JP6874744B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolytic solution secondary battery including a negative electrode containing silicon oxide and graphite.

Silicon materials such as silicon and silicon oxide are known as negative electrodes for non-aqueous electrolyte secondary batteries.

In Example 2 of Patent Document 1, _{SiO particles phase-separated into microcrystalline Si and amorphous SiO 2} and scaly artificial graphite are composited at a weight mixing ratio of 1: 1 using a ball mill. After the particles were formed, the surface of the composite particles was coated with 20% by weight of carbon by a CVD method to prepare carbon-coated composite particles having a number average particle size of 10 μm, and the carbon-coated composite particles were 10% by weight and used as a carbon material. A mixture of 40% by weight of MCMB, 30% by weight of natural graphite, and 20% by weight of artificial graphite is used as a negative electrode active material, and 97% by weight of the negative electrode active material and 3% by weight of a binder (SBR and CMC) are used. It is described that a non-aqueous electrolyte secondary battery having a negative electrode having a negative electrode mixture layer consisting of% was prepared.

In Patent Document 2, "the pore ratio of the negative electrode active material layer is 10% or more and 60% or less", and "the amount of the electrolytic solution with respect to the negative electrode active material layer" is "the pore volume of the negative electrode active material layer (the pore volume of the negative electrode active material layer). It is described that "1 times or more and 35 times or less of cm ³ )", and an example in which the negative electrode active material does not contain graphite and consists only of silicon is described. In Examples 25 to 36, amorphous Si is used as the negative electrode. It occupies 70% by volume of the agent layer.

Patent No. 4965790 Japanese Unexamined Patent Publication No. 2008-262768

In general, in a non-aqueous electrolyte secondary battery, it is desired that the pores of the electrode mixture layer are always filled with the non-aqueous electrolyte, and a sufficient amount of the non-aqueous electrolyte (electrolyte solution) is injected for this purpose. There is a need to. Since the pore volume of the electrode mixture layer increases or decreases as the negative electrode active material expands and contracts with charge and discharge, if the amount of non-aqueous electrolyte injected is insufficient, the non-aqueous electrolyte will be generated during the charge and discharge process. The inside of the pores cannot be sufficiently filled, causing a decrease in capacity. However, the coefficient of thermal expansion of the negative electrode active material due to occlusion of lithium ions is remarkably large, about 300% for silicon oxide, while it is about 10% for graphite. Therefore, it is considered appropriate for a general graphite negative electrode or a non-aqueous electrolyte secondary battery using a negative electrode having a low content of silicon material, as opposed to a non-aqueous electrolyte secondary battery containing a certain amount or more of silicon oxide. Even if the amount of liquid is applied, the non-aqueous electrolyte in the pores is likely to be depleted due to the repeated changes in the pore volume of the negative electrode mixture as the negative electrode active material expands and contracts due to charging and discharging, resulting in sufficient cycle performance. Will not be obtained.

For example, the technique described in Patent Document 2 is applied to a non-aqueous electrolyte secondary battery provided with a negative electrode mixture layer containing silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40. However, there is a problem that it is difficult to determine an appropriate injection amount and it cannot be adopted.

Amount of injection of non-aqueous electrolyte into a non-aqueous electrolyte secondary battery having a negative electrode having a negative electrode mixture layer containing silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40. There was a need for a technology that would make the above appropriate.

The configuration and the action and effect of the present invention will be described with technical ideas. However, the mechanism of action includes estimation, and its correctness does not limit the present invention. It should be noted that the present invention can be practiced in various other forms without departing from its spirit or major features. Therefore, the embodiments or experimental examples described below are merely examples in all respects and should not be construed in a limited manner. Furthermore, all modifications and modifications that fall within the equivalent scope of the claims are within the scope of the present invention.

In the present invention, a negative electrode containing a silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40 and having a negative electrode mixture layer having pores, a positive electrode, and non-aqueous electrolysis. The silicon oxide comprising a liquid and the low crystalline carbon contains 70% by mass or more of the silicon oxide, and the porosity of the negative electrode mixture layer is 68% or less (however, "38% or more"). The non-aqueous electrolyte secondary battery has a mass ratio of the non-aqueous electrolyte solution to 10.5 or more with respect to the mass of silicon contained in the negative electrode mixture layer in terms of atomic weight. (In the specification of the present application, the "non-aqueous electrolyte" is also referred to as "non-aqueous electrolyte", and the "non-aqueous electrolyte secondary battery" is also referred to as "non-aqueous electrolyte secondary battery".)

