JP6853944B2 - Power storage element - Google Patents

Description

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

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

The reaction layer of the battery described in Patent Document 1 is produced by applying a slurry in which scaly graphite powder and a binder are dispersed in a solvent to a current collector. The reaction layer is prepared by orienting the scaly graphite powder in the slurry with a magnetic field. By the magnetic field, the scaly graphite powder is oriented so that its thickness direction is substantially perpendicular to the current collector.

In the battery described in Patent Document 1, the capacity may decrease after repeated charging and discharging, or the output performance may not be sufficiently exhibited.

Japanese Unexamined Patent Publication No. 2006-127823

An object of the present embodiment is to provide a power storage element in which a decrease in capacity is suppressed after repeated charging and discharging and an output performance is improved.

The power storage element of the present embodiment includes an electrode having a current collecting foil and an active material layer, the active material layer contains active material particles and scaly graphite, and the average angle of the scaly graphite with respect to the current collecting foil is , 20 ° or more and 56 ° or less. Since the average angle of the scaly graphite with respect to the current collecting foil is 20 ° or more and 56 ° or less, the active material layer secures the conductive path in the thickness direction between the current collecting foil and the active material layer by the scaly graphite. It is possible to suppress variations in conductivity in the plane direction of. Therefore, the electronic resistance between the current collector foil and the active material layer can be suppressed low. As a result, the output performance is improved. Further, with the above configuration, it is possible to suppress a decrease in capacity after repeated charging and discharging.

In the above-mentioned power storage element, a plurality of active material particles may be in contact with each of the peripheral portions of one scaly graphite. With such a configuration, a conductive path between the active material particles is secured through the scaly graphite. As such a conductive path is secured, the output performance is further improved, and the decrease in capacitance after repeated charging and discharging is further suppressed.

According to the present embodiment, it is possible to provide a power storage element in which a decrease in capacity is suppressed after repeated charging and discharging and an output performance is improved.

FIG. 1 is a perspective view of a power storage element according to the present embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. FIG. 4 is a diagram for explaining the configuration of the electrode body of the power storage element according to the embodiment. FIG. 5 is a cross-sectional view (VV cross section of FIG. 4) of the superposed positive electrode, negative electrode, and separator. FIG. 6 is a cross-sectional view schematically showing the metal leaf of the positive electrode and the positive electrode active material layer. FIG. 7 is a perspective view of a power storage device including a power storage element according to the same embodiment. FIG. 8 is a graph showing the results of the output performance of the batteries of each test example and the capacity retention rate after the cycle test.

Hereinafter, an embodiment of the power storage element according to the present invention will be described with reference to FIGS. 1 to 6. 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 6, the power storage element 1 includes an electrode body 2 including a positive electrode 11 and a negative electrode 12, a case 3 accommodating the electrode body 2, and an external terminal 7 arranged outside the case 3. It is provided with an external terminal 7 that is electrically connected to the electrode body 2. 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 (current collecting foil) and an 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 active material layer 112 overlaps both surfaces of the metal foil 111. The thickness of the positive electrode 11 is usually 40 μm or more and 150 μm or less.

The metal foil 111 is strip-shaped. The metal foil 111 of the positive electrode 11 of the present embodiment is, for example, an aluminum foil. The positive electrode 11 has an uncoated 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 lateral direction of the band shape.

The positive electrode active material layer 112 contains a particulate active material (active material particles), a particulate conductive auxiliary agent, 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 4 mg / cm ² or more and 17 mg / cm ² or less. The density of the positive electrode active material layer 112 is usually 1.5 g / cm ³ or more and 3.0 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 active material of the positive electrode 11 is a compound that can occlude and release lithium ions. The average particle size D50 of the active material of the positive electrode 11 is usually 2 μm or more and 5 μm or less. The average particle size D50 is measured by the method described in the Examples.

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 , 0 ≦ q ≦ 1, 0 ≦ r ≦ 1, 0 ≦ s ≦ 1, and 1.7 ≦ t ≦ 2.3). It should be noted 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.

