Battery pack

Abstract

To provide a battery pack in which a phenomenon that a capacitance is increased due to thinning caused by a load and variations occur in a deterioration degree of an electrode due to an overcharge when the battery pack is charged in an electrode that is positioned on lower side in a lamination direction of the battery pack is suppressed.SOLUTION: A battery pack includes: a collector; and a plurality of electrodes that include a negative electrode mixture layer provided on one surface of the collector and a positive electrode mixture provided on the other surface of the collector, in which the electrodes are alternately laminated via an electrolyte layer. A basis weight (mg / cm2) of a negative electrode mixture or a positive electrode mixture in the negative electrode mixture layer or the positive electrode mixture layer of the electrode positioned on an upper side of a lamination direction of the battery pack is larger than a basis weight (mg / cm2) of the negative electrode mixture or the positive electrode mixture in the negative electrode mixture layer or the positive electrode mixture layer of the electrode positioned on the lower side in the lamination direction of the battery pack.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a battery pack. [Background technology]

[0002] A lithium-ion secondary battery has been disclosed in which the amount of positive electrode active material per unit area of ​​the current collector in the positive electrode arranged toward the center in the stacking direction is greater than the amount of positive electrode active material per unit area of ​​the current collector in the positive electrode arranged away from the center in the stacking direction, with the aim of increasing battery capacity while suppressing a decrease in charge / discharge rate characteristics (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-46758 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in a battery pack, the electrodes located at the bottom in the stacking direction become thinner due to the load of the electrodes located at the top in the stacking direction, and the distance of material transfer within the electrode decreases, so the internal resistance decreases and the capacity increases. For this reason, in a battery pack connected in series in the stacking direction, when charging, the SOC (State of Charge) varies depending on the position of the cells (single cells) in the stacking direction, and there is a risk that the degree of deterioration of the electrodes will also vary due to overcharging.

[0005] The problem that one embodiment of the present disclosure aims to solve is to provide a battery pack in which the electrodes located lower in the stacking direction of the battery pack (the electrodes closer to the direction of gravity) have a larger capacity due to thinning caused by load, and in which the phenomenon of variation in the degree of deterioration of the electrodes due to overcharging when the battery pack is charged is suppressed. It should be noted that "upper side in the stacking direction" refers to the antigravity direction, and "lower side in the stacking direction" refers to the gravity direction. [Means for solving the problem]

[0006] Means for solving the above problems include the following aspects. <1> A battery pack comprising a plurality of electrodes, each of which has a current collector, a negative electrode mixture layer provided on one surface of the current collector, and a positive electrode mixture layer provided on the other surface of the current collector, the electrodes being alternately stacked with an electrolyte layer interposed therebetween, The weight per unit area (mg / cm2) of the negative electrode mixture layer or the positive electrode mixture layer of the electrode located on the upper side in the stacking direction of the battery pack 2 ) is the basis weight (mg / cm2) of the negative electrode mixture or the positive electrode mixture in the negative electrode mixture layer or the positive electrode mixture layer of the electrode located at the lower side in the stacking direction of the battery pack. 2 ), Battery pack. <2> The density (g / cm) of the negative electrode active material or positive electrode active material in the negative electrode mixture layer or positive electrode mixture layer of the electrode located on the upper side in the stacking direction of the battery pack. 3 ) is the density (g / cm 3 ) of the negative electrode active material or positive electrode active material in the negative electrode mixture layer or positive electrode mixture layer of the electrode located at the lower side in the stacking direction of the battery pack. 3 ), <1> The battery pack according to claim 1. Effect of the Invention

[0007] According to the present disclosure, a battery pack is provided in which the electrodes located lower in the stacking direction of the battery pack (toward the direction of gravity) have a greater capacity due to thinning caused by load, and in which the phenomenon of variation in the degree of deterioration of the electrodes due to overcharging when the battery pack is charged is suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the structure of a battery pack according to the present disclosure. [Diagram 2]FIG. 2 is a plot showing the relationship between the ratio of the capacity (mAh / g) of the positive or negative electrode of the cell (single cell) located at the top to the capacity (mAh / g) of the positive or negative electrode of the cell (single cell) located at the bottom of the battery pack of the present disclosure and time (number of days of storage). [Diagram 3] FIG. 3 is a plot showing the relationship between the difference (%) in initial capacity (mAh / g) between the positive electrode or negative electrode of the cell (single cell) located at the top of the battery pack of the present disclosure and the positive electrode or negative electrode of the cell (single cell) located at the bottom, and the number of years of use (years). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described. The description is for illustrating the embodiments and is not intended to limit the scope of the present disclosure.

