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] This disclosure relates to a battery pack. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-46758 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in a battery pack, electrodes located on the lower side in the stacking direction become thinner due to the load of electrodes located higher up in the stacking direction, reducing the mass transfer distance within the electrode, which in turn reduces internal resistance and increases capacity. For this reason, in a battery pack connected in series in the stacking direction, variations in the State of Charge (SOC) occur during charging depending on the position of the cells (single cells) in the stacking direction, and overcharging may also cause variations in the degree of electrode degradation.

[0005] One embodiment of this disclosure aims to solve the problem of the electrode located on the lower side (gravity side) in the stacking direction increasing in capacity due to thinning caused by load, and of the electrode degradation rate varying due to overcharging when the battery pack is charged, by suppressing this phenomenon. Note that "upper side in the stacking direction" refers to the anti-gravity direction, and "lower side in the stacking direction" refers to the gravity direction.

Means for Solving the Problem

[0006] The means for solving the above problems include the following aspects. <1> A laminated battery having a plurality of electrodes including a current collector, a negative electrode composite layer provided on one surface of the current collector, and a positive electrode composite layer provided on the other surface of the current collector, and the electrodes being alternately laminated via an electrolyte layer, The basis 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 on the upper side in the stacking direction of the laminated battery is larger than the basis 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 on the lower side in the stacking direction of the laminated battery, Laminated battery. <2> The density (g / cm 3 ) of the negative electrode active material or positive electrode active material in the negative electrode composite or positive electrode composite in the negative electrode composite layer or positive electrode composite layer of the electrode located on the upper side in the stacking direction of the laminated battery is larger than the density (g / cm 3 ) of the negative electrode active material or positive electrode active material in the negative electrode composite or positive electrode composite in the negative electrode composite layer or positive electrode composite layer of the electrode located on the lower side in the stacking direction of the laminated battery. The laminated battery according to <1>.

Advantages of the Invention

[0007] According to the present disclosure, a laminated battery is provided in which the lower the electrode located on the lower side (gravity direction side) in the stacking direction of the laminated battery, the more the capacity increases due to thinning by the load, and when the laminated battery is charged, the phenomenon that the degree of deterioration of the electrode varies due to overcharging 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 the laminated battery of the present disclosure. [Figure 2]Figure 2 is a plot showing the relationship between the ratio of the capacity (mAh / g) of the positive or negative electrode of the uppermost cell (single cell) to the capacity (mAh / g) of the positive or negative electrode of the lowermost cell (single cell) of the battery pack of this disclosure, and time (number of days of storage). [Figure 3] Figure 3 is a plot showing the relationship between the difference (%) in initial capacity (mAh / g) between the positive or negative electrode of the uppermost cell (single cell) and the positive or negative electrode of the lowermost cell (single cell) of the battery pack of this disclosure, and the number of years of use. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure are described below. The description is illustrative and does not limit the scope of this disclosure.

[0010] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages within this 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 stages. Furthermore, in the numerical ranges described within this embodiment, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

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

[0012] In this specification, when embodiments are described with reference to the drawings, the configuration of the embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the members in each figure are conceptual, and the relative relationships between the sizes of the members are not limited thereto.

[0013] In this specification, each component may contain multiple substances. In this embodiment, when referring to the amount of each component in the composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

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

[0015] <Battery pack> The battery pack disclosed herein is A battery pack having a current collector, a negative electrode composite layer provided on one side of the current collector, and a plurality of electrodes provided on the other side of the current collector, wherein the electrodes are alternately stacked with an electrolyte layer in between, The basis weight (mg / cm³) 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 on the upper side in the stacking direction of the aforementioned battery pack. 2 ) is the basis weight (mg / cm³) 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 lower in the stacking direction of the battery pack. 2 ) are each larger than It is a battery pack. With the above configuration, electrodes located on the lower side (gravity side) of the stacking direction of the battery pack increase in capacity due to thinning caused by the load, and when the battery pack is charged, the phenomenon of variations in the degree of electrode degradation due to overcharging can be suppressed.

