Electric energy storage element, method for manufacturing same, and electric energy storage device

Abstract

An electricity storage element according to one embodiment of the present invention is provided with: an electrode body that comprises a positive electrode, a negative electrode and a separator; a nonaqueous electrolyte; and a container that contains the electrode body and the nonaqueous electrolyte. The positive electrode contains a positive electrode active material; the positive electrode active material contains a plurality of particles that satisfy at least one of the conditions (1) and (2) described below; and the electrode body is in a pressed state. (1) A plurality of primary particles that do not form secondary particles (2) A plurality of secondary particles, each of which is formed of a plurality of aggregated primary particles, wherein the ratio of the average diameter of the secondary particles to the average diameter of the primary particles that form the secondary particles is less than 11

Description

Technical Field

[0001] The present disclosure relates to a power storage element, a method for manufacturing the same, and a power storage device.

Background Art

[0002] Secondary batteries typified by lithium ion secondary batteries are used in electronic devices such as personal computers and communication terminals, and automobiles because of their high energy density.

[0003] As the secondary battery, for example, a flat non-aqueous electrolyte secondary battery including a flat electrode body having a structure in which a positive electrode plate and a negative electrode plate are laminated via a separator and a non-aqueous electrolyte, wherein a pressure is applied to the flat portion of the flat non-aqueous electrolyte secondary battery from the outside in the lamination direction of the positive electrode plate, the negative electrode plate, and the separator, so that a pressure of 8.83×10 -2 MPa or more is applied to the electrode body, is disclosed (see Japanese Patent Application Laid-Open No. 2018-26352).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the flat non-aqueous electrolyte secondary battery, the resistance may increase when charging and discharging are repeated.

[0006] In view of the above circumstances, an object of the present invention is to provide a power storage element in which an increase in resistance associated with charge and discharge cycles is suppressed, a method for manufacturing the same, and a power storage device including the power storage element.

Means for Solving the Problems

[0007] The energy storage element according to one aspect of the present invention includes an electrode body including 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 positive electrode contains a positive electrode active material, and the positive electrode active material contains a plurality of particles that satisfy at least one of the following conditions (1) and (2), and the electrode body is in a pressed state. (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, and a plurality of secondary particles in which the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

[0008] A method for manufacturing an energy storage element according to another aspect of the present invention is a method for manufacturing an energy storage element including an electrode body including 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, and includes pressing the electrode body. The positive electrode contains a positive electrode active material, and the positive electrode active material contains a plurality of particles that satisfy at least one of the following conditions (1) and (2). (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, and a plurality of secondary particles in which the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

[0009] An energy storage device according to another aspect of the present invention includes the one or more energy storage elements and a pressing member, and the pressing member presses the electrode body of the energy storage element by pressing the container. [Effect of the Invention]

[0010] According to the energy storage element according to one aspect of the present invention, an increase in resistance associated with charge and discharge cycles can be suppressed.

[0011] According to the method for manufacturing an energy storage element according to another aspect of the present invention, an energy storage element in which an increase in resistance associated with charge and discharge cycles is suppressed can be manufactured.

[0012] According to the power storage device according to another aspect of the present invention, an increase in resistance associated with charge and discharge cycles can be suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0014] First, an overview of the power storage element, the method for manufacturing the power storage element, and the power storage device disclosed in this specification will be described.

[0015] The power storage element according to one aspect of the present invention includes an electrode body including 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 positive electrode contains a positive electrode active material, and the positive electrode active material contains a plurality of particles that satisfy at least one of the following conditions (1) and (2), and the electrode body is in a pressed state. (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, and a plurality of secondary particles in which the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

[0016] When the charge and discharge of the power storage element are repeated, the positive electrode active material expands. When secondary particles formed by aggregation of a plurality of primary particles are used as the positive electrode active material, cracks are generated at the grain boundaries of the plurality of primary particles due to this expansion, and the resistance at the surface of the positive electrode active material increases due to the generation of these cracks. The larger the number of primary particles constituting the secondary particles, the more significant the increase in resistance due to the generation of cracks.

[0017] However, according to the energy storage element, the plurality of particles included in the positive electrode active material are a plurality of primary particles that do not form secondary particles, or are secondary particles formed by aggregation of a plurality of primary particles. In addition to the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles being within the above range, in a state where the electrode body is pressed, expansion of the positive electrode active material accompanying repeated charge and discharge is suppressed. By suppressing this expansion, generation of the above cracks is reduced, and an increase in resistance on the surface of the positive electrode active material is reduced. Therefore, according to the energy storage element, an increase in resistance accompanying charge and discharge cycles can be suppressed.

[0018] Here, the pressure applied to the electrode body may be 0.1 MPa or more.

[0019] If the pressure is 0.1 MPa or more in this way, an increase in resistance accompanying charge and discharge cycles can be more suppressed.

[0020] Here, the positive electrode active material is a transition metal oxide containing nickel, and the product of the BET specific surface area and the median diameter of the positive electrode active material may be 4.5 or less.

[0021] When secondary particles formed by aggregation of a plurality of primary particles are used as the positive electrode active material, due to unevenness on the surface of the secondary particles and cracks generated at the grain boundaries of the primary particles, the BET specific surface area of the positive electrode active material increases, and the contact area between the positive electrode active material and the non-aqueous electrolyte increases. As a result, the resistance on the surface of the positive electrode active material increases. Therefore, it is presumed that the closer the positive electrode active material particles are to an ideal sphere without unevenness or cracks on the surface, the more the increase in resistance due to the reaction with the non-aqueous electrolyte is reduced. In an ideal sphere, the BET specific surface area is expressed by the following formula. BET specific surface area (m 2 / g) = 4π × (median diameter (μm) / 2) 2 / {(4π / 3) × (median diameter (μm) / 2) 3 × true density (g / cm 3 )} By transforming the above formula, the following formula is derived. BET specific surface area (m2 / g)×Median diameter (μm) = 6 / True density (g / cm 3 ) Here, as an example of a transition metal oxide containing nickel, the true density of LiNiO2 is about 4.7 (g / cm 3 ). Therefore, in the case of an ideal sphere, the product of the BET specific surface area and the median diameter is about 1.3. In reality, since the positive electrode active material particles have minute irregularities and cracks on the surface, the product of the BET specific surface area and the median diameter becomes larger than 1.3. However, by setting such a product to 4.5 or less, an increase in resistance associated with charge-discharge cycles can be more effectively suppressed. When the positive electrode active material contains a plurality of particles satisfying at least one of the following conditions (1) and (2), the product of the BET specific surface area and the median diameter can be reduced. (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, and a plurality of secondary particles in which the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

