Non-aqueous electrolyte secondary battery

Abstract

In a non-aqueous electrolyte secondary battery according to an embodiment, a positive electrode includes a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the surface of particles of the composite oxide. The sulfonic acid compound is represented by formula (I).　In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2. A negative electrode includes a silicon-containing material (50). The silicon-containing material (50) contains an ion-conducting phase (51) and a Si phase (52) dispersed in the ion-conducting phase (50), and the size of the Si phase (52) is 110 nm or less.

Description

Nonaqueous electrolyte secondary battery

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

[0002] In Patent Document 1, Li ４ Ti ５ O １２ Patent Document 1 describes that the use of this active material as a negative electrode active material can suppress the resistance change of a battery before and after storage in a charged state.

[0003] Japanese Patent Application Laid-Open No. 2018-6164

[0004] In non-aqueous electrolyte secondary batteries, it is important to improve output characteristics and cycle characteristics while maintaining high capacity. Conventional techniques including those described in Patent Document 1 have not been able to adequately address these challenges, and there is still much room for improvement.

[0005] A nonaqueous electrolyte secondary battery according to the present disclosure is a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode contains a lithium-containing transition metal composite oxide and a sulfonic acid compound present on particle surfaces of the composite oxide, and the sulfonic acid compound is a compound represented by formula (I): In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2. The negative electrode includes a silicon-containing material. The silicon-containing material includes an ion-conducting phase and a Si phase dispersed in the ion-conducting phase, and the size of the Si phase is 110 nm or less.

[0006] The nonaqueous electrolyte secondary battery according to the present disclosure has a high capacity and excellent output characteristics and cycle characteristics.

[0007] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; 2 is a diagram showing a cross section of a particle of a silicon-containing material according to an embodiment of the present invention;

[0008] As a result of the inventors' investigations, it has been found that the presence of a sulfonic acid compound represented by the above formula (I) on the particle surface of a lithium-containing transition metal composite oxide used as a positive electrode active material can realize a nonaqueous electrolyte secondary battery with high capacity and low resistance. This is thought to be because the function of the sulfonic acid compound reduces the reaction resistance at the positive electrode, making it possible to deepen the charge-discharge depth. However, a new problem has arisen: deterioration in cycle characteristics, accompanied by the deepening charge-discharge depth due to the reduced reaction resistance. This deterioration in cycle characteristics is thought to be primarily due to the fact that the deepening charge-discharge depth causes greater expansion and contraction of the negative electrode mixture layer, resulting in insufficient diffusion of the electrolyte in the negative electrode mixture layer and resulting in non-uniform battery reactions.

[0009] Therefore, the inventors have succeeded in improving output characteristics and cycle characteristics while ensuring high capacity by using a lithium-containing transition metal composite oxide having a specific sulfonic acid compound attached to the particle surface as the positive electrode active material and a silicon-containing material having an Si phase size of 110 nm or less dispersed in an ion-conducting phase as the negative electrode active material. It is believed that the nonaqueous electrolyte secondary battery according to the present disclosure has improved cycle characteristics because the expansion and contraction of the negative electrode mixture layer is kept small even when the negative electrode is charged and discharged deeply.

[0010] The sulfonic acid compound represented by the above formula (I) functions specifically when applied to the particle surface of a lithium-containing transition metal composite oxide, reducing the reaction resistance at the positive electrode and deepening the charge / discharge depth of the positive electrode. However, simply applying a sulfonic acid compound to the positive electrode does not result in a battery with high capacity and excellent output and cycle characteristics. As a result of the inventors' studies, it has been found that, as described above, using a specific silicon-containing material as the negative electrode active material is important to realize such a battery. By setting the Si phase size of the silicon-containing material to 110 nm or less, the cycle characteristics are specifically improved compared to when a silicon-containing material with a Si phase size exceeding 110 nm is used.

[0011] 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.

[0012] In the embodiment described below, a nonaqueous electrolyte secondary battery 10 is exemplified, which is a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical outer can 16 with a bottom, but the outer can of the battery is not limited to a cylindrical outer can. Other embodiments of the nonaqueous electrolyte secondary battery according to the present disclosure include a prismatic battery having a prismatic outer can, a coin-shaped battery having a coin-shaped outer can, and a pouch-shaped battery having an outer can made of a laminate sheet including a metal layer and a resin layer. In addition, the electrode assembly is not limited to a wound type, and may be a stacked type electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0013] FIG. 1 is a schematic diagram illustrating an axial cross section of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte, and an outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 has 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 is a cylindrical metal container with a bottom and an open end in the axial direction, and the opening of the outer can 16 is closed by a sealing member 17. Hereinafter, for convenience of explanation, the sealing member 17 side of the battery is referred to as the top, and the bottom side of the outer can 16 is referred to as the bottom.

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

[0015] The liquid electrolyte (electrolytic solution) contains 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] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesins, acrylic resins, and polyether resins. 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, halide-based solid electrolytes, etc.).

[0017] 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 deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length 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.

[0018] 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.

[0019] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0020] 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.

[0021] The positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode assembly 14, particularly the positive electrode active material that constitutes the positive electrode 11 and the negative electrode active material that constitutes the negative electrode 12, will be described in detail below.