The active material of the positive electrode 11 is, for example, _{a polyanion represented by Li p Meu} (XO _v ) _w (Me represents one or more transition metals, and X represents, for example, P, Si, B, V). It may be a compound. However, 0 <p ≦ 1.3, 0.8 ≦ u ≦ 1.2, 3.8 ≦ v ≦ 4.2, and 0.8 ≦ w ≦ 1.2. Examples of the polyanion compound include LiFePO ₄ , LiMnPO ₄ , LiMnSiO ₄ , LiCoPO ₄ F, LiFePO ₄ F 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 contains a carbonaceous material containing 98% by mass or more of carbon as a conductive auxiliary agent. The positive electrode active material layer 112 contains at least scaly graphite as a conductive auxiliary agent. The positive electrode active material layer 112 may further contain, for example, Ketjen Black (registered trademark), acetylene black, graphite other than scaly graphite, and the like as a conductive auxiliary agent. In the positive electrode active material layer 112, the proportion of scaly graphite in the conductive auxiliary agent may be 95% by mass or more.

Scaly graphite is usually plate-shaped. The scaly graphite has a structure in which layers formed by covalently bonding carbon atoms are laminated, and the direction of such lamination usually corresponds to the thickness direction of the scaly graphite. Scaly graphite includes expanded graphite. Expanded graphite is produced, for example, by allowing an inorganic substance such as sulfuric acid to penetrate between layers of scaly graphite. Expanded graphite is produced, for example, by heating and expanding a material in which an inorganic substance has penetrated between layers of scaly graphite.

The scaly graphite of the positive electrode active material layer 112 is oriented at an average angle of 20 ° or more and 56 ° or less with respect to the metal foil 111. Such an average angle is measured in detail as follows. The positive electrode 11 is cut in the thickness direction, and the cross section formed by the cutting is observed with an electron microscope. At least 100 scaly graphites are randomly selected in cross section. However, when selecting the scaly graphite, the scaly graphite in contact with the metal foil 111 and the scaly graphite having at least a part exposed on the surface of the positive electrode active material layer 112 are excluded. The angle (acute angle) between the straight line passing through the long side of the rectangle having the smallest area circumscribing the cross section of each selected scaly graphite and the surface of the metal foil 111 is measured. Obtain the average value of the measured angles.

When measuring the average angle of scaly graphite with respect to the metal foil 111 of the manufactured power storage element, it is measured after constant voltage discharge. For example, after discharging to 3.0 V at a 1 C rate, constant voltage discharge is performed at 3.0 V for 5 hours, the power storage element is disassembled, the positive electrode 11 is taken out, and the positive electrode 11 is washed. The washed positive electrode 11 is cut in the thickness direction as described above, the cross section processed by the cross section polisher (CP) is observed with an electron microscope, and the above average angle is measured.

In the positive electrode active material layer 112, the above-mentioned average angle (average orientation angle) of the scaly graphite can be adjusted as follows when the positive electrode 11 is manufactured. After applying a mixture (described later) containing active material particles and scaly graphite to the metal leaf 111, a magnetic field is applied in the thickness direction of the metal leaf 111 to apply the plate-shaped scaly graphite to the surface of the metal foil 111. Orient almost vertically. That is, the scaly graphite is oriented so that the thickness direction of the scaly graphite and the thickness direction of the metal leaf 111 are substantially perpendicular to each other. At this time, by increasing the magnetic flux density of the applied magnetic field, the scaly graphite can be oriented in a more vertical direction. Then, the applied mixture is pressed at an appropriate pressure. By lowering the pressing pressure during pressing, the average orientation angle of the scaly graphite can be increased. In this way, the average angle of the scaly graphite with respect to the metal foil 111 is adjusted to 20 ° or more and 56 ° or less.

The aspect ratio of scaly graphite may be 10 or more.
In the cross section of the positive electrode active material layer 112 in the thickness direction, the average aspect ratio (vertical length to horizontal length) of the scaly graphite may be 10 or more. The average aspect ratio is usually 100 or less. Each vertical length when measuring the above aspect ratio is the length of a straight line segment passing through both ends of each scaly graphite in the above cross section. On the other hand, the horizontal length when measuring the aspect ratio is the length of the thickest portion of the thickness length of the scaly graphite in the cross section. The length and width of at least 100 randomly selected scaly graphites are measured, and the average aspect ratio of the scaly graphites is calculated.

