Nonaqueous electrolyte secondary battery

Abstract

In a nonaqueous electrolyte secondary battery as an example of an embodiment, a positive electrode includes a lithium-containing transition metal composite oxide and a sulfonic acid compound present on a particle surface of the composite oxide. 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 (50). The silicon-containing material (50) contains an ion-conducting phase (51) and a Si phase (52) dispersed in the ion-conducting phase (51), and the size of the Si phase (52) is 110 nm or less. # imgabs0 #

Description

Technical Field

[0001] The present disclosure relates to a nonaqueous electrolyte secondary battery. Background Art

[0002] Patent document 1 proposes: 4 Ti 5 O 12 An active material having a surface layer composed of a lithium sulfonate compound formed on the surface of lithium titanate particles as a main component. Patent Document 1 states that by using this active material in a negative electrode active material, a change in resistance of a battery before and after charge storage can be suppressed.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-6164 Summary of the invention

[0006] In non-aqueous electrolyte secondary batteries, it is an important issue to improve output characteristics and cycle characteristics while ensuring high capacity. The prior art including Patent Document 1 cannot fully address such issues, and there is still much room for improvement.

[0007] The nonaqueous electrolyte secondary battery disclosed herein comprises: a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode comprises a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the surface of particles of the composite oxide, wherein the sulfonic acid compound is a compound represented by formula (I),

[0008] [Chemical formula 1]

[0009]

[0010] In formula (I), 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 less than 110 nm.

[0011] The nonaqueous electrolyte secondary battery disclosed herein has a high capacity and is excellent in output characteristics and cycle characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a cross-sectional view of a nonaqueous electrolyte secondary battery as an example of the embodiment.

[0013] Figure 2 This is a diagram showing a cross section of a particle of a silicon-containing material as an example of an embodiment. DETAILED DESCRIPTION

[0014] The research results of the present inventors have confirmed that: by the presence of the sulfonic acid compound shown in the above formula (I) on the surface of the particles of the lithium-containing transition metal composite oxide used as the positive electrode active material, a non-aqueous electrolyte secondary battery with high capacity and low resistance can be realized. It is believed that the reason is that the reaction resistance in the positive electrode is reduced by the function of the sulfonic acid compound, which can deepen the charge and discharge depth. However, the charge and discharge depth is deepened with the reduction of the reaction resistance, and a new problem such as reduced cycle characteristics is generated. It is believed that the main reason for the reduction in the above-mentioned cycle characteristics is that the expansion and contraction of the negative electrode mixture layer increases due to the deepening of the charge and discharge depth, and the diffusion of the electrolyte in the negative electrode mixture layer becomes insufficient and the battery reaction becomes uneven.

[0015] Therefore, the inventors of the present invention have successfully ensured high capacity and improved output characteristics and cycle characteristics by using a lithium-containing transition metal composite oxide having a specific sulfonic acid compound attached to the particle surface as a positive electrode active material and using a silicon-containing material having a Si phase of 110 nm or less dispersed in an ion-conducting phase as a negative electrode active material. According to the non-aqueous electrolyte secondary battery disclosed in the present invention, it is believed that even if the charge and discharge depth of the negative electrode becomes deeper, the expansion and contraction of the negative electrode mixture layer is suppressed to a small extent, thereby improving the cycle characteristics.

[0016] The sulfonic acid compound shown in the above formula (I) specifically functions when applied to the surface of particles containing lithium transition metal composite oxides to reduce the reaction resistance in the positive electrode and deepen the charge and discharge depth of the positive electrode. However, a battery with high capacity, excellent output characteristics and cycle characteristics cannot be achieved by simply applying the sulfonic acid compound to the positive electrode. The research results of the present inventors show that, in order to achieve such a battery, it is important to use a specific silicon-containing material as the negative electrode active material as described above. By setting the size of the Si phase of the silicon-containing material to less than 110 nm, the cycle characteristics are specifically improved compared to the case where a silicon-containing material with a Si phase size exceeding 110 nm is used.

[0017] Hereinafter, an example of an embodiment of the nonaqueous electrolyte secondary battery of the present disclosure will be described in detail with reference to the drawings. It should be noted that a configuration in which each component of a plurality of embodiments and modifications described below is selectively combined is included in the scope of the present disclosure.

[0018] In the embodiment described below, a cylindrical battery, i.e., a non-aqueous electrolyte secondary battery 10, is exemplified in which a wound electrode body 14 is housed in an outer can 16 having a bottomed cylindrical shape, but the outer shell of the battery is not limited to a cylindrical outer can. As other embodiments of the non-aqueous electrolyte secondary battery disclosed herein, a square battery having a square outer can, a coin-shaped battery having a coin-shaped outer can, and a bag-type battery having an outer shell composed of a laminate sheet including a metal layer and a resin layer can be listed. In addition, the electrode body is not limited to a wound type, and may also be a stacked electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked with a separator.

[0019] Figure 1 Schematic diagram of an axial cross section of a nonaqueous electrolyte secondary battery 10 as an example of an embodiment. Figure 1 As shown, the nonaqueous electrolyte secondary battery 10 includes a wound electrode body 14, a nonaqueous electrolyte, and an outer can 16 for storing the electrode body 14 and the nonaqueous electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a winding structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween. The outer can 16 is a metal container in a bottomed cylindrical shape with one end side open in the axial direction, and the opening of the outer can 16 is blocked by a sealing body 17. In the following, for convenience of description, the sealing body 17 side of the battery is set as the upper side, and the bottom side of the outer can 16 is set as the lower side.

[0020] The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity) and may be a liquid electrolyte (electrolyte) or a solid electrolyte.

[0021] The liquid electrolyte (electrolyte) 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 thereof. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents thereof. The non-aqueous solvent may also contain a halogen-substituted product (e.g., fluoroethylene carbonate, etc.) in which at least a portion of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF 6 And other lithium salts.

