TITLE OF THE INVENTION: BAG-PACKED POSITIVE ELECTRODE PLATE, LAYERED ELECTRODE ASSEMBLY, AND ENERGY STORAGE DEVICE

TECHNICAL FIELD

[0001]

The present invention relates to a bag-packed positive electrode plate, a layered electrode assembly, and an energy storage device.

BACKGROUND ART

[0002]

A chargeable and dischargeable energy storage device has been used in various equipment such as a mobile phone or an electric vehicle.

Recently, along with a realization of higher output and higher performance of these equipment, an energy storage device which is smaller in size and having a larger electric capacity (larger energy density) has been requested.

[0003]

In general, the energy storage device includes a layered electrode assembly which is formed by alternately stacking a positive electrode plate having a surface on which a positive active material layer is formed and a negative electrode plate having a surface on which a negative active material layer is formed with a separator having electric insulation property sandwiched between the positive electrode plate and the negative electrode plate. To increase an electric capacity per unit volume in such an energy storage device, it is effective to reduce a thickness of the separator. To satisfy such a request, an energy storage device where a separator is formed of a porous resin film has been put into practice.

[0004]

In an energy storage device, there is a possibility that metal precipitation (lithium dendrite, for example) which is formed on a negative electrode by electrodeposition penetrates a separator thus causing minute short-circuiting between a positive electrode plate and a negative electrode plate. To eliminate such a possibility, there has been known a

configuration of a layered electrode assembly which can suppress mixing of metal species which generate metal ions capable of forming a precipitation on an electrolyte in the vicinity of the positive electrode plate and can suppress electrodeposition caused by contacting of metal ions with a negative electrode using a bag-packed electrode plate which is formed into a bag shape by welding outer peripheries of a pair of separators which sandwiches the positive electrode plate or the negative electrode plate therebetween to each other.

[0005]

A welded portion of the separators does not contribute to charging and discharging and hence, when a space in the inside of an energy storage device is occupied only by the welded portion of the separators, there may be a possibility that such a configuration obstructs the increase of energy density of the energy storage device. In the energy storage device, when the positive electrode plate projects from the negative electrode plate as viewed in a plan view, an electric current is concentrated on an end portion of the negative electrode plate so that electrodeposition is locally accelerated and hence, it is preferable that the positive electrode plate be disposed so as not to project from the negative electrode plate as viewed in a plan view. Accordingly, by using a layered electrode assembly formed by stacking a bag-packed positive electrode plate and a negative electrode plate which is not bag-packed, the space efficiency can be enhanced thus increasing energy density of the energy storage device.

[0006]

With respect to an energy storage device, there may be a case which is not a normal in-use case of the energy storage device, for example, a case where an object other than the energy storage device is pressed to the energy storage device (for example, an automobile on which the energy storage device is mounted being involved in a traffic accident). In such a case, there is a possibility that the object pierces a layered electrode assembly so that a positive electrode plate and a negative electrode plate are short-circuited thus giving rise to a sharp increase of a temperature in the layered electrode assembly.

[0007]

JP-A-2016- 190499 discloses a technique where an object other than an energy storage device minimally penetrates a separator with the use of a separator which is formed by stacking a porous layer containing inorganic fine particles and a binder resin in a resin film. However, even with the use of configuration described in the patent document, it is not possible to completely prevent the object from penetrating the layered electrode assembly.

[0008] JP-A-2015-213073 discloses a method where a layer which contains inorganic fine particles and a binder resin is disposed on a non-coated portion of a positive electrode. With such a method, even when a foreign substance penetrates a separator which opposedly faces the non-coated portion of the positive electrode, an energy storage device can ensure safety. However, there exists a drawback that coating of the layer which contains the inorganic fine particles and the binder resin to the positive electrode non-coated portion makes the method complicated thus pushing up a manufacturing cost of an energy storage device.

PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0009]

Patent Document l: JP-A-2016- 190499

Patent Document 2- JP-A-2015-213073

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0010]

Inventors of the present invention have studied the generation of heat when an object other than an energy storage device penetrates a layered electrode assembly. As a result of such studies, the inventors of the present invention have confirmed that the generation of heat is relatively liable to become large in a case where the object other than the energy storage device penetrates a region of an electrode plate on which an active material is not stacked (specifically a tab portion which extends for connecting the electrode plate to an electrode terminal of the energy storage device) compared to a case where the object other than the energy storage device penetrates a region of an electrode plate on which the active material is stacked.

[0011]

It is an object of the present invention to provide a bag-packed positive electrode plate, a layered electrode assembly, and an energy storage device which can suppress the generation of heat when an object other than the energy storage device penetrates a tab.

MEANS FOR SOLVING THE PROBLEMS

[0012]

A bag-packed positive electrode plate according to one aspect of the present invention includes ^: a positive electrode plate having a tab; and a pair of separators which sandwiches the positive electrode plate

therebetween, wherein each of the separators has^ a resin layer! a heat resistant layer stacked on the resin layer! and an adhesive layer stacked on a surface of the heat resistant layer which opposedly faces the positive electrode plate, and the adhesive layers of the pair of separators are adhered to the tab.

ADVANTAGES OF THE INVENTION

[0013]

In the bag-packed positive electrode plate according to one aspect of the present invention, the adhesive layers of the pair of separators are adhered to the tab and hence, it is possible to suppress the generation of heat when an object other than an energy storage device penetrates the tab. BRIEF DESCRIPTION OF THE DRAWINGS [0014]

Fig. 1 is a schematic exploded perspective view showing a

configuration of an energy storage device according to one embodiment of the present invention.

Fig. 2 is a schematic partially enlarged cross-sectional view of a layered electrode assembly of the energy storage device shown in Fig. 1.

Fig. 3 is a schematic plan view of a bag-packed positive electrode plate of the energy storage device shown in Fig. 1.

