PTC Functional Composition, PTC Functional Composition Layer, Coated Current Collector for Non-aqueous Electrolyte Secondary Battery, Electrode for Non-aqueous Electrolyte Secondary Battery, and Non-aqueous Electrolyte Secondary Battery

Abstract

To provide a PTC functional composition which can achieve both of a satisfactory PTC function and a battery performance in a nonaqueous electrolyte secondary battery.SOLUTION: A PTC functional composition comprises a carbon material, a binding agent, and a thermoplastic resin. The carbon material is a granular material having electrical conductivity. The total amount (DBP absorption) of dibutylphthalate absorbed by the carbon material is 30 cc / 100 g or more and 120 cc / 100 g or less. The carbon material has primary particles of which the particle diameter is 20 nm or more and 300 nm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a PTC functional composition, a PTC functional composition layer for a non-aqueous electrolyte secondary battery containing the PTC functional composition, a coated current collector for a non-aqueous electrolyte secondary battery provided with the PTC functional composition layer, an electrode for a non-aqueous electrolyte secondary battery provided with the coated current collector, and a non-aqueous electrolyte secondary battery provided with the electrode.

Background Art

[0002] Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are widely used as power sources for smartphones, notebook computers, etc., and recently are also used for large batteries such as in-vehicle applications. On the other hand, while lithium-ion secondary batteries have the advantage of high energy density, since they use a non-aqueous electrolyte, sufficient safety measures are required. In recent years, with the increase in battery size, ensuring safety has become even more important.

[0003] Therefore, in lithium-ion secondary batteries, a so-called shutdown function that spontaneously and safely stops charging and discharging in the event of an accident such as a failure is required, and this function is imparted to the separator inside the battery. However, there are cases where the shutdown by the separator is incomplete and the temperature further rises above the melting point of the separator, or the separator melts due to an increase in external temperature and an internal short circuit occurs, and countermeasures for further improving safety are required.

[0004] As a countermeasure, a technique of forming a positive temperature coefficient (PTC) functional composition in a current collector or an active material layer constituting an electrode of a lithium secondary battery has been proposed (see, for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the present inventor has noticed that the PTC functional compositions described in Patent Documents 1 to 3 may not exhibit a sufficient PTC function or may cause a decrease in battery performance.

[0007] As a result of intensive studies to solve the above-described problems, the present invention has been completed for the first time by finding that a PTC functional composition in which the connection between the particles of the contained carbon material is relatively weak and the primary particle size of the carbon material is within a predetermined range can achieve both a sufficient PTC function and battery performance in a non-aqueous electrolyte secondary battery.

Means for Solving the Problems

[0008] That is, the PTC functional composition according to the present invention is a PTC functional composition containing a carbon material, a binder, and a thermoplastic resin, wherein the carbon material is in the form of conductive particles, and the total amount of dibutyl phthalate absorbed by the carbon material (DBP absorption amount) is 30 cc / 100 g or more and 120 cc / 100 g or less, and the primary particle size of the carbon material is 20 nm or more and 300 nm or less.

[0009] According to the PTC functional composition configured as described above, since the DBP absorption amount and the primary particle size of the carbon material are within the ranges described above, respectively, the connection between the particles is relatively weak, and the shielding effect of the conductivity between the carbon materials due to the volume expansion of the thermoplastic resin when the internal temperature of the battery rises can be sufficiently exhibited. On the other hand, at normal temperature, a conductive path is easily formed between the carbon materials, and even when a PTC functional composition layer containing the PTC functional composition is formed in the battery, deterioration of battery characteristics such as cycle life can be reduced.

[0010] The peak area (A -1 ) around 1350 cm measured by Raman spectroscopy of the carbon material D and the ratio R value (A -1 ) of the peak area (A G ) around 1580 cm D / A G ) are preferably 2.2 or more and 3.5 or less. When the ratio R value (A D / A G ) of the carbon material is within the above-mentioned range, the crystallinity of the surface of the carbon material particles is relatively low (amorphous). When the surface of the carbon material particles is moderately amorphous, the interaction with the thermoplastic resin becomes strong and it is easily affected by the volume expansion of the thermoplastic resin. Therefore, it is considered that the effect of cutting the conductive path of the carbon material accompanying the volume expansion of the thermoplastic resin can be sufficiently exerted.

[0011] For the same reason, the peak half-width at half maximum (G-FWHM) around 1580 cm measured by Raman spectroscopy of the carbon material is preferably 95 cm -1 or more and 150 cm -1 or less. -1

[0012] The total specific surface area of the carbon material is preferably 7 m 2 / g or more and 100 m 2 / g or less.

[0013] The volume density of the carbon material under a pressure of 60 MPa is preferably 1.0 g / cc or more and 1.6 g / cc or less.

[0014] The volume resistivity of the carbon material under a pressure of 60 MPa is preferably 0.020 Ωcm or more and 0.10 Ωcm or less.

