JP2018098138A - Power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage element in which the difference in amount of discharged electricity between high and low rates is reduced.SOLUTION: A power storage element comprises: an electrode having an active material layer. A particle size frequency distribution of particles included in the active material layer on a volume basis has a peak in each of a first range of 0.5 to 2.0 μm, exclusive 2.0 μm in particle size, a second range of 2.0 to 10 μm, exclusive 10 μm in particle size, and a third range of 10 μm or more in particle size. Supposing that the frequencies (%) of the peaks in the first, second and third ranges are P1, P2 and P3 respectively, the particle size of particles at the peak in the second range is D2, and the particle size of particles of the peak in the third range is D3, they satisfy all the following relational expressions (1)-(3): 0.6≤[P2/P1] (1); 0.1≤[P3/P2]≤0.7 (2); and 4.5≤[D3/D2]≤10.5 (3). Further, as to the power storage element, it is preferred that the following relational expression (4) is satisfied: [P2/P1]≤2.0 (4).SELECTED DRAWING: None

Description

  The present invention relates to a power storage device such as a lithium ion secondary battery.

  Conventionally, a lithium ion secondary battery including an electrode having a current collector and an active material layer containing active material particles is known (for example, Patent Document 1).

In the battery described in Patent Document 1, the active material layer includes monoclinic β-type titanium composite oxide particles and spinel lithium titanate particles. In the battery described in Patent Document 1, when the frequency distribution of the particle size of particles contained in the active material layer is measured by a laser diffraction scattering method, the first peak P1 appears in the range of 0.3 μm to 3 μm, and 5 μm. The second peak P2 appears in the range of 20 μm or less, and the ratio F _P1 / _FP 2 of the frequency FP1 of the first peak P1 to the frequency _FP2 of the second peak _P2 is 0.4 or more and 2.3 or less. It is.

  In the battery described in Patent Document 1, there is a case where the difference in discharge electricity between the high rate and the low rate may be large, and the difference in discharge electricity between the high rate and the low rate is suppressed from increasing. There is a demand for a storage element.

JP 2013-105703 A

  This embodiment makes it a subject to provide the electrical storage element by which the difference in the amount of discharge electricity with a high rate and a low rate was suppressed.

The power storage device of the present embodiment includes an electrode having an active material layer, and the particle size frequency distribution based on the volume of particles contained in the active material layer is a first range in which the particle size is 0.5 μm or more and less than 2.0 μm, Each of the second range having a particle size of 2.0 μm or more and less than 10 μm and the third range having a particle size of 10 μm or more have peaks, and the frequency of peaks in the first range, the second range, and the third range ( %) Is P1, P2, and P3, the particle diameter of the second range peak particle is D2, and the particle diameter of the third range peak particle is D3. Satisfy all (3).
0.6 ≦ [P2 / P1] Relational expression (1)
0.1 ≦ [P3 / P2] ≦ 0.7 Relational expression (2)
4.5 ≦ [D3 / D2] ≦ 10.5 Relational expression (3)
With such a configuration, it is possible to provide an energy storage device in which an increase in the difference in the amount of discharged electricity between the high rate and the low rate is suppressed.

In the above electricity storage device, the relational expression (1) may further satisfy the following relational expression (4). With such a configuration, it is possible to suppress a decrease in output performance after repeated charging and discharging.
[P2 / P1] ≦ 2.0 Relational expression (4)

  According to the present embodiment, it is possible to provide a power storage device in which an increase in the amount of discharge electricity between a high rate and a low rate is suppressed.

FIG. 1 is a perspective view of a power storage device according to this embodiment. 2 is a cross-sectional view taken along the line II-II in FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is a view for explaining the configuration of the electrode body of the energy storage device according to the embodiment. FIG. 5 is a cross-sectional view of the superimposed positive electrode, negative electrode, and separator (VV cross-section in FIG. 4). FIG. 6 is a perspective view of a power storage device including the power storage element according to the embodiment. FIG. 7 is an example of a particle size frequency distribution diagram based on the volume of particles contained in the active material layer.

  Hereinafter, an embodiment of a power storage device according to the present invention will be described with reference to FIGS. Examples of the power storage element include a primary battery, a secondary battery, and a capacitor. In the present embodiment, a chargeable / dischargeable secondary battery will be described as an example of a power storage element. In addition, the name of each component (each component) of this embodiment is a thing in this embodiment, and may differ from the name of each component (each component) in background art.

  The electricity storage device 1 of the present embodiment is a nonaqueous electrolyte secondary battery. More specifically, the electricity storage element 1 is a lithium ion secondary battery that utilizes electron movement that occurs in association with movement of lithium ions. This type of power storage element 1 supplies electric energy. The electric storage element 1 is used singly or in plural. Specifically, the storage element 1 is used as a single unit when the required output and the required voltage are small. On the other hand, power storage element 1 is used in power storage device 100 in combination with other power storage elements 1 when at least one of a required output and a required voltage is large. In the power storage device 100, the power storage element 1 used in the power storage device 100 supplies electric energy.

  As shown in FIGS. 1 to 5, the storage element 1 includes an electrode body 2 including a positive electrode 11 and a negative electrode 12, a case 3 that houses the electrode body 2, and an external terminal 7 that is disposed outside the case 3. And an external terminal 7 that is electrically connected to the electrode body 2. In addition to the electrode body 2, the case 3, and the external terminal 7, the power storage element 1 includes a current collector 5 that electrically connects the electrode body 2 and the external terminal 7.

