Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery (10) comprises a positive electrode (11), a negative electrode (12), and a non-aqueous electrolyte, wherein the negative electrode (12) has a negative electrode mixture layer containing a negative electrode active material including a Si-based material, the positive electrode (11) has a positive electrode mixture layer containing a positive electrode active material and a conductive agent, the positive electrode active material includes a positive electrode active material A composed of polycrystalline particles and a positive electrode active material B composed of single-crystalline particles, the average particle diameter (DB) of the positive electrode active material B is smaller than the average particle diameter (DA) of the positive electrode active material A, and the conductive agent contains single-walled carbon nanotubes and multi-walled carbon nanotubes.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to technology for non-aqueous electrolyte secondary batteries.

[0002] A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery includes, for example, a positive electrode having a positive electrode mixture layer disposed on a positive electrode core, a negative electrode having a negative electrode mixture layer disposed on a negative electrode core, and a non-aqueous electrolyte.

[0003] For example, Patent Document 1 discloses that in order to improve battery characteristics compared to conventional methods, a first long carbon material having a first length and a second long carbon material having a second length greater than the first length are used as conductive agents contained in a positive electrode mixture layer.

[0004] International Publication No. 2020 / 105729

[0005] However, in the prior art, there is room for improvement in the resistance increase that accompanies charge / discharge cycles of secondary batteries, and in the rapid charge characteristics.

[0006] Therefore, an object of the present disclosure is to provide a non-aqueous electrolyte secondary battery that suppresses an increase in resistance due to charge / discharge cycles and has excellent rapid charging characteristics.

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode mixture layer including a negative electrode active material including a Si-based material. The positive electrode has a positive electrode mixture layer including a positive electrode active material and a conductive agent. The positive electrode active material includes a positive electrode active material A that is a polycrystalline particle and a positive electrode active material B that is a single-crystal particle. The positive electrode active material B has an average particle size (D Ｂ ) is the average particle size (D Ａ ) and the conductive agent contains single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0008] According to one aspect of the present disclosure, it is possible to provide a nonaqueous electrolyte secondary battery that suppresses an increase in resistance due to charge / discharge cycles and has excellent rapid charge characteristics.

[0009] 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment;

[0010] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode mixture layer including a negative electrode active material including a Si-based material. The positive electrode has a positive electrode mixture layer including a positive electrode active material and a conductive agent. The positive electrode active material includes a positive electrode active material A that is a polycrystalline particle and a positive electrode active material B that is a single-crystal particle. The positive electrode active material B has an average particle size (D Ｂ ) is the average particle size (D Ａ ) and the conductive agent contains single-walled carbon nanotubes and multi-walled carbon nanotubes. The nonaqueous electrolyte secondary battery according to one aspect of the present disclosure exhibits the effects of suppressing an increase in resistance due to charge / discharge cycles and exhibiting excellent rapid charging characteristics. The reason for this effect is not fully understood, but the following is presumed.

[0011] According to the present disclosure, the negative electrode mixture layer contains a Si-based material, thereby increasing the capacity of the battery. Furthermore, the positive electrode mixture layer contains positive electrode active materials A and B with different average particle sizes, thereby improving the packing of the positive electrode active material, thereby also increasing the capacity of the battery. Typically, using positive electrode active materials with different average particle sizes tends to cause uneven reactions within the positive electrode mixture layer, which can lead to deterioration of positive electrode active materials with smaller average particle sizes. For this reason, the use of single-crystal particles, which have excellent durability, for positive electrode active materials with smaller average particle sizes is considered. However, because single-crystal particles have poor electronic conductivity, simply replacing them can easily lead to a decrease in rapid charging performance. However, in the present disclosure, single-walled carbon nanotubes and multi-walled carbon nanotubes are used as the conductive agent in the positive electrode mixture layer, thereby enabling the reduction of the resistance of the positive electrode mixture layer containing single-crystal particles. Specifically, multi-walled carbon nanotubes, which generally have short fiber lengths, are arranged between positive electrode active material particles, and single-walled carbon nanotubes, which generally have longer fiber lengths than multi-walled carbon nanotubes, are arranged so as to straddle multiple positive electrode active material particles, thereby establishing a continuous electron conduction path throughout the positive electrode mixture layer, thereby enabling low resistance of the positive electrode mixture layer containing single-crystalline particles. As a result, it is believed that excellent rapid charging characteristics can be exhibited. Furthermore, the use of single-walled carbon nanotubes and multi-walled carbon nanotubes enables low resistance of the positive electrode mixture layer with a small amount of conductive agent, thereby enabling the maintenance of a certain amount of voids in the positive electrode mixture layer. This allows, for example, the retention of electrolyte expelled by swelling of the negative electrode mixture layer during charging in the positive electrode mixture layer. In other words, it is believed that this suppresses depletion of electrolyte in the electrode, thereby suppressing resistance increases with charge / discharge cycles and improving rapid charging characteristics.

[0012] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described below. The drawings referred to in the following embodiment are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual battery.

[0013] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery 10 shown in FIG. 1 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, a nonaqueous electrolyte, insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a cylindrical case body 16 with a bottom and a sealing body 17 that closes the opening of the case body 16. Note that, instead of the wound electrode assembly 14, other electrode bodies may be used, such as a laminated electrode body formed by alternately stacking positive and negative electrodes with separators interposed therebetween. Examples of the battery case 15 include cylindrical, prismatic, coin-shaped, or button-shaped metal cases, and resin cases (so-called pouch-shaped cases) formed by laminating resin sheets.