The low-crystalline carbon, a peak attributed to Dband of 1360 ± 40 cm ^-1 obtained by Raman spectroscopy intensity I _D and 1580 between the intensity I _G of the peak attributed to the Gband of ± 20 cm ^-1 ratio value, ie, R value as an index of disturbance of a hexagonal carbon layer (= I _D / I _G) is referred to a carbonaceous material is 0.18 ≧ R.

The silicon oxide is _{a material represented by SiO x} (0 ≦ x ≦ 2), and may be a mixture of silicon and silicon oxide or a co-crystal, regardless of whether it is crystalline (amorphous) or not. Absent. The value of x is preferably 0.8 or more. Further, 1.2 or less is preferable.

Silicon oxide with low crystalline carbon is a material composed of composite particles of low crystalline carbon and silicon oxide, a material in which the surface of silicon oxide particles is coated with low crystalline carbon, and low crystalline carbon. It may be any material in which the surface of the composite particles of carbon and silicon oxide is coated with low crystalline carbon.

The mass of graphite contained in the negative electrode mixture layer and the mass of low crystalline carbon contained in the negative electrode mixture layer can be quantified separately by differential scanning calorimetry (TG).

When the negative electrode is composed of a negative electrode current collector and a negative electrode mixture layer, in defining the value of the porosity of the negative electrode mixture layer, the negative electrode current collector is a member having no pores such as a plate shape or a foil shape. If the negative electrode current collector is excluded from the negative electrode mixture layer, and if the negative electrode current collector has pores such as a mesh shape or a fibrous shape, the negative electrode current collector is a negative electrode combination. It shall be contained in the agent layer. Further, in defining the porosity value of the negative electrode mixture layer, it is assumed that the negative electrode mixture layer does not contain a non-aqueous electrolyte.

The atomic weight-converted silicon mass contained in the negative electrode mixture layer is the atomic weight-converted silicon mass of the silicon oxide contained in the entire negative electrode mixture layer contained in the negative electrode, for example, the chemical composition of the entire negative electrode mixture layer. When 10 g of silicon oxide represented by the formula SiO _x (x = 1.00) is contained, the mass of silicon converted to atomic weight is 10 g × [Si / SiO] = 6.37 g. The amount of Si element can be quantified by ICP emission spectroscopic analysis.

The mass of the non-aqueous electrolyte used in calculating the mass ratio of the non-aqueous electrolyte to the mass of the atomic weight-converted silicon contained in the negative electrode mixture layer is the mass of all the non-aqueous electrolyte solutions stored in the battery case. Includes a non-aqueous electrolyte solution contained or adhered to all members in the battery case, such as a negative electrode, a positive electrode, and a separator.

According to the present invention, a non-aqueous electrolyte secondary battery comprising a negative electrode having a negative electrode mixture layer containing silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40. Since the amount of the water electrolyte can be made appropriate, it is possible to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance.

FIG. 5 is a graph showing the relationship between the mass ratio of the non-aqueous electrolyte and the capacity retention rate with respect to the mass of silicon contained in the negative electrode mixture layer in terms of atomic weight for Examples and Comparative Examples. 6 is a graph plotted according to the index described in Patent Document 2 with respect to Examples and Comparative Examples.

The negative electrode mixture layer included in the negative electrode of the non-aqueous electrolyte secondary battery according to the present invention contains 40% by mass or more of graphite, so that a network of graphite is formed and a shape-retaining action is exerted. Even if it is repeated, the shape and size of the pores at the time of preparing the mixture can be maintained to some extent.

In the present invention, the porosity of the negative electrode mixture layer shall be measured in the state of the end of discharge. Since it can be said that the negative electrode in the state before the electrolytic solution is injected is in the discharge end state, it can be used for measurement as it is. Regarding the negative electrode included in the completed battery, it is necessary to take out the negative electrode after the battery is sufficiently discharged with a discharge current of 0.1 C or less, and then measure in a state where the electrolytic solution is sufficiently removed. As a method for sufficiently removing the electrolytic solution, a method such as physical removal by a centrifuge or the like, washing with a low-viscosity organic solvent (ethanol, diethyl carbonate, etc.), and drying under reduced pressure can be performed in combination. However, when there is a concern that the binder may affect the porosity state due to swelling by a low-viscosity organic solvent, such as a negative electrode containing polyvinylidene fluoride (PVdF), it is used for cleaning. It is required to pay attention to the selection of the viscous organic solvent or not to wash with the low-viscosity organic solvent.

