JP2017168302A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device which can adequately prevent an overcharged state from being continued.SOLUTION: A power storage device comprises: a positive electrode; a negative electrode; a separator disposed between the positive and negative electrodes; and an electrolyte solution impregnated into the separator. At least one of the positive and negative electrodes has: an electrode base material; a conductive layer overlying on the electrode base material and including polyvinylidene fluoride and a conductive assistant; and an active material layer overlying the conductive layer. The electrolyte solution includes 0.5-4.0 mass% of biphenyl. The conductive layer includes 2 g/mor more of the polyvinylidene fluoride.SELECTED DRAWING: None

Description

  The present invention relates to a power storage element.

  2. Description of the Related Art Conventionally, an electricity storage element formed by accommodating an electrode structure and an electrolytic solution in a container is known. In this type of power storage device, the electrode structure includes a positive electrode sheet including a current collector and an active material layer laminated on the current collector, and a current collector and an active material laminated on the current collector. A negative electrode sheet including a layer, and a separator disposed between the positive electrode sheet and the negative electrode sheet.

  As the electric storage element, there is a battery having a conductive layer including a polyvinylidene fluoride as a binder and a conductive material, the conductive layer being disposed between the positive electrode current collector and the active material layer. Known (for example, Patent Document 1).

  The battery described in Patent Document 1 may be in an overcharged state. In the battery described in Patent Document 1, when the battery is overcharged, the temperature of the conductive layer rises due to heat generated by Joule heat. This rise in temperature causes the polyvinylidene fluoride to expand (increase in volume) and increase the electrical resistance of the conductive layer. As a result, the current between the current collector and the active material layer is interrupted, and the overcharged state of the battery can be cut off.

  However, in the nonaqueous electrolyte secondary battery described in Patent Document 1, it may not always be possible to sufficiently prevent the overcharged state from continuing.

JP 2006-4739 A

  This embodiment makes it a subject to provide the electrical storage element which can fully prevent that an overcharge state continues.

The electricity storage device of the present embodiment includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolytic solution impregnated in the separator, and at least one of the positive electrode and the negative electrode is an electrode substrate. And a conductive layer containing polyvinylidene fluoride and a conductive auxiliary agent, which is superimposed on the electrode substrate, and an active material layer superimposed on the conductive layer, and the electrolytic solution contains biphenyl in an amount of 0.5% by mass or more and 4.0% by mass. % Or less, and the conductive layer contains ² g / m ² or more of polyvinylidene fluoride.

In the above electricity storage element, since the conductive layer contains ² g / m ² or more of polyvinylidene fluoride, when the temperature of the conductive layer rises due to an overcharged state, the polyvinylidene fluoride expands and the electric resistance of the conductive layer Becomes larger. Thereby, the electroconductivity between an electrode base material and a positive electrode active material layer can be reduced comparatively early. In addition, since the electrolytic solution contains 0.5% by mass or more of biphenyl, when the overcharged state occurs, biphenyl generates heat, thereby promoting the temperature rise of the conductive layer. As the temperature rise is promoted, the polyvinylidene fluoride expands early. Therefore, the electrical resistance of the conductive layer increases early, and the current between the electrode base material and the positive electrode active material layer is interrupted early. In addition, since electrolyte solution contains 4.0 mass% or less of biphenyl, normal charging / discharging reaction is not prevented by biphenyl. Thus, according to the electricity storage device having the above configuration, it is possible to sufficiently prevent the overcharge state from continuing.

  In the above electricity storage device, the mass ratio of polyvinylidene fluoride to biphenyl may be 1.4 or more and 22 or less. When the above-mentioned mass ratio is 1.4 or more and 22 or less, it is possible to more sufficiently prevent the overcharge state from continuing.

  According to the present embodiment, it is possible to provide a storage element in which the overcharge state is sufficiently prevented from continuing.

FIG. 1 is a perspective view of a power storage device according to this embodiment. FIG. 2 is a front view of the energy storage device according to the embodiment. 3 is a cross-sectional view taken along line III-III in FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a perspective view of a state in which a part of the energy storage device according to the embodiment is assembled, and is a perspective view of a state in which a liquid filling tap, an electrode body, a current collector, and an external terminal are assembled to a lid plate. is there. FIG. 6 is a view for explaining the configuration of the electrode body of the energy storage device according to the embodiment. FIG. 7 is a cross-sectional view of the superimposed positive electrode, negative electrode, and separator (cross section VII-VII in FIG. 6). FIG. 8 is a perspective view of a power storage device including the power storage element according to the embodiment.

