Stacked battery and stacked battery design method

Abstract

To provide a stacked cell improved in safety in a case where internal short-circuiting occurs.SOLUTION: A stacked cell 10 comprises: a single cell laminate 40 configured by stacking single cells 30 in series over in a multistage manner via internal collectors 20; and a pair of external collectors 50 connected to electrode layers in one end and the other end of the single cell laminate 40. In the stacked cell 10, when volume resistivity of the internal collector 20 is defined as ρv[Ω m], a thickness of the internal collector 20 is defined as t[m], a maximum heat flow rate of a short-circuited part in a case where short-circuiting occurs and thermal runaway does not start is defined as Wx [W] and a voltage of the single cell 30 at the time of full charge is defined as Vmax [V], a value expressed by ρv / (π×t) is equal to or greater than a safety reference value which is determined on the basis of the heat flow rate Wx and the voltage Vmax.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a stacked battery and a method for designing a stacked battery. [Background technology]

[0002] Conventionally, a stacked battery has been known that includes a cell stack in which cells are stacked in series in multiple stages via internal current collectors, and a pair of external current collectors connected to electrode layers at one end and the other end of the cell stack. Such a stacked battery is also called a bipolar battery, and is assembled, for example, using bipolar electrodes in which electrode layers of different polarities are formed on the front and back of an internal current collector. It has been proposed that, in such a stacked battery, the electrical resistance in the planar direction of the external current collector connected to the end of the cell stack be made smaller than the electrical resistance in the stacking direction of the cell stack (see, for example, Patent Document 1). This is believed to suppress variations in current density in the cell stack and to inhibit deterioration of the cell stack that may occur due to variations in current density. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-159570 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although Patent Document 1 can suppress deterioration of the cell stack, it does not consider safety in the event of an internal short circuit.

[0005] The present disclosure has been made in view of these problems, and has as its main object to provide a stacked battery that is highly safe in the event of an internal short circuit. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present inventors have conducted extensive research and discovered that, by adjusting the resistance in the planar direction of the internal current collector, even if an internal short circuit occurs in a stacked battery, the current flowing to the internal short circuit portion can be suppressed, and heat generation at the internal short circuit portion can be suppressed to a level that does not lead to thermal runaway, which led to the completion of the presently disclosed invention.

[0007] That is, the stacked battery of the present disclosure has: a cell stack in which cells are stacked in series in multiple stages with internal current collectors interposed therebetween; and a pair of external current collectors connected to electrode layers at one end and the other end of the cell stack, When the volume resistivity of the internal current collector is ρv [Ω m], the thickness of the internal current collector is t [m], the maximum heat flow rate at the short-circuited portion when thermal runaway does not start in the event of an internal short circuit is Wx [W], and the voltage of the cell when fully charged is Vmax [V], the value expressed by ρv / (π×t) is equal to or greater than the safety standard value determined based on the heat flow rate Wx and the voltage Vmax.

[0008] The method for designing a stacked battery according to the present disclosure includes: A method for designing a stacked battery including a cell stack in which cells are stacked in series in multiple stages with internal current collectors interposed therebetween, and a pair of external current collectors connected to electrode layers at one end and the other end of the cell stack, When the volume resistivity of the internal current collector is ρv [Ω m], the thickness of the internal current collector is t [m], the maximum heat flow rate of the short-circuited portion when thermal runaway does not start in the event of an internal short circuit is Wx [W], and the voltage of the cell when fully charged is Vmax [V], a member is adopted as the internal current collector such that the value expressed by ρv / (π×t) is equal to or greater than the safety standard value established based on the heat flow rate Wx and the voltage Vmax. [Effects of the Invention]

