Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery can achieve both high capacity and good quick charge cycle characteristics. A negative electrode mixture layer of the non-aqueous electrolyte secondary battery includes a first negative electrode mixture layer facing a negative electrode current collector and a second negative electrode mixture layer facing a positive electrode. Each of the first negative electrode mixture layer and the second negative electrode mixture layer contains a negative electrode active material, a first CMC having an etherification degree of 0.7 or less, a second CMC having an etherification degree of more than 0.7 but not more than 1.8, the content of the first CMC in the first negative electrode mixture layer is 30 mass% or more with respect to the total mass of the CMC included in the first negative electrode mixture layer, the content of the second CMC in the second negative electrode mixture layer is 40 mass% or more with respect to the total mass of the CMC included in the second negative electrode mixture layer, and the mass per unit area in one surface of the negative electrode mixture layer is 100-250 g / m2.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion batteries have been widely used in applications requiring high capacity, such as automotive applications and power storage applications. Furthermore, non-aqueous electrolyte secondary batteries are required to have various performance characteristics, such as rapid charging performance and good cycle characteristics. Because electrodes, which are key components of batteries, have a significant impact on these performance characteristics, many studies have been conducted on electrodes. For example, Patent Document 1 discloses a technology in which, for the purpose of improving liquid absorption and adhesion, a negative electrode mixture layer has a two-layer structure, in which the layer on the current collector side contains CMC with a relatively low degree of etherification, and the layer on the surface side contains CMC with a relatively high degree of etherification.

[0003] JP 2013-45558 A

[0004] In recent years, increasing the thickness of the negative electrode mixture layer has been considered from the viewpoint of increasing capacity. However, increasing the thickness tends to reduce the permeability of the non-aqueous electrolyte into the negative electrode mixture layer, resulting in a decrease in rapid charge cycle performance. The technology disclosed in Patent Document 1 does not consider increasing the thickness of the negative electrode mixture layer, and there is still room for improvement.

[0005] The non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the surface of the negative electrode current collector. The negative electrode mixture layer includes a first negative electrode mixture layer facing the negative electrode current collector and a second negative electrode mixture layer facing the positive electrode. The first negative electrode mixture layer and the second negative electrode mixture layer each contain a negative electrode active material, a first carboxymethyl cellulose having a degree of etherification of 0.7 or less, and a second carboxymethyl cellulose having a degree of etherification of more than 0.7 and 1.8 or less. The content of the first carboxymethyl cellulose in the first negative electrode mixture layer is 30% by mass or more relative to the total mass of carboxymethyl cellulose contained in the first negative electrode mixture layer, the content of the second carboxymethyl cellulose in the second negative electrode mixture layer is 40% by mass or more relative to the total mass of carboxymethyl cellulose contained in the second negative electrode mixture layer, and the mass per unit area of ​​one side of the negative electrode mixture layer is 100 g / m ２More than 250g / m ２ The present invention is characterized by the following:

[0006] According to the nonaqueous electrolyte secondary battery according to the present disclosure, the capacity retention rate during rapid charge cycles can be improved, and therefore both high capacity and good rapid charge cycle characteristics can be achieved.

[0007] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention;

[0008] As described above, it is an important challenge to increase the capacity of a battery by increasing its thickness while improving the capacity retention rate during rapid charging cycles. In particular, for automotive batteries, high capacity and minimal capacity loss during repeated rapid charging, i.e., excellent rapid charging cycle characteristics, are strongly desired. By forming a negative electrode mixture layer into a two-layer structure, in which the layer on the current collector side contains a CMC with a relatively low degree of etherification and the layer on the surface side contains a CMC with a relatively high degree of etherification, it is possible to improve the liquid absorption and adhesion to a certain extent. However, the inventors' investigations have revealed that in a thick negative electrode mixture layer, rapid charging cycle characteristics may be deteriorated even when the above-mentioned configuration is used.

[0009] The inventors further conducted extensive research into the above-mentioned problems, and found that the mass per unit area on one side was 100 g / m ２ More than 250g / m ２ The inventors have found that by thickening the anode mixture layer as described below, the anode mixture layer includes a first anode mixture layer facing the anode current collector and a second anode mixture layer facing the positive electrode, and the contents of the first carboxymethyl cellulose in the first anode mixture layer and the second carboxymethyl cellulose in the second anode mixture layer are set within predetermined ranges, it is possible to uniquely achieve both high capacity and good rapid charging cycle characteristics.

[0010] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the respective components of the multiple embodiments and variations described below are included within the scope of the present disclosure.

[0011] In the following, a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical outer can 16 with a bottom is exemplified as a nonaqueous electrolyte secondary battery, but the outer can of the battery is not limited to a cylindrical outer can. The nonaqueous electrolyte secondary battery according to the present disclosure may be, for example, a prismatic battery having a prismatic outer can, a coin battery having a coin-shaped outer can, or a laminate battery having an outer can made of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode assembly is not limited to a wound type, and may be a laminated type electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0012] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 is a cylindrical battery including an electrode assembly 14, a nonaqueous electrolyte, a cylindrical outer can 16 with a bottom that accommodates the electrode assembly 14 and the nonaqueous electrolyte, and a sealing member 17 that closes the opening of the outer can 16. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 has a groove 22 formed in its sidewall, and the sealing member 17 is supported by the groove 22 and closes the opening of the outer can 16. Hereinafter, for convenience of explanation, the sealing member 17 side of the nonaqueous electrolyte secondary battery 10 is referred to as the top, and the bottom side of the outer can 16 is referred to as the bottom.