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

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

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

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

  The positive electrode 11 is disposed between the metal foil 111 and the active material layer 112, the metal foil (positive electrode base material) 111, the active material layer 112 disposed so as to cover the surface of the metal foil 111 and containing the active material. And a porous conductive layer 113 formed. In the present embodiment, the conductive layer 113 overlaps both surfaces of the metal foil 111. The active material layer 112 overlaps with one surface of each conductive layer 113. The active material layers 112 are respectively disposed on both sides of the metal foil 111 in the thickness direction, and similarly, the conductive layers 113 are respectively disposed on both sides of the metal foil 111 in the thickness direction. The thickness of the positive electrode 11 is usually 40 μm or more and 150 μm or less.

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

  The positive electrode active material layer 112 includes a particulate active material, a particulate conductive aid, and a binder. In the positive electrode active material layer 112, the content of the active material is usually 88% by mass to 95% by mass, the content of the conductive auxiliary agent is 2.5% by mass to 6.0% by mass, Content is 2.5 mass% or more and 6.0 mass% or less.

The basis weight of the positive electrode active material layer 112 is usually 5 mg / cm ² or more and 10 mg / cm ² or less. The density of the positive electrode active material layer 112 is usually 1.9 g / cm ³ or more and 2.8 g / cm ³ or less. The basis weight and the density are densities in 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 diameter D50 of the active material of the positive electrode 11 is usually 3 μm or more and 8 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, for _example, Li p _MeO t (Me represents one or more transition metal) complex oxide represented by _{(Li p Co s O 2,} Li p Ni q O _{2, Li p Mn r O 4} , Li p Ni q Co s Mn r O 2 , etc.), _{or, Li y Me u (XO v} ) w (Me represents one or more transition metals, X is e.g. P, Si, B, a polyanion compounds represented by the representative of the _{V) (Li y Fe u PO} 4, Li y Mn u PO 4, Li y Mn u SiO 4, Li y Co u PO 4 F , etc.).

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

Additional such _{Li p Ni q Mn r Co s} O lithium-metal composite oxide represented by the chemical composition of the _t, for _{example, LiNi 1/3 Co 1/3 Mn 1/3 O} 2, LiNi 1/6 Co 1 _{/ 6} Mn _2/3 O ₂ , LiCoO ₂ and the like.

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

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

  The conductive layer 113 includes a particulate conductive additive and a binder (binder). Note that the conductive layer 113 does not include a positive electrode active material. The conductive layer 113 is formed to be porous by a gap between conductive assistants. The conductive layer 113 is impregnated with an electrolyte solution described later. The conductive layer 113 has conductivity because it includes a conductive additive. The conductive layer 113 serves as an electron path between the metal foil 111 and the positive electrode active material layer 112, and maintains electrical conductivity therebetween. The conductivity of the conductive layer 113 is usually higher than the conductivity of the positive electrode active material layer 112.

  The conductive layer 113 is disposed between the metal foil 111 and the positive electrode active material layer 112. The conductive layer 113 containing a binder (binder) has sufficient adhesion to the metal foil 111. The conductive layer 113 has sufficient adhesion to the positive electrode active material layer 112.

The thickness of the conductive layer 113 is usually 10 μm or more and 50 μm or less. The basis weight of the conductive layer 113 is usually 1 g / m ² or more and 6 g / m ² or less. The density of the conductive layer 113 is usually 5 g / cm ³ or more and 10 g / cm ³ or less. Note that the basis weight and density of the conductive layer 113 are amounts on one side of the metal foil 111.

The conductive additive of the conductive layer 113 is a carbonaceous material containing 98% by mass or more of carbon. The electric conductivity of the carbonaceous material is usually 10 ⁻⁶ S / m or more. Examples of the carbonaceous material include ketjen black (registered trademark), acetylene black, and graphite. The conductive layer 113 of this embodiment has acetylene black as a conductive additive. The average particle diameter D50 of the conductive assistant is usually 20 nm or more and 150 nm or less.

  The binder of the conductive layer 113 includes at least polyvinylidene fluoride (PVdF). The binder is a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide , Polyimide, polyamideimide, polyethylene oxide (polyethylene glycol), polypropylene oxide (polypropylene glycol), polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyolefin, nitrile- A synthetic polymer compound such as butadiene rubber may be further included. Further, the binder of the conductive layer 113 may include natural polymer compounds such as chitosan and chitosan derivatives, cellulose and cellulose derivatives, for example.

