Method of use of nonaqueous electrolyte power storage device and apparatus

Abstract

To provide a method of use of nonaqueous electrolyte power storage device with a silicon-based active material where resistance is low in a low temperature environment in comparison with a nonaqueous electrolyte power storage device having the same discharge capacity and capacity maintenance ratio is high in a charge / discharge cycle, and an apparatus which can use the nonaqueous electrolyte power storage device with a silicon-based active material as the such application use.SOLUTION: A method of use of nonaqueous electrolyte power storage device comprises the step of: discharging nonaqueous electrolyte power storage device until lower limit voltage. The nonaqueous electrolyte power storage device includes a negative electrode with anode active material layer including metal silicon nanoparticle. Content of the metal silicon nanoparticle in the anode active material layer is 6 mass% or more. The lower limit voltage is lower than voltage corresponding to a local maximum value at the lowest voltage side by 0.04 V or more and 0.20 V or less in a dQ / dV curve which is obtained when the nonaqueous electrolyte power storage device discharges quantity of electricity corresponding rating capacity from a fully charged state.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and device for using a non-aqueous electrolyte electricity storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc., due to their high energy density. Non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. As non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used.

[0003] There is known a non-aqueous electrolyte storage element that uses a silicon material (silicon-based active material) containing silicon element such as metal silicon or silicon oxide as the negative electrode active material (see Patent Document 1). Silicon-based materials have advantages such as a larger discharge capacity per mass compared to carbon materials (carbon-based active materials) such as graphite. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-053152 A Summary of the Invention [Problem to be solved by the invention]

[0005] A nonaqueous electrolyte storage element using a silicon-based active material has a disadvantage in that it has a low capacity retention rate in charge-discharge cycles. In addition, in a nonaqueous electrolyte storage element, it is desirable to have low resistance in a low-temperature environment, for example, in terms of regenerative power acceptance and output performance in a low-temperature environment.

[0006] The present invention aims to provide a method for using a nonaqueous electrolyte storage element that uses a silicon-based active material, which has low resistance in a low-temperature environment and a high capacity retention rate in charge-discharge cycles when compared with a nonaqueous electrolyte storage element having the same discharge capacity, and to provide an apparatus capable of such use for a nonaqueous electrolyte storage element that uses a silicon-based active material. [Means for solving the problem]

[0007] A method of using a nonaqueous electrolyte storage element according to one embodiment of the present invention comprises discharging the nonaqueous electrolyte storage element to a lower limit voltage, the nonaqueous electrolyte storage element comprising a negative electrode having a negative electrode active material layer containing metal silicon nanoparticles, the content of the metal silicon nanoparticles in the negative electrode active material layer being 6 mass % or more, and the lower limit voltage being in the range of 0.04 V to 0.20 V lower than the voltage corresponding to the maximum on the lowest voltage side in a dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state with an amount of electricity equivalent to the rated capacity.

[0008] Another embodiment of the present invention provides a device comprising a nonaqueous electrolyte storage element having a negative electrode having a negative electrode active material layer containing metal silicon nanoparticles, wherein the content of the metal silicon nanoparticles in the negative electrode active material layer is 6 mass % or more, and the lower limit voltage of the nonaqueous electrolyte storage element is set in a range of 0.04 V to 0.20 V lower than the voltage corresponding to the maximum on the lowest voltage side in a dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state with an amount of electricity equivalent to the rated capacity. Effect of the Invention

[0009] According to one aspect of the present invention, it is possible to provide a method for using a nonaqueous electrolyte storage element that uses a silicon-based active material, which has low resistance in a low-temperature environment and a high capacity retention rate in charge-discharge cycles when compared with a nonaqueous electrolyte storage element having the same discharge capacity, and an apparatus capable of such use for a nonaqueous electrolyte storage element that uses a silicon-based active material. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing a nonaqueous electrolyte electricity storage element used in one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements used in one embodiment of the present invention. [Diagram 3] FIG. 3 shows the dQ / dV curve obtained when the nonaqueous electrolyte storage element of Reference Example A was discharged from 4.25V to 2.75V. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] First, an outline of a method and device for using the nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0012] (1) A method of using a nonaqueous electrolyte storage element according to one embodiment of the present invention comprises discharging a nonaqueous electrolyte storage element to a lower limit voltage, the nonaqueous electrolyte storage element comprising a negative electrode having a negative electrode active material layer containing metal silicon nanoparticles, the content of the metal silicon nanoparticles in the negative electrode active material layer being 6 mass % or more, and the lower limit voltage being in a range of 0.04 V to 0.20 V lower than a voltage corresponding to a maximum on the lowest voltage side in a dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state with an amount of electricity equivalent to a rated capacity.

