JP7753115B2 - Battery module - Google Patents

Description

The present invention relates to a battery module made up of multiple stacked all-solid-state batteries.

In order to maintain low interfacial resistance between the solid electrolyte and the active material layers of the positive and negative electrodes, the electrode assembly, which has a laminated structure of the positive electrode, solid electrolyte, and negative electrode, is pressurized in the stacking direction (see, for example, Patent Document 1). For example, a pressing mechanism that presses the exterior member that houses the electrode assembly in the thickness direction is disposed on the outside of the exterior member, and the pressing force generated by the pressing mechanism presses the all-solid-state battery in the stacking direction.

JP 2013-062174 A

However, with all-solid-state batteries like the one described above, if the all-solid-state battery reaches a certain temperature or higher and the lithium metal melts, the pressure applied by the pressing mechanism can push the molten lithium out.

The problem that the present invention aims to solve is to provide a battery module that can prevent molten lithium from being extruded to the outside even when the temperature of the all-solid-state battery exceeds a predetermined value and the lithium metal melts.

The present invention solves the above problem by having the pressure mechanism form a guide path through the surface pressure distribution when the temperature of the all-solid-state battery reaches or exceeds the melting point of lithium, and then guide the molten lithium to the buffer section through this guide path.

According to the present invention, when the temperature of the all-solid-state battery reaches or exceeds the melting point of lithium, the pressure mechanism forms a guide path through the surface pressure distribution, and this guide path guides the molten lithium to the buffer section, thereby preventing the molten lithium from being pushed out to the outside.

FIG. 1 is a perspective view showing an example of a battery module according to an embodiment of the present invention. 2A is a cross-sectional view taken along line IIa-IIa in FIG. 1, and FIG. 2B is a cross-sectional view taken along line IIb-IIb in FIG. 2A. FIG. 3 is a cross-sectional view showing a modification of the first adhesive and the second adhesive in the battery module according to the embodiment of the present invention.

The battery module according to this embodiment will be described with reference to the drawings. Figure 1 is a perspective view showing an example of a battery module according to this embodiment. Figure 2(a) is a cross-sectional view taken along line IIa-IIa in Figure 1, and Figure 2(b) is a cross-sectional view taken along line IIb-IIb in Figure 2(a).

The battery module 1 in this embodiment is mounted on a mobile object such as an automobile. The use of the battery module 1 is not particularly limited, and it may be mounted on, for example, an electronic device. As shown in FIG. 1 , the battery module 1 includes a battery pack 2 and a pressure mechanism 3 that applies surface pressure to the battery pack 2.

As shown in FIG. 1 , the pressure mechanism 3 applies surface pressure to both end surfaces of the battery pack 2 in the stacking direction of the battery pack 2 (the X direction in the figure). The pressure mechanism 3 includes a first plate 31, a second plate 32, and multiple (four in this example) fasteners 33. The first and second plates 31, 32 are rigid plates made of metal or other materials, and sandwich the battery pack 2 from both ends in the stacking direction. The fasteners 33 fasten the first and second plates 31, 32 together so that the distance between them can be adjusted. The fasteners 33 press the first and second plates 31, 32 toward the battery pack 2, causing the first and second plates 31, 32 to apply surface pressure to the battery pack 2.

As shown in Figures 1 and 2(a), the battery pack 2 includes a plurality of (eight in this example) all-solid-state batteries 20, a plurality of (nine in this example) bus bars 21, a first adhesive 22 interposed between the all-solid-state batteries 20, and a second adhesive 23 interposed between the all-solid-state batteries 20.

The all-solid-state battery 20 shown in FIG. 2(a) is in a charged state. This charged state refers to a state in which the SOC (State of Charge) is greater than 0%. As will be described in detail later, in the all-solid-state battery 20 of this embodiment, an anode layer 207 made of lithium metal is deposited on the anode current collector 205 during charging. Conversely, when the all-solid-state battery 20 is in a fully discharged state, the anode layer 207 disappears. Note that a fully discharged state refers to a state in which the SOC of the all-solid-state battery 20 is 0%. Furthermore, the all-solid-state battery 20 is not limited to one in which an anode layer is not present when fully charged, and may be one in which an anode layer is present when fully discharged.

As shown in FIG. 2(a), this all-solid-state battery 20 includes a positive electrode current collector 201, a positive electrode tab 202, a positive electrode layer 203, a solid electrolyte layer 204, a negative electrode current collector 205, a negative electrode tab 206, a negative electrode layer 207, and an exterior member 208. Hereinafter, the laminate formed by stacking the positive electrode current collector 201, the positive electrode tab 202, the positive electrode layer 203, the solid electrolyte layer 204, the negative electrode current collector 205, the negative electrode tab 206, and the negative electrode layer 207 may be referred to as the electrode assembly.

