JP2021044250A - Power storage element - Google Patents

Abstract

To provide a power storage element in which an electrode is prevented from being bent by pressing.SOLUTION: A power storage element includes an electrode including a foil-shaped electrode base material, and an active material layer superimposed on the electrode base material and containing a particulate active material, and the particle size D50 and the particle size D90 of the active material satisfy a relational expression of 0.39 ≤ particle size D50 / (particle size D50 + particle size D90) ≤ 0.43 (In the formula, the particle size D50 is the particle size at which the volume integration is 50% in the particle size distribution, and the particle size D90 is the particle size at which the volume integration is 90% in the particle size distribution).SELECTED DRAWING: Figure 1

Description

The present invention relates to a power storage element.

Conventionally, a non-aqueous electrolyte secondary battery has been known in which a positive electrode and a negative electrode are provided as electrodes, and the electrode has a foil-shaped electrode base material and an active material layer containing a particulate active material and superposed on the electrode base material. Has been done.

As the positive electrode active material that can be used in this type of non-aqueous electrolyte secondary battery, an active material obtained from a particulate nickel-cobalt composite hydroxide having a specific composition and a specific particle size can be considered (for example). Patent Document 1). According to Patent Document 1, when the particle size of such a composite hydroxide is measured and the particle sizes that are the volume integration values of 10%, 50%, and 90% are D10, D50, and D90, (D50-D10) / D50≤ It is stated that 0.25 and (D90-D10) / D50 ≦ 0.25 are satisfied.

However, in a battery containing the active material obtained as described above in the electrode, the electrode may be bent by being pressed, for example, during manufacturing.

Japanese Unexamined Patent Publication No. 2014-144894

An object of the present invention is to provide a power storage element in which the electrodes are prevented from being bent by a press.

The power storage element of the present invention includes an electrode having a foil-shaped electrode base material and an active material layer superimposed on the electrode base material and containing a particulate active material.
The particle size D50 and the particle size D90 of the active material satisfy the relational expression of 0.39 ≤ particle size D50 / (particle size D50 + particle size D90) ≤ 0.43 (in the formula, the particle size D50 has a particle size distribution. The particle size D90 is the particle size at which the volume integration is 50%, and the particle size D90 is the particle size at which the volume integration is 90% in the particle size distribution.)
The mechanism by which an electrode whose bending is suppressed by pressing is obtained by satisfying the relational expression is not always clear, but it is presumed to be as follows. That is, according to the power storage element having such a configuration, since the particle size of the active material satisfies the above relational expression, even if the electrode is pressed, smaller particles appropriately enter between the larger particles in the active material layer. .. As the small particles enter between the large particles, the compressive force in the thickness direction is dispersed in the plane direction of the active material layer. Therefore, it is possible to prevent the compressive force from being concentrated on a part of the electrode base material. As a result, the active material layer is pressed against the electrode base material with a relatively uniform force. Since the force is applied to the electrode base material relatively evenly, it is possible to prevent the electrode base material from stretching due to a non-uniform compressive force. Therefore, it is possible to prevent the electrode from bending so as to undulate in the thickness direction. Further, for example, in the case of an electrode in which the electrode base material is exposed along one side of a rectangular electrode base material, when pressed, the electrode tends to bend with the exposed side inside. However, since the non-uniform elongation of the electrode base material is suppressed as described above, the bending of the electrode can be suppressed. As described above, according to the power storage element having such a configuration, it is possible to suppress the bending of the electrodes.

In the above power storage element, the electrode may be a positive electrode. Active material of the positive _{electrode, Li v Ni w Mn x Co} y O z lithium-metal composite oxide represented by the chemical composition (but is 0 <v ≦ 1.3, a w + x + y = 1, 0 <w <1, 0 <x <1, 0 <y <1, 1.7 ≦ z ≦ 2.3).

In the above-mentioned power storage element, the electrode has a coating portion in which the electrode base material is covered by overlapping the active material layer on the electrode base material and an exposed portion in which the active material layer does not overlap the electrode base material and the electrode base material is exposed. And may have. When the electrode having the covering portion and the exposed portion is pressed, a stronger force is applied to the covering portion by the thickness of the active material layer. However, even if the electrode has a coated portion and an exposed portion, it is possible to prevent the electrode from being bent by the press because the force is applied relatively evenly from the coated portion to the electrode base material.

