JP7209558B2 - bipolar secondary battery - Google Patents

Description

The present invention relates to a bipolar secondary battery.

2. Description of the Related Art In recent years, various electric vehicles are expected to spread toward solving environmental and energy problems. Batteries are being developed earnestly as in-vehicle power sources such as power sources for driving motors, which hold the key to popularization of these electric vehicles. Batteries intended for use in vehicle power sources are required to have extremely high output characteristics compared to batteries used in mobile phones, laptop computers, and the like.

For example, Patent Document 1 discloses a gas adsorption layer in the gap between an electrode group and a laminate film sealing portion in order to efficiently adsorb gas generated by charge and discharge reactions while maintaining volumetric energy density and battery characteristics. A laminated battery is disclosed in which the

JP 2011-249269 A

However, according to the technique described in Patent Document 1, since the gas adsorption layer is immersed in the electrolytic solution, the amount of gas adsorption is reduced and the gas may remain inside the laminate film. In addition, there is a problem that the gas causes stress in the electrode assembly, which may cause the current collector to break or the electrode active material layer to collapse, thereby degrading the battery performance.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide means for efficiently absorbing gas generated by charge/discharge reactions and suppressing degradation of battery performance.

A bipolar secondary battery of the present invention for achieving the above object includes a power generation element in which a plurality of single cells each having a positive electrode, a negative electrode, a separator, and an insulating member are laminated and sealed inside an outer package. have a structure. The positive electrode is formed by forming a positive electrode active material layer on a positive electrode current collector, and the negative electrode is formed by forming a negative electrode active material layer on a negative electrode current collector. The separator is sandwiched between the positive electrode active material layer and the negative electrode active material layer. The insulating member is disposed on the outer periphery of the positive electrode current collector, the negative electrode current collector, and the separator, seals the positive electrode active material layer between the positive electrode current collector and the separator, and seals the positive electrode active material layer between the positive electrode current collector and the separator. to seal the negative electrode active material layer. Then, the positive electrode current collector and the negative electrode current collector have gas permeability, and in the non-electrode portion where the positive electrode active material layer and the negative electrode active material layer are not formed, the positive electrode current collector of one single cell and the A gas adsorbent is disposed between the positive electrode current collector and the negative electrode current collector of another adjacent unit cell.

According to the present invention, the gas generated by the charge/discharge reaction permeates the positive electrode current collector and the negative electrode current collector and is adsorbed by the gas adsorbent arranged outside the single cell. Therefore, the gas generated by the charge/discharge reaction is efficiently adsorbed, and deterioration of battery performance can be suppressed.

1 is a perspective view showing a battery according to one embodiment of the present invention; FIG. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1 and schematically showing the overall structure of the battery; 1 is a cross-sectional view showing a single cell of a battery; FIG. FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 1 and showing a gas adsorbent in the battery; FIG. 5 is a cross-sectional view showing a gas adsorbent according to Modification 1; FIG. 11 is a cross-sectional view showing a gas adsorbent according to modification 2; FIG. 11 is a cross-sectional view showing a gas adsorbent according to modification 3; FIG. 11 is a cross-sectional view showing a gas adsorbent according to modification 4; 4B is a cross-sectional view showing the thickness of the gas adsorbent in the stacking direction in the battery shown in FIG. 4A. FIG. 4B is a cross-sectional view showing the width of the gas adsorbent in the plane direction in the battery shown in FIG. 4A. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the claims and is not limited only to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios. In this specification, "X to Y" indicating a range means "X or more and Y or less".

<Bipolar secondary battery>
As an example of a bipolar secondary battery according to an embodiment of the present invention, a bipolar lithium ion secondary battery, which is a type of non-aqueous electrolyte secondary battery, will be described. Here, the bipolar lithium ion secondary battery is a secondary battery that includes series-connected bipolar electrodes and performs charging and discharging by moving lithium ions between a positive electrode and a negative electrode. In the following description, the bipolar lithium ion secondary battery is also simply referred to as "battery".

FIG. 1 is a perspective view showing a battery 10 according to one embodiment of the invention. FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1, showing an outline of the overall structure of the battery 10. As shown in FIG. FIG. 3 is a cross-sectional view showing a single cell 20 of battery 10. As shown in FIG. 4A is a cross-sectional view taken along line 4-4 of FIG. 1, showing a gas adsorbent in the battery. FIG.