[0014] The non-aqueous electrolyte has, for example, ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0015] The liquid electrolyte (electrolytic solution) contains, for example, 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

[0016] Furthermore, examples of the solid electrolyte that can be used include solid or gel polymer electrolytes, inorganic solid electrolytes, and the like. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, and the like).

[0017] The case body 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports the sealing body 17. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and supports the sealing body 17 on its upper surface.

[0018] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and all components except for the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the nonaqueous electrolyte secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, 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 ruptures, and gas is discharged from the opening of the cap 27.

[0019] 1 , a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode lead 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom of the case body 16. The positive electrode lead 20 is connected by welding or the like to the underside of a filter 23, which is the bottom plate of the sealing body 17, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner bottom surface of the case body 16, and the case body 16 serves as the negative electrode terminal.

[0020] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the nonaqueous electrolyte secondary battery 10 will be further described below.

[0021] The positive electrode 11 includes, for example, a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode mixture layer may be disposed on only one surface of the positive electrode core, or on both surfaces of the positive electrode core.

[0022] The positive electrode core constituting the positive electrode 11 may be, for example, a metal foil such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on the surface layer. The thickness of the positive electrode core is, for example, 10 μm or more and 50 μm or less. The positive electrode mixture layer contains a positive electrode active material and a conductive agent. The positive electrode mixture layer may also contain a binder, etc.

[0023] The positive electrode active material includes a positive electrode active material A that is a polycrystalline particle and a positive electrode active material B that is a single-crystal particle. The single-crystal particles include not only particles that are completely separated into individual primary particles, but also particles that are aggregates of several to a dozen (specifically, 2 to 19) primary particles. The polycrystalline particles refer to particles (secondary particles) that are aggregates of several tens or more (specifically, 20 or more) primary particles.

[0024] The average particle size (D Ｂ ) is the positive electrode active material A (D Ａ ) is sufficient, but for example, in terms of further improving the filling property of the positive electrode active material, or further improving the rapid charge characteristics and the increase in resistance accompanying charge / discharge cycles, it is preferable to have a smaller D Ａ / D Ｂis preferably 2 or more and 6 or less, more preferably 3 or more and 5 or less, and even more preferably 3 or more and 4 or less. The average particle size of the positive electrode active material B of single-crystal particles may be, for example, in the range of 2 μm to 20 μm, and the average particle size of the positive electrode active material A of polycrystalline particles may be, for example, in the range of 5 μm to 25 μm. The average particle size in the present disclosure is the volume-average particle size measured by a laser diffraction method, and is the median diameter at which the volume integrated value in the particle size distribution is 50%. The average particle size can be measured by the laser diffraction method, for example, using a Microtrac Bell MT3000II.

[0025] Examples of the positive electrode active materials A and B include lithium-containing metal composite oxides. The lithium-containing metal composite oxide may contain, for example, Ni, Co, Mn, Al, Zr, B, Mg, Sc, Y, Ti, Fe, Cu, Zn, Cr, Pb, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, or Si. Among these, for example, in order to increase the capacity of the battery, it is preferable to contain 85 mol% or more of Ni relative to the total molar amount of metal elements excluding lithium, and it is preferable to contain at least one of Al and Mn in order to further suppress deterioration of charge-discharge cycle characteristics. The lithium-containing metal composite oxide of the positive electrode active material A and the lithium-containing metal composite oxide of the positive electrode active material B may have the same composition or different compositions.

[0026] The total mass of the positive electrode active material A and the positive electrode active material B (M Ａ +M Ｂ ) the mass of the positive electrode active material B (M Ｂ ) ratio ((M Ｂ / (M Ａ +M Ｂ )) × 100) is preferably 10% by mass or more and 40% by mass or less, more preferably 20% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less, in terms of being able to further improve, for example, rapid charging characteristics and an increase in resistance accompanying charge / discharge cycles. The total mass of the positive electrode active material A and the positive electrode active material B is preferably 90% by mass or more and more preferably 95% by mass or more with respect to the total mass of the positive electrode mixture layer.

[0027] The conductive agent includes single-walled carbon nanotubes and multi-walled carbon nanotubes. Single-walled carbon nanotubes (SWCNTs) are carbon nanostructures in which a single layer of graphene sheets forms a cylindrical shape, while multi-walled carbon nanotubes (MWCNTs) are carbon nanostructures in which two or more layers of graphene sheets are concentrically stacked to form a cylindrical shape. A graphene sheet refers to a layer in which carbon atoms in sp2 hybrid orbitals that form graphite crystals are located at the vertices of a regular hexagon. The shape of the carbon nanotubes is not limited. Examples of such shapes include needles, cylindrical tubes, fishbone-shaped (fishbone or cup-stacked), playing card-shaped (platelets), and coil-shaped.