In the power storage element, the electrodes may be stacked in the thickness direction.

According to the present invention, it is possible to prevent the electrode from being bent by the press.

FIG. 1 is a perspective view of a power storage element according to the present embodiment. FIG. 2 is a front view of the power storage element according to the same embodiment. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. FIG. 5 is a perspective view of a state in which a part of the power storage element according to the same embodiment is assembled, and is a perspective view of a state in which the liquid injection plug, the electrode body, the current collector, and the external terminal are assembled to the lid plate. is there. FIG. 6 is a diagram for explaining the configuration of the electrode body of the power storage element according to the embodiment. FIG. 7 is a cross-sectional view taken along the line VII-VII of FIG. FIG. 8 is a perspective view of a power storage device including a power storage element according to the same embodiment. FIG. 9 is a graph showing the curvature value of the positive electrode.

Hereinafter, an embodiment of the power storage element according to the present invention will be described with reference to FIGS. 1 to 7. The power storage element includes a secondary battery, a capacitor, and the like. In the present embodiment, a rechargeable secondary battery will be described as an example of the power storage element. The name of each component (each component) of the present embodiment is that of the present embodiment, and may be different from the name of each component (each component) in the background technology.

The power storage element 1 of the present embodiment is a non-aqueous electrolyte secondary battery. More specifically, the power storage element 1 is a lithium ion secondary battery that utilizes electron transfer generated by the movement of lithium ions. This type of power storage element 1 supplies electrical energy. The power storage element 1 is used alone or in a plurality. Specifically, the power storage element 1 is used alone when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, the power storage element 1 is used in the power storage device 100 in combination with the other power storage element 1. In the power storage device 100, the power storage element 1 used in the power storage device 100 supplies electrical energy.

As shown in FIGS. 1 to 7, the power storage element 1 includes an electrode body 2 including a positive electrode 11 and a negative electrode 12 as electrodes, a case 3 accommodating the electrode body 2, and an external terminal arranged outside the case 3. An external terminal 7 which is 7 and conducts with the electrode body 2 is provided. Further, the power storage element 1 has a current collector 5 or the like that conducts the electrode body 2 and the external terminal 7 in addition to the electrode body 2, the case 3, and the external terminal 7.

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

The positive electrode 11 has a metal foil 111 (positive electrode base material) and a positive electrode active material layer 112 that is overlapped with the metal foil 111 and contains an active material. In the present embodiment, the positive electrode active material layer 112 is laminated on both sides of the metal foil 111, respectively. The thickness of the positive electrode 11 is usually 40 μm or more and 200 μm or less. The metal foil 111 is strip-shaped. The metal leaf 111 of the positive electrode of the present embodiment is, for example, an aluminum foil.

The positive electrode active material layer 112 contains an active material and a binder. Specifically, the positive electrode active material layer 112 contains 85% by mass or more and 95% by mass or less of the active material, and 2% by mass or more and 10% by mass or less of the binder. The thickness of the positive electrode active material layer 112 is usually 10 μm or more and 100 μm or less. The basis weight of the positive electrode active material layer 112 is usually 5.0 mg / cm ² or more and 15.0 mg / cm ² or less. The positive electrode active material layer 112 usually has a packing density of ^{1 g / cm 3} or more and 4 g / cm ^{3 or less when pressed.}

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 in the form of particles.

The particle size D50 and the particle size D90 of the active material of the positive electrode 11 satisfy the relational expression of 0.39 ≤ particle size D50 / (particle size D50 + particle size D90) ≤ 0.43 (in the formula, the particle size D50 is The particle size is such that the volume integration is 50% in the particle size distribution, and the particle size D90 is the particle size in which the volume integration is 90% in the particle size distribution). That is, in the particle size distribution of the active material of the positive electrode 11, the particle size D50 having a volume integration of 50% and the particle size D90 having a volume integration of 90% satisfy the above relational expression.

The particle size D50 is usually 2 μm or more and 10 μm or less. The particle size D50 may be 3 μm or more and 8 μm or less.

