JP7553243B2 - Battery pack - Google Patents

Description

The present invention relates to a battery pack.

In recent years, there has been an increasing demand for deeper diving depths and longer diving times for deep-sea equipment, submersible research vessels, and submersible work robots, and there is also an increasing demand for larger capacity batteries to power these devices as their main power sources or the instruments and communication devices installed on them.

Furthermore, batteries used in the deep sea are required to be configured for use in a high-pressure environment, and Patent Document 1 discloses a battery for use in the deep sea that is equipped with a pressure equalizing device having an expandable bellows.

Patent document 2 also discloses a single cell made of a lithium-ion battery, and describes stacking multiple cells in series for use as a stacked battery module.

JP 2007-18573 A JP 2018-125213 A

The present inventors have investigated whether the lithium ion battery described in Patent Document 2 can be used in a high-pressure environment.
The lithium ion battery described in Patent Document 2 has a single cell including an electrolyte, in which a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector are laminated in this order, and is provided with a fixing part that is disposed between the positive electrode current collector and the negative electrode current collector to fix the peripheral portion of the separator between the positive electrode current collector and the negative electrode current collector, and that seals the positive electrode active material layer, the separator, and the negative electrode active material layer.

When a lithium-ion battery formed by stacking the single cells described in Patent Document 2 was used in a high-pressure environment, the gaps between the positive electrode active material layer and the negative electrode active material layer and the surrounding fixing parts could become significantly recessed. When such a recess occurs, there is a concern that stress concentration will occur in the recess, causing cracks in the positive electrode current collector and/or the negative electrode current collector.

From the above investigations, it was thought that some improvement was necessary to make the lithium ion battery described in Patent Document 2 into a battery that could be used in a high-pressure environment.
The battery described in Patent Document 1 is intended for use in a high-pressure environment, but since this battery has a different basic battery configuration, it was difficult to improve the battery described in Patent Document 2 by referring to the configuration described in Patent Document 1.

The present invention was made in consideration of the above problems, and aims to provide a battery pack suitable for use in high-pressure environments.

The present invention relates to an assembled battery having two or more single cells having a stacking unit consisting of a set of a positive electrode collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode collector stacked in order, and an annular frame member arranged around the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode collector and the negative electrode collector, wherein the difference in thickness between the portion where the frame member is present and the portion where the stacking unit is present is 0.3 mm or less for the single cells constituting the assembled battery, and the gap between the frame member and the stacking unit is 0.5 mm or less for the single cells constituting the assembled battery; and This battery assembly includes two or more single cells each having a stacking unit made of a negative electrode current collector and an annular frame member arranged around the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector and the negative electrode current collector, and is characterized in that a step filler is provided on the frame member and on the gap between the frame member and the stacking unit, on the positive electrode current collector and/or the negative electrode current collector, and the step filler is provided so that the difference between the thickness at the location where the frame member is present, the thickness at the location between the location where the frame member is present and the location where the stacking unit is present, and the thickness at the location where the stacking unit is present is 0.3 mm or less.

The present invention provides a battery pack suitable for use in high-voltage environments.

FIG. 1 is a cross-sectional view showing a schematic diagram of an example of a unit cell constituting the battery pack of the present invention. FIG. 2 is a top view for explaining how to determine the gap between the frame member and the stack unit. FIG. 3 is a cross-sectional view that shows a schematic example of a unit cell in which there is a large difference in thickness between a portion where a frame member is present and a portion where a laminate unit is present, and there is a large gap between the frame member and the laminate unit. FIG. 4 is a cross-sectional view that illustrates an example of a battery pack in which the unit cells shown in FIG. 3 are stacked. FIG. 5 is a cross-sectional view that illustrates an example of a battery pack in which the unit cells shown in FIG. 1 are stacked. FIG. 6 is a cross-sectional view that illustrates a schematic diagram of another example of a unit cell that constitutes the battery pack of the present invention. FIG. 7 is a cross-sectional view that shows a schematic example of a battery pack in which a step filler is provided on the outside of the battery pack. FIG. 8 is a photograph showing an enlarged view of a part of the upper surface of the laminate cell of Example 1. FIG. 9 is a photograph showing an enlarged view of a part of the upper surface of the laminate cell of Example 2. FIG. 10 is a photograph showing an enlarged view of a portion of the upper surface of the laminate cell of Comparative Example 1. FIG. 11 is a photograph showing an enlarged view of a portion of the upper surface of the laminate cell of Comparative Example 2. FIG. 12 is a photograph showing an enlarged view of a portion of the upper surface of the laminate cell of Comparative Example 3. FIG. 13 is a photograph showing an enlarged view of a part of the upper surface of the laminate cell of Example 5.

The present invention will be described in detail below.
In this specification, the term "lithium ion battery" is intended to include the concept of a lithium ion secondary battery.

First Embodiment
A first embodiment of a battery pack of the present invention is an assembled battery including two or more single cells each having a stacking unit including a set of a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector, which are stacked in order, and an annular frame member disposed around the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector and the negative electrode current collector,
With respect to the unit cells constituting the assembled battery, the difference in thickness between a portion where the frame member is present and a portion where the laminated unit is present is 0.3 mm or less;
The battery pack is characterized in that the gap between the frame member and the stacking unit is 0.5 mm or less for each cell constituting the battery pack.

