Stackable battery

Abstract

Stack battery (100), comprising: a plurality of cells (10) in a thickness direction, wherein the plurality of cells (10) are electrically connected in parallel; each of the plurality of cells (10) includes a cathode current collector (4), a cathode active material layer (1), a solid electrolyte layer (3), an anode active material layer (2) and an anode current collector (5) in this order; the stacked battery (100) includes a surface-side cell located on a surface side of the stacked battery (100) and a center-side cell located on a center side other than the surface-side cell; and the surface cell and the middle cell satisfy at least one of: Condition i), according to which a strain rate of the cathode current collector (4) in the surface-side cell is lower than a strain rate of the cathode current collector (4) in the middle-side cell; and Condition ii) according to which a strain rate of the anode current collector (5) in the surface-side cell is lower than a strain rate of the anode current collector (5) in the middle-side cell, characterized in that condition i) further satisfies at least one of: Condition i-1) the material for the cathode current collector (4) in the surface-side cell is a material having a lower strain rate than that of the material for the cathode current collector (4) in the center-side cell; and Condition i-2) the thickness of the cathode current collector (4) in the surface-side cell is less than the thickness of the cathode current collector (4) in the center-side cell; and condition ii) further satisfies at least one of: Condition ii-1) the material for the anode current collector (5) in the surface-side cell is a material having a lower strain rate than that of the material for the anode current collector (5) in a center-side cell; and Condition ii-2) the thickness of the anode current collector (5) in the surface-side cell is less than the thickness of the anode current collector (5) in the center-side cell.

Description

TECHNICAL FIELD

[0001] The present invention relates to a stack battery. STATE OF THE ART

[0002] Stacked batteries are known that include a plurality of cells in a thickness direction; each of the plurality of cells includes a cathode current collector, a cathode active material layer, a solid electrolyte layer, an anode active material layer, and an anode current collector in this order. For example, Patent Literature 1 discloses a lithium-ion secondary battery comprising a plurality of unit cells, each of the plurality of unit cells including: a cathode layer provided with a cathode current collector and a cathode mixture layer; a solid electrolyte layer; and an anode layer provided with an anode current collector and an anode mixture layer. Furthermore, Patent Literature 1 discloses a nail penetration test as a method for evaluating the safety of solid-state batteries.

[0003] Also, for example, Patent Literature 2 discloses a method for manufacturing a stack-type solid-state battery, wherein: the stack-type solid-state battery includes a plurality of solid-state battery cells connected in a bipolar form or a monopolar form; and each of the plurality of solid-state battery cells includes a cathode current collector layer, a cathode active material layer, a solid electrolyte layer, an anode active material layer, and an anode current collector layer.

[0004] Patent Literature 3 discloses a prior art laminated battery.

[0005] Patent Literature 4 discloses a prior art spherical silicon-carbon nanocomposite used as an anode material for lithium-ion batteries. LIST OF CITIONS Patent Literature 1: JP 2016-207614 A Patent Literature 2: JP 2016-136490 A Patent literature 3: WO 2017 / 038042 A1 Patent literature 4: DE 10 2014 210 613 A1 SUMMARY OF THE INVENTIONTechnical Problem

[0006] As described above, the nail penetration test is known as a method for assessing the safety of solid-state batteries. The nail penetration test involves penetrating a solid-state battery with a conductive nail and observing changes (such as temperature changes) when an internal short circuit occurs within the battery.

[0007] From detailed studies of the nail penetration test on stacked batteries with a plurality of solid-state battery cells electrically connected in parallel, the present inventors have obtained the new knowledge that the resistance of a short-circuit part (short-circuit resistance) in each cell varies greatly with cell location. When a cell with low short-circuit resistance and a cell with high short-circuit resistance are combined, a current flows from the cell with high short-circuit resistance to the cell with low short-circuit resistance. Hereinafter, this may be referred to as a "leakage current." When the leakage current occurs, the temperature of the cell with low short-circuit resistance (the cell into which the current has flowed) increases, and as a result, the battery materials are likely to deteriorate.

