JP6349080B2 - Fine particle mixture for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a fine particle mixture for a nonaqueous electrolyte secondary battery, an electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.

  In recent years, as the capacity and the resistance of lithium ion secondary batteries have increased, the thickness of the separator has been reduced. On the other hand, from the viewpoint of improving safety, higher insulation performance (short-circuit prevention performance) is required than ever.

  In this regard, Patent Document 1 discloses a technique in which a non-woven fabric using heat-resistant organic fibers contains thermally expandable fine particles that can be thermally expanded. According to this technique, even when a sudden exothermic reaction occurs due to an internal short circuit or the like, it is possible to suppress the loss of the insulating properties of the separator.

JP 2007-273127 A

  However, the nonwoven fabric separator has a problem that it is difficult to reduce the film thickness. On the other hand, as a separator for a lithium ion secondary battery, a polyolefin-based porous film is known, and this porous film is currently mainstream. As a material for the polyolefin-based porous film, polyethylene, polypropylene, and the like are known.

  Polyolefin porous membranes have the advantage that they can be made thinner than nonwoven separators. However, when the polyolefin-based porous film is thinned, the strength of the film is lowered, and there is a problem that the film is easily broken and the insulating performance is lowered. Examples of a method for solving this problem include application of an inorganic filler and clothing with a highly elastic polymer. However, these methods inevitably increase the film thickness and increase the manufacturing cost. Furthermore, thinning of the polyolefin-based porous film is approaching its limit, and further thinning has been extremely difficult.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to reduce the thickness of the separator of the nonaqueous electrolyte secondary battery and to improve the insulating performance of the separator. An object is to provide a fine particle mixture for a non-aqueous electrolyte secondary battery, an electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

  In order to solve the above problems, according to one aspect of the present invention, swelling fine particles that swell in an electrolyte solution of a non-aqueous electrolyte secondary battery, swelling property to an electrolyte solution is lower than swelling fine particles, and thermal expansion There is provided a fine particle mixture for a non-aqueous electrolyte secondary battery, characterized by comprising a thermally expandable fine particle having a property and an average particle size of 0.05 μm to 0.5 μm.

  The fine particle mixture for a non-aqueous electrolyte secondary battery according to this aspect functions as a separator of the non-aqueous electrolyte secondary battery by foaming after being disposed on the electrode, for example. Since this separator is obtained by foaming a fine particle mixture, the separator can be made thinner than the polyolefin-based porous film, and the insulation is improved as compared with the polyolefin-based separator. Furthermore, this separator can be produced at a lower cost than a polyolefin-based porous membrane. Furthermore, a non-aqueous electrolyte secondary battery using this separator can realize a cycle life comparable to a non-aqueous electrolyte secondary battery using a polyolefin-based porous membrane.

  Here, the thermally expandable fine particles may be a copolymer of a foaming monomer and a stabilizing monomer having a higher stability in the non-aqueous electrolyte secondary battery than the foamable monomer. The expandable fine particles are stably present in the nonaqueous electrolyte secondary battery. That is, the insulating property of the separator produced by foaming the fine particle mixture is improved.

  Further, the foamable monomer may contain a diazo compound, and in this case, the thermally expandable fine particles can be easily foamed.

  Further, the diazo compound may have a structure represented by the following chemical formula I. In this case, the thermally expandable fine particles can be easily foamed.

  In Chemical Formula I, R1 is a hydrogen atom or a methyl group, R2 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R3 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R4 is hydrogen, a methyl group, an acryl group, or a methacryl group. Or a glycidyl group, X represents a direct bond or an alkylene group having 1 to 6 carbon atoms.

  The diazo compound may have a structure represented by the following chemical formula II, and in this case, the thermally expandable fine particles can be easily foamed.

  In Formula II, R1 is a hydrogen atom or methyl group, R2 is hydrogen or an alkyl group having 1 to 6 carbon atoms, A is a methylene group or carbonyl group, Q is a methylene group or methine group, T is a direct bond, a double bond, methylene Represents a group, oxygen or NH group.

  Further, the foaming temperature of the foamable monomer may be 120 ° C. or more and 250 ° C. or less. In this case, the thermally expandable fine particles can be easily foamed.

  According to another aspect of the present invention, there is provided an electrode active material layer, and a separator provided on the electrode active material layer, wherein the fine particle mixture for a nonaqueous electrolyte secondary battery is foamed. An electrode for a non-aqueous electrolyte secondary battery is provided.

  Since the electrode for nonaqueous electrolyte secondary batteries according to this aspect includes a separator produced by foaming the above fine particle mixture, the separator can be thinned. In addition, the non-aqueous electrolyte secondary battery using this electrode has improved insulating properties.

  According to another aspect of the present invention, there is provided a nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery.

  According to this viewpoint, the separator of the nonaqueous electrolyte secondary battery can be made thin, and the insulating performance of the separator can be improved.

  As described above, the fine particle mixture according to the present invention can reduce the thickness of the separator of the nonaqueous electrolyte secondary battery and can improve the insulating performance of the separator.

It is a sectional side view which shows the structure of the lithium ion secondary battery which concerns on embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(Configuration of lithium ion secondary battery)
First, based on FIG. 1, the structure of the lithium ion secondary battery 10 which concerns on 1st Embodiment is demonstrated.

The lithium ion secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator layer 40. The charge ultimate voltage (redox potential) of the lithium ion secondary battery 10 is, for example, 4.3 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V or less, particularly 4.5 V or more and 5.0 V or less. The form of the lithium ion secondary battery 10 is not particularly limited. That is, the lithium ion secondary battery 10 may be any one of a cylindrical shape, a square shape, a laminate shape, a button shape, and the like.

  The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22. The current collector 21 may be any conductor as long as it is a conductor, and is made of, for example, aluminum, stainless steel, nickel-coated steel, or the like.