[0022] [Positive Electrode] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 31 disposed on the positive electrode core 30. The positive electrode core 30 can be made of a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film having such a metal disposed on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode core 30 except for the portion to which the positive electrode lead 20 is connected. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder to the surface of the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0023] Examples of the conductive agent contained in the positive electrode mixture layer 31 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 31 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. The content of the conductive agent and the binder is, for example, 0.1% by mass or more and 5% by mass or less, relative to the mass of the positive electrode mixture layer 31.

[0025] The positive electrode 11 contains a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the particle surfaces of the composite oxide. The lithium-containing transition metal composite oxide having the sulfonic acid compound attached to the particle surfaces functions as a positive electrode active material. The sulfonic acid compound is a compound represented by formula (I). In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.

[0026] The sulfonic acid compound represented by formula (I) (hereinafter sometimes simply referred to as "sulfonic acid compound") functions specifically when applied to the particle surface of a lithium-containing transition metal oxide, reducing the reaction resistance in the positive electrode 11 and improving the output characteristics of the battery. Furthermore, the reduced resistance makes it possible to increase the charge / discharge depth, thereby achieving a high capacity. Even a very small amount of the sulfonic acid compound can exert this effect, but it is preferable for it to be present on the particle surface of the composite oxide in an amount of 0.01% by mass or more relative to the lithium-containing transition metal composite oxide. The content of the sulfonic acid compound is more preferably 0.05% by mass or more, and particularly preferably 0.10% by mass or more, relative to the lithium-containing transition metal composite oxide.

[0027] The upper limit of the content of the sulfonic acid compound is not particularly limited, but from the viewpoint of achieving both output characteristics and cycle characteristics, it is preferably 2.0 mass% relative to the lithium-containing transition metal composite oxide, more preferably 1.5 mass%, and particularly preferably 1.0 mass%. An example of a suitable content of the sulfonic acid compound relative to the lithium-containing transition metal composite oxide is 0.05 mass% to 1.50 mass%, 0.1 mass% to 1.0 mass%, or 0.2 mass% to 0.7 mass%.

[0028] The positive electrode active material may be composed essentially of lithium-containing transition metal composite oxide particles having a sulfonic acid compound attached to the particle surface as the main component (the component with the highest mass percentage). The positive electrode active material may also contain composite oxides or other compounds other than the composite particles, as long as the objectives of the present disclosure are not impaired. For example, a composite oxide having no sulfonic acid compound attached to the particle surface may be included as part of the positive electrode active material.

[0029] The lithium-containing transition metal oxide preferably has a layered rock salt structure. When a sulfonic acid compound is applied to a composite oxide having a layered rock salt structure, the above-mentioned effect becomes more pronounced. Examples of the layered rock salt structure of the lithium-containing transition metal oxide 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, from the viewpoints of high capacity and stability of the crystal structure, a layered rock salt structure belonging to the space group R-3m is preferred. The layered rock salt structure of the lithium-containing transition metal oxide includes a transition metal layer, a Li layer, and an oxygen layer.

[0030] The lithium-containing transition metal oxide is a composite oxide containing, in addition to Li, metal elements such as Ni, Co, Mn, and Al. The metal element constituting the lithium-containing transition metal oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, and Mn.

[0031] From the viewpoint of increasing capacity, the lithium-containing transition metal oxide preferably contains 70 mol% or more, more preferably 80 mol% or more, of Ni relative to the total number of moles of metal elements excluding Li. The effect of adding a sulfonic acid compound is more pronounced when a lithium-containing transition metal oxide with a high Ni content is used. The Ni content may be 85 mol% or more, or even 90 mol% or more, relative to the total number of moles of metal elements excluding Li. The upper limit of the Ni content is, for example, 95 mol%.

[0032] For example, the Al content is 4 mol% or more and 15 mol% or less, and the Co content is 1.5 mol% or less, relative to the total number of moles of metal elements excluding Li. If the Al content is within this range, the crystal structure is stabilized and contributes to improving cycle characteristics compared to when the content is outside this range. Although Co does not need to be substantially added, adding a small amount of Co tends to improve battery performance. Furthermore, the Mn content is, for example, 4 mol% or more and 15 mol% or less, relative to the total number of moles of metal elements excluding Li.

[0033] The lithium-containing transition metal oxide has the general formula Li ａ Ni ｘ Al ｙ Co ｚ M1 ｗ O ２－ｂ (wherein 0.8≦a≦1.2, 0.85≦x≦0.95, 0.04≦y≦0.15, 0≦z≦0.015, 0≦w≦0.15, 0≦b<0.05, x+y+z+w=1, and M1 is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn.) Preferably, M1 is Mn.

[0034] The content of elements constituting the lithium-containing transition metal composite oxide can be measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0035] The lithium-containing transition metal composite oxide is, for example, a secondary particle formed by the aggregation of a plurality of primary particles. The volume-based median diameter (D50) of the composite oxide is not particularly limited, but is, for example, 3 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less. When the composite oxide is a secondary particle formed by the aggregation of primary particles, the D50 of the composite oxide refers to the D50 of the secondary particles. D50 refers to 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 composite oxide (as well as that of the negative electrode active material) can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0036] The average particle size of the primary particles constituting the lithium-containing transition metal composite oxide is, for example, 0.05 μm or more and 1 μm or less, and is calculated by averaging the diameters of the circumscribed circles of the primary particles extracted by analyzing scanning electron microscope (SEM) images of the cross sections of the secondary particles.

[0037] The sulfonic acid compound present on the particle surface of the lithium-containing transition metal composite oxide is the compound represented by formula (I) as described above. In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2. A is preferably a Group 1 element. Among these, Li or Na is more preferred, and Li is particularly preferred.

