Non-aqueous electrolyte secondary battery and positive electrode for the same

Abstract

To provide a positive electrode for a non-aqueous electrolyte secondary battery capable of maintaining electric resistance and cycle characteristics within an appropriate range while improving safety by sufficiently suppressing rise in internal temperature of the battery.SOLUTION: A positive electrode for a non-aqueous electrolyte secondary battery includes a positive electrode active material and inorganic particles. The inorganic particles contain boron. D50, which is a 50% integrated value of a particle size distribution of a particle size volume basis in the particle size distribution determined by a laser diffraction / scattering method of the inorganic particles, is between 0.3 μm or more and 8.0 μm or less. A ratio of a long diameter relative to a short diameter (a long diameter / a short diameter) of the inorganic particles is 3.0 or more and 30 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery including the same.

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 the size of the battery, ensuring safety has become even more important.

[0003] For example, when a lithium-ion secondary battery is placed in a high-temperature environment, etc., the positive electrode of the lithium-ion secondary battery may generate heat, or heat may be generated by the oxidative decomposition reaction of the electrolyte by oxygen radicals generated from the positive electrode, causing an increase in the internal temperature of the battery. When the internal temperature of the battery becomes very high due to such causes, a short circuit is likely to occur due to the shrinkage of the separator included in the lithium-ion secondary battery, and there is a risk that the internal temperature of the battery will further increase.

[0004] Therefore, in order to suppress the increase in the internal temperature of the lithium-ion secondary battery and ensure safety, a method of adding boron nitride as a heat-conductive particle to the positive electrode (Patent Document 1) has been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, according to the studies by the present inventors, it has been found that simply containing boron nitride in the positive electrode may not be able to sufficiently suppress the internal temperature of the battery. In addition, when boron nitride is contained in the positive electrode, the battery resistance of the battery may increase or the cycle characteristics may deteriorate.

[0007] The present invention has been made in view of the above-described problems, and an object thereof is to provide a positive electrode for a non-aqueous electrolyte secondary battery that can sufficiently suppress an increase in the internal temperature of the battery to improve safety while maintaining electrical resistance and cycle characteristics.

Means for Solving the Problems

[0008] That is, the present invention is as follows. [1] A positive electrode for a non-aqueous electrolyte secondary battery including a positive electrode active material and inorganic particles, wherein the inorganic particles contain boron, the D50 of the inorganic particles is 0.3 μm or more and 8.0 μm or less, and the ratio (major axis / minor axis) of the major axis to the minor axis of the inorganic particles is 3.0 or more and 30 or less, a positive electrode for a non-aqueous electrolyte secondary battery. [2] The positive electrode for a non-aqueous electrolyte secondary battery according to [1], wherein the ratio B / A of the D50 (A) of the positive electrode active material to the D50 (B) of the inorganic particles is 0.010 or more and 0.8 or less. [3] The positive electrode for a non-aqueous electrolyte secondary battery according to [1] or [2], wherein the inorganic particles are boron nitride (BN). [4] The BET specific surface area of the inorganic particles calculated from the adsorption isotherm measured by adsorbing nitrogen on the inorganic particles is 1 m 2 / g or more and 50 m 2 / g or less, the positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [3]. [5] A positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector, wherein the inorganic particles are contained in the positive electrode mixture layer, The positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein the content of the inorganic particles is in the range of 0.1% by mass or more and 5.0% by mass or less with respect to 100% by mass of the positive electrode composite material layer. [6] A positive electrode current collector, a positive electrode composite material layer formed on the positive electrode current collector, and a temperature rise suppression layer laminated on the side opposite to the current collector of the positive electrode composite material layer. The inorganic particles are contained in the temperature rise suppression layer. The positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein the content of the inorganic particles is in the range of 40% by mass or more and 99% or less with respect to 100% by mass of the temperature rise suppression layer. [7] The positive electrode for a non-aqueous electrolyte secondary battery according to [6], wherein the content of the binder is in the range of 1% by mass or more and 60% by mass or less with respect to 100% by mass of the temperature rise suppression layer. [8] The positive electrode for a non-aqueous electrolyte secondary battery according to [6], wherein the thickness of the temperature rise suppression layer is 0.1 or more and 5 μm or less. [9] A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, The non-aqueous electrolyte secondary battery, wherein the positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [8].

Effect of the Invention

[0009] According to the present invention, since the D50 and the major axis / minor axis of the boron-containing inorganic particles containing inorganic particles in the positive electrode are within a predetermined range, when the temperature inside the battery starts to rise, an endothermic reaction occurs in the inorganic particles and the electrolyte decomposition reaction is suppressed, thereby sufficiently suppressing the rise in the internal temperature in the non-aqueous electrolyte secondary battery and improving the safety, while maintaining the electrical resistance and cycle characteristics of the non-aqueous electrolyte secondary battery.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0011] Hereinafter, the specific configuration of the non-aqueous electrolyte secondary battery according to one embodiment of the present invention will be described. <1. Basic Configuration of Non-Aqueous Electrolyte Secondary Battery> As shown in FIG. 1, the non-aqueous electrolyte secondary battery 100 according to the present embodiment is a lithium ion secondary battery including a positive electrode 1, a negative electrode 2, a separator 3, a non-aqueous electrolyte 4, and a casing 5 that houses these components inside. Note that FIG. 1 is a schematic cross-sectional view showing the cross-section of the non-aqueous electrolyte secondary battery 100. The form of the lithium ion secondary battery is not particularly limited, and for example, it may be any of a cylindrical shape, a rectangular shape, a laminate shape, or a button shape.