The positive electrode active material layer 22 includes at least a positive electrode active material, and may further include a conductive agent and a binder. The positive electrode active material is, for example, a solid solution oxide containing lithium, but is not particularly limited as long as the material can electrochemically occlude and release lithium ions. The solid solution oxide is, for example, Li _a Mn _x Co _y Ni _z O ₂ (1.150 ≦ a ≦ 1.430, 0.45 ≦ x ≦ 0.6, 0.10 ≦ y ≦ 0.15,. 20 ≦ z ≦ 0.28), LiMn _x Co _y Ni _z O ₂ (0.3 ≦ x ≦ 0.85, 0.10 ≦ y ≦ 0.3, 0.10 ≦ z ≦ 0.3), LiMn _1.5 Ni _0.5 O ₄ .

  The conductive agent is, for example, carbon black such as ketjen black or acetylene black, natural graphite, artificial graphite, or the like, but is not particularly limited as long as it is intended to increase the conductivity of the positive electrode.

  Examples of the binder include polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile butadiene rubber, and acrylonitrile butadiene rubber. Fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, nitrocellulose, and the like, and a positive electrode active material and a conductive agent on the current collector 21. Bind There is no particular limitation as long as it can be used.

  The positive electrode active material layer 22 is produced, for example, by the following manufacturing method. That is, first, a positive electrode mixture is prepared by dry-mixing a positive electrode active material, a conductive agent, and a binder. Next, the positive electrode mixture is dispersed in a suitable organic solvent to form a positive electrode mixture slurry (slurry). The positive electrode mixture slurry is applied onto the current collector 21, dried, and rolled to produce a positive electrode active slurry. A material layer is formed.

The negative electrode 30 includes a current collector 31 and a negative electrode active material layer 32. The current collector 31 may be any conductor as long as it is a conductor, for example, aluminum, stainless steel, nickel-plated steel, or the like. The negative electrode active material layer 32 may be any material as long as it is used as a negative electrode active material layer of a lithium ion secondary battery. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a binder. Examples of the negative electrode active material include graphite active material (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), fine particles of silicon or tin or oxides thereof and graphite active material. , Silicon or tin fine particles, alloys based on silicon or tin, and titanium oxide compounds such as Li ₄ Ti ₅ O ₁₂ . The oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). Examples of the negative electrode active material include metallic lithium and the like in addition to these. The binder is also the same as the binder constituting the positive electrode active material layer 22. The mass ratio between the positive electrode active material and the binder is not particularly limited, and the mass ratio employed in the conventional lithium ion secondary battery is also applicable in this embodiment.

  The negative electrode active material layer 32 is produced by the following manufacturing method, for example. That is, first, a negative electrode mixture is prepared by dry-mixing a negative electrode active material and a binder. Subsequently, the negative electrode mixture is dispersed in a suitable solvent to form a negative electrode mixture slurry (slurry). The negative electrode mixture slurry is coated on the current collector 31, dried, and rolled to form a negative electrode active material. Layer 32 is formed.

  The separator layer 40 includes a separator and a non-aqueous electrolyte. The separator is obtained by foaming a fine particle mixture. Here, the fine particle mixture includes swellable fine particles and thermally expandable fine particles.

  Swellable fine particles are fine particles that are swollen by a non-aqueous electrolyte. The swellable fine particles have a role of ensuring the conductivity of the separator. The swellable fine particles may or may not have thermal expansibility. However, when the swellable fine particles are thermally expanded, the swellable fine particles can be thermally expanded in the same manner as the thermally expandable fine particles. That is, the swellable fine particles after thermal expansion (after foaming) and the thermal expandable fine particles after thermal expansion are uniformly dispersed in the separator. Thereby, the insulation performance of the separator can be further improved, and the conductivity can be more reliably ensured. When the swellable fine particles have thermal expansibility, the swellable fine particles can thermally expand to form a large number of pores therein. Therefore, the swellable fine particles can contain more electrolytic solution.

  When the swellable fine particles have thermal expansibility, the material constituting the swellable fine particles is any of foamable monomers, butyl acrylate, triethylene glycol diacrylate, acrylic acid, styrene, acrylonitrile, and acrylamide, which will be described later Examples thereof include a copolymer with one or more kinds.

  When the swellable fine particles do not have thermal expansibility, as the material constituting the swellable fine particles, the above foamable monomer is replaced with 2-hydroxydiethyl acrylate, styrene, acrylonitrile, acrylamide, or N-isopropylamide. And the like.

  The heat-expandable fine particles have a lower swelling property to the electrolytic solution than the swellable fine particles and have a heat-expandable property. The thermally expandable fine particles are thermally expanded (foamed) to suppress a short circuit between the electrodes. Further, the thermally expandable fine particles are stably present in the lithium ion secondary battery 10. That is, it hardly swells with respect to the electrolytic solution and hardly reacts with the electrode. Therefore, the thermally expandable fine particles after foaming function as a skeleton of the separator.

  The thermally expandable fine particles are preferably a copolymer of a foaming monomer and a stabilizing monomer having higher stability in the lithium ion secondary battery than the foamable monomer. When the heat-expandable fine particles become a copolymer of these monomers, the heat-expandable fine particles are hardly swelled in the electrolytic solution.

  The foamable monomer can be used without particular limitation as long as it is a resin that foams when heated, but a low volatility monomer is preferred. This is because when thermally expandable fine particles containing a highly volatile foamable monomer are introduced into the electrolyte, volatile components may be eluted into the electrolyte.

  The foamable monomer preferably foams between 120 ° C and 250 ° C. The foamable monomer preferably comprises a diazo compound. The diazo compound decomposes when heated. And a diazo compound foams with the nitrogen gas which is a decomposition product. The diazo compound preferably has a structure represented by the following chemical formula I or chemical formula II.

