JP7219783B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present technology relates to non-aqueous electrolyte secondary batteries.

WO2016/024394 discloses an intermediate layer.

WO2016/024394

A positive electrode of a non-aqueous electrolyte secondary battery (hereinafter may be abbreviated as "battery") generally includes a positive electrode base material and a positive electrode active material layer. The positive electrode active material layer can be formed by applying slurry to the surface of the positive electrode substrate and drying the slurry. Conventionally, in order to reduce the interfacial resistance between the positive electrode active material layer and the positive electrode substrate, it has been proposed to form an underlayer between the positive electrode active material layer and the positive electrode substrate. The underlayer corresponds to the intermediate layer of Patent Document 1.

The underlayer contains carbon black (CB). CB is a conductive material. CB is an aggregate of fine particles. The underlayer does not contain a positive electrode active material. The underlayer does not contribute to battery capacity. From the viewpoint of energy density, the underlying layer is required to be formed as thin as possible.

Carbon nanotubes (CNTs) have been investigated as conductive materials. CNTs exhibit higher electrical conductivity than CBs. The interfacial resistance is expected to be reduced by including CNTs in the underlayer.

However, the inclusion of CNTs in the underlayer may rather increase the interfacial resistance between the positive electrode active material layer and the positive electrode substrate. Furthermore, the adhesion between the positive electrode active material layer and the positive electrode base material may deteriorate. This is probably because it is difficult to uniformly disperse fibrous CNTs in a thin underlayer.

An object of the present technology is to reduce interfacial resistance between a positive electrode active material layer and a positive electrode substrate.

The configuration and effects of the present technology will be described below. However, the mechanism of action of this specification includes speculation. The mechanism of action does not limit the scope of this technology.

[1] A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer is arranged on the surface of the positive electrode substrate. The positive electrode active material layer includes a first layer and a second layer. The first layer is interposed between the positive electrode substrate and the second layer. The first layer is in direct contact with the surface of the positive electrode substrate. The positive electrode active material layer contains a positive electrode active material and carbon nanotubes. The first layer contains carbon nanotubes with a mass fraction of 0.4% or more. The second layer does not contain carbon nanotubes. Carbon nanotubes have aspect ratios of 4000 or greater.

The first layer of this technology is, so to speak, the lower layer. The first layer includes an interface between the positive electrode active material layer and the positive electrode substrate. According to the new findings of the present technology, coexistence of CNTs having an aspect ratio of 4000 or more and the positive electrode active material at the interface between the positive electrode active material layer and the positive electrode substrate can improve the dispersibility of CNTs. As a result, a reduction in interfacial resistance is expected. Furthermore, improvement in adhesion between the positive electrode active material layer and the positive electrode substrate is also expected.

The second layer of this technology is, so to speak, the upper layer. The second layer does not contain CNTs. CNTs are currently expensive. If the entire positive electrode active material layer contains CNTs, the manufacturing cost may increase. By locally arranging CNTs at the interface (first layer) with the positive electrode substrate, an increase in manufacturing cost can be reduced.

[2] The first layer may contain, for example, 0.6% or less of carbon nanotubes in mass fraction.

[3] The carbon nanotube may have an aspect ratio of 13333 or less, for example.

FIG. 1 is a schematic diagram showing an example of the configuration of a non-aqueous electrolyte secondary battery according to this embodiment. FIG. 2 is a schematic diagram showing an example of the configuration of the electrode body in this embodiment. FIG. 3 is a schematic cross-sectional view showing an example of the positive electrode in this embodiment.

Hereinafter, embodiments of the present technology (also referred to as “present embodiments” in this specification) will be described. However, the following description does not limit the scope of this technology. For example, references to actions and effects in this specification do not limit the scope of the present technology to a range in which all the actions and effects are exhibited.

