JP2021163583A - Power storage element - Google Patents

Abstract

To provide a power storage element capable of suppressing occurrence of metal precipitation on a negative electrode during charging at a high rate.SOLUTION: A power storage element 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. The negative electrode has a sheet-shaped current collecting base material 51, and the negative electrode active material layer overlapped with at least one surface of the current collecting base material. The current collecting base material has a main body portion 511, and a tab portion 512 protruding outward from the main body portion. The negative electrode active material layer extends beyond the boundary between the main body portion and the tab portion to overlap a part of the tab portion, and satisfies at least one of the following conditions: (1) the mass of the negative electrode active material layer per unit area is larger at the tab portion than at the main body portion; and (2) the thickness of the negative electrode active material layer is thicker at the tab portion than at the main body portion.SELECTED DRAWING: Figure 3

Description

The present invention relates to a power storage element.

Patent Document 1 describes an electrode set in which a positive electrode and a negative electrode have an insulated layered structure, and the positive electrode and the negative electrode are electrically connected to electrode terminals in a laminated state with a plurality of positive electrode tabs and negative electrode tabs, respectively. It is a power storage device equipped with a three-dimensional structure.
The negative electrode is formed by applying a first active material and a second active material having a larger capacity per mass than the first active material to form a negative electrode active material layer. At least the capacity per area of the negative electrode active material layer in the tab side edge region in the protruding direction of the negative electrode tab is larger than the capacity per area of the negative electrode active material layer in the central region in the protruding direction of the negative electrode tab. A power storage device, characterized in that the mixing ratio of the first active material and the second active material is adjusted and applied so as to be large, is described.

Japanese Unexamined Patent Publication No. 2016-12541

An object of the present invention is to provide a power storage element capable of suppressing metal precipitation at a negative electrode during charging at a high rate.

The power storage element according to one aspect of the present invention is
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 are provided.
The negative electrode has a sheet-shaped current collecting base material and the negative electrode active material layer overlapped with 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 extends beyond the boundary between the main body portion and the tab portion and also overlaps a part of the tab portion, and the following conditions:
(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;
(2) The thickness of the negative electrode active material layer is thicker in the tab portion than in the main body portion;
Satisfy at least one of the above.

The power storage element according to one aspect of the present invention is prevented from causing metal precipitation at the negative electrode during charging at a high rate.

FIG. 1 is a perspective view of a power storage element according to the present embodiment. FIG. 2 is a perspective view of a wound electrode body of the power storage element according to the present embodiment. FIG. 3 is a cross-sectional view of the laminated negative electrode (tab portion of the current collecting base material) and the positive electrode cut in the thickness direction. FIG. 4 is a schematic view 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 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 is
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 are provided.
The negative electrode 50 has a sheet-shaped current collecting base material 51 and the negative electrode active material layer 52 that overlaps at least one surface of the current collecting base material 51.
The current collecting base material 51 has a main body portion 511 and a tab portion 512 protruding outward from the main body portion 511.
The negative electrode active material layer 52 extends beyond the boundary between the main body portion 511 and the tab portion 512 and also overlaps a part of the tab portion 512, and 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;
(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;
Satisfy at least one of the above.

According to the power storage element 1, the precipitation of metal on the negative electrode is suppressed during charging at a high rate. The reason why such an effect occurs is presumed as follows, for example.
That is, in the above-mentioned power storage element 1, the current tends to concentrate at the tab portion 512 of the negative electrode 50 during charging. In the negative electrode active material layer 52 that overlaps the tab portion 512, metal precipitation is likely to occur due to the influence of current concentration. On the other hand, in the case of (1), the mass of the negative electrode active material layer 52 in the tab portion 512 of the negative electrode 50 is larger than that of the main body portion 511, so that the amount of the negative electrode active material per unit area is the tab portion 512. Is getting bigger. 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 prevent metal ions that have not been incorporated into the negative electrode active material from becoming metal and precipitating at the negative electrode. Further, 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 of the main body portion 511, the amount of the negative electrode active material per unit area becomes larger in the tab portion 512. There is. Therefore, similarly, it is possible to suppress the occurrence of metal precipitation on the negative electrode. This suppression is particularly effective when charging at a high rate. However, it is not limited to the above reasons.
The high rate is, for example, a charging speed of 2C or more (when the magnitude of the current for fully charging the rated capacity of the battery in 1 hour is defined as 1C).

