secondary battery with non-aqueous electrolyte

Abstract

A non-aqueous electrolyte secondary battery (100) comprising: a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode current collector (52), a positive electrode active material layer (54) formed on the positive electrode current collector (52), and a heat-resistant layer (56) formed on the positive electrode current collector (52) and adjacent to the positive electrode active material layer (54), the positive electrode active material layer (54) contains a positive electrode active material, the active material of the positive electrode is porous particles in which primary particles are aggregated and at least two or more pores are formed, the positive electrode active material has a dibutyl phthalate oil absorption of 26.5 ml / 100 g or more and 45.0 ml / 100 g or less, the heat-resistant layer (56) contains an inorganic filler and a ratio of a tamped density of the positive electrode active material to a tamped density of the inorganic filler is 1.32 or more and 2.44 or less.

Description

Background of the invention 1. Field of the invention

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery. This application claims foreign priority from Japanese patent application JP 2019-108717 A, filed on June 11, 2019, which is hereby incorporated by reference. 2. Description of the related art

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries have been suitably used for portable power supplies for computers and mobile devices, and for power supplies for driving vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs).

[0003] The positive electrode of a nonaqueous electrolyte secondary battery generally has a structure in which a positive electrode active material layer is provided on a positive electrode current collector. A technology is known in which, in order to reduce a short circuit between the positive electrode and the negative electrode, a heat-resistant layer is provided on a portion of a positive electrode current collector adjacent to the positive electrode active material layer (see, for example, Japanese Patent Application JP 2017-143004 A).Such a positive electrode is manufactured as follows: Generally, a slurry containing the components constituting the positive electrode active material layer (hereinafter also referred to as "positive electrode slurry") is applied to a positive electrode current collector and dried to form a positive electrode active material layer. Then, a slurry containing the components constituting the heat-resistant layer (hereinafter also referred to as "heat-resistant layer slurry") is applied so as to be adjacent to the positive electrode active material layer and dried. JP 2012-74359 A also discloses a two-step process for producing a positive electrode active material layer and then a heat-resistant layer of a battery.JP 2013 - 65 409 A discloses a positive electrode lithium secondary battery in which a positive electrode active material layer is formed on a positive electrode current collector. Summary of the invention

[0004] However, as described above, when the heat-resistant layer is formed after the positive electrode active material layer is formed, as shown in the drawings in Japanese Patent Application JP 2017-143004 A, a tapered portion with a gradually decreasing thickness is formed at the end of the positive electrode active material layer due to the surface tension of the positive electrode slurry. Since the tapered portion does not contribute to the charging and discharging of the nonaqueous electrolyte battery, the longer the tapered portion becomes, the lower the battery capacity becomes.

[0005] Therefore, the inventors attempted to simultaneously apply the positive electrode slurry and the heat-resistant layer slurry to minimize the formation of the tapered portion. As a result, the applied positive electrode slurry and the applied heat-resistant layer slurry are brought adjacent to each other, thus increasing the inclination angle of the tapered portion of the positive electrode active material layer, and preventing the tapered portion from becoming longer. However, a phenomenon of mixing is observed at the interface between the positive electrode active material layer and the heat-resistant layer.In addition, new problems have recently been discovered in that when a positive electrode in which such mixing occurs is used, the active material layer of the positive electrode expands and contracts (expands and contracts) according to the charging and discharging of the non-aqueous electrolyte secondary battery, and the heat-resistant layer peels off due to the stress caused by the expansion and contraction.

[0006] Thus, the object of the present disclosure is to provide a non-aqueous electrolyte secondary battery that can be manufactured while limiting mixing at the interface between the positive electrode active material layer and the heat-resistant layer even when the positive electrode slurry and the heat-resistant layer slurry are applied simultaneously.

[0007] The nonaqueous electrolyte secondary battery disclosed herein comprises a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and a heat-resistant layer formed on the positive electrode current collector and adjacent to the positive electrode active material layer. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material is porous particles in which primary particles are aggregated. The dibutyl phthalate oil absorption of the positive electrode active material is 26.5 ml / 100 g or more and 45.0 ml / 100 g or less. The heat-resistant layer contains an inorganic filler.The ratio of the tamped density of the positive electrode active material to the tamped density of the inorganic filler is 1.32 or more and 2.44 or less.

