JP7130525B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries, especially lithium-ion secondary batteries, have high energy density and are widely used as batteries for personal computers, mobile phones, personal digital assistants, etc. Recently, they have been widely used in consumer products such as power tools and vacuum cleaners. It is being developed as a battery for automobiles and a battery for automobiles.

As non-aqueous electrolyte secondary batteries, for example, non-aqueous electrolyte secondary batteries as described in Patent Documents 1 and 2 are known.

Japanese Patent No. 5569515 JP 2009-146822 A

However, the conventional technology as described above has room for improvement from the viewpoint of charge capacity after high-rate discharge.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to realize a non-aqueous electrolyte secondary battery having excellent charge capacity after high-rate discharge.

A non-aqueous electrolyte secondary battery according to aspect 1 of the present invention includes a porous layer containing an inorganic filler and a resin, a positive electrode, a negative electrode, and a non-aqueous electrolyte. The expansion coefficient is 11 ppm/° C. or less, and the porous layer has a frequency of 2455 MHz after being impregnated with a solution containing propylene carbonate, a polyoxyalkylene type nonionic surfactant and water in a weight ratio of 85:12:3. The temperature rise rate of the porous layer surface from the start of irradiation to 15 seconds after irradiation measured while irradiating with microwaves of 1800 W is 0.93 ° C./sec or more and 1.25 ° C./sec or less, The non-aqueous electrolytic solution contains 0.5 ppm or more and 300 ppm or less of an additive whose ionic conductivity decrease rate L represented by the following formula (A) is 1.0% or more and 6.0% or less.
L=(LA−LB)/LA (A)
(In formula (A), LA is a mixed solvent containing ethylene carbonate, ethylmethyl carbonate and diethyl carbonate at a volume ratio of 3:5:2, and LiPF ₆ was dissolved so that its concentration was 1 mol/L. Represents the ionic conductivity (mS/cm) of the reference electrolyte solution, and LB represents the ionic conductivity (mS/cm) of the electrolyte solution obtained by dissolving 1.0% by weight of an additive in the reference electrolyte solution. .)
Further, in the non-aqueous electrolyte secondary battery according to aspect 2 of the present invention, in aspect 1, the porous layer is laminated on one side or both sides of the polyolefin porous film.

Further, in the non-aqueous electrolyte secondary battery according to aspect 3 of the present invention, in aspect 1 or 2, the porous layer is polyolefin, (meth)acrylate resin, fluorine-containing resin, polyamide resin, polyester It contains one or more resins selected from the group consisting of resins and water-soluble polymers.

Further, in the non-aqueous electrolyte secondary battery according to aspect 4 of the present invention, in aspect 3, the polyamide-based resin is an aramid resin.

Further, the non-aqueous electrolyte secondary battery according to aspect 5 of the present invention is the non-aqueous electrolyte secondary battery according to any one of aspects 1 to 4, wherein the non-aqueous electrolyte contains an electrolyte containing lithium.

Further, in the non-aqueous electrolyte secondary battery according to aspect 6 of the present invention, in any one of aspects 1 to 5, the non-aqueous electrolyte contains an aprotic polar solvent.

According to one aspect of the present invention, a non-aqueous electrolyte secondary battery having excellent charge capacity after high-rate discharge can be realized.

It is a figure which shows an example of the temperature change of the porous layer surface.

An embodiment of the invention will be described below, but the invention is not limited thereto. The present invention is not limited to the configurations described below, and can be modified in various ways within the scope of the claims, by appropriately combining technical means disclosed in different embodiments. The resulting embodiment is also included in the technical scope of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less".

A non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a porous layer containing an inorganic filler and a resin, a positive electrode, a negative electrode, and a non-aqueous electrolyte. The porous layer has a coefficient of thermal expansion of 11 ppm/° C. or less, and the porous layer is impregnated with a solution containing propylene carbonate, a polyoxyalkylene-type nonionic surfactant, and water in a weight ratio of 85:12:3, and then subjected to frequency The rate of temperature rise of the surface of the porous layer from the start of irradiation to 15 seconds after irradiation, which is measured while irradiating microwaves of 2455 MHz at an output of 1800 W, is 0.93° C./second or more and 1.25° C./second or less. , the nonaqueous electrolytic solution contains 0.5 ppm or more and 300 ppm or less of an additive having an ionic conductivity decrease rate L represented by the following formula (A) of 1.0% or more and 6.0% or less.
L=(LA−LB)/LA (A)
In formula (A), LA is a mixed solvent containing ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate at a volume ratio of 3:5:2, and LiPF ₆ is dissolved to a concentration of 1 mol/L. LB represents the ionic conductivity (mS/cm) of the electrolytic solution for reference, and LB represents the ionic conductivity (mS/cm) of the electrolytic solution obtained by dissolving 1.0% by weight of the additive in the reference electrolytic solution.

Adjust the thermal expansion coefficient of the inorganic filler contained in the porous layer and the temperature rise rate of the surface of the porous layer to an appropriate range, and specify the ionic conductivity decrease rate and content of the additive contained in the non-aqueous electrolyte. By adjusting the range of , the flow of ions in the non-aqueous electrolyte secondary battery comprising these is adjusted to a suitable one, and as a result, the charge capacity of the non-aqueous electrolyte secondary battery after high-rate discharge is maintained high. can do.

[Porous layer]
In one embodiment of the present invention, the porous layer can be arranged between the polyolefin porous film and at least one of the positive electrode and the negative electrode as a member constituting the non-aqueous electrolyte secondary battery. The porous layer may be formed on one side or both sides of the polyolefin porous film. Alternatively, the porous layer may be formed on the active material layer of at least one of the positive electrode and the negative electrode. Alternatively, the porous layer may be arranged between and in contact with the polyolefin porous film and at least one of the positive electrode and the negative electrode. The porous layer arranged between the polyolefin porous film and at least one of the positive electrode and the negative electrode may be one layer or two layers or more. The porous layer is preferably an insulating porous layer containing a resin.

When a porous layer is laminated on one side of the polyolefin porous film described later, which is a separator for a non-aqueous electrolyte secondary battery, the porous layer is preferably the surface of the polyolefin porous film facing the positive electrode. is laminated to More preferably, the porous layer is laminated on the surface in contact with the positive electrode.

It is believed that the charge capacity after high-rate discharge is affected by the denseness of the porous layer. The lower the density of the porous layer, the easier it is for lithium ions to permeate, so the charge capacity after high-rate discharge is improved. On the other hand, the higher the density of the porous layer, the more difficult it is for lithium ions to permeate.

The pore structure of the porous layer is one of the factors that affect the denseness of the porous layer. The pore structure of the porous layer may include the area of the inner walls of the pores, the tortuosity of the pores, and the like. It is thought that the smaller the area of the inner wall of the voids and the degree of tortuosity of the voids, the lower the density of the porous layer, and conversely, the greater the area of the inner walls of the voids and the degree of tortuosity of the voids, the higher the density of the porous layer. be done.