[0022] A method for manufacturing a power storage element according to another aspect of the present invention is a method for manufacturing a power storage element including an electrode body including 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 method including pressing the electrode body, the positive electrode including a positive electrode active material, and the positive electrode active material including a plurality of particles satisfying at least one of the following conditions (1) and (2). (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, and a plurality of secondary particles in which the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

[0023] According to this method for manufacturing a power storage element, a power storage element can be manufactured in which the plurality of particles included in the positive electrode active material are a plurality of primary particles that do not form secondary particles, or secondary particles formed by aggregation of a plurality of primary particles, and in addition to the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles being within the above range, the electrode body is in a pressed state. Therefore, as described above, according to the method for manufacturing the storage element, it is possible to manufacture a storage element in which an increase in resistance associated with charge-discharge cycles is suppressed.

[0024] Here, the pressure applied to the electrode body may be 0.1 MPa or more.

[0025] Thus, if the pressure is 0.1 MPa or more, it is possible to manufacture a storage element in which an increase in resistance associated with charge-discharge cycles is further suppressed.

[0026] Here, the method for manufacturing the storage element may further include initially charging and discharging the storage element, and may perform pressing the electrode body after the initial charging and discharging.

[0027] If the electrode body is pressed after the initial charging and discharging in this way, the gas generated by the decomposition of the non-aqueous electrolyte due to the initial charging and discharging can be discharged from inside the electrode body. When gas exists between the positive and negative electrodes, it becomes one of the causes of an increase in the resistance between the positive and negative electrodes. Therefore, it is possible to manufacture a storage element having a low initial resistance and in which an increase in resistance associated with charge-discharge cycles is suppressed.

[0028] A power storage device according to another aspect of the present invention includes the one or more power storage elements and a pressing member, and the pressing member presses the electrode body of the power storage element by pressing the container.

[0029] According to this power storage device, since the electrode body of the power storage element is in a state of being pressed by the pressing member, as described above, an increase in resistance associated with charge-discharge cycles can be suppressed.

[0030] The configuration of the power storage element, the configuration of the power storage device, the method for manufacturing the power storage element, and the method for manufacturing the power storage device according to an embodiment of the present invention, as well as other embodiments, 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.

[0031] <Configuration of the energy storage element> The energy storage element according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode usually form an electrode body laminated or wound via a separator. This electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. As an example of the energy storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as "secondary battery") will be described.

[0032] (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.

[0033] The positive electrode substrate has conductivity. Having "conductivity" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 Ω·cm or less, and "non-conductive" means that the above volume resistivity is 10 7 Ω·cm or more. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, and 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, and a porous material, 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 aluminum or an aluminum alloy include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0034] 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 unit volume of the secondary battery. The "average thickness" refers to the value obtained by dividing the punching mass when punching out a substrate of a predetermined area by the true density and the punching area of the substrate. The same definition applies when using the "average thickness" for other members, etc.

[0035] 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 for example, it contains a binder and a conductive agent.

[0036] 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, a thickener, and a filler as necessary.

[0037] 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, etc. 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), 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), Li[Li x Niγ Mn β Co (1-x-γ-β) O2(0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1), 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), etc. are exemplified. As the lithium transition metal composite oxide having a spinel crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) O4, etc. are exemplified. As the polyanion compound, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. are exemplified. As the chalcogen compound, titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. are exemplified. 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 used in combination.

[0038] As the above positive electrode active material, a lithium transition metal composite oxide containing nickel is preferable, a lithium transition metal composite oxide containing nickel, cobalt, and manganese or aluminum is more preferable, and a lithium transition metal composite oxide containing nickel, cobalt, and manganese 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 increase the energy density, etc.

[0039] The positive electrode active material is particles (powder). More specifically, the positive electrode active material contains a plurality of particles that satisfy at least one of the following conditions (1) and (2). (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, wherein the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

[0040] When the positive electrode active material satisfies the conditions of (1) above, the average diameter of the primary particles is preferably, for example, 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 7 μm or less. The "average diameter of the primary particles" means a value obtained by measuring the average diameter of at least 50 primary particles in a scanning electron microscope image of a cross section obtained by cutting the positive electrode active material layer in the thickness direction and averaging the measured values. The average diameter of each primary particle is obtained as follows. The shortest diameter passing through the center of the minimum circumscribed circle of the primary particle is defined as the minor axis, and the diameter passing through the center and perpendicular to the minor axis is defined as the major axis. The average value of the major axis and the minor axis is defined as the average diameter of the primary particle. When there are two or more shortest diameters, the diameter that is the longest among the perpendicular diameters is defined as the minor axis.

[0041] When the positive electrode active material satisfies the conditions of (2) above, the upper limit of the ratio of the average diameter of the secondary particles to the average diameter of the primary particles is less than 11, preferably 8, more preferably 6, even more preferably 4, and even more preferably 3 in some cases. By the ratio being less than the upper limit, the occurrence of cracks associated with charge-discharge cycles can be more reliably reduced, and an increase in resistance can be more reliably suppressed. The lower limit of the ratio of the average diameter of the secondary particles to the average diameter of the primary particles may be 1. Note that due to the difference between the measurement method of the average diameter of the primary particles and the measurement method of the average diameter of the secondary particles, the lower limit of the ratio of the average diameter of the secondary particles to the average diameter of the primary particles does not necessarily have to be 1, and may be less than 1, for example, 0.9.

