Non-aqueous electrolyte solution storage element and manufacturing method of them

Abstract

To provide a non-aqueous electrolyte power storage element having a small amount of non-aqueous electrolyte and excellent output performance after charge and discharge cycles, and provide a manufacturing method for such a non-aqueous electrolyte power storage element.SOLUTION: A non-aqueous electrolyte power storage element according to one aspect of the present invention, includes: an electrode body having a positive electrode, a negative electrode, and a separator; a non-aqueous electrolyte solution; and a container containing the electrode body and the non-aqueous electrolyte solution, in which the negative electrode includes a solid graphite and satisfies the following formula (1): A=(Vp+Vn+Vs)X...(1) (In the formula (1), A is the amount of the non-aqueous electrolyte in the container (cm3). Vp is the total void volume of the positive electrode (cm3). Vn is the total void volume of the negative electrode (cm3). Vs is the total void volume (cm3) of the separator. X is the number greater than or equal to 1.15 or more and less than 1.25.)SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte storage element and a method for manufacturing the same.

Background Art

[0002] Non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, and automobiles because of their high energy density. A non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring charge-transporting ions between both electrodes. In addition, 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 popular.

[0003] As a non-aqueous electrolyte storage element, one including an electrode body in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are stacked via a separator is common. Such an electrode body is housed in a container together with a non-aqueous electrolyte to constitute a non-aqueous electrolyte storage element. As the negative electrode active material, carbon materials such as graphite are widely used (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] From the viewpoints of weight reduction of the non-aqueous electrolyte storage element and reduction of raw material costs, etc., it is preferable that the non-aqueous electrolyte accommodated in the container is as little as possible. However, when the amount of the non-aqueous electrolyte is small, sufficient charge and discharge performance cannot be exhibited, and particularly, a decrease in output accompanying charge and discharge cycles is likely to occur.

[0006] An object of the present invention is to provide a non-aqueous electrolyte storage element in which the amount of the non-aqueous electrolyte is small and the output performance after charge and discharge cycles is excellent, and a method for manufacturing such a non-aqueous electrolyte storage element.

Means for Solving the Problems

[0007] The non-aqueous electrolyte storage element according to one aspect of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that houses the electrode body and the non-aqueous electrolyte. The negative electrode contains solid graphite and satisfies the following formula (1). A = (Vp + Vn + Vs)X ···(1) (In formula (1), A is the amount (cm 3 ) of the non-aqueous electrolyte in the container. Vp is the total void volume (cm 3 ) of the positive electrode. Vn is the total void volume (cm 3 ) of the negative electrode. Vs is the total void volume (cm 3 ) of the separator. X is a number of 1.15 or more and less than 1.25.)

[0008] The method for manufacturing a non-aqueous electrolyte storage element according to another aspect of the present invention includes housing an electrode body having a positive electrode, a negative electrode, and a separator and a non-aqueous electrolyte in a container. The negative electrode contains solid graphite and satisfies the following formula (2). A’ = (Vp’·Ep + Vn’·En + Vs)X ···(2) (In formula (2), A’ is the amount (cm 3 ) of the non-aqueous electrolyte to be housed in the container. Vp’ is the total void volume (cm 3 ) of the positive electrode before charge and discharge, and Ep is the expansion rate of the positive electrode after charge and discharge. Vn’ is the total void volume (cm 3) and En is the expansion rate of the negative electrode after charge and discharge. Vs is the total void volume of the separator (cm 3 )). X is a number between 1.15 and 1.25 inclusive. )

Advantages of the Invention

[0009] According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte storage element with a small amount of non-aqueous electrolyte and excellent output performance after charge and discharge cycles, and a method for manufacturing such a non-aqueous electrolyte storage element.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0011] First, an overview of the non-aqueous electrolyte storage element disclosed by this specification will be described.

[0012] [1] A non-aqueous electrolyte storage element according to one aspect of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that houses the electrode body and the non-aqueous electrolyte. The negative electrode contains solid graphite and satisfies the following formula (1). A = (Vp + Vn + Vs)X ···(1) (In formula (1), A is the amount of the non-aqueous electrolyte in the container (cm 3 ). Vp is the total void volume of the positive electrode (cm3 ) is. Vn is the total void volume of the negative electrode (cm 3 ) is. Vs is the total void volume of the separator (cm 3 ) is. X is a number greater than or equal to 1.15 and less than 1.25.)

[0013] In the non-aqueous electrolyte storage element described in the above [1], the amount of the non-aqueous electrolyte is small and the output performance after charge and discharge cycles is also excellent. The reason for this is not clear, but the following reasons are presumed. In the non-aqueous electrolyte storage element described in the above [1], X in the above formula (1), that is, the ratio of the amount of the non-aqueous electrolyte to the total void volume of the positive electrode, the negative electrode, and the separator (A / (Vp+Vn+Vs)) is less than 1.25, and the amount of the non-aqueous electrolyte is small. Further, ordinary graphite used as the negative electrode active material usually has voids inside and has a large expansion and contraction accompanying charge and discharge. In a non-aqueous electrolyte storage element using such ordinary graphite, during charging, the separator is compressed with a large displacement due to the expansion of the negative electrode active material, and a large amount of the non-aqueous electrolyte impregnated in the voids of the separator is released outside the separator. For this reason, when the amount of the non-aqueous electrolyte is reduced in a non-aqueous electrolyte storage element using ordinary graphite, the non-aqueous electrolyte in the voids of the separator is likely to be depleted with repeated charge and discharge, and the output performance deteriorates. On the other hand, dense graphite has a small expansion and contraction accompanying charge and discharge. Therefore, in a non-aqueous electrolyte storage element using dense graphite, the separator is not compressed so much even during charging, and the amount of the non-aqueous electrolyte released from the voids of the separator is small. For this reason, when the amount of the non-aqueous electrolyte is reduced in a non-aqueous electrolyte storage element using dense graphite, the non-aqueous electrolyte in the voids of the separator is difficult to be depleted even with repeated charge and discharge, and the deterioration of the output performance is suppressed. For such reasons, in the non-aqueous electrolyte storage element described in the above [1], it is presumed that the effect that the amount of the non-aqueous electrolyte is small and the output performance after charge and discharge cycles is also excellent is exhibited.

