Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte secondary battery is characterized in that: the negative electrode has a negative electrode active material that contains a Si-containing material; the Si-containing material contains a composite material having a carbon phase and a silicon phase that is dispersed in the carbon phase; the non-aqueous electrolyte contains a heterocyclic compound that contains a heterocycle and at least one electron-withdrawing group R; the electron-withdrawing group R contains oxygen and / or nitrogen; and the heterocycle contains nitrogen and sulfur.

Description

Non-aqueous electrolyte secondary battery

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

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

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery that uses a non-aqueous electrolyte containing a thiazole compound.

[0004] International Publication No. 2023 / 145896

[0005] By using a non-aqueous electrolyte containing a thiazole compound, it is possible to reduce battery resistance. However, when a Si-containing material is used as the negative electrode active material, the effect of the thiazole compound in reducing battery resistance may not be sufficiently obtained.

[0006] Therefore, an object of the present disclosure is to improve the reduction of battery resistance in a non-aqueous electrolyte secondary battery that uses a Si-containing material as the negative electrode active material.

[0007] One aspect of the present disclosure is a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material including a Si-containing material, the Si-containing material including a composite material having a carbon phase and a silicon phase dispersed within the carbon phase, the non-aqueous electrolyte including at least one heterocyclic compound including an electron-withdrawing group R and a heterocycle, the electron-withdrawing group R including oxygen and / or nitrogen, and the heterocycle including nitrogen and sulfur.

[0008] According to one aspect of the present disclosure, in a nonaqueous electrolyte secondary battery using a Si-containing material as a negative electrode active material, it is possible to improve reduction in battery resistance.

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

[0010] A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure is a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte. The negative electrode has a negative electrode active material containing a Si-containing material. The Si-containing material includes a composite material having a carbon phase and a silicon phase dispersed within the carbon phase. The nonaqueous electrolyte includes a heterocyclic compound containing at least one electron-withdrawing group R and a heterocycle, wherein the electron-withdrawing group R contains oxygen and / or nitrogen, and the heterocycle contains nitrogen and sulfur. According to the present disclosure, the heterocyclic compound (thiazole compound) is reductively decomposed during battery charging and discharging, forming a coating on the negative electrode surface. Because the coating derived from the heterocyclic compound has high ion conductivity, the formation of this coating on the negative electrode surface reduces battery resistance. Meanwhile, Si-containing materials generally tend to undergo particle cracking and new interface formation due to expansion and contraction during charging and discharging. When a new interface is formed on the particles of the Si-containing material, a coating is formed on the formed new interface due to the reductive decomposition of the heterocyclic compound. Therefore, when a Si-containing material that easily forms a new interface is used, the consumption of the heterocyclic compound due to reductive decomposition increases, which increases the amount of coating formed on the negative electrode surface, and the battery resistance reduction effect may not be sufficiently achieved. However, among Si-containing materials, the composite material used in the present disclosure minimizes the generation of new interfaces due to charge and discharge, thereby reducing the consumption of the heterocyclic compound due to reductive decomposition. As a result, an appropriate amount of coating is formed on the negative electrode surface, which is thought to sufficiently reduce the battery resistance.

[0011] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described below. The drawings referred to in the following embodiment are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual battery.

[0012] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery 10 shown in FIG. 1 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, a nonaqueous electrolyte, insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a cylindrical outer can 16 with a bottom and a sealing member 17 that closes the opening of the outer can 16. Note that, instead of the wound electrode assembly 14, other electrode assembly configurations may be used, such as a laminated electrode assembly formed by alternately stacking positive and negative electrodes with separators interposed therebetween. Examples of the battery case 15 include cylindrical, prismatic, coin-shaped, or button-shaped metal cases, and resin cases (so-called pouch-shaped cases) formed by laminating resin sheets.

[0013] The outer can 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure airtightness inside the battery. The outer can 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports the sealing body 17. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its upper surface.

[0014] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and all components except for the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the nonaqueous electrolyte secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0015] 1 , a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode lead 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom of the outer can 16. The positive electrode lead 20 is connected by welding or the like to the underside of a filter 23, which is the bottom plate of the sealing body 17, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner bottom surface of the outer can 16, and the outer can 16 serves as the negative electrode terminal.

