JP2021158109A - Energy storage device - Google Patents

Abstract

To provide an energy storage device in which a space of a winding center portion of an electrode assembly is relatively small and an increase in the air permeance of a separator including a wet film is suppressed.SOLUTION: An energy storage device includes: a winding type electrode assembly including a negative electrode containing a negative active material, a positive electrode, and a separator disposed between the positive electrode and the negative electrode; a case housing the electrode assembly; and a spacer disposed between the electrode assembly and an inner surface of the case in the case. The separator has a wet film, the negative active material is a carbonaceous material or lithium titanate, and the spacer is harder than the separator.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power storage element.

Patent Document 1 describes a case, an electrode assembly housed in the case, and an electrode assembly having a layered structure in which a first electrode and a second electrode having a polarity different from that of the first electrode are insulated by a separator. A power storage device including, the separator includes a first separator and a second separator having a ceramic layer, the first electrode or the second electrode is sandwiched between the second separator, and the second separator. A power storage device, characterized in that one separator is arranged in this order, is described.

Japanese Unexamined Patent Publication No. 2014-220079

An object of the present invention is to provide a power storage element in which the space of the winding center portion of the electrode body is relatively small and the increase in air permeability of the separator having a wet film is suppressed.

The power storage element according to one aspect of the present invention includes a negative electrode containing a negative electrode active material, a positive electrode, and a wound electrode body having a positive electrode and a separator arranged between the positive electrode and the negative electrode.
A case containing the electrode body and
A spacer arranged between the electrode body and the inner surface of the case inside the case is provided.
The separator has a wet film and
The negative electrode active material is a carbonaceous material or lithium titanate.
The spacer is harder than the separator.

In the power storage element according to one aspect of the present invention, the space at the center of winding of the electrode body is relatively small, and the increase in air permeability of the separator having a wet film is suppressed.

FIG. 1 is a perspective view of a power storage element according to the present embodiment. FIG. 2 is a schematic cross-sectional view of the position of line II-II in FIG. FIG. 3 is a schematic cross-sectional view of the position of line III-III in FIG. FIG. 4 is a perspective view of a wound electrode body of the power storage element according to the present embodiment. FIG. 5 is a schematic view of a power storage device including a plurality of power storage elements according to the present embodiment.

First, the outline of the power storage element disclosed by the present specification will be described.

The power storage element 1 according to one aspect of the present invention includes a winding type electrode body 2 having a negative electrode containing a negative electrode active material, a positive electrode, and a separator 60 arranged between the positive electrode and the negative electrode.
Case 3 containing the electrode body 2 and
A spacer 70 arranged between the electrode body 2 and the inner surface of the case inside the case 3 is provided.
The separator 60 has a wet film and
The negative electrode active material is a carbonaceous material or lithium titanate.
The spacer 70 is harder than the separator 60.

The power storage element 1 includes a winding type electrode body 2. In the winding type electrode body 2, a space z is formed in the winding center portion. In general, the innermost portion of such an electrode body 2 can be deformed so as to protrude toward the space z side of the winding center portion, so that the distance between the positive electrode and the negative electrode in the deformed inner portion increases. It may end up. Therefore, in the winding type electrode body 2 housed in the case 3, it is desired that the space z at the center of winding is as small as possible.
Therefore, as in the present embodiment, by arranging a relatively hard spacer 70 (gap filling member) between the case 3 and the electrode body 2, the space z in the winding center portion is increased by the amount of the spacer 70 arranged. It can be made smaller. Therefore, in the power storage element 1 of the present embodiment, the space z of the winding center portion of the electrode body 2 is relatively small.
However, since the electrode body 2 housed in the case 3 can expand with charging and discharging, the electrode body 2 is pressed from the outside by the inner surface of the case 3 due to the reaction force when expanding. Therefore, the pores of the separator 60 may be crushed and the air permeability of the separator 60 may increase. In particular, since the separator 60 has a wet film, there are many curved pores in the wet film, so that an increase in air permeability due to crushing of the pores tends to be a problem.
On the other hand, as in the present embodiment, the expansion of the electrode body 2 can be suppressed by using a carbonaceous material having a small expansion coefficient or lithium titanate as the negative electrode active material. Since the expansion of the electrode body 2 can be suppressed, it is possible to suppress the inner surface of the case from pressing the electrode body 2 due to the reaction force of the expansion force. As a result, it is possible to suppress the crushing of the pores of the wet film and suppress the increase in the air permeability of the separator.
As described above, in the power storage element 1 of the present embodiment, the space z of the winding center portion of the electrode body 2 is relatively small, and the increase in the air permeability of the separator having the wet film is suppressed.

Here, the negative electrode active material may be non-graphitic carbon as a carbonaceous material.
As a result, the expansion of the negative electrode active material can be suppressed more sufficiently, so that the increase in the air permeability of the separator having the wet film can be further suppressed for the same reason as described above.

Further, the case 3 may be held so as to have a fixed size. In this case, the air permeability of the separator may increase easily.
For example, when the electrode body that occupies most of the internal volume of the case 3 is housed in the case 3, if the case is held so as to have a fixed size, the inner surface of the case 3 is relatively relative to the electrode body 2. Large pressure (reaction force) can be applied. Due to this pressure (reaction force), the pores of the wet film are likely to be crushed, and the air permeability of the separator 60 is likely to increase.
As described above, since the case 3 is held so as to have a fixed size, the power storage element 1 in which the air permeability of the separator 60 can be easily increased has the above-mentioned configuration (the negative electrode active material is a carbonaceous material or titanium). By having lithium titanate), the effect of suppressing an increase in the air permeability of the separator 60 can be particularly expected.

Further, when the spacer 70 and the separator 60 are each ^{compressed by an indenter having a surface area of 3680 mm 2 with} a load of 7 kN, the displacement amount of the separator 60 may be 0.1 mm / mm or more larger than the displacement amount of the spacer 70.
By using the spacer 70 whose displacement amount is equal to or less than the displacement amount of the separator 60 as described above, the spacer 70 is less likely to be deformed by the compressive force. Therefore, the electrode body 2 can receive a larger reaction force when expanding from the spacer 70. Due to this force, the pores of the wet film are likely to be crushed, and the air permeability of the separator 60 is likely to increase.
As described above, the power storage element 1 in which the air permeability of the separator 60 can easily increase has the above-mentioned configuration (the negative electrode active material is a carbonaceous material or lithium titanate), so that the air permeability of the separator 60 increases. Especially the suppressed effect can be expected.