[0042] The average diameter of the primary particles can be appropriately set in consideration of the relationship with the average diameter of the secondary particles so that, for example, the ratio of the average diameter of the secondary particles to the average diameter of the primary particles is less than 11. For example, the average diameter of the primary particles is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 7 μm or less. When the positive electrode active material includes a plurality of primary particles that do not form secondary particles and secondary particles formed by aggregation of the plurality of primary particles, it is preferable that both the average diameter of the primary particles independently included and the average diameter of the primary particles constituting the secondary particles are within the above range. When the positive electrode active material includes only secondary particles, it is preferable that the average diameter of the primary particles constituting the secondary particles is within the above range.

[0043] By setting the average diameter of the primary particles 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 diameter of the primary particles to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. In addition, by setting the average diameter of the primary particles within the above range, it becomes easier to make the ratio of the average diameter of the secondary particles to the average diameter of the primary particles less than 11, so that an increase in resistance associated with charge and discharge cycles can be more reliably suppressed.

[0044] The average diameter of the secondary particles can be appropriately set in consideration of the relationship with the average diameter of the primary particles so that, for example, the ratio of the average diameter of the secondary particles to the average diameter of the primary particles is less than 11. For example, the average diameter of the secondary particles is preferably 1 μm or more and 20 μm or less, and more preferably 2 μm or more and 15 μm or less. When a composite of the positive electrode active material and another material is used as the secondary particles, the average diameter of the composite is taken as the average diameter of the secondary particles. The "average diameter of the secondary particles" 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 the laser diffraction / scattering method for a dilution obtained by diluting the particles with a solvent in accordance with JIS-Z-8825 (2013).

[0045] By setting the average diameter of the secondary particles 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 diameter of the secondary particles to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. In addition, by setting the average diameter of the secondary particles within the above range, it becomes easier to make the ratio of the average diameter of the secondary particles to the average diameter of the primary particles less than 11, so that an increase in resistance associated with charge-discharge cycles can be more reliably suppressed.

[0046] The upper limit of the product of the BET specific surface area and the median diameter of the positive electrode active material is not particularly limited, but is preferably 4.5 or less, more preferably 4.0 or less, still more preferably 3.0 or less, and even more preferably 2.5 or less in some cases. By setting the product of the BET specific surface area and the median diameter to be equal to or less than the above upper limit, an increase in resistance associated with charge-discharge cycles can be more suppressed. The lower limit of the product of the BET specific surface area and the median diameter of the positive electrode active material is not particularly limited, but may be 1.3.

[0047] The upper limit of the BET specific surface area of the positive electrode active material is not particularly limited. For example, 1.0 m 2 / g is preferable, and 0.7 m 2 / g is more preferable. The lower limit of the BET specific surface area of the positive electrode active material is not particularly limited. For example, 0.2 m 2 / g is preferable, and 0.3 m 2 / g is more preferable. By setting the BET specific surface area of the positive electrode active material within the above range, the contact area between the non-aqueous electrolyte and the positive electrode active material particles can be reduced, so that an increase in resistance associated with charge-discharge cycles can be more suppressed. The "BET specific surface area of the positive electrode active material" is obtained by immersing the positive electrode active material in liquid nitrogen and measuring the pressure and nitrogen adsorption amount at that time based on the physical adsorption of nitrogen molecules on the particle surface by supplying nitrogen gas. Specifically, the BET specific surface area is measured by the following method. Using a specific surface area measuring device (trade name: MONOSORB) manufactured by Yuasa Ionics Co., Ltd., the nitrogen adsorption amount (m 2 ) for the sample is determined by the single-point method. The value obtained by dividing the obtained adsorption amount by the mass (g) of the sample is the BET specific surface area (m 2Set it as ( / g). In the measurement, gas adsorption by cooling using liquid nitrogen is performed. Also, preheating is carried out at 120 °C for 15 minutes before cooling. The input amount of the measurement sample shall be 0.5 g ± 0.01 g. The sample of the positive electrode active material used for the measurement of the BET specific surface area is prepared by the following method. Discharge the energy storage element at a current of 0.1 C until the discharge cut-off voltage during normal use is reached to make it in a fully discharged state. Here, "during normal use" means the case where the energy storage element is used by adopting the discharge conditions recommended or specified for the energy storage element. Disassemble the fully discharged energy storage element, take out the positive electrode as the working electrode, assemble a half-cell with metallic Li as the counter electrode, and discharge at a current of 0.1 C until the positive electrode potential reaches 3.0 V (vs. Li / Li + )). Disassemble the half-cell, thoroughly wash the taken-out positive electrode with dimethyl carbonate, and then perform drying under reduced pressure at room temperature. Peel off the positive electrode mixture layer from the dried positive electrode using, for example, a spatula, and remove the binder, conductive agent, etc. to separate the positive electrode active material, which is used as the sample of the positive electrode active material in the measurement of the BET specific surface area. The removal of the binder is performed by immersing the positive electrode mixture layer in an organic solvent or the like and then filtering. The removal of the conductive agent is performed by heat treatment at about 750 °C in an air atmosphere. The operations from the disassembly of the battery to the drying under reduced pressure are carried out in a dry atmosphere with a dew point of -40 °C or lower.

[0048] The median diameter of the positive electrode active material is preferably, for example, 0.5 μm or more and 20 μm or less, more preferably 1 μm or more and 15 μm or less. By setting the median diameter 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 median diameter to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. The "median diameter of the positive electrode active material" means a value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) based on the particle size distribution measured by the laser diffraction / scattering method for a dilution obtained by diluting the positive electrode active material particles with a solvent conforms to JIS-Z-8825 (2013). When the positive electrode active material is a plurality of primary particles that do not form secondary particles, the average diameter of the primary particles may not match the median diameter due to the difference between the measurement method of the average diameter of the primary particles and the measurement method of the median diameter. When the positive electrode active material is a plurality of secondary particles formed by aggregation of a plurality of primary particles and the ratio of the average diameter to the average diameter of the primary particles is less than 11, the above median diameter is equal to the average diameter of the secondary particles.

[0049] In order to obtain primary particles that do not form secondary particles and secondary particles in which primary particles are aggregated at 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 methods. In addition, a plurality of primary particles can be sintered to have a large particle size by increasing the firing temperature of the active material or increasing the firing time.

[0050] 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 the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer.