[0015] When the total solid content of the PTC functional composition is 100 parts by mass, the content of the carbon material is preferably 10 parts by mass or more and 70 parts by mass or less, the content of the binder is preferably 1 part by mass or more and 50 parts by mass or less, and the content of the thermoplastic resin is preferably 5 parts by mass or more and 65 parts by mass or less. ​

[0016] The present invention includes a PTC functional composition layer containing a PTC functional composition as described above, a coated current collector for a non-aqueous electrolyte secondary battery in which the PTC functional composition layer is formed on a current collector, an electrode for a non-aqueous electrolyte secondary battery including the coated current collector for a non-aqueous electrolyte secondary battery, or a non-aqueous electrolyte secondary battery including the electrode for a non-aqueous electrolyte secondary battery.

Effects of the Invention

[0017] According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery capable of achieving both a sufficient PTC function and battery performance for practical use.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the specific configuration of a secondary battery according to an embodiment of the present invention will be described. <1. Basic Configuration of Non-Aqueous Electrolyte Secondary Battery> The lithium ion secondary battery according to the present embodiment includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The charging cut-off voltage (redox potential) of this lithium ion secondary battery is, for example, 4.0 V (vs. Li / Li+) or more and 5.0 V or less, particularly 4.2 V or more and 5.0 V or less. The form of the lithium ion secondary battery is not particularly limited, and for example, it may be any of a cylindrical shape, a prismatic shape, a laminate shape, or a button shape.

[0019] (1-1. Positive Electrode) The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. The positive electrode current collector may be any conductor, and for example, it is preferably in the form of a plate or foil and is composed of aluminum, stainless steel, nickel-coated steel, or the like. The positive electrode mixture layer contains at least a positive electrode active material, and may further contain a conductive agent and a positive electrode binder.

[0020] The positive electrode active material is, for example, a transition metal oxide or solid solution oxide containing lithium, and is not particularly limited as long as it can electrochemically occlude and release lithium ions. Examples of the transition metal oxide containing lithium include, for example, Li 1.0 Ni 0.88 Co 0.1 Al 0.01 Mg 0.01 O2 and the like can be mentioned. In addition to these, Li·Co-based composite oxides such as LiCoO2, LiNi x Co y Mn z O2 and other Li·Ni·Co·Mn-based composite oxides, Li·Ni-based composite oxides such as LiNiO2, or Li·Mn-based composite oxides such as LiMn2O4 can be exemplified. Examples of the solid solution oxide include Li a Mn x Co y Ni z O2 (1.150 ≤ a ≤ 1.430, 0.45 ≤ x ≤ 0.6, 0.10 ≤ y ≤ 0.15, 0.20 ≤ z ≤ 0.28), LiMn 1.5 Ni 0.5 O4 and the like can be exemplified. The content (content ratio) of the positive electrode active material is not particularly limited as long as it is applicable to the positive electrode mixture layer of the non-aqueous electrolyte secondary battery. Further, these compounds may be used alone or in combination of plural kinds.

[0021] The conductive agent is not particularly limited as long as it can enhance the conductivity of the positive electrode. Specific examples of the conductive agent include those containing one or more selected from carbon black, natural graphite, artificial graphite, and fibrous carbon. Examples of the carbon black include furnace black, channel black, thermal black, ketjen black, acetylene black, and the like. Examples of the fibrous carbon include carbon nanotubes, graphene, carbon nanofibers, and the like. The content of the conductive agent is not particularly limited as long as it is applicable to the positive electrode mixture layer of the non-aqueous electrolyte secondary battery.

[0022] Examples of the binder for the positive electrode include fluorine-containing resins such as polyvinylidene fluoride, ethylene-containing resins such as styrene-butadiene rubber, ethylene-propylene-diene terpolymer, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, polyvinyl alcohol, carboxy methyl cellulose or carboxy methyl cellulose derivatives (such as salts of carboxy methyl cellulose), or nitrocellulose. The binder for the positive electrode is not particularly limited as long as it can bind the positive electrode active material and the conductive agent onto the positive electrode current collector.

[0023] (1-2. Negative electrode) The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode current collector may be any conductor, and is preferably, for example, in the form of a plate or foil and composed of copper, stainless steel, nickel-plated steel, or the like.

[0024] The negative electrode mixture layer contains at least a negative electrode active material, and may further contain a conductive agent and a binder for the negative electrode. The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. For example, graphite active materials (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), Si-based active materials or Sn-based active materials (e.g., a mixture of fine particles of silicon (Si) or tin (Sn) or their oxides and a graphite active material, fine particles of silicon or tin, an alloy based on silicon or tin), metallic lithium, and Li4Ti5O 12 titanium oxide compounds such as the like, lithium nitride, etc. can be considered. As the negative electrode active material, one of those listed above may be used, or two or more of them may be used in combination. Note that the oxide of silicon is represented by SiOx (0 ≦ x ≦ 2).

[0025] The conductive agent is not particularly limited as long as it can enhance the conductivity of the negative electrode. For example, the same ones as those described in the section of the positive electrode can be used.