The particle size D90 is usually 3 μm or more and 15 μm or less. The particle size D90 may be 4 μm or more and 11 μm or less.

The above-mentioned particle size D50 is an average particle size (also referred to as a median diameter) in which a volume cumulative distribution is drawn from the small diameter side in the particle size distribution and the volume accumulation frequency is 50%. The particle size D50 is a value of D50 obtained by measuring with a laser diffraction / scattering type particle size distribution measuring device. The particle size D90 is the same as the particle size D50 except that the volume accumulation frequency is 90%. The measurement conditions for the particle size D50 and the particle size D90 will be described in detail in Examples.

The particle size D10 measured in the same manner as described above and having a volume integration of 10% is usually 1 μm or more and 5 μm or less.

The active material of the positive electrode 11 is, for example, a lithium metal oxide. Specifically, the active material of the positive electrode is, for example, _{a composite oxide represented by Li v} MeO _z (Me represents one or more transition metals) (L _v Co _y O ₂ , Li _v Ni _w O). _{2, Li v Mn x O 4} , Li v Ni w Co y Mn x O 2 , etc.), _{or, Li a Me b (XO c} ) d (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 a Fe b PO} 4, Li a Mn b PO 4, Li a Mn b SiO 4, Li a Co b PO 4 F , etc.).

In this embodiment, the active material of the positive electrode _{11, Li v Ni w Mn x Co} y O z lithium-metal composite oxide represented by the chemical composition (provided that at 0 <v ≦ 1.3, w + x + y = 1 , 0 <w <1, 0 <x <1, 0 <y <1, 1.7 ≦ z ≦ 2.3). Additional such _{Li v Ni w Mn x Co y} O lithium-metal composite oxide represented by the chemical composition of _z is, for _{example, LiNi 1/3 Co 1/3 Mn 1/3 O} 2, LiNi 1/6 Co 2 _{/ 3} Mn _1/6 O ₂ and the like.

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

The positive electrode active material layer 112 may further have a conductive auxiliary agent such as Ketjen Black (registered trademark), acetylene black, and graphite. The positive electrode active material layer 112 of the present embodiment has acetylene black as a conductive auxiliary agent.

The negative electrode 12 has a metal foil 121 (negative electrode base material) and a negative electrode active material layer 122 that is overlapped with the metal foil 121 and contains an active material. In the present embodiment, the negative electrode active material layer 122 is laminated on both sides of the metal foil 121, respectively. The metal foil 121 is strip-shaped. The metal leaf 121 of the negative electrode of the present embodiment is a copper foil. The thickness of the negative electrode 12 is usually 40 μm or more and 200 μm or less.

The negative electrode active material layer 122 has an active material and a binder. The negative electrode active material layer 122 is arranged so as to face the positive electrode 11 via the separator 4. The thickness of the negative electrode active material layer 122 is usually 10 μm or more and 100 μm or less.

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. The active material of the negative electrode 12 is in the form of particles. The active material of the negative electrode of the present embodiment is non-graphitized carbon.

The particle size D50 of the active material of the negative electrode 12 (similar to the particle size D50 of the active material of the positive electrode 11) is usually 2 μm or more and 10 μm or less. Such a particle size D50 may be 2 μm or more and 8 μm 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 polyvinylidene fluoride.

The negative electrode active material layer 122 may further have a conductive auxiliary agent such as Ketjen Black (registered trademark), acetylene black, and graphite. The negative electrode active material layer 122 of the present embodiment does not have a conductive auxiliary agent.

The separator 4 is a member having an insulating property. The separator 4 has a strip shape. The separator 4 is arranged between the positive electrode 11 and the negative electrode 12. As a result, in the electrode body 2 (specifically, the laminated body 22), the positive electrode 11 and the negative electrode 12 are insulated from each other. Further, the separator 4 holds the electrolytic solution in the case 3. As a result, when the power storage element 1 is charged and discharged, lithium ions move between the positive electrode 11 and the negative electrode 12 which are alternately laminated with the separator 4 in between.

The separator 4 is made porous by, for example, a woven fabric, a non-woven fabric, or a porous membrane. Examples of the material of the separator 4 include polymer compounds, glass, and ceramics. Examples of the polymer compound include polyesters such as polyacrylonitrile (PAN), polyamide (PA) and polyethylene terephthalate (PET), polyolefins (PP) such as polypropylene (PP) and polyethylene (PE), and cellulose. ..