As used herein, "comprise, include," "have," and variations thereof (e.g., "be composed of," "encompass, involve," Descriptions of "contain", "carry, support", "hold", etc.] are open-ended. An open-ended form may or may not contain additional elements in addition to the required elements. The statement "consist of" is closed form. The statement "consist essentially of" is in semi-closed form. The semi-closed format may further include additional elements in addition to the essential elements to the extent that the purpose of the present technology is not impaired. For example, elements normally assumed in the field to which the present technology belongs (for example, unavoidable impurities and the like) may be included as additional elements.

As used herein, the expressions “may” and “can” are used in a permissive sense rather than in a mandatory sense “in a must” sense. It is used in the sense of "having the possibility of...".

In this specification, the singular forms (a, an, the) include the plural forms unless otherwise specified. For example, "particle" can include not only "one particle" but also "aggregate of particles (powder, powder, particle group)".

In this specification, numerical ranges such as "0.4% to 0.6%" and "0.4 to 0.6%" include upper and lower limits unless otherwise specified. That is, "0.4% to 0.6%" and "0.4 to 0.6%" indicate numerical ranges of "0.4% to 0.6%". Also, numerical values arbitrarily selected from within the numerical range may be used as the new upper and lower limits. For example, a new numerical range may be set by arbitrarily combining numerical values within the numerical range with numerical values described in other parts of the specification, tables, drawings, and the like.

In this specification, when a compound is expressed by a stoichiometric composition formula such as "LiCoO ₂ ", the stoichiometric composition formula is merely a representative example. Composition ratios may be non-stoichiometric. For example, when lithium cobalt oxide is expressed as “LiCoO ₂ ”, the composition ratio of lithium cobalt oxide is not limited to “Li/Co/O=1/1/2” unless otherwise specified. It may contain Li, Co and O in a compositional ratio. Doping and substitution with trace elements are also permissible.

Geometric terms (eg, "perpendicular," etc.) herein are not to be taken in a strict sense. For example, "perpendicular" may deviate somewhat from "perpendicular" in the strict sense. Geometric terms herein may include, for example, design, work, manufacturing, etc. tolerances, errors, and the like. The dimensional relationships in each drawing may not match the actual dimensional relationships. Dimensional relationships (length, width, thickness, etc.) in each figure may be changed to facilitate understanding of the present technology. Furthermore, some configurations may be omitted.

<Non-aqueous electrolyte secondary battery>
FIG. 1 is a schematic diagram showing an example of the configuration of a non-aqueous electrolyte secondary battery according to this embodiment.
Battery 100 can be used in any application. The battery 100 may be used as a main power source or a power assist power source in, for example, an electric vehicle. A battery module or an assembled battery may be formed by connecting a plurality of batteries 100 . Battery 100 may have a rated capacity of, for example, 1-200 Ah.

Battery 100 includes an exterior body 90 . The exterior body 90 is square (flat rectangular parallelepiped). However, the rectangular shape is an example. The exterior body 90 can have any form. The exterior body 90 may be, for example, cylindrical or pouch-shaped. The exterior body 90 may be made of an Al alloy, for example. The exterior body 90 houses the electrode body 50 and an electrolytic solution (not shown). The exterior body 90 may include, for example, a sealing plate 91 and an exterior can 92 . The sealing plate 91 closes the opening of the outer can 92 . For example, the sealing plate 91 and the outer can 92 may be joined by laser welding or the like.

A positive terminal 81 and a negative terminal 82 are provided on the sealing plate 91 . The sealing plate 91 may be further provided with an inlet (not shown) and a gas exhaust valve (not shown). The electrolytic solution can be injected into the exterior body 90 through the injection port. The electrode body 50 is connected to the positive terminal 81 by the positive collector member 71 . The positive current collecting member 71 may be, for example, an Al plate. The electrode body 50 is connected to the negative electrode terminal 82 by the negative current collecting member 72 . The negative electrode current collecting member 72 may be, for example, a Cu plate or the like.