MODE FOR CARRYING OUT THE INVENTION

[0015]

A bag-packed positive electrode plate according to one aspect of the present invention includes ^: a positive electrode plate having a tab; and a pair of separators which sandwiches the positive electrode plate

therebetween, wherein each of the separators has^ a resin layer! a heat resistant layer stacked on the resin layer! and an adhesive layer stacked on a surface of the heat resistant layer which opposedly faces the positive electrode plate, and the adhesive layers of the pair of separators are adhered to the tab.

[0016]

In the bag-packed positive electrode plate according to one aspect of the present invention, the separator has the resin layer, the heat resistant layer and the adhesive layer, and the adhesive layer is adhered to the tab of the positive electrode plate. Accordingly, it is considered that even when an object other than the energy storage device penetrates the tab, a state where the separator is adhered to the tab can be maintained and hence, a contact area between a negative electrode plate and the tab can be decreased whereby a short circuit current between the positive electrode plate and the negative electrode plate can be reduced thus suppressing the generation of heat.

[0017]

In the bag-packed positive electrode plate according to one aspect of the present invention, an average distance between an active material stacked region of the positive electrode plate and an adhered region of the adhesive layer to the tab is preferably set to 500 μηι or below, and more preferably set to 300 μηι or below. With such a configuration, it is possible to acquire a relatively large heat generation suppressing effect when an object other than the energy storage device penetrates the tab while ensuring an easy manufacture of the energy storage device.

[0018]

In the bag-packed positive electrode plate according to one aspect of the present invention, it is preferable that the adhesive layer be formed of a mixed material which contains ^: particles including an electrolyte solution and exhibiting ion conductivity! and a binder. With such a configuration, ion conductivity of the adhesive layer can be relatively increased and hence, an output of the energy storage device can be increased.

[0019]

A layered electrode assembly according to another aspect of the present invention includes ^: a plurality of the bag-packed positive electrode plates! and a plurality of negative electrode plates, wherein the bag-packed positive electrode plate and the negative electrode plate are alternately stacked with each other. The layered electrode assembly includes the bag- packed positive electrode plates and hence, the generation of heat when an object other than the energy storage device penetrates the tab can be suppressed.

[0020]

In the layered electrode assembly according to one aspect of the present invention, it is preferable that an adhered region of the adhesive layer to the tab extend to the outside of the negative electrode plate as viewed in a plan view. With such a configuration, the tab is further minimally brought into contact with the negative electrode plate when an object other than the energy storage device penetrates the tab thus suppressing the generation of heat with more certainty.

[0021]

An energy storage device according to another aspect of the present invention includes ^: the layered electrode assembly! and an outer case which accommodates the layered electrode assembly therein. The energy storage device can suppress the generation of heat when an object other than the energy storage device penetrates the tab.

[0022]

Fig. 1 shows an energy storage device according to one embodiment of the present invention. The energy storage device includes a layered electrode assembly 1, and an outer case 2 which accommodates the layered electrode assembly 1 therein. An electrolyte (electrolyte solution) is filled in the outer case 2. The energy storage device further includes a positive electrode terminal 3 and a negative electrode terminal 4 which project from the outer case 2 and are electrically connected to the layered electrode assembly 1.

[0023]

As shown in Fig. 2, the layered electrode assembly 1 includes a plurality of bag-packed positive electrode plates 5 and a plurality of negative electrode plates 6, wherein the bag-packed positive electrode plate 5 and the negative electrode plate 6 are alternately stacked with each other.

[0024]

Each bag-packed positive electrode plate 5 includes a positive electrode plate 7, and a pair of separators 8 which sandwiches the positive electrode plate 7 therebetween. The pair of separators 8 may be two sheets opposedly facing each other, or may be formed by folding one sheet in two.

[0025]

It is preferable that a width of the bag-packed positive electrode plate 5 be set equal to or below a width of the negative electrode plate 6. To be more specific, in the bag-packed positive electrode plate 5, a width of the separator 8 having an approximately rectangular planar shape is set equal to or below a width of the negative electrode plate 6 having an

approximately rectangular planar shape. In such a layered electrode assembly 1, a whole surface of the positive electrode plate 7 held inside the separator 8 as viewed in a plan view is made to opposedly face the negative electrode plate 6 without projecting from the negative electrode plate 6 as viewed in a plan view. That is, the positive electrode plate 7 is embraced within a projection region of the negative electrode plate 6. Accordingly, in the layered electrode assembly 1 and the energy storage device, there is no possibility that a current density is increased on an outer peripheral portion of the negative electrode plate 6 so that electrodeposition is locally

accelerated and hence, short-circuiting caused by the electrodeposition can be prevented.

[0026]

A lower limit of the difference between a width of the bag-packed positive electrode plate 5 and a width of the negative electrode plate 6 (a value obtained by subtracting the width of the bag-packed positive electrode plate 5 from the width of the negative electrode plate 6) is preferably set to 0 mm, and an upper limit of the difference between the width of the bag- packed positive electrode plate 5 and the width of the negative electrode plate 6 is preferably set to 2 mm, and more preferably set to 1.0 mm. By setting the difference between the width of the bag-packed positive electrode plate 5 and the width of the negative electrode plate 6 to the above- mentioned lower limit or above, the bag-packed positive electrode plate 5 and the negative electrode plate 6 can be easily stacked to each other such that the positive electrode plate 7 does not project from the negative electrode plate 6. Further, by setting the difference between the width of the bag-packed positive electrode plate 5 and the width of the negative electrode plate 6 to the above-mentioned upper limit or below, it is possible to prevent the difference in area between the positive electrode plate 7 and the negative electrode plate 6 from increasing unnecessarily thus increasing energy density of the layered electrode assembly 1 and energy density of the energy storage device.