[0026] The binder for the negative electrode is not particularly limited as long as it can bind the negative electrode active material and the conductive agent onto the negative electrode current collector. The binder for the negative electrode may be, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), a metal salt of carboxymethyl cellulose (CMC), etc. One type of binder may be used alone, or a binder containing two or more types may also be used.

[0027] (1 - 3. Separator) The separator is not particularly limited and may be any separator as long as it can be used as a separator for a lithium-ion secondary battery. As the separator, it is preferable to use alone or in combination a porous film, a nonwoven fabric, or the like that exhibits excellent high-rate discharge performance. Examples of the resin constituting the separator include polyolefin-based resins typified by polyethylene, polypropylene, etc., polyester-based resins typified by polyethylene terephthalate, polybutylene terephthalate, etc., polyvinylidene difluoride, vinylidene difluoride-hexafluoropropylene copolymer, vinylidene difluoride-perfluoroninylether copolymer, vinylidene difluoride-tetrafluoroethylene copolymer, vinylidene difluoride-trifluoroethylene copolymer, vinylidene difluoride-fluoroethylene copolymer, vinylidene difluoride-hexafluoroacetone copolymer, vinylidene difluoride-ethylene copolymer, vinylidene difluoride-propylene copolymer, vinylidene difluoride-trifluoropropylene copolymer), vinylidene difluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene difluoride-ethylene-tetrafluoroethylene copolymer, and the like can be mentioned. The porosity of the separator is not particularly limited, and the porosity of the separator of a conventional lithium ion secondary battery can be arbitrarily applied.

[0028] On the surface of the separator, there may be a heat-resistant layer containing inorganic particles for improving heat resistance, or a layer containing an adhesive for adhering to the electrode to fix the battery element. Examples of the aforementioned inorganic particles include Al2O3, AlOOH, Mg(OH)2, SiO2, and the like. Examples of the adhesive include vinylidene difluoride-hexafluoropropylene copolymer, acid-modified vinylidene fluoride polymer, styrene-(meth)acrylate copolymer, and the like.

[0029] (1-4. Non-aqueous electrolyte) The non-aqueous electrolyte can be used without particular limitation as the same type as the non-aqueous electrolyte conventionally used in lithium-ion secondary batteries. The non-aqueous electrolyte has a composition in which an electrolyte salt is contained in a non-aqueous solvent which is a solvent for the electrolyte. Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, vinylene carbonate; cyclic esters such as γ-butyrolactone, γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate; chain esters such as methylformate, methylacetate, methylbutyrate, ethyl propionate, propyl propionate; tetrahydrofuran or its derivatives, 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, 1,4-dibutoxyethane), or ethers such as methyldiglyme, ethylene glycol monopropyl ether, propylene glycol monopropyl ether, nitriles such as acetonitrile, benzonitrile, dioxolane or its derivatives, ethylene sulfide, sulfolane, sultone or its derivatives, etc. can be used alone or in a mixture of two or more thereof. When using a mixture of two or more of the non-aqueous solvents, the mixing ratio of each non-aqueous solvent can be the mixing ratio used in conventional lithium ion secondary batteries.,

[0030] Examples of the electrolyte salt include LiClO4, LiBF4, LiAsF6, LiPF6, LIPF6-x(C n F 2n+1 )x [where 1 < x < 6, n = 1 or 2], LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10, inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K) such as NaClO4, NaI, NaSCN, NaBr, KClO4, KSCN, organic ion salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiC(C2F5SO2)3, (CH3)4NBF4, (CH3)4NBr, (C2H5)4NClO4, (C2H5)4NI, (C3H7)4NBr, (n-C4H9)4NClO4, (n-C4H9)4NI, (C2H5)4N-maleate, (C2H5)4N-benzoate, (C2H5)4N-phtalate, lithium stearyl sulfonic acid, lithium octyl sulfonic acid, lithium dodecyl benzene sulfonic acid, etc. These ionic compounds can be used alone or in combination of two or more. Note that the concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte used in conventional lithium-ion secondary batteries, and there is no particular limitation. In this embodiment, it is preferable to use a non-aqueous electrolyte containing the above-mentioned lithium compound (electrolyte salt) at a concentration of about 0.8 mol / l or more and 1.5 mol / l or less.

[0031] In addition, various additives may be added to the non-aqueous electrolyte. Such additives include negative electrode acting additives, positive electrode acting additives, ester-based additives, carbonate ester-based additives, sulfate ester-based additives, phosphate ester-based additives, borate ester-based additives, acid anhydride-based additives, and electrolyte-based additives, etc. 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.

[0032] <2. Manufacturing method of the non-aqueous electrolyte secondary battery according to this embodiment> Next, a method for manufacturing a lithium-ion secondary battery will be described. The positive electrode is fabricated as follows. First, a mixture of a positive electrode active material, a conductive agent, and a positive electrode binder in a desired ratio is dispersed in a solvent for the positive electrode slurry to form the positive electrode slurry. Next, this positive electrode slurry is applied onto a positive electrode current collector and dried to form a positive electrode mixture layer. Note that the coating method is not particularly limited. Examples of the coating method include a knife coater method, a gravure coater method, a reverse roll coater, a slit die coater, etc. The following respective coating steps are also performed by a similar method. Next, the positive electrode mixture layer is pressed by a press machine to a desired density. Thereby, the positive electrode is fabricated.