The porosity of the negative electrode mixture is measured according to the following conditions and procedures. The same applies to the following examples.
Device name: Mercury porosimeter manufactured by Micrometrics (model number: WIN9400)
Pore diameter measurement range: 0.005 to 20 μm
Measurement principle: D = -4σcosθ / P
(D: pore diameter, P: mercury pressure, σ: surface tension, θ: contact angle)
However, θ = 130 ° and σ = 484 mN / cm were used.

In the above measurement, the mixture volume is _{the difference between the sample tube volume (V stem} ) and the mercury input volume (V _Hg ). Therefore, if the apparent volume is V _app and the true volume is V _true , V _app is mercury. It is the volume of the mixture before press-fitting, and V _true is the volume of the mixture when mercury is press-fitted to D = 0.005 μm (P = 230 MPa). Here, assuming that the mixture weight measured in advance is w, it is represented by the apparent density d _app = w / V _app and the true density d _true = w / V _true , and the porosity p (%) is p ( %) = (1-d _app / d _true ) × 100.

By setting the mass ratio of the non-aqueous electrolyte to the mass of the atomic weight-converted silicon contained in the negative electrode mixture layer to 10.5 or more, the amount of the non-aqueous electrolyte contained in the pores of the negative electrode mixture layer is sufficient. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance. The mass ratio is more preferably 12.5 or more. Moreover, 15.5 or less is preferable.

The silicon oxide having low crystalline carbon preferably contains 70% by mass or more of the silicon oxide. The particle size of the silicon oxide having low crystalline carbon is preferably 0.3 to 8 μm, more preferably 2 to 6 μm.

(Measurement of particle size)
In the following examples, the particle size distribution was measured according to the following conditions and procedures. A Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. was used as the measuring device. The measuring device includes a computer equipped with an optical table, a sample supply unit, and control software, and a wet cell having a laser light transmitting window is installed in the optical table. The measurement principle is a method in which a wet cell in which a dispersion liquid in which a measurement target sample is dispersed in a dispersion solvent circulates is irradiated with laser light, and the scattered light distribution from the measurement sample is converted into a particle size distribution. The dispersion is stored in the sample supply section and circulated and supplied to the wet cell by a pump. Ultrasonic vibration is constantly applied to the sample supply unit. In this measurement, water was used as the dispersion solvent. In addition, Microtrac DHS for Win98 (MT3000) was used as the measurement control software. For the "substance information" to be set and input to the measuring device, 1.33 is set as the "refractive index" of the solvent, "TRANSPARENT" is selected as the "transparency", and "non-spherical" is selected as the "spherical particle". Was selected. Perform the "Set Zero" operation prior to sample measurement. The "Set zero" operation is an operation to subtract the influence of disturbance elements (glass, dirt on the glass wall surface, glass unevenness, etc.) other than the scattered light from the particles on the subsequent measurement, and the sample supply part is supplied with a dispersion solvent. A background operation is performed in a state where only a certain amount of water is put in and only water, which is a dispersion solvent, is circulated in the wet cell, and the background data is stored in the computer. Then, perform the "Sample LD (Sample Loading)" operation. The Sample LD operation is an operation for optimizing the sample concentration in the dispersion liquid that is circulated and supplied to the wet cell at the time of measurement, and manually reaches the optimum amount of the sample to be measured in the sample supply unit according to the instruction of the measurement control software. It is an operation to put in. Then, the measurement operation is performed by pressing the "measurement" button. The measurement operation is repeated twice, and the measurement result is output from the computer as the average value. The measurement results are based on the particle size distribution histogram and the respective values of D10, D50 and D90 (D10, D50 and D90 have particle sizes of 10%, 50% and 90%, respectively, in the particle size distribution of the secondary particles). To be acquired. Of these, the value of D50 is adopted as the "particle size".