[0012] (1-1. Positive Electrode) The positive electrode 1 includes a positive electrode current collector 11 and a positive electrode composite layer 12 formed on the positive electrode current collector 11. The positive electrode current collector 11 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 composite layer 12 contains a positive electrode active material and may further contain a conductive agent and a positive electrode binder.

[0013] The positive electrode active material is, for example, a transition metal oxide or a solid solution oxide containing lithium, and is not particularly limited as long as it can electrochemically occlude and release lithium ions. The shape of the positive electrode active material is not particularly limited, but is preferably particulate. 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 O 2 and the like. In addition to these, Li·Co-based composite oxides such as LiCoO 2 and the like, Li·Ni·Co·Mn-based composite oxides such as LiNi x Co y Mn z O 2 and the like, Li·Ni-based composite oxides such as LiNiO 2 and the like, or Li·Mn-based composite oxides such as LiMn 2 O 4 and the like can be exemplified. Examples of the solid solution oxide include Li a Mn x Co y Ni z O 2 (1.150 ≦ a ≦ 1.430, 0.45 ≦ x ≦ 0.6, 0.10 ≦ y ≦ 0.15, 0.20 ≦ z ≦ 0.28), LiMn 1.5 Ni 0.5 O 4 and the like. Note that 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 12 of the non-aqueous electrolyte secondary battery 100. These compounds may be used alone or in combination of multiple types.

[0014] The conductive agent is not particularly limited as long as it can enhance the conductivity of the positive electrode 1. Specific examples of the conductive agent include, for example, those containing one or more selected from carbon black, natural graphite, artificial graphite, fibrous carbon, and sheet-like 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, carbon nanofibers, and the like, and examples of the sheet-like carbon include graphene and the like. The content of the conductive agent in the positive electrode composite material layer 12 is not particularly limited, but from the viewpoint of achieving both conductivity and battery capacity, it is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less, based on the entire positive electrode composite material layer 12.

[0015] 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 11.

[0016] (1-2. Negative electrode) The negative electrode 2 includes a negative electrode current collector 21 and a negative electrode composite material layer 22 formed on the negative electrode current collector 21. The negative electrode current collector 21 may be any conductor, and for example, it is preferably in the form of a plate or foil and is composed of copper, stainless steel, nickel-plated steel, etc.

[0017] The negative electrode composite material layer 22 may contain 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 (for example, 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 Li 4 Ti 5 O 12 titanium oxide-based compounds such as, and lithium nitride, etc. are conceivable. As the negative electrode active material, one of those listed above may be used, or two or more kinds may be used in combination. Note that the oxide of silicon is represented by SiOx (0 ≤ x ≤ 2).

[0018] The conductive agent is not particularly limited as long as it can enhance the conductivity of the negative electrode 2. For example, the same ones as those described in the section of the positive electrode 1 can be used. The content of the conductive agent in the negative electrode composite material layer 22 is not particularly limited, but from the viewpoint of achieving both conductivity and battery capacity, it is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.5% by mass or more and 3% by mass or less with respect to the entire negative electrode composite material layer 22.

[0019] The binder for the negative electrode may be any material that can bind the negative electrode active material and the conductive agent onto the negative electrode current collector 21, and is not particularly limited. Examples of the binder for the negative electrode include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), metal salts of carboxymethyl cellulose (CMC), and the like. One type of binder may be used alone, or two or more types may be contained.

[0020] (1-3. Separator) The separator 3 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 3, it is preferable to use alone or in combination a porous film, a nonwoven fabric, etc. that exhibit excellent high-rate discharge performance. Examples of the resin constituting the separator 3 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 3 is not particularly limited, and the porosity of the separator of a conventional lithium ion secondary battery can be arbitrarily applied.

[0021] The separator 3 may further include a surface layer that covers the surface of the above-mentioned porous film or non-woven fabric. The surface layer may contain an adhesive for adhering to the electrode and fixing the battery element. Examples of the adhesive include vinylidene difluoride-hexafluoropropylene copolymer, acid-modified vinylidene fluoride polymer, styrene-(meth)acrylate copolymer, and the like.