Here, the ratio (B / A) of the cross-sectional area (A) of 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. It may be as follows.
As a result, it is possible to further suppress the occurrence of metal precipitation on the negative electrode during charging at a high rate.

As an example of the power storage element according to the embodiment of the present invention, the configuration of the non-aqueous electrolyte power storage element, the configuration of the non-aqueous electrolyte power storage device, the method for manufacturing the non-water electrolyte power storage element, 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 (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 container for accommodating the non-aqueous electrolyte. The electrode body 2 is usually wound in a laminated type in which a plurality of positive electrodes 40 and a plurality of negative electrodes 50 are laminated via a separator 60, or in a state in which a positive electrode 40 and a negative electrode 50 are laminated via a separator 60. It is a winding type (described in detail below). 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 and 2, 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.
The power storage element 1 of the present embodiment includes an electrode body 2 housed in a case 3. The case 3 has a flat rectangular parallelepiped shape, and has a case main body 31 that opens toward one side and a long and thin rectangular lid 32 that covers the opening of the case main body 31. The two external terminals 4 and 5 are arranged apart from each other in the long side direction of the lid 32.

As shown in FIGS. 2 and 3, 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 the electrode body 2. Is formed. 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 opening direction of the case body 31.

The electrode body 2 has a plurality of positive electrode tab portions 412 in which one long side in the width direction of the strip-shaped positive electrode 40 protrudes. The tab portions 412 of the plurality of positive electrodes are formed of a part of the positive electrode base material 41 (current collecting base material 41). Similarly, the electrode body 2 has a plurality of tab portions 512 (tab portions 512 of the negative electrode) in which one long side in the width direction of the strip-shaped negative electrode 50 protrudes. The plurality of tab portions 512 (negative electrode tab portions 512) are composed of a part of the negative electrode base material 51 (current collector base material 51).
The tab portions 412 of the plurality of positive electrodes of the positive electrode 40 are arranged side by side in the direction in which the positive electrode 40 and the negative electrode 50 are laminated. The same applies to the plurality of tab portions 512 of the negative electrode 50 (tab portions 512 of the negative electrode). Further, the tab portions 412 of the plurality of positive electrodes of the positive electrode 40 and the plurality of tab portions 512 (tab portions 512 of the negative electrode) of the negative electrode 50 are the lids of the case 3 as well as the two external terminals 4 and 5 which are separated from each other. They are arranged apart from each other in the long side direction of 32.

(Positive electrode)
The positive electrode 40 has a positive electrode base material 41 (a positive electrode current collecting 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, as shown in FIG. 3, the positive electrode active material layer 42 is laminated on both sides of the positive electrode base material 41 (the positive electrode current collecting base material 41).
The positive electrode base material 41 (current collecting base material 41 of the positive electrode) has a main body portion of the positive electrode and a tab portion 412 of the positive electrode protruding outward from the main body portion of the positive electrode. 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 (current collecting base material 41 of the positive electrode) is exposed.
The edge of the positive electrode active material layer 42 is arranged inside the edge of the negative electrode active material layer 52 facing each other via the separator 60.
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 collecting 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 (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, 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, 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 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 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 composite 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 the laser diffraction / scattering method for 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, polyacrylics, and polyimides; ethylene-propylene-diene rubber (EPDM), sulfone. Elastomers such as chemicalized EPDM, styrene-butadiene rubber (SBR), fluororubber; and thermoplastic polymers can be mentioned. 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.

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. When a thickener is used, 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 technique disclosed herein can be preferably carried out in a manner in which the positive electrode active material layer 42 does not contain the thickener.

The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, inorganic oxides such as aluminosilicate, magnesium hydroxide, calcium hydroxide, and hydroxide. Hydroxides such as aluminum, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, Mineral resource-derived substances such as apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, and mica, or man-made products thereof and the like can be mentioned. When a filler is used, 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 technique disclosed herein can be preferably carried out in a manner in which the positive electrode active material layer 42 does not contain the above filler.