[0008] With such a structure, a nonaqueous electrolyte secondary battery is provided which can be manufactured while limiting mixing at the interface between the positive electrode active material layer and the heat-resistant layer even when the positive electrode slurry and the heat-resistant layer slurry are applied simultaneously.

[0009] According to a desirable aspect of the non-aqueous electrolyte secondary battery disclosed herein, the positive electrode active material has a dibutyl phthalate oil absorption of 31.8 ml / 100 g or more and 45.0 ml / 100 g or less.

[0010] With such a structure, the non-aqueous electrolyte secondary battery can be manufactured with high yield because a positive electrode slurry with suitable viscosity and favorable coatability can be easily prepared. Short description of the drawings Fig. 1 is a cross-sectional view schematically showing the internal structure of a lithium-ion secondary battery according to an embodiment of the present disclosure; Fig. 2 is a schematic view showing the structure of a wound electrode body of a lithium ion secondary battery according to an embodiment of the present disclosure; Fig. 3 is a schematic cross-sectional view of a positive electrode of a lithium-ion secondary battery according to an embodiment of the present disclosure; and Fig. 4 is an enlarged view of the interior of the rectangular frame A in Fig.3. Description of the preferred embodiments

[0011] Embodiments of the present disclosure are described below. Here, components other than those specifically mentioned in this description that are required for implementing the present disclosure (for example, general configurations and manufacturing processes of a non-aqueous electrolyte secondary battery that do not characterize the present disclosure) may be recognized by a person skilled in the art as design elements based on the related art. The present disclosure can be implemented based on the contents disclosed in this description and general technical knowledge in the field.

[0012] Here, “secondary battery” in this specification refers to an energy storage device in general that can be repeatedly charged and discharged, and is a term that includes a so-called storage battery and a storage element such as an electric double-layer capacitor.

[0013] Furthermore, “lithium ion secondary battery” in this specification refers to a secondary battery that uses lithium ions as charge carriers and realizes charging and discharging according to the movement of charges involving lithium ions between positive and negative electrodes.

[0014] Furthermore, “slurry” in this specification refers to a liquid mixture in which at least a part of a solid content is dispersed in a solvent, and includes a so-called slurry, paste and ink.

[0015] Although the present disclosure will be described in detail below using a flat rectangular lithium ion secondary battery as an example, the present disclosure is not intended to be limited to what is described in these embodiments.

[0016] The Fig.The lithium-ion secondary battery 100 shown in FIG. 1 is a sealed battery composed of a flat-wound electrode body 20 and a nonaqueous electrolyte 80 housed in a flat rectangular battery case (i.e., an outer container) 30. A positive electrode terminal 42 and a negative electrode terminal 44 for external connection and a thin safety valve 36 configured to release internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or higher are provided in the battery case 30. Additionally, an injection port (not shown) through which the nonaqueous electrolyte 80 is injected is provided in the battery case 30. The positive electrode terminal 42 is electrically connected to a positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector plate 44a.Regarding the material of the battery case 30, for example, a lightweight metal material with favorable thermal conductivity such as aluminum is used.

[0017] As in Fig. 1 and Fig. 2, the wound electrode body 20 has a shape in which an elongated positive electrode sheet 50 and an elongated negative electrode sheet 60 are superimposed on each other with two elongated separator sheets 70 arranged therebetween and wound in the longitudinal direction.

[0018] As in Fig. 2 and Fig.3, the positive electrode sheet 50 includes an elongated positive electrode current collector 52 and a positive electrode active material layer 54 formed on the positive electrode current collector 52. In the illustrated example, the positive electrode active material layer 54 is provided on both surfaces of the positive electrode current collector 52, but may be provided on one surface. In addition, the positive electrode current collector 52 has a portion (positive electrode current collector exposed portion) 52a in which the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed. As shown in Fig.As shown in Figure 2, the exposed portion of the positive electrode current collector 52a is formed to protrude outward from one end of the wound electrode body 20 in the direction of the winding axis (i.e., in the sheet width direction, which is orthogonal to the longitudinal direction). The positive electrode current collector plate 42a is connected to the exposed portion of the positive electrode current collector 52a.