[0008] The present invention has been made in view of the above circumstances, and a main object thereof is to provide a stacked battery in which the unevenness of a short-circuit resistance between a plurality of cells is suppressed. Solution to the problem

[0009] To achieve the object, the present invention provides a stacked battery comprising: a plurality of cells in a thickness direction, the plurality of cells being electrically connected in parallel; each of the plurality of cells includes a cathode current collector, a cathode active material layer, a solid electrolyte layer, an anode active material layer, and an anode current collector in this order; the stacked battery includes a surface-side cell located on a surface side of the stacked battery and a center-side cell located on a center side other than the surface-side cell; and the surface-side cell and the center-side cell satisfy at least one of: condition i) that a strain rate of the cathode current collector in the surface-side cell is lower than a strain rate of the cathode current collector in the center-side cell;and condition ii) that a strain rate of the anode current collector in the surface-side cell is lower than a strain rate of the anode current collector in the center-side cell. The present invention is characterized in that condition i) further satisfies at least one of: Condition i-1) the material for the cathode current collector in the surface-side cell is a material with a lower strain rate than that of the material for the cathode current collector in the middle-side cell; and Condition i-2) the thickness of the cathode current collector in the surface-side cell is less than the thickness of the cathode current collector in the center-side cell; and condition ii) further satisfies at least one of: Condition ii-1) the material for the anode current collector in the surface-side cell is a material having a lower strain rate than that of the material for the anode current collector in a center-side cell; and Condition ii-2) the thickness of the anode current collector in the surface-side cell is less than the thickness of the anode current collector in the center-side cell.

[0010] According to the present invention, since the surface-side cell and the center-side cell satisfy at least one of condition i) and condition ii), the unevenness of the short-circuit resistance between the plurality of cells can be suppressed in the stacked battery.

[0011] In the invention, when each of the plurality of cells is numbered in an order along the thickness direction of the stacked battery as a 1st cell to an Nth cell, where N ≥ 3, the surface-side cell may be a cell belonging to a cell region A including the 1st cell to an (N / 3)th cell.

[0012] In the invention, the center cell may be a cell belonging to a cell range B including a ((N / 3) + 1)th cell to a (2N / 3)th cell.

[0013] In the invention, an average strain rate of the cathode current collector in the cell region A may be lower than an average strain rate of the cathode current collector in the cell region B.

[0014] In the invention, an average strain rate of the anode current collector in the cell region A may be lower than an average strain rate of the anode current collector in the cell region B.

[0015] In the invention, when each of the plurality of cells is numbered in order along the thickness direction of the stacked battery as a 1st cell to an Nth cell, where N ≥ 60, the surface-side cell may be a cell belonging to a cell region C including the 1st cell to a 20th cell.

[0016] In the invention, the center cell may be a cell belonging to a cell range D including a 21st cell up to a 40th cell.

[0017] In the invention, an average strain rate of the cathode current collector in the cell region C may be lower than an average strain rate of the cathode current collector in the cell region D.

[0018] In the invention, an average strain rate of the anode current collector in the cell region C may be lower than an average strain rate of the anode current collector in the cell region D.

[0019] In the invention, the anode active material layer may include Si or a Si alloy as an anode active material. Advantageous effects of the invention

[0020] The stacked battery in the present invention is effective to suppress unequal short-circuit resistance between a plurality of cells. Short description of the drawings Fig. 1 is a schematic cross-sectional view showing an example of the stacked battery of the present invention; Fig. 2 is a schematic cross-sectional view explaining a nail penetration test; Fig.Figure 3 is a graph showing the relationship between cell location and short-circuit resistance; Fig. Figure 4 is an equivalent circuit diagram explaining a leakage current; Fig. 5 is a schematic cross-sectional view explaining a nail penetration test; Fig. 6A to 6E are schematic cross-sectional views exemplifying a method for manufacturing a two-stack cell; and Fig. Figure 7 is a graph illustrating an example of a stress profile in a nail penetration test. Description of embodiments

[0021] The stack battery of the present invention will be described in detail below. Fig. 1 is a schematic cross-sectional view showing an example of the stacked battery of the present invention. Fig.The stacked battery 100 shown in Figure 1 comprises a plurality of cells 10 (10A, 10B to 10H to 10N) in a thickness direction; and each of the plurality of cells 10 includes a cathode current collector 4, a cathode active material layer 1, a solid electrolyte layer 3, an anode active material layer 2, and an anode current collector 5 in this order. Furthermore, the plurality of cells 10 are electrically connected in parallel. A method for connecting the cells in parallel is not particularly limited, and for example, the methods shown in Fig.The cells 10A and 10B shown in Figure 1 are connected in parallel such that the cells share the anode current collector 5. Furthermore, two adjacent cells may or may not share the cathode current collector 4 or the anode current collector 5. By providing, for example, a two-layer cathode current collector 4 or a two-layer anode current collector 5 in the latter case, the two adjacent cells have the cathode current collector 4 or the anode current collector 5 individually between the cells.