  The electrode body 2 is formed by winding a laminated body 22 in which the positive electrode 11 and the negative electrode 12 are laminated with the separator 4 being insulated from each other.

  The positive electrode 11 includes a metal foil 111 (current collector foil) and an active material layer 112 that is stacked on the surface of the metal foil 111 and includes an active material. In the present embodiment, the active material layer 112 overlaps both surfaces of the metal foil 111. In addition, the thickness of the positive electrode 11 is usually 40 μm or more and 150 μm or less.

  The metal foil 111 has a strip shape. The metal foil 111 of the positive electrode 11 of this embodiment is, for example, an aluminum foil. The positive electrode 11 has an uncovered portion (a portion where the positive electrode active material layer is not formed) 115 of the positive electrode active material layer 112 at one edge portion in the width direction, which is the short direction of the band shape.

The positive electrode active material layer 112 includes a particulate active material (active material particles), a particulate conductive aid, and a binder. The thickness of the positive electrode active material layer 112 (for one layer) is usually 12 μm or more and 70 μm or less. The basis weight of the positive electrode active material layer 112 (for one layer) is usually 6 mg / cm ² or more and 17 mg / cm ² or less. Density of the positive electrode active material layer 112 may also be 2.00 g / cm ³ or more 3.00 g / cm ³ or less, or may be 2.32 g / cm ³ or more 2.83 g / cm ³ or less. The basis weight and density are for one layer arranged so as to cover one surface of the metal foil 111.

The volume-based particle size frequency distribution of the particles contained in the positive electrode active material layer 112 includes a first range in which the particle size is 0.5 μm or more and less than 2.0 μm, a second range in which the particle size is 2.0 μm or more and less than 10 μm, and , Each has a peak in the third range of particle diameters of 10 μm or more and 100 μm or less. The frequency (%) of the peaks in the first range, the second range, and the third range are P1, P2, and P3, the particle diameter (μm) of the peak in the second range is D2, and the peak in the third range When the particle diameter (μm) is D3, the following relational expressions (1) to (3) are all satisfied. Relational expression (1) may further satisfy the following relational expression (4).
0.6 ≦ [P2 / P1] Relational expression (1)
0.1 ≦ [P3 / P2] ≦ 0.7 Relational expression (2)
4.5 ≦ [D3 / D2] ≦ 10.5 Relational expression (3)
[P2 / P1] ≦ 2.0 Relational expression (4).

  The presence of a peak in each of the above ranges is confirmed by the following method. In a graph of a curve obtained by differentiating a particle size frequency distribution curve once, a point where the numerical value on the vertical axis of such a curve changes from positive to negative (0) It is determined that there is a peak. The particle diameter corresponding to the portion that changes from positive to negative is the particle diameter at the peak of the peak in the particle size frequency distribution curve. When there are a plurality of peaks in each range, the largest peak in each range is adopted.

  The positive electrode active material layer 112 includes, as active material particles, primary particles of active material and secondary particles in which a plurality of primary particles are aggregated. Specifically, the positive electrode active material layer 112 includes primary particles that exist independently independently of each other, and secondary particles in which a plurality of primary particles are condensed. The primary particles present in the positive electrode active material layer 112 are present alone or aggregate to form secondary particles. The secondary particles include at least secondary particles having two or more hollow portions having a pore size larger than the average primary particle size.

  For the positive electrode active material layer 112 having a peak in each of the above ranges, for example, active material particles having an average primary particle diameter of a specific size and an active material particle having an average particle diameter D50 of a specific size are adopted. Is obtained. For example, the positive electrode active material layer 112 having a peak in each of the above ranges has an average primary particle diameter of 0.5 μm or more and less than 2.0 μm, an average particle diameter D50 of 2.0 μm or more and less than 10 μm, and an average particle diameter. It is obtained by adopting active material particles having D90 of 10 μm or more. In addition, the positive electrode active material layer 112 having a peak in each of the above ranges can be obtained by, for example, mixing the powders of active material particles having different average particle sizes at an appropriate mixing ratio to produce the positive electrode active material layer 112. Can be prepared. For example, the positive electrode active material layer 112 having a peak in each of the ranges described above includes an active material particle powder having an average particle diameter D50 of 2.0 μm or more and less than 10 μm, and an active material particle powder having an average particle diameter D50 of 10 μm or more. It is obtained by mixing the body. Moreover, the value of each said relational expression can be adjusted by changing the press pressure at the time of producing the specific surface area of the positive electrode active material or the positive electrode 11, for example. By increasing the pressing pressure, it is possible to increase the frequency of the peak in the first range where the particle diameter is 0.5 μm or more and less than 2.0 μm. The value of each of the above relational expressions can be adjusted, for example, by changing the mixing ratio of powders of active material particles having different average particle diameters.

The specific surface area of the active material, 0.3 m ² / g or more 3.0 m ² / g by mass or less well, may is 1.0 m ² / g or more 2.0 m ² / g or less. The specific surface area of the active material is calculated from the amount of nitrogen adsorbed [m ² ] with respect to the measurement sample obtained by the one-point method, using a specific surface area measuring device (trade name: MONOSORB) manufactured by Yuasa Ionics. Specifically, the input amount of the measurement sample is 0.5 g ± 0.01 g, and the preheating is 120 ° C. for 15 minutes. Moreover, it cools using liquid nitrogen and measures the nitrogen gas adsorption amount of a cooling process. The specific surface area is calculated by dividing the measured adsorption amount (m ² ) by the active material mass (g).