A battery 10 of the present embodiment will be outlined with reference to FIGS. 1 to 4. FIG. A battery 10 has a power generation element 11 in which a plurality of single cells 20 are stacked. The single cell 20 includes a positive electrode 30a, a negative electrode 30b, a separator 40, and an insulating member 50. The positive electrode 30a is formed by forming a positive electrode active material layer 32a on a positive electrode current collector 31a. The negative electrode 30b is formed by forming a negative electrode active material layer 32b on a negative electrode current collector 31b. The separator 40 is sandwiched between the positive electrode active material layer 32a and the negative electrode active material layer 32b. The insulating member 50 is disposed on the positive electrode current collector 31a, the negative electrode current collector 31b, and the outer peripheral portion 60 of the separator 40, seals the positive electrode active material layer 32a between the positive electrode current collector 31a and the separator 40, and seals the positive electrode active material layer 32a between the positive electrode current collector 31a and the separator. A negative electrode active material layer 32b is sealed between the current collector 31b and the separator 40 . The positive electrode current collector 31a and the negative electrode current collector 31b have gas permeability. In the non-electrode portion 70 where the positive electrode active material layer 32a and the negative electrode active material layer 32b are not formed, the positive electrode current collector 31a of one unit cell 20 and the other unit cell 20 adjacent to the positive electrode current collector 31a A gas adsorbent 80 is arranged between it and the negative electrode current collector 31b. The configuration of the battery 10 will be described in detail below.

As shown in FIG. 2, the battery 10 has a structure in which a power generation element 11 having a plurality of stacked single cells 20 is sealed inside an exterior body 12 in order to prevent impact from the outside and environmental deterioration. The power generation element 11 is a laminate of single cells 20 and is a part that contributes to charge/discharge reactions. It is preferable to adjust the number of times the unit cells 20 are stacked according to the desired voltage. Also, in this specification, the direction in which the plurality of unit cells 20 are stacked is referred to as a "stacking direction" and is indicated by an arrow Z in the drawing. A plane orthogonal to the stacking direction is called a "plane direction" and indicated by an arrow X and an arrow Y in the figure.

As shown in FIG. 2, the positive electrode 30a and the negative electrode 30b are formed with a positive electrode active material layer 32a electrically coupled to one surface of the current collector 31 and electrically connected to the opposite surface of the current collector 31. A bipolar electrode 35 having a bonded negative electrode active material layer 32b is formed. The current collector 31 has a laminated structure (two-layer structure) in which a positive electrode current collector 31a and a negative electrode current collector 31b are combined.

In the battery 10, a positive collector plate (positive tab) 34a is arranged adjacent to the positive collector 31a, and a negative collector plate (negative tab) 34b is arranged adjacent to the negative collector 31b. there is As also shown in FIG. 1 , the positive electrode collector plate (positive electrode tab) 34 a is extended and led out from the exterior body 12 . Similarly, the negative electrode current collecting plate (negative electrode tab) 34 b is extended and led out from the exterior body 12 .

[Single cell]
As shown in FIGS. 2 and 3, the single cell 20 includes a positive electrode 30a, a negative electrode 30b, a separator 40, and an insulating member 50. As shown in FIGS. An electrolyte layer is formed by holding the electrolyte in the separator 40 . In the single cell 20 of the present embodiment, the positive electrode active material layer 32a and the negative electrode active material layer 32b contain an electrolytic solution.

The positive electrode 30a is formed by forming a positive electrode active material layer 32a on one surface of a positive electrode current collector 31a. The negative electrode 30b is formed by forming a negative electrode active material layer 32b on one surface of a negative electrode current collector 31b. The positive electrode active material layer 32a and the negative electrode active material layer 32b are arranged to face each other with the separator 40 interposed therebetween. The positive electrode current collector 31a and the negative electrode current collector 31b are located in the outermost layers of the single cell 20 . The positive electrode current collector 31 a and the negative electrode current collector 31 b have gas permeability, and can discharge gas generated by charge/discharge reactions to the outside of the unit cell 20 .

