Multilayer lithium-ion secondary battery

Abstract

In this multilayer lithium-ion secondary battery, a positive electrode includes a positive electrode current collector, a positive electrode active material layer, an exposed portion (a) in which the positive electrode active material layer is not laminated on one end of the positive electrode current collector, and an insulating layer between the positive electrode active material layer and the exposed portion (a). A negative electrode includes a negative electrode current collector, a negative electrode active material layer, and an exposed portion (b) in which the negative electrode active material layer is not laminated on one end of the negative electrode current collector, the negative electrode active material included in the negative electrode active material layer including a silicon-based active material. When the lamination direction of the negative electrode, a separator, and the positive electrode is defined as a z-direction, the direction from the center of the positive electrode collector (101) toward the center of the exposed part (a), which is perpendicular to the z-direction, is defined as the x-direction, the length of the negative electrode active material layer in the x-direction is defined as X1, and the length of the positive electrode active material layer is defined as Y1, the ratio of X1 to Y1 (X1 / Y1) is greater than 1.000 and 1.200 or less, the center (c) of the negative electrode active material layer and the center (d) of the positive electrode active material layer do not overlap in the x-direction, and the center (d) is positioned closer to the exposed part (a) than the center (c).

Description

Stacked lithium-ion secondary battery

[0001] This invention relates to a stacked lithium-ion secondary battery.

[0002] Carbon-based and silicon-based active materials are known as negative electrode active materials for lithium-ion secondary batteries. Silicon-based active materials are attracting attention because they can produce lithium-ion secondary batteries with higher capacity compared to those using carbon-based active materials. An example of a lithium-ion secondary battery technology using silicon-based active materials as the negative electrode active material is the one described in Patent Document 1.

[0003] Patent Document 1 describes a negative electrode that can simultaneously improve lifespan characteristics and output characteristics, comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises a silicon-based active material, a first conductive material containing graphite, a second conductive material containing single-walled carbon nanotubes, and a binder, the binder comprising a cellulose-based compound and a rubber-based compound, the first conductive material being contained in the negative electrode active material layer in an amount of 15% to 25% by weight, the second conductive material being contained in the negative electrode active material layer in an amount of 0.15% to 2.5% by weight, and the second conductive material and the binder being contained in the negative electrode active material layer in a weight ratio of 1.5:99.5 to 20.0:80.0.

[0004] Special Publication No. 2024-503357

[0005] According to the inventors' research, in stacked lithium-ion secondary batteries that use silicon-based active material for the negative electrode to increase capacity, the silicon-based active material expands during battery charging, causing the entire negative electrode active material layer to stretch. As a result, the negative electrode active material layer may come into contact with the exposed portion of the positive electrode current collector.

[0006] The present invention provides a stacked lithium-ion secondary battery that has high capacity and can suppress contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer.

[0007] The inventors of the present invention have intensively studied to achieve the above problems. As a result, by devising the arrangement of the positive electrode active material layer and the negative electrode active material layer, it has been found that the contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer can be suppressed while using a silicon-based active material for the negative electrode active material.