[0038] In formula (I), R is preferably an alkyl group. The number of carbon atoms in the alkyl group is preferably 5 or less, more preferably 3 or less. From the viewpoint of reducing reaction resistance, a suitable example of R is an alkyl group having 3 or less carbon atoms, and among these, a methyl group is preferred. In R, some of the hydrogen atoms bonded to the carbon may be substituted with fluorine. In formula (I), n is preferably 1.

[0039] Specific examples of the sulfonic acid compound include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, sodium ethanesulfonate, magnesium methanesulfonate, lithium fluoromethanesulfonate, etc. Among these, at least one selected from the group consisting of lithium methanesulfonate, lithium ethanesulfonate, and sodium methanesulfonate is preferred, with lithium methanesulfonate being particularly preferred.

[0040] The sulfonic acid compound is present, for example, uniformly over the entire particle surface of the lithium-containing transition metal composite oxide. The presence of the sulfonic acid compound on the particle surface of the composite oxide can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectrum obtained by FT-IR, the positive electrode active material containing lithium methanesulfonate exhibits, for example, a peak at 1238 cm －１ , 1175 cm －１ , 1065 cm －１ , 785 cm －１ It has an absorption peak around 1238 cm －１ , 1175 cm －１ , 1065 cm －１ The peak around 785 cm is due to the SO stretching vibration of lithium methanesulfonate. －１ The peak around this position is a peak due to the C-S stretching vibration derived from lithium methanesulfonate.

[0041] For positive electrode active materials containing sulfonic acid compounds other than lithium methanesulfonate, the presence of the sulfonic acid compounds can be confirmed from the absorption peaks attributable to the sulfonic acid compounds in the infrared absorption spectrum. The presence of the sulfonic acid compounds on the particle surfaces of the lithium-containing transition metal composite oxide can also be confirmed by ICP, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), synchrotron XRD measurement, TOF-SIMS, etc.

[0042] The positive electrode active material, which is one example of the embodiment, can be produced by the following method: Note that the production method described here is only an example, and the method for producing the positive electrode active material is not limited to this method.

[0043] First, a metal oxide containing a metal element such as Ni, Co, Mn, or Al is synthesized. Next, the metal oxide is mixed with a lithium compound and calcined to obtain a lithium-containing transition metal composite oxide. The metal oxide can be synthesized, for example, by adding an alkaline solution such as sodium hydroxide dropwise to a stirred solution of a metal salt containing Ni, Co, Mn, Al, or the like, and adjusting the pH to the alkaline side (e.g., 8.5 to 12.5), thereby precipitating (co-precipitating) a composite hydroxide containing a metal element such as Ni, Co, Mn, or Al, and then heat-treating the composite hydroxide. The heat-treatment temperature is not particularly limited, but an example is 300°C to 600°C.

[0044] The lithium compound includes Li ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２ Examples of suitable lithium compounds include lithium ions, ...

[0045] The mixture of the metal oxide and the lithium compound is fired, for example, in an oxygen atmosphere. The mixture may be fired through multiple temperature-raising processes. The firing process includes, for example, a first temperature-raising process in which the temperature is raised to 450°C or higher and 680°C or lower at a temperature-raising rate of 1.0°C / min or higher and 5.5°C / min or lower, and a second temperature-raising process in which the temperature is raised to a temperature exceeding 680°C at a temperature-raising rate of 0.1°C / min or higher and 3.5°C / min or lower. The maximum temperature reached in the firing process may be set to 700°C or higher and 850°C or lower, and the mixture may be held at this temperature for 1 hour or higher and 10 hours or lower.

[0046] Next, the fired product (lithium-containing transition metal composite oxide) is washed with water and dehydrated to obtain a cake-like composition. This washing step removes any remaining alkaline components. The washing and dehydration can be performed by a conventionally known method. The cake-like composition is then dried to obtain a powder-like composition. The drying step may be performed in a vacuum atmosphere. An example of drying conditions is a temperature of 150°C to 400°C for 0.5 hours to 15 hours.

[0047] The sulfonic acid compound is added, for example, to the cake-like composition obtained in the washing step or the powder-like composition obtained in the drying step. At this time, a sulfonic acid solution may be added instead of or together with the sulfonic acid compound. This results in a positive electrode active material in which the sulfonic acid compound adheres to the particle surfaces of the lithium-containing transition metal composite oxide. The sulfonic acid compound may be added as an aqueous dispersion. The sulfonic acid solution is preferably an aqueous solution of sulfonic acid. The sulfonic acid concentration in the sulfonic acid solution is, for example, 0.5% by mass or more and 40% by mass or less.

[0048] Since a certain amount of lithium compound remains in the cake-like composition, adding a sulfonic acid solution to the cake-like composition causes the Li dissolved in the water in the cake to react with the sulfonic acid, thereby producing lithium sulfonate.

[0049] [Negative Electrode] The negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 41 disposed on the negative electrode core 40. The negative electrode core 40 may be a foil of a metal 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 41 contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core 40, excluding the portion to which the negative electrode lead 21 is connected. The negative electrode 12 can be fabricated, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40. The negative electrode mixture layer 41 may also contain a conductive agent such as CNT.