The graphite contained in the negative electrode mixture layer preferably has a particle size of 8 to 25 μm, more preferably 10 to 15 μm. The form is not particularly limited, but scaly, fibrous, and needle-shaped graphite is preferable from the viewpoint that the shape-retaining action of the negative electrode mixture is preferably exhibited. Any graphite may be used as long as it has high crystallinity, but the surface spacing d _{002 of} 002 planes obtained by the X-ray diffraction method is 3.35 in that it has a large charge / discharge capacity and excellent conductivity. It is preferable that the R value is ~ 3.40 Å and the R value by Raman spectroscopy is R ≦ 0.17.

In the present invention, the volume of the positive electrode, the separator, the battery case, etc. other than the negative electrode is not specified, but the amount of the positive electrode provided in the battery is determined by design according to the amount of the negative electrode. Since the internal volume is also determined by design from the viewpoint of energy density, by defining the relationship between the mass of silicon contained in the negative electrode and the mass of all non-aqueous electrolytes stored in the battery case. , The effect of the present invention is surely achieved.

Examples of the binder used for the negative electrode include polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), vinylidene fluoride-hexafluoropropylene copolymer P (VdF-HFP), and polyimide ( PI), polyamideimide (PAI), polyacrylic acid, methyl polyacrylate, polymethyl methacrylate (PMMA), polyacrylonitrile (PAN) and the like can be used alone or in combination. Among these, polyimide (PI) or polyamide-imide (PAI) is preferable because it can withstand a large volume change of silicon oxide.

The amount of the binder added may be any amount as long as the battery characteristics can be maintained, but is preferably 1 to 30% by mass, more preferably 2 to 20% by mass of the entire negative electrode mixture.

As a method of supporting the negative electrode mixture on the current collector, a silicon oxide having low crystalline carbon, graphite, and a binder are mixed in a dispersion medium to obtain a paste, which is then used. After coating on the current collector, the dispersion medium is dried to obtain a current collector containing the mixture, and the thickness can be adjusted by pressing the current collector to obtain the set porosity. Further, as the binder, the monomers, oligomers, etc. of those listed above can also be used. In this case, the curing treatment can be appropriately performed by heating, irradiating with ultraviolet rays, or the like.

The type of dispersion medium may be any type as long as it can dissolve or disperse the binder or its monomer or oligomer. For example, when polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer P (VdF-HFP), polyimide (PI), polyamideimide (PAI), polyacrylonitrile (PAN), or the like is used, N -When methylpyrrolidone is carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid, or the like, water can be used.

The mixer used to obtain the paste may be any mixer that can be uniformly mixed. For example, powder mixers such as V-type mixers, S-type mixers, scouring machines, ball mills, and planetary ball mills can be mixed dry or wet.

The positive electrode is not limited as long as it has a capacity corresponding to the negative electrode. The positive electrode active material is not limited, and is, for example, lithium iron phosphate (LiFePO ₄ ), lithium iron manganese phosphate (for example, LiFe _0.9 Mn _0.1 PO ₄ ), lithium titanate (Li ₄ Ti ₅ O ₁₂ ). , Tunganoic acid (WO ₃ ), as the lithium transition metal composite oxide, spinel type lithium manganese oxide represented by _{LiMn 2} O ₄ etc., spinel type lithium nickel manganese oxide represented by _{LiNi 1.5} Mn ₀₅ O _{4 etc.} Lithium transition metal oxides having a spinel-type crystal structure typified by objects, LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li _1.1 Co _2/3 Ni _1/6 LiMeO _{type 2} (Me is a transition metal) lithium transition metal composite oxide having an α-NaFeO ₂ structure represented by Mn _1/6 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O _{2, etc., LiMePO 4} (Me is Co or Mn-containing transition metals), lithium transition metal phosphate compounds such as _{Li 3} V ₂ (PO ₄ ) _{3, and the like.} Alternatively, a so-called "lithium excess type" lithium transition metal composite oxide which can be described as _{Li 1 +} αMe _1- αO _{2 (α> 0) may be used.} Here, the Li / Me ratio is preferably 1.25 to 1.6. When the Li / Me ratio is β, β = (1 + α) / (1-α). Therefore, for example, when Li / Me is 1.5, α = 0.2. Further, in these oxides, a part of the transition metal can be replaced with a typical metal. When a charged positive electrode active material such as lithium titanate or tungsten acid is used, lithium can be occluded in advance in either the negative electrode or the positive electrode.