[0028] The fiber lengths of the single-walled carbon nanotubes and the multi-walled carbon nanotubes may be, for example, 500 μm or more and 2000 μm or less, or 0.1 μm or more and 50 μm or less. The fiber length of the carbon nanotubes can be determined by measuring the lengths of 50 arbitrary carbon nanotubes using a field emission scanning electron microscope (FE-SEM) and taking the arithmetic average. The fiber length (L) of the multi-walled carbon nanotubes is advantageous in that it makes it easier to establish a continuous electron conduction path throughout the positive electrode mixture layer and can further reduce the resistance of the positive electrode mixture layer. Ｍ ) is the fiber length of the single-walled carbon nanotube (L Ｓ ), and L Ｍ / L Ｓ is more preferably 0.00005 or more and 0.1 or less.

[0029] The outermost diameter (i.e., fiber diameter) of the single-walled carbon nanotube and the multi-walled carbon nanotube may be, for example, 0.5 nm or more and 20 nm or less, or 1 nm or more and 10 nm or less. The outermost diameter of the carbon nanotube can be determined by measuring the outer diameters of 50 arbitrary carbon nanotubes using a field emission scanning electron microscope (FE-SEM) or a transmission electron microscope (TEM) and taking the arithmetic average.

[0030] Multi-walled carbon nanotubes are advantageous in that they can improve rapid charging characteristics and the increase in resistance that accompanies charge-discharge cycles, for example, and have a BET specific surface area of ​​200 m ２ It is preferable that the single-walled carbon nanotube contains a multi-walled carbon nanotube having a BET specific surface area of ​​300 m / g or more, for example, in that it can further improve rapid charging characteristics and the increase in resistance that accompanies charge-discharge cycles. ２ The upper limit of the BET specific surface area of ​​the multi-walled carbon nanotubes is, for example, 500 m ２ The upper limit of the BET specific surface area of ​​the single-walled carbon nanotube is, for example, 600 m ２ The specific surface area of ​​the carbon nanotubes can be determined by the BET method, which is a general method for measuring specific surface area, using a specific surface area measuring device based on a gas adsorption method.

[0031] The content of the multi-walled carbon nanotubes is preferably 0.01 parts by mass or more and 0.5 parts by mass or less, more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, and more preferably 0.2 parts by mass or more and 0.5 parts by mass or less, relative to 100 parts by mass of the positive electrode active material, in order to further improve, for example, the rapid charging characteristics and the increase in resistance due to charge / discharge cycles. Furthermore, the content of the single-walled carbon nanotubes contained in the positive electrode mixture layer 32 is preferably 0.0001 parts by mass or more and 0.02 parts by mass or less, more preferably 0.005 parts by mass or more and 0.02 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.02 parts by mass or less, relative to 100 parts by mass of the positive electrode active material, in order to further improve, for example, the rapid charging characteristics and the increase in resistance due to charge / discharge cycles.

[0032] It is preferable that single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) are substantially free of metal catalysts within the tubes. Carbon nanotubes are generally synthesized using metal catalysts, but if metal catalysts remain within the carbon nanotubes, the metal catalysts may cause deterioration of the positive electrode 11 and reduce the characteristics of the secondary battery. Therefore, it is preferable to remove the metal catalysts from the carbon nanotubes, for example, by washing them with an acidic aqueous solution. Here, "substantially free of metal catalysts" means that the metal catalysts are contained only at the lower limit of detection by ICP-AES.

[0033] Examples of the binder include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyethylene oxide (PEO), etc. The content of the binder may be, for example, in the range of 0.1 mass % to 5 mass % with respect to the total mass of the positive electrode mixture layer.

[0034] The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, carbon nanotubes, and the like to a positive electrode core, drying the coating, and then rolling the coating to form a positive electrode mixture layer on the positive electrode core. To improve the dispersibility of the carbon nanotubes, it is preferable to add at least one of a hydrogenated nitrile butadiene copolymer (HNBR) and a cellulose derivative to the positive electrode mixture slurry. In other words, by including a hydrogenated nitrile butadiene copolymer and a cellulose derivative in the positive electrode mixture layer, the carbon nanotubes in the positive electrode mixture layer remain highly dispersed, which may further reduce the resistance of the positive electrode mixture layer and improve rapid charging characteristics. The thickness of the positive electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode core.

[0035] The porosity of the positive electrode mixture layer is preferably, for example, 22% or more. When the porosity of the positive electrode mixture layer satisfies the above range, for example, it becomes easy for the positive electrode mixture layer to retain the electrolyte discharged due to swelling of the negative electrode mixture layer during charging. This may suppress depletion of the electrolyte in the electrode and further improve rapid charging characteristics and resistance increase associated with charge / discharge cycles. The upper limit of the porosity of the positive electrode mixture layer may be 40% or less. The porosity of the positive electrode mixture layer can be adjusted, for example, by the content of carbon nanotubes. The porosity of the positive electrode mixture layer can also be adjusted, for example, by the rolling force of the coating film of the positive electrode mixture slurry.

[0036] The porosity of the positive electrode mixture layer is measured as follows. A portion of the positive electrode 11 removed from a discharged nonaqueous electrolyte secondary battery is cut out and processed using an ion milling device (e.g., IM4000PLUS, manufactured by Hitachi High-Technologies Corporation) to expose a cross section of the positive electrode mixture layer. A backscattered electron image of the exposed cross section of the positive electrode mixture layer is captured using a scanning electron microscope. The cross-sectional image of the positive electrode mixture layer obtained above is imported into a computer and binarized using image analysis software (e.g., ImageJ, manufactured by the National Institutes of Health, USA). A binarized image is obtained in which particle cross sections in the cross-sectional image are converted into black and voids between particles are converted into white. The area of ​​the white region in this binarized image is determined, and the ratio of the area of ​​the white region to the area of ​​the cross-sectional image of the positive electrode mixture layer is calculated, thereby determining the porosity of the positive electrode mixture layer.