[0019] Furthermore, the positive electrode sheet 50 includes a heat-resistant layer 56 formed on the positive electrode current collector 52. The heat-resistant layer 56 is disposed adjacent to the positive electrode active material layer 54 and is positioned between the positive electrode active material layer 54 and the exposed portion of the positive electrode current collector 52a in a plane direction of the positive electrode sheet 50. In other words, the heat-resistant layer 56 is positioned at the boundary between the positive electrode active material layer 54 and the exposed portion of the positive electrode current collector 52a. In the illustrated example, the heat-resistant layer 56 is provided on both surfaces of the positive electrode current collector 52, but it may be provided on one surface.

[0020] In the present embodiment, as shown in Fig.4, the end of the positive electrode active material layer 54 is inclined. The inclination angle at the end of the positive electrode active material layer 54 can be expressed as an angle θ formed by the boundary line 58 between the positive electrode active material layer 54 and the heat-resistant layer 56 and the positive electrode current collector 52 on the positive electrode active material layer 54 side. In order to increase the capacity of the lithium-ion secondary battery 100, the angle θ is desirably 45 degrees or more, more desirably 50 degrees or more, and even more desirably 55 degrees or more. In addition, the angle θ is desirably less than 90 degrees, more desirably 85 degrees or less, and even more desirably 75 degrees or less. Here, when the boundary line 58 is not a straight line, the angle θ can be obtained by a straight line approximation.

[0021] Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include an aluminum foil.

[0022] The positive electrode active material layer 54 contains a positive electrode active material.

[0023] Examples of the positive electrode active material include lithium transition metal oxides (for example, LiNi 1l3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4 and LiNi 0,5 Mn 1,5 O4) and lithium transition metal phosphate compounds (for example LiFePO4).

[0024] In the present embodiment, the positive electrode active material is porous particles in which primary particles are aggregated. That is, the positive electrode active material is in the form of secondary particles in which primary particles are aggregated, and the secondary particles have a porous structure. The porous structure means a structure with at least two or more pores in the secondary particle. In the porous structure, the pores desirably have a 3D network structure.

[0025] The average particle size of the secondary particles of the positive electrode active material is not specifically limited and is desirably 0.1 μm or more, more desirably 2 μm or more, and even more desirably 5 μm or more. Furthermore, the average particle size of the secondary particles of the positive electrode active material is desirably 20 μm or less, and more desirably 15 μm or less.

[0026] The “average particle size” in this description refers to a particle size (D 50 , also called mean diameter), which corresponds to a cumulative abundance of 50 vol% from the fine particle end with small particle size in a volume-based particle size distribution based on a general laser diffraction and light scattering method.

[0027] The tamped density of the positive electrode active material is not specifically limited and is desirably 0.75 g / ml or more, more desirably 0.9 g / ml or more, and even more desirably 1.0 g / ml or more. Furthermore, the tamped density of the positive electrode active material is desirably 1.66 g / ml or less, and more desirably 1.6 g / ml or less.

[0028] Here, the tapped density of the positive electrode active material can be measured according to a method defined in JIS K 1469:2003 using a general tapped density measuring device.

[0029] The content of the positive electrode active material in the positive electrode active material layer 54 is not specifically limited and is desirably 82 mass% or more and 98 mass% or less, and more desirably 85 mass% or more and 95 mass% or less.

[0030] The positive electrode active material layer 54 may contain components other than the positive electrode active material, such as trilithium phosphate, a conductive material, a binder, and the like. For the conductive material, for example, carbon black such as acetylene black AB and other carbon materials (e.g., graphite) may be suitably used. For the binder, for example, polyvinylidene fluoride (PVdF) or the like may be used.

[0031] The content of trilithium phosphate in the active material layer of the positive electrode 54 is not specifically limited and is desirably 1 mass% or more and 15 mass% or less, and more desirably 2 mass% or more and 12 mass% or less.

[0032] The content of the conductive material in the active material layer of the positive electrode 54 is not specifically limited and is desirably 1 mass% or more and 15 mass% or less, and more desirably 3 mass% or more and 13 mass% or less.

