JP7411161B2 - Energy storage element - Google Patents

Description

The present invention relates to a power storage element.

Patent Document 1 discloses an electrode assembly in which a positive electrode and a negative electrode have an insulated layered structure, and each of the positive electrode and the negative electrode has a plurality of positive electrode tabs and negative electrode tabs stacked and electrically connected to an electrode terminal. A power storage device comprising a three-dimensional structure,
In the negative electrode, a first active material and a second active material having a larger capacity per mass than the first active material are coated to form a negative electrode active material layer, and the negative electrode active material layer includes: At least the capacity per area of the negative electrode active material layer in the tab side edge region in the projecting direction of the negative electrode tab is greater than the capacity per area of the negative electrode active material layer in the central region in the projecting direction of the negative electrode tab. There is described a power storage device characterized in that the first active material and the second active material are applied in such a manner that the mixing ratio of the first active material and the second active material increases.

Japanese Patent Application Publication No. 2016-12541

An object of the present invention is to provide a power storage element that can suppress metal deposition on the negative electrode during high-rate charging.

A power storage element according to one aspect of the present invention includes:
A positive electrode having a positive electrode active material layer, and a negative electrode having a negative electrode active material layer facing the positive electrode active material layer,
The negative electrode has a sheet-like current collecting base material and the negative electrode active material layer overlapping at least one surface of the current collecting base material,
The current collecting base material has a main body portion and a tab portion protruding outward from the main body portion,
The negative electrode active material layer crosses the boundary between the main body part and the tab part and overlaps a part of the tab part, and the following conditions are met:
(1) The mass per unit area of the negative electrode active material layer is larger in the tab portion than in the main body portion; and
(2) the thickness of the negative electrode active material layer is thicker in the tab portion than in the main body portion;
satisfies at least one of the following.

In the electricity storage element according to one aspect of the present invention, metal precipitation on the negative electrode is suppressed during high-rate charging.

FIG. 1 is a perspective view of a power storage element according to this embodiment. FIG. 2 is a perspective view of a wound electrode body of a power storage element according to this embodiment. FIG. 3 is a cross-sectional view of the laminated negative electrode (tab portion of the current collecting base material) and positive electrode cut in the thickness direction. FIG. 4 is a schematic diagram of a part of the negative electrode viewed from one side in the thickness direction. FIG. 5 is a cross-sectional view of a part of the negative electrode cut in the thickness direction. FIG. 6 is a schematic diagram of a power storage device including a plurality of power storage elements according to the present embodiment.

First, an overview of the power storage element disclosed in this specification will be explained.

The power storage element 1 according to one aspect of the present invention includes:
A positive electrode 40 having a positive electrode active material layer 42, and a negative electrode 50 having a negative electrode active material layer 52 facing the positive electrode active material layer 42,
The negative electrode 50 includes a sheet-shaped current collecting base material 51 and the negative electrode active material layer 52 overlapping at least one surface of the current collecting base material 51,
The current collecting base material 51 has a main body part 511 and a tab part 512 protruding outward from the main body part 511,
The negative electrode active material layer 52 crosses the boundary between the main body part 511 and the tab part 512 and overlaps a part of the tab part 512 under the following conditions:
(1) The mass per unit area of the negative electrode active material layer 52 is larger in the tab portion 512 than in the main body portion 511; and
(2) the negative electrode active material layer 52 is thicker in the tab portion 512 than in the main body portion 511;
satisfies at least one of the following.

According to the power storage element 1 described above, metal precipitation at the negative electrode is suppressed during high-rate charging. The reason why such an effect occurs is presumed to be as follows, for example.
That is, in the electricity storage element 1 described above, current tends to concentrate at the tab portion 512 of the negative electrode 50 during charging. In the negative electrode active material layer 52 overlapping the tab portion 512, metal deposition is likely to occur due to the influence of current concentration. On the other hand, in the case of (1), the mass per unit area of the negative electrode active material layer 52 in the tab portion 512 of the negative electrode 50 is larger than that in the main body portion 511, so that the amount of negative electrode active material per unit area is smaller than that in the tab portion 512. is larger. As a result, more metal ions such as Li ions are incorporated into the negative electrode active material during charging. Therefore, it is possible to suppress metal ions that have not been incorporated into the negative electrode active material from becoming metal and precipitating in the negative electrode. In the case of (2), since the thickness of the negative electrode active material layer 52 in the tab portion 512 of the negative electrode 50 is thicker than that in the main body portion 511, the amount of negative electrode active material per unit area becomes larger in the tab portion 512. There is. Therefore, metal precipitation at the negative electrode can be similarly suppressed. This suppression is particularly effective during high rate charging. However, this should not be interpreted as being limited to the above reasons.
Note that the high rate is, for example, a charging speed of 2C or more (when the magnitude of the current that completely charges the rated capacity of the battery in one hour is defined as 1C).

Here, the ratio (B/A) of the cross-sectional area (A) at the tab portion 512 of the current collecting base material 51 of the negative electrode 50 to the surface area (B) of the positive electrode active material layer 42 is 30,000 or more and 150,000 The following may be used.
Thereby, it is possible to further suppress metal precipitation at the negative electrode during high-rate charging.

As an example of a power storage element according to an embodiment of the present invention, a configuration of a non-aqueous electrolyte power storage element, a configuration of a non-aqueous electrolyte power storage device, a method for manufacturing a non-aqueous electrolyte power storage element, and other embodiments will be described in detail. Note that 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 art.