[0027] In the layered electrode assembly 1, by positioning the separator 8 of the bag-packed positive electrode plate 5 with respect to the negative electrode plate 6, the positive electrode plate 7 can be relatively easily positioned with respect to the negative electrode plate 6. Accordingly, in the layered electrode assembly 1, even when a ratio of an area of the positive electrode plate 7 with respect to an area of the negative electrode plate 6 is relatively increased, electrodeposition on the outer edge portion of the negative electrode plate 6 is not accelerated and hence, energy density can be relatively increased.

[0028]

The positive electrode plate 7 includes^ a foil-like or sheet-like positive electrode current collector 9 having conductivity! and a positive active material layer 10 which is stacked on a surface of the positive electrode current collector 9. To be more specific, the positive electrode plate 7 is configured to include an active material stacked region having a rectangular shape as viewed in a plan view where the positive active material layer 10 is stacked on a surface of the positive electrode current collector 9! and a positive electrode tab 11 which extends from the active material stacked region in a strip shape having a width smaller than a width of the active material stacked region and is connected to the positive electrode terminal 3.

[0029]

As a material for forming the positive electrode current collector 9, a metal material such as aluminum, copper, iron or nickel, or an alloy of such metal materials is used. Among these metal materials, from a viewpoint of taking a balance between a level of conductivity and a cost, aluminum, an aluminum alloy, copper, and a copper alloy are preferably used, and aluminum and an aluminum alloy are more preferably used. Further, as the configuration of the positive electrode current collector 9, a foil, a vapor deposition film and the like can be named. From a viewpoint of a cost, the positive electrode current collector 9 is preferably formed of a foil. That is, the positive current collector 9 is preferably made of an aluminum foil. As aluminum or an aluminum alloy, A1085P, A3003P prescribed in JIS-H4000 (2014) or the like can be exemplified.

[0030]

A lower limit of an average thickness of the positive electrode current collector 9 is preferably set to 5 μηι, and more preferably set to 10 μηι. On the other hand, an upper limit of the average thickness of the positive electrode current collector 9 is preferably set to 50 μηι, and more preferably set to 40 μηι. By setting the average thickness of the positive electrode current collector 9 to the above-mentioned lower limit or above, the positive electrode current collector 9 can acquire a sufficient strength. Further, by setting the average thickness of the positive electrode current collector 9 to the above-mentioned upper limit or below, energy density of the energy storage device can be increased.

[0031]

The positive active material layer 10 is made of a so-called positive electrode mixture containing a positive active material. The positive electrode mixture which forms the positive active material layer 10 contains arbitrary components such as a conductive agent, a binder, a thickening agent, a filler and the like when necessary.

[0032]

As the positive active material, for example, a composite oxide expressed by Li _x MO _y (M indicating at least one kind of transition metal) (Li _x Co02, Li _x Ni02, Li _x Mn204, Li _x Mn03, Li _x Ni _a Co(i- _a )02, Li _x Ni _a MnpCoa- _a -p)O2, Li _x Ni _a Mn(2-a)04 or the like), or a polyanion compound expressed by

Li _w Me _x (XOy)z (Me indicating at least one kind of transition metal, X being P, Si, B, V or the like, for example) (LiFeP0 ₄ , LiMnP0 ₄ , LiNiP0 ₄ , L1C0PO4, Li3V2(P0 ₄ )3, Li2MnSi0 ₄ , Li2CoPO ₄ F or the like) can be named. An element or a polyanion in these compounds may be partially replaced with other elements or other anion species. In the positive active material layer 10, one kind of these compounds may be used singly or these compounds may be used in a state where two or more kinds of compounds are mixed. Further, it is preferable that the crystal structure of the positive active material be a layered structure or a spinel structure.

[0033]

A lower limit of a content of the positive active material in the positive active material layer 10 is preferably set to 50 mass%, and more preferably set to 70 mass%, and still further preferably set to 80 mass%. On the other hand, an upper limit of the content of the positive active material in the positive active material layer 10 is preferably set to 99 mass%, and more preferably set to 94 mass%. By setting the content of the positive active material within the above-mentioned range, energy density of the energy storage device can be increased.

[0034] The conductive agent is not particularly limited provided that the conductive agent is made of a conductive material which does not adversely affect battery performance. As such a conductive agent, natural or artificial graphite, carbon black such as furnace black, acetylene black and Ketjen black, metal, conductive ceramics and the like can be named. As the shape of the conductive agent, a powdery form, a fibrous form and the like can be named.

[0035]

A lower limit of a content of the conductive agent in the positive active material layer 10 is preferably set to 0.1 mass%, and more preferably set to 0.5 mass%. On the other hand, an upper limit of the content of the conductive agent is preferably set to 10mass%, and more preferably set to 5 mass%. By setting the content of the conductive agent within the above- mentioned range, energy density of the energy storage device can be increased.

[0036]

As a material of the binder, for example, a fluororesin

(polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and the like), a thermoplastic resin such as polyethylene, polypropylene and polyimide, elastomer such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and the like, for example, polysaccharide polymer and the like can be named.

[0037]

A lower limit of a content of the binder in the positive active material layer 10 is preferably set to 1 mass%, and more preferably set to 2 mass%. On the other hand, an upper limit of the content of the binder is preferably set to 10 mass%, and more preferably set to 5 mass%. By setting the content of the binder within the above-mentioned range, the positive active material can be held in a stable manner.

[0038]

As a material of the thickening agent, polysaccharide polymer such as carboxymethyl cellulose (CMC), methyl cellulose and the like can be named. Further, when the thickening agent has a functional group reactable with lithium, it is preferable to preliminarily deactivate the functional group by methylation or the like.

[0039]

A material of the filler is not particularly limited provided that the battery performance is not adversely affected by the material. As a main component of the filler, a polyolefin such as polypropylene and polyethylene, silica, alumina, zeolite, glass, carbon and the like can be named.