[0013] The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0014] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal and width directions. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11. The electrode assembly 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0015] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0016] The negative electrode 12 is disposed on the outer peripheral surface of the electrode body 14, and an exposed portion may be provided in which the surface of the negative electrode current collector (see FIG. 2 described later) constituting the negative electrode 12 is exposed. In this case, the exposed portion may be in contact with the inner peripheral surface of the outer can 16, and the negative electrode 12 and the outer can 16 may be electrically connected.

[0017] A gasket 28 is provided between the outer can 16 and the sealing body 17, ensuring airtightness inside the battery and preventing electrical contact between the outer can 16 and the sealing body 17. The outer can 16 has a groove 22 formed on its side surface that protrudes inward and supports the sealing body 17. The groove 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the outer can 16 by the groove 22 and the open end of the outer can 16 that is crimped to the sealing body 17.

[0018] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0019] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode assembly 14, with the negative electrode 12 being particularly described in detail below.

[0020] [Positive Electrode] The positive electrode 11 includes a positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector. The positive electrode current collector can be a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film with such a metal disposed on the surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode current collector except for the portion where the positive electrode lead 20 is connected. A protective layer containing inorganic particles and a binder may be provided between the positive electrode current collector and the positive electrode mixture layer, or on the positive electrode mixture layer. The positive electrode 11 can be fabricated, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder to the positive electrode current collector, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode current collector.

[0021] The positive electrode active material uses a lithium-containing composite oxide containing transition metal elements such as Ni, Co, and Mn. Examples of metal elements contained in the lithium-containing composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. Examples of suitable composite oxides include lithium-containing composite oxides containing Ni, Co, and Mn, and lithium-containing composite oxides containing Ni, Co, and Al. One type of lithium-containing composite oxide may be used alone, or multiple types may be used in combination.

[0022] The lithium-containing composite oxide has, for example, a layered rock salt structure. Examples of the layered rock salt structure include a layered rock salt structure belonging to the space group R-3m and a layered rock salt structure belonging to the space group C2 / m. Among these, a layered rock salt structure belonging to the space group R-3m is preferred from the viewpoints of increasing capacity and stability of the crystal structure.

[0023] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, conductive whiskers, etc. One type of conductive agent may be used alone, or multiple types may be used in combination.

[0024] Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. One type of binder may be used alone, or multiple types may be used in combination.

[0025] [Negative Electrode] Fig. 2 is a cross-sectional view of the negative electrode 12 cut in the longitudinal direction. As shown in Fig. 2, the negative electrode 12 has a negative electrode current collector 30 and a negative electrode mixture layer 33 disposed on the surface of the negative electrode current collector 30. The negative electrode mixture layer 33 has a multi-layer structure and includes a first negative electrode mixture layer 31 facing the negative electrode current collector 30 and a second negative electrode mixture layer 32 facing the positive electrode 11.

[0026] The ratio of the thickness of the first anode mixture layer 31 to the thickness of the second anode mixture layer 32 is, for example, in the range of 8:2 to 5:5. That is, the thickness of the first anode mixture layer 31 is equal to or greater than the thickness of the second anode mixture layer 32, and the thickness of the first anode mixture layer 31 is preferably from 1 to 4 times the thickness of the second anode mixture layer 32. This can more significantly improve the adhesion of the anode mixture layer 33 to the anode current collector 30.

[0027] The thickness of the negative electrode mixture layer 33 when applied to one side is, for example, 30 μm or more and 100 μm or less. By making the thickness of the negative electrode mixture layer 33 50 μm or more, it is possible to more significantly improve the battery capacity. Furthermore, by making the thickness of the negative electrode mixture layer 33 100 μm or less and appropriately incorporating CMC into the first negative electrode mixture layer 31 and the second negative electrode mixture layer 32 as described below, it is possible to further improve the rapid charge cycle characteristics.

[0028] The mass per unit area of ​​one surface of the negative electrode mixture layer 33 is preferably 100 g / m ２ More than 250g / m ２ More preferably, 150 g / m or less. ２ 220g / m or more ２ The mass per unit area of ​​one surface of the negative electrode mixture layer 33 is set to 100 g / m ２ By setting the thickness to 250 g / m or more, it is possible to increase the thickness of the negative electrode mixture layer 33 and thereby increase the capacity of the battery. ２ As will be described below, by appropriately adding CMC to the first negative electrode mixture layer 31 and the second negative electrode mixture layer 32, the rapid charge cycle characteristics can be improved.

[0029] The negative electrode current collector 30 can be a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a nickel alloy, or a film having such a metal disposed on its surface. The negative electrode mixture layer 33 contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode current collector 30 except for the portion where the negative electrode lead 21 is connected. A protective layer containing inorganic particles and a binder may be provided between the negative electrode current collector 30 and the negative electrode mixture layer 33 or on the negative electrode mixture layer 33. The negative electrode 12 can be produced, for example, by sequentially applying two types of negative electrode mixture slurries containing a negative electrode active material and a binder to the surface of the negative electrode current collector 30, drying the coating, and then compressing the coating to form a negative electrode mixture layer 33 containing two layers on both sides of the negative electrode current collector 30.