[0022] The stacked battery 100 also includes a surface-side cell 10X located on a surface side of the stacked battery 100, and a center-side cell 10Y located on a center side other than the surface-side cell 10X. Furthermore, the surface-side cell 10X and the center-side cell 10Y have a configuration such that they satisfy at least one of: Condition i), according to which a strain rate of the cathode current collector 4 in the surface-side cell 10X is lower than a strain rate of the cathode current collector 4 in the center-side cell 10Y; and Condition ii) that a strain rate of the anode current collector 5 in the surface-side cell 10X is lower than a strain rate of the anode current collector 5 in the center-side cell 10Y.

[0023] According to the present invention, since the surface-side cell and the center-side cell satisfy at least one of condition i) and condition ii), the short-circuit resistance disparity among the plurality of cells in the stacked battery can be suppressed. As described above, the present inventors have obtained a new insight from detailed studies of the nail penetration test on stacked batteries with a plurality of cells electrically connected in parallel that the resistance of a short-circuit part (short-circuit resistance) in each cell varies greatly with the cell location.

[0024] This new finding is now discussed with reference to Fig. 2. As explained in Fig. As shown in Figure 2, a nail 110 has penetrated into the stacked battery 100, which comprises a plurality of cells 10 (10A, 10B to 10H to 10N) connected electrically in parallel. For this reason, a short-circuit resistance R (R A , R B to RH to R N ) with respect to each cell 10. As a result of such detailed studies, as for example in Fig. As shown in Figure 3, it was found that the surface-side cell 10A had a lower short-circuit resistance than the center-side cell 10H. In other words, it was found that there was an inequality in short-circuit resistance among the majority of cells.

[0025] When a cell with low short-circuit resistance and a cell with high short-circuit resistance are combined, a current flows from the cell with high short-circuit resistance into the cell with low short-circuit resistance. If, for example, Fig. 4, a short circuit occurs within a stack battery comprising the electrically parallel connected cell 10A and cell 10H, in which the short circuit resistance R Athe cell 10A is lower than the short-circuit resistance R H of cell 10H, according to Ohm's law, a leakage current I flows from cell 10H into cell 10A. When the leakage current I occurs, the temperature of cell 10A rises due to Joule heating; as a result, deterioration of the battery material easily occurs.

[0026] Although the reason why the short-circuit resistance inequality exists between the majority of cells is not entirely clear, the following is suspected. For example, as in Fig. 5, it is assumed that by penetrating the nail 110 into the cell 10 on the surface side (such as the location P1 in Fig. 3) of the stacked battery, a state in which the cathode current collector 4 and the anode current collector 5 are in contact and a state in which the cathode active material layer 1 and the anode current collector 5 are in contact occur.

[0027] However, since on the middle side (such as the location P2 in Fig. 3) In the stacked battery, the nail drags the fragments of each element along with it as it penetrates. A state where the cathode current collector and the anode current collector are not in contact, and a state where the cathode active material layer and the anode current collector are not in contact, are likely to occur. For example, the "non-contact state" can be considered to be a state where the fragment of the solid electrolyte layer exists between the two, and a state where a void exists between the two. As a result, the short-circuit resistance is higher on the center side of the stacked battery.

[0028] Furthermore, the behavior of the short-circuit resistance on the surface side opposite to the nail penetration surface of the stacked battery (such as the location P3 in Fig.3), may vary depending on the nature of the stacked battery; however, in the two Reference Examples 1 and 2 described later, the short-circuit resistance was reduced. The reason for this is believed to be that the nail, as it penetrates, carries most of the fragment of each element, and therefore the cathode current collector and the anode current collector are in an electrically connected state through the fragment with high electron conductivity.

[0029] On the other hand, in the present invention, since the surface-side cell and the middle-side cell satisfy at least one of condition i) and condition ii), in the stacked battery, the inequality in short-circuit resistance among the plurality of cells can be suppressed. Generally, a current collector with a low strain rate is not easily deformed upon nail penetration, and a current collector with a high strain rate is easily deformed upon nail penetration. Therefore, by using a current collector with a relatively low strain rate for the surface-side cell with low short-circuit resistance and using a current collector with a relatively high strain rate for the middle-side cell with high short-circuit resistance, the inequality in short-circuit resistance among the plurality of cells can be suppressed.Incidentally, in the present invention, only one comprehensive term, “current collector,” can be used for a cathode current collector and an anode current collector.