[0014] "Solid" in the solid graphite means that the interior of the graphite particles is filled and there are substantially no voids. More specifically, "solid" means that in the cross-section of the particles observed in the SEM image obtained using a scanning electron microscope (SEM), the area ratio (void ratio) of the voids inside the particles to the total area of the particles is 2% or less. The "area ratio (void ratio) of the voids inside the particles to the total area of the particles" in the graphite particles is determined by the following procedure. (1) Preparation of the measurement sample Fix the negative electrode to be measured with a thermosetting resin. For the negative electrode fixed with the resin, expose the cross-section by the ion milling method to prepare a measurement sample. The negative electrode to be measured is prepared by the following procedure. If the negative electrode before assembling the non-aqueous electrolyte storage element can be prepared, it is used as it is. When preparing from the assembled non-aqueous electrolyte storage element, first discharge the non-aqueous electrolyte storage element at a constant current of 0.1C to the discharge cut-off voltage during normal use to make it in a discharged state. Disassemble the discharged non-aqueous electrolyte storage element, take out the negative electrode, thoroughly wash the components attached to the negative electrode with dimethyl carbonate (DMC), and then perform vacuum drying at room temperature for 24 hours. The operations from disassembling the non-aqueous electrolyte storage element to preparing the negative electrode to be measured are carried out in a dry air atmosphere with a dew point of -40°C or lower. Here, "during normal use" means the case where the non-aqueous electrolyte storage element is used by adopting the charge and discharge conditions recommended or specified for the non-aqueous electrolyte storage element, and when a charger for the non-aqueous electrolyte storage element is prepared, it means the case where the non-aqueous electrolyte storage element is used by applying the charger. (2) Acquisition of the SEM image For the acquisition of the SEM image, JSM-7001F (manufactured by JEOL Ltd.) is used as the SEM. The SEM image shall observe the secondary electron image. The acceleration voltage is set to 5 kV. The observation magnification is set to a magnification at which 3 or more and 15 or fewer graphite particles appear in one field of view. The obtained SEM image is saved as an image file. In addition, various conditions such as the spot diameter, working distance, irradiation current, brightness, and focus are appropriately set so that the contour of the graphite particles is clear. (3) Cutting out the contour of the graphite particles Using the image clipping function of the image editing software Adobe Photoshop Elements 11, clip the outline of the graphite particles from the acquired SEM image. This clipping of the outline is performed by selecting the outside of the outline of the graphite particles using the Quick Selection tool and editing the area outside the graphite particles to a black background. At this time, if the number of graphite particles for which the outline could be clipped is less than 3, acquire the SEM image again and repeat the process until the number of graphite particles for which the outline could be clipped is 3 or more. (4) Binarization processing For the image of the first graphite particle among the clipped graphite particles, using the image analysis software PopImaging 6.00, set the density that is 20% lower than the density at which the intensity is maximum as the threshold value and perform binarization processing. By calculating the area on the higher density side through the binarization processing, the "area S1 of the voids inside the particle" is obtained. Next, for the image of the same first graphite particle as before, perform binarization processing with a density of 10% as the threshold value. By determining the outer edge of the graphite particle through the binarization processing and calculating the area inside the outer edge, the "total area S0 of the particle" is obtained. Using the calculated S1 and S0, calculate the ratio of S1 to S0 (S1 / S0) to calculate the "area ratio R1 of the voids inside the particle to the total area of the particle" for the first graphite particle. For the images of the second and subsequent graphite particles among the clipped graphite particles, perform the above binarization processing respectively to calculate the area S1 and the area S0. Based on the calculated area S1 and area S0, calculate the area ratios R2, R3,... of the voids of the respective graphite particles. (5) Determination of the area ratio of voids By calculating the average value of all the area ratios R1, R2, R3,... of the voids calculated through the binarization processing, the "area ratio (void ratio) of the voids inside the particle to the total area of the particle" is determined. Note that instead of the scanning electron microscope used for the above "acquisition of SEM image", the image editing software used for the "clipping of the outline of the graphite particles", and the image analysis software used for the "binarization processing", devices and software capable of equivalent measurement, image editing, and image analysis may be used.

[0015] "Graphite" refers to a carbon material with an average lattice plane spacing (d 002 ) of the (002) plane determined by X-ray diffraction method of 0.33 nm or more and less than 0.34 nm before charge-discharge or in a discharged state. Here, the "discharged state" of the carbon material means a state in which lithium ions that can be occluded and released with charge-discharge are sufficiently released from the carbon material serving as the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the working electrode and metallic Li as the counter electrode, it is a state where the open circuit voltage is 0.7 V or more.

[0016] The amount (A) of the non-aqueous electrolyte in the container and the total void volumes (Vp, Vn, and Vs) of the positive electrode, negative electrode, and separator are values obtained by the following methods.

[0017] (Amount of non-aqueous electrolyte in the container) Measure the mass W1 of the non-aqueous electrolyte storage element. Disassemble the non-aqueous electrolyte storage element, wash each component member with DMC, and then dry it. Measure the mass W2 of all the component members after drying. Here, all the component members refer to all the members other than the non-aqueous electrolyte that constitute the non-aqueous electrolyte storage element. Let the difference (W1 - W2) between the mass W1 of the non-aqueous electrolyte storage element and the mass W2 of all the component members after drying be the mass W3 of the non-aqueous electrolyte in the container. Calculate the amount (volume) of the non-aqueous electrolyte in the container from the mass W3 of the non-aqueous electrolyte in the container and the density of the non-aqueous electrolyte. The density of the non-aqueous electrolyte shall be the value at 20°C.