The width of the separator 4 (the dimension of the strip shape in the lateral direction) is slightly larger than the width of the negative electrode active material layer 122. The separator 4 is arranged between the positive electrode 11 and the negative electrode 12 in which the positive electrode active material layer 112 and the negative electrode active material layer 122 are overlapped with each other in a state of being displaced in the width direction so as to overlap each other.

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 of being insulated by the separator 4. That is, in the electrode body 2 of the present embodiment, the laminated body 22 of the positive electrode 11, the negative electrode 12, and the separator 4 is wound.

The positive electrode 11 and the negative electrode 12 have a coating portion 104 in which the metal foil (electrode base material) is covered by overlapping the active material layer on the metal foil (electrode base material), and the active material on the metal foil (electrode base material), respectively. It has an exposed portion 105 in which the layers do not overlap and the metal foil (electrode base material) is exposed. The exposed portion 105 is formed along one end edge in the width direction of the strip-shaped metal foil (electrode base material).

In a state where the positive electrode 11 and the negative electrode 12 are laminated, as shown in FIG. 6, the exposed portion 105 of the positive electrode 11 and the exposed portion 105 of the negative electrode 12 do not overlap. That is, the exposed portion 105 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 exposed portion 105 of the negative electrode 12 extends in the width direction (positive electrode 11) from the region where the positive electrode 11 and the negative electrode 12 overlap. (In the direction opposite to the protruding direction of the exposed portion 105). The electrode body 2 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 4, that is, the laminated body 22, in a laminated state. The exposed laminated portion 26 in the electrode body 2 is formed by the portion where only the exposed portion 105 of the positive electrode 11 or the exposed portion 105 of the negative electrode 12 is laminated. In this way, the positive electrode 11 is stacked in the thickness direction via the negative electrode 12 and the separator 4. The negative electrode 12 is stacked in the thickness direction via the positive electrode 11 and the separator 4.

The exposed laminated portion 26 is a portion of the electrode body 2 that is electrically connected to the current collector 5. The exposed laminated portion 26 has two portions (divided exposed laminated portion) 261 sandwiching the hollow portion 27 (see FIG. 6) in the winding center direction of the wound positive electrode 11, negative electrode 12, and separator 4. It is divided into.

The exposed laminated portion 26 configured as described above is provided at each pole of the electrode body 2. That is, the exposed laminated portion 26 in which only the exposed portion 105 of the positive electrode 11 is laminated constitutes the exposed laminated portion of the positive electrode 11 in the electrode body 2, and the exposed laminated portion 26 in which only the exposed portion 105 of the negative electrode 12 is laminated constitutes the electrode body. The exposed laminated portion of the negative electrode 12 in No. 2 is formed.

The case 3 has a case main body 31 having an opening and a lid 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, the current collector 5, and the like. Case 3 is formed of a metal that is resistant to electrolytes. The case 3 is formed of, for example, aluminum or an aluminum-based metal material such as an aluminum alloy. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material in which a resin such as nylon is adhered to aluminum.

The electrolytic solution is a non-aqueous electrolyte solution. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. The organic solvent is, for example, cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Electrolyte salts are LiClO ₄ , LiBF _{4 , LiPF 6} , and the like.

_{The electrolytic solution is, for example, a solution in which 0.5 to 1.5 mol / L of LiPF 6} is dissolved in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed in a predetermined volume ratio.

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

In the following, as shown in FIG. 1, the long side direction of the lid plate 32 is the X-axis direction, the short side direction of the lid plate 32 is the Y-axis direction, and the normal direction of the lid plate 32 is the Z-axis direction.

The case body 31 has a square tube shape (that is, a bottomed square tube shape) in which one end in the opening direction (Z-axis direction) is closed.

The lid plate 32 is a plate-shaped member that closes the opening of the case body 31. Specifically, the lid plate 32 comes into contact with the case body 31 so as to close the opening of the case body 31. More specifically, the peripheral edge of the lid plate 32 is overlapped with the peripheral edge of the opening of the case body 31 so that the lid plate 32 closes the opening. The boundary portion between the lid plate 32 and the case body 31 is welded in a state where the opening peripheral edge portion and the lid plate 32 are overlapped with each other. As a result, the case 3 is configured.