[0033] The negative electrode is also fabricated in the same manner as the positive electrode. First, a mixture of the materials constituting the negative electrode mixture layer is dispersed in a solvent for the negative electrode slurry to produce the negative electrode slurry. Next, the negative electrode slurry is applied onto a negative electrode current collector and dried to form a negative electrode mixture layer. Next, the negative electrode mixture layer is pressed by a press machine to a desired density. Thereby, the negative electrode is fabricated.

[0034] Next, an electrode structure is fabricated by sandwiching a separator between the positive electrode and the negative electrode. Next, the electrode structure is processed into a desired form (e.g., cylindrical, rectangular, laminated, button-shaped, etc.) and inserted into a container of that form. Next, a non-aqueous electrolyte is injected into the container to impregnate each pore in the separator and the voids of the positive electrode and the negative electrode with the electrolyte. Thereby, a lithium-ion secondary battery is fabricated.

[0035] <3. Characteristic Configuration of the Non-aqueous Electrolyte Secondary Battery According to the Present Embodiment> Hereinafter, the characteristic configuration of the non-aqueous electrolyte secondary battery according to the present embodiment will be described.

[0036] (3-1. PTC Functional Composition Layer) The above-described positive electrode and negative electrode further include a PTC functional composition layer containing a positive temperature coefficient (PTC) functional composition. The PTC functional composition layer may be formed between the positive electrode current collector and the negative electrode current collector. For example, it is preferably provided between the positive electrode current collector and the positive electrode mixture layer and / or between the negative electrode current collector and the negative electrode mixture layer. In the present embodiment, the PTC functional composition layer is provided both between the positive electrode current collector and the positive electrode mixture layer and between the negative electrode current collector and the negative electrode mixture layer.

[0037] The PTC functional composition contains a carbon material, a binder, and a thermoplastic resin. The carbon material is in the form of conductive particles, such as amorphous carbon like carbon black. This carbon material has relatively weak connections between carbon material particles.

[0038] The degree of connection (connection strength) between carbon material particles can be defined, for example, by the total amount of dibutyl phthalate absorbed by the carbon material (total DBP absorption amount) and the primary particle size of the carbon material particles. For a carbon material with a certain primary particle size, when its total DBP absorption amount increases, it indicates that the structure of the aggregates formed by the aggregation of primary particles becomes more complex, that is, it is considered that more primary particles are aggregated together.

[0039] The carbon material used in the PTC functional composition according to the present embodiment has a total DBP absorption amount in the range of 30 cc / 100 g or more and 120 cc / 100 g or less, and its primary particle size is in the range of 20 nm or more and 300 nm or less. The volume expansion of the thermoplastic resin at high temperature can easily block the connection between carbon material particles, and at room temperature, the carbon material particles can form a conduction path without problems. The range of the total DBP absorption amount is more preferably 30 cc / 100 g or more and 110 cc / 100 g or less. The primary particle size is more preferably in the range of 25 nm or more and 300 nm or less, and particularly preferably in the range of 30 nm or more and 300 nm or less.

[0040] Also, when performing Raman spectroscopy on the carbon material, the peak area (A -1 around 1350 cm D ) and the peak area (A -1 around 1580 cm G ) ratio (A D / A G , also referred to as the R value.) is 2.2 or more and 3.5 or less, or the peak full width at half maximum (G-FWHM) around 1580 cm -1 is 95 cm -1 or more and 150 cm -1 or less, then the crystallinity (graphitization degree) of the carbon material is low, and it is considered that the surface is relatively rough or there are relatively many functional groups. If the surface of the carbon material particles is relatively rough, the adhesion force with the surrounding thermoplastic resin increases, and the carbon material particles are likely to follow the thermoplastic resin during the volume expansion of the thermoplastic resin. As a result, it is preferable because the PTC function is easily exhibited. The R value is more preferably 2.3 or more and 3.3 or less. Also, the G-FWHM is more preferably 98 cm -1 or more and 115 cm -1 or less, and particularly preferably 98 cm -1 or more and 110 cm -1 or less.

[0041] The total specific surface area of the carbon material is one of the factors affecting the degree of connection between carbon materials, similar to the primary particle diameter described above. For the carbon material used in this embodiment, its total specific surface area is preferably 7 m 2 / g or more and 100 m 2 / g or less, more preferably 7 m 2 / g or more and 70 m 2 / g or less, and particularly preferably 7 m 2 / g or more and 60 m 2 / g or less.

[0042] The volume density of the carbon material under a pressure of 60 MPa is also one of the factors affecting the degree of connection between carbon materials, similar to the primary particle size described above. For the carbon material used in this embodiment, its volume density is preferably 1.0 g / cc or more and 1.6 g / cc or less, and more preferably 1.0 g / cc or more and 1.5 g / cc or less. The volume density of the carbon material under a pressure of 60 MPa is defined by the measurement method described in detail in the examples.