[0016] The non-aqueous electrolyte, the positive electrode 11, the negative electrode 12, and the separator 13 will be described below.

[0017] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and a heterocyclic compound containing at least one electron-withdrawing group R and a heterocycle. Hereinafter, the heterocycle and the heterocyclic compound may be referred to as "heterocycle (H)" and "heterocyclic compound (C)," respectively. The electron-withdrawing group R contains oxygen and / or nitrogen. The heterocycle (H) contains nitrogen and sulfur. As described above, the inclusion of the heterocyclic compound (C) in the non-aqueous electrolyte forms a coating on the surface of the negative electrode, leading to a reduction in battery resistance.

[0018] The non-aqueous electrolyte may contain only one type of compound as the heterocyclic compound (C), or may contain multiple types of compounds.

[0019] The electron-withdrawing group R contained in the heterocyclic compound (C) may contain only one of oxygen and nitrogen, or may contain both. For example, the electron-withdrawing group R may be a carbonyl group (—C(═O)—), a nitrile group (—C≡N), a sulfonyl group (—S(═O)—), or a hydroxyl group (—S(═O)—) in order to further reduce the battery resistance. ２ The hydroxy group, which is the electron-withdrawing group R, may be bonded to a carbon atom constituting a saturated hydrocarbon group (e.g., an alkyl group or an alkylene group). The nitrile group may be contained in a thionitrile group. The sulfonyl group may be a sulfonate ester bond (-S(=O)２ —O—). The C═O moiety contained in an isocyanate group and an isothiocyanate group is not usually considered to be a carbonyl group. Therefore, in this specification, the C═O moiety contained in an isocyanate group and an isothiocyanate group is not considered to be a carbonyl group.

[0020] The carbonyl group may be contained in at least one selected from the group consisting of an aldehyde group (-CHO), a ketone, an amide bond (C(=O)-N), an ester bond (COO), and a carboxy group (-COOH). That is, the electron-withdrawing group R may be at least one selected from the group consisting of an aldehyde group, a carbonyl group contained in a ketone, an amide bond, an ester bond, and a carboxy group.

[0021] The number of electron-withdrawing groups R contained in the heterocyclic compound (C) may be 1, 2 or more, 5 or more, or 5 or less. The number of heterocycles (H) contained in the heterocyclic compound (C) may be 1, 2, 3 or less, or 3 or more.

[0022] The heterocycle (H) contains nitrogen and sulfur. The heterocycle (H) may or may not have aromaticity. The number of atoms constituting the heterocycle (H) may be in the range of 5 to 8, or in the range of 5 to 7, or may be 5 or 6. That is, the heterocycle (H) may be a five-membered ring, a six-membered ring, a seven-membered ring, or an eight-membered ring.

[0023] The heterocycle (H) may satisfy the following conditions (1) and / or (2), or may satisfy the following conditions (1) and (3): (1) The heterocycle (H) is composed of one nitrogen atom, one sulfur atom, and multiple carbon atoms; (2) The nitrogen atom forms a double bond with one adjacent carbon atom that constitutes the heterocycle (H); and (3) The nitrogen atom forms a single bond with each of the two adjacent carbon atoms that constitute the heterocycle (H).

[0024] The heterocycle (H) may be a thiazole ring represented by the following formula:

[0025]

[0026] The heterocycle (H) may be a thiomorpholine ring represented below.

[0027]

[0028] The heterocycle (H) may be a thiazepine ring represented by the following formula: The thiazepine ring may be a 1,3-thiazepine ring or a 1,4-thiazepine ring.

[0029]

[0030] The heterocycle (H) may contain at least one ring selected from the group consisting of a thiazole ring, a thiomorpholine ring, and a thiazepine ring.

[0031] The structure of the heterocyclic compound (C) other than the heterocycle (H) and the electron-withdrawing group R is not limited as long as the effects of the present disclosure are obtained. The portion other than the heterocycle (H) and the electron-withdrawing group R may be composed only of hydrocarbons. Examples of hydrocarbons include hydrocarbon groups (including hydrocarbon chains). Examples of hydrocarbons include aliphatic hydrocarbons and aromatic hydrocarbons. The heterocyclic compound (C) may contain an ether bond, a thioether bond, nitrogen not included in the electron-withdrawing group R, etc.