  In Chemical Formula I, R1 is a hydrogen atom or a methyl group, R2 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R3 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R4 is hydrogen, a methyl group, an acryl group, or a methacryl group. Or a glycidyl group, X represents a direct bond or an alkylene group having 1 to 6 carbon atoms.

化学式ＩＩ中、Ｒ１は水素原子又はメチル基、Ｒ２は水素又は炭素数１〜６のアルキル基、Ａはメチレン基又はカルボニル基、Ｑはメチレン基又はメチン基、Ｔは直結、二重結合、メチレン基、酸素、またはＮＨ基を表す。

In Formula II, R1 is a hydrogen atom or methyl group, R2 is hydrogen or an alkyl group having 1 to 6 carbon atoms, A is a methylene group or carbonyl group, Q is a methylene group or methine group, T is a direct bond, a double bond, methylene Represents a group, oxygen or NH group.

  When the heat-expandable fine particles are composed only of a diazo compound, the heat-expandable fine particles easily react with the electrode active material and easily swell in the electrolytic solution. Therefore, when thermally expandable fine particles are added to the electrolytic solution, the thermally expandable fine particles react with the electrode and swell with the electrolytic solution. As a result, problems such as an increase in internal resistance and a decrease in cycle life of the lithium ion secondary battery 10 may occur.

  Therefore, in this embodiment, the thermally expandable fine particles are a copolymer of a foaming monomer and a stabilizing monomer having higher stability in the lithium ion secondary battery than the foamable monomer. The stabilizing monomer is less likely to swell in the electrolyte solution than the foamable monomer. In addition, the stabilizing monomer is less likely to react with the electrode active material than the foamable monomer. Examples of the stabilizing monomer include acrylonitrile and acrylic acid. As a result, the thermally expandable fine particles are stabilized in the lithium ion secondary battery. That is, the heat-expandable fine particles are less likely to swell in the electrolytic solution and are less likely to react with the electrode.

  The average particle size of the fine particle mixture is 0.05 μm to 0.5 μm. Here, the average particle diameter is a D50 value of the diameter when each fine particle is regarded as a sphere. For example, when the average particle size is less than 0.05 μm, for example, a laser diffraction / scattering particle size distribution measuring apparatus (for example, Microtrac MT3000 manufactured by Nikkiso Co., Ltd.) is sufficient even if the thermally expandable fine particles are thermally expanded. As a result, the insulating performance of the separator may be insufficient. On the other hand, when the average particle size is larger than 0.5 μm, the separator becomes thicker.

  Since the separator according to the present embodiment is obtained by foaming a fine particle mixture, the separator can be made thinner than the polyolefin-based porous film, and the insulating property is improved as compared with the polyolefin-based separator. Furthermore, the separator according to this embodiment can be produced at a lower cost than the polyolefin-based porous membrane. Furthermore, as will be described later, the lithium ion secondary battery 10 according to the present embodiment can realize a cycle life comparable to that of a lithium ion secondary battery using a polyolefin-based porous film.

  As the non-aqueous electrolyte, the same non-aqueous electrolyte as conventionally used for lithium secondary batteries can be used without any particular limitation. The nonaqueous electrolytic solution has a composition in which an electrolyte salt is contained in a nonaqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate (vinyl carbonate), and the like. ); Cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate chain carbonates such as ethyl carbonate; chain esters such as methyl formate, methyl acetate, butyric acid methyl; tetrahydrofuran (tetrahydrofuran) or derivatives thereof; 1,3- Ethers such as dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyl diglyme; Nitriles such as acetonitrile and benzonitrile e) class; dioxolane or a derivative thereof; ethylene sulfide, sulfolane, sultone, or a derivative thereof alone or a mixture of two or more thereof, etc. It is not limited to.

Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiPF _6-x (C _n F _{2n + 1} ) _x [where 1 <x <6, n = 1or2], LiSCN, LiBr, Inorganic ions containing one kind of lithium (Li), sodium (Na) or potassium (K) such as LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN Salt, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) _{3, LiC (C 2 F 5} SO 2) 3, (CH 3) 4 NBF 4, (CH 3) 4 NBr, (C 2 H 5) 4 NClO 4, _{C 2 H 5) 4 NI,} (C 3 H 7) 4 NBr, (n-C 4 H 9) 4 NClO 4, (n-C 4 H 9) 4 NI, (C 2 H 5) 4 N-maleate , (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, lithium stearyl sulfonate (octyl sulfonic acid), lithium dodecylbenzene sulfonate (lithium dodecylbenzene sulfonate) organic ion salts such as dodecyl benzene sulphonic acid) and the like, and these ionic compounds can be used alone or in admixture of two or more. The concentration of the electrolyte salt may be the same as that of the nonaqueous electrolytic solution used in the conventional lithium secondary battery, and is not particularly limited. In this embodiment, a nonaqueous electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.8 to 1.5 mol / L can be used.

  Various additives may be added to the nonaqueous electrolytic solution. Examples of such additives include a negative electrode action additive, a positive electrode action additive, an ester additive, a carbonate ester additive, a sulfate ester additive, a phosphate ester additive, and a borate ester additive. Additive, acid anhydride additive, electrolyte additive and the like. Any one of these may be added to the non-aqueous electrolyte, or a plurality of types of additives may be added to the non-aqueous electrolyte.

(Method for producing lithium ion secondary battery)
Next, a method for manufacturing the lithium ion secondary battery 10 will be described. The positive electrode 20 is produced as follows. First, a slurry is formed by dispersing a mixture of a positive electrode active material, a conductive agent, and a binder in a solvent (for example, N-methyl-2-pyrrolidone). Next, the positive electrode active material layer 22 is formed by forming (for example, coating) the slurry on the current collector 21 and drying the slurry. The coating method is not particularly limited. Examples of the coating method include a knife coater method and a gravure coater method. The following coating steps are also performed by the same method. Next, the positive electrode active material layer 22 is pressed by a press machine. Thereby, the positive electrode 20 is produced.