[0018] (Total void volume of the positive electrode) The positive electrode to be measured is prepared by the following procedure. Discharge the non-aqueous electrolyte storage element at a constant current of 0.1 C to the discharge cut-off voltage during normal use, and set it to the discharged state. Disassemble the non-aqueous electrolyte storage element in this discharged state, take out the positive electrode, wash it with DMC, and then dry it. The total void volume of the positive electrode is the sum of the total void volumes of the respective members constituting the positive electrode. For example, when the positive electrode consists of a non-porous substrate, i.e., a substrate having no voids, and a positive electrode active material layer, the total void volume of the positive electrode is equal to the total void volume of the positive electrode active material layer. The total void volume of the positive electrode active material layer is determined from the difference (V1 - V2) between the apparent volume (volume including voids) V1 of the positive electrode active material layer and the sum V2 of the solid volumes of the respective materials constituting the positive electrode active material layer. The apparent volume of the positive electrode active material layer is calculated from the length, average thickness, and width of the positive electrode active material layer. The average thickness is taken as the average of the measured values at any five locations (the same applies to the average thickness hereinafter). The sum V2 of the solid volumes of the respective materials constituting the positive electrode active material layer is calculated from the content of the respective materials constituting the positive electrode active material layer and the true density of each material.

[0019] (Total void volume of the negative electrode) The total void volume of the negative electrode is determined in the same manner as the total void volume of the positive electrode.

[0020] (Total void volume of the separator) The non-aqueous electrolyte storage element is disassembled, and the removed separator is washed with DMC and then dried. The length, average thickness, and width of the dried separator are measured, and the apparent volume (volume including voids) of the separator is calculated. Further, the porosity of the dried separator on a volume basis is measured by the mercury intrusion method. Here, among the pore distributions obtained by the mercury intrusion method, the range of pore diameters from 0.01 μm to 2 μm is extracted as the pore distribution of the separator, and the porosity of the separator is calculated. The total void volume of the separator is calculated as the product of the apparent volume of the separator and the porosity. Note that the porosity of the separator is the ratio of the voids (pores) to the apparent volume and may also be referred to as the void fraction of the separator.

[0021] In addition, a nonaqueous electrolyte storage element is usually completed through initial charging and discharging after assembly. In addition, the positive electrode and the negative electrode expand due to the initial charging and discharging. Therefore, the total pore volume of each of the positive electrode and the negative electrode that have not been charged and discharged is usually different from the total pore volume of each of the positive electrode and the negative electrode that have been initially charged and discharged in the nonaqueous electrolyte storage element. The total pore volume of each of the positive electrode and the negative electrode of the nonaqueous electrolyte storage element according to one aspect of the present invention is the total pore volume of each of the positive electrode and the negative electrode that have been initially charged and discharged. On the other hand, the total pore volume of the separator is usually the same value before and after charging and discharging.

[0022] [2] In the nonaqueous electrolyte storage element according to the above item [1], the container may be constrained to have a constant, predetermined dimension.

[0023] When the container is constrained, the charge / discharge performance tends to be improved due to the increased adhesion between the particles (active material particles, conductive agent, etc.) constituting the positive electrode and the negative electrode or between the active material layer and the substrate. On the other hand, when the container is generally constrained, the separator is likely to be compressed due to the expansion of the negative electrode active material, and the nonaqueous electrolyte in the voids of the separator is likely to be depleted with repeated charging and discharging, and the output performance is likely to decrease. Therefore, in the case of the nonaqueous electrolyte storage element described in [2] above, in which one aspect of the present invention is applied to a nonaqueous electrolyte storage element in which the container is constrained to be constant at a predetermined dimension, the effect of using a small amount of nonaqueous electrolyte and having excellent output performance after charge / discharge cycles is particularly remarkable.

[0024] [3] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes housing an electrode assembly having a positive electrode, a negative electrode, and a separator, and a nonaqueous electrolyte in a container, wherein the negative electrode contains solid graphite and satisfies the following formula (2): A'=(Vp'·Ep+Vn'·En+Vs)X ···(2) (In formula (2), A' is the amount (cm) of the nonaqueous electrolyte contained in the container. 3 ) Vp' is the total void volume (cm) of the positive electrode before charging and discharging. 3 ), Ep is the expansion rate of the positive electrode after charging and discharging, Vn' is the total void volume (cm) of the negative electrode before charging and discharging 3) and En is the expansion rate of the negative electrode after charge and discharge. Vs is the total void volume of the separator (cm 3 ). X is a number greater than or equal to 1.15 and less than or equal to 1.25.)

[0025] According to the method for manufacturing a non-aqueous electrolyte storage element described in [3] above, it is possible to manufacture a non-aqueous electrolyte storage element with a small amount of non-aqueous electrolyte and excellent output performance after charge and discharge cycles.

[0026] The total void volume (Vp') of the positive electrode before charge and discharge, the total void volume (Vn') of the negative electrode before charge and discharge, and the total void volume (Vs) of the separator are determined by the above-described method for the positive electrode, negative electrode, and separator that have not been charged and discharged and that constitute the electrode body before formation. The total void volume (Vs) of the separator does not usually change before and after charge and discharge as described above. Also, the expansion rate (Ep) of the positive electrode after charge and discharge and the expansion rate (En) of the negative electrode after charge and discharge are values determined by the types of the positive electrode active material and the negative electrode active material, charge and discharge conditions, etc., and are obtained from the apparent volumes of the positive electrode and the negative electrode before and after charge and discharge, respectively. The apparent volume of the positive electrode is calculated from the length, average thickness, and width of the positive electrode. The apparent volume of the negative electrode is calculated from the length, average thickness, and width of the negative electrode.

[0027] A non-aqueous electrolyte storage element, a power storage device, a method for manufacturing a non-aqueous electrolyte storage element, and other embodiments according to an embodiment of the present invention will be described in detail. Note that the names of the respective constituent members (each constituent element) used in each embodiment may be different from the names of the respective constituent members (each constituent element) used in the background art.

[0028] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte energy storage device according to an embodiment of the present invention (hereinafter, also simply referred to as an "energy storage device") includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, or a wound type in which a positive electrode and a negative electrode are wound in a state of being laminated via a separator. The non-aqueous electrolyte exists in a state contained in the positive electrode, the negative electrode, and the separator. As an example of the non-aqueous electrolyte energy storage device, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as a "secondary battery") will be described.