<Configuration of non-aqueous electrolyte storage element>
A non-aqueous electrolyte storage device (hereinafter also simply referred to as a "power storage device") according to an 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 container containing a non-aqueous electrolyte. The electrode body 2 is usually a laminated type in which a plurality of positive electrodes 40 and a plurality of negative electrodes 50 are laminated with a separator 60 in between, or a laminated type in which a plurality of positive electrodes 40 and a negative electrode 50 are laminated with a separator 60 in between. It is a wound type (described in detail below). The non-aqueous electrolyte exists in the positive electrode 40, negative electrode 50, and separator 60. A nonaqueous electrolyte secondary battery (particularly a lithium ion secondary battery, hereinafter also simply referred to as a "secondary battery") will be described below as an example of a nonaqueous electrolyte storage element, but the scope of application of the present invention will be limited. Not my intention.

As shown in FIGS. 1 and 2, the power storage element 1 of this embodiment includes a wound-type electrode body 2 and a case 3 that houses the electrode body 2. Furthermore, the power storage element 1 includes two external terminals (a positive terminal 4 and a negative terminal 5) that are attached to the case 3 in a state where at least a portion thereof is exposed or are constituted by at least a portion of the case 3. The electrode body 2 is connected to each external terminal 4, 5 within the case 3 via a current collecting member or the like.
The power storage element 1 of this embodiment includes an electrode body 2 housed in a case 3. The case 3 has a flat rectangular parallelepiped shape and includes a case body 31 that is open toward one side and a long and narrow rectangular lid 32 that covers the opening of the case body 31. The two external terminals 4 and 5 are spaced apart from each other in the long side direction of the lid body 32.

As shown in FIGS. 2 and 3, the electrode body 2 includes a long sheet-like positive electrode 40, a long sheet-like negative electrode 50, and two sheet-like separators 60, 60, which are stacked one on top of the other, and are further wound. has been formed. The two separators 60, 60 are arranged to electrically insulate the positive electrode 40 and the negative electrode 50, respectively. In this embodiment, the electrode body 2 is a flat wound body. The electrode body 2 is arranged in the case 3 so that the direction of the winding axis of the electrode body 2 is the same as the opening direction of the case body 31.

The electrode body 2 has a plurality of positive electrode tab portions 412 from which one long side in the width direction of the strip-shaped positive electrode 40 projects. The tab portions 412 of the plurality of positive electrodes are constituted by a part of the positive electrode base material 41 (current collection base material 41). Further, the electrode body 2 similarly includes a plurality of tab portions 512 (negative electrode tab portions 512) in which one long side in the width direction of the strip-shaped negative electrode 50 projects. The plurality of tab portions 512 (negative electrode tab portions 512) are constituted by a part of the negative electrode base material 51 (current collection base material 51).
The plurality of positive electrode tab portions 412 of the positive electrode 40 are arranged in line in the direction in which the positive electrode 40 and the negative electrode 50 are stacked. The same applies to the plurality of tab portions 512 (negative electrode tab portions 512) of the negative electrode 50. Further, the plurality of positive electrode tab portions 412 of the positive electrode 40 and the plurality of tab portions 512 (negative electrode tab portions 512) of the negative electrode 50 are connected to the lid of the case 3 in the same manner as the two external terminals 4 and 5 spaced apart from each other. 32 are spaced apart from each other in the long side direction.

(positive electrode)
The positive electrode 40 includes a positive electrode base material 41 (positive electrode current collecting base material 41), and a positive electrode active material layer 42 disposed on the positive electrode base material 41 directly or via an intermediate layer (not shown). In this embodiment, as shown in FIG. 3, positive electrode active material layers 42 are stacked on both sides of a positive electrode base material 41 (positive electrode current collection base material 41).
The positive electrode base material 41 (positive electrode current collecting base material 41) has a positive electrode main body portion and a positive electrode tab portion 412 protruding outward from the positive electrode main body portion. The positive electrode active material layer 42 overlaps the main body portion of the positive electrode and does not overlap the tab portion 412 of the positive electrode. In the tab portion 412 of the positive electrode, the positive electrode base material 41 (the current collecting base material 41 of the positive electrode) is exposed.
The edge of the positive electrode active material layer 42 is arranged on the inner side of the edge of the negative electrode active material layer 52, which is opposed to the positive electrode active material layer 42 with the separator 60 interposed therebetween.
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 (current collection base material 41) has electrical conductivity. Whether or not it has "conductivity" is determined by using a volume resistivity of 10 ⁷ Ω·cm as a threshold value, which is measured in accordance with JIS-H-0505 (1975). As the material of the positive electrode base material 41, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum or aluminum alloy is preferred from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode base material 41 include foil, vapor deposited film, etc., and foil is preferable from the viewpoint of cost. Therefore, as the positive electrode base material 41, aluminum foil or aluminum alloy foil is preferable. 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 (current collector 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, even more 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 within the above range, the energy density per volume of the secondary battery can be increased while increasing the strength of the positive electrode base material 41.

The intermediate layer is a layer disposed between the positive electrode base material 41 and the positive electrode active material layer 42. The intermediate layer reduces contact resistance between the positive electrode base material 41 and the positive electrode active material layer 42 by containing conductive particles such as carbon particles. The structure 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, a thickener, and a filler, as necessary.

