Battery pack

Abstract

The invention relates to a battery pack. The battery pack has a plurality of electrodes each having 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 laminated via electrolyte layers. Mass per unit area (mg / cm2) of negative electrode mixture or positive electrode mixture in negative electrode mixture layer or positive electrode mixture layer of electrode positioned on upper side in stacking direction of battery pack The mass per unit area (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 opposite lower side in the stacking direction of the battery pack is greater than the mass per unit area (mg / cm < 2 >).

Description

Technical Field

[0001] The present disclosure relates to battery packs. Background Art

[0002] In order to suppress the reduction of charge and discharge rate characteristics and increase battery capacity, a lithium-ion secondary battery has been disclosed, in which the amount of positive electrode active material per unit area of ​​the collector of the positive electrode arranged on the center side of the stacking direction is greater than the amount of positive electrode active material per unit area of ​​the collector of the positive electrode arranged on the side away from the center of the stacking direction (refer to Japanese Patent No. 2019-46758). Summary of the invention

[0003] However, in a battery pack, the electrode located at the lower side in the stacking direction is thinned due to the load of the electrode located at the upper side in the stacking direction, and the distance of material movement in the lower electrode is reduced, so the internal resistance is reduced and the capacity is increased. Therefore, for a battery pack in which battery cells are connected in series in the stacking direction, when charging, the SOC (State of Charge) fluctuates depending on the position of the battery cell (single battery) in the stacking direction, and due to overcharging, the degree of electrode deterioration may also fluctuate (deviation).

[0004] The problem to be solved by one embodiment of the present disclosure is to provide a battery pack that suppresses the following phenomenon, namely, the thinning of electrodes located on the lower side (gravity direction side) in the stacking direction of the battery pack increases due to the load, thereby causing fluctuations in the degree of electrode deterioration due to overcharging when charging the battery pack.

[0005] It should be noted that “the upper side in the stacking direction” refers to the direction against gravity, and “the lower side in the stacking direction” refers to the direction of gravity.

[0006] Means for solving the above-mentioned problems include the following.

[0007] <1> A battery pack, the battery pack comprising a plurality of electrodes, the electrodes comprising: a current collector, a negative electrode composite layer provided on one side of the current collector, and a positive electrode composite layer provided on the other side of the current collector, wherein the electrodes are alternately stacked via an electrolyte layer, and the unit area mass (mg / cm2) 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 respectively greater than the unit area mass (mg / cm2) 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 relative to the stacking direction of the battery pack. 2 )big.

[0008] <2> The battery pack according to <1>, wherein the density (g / cm2) of the negative electrode active material or the positive electrode active 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 3 ) is respectively greater than the density (g / cm2) 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 relative to the stacking direction of the battery pack. 3 )big.

[0009] According to the present disclosure, a battery pack can be provided that suppresses the phenomenon in which the electrode located on the lower side (gravity direction side) in the stacking direction of the battery pack becomes thinner due to load and the capacity increases, thereby suppressing the fluctuation (deviation) in the degree of electrode deterioration due to overcharging when charging the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0011] Figure 1 This is a schematic cross-sectional view showing an example of the structure of the battery pack of the present disclosure.

[0012] Figure 2 A coordinate graph showing the relationship between the ratio of the capacity (mAh / g) of the positive or negative electrode of the battery cell (single cell) located at the top and the capacity (mAh / g) of the positive or negative electrode of the battery cell (single cell) located at the bottom and time (number of days of storage) of the battery pack of the present invention.

[0013] Figure 3 A coordinate graph showing the relationship between the difference (%) in initial capacity (mAh / g) between the positive or negative electrode of the uppermost battery cell (single cell) and the positive or negative electrode of the lowermost battery cell (single cell) of the battery pack of the present invention and the years of use (years). DETAILED DESCRIPTION

[0014] The following description is for illustration of the embodiments and does not limit the scope of the present disclosure.