The conductive layer 113 usually contains 20% by mass or more and 50% by mass or less of a carbonaceous material as a conductive assistant, and contains 50% by mass or more and 95.5% by mass or less of a binder (PVdF). The conductive layer 113 preferably contains 90% by mass or less of a binder (PVdF). The conductive layer 113 contains ² g / m ² or more of a binder (PVdF). The conductive layer 113 usually contains 5 g / m ² or less of binder (PVdF).

  The negative electrode 12 includes a metal foil (negative electrode base material) 121 and a negative electrode active material layer 122 formed on the metal foil 121. In the present embodiment, the negative electrode active material layer 122 is overlaid on both surfaces of the metal foil 121. The metal foil 121 has a strip shape. The metal foil 121 of the negative electrode of this embodiment is, for example, a copper foil. The negative electrode 12 has an uncoated portion 125 of the negative electrode active material layer 122 (a portion where the negative electrode active material layer is not formed) at one end edge in the width direction, which is the short direction of the belt shape. The thickness of the negative electrode 12 is usually 30 μm or more and 150 μm or less.

  The negative electrode active material layer 122 includes a particulate active material and a binder. The negative electrode active material layer 122 is disposed so as to face the positive electrode 11 with the separator 4 interposed therebetween. The width of the negative electrode active material layer 122 is larger than the width of the positive electrode active material layer 112. The thickness of the negative electrode active material layer 122 is usually 10 μm or more and 50 μm or less.

  In the negative electrode active material layer 122, the ratio of the binder may be 5% by mass or more and 10% by mass or less with respect to the total mass of the negative electrode active material and the binder.

  The active material of the negative electrode 12 can contribute to the electrode reaction of the charge reaction and the discharge reaction in the negative electrode 12. For example, the active material of the negative electrode 12 has an alloying reaction with carbon materials such as graphite and amorphous carbon (non-graphitizable carbon and graphitizable carbon), or lithium ions such as silicon (Si) and tin (Sn). The resulting material. The active material of the negative electrode of this embodiment is amorphous carbon. More specifically, the negative electrode active material is non-graphitizable carbon. The average particle diameter D50 of the active material of the negative electrode 12 is usually 1 μm or more and 10 μm or less.

The weight per unit area (one layer) of the negative electrode active material layer 122 is usually 2.5 mg / cm ² or more and 5.0 mg / cm ² or less. The density (one layer) of the negative electrode active material layer 122 is usually 1 g / cm ³ or more and 3 g / cm ³ or less.

  The binder used for the negative electrode active material layer 122 is the same as the binder used for the positive electrode active material layer 112. The binder of this embodiment is polyvinylidene fluoride.

  The negative electrode active material layer 122 may further include a conductive additive such as ketjen black (registered trademark), acetylene black, or graphite.

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

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

  The separator substrate is configured to be porous by, for example, a woven fabric, a nonwoven fabric, or a porous film. Examples of the material for the separator substrate include polymer compounds, glass, and ceramics. Examples of the polymer compound include polyesters such as polyacrylonitrile (PAN), polyamide (PA), and polyethylene terephthalate (PET), polyolefins (PO) such as polypropylene (PP) and polyethylene (PE), and cellulose. .

  The width of the separator 4 (the dimension of the strip shape in the short direction) is slightly larger than the width of the negative electrode active material layer 122. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 that are stacked in a state of being displaced in the width direction so that the positive electrode active material layer 112 and the negative electrode active material layer 122 overlap. At this time, as shown in FIG. 6, the non-covered portion 115 of the positive electrode 11 and the non-covered portion 125 of the negative electrode 12 do not overlap. That is, the uncovered portion 115 of the positive electrode 11 protrudes in the width direction from the region where the positive electrode 11 and the negative electrode 12 overlap, and the non-covered portion 125 of the negative electrode 12 extends from the region where the positive electrode 11 and the negative electrode 12 overlap in the width direction ( It protrudes in a direction opposite to the protruding direction of the non-covering portion 115 of the positive electrode 11. The electrode body 2 is formed by winding the stacked positive electrode 11, negative electrode 12, and separator 4, that is, the stacked body 22. The portion where only the uncovered portion 115 of the positive electrode 11 or the uncovered portion 125 of the negative electrode 12 is stacked constitutes the uncoated stacked portion 26 in the electrode body 2.

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

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

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

  The electrolytic solution contains 0.5% by mass or more and 4.0% by mass or less of biphenyl. The electrolytic solution preferably contains 0.5% by mass to 3.0% by mass of biphenyl. The mass ratio of polyvinylidene fluoride in the conductive layer 113 to biphenyl in the electrolytic solution is usually 1.4 or more and 22 or less. Such a mass ratio is preferably 4 or more and 21 or less.

