JP2018098140A - Power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage element in which the increase of the difference in amount of discharged electricity between high and low rates is suppressed.SOLUTION: A power storage element comprises: an electrode body having, as its electrodes, a positive electrode and a negative electrode; and an electrolyte solution. The electrode body has a separator base disposed between the positive and negative electrodes. The positive and negative electrodes each have an active material layer containing active material particles. The active material layer of the positive electrode is opposed to the active material layer of the negative electrode through the separator base. The porosity of the active material layer of at least one of the electrodes on one side in a thickness direction thereof is different from that on the other side. The porosity on the one side located closer to the separator base is lower than that on the other side. The electrode body further has a high-porosity layer which is higher, in porosity, than the separator base, and which is disposed between the active material layer having a porosity changed therein and the separator base.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 a negative electrode and an electrolyte, wherein the negative electrode includes a current collector and a negative electrode material layer formed on the current collector and containing a negative electrode active material. Is known (for example, Patent Document 1).

  In the battery described in Patent Document 1, when the negative electrode material layer is divided in half in the thickness direction, the negative electrode material layer on the current collector side is A1, and the negative electrode material layer on the opposite side of the current collector side is A2, The average porosity of A1 is higher than the average porosity of A2.

  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 2003-077752 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 electricity storage device of the present embodiment includes an electrode body having a positive electrode and a negative electrode as electrodes, and an electrolytic solution, and the electrode body includes a separator base disposed between the positive electrode and the negative electrode, and the positive electrode and the negative electrode Each has an active material layer containing active material particles, and the active material layer of the positive electrode and the active material layer of the negative electrode face each other through the separator substrate, and the voids of the active material layer of at least one of the electrodes The rate is different between one side and the other side in the thickness direction, and is lower than the other side at one side close to the separator base material. The electrode body has a higher porosity than the separator base material and has different porosity ratios. It further has a high void layer disposed between the material layer and the separator substrate. In such a configuration, in the other portion where the porosity of the active material layer is high, the amount of the electrolyte solution that has entered the gap is large due to the high porosity. On the other hand, the electrolytic solution is easily supplied from the high void layer to one portion where the porosity of the active material layer is low. As a result, the active material layer is impregnated with a sufficient amount of the electrolyte solution that contributes to the discharge reaction. Therefore, the discharge reaction easily proceeds efficiently at a high rate or a low rate, and a sufficient amount of electricity can be discharged at any time. Therefore, it is possible to provide a power storage element in which the difference in the amount of discharged electricity between the high rate and the low rate is suppressed.

  In the electric storage element, the one porosity close to the separator base material may be 38% or more. Such a configuration further suppresses an increase in the difference in discharge electricity amount between the high rate and the low rate.

  In the above electricity storage device, each of the positive electrode and the negative electrode has an active material layer whose porosity is lower in one direction than the other in the thickness direction, and the high void layer is formed between the active material layer of the positive electrode and the separator substrate. It may be arranged both between and between the active material layer of the negative electrode and the separator substrate. Such a configuration further suppresses an increase in the difference in discharge electricity amount between the high rate and the low rate.

  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 cross-sectional view schematically showing an electrode, a high void layer, and a separator base material. FIG. 7 is a perspective view of a power storage device including the power storage element according to the embodiment.

  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 6, 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 (separator base material 41) being insulated from each other. The electrode body 2 preferably has a high void layer 8 having a higher porosity than the separator substrate 41 between the positive electrode or negative electrode 12 and the separator substrate 41.

  The positive electrode 11 includes a metal foil 111 (current collector foil) and a positive electrode active material layer 112 that is superimposed on the surface of the metal foil 111 and contains an active material. In the present embodiment, the positive electrode 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 metal foil 111 may be formed with a through hole penetrating in the thickness direction.