[0032] The molecular weight of the heterocyclic compound (C) may be 100 or more, or 130 or more, and may be 400 or less, or 370 or less.

[0033] As the heterocyclic compound (C), a compound that dissolves in the non-aqueous solvent of the non-aqueous electrolyte is preferably used.

[0034] Examples of the heterocyclic compound (C) include 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, ethyl 2-ethynyl-4-methylthiazole-5-carboxylate, N-benzyl-2-ethynyl-4-methylthiazole-5-carboxamide, 4-methyl-5-(2-thiocyanatoethyl)thiazole, perfluorophenyl 4,5-dimethylthiazole-2-sulfonate, 2-(trimethylsilyl)thiazole-4-carbaldehyde, 4-(((tert-butyl Examples of the thiocyanate include 1-(5-(hydroxymethyl)-4-methylthiazol-2-yl)ethan-1-one, 5-isocyanato-4-methyl-2-phenylthiazole, 5-isocyanato-4-methyl-2-(pyrazin-2-yl)thiazole, 2-ethylthiomorpholine-4-carbaldehyde, 2,3-dimethylthiomorpholine-4-carbaldehyde, 2-methyl-4-thiocyanatobenzo[b][1,4]thiazepine, and 4-methyl-2-thiocyanatobenzo[b][1,4]thiazepine. Among these, it is preferable that the heterocyclic compound (C) contains at least one selected from the group consisting of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, 2-ethylthiomorpholine-4-carbaldehyde, and 2,3-dimethylthiomorpholine-4-carbaldehyde, in that it is possible to further improve the reduction in battery resistance.

[0035] The heterocyclic compound (C) may be a commercially available compound, or may be synthesized according to a known synthesis method.

[0036] The content of the heterocyclic compound (C) in the non-aqueous electrolyte may be 0.1 mass % or more, 0.5 mass % or more, or 1.0 mass % or more, and may be 10.0 mass % or less, 5.0 mass % or less, or 3.0 mass % or less. By setting the content within the above range, it is possible to further reduce the battery resistance.

[0037] The content of the heterocyclic compound (C) in the non-aqueous electrolyte is determined using gas chromatography under the following conditions. Used equipment: GC-2010 Plus, manufactured by Shimadzu Corporation. Column: HP-1 (film thickness 1 μm, inner diameter 0.32 mm, length 60 m), manufactured by J&W. Column temperature: heated from 50°C to 90°C at a heating rate of 5°C / min, maintained at 90°C for 15 minutes, then heated from 90°C to 250°C at a heating rate of 10°C / min, and maintained at 250°C for 15 minutes. Split ratio: 1 / 50. Linear velocity: 30.0 cm / sec. Injection port temperature: 270°C. Injection volume: 1 μL. Detector: FID 290°C (sens. 10 １ )

[0038] Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The non-aqueous electrolyte may contain only one non-aqueous solvent, or may contain two or more non-aqueous solvents.

[0039] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０Examples of the lithium salts include lithium carboxylates, lower aliphatic carboxylates, LiCl, LiBr, LiI, borates, and imide salts. Examples of the borates include lithium difluorooxalate borate and lithium bis(oxalate) borate. Examples of the imide salts include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ The non-aqueous electrolyte may contain only one type of electrolyte salt or may contain two or more types of electrolyte salts. The concentration of the electrolyte salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0040] (Positive Electrode) The positive electrode 11 includes, for example, a positive electrode core and a positive electrode composite layer disposed on the positive electrode core. The positive electrode composite layer may be disposed on only one surface of the positive electrode core, or on both surfaces of the positive electrode core. The positive electrode composite layer includes, for example, a positive electrode active material, a conductive material, a binder, and the like. The positive electrode 11 is obtained, for example, by applying and drying a positive electrode composite slurry containing the positive electrode active material, etc., onto the positive electrode core, forming a positive electrode composite layer on the positive electrode core, and then rolling the positive electrode composite layer.

[0041] The positive electrode core may be, for example, a metal foil such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on the surface thereof. The thickness of the positive electrode core is, for example, 10 μm or more and 50 μm or less.