[0022] (1-4. Non-aqueous electrolyte) The non-aqueous electrolyte 4 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 4 has a composition in which an electrolyte salt is contained in a non-aqueous solvent that is a solvent for the electrolyte solution. 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 and benzonitrile, dioxolane or its derivatives, ethylene sulfide, sulfolane, sultone or its derivatives, etc. can be used alone or in combination of two or more thereof. When the non-aqueous solvents are used in combination of two or more, the mixing ratio of each non-aqueous solvent can be the mixing ratio used in conventional lithium ion secondary batteries.,

[0023] As the electrolyte salt, for example, LiClO 4 , LiBF 4 , LiAsF 6 , LiPF 6 , LIPF 6 -x(C n F 2n+1 )x [provided that 1 < x < 6, n = 1 or 2], LiSCN, LiBr, LiI, Li 2 SO 4 , Li 2 B 10 Cl 10 , NaClO 4 , NaI, NaSCN, NaBr, KClO 4 , KSCN and other inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), LiCF 3 SO 3 , LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 )(C 4 F 9SO 2 )、LiC(CF 3 SO 2 ) 3 、LiC(C 2 F 5 SO 2 ) 3 、(CH 3 ) 4 NBF 4 、(CH 3 ) 4 NBr、(C 2 H 5 ) 4 NClO 4 、(C 2 H 5 ) 4 NI、(C 3 H 7 ) 4 NBr、(n-C 4 H 9 ) 4 NClO 4 、(n-C 4 H 9 ) 4 NI、(C 2 H 5 ) 4 N-maleate、(C 2 H 5 ) 4 N-benzoate、(C 2 H 5 ) 4 N-phtalate, lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzenesulfonate and other organic ion salts can be mentioned, and these ionic compounds can be used alone or in combination of two or more. The concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte used in a conventional lithium-ion secondary battery, and there is no particular limitation. In this embodiment, it is preferable to use the non-aqueous electrolyte 4 containing the lithium compound (electrolyte salt) as described above at a concentration of about 0.8 mol / l or more and 1.5 mol / l or less.

[0024] In addition, various additives may be added to the non-aqueous electrolyte 4. Examples of 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. 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.

[0025] <2. Characteristic Configuration of Non-Aqueous Electrolyte Secondary Battery According to This Embodiment> Hereinafter, the characteristic configuration of the non-aqueous electrolyte secondary battery 100 according to this embodiment will be described. The positive electrode 1 of the non-aqueous electrolyte secondary battery 100 according to this embodiment contains a positive electrode active material and inorganic particles for non-aqueous electrolyte secondary batteries (hereinafter, also simply referred to as inorganic particles). In this embodiment, as described above, the positive electrode 1 includes a positive electrode current collector 11 and a positive electrode mixture layer 12, and the positive electrode mixture layer 12 contains the above-described positive electrode active material and inorganic particles. The inorganic particles function as heat generation suppression additives that suppress the rise in the internal temperature of the non-aqueous electrolyte secondary battery 100.

[0026] The particle size of the inorganic particles is such that D50(B), which is the integrated value of 50% of the particle size distribution based on volume, is 0.3 μm or more and 8.0 μm or less. The shape of the inorganic particles may be any of spherical, scaly, columnar, and needle-like shapes, but scaly ones are preferred. The aspect ratio (major axis / minor axis) of the inorganic particles is 3.0 or more and 30 or less. The aspect ratio is preferably 3.0 or more and 20 or less, and more preferably 3.0 or more and 15 or less. Here, the major axis refers to the largest diameter of the particle, and the minor axis refers to the smallest diameter of the particle. For example, when the particle is scaly (flaky), the major axis may refer to the longest diameter of the flake, and the minor axis may refer to the thickness of the scale (flake). As the method for measuring the major axis and the minor axis, for example, a method of calculating D50 which is the integrated value of 50% of the particle size distribution based on particle volume in the particle size distribution obtained by the laser diffraction / scattering method, a method of calculating the major axis and / or the minor axis from a scanning electron microscope image, etc. can be mentioned. As these measurement methods, only one of the above-mentioned methods may be used, or both may be used in combination and then a method with higher accuracy may be adopted. For example, when the particles are scaly (flaky) and the thickness is sufficiently small and it is difficult to accurately measure the thickness in the method of calculating D50, it is also possible to measure the aforementioned D50 as the major axis and calculate the minor axis from the scanning electron microscope image as the minor axis.

[0027] It is preferable that the ratio B / A of D50(A) which is the integrated value of 50% of the particle size distribution based on particle volume of the positive electrode active material contained in the positive electrode composite material layer and D50(B) of the inorganic particles is 0.010 or more and 0.8 or less, more preferably 0.010 or more and 0.6 or less, still more preferably 0.010 or more and 0.4 or less, and particularly preferably 0.010 or more and 0.2 or less.

[0028] The inorganic particles contain boron, specifically, those containing one or more selected from the group consisting of boron nitride and zirconium boride, and more preferably boron nitride (BN).

[0029] The BET specific surface area of the inorganic particles calculated by the adsorption isotherm measured by adsorbing nitrogen to the inorganic particles is 1 m 2 / g or more and 50 m 2 / g or less, preferably 5 m 2 / g or more and 48 m 2 / g or less, more preferably 10 m 2 / g or more and 48 m 2 / g or less.

[0030] The content of the inorganic particles contained in the positive electrode composite material layer is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.3% by mass or more and 3.0% by mass or less, and even more preferably 0.5% by mass or more and 2.0% by mass or less.