[0013] The method of using the nonaqueous electrolyte storage element described in (1) above is a method of using a nonaqueous electrolyte storage element using a silicon-based active material, which has a low resistance in a low-temperature environment and a high capacity retention rate in a charge-discharge cycle when compared with a nonaqueous electrolyte storage element having the same discharge capacity. The reason for this is unclear, but the following reason is presumed. Metal silicon nanoparticles have a small particle size, so that the amount of change in volume due to expansion and contraction during charge and discharge is small compared with those with a large particle size, and cracks are less likely to occur. The use of such metal silicon nanoparticles is considered to be one of the factors that causes the high capacity retention rate in a charge-discharge cycle. In addition, in a nonaqueous electrolyte storage element using metal silicon as the negative electrode active material, if discharge is not performed until a predetermined negative electrode potential is reached, the formation of a crystalline silicide (typically crystalline lithium silicide) that does not substantially contribute to charge and discharge in a state where charge transport ions are absorbed is promoted, and the discharge capacity in a predetermined voltage range is reduced. In contrast, when discharging is performed until a certain negative electrode potential is reached, charge-transporting ions are released from the crystalline silicide and the crystalline silicide changes to amorphous silicon, suppressing the formation of crystalline silicide that does not substantially contribute to charging and discharging. This suppresses changes in the shape of the discharge curve and reduces the decrease in discharge capacity in a certain voltage range. When the charge-transporting ions are lithium ions, the change from crystalline silicide to amorphous silicon usually occurs when the negative electrode potential reaches about 0.45 V (vs. Li / Li +) or more. This change corresponds to the lowest voltage maximum in the dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state with an amount of electricity equivalent to the rated capacity. That is, by discharging the nonaqueous electrolyte storage element to a voltage 0.04V or more lower than the voltage (hereinafter also referred to as the "peak voltage") corresponding to the lowest voltage maximum in the dQ / dV curve, the crystalline silicide is converted to amorphous silicon, and the decrease in the discharge capacity in the charge-discharge cycle is suppressed. On the other hand, when the nonaqueous electrolyte storage element is discharged to a voltage 0.20V or more lower than the peak voltage, even the metal silicon nanoparticles are likely to crack, so that the discharge capacity in the charge-discharge cycle is likely to decrease. In addition, by using metal silicon nanoparticles as the silicon-based active material and setting the content of the metal silicon nanoparticles in the negative electrode active material layer to 6% by mass or more, the negative electrode active material layer can be made thinner when a nonaqueous electrolyte storage element with the same discharge capacity is designed, and the resistance of the nonaqueous electrolyte storage element in a low-temperature environment can be reduced. For these reasons, it is presumed that the method of using the nonaqueous electrolyte storage element described above in (1) is a method of using a nonaqueous electrolyte storage element that uses a silicon-based active material, and that the resistance in a low-temperature environment is lower and the capacity retention rate during charge-discharge cycles is higher when compared with nonaqueous electrolyte storage elements having the same discharge capacity.

[0014] The dQ / dV curve used is obtained under the following conditions: First, the nonaqueous electrolyte storage element is fully charged at 25° C. After a 30-minute pause, a constant current discharge is performed at a discharge current of 0.2 C at 25° C., with an amount of electricity equivalent to the rated capacity of the nonaqueous electrolyte storage element. The capacity (Q) is calculated based on the voltage and current data during this constant current discharge process, and the amount of change (dQ / dV) in the capacity (Q) relative to the voltage (V) is calculated as capacity change data to obtain a dQ / dV curve. Here, the fully charged state refers to a state in which the nonaqueous electrolyte storage element is fully charged using a dedicated charger if one is available for the element, or a state in which the nonaqueous electrolyte storage element is fully charged using a dedicated charger if no dedicated charger is available, and refers to a state in which the nonaqueous electrolyte storage element is charged using a constant current constant voltage (CCCV) charge method with a charging current of 1C and a charging completion time of 3 hours, using an upper limit charging voltage for the nonaqueous electrolyte storage element as the charging voltage. The rated capacity is the capacity used to indicate the capacity of a nonaqueous electrolyte storage element. That is, the rated capacity is the capacity indicated on the nonaqueous electrolyte storage element or its instruction manual, etc. When the capacity is not indicated on the nonaqueous electrolyte storage element or its instruction manual, etc., the rated capacity refers to the discharge capacity when the nonaqueous electrolyte storage element, which has been fully charged by the above-mentioned method, is discharged at a constant current (CC) at a discharge current of 0.2 C to the lower limit voltage of the discharge of the nonaqueous electrolyte storage element.

[0015] (2) In the method for using the nonaqueous electrolyte electricity storage element described above in (1), the metal silicon nanoparticles may form a composite with a carbon material.

[0016] When metal silicon nanoparticles form a composite with a carbon material, advantages are obtained such as improved electronic conductivity and suppressed reaction with the nonaqueous electrolyte, etc. Therefore, the method of using the nonaqueous electrolyte storage element described in (2) above has a lower resistance in a low-temperature environment and a higher capacity retention rate in charge-discharge cycles when compared with nonaqueous electrolyte storage elements having the same discharge capacity.

[0017] (3) A device according to another embodiment of the present invention comprises a nonaqueous electrolyte storage element including a negative electrode having a negative electrode active material layer containing metal silicon nanoparticles, wherein the content of the metal silicon nanoparticles in the negative electrode active material layer is 6 mass % or more, and the lower limit voltage of the nonaqueous electrolyte storage element is set in a range of 0.04 V to 0.20 V lower than the voltage corresponding to the maximum on the lowest voltage side in a dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state with an amount of electricity equivalent to the rated capacity.

[0018] The device described in (3) above has a lower resistance in a low-temperature environment than a nonaqueous electrolyte storage element using a silicon-based active material when compared with a nonaqueous electrolyte storage element having the same discharge capacity, and can be used with a high capacity retention rate during charge-discharge cycles.

[0019] A nonaqueous electrolyte storage element used in a method for using the nonaqueous electrolyte storage element according to one embodiment of the present invention, a manufacturing method thereof, a method for using the nonaqueous electrolyte storage element, a storage device, an apparatus, and other embodiments will be described in detail below. Note that the names of the components (components) used in each embodiment may differ from the names of the components (components) used in the background art.

[0020] <Non-aqueous electrolyte electricity storage element> The nonaqueous electrolyte storage element used in the method of using the nonaqueous electrolyte storage element according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and a separator, a nonaqueous electrolyte, and a container that contains the electrode assembly and the nonaqueous electrolyte. The electrode assembly is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated with a separator interposed therebetween, or a wound type in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween and wound. The nonaqueous electrolyte exists in a state in which it is permeated into the positive electrode, the negative electrode, and the separator. As an example of the nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter, also simply referred to as a "secondary battery") will be described.