[0042] The positive electrode active material may be, for example, a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, or Mn. Metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. Examples of suitable composite oxides include lithium transition metal composite oxides containing Ni, Co, and Mn, and lithium transition metal composite oxides containing Ni, Co, and Al. One type of lithium transition metal composite oxide may be used alone, or multiple types may be used in combination.

[0043] The lithium transition metal composite oxide has, for example, a layered rock salt structure. Examples of the layered rock salt structure include a layered rock salt structure belonging to the space group R-3m and a layered rock salt structure belonging to the space group C2 / m. Among these, a layered rock salt structure belonging to the space group R-3m is preferred from the viewpoints of high capacity and stability of the crystal structure. The content of the positive electrode active material is, for example, 90% by mass or more and 99% by mass or less with respect to the mass of the positive electrode mixture layer.

[0044] Examples of conductive materials include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. One type of conductive material may be used alone, or multiple types may be used in combination. The content of the conductive material may be, for example, 0.1% by mass or more and 5% by mass or less with respect to the total mass of the positive electrode mixture layer.

[0045] Examples of binders 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, acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer, styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), and polyethylene oxide (PEO). One type of binder may be used alone, or multiple types may be used in combination. The content of the binder may be 0.6% by mass or more and 1.5% by mass or less with respect to the total mass of the positive electrode mixture layer.

[0046] (Negative Electrode) The negative electrode 12 has, for example, a negative electrode core and a negative electrode composite layer disposed on the negative electrode core. The negative electrode composite layer may be disposed on only one surface of the negative electrode core, or on both surfaces of the negative electrode core. The negative electrode composite layer contains, for example, a negative electrode active material, a binder, and the like. The negative electrode 12 is obtained, for example, by applying and drying a negative electrode composite slurry containing the negative electrode active material, etc., onto the negative electrode core, thereby forming a negative electrode composite layer on the negative electrode core, and then rolling the negative electrode composite layer.

[0047] The negative electrode core may be made of a metal foil such as copper or a copper alloy that is stable within the potential range of the negative electrode 12, or a film having such a metal disposed on the surface thereof. The thickness of the negative electrode core is, for example, 5 μm or more and 50 μm or less.

[0048] The negative electrode composite layer includes a negative electrode active material containing a Si-containing material. The Si-containing material includes a composite material including a carbon phase and a silicon phase (silicon particles in one respect) dispersed within the carbon phase. Hereinafter, this composite material may be referred to as a SiC material.

[0049] The SiC material may exist in the form of particles having, for example, a sea-island structure. For example, silicon phases (islands) are dispersed in a carbon phase matrix (sea) and covered by the carbon phase. In the sea-island structure, contact between the silicon phase and the non-aqueous electrolyte is limited, thereby suppressing side reactions. Furthermore, stress generated by the expansion and contraction of the silicon phase is alleviated by the carbon phase matrix. For these reasons, it is believed that the SiC material suppresses the generation of new interfaces due to the charging and discharging of the battery. Furthermore, as described above, the combination of the SiC material with the heterocyclic compound (C) can improve the reduction of battery resistance.

[0050] The carbon phase, which is an ion-conducting phase, may be composed of, for example, amorphous carbon (amorphous carbon), rather than a material with a developed graphite-type crystal structure, such as graphite. Examples of amorphous carbon that constitutes the carbon phase include hard carbon, soft carbon, and other amorphous carbon. Amorphous carbon is a carbon material in which the average interplanar spacing d002 of the (002) plane measured by X-ray diffraction exceeds 0.34 nm.

[0051] The content of the carbon phase in the SiC material may be, for example, 10 mass % or more, 20 mass % or more, or 30 mass % or more, and may be 60 mass % or less, or 50 mass % or less. Within such a range, for example, electrical connection between the SiC material and its surroundings is easily maintained.

[0052] The silicon phase includes at least one of elemental silicon and a silicon alloy. The average particle size of the silicon phase may be 1 nm or more, or 5 nm or more. The average particle size may be 1000 nm or less, 500 nm or less, 200 nm or less, 100 nm or less, or 50 nm or less. A fine silicon phase is preferable in that it reduces volume change during charge and discharge and improves the structural stability of the SiC material.

