JP6632957B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a nonaqueous electrolyte secondary battery provided with a negative electrode containing silicon oxide and graphite.

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

In Example 2 of Patent Literature 1, there is disclosed a method in which SiO particles which are phase-separated into microcrystalline Si and amorphous SiO ₂ and flaky artificial graphite are mixed at a weight mixing ratio of 1: 1 using a ball mill. After forming the particles, the surface of the composite particles is coated with 20% by weight of carbon by a CVD method to prepare carbon-coated composite particles having a number average particle diameter of 10 μm, and 10% by weight of the carbon-coated composite particles 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 was used as a negative electrode active material, and 97% by weight of the negative electrode active material and 3% by weight of binders (SBR and CMC) were used. It is described that a non-aqueous electrolyte secondary battery provided with a negative electrode provided with a negative electrode mixture layer composed of

Patent Literature 2 discloses that “the porosity of the negative electrode active material layer is 10% or more and 60% or less” and that “the amount of the electrolytic solution with respect to the negative electrode active material layer” is “the porosity of the negative electrode active material layer ( cm ³⁾ 1 times or more, it is described that a 35-fold or less ", examples where the anode active material consists only of silicon free of graphite is described, amorphous Si in examples 25 to 36 is the negative electrode It accounts for 70% by mass of the agent layer.

Patent No. 4965790 JP 2008-262768 A

  Generally, 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) is injected for this purpose. There is a need to. Since the pore volume of the electrode mixture layer increases and decreases with the expansion and contraction of the negative electrode active material due to charge and discharge, if the injection amount of the nonaqueous electrolyte is insufficient, the nonaqueous electrolyte is charged during the charge and discharge process. It is not possible to sufficiently fill the pores, causing a reduction in capacity. However, the volume expansion coefficient of the negative electrode active material due to occlusion of lithium ions is about 10% in graphite, and about 300% in silicon oxide. Therefore, it is considered appropriate for a non-aqueous electrolyte secondary battery using a general graphite negative electrode or a negative electrode having a low silicon material content with respect to a non-aqueous electrolyte secondary battery containing a certain amount of silicon oxide. Even when the liquid volume is applied, the pore volume of the negative electrode mixture repeatedly changes with the expansion and contraction of the negative electrode active material due to charge and discharge, so that the nonaqueous electrolyte in the holes is easily depleted, and sufficient cycle performance Will not be obtained.

  For example, a technique described in Patent Document 2 is applied to a nonaqueous electrolyte secondary battery including a negative electrode mixture layer including a 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 nonaqueous electrolyte injected into a nonaqueous electrolyte secondary battery including a negative electrode including a negative electrode mixture layer including a silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40. There has been a demand for a technique for making the appropriate.

  The configuration, operation and effect of the present invention will be described together with technical ideas. However, the mechanism of action includes an estimation, and its correctness is not intended to limit the present invention. Note that the present invention can be embodied in various other forms without departing from the spirit or main characteristics thereof. Therefore, the following embodiments or experimental examples are merely examples in all aspects and should not be interpreted in a limited manner. Furthermore, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The present invention provides a negative electrode composite having a porosity capable of absorbing a volume change of the silicon oxide caused by charging and discharging, comprising a silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40. A negative electrode provided with an agent layer, a positive electrode, and a non-aqueous electrolyte, wherein the silicon oxide is a material represented by SiO _x (0.8 ≦ x ≦ 1.2), The silicon oxide with carbon contains silicon oxide in an amount of 70% by mass or more, and the mass ratio of the nonaqueous electrolyte to the mass of silicon in atomic weight contained in the negative electrode mixture layer is 10.5 or more. Ri is a non-aqueous electrolyte secondary battery capacity retention rate, characterized in der Rukoto more than 75%. (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, that is, a carbonaceous material whose R value (= I _D / I _G ), which is an index of the disorder of the carbon hexagonal mesh plane, is 0.18 ≧ R.

In the present invention, the silicon oxide is a material represented by SiO _x ( 0.8 ≦ x ≦ 1.2 ), which may be a mixture or eutectic of silicon and silicon oxide, Crystallinity).

Silicon oxide with low crystalline carbon refers to 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, Any material may be used in which the surface of the composite particles of carbon and silicon oxide is coated with low-crystalline carbon. In the present invention, the silicon oxide having low crystalline carbon contains the silicon oxide in an amount of 70% by mass or more.