In the cross section of the positive electrode active material layer 112 in the thickness direction, the vertical average length of the scaly graphite is usually 10 μm or more and 20 μm or less. The average length of such a vertical length is measured according to the method of measuring the vertical length when measuring the aspect ratio described above. The average thickness of scaly graphite is usually 0.1 μm or more and 2.0 μm or less. Such an average thickness is measured according to the method for measuring the horizontal length when measuring the aspect ratio described above.

In the positive electrode active material layer 112, as shown in FIG. 6, a plurality of active material particles A are in contact with the peripheral portion of one scaly graphite B, respectively. The plurality of active material particles A in contact with one scaly graphite B may be separated from each other. Further, a plurality of scaly graphite B may be in contact with one active material particle A.

In the positive electrode active material layer 112, the average particle size D50 of the active material particles may be smaller than the average length of the scaly graphite. In such a cross section, the ratio of the average length of scaly graphite to the average particle size D50 of the active material particles may be 2 or more and 10 or less. The average particle size D50 of the active material particles is measured by the method described in the Examples. The average length of the scaly graphite is measured by the same method as the above-described method for measuring the vertical length of the scaly graphite.

In the positive electrode active material layer 112, the mass ratio of scaly graphite to the active material particles may be 1% by mass or more and 10% by mass or less.

The negative electrode 12 has 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 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, for example, a copper foil. The negative electrode 12 has an uncoated 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 lateral direction of the band 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 arranged so as to face the positive electrode 11 via the separator 4. 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 undergoes an alloying reaction with a carbon material such as graphite or amorphous carbon (non-graphitized carbon, easily graphitized carbon) or lithium ions such as silicon (Si) and tin (Sn). The resulting material. The active material of the negative electrode of this embodiment is amorphous carbon. More specifically, the active material of the negative electrode is non-graphitized carbon.

The thickness of the negative electrode active material layer 122 (for one layer) is usually 10 μm or more and 50 μm or less. The basis weight (for one layer) of the negative electrode active material layer 122 is usually 3 mg / cm ² or more and 10 mg / cm ² or less. The density (for one layer) of the negative electrode active material layer 122 is usually 0.9 g / cm ³ or more and 1.6 g / cm ³ or less.

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 2% 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 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.

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 separator 4 is a member having an insulating property. 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 has a strip shape. The separator 4 has a porous separator base material. The separator 4 is arranged 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 the present embodiment has only the separator base material 41.

The separator base material 41 is made porous by, for example, a woven fabric, a non-woven fabric, or a porous membrane. Examples of the material of the separator base material 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. At this time, as shown in FIG. 4, the uncoated portion 115 of the positive electrode 11 and the uncoated portion 125 of the negative electrode 12 do not overlap. That is, the uncoated 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 uncoated portion 125 of the negative electrode 12 protrudes in the width direction from the region where the positive electrode 11 and the negative electrode 12 overlap. It protrudes in the direction opposite to the protruding direction of the uncoated portion 115 of the positive electrode 11. 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 uncoated laminated portion 26 in the electrode body 2 is formed by the portion where only the uncoated portion 115 of the positive electrode 11 or the uncoated portion 125 of the negative electrode 12 is laminated.

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

The uncoated laminated portion 26 configured as described above is provided at each electrode of the electrode body 2. That is, the uncoated laminated portion 26 in which only the uncoated portion 115 of the positive electrode 11 is laminated constitutes the uncoated laminated portion of the positive electrode 11 in the electrode body 2, and only the uncoated 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 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 of the present embodiment is obtained by dissolving _{0.5 to 1.5 mol / L of 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 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.

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. 2, 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 current collector 5 is arranged in the uncoated laminated portion 26 of the positive electrode 11 of the electrode body 2 and the uncoated 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) in a state of being housed in a bag-shaped insulating cover 6 that insulates the electrode body 2 and the case 3 is the case 3. It is housed inside.

Next, a method of manufacturing the power storage element 1 of the above embodiment will be described.