FIG. 2 is a schematic diagram showing an example of the configuration of the electrode body in this embodiment.
The electrode body 50 is of a wound type. Electrode body 50 includes positive electrode 10 , separator 30 and negative electrode 20 . That is, battery 100 includes positive electrode 10, negative electrode 20, and an electrolyte. The positive electrode 10, the separator 30 and the negative electrode 20 are all belt-shaped sheets. The electrode assembly 50 may include multiple separators 30 . The electrode body 50 is formed by laminating the positive electrode 10, the separator 30 and the negative electrode 20 in this order and winding them in a spiral shape. Either the positive electrode 10 or the negative electrode 20 may be sandwiched between the separators 30 . Both the positive electrode 10 and the negative electrode 20 may be sandwiched between separators 30 . The electrode body 50 may be flattened after winding. Note that the winding type is an example. The electrode body 50 may be, for example, a stacked type.

《Positive electrode》
The positive electrode 10 includes a positive electrode substrate 11 and a positive electrode active material layer 12 . The positive electrode substrate 11 is a conductive sheet. The positive electrode base material 11 may be, for example, an Al alloy foil or the like. The positive electrode substrate 11 may have a thickness of, for example, 10-30 μm. The positive electrode active material layer 12 is arranged on the surface of the positive electrode substrate 11 . The positive electrode active material layer 12 may be arranged, for example, only on one side of the positive electrode substrate 11 . The positive electrode active material layer 12 may be arranged on both front and back surfaces of the positive electrode substrate 11, for example. The positive electrode substrate 11 may be exposed at one end in the width direction of the positive electrode 10 (the X-axis direction in FIG. 2). A positive current collecting member 71 may be bonded to the exposed portion of the positive electrode substrate 11 .

(Positive electrode active material layer)
The positive electrode active material layer 12 may have a thickness of, for example, 10 to 200 μm, a thickness of 50 to 150 μm, or a thickness of 50 to 100 μm. good. The positive electrode active material layer 12 may have a density of, for example, 3.3-3.8 g/cm ³ . The density of the positive electrode active material layer 12 is obtained by dividing the mass of the positive electrode active material layer 12 by the apparent volume of the positive electrode active material layer 12 .

The positive electrode active material layer 12 contains a positive electrode active material and a conductive material. The conductive material contains CNTs. That is, the positive electrode active material layer 12 contains a positive electrode active material and CNTs. The conductive material may further contain CB, for example. The positive electrode active material layer 12 may further contain, for example, a binder.

(Positive electrode active material)
The positive electrode active material is particles. The positive electrode active material can have any size. The positive electrode active material may have, for example, a D50 of 1-30 μm, or a D50 of 5-20 μm. "D50" as used herein is defined as the particle size at which the cumulative frequency from the smaller particle size is 50% in the volume-based particle size distribution. The volume-based particle size distribution can be measured with a laser diffraction particle size distribution analyzer.

The positive electrode active material can reversibly occlude and release lithium ions. The positive electrode active material can have any crystal structure. The positive electrode active material may have, for example, a layered rock salt structure, a spinel structure, an olivine structure, or the like. The positive electrode active material can have any chemical composition. The chemical composition of the positive electrode active material can be measured by, for example, ICP-AES (inductively coupled plasma-atomic emission spectrometry). The positive electrode active material may contain nickel (Ni), for example.

The positive electrode active material may have, for example, a chemical composition represented by the following formula (I).
Li1 _{- aNixMe1 -xO2 (} I)
In the above formula (I), "a" satisfies the relationship "-0.3≤a≤0.3". “x” satisfies the relationship “0.3≦x≦1.0”. "Me" is cobalt (Co), manganese (Mn), aluminum (Al), zirconium (Zr), boron (B), magnesium (Mg), iron (Fe), copper (Cu), zinc (Zn), Tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb), titanium (Ti), At least one selected from the group consisting of silicon (Si), vanadium (V), chromium (Cr) and germanium (Ge).