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 (a negative electrode current collecting 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, as shown in FIG. 3, the negative electrode active material layer 52 is laminated on both sides of the negative electrode base material 51 (the negative electrode current collecting base material 51).
The negative electrode base material 51 (negative electrode current collecting base material 51) has a main body portion 511 and a tab portion 512 (negative electrode tab portion 512) protruding outward from the main body portion 511. As shown in FIG. 4, for example, the negative electrode active material layer 52 overlaps the entire main body portion 511, and also overlaps a part of the tab portion 512 beyond the boundary between the main body portion 511 and the tab portion 512. The negative electrode base material 51 (negative electrode current collecting base material 51) is exposed in most of the tab portion 512.
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.

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 above-mentioned power storage element 1, the current tends to concentrate at the tab portion 512 of the negative electrode 50 during charging. In the negative electrode active material layer 52 that overlaps the tab portion 512, metal precipitation is likely to occur due to the influence of current concentration. On the other hand, in the case of (1), the mass of the negative electrode active material layer 52 in the tab portion 512 of the negative electrode 50 is larger than that of the main body portion 511, so that the amount of the negative electrode active material per unit area is the tab portion 512. Is getting bigger. 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 prevent metal ions that have not been incorporated into the negative electrode active material from becoming metal and precipitating at the negative electrode. Further, 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 of the main body portion 511, the amount of the negative electrode active material per unit area becomes larger in the tab portion 512. There is. Therefore, similarly, it is possible to suppress the occurrence of metal precipitation on the negative electrode. This suppression is particularly effective when charging at a high rate.

When the above condition (1) is satisfied, the mass (grain amount) W2 of the negative electrode active material layer 52 overlapping the main body portion 511 per unit area is the mass per unit area of the negative electrode active material layer 52 overlapping the tab portion 512. It may be smaller than W1 (that is, W1> W2), and is not particularly limited. In W2, when the negative electrode active material layers 52 are formed on both sides of the negative electrode base material 51, 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 preferably 0.1 g / 100 cm ^{2 or more per 100 cm 2 of} an area, and is 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, and further preferably 0.48 g / 100 cm ² or more. In some embodiments, W2 may be 0.50 g / 100 cm ² or greater and 0.52 g / 100 cm ² or greater. 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, still 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. The value of W2 represents the mass of the negative electrode active material layer 52 that overlaps the entire main body portion 511 as ^{the mass per 100 cm 2 of the area.} The area of the negative electrode active material layer 52 that overlaps the entire main body 511 has a predetermined size, but is arbitrary, and ^{the unit "g / 100 cm 2} " is the area of the negative electrode active material layer 52 that overlaps the entire main body 511. Has 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 should be larger than the mass W2 per unit area of the negative electrode active material layer 52 overlapping the main body portion 511. It suffices, and is not particularly limited. In W1, when the negative electrode active material layer 52 is formed on both sides of the negative electrode base material 51, 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). Value).
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 represented by the following formula (I). Meet.
1.0 <W1 / W2 ≦ 1.2 Equation (I)
By satisfying the above formula (I), it is possible to more reliably suppress the occurrence of metal precipitation on the negative electrode during charging at a high rate. The techniques disclosed herein include, for example, the relationship between W1 and W2.
1.005 ≤ W1 / W2 ≤ 1.150 Equation (II),
Furthermore, 1.008 ≦ W1 / W2 ≦ 1.100 equation (III),
In particular, it can be carried out in the embodiment of 1.010 ≦ W1 / W2 ≦ 1.050 equation (IV).
W1 is obtained by dividing the mass of the negative electrode active material layer 52 that overlaps the area of the portion where the negative electrode active material layer 52 overlaps the part of the tab portion 512. 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 (negative electrode active material layers 52 on both sides of the negative electrode base material 51). Is formed, the total value of the average thickness of each layer) 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, the mixture composition is applied more in the tab portion 512 while the main body portion. It is better to apply less in 511. In this way, the negative electrode active material layer 52 satisfying the above-mentioned relationship of W2 <W1 can be easily formed by using the same mixture composition. In this case, the mass of the negative electrode active material per unit volume may be the same in the entire negative electrode active material layer 52. Further, the mass of the negative electrode active material layer per unit volume may be the same in the entire negative electrode active material layer 52.