The positive electrode current collector 201 is a conductive plate-like (or foil-like) member and is made of, for example, a metal or a conductive resin, although it is not particularly limited thereto. Examples of metals that can be used include aluminum, nickel, iron, stainless steel, titanium, and copper. Alternatively, a clad material of nickel and aluminum, or a clad material of copper and aluminum may also be used. Examples of conductive resins include resins in which a conductive filler is added to a non-conductive polymer material.

Like the positive electrode current collector 201, the positive electrode tab 202 is a conductive plate-like (or foil-like) member and is made of, for example, but not limited to, a metal or a conductive resin. The metal and conductive resin may be made of the same materials as those used to make the positive electrode current collector 201. One end of the positive electrode tab 202 is connected to the positive electrode current collector 201, and the other end extends outside the exterior member 208. The positive electrode tab 202 is electrically connected to the negative electrode tab 206 of another all-solid-state battery 20 via a bus bar 21.

The positive electrode layer 203 is formed on the main surface of the positive electrode current collector 201. This positive electrode layer 203 contains at least a positive electrode active material capable of absorbing and releasing lithium (Li) metal, and although not particularly limited, preferably contains a positive electrode active material containing sulfur. The sulfur-containing positive electrode active material may be a material that utilizes the oxidation-reduction reaction of sulfur to release lithium ions during charging and absorb lithium ions during discharging. The type of sulfur-containing positive electrode active material is not particularly limited, but particles or thin films of elemental sulfur (S), organic sulfur compounds, or inorganic sulfur compounds can be used.

The organic sulfur compound is not particularly limited, but examples thereof include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polycarbon sulfide, etc. The inorganic sulfur compound is not particularly limited, but examples thereof include S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li ₂ S, MoS ₂ , MoS ₃ , etc. Note that a positive electrode active material that does not contain sulfur may also be used.

A solid electrolyte layer 204 is interposed between the positive electrode layer 203 and the negative electrode layer 207. When the all-solid-state battery 20 is fully discharged, the solid electrolyte layer 204 is in contact with the negative electrode current collector 205. As the solid electrolyte, for example, a sulfide solid electrolyte or an oxide solid electrolyte can be used, but it is preferable to use a sulfide solid electrolyte.

Examples of the sulfide solid electrolyte include LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ S-P ₂ S ₅ , LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS ₄ , Li ₃ PS ₄ , Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S—SiS ₂ —LiBr, Li ₂ S—SiS ₂ —LiCl, Li ₂ S—SiS ₂ —B ₂ S ₃ —LiI, Li ₂ S—SiS ₂ —P ₂ S ₅ —LiI, Li ₂ S—B ₂ S ₃ , Li ₂ S—P ₂ S ₅ —Z _m S _n (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ —Li _x MO _y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). The term "Li ₂ S-P ₂ S ₅ " means a sulfide solid electrolyte obtained using a raw material composition containing Li ₂ S and P ₂ S ₅ , and the same applies to the other descriptions above. Alternatively, sulfide glass or the like may be used as the sulfide solid electrolyte.

The oxide solid electrolyte may be, for example, a compound having a NASICON structure. Examples of the compound having a NASICON structure include a compound (LAGP) represented by the general formula Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ (0≦x≦2) and a compound (LATP) represented by the general formula Li1 _{+xAlxTi2 - x} ( _PO4 ) ₃ (0 _≦ x _{≦ 2} ). Other examples of the oxide solid electrolyte include LiLaTiO (e.g., Li0.34La0.51TiO3), LiPON ₍ e.g. _{, Li2.9PO3.3N0.46} ) _, and LiLaZrO ₍ e.g. _{, Li7La3Zr2O12} ).

Like the positive electrode current collector 201, the negative electrode current collector 205 is a conductive plate-shaped (or foil-shaped) member and is not particularly limited, but is made of, for example, a metal or a conductive resin. The metal and conductive resin may be made of the same materials as those used to make the positive electrode current collector 201 described above.

Like the negative electrode current collector 205, the negative electrode tab 206 is a conductive plate-like (or foil-like) member and is made of, for example, but not limited to, a metal or a conductive resin. The metal and conductive resin may be made of the same materials as those used to make the negative electrode current collector 205. One end of the negative electrode tab 206 is connected to the negative electrode current collector 205, and the other end extends outside the exterior member 208. The negative electrode tab 206 is electrically connected to the positive electrode tab 202 of another all-solid-state battery 20 via a bus bar 21.

The anode layer 207 is a lithium metal layer composed primarily of lithium metal that is released from the cathode layer 203, reaches the main surface of the anode current collector 205 via the solid electrolyte layer 204, and precipitates thereon as the all-solid-state battery 20 is charged. The volume of this lithium metal layer increases as alkali metal precipitates as the all-solid-state battery 20 is charged, but decreases as the alkali metal disappears (moves toward the cathode layer 203) as the battery is discharged.

