JP2019175777A - Lithium ion battery separator - Google Patents

Abstract

To provide a lithium ion battery separator capable of reducing internal resistance of the lithium ion battery.SOLUTION: The lithium ion battery separator includes: a resin porous membrane; and an inorganic particle layer containing inorganic particles. The inorganic particle layer includes: an inorganic particle layer A containing magnesium hydroxide having an average particle diameter of 2.0 to 4.0 μm; and an inorganic particle layer B containing magnesium hydroxide with an average particle size of 0.5 μm or more and less than 2.0 μm.SELECTED DRAWING: None

Description

  The present invention relates to a separator for a lithium ion battery.

  Lithium ion batteries incorporate a lithium ion battery separator. The separator for lithium ion batteries plays a role of preventing direct contact between the positive electrode and the negative electrode in the lithium ion battery. That is, the lithium ion battery separator separates the positive electrode and the negative electrode so as not to cause an internal short circuit (internal short circuit). In order to reduce the internal resistance of the lithium ion battery, vacancies capable of efficiently transmitting electrolyte ions must be formed in the lithium ion battery separator. Therefore, the lithium ion battery separator needs to be porous.

  Conventionally, a resin porous film made of a polyolefin resin such as polyethylene or polypropylene has been used as a separator for a lithium ion battery. However, when such a resin porous membrane is used as a separator for a lithium ion battery, the battery melts and contracts when the battery abnormally generates heat, and the shutdown characteristic that isolates the positive and negative electrodes is lost, resulting in a significant internal short circuit. There was a problem that occurred.

In order to solve such a problem, a lithium ion battery separator in which an inorganic particle layer containing inorganic particles is provided on a resin porous membrane has been disclosed (for example, see Patent Document 1). Further, as in Patent Document 2, a secondary battery separator having a plurality of inorganic particle layers is also disclosed. The separator for a secondary battery of Patent Document 2 includes a first porous coating layer including first inorganic particles having a BET surface area of less than 10 m ² / g, and a second inorganic material having a BET surface area of 10 to 50 m ² / g. It is characterized by comprising a second porous coating layer containing particles. Specifically, in the secondary battery separator of Patent Document 2, alumina particles having an average particle diameter of 0.7 μm are used in the first porous coating layer, and an average particle diameter of 0.4 μm is used in the second porous coating layer. Alumina particles are used. However, even if the coating amount (thickness) of the porous coating layer is lowered, there is a drawback that the internal resistance of the lithium ion battery is high.

International Publication No. 2008/156033 Pamphlet JP-T-2015-524991

  The subject of this invention is providing the separator for lithium ion batteries which can make internal resistance of a lithium ion battery low.

  The present inventors have found the following invention as means for solving the above problems.

(1) In a lithium ion battery separator comprising a porous resin membrane and an inorganic particle layer containing inorganic particles,
As the inorganic particle layer, an inorganic particle layer A containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm, and an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm, Have
A separator for a lithium ion battery having a configuration in which an inorganic particle layer A and an inorganic particle layer B are laminated in this order on one surface of the resin porous membrane.

(2) In a lithium ion battery separator comprising a resin porous membrane and an inorganic particle layer containing inorganic particles,
As the inorganic particle layer, an inorganic particle layer A containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm, and an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm, Have
A separator for a lithium ion battery, characterized in that an inorganic particle layer A is provided on one side of the resin porous membrane and an inorganic particle layer B is provided on the other side.

(3) In a separator for a lithium ion battery comprising a resin porous membrane and an inorganic particle layer containing inorganic particles,
As the inorganic particle layer, an inorganic particle layer A containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm, and an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm, Have
A separator for a lithium ion battery having a structure in which an inorganic particle layer B and an inorganic particle layer A are laminated in this order on one surface of the resin porous membrane.