[0030] Also, the problem of preventing short-circuit resistance inequality among a plurality of cells is a problem that never occurs in a single cell; that is, it is a problem specific to a stacked battery. Furthermore, since all the constituent elements in a typical solid-state stacked battery are solids, the pressure applied to the stacked battery during a nail penetration test is extremely high. Since high pressures such as 100 MPa or more are applied at the nail penetration portion, and especially 400 MPa at the nail tip portion, it is important to control the short-circuit resistance under high-pressure conditions. On the other hand, in a liquid-based battery, since there is a void in the electrode into which the liquid electrolyte penetrates, the pressure applied to the battery during a nail penetration test is much lower.This means that controlling the short-circuit resistance under a high-pressure condition based on the liquid-based battery technology is difficult to imagine. 1. Strain rate of the current collector

[0031] The stacked battery of the present invention includes a surface-side cell located on a surface side of the stacked battery, and a center-side cell located on a center side other than the surface-side cell. Furthermore, the surface-side cell and the center-side cell satisfy at least one of: condition i) that a strain rate of the cathode current collector in the surface-side cell is lower than a strain rate of the cathode current collector in the center-side cell; and condition ii) that a strain rate of the anode current collector in the surface-side cell is lower than a strain rate of the anode current collector in the center-side cell.

[0032] The stacked battery of the present invention typically satisfies at least one of: including two or more types of cathode current collectors with different strain rates, and including two or more types of anode current collectors with different strain rates. Here, in the present invention, "surface-side cell" and "center-side cell" are used to specify the current collectors with different strain rates. For example, consider a case of a stacked battery including two types of cathode current collectors (cathode current collector α and cathode current collector β) with different strain rates. Incidentally, the strain rates are such that cathode current collector α < cathode current collector β.If a plurality of cells including the cathode current collector α exist on the surface side of the stacked battery, then any one of the plurality of cells can be designated as the surface-side cell. However, if a plurality of cells including the cathode current collector β exist on the middle side of the stacked battery, then any one of the plurality of cells can be designated as the middle-side cell.Also, for example, if the stacked battery includes three or more types of cathode current collectors with different strain rates, when comparing two cathode current collectors with different strain rates, if the size relationship of the strain rates and the location relationship of the two cathode current collectors (cells) meet the specific conditions, the cell containing one cathode current collector is designated as the surface-side cell, and the cell containing the other cathode current collector is designated as the center-side cell. Although the explanation is otherwise given using the cathode current collector as an example, the same largely applies to the anode current collector.

[0033] For example, if the strain rate of the cathode current collector in the surface-side cell is considered E1 and the strain rate of the cathode current collector in the middle-side cell is considered E2, the value of E2 / E1 is 1.1 or more, and may be 1.7 or more. Meanwhile, the value of E2 / E1 is 10 or less, for example. Similarly, if the strain rate of the anode current collector in the surface-side cell is considered E3 and the strain rate of the anode current collector in the middle-side cell is considered E4, a preferable range of E4 / E3 is similar to that of E2 / E1. The strain rate of the cathode current collector and the anode current collector can be obtained by measuring a fracture strain according to JIS 2201.

[0034] In the present invention, the strain rate of the cathode current collector in the surface-side cell is preferably lower than the strain rate of the cathode current collector in the middle-side cell. Similarly, in the present invention, the strain rate of the anode current collector in the surface-side cell is preferably lower than the strain rate of the anode current collector in the middle-side cell. The strain rate of the current collectors can be adjusted, for example, based on the properties of the current collector.

[0035] The material for the cathode current collector in the surface-side cell may be a material with a lower strain rate than that of the cathode current collector in the middle-side cell. Similarly, the material for the anode current collector in the surface-side cell may be a material with a lower strain rate than that of the anode current collector in the middle-side cell. If the current collector materials are different, the strain rates will also be different. For example, the strain rate of SUS is lower than the strain rate of Al. In the surface-side cell and the middle-side cell, the cathode current collectors may contain the same material, and the anode current collectors may contain different materials. Similarly, the cathode current collectors may contain different materials, and the anode current collectors may contain the same material.

[0036] The thickness of the cathode current collector in the surface-side cell may be thinner than the thickness of the cathode current collector in the middle-side cell. Similarly, the thickness of the anode current collector in the surface-side cell may be thinner than the thickness of the anode current collector