When the above condition (1) is satisfied, in another preferable aspect, 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 substantially the same. .. For example, even if the thickness of the negative electrode active material layer 52 is the same as a whole, the unit of the negative electrode active material layer 52 is that 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 mass per area may be larger in the tab portion 512 than in the main body portion 511. In such an 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, the content of the negative electrode active material is larger. While the agent composition is applied to the tab portion 512, it is preferable to apply the mixture composition having a lower content of the negative electrode active material to the main body portion 511 so as to have the same thickness as 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 part of the negative electrode active material layer 52 may be thicker than that of the main body portion 511. For example, as shown in FIG. 5, the thickness gradually decreases toward the tip of the tab portion 512. May be good. 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 may be thinner than the average thickness T1 of the negative electrode active material layer 52 overlapping the tab portion 512 ( That is, T2 <T1), and is not particularly limited. T2 is the total value of the average thickness of each layer when the negative electrode active material layer 52 is formed on both surfaces of the negative electrode base material 51. It is appropriate that T2 (total value of average thickness) is, for example, 50 μm or more, usually 70 μm or more, and typically 80 μm or more. T2 is preferably 90 μm or more, more preferably 100 μm or more, still more preferably 110 μm or more. In some embodiments, T2 may be 115 μm or greater and 120 μm or greater. Further, T2 can be, for example, 250 μm or less. T2 is preferably 200 μm or less, more preferably 180 μm or less, still 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 may be thicker than the average thickness T2 of the negative electrode active material layer 52 overlapping the main body portion 511. There is no particular limitation. T1 is the total value of the average thickness of each layer when the negative electrode active material layer 52 is formed on both surfaces of the negative electrode base material 51. 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 (ie, T1-T2) is. For example, it is 0.05 μm or more, and typically 0.1 μm or more. Further, T1-T2 may be, for example, 20 μm or less (typically 10 μm or less), or may be, for example, 5 μm or less.
The average thickness is calculated by averaging the measured values of at least five randomly selected thicknesses. The average thickness T2 of the negative electrode active material layer 52 overlapping the main body portion 511 is obtained by measuring the thickness of the negative electrode active material layer 52 overlapping the central portion of the main body portion 511. On the other hand, the average thickness T1 of the negative electrode active material layer 52 overlapping the tab portion 512 measures 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. However, it is obtained by averaging a plurality of measured values. In other words, the measurement site of the average thickness T1 is the central site of the region where the negative electrode active material layer 52 overlaps in the tab portion 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, the mixture composition is applied more in the tab portion 512. On the other hand, it is better to apply less on the main body 511. In this case, the mass of the negative electrode active material per unit volume may be the same in the entire negative electrode active material layer 52. Further, the mass per unit volume may be the same in the entire negative electrode active material layer 52.

In the power storage element 1 of the present embodiment, the ratio (B / A) of the cross-sectional area (A) of 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. It may be 000 or more and 150,000 or less.
Specifically, the surface area (B) of the positive electrode active material layer 42 that causes a charge / discharge reaction between the negative electrode active material layer 52 that overlaps the main body portion 511 and the tab portion 512, and the negative electrode through which the current associated with the charge / discharge reaction passes. Even if the ratio (B / A) of the 50 current collecting base materials 51 to the cross-sectional area (A) at the tab portion 512 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 the occurrence of metal precipitation on the negative electrode during charging at a high rate.

The cross-sectional area of the tab portion 512 is the cross-sectional area of a 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 the current collecting clips as the current collecting member, as shown in FIG. 5, the cross-sectional area of the portion (indicated by Z) where the tab portion 512 is sandwiched by the current collecting clip is adopted. do.
Further, when one current collecting base material 51 has a plurality of tab portions 512 as in the power storage element 1 of the present embodiment, the cross-sectional area (A) of the tab portions 512 is the total cross-sectional area of each tab portion 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 generates an electric current passing through each of the target tab portions 512. In this case, the average cross-sectional area of each tab portion 512 (that is, the value obtained by dividing the total area of the 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. It may also be 006Cm ² or less, preferably 0.004 cm ² or more 0.005 cm ² or less. The surface area of the positive electrode active material layer 42 per 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 less than or equal to, preferably 120 cm ² or more and 700 cm ² or less.
When the electrode body is the so-called laminated type described above, the above ratio (B / A) is calculated for each positive electrode and each negative electrode facing each other via the separator. At least one set of positive electrode and negative electrode facing each other via the separator may satisfy the numerical range of the above ratio (B / A). Preferably, the above numerical range of ratio (B / A) is satisfied for all positive and negative electrodes.