[0040]

A lower limit of an average thickness of the positive active material layer 10 is preferably set to 10 μηι, and more preferably set to 20 μηι. On the other hand, an upper limit of the average thickness of the positive active material layer 10 is preferably set to 100 μηι, and more preferably set to 80 μηι. By setting the average thickness of the positive active material layer 10 to the above-mentioned lower limit or above, the reaction at the positive electrode can be sufficiently activated. Further, by setting the average thickness of the positive active material layer 10 to the above-mentioned upper limit or below, energy density of the energy storage device can be increased.

[0041]

The separator 8 includes a sheet-like resin layer 12, a heat resistant layer 13 which is stacked on a surface of the resin layer 12 which opposedly faces the positive electrode plate 7, and an adhesive layer 14 which is stacked on a surface of the heat resistant layer 13 which opposedly faces the positive electrode plate 7.

[0042]

As shown in Fig. 3, in the bag-packed positive electrode plate 5, the adhesive layers 14 of the pair of separators 8 are adhered to each other outside the active material stacked region of the positive electrode plate 7 as viewed in a plan view (the adhered region of the separator 8 being indicated by hatching in Fig. 3). The adhesion of the adhesive layers 14 of the pair of separators 8 outside the active material stacked region of the positive electrode plate 7 may be performed continuously along an outer edge of the active material stacked region of the positive electrode plate 7. However, as shown in Fig. 3, by performing the adhesion of the adhesive layers 14 intermittently, pouring of an electrolyte solution to the separator 8 can be accelerated.

[0043]

The adhesive layer 14 of the separator 8 may be adhered to the positive active material layer 10. By adhering the adhesive layer 14 to the positive active material layer 10, it is possible to prevent the intrusion of foreign substances which generate metal ions between the positive electrode pate 7 and the separator 8 thus suppressing internal short-circuiting caused by electrodeposition of the layered electrode assembly 1.

[0044]

The adhesive layer 14 of the separator 8 is adhered to the positive electrode tab 11. In a situation where an accident which is not a normal in- use state occurs, there may be a case where the object other than the energy storage device penetrates the positive electrode tab 11 so that the positive electrode tab 11 is broken and a portion which is bent in a tongue shape or a burr-shape is formed and extends toward the negative electrode plate 6. Also in such a case, by adhering the adhesive layer 14 also to the positive electrode tab 11 as described above, the separator 8 is maintained in an adhered state to the surface of the broken positive electrode tab 11 is maintained and hence, a contact area between the positive electrode tab 11 and the negative electrode plate 6 is reduced. With such a configuration, a short-circuit current between the positive electrode tab 11 and the negative electrode plate 6 is reduced thus suppressing the generation of heat caused by a short circuit current when the object other than the energy storage device penetrates the tab.

[0045]

The positive active material layer 10 has a relatively large

thickness. Accordingly, to prevent an excessively large stress from acting on the separator 8 from the positive active material layer 10, a gap may be formed between an active material stacked region of the positive electrode plate 7 and an adhered region of the adhesive layer 14 to the positive electrode tab 11. In this case, although it depends on a thickness of the positive active material layer 10, an upper limit of an average distance D (see Fig. 2) between the active material stacked region of the positive electrode plate 7 and the adhered region of the adhesive layer 14 to the positive electrode tab 11 is preferably set to 500 μηι, more preferably set to 300 μηι, and further more preferably set to 200 μηι. By setting the average distance D between the active material stacked region of the positive electrode plate 7 and the adhered region of the adhesive layer 14 to the positive electrode tab 11 to the above-mentioned upper limit or below, it is possible to effectively suppress the contact of the positive electrode tab 11 to the negative electrode plate 6 when an object other than the energy storage device penetrates the positive electrode tab 11.

[0046]

The resin layer 12 is formed of a porous resin film.

[0047]

As a main component of the resin layer 12, for example,

polyethylene (PE), polypropylene (PP), ethylene-vinyl acetate copolymer, ethylene-methylacrylate copolymer, ethylene-ethyl acrylate copolymer, a polyolefin derivative such as chlorinated polyethylene, polyolefin such as ethylene-propylene copolymer, or polyester such as polyethylene- telephthalate and copolyester can be adopted. Among these components, as the main component of the resin layer 12, polyethylene and

polypropylene excellent in electrolyte solution resistance, durability and weldability are suitably used. Here, "main component" means a component having a largest mass content.

[0048]

A lower limit of an average thickness of the resin layer 12 is preferably set to 5 μηι, and more preferably set to 10 μηι. On the other hand, an upper limit of the average thickness of the resin layer 12 is preferably set to 30 μηι, and more preferably set to 20 μηι. By setting the average thickness of the resin layer 12 to the above-mentioned lower limit or above, it is possible to prevent breaking of the resin layer 12 at the time of adhering the separators 8 to each other. Further, by setting the average thickness of the resin layer 12 to the above-mentioned upper limit or below, energy density of the energy storage device can be increased.

[0049]

The heat resistant layer 13 is configured to contain a large number of inorganic particles, and a binder for connecting the inorganic particles to each other.

[0050]

As a main component of the inorganic particles, for example, alumina, silica, zirconia, titania, magnesia, ceria, yttria, an oxide such as a zinc oxide and an iron oxide, a nitride such as a silicon nitride, a titanium nitride and a boron nitride, silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate or the like can be named. Among these components, as the main component of the inorganic particles in the heat resistant layer 13, alumina, silica and titania are particularly preferable.