The present inventors focused on the rate of temperature rise on the surface of the porous layer as a parameter reflecting the denseness of the porous layer. The lower the denseness of the porous layer, the smaller the rate of temperature rise on the surface of the porous layer. On the other hand, the higher the denseness of the porous layer, the faster the rate of temperature rise on the surface of the porous layer.

The porous layer in one embodiment of the present invention is impregnated with a solution containing propylene carbonate, a polyoxyalkylene type nonionic surfactant and water in a weight ratio of 85:12:3, and then subjected to microwaves with a frequency of 2455 MHz. The rate of temperature rise of the surface of the porous layer is 0.93° C./second or more and 1.25° C./second or less from the start of irradiation to 15 seconds after irradiation, which is measured while irradiating at an output of 1800 W. The temperature rise rate of the surface of the porous layer is preferably 0.95° C./second or more, more preferably 0.97° C./second or more. Moreover, the temperature rise rate of the surface of the porous layer is preferably 1.23° C./second or less, more preferably 1.20° C./second or less.

FIG. 1 is a diagram showing an example of temperature changes on the surface of a porous layer. The rate of temperature rise from the start of irradiation until 15 seconds later corresponds to the slope at which the contribution rate (R ² ) maximizes when the curve in the area surrounded by the solid line in FIG. 1 is linearly approximated.

If the rate of temperature rise of the surface of the porous layer is 1.25° C./sec or less, the denseness of the porous layer is not too high. That is, the flow path for lithium ions is not too long and narrow, and the flow path is not too branched. Therefore, since lithium ions easily permeate the porous layer, the charge capacity after high-rate discharge of the non-aqueous electrolyte secondary battery can be improved. Further, when the temperature rise rate is 0.93° C./second or more, the porous layer has a certain degree of denseness, so strength and safety are ensured.

As used herein, a polyoxyalkylene-type nonionic surfactant means a polymer having an oxyalkylene group and acting as a nonionic surfactant. The polyoxyalkylene-type nonionic surfactant is not particularly limited as long as it can promote the permeation of the solution into the porous layer. The heat generated by the polyoxyalkylene-type nonionic surfactant is insignificant compared to that of water, and therefore, it is believed that the difference in the structure of the polyoxyalkylene-type nonionic surfactant does not have a large effect on the calorific value. It's for. Examples of polyoxyalkylene-type nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene tridecyl ethers, polyoxyalkylene polycyclic phenyl ethers, polyoxyalkylene aryl ethers, and formula (1) below. can be used.

(Where m = 5-10, n = 10-25, and the arrangement of each repeating unit may be block, random or alternating.)
The compound represented by the formula (1) can also be called an ethylene oxide/propylene oxide copolymer. A specific example of the polyoxyalkylene-type nonionic surfactant composed of the compound is commercially available SN Wet 980 (manufactured by San Nopco Co., Ltd.). SN Wet 980 is composed of a compound represented by the formula (1) having an average value of 7 for m and an average value of 19 for n.

Further, the porous layer contains an inorganic filler having a thermal expansion coefficient of 11 ppm/°C or less at -40°C to 200°C. In this specification, the inorganic filler means a filler composed of an inorganic substance. The thermal expansion coefficient of the inorganic filler can affect the uniformity of the component and void distribution in the porous layer, as well as the uniformity of void deformation during battery operation. This is probably because the coefficient of thermal expansion of the inorganic filler can affect whether or not the distribution of constituent components and voids can be easily homogenized during formation of the porous layer. The more uniformly the pores and components are distributed within the porous layer, or the higher the uniformity of pore deformation during battery operation, the easier it is for lithium ions to permeate the porous layer. Therefore, the charge capacity of non-aqueous electrolyte secondary batteries after high-rate discharge tends to improve.

If the thermal expansion coefficient of the inorganic filler at −40° C. to 200° C. is 11 ppm/° C. or less, a porous layer in which voids and constituent components are uniformly distributed can be obtained. Moreover, the deformation of the voids of the porous layer is small during operation of the battery. Therefore, since lithium ions easily permeate the porous layer, the charge capacity after high-rate discharge of the non-aqueous electrolyte secondary battery can be improved.

The coefficient of thermal expansion is preferably greater than 0 ppm/°C, more preferably 1 ppm/°C or more. When the porous layer deforms due to the heat generated during operation of the non-aqueous electrolyte secondary battery, stress concentrates on the contact portion between the inorganic filler and the binder resin that make up the porous layer, causing the inside of the porous layer to The pore structure may change irreversibly, resulting in adverse effects on battery characteristics. If the coefficient of thermal expansion is within the above range, such adverse effects can be avoided.

The lower limit of the content of the inorganic filler in the porous layer is preferably 50% by weight or more, and 70% by weight or more, based on the total weight of the inorganic filler and the resin constituting the porous layer. is more preferable, and 90% by weight or more is even more preferable. On the other hand, the upper limit of the content of the inorganic filler in the porous layer is preferably 99% by weight or less, more preferably 98% by weight or less. From the viewpoint of heat resistance, the content of the inorganic filler is preferably 50% by weight or more. Moreover, the content of the inorganic filler is preferably 99% by weight or less from the viewpoint of adhesion between the inorganic fillers. In addition, by containing the inorganic filler, the slipperiness and heat resistance of the separator having the porous layer can be improved.

The inorganic filler is preferably a filler that is stable in a non-aqueous electrolyte and electrochemically stable. From the viewpoint of ensuring battery safety, the inorganic filler is preferably a filler having a heat resistance temperature of 150° C. or higher.

The inorganic filler is preferably an inorganic filler containing an oxygen element. In this specification, the inorganic filler containing oxygen element means a filler composed of an inorganic material containing oxygen element. Examples of inorganic materials containing oxygen include barium zirconate titanate, calcium titanate, aluminum titanate, and borosilicate glass, but are not limited to these.

Furthermore, the atomic composition percentage of oxygen in the inorganic filler containing oxygen element is preferably 60 at % or more. If the atomic composition percentage of oxygen is 60 at % or more, the inorganic fillers repel each other and are easily dispersed. Therefore, the inorganic fillers are unlikely to interact with each other, and the constituent components can be dispersed more uniformly. Therefore, by controlling the atomic composition percentage of oxygen contained in the inorganic filler, it is also possible to adjust the rate of temperature rise on the surface of the porous layer.

The shape of the inorganic filler may vary depending on the method for producing the inorganic filler and/or the conditions for dispersing the inorganic filler when preparing the coating liquid for forming the porous layer. The inorganic filler may have any shape, such as a gourd shape obtained by thermal fusion between spherical, oval, rectangular, or spherical particles, or an irregular shape without a specific shape. . From the viewpoint of ion permeability and liquid retention of the porous layer, the shape of the inorganic filler is more preferably gourd-shaped or amorphous.