[0031] <3. Manufacturing Method of Non-aqueous Electrolyte Secondary Battery According to this Embodiment> Next, a manufacturing method of the non-aqueous electrolyte secondary battery 100 according to this embodiment will be described. (3-1. Manufacturing Method of Positive Electrode) The positive electrode 1 is manufactured, for example, as follows. First, a mixture of a positive electrode active material, a conductive agent, a binder for positive electrode, and the inorganic particles in a desired ratio is dispersed in a solvent for positive electrode slurry to form a positive electrode slurry. Next, this positive electrode slurry is applied onto the positive electrode current collector 11 and dried to form the positive electrode composite material layer 12. 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 the same method. Next, the positive electrode composite material layer 12 is pressed by a press machine to have a desired density. Thereby, the positive electrode 1 is manufactured.

[0032] (3-2. Manufacturing Method of Negative Electrode) The negative electrode 2 may also be manufactured in the same manner as the positive electrode 1. First, a mixture of the materials constituting the negative electrode composite material layer 22 is dispersed in a solvent for negative electrode slurry to produce a negative electrode slurry. Next, the negative electrode slurry is applied onto the negative electrode current collector 21 and dried to form the negative electrode composite material layer 22. Next, the negative electrode composite material layer 22 is pressed by a press machine to have a desired density. Thereby, the negative electrode 2 is manufactured.

[0033] (3-3. Manufacturing Method of Non-aqueous Electrolyte Secondary Battery) Next, an electrode structure is fabricated by sandwiching the separator 3 between the positive electrode 1 and the negative electrode 2. Next, the electrode structure is processed into a desired form (e.g., cylindrical, rectangular, laminated, button-shaped, etc.) and inserted into a container 5 of that form. Next, a non-aqueous electrolyte is injected into the container to impregnate the electrolyte 4 into each pore in the separator 3 and the voids of the positive electrode 1 and the negative electrode 2. A lithium-ion secondary battery can be fabricated through the above steps.

[0034] <4. Effects of this Embodiment> According to the non-aqueous electrolyte secondary battery 100 configured as described above, even in an environment where the internal temperature is likely to rise due to battery abnormalities such as internal short circuits, the rise in the internal temperature of the non-aqueous electrolyte secondary battery 100 can be sufficiently suppressed. Furthermore, the electrical resistance of the non-aqueous electrolyte secondary battery 100 can be kept small, and the cycle characteristics can be improved.

[0035] <5. Other Embodiments of the Present Invention> The present invention is not limited to the above-described embodiments. The positive electrode 1 of the non-aqueous electrolyte secondary battery 100 according to this embodiment may further include a temperature rise suppression layer 13 laminated on the surface of the positive electrode composite layer 12 opposite to the positive electrode current collector 11, as shown in FIG. 2. The temperature rise suppression layer 13 contains, for example, the inorganic particles and a binder for binding the inorganic particles in the temperature rise suppression layer to each other and the temperature rise suppression layer 13 and the positive electrode composite layer 12. Note that FIG. 2 is a schematic cross-sectional view showing a cross-section of the non-aqueous electrolyte secondary battery 100.

[0036] The content of the inorganic particles in the temperature rise suppression layer 13 is preferably in the range of 40% by mass or more and 99% by mass or less, more preferably 60% by mass or more and 99% by mass or less, and particularly preferably 80% by mass or more and 99% by mass or less with respect to the entire temperature rise suppression layer 13 (100% by mass). The content of the inorganic particles in the positive electrode composite layer 12 or the temperature rise suppression layer 13 can be measured by the following method. First, a cross-sectional sample containing only the positive electrode active material layer 12 or only the temperature rise suppression layer 13 is prepared using a cross-section sample preparation apparatus such as a cross-section polisher. SEM-EDS observation is performed at at least three locations including the vicinity of the center and both ends in the prepared cross-sectional sample, and the mass of boron is quantitatively analyzed due to its inclusion in the cross-sectional sample. From the results of the above-described SEM-EDS observation, the molecular structure constituting the inorganic particles is also specified. Based on the molecular structure of the specified inorganic particles and the mass of boron, the mass of the inorganic particles contained in the cross-sectional sample is calculated. Based on the mass of the inorganic particles calculated in this way and the mass of the cross-sectional sample, the content of the inorganic particles in the positive electrode composite material layer 12 or the temperature rise suppression layer 13 can be calculated. The apparatus and conditions used for the measurement are as follows. Measuring apparatus: Field emission scanning electron microscope JSM-7800F (FE-SEM, manufactured by JEOL Ltd.) Energy dispersive analyzer JED100mm (EDS, manufactured by JEOL Ltd.) Acceleration voltage: 4 kV

[0037] As the binder, for example, those listed as the positive electrode binder can be used. From the viewpoint of sufficiently suppressing the rise in the internal temperature while exhibiting sufficient binding force, the content of the binder in the temperature rise suppression layer 13 is preferably in the range of 1% by mass or more and 99% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and particularly preferably 1% by mass or more and 30% by mass or less with respect to the entire temperature rise suppression layer 13 (100% by mass).