[0053] The average particle size of the silicon phase can be measured by observing the cross section of particles of the Si-containing material using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Specifically, it can be determined by averaging the maximum diameters of 100 randomly selected silicon phase particles.

[0054] The crystallite size of the silicon phase may be 30 nm or less, or 20 nm or less. When the crystallite size is 30 nm or less, the volume change of the SiC material due to expansion and contraction of the silicon phase during charge and discharge can be further reduced. When the crystallite size is 20 nm or less, the expansion and contraction of the silicon phase are uniformed, microcracks in the silicon phase are reduced, and cycle characteristics can be further improved.

[0055] The crystallite size of the silicon phase is calculated by Scherrer's formula from the half-width of the diffraction peak attributable to the (111) plane of the silicon phase (simple element Si) in the X-ray diffraction pattern.

[0056] The content of the silicon phase in the SiC material may be, for example, 10% by mass or more, 20% by mass or more, or 30% by mass or more, and may be 80% by mass or less, or 70% by mass or less. Within such a range, for example, a high capacity of the negative electrode can be achieved.

[0057] The intra-particle porosity of the SiC material may be, for example, 6% or more, or 8% or more, or 20% or less, or 18% or less. In such a range, the generation of new interfaces during charge and discharge is further suppressed, leading to a further reduction in battery resistance.

[0058] The internal particle porosity of the SiC material is determined by the following method. The negative electrode composite layer on the negative electrode core is cut using a cross-section polisher, and the cut surface is observed using an SEM. Multiple particle cross sections of the SiC material are randomly selected from the obtained SEM image, and for each selected particle cross section, an outline along the particle surface and a contour line of the internal voids present within the area surrounded by the outline line are drawn. Based on the drawn outline and contour line, the total cross-sectional area of ​​the SiC material particles and the total area of ​​the internal voids are measured, and the internal particle porosity ((total area of ​​internal voids / total cross-sectional area of ​​particles) × 100) is calculated. The internal particle porosity of the SiC material is the average value of the internal particle porosities calculated for 100 particle cross sections of the SiC material.

[0059] The specific surface area of ​​the SiC material is, for example, 5 m ２ / g or more, or 8% m ２ / g or more, ２ / g or less, or 18m ２ In such a range, the generation of new interfaces during charge and discharge is further suppressed, which leads to a further reduction in the battery resistance.

[0060] The specific surface area of ​​the SiC material is determined by the BET method, a general method for measuring specific surface area, using a specific surface area measuring device based on gas adsorption (Macsorb (registered trademark) HM model-1201, manufactured by Mountec Co., Ltd.).

[0061] The average pore size of the SiC material may be, for example, 1 nm or more, or 5 nm or more, or 45 nm or less, or 40 nm or less, In such a range, the generation of new interfaces during charge and discharge is further suppressed, leading to a further reduction in battery resistance.

[0062] The average pore diameter of a SiC material refers to the pore diameter D50 at which the cumulative volume is 50% in the pore diameter distribution of the SiC material measured with a mercury intrusion porosimeter. The pore diameter distribution represents the relationship between the pore diameter and the volume (frequency) occupied by pores of that pore diameter. The cumulative volume is calculated by integrating the volumes of pores of the smallest diameter in order.

[0063] The average particle size of the SiC material may be 1 μm or more, or 5 μm or more, or may be 20 μm or less, 15 μm or less, or 10 μm or less. The average particle size of the SiC material is the median diameter (diameter at 50% cumulative volume) in a volume-based particle size distribution measured with a laser diffraction / scattering particle size distribution analyzer.

[0064] The following is an example of a method for producing a SiC material. According to the production method described below, the intra-particle porosity, specific surface area, average pore size, etc. of the SiC material can be adjusted to fall within the aforementioned ranges.

[0065] (a) Production Example 1 SiC material particles can be obtained, for example, by pulverizing a mixture of a carbon source and raw silicon while stirring it in a ball mill or the like to form fine particles, and then heat-treating the mixture in an inert atmosphere. Examples of carbon sources that can be used include petroleum resins such as coal pitch, petroleum pitch, and tar, as well as sugars and water-soluble resins such as carboxymethyl cellulose (CMC), polyvinylpyrrolidone, cellulose, and sucrose. When mixing the carbon source and raw silicon, the carbon source and raw silicon may be dispersed in a dispersion medium such as alcohol. After drying the milled mixture, the mixture is heated in an inert gas atmosphere, for example, at a temperature of 600°C or higher and 1000°C or lower, to carbonize the carbon source and form a carbon phase.