  In the particle size frequency distribution, the frequency with respect to the particle size of the active material and the conductive additive is represented. On the other hand, the binder has a small influence on the result of the particle size frequency distribution. The particle size frequency distribution is obtained by measurement using a laser diffraction / scattering type particle size distribution measuring apparatus. The particle size frequency distribution is determined on the basis of the volume of the particles. The measurement conditions are explained in detail in the examples.

  In addition, in the particle size frequency distribution obtained with the particles (active material particles) after the treatment for removing the conductive additive from the positive electrode active material layer 112, the above relational expressions (1) to (4) may be satisfied. .

  The average primary particle diameter of the active material particles in the positive electrode active material layer 112 is usually 0.1 μm or more and 2.0 μm or less. The average primary particle diameter is obtained by measuring the diameters of at least 100 primary particle diameters and averaging the measured values in a scanning electron microscope observation image of the cross section in the thickness direction of the positive electrode active material layer 112. If the primary particles are not spherical, the longest diameter is measured as the diameter.

  The peak frequency P1 in the first range may be 1% or more and 4% or less. The peak frequency P2 in the second range may be 1% or more and 5% or less. The peak frequency P3 in the third range may be not less than 0.1% and not more than 4.0%. Accordingly, [P2 / P1] may be not less than 0.71 and not more than 1.65. [P3 / P2] may be 0.11 or more and 0.67 or less.

  The particle diameter (μm) (hereinafter referred to as D1) of the peak in the first range may be 0.7 μm or more and 1.5 μm or less. The particle diameter D2 of the peak in the second range may be 2 μm or more and 5 μm or less. The particle diameter D3 of the peak in the third range may be 10 μm or more and 30 μm or less. Accordingly, [D2 / D1] may be 2 or more and 7 or less. [D3 / D2] may be 5 or more and 10 or less.

The active material of the positive electrode 11 is a compound that can occlude and release lithium ions. The active material of the positive electrode 11 is, for example, a lithium metal oxide. Specifically, the active material of the positive electrode, for _example, Li p _MeO t (Me represents one or more transition metal) complex oxide represented by _{(Li p Co s O 2,} Li p Ni q O _{2, Li p Mn r O 4} , Li p Ni q Co s Mn r O 2 , etc.), _{or, Li p Me u (XO v} ) w (Me represents one or more transition metals, X is e.g. P, Si, B, a polyanion compounds represented by the representative of the _{V) (Li p Fe u PO} 4, Li p Mn u PO 4, Li p Mn u SiO 4, Li p Co u PO 4 F , etc.).

In this embodiment, the active material of the positive electrode _{11, Li p Ni q Mn r Co} s O lithium-metal composite oxide represented by the chemical composition of the _t (where a 0 <p ≦ 1.3, q + r + s = 1 0 ≦ q ≦ 1, 0 ≦ r ≦ 1, 0 ≦ s ≦ 1, and 1.7 ≦ t ≦ 2.3. Note that 0 <q <1, 0 <r <1, and 0 <s <1.

Additional such _{Li p Ni q Mn r Co s} O lithium-metal composite oxide represented by the chemical composition of the _t, for _{example, LiNi 1/3 Co 1/3 Mn 1/3 O} 2, LiNi 1/6 Co 1 _{/ 6} Mn _2/3 O ₂ , LiCoO ₂ and the like. At this time, trace element other than the chemical composition may be included in the lithium metal composite oxide.

  Examples of the binder used for the positive electrode active material layer 112 include polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, and polymethacrylic acid. Acid, styrene butadiene rubber (SBR). The binder of this embodiment is polyvinylidene fluoride.

  The conductive additive of the positive electrode active material layer 112 is a carbonaceous material containing 98% by mass or more of carbon. Examples of the carbonaceous material include ketjen black (registered trademark), acetylene black, and graphite. The positive electrode active material layer 112 of this embodiment has acetylene black as a conductive additive.

  The positive electrode active material layer 112 usually contains 2% by mass or more and 8% by mass or less of a conductive additive, and contains 1% by mass or more and 6% by mass of a binder. The proportion of the conductive additive and the binder contained in the positive electrode active material layer 112 may be 1% by mass or more and 3% by mass or less of the conductive auxiliary with respect to the binder.

  The negative electrode 12 includes a metal foil 121 (current collector foil) and a negative electrode active material layer 122 formed on the metal foil 121. In the present embodiment, the negative electrode active material layer 122 is overlaid on both surfaces of the metal foil 121. The metal foil 121 has a strip shape. The metal foil 121 of the negative electrode of this embodiment is, for example, a copper foil. The negative electrode 12 has a non-covered portion (a portion where the negative electrode active material layer is not formed) 125 of the negative electrode active material layer 122 at one edge portion in the width direction which is the short direction of the belt shape. The thickness of the negative electrode 12 is usually 40 μm or more and 150 μm or less.

  The negative electrode active material layer 122 includes a particulate active material (active material particles) and a binder. The negative electrode active material layer 122 is disposed so as to face the positive electrode 11 with the separator 4 interposed therebetween. The width of the negative electrode active material layer 122 is larger than the width of the positive electrode active material layer 112.

  The active material of the negative electrode 12 can contribute to the electrode reaction of the charge reaction and the discharge reaction in the negative electrode 12. For example, the active material of the negative electrode 12 has an alloying reaction with carbon materials such as graphite and amorphous carbon (non-graphitizable carbon and graphitizable carbon), or lithium ions such as silicon (Si) and tin (Sn). The resulting material. The active material of the negative electrode of this embodiment is amorphous carbon. More specifically, the negative electrode active material is non-graphitizable carbon.