[0038] The thickness of the temperature rise suppression layer 13 is preferably 0.1 μm or more and 5 μm or less. By setting the thickness of the temperature rise suppression layer 13 to 0.1 μm or more, a sufficient heat generation suppression effect can be achieved. Also, by setting the thickness of the temperature rise suppression layer 13 to 5 μm or less, an increase in electrical resistance and a decrease in the energy density of the battery due to the provision of the temperature rise suppression layer 13 can be suppressed. The thickness of the temperature rise suppression layer 13 is more preferably 0.5 μm or more and 5 μm or less, and particularly preferably 1 μm or more and 4 μm or less. The thickness of the temperature rise suppression layer 13 can be measured, for example, by the following procedure. First, a cross-sectional sample obtained by cutting the positive electrode 1 along its thickness direction is created using a cross-polisher or the like. The created cross-sectional sample is observed with a scanning electron microscope (SEM), and the thickness of the temperature rise suppression layer 13 is calculated from this SEM image. Specifically, the thicknesses at at least three locations including near the center and both ends of the temperature rise suppression layer 13 in the cross-sectional sample are measured, and the average value is taken as the thickness of the temperature rise suppression layer. After setting the content of the inorganic particles in the temperature rise suppression layer 13 within the above-described preferred range, by setting the thickness in the temperature rise suppression layer 13 within the above-described range, the content of the inorganic particles can be adjusted within a preferred range similar to the case where inorganic particles are contained in the positive electrode composite material layer 12 (that is, preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.3% by mass or more and 3.0% by mass or less, and even more preferably 0.5% by mass or more and 2.0% by mass or less with respect to the entire positive electrode composite material layer 12).

[0039] When a positive electrode provided with a temperature rise suppression layer is used, in the above-described manufacturing process of the positive electrode, a positive electrode composite material layer containing no inorganic particles is formed on the positive electrode current collector, and a temperature rise suppression layer slurry containing inorganic particles, a binder, and an appropriate solvent is applied and dried on this positive electrode composite material layer to form the temperature rise suppression layer. 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

[0040] 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.

[0041] <Fabrication of the positive electrode> (Example 1) LiCoO 2 (D50: 17 μm), acetylene black, polyvinylidene fluoride, and boron nitride A (manufactured by Resonac Co., Ltd., product number: BN-UHP) with the physical properties shown in Table 1 as inorganic particles were dispersed and mixed in an N-methyl-2-pyrrolidone solvent at a mass ratio of solid content of 96.7:1.0:1.3:1.0 to prepare a positive electrode composite slurry. Next, after drying, the slurry was coated and dried on one or both sides of an aluminum current collector foil so that the coating amount (areal density) of the composite after drying was 20.20 mg / cm 2 on one side, and then pressed with a roll press machine so that the density of the composite layer was 4.15 g / cc to fabricate a positive electrode.

[0042] (Examples 2-7, Comparative Examples 2-8) Positive electrodes of Examples 2-7 and Comparative Examples 6-7 were fabricated in the same procedure as in Experimental Example 1, except that boron nitrides B-I with the physical properties shown in Table 1 were added as inorganic particles. Aluminum diboride (AlB 2 ), magnesium diboride (MgB 2 ), titanium diboride (TiB 2 ), niobium diboride (NbB 2 ), and aluminum hydroxide were added as inorganic particles, and positive electrodes of Comparative Examples 2-5 and 8 were fabricated in the same procedure as in Experimental Example 1.

[0043] (Example 8) LiCoO 2 (D50: 17 μm), acetylene black, polyvinylidene fluoride, and boron nitride A with the physical properties shown in Table 1 as inorganic particles were dispersed and mixed in an N-methyl-2-pyrrolidone solvent at a mass ratio of solid content of 97.2:1.0:1.3:0.5 to prepare a positive electrode composite slurry. Next, after drying, the coating amount (areal density) of the composite after drying was 20.10 mg / cm 2The slurry was coated and dried on one or both sides of the aluminum current collector foil so as to obtain a certain state, and then pressed by a roll press machine so that the density of the composite layer became 4.15 g / cc to fabricate the positive electrode.

[0044] (Example 9) LiCoO 2 (D50: 17 μm), acetylene black, polyvinylidene fluoride, and boron nitride A with the physical properties shown in Table 1 as inorganic particles were dispersed and mixed in an N-methyl-2-pyrrolidone solvent at a mass ratio of solid content of 95.7:1.0:1.3:2.0 to prepare a positive electrode composite slurry. Next, after the slurry was coated and dried on one or both sides of the aluminum current collector foil so that the coated amount (areal density) of the composite after drying became 20.40 mg / cm 2 on one side, it was pressed by a roll press machine so that the density of the composite layer became 4.15 g / cc to fabricate the positive electrode.