[0008] [1] A laminated lithium ion secondary battery in which a positive electrode and a negative electrode are alternately laminated via a separator, wherein the positive electrode includes a positive electrode current collector, a positive electrode active material layer laminated on at least one surface of the positive electrode current collector, an exposed portion a at one end of the positive electrode current collector where the positive electrode active material layer is not laminated, and an insulating layer positioned between the positive electrode active material layer and the exposed portion a; the negative electrode includes a negative electrode current collector, a negative electrode active material layer laminated on at least one surface of the negative electrode current collector, and an exposed portion b at one end of the negative electrode current collector where the negative electrode active material layer is not laminated; the negative electrode active material included in the negative electrode active material layer includes a silicon-based active material; the lamination direction of the negative electrode, the separator, and the positive electrode is defined as the z direction, a direction perpendicular to the z direction and from the center of the positive electrode current collector toward the center of the exposed portion a is defined as the x direction; when the length of the negative electrode active material layer in the x direction is X １ and the length of the positive electrode active material layer is Y １ , the ratio (X １ / Y １ ) of X １ to Y １ is more than 1.000 and less than or equal to 1.200; in the x direction, the center c of the negative electrode active material layer and the center d of the positive electrode active material layer do not overlap, and the center d is positioned closer to the exposed portion a side than the center c. A laminated lithium ion secondary battery. [2] The laminated lithium ion secondary battery according to [1], wherein in the x direction, the center e of the separator is positioned between the center c and the center d. [3] When the distance between the center e and the center c in the x direction is X ２ , the ratio (X １ / X ２ ) of X ２ to X １[2] The stacked lithium-ion secondary battery, wherein the ratio is 0.0001 or more and 0.0100 or less. [4] In the x direction, the distance between the center e and the center d is Y ２ In that case, Y １ Y ２ The ratio (Y ２ / Y １ A stacked lithium-ion secondary battery according to [2] or [3], wherein the ratio is 0.0001 or more and 0.0100 or less. [5] In the x direction, the distance between the center c and the center d is Y ３ In that case, Y １ Y ３ The ratio (Y ３ / Y １ A stacked lithium-ion secondary battery according to any one of [1] to [4], wherein the x-axis is 0.0002 or more and 0.0200 or less. [6] In the x-direction, when the length of the separator is Z, the x-axis relative to Z １ The ratio (X １ A stacked lithium-ion secondary battery according to any one of [1] to [5], wherein / Z) is 0.900 or more and less than 1.000. [7] In the x direction, the sum of the length of the insulating layer and the length of the positive electrode active material layer is Y ４ In that case, Y ４ The X １ The ratio (X １ / Y ４ A stacked lithium-ion secondary battery according to any one of [1] to [6], wherein the ratio is 0.900 or more and less than 1.000. [8] In the x direction, the sum of the length of the insulating layer and the length of the positive electrode active material layer is Y ４ Let X be the length of the negative electrode active material layer in the fully charged state. ３ In that case, Y ４ The X ３ The ratio (X ３ / Y ４A stacked lithium-ion secondary battery according to any one of [1] to [7], wherein the ratio is 0.910 or more and less than 1.020. [9] A stacked lithium-ion secondary battery according to any one of [1] to [8], wherein in the x direction, the end of the negative electrode active material layer on the exposed portion a side in the fully charged state is located on the exposed portion b side of the boundary between the insulating layer and the exposed portion a.

[10] The silicon-based active material is SiO ｘ A stacked lithium-ion secondary battery according to any one of [1] to [9], comprising one or more selected from the group consisting of (0 < x ≤ 2), Si / C including Si-C composite particles containing silicon and carbon materials, and Si.

[0009] According to the present invention, it is possible to provide a stacked lithium-ion secondary battery that has high capacity and can suppress contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer.

[0010] This is a schematic cross-sectional view illustrating an example of a stacked lithium-ion secondary battery according to this embodiment. This is a schematic cross-sectional view illustrating an example of a stacked lithium-ion secondary battery according to this embodiment. This is an enlarged view of the central part A of Figure 2, illustrating a schematic cross-sectional view illustrating an example of the positional relationship between the positive electrode active material layer, separator, and negative electrode active material layer of the stacked lithium-ion secondary battery according to this embodiment. This is a schematic cross-sectional view illustrating an example of a stacked lithium-ion secondary battery according to this embodiment in a fully charged state. This is a schematic cross-sectional view illustrating the case in which the exposed portion of the positive electrode current collector and the negative electrode active material layer are in contact in a fully charged state.

[0011] Embodiments of the present invention will be described below with reference to the drawings. In all drawings, similar components are denoted by the same reference numerals, and their descriptions are omitted as appropriate. Also, the drawings are schematic diagrams and do not necessarily correspond to the actual dimensional ratios. In the specification, unless otherwise specified, the notation "A to B" regarding numerical ranges means A or more and B or less. For example, 1 to 5% means 1% or more and 5% or less.

[0012] <Stacked Lithium-Ion Secondary Battery> The stacked lithium-ion secondary battery of this embodiment will be described with reference to the figures. Figures 1 and 2 are schematic cross-sectional views illustrating an example of the stacked lithium-ion secondary battery of this embodiment, and Figure 3 is an enlarged view of the central part A of Figure 2, and is a schematic cross-sectional view illustrating an example of the positional relationship between the positive electrode active material layer, separator, and negative electrode active material layer of the stacked lithium-ion secondary battery of this embodiment.