[0015] In the present specification, a numerical range expressed using "to" indicates a range including the numerical values ​​described before and after "to" as the minimum value and the maximum value, respectively.

[0016] In the numerical range recorded in stages in the present embodiment, the upper limit or lower limit recorded in a numerical range can be replaced by the upper limit or lower limit of the numerical range recorded in other stages. In addition, in the numerical range recorded in the present embodiment, the upper limit or lower limit of the numerical range can be replaced by the value shown in the embodiment.

[0017] In the present specification, the term "step" refers not only to an independent step but also to a step that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0018] In this specification, when the embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the sizes of the components in each figure are conceptual, and the relative relationship between the sizes of the components is not limited to this.

[0019] In this specification, each component may include a plurality of substances corresponding thereto. In this embodiment, when the amount of each component in the composition is mentioned, if there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of the plurality of substances present in the composition.

[0020] In this specification, "particle size" refers to the volume average median diameter D 50 .

[0021] <Battery Pack>

[0022] The battery pack disclosed in the present invention is a battery pack having a plurality of electrodes, each of which has: a current collector, a negative electrode composite layer provided on one side of the current collector, and a positive electrode composite layer provided on the other side of the current collector, and the electrodes are alternately stacked via an electrolyte layer, and the unit area mass (mg / cm2) 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 respectively greater than the unit area mass (mg / cm2) 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 relative to the stacking direction of the battery pack. 2 )big.

[0023] The above-mentioned structure can suppress the phenomenon that "the electrodes located on the lower side (gravity direction side) in the stacking direction of the battery pack become thinner due to the load and the capacity increases, thereby causing fluctuations (deviations) in the degree of electrode deterioration due to overcharging when charging the battery pack."

[0024] The battery pack of the present disclosure will be described below with reference to the drawings.

[0025] <Battery Pack>

[0026] Figure 1 1 is a schematic cross-sectional view showing an example of the structure of the battery pack disclosed in the present invention. Figure 1 As shown, the battery pack 100 has a plurality of electrodes 1, each electrode 1 having a current collector C, a negative electrode composite layer 1a disposed on one surface of the current collector C, and a positive electrode composite layer 1b disposed on the other surface of the current collector C, and the electrodes are alternately stacked via an electrolyte layer S.

[0027] In the battery pack 100 of the present disclosure, the unit area mass (mg / cm2) 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 of the electrode 1 located on the upper side in the stacking direction of the battery pack 100 is 2 ) is respectively greater than the unit area mass (mg / cm2) 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 of the electrode 1 located at the lower side in the stacking direction of the battery pack. 2 )big.

[0028] like Figure 1 As shown, the battery pack 100 of the present disclosure preferably has a positive terminal electrode 2a composed of a positive electrode composite layer 1b and a current collector C at the uppermost portion. Also, the battery pack 100 of the present disclosure preferably has a negative terminal electrode 2b composed of a negative electrode composite layer 1a and a current collector C at the lowermost portion.

[0029] (electrode)

[0030] The electrode comprises: a current collector, a negative electrode composite material layer provided on one side of the current collector, and a positive electrode composite material layer provided on the other side of the current collector. The electrode can be easily obtained by applying one of the negative electrode composite material or the positive electrode composite material to one side of the current collector and drying it, and then applying the other composite material to the other side in the same manner and drying it. The electrode can be pressed and cut as needed.

[0031] -Current Collector-

[0032] Examples of the current collector include current collectors 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 can be appropriately selected from one or more metal members depending on the purpose.

[0033] The thickness of the current collector is not particularly limited, and may be, for example, 0.1 μm to 1000 μm.

[0034] - Negative electrode composite layer -

[0035] The negative electrode composite layer includes a negative electrode active material, a conductive agent and a binder.

[0036] Examples of the negative electrode active material include lithium-based active materials such as metallic lithium, carbon-based active materials such as graphite, lithium titanate (e.g., Li4Ti5O 12 ) and other oxide-based active materials, and Si-based active materials such as Si single substance.