[0045] (Examples 10 - 12, Comparative Examples 1, 9 - 10) LiCoO 2 , acetylene black, and polyvinylidene fluoride were dispersed and mixed in an N-methyl-2-pyrrolidone solvent so as to have a ratio of 97.7:1.0:1.3 in terms of mass ratio of dry powder (solid content) without solvent to prepare a positive electrode composite slurry. Next, after the slurry was coated and dried on one or both sides of the aluminum current collector so that the coated amount (areal density) of the composite after drying became 20.0 mg / cm 2 on one side, it was pressed by a roll press machine so that the density of the positive electrode composite layer became 4.15 g / cc to form the positive electrode composite layer. For Examples 10 to 12, Comparative Example 9, and Comparative Example 10, an inorganic particle (boron nitride A, B, D, H, I) described in Table 1 and polyvinylidene fluoride as a binder were dispersed and mixed in an N-methyl-2-pyrrolidone solvent to prepare a composite slurry for the temperature rise suppression layer. The inorganic particles and the binder were mixed so that the mass ratio was X:100 - X (X is the mass ratio of the inorganic particles described in Table 1, that is, the mass% in the temperature rise suppression layer). This composite slurry for the temperature rise suppression layer was applied to the surface of the positive electrode current collector of the positive electrode composite layer on the side opposite to the positive electrode current collector so as to have the thickness shown in Table 1 to form a coating layer, and dried under the conditions of a drying temperature of 100°C and a drying time of 600 seconds to form a temperature rise suppression layer. The content of the inorganic particles in the temperature rise suppression layer in Examples 10 to 12, Comparative Example 9, and Comparative Example 10 was adjusted to be 1 mass% with respect to the entire positive electrode composite layer. The coating thickness of the composite slurry for the temperature rise suppression layer can be measured by the following method. The average thickness of the positive electrode 1 before applying the composite slurry for the temperature rise suppression layer and the average thickness of the positive electrode 1 after application were measured respectively with a constant pressure thickness measuring instrument (manufactured by Teclock). Then, the difference in the average thickness of the positive electrode before and after application was calculated, and this was taken as the coating thickness of the composite slurry for the temperature rise suppression layer. Since this coating thickness does not change in the subsequent drying process, it can be directly used as the thickness of the temperature rise suppression layer.

[0046] <Negative electrode fabrication> (Examples 1-12, Comparative Examples 1-10) Artificial graphite, sodium carboxymethyl cellulose salt (CMC), and styrene-butadiene-based aqueous dispersion were dissolved and dispersed in an aqueous solvent so that the mass ratio was 97.5:1.0:1.5 as dry powders (solid content) without solvents respectively to prepare a negative electrode composite slurry. Next, the negative electrode composite slurry was applied and dried on one or both sides of a copper foil as a negative electrode current collector so that the dried composite coating amount (areal density) became 15.0 mg / cm 2 Then, it was pressed with a roll press so that the density of the negative electrode composite layer became 1.65 g / cc to fabricate a negative electrode.

[0047] <Secondary battery cell fabrication> (Examples 1-12, Comparative Examples 1-10) Through a porous separator made of polypropylene, a plurality of positive and negative electrodes were laminated so that the designed battery capacity became 300 mAh to produce an electrode laminate. At this time, for the positive and negative electrodes arranged inside the electrode laminate, those with composite layers formed on both sides of the current collector were used, and for the positive or negative electrode arranged on the outermost layer, those with the composite layer formed on only one side were used. Specifically, a positive electrode (5 pieces on both sides) with an electrode plate area of 8.5 cm 2 and a negative electrode (4 pieces on both sides and 2 pieces on one side) with an electrode plate area of 10.0 cm 2 were produced. Next, nickel and aluminum lead wires were welded to the negative and positive electrodes of the above-mentioned electrode laminate in an aluminum laminate film, respectively, and then stored in a state where the lead wires were drawn out to the outside, and an electrolytic solution was injected and sealed under reduced pressure to produce a secondary battery cell before initial charging. As the electrolytic solution, a solvent in which ethylene carbonate / dimethyl carbonate / fluoroethylene carbonate was mixed at 15 / 80 / 5 (volume ratio) and 1.3 M LiPF 6 and 1 mass% of vinylene carbonate were dissolved was used.

[0048] <Evaluation of Inorganic Particles> The evaluation of the inorganic particles used in the examples and comparative examples was carried out as follows.

[0049] (Specific Surface Area) The specific surface area of the inorganic particles (BET specific surface area calculated based on the adsorption isotherm measured by adsorbing water vapor) was measured in accordance with JIS K6217-2 using a gas adsorption amount measuring device (BELSORP manufactured by MicrotracBEL Corporation).

[0050] (Evaluation of Particle Size) The particle sizes of the inorganic particles and the positive electrode active material were evaluated with the integrated value 50% of the particle size volume-based particle size distribution obtained by the laser diffraction / scattering method as D50. The D50 (A) of the positive electrode active material and the D50 (B) of the inorganic particles were measured under the following apparatus and conditions, and the ratio B / A of the particle sizes of the inorganic particles and the positive electrode active material was also calculated from the value A and the value B. Measuring apparatus: Laser diffraction / scattering type particle size distribution measuring apparatus MT3300 (manufactured by MicrotracBEL Corporation) Permeability: permeation Shape: non-spherical Circulation speed: 7 Measurement time: 30 seconds Number of repetitions: 3 Refractive index: a. Inorganic particles: 1.65 - 0.00i b. Ethanol solvent: 1.36 - 0.00i c. Positive electrode active material: 2.09 - 0.00i

[0051] (Measurement of the ratio of the major axis to the minor axis of inorganic particles) The average particle size (D50) obtained by the above laser diffraction / scattering method was taken as the major axis of the inorganic particles. After attaching the inorganic particles onto a carbon tape, a scanning electron microscope image of the inorganic particles was obtained using a scanning electron microscope JSM-7800F (manufactured by JEOL Ltd.). Among the inorganic particles included in the obtained scanning electron microscope image, 100 arbitrary particles imaged from a direction perpendicular to the thickness direction were selected and their thicknesses were measured, and the arithmetic mean thereof was taken as the minor axis of the inorganic particles. From the major axis and minor axis calculated by the method described above, the ratio of the major axis to the minor axis (major axis / minor axis), that is, the aspect ratio, was calculated.