The resin contained in the porous layer is preferably insoluble in the electrolyte of the battery and electrochemically stable within the range of use of the battery. Examples of the resin include polyolefins; (meth)acrylate resins; fluorine-containing resins; polyamide resins; polyimide resins; polyester resins; ; Polycarbonate, polyacetal, polyether ether ketone and the like.

Among the above resins, polyolefins, polyester resins, (meth)acrylate resins, fluorine-containing resins, polyamide resins and water-soluble polymers are preferred.

Preferred polyolefins include polyethylene, polypropylene, polybutene, and ethylene-propylene copolymers.

As polyamide-based resins, aramid resins such as aromatic polyamides and wholly aromatic polyamides are preferred.

Specific examples of aramid resins include poly(paraphenylene terephthalamide), poly(metaphenylene isophthalamide), poly(parabenzamide), poly(methabenzamide), poly(4,4'-benzanilide terephthalate amide), poly(paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly(metaphenylene-4,4′-biphenylenedicarboxylic acid amide), poly(paraphenylene-2,6-naphthalenedicarboxylic acid amide), Poly(metaphenylene-2,6-naphthalenedicarboxylic acid amide), poly(2-chloroparaphenylene terephthalamide), paraphenylene terephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer, metaphenylene terephthalamide/2 , 6-dichloroparaphenylene terephthalamide copolymer. Among these, poly(paraphenylene terephthalamide) is more preferable.

Aromatic polyesters such as polyarylates and liquid crystalline polyesters are preferable as the polyester-based resin.

Rubbers include styrene-butadiene copolymer and its hydride, methacrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl acetate, etc. can be mentioned.

Examples of resins having a melting point or glass transition temperature of 180° C. or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, and polyetheramide.

Examples of water-soluble polymers include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, and polymethacrylic acid.

Examples of fluorine-containing resins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. coalescence, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichlorethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride-hexafluoro Examples include propylene-tetrafluoroethylene copolymers and ethylene-tetrafluoroethylene copolymers. Among them, when the porous layer is arranged facing the positive electrode, it is easy to maintain various performances such as rate characteristics and resistance characteristics of the non-aqueous electrolyte secondary battery due to oxidation deterioration during battery operation. A fluororesin is preferred.

The porous layer in the present embodiment is preferably arranged between the nonaqueous electrolyte secondary battery separator and the positive electrode active material layer of the positive electrode. In the following description of the physical properties of the porous layer, a porous layer disposed between a separator for a non-aqueous electrolyte secondary battery and a positive electrode active material layer included in a positive electrode when used as a non-aqueous electrolyte secondary battery at least refers to the physical properties of

The average film thickness of the porous layer is preferably in the range of 0.5 μm to 10 μm per one porous layer, and in the range of 1 μm to 5 μm, from the viewpoint of ensuring adhesion with the electrode and high energy density. is more preferable.

When the film thickness of the porous layer is 0.5 μm or more per layer, it is possible to sufficiently suppress internal short circuits due to breakage of the non-aqueous electrolyte secondary battery, etc., and the amount of electrolyte retained in the porous layer. is sufficient.

On the other hand, if the film thickness of the porous layer exceeds 10 μm per layer, the permeation resistance of lithium ions increases in the non-aqueous electrolyte secondary battery, and the positive electrode may deteriorate after repeated cycles. Therefore, in the non-aqueous electrolyte secondary battery, the rate characteristics and cycle characteristics may deteriorate. In addition, since the distance between the positive electrode and the negative electrode increases, the internal volumetric efficiency of the non-aqueous electrolyte secondary battery may decrease.

The basis weight per unit area of the porous layer can be appropriately determined in consideration of the strength, film thickness, weight and handleability of the porous layer. The basis weight per unit area of the porous layer is preferably 0.5 to 20 g/m ² and more preferably 0.5 to 10 g/m ² per one porous layer.

By setting the basis weight per unit area of the porous layer within these numerical ranges, the weight energy density and volume energy density of the non-aqueous electrolyte secondary battery can be increased. If the basis weight of the porous layer exceeds the above range, the non-aqueous electrolyte secondary battery tends to be heavy.

The porosity of the porous layer is preferably 20 to 90% by volume, more preferably 30 to 80% by volume, so as to obtain sufficient ion permeability. Moreover, the pore size of the pores of the porous layer is preferably 1.0 μm or less, more preferably 0.5 μm or less. By setting the pore diameters of the pores to these sizes, the non-aqueous electrolyte secondary battery can obtain sufficient ion permeability.

[Method for producing porous layer]
A porous layer can be formed using a coating liquid obtained by dissolving or dispersing a resin in a solvent and dispersing an inorganic filler. The solvent can be said to be a solvent for dissolving the resin and also a dispersion medium for dispersing the resin or the inorganic filler. Methods for forming the coating liquid include, for example, a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, a media dispersion method, and the like.

Methods for forming a porous layer include, for example, a method of directly applying a coating liquid to the surface of a substrate and then removing the solvent; A method in which a porous layer is formed, this porous layer and a substrate are pressed together, and then the support is peeled off; a method of removing the solvent after peeling; and a method of removing the solvent after performing dip coating by immersing the substrate in the coating solution.

The solvent is preferably a solvent that does not adversely affect the substrate, uniformly and stably dissolves the resin, and uniformly and stably disperses the inorganic filler. Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, acetone and water.

The coating liquid may appropriately contain a dispersant, a plasticizer, a surfactant, a pH adjuster, and the like as components other than the resin and the inorganic filler.

In addition to the polyolefin porous film described later, other films, positive electrodes and negative electrodes can be used as the base material.

As a method for applying the coating liquid to the base material, conventionally known methods can be employed, and specific examples include the gravure coater method, the dip coater method, the bar coater method and the die coater method. .

Drying is generally used to remove the solvent. Alternatively, drying may be performed after replacing the solvent contained in the coating liquid with another solvent.

The shear viscosity of the coating liquid is preferably 1 Pa·s or less, more preferably 0.5 Pa·s or less. When the shear viscosity is high, the constituent components tend to interact with each other, and the resulting porous layer tends to be highly dense. When the shear viscosity of the coating liquid is 1 Pa·s or less, the denseness of the porous layer does not become too high, and the constituent components can be dispersed more uniformly. Therefore, by controlling the shear viscosity of this coating liquid, the rate of temperature rise on the surface of the porous layer can be controlled. In addition, this makes it possible to control the permeation of lithium ions.

In this specification, the shear viscosity is continuously sheared at interval 1 at a shear rate of 0.1 to 1000 [1/sec] and at interval 2 at a shear rate of 1000 to 0.1 [1/sec]. It refers to the shear viscosity at a shear rate of 0.4 [1/sec] in interval 2 when the viscosity is measured.

[Non-aqueous electrolyte]
The non-aqueous electrolyte in one embodiment of the present invention contains an additive whose ionic conductivity decrease rate L represented by the following formula (A) is 1.0% or more and 6.0% or less. contains.
L=(LA−LB)/LA (A)
In formula (A), LA is a mixed solvent containing ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate at a volume ratio of 3:5:2, and LiPF ₆ is dissolved to a concentration of 1 mol/L. represents the ionic conductivity (mS/cm) of the electrolytic solution for LB represents the ionic conductivity (mS/cm) of an electrolytic solution obtained by dissolving 1.0% by weight of an additive in the reference electrolytic solution.