[0021] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0022] The positive electrode substrate is conductive. Whether or not it has "conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 -2The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. The positive electrode substrate may be a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferred from the viewpoint of cost. Therefore, aluminum foil or an aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or an aluminum alloy include A1085, A3003, A1N30, etc., as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0023] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, further preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate and to increase the energy density per volume of the nonaqueous electrolyte storage element.

[0024] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0025] The positive electrode active material layer contains a positive electrode active material and, as necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0026] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of absorbing and releasing lithium ions is usually used. As the positive electrode active material, for example, α-NaFeO 2 Lithium transition metal composite oxides having a crystalline structure, lithium transition metal composite oxides having a spinel crystalline structure, polyanion compounds, chalcogen compounds, sulfur, etc. 2As an example of a lithium transition metal composite oxide having a crystalline structure, Li[Li x Ni (1-x) ]O 2 (0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O 2 (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1-x) ]O 2 (0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O 2 (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O 2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O 2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn 2 O 4 , Li x Ni γ Mn (2-γ) O 4 Examples of polyanion compounds include LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 , Li 3 V 2 (PO 4 ) 3 , Li 2 MnSiO 4 , Li 2 CoPO 4Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination.

[0027] The positive electrode active material is preferably a lithium transition metal composite oxide, such as α-NaFeO 2 A lithium transition metal composite oxide having a C-type crystal structure is more preferable. The method of using the nonaqueous electrolyte storage element according to one embodiment of the present invention can be particularly suitably applied to a nonaqueous electrolyte storage element using such a positive electrode active material.

[0028] The positive electrode active material is usually a particle (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material can be easily manufactured or handled. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. In addition, when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "average particle size" means a value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by a laser diffraction / scattering method for a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0029] In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, etc. are used. Examples of the pulverization method include a method using 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 airflow type jet mill, or a sieve. During pulverization, wet pulverization in the presence of water or an organic solvent such as hexane can also be used. As a classification method, a sieve, an air classifier, etc. are used as necessary for both dry and wet methods.

[0030] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the positive electrode active material in the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0031] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbon materials, metals, and conductive ceramics. In this specification, the carbon material is usually a material in which the most abundant element on a mass basis is carbon element, and does not include non-carbonized polymer compounds. Examples of carbon materials include graphite, non-graphitic carbon, graphene carbon, and the like. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene carbon include graphene, carbon nanotube (CNT), and fullerene. Examples of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. In addition, these materials may be used in a composite form. For example, a material in which carbon black and CNT are composited may be used. Among these, carbon black is preferable from the viewpoint of electronic conductivity and coatability, and acetylene black is preferable among them.

[0032] The content of the conductive agent in the positive electrode active material layer is preferably from 1 mass % to 10 mass %, more preferably from 3 mass % to 9 mass %. By setting the content of the conductive agent in the above range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0033] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, polyimide, etc.; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, etc.

[0034] The content of the binder in the positive electrode active material layer is preferably from 1% by mass to 10% by mass, and more preferably from 3% by mass to 9% by mass. By setting the content of the binder in the above range, the positive electrode active material can be stably maintained.

[0035] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0036] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, poorly soluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, and mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0037] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0038] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode.

[0039] The negative electrode substrate has electrical conductivity. Metals such as copper, nickel, stainless steel, and nickel-plated steel, or alloys thereof, and carbon materials are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor deposition films, meshes, and porous materials, and foils are preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0040] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, further preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate and to increase the energy density per volume of the nonaqueous electrolyte storage element.

[0041] The negative electrode active material layer contains metal silicon nanoparticles. The negative electrode active material layer preferably contains a carbon material, and may further contain optional components such as a binder, a thickener, and a filler as necessary. The optional components such as the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode.

[0042] Metal silicon nanoparticles are components that function as negative electrode active materials. Metal silicon is typically silicon alone, and may also be an alloy of silicon element and other metal elements. Metal silicon may, for example, exhibit p-type semiconductor properties including elements such as boron and aluminum, or may exhibit n-type semiconductor properties including elements such as phosphorus and arsenic. Elements other than the above-mentioned elements may be included in small amounts. For example, the content of silicon element in metal silicon nanoparticles in a state in which the nonaqueous electrolyte storage element is discharged to the lower limit voltage is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0043] Metal silicon nanoparticles are nanoparticles made of metal silicon. In the metal silicon nanoparticles, a part or the whole of the surface may be oxidized. Nanoparticles refer to particles having an average primary particle diameter of 1 nm or more and less than 1,000 nm. The average primary particle diameter of the metal silicon nanoparticles is preferably 5 nm or more and 500 nm or less, more preferably 10 nm or more and 300 nm or less, and even more preferably 15 nm or more and 200 nm or less. By having the average primary particle diameter of the metal silicon nanoparticles in the above range, it is possible to lower the resistance in a low-temperature environment and to increase the capacity retention rate in a charge-discharge cycle when compared with a nonaqueous electrolyte storage element having the same discharge capacity.

[0044] The "average primary particle diameter" of metal silicon nanoparticles is the average value of the primary particle diameters of any 100 primary particles constituting the metal silicon nanoparticles observed under a scanning electron microscope (SEM). A primary particle is a particle in which no grain boundaries are observed in appearance when observed under the SEM. The primary particle diameter of a primary particle is determined as follows. The shortest diameter passing through the center of the minimum circumscribing circle of the primary particle is defined as the minor diameter, and the diameter passing through the center and perpendicular to the minor diameter is defined as the major diameter. The average of the major diameter and minor diameter is defined as the primary particle diameter. When there are two or more shortest diameters, the diameter perpendicular to the minor diameter is defined as the minor diameter.