[0050] As in the case of the positive electrode 11, the binder contained in the negative electrode mixture layer 41 can be a fluorine-containing resin, an olefin resin, PAN, a polyimide, a polyamide, an acrylic resin, or the like. However, polyvinyl acetate, styrene-butadiene rubber (SBR), or the like can also be used. Among these, SBR is preferably used. One type of binder may be used alone, or multiple types may be used in combination. The content of the binder is, for example, 0.1% by mass or more and 5% by mass or less, relative to the mass of the negative electrode mixture layer 41. In addition, the negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. These function as thickeners in the negative electrode mixture slurry.

[0051] FIG. 2 is a schematic diagram showing a particle cross section of a silicon-containing material 50. The negative electrode 12 includes a silicon-containing material 50 having a particle cross section as shown in FIG. 2. The silicon-containing material 50 is contained in the negative electrode mixture layer 41 and functions as a negative electrode active material that absorbs and releases Li ions during charging and discharging of the battery. The silicon-containing material 50 includes an ion-conducting phase 51 and a Si phase 52 dispersed in the ion-conducting phase 51. The size of the Si phase 52 is 110 nm or less. In a nonaqueous electrolyte secondary battery 10 in which the above sulfonic acid compound is applied to the positive electrode 11, the cycle characteristics change specifically at a Si phase size of 110 nm or less. When the size of the Si phase 52 of the silicon-containing material 50 is 110 nm or less, the cycle characteristics are significantly improved.

[0052] Although it is possible to use only the silicon-containing material 50 as the negative electrode active material, the negative electrode 12 preferably contains both a carbon material and the silicon-containing material 50. The combined use of the carbon material and the silicon-containing material 50 makes it easier to achieve both high capacity and excellent cycle characteristics. The negative electrode 12 may contain, for example, as the negative electrode active material, a silicon-containing material other than the silicon-containing material 50, or a material containing another element that forms an alloy with Li, but in this embodiment, the negative electrode 12 essentially contains only the carbon material and the silicon-containing material 50.

[0053] The content of the carbon material is preferably higher than the content of the silicon-containing material 50. From the viewpoint of improving cycle characteristics, the content of the silicon-containing material 50 is preferably 40 mass% or less, more preferably 35 mass% or less, and particularly preferably 30 mass% or less, of the total mass of the negative electrode active material. In a nonaqueous electrolyte secondary battery in which a sulfonic acid compound is added to the positive electrode 11, if the silicon-containing material 50 is completely absent, not only the battery capacity but also the cycle characteristics decrease. From the viewpoint of increasing capacity and improving cycle characteristics, the content of the silicon-containing material 50 is preferably 5 mass% or more of the total mass of the negative electrode active material.

[0054] An example of a suitable range for the content of silicon-containing material 50 is 5% by mass or more and 35% by mass or less, more preferably 5% by mass or more and 30% by mass or less, or 5% by mass or more and 25% by mass or less, of the total mass of the negative electrode active material. Note that, as described above, negative electrode 12 may contain a silicon-containing material other than silicon-containing material 50 within a range that does not impair the objectives of the present disclosure. For example, the average size of the Si phase of the silicon-containing material contained in negative electrode 12 may be 110 nm or less, and a silicon-containing material whose Si phase size exceeds 110 nm may be contained.

[0055] 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 them, it is preferable to use at least artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, and amorphous graphite, or a mixture thereof. The volume-based D50 of the carbon material is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less.

[0056] Soft carbon and hard carbon are classified as amorphous carbons with an undeveloped graphite crystal structure. More specifically, they refer to carbon components having a d(002) interplanar spacing of 0.342 nm or more as determined by X-ray diffraction. Soft carbon is also called graphitizable carbon, and is carbon that is more easily graphitized by high-temperature treatment than hard carbon. Hard carbon is also called non-graphitizable carbon. Note that, in the configuration of the present invention, it is not necessary to clearly distinguish between soft carbon and hard carbon. Graphite and at least one amorphous carbon of soft carbon and hard carbon may be used in combination as the negative electrode active material.

[0057] As described above, the silicon-containing material 50 includes an ion-conducting phase 51 and an Si phase 52 dispersed in the ion-conducting phase 51. The silicon-containing material 50 is a composite particle composed of the ion-conducting phase 51 and the Si phase 52. The D50 of the silicon-containing material 50 is generally smaller than the D50 of graphite. The volume-based D50 of the silicon-containing material 50 is, for example, 1 μm or more and 20 μm or less, or 1 μm or more and 15 μm or less. Note that one type of silicon-containing material 50 may be used alone, or two or more types may be used in combination.

[0058] The ion-conducting phase 51 is, for example, 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 made of Si and an element more electropositive than Si, such as NiSi, Mg ２ Si, TiSi ２The Si phase 52 is formed by dispersing Si in the form of fine particles. The ion-conducting phase 51 is a continuous phase formed by an aggregation of particles that are finer than the Si phase 52.

[0059] As described above, the size of the Si phase 52 in the silicon-containing material 50 is 110 nm or less. It is preferable that the average size of the Si phase 52 contained in one particle of the silicon-containing material 50 is 110 nm or less. The Si phase 52 is dispersed in the ion-conducting phase 51 in the form of fine particles in the cross section of the particle of the silicon-containing material 50. Therefore, hereinafter, the average size of the Si phase 52 may be referred to as the "average particle size." The average particle size of the Si phase is calculated by randomly selecting 100 silicon-containing materials, capturing SEM images of the cross sections of each particle, and averaging the diameters of the circumscribing circles α of the Si phases extracted by image analysis. The particle cross sections can be prepared by a cross-section polisher (CP) method.