  The negative electrode 30 is also produced in the same manner as the positive electrode 20. First, a slurry is formed by dispersing a mixture of a negative electrode active material and a binder in a solvent (eg, N-methyl-2-pyrrolidone, water). Next, the negative electrode active material layer 32 is formed by forming (for example, coating) the slurry on the current collector 31 and drying the slurry. Next, the negative electrode active material layer 32 is pressed by a press. Thereby, the negative electrode 30 is produced.

  The slurry of the fine particle mixture is applied to at least one of the positive electrode active material layer 22 and the negative electrode active material layer 32 and dried to form a separator. Subsequently, an electrode structure is produced by sandwiching the separator between the positive electrode 20 and the negative electrode 30. Next, the electrode structure is processed into a desired shape (for example, a cylindrical shape, a square shape, a laminate shape, a button shape, etc.) and inserted into a container of the shape. Next, by injecting the electrolytic solution having the above composition into the container, each pore in the separator is impregnated with the electrolytic solution. Thereby, a lithium ion secondary battery is produced.

(Synthesis example 1 of foaming monomer)
First, a synthesis example of the foamable monomer used in this example will be described. In Synthesis Example 1, N-monoacrylazodicarbonamide was synthesized as a foamable monomer by the following method.

  50 g (0.43 mol, 1 equivalent) of azodicarbonamide and 500 g of anhydrous N, N-dimethylformamide (DMF) in a 1 liter three-necked flask equipped with a condenser, a thermometer, and a dropping funnel under a nitrogen atmosphere Then, 500 g (6.32 mol, 14.7 equivalents) of anhydrous pyridine was added, and the mixture was cooled to 5 ° C. in an ice bath while stirring with a magnetic stirrer.

  Next, 39 g (0.43 mol, 1.0 equivalent) of acrylic acid chloride was added to the dropping funnel, and acrylic acid chloride was added dropwise to the mixed solution while maintaining the temperature of the mixed solution at 30 ° C. or lower. After completion of the dropping, the ice bath was replaced with an oil bath, and the mixture was heated and stirred at 40 ° C. for 2 hours. Next, after cooling the reaction solution to room temperature, the reaction solution was poured into 1000 ml of water and stirred. This solution was transferred to a 3000 ml separatory funnel and extracted three times with 300 ml of ethyl acetate. All the organic layers were collected, and the collected product was washed twice with 500 ml of water and once with 300 ml of saturated brine, and dried over anhydrous magnesium sulfate. After removing anhydrous magnesium sulfate by suction filtration from the collected material after drying, it was concentrated with a rotary evaporator (bath temperature 40 ° C.). The concentrate was further dried with a vacuum dryer (40 ° C./133 Pa) for 6 hours. As a result, 55 g (yield 75%) of N-monoacrylazodicarbonamide was obtained.

(Synthesis example 2 of foamable monomer)
The same treatment as in the foaming monomer synthesis example 1 was performed except that 45 g (0.43 mol, 1.0 equivalent) of methacrylic acid chloride was used instead of acrylic acid chloride. As a result, 58 g (yield 73%) of N-monoacrylic azodicarbonamide was obtained.

(Synthesis example 3 of foaming monomer)
The same treatment as in the foaming monomer synthesis example 1 was performed, except that 80 g (0.88 mol, 2.05 equivalent) of acrylic acid chloride was used. Thereby, 78 g (yield 81%) of N, N′-diacrylazodicarbonamide (N, N′-diacrylic azodic bonamide) was obtained.

(Synthesis example 4 of foaming monomer)
The same treatment as in the foaming monomer synthesis example 4 was performed except that 92.3 g (0.88 mol, 2.05 equivalents) of methacrylic acid chloride was used instead of acrylic acid chloride. As a result, 85 g (yield 78%) of N, N′-dimethacrylic azodicarbonamide was obtained.

(Synthesis example 1 of thermally expandable fine particles)
Next, a synthesis example of the microcapsules used in this example will be described. In Synthesis Example 1, thermally expandable fine particles having an average particle diameter of 80 nm were produced by the following treatment. To a 0.5 liter three-necked flask (Flask) equipped with a stirrer, thermometer, condenser, and liquid feed pump, 240 g of water, 300 mg of sodium dodecylbenzenesulfonate (SDBS) as a surfactant (0 .86 mmol, 0.005 parts by mass (external number) with respect to the total mass of monomers), and 150 mg of zinc stearate as a foaming aid were added to prepare a first mixed solution.

  Next, the pressure in the three-necked flask was reduced to 2600 Pa with a diaphragm pump and then returned to normal pressure with nitrogen three times to remove dissolved oxygen from the first mixture. While maintaining the inside of the flask in a nitrogen atmosphere and heating the first mixed solution with an oil bath so that the temperature in the flask becomes 65 ° C., 0.102 g (0.447 mmol, thermally expandable fine particles) of ammonium persulfate (ammonium) 0.05 mol (mol)% (outside number)) was added to the first mixed liquid with respect to the total number of moles of the monomer.

  Immediately after adding ammonium persulfate, 30 g of N-monoacrylazodicarbonamide (Synthesis Example 1) (176.3 mmol, 50.0 parts by mass relative to the total mass of monomers of the thermally expandable fine particles), acrylonitrile (sum) 25 g (471.2 mmol, 41.7 parts by mass based on the total mass of monomers of the thermally expandable fine particles), 3 g (23.4 mmol, heat) of butyl acrylate (manufactured by Wako Pure Chemical Industries) 5.0 parts by mass with respect to the total mass of monomers of the expandable fine particles), 2 g of acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) (27.8 mmol, 3.3 parts by mass with respect to the total mass of monomers of the thermally expandable fine particles) The mixture (second mixed solution) was added dropwise to the first mixed solution over a period of 1 hour using a feed pump.