[0066] A pore-forming material may be mixed into the mixture of the carbon source and raw silicon. The SiC material particles can be made porous by removing the pore-forming material from the fired product. The internal porosity of the SiC material particles can be controlled by the amount of pore-forming material mixed. The pore-forming material is not particularly limited, but for example, a powder that easily dissolves in an acidic aqueous solution that barely dissolves the silicon phase may be used. Examples of such powder pore-forming agents include oxides of transition metals (e.g., Cu, Fe, etc.). The median diameter in the volume-based particle size distribution of the pore-forming agent is appropriately selected depending on the desired pore size distribution of the SiC material particles. The acid used in the acidic aqueous solution may be, for example, dilute sulfuric acid.

[0067] Furthermore, the internal particle porosity of the SiC material particles can be controlled to a target value by the manufacturing method. Examples of such methods include selecting the material that constitutes the ion-conductive phase and applying pressure to the silicon-containing material while heating it before pulverization. The heating temperature may be, for example, 300°C to 800°C. For example, if the material used to form the ion-conductive phase contains a substance that is removed by heating, the greater the amount of substance that is removed by heating, the more voids there will be in the formed ion-conductive phase, and the larger the internal particle porosity, specific surface area, and / or average pore size will tend to be.

[0068] (b) Production Example 2: While stirring porous carbon in a heated reactor, a silicon-containing source gas is flowed into the reactor. This deposits amorphous silicon inside the pores of the porous carbon. The deposition forms a particulate silicon phase dispersed within the carbon phase (porous carbon). The reactor may be heated to a temperature in the range of 500 to 700°C (e.g., 600°C). An example of the source gas is a mixture of monosilane (SiH4) and a carrier gas (e.g., nitrogen gas). The starting porous carbon may have an average pore diameter in the range of 2 to 10 nm and an average particle size (median diameter D50) in the range of 5 to 7 μm. Porous carbons that can be used include activated carbon, carbon aerogel, carbon foam, graphite, and nanoporous carbon.

[0069] The negative electrode active material may contain a conventionally known Si-containing material other than a SiC material, as long as the effects of the present disclosure are not impaired. The content ratio of the conventionally known Si-containing material other than a SiC material in the negative electrode active material may be 1 mass % or less, 0.5 mass % or less, or 0 mass %.

[0070] The content ratio of the SiC material in the negative electrode active material may be 0.5% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 20% by mass or less, 18% by mass or less, or 15% by mass or less, from the viewpoint of increasing the capacity of the battery or further reducing the battery resistance, etc.

[0071] The negative electrode active material may contain, in addition to Si-containing materials including SiC materials, materials other than Si-containing materials that can reversibly absorb and release lithium ions. Examples of materials other than Si-containing materials include natural graphite such as flake graphite, lump graphite, and earthy graphite, and carbon materials such as lump artificial graphite and artificial graphite such as graphitized mesophase carbon microbeads. The content ratio of the carbon material in the negative electrode active material may be, for example, 70% by mass or more, or 80% by mass or more. Furthermore, for example, metals that alloy with lithium, such as Sn, alloys containing such metals, compounds containing such metals, etc. may also be used.

[0072] Examples of the binder include the same materials as those used in the positive electrode 11. The negative electrode mixture layer may also contain a conductive material.

[0073] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0074] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0075] Example 1 Preparation of Positive Electrode A positive electrode composite slurry was prepared by mixing lithium cobalt oxide, acetylene black, and polyvinylidene fluoride, which are positive electrode active materials, in a solids mass ratio of 100:1:1, and using N-methylpyrrolidone (NMP) as a dispersion medium. The slurry was applied to both sides of a positive electrode core made of aluminum foil, and the coating was dried and rolled to obtain a positive electrode having positive electrode composite layers formed on both sides of the positive electrode core.

