used.

  As thickness of the electrode foil used for this indication, it can be set as 10 micrometers or more and 100 micrometers or less, for example.

<Oxide layer>
The oxide layer formed on the surface of the electrode foil in the present disclosure is a layer containing a silicate compound represented by the general formula M ₂ O · nSiO ₂ .

  M in the formula represents at least one selected from sodium, potassium, and tetraalkylammonium. Examples of tetraalkylammonium include tetramethylammonium and tetraethylammonium. From the viewpoint of improving alkali resistance, M is preferably at least one selected from sodium and potassium, more preferably potassium.

  N in the formula represents a number of 0.5 or more and 6.0 or less. n is 0.5 or more, preferably 1.0 or more, more preferably 1.5 or more, from the viewpoint of suppressing an increase in the surface resistance of the current collector and from the viewpoint of not reducing the performance of the lithium ion battery. Preferably, it is 2.0 or more, and from the viewpoint of solubility in water, it is 6.0 or less, preferably 4.0 or less, and more preferably 3.5 or less.

The content of the silicate compound represented by the general formula M ₂ O · nSiO ₂ in the oxide layer in the present disclosure is preferably 95% by mass or more and 100% by mass or less, and 98% by mass or more from the viewpoint of not deteriorating battery performance. 100 mass% or less is more preferable, and 99 mass% or more and 100 mass% is still more preferable.

In the present disclosure, the coating amount of the oxide layer on the electrode foil is 10 μg / cm ² or more and preferably 20 μg / cm ² or more in terms of solid content per unit volume of the electrode foil surface from the viewpoint of improving alkali resistance. And from a viewpoint of suppressing the raise of the surface resistance of a collector, it is 35 microgram / cm < ² > or less, and 30 microgram / cm < ² > or less is preferable.

The current collector according to the present disclosure is obtained by applying an aqueous solution of a silicate compound represented by the general formula M ₂ O · nSiO ₂ (hereinafter, also simply referred to as “oxide aqueous solution”) to the surface of the electrode foil and drying it. be able to. The concentration of the aqueous oxide solution may be about 5% by mass or more and about 10% by mass in terms of SiO ₂ solid content. As a solvent for the aqueous oxide solution, for example, water can be used.

  From the viewpoint of suppressing an increase in the surface resistance of the current collector, the resistance value of the current collector according to the present disclosure has a resistance variation rate of ± 900% with respect to the surface resistance of the electrode foil before applying the oxide. The following is preferable, and it is more preferably within ± 10%.

  In one embodiment, the current collector according to the present disclosure can be suitably used for an electrode for a lithium ion battery, particularly a positive electrode.

[Electrode for lithium ion battery]
In one embodiment of the present disclosure, an electrode for a lithium ion battery including a current collector according to the present disclosure and a mixture layer formed on the current collector (hereinafter, also referred to as “electrode according to the present disclosure”). About.

  In one embodiment, the mixture layer is prepared by preparing a mixture paste (slurry) containing an active material, a conductive material, a binder, a solvent, and, if necessary, optional components such as a thickener. After the agent paste is applied to the current collector according to the present disclosure and dried, the paste is pressed as necessary to be processed into a predetermined size. The mixing ratio of each component contained in the mixture paste can be arbitrarily adjusted according to the suitability of the battery.

As an active material (positive electrode active material) when the electrode is a positive electrode, any active material capable of occluding and releasing lithium and capable of charge / discharge reaction may be used. For example, LiCoO ₂ , LiNiO ₂ , Li ₂ Lithium metal composite oxides such as MnO ₄ are listed. These compounds may be partially element-substituted. In particular, when a composite oxide containing LiNiO ₂ as a main component is used as a positive electrode active material and a positive electrode mixture paste is prepared using water as a solvent, the elution of LiOH is strong and the positive electrode mixture paste exhibits a strong alkalinity of about pH 12. The current collector according to the present disclosure can be effectively used when used for a positive electrode mainly composed of LiNiO ₂ as a positive electrode active material. The average particle diameter of the positive electrode active material can be, for example, 2 μm or more and 40 μm or less.