[0037] The negative electrode 12 includes, for example, a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode mixture layer may be formed on only one side of the negative electrode core, or on both sides. Examples of the negative electrode core include a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The thickness of the negative electrode core is, for example, 5 μm or more and 50 μm or less. The negative electrode mixture layer includes a negative electrode active material containing a Si-based material. The negative electrode mixture layer may also include a binder. The negative electrode 12 can be fabricated, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and the like onto the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on the negative electrode core. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode core.

[0038] Examples of the Si-based material include Si, Si alloys, and Si compounds. The Si-based material may also be a composite particle containing an ion-conducting phase and a silicon phase (silicon particles in one respect) dispersed within the ion-conducting phase. The ion-conducting phase is a phase that conducts ions, and examples thereof include a silicate phase, a carbon phase, and a silicon oxide phase.

[0039] The carbon phase may be composed of, for example, amorphous carbon. Examples of amorphous carbon constituting the carbon layer include hard carbon, soft carbon, and other amorphous carbon. Amorphous carbon has an average interplanar spacing d of (002) planes measured by, for example, X-ray diffraction. ００２ The carbon material has a particle size of more than 0.34 nm.

[0040] The main component of the silicon oxide phase (for example, 95% by mass or more and 100% by mass or less) may be silicon dioxide. The composition of the composite particles containing the silicon oxide phase and the silicon phase dispersed therein is generally SiO ｘ It can be expressed as: SiO ｘ is a material in which silicon particles are amorphous SiO ２ The oxygen content ratio x to silicon is preferably, for example, 0.5≦x<2.0, and more preferably 0.8≦x≦1.5.

[0041] The silicate phase may satisfy the following conditions (1) and / or (2): (1) The silicate phase contains at least one element selected from the group consisting of alkali metal elements and Group 2 elements (Group 2 elements of the long periodic table). (2) The silicate phase contains element L. The element L is at least one element selected from the group consisting of B, Al, Zr, Nb, Ta, V, lanthanoids, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W. Lanthanoids is a collective term for 15 elements ranging from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71.

[0042] Regarding the above condition (1), examples of alkali metal elements include lithium (Li), potassium (K), and sodium (Na). Examples of Group 2 elements include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The inclusion of an alkali metal element and / or a Group 2 element may reduce the irreversible capacity of the silicate phase. A silicate phase containing lithium (hereinafter, sometimes referred to as a "lithium silicate phase") is preferable in terms of, for example, a small irreversible capacity and a high initial charge / discharge efficiency.

[0043] The lithium silicate phase may be an oxide phase containing Li, Si, and O, and may contain other elements. The atomic ratio of O to Si in the lithium silicate phase, O / Si, is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase, Li / Si, is, for example, greater than 0 and less than 4.

[0044] The lithium silicate phase has the formula: Li ２ｚ SiO （２＋ｚ） The lithium silicate phase may contain or be composed of a lithium silicate phase represented by (0<z<2). Preferably, z satisfies the relationship 0<z<1, and z=1 / 2 (i.e., Li ２ Si ２ O ５ ) is more preferred.

[0045] The Si-based material may also include composite particles containing an ion-conducting phase and a silicon phase dispersed within the ion-conducting phase, and a coating layer covering at least a portion of the surface of the composite particles.

[0046] The coating layer present on the surface of the composite particle may include, for example, a conductive layer. Forming a conductive layer on the surface of the composite particle may increase the conductivity of the Si-based material. A conductive material containing carbon is preferred as the conductive material constituting the conductive layer. Examples of conductive materials containing carbon include conductive carbon materials. Examples of conductive carbon materials include carbon black, graphite, and amorphous carbon (amorphous carbon) with low crystallinity. Amorphous carbon is preferred because it has a strong buffering effect on the silicon phase, which changes in volume during charging and discharging. The amorphous carbon may be either easily graphitized carbon (soft carbon) or difficult-to-graphitize carbon (hard carbon). Examples of carbon black include acetylene black and ketjen black. The thickness of the conductive layer may be, for example, in the range of 1 to 200 nm. The thickness of the conductive layer can be measured by observing the cross section of the Si-containing material using a SEM or TEM (transmission electron microscope).

[0047] The content of the Si-based material is preferably 5% by mass or more relative to the total mass of the negative electrode active material, from the viewpoint of increasing the capacity of the secondary battery, etc. Furthermore, from the viewpoint of increasing the capacity of the secondary battery and suppressing swelling of the negative electrode, the content of the Si-based material is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, relative to the total amount of the negative electrode active material.

[0048] In addition to the Si-based material, the negative electrode active material may also contain a material other than the Si-based material that can reversibly absorb and release lithium ions. Examples of materials other than the Si-based material include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and carbon materials such as lump artificial graphite and artificial graphite such as graphitized mesophase carbon microbeads. Furthermore, for example, a metal that alloys with lithium, such as Sn, an alloy containing such a metal, or a compound containing such a metal may also be used. Examples of binders include the same materials as those used in the positive electrode 11. The negative electrode mixture layer may also contain a conductive agent.