[0037] The shape of the negative electrode active material is not particularly limited, and may be, for example, spherical (eg, spherical, ellipsoidal, etc.), fibrous, etc.

[0038] When the shape of the negative electrode active material is spherical, the particle size of the negative electrode active material is, for example, 0.1 μm to 100 μm.

[0039] The specific surface area of ​​the negative electrode active material is, for example, 0.1 m 2 / g~1500m 2 / g.

[0040] Examples of the conductive agent include carbon materials such as acetylene black, Ketjen black, vapor grown carbon fiber (VGCF (registered trademark)), and carbon nanotubes (CNT).

[0041] The content of the conductive agent is, for example, 3% by mass to 5% by mass based on the negative electrode active material.

[0042] Examples of the binder include polyvinylidene fluoride (PVDF) / NMP-based, styrene butadiene rubber (SBR) / water-based, and polytetrafluoroethylene (PTFE) / water-based binders.

[0043] The content of the binder is, for example, 3% by mass to 5% by mass based on the negative electrode active material.

[0044] - Positive electrode composite layer -

[0045] The positive electrode composite layer includes a positive electrode active material, a conductive agent and a binder.

[0046] Examples of the positive electrode active material include lithium composite oxides. Examples of the lithium composite oxides include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc.

[0047] The lithium composite oxide may contain at least one selected from F, Cl, N, S, Br, and I.

[0048] The shape of the positive electrode active material is not particularly limited, and may be, for example, spherical (eg, spherical, ellipsoidal, etc.), fibrous, or the like.

[0049] The particle size of the positive electrode active material is, for example, 0.1 μm to 30 μm.

[0050] The specific surface area of ​​the positive electrode active material is, for example, 0.1 m 2 / g~100m 2 / g.

[0051] As the conductive agent, the same conductive agent as exemplified in the negative electrode mixed material layer can be used.

[0052] The content of the conductive agent is, for example, 3% by mass to 5% by mass based on the positive electrode active material.

[0053] As the binder, the same binder as exemplified in the negative electrode mixed material layer can be used.

[0054] The content of the binder is, for example, 3% by mass to 5% by mass based on the positive electrode active material.

[0055] In the battery pack of the present disclosure, the mass per unit area (mg / cm2) 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 relative to the stacking direction of the battery pack is 2 ) is respectively greater than the unit area mass (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 relative to the stacking direction of the battery pack. 2 ) is large. As a result, the capacity of the electrode increases, and the portion of the electrode located on the upper side corresponding to the difference in internal resistance of the electrode located on the relatively lower side is alleviated, thereby making it easy to suppress the phenomenon that the electrode located on the lower side in the stacking direction of the battery pack increases in capacity due to thinning caused by load, thereby causing fluctuations in the degree of electrode deterioration due to overcharging when charging the battery pack.

[0056] Therefore, the coating of the negative electrode composite or the positive electrode composite (hereinafter referred to as "coating" for simplicity) is preferably performed in the following manner: the unit area mass (mg / cm 2 ) is respectively greater than the unit area mass (mg / cm) of the negative electrode composite or the positive electrode composite of the electrode located at the lower side relative to the stacking direction of the battery pack. 2 )big.

[0057] The coating is preferably performed in the following manner: the mass per unit area (mg / cm2) 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 uppermost portion of the battery pack is 2 ) For example, 10 mg / cm 2 ~50mg / cm 2 The coating is preferably carried out in the following manner: the unit area mass (mg / cm 2 ) For example, 10 mg / cm 2~50mg / cm 2 .

[0058] In addition, for example, when the thickness of the battery pack is 100 mm, the coating may be carried out at a unit area mass (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 ) The unit area mass (mg / cm) of the negative electrode composite or positive electrode composite that is the electrode located at the bottom in the stacking direction of the battery pack 2 ) can be carried out in a manner of 100.5% to 102% of ), for example, it can be carried out in a manner of 101%.