The insulating member 50 liquid-tightly seals the positive electrode active material layer 32a, the negative electrode active material layer 32b, and the separator 40 at the outer peripheral portion 60, thereby preventing liquid junction due to leakage of the electrolyte. In addition, the positive electrode current collector 31a and the negative electrode current collector 31b are electrically separated in the single cell 20 to prevent a short circuit due to contact between the positive electrode current collector 31a and the negative electrode current collector 31b. In this specification, the positive electrode current collector 31a, the negative electrode current collector 31b, and the outer peripheral portion 60 of the separator 40 refer to a region heat-sealed with the insulating member 50 interposed therebetween (the region surrounded by the dashed line in FIG. 3). defined as

Any material can be used for the insulating member 50 as long as it has insulating properties, sealing properties (liquid-tightness), heat resistance under the battery operating temperature, and the like. For example, acrylic resin, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber (ethylene-propylene-diene rubber: EPDM), and the like can be used. Alternatively, an isocyanate-based adhesive, an acrylic resin-based adhesive, a cyanoacrylate-based adhesive, or the like may be used, or a hot-melt adhesive (urethane resin, polyamide resin, polyolefin resin) or the like may be used. Among them, polyethylene resin and polypropylene resin are preferably used as constituent materials of the insulating layer from the viewpoint of corrosion resistance, chemical resistance, ease of production (film forming property), economy, etc., and amorphous polypropylene resin is the main component. It is preferable to use a resin obtained by copolymerizing ethylene, propylene, and butene.

[Gas adsorbent]
As shown in FIG. 4A, the gas adsorbent 80 is placed between two single cells 20, that is, the positive electrode current collector 31a of one single cell 20 and the other single cell 20 adjacent to the positive electrode current collector 31a. is arranged in the non-electrode portion 70 between the negative electrode current collector 31b. In this specification, the non-electrode portion 70 is defined as a region where the positive electrode active material layer 32a and the negative electrode active material layer 32b are not formed (region surrounded by broken lines in FIG. 4A). By disposing the gas adsorbent 80 between the positive electrode current collector 31a and the negative electrode current collector 31b, the gas is discharged to the outside of the unit cell 20 through the positive electrode current collector 31a and the negative electrode current collector 31b. Gas is quickly adsorbed by the gas adsorbent 80 . This prevents the single cell 20 from being compressed by the stored gas, and suppresses deterioration in battery performance due to breakage of the current collector 31 caused by distortion of the non-electrode portion 70, collapse of the electrode active material layer 32, and the like. . In addition, since the gas adsorbent 80 is arranged outside the single cell 20, it does not come into contact with the electrolyte (electrolyte solution), so that the gas adsorption amount can be prevented from decreasing.

4B to 4E are cross-sectional views showing gas adsorbents 80 according to modified examples 1 to 4, respectively. As shown in FIGS. 4B to 4E, the shape of gas adsorbent 80 is not particularly limited. For example, Modification 1 shown in FIG. 4B has a shape in which a plurality of gas adsorbents 80 are aligned in the plane direction. In modification 2 shown in FIG. 4C, the cross section of the gas adsorbent 80 has an elliptical shape. Modification 3 shown in FIG. 4D has a shape in which a plurality of gas adsorbents are arranged in a row in the stacking direction. Modification 4 shown in FIG. 4E has a shape in which part of the gas adsorbent 80 is arranged in the outer peripheral portion 60 .

FIG. 5A is a cross-sectional view showing the thickness of gas adsorbent 80 in the stacking direction in the battery shown in FIG. 4A. As shown in FIG. 5A, in the stacking direction (arrow Z in the drawing), the thickness t1 of the gas adsorbent 80 is the sum of the thickness t2 of the positive electrode active material layer 32a and the thickness t3 of the negative electrode active material layer 32b. Below is (t1≦t2+t3). In this specification, the thickness t1 of the gas adsorbent 80 is defined as the maximum thickness of the gas adsorbent 80 . When a plurality of gas adsorbents 80 are arranged in a row in the stacking direction as in Modification 3 shown in FIG. 4D, the total thickness of the plurality of gas adsorbents 80 is defined as the maximum value. On the other hand, in this specification, the sum of the thickness t2 of the positive electrode active material layer 32a and the thickness t3 of the negative electrode active material layer 32b is defined as the minimum value of the sum. By setting the thickness t1 of the gas adsorbent 80 within the above range, excess space is less likely to occur when the unit cells 20 are stacked, so a battery with a high energy density can be obtained. In addition, this makes it difficult for other members (eg, the positive electrode 30a, the negative electrode 30b, the separator 40, etc.) to be distorted. is suppressed.

