JP2018037351A - Slurry for forming electrode protective layer, electrode, separator laminate, and manufacturing method for electrode and separator laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slurry for forming an electrode protective layer capable of reducing agglomeration of aluminum oxide particles, and the like.SOLUTION: The slurry for forming an electrode protective layer for a power storage device of the present invention includes aluminum oxide particles, resin and a solvent. The resin contains at least one member selected from the group consisting of polyvinyl butyral, polyvinyl pyrrolidone, and an amine salt of a polymer having an acid group.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a slurry for forming an electrode protective layer, an electrode and a separator laminate, and methods for producing them.

  An electrode protective layer containing electrically insulating particles may be provided between a positive electrode and a negative electrode in a power storage device such as a lithium ion secondary battery in order to increase resistance to a short circuit. The electrode protective layer is usually formed by applying a slurry containing electrically insulating particles and a binder to an active material layer or a separator (for example, Patent Document 1).

Japanese Patent Laying-Open No. 2015-185353

  However, in the conventional slurry for forming an electrode protective layer, the electrically insulating particles in the slurry sometimes aggregate in the slurry coating process. When the electrically insulating particles are aggregated, problems such as failure to uniformly apply the slurry to the active material layer or the separator and formation of an electrode protective layer having a desired thickness occur.

  The present invention has been made in view of the above problems, and a slurry for forming an electrode protective layer capable of reducing aggregation of aluminum oxide particles among electrically insulating particles, an electrode and separator laminate including an electrode protective layer, and production thereof It aims to provide a method.

  The slurry for forming an electrode protective layer according to an embodiment of the present invention includes aluminum oxide particles, a resin, and a solvent. The resin is made of polyvinyl butyral, polyvinyl pyrrolidone, and a polymer amine salt having an acid group. At least one selected from the group consisting of:

  Here, the total content of the polyvinyl butyral, the polyvinyl pyrrolidone, and the amine salt of the polymer having an acid group may be 1 part by mass or more with respect to 100 parts by mass of the aluminum oxide particles.

  The resin may further include a fluororesin.

  The solvent may be an organic solvent.

  The average primary particle diameter of the aluminum oxide particles may be 3 μm or less.

  Furthermore, the slurry may not contain polyethylene oxide.

  An electrode according to one embodiment of the present invention includes a current collector, an active material layer formed over the current collector, and an electrode protection layer provided over the active material layer, and the electrode protection layer includes And aluminum oxide particles and a resin, and the resin contains at least one selected from the group consisting of polyvinyl butyral, polyvinyl pyrrolidone, and an amine salt of a polymer having an acid group.

  A separator laminate according to an embodiment of the present invention includes a separator and an electrode protective layer provided on the separator, and the electrode protective layer includes aluminum oxide particles and a resin. It contains at least one selected from the group consisting of butyral, polyvinylpyrrolidone, and an amine salt of a polymer having an acid group.

  The manufacturing method of the electrode or separator laminated body which concerns on one form of this invention is equipped with the process of apply | coating the above-mentioned slurry for electrode protective layer formation to an active material layer or a separator, and forming an electrode protective layer.

  According to the present invention, aggregation of aluminum oxide particles in the electrode protective layer forming slurry can be reduced.

It is a schematic sectional drawing of the lithium ion secondary battery and electrode which concern on one Embodiment of this invention. It is a mimetic diagram showing the coating device concerning one embodiment of the present invention. It is a graph which shows a time-dependent change of the average particle diameter (D50) of the aluminum oxide particle in the Example of this invention. It is a graph which shows the particle size distribution of the aluminum oxide particle in the Example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  The slurry for forming an electrode protective layer for a power storage device according to an embodiment of the present invention includes aluminum oxide particles, a resin, and a solvent.

(Aluminum oxide particles)
The aluminum oxide particles (alumina particles) contained in the slurry according to the present embodiment are electrically insulating particles that are the main component of the electrode protective layer.