[0051]

A lower limit of an average particle size of the inorganic particles contained in the heat resistant layer 13 is preferably set to 1 nm, and more preferably set to 7 nm. On the other hand, an upper limit of the average particle size of the inorganic particles is preferably set to 5 μηι, and more preferably set to 1 μηι. By setting the average particle size of the inorganic particles to the above-mentioned lower limit or above, a ratio of the binder contained in the heat resistant layer 13 is decreased thus enhancing heat resistance of the heat resistant layer 13. By setting the average particle size of the inorganic particles to the above-mentioned upper limit or below, it is possible to provide the homogenized heat resistant layer 13. Here, "average particle size" means a value measured in accordance with JIS- R1670 using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

[0052]

As a main component of the binder in the heat resistant layer 13, for example, a fluororesin such as polyvinylidene fluoride,

polytetrafluoroethylene, fluororubber such as vinylidene fluoride- hexafluoropropylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer, and hydride of styrene-butadiene copolymer, acrylonitrile- butadiene copolymer and hydride of acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer and hydride of acrylonitrile- butadiene- styrene copolymer, synthetic rubber such as methacrylic ester- acrylic ester copolymer, styrene-acrylic ester copolymer, and acrylonitrile- acrylic ester copolymer, cellulose derivative such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and ammonium salt of carboxymethyl cellulose, polyetherimide, polyamidimide, polyamide, polyimide such as precursor (polyamic acid or the like) of polyamide, ethylene acrylic acid copolymer such as ethylene-ethyl acrylate copolymer, polyvinyl alcohol (PVA), polyvinyl butylal (PVB), polyvinyl pyrrolidone (PVP), polyvinyl acetate, polyurethane, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyester or the like can be named.

[0053]

A lower limit of an average thickness of the heat resistant layer 13 is preferably set to 2 μηι, and more preferably set to 4 μηι. On the other hand, an upper limit of the average thickness of the heat resistant layer 13 is preferably set to 10 μηι, and more preferably set to 6 μηι. By setting the average thickness of the heat resistant layer 13 to the above-mentioned lower limit or above, it is possible to prevent breaking of the heat resistant layer 13 at the time of adhering the separators 8. Further, by setting the average thickness of the heat resistant layer 13 to the above-mentioned upper limit or below, energy density of the energy storage device can be increased.

[0054]

The adhesive layer 14 can be made of a material exhibiting ion conductivity and having adhesiveness. To be more specific, the adhesive layer 14 can be made of a mixed material containing particles which possess ion conductivity by including an electrolyte solution, and a binder which possesses adhesiveness. It is preferable that the adhesive layer 14 have continuous pores so as to allow a liquid and a gas to pass therethrough.

[0055]

A lower limit of an average thickness of the adhesive layer 14 is preferably set to 0.1 μηι, more preferably set to 0.2 μπι, and further more preferably set to 0.4 μηι. On the other hand, an upper limit of the average thickness of the adhesive layer 14 is preferably set to 5 μηι, more preferably set to 3 μηι, and further more preferably set to 1.2 μηι. By setting the average thickness of the adhesive layer 14 to the above-mentioned lower limit or above, sufficient adhesiveness can be acquired. Further, by setting the average thickness of the adhesive layer 14 to the above-mentioned upper limit or below, sufficient ion conductivity can be acquired.

[0056]

As a material of the particles of the adhesive layer 14 which exhibits ion conductivity by including an electrolyte solution, for example, an inorganic solid electrolyte, a pure solid polymer electrolyte, a gel polymer electrolyte and the like can be named. Among these materials, the gel polymer electrolyte which can increase ion conductivity and is homogenous thus enabling the easy adjustment of a particle size is particularly

preferably used.

[0057]

The gel polymer electrolyte is a material which can facilitate handling thereof by turning an electrolyte solution into a gel state by polymer. As a polymer which turns an electrolyte solution into a gel state, for example, vinylidene fluoride-hexafluoropropylene copolymer,

polymethylmethacrylic acid, polyacrylonitrile and the like can be named.

[0058]

As an electrolyte solution of the gel polymer electrolyte, an organic electrolyte solution formed by dissolving a support electrolyte in an organic solvent is used. As the support electrolyte, a lithium salt is preferably used. Although a lithium salt is not particularly limited, for example, LiPF ₆ , LiAsFe, LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiC10 ₄ , CF ₃ S0 ₃ Li, C ₄ F ₉ S0 ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi, (CF ₃ S0 ₂ ) ₂ NLi, (C ₂ F ₅ S0 ₂ )NLi and the like can be named. Among these materials, LiPF6, LiC10 ₄ , CF3S0 ₃ Li which are easily dissolved in an organic solvent and exhibit a high dissociation degree are particularly preferably used.

[0059]

An organic solvent used in an electrolyte solution is not particularly limited provided that the organic solvent can dissolve a support electrolyte. For example, carbonates such as a dimethyl carbonate (DMC), an ethylene carbonate (EC), a diethyl carbonate (DEC), a propylene carbonate (PC), a butylene carbonate (BC), and an methyl-ethyl carbonate (MEC), for example, esters such as γ-butyrolactone and methyl formate, for example, ethers such as 1,2- dimethoxy- ethane and tetrahydrofuran, sulfur- containing compounds such as sulfolane and dimethylsulioxide and the like can be used singly or in combination of plural kinds of these materials. Among these materials, carbonates having a high dielectric constant and having a wide stable potential region are particularly preferably used.

[0060]

A lower limit of concentration of the support electrolyte in the electrolyte solution is preferably set to 1 mass%, and more preferably set to 5 mass%. On the other hand, an upper limit of the concentration of the support electrolyte in the electrolyte solution is preferably set to 30 mass%, and more preferably set to 20 mass%. By setting the concentration of the support electrolyte in the electrolyte solution within the above-mentioned range, relatively large ion conductivity can be obtained.

[0061]

A lower limit of an average particle size of the solid electrolyte particles is preferably set to 0.1 μηι, and more preferably set to 0.2 μηι. On the other hand, an upper limit of the average particle size of the solid electrolyte particles is preferably set to 2 μηι, and more preferably set to 1 μηι. By setting the average particle size of the solid electrolyte particles to the above-mentioned lower limit or above, it is possible to easily impart ion conductivity to the adhesive layer 14 by bringing solid electrolyte particles into contact with each other. Further, by setting the average particle size of the solid electrolyte particles to the above-mentioned upper limit or below, the adhesive layer 14 can be easily formed into a homogenized film shape.