The positive electrode active material may have, for example, a chemical composition represented by formula (II) below.
Li1 _{- aNixCoyMn1 -xyO2 ( II} )
In the above formula (II), "a" satisfies the relationship "-0.3≤a≤0.3". “x” satisfies the relationship “0.5≦x≦0.8”. “y” satisfies the relationship “0.2≦y≦0.5”.

(carbon nanotube)
CNT is a conductive material. CNT is an aggregate of hollow carbon fibers. CNTs may consist essentially of carbon. CNTs may contain at least one selected from the group consisting of, for example, SWNTs (single-walled carbon nanotubes), DWNTs (double-walled carbon nanotubes), and MWNTs (multi-walled carbon nanotubes).

CNTs have an aspect ratio of 4000 or more. When the CNTs have an aspect ratio of 4000 or more, the dispersibility of the CNTs at the interface between the positive electrode active material layer 12 and the positive electrode substrate 11 can be improved. The CNTs may have an aspect ratio of 13333 or less, for example. CNTs may have an aspect ratio of, for example, 4000-10000, or an aspect ratio of 6000-8000.

Aspect ratio is the ratio of length to diameter. The "aspect ratio" used herein is determined by dividing the average length of CNTs by the average diameter of CNTs. The average length and average diameter can each be the arithmetic mean of measurements on 10 CNTs. The length and diameter of individual CNTs can be measured in SEM (scanning electron microscope) images. The acceleration voltage of the SEM can be on the order of 5 kV. The magnification of the SEM image can be about 50,000 times (1024×1280 pixels).

The CNTs may, for example, have an average length of 1-100 μm, or an average length of 10-50 μm. The average length of CNTs may be greater than, for example, the D50 of the positive electrode active material. Since the average length of CNTs is larger than the D50 of the positive electrode active material, for example, a reduction in interfacial resistance is expected. The CNTs may, for example, have an average diameter of 1-100 nm, or an average diameter of 5-10 nm.

(Carbon black)
CB is a conductive material. CB has electronic conductivity. CB is an aggregate of fine particles. CB is a type of amorphous carbon. CB may consist essentially of carbon. CB may contain, for example, at least one selected from the group consisting of acetylene black, Ketjenblack (registered trademark), furnace black, channel black, and thermal black. Part of the CB may be graphitized.

(Binder)
The binder can contain optional ingredients. The binder is, for example, selected from the group consisting of polyvinylidene fluoride (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), polytetrafluoroethylene (PTFE) and polyacrylic acid (PAA). may contain at least one of

《Multilayer structure》
FIG. 3 is a schematic cross-sectional view showing an example of the positive electrode in this embodiment.
The positive electrode active material layer 12 has a multilayer structure. That is, positive electrode active material layer 12 includes first layer 1 and second layer 2 . The first layer 1 is interposed between the positive electrode substrate 11 and the second layer 2 .

As long as it includes the first layer 1 and the second layer 2, the positive electrode active material layer 12 may include additional layers (not shown). The additional layer has a different composition than the first layer 1 and the second layer 2 . For example, additional layers may be formed between the first layer 1 and the second layer 2 . For example, an additional layer may be formed between the surface of the positive electrode active material layer 12 and the second layer 2 .

The first layer 1 is, so to speak, the lower layer. The first layer 1 includes an interface with the positive electrode substrate 11 . That is, the first layer 1 is in direct contact with the surface of the positive electrode substrate 11 . The second layer 2 is, so to speak, an upper layer. The second layer 2 is arranged closer to the surface side of the positive electrode active material layer 12 than the first layer 1 is. The second layer 2 may be exposed on the surface of the positive electrode active material layer 12 . The second layer 2 may form the surface of the positive electrode active material layer 12 .

The first layer 1 has a different conductive material composition than the second layer 2 . That is, the first layer 1 contains CNTs. The second layer 2 does not contain CNTs. The first layer 1 contains 0.4% or more of CNT in mass fraction. If the mass fraction of CNTs in the first layer 1 is less than 0.4%, interfacial resistance may increase, for example. The first layer 1 contains a positive electrode active material. Coexistence of the CNTs and the positive electrode active material at the interface between the positive electrode active material layer 12 and the positive electrode substrate 11 is expected to reduce interfacial resistance and improve adhesion. For example, the first layer 1 may consist essentially of 0.4-0.6% CNTs, 0.1-5% binder, and the balance positive electrode active material in terms of mass fraction. The mass fraction here is defined as the mass of the entire first layer 1 being 100%.