FIG. 5B is a cross-sectional view showing the width of gas adsorbent 80 in the plane direction in the battery shown in FIG. 4A. As shown in FIG. 5B, the width w1 of the gas adsorbent 80 is less than or equal to the distance w2 from the end of the negative electrode active material layer 32b to the end of the insulating member 50 in the planar direction (arrow X in the drawing). In this specification, the width w1 of the gas adsorbent 80 is defined as the maximum width of the gas adsorbent 80 . When a plurality of gas adsorbents 80 are arranged in a row in the plane direction as in Modification 1 shown in FIG. 4B, the total width of the plurality of gas adsorbents 80 is defined as the maximum value. On the other hand, in this specification, the distance w2 from the end of the negative electrode active material layer 32b to the end of the insulating member 50 is defined as the minimum value of the distance. By setting the width w1 of the gas adsorbent 80 within the above range, it is possible to prevent the gas adsorbent 80 from being arranged in the region where the electrode 30 is laminated or the region where the insulating member 50 is laminated. As a result, excess space is less likely to occur, so a battery with a high energy density can be obtained. In addition, this makes it difficult for other members (eg, the positive electrode 30a, the negative electrode 30b, the separator 40, etc.) to be distorted. is suppressed.

Any material can be used as the material constituting the gas adsorbent 80 as long as it can adsorb gases (eg, H ₂ , H ₂ O, CO, CO ₂ , etc.) generated by charge/discharge reactions. Examples include silica gel, zeolite, and activated carbon. , copper chloride, metal stearates, hydrotalcite, hydrogen storage alloys, activated alumina, transition metal oxides, soda lime, calcium oxide, magnesium oxide, ascarite and the like. These materials may be used alone or in combination of two or more.

[Voltage detection terminal]
As shown in FIG. 4A, battery 10 according to one embodiment of the present invention has voltage detection terminals 90 on outer peripheral portion 60 . The voltage detection terminal 90 is arranged between the surface of the positive electrode current collector 31 a that is not in contact with the insulating member 50 and the surface of the negative electrode current collector 31 b that is not in contact with the insulating member 50 . A lead wire 91 is connected to the voltage detection terminal 90 . The lead wire 91 is connected to a controller (not shown), and a detection signal is input to the controller.

The material constituting the voltage detection terminal 90 may be any material as long as it has conductivity, and is composed of a conductive material. Examples of conductive materials include metal materials. Metal materials include aluminum, nickel, iron, stainless steel, titanium, and copper.

[Current collector]
The current collector 31 (positive electrode current collector 31a, negative electrode current collector 31b) has a function of mediating transfer of electrons from one surface in contact with the positive electrode active material layer 32a to the other surface in contact with the negative electrode active material layer 32b. have In addition, the current collector 31 can discharge the gas generated by the charge/discharge reaction to the outside of the single cell 20 . The current collector 31 is composed of a gas-permeable resin current collector. The resin current collector is made by dispersing a conductive filler in a polymeric material.

Specifically, the polymeric material that is the constituent material of the resin current collector preferably contains at least one selected from the group consisting of polyethylene (PE), polypropylene (PP) and aramid (aromatic polyamide). . These polymer materials have sufficient gas permeability and can discharge the gas generated by the charge/discharge reaction to the outside of the single cell 20 .

Any electrically conductive filler can be used without particular limitation. Examples of materials having excellent conductivity, potential resistance, or lithium ion blocking properties include metals and conductive carbon. The metal is not particularly limited, but at least one metal selected from the group consisting of nickel, titanium, aluminum, copper, platinum, iron, chromium, tin, zinc, indium, antimony, and potassium, or these metals It is preferable to include an alloy or metal oxide containing. Also, the conductive carbon is not particularly limited. Preferably, from the group consisting of acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjenblack (registered trademark), carbon nanotube (CNT), carbon nanohorn, carbon nanoballoon, and fullerene It is preferable to include at least one selected.