The positive electrode active material layer 112 contains 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. The density of the positive electrode active material layer 112 is usually 1.0 g / cm ³ or more and 6.0 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 porosity of the positive electrode active material layer 112 may be different between one side and the other side in the thickness direction. Specifically, the porosity of the positive electrode active material layer 112 is lower on the side closer to the separator substrate 41 (one side) and higher on the side closer to the metal foil 111 (the other side). That is, the porosity of the positive electrode active material layer 112 is higher on the side closer to the metal foil 111 (the side farther from the separator base 41) than on the side closer to the separator base 41. As shown in FIG. 6, for example, the positive electrode active material layer 112 is formed to be porous by the gaps between the plurality of active material particles A. The area ratio of the gap per unit area of the cross section of the active material layer is lower on the side closer to the separator substrate 41 (one side). It is confirmed that the porosity is different in the thickness direction by comparing the porosity of one and the other when the thickness of the positive electrode active material layer 112 is halved. Specifically, it is as follows. First, the discharged battery is disassembled in a dry atmosphere. A part of the positive electrode 11 is cut out from the disassembled battery, the active material layer 112 of the positive electrode 11 is washed with dimethyl carbonate, and then vacuum-dried for 2 hours or more. In observation with a scanning electron microscope (SEM) of a cross section obtained by cutting the positive electrode active material layer 112 in the thickness direction in the positive electrode 11 after drying, observation of a square having half the length of the positive electrode active material layer 112 as four sides Set the image. Observation images are set for one and the other in the thickness direction. By calculating the ratio of the area occupied by the voids to the total area of the observation image, the respective void ratios are obtained.

  The porosity close to the metal foil 111 in the positive electrode active material layer 112 may be 3 points or more and 5 points or less higher than the porosity close to the separator substrate 41. The porosity closer to the metal foil 111 in the positive electrode active material layer 112 is usually 35% or more and 50% or less. On the other hand, the porosity close to the separator substrate 41 is usually 25% or more and 45% or less. The porosity closer to the separator substrate 41 may be 35% or more, or 38% or more.

  The porosity in the positive electrode active material layer 112 is varied in the thickness direction by, for example, applying a mixture (described later) for forming the positive electrode active material layer 112 a plurality of times to produce the positive electrode active material layer 112. be able to. Specifically, after applying a mixture having a lower solid content to the metal foil 111, the one closer to the metal foil 111 than to the separator base 41 is further applied by further applying a mixture having a higher solid content. Thus, the positive electrode active material layer 112 having a high porosity can be manufactured. Further, for example, after a mixture for forming the positive electrode active material layer 112 is applied once to the metal foil 111, the mixture is dried at a relatively high temperature, and the metal foil 111 side and the surface side It is possible to adopt a method that causes a difference in porosity. Thereby, the positive electrode active material layer 112 having a higher porosity in the direction closer to the metal foil 111 than in the direction closer to the separator substrate 41 can be produced.

  The active material of the positive electrode 11 is a compound that can occlude and release lithium ions. The average primary particle diameter of the active material of the positive electrode 11 is usually 0.5 μm or more and 2.0 μm or less. The average primary particle size is measured as follows. The positive electrode 11 is cut in the thickness direction, and the cross section of the positive electrode active material layer 112 that appears by cutting is observed with a scanning electron microscope. The primary particles of at least 100 active material particles in the cross section are randomly selected. Measure and average the particle size of the selected primary particles. When the active material particles are not spherical, the longest diameter is measured.

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, a _{Li p Mn r O 4, Li} p Ni q Co s Mn r O 2 , etc.).

More specifically, 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 And 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 positive electrode active material layer 112 contains a carbonaceous material containing 98% by mass or more of carbon as a conductive additive. The positive electrode active material layer 112 can contain, for example, ketjen black (registered trademark), acetylene black, graphite or the like as a conductive additive.

  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 active material layer 112 with the separator 4 (separator base material 41) 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 is a graphite such as natural graphite or artificial graphite, a carbon material such as amorphous carbon (non-graphitizable carbon, graphitizable carbon), silicon (Si), tin (Sn), or the like. It is a material that causes an alloying reaction with lithium ions. The active material of the negative electrode of the present embodiment is graphite, specifically, natural graphite.