  The separator for a lithium ion battery of the present invention has a resin porous membrane and inorganic particle layers A and B, and the inorganic particle layer A contains magnesium hydroxide having an average particle diameter of 2.0 to 4.0 μm as inorganic particles. In addition, since the inorganic particle layer B contains magnesium hydroxide having an average fiber diameter of 0.5 μm or more and less than 2.0 μm as inorganic particles, the internal resistance of the lithium ion battery can be further reduced.

<Separator for lithium ion battery>
The separator (1) for lithium ion batteries of the present invention comprises an inorganic particle layer A containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm on one side of a resin porous membrane, and an average particle size of 0.5 μm. The separator for lithium ion batteries is characterized in that the inorganic particle layer B containing magnesium hydroxide of less than 2.0 μm is laminated in this order.

  The lithium ion battery separator (2) of the present invention is provided with an inorganic particle layer A containing magnesium hydroxide having an average particle diameter of 2.0 to 4.0 μm on one surface of a resin porous membrane, and on the other surface. A separator for a lithium ion battery having a structure in which an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm is provided.

  The lithium ion battery separator (3) of the present invention comprises an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm on one side of a resin porous membrane; A separator for a lithium ion battery having a structure in which an inorganic particle layer A containing magnesium hydroxide of 0 to 4.0 μm is laminated in this order.

  In the present invention, the resin porous membrane is preferably made of polyolefin. A large number of micropores are formed inside the resin porous membrane, and the micropores are connected to each other so that gas or liquid can pass from one surface to the other. Examples of the polyolefin include polyethylene, polypropylene, and polymethylpentene. One type of polyolefin may be used, or two or more types of polyolefin may be used. More preferred polyolefins are polyethylene and polypropylene.

  The porosity of the resin porous membrane is preferably 20 to 60%. When the porosity is less than 20%, the internal resistance of the lithium ion battery separator may become too high. Further, when the porosity exceeds 60%, the shutdown characteristics may be deteriorated.

  The thickness of the resin porous membrane is preferably 5 to 20 μm, more preferably 6 to 18 μm, and further preferably 6 to 15 μm. If the thickness is less than 5 μm, sufficient strength may not be obtained. When thickness exceeds 20 micrometers, the output of a lithium ion battery may fall. The thickness in the present invention is a value measured with a 5N load using an outer micrometer defined in JIS B 7502.

  In the lithium ion battery separators (1) to (3) of the present invention, the inorganic particle layer A is obtained by a method of applying a coating liquid a containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm. .

  The average particle diameter in the present invention is a volume-based 50% particle diameter (D50) determined from particle size distribution measurement by a laser diffraction method.

  The average particle diameter of magnesium hydroxide in the inorganic particle layer A is more preferably 2.2 to 3.7 μm, and further preferably 2.5 to 3.5 μm.

The coating amount (absolutely dry) of the inorganic particle layer A is preferably 1.0 to 8.0 g / m ² , more preferably 1.5 to 7.0 g / m ² , and still more preferably 1. 5 to 6.0 g / m ² . When the coating amount exceeds 8.0 g / m ² , the thickness of the lithium ion battery separator may become too thick. When the coating amount is less than 1.0 g / m ² , coating defects may occur.

  In the lithium ion battery separators (1) to (3) of the present invention, the inorganic particle layer B is obtained by a method of applying a coating liquid b containing magnesium hydroxide having an average particle size of 0.5 μm or more and 2.0 μm or less. It is done.

  The average particle diameter of magnesium hydroxide in the inorganic particle layer B is more preferably 0.5 to 1.5 μm, further preferably 0.5 to 1.3 μm, and particularly preferably 0.5 to 1.0 μm. It is.

The coating amount (absolute dryness) of the inorganic particle layer B is preferably 1.0 to 8.0 g / m ² , more preferably 1.5 to 7.0 g / m ² , and still more preferably 1. 5 to 6.0 g / m ² . When the coating amount exceeds 8.0 g / m ² , the thickness of the lithium ion battery separator may become too thick. When the coating amount is less than 1.0 g / m ² , coating defects may occur.

  The medium for preparing the coating liquid containing magnesium hydroxide is not particularly limited as long as it can uniformly dissolve or disperse the organic polymer binder and magnesium hydroxide. For example, aromatic hydrocarbons such as toluene, cyclic ethers such as tetrahydrofuran (THF), ketones such as methyl ethyl ketone (MEK), alcohols such as isopropanol, N-methyl-2-pyrrolidone ( N-methylpyrrolidone (NMP), N, N-dimethylacetamide (N, N-dimethylacetamide, DMAc), N, N-dimethylformamide (N, N-dimethylformamide, DMF), dimethyl sulfoxide (Dimethyl sulfDMide, water, etc.) Can be used as needed. Moreover, you may mix and use these media as needed. The medium to be used is preferably one that does not expand or dissolve the resin porous membrane.

  Examples of the method for applying the coating liquid include a blade, a rod, a reverse roll, a lip, a die, a curtain, an air knife, and the like. Various coating methods, flexographic, screen, offset, gravure, ink jet, and other printing methods, transfer methods such as roll transfer and film transfer are required. It can be selected and used accordingly.

  The inorganic particle layers A and B preferably contain an organic polymer binder. The organic polymer binder is not particularly limited as long as it is suitable for use in the inorganic particle layer of the separator. Specifically, for example, ethylene-vinyl acetate copolymer (EVA), (meth) acrylate copolymer, fluorine-based rubber, styrene butadiene copolymer resin (SBR), polyvinyl alcohol (PVA), polyvinyl butyral (PVB) In addition, resins such as polyvinyl pyrrolidone (PVP) and polyurethane can be used, and a resin in which a crosslinked structure is introduced into some of these resins to prevent dissolution in a non-aqueous electrolyte can also be used. These organic polymer binders may be used alone or in combination of two or more. Among these, SBR and (meth) acrylate copolymer are particularly preferable. In the inorganic particle layers A and B, the same organic polymer binder may be used, or different organic polymer binders may be used.

  The content of the organic polymer binder in the inorganic particle layers A and B is preferably 0.8% by mass or more and 9.0% by mass or less, more preferably 1.0% by mass or more and 8.0% by mass or less, and 1.2% by mass. % To 6.0% by mass is more preferable. When the content of the organic polymer binder is less than 0.8% by mass, the adhesion between the inorganic particles in the inorganic particle layer is insufficient, and the inorganic particles may peel off. When the content is more than 9.0% by mass, the internal resistance May be higher.

<Lithium ion battery>
The lithium ion battery in the present invention means a lithium ion secondary battery or a lithium ion polymer secondary battery.

  The negative electrode active material of the lithium ion battery is not particularly limited, but it is preferable to use a negative electrode active material having an equilibrium potential of 1 V (vs Li + / Li) or less for inserting and extracting lithium ions. By using such a negative electrode active material, a battery having a large potential difference between the positive and negative electrodes, that is, a large amount of energy that can be stored can be obtained. As the negative electrode active material satisfying this condition, for example, a carbon material such as graphite, hard carbon, low crystalline carbon, graphite coated with amorphous carbon, carbon nanotube, or a mixture thereof can be used. Further, not only a carbon-based material but also a negative electrode material containing Si, Sn, N, or the like can be used.

The positive electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), spinel-type lithium manganate (LiMn ₂ O ₄ ), and a general formula: LiNi _x Co _y Mn _z O ₂ (x + y + z = 1) And composite metal oxides such as lithium vanadium compound (LiV ₂ O ₅ ) and olivine-type LiMPO ₄ (wherein M represents Co, Ni, Mn or Fe).

  As an electrolyte for a lithium ion battery, a solution obtained by dissolving a lithium salt in an organic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, dimethoxymethane, or a mixed solvent thereof is used. Examples of the lithium salt include lithium hexafluorophosphate and lithium tetrafluoroborate. As solid electrolyte, what melt | dissolved lithium salt in gel-like polymers, such as polyethyleneglycol, its derivative (s), polymethacrylic acid derivative, polysiloxane, its derivative (s), polyvinylidene fluoride, is used.

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

<Resin porous membrane 1>
A polypropylene porous film having a thickness of 15 μm and a porosity of 42% was used as the resin porous film.

<Preparation of coating liquid a1>
100 parts by mass of magnesium hydroxide having an average particle size of 2.0 μm was dispersed in 150 parts by mass of water. Next, 75 parts by mass of a 2% by mass aqueous solution of carboxymethyl cellulose sodium salt having a viscosity of 200 mPa · s at 25 ° C. of the 1% by mass aqueous solution was added and mixed with stirring. Subsequently, 10 parts by mass of a carboxy-modified styrene-butadiene copolymer resin emulsion (solid content concentration: 50% by mass) having a glass transition point of -18 ° C. and an average particle size of 0.2 μm was added and stirred and mixed. Finally, preparation water was added so that the solid content concentration was 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 2.0 μm was changed to magnesium hydroxide having an average particle diameter of 3.0 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 2.0 μm was changed to magnesium hydroxide having an average particle diameter of 4.0 μm.

<Preparation of coating liquid b1>
100 parts by mass of magnesium hydroxide having an average particle size of 0.5 μm was dispersed in 150 parts by mass of water. Next, 75 parts by mass of a 2% by mass aqueous solution of carboxymethyl cellulose sodium salt having a viscosity of 200 mPa · s at 25 ° C. of the 1% by mass aqueous solution was added and mixed with stirring. Subsequently, 10 parts by mass of a carboxy-modified styrene-butadiene copolymer resin emulsion (solid content concentration: 50% by mass) having a glass transition point of -18 ° C. and an average particle size of 0.2 μm was added and stirred and mixed. Finally, adjustment water was added so that the solid content concentration was 25% by mass to prepare a coating liquid b1.

<Preparation of coating liquid b2>
A coating solution b2 was prepared in the same manner as the coating solution b1, except that magnesium hydroxide having an average particle size of 0.5 μm was changed to magnesium hydroxide having an average particle size of 1.0 μm.

<Preparation of coating liquid b3>
A coating solution b3 was prepared in the same manner as the coating solution b1, except that magnesium hydroxide having an average particle size of 0.5 μm was changed to magnesium hydroxide having an average particle size of 1.5 μm.

<Preparation of coating liquid c1>
100 parts by mass of alumina having an average particle diameter of 0.7 μm was dispersed in 150 parts by mass of water. Next, 75 parts by mass of a 2% by mass aqueous solution of carboxymethyl cellulose sodium salt having a viscosity of 200 mPa · s at 25 ° C. of the 1% by mass aqueous solution was added and mixed with stirring. Subsequently, 10 parts by mass of a carboxy-modified styrene-butadiene copolymer resin emulsion (solid content concentration: 50% by mass) having a glass transition point of -18 ° C. and an average particle size of 0.2 μm was added and stirred and mixed. Finally, adjustment water was added so that the solid content concentration was 25% by mass to prepare a coating liquid c1.

<Preparation of coating liquid c2>
A coating solution c2 was prepared in the same manner as the coating solution c1 except that the alumina having an average particle size of 0.7 μm was changed to alumina having an average particle size of 0.4 μm.

<Separator for lithium ion battery>
(Example 1-1)
After coating and drying the coating liquid a1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ² , Furthermore, the coating liquid b1 was coated and dried on the same coated surface with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 2.0 g / m ² , thereby obtaining a lithium ion battery separator. .

(Example 1-2)
After coating and drying the coating liquid a2 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ² , the same coated surface is further obtained. Then, the coating liquid b2 was applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 2.0 g / m ² to obtain a separator for a lithium ion battery.

(Example 1-3)
After coating and drying the coating liquid a3 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 1.5 g / m ² , the same coated surface is further obtained. The coating solution b3 was applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 1.5 g / m ² to obtain a lithium ion battery separator.

(Example 1-4)
After coating / drying the coating liquid a1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ² , the same coated surface is further obtained. Then, the coating liquid b2 was applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 2.0 g / m ² to obtain a separator for a lithium ion battery.

(Example 1-5)
After coating / drying the coating liquid a1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ² , the same coated surface is further obtained. The coating solution b3 was applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 1.5 g / m ² to obtain a lithium ion battery separator.

(Comparative Example 1-1)
After coating and drying the coating liquid c1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ² , the same coated surface is further obtained. Then, the coating liquid c2 was coated and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 2.0 g / m ² to obtain a lithium ion battery separator. The inorganic particle layer obtained by applying the coating liquid c1 is referred to as “inorganic particle layer C”, and the inorganic particle layer obtained by applying the coating liquid c2 is referred to as “inorganic particle layer D”.

(Example 2-1)
After coating and drying the coating liquid a1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ² , the resin porous membrane is obtained. On the other surface of 1, a coating liquid b1 is coated and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ^2, and a lithium ion battery separator Got.

(Example 2-2)
After coating and drying the coating liquid a2 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) becomes 2.0 g / m ² , the resin porous film is further formed. On the other surface of the membrane 1, the coating liquid b2 is coated and dried with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ^2, and is used for a lithium ion battery. A separator was obtained.

(Example 2-3)
After coating and drying the coating liquid a3 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 1.5 g / m ² , the resin porous film is further formed. On the other side of the membrane 1, the coating liquid b3 is applied and dried with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ^2, and is used for a lithium ion battery. A separator was obtained.

(Example 2-4)
After coating and drying the coating liquid a1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ² , the resin porous film is further formed. On the other surface of the membrane 1, the coating solution b1 is coated and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 3.0 g / m ^2, and used for a lithium ion battery. A separator was obtained.

(Example 2-5)
After coating and drying the coating liquid a1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ² , the resin porous film is further formed. On the other side of the membrane 1, the coating liquid b2 is applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 1.5 g / m ^2, and is used for a lithium ion battery. A separator was obtained.

(Example 2-6)
After coating and drying the coating liquid b1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ² , the resin porous On the other side of the membrane 1, the coating liquid a2 is applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ^2, and is used for a lithium ion battery. A separator was obtained.

(Comparative Example 2-1)
After coating and drying the coating liquid c1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ² , the resin porous film is further formed. On the other side of the membrane, the coating liquid c2 is coated and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ^2, and a lithium ion battery separator Got.

(Example 3-1)
After coating and drying the coating liquid b1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 1.5 g / m ² , Further, on the same coated surface, the coating liquid a1 was applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 2.5 g / m ² to obtain a lithium ion battery separator. .

(Example 3-2)
After coating and drying the coating liquid b2 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 1.5 g / m ² , the same coated surface is further applied. Then, the coating liquid a2 was coated and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 2.0 g / m ² to obtain a lithium ion battery separator.

(Example 3-3)
After coating and drying the coating liquid b3 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 1.5 g / m ² , the same coated surface is further applied. Then, the coating liquid a3 was coated and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 1.5 g / m ² to obtain a lithium ion battery separator.

(Example 3-4)
After coating / drying the coating liquid b1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.0 g / m ² , the same coated surface is further obtained. Then, the coating liquid a2 was coated and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 2.0 g / m ² to obtain a lithium ion battery separator.

(Example 3-5)
After coating and drying the coating liquid b1 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolutely dry) is 2.5 g / m ² , the same coated surface is further applied. The coating liquid a3 was applied and dried with a kiss reverse gravure coater so that the coating amount (absolutely dry) was 1.0 g / m ² to obtain a lithium ion battery separator.

(Comparative Example 3-1)
After coating and drying the coating liquid c2 on the resin porous membrane 1 with a kiss reverse gravure coater so that the coating amount (absolute dryness) is 2.0 g / m ² , the same coated surface is further applied. The coating liquid c1 was applied and dried with a kiss reverse gravure coater such that the coating amount (absolutely dry) was 2.0 g / m ² to obtain a lithium ion battery separator.

  The following evaluation was performed about the separator for lithium ion batteries of an Example and a comparative example, and the lithium ion battery using the same, and the result was shown in Table 1.

<Lithium ion battery>
[Production of lithium-ion batteries]
Using each of the lithium ion battery separators described above, lithium manganate as the positive electrode, mesocarbon microbead as the negative electrode, and 1 mol / L diethyl carbonate (DEC) / lithium hexafluorophosphate (LiPF ₆ ) as the electrolyte A lithium ion battery having a design capacity of 30 mAh using a mixed solvent solution of ethylene carbonate (EC) (capacity ratio 7/3) was produced.

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

◎: Internal resistance less than 5Ω ○: Internal resistance of 5Ω to less than 6Ω △: Internal resistance of 6Ω to less than 7Ω ×: Internal resistance of 7Ω or more

  As shown in Table 1, in the separators for lithium ion batteries prepared in Examples 1-1 to 1-5, the inorganic particle layer A and the inorganic particle layer B are arranged in this order on one side of the resin porous membrane. Due to the laminated structure, the internal resistance of the lithium ion battery was low and excellent.

  Moreover, the separator for lithium ion batteries produced in Examples 2-1 to 2-6 is provided with the inorganic particle layer A on one surface of the resin porous membrane and the inorganic particle layer B on the other surface. Therefore, the internal resistance of the lithium ion battery was low and excellent.

  As shown in Table 1, in the separators for lithium ion batteries produced in Examples 3-1 to 3-5, the inorganic particle layer B and the inorganic particle layer A are arranged in this order on one side of the resin porous membrane. Due to the laminated structure, the internal resistance of the lithium ion battery was low and excellent.

  The separator for a lithium ion battery produced in Comparative Example 1-1 includes an inorganic particle layer C containing alumina having an average particle diameter of 0.7 μm and alumina having an average particle diameter of 0.4 μm on one surface of the resin porous membrane. Although the inorganic particle layer D has a configuration laminated in this order, the internal resistance of the lithium ion battery was high.

  The separator for a lithium ion battery produced in Comparative Example 2-1 was provided with an inorganic particle layer C containing alumina having an average particle diameter of 0.7 μm on one surface of a resin porous membrane, and an average particle on the other surface. Although the inorganic particle layer D containing alumina having a diameter of 0.4 μm was provided, the internal resistance of the lithium ion battery was high.

  The separator for a lithium ion battery produced in Comparative Example 3-1 includes an inorganic particle layer D containing alumina having an average particle diameter of 0.4 μm and alumina having an average particle diameter of 0.7 μm on one surface of the resin porous membrane. The inorganic particle layer C has a configuration in which the layers are stacked in this order, but the internal resistance of the lithium ion battery is high.

  As an application example of the present invention, a lithium ion battery separator is suitable.

Claims (3)

In a lithium ion battery separator comprising a resin porous membrane and an inorganic particle layer containing inorganic particles,
As the inorganic particle layer, an inorganic particle layer A containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm, and an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm, Have
A separator for a lithium ion battery having a configuration in which an inorganic particle layer A and an inorganic particle layer B are laminated in this order on one surface of the resin porous membrane. In a lithium ion battery separator comprising a resin porous membrane and an inorganic particle layer containing inorganic particles,
As the inorganic particle layer, an inorganic particle layer A containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm, and an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm, Have
A separator for a lithium ion battery, characterized in that an inorganic particle layer A is provided on one side of the resin porous membrane and an inorganic particle layer B is provided on the other side. In a lithium ion battery separator comprising a resin porous membrane and an inorganic particle layer containing inorganic particles,
As the inorganic particle layer, an inorganic particle layer A containing magnesium hydroxide having an average particle size of 2.0 to 4.0 μm, and an inorganic particle layer B containing magnesium hydroxide having an average particle size of 0.5 μm or more and less than 2.0 μm, Have
A separator for a lithium ion battery having a structure in which an inorganic particle layer B and an inorganic particle layer A are laminated in this order on one surface of the resin porous membrane.