[0013] The stacked lithium-ion secondary battery (500) of this embodiment has a positive electrode (100) and a negative electrode (300) alternately stacked with a separator (201) in between. The positive electrode (100) includes a positive electrode current collector (101), a positive electrode active material layer (105) stacked on at least one surface of the positive electrode current collector (101), an exposed portion a at one end of the positive electrode current collector (101) where the positive electrode active material layer (105) is not stacked, and an insulating layer (103) between the positive electrode active material layer (105) and the exposed portion a. The negative electrode (300) includes a negative electrode current collector (303) and a negative electrode current collector. The negative electrode active material layer (301) is laminated on at least one surface of (303), and the negative electrode current collector (303) has an exposed portion b at one end where the negative electrode active material layer (301) is not laminated, wherein the negative electrode active material contained in the negative electrode active material layer (301) includes a silicon-based active material, the lamination direction of the negative electrode (300), separator (201), and positive electrode (100) is the z direction, the direction perpendicular to the z direction and moving from the center of the positive electrode current collector (101) toward the center of the exposed portion a is the x direction, and the length of the negative electrode active material layer (301) in the x direction is X １ Let Y be the length of the positive electrode active material layer (105). １ In that case, Y １ The X １ The ratio (X １ / Y １ The value is greater than 1.000 and less than or equal to 1.200, and in the x-direction, the center c of the negative electrode active material layer (301) and the center d of the positive electrode active material layer (105) do not overlap, and the center d is located closer to the exposed portion a than the center c.

[0014] According to the inventors' research, when a silicon-based active material is used as the negative electrode active material, it has become clear that during charging or when the lithium-ion secondary battery is fully charged, the end of the negative electrode active material layer opposite to the exposed portion reaches the exposed portion of the positive electrode current collector, making short circuits due to contact likely. This is thought to be because silicon-based active materials undergo large volume changes with charging and discharging, and during charging, the negative electrode active material layer expands significantly in the planar direction, causing it to protrude beyond the design dimensions towards the exposed portion of the positive electrode current collector, making contact more likely. The inventors diligently conducted research to solve the above problem. As a result, X １ / Y １ We have discovered for the first time that, by satisfying a predetermined range and by positioning the center d of the positive electrode active material layer on the exposed part a side of the negative electrode active material layer than the center c of the negative electrode active material layer in the x direction, it is possible to suppress contact between the exposed part of the positive electrode current collector and the negative electrode active material layer, even when using a silicon-based active material for the negative electrode active material. The reason for this is thought to be as follows. First, X １ / Y １ The lower limit of X contributes to ensuring battery safety. Specifically, X １ / Y １ The lower limit of X functions to ensure the basic safety of the battery by making the negative electrode active material layer larger than the positive electrode active material layer, thereby reliably receiving lithium ions released from the positive electrode during charging on the negative electrode side and suppressing the deposition of metallic lithium. On the other hand, X １ / Y １ The relationship between the upper limit and the center position contributes to solving the above problem. In detail, first X １ / Y １By setting an upper limit, it is possible to suppress contact between the negative electrode active material layer and the exposed portion of the positive electrode current collector when the negative electrode active material layer expands. Furthermore, since it is possible to suppress the increase in the size of the electrode body, such as when it is laminated via a positive electrode and negative electrode separator, the capacity density per unit size of the battery is hardly impaired. In addition, by aligning the center d towards the exposed portion a, the end of the negative electrode active material layer can be separated from the exposed portion of the positive electrode current collector, and as a result, contact with the exposed portion of the positive electrode current collector can be further suppressed. Thus, even if the negative electrode active material layer stretches due to the expansion of the silicon-based active material, it is possible to suppress it from reaching the exposed portion of the positive electrode current collector, and thus it is thought that contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer can be suppressed.

[0015] The aforementioned X １ / Y １ From the viewpoint of suppressing lithium deposition on the surface of the negative electrode active material layer during charging and further improving the cycle characteristics of the stacked lithium-ion secondary battery, and from the viewpoint of suppressing contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer, the ratio is greater than 1.000, preferably 1.001 or more, more preferably 1.002 or more, even more preferably 1.003 or more, even more preferably 1.004 or more, and 1.200 or less, preferably 1.150 or less, more preferably 1.100 or less, even more preferably 1.050 or less, even more preferably 1.020 or less, and even more preferably 1.010 or less. １ / Y １ For similar reasons, the value of X is greater than 1.000 and less than or equal to 1.200, preferably greater than 1.000 and less than or equal to 1.150, more preferably 1.001 to 1.100, even more preferably 1.002 to 1.050, even more preferably 1.003 to 1.020, and even more preferably 1.004 to 1.010. １ / Y １ As long as the above range is satisfied and the centers c and d satisfy the above positional relationship, contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer can be suppressed even when a silicon-based active material is used for the negative electrode active material.