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 0.3 g / 100 cm ² or more and 1.0 g / 100 cm ² or less. The density (one layer) of the negative electrode active material layer 122 is usually 0.5 g / cm ³ or more and 6.0 g / cm ³ or less.

  Similar to the positive electrode active material layer 112, the porosity of the negative electrode active material layer 122 may be different in the thickness direction. Specifically, the porosity of the negative electrode active material layer 122 may be lower near the separator base material 41 and higher near the metal foil 121. That is, the porosity of the negative electrode active material layer 122 may be higher near the metal foil 121 than near the separator base material 41. The porosity of the negative electrode active material layer 122 is measured in the same manner as the porosity of the positive electrode active material layer 112 described above.

  The binder used for the negative electrode active material layer is the same as the binder used for the positive electrode active material layer. 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 (separator base material 41). 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 41. 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 porosity of the separator substrate 41 is higher than the porosity of the positive electrode active material layer 112 closer to the metal foil 111, and is usually 40% or more and 70% or less.

  As with the method for measuring the porosity of the positive electrode active material layer 112 described above, the porosity of the separator substrate 41 is determined by using a part of the separator 4 cut out from the battery disassembled at the time of the measurement. Obtained from the observed image. The porosity of the separator base material 41 can be changed, for example, by adopting a separator base material 41 having a different air resistance.

  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 the present embodiment includes the high void layer 8 disposed between the positive electrode active material layer 112 or the negative electrode active material layer 122 and the separator base material 41. The electrode body 2 may have the high void layer 8 both between the positive electrode active material layer 112 and the separator base material 41 and between the negative electrode active material layer 122 and the separator base material 41. The porosity of the negative electrode active material layer 122 may be different in the thickness direction, similar to the porosity of the positive electrode active material layer 112 described above. The porosity of the high porosity layer 8 is higher than the porosity of the separator substrate 41. The porosity of the high porosity layer 8 is higher than the porosity of the positive electrode active material layer 112 (or negative electrode active material layer 122) closer to the separator substrate 41 and closer to the metal foil 111 (or metal foil 121). It is higher than the porosity. The porosity of the high void layer 8 is usually 55% or more and 85% or less.

  The porosity of the high porosity layer 8 is the same as the method for measuring the porosity of the positive electrode active material layer 112 described above, using a part of the high porosity layer 8 cut out from the battery disassembled at the time of the measurement. Obtained from the observation image of the microscope. The porosity of the high void layer 8 is obtained by, for example, reducing the amount of inorganic particles and binder (described later) in the composition containing a solvent prepared to form the high void layer 8 (reduce the solid content). Can be high.

The high void layer 8 includes inorganic particles having at least electrical insulation, and further includes a binder. The electrical insulation property of the high void 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 high void layer 8 is less than 10 ⁻⁶ S / m.

The high void layer 8 is formed porous by voids between the 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 high void layer 8 usually contains 30% by mass to 99% by mass of inorganic particles. The high void layer 8 usually contains 1% by mass or more and 70% 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 calcium fluoride, barium fluoride, and barium sulfate. Examples of the covalently bonded crystal particles include silicon and diamond particles. 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.

  The binder of the high void layer 8 includes, for example, 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 high void layer 8 is disposed between the separator base 41 and the positive electrode active material layer 112 or the negative electrode active material layer 122 by being formed on the surface of the positive electrode active material layer 112 or the negative electrode active material layer 122. Also good. Further, the high void layer 8 may be disposed between the separator base material 41 and the positive electrode active material layer 112 or the negative electrode active material layer 122 by being formed on the surface of the separator base material 41.

  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. At this time, after applying a mixture with a lower solid content to the metal foil, by further applying a mixture with a higher solid content, the porosity differs in the thickness direction, and the porosity closer to the metal foil A high active material layer can be formed. After applying the mixture, the solvent contained in the mixture can be volatilized by heating or the like. When the mixture is applied once, the volatilization rate of the solvent can be increased by relatively increasing the temperature during heating, and an active material layer having a higher porosity can be formed closer to the metal foil. 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. Similarly, the negative electrode 12 can be manufactured.