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

  When the negative electrode is composed of the negative electrode current collector and the 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 pore portion, such as a plate shape, a foil shape, or the like. , The negative electrode current collector is excluded from the negative electrode mixture layer, and when the negative electrode current collector has a pore portion such as a mesh shape, a fibrous shape, or the like, the negative electrode current collector is Shall be included in the agent layer. In defining the value of the porosity of the negative electrode mixture layer, the negative electrode mixture layer does not contain a nonaqueous electrolyte.

The mass of silicon in terms of atomic weight contained in the negative electrode mixture layer is the mass of silicon in terms of atomic weight with respect to the silicon oxide contained in the entire negative electrode mixture layer provided in the negative electrode. When 10 g of the silicon oxide represented by the formula SiO _x (x = 1.00) is contained, the mass of silicon in terms of atomic weight is 10 g × [Si / SiO] = 6.37 g. The Si element amount can be quantified by ICP emission spectroscopy.

  The mass of the non-aqueous electrolyte used to calculate 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 electrolytes contained in the battery case of the battery. And includes a non-aqueous electrolyte contained or adhered to all members in a battery case, such as a negative electrode, a positive electrode, and a separator.

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

4 is a graph showing a relationship between a mass ratio of a nonaqueous electrolyte to a mass of silicon in terms of an atomic weight contained in a negative electrode mixture layer and a capacity retention ratio in Examples and Comparative Examples. 9 is a graph plotted according to an index described in Patent Document 2 for Examples and Comparative Examples.

The negative electrode mixture layer included in the negative electrode of the nonaqueous electrolyte secondary battery according to the present invention contains a graphite of 40 % by mass or more, so that a network of graphite is formed, and a shape maintaining action is exhibited, so that charging and discharging are performed. Even if it is repeated, the shape and size of the holes at the time of preparing the mixture can be maintained to some extent.

  The negative electrode mixture layer preferably has a porosity of 38% or more in a discharge end state, and since such a porosity can absorb a volume change of silicon oxide due to charge and discharge, the negative electrode mixture layer has a porosity of 38% or more. The nonaqueous electrolyte secondary battery can suppress the change in the volume of the agent layer and have a sufficient capacity retention ratio with repeated charge / discharge cycles. The porosity is more preferably 40% or more, and further preferably 68% or less.

  In the present invention, the porosity of the negative electrode mixture layer is measured in a state of a discharge end. The negative electrode in a state before the electrolyte solution is injected can be said to be in a discharged state, and thus 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 at a discharge current of 0.1 C or less, and then take out the negative electrode, and then perform measurement in a state where the electrolyte is sufficiently removed. As a method for sufficiently removing the electrolytic solution, a combination of techniques such as physical removal by a centrifuge, washing with a low-viscosity organic solvent (ethanol, diethyl carbonate, etc.), and drying under reduced pressure can be used. However, if there is a concern that the swelling of the binder with a low-viscosity organic solvent will affect the porosity state, as in the case of a negative electrode containing polyvinylidene fluoride (PVdF), for example, It is required to pay attention to the selection of the organic solvent having a high viscosity or not to perform the washing with the organic solvent having a low viscosity.

The porosity of the negative electrode mixture is measured according to the following conditions and procedures. The same applies to the following embodiments.
Device name: Micrometrics, mercury porosimeter (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 are used.

In the above measurement, since the mixture volume is the difference between the sample tube volume (V _stem ) and the mercury input volume (V _Hg ), if the apparent volume is V _app and the true volume is V _true , V _app is mercury V _true is the volume of the mixture before the injection, and V _true is the volume of the mixture when mercury is injected to D = 0.005 μm (P = 230 MPa). Here, assuming that the mixture weight measured in advance is w, 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 nonaqueous electrolyte to the mass of the silicon in terms of atomic weight contained in the negative electrode mixture layer to 10.5 or more, the amount of the nonaqueous electrolyte contained in the pores of the negative electrode mixture layer can be sufficiently increased. Therefore, a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle performance can be provided. The mass ratio is more preferably 12.5 or more. Moreover, 15.5 or less is preferable.