[0016] Figure 5 is a schematic cross-sectional view illustrating the case in which the exposed portion of the positive electrode current collector and the negative electrode active material layer come into contact when the battery is fully charged. If the positional relationship between the positive electrode active material layer (105), the insulating layer (103), and the negative electrode active material layer (308), as well as the lengths of the positive electrode active material layer (105) and the negative electrode active material layer (308), are not designed with consideration for the expansion of the negative electrode active material layer (308), which contains silicon-based active material, due to charging, then during charging or when the lithium-ion secondary battery is fully charged, the end of the negative electrode active material layer (308) opposite to the exposed portion b may reach the exposed portion of the positive electrode current collector (101) and come into contact.

[0017] Furthermore, the state in which contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer is suppressed means that, as shown in Figure 4, even in a fully charged state, the end portion (304) of the negative electrode active material layer (306) on the exposed portion a side does not come into contact with the exposed portion a of the positive electrode current collector (101).

[0018] In this embodiment, the center e of the separator (201) of the stacked lithium-ion secondary battery is preferably located between the center c and the center d in the x direction, from the viewpoint of further suppressing contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer.

[0019] In the stacked lithium-ion secondary battery of this embodiment, the distance between the center e and the center c in the x direction is X ２ In that case, the above X １ The X ２ The ratio (X ２ / X １ From the viewpoint of further suppressing contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer, the ratio (X) is preferably 0.0001 or higher, more preferably 0.0005 or higher, even more preferably 0.0010 or higher, even more preferably 0.0015 or higher, even more preferably 0.0020 or higher, and also preferably 0.0100 or lower, more preferably 0.0080 or lower, even more preferably 0.0050 or lower, even more preferably 0.0045 or lower, and even more preferably 0.0040 or lower. ２ / X １For similar reasons, the coefficient is preferably 0.0001 to 0.0100, more preferably 0.0005 to 0.0080, even more preferably 0.0010 to 0.0050, even more preferably 0.0015 to 0.0045, and even more preferably 0.0020 to 0.0040.

[0020] In the stacked lithium-ion secondary battery of this embodiment, the distance between the center e and the center d in the x direction is Y. ２ In that case, Y １ Y ２ The ratio (Y ２ / Y １ From the viewpoint of further suppressing contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer, the ratio (Y) is preferably 0.0001 or higher, more preferably 0.0005 or higher, even more preferably 0.0010 or higher, even more preferably 0.0015 or higher, and preferably 0.0100 or lower, more preferably 0.0080 or lower, even more preferably 0.0070 or lower, and even more preferably 0.0060 or lower. ２ / Y １ For similar reasons, the coefficient is preferably 0.0001 to 0.0100, more preferably 0.0005 to 0.0080, even more preferably 0.0010 to 0.0070, and even more preferably 0.0015 to 0.0060.

[0021] In the stacked lithium-ion secondary battery of this embodiment, the distance between the center c and the center d in the x direction is Y. ３ In that case, Y １ Y ３ The ratio (Y ３ / Y １ The ratio (Y) is preferably 0.0002 or higher, more preferably 0.0005 or higher, even more preferably 0.0010 or higher, even more preferably 0.0030 or higher, and preferably 0.0200 or lower, more preferably 0.0150 or lower, even more preferably 0.0100 or lower, and even more preferably 0.0090 or lower, from the viewpoint of further suppressing contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer. ３ / Y １For similar reasons, the coefficient is preferably 0.0002 to 0.0200, more preferably 0.0005 to 0.0150, even more preferably 0.0010 to 0.0100, and even more preferably 0.0030 to 0.0090.

[0022] When the length of the separator (201) of the stacked lithium-ion secondary battery in this embodiment is Z in the x-direction, the x-direction is given by the x-direction of Z. １ The ratio (X １ From the viewpoint of further suppressing contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer, the ratio (X) is preferably 0.900 or higher, more preferably 0.920 or higher, even more preferably 0.940 or higher, even more preferably 0.960 or higher, even more preferably 0.970 or higher, and preferably less than 1.000, more preferably 0.999 or lower, even more preferably 0.996 or lower, even more preferably 0.993 or lower, and even more preferably 0.990 or lower. １ For similar reasons, the value of / Z is preferably 0.900 or more and less than 1.000, more preferably 0.920 or more and 0.999 or less, even more preferably 0.940 or more and 0.996 or less, even more preferably 0.960 or more and 0.993 or less, and even more preferably 0.970 or more and 0.990 or less.