First, a case where the unit cells constituting the battery pack are the unit cells of the first embodiment will be described.
FIG. 1 is a cross-sectional view showing a schematic diagram of an example of a unit cell constituting the battery pack of the present invention.
The single battery 100 shown in FIG. 1 has a positive electrode current collector 11, a positive electrode active material layer 13, a separator 30, a negative electrode active material layer 23, and a negative electrode current collector 21 laminated in this order, with the positive electrode current collector 11 and the negative electrode current collector 21 as the outermost layers.
The positive electrode current collector 11 , the positive electrode active material layer 13 , the separator 30 , the negative electrode active material layer 23 and the negative electrode current collector 21 constitute a laminate unit 50 .

The stacking unit 50 is a position where all of the elements, i.e., the positive electrode collector 11, the positive electrode active material layer 13, the separator 30, the negative electrode active material layer 23, and the negative electrode collector 21, are present in the vertical direction in the cross section shown in FIG. 1, and is the region indicated by a double-headed arrow (reference symbol 50) in FIG. 1.
A region of the positive electrode current collector 11 that is not in contact with the positive electrode active material layer 13 and a region of the negative electrode current collector 21 that is not in contact with the negative electrode active material layer 23 are not included in the laminate unit.

Between the positive electrode current collector 11 and the negative electrode current collector 21 , an annular frame member 40 is disposed around the positive electrode active material layer 13 , the separator 30 and the negative electrode active material layer 23 .
The unit cell is sealed by a frame member 40, a positive electrode current collector 11, and a negative electrode current collector 21, and an electrolyte is enclosed.
The annular frame member means a structure that is annular when the unit cell is viewed from above, and is a structure in which stack units can be disposed within the ring of the frame member.
The frame member may be one annular frame member formed by joining a frame member arranged around the positive electrode active material and a frame member arranged around the negative electrode active material.
In FIG. 1, there is no distinction between a member that has been joined together to form a single annular frame member and a member that was originally a single annular frame member, and they are shown as a single annular frame member 40.

In the unit cell, the difference in thickness between the portion where the frame member is present and the portion where the laminate unit is present is 0.3 mm or less.
The thicknesses of the portion where the frame member is present and the portion where the laminate unit is present include the thicknesses of the positive electrode current collector and the negative electrode current collector, respectively.
The thickness of the portion where the frame member is present is indicated by a double-headed arrow _T1 in FIG. 1, and the thickness of the portion where the laminate unit is present is indicated by a double-headed arrow _T2 in FIG.

The difference in thickness between the portion where the frame member exists and the portion where the laminate unit exists is determined as follows.
The thickness is measured at five or more points in the area where the frame member is present, and the average thickness is defined as the thickness of the area where the frame member is present (frame member thickness).Similarly, the thickness is measured at five or more points in the area where the laminate unit is present, and the average thickness is defined as the thickness of the area where the laminate unit is present (lamination unit thickness).
The absolute value of the difference between the thickness of the frame member and the thickness of the laminate unit is defined as the difference in thickness between the portion where the frame member is present and the portion where the laminate unit is present.

It is also preferable that the difference between the total thickness of the positive electrode active material layer, the separator and the negative electrode active material layer and the thickness of the frame member is 0.3 mm or less.
The total thickness of the positive electrode active material layer, the separator, and the negative electrode active material layer is indicated by a double-headed arrow _T4 in FIG. 1, and the thickness of the frame member is indicated by a double-headed arrow _T3 in FIG. 1.
The cell shown in FIG. 1 has a configuration in which the difference in thickness between the portion where the frame member is present and the portion where the laminate unit is present is reduced by matching the thickness of the frame member with the total thickness of the positive electrode active material layer, the separator, and the negative electrode active material layer.

By reducing the difference in thickness between the area where the frame member is present and the area where the stacking unit is present, the step between the area where the frame member is present and the area where the stacking unit is present is reduced when the single cells are stacked. This prevents stress concentration between the frame member and the stacking unit when pressure is applied to the battery pack.

In addition, for each of the cells constituting the battery pack, the gap between the frame member and the stacking unit is 0.5 mm or less.
The method of determining the gap between the frame member and the stacking unit in the unit cell will be described with reference to the drawings.
FIG. 2 is a top view for explaining how to determine the gap between the frame member and the stack unit.
The cell is viewed from above, and the gap (distance) between the frame member and the stacking unit is measured at four or more measurement points, and the average value is taken as the gap between the frame member and the stacking unit.
When the shape of the laminate unit in top view is polygonal, the center of each side constituting the polygon is set as the measurement site.
2, the gaps between the frame member 40 and the laminate unit 50 are indicated by double-headed arrows _W1 , _W2 , _W3 , and _W4 at the center of each side of a rectangle. The average value of _W1 , _W2 , _W3 , and _W4 is defined as the gap between the frame member and the laminate unit.

If the gap between the frame member and the stacking unit defined in this manner is small, there is little room for a dent to form in the gap between the frame member and the stacking unit when pressure is applied to a battery pack formed by stacking single cells, and the problem of stress concentration in the dent is less likely to occur.
The gap between the frame member and the laminate unit is preferably 0.3 mm or less, more preferably 0.1 mm or less. The lower limit of the gap between the frame member and the laminate unit is preferably 0 mm, and the lower limit of the gap between the frame member and the laminate unit is preferably 0.05 mm.