[0009] This stacked battery and stacked battery design method can improve safety in the event of an internal short circuit. The reason for this effect is presumed to be as follows. For example, the value expressed as ρv / (π×t) corresponds to the resistance in the surface direction of the internal current collector (the direction perpendicular to the stacking direction), and if this value is appropriate, the current flowing to the short-circuited part is suppressed even if an internal short circuit occurs, so heat generation in the short-circuited part is kept to a level that does not lead to thermal runaway. This can improve safety in the event of an internal short circuit. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing the outline of the configuration of a stacked battery 10. FIG. [Figure 2] FIG. 3 is an explanatory diagram showing the current flow in the stacked battery 10 under normal conditions. [Figure 3] FIG. 3 is an explanatory diagram showing the current flow in the stacked battery 10 when an internal short circuit occurs. [Figure 4] FIG. 4 is an explanatory diagram showing the flow of current in the internal current collector 20 when an internal short circuit occurs. [Figure 5] FIG. 10 is an explanatory diagram showing the resistance when a current flows from the outer periphery of an imaginary circle to a short-circuited portion. [Figure 6] Graph showing the change in heat flow when the short-circuit resistance is changed. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Stacked battery] A laminated battery according to an embodiment will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the outline of the configuration of a laminated battery 10 according to an example of the present disclosure. FIG. 2 is an explanatory diagram showing the current flow in the laminated battery 10 under normal conditions. FIG. 3 is an explanatory diagram showing the current flow in the laminated battery 10 when an internal short circuit occurs. FIG. 4 is an explanatory diagram showing the current flow in the internal current collector 20 when an internal short circuit occurs (however, the diagram shows the current flow from an imaginary circle with a diameter D centered on the short circuit to the short circuit). FIG. 5 is an explanatory diagram showing the resistance when current flows from the outer periphery of the imaginary circle to the short circuit. FIG. 6 is a graph showing the change in heat flow when the short circuit resistance is changed.

[0012] The stacked battery 10 includes a cell stack 40 in which cells 30 are stacked in multiple stages, and a pair of external current collectors 50. Each cell 30 includes a positive electrode layer 32, a negative electrode layer 34, and an ion-conducting medium 36 interposed between the positive electrode layer 32 and the negative electrode layer 34. Here, the ion-conducting medium 36 is impregnated in a separator 38 interposed between the positive electrode layer 32 and the negative electrode layer 34. The cell stack 40 is stacked in multiple stages so that the cells 30 are connected in series via the internal current collector 20, i.e., so that the positive electrode layers 32 and the negative electrode layers 34 alternate. This cell stack 40 has a structure in which a bipolar electrode BP is stacked, with the positive electrode layer 32 on one side of the internal current collector 20 and the negative electrode layer 34 on the other side. The cell stack 40 and the external current collector 50 are housed in an exterior case 60.

[0013] The stacked battery 10 may be an ion secondary battery in which carrier ions are absorbed and released (inserted and desorbed) in the positive electrode layer 32 and the negative electrode layer 34. Examples of carrier ions include Group 1 (alkali metal) ions such as lithium ions, sodium ions, and potassium ions, and Group 2 ions such as magnesium ions, strontium ions, and calcium ions. Here, the case in which the stacked battery 10 is a lithium ion secondary battery in which lithium ions are carrier ions will be mainly described.

[0014] In the stacked battery 10, when the volume resistivity of the internal current collector 20 is ρv [Ω·m], the thickness of the internal current collector 20 is t [m], the maximum heat flow rate (amount of heat generated) at the short circuited portion when thermal runaway does not start in the event of an internal short circuit is Wx [W], and the voltage of the cell 30 when fully charged is Vmax [V], the value expressed by ρv / (π×t) satisfies or exceeds the safety standard value determined based on the heat flow rate Wx and the voltage Vmax. Note that in this specification, the volume resistivity ρv is the volume resistivity at 100°C.

[0015] The voltage Vmax of the cells 30 when fully charged can be calculated by dividing the rated voltage set for the stacked battery 10 by the number of cells 30. For example, in lithium ion batteries, the voltage Vmax is often set to 4.1 V.

[0016] The maximum heat flow rate Wx (hereinafter referred to as the safe heat flow rate) at the short circuit point that will prevent thermal runaway from occurring in the event of an internal short circuit can be determined experimentally. Here, as an example of an experiment to determine the safe heat flow rate Wx, we describe the determination of the safe heat flow rate Wx for a lithium-ion battery with a voltage Vmax of 4.1 V and a capacity of 1 Ah per cell 30. In this experiment, a lithium-ion battery (with only one cell 30) was fully charged to 4.1 V, with a voltage Vmax of 4.1 V and a capacity of 1 Ah per cell 30. The resistance of the short circuit (short-circuit resistance Rs [Ω]) was varied, and a nail penetration test was conducted multiple times at room temperature to check for the occurrence of intense smoke or fire due to thermal runaway. The resistance of the short circuit point was varied by adjusting the nail penetration depth based on a previously determined relationship between the nail penetration depth and the DC resistance between the terminals of the uncharged lithium-ion battery. The results are shown in Table 1. In Table 1, the heat flow rate Wc is calculated by the voltage Vmax (4.1V) when fully charged and the short-circuit resistance Rs immediately after the short circuit: Wc = Vmax 2 This value was calculated using the formula / Rs.