The lid plate 32 has a contour shape corresponding to the opening peripheral edge of the case body 31 in the Z-axis direction. That is, the lid plate 32 is a rectangular plate material that is long in the X-axis direction when viewed in the Z-axis direction. The four corners of the lid plate 32 are arcuate.

The lid plate 32 has a gas discharge valve 321 capable of discharging 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 injection hole is sealed (closed) by the injection plug 326. The liquid injection plug 326 is fixed to the case 3 (the lid plate 32 in the example of the present embodiment) by welding.

The external terminal 7 is a portion that is electrically connected to the external terminal 7 of another power storage element 1 or an external device or the like. 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 an aluminum alloy, or a copper-based metal material such as copper or a 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 that extends along the lid plate 32. Specifically, the external terminal 7 has a rectangular plate shape in the Z-axis direction.

The current collector 5 is arranged 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 electrically connected to the electrode body 2 via the clip member 50. That is, the power storage element 1 includes a clip member 50 that connects the electrode body 2 and the current collector 5 so as to be energized.

The current collector 5 is formed of a conductive member. As shown in FIG. 3, the current collector 5 is arranged along the inner surface of the case 3.

The current collector 5 is arranged on the positive electrode 11 and the negative electrode 12 of the power storage element 1, respectively. In the power storage element 1 of the present embodiment, the storage element 1 is arranged in the exposed laminated portion 26 of the positive electrode 11 of the electrode body 2 and the exposed laminated portion 26 of the negative electrode 12 in the case 3, 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 power storage element 1 of the present embodiment, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) housed in the bag-shaped insulating cover 6 is housed in the case 3.

Next, a method of manufacturing the power storage element of the above embodiment will be described.

In the method for manufacturing the power storage element 1, a mixture containing an active material is applied to a metal foil (electrode base material) to form an active material layer, and electrodes (positive electrode 11 and negative electrode 12) are produced. Next, the positive electrode 11, the separator 4, and the negative electrode 12 are superposed to form the electrode body 2. Subsequently, the electrode body 2 is put into the case 3, and the electrolytic solution is put into the case 3 to assemble the power storage element 1.

In the production of the electrode (positive electrode 11), an active material layer (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. When applying the mixture to the metal foil, the mixture is applied so that one end in the width direction of the strip-shaped metal foil is not covered with the mixture. As a result, the electrode (positive electrode 11) includes a covering portion 104 in which the metal foil is covered by the active material layer overlapping the metal foil, and an exposed portion 105 in which the metal foil is exposed without the active material layer overlapping the metal foil. Will have. As a coating method for forming the active material layer, a general method is adopted. The negative electrode is also manufactured in the same manner. Subsequently, the electrode (positive electrode 11) is pressed with a roll. The press pressure is usually 1000 N / cm or more and 24000 N / cm or less. Due to the thickness of the active material layer, a larger force is applied to the covering portion 104 by pressing than to the exposed portion 105. As the metal foil in the covering portion 104 is compressed more strongly, the thickness of the metal foil in the covering portion 104 becomes thinner than the thickness of the metal foil in the exposed portion 105, and the electrode may bend due to the variation in the thickness of the metal foil. ..

In the formation of the electrode body 2, the electrode body 2 is formed by winding the laminated body 22 having the separator 4 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 superposed so that the positive electrode active material layer 112 and the negative electrode active material layer 122 face each other via the separator 4 to form the laminated body 22. Subsequently, the laminated body 22 is wound to form the electrode body 2.

In assembling the power storage element 1, the electrode body 2 is put into the case body 31 of the case 3, the opening of the case body 31 is closed with the lid plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case body 31 with the lid plate 32, the electrode body 2 is inserted inside the case body 31, the positive electrode 11 and one external terminal 7 are made conductive, and the negative electrode 12 and the other external terminal 7 are connected. The opening of the case body 31 is closed with the lid plate 32 in a conductive state. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 through the injection hole of the lid plate 32 of the case 3.