The thickness of the negative electrode active material layer 122 (for one layer) is usually 10 μm or more and 50 μm or less. The basis weight (one layer) of the negative electrode active material layer 122 is usually 3 mg / cm ² or more and 10 mg / cm ² or less. The density (one layer) of the negative electrode active material layer 122 is usually 0.50 g / cm ³ or more and 6.00 g / cm ³ or less.

  The binder used for the negative electrode active material layer 122 is the same as the binder used for the positive electrode active material layer 112. The binder of this embodiment is styrene butadiene rubber (SBR).

  In the negative electrode active material layer 122, the ratio of the binder may be 1% by mass or more and 10% by mass or less with respect to the total mass of the active material particles and the binder.

  The negative electrode active material layer 122 may further include a conductive additive such as ketjen black (registered trademark), acetylene black, or graphite. The negative electrode active material layer 122 of this embodiment does not have a conductive additive.

  In the electrode body 2 of the present embodiment, the positive electrode 11 and the negative electrode 12 configured as described above are wound in a state where they are insulated by the separator 4. That is, in the electrode body 2 of the present embodiment, the stacked body 22 of the positive electrode 11, the negative electrode 12, and the separator 4 is wound. The separator 4 is a member having insulating properties. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12. Thereby, in the electrode body 2 (specifically, the laminated body 22), the positive electrode 11 and the negative electrode 12 are insulated from each other. The separator 4 holds the electrolytic solution in the case 3. Thereby, at the time of charging / discharging of the electrical storage element 1, lithium ion moves between the positive electrode 11 and the negative electrode 12 which are laminated | stacked alternately on both sides of the separator 4. FIG.

  The separator 4 has a strip shape. The separator 4 has a porous separator base material. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 in order to prevent a short circuit between the positive electrode 11 and the negative electrode 12. The separator 4 of this embodiment has only the separator base material 41.

  The separator base material 41 is configured to be porous. The separator base material 41 is, for example, a woven fabric, a nonwoven fabric, or a porous film. Examples of the material for the separator substrate include polymer compounds, glass, and ceramics. Examples of the polymer compound include a group consisting of polyester such as polyacrylonitrile (PAN), polyamide (PA), polyethylene terephthalate (PET), polyolefin (PO) such as polypropylene (PP) and polyethylene (PE), and cellulose. The at least 1 sort selected from more is mentioned.

The electrode body 2 of this embodiment has the inorganic porous layer 8 arrange | positioned between the separator base material 41 and the positive electrode active material layer 112. FIG. The inorganic porous layer 8 includes inorganic particles having at least electrical insulation, and further includes a binder. The electrical insulation property of the inorganic porous layer 8 is higher than the electrical insulation properties of the positive electrode active material layer 112 and the negative electrode active material layer 122. The electrical conductivity of the inorganic porous layer 8 is less than 10 ⁻⁶ S / m. The inorganic porous layer 8 may also be disposed between the separator base material 41 and the negative electrode active material layer 122.

The inorganic porous layer 8 is formed porous by voids between inorganic particles so that Li ions and the like can move between the positive electrode 11 and the negative electrode 12. The inorganic particles contain 95% by mass or more of an insulating material having an electric conductivity of less than 10 ⁻⁶ S / m.

  The inorganic porous layer 8 usually contains 30% by mass or more and 99% by mass or less of inorganic particles. The inorganic porous layer 8 usually contains 1% by mass or more and 10% by mass or less of a binder.

Examples of the inorganic particles include oxide particles, nitride particles, ionic crystal particles, covalently bonded crystal particles, clay particles, mineral resource-derived substances, or particles of these artificial substances. Examples of the oxide particles (metal oxide particles) include particles such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₂ , ZrO, and alumina-silica composite oxide. Examples of the nitride particles include particles such as aluminum nitride and silicon nitride. Examples of the ionic crystal particles include particles of calcium fluoride, barium fluoride, barium sulfate, and the like. Examples of the covalently bonded crystal particles include particles such as silicon and diamond. Examples of the clay particles include particles such as talc and montmorillonite. Examples of particles of mineral resource-derived substances or those artificial substances include particles of boehmite (alumina hydrate), zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, and the like. A fired body obtained by firing a natural mineral containing a hydrate (for example, the above-mentioned clay or mineral resource-derived substance) can also be employed. In this embodiment, the inorganic particles are Al ₂ O ₃ particles.

  Examples of the binder of the inorganic porous layer 8 include polyacrylonitrile, polyvinylidene fluoride (PVdF), a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, Examples include sphazene, polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, or polycarbonate.

  The width of the separator 4 (the dimension of the strip shape in the short direction) is slightly larger than the width of the negative electrode active material layer 122. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 that are stacked in a state of being displaced in the width direction so that the positive electrode active material layer 112 and the negative electrode active material layer 122 overlap. At this time, as shown in FIG. 4, the non-covered portion 115 of the positive electrode 11 and the non-covered portion 125 of the negative electrode 12 do not overlap. That is, the uncovered portion 115 of the positive electrode 11 protrudes in the width direction from the region where the positive electrode 11 and the negative electrode 12 overlap, and the non-covered portion 125 of the negative electrode 12 extends from the region where the positive electrode 11 and the negative electrode 12 overlap in the width direction ( It protrudes in a direction opposite to the protruding direction of the non-covering portion 115 of the positive electrode 11. The electrode body 2 is formed by winding the stacked positive electrode 11, negative electrode 12, and separator 4, that is, the stacked body 22. The portion where only the uncovered portion 115 of the positive electrode 11 or the uncovered portion 125 of the negative electrode 12 is stacked constitutes the uncoated stacked portion 26 in the electrode body 2.