[0030] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. The negative electrode active material may be an element that alloys with Li, such as silicon (Si) or tin (Sn), or a material containing such an element. Among these, a silicon-containing material containing Si is preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, may also be used as the negative electrode active material. One type of negative electrode active material may be used alone, or multiple types may be used in combination. The negative electrode mixture layer 33 may contain a conductive agent such as CNT. The conductive agent may be the same as that used in the positive electrode 11.

[0031] The carbon material functioning as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. Among these, graphite is preferably used as the carbon material. The graphite may be artificial graphite such as massive artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, or amorphous graphite, or a mixture thereof. Furthermore, from the viewpoint of improving rapid charge / discharge, it is preferable that the upper layer contains artificial graphite.

[0032] The volume-based D50 of graphite is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less. The D50 of the negative electrode active material particles means the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size. The particle size distribution of the lithium-containing composite oxide can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by Microtrac-Bell Co., Ltd.) using water as a dispersion medium.

[0033] The silicon-containing material functioning as the negative electrode active material may be any material containing Si, and examples thereof include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The D50 of silicon-containing materials is generally smaller than the D50 of graphite. The volume-based D50 of silicon-containing materials is, for example, 1 μm or more and 20 μm or less, or 1 μm or more and 15 μm or less.

[0034] A suitable silicon-containing material (composite material) is a composite particle containing an ion-conducting phase and Si particles dispersed in the ion-conducting phase. An example of a suitable ion-conducting phase is at least one selected from the group consisting of a silicate phase, a carbon phase, a silicide phase, and a silicon oxide phase. The silicide phase is a phase of a compound consisting of Si and an element more electropositive than Si, such as NiSi, Mg ２ Si, TiSi ２ The ion-conducting phase is a continuous phase composed of an aggregate of particles that are finer than Si particles.

[0035] The composite material may have a conductive layer covering the surface of the ion-conducting phase. The conductive layer is made of a material with higher conductivity than the ion-conducting layer and forms a good conductive path in the negative electrode mixture layer 33. The conductive layer is, for example, a carbon coating made of a conductive carbon material. Examples of the conductive carbon material that can be used include carbon black such as acetylene black and ketjen black, graphite, and amorphous carbon (amorphous carbon) with low crystallinity.

[0036] An example of a suitable Si-containing composite material has a sea-island structure in which fine Si particles are dispersed uniformly in an amorphous silicon oxide phase, and the overall structure is represented by the general formula SiO ｘ(0.5≦x≦1.6). The main component of the silicon oxide may be silicon dioxide. The silicon oxide phase may be doped with Li.

[0037] Another example of a suitable Si-containing composite material is a composite particle having a sea-island structure in which fine Si particles are uniformly dispersed in an amorphous silicate phase. A suitable silicate phase is a lithium silicate phase containing Li. The lithium silicate phase can be, for example, represented by the general formula Li ２ｚ SiO （２＋ｚ） (0<z<2). The lithium silicate phase contains Li ４ SiO ４ It is preferable that (Z=2) is not included. ４ SiO ４ is an unstable compound and reacts with water to become alkaline, which may cause Si to change and lead to a decrease in charge / discharge capacity. The lithium silicate phase is considered to be a suitable phase for Li, from the viewpoints of stability, productivity, Li ion conductivity, etc. ２ SiO ３ (Z=1) or Li ２ Si ２ O ５ It is preferable that (Z=1 / 2) is used as the main component.

[0038] Another example of a suitable Si-containing composite material is a composite particle having a sea-island structure in which fine Si particles are substantially uniformly dispersed in a carbon phase. The carbon phase is preferably an amorphous carbon phase. The carbon phase may contain a crystalline phase component, but preferably contains a larger amount of amorphous phase components. The composite material may contain particles whose ion-conducting phase is an amorphous carbon phase. The amorphous carbon phase is, for example, composed of a carbon material having an average interplanar spacing of (002) planes of more than 0.34 nm as measured by X-ray diffraction. The composite material containing a carbon phase may or may not have a conductive layer separate from the carbon phase.

[0039] From the viewpoint of achieving high capacity, the content of the silicon-containing material in the negative electrode mixture layer 33 is preferably 1 mass% or more, more preferably 2 mass% or more, and particularly preferably 3 mass% or more, relative to the total mass of the negative electrode active material. The upper limit of the content of the silicon-containing material is not particularly limited, but is, for example, 10 mass%. The content of the negative electrode active material in the negative electrode mixture layer 33 is, for example, 90 mass% or more and 99.5 mass% or less, or 95 mass% or more and 99 mass% or less, relative to the total mass of the negative electrode mixture layer 33.