[0017] [Table 1]

[0018] As shown in Table 1, it was found that with the lithium-ion battery used in the experiment, no signs of thermal runaway appeared until the heat flow Wc at the short circuit point reached 50 W, but signs of thermal runaway appeared when the heat flow Wc at the short circuit point exceeded 50 W. From these results, the safe heat flow Wx was determined to be 50 W. Similar results can be obtained with any lithium-ion battery.

[0019] The safety standard value can be determined by calculation using the above-mentioned safe heat flow rate Wx and voltage Vmax. In this case, factors other than the safe heat flow rate Wx and voltage Vmax (for example, the influence of the resistance of the short circuit, which will be described in detail later) may be taken into consideration. The safety standard value is, for example, Vmax 2 / 8Wx. That is, the stacked battery 10 may satisfy the following formula (1).

[0020]

number

[0021] The safety standard value is, for example, Vmax 2 / 400. That is, the stacked battery 10 may satisfy the following formula (2): When the safe heat flow rate Wx (50 W) calculated as above is substituted into formula (1), formula (2) is obtained.

[0022]

number

[0023] The safety standard value may be 42 mΩ. When the above-mentioned Vmax=4.1 V is applied to equation (2), the safety standard value becomes 42 mΩ. Taking into account the influence of the resistance of the short-circuited portion, for example, the safety standard value may be set to 40 mΩ or 39 mΩ.

[0024] The upper limit of the value of ρv / (π×t) is not particularly limited, but may be, for example, 1 Ω or less.

[0025] The internal current collector 20 is made of a sheet-like conductive material. The internal current collector 20 is made of a material whose value expressed by ρv / (π×t) satisfies or exceeds the safety standard value determined based on the safe heat flow rate Wx and voltage Vmax.

[0026] The volume resistivity ρv of the internal current collector 20 is, for example, 40×10 -8It may be 50×10 Ω·m or more. -8 It may be 60×10 Ω·m or more. -8 In this way, the thickness of the internal current collector 20 can be made extremely thin to satisfy the formula (1). In addition, the volume resistivity ρv of the internal current collector 20 can be set to, for example, 100×10 -8 It may be Ω·m or less, and 90×10 -8 It may be 80×10 Ω·m or less. -8 The electrical resistance may be Ω·m or less. This reduces the internal resistance during normal charging and discharging. Stainless steel such as SUS316 or SUS304, titanium, carbon, etc., can be suitably used as the material for the current collector. The current collector may be circular, for example, and may have a larger diameter than the positive electrode layer 32, the negative electrode layer 34, and the separator 38.

[0027] The thickness t of the internal current collector 20 may be, for example, 10 μm or less, or 8 μm or less. The thickness t of the internal current collector 20 is preferably 6.3 μm or less, and more preferably 5.9 μm or less. The thickness t of the internal current collector 20 may be, for example, 0.1 μm or more, 1 μm or more, or 5 μm or more.

[0028] The positive electrode layer 32 includes a positive electrode active material. The positive electrode layer 32 may be formed, for example, by mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode mixture, drying the mixture, and compressing it to increase electrode density as needed. Examples of the positive electrode active material include sulfides containing transition metal elements and oxides containing lithium and transition metal elements. Examples of the former include transition metal sulfides such as TiS2, TiS3, MoS3, and FeS2. Examples of the latter include lithium manganese composite oxide, lithium cobalt composite oxide, lithium nickel composite oxide, lithium nickel cobalt manganese composite oxide, lithium vanadium composite oxide, and lithium iron phosphate compounds. Conductive materials include graphite (e.g., natural graphite (e.g., scaly graphite, flake graphite) and artificial graphite), acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (e.g., copper, nickel, aluminum, silver, and gold), either singly or in combination. Binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and fluororubber; thermoplastic resins such as polypropylene and polyethylene; ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR), either singly or in combination. Solvents include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

[0029] The negative electrode layer 34 includes a negative electrode active material. The negative electrode layer 34 may be formed, for example, by mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like negative electrode mixture, drying the mixture, and compressing it to increase electrode density as needed. Examples of negative electrode active materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. The conductive material, binder, and solvent may be the same as those used in the positive electrode layer 32.