The additive is not particularly limited as long as it is a compound that satisfies that the ionic conductivity decrease rate L represented by formula (A) is 1.0% or more and 6.0% or less. Such compounds include, for example, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethyl phosphate, vinylene carbonate, propanesultone, 2,6-di -tert-butyl-4-methylphenol, 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenzo[d , f][1,3,2]dioxaphosphepine, tris(2,4-di-tert-butylphenyl) phosphate, 2-[1-(2-hydroxy-3,5-di-tert- pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, dibutylhydroxytoluene, and the like.

The non-aqueous electrolyte contains an electrolyte and an organic solvent. Examples of the electrolyte include an electrolyte containing lithium. Examples of lithium-containing electrolytes include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , Metal salts such as Li ₂ B ₁₀ Cl ₁₀ , lower aliphatic carboxylic acid lithium salts and lithium salts such as LiAlCl ₄ can be mentioned. Only one type of the electrolyte may be used, or two or more types may be used in combination.

Organic solvents constituting the non-aqueous electrolyte include, for example, carbonates, ethers, esters, nitriles, amides, carbamates, sulfur-containing compounds, and fluorine groups introduced into these organic solvents. Aprotic polar solvents such as fluorine-containing organic solvents are included. Only one type of the organic solvent may be used, or two or more types may be used in combination.

Like the reference electrolyte, the organic solvent is preferably a mixed solvent containing a cyclic compound such as ethylene carbonate and a chain compound such as ethylmethyl carbonate or diethyl carbonate. The mixed solvent contains the cyclic compound and the chain compound preferably in a volume ratio of 2:8 to 4:6, more preferably in a volume ratio of 2:8 to 3:7, and particularly preferably. contains in a volume ratio of 3:7. A mixed solvent in which a cyclic compound and a chain compound are mixed at a volume ratio of 3:7 is an organic solvent that is particularly commonly used for non-aqueous electrolytes in non-aqueous electrolyte secondary batteries.

The additive in one embodiment of the present invention reduces the ionic conductivity of the reference electrolyte. The reason why the addition of the additive to the non-aqueous electrolyte can suppress the decrease in the charge capacity after high-rate discharge is, for example, as follows. By adding the additive, the degree of dissociation of ions in the non-aqueous electrolyte can be lowered. This can reduce the depletion of ions at the separator-electrode interface during charging and discharging, especially when the battery is operated at high speeds. It is considered that this can suppress the decrease in charge capacity after high-rate discharge.

From the viewpoint of reducing depletion of ions in the vicinity of the electrode, the non-aqueous electrolytic solution contains the additive at 0.5 ppm or more, preferably at 20 ppm or more, and more preferably at 45 ppm or more.

On the other hand, when the content of the additive is excessively high, the degree of dissociation of ions in the entire non-aqueous electrolyte is excessively lowered, which is thought to impede the flow of ions in the entire non-aqueous electrolyte secondary battery. be done. Therefore, the battery characteristics such as the charge capacity after high-rate discharge may rather deteriorate. From the viewpoint of suppressing inhibition of ion flow in the entire non-aqueous electrolyte secondary battery, the non-aqueous electrolyte contains the additive at 300 ppm or less, preferably at 250 ppm or less, and at 180 ppm or less. is more preferred.

Here, in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the degree of dissociation of ions near the positive electrode when charging and discharging are repeated, particularly when the battery is operated at high speed, is Strongly influenced by the amount of additive.

Therefore, in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the dissociation degree of ions in the vicinity of the positive electrode can be suitably reduced regardless of the type of non-aqueous electrolyte. That is, 0.5 ppm or more and 300 ppm or less of the additive is contained regardless of the type and amount of the electrolyte contained in the non-aqueous electrolyte, and the type of the organic solvent contained, thereby dissociating ions near the positive electrode. degree can be suitably reduced. As a result, a decrease in charge capacity after high-rate discharge can be suppressed.

The method for controlling the content of the additive in the non-aqueous electrolyte to 0.5 ppm or more and 300 ppm or less is not particularly limited. A method of dissolving the additive in advance in the non-aqueous electrolyte to be injected into the container serving as the housing of the liquid secondary battery so that the content is 0.5 ppm or more and 300 ppm or less. can.

[Positive electrode]
The positive electrode in one embodiment of the present invention is not particularly limited as long as it is generally used as a positive electrode for non-aqueous electrolyte secondary batteries. For example, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder is formed on a positive electrode current collector can be used as the positive electrode. The active material layer may further contain a conductive agent.

Examples of the positive electrode active material include materials that can be doped/dedoped with metal ions such as lithium ions or sodium ions. Specific examples of such materials include lithium composite oxides containing at least one type of transition metal such as V, Mn, Fe, Co and Ni.

Examples of the conductive agent include natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and carbonaceous materials such as sintered organic polymer compounds. Only one type of the conductive agent may be used, or two or more types may be used in combination.

Examples of the binder include fluorine-based resins such as polyvinylidene fluoride (PVDF), acrylic resins, and styrene-butadiene rubber. In addition, the binder also has a function as a thickener.

Examples of the positive electrode current collector include conductors such as Al, Ni, and stainless steel. Among them, Al is more preferable because it is easy to process into a thin film and is inexpensive.

Methods for producing the positive electrode sheet include, for example, a method of pressure-molding a positive electrode active material, a conductive agent and a binder on a positive electrode current collector; is made into a paste, the paste is applied to the positive electrode current collector, and after drying, pressure is applied to fix it to the positive electrode current collector;

[Negative electrode]
The negative electrode in one embodiment of the present invention is not particularly limited as long as it is generally used as a negative electrode for non-aqueous electrolyte secondary batteries. For example, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder is formed on a negative electrode current collector can be used as the negative electrode. The active material layer may further contain a conductive agent.

Examples of the negative electrode active material include materials capable of doping/dedoping metal ions such as lithium ions or sodium ions. Examples of such materials include carbonaceous materials. Examples of carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black and pyrolytic carbons.

Examples of the negative electrode current collector include Cu, Ni, and stainless steel. Cu is more preferable because it is difficult to form an alloy with lithium and is easy to process into a thin film.

Examples of the method for producing the negative electrode sheet include a method of pressure-molding a negative electrode active material on a negative electrode current collector; a method in which the coating is applied to the surface, dried, and then pressed to adhere to the negative electrode current collector; and the like. The paste preferably contains the conductive agent and the binder.

[Polyolefin porous film]
A non-aqueous electrolyte secondary battery in one embodiment of the present invention may include a polyolefin porous film. Hereinafter, the polyolefin porous film may be simply referred to as "porous film". The porous film has a polyolefin resin as a main component and has a large number of interconnected pores therein, allowing gas and liquid to pass from one surface to the other surface. The porous film alone can serve as a separator for a non-aqueous electrolyte secondary battery. It can also be used as a base material of a laminated separator for a non-aqueous electrolyte secondary battery in which the above porous layer is laminated.