[0023] In this embodiment of the stacked lithium-ion secondary battery, the sum of the length of the insulating layer (103) and the length of the positive electrode active material layer (105) in the x-direction is Y. ４ In that case, Y ４ The X １ The ratio (X １ / Y ４ From the viewpoint of further suppressing contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer, the ratio (X) is preferably 0.900 or higher, more preferably 0.920 or higher, even more preferably 0.940 or higher, even more preferably 0.960 or higher, even more preferably 0.970 or higher, and less than 1.000, more preferably 0.999 or lower, even more preferably 0.998 or lower, even more preferably 0.996 or lower, and even more preferably 0.995 or lower. １ / Y ４is, for the same reason, preferably 0.900 or more and less than 1.000, more preferably 0.920 or more and 0.999 or less, still more preferably 0.940 or more and 0.998 or less, still more preferably 0.960 or more and 0.996 or less, still more preferably 0.970 or more and 0.995 or less.

[0024] Let the total value of the length of the insulating layer (103) and the length of the positive electrode active material layer (105) in the x direction of the laminated lithium ion secondary battery of the present embodiment be Y. ４ And let the length of the negative electrode active material layer (306) in the fully charged state be X. ３ When this is done, the ４ ratio of X ３ to Y ３ (X ４ / Y ３ ) is preferably 0.910 or more, more preferably 0.930 or more, still more preferably 0.950 or more, still more preferably 0.970 or more, still more preferably 0.980 or more from the viewpoint of further suppressing the contact between the exposed portion of the positive electrode current collector and the negative electrode active material layer, and is preferably less than 1.020, more preferably less than 1.015, still more preferably less than 1.010, still more preferably less than 1.005, still more preferably less than 1.000. Also, this ratio (X ４ / Y

[0025] ) is, for the same reason, preferably 0.910 or more and less than 1.020, more preferably 0.930 or more and less than 1.015, still more preferably 0.950 or more and less than 1.010, still more preferably 0.970 or more and less than 1.005, still more preferably 0.980 or more and less than 1.000.

[0026] <Negative electrode> The laminated lithium ion secondary battery of the present embodiment includes a negative electrode. The negative electrode of the present embodiment includes a negative electrode current collector, a negative electrode active material layer laminated on at least one surface of the negative electrode current collector, and an exposed portion b where the negative electrode active material layer is not laminated at one end of the negative electrode current collector.

[0027] (Negative electrode active material layer) The negative electrode active material contained in the negative electrode active material layer of the present embodiment includes a silicon-based active material from the viewpoint of improving the battery capacity of the obtained lithium ion secondary battery.

[0028] The silicon-based active material of the present embodiment preferably includes SiO ｘ (0 < x ≤ 2), Si / C containing Si-C composite particles containing silicon and a carbon material, and one or more selected from the group consisting of Si, more preferably SiO ｘ (0 < x ≤ 2), and one or more selected from the group consisting of Si / C containing Si-C composite particles containing silicon and a carbon material, and more preferably contains Si / C containing Si-C composite particles containing silicon and a carbon material.

[0029] When the total amount of the negative electrode active material layer is 100 parts by mass, the content of the silicon-based active material in the negative electrode active material layer of the present embodiment is preferably 5 parts by mass or more and 40 parts by mass or less, more preferably 10 parts by mass or more and 30 parts by mass or less.

[0030] The negative electrode active material contained in the negative electrode active material layer of the present embodiment may further contain an active material other than the silicon-based active material as necessary. For example, it is preferable to further contain a carbon-based active material. Examples of the carbon-based active material include graphite, amorphous carbon, diamond-like carbon, fullerene, carbon nanotube, carbon nanohorn, etc. Among these, it is preferable to contain graphite. Also, the type of graphite is not particularly limited, but from the viewpoint of further improving the battery performance of the laminated lithium ion secondary battery, it is preferably artificial graphite, and more preferably artificial graphite having a surface coating. Also, it is preferably powdered graphite, and more preferably contains secondary particles.

[0031] When the total amount of the negative electrode active material layer in this embodiment is 100 parts by mass, the content of carbon-based active material in the negative electrode active material layer is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 70 parts by mass or more, even more preferably 75 parts by mass or more, and preferably 95 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 88 parts by mass or less, and even more preferably 85 parts by mass or less. Also, when the total amount of the negative electrode active material layer in this embodiment is 100 parts by mass, the content of carbon-based active material in the negative electrode active material layer is preferably 50 parts by mass or more and 95 parts by mass or less, more preferably 60 parts by mass or more and 90 parts by mass or less, even more preferably 70 parts by mass or more and 88 parts by mass or less, and even more preferably 75 parts by mass or more and 85 parts by mass or less.

[0032] The negative electrode active material layer of this embodiment preferably comprises a negative electrode active material and a binder, and more preferably comprises a negative electrode active material, a binder and a conductive additive.

