JP2022092808A - All-solid battery - Google Patents

Abstract

To provide an all-solid battery capable of suppressing fluctuation in restraint pressure associated with charge and discharge.SOLUTION: Provided is an all-solid battery having a negative electrode current collector, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. The negative electrode active material layer contains an Si-based active material as a negative electrode active material. The negative electrode current collector is a nickel foil having a through-hole penetrating in a thickness direction, an opening area ratio by the through-hole being 16% or more and 40% or less.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an all-solid-state battery.

The all-solid-state battery is a battery having a solid electrolyte layer between the positive electrode layer and the negative electrode layer, and has an advantage that the safety device can be easily simplified as compared with a liquid-based battery having an electrolytic solution containing a flammable organic solvent. Have.

It has been proposed to use a metal foil having a large number of through holes as a current collector of a battery (Patent Documents 1 to 3). For example, in Patent Document 1, by providing a through hole, the active material layer is suppressed from being separated from the current collector. Further, as a negative electrode active material used for the negative electrode layer of a battery, an active material containing Si (Si-based active material) is known (Patent Document 4).

Japanese Unexamined Patent Publication No. 05-290853 Japanese Unexamined Patent Publication No. 2017-004914 Japanese Unexamined Patent Publication No. 2000-294250 Japanese Unexamined Patent Publication No. 2020-091974

The Si-based active material has an advantage that the theoretical capacity per volume is large, but on the other hand, the volume change due to charge / discharge is large. Since the young rate of the electrode of the all-solid-state battery is higher than that of the liquid-based battery, when a Si-based active material having a large expansion and contraction is used as the negative electrode active material, the fluctuation of the restraining pressure of the all-solid-state battery may be large. If the fluctuation of the confining pressure is large, a short circuit may occur due to peeling or sliding of the negative electrode active material layer.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an all-solid-state battery capable of suppressing fluctuations in restraining pressure due to charging and discharging.

In order to solve the above problems, in the present disclosure, an all-solid-state battery having a negative electrode current collector, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order is the negative electrode. The active material layer contains a Si-based active material as a negative electrode active material, and the negative electrode current collector has through holes penetrating in the thickness direction, and the opening area ratio of the through holes is 16% or more and 40% or less. Provided is an all-solid-state battery which is a nickel foil.

According to the present disclosure, by using a nickel foil having a through hole and a predetermined opening area ratio as a negative electrode current collector, fluctuations in the restraining pressure due to expansion and contraction of the Si-based active material due to charging and discharging are performed. It is possible to provide an all-solid-state battery in which the amount of electricity is suppressed.

In the present disclosure, it is possible to provide an all-solid-state battery in which fluctuations in restraining pressure due to charging and discharging are suppressed.

It is a schematic sectional drawing which shows an example of the all-solid-state battery in this disclosure. It is a schematic sectional drawing which shows another example of the all-solid-state battery in this disclosure. It is a figure for demonstrating the measuring method of the restraint pressure fluctuation in an Example and a comparative example.

Hereinafter, the all-solid-state battery in the present disclosure will be described in detail.

FIG. 1 is a schematic cross-sectional view showing an example of the all-solid-state battery of the present disclosure. The all-solid-state battery 10 shown in FIG. 1 has a negative electrode current collector 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5 in this order in the thickness direction. In the present disclosure, the negative electrode active material layer 2 contains a Si-based active material as the negative electrode active material, the negative electrode current collector 1 has a through hole penetrating in the thickness direction, and the opening area ratio by the through hole is 16. It is characterized by being a nickel foil having a percentage of% or more and 40% or less.

As described above, since the conventional all-solid-state battery using the Si-based active material as the negative electrode active material has a high young rate of the electrode, the expansion and contraction of the Si-based active material during charging and discharging affects the entire battery. , The fluctuation of the restraining pressure of the all-solid-state battery is large.

On the other hand, in the all-solid-state battery in the present disclosure, the negative electrode current collector is a nickel foil having through holes penetrating in the thickness direction and having an opening area ratio of 16% or more through the through holes. In the present disclosure, by using a nickel foil having an opening area ratio of through holes of a predetermined value or more, for example, during charging, when pressure is applied in the stacking direction due to expansion of the Si-based active material, the through holes are formed. The nickel foil can be elastically deformed so as to be crushed. Therefore, it is possible to suppress fluctuations in the restraining pressure of the all-solid-state battery due to expansion and contraction of the Si-based active material. In addition, cracking, peeling, and slipping of the negative electrode active material layer due to expansion and contraction of the Si-based active material can be suppressed. On the other hand, when the opening area ratio is 40% or less, the nickel foil has sufficient strength, so that tearing or the like due to a press during battery manufacturing can be suppressed. Further, in the all-solid-state battery in the present disclosure, since the active material can be filled in the through hole of the negative electrode current collector, the negative electrode capacity can be increased. It is also possible to improve the adhesion between the negative electrode current collector and the negative electrode active material layer.