[0022] As a solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. are used. The polymer electrolyte, for example, contains a lithium salt and a matrix polymer, or contains a non-aqueous solvent, a lithium salt and a matrix polymer. As a matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. As a polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. are used. As an inorganic solid electrolyte, for example, a well-known material in an all-solid-state lithium-ion secondary battery, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halide-based solid electrolyte, etc.) is used.

[0023] The positive electrode 11, the negative electrode 12, and the separator 13 constituting the electrode body 14 are all strip-shaped long bodies, and are alternately stacked in the radial direction of the electrode body 14 by being wound into a spiral shape. The negative electrode 12 is formed to be one circle larger than the positive electrode 11 to prevent the precipitation of lithium. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length direction and the width direction. The separator 13 is formed to be at least one circle larger than the positive electrode 11, for example, two sheets are arranged in a manner of clamping the positive electrode 11. The electrode body 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.

[0024] Insulating plates 18 and 19 are disposed above and below the electrode body 14 , respectively. Figure 1 In the example shown, the positive electrode lead 20 extends to the sealing body 17 side through the through hole of the insulating plate 18, and the negative electrode lead 21 extends to the bottom side of the outer can 16 through the outer side of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the top plate of the sealing body 17, that is, the cover 27 electrically connected to the internal terminal plate 23 serves as the positive terminal. The negative electrode lead 21 is connected to the bottom inner surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative terminal.

[0025] A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness inside the battery. A groove portion 22 is formed on the outer can 16, in which a part of the side portion protrudes inward and supports the sealing body 17. The groove portion 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and the sealing body 17 is supported by its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 through the groove portion 22 and the open end of the outer can 16 fastened to the sealing body 17.

[0026] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26 and a cover 27 are stacked in order from the electrode body 14 side. The components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and an insulating member 25 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat release, the lower valve body 24 is deformed and broken in a manner that pushes the upper valve body 26 toward the cover 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 breaks, and the gas is discharged from the opening of the cover 27.

[0027] Hereinafter, the positive electrode 11 , the negative electrode 12 , and the separator 13 constituting the electrode body 14 , in particular, the positive electrode active material constituting the positive electrode 11 and the negative electrode active material constituting the negative electrode 12 will be described in detail.

[0028] [positive electrode]

[0029] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 31 arranged on the positive electrode core 30. The positive electrode core 30 can use a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, titanium, or a thin film of the metal arranged on the 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 connected to the positive electrode lead 20. The positive electrode 11 can be manufactured, 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 to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0030] 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 (CNTs), carbon nanofibers, graphene, metal fibers, metal powders, conductive whiskers, etc. The conductive agent may be used alone or in combination of two or more.

[0031] As the binder contained in the positive electrode mixture layer 31, fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be exemplified; olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, ethylene-propylene-butadiene copolymer; acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, ethylene-acrylic acid copolymer, etc. In addition, these resins can also be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. The binder can be used alone or in combination. The content of the conductive agent and the binder relative to the mass of the positive electrode mixture layer 31 is, for example, 0.1% by mass or more and 5% by mass or less.

[0032] The positive electrode 11 includes a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the surface of the composite oxide particles. The lithium-containing transition metal composite oxide with the sulfonic acid compound attached to the particle surface functions as a positive electrode active material. The sulfonic acid compound is a compound represented by formula (I).

[0033] [Chemical formula 2]

[0034]

[0035] In formula (I), A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.

[0036] The sulfonic acid compound represented by formula (I) (hereinafter sometimes referred to as "sulfonic acid compound") acts specifically when applied to the surface of particles of lithium-containing transition metal oxide to reduce the reaction resistance in the positive electrode 11 and improve the output characteristics of the battery. In addition, with the reduction of resistance, the depth of charge and discharge can be deepened, and high capacity can be achieved. The sulfonic acid compound can exert this effect even in a very small amount, but it is preferably 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 relative to the lithium-containing transition metal composite oxide, and particularly preferably 0.10% by mass or more.

[0037] The upper limit of the content of the sulfonic acid compound is not particularly limited, but from the viewpoint of taking both output characteristics and cycle characteristics into consideration, it is preferably 2.0% by mass, more preferably 1.5% by mass, and particularly preferably 1.0% by mass relative to the lithium-containing transition metal composite oxide. An example of a suitable content of the sulfonic acid compound is 0.05% by mass or more and 1.50% by mass or less, 0.1% by mass or more and 1.0% by mass or less, or 0.2% by mass or more and 0.7% by mass or less relative to the lithium-containing transition metal composite oxide.

[0038] The positive electrode active material may be a composite particle of a lithium-containing transition metal composite oxide with a sulfonic acid compound attached to the particle surface as the main component (the component with the highest mass ratio), or may be substantially composed of only the composite particle. It should be noted that, within the scope of not impairing the purpose of the present disclosure, the positive electrode active material may also contain a composite oxide other than the composite particle, or other compounds. For example, as part of the positive electrode active material, a composite oxide without a sulfonic acid compound attached to the particle surface may also be included.

[0039] The lithium-containing transition metal oxide preferably has a layered rock salt structure. When the sulfonic acid compound is applied to a composite oxide with a layered rock salt structure, the above effect becomes more significant. As the layered rock salt structure of the lithium-containing transition metal oxide, for example, a layered rock salt structure belonging to the space group R-3m, a layered rock salt structure belonging to the space group C2 / m, etc. can be listed. Among them, from the viewpoint 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 comprises a transition metal layer, a Li layer and an oxygen layer.

[0040] The lithium-containing transition metal oxide is a composite oxide containing metal elements such as Ni, Co, Mn, and Al in addition to Li. 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 them, it is preferred to contain at least one selected from Co, Ni, and Mn.

[0041] From the viewpoint of high 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 molar number of metal elements excluding Li. In addition, the effect of adding the sulfonic acid compound is more significant when using a lithium-containing transition metal oxide with a high Ni content. The Ni content can be 85 mol% or more, or 90 mol% or more relative to the total molar number of metal elements excluding Li. The upper limit of the Ni content is, for example, 95 mol%.