[0052] [Evaluation of secondary battery] (Cycle characteristics) The secondary battery cells fabricated in Examples 1 to 12 and Comparative Examples 1 to 10 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 the current reached 0.05 CA. Subsequently, constant current discharging was performed at 0.1 CA down to 3.0 V. Further, in the thermostat at 25°C, constant current charging at 0.2 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.2 CA were carried out for one cycle under the conditions of a charge termination voltage of 4.3 V and a discharge termination voltage of 3.0 V, and the initial discharge capacity was measured. This secondary battery was subjected to a life test of 100 cycles of constant current charging at 0.5 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.5 CA under the conditions of a charge termination voltage of 4.3 V and a discharge termination 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 by dividing it by the initial discharge capacity, the capacity retention rate after 100 cycles was measured.

[0053] (Heating Test) The secondary battery cells fabricated in Examples 1 to 12 and Comparative Examples 1 to 10 were subjected to constant current charging at 0.1 CA of the designed capacity up to 4.42 V in a thermostat at 25°C, followed by constant voltage charging at 4.42 V until the current reached 0.05 CA. Subsequently, constant current discharging was performed at 0.1 CA down to 3.0 V. Further, in the thermostat at 25°C, after performing 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 charge termination voltage of 4.42 V and a discharge termination voltage of 3.0 V, the cell that was again charged at constant current / constant voltage up to 4.42 V was taken as the initial cell. This initial cell was placed in a thermostat heated to 165°C for 1 hour, and when the voltage of the battery dropped below 4.2 V, it was regarded as "abnormal occurrence", and the abnormal occurrence rate of 10 battery tests was evaluated.

[0054] (Nail Piercing Test) In the above-mentioned initial cell, a nail with a diameter of 3 mm was pierced into the center of the cell at a speed of 1 mm / s, and the nail piercing test was carried out. When the external temperature of the battery reached 50°C or higher 5 seconds after the nail was pierced, it was regarded as "abnormal occurrence", and the abnormal occurrence rate of 10 battery tests was evaluated.

[0055] (Overcharge Test) The above initial cells were further subjected to constant current charging at 3CA up to 12V, and when the external battery temperature reached 50°C or higher after 10 minutes of constant voltage charging after reaching 12V, it was regarded as "abnormal occurrence", and the abnormal occurrence rate of 10 battery tests was evaluated.

[0056] (Evaluation of cell resistance (Ω)) It was measured by the alternating current impedance (EIS) method at 25°C in a fully charged initial cell. As the measurement conditions, the frequency range was 100 kHz to 100 mHz, and the applied voltage was 10 mV. Also, as the measurement device using this EIS method, a VMP-3 Potentiostat manufactured by BioLogic was used. The size of the semi-circular arc of the Nyquist plot obtained as a result of the measurement was taken as the cell resistance.

[0057] (Evaluation results) Table 1 shows the types and physical properties of the inorganic particles used in the examples and comparative examples described above. Also, the evaluation results for the secondary battery cells of Examples 1 to 12 and Comparative Examples 1 to 10 are summarized in Table 2.

[0058]

Table 1

[0059]

Table 2

[0060] (Confirmation of heat generation behavior in the coexistence of a charging positive electrode and an electrolytic solution) The initial cells of the fully charged secondary battery cells fabricated in Example 1 and Comparative Example 1 described in Table 1 and Table 2 were disassembled in a glove box, and the positive electrode obtained by washing and drying the positive electrode with a dimethyl carbonate solvent was designated as the "charged positive electrode". 2.0 mg of the "charged positive electrode" and 1.0 mg of the same electrolyte used when fabricating the secondary battery cell were placed in a dedicated sealed container and sealed. Then, using a differential scanning calorimeter (DSC, manufactured by Hitachi High-Technologies Corporation), and in accordance with the provisions of JIS K7121, the temperature was raised at a rate of 5 K / min, and the heat generation behavior was evaluated. The results are shown in Figure 3. The solid line represents Comparative Example 1, and the dashed line represents Example 1, respectively.

[0061] <Evaluation of oxygen capture ability> The initial cells of the fully charged secondary battery cells fabricated in Example 1 and Comparative Example 1 described in Table 1 and Table 2 were disassembled in a glove box, and the positive electrode obtained by washing and drying the positive electrode with a dimethyl carbonate solvent was designated as the "charged positive electrode". 70.0 mg of the "charged positive electrode" was placed in a dedicated alumina pan and put into a thermogravimetric-differential thermal analyzer (TG-DTA, Thermo plus EVO TG8120 manufactured by Rigaku Corporation). The temperature was raised at 10 K / min under a He atmosphere, and the generated oxygen gas (m / z = 32) was analyzed using a mass spectrometer (GC-MS, GCMS QP 2010Plus manufactured by Shimadzu Corporation). The results are shown in Figure 5. The solid line represents Comparative Example 1, and the dashed line represents Example 1, respectively.