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.
Note that the high void layer 8 is formed by, for example, applying a composition containing inorganic particles, a binder, and a solvent to the surface of the separator base 41 or an active material layer of at least one of the positive electrode 11 and the negative electrode 12. It can be formed by applying to the surface. And when winding as mentioned above, the laminated body 22 on which the high void layer 8 was also laminated is wound.

  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 body 2 having a positive electrode 11 and a negative electrode 12 as electrodes, and an electrolytic solution. The electrode body 2 has a separator substrate 41 disposed between the positive electrode 11 and the negative electrode 12. The positive electrode 11 and the negative electrode 12 have a positive electrode active material layer 112 and a negative electrode active material layer 122 containing active material particles, respectively. The positive electrode active material layer 112 and the negative electrode active material layer 122 face each other with the separator base material interposed therebetween. The porosity of the positive electrode active material layer 112 or the negative electrode active material layer 122 is different between one side and the other side in the thickness direction, and is lower than the other side on one side close to the separator substrate 41. The electrode body 2 further includes a high void layer 8 disposed between the positive electrode active material layer 112 and the separator substrate 41 having a higher porosity than the separator substrate 41 and having a different porosity. In such a configuration, in the other portion where the porosity of the positive electrode active material layer 112 or the negative electrode active material layer 122 is high, a larger amount of electrolyte exists in the space because the porosity is higher. On the other hand, the electrolytic solution is likely to be supplied from the high void layer 8 having a relatively high porosity to one portion where the porosity of the positive electrode active material layer 112 or the negative electrode active material layer 122 is low. Thereby, the positive electrode active material layer 112 or the negative electrode active material layer 122 is impregnated with a sufficient amount of the electrolyte solution that contributes to the discharge reaction. Therefore, the discharge reaction easily proceeds efficiently at a high rate or a low rate, and a sufficient amount of electricity can be discharged at any time. Therefore, it is possible to provide a power storage element in which 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 porosity (one side) closer to the separator base material 41 of the positive electrode active material layer 112 or the negative electrode active material layer 122 may be 38% or more. Such a configuration further suppresses an increase in the difference in discharge electricity amount between the high rate and the low rate.

  In the power storage device 1, the high void layer 8 is disposed between both the positive electrode active material layer 112 and the separator base material 41 and between the negative electrode active material layer 122 and the separator base material 41. Also good. The porosity of each of the positive electrode active material layer 112 and the negative electrode active material layer 122 is different in the thickness direction, and may be lower on the side (one side) closer to the side farther from the separator substrate 41 (the other side). Such a configuration further suppresses an increase in the difference in discharge electricity amount between the high rate and the low rate.

  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. 7 (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) was produced as shown below.

Example 1
(1) Production of positive electrode N-methyl-2-pyrrolidone (NMP) as an organic solvent, conductive auxiliary agent (acetylene black), binder (PVdF), active material particles (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) was mixed and kneaded to prepare two types of mixture for the positive electrode. First, a low solid content mixture was prepared in which the blending amounts of the conductive assistant, the binder, and the active material particles were 4.5 mass%, 4.5 mass%, and 91 mass%, respectively. Next, a high solid content mixture was prepared in which the blending amounts of the conductive assistant, the binder, and the active material particles were 4.5 mass%, 4.5 mass%, and 91 mass%, respectively. At this time, a mixture with a high solid content was prepared by reducing the amount of the organic solvent to a mixture with a low solid content. The prepared low solid content mixture was applied to both sides of an aluminum foil (thickness: 15 μm) so that the coating amount after drying (weight per unit area) was 4.3 mg / cm ² . On the applied mixture, a high solid content mixture was applied so that the coating amount after drying (one basis weight) was 4.3 mg / cm ² . After drying, a roll press was performed at a predetermined pressure. Thereafter, it was vacuum dried to remove moisture and the like. The thickness of the active material layer (for one layer) was 32 μm. The density of the active material layer was 2.69 g / cm ³ .