[0033] The content of the binder in the active material layer of the positive electrode 54 is not specifically limited and is desirably 1 mass% or more and 15 mass% or less, and more desirably 1.5 mass% or more and 10 mass% or less.

[0034] The heat-resistant layer 56 contains an inorganic filler. Typically, the heat-resistant layer 56 also contains a binder.

[0035] The shape of the inorganic filler is not specifically limited and may be a particle shape, a fiber shape, a plate shape, a flake shape, or the like.

[0036] Regarding the inorganic filler, those with insulating properties and heat resistance are used. Specific examples include inorganic oxides such as alumina (Al2O3), magnesium oxide (MgO), silicon dioxide (SiO2), and titanium dioxide (TiO2); nitrides such as aluminum nitride and silicon nitride; metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide; clay minerals such as mica, talc, boehmite, zeolite, apatite, and kaolin; and glass fibers. These can be used alone, or two or more of them can be used in combination. Among them, alumina, boehmite, and magnesium oxide are desirable.

[0037] The average particle size of the inorganic filler is not specifically limited and is desirably 0.1 µm or more, and more desirably 0.5 µm or more. Furthermore, the average particle size of the inorganic filler is desirably 10 µm or less, and more desirably 5 µm or less.

[0038] The tapped density of the inorganic filler is not specifically limited and is desirably 0.4 g / ml or more, and more desirably 0.57 g / ml or more. Furthermore, the tapped density of the inorganic filler is desirably 1.2 g / ml or less, and more desirably 1.0 g / ml or less.

[0039] Here, the tapped density of the inorganic filler can be measured by a method defined in JIS K 1469:2003 using a general tapped density measuring device.

[0040] Examples of the binders include an acrylic binder, styrene-butadiene rubber (SBR), and a polyolefin binder, and a fluoropolymer such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE) may also be used.

[0041] The content of the binder in the heat-resistant layer 56 is not specifically limited and is, for example, 1 mass% or more and 30 mass% or less, and desirably 3 mass% or more and 25 mass% or less.

[0042] The mixing of the positive electrode active material layer 54 and the heat-resistant layer 56 is caused by mixing a positive electrode slurry and a heat-resistant layer slurry when the positive electrode slurry and the heat-resistant layer slurry are applied simultaneously. To limit such mixing, it is necessary to control a gap between positive electrode active materials in the applied positive electrode slurry and a gap between inorganic fillers in the applied heat-resistant layer slurry.

[0043] The inventors considered using a tapped density as an index for these spaces. However, in porous particles in which primary particles are aggregated, voids within the porous particles can also affect the tapped density. For example, the tapped density of a positive electrode active material with a small pore volume in porous particles and a large inter-particle spacing can be the same as the tapped density of a positive electrode active material with a large pore volume in porous particles and a small inter-particle spacing. Therefore, the inventors considered using DBP oil absorption as an index for voids in porous particles.

[0044] As a result of extensive studies, the inventors have found, as shown in the examples described below, that when the DBP oil absorption of the positive electrode active material is within a certain range and a ratio of the tapped density of the positive electrode active material to the tapped density of the inorganic filler is within a certain range, it is possible to limit mixing at an interface between the positive electrode active material layer and the heat-resistant layer when the positive electrode slurry and the heat-resistant layer slurry are applied simultaneously.

[0045] Here, in the present embodiment, the DBP oil absorption of the positive electrode active material is 26.5 ml / 100 g or more and 45.0 ml / 100 g or less.

[0046] In addition, the ratio of the tamped density of the positive electrode active material to the tamped density of the inorganic filler (tamped density of the positive electrode active material / tamped density of the inorganic filler) is 1.32 or more and 2.44 or less.

[0047] The DBP oil absorption of the positive electrode active material is desirably 31.8 ml / 100 g or more and 45.0 ml / 100 g or less, and more desirably 31.8 ml / 100 g or more and 39.4 ml / 100 g or less, because a positive electrode slurry with a suitable viscosity and favorable coatability is easy to prepare.

[0048] Here, the DBP oil absorption of the positive electrode active material can be measured using dibutyl phthalate (DBP) as a reagent liquid and according to a method defined in JIS K 6217-4:2008.

