JP2021197219A - Bipolar type all-solid battery - Google Patents

Abstract

To mainly provide a bipolar type all-solid battery which can suppress an internal short circuit.SOLUTION: In the disclosure hereof, the above problem is solved by providing a bipolar type all-solid battery comprising a plurality of battery cells each having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer containing lithium metal as a negative electrode active material, and a negative electrode current collector in this order. The plurality of battery cells are laminated along a thickness direction and they are electrically connected in series. The bipolar type all-solid battery further comprises a porous metal layer between the positive electrode current collector of one battery cell, and the negative electrode current collector of the other battery cell in a pair of the battery cells.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a bipolar 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. Further, as an all-solid-state battery, a series-stacked all-solid-state battery capable of achieving high energy density and high output density is attracting attention. Disclosed is a bipolar all-solid-state battery comprising a unit cell with an all-solid-state electrolyte in the center, and the collector forming a bipolar structure through surface contact when each unit cell is connected.

Japanese Unexamined Patent Publication No. 2018-186074

For example, by stacking a pair of battery cells so that the positive electrode collector of one battery cell and the negative electrode current collector of the other battery cell are in contact with each other, a bipolar all-solid-state battery connected in series can be obtained. At this time, if the electrical connection between the positive electrode current collector and the negative electrode current collector is non-uniform, a portion where the current density becomes excessive locally occurs during charging, and lidendrite is likely to occur in the negative electrode active material layer. .. When the Lidendrite grows, penetrates the solid electrolyte layer and reaches the positive electrode active material layer, an internal short circuit occurs.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a bipolar all-solid-state battery capable of suppressing an internal short circuit.

In order to solve the above problems, in the present disclosure, a battery having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer containing metallic lithium as a negative electrode active material, and a negative electrode current collector in this order. A plurality of cells are provided, and the plurality of battery cells are stacked along the thickness direction and electrically connected in series, and in the pair of the battery cells, with the positive electrode current collector of one of the battery cells. Provided is a bipolar all-solid-state battery having a foamed metal layer between the negative electrode current collector and the negative electrode current collector of the other battery cell.

According to the present disclosure, by providing a foamed metal layer between a pair of battery cells, it is possible to obtain a bipolar all-solid-state battery capable of suppressing an internal short circuit.

The bipolar all-solid-state battery in the present disclosure has an effect that the occurrence of an internal short circuit can be suppressed.

It is a schematic plan view and a schematic sectional view illustrating the bipolar type all-solid-state battery in the present disclosure.

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

1 (a) is a schematic plan view illustrating the bipolar type all-solid-state battery in the present disclosure, and FIG. 1 (b) is a sectional view taken along the line AA of FIG. 1 (a). As shown in FIG. 1 (b), the bipolar all-solid-state battery 10 includes battery cells C1 and C2. The battery cells C1 and C2 each have a positive electrode current collector 1, a positive electrode active material layer 2, a solid electrolyte layer 3, a negative electrode active material layer 4, and a negative electrode current collector 5 in this order along the thickness direction. Further, the negative electrode active material layer 4 contains metallic lithium as the negative electrode active material. The battery cells C1 and C2 are stacked along the thickness direction and electrically connected in series. Further, in the pair of battery cells C1 and C2, the foamed metal layer 6 is arranged between the positive electrode current collector 1 of the battery cell C2 and the negative electrode current collector 5 of the battery cell C1.

According to the present disclosure, by providing a foamed metal layer between a pair of battery cells, it is possible to obtain a bipolar all-solid-state battery capable of suppressing an internal short circuit. Here, as described above, in the bipolar type all-solid-state battery, if the electrical connection between the positive electrode current collector and the negative electrode current collector facing each other is non-uniform, the current density locally becomes excessive during charging. Is generated, and Lidendrite is likely to occur in the negative electrode active material layer.

In particular, when the positive electrode active material layer in the battery cell is a powder compact, the electrical connection between the positive electrode active material layer and the positive electrode current collector tends to be non-uniform, and accompanying this, the opposing positive electrode current collector and the positive electrode current collector and the positive electrode current collector and the positive electrode current collector are likely to be non-uniform. The electrical connection of the negative electrode current collector also tends to be non-uniform. As a result, an internal short circuit due to Lidendrite is likely to occur. Further, when metallic lithium is used as the negative electrode active material, since metallic lithium is soft, an internal short circuit due to Lidendrite is likely to occur.

On the other hand, in the present disclosure, by providing a foamed metal layer having good elasticity and a concavo-convex structure on the surface between the pair of battery cells, the positive electrode current collector and the negative electrode collector facing each other are provided. The electrical connection of the electric body can be made uniform in the in-plane direction (direction perpendicular to the stacking direction of the battery cells). As a result, Li dendrite is less likely to occur, and the occurrence of an internal short circuit can be suppressed.

1. 1. Battery cell The battery cell in the present disclosure has a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order.