A laminate obtained by laminating the porous layer on at least one surface of the polyolefin porous film is also referred to herein as a "laminated separator for a non-aqueous electrolyte secondary battery" or a "laminated separator". . Moreover, the separator for non-aqueous electrolyte secondary batteries in one embodiment of the present invention may further include other layers such as an adhesive layer, a heat-resistant layer, and a protective layer in addition to the polyolefin porous film.

The proportion of polyolefin in the porous film is 50% by volume or more, more preferably 90% by volume or more, and even more preferably 95% by volume or more, of the entire porous film. Further, the polyolefin more preferably contains a high molecular weight component having a weight average molecular weight of 5×10 ⁵ to 15×10 ⁶ . In particular, when the polyolefin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more, the strength of the separator for non-aqueous electrolyte secondary batteries is improved, which is more preferable.

Specific examples of the polyolefin, which is a thermoplastic resin, include homopolymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene and 1-hexene. Or a copolymer is mentioned. Examples of the homopolymer include polyethylene, polypropylene, and polybutene. Further, examples of the copolymer include an ethylene-propylene copolymer.

Among these, polyethylene is more preferable because it can prevent the flow of excessive current at a lower temperature. It should be noted that blocking the flow of this excessive current is also called shutdown. Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more. Among them, ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more is more preferable.

The thickness of the porous film is preferably 4 to 40 μm, more preferably 5 to 30 μm, even more preferably 6 to 15 μm.

The basis weight per unit area of the porous film can be appropriately determined in consideration of strength, film thickness, weight and handleability. However, the basis weight is preferably 4 to 20 g/m ² and more preferably 4 to 12 g/m ² so that the weight energy density and volume energy density of the non-aqueous electrolyte secondary battery can be increased. more preferably 5 to 10 g/m ² .

The air permeability of the porous film is preferably 30 to 500 sec/100 mL, more preferably 50 to 300 sec/100 mL in Gurley value. Sufficient ion permeability can be obtained by the porous film having the air permeability. The air permeability of the laminated separator for a non-aqueous electrolyte secondary battery in which the above porous layer is laminated on a porous film is preferably 30 to 1000 sec/100 mL, more preferably 50 to 800 sec/100 mL in Gurley value. is more preferable. The laminated separator for a non-aqueous electrolyte secondary battery can obtain sufficient ion permeability in a non-aqueous electrolyte secondary battery by having the above air permeability.

The porosity of the porous film is preferably 20 to 80% by volume so as to increase the retention amount of the electrolytic solution and to obtain the function of reliably preventing the flow of excessive current at a lower temperature. It is more preferably 30 to 75% by volume. In addition, the pore diameter of the pores of the porous film is 0.3 μm or less so that sufficient ion permeability can be obtained and particles can be prevented from entering the positive electrode and the negative electrode. is preferable, and 0.14 μm or less is more preferable.

[Method for producing polyolefin porous film]
The method for producing the porous film is not particularly limited. For example, a sheet-like polyolefin resin composition is produced by kneading a polyolefin resin, a pore-forming agent such as an inorganic filler and a plasticizer, and optionally an antioxidant or the like and then extruding the mixture. After removing the pore-forming agent from the sheet-shaped polyolefin resin composition with an appropriate solvent, the polyolefin porous film can be produced by stretching the polyolefin resin composition from which the pore-forming agent has been removed. can.

The inorganic filler is not particularly limited, and includes inorganic fillers, specifically calcium carbonate and the like. The plasticizer is not particularly limited, and examples thereof include low-molecular-weight hydrocarbons such as liquid paraffin.

Specifically, a method including the steps shown below can be mentioned.
(A) a step of kneading an ultra-high molecular weight polyethylene, a low molecular weight polyethylene having a weight average molecular weight of 10,000 or less, a pore forming agent such as calcium carbonate or a plasticizer, and an antioxidant to obtain a polyolefin resin composition;
(B) A step of rolling the obtained polyolefin resin composition with a pair of rolling rollers, cooling it step by step while pulling it with winding rollers with different speed ratios, and forming a sheet;
(C) A step of removing the pore-forming agent from the obtained sheet with a suitable solvent.
(D) A step of stretching the sheet from which the pore-forming agent has been removed at an appropriate stretching ratio.

[Method for manufacturing laminated separator for non-aqueous electrolyte secondary battery]
As a method for producing a laminated separator for a non-aqueous electrolyte secondary battery in one embodiment of the present invention, for example, in the above-mentioned "method for producing a porous layer", the above-mentioned base material for applying the coating liquid is used. A method using a polyolefin porous film can be mentioned.

In other words, the porous layer is laminated on one side or both sides of the polyolefin porous film to obtain a laminated separator for a non-aqueous electrolyte secondary battery.

[Method for producing non-aqueous electrolyte secondary battery]
As a method for manufacturing the non-aqueous secondary battery according to one embodiment of the present invention, a conventionally known manufacturing method can be adopted. For example, a non-aqueous electrolyte secondary battery member is formed by arranging a positive electrode, a polyolefin porous film and a negative electrode in this order. Here, the porous layer may exist between the polyolefin porous film and at least one of the positive electrode and the negative electrode. Next, the non-aqueous electrolyte secondary battery member is placed in a container that serves as a housing for the non-aqueous electrolyte secondary battery. After filling the inside of the container with the non-aqueous electrolyte, the container is sealed while reducing the pressure. Thereby, a non-aqueous electrolyte secondary battery according to one embodiment of the present invention can be manufactured.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Measuring method]
Various measurements in Examples and Comparative Examples were performed by the following methods.

(1) Film thickness (unit: μm)
The film thicknesses of the non-aqueous electrolyte secondary battery separator and the porous layer were measured using a high-precision digital length measuring machine (VL-50) manufactured by Mitutoyo Corporation. The thickness of the porous layer was obtained by subtracting the thickness of the portion where the porous layer was not formed from the thickness of the portion where the porous layer was formed in each laminate.

(2) Shear viscosity The shear viscosity of the coating liquids used in Examples 1 to 5 and Comparative Examples 1 to 4 was measured continuously at intervals 1 and 2 under the following conditions using a rheometer (MCR301 manufactured by Anton Paar). It was measured. The shear viscosity at a shear rate of 0.4 [1/sec] in this interval 2 was employed.
Jig used: cone plate (CP-50-1), measurement position: 1 mm, measurement temperature: 25°C
Interval 1 shear rate: 0.1 to 1000 [1/sec],
Shear rate of interval 2: 1000 to 0.1 [1/sec].