[0029] An embodiment of the present invention may be a non-aqueous electrolyte energy storage device including a wound type electrode body. In a general conventional wound type electrode body, the non-aqueous electrolyte can penetrate into the electrode body only from the end face in the winding axis direction. Therefore, when the amount of the non-aqueous electrolyte is reduced in a non-aqueous electrolyte energy storage device including a conventional wound type electrode body, the depletion of the non-aqueous electrolyte in the electrode body tends to occur particularly easily with repeated charge and discharge. Therefore, when an embodiment of the present invention is applied to a non-aqueous electrolyte energy storage device including a wound type electrode body, the effect that the amount of the non-aqueous electrolyte is small and the output performance after charge and discharge cycles is excellent can be obtained particularly remarkably.

[0030] (Positive Electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate.

[0031] The positive electrode substrate has conductivity. Whether it has "conductivity" or not is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975) being 10 -2It is determined with Ω·cm as the threshold value. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferable from the viewpoint of cost. Therefore, an aluminum foil or an aluminum alloy foil is preferable as the positive electrode substrate. Examples of the aluminum or aluminum alloy include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0032] The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. 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 while increasing the energy density per volume of the non-aqueous electrolyte storage element.

[0033] 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. For example, it contains a binder and a conductive agent.

[0034] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder (binding agent), a thickener, a filler, etc. as necessary.

[0035] 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 that can occlude and release lithium ions is usually used. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2-type crystal structure, lithium transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. Examples of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure include Li[Li x Ni (1-x) O2 (0 ≦ x < 0.5), Li[Li x Ni γ Co (1-x-γ) O2 (0 ≦ x < 0.5, 0 < γ < 1, 0 < 1 - x - γ), Li[Li x Co (1-x) O2 (0 ≦ x < 0.5), Li[Li x Ni γ Mn (1-x-γ) O2 (0 ≦ x < 0.5, 0 < γ < 1, 0 < 1 - x - γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) O2 (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) O2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1, 0 < 1 - x - γ - β), etc. Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ)Examples include O4. Examples of the polyanion compound include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species composed of other elements. These materials may have their surfaces 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 mixed and used.

[0036] As the positive electrode active material, a lithium transition metal composite oxide is preferable, a lithium transition metal composite oxide containing a nickel element, a cobalt element, and a manganese element or an aluminum element is more preferable, and a lithium transition metal composite oxide containing a nickel element, a cobalt element, and a manganese element is even more preferable. This lithium transition metal composite oxide preferably has an α-NaFeO2 type crystal structure. By using such a lithium transition metal composite oxide, it is possible to further improve the output performance after charge-discharge cycles, increase the energy density, etc.

[0037] The materials of the positive electrode active material may be used alone or two or more of them may be mixed and used. Among them, the positive electrode active material preferably contains a lithium transition metal composite oxide at a ratio of 50% by mass or more (preferably 70% to 100% by mass, more preferably 80% to 100% by mass) of all the positive electrode active materials used, and it is more preferable to use a positive electrode active material consisting essentially of only a lithium transition metal composite oxide.

[0038] The positive electrode active material is usually in the form of particles (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 be equal to or greater than the above lower limit, the production or handling of the positive electrode active material becomes easier. By setting the average particle size of the positive electrode active material to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. When a composite of the positive electrode active material and other materials is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material.

[0039] To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. Examples of the pulverization method include methods 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 air flow type jet mill, or a sieve. During pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As the classification method, a sieve, an air classifier, or the like is used as needed for both dry and wet processes.

[0040] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less. By setting the content of all the positive electrode active materials within the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer.

[0041] The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), fullerenes, and the like. Examples of the shape of the conductive agent include powder form, fibrous form, and the like. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Further, these materials may be used in a composite form. For example, a material in which carbon black and CNTs are compounded may be used. Among these, carbon black is preferable from the viewpoints of electron conductivity and coatability, and among them, acetylene black is particularly preferable.

[0042] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte storage element can be increased.

[0043] Examples of the binder 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, and the like.

[0044] The content of the binder in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the positive electrode active material can be stably held.

[0045] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. 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. When the positive electrode active material layer contains a thickener, the content of the thickener in the positive electrode active material layer can be, for example, 0.1% by mass or more and 10% by mass or less. The content of the thickener in the positive electrode active material layer may be 5% by mass or less, may be 1% by mass or less, or may be 0% by mass.

[0046] 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 aluminosilicate, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic 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. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer can be, for example, 0.1% by mass or more and 10% by mass or less. The content of the filler in the positive electrode active material layer may be 5% by mass or less, may be 1% by mass or less, or may be 0% by mass.

[0047] The positive electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, and I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, and Nb as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0048] The positive electrode can be fabricated, for example, by applying a positive electrode mixture paste directly onto the positive electrode substrate or via an intermediate layer, and then drying it. After drying, pressing or the like may be performed as necessary. The positive electrode mixture paste contains each component constituting the positive electrode active material layer, such as a positive electrode active material, and optional components such as a conductive agent and a binder. The positive electrode mixture paste usually further contains a dispersion medium.

[0049] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected, for example, from the configurations exemplified for the above positive electrode.

[0050] The negative electrode substrate has conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, or alloys thereof, carbonaceous materials, etc. are used. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate include a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferred from the viewpoint of cost. Therefore, a copper foil or a copper alloy foil is preferred as the negative electrode substrate. Examples of the copper foil include a rolled copper foil, an electrolytic copper foil, etc.

[0051] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, still more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per unit volume of the non-aqueous electrolyte storage element.

[0052] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary. The optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the above positive electrode.

[0053] The negative electrode active material layer may contain, as components other than the negative electrode active material, conductive agent, binder, thickener, and filler, typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc.

[0054] The negative electrode active material contains mesocarbon microbeads. By including mesocarbon microbeads in the negative electrode active material, in the non-aqueous electrolyte storage element according to one embodiment of the present invention with a small amount of non-aqueous electrolyte, the output performance after charge and discharge cycles can be enhanced.