[0060] In the negative electrode 12, when the size of the Si phase is measured for all silicon-containing materials contained in the negative electrode mixture layer 41 or for 100 silicon-containing materials randomly selected from all silicon-containing materials, the average particle size of the Si phase is 110 nm or less. Note that, as long as the average particle size of the Si phase is 110 nm or less throughout the negative electrode mixture layer 41, a silicon-containing material having an average particle size of the Si phase exceeding 110 nm may be used. However, when two or more types of materials are used, it is preferable that all of the materials be silicon-containing materials 50 in which the average particle size of the Si phase 52 is 110 nm or less.

[0061] As described above, the Si phase 52 contained in each particle of the silicon-containing material 50 may have an average particle size of 110 nm or less, but all of the particles may have particle sizes of 110 nm or less. The average particle size of the Si phase 52 is preferably 100 nm or less, more preferably 90 nm or less, and particularly preferably 80 nm or less. In this case, particle expansion due to charge and discharge can be effectively suppressed while maintaining a high capacity, resulting in a more significant improvement in cycle characteristics.

[0062] The average grain size of the Si phase 52 may be 50 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. The lower limit of the average grain size of the Si phase 52 is not particularly limited, but is, for example, 1 nm. Examples of suitable ranges for the average grain size of the Si phase 52 may be 1 nm or more and 50 nm or less, 1 nm or more and 40 nm or less, 1 nm or more and 30 nm or less, 5 nm or more and 30 nm or less, or 10 nm or more and 30 nm or less. When the average grain size of the Si phase 52 is within this range, the effect of improving the cycle characteristics is greater than when the average grain size is outside this range.

[0063] The silicon-containing material 50 may have a conductive layer covering the surface of the ion-conducting phase 51. The conductive layer is made of a material with higher conductivity than the ion-conducting phase 51 and forms a good conductive path in the negative electrode mixture layer 41. The conductive layer is, for example, a carbon coating made of a conductive carbon material. Examples of conductive carbon materials that can be used include carbon black such as acetylene black and ketjen black, graphite, and amorphous carbon (amorphous carbon) with low crystallinity. The thickness of the conductive layer is preferably 1 nm to 200 nm, or 5 nm to 100 nm, taking into consideration ensuring conductivity and the diffusibility of Li ions into the particles. The thickness of the conductive layer can be measured by observing the cross section of the composite material using a SEM or a transmission electron microscope (TEM).

[0064] The ion-conducting phase 51 may contain at least one element selected from the group consisting of Group 1 and Group 2 elements of the periodic table. The ion-conducting phase 51 may be a silicon oxide phase doped with Li. The ion-conducting phase 51 may also contain at least one element selected from the group consisting of B, Al, Zr, Nb, Ta, V, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, W, and lanthanoids.

[0065] A suitable example of the silicon-containing material 50 has a sea-island structure in which fine Si (Si phase 52) is dispersed substantially uniformly in an amorphous silicon oxide phase (ion-conducting phase 51), and is represented as a general formula SiO ｘThe silicon oxide may be mainly composed of silicon dioxide. The silicon oxide phase may be doped with Li. The oxygen to Si content (x) is, for example, 0.5≦x<2.0, and preferably 0.8≦x≦1.5.

[0066] Another example of a suitable silicon-containing material 50 is a composite particle having an island-in-sea 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, a compound 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.

[0067] Another example of a suitable silicon-containing material 50 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 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.

[0068] The silicon-containing material 50 is, for example, a silicon-containing material obtained by converting alkoxysilane into SiO ２ After synthesizing the nanoparticles, SiO ２The nanoparticles are obtained by synthesizing a polymer containing nanoparticles, carbonizing the polymer, and reducing the polymer (see the examples below for details). In this case, the composite particles are formed in which fine Si particles are dispersed uniformly in an amorphous carbon phase. The size of the Si phase 52 can be adjusted by, for example, grinding the SiO ２ The nanoparticles can be reduced in size by a prolonged milling process. For example, the milling can be continued for 100 hours or more, and the SiO ２ The process is continued until the average particle size of the nanoparticles reaches the target particle size. At this time, isopropyl alcohol is added to the pulverization process, and the SiO ２ This promotes the miniaturization of nanoparticles.

[0069] From the viewpoint of improving cycle characteristics, the particle expansion coefficient of the silicon-containing material 50 is preferably 210% or less, and more preferably 170% or less.

[0070] The particle expansion coefficient of the silicon-containing material 50 is measured by the following method. (1) A battery to be evaluated is disassembled, and the negative electrode plate is cut out. A single-electrode cell is prepared using metallic Li as the counter electrode and an ionic liquid as the electrolyte, with the particle cross-section of the silicon-containing material exposed. (2) The single-electrode cell is charged at 0.002 C in a 25°C environment until the cell voltage reaches 5 mV, and then discharged at 0.05 C until the cell voltage reaches 1.0 V, and the particle cross-section of the silicon-containing material is observed in situ using an SEM. (3) From the change in the particle cross-sectional area of ​​the silicon-containing material, the particle volume (V1) of the silicon-containing material in the charged state and the particle volume (V2) of the silicon-containing material in the discharged state are determined, and the particle expansion coefficient (V1 x 100 / V2) is calculated.