In the power storage element 1 of the present embodiment configured as described above, the particle size D50 and the particle size D90 of the active material of the positive electrode 11 are 0.39 ≤ particle size D50 / (particle size D50 + particle size D90) ≤ 0. Satisfy the relational expression of .43. The mechanism by which an electrode whose bending is suppressed by pressing is obtained by satisfying the relational expression is not always clear, but it is presumed to be as follows. That is, since the particle size of the active material of the positive electrode 11 satisfies the above relational expression, even if the positive electrode 11 is pressed, smaller particles appropriately enter between the larger particles in the positive electrode active material layer 112. As the small particles enter between the large particles, the compressive force in the thickness direction is dispersed in the plane direction of the positive electrode active material layer 112. Therefore, it is possible to prevent the compressive force from being concentrated on a part of the positive electrode base material (metal foil 111). As a result, the positive electrode active material layer 112 is pressed against the positive electrode base material (metal foil 111) with a relatively uniform force. Since the force is applied relatively evenly to the positive electrode base material (metal foil 111), the positive electrode base material (metal leaf 111) is prevented from stretching due to the non-uniform compressive force. Therefore, it is possible to prevent the positive electrode 11 from bending so as to undulate in the thickness direction. Further, the positive electrode 11 in which a part of the positive electrode base material (metal foil 111) is exposed without overlapping with the active material can be prevented from bending and bending. That is, the positive electrode 11 in which the positive electrode base material (metal foil 111) is exposed along one side of the rectangular positive electrode base material (metal foil 111) is prevented from being curved with the exposed side inward. As described above, according to the power storage element 1 of the present embodiment, it is possible to suppress the bending of the positive electrode 11.

In the above-mentioned power storage element 1, the positive electrode 11 has a covering portion 104 and an exposed portion 105. When the positive electrode 11 having the covering portion 104 and the exposed portion 105 is pressed in the thickness direction, a stronger force is applied to the covering portion 104 by the thickness of the positive electrode active material layer 112. However, even if the positive electrode 11 has a coated portion and an exposed portion, the positive electrode 11 is more reliably suppressed from being bent by the press because the force is applied relatively evenly from the coated portion to the positive electrode base material (metal foil 111). it can.

In the power storage element 1, the positive electrodes 11 are stacked in the thickness direction. The negative electrodes 12 are also stacked in the thickness direction. Specifically, the positive electrode 11 and the negative electrode 12 are laminated on the laminated body 22, and the laminated body 22 is wound to form the electrode body 2. As described above, since the positive electrode 11 is suppressed from being wavy or curved and bent, the distance between the electrodes can be made more uniform in the electrode body 2.

In the above-mentioned power storage element 1, since the particle size D50 of the active material contained in the positive electrode active material layer 112 is 2 μm or more and 10 μm or less, the particle size of the active material is relatively small. It can have sufficient output.

The power storage element of the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. In addition, some of the configurations of certain embodiments can be deleted.

In the above embodiment, the electrodes (positive electrode and negative electrode) in which the layer containing the active material is in direct contact with the metal foil have been described in detail, but in the present invention, at least one of the positive electrode and the negative electrode is a binder and a conductive auxiliary agent. May have a conductive layer containing. At least one of the positive electrode active material layer 112 and the negative electrode active material layer 122 may have a conductive layer, and the conductive layer may be arranged on the surface of the active material layer in contact with the electrode base material (metal foil).

In the above embodiment, the electrodes in which the active material layer is arranged on both sides of the metal leaf of each electrode have been described, but in the power storage element of the present invention, the positive electrode 11 or the negative electrode 12 has the active material layer on one side of the metal leaf. It may be provided only on the side.

In the above embodiment, the power storage element in which the electrode containing the active material satisfying the above relational expression is the positive electrode has been described, but in the power storage element of the present invention, the electrode containing the active material satisfying the above relational expression is the negative electrode. May be good.

In the above embodiment, the power storage element 1 including the electrode body 2 in which the laminated body 22 is wound has been described in detail, but the power storage element of the present invention may include the laminated body 22 which is not wound. Specifically, the power 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, but the type and size (capacity) of the power storage element 1 are arbitrary. is there. Further, in the above embodiment, the lithium ion secondary battery has been described as an example of the power storage element 1, but the present invention is not limited to this. For example, the present invention can be applied to various secondary batteries and other storage elements of capacitors such as electric double layer capacitors.