The exterior member 208 houses the electrode assembly. This exterior member 208 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order. The fusion portion is made of, for example, polyethylene or polypropylene, the metal portion is made of, for example, aluminum foil, and the protection layer is made of, for example, nylon.

As shown in FIG. 2(b), the exterior member 208 in this embodiment has a substantially rectangular planar shape. As shown in FIG. 2(a), this exterior member 208 is formed by folding a strip-shaped film at folding portion 208a, and then bonding and sealing three sides of the rectangle with sealing material 209. This bonding process forms first to third seal portions 208b to 208d. Note that, while this embodiment illustrates a case in which three sides of the film are bonded using sealing material 209, this is not limiting. For example, the first to third seal portions 208b to 208d may be formed by heat-sealing the adhesive layer of the exterior member 208.

The buffer section 208e stores molten lithium that melts from the negative electrode layer 207 when the temperature of the all-solid-state battery 20 reaches or exceeds the melting point of lithium. The melting point of lithium is, for example, approximately 180°C. In this embodiment, the buffer section 208e is an internal space formed between the folded section 208a of the exterior member 208 and the electrode body. Because the exterior member 208 has a metal layer made of aluminum foil or the like, this metal layer prevents the molten lithium stored in the buffer section 208e from leaking out of the all-solid-state battery 20 at the folded section 208a. However, if the molten lithium reaches the first to third seal sections 208b to 208d, there is a risk that the molten lithium will leak out because the melting point of the seal material 209 is at most approximately 160°C.

In this embodiment, the buffer portion 208e is provided at the bottom of the battery module 1. This makes it easier for the molten lithium to flow into the buffer portion 208e due to gravity, preventing the molten lithium from leaking out of the all-solid-state battery 20.

In addition, in this embodiment, the buffer section 208 is provided on the long side of the rectangle, and the length of the buffer section 208 is longer than the short side of the rectangle. This shortens the distance that the molten lithium travels to the buffer section 208, and also allows the volume of the buffer section 208 to be increased within the all-solid-state battery 20.

As shown in Figures 2(a) and 2(b), the above-described plurality of all-solid-state batteries 20 are bonded to one another via a first adhesive 22 and a second adhesive 23. As shown in Figure 2(b), the first adhesive 22 is provided in a first region _R1 on the main surface of the all-solid-state battery 20. On the other hand, the second adhesive 23 is provided in a second region _R1 on the main surface of the all-solid-state battery 20. In this embodiment, the first and second regions _R1 , _R2 have rectangular planar shapes, and the second region _R2 is provided below the first region _R1 . In other words, the second region _R2 is provided closer to the buffer section 208e than the first region _R1 .

The first adhesive 22 and the second adhesive 23 are made of adhesives with different softening points, with the softening point _T1 of the first adhesive 22 being higher than the softening point _T2 of the second adhesive 23 ( _T1 > _T2 ). The softening point _T1 of the first adhesive 22 may be, for example, higher than 100°C ( _T1 > 100°C), and the softening point _T2 of the second adhesive 23 may be, for example, 100°C or higher and 180°C or lower (180°C ≧ _T2 ≧ 100°C). Examples of materials constituting the first adhesive 22 include adhesive resins such as epoxy resin and silicone resin. The second adhesive 23 may also be made of the same resin as the material constituting the first adhesive 22. Note that the materials constituting the first adhesive 22 and the second adhesive 23 may be different materials.

When the temperature of the all-solid-state battery 20 is within the normal range (e.g., below 100°C), the first and second adhesives 22, 23 are not softened and have approximately the same hardness, so the pressure mechanism 3 applies a uniform surface pressure to the surface of the all-solid-state battery 20.

On the other hand, when the temperature of the all-solid-state battery 20 is abnormally high (for example, above 180°C, which is the melting point of lithium), the second adhesive 23, which has a low softening point, is softer than the first adhesive 22, which has a high softening point. Therefore, the surface pressure applied to the surface of the all-solid-state battery 20 is high in the first region _R1 where the first adhesive 22 is formed, and low in the second region _R2 where the second adhesive 23 is formed. Therefore, molten lithium melted from the anode layer 207 tends to flow from the first region _R1 to the second region R2 in a plan view of the all-solid-state battery _20. That is, the molten lithium is guided to the buffer portion 208e along the guide path 24 formed by the surface pressure distribution by the pressurizing mechanism 3.

The shapes of the first adhesive 22 and the second adhesive 23 are not limited to those described above. For example, the first adhesive 22 may be U-shaped, with the second adhesive 23 provided inside the first adhesive 22. Such modifications will be described with reference to the drawings. Figure 3 is a cross-sectional view showing a modification of the first adhesive and the second adhesive in the battery module of this embodiment.