For comparison with the battery pack of the present invention, a problem that occurs when there is a large difference in thickness between the portion where the frame member is present and the portion where the laminate unit is present, and there is a large gap between the frame member and the laminate unit, will be described.
FIG. 3 is a cross-sectional view that shows a schematic example of a unit cell in which there is a large difference in thickness between a portion where a frame member is present and a portion where a laminate unit is present, and there is a large gap between the frame member and the laminate unit.

The single battery 500 shown in FIG. 3 has a positive electrode current collector 11, a positive electrode active material layer 13, a separator 30, a negative electrode active material layer 23, and a negative electrode current collector 21 laminated in this order, with the positive electrode current collector 11 and the negative electrode current collector 21 as the outermost layers.
The positive electrode current collector 11 , the positive electrode active material layer 13 , the separator 30 , the negative electrode active material layer 23 and the negative electrode current collector 21 constitute a laminate unit 50 .
Between the positive electrode current collector 11 and the negative electrode current collector 21 , an annular frame member 40 is disposed around the positive electrode active material layer 13 , the separator 30 and the negative electrode active material layer 23 .

In this single battery 500, since the thickness of the frame member (thickness indicated by double arrow _t3 ) is thin, the thickness _t1 of the portion where the frame member exists is thinner than the thickness _t2 of the portion where the laminate unit exists.
Furthermore, the gap (the width indicated by the double-headed arrow w) between the frame member and the stack unit is large.

FIG. 4 is a cross-sectional view that illustrates an example of a battery pack in which the unit cells shown in FIG. 3 are stacked.
The battery pack 600 shown in FIG. 4 is formed by stacking five of the unit cells 500 shown in FIG.
4 is a schematic diagram showing a state in which pressure is applied to the battery pack 600 in a high-pressure environment. It can be seen that when pressure is applied to the battery pack 600, the gap between the frame member and the stacking unit is significantly recessed. When such a recess occurs, stress is concentrated in the recess, which may cause cracks in the positive electrode current collector and/or the negative electrode current collector.

On the other hand, a battery pack having two or more unit cells as shown in FIG. 1 is one example of the battery pack of the present invention.
FIG. 5 is a cross-sectional view that illustrates an example of a battery pack in which the unit cells shown in FIG. 1 are stacked.
The battery pack 300 shown in FIG. 5 is formed by stacking five of the unit cells 100 shown in FIG.
FIG. 5 shows a schematic diagram of a state in which pressure is applied to the battery pack 300 in a high-pressure environment.
In the cells 100 constituting the battery pack 300, the difference in thickness between the portion where the frame member is present and the portion where the stack unit is present is small, so that when the cells are stacked, the step between the portion where the frame member is present and the portion where the stack unit is present is small, thereby preventing stress concentration between the frame member and the stack unit when pressure is applied to the battery pack.
In addition, since the gap between the frame member and the stacking unit of the single cells 100 that make up the battery pack 300 is small, when pressure is applied to a battery pack made up of stacked single cells, there is little room for a dent to form in the gap between the frame member and the stacking unit, making it less likely that the problem of stress concentration in the dent will occur.

A preferred embodiment of each of the components constituting the unit cell will be described below.
The positive electrode active material layer contains a positive electrode active material.
Positive electrode active materials include composite oxides of lithium and transition metals {composite oxides containing one type of transition metal (LiCoO ₂ , LiNiO 2 , LiAlMnO ₄ , LiMnO ₂ , LiMn ₂ O ₄ , etc.), composite oxides containing two types of transition metal elements ₍ for example, LiFeMnO ₄ , LiNi _1-x Co _x O ₂ , LiMn _1-y Co _y O ₂ , LiNi _1/3 Co _1/3 Al _1/3 O ₂ , and LiNi _0.8 Co _0.15 Al _0.05 O ₂ ), and composite oxides containing three or more types of metal elements [for example, LiM _a M' _b M'' _c O ₂ (M, M' and M'' are different transition metal elements satisfying a+b+c=1, for example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), etc.}, lithium-containing transition metal phosphates (for example, LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ and LiNiPO ₄ ), transition metal oxides (for example, MnO ₂ and V ₂ O ₅ ), transition metal sulfides (for example, MoS ₂ and TiS ₂ ), and conductive polymers (for example, polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene and polyvinylcarbazole), and two or more of them may be used in combination.
The lithium-containing transition metal phosphate may have some of the transition metal sites substituted with other transition metals.

The positive electrode active material is preferably a coated positive electrode active material coated with a conductive assistant and a coating resin.
When the positive electrode active material is coated with a coating resin, the volume change of the electrode is mitigated, and the expansion of the electrode can be suppressed.

Examples of the conductive assistant include metal-based conductive assistants [aluminum, stainless steel (SUS), silver, gold, copper, titanium, etc.], carbon-based conductive assistants [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.)], and mixtures thereof.
These conductive assistants may be used alone or in combination of two or more kinds thereof. They may also be used as alloys or metal oxides.
Among these, from the viewpoint of electrical stability, aluminum, stainless steel, silver, gold, copper, titanium, carbon-based conductive assistants, and mixtures thereof are more preferable, silver, gold, aluminum, stainless steel, and carbon-based conductive assistants are even more preferable, and carbon-based conductive assistants are particularly preferable.
Furthermore, these conductive assistants may be formed by coating a particulate ceramic material or a resin material with a conductive material (preferably a metal one of the conductive assistants described above) by plating or the like.

The shape (form) of the conductive additive is not limited to a particulate form, and may be a form other than a particulate form, and may be a form that is in practical use as a so-called filler-based conductive additive, such as carbon nanofibers or carbon nanotubes.