[0010] In this specification, a numerical range indicated using "~" indicates a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present embodiment, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in the present embodiment. In addition, in the numerical ranges described in the present embodiment, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.

[0011] In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0012] In this specification, when an embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the size of the members in each drawing is conceptual, and the relative relationship between the sizes of the members is not limited to this.

[0013] In the present specification, each component may contain a plurality of corresponding substances. In the present embodiment, when the amount of each component in the composition is mentioned, in the case where a plurality of substances corresponding to each component are present in the composition, the amount means the total amount of the plurality of substances present in the composition, unless otherwise specified.

[0014] In this specification, "particle size" refers to the volume average median diameter D 50 means...

[0015] <Battery pack> The battery pack according to the present disclosure includes: A battery pack comprising a plurality of electrodes, each of which has a current collector, a negative electrode mixture layer provided on one surface of the current collector, and a positive electrode mixture layer provided on the other surface of the current collector, the electrodes being alternately stacked with an electrolyte layer interposed therebetween, The weight per unit area (mg / cm2) of the negative electrode mixture layer or the positive electrode mixture layer of the electrode located on the upper side in the stacking direction of the battery pack 2 ) is the basis weight (mg / cm2) of the negative electrode mixture or the positive electrode mixture in the negative electrode mixture layer or the positive electrode mixture layer of the electrode located at the lower side in the stacking direction of the battery pack. 2 ), respectively. It is a battery pack. With the above configuration, the electrodes located lower in the stacking direction of the battery pack (the electrodes closer to the direction of gravity) have a larger capacity due to thinning caused by the load, and this makes it possible to suppress the phenomenon in which variations in the degree of deterioration of the electrodes occur due to overcharging when the battery pack is charged.

[0016] Hereinafter, the battery pack of the present disclosure will be described with reference to the drawings.

[0017] <Battery pack> Fig. 1 is a schematic cross-sectional view showing an example of the structure of a battery pack according to the present disclosure. As shown in Fig. 1, a battery pack 100 has a current collector C, a negative electrode composite layer 1a provided on one surface of the current collector C, and a positive electrode composite layer 1b provided on the other surface of the current collector C. The electrodes are alternately stacked with an electrolyte layer S interposed therebetween. The battery pack 100 of the present disclosure has a negative electrode composite material or positive electrode composite material basis weight (mg / cm 2 ) in the negative electrode composite material layer 1 a or the positive electrode composite material layer 1 b of the electrode 1 located on the upper side in the stacking direction of the battery pack 100. 2 ) is the basis weight (mg / cm 2 ) of the negative electrode mixture or the positive electrode mixture in the negative electrode mixture layer 1 a or the positive electrode mixture layer 1 b of the electrode 1 located at the lower side in the stacking direction of the battery pack. 2 ) respectively. 1, the battery pack 100 of the present disclosure preferably has, at the top, a positive terminal electrode 2a made of a positive electrode composite layer 1b and a current collector C. The battery pack 100 of the present disclosure preferably has, at the bottom, a negative terminal electrode 2b made of a negative electrode composite layer 1a and a current collector C.

[0018] (electrode) The electrode has a current collector, a negative electrode mixture layer provided on one surface of the current collector, and a positive electrode mixture layer provided on the other surface of the current collector. The electrode can be easily obtained by coating the current collector with one of the negative electrode mixture or the positive electrode mixture and drying it, and then coating the other in the same manner and drying it. The electrode may be pressed and cut as necessary.

[0019] -Current collector- Examples of the current collector include those made of metal members such as Cu, Al, Fe, Co, Ni, Cr, Ni-plated steel, stainless steel, etc. The metal member constituting the current collector may be appropriately selected from one or more metal members depending on the purpose.

[0020] The thickness of the current collector is not particularly limited and may be, for example, 0.1 μm to 1,000 μm.

[0021] -Negative electrode composite layer- The negative electrode mixture layer contains a negative electrode active material, a conductive agent, and a binder.