In the above embodiment, the exposed portion is provided at one end of the strip-shaped metal foil in the lateral direction, but the present invention is not limited to such an embodiment. That is, the exposed portion may be provided at two or more sides of the metal foil. Specifically, the exposed portions may be provided along both ends of the strip-shaped metal foil in the lateral direction. If the electrode is provided with an exposed portion along one end of the metal foil in the lateral direction as in the above embodiment, the metal foil (specifically, the covering portion) is provided at the time of pressing. And the exposed part), the electrode is easily curved because the force is applied asymmetrically. However, even with such an electrode, the effect of suppressing curvature is remarkably exhibited.

The power storage element 1 (for example, a battery) may be used in a power storage device 100 (a battery module when the power storage element is a battery) as shown in FIG. 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 non-aqueous electrolyte secondary battery (lithium ion secondary battery) was manufactured as shown below.

(Example 1)
(1) Preparation of Positive Electrode An active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having a predetermined particle size distribution was prepared. The particle size D50 of the active material determined from the particle size distribution was 3.8 μm, and the particle size D90 was 5.0 μm. A mixture for the positive electrode was prepared by mixing and kneading N-methyl-2-pyrrolidone (NMP) as a solvent, a conductive auxiliary agent (acetylene black), a binder (PVdF), and an active material. .. The blending amounts of the conductive auxiliary agent, the binder, and the active material were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. The prepared mixture for the positive electrode was applied to both sides of the aluminum foil (thickness of 15 μm) so that the coating amount (basis weight) after drying was 17.2 mg / cm ² . After drying, a roll press was performed. The roll press was performed so that the packing density of the active material layer was 2.7 g / cm ^3. Then, it was vacuum dried to remove water. The thickness of the active material layer (for one layer) was 32 μm.
The particle size distribution of the active material of the positive electrode was measured using a laser diffraction / scattering type particle size distribution measuring device. Then, the particle size D50 and the particle size D90 were obtained from the particle size distribution. The particle size D10 was also determined in the same manner. The details of the measurement conditions are as follows.
・ Device name, model, manufacturer name Manufacturer: Microtrack Bell Co., Ltd. Device: Laser diffraction / scattering type particle size distribution measuring device Model: MT3000EXII
-Pretreatment Dispersion medium: Distilled water Dispersant: Product name "Extran MA02 Neutral" (Merck) 0.5% (Diluted water diluted with 0.5% Extran MA02 Neutral was used as the solvent. )
-Circulate the solution prepared by pretreatment in the bath of the sampling circulator (SDC (Sample Delivery Controller)), and add the sample (powder of active material) little by little so that the transmittance becomes 0.85 ± 0.05. did.
Dispersion Dispersion condition: Cardiovascular system (SDC (Sample Delivery Controller)
After putting the sample (active material) into), ultrasonic waves were irradiated at an output of 40 W for 120 sec while circulating at a flow velocity of 24 mL / sec.
-Measurement conditions After dispersion, measurement was performed 5 times with a measurement time of 10 sec, and the results of 5 times were averaged.

(2) Preparation of Negative Electrode As the active material, particulate non-graphitized carbon having a particle size D50 of 4 μm was used. Moreover, PVdF was used as a binder. The mixture for the negative electrode was prepared by mixing and kneading NMP, a binder, and an active material as solvents. The binder was blended so as to be 7% by mass, and the active material was blended so as to be 93% by mass. The prepared mixture for the negative electrode was applied to both sides of the copper foil (10 μm thickness) so that the coating amount (weight) after drying was 7.9 mg / cm ^2. After drying, a roll press was performed and vacuum dried to remove water. The thickness of the active material layer (for one layer) was 35 μm.

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

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

(5) Arrangement of Electrode Body in Case Using the above positive electrode, the above negative electrode, the above electrolytic solution, the separator, and the case, a battery was manufactured by a general method.
First, a sheet-like material formed by arranging and laminating a separator between the positive electrode and the negative electrode was wound around. Next, the wound electrode body was placed in the case body of the aluminum square battery case as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to each of the two external terminals. Furthermore, a lid plate was attached to the case body. The above electrolytic solution was injected into the case through a liquid injection port formed on the lid plate of the case. Finally, the case was sealed by sealing the injection port of the case.