[0033] Examples of conductive additives in the negative electrode active material layer of this embodiment include carbon fibers such as carbon nanofibers; carbon blacks such as acetylene black and Ketjenblack; and carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. One of these may be used alone, or two or more may be used in combination. Among these, the conductive additive in the negative electrode active material layer of this embodiment preferably contains a carbon material, more preferably contains carbon nanotubes, and even more preferably contains single-walled carbon nanotubes, from the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery.

[0034] In this embodiment, the content of the conductive additive in the negative electrode active material layer is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, even more preferably 0.05 parts by mass or more, even more preferably 0.07 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 1.0 part by mass or less, even more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less, when the total amount of the negative electrode active material layer is 100 parts by mass, for the same reasons.

[0035] Examples of binders in the negative electrode active material layer of this embodiment include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); polycarboxylic acid polymers such as poly(meth)acrylic acid; conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; synthetic rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile-butadiene rubber (NBR); and polysaccharides such as carboxymethylcellulose (CMC), xanthan gum, guar gum, and pectin. One of these may be used alone, or two or more may be used in combination. Among these, the binder in the negative electrode active material layer of this embodiment preferably comprises one or more selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, from the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery, more preferably comprises one or more selected from the group consisting of polyvinylidene fluoride, polycarboxylic acid polymer, and styrene-butadiene rubber, even more preferably comprises a polycarboxylic acid polymer, and even more preferably comprises poly(meth)acrylic acid.

[0036] From the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery, the binder content in the negative electrode active material layer of this embodiment is preferably 0.1 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 2.0 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 5.0 parts by mass or less, when the total amount of the negative electrode active material layer is 100.0 parts by mass. From the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery, the binder content in the negative electrode active material layer of this embodiment is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 2.0 parts by mass or more and 5.0 parts by mass or less, when the total amount of the negative electrode active material layer is 100.0 parts by mass.

[0037] The thickness of the negative electrode active material layer in this embodiment is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 50 μm or more, and preferably 250 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less, from the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery. The thickness of the negative electrode active material layer in this embodiment is preferably 10 μm or more and 250 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 50 μm or more and 150 μm or less, from the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery.

[0038] From the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery, the density of the negative electrode active material layer in this embodiment is preferably 0.50 g / cm³. ３ More preferably, 1.00 g / cm³ ３ More preferably, 1.30 g / cm³ ３ The above is true, and preferably 3.00 g / cm³. ３ More preferably, 2.50 g / cm³ ３ More preferably, 2.00 g / cm³ ３ The following applies. From the viewpoint of further improving the battery performance of the stacked lithium-ion secondary battery, the density of the negative electrode active material layer in this embodiment is preferably 0.50 g / cm³. ３ 3.00g / cm or more ３More preferably, 1.00 g / cm³ ３ 2.50g / cm or more ３ More preferably, 1.30 g / cm³ ３ 2.00g / cm or more ３ The following applies:

[0039] The negative electrode current collector in this embodiment may be made of, for example, copper, stainless steel, nickel, titanium, or an alloy thereof. The shape of the negative electrode current collector may be, for example, foil, a flat plate, or a mesh. The thickness of the negative electrode current collector is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

[0040] <Method for Manufacturing a Stacked Lithium-Ion Secondary Battery> The stacked lithium-ion secondary battery of this embodiment includes, for example, a positive electrode (100) comprising a positive electrode current collector (101) made of a metal such as aluminum foil, and a positive electrode active material layer (105) and an insulating layer (103) provided on at least one side thereof, and a negative electrode (300) comprising a negative electrode current collector (303) made of a metal such as copper foil, and a negative electrode active material layer (301) containing negative electrode active material provided thereon. The positive electrode (100) and the negative electrode (300) are stacked via a separator (201) made of a nonwoven fabric or a polypropylene microporous film, etc., such that the positive electrode active material layer (105) and the negative electrode active material layer (301) face each other. This electrode body is housed in a container formed of an outer casing made of, for example, an aluminum laminate film. Furthermore, for example, a positive electrode tab is connected to the positive electrode current collector (101), and a negative electrode tab is connected to the negative electrode current collector (303), with these tabs extending outside the container. In Figures 1 and 2, one end of the separator (201) faces the negative electrode current collector (303) at a negative x-direction position relative to the end of the negative electrode active material layer (301), and the other end of the separator faces the insulating layer (103) at a positive x-direction position relative to the end of the negative electrode active material layer (301). However, it may also be positioned to face the positive electrode current collector (101) at a positive x-direction position relative to the end of the insulating layer (103). An electrolyte solution is injected into the container and sealed. The container can have a structure that houses an electrode group in which multiple positive and negative electrodes are stacked via separators, or a structure that houses a single electrode. Alternatively, the structure may include an electrode body or electrode group in which a positive electrode and a negative electrode are wound together with a separator in between, but the configuration of the electrode body is not limited to these.