  The uncoated laminated portion 26 is a portion that is electrically connected to the current collector 5 in the electrode body 2. The non-coated laminated portion 26 has two parts (halved uncoated laminated portions) across the hollow portion 27 (see FIG. 4) in the winding center direction view of the wound positive electrode 11, negative electrode 12, and separator 4. ) 261.

  The uncoated laminated portion 26 configured as described above is provided on each electrode of the electrode body 2. That is, the non-coated laminated portion 26 in which only the non-coated portion 115 of the positive electrode 11 is laminated constitutes the non-coated laminated portion of the positive electrode 11 in the electrode body 2, and the non-coated laminated layer in which only the non-coated portion 125 of the negative electrode 12 is laminated. The portion 26 constitutes an uncoated laminated portion of the negative electrode 12 in the electrode body 2.

  The case 3 includes a case main body 31 having an opening and a cover plate 32 that closes (closes) the opening of the case main body 31. The case 3 houses the electrolytic solution in the internal space together with the electrode body 2 and the current collector 5. Case 3 is formed of a metal having resistance to the electrolytic solution. The case 3 is made of an aluminum-based metal material such as aluminum or an aluminum alloy, for example. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material obtained by bonding a resin such as nylon to aluminum.

The electrolytic solution is a non-aqueous electrolytic solution. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrolyte salt is LiClO ₄ , LiBF ₄ , LiPF ₆ or the like. The electrolytic solution of this embodiment is obtained by dissolving 0.5 to 1.5 mol / L LiPF ₆ in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a predetermined ratio.

  The case 3 is formed by joining the peripheral edge of the opening of the case main body 31 and the peripheral edge of the rectangular lid plate 32 in an overlapping state. The case 3 has an internal space defined by the case main body 31 and the lid plate 32. In this embodiment, the opening peripheral part of the case main body 31 and the peripheral part of the cover plate 32 are joined by welding.

  In the following, as shown in FIG. 1, the long side direction of the cover plate 32 is the X-axis direction, the short side direction of the cover plate 32 is the Y-axis direction, and the normal direction of the cover plate 32 is the Z-axis direction. The case body 31 has a rectangular tube shape (that is, a bottomed rectangular tube shape) in which one end in the opening direction (Z-axis direction) is closed. The lid plate 32 is a plate-like member that closes the opening of the case body 31.

  The cover plate 32 has a gas discharge valve 321 that can discharge the gas in the case 3 to the outside. The gas discharge valve 321 discharges gas from the inside of the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. The gas discharge valve 321 is provided at the center of the lid plate 32 in the X-axis direction.

  The case 3 is provided with a liquid injection hole for injecting an electrolytic solution. The liquid injection hole communicates the inside and the outside of the case 3. The liquid injection hole is provided in the lid plate 32. The liquid injection hole is sealed (closed) by a liquid injection stopper 326. The liquid filling tap 326 is fixed to the case 3 (the cover plate 32 in the example of the present embodiment) by welding.

  The external terminal 7 is a part that is electrically connected to the external terminal 7 of another power storage element 1 or an external device. The external terminal 7 is formed of a conductive member. For example, the external terminal 7 is formed of a highly weldable metal material such as an aluminum-based metal material such as aluminum or aluminum alloy, or a copper-based metal material such as copper or copper alloy.

  The external terminal 7 has a surface 71 to which a bus bar or the like can be welded. The surface 71 is a flat surface. The external terminal 7 has a plate shape extending along the lid plate 32. Specifically, the external terminal 7 has a rectangular plate shape when viewed in the Z-axis direction.

  The current collector 5 is disposed in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be energized. The current collector 5 of the present embodiment is connected to the electrode body 2 through the clip member 50 so as to be energized. That is, the electrical storage element 1 includes a clip member 50 that connects the electrode body 2 and the current collector 5 so as to allow energization.

  The current collector 5 is formed of a conductive member. As shown in FIG. 2, the current collector 5 is disposed along the inner surface of the case 3. The current collector 5 is disposed on each of the positive electrode 11 and the negative electrode 12 of the power storage element 1. In the power storage device 1 of the present embodiment, the current collectors 5 are disposed in the case 3 on the uncoated stacked portion 26 of the positive electrode 11 and the uncoated stacked portion 26 of the negative electrode 12, respectively.

  The current collector 5 of the positive electrode 11 and the current collector 5 of the negative electrode 12 are formed of different materials. Specifically, the current collector 5 of the positive electrode 11 is formed of, for example, aluminum or an aluminum alloy, and the current collector 5 of the negative electrode 12 is formed of, for example, copper or a copper alloy.

  In the electricity storage device 1 of the present embodiment, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) housed in a bag-like insulating cover 6 that insulates the electrode body 2 and the case 3 is the case 3. Housed inside.

  Next, the manufacturing method of the electrical storage element 1 of the said embodiment is demonstrated.

  In the manufacturing method of the electrical storage element 1, first, the mixture containing an active material is apply | coated to metal foil (current collection foil), an active material layer is formed, and an electrode (the positive electrode 11 and the negative electrode 12) is produced. Next, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped to form the electrode body 2. Subsequently, the electrode body 2 is put in the case 3 and the electrolytic solution is put in the case 3 to assemble the power storage element 1.