(2) Production of negative electrode As active material particles, natural graphite particles were used. As the binder, styrene butadiene rubber was used. The mixture for the negative electrode was prepared by mixing and kneading water as a solvent, a binder, carboxymethyl cellulose (CMC), and active material particles. CMC was blended so as to be 1.0 mass%, a binder was blended so as to be 2.0 mass%, and active material particles were blended so as to be 97.0 mass%. The prepared negative electrode mixture was applied on both sides of a copper foil (thickness: 10 μm) so that the coating amount after drying (one basis weight) was 3.8 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 39 μm. The density of the active material layer was 0.974 g / cm ³ .

(3) Separator (Separator base material)
A polyethylene microporous film having a thickness of 22 μm was used as the separator substrate. The air resistance of the polyethylene microporous membrane was 100 seconds / 100 cc.

(4) High void layer (inorganic porous layer)
A composition containing 95% by mass of inorganic particles (alumina particles), 5% by mass of a binder (specifically, polyvinylidene fluoride) and a solvent was prepared, and such a composition was applied to one side of a separator substrate. . The solvent was volatilized by heating to form a high void layer (inorganic porous layer) on the separator substrate. In addition, before winding an electrode body as follows, it arrange | positioned so that a high void layer might contact a positive electrode active material layer.

(5) 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.

(6) Arrangement of electrode body in case A battery was manufactured by a general method using the above positive electrode, the above negative electrode, the above electrolytic solution, a separator, a high void layer, and a case.
First, a sheet-like material in which a separator was disposed between the positive electrode and the negative electrode and laminated was wound. 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.

(Examples 2-15, Comparative Examples 1-10)
A battery was produced in the same manner as in Example 1 except that the porosity of the positive electrode active material layer, the separator base material, and the high void layer was changed as shown in Table 1.
Specifically, in Examples 1 to 15 and Comparative Examples 1 to 10 (excluding Comparative Examples 2, 6, and 8), after applying the low solid content mixture, the high solid content mixture was applied as described above. By coating, positive electrode active material layers having different porosity in the thickness direction were produced.
On the other hand, in Comparative Examples 2, 6, and 8, a positive electrode active material layer in which the porosity does not differ in the thickness direction was produced by applying a predetermined solid content mixture only once.
In each example and each comparative example shown in Table 1 (except for Comparative Examples 1 and 5), a high void layer was formed on one surface of the separator substrate.
In each example and each comparative example shown in Table 2 (excluding comparative example 7), the composition of the positive electrode active material layer was applied to the surface of the positive electrode active material layer by applying a composition for a high void layer. A high void layer was formed on top.
Note that none of the negative electrode active material layers was formed so that the porosity in the thickness direction was different.

<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.

  Tables 1 and 2 show the evaluation results of the discharge rate characteristics of the manufactured batteries. As can be seen from Tables 1 and 2, in the batteries of the examples, the difference in the amount of discharge electricity between the high rate and the low rate 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: High void layer (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 (3)

An electrode body having a positive electrode and a negative electrode as electrodes, and an electrolyte solution,
The electrode body has a separator substrate disposed between the positive electrode and the negative electrode,
The positive electrode and the negative electrode each have an active material layer containing active material particles,
The active material layer of the positive electrode and the active material layer of the negative electrode are opposed to each other through the separator substrate,
The porosity of the active material layer of at least one of the electrodes is different between one and the other in the thickness direction, and lower than the other in the one near the separator substrate,
The said electrode body is a electrical storage element which has a high porosity layer arrange | positioned between the said active material layer from which the porosity is higher than the said separator base material, and the said porosity differs, and the said separator base material.   The power storage element according to claim 1, wherein the one porosity close to the separator substrate is 38% or more. Each of the positive electrode and the negative electrode has an active material layer in which the porosity is lower on the one side than the other in the thickness direction,
The high void layer is disposed between the active material layer of the positive electrode and the separator base material, and between the active material layer of the negative electrode and the separator base material, respectively. Or the electrical storage element of 2.