[0041] Lithium-ion secondary batteries can be manufactured according to known methods. For electrodes, for example, laminates can be used. For the outer casing, metal casings or aluminum laminate casings can be used as appropriate.

[0042] In the lithium-ion secondary battery of this embodiment, the positive electrode preferably comprises a positive electrode active material layer containing a positive electrode active material and a positive electrode current collector. The positive electrode active material layer of this embodiment preferably comprises a positive electrode active material and a binder, and more preferably comprises a positive electrode active material, a binder and a conductive additive.

[0043] The positive electrode active material in the positive electrode active material layer of this embodiment may be, for example, a composite oxide of lithium and a transition metal such as lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-nickel-manganese composite oxide, lithium-nickel-cobalt composite oxide, lithium-nickel-aluminum composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-manganese-cobalt composite oxide, lithium-nickel-manganese-aluminum composite oxide, lithium-nickel-cobalt-manganese-aluminum composite oxide; TiS ２ FeS, MoS ２ Transition metal sulfides such as MnO, V ２ O ５ , V ６ O １３ , TiO ２ Examples include transition metal oxides such as olivine-type lithium phosphate oxide, and these may be used individually or in combination of two or more.

[0044] Examples of conductive additives in the positive electrode active material layer of this embodiment include carbon fibers such as carbon nanofibers; carbon blacks such as acetylene black and Ketjenblack; and carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. One of these may be used alone, or two or more may be used in combination.

[0045] Examples of binders in the positive electrode active material layer of this embodiment include fluorine-based binders such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); and aqueous binders such as styrene-butadiene rubber. One of these may be used alone, or two or more may be used in combination.

[0046] The positive electrode current collector of this embodiment may be made of, for example, aluminum, stainless steel, nickel, titanium, or an alloy thereof. The shape of the positive electrode current collector may be, for example, foil, a flat plate, or a mesh. The thickness of the positive electrode current collector is not particularly limited, but for example, it is 1 μm or more and 50 μm or less.

[0047] The electrolyte in this embodiment may include, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and butylene carbonate (BC); linear carbonates such as ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and dipropyl carbonate (DPC); aliphatic carboxylic acid esters; γ-lactones such as γ-butyrolactone; linear ethers; and organic solvents such as cyclic ethers, to which lithium hexafluoride phosphate (LiPF) is added. ６ ), lithium borofluoride (LiBF ４ ), LiFSI, lithium perchlorate (LiClO ４ Examples include solutions of lithium salts such as ), and the organic solvent may be used alone or in combination of two or more.

[0048] The separator of this embodiment is, for example, mainly made of a porous membrane, woven fabric, nonwoven fabric, etc., and as the resin component, for example, polyolefin resins such as polypropylene and polyethylene, polyester resins, acrylic resins, styrene resins, or nylon resins can be used. In addition, if necessary, a layer containing inorganic particles may be formed in the separator, and examples of inorganic particles include insulating oxides, nitrides, sulfides, carbides, etc.

[0049] As the outer casing of this embodiment, for example, a case or can made of a flexible film can be used, and from the viewpoint of reducing the weight of the battery, it is preferable to use a flexible film. The flexible film can be one in which a resin layer is provided on both the front and back surfaces of a metal base layer. The metal layer can be selected to have barrier properties such as preventing leakage of electrolyte and intrusion of moisture from the outside, and can be made of aluminum, stainless steel, etc. A heat-sealable resin layer, such as a modified polyolefin, is provided on at least one surface of the metal layer. The outer casing is formed by facing the heat-sealable resin layers of the flexible film toward each other and heat-sealing the area around the part that houses the electrode laminate. A resin layer such as a nylon film or polyester film can be provided on the surface of the outer casing opposite to the surface on which the heat-sealable resin layer is formed.

[0050] The stacked lithium-ion secondary battery of this embodiment has a high capacity because the negative electrode active material contains a silicon-based active material. Furthermore, since contact between the negative electrode active material layer and the exposed portion of the positive electrode current collector due to the expansion of the silicon-based active material during battery charging can be suppressed, the battery's cycle characteristics can be improved. Such a stacked lithium-ion secondary battery is particularly suitable for use as a vehicle battery or a fixed-type battery.

[0051] The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can also be adopted.