[0040] The first negative electrode mixture layer 31 and the second negative electrode mixture layer 32 each contain a negative electrode active material, a first carboxymethyl cellulose (hereinafter referred to as the first CMC) having a degree of etherification of 0.7 or less, and a second carboxymethyl cellulose (hereinafter referred to as the second CMC) having a degree of etherification of more than 0.7 and 1.8 or less. The content of the first CMC in the first negative electrode mixture layer 31 is 30% by mass or more relative to the total mass of the CMC contained in the first negative electrode mixture layer 31, and the content of the second CMC in the second negative electrode mixture layer 32 is 40% by mass or more relative to the total mass of the CMC contained in the second negative electrode mixture layer 32. This allows the negative electrode mixture layer 33 to have both good liquid absorption and adhesion, resulting in a battery with high capacity and good rapid charge cycle characteristics.

[0041] The content of the first CMC in the first negative electrode mixture layer 31 is preferably 40 mass% or more, and more preferably 50 mass% or more, relative to the total mass of the CMC contained in the first negative electrode mixture layer 31. The content of the first CMC in the first negative electrode mixture layer 31 is preferably 90 mass% or less, more preferably 80 mass% or less, and particularly preferably 70 mass% relative to the total mass of the CMC contained in the first negative electrode mixture layer 31.

[0042] The content of the second CMC in the second negative electrode mixture layer 32 is preferably 45 mass% or more, and more preferably 50 mass% or more, relative to the total mass of the CMC contained in the second negative electrode mixture layer 32. The content of the second CMC in the second negative electrode mixture layer 32 is preferably 90 mass% or less, more preferably 80 mass% or less, and particularly preferably 70 mass% relative to the total mass of the CMC contained in the second negative electrode mixture layer 32.

[0043] The lower limit of the degree of etherification of the first CMC is not particularly limited, but is, for example, 0.1. The degree of etherification of the second CMC is preferably 1.0 or more and 1.8 or less, more preferably 1.2 or more and 1.7 or less.

[0044] Carboxymethyl cellulose (CMC) is a water-soluble polymer in which some of the hydroxyl groups in the cellulose backbone are substituted with carboxymethyl groups. The degree of substitution by carboxymethyl groups is expressed as the degree of etherification. The degree of etherification of CMC can be measured as follows.

[0045] [Method for measuring the degree of etherification of CMC] Approximately 1 g of sample is weighed into a flask and dissolved in an appropriate amount of pure water. Approximately 5 mL of 0.05 M (N / 10) aqueous sulfuric acid is added using a pipette, boiled for several minutes, and cooled. After this, phenolphthalein indicator is added and titration is performed with 0.1 M (N / 10) aqueous sodium hydroxide. Calculate the alkalinity using the following formula: Alkalinity = 5 x F' - mL of 0.1 M (N / 10) aqueous sodium hydroxide x F / sample (g of anhydrous equivalent) F: Factor of 0.1 M (N / 10) aqueous sodium hydroxide F': Factor of 0.05 M (N / 10) aqueous sulfuric acid Approximately 1 g of sample is weighed out, placed in a crucible, and incinerated at 500°C or higher. After cooling, the crucible is transferred to a beaker, an appropriate amount of pure water is added, and then 50 mL of 0.05 M (N / 10) aqueous sulfuric acid is accurately added and boiled for several tens of minutes. After cooling, add phenolphthalein indicator and titrate with 0.1M (N / 10) aqueous sodium hydroxide solution. A blank titration is carried out in the same manner using this method. The degree of etherification is calculated using the following formula: A = (blank titration mL - sample titration mL) x F / sample (anhydrous equivalent g) - alkalinity F: Factor of 0.1M (N / 10) aqueous sodium hydroxide solution The above A refers to the number of mL of 0.05M (N / 10) aqueous sulfuric acid consumed to neutralize the bound sodium in 1 g of sample. The above A is used to calculate the degree of etherification as follows: Degree of etherification (DS) = 162A / (10000 - 80A)

[0046] The CMC content in the negative electrode mixture layer 33 is preferably 0.2% by mass or more and 3% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less, and particularly preferably 1% by mass or more and 3% by mass or less, relative to the total mass of the negative electrode active material. Within this range, rapid charge cycle characteristics are more significantly improved. Note that if the CMC content in the negative electrode mixture layer 33 exceeds 3% by mass, the battery capacity may decrease.

[0047] The content of the second CMC in the second negative electrode mixture layer 32 is preferably greater than the content of the second CMC in the first negative electrode mixture layer 31 .

[0048] The first CMC and the second CMC comprise carboxymethyl cellulose (CMC) or a similar derivative thereof. Examples of similar derivatives of CMC include sodium salt, lithium salt, ammonium salt, potassium salt, rubidium salt, and cesium salt of CMC, with the sodium salt (CMC-Na) or lithium salt (CMC-Li) being preferred. CMC-Na is generally a partially neutralized salt in which some of the carboxyl groups are neutralized. The weight-average molecular weight of CMC-Na is, for example, 200,000 or more and 1,000,000 or less, preferably 200,000 or more and 500,000 or less.

[0049] The CMC or its analogous derivative contained in the negative electrode mixture layer 33 functions as a binder and also as a thickener for imparting an appropriate viscosity to the negative electrode mixture slurry. The negative electrode mixture layer 33 preferably contains a binder other than CMC or its analogous derivative. Each negative electrode mixture layer 33 may contain the same binder as that used in the positive electrode 11, but preferably contains styrene-butadiene rubber (SBR). Furthermore, from the perspective of suppressing swelling and shrinkage of silicon, it is more preferable to add a polyacrylic acid (PAA)-based material. Not only the adhesiveness of the SBR binder, but also the toughness of the PAA binder suppresses swelling and shrinkage of silicon, contributing to improved cycle life.