As shown in FIG. 3, the first adhesive 22B has a downward U-shape. This first adhesive 22B has first to third strip-shaped portions 22a to 22c and an opening 22d. The first strip-shaped portion 22a is located on the positive and negative electrode tabs 202 and 206 side of the all-solid-state battery 20 and extends along the width direction of the all-solid-state battery 20 (the Y direction in the figure).

On the other hand, the second strip portion 22b is located on the buffer portion 208e side of the all-solid-state battery 20 and extends along the height direction of the all-solid-state battery 20 (Z direction in the figure). The second strip portion 22b is connected to one end of the first strip portion 22a. The third strip portion 22c is also located on the buffer portion 208e side of the all-solid-state battery 20 and extends along the height direction of the all-solid-state battery 20 (Z direction in the figure). The third strip portion 22c is spaced apart from the second strip portion 22b and connected to the other end of the first strip portion 22a. An opening 22d is provided between the second and third strip portions 22b, 22c. In other words, the opening 22d is formed toward the buffer portion 208e side.

A second adhesive 23B is provided inside this opening 22d. As in the above embodiment, the second adhesive 23B is provided on the buffer portion 208e side. The upper end and left and right ends of this second adhesive 23B are in contact with the first adhesive 22B, while the lower end is open to the buffer portion 208e side.

In this modified example, by surrounding the second adhesive 23B on three sides with the U-shaped first adhesive 22B, a three-way guide path 24 can be formed, allowing the molten lithium to concentrate in the buffer portion 208e.

With the battery module 1 described above, when the temperature of the all-solid-state battery 20 reaches or exceeds the melting point of lithium, the guide path 24 formed by the surface pressure distribution of the pressure applied by the pressure mechanism 3 can guide the molten lithium to the buffer portion 208e, thereby preventing the molten lithium from being pushed out of the battery module 1. Furthermore, when the temperature of the all-solid-state battery 20 is normal, no surface pressure distribution occurs and uniform surface pressure is applied to the all-solid-state battery 20, preventing a decrease in the battery performance of the all-solid-state battery 20.

Furthermore, as in this embodiment, by providing a buffer portion 208e on only one side of the all-solid-state battery 20 and guiding molten lithium to the buffer portion 208e via the guide path 24, it is possible to suppress a decrease in energy density.

Although embodiments of the present invention have been described above, these embodiments have been described to facilitate understanding of the present invention and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

For example, in the above embodiment, the internal space of the all-solid-state battery 20 is used as the buffer portion 208e from the viewpoint of improving the volumetric energy density of the battery module 1, but this is not limiting. A buffer portion made of a material with a higher melting point than lithium may be attached to a seal portion or the like of the all-solid-state battery 20, and a guide path may be set in the buffer portion to allow the molten lithium to move freely.

1... Battery module 2... Battery pack 20... All-solid-state battery (cell)
DESCRIPTION OF SYMBOLS 201...Positive electrode current collector 202...Positive electrode tab 203...Positive electrode layer 204...Solid electrolyte layer 205...Anode current collector 206...Anode tab 207...Anode layer 208...Exterior member 208a...Folded portion 208b-208d...First to third sealing portions 208e...Buffer portion R ₁ , R ₂ ...First and second regions 209...Sealing material 21...Bus bar 22, 22B...First adhesive 22a-22c...Strip portion 22d...Opening 23, 23B...Second adhesive 24...Guiding path 3...Pressure mechanism 31...First plate 32...Second plate 33...Fastener

Claims (4)

a battery pack including a plurality of stacked all-solid-state batteries each including a negative electrode including a lithium metal layer;
a pressure mechanism that applies a surface pressure to the battery pack along a stacking direction of the battery pack;
a buffer section capable of storing molten lithium melted from the lithium metal layer;
a guide path for guiding the molten lithium to the buffer portion,
The pressure mechanism forms the guide path by a surface pressure distribution when the temperature of the all-solid-state battery reaches or exceeds the melting point of lithium. The battery module according to claim 1,
the all-solid-state battery has a surface to which a surface pressure is applied by the pressurizing mechanism,
The surface is
a U-shaped first region having an opening;
a second region located inside the first region and having a surface pressure applied thereto that is smaller than that applied to the first region;
The opening of the first region is located on the buffer portion side of the battery module. The battery module according to claim 1 or 2,
The buffer unit is a battery module provided at a lower portion of the battery module. The battery module according to any one of claims 1 to 3,
the buffer portion is provided on one side of the all-solid-state battery,
The length of one side on which the buffer portion is provided is longer than the length of the other side of the all-solid-state battery.