The power storage element 1 may include an insulating sheet 80 that covers the electrode body 2 and insulates between the electrode body 2 and the case 3, the case 3 is made of metal, and the spacer 70 is the electrode body 2. It may be arranged between the insulation sheet 80 and the insulating sheet 80.
Since the case 3 is made of metal, the strength of the case 3 is increased, so that the deformation of the case 3 can be suppressed even when the electrode body 2 is expanded. Therefore, the electrode body 2 is more likely to be pressed by the inner surface of the case, and the air permeability of the separator 60 can be further increased. Even in the above-mentioned power storage element configured in this way, as described above, the negative electrode active material is a carbonaceous material or lithium titanate, and the spacer is harder than the separator, so that the air permeability is high. Can be effectively suppressed from increasing the air permeability of the separator 60, which tends to increase.

The configuration of the non-aqueous electrolyte storage element 1 according to the embodiment of the present invention, the configuration of the non-aqueous electrolyte storage device, the method for manufacturing the non-aqueous electrolyte storage element 1, and other embodiments will be described in detail. The name of each component (each component) used in each embodiment may be different from the name of each component (each component) used in the background technology.

<Structure of non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage element 1 (hereinafter, also simply referred to as “storage element”) according to the embodiment of the present invention includes an electrode body 2 having a positive electrode 40, a negative electrode 50, and a separator 60, a non-aqueous electrolyte, and the electrode body. 2 and a case 3 for accommodating a non-aqueous electrolyte are provided. The electrode body 2 is a winding type (hereinafter, described in detail) in which the positive electrode 40 and the negative electrode 50 are wound in a laminated state via a separator 60. The non-aqueous electrolyte exists in a state of being contained in the positive electrode 40, the negative electrode 50, and the separator 60. Hereinafter, a non-aqueous electrolyte secondary battery (particularly, a lithium ion secondary battery, hereinafter also simply referred to as a “secondary battery”) will be described as an example of a non-aqueous electrolyte power storage element, but the scope of application of the present invention is limited. Not intended.

As shown in FIGS. 1 to 4, the power storage element 1 of the present embodiment includes a wound electrode body 2 in a wound state and a case 3 accommodating the electrode body 2. Further, the power storage element 1 includes two external terminals (positive electrode terminal 4 and negative electrode terminal 5) that are attached to the case 3 with at least a part exposed or are composed of at least a part of the case 3. The electrode body 2 is connected to each of the external terminals 4 and 5 in the case 3 via a current collector or the like.

As shown in FIG. 4, the electrode body 2 is formed by stacking a long sheet-shaped positive electrode 40, a long sheet-shaped negative electrode 50, and two sheet-shaped separators 60 and 60, and further winding them. Has been done. The two separators 60 and 60 are arranged so as to electrically insulate the positive electrode 40 and the negative electrode 50, respectively. In the present embodiment, the electrode body 2 is a flat wound body. The electrode body 2 is arranged in the case 3 so that the winding axis direction of the electrode body 2 is the same as the direction perpendicular to the opening direction of the case body 31. As shown in FIG. 2, a space z is slightly formed in the winding center portion of the electrode body 2.

(Positive electrode)
The positive electrode 40 has a positive electrode base material 41 and a positive electrode active material layer 42 arranged directly on the positive electrode base material 41 or via an intermediate layer (not shown). In the present embodiment, the positive electrode active material layers 42 are laminated on both sides of the positive electrode base material 41. The positive electrode active material layer 42 causes a charge / discharge reaction with the negative electrode active material layer 52.

The positive electrode base material 41 has conductivity. Whether it has a "conductive" is the volume resistivity is measured according to JIS-H-0505 (1975 years) is equal to 10 ⁷ Ω · cm as a threshold value. As the material of the positive electrode base material 41, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode base material 41 include a foil and a vapor-deposited film, and the foil is preferable from the viewpoint of cost. Therefore, the positive electrode base material 41 is preferably an aluminum foil or an aluminum alloy foil. Examples of aluminum or aluminum alloy include A1085 and A3003 specified in JIS-H-4000 (2014).

The average thickness of the positive electrode base material 41 is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, further preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode base material 41 in the above range, it is possible to increase the strength of the positive electrode base material 41 and the energy density per volume of the secondary battery.

The intermediate layer is a layer arranged between the positive electrode base material 41 and the positive electrode active material layer 42. The intermediate layer contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material 41 and the positive electrode active material layer 42. The composition of the intermediate layer is not particularly limited, and includes, for example, a resin binder and conductive particles.

The positive electrode active material layer 42 contains a positive electrode active material. The positive electrode active material layer 42 contains optional components such as a conductive agent, a binder (binding agent), a thickener, and a filler, if necessary.

The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the positive electrode active material include _{a lithium transition metal composite oxide having an α-NaFeO type 2} crystal structure, a lithium transition metal composite oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, sulfur and the like. Examples of the lithium transition metal composite oxide having an _{α-NaFeO type 2 crystal structure include Li [Li x} Ni _(1-x) ] O ₂ (0 ≦ x <0.5) and Li [Li _x Ni _γ Co _{( 1-x-γ)] O} 2 (0 ≦ x <0.5,0 <γ <1), Li [Li x Co (1-x)] O 2 (0 ≦ x <0.5), Li [ Li _x Ni _γ Mn _(1-x-γ) ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Ni _γ Mn _β Co _(1-x-γ-β) ] O ₂ (0 ≦ x <0.5, 0 <γ, 0 <β, 0.5 <γ + β <1), Li [Li _x Ni _γ Co _β Al _(1-x-γ-β) ] O ₂ ( Examples thereof include 0 ≦ x <0.5, 0 <γ, 0 <β, 0.5 <γ + β <1). Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ . Examples of the polyanion compound include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like. The atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface of these materials may be coated with other materials. In the positive electrode active material layer 42, one of these materials may be used alone, or two or more of these materials may be mixed and used.