[0016] The battery pack described herein will be explained below with reference to the drawings.

[0017] <Battery pack> Figure 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 Figure 1, the battery pack 100 has a current collector C, a plurality of electrodes 1 having a negative electrode composite layer 1a provided on one side of the current collector C, and a positive electrode composite layer 1b provided on the other side of the current collector C, and the electrodes are alternately stacked with an electrolyte layer S in between. The laminated battery 100 of the present disclosure has a basis weight (mg / cm 2 ) of the negative electrode composite material or the positive electrode composite material in the negative electrode composite material layer 1a or the positive electrode composite material layer 1b located on the upper side in the stacking direction of the laminated battery 100, which is respectively larger than 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 1a or the positive electrode composite material layer 1b located on the lower side in the stacking direction of the laminated battery. As shown in FIG. 1, the laminated battery 100 of the present disclosure preferably has a positive electrode terminal electrode 2a composed of a positive electrode composite material layer 1b and a current collector C at the uppermost part. Further, the laminated battery 100 of the present disclosure preferably has a negative electrode terminal electrode 2b composed of a negative electrode composite material layer 1a and a current collector C at the lowermost part.

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

[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, and stainless steel. The metal member forming the current collector may be appropriately selected from one or more metal members according to the purpose.

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

[0021] -Negative electrode composite material layer- The negative electrode composite material 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, oxide-based active materials such as lithium titanate (for example, Li4Ti5O 12 ), and Si-based active materials such as elemental Si.

[0023] The shape of the negative electrode active material is not particularly limited. For example, it may be spherical (e.g., perfectly spherical, ellipsoidal, etc.), fibrous, etc.

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

[0025] For example, the specific surface area of ​​the negative electrode active material is 0.1 m². 2 / g~1,500m 2 It is / g.

[0026] Examples of negative conductive agents include carbon materials such as acetylene black, Ketjenblack, vapor-processed carbon fiber (VGCF®), and carbon nanotubes (CNTs).

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

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

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

[0030] -Positive electrode composite layer- The positive electrode composite layer includes a positive electrode active material, a conductive agent, and a binder. Examples of positive electrode active materials include lithium composite oxides. Examples of lithium composite oxides include lithium cobaltate, lithium nickelate, lithium manganeseate, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Examples include O2. 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. For example, it may be spherical (e.g., perfectly spherical, ellipsoidal, etc.), fibrous, etc.

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

[0033] For example, the specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g~100m 2 It is / g.

[0034] As the conductive agent, the same one as that exemplified in the negative electrode composite layer can be used.

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

[0036] For the binder, the same type as that exemplified for the positive electrode composite layer can be used.

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

[0038] In the battery pack of this disclosure, the basis weight (mg / cm³) 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 on the upper side in the stacking direction of the battery pack. 2 ) is the basis weight (mg / cm³) 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 lower in the stacking direction of the battery pack. 2 These values ​​are larger than the values ​​shown. As a result, the capacitance of the electrodes increases, and the difference in internal resistance between electrodes located lower down is mitigated. Therefore, electrodes located lower down in the stacking direction of the battery pack have increased capacitance due to thinning caused by the load, and when the battery pack is charged, the phenomenon of variations in the degree of electrode degradation due to overcharging is more easily suppressed.

[0039] Therefore, the coating of the negative electrode composite material or positive electrode composite material (hereinafter simply referred to as "coating" for simplicity) is performed on the electrodes located higher up in the stacking direction of the battery pack, and the basis weight (mg / cm²) of the negative electrode composite material or positive electrode composite material is used.2 ) is the basis weight (mg / cm³) of the negative electrode composite material or positive electrode composite material of the electrode located lower in the stacking direction of the battery pack. 2 It is preferable that the results be made so that each of them is greater than ).