[0042] Relative to the total molar number of metal elements excluding Li, for example, the content of Al is 4 mol% or more and 15 mol% or less, and the content of Co is 1.5 mol% or less. If the content of Al is within this range, the stabilization of the crystal structure helps to improve the cycle characteristics compared to the case where the content is not within this range. Co may not be substantially added, but there is a tendency to improve battery performance by adding a small amount of Co. In addition, the content of Mn is, for example, 4 mol% or more and 15 mol% or less relative to the total molar number of metal elements excluding Li.

[0043] The lithium-containing transition metal oxide may be of 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, M1 is at least one element selected from the group consisting of Mn, Fe, Ti, Si, Nb, Zr, Mo and Zn.) A composite oxide represented by M1 is preferably Mn.

[0044] The content of elements constituting the lithium-containing transition metal composite oxide can be measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0045] The lithium-containing transition metal composite oxide is, for example, a secondary particle formed by the aggregation of multiple primary particles. The volume-based median particle size (D50) of the composite oxide is not particularly limited, and as an example, is 3 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less. In the case where 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 particle. D50 refers to the particle size at which the cumulative frequency from the smaller particle size in the volume-based particle size distribution becomes 50%. The particle size distribution of the composite oxide (the same is true for the negative electrode active material) can be measured using a laser diffraction particle size distribution measuring device (for example, MT3000II manufactured by MicrotracBEL Corp.) and water as the dispersion medium.

[0046] The average particle size of the primary particles constituting the lithium-containing transition metal composite oxide is, for example, 0.05 μm to 1 μm. The average particle size of the primary particles is calculated by averaging the diameters of the circumscribed circles of the primary particles extracted by analyzing a scanning electron microscope (SEM) image of a cross section of the secondary particles.

[0047] The sulfonic acid compound present on the surface of the particles of the lithium-containing transition metal composite oxide is a compound represented by formula (I) as described above.

[0048] [Chemical formula 3]

[0049]

[0050] In formula (I), A is an element of Group 1 or Group 2, R is a hydrocarbon group, and n is 1 or 2. A is preferably an element of Group 1. Among them, Li or Na is more preferred, and Li is particularly preferred.

[0051] In formula (I), R is preferably an alkyl group. The carbon number of the alkyl group is preferably 5 or less, and more preferably 3 or less. From the viewpoint of reducing the reaction resistance, an example of suitable R is an alkyl group with a carbon number of 3 or less, wherein a methyl group is preferred. It should be noted that in R, a part of the hydrogen bonded to the carbon may also be substituted by fluorine. In addition, n in formula (I) is preferably 1.

[0052] Specific examples of the sulfonic acid compound include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, sodium ethanesulfonate, magnesium methanesulfonate, lithium fluoromethanesulfonate, etc. Among them, at least one selected from the group consisting of lithium methanesulfonate, lithium ethanesulfonate and sodium methanesulfonate is preferred, and lithium methanesulfonate is particularly preferred.

[0053] The sulfonic acid compound is, for example, uniformly present on the entire surface of the particles of the lithium-containing transition metal composite oxide. The presence of the sulfonic acid compound on the surface of the composite oxide particles 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, for example, has a wavelength of 1238 cm -1 、1175cm -1 、1065cm -1 、785cm -1 There is an absorption peak near 1238cm -1 、1175cm -1 、1065cm -1 The peaks near 785 cm are due to the SO stretching vibration of lithium methanesulfonate. -1 The nearby peaks are peaks due to CS stretching vibration derived from lithium methanesulfonate.

[0054] For positive electrode active materials containing sulfonic acid compounds other than lithium methanesulfonate, the presence can also be confirmed by the absorption peak of the sulfonic acid compound source of the infrared absorption spectrum. It should be noted that the presence of the sulfonic acid compound on the particle surface of the lithium-containing transition metal composite oxide can also be confirmed by ICP, atomic absorption spectrometry, X-ray photoelectron spectroscopy (XPS), synchrotron radiation XRD measurement, TOF-SIMS, etc.

[0055] The positive electrode active material as an example of the embodiment can be produced by the following method. It should be noted that the production method described here is an example, and the production method of the positive electrode active material is not limited to this method.

[0056] First, a metal oxide containing metal elements such as Ni, Co, Mn, and Al is initially synthesized. Secondly, the metal oxide and a lithium compound are mixed and calcined to obtain a lithium-containing transition metal composite oxide. The metal oxide can be synthesized, for example, in the following manner: a solution containing a metal salt of Ni, Co, Mn, Al, etc. is stirred while an alkaline solution such as sodium hydroxide is added dropwise to adjust the pH to the alkaline side (for example, 8.5 or more and 12.5 or less), thereby allowing a composite hydroxide containing metal elements such as Ni, Co, Mn, and Al to precipitate (coprecipitate), and the composite hydroxide is heat-treated to enable synthesis. The heat treatment temperature is not particularly limited, and as an example, is 300°C or more and 600°C or less.

[0057] Examples of lithium compounds include Li 2 CO 3 、LiOH、Li 2 O 2 , Li 2 O、LiNO 3 、LiNO 2 , Li 2 SO 4 、LiOH·H 2 O, LiH, LiF, etc. The metal oxide and the lithium compound are mixed, for example, in a manner such that the molar ratio of the metal element in the metal oxide to the Li in the lithium compound is 1:0.98 or more and 1:1.1 or less. It should be noted that when mixing the metal oxide and the lithium compound, other metal raw materials may be added as needed.

[0058] The mixture of the metal oxide and the lithium compound is calcined, for example, in an oxygen atmosphere. The mixture may also be calcined through multiple temperature rising processes. The calcination process, for example, includes the following steps: a first temperature rising process, heating to 450°C to 680°C at a temperature rising rate of 1.0°C / min to 5.5°C / min; and a second temperature rising process, heating to a temperature exceeding 680°C at a temperature rising rate of 0.1°C / min to 3.5°C / min. The maximum reaching temperature of the calcination process may be set to 700°C to 850°C, and the temperature may be maintained for 1 hour to 10 hours.