The positive electrode active material is usually particles (powder). The average particle size of the positive electrode active material is preferably 0.1 μm or more and 20 μm or less, for example. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer 42 is improved. When a complex of a positive electrode active material and another material is used, the average particle size of the complex is taken as the average particle size of the positive electrode active material. The "average particle size" is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by laser diffraction / scattering method with respect to a diluted solution obtained by diluting the particles with a solvent. -2 (2001) means a value at which the volume-based integrated distribution calculated in accordance with (2001) is 50%.

A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

The content of the positive electrode active material in the positive electrode active material layer 42 is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and further preferably 80% by mass or more and 95% by mass or less. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer 42.

(Arbitrary ingredient)
The conductive agent is not particularly limited as long as it is a conductive material. Examples of such a conductive agent include carbonaceous materials, metals, conductive ceramics and the like. Examples of the carbonaceous material include graphitized carbon, non-graphitized carbon, graphene-based carbon and the like. Examples of non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerenes. Examples of the shape of the conductive agent include powder and fibrous. As the conductive agent, one of these materials may be used alone, or two or more of these materials may be mixed and used. Further, these materials may be used in combination. For example, a material in which carbon black and CNT are composited may be used. Among these, carbon black is preferable from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferable.

When a conductive agent is used, the content of the conductive agent in the positive electrode active material layer 42 is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the secondary battery can be increased.

Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyacrylic, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfone. Examples thereof include elastomers such as propylene propylene rubber, styrene butadiene rubber (SBR), and fluororubber; and thermoplastic polymers. Of these, solvent-based binders such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.) are preferable.

When a binder is used, the content of the binder in the positive electrode active material layer 42 is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the binder content within the above range, the active material can be stably retained.

When a thickener is used, examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

The filler is not particularly limited. When a filler is used, the filler includes polyolefins such as polypropylene and polyethylene, silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, inorganic oxides such as aluminosilicate, and magnesium hydroxide. Hydroxides such as calcium hydroxide and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, Examples thereof include mineral resource-derived substances such as montmorillonite, boehmite, zeolite, apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, and mica, or man-made products thereof.

The positive electrode active material layer 42 includes typical non-metal elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba. Main group elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as positive electrode active materials, conductive agents, binders, thickeners, etc. It may be contained as a component other than the filler.

(Negative electrode)
The negative electrode 50 has a negative electrode base material 51 and a negative electrode active material layer 52 arranged directly on the negative electrode base material 51 or via an intermediate layer. The configuration of the intermediate layer is not particularly limited, and for example, it can be selected from the configurations exemplified by the positive electrode 40.

In the present embodiment, the negative electrode active material layers 52 are laminated on both sides of the negative electrode base material 51.
The edge of the negative electrode active material layer 52 is arranged outside the edge of the positive electrode active material layer 42 facing each other via the separator 60.

The negative electrode base material 51 has conductivity. As the material of the negative electrode base material 51, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof are used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode base material 51 include a foil and a vapor-deposited film, and the foil is preferable from the viewpoint of cost. Therefore, the negative electrode base material 51 is preferably a copper foil or a copper alloy foil. Examples of the copper foil include rolled copper foil, electrolytic copper foil and the like.

The average thickness of the negative electrode base material 51 is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, further preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material 51 in the above range, it is possible to increase the strength of the negative electrode base material 51 and the energy density per volume of the secondary battery.

The negative electrode active material layer 52 contains a negative electrode active material. The negative electrode active material layer 52 contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified by the positive electrode 40.

The negative electrode active material layer 52 includes typical non-metal elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba. , Etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W as negative electrode active materials, conductive agents, binders, etc. , Thickener, may be contained as a component other than the filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. In this embodiment, the negative electrode active material is a carbonaceous material or lithium titanate. Examples of the negative electrode active material include _{lithium titanate such as Li 4} Ti ₅ O ₁₂ , Li ₂ TiO _{3 , and LiTIO 2} ; graphite (graphite), non-graphitizable carbon (graphitizable carbon or non-graphitizable carbon), and the like. Examples include graphite materials. In the negative electrode active material layer 52, one of these materials may be used alone, or two or more of these materials may be mixed and used.
In the present embodiment, since the negative electrode active material is at least one of a carbonaceous material and lithium titanate, expansion of the negative electrode due to charging can be suppressed. Therefore, the expansion of the electrode body 2 at the time of charging / discharging can be suppressed. Therefore, the pressing force on which the inner surface of the case 3 compresses the electrode body 2 can be weakened by the reaction force of expansion. Therefore, it is possible to suppress an increase in the air permeability of the separator having a wet film.

_{“Graphite” refers to a carbonaceous material having an average lattice spacing (d 002} ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. .. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material having stable physical properties can be obtained.

_{“Non-graphitic carbon” is a carbonaceous material having an average lattice spacing (d 002} ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. To say. Examples of non-graphitizable carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-graphic carbon include a resin-derived material, a petroleum pitch or a petroleum pitch-derived material, a petroleum coke or a petroleum coke-derived material, a plant-derived material, an alcohol-derived material, and the like.

Here, the "discharged state" refers to a state in which the open circuit voltage is 0.7 V or more in a unipolar battery in which the negative electrode 50 containing a carbonaceous material as the negative electrode active material is used as the working electrode and the metal Li is used as the counter electrode. say. Since the potential of the metal Li counter electrode in the open circuit state is substantially equal to the redox potential of Li, the open circuit voltage in the single pole battery is substantially equal to the potential of the negative electrode 50 containing the carbonaceous material with respect to the redox potential of Li. Is. That is, the fact that the open circuit voltage of the single-pole battery is 0.7 V or more means that lithium ions that can be occluded and discharged are sufficiently released from the carbonaceous material that is the negative electrode active material. do.

The “non-graphitizable carbon” _{refers to a carbonaceous material in which d 002} is 0.36 nm or more and 0.42 nm or less.

The “graphitizable carbon” _{refers to a carbonaceous material in which d 002} is 0.34 nm or more and less than 0.36 nm.