[0045] The lower limit of the content of the metal silicon nanoparticles in the negative electrode active material layer is 6% by mass, preferably 7% by mass, and more preferably 8% by mass. By having the content of the metal silicon nanoparticles in the negative electrode active material layer be equal to or greater than the above lower limit, it is possible to lower the resistance in a low-temperature environment and increase the energy density when compared with a nonaqueous electrolyte storage element having the same discharge capacity. The upper limit of the content of the metal silicon nanoparticles in the negative electrode active material layer may be, for example, 80% by mass, or may be 50% by mass, 40% by mass, 30% by mass, 20% by mass, or 10% by mass. The content of the metal silicon nanoparticles in the negative electrode active material layer may be within a range that combines any of the above lower limits and any of the above upper limits.

[0046] The metal silicon nanoparticles preferably form a composite with a carbon material. The composite of the metal silicon nanoparticles and the carbon material (hereinafter, simply referred to as the "composite") may be a composite in which the primary or secondary particles of the metal nanoparticles are coated with a carbon material, or a composite in which the metal silicon nanoparticles are arranged in the skeleton of a porous carbon material. The shape of the composite is not particularly limited, and may be, for example, particulate. Examples of the carbon material constituting the composite include those exemplified as the carbon material of the conductive agent. The carbon material constituting the composite may function as a negative electrode active material. The composite may be produced by a known method.

[0047] The content of the metal silicon nanoparticles in the composite is preferably 10% by mass to 80% by mass, more preferably 20% by mass to 60% by mass, and even more preferably 30% by mass to 50% by mass. By having the content of the metal silicon nanoparticles in the composite within the above range, the discharge capacity, electrical conductivity, etc. are optimized in a well-balanced manner.

[0048] The composite may further contain components other than the metal silicon nanoparticles and the carbon material, provided that the combined content of the metal silicon nanoparticles and the carbon material in the composite is preferably 90 mass % or more, more preferably 99 mass % or more.

[0049] The content of the composite in the negative electrode active material layer is preferably 10% by mass or more and 80% by mass or less, more preferably 12% by mass or more and 60% by mass or less, even more preferably 14% by mass or more and 40% by mass or less, and even more preferably 16% by mass or more and 30% by mass or less.

[0050] The negative electrode active material layer preferably contains a carbon material that does not form a composite. The carbon material may function as a negative electrode active material or as a conductive agent. The carbon material is preferably graphite or non-graphitic carbon, more preferably graphite. By including such a carbon material in the negative electrode active material layer, it is possible to suppress the expansion and contraction of the metal silicon nanoparticles and further increase the capacity retention rate.

[0051] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of availability of materials with stable physical properties.

[0052] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitizable carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0053] Here, the "discharged state" of the carbon material means a state in which the carbon material, which is a negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material, which is a negative electrode active material. For example, in a half cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode, the open circuit voltage is 0.7 V or more.

[0054] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0055] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0056] The negative electrode active material layer may contain a carbon material that is usually used as a conductive agent, such as carbon black or CNT. CNT is preferable as such a carbon material. The content of CNT in the negative electrode active material layer is preferably 0.01% by mass or more and 1% by mass or less, and more preferably 0.02% by mass or more and 0.5% by mass or less. By containing such a small amount of CNT in the negative electrode active material layer, it is possible to lower the resistance in a low-temperature environment and to increase the capacity retention rate in a charge-discharge cycle, when compared with a nonaqueous electrolyte storage element having the same discharge capacity.

[0057] The content of the carbon material (both the carbon material constituting the composite and the carbon material not constituting the composite) in the negative electrode active material layer is preferably 50% by mass or more and 94% by mass or less, more preferably 70% by mass or more and 93% by mass or less, even more preferably 80% by mass or more and 92% by mass or less, and even more preferably 86% by mass or more and 91% by mass or less.

[0058] The binder content in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 4% by mass. By setting the binder content within the above range, it is possible to stably hold metal silicon nanoparticles, etc.

[0059] The content of the thickener in the negative electrode active material layer is preferably 0.1% by mass to 5% by mass, more preferably 0.5% by mass to 3% by mass. By setting the content of the thickener in the above range, it is possible to improve the coatability when forming the negative electrode active material layer by coating the negative electrode mixture paste.

[0060] The negative electrode active material layer may contain a negative electrode active material other than metal silicon nanoparticles and carbon materials, and a conductive agent other than carbon materials. However, the lower limit of the total content of the metal silicon nanoparticles, carbon materials (both carbon materials constituting a composite and carbon materials not constituting a composite), binder and thickener in the negative electrode active material layer is preferably 95 mass%, and may be 98 mass%, 99 mass% or 99.5 mass%. When the negative electrode active material layer is mainly composed of these components, it is possible to lower the resistance compared with nonaqueous electrolyte storage elements having the same discharge capacity, and to increase the capacity retention rate in charge and discharge cycles.

[0061] The negative electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0062] (Separator) The separator can be appropriately selected from known separators. For example, a separator consisting of only a substrate layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer, etc. can be used as the separator. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, a porous resin film is preferred from the viewpoint of strength, and a nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention. As the material of the substrate layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidation decomposition resistance. A material obtained by combining these resins may be used as the substrate layer of the separator.

[0063] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C under an air atmosphere at 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials with a mass loss of a predetermined amount or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the nonaqueous electrolyte storage element.

[0064] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0065] As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of the polymer gel has the effect of suppressing leakage. As the separator, the above-mentioned porous resin film or nonwoven fabric may be used in combination with the polymer gel.