The amount of the conductive filler to be added is not particularly limited as long as it can impart sufficient conductivity to the current collector 31, and is preferably about 5 to 35% by volume.

[Electrode active material layer]
The electrode active material layer 32 (positive electrode active material layer 32a, negative electrode active material layer 32b) contains an electrode active material (positive electrode active material or negative electrode active material) and an electrolytic solution. In addition, the electrode active material layer 32 may contain a coating agent (coating resin, conductive aid), a conductive member, etc., if necessary. Furthermore, the electrode active material layer 32 may contain an ion-conducting polymer or the like as necessary.

The electrolytic solution contained in the electrode active material layer 32 can function as a dispersion medium for the electrode active material in the slurry preparation process. From the viewpoint of reducing man-hours by omitting the step of injecting the electrolytic solution in the step after forming the electrode 30, the electrolytic solution of the electrode active material layer 32 has the same composition as the electrolytic solution contained in the separator 40 of the battery 10. is preferred.

In the battery 10, the positive electrode active material layer 32a and the negative electrode active material layer 32b contain an electrolytic solution. In this configuration, it is not necessary to dry the obtained coating film by heating after coating the electrode active material slurry to obtain the coating film. As a result, cracking of the electrode active material layer 32 can be suppressed, and manufacturing costs required for the drying process can be reduced.

The electrolytic solution has a form in which a lithium salt is dissolved in a solvent. Examples of the solvent that constitutes the electrolytic solution include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. Lithium salts include inorganic acid lithium salts such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ LiClO ₄ , Li[(FSO ₂ ) ₂ N] (LiFSI), LiN(CF ₃ SO ₂ ) ₂ , LiN( Lithium salts of organic acids such as C ₂ F ₅ SO ₂ ) ₂ and LiC(CF ₃ SO ₂ ) ₃ are included.

(Positive electrode active material)
Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li(Ni—Mn—Co)O ₂ and lithium- Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, and the like. In some cases, two or more positive electrode active materials may be used together. From the viewpoint of capacity and output characteristics, lithium-transition metal composite oxides are preferably used as the positive electrode active material. A composite oxide containing lithium and nickel is more preferably used. More preferably, Li(Ni-Mn-Co)O ₂ and those in which a part of these transition metals are replaced with other elements (hereinafter simply referred to as "NMC composite oxide"), or lithium-nickel-cobalt - Aluminum composite oxide (hereinafter simply referred to as "NCA composite oxide") or the like is used. The NMC composite oxide has a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co are arranged in an orderly manner) atomic layers are alternately stacked via oxygen atomic layers. In addition, one Li atom is contained per transition metal atom, and the amount of Li that can be taken out is double that of the spinel-based lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained.

(Negative electrode active material)
Examples of the negative electrode active material include carbon materials such as graphite (graphite), soft carbon and hard carbon, lithium-transition metal composite oxides (eg, Li ₄ Ti ₅ O ₁₂ ), metal materials (tin, silicon), lithium Alloy negative electrode materials (eg, lithium-tin alloys, lithium-silicon alloys, lithium-aluminum alloys, lithium-aluminum-manganese alloys, etc.). In some cases, two or more kinds of negative electrode active materials may be used together. Carbon materials, lithium-transition metal composite oxides, and lithium alloy negative electrode materials are preferably used as the negative electrode active material from the viewpoint of capacity and output characteristics. Needless to say, negative electrode active materials other than those described above may be used. In addition, coating resins such as (meth)acrylate copolymers have the property of being particularly prone to adhere to carbon materials. Therefore, from the viewpoint of providing a structurally stable electrode material, it is preferable to use a carbon material as the negative electrode active material.

(Conductivity aid)
The conductive aid is used together with the coating resin as a coating agent that coats the surface of the electrode active material. The conductive aid forms an electron conduction path in the coating agent and reduces the electron transfer resistance of the electrode active material layer 32, thereby contributing to the improvement of high-rate output characteristics of the battery.