The positive electrode active material can be appropriately selected from known positive electrode active materials. As a positive electrode active material for a lithium ion secondary battery, a material that can insert and release lithium ions is usually used. Examples of the positive electrode active material include a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, a lithium transition metal composite oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, and sulfur. Examples of lithium transition metal composite oxides having α-NaFeO type ₂ crystal structure include Li[Li _x Ni _(1-x) ]O ₂ (0≦x<0.5), 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 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 crystal structure include LixMn 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 chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, and the like. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer 42, one type of these materials may be used alone, or two or more types may be used in combination.

The positive electrode active material is usually particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to be equal to or larger than the above lower limit, manufacturing or handling of the positive electrode active material becomes easier. By setting the average particle size of the positive electrode active material to be less than or equal to the above upper limit, the electronic conductivity of the positive electrode active material layer 42 is improved. In addition, when using a composite of a positive electrode active material and another material, let the average particle diameter of the composite be the average particle diameter of the positive electrode active material. "Average particle size" is based on the particle size distribution measured by laser diffraction/scattering method on a diluted solution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013). -2 (2001), meaning the value at which the volume-based cumulative distribution calculated in accordance with 2001 is 50%.

A pulverizer, classifier, etc. are used to obtain powder with a predetermined particle size. Examples of the pulverization method include methods using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, swirling jet mill, or sieve. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane is present can also be used. As for the classification method, a sieve, a wind classifier, etc. may be used, both dry and wet, as necessary.

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 even more 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.

(optional ingredient)
The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents 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, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, Ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Examples of the shape of the conductive agent include powder, fiber, and the like. As the conductive agent, one type of these materials may be used alone, or two or more types may be used in combination. Further, these materials may be used in combination. For example, a composite material of carbon black and CNT may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coatability, and acetylene black is particularly preferred.

When using a conductive agent, 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 within the above range, the energy density of the secondary battery can be increased.

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

When using a binder, 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, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the active material can be stably held.

Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. 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. When using a thickener, the content of the thickener in the positive electrode active material layer 42 is preferably 8% by mass or less, more preferably 5% by mass or less. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer 42 does not contain the above-mentioned thickener.

The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate, magnesium hydroxide, calcium hydroxide, and hydroxide. Hydroxides such as aluminum, carbonates such as calcium carbonate, poorly soluble ionic crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, Examples include substances derived from mineral resources such as apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. When using a filler, the content of the filler in the positive electrode active material layer 42 is preferably 8% by mass or less, more preferably 5% by mass or less. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer 42 does not contain the filler.

The positive electrode active material layer 42 is made of typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba. Typical metal 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, It may be contained as a component other than filler.

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

In this embodiment, as shown in FIG. 3, negative electrode active material layers 52 are stacked on both sides of a negative electrode base material 51 (negative electrode current collection base material 51).
The negative electrode base material 51 (negative electrode current collecting base material 51) has a main body part 511 and a tab part 512 (negative electrode tab part 512) protruding outward from the main body part 511. For example, as shown in FIG. 4, the negative electrode active material layer 52 overlaps the entire body portion 511, and also overlaps a portion of the tab portion 512 across the boundary between the body portion 511 and the tab portion 512. In most of the tab portion 512, the negative electrode base material 51 (negative electrode current collection base material 51) is exposed.
The edge of the negative electrode active material layer 52 is arranged on the outer side of the edge of the positive electrode active material layer 42 that faces the negative electrode active material layer 52 with the separator 60 interposed therebetween.

In this embodiment, at least one of the following (1) and (2) is satisfied.
(1) The mass per unit area of the negative electrode active material layer 52 is larger in the tab portion 512 than in the main body portion 511.
(2) The thickness of the negative electrode active material layer 52 is thicker in the tab portion 512 than in the main body portion 511.
In the electricity storage element 1 described above, current tends to concentrate at the tab portion 512 of the negative electrode 50 during charging. In the negative electrode active material layer 52 overlapping the tab portion 512, metal deposition is likely to occur due to the influence of current concentration. On the other hand, in the case of (1), the mass per unit area of the negative electrode active material layer 52 in the tab portion 512 of the negative electrode 50 is larger than that in the main body portion 511, so that the amount of negative electrode active material per unit area is smaller than that in the tab portion 512. is larger. As a result, more metal ions such as Li ions are incorporated into the negative electrode active material during charging. Therefore, it is possible to suppress metal ions that have not been incorporated into the negative electrode active material from becoming metal and precipitating in the negative electrode. In the case of (2), since the thickness of the negative electrode active material layer 52 in the tab portion 512 of the negative electrode 50 is thicker than that in the main body portion 511, the amount of negative electrode active material per unit area becomes larger in the tab portion 512. There is. Therefore, metal precipitation at the negative electrode can be similarly suppressed. This suppression is particularly effective during high rate charging.