[0051] (Optional component) 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, etc. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerenes, etc. Examples of the shape of the conductive agent include powder form, fibrous form, etc. As the conductive agent, one of these materials may be used alone, or two or more thereof may be mixed and used. Further, these materials may be used in a composite form. For example, a material in which carbon black and CNT are composite may be used. Among these, carbon black is preferable from the viewpoints of electron conductivity and coatability, and acetylene black is particularly preferable.

[0052] The content of the conductive agent in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% 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 secondary battery can be increased.

[0053] 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, etc.

[0054] The content of the binder in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the active material can be stably held.

[0055] 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.

[0056] 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, and magnesium oxide, 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 substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, or artificial products thereof.

[0057] 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.

[0058] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly or via an intermediate layer on the negative electrode substrate. The configuration of the intermediate layer is not particularly limited, and can be selected, for example, from the configurations exemplified for the positive electrode above.

[0059] The negative electrode substrate has conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or alloys thereof are used. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate include foil, vapor deposition film, mesh, porous material, etc., and foil is preferred from the perspective of cost. Therefore, a copper foil or a copper alloy foil is preferred as the negative electrode substrate. Examples of the copper foil include rolled copper foil, electrolytic copper foil, etc.

[0060] 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, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the secondary battery.

[0061] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer may contain optional components such as a conductive agent, a binder, a thickening agent, and a filler as required. The optional components such as the conductive agent, the binder, the thickening agent, and the filler can be selected from the materials exemplified in the above positive electrode.

[0062] The negative electrode active material layer may contain 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. as components other than the negative electrode active material, the conductive agent, the binder, and the filler.

[0063] The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium-ion secondary battery, a material that can usually occlude and release lithium ions is generally used. Examples of the negative electrode active material include metallic Li; metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxide, Ti oxide, and Sn oxide; Li4Ti5O 12 、LiTiO 2、Titanium-containing oxides such as TiNb2O7; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite (graphite), non-graphitic carbon (easily graphitizable carbon or hardly graphitizable carbon), etc. Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

[0064] "Graphite" refers to a carbon material having an average lattice plane spacing (d 002 ) of 0.33 nm or more and less than 0.34 nm as determined by X-ray diffraction before charge-discharge or in the discharged state. Examples of graphite include natural graphite and artificial graphite. From the viewpoint of obtaining a material with stable physical properties, artificial graphite is preferred.

[0065] "Non-graphitic carbon" refers to a carbon material having an average lattice plane spacing (d 002 ) of 0.34 nm or more and 0.42 nm or less as determined by X-ray diffraction before charge-discharge or in the discharged state. Examples of non-graphitic carbon include hardly graphitizable carbon and easily graphitizable carbon. Examples of non-graphitic carbon include, for example, resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, alcohol-derived materials, etc.

[0066] Here, the "discharged state" means a state in which lithium ions that can be occluded and released with charge-discharge are sufficiently released from the carbon material that is 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.

[0067] "Hardly graphitizable carbon" refers to a carbon material having the above d 002 of 0.36 nm or more and 0.42 nm or less.

[0068] "Easily graphitizable carbon" refers to a carbon material having the above d 002 of 0.34 nm or more and less than 0.36 nm.

[0069] The negative electrode active material is usually in the form of particles (powder). The average diameter of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is, for example, a carbon material, a titanium-containing oxide, or a polyphosphoric acid compound, its average diameter may preferably be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, a Si oxide, a Sn oxide, or the like, its average diameter may be 1 nm or more and 1 μm or less. By setting the average diameter of the negative electrode active material to be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average diameter of the negative electrode active material to be equal to or less than the above upper limit, the electron conductivity of the active material layer is improved. To obtain a powder 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. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of a foil.

[0070] The content of the negative electrode active material 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. By setting the content of the negative electrode active material within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0071] (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 in which a heat-resistant layer containing heat-resistant particles and a binder is 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 woven fabric, non-woven fabric, porous resin film, and the like. 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, aramids, and the like 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.

[0072] 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.

[0073] From the viewpoint of strength, the porosity of the separator is preferably 80% by volume or less, and from the viewpoint of discharge performance, it is preferably 20% by volume or more. Here, the "porosity" is a value based on volume and means the measured value by a mercury porosimeter.

[0074] 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, polyvinyl pyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing liquid leakage. As the separator, a porous resin film or non-woven fabric as described above and a polymer gel may be used in combination.

[0075] (Non-aqueous electrolyte) The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0076] 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 halogens may also be used.

[0077] 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.

[0078] 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.

[0079] 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 cyclic carbonate and a chain carbonate in combination. By using a cyclic carbonate, dissociation of the electrolyte salt can be promoted to improve the ionic conductivity of the non-aqueous electrolyte. 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.

[0080] As the electrolyte salt, it 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 preferable.

[0081] 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(oxalato)borate (LiBOB), lithium difluorooxalate borate (LiFOB), lithium bis(oxalato)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, etc. Among these, inorganic lithium salts are preferable, and LiPF6 is more preferable.

[0082] 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, still more preferably 0.5 mol / dm 3 or more and 1.7 mol / dm 3 or less, and most preferably 0.7 mol / dm 31.5 mol / dm or less is particularly preferred. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased. 3 It is particularly preferable that it is as follows. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0083] The non-aqueous electrolyte may contain an additive in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additive include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate) difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl) imide (LiFSI); aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halogenated compounds 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, 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, propane sultone, propene sultone, butane sultone, 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, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tetrakis(trimethylsilyl) titanate, lithium monofluorophosphate, lithium difluorophosphate, and the like.These additives may be used individually or in combination of two or more thereof.

[0084] 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, the capacity retention performance or cycle performance after high-temperature storage can be improved, or the safety can be further improved.

[0085] As the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

[0086] As the solid electrolyte, any material having ion conductivity such as lithium, sodium, calcium, etc. and being solid at normal temperature (for example, from 15°C to 25°C) can be selected. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes, and the like.

[0087] As the sulfide solid electrolyte, in the case of a lithium-ion secondary battery, for example, Li2S-P2S5, LiI-Li2S-P2S5, Li 10 Ge-P2S 12 and the like can be mentioned.