[0076] [Fabrication of Negative Electrode] Graphite, the SiC material prepared by the method of Production Example 2, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a solid mass ratio of 90:10:1:1, and an appropriate amount of water was added to prepare a negative electrode composite slurry. The slurry was applied to both sides of a copper foil serving as a negative electrode core, and the coating was dried and rolled to obtain a negative electrode having a negative electrode composite layer formed on both sides of the negative electrode core.

[0077] The SiC material has an internal particle porosity of 3.7% and a specific surface area of ​​2 m ２ / g and the average pore diameter was 2 nm.

[0078] [Preparation of non-aqueous electrolyte] 1.0 mass % of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, which is a heterocyclic compound (C), was added to a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7, to prepare a non-aqueous electrolyte solution containing lithium hexafluorophosphate (LiPF６ A non-aqueous electrolyte was prepared by dissolving 1.0 mol / L of ammonium hydroxide in water.

[0079] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] (1) A positive electrode lead was attached to the positive electrode, and a negative electrode lead was attached to the negative electrode. A separator made of a polyethylene microporous film was then interposed between the positive and negative electrodes, and the resulting structure was wound to produce a wound electrode assembly. (2) Insulating plates were placed on the top and bottom of the electrode assembly, respectively, and the negative electrode lead was welded to the outer can, and the positive electrode lead was welded to a sealing member, and the electrode assembly was then housed in the outer can. (3) A non-aqueous electrolyte was injected into the outer can using a reduced pressure method, and the opening of the outer can was sealed with a sealing member via a gasket. This resulted in a non-aqueous electrolyte secondary battery.

[0080] Example 2 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a SiC material was fabricated based on Production Example 1. The SiC material had an internal particle porosity of 11.2% and a specific surface area of ​​13 m ２ / g and the average pore diameter was 15 nm.

[0081] Example 3 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 2, except that coal pitch with a low fixed carbon content was used in the production of the SiC material. The SiC material had an internal particle porosity of 11.0% and a specific surface area of ​​11 m. ２ / g and the average pore diameter was 40 nm.

[0082] Example 4 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 2, except that 2-ethylthiomorpholine-4-carbaldehyde was added as the additive compound.

[0083] Comparative Example 1 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a SiO material (SiOx (x=1)) was used as the Si-containing material used as the negative electrode active material, and 4,5-dimethyl-1,3-thiazole-2-carbaldehyde was not added as the additive compound.

[0084] Comparative Example 2 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the SiO material of Comparative Example 1 was used.

[0085] Comparative Example 3 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 2, except that 4,5-dimethyl-1,3-thiazole-2-carbaldehyde was not added as the additive compound.

[0086] Comparative Example 4 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 2, except that thiazole was added as the additive compound.

[0087] [Measurement of Battery Resistance] The nonaqueous electrolyte secondary batteries of each Example and Comparative Example were charged to 50% SOC at a constant current of 0.5 C in an environment of 25°C. The voltage at this time was designated as V0. Next, the batteries were discharged for 10 seconds at a constant current of 0.5 C. The voltage at this time was designated as V1. The direct current resistance (DCR) was then calculated using the following formula. This was designated as the battery resistance, and the battery resistances of each Example and Comparative Example are summarized in Table 1. However, in Table 1, the battery resistance of Comparative Example 1 is set as the reference (100), and the battery resistances of the other Examples and Comparative Examples are shown relative to each other. DCR = (V0 - V1) / 0.5 C

[0088]

[0089] As in Examples 1 to 4, a sufficient effect of reducing battery resistance was achieved by using a SiC material as the negative electrode active material and adding a heterocyclic compound containing an electron-withdrawing group R containing oxygen and / or nitrogen and a heterocyclic ring containing nitrogen and sulfur to the non-aqueous electrolyte. On the other hand, as in Comparative Examples 2 to 4, when a SiC material was not used as the negative electrode active material or when a heterocyclic compound containing an electron-withdrawing group R containing oxygen and / or nitrogen and a heterocyclic ring containing nitrogen and sulfur was not added to the non-aqueous electrolyte, a sufficient effect of reducing battery resistance was not achieved.