The porosity of the positive electrode mixture layer is preferably 20 to 40%, more preferably 26 to 34%. The pore volume of the positive electrode mixture layer is preferably 1.7 to 3.4 cc, more preferably 2.2 to 2.9 cc per 1 g of the atomic weight-converted silicon contained in the negative electrode mixture layer.

The powder of the positive electrode active material preferably has an average particle size of 100 μm or less. In particular, 30 μm or less is more preferable for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. A crusher or a classifier is used to obtain the powder in a predetermined shape. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. The classification method is not particularly limited, and a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

In addition to the main constituents, the positive electrode may contain a conductive agent, a binder, a thickener, a filler and the like as other constituents.

The conductive agent is not limited as long as it is an electronically conductive material that does not adversely affect the battery performance, but is usually natural graphite (scaly graphite, scaly graphite, earthy graphite, etc.), artificial graphite, carbon black, acetylene black, etc. Conductive materials such as Ketjen black, carbon whiskers, carbon fibers, and conductive ceramic materials can be included as one kind or a mixture thereof.

Among these, acetylene black is desirable as the conductive agent from the viewpoint of electron conductivity and coatability. The amount of the conductive agent added is preferably 0.1% by mass to 50% by mass, particularly preferably 0.5% by mass to 30% by mass, based on the total mass of the positive electrode or the negative electrode. The ideal is uniform mixing. Therefore, it is possible to mix powder mixers such as V-type mixers, S-type mixers, scouring machines, ball mills, and planetary ball mills in a dry or wet manner.

Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, and polyacrylonitrile (PAN), ethylene-propylene-dienter polymer (EPDM), and the like. Polymers having rubber elasticity such as sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by mass, particularly preferably 2 to 30% by mass, based on the total mass of the positive electrode.

The filler may be any material that does not adversely affect the battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The amount of the filler added is preferably 30% by mass or less with respect to the total mass of the positive electrode or the negative electrode.

For the positive electrode, the main constituents (positive electrode active material for the positive electrode, negative electrode material for the negative electrode) and other materials are kneaded to form a kneading agent, which is then mixed with an organic solvent such as N-methylpyrrolidone or toluene or water. , The obtained mixed solution is preferably applied on a current collector described in detail below, or pressure-bonded and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours to be suitably produced. Regarding the coating method, for example, a roller coating such as an applicator roll, a gravure roll coating, a die coating, a screen coating, a doctor blade method, a spin coating, a bar coater, or the like is used to apply the coating to an arbitrary thickness and an arbitrary shape. It is desirable, but not limited to these.

As the separator, it is preferable to use a porous membrane, a non-woven fabric, or the like exhibiting excellent high-rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, foot Vinylidene-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene Examples thereof include a copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like. A microporous membrane made of an ethylene-propylene copolymer coated with an insulating powder such as alumina can also be preferably used.

The thickness of the separator is preferably 16 to 30 μm, more preferably 20 to 27 μm. This is because it is desirable that it is 16 μm or more in order to have sufficient insulating properties, and it is desirable that it is 30 μm or less in order not to impair the energy density of the battery.

The porosity of the separator is preferably 0.4 to 0.7, more preferably 0.5 to 0.6. When the porosity of the separator is 0.4 to 0.7 (preferably 0.5 to 0.6), the pore volume of the separator is based on 1 g of the atomic weight-converted silicon contained in the negative electrode mixture layer. It is 1.3 to 3.4 cc (preferably 2.0 to 2.5 cc).

The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Examples of the non-aqueous solvent used for the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butylolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; Chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane, methyl diglime; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sulton or derivatives thereof, etc. alone or two or more thereof Mixtures and the like can be mentioned, but the present invention is not limited to these.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF _{4 , LiAsF 6} , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN and other inorganic ionic salts containing one of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅₎ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ , NClO ₄ , (n-) C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthate, lithium stearyl sulfonate, lithium octyl sulfonate , Organic ionic salts such as lithium dodecylbenzenesulfonate, etc., and these ionic compounds can be used alone or in combination of two or more.

The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to surely obtain a non-aqueous electrolyte battery having high battery characteristics. It is .5 mol / l.