Examples of conductive aids include metals such as aluminum, stainless steel, silver, gold, copper, and titanium, alloys containing these metals, or metal oxides; graphite, carbon fiber (specifically, vapor growth carbon fiber ( VGCF), etc.), carbon nanotubes (CNT), carbon black (specifically, acetylene black, Ketjenblack (registered trademark), furnace black, channel black, thermal lamp black, etc.). is not limited to In addition, a particulate ceramic material or resin material coated with the above metal material by plating or the like can also be used as a conductive aid. Among these conductive aids, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon. , silver, gold, and carbon, and more preferably at least one carbon. These conductive aids may be used alone or in combination of two or more.

The shape of the conductive aid is preferably particulate or fibrous. When the conductive agent is particulate, the shape of the particles is not particularly limited, and may be powdery, spherical, rod-like, needle-like, plate-like, columnar, amorphous, scaly, spindle-like, or the like. I don't mind. The average particle size (primary particle size) of the conductive aid in the form of particles is preferably 100 nm or less. In this specification, the term "particle size" means the maximum distance between any two points on the contour line of the conductive aid. The value of "average particle size" is the average value of the particle size of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

(Conductive member)
The conductive member has a function of forming an electron conduction path in the electrode active material layer 32 . In particular, at least part of the conductive member preferably forms a conductive path that electrically connects the two main surfaces of the electrode active material layer 32 . With such a configuration, the electron transfer resistance in the thickness direction in the electrode active material layer 32 is further reduced, so that the high-rate output characteristics of the battery can be further improved. Whether or not at least a part of the conductive member forms a conductive path that electrically connects the two main surfaces of the electrode active material layer 32 can be determined using an SEM or an optical microscope. can be confirmed by observing the cross section of

The conductive member is preferably a conductive fiber having a fibrous form. Specifically, carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers made by uniformly dispersing highly conductive metals and graphite in synthetic fibers, and fiberizing metals such as stainless steel. metal fibers, conductive fibers obtained by coating the surfaces of organic fibers with metal, and conductive fibers obtained by coating the surfaces of organic fibers with a resin containing a conductive substance. Among them, carbon fiber is preferable because of its excellent conductivity and light weight.

In the battery 10 of the present embodiment, the thickness of the electrode active material layer 32 for the positive electrode active material layer 32a is preferably 150 to 1500 μm, more preferably 180 to 950 μm, even more preferably 200 to 800 μm. be. The thickness of the negative electrode active material layer 32b is preferably 150-1500 μm, more preferably 180-1200 μm, and even more preferably 200-1000 μm. If the thickness of the electrode active material layer 32 is equal to or greater than the above lower limit, the energy density of the battery can be sufficiently increased. On the other hand, if the thickness of the electrode active material layer 32 is equal to or less than the above upper limit, the structure of the electrode active material layer 32 can be sufficiently maintained.

In the battery 10 of the present embodiment, the constituent members of the electrode active material layer 32 include the electrode active material described above, a conductive member used as necessary, an ion conductive polymer, a lithium salt, and a coating agent (for coating). A member other than the resin and conductive aid) may be used as appropriate. However, from the viewpoint of improving the energy density of the battery, it is preferable not to include members that do not contribute much to the progress of the charge-discharge reaction. For example, it is preferable not to use a binder as much as possible to bind the electrode active material and other members and to maintain the structure of the electrode active material layer 32 . Examples of binders having the above functions include solvent-based binders such as polyvinylidene fluoride (PVdF) and water-based binders such as styrene-butadiene rubber (SBR). Specifically, the content of the binder is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 100% by mass of the total solid content contained in the electrode active material layer 32. is 2% by mass or less, particularly preferably 1% by mass or less, and most preferably 0% by mass.

[Separator]
The separator 40 holds an electrolyte and is between the positive electrode active material layer 32a and the negative electrode active material layer 32b to prevent the two from coming into direct contact with each other. The electrolyte used in the separator 40 of this embodiment is not particularly limited, and examples thereof include electrolytic solutions and gel polymer electrolytes. By using these electrolytes, high lithium ion conductivity can be ensured.

Examples of the form of the separator 40 include a porous sheet separator and a non-woven fabric separator made of a polymer or fiber that absorbs and retains the electrolyte.