[0062]

As a shape of the solid electrolyte particles, a shape having small sphericity such as a rod shape, a conical shape, a plate shape, for example, is preferable so as to increase ion conductivity by accelerating contact between the solid electrolyte particles, for example.

[0063]

As a binder in the adhesive layer 14, it is sufficient that the binder have adhesiveness to the solid electrolyte particles and the positive active material layer 10. A resin capable of being adhered to the positive active material layer 10 by being heated at a relatively low temperature, that is, a polymer material having a relatively low glass transition point and exhibiting adhesiveness is preferably used. [0064]

A lower limit of the glass transition point of the binder is preferably set to -50°C, and more preferably set to -45°C. On the other hand, an upper limit of the glass transition point of the binder is preferably set to 80°C, and more preferably set to 45°C. By setting the glass transition point of the binder to the above-mentioned lower limit or above, a strength of the adhesive layer 14 can be ensured. Further, by setting the glass transition point of the binder to the above-mentioned upper limit or below, the separator 8 can be adhered to the positive electrode plate 7 and the opposedly facing separator 8 at a temperature where the resin layer 12 is not damaged.

[0065]

As a main component of the binder, for example, an acrylic polymer and the like can be named. As the acrylic polymer, a nitrile -group - containing acrylic polymer which includes a monomer unit having a nitrile group and a (meth)acrylate acid ester monomer unit is preferably used. Here, the monomer unit having a nitrile group is a structural unit obtained by polymerizing acrylonitrile, methacrylonitrile or the like, for example, and a (meth)acrylate acid ester monomer unit is a monomer unit derived from a compound expressed by (in the formula, R ¹ indicating a hydrogen atom or a methyl group, and R ² indicating an alkyl group or a cycloalkyl group). The nitrile group containing acrylic polymer may contain an ethylenic unsaturated acid monomer unit obtained by

polymerizing an ethylenic unsaturated acid monomer in addition to the monomer unit having a nitrile group and the (meth)acrylate acid ester monomer unit. Further, nitrile group containing acrylic polymer may be formed in a cross-linking manner.

[0066]

A lower limit of a ratio of the solid electrolyte particles in the adhesive layer 14 is preferably set to 70 mass%, and more preferably set to 80 mass%. On the other hand, an upper limit of the ratio of the solid electrolyte particles in the adhesive layer 14 is preferably set to 95 mass%, and more preferably set to 90 mass%. By setting the ratio of the solid electrolyte particles in the adhesive layer 14 to the above-mentioned lower limit or above, it is possible to impart sufficient ion conductivity to the adhesive layer 14. Further, by setting the ratio of the solid electrolyte particles in the adhesive layer 14 to the above-mentioned upper limit or below, it is possible to impart sufficient adhesiveness to the adhesive layer 14 while setting a ratio of the binder to the adhesive layer 14 to a fixed value or more relatively.

[0067]

The bag-packed positive electrode plate 5 can be manufactured by a method including the steps οΐ ^' - sandwiching the positive electrode plate 7 by the pair of separators 8 each having the resin layer 12, the heat resistant layer 13, and the adhesive layer 14 (stacking step); and sandwiching a layered product of the positive electrode plate 7 and the pair of separators 8 by a heating mold which is heated to a temperature lower than a melting point of the resin layer 12 (pressing step).

[0068]

In the stacking step, the adhesive layers 14 of the separators 8 are respectively brought into contact with the positive electrode plate 7, and the positive electrode plate 7 and the pair of separators 8 are stacked to each other such that the separators 8 envelope the active material stacked region of the positive electrode plate 7 as viewed in a plan view.

[0069]

In the pressing step, a pair of heating molds is heated to a

temperature below a melting point of the resin layer 12 and equal to or above a glass transition point of the binder of the adhesive layer 14, and the layered product formed of the positive electrode plate 7 and the pair of separators 8 is sandwiched and pressurized by the pair of heating molds.

[0070]

The heating molds are configured to have a convex shape portion respectively such that, outside the active material stacked region of the positive electrode plate 7 as viewed in a plan view, the heating molds make the adhesive layers 14 adhere to adhesive layer 14 of the separator 8 which opposedly face each other and the positive electrode tab 11 by pressure bonding.

[0071]

The negative electrode plates 6 are stacked in the layered electrode assembly 1 without being bag-packed unlike the positive electrode plates 7.

[0072]

The negative electrode plate 6 includes^ a foil-like or sheet-like negative electrode current collector 15 having conductivity! and a negative active material layer 16 which is stacked on a surface of the negative electrode current collector 15. To be more specific, the negative electrode plate 6 is configured to include ^: an active material stacked region having a rectangular shape as viewed in a plan view where the active material layer 12 is stacked on a surface of the negative electrode current collector 15; and a negative electrode tab 17 which extends from the active material stacked region in a strip shape having a width smaller than a width of the active material stacked region and is connected to the negative electrode terminal 4.

[0073]

Although the negative electrode current collector 15 can be formed substantially in the same manner as the above-mentioned positive electrode current collector 9, copper or a copper alloy is preferably used as a material for forming the negative electrode current collector 15. That is, a copper foil is preferably used as the negative electrode current collector 15 of the negative electrode plate 6. As a copper foil, a rolled copper foil, an electrolytic copper foil and the like can be exemplified.