  The average primary particle size of the alumina particles can be 3 μm or less, can be 1.8 μm or less, and can be 1.2 μm or less. The average primary particle diameter of the alumina particles is, for example, 0.3 to 1.2 μm. In general, when the primary particle diameter of alumina particles is as small as these, aggregation easily occurs, but even in this case, according to the slurry of this embodiment, the aggregation of alumina particles is effectively suppressed. be able to. In addition, the average primary particle diameter of an alumina particle can be made into the number average of the fixed direction tangent diameter (Feret diameter) based on a cross-sectional scanning electron microscope (SEM) photograph, for example.

(resin)
The resin contained in the slurry according to the present embodiment includes a specific resin selected from the group consisting of polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), and a polymer amine salt having an acid group. These specific resins may be used alone or in combination of two or more. These specific resins help disperse the alumina particles in the slurry and reduce agglomeration of the alumina particles. Further, these specific resins function as a binder for bonding the alumina particles and the alumina particles, or the alumina particles and the active material layer or the separator after the solvent is dried.

(Amine salt of polymer having acid group)
Polymeric amine salts having acid groups are generally known as anionic dispersants. Examples of acid groups are carboxy groups and phosphate groups. Examples of amines that form amine salts are alkylol amines, ammonia, and other primary, secondary, or tertiary amines. Examples of the polymer are polyester, polyether, polyacrylic acid, polyurethane, fatty acid, and a copolymer of polyester and polyether. The acid value and the amine value of the polymer amine salt having an acid group can be 35 to 150 mgKOH / g, and 70 to 100 mgKOH. Here, an example of an amine salt of a polymer having an acid group is an alkylol ammonium salt of a polymer having a phosphate group. For example, a commercially available product such as DISPERBYK-180 (manufactured by BYK Japan) can do.

(Other resins)
The slurry according to the present embodiment may contain other resins other than the specific resin. Examples of other resins include resins generally used as a dispersant or binder for alumina particles, and examples thereof include fluororesins. The fluororesin is not highly effective in dispersing the alumina particles, but functions as a good binder after the solvent is dried. Examples of the fluororesin are PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and fluororubber.

(Other ingredients)
The slurry according to this embodiment can contain other components other than the alumina particles, the resin, and the solvent. Examples of other components include a thickener. As other components, polyethylene oxide may not be contained.

(solvent)
The solvent is not particularly limited as long as it can dissolve / disperse the resin, and for example, an organic solvent can be used. Examples of the organic solvent include tetrahydrofuran, methyl ethyl ketone, dimethylformamide, dimethylacetamide, tetramethylurea, dimethyl sulfoxide, trimethyl phosphate, and N-methyl-2-pyrrolidone (NMP), and NMP is preferable.

(Ratio of each component)
Here, in the slurry, the entire component remaining as a solid after the slurry is dried is called a total solid content. The total solid content does not include a solvent, and includes alumina particles and a resin.

  The ratio of the total solid content in the slurry can be 20% by mass or more, 30% by mass or more, or 35% by mass or more. The ratio of the total solid content in the slurry can be 80% by mass or less, 70% by mass or less, or 65% by mass or less.

  The proportion of alumina particles in the total solid content can be 50% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more. The proportion of alumina particles in the total solid content can be 99% by mass or less, 98% by mass or less, 95% by mass or less, or 92% by mass or less.

  The ratio of the whole resin to the total solid content can be 25% by mass or less, 20% by mass or less, or 15% by mass or less. The ratio of the whole resin to the total solid content can be 1% by mass or more, 5% by mass or more, or 10% by mass or more.

  The total ratio of the specific resin in the total solid content may be 24% by mass or less, 19% by mass or less, or 14% by mass or less. The total ratio of the specific resin in the total solid content may be 0.5% by mass or more, 4% by mass or more, or 9% by mass or more.