[0049] As in Fig.2, the negative electrode sheet 60 includes an elongated negative electrode current collector 62 and a negative electrode active material layer 64 formed on the negative electrode current collector 62. In the illustrated example, the negative electrode active material layer 64 is provided on both surfaces of the negative electrode current collector 62, but may be provided on one surface. Moreover, the negative electrode current collector 62 has a part (negative electrode current collector exposed part) 62a in which the negative electrode current collector 62 is exposed without the negative electrode active material layer 64 being formed. The exposed part of the negative electrode current collector 62a is formed so as to extend from the other end of the wound electrode body 20 toward the axis of the winding (ie,a direction orthogonal to the longitudinal direction of the sheet width). The negative electrode current collector plate 44a is connected to the exposed part of the negative electrode current collector 62a.

[0050] Examples of the negative electrode current collector 62 constituting the negative electrode sheet 60 include a copper foil. The negative electrode active material layer 64 contains a negative electrode active material. Regarding the negative electrode active material, for example, carbon materials such as graphite, hard carbon, and soft carbon can be used. The negative electrode active material layer 64 may contain components other than the active material, such as a binder, a thickener, and the like. Regarding the binder, for example, styrene-butadiene rubber (SBR) or the like can be used. Regarding the thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.

[0051] Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, or the like. Such a porous sheet may have a single-layer structure or a laminated structure in which two or more layers are laminated (for example, a three-layer structure in which a PP layer is laminated to both surfaces of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0052] In the present embodiment, a non-aqueous electrolyte solution is used for the non-aqueous electrolyte 80. Typically, the non-aqueous electrolyte 80 contains a non-aqueous solvent and a conductive salt.

[0053] Regarding the non-aqueous solvent, organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones used for an electrolytic solution of a general lithium-ion secondary battery can be used without particular limitation. Among them, carbonates are desirable, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). These non-aqueous solvents can be used alone, or two or more of them can be used in combination as appropriate.

[0054] Regarding the conducting salt, lithium salts such as LiPF6, LiBF4, and LiClO4 (preferably LiPF6) can be suitably used. The concentration of the conducting salt is desirably 0.7 mol / L or more and 1.3 mol / L or less.

[0055] Here, the non-aqueous electrolyte 80 may contain various additives, for example, a gas generating agent such as biphenyl (BP) and cyclohexylbenzene (CHB); a film former such as oxalato complex compounds containing boron atoms and / or phosphorus atoms and vinylene carbonate (VC); a dispersant; a thickener, and the like, as long as the effects of the present disclosure are not substantially impaired.

[0056] The lithium-ion secondary battery 100 constructed as described above can be manufactured while limiting mixing at the interface between the positive electrode active material layer and the heat-resistant layer, even if a positive electrode slurry and a heat-resistant layer slurry are simultaneously coated. In the lithium-ion secondary battery 100 manufactured while limiting mixing of the positive electrode active material layer and the heat-resistant layer, even if simultaneous coating is performed, the decrease in capacity due to the tapered part at the end of the positive electrode active material layer and the like is limited, and furthermore, peeling of the heat-resistant layer due to stress or wear is prevented.Stresses caused by expansion and contraction of the positive electrode active material layer when the non-aqueous electrolyte secondary battery is charged and discharged.

[0057] The method for manufacturing the lithium-ion secondary battery 100 is not particularly limited. A suitable manufacturing method includes a step of simultaneously coating a positive electrode slurry containing a positive electrode active material and a heat-resistant layer slurry containing an inorganic filler on the positive electrode current collector 52 so that the positive electrode slurry and the heat-resistant layer slurry are adjacent to each other (simultaneous coating step), a step of obtaining a positive electrode by drying the applied positive electrode slurry and heat-resistant layer slurry (positive electrode manufacturing step), and a step of assembling the lithium-ion secondary battery 100 using the positive electrode (battery assembly step).In the manufacturing process, the positive electrode active material is porous particles in which primary particles are aggregated. Furthermore, the dibutyl phthalate oil absorption of the positive electrode active material is 26.5 ml / 100 g or more and 45.0 ml / 100 g or less. Furthermore, the ratio of the tapped density of the positive electrode active material to the tapped density of the inorganic filler is 1.32 or more and 2.44 or less.