[0022] Examples of the negative electrode active material include Li-based active materials such as metallic lithium, carbon-based active materials such as graphite, and lithium titanate (e.g., Li4Ti5O 12 and Si-based active materials such as simple silicon.

[0023] The shape of the negative electrode active material is not particularly limited, and may be, for example, spherical (e.g., perfect sphere, oval sphere, etc.), fibrous, etc.

[0024] When the negative electrode active material has a spherical shape, the particle size of the negative electrode active material is, for example, 0.1 μm to 100 μm.

[0025] The specific surface area of ​​the negative electrode active material is, for example, 0.1 m 2 / g~1,500m 2 / g.

[0026] Examples of the negative conductive agent include carbon materials such as acetylene black, ketjen black, vapor grown carbon fiber (VGCF (registered trademark)), and carbon nanotubes (CNT).

[0027] The content of the conductive agent is, for example, 3% by mass to 5% by mass with respect to the negative electrode active material.

[0028] Examples of the binder include polyvinylidene fluoride (PVDF) / NMP-based, styrene butadiene rubber (SBR) / water-based, and polytetrafluoroethylene (PTFE) / water-based binders.

[0029] The content of the binder is, for example, 3% by mass to 5% by mass with respect to the negative electrode active material.

[0030] -Positive electrode mixture layer- The positive electrode mixture layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material may be, for example, a lithium composite oxide. Examples of the lithium composite oxide include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. The lithium composite oxide may contain at least one element selected from the group consisting of F, Cl, N, S, Br and I.

[0031] The shape of the positive electrode active material is not particularly limited, and may be, for example, spherical (e.g., perfect sphere, oval sphere, etc.), fibrous, etc.

[0032] The particle size of the positive electrode active material is, for example, 0.1 μm to 30 μm.

[0033] The specific surface area of ​​the positive electrode active material is, for example, 0.1 m 2 / g~100m 2 / g.

[0034] As the conductive agent, the same ones as those exemplified for the negative electrode mixture layer can be used.

[0035] The content of the conductive agent layer is, for example, 3% by mass to 5% by mass with respect to the positive electrode active material.

[0036] As for the binder, the same binders as those exemplified for the positive electrode mixture layer can be used.

[0037] The content of the binder is, for example, 3% by mass to 5% by mass with respect to the positive electrode active material.

[0038] In the battery pack of the present disclosure, the basis weight (mg / cm 2 ) of the negative electrode composite material or the positive electrode composite material in the negative electrode composite material layer or the positive electrode composite material layer of the electrode located on the upper side in the stacking direction of the battery pack is 2 ) is the basis weight (mg / cm2) of the negative electrode composite material or positive electrode composite material in the negative electrode composite material layer or positive electrode composite material layer of the electrode located at the lower side in the stacking direction of the battery pack. 2 ) are greater than the capacitance of the electrodes. This increases the capacity of the electrodes and reduces the difference in internal resistance with the electrodes located further down, so that the electrodes located further down in the stacking direction of the battery pack have a larger capacity due to thinning caused by the load, and when the battery pack is charged, the phenomenon of variation in the degree of deterioration of the electrodes due to overcharging is easily suppressed.

[0039] Therefore, the coating of the negative electrode composite or the positive electrode composite (hereinafter, for the sake of simplicity, simply referred to as "coating") is carried out based on the basis weight (mg / cm2) of the negative electrode composite or the positive electrode composite of the electrode located at the upper side in the stacking direction of the battery pack.2 ) is the basis weight (mg / cm2) of the negative electrode composite or positive electrode composite of the electrode located at the lower side in the stacking direction of the battery pack. 2 ) are preferably greater than

[0040] The coating is performed by applying a coating weight (mg / cm2) of the negative electrode mixture or the positive electrode mixture layer of the electrode located at the top of the battery pack. 2 ) for example, 10 mg / cm 2 ~50mg / cm 2 The coating is preferably performed so that the coating weight (mg / cm 2 ) of the negative electrode composite or positive electrode composite in the negative electrode composite layer or positive electrode composite layer of the electrode located at the bottom of the battery pack is 2 ) for example, 10 mg / cm 2 ~50mg / cm 2 It is preferable that the above-mentioned is carried out so as to satisfy the above-mentioned condition.