The negative electrode active material is preferably non-graphitic carbon. Since the negative electrode active material is non-graphitic carbon having a smaller expansion coefficient due to charging, the expansion of the electrode body 2 due to charging and discharging can be further suppressed. Therefore, the pressing force on which the inner surface of the case 3 compresses the electrode body 2 can be further weakened by the reaction force of expansion. Therefore, an increase in air permeability of the separator having a wet film can be further suppressed.

The negative electrode active material is usually particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. The average particle size of the negative electrode active material may be 1 μm or more and 100 μm or less. By setting the average particle size of the negative electrode active material to be equal to or higher than the above lower limit, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electron conductivity of the negative electrode active material layer is improved. A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. The pulverization method and the powder grade method can be selected from, for example, the methods exemplified by the positive electrode 40.

The content of the negative electrode active material in the negative electrode active material layer 52 is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer 52.

(Separator)
The separator 60 can be appropriately selected from known separators. As the separator 60, for example, a separator 60 composed of only a base material layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one surface or both surfaces of the base material layer can be used. As the material of the base material layer of the separator 60, a porous resin film is preferable from the viewpoint of strength. As the material of the base material layer of the separator 60, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. As the base material layer of the separator 60, a material in which these resins are composited may be used.

The separator 60 has a base material layer (separator base material). The base material layer of the separator 60 is a wet film.

The wet film of the separator can be produced by a known production method. An example of a method for producing a separator formed only of a wet film as a base material layer is shown below.
For example, a polymer such as polyethylene or polypropylene, an additive if necessary, and an extract such as liquid paraffin are mixed and melted by heating. The melt is discharged from, for example, a T-die and cast onto a temperature controlled cooling roll. As a result, a sheet in which the polymer and liquid paraffin are phase-separated is formed. Then, the sheet is set in a biaxial tenter stretching machine, and the sheet is biaxially stretched so as to have a predetermined stretching ratio to form a film. Biaxial stretching may or may not be performed simultaneously. The film is placed in a solvent (for example, methylene chloride, methyl ethyl ketone, etc.) that dissolves the extract in the film, and the extract is extracted and removed. In addition, the solvent is removed by a drying process. Subsequently, the film is guided to a TD tenter heat fixing machine, and the heat fixing treatment is performed at a predetermined temperature to prepare a wet film.

The pores of the wet film produced as described above are formed by extracting and removing the object to be extracted. Therefore, the pores of the wet film are formed so as to expand three-dimensionally regardless of the thickness direction or the surface direction of the film. Therefore, the pores of the wet film tend to collapse more easily than the pores of the dry film when a compressive force is applied in the thickness direction. Therefore, the separator having a wet film tends to have an increased air permeability after being subjected to a compressive force.

The air permeability of the separator 60 is measured according to, for example, JIS P-8117. For example, using a Garley type air permeability meter, the time (seconds) through which 100 cc of air passes in a circle having a predetermined area is measured as the air permeability (seconds / 100 cc).

The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500 ° C. in an air atmosphere of 1 atm, and are heated from room temperature to 800 ° C. in an air atmosphere of 1 atm. It is more preferable that the mass reduction at the time is 5% or less. Inorganic compounds can be mentioned as a material whose mass loss when heated is less than or equal to a predetermined value. As inorganic compounds, for example, oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminosilicate; magnesium hydroxide, water. Hydroxides such as calcium oxide and aluminum hydroxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride and barium fluoride Covalently bonded crystals such as silicon and diamond; talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, mica and other mineral resource-derived substances or man-made products thereof. .. As the inorganic compound, a simple substance or a complex of these substances may be used alone, or two or more kinds thereof may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the power storage element 1.

The porosity of the separator 60 is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value, and means a value measured by a mercury porosity meter.

(Spacer)
As shown in FIGS. 2 and 3, the spacer 70 is arranged between the inner surface of the case 3 (case body 31) and the electrode body 2 and is housed inside the case 3 (in FIG. 1, the spacer 70 is housed in the case 3). Not shown). The shape of the spacer 70 is, for example, a sheet. Two spacers 70, 70 may be housed in the case 3.
The two spacers 70, 70 are arranged in the case 3, for example, so as to be in contact with both flat outer surfaces of the flat electrode body 2.
The spacer 70 may be fixed to the inner surface of the case by an adhesive, heat welding, or the like, or may be simply sandwiched by the electrode body 2 and the inner surface of the case and held by pressure from both sides.
For example, the entire one surface of the sheet-shaped spacer 70 may be fixed to the inner surface of the case (surface adhesion, etc.), and a part of one surface of the sheet-shaped spacer 70 may be fixed to the inner surface of the case by, for example, point adhesion. It may have been done.

The power storage element 1 of the present embodiment may include an insulating sheet 80 arranged so as to cover the inner surface of the case body 31 inside the case 3 in order to insulate the electrode body 2 and the case 3. The insulating sheet 80 is, for example, a resin sheet. The insulating sheet 80 is arranged between the inner surface of the case body 31 and the electrode body 2. The insulating sheet 80 may be arranged so as to cover the electrode body 2. The material of the insulating sheet 80 is not particularly limited as long as it is an electrically insulating (non-conductive) material, and for example, a polyolefin resin such as polyethylene or polypropylene, a polyimide resin, or a resin such as a polyamide resin can be used. From the viewpoint of ease of manufacture, the material of the insulating sheet 80 is preferably a polyolefin resin, and more preferably at least one of polyethylene (PE) and polypropylene (PP).
The insulating sheet 80 may be formed in a bag shape and arranged in the case main body 31 by bending a sheet-shaped member or fusing or welding a plurality of sheet-shaped members.
The spacer 70 may be fixed to the insulating sheet 80 by the same surface adhesion or point adhesion as described above. It is preferable that the spacer 70 and the insulating sheet 80 fixed in this way are made of the same material. By using the same material, it becomes easier to fix the spacer 70 and the insulating sheet 80 by surface adhesion or point adhesion.