  The particle diameter 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. Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. was used as a measuring device. The measuring device includes an optical bench, a sample supply unit, and a computer on which control software is mounted. The optical bench is provided with a wet cell having a laser light transmission window. The measurement principle is a method of irradiating a wet cell in which a dispersion liquid in which a sample to be measured is dispersed in a dispersion solvent is circulated with laser light, and converting a scattered light distribution from the measurement sample into a particle size distribution. The dispersion is stored in the sample supply unit and circulated and supplied to the wet cell by a pump. Ultrasonic vibration is always applied to the sample supply unit. In this measurement, water was used as a dispersion solvent. Microtrac DHS for Win98 (MT3000) was used as measurement control software. As 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 set as the “spherical particle”. Was selected. Perform “Set Zero” operation before measuring the sample. The “Set zero” operation is an operation to subtract the influence of disturbance elements other than the scattered light from the particles (glass, stain on the glass wall surface, glass irregularities, etc.) on the subsequent measurement. A background operation is performed in a state where only certain water is charged and only water as a dispersion solvent circulates in the wet cell, and the background data is stored in a computer. Then, perform “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 during measurement, and reaches the optimal amount of the sample to be measured manually to the sample supply unit according to the instruction of the measurement control software. This is the operation to enter. Subsequently, a measurement operation is performed by pressing a “measure” button. The measurement operation is repeated twice, and the measurement result is output from the computer as an average value. The measurement result is a particle size distribution histogram, and each value of D10, D50, and D90 (D10, D50, and D90 are particle sizes at which the cumulative volume in the particle size distribution of the secondary particles is 10%, 50%, and 90%, respectively). Is obtained. Among them, the value of D50 is adopted as “particle size”.

The graphite included 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, or acicular graphite is preferable from the viewpoint that the shape-retaining action of the negative electrode mixture is suitably exhibited. Any graphite may be used as long as it has high crystallinity. However, in view of a large charge / discharge capacity and excellent conductivity, the 002 plane spacing d ₀₀₂ obtained by the X-ray diffraction method is 3.35. It is preferable that the R value by Raman spectroscopy is R ≦ 0.17.

  In the present invention, the positive electrode, the separator, the container, etc., the volume and the like other than the negative electrode is not specified, but the amount of the positive electrode provided in the battery is determined by design corresponding to the amount of the negative electrode, the battery case, Since the internal volume is also almost 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 electrolyte solutions contained in the battery case of the battery. Thus, the effects of the present invention are reliably 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), polyimide ( PI), polyamide imide (PAI), polyacrylic acid, polymethyl acrylate, polymethyl methacrylate (PMMA), polyacrylonitrile (PAN) and the like can be used alone or in combination. Among these, polyimide (PI) and polyamideimide (PAI) are preferable because they can withstand a large volume change of silicon oxide.

  The amount of the binder added may be any 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 whole 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, and this is obtained. After being applied on the current collector, the dispersion medium is dried to obtain a current collector provided with the mixture, and the thickness is adjusted by pressing, so that the porosity can be set. Further, as the binder, monomers or oligomers of the above-mentioned ones can also be used. In this case, a curing treatment can be appropriately performed by heating, irradiation with ultraviolet light, or the like.

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

  Any mixer can be used for obtaining the paste as long as it can be uniformly mixed. For example, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, and a planetary ball mill can be mixed in a dry or wet manner.

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. For example, lithium iron phosphate (LiFePO ₄ ), lithium manganese iron phosphate (eg, LiFe _0.9 Mn _0.1 PO ₄ ), lithium titanate (Li ₄ Ti ₅ O ₁₂ ) , Tungstic acid (WO ₃ ), and lithium transition metal composite oxides include spinel-type lithium manganese oxide represented by LiMn ₂ O _{4 and the} like, and spinel-type lithium nickel manganese oxide represented by LiNi _1.5 Mn ₀₅ O _{4 and the} like Transition metal oxide having a spinel-type crystal structure typified by a material, LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li _1.1 Co _2/3 Ni _{1/6 Mn 1/6 O 2, LiNi 0.8 Co} 0.15 Al 0.05 O 2 , etc. LiMeO ₂ type with alpha-NaFeO ₂ structure represented by (Me is a transition metal) lithium transition metal composite Product, LiMePO ₄ (transition metal Me is containing Co or _{Mn), Li 3 V 2 (} PO 4) transition metal phosphate lithium compound such as _3, and the like. Further, a so-called “lithium-excess type” lithium transition metal composite oxide that can be expressed as Li ₁₊ αMe ₁₋ αO ₂ (α> 0) may be used. Here, the Li / Me ratio is preferably from 1.25 to 1.6. When the Li / Me ratio is β, β = (1 + α) / (1−α). For example, when Li / Me is 1.5, α = 0.2. 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 tungstic acid is used, lithium can be stored in advance in either the negative electrode or the positive electrode as appropriate.