[0066] (Non-aqueous electrolyte) The nonaqueous electrolyte may be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolyte solution. The nonaqueous electrolyte solution includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0067] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylates, phosphates, sulfonates, ethers, amides, and nitriles. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are substituted with halogens may be used.

[0068] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0069] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferable.

[0070] As the non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. By using a cyclic carbonate, it is possible to promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, it is possible to keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a chain carbonate in combination, it is preferable that the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is, for example, in the range of 5:95 to 50:50.

[0071] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferred.

[0072] The lithium salt is LiPF 6 , LiPO 2 F 2 , LiBF 4 , LiClO 4 , LiN(SO 2 F) 2 inorganic lithium salts such as lithium oxalate (LiBOB), lithium difluorooxalate (LiFOB), lithium bis(oxalate) difluorophosphate (LiFOP), and other lithium oxalates; LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ), LiC(SO 2 CF 3 ) 3 , LiC(SO 2 C 2 F 5 )3 Among these, inorganic lithium salts are preferred, and LiPF 6 is more preferred.

[0073] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 More preferably, it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 More preferably, it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the nonaqueous electrolyte can be increased.

[0074] The nonaqueous electrolyte may contain additives in addition to the nonaqueous solvent and the electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0075] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0076] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

[0077] The solid electrolyte can be selected from any material that has ion conductivity such as lithium, sodium, calcium, etc., and is solid at room temperature (e.g., 15° C. to 25° C.). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes.

[0078] As the sulfide solid electrolyte, in the case of a lithium ion secondary battery, for example, Li 2 SP 2 S 5 , LiI-Li 2 SP 2 S 5 , Li 10 Ge-P 2 S 12 etc.

[0079] The shape of the nonaqueous electrolyte storage element is not particularly limited, and examples thereof include a cylindrical battery, a square battery, a flat battery, a coin battery, and a button battery.

[0080] Fig. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched therebetween is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0081] <Method of Manufacturing Nonaqueous Electrolyte Storage Element> The method for producing the nonaqueous electrolyte storage element can be appropriately selected from known methods. The method for producing the nonaqueous electrolyte storage element can include, for example, preparing an electrode body, preparing a nonaqueous electrolyte, and housing the electrode body and the nonaqueous electrolyte in a container. The preparation of the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0082] Preparing the positive electrode and the negative electrode may mean fabricating the positive electrode and the negative electrode. In preparing the positive electrode and the negative electrode, it is preferable to prepare the positive electrode and the negative electrode so that the discharge capacity of the nonaqueous electrolyte storage element is limited by the negative electrode. In this way, when the negative electrode potential is 0.45V (vs. Li / Li) when the nonaqueous electrolyte storage element is discharged to a predetermined lower limit voltage, the negative electrode potential is 0.45V (vs. Li / Li) when the negative electrode potential is 0.45V (vs. Li / Li) when the nonaqueous electrolyte storage element is discharged to a predetermined lower limit voltage. + ) and thus a nonaqueous electrolyte storage element in which a change from crystalline silicide to amorphous silicon occurs can be effectively obtained. Specifically, for example, by providing a positive electrode active material layer and a negative electrode active material layer such that the initial irreversible capacity ratio (positive electrode / negative electrode) per unit area of ​​the positive electrode and the negative electrode is less than 1.0, a negative electrode-limited nonaqueous electrolyte storage element can be effectively obtained.

[0083] The method of housing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be injected through an injection port formed in the container, and then the injection port may be sealed.

[0084] <Method of using non-aqueous electrolyte storage element> A method of using a nonaqueous electrolyte storage element according to one embodiment of the present invention comprises discharging the nonaqueous electrolyte storage element to a lower limit voltage, the lower limit voltage being in a range of 0.04 V to 0.20 V lower than the voltage (peak voltage) corresponding to the maximum on the lowest voltage side in a dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state with an amount of electricity equivalent to the rated capacity. By discharging the nonaqueous electrolyte storage element to a lower limit voltage in such a range, the resistance in a low-temperature environment is lower compared to nonaqueous electrolyte storage elements having the same discharge capacity, and the capacity retention rate in charge-discharge cycles can be increased.

[0085] For example, the positive electrode active material of the nonaqueous electrolyte storage element according to one embodiment of the present invention is a lithium transition metal composite oxide (preferably, α-NaFeO 2 In the case of a lithium-transition metal composite oxide having a L-type crystal structure, the "fully charged state" of the nonaqueous electrolyte storage element may be a state in which the voltage is 4.25 V, and "when an amount of electricity equivalent to the rated capacity has been discharged" may be when the voltage has been discharged from 4.25 V to 2.75 V.

[0086] For example, in the dQ / dV curve of the nonaqueous electrolyte storage element of Reference Example A shown in Fig. 3, which will be described later, the peak voltage is 3.22 V. In this case, the lower limit voltage is set in the range of 3.02 V (= 3.22 - 0.20 V) to 3.18 V (= 3.22 V - 0.04 V). The lower limit voltage is preferably in the range of 0.05 V to 0.18 V lower than the peak voltage, and more preferably in the range of 0.06 V to 0.16 V lower.

[0087] In the method of using the nonaqueous electrolyte storage element according to one embodiment of the present invention, it is not necessary to discharge to the lower limit voltage in all discharges. That is, charging may be performed without discharging to the lower limit voltage. In other words, the method of use may be performed by discharging the nonaqueous electrolyte storage element to the lower limit voltage at least once. However, in the method of using the nonaqueous electrolyte storage element according to one embodiment of the present invention, it is preferable to repeatedly discharge the nonaqueous electrolyte storage element to the lower limit voltage and charge the nonaqueous electrolyte storage element discharged to the lower limit voltage. By using the nonaqueous electrolyte storage element in this way, the effect of a high capacity retention rate in a charge / discharge cycle is particularly well achieved.