[0062] In addition, Figure 4 shows a graph of the cell resistance of the secondary battery cells fabricated in Example 1 and Comparative Example 1. The solid line represents Comparative Example 1, and the dashed line represents Example 1, respectively.

[0063] <Considerations on Examples and Comparative Examples> From the results in Table 2, in Examples 1 to 12, not only Comparative Example 1 which does not contain inorganic particles in the positive electrode, but also Comparative Examples 2 to 7, 9, and 10 in which the D50 and aspect ratio of the inorganic particles containing boron are outside the ranges defined in the present invention, and Comparative Example 8 using inorganic particles not containing boron, it can be seen that even under high-temperature conditions, external impacts such as nail punctures, and conditions where the internal temperature of the battery is likely to rise such as overcharging, the occurrence rate of abnormalities caused by the rise in the internal temperature of the battery could be sufficiently reduced. In FIG. 3, both of the two peaks confirmed in the solid-line graph showing the heat generation behavior of Comparative Example 1 shifted to the high-temperature side in the broken-line graph showing the heat generation behavior of Example 2, and the height of the peaks also decreased, indicating that the rise in the internal temperature of the battery is suppressed in the examples. In non-aqueous electrolyte secondary batteries, it is known that heat generation is accelerated by the decomposition reaction of oxygen generated by the collapse of the active material structure during temperature rise with the electrolyte, conductive agent, etc. From the analysis results of the generated oxygen gas in Example 1 and Comparative Example 1 shown in FIG. 5, it can be seen that the amount of oxygen released in Example 1 is significantly lower than that in Comparative Example 1. Thus, it can be inferred that in Example 1, the inorganic particles capture oxygen, suppressing the heat generation reaction between oxygen and the electrolyte, etc., and suppressing the rise in the internal temperature of the battery. Also, from the results in Table 2 and FIG. 4, in Examples 1 to 12, the internal resistance is 1.6 or less, and it can be seen that there are some examples that are almost the same as Comparative Example 1 which does not contain inorganic particles, or rather lower than Comparative Example 1. Also, from the results in Table 2, it was possible to maintain a value that is sufficiently practical and almost the same as Comparative Example 1, at 90% or more, for the cycle characteristics. From the above experimental results, according to the present invention, by setting the D50 and aspect ratio of the inorganic particles containing nitrogen atoms within a predetermined range, while sufficiently suppressing the rise in the internal temperature of the battery, it was confirmed that an increase in cell resistance and a decrease in cycle characteristics can be suppressed, and these battery performances can be maintained within an appropriate range.

Explanation of Reference Numerals

[0064] 100···Non-aqueous electrolyte secondary battery 1 ···Positive electrode 11 ···Positive electrode current collector 12 ···Positive electrode composite layer 13 ···Temperature rise suppression layer 2 ···Negative electrode 21 ···Negative electrode current collector 22 ···Negative electrode composite layer 3 ···Separator 4 ···Non-aqueous electrolyte 5 ···Container

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery comprising a positive electrode active material and inorganic particles, The inorganic particles contain boron, The inorganic particles have a particle size distribution determined by a laser diffraction / scattering method, and a particle size distribution (D50) of 0.3 μm or more and 8.0 μm or less, the particle size distribution being defined as a cumulative 50% value of the particle size distribution on a volume basis. The ratio of the major axis to the minor axis of the inorganic particles (major axis / minor axis) is 3.0 or more and 30 or less.

2. 2. The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio (B / A) of D50(A), which is an integrated value 50% of a particle size distribution based on a volume of particle diameter in a particle size distribution of the positive electrode active material obtained by a laser diffraction / scattering method, to D50(B), which is an integrated value 50% of a particle size distribution based on a volume of particle diameter in a particle size distribution of the inorganic particles obtained by a laser diffraction / scattering method, is 0.010 or more and 0.8 or less.

3. 2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the inorganic particles contain boron nitride (BN).

4. The inorganic particles are allowed to adsorb nitrogen and the BET specific surface area of ​​the inorganic particles calculated from an adsorption isotherm is 1 m 2 / g or more 50m 2 2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode has a molecular weight of 1 / g or less.

5. A positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, The positive electrode mixture layer contains inorganic particles, 2 . The positive electrode for a non-aqueous electrolyte secondary battery in accordance with claim 1 , wherein the content of the inorganic particles is in the range of 0.1% by mass to 5.0% by mass with respect to 100% by mass of the positive electrode mixture layer.

6. a positive electrode current collector; a positive electrode mixture layer on the positive electrode current collector; and a temperature rise suppression layer on the positive electrode mixture layer on a side opposite to the current collector, the temperature rise suppression layer contains the inorganic particles, 2 . The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1 , wherein a content of the inorganic particles relative to 100% by mass of the temperature rise suppression layer is in the range of 40% by mass or more and 99% by mass or less.

7. 7. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 6, wherein the temperature rise suppression layer has a thickness of 0.1 μm or more and 5 μm or less.

8. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution, 8. A non-aqueous electrolyte secondary battery, wherein the positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery according to claim 1.

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