  Subsequently, after the liquid mixture (3rd liquid mixture) of a 1st and 2nd liquid mixture was stirred for 4 hours, reaction temperature was heated up to 80 degreeC and stirring was continued for further 1 hour. Thereby, each monomer was emulsion-polymerized. That is, thermally expandable fine particles were produced. Next, the thermally expandable fine particle dispersion was cooled to room temperature, and then filtered through a 100 (mesh) filter to remove aggregates. Thereby, the thermally expandable fine particle dispersion was purified.

  Next, about 1 ml of the thermally expandable fine particle dispersion was weighed into an aluminum pan, dried on a hot plate heated to 160 ° C. for 15 minutes, and the nonvolatile content was calculated from the residue weight. 19.6% by mass (yield 98%) with respect to the total mass of the conductive fine particle dispersion. In addition, the average particle diameter (D50) of the thermally expandable fine particles was measured by a laser (laser) diffraction scattering type particle size distribution measuring apparatus (Microtrac MT3000, manufactured by Nikkiso Co., Ltd.).

(Synthesis example 2 of thermally expandable fine particles)
The same treatment as in Synthesis Example 1 of thermally expandable fine particles was performed except that 150 mg of sodium dodecylbenzenesulfonate (0.43 mmol, 0.0025 parts by mass (external number) with respect to the total monomer mass of the thermally expandable fine particles) was used. went. Thereby, thermally expandable fine particles according to Synthesis Example 2 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). Moreover, the average particle diameter was 150 nm.

(Synthesis example 3 of thermally expandable fine particles)
The same treatment as in Synthesis Example 1 of thermally expandable fine particles was performed except that 190 g of water and 60 mg of sodium dodecylbenzenesulfonate (0.17 mmol, 0.001 part by mass (external number) with respect to the total mass of monomers) were used. . Thereby, thermally expandable fine particles according to Synthesis Example 3 were obtained. The nonvolatile content was 23.7% by mass (yield 99%). The average particle size of the thermally expandable fine particles was 300 nm.

(Synthesis example 4 of thermally expandable fine particles)
Instead of N-monoacrylazodicarbonamide, 30 g (162.9 mmol, 50.0 parts by mass with respect to the total mass of monomers of thermally expandable fine particles) of N-monomethacrylazodicarbonamide (Synthesis Example 2 of foaming monomer) The same treatment as in Synthesis Example 1 of thermally expandable fine particles was performed except that it was used. Thereby, thermally expandable fine particles according to Synthesis Example 4 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). The average particle size of the thermally expandable fine particles was 100 nm.

(Synthesis example 5 of thermally expandable fine particles)
30 g of N-monomethacrylazodicarbonamide (Synthesis Example 2 of foamable monomer) instead of N-monoacrylazodicarbonamide (162.9 mmol, 50.0 parts by mass with respect to the total mass of monomers of the thermally expandable fine particles), The same treatment as in Synthesis Example 1 of thermally expandable fine particles was performed except that 150 mg of sodium dodecylbenzenesulfonate (0.43 mmol, 0.0025 parts by mass (external number) with respect to the total monomer mass of the thermally expandable fine particles) was used. went. Thereby, thermally expandable fine particles according to Synthesis Example 5 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). The average particle size of the thermally expandable fine particles was 150 nm.

(Synthesis example 6 of thermally expandable fine particles)
Using 190 g of water, instead of N-monoacrylazodicarbonamide, 30 g of N-monomethacrylazodicarbonamide (Expandable Monomer Synthesis Example 2) (162.9 mmol, 50. 0 parts by mass), and 60 mg (0.17 mmol, 0.001 part by mass (outside number) of the total monomer mass of the thermally expandable fine particles) of sodium dodecylbenzenesulfonate was used. The same processing as in Synthesis Example 1 was performed. Thereby, thermally expandable fine particles according to Synthesis Example 6 were obtained. The nonvolatile content was 23.5% by mass (yield 98%). The average particle diameter of the thermally expandable fine particles was 320 nm.

(Synthesis example 7 of thermally expandable fine particles)
Instead of N-monoacrylazodicarbonamide, 30 g (133.8 mmol) of N, N′-diacrylazodicarbonamide (Synthesis Example 3 of expandable monomer), 50.0 mass relative to the total monomer mass of the thermally expandable fine particles Part) and using sodium dodecylbenzenesulfonate 150 mg (0.43 mmol, 0.0025 parts by mass (external number) with respect to the total monomer mass of the thermally expandable particles)) 1 was performed. Thereby, thermally expandable fine particles according to Synthesis Example 7 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). The average particle size of the thermally expandable fine particles was 100 nm.

(Synthesis example 8 of thermally expandable fine particles)
Instead of N-monoacrylazodicarbonamide, 30 g (118.9 mmol of N, N′-dimethacrylacrylazodicarbonamide (Synthesis Example 4 of expandable monomer), 50.0 with respect to the total monomer mass of the thermally expandable fine particles Parts by weight) and using 150 mg of sodium dodecylbenzenesulfonate (0.43 mmol, 0.0025 parts by mass (external number) with respect to the total mass of the monomer) as in Synthesis Example 1 of thermally expandable fine particles Processed. Thereby, thermally expandable fine particles according to Synthesis Example 8 were obtained. The nonvolatile content was 19.6% by mass (yield 98%). The average particle diameter of the thermally expandable fine particles was 160 nm.

(Synthesis example 1 of swellable fine particles (with thermal expansion))
In a 0.5 liter three-necked flask equipped with a stirrer, thermometer, condenser, and liquid feed pump, 240 g of water, 60 mg of sodium dodecylbenzenesulfonate as a surfactant (0.172 mmol, total monomer mass of swellable fine particles) 0.001 part by mass) and 150 mg of zinc stearate as a foaming aid was added to prepare a first mixed solution.