[0059] Next, the calcined product (lithium-containing transition metal composite oxide) is washed with water and dehydrated to obtain a cake-like composition. The residual alkali component can be removed by this washing process. The washing and dehydration can be carried out using existing known methods. Next, the cake-like composition is dried to obtain a powdery composition. The drying process can be carried out under a vacuum atmosphere. An example of drying conditions is to perform at a temperature of more than 150° C. and less than 400° C. for more than 0.5 hours and less than 15 hours.

[0060] 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 the sulfonic acid compound, or the sulfonic acid solution may be added together with the sulfonic acid compound. Thus, a positive electrode active material having a sulfonic acid compound attached to the surface of particles of the lithium-containing transition metal composite oxide can be obtained. The sulfonic acid compound may be added in the form of an aqueous dispersion. In addition, the sulfonic acid solution is preferably an aqueous solution of sulfonic acid. The concentration of sulfonic acid in the sulfonic acid solution is, for example, 0.5% by mass or more and 40% by mass or less.

[0061] It should be noted that a certain amount of lithium compound remains in the cake-like composition. Therefore, by adding the sulfonic acid solution to the cake-like composition, Li dissolved in water in the cake reacts with the sulfonic acid to obtain lithium sulfonate.

[0062] [negative electrode]

[0063] The negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 41 arranged on the negative electrode core 40. As the negative electrode core 40, a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, nickel alloy, or a thin film having the metal arranged on the surface, or the like can be used. 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 except for the portion connected to the negative electrode lead 21. The negative electrode 12 can be produced, 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 the coating to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40. It should be noted that the negative electrode mixture layer 41 may also contain a conductive agent such as CNT.

[0064] The binder contained in the negative electrode mixture layer 41 may be fluorine-containing resin, olefin resin, PAN, polyimide, polyamide, acrylic resin, etc., as in the case of the positive electrode 11, but polyvinyl acetate, styrene-butadiene rubber (SBR), etc. may also be used. Among them, SBR is preferably used. One type of binder may be used alone, or a plurality of types may be used in combination. The content of the binder relative to the mass of the negative electrode mixture layer 41 is, for example, 0.1% by mass or more and 5% by mass or less. In addition, the negative electrode mixture layer 41 preferably includes CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. These function as thickeners in the negative electrode mixture slurry.

[0065] Figure 2 Schematic diagram of a cross section of a particle of a silicon-containing material 50. The negative electrode 12 includes Figure 2A silicon-containing material 50 having a particle cross-section as shown. The silicon-containing material 50 is contained in the negative electrode mixture layer 41, and acts as a negative electrode active material that absorbs and releases Li ions during the charge and discharge of the battery. The silicon-containing material 50 includes an ion conductive phase 51 and a Si phase 52 dispersed in the ion conductive phase 51. In addition, the size of the Si phase 52 is less than 110nm. In the non-aqueous electrolyte secondary battery 10 using the above-mentioned sulfonic acid compound in the positive electrode 11, the cycle characteristics specifically change with the Si phase size of 110nm as the boundary. When the size of the Si phase 52 of the silicon-containing material 50 is less than 110nm, the cycle characteristics specifically improve.

[0066] The negative electrode 12 may use only the silicon-containing material 50 as the negative electrode active material, but preferably contains a carbon material and a silicon-containing material 50. By using the carbon material and the silicon-containing material 50 in combination, it is easy to achieve both high capacity and excellent cycle characteristics. The negative electrode 12 may also contain, for example, a silicon-containing material other than the silicon-containing material 50, or a material containing other elements that can form an alloy with Li as a negative electrode active material, but in this embodiment, it substantially contains only a carbon material and a silicon-containing material 50.

[0067] The content of the carbon material is preferably higher than the content of the silicon-containing material 50. From the viewpoint of improving the cycle characteristics, the content of the silicon-containing material 50 is preferably less than 40% by mass of the total mass of the negative electrode active material, more preferably less than 35% by mass, and particularly preferably less than 30% by mass. It should be noted that in a non-aqueous electrolyte secondary battery in which a sulfonic acid compound is added to the positive electrode 11, in the absence of the silicon-containing material 50, not only the battery capacity is reduced, but also the cycle characteristics are reduced. From the viewpoint of high capacity and improved cycle characteristics, the content of the silicon-containing material 50 is preferably more than 5% by mass of the total mass of the negative electrode active material.

[0068] An example of a suitable range of the content of the silicon-containing material 50 is 5% by mass or more and 35% by mass or less of the total mass of the negative electrode active material, 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. It should be noted that, as described above, within the scope that does not impair the purpose of the present disclosure, the negative electrode 12 may also include a silicon-containing material other than the silicon-containing material 50. For example, the average size of the Si phase of the silicon-containing material included in the negative electrode 12 may be less than 110 nm, and may also include a silicon-containing material whose Si phase size exceeds 110 nm.

[0069] The carbon material acting 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, as the carbon material, it is preferred to use at least artificial graphite such as blocky artificial graphite (MAG), graphitized mesophase carbon microbeads (MCMB), natural graphite such as flaky graphite, blocky graphite, and earthy 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.

[0070] Soft carbon and hard carbon are classified as amorphous carbon with an underdeveloped graphite crystal structure. More specifically, it refers to a carbon component with a d(002) interplanar spacing of 0.342 nm or more based on X-ray diffraction. Soft carbon is also called graphitizable carbon, which is carbon that is easily graphitized by high temperature treatment compared to hard carbon. Hard carbon is also called difficult to graphitize carbon. It should be noted that in the composition of the present invention, there is no need to clearly distinguish between soft carbon and hard carbon. As a negative electrode active material, graphite and at least one amorphous carbon of soft carbon and hard carbon can also be used in combination.