In the method for manufacturing the power storage element 1, first, a mixture containing an active material is applied to a metal foil (current collector foil) 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), 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 adopted. A magnetic field is applied to the positive electrode active material layer 112 after coating so that the direction of the magnetic field lines is not parallel to the surface of the metal foil 111, specifically, the vertical direction, and the scaly graphite is oriented. .. Then, the positive electrode active material layer 112 is roll-pressed at a predetermined pressure. By changing the magnetic flux density of the applied magnetic field and changing the press pressure, the average angle of the scaly graphite with respect to the surface of the metal foil 111 can be adjusted. Further, the density of the positive electrode active material layer 112 can be adjusted by changing the press pressure. The negative electrode 12 is manufactured in the same manner without applying a magnetic field.

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. 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 average angle of the scaly graphite with respect to the metal foil 111 in the positive electrode active material layer 112 is 20 ° or more and 56 ° or less. Since the average angle of the scaly graphite with respect to the metal foil 111 is 20 ° or more and 56 ° or less, the positive electrode while ensuring the conductive path in the thickness direction between the metal foil 111 and the positive electrode active material layer 112 by the scaly graphite. It is possible to suppress variations in the conductivity of the active material layer 112 in the plane direction. Therefore, the electronic resistance between the metal foil 111 and the positive electrode active material layer 112 can be suppressed low. As a result, the output performance is improved. Further, with the above configuration, it is possible to suppress a decrease in capacity after repeated charging and discharging (after a cycle).

In the power storage element 1, the plurality of the active material particles may be in contact with each of the peripheral portions of the scaly graphite. With such a configuration, a conductive path between the active material particles is secured through the scaly graphite. As such a conductive path is secured, the output performance is further improved, and the decrease in capacitance after repeated charging and discharging (after the cycle) is further suppressed.

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 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, but in the present invention, the positive electrode is a conductive layer containing a binder and a conductive auxiliary agent and is an active material layer. It may have a conductive layer arranged between the metal foil and the 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 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 non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) capable of charging and discharging 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.

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. 7. 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.

(Test Example 1)
(1) Preparation of positive electrode N-methyl-2-pyrrolidone (NMP) as an organic solvent, a conductive auxiliary agent (scaly graphite), a binder (PVdF), and active material particles (LiNi _1/3 Co _1/3). Mn _1/3 O ₂ ) was mixed and kneaded to prepare a mixture for the positive electrode. The blending amounts of the conductive auxiliary agent, the binder, and the active material particles 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 15 μm) so that the coating amount (basis weight) after drying was 8.61 mg / cm ² . After drying, a magnetic field was applied at a predetermined magnetic flux density so that the direction of the magnetic field lines was the direction of the thickness of the aluminum foil. Further, a roll press was performed at a predetermined pressure. Then, 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 .
The average particle size D50 of the active material was 4 μm as a result of measurement as follows.
Specifically, the active material layer of the positive electrode was taken out from the battery once manufactured. The active material layer was washed with dimethyl carbonate, vacuum dried for 2 hours or more, and then pretreated to disperse the active material layer in N-methylpyrrolidone (NMP). Then, the active material and the conductive auxiliary agent were separated by the difference in specific gravity, and the active material was taken out. A laser diffraction type particle size distribution measuring device (“SALD2200” manufactured by Shimadzu Corporation) was used as the measuring device, and the dedicated application software DMSver2 was used as the measurement control software. As a specific measurement method, a scattering type measurement mode is adopted, and a wet cell in which a dispersion liquid in which a measurement sample (active material particles) is dispersed is placed in an ultrasonic environment for 2 minutes and then irradiated with laser light. Then, the scattered light distribution was obtained from the measurement sample. Then, the scattered light distribution is approximated by a lognormal distribution, and the particle size corresponding to a cumulative degree of 50% (D50) within the range in which the minimum is 0.021 μm and the maximum is 2000 μm in the particle size distribution (horizontal axis, σ). The average diameter was used. The dispersion also contains a surfactant.

(2) Preparation of negative electrode Amorphous carbon (non-graphitized carbon) particles were used as the active material particles. Styrene-butadiene rubber was used as the binder. 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. The CMC was blended so as to be 1.0% by mass, the binder was blended so as to be 2.0% by mass, and the active material particles were blended so as to be 97.0% by mass. The prepared mixture for the negative electrode was applied to both sides of the copper foil (thickness 10 μm) so that the coating amount (weight) after drying was 3.8 mg / cm ^2. After drying, a roll press was performed and vacuum dried to remove water 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 A polyethylene microporous membrane having a thickness of 22 μm was used as the separator base material. The air permeability resistance 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.