[0049] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0050] The nonaqueous electrolyte secondary battery of this embodiment is preferably applied to a battery having a relatively large capacity, since it suppresses an increase in resistance due to charge / discharge cycles and exhibits excellent rapid charging characteristics. For example, ２ ), in a temperature environment of 25 ° C, after charging at a constant current of 1 C to 4.2 V, and then charging at a constant voltage of 4.2 V until the current value becomes 0.02 C, when discharging from 4.2 V to 2.5 V at a constant current of 0.05 C, the battery capacity when B (Ah) is B, B / A>40 Ah / m ２ It is preferable that the positive electrode mixture layer is a nonaqueous electrolyte secondary battery that satisfies the above condition. When the positive electrode mixture layer is provided on both the front surface side of the positive electrode core and the back surface of the positive electrode mixture layer, the area A of the positive electrode mixture layer is the sum of the areas of the front surface and the back surface.

[0051] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0052] Example 1 [Preparation of Positive Electrode Active Material of Polycrystalline Particles] [Ni ０．８ Co ０．１５ Al ０．０５ ](OH) ２ and LiOH were mixed in an Ishikawa-type mortar so that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.1:1.0. This mixture was then fired at 730°C for 50 hours in an oxygen atmosphere, and the fired product was pulverized to obtain a polycrystalline particle positive electrode active material.

[0053] The polycrystalline particles of the positive electrode active material were embedded in a resin, and cross sections of the particles were prepared by cross-section polishing (CP) and observed by SEM. As a result, the polycrystalline particles of the positive electrode active material were particles in a state where several hundred or more primary particles were aggregated. The average particle size of the polycrystalline particles of the positive electrode active material was 12 μm.

[0054] [Preparation of Positive Electrode Active Material of Single Crystal Particles] ０．８ Co ０．１５ Al ０．０５ ](OH) ２ and LiOH were mixed in an Ishikawa-type mortar so that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.1:1.0. This mixture was then fired at 800°C for 50 hours in an oxygen atmosphere, and the fired product was pulverized to obtain a positive electrode active material in the form of single-crystal particles.

[0055] The positive electrode active material of single crystal particles was embedded in a resin, and a cross section of the particle was prepared by cross-section polishing (CP) and observed by SEM. As a result, the positive electrode active material of single crystal particles was present in a state where it was completely separated into individual primary particles, or in a state where 2 to 10 primary particles were present together. The average particle size of the positive electrode active material of single crystal particles was 4 μm.

[0056] [Preparation of Positive Electrode] 100 parts by mass of a positive electrode active material obtained by mixing a polycrystalline particle positive electrode active material and a single-crystalline particle positive electrode active material in a mass ratio of 80:20, 0.01 parts by mass of multi-walled carbon nanotubes (MWCNT), 0.0001 parts by mass of single-walled carbon nanotubes, and 1 part by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to both sides of an aluminum foil positive electrode core, and the coating was dried and rolled to obtain a positive electrode having a positive electrode mixture layer formed on the positive electrode core.

[0057] [Fabrication of Negative Electrode] 95 parts by mass of graphite, 5 parts by mass of silicon oxide (SiO), 1 part by mass of carboxymethyl cellulose, and 1 part by mass of styrene-butadiene rubber were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both sides of a copper foil serving as a negative electrode core, and the coating was dried and rolled to obtain a negative electrode having a negative electrode mixture layer formed on the negative electrode core.

[0058] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:7, to prepare a non-aqueous electrolyte solution containing lithium hexafluorophosphate (LiPF ６ ) was dissolved in a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte solution.

[0059] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] (1) A positive electrode lead was attached to the positive electrode, and a negative electrode lead was attached to the negative electrode. A separator made of a polyethylene microporous film was then interposed between the positive and negative electrodes, and the resulting structure was wound to produce a wound electrode assembly. (2) Insulating plates were placed above and below the electrode assembly, and the negative electrode lead was welded to the case body and the positive electrode lead was welded to a sealing member, and the electrode assembly was housed within the case body. (3) A non-aqueous electrolyte was injected into the case body under reduced pressure, and the opening of the case body was then sealed with a sealing member via a gasket. This resulted in a non-aqueous electrolyte secondary battery.

[0060] Comparative Example 1: The positive electrode active material made of single-crystal particles was replaced with a positive electrode active material made of polycrystalline particles having an average particle size of 4 μm. The polycrystalline particles having an average particle size of 4 μm were produced in the same manner as in the production of the polycrystalline particles having an average particle size of 12 μm described above, except that the fired material was pulverized to an average particle size of 4 μm. In addition, single-walled carbon nanotubes were not used, and the amount of multi-walled carbon nanotubes added was 0.2 parts by mass. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except for the above.

[0061] Comparative Example 2 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material made of single-crystal particles was changed to a positive electrode active material made of polycrystalline particles having an average particle size of 4 μm.

[0062] <Comparative Example 3> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material made of single-crystalline particles was changed to a positive electrode active material made of polycrystalline particles having an average particle size of 4 μm, and that multi-walled carbon nanotubes were not used and the amount of single-walled carbon nanotubes added was 0.01 parts by mass.

[0063] Comparative Example 4 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that no single-crystal particle positive electrode active material was used, no single-walled carbon nanotubes were used, and the amount of multi-walled carbon nanotubes added was 0.2 parts by mass.