[0055] In the cross-section of the mesocarbon microbeads observed in the above SEM image, the area ratio (porosity) of the voids inside the particles to the total area of the particles is 2% or less, more preferably 1% or less, and even more preferably 0.5% or less. The lower limit of this area ratio (porosity) may be 0% or may be 0.1%.

[0056] The mesocarbon microbeads may be natural graphite or artificial graphite, but natural graphite is preferred. By using natural graphite (meso-natural graphite) as the mesocarbon microbeads, the output performance after charge and discharge cycles of the non-aqueous electrolyte storage element can be further enhanced, etc.

[0057] Natural graphite refers to the general term for graphite mined from natural resources. The shape of massive natural graphite is not particularly limited, and examples include flake graphite, massive graphite (scaly graphite), and earthy graphite. The massive natural graphite may be spherical natural graphite particles obtained by spheroidizing flake natural graphite or the like. Natural graphite may be such that in an X-ray diffraction pattern using CuKα rays measured before charge-discharge or in a discharged state, four peaks appear in the range of diffraction angle 2θ from 40° to 50°. These four peaks are said to be two peaks derived from a hexagonal crystal structure and two peaks derived from a rhombohedral crystal structure. In the case of artificial graphite, generally, only two peaks derived from a hexagonal crystal structure appear. In the X-ray diffraction pattern, the ratio of the peak intensity derived from the (012) plane to the peak intensity derived from the (100) plane ((012) / (100)) is preferably 0.3 or more, and more preferably 0.4 or more. The ratio of the peak intensities ((012) / (100)) is preferably 0.6 or less. Here, the (100) plane is derived from a hexagonal crystal structure, and the (012) plane is derived from a rhombohedral crystal structure.

[0058] The average particle size of the massive graphite is, for example, preferably 1 μm or more and 50 μm or less, more preferably 5 μm or more and 30 μm or less, even more preferably 7 μm or more and 20 μm or less, and still more preferably 9 μm or more and 15 μm or less. When the average particle size of the massive graphite is within the above range, the output performance after charge-discharge cycles of the non-aqueous electrolyte storage element can be further enhanced. In order to obtain the massive graphite with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the classification method can be selected, for example, from the methods exemplified for the positive electrode above.

[0059] The content of the massive graphite in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, more preferably 90% by mass or more and 98% by mass or less, and may be even more preferably 95% by mass or more, 97% by mass or more, or 98% by mass or more. By setting the content of the massive graphite within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer, and further enhance the output performance after charge-discharge cycles.

[0060] The negative electrode active material may contain other negative electrode active materials than solid graphite. As other negative electrode active materials, hollow graphite (graphite other than solid graphite, and graphite having an area ratio of voids in the particles to the total area of the particles in the cross-section of the graphite observed in the SEM image exceeding 2%) and various other conventionally known negative electrode active materials can be used. However, the proportion of solid graphite in all the negative electrode active materials contained in the negative electrode active material layer is preferably 90% by mass or more, more preferably 99% by mass or more, and may be substantially 100% by mass. Thus, by increasing the proportion of solid graphite contained in the negative electrode active material, the effects of solid graphite are particularly sufficiently produced, and the output performance after charge-discharge cycles becomes more excellent.

[0061] The content of all the negative electrode active materials in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. The content of all the negative electrode active materials in the negative electrode active material layer may be 95% by mass or more, 97% by mass or more, or 98% by mass or more. By setting the content of all the negative electrode active materials within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0062] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer may be, for example, 1% by mass or more and 10% by mass or less. The content of the conductive agent in the negative electrode active material layer is preferably 5% by mass or less, and may be more preferably 2% by mass or less, 1% by mass or less, 0.1% by mass or less, or 0% by mass. When the content of the conductive agent in the negative electrode active material layer is small or the conductive agent is not contained, the content of the negative electrode active material can be increased, and the energy density and the like can be increased.

[0063] The content of the binder in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. By setting the content of the binder within the above range, the negative electrode active material can be stably held.

[0064] The content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 5% by mass or less.

[0065] When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be, for example, 0.1% by mass or more and 10% by mass or less. The content of the filler in the negative electrode active material layer may be 5% by mass or less, may be 1% by mass or less, or may be 0% by mass. When the content of the filler in the negative electrode active material layer is small or the filler is not contained, the content of the negative electrode active material can be increased, and the energy density and the like can be increased.

[0066] The negative electrode can be produced, for example, by applying a negative electrode mixture paste directly to a negative electrode substrate or via an intermediate layer and then drying it. After drying, pressing or the like may be performed as necessary. The negative electrode mixture paste contains a negative electrode active material including mesocarbon microbeads, and components constituting the negative electrode active material layer such as a conductive agent and a binder which are optional components. The negative electrode mixture paste usually further contains a dispersion medium.

[0067] (Separator) The separator can be appropriately selected from known separators. As the separator, for example, a separator composed only of a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of the base material layer, or the like can be used. Examples of the shape of the base material layer of the separator include a woven fabric, a non-woven fabric, and a porous resin film. Among these shapes, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of the liquid retention property of the non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of the shut-down function, and polyimides and aramids are preferable from the viewpoint of oxidation decomposition resistance. A composite material of these resins may be used as the base material layer of the separator. The content ratio of the resin in the base material layer may be 90% by mass or more, may be 99% by mass or more, or may be 100% by mass.

[0068] 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 in an air atmosphere at 1 atm, 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 value 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 ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; and 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 combination, or two or more of them may be mixed and used. Among these inorganic compounds, from the viewpoint of the safety of the energy storage element, silicon oxide, aluminum oxide, or aluminosilicate is preferable.

[0069] In one embodiment of the present invention, the separator may be a single-layer separator composed only of a resin base material layer. Further, the separator may be a single-layer separator composed only of a porous resin film made of polyolefin as the base material layer. The base material layer may be a single layer or a multilayer of two or more layers (for example, two or more layers and five or less layers, preferably three layers) made of different resins.