[0040] The coating process involves the basis weight (mg / cm³) 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 top of the battery pack. 2 For example, 10 mg / cm³ 2 ~50 mg / cm³ 2 It is preferable that the coating is carried out in such a manner. The coating is carried out in such a manner that the basis weight (mg / cm³) 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 bottom of the battery pack is 2 For example, 10 mg / cm³ 2 ~50 mg / cm³ 2 It is preferable that the procedure be carried out in such a manner.

[0041] Furthermore, in coating, for example, if the thickness of the battery pack is 100 mm, the basis weight (mg / cm²) of the negative electrode composite material or positive electrode composite material of the electrode located at the top of the battery pack is... 2 ) is the basis weight (mg / cm²) of the negative electrode composite material or positive electrode composite material of the electrode located at the bottom of the stacking direction. 2 The process may be carried out to achieve a value between 100.5% and 102%, for example, to achieve 101%.

[0042] Furthermore, in coating, for example, if the stacking thickness of the battery pack is 200 mm, the basis weight (mg / cm²) of the negative electrode composite material or positive electrode composite material of the electrode located at the top of the battery pack is... 2 ) is the basis weight (mg / cm³) of the negative electrode composite material or positive electrode composite material of the electrode located at the bottom of the battery pack. 2 The process may be carried out to achieve 101% to 104% of the result, for example, to achieve 102%.

[0043] Basis weight (mg / cm³) 2 ) can be found as follows: (1) A negative electrode mixture or a positive electrode mixture is applied to the current collector and dried to form a negative electrode mixture layer or a positive electrode mixture layer. (2) Measure the area and weight of the negative electrode composite layer or the positive electrode composite layer, and calculate the basis weight (= weight of positive electrode composite or negative electrode composite / area of ​​positive electrode composite layer or negative electrode composite layer).

[0044] Furthermore, the coating process involves the density (g / cm³) 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 on the upper side in the stacking direction of the battery pack. 3 ) is the density (g / cm³) 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 lower in the stacking direction of the battery pack. 3 It is preferable that these values ​​be made larger than the above. This increases the capacitance of the electrodes and mitigates the difference in internal resistance, so that electrodes located on the lower side in the stacking direction of the battery pack have increased capacitance due to thinning caused by the load, and when the battery pack is charged, the phenomenon of variations in the degree of electrode degradation due to overcharging is more easily suppressed.

[0045] The coating process involves the density (g / cm³) of the negative electrode composite layer or positive electrode composite layer of the electrode located at the top of the battery pack. 3 For example, 1 g / cm³ 3 ~5g / cm 3 It is preferable that the coating be carried out in such a way that the density (g / cm³) 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 bottom of the stacking direction of the battery pack is reduced. 3 For example, 1 g / cm³ 3 ~5g / cm 3 It is preferable that the procedure be carried out in such a manner.

[0046] Furthermore, the coating may be carried out such that, for example, when the thickness of the battery pack in the stacking direction is 100 mm, 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 100.5% to 102% 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 bottom of the stacking direction, for example, it may be 101%.

[0047] Furthermore, the coating may be carried out such that, for example, when the thickness of the battery pack in the stacking direction is 200 mm, 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 bottom of the stacking direction, for example, it may be 102%.

[0048] Density (g / cm 3 ) is the basis weight (mg / cm³). 2 This can be determined by dividing the value 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 this disclosure can be obtained by alternately stacking the electrodes and the electrolyte layer S.

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

[0051] If the electrolytic layer S is a solid electrolyte layer, the solid electrolyte can be, for example, lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X Examples of solid electrolytes include oxide solid electrolytes such as (PO4)3, Li-SiO glass, and Li-Al-SO glass; 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, and Li2S-P2S5-GeS2. The solid electrolyte layer can be obtained by pressing the solid electrolyte.