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

The case 3 is formed by joining the peripheral edge of the opening of the case main body 31 and the peripheral edge of the rectangular lid plate 32 in an overlapping state. The case 3 has an internal space defined by the case main body 31 and the lid plate 32. In this embodiment, the opening peripheral part of the case main body 31 and the peripheral part of the cover plate 32 are joined by welding.
In the following, as shown in FIG. 1, the long side direction of the cover plate 32 is the X-axis direction, the short side direction of the cover plate 32 is the Y-axis direction, and the normal direction of the cover plate 32 is the Z-axis direction.

  The case body 31 has a rectangular tube shape (that is, a bottomed rectangular tube shape) in which one end in the opening direction (Z-axis direction) is closed. The lid plate 32 is a plate-like member that closes the opening of the case body 31.

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

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

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

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

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

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

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

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

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

  In the manufacturing method of the electrical storage element 1, the mixture containing an active material is apply | coated to metal foil, an active material layer is formed, and an electrode (the positive electrode 11 and the negative electrode 12) is produced. Note that in the production of the positive electrode 11, the conductive material 113 containing a conductive additive is formed on the metal foil 111, and then the active material layer 112 is formed. Next, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped to form the electrode body 2. Subsequently, the electrode body 2 is put in the case 3 and the electrolytic solution is put in the case 3 to assemble the power storage element 1.

  In the production of the electrode (positive electrode 11), a conductive layer 113 is formed by applying a composition for a conductive layer containing a conductive additive, a binder, and a solvent to both surfaces of a metal foil and drying the composition. . Further, the positive electrode active material layer 112 is formed by applying a mixture containing an active material, a binder, and a solvent to each conductive layer. By adjusting the coating amount, the basis weight of the conductive layer 113 and the positive electrode active material layer 112 can be adjusted. As a coating method for forming the conductive layer 113 and the positive electrode active material layer 112, a general method is employed. The applied conductive layer 113 and positive electrode active material layer 112 are roll-pressed at a predetermined temperature and a predetermined pressure. By adjusting the pressing pressure, the density of the conductive layer 113 and the positive electrode active material layer 112 can be adjusted. After pressing, vacuum drying is performed. Note that a negative electrode is similarly formed without forming a conductive layer.

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

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

The electrolyte solution of the electricity storage device 1 of the present embodiment configured as described above contains 0.5% by mass or more and 4.0% by mass or less of biphenyl. In addition, since the conductive layer 113 contains ² g / m ² or more of polyvinylidene fluoride, when the temperature of the conductive layer 113 rises due to an overcharged state, the polyvinylidene fluoride expands and the electric resistance of the conductive layer 113 is reduced. growing. Thereby, the electrical conductivity between the metal foil 111 and the positive electrode active material layer 112 can be reduced relatively early. In addition, since the electrolytic solution contains 0.5% by mass or more of biphenyl, when the overcharged state occurs, the biphenyl generates heat, and thus the temperature rise of the conductive layer 113 is promoted. As the temperature rise is promoted, the polyvinylidene fluoride expands early. Accordingly, the electrical resistance of the conductive layer 113 increases early, and the current between the metal foil 111 and the positive electrode active material layer 112 is interrupted early. In addition, since electrolyte solution contains 4.0 mass% or less of biphenyl, normal charging / discharging reaction is not prevented by biphenyl. Thus, according to the electric storage element 1 having the above configuration, it is possible to sufficiently prevent the overcharge state from continuing.

  In addition, an overcharge state is a state in which the electrical storage element 1 enters a state in which electric charge is stored exceeding the full charge state.

In the above electricity storage element 1, the conductive layer 113 contains 95.5% by mass or less of polyvinylidene fluoride, or the conductive layer 113 contains 5 g / m ² or less of polyvinylidene fluoride, so that the conductive layer 113 is more It can have sufficient conductivity.

  In said electrical storage element 1, mass ratio of the polyvinylidene fluoride with respect to biphenyl is 1.4 or more and 22 or less. When the above-mentioned mass ratio is 1.4 or more and 22 or less, it is possible to more sufficiently prevent the overcharge state from continuing.

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

  In the above embodiment, the negative electrode in which the active material layer containing the active material is in direct contact with the metal foil has been described in detail. However, in the present invention, the negative electrode may have a conductive layer containing PVdF and a conductive additive. .