  From the viewpoint of further reducing the aggregation of the alumina particles, the content of the specific resin is preferably 1 part by mass or more, more preferably 3 parts by mass or more, with respect to 100 parts by mass of the alumina particles. The amount is more preferably 4 parts by mass or more, and particularly preferably 10 parts by mass or more. Content of the said specific resin can be 40 mass parts or less with respect to 100 mass parts of alumina particles, can be 30 mass parts or less, and can be 25 mass parts or less.

  The slurry for forming an electrode protective layer according to the present embodiment is agglomeration of alumina particles by using a specific resin selected from the group consisting of PVB, PVP, and an amine salt of a polymer having an acid group among resins. Can be significantly reduced. Among the many resins used as dispersants, the reason why the aggregation of alumina is remarkably reduced when these specific resins are used is not clear, but the surface of alumina particles having many basic points and these specifics It is presumed that this is because of good compatibility with other resins.

(Power storage device and electrode)
Next, an electrode for a power storage device manufactured using the electrode protective layer forming slurry will be described. The electrode according to the present embodiment includes a current collector, an active material layer formed on the current collector, and an electrode protective layer formed on the active material layer.

  FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery 100 as an example of a power storage device including an electrode according to the present embodiment. The lithium ion secondary battery 100 includes a negative electrode (electrode) 10, a separator 22, a positive electrode (electrode) 30, a case 70, and an electrolytic solution. The laminated body of the negative electrode 10, the separator 22, and the positive electrode 30 constitutes an electrode assembly.

  The negative electrode (electrode) 10 includes a negative electrode current collector 12, a negative electrode active material layer 14 formed on the negative electrode current collector 12, and an electrode protection layer 24 formed on the negative electrode active material layer 14. The negative electrode active material layer 14 includes a material capable of inserting and extracting lithium. The negative electrode active material layer 14 may be provided on both surfaces of the negative electrode current collector 12 as shown in FIG. 1, or may be provided on only one surface of the negative electrode current collector 12.

  The positive electrode (electrode) 30 includes a positive electrode current collector 32, a positive electrode active material layer 34 formed on the positive electrode current collector 32, and an electrode protective layer 24 formed on the positive electrode active material layer 34. As shown in FIG. 1, the positive electrode active material layer 34 may be provided on both surfaces of the positive electrode current collector 32, or may be provided on only one surface of the positive electrode current collector 32.

  Here, in the lithium ion secondary battery 100 shown in FIG. 1, both the negative electrode 10 and the positive electrode 30 include the electrode protective layer 24 on the active material layer, but only one of the negative electrode 10 and the positive electrode 30 is on the active material layer. The electrode protective layer 24 may be provided. Moreover, the electrode protective layer 24 may be formed on the separator 22 instead of being formed on the active material layer of the electrode.

  The negative electrode current collector 12 and the positive electrode current collector 32 can be made of a conductive material. Examples of the conductive material include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, and conductive resins.

  The negative electrode active material layer 14 can include a negative electrode active material and a binder. The negative electrode active material can be a known negative electrode active material, for example, graphite such as graphite, highly oriented graphite, mesocarbon microbeads, carbon such as hard carbon and soft carbon, alkali metals such as lithium and sodium, and SiOx. Examples include metal oxides and boron-added carbon. The binder may be, for example, a fluorine resin such as PVDF, PTFE, or fluororubber, a thermoplastic resin such as polypropylene or polyethylene, an imide resin such as polyimide or polyamideimide, or an alkoxysilyl group-containing resin.

  The positive electrode active material layer 34 can include a positive electrode active material and a binder. As the positive electrode active material, a known positive electrode active material can be used. For example, a lithium metal composite oxide such as a lithium cobalt composite oxide, a lithium nickel composite oxide, or a lithium manganese composite oxide can be used. . Also, other metal compounds or polymer materials can be used as the positive electrode active material. Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, and disulfides such as titanium sulfide and molybdenum sulfide. Examples of the polymer material include conductive polymers such as polyaniline and polythiophene. The binder contained in the positive electrode active material layer 34 can be the same as the binder contained in the negative electrode active material layer 14.