[0088] The shape of the power storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery, a flat battery, a coin-type battery, a button-type battery, and the like. FIG. 1 shows a power storage element 1 (non-aqueous electrolyte power storage element) as an example of a prismatic battery. Note that the figure is a perspective view of the inside of the case. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed 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.

[0089] (State where the electrode body is pressed) The power storage element 1 of this embodiment is in a state where the electrode body 2 is pressed in the situation where the power storage element 1 is used. That is, the power storage element 1 of this embodiment is used in a state where the electrode body 2 is pressed. For example, as will be described later, by pressing the container 3 with a pressing member 6 (see FIG. 3), the electrode body 2 can be brought into a state of being pressed in the thickness direction. By reducing the pressure (negative pressure) by sucking the gas in the container 3 or the like, the electrode body 2 may be brought into a state of being pressed in the thickness direction. In addition to the electrode body 2, by inserting a spacer (not shown) into the container 3, the electrode body 2 may be in a pressed state. Generally, the electrode body 2 increases in thickness after manufacture by impregnating with a non-aqueous electrolyte or by performing initial charge and discharge. Therefore, when using a highly rigid container 3, an electrode body 2 having a thickness substantially the same as the inner dimension of the container 3 is housed in the container 3, and a non-aqueous electrolyte is injected and initial charge and discharge is performed, so that the electrode body 2 can be brought into a state of being pressed by the container 3.

[0090] In a state where the electrode body 2 is pressed, the pressure applied to the electrode body 2 is preferably 0.1 MPa or more, more preferably 0.1 MPa or more and 2 MPa or less, and even more preferably 0.1 MPa or more and 1 MPa or less. The pressure applied to the electrode body 2 means a value measured by a strain gauge type load cell. By setting the pressure to be equal to or higher than the lower limit, the expansion of the positive electrode active material accompanying the charge and discharge cycle can be suppressed, and the occurrence of cracks can be more reliably suppressed. On the other hand, by setting the pressure to be equal to or lower than the upper limit, a decrease in durability due to excessive pressing of the electrode body can be suppressed.

[0091] <Configuration of the power storage device> The energy storage element of this embodiment can be mounted as an energy storage device (battery module) configured by aggregating a plurality of energy storage elements 1 in an automotive power source such as an electric vehicle (EV), a hybrid vehicle (HEV), or a plug-in hybrid vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage. In this case, the technology of the present invention may be applied to at least one energy storage element included in the energy storage device.

[0092] The energy storage device of this embodiment includes the energy storage element and the pressing member of the above-described embodiment, and the pressing member presses the electrode body by pressing the container. FIG. 2 shows an example of a battery pack 30 in which energy storage devices 20 in which two or more electrically connected energy storage elements 1 are aggregated are further aggregated. The battery pack 30 may include a bus bar (not shown) for electrically connecting two or more energy storage elements 1, a bus bar (not shown) for electrically connecting two or more energy storage devices 20, and the like. The energy storage device 20 or the battery pack 30 may include a state monitoring device (not shown) for monitoring the state of one or more energy storage elements.

[0093] FIG. 2 shows an aspect in which the energy storage device 20 has a plurality of energy storage elements 1 that are rectangular batteries as shown in FIG. 1. As shown in FIG. 3, the energy storage device 20 includes a plurality of energy storage elements 1 arranged such that side surfaces face each other and are spaced apart from each other, and a pressing member 6.

[0094] (Pressing member) As shown in FIG. 3, the pressing member 6 includes two (i.e., paired) pressing portions 61 that respectively press the outer surfaces of the two energy storage elements 1 arranged on the outermost sides in the arrangement direction of the plurality of energy storage elements 1, one or more spacer portions 62 arranged between the plurality of energy storage elements 1, one or more support portions 63 arranged along the arrangement direction between the two pressing portions 61 and supporting the two pressing portions 61, and one or more pressing force adjusting portions 64 configured to connect the two pressing portions 61 and the one or more support portions 63 and adjust the pressing force of the two pressing portions 61 on the plurality of energy storage elements 1.

[0095] [Pressing portion] The two pressing portions 61 in 2 contact the outer surfaces of the two outermost power storage elements 1 and press these power storage elements 1. The pressing portion 61 is not particularly limited and is appropriately set so as to contact the side surface of the power storage element and be able to press the power storage element 1. Examples of the pressing portion 61 include a metal plate, a resin plate, and the like. As shown in FIG. 3, the shape of the pressing portion 61 can be, for example, a rectangular shape. In the embodiment shown in FIG. 3, the pressing portion 61 has one or a plurality (4 in FIG. 3) of screw holes (not shown) into which the pressing force adjusting portion 64 is screwed. In FIG. 3, in addition to the pressing force adjusting portion 64 being screwed into one (front side) of the two pressing portions 61, the pressing force adjusting portion 64 is also screwed into the other (rear side) pressing portion 61 in the same manner.

[0096] [Spacer portion] One or a plurality of spacer portions 62 are arranged between the plurality of power storage elements 1 so as to contact these plurality of power storage elements 1 and transmit the pressing force from the pressing portion 61 to the adjacent power storage elements 1. The spacer portion 62 is not particularly limited and is appropriately set so as to be able to transmit the pressing force to the adjacent power storage elements 1. Examples of the spacer portion 62 include a metal plate, a resin plate, and the like. As shown in FIG. 3, the shape of the spacer portion 62 can be, for example, a rectangular shape. As shown in FIG. 3, for example, the outer peripheral edge of the side surface of the spacer portion 62 that contacts the power storage element 1 can be formed smaller than the outer peripheral edge of the side surface of the power storage element 1. By forming it in this way, the pressing force from the pressing portion 61 can be efficiently transmitted to the power storage element 1. The number of the spacer portions 62 may be 1 or more and is not particularly limited. For example, the number of the spacer portions 62 can be appropriately set according to the number of the power storage elements 1 included in the power storage device 20.

[0097] [Support portion] One or a plurality of support portions 63 are connected to the two pressing portions 61 to support these pressing portions 61. The support portion 63 is not particularly limited and can be appropriately set so as to support the pressing portion 61. Examples of the support portion 63 include a metal plate, a resin plate, and the like. As shown in FIG. 3, the shape of the support portion 63 can be, for example, a rectangular shape. The support portion 63 can be arranged to contact, for example, a side surface perpendicular to the arrangement direction in the plurality of power storage elements 1. The support portion 63 is connected to the pressing portion 61 by a pressing force adjusting portion 64. The length of the support portion 63 in the above arrangement direction can be appropriately set to a length that can adjust the pressing force from the pressing portion 62 to a desired value.

