JP2017123269A - Separator electrode integrated storage element for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Abstract

An object of the present invention is to provide a separator electrode integrated power storage device capable of realizing a lithium ion secondary battery having a low internal resistance and a low internal short-circuit failure rate, and a lithium ion secondary battery using the same.
SOLUTION: In a separator electrode integrated power storage element for a lithium ion secondary battery obtained by joining and integrating a separator to an electrode surface, the separator includes a porous layer containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm. A separator electrode integrated power storage element for a lithium ion secondary battery, and a lithium ion secondary battery using the same.
[Selection figure] None

Description

  The present invention relates to a separator electrode integrated power storage element for a lithium ion secondary battery and a lithium ion secondary battery using the same.

  Conventionally, as a lithium ion secondary battery separator (hereinafter sometimes abbreviated as “separator”) used in a lithium ion secondary battery (hereinafter sometimes abbreviated as “battery”), polyethylene and polypropylene have been used. A resin porous membrane made of a polyolefin resin such as has been used. However, when such a resin porous membrane is used as a separator, there is a problem in that when the battery is abnormally heated, it melts and contracts, and the function of isolating the positive and negative electrodes is lost, resulting in a significant short circuit. Further, when the thickness of the separator is reduced in order to reduce the internal resistance, there is a problem that the mechanical strength is lowered and the separator is easily broken during battery production.

  In order to solve such a problem, a separator electrode integrated power storage element in which a porous layer made of inorganic fine particles and a binder is integrally formed on the surface of an electrode active material has been proposed (for example, see Patent Document 1). However, this separator electrode-integrated power storage element has a problem that the porous layer (separator) is easily damaged during battery manufacture, and the internal short circuit easily occurs.

Japanese Patent No. 3253632

  The present invention is intended to solve the above problems. That is, an object of the present invention is to provide a separator electrode integrated power storage device that can realize a lithium ion secondary battery having a low internal resistance and a low internal short-circuit defect rate, and a lithium ion secondary battery using the same.

  The present inventor has found the following invention as means for solving the above problems.

(1) In a lithium ion secondary battery separator electrode integrated electricity storage device obtained by joining and integrating a separator to the electrode surface, the separator is a porous layer containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm. A separator electrode-integrated power storage element for a lithium ion secondary battery.

(2) A lithium ion secondary battery using the separator electrode-integrated electric storage element for lithium ion secondary battery according to (1) above.

  According to the present invention, a porous layer containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm is used as a separator, and the separator is integrally bonded to the surface of the electrode without impairing mechanical strength. The porous layer can be thinned. This thinning can contribute to the reduction of internal resistance. In addition, since the porous layer easily adheres to the electrode active material and the layer strength becomes strong, there are obtained effects that it is difficult for defects to occur during battery manufacture, and internal short circuit failure hardly occurs.

<Lithium ion secondary battery>
The lithium ion secondary battery in the present invention refers to a battery comprising an electrode that can occlude and release lithium ions, and an electrolytic solution or a solid electrolyte. The negative electrode active material of the lithium ion secondary battery is selected from carbon materials such as graphite and coke, metallic lithium, aluminum (Al), silicon (Si), tin (Sn), nickel (Ni), and lead (Pb). One or more alloys of (semi) metal and lithium (Li), metal oxides such as SiO, SnO, Fe ₂ O ₃ , WO ₂ , Nb ₂ O ₅ , Li _4/3 Ti _5/3 O ₄ , Nitride such as Li _0.4 CoN is used. Examples of the positive electrode active material include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium titanium oxide (LTO), lithium nickel manganese oxide (LTO), and lithium nickel manganese oxide (LTO). Lithium-nickel-manganese oxide) and lithium iron phosphate are used. Lithium iron phosphate further includes manganese (Mn), chromium (Cr), cobalt (Co), copper (Cu), nickel, vanadium (V), molybdenum (Mo), titanium (Ti), zinc (Zn), It may be a composite with one or more metals selected from aluminum (Al), gallium (Ga), magnesium (Mg), boron (B), and niobium (Nb).