[0050] The negative electrode mixture layer 33 preferably contains 0.5 mass % or more and 5 mass % or less of SBR relative to the total mass of the negative electrode active material, and the content of SBR in the first negative electrode mixture layer 31 is preferably 1.2 times or more the content of SBR in the second negative electrode mixture layer 32. This more significantly improves the adhesion of the negative electrode mixture layer 33.

[0051] The first CMC and the second CMC each preferably have a 1% aqueous solution viscosity of 500 mPa·s or more. The 1% aqueous solution viscosity of the first CMC is more preferably 1000 mPa·s or more and 9000 mPa·s or less. The 1% aqueous solution viscosity of the second CMC is more preferably 1000 mPa·s or more and 5000 mPa·s or less.

[0052] The ratio of the 1% aqueous viscosity of the first CMC to the 1% aqueous viscosity of the second CMC (1% aqueous viscosity of the first CMC / 1% aqueous viscosity of the second CMC) is preferably 0.5 or more and 9.0 or less, more preferably 1.0 or more and 3.0 or less. This further improves the adhesion between the first negative electrode mixture layer and the second negative electrode mixture layer, thereby suppressing peeling between the negative electrode mixture layer and the negative electrode current collector. When a silicon-containing material with a large expansion and contraction rate during charge and discharge is used as the negative electrode active material, the negative electrode mixture layer may peel from the negative electrode current collector, adversely affecting the rapid charge cycle performance. However, by improving the adhesion between the negative electrode mixture layer and the negative electrode current collector, the negative electrode mixture layer can be thickened while maintaining high rapid charge cycle performance.

[0053] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. The separator 13 may have, for example, a multi-layer structure including a thermoplastic resin layer such as polyolefin and a cellulose fiber layer, a two-layer structure of polyethylene (PE) / polypropylene (PP), or a three-layer structure of PE / PP / PE. A filler layer including an inorganic filler or a layer of a highly heat-resistant resin such as aramid resin may be provided on the surface of the separator 13.

[0054] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0055] Example 1 [Fabrication of Positive Electrode] LiCo was used as the positive electrode active material. ０．９７９ Zr ０．００１ Mg ０．０１ Al ０．０１ O ２ A lithium-containing composite oxide represented by the formula (I) was used. The positive electrode active material, carbon black, and polyvinylidene fluoride were mixed in a solids mass ratio of 95:2.5:2.5, and a positive electrode mixture slurry was prepared using N-methyl-2-pyrrolidone (NMP) as a dispersion medium. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil (thickness 15 μm) by the doctor blade method, and the coating was dried and compressed using a rolling roller. Thereafter, the positive electrode current collector was cut to a predetermined electrode size, and a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector was obtained. Note that an exposed portion in which the surface of the positive electrode core was exposed was provided in a part of the positive electrode.

[0056] [Fabrication of Negative Electrode] As a negative electrode active material, SiO Ｘ(X=1) and graphite with a median diameter of 22 μm were used. Furthermore, as the first CMC, a sodium salt of carboxymethyl cellulose (CMC-Na) with a degree of etherification (DS) of 0.7 and a 1% aqueous solution viscosity of 3000 mPa·s was used, and as the second CMC, a sodium salt of carboxymethyl cellulose (CMC-Na) with a degree of etherification (DS) of 1.2 and a 1% aqueous solution viscosity of 1500 mPa·s was used. SiO Ｘ Anode mixture slurry A was prepared by mixing anode mixture slurry A (X=1), graphite, a first CMC, a second CMC, and styrene-butadiene rubber (SBR) in a solid mass ratio of 3.0:97.0:0.7:0.3:1.5, and using water as a dispersion medium. Ｘ (X = 1), graphite, a first CMC, a second CMC, and styrene butadiene rubber (SBR) were mixed in a solids mass ratio of 3.0:97.0:0.3:0.7:0.7, and water was used as a dispersion medium to prepare a negative electrode mixture slurry B. Next, the negative electrode mixture slurry A was applied to both sides of a negative electrode current collector made of copper foil (thickness 10 μm) by a doctor blade method to form a first coating film, and after drying the first coating film, the negative electrode mixture slurry B was applied to the first coating film by a doctor blade method to form a second coating film, and the second coating film was dried. The mass per unit area of ​​one side was adjusted to 150 g / m so that the thickness ratio of the first negative electrode mixture layer to the second negative electrode mixture layer was 7:3. ２ The slurry was applied to the negative electrode core. The coating was then compressed using a rolling roller, and the negative electrode current collector was cut to a predetermined electrode size, resulting in a negative electrode in which a two-layer structure of negative electrode mixture layers including a first negative electrode mixture layer and a second negative electrode mixture layer was formed on both sides of the negative electrode current collector. An exposed portion in which the surface of the negative electrode core was exposed was provided in a part of the negative electrode.