[0059] For example, when the thickness of the battery pack in the stacking direction is 200 mm, the coating may be carried out at a unit area mass (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 ) The mass per unit area of ​​the negative electrode composite or positive electrode composite material that becomes the electrode at the bottom of the battery pack (mg / cm 2 ) can be carried out in a manner of 101% to 104%, for example, it can be carried out in a manner of 102%.

[0060] Mass per unit area (mg / cm 2 ) can be obtained as follows.

[0061] (1) A negative electrode composite material or a positive electrode composite material is coated on a current collector and dried to form a negative electrode composite material layer or a positive electrode composite material layer.

[0062] (2) The area and weight of the negative electrode composite layer or the positive electrode composite layer are measured to calculate the mass per unit area (=weight of the positive electrode composite layer or the negative electrode composite layer / area of ​​the positive electrode composite layer or the negative electrode composite layer).

[0063] In addition, the coating is preferably performed in such a manner that the density (g / cm 3 ) is respectively greater than the density (g / cm2) of the negative electrode active material or the positive electrode active material in the negative electrode composite layer or the positive electrode composite layer of the electrode located at the lower side in the stacking direction of the battery pack. 3 ) is large. As a result, the portion of the increase in the capacity of the electrode corresponding to the difference in internal resistance is mitigated, and therefore, it is easy to suppress the phenomenon that the electrode located at the lower side in the stacking direction of the battery pack increases in capacity due to thinning caused by load, thereby causing fluctuations in the degree of electrode deterioration due to overcharging when charging the battery pack.

[0064] The coating is preferably performed in the following manner: the density (g / cm 3) For example, 1g / cm 3 ~5g / cm 3 The coating is preferably carried out in the following manner: the density (g / cm 3 ) For example, 1g / cm 3 ~5g / cm 3 .

[0065] In addition, for example, when the thickness of the battery pack in the stacking direction is 100 mm, the coating can be carried out in a manner that the density of the negative electrode active material or the positive electrode active material in the negative electrode composite layer or the positive electrode composite layer of the electrode located at the top of the battery pack becomes 100.5% to 102% of the density of the negative electrode active material or the positive electrode active material in the negative electrode composite layer or the positive electrode composite layer of the electrode located at the bottom of the battery pack in the stacking direction, for example, it can be carried out in a manner that becomes 101%.

[0066] In addition, for example, when the thickness of the battery pack in the stacking direction is 200 mm, the coating can be carried out in a manner that the density of the negative electrode active material or the positive electrode active material in the negative electrode composite layer or the positive electrode composite layer of the electrode located at the top of the battery pack becomes 101% to 104% of the density of the negative electrode active material or the positive electrode composite layer of the electrode located at the bottom of the battery pack in the stacking direction, for example, it can be carried out in a manner that it becomes 102%.

[0067] Density (g / cm 3 ) can be passed through the mass per unit area (mg / cm 2 ) divided by the thickness (cm) of the positive electrode active material layer or the negative electrode active material layer.

[0068] (Battery Pack)

[0069] The battery pack of the present disclosure can be obtained by alternately stacking the electrodes and the electrolyte layers S.

[0070] -Electrolyte layer S-

[0071] The electrolyte layer S may include a solid electrolyte layer, or may include a separator and an electrolytic solution.

[0072] When the electrolytic layer S is a solid electrolyte layer, examples of the solid electrolyte include lithium lanthanum zirconate, LiPON, Li 1+x Al x Ge 2-x(PO4)3, Li-SiO glass, Li-Al-SO glass and other oxide solid electrolytes; 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 and other sulfide solid electrolytes. The solid electrolyte layer can be obtained by pressing the solid electrolyte.