[0041] In addition, when the thickness of the battery pack is 100 mm, for example, the coating is performed by applying a coating weight (mg / cm 2 ) of the negative electrode composite material or the positive electrode composite material of the electrode located at the top of the battery pack. 2 ) is the basis weight (mg / cm2) of the negative electrode mixture or positive electrode mixture of the electrode located at the bottom in the stacking direction. 2 ) may be 100.5% to 102%, for example, 101%.

[0042] In addition, when the thickness of the battery pack in the stacking direction is 200 mm, the coating is performed by adjusting the basis weight (mg / cm2) of the negative electrode composite material or the positive electrode composite material of the electrode located at the top of the battery pack. 2 ) is the basis weight (mg / cm2) of the negative electrode composite or positive electrode composite of the electrode located at the bottom of the battery pack. 2 ) may be 101% to 104%, for example, 102%.

[0043] Weight per unit area (mg / cm 2 ) can be found as follows: (1) A negative electrode mixture or a positive electrode mixture is applied to a current collector and then dried to form a negative electrode mixture layer or a positive electrode mixture layer. (2) The area and weight of the negative electrode composite layer or the positive electrode composite layer are measured, and the basis weight (= weight of positive electrode composite or negative electrode composite / area of ​​positive electrode composite layer or negative electrode composite layer) is calculated.

[0044] In addition, the coating is performed based on the density (g / cm) of the negative electrode active material or the positive electrode active material in the negative electrode mixture layer or the positive electrode mixture layer of the electrode located on the upper side in the stacking direction of the battery pack. 3 ) is the density (g / cm 3 ) of the negative electrode active material or positive electrode active material in the negative electrode mixture layer or positive electrode mixture layer of the electrode located lower in the stacking direction of the battery pack. 3 ) is preferably set to be greater than the internal resistance difference. This increases the capacity of the electrodes and reduces the difference in internal resistance, so that the electrodes located lower in the stacking direction of the battery pack have a larger capacity due to thinning caused by the load, which makes it easier to suppress the phenomenon in which the deterioration degree of the electrodes varies due to overcharging when the battery pack is charged.

[0045] The coating is performed based on the density (g / cm) of the negative electrode active material or the positive electrode active material in the negative electrode mixture layer or the positive electrode mixture layer of the electrode located at the top of the battery pack. 3 ) for example, 1g / cm 3 ~5g / cm 3 The coating is preferably performed so that the density (g / cm 3 ) of the negative electrode active material or the positive electrode active material in the negative electrode mixture layer or the positive electrode mixture layer of the electrode located at the bottom in the stacking direction of the battery pack is 100%. 3 ) for example, 1g / cm 3 ~5g / cm 3 It is preferable that the above-mentioned is carried out so as to satisfy the above-mentioned condition.

[0046] Furthermore, when the thickness of the battery pack in the stacking direction is 100 mm, for example, the coating may be performed so that the density of the negative electrode active material or positive electrode active material in the negative electrode mixture layer or positive electrode mixture layer of the electrode located at the top of the battery pack is 100.5% to 102% of the density of the negative electrode active material or positive electrode active material in the negative electrode mixture layer or positive electrode mixture layer of the electrode located at the bottommost in the stacking direction, for example, 101%.

[0047] Furthermore, when the thickness of the battery pack in the stacking direction is 200 mm, for example, the coating may be performed so that the density of the negative electrode active material or positive electrode active material in the negative electrode composite layer or positive electrode composite layer of the electrode located at the top of the battery pack is 101% to 104% of the density of the negative electrode active material or positive electrode active material in the negative electrode composite layer or positive electrode composite layer of the electrode located at the bottommost part in the stacking direction, for example, 102%.

[0048] Density (g / cm 3 ) is the basis weight (mg / cm 2 ) by the thickness (cm) of the positive electrode active material layer or the negative electrode active material layer.

[0049] (Battery pack) The battery pack of the present disclosure can be obtained by alternately stacking the electrodes and the electrolyte layers S.

[0050] -Electrolyte layer S- The electrolyte layer S may include a solid electrolyte layer or a separator and an electrolyte solution.

[0051] When the electrolytic layer S is a solid electrolyte layer, the solid electrolyte may be, for example, lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X oxide solid electrolytes such as (PO4)3, Li-SiO-based glass, Li-Al-SO-based glass, etc.; and sulfide solid electrolytes such as Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5-GeS2, etc. The solid electrolyte layer can be obtained by pressing the solid electrolyte.