[0071] The expansion rate of the negative electrode mixture layer 41 during charging per discharge capacity is preferably 50% / (mAh / g) or less, and more preferably 48% / (mAh / g) or less. Here, the discharge capacity is the discharge capacity per gram of negative electrode active material. In this case, the improvement in cycle characteristics is more significant compared to when the expansion rate of the negative electrode mixture layer 41 during charging exceeds 550%. The expansion rate of the negative electrode mixture layer 41 during charging can be controlled by the amount of silicon-containing material 50 added and the particle expansion rate. The lower limit of the expansion rate of the negative electrode mixture layer 41 during charging per discharge capacity is not particularly limited, but is, for example, 40% / (mAh / g). A charge expansion rate of 40% / (mAh / g) or more makes it easier to achieve a higher capacity than when the expansion rate is less than 40% / (mAh / g).

[0072] The expansion rate during charge per discharge capacity of the negative electrode mixture layer 41 is measured by the following method. (1) A battery to be evaluated is disassembled, and the negative electrode is cut out. A single-electrode cell is prepared using metallic Li as a counter electrode and an ionic liquid as an electrolyte. (2) The single-electrode cell is charged at 0.1 C in a temperature environment of 25°C until the cell voltage reaches 5 mV, and then discharged at 0.1 C until the cell voltage reaches 1.0 V, and the discharge capacity (mAh / g) per 1 g of negative electrode active material is determined. (3) The thickness (T1) of the negative electrode mixture layer in a charged state and the thickness (T2) of the negative electrode mixture layer in a discharged state are determined, and the increase rate of the thickness (T1 × 100 / T2 − 100) is calculated. This is then divided by the discharge capacity (mAh / g) per 1 g of active material in the negative electrode mixture to calculate the expansion rate during charge per discharge capacity of the negative electrode mixture layer.

[0073] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. 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.

[0074] A filler layer containing an inorganic filler may be disposed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13. In addition, a highly heat-resistant resin layer (heat-resistant layer) such as an aramid resin may be disposed on the surface of the separator 13. The separator 13 may have, for example, a substrate made of a porous sheet and a filler layer or heat-resistant layer disposed on the substrate.

[0075] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0076] Example 1 Synthesis of Positive Electrode Active Material [Ni ０．９０ Al ０．０５ Mn ０．０５ ](OH) ２ The composite hydroxide represented by the formula (I) was calcined at 500°C for 8 hours to obtain an oxide (Ni ０．９０ Al ０．０５ Mn ０．０５ O ２ Next, LiOH and the composite oxide were mixed so that the molar ratio of Li to the total amount of Ni, Al, and Mn was 1.03:1 to obtain a mixture. This mixture was then subjected to an oxygen flow (10 cm) with an oxygen concentration of 95%. ３ The mixture was fired at a temperature rising rate of 2.0°C / min from room temperature to 650°C, and then at a temperature rising rate of 0.5°C / min from 650°C to 780°C, thereby obtaining a lithium-containing transition metal composite oxide.

[0077] Water was added to the obtained lithium-containing transition metal composite oxide so that the slurry concentration was 1500 g / L, and the mixture was stirred for 15 minutes and filtered to obtain a cake-like composition. Powdered lithium methanesulfonate was added to this cake-like composition. The amount of lithium methanesulfonate added was 0.1 mass% based on the total mass of the lithium-containing transition metal composite oxide. After the addition of lithium methanesulfonate, the mixture was dried under vacuum at 180°C for 2 hours to obtain a positive electrode active material. The presence of lithium methanesulfonate on the particle surface of the composite oxide was confirmed by Fourier transform infrared spectroscopy (FT-IR).

[0078] [Preparation of Positive Electrode] The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 98:1:1, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to a positive electrode core made of aluminum foil, the coating was dried and compressed, and then the positive electrode core was cut to a predetermined electrode size to obtain a positive electrode with a positive electrode mixture layer formed on both sides of the positive electrode core. Note that an exposed portion was provided in part of the positive electrode, exposing the surface of the positive electrode core.

[0079] [Synthesis of silicon-containing material] Tetraethylorthosilane (TEOS) and cetyltrimethylammonium bromide (CTAB) were mixed in a mixed solution of ethanol / water / ammonia to prepare SiO modified with CTAB. ２ Nanoparticles were obtained. ２ The nanoparticles were milled for 300 hours using a bead mill with the addition of isopropyl alcohol, and then polymerized with resorcinol and formaldehyde to produce SiO ２ Polymer particles containing nanoparticles were obtained. The ratio of resorcinol to TEOS was approximately 0.5:1. The obtained polymer particles were dried and then heated to 800°C in a nitrogen atmosphere to carbonize the polymer. The polymer was then mixed with magnesium powder and heated to 650°C in an argon atmosphere to carry out a magnesium thermal reduction reaction. ２MgO was dissolved from the particles after the reaction in an O / ethanol solution, washed with ethanol, and then dried to obtain a mesoporous silicon-containing material in which a Si phase was dispersed in an amorphous carbon phase.

[0080] One hundred particles were randomly selected from the SEM image of the cross section of the obtained silicon-containing material, and the average size (average particle size) of the Si phase was determined by the above method (the same applies to the following Examples and Comparative Examples). The average particle size of the Si phase was 5 nm.

[0081] [Preparation of Negative Electrode] The negative electrode active material was a mixture of the silicon-containing material and artificial graphite in a mass ratio of 10:90. This negative electrode active material was mixed with a dispersion of carboxymethylcellulose sodium (CMC-Na) and styrene-butadiene rubber (SBR) in a solids mass ratio of 100:1:1, and a negative electrode mixture slurry was prepared using water as the dispersion medium. This negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, and the coating was dried. The coating was then rolled using a roller and cut to a predetermined electrode size, resulting in a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core. An exposed portion was provided in part of the negative electrode, exposing the surface of the negative electrode core.