[0030] The ion-conducting medium 36 may be a non-aqueous electrolyte solution containing a supporting salt, a non-aqueous gel electrolyte solution, or the like. Examples of solvents for non-aqueous electrolyte solutions include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, which may be used alone or in combination. Specific examples of carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; and γ-butyl carbonate. Examples of supporting salts include cyclic esters such as lactone and γ-valerolactone, chain esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane, nitriles such as acetonitrile and benzonitrile, furans such as tetrahydrofuran and methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Examples of supporting salts include LiPF, LiBF, LiAsF, LiCF, LiN(CF,SO), LiC(CF,SO), LiSbF, LiSiF, LiAlF, LiSCN, LiClO, LiCl, LiF, LiBr, LiI, and LiAlCl. The concentration of this supporting salt in the electrolyte is preferably 0.1 mol / L to 5 mol / L, and more preferably 0.5 mol / L to 2 mol / L.

[0031] The separator 38 insulates the positive electrode layer 32 from the negative electrode layer 34 without impeding ionic conduction of carrier ions. In other words, the separator 38 is configured to allow carrier ions to pass through but not electrons. The separator 38 may be made of any material as long as it can withstand the range of use of the stacked battery 10. Examples of the separator 38 include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous membranes made of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination. The thickness of the separator 38 is preferably 5 μm or more, more preferably 8 μm or more, and may be 10 μm or more. A thickness of 5 μm or more is preferable for ensuring insulation. The thickness of the separator 38 is preferably 15 μm or less, more preferably 10 μm or less. A thickness of 15 μm or less is preferable for preventing a decrease in ionic conductivity and for further reducing the volume occupied by the cell.

[0032] A pair of external current collectors 50 are provided so as to contact the outer electrode layers of each of the two cells 30 located at both ends of the cell stack 40. The external current collectors 50 can be made of, for example, copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymers, conductive glass, Al-Cd alloys, or materials such as copper whose surfaces have been treated with carbon, nickel, titanium, or silver to improve adhesion, conductivity, and reduction resistance. The external current collectors 50 can be made of the same material as the internal current collectors 20 or a different material. The external current collectors 50 can be made by stacking multiple current collectors similar to the internal current collectors 20, or by stacking a current collector similar to the internal current collector 20 with another current collector. The external current collectors 50 can be in the form of a sheet, a net, a punched or expanded material, a lath, a porous material, a foam, a fiber group formation, or the like. The thickness of the external current collector 50 is preferably the same as or thicker than the internal current collector 20. The thickness of the external current collector 50 may be, for example, 500 μm or less. One and the other external current collectors 50 may be made of the same material and have the same shape, or may be different in at least one of the material and the shape.

[0033] The exterior case 60 houses the cell stack 40 and the external current collectors 50 and has openings that expose portions of each external current collector 50. The exterior case 60 is formed, for example, in a cylindrical shape. The material of the exterior case 60 may be, for example, a laminate film, or may be, for example, a polymer-metal composite film in which a heat-sealable resin film, a metal foil, and a rigid resin film are laminated in this order from the inside to the outside. Examples of the heat-sealable resin film that can be used include polyethylene, ionomer, and ethylene vinyl acetate. Examples of the metal foil that can be used include aluminum foil and nickel foil. Examples of the rigid resin that can be used include polyethylene terephthalate and nylon. The internal current collector 20 may be fixed to the exterior case 60 by, for example, heat-sealing the heat-sealable resin film.

[0034] In the laminated battery 10 described above, during normal charge and discharge, current flows in the thickness direction of the internal current collector 20 (see the outline arrows) as shown in FIG. 2 . On the other hand, when an internal short circuit occurs, current flows in the plane direction of the internal current collector 20 (see the outline arrows) as shown in FIGS. 3 and 4 . Here, if the resistance in the plane direction of a virtual circle of diameter D centered on the short circuit (assumed to be a point) in the internal current collector 20 is Rx [Ω], the value of Rx can be calculated using the following formula. First, by dividing the virtual circle of diameter D into infinitesimal sections in the radial direction, as shown in FIG. 5A , it can be approximated by an isosceles triangle (thickness t) with a base length of ΔπD [m] and the remaining two sides of lengths D / 2 [m], as shown in FIG. 5B . The average resistance in this isosceles triangle can be approximated by the resistance of a rectangle (thickness t) with a width of π × D / 2 [m] and a length (direction of current flow) of D / 2 [m], as shown in FIG. 5B . Using this, the resistance Rx is calculated as follows: Rx={ρv×(D / 2)} / {π×(D / 2)×t}=ρv / (π×t).