[0098] The number of the support portions 63 may be 1 or more and is not particularly limited. As shown in FIG. 3, for example, the number of the support portions 63 is 2, and the two support portions 63 can be respectively connected to the two pressing portions 61. In the embodiment shown in FIG. 3, the support portion 63 has one or a plurality (two each on each end surface in FIG. 3) of screw holes (not shown) into which the pressing force adjusting portion 64 is screwed at both end surfaces in the above arrangement direction.

[0099] [Pressing force adjusting portion] One or a plurality of pressing force adjusting portions 64 connect the two pressing portions 61 and adjust the pressing force of the two pressing portions 61 on the plurality of power storage elements 1. In the embodiment shown in FIG. 3, the pressing force adjusting portion 64 connects the two pressing portions 61 via the support portion 63. The pressing force adjusting portion 64 is not particularly limited and can be appropriately set so as to connect the two pressing portions 61 in this way and adjust the pressing force of these pressing portions 61.

[0100] As shown in FIG. 3, for example, the pressing force adjustment part 64 may be formed by a screw member screwed into the pressing part 61 and the support part 63. As described above, in FIG. 3, in addition to the pressing force adjustment part 64 being screwed into one (front side) pressing part 61 out of the two pressing parts 61, the pressing force adjustment part 64 is also screwed into the other (rear side) pressing part 61 in the same manner. In this mode, by adjusting the screwing amount of the pressing force adjustment part 64 with respect to the pressing part 61 and the support part 63, the pressing force applied by the pressing part 61 to the power storage element 1 can be adjusted. For example, by adjusting the screwing amount of the pressing force adjustment part 64 in the direction in which the distance between the two pressing parts 61 becomes smaller, the pressing force applied by these pressing parts 61 to the power storage element 1 can be increased. On the other hand, by adjusting the screwing amount of the pressing force adjustment part 64 in the direction in which the distance between the two pressing parts 61 becomes larger, the pressing force applied by these pressing parts 61 to the power storage element 1 can be decreased.

[0101] Thus, when the pressing force adjustment part 64 is formed by a screw member, the pressing force can be adjusted only by adjusting the screwing amount, so that the adjustment of the pressing force becomes easy. The pressing force can be set so that the pressure applied to the electrode body 2 becomes 0.1 MPa as described above.

[0102] The number of the pressing force adjustment parts 64 may be 1 or more and is not particularly limited. As shown in FIG. 2, for example, the number of the pressing force adjustment parts 64 can be set to 8 (4 for each pressing part 61).

[0103] The battery pack 30 can include one or a plurality of power storage devices 20. When the battery pack 30 includes one power storage device 20, this power storage device 20 can correspond to the battery pack 30. When the battery pack 30 includes a plurality of power storage devices 20 as shown in FIG. 2, these plurality of power storage devices 20 can be connected by a connecting member (not shown).

[0104] <Method for manufacturing a power storage element> The manufacturing method of the energy storage element of the present embodiment is a method for manufacturing the energy storage element of the present embodiment described above, and includes pressing the electrode body. The manufacturing method further includes preparing the electrode body, preparing the non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. That is, the manufacturing method includes preparing the electrode body, preparing the non-aqueous electrolyte, housing the electrode body and the non-aqueous electrolyte in a container, and pressing the electrode body in a state where the electrode body and the non-aqueous electrolyte are housed in the container.

[0105] 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 with a separator interposed therebetween.

[0106] Housing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when using a non-aqueous electrolytic solution as the non-aqueous electrolyte, after injecting the non-aqueous electrolytic solution from the injection port formed in the container, the injection port may be sealed.

[0107] As for pressing the electrode body, for example, as described above, pressing the container with a pressing member can be adopted. In this case, as described above, the container can be pressed with a pressing member so that the pressure applied to the electrode body is 0.1 MPa or more. Or as described above, by using a container with high rigidity and an electrode body whose thickness becomes larger than the inner dimension of the container after charge and discharge, and performing injection of the non-aqueous electrolyte and initial charge and discharge, the electrode body can also be pressed.

[0108] The manufacturing method may further include initially charging and discharging the storage element, and may perform the pressing after the initial charging and discharging. That is, in the manufacturing method, the storage element may be initially charged and discharged in a state where the electrode body and the non-aqueous electrolyte are housed in the container, and the electrode body may be pressed after the initial charging and discharging. The number of times of the initial charging and discharging before pressing is not particularly set, but can be one or more, and one time is preferable. That is, it is preferable to press the electrode body after the first charge and discharge. By making the electrode body in a pressed state after the first charge and discharge, the gas generated by the first charge and discharge can be discharged from inside the electrode body. Thereby, the initial resistance can be reduced. Therefore, according to the manufacturing method, a storage element with a reduced initial resistance and suppressed increase in resistance accompanying charge and discharge cycles can be manufactured.

[0109] <Manufacturing Method of Storage Device> The manufacturing method of the storage device according to the present embodiment includes arranging the above-described one or more storage elements and bringing the arranged storage elements into a state of being pressed by a pressing member. For example, when manufacturing a storage device in the aspect shown in FIGS. 2 and 3, the manufacturing method of the storage device includes arranging a plurality of storage elements and a spacer portion 62 disposed between the plurality of storage elements 1 so as to be in contact with the plurality of storage elements 1, contacting two pressing portions 61 with the outer surfaces of the two storage elements 1 located on both outer sides in the arrangement direction of the plurality of storage elements 1, respectively, arranging one or more support portions 63 between the two pressing portions 61, and connecting each pressing portion 61 and each support portion 63 with one or more pressing force adjusting portions 64. The manufacturing method may also include manufacturing the storage device 20 by bringing the plurality of storage elements 1 into a state of being pressed by the pressing member 6, and connecting the manufactured plurality of storage devices 20.