The size of the spacer 70 is not particularly limited as long as it can be accommodated in the case 3. As shown in FIG. 3, when the flat electrode body 2 and the spacer 70 housed in the case 3 are viewed in the thickness direction of the electrode body 2, the size of one sheet-shaped spacer 70 is the electrode. It may be smaller than the size of body 2. In this case, the spacer 70 is arranged in the case 3 so that all one side of the sheet-shaped spacer 70 is in contact with the flat outer surface of the flat electrode body 2.
Similarly, when the electrode body 2 and the spacer 70 are viewed as shown in FIG. 3, the ratio of the area of the spacer 70 to the area of the electrode body 2 may be 0.6 or more, preferably 0. 8 or more.
When the size of the spacer 70 is in the above range, the space z of the winding center portion of the electrode body 2 can be made smaller.
When looking at the electrode body 2 and the spacer 70 as shown in FIG. 3, the ratio of the area of the spacer 70 to the area of the electrode body 2 may be 1.0 or less.

In the flat electrode body 2, the positive electrode active material layer 42 and the negative electrode active material layer 52 face each other with the separator 60 interposed therebetween. In the winding axis direction of the electrode body 2, both end edges of the negative electrode active material layer 52 are arranged outside the both end edges of the positive electrode active material layer 42. In other words, both ends of the negative electrode active material layer 52 in the winding axis direction have portions that do not face the positive electrode active material layer 42.
Therefore, the flat electrode body 2 has a facing region in which the positive electrode active material layer 42 and the negative electrode active material layer 52 face each other when viewed in the thickness direction. It is preferable that the length of the spacer 70 is equal to or longer than the length of the facing region in the winding axis direction, and the spacer 70 is arranged so as to cover the entire facing region in the winding axis direction. In other words, both end edges of the spacer 70 in the winding axis direction overlap with both end edges of the facing region or protrude outward from both end edges of the facing region when the electrode body is viewed in the thickness direction. Is preferable.
With such a configuration, the spacer 70 can more sufficiently suppress the increase in the distance between the positive electrode active material layer 42 and the negative electrode active material layer 52. Therefore, it is possible to suppress a non-uniform charge / discharge reaction in the power storage element.

The flat and wound electrode body 2 has a flat portion 21 in which the sheet-shaped positive electrode 40 and the negative electrode 50 are stacked in a flat state, and a folded portion in which the stacked sheet-shaped positive electrode 40 and the negative electrode 50 are folded back. 22 and. At the folded-back portion 22, the positive electrode 40 and the negative electrode 50 are bent so as to surround the winding shaft. When the electrode body 2 is viewed in the winding axis direction, the folded portions 22 are arranged at both ends of the flat portion 21. A boundary portion y exists at a portion where the positive electrode 40 and the negative electrode 50 stacked on the flat portion 21 begin to bend along the winding circumferential direction (see FIGS. 2 and 3). There are four boundary portions y so as to extend linearly in the winding axis direction.
When the flat and wound electrode body 2 is viewed in the winding axis direction, it is preferable that both end edges of the spacer 70 are arranged inside the boundary portion y between the flat portion 21 and the folded portion 22. .. In other words, it is preferable that the spacer 70 is arranged so that the boundary portion y between the flat portion 21 and the folded portion 22 is not directly subjected to the compressive force by the spacer 70.
The boundary portion y between the flat portion 21 and the folded portion 22 is a portion that is not easily compressed and deformed even if a compressive force is applied in the thickness direction of the electrode body 2. In other words, the flat portion 21 is more likely to be compressed and deformed than the boundary portion y between the flat portion 21 and the folded portion 22. Therefore, since the edge of the spacer 70 is arranged inside the boundary portion y between the flat portion 21 and the folded portion 22, the spacer 70 is more likely to apply a force for compressing the electrode body 2 from the outside.

As described above, the shape of the spacer 70 is preferably, for example, a sheet shape, and is preferably a flat flat plate shape having no bent portion or curved portion. Since the spacer 70 has a flat plate shape, the number or thickness of the spacer 70 can be easily changed according to the tolerance (difference with respect to the reference dimension) of the internal space of the electrode body 2 or the case 3. Therefore, since the desired reference design can be appropriately adjusted, it is possible to easily reduce the space z in the winding center portion.

The material of the spacer 70 is not particularly limited. The spacer 70 may be made of, for example, a polyolefin resin such as polyethylene or polypropylene, a polyimide resin, or a resin such as a polyamide resin. The material of the spacer 70 is preferably a polyolefin resin such as polyethylene (PE) or polypropylene (PP) because it has good stability with respect to the electrolytic solution and is easy to handle.

The spacer 70 is harder than the separator 60 (base layer of the wet film). The hardness can be quantified by the amount of displacement when the spacer 70 and the separator 60 are each compressed with a predetermined load (detailed later).
The smaller the amount of displacement, the harder it is, and the larger the amount of displacement, the softer it is. Therefore, the displacement amount in the spacer 70 is smaller than the displacement amount in the separator 60.
Since the spacer 70 is harder than the separator 60 as described above, the spacer 70 is less likely to be deformed than the separator 60. Therefore, when the electrode body 2 is pressed by the inner surface of the case via the spacer 70 due to the reaction force when the electrode body 2 expands, the spacer 70 can further suppress the electrode body 2 from expanding outward. Therefore, the expansion becomes easier to go inward, and the space z at the winding center portion of the electrode body 2 can be reduced.

For example, the hardness of the spacer 70 and the separator 60 may be quantified by the following method to quantify the difference in hardness.
Specifically, when the spacer 70 and the separator 60 are each compressed with a load of 7 kN, the displacement amount of the separator 60 may be 0.1 mm / mm or more than the displacement amount of the spacer 70. The difference in the amount of such displacement may be 0.3 mm / mm or less.
Since the spacer 70 is harder than the separator 60 when the difference in displacement amount is 0.1 mm / mm or more as described above, the outward expansion of the electrode body 2 is further suppressed for the above reason. Can be done.
Since the above-mentioned displacement amount is expressed per 1 mm in thickness, the thickness of the spacer 70 or the separator 60 when measuring the displacement amount may be different, and may be substantially the same thickness. For example, a plurality of spacers 70 or separators 60 may be superposed and a load of 7 kN may be applied with a total thickness of about 1 mm or more and 2 mm or less. The area of the indenter when a load is applied may be 3000 mm ² or more, or 4000 mm ² or less. The surface area of the indenter is preferably ^{3680 mm 2.}

Two spacers 70 may be arranged in the case 3 so as to sandwich the electrode body 2 as described above, and are in contact with only one flat portion (one surface of the flat portion) of the flat electrode body 2. As described above, it may be arranged in the case 3.