All the CNTs contained in the positive electrode active material layer 12 may be contained in the first layer 1 , or some of the CNTs may be contained in the first layer 1 .

Since the second layer 2 does not contain CNTs, an increase in manufacturing costs can be reduced. The second layer 2 may contain CB, for example. For example, the second layer 2 may consist essentially of 0.1-5% CB, 0.1-5% binder, and the balance positive electrode active material. The mass fraction here is defined as the mass of the entire second layer 2 being 100%.

The thickness of the first layer 1 may be larger than, for example, D50 of the positive electrode active material. The first layer 1 may for example have a thickness of 10-50 μm, or a thickness of 20-32.5 μm. The second layer 2 may have the same thickness as the first layer 1 or may have a different thickness. For example, when the thickness of the first layer 1 is defined as T1 and the thickness of the second layer 2 is defined as T2, the relationship "0.1≤T1/T2≤1" may be satisfied. However, the relationship “0.1≦T1/T2≦0.5” may be satisfied. Since the first layer 1 is thinner than the second layer 2, for example, a reduction in manufacturing costs is expected.

《Negative electrode》
The negative electrode 20 may include, for example, a negative electrode substrate 21 and a negative electrode active material layer 22 . The negative electrode base material 21 is a conductive sheet. The negative electrode base material 21 may be, for example, a Cu alloy foil or the like. The negative electrode substrate 21 may have a thickness of, for example, 5-30 μm. The negative electrode active material layer 22 may be arranged on the surface of the negative electrode substrate 21 . The negative electrode active material layer 22 may be arranged, for example, only on one side of the negative electrode substrate 21 . The negative electrode active material layer 22 may be arranged, for example, on both front and back surfaces of the negative electrode substrate 21 . The negative electrode substrate 21 may be exposed at one end in the width direction (the X-axis direction in FIG. 2) of the negative electrode 20 . A negative current collecting member 72 may be bonded to the exposed portion of the negative electrode substrate 21 .

The negative electrode active material layer 22 may have a thickness of, for example, 10-200 μm. The negative electrode active material layer 22 contains a negative electrode active material. The negative electrode active material can contain any component. The negative electrode active material contains, _for example, at least one selected from _the group consisting of graphite, soft carbon, hard carbon, Si, SiO, Si-based alloys, Sn, SnO, Sn-based alloys, and _Li4Ti5O12 . may be

The negative electrode active material layer 22 may further contain, for example, a binder in addition to the negative electrode active material. For example, the negative electrode active material layer 22 may substantially consist of a binder of 0.1 to 10% by mass and the balance of the negative electrode active material. The binder can contain optional ingredients. The binder may contain, for example, at least one selected from the group consisting of carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR).

《Separator》
At least part of the separator 30 is interposed between the positive electrode 10 and the negative electrode 20 . The separator 30 separates the positive electrode 10 and the negative electrode 20 . Separator 30 may have a thickness of, for example, 10-30 μm.

Separator 30 is a porous sheet. The separator 30 is permeable to the electrolyte. Separator 30 may have an air permeability of, for example, 100-400 s/100 mL. "Air permeability" in this specification indicates "air resistance" defined in "JIS P 8117:2009". Air permeability is measured by the Gurley test method.

Separator 30 is electrically insulating. The separator 30 may contain, for example, polyolefin-based resin. The separator 30 may be substantially made of polyolefin resin, for example. The polyolefin-based resin may contain, for example, at least one selected from the group consisting of polyethylene (PE) and polypropylene (PP). The separator 30 may have, for example, a single layer structure. The separator 30 may, for example, consist essentially of a PE layer. The separator 30 may have a multilayer structure, for example. The separator 30 may be formed, for example, by laminating a PP layer, a PE layer, and a PP layer in this order. For example, a heat-resistant layer (ceramic particle layer) or the like may be formed on the surface of the separator 30 .