[0043] The volume resistivity of the carbon material under a pressure of 60 MPa is also one of the factors affecting the degree of connection between carbon materials, similar to the total DBP absorption amount and the primary particle size of the carbon material particles described above. For the carbon material used in this embodiment, its volume resistivity under a pressure of 60 MPa is preferably 0.020 Ωcm or more and 0.10 Ωcm or less, and more preferably 0.02 Ωcm or more and 0.075 Ωcm or less. The volume resistivity of the carbon material under a pressure of 60 MPa is defined by the measurement method described in detail in the examples.

[0044] The amorphous carbon is not particularly limited as long as it satisfies the above-mentioned properties, such as carbon black. Specific examples of carbon black include, for example, furnace black, channel black, thermal black, ketjen black, acetylene black, and the like. Among these, furnace black produced by the furnace method is preferable because its production method can easily adjust the total DBP absorption amount, primary particle size, etc. within the above-mentioned ranges.

[0045] The binder is not particularly limited as long as it can bind the carbon material and the thermoplastic resin. Specific examples of the binder include, for example, metal salts of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), and the like.

[0046] The thermoplastic resin is not particularly limited as long as it is generally used in PTC functional compositions. Specific examples of the thermoplastic resin include, for example, linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyvinyl acetate (PVAc), polyurethane (PUR), polytetrafluoroethylene (PTFE), polymethyl methacrylate resin (PMMA), polyamide (PA), polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE, modified PPE, PPO), polyethylene terephthalate (PET), glass fiber reinforced polyethylene terephthalate (GF-PET), polybutylene terephthalate (PBT), cyclic polyolefin (COP), polyphenylene sulfide (PPS), polysulfone (PSF), polyethersulfone (PES), amorphous polyarylate (PAR), polyetheretherketone (PEEK), thermoplastic polyimide (PI), polyamideimide (PAI), and the like.

[0047] As the content ratio of each component constituting the PTC functional composition, for example, when the total solid content excluding liquid components such as solvents from the PTC functional composition is 100 parts by mass, the content of the carbon material is 10 parts by mass or more and 70 parts by mass or less, the content of the binder is 1 part by mass or more and 50 parts by mass or less, and the content of the thermoplastic resin is 5 parts by mass or more and 65 parts by mass or less. When the total solid content excluding liquid components such as solvents from the PTC functional composition is 100 parts by mass, it is more preferable that the content of the carbon material is 15 parts by mass or more and 65 parts by mass or less, the content of the binder is 4 parts by mass or more and 40 parts by mass or less, and the content of the thermoplastic resin is 10 parts by mass or more and 60 parts by mass or less. Note that the total solid content of the PTC functional composition refers to, for example, the total mass of the solid remaining after all the liquid parts are volatilized by drying, that is, it is equal to the total mass of the powders of each component used when preparing the PTC functional composition.

[0048] (3-2. Method for Producing PTC Functional Composition Layer) The above-described PTC functional composition suspended in a solvent such as water or NMP to form a slurry is applied onto a positive current collector or a negative current collector so that the thickness after drying is 0.1 μm or more and 5 μm or less, more preferably 0.3 μm or more and 2 μm or less, and then dried to form it. In this specification, the current collector with the PTC functional composition layer formed on its surface is referred to as a coated current collector. If the thickness of the PTC functional composition layer of the coated current collector is 0.1 μm or more, it is preferable because the PTC function can be sufficiently exhibited during abnormal heat generation. Also, if the thickness of the PTC functional composition layer of the coated current collector is 5 μm or less, it is preferable because the content ratio of the active material in the electrode can be ensured and the decrease in battery capacity can be suppressed. A secondary battery electrode serving as a positive electrode or a negative electrode can be produced by forming a paste layer on the PTC functional composition layer provided on this coated current collector. More specifically, the positive electrode can be formed by forming a positive electrode mixture layer on the PTC functional composition layer of a coated current collector for the positive electrode, which includes a PTC functional composition layer and a positive current collector. Similarly, the negative electrode can be formed by forming a negative electrode mixture layer on the PTC functional composition layer of a coated current collector for the negative electrode, which includes a PTC functional composition layer and a negative current collector.

[0049] <4. Effects of this Embodiment> According to the non-aqueous electrolyte secondary battery configured as described above, it is possible to achieve both a sufficient PTC function and battery characteristics such as cycle life.

[0050] <5. Other Embodiments of the Present Invention> The present invention is not limited to the embodiments described above. In the above-described embodiments, the formation of a PTC functional composition layer between the current collector and the mixture layer using the PTC functional composition according to the present invention has been described. However, by incorporating the PTC functional composition into the positive electrode mixture layer and / or the negative electrode mixture layer, the positive electrode mixture layer and / or the negative electrode mixture layer may be provided with a PTC function. Needless to say, the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit thereof.