[0070] From the perspective of strength, the porosity of the separator is preferably 80% by volume or less, more preferably 70% by volume or less, and even more preferably 60% by volume or less. From the perspective of discharge performance, it is preferably 20% by volume or more, more preferably 30% by volume or more, even more preferably 40% by volume or more, and may be 45% by volume or more or 50% by volume or more. In addition, since the separator with a porosity above the above lower limit is compressed even under a relatively weak pressure, non-aqueous electrolyte is likely to be released from the voids of the separator during charging. Therefore, when an embodiment of the present invention is applied to a non-aqueous electrolyte storage element equipped with such a separator, the amount of non-aqueous electrolyte is small, and the effect of excellent output performance after charge-discharge cycles is particularly remarkable.

[0071] The average thickness of the separator is preferably 5 μm or more and 30 μm or less, more preferably 8 μm or more and 25 μm or less, and even more preferably 12 μm or more and 20 μm or less. When the average thickness of the separator is within the above range, the output performance of the non-aqueous electrolyte storage element after charge-discharge cycles can be further enhanced.

[0072] The ratio (Vs / (Vp + Vn + Vs)) of the total void volume (Vs) of the separator to the sum of the total void volume (Vp) of the positive electrode, the total void volume (Vn) of the negative electrode, and the total void volume (Vs) of the separator is preferably 0.1 or more and 0.6 or less, more preferably 0.2 or more and 0.5 or less, and even more preferably 0.25 or more and 0.4 or less. When the above ratio (Vs / (Vp + Vn + Vs)) is within the above range, the output performance of the non-aqueous electrolyte storage element after charge-discharge cycles can be further enhanced. The above ratio (Vs / (Vp + Vn + Vs)) can be adjusted, for example, by the average thickness, porosity, etc. of the separator. It can also be adjusted by the types of the positive electrode active material and the negative electrode active material, the thicknesses of the positive electrode active material layer and the negative electrode active material layer, etc.

[0073] (Non-aqueous electrolyte) The non-aqueous electrolyte usually contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0074] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, nitriles, etc. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are substituted with halogen atoms may be used.

[0075] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene 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.

[0076] 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 preferred.

[0077] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination. By using a cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte can be improved. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0078] 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, and the like. Among these, lithium salts are preferred.

[0079] Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, LiN(SO2F)2, lithium oxalate salts such as lithium bis(oxalate) difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0080] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm 3 or more and 2.5 mol / dm 3 or less at 20°C and 1 atm, more preferably 0.3 mol / dm 3 or more and 2.0 mol / dm 3 or less, even more preferably 0.5 mol / dm 3 or more and 1.7 mol / dm 3 or less, and particularly preferably 0.7 mol / dm 3 or more and 1.5 mol / dm 3 or less. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0081] The non-aqueous electrolyte may contain an additive in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additive include aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; vinylene carbonate, methyl vinylene carbonate, ethyl vinylene 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-propenesultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butenesultone, perfluorooctane, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tetrakis(trimethylsilyl) titanate, etc. These additives may be used alone or in combination of two or more.

[0082] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, still more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less with respect to the mass of the entire non-aqueous electrolyte. 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, or to further improve the safety.

[0083] The non-aqueous electrolyte storage element according to one embodiment of the present invention satisfies the following formula (1). A = (Vp + Vn + Vs)X ···(1) In formula (1), A is the amount (cm 3 ) of the non-aqueous electrolyte in the container. Vp is the total void volume (cm 3 ) of the positive electrode. Vn is the total void volume (cm 3 ) of the negative electrode. Vs is the total void volume (cm 3 ) of the separator. X is a number of 1.15 or more and less than 1.25. The lower limit of X may be 1.16, 1.18 or 1.20. By X being not less than the above lower limit, the output performance after charge and discharge cycles can be enhanced. The upper limit of X may be 1.24, 1.20 or 1.18. By X being not more than the above upper limit, the amount of the non-aqueous electrolyte can be reduced, and the weight reduction of the non-aqueous electrolyte storage element, the reduction of raw material costs, etc. can be achieved.

[0084] The shape of the non-aqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a rectangular battery, a flat battery, a coin-type battery, a button-type battery, etc.

[0085] Fig. 1 shows a non-aqueous electrolyte storage element 1 as an example of a rectangular battery. Note that the figure is a perspective view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a rectangular 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.

[0086] <Electricity storage device> The nonaqueous electrolyte storage element of the present embodiment 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), a plug-in hybrid electric vehicle (PHEV), etc., a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one of the nonaqueous electrolyte storage elements included in the electricity storage unit.

[0087] The electricity storage device 80 shown in FIG. 2 has a plurality of nonaqueous electrolyte storage elements 10. The plurality of nonaqueous electrolyte storage elements 10 are arranged in a row with spacers 81 interposed therebetween and housed in a housing 82. The nonaqueous electrolyte storage elements 10 are electrically connected to each other by a bus bar (not shown). In the electricity storage device 80, the flat plate 84 presses each of the nonaqueous electrolyte storage elements 10 via the spacers 81 as the nut 83 rotates. That is, in the electricity storage device 80, the nut 83 and the flat plate 84 form a pressing member. The container of the nonaqueous electrolyte storage element 10 is pressed (compressed) by such a pressing member, and the container of the nonaqueous electrolyte storage element 10 is in a state of being constrained so as to be constant in a predetermined dimension (so as to have a constant thickness in the thickness direction of the electrode body). The specific structure of the nonaqueous electrolyte storage element 10 provided in the electricity storage device 80 is similar to that of the nonaqueous electrolyte storage element 1 shown in FIG. 1. The container of the nonaqueous electrolyte storage element may be constrained by a configuration other than that shown in FIG. 2. The container does not need to be pressed as long as it is constrained so that the shape of the container is restricted. In addition, a plurality of nonaqueous electrolyte storage elements do not need to be pressed as a whole, and one nonaqueous electrolyte storage element may be pressed and the container may be constrained. When one embodiment of the present invention is applied to a nonaqueous electrolyte storage element or a storage device in which the container is constrained, the effects of a small amount of nonaqueous electrolyte and excellent output performance after charge / discharge cycles are particularly notable.