[0088] The method of using the nonaqueous electrolyte storage element according to one embodiment of the present invention may further include discharging the nonaqueous electrolyte storage element to a lower limit voltage when the lower limit voltage has not been reached before the nonaqueous electrolyte storage element is charged. This additional discharge can be performed, for example, by switching to an additional discharge mode for an apparatus including the nonaqueous electrolyte storage element when the nonaqueous electrolyte storage element is not normally used (for example, at night), and using the nonaqueous electrolyte storage element as such an apparatus, or by discharging the nonaqueous electrolyte storage element before charging when the nonaqueous electrolyte storage element has not reached the lower limit voltage when attempting to charge the nonaqueous electrolyte storage element using a charger. The method of use may also include charging the additionally discharged electricity to another nonaqueous electrolyte storage element. In this case, the other nonaqueous electrolyte storage element for charging the additionally discharged electricity may be provided, for example, in a charger, or may be provided in the same apparatus as the nonaqueous electrolyte storage element that performs the additional discharge.

[0089] On the other hand, the method of using the nonaqueous electrolyte storage element according to one embodiment of the present invention may further include discharging to a voltage below the lower limit voltage. For example, the nonaqueous electrolyte storage element may be discharged to a voltage below the lower limit voltage during maintenance, emergency, etc. During maintenance, the nonaqueous electrolyte storage element is discharged to a voltage below the lower limit voltage, so that crystalline lithium silicide formed to some extent on the negative electrode is converted to amorphous silicon, and the discharge capacity tends to recover. In addition, for example, in an electric vehicle (EV), the nonaqueous electrolyte storage element may be discharged to a voltage below the lower limit voltage for emergency use, such as when the nonaqueous electrolyte storage element reaches the lower limit voltage during operation.

[0090] That is, a lower limit voltage in the range of 0.04 V to 0.20 V lower than the peak voltage may be set as the first lower limit voltage corresponding to normal use, and a lower limit voltage lower than the first lower limit voltage may be set as the second lower limit voltage corresponding to maintenance, emergency, etc. The second lower limit voltage may be, for example, in the range of more than 0.20 V to 0.50 V lower than the peak voltage, or may be in the range of more than 0.20 V to 0.47 V lower.

[0091] The method of using the nonaqueous electrolyte storage element according to one embodiment of the present invention can be applied to nonaqueous electrolyte storage elements for various conventional applications. Among the various applications, the method is particularly suitable for applications in which the repeated discharging of the nonaqueous electrolyte storage element to a predetermined lower limit voltage can be relatively controlled, such as electric vehicles (EVs), plug-in hybrid vehicles (PHEVs), and power storage sources.

[0092] <Electricity storage device> The nonaqueous electrolyte storage element can be mounted as an electricity storage unit (battery module) comprising a plurality of nonaqueous electrolyte storage elements assembled together in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte storage element included in the electricity storage unit. In other words, the method of using the nonaqueous electrolyte storage element of the present invention can also be applied to such an electricity storage unit.

[0093] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, a bus bar (not shown) that electrically connects two or more electricity storage units 20, and the like. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements.

[0094] <Equipment> An apparatus including a nonaqueous electrolyte storage element or a storage device including a plurality of nonaqueous electrolyte storage elements is also included in one aspect of the present invention. Specifically, an apparatus according to one embodiment of the present invention includes a nonaqueous electrolyte storage element including a negative electrode having a negative electrode active material layer including metal silicon nanoparticles, and the content of the metal silicon nanoparticles in the negative electrode active material layer is 6% by mass or more, and the lower limit voltage of the nonaqueous electrolyte storage element is set in a range of 0.04 V to 0.20 V lower than the voltage corresponding to the lowest voltage maximum in the dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state to an amount of electricity equivalent to the rated capacity. The apparatus according to one embodiment of the present invention has a low resistance in a low temperature environment compared to a nonaqueous electrolyte storage element using a silicon-based active material, and can be used with a high capacity retention rate in a charge / discharge cycle. The apparatus includes, but is not limited to, electronic devices such as personal computers and communication terminals, home appliances, automobiles (EV, HEV, PHEV, etc.), power storage devices, and other industrial equipment.

[0095] In this device, the lower limit voltage of the nonaqueous electrolyte storage element is set to a range of 0.04 V to 0.20 V lower than the peak voltage. In such a device, the method for using a nonaqueous electrolyte storage element according to one embodiment of the present invention is applied by discharging the nonaqueous electrolyte storage element to the lower limit voltage. Specific and preferred aspects of the nonaqueous electrolyte storage element provided in this device are the same as the specific and preferred aspects of the nonaqueous electrolyte storage element used in the method for using a nonaqueous electrolyte storage element according to one embodiment of the present invention described above.

[0096] The device including the nonaqueous electrolyte storage element or the storage device including a plurality of nonaqueous electrolyte storage elements may be set with the first lower limit voltage corresponding to normal use and the second lower limit voltage corresponding to emergency situations, etc. In this case, for example, the lower limit voltage may be set to the first lower limit voltage in normal conditions, and may be able to be switched to the second lower limit voltage as necessary. The device is preferably equipped with a control device that controls the lower limit voltage and charging / discharging, etc. The device may further include the above-mentioned additional discharge function, another nonaqueous electrolyte storage element for charging the additionally discharged electricity, etc.