[0064] Comparative Example 5 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material made of single crystal particles was not used.

[0065] Comparative Example 6 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that no single-crystal particle positive electrode active material was used, no multi-walled carbon nanotubes were used, and the amount of single-walled carbon nanotubes added was 0.01 parts by mass.

[0066] Comparative Example 7 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that no single-walled carbon nanotubes were used and the amount of multi-walled carbon nanotubes added was 0.2 parts by mass.

[0067] Comparative Example 8 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that no multi-walled carbon nanotubes were used and the amount of single-walled carbon nanotubes added was 0.01 parts by mass.

[0068] [Rapid Charge Test] In an environment of 25°C, the nonaqueous electrolyte secondary batteries of Example 1 and each Comparative Example were charged at a constant current of 1 C until the battery voltage reached 4.2 V, and then discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. This charge / discharge cycle was counted as one cycle, and 300 cycles were performed. The capacity retention rate in the rapid charge test was calculated using the following formula, and the results are summarized in Table 1. Note that the capacity retention rates in the rapid charge test shown in Table 1 are shown relative to the capacity retention rate of Comparative Example 1 (100). A capacity retention rate of more than 100 can be evaluated as having excellent rapid charge characteristics. Capacity retention rate = (discharge capacity at 300th cycle / initial discharge capacity) x 100

[0069] [Measurement of Resistance Increase Rate in Charge-Discharge Cycle Test] In an environment of 25°C, the nonaqueous electrolyte secondary batteries of Example 1 and each Comparative Example were charged to an SOC of 50% at a constant current of 0.5 C. The voltage at this time was designated as V0. Next, the batteries were discharged at a constant current of 0.5 C for 10 seconds. The voltage at this time was designated as V1. The direct current resistance (DCR) was then calculated using the following formula. This was designated as the initial resistance. DCR = (V0 - V1) / 0.5 C

[0070] Next, in an environment of 25°C, the nonaqueous electrolyte secondary batteries of Example 1 and each Comparative Example were charged at a constant current of 0.5 C until the voltage reached 4.2 V, and then charged at a constant voltage of 0.05 C. Thereafter, the batteries were discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. This charge / discharge cycle was counted as one cycle, and 300 cycles were performed. Then, the DC resistance of the nonaqueous electrolyte secondary batteries of Example 1 and each Comparative Example after 300 cycles was measured using the same method as above. This was defined as the resistance after the charge / discharge cycles.

[0071] The initial resistance and the resistance after charge-discharge cycles were applied to the following formula to determine the resistance increase rate, and the results are summarized in Table 1. Note that the resistance increase rates shown in Table 1 are shown relative to the resistance increase rate of Comparative Example 1, which is set as the reference (100), for Example 1 and each Comparative Example. When the resistance increase rate is less than 100, it can be evaluated that the resistance increase due to charge-discharge cycles has been suppressed. Resistance increase rate = (resistance after charge-discharge cycles / initial resistance) x 100

[0072]

[0073] As shown in Table 1, Example 1 had a higher capacity retention rate in the rapid charge test and a lower resistance increase rate in the charge-discharge cycle test than Comparative Example 1. Comparative Examples 2 to 8 did not exhibit the desirable effects of both a higher capacity retention rate in the rapid charge test and a lower resistance increase rate in the charge-discharge cycle test than Comparative Example 1. From these results, it can be seen that the negative electrode has a negative electrode mixture layer containing a negative electrode active material containing a Si-based material, the positive electrode has a positive electrode mixture layer containing a positive electrode active material and a conductive agent, the positive electrode active material includes a positive electrode active material A of polycrystalline particles and a positive electrode active material B of single-crystal particles, and the average particle size (D Ｂ ) is the average particle size (D Ａ ) and the conductive agent includes single-walled carbon nanotubes and multi-walled carbon nanotubes, the nonaqueous electrolyte secondary battery can be said to suppress an increase in resistance due to charge-discharge cycles and have excellent rapid charge characteristics.

[0074] Example 2 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a positive electrode active material made of polycrystalline particles and a positive electrode active material made of single crystal particles were mixed in a mass ratio of 90:10, and the resistance increase rate in the rapid charge test and the charge / discharge cycle test was measured.

[0075] Example 3 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material of polycrystalline particles and the positive electrode active material of single crystal particles were mixed in a mass ratio of 70:30, and the resistance increase rate in the rapid charge test and the charge / discharge cycle test was measured.

[0076] Example 4 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material of polycrystalline particles and the positive electrode active material of single crystal particles were mixed in a mass ratio of 60:40, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured.

[0077] The results of the capacity retention rate in the rapid charge test and the resistance increase rate in the charge-discharge cycle test for Examples 1 to 4 and Comparative Example 2 are summarized in Table 2. Note that the capacity retention rate and resistance increase rate shown in Table 2 are shown relative to the value for Comparative Example 2 (100).

[0078]

[0079] As shown in Table 2, the total mass (M Ａ +M Ｂ ) relative to the mass (M Ｂ ) ratio ((M Ｂ / (M Ａ +M Ｂ Examples 1 to 4, in which the mass (M )) × 100) of the positive electrode active material B is 10 mass % or more and 40 mass % or less, suppress an increase in resistance due to charge / discharge cycles and have excellent rapid charge characteristics, compared to Comparative Example 2, in which no positive electrode active material of single crystal particles is used. Among Examples 1 to 4, the positive electrode active material B is Ｂ Examples 1, 3 and 4 in which the ratio of the mass (M Ｂ Examples 1 and 3 in which the ratio of ) is 20% or more and 30% or less are preferred.