"Electrolytes"
The electrolyte is a liquid electrolyte. The electrolytic solution contains a solvent and a supporting electrolyte. Solvents are aprotic. Solvents may contain optional ingredients. Solvents include, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME ), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL).

The supporting electrolyte is dissolved in the solvent. The supporting electrolyte may contain, for example, at least one selected from the group consisting of LiPF ₆ , LiBF ₄ and LiN(FSO ₂ ) ₂ . The supporting electrolyte may have, for example, a molar concentration of 0.5-2.0 mol/L, or a molar concentration of 0.8-1.2 mol/L.

The electrolytic solution may further contain optional additives in addition to the solvent and the supporting electrolyte. For example, the electrolyte may contain additives in a mass fraction of 0.01 to 5%. The additive is at least selected from the group consisting of, for example, vinylene carbonate (VC), lithium difluorophosphate ( _LiPO2F2 ), lithium fluorosulfonate ( _FSO3Li ), and lithium bisoxalatoborate (LiBOB) _. You may contain 1 type.

As long as the electrolyte is non-aqueous, it may be, for example, a gel electrolyte or a solid electrolyte. A solid electrolyte can also function as a separator. That is, the solid electrolyte layer may separate the positive electrode and the negative electrode.

Hereinafter, examples of the present technology (also referred to as “present examples” in this specification) will be described. However, the following description does not limit the scope of this technology.

<Production of positive electrode>
No. Positive electrodes according to 1 to 7 were produced.

《No. 1>>
The following materials were prepared.
_{Positive electrode} active _material : _{LiNi0.55Co0.20Mn0.25O2}
Conductive material: CB (acetylene black)
CNT (average diameter 7.5 nm, aspect ratio 4000)
Binder: PVdF (weight average molecular weight 1,100,000)
Dispersion medium: N-methyl-2-pyrrolidone Positive electrode substrate: Al foil (thickness 15 μm)

A first slurry was prepared by mixing the positive electrode active material, the CNTs, the binder, and the dispersion medium. The compounding ratio of the solid content was "positive electrode active material/binder/CNT=97.5/0.4/0.6 (mass ratio)".

A second slurry was prepared by mixing the positive electrode active material, CB, binder, and dispersion medium. The compounding ratio of the solid content was "positive electrode active material/binder/CB=97.5/1/1.5 (mass ratio)".

The first slurry was applied to the surface of the positive electrode substrate by a die coater and dried to form a first layer. A second slurry was applied to the surface of the first layer by a die coater and dried to form a second layer. Thus, a positive electrode active material layer was formed. The discharge amount of the second slurry was the same as the discharge amount of the first slurry. The basis weight of the positive electrode active material layer (the total basis weight of the first layer and the second layer) was 220 mg/10 cm ² . Similarly, a positive electrode active material layer was also formed on the back surface of the positive electrode substrate. That is, positive electrode active material layers were formed on both the front and back surfaces of the positive electrode substrate. The positive electrode active material layer was compressed by a rolling mill. The positive electrode active material layer (one side) after compression had a thickness of 65 μm. From the above, No. A positive electrode according to No. 1 was manufactured.

《No. 2 to 6>>
Except that the CNT compounding amount and aspect ratio in the first slurry (first layer) are changed, No. Various positive electrodes were produced (see Table 1 below) in the same manner as the positive electrode according to No. 1.