  In producing the electrode (positive electrode 11), the positive electrode active material layer 112 is formed by applying a mixture containing an active material, a binder, and a solvent to both surfaces of the metal foil. By changing the coating amount of the mixture, the thickness and basis weight of the positive electrode active material layer 112 can be adjusted. As a coating method for forming the positive electrode active material layer 112, a general method is employed. Further, the positive electrode active material layer 112 is roll-pressed at a predetermined pressure. By changing the pressing pressure, the thickness and density of the positive electrode active material layer 112 can be adjusted. If necessary, a composition containing inorganic particles, a binder, and a solvent is applied to the positive electrode active material layer 112 to form an inorganic porous layer. In addition, the negative electrode 12 is produced in the same manner as described above without forming the inorganic porous layer.

  In the formation of the electrode body 2, the electrode body 2 is formed by winding a laminate 22 in which the separator 4 is sandwiched between the positive electrode 11 and the negative electrode 12. Specifically, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped so that the positive electrode active material layer 112 and the negative electrode active material layer 122 face each other through the separator 4, thereby forming the laminate 22. The laminated body 22 is wound to form the electrode body 2.

  In assembling the electricity storage element 1, the electrode body 2 is inserted into the case body 31 of the case 3, the opening of the case body 31 is closed with the cover plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case main body 31 with the cover plate 32, the electrode body 2 is inserted into the case main body 31, the positive electrode 11 and the one external terminal 7 are electrically connected, and the negative electrode 12 and the other external terminal 7 are connected to each other. In the conductive state, the opening of the case body 31 is closed with the lid plate 32. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 from the injection hole of the cover plate 32 of the case 3.

The electricity storage device 1 of the present embodiment configured as described above includes an electrode having an active material layer, and the particle size frequency distribution on the volume basis of particles contained in the active material layer has a particle size of 0.5 μm or more 2 Each having a peak in the first range of less than 0.0 μm, the second range of the particle size of 2.0 μm or more and less than 10 μm, and the third range of the particle size of 10 μm or more, the first range, the second range, and When the frequency (%) of the peak in the third range is P1, P2, and P3, the particle size of the particles in the second range is D2, and the particle size of the particles in the third range is D3 The following relational expressions (1) to (3) are all satisfied.
0.6 ≦ [P2 / P1] Relational expression (1)
0.1 ≦ [P3 / P2] ≦ 0.7 Relational expression (2)
4.5 ≦ [D3 / D2] ≦ 10.5 Relational expression (3)
Since the relational expression (2) of 0.1 ≦ [P3 / P2] ≦ 0.7 and the relational expression (3) of 4.5 ≦ [D3 / D2] ≦ 10.5 are satisfied, the particle diameter is The size and amount of particles between the largest peak and the next largest peak are within an appropriate range. Thereby, it is considered that particles having a small particle diameter enter between the particles on the large particle diameter side, and a gap between the particles is appropriately secured. Therefore, it is considered that the amount of the electrolytic solution retained in the active material layer is appropriately secured, the charge / discharge reaction proceeds efficiently, and the output performance is improved regardless of whether the rate is high or low. In addition, it is thought that said effect is exhibited on the conditions with comparatively few particle | grains of the smallest particle diameter so that the relational expression (1) of 0.6 <= [P2 / P1] is satisfy | filled. It is done.
With such a configuration, it is possible to provide an energy storage device in which an increase in the difference in the amount of discharged electricity between the high rate and the low rate is suppressed.

In the above electricity storage device 1, the relational expression (1) may further satisfy the following relational expression (4).
[P2 / P1] ≦ 2.0 Relational expression (4)
With such a configuration, it is possible to suppress a decrease in output performance after repeated charging and discharging.

  In addition, the electrical storage element of this invention is not limited to the said embodiment, Of course, a various change can be added in the range which does not deviate from the summary of this invention. For example, the configuration of another embodiment can be added to the configuration of a certain embodiment, and a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment. Furthermore, a part of the configuration of an embodiment can be deleted.

  In the above embodiment, the positive electrode in which the active material layer containing the active material is in direct contact with the metal foil has been described in detail. However, in the present invention, the positive electrode is a conductive layer containing a binder and a conductive auxiliary agent, and the active material layer And a conductive layer disposed between the metal foil and the metal foil.

  In the above embodiment, the electrodes in which the active material layers are disposed on both sides of the metal foil of each electrode have been described. However, in the electricity storage device of the present invention, the positive electrode 11 or the negative electrode 12 has the active material layer on one side of the metal foil. It may be provided only on the side.

  In the said embodiment, although the electrical storage element 1 provided with the electrode body 2 by which the laminated body 22 was wound was demonstrated in detail, the electrical storage element of this invention may be provided with the laminated body 22 which is not wound. Specifically, the storage element may include an electrode body in which a positive electrode, a separator, a negative electrode, and a separator each formed in a rectangular shape are stacked a plurality of times in this order.

  In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described. However, the type and size (capacity) of the power storage element 1 are arbitrary. is there. Moreover, although the lithium ion secondary battery was demonstrated as an example of the electrical storage element 1 in the said embodiment, it is not limited to this. For example, the present invention can be applied to various secondary batteries, other primary batteries, and power storage elements of capacitors such as electric double layer capacitors.