[0052] When the electrolyte layer S consists of a separator and an electrolyte solution, the separator can be, for example, a resin sheet such as polyethylene (PE) or polypropylene (PP). The electrolyte solution contains a predetermined electrolyte and a solvent, and examples of predetermined electrolytes include LiPF6, LiBF4, LiAsF6, Li(CF3SO2)2N, Li(C2F5SO2)2N, LiTaF6, LiClO4, and LiCF3SO3.

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

[0054] In the battery pack of this disclosure, the stacking thickness of the battery pack is 100 mm, and the stacking thickness of each cell (single cell) is 0.5 mm. Assuming that after 10 years of use, the thickness of the positive or negative electrode of the topmost cell (single cell) of the battery pack is 1.018 times the thickness of the positive or negative electrode of the bottommost cell (single cell), then, as shown in Figure 3, the difference in initial capacity (mAh / g) between the positive or negative electrode of the topmost cell (single cell) and the positive or negative electrode of the bottommost cell (single cell) may be 1.8%. Furthermore, in this case, after 10 years of use, the difference in capacity (mAh / g) between the positive or negative electrode of the topmost cell (single cell) and the positive or negative electrode of the bottommost cell (single cell) may become 0%.

[0055] In the battery pack of this disclosure, the stacking thickness of the battery pack is 100 mm, and the stacking thickness of each cell (single cell) is 0.5 mm. Assuming that after 10 years of use, the thickness of the positive or negative electrode of the topmost cell (single cell) of the battery pack is 1.009 times the thickness of the positive or negative electrode of the bottommost cell (single cell), then, as shown in Figure 3, the difference in initial capacity (mAh / g) between the positive or negative electrode of the topmost cell (single cell) and the positive or negative electrode of the bottommost cell (single cell) may be 0.9%. Furthermore, in this case, after 5 years of use, the difference in capacity (mAh / g) between the positive or negative electrode of the topmost cell (single cell) and the positive or negative electrode of the bottommost cell (single cell) may become 0%.

[0056] In the two examples above, the former is preferable 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. Also, the latter is preferable 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 the 10-year usage period.

[0057] Furthermore, assuming that no thinning of the electrodes occurs due to the load, the difference in initial capacity (mAh / g) may be 0%, as shown in Figure 3.

[0058] Furthermore, the battery pack of this disclosure is 1m 2If the weight per cell is 3N, the surface pressure difference between the top and bottom of the battery pack will be 3kPa. Due to this surface pressure difference, the difference in internal resistance between the positive or negative electrode of the cell located at the top of the battery pack and the positive or negative electrode of the cell located at the bottom of the battery pack may be 1μΩ. Also, due to this surface pressure difference, the temperature difference between the positive or negative electrode of the cell located at the top of the battery pack and the positive or negative electrode of the cell located at the bottom of the battery pack may be 0.2℃. Based on this surface pressure difference, after 10 years of use, the difference in capacity (mAh / g) between the positive or negative electrode of the cell located at the top of the battery pack and the positive or negative electrode of the cell located at the bottom of the battery pack can be 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 approximate weight (mg / cm²) of the electrode of the nth cell (single cell) located from the top of the battery pack. 2 )

Claims

1. A battery pack having a current collector, a negative electrode composite layer provided on one side of the current collector, and a plurality of electrodes provided on the other side of the current collector, wherein the electrodes are alternately stacked with an electrolyte layer in between, 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 on the upper side in the stacking direction of the aforementioned battery pack. 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 lower in the stacking direction of the battery pack. ２ ) are each larger than Battery pack.

2. The density (g / cm³) of the negative electrode composite material or positive electrode composite material in the negative electrode composite material or positive electrode composite material in the negative electrode composite material or positive electrode composite material of the electrode located above in the stacking direction. ３ ) is the density (g / cm³) 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 lower in the stacking direction. ３ The battery pack according to claim 1, wherein each of the following is larger than ).

Images