When the above condition (1) is satisfied, the mass per unit area (fabric weight) W2 of the negative electrode active material layer 52 overlapping the main body part 511 is the mass per unit area of the negative electrode active material layer 52 overlapping the tab part 512. It is not particularly limited as long as it is smaller than W1 (that is, W1>W2). When the negative electrode active material layers 52 are formed on both sides of the negative electrode base material 51, W2 is the mass per unit area of the negative electrode active material layer 52 overlapping on one surface (the mass per unit area of two layers). half the value). For example, W2 is suitably 0.1 g/100 cm ² or more per 100 cm 2 of area, usually 0.2 g/100 cm ^{2 or} more, typically 0.3 g/100 cm ² or more. W2 is preferably 0.40 g/100 cm ² or more, more preferably 0.45 g/100 cm ² or more, even more preferably 0.48 g/100 cm ² or more. In some embodiments, W2 may be 0.50 g/100 cm ² or more, or 0.52 g/100 cm ² or more. Further, W2 can be, for example, 1.0 g/100 cm ² or less. W2 is preferably 0.8 g/100 cm ² or less, more preferably 0.7 g/100 cm ² or less, even more preferably 0.65 g/100 cm ² or less. In some embodiments, W2 may be 0.60 g/100 cm ² or less, or 0.55 g/100 cm ² or less. Note that the above value of W2 represents the mass of the negative electrode active material layer 52 that overlaps the entire main body portion 511 in terms of mass per 100 cm ² of area. The area of the negative electrode active material layer 52 that overlaps the entire main body portion 511 has a predetermined size, but is arbitrary, and the unit “g/100cm ² ” is the area of the negative electrode active material layer 52 that overlaps the entire main body portion 511. There is no direct relationship.

When the above condition (1) is satisfied, the mass W1 per unit area of the negative electrode active material layer 52 overlapping the tab portion 512 must be larger than the mass W2 per unit area of the negative electrode active material layer 52 overlapping the main body portion 511. Good, but not particularly limited. When the negative electrode active material layers 52 are formed on both sides of the negative electrode base material 51, W1 is the mass per unit area of the negative electrode active material layer 52 overlapping on one surface (half the mass per unit area of two layers). ).
In some embodiments, the mass W1 per unit area of the negative electrode active material layer 52 overlapping the tab portion 512 and the mass W2 per unit area of the negative electrode active material layer 52 overlapping the main body portion 511 are expressed by the following formula (I). satisfy.
1.0<W1/W2≦1.2 Formula (I)
By satisfying the above formula (I), it is possible to more reliably suppress metal precipitation on the negative electrode during high-rate charging. In the technology disclosed herein, for example, the relationship between W1 and W2 is
1.005≦W1/W2≦1.150 formula (II),
Furthermore, 1.008≦W1/W2≦1.100 formula (III),
In particular, it can be implemented in an embodiment where 1.010≦W1/W2≦1.050 formula (IV).
Note that W1 is the area of the portion where the negative electrode active material layer 52 overlaps with a portion of the tab portion 512, and is determined by dividing the mass of the negative electrode active material layer 52 overlapping that portion. Therefore, the area for calculating W1 is relatively small but arbitrary, and is not limited to 100 cm ² .

When the above condition (1) is satisfied, in a preferred embodiment, the average thickness of the negative electrode active material layer 52 overlapping the tab portion 512 is thicker than the average thickness of the negative electrode active material layer 52 overlapping the main body portion 511. That is, the mass per unit area of the negative electrode active material layer 52 is larger in the tab portion 512 than in the main body portion 511, and the average thickness of the negative electrode active material layer 52 (the negative electrode active material layer 52 on both sides of the negative electrode base material 51 is formed, the sum of the average thicknesses of the respective layers) is thicker in the tab portion 512 than in the main body portion 511. In such an embodiment, in order to make the average thickness of the negative electrode active material layer 52 thicker in the tab portion 512 than in the main body portion 511, for example, while applying more of the mixture composition in the tab portion 512, It is better to apply less amount in 511. In this way, the negative electrode active material layer 52 satisfying the above relationship W2<W1 can be easily formed using the same mixture composition. In this case, the mass of the negative electrode active material per unit volume may be the same throughout the negative electrode active material layer 52. Further, the mass of the negative electrode active material layer per unit volume may be the same throughout the negative electrode active material layer 52.

When the above condition (1) is satisfied, in another preferred embodiment, the thickness of the negative electrode active material layer 52 overlapping the main body portion 511 and the thickness of the negative electrode active material layer 52 overlapping the tab portion 512 are approximately the same. . For example, even if the thickness of the entire negative electrode active material layer 52 is the same, because the mass per unit volume of the negative electrode active material layer 52 is larger in the tab portion 512 than in the main body portion 511, the unit of the negative electrode active material layer 52 is The mass per area may be larger in the tab portion 512 than in the main body portion 511. In this embodiment, in order to make the mass per unit area of the negative electrode active material layer 52 formed with the same thickness larger in the tab portion 512 than in the main body portion 511, for example, if the content of the negative electrode active material is higher, While applying the agent composition to the tab portion 512, it is preferable to apply a mixture composition containing a smaller amount of negative electrode active material to the main body portion 511 so as to have the same thickness as the thickness in the tab portion.

On the other hand, when the above condition (2) is satisfied, for example, as shown in FIG. 5, the maximum thickness of the negative electrode active material layer 52 is thicker in the tab portion 512 than in the main body portion 511. In the tab portion 512, the thickness of at least a portion of the negative electrode active material layer 52 only needs to be thicker than the main body portion 511, and for example, as shown in FIG. Good too. On the other hand, the thickness of the negative electrode active material layer 52 may be thicker in the tab portion 512 than in the main body portion 511 so as to have a step, for example.