As described above, the case 3 may be held so as to have a fixed size while accommodating the electrode body 2 in the internal space.
The "storage element held so as to have a fixed size" is set in, for example, the power storage device 100 configured by arranging a plurality of power storage elements 1 so as to be arranged in one direction.
Whether or not the power storage element 1 is held so as to have a fixed size in the power storage device 100 can be determined by comparison with the power storage device 100 of the same design. In the similarly designed power storage device 100, a plurality of power storage elements 1 arranged in one direction are fixed in the same number (as a power storage device to be compared), and the plurality of power storage elements 1 are fixed in a fixed position. It means a power storage device 100 in which a tool is configured to have a similar shape (as a power storage device to be compared).
When the difference in the total lengths of the compared power storage devices 100 is less than 3% with respect to the power storage device 100 similarly designed in this way, each power storage element 1 in the compared power storage devices 100 has a fixed size. It is held so as to be. Here, the power storage device 100 similarly designed and the power storage device 100 to be compared are compared after being appropriately discharged so that the voltage of the power storage device 100 becomes the same.
Even when the power storage device 100 is composed of one power storage element 1 and a fixture, is the power storage element 1 held so as to have a fixed size by comparing with the similarly designed power storage device 100? Whether or not it can be determined.
The power storage element 1 held so as to have a fixed size is, for example, each power storage element 1 constituting the power storage device as described above.
When the power storage element 1 constituting the power storage device 100 is held in a fixed size, it is difficult to individually adjust the pressure applied to each power storage element. Therefore, a relatively large pressure may be applied depending on the power storage element 1. Therefore, the pores of the wet film of the separator 60 contained in the electrode body 2 are more likely to be crushed, and the air permeability of the separator 60 is likely to increase.

In the present embodiment, the flat electrode body 2 is arranged in the case 3 so as not to have a gap with the inner surface of the case 3 in the thickness direction. As the case 3, preferably, a case 3 that does not easily swell is adopted. In other words, in order to hold the power storage element 1 so as to have a fixed size, the volume increase rate of the case 3 after the electrode body 2 is housed is less than a predetermined% (for example, less than 10%). preferable. The difference between the case length before accommodating the flat electrode body 2 and the case length after accommodating (the case length in the thickness direction of the electrode body 2) may be less than 20%. Examples of such a case 3 include a square-shaped (rectangular parallelepiped) case 3 formed of a metal plate having a thickness of 0.3 mm or more. The case 3 may be made of a metal plate having a thickness of 1.5 mm or less. Examples of the metal include aluminum (including aluminum alloy) and stainless steel.
Since the case 3 is hard to swell, the electrode body 2 housed in the case 3 is pressed from the outside. As the electrode body 2 is pressed from the outside, the space z at the winding center portion of the electrode body 2 becomes narrower.

In the power storage element 1 of the present embodiment, in a state where the flat electrode body 2 and the spacer 70 are housed in the case 3, the electrode body 2 and the spacer 70 and the like occupy in the thickness direction in the central portion of the electrode body 2. The ratio is as follows.
Specifically, in the cross section (cross section shown in FIG. 2) in which the power storage element 1 (state in which the electrode body 2 is housed in the case 3) is cut in a plane perpendicular to the winding axis direction of the electrode body 2, the thickness of the electrode body 2 is thick. It is preferable that (A), the total thickness (B) of the spacer 70, and the distance (C) between the inner surfaces facing each other in the case body 31 satisfy the following relationship.
0.95C ≤ A + B ≤ 1.00C
B / A = 0.01 or more and 0.08 or less A / C = 0.90 or more and 0.99 or less B / C = 0.01 or more and 0.08 or less

(Non-aqueous electrolyte)
The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, carboxylic acid ester, phosphoric acid ester, sulfonic acid ester, ether, amide, nitrile and the like. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are replaced with halogen may be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate. (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned. Among these, EC or PC is preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis (trifluoroethyl) carbonate. Of these, DMC or EMC is preferable.

As the non-aqueous solvent, it is preferable to use cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. By using the cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte solution can be improved. By using the chain carbonate, the viscosity of the non-aqueous electrolytic solution can be kept low. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like. Of these, lithium salts are preferred.

Lithium salts include inorganic lithium salts such _{as LiPF 6} , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) _{2 , LiSO 3} CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO _2). C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _{3 and} other halogenated hydrocarbon groups Examples thereof include lithium salts having. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The content of the electrolyte salt in the nonaqueous electrolytic solution, under 20 ° C. 1 atm, preferable to be 0.1 mol / dm ³ or more 2.5 mol / dm ³ or less, 0.3 mol / dm ³ or more 2.0 mol / dm more preferable to be ³ or less, more preferable to be 0.5 mol / dm ³ or more 1.7 mol / dm ³ or less, and particularly preferably 0.7 mol / dm ³ or more 1.5 mol / dm ³ or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte solution can be increased.

The non-aqueous electrolyte solution may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additive include halogenated carbonate esters such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium bis (oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis (oxalate). ) Sulfonic acid ester such as difluorophosphate (LiFOP); imide salt such as lithium bis (fluorosulfonyl) imide (LiFSI); partial hydride of biphenyl, alkylbiphenyl, terphenyl, terphenyl, cyclohexylbenzene, t-butylbenzene , T-Amilbenzene, diphenyl ether, dibenzofuran and other aromatic compounds; partial halides of said aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2 , 5-Difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole and other halogenated anisole compounds; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, anhydrous. Citraconic acid, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sulton, propensulton, butane sulton, methyl methanesulphonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, sulfuric acid Ester, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxy Methyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisol, diphenyldisulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tritrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate , Lithium difluorophosphate and the like. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolyte solution is preferably 0.01% by mass or more and 10% by mass or less, preferably 0.1% by mass or more and 7% by mass or less, based on the total mass of the non-aqueous electrolyte solution. It is more preferable to have it, more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less. By setting the content of the additive in the above range, it is possible to improve the capacity maintenance performance or the cycle performance after high temperature storage, and further improve the safety.