The volume of the gap between the power generation element provided with the positive electrode, the negative electrode and the separator and the electric tank for accommodating the positive electrode, the negative electrode and the separator is sufficient to sufficiently hold the electrolytic solution in the electric tank, and the maximum volume of the negative electrode. As long as it can tolerate expansion, it is not particularly limited, but it must not be larger than necessary from the viewpoint of energy density. The volume of the gap between the power generation element and the battery tank at the time of battery assembly is preferably 3.5 to 7.5 cc, more preferably 4.5 to 6 per 1 g of the atomic weight-converted silicon contained in the negative electrode mixture layer. It is .5 cc.

The configuration of the non-aqueous electrolyte secondary battery is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll-shaped separator, a square battery, and a flat battery.

Hereinafter, the present invention will be described in more detail by exemplifying examples, but the present invention is not limited to the following embodiments.

(Example 1)
(Creation of silicon oxide with low crystalline carbon)
A silicon oxide having low crystalline carbon (hereinafter referred to as "SiO-C") is obtained by coating the surface of SiO particles with low crystalline carbon by a method (CVD) of thermally decomposing benzene gas at 1000 ° C. in an argon atmosphere. Also called). The coating amount of low crystalline carbon was set to 5% by mass with respect to the mass of SiO-C. The number average particle size of SiO-C was 5 μm. In SiO-C used in this example, the SiO particles are _{phase-separated into microcrystalline Si and amorphous SiO 2,} and the diffraction angle (2θ) is 46 from the X-ray diffraction pattern using CuKα rays. The main diffraction peak of Si was shown in the range of ° to 49 °, and the half width of this diffraction peak was less than 3 °. The R value by Raman spectroscopy was 0.21.

(Creation of negative electrode)
As the graphite, scaly artificial graphite (manufactured by TIMCAL) having a particle size of 10 μm was used. The "SiO-C" and the graphite were weighed at a mass ratio of 40:60 and manually mixed in a mixing pot until uniform. Further, N-methylpyrrolidone (NMP) as a solvent and polyamide-imide resin as a binder were weighed so as to have a mass ratio of 94: 6, and were sufficiently mixed with a Dalton mixer to prepare a negative electrode paste. .. After applying the negative electrode paste to both sides of an electrolytic copper foil having a thickness of 10 μm, which is a negative electrode current collector, the negative electrode paste is subjected to a drying step and a pressing step, and then a curing process is carried out at 300 ° C. for 12 hours under vacuum conditions. A negative electrode plate in which the agent layer was formed on both sides of the negative electrode current collector was produced. The mass of the negative electrode mixture layer formed on one surface of the negative electrode current collector is 2.8 mg / cm ² , and the porosity of the negative electrode mixture layer is 40%.

(Creation of positive electrode)
Using NMP as a solvent _{, 93: a positive electrode active material represented by the composition formula LiCo 1/3} Ni _1/3 Mn _1/3 O ₂ , acetylene black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder. A positive electrode paste containing a mass ratio of 3: 4 was prepared. After applying the positive electrode paste to both sides of a 15 μm-thick aluminum foil that is a positive electrode current collector, a positive electrode mixture layer is formed on both sides of the positive electrode current collector through a drying step and a pressing step. Made. The mass of the positive electrode mixture layer formed on one surface of the positive electrode current collector is 17.4 mg / cm ² , and the thickness of the positive electrode plate including the positive electrode current collector and the positive electrode mixture layers formed on both sides is 134 μm. Is. The porosity of the positive electrode mixture layer is 34%. At this time, the pore volume of the positive electrode mixture layer is 2.77 cc per 1 g of the atomic weight-converted silicon contained in the negative electrode mixture layer.

(Separator)
As a separator, a polyethylene microporous membrane having a porosity of 0.5 and a thickness of 27 μm was used. At this time, the pore volume of the separator is 2.25 cc per 1 g of the atomic weight-converted silicon contained in the negative electrode mixture layer.

(Electric tank)
An aluminum battery was used as the battery. The volume of the gap between the power generation element composed of the positive electrode, the negative electrode and the separator and the inside of the battery case is 6.0 cc per 1 g of the atomic weight-converted silicon contained in the negative electrode mixture layer. (However, the volume of the gap becomes smaller as the porosity of the negative electrode mixture layer increases, and the volume of the gap is 4.5 in Examples 7 and 8 and Comparative Example 3 described later.)