When the above condition (2) is satisfied, the average thickness T2 of the negative electrode active material layer 52 overlapping the main body portion 511 only needs to be thinner than the average thickness T1 of the negative electrode active material layer 52 overlapping the tab portion 512 ( In other words, it is sufficient that T2<T1), and is not particularly limited. When the negative electrode active material layers 52 are formed on both sides of the negative electrode base material 51, T2 is the total value of the average thickness of each layer. T2 (total average thickness) is, for example, suitably 50 μm or more, usually 70 μm or more, typically 80 μm or more. T2 is preferably 90 μm or more, more preferably 100 μm or more, even more preferably 110 μm or more. In some embodiments, T2 may be greater than or equal to 115 μm, or greater than or equal to 120 μm. Further, T2 can be, for example, 250 μm or less. T2 is preferably 200 μm or less, more preferably 180 μm or less, even more preferably 160 μm or less. In some embodiments, T2 (total average thickness) may be 150 μm or less, or 140 μm or less.

When the above condition (2) is satisfied, the average thickness T1 of the negative electrode active material layer 52 overlapping the tab portion 512 only needs to be thicker than the average thickness T2 of the negative electrode active material layer 52 overlapping the main body portion 511, Not particularly limited. When the negative electrode active material layers 52 are formed on both sides of the negative electrode base material 51, T1 is the total value of the average thickness of each layer. In some embodiments, the difference between the average thickness T1 of the negative electrode active material layer 52 overlapping the tab portion 512 and the average thickness T1 of the negative electrode active material layer 52 overlapping the main body portion 511 (i.e., T1−T2) is as follows: For example, it is 0.05 μm or more, typically 0.1 μm or more. Further, T1-T2 may be, for example, 20 μm or less (typically 10 μm or less), for example, 5 μm or less).
Note that the average thickness is calculated by averaging thickness measurements at at least five randomly selected locations. The average thickness T2 of the negative electrode active material layer 52 overlapping the main body part 511 is determined by measuring the thickness of the negative electrode active material layer 52 overlapping the central part of the main body part 511. On the other hand, the average thickness T1 of the negative electrode active material layer 52 overlapping the tab portion 512 is determined by measuring the thickness at the midpoint from the boundary C between the main body portion 511 and the tab portion 512 to the edge B of the negative electrode active material layer 52. It is calculated by averaging multiple measurements. In other words, the part where the average thickness T1 is measured is the central part of the region where the negative electrode active material layers 52 overlap in the tab part 512.

When the above condition (2) is satisfied, in order to make the average thickness of the negative electrode active material layer 52 thicker in the tab portion 512 than in the main body portion 511, for example, more of the mixture composition is applied to the tab portion 512. On the other hand, it is preferable to apply less amount in the main body portion 511. In this case, the mass of the negative electrode active material per unit volume may be the same throughout the negative electrode active material layer 52. Further, the entire negative electrode active material layer 52 may have the same mass per unit volume.

In the electricity storage element 1 of this embodiment, the ratio (B/A) of the cross-sectional area (A) at the tab portion 512 of the current collecting base material 51 of the negative electrode 50 to the surface area (B) of the positive electrode active material layer 42 is 30. ,000 or more and 150,000 or less.
Specifically, the surface area (B) of the positive electrode active material layer 42 that causes a charging/discharging reaction with the negative electrode active material layer 52 overlapping the main body portion 511 and the tab portion 512, and the negative electrode through which current accompanying the charging/discharging reaction described above passes. Even if the ratio (B/A) to the cross-sectional area (A) of the tab portion 512 of the current collecting base material 51 of No. 50 is 30,000 or more and 150,000 or less (for example, 30,000 or more and 125,000 or less) good.
With such a configuration, it is possible to further suppress metal precipitation on the negative electrode during high-rate charging.

The above cross-sectional area of the tab portion 512 is the cross-sectional area of the portion where the current collecting member attached to the tab portion 512 for connecting the tab portion 512 and the external terminal 5 is in contact with the tab portion 512. For example, when the tab portion 512 is sandwiched between current collecting clips serving as current collecting members, the cross-sectional area of the portion (indicated by Z) where the tab portion 512 is sandwiched between the current collecting clips is adopted as shown in FIG. do.
Moreover, when one current collection base material 51 has a plurality of tab parts 512 like the electricity storage element 1 of this embodiment, the cross-sectional area (A) of the tab part 512 is the total cross-sectional area of each tab part 512. area (total area). The surface area (B) of the positive electrode active material layer 42 at this time is the total area of the positive electrode active material layer 42 that causes a current to flow through each targeted tab portion 512. In this case, the average cross-sectional area of each tab portion 512 (that is, the value obtained by dividing the total cross-sectional area of each tab portion 512 by the number of each tab portion 512) is not particularly limited, but is 0.003 cm ² or more. 006 cm ² or less, preferably 0.004 cm ² or more and 0.005 cm ² or less. Further, the surface area of the positive electrode active material layer 42 per one tab portion 512 (that is, the value obtained by dividing the total area of the positive electrode active material layer 42 by the number of tab portions 512) is not particularly limited, but is 100 cm ² or more and 750 cm ² It may be below, preferably 120 cm ² or more and 700 cm ² or less.
Note that when the electrode body is of the so-called laminated type described above, the above ratio (B/A) is calculated for each positive electrode and each negative electrode that face each other with a separator in between. At least one set of a positive electrode and a negative electrode facing each other with a separator in between may satisfy the above numerical range of the ratio (B/A). Preferably, the above numerical range of the ratio (B/A) is satisfied for all the positive electrodes and negative electrodes.