[0080] Example 5 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a positive electrode active material made of polycrystalline particles having an average particle size of 10 μm and a positive electrode active material made of single-crystalline particles having an average particle size of 5 μm were used, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured.

[0081] Example 6 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a positive electrode active material made of polycrystalline particles having an average particle size of 12 μm and a positive electrode active material made of single-crystalline particles having an average particle size of 3 μm were used, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured.

[0082] Example 7 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a positive electrode active material made of polycrystalline particles having an average particle size of 15 μm and a positive electrode active material made of single-crystalline particles having an average particle size of 3 μm were used, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured.

[0083] Example 8 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a positive electrode active material made of polycrystalline particles having an average particle size of 12 μm and a positive electrode active material made of single-crystalline particles having an average particle size of 2 μm were used, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured.

[0084] The results of the capacity retention rate in the rapid charge test and the resistance increase rate in the charge cycle test for Examples 1, 5 to 8 and Comparative Example 2 are summarized in Table 3. Note that the capacity retention rate and resistance increase rate shown in Table 3 are shown relative to the value for Comparative Example 2 (100).

[0085]

[0086] As shown in Table 3, the average particle size (D Ｂ ) to the average particle size (D Ａ ) ratio (D Ａ / D Ｂ Examples 1, 5 to 8, in which the ratio of the positive electrode active material to the single-crystal particles is 2 or more and 6 or less, suppress the increase in resistance due to charge / discharge cycles and have excellent rapid charge characteristics compared to Comparative Example 2, in which a positive electrode active material made of single-crystal particles is not used. Among Examples 1, 5 to 8, D Ａ / D Ｂ Examples 1, 6 and 7 are preferred in which D is 3 or more and 5 or less. Furthermore, among Examples 1, 6 and 7, D is more preferred in that it can further suppress the increase in resistance due to charge / discharge cycles. Ａ / D Ｂ Examples 1 and 6 in which is 3 or more and 4 or less are preferred.

[0087] Example 9 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the amount of multi-walled carbon nanotubes added was 0.01 parts by mass and the amount of single-walled carbon nanotubes added was 0.0001 parts by mass, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured. The porosity of the positive electrode mixture layer was 24%.

[0088] Example 10 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the amount of multi-walled carbon nanotubes added was 0.2 parts by mass and the amount of single-walled carbon nanotubes added was 0.01 parts by mass, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured. The porosity of the positive electrode mixture layer was 23%.

[0089] Example 11 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the amount of multi-walled carbon nanotubes added was 0.5 parts by mass and the amount of single-walled carbon nanotubes added was 0.02 parts by mass, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured. The porosity of the positive electrode mixture layer was 22%.

[0090] Comparative Example 9 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that no multi-walled carbon nanotubes or single-walled carbon nanotubes were used and 1 part by mass of acetylene black was added, and the resistance increase rate in the rapid charge test and the charge-discharge cycle test was measured. The porosity of the positive electrode mixture layer was 20%.

[0091] The porosity of the positive electrode mixture layer in Example 1 and Comparative Example 2 was measured and found to be 23% in both Example 1 and Comparative Example 2.

[0092] The results of the capacity retention rate in the rapid charge test and the resistance increase rate in the charge-discharge cycle test for Examples 1, 9 to 11 and Comparative Examples 2 and 9 are summarized in Table 4. Note that the capacity retention rate and resistance increase rate shown in Table 4 are shown relative to the value for Comparative Example 2 (100) for each Example and Comparative Example 9.

[0093]

[0094] Examples 1 and 9 to 11 used, as the positive electrode active materials, a positive electrode active material A made of polycrystalline particles and a positive electrode active material B made of single-crystalline particles having an average particle size smaller than that of the positive electrode active material A, and the content of the multi-walled carbon nanotubes as the conductive agent was 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the positive electrode active material, and the content of the single-walled carbon nanotubes as the conductive agent was 0.0001 parts by mass or more and 0.02 parts by mass or less per 100 parts by mass of the positive electrode active material. As shown in Table 4, Examples 1 and 9 to 11, which use single-walled carbon nanotubes and multi-walled carbon nanotubes as the conductive agent, suppress the increase in resistance with charge / discharge cycles and exhibit superior rapid charge characteristics compared to Comparative Example 2, which does not use a positive electrode active material made of single-crystalline particles. In Comparative Example 9, which uses, as the positive electrode active materials, a positive electrode active material A made of polycrystalline particles and a positive electrode active material B made of single-crystalline particles having an average particle size smaller than that of the positive electrode active material A, but which uses acetylene black instead of carbon nanotubes as the conductive agent, both the increase in resistance with charge / discharge cycles and the rapid charge characteristics are worse than those of Comparative Example 2.