1. 1. Negative electrode current collector The negative electrode current collector in the present disclosure is a nickel foil having through holes penetrating in the thickness direction. The opening area ratio by the through hole is 16% or more, and may be 24% or more. If it is equal to or more than the above value, the fluctuation of the restraining pressure of the all-solid-state battery can be suppressed. If it is smaller than the above value, the effect of suppressing the fluctuation of the restraining pressure due to the through hole cannot be sufficiently obtained. In the present specification, the opening area ratio is the total area of the through holes with respect to the area of the entire nickel foil (including the through holes) in the plan view of the nickel foil.

On the other hand, the opening area ratio due to the through hole is 40% or less, and may be 32% or less. When it is not more than the above value, the decrease in the strength of the current collector can be suppressed, and for example, the foil tearing at the time of manufacturing the battery can be suppressed.

The number of through holes in the nickel foil is not particularly limited as long as it is one or more, but for example, it may be two or more, and may be 10 or more or 100 or more. Further, when the number of through holes is two or more, it is preferable that the through holes are not biased to a part of the region in the nickel foil and are evenly distributed. This is because the fluctuation of the restraining pressure can be suppressed evenly by arranging the plurality of through holes evenly distributed.

The hole diameter (opening diameter) of the through hole of the negative electrode current collector is not particularly limited. The lower limit of the opening diameter of the negative electrode current collector is, for example, 1 μm or more, and may be 10 μm or more. The upper limit is, for example, 300 μm or less, and may be 200 μm or less. The opening diameter referred to here is the diameter of the circumscribed circle of the opening of the through hole. The diameter of the circumscribed circle is a value averaged by observing the surface of the current collector with a microscope or the like.

The shape of the through hole is not particularly limited, and examples thereof include a round shape, a quadrangle shape, a rhombus shape, a hexagonal shape, a hexagonal shape, a square shape, a star shape, and a cross shape.

The thickness of the nickel foil as the negative electrode current collector is not particularly limited, but may be, for example, 10 μm or more, or 20 μm or more. On the other hand, for example, it may be 50 μm or less and 40 μm or less. It is preferable that the negative electrode current collector and the negative electrode active material layer are in direct contact with each other.

2. 2. Negative electrode active material layer The negative electrode active material layer in the present disclosure contains a Si-based active material as a negative electrode active material. The Si-based active material is preferably an active material that can be alloyed with Li. Examples of the Si-based active material include simple substances of Si, Si alloys, and Si oxides. The Si alloy preferably contains a Si element as a main component. The ratio of the Si element in the Si alloy may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more.

The content of the Si-based active material is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the ratio of the Si-based active material is, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

The average particle size (D ₅₀ ) of the Si-based active material is not particularly limited, but is, for example, 5 μm or more, and may be 10 μm or more. On the other hand, the average particle size (D ₅₀ ) is, for example, 20 μm or less, and may be 15 μm or less. The average particle size (D ₅₀ ) can be calculated from, for example, measurement by a laser diffraction type particle size distribution meter or a scanning electron microscope (SEM).

Further, the negative electrode active material layer in the present disclosure may further contain at least one of a conductive material, a binder and a solid electrolyte, if necessary. Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB); and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). .. Examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR); and fluoride-based binders such as polyvinylidene fluoride (PVDF). The solid electrolyte will be described in "3. Solid electrolyte layer". The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

3. 3. Solid electrolyte layer The solid electrolyte layer is a layer formed between the positive electrode active material layer and the negative electrode active material layer, and is a layer containing at least a solid electrolyte. Further, the solid electrolyte layer may contain only the solid electrolyte, or may further contain a binder.

Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes; and organic polymer electrolytes such as polymer electrolytes. Among these, a sulfide solid electrolyte is particularly preferable. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

4. Positive electrode active material layer The positive electrode active material layer contains at least a positive electrode active material, and may contain a conductive material, a solid electrolyte, and a binder, if necessary. Examples of the positive electrode active material include an oxide active material. Examples of the oxide active material include rock salt layered active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , Li ₄ Examples thereof include spinel-type active materials such as Ti ₅ O ₁₂ and Li (Ni _0.5 Mn _1.5 ) O ₄ , and olivine-type active materials such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , and LiCoPO ₄ . The surface of the positive electrode active material may be coated with an ion conductive oxide. Examples of the ion conductive oxide include LiNbO ₃ .