[0035] As can be seen from the above calculation results, the diameter D is not involved in the resistance Rx. This shows that the resistance Rx of the current flowing in the planar direction of the internal current collector 20 from the outer periphery toward the short-circuited part (or from the short-circuited part toward the outer periphery) when an internal short circuit occurs is determined only by the volume resistivity ρv of the internal current collector 20 and the thickness t of the internal current collector 20, regardless of the size of the electrode or the position of the short-circuited part. Therefore, the resistance in the planar direction of the internal current collector 20 is equal to the above-mentioned resistance Rx = ρv / (π×t). In other words, ρv / (π×t) corresponds to the resistance in the planar direction of the internal current collector 20.

[0036] Incidentally, when an internal short circuit occurs in a battery, local heat generation occurs at the short-circuited portion, and if the heat flow rate Ws [W] at the short-circuited portion (local heat generation) exceeds a predetermined value (the above-mentioned safe heat flow rate Wx [W]), thermal runaway may occur. The heat flow rate Ws at the short-circuited portion varies depending on the short-circuit resistance (resistance of the short-circuited portion) Rs [Ω]. FIG. 6 is a graph showing calculated changes in the heat flow rate Ws at the short-circuited portion, the heat flow rate inside the battery (heat flow rate due to the battery's internal resistance Ri [Ω]) Wi, and the sum of these, Wi + Ws, when the short-circuit resistance Rs is changed. This graph applies not only to the laminated battery 10 of the present disclosure but also to general batteries. In FIG. 6, for ease of explanation, the battery voltage is normalized to 1 V and the internal resistance Ri to 1 Ω. Note that in FIG. 6, the heat flow rate Wi is calculated as Wi = 1 / (1 + Rs) 2 The heat flow rate Ws is expressed as Ws=Rs / (1+Rs) 2 It is expressed as:

[0037] As shown in Figure 6, the heat flow rate Ws at the short circuit is maximum when the short circuit resistance Rs is equal to the battery's internal resistance Ri, and this value is calculated to be 25% of Wi + Ws (≒ Wi), which is the total heat generation amount when the battery is short-circuited with zero resistance (when the short circuit resistance Rs approaches zero).From this, it can be seen that in a battery configured so that the heat flow rate Wi when short-circuited with zero resistance is four times or less the above-mentioned safe heat flow rate Wx, that is, so that Wi≦4Wx, the heat flow rate Ws at the short circuit will be less than the safe heat flow rate Wx, and thermal runaway will not occur.

[0038] Applying this to the stacked battery 10, it can be assumed that the heat flow rate Wi when a short circuit occurs with zero resistance is equivalent to the heat flow rate when the two internal current collectors 20 sandwiching the shorted cell 30 are shorted with zero resistance. The resistance in the surface direction of each internal current collector 20 is expressed as ρv / (π×t) as described above. Furthermore, since the voltage between the two internal current collectors 20 sandwiching the shorted cell 30 is Vmax at most, the voltage applied to each internal current collector 20 is Vmax / 2 at most. From the above, the heat flow rate Wi when the stacked battery 10 is shorted with zero resistance can be expressed as Wi={2×(Vmax / 2) 2} / {ρv / (π×t)}=Vmax 2×π×t / 2ρv. Therefore, if the heat flow rate Wi thus determined satisfies Wi≦4Wx, that is, if the above-described formula (1) is satisfied, thermal runaway will not occur even if an internal short circuit occurs. Therefore, in a stacked battery 10 that satisfies formula (1), safety in the event of an internal short circuit can be improved. According to formula (1), when the safe heat flow rate Wx is 50 W, safety in the event of an internal short circuit can be improved if formula (2) is satisfied. Furthermore, when the safe heat flow rate Wx is 50 W and the voltage Vmax is 4.1 V, safety in the event of an internal short circuit can be improved if the value of ρv / (π×t) is 42 mΩ or more. Therefore, the safety standard value can be set to, for example, 42 mΩ.

[0039] In an actual battery, a short circuit does not occur with zero resistance, and a resistance of several mΩ occurs at the short circuited portion. Taking this into consideration, for example, when the safe heat flow rate Wx is 50 W and the voltage Vmax is 4.1 V, if the value of ρv / (π×t) is 39 mΩ or more (preferably 40 mΩ or more), thermal runaway will not occur and safety in the event of an internal short circuit can be improved. Therefore, the safety standard value may be, for example, 40 mΩ or 39 mΩ. The material of the internal current collector 20 should have a volume resistivity of 78×10 at 100°C. -8 In the case of using SUS304 with a resistance of Ω·m, if the thickness of the internal current collector 20 is 6.3 μm or less, the value of ρv / (π×t) can be 39 mΩ or more, if the thickness of the internal current collector 20 is 6.2 μm or less, the value of ρv / (π×t) can be 40 mΩ or more, and if the thickness of the internal current collector 20 is 5.9 μm or less, the value of ρv / (π×t) can be 42 mΩ or more.