Examples

[0051] Hereinafter, the present invention will be described in more detail based on specific examples. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples. (Example 1) A coated current collector for a non-aqueous electrolyte secondary battery was produced by the following procedure or steps. <Production of PTC Functional Composition> As the conductive carbon material, 56 g of carbon black (DBP absorption 42 cc / 100 g, primary particle diameter 122 nm, specific surface area 19 m2 / g) and 560 g of a 2.5% aqueous solution of sodium carboxymethyl cellulose (CMC) as a binder (14 g as solid content) were put into 100 g of water and mixed with a mixer at 3000 revolutions for 20 minutes. Then, this mixed solution was put into the tank of NanoVator manufactured by Yoshida Kogyo Kikai Co., Ltd. The mixed solution in the tank was conveyed to a slurry pump by a pressure pump and injected into a straight nozzle (nozzle diameter 150 μm) by the slurry pump at a pressure of 80 MPa. The mixed solution that passed through the straight nozzle and was subjected to high-pressure dispersion treatment was recovered in a 2-L container through a heat exchanger. To the recovered mixed solution, 120 g of a 25% aqueous solution of high-density polyethylene (HDPE, High Density Polyethylene) as a thermoplastic resin (30 g as solid content) was further added and mixed with a mixer at a speed of 500 revolutions per minute for 10 minutes to obtain a PTC functional composition. The solid content obtained by removing moisture from the obtained PTC functional composition was 12%.

[0052] <Formation of PTC Functional Composition Layer> On an aluminum foil with a thickness of 10 μm serving as a current collector (copper foil in Example 17), the PTC functional composition prepared as described above was coated using a gravure coater. The PTC functional composition coated on the current collector was heated and dried at 130°C for 5 minutes to obtain a coated current collector having a PTC functional composition layer with a thickness of 1.5 μm.

[0053] (Examples 2 to 9, 11 to 20, Comparative Examples 1 to 4) In each example and each comparative example, except that the raw materials and ratios of the physical properties shown in Table 1 were changed, a coated current collector was produced in the same procedure as in Example 1. For Comparative Example 1, a current collector without a PTC functional composition layer was used in the following respective steps and experiments.

[0054] (Example 10) Using the conductive carbon materials obtained by mixing 15 parts by mass each of the carbon blacks used in Examples 3 and 8, and changing other raw materials and ratios as shown in Table 1, a coated current collector was produced in the same procedure as in Example 1.

[0055] (Negative electrode fabrication) An artificial graphite, sodium carboxymethyl cellulose (CMC), and a styrene-butadiene-based aqueous dispersion were dissolved and dispersed in an aqueous solvent at a mass ratio of solid content of 97.5:1.0:1.5 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied and dried on the PTC functional composition layer of the above-mentioned coated current collector or on one side of the current collector so that the applied amount (surface density) of the dried mixture was 20.5 mg / cm 2 on one side, and then pressed with a roll press so that the density of the mixture layer was 1.65 g / cc to fabricate a negative electrode.

[0056] (Positive electrode fabrication) Li 1.0 Ni 0.88 Co 0.1 Al 0.01 Mg 0.01 O2, acetylene black, and polyvinylidene fluoride were dispersed and mixed in an N-methyl-2-pyrrolidone solvent at a mass ratio of solid content of 97.7:1.0:1.3 to prepare a positive electrode mixture slurry. Next, the slurry was applied and dried on the PTC functional composition layer of the above-mentioned coated current collector or on one side of the current collector so that the applied amount (surface density) of the dried mixture was 24.0 mg / cm 2 on one side, and then pressed with a roll press so that the density of the mixture layer was 3.65 g / cc to fabricate a positive electrode.

[0057] (Secondary battery cell fabrication) After welding nickel and aluminum lead wires to the above-mentioned single-sided negative electrode and single-sided positive electrode respectively, a single-layer electrode body was fabricated by sandwiching a porous polypropylene separator between one negative electrode and one positive electrode. Next, the above single-layer electrode body was stored in an aluminum laminate film with the lead wires drawn out to the outside, and an electrolytic solution was injected and sealed under reduced pressure to fabricate a secondary battery cell before initial charging. As the electrolytic solution, a solution in which 1.3 M of LiPF6 and 1% by mass of vinylene carbonate were dissolved in a solvent obtained by mixing ethylene carbonate / dimethyl carbonate / fluoroethylene carbonate at 15 / 80 / 5 (volume ratio) was used.