  Next, the pressure in the three-necked flask was reduced to 2600 Pa with a diaphragm pump, and the operation of returning to normal pressure with nitrogen was repeated three times to remove dissolved oxygen from the first mixed solution. The flask was kept in a nitrogen atmosphere, and the first mixture was stirred and heated in an oil bath so that the temperature in the flask was 65 ° C. Thereafter, 0.05 g of ammonium persulfate (0.220 mmol, 0.05 mol% (external number) with respect to the total number of moles of the monomer of the swellable fine particles) was added to the first mixed solution.

  Immediately after adding ammonium persulfate to the first mixture, 15 g of N-monoacrylazodicarbonamide (Synthesis Example 1) (88.2 mmol, 25.0 parts by mass relative to the total monomer mass of the swellable fine particles), acrylic acid Butyl (manufactured by Wako Pure Chemical Industries, Ltd.) 40 g (312.1 mmol, 66.7 parts by mass based on the total monomer mass of the swellable fine particles), triethylene glycol diacrylate (Kyoeisha Chemical Co., Ltd. 3EG-A) 3 g (12.0 mmol) , 5.0 parts by mass with respect to the total mass of monomers of the swellable fine particles), and 2 g of acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) (27.8 mmol, 3.3 parts by mass with respect to the total mass of monomers of the swellable fine particles) The mixture (second mixture) was added dropwise to the first mixture over a period of 1 hour with a feed pump.

  After completion of the dropwise addition, the mixed liquid of the first and second mixed liquids (third mixed liquid) was stirred for 4 hours, and then the reaction temperature was raised to 80 ° C. and stirring was continued for another 1 hour. Thereby, each monomer was emulsion-polymerized. That is, swellable fine particles were produced. The dispersion of the swellable fine particles was cooled to room temperature and then filtered through a 100 mesh filter to remove aggregates. Thereby, the swellable fine particle dispersion was purified. About 1 ml of the swellable fine particle dispersion was weighed into an aluminum pan, dried on a hot plate heated to 160 ° C. for 15 minutes, and the non-volatile content was calculated from the weight of the residue. The result was 19.5% by mass (yield 98%). It was. Further, the average particle diameter of the swellable fine particles was 90 nm.

(Synthesis example 2 of swellable fine particles (with thermal expansion))
All except that 15 g of N-monomethacrylazodicarbonamide (Synthesis Example 2) (81.5 mmol, 25.0 parts by mass relative to the total mass of the monomer of the swellable fine particles) was used instead of N-monoacrylazodicarbonamide By performing the same treatment as in the synthesis example 1 of the swellable fine particles, the swellable fine particles according to the synthesis example 2 of the swellable fine particles were obtained. The nonvolatile content was 19.5% by mass (yield 98%). Further, the average particle diameter of the swellable fine particles was 95 nm.

(Synthesis example 3 of swelling fine particles (no thermal expansion))
Synthesis Example 1 of swellable fine particles, except that 15 g of 2-hydroxyethyl acrylate (129.2 mmol, 25.0 parts by mass with respect to the total monomer mass of the swellable fine particles) was used instead of N-monoacrylazodicarbonamide By performing the same treatment, swellable fine particles according to Synthesis Example 3 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). Moreover, the average particle diameter of the swellable fine particles was 100 nm.

(Synthesis example 4 of swelling fine particles (no thermal expansion))
The same treatment as in Synthesis Example 1 of the swellable fine particles was performed except that 15 g of styrene (144.0 mmol, 25.0 parts by mass relative to the total monomer mass of the swellable fine particles) was used instead of N-monoacrylazodicarbonamide. As a result, swellable fine particles according to Synthesis Example 4 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). The average particle size of the swellable fine particles was 105 nm.

(Synthesis example 5 of swelling fine particles (no thermal expansion))
The same treatment as in Synthesis Example 1 of the swellable fine particles was performed except that 15 g of acrylonitrile (283.0 mmol, 25.0 parts by mass with respect to the total monomer mass of the swellable fine particles) was used instead of N-monoacrylazodicarbonamide. As a result, swellable fine particles according to Synthesis Example 5 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). Further, the average particle diameter of the swellable fine particles was 95 nm.

(Synthesis Example 6 of swelling fine particles (no thermal expansion))
The same as Synthesis Example 1 of the swellable fine particles, except that 15 g of N-isopropylacrylamide (133.0 mmol, 25.0 parts by mass with respect to the total monomer mass of the swellable fine particles) was used instead of N-monoacrylazodicarbonamide. As a result of the treatment, swellable fine particles according to Synthesis Example 6 were obtained. The nonvolatile content was 19.5% by mass (yield 98%). Moreover, the average particle diameter of the swellable fine particles was 100 nm.

(Evaluation of foamability)
100 parts by mass of the aqueous dispersion obtained in Synthesis Examples 1 to 12 of the thermally expandable fine particles and Synthetic Examples 1 and 2 of the swellable fine particles (with thermal expansion) and a 1% by mass aqueous solution of carboxymethyl cellulose (based on the total mass of the aqueous solution) 25 parts by mass of each containing 1% by mass of carboxymethylcellulose) was stirred for 3 minutes with a planetary stirrer (Thinky Awatake Vitaro, rotation speed 800 rpm, revolution speed 2000 rpm) to prepare an experimental mixture. .

  Next, the experimental mixed solution was applied on a glass substrate with a bar coater with a gap adjusted so that the film thickness after drying was 3 μm, and dried with an air blow dryer at 80 ° C. Thereby, the coating film for experiment was produced. Subsequently, this coating film was heated to 160 ° C. on a hot plate, and the film thickness after foaming was measured. The results are summarized in Table 1.