[0097] <Other embodiments> The method of using the nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0098] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0099] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode. EXAMPLES

[0100] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0101] [Reference example A] (Preparation of positive electrode) As a positive electrode active material, α-NaFeO 2 Lithium transition metal composite oxide with LiNi type crystal structure 1 / 2 Mn 3 / 10 Co 1 / 5 O 2 was prepared. A positive electrode mixture paste was prepared by mixing the positive electrode active material, acetylene black, and PVDF in a mass ratio of 93.0:3.5:3.5 in terms of solid content, and containing N-methylpyrrolidone (NMP) as a dispersion medium. The positive electrode mixture paste was applied to one side of an aluminum foil as a positive electrode substrate, and pressed after drying to prepare a positive electrode having a positive electrode active material layer disposed on one side of the positive electrode substrate.

[0102] (Preparation of negative electrode) A composite of metal silicon nanoparticles and a carbon material was prepared. The metal silicon nanoparticles were particles of elemental silicon (Si) with an average primary particle diameter of 98 nm. The composite was an agglomerate of metal silicon nanoparticles coated with a carbon material. The content of metal silicon nanoparticles in the composite was 41.7 mass%. The composite, graphite, CNT, SBR and CMC were contained in a mass ratio of 20.0:76.9:0.1:2.0:1.0 in terms of solid content, and a negative electrode mixture paste containing water as a dispersion medium was prepared. The negative electrode mixture paste was applied to one side of a copper foil as a negative electrode substrate, and pressed after drying to prepare a negative electrode in which a negative electrode active material layer was disposed on one side of the negative electrode substrate. The content of metal silicon nanoparticles in the obtained negative electrode active material layer was 8.3% by mass. The coating amounts of the positive electrode mixture paste and the negative electrode mixture paste were adjusted so that the initial irreversible capacity ratio per unit area of ​​the positive electrode and the negative electrode (positive electrode / negative electrode) was 0.61.

[0103] (Preparation of non-aqueous electrolyte) LiPF was added to a mixed solvent of EC, EMC, and DMC in a volume ratio of 30:35:35. 6 to 1.0 mol / dm 3 to give a non-aqueous electrolyte.

[0104] (Assembly of non-aqueous electrolyte storage element) The positive electrode and the negative electrode were laminated with a polyolefin microporous membrane as a separator therebetween to prepare an electrode assembly, which was then housed in a container made of a metal resin composite film, and the nonaqueous electrolyte was poured into the container, which was then sealed by heat welding.

[0105] (Initial charge / discharge) Next, three cycles of initial charge and discharge were performed at 25°C in the following manner. In the first cycle, constant current and constant voltage charging was performed with a charging current of 0.2C, a charging end voltage of 4.25V, and a charging end time of 7 hours, followed by a rest period of 10 minutes. Then, constant current discharging was performed with a discharging current of 0.2C and a discharging end voltage of 2.75V, followed by a rest period of 10 minutes. In the second and third cycles, constant current and constant voltage charging was performed with a charging current of 1C, a charging end voltage of 4.25V, and a charging end time of 3 hours, followed by a rest period of 10 minutes. Then, constant current discharging was performed with a discharging current of 1C and a discharging end voltage of 2.75V, followed by a rest period of 10 minutes. Through the above operations, a nonaqueous electrolyte storage element of Reference Example A was obtained.

[0106] The nonaqueous electrolyte storage element of Reference Example A was charged at a constant current and constant voltage with a charging current of 1C, a charge cut-off voltage of 4.25V, and a charging time of 3 hours, until it was fully charged. After a 10-minute pause, it was discharged at a constant current of 0.2C to 2.75V, and a dQ / dV curve was obtained. It can be considered that the amount of electricity equivalent to the rated capacity of the nonaqueous electrolyte storage element of Reference Example A was discharged by this constant current discharge. The obtained dQ / dV curve is shown in FIG. 3. The lowest voltage maximum in the dQ / dV curve appeared at 3.22V. That is, the peak voltage (V1) was 3.22V.

[0107] [Reference example B] In the preparation of the negative electrode mixture paste, the mass ratio of the composite, graphite, CNT, SBR and CMC in terms of solid content was 10.0:86.9:0.1:2.0:1.0, and the initial irreversible capacity ratio (positive electrode / negative electrode) was 0.69 and the discharge capacity was the same as that of the nonaqueous electrolyte storage element of Reference Example A, except that the coating amount of the positive electrode mixture paste and the negative electrode mixture paste was adjusted. The content of the metal silicon nanoparticles in the negative electrode active material layer of this nonaqueous electrolyte storage element was 4.2 mass%. In addition, the peak voltage (V1) of this nonaqueous electrolyte storage element was 3.20V.

[0108] [Reference example C] The nonaqueous electrolyte storage element of Reference Example C was obtained in the same manner as Reference Example A, except that silicon oxide (SiO) was used instead of the composite of metal silicon nanoparticles and a carbon material, the mass ratio of silicon oxide, graphite, CNT, SBR and CMC in terms of solid content was set to 20.0:76.9:0.1:2.0:1.0 in the preparation of the negative electrode mixture paste, the initial irreversible capacity ratio (positive electrode / negative electrode) was 0.67, and the coating amount of the positive electrode mixture paste and the negative electrode mixture paste was adjusted so that the discharge capacity was the same as that of the nonaqueous electrolyte storage element of Reference Example A. The silicon oxide was obtained by doping lithium ions into silicon oxide having an average particle size of 5 μm and coating it with a carbon material. The peak voltage (V1) of this nonaqueous electrolyte storage element was 3.23 V.

[0109] [Reference example D] In the preparation of the negative electrode mixture paste, the mass ratio of silicon oxide, graphite, CNT, SBR and CMC in terms of solid content was set to 10.0:86.9:0.1:2.0:1.0, and the coating amounts of the positive electrode mixture paste and the negative electrode mixture paste were adjusted so that the initial irreversible capacity ratio (positive electrode / negative electrode) was 0.76 and the discharge capacity was the same as that of the nonaqueous electrolyte storage element of Reference Example A. A nonaqueous electrolyte storage element of Reference Example D was obtained in the same manner as in Reference Example C. The peak voltage (V1) of this nonaqueous electrolyte storage element was 3.17V.