[0057] [Preparation of non-aqueous electrolyte] Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7 (at 25°C and 1 atmosphere), and then 2 mass% of vinylene carbonate and LiPF 6 were added to the mixed solvent. ６ was added to give a concentration of 1 mol / L to obtain a non-aqueous electrolyte.

[0058] [Preparation of Test Cell (Non-Aqueous Electrolyte Secondary Battery)] A positive electrode lead was attached to the exposed portion of the positive electrode, and a negative electrode lead was attached to the exposed portion of the negative electrode. The positive and negative electrodes were spirally wound with a separator made of a polyethylene microporous membrane interposed therebetween. Polypropylene tape was attached to the outermost surface of the wound body, and the wound body was then pressed radially to produce a flat wound electrode body. Under an argon atmosphere, the electrode body and non-aqueous electrolyte were placed in a cup-shaped container of an outer casing composed of a laminate sheet having a five-layer structure of a polypropylene layer / adhesive layer / aluminum alloy layer / adhesive layer / polypropylene layer. The pressure inside the outer casing was then reduced, allowing the electrode body to be impregnated with the non-aqueous electrolyte. The opening of the outer casing was sealed, producing a non-aqueous electrolyte secondary battery measuring 62 mm in height, 35 mm in width, and 3.6 mm in thickness.

[0059] [Measurement of Peel Strength] The negative electrode was cut to a predetermined size to prepare a test specimen. Using Nitto Denko double-sided tape #515, the negative electrode mixture layer on one side of the test specimen was attached to a stainless steel substrate with a smooth surface, and the stainless steel substrate to which the test specimen was fixed was positioned horizontally. One end of the negative electrode current collector in the longitudinal direction of the test specimen was fixed to a movable jig of a tensile tester (A&D Corporation's Tensilon Universal Tester RTC1210). The negative electrode current collector was set to peel off in a direction 90° relative to the substrate surface of the stainless steel substrate, and the movable jig was then moved to peel off the negative electrode mixture layer of the test specimen from the negative electrode current collector at a speed of 100 mm / min. The tensile direction was always maintained at 90° relative to the substrate surface of the stainless steel substrate to which the test specimen was fixed. A stable tensile strength value was read when 30 mm or more of the test specimen had peeled off. The above measurements were performed on five test specimens, and the average of the measured values ​​was taken as the peel strength (N / m). By increasing the peel strength, it is possible to suppress the deterioration of the rapid charging cycle characteristics.

[0060] [Measurement of Liquid Absorption Time] The negative electrode was dried for 10 hours in a thermostatic chamber heated to 200°C under a nitrogen atmosphere and then cut into a 5 cm x 5 cm test piece. 3.0 μL of polypropylene carbonate (PC) was dropped vertically onto the surface of the test piece, and the time until the PC was absorbed into the sample was measured visually. Six measurements were performed, and the average value was taken as the liquid absorption time. The shorter the liquid absorption time, the smoother the exchange of non-aqueous electrolyte from the surface of the negative electrode mixture layer to the current collector side, so that the non-aqueous electrolyte discharged from the negative electrode mixture layer during discharge is quickly absorbed into the negative electrode mixture layer during charge. Therefore, the shorter the liquid absorption time, the more suppressed the deterioration of rapid charge cycle characteristics.

[0061] [Evaluation of rapid charge cycle characteristics (capacity retention)] In a temperature environment of 25°C, the test cell was subjected to constant current charging at 0.7 C until the cell voltage reached 4.2 V, and then constant voltage charging at 4.2 V down to 0.05 C. Thereafter, constant current discharging was performed at 1.0 C until the cell voltage reached 2.75 V. This charge / discharge cycle was repeated 100 times, and the capacity retention was calculated using the following formula: Capacity retention = (discharge capacity at 100th cycle / discharge capacity at 1st cycle) × 100

[0062] Example 2 A negative electrode and a test cell were fabricated and evaluated in the same manner as in Example 1, except that the CMC content in the negative electrode mixture layer was changed to 0.5 mass % in the fabrication of the negative electrode. Specifically, in the preparation of negative electrode mixture slurry A, the mixing ratio of the first CMC to the second CMC was changed to 0.35:0.15 relative to 100 parts by mass of the negative electrode active material, and in the preparation of negative electrode mixture slurry B, the mixing ratio of the first CMC to the second CMC was changed to 0.15:0.35 relative to 100 parts by mass of the negative electrode active material.

[0063] Example 3 A negative electrode and a test cell were fabricated and evaluated in the same manner as in Example 1, except that the CMC content in the negative electrode mixture layer was changed to 3.0 mass% in the fabrication of the negative electrode. Specifically, in the preparation of negative electrode mixture slurry A, the mixing ratio of the first CMC to the second CMC was changed to 2.1:0.9 relative to 100 parts by mass of the negative electrode active material, and in the preparation of negative electrode mixture slurry B, the mixing ratio of the first CMC to the second CMC was changed to 0.9:2.1 relative to 100 parts by mass of the negative electrode active material.

[0064] Example 4 A negative electrode and a test cell were produced and evaluated in the same manner as in Example 1, except that in the preparation of the negative electrode, the mixing ratio of the first CMC to the second CMC when preparing the negative electrode mixture slurry A was changed to 0.5:0.5 relative to 100 parts by mass of the negative electrode active material.