The electrolyte of the lithium ion secondary battery includes propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dimethoxyethane ( A solution obtained by dissolving a lithium salt in an organic solvent such as dimethyloxyethane (DME), dimethoxymethane (DMM), or a mixed solvent thereof is used. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ). As solid electrolyte, what melt | dissolved lithium salt in gel-like polymers, such as polyethyleneglycol, its derivative (s), a poly (meth) acrylic acid derivative, polysiloxane, its derivative, polyvinylidene fluoride, is used.

  The positive electrode and the negative electrode for lithium ion secondary batteries preferably contain a conductive auxiliary. Although it does not restrict | limit especially as a conductive support agent, Carbon black, Ketjen black (the Ketjen Black International company make, registered trademark), acetylene black, carbon whisker, carbon nanofiber, carbon nanotube, carbon fiber, natural graphite, artificial graphite; Examples thereof include particles of titanium dioxide, ruthenium oxide, aluminum, nickel, silver, and metal fibers. 0.1-20 mass parts is preferable with respect to 100 mass parts of electrode active materials, and, as for the compounding quantity of a conductive support agent, 2-10 mass parts is more preferable.

  The binder used for the positive electrode and the negative electrode for lithium ion secondary batteries is not particularly limited as long as it has resistance to electrolytic solution, voltage resistance, and resistance to oxidation-reduction reaction. Polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate , Polyethylene terephthalate, polybutylene terephthalate, polyamide, polyamideimide, polytetrafluoroethylene, polyimide, polyethylene naphthalate, polyphenylene sulfide, etc., cellulose derivatives such as carboxymethylcellulose, starch and its derivatives, casein, sodium alginate Water-soluble resins such as polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyvinyl methyl ether, polyethylene glycol, Chi Ren butadiene rubbers, and rubbers such as acrylonitrile-butadiene rubber. As for the compounding quantity of a binder, 0.05-25 mass parts is preferable with respect to 100 mass parts of electrode active materials.

  It is preferable that the thickness of the positive electrode and negative electrode for lithium ion secondary batteries is 10-300 micrometers. If the thickness is smaller than 10 μm, it may be difficult to obtain a sufficient electric capacity in the lithium ion battery, and if the thickness exceeds 300 μm, the internal resistance may increase.

  As a method for producing a positive electrode for a lithium ion secondary battery, a positive electrode active material, a conductive agent, and a binder are dry-kneaded or wet-kneaded, and then formed into a sheet shape or a rod shape by a press molding method or an extrusion molding method, and punched or cut. In addition, there are known a production method in which an electrode slurry containing an electrode active material, a conductive agent, and a binder is applied to the surface of the current collector and dried. Any method can be applied in the present invention. Although it does not specifically limit as a coating method of an electrode slurry, A dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a die coating method, a screen printing method, etc. are applicable.

  As a method for producing a negative electrode for a lithium ion secondary battery, a negative electrode active material and a binder are dry-kneaded or wet-kneaded, formed into a sheet shape or a rod shape by a press molding method or an extrusion molding method, stamped, or cut and collected. There are known a production method in which an electrode slurry containing an electrode active material, a conductive agent, and a binder is applied to the surface of a current collector and dried. Any method can be applied in the present invention. Although it does not specifically limit as a coating method of an electrode slurry, A dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a die coating method, a screen printing method, etc. are applicable.

  The material for the current collector includes a conductive material, and examples thereof include gold, silver, copper, aluminum, nickel, and platinum. In particular, aluminum is preferable as the positive electrode current collector, and copper is preferable as the negative electrode current collector. Examples of the shape of the current collector include, but are not limited to, a plate shape, a fiber shape, a sheet shape, a film shape, and a mesh shape.

<Separator electrode integrated storage element>
In the separator electrode integrated electricity storage device of the present invention, the porous layer containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm is a coating liquid containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm. Is obtained by coating the electrode surface.

  The average particle diameter in the present invention is a volume average particle diameter (D50) obtained from a particle size distribution measurement by a laser diffraction method.

  The average particle diameter of magnesium hydroxide in the porous layer containing magnesium hydroxide having an average particle diameter of 0.5 to 3.0 μm of the present invention is more preferably 0.5 to 2.0 μm, and 0.5 to 1.5 μm. Is more preferable. When the average particle diameter is smaller than 0.5 μm, the internal resistance of the battery is increased, and when it is larger than 3.0 μm, an internal short circuit failure is likely to occur.