[0090] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material including a Si-containing material, the Si-containing material including a composite material having a carbon phase and a silicon phase dispersed within the carbon phase, the non-aqueous electrolyte including at least one electron-withdrawing group R and a heterocyclic compound including a heterocycle, the electron-withdrawing group R including oxygen and / or nitrogen, and the heterocycle including nitrogen and sulfur. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the content of the silicon phase in the composite material is 10% by mass or more and 80% by mass or less. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the silicon phase includes at least one of elemental silicon and a silicon alloy. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the content of the carbon phase in the composite material is 10% by mass or more and 60% by mass or less. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the intra-particle porosity of the composite material is 6% or more and 20% or less. Configuration 6: The specific surface area of ​​the composite material is 5 m ２ / g or more, 20m ２ / g or less. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the average pore size of the composite material is 1 nm or more and 45 nm or less. Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the content of the composite material in the negative electrode active material is 0.5 mass % or more and 20 mass % or less. Configuration 9: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 8, wherein the electron-withdrawing group R contains at least one selected from the group consisting of a carbonyl group, a nitrile group, a sulfonyl group, an isocyanate group, an isothiocyanate group, and a hydroxy group, and the hydroxy group is bonded to a carbon constituting a saturated hydrocarbon group. Configuration 10: The nonaqueous electrolyte secondary battery according to Configuration 9, wherein the carbonyl group is contained in at least one selected from the group consisting of an aldehyde group, a ketone, an amide bond, an ester bond, and a carboxy group. Configuration 11: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 10, wherein the heterocycle includes at least one selected from the group consisting of a thiazole ring, a thiomorpholine ring, and a thiazepine ring.Configuration 12: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 11, wherein the heterocyclic compound includes at least one selected from the group consisting of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, 2-ethylthiomorpholine-4-carbaldehyde, and 2,3-dimethylthiomorpholine-4-carbaldehyde.Configuration 13: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 12, wherein the content of the heterocyclic compound in the nonaqueous electrolyte is 0.1% by mass or more and 3% by mass or less.

[0091] REFERENCE SIGNS LIST 10 nonaqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 battery case, 16 outer can, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 protruding portion, 23 filter, 24 lower valve body, 25 insulator, 26 upper valve body, 27 cap, 28 gasket

Claims

1. A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material including a Si-containing material, the Si-containing material including a composite material having a carbon phase and a silicon phase dispersed within the carbon phase, the non-aqueous electrolyte including at least one heterocyclic compound including an electron-withdrawing group R and a heterocycle, the electron-withdrawing group R including oxygen and / or nitrogen, and the heterocycle including nitrogen and sulfur.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of said silicon phase in said composite material is 10 mass % or more and 80 mass % or less.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the silicon phase includes at least one of elemental silicon and a silicon alloy.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of said carbon phase in said composite material is 10 mass % or more and 60 mass % or less.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the composite material has an internal particle porosity of 6% or more and 20% or less.

6. The specific surface area of ​​the composite material is 5 m ２ / g or more, 20m ２ 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte content is 0.1 / g or less.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the composite material has an average pore size of 1 nm or more and 45 nm or less.

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of said composite material in said negative electrode active material is 0.5 mass % or more and 20 mass % or less.

9. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electron-withdrawing group R comprises at least one selected from the group consisting of a carbonyl group, a nitrile group, a sulfonyl group, an isocyanate group, an isothiocyanate group, and a hydroxy group, and the hydroxy group is bonded to a carbon constituting a saturated hydrocarbon group.

10. The nonaqueous electrolyte secondary battery according to claim 9, wherein the carbonyl group is contained in at least one selected from the group consisting of an aldehyde group, a ketone, an amide bond, an ester bond, and a carboxy group.

11. The nonaqueous electrolyte secondary battery according to claim 1, wherein the heterocycle includes at least one selected from the group consisting of a thiazole ring, a thiomorpholine ring, and a thiazepine ring.

12. The nonaqueous electrolyte secondary battery according to claim 1, wherein the heterocyclic compound includes at least one selected from the group consisting of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, 2-ethylthiomorpholine-4-carbaldehyde, and 2,3-dimethylthiomorpholine-4-carbaldehyde.

13. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the heterocyclic compound in the nonaqueous electrolyte is 0.1% by mass or more and 3% by mass or less.

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