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. When a binder is used, it is preferable to use an aqueous binder such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, and 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, 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, 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 a conductive agent is used, 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 here can be preferably carried out in a manner in which the negative electrode active material layer 52 does not contain the above-mentioned conductive agent. When a filler is used, 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 carried out in a manner in which the negative electrode active material layer 52 does not contain the above filler.

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. As the negative electrode active material, e.g., metal Li; Si, metal or metalloid, such as Sn; Si oxide, Ti oxide, a metal oxide such as Sn oxide or semi-metal _oxide; Li ₄ Ti 5 _O1 2, Titanium-containing oxides such as LiTIO ₂ and TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite (graphite) and non-graphitable carbon (easy graphitable carbon or non-graphitizable carbon) can be mentioned. Be done. Among these materials, graphite and non-graphitic carbon are preferable. 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.

_{“Graphite” refers to a carbon 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” refers to a carbon 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. 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" means 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 carbon material as the negative electrode active material is used as the working electrode and the metal Li is used as the counter electrode. .. 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 carbon material with respect to the redox potential of Li. be. 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 carbon material that is the negative electrode active material during charging and discharging. ..

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

The “graphitizable carbon” _{refers to a carbon material having d 002} of 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 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 52 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. 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, 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 having a heat-resistant layer containing heat-resistant particles and a binder formed on one surface or both surfaces of the base material layer can be used. Examples of the material of the base material layer of the separator 60 include a woven fabric, a non-woven fabric, and a porous resin film. Among these materials, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. 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 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 of the above is 5% or less. Inorganic compounds can be mentioned as materials whose mass reduction 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.

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, polymethylmethacrylate, polyvinylacetate, polyvinylpyrrolidone, polyvinylidene fluoride and the like. The use of polymer gel has the effect of suppressing liquid leakage. As the separator 60, a polymer gel may be used in combination with the above-mentioned porous resin film, non-woven fabric, or the like.

(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), vinyl ethylene 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. Of these, EC 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, 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 oxalate esters such as lithium bis (oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis (oxalate) difluorophosphate (LiFOP); biphenyl, alkylbiphenyl, terphenyl, etc. Partially hydride of terphenyl, aromatic compounds such as cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; said aromatics such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene 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, anhydrous Maleic acid, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sulton, propensulton, butane sulton, methyl methanesulfonate, busulfane, methyl toluenesulfonate, Dimethyl sulphate, ethylene sulphate, 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, thioanisol, diphenyldisulfide, dipyridinium disulfide, perfluorooctane, tritrimethylsilyl borate, tritrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, mono Examples thereof include lithium fluorophosphate. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolytic solution is preferably 0.01% by mass or more and 10% by mass or less, and is 0.1% by mass or more and 7% by mass or less with respect to the total mass of the non-aqueous electrolytic 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.

As the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material having ionic conductivity such as lithium, sodium and calcium and being 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 lithium ion secondary battery include Li _{2 SP 2} S ₅ , Li I-Li _{2 SP 2} S ₅ , Li ₁₀ Ge-P ₂ S ₁₂ , and the like as the sulfide solid electrolyte. ..

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 the 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 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.
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. 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.

<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 an 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 via the separator 60.

Containing the non-aqueous electrolyte in a container 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 container, 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.