[0071] As described above, the silicon-containing material 50 includes an ion-conducting phase 51 and a 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, greater than 1 μm and less than 20 μm, or greater than 1 μm and less than 15 μm. It should be noted that the silicon-containing material 50 may be used alone or in combination of two or more.

[0072] The ion conductive 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 composed of Si and an element with a higher electropositive property than Si, and examples thereof include NiSi, Mg 2 Si、TiSi 2 The Si phase 52 is formed by dispersing Si in fine particles. The ion conductive phase 51 is a continuous phase composed of a collection of particles finer than the Si phase 52 .

[0073] As described above, the size of the Si phase 52 of the silicon-containing material 50 is less than 110 nm. The average value of the size of the Si phase 52 contained in one particle of the silicon-containing material 50 is preferably less than 110 nm. The Si phase 52 is dispersed in the ion conductive phase 51 in the particle cross section of the silicon-containing material 50 in the form of fine particles. Therefore, hereinafter, the average value of the size of the Si phase 52 is sometimes referred to as the "average particle size". The average particle size of the Si phase is calculated as follows: 100 silicon-containing materials are randomly selected, an SEM image of the cross section of each particle is taken, and the diameter of the circumscribed circle α of the Si phase extracted by image analysis is averaged and calculated. The particle cross section can be made using the cross-section polishing (CP) method.

[0074] In the negative electrode 12, for all silicon-containing materials contained in the negative electrode mixture layer 41, or 100 silicon-containing materials randomly selected from all silicon-containing materials, when the size of the Si phase is measured, the average particle size of the Si phase is less than 110nm. It should be noted that as long as the average particle size of the Si phase in the entire negative electrode mixture layer 41 is less than 110nm, a silicon-containing material having an average particle size of the Si phase exceeding 110nm can also be used. However, when using more than two materials, all materials are preferably silicon-containing materials 50 having an average particle size of the Si phase 52 of less than 110nm.

[0075] As described above, the average particle size of the Si phase 52 contained in one particle of the silicon-containing material 50 may be 110 nm or less, and the total particle size may be 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, it is possible to effectively suppress particle expansion accompanying charge and discharge while maintaining high capacity, and the effect of improving cycle characteristics becomes more significant.

[0076] The average particle size of the Si phase 52 may also be less than 50 nm, less than 30 nm, less than 20 nm, or less than 10 nm. The lower limit of the average particle size of the Si phase 52 is not particularly limited, for example, 1 nm. An example of a suitable range of the average particle size of the Si phase 52 may be more than 1 nm and less than 50 nm, more than 1 nm and less than 40 nm, more than 1 nm and less than 30 nm, more than 5 nm and less than 30 nm, or more than 10 nm and less than 30 nm. If the average particle size of the Si phase 52 is within this range, the improvement effect of the cycle characteristics is improved compared to the case where the average particle size is not within this range.

[0077] The silicon-containing material 50 may also have a conductive layer covering the surface of the ion-conductive phase 51. The conductive layer is made of a material with higher conductivity than the ion-conductive phase 51, forming 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. As the conductive carbon material, carbon black such as acetylene black and Ketjen black, graphite, amorphous carbon with low crystallinity, etc. can be used. Considering the ensuring of conductivity and the diffusivity of Li ions into the particles, the thickness of the conductive layer is preferably 1 nm or more and 200 nm or less, or 5 nm or more and 100 nm or less. The thickness of the conductive layer can be measured by observing the cross-section of the composite material using SEM or a transmission electron microscope (TEM).

[0078] The ion-conductive phase 51 may also contain at least one selected from the group consisting of elements of Group 1 and Group 2 of the periodic table. The ion-conductive phase 51 may also be a silica phase doped with Li. Additionally, the ion-conductive phase 51 may contain at least one 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 lanthanide elements.

[0079] A suitable example of the silicon-containing material 50 is a composite particle having an island structure in which fine Si (Si phase 52) is substantially uniformly dispersed in an amorphous silica phase (ion-conductive phase 51), and is generally represented by the general formula SiO x (0 < x ≤ 2). The main component of the silica may also be silicon dioxide. Additionally, Li may be doped in the silica phase. The content ratio (x) of oxygen to Si is, for example, 0.5 ≤ x < 2.0, preferably 0.8 ≤ x ≤ 1.5.

[0080] Another example of a suitable silicon-containing material 50 is a composite particle having an island structure in which fine Si is substantially uniformly dispersed in an amorphous silicate phase. A suitable silicate phase is a lithium silicate phase containing Li. The lithium silicate phase is, for example, a phase of a composite oxide represented by the general formula Li 2z SiO (2+z) (0 < z < 2). It is preferred that the lithium silicate phase does not contain Li 4 SiO 4 (Z = 2). Li 4 SiO 4 is an unstable compound, reacts with water and shows alkalinity, and thus sometimes deteriorates Si, resulting in a reduction in charge-discharge capacity. From the viewpoints of stability, productivity, Li ion conductivity, etc., the lithium silicate phase is preferably Li 2 SiO 3 (Z = 1) or Li 2 Si 2 O 5(Z=1 / 2) is the main component.

[0081] Another example of a suitable silicon-containing material 50 is a composite particle having a sea island structure in which fine Si is roughly uniformly dispersed in a carbon phase. The carbon phase is preferably an amorphous carbon phase. The carbon phase may also contain a crystalline phase component, but preferably the amorphous phase component is more. The amorphous carbon phase is composed of a carbon material whose average interplanar spacing of the (002) plane measured by, for example, X-ray diffraction exceeds 0.34 nm. It should be noted that the composite material containing the carbon phase may have a conductive layer different from the carbon phase, or may not have the conductive layer.