  As a medium for preparing a coating liquid containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm, a binder and magnesium hydroxide having an average particle size of 0.5 to 3.0 μm can be uniformly dissolved or dispersed. If it is a thing, it will not specifically limit, For example, aromatic hydrocarbons, such as toluene, Furans, such as tetrahydrofuran, Ketones, such as methyl ethyl ketone (methyl ethyl ketone), Alcohols, such as isopropanol, N-methyl-2-pyrrolidone , N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, water and the like can be used as necessary. Moreover, you may mix and use these media as needed. In addition, the medium to be used is preferably one that does not dissolve the nonwoven fabric substrate.

  Examples of the method of coating a coating solution containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm on the electrode include various coatings such as blades, rods, reverse rolls, lips, dies, curtains, and air knives. Various printing methods such as a method, flexo, screen, offset, gravure, and inkjet, and a transfer method such as roll transfer and film transfer can be selected and used as necessary.

The coating amount of the porous layer (bone dry) is preferably from 2.0~20.0g / ^{m 2,} more preferably ^{2.5~17.0g / m 2, 3.0~15.0g / m} 2 Is more preferable. If it exceeds 20.0 g / m ² , the thickness of the porous layer becomes thick and the internal resistance may increase, and if it is less than 2.0 g / m ² , an internal short circuit may easily occur.

  The thickness (absolute dryness) of the porous layer is preferably 1.0 to 20.0 μm, more preferably 1.5 to 17.0 μm, and even more preferably 2.0 to 15.0 μm. If it exceeds 20.0 μm, the thickness of the porous layer becomes thick and the internal resistance may be increased. If it is less than 1.0 μm, an internal short circuit may easily occur.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to an Example.

<Preparation of coating liquid a1>
100 mass parts of magnesium hydroxide having an average particle size of 0.5 μm dispersed in 150 mass parts of water, 75 mass of a 2 mass% aqueous solution of carboxymethyl cellulose having a viscosity of 200 mPa · s of a 1 mass% aqueous solution at 25 ° C. Parts are added and stirred, and 10 parts by weight of a carboxy-modified styrene-butadiene copolymer resin emulsion (solid content concentration 50% by weight) having a glass transition point of -18 ° C. and a volume average particle size of 0.2 μm is added and stirred. Finally, adjustment water was added to adjust the solid content concentration to 25% by mass to prepare a coating liquid a1.

<Preparation of coating liquid a2>
A coating liquid a2 was prepared in the same manner as the coating liquid a1, except that magnesium hydroxide having an average particle diameter of 0.5 μm was changed to magnesium hydroxide having an average particle diameter of 1.0 μm.

<Preparation of coating liquid a3>
A coating liquid a3 was prepared in the same manner as the coating liquid a1, except that magnesium hydroxide having an average particle diameter of 0.5 μm was changed to magnesium hydroxide having an average particle diameter of 1.5 μm.

<Preparation of coating liquid a4>
A coating liquid a4 was prepared in the same manner as the coating liquid a1, except that magnesium hydroxide having an average particle diameter of 0.5 μm was changed to magnesium hydroxide having an average particle diameter of 2.0 μm.

<Preparation of coating liquid a5>
A coating liquid a5 was prepared in the same manner as the coating liquid a1, except that magnesium hydroxide having an average particle diameter of 0.5 μm was changed to magnesium hydroxide having an average particle diameter of 3.0 μm.

<Preparation of coating liquid b1>
A coating solution b1 was prepared in the same manner as the coating solution a1, except that magnesium hydroxide having an average particle size of 0.5 μm was changed to magnesium hydroxide having an average particle size of 0.2 μm.

<Preparation of coating liquid b2>
A coating solution b2 was prepared in the same manner as the coating solution a1, except that magnesium hydroxide having an average particle size of 0.5 μm was changed to magnesium hydroxide having an average particle size of 3.5 μm.

<Preparation of coating liquid c1>
A coating solution c1 was prepared in the same manner as the coating solution a1, except that magnesium hydroxide having an average particle size of 0.5 μm was changed to alumina hydrate having an average particle size of 2.0 μm.