[0082] [Preparation of non-aqueous electrolyte] LiPF 6 was dissolved in a mixed solvent of ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4 (25°C). ６ was dissolved in the solution at a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte solution.

[0083] [Fabrication of Test Cell (Non-Aqueous Electrolyte Secondary Battery)] An aluminum lead was attached to the exposed portion of the positive electrode, and a nickel lead was attached to the exposed portion of the negative electrode. The positive electrode and the negative electrode were spirally wound with a polyolefin separator interposed therebetween, and then pressed radially to form a flat wound electrode assembly. This electrode assembly was housed in an exterior body made of an aluminum laminate sheet, and the non-aqueous electrolyte solution was poured into it. The opening of the exterior body was then sealed to obtain a test cell.

[0084] Example 2 A test cell was produced in the same manner as in Example 1, except that in the synthesis of the positive electrode active material, the amount of lithium methanesulfonate added to the lithium-containing transition metal composite oxide was changed to 0.3 mass %.

[0085] Example 3 A test cell was produced in the same manner as in Example 1, except that in the synthesis of the positive electrode active material, the amount of lithium methanesulfonate added to the lithium-containing transition metal composite oxide was changed to 0.5% by mass.

[0086] Example 4 A test cell was produced in the same manner as in Example 1, except that in the synthesis of the positive electrode active material, the amount of lithium methanesulfonate added to the lithium-containing transition metal composite oxide was changed to 1.0 mass %.

[0087] Example 5 A test cell was fabricated in the same manner as in Example 3, except that a mixture of the silicon-containing material and artificial graphite in a mass ratio of 20:80 was used as the negative electrode active material.

[0088] Example 6 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 3, except that a silicon-containing material with an average particle size of the Si phase of 20 nm was used as the negative electrode active material. The silicon-containing material was synthesized as follows. [Synthesis of silicon-containing material] Tetraethylorthosilane (TEOS) and cetyltrimethylammonium bromide (CTAB) were mixed in a mixed solution of ethanol / water / ammonia to form SiO modified with CTAB. ２ Nanoparticles were obtained. ２ The nanoparticles were milled for 200 hours using a bead mill with the addition of isopropyl alcohol, and then polymerized with resorcinol and formaldehyde to produce SiO ２ Polymer particles containing nanoparticles were obtained. The ratio of resorcinol to TEOS was approximately 0.5:1. The obtained polymer particles were dried and then heated to 800°C in a nitrogen atmosphere to carbonize the polymer. The polymer was then mixed with magnesium powder and heated to 650°C in an argon atmosphere to carry out a magnesium thermal reduction reaction. ２MgO was dissolved from the particles after the reaction in an O / ethanol solution, washed with ethanol, and then dried to obtain a mesoporous silicon-containing material in which a Si phase was dispersed in an amorphous carbon phase.

[0089] Example 7 A test cell was prepared in the same manner as in Example 6, except that a mixture of the silicon-containing material used in Example 6 and artificial graphite in a mass ratio of 20:80 was used as the negative electrode active material.

[0090] Example 8 A test cell was produced in the same manner as in Example 3, except that sodium methanesulfonate was used instead of lithium methanesulfonate in synthesizing the positive electrode active material.

[0091] Example 9 A test cell was produced in the same manner as in Example 3, except that lithium ethanesulfonate was used instead of lithium methanesulfonate in synthesizing the positive electrode active material.

[0092] Example 10 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3, except that a silicon-containing material having an average particle size of the Si phase of 100 nm was used as the negative electrode active material. The silicon-containing material was synthesized as follows. [Synthesis of Silicon-Containing Material] SiO ２ A silicon-containing material was synthesized in the same manner as in Example 1, except that the nanoparticles were pulverized using a bead mill for 100 hours.

[0093] Example 11 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3, except that a silicon-containing material having an average particle size of the Si phase of 80 nm was used as the negative electrode active material. The silicon-containing material was synthesized as follows. [Synthesis of Silicon-Containing Material] SiO ２ A silicon-containing material was synthesized in the same manner as in Example 1, except that the nanoparticles were pulverized using a bead mill for 150 hours.

[0094] Comparative Example 1 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that lithium methanesulfonate was not used in the synthesis of the positive electrode active material, and a silicon-containing material having an average particle size of the Si phase of 120 nm was used as the negative electrode active material. The silicon-containing material was synthesized as follows. [Synthesis of Silicon-Containing Material] SiO ２ A silicon-containing material was synthesized in the same manner as in Example 1, except that the nanoparticles were pulverized using a bead mill for 50 hours.

[0095] Comparative Example 2 A test cell was produced in the same manner as in Example 1, except that lithium methanesulfonate was not used in the synthesis of the positive electrode active material.

[0096] Comparative Example 3 A test cell was produced in the same manner as in Example 3, except that lithium succinate was used instead of lithium methanesulfonate in synthesizing the positive electrode active material.

[0097] Comparative Example 4 A test cell was produced in the same manner as in Example 3, except that lithium oxalate was used instead of lithium methanesulfonate in synthesizing the positive electrode active material.

[0098] Comparative Example 5 A test cell was produced in the same manner as in Example 3, except that the silicon-containing material used in Comparative Example 1 was used as the silicon-containing material.