[0073] When the electrolyte layer S is a separator and an electrolyte, the separator may be, for example, a resin sheet such as polyethylene (PE) or polypropylene (PP). In addition, the electrolyte contains a predetermined electrolyte and a solvent, and as the predetermined electrolyte, LiPF6, LiBF4, LiAsF6, Li(CF3SO2)2N, Li(C2F5SO2)2N, LiTaF6, LiClO4, LiCF3SO3, etc. may be cited.

[0074] Examples of the solvent include cyclic carbonate solvents such as ethylene carbonate (EC) and propylene carbonate (PC); chain carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The concentration of the electrolyte solution is, for example, 0.1 to 1 mol / L.

[0075] For the battery pack of the present disclosure, assuming that the thickness of the battery pack in the stacking direction is 100 mm, and the thickness of the battery cells (single cells) in the stacking direction is 0.5 mm, after 10 years of use, the thickness of the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack is 1.018 times the thickness of the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack. Figure 3 As shown in FIG. 1 , the difference in initial capacity (mAh / g) between the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack may be 1.8%. In addition, in this case, after 10 years of use, the difference in capacity (mAh / g) between the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack may be 0%.

[0076] For the battery pack of the present disclosure, assuming that the thickness of the battery pack in the stacking direction is 100 mm, and the thickness of the battery cells (single cells) in the stacking direction is 0.5 mm, after 10 years of use, the thickness of the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack is 1.009 times the thickness of the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack. Figure 3 As shown in FIG. 1 , the difference in initial capacity (mAh / g) between the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack may be 0.9%. In addition, in this case, after 5 years of use, the difference in capacity (mAh / g) between the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack may be 0%.

[0077] In the above two examples, from the viewpoint of suppressing the difference in capacity (mAh / g) between the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack after 10 years of use, the former is preferred. In addition, from the viewpoint of suppressing the difference in capacity (mAh / g) between the positive electrode or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive electrode or negative electrode of the battery cell (single cell) located at the bottom of the battery pack during the 10-year use period, the latter is preferred.

[0078] Furthermore, assuming that no load-induced thinning of the electrode occurs, Figure 3 As shown, the difference in initial capacity (mAh / g) sometimes becomes 0%.

[0079] In addition, the battery pack of the present disclosure has a 2 When the weight is 3N, the surface pressure difference between the top and bottom of the battery pack becomes 3kPa. Due to this surface pressure difference, the difference in internal resistance between the positive or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive or negative electrode of the battery cell (single cell) located at the bottom of the battery pack sometimes becomes 1μΩ. In addition, due to this surface pressure difference, the temperature difference between the positive or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive or negative electrode of the battery cell (single cell) located at the bottom of the battery pack sometimes becomes 0.2°C. Moreover, due to this surface pressure difference, after 10 years of use, the difference in capacity (mAh / g) between the positive or negative electrode of the battery cell (single cell) located at the top of the battery pack and the positive or negative electrode of the battery cell (single cell) located at the bottom of the battery pack is according to Figure 2 The calculated value is 1.8%. In this case, the higher the temperature, the greater the tendency of capacity reduction.

Claims

1. A battery pack, the battery pack comprising a plurality of electrodes, the electrodes comprising: a current collector, a negative electrode composite layer provided on one side of the current collector, and a positive electrode composite layer provided on the other side of the current collector, wherein the electrodes are alternately stacked via an electrolyte layer, The mass per unit area (mg / cm2) 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 2 ) is respectively greater than the unit area mass (mg / cm2) 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 relative to the stacking direction of the battery pack. 2 )big.

2. The battery pack according to claim 1, wherein: Density (g / cm2) of the negative active material or positive active material in the negative composite material or positive composite material of the electrode located on the upper side in the stacking direction 3 ) is respectively greater than the density (g / cm2) of the negative electrode active material or the positive electrode active material in the negative electrode composite material layer or the positive electrode composite material layer of the electrode located at the lower side relative to the stacking direction. 3 )big.

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