[0082] The silicon-containing material 50 can be synthesized by using alkoxysilane as a raw material, for example, SiO 2 Nanoparticles after synthesis and encapsulation of SiO 2 The nanoparticles are polymerized and the polymer is carbonized and reduced (for details, refer to the examples described later). In this case, the amorphous carbon phase is a composite particle in which fine Si is dispersed roughly uniformly. The size of the Si phase 52 is obtained by, for example, using a bead mill to crush SiO 2 Nanoparticles can be reduced by pulverizing for a long time. The pulverization is continued for more than 100 hours until SiO 2 The average particle size of the nanoparticles reaches the target particle size. At this time, by adding isopropyl alcohol for pulverization, the SiO 2 Nanoparticle miniaturization.

[0083] From the viewpoint of improving cycle characteristics, the particle expansion rate of the silicon-containing material 50 is preferably 210% or less, and more preferably 170% or less.

[0084] The particle expansion rate of the silicon-containing material 50 is measured by the following method.

[0085] (1) The battery to be evaluated was dismantled and the negative electrode plate was cut out. Metal Li was used as the counter electrode and an ionic liquid was used as the electrolyte to prepare a monopolar battery cell in which the cross section of the silicon-containing material particles was exposed.

[0086] (2) The monopolar battery cell was charged at 0.002C until the battery cell voltage reached 5 mV under a temperature environment of 25°C, and then discharged at 0.05C until the battery cell voltage reached 1.0V. The cross section of the silicon-containing material particles was observed in situ using a SEM.

[0087] (3) Based on the change in the cross-sectional area of ​​the silicon-containing material particles, the volume of the silicon-containing material particles in the charged state (V1) and the volume of the silicon-containing material particles in the discharged state (V2) are determined, and the particle expansion ratio (V1×100 / V2) is calculated.

[0088] The expansion rate of the negative electrode mixture layer 41 during charge per unit 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 1g of the negative electrode active material. In this case, the improvement effect of the cycle characteristics becomes more significant compared to the case where the expansion rate of the negative electrode mixture layer 41 during charge exceeds 550%. The expansion rate of the negative electrode mixture layer 41 during charge can be controlled by the amount of silicon-containing material 50 added and the above-mentioned particle expansion rate. The lower limit of the expansion rate of the negative electrode mixture layer 41 during charge per unit discharge capacity is not particularly limited, and as an example, it is 40% / (mAh / g). If the expansion rate during charge is 40% / (mAh / g) or more, it becomes easier to achieve high capacity compared to the case where it is less than 40% / (mAh / g).

[0089] The expansion rate of the negative electrode mixture layer 41 per unit discharge capacity during charging was measured by the following method.

[0090] (1) The battery to be evaluated was dismantled and the negative electrode was cut out. Metal Li was used as the counter electrode and an ionic liquid was used as the electrolyte to prepare a monopolar battery cell.

[0091] (2) The monopolar battery cell was charged at 0.1 C until the cell voltage reached 5 mV under a temperature environment of 25° C., and then discharged at 0.1 C until the cell voltage reached 1.0 V. The discharge capacity (mAh / g) per 1 g of the negative electrode active material was determined.

[0092] (3) Determine the thickness of the negative electrode mixture layer in the charged state (T1) and the thickness of the negative electrode mixture layer in the discharged state (T2), calculate the rate of increase of the thickness (T1×100 / T2-100), and divide it by the discharge capacity per 1g of active material in the negative electrode mixture (mAh / g) to calculate the expansion rate of the negative electrode mixture layer during charging per unit discharge capacity.

[0093] [Separator]

[0094] As the separator 13, a porous sheet having ion permeability and insulation is used. As specific examples of the porous sheet, microporous films, woven fabrics, non-woven fabrics, etc. can be cited. As the material of the separator 13, suitable materials are polyolefins such as polyethylene and polypropylene, cellulose, etc. The separator 13 can be a single-layer structure or a multi-layer structure. The separator 13 can 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.

[0095] A filler layer containing an inorganic filler may also be arranged at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of the inorganic filler include oxides containing metal elements such as Ti, Al, Si, and Mg, phosphate compounds, and the like. The filler layer may 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 resin layer (heat-resistant layer) having high heat resistance such as an aromatic polyamide resin may also be arranged on the surface of the separator 13. The separator 13 may also have, for example, a substrate formed of a porous sheet and a filler layer or a heat-resistant layer arranged on the substrate.

[0096] Example

[0097] Hereinafter, the present disclosure will be further described based on examples, but the present disclosure is not limited to these examples.

[0098] <Example 1>

[0099] [Synthesis of positive electrode active material]

[0100] The [Ni 0.90 Al 0.05 Mn 0.05 ](OH) 2 The composite hydroxide shown was calcined at 500°C for 8 hours to obtain an oxide (Ni 0.90 Al 0.05 Mn 0.05 O 2 Then, 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. The mixture was heated under an oxygen gas flow with an oxygen concentration of 95% (per 10 cm 3 The mixture was calcined at a rate of 2 mL / min and a flow rate of 5 L / min per 1 kg of the mixture) from room temperature to 650°C at a heating rate of 2.0°C / min, and then calcined from 650°C to 780°C at a heating rate of 0.5°C / min to obtain a lithium-containing transition metal composite oxide.

[0101] Water is added to the obtained lithium-containing transition metal composite oxide so that the slurry concentration becomes 1500g / L, stirred for 15 minutes, and filtered to obtain a cake-like composition. Powdered lithium methanesulfonate is added to the cake-like composition. The amount of lithium methanesulfonate added is 0.1% by mass relative to the total mass of the lithium-containing transition metal composite oxide. After adding lithium methanesulfonate, it is dried under vacuum atmosphere at 180°C for 2 hours to obtain a positive electrode active material. It should be noted that the presence of lithium methanesulfonate on the particle surface of the composite oxide was confirmed by Fourier transform infrared spectroscopy (FT-IR).

[0102] [Production of positive electrode]

[0103] The positive electrode active material, acetylene black and polyvinylidene fluoride are mixed in a mass ratio of 98:1:1, and N-methyl-2-pyrrolidone (NMP) is used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to the positive electrode core formed by aluminum foil, and after the coating is dried and compressed, the positive electrode core is cut into a specified electrode size to obtain a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode core. It should be noted that an exposed portion exposed on the surface of the positive electrode core is provided on a part of the positive electrode.