(Test Examples 2 to 6)
A battery was manufactured in the same manner as in Test Example 1 except that the average angle of the scaly graphite with respect to the surface of the metal foil was set to each angle shown in Table 1 by changing the magnetic flux density of the applied magnetic field.

<Evaluation of output performance>
The output performance of each battery was evaluated by measuring the direct current resistance (DCR) of the batteries.
1. 1. It was charged to 4.2 V with a constant current of 5 A at 25 ° C., and further charged with a constant voltage of 4.2 V for a total of 3 hours. Then, the initial discharge capacity C1 was measured by discharging at a constant current of 5 A under the condition of a final voltage of 2.4 V.
2. At 25 ° C., a constant current of 5 A was charged to a voltage equivalent to 50% of the initial capacity, and the voltage was further charged for a total of 2 hours.
3. 3. A constant current discharge of 2C1 [A] was performed at 25 ° C., and the current value A1 and the voltage value V1 1 second after the start of the discharge were measured.
4. Above 3. The subsequent battery was discharged at 25 ° C. at a constant current of 5 A under the condition of a final voltage of 2.4 V.
5. Above 2. After charging under the conditions of (1), a constant current discharge of 4C1 [A] was performed at 25 ° C., and the current value A2 and the voltage value V2 1 second after the start of the discharge were measured.
6. Above 4. Discharge under the conditions of 2. above. After charging under the conditions of (1), constant current discharge of 6C1 [A] was performed, and the current value A3 and the voltage value V3 1 second after the start of discharge were measured.
7. Above 4. Discharge under the conditions of 2. above. After charging under the conditions of (1), a constant current discharge of 8C1 [A] was performed, and the current value A4 and the voltage value V4 1 second after the start of the discharge were measured.
8. Above 4. Discharge under the conditions of 2. above. After charging under the conditions of (1), a constant current discharge of 10C1 [A] was performed, and the current value A5 and the voltage value V5 1 second after the start of the discharge were measured.
9. The measured A1 to A5 were plotted on the X-axis and V1 to V5 were plotted on the Y-axis, and the slope was calculated by the method of least squares. From the relationship of V = IR, the calculated slope was defined as the direct current resistance R (DCR).

<Evaluation of capacity retention rate after repeated charging / discharging (after cycle test)>
8. Above. The subsequent battery was discharged at 25 ° C. at a constant current of 5 A under the condition of a final voltage of 2.4 V.
A charge / discharge cycle was performed for 1000 hours at 25 ° C. under the condition of 8C1 [A] in the range of the amount of electricity equivalent to 20% of the initial capacity (SOC 20%) to the amount of electricity equivalent to 80% of the initial capacity (SOC 80%). ..
After the cycle, the battery was charged at 25 ° C. with a constant current of 5 A to 4.2 V, and further charged with a constant voltage of 4.2 V for a total of 3 hours. Then, the discharge capacity C2 after the cycle was measured by discharging at a constant current of 5 A under the condition of a final voltage of 2.4 V.
The capacity retention rate (C2 / C1) was calculated from the measured C1 and C2.

Table 1 shows the evaluation results of the output performance of the batteries manufactured in each test example and the evaluation results of the capacity retention rate after repeated charging and discharging. Further, FIG. 8 shows a graph of the results in Table 1.

As can be seen from Table 1 and FIG. 8, in each test example in which the average angle of the scaly graphite with respect to the metal foil is 20 ° or more and 56 ° or less, the decrease in capacity after repeated charging and discharging is suppressed. Moreover, the output performance is improved.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
26: Uncoated 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: Positive electrode metal foil (current collector foil), 112: Positive electrode active material layer,
12: Negative electrode,
121: Negative electrode metal foil (current collector foil), 122: Negative electrode active material layer,
91: Bus bar member,
100: Power storage device.

Claims (2)

Equipped with an electrode having a current collecting foil and an active material layer,
The active material layer contains active material particles and scaly graphite.
A power storage element having an average angle of the scaly graphite with respect to the current collecting foil of 20 ° or more and 49 ° or less. The power storage element according to claim 1, wherein the plurality of the active material particles are in contact with each of the peripheral portions of the scaly graphite.

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