[0065] Example 5 A negative electrode and a test cell were produced and evaluated in the same manner as in Example 1, except that in the preparation of the negative electrode, the mixing ratio of the first CMC to the second CMC when preparing the negative electrode mixture slurry B was changed to 0.5:0.5 relative to 100 parts by mass of the negative electrode active material.

[0066] Example 6 In the preparation of the negative electrode, the mixing ratio of the first CMC to the second CMC when preparing the negative electrode mixture slurry A was changed to 0.5:0.5 relative to 100 parts by mass of the negative electrode active material, and the mixing ratio of the first CMC to the second CMC when preparing the negative electrode mixture slurry B was changed to 0.5:0.5 relative to 100 parts by mass of the negative electrode active material. Except for this, a negative electrode and a test cell were prepared and evaluated in the same manner as in Example 1.

[0067] Example 7 A negative electrode and a test cell were produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a sodium salt of carboxymethyl cellulose (CMC-Na) having a degree of etherification (DS) of 1.8 and a 1% aqueous solution viscosity of 1100 mPa·s was used as the second CMC.

[0068] Example 8 A negative electrode and a test cell were produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a sodium salt of carboxymethyl cellulose (CMC-Na) having a degree of etherification (DS) of 0.3 and a 1% aqueous solution viscosity of 2700 mPa·s was used as the first CMC.

[0069] <Example 9> In the production of the negative electrode, the mass per unit area of ​​one side was set to 220 g / m ２ A negative electrode and a test cell were prepared and evaluated in the same manner as in Example 1, except for the above change.

[0070] Example 10 A negative electrode and a test cell were produced and evaluated in the same manner as in Example 1, except that in the production of the negative electrode, a sodium salt of carboxymethyl cellulose (CMC-Na) having a degree of etherification (DS) of 0.7 and a 1% aqueous solution viscosity of 1000 mPa·s was used as the first CMC, and a sodium salt of carboxymethyl cellulose (CMC-Na) having a degree of etherification (DS) of 1.2 and a 1% aqueous solution viscosity of 1000 mPa·s was used as the second CMC.

[0071] Example 11 In the preparation of the negative electrode, a lithium salt of carboxymethyl cellulose (CMC-Li) having a degree of etherification (DS) of 0.7 and a 1% aqueous solution viscosity of 3000 mPa·s was used as the first CMC, and a lithium salt of carboxymethyl cellulose (CMC-Li) having a degree of etherification (DS) of 1.2 and a 1% aqueous solution viscosity of 1500 mPa·s was used as the second CMC. Except for this, a negative electrode and a test cell were prepared and evaluated in the same manner as in Example 1.

[0072] Example 12 A negative electrode and a test cell were produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, the thickness ratio of the first negative electrode mixture layer to the second negative electrode mixture layer was set to 5:5.

[0073] <Comparative Example 1> In the production of the negative electrode, the negative electrode mixture slurry B was not applied, and the mass per unit area of ​​one side was 150 g / m ２A negative electrode and a test cell were produced and evaluated in the same manner as in Example 1, except that only the negative electrode mixture slurry A was applied so that ...

[0074] <Comparative Example 2> In the preparation of the negative electrode, a negative electrode and a test cell were prepared and evaluated in the same manner as in Example 1, except that, in preparing the negative electrode mixture slurry A, the first CMC was not used and only the second CMC was added in an amount of 1.0 part by mass per 100 parts by mass of the negative electrode active material.

[0075] <Comparative Example 3> In the preparation of the negative electrode, a negative electrode and a test cell were prepared and evaluated in the same manner as in Example 1, except that, in preparing the negative electrode mixture slurry B, the second CMC was not used and only the first CMC was added in an amount of 1.0 part by mass per 100 parts by mass of the negative electrode active material.

[0076] The evaluation results of the negative electrodes and test cells in the examples and comparative examples are shown in Table 1. The negative electrode peel strength, negative electrode liquid absorption time, and capacity retention rate shown in Table 1 are relative values ​​when the negative electrode peel strength, negative electrode liquid absorption time, and capacity retention rate of Example 1 are each set to 100.

[0077]

[0078] As shown in Table 1, the examples use negative electrodes with peel strengths and liquid absorption times within appropriate ranges, and therefore the test cells of the examples all have high capacity retention rates. On the other hand, the negative electrode of Comparative Example 1 does not have a two-layer structure, so the liquid absorption time is long, and the capacity retention rate of the test cell of Comparative Example 1 is poorer than that of the examples. Furthermore, the negative electrode of Comparative Example 2 does not contain a first CMC in the first negative electrode mixture layer, so the peel strength is low, and the capacity retention rate of the test cell of Comparative Example 2 is poorer than that of the examples. Furthermore, the negative electrode of Comparative Example 3 does not contain a second CMC in the second negative electrode mixture layer, so the liquid absorption time is long, and the capacity retention rate of the test cell of Comparative Example 3 is poorer than that of the examples.