[0058] <Physical Property Evaluation of Conductive Carbon Materials> Regarding the evaluation of the conductive carbon materials used in the examples and comparative examples, the following was carried out. (Total DBP Absorption, Total Specific Surface Area, Primary Particle Size of Carbon Materials) For the carbon materials, the DBP absorption was measured in accordance with JIS K6217-4 using an absorption amount / oil supply measuring device (S-500 manufactured by Koizumi Sokki Seisakusho). Specifically, 10 g of the sample was introduced, and the measurement was carried out while rotating at a dropping rate of 4 ml / min and 100 revolutions / min until the maximum value of torque was confirmed. The value calculated from the dropping oil amount when the torque showed 70% of the maximum torque within the range from the start of measurement to the maximum torque was taken as the DBP absorption. The total DBP absorption was the weighted average value of the DBP absorption of each carbon material and the mixing ratio. Also, the specific surface area was measured in accordance with JIS K6217-2 using a gas adsorption amount measuring device (BELSORP manufactured by Microtrac BEL). Specifically, 0.3 g of the sample was filled into the cell, pre-treated by heating at 200 °C for 4 hours, cooled to liquid nitrogen temperature, saturated with nitrogen gas adsorption, and then heated to room temperature to measure the amount of desorbed gas. From the obtained results, it was calculated by the normal BET method. The total specific surface area was the weighted average value of the specific surface area of each carbon material and the mixing ratio. The primary particle size was the average of the particle sizes measured by an electron microscope.

[0059] (Raman Spectroscopic Analysis) Using the NRS-5100 from JASCO Corporation as a microscopic laser Raman spectrometer, measurements were performed at an excitation wavelength of 532.36 nm. The measurement conditions are as follows. Exposure time: 10 seconds Number of integrations: 20 times Diffraction grating: 300 lines / mm (600 nm) Among the Raman spectra of the entire measured region, curve fitting was performed on the spectra in the range of 800 cm -1 ~2000 cm -1 and the peak area (A -1 ) around 1350 cm D and the ratio (A -1 ) of the peak area (A G ) around 1580 cm D / A G ) around 1580 cm -1 were obtained, and the full width at half maximum (G-FWHM) of the peak around 1580 cm was obtained.

[0060] (Volume density and powder resistance under 60 MPa pressure) Using the MCP-PD51 from Nitto Seiko Analytic Co., Ltd., the volume density when carbon material powder filled in a cylindrical cylinder was pressure-molded with a hydraulic press, and the volume resistivity of the pressure-molded powder were measured. The measurement conditions are as follows. Load: 18.85 kN Electrode interval: 3.0 mm Electrode radius: 0.7 mm Sample radius: 10.0 mm Probe used: 4-probe

[0061] <Evaluation of secondary battery> (Resistance measurement) The secondary battery cells fabricated in Examples 1 to 20 and Comparative Examples 1 to 4 were subjected to constant current charging at 0.1 CA of the designed capacity up to 4.3 V in a thermostat at 25°C, followed by constant voltage charging at 4.3 V until it reached 0.05 CA. Subsequently, constant current discharging was performed at 0.1 CA until 3.0 V. Further, in a thermostat at 25°C, a cell that was subjected to one cycle of constant current charging at 0.2 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.2 CA under the conditions of a charging cut-off voltage of 4.3 V and a discharging cut-off voltage of 3.0 V was used as the initial cell, and resistance measurement was carried out at 25°C and 1 kHz using an impedance analyzer (RM3544 manufactured by Hioki E.E. Corporation) to obtain the initial resistance value at 25°C. Thereafter, the initial cell was heated at a heating rate of 10°C / min up to 150°C, and resistance measurement was performed at 150°C in the same manner as described above to obtain the resistance value at 150°C.

[0062] (Cycle characteristics) The secondary battery cells fabricated in Examples 1 to 20 and Comparative Examples 1 to 4 were subjected to constant current charging at 0.1 CA of the designed capacity up to 4.3 V in a thermostat at 25°C, followed by constant voltage charging at 4.3 V until it reached 0.05 CA. Subsequently, constant current discharging was performed at 0.1 CA until 3.0 V. Further, in a thermostat at 25°C, one cycle of constant current charging at 0.2 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.2 CA was carried out under the conditions of a charging cut-off voltage of 4.3 V and a discharging cut-off voltage of 3.0 V, and the initial discharge capacity was measured. This secondary battery was subjected to 100 cycles of a life test in which constant current charging was performed at 0.5 CA, constant voltage charging was performed at 0.05 CA, and constant current discharging was performed at 0.5 CA under the conditions of a charging cut-off voltage of 4.3 V and a discharging cut-off voltage of 3.0 V at a temperature of 45°C. Then, after 100 cycles, the discharge capacity at constant current charging of 0.2 CA, constant voltage charging of 0.05 CA, and discharging of 0.2 CA was measured and divided by the initial discharge capacity to measure the capacity retention rate after 100 cycles.

[0063] (Evaluation results) The raw materials, physical properties, and compositions used in the examples and comparative examples described above are shown in Table 1. Also, the evaluation results of Examples 1 to 20 and Comparative Examples 1 to 4 are summarized in Table 2.

[0064]

Table 1

[0065] [Table 2]

[0066] (Consideration on the Results of Examples and Comparative Examples) As shown in Table 2, when a non-aqueous electrolyte secondary battery including a PTC functional composition layer containing the PTC functional composition according to the present invention is used, it was confirmed that when the internal temperature of the battery increased, the internal resistance of the battery increased significantly. From this, for example, when the battery generates abnormal heat due to an internal short circuit or the like, it is considered that the resistance of the current collector increases and the current is cut off, thereby avoiding ignition of the battery.