In the above embodiment, the electrode body in which the positive electrode 40 and the negative electrode 50 are laminated via the separator 60 has been described, but the electrode body may not include the separator 60. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state where a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

In the above embodiment, the so-called winding type electrode body has been described in detail, but the electrode body may 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 described in more detail with reference to Examples. The present 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. Each of the positive electrode and the negative electrode has a sheet-shaped current collecting base material and an active material layer overlapped on 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)
The above raw materials were mixed and kneaded to prepare a mixture composition for a positive electrode. The prepared mixture composition for positive electrodes is collected from aluminum foil (a collection of positive electrodes having a thickness of 12 μm) so that the mass (grain amount) per unit area of the positive electrode active material layer after drying is 1.7 g / 100 cm ^2. It was applied to both sides of the electrical substrate). After drying by heating, a roll press was performed. Then, it was vacuum dried to remove moisture and the like. The thickness of the active material layer (for 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: Hydroactive material: Particle-like amorphous carbon (non-graphitized carbon) (97.4 parts by mass)
Binder: SBR (2.0 parts by mass)
Thickener: CMC (0.6 parts by mass)
The above raw materials were mixed and kneaded to prepare a mixture composition for a negative electrode. The prepared mixture composition for the negative electrode was applied to both sides of a copper foil (a current collecting base material for a negative electrode having a thickness of 8 μm). The coating was applied so that the mass (weight of basis weight, one layer) of the negative electrode active material layer overlapping the main body of the copper foil was 0.539 g / 100 cm ^2. After drying by heating, a roll press was performed. Then, it was vacuum dried to remove moisture and the like. The thickness of the active material layer after pressing was 61 μm (for one layer), that is, 122 μm (for 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 portion (central portion) and a tab portion protruding outward from the main body portion. The negative electrode active material layer extends beyond the boundary between the main body portion and the tab portion and also overlaps a part of 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 the production of the negative electrode, by applying the mixture composition more in the tab portion, the mass per unit area of the negative electrode active material layer overlapping the tab portion is increased, and the negative electrode active material layer overlapping the tab portion is increased. The average thickness of was increased.

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

(4) Preparation of non-aqueous electrolytic solution As the non-aqueous electrolytic solution, one prepared by the following method was used. As the non-aqueous solvent, a solvent obtained by mixing 1 part by volume of propylene carbonate 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 solution was prepared.

(5) Arrangement of Electrode Body in Case Using the above positive electrode, the above negative electrode, the above non-aqueous electrolyte solution, the separator, and the case, a lithium ion secondary battery was assembled by a general method.
First, a sheet-like material formed by arranging and laminating a separator between the positive electrode and the negative electrode was wound around. Next, the wound electrode body was placed in the case body of the aluminum square battery case as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to each of the two external terminals. Furthermore, a lid was attached to the case body. The above non-aqueous electrolytic solution was injected into the case through a liquid injection port formed on the lid of the case. Finally, the case was sealed by sealing the 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 precipitation during high-rate charging>
The magnitude (current value) of the current that can be fully charged to the rated capacity of each battery in one hour is defined as 1C. After defining the current value in this way, the current value of 3C is used for constant current charging up to the upper limit voltage (4.32V in this example), and the current value of 1 / 3C is the lower limit voltage (2.4V in this example). ) Was carried out for 10 cycles in a charge / discharge test in which a constant current was discharged. Then, 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 of 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 power storage element of the example, the precipitation of metal on the negative electrode was suppressed during charging at a high rate. On the other hand, in the power storage element of the comparative example, metal precipitation occurred at the negative electrode when charging at a high rate.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
3: Case, 31: Case body, 32: Cover body,
4: Positive electrode terminal, 5: Negative electrode terminal,
40: Positive electrode,
41: Positive electrode current collecting base material (positive electrode base material), 42: Positive electrode active material layer, 412: Positive electrode tab portion,
50: Negative electrode,
51: Current collecting base material of negative electrode (negative electrode base material), 511: Main body part, 512: Tab part (tab part of negative electrode),
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 are provided.
The negative electrode has a sheet-shaped current collecting base material and the negative electrode active material layer overlapped with 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 extends beyond the boundary between the main body portion and the tab portion and also overlaps a part of the tab portion, and the following conditions:
(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;
(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 above. The ratio (B / A) of the cross-sectional area (A) of the current collecting base material at the tab portion to the surface area (B) of the positive electrode active material layer is
The power storage element according to claim 1, wherein the power storage element is 30,000 or more and 150,000 or less.

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