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that an active material having a particle size D50 of 3.9 μm and a particle size D90 of 5.7 μm was used in the production of the positive electrode.

(Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that an active material having a particle size D50 of 5.6 μm and a particle size D90 of 8.8 μm was used in the production of the positive electrode.

(Example 4)
In the production of the positive electrode, except that an active material having a particle size D50 of 6.0 μm, a particle size D90 of 9.0 μm, and a composition of LiNi _1/6 Co _2/3 Mn _1/6 O _{2 was used.} Manufactured a lithium ion secondary battery in the same manner as in Example 1.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that an active material having a particle size D50 of 5.1 μm and a particle size D90 of 8.2 μm was used in the production of the positive electrode.

(Comparative Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that an active material having a particle size D50 of 5.5 μm and a particle size D90 of 8.8 μm was used in the production of the positive electrode.

(Comparative Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that an active material having a particle size D50 of 5.7 μm and a particle size D90 of 7.3 μm was used in the production of the positive electrode.

<Evaluation of cathode bending (curving) by pressing>
The curvature value of the positive electrode was measured as follows. First, the positive electrode was vacuum-dried, and the positive electrode after vacuum-drying was cut off to a length of 2 m. Next, the cut positive electrode was arranged so that the longitudinal direction of the 5 m straight metal scale and the longitudinal direction of the positive electrode were substantially parallel to each other. One end (corner) of the exposed portion in the longitudinal direction and the other end (corner) were grounded to the metal scale. The distance of the gap from the edge of the exposed portion to the metal scale was measured at a portion 1 m from one end in the longitudinal direction of the exposed portion (that is, the central portion in the longitudinal direction of the positive electrode). In the measurement, a scale loupe having a minimum unit of 0.1 mm was used, and the measured value was a curvature value (mm).

Tables 1 and 9 show the results of evaluation of the bending (curving) of the positive electrode in the batteries of each Example and each Comparative Example. As can be seen from Table 1 and FIG. 9, in the battery of the example satisfying the above relational expression, the bending of the electrode could be suppressed as compared with the battery of the comparative example. In particular, when 0.40 ≤ particle size D50 / (particle size D50 + particle size D90) ≤ 0.41, it was found that the curvature value can be made smaller.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
26: Exposed laminated part,
3: Case, 31: Case body, 32: Lid plate,
4: Separator,
5: Current collector, 50: Clip member, 6: Insulation cover,
7: External terminal, 71: Surface,
11: Positive electrode,
111: Metal leaf of positive electrode (positive electrode base material), 112: Positive electrode active material layer,
12: Negative electrode,
121: Metal leaf of negative electrode (negative electrode base material), 122: Negative electrode active material layer,
104: Cover, 105: Exposed,
91: Bus bar member,
100: Power storage device.

Claims (5)

An electrode having a foil-shaped electrode base material and an active material layer superimposed on the electrode base material and containing a particulate active material is provided.
The particle size D50 and the particle size D90 of the active material satisfy the relational expression of 0.39 ≤ particle size D50 / (particle size D50 + particle size D90) ≤ 0.43 (in the formula, the particle size D50 is the particle size distribution). The particle size D90 is the particle size at which the volume integration is 50%, and the particle size D90 is the particle size at which the volume integration is 90% in the particle size distribution). The power storage element according to claim 1, wherein the electrode is a positive electrode. The active _{material, Li v Ni w Mn x Co} y O z lithium-metal composite oxide represented by the chemical composition (but is 0 <v ≦ 1.3, a w + x + y = 1, 0 <w < The power storage element according to claim 2, wherein 1 is, 0 <x <1, 0 <y <1, and 1.7 ≦ z ≦ 2.3). The electrode is exposed to a coating portion in which the electrode base material is covered by overlapping the active material layer on the electrode base material and an exposed portion in which the active material layer is not overlapped on the electrode base material and the electrode base material is exposed. The power storage element according to any one of claims 1 to 3, further comprising a part. The power storage element according to any one of claims 1 to 4, wherein the electrodes are stacked in the thickness direction.

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