The ratio of the coating resin to the conductive additive is not particularly limited, but from the viewpoint of the internal resistance of the battery, the weight ratio of the coating resin (resin solids weight):conductive additive is preferably 1:0.01 to 1:50, and more preferably 1:0.2 to 1:3.0.

As a coating resin, those described in JP 2017-054703 A as a coating resin for non-aqueous secondary battery active materials can be suitably used.

The positive electrode active material layer may contain a conductive assistant other than the conductive assistant contained in the coated positive electrode active material.
As the conductive assistant, the same conductive assistant as that contained in the coated positive electrode active material described above can be suitably used.

The positive electrode active material layer preferably contains a positive electrode active material and is a non-binding material that does not contain a binder that binds the positive electrode active material together.
Here, non-bound material means that the positive electrode active material is not fixed in position by a binding material (also called a binder), and the positive electrode active materials are not irreversibly fixed to each other or to the current collector.

The positive electrode active material layer may contain an adhesive resin.
As the adhesive resin, for example, a resin for coating a non-aqueous secondary battery active material described in JP 2017-054703 A in which a small amount of an organic solvent is mixed to adjust the glass transition temperature to room temperature or lower, and a resin described as an adhesive in JP 10-255805 A can be suitably used.
The adhesive resin means a resin that does not solidify even when dried by volatilizing the solvent component and has adhesiveness (the property of adhering by applying slight pressure without using water, solvent, heat, etc.) On the other hand, the solution-drying type electrode binder used as a binding material means a material that dries and solidifies by volatilizing the solvent component, thereby firmly adhering and fixing active materials to each other.
Therefore, the solution drying type electrode binder (binding material) and the adhesive resin are different materials.

The thickness of the positive electrode active material layer is not particularly limited, but from the viewpoint of battery performance, it is preferably 150 to 600 μm, and more preferably 200 to 450 μm.

The negative electrode active material layer contains a negative electrode active material.
The negative electrode active material may be a known negative electrode active material for lithium ion batteries, and may be, for example, a carbon-based material [graphite, non-graphitizable carbon, amorphous carbon, resin baked bodies (e.g., phenolic resin, furan resin, etc. baked and carbonized), cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), and carbon fibers, etc.], a silicon-based material [silicon, silicon oxide (SiOx), silicon-carbon composites (carbon particles whose surfaces are coated with silicon and/or silicon carbide, silicon particles or silicon oxide particles whose surfaces are coated with carbon and/or silicon carbide, silicon carbide, etc.)], and ... Examples of the conductive material include silicon alloys (silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper alloy, silicon-tin alloy, etc.), conductive polymers (for example, polyacetylene, polypyrrole, etc.), metals (tin, aluminum, zirconium, titanium, etc.), metal oxides (titanium oxide, lithium-titanium oxide, etc.), metal alloys (for example, lithium-tin alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.), and mixtures of these with carbon-based materials.

The negative electrode active material may be a coated negative electrode active material coated with a conductive assistant and a coating resin similar to the coated positive electrode active material described above.
As the conductive assistant and the coating resin, the same conductive assistant and coating resin as those in the coated positive electrode active material described above can be suitably used.

The negative electrode active material layer may also contain a conductive assistant other than the conductive assistant contained in the coated negative electrode active material. As the conductive assistant, the same conductive assistant as the conductive assistant contained in the coated positive electrode active material described above can be suitably used.

The negative electrode active material layer, like the positive electrode active material layer, is preferably a non-binding material that does not contain a binder that binds the negative electrode active materials together. Also, like the positive electrode active material layer, it may contain an adhesive resin.

The thickness of the negative electrode active material layer is not particularly limited, but from the viewpoint of battery performance, it is preferably 150 to 600 μm, and more preferably 200 to 450 μm.

Examples of materials constituting the positive electrode current collector and the negative electrode current collector (hereinafter collectively referred to simply as current collectors) include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, as well as baked carbon, conductive polymer materials, conductive glass, and the like.
Of these materials, from the viewpoints of weight reduction, corrosion resistance, and high electrical conductivity, aluminum is preferred for the positive electrode current collector, and copper is preferred for the negative electrode current collector.

The current collector is preferably a resin current collector made of a conductive polymer material.
The shape of the current collector is not particularly limited, and may be a sheet-like current collector made of the above-mentioned material, or a deposition layer made of fine particles made of the above-mentioned material.
The thickness of the current collector is not particularly limited, but is preferably 50 to 500 μm.

The conductive polymer material constituting the resin collector may be, for example, a conductive polymer or a resin to which a conductive agent has been added as necessary.
As the conductive agent constituting the conductive polymer material, the same conductive assistant as that contained in the coated positive electrode active material described above can be suitably used.

Examples of resins constituting the conductive polymer material include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyethernitrile (PEN), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin, and mixtures thereof.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferred, and polyethylene (PE), polypropylene (PP) and polymethylpentene (PMP) are more preferred.

In addition, a collector having a metal layer provided on one or both sides of a resin collector may be used as the current collector. Examples of metals include copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, which are listed as examples of metals constituting the current collector itself. Methods for providing the metal layer include metal vapor deposition and sputtering.

Examples of separators include known separators for lithium ion batteries, such as porous films made of polyethylene or polypropylene, laminated films of porous polyethylene film and porous polypropylene, nonwoven fabrics made of synthetic fibers (polyester fibers, aramid fibers, etc.) or glass fibers, and those with ceramic particles such as silica, alumina, or titania attached to their surfaces.