  The electrode protective layer 24 is formed by applying the electrode protective layer forming slurry and then drying the solvent, and includes the alumina particles and the specific resin, and is porous. The porosity of the electrode protective layer 24 can be 40 to 85%. The thickness of the electrode protective layer 24 can be, for example, 1 to 10 μm.

  The separator 22 is not particularly limited as long as it separates the negative electrode 10 and the positive electrode 30 and prevents a short circuit of current due to contact between both electrodes, and allows metal ions to pass therethrough, and a known separator can be used. Examples of the separator include a porous film made of a polyolefin resin such as polyethylene or polypropylene, and a woven or non-woven fabric made of polypropylene, polyethylene terephthalate, methylcellulose, or the like.

  The electrolytic solution is not particularly limited, and can be, for example, an organic solvent in which an electrolyte such as a lithium salt is dissolved. The electrolytic solution may be retained in a polymer and used as a polymer electrolyte.

  Case 70 accommodates negative electrode 10, separator 22, positive electrode 30, and electrolyte. A negative electrode lead 16 and a positive electrode lead 36 are connected to the tab portion 12 t of the negative electrode current collector 12 and the tab portion 32 t of the positive electrode current collector 32, respectively. One ends of the negative electrode lead 16 and the positive electrode lead 36 are out of the case 70.

(Method for manufacturing electrode for power storage device)
Next, a method for manufacturing an electrode for a power storage device according to this embodiment will be described. The manufacturing method of the electrode which concerns on this embodiment is equipped with the process of apply | coating a slurry on an active material layer and forming an electrode protective layer.

  The slurry can be applied onto the active material layer using, for example, a coating apparatus 200 as shown in FIG. The coating apparatus 200 includes a slurry circulation path L1, a stirring unit 110, a pump 130, a filter 150, and a coating unit 170. First, in the stirring unit 110, the alumina particles and the resin are dissolved or dispersed in a solvent to prepare the electrode protective layer forming slurry S. The slurry S prepared in the stirring unit 110 is supplied to the coating unit 170 through the filter 150 by the pump 130. In the coating unit 170, the slurry S is applied to the active material layer, and the remaining slurry S without being applied to the active material layer is returned to the stirring unit 110. As described above, the slurry S is circulated in the coating apparatus 200 through the circulation path L1 while the coating apparatus 200 is in operation.

  The stirring unit 110 is, for example, a homodisper or a planetary mixer, and a planetary mixer is preferable from the viewpoint of further reducing the aggregation of alumina particles.

  In the coating unit 170, for example, a known coating machine such as a die coater, a gravure coater, a reverse roll coater, a squeeze roll coater, a curtain coater, a blade coater, or a knife coater is used, and a slurry is formed on the surface of the active material layer. S is applied. Thereafter, the coated slurry S is dried to remove the solvent, whereby an electrode for a power storage device in which an electrode protective layer is formed on the active material layer is obtained.

  The thickness of the electrode protective layer formed using the slurry needs to be sufficiently thin and constant as about 1 to 10 μm, but when the alumina particles in the slurry are aggregated, the thickness of the electrode protective layer is sufficiently thin and constant. Is difficult. In the conventional slurry, the electrically insulating particles in the slurry easily aggregate. In contrast, according to the slurry for forming an electrode protective layer for a power storage device according to this embodiment, aggregation of alumina particles in the slurry is reduced. Thereby, a sufficiently thin electrode protection layer having a constant thickness can be continuously applied for a long time.