As the electrolytic solution, the same electrolytic solution as that used for the electrode active material layer 32 described above can be used. The lithium salt concentration in the electrolytic solution is preferably 0.1 to 3.0M, more preferably 0.8 to 2.2M. In addition, when using an additive, the amount used is preferably 0.5 to 10% by mass, more preferably 0.5 to 5% by mass, with respect to 100% by mass of the electrolytic solution before adding the additive. be.

Examples of additives include vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinylethylene carbonate, 1,2-divinylethylene carbonate, 1-methyl- 1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate, allylethylene carbonate, vinyloxymethylethylene carbonate, allyloxymethylethylene carbonate, acryloxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate and the like. Among them, vinylene carbonate, methylvinylene carbonate and vinylethylene carbonate are preferred, and vinylene carbonate and vinylethylene carbonate are more preferred. These cyclic carbonates may be used alone or in combination of two or more.

A gel polymer electrolyte has a structure in which the electrolyte solution is injected into a matrix polymer (host polymer) made of an ion-conducting polymer. The use of a gel polymer electrolyte as the electrolyte is excellent in that the fluidity of the electrolyte is eliminated and the ionic conductivity between layers is blocked, thereby facilitating the use. Examples of ion conductive polymers used as matrix polymers (host polymers) include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene ( PVdF-HEP), polymethyl methacrylate (PMMA) and copolymers thereof.

The matrix polymer of the gel polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, an appropriate polymerization initiator is used to subject a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte to thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, or the like. A polymerization treatment may be applied.

[Exterior body]
In the present embodiment shown in FIGS. 1 and 2, the exterior body 12 is configured in a bag shape by a flexible laminate film, but is not limited to this, and is made of a rigid material, for example. A cell case or the like may be used. From the viewpoint that it has excellent high output and cooling performance and can be suitably used as a battery for large equipment such as EV and HEV, the exterior body 12 is preferably composed of a laminate film, and a laminate film containing aluminum. is particularly preferred. As the laminate film containing aluminum, for example, a laminate film having a three-layer structure in which polypropylene (PP), aluminum, and nylon are laminated in this order can be used, but the film is not limited to these.

As described above, the battery 10 according to this embodiment has the power generation element 11 in which a plurality of single cells 20 are stacked. The unit cell 20 includes a positive electrode 30a, a negative electrode 30b, a separator 40, and an insulating member 50. The positive electrode 30a is formed by forming a positive electrode active material layer 32a on a positive electrode current collector 31a. The negative electrode 30b is formed by forming a negative electrode active material layer 32b on a negative electrode current collector 31b. The separator 40 is sandwiched between the positive electrode active material layer 32a and the negative electrode active material layer 32b. The insulating member 50 is disposed on the positive electrode current collector 31a, the negative electrode current collector 31b, and the outer peripheral portion 60 of the separator 40, seals the positive electrode active material layer 32a between the positive electrode current collector 31a and the separator 40, and seals the positive electrode active material layer 32a between the positive electrode current collector 31a and the separator. A negative electrode active material layer 32b is sealed between the current collector 31b and the separator 40 . The positive electrode current collector 31a and the negative electrode current collector 31b have gas permeability. In the non-electrode portion 70 where the positive electrode active material layer 32a and the negative electrode active material layer 32b are not formed, the positive electrode current collector 31a of one unit cell 20 and the other unit cell 20 adjacent to the positive electrode current collector 31a A gas adsorbent 80 is arranged between it and the negative electrode current collector 31b. With this configuration, the gas discharged to the outside of the single cell 20 through the positive electrode current collector 31 a and the negative electrode current collector 31 b is quickly adsorbed by the gas adsorbent 80 . This prevents the single cell 20 from being compressed by the stored gas, and suppresses deterioration in battery performance due to breakage of the current collector 31 caused by distortion of the non-electrode portion 70, collapse of the electrode active material layer 32, and the like. . In addition, since the gas adsorbent 80 is arranged outside the single cell 20, it does not come into contact with the electrolyte (electrolyte solution), so that the gas adsorption amount can be prevented from decreasing.