  From Table 1, it was found that any fine particles can realize a sufficient film thickness as a separator by expansion.

(Preparation of fine particle mixture)
A fine particle mixture was prepared by mixing the thermally expandable fine particle dispersion and the swellable fine particle dispersion in the combinations shown in Table 2. The mixing ratio (volume ratio) of each dispersion was 1: 1.

(Preparation Example 1 of Negative Electrode Mixture Slurry)
Next, a preparation example of the negative electrode mixture slurry will be described. Mix 95% by weight of artificial graphite, 2% by weight of acetylene black, 2% by weight of styrene butadiene copolymer (SBR), and 1% by weight of carboxymethylcellulose (CMC), and add water to adjust the viscosity. A negative electrode mixture slurry was prepared. In addition, the non volatile matter in a negative mix slurry (slurry) was 48 mass% with respect to the total mass of a slurry.

(Negative electrode production example 1)
Next, an example of manufacturing a negative electrode will be described. The gap of the bar coater was adjusted so that the coating amount (area density) after drying was 9.55 mg / cm ² . Next, the negative electrode mixture slurry prepared in Preparation Example 1 was uniformly applied to a copper foil (current collector, 10 μm) using this bar coater. Next, the negative electrode mixture slurry was dried for 15 minutes by a blow type dryer set at 80 ° C. Subsequently, the negative electrode mixture after drying was pressed by a roll press machine so that the mixture density was 1.65 g / cm ³ . Subsequently, the negative electrode mixture was vacuum-dried at 150 ° C. for 6 hours to produce a sheet-shaped negative electrode including a negative electrode current collector and a negative electrode active material layer. This negative electrode corresponds to the first embodiment.

(Negative electrode preparation example 2 (preparation example of negative electrode with separator))
To the sheet-like negative electrode prepared in negative electrode preparation example 1, 100 parts by weight of the fine particle mixture prepared in preparation example 1 and 25 parts by weight of a 1% by weight aqueous solution of carboxymethylcellulose were mixed, and the thickness of the coating layer after drying was 3 μm. After coating with a bar coater adjusted so as to be, it was dried with an air blow dryer at 80 ° C. for 15 minutes. Next, the dried coating film was further vacuum-dried at 80 ° C. for 1 hour and 160 ° C. for 1 hour to form a separator on the negative electrode. That is, a negative electrode with a separator was produced.

(Negative electrode preparation examples 3 to 14 (preparation example of negative electrode with separator))
A separator-attached negative electrode according to negative electrode preparation examples 3 to 14 was manufactured by performing the same treatment as negative electrode preparation example 2 except that the fine particle mixture prepared in Preparation Examples 2 to 13 was used.

(Example of positive electrode mixture slurry preparation)
Next, a preparation example of the positive electrode mixture slurry will be described. Solid solution oxide Li _1.20 Mn _0.55 Co _0.10 Ni _0.15 O ₂ 96% by mass, Ketjenblack 2% by mass, polyvinylidene fluoride (PVDF) 2% by mass with N-methyl-2 -A positive electrode mixture slurry was formed by dispersing in pyrrolidone. The non-volatile content in the positive electrode mixture slurry was 50% by mass.

(Positive electrode production example 1)
Next, a positive electrode manufacturing example will be described. The gap of the bar coater was adjusted so that the coating amount (area density) after drying was 22.7 mg / cm ² . Next, a positive electrode active material layer was prepared by coating the positive electrode mixture slurry on the aluminum current collector foil, which is a current collector, and drying it with this bar coater. The positive electrode mixture after drying was pressed with a roll press so that the mixture density was 3.9 g / cm ³ . Subsequently, the positive electrode mixture was vacuum-dried at 80 ° C. for 6 hours to produce a sheet-like positive electrode including a positive electrode current collector and a positive electrode active material layer. This positive electrode corresponds to the first embodiment.

(Positive electrode preparation example 2 (preparation example of positive electrode with separator))
To the sheet-like positive electrode prepared in Positive Electrode Preparation Example 1, 100 parts by mass of the fine particle mixture prepared in Preparation Example 1 and a mixed liquid of 25 parts by mass of a 1% by mass aqueous solution of carboxymethyl cellulose had a coating layer thickness of 3 μm after drying. After coating with a bar coater adjusted so as to be, it was dried with an air blow dryer at 80 ° C. for 15 minutes. Next, the dried coating film was further vacuum-dried at 80 ° C. for 1 hour and 160 ° C. for 1 hour to form a separator on the positive electrode. That is, a positive electrode with a separator was produced.

(Positive electrode production examples 3 to 14)
A positive electrode with a separator according to positive electrode preparation examples 3 to 14 was manufactured by performing the same process as positive electrode preparation example 2 except that the fine particle mixture prepared in Preparation Examples 2 to 13 was used.

(Cell production example 1)
The positive electrode produced in the positive electrode production example 1 was cut into a circle having a diameter of 1.3 cm, and the negative electrode with a separator produced in the negative electrode production example 2 was cut into a circle having a diameter of 1.55 cm.

Then, in a stainless steel coin outer container having a diameter of 2.0 cm, a positive electrode having a diameter of 1.3 cm, a negative electrode having a diameter of 1.55 cm, and a spacer having a diameter of 1.5 cm as a spacer. A 200 μm thick copper plate cut in a circle was superposed in this order. Then, the electrolyte (1.5 M LiPF ₆ ethylene carbonate (EC) / diethyl carbonate (DEC) / fluoroethylene carbonate (FEC) = 10/70/20 mixed solution (volume ratio)) is dropped in the container to the extent that it does not overflow. It was. Next, a stainless steel cap was put on the container via polypropylene packing, and the container was sealed with a caulking device for producing a coin battery. This produced the lithium ion secondary battery.