The negative electrode base material 51 has electrical conductivity. As the material of the negative electrode base material 51, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or alloys thereof are used. Among these, copper or copper alloy is preferred. Examples of the negative electrode base material 51 include foil, vapor deposited film, etc., and foil is preferable from the viewpoint of cost. Therefore, as the negative electrode base material 51, copper foil or copper alloy foil is preferable. Examples of 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, even more 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 within the above range, the energy density per volume of the secondary battery can be increased while increasing the strength of the negative electrode base material 51.

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, as necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the positive electrode 40 above. When a binder is used, it is preferable to use a water-based binder such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, or styrene-butadiene rubber (SBR). The binder content in the negative electrode active material layer 52 is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the active material can be stably held. When using a thickener, the content of the thickener in the negative electrode active material layer 52 is preferably 0.5% by mass or more and 8% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. When using a conductive agent, the content of the conductive agent in the negative electrode active material layer 52 is preferably 8% by mass or less, more preferably 5% by mass or less. The technique disclosed herein can be preferably implemented in an embodiment in which the negative electrode active material layer 52 does not contain the above-mentioned conductive agent. When using a filler, the content of the filler in the negative electrode active material layer 52 is preferably 8% by mass or less, more preferably 5% by mass or less. The technique disclosed herein can be preferably implemented in an embodiment in which the negative electrode active material layer 52 does not contain the filler.

The negative electrode active material layer 52 is made of typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and other transition metal elements are used as negative electrode active materials, conductive agents, and binders. , thickeners, and fillers.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As a negative electrode active material for a lithium ion secondary battery, a material that can insert and release lithium ions is usually used. Examples of negative electrode active materials include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li ₄ Ti ₅ O1 ₂ , Examples include titanium-containing oxides such as LiTiO ₂ and TiNb ₂ O ₇ ; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon); It will be done. Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer 52, one type of these materials may be used alone, or two or more types may be used in combination.

"Graphite" refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane of 0.33 nm or more and less than 0.34 nm before charging and discharging or in a discharge state, as determined by X-ray diffraction. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

"Non-graphitic carbon" refers to a carbon material whose average lattice spacing (d ₀₀₂ ) of the (002) plane is 0.34 nm or more and 0.42 nm or less, as determined by X-ray diffraction before charging and discharging or in a discharge state. say. Examples of non-graphitic carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, alcohol-derived materials, and the like.

Here, the "discharge state" refers to a state in which the open circuit voltage is 0.7 V or more in a monopolar battery using the negative electrode 50 containing a carbon material as the negative electrode active material as the working electrode and metal Li as the counter electrode. . Since the potential of the metal Li counter electrode in an open circuit state is approximately equal to the oxidation-reduction potential of Li, the open-circuit voltage in the monopolar battery is approximately equal to the potential of the negative electrode 50 containing the carbon material with respect to the oxidation-reduction potential of Li. be. In other words, if the open circuit voltage of the monopolar battery is 0.7 V or more, it means that a sufficient amount of lithium ions, which can be intercalated and released during charging and discharging, is released from the carbon material that is the negative electrode active material. .

"Non-graphitizable carbon" refers to a carbon material in which the above d ₀₀₂ is 0.36 nm or more and 0.42 nm or less.

"Graphitizable carbon" refers to a carbon material in which the above d ₀₀₂ is 0.34 nm or more and less than 0.36 nm.

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. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphoric acid compound, the average particle size thereof may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size thereof may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or larger than the above lower limit, manufacturing or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the negative electrode active material layer 52 is improved. A pulverizer, classifier, etc. are used to obtain powder with a predetermined particle size. The pulverization method and powder-grading method can be selected from, for example, the methods exemplified for the positive electrode 40 above. When the negative electrode active material is a metal such as metal Li, the negative electrode active material may be in the form of a foil.

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, 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 consisting 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 or both surfaces of the base material layer, etc. can be used. Examples of the material for the base layer of the separator 60 include woven fabric, nonwoven fabric, and porous resin film. Among these materials, a porous resin film is preferred from the viewpoint of strength, and a nonwoven fabric is preferred from the viewpoint of liquid retention of the nonaqueous electrolyte. The material for the base layer of the separator 60 is preferably polyolefin, such as polyethylene or polypropylene, from the viewpoint of a shutdown function, and preferably polyimide, aramid, etc. from the viewpoint of oxidative decomposition resistance. A composite material of these resins may be used as the base material layer of the separator 60.

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 when heated to 800°C in an air atmosphere of 1 atm. It is more preferable that the mass reduction is 5% or less. Inorganic compounds are examples of materials whose mass loss is less than a predetermined value. Examples of inorganic compounds include 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; Hardly soluble ionic crystals such as calcium fluoride and barium fluoride Covalent crystals such as silicon and diamond; Substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. . As the inorganic compound, these substances may be used alone or in combination, or two or more types may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of 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, "porosity" is a value based on volume, and means a value measured with a mercury porosimeter.

As the separator 60, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyvinylidene fluoride, and the like. Use of polymer gel has the effect of suppressing liquid leakage. As the separator 60, a porous resin film or nonwoven fabric as described above and a polymer gel may be used in combination.