[0110] <Other Embodiments> Furthermore, the energy storage element, the method for manufacturing the energy storage element, and the energy storage device of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or a well-known technique. Further, a part of the configuration of one embodiment may be deleted. In addition, a well-known technique may be added to the configuration of one embodiment.

[0111] In the above embodiment, the case where the energy storage element is used as a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) capable of charge and discharge has been described. However, the type, shape, dimensions, capacity, etc. of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, or capacitors such as lithium ion capacitors.

[0112] In the energy storage element and the energy storage device of the above embodiment, the mode in which a plurality of energy storage elements are pressed by a pressing member has been described. However, alternatively, a mode in which one energy storage element is pressed by a pressing member may be adopted.

[0113] In the energy storage device of the above embodiment, the mode in which the pressing member has a plurality of support portions has been described. However, alternatively, for example, a mode in which the pressing member has one support portion may also be adopted. In this case, for example, the support portion is in contact with each bottom surface of the plurality of energy storage elements and both outer side surfaces in a direction perpendicular to the above-described arrangement direction of the plurality of energy storage elements, and is bent so that the upper part is open (that is, the cross-sectional shape viewed in the arrangement direction is U-shaped). It can be formed by one bent plate.

[0114] In the energy storage device of the above embodiment, the mode in which the pressing force adjustment portion is formed by a screw member has been described. However, alternatively, as the pressing force adjustment portion, a connecting member other than the screw member that connects the two pressing portions and one or a plurality of support portions so that the distance between the two pressing portions can be adjusted may be adopted.

[0115] In the energy storage device of the above embodiment, the aspect in which the pressing member has the spacer portion and the support portion has been described. However, other aspects in which the pressing member does not include the spacer portion and the support portion can also be adopted. In this case, for example, two pressing portions can be directly connected by one or a plurality of pressing force adjusting portions.

Example

[0116] Hereinafter, the present invention will be described more specifically by way of examples. The present invention is not limited to the following examples.

[0117] [Example 1] (Fabrication of positive electrode plate) As the positive electrode active material, LiNi having an average primary particle diameter of 2.0 μm, a median diameter and an average secondary particle diameter of 4.4 μm, and a BET specific surface area of 0.6 m 2 / g 0.6 Mn 0.2 Co 0.2 O2 powder was used. A positive electrode binder paste containing the positive electrode active material: polyvinylidene fluoride (PVDF): acetylene black (AB) in a ratio of 90:5:5 (in terms of solid content) by mass was prepared. This positive electrode binder paste was applied to both sides of an aluminum foil as a positive electrode substrate so that the coating amount of the positive electrode active material was 0.0128 g / cm 2 Then, the positive electrode active material layer was formed by drying and pressing, and a positive electrode was obtained.

[0118] (Measurement of average diameter of primary particles) The average diameter of the above primary particles was determined by measuring the diameters of at least 50 primary particles in a scanning electron microscope image of a cross section obtained by cutting the formed positive electrode active material layer in the thickness direction by the method described above and averaging the measured values.

[0119] (Measurement of average diameter of secondary particles and median diameter of positive electrode active material) The average diameter of the secondary particles was measured by the following method. Based on the particle size distribution measured by the laser diffraction / scattering method for a dilution obtained by diluting the particles with a solvent in accordance with JIS-Z-8825 (2013), the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001) becomes 50% was determined. The measured value was taken as the average diameter of the secondary particles and the median diameter of the positive electrode active material.

[0120] (Measurement of BET specific surface area) The BET specific surface area of the positive electrode active material (here, secondary particles) was measured by the following method. Using a specific surface area measuring device (trade name: MONOSORB) manufactured by Yuasa Ionics, the nitrogen adsorption amount (m 2 ) for the sample was determined by the single-point method. The value obtained by dividing the obtained adsorption amount by the mass (g) of the sample was taken as the BET specific surface area (m 2 / g). In the measurement, gas adsorption was performed by cooling using liquid nitrogen. Also, preliminary heating was performed at 120°C for 15 minutes before cooling. The input amount of the measurement sample was set to 0.5 g ± 0.01 g.

[0121] (Fabrication of negative electrode plate) Graphite was used as the negative electrode active material. A negative electrode binder paste containing the negative electrode active material, SBR, and CMC in a mass ratio of 97:2:1 was prepared. This negative electrode binder paste was applied to both sides of a copper foil as a negative electrode substrate so that the coating amount of the negative electrode active material was 0.0070 g / cm 2 , and a negative electrode was obtained by drying and pressing.

[0122] (Preparation of non-aqueous electrolyte) LiPF6 was dissolved as an electrolyte salt in a non-aqueous solvent obtained by mixing EC:DMC:EMC in a volume ratio of 30:40:30 at a concentration of 1.2 mol / dm 3 to obtain a non-aqueous electrolyte.

[0123] (Fabrication of energy storage element) As the separator, a microporous polyolefin film having an inorganic heat-resistant layer formed on its surface was used. Through this separator, the positive electrode and the negative electrode were laminated and wound to produce a wound electrode body. This electrode body was housed in an aluminum container, the non-aqueous electrolyte was injected therein, and then it was sealed.

[0124] After this sealing, charge and discharge were performed once as the initial charge and discharge, and then, by making the pressing member press both side faces of the container, the power storage element of Example 1 was obtained. At this time, as shown in Table 1, the container was pressed with the pressing member so that the pressure applied to the electrode body became 0.1 MPa. In this power storage element, since the container was in a pressed state, the electrode body in the container was in a pressed state. The pressure applied to the electrode body was measured with a strain gauge type load cell.

[0125] As the pressing member, a pressing member including two metal plate-like pressing parts arranged in parallel so as to contact both side faces of the container and one pressing force adjusting part that can be screwed into the two pressing parts to connect these pressing parts and adjust the distance therebetween (that is, the pressing force) was used. By this pressing force adjusting part, one power storage element was made to be in a pressed state. The adjustment of the above pressure was performed by adjusting the screwing amount of the pressing force adjusting part.