The shape of the power storage element 1 of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a laminated film type battery, a square type battery, a flat type battery, a coin type battery, and a button type battery.
FIG. 1 shows a power storage element 1 (non-aqueous electrolyte power storage element) as an example of a square battery. The electrode body 2 having the positive electrode 40 and the negative electrode 50 wound around the separator 60 is housed in a square case 3 (container). The positive electrode 40 is electrically connected to the positive electrode terminal 4 via the positive electrode lead 45. The negative electrode 50 is electrically connected to the negative electrode terminal 5 via the negative electrode lead 55.

<Configuration of non-aqueous electrolyte power storage device>
The power storage element 1 of the present embodiment is used as a power source for automobiles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV), a power source for electronic devices such as a personal computer and a communication terminal, or a power storage device. It can be mounted on a power source or the like as a power storage unit 10 (battery module) composed of a plurality of power storage elements 1. In this case, the technique of the present invention may be applied to at least one power storage element 1 included in the power storage device 100.
FIG. 5 shows an example of a power storage device 100 in which a power storage unit 10 in which two or more electrically connected power storage elements 1 are assembled is further assembled. The power storage device 100 may include a bus bar (not shown) that electrically connects two or more power storage elements 1, a bus bar (not shown) that electrically connects two or more power storage units 10. The power storage unit 10 or the power storage device 100 may include a condition monitoring device (not shown) that monitors the state of one or more power storage elements 1.

The power storage device 100 may be provided with a fixture for fixing the plurality of power storage elements 1 at a fixed position. The power storage element 1 in the power storage device 100 may be held in a fixed size by being fixed by the fixture.
For example, the power storage device 100 includes a pair of end plates arranged so as to sandwich a plurality of power storage elements 1 and 1 arranged in one direction from both ends in the arrangement direction, and a frame connecting the pair of end plates. May be good. As a result, the power storage element 1 can be held at a fixed size as described above.

<Manufacturing method of non-aqueous electrolyte power storage element>
The method for manufacturing the power storage element 1 of the present embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing the electrode body 2, preparing the non-aqueous electrolyte, and accommodating the electrode body 2 and the non-aqueous electrolyte in the case 3. Preparing the electrode body 2 includes preparing the positive electrode 40 and the negative electrode 50, and forming the electrode body 2 by laminating or winding the positive electrode 40 and the negative electrode 50 via the separator 60.

Containing the non-aqueous electrolyte in Case 3 can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte solution, the non-aqueous electrolyte solution may be injected from the injection port formed in the case 3 and then the injection port may be sealed.

<Other Embodiments>
The power storage element of the present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described, but the type, shape, dimensions, capacity, etc. of the power storage element are arbitrary. be. The present invention can also be applied to capacitors such as various secondary batteries, electric double layer capacitors and lithium ion capacitors.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples.

As shown below, a non-aqueous electrolyte secondary battery (lithium ion secondary battery) of each Example and each Comparative Example was manufactured.

<Battery manufacturing>
A positive electrode active material layer having a thickness of 81 μm on one side (the positive electrode active material is a lithium transition metal composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ )) is formed on both sides of a 12 μm thick aluminum foil. , A positive electrode was prepared.
A negative electrode active material layer having a thickness of 78 μm on one side (the negative electrode active material is non-graphitizable carbon, graphite, or silicon shown in Table 1) was formed on both sides of a copper foil having a thickness of 8 μm to prepare a negative electrode.
The positive electrode and the negative electrode are overlapped with each other via a separator having a wet polyethylene film having a thickness of 20 μm as a base material layer, and further wound to obtain dimensions of 116 mm in width, 10.6 mm in thickness, and 57 mm in height. As described above, a wound electrode body was produced.
Further, two spacers having a thickness of 0.15 mm and a width of 96.0 x a height of 56.3 mm are provided, and the case body (width 120 mm, thickness 12.5 mm (interval in the thickness direction of the internal space is 11.5 mm). ), Height 65 mm). Two spacers were arranged in the case body so that the electrode body was sandwiched between the two spacers from both sides when the flat electrode body was inserted into the case body. After that, the electrode body was inserted into the case body and the case was sealed so that the spacers were in contact with each flat surface portion of the electrode body.
_{As the non-aqueous electrolyte solution, LiPF 6} was dissolved in a non-aqueous solvent so that the salt concentration was 1.2 mol / L to prepare a non-aqueous electrolyte solution. Then, according to the following measurement, it was appropriately injected into the case. Here, as the non-aqueous solvent, in Example 1 and Comparative Example 2, propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were used as PC: DMC: EMC = 30: 35: 35 ( A mixture was used so as to be (% by volume). In Example 2 and Comparative Example 1, ethylene carbonate (EC), DMC, and EMC were mixed so as to have EC: DMC: EMC = 30: 35: 35 (volume%).

<Measurement of spacer hardness and separator hardness used in battery manufacturing>
When 10 spacers with a thickness of 0.15 mm are stacked and a load of 7 kN is applied by an indenter ^{with a surface area of 3680 mm 2} and held for 1 minute using a universal testing machine Autograph (AG-X manufactured by Shimadzu Corporation). The amount of displacement of was measured. The amount of displacement per 1 mm of thickness was calculated.
As a result, the displacement amount (per 1 mm) of the spacer (polypropylene medium substance) used in Examples 1 and 2 and Comparative Example 1 was 0.10 mm / mm.
The displacement amount (per 1 mm) of the spacer (porous material made of polyurethane) used in Comparative Example 2 was 0.77 mm / mm.
On the other hand, with 50 separators with a thickness of 20 μm (0.020 mm) stacked, a load of 7 kN was applied by an indenter ^{with a surface area of 3680 mm 2 using a universal testing machine Autograph (AG-X manufactured by Shimadzu Corporation).} The amount of displacement when held for 1 minute was measured. This measured value was taken as the amount of displacement per 1 mm of thickness.
As a result, the displacement amount (per 1 mm) of the separator used in each Example and each Comparative Example was 0.21 mm / mm.