(1) Negative electrode current collector As the material of the negative electrode current collector, any current collector material can be used, and examples thereof include SUS (stainless steel), copper, nickel, and carbon. Further, as the shape of the negative electrode current collector, for example, a foil shape can be mentioned. The thickness of the negative electrode current collector is, for example, 0.1 μm or more, and may be 1 μm or more. On the other hand, the thickness of the negative electrode current collector is, for example, 1 mm or less, and may be 100 μm or less.

(2) Negative electrode active material layer The negative electrode active material layer in the present disclosure contains metallic lithium. Examples of the shape of metallic lithium include a foil shape. Further, the negative electrode active material layer in the present disclosure may be a precipitation type layer by charging. That is, immediately after the battery cell is manufactured, the negative electrode active material layer does not exist between the solid electrolyte layer and the negative electrode current collector, and charging causes precipitation of metallic lithium between the solid electrolyte layer and the negative electrode current collector. A negative electrode active material layer may be formed.

(3) Solid electrolyte layer The solid electrolyte layer in the present disclosure contains at least a solid electrolyte. The solid electrolyte is preferably an inorganic solid electrolyte. Examples of the inorganic solid electrolyte include a sulfide solid electrolyte, an oxide solid electrolyte, and a nitride solid electrolyte.

The shape of the solid electrolyte is preferably particulate. The average particle size (D ₅₀ ) of the solid electrolyte is, for example, 0.01 μm or more. On the other hand, the average particle size (D ₅₀ ) of the solid electrolyte is, for example, 10 μm or less, and may be 5 μm or less. The Li ion conductivity of the solid electrolyte at 25 ° C. is, for example, 1 × 10 ^-4 S / cm or more, and ^{preferably 1 × 10 -3} S / cm or more.

The content of the solid electrolyte in the solid electrolyte layer is, for example, 70% by weight or more, and may be 90% by weight or more. The solid electrolyte layer may contain a binder, if necessary. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 300 μm or less. The solid electrolyte layer may be a powder compact.

(4) Positive Electrode Active Material Layer The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material is not particularly limited, and examples thereof include an oxide active material and a sulfur-based 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 , and LiMn 2} O ₄ and 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. Further, as the oxide active material, Li _{1 + x} Mn _{2- xy My} O ₄ (M is at least one of Al, Mg, Co, Fe, Ni and Zn, 0 <x + y <2). A spinel active material, lithium titanate, may be used. Further, the sulfur-based active material is an active material containing at least S element. The sulfur-based active substance may or may not contain the Li element. Examples of the sulfur-based active material include elemental sulfur, lithium sulfide (Li ₂ S), and lithium polysulfide (Li ₂ Sx, 2 ≦ x ≦ 8).

The positive electrode active material layer may contain at least one of a solid electrolyte, a conductive material and a binder, if necessary. As the solid electrolyte, the solid electrolyte described in the above "(3) Solid electrolyte layer" can be exemplified. The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 300 μm or less. The positive electrode active material layer may be a powder compact. The positive electrode active material layer, which is a powder compact, can have a higher capacity than, for example, a coated body (a positive electrode active material layer manufactured by a coating method).

(5) Positive Electrode Collector As the material of the positive electrode current collector, any current collector material can be used, and examples thereof include SUS, aluminum, nickel, iron, titanium, and carbon. Further, as the shape of the positive electrode current collector, for example, a foil shape can be mentioned. The thickness of the positive electrode current collector is, for example, 0.1 μm or more, and may be 1 μm or more. On the other hand, the thickness of the positive electrode current collector is, for example, 1 mm or less, and may be 100 μm or less.

(6) Battery cell The plan view shape of the battery cell is not particularly limited, and examples thereof include a circle and a rectangle. The size of the battery cell is, for example, 5 mm or more and 30 mm or less. The size of the battery cell means the diameter when the plan view shape is a circle, and means the length of the long side when the plan view shape is a rectangle. The thickness of the battery cell may be, for example, 30 μm or more, 50 μm or more, 100 μm or more, or 500 μm or more. On the other hand, the thickness of the battery cell is, for example, 5 mm or less.

The positive electrode active material layer and the solid electrolyte layer constituting the battery cell can be produced by powder forming (press forming) the respective constituent materials. Further, the battery cell is manufactured, for example, by laminating 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 on a cylindrical mold and pressurizing the battery cell. be able to. As a result, a so-called pellet battery is obtained. Further, the battery cell may be a sintered body and may not be a sintered body.

2. 2. Foamed Metal Layer The foamed metal layer in the present disclosure is a layer arranged between a positive electrode current collector of one battery cell and a negative electrode current collector of the other battery cell in a pair of battery cells. Since the foamed metal layer has pores inside, it has good elasticity during pressing. Further, the foamed metal layer has an uneven structure associated with pores on the surface. Furthermore, the foamed metal layer usually has electron conductivity.

The foamed metal constituting the foamed metal layer is not particularly limited, and examples thereof include simple substances such as nickel, aluminum, copper, and iron, and alloys containing at least one of these metals. The foamed metal may be a continuous pore body (open cell body) or a single pore body (single bubble body). Further, the porosity of the foamed metal is, for example, 50% or more, and may be 70% or more.