[0104] [Synthesis of Silicon-Containing Materials]

[0105] In a mixture of ethanol / water / ammonia, tetraethoxysilane (TEOS) and hexadecyltrimethylammonium bromide (CTAB) were mixed to obtain SiO modified with CTAB. 2 Nanoparticles. For the obtained SiO 2 The nanoparticles were crushed by adding isopropyl alcohol using a bead mill for 300 hours. Then, resorcinol and formaldehyde were added to polymerize the nanoparticles to obtain nanoparticles encapsulating SiO 2 Nanoparticle polymer particles. At this time, the ratio of resorcinol to TEOS was set to about 0.5:1. The obtained polymer particles were dried, heated to 800°C in a nitrogen atmosphere to carbonize the polymer, and then mixed with magnesium powder and heated at 650°C in an argon atmosphere to perform a magnesium thermal reduction reaction. HCl / H 2 O / ethanol solution was used to dissolve MgO from the particles after the reaction, and after washing with ethanol, drying was performed to obtain a mesoporous silicon-containing material in which a Si phase was dispersed in an amorphous carbon phase.

[0106] 100 particles were randomly selected from the SEM image of the cross section of the obtained silicon-containing material particles, and the average value of the size of the Si phase (average particle size) 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.

[0107] [Production of negative electrode]

[0108] As the negative electrode active material, a mixture of the above silicon-containing material and artificial graphite in a mass ratio of 10:90 is used. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na) and a dispersant of styrene-butadiene rubber (SBR) are mixed in a solid component mass ratio of 100:1:1, and water is used as a dispersion medium to prepare a negative electrode mixture slurry. The negative electrode mixture slurry is applied to both sides of a negative electrode core formed of copper foil, and after the coating film is dried, the coating film is rolled using a roller and cut into a specified electrode size to obtain a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode core. It should be noted that an exposed portion where the surface of the negative electrode core is exposed is provided on a part of the negative electrode.

[0109] [Preparation of non-aqueous electrolyte]

[0110] LiPF was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (MEC) and dimethyl carbonate (DMC) at a volume ratio of 3:3:4 (25°C) at a concentration of 1.2 mol / L. 6 A non-aqueous electrolyte was prepared.

[0111] [Fabrication of test battery cell (non-aqueous electrolyte secondary battery)]

[0112] An aluminum lead was installed on the exposed portion of the positive electrode, and a nickel lead was installed on 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 press-formed in the radial direction to produce a flat wound electrode body. The electrode body was housed in an outer shell composed of an aluminum laminate sheet, and after the non-aqueous electrolyte was injected, the opening of the outer shell was sealed to obtain a test battery cell.

[0113] <Example 2>

[0114] A test cell was prepared in the same manner as in Example 1 except that the amount of lithium methanesulfonate added to the lithium-containing transition metal composite oxide was changed to 0.3 mass % in the synthesis of the positive electrode active material.

[0115] <Example 3>

[0116] A test cell was prepared in the same manner as in Example 1 except that the amount of lithium methanesulfonate added to the lithium-containing transition metal composite oxide was changed to 0.5 mass % in the synthesis of the positive electrode active material.

[0117] <Example 4>

[0118] A test cell was prepared in the same manner as in Example 1 except that the amount of lithium methanesulfonate added to the lithium-containing transition metal composite oxide was changed to 1.0 mass % in the synthesis of the positive electrode active material.

[0119] <Example 5>

[0120] A test cell was prepared in the same manner as in Example 3 except that a mixture of the silicon-containing material and artificial graphite at a mass ratio of 20:80 was used as the negative electrode active material.

[0121] <Example 6>

[0122] A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3 except that a silicon-containing material having an average particle size of 20 nm of the Si phase was used as the negative electrode active material. The synthesis method of the silicon-containing material is as follows.

[0123] [Synthesis of Silicon-Containing Materials]

[0124] In a mixture of ethanol / water / ammonia, tetraethoxysilane (TEOS) and hexadecyltrimethylammonium bromide (CTAB) were mixed to obtain SiO modified with CTAB. 2 Nanoparticles. For the obtained SiO 2 The nanoparticles were crushed by adding isopropyl alcohol using a bead mill for 200 hours. Then, resorcinol and formaldehyde were added to polymerize the nanoparticles to obtain nanoparticles encapsulating SiO 2 Nanoparticle polymer particles. At this time, the ratio of resorcinol to TEOS was set to about 0.5:1. The obtained polymer particles were dried, heated to 800°C in a nitrogen atmosphere to carbonize the polymer, and then mixed with magnesium powder and heated at 650°C in an argon atmosphere to perform a magnesium thermal reduction reaction. HCl / H 2 O / ethanol solution was used to dissolve MgO from the particles after the reaction, and after washing with ethanol, drying was performed to obtain a mesoporous silicon-containing material in which a Si phase was dispersed in an amorphous carbon phase.

[0125] <Example 7>

[0126] A test cell was prepared in the same manner as in Example 6 except that the silicon-containing material and artificial graphite used in Example 6 were mixed at a mass ratio of 20:80 as the negative electrode active material.

[0127] <Example 8>

[0128] A test cell was produced in the same manner as in Example 3 except that sodium methanesulfonate was used instead of lithium methanesulfonate in the synthesis of the positive electrode active material.

[0129] <Example 9>

[0130] A test cell was prepared in the same manner as in Example 3 except that lithium ethanesulfonate was used instead of lithium methanesulfonate in the synthesis of the positive electrode active material.

[0131] <Example 10>

[0132] A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3 except that a silicon-containing material having an average particle size of 100 nm of the Si phase was used as the negative electrode active material. The synthesis method of the silicon-containing material is as follows.

[0133] [Synthesis of Silicon-Containing Materials]

[0134] For SiO 2 The 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.

[0135] <Example 11>

[0136] A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3 except that a silicon-containing material having an average particle size of 80 nm of the Si phase was used as the negative electrode active material. The synthesis method of the silicon-containing material is as follows.