(3) Atomic Composition Percentage of Oxygen Contained in Inorganic Filler A method for calculating the atomic composition percentage [at %] of oxygen contained in the inorganic filler of Example 1 is shown below.
_{Chemical formula} : _{BaTi0.8Zr0.2O3}
Ba:Ti:Zr:O=1:0.8:0.2:3
Atomic composition percentage of oxygen [at%] = 3/(1 + 0.8 + 0.2 + 3) x 100 = 60 [at%]
For the inorganic fillers used in Examples 2 to 5 and Comparative Examples 1 to 4, the atomic composition percentage of oxygen was calculated by the same calculation method.

(4) Separator temperature change behavior measurement during microwave irradiation A test piece of 4 cm × 4 cm was prepared from the laminates for non-aqueous electrolyte secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 4 prepared as described later. The specimen was cut out and impregnated with a solution containing propylene carbonate, SN Wet 980 (manufactured by San Nopco Co., Ltd.) and water at a weight ratio of 85:12:3. After that, these test pieces were spread on a Teflon (registered trademark) sheet (size: 12 cm x 10 cm). The test piece was folded in half such that an optical fiber thermometer (Neoptix Reflex thermometer manufactured by Astec Co., Ltd.) coated with Teflon (registered trademark) was sandwiched between the porous layer surfaces. After that, in order to ensure contact between the thermometer and the surface of the porous layer, a PTFE plate was placed on the test piece except for 1 mm around the thermometer to prevent floating.

Next, after fixing the test piece impregnated with the solution and sandwiching the thermometer in a microwave irradiation device (manufactured by Micro Denshi Co., Ltd., 9 kW microwave oven, frequency 2455 MHz) equipped with a turntable, The test piece was irradiated with microwaves at 1800 W for 2 minutes.

The temperature change of the test piece during microwave irradiation was measured every 0.2 seconds with the optical fiber thermometer.

The temperature rise rate of the porous layer surface (° C./s ).

(5) Measurement of thermal expansion coefficient The thermal expansion coefficient (ppm/°C) at -40°C to 200°C of the inorganic fillers used in Examples 1 to 5 and Comparative Examples 1 to 4 was measured using TMA402 F1Hyperion (manufactured by NETZSCH). was measured under the following conditions.
Measurement atmosphere: helium, measurement load: 0.02 N, heating rate: 5°C/min, reference sample: quartz, measurement method: compression mode.

(6) Decrease rate of ionic conductivity (%)
LiPF ₆ was dissolved in a mixed solvent obtained by mixing ethylene carbonate, ethylmethyl carbonate and diethyl carbonate at a volume ratio of 3:5:2 to a concentration of 1 mol/L to obtain a reference electrolytic solution. got After each additive was added to the reference electrolytic solution so as to be 1% and dissolved, the ionic conductivity (mS/cm) was measured. The ionic conductivity was measured using an electrical conductivity meter (ES-71) manufactured by Horiba, Ltd.
The ionic conductivity decrease rate is represented by the following formula (A).

L=(LA−LB)/LA (A)
L: ionic conductivity decrease rate (%),
LA: ionic conductivity (mS/cm) before adding additives,
LB: ionic conductivity (mS/cm) after addition of additive.

(7) Battery characteristics of non-aqueous electrolyte secondary battery A non-aqueous electrolyte secondary battery assembled as described below was charged at 25 ° C. with a voltage range of 4.1 to 2.7 V and a charging current value of 0.2 C. Four initial charge/discharge cycles were performed at 25° C., with -CV charge (final current condition of 0.02 C) and CC discharge at a discharge current value of 0.2 C being one cycle.

In addition, the current value for discharging the rated capacity based on the discharge capacity at the rate of 1 hour in 1 hour is assumed to be 1C. Further, CC-CV charging is a charging method in which charging is performed with a set constant current, and after reaching a predetermined voltage, the voltage is maintained while reducing the current. CC discharge is a method of discharging to a predetermined voltage with a set constant current. These are the same as below.

CC-CV charging with a charging current value of 1C (final current condition of 0.02C), discharging current values of 0.2C, 1C, and 2C in the order of CC A discharge was performed. Three cycles of charging and discharging were performed at 55° C. for each rate. At this time, the voltage range was set to 2.7V to 4.2V. At this time, the charge capacity at the time of 1C charge in the third cycle when measuring the 2C discharge rate characteristics was measured, and this was taken as the charge capacity after high rate discharge. The design capacity of the non-aqueous electrolyte secondary batteries manufactured in Examples and Comparative Examples was 20.5 mAh.

[Example 1]
<Production of porous layer>
(Manufacture of coating liquid)
Barium titanate zirconate (manufactured by Sakai Chemical Industry Co., Ltd., BTZ-01-8020) as an inorganic filler, vinylidene fluoride-hexafluoropropylene copolymer (manufactured by Arkema Co., Ltd.: trade name "KYNAR2801") as a binder resin, solvent N-methyl-2-pyrrolidone (manufactured by Kanto Kagaku Co., Ltd.) was mixed as follows.

First, 10 parts by weight of a vinylidene fluoride-hexafluoropropylene copolymer was added to 90 parts by weight of barium zirconate titanate to obtain a mixture. Next, the solvent is added to the obtained mixture so that the concentration of the solid content (barium titanate zirconate and vinylidene fluoride-hexafluoropropylene copolymer) is 40% by weight, and the mixture is Obtained. The resulting mixture was stirred and mixed using a rotation/revolution mixer (Awatori Mixer, manufactured by Thinky Co., Ltd.) and a thin-film swirl type high-speed mixer (Filmix, manufactured by Primix Co., Ltd.) to obtain a uniform coating liquid. .

(Production of porous layer)
The resulting coating solution was applied to one side of a polyethylene porous film (thickness: 12 μm, porosity: 44%) as a separator for non-aqueous electrolyte secondary batteries by a doctor blade method. The obtained coating film was dried at 80° C. to form a porous layer 1 on one side of the separator for a non-aqueous electrolyte secondary battery. Thus, a laminate 1 having a separator for a non-aqueous electrolyte secondary battery and a porous layer 1 was obtained. At this time, the clearance of the doctor blade was adjusted so that the basis weight of the porous layer 1 was 7 g/m ² . Table 1 shows the measurement results of various physical properties of the coating liquid, the inorganic filler, and the laminate 1.

<Production of non-aqueous electrolyte secondary battery>
(Preparation of positive electrode)
A commercial positive electrode made by coating LiNi _0.5 Mn _0.3 Co _0.2 O ₂ /conducting agent/PVDF (92/5/3 weight ratio) on aluminum foil was used. The commercially available positive electrode is coated with aluminum foil so that the size of the portion where the positive electrode active material layer is formed is 40 mm × 35 mm, and the portion where the positive electrode active material layer is not formed with a width of 13 mm remains on the outer periphery. It was cut out and used as a positive electrode for a non-aqueous electrolyte secondary battery, which will be described later. The positive electrode active material layer had a thickness of 58 μm and a density of 2.50 g/cm ³ .