[0088] <Method of Manufacturing Nonaqueous Electrolyte Storage Element> A method for manufacturing a non-aqueous electrolyte storage element according to an embodiment of the present invention includes accommodating an electrode body having a positive electrode, a negative electrode, and a separator, and a non-aqueous electrolyte in a container, wherein the negative electrode contains solid graphite and satisfies the following formula (2). A’=(Vp’·Ep+Vn’·En+Vs)X ···(2) In formula (2), A’ is the amount (cm 3 ) of the non-aqueous electrolyte accommodated in the container. Vp’ is the total void volume (cm 3 ) of the positive electrode before charge and discharge, and Ep is the expansion rate of the positive electrode after charge and discharge. Vn’ is the total void volume (cm 3 ) of the negative electrode before charge and discharge, and En is the expansion rate of the negative electrode after charge and discharge. Vs is the total void volume (cm 3 ) of the separator. X is a number greater than or equal to 1.15 and less than 1.25. The lower limit of X in formula (2) may be 1.16, 1.18, or 1.20. The upper limit of X in formula (2) may be 1.24, 1.20, or 1.18.

[0089] Ep (expansion rate of the positive electrode after charge and discharge) and En (expansion rate of the negative electrode after charge and discharge) in the above formula (2) are values determined by the types of the positive electrode active material and the negative electrode active material, charge and discharge conditions, etc. For example, when the positive electrode active material is a lithium transition metal composite oxide containing nickel element, cobalt element, and manganese element and having an α-NaFeO2 type crystal structure, Ep (expansion rate of the positive electrode after charge and discharge) is usually 1.00 or more and 1.05 or less. When the negative electrode active material is only solid graphite, En (expansion rate of the negative electrode after charge and discharge) is usually 1.00 or more and 1.20 or less.

[0090] The accommodation of the electrode body and the non-aqueous electrolyte in the container is usually carried out in the order of first accommodating the electrode body and then accommodating the non-aqueous electrolyte. The accommodation of the non-aqueous electrolyte is performed, for example, by injecting the non-aqueous electrolyte from an injection port formed in the container and then sealing the injection port. In the case of a non-aqueous electrolyte storage element in which the container is constrained to be constant at a predetermined dimension, the non-aqueous electrolyte may be injected in a state where the container is constrained to be constant at a predetermined dimension, or the container may be constrained to be constant at a predetermined dimension after injecting the non-aqueous electrolyte in a state where the container is not constrained. However, from the viewpoint of productivity and the like, the latter is preferable.

[0091] The manufacturing method preferably further includes performing an initial charge and discharge on the uncharged and discharged storage element in which the electrode body and the non-aqueous electrolyte are accommodated in the container. By the initial charge and discharge, the positive electrode and the negative electrode expand at expansion rates Ep and En, respectively, and a non-aqueous electrolyte storage element according to an embodiment of the present invention is obtained.

[0092] The manufacturing method may further include preparing the electrode body and preparing the non-aqueous electrolyte. Preparing the electrode body includes preparing the positive electrode and the negative electrode and forming the electrode body by laminating or winding the positive electrode and the negative electrode via a separator.

[0093] <Other Embodiments> In addition, the non-aqueous electrolyte storage element of the present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added with the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. Further, a part of the configuration of one embodiment can be deleted. In addition, a well-known technique can be added to the configuration of one embodiment.

[0094] In the above-described embodiment, the case where the non-aqueous electrolyte storage element is used as a rechargeable non-aqueous electrolyte secondary battery (lithium-ion secondary battery) has been described. However, the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries. The non-aqueous electrolyte storage element of the present invention may be in a form in which the container is not constrained to be constant at a predetermined dimension. For example, the non-aqueous electrolyte storage element of the present invention may be in a form in which the container is constrained to be constant at a predetermined dimension after passing through a predetermined charge-discharge cycle.

Example

[0095] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

[0096] [Example 1] (Fabrication of positive electrode) LiNi, which is a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium were used to prepare a positive electrode mixture paste. The mass ratio of the positive electrode active material, AB, and PVDF was 93:3.5:3.5 (in terms of solid content). The positive electrode mixture paste was applied to both sides of an aluminum foil as a positive electrode substrate so that the coating mass of the solid content was 6.19 mg / cm 2 and dried. Thereafter, roll pressing was performed to obtain a positive electrode. The total void volume (Vp') of the obtained positive electrode before charge and discharge was 6.31 cm 3 .

[0097] (Fabrication of negative electrode) A negative electrode mixture paste was prepared using mesoporous natural graphite (porosity 0.45%, average particle size 9.9 μm) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, carboxymethyl cellulose (CMC) as the thickener, and water as the dispersion medium. The mass ratio of graphite, SBR, and CMC was 98:1:1 (in terms of solid content). The negative electrode mixture paste was applied to both sides of a copper foil serving as the negative electrode substrate so that the coating mass of the solid content was 3.83 mg / cm 2 and dried. Then, roll pressing was performed to obtain a negative electrode. The total void volume (Vn’) of the obtained negative electrode before charge and discharge was 9.39 cm 3 .

[0098] (Non-aqueous electrolyte) LiPF6 was dissolved in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 30:70 to obtain a non-aqueous electrolyte at a concentration of 1.2 mol / dm 3 .

[0099] (Separator) A polyolefin microporous membrane was used as the separator. The total void volume (Vs) of the prepared separator was 6.71 cm 3 , the porosity was 52% by volume, and the average thickness was 18 μm.