[0137] [Synthesis of Silicon-Containing Materials]

[0138] For SiO 2 The 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.

[0139] <Comparative Example 1>

[0140] A nonaqueous electrolyte secondary battery was prepared 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 Si phase particle size of 120 nm was used as the negative electrode active material. The synthesis method of the silicon-containing material is as follows.

[0141] [Synthesis of Silicon-Containing Materials]

[0142] For SiO 2 The 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.

[0143] <Comparative Example 2>

[0144] 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.

[0145] <Comparative Example 3>

[0146] A test cell was produced in the same manner as in Example 3 except that lithium succinate was used instead of lithium methanesulfonate in the synthesis of the positive electrode active material.

[0147] <Comparative Example 4>

[0148] A test cell was prepared in the same manner as in Example 3 except that lithium oxalate was used instead of lithium methanesulfonate in the synthesis of the positive electrode active material.

[0149] <Comparative Example 5>

[0150] A test cell was prepared 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.

[0151] The output characteristics and cycle characteristics (capacity retention rate) of each test battery cell of the embodiment and the comparative example were evaluated by the following method, and the evaluation results are shown in Table 1. The output characteristics of each test battery cell shown in Table 1 are relative values ​​when the value of the test battery cell of Comparative Example 2 is set to 100, and a larger value indicates a better output characteristic.

[0152] [Evaluation of initial output characteristics (discharge load characteristics)]

[0153] For the above test battery cell, under a temperature environment of 25°C, constant current charging was performed at 0.3It until the battery voltage reached 4.2V, and then constant voltage charging was performed at 4.2V until the current value reached 0.02It. Then, constant current discharge was performed at 0.2It until the battery voltage reached 2.5V. Then, constant current charging was performed again at 0.3It until the battery voltage reached 4.2V, and then constant voltage charging was performed at 4.2V until the current value reached 0.02It. Then, constant current discharge was performed at 0.5It until the battery voltage reached 2.5V. Using the value of the discharge capacity at this time, the discharge load characteristic was calculated according to the following formula.

[0154] Discharge load characteristic (%) = (discharge capacity at 0.5 It / discharge capacity at 0.02 It)

[0155] [Evaluation of cycle characteristics (capacity retention rate after cycle test)]

[0156] The test battery cell was charged at a constant current of 0.3 It until the battery voltage reached 4.2 V under a temperature environment of 25°C, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 It. Then, the battery was discharged at a constant current of 0.5 It until the battery voltage reached 2.5 V. This charge and discharge was regarded as one cycle, and 300 cycles were performed. The discharge capacity of the first cycle and the discharge capacity of the 300th cycle were obtained, and the capacity retention rate was calculated according to the following formula.

[0157] Capacity retention rate (%) = (300th cycle discharge capacity ÷ 1st cycle discharge capacity) × 100

[0158] [Table 1]

[0159]

[0160] As shown in Table 1, the test battery cells of the embodiment have higher discharge load characteristics and better output characteristics than the test battery cells of Comparative Examples 1 to 4. In addition, the test battery cells of the embodiment have higher capacity retention rates after cycle tests and better cycle characteristics than the test battery cells of Comparative Example 5. That is, the test battery cells of the embodiment have both excellent output characteristics and cycle characteristics. As in the test battery cells of Comparative Example 5, it is difficult to ensure both improved output characteristics and good cycle characteristics, but the test battery cells of the embodiment have good cycle characteristics despite high output characteristics.

[0161] The test cell of Comparative Example 1, which did not use a sulfonic acid compound as the positive electrode and used a silicon-containing compound having an average particle size of more than 110 nm of the Si phase as the negative electrode active material, had lower output characteristics than the test cell of the embodiment. Furthermore, the capacity retention rate of the test cell of Comparative Example 1 was the same as that of Example 10 (output characteristic: 102.0), which had the lowest capacity retention rate among the embodiments.

[0162] When a sulfonic acid compound is used as the positive electrode, if a silicon-containing compound having an average particle size of the Si phase exceeding 110 nm is used as the negative electrode active material (Comparative Example 5), the capacity retention rate is greatly reduced. That is, it can be understood from the Examples and Comparative Example 5 that when a sulfonic acid compound is used as the positive electrode, the capacity retention rate is greatly improved by using a silicon-containing compound having an average particle size of the Si phase of less than 110 nm as the negative electrode active material.

[0163] It should be noted that when lithium succinate and lithium oxalate were used instead of lithium methanesulfonate (Comparative Examples 3 and 4), the output characteristics were lower than when no acid salt was added to the positive electrode (Comparative Example 2).

[0164] The present disclosure is further illustrated by the following embodiments.

[0165] Configuration 1: A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte,

[0166] The positive electrode comprises a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the surface of the composite oxide particles.

[0167] The aforementioned sulfonic acid compound is a compound represented by formula (I),

[0168]

[0169] In formula (I), A is a Group 1 or Group 2 element, R is a hydrocarbon group, n is 1 or 2,

[0170] The negative electrode comprises a silicon-containing material,

[0171] The silicon-containing material includes an ion-conducting phase and a Si phase dispersed in the ion-conducting phase, and a size of the Si phase is 110 nm or less.

[0172] 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.

[0173] Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein A in formula (I) is Li or Na.

[0174] 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.

[0175] 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.

[0176] Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the negative electrode mixture layer contains a carbon material and the silicon-containing material as negative electrode active materials.

[0177] Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the ion conductive 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.

[0178] Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein a size of the Si phase is 1 nm or more and 50 nm or less.

[0179] Description of Reference Numerals

[0180] 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 groove portion, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cover, 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 conductive phase, 52 Si phase.

Claims

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

2. The nonaqueous electrolyte secondary battery according to claim 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.

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 the 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 includes a carbon material and the silicon-containing material as negative electrode active materials.

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 greater than or equal to 1 nm and less than or equal to 50 nm.

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