The positive electrode active material layer and the negative electrode active material layer contain an electrolyte.
As the electrolytic solution, a known electrolytic solution containing an electrolyte and a non-aqueous solvent, which is used in the production of known lithium ion batteries, can be used.

As the electrolyte, those used in known electrolytic solutions can be used, for example, lithium salts of inorganic acids such as LiN( _FSO2 ) ₂ , _LiPF6 , _LiBF4 , _LiSbF6 , _LiAsF6 , and _LiClO4 , and lithium salts of organic acids such as LiN( _CF3SO2 ) ₂ , _LiN ( _{C2F5SO2 ) 2} , and LiC( _CF3SO2 ) ₃ . Among these, imide-based electrolytes [LiN( _FSO2 ) ₂ , LiN( _CF3SO2 ) _{2, LiN(C2F5SO2)2, and LiC(CF3SO2 ) 3 , etc. ] and LiPF6} are preferred from the viewpoint of battery output and _charge /discharge cycle characteristics.

The non-aqueous solvent may be any of those used in known electrolytic solutions, such as lactone compounds, cyclic or chain carbonates, chain carboxylates, cyclic or chain ethers, phosphates, nitrile compounds, amide compounds, sulfones, sulfolane, and mixtures thereof.

The electrolyte concentration of the electrolytic solution is preferably 1 to 5 mol/L, more preferably 1.5 to 4 mol/L, and even more preferably 2 to 3 mol/L.
If the electrolyte concentration of the electrolytic solution is less than 1 mol/L, the battery may not exhibit sufficient input/output characteristics, whereas if it exceeds 5 mol/L, the electrolyte may precipitate.
The electrolyte concentration of the electrolytic solution can be confirmed by extracting the electrolytic solution constituting the lithium ion battery electrode or the lithium ion battery without using a solvent or the like and measuring the concentration.

The material for the frame member is not particularly limited as long as it is durable against the electrolyte, but a polymer material is preferable, and a thermosetting polymer material is more preferable.
Specific examples include epoxy resins, polyolefin resins, polyurethane resins, and polyvinylidene fluoride resins, with epoxy resins being preferred because of their high durability and ease of handling.

Second Embodiment
A second embodiment of the battery pack of the present invention is an assembled battery including two or more single cells each having a lamination unit including a set of a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector, which are laminated in order, and an annular frame member disposed around the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector and the negative electrode current collector,
a step filler is provided on the frame member, and on the positive electrode current collector and/or the negative electrode current collector in a gap between the frame member and the stacking unit;
The above-mentioned step filling material is
a thickness at a portion where the frame member is present; and
a thickness at a portion between a portion where the frame member is present and a portion where the laminate unit is present;
The laminated unit is characterized in that the difference in thickness between the laminated unit and the portion where the laminated unit is present is set to 0.3 mm or less.

The following describes a case where the unit cells constituting the battery pack are the unit cells of the second embodiment.
In the unit cell of the second embodiment, step fillers are provided on the frame member, and on the gaps between the frame member and the stack units, and on the positive electrode current collector and/or the negative electrode current collector.
The step filler is provided so that the difference between the thickness at the portion where the frame member is present, the thickness at the portion between the portion where the frame member is present and the portion where the laminate unit is present, and the thickness at the portion where the laminate unit is present is 0.3 mm or less.

FIG. 6 is a cross-sectional view that illustrates a schematic diagram of another example of a unit cell that constitutes the battery pack of the present invention.
In the single battery 200 shown in FIG. 6 , a positive electrode current collector 11, a positive electrode active material layer 13, a separator 30, a negative electrode active material layer 23, and a negative electrode current collector 21 are laminated in this order, with the positive electrode current collector 11 and the negative electrode current collector 21 being the outermost layers.
The positive electrode current collector 11 , the positive electrode active material layer 13 , the separator 30 , the negative electrode active material layer 23 and the negative electrode current collector 21 constitute a laminate unit 50 .
Between the positive electrode current collector 11 and the negative electrode current collector 21 , an annular frame member 40 is disposed around the positive electrode active material layer 13 , the separator 30 and the negative electrode active material layer 23 .

Furthermore, step fillers 60 are provided on the positive electrode current collector 11 on the frame member 40, on the positive electrode current collector 11 in the gap between the frame member 40 and the stacking unit 50, on the negative electrode current collector 21 on the frame member 40, and on the negative electrode current collector 21 in the gap between the frame member 40 and the stacking unit 50.
The step filler 60 is not provided on the positive electrode current collector 11 in contact with the positive electrode active material layer 13 , and is not provided on the negative electrode current collector 21 in contact with the negative electrode active material layer 23 .

The gap filling material is provided so as to fill gaps in the area where the frame member is present, the area between the area where the frame member is present and the area where the laminate unit is present, and the area where the laminate unit is present.
When the step filling material is not taken into consideration, the thickness _t1 of the portion where the frame member exists is much thinner than the thickness _t2 of the portion where the laminate unit exists.
By providing the step filler on the current collector on the frame member, the thickness _T1 of the portion where the frame member is present becomes thicker, and the difference between the thickness _T1 of the portion where the frame member is present and the thickness _t2 of the portion where the laminate unit is present becomes smaller.
Furthermore, by providing the step filler on the current collector above the gap between the frame member and the laminate unit, the thickness _T5 at the portion between the portion where the frame member is present and the portion where the laminate unit is present becomes thicker, and the difference between thickness _T5 , thickness _T1 of the portion where the frame member is present, and thickness _t2 of the portion where the laminate unit is present becomes smaller.
Specifically, the step filler is provided so that the difference between the thickness _T1 of the portion where the frame member is present, the thickness _T5 of the portion between the portion where the frame member is present and the portion where the laminate unit is present, and the thickness _t2 of the portion where the laminate unit is present is 0.3 mm or less.