  As the active material (negative electrode active material) when the electrode is a negative electrode, a material capable of occluding and releasing lithium ions is used, for example, one or more carbon materials selected from natural graphite, artificial graphite, and coke, A silicon material, a titanium material, a tin material, etc. are mentioned.

  The conductive material is for efficiently performing the charge / discharge reaction of the mixture and enhancing the electrical conductivity. Examples thereof include carbon materials such as acetylene black, ketjen black, and graphite. A mixture of more than one species can be used.

  The binder has a bonding function between the mixture and a bonding function between the mixture and the core material. For example, sodium polyacrylate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) And styrene butadiene rubber (SBR), and the like. These may be used alone or in combination of two or more.

  Examples of the solvent include organic solvents such as N-methyl-2-pyrrolidone (NMP) or water, and water is preferable from the viewpoint of manifesting the effects of the present disclosure.

  Examples of the thickener include water-soluble polymers such as carboxymethyl cellulose.

[Lithium ion battery]
In one embodiment, the present disclosure relates to a lithium ion battery (hereinafter, also referred to as “battery according to the present disclosure”) including the current collector according to the present disclosure. In one embodiment, a battery according to the present disclosure includes the electrode according to the present disclosure described above and an electrolytic solution.

  The shape of the battery according to the present disclosure may be any shape such as a coin shape, a cylindrical shape, a square shape, and a stacked shape.

  The battery according to the present disclosure can be manufactured by a known method for manufacturing a lithium ion battery. As one embodiment of a method for producing a lithium ion battery, for example, two electrodes (a positive electrode and a negative electrode) are overlapped via a separator, wound or stacked into a battery shape, and inserted into a battery container or a laminate container. , And a method of injecting an electrolyte into the container and sealing it.

  In one embodiment, the separator is a member having a function of insulating between the positive electrode and the negative electrode and further holding an electrolyte solution. As the separator, for example, a thin microporous film such as polyethylene, polypropylene, or a laminate thereof can be used.

As the electrolytic solution, a solution in which an electrolyte is dissolved in an organic solvent can be usually used. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; these may be used alone or in combination of two or more. . The electrolyte refers to an ionic compound having a function of conducting electricity by dissolving in an organic solvent. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ CO ₂ , LiCl, LiBr, and LiSCN. You may use together.

  Hereinafter, although an example explains this indication, this indication is not limited to this.

1. Preparation of current collector (Examples 1 to 5 and Comparative Examples 1 to 14)
An aqueous oxide solution having a composition concentration shown in Table 1 was prepared, and this was absorbed by Kimwipe (manufactured by Nippon Paper Crecia; paper waste). Next, an aluminum foil having a thickness of 20 μm is cut into a size of 7 cm × 20 cm, and half of the aluminum foil (7 cm × 10 cm) is rubbed with a Kim wipe that has absorbed the aqueous oxide solution, and the oxide is applied to the surface of the aluminum foil. A current collector (Examples 1 to 5 and Comparative Examples 2 to 14) in which an oxide layer was formed on the surface of the aluminum foil was produced. The oxide layer formed on each current collector consists of only oxides having the composition shown in Table 1 (content in the oxide layer: 100% by mass). From the change in the weight of the aluminum foil before and after the oxide coating, the weight (μg / cm ² ) of the oxide layer formed on the surface of the aluminum foil was calculated and used as the coating amount. The calculation results are shown in Table 1.
As the current collector of Comparative Example 1, an untreated aluminum foil, that is, an aluminum foil on which no oxide layer was formed was used.

2. Measurement of resistance and resistance fluctuation rate of current collector The resistance (Ω) of the current collector surface was measured by a four-terminal four-single-needle method using a low resistivity meter (Mitsubishi, “Loresta-GP”). . The resistance fluctuation rate is shown as a relative value (%) with respect to the resistance value of Comparative Example 1. The results are shown in Table 1.