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

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic esters, phosphoric esters, sulfonic esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are replaced with halogens may be used.

Examples of cyclic carbonates 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. Among these, EC is preferred.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate, bis(trifluoroethyl) carbonate, and the like. Among these, EMC is preferred.

As the nonaqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a cyclic carbonate and a chain carbonate together. By using a cyclic carbonate, it is possible to promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. By using chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When a cyclic carbonate and a chain carbonate are used together, 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 electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, and the like. Among these, lithium salts are preferred.

Examples of 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 Halogenated _{hydrocarbon groups} such _{as C2F5 ) 2} , LiN( _SO2CF3 )( _{SO2C4F9 )} , LiC( _{SO2CF3 ) 3} , LiC _{( SO2C2F5} ) _3, etc. Examples include lithium salts with Among these, inorganic lithium salts are preferred, and LiPF ₆ is more preferred.

The content of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol/dm ³ or more and 2.5 mol/dm 3 or less, and 0.3 mol/dm ^{3 or} more and 2.0 mol/dm at 20° C. and 1 atmosphere. It is more preferably ³ or less, even more preferably 0.5 mol/dm ³ or more and 1.7 mol/dm ³ or less, particularly preferably 0.7 mol/dm ³ or more and 1.5 mol/dm ³ or less. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include oxalate esters such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); biphenyl, alkylbiphenyl, terphenyl, Aromatic compounds such as partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; the above aromatics such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, etc. Partial halides of group compounds; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, anhydride Maleic acid, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, propene sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, Dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4 -Methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, mono Examples include lithium fluorophosphate. These additives may be used alone or in combination of two or more.

The content of the additive contained in the nonaqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, and 0.1% by mass or more and 7% by mass or less based on the mass of the entire nonaqueous electrolyte. It is more preferable if it is present, more preferably from 0.2% by mass to 5% by mass, and particularly preferably from 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, capacity retention performance or cycle performance after high-temperature storage can be improved, and safety can be further improved.

A solid electrolyte may be used as the non-aqueous electrolyte, or a non-aqueous electrolyte and a solid electrolyte may be used together.

The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (for example, 15° C. to 25° C.). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes, and the like.

Examples of the sulfide solid electrolyte in the case of a lithium ion secondary battery include Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ S ₅ , Li ₁₀ Ge-P ₂ S ₁₂ , and the like. .

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

<Configuration of non-aqueous electrolyte power storage device>
The power storage element 1 of this embodiment is used as a power source for automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs), power sources for electronic devices such as personal computers and communication terminals, or for power storage. It can be installed in a power source or the like as a power storage unit 10 (battery module) configured by collecting a plurality of power storage elements 1. In this case, the technology of the present invention may be applied to at least one power storage element 1 included in the power storage device.
FIG. 6 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. 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, and the like. The power storage unit 10 or the power storage device 100 may include a state monitoring device (not shown) that monitors the state of one or more power storage elements 1.

<Method for manufacturing non-aqueous electrolyte storage element>
A method for manufacturing the electricity storage element 1 of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing the electrode body 2, preparing a non-aqueous electrolyte, and accommodating the electrode body 2 and the non-aqueous electrolyte in a container. 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 with the separator 60 in between.

The method of accommodating the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a nonaqueous electrolyte is used as the nonaqueous electrolyte, the injection port may be sealed after the nonaqueous electrolyte is injected through an injection port formed in the container.

<Other embodiments>
Note that the power storage element of the present invention is not limited to the above embodiments, and various changes 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 known technique. Additionally, some of the configurations of certain embodiments may be deleted. Furthermore, well-known techniques can be added to the configuration of a certain embodiment.

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

In the above embodiment, an electrode body in which the positive electrode 40 and the negative electrode 50 are stacked with the separator 60 in between is described, but the electrode body does not need to include the separator 60. For example, the positive electrode and the negative electrode may be in direct contact with each other with a non-conductive layer formed on the active material layer of the positive electrode or the negative electrode.

In the above embodiment, a so-called wound type electrode body has been described in detail, but the electrode body may also be a laminated type in which a sheet-shaped positive electrode, a sheet-shaped separator, and a sheet-shaped negative electrode are repeatedly stacked. good.

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

A non-aqueous electrolyte secondary battery (lithium ion secondary battery) was manufactured as shown below.

(Example 1)
The lithium ion secondary battery according to this example includes a positive electrode having a positive electrode active material layer, and a negative electrode having a negative electrode active material layer facing the positive electrode active material layer. The positive electrode and the negative electrode each have a sheet-like current collecting base material and an active material layer overlapping both sides of the current collecting base material.
(1) Preparation of positive electrode Solvent: N-methyl-2-pyrrolidone (NMP)
Conductive agent: carbon black (4.0 parts by mass)
Particles of active material (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ): (94.5 parts by mass)
Binder: PVDF (1.5 parts by mass)
A mixture composition for a positive electrode was prepared by mixing and kneading the above raw materials. The prepared mixture composition for a positive electrode was placed on aluminum foil (a collection of positive electrodes with ^a thickness of 12 μm) so that the mass per unit area (fabric weight) of the positive electrode active material layer after drying was 1.7 g/100 cm2. It was applied to both sides of the electronic base material). After drying by heating, roll pressing was performed. Thereafter, it was vacuum dried to remove moisture and the like. The thickness of the active material layer (one layer) after pressing was 51 μm. The mass of the positive electrode active material layer per unit volume was 3.3 g/cm ³ .