[0074]

The negative active material layer 16 is made of a so-called negative electrode plate mixture containing a negative active material. The negative electrode plate mixture which forms the negative active material layer 16 contains arbitrary components such as a conductive agent, a binder, a thickening agent, a filler and the like when necessary. As the arbitrary components such as a conductive agent, a binder, a thickening agent, a filler and the like used for forming the negative active material layer 16, arbitrary components substantially equal to the arbitrary components used for forming the positive active material layer 10 can be used. [0075]

As the negative active material, a material which can occlude and discharge lithium ions is preferably used. As a specific negative active material, metal such as lithium or a lithium alloy, for example, a metal oxide, a polyphosphoric acid compound, a carbon material such as graphite, non- crystalline carbon (easily graphitizable carbon or hardly graphitizable carbon), for example, or the like can be named.

[0076]

Among the above-mentioned negative active materials, from a viewpoint of setting a discharge capacity per unit opposedly facing area between the positive electrode plate 7 and the negative electrode plate 6 within a preferable range, it is preferable to use Si, an Si oxide, Sn, an Sn oxide or a combination of these materials. It is particularly preferable to use an Si oxide. Si and Sn can have a discharge capacity approximately three times as large as a discharge capacity of graphite when Si and Sn are used in the form of an oxide.

[0077]

When an Si oxide is used as the negative active material, a ratio of the number of atoms of oxygen (O) contained in an Si oxide with respect to the number of atoms of Si is preferably set to more than 0 to less than 2. That is, as Si oxide, a compound expressed as SiO _x (0 < x < 2) is preferably used. Further, the ratio of the number of atoms of O with respect to the number of atoms of Si is preferably set to a value which falls within a range of from 0.5 to 1.5 inclusive.

[0078] As the negative active material, the above-mentioned materials may be used in a single form, or two or more kinds of the materials may be used by mixing. For example, by using an Si oxide and other negative active materials by mixing, both discharge capacities per unit opposedly facing area between the positive electrode plate 7 and the negative electrode plate 6 and a ratio of a mass of the positive active material with respect to a mass of a negative active material described later can be adjusted to suitable values. As other negative active materials used by being mixed with an Si oxide, carbon materials such as graphite, hard carbon, soft carbon, coke, acetylene black, Ketjen black, vapor phase growth carbon fibers, fullerene, and activated carbon can be named. Among these carbon materials, only one kind of material may be mixed with an Si oxide, or two or more kinds of materials may be mixed with an Si oxide in an arbitrary combination or at an arbitrary ratio. Among these other negative active materials, graphite having a relatively low charge- discharge potential is preferably used. By using graphite as the negative active material, it is possible to obtain a secondary battery element having high energy density. As graphite used in a form that graphite is mixed with an Si oxide, flaky graphite, spherical graphite, artificial graphite, natural graphite and the like can be named. Among these graphite, flaky graphite which can easily maintain its contact with Si oxide particle surfaces even when charging and discharging of the energy storage device are repeated is preferably used.

[0079]

A lower limit of a content of an Si oxide in the negative active material is preferably set to 30 mass%, more preferably set to 50 mass%, and further more preferably set to 70 mass%. On the other hand, an upper limit of the content of the Si oxide is usually set to 100 mass%, and preferably set to 90 mass%.

[0080]

It is preferable that the above-mentioned Si oxide (a material expressed by a general formula SiO _x ) include both an S1O2 phase and an Si phase. In such an Si oxide, lithium is occluded in or discharged from Si in a matrix of S1O2 and hence, such an Si oxide exhibits a small change in volume and exhibits an excellent charge- discharge cycle characteristic.

[0081]

An average particle size of the Si oxide is preferably set to a value which falls within a range of from 1 μηι to 15 μηι inclusive. By setting the average particle size of the Si oxide within the above-mentioned range, a charge- discharge cycle characteristic of the energy storage device can be enhanced.

[0082]

As the Si oxide, various Si oxides can be used ranging from a high crystalline Si oxide to an amorphous Si oxide. Further, as the Si oxide, an Si oxide which is washed by an acid such as a hydrogen fluoride or a sulfuric acid, or an Si oxide which is reduced by hydrogen may be used.

[0083]

Further, the negative active material layer 16 may contain^ a small amount of a typical nonmetallic element such as B, N, P, F, CI, Br, I; a typical metallic element such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge! and a transition metallic element such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W in addition to an Si oxide.

[0084]

A lower limit of a content of the negative active material in the negative active material layer 16 is preferably set to 60 mass%, more preferably set to 80 mass%, and further more preferably set to 90 mass%. On the other hand, an upper limit of the content of the negative active material is preferably set to 99 mass%, and more preferably set to 98 mass%. By setting the content of the negative active material particles within the above-mentioned range, energy density of the energy storage device can be increased.

[0085]

A lower limit of a content of a binder in the negative active material layer 16 is preferably set to 1 mass%, and more preferably set to 5 mass%. On the other hand, an upper limit of the content of the binder is preferably set to 20 mass%, and more preferably set to 15 mass%. By setting the content of the binder within the above-mentioned range, the negative active material can be held in a stable manner.

[0086]

A lower limit of an average thickness of the negative active material layer 16 is preferably set to 10 μηι, and more preferably set to 20 μηι. On the other hand, an upper limit of the average thickness of the negative active material layer 16 is preferably set to 100 μηι, and more preferably set to 80 μηι. By setting the average thickness of the negative active material layer 16 to the above-mentioned lower limit or above, a reaction at the negative electrode can be sufficiently activated. Further, by setting the average thickness of the negative active material layer 16 to the above- mentioned upper limit or below, energy density of the energy storage device can be increased.

[0087]

The outer case 2 is a hermetically-closed container which

accommodates the layered electrode assembly 1 therein and in which an electrolyte is sealed.

[0088]

As a material for forming the outer case 2, provided that the material has sealability capable of sealing electrolyte and a strength capable of protecting the layered electrode assembly 1, a resin or the like may be used, for example. However, metal is preferably used. In other words, although the outer case 2 may be a bag-shaped body formed of laminated film and having flexibility or the like, for example, it is preferable to use a robust metal case capable of protecting the layered electrode assembly 1 with more certainty.