[0067] On the other hand, in Comparative Example 1 not provided with a PTC functional composition layer and Comparative Examples 2 to 3 in which the total DBP absorption amount of the conductive carbon material is large, no significant increase in the internal resistance of the battery was observed even when the internal temperature of the battery increased. First, in Comparative Example 1, since there is no PTC functional composition layer, there is no effect of increasing the resistance during heat generation. In Comparative Examples 2 to 3, the total DBP absorption amount of the conductive carbon material exceeds 120 cc / 100 g. As described above, a large total DBP absorption amount of the carbon material indicates that the connection between the conductive carbon materials is strong. Therefore, in these Comparative Examples 2 to 3, it is considered that the effect of increasing the resistance due to the volume expansion of the thermoplastic resin is impaired because the connection between the carbon materials is too strong. In addition, in Comparative Examples 2 to 3, the R value (A D / A G ) in the Raman spectroscopic measurement of the conductive carbon material is small, indicating that the crystallinity is mainly high on the surface and the defects and functional groups are relatively few.

[0068] From these results, in Comparative Examples 2 to 3, it is considered that the volume expansion of the conductive carbon material due to the volume expansion of the resin during heat generation was insufficient, so the effect of blocking the conductivity between the carbon materials was small. In Comparative Example 4 using graphite as the conductive carbon material, although the total DBP absorption amount of the carbon material is small and the connection between the graphites is weak, it can be seen that the initial resistance is large and the 100-cycle capacity retention rate decreases. This is presumably because, even though the R value is very small and the crystallinity is high in Raman spectroscopic measurement, when using graphite with a large particle size, the formation of conductive paths between the graphites is insufficient.

[0069] In addition to Examples 1 to 20 described above, for example, when using the same materials as in Example 8 and setting the content of the carbon material to 10 parts by mass, the content of the binder to 30 parts by mass, and the content of the thermoplastic resin to 60 parts by mass, when the content of the carbon material is 70 parts by mass, the content of the binder is 15 parts by mass, and the content of the thermoplastic resin is 15 parts by mass, when the content of the binder is 50 parts by mass, the content of the carbon material is 30 parts by mass, and the content of the thermoplastic resin is 20 parts by mass, and when using the same materials as in Example 3 and setting the content of the thermoplastic resin to 5 parts by mass, the content of the carbon material to 65 parts by mass, and the content of the binder to 30 parts by mass, although secondary batteries showing cycle retention rates equivalent to those of Examples 1 to 20 could be fabricated, the increase in cell impedance at 150 °C was inferior compared to Examples 1 to 20. Also, as shown in Example 19, when the content of the binder was reduced to 1 part by mass, it was found that the temperature change of the impedance became smaller compared to Examples 1 to 18 and 20, and the cycle retention rate also decreased slightly. From these results, it can be seen that the content ratios of the carbon material, the binder, and the thermoplastic resin are preferably within the ranges implemented in Examples 1 to 20, and more preferably within the ranges described in Examples 1 to 18 and 20.

Claims

1. A PTC functional composition containing a carbon material, a binder, and a thermoplastic resin, wherein the carbon material is in the form of conductive particles, the total amount of dibutyl phthalate absorbed by the carbon material (DBP absorption amount) is 30 cc / 100 g or more and 120 cc / 100 g or less, and the primary particle diameter of the carbon material is 20 nm or more and 300 nm or less, and the peak half-width (G-FWHM) near 1580 cm−1 measured by Raman spectroscopy of the carbon material is 95 cm−1 or more and 150 cm−1 or less. The PTC functional composition is characterized by this.

2. The peak area (A －１ ) around 1350 cm Ｄ measured by Raman spectroscopy of the carbon material and the peak area (A －１ ) around 1580 cm Ｇ have a ratio (A Ｄ / A Ｇ ) of 2.2 or more and 3.5 or less. The PTC functional composition according to claim 1.

3. The total specific surface area of the carbon material is 7 m 2 / g or more and 100 m 2 / g or less, and the PTC functional composition according to claim 1 or 2.

4. The PTC functional composition according to any one of Claims 1 to 3, wherein the bulk density of the carbon material under a pressure of 60 MPa is 1.0 g / cc or more and 1.6 g / cc or less.

5. When the total solid content is 100 parts by mass, the content of the carbon material is 10 parts by mass or more and 70 parts by mass or less, the content of the binder is 1 part by mass or more and 50 parts by mass or less, and the content of the thermoplastic resin is 5 parts by mass or more and 65 parts by mass or less. The PTC functional composition according to any one of Claims 1 to 4.

6. A PTC functional composition layer containing the PTC functional composition according to any one of Claims 1 to 5.

7. A coated current collector for a non-aqueous electrolyte secondary battery provided with the PTC functional composition layer according to Claim 6.

8. An electrode for a non-aqueous electrolyte secondary battery provided with the coated current collector for a non-aqueous electrolyte secondary battery according to Claim 7.

9. A non-aqueous electrolyte secondary battery provided with the electrode for a non-aqueous electrolyte secondary battery according to Claim 8.

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