In the battery 10, the thickness t1 of the gas adsorbent 80 in the stacking direction (arrow Z in the figure) is equal to or less than the sum of the thickness t2 of the positive electrode active material layer 32a and the thickness t3 of the negative electrode active material layer 32b (t1 ≤ t2+t3). By configuring in this way, it becomes difficult for an extra space to be generated when the unit cells 20 are stacked, so that a battery having a high energy density can be obtained. In addition, this makes it difficult for other members (eg, the positive electrode 30a, the negative electrode 30b, the separator 40, etc.) to be distorted. is suppressed.

In the battery 10, the width w1 of the gas adsorbent 80 in the planar direction (arrow X in the drawing) is less than or equal to the distance w2 from the end of the negative electrode active material layer 32b to the end of the insulating member 50. FIG. By configuring in this way, it is possible to prevent the gas adsorbent 80 from being arranged in the region where the electrode 30 is laminated or the region where the insulating member 50 is laminated. As a result, excess space is less likely to occur, so a battery with a high energy density can be obtained. In addition, this makes it difficult for other members (eg, the positive electrode 30a, the negative electrode 30b, the separator 40, etc.) to be distorted. is suppressed.

Examples are shown below.

<Example 1>
A bipolar secondary battery is manufactured by using gas-permeable resin current collectors in which acetylene black is dispersed in polypropylene (PP) as the positive electrode current collector and the negative electrode current collector, and using activated carbon as the gas adsorbent. bottom.

<Example 2>
A bipolar secondary battery was manufactured in the same manner as in Example 1, except that copper chloride (CuCl ₂ ) was used as the gas adsorbent.

<Comparative Example 1>
A bipolar secondary battery was manufactured in the same manner as in Example 1, except that no gas adsorbent was provided.

<Results>
Table 1 shows the results regarding the presence or absence of cell damage after the charge/discharge test was performed on the bipolar secondary batteries of Example 1, Example 2, and Comparative Example 1. As shown in Table 1, by using a gas-permeable resin current collector as in Examples 1 and 2 and arranging the gas adsorbent at a specific position, cell damage due to charge-discharge reactions is suppressed. shown to be done. On the other hand, as in Comparative Example 1, even when a gas-permeable resin current collector is used, when the gas adsorbent is not arranged, cell damage occurs after the charge-discharge reaction, and the battery performance is maintained. couldn't.

10 batteries,
11 power generation element,
12 outer body,
20 single cells,
30 electrodes,
30a positive electrode,
30b negative electrode,
31 current collector,
31a positive electrode current collector,
31b negative electrode current collector,
32 electrode active material layer,
32a positive electrode active material layer,
32b negative electrode active material layer,
34a positive collector plate (positive tab),
34b negative electrode current collector (negative electrode tab)
35 bipolar electrodes,
40 separator,
50 insulating member,
60 outer periphery,
70 non-electrode part,
80 gas adsorbent,
90 voltage detection terminal,
91 leads.

Claims (3)

a positive electrode in which a positive electrode active material layer is formed on a positive electrode current collector;
a negative electrode in which a negative electrode active material layer is formed on a negative electrode current collector;
a separator sandwiched between the positive electrode active material layer and the negative electrode active material layer;
The positive electrode current collector, the negative electrode current collector, and the separator are arranged in the outer periphery, and the positive electrode active material layer is sealed between the positive electrode current collector and the separator, and the negative electrode current collector and the separator are arranged. an insulating member that seals the negative electrode active material layer between itself and a separator;
has a structure in which a power generation element in which a plurality of single cells are stacked is sealed inside the exterior body,
The positive electrode current collector and the negative electrode current collector have gas permeability,
In the non-electrode portion where the positive electrode active material layer and the negative electrode active material layer are not formed, the positive electrode current collector of one of the single cells and the negative electrode of the other single cell adjacent to the positive electrode current collector A bipolar secondary battery in which a gas adsorbent is placed between a current collector. 2. The bipolar secondary battery according to claim 1, wherein the thickness of said gas adsorbent in the stacking direction is equal to or less than the sum of the thickness of said positive electrode active material layer and the thickness of said negative electrode active material layer. 3. The bipolar secondary battery according to claim 1, wherein the width of said gas adsorbent in the planar direction is equal to or less than the distance from the edge of said negative electrode active material layer to the edge of said insulating member.

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