[0052] It should be noted that the present invention is not limited to the embodiments described above, and any modifications, improvements, etc., that can achieve the objectives of the present invention are included in the present invention.

[0053] This application claims priority based on Japanese Patent Application No. 2025-011348, filed on 27 January 2025, and incorporates all of its disclosures herein.

[0054] a Exposed part a b Exposed part b 100 Positive electrode 101 Positive electrode current collector d Center of positive electrode active material layer 103 Insulating layer 104 Boundary between insulating layer and exposed part a 105 Positive electrode active material layer 201 Separator e Center of separator 300 Negative electrode 301 Negative electrode active material layer c Center of negative electrode active material layer 303 Negative electrode current collector 304 End of negative electrode active material layer on the exposed part a side 305 Negative electrode 306 Negative electrode active material layer 307 Negative electrode 308 Negative electrode active material layer 500 Stacked lithium-ion secondary battery

Claims

1. A stacked lithium-ion secondary battery in which a positive electrode and a negative electrode are alternately stacked with a separator in between, wherein the positive electrode includes a positive electrode current collector, a positive electrode active material layer stacked on at least one surface of the positive electrode current collector, an exposed portion a at one end of the positive electrode current collector where the positive electrode active material layer is not stacked, and an insulating layer located between the positive electrode active material layer and the exposed portion a, the negative electrode includes a negative electrode current collector, a negative electrode active material layer stacked on at least one surface of the negative electrode current collector, and an exposed portion b at one end of the negative electrode current collector where the negative electrode active material layer is not stacked, the negative electrode active material contained in the negative electrode active material layer includes a silicon-based active material, the stacking direction of the negative electrode, the separator, and the positive electrode is defined as the z direction, the direction perpendicular to the z direction and moving from the center of the positive electrode current collector toward the center of the exposed portion a is defined as the x direction, and the length of the negative electrode active material layer in the x direction is defined as X １ Let Y be the length of the positive electrode active material layer. １ In that case, Y １ The X １ The ratio (X １ / Y １ A stacked lithium-ion secondary battery wherein the x-axis is greater than 1.000 and less than or equal to 1.200, and in the x-direction, the center c of the negative electrode active material layer and the center d of the positive electrode active material layer do not overlap, and the center d is located closer to the exposed portion a than the center c.

2. The stacked lithium-ion secondary battery according to claim 1, wherein, in the x-direction, the center e of the separator is located between the center c and the center d.

3. In the x direction, let the distance between the center e and the center c be X ２ When this is done, the X １ For the X ２ Ratio of X (X ２ / X １ ) is 0.0001 or more and 0.0100 or less. The laminated lithium ion secondary battery according to claim 2 4. In the x-direction, the distance between the center e and the center d is Y. ２ In that case, Y １ Y ２ The ratio (Y ２ / Y １ A stacked lithium-ion secondary battery according to claim 2 or 3, wherein the coefficient of 5. In the x-direction, the distance between the center c and the center d is Y. ３ In that case, Y １ Y ３ The ratio (Y ３ / Y １ A stacked lithium-ion secondary battery according to any one of claims 1 to 4, wherein the ratio is 0.0002 or more and 0.0200 or less.

6. When the length of the separator is Z in the x-direction, the x-direction is given by the x-direction. １ The ratio (X １ A stacked lithium-ion secondary battery according to any one of claims 1 to 5, wherein / Z) is 0.900 or more and less than 1.

000.

7. In the x-direction, the sum of the length of the insulating layer and the length of the positive electrode active material layer is Y ４ In that case, Y ４ The X １ The ratio (X １ / Y ４ A stacked lithium-ion secondary battery according to any one of claims 1 to 6, wherein the ratio is 0.900 or more and less than 1.

000.

8. In the x-direction, the sum of the length of the insulating layer and the length of the positive electrode active material layer is Y ４ Let X be the length of the negative electrode active material layer in the fully charged state. ３ In that case, Y ４ The X ３ The ratio (X ３ / Y ４ A stacked lithium-ion secondary battery according to any one of claims 1 to 7, wherein the ratio is 0.910 or more and less than 1.

020.

9. The stacked lithium-ion secondary battery according to any one of claims 1 to 8, wherein, in the x-direction, the end of the negative electrode active material layer on the exposed portion a side in the fully charged state is located on the exposed portion b side of the boundary between the insulating layer and the exposed portion a.

10. The silicon-based active material is SiO ｘ A stacked lithium-ion secondary battery according to any one of claims 1 to 9, comprising one or more selected from the group consisting of (0 < x ≤ 2), Si / C including Si-C composite particles containing silicon and carbon materials, and Si.

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