[0089]

As an electrolyte sealed in the outer case 2 together with the layered electrode assembly 1, a known electrolyte solution usually used in the energy storage device can be used. For example, a solution obtained by dissolving lithium hexafluorophosphate (LiPFe) or the like in a solvent containing: a cyclic carbonate such as an ethylene carbonate (EC), a propylene carbonate (PC) or a butylene carbonate (BC); or a chain carbonate such as a diethyl carbonate (DEC), a dimethyl carbonate (DMC) or an ethyl- methyl carbonate (EMC) can be used. [0090]

The above-mentioned embodiment is not intended to limit the configuration of the present invention. Accordingly, it should be construed that the above-mentioned embodiment can be modified by omission, replacement or addition of constitutional elements of respective parts of the embodiment based on the description of this specification and the common general technical knowledge, and all these modifications also fall within the scope of the present invention.

EXAMPLES

[0091]

Hereinafter, although the present invention will be explained in detail with reference to examples, the present invention is not construed to restrict the present invention by the description of the examples.

[0092]

A positive electrode plate and separators were prepared. The positive electrode plate was prepared by stacking a positive electrode active material layer on an aluminum-foil-made positive electrode current collector. The separator was prepared by stacking a heat resistant layer having a thickness of 4 μηι on a resin layer having a thickness of 16 μηι and formed of a plurality of large-thickness film layers made of polyethylene and polypropylene respectively, and by stacking an adhesive layer having a thickness of 1 μηι and containing non-aqueous electrolyte particles and a binder on the heat resistant layer. The positive electrode plate was sandwiched between the pair of separators in a state where the adhesive layers of the pair of separators are disposed inside. By performing thermal pressing using heating molds, the adhesive layers of the separators were welded to each other outside an active material stacked region of the positive electrode plate and, at the same time, by making the adhesive layers of the separators adhere to the tab of the positive electrode plate, an example of the bag-packed positive electrode plate according to the present invention was obtained. Forty bag-packed positive electrode plates and forty negative electrode plates were stacked in such a manner that the bag- packed positive electrode plate and the negative electrode plate are stacked alternately, these electrode plates were accommodated in an aluminum- made box- shaped outer case, and an electrolyte solution was poured into the outer case thus forming an energy storage device according to an example of the present invention.

[0093]

In the examples of the energy storage device, a capacity was 40 Ah, energy density on a weight basis was 107 Hh/kg, and energy density on a volume basis was 241 Wh/L.

[0094]

Energy storage devices according to comparison examples were prepared in the same manner except for that a heat resistant layer having a thickness of 4 μηι was stacked on a resin layer having a thickness of 16 μηι, and the energy storage devices of the comparison examples had no adhesive layers. A capacity, energy density on a weight basis and energy density on a volume basis of the energy storage devices of the comparison examples were set equal to those of the energy storage devices according to the examples of the present invention. [0095]

A plurality of energy storage devices according to the examples and a plurality of energy storage devices according to the comparison examples were prepared. Tests were carried out in such a manner that a nail- shaped body made of SUS304 having a diameter of 1 mm and a distal end angle of 30° was driven at a speed of 80 mm/sec such that the nail-shaped body penetrated an active material stacked region of a negative electrode plate and a tab of a positive electrode plate, and a change in temperature at the center of the energy storage device and a change in temperature at an edge of the energy storage device in the vicinity of a position where the nail- shaped body was inserted was measured. The tests were performed by changing a driven depth of the nail-shaped body.

[0096]

A result of the above-mentioned tests is collectively shown in Table

1.

[0097]

[Table l]

[0098]

In the energy storage devices of the comparison examples, even when the nail-shaped body was driven into the active material layer of the negative electrode and the tab of the positive electrode by only 7 mm, a temperature was increased to 100°C or above, and when the nail-shaped body was driven into the active material layer of the negative electrode and the tab of the positive electrode by 9 mm, a temperature was increased to 300° C or above even at the center and was increased to 600° or above at the edge part. To the contrary, in the energy storage devices of the examples according to the present invention, when the nail-shaped body was driven into the active material layer of the negative electrode and the tab of the positive electrode by 7 mm to 9 mm, the maximum temperature reached was approximately 20° C, and there was no generation of heat which becomes a problem. In the energy storage devices of the example according to the present invention, even when a driven depth of the nail-shaped body was increased to 32 mm, a temperature could be retained at 65°C even at the edge part which exhibits a high temperature. Accordingly, the temperature of the energy storage device was not increased to a temperature which causes a burn on a hand of a user even when the user erroneously touches the edge part.

[0099]

As has been described heretofore, by using the separator having the adhesive layer and by adhering the adhesive layer of the separator to the positive electrode tab, the generation of heat in a nail driven state can be largely suppressed.

INDUSTRIAL APPLICABILITY

[0100]

The bag-packed positive electrode plate, the layered electrode assembly, and the energy storage device according to the present invention are preferably applicable to a secondary battery, and are particularly preferably used as a power source for a vehicle such as an electric vehicle or a plug-in hybrid electric vehicle (PHEV).

DESCRIPTION OF REFERENCE SIGNS [0101]

l: layered electrode assembly

2- outer case

3 ^: positive electrode terminal

4 ^' · negative electrode terminal

5: bag-packed positive electrode plate

6: negative electrode plate

T- positive electrode plate

8^ separator

9 ^: positive electrode current collector

10^ positive active material layer

11: positive electrode tab

12 ^' · resin layer

13: heat resistant layer

14: adhesive layer

15: negative electrode current collector

16^ negative active material layer

IT- negative electrode tab

D: distance between active material stacked region of positive electrode plate and adhered region of adhesive layer to positive electrode tab