[0099] The output characteristics and cycle characteristics (capacity retention rate) of each test cell of the Examples and Comparative Examples were evaluated by the following methods, and the evaluation results are shown in Table 1. The output characteristics of each test cell shown in Table 1 are relative values ​​when the value of the test cell of Comparative Example 2 is set to 100, and a larger value indicates better output characteristics.

[0100] [Evaluation of Initial Output Characteristics (Discharge Load Characteristics)] The test cell was charged at a constant current of 0.3 It in a temperature environment of 25°C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 0.02 It at 4.2 V. It was then discharged at a constant current of 0.2 It until the battery voltage reached 2.5 V. It was then charged at a constant current of 0.3 It again until the battery voltage reached 4.2 V, and then charged at a constant voltage of 0.02 It at 4.2 V. It was then discharged at a constant current of 0.5 It until the battery voltage reached 2.5 V. The discharge capacity values ​​at this time were used to calculate the discharge load characteristics according to the following formula: Discharge load characteristics (%) = (Discharge capacity at 0.5 It / Discharge capacity at 0.02 It)

[0101] [Evaluation of Cycle Characteristics (Capacity Retention Rate after Cycle Test)] The test cell was charged at a constant current of 0.3 It at a temperature of 25°C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 It. Subsequently, the test cell was discharged at a constant current of 0.5 It until the battery voltage reached 2.5 V. This charge / discharge cycle constituted one cycle, and 300 cycles were repeated. The discharge capacity at the first cycle and the discharge capacity at the 300th cycle were determined, and the capacity retention rate was calculated according to the following formula: Capacity retention rate (%) = (Discharge capacity at the 300th cycle / Discharge capacity at the first cycle) × 100

[0102]

[0103] As shown in Table 1, all of the test cells of the Examples have higher discharge load characteristics and superior output characteristics than the test cells of Comparative Examples 1 to 4. Furthermore, all of the test cells of the Examples have higher capacity retention rates after cycle testing and superior cycle characteristics than the test cell of Comparative Example 5. That is, the test cells of the Examples achieve both excellent output characteristics and cycle characteristics. As with the test cell of Comparative Example 5, when output characteristics are improved, it becomes difficult to ensure good cycle characteristics. However, the test cells of the Examples have good cycle characteristics despite their high output characteristics.

[0104] The test cell of Comparative Example 1, which did not use a sulfonic acid compound in the positive electrode and used a silicon-containing compound with an average particle size of the Si phase exceeding 110 nm as the negative electrode active material, had lower output characteristics than the test cells of Examples 1 and 2. Furthermore, the capacity retention rate of the test cell of Comparative Example 1 was similar to that of Example 10, which had the lowest capacity retention rate among the Examples (output characteristic: 102.0).

[0105] When a sulfonic acid compound is used in the positive electrode, the capacity retention rate is significantly reduced when a silicon-containing compound with an Si phase having an average particle size of more than 110 nm is used as the negative electrode active material (Comparative Example 5). In other words, it can be seen from the examples and Comparative Example 5 that when a sulfonic acid compound is used in the positive electrode, the capacity retention rate is significantly improved by using a silicon-containing compound with an Si phase having an average particle size of 110 nm or less as the negative electrode active material.

[0106] When lithium succinate and lithium oxalate were used instead of lithium methanesulfonate (Comparative Examples 3 and 4), the output characteristics were actually lower than when no acid salt was added to the positive electrode (Comparative Example 2).

[0107] The present disclosure is further described by the following embodiments: Configuration 1: A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the particle surface of the composite oxide, and the sulfonic acid compound is a compound represented by formula (I): wherein A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2; the negative electrode comprises a silicon-containing material, the silicon-containing material comprising an ion-conducting phase and a Si phase dispersed in the ion-conducting phase, the size of the Si phase being 110 nm or less. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the sulfonic acid compound is present in an amount of 0.1 mass % or more and 1.0 mass % or less relative to the lithium-containing transition metal composite oxide. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein A in Formula (I) is Li or Na. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein R in Formula (I) is an alkyl group having 3 or less carbon atoms. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the lithium-containing transition metal composite oxide has a layered rock salt structure. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the negative electrode mixture layer contains, as negative electrode active materials, a carbon material and the silicon-containing material. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the 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. Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the size of the Si phase is 1 nm or more and 50 nm or less.

[0108] 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 Positive electrode core, 31 Positive electrode mixture layer, 40 Negative electrode core, 41 Negative electrode mixture layer, 50 Silicon-containing material, 51 Ion-conducting phase, 52 Si phase

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the particle surface of the composite oxide, and the sulfonic acid compound is a compound represented by formula (I): wherein A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2; the negative electrode comprises a silicon-containing material; the silicon-containing material comprises an ion-conducting phase and a Si phase dispersed in the ion-conducting phase, and the size of the Si phase is 110 nm or less.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the sulfonic acid compound is present in an amount of 0.1% by mass or more and 1.0% by mass or less relative to the lithium-containing transition metal composite oxide.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein A in formula (I) is Li or Na.

4. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein R in formula (I) is an alkyl group having 3 or less carbon atoms.

5. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the lithium-containing transition metal composite oxide has a layered rock salt structure.

6. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the negative electrode contains, as negative electrode active materials, a carbon material and the silicon-containing material.

7. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the 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.

8. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the size of the Si phase is 1 nm or more and 50 nm or less.

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