The ratio of the positive electrode active material in the positive electrode active material layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the ratio of the positive electrode active material is, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less. The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

The solid electrolyte, the conductive material, and the binder are the same as those described in "1. Negative electrode active material layer" above, and thus the description thereof is omitted here.

5. Positive Electrode Collector The material of the positive electrode current collector is not particularly limited, and examples thereof include SUS, aluminum, nickel, iron, titanium, and carbon.

6. Specific Embodiment of All-Solid State Battery The type of all-solid-state battery in the present disclosure is not particularly limited, but is typically a lithium ion battery. Further, the all-solid-state battery in the present disclosure may be a primary battery or a secondary battery, but a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful as an in-vehicle battery, for example.

The all-solid-state battery in the present disclosure may be a single battery or a laminated battery. The laminated battery may be a monopolar type laminated battery (parallel connection type laminated battery) or a bipolar type laminated battery (series connection type laminated battery). Examples of the shape of the battery include a coin type, a laminated type, a cylindrical type, and a square type.

FIG. 2 is a schematic cross-sectional view showing another example of the all-solid-state battery in the present disclosure, and is a schematic cross-sectional view showing a state in which a plurality of power generation units are connected in parallel. In the all-solid-state battery 100 shown in FIG. 2, the negative electrode current collector 1 and the first negative electrode active material layer 2a, the first solid electrolyte layer 3a, and the first are arranged in order from one surface s11 of the negative electrode current collector 1. The second negative electrode active material layer 2b, the second solid electrolyte layer 3b, and the second positive electrode activity arranged in order from the positive electrode active material layer 4a and the first positive electrode current collector 5a and the other surface s12 of the negative electrode current collector 1. It has a material layer 4b and a second positive electrode current collector 5b. The first positive electrode current collector 5a and the second positive electrode current collector 5b are connected to form a positive electrode tab 5t. A negative electrode tab 1t is connected to the negative electrode current collector 1. Further, an insulating property is provided between the second positive electrode current collector 5b and the side surface of the negative electrode (negative electrode current collector 1, first negative electrode active material layer 2a, second negative electrode active material layer 2b) to prevent a short circuit. The protective layer 7 is arranged.

In the present disclosure, the negative electrode active material layer 2 contains a Si-based active material as the negative electrode active material, the negative electrode current collector 1 has a through hole penetrating in the thickness direction, and the opening area ratio by the through hole is 16. % Or more and 40% or less of the nickel foil. Such a nickel foil pushes through holes when pressure is applied in the stacking direction due to expansion of the Si-based active material in the first negative electrode active material layer 2a and the second negative electrode active material layer 2b, for example, during charging. It can be elastically deformed to be crushed. Therefore, it is possible to suppress fluctuations in the restraining pressure of the all-solid-state battery due to expansion and contraction of the Si-based active material.

For example, in an all-solid-state battery containing an inorganic solid electrolyte, it is necessary to press the electrode body at a very high pressure in order to form a good ion conduction path. At this time, in the all-solid-state battery shown in FIG. 2, since the configurations of the other layers are symmetrical with respect to the negative electrode current collector, the stress due to the difference in elasticity between the positive electrode active material layer and the negative electrode active material layer is increased. There is an advantage that it is unlikely to occur.

The present disclosure is not limited to the above embodiment. The above embodiment is an example, and any object having substantially the same structure as the technical idea described in the claims of the present disclosure and having the same effect and effect is the present invention. Included in the technical scope of the disclosure.

[Preparation of evaluation cell]
(Example 1)
Si _- based negative electrode active material (Si alone), dispersion medium (butyl butyrate), binder (5 wt% butyl butyrate solution of PVdF-based binder), and sulfide solid electrolyte (Li 2SP ₂ containing LiBr and LiI). A paste _- like negative electrode composition was prepared by mixing S5 glass ceramic) and a conductive material (VGCF). This composition was applied onto a Ni foil having through holes (negative electrode current collector opening area ratio 16%, thickness 24 μm) and dried to form a negative electrode active material layer.

Positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), dispersion medium (butyl butyrate), binder (5 wt% butyl butyrate solution of PVdF-based binder), and sulfide solid electrolyte (LiBr, A Li ₂ SP ₂ S ₅ series glass ceramic containing LiI) and a conductive material (VGCF) were mixed to prepare a paste-like positive electrode composition. This composition was applied onto an aluminum foil (positive electrode current collector) having a thickness of 10 μm and dried to form a positive electrode active material layer.

A solid electrolyte by mixing a dispersion medium (heptane), a binder (a _{5 wt% heptane solution of butadiene rubber) and a sulfide solid electrolyte (Li 2SP 2S 5 glass ceramic} containing LiBr and LiI). The composition was prepared. This composition was applied to an aluminum foil (substrate) and dried to form a solid electrolyte layer.

The solid electrolyte layer was laminated on the positive electrode active material layer and pressed so that the solid electrolyte layer was in contact with the positive electrode active material layer. Then, the substrate (aluminum foil) of the solid electrolyte layer was peeled off, and the negative electrode active material layer was laminated and pressed so that the solid electrolyte layer was in contact with the negative electrode active material layer. In this way, an evaluation cell as shown in FIG. 3A was produced. The thickness of the positive electrode active material layer (density 3.7 g / cc) is 70.0 μm, the thickness of the solid electrolyte layer is 15.0 μm, and the thickness of the negative electrode active material layer (density 1.8 g / cc) is 45.3 μm. Met. The electrode area was 1 cm ² .

(Examples 2 to 4, Comparative Examples 1 to 3)
An evaluation cell was obtained in the same manner as in Example 1 except that a Ni foil having an opening area ratio shown in Table 1 was used as the negative electrode current collector.

[Evaluation of restraint pressure fluctuation]
Four evaluation cells prepared in Example 1 above were set in a jig as shown in FIG. 3 (b), fluctuations in the restraint pressure were measured by a load cell, and the effect of suppressing the fluctuations in the restraint pressure was evaluated. Specifically, the effect of suppressing fluctuations in restraint pressure was evaluated from the following equation. The results are shown in Table 1.
Constriction pressure fluctuation (ΔMPa / mAh) = (constraint pressure at the end of charging (MPa) -constraint pressure at the start of charging (MPa)) / (number of cells x capacity at the end of charging (mAh))
Similarly, the evaluation cells of Examples 2 to 4 and Comparative Examples 1 to 3 were also evaluated.

[Negative electrode active material layer crack]
In the 2C charge / discharge cycle evaluation (n = 4) of the above evaluation cell, the case where 10 cycles of charge / discharge are performed and the capacity retention rate at the 10th cycle is 90% or less exists even at n = 1 is defined as x. , Others were evaluated as 〇. In the cell whose evaluation result was ×, it was confirmed that the active material layer cracked due to the large fluctuation of the restraining pressure at the time of cell dismantling.

[Ripped foil]
The presence or absence of foil tearing caused by pressing the positive electrode, the solid electrolyte layer, and the negative electrode during battery production was evaluated (n = 5 under the same pressing conditions). Those in which tearing occurred even with n = 1 were evaluated as x, and those in which no tear occurred were evaluated as 〇. The tearing of the negative electrode current collector foil (Ni foil) occurred at the boundary between the coated portion and the uncoated portion of the composition for the negative electrode active material layer on the negative electrode current collector foil.

[criterion]
The characteristic range in which the evaluation result of [negative electrode active material layer crack] was 〇 and the evaluation result of [foil tear] was 〇 was evaluated as 〇.

From the results in Table 1, the all-solid-state batteries (Examples 1 to 4) of the present disclosure using a nickel foil having an opening area ratio of 16% or more and 40% or less as a negative electrode current collector suppress fluctuations in restraining pressure. It was possible and no foil tear occurred during battery manufacturing. Further, in the all-solid-state battery in the present disclosure, since the through hole of the nickel foil is filled with the negative electrode active material, the degree of the negative electrode is increased, and the negative / positive capacity ratio can be improved.

1 ... Negative electrode current collector (nickel foil with through holes)
2 ... Negative electrode active material layer 3 ... Solid electrolyte layer 4 ... Positive electrode active material layer 5 ... Positive electrode current collector 10, 100 ... All-solid-state battery

Claims (1)

An all-solid-state battery having a negative electrode current collector, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order.
The negative electrode active material layer contains a Si-based active material as a negative electrode active material, and the negative electrode active material layer contains a Si-based active material.
The negative electrode current collector is an all-solid-state battery which is a nickel foil having a through hole penetrating in the thickness direction and having an opening area ratio of 16% or more and 40% or less.

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