  The porosity of the positive electrode mixture layer is preferably from 20 to 40%, more preferably from 26 to 34%. The pore volume of the positive electrode mixture layer is preferably from 1.7 to 3.4 cc, more preferably from 2.2 to 2.9 cc, per gram of the atomic weight of 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, the thickness is preferably 30 μm or less for the purpose of improving the high output characteristics of the nonaqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air jet mill, a sieve, and the like are used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed in both dry and wet methods.

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

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (scale graphite, flake graphite, earth graphite, etc.), artificial graphite, carbon black, acetylene black, Conductive materials such as Ketjen black, carbon whiskers, carbon fibers, and conductive ceramic materials can be included as one type or a mixture thereof.

  Among these, acetylene black is preferable as the conductive agent from the viewpoints of electron conductivity and coatability. The amount of the conductive agent to be 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. Where the ideal is homogeneous mixing. Therefore, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, and a planetary ball mill can be mixed 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-diene terpolymer (EPDM); Polymers having rubber elasticity such as sulfonated EPDM, styrene butadiene rubber (SBR), and fluororubber can be used as one kind or as a mixture of two or more kinds. The addition amount of the binder is preferably from 1 to 50% by mass, and particularly preferably from 2 to 30% by mass, based on the total mass of the positive electrode.

  Any filler may be used as long as it does not adversely affect battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by mass or less based on the total mass of the positive electrode or the negative electrode.

  The positive electrode is prepared by kneading the main components (a positive electrode active material in the positive electrode, a negative electrode material in the negative electrode) and other materials to form a mixture, and mixing the mixture with water or an organic solvent such as N-methylpyrrolidone or toluene or water. The obtained liquid mixture is applied onto a current collector described in detail below, or is pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours to be suitably prepared. For the application method, for example, using a means such as roller coating such as an applicator roll, gravure roll coating, die coating, screen coating, a doctor blade method, spin coating, a bar coater, and the like, apply to an arbitrary thickness and an arbitrary shape. However, the present invention is not limited thereto.

  As the separator, it is preferable to use a porous film or a nonwoven fabric exhibiting excellent high-rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include, for example, polyethylene, a polyolefin resin represented by polypropylene, a polyester resin represented by polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer. A material obtained by applying an insulating powder such as alumina to a microporous film made of an ethylene-propylene copolymer or the like can also be suitably used.

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

  The porosity of the separator is preferably from 0.4 to 0.7, more preferably from 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 as follows: per 1 g of atomic mass-converted silicon contained in the negative electrode mixture layer, 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 propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, cyclic carbonates such as vinylene carbonate; γ-butyrolactone, cyclic esters such as 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 and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof. Examples of the conductor include a single conductor or a mixture of two or more conductors, but are not limited thereto.

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, and NaBr. , KClO ₄ , KSCN, etc., inorganic ion salts containing one kind 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-ma eATE, include _{(C 2 H 5) 4 N} -benzoate, (C 2 H 5) 4 N-pht h alate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts such as lithium dodecylbenzenesulfonate 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 from 0.1 mol / l to 5 mol / l, more preferably from 0.5 mol / l to 2 mol / l in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. 0.5 mol / l.

  The volume of the gap between the power generating element including the positive electrode, the negative electrode, and the separator, and the battery case housing the power generating element is sufficient to hold the electrolyte sufficiently in the battery case, and the maximum volume of the negative electrode There is no particular limitation as long as expansion is permissible, but it should not be unnecessarily large from the viewpoint of energy density. The volume of the gap between the power generating element and the battery case at the time of assembling the battery is preferably 3.5 to 7.5 cc, more preferably 4.5 to 6 cc, per gram of the atomic weight of silicon contained in the negative electrode mixture layer. 0.5 cc.

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

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

(Example 1)
(Preparation of silicon oxide with low crystalline carbon)
The surface of SiO particles is coated with low-crystalline carbon by a method of thermally decomposing benzene gas at 1000 ° C. in an argon atmosphere, and silicon oxide having low-crystalline carbon (hereinafter “SiO-C”) is coated. ). The coating amount of low crystalline carbon was 5% by mass with respect to the mass of SiO-C. The number average particle diameter of SiO-C was 5 μm. In the SiO-C used in this example, the SiO particles were phase-separated into microcrystalline Si and amorphous SiO _2, and the diffraction angle (2θ) was 46 from the X-ray diffraction pattern using CuKα radiation. The main diffraction peak of Si was shown in the range of ° to 49 °, and the half value width of this diffraction peak was less than 3 °. The R value measured by Raman spectroscopy was 0.21.