<Preparation of electrode B1>
A slurry in which 85% by mass of mesocarbon microbeads, 10% by mass of acetylene black and 5% by mass of polyvinylidene fluoride were mixed and dispersed in N-methyl-2-pyrrolidone was prepared, and copper having a thickness of 20 μm was prepared. After applying and rolling on both surfaces of the foil, vacuum drying was performed at 150 ° C. for 2 hours to prepare a negative electrode for a lithium ion battery having a thickness of 100 μm, and this was designated as an electrode B1.

<Preparation of electrode C1>
A slurry in which 90% by mass of LiMn ₂ O ₄ , 5% by mass of acetylene black and 5% by mass of polyvinylidene fluoride were mixed and dispersed in N-methyl-2-pyrrolidone was prepared, and both sides of an aluminum foil having a thickness of 20 μm were prepared. After being applied and rolled, the film was vacuum dried at 150 ° C. for 2 hours to produce a positive electrode for a lithium ion battery having a thickness of 100 μm, which was designated as electrode C1.

<Separator electrode integrated storage element>
Example 1
The coating liquid a1 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated electricity storage element having a porous layer thickness of 2 μm.

(Example 2)
The coating liquid a2 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated power storage element having a porous layer thickness of 4 μm.

(Example 3)
A coating liquid a3 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated electricity storage element having a porous layer thickness of 15 μm.

Example 4
A coating liquid a4 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated electricity storage element having a porous layer thickness of 17 μm.

(Example 5)
A coating liquid a5 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated power storage element having a porous layer thickness of 20 μm.

(Example 6)
The coating liquid a1 was applied to the electrode surface of the electrode C1 using a wire bar and dried to obtain a separator electrode integrated electricity storage element having a porous layer thickness of 3 μm.

(Example 7)
The coating liquid a1 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated power storage device (negative electrode side device) having a porous layer thickness of 4 μm. Further, the coating liquid a1 was applied to the electrode surface of the electrode C1 using a wire bar and dried to obtain a separator electrode integrated power storage device (positive electrode side device) having a porous layer thickness of 4 μm.

(Comparative Example 1)
The coating liquid b1 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated electricity storage element having a porous layer thickness of 10 μm.

(Comparative Example 2)
The coating liquid b2 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated power storage element having a porous layer thickness of 17 μm.

(Comparative Example 3)
The coating liquid c1 was applied to the electrode surface of the electrode B1 using a wire bar and dried to obtain a separator electrode integrated power storage element having a porous layer thickness of 15 μm.

<Production of lithium ion secondary battery>
(Examples 1-5)
The separator electrode-integrated electricity storage element of Examples 1 to 5 and the electrode C1 were wound so that the separators were interposed between the electrodes, respectively, and a DEC / EC (capacity ratio: 7/3) mixed solvent solution of LiPF ₆ ( A lithium ion secondary battery having a design capacity of 30 mAh using a concentration of 1 mol / L was produced.

(Example 6)
The separator electrode-integrated power storage device of Example 6 and the electrode B1 were wound so that the separators were interposed between the electrodes, respectively, and a DEC / EC (capacity ratio 7/3) mixed solvent solution (concentration 1 mol) of LiPF ₆ was used as the electrolyte. / L) was used to produce a lithium-ion secondary battery with a design capacity of 30 mAh.

(Example 7)
The positive electrode side element and the negative electrode side element of the separator electrode integrated power storage element of Example 7 were wound so that the separator was interposed between the electrodes, respectively, and LiPF ₆ DEC / EC (capacity ratio 7/3) mixed in the electrolyte solution A lithium ion secondary battery with a designed capacity of 30 mAh using a solvent solution (concentration 1 mol / L) was produced.

(Comparative Examples 1-3)
The separator electrode-integrated electricity storage element of Comparative Examples 1 to 3 and the electrode C1 were wound so that the separators were interposed between the electrodes, respectively, and the electrolyte solution was a LiPF ₆ DEC / EC (capacity ratio 7/3) mixed solvent solution ( A lithium ion secondary battery having a design capacity of 30 mAh using a concentration of 1 mol / L was produced.