[0058] The positive electrode slurry contains components that form the positive electrode active material layer 54 and a solvent. The heat-resistant layer slurry contains components that form the heat-resistant layer 56 and a solvent. The positive electrode slurry and the heat-resistant layer slurry can be prepared according to known methods, and the concentrations of these solid contents are desirably 45 mass% or more, and more desirably 50 mass% or more and 80 mass% or less, respectively. The viscosities of the positive electrode slurry and the heat-resistant layer slurry are desirably more than 2,000 mPa s and less than 15,000 mPa s.

[0059] In the simultaneous coating step, it is desirable to use a die coater. Using a die coater allows these slurries to be applied simultaneously and easily from the same die head, so that the positive electrode slurry and the heat-resistant layer slurry are adjacent to each other.

[0060] The other operations of the simultaneous coating step and other steps can be carried out according to a known method.

[0061] The lithium-ion secondary battery 100 can be used for various applications. Examples of suitable applications include motive power sources mounted in vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). The lithium-ion secondary battery 100 can also be used in the form of a battery pack, in which multiple cells are typically connected in series and / or parallel.

[0062] The rectangular lithium-ion secondary battery 100 including the flat-wound electrode body 20 is described here as an example. However, the lithium-ion secondary battery may be configured as a lithium-ion secondary battery including a stack-type electrode body. In addition, the lithium-ion secondary battery may be configured as a cylindrical lithium-ion secondary battery, a laminate-type lithium-ion secondary battery, or the like. Furthermore, the technology disclosed herein can be applied to nonaqueous electrolyte secondary batteries other than lithium-ion secondary batteries.

[0063] While examples related to the present disclosure are described below, the present disclosure is not intended to be limited to those shown in the examples. Manufacturing a lithium-ion secondary battery

[0064] Using a dispersing machine, acetylene black (AB) as a conductive material, polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidone (NMP) were mixed to obtain a slurry. A mixed powder of LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (LNCM) as a positive electrode active material and Li3PO4 were added to the slurry, and the solids were then uniformly dispersed therein to prepare a positive electrode slurry. Note that the positive electrode slurry was prepared such that LNCM: Li3PO4: AB: PVdF = 87:3:8:2 (mass ratio). In this case, LNCMs with DBP oil absorption and tapped density shown in Table 1 were used.

[0065] Using a dispersing machine, boehmite as an inorganic filler, PVdF as a binder, and NMP were mixed to prepare a heat-resistant layer slurry. In this case, boehmite was used with a tapped density shown in Table 1.

[0066] The positive electrode slurry and the heat-resistant layer slurry were simultaneously applied from the same die head to both surfaces of an elongated aluminum foil strip using a die coater and then dried to prepare a positive electrode sheet. The application was performed so that the heat-resistant layer slurry was adjacent to the positive electrode slurry.

[0067] In this way, the positive electrode sheet was coated with the Fig. 3 shown form.

[0068] Natural graphite (C) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed with deionized water in a mass ratio of C:SBR:CMC = 98:1:1 to prepare a negative electrode slurry. The negative electrode slurry was applied to both surfaces of an elongated copper foil in tape form, dried, and then pressed to prepare a negative electrode sheet.

[0069] A porous polyolefin sheet with a three-layer structure of PP / PE / PP was manufactured as a separator.

[0070] The prepared positive electrode sheet and the prepared negative electrode sheet and the two prepared separator sheets were laminated, wound, and then pressed into a flat shape from a lateral direction to prepare a flat wound electrode body.

[0071] Next, a positive electrode terminal and a negative electrode terminal were connected to the wound electrode body and housed in a rectangular battery case having an injection port for electrolyte solution.

[0072] Subsequently, a non-aqueous electrolyte was injected through the injection port of the battery case, and the injection port was hermetically sealed. Regarding the non-aqueous electrolyte, an electrolyte was used in which LiPF6 was dissolved as a conductive salt at a concentration of 1.1 mol / L in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) with a volume ratio of EC:EMC:DMC = 3:4:3.