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

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

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

  The power storage element 1 (for example, a battery) may be used in a power storage device 100 as shown in FIG. 8 (a battery module when the power storage element is a battery). The power storage device 100 includes at least two power storage elements 1 and a bus bar member 91 that electrically connects two (different) power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element.

  A nonaqueous electrolyte secondary battery (lithium ion secondary battery) was produced as shown below.

Example 1
(1) Preparation of positive electrode Composition for conductive layer by mixing and kneading N-methyl-2-pyrrolidone (NMP), conductive additive (acetylene black) and binder (PVdF) as a solvent. Was prepared. The blending amounts of the conductive assistant and the binder (PVdF) were 17% by mass and 83% by mass, respectively. The prepared composition for a conductive layer was applied to both sides of an aluminum foil (15 μm thickness) so that the coating amount (weight per unit area) after drying was 2.4 g / m ² and dried. Accordingly, the binder (PVdF) content in the conductive layer was 2.0 g / m ² .
Next, N-methyl-2-pyrrolidone (NMP) as a solvent, a conductive additive (acetylene black), a binder (PVdF), and an active material (LiNi _1/3 Co _1/3 ) having an average particle diameter D50 of 5 μm. A mixture for Mn _1/3 O ₂ ) was mixed and kneaded to prepare a mixture for positive electrode. The blending amounts of the conductive assistant, binder, and active material were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. The prepared positive electrode mixture was applied to the conductive layer so that the coating amount (weight per unit area) after drying was 8.61 mg / cm ² . After drying, a roll press was performed. Thereafter, it was vacuum dried to remove moisture and the like. The thickness of the active material layer (for one layer) after pressing was 30 μm. The density of the active material layer was 2.69 g / cm ³ . The thickness of the conductive layer after pressing was 32 μm. The density of the conductive layer was 7.3 g / cm ³ .

(2) Production of Negative Electrode As the active material, particulate amorphous carbon (non-graphitizable carbon) having an average particle diameter D50 of 4 μm was used. Moreover, PVdF was used as the binder. The negative electrode mixture was prepared by mixing and kneading NMP as a solvent, a binder, and an active material. The binder was blended so as to be 7% by mass, and the active material was blended so as to be 93% by mass. The prepared negative electrode mixture was applied to both surfaces of a copper foil (thickness: 10 μm) so that the coating amount (weight per unit area) after drying was 4.0 mg / cm ² . After drying, roll pressing was performed and vacuum drying was performed to remove moisture and the like. The thickness of the active material layer (for one layer) was 35 μm. The density of the active material layer was 1.12 g / cm ³ .

(3) Separator A polyethylene microporous film having a thickness of 22 μm was used as a separator (separator substrate). 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 a non-aqueous solvent, a solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed in a volume of 1: 1: 1 by volume is used, and LiPF ₆ is added to the non-aqueous solvent so that the salt concentration becomes 1 mol / L. Was dissolved to prepare an electrolytic solution. Moreover, the electrolyte solution was prepared so that biphenyl content might be 1.0 mass%.

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

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the electrolytic solution was prepared so that the biphenyl content was 2.0% by mass.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolytic solution containing no biphenyl was prepared.

(Comparative Example 2)
Except that the electrolyte was prepared so that the biphenyl content was 2.0% by mass, and the binder (PVdF) content in the conductive layer was 1.6 g / m ² , the same as in Example 1. A lithium ion secondary battery was manufactured.

<Evaluation of overcharge prevention performance>
Each manufactured battery was overcharged as follows. The battery was charged under the conditions of a start voltage of 4.03 V, a start temperature of 25 ° C., an energization current of 200 A, an upper limit voltage (8.4 V), and a charge depth (150 to 200% predetermined charge depth), and the time until burst was measured.

  In the battery of the example, it was possible to sufficiently prevent the overcharged state from continuing. On the other hand, the battery of the comparative example could not sufficiently prevent the overcharged state from continuing.

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

Claims (2)

A positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte impregnated in the separator,
At least one of the positive electrode and the negative electrode has an electrode substrate, a conductive layer superimposed on the electrode substrate and containing polyvinylidene fluoride and a conductive additive, and an active material layer superimposed on the conductive layer,
The electrolytic solution contains 0.5% by mass to 4.0% by mass of biphenyl,
The conductive layer contains ² g / m ² or more of the polyvinylidene fluoride.   The power storage element according to claim 1, wherein a mass ratio of the polyvinylidene fluoride to the biphenyl is 1.4 or more and 22 or less.