The thickness of the foamed metal layer is not particularly limited, but may be, for example, 20 μm or more, and may be 50 μm or more. If the metal foam layer is too thin, it may not be possible to make the electrical connections between the opposing positive and negative current collectors uniform in the in-plane direction. On the other hand, the thickness of the foamed metal layer is, for example, 3000 μm or less, and may be 1500 μm or less. If the metal foam layer is too thick, the energy density of the bipolar all-solid-state battery may decrease.

The plan view shape of the foamed metal layer is not particularly limited, and examples thereof include a circle and a rectangle. The size of the foamed metal layer is, for example, 5 mm or more and 30 mm or less. The size of the foamed metal layer means the diameter when the plan view shape is a circle, and means the length of the long side when the plan view shape is a rectangle. The area of the foamed metal layer is, for example, 70% or more, may be 80% or more, or 90% or more, with respect to the area of the overlapping region where the positive electrode current collector and the negative electrode current collector overlap in a plan view. It may be.

3. 3. Bipolar all-solid-state battery The bipolar all-solid-state battery in the present disclosure includes a plurality of battery cells. The number of battery cells is at least 2 or more, and may be 3 or more, 5 or more, or 10 or more. On the other hand, the number of battery cells is, for example, 200 or less. The bipolar all-solid-state battery is usually a lithium-ion battery. Further, the bipolar type all-solid-state battery is usually a secondary battery that can be charged and discharged.

The bipolar all-solid-state battery may have a battery case for accommodating a plurality of battery cells. Examples of the shape of the bipolar all-solid-state battery include a coin type, a laminated type, a cylindrical type, and a square type. Further, the bipolar all-solid-state battery may have a restraining jig that applies a restraining pressure to a plurality of battery cells in the thickness direction. The confining pressure is, for example, 0.1 MPa or more, may be 1 MPa or more, or may be 5 MPa or more. On the other hand, the restraining pressure is, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

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.

(Example 1)
Negative electrode current collector (Cu foil), negative electrode active material layer (metal Li), solid electrolyte layer (sulfide solid electrolyte and binder), positive electrode active material layer (LiNi _1/3 Co _1/3 Mn _{1) in a ceramic cylinder. / 3} O ₂ , sulfide solid electrolyte, conductive material and binder) and a positive electrode current collector (Al foil) were put in and uniaxially pressed. Then, a pellet battery was manufactured by punching with a SUS pin. Another pellet battery was manufactured by the same procedure. Nickel foam (foamed metal layer) was placed on the upper part of the positive electrode current collector of the produced pellet battery, and the negative electrode current collector of another pellet battery was layered on the upper part so as to be in contact with the negative electrode collector. The prepared laminate was placed in a cylindrical container and screw-constrained at a pressure of 20 kgf to obtain a bipolar all-solid-state battery.

(Comparative Example 1)
A bipolar all-solid-state battery was obtained in the same manner as in Example 1 except that a SUS plate was used instead of nickel foam.

(Comparative Example 2)
A bipolar all-solid-state battery was obtained in the same manner as in Example 1 except that nickel foam was not used.

(evaluation)
Charge / discharge tests were performed on the bipolar all-solid-state batteries obtained in Example 1 and Comparative Examples 1 and 2. The charge / discharge test was performed in a constant temperature bath at 60 ° C. with a current value of 0.5 mA / cm ² and a voltage range of 4.0 V-8.74 V using a charge / discharge device (HJ1001SD8 manufactured by Hokuto Denko Co., Ltd.). The evaluation results are shown in Table 1.

In the bipolar all-solid-state battery (Example 1) manufactured using nickel foam, the capacity per positive electrode active material was 125 mAh / g, and the battery could be charged and discharged at an average discharge voltage of 7.6 V. On the other hand, a bipolar all-solid-state battery manufactured by using a SUS plate instead of nickel foam (Comparative Example 1) and a bipolar all-solid-state battery in which each pellet battery is directly coupled without using nickel foam (Comparative Example 2). In), a short circuit occurred during charging and evaluation could not be performed. In Comparative Examples 1 and 2, it is considered that the electrical connection between the positive electrode current collector and the negative electrode current collector was non-uniform, and an internal short circuit due to the Lidendrite occurred.

1 ... Positive electrode current collector 2 ... Positive electrode active material layer 3 ... Solid electrolyte layer 4 ... Negative electrode active material layer 5 ... Negative electrode current collector 6 ... Foamed metal layer C ... Battery cell 10 ... Bipolar all-solid-state battery

Claims (1)

A plurality of battery cells having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer containing metallic lithium as a negative electrode active material, and a negative electrode current collector in this order are provided.
The plurality of battery cells are stacked along the thickness direction and electrically connected in series.
A bipolar all-solid-state battery having a foamed metal layer between the positive electrode current collector of one of the battery cells and the negative electrode current collector of the other battery cell in the pair of battery cells.

Images