《No. 7>>
A second slurry was prepared by mixing the positive electrode active material, CB, binder, and dispersion medium. The positive electrode active material layer was formed by applying the second slurry to the surface of the positive electrode substrate with a die coater and drying it. The basis weight of the positive electrode active material layer was 220 mg/10 cm ² . Similarly, a positive electrode active material layer was also formed on the back surface of the positive electrode substrate. That is, positive electrode active material layers were formed on both the front and back surfaces of the positive electrode substrate. The positive electrode active material layer was compressed by a rolling mill. The positive electrode active material layer after compression had a thickness of 65 μm. From the above, No. A positive electrode according to No. 7 was manufactured. No. The positive electrode active material layer according to No. 7 has a single layer structure.

<Evaluation>
《Interface resistance》
The interfacial resistance was evaluated by the area resistivity (unit: Ω·cm ² ) at the interface between the positive electrode active material layer and the positive electrode substrate. The area resistivity was measured by an electrode resistance measurement system "product name RM2610" manufactured by Hioki Electric Co., Ltd. A swelling treatment was applied to the positive electrode active material layer after compression. The positive electrode active material layer after swelling was dried again. After drying the positive electrode active material layer, the area resistivity at the interface between the positive electrode active material layer and the positive electrode substrate was measured. It is considered that the lower the area resistivity, the lower the interfacial resistance.

《Adhesion》
Adhesion was evaluated by 90° peel adhesion (unit: mN/cm). The 90° peeling adhesive strength was measured according to "JIS Z 0237:2009". A test piece was cut from the positive electrode. The planar size of the test piece was "25 mm x 20 mm (width x length)". The positive electrode active material layer was attached to the metal plate with a double-sided tape (width 15 mm). The metal plate was a SUS304 steel plate. A tensile tester pulled the specimen off the metal plate at an angle of 90°. The tension was measured at predetermined intervals during peeling. The arithmetic mean value of tension was taken as cohesion. It is considered that the higher the adhesive strength, the better the adhesion.

<Results>
In this example, it is considered that the interfacial resistance is reduced when the area resistivity is 0.16 Ω·cm ² or less. Adhesion is considered sufficient when the adhesive strength is 115 mN/cm or more.

No. In 1 and 2, the interfacial resistance is reduced. Furthermore, No. In 1 and 2, sufficient adhesion is also obtained. No. In 1 and 2, the CNT has an aspect ratio of 4000 or more. No. In 1 and 2, the first layer (lower layer) contains 0.4% or more of CNT in mass fraction.

This embodiment and this example are illustrative in all respects. This embodiment and this example are not restrictive. The scope of the present technology includes all changes within the meaning and range of equivalence to the description of the claims. For example, it is planned from the beginning that arbitrary configurations are extracted from this embodiment and this example and they are arbitrarily combined.

1 first layer, 2 second layer, 10 positive electrode, 11 positive electrode base material, 12 positive electrode active material layer, 20 negative electrode, 21 negative electrode base material, 22 negative electrode active material layer, 30 separator, 50 electrode body, 71 positive electrode current collecting member , 72 negative electrode collector, 81 positive electrode terminal, 82 negative electrode terminal, 90 exterior body, 91 sealing plate, 92 exterior can, 100 battery (non-aqueous electrolyte secondary battery).

Claims (3)

comprising a positive electrode, a negative electrode and an electrolyte;
The positive electrode includes a positive electrode base material and a positive electrode active material layer,
The positive electrode active material layer is arranged on the surface of the positive electrode base material,
The positive electrode active material layer includes a first layer and a second layer,
The first layer is interposed between the positive electrode substrate and the second layer,
The first layer is in direct contact with the surface of the positive electrode substrate,
The positive electrode active material layer contains a positive electrode active material and carbon nanotubes,
The first layer contains the carbon nanotubes at a mass fraction of 0.4% or more,
the second layer does not contain the carbon nanotube,
The carbon nanotubes have an aspect ratio of 4000 or more,
Non-aqueous electrolyte secondary battery. The first layer contains the carbon nanotubes in a mass fraction of 0.6% or less,
The non-aqueous electrolyte secondary battery according to claim 1. The carbon nanotubes have an aspect ratio of 13333 or less,
The non-aqueous electrolyte secondary battery according to claim 1 or 2.

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