(Cell production examples 2 to 30)
A lithium ion secondary battery according to Cell Preparation Examples 2 to 38 was manufactured by performing the same treatment as in Cell Preparation Example 1 except that the positive electrode, negative electrode, and separator shown in Table 3 were used.

(Evaluation of cycle life)
The lithium ion secondary battery produced in each of the production examples was charged at a constant current-constant voltage of 0.1 C to 4.2 V and 0.04 mA at 25 ° C., and then discharged to 2.5 V at a constant current of 0.1 C. One cycle was performed under the following conditions. Next, after charging to 4.2 V and 0.04 mA at a current-constant voltage of 1.0 C, 100 cycles were performed under the condition of discharging to 2.5 V at a constant current of 1.0 C. Next, the discharge capacity retention rate (percentage) was calculated by dividing the discharge capacity after 100 cycles by the discharge capacity after 1 cycle. The larger the capacity retention rate, the better the cycle life. The measurement of the discharge capacity was performed by TOSCAT3000 Toyo System Corporation. The evaluation results are summarized in Table 3.

  Since the negative electrode preparation examples 2 to 14 and the positive electrode preparation examples 2 to 14 are prepared using the fine particle mixture according to this embodiment, they correspond to the examples of this embodiment. Moreover, since the lithium ion secondary battery which concerns on cell preparation examples 1-29 uses the fine particle mixture for any 1 or more types of components among a positive electrode and a negative electrode, it corresponds to the Example of this embodiment. . Since Cell Preparation Example 30 does not use the fine particle mixture of this embodiment, it corresponds to a comparative example.

  According to Table 3, it was found that the lithium ion secondary battery according to this example realized a cycle life comparable to that of a lithium ion secondary battery using a polyolefin-based porous membrane.

  As described above, the fine particle mixture according to the present embodiment functions as a separator of a lithium ion secondary battery by foaming at least the thermally expandable fine particles. Since this separator is obtained by foaming a fine particle mixture, the separator can be made thinner than the polyolefin-based porous film, and the insulation is improved as compared with the polyolefin-based separator. Furthermore, this separator can be produced at a lower cost than a polyolefin-based porous membrane. Furthermore, a lithium ion secondary battery using this separator can realize a cycle life comparable to that of a lithium ion secondary battery using a polyolefin-based porous membrane. That is, by using the fine particle mixture according to the present embodiment, a lithium ion secondary battery having a good cycle life can be produced without using a conventional separator.

  Here, the thermally expandable fine particles may be a copolymer of a foaming monomer and a stabilizing monomer having a higher stability in the lithium ion secondary battery than the foamable monomer. The fine particles are stably present in the lithium ion secondary battery. That is, the insulating property of the separator produced by foaming the fine particle mixture is improved.

  Further, the foamable monomer may contain a diazo compound, and in this case, the thermally expandable fine particles can be easily foamed.

  Further, the diazo compound may have a structure represented by the chemical formula I or II, and in this case, the thermally expandable fine particles can be easily foamed.

  Further, the foaming temperature of the foamable monomer may be 120 ° C. or more and 250 ° C. or less. In this case, the thermally expandable fine particles can be easily foamed.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, in the above embodiment, the present invention is applied to a lithium ion secondary battery, but it is needless to say that the present invention may be applied to other nonaqueous electrolyte secondary batteries.

10, 10a, 10b Lithium ion secondary battery 20 Positive electrode 21 Current collector 22 Positive electrode active material layer 30 Negative electrode 31 Current collector 32 Negative electrode active material layer 40 Separator layer

Claims (8)

Swellable fine particles that swell in the electrolyte of the non-aqueous electrolyte secondary battery;
A thermally expandable fine particle having a swelling property to the electrolyte solution lower than that of the swellable fine particle and having a heat expandability,
A fine particle mixture for a non-aqueous electrolyte secondary battery, wherein the average particle size is 0.05 μm to 0.5 μm.   The heat-expandable fine particle is a copolymer of a foaming monomer and a stabilizing monomer having higher stability in a non-aqueous electrolyte secondary battery than the foamable monomer. The fine particle mixture for a non-aqueous electrolyte secondary battery as described. The fine particle mixture for a nonaqueous electrolyte secondary battery according to claim 2, wherein the foamable monomer contains a diazo compound. The fine particle mixture for a nonaqueous electrolyte secondary battery according to claim 3, wherein the diazo compound has a structure represented by the following chemical formula I:

In Chemical Formula I, R1 is a hydrogen atom or a methyl group, R2 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R3 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R4 is hydrogen, a methyl group, an acryl group, or a methacryl group. Or a glycidyl group, X represents a direct bond or an alkylene group having 1 to 6 carbon atoms. 5. The fine particle mixture for a nonaqueous electrolyte secondary battery according to claim 3, wherein the diazo compound has a structure represented by the following chemical formula II.

In Formula II, R1 is a hydrogen atom or methyl group, R2 is hydrogen or an alkyl group having 1 to 6 carbon atoms, A is a methylene group or carbonyl group, Q is a methylene group or methine group, T is a direct bond, a double bond, methylene group, an oxygen or display the NH group,, X is to display the direct or alkylene group having 1 to 6 carbon atoms.   The fine particle mixture for a non-aqueous electrolyte secondary battery according to any one of claims 2 to 5, wherein a foaming temperature of the foamable monomer is 120 ° C or higher and 250 ° C or lower. An electrode active material layer;
Wherein provided on the electrode active material layer, have a, a separator for a non-aqueous electrolyte secondary battery particulate mixture was foamed according to any one of claims 1 to 6,
The electrode for a non-aqueous electrolyte secondary battery , wherein the separator includes the thermally expandable fine particles dispersed and foamed in the separator and the swellable fine particles dispersed in the separator . A nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery according to claim 7.

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