[0040] As described above, in the stacked battery 10, the value expressed by ρv / (π×t) is equal to or greater than the predetermined value (safety standard value) determined based on the safe heat flow rate Wx and the voltage Vmax, so thermal runaway does not occur even if an internal short circuit occurs. This improves safety when an internal short circuit occurs.

[0041] [Stacked battery design method] The stacked battery design method is a method for designing the stacked battery 10 described above. In this design method, a material for which the value expressed by ρv / (π×t) is equal to or greater than the safety standard value established based on the safe heat flow rate Wx and voltage Vmax is used as the internal current collector. The safe heat flow rate Wx and voltage Vmax vary depending on the materials and amounts used of the positive electrode active material, negative electrode active material, ion conductive medium, etc. (also referred to as battery configuration), and the safety standard value also varies depending on these differences in battery configuration. Therefore, by designing the material (volume resistivity ρv) and thickness t of the internal current collector 20 so that the value expressed by ρv / (π×t) is equal to or greater than the safety standard value corresponding to the battery configuration, a stacked battery with high safety in the event of an internal short circuit can be realized.

[0042] The present disclosure is not limited to the above-described embodiment and may be embodied in various forms within the technical scope of the present disclosure. For example, in the above-described embodiment, an electrolyte solution is used as the ion conductive medium 36. However, a solid electrolyte may be used instead of the electrolyte solution, and the stacked battery 10 may be an all-solid-state battery. The separator 38 may also be omitted. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes. Examples of inorganic solid electrolytes include nitrides, halides, oxyacid salts, and phosphorus sulfide compounds of Li. More specifically, examples of such solid electrolytes include Li4SiO4, Li4SiO4-LiI-LiOH, xLi3PO4-(1-x)Li4SiO4, Li2SiS3, and Li3PO4-Li2S-SiS2. Examples of organic solid electrolytes include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene, and derivatives thereof. These may be used alone or in combination. [Industrial Applicability]

[0043] The present disclosure is applicable to the field of the battery industry. [Explanation of symbols]

[0044] 10 battery stack, 20 internal current collector, 30 cell, 32 positive electrode layer, 34 negative electrode layer, 36 ionically conductive medium, 38 separator, 40 cell stack, 50 external current collector, 60 outer case, BP bipolar electrode.

Claims

1. a cell stack in which cells are stacked in series in multiple stages with internal current collectors interposed therebetween; and a pair of external current collectors connected to electrode layers at one end and the other end of the cell stack, where ρv [Ω m] is the volume resistivity of the internal current collector, t [m] is the thickness of the internal current collector, Wx [W] is the maximum heat flow rate at the short-circuited portion when thermal runaway does not start in the event of an internal short circuit, and Vmax [V] is the voltage of the cell when fully charged, a value expressed by ρv / (π×t) is equal to or greater than a safety standard value determined based on the heat flow rate Wx and the voltage Vmax, and satisfies the following formula (1): Stacked battery. [Equation 1]

2. The unit cell stack has a structure in which bipolar electrodes having electrode layers of different polarities on the front and back of the internal current collector are stacked. The laminated battery according to claim 1 .

3. The laminated battery according to claim 1 or 2, which satisfies the following formula (2): [Equation 2]

4. The laminated battery according to any one of claims 1 to 3, wherein the safety standard value is 40 mΩ.

5. 5. The stacked battery according to claim 1, wherein the internal current collector is made of stainless steel and has a thickness of 6.3 μm or less.

6. A method for designing a stacked battery including a cell stack in which cells are stacked in series in multiple stages with internal current collectors interposed therebetween, and a pair of external current collectors connected to electrode layers at one end and the other end of the cell stack, When the volume resistivity of the internal current collector is ρv [Ω m], the thickness of the internal current collector is t [m], the maximum heat flow rate of the short-circuited portion when thermal runaway does not start in the event of an internal short circuit is Wx [W], and the voltage of the cell when fully charged is Vmax [V], a value expressed by ρv / (π×t) is equal to or greater than a safety standard value determined based on the heat flow rate Wx and the voltage Vmax, and a member that satisfies the following formula (1) is adopted as the internal current collector: How to design stacked batteries. [Equation 1]

Images