[0073] In this way, lithium ion secondary batteries of Examples and Comparative Examples were manufactured. Evaluation of the mixing of the positive electrode active material layer and the heat-resistant layer

[0074] Using an electron probe microanalyzer (EPMA), cross-sectional images of the generated positive electrodes were obtained, and elemental mapping was performed on the images. Based on the elemental mapping results, it was determined whether the positive electrode active material layer and the heat-resistant layer were intermingled. The results are shown in Table 1. Evaluation of slurry viscosity

[0075] The viscosity of the prepared positive electrode slurry was measured using a B-type viscometer under a rotational speed of 20 rpm. The results are shown in Table 1. Table 1 DBP oil absorption of the positive electrode active material (ml / 100 g) Tapped density Tamped density ratio of active material of the positive electrode / inorganic filler Viscosity of the slurry (mPa s) Mixing at the interface Positive electrode active material (g / ml) Inorganic filler (g / ml) Side of the active material layer of the positive electrode Side of the heat-resistant layer Example 1 31,8 1,1 0,68 1,62 7005 No No Example 2 35,7 1,56 0,68 2,29 7977 No No Example 3 39,4 1,37 0,68 2,01 9477 No No Example 4 39,4 1,37 0,78 1,76 9004 No No Example 5 45 0,81 0,57 1,42 12927 No No Example 6 35,7 1,56 1 1,56 8975 No No Example 7 40,1 0,75 0,57 1,32 11282 No No Example 8 26,5 1,66 0,68 2,44 1770 No No Comparison example 1 40,1 0,75 0,68 1,10 5545 Yes No Comparison example 2 47 0,73 0,68 1,07 15657 Yes No Comparison example 3 40,1 0,75 1 0,75 8824 Yes No Comparison example 4 30,3 0,7 0,68 1,03 6730 Yes No Comparison example 5 22,2 2,01 0,68 2,96 1620 No Yes Comparison example 6 29,1 1,88 0,68 2,76 3630 No Yes Comparison example 7 31,9 1,67 0,68 2,46 5939 No Yes Comparison example 8 37,5 1,95 0,68 2,87 11203 No Yes Comparison example 9 35,7 1,56 0,57 2,74 10485 No Yes

[0076] Based on the results of Table 1, it is clear that when the positive electrode active material was porous particles in which primary particles were aggregated, the dibutyl phthalate oil absorption of the positive electrode active material was 26.5 ml / 100 g or more and 45.0 ml / 100 g or less, and a ratio of the tapped density of the positive electrode active material to the tapped density of the inorganic filler was 1.32 or more and 2.44 or less, whereby mixing at the interface between the positive electrode active material layer and the heat-resistant layer was limited.

[0077] Based on the above results, it is clear that according to the nonaqueous electrolyte secondary battery disclosed herein, it is possible to provide a nonaqueous electrolyte secondary battery that can be produced while limiting mixing at the interface between the positive electrode active material layer and the heat-resistant layer even when a positive electrode slurry and a heat-resistant layer slurry are applied simultaneously.

[0078] While specific examples of the present disclosure have been described in detail above, these are only examples and do not limit the scope of the claims. The technology described in the claims encompasses various modifications and variations of the specific examples exemplified above.

Claims

[1] A non-aqueous electrolyte secondary battery (100) comprising: a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode current collector (52), a positive electrode active material layer (54) formed on the positive electrode current collector (52), and a heat-resistant layer (56) formed on the positive electrode current collector (52) and adjacent to the positive electrode active material layer (54), the positive electrode active material layer (54) contains a positive electrode active material, the active material of the positive electrode is porous particles in which primary particles are aggregated and at least two or more pores are formed, the positive electrode active material has a dibutyl phthalate oil absorption of 26.5 ml / 100 g or more and 45.0 ml / 100 g or less, the heat-resistant layer (56) contains an inorganic filler and a ratio of a tamped density of the positive electrode active material to a tamped density of the inorganic filler is 1.32 or more and 2.44 or less. [2] The non-aqueous electrolyte secondary battery (100) according to claim 1, wherein the positive electrode active material has a dibutyl phthalate oil absorption of 31.8 ml / 100 g or more and 45.0 ml / 100 g or less.

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