As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the said embodiment. For example, in the above embodiment, slurry is applied to the surface of the negative electrode active material layer 14 or the positive electrode active material layer 34 to form the electrode protective layer 24, thereby forming the negative electrode 10 and the positive electrode 30 having the electrode protective layer 24. doing. However, slurry is applied to the surface of the separator 22 (which may be single-sided or double-sided) to form the electrode protective layer 24, and a separator laminate 40 (see FIG. 1) including the separator 22 and the electrode protective layer 24 is formed. It is also possible to do.
The electrode protective layer and the electrode of the present invention can be used for various power storage devices such as secondary batteries other than lithium ion secondary batteries or capacitors.

  EXAMPLES Hereinafter, although an invention is concretely demonstrated based on an Example, this invention is not limited to a following example.

<Test Example 1>
(Examples 1-3)
50 parts by mass of NMP, 44.5 parts by mass of alumina particles (average primary particle size: 1 μm), and 1.5 parts by mass of resin were mixed to prepare a slurry. The slurry was stirred at a rotation speed of 1000 rpm using a homodisper. As the resin, PVB (“ESREC BL-1”, manufactured by Sekisui Chemical Co., Ltd., weight average molecular weight 19000) is used in Example 1, and polymer alkylol ammonium salt having a phosphate group (“DISPERBYK-” is used in Example 2. 180 ", manufactured by Big Chemie Japan, acid value: 94 mgKOH / g, amine value: 94 mgKOH / g), in Example 3, PVP (" polyvinylpyrrolidone K-30 ", manufactured by Nippon Shokubai Co., Ltd., viscosity average molecular weight: 40,000) were used respectively. After stirring for 90 minutes, 4.0 parts by mass of PVDF (weight average molecular weight: 280,000) was further added to the slurry, and the mixture was stirred using a homodisper at a rotation speed of 1500 rpm for 30 minutes. The volume-based particle size distribution of alumina particles was determined by laser diffraction, and the value of D50 was defined as the average particle diameter of the alumina particles. The change with time of the average particle diameter of the alumina particles is shown in FIG.

(Comparative Examples 1 and 2)
A slurry was prepared by mixing 52 parts by mass of NMP, 46.4 parts by mass of alumina particles (average primary particle size: 1 μm), and 1.6 parts by mass of polyvinyl alcohol (PVA). The slurry was stirred at a rotation speed of 1000 rpm using a homodisper. As PVA, in Comparative Example 1, “JR-05” manufactured by Nippon Vinegar Poval Co., Ltd. was used, and in Comparative Example 2, “JP-05” of the same company was used. The change with time of the average particle diameter of the alumina particles is shown in FIG.

(Comparative Example 3)
50 parts by mass of NMP, 44.5 parts by mass of alumina particles (average primary particle size: 1 μm), and 5.5 parts by mass of PVDF were mixed to prepare a slurry. The slurry was stirred for 30 minutes at a rotation speed of 1000 rpm using a homodisper. The change with time of the average particle diameter of the alumina particles is shown in FIG.

(Evaluation)
When PVB (Example 1), a polymer amine salt having an acid group (Example 2), or PVP (Example 3) is used as the resin, PVA (Comparative Examples 1 and 2) or PVDF ( The average particle diameter of the alumina particles was smaller than when Comparative Example 3) was used. This result shows that the aggregation of alumina particles was reduced in Examples 1 to 3. In Examples 1 to 3, even when PVDF was added to the slurry, the dispersibility of the alumina particles could be kept good.

<Test Example 2>
Example 4
50 parts by mass of NMP, 44.5 parts by mass of alumina particles (average primary particle size: 1 μm), 5.0 parts by mass of PVDF (weight average molecular weight: 280,000), 0.5 parts by mass of PVB, Were mixed and stirred for 1 hour using a homodisper to prepare a slurry. The particle size distribution of alumina particles in the slurry after stirring was determined by a laser diffraction method.

(Example 5)
A slurry was prepared in the same manner as in Example 4 except that the blending amount of PVB was 1.5 parts by mass and the blending amount of PVDF was 4.0 parts by mass, and the particle size distribution of alumina particles was obtained. The results are shown in FIG.