(Examples 1 and 2)
A lithium ion secondary battery was manufactured as described above using the negative electrode active material shown in Table 1. The spacer and the separator are the same in Examples 1 and 2.

(Comparative Examples 1 and 2)
A lithium ion secondary battery was manufactured as described above using the negative electrode active material, the spacer, and the separator shown in Table 1.
In Comparative Example 1, the same spacers and separators as in Example 1 were used, and negative electrode active materials different from those used in Example 1 were used.
In Comparative Example 2, a porous body (same size) different from that of Example 1 was used as the spacer.

Table 1 shows the results of evaluations described below for the lithium ion secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2.

<Measurement of space width at the center of winding of the electrode body>
The case was held in a fixed size so that the case in which the electrode body was inserted had the size before the electrode body was inserted. In that state, an X-ray CT image of the winding center portion of the electrode body was acquired using an X-ray CT scanning apparatus (microfocus X-ray CT system inspexio SMX-225CT FRD HR Plus manufactured by Shimadzu Corporation). The X-ray CT image obtained a cross section of the wound electrode body when cut on a plane perpendicular to the direction connecting the folded portions. In other words, the cross section when the electrode body was cut was obtained along the virtual plane facing in the vertical direction in FIG.
In the acquired X-ray CT image, a region having a width of 1 mm from 34.5 mm to 35.5 mm was image-processed from the edge of the negative electrode active material layer toward the inside. Specifically, the image was binarized in order to distinguish the portion of the electrode and the separator in that region from the space of the winding center portion of the electrode body.
The spatial width of the winding center portion was calculated by counting the number of pixels (pix) of the spatial portion that was represented in black by binarization.
The space width (space size) was calculated using a converted value of 1 pix = 77 μm (1 mm = 13 pix). For example, when the number of counted pixels is 200 pix, the space width is (200/13) × 0.077 = 1.185 mm.

<Measurement of reaction force applied as the electrode body expands>
The battery after acquiring the X-ray CT image was held in a state where the entire long side surface of the case was in contact with the jig using a jig with a load cell (LCX-A-ID manufactured by Kyowa Electric Co., Ltd.). At this time, the size of the case in which the electrode body was housed was held so as to be the same as the size of the case before the electrode body was housed. Then, it was put into a charged state by being charged with a constant current until the utilization rate of the negative electrode active material became 0.5. The capacity of the negative electrode active material is 372 mAh / g in the case of graphitizable carbon, 372 mAh / g in the case of graphite, and 4200 mA / g in the case of Si, as values when the utilization rate is 1.0. The value of was used.
The value measured by the load cell was used as the reaction force applied to the electrode body in the charged state.

<Measurement of air permeability increase rate of separator>
Apart from the battery manufactured as described above, the electrode body of the battery (provided with a wet film separator) designed in the same manner as in Example 1 and the separator in Example 1 are made of a dry film (polypropylene / polyethylene / polypropylene) having a thickness of 20 μm. The electrode body changed to the three-layer structure of the above was prepared.
Using the universal testing machine Autograph (AG-X manufactured by Shimadzu Corporation), a predetermined load (various loads) is applied to each electrode body without the case inserted for 1 minute, and the electrode body after the load is applied. Was disassembled, and the air permeability of the separator was measured.
The air permeability of each separator to which the load was applied was calculated as a relative value, assuming that the air permeability of the separator (unused one not used for manufacturing the electrode body) before the load was applied was 100%. The results are shown in Tables 2 and 3.
From the calculated plot showing the relationship between each air permeability ratio and the load, an approximate curve (quadratic function, intercept is 100) was created by the least squares method.
It is assumed that the reaction force applied to the electrode body in the charged state is the pressure itself applied to the separator. Using the above approximate curve, the air permeability ratio of the separator, which corresponds to the above reaction force value, is obtained, and by subtracting 100% from the air permeability ratio, the air permeability increase rate of each battery ( (See Table 1) was calculated.

As can be seen from Table 1, in the power storage element of the present embodiment, the space at the center of winding of the electrode body is relatively small, and the increase in air permeability of the separator having a wet film is suppressed.
As can be seen from Tables 2 and 3, a power storage element (battery) having a separator having a wet film as a base material has a higher air permeability of the separator than a power storage element having a dry film separator. It can be said that it has a peculiar problem that it is easy to rise.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body, 21: Flat part, 22: Folded part,
y: boundary part, z: space at the winding center part of the electrode body,
3: Case, 31: Case body, 32: Cover body,
4: Positive electrode terminal, 5: Negative electrode terminal,
40: Positive electrode,
41: Positive electrode base material, 42: Positive electrode active material layer,
50: Negative electrode,
51: Negative electrode base material, 52: Negative electrode active material layer,
60: Separator, 70: Spacer, 80: Insulation sheet,
10: Power storage unit, 100: Power storage device.

Claims (5)

A wound electrode body having a negative electrode containing a negative electrode active material, a positive electrode, and a separator arranged between the positive electrode and the negative electrode.
A case containing the electrode body and
A spacer arranged between the electrode body and the inner surface of the case inside the case is provided.
The separator has a wet film and
The negative electrode active material is a carbonaceous material or lithium titanate.
A power storage element in which the spacer is harder than the separator. The power storage element according to claim 1, wherein the negative electrode active material is non-graphitic carbon as the carbonaceous material. The power storage element according to claim 1 or 2, wherein the case is held so as to have a fixed size. Each said spacer and said separator, when compressed under a load 7kN by indenter surface area 3680Mm ^2, the displacement amount of the separator is greater than 0.1 mm / mm than the displacement amount of the spacer, of claims 1 to 3 The power storage element according to any one item. An insulating sheet that covers the electrode body and insulates between the electrode body and the case is provided.
The case is made of metal
The power storage element according to any one of claims 1 to 4, wherein the spacer is arranged between the electrode body and the insulating sheet.

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