When a step filler is provided, the difference between the thickness at the area where the frame member is present, the thickness between the area where the frame member is present and the area where the laminate unit is present, and the thickness at the area where the laminate unit is present is calculated by measuring the thickness at five or more points at each area, calculating the average value, and then calculating the difference between the maximum and minimum values of the average values.

In FIG. 6, on the positive electrode side, a step filler 60 is provided on the lower side of the positive electrode current collector 11 outside the frame member 40. However, when a step filler is provided on the outside of the current collector regardless of the top or bottom in the drawing, it is said that "a step filler is provided on the current collector."

In the cell of the second embodiment as well, the gap between the frame member and the stack unit is preferably 0.5 mm or less.
Furthermore, by using the unit cell of the second embodiment, the same effects as those obtained by using the unit cell of the first embodiment can be obtained.
That is, when pressure is applied to the battery pack, stress concentration between the frame member and the laminated units is prevented.
Furthermore, since there are small gaps within the cells when pressure is applied to a battery pack made up of stacked cells, there is little room for dents to form in the cells, making it less likely that the problem of stress concentration in the dents will occur.

Each component constituting the unit cell of the second embodiment can be similar to each component constituting the unit cell of the first embodiment, and therefore detailed description thereof will be omitted.
In the battery of the second embodiment, the material of the step filler is not particularly limited, but is preferably a resin material, which may be applied to the current collector and cured, and examples of the material include epoxy resin, polyolefin resin, polyurethane resin, and polyvinylidene fluoride resin.

Next, a method for manufacturing the unit cell and the battery pack will be described.
The cell 100 can be manufactured as follows.
The positive electrode current collector 11 is joined to one frame surface of the annular frame member, and one end of the frame member is sealed. Then, the frame member is filled with a positive electrode active material that will become the positive electrode active material layer 13. At this time, it is preferable to fill the frame member with as much positive electrode active material as possible so that no gap occurs between the frame member and the positive electrode active material layer. Then, a separator is placed on the other frame surface of the frame member.
Similarly, the negative electrode current collector 21 is joined to one frame surface of the annular frame member, and one end of the frame member is sealed. Next, the frame member is filled with a negative electrode active material that will become the negative electrode active material layer 23. At this time, it is preferable to fill the frame member with as much negative electrode active material as possible so that no gap occurs between the frame member and the negative electrode active material layer. Next, a separator is placed on the other frame surface of the frame member.
The frame members are then bonded together and sealed to obtain the unit cell 100 .
The two bonded frame members are joined together to form the frame member 40.
In the above example, separators are placed in both the frame member filled with the positive electrode active material and the frame member filled with the negative electrode active material, and the two separators are stacked to form separator 30, but the separator may be placed in only one of the frame members.
It is preferable to adjust the thickness of the frame member so that the difference between the total thickness of the positive electrode active material layer, the separator, and the negative electrode active material layer and the thickness of the frame member is 0.3 mm or less. The unit cell manufactured in this manner is the unit cell of the first embodiment.

In addition, after producing a single battery without adjusting the thickness of the frame member, a step filler is provided to fill in the steps at the location where the frame member is present, the location between the location where the frame member is present and the location where the stacking unit is present, and the location where the stacking unit is present, thereby making it possible to manufacture the single battery of the second embodiment.
The step filling material can be provided on the current collector by applying a resin material constituting the step filling material and curing it.

A plurality of the thus manufactured single cells are stacked to manufacture a battery pack.
When stacking the single cells, the single cells are stacked in the same orientation so that the positive electrode current collector of one cell is in contact with the negative electrode current collector of an adjacent cell, thereby obtaining a battery pack in which multiple single cells are connected in series.

Furthermore, even if a battery pack is manufactured in which a step filler is provided on the outside of the battery pack, a battery pack suitable for use in a high-pressure environment can be provided.
FIG. 7 is a cross-sectional view that shows a schematic example of a battery pack in which a step filler is provided on the outside of the battery pack.
The battery pack 400 shown in Fig. 7 is based on an assembled battery formed by stacking unit cells, such as the battery pack 600 shown in Fig. 4, in which there is a large difference in thickness between the portion where the frame member is present and the portion where the stacking unit is present. In the battery pack 400, the battery pack 600 shown in Fig. 4 is surrounded by an outer frame member 410, an upper frame member 420, and a lower frame member 430. Step fillers 60 are provided in the gaps between the battery pack 600 and each frame member.
As the step filling material 60, the step filling material constituting the unit cell of the second embodiment can be used.
7 as a whole, the step between the outer frame member 410 and the battery assembly 600 is small, which prevents stress concentration between the outer frame member 410 and the battery assembly 600 when pressure is applied to the battery assembly 400. This makes it possible to provide a battery assembly suitable for use in high-pressure environments.

The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples as long as they do not deviate from the spirit of the present invention. Note that, unless otherwise specified, parts are parts by weight and % is % by weight.