[0079] The present disclosure is further illustrated by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on a surface of the negative electrode current collector, the negative electrode mixture layer including a first negative electrode mixture layer facing the negative electrode current collector and a second negative electrode mixture layer facing the positive electrode, the first negative electrode mixture layer and the second negative electrode mixture layer each containing a negative electrode active material, a first carboxymethyl cellulose having a degree of etherification of 0.7 or less, and a second carboxymethyl cellulose having a degree of etherification of more than 0.7 and 1.8 or less, the content of the first carboxymethyl cellulose in the first negative electrode mixture layer being 30 mass% or more relative to the total mass of carboxymethyl cellulose contained in the first negative electrode mixture layer, and the content of the second carboxymethyl cellulose in the second negative electrode mixture layer being 40 mass% or more relative to the total mass of carboxymethyl cellulose contained in the second negative electrode mixture layer, The mass per unit area of ​​one surface of the negative electrode mixture layer is 100 g / m ２ More than 250g / m ２A nonaqueous electrolyte secondary battery having a thickness of 0.5% to 5% by mass of styrene-butadiene rubber relative to the total mass of the negative electrode active material, and a content of the styrene-butadiene rubber in the first negative electrode mixture layer is 1.2 times or more the content of the styrene-butadiene rubber in the second negative electrode mixture layer. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the ratio of the thickness of the first negative electrode mixture layer to the thickness of the second negative electrode mixture layer is in the range of 8:2 to 5:5. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the negative electrode mixture layer contains 0.5% to 5% by mass of styrene-butadiene rubber relative to the total mass of the negative electrode active material, and the content of the styrene-butadiene rubber in the first negative electrode mixture layer is 1.2 times or more the content of the styrene-butadiene rubber in the second negative electrode mixture layer. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the content of the second carboxymethyl cellulose in the second negative electrode mixture layer is greater than the content of the second carboxymethyl cellulose in the first negative electrode mixture layer. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the first carboxymethyl cellulose and the second carboxymethyl cellulose contain carboxymethyl cellulose or a derivative similar thereto.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the content of carboxymethyl cellulose in the negative electrode mixture layer is 0.2 mass % or more and 3 mass % or less, relative to the total mass of the negative electrode active material.Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the first carboxymethyl cellulose and the second carboxymethyl cellulose both have a 1% aqueous solution viscosity of 500 mPa·s or more.Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the negative electrode active material contains a silicon-containing material.Configuration 9: The nonaqueous electrolyte secondary battery according to claim 1, wherein the silicon-containing material contains an ion-conducting phase and Si particles dispersed in the ion-conducting phase, and the ion-conducting phase is at least one selected from a silicon oxide phase, a silicate phase, and a carbon phase. Configuration 10: The nonaqueous electrolyte secondary battery of configuration 8, wherein the silicon-containing material is SiOx (0.5≦x≦1.6).

[0080] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Negative electrode current collector, 31 First negative electrode mixture layer, 32 Second negative electrode mixture layer

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on a surface of the negative electrode current collector, the negative electrode mixture layer includes a first negative electrode mixture layer facing the negative electrode current collector and a second negative electrode mixture layer facing the positive electrode, the first negative electrode mixture layer and the second negative electrode mixture layer each contain a negative electrode active material, a first carboxymethylcellulose having a degree of etherification of 0.7 or less, and a second carboxymethylcellulose having a degree of etherification of more than 0.7 and 1.8 or less, the content of the first carboxymethylcellulose in the first negative electrode mixture layer is 30 mass% or more with respect to a total mass of carboxymethylcellulose contained in the first negative electrode mixture layer, and the content of the second carboxymethylcellulose in the second negative electrode mixture layer is 40 mass% or more with respect to a total mass of carboxymethylcellulose contained in the second negative electrode mixture layer, The mass per unit area of ​​one surface of the negative electrode mixture layer is 100 g / m ２ More than 250g / m ２ The non-aqueous electrolyte secondary battery is as follows:

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the thickness of the first negative electrode mixture layer to the thickness of the second negative electrode mixture layer is in the range of 8:2 to 5:

5.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode mixture layer contains 0.5 mass % or more and 5 mass % or less of styrene-butadiene rubber relative to the total mass of the negative electrode active material, and the content of styrene-butadiene rubber in the first negative electrode mixture layer is 1.2 times or more the content of styrene-butadiene rubber in the second negative electrode mixture layer.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the second carboxymethyl cellulose in the second negative electrode mixture layer is equal to or greater than the content of the second carboxymethyl cellulose in the first negative electrode mixture layer.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first carboxymethyl cellulose and the second carboxymethyl cellulose include carboxymethyl cellulose or a derivative similar thereto.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of carboxymethyl cellulose in the negative electrode mixture layer is 0.2 mass % or more and 3 mass % or less with respect to the total mass of the negative electrode active material.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first carboxymethyl cellulose and the second carboxymethyl cellulose each have a 1% aqueous solution viscosity of 500 mPa·s or more.

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material includes a silicon-containing material.

9. The nonaqueous electrolyte secondary battery according to claim 8, wherein the silicon-containing material comprises an ion-conducting phase and Si particles dispersed in the ion-conducting phase, and the ion-conducting phase is at least one selected from a silicon oxide phase, a silicate phase, and a carbon phase.

10. The nonaqueous electrolyte secondary battery according to claim 8, wherein the silicon-containing material is SiOx (0.5≦x≦1.6).

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