[0100] (Assembly of non-aqueous electrolyte storage element) The above positive electrode and the above negative electrode were wound in a state of being overlapped via the above separator to obtain an electrode body. The obtained electrode body was housed in a container, and further the above non-aqueous electrolyte was housed to obtain an uncharged storage element. Initial charge and discharge were performed on the obtained uncharged storage element under the following conditions. In a constant temperature bath at 25°C, constant current charging was performed with a charging current of 1.0C and a charging cut-off voltage of 4.10V, and then constant voltage charging was performed at 4.10V. The end condition of charging was until the total charging time reached 3 hours. Then, a 10-minute rest period was provided. Constant current discharge was performed with a discharge current of 1.0C and a discharge cut-off voltage of 2.50V. Then, pressing members were attached to both sides of the container, and the container was constrained by the pressing members so as to be constant at a predetermined dimension, thereby obtaining the non-aqueous electrolyte storage element of Example 1. In the non-aqueous electrolyte storage element of Example 1 obtained, the amount (A) of the non-aqueous electrolyte in the container determined by the above method was 26.75 cm 3 , the total void volume (Vp) of the positive electrode was 6.38 cm 3 , the total void volume (Vn) of the negative electrode was 9.92 cm 3 , the total void volume (Vs) of the separator was 6.71 cm 3 , X in the above formula (1) was 1.16. Also, the expansion rate (Ep) of the positive electrode after charge and discharge was 1.011, and the expansion rate (En) of the negative electrode after charge and discharge was 1.056. It was confirmed that the measured amount of the non-aqueous electrolyte in the container was substantially equal to the amount of the non-aqueous electrolyte contained in the container.

[0101] [Examples 2 and Comparative Examples 1 to 16] Except for using the negative electrode active material described in Table 1 and changing the amount of the non-aqueous electrolyte to be accommodated so that X in the above formula (1) becomes the value described in Table 1, each non-aqueous electrolyte storage element of Examples 2 and Comparative Examples 1 to 16 was obtained in the same manner as in Example 1. Note that the hollow natural graphite in Table 1 had a porosity of 3% and an average particle size of 9.1 μm.

[0102] [Evaluation] (1) Initial output For each of the obtained non-aqueous electrolyte storage elements, constant current charging was performed at 25°C with a current of 1.0C to make the SOC 50%. Subsequently, discharge was performed for 30 seconds each at a current of 0.2C, 0.5C, or 1.0C. After each discharge, constant current charging was performed at a current of 1.0C to make the SOC 50%. The relationship between the current in each discharge and the voltage at the 10th second after the start of discharge was plotted, and the DC resistance was obtained from the slope of the straight line obtained from the three points of the plot. The output 10 seconds after the start of discharge was calculated from the obtained DC resistance and used as the initial output. The initial output of each non-aqueous electrolyte storage element is shown in Table 1 and FIG. 3 as a relative value (%) with the value of the non-aqueous electrolyte storage element in which X is 1.50 and the same negative electrode active material is used as the reference (100%). (2) Charge and discharge cycle test Next, for each non-aqueous electrolyte storage element, constant current charging was performed at a current of 1.0 C at 25°C to set the SOC to 20%. Subsequently, after storing in a thermostat at 60°C for 4 hours, constant current charging was performed at a current of 40 A until the voltage corresponding to an SOC of 80% was reached, and then constant current discharging was performed at a current of 40 A until the voltage corresponding to an SOC of 20% was reached. The above charging and discharging cycles were repeated 3,000 hours without providing a rest time after the above charging and discharging. (3) Output after charge-discharge cycles Thereafter, the output after the charge-discharge cycle test was determined by the same procedure as the procedure for determining the initial output. Regarding the output after the charge-discharge cycle of each non-aqueous electrolyte storage element, it is shown in Table 1 and FIG. 4 as a relative value (%) with the value of the non-aqueous electrolyte storage element having X = 1.50 and using the same negative electrode active material as the reference (100%).

[0103]

Table 1

[0104] As shown in Table 1 and FIG. 3, when the value of X indicating the relative amount of the non-aqueous electrolyte is less than 1.10, the initial output significantly decreases. However, in the initial output, there is almost no difference between the case where the negative electrode active material is solid natural graphite and the case where it is hollow natural graphite. On the other hand, as shown in Table 1 and FIG. 4, in the output after the charge-discharge cycle, when the negative electrode active material is hollow natural graphite, the output after the charge-discharge cycle significantly decreases when the value of X is less than 1.25. In contrast, when the negative electrode active material is solid natural graphite, even if the value of X is lowered to 1.10, the output after the charge-discharge cycle hardly changes. From such results, it can be confirmed that a non-aqueous electrolyte storage element using solid graphite as the negative electrode active material and having a value of X of 1.15 or more and less than 1.25 has the effect of having a small amount of non-aqueous electrolyte and excellent output performance after the charge-discharge cycle.

Industrial Applicability

[0105] The present invention can be applied to electronic devices such as personal computers and communication terminals, and non-aqueous electrolyte storage elements used as power sources for automobiles and the like.

Explanation of Signs

[0106] 1, 10 Non-aqueous electrolyte storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 80 Power storage device 81 Spacer 82 Housing 83 Nut 84 Flat plate

Claims

1. An electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte are provided, wherein the negative electrode contains solid graphite, and the non-aqueous electrolyte storage element satisfies the following formula (1). A = (Vp + Vn + Vs)X...(1) (In formula (1), A is the amount (cm ３ ) of the non-aqueous electrolyte in the container. Vp is the total void volume (cm ３ ) of the positive electrode. Vn is the total void volume (cm ３ ) of the negative electrode. Vs is the total void volume (cm ３ ) of the separator. X is a number greater than or equal to 1.15 and less than 1.25.)

2. The non-aqueous electrolyte storage element according to Claim 1, wherein the container is constrained to be constant with a predetermined dimension.

3. A method for manufacturing a non-aqueous electrolyte storage element, comprising housing an electrode body having a positive electrode, a negative electrode, and a separator, and a non-aqueous electrolyte in a container, wherein the negative electrode contains solid graphite, and satisfies the following formula (2). A' = (Vp'·Ep + Vn'·En + Vs)X...(2) (In Formula (2), A' is the amount (cm ３ ) of the non-aqueous electrolyte accommodated in the container. Vp' is the total void volume (cm ３ ) of the positive electrode before charge and discharge, and Ep is the expansion ratio of the positive electrode after charge and discharge. Vn' is the total void volume (cm ３ ) of the negative electrode before charge and discharge, and En is the expansion ratio of the negative electrode after charge and discharge. Vs is the total void volume (cm ３ ) of the separator. X is a number of 1.15 or more and 1.25 or less.)

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