[0110] (Measurement of DC resistance in a low temperature environment) Next, for each nonaqueous electrolyte storage element, a voltage equivalent to a 50% state of charge (SOC) was set as the charge end voltage in a thermostatic layer at 25°C, and constant current constant voltage charging was performed with a charging current of 1C and a charge end current of 0.01C. In this way, the SOC was adjusted to 50%. After that, the nonaqueous electrolyte storage element was stored in a thermostatic chamber at -10°C for 3 hours, and then discharged at a constant current of 0.1C, 0.2C, or 0.3C for 30 seconds. After each discharge, constant current charging was performed at a current of 0.05C to adjust the SOC to 50%. The relationship between the current and the voltage 1 second after the start of discharge in each discharge was plotted, and the direct current resistance (DCR) in a low temperature environment was calculated from the slope of the straight line obtained from the plot of the three points. The calculated direct current resistance (DCR) is shown in Table 1.

[0111] [Table 1]

[0112] As shown in Table 1, the nonaqueous electrolyte storage elements of Reference Examples C and D, in which silicon oxide (SiO) was used as the silicon-based active material, had high direct current resistance (DCR) in a low-temperature environment. In addition, when metal silicon nanoparticles (Si) were used as the silicon-based active material, the nonaqueous electrolyte storage element of Reference Example B, in which the content of metal silicon nanoparticles (Si) in the negative electrode active material layer was less than 6 mass%, had high direct current resistance (DCR) in a low-temperature environment. In contrast, the nonaqueous electrolyte storage element of Reference Example A, in which the content of metal silicon nanoparticles (Si) in the negative electrode active material layer was 6 mass% or more, had low direct current resistance (DCR) in a low-temperature environment.

[0113] [Test example] Five nonaqueous electrolyte storage elements were assembled with the same recipe and procedure as in Reference Example A, and five nonaqueous electrolyte storage elements A1 to A5 were obtained by performing initial charging and discharging under the same conditions as above. Five nonaqueous electrolyte storage elements were assembled with the same recipe and procedure as in Reference Example B, and five nonaqueous electrolyte storage elements B1 to B5 were obtained by performing initial charging and discharging under the same conditions as above. Five nonaqueous electrolyte storage elements were assembled with the same recipe and procedure as in Reference Example C, and five nonaqueous electrolyte storage elements C1 to C5 were obtained by performing initial charging and discharging under the same conditions as above. Five nonaqueous electrolyte storage elements were assembled with the same recipe and procedure as in Reference Example D, and five nonaqueous electrolyte storage elements D1 to D5 were obtained by performing initial charging and discharging under the same conditions as above.

[0114] (Measurement of capacity retention rate during charge / discharge cycles) Next, a charge-discharge cycle test was performed on each nonaqueous electrolyte storage element in the following manner. In a thermostatic chamber at 25°C, constant current and constant voltage charging was performed with a charging current of 1.0C, a charge cut-off voltage of 4.25V, and a charge end time of 3 hours, followed by a rest period of 10 minutes. Then, constant current discharging was performed with a discharge current of 0.2C and a discharge cut-off voltage of the lower limit voltage (V2) shown in Table 2, followed by a rest period of 10 minutes. This charge-discharge cycle was repeated 700 times. The percentage of the discharge capacity at the 700th cycle to the discharge capacity at the 1st cycle in this charge-discharge cycle test was calculated as the capacity retention rate in the charge-discharge cycle. The difference (V1-V2) between the peak voltage (V1) and the lower limit voltage (V2) and the calculated capacity retention rate are shown in Table 2.

[0115] [Table 2]

[0116] As shown in Table 2, among test examples A1 to A5 in which the content of metal silicon nanoparticles (Si) in the negative electrode active material layer was 6 mass% or more, the nonaqueous electrolyte storage elements of test examples A2 and A3 in which the lower limit voltage (V2) was set in a range of 0.04 V or more and 0.20 V or less lower than the peak voltage (V1) had high capacity retention during charge-discharge cycles. [Industrial Applicability]

[0117] The present invention is applicable to electronic devices such as personal computers and communication terminals, and methods of using nonaqueous electrolyte storage elements mounted in automobiles and the like. [Explanation of symbols]

[0118] 1. Non-aqueous electrolyte storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy Storage Unit 30 Energy storage device

Claims

1. Discharging the nonaqueous electrolyte storage element to a lower limit voltage; the nonaqueous electrolyte storage element comprises a negative electrode having a negative electrode active material layer containing metal silicon nanoparticles; The content of the metal silicon nanoparticles in the negative electrode active material layer is 6% by mass or more, a lower limit voltage in the range of 0.04 V to 0.20 V lower than a voltage corresponding to a maximum on the lowest voltage side in a dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state by an amount of electricity equivalent to a rated capacity.

2. 2. The method for using the nonaqueous electrolyte electricity storage element according to claim 1, wherein the metal silicon nanoparticles form a composite with a carbon material.

3. A non-aqueous electrolyte electricity storage element is provided, the non-aqueous electrolyte storage element comprising a negative electrode having a negative electrode active material layer containing metal silicon nanoparticles; The content of the metal silicon nanoparticles in the negative electrode active material layer is 6% by mass or more, The lower limit voltage of the nonaqueous electrolyte storage element is set to a range of 0.04 V to 0.20 V lower than the voltage corresponding to the maximum on the lowest voltage side in a dQ / dV curve obtained when the nonaqueous electrolyte storage element is discharged from a fully charged state by an amount of electricity equivalent to a rated capacity.

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