(Preparation of negative electrode)
A commercial negative electrode prepared by coating a copper foil with graphite/styrene-1,3-butadiene copolymer/sodium carboxymethylcellulose (98/1/1 weight ratio) was used. The commercially available negative electrode is coated with copper foil so that the size of the portion where the negative electrode active material layer is formed is 50 mm × 40 mm, and the portion where the negative electrode active material layer is not formed with a width of 13 mm remains on the outer periphery. It was cut out and used as a negative electrode for a non-aqueous electrolyte secondary battery, which will be described later. The negative electrode active material layer had a thickness of 49 μm and a density of 1.40 g/cm ³ .

(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2 to a concentration of 1 mol/L to obtain an electrolyte stock solution 1. Electrolyte stock solution 1 is an aprotic polar solvent electrolyte containing Li ⁺ ions.

Addition liquid 1 was obtained by adding diethyl carbonate to 10.3 mg of dibutyl hydroxytoluene (BHT, rate of decrease in ionic conductivity: 5.3%) and dissolving the solution to 5 mL. 300 μL of additive solution 1 and 1700 μL of electrolyte solution undiluted solution 1 were mixed to obtain non-aqueous electrolyte solution 1 . Table 2 shows the content of the additive in the non-aqueous electrolyte 1.

(Assembly of non-aqueous electrolyte secondary battery)
Using the positive electrode, the negative electrode, the laminate 1 and the non-aqueous electrolyte 1, a non-aqueous electrolyte secondary battery 1 was manufactured by the method described below.

A non-aqueous electrolyte secondary battery member 1 was obtained by laminating the positive electrode, the laminate 1 with the porous layer facing the positive electrode side, and the negative electrode in this order in the laminate pouch. At this time, the positive electrode and the negative electrode were arranged such that the entire main surface of the positive electrode active material layer of the positive electrode was included in the range of the main surface of the negative electrode active material layer of the negative electrode. That is, the positive electrode and the negative electrode were arranged so that the entire main surface of the positive electrode active material layer of the positive electrode overlapped the main surface of the negative electrode active material layer of the negative electrode.

Subsequently, the non-aqueous electrolyte secondary battery member 1 was placed in a prefabricated bag formed by laminating an aluminum layer and a heat seal layer. Further, 0.23 mL of the non-aqueous electrolyte 1 was put into this bag. Then, the non-aqueous electrolyte secondary battery 1 was produced by heat-sealing the bag while decompressing the inside of the bag.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 1 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Example 2]
<Production of non-aqueous electrolyte secondary battery>
(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3:7 so that the concentration thereof became 1 mol/L, whereby an electrolytic stock solution 2 was obtained.

Addition liquid 2 was obtained by adding diethyl carbonate to 10.0 mg of vinylene carbonate (VC, rate of decrease in ionic conductivity: 1.3%) and dissolving the solution to 5 mL. 200 μL of additive liquid 2 and 1800 μL of electrolyte undiluted solution 2 were mixed, and 900 μL of electrolyte undiluted solution 2 was added to 100 μL of the mixed liquid of additive liquid 2 and electrolyte undiluted solution 2 to obtain additive liquid 3 . 50 μL of additive solution 3 and 1950 μL of electrolyte undiluted solution 2 were mixed to obtain non-aqueous electrolyte solution 2 . Table 2 shows the content of the additive in the non-aqueous electrolyte 2.

(Assembly of non-aqueous electrolyte secondary battery)
A non-aqueous electrolyte secondary battery 2 was produced in the same manner as in Example 1, except that the non-aqueous electrolyte 2 was used instead of the non-aqueous electrolyte 1 .

After that, the charge capacity of the non-aqueous electrolyte secondary battery 2 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Example 3]
<Production of laminate including separator for non-aqueous electrolyte secondary battery and porous layer>
In the same manner as in Example 1, except that calcium titanate (manufactured by Toshima Seisakusho, D50 = 0.3 μm) was used as the inorganic filler, instead of the porous layer 1 on one side of the separator for a non-aqueous electrolyte secondary battery A porous layer 2 was formed. As a result, a laminate 2 including a separator for a non-aqueous electrolyte secondary battery and the porous layer 2 was obtained. Table 1 shows the measurement results of various physical properties of the coating liquid, the inorganic filler, and the laminate 2.

<Production of non-aqueous electrolyte secondary battery>
(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate in a volume ratio of 4:4:2 so that the concentration thereof became 1 mol/L, thereby obtaining an electrolytic stock solution 3. rice field.

Diethyl carbonate was added to 11.2 mg of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irg.1010, rate of decrease in ionic conductivity: 4.0%) and dissolved. to 5 mL to obtain additive solution 4. 90 μL of additive solution 4 and 1910 μL of electrolyte undiluted solution 3 were mixed to obtain non-aqueous electrolyte solution 3 . Table 2 shows the content of the additive in the non-aqueous electrolyte 3.

(Assembly of non-aqueous electrolyte secondary battery)
A non-aqueous electrolyte secondary was prepared in the same manner as in Example 1 except that the laminate 2 was used instead of the laminate 1 and the non-aqueous electrolyte 3 was used instead of the non-aqueous electrolyte 1. A battery 3 was produced.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 3 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Example 4]
<Production of non-aqueous electrolyte secondary battery>
(Preparation of non-aqueous electrolyte)
90 μL of additive solution 4 and 1910 μL of electrolyte undiluted solution 1 were mixed to obtain non-aqueous electrolyte solution 4 . Table 2 shows the content of the additive in the non-aqueous electrolyte 4.

(Assembly of non-aqueous electrolyte secondary battery)
Non-aqueous electrolyte secondary was prepared in the same manner as in Example 1 except that the laminate 2 was used instead of the laminate 1 and the non-aqueous electrolyte 4 was used instead of the non-aqueous electrolyte 1. A battery 4 was produced.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 4 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Example 5]
<Production of laminate including separator for non-aqueous electrolyte secondary battery and porous layer>
In the same manner as in Example 1 except that aluminum titanate (manufactured by Toshima Seisakusho, D50 = 0.9 µm) was used as the inorganic filler, a porous A quality layer 3 was formed. As a result, a laminate 3 having a separator for a non-aqueous electrolyte secondary battery and a porous layer 3 was obtained. Table 1 shows the measurement results of various physical properties of the coating liquid, the inorganic filler, and the laminate 3.

<Production of non-aqueous electrolyte secondary battery>
(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, ethylmethyl carbonate and diethyl carbonate in a volume ratio of 2:5:3 to a concentration of 1 mol/L to obtain an electrolytic stock solution 4. rice field. 90 μL of additive solution 4 and 1910 μL of electrolyte undiluted solution 4 were mixed to obtain non-aqueous electrolyte solution 5 . Table 2 shows the content of the additive in the non-aqueous electrolyte 5.