  The power storage element 1 (for example, a battery) may be used in a power storage device 100 as shown in FIG. 6 (a battery module when the power storage element is a battery). The power storage device 100 includes at least two power storage elements 1 and a bus bar member 91 that electrically connects two (different) power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element.

  A nonaqueous electrolyte secondary battery (lithium ion secondary battery) having a rated capacity of 5 Ah was manufactured as shown below.

Example 1
(1) Preparation of positive electrode N-methyl-2-pyrrolidone (NMP), a conductive additive (acetylene black), a binder (PVdF), and an active material (LiNi _1/3 Co _1/3 Mn _1/3 ) as a solvent O ₂ ) particles were mixed and kneaded to prepare a positive electrode mixture. The blending amounts of the conductive assistant, binder, and active material were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. The prepared positive electrode mixture was applied to both surfaces of an aluminum foil (thickness: 15 μm) so that the coating amount (weight per unit area) after drying was 8.61 mg / cm ² . After drying, a roll press was performed. Thereafter, it was vacuum dried to remove moisture and the like. The thickness of the active material layer (for one layer) after pressing was 32 μm. The density of the active material layer was 2.71 g / cm ³ . The specific surface area of the active material used was 1.5 m ² / g. Moreover, what has 2-10 hollow parts was used as particle | grains of an active material.

(2) Production of negative electrode As the active material, particulate amorphous carbon (non-graphitizable carbon) was used. Moreover, PVdF was used as the binder. The negative electrode mixture was prepared by mixing and kneading NMP as a solvent, a binder, and an active material. The binder was blended so as to be 7% by mass in the solid content, and the active material was blended so as to be 93% by mass. The prepared negative electrode mixture was applied to both sides of a copper foil (thickness: 8 μm) so that the coating amount (weight per unit area) after drying was 4.0 mg / cm ² . After drying, roll pressing was performed and vacuum drying was performed to remove moisture and the like. The thickness of the active material layer (for one layer) was 35 μm. The density of the active material layer was 1.13 g / cm ³ .

(3) Separator (separator base material) and inorganic porous layer What formed the inorganic porous layer on the surface of a separator base material was produced. The separator substrate is a polyethylene microporous film having a thickness of 15 μm. The inorganic porous layer has a thickness of 6 μm and contains 95% by mass of alumina particles and 5% by mass of polyvinylidene fluoride. The air resistance of the laminate of the separator and the inorganic porous layer was 100 seconds / 100 cc.

(4) Preparation of electrolytic solution As the electrolytic solution, one prepared by the following method was used. As a non-aqueous solvent, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume of 1 part by volume, and LiPF ₆ was dissolved in this non-aqueous solvent so that the salt concentration was 1 mol / L. An electrolyte solution was prepared.

(5) Arrangement of electrode body in case A battery was manufactured by a general method using the positive electrode, the negative electrode, the electrolytic solution, the separator, and the case.
First, a sheet-like material in which a separator was disposed between the positive electrode and the negative electrode and laminated was wound. The inorganic porous layer was disposed between the separator substrate and the positive electrode. Next, the wound electrode body was placed in the case body of an aluminum square battery case as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to the two external terminals, respectively. Further, a lid plate was attached to the case body. The above electrolytic solution was injected into the case from a liquid injection port formed on the cover plate of the case. Finally, the case was sealed by sealing the liquid injection port of the case.

-About the particle size frequency distribution of the particles contained in the positive electrode active material layer After charging the battery until it reaches 4.2 V at a 1.0 C rate, the battery is further discharged for 3 hours at a constant voltage of 4.2 V, and then 1 A constant current was discharged to 2.0 V at a 0.0 C rate. Subsequently, a constant voltage discharge was performed at 2.0 V for 5 hours. The battery was disassembled in a dry atmosphere. A part of the positive electrode (1 cm × 1 cm) was cut out from the disassembled battery, the cut out positive electrode was immersed in NMP having a mass of 50 times or more, and subjected to pretreatment by ultrasonic dispersion for 15 minutes, whereby the positive electrode active material layer and the metal The foil was separated and the metal foil was removed. A dispersion containing a measurement sample (active material and conductive additive) was prepared using the positive electrode active material layer subjected to ultrasonic treatment. In the measurement of the particle size frequency distribution of the measurement sample, a laser diffraction particle size distribution measuring device (“MT3000” manufactured by Microtrac Bell Co.) was used as the measuring device, and the attached application software was used as the measurement control software. As a specific measurement method, a scattering type measurement mode is adopted, and the wet cell in which the dispersion liquid circulates is placed in an ultrasonic environment for 2 minutes, and then irradiated with laser light, and the scattered light distribution from the measurement sample. Got. Then, the measurement was performed by approximating the scattered light distribution by a lognormal distribution.

・ Each frequency (%) of peak in the first range, peak in the second range, peak in the third range
The frequency (%) of each peak in the first range where the particle size is 0.5 μm or more and less than 2.0 μm, the second range where the particle size is 2.0 μm or more and less than 10 μm, and the third range where the particle size is 10 μm or more. , P1, P2, and P3, respectively.
The particle diameter of the particles in the second range peak was D2, and the particle diameter of the particles in the third range peak was D3. Each particle size was calculated by the above-mentioned attached application software.