[0095] Among Examples 1 and 9 to 11, Examples 1, 10, and 11 are preferred in that they exhibit better rapid charging characteristics, as they contain multi-walled carbon nanotubes in an amount of 0.1 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the positive electrode active material, and contain single-walled carbon nanotubes in an amount of 0.005 parts by mass or more and 0.02 parts by mass or less per 100 parts by mass of the positive electrode active material. Furthermore, among Examples 1, 10, and 11, Examples 10 and 11 are preferred in that they contain multi-walled carbon nanotubes in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the positive electrode active material, and contain single-walled carbon nanotubes in an amount of 0.01 parts by mass or more and 0.02 parts by mass or less per 100 parts by mass of the positive electrode active material, as they can further suppress an increase in resistance due to charge-discharge cycles.

[0096] The present disclosure will be further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode mixture layer containing a negative electrode active material containing a Si-based material, the positive electrode has a positive electrode mixture layer containing a positive electrode active material and a conductive agent, the positive electrode active material includes a positive electrode active material A of polycrystalline particles and a positive electrode active material B of single-crystal particles, and the positive electrode active material B has an average particle size (D Ｂ ) is the average particle size (D Ａ ) of the positive electrode active material B, and the conductive agent contains single-walled carbon nanotubes and multi-walled carbon nanotubes. Ｂ ) relative to the average particle size (D Ａ ) ratio (D Ａ / D Ｂ ) is 2 or more and 6 or less. Ａ +M Ｂ ) the mass of the positive electrode active material B (M Ｂ ) ratio ((M Ｂ / (M Ａ +M Ｂ )) × 100) is 10 mass % or more and 40 mass % or less. Configuration 5: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 4, wherein the content of the multi-walled carbon nanotubes is 0.01 mass parts or more and 0.5 mass parts or less per 100 mass parts of the positive electrode active material, and the content of the single-walled carbon nanotubes is 0.0001 mass parts or more and 0.02 mass parts or less per 100 mass parts of the positive electrode active material. Configuration 6: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 4, wherein the area of ​​the positive electrode mixture layer is A (m ２ ) and in a temperature environment of 25°C, charge it at a constant current of 1C until it reaches 4.2V, then charge it at a constant voltage of 4.2V until the current value reaches 0.02C, and then discharge it from 4.2V to 2.5V at a constant current of 0.05C. When the battery capacity is B (Ah), B / A>40Ah / m ２The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the positive electrode mixture layer contains at least one of hydrogenated nitrile butadiene copolymer (HNBR) and a cellulose derivative. ２ / g or more of multi-walled carbon nanotubes, and the single-walled carbon nanotubes have a BET specific surface area of ​​300 m ２ / g or more of single-walled carbon nanotubes. Configuration 9: The secondary battery of any one of configurations 1 to 8, wherein the single-walled carbon nanotubes and the multi-walled carbon nanotubes are substantially free of a metal catalyst. Configuration 10: The secondary battery of any one of configurations 1 to 9, wherein the content of the Si-based material is 5 mass% or more with respect to the total mass of the negative electrode active material.

[0097] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding portion, 23 Filter, 24 Lower valve body, 25 Insulator, 26 Upper valve body, 27 Cap, 28 Gasket.

Claims

1. A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode mixture layer containing a negative electrode active material containing a Si-based material, the positive electrode has a positive electrode mixture layer containing a positive electrode active material and a conductive agent, the positive electrode active material includes a positive electrode active material A of polycrystalline particles and a positive electrode active material B of single-crystal particles, and the average particle size (D Ｂ ) is the average particle size (D Ａ ) smaller than 1.0 V, and the conductive agent contains single-walled carbon nanotubes and multi-walled carbon nanotubes.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode mixture layer has a porosity of 22% or more.

3. The average particle size (D Ｂ ) relative to the average particle size (D Ａ ) ratio (D Ａ / D Ｂ 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein ) is 2 or more and 6 or less.

4. The total mass (M Ａ +M Ｂ ) the mass of the positive electrode active material B (M Ｂ ) ratio ((M Ｂ / (M Ａ +M Ｂ 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the total mass of the electrolyte to the total mass of the nonaqueous electrolyte is 10% by mass or more and 40% by mass or less.

5. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the content of the multi-walled carbon nanotubes is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the positive electrode active material, and the content of the single-walled carbon nanotubes is 0.0001 parts by mass or more and 0.02 parts by mass or less per 100 parts by mass of the positive electrode active material.

6. The area of the positive electrode mixture layer is A (m ２ ) and in a temperature environment of 25°C, charge it at a constant current of 1C until it reaches 4.2V, then charge it at a constant voltage of 4.2V until the current value reaches 0.02C, and then discharge it from 4.2V to 2.5V at a constant current of 0.05C. When the battery capacity is B (Ah), B / A>40Ah / m ２ The nonaqueous electrolyte secondary battery according to claim 1 or 2, which satisfies the above.

7. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the positive electrode mixture layer contains at least one of hydrogenated nitrile butadiene copolymer (HNBR) and a cellulose derivative.

8. The multi-walled carbon nanotubes have a BET specific surface area of 200 m ２ / g or more of multi-walled carbon nanotubes, and the single-walled carbon nanotubes have a BET specific surface area of 300 m ２ 3. The nonaqueous electrolyte secondary battery according to claim 1, comprising single-walled carbon nanotubes in an amount of 1 / g or more.

9. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the single-walled carbon nanotubes and the multi-walled carbon nanotubes are substantially free of a metal catalyst.

10. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the content of the Si-based material is 5 mass % or more relative to the total mass of the negative electrode active material.

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