(Example 6)
A slurry was prepared in the same manner as in Example 4 except that the blending amount of PVB was 2.5 parts by mass and the blending amount of PVDF was 3.0 parts by mass, and the particle size distribution of alumina particles was obtained. The results are shown in FIG.

(Example 7)
A slurry was prepared in the same manner as in Example 4 except that the blending amount of PVB was 5.5 parts by mass and PVDF was not blended, and the particle size distribution of alumina particles was obtained. The results are shown in FIG.

(Example 8)
A slurry was prepared in the same manner as in Example 7 except that the slurry was stirred using a planetary mixer instead of the homodisper, and the particle size distribution of the alumina particles was determined. The results are shown in FIG.

(Comparative Example 4)
A slurry was prepared in the same manner as in Example 4 except that PVB was not used and the amount of PVDF was 5.5 parts by mass, and the particle size distribution of alumina particles was determined. The results are shown in FIG.

(Evaluation)
When PVB was used as the resin (Examples 4 to 8), alumina particles having a small particle diameter were seen more frequently than when PVDF was used as the resin (Comparative Example 4). In addition, the frequency of large aggregates having a particle size of 10 μm or more was also reduced. These results show that the aggregation of alumina particles was reduced in Examples 4 to 8. Moreover, the higher the blending amount of PVB, the higher the frequency of alumina particles having a smaller particle diameter. This result shows that the aggregation of alumina particles was further reduced as the blending amount of PVB was higher (Examples 4 to 8). Furthermore, when the slurry was stirred using a planetary mixer, the aggregation of alumina particles could be further reduced than when the slurry was stirred using a homodisper (Examples 7 and 8).

  DESCRIPTION OF SYMBOLS 10 ... Negative electrode (electrode), 12 ... Negative electrode collector, 14 ... Negative electrode active material layer, 16 ... Negative electrode lead, 22 ... Separator, 24 ... Electrode protective layer, 30 ... Positive electrode (electrode), 32 ... Positive electrode collector, 34 ... Positive electrode active material layer, 36 ... Positive electrode lead, 40 ... Separator laminate, 100 ... Lithium ion secondary battery, 110 ... Stirring unit, 130 ... Pump, 150 ... Filter, 170 ... Coating unit, 200 ... Coating device .

Claims (9)

Including aluminum oxide particles, resin, and solvent,
The electrode protective layer forming slurry, wherein the resin contains at least one selected from the group consisting of polyvinyl butyral, polyvinyl pyrrolidone, and an amine salt of a polymer having an acid group.   The total content of the polyvinyl butyral, the polyvinyl pyrrolidone, and the amine salt of the polymer having the acid group is 1 part by mass or more with respect to 100 parts by mass of the aluminum oxide particles. slurry.   The slurry according to claim 1 or 2, wherein the resin further contains a fluororesin.   The slurry according to any one of claims 1 to 3, wherein the solvent is an organic solvent.   The slurry as described in any one of Claims 1-4 whose average primary particle diameter of the said aluminum oxide particle is 3 micrometers or less.   The slurry as described in any one of Claims 1-5 which does not contain a polyethylene oxide. A current collector, an active material layer formed on the current collector, and an electrode protective layer provided on the active material layer, the electrode protective layer including aluminum oxide particles and a resin ,
The electrode, wherein the resin contains at least one selected from the group consisting of polyvinyl butyral, polyvinyl pyrrolidone, and an amine salt of a polymer having an acid group. A separator and an electrode protective layer provided on the separator, the electrode protective layer comprising aluminum oxide particles and a resin;
A separator laminate, wherein the resin contains at least one selected from the group consisting of polyvinyl butyral, polyvinylpyrrolidone, and an amine salt of a polymer having an acid group.   The manufacturing method of an electrode or a separator laminated body provided with the process of apply | coating the slurry for electrode protective layer formation as described in any one of Claims 1-6 to an active material layer or a separator, and forming an electrode protective layer.

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