<Preparation of coating resin solution>
Into a four-neck flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel, and a nitrogen gas inlet tube, 83 parts of ethyl acetate and 17 parts of methanol were placed and heated to 68°C.
Next, a monomer blend solution containing 242.8 parts of methacrylic acid, 97.1 parts of methyl methacrylate, 242.8 parts of 2-ethylhexyl methacrylate, 52.1 parts of ethyl acetate, and 10.7 parts of methanol was mixed with a four-neck flask and an initiator solution containing 0.263 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) dissolved in 34.2 parts of ethyl acetate was continuously dropped into the flask over 4 hours with a dropping funnel while blowing nitrogen into the flask, and radical polymerization was carried out. After the dropwise addition, an initiator solution containing 0.583 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) dissolved in 26 parts of ethyl acetate was continuously added over 2 hours with a dropping funnel. Furthermore, polymerization was continued at the boiling point for 4 hours. After removing the solvent to obtain 582 parts of resin, 1,360 parts of isopropanol was added to obtain a coating resin solution consisting of a vinyl resin with a resin concentration of 30% by weight.

<Preparation of Positive Electrode Composition>
94 parts _{of LiNi0.8Co0.15Al0.05O2 powder was} placed in a _universal mixer and stirred at room temperature (25°C) and 150 rpm. The above-mentioned coating resin solution (resin solid content concentration: 30% by mass) was added dropwise over 60 minutes to make the resin solid content 3 parts, and then stirred for another 30 minutes.
Next, while stirring, 3 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Company, Ltd.] (average particle diameter (primary particle diameter): 0.036 μm) was added in three separate batches, and the mixture was heated to 70° C. while stirring for 30 minutes, and then the pressure was reduced to 100 mmHg and maintained for 30 minutes to obtain coated positive electrode active material particles.
100 parts of the coated positive electrode active material particles and 6 parts of carbon fiber (DonaCarbo Milled S-243, manufactured by Osaka Gas Chemicals Co., Ltd.: average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS/cm) were dry-blended to obtain a positive electrode material mixture. Then, 11 parts of the electrolyte were added to the positive electrode material mixture and mixed in a mixer to obtain a positive electrode composition.

<Preparation of negative electrode composition>
88 parts of non-graphitizable carbon [Carbotron (registered trademark) PS (F) manufactured by Kureha Battery Materials Japan Co., Ltd.] was placed in a universal mixer, and while stirring at room temperature (25° C.) and 150 rpm, a coating resin solution (resin solids concentration: 30% by weight) was added dropwise over 60 minutes to make the resin solids 6 parts, and the mixture was further stirred for 30 minutes.
Next, while stirring, 6 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.] (average particle diameter (primary particle diameter): 0.036 μm) was mixed in three batches, and the mixture was heated to 70° C. while stirring for 30 minutes, and the pressure was reduced to 0.01 MPa and maintained for 30 minutes to obtain coated negative electrode active material particles.
100 parts of the coated negative electrode active material particles and 1 part of carbon fiber (DonaCarbo Milled S-243, manufactured by Osaka Gas Chemicals Co., Ltd.: average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS/cm) were dry-blended to obtain a negative electrode material mixture. Thereafter, 0.11 parts of an electrolyte was added to the negative electrode material mixture and mixed in a mixer to obtain a negative electrode composition.

<Preparation of Electrolyte Solution>
LiPF ₆ was dissolved at a ratio of 1 mol/L in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1:1) to obtain an electrolyte solution.

<Production of Positive Electrode Current Collector>
A positive electrode resin current collector material was obtained by melt-kneading 69.7 parts of polypropylene (PP) [trade name "Sunallomer PC630S", manufactured by Sunallomer Co., Ltd.], 25.0 parts of acetylene black [Denka Black (registered trademark), manufactured by Denka Co., Ltd.], and 5.0 parts of a dispersant [trade name "UMEX 1001 (acid-modified polypropylene)", manufactured by Sanyo Chemical Industries, Ltd.] in a twin-screw extruder at 180°C, 100 rpm, and a residence time of 5 minutes. The obtained positive electrode resin current collector material was passed through a T-die extrusion film molding machine and then rolled multiple times with a hot press machine to obtain a positive electrode current collector with a film thickness of 42 μm.

<Production of negative electrode current collector>
A negative electrode resin current collector material was obtained by melt-kneading 70 parts of polypropylene (trade name "SunAllomer PL500A", manufactured by SunAllomer Co., Ltd.), 25 parts of nickel particles (manufactured by Vale Corporation), and 5 parts of a dispersant (trade name "UMEX 1001", manufactured by Sanyo Chemical Industries, Ltd.) in a twin-screw extruder at 200° C. and 200 rpm. The obtained negative electrode resin current collector material was passed through a T-die extrusion film molding machine and then rolled multiple times with a hot press machine to obtain a negative electrode resin current collector roll having a thickness of 45 μm.
A copper metal layer was formed to a thickness of 5 nm on one side of this negative electrode resin current collector raw sheet by vacuum deposition to obtain a negative electrode current collector having a metal layer on one side.