(Assembly of non-aqueous electrolyte secondary battery)
Non-aqueous electrolyte secondary was prepared in the same manner as in Example 1 except that the laminate 3 was used instead of the laminate 1 and the non-aqueous electrolyte 5 was used instead of the non-aqueous electrolyte 1. A battery 5 was produced.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 5 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Comparative Example 1]
<Production of non-aqueous electrolyte secondary battery>
(Preparation of non-aqueous electrolyte)
Diethyl carbonate was added to 9.7 mg of tris-(4-t-butyl-2,6-dimethyl-3-hydroxybenzyl) isocyanurate (Cyanox 1790, rate of decrease in ionic conductivity: 6.1%) and dissolved. Addition liquid 5 was obtained by adjusting the volume to 5 mL. 90 μL of additive solution 5 and 1910 μL of electrolyte undiluted solution 1 were mixed to obtain non-aqueous electrolyte solution 6 . Table 2 shows the content of the additive in the non-aqueous electrolyte 6.

(Assembly of non-aqueous electrolyte secondary battery)
Non-aqueous electrolyte secondary was prepared in the same manner as in Example 1 except that the laminate 2 was used instead of the laminate 1 and the non-aqueous electrolyte 6 was used instead of the non-aqueous electrolyte 1. A battery 6 was produced.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 6 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Comparative Example 2]
<Production of laminate including separator for non-aqueous electrolyte secondary battery and porous layer>
A porous layer 1 was formed on one side of a separator for a non-aqueous electrolyte secondary battery in the same manner as in Example 1 except that borax passed through a sieve with an opening of 53 μm (manufactured by Wako Pure Chemical Industries) was used as the inorganic filler. A porous layer 4 was formed instead. As a result, a laminate 4 of the non-aqueous electrolyte secondary battery separator and the porous layer 4 was obtained. Table 1 shows the measurement results of various physical properties of the coating liquid, the inorganic filler, and the laminate 4.

<Production of non-aqueous electrolyte secondary battery>
(Assembly of non-aqueous electrolyte secondary battery)
Non-aqueous electrolyte secondary was prepared in the same manner as in Example 1 except that the laminate 4 was used instead of the laminate 1 and the non-aqueous electrolyte 4 was used instead of the non-aqueous electrolyte 1. A battery 7 was produced.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 7 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Comparative Example 3]
<Production of laminate including separator for non-aqueous electrolyte secondary battery and porous layer>
A porous layer 5 was formed instead of the porous layer 1 on one side of the separator for a non-aqueous electrolyte secondary battery in the same manner as in Example 1 except that alumina (AKP3000 manufactured by Sumitomo Chemical Co., Ltd.) was used as the inorganic filler. formed. As a result, a laminate 5 of the non-aqueous electrolyte secondary battery separator and the porous layer 5 was obtained. Table 1 shows the measurement results of various physical properties of the coating liquid, the inorganic filler, and the laminate 5.

<Production of non-aqueous electrolyte secondary battery>
(Assembly of non-aqueous electrolyte secondary battery)
Non-aqueous electrolyte secondary was prepared in the same manner as in Example 1 except that the laminate 5 was used instead of the laminate 1 and the non-aqueous electrolyte 4 was used instead of the non-aqueous electrolyte 1. A battery 8 was produced.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 8 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

[Comparative Example 4]
<Production of non-aqueous electrolyte secondary battery>
(Assembly of non-aqueous electrolyte secondary battery)
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the laminate 2 was used instead of the laminate 1 and the electrolyte undiluted solution 1 was used instead of the non-aqueous electrolyte 1. 9 was made.

After that, the charge capacity of the non-aqueous electrolyte secondary battery 9 obtained by the above-described method after high-rate discharge was measured. Table 2 shows the results.

As shown in Tables 1 and 2, the non-aqueous electrolyte secondary batteries of Examples 1-5 are superior to the non-aqueous electrolyte secondary batteries of Comparative Examples 1-4 in charge capacity after high-rate discharge. It turns out that there is In the non-aqueous electrolyte secondary batteries of Examples 1 to 5, the thermal expansion coefficient of the inorganic filler is 1 ppm/° C. or more and 11 ppm/° C. or less, and the temperature rise rate of the porous layer surface is 0.93° C./ 0.5 ppm or more and 300 ppm or less of an additive whose ionic conductivity decrease rate is 1.0% or more and 6.0% or less in the non-aqueous electrolyte. contains. On the other hand, in Comparative Example 1, the ionic conductivity decrease rate of the additive exceeds 6.0%. In Comparative Example 2, the thermal expansion coefficient of the inorganic filler exceeds 11 ppm/°C, and the temperature rise rate of the porous layer surface is less than 0.93°C/sec. In Comparative Example 3, the temperature rise rate of the surface of the porous layer exceeds 1.25°C/sec. Comparative Example 4 contains no additive.

A non-aqueous electrolyte secondary battery according to an embodiment of the present invention maintains a high charge capacity after high-rate discharge. Therefore, it can be suitably used for various applications, particularly as a battery for consumer use such as power tools and vacuum cleaners, and a battery for vehicle use, which requires high-rate discharge.

Claims (6)

A porous layer containing an inorganic filler and a resin, a positive electrode, a negative electrode and a non-aqueous electrolyte,
The thermal expansion coefficient of the inorganic filler at -40°C to 200°C is 11 ppm/°C or less,
The porous layer was impregnated with a solution containing propylene carbonate, a polyoxyalkylene-type nonionic surfactant, and water at a weight ratio of 85:12:3, and then irradiated with microwaves at a frequency of 2455 MHz at an output of 1800 W. The measured temperature rise rate of the surface of the porous layer from the start of irradiation to 15 seconds after is 0.93° C./second or more and 1.25° C./second or less,
The non-aqueous electrolytic solution contains 0.5 ppm or more and 300 ppm or less of an additive whose ionic conductivity decrease rate L represented by the following formula (A) is 1.0% or more and 6.0% or less ,
L=(LA−LB)/LA (A)
(In formula (A), LA is a mixed solvent containing ethylene carbonate, ethylmethyl carbonate and diethyl carbonate at a volume ratio of 3:5:2, and LiPF ₆ was dissolved so that its concentration was 1 mol/L. Represents the ionic conductivity (mS/cm) of the reference electrolyte solution, and LB represents the ionic conductivity (mS/cm) of the electrolyte solution obtained by dissolving 1.0% by weight of an additive in the reference electrolyte solution. .)
Said additives include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethyl phosphate, vinylene carbonate, propanesultone, 6-[3-(3-t -butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepine, tris phosphate (2,4-di-tert-butylphenyl) and 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate A non-aqueous electrolyte secondary battery selected from the group. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein said porous layer is laminated on one side or both sides of a polyolefin porous film. Claim 1 or 2, wherein the porous layer contains one or more resins selected from the group consisting of polyolefins, (meth)acrylate resins, fluorine-containing resins, polyamide resins, polyester resins and water-soluble polymers. The non-aqueous electrolyte secondary battery described. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein said polyamide resin is an aramid resin. 5. The non-aqueous electrolyte secondary battery in accordance with claim 1, wherein said non-aqueous electrolyte contains an electrolyte containing lithium. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the non-aqueous electrolyte contains an aprotic polar solvent.

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