[Evaluation of internal resistance]
5 cycles in the sequence of “60 mA constant current charging → 4.2 V constant voltage charging (1 hour) → constant current discharge at 60 mA → next cycle when 2.8 V is reached” for each lithium ion secondary battery produced. After performing the break-in charge / discharge, “60 mA constant current charge → 4.2 V constant voltage charge (1 hour) → 6 mA constant current discharge for 30 minutes (discharge amount 3 mAh) → Measure the voltage immediately before the end of discharge (voltage a) → 60mA constant current charge → 4.2V constant voltage charge (1 hour) → 90mA constant current discharge for 2 minutes (discharge amount 3mAh) → Measurement of voltage (voltage b) just before the end of discharge ” The internal resistance was determined by the equation (voltage a−voltage b) / (90 mA−6 mA) ”. The results are shown in Table 1.

○: Internal resistance 4Ω or less △: Internal resistance 4Ω or more and less than 5Ω ×: Internal resistance 5Ω or more

[Internal short-circuit failure rate]
The separator electrode-integrated electricity storage elements of Examples 1 to 6 and Comparative Examples 1 to 3 and the aluminum foil were wound so that the separators were interposed between the electrodes, respectively, to produce an electrode group. About the separator electrode integrated element of Example 7, the positive electrode side element and the negative electrode side element were wound so that the separator was interposed between the electrodes, respectively, and an electrode group was produced. About the nonwoven fabric coating separator of the comparative example 4, the separator was wound so that it might interpose between the electrodes which consist of two sheets of aluminum foil, and the electrode group was produced. The prepared electrode group was not impregnated with the electrolytic solution, and the presence or absence of a short circuit was confirmed by examining the conduction between the electrodes with a tester. The internal short-circuit failure rate was calculated from the number of shorts with respect to the total number of electrode groups by inspecting 200 electrode groups. The results are shown in Table 1.

○: Internal short circuit failure rate less than 1% △: Internal short circuit failure rate 1% or more and less than 2% ×: Internal short circuit failure rate 2% or more

  As shown in Table 1, the separator electrode-integrated electricity storage devices produced in Examples 1 to 7 are mechanical because the separator is a porous layer containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm. The separator could be made thin without impairing the strength, and the internal resistance could be lowered. Moreover, since the strength of the porous layer was strong and defects were unlikely to occur during battery production, the internal short-circuit defect rate was low and excellent.

  In Examples 1 to 5, the porous layer is formed on the negative electrode side, in Example 6 on the positive electrode side, and in Example 7 on both the positive electrode side and the negative electrode side. Was low and excellent.

  On the other hand, the separator electrode-integrated energy storage device produced in Comparative Example 1 has an average particle diameter of magnesium hydroxide in the porous layer smaller than 0.5 μm. Worsened.

  In the separator electrode-integrated electricity storage device produced in Comparative Example 2, the average particle size of magnesium hydroxide in the porous layer is larger than 3.0 μm, so that the strength of the porous layer is weakened and the internal short circuit defect rate is deteriorated. did.

  Since the separator electrode-integrated electricity storage device produced in Comparative Example 3 did not contain magnesium hydroxide having an average particle size of 0.5 to 3.0 μm, the strength of the porous layer was weakened and the internal short circuit defect rate was deteriorated.

  When Examples 1 to 7 are compared, when the thickness of the porous layer in the separator electrode integrated power storage element is reduced, the internal short-circuit failure rate tends to increase. In Example 1 in which the porous layer is the thinnest, The defect rate was slightly higher. Further, when the thickness of the porous layer in the separator electrode integrated electricity storage element was increased, the internal resistance tended to increase, and in Example 5 where the porous layer was the thickest, the internal resistance was slightly increased.

  As an application example of the present invention, a separator electrode integrated power storage element for lithium ion secondary batteries and a lithium ion secondary battery are suitable.

Claims (2)

  In the separator electrode integrated power storage element for a lithium ion secondary battery, in which the separator is bonded and integrated to the electrode surface, the separator is a porous layer containing magnesium hydroxide having an average particle size of 0.5 to 3.0 μm. A separator electrode integrated power storage element for a lithium ion secondary battery.   A lithium ion secondary battery using the separator electrode-integrated power storage element for a lithium ion secondary battery according to claim 1.