(2) Preparation of negative electrode Solvent: Water Active material: Particulate amorphous carbon (non-graphitizable carbon) (97.4 parts by mass)
Binder: SBR (2.0 parts by mass)
Thickener: CMC (0.6 parts by mass)
A mixture composition for a negative electrode was prepared by mixing and kneading the above raw materials. The prepared mixture composition for a negative electrode was applied to both sides of a copper foil (current collector base material for a negative electrode having a thickness of 8 μm). The negative electrode active material layer overlapping the main body of the copper foil was coated so that the mass per unit area (fabric weight, one layer) was 0.539 g/100 cm ² . After drying by heating, roll pressing was performed. Thereafter, it was vacuum dried to remove moisture and the like. The thickness of the active material layer after pressing was 61 μm (one layer), that is, 122 μm (two layers). The mass of the negative electrode active material layer per unit volume was 0.9 g/cm ³ .
The current collecting base material of the negative electrode has a main body (center part) and a tab part protruding outward from the main body. The negative electrode active material layer also overlaps a part of the tab portion beyond the boundary between the main body portion and the tab portion. In this example, a negative electrode was produced in which the mass per unit area of the negative electrode active material layer was set to be larger in the tab portion than in the main body portion.
In addition, in producing the negative electrode, by applying more of the mixture composition on the tab portion, the mass per unit area of the negative electrode active material layer overlapping the tab portion can be increased, and the mass per unit area of the negative electrode active material layer overlapping the tab portion can be increased. The average thickness of

(3) Separator (separator base material)
A microporous polyethylene membrane having a thickness of 14 μm was used as a separator base material. A separator was constructed using only this separator base material.

(4) Preparation of non-aqueous electrolyte The non-aqueous electrolyte prepared by the following method was used. As a non-aqueous solvent, a mixture of 1 part by volume of propylene carbonate and ethyl methyl carbonate was used, and LiPF ₆ was dissolved in this non-aqueous solvent so that the salt concentration was 1.2 mol/dm ³ . A non-aqueous electrolyte was prepared.

(5) Arranging the electrode body in the case A lithium ion secondary battery was assembled by a general method using the above positive electrode, the above negative electrode, the above nonaqueous electrolyte, the separator, and the case.
First, a sheet-like material in which a separator was laminated and arranged between the positive electrode and the negative electrode was wound. Next, the wound electrode body was placed inside a case body of an aluminum rectangular battery case. Subsequently, the positive electrode and the negative electrode were electrically connected to each of the two external terminals. Furthermore, a lid was attached to the case body. The above-mentioned non-aqueous electrolyte was injected into the case through a liquid injection port formed in the lid of the case. Finally, the case was sealed by sealing the liquid injection port of the case.

(Examples 2 to 5)
A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the configuration was changed to that shown in Table 1.

(Comparative Examples 1 to 4)
A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the configuration was changed to that shown in Table 1.

<Evaluation of metal deposition during high-rate charging>
The magnitude of the current (current value) that can fully charge each battery to its rated capacity in one hour was defined as 1C. After defining the current value in this way, constant current charging is performed at a current value of 3C to the upper limit voltage (4.32V in this example), and at a current value of 1/3C to the lower limit voltage (2.4V in this example). ) A charge/discharge test was conducted for 10 cycles with constant current discharge. Thereafter, the battery was disassembled and the presence or absence of metal (Li) precipitation on the surface of the negative electrode was confirmed.

Table 1 shows the results of the above evaluation for the lithium ion secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 4.

As can be seen from Table 1, in the electricity storage elements of Examples, metal precipitation at the negative electrode was suppressed during high rate charging. On the other hand, in the electricity storage element of the comparative example, metal precipitation occurred on the negative electrode during high-rate charging.

1: Energy storage element (non-aqueous electrolyte secondary battery),
2: electrode body,
3: Case, 31: Case body, 32: Lid body,
4: Positive terminal, 5: Negative terminal,
40: positive electrode,
41: Current collecting base material of positive electrode (positive electrode base material), 42: Positive electrode active material layer, 412: Tab portion of positive electrode,
50: negative electrode,
51: negative electrode current collecting base material (negative electrode base material), 511: main body part, 512: tab part (negative electrode tab part),
52: negative electrode active material layer,
60: separator,
10: Power storage unit, 100: Power storage device.

Claims (2)

A positive electrode having a positive electrode active material layer, and a negative electrode having a negative electrode active material layer facing the positive electrode active material layer,
The negative electrode has a sheet-like current collecting base material and the negative electrode active material layer overlapping at least one surface of the current collecting base material,
The current collecting base material has a main body portion and a tab portion protruding outward from the main body portion,
The negative electrode active material layer crosses the boundary between the main body part and the tab part and overlaps a part of the tab part, and the following conditions are met:
(1) The mass per unit area of the negative electrode active material layer is larger in the tab portion than in the main body portion; and
(2) the thickness of the negative electrode active material layer is thicker in the tab portion than in the main body portion;
A power storage element that satisfies at least one of the following. The ratio (B/A) of the cross-sectional area (A) at the tab portion of the current collecting base material to the surface area (B) of the positive electrode active material layer is:
The energy storage element according to claim 1, wherein the energy storage element is 30,000 or more and 150,000 or less.