[0052] When the electrolyte layer S is composed of a separator and an electrolytic solution, examples of the separator include resin sheets such as polyethylene (PE) and polypropylene (PP), etc. The electrolytic solution includes a predetermined electrolyte and a solvent, and examples of the predetermined electrolyte include LiPF6, LiBF4, LiAsF6, Li(CF3SO2)2N, Li(C2F5SO2)2N, LiTaF6, LiClO4, LiCF3SO3, etc.

[0053] Examples of the solvent include cyclic carbonate solvents such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), etc. The concentration of the electrolyte is, for example, 0.1 to 1 mol / L.

[0054] In the battery pack of the present disclosure, if the thickness of the battery pack in the stacking direction is 100 mm, and the thickness of each cell (single cell) in the stacking direction is 0.5 mm, and if it is assumed that the thickness of the positive or negative electrode of the cell (single cell) located at the top of the battery pack is 1.018 times the thickness of the positive or negative electrode of the cell (single cell) located at the bottom after 10 years of use, the difference in initial capacity (mAh / g) between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom may be 1.8%, as shown in Figure 3. In this case, after 10 years of use, the difference in capacity (mAh / g) between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom may be 0%.

[0055] In the battery pack of the present disclosure, if the thickness of the battery pack in the stacking direction is 100 mm, and the thickness of each cell (single cell) in the stacking direction is 0.5 mm, and if it is assumed that the thickness of the positive or negative electrode of the cell (single cell) located at the top of the battery pack is 1.009 times the thickness of the positive or negative electrode of the cell (single cell) located at the bottom after 10 years of use, the difference in initial capacity (mAh / g) between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom may be 0.9%, as shown in Figure 3. In this case, after 5 years of use, the difference in capacity (mAh / g) between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom may be 0%.

[0056] Of the two examples, the former is preferred from the viewpoint of minimizing the difference in capacity (mAh / g) between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom after 10 years of use, while the latter is preferred from the viewpoint of minimizing the difference in capacity (mAh / g) between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom during 10 years of use.

[0057] If it is assumed that the electrodes do not become thinner due to the load, the difference in initial capacity (mAh / g) may be 0%, as shown in FIG.

[0058] In addition, the battery pack of the present disclosure is 2When the weight per cell is 3N, the surface pressure difference between the top and bottom of the battery pack is 3kPa. Due to this surface pressure difference, the difference in internal resistance between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom of the battery pack can be 1μΩ. Also, due to this surface pressure difference, the temperature difference between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom of the battery pack can be 0.2℃. Due to this surface pressure difference, the difference in capacity (mAh / g) between the positive or negative electrode of the cell (single cell) located at the top of the battery pack and the positive or negative electrode of the cell (single cell) located at the bottom of the battery pack after 10 years of use is calculated to be 1.8% from Figure 2. In this case, the higher the temperature, the greater the tendency for capacity to decrease. [Explanation of symbols]

[0059] 100 battery packs 1 electrode 1a Negative electrode composite layer 1b Positive electrode composite layer C Current collector S electrolyte layer 2a Positive terminal electrode 2b Negative terminal electrode d n The electrode weight (mg / cm2) of the nth cell (single cell) from the top of the battery pack 2 )

Claims

1. A battery pack comprising a plurality of electrodes, each of which has a current collector, a negative electrode mixture layer provided on one surface of the current collector, and a positive electrode mixture layer provided on the other surface of the current collector, the electrodes being alternately stacked with an electrolyte layer interposed therebetween, The weight per unit area (mg / cm) of the negative electrode mixture layer or the positive electrode mixture layer of the electrode located on the upper side in the stacking direction of the battery pack ２ ) is the basis weight (mg / cm) of the negative electrode composite material or the positive electrode composite material in the negative electrode composite material layer or the positive electrode composite material layer of the electrode located at the lower side in the stacking direction of the battery pack. ２ ) are larger than Battery pack.

2. The density (g / cm) of the negative electrode active material or positive electrode active material in the negative electrode mixture layer or positive electrode mixture layer of the electrode located on the upper side in the stacking direction ３ ) is the density (g / cm) of the negative electrode active material or positive electrode active material in the negative electrode mixture layer or positive electrode mixture layer of the electrode located lower in the stacking direction. ３ 2. The battery pack according to claim 1 , wherein each of said first and second terminals is greater than one of said first and second terminals.

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