Example 1
An annular frame member made of epoxy resin and having a rectangular shape when viewed from above was prepared.
One end of the positive electrode current collector was joined to one of the frame surfaces of the frame member. The frame member was filled with a positive electrode composition, and a separator was placed on the other frame surface of the frame member.
A frame member other than the frame member filled with the positive electrode composition was prepared, and one end of the negative electrode current collector was joined to one frame surface of the frame member in the same manner as above, with the metal layer in a direction in which it contacted the negative electrode composition. The negative electrode composition was filled in the frame member, and a separator was placed on the other frame surface of the frame member.
The frame member filled with the positive electrode composition and the frame member filled with the negative electrode composition were attached to each other with the separators facing each other, and sealed to obtain a unit cell.
The dimensions of this unit cell were adjusted so that the difference between the total thickness of the positive electrode active material layer, the separator and the negative electrode active material layer and the thickness of the frame member was 0 mm.
In addition, the electrode composition was filled so that the gap between the frame member and the laminate unit was 0 mm.
In this unit cell, the difference in thickness between the portion where the frame member is present and the portion where the laminate unit is present is 0 mm.

(Examples 2 to 4, Comparative Examples 1 to 3)
A single cell was fabricated by changing the thickness of the frame member or by changing the gap between the frame member and the stack unit.
Table 1 shows the difference in thickness between the portion where the frame member is present and the portion where the laminate unit is present in each unit cell.

(Preparation of assembled battery and pressure test)
Eight of the cells obtained in each of the Examples and Comparative Examples were stacked to obtain a battery pack, and the entire battery pack was covered with an aluminum laminate film and evacuated (vacuum-packed) to simulate a high-pressure environment.

(Observation of Appearance)
After the pressure test, the aluminum laminate cell was observed for the presence or absence of dents in the gap between the frame member and the laminate unit. The observation results are shown in Table 1.

(Observation of the current collector)
After the pressure test, the aluminum laminate cell was opened and the state of the current collector of the unit cell was observed.
The current collector was observed for the presence or absence of cracks, and the observation results are shown in Table 1.

The drawings show photographs showing the presence or absence of dents in Examples 1 and 2 and Comparative Examples 1, 2, and 3. Each drawing shows an enlarged photograph of the vicinity of a vertex of a laminate unit having a rectangular shape when viewed from above.
FIG. 8 is a photograph showing an enlarged view of a portion of the upper surface of the laminate cell of Example 1, and FIG. 9 is a photograph showing an enlarged view of a portion of the upper surface of the laminate cell of Example 2.
The black lines in Figs. 8 and 9 are marks (indicating the vertices of the rectangular laminate units) for observation under a microscope.
FIG. 10 is a photograph showing an enlarged portion of the upper surface of the laminate cell of Comparative Example 1, FIG. 11 is a photograph showing an enlarged portion of the upper surface of the laminate cell of Comparative Example 2, and FIG. 12 is a photograph showing an enlarged portion of the upper surface of the laminate cell of Comparative Example 3.

As shown in Figures 8 and 9, in Examples 1 and 2, no dents are seen in the gaps between the frame member and the laminated member. On the other hand, as shown in Figures 10, 11, and 12, in Comparative Examples 1 to 3, dents are seen in the gaps between the frame member and the laminated member.

These results show that in the battery packs of Examples 1 to 4, stress concentration between the frame member and the stacking unit was prevented when pressure was applied, and cracks were prevented from occurring in the current collector.

Example 5
After producing the single battery of Comparative Example 3, an epoxy resin was applied as a step filler and cured so as to fill in the steps at the area where the frame member was present, the area between the area where the frame member was present and the area where the laminate unit was present, and the area where the laminate unit was present.
In this unit cell, the difference in thickness between the portion where the frame member is present, the portion between the portion where the frame member is present and the portion where the laminate unit is present, and the portion where the laminate unit is present is 0 mm.
A battery pack was fabricated in the same manner as in Example 1, and a pressure test was carried out. As a result, no dents were found in the gaps between the frame members and the stacking units, and no cracks were found in the current collectors.
FIG. 13 is a photograph showing an enlarged view of a part of the upper surface of the laminate cell of Example 5.
As shown in FIG. 13, in Example 5 as well, no depressions were observed in the gaps between the frame member and the laminated members.

The battery pack of the present invention is particularly useful as a battery for use in high-pressure environments.

REFERENCE SIGNS LIST 11 Positive electrode current collector 13 Positive electrode active material layer 21 Negative electrode current collector 23 Negative electrode active material layer 30 Separator 40 Frame member 50 Laminate unit 60 Step filler 100, 200, 500 Single cell 300, 400, 600 Assembled battery 410 Outer frame member 420 Upper frame member 430 Lower frame member

Claims (3)

A battery pack including two or more unit cells each having a stacking unit including a set of a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector, which are stacked in order, and an annular frame member disposed around the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector and the negative electrode current collector,
With respect to the unit cells constituting the assembled battery, the difference in thickness between a portion where the frame member is present and a portion where the laminated unit is present is 0.3 mm or less;
A battery pack, wherein a gap between the frame member and the stacking unit of each of the cells constituting the battery pack is 0.05 mm or more and 0.5 mm or less. The battery pack according to claim 1, wherein the difference between the total thickness of the positive electrode active material layer, the separator, and the negative electrode active material layer and the thickness of the frame member is 0.3 mm or less. A battery pack including two or more unit cells each having a stacking unit including a set of a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector, which are stacked in order, and an annular frame member disposed around the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector and the negative electrode current collector,
a step filler is provided on the frame member, and on a positive electrode current collector and/or a negative electrode current collector in a gap between the frame member and the stacking unit;
The step filling material is
a thickness at a portion where the frame member is present; and
a thickness at a portion between the portion where the frame member is present and the portion where the laminate unit is present;
a difference in thickness between the laminated unit and a portion where the laminated unit is present is set to be 0.3 mm or less.

Images