(Non-aqueous electrolyte)
_{The non-aqueous electrolyte contains 1 mol / l of LiPF 6} dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 7, and 2% by mass of vinylene carbonate (VC). Was added. The non-aqueous electrolyte was injected into the electric tank containing the power generation element, and finally the injection port was sealed. Here, the amount of the non-aqueous electrolyte injected is such that the mass ratio of the non-aqueous electrolyte to the mass of silicon contained in the negative electrode mixture layer in terms of atomic weight is 10.5. In this way, the non-aqueous electrolyte battery according to Example 1 was assembled.

(Examples 2 and 3 and Comparative Examples 1 and 2)
Except that the injection amount of the non-aqueous electrolyte was changed and the mass ratio of the non-aqueous electrolyte to the mass of the atomic weight-converted silicon contained in the negative electrode mixture layer was different as shown in Table 1, it was different from that of Example 1. In the same manner, the non-aqueous electrolyte batteries according to Examples 2 and 3 and Comparative Examples 1 and 2 were assembled.

(Examples 4 to 8 and Comparative Example 3)
In the production of the negative electrode, Example 1 except that the porosity of the negative electrode mixture layer was changed as shown in Table 1 by changing the conditions of the pressing process, and the injection amount was also set to the value shown in Table 1. The non-aqueous electrolyte batteries according to Examples 4 to 8 and Comparative Example 3 were assembled in the same manner as in the above.

(Charge / discharge cycle test)
A charge / discharge cycle test was performed on the non-aqueous electrolyte batteries according to Examples 1 to 7 and Comparative Examples 1 and 2 assembled in this manner. The charging was a constant current constant voltage charging with a current of 1CA and a voltage of 4.2V, and the charging time was 3 hours. The discharge was a constant current discharge with a current of 1CA and a final voltage of 2.75V. A 10-minute pause process was provided between charging and discharging, and between discharging and charging. Charging and discharging under such conditions was repeated for 150 cycles. For each non-aqueous electrolyte battery, the percentage of the discharge capacity (mAh) at the 150th cycle with respect to the discharge capacity (mAh) at the first cycle was determined, and the capacity retention rate (%) is also shown in Tables 1 and 2.

FIG. 1 is a diagram in which the results of the capacity retention rates shown in Table 1 are plotted in relation to the mass ratio of the non-aqueous electrolyte to the mass of silicon contained in the negative electrode mixture layer in terms of atomic weight. It can be seen that a non-aqueous electrolyte secondary battery having an excellent capacity retention rate of 75% or more can be provided by setting the mass ratio of the non-aqueous electrolyte to the mass of silicon contained in the negative electrode mixture layer in terms of atomic weight to 10.5 or more. ..

Patent Document 2 describes that "the amount of electrolyte with respect to the negative electrode active material layer" is "1 times or more and 35 times or less the ^{pore volume (cm 3) of the negative electrode active material layer", respectively.} For the Examples and Comparative Examples of the above, the value obtained by dividing the amount of the non-aqueous electrolyte with respect to the negative electrode mixture layer by the pore volume of the negative electrode mixture layer was obtained, and it is also shown in Table 1 and the result of the capacity retention rate The relationship is plotted and shown in FIG. From FIG. 2, in a non-aqueous electrolyte secondary battery having a negative electrode having a negative electrode mixture layer containing silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40, the negative electrode Since no correlation is observed with the value obtained by dividing the amount of non-aqueous electrolyte with respect to the mixture layer by the pore volume of the negative electrode mixture layer, even if the above value is in the range of 1 to 35, the performance is not necessarily good. It turns out that a non-aqueous electrolyte secondary battery cannot be provided.

Claims (1)

A negative electrode containing a silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40 and having a negative electrode mixture layer having pores, a positive electrode, and a non-aqueous electrolytic solution. The silicon oxide provided with the low crystalline carbon contains 70% by mass or more of the silicon oxide, and the porosity of the negative electrode mixture layer is 68% or less (however, "38% or more" is excluded). A non-aqueous electrolyte secondary battery in which the mass ratio of the non-aqueous electrolyte solution to the mass of the atomic weight-converted silicon contained in the negative electrode mixture layer is 10.5 or more.

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