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

(Creation of positive electrode)
Using NMP as a solvent, 93: a positive electrode active material represented by a composition formula of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , acetylene black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder 93: A positive electrode paste containing at a mass ratio of 3: 4 was prepared. After applying the positive electrode paste on both sides of a 15 μm thick aluminum foil that is a positive electrode current collector, through a drying step and a pressing step, a positive electrode plate having a positive electrode mixture layer formed on both surfaces of the positive electrode current collector is formed. Produced. The mass of the positive electrode mixture layer formed on one surface of the positive electrode current collector was 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 surfaces was 134 μm. It 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 atomic mass of silicon contained in the negative electrode mixture layer.

(Separator)
As the separator, a microporous polyethylene 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 atomic mass of silicon contained in the negative electrode mixture layer.

(Battery case)
As the battery case, an aluminum battery case was used. The volume of the gap between the power generation element including 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 of silicon contained in the negative electrode mixture layer. (However, the volume of the gap is smaller as the porosity of the negative electrode mixture layer is larger, 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 was prepared by dissolving 1 mol / l LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 7, and further 2% by mass of vinylene carbonate (VC). Was used. The non-aqueous electrolyte was injected into the battery case containing the power generating element, and the injection port was sealed at last. Here, as for the injection amount of the non-aqueous electrolyte, 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 10.5. Thus, the nonaqueous electrolyte battery according to Example 1 was assembled.

(Examples 2 and 3 and Comparative Examples 1 and 2)
Example 1 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 silicon in terms of atomic weight contained in the negative electrode mixture layer was changed as shown in Table 1. Similarly, 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 preparation of the negative electrode, Example 1 was repeated except that the porosity of the negative electrode mixture layer was changed as shown in Table 1 by changing the conditions of the pressing step, and the injection amount was also the value shown in Table 1. In the same manner as in the above, non-aqueous electrolyte batteries according to Examples 4 to 8 and Comparative Example 3 were assembled.

(Charge / discharge cycle test)
The non-aqueous electrolyte batteries according to Examples 1 to 7 and Comparative Examples 1 and 2 assembled in this manner were subjected to a charge / discharge cycle test. The charging was performed at a constant current and constant voltage with a current of 1 CA and a voltage of 4.2 V, and the charging time was 3 hours. The discharge was a constant current discharge at a current of 1 CA and a cutoff voltage of 2.75 V. Between the charge and the discharge, and between the discharge and the charge, a pause process of 10 minutes was provided. The charge and discharge under such conditions were repeated for 150 cycles. For each of the nonaqueous electrolyte batteries, the percentage of the discharge capacity (mAh) at the 150th cycle relative to the discharge capacity (mAh) at the first cycle was determined, and the results are shown in Tables 1 and 2 as the capacity retention rate (%).
The “capacity maintenance rate” specified in claim 1 means the capacity maintenance rate (%) obtained by the above method.

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

Patent Literature 2 describes that “the amount of the electrolytic solution with respect to the negative electrode active material layer” is “1 to 35 times the pore volume (cm ³ ) of the negative electrode active material layer”. For Examples and Comparative Examples, the value obtained by dividing the amount of the nonaqueous electrolyte with respect to the negative electrode mixture layer by the pore volume of the negative electrode mixture layer was obtained, and the results are shown in Table 1 together with the results of the capacity retention. The relationship was plotted and shown in FIG. From FIG. 2, in the nonaqueous electrolyte secondary battery including the negative electrode including the negative electrode mixture layer including the silicon oxide having low crystalline carbon and graphite at a mass ratio of 30:70 to 60:40, the negative electrode Since there is no correlation with the value obtained by dividing the amount of the non-aqueous electrolyte with respect to the mixture layer by the pore volume of the negative electrode mixture layer, even if the value is in the range of 1 to 35, it is not necessarily required to obtain good performance. It turns out that a nonaqueous electrolyte secondary battery cannot be provided.

Claims (1)

A silicon oxide having low crystalline carbon and graphite in a mass ratio of 30:70 to 60:40, and a negative electrode mixture layer having a porosity capable of absorbing a volume change of the silicon oxide due to charge and discharge. A negative electrode, a positive electrode, and a non-aqueous electrolyte, wherein the silicon oxide is a material represented by SiO _x (0.8 ≦ x ≦ 1.2), and includes the low-crystalline carbon. The silicon oxide contains the silicon oxide in an amount of 70% by mass or more, and the mass ratio of the nonaqueous electrolyte to the mass of the atomic weight-converted silicon contained in the negative electrode mixture layer is 10.5 or more; Is 75% or more.

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