3. Production of positive electrode (Examples 1 to 5 and Comparative Examples 1 to 14)
[Preparation of positive electrode active material]
First, by adding a predetermined ratio of Co and Al sulfate to a NiSO ₄ aqueous solution, a saturated aqueous solution is prepared, and an alkaline solution in which sodium hydroxide is dissolved is slowly dropped and neutralized while stirring the saturated aqueous solution. A ternary nickel hydroxide Ni _0.7 Co _0.2 Al _0.1 (OH) ₂ precipitate was produced by coprecipitation. The precipitate was filtered, washed with water, and dried at 80 ° C. The average particle diameter of the obtained nickel hydroxide was about 10 μm.
Next, the obtained nickel hydroxide Ni _0.7 Co _0.2 Al _0.1 (OH) ₂ was heat-treated at 900 ° C. for 10 hours in the atmosphere to obtain nickel oxide Ni _0.7 Co _0.2 Al _0.1 O. Then, lithium hydroxide monohydrate is added so that the sum of the number of atoms of Ni, Co, and Al and the number of atoms of Li are equal, and a heat treatment is performed at 800 ° C. for 10 hours in dry air. A lithium nickel composite oxide represented by the formula LiNi _0.7 Co _0.2 Al _0.1 O ₂ was obtained as a positive electrode active material. The average particle size of the positive electrode active material was 10 μm.

[Preparation of positive electrode paste]
The positive electrode active material, conductive material (acetylene black, manufactured by Denka Co., “HS-100”), binder (sodium polyacrylate, manufactured by Wako Pure Chemical Industries, Ltd., “high viscosity”) and water are mixed, and positive electrode paste Was prepared. Here, the mass ratio of the positive electrode active material, the conductive material, and the binder was 94: 3: 3 (in terms of solid content). For the mixing, kneading using a disper was performed. The solid content (mass%) in the positive electrode paste was 50 mass%. The solid content (% by mass) in the positive electrode paste is the total amount (% by mass) of the solid content of the positive electrode active material, the conductive material and the binder contained in the positive electrode paste.
Next, on the current collector, the prepared positive electrode paste was applied with a bar coater with the thickness adjusted so that the gap width was 180 μm and the coating amount after drying was 10 mg / cm ² . The coating film was dried at 100 ° C. for 12 hours using an air dryer, and a positive electrode having a positive electrode mixture layer on the current collector was produced.

4). Evaluation of Alkali Resistance (Corrosion Resistance) The state of the positive electrode mixture layer (coating film) formed on the current collector was visually observed, and the alkali resistance was evaluated according to the following evaluation criteria. The results are shown in Table 1. When neither cracking nor surface roughness is confirmed, it indicates that the current collector is excellent in alkali resistance.
[Evaluation criteria]
A: Cracks and surface roughness were not confirmed. B: Cracks were not confirmed, but surface roughness was confirmed. C: Cracks were confirmed.

According to Table 1, the current collectors of Examples 1 to 5 have a resistance variation rate as compared with Comparative Examples 1 to 11 in which the coating amount of the oxide layer is not within a predetermined range (10 to 35 μg / cm ² ). Further, no crack was confirmed in the coating film, and a smooth film was obtained. That is, it was found that the current collectors of Examples 1 to 5 were excellent in alkali resistance. In addition, the current collectors of Comparative Examples 12 to 14 in which M in the general formula M ₂ O · nSiO ₂ was Li had a coating amount of the oxide layer within a predetermined range, and the resistance variation rate was small. The surface roughness of the film was confirmed, and it was found that the alkali resistance was not good.

  According to the present disclosure, a current collector excellent in alkali resistance can be provided. Since the current collector of the present disclosure is excellent in alkali resistance, it is suitably used for lithium ion batteries, lithium ion capacitors, and other power storage devices.

Claims (4)

An electrode foil containing aluminum, and an oxide layer covering the surface of the electrode foil,
The oxide layer has a general formula M ₂ O · nSiO ₂ (wherein M represents at least one selected from sodium, potassium and tetraalkylammonium, and n is 0.5 or more and 6.0 or less) A layer containing a silicic acid compound represented by
The current collector for a lithium ion battery, wherein a coating amount of the oxide layer on the electrode foil is 10 μg / cm ² or more and 35 μg / cm ² or less in terms of solid content.   The current collector according to claim 1, wherein M in the formula is at least one selected from sodium and potassium.   The current collector according to claim 1, wherein M in the formula is potassium.   A lithium ion battery comprising the current collector according to claim 1.