-Density of positive electrode active material layer After discharging the battery to 2.0 V at a current of 5 A, the battery was held at 2.0 V for 5 hours. After holding, the electrode assembly was taken out from the inside of the case in a dry room or an argon atmosphere glove box. Each of the positive electrode and the negative electrode taken out from the electrode body was washed three times or more with DMC having a purity of 99.9% or more and a water content of 20 ppm or less. Thereafter, DMC was removed by vacuum drying. Then, a test piece having a set area S (cm ² ), for example, 4 cm ² (2 cm × 2 cm) was cut out, and the thickness T1 (cm) and the weight W1 (g) were measured. The active material layer and the metal foil were separated by immersing in pure water. After the separation, the thickness T2 (cm) and the weight W2 (g) of the metal foil were measured. The density of the active material layer was calculated by {(W1-W2) / (T1-T2)} / S.

(Examples 2-16, Comparative Examples 1-8)
A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the configuration of the battery was changed to the configuration shown in Table 1.

  As an example, FIG. 7 shows the particle size frequency distribution on the volume basis of the particles contained in the positive electrode active material layer for the battery of Example 1. In addition, Table 1 shows the configuration of each manufactured battery and the results of each evaluation described below for each battery.

<Evaluation of difference in discharge electricity quantity (discharge rate characteristics) between high rate and low rate>
The battery charged to 4.2 V was discharged to 2.4 V with a discharge current of 40 A, and the amount of discharge C1 during 40 A discharge was measured.
The battery in which the above measurement was performed was charged to 4.2 V and discharged to 2.4 V with a discharge current of 200 A, thereby measuring the discharge electricity amount C2 at the time of 200 A discharge.
The value calculated by the formula of [C2 / C1] × 100 was taken as the discharge rate characteristic.

<Output performance after repeated charge and discharge>
-Confirmation of discharge capacity For each battery, 5A charging current in a constant temperature bath at 25 ° C, 4.2V constant current constant voltage charging for 3 hours, after 10 minutes rest, 2.4V at 5A discharge current The discharge capacity of the battery was measured by performing a constant current discharge until.
-Initial output confirmation test The battery whose discharge capacity was measured was adjusted to 50% SOC (state of charge, state of charge) in a constant temperature bath at 25 ° C, and discharged at a current value of 60 A for 10 seconds. After a rest of 60 seconds, a constant current was discharged to 2.4 V at a current value of 2.5 A, and then the same amount of electricity as that generated by the discharge was charged at a current value of 2.5 A. After resting for 300 seconds, discharging at each current value was performed under the same conditions except that the discharge current value was changed to 90A, 120A, 150A, and 200A. Thereafter, each discharge current value was plotted on the horizontal axis and the voltage of the first second of each current value was plotted on the vertical axis, and an approximate straight line was created by the least square method. The slope of the straight line was taken as the resistance R of the battery. Based on the calculated R, the battery output P was calculated by the following equation.
P [W] =
2.5V x (50% SOC open circuit voltage (3.65V) -2.4V) / R
-Charging / discharging cycle test A battery adjusted to 50% SOC is held at 55 ° C for 4 hours, 40A constant current charging is performed until the SOC reaches 80%, and then 40A constant current discharging is performed from SOC 80% to SOC 20%. Thus, a charging voltage V80 of SOC 80% and a discharging voltage V20 of SOC 20% were determined.
A cycle test was continuously performed without setting a rest time under a constant current condition of 55 ° C. and 40 A under the condition that the cut-off voltage during charging was V80 and the cut-off voltage during discharge was V20. The cycle time was 3000 hours in total. After the end of the 3000 hour cycle test, it was held at 25 ° C. for 4 hours, and the aforementioned output confirmation test was conducted. The output reduction rate was calculated from the formula of output reduction rate = 100−P2 / P1 × 100, where P1 is the output before the cycle test (initial output) and P2 is the output after the cycle test (output after degradation).

As can be seen from Table 1, in the battery of the example in which all of the above relational expressions (1) to (3) are satisfied, an increase in the difference in the amount of discharged electricity between the high rate and the low rate is suppressed. It was done.
Moreover, as can be seen from Table 1, in the battery of the example in which all of the above relational expressions (1) to (4) are satisfied, the decrease in output performance after repeated charging and discharging was suppressed.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
26: Uncoated laminated part,
3: Case, 31: Case body, 32: Cover plate,
4: Separator,
5: current collector, 50: clip member,
6: Insulation cover
7: External terminal, 71: Surface,
8: inorganic porous layer,
11: positive electrode,
111: positive electrode metal foil (current collector foil), 112: positive electrode active material layer,
12: negative electrode,
121: negative electrode metal foil (current collector foil), 122: negative electrode active material layer,
91: Bus bar member,
100: Power storage device.

Claims (2)

Comprising an electrode having an active material layer;
The particle size frequency distribution on a volume basis of the particles contained in the active material layer is a first range in which the particle size is 0.5 μm or more and less than 2.0 μm, a second range in which the particle size is 2.0 μm or more and less than 10 μm, and Each particle has a peak in the third range of 10 μm or more,
The frequency (%) of the peak in the first range, the second range, and the third range is P1, P2, and P3, respectively, the particle diameter of the particles in the peak in the second range is D2, and the first An electricity storage element that satisfies all of the following relational expressions (1) to (3) when the particle diameter of the particles in the three ranges of peaks is D3.
0.6 ≦ [P2 / P1] Relational expression (1)
0.1 ≦ [P3 / P2] ≦ 0.7 Relational expression (2)
4.5 ≦ [D3 / D2] ≦ 10.5 Relational expression (3) The electrical storage element according to claim 1, wherein the relational expression (1) further satisfies the following relational expression (4).
[P2 / P1] ≦ 2.0 Relational expression (4)