[0126] [Example 2, Comparative Examples 1 to 3] As the positive electrode active material, except that the average diameter of primary particles, the average diameter of secondary particles, the ratio of the average diameter of secondary particles to the average diameter of primary particles, the median diameter, and the BET specific surface area are the values shown in Table 1, the power storage element of Example 2 was produced in the same manner as in Example 1. The power storage element of Comparative Example 1 was produced in the same manner as in Example 2 except that pressing by the pressing member was not performed. As the positive electrode active material, except that the average diameter of primary particles, the average diameter of secondary particles, the ratio of the average diameter of secondary particles to the average diameter of primary particles, the median diameter, and the BET specific surface area are the values shown in Table 1 and the pressure applied to the electrode body is the value shown in Table 1, the power storage element of Comparative Example 2 was produced in the same manner as in Example 1. The power storage element of Comparative Example 3 was produced in the same manner as in Comparative Example 2 except that pressing by the pressing member was not performed.

[0127] (Measurement of Initial Discharge Capacity) For each of the obtained energy storage elements, with the charge termination voltage set to 4.25 V, under a temperature environment of 25 °C, after constant current charging at a current value of 0.1 C, constant voltage charging was performed. The end condition of charging was until the charging current reached 0.01 C. After providing a 10-minute rest, with the discharge termination voltage set to 2.75 V, constant current discharge was performed at a current value of 0.2 C. After providing a 10-minute rest, with the charge termination voltage set to 4.25 V, under a temperature environment of 25 °C, after constant current charging at a current value of 0.2 C, constant voltage charging was performed. The end condition of charging was until the charging current reached 0.01 C. After providing a 10-minute rest, with the discharge termination voltage set to 2.75 V, constant current discharge was performed at a current value of 0.2 C. This discharge capacity was defined as the "initial discharge capacity".

[0128] (Charge and Discharge Cycle Test) After storing each energy storage element in a constant temperature bath at 60 °C for 4 hours, with the charge termination voltage set to 4.25 V for each, after constant current charging at a current value of 2 C, constant voltage charging was performed. The end condition of charging was until the charging current reached 0.01 C. Next, a 10-minute rest was provided after charging. Then, with the discharge termination voltage set to 2.75 V, constant current discharge was performed at a current value of 2 C, and a 10-minute rest was provided. These charging and discharging steps were regarded as one cycle, and this cycle was repeated 300 times. Charging, discharging, and resting were all carried out in a constant temperature bath at 60 °C.

[0129] (Increase Rate of Low Temperature DC Resistance (DCR) after Charge and Discharge Cycle Test) The increase rate of the low-temperature direct current resistance (DCR) of the energy storage element after the charge-discharge cycle test was evaluated. For each energy storage element before the charge-discharge cycle test and after the charge-discharge cycle test of 300 cycles, in a constant temperature bath at 25°C, an amount of electricity corresponding to 50% of the initial discharge capacity was charged at a constant current with a current value of 0.1C. Under this condition, the state of charge (SOC) of each energy storage element was set to 50%. Next, after each energy storage element was stored in a constant temperature bath at -10°C for 4 hours, it was discharged for 10 seconds at current values of 0.1C, 0.2C, and 0.3C, respectively. After each discharge ended, constant current charging was performed at a current value of 0.1C to set the SOC to 50%. From the current-voltage performance graph obtained by plotting the voltage 10 seconds after the start of discharge on the vertical axis and the discharge current value on the horizontal axis, the DCR value, which is the value corresponding to the slope, was obtained. Then, the value representing the increase rate of "DCR after the charge-discharge cycle test" relative to "DCR before the charge-discharge cycle test" as a percentage was defined as the "low-temperature DCR increase rate (%)" and was obtained by the following formula. Low-temperature DCR increase rate = (DCR after the charge-discharge cycle test) / (DCR before the charge-discharge cycle test) × 100 - 100 The results are shown in Table 1 below.

[0130]

Table 1

[0131] As shown in Table 1, it was shown that when the ratio of the average diameter of the secondary particles to the average diameter of the primary particles is less than 11 and the electrode body is in a pressed state, an increase in resistance associated with the charge-discharge cycle can be suppressed. Furthermore, in addition to the above ratio being less than 11, it was shown that when the pressure applied to the electrode body is 0.1 MPa or more, an increase in resistance associated with the charge-discharge cycle can be more effectively suppressed. Also, it was shown that when the product of the BET specific surface area and the median diameter of the positive electrode active material is 4.5 or less, an increase in resistance associated with the charge-discharge cycle can be more effectively suppressed.

Description of Symbols

[0132] 1 Energy storage element 2 Electrode body 3 Container 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 6 Pressing member 61 Pressing part 62 Spacer part 63 Support part 64 Pressing force adjustment part 20 Power storage device 30 Battery pack

Claims

1. An electrode body including 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, the positive electrode contains a positive electrode active material, the positive electrode active material contains a plurality of particles satisfying at least one of the following conditions (1) and (2), a power storage element in a state where the electrode body is pressed. (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, and a plurality of secondary particles in which the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

2. The power storage element according to Claim 1, wherein the pressure applied to the electrode body is 0.1 MPa or more.

3. The power storage element according to Claim 1 or 2, wherein the positive electrode active material is a transition metal oxide containing nickel, and the product of the BET specific surface area and the median diameter of the positive electrode active material is 4.5 or less.

4. A method for manufacturing a power storage element including an electrode body including 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, comprising pressing the electrode body, the positive electrode contains a positive electrode active material, a method for manufacturing a power storage element, wherein the positive electrode active material contains a plurality of particles satisfying at least one of the following conditions (1) and (2). (1) A plurality of primary particles that do not form secondary particles (2) Secondary particles formed by aggregation of a plurality of primary particles, and a plurality of secondary particles in which the ratio of the average diameter of the secondary particles to the average diameter of the primary particles forming the secondary particles is less than 11

5. The method for manufacturing a power storage element according to Claim 4, wherein the pressure applied to the electrode body is 0.1 MPa or more.

6. further comprising initially charging and discharging the power storage element, The method for manufacturing a power storage element according to Claim 4 or 5, wherein the electrode body is pressed after the initial charging and discharging.

7. One or a plurality of power storage elements according to any one of Claims 1 to 3, and a pressing member, a power storage device in which the pressing member presses the electrode body of the power storage element by pressing the container.

Images