JP5219099B2 - Battery separator material, battery separator manufacturing method, battery separator, and secondary battery - Google Patents

Description

  The present invention particularly relates to a battery separator.

  The secondary battery is composed of a positive electrode, a negative electrode, and a separator. The separator has heretofore been configured using a polyethylene microporous membrane or a polypropylene microporous membrane.

Japanese Patent Publication No. 6-104736 JP-A-5-222236 JP-A-5-222237 JP-A-4-261441 JP-A-8-12799 JP-A-11-279324

  The physical properties required as a separator include the following physical properties.

  Mechanical strength (puncture strength) is necessary from the viewpoint of battery assembly characteristics. In particular, in the case of a lithium ion secondary battery separator, it is said that high mechanical strength (puncture strength) is required.

  High ion permeability is necessary from the viewpoint of the output characteristics of the battery. The output characteristics of the battery are current characteristics (for example, discharge performance at a large current and discharge performance at low temperature) and life characteristics (for example, cycle characteristics and high temperature storage characteristics). Such characteristics are better as the ion permeability of the separator is higher.

  Secondary batteries have increased in output and capacity. For this reason, secondary batteries are required to have high safety. From the viewpoint of safety, the separator is required to have the following characteristics. That is, when the inside of the battery is overheated, the separator is melted, thereby covering the electrode. That is, if the electrode is covered by melting of the separator, the current is interrupted. Therefore, heat generation is suppressed and safety is ensured.

  High power is required for batteries of electric vehicles, particularly hybrid electric vehicles. For high output, high ion permeability is desired. For this purpose, it is desired that the separator (microporous membrane) has a large pore size and a large porosity. However, enlarging the hole diameter or increasing the porosity causes a disadvantage that the capacity is reduced due to self-discharge or the current interruption performance during the heat generation is reduced.

  Electrolyte injection for battery manufacturing is a difficult process. Because there are almost no voids in the battery can, it is difficult to inject the electrolyte uniformly and rapidly. However, uniform and rapid injection of the electrolyte is also an important requirement.

  The problem to be solved by the present invention is to provide a separator that satisfies the above requirements. That is, to provide a separator having high mechanical strength (puncture strength), excellent ion permeability, and excellent battery output characteristics, safety, and productivity at a low cost.

  While eagerly pursuing research to solve the above problems, that is, while investigating the above characteristics by incorporating a separator made of a number of resin films into a non-aqueous secondary battery, As a result, it has been found that the separator exhibits far superior features as compared with a separator made of polyethylene porous membrane or a separator made of polypropylene porous membrane.

  The present invention has been achieved based on the above findings.

That is, the above problem is
A battery separator material,
The material is a battery separator material characterized in that it is a polyurethane porous membrane.

  This battery separator material is preferably solved by a battery separator material having an average pore diameter of 5 μm or less.

The battery separator material is preferably a battery separator material having a water permeability of 0 to 2000 L / m ² · hr · atm.

  This battery separator material is preferably solved by a battery separator material having an air permeability of 50 to 400 sec.

  This battery separator material is preferably solved by a battery separator material having a porosity of 5 to 60%.

  This battery separator material is preferably solved by a battery separator material having a puncture strength of 300 g or more.

The above issues are
A method for manufacturing a battery separator,
The battery separator is manufactured using the polyurethane porous membrane, and the battery separator manufacturing method is used.

The above issues are
A battery separator,
It solves by the separator for batteries characterized by comprising using the above-mentioned polyurethane porous membrane.

The above issues are
A positive electrode;
A negative electrode,
This is solved by a secondary battery comprising the battery separator.

  The above-mentioned secondary battery, preferably a non-aqueous secondary battery, is solved by the secondary battery.

  A separator with high mechanical strength (puncture strength), excellent ion permeability, and excellent battery output characteristics, safety, and productivity. A high-performance secondary battery can be obtained at low cost.

  The first aspect of the present invention is a material for a battery separator. This material is a polyurethane porous membrane.

  A preferred polyurethane porous membrane has an average pore size of 5 μm or less (more preferably 3 μm or less, more preferably 2 μm or less, particularly preferably 1 μm or less, more preferably 0.01 μm or more, still more preferably 0.1 μm or more, particularly. The polyurethane porous membrane was preferably 0.3 μm or more. Here, the average pore diameter is a value measured by a mercury intrusion method. From the obtained pore distribution data, the point (mode diameter) having the largest injection volume at 10 μm or less was defined as the average pore diameter. Patent Document 6 points out that when the average pore diameter is larger than 0.25 μm, for example, when used as a separator for a lithium ion secondary battery, precipitation of metallic lithium due to current concentration tends to occur. However, surprisingly, when a polyurethane porous membrane was used, even a value exceeding 0.25 μm was preferred. This difference was thought to be due to the chemical bond structure and pore structure unique to the polyurethane porous membrane.

A preferred polyurethane porous membrane was a polyurethane porous membrane having a porosity of 5 to 60% (more preferably 55% or less, more preferably 40% or less, 15% or more). Here, a 20 cm square sample is prepared for the porosity, and the formula [porosity (%) = (volume (cm ³ ) −weight (g) / membrane density) / volume (cm ³ )] from the volume and weight. × 100]. If the porosity is too small, the permeability of ions and the like is not sufficient, and the function as a battery separator is difficult to be achieved. On the other hand, when the porosity is too large, the mechanical strength becomes weak and the safety as a battery separator is lowered. For this reason, a polyurethane porous membrane having the above-mentioned porosity was preferred.

Preferred polyurethane porous membrane, the water permeability is ^{0~2000L / m 2 · hr · atm} ( more preferably 900L ^/ m 2 · hr · atm or less. More preferably 500L ^/ m 2 · hr · atm or less. More preferably 200 L / m ² · hr · atm or less, in particular 50 L / m ² · hr · atm or less). The water permeation amount is the water permeation amount per unit time, unit pressure, unit area, and thickness of 25 μm of the microporous membrane. Here, the water permeation amount is a unit based on the water permeation amount (cm ³ ) when 120 seconds have passed after a porous membrane is set in a stainless steel permeation cell having a diameter of 42 mm and water is filtered at a differential pressure of 0.5 atm. Calculate the amount of water per time, unit pressure, unit area,
This was multiplied by the film thickness (μm) / 25 (μm) to obtain a water permeability of 25 μm (L / m ² · hr · atm). When the amount of water permeation was too large, the liquid retaining property of the electrolytic solution deteriorated and the output performance of the battery deteriorated. And the discharge capacity at the time of a large current was so large that the amount of water permeation was small. For these reasons, a polyurethane porous membrane having a water permeability of the above value was preferred.

  A preferable polyurethane porous membrane was a polyurethane porous membrane having an air permeability of 50 to 400 sec (more preferably 60 sec or more, more preferably 70 sec or more, more preferably 200 sec or less, and further preferably 150 sec or less). Here, the air permeability is a value measured by a Gurley type air permeability meter according to JIS P-8117, and is a value converted per thickness of 25 μm. That is, when the air permeability is too small, a short circuit is likely to occur between the positive electrode and the negative electrode. Conversely, when the air permeability is too high, the discharge capacity at low temperatures tends to decrease. For this reason, a polyurethane porous membrane having the above-mentioned air permeability was preferred.

A preferred polyurethane porous membrane was a polyurethane porous membrane having a permeability index of 0 to 20 (more preferably 15 or less, still more preferably 5 or less). The permeability index is an index expressed by water permeability (L / m ² · hr · atm) / air permeability (sec). When the permeability index was too large, the temperature increase at the time of overcharging was abrupt, which was not preferable.

  A preferable polyurethane porous membrane is a polyurethane porous membrane having a puncture strength of 300 g or more (there is no particular limitation on the upper limit value, but in reality, 1000 g or less, more preferably 600 g or less). When the puncture strength is too small, the polyurethane porous membrane (separator) is easily broken. If it breaks, there is a risk of a short circuit. Therefore, from the viewpoint of safety, a polyurethane porous membrane having the above-mentioned puncture strength was preferred.

  The second aspect of the present invention is a method for producing a battery separator. The battery separator is manufactured by using polyurethane. In particular, it is produced by using the polyurethane having the above characteristics. The polyurethane porous membrane constituting the battery separator thus obtained has the above characteristics.

  The third aspect of the present invention is a battery separator. The battery separator is constructed using the polyurethane porous membrane.

  The fourth aspect of the present invention is a battery. The battery includes a positive electrode, a negative electrode, and the battery separator. This battery is, for example, a non-aqueous secondary battery.

  The battery separator (porous membrane) of the present invention is made of polyurethane. The polyurethane preferably comprises a bifunctional or higher functional isocyanate component, a polyol component having two or more active hydrogens, and a chain extension component.

  Examples of the isocyanate component (compound) include 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, naphthalene diisocyanate, 1,4-phenylene diisocyanate, Ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, hydrogenated 4,4′-diphenylmethane diisocyanate, 4-cyclohexane diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tetraethyl xylylene diisocyanate Can be mentioned. In addition, a polyfunctional polyisocyanate compound having three or more functions may be used.

  Examples of the polyol component (compound) include polyether polyols, polyester polyols, and acrylic polyols.

  Polyether propylene polyols obtained by adding propylene oxide to one or more polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin and trimethylolpropane Polyoxyethylene polyols obtained by adding ethylene oxide, polyols obtained by adding styrene oxide or butylene oxide, or polyoxytetramethylene polyol obtained by ring-opening polymerization of tetrahydrofuran to the polyhydric alcohol Or a copolymer using two or more of the above cyclic ethers.

  Examples of the polyester polyols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, cyclohexanediol, glycerin, trimethylolpropane, pentaesitol, other low molecular weight polyhydric alcohols, and glutar Condensation polymers with one or more of acid, adipic acid, pimelic acid, suberic acid, sebacic acid, terephthalic acid, isophthalic acid, dimer acid, hydrogenated dimer acid, other low molecular weight dicarboxylic acid or oligomeric acid, propionlactone, Examples thereof include polyols such as ring-opening polymers of cyclic esters such as caprolactone and valerolactone.

  Examples of the acrylic polyols include phenol resin polyols, epoxy polyols, polybutadiene polyols, polyisoprene polyols, polyester-polyether polyols, acrylonitrile-based polyols, and polycarbonate polyols.

  Examples of the chain extending component, particularly a chain extending component having an active hydrogen (chain extending agent) include compounds having a molecular weight of about 500 or less. For example, aliphatic low molecular diols typified by ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane and the like, triols, methylenebis-o-chloroaniline, cyclohexylmethane-4,4′-diamine Aromatic diamines such as 1,4-bishydroxyethoxybenzene and the like.

  Various methods can be adopted as a method for producing the battery separator (porous membrane) of the present invention using the polyurethane. For example, a porous film can be obtained using a known wet molding method. Alternatively, a porous film can be obtained by using a technique in which a foaming agent is added. The wet molding method is suitable as a method of obtaining a battery separator made of a polyurethane porous membrane. That is, a polyurethane microporous membrane can be easily obtained by coagulating the polyurethane composition in water, followed by washing and drying.

  The polyurethane porous membrane constituting the battery separator may be in the form of a polyurethane composition. That is, the polyurethane porous membrane may contain various additives. Examples of the additive include a crosslinking agent, a water repellent, a pigment, a wettability improver, an antifoaming agent, an antioxidant, and an ultraviolet ray preventing agent.

  Examples of the crosslinking agent include a polyisocyanate crosslinking agent, a carbodiimide crosslinking agent, an epoxy crosslinking agent, an ethyleneimine crosslinking agent, and an oxazoline crosslinking agent. Polyvalent metal salts such as calcium and magnesium may be used.

  As said water repellent, a fluorine-type water repellent is mentioned, for example. The inclusion of a water repellent is preferable because it reduces the amount of water permeation in the polyurethane porous membrane (battery separator). A typical example of the fluorine-based water repellent is a compound having a perfluoroalkyl group. For example, a fluoroalkyl group-containing polymerizable compound such as acrylic acid (methacrylic acid) having a perfluoroalkyl group, ethylene, vinyl acetate, vinyl fluoride, styrene, acrylic acid (methacrylic acid), and alkyl esters thereof And copolymers with one or more of maleic anhydride, chloroprene, butadiene, vinyl alkyl ketone, vinyl alkyl ether, acrylamide, methacrylamide, glycidyl acrylate, and the like.

  The polyurethane composition may contain inorganic or organic fine particles. For example, inorganic fine particles such as silica, silica sol, colloidal silica, alumina, alumina sol, zinc oxide, boron, boron oxide, calcium oxide, magnesium oxide, and barium oxide may be contained. Alternatively, organic fine particles such as polyethylene, acrylic polymer, polystyrene, and silicone polymer may be contained.

The battery separator not only separates the positive electrode and the negative electrode, but also has a function of holding the electrolyte and ensuring ionic conductivity between the positive electrode and the negative electrode. The electrolytic solution is generally composed of a supporting salt and a solvent. Lithium salt is mainly used as the supporting salt in the lithium secondary battery. As the lithium salt, for _{example, LiClO 4, LiBF 4, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, lower aliphatic lithium _carboxylate, LiAlCl 4, LiCl, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate and the like can be mentioned. Of course, not only one type but also two or more types may be mixed. LiBF ₄ and LiPF ₆ are particularly preferred lithium salts. The concentration of the supporting salt is not particularly limited, but is preferably 0.2 to 3 mol per liter of the electrolytic solution. Solvents constituting the electrolyte include, for example, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, methyl acetate, 1,2-dimethoxy. Ethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, dioxane, acetonitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3 -Aprotic properties such as methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone Solvents. Of course, not only one type but also two or more types may be mixed. A carbonate-based solvent is particularly preferable. Among these, a mixture of a cyclic carbonate and an acyclic carbonate is particularly preferable. As the cyclic carbonate, for example, ethylene carbonate and propylene carbonate are preferable examples. Preferred examples of the acyclic carbonate include diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate. The entire amount of the electrolytic solution may be injected once, but it is preferable to inject it in two or more times. When injecting in two or more times, each solution may have the same composition, but a different composition (for example, a non-aqueous solvent or a non-aqueous solvent having a higher viscosity than the solvent after injecting a solution in which a lithium salt is dissolved in the non-aqueous solvent). Or a solution in which a lithium salt is dissolved in a solvent or a non-aqueous solvent may be injected). In order to shorten the time for injecting the electrolyte, the battery can may be decompressed, or centrifugal force or ultrasonic waves may be applied to the battery can.

  A battery (secondary battery, in particular, a non-aqueous secondary battery, in particular, a lithium ion secondary battery) is configured using the battery separator. In addition to the battery separator, the battery includes a positive electrode and a negative electrode. The positive electrode is configured using a positive electrode active material. The positive electrode active material is preferably a lithium-containing transition metal oxide. The lithium-containing transition metal oxide is an oxide mainly containing lithium and at least one transition metal element selected from the group of Ti, V, Cr, Mn, Fe, Co, Ni, Mo, W and the like. . It can be synthesized by a method of mixing and firing a lithium compound and a transition metal compound or by a solution reaction. The negative electrode is composed of a compound (negative electrode material) that can occlude and release lithium ions. Examples of such a negative electrode material include metal lithium, lithium alloy, carbonaceous compound, inorganic oxide, inorganic chalcogen compound, metal complex, and organic polymer compound. These can be used alone or in combination. The conductive agent used in the mixture of the present invention may be anything as long as it is an electron conductive material that does not cause a chemical change in the constructed battery. Specific examples include natural graphite such as scaly graphite, scaly graphite and earthy graphite, high-temperature fired bodies such as petroleum coke, coal coke, celluloses, saccharides and mesophase pitch, and graphite such as artificial graphite such as vapor-grown graphite. , Carbon blacks such as acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, etc., carbon materials such as asphalt pitch, coal tar, activated carbon, mesofuse pitch, polyacene, conductivity of metal fibers, etc. Examples thereof include fibers, metal powders such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium oxide. In the present invention, a binder is used to hold the electrode mixture. Examples of the binder include polysaccharides, thermoplastic resins, and polymers having rubber elasticity.

  Hereinafter, specific examples will be given and described in detail.

[Example 1]
(Preparation of electrolyte)
A non-aqueous solvent of EC (ethylene carbonate): DEC (diethyl carbonate) = 50: 50 (weight ratio) was prepared. LiPF ₆ was dissolved in this solvent. Then, an electrolyte (LiPF ₆ concentration: 1M) was obtained.
[Lithium secondary battery]
80 parts by weight of LiCoO ₂ (positive electrode active material), 10 parts by weight of acetylene black (conductive agent), and 10 parts by weight of polyvinylidene fluoride (binder) were mixed. To this, 1-methyl-2-pyrrolidone was added to form a slurry. This slurry was applied on an aluminum foil. Then, it dried and pressure-molded and comprised the positive electrode.
90 parts by weight of natural graphite (negative electrode active material) and 10 parts by weight of polyvinylidene fluoride (binder) were mixed. To this, 1-methyl-2-pyrrolidone was added to form a slurry. This slurry was applied on a copper foil. Then, it dried and pressure-molded and comprised the negative electrode.
A microporous polyurethane film (Rustre FGX manufactured by Hiramatsu Sangyo Co., Ltd .: Rustre is a registered trademark) was prepared as a separator. The electrolyte solution was poured into this to produce a coin-type battery (diameter 20 mm, thickness 3.2 mm).

[Comparative Example 1]
In Example 1, a coin-type battery (diameter 20 mm, thickness 3.2 mm) was prepared in the same manner except that microporous polypropylene (Celgard Inc. cell guard) was used instead of the microporous polyurethane film. Produced.

[Characteristic]
Using the coin battery of each of the above examples, it was charged at a constant current constant voltage of 0.8 mA at room temperature (20 ° C.) for 5 hours to a final voltage of 4.2 V, and then at a constant current of 0.8 mA, a final voltage of 2 Discharged to 7V. Then, after charging and discharging under the same conditions and measuring the discharge capacity, the discharge capacity was measured by setting only the discharge current to 4.0 mA. The results are shown in Table-1.
Table-1
Example 1 Comparative Example 1
Porous film Porous polyurethane film Porous polypropylene film thickness (μm) 25 25
Puncture strength (g) 350 340
Average pore diameter (μm) 0.8 0.15
Porosity (%) 30 44
Air permeability (sec) 120 130
Water permeability (L / m ² · hr · atm) 0 920
Permeability index 0 8.4
Relative discharge capacity (0.8 mA) 100 100
Relative discharge capacity (4.0 mA) 80 60

As can be seen from Table 1, the present invention has a large relative discharge capacity at the high rate.

[Example 2]
A non-aqueous solvent of EC (ethylene carbonate): DEC (diethyl carbonate) = 50: 50 (weight ratio) was prepared.
A microporous polyurethane film (Rustre FGX manufactured by Hiramatsu Sangyo Co., Ltd .: Rustre is a registered trademark) as a separator material was prepared. The film was cut into 5 × 50 mm strips, and 10 mm from the tip was immersed perpendicularly to the liquid surface of the solvent. The time from immediately after immersion until the above-mentioned solvent rose 5 mm along the film was measured by the capillary effect.

[Comparative Example 2]
In Example 2, the same procedure was performed except that microporous polypropylene (Celgard Inc. cell guard) was used instead of the microporous polyurethane film, and the solvent rising time was measured.

[Characteristic]
Table-2
Example 2 Comparative Example 2
Solvent rise time (sec) 487 1200 or more

As can be seen from Table-2, the present invention has a high affinity with the solvent, and the injection of the electrolytic solution is quick.

Claims (10)

A battery separator material,
The material has a water permeability of 0 to 50 L / m ² · hr · atm , an air permeability of 50 to 400 sec, a permeability index represented by the water permeability / the air permeability of 0 to 20, and a porosity of A battery separator material, characterized by being a polyurethane porous membrane having an average pore diameter of 5 to 60% and an average pore size of 0.01 to 5 μm . The battery separator material according to claim 1, wherein the air permeability is 70 to 150 sec. The battery separator material according to claim 1 or claim 2, wherein the permeability index is 0-5. 4. The battery separator material according to claim 1, wherein the porosity is 15 to 40% . The battery separator material according to any one of claims 1 to 4, wherein an average pore diameter is 0.3 to 2 µm. 6. The battery separator material according to claim 1, wherein the puncture strength is 300 to 1000 g. A method for manufacturing a battery separator,
A battery separator is produced using the polyurethane porous membrane according to any one of claims 1 to 6. A method for producing a battery separator. A battery separator,
A battery separator comprising the polyurethane porous membrane according to any one of claims 1 to 6. A positive electrode;
A negative electrode,
A secondary battery comprising the battery separator according to claim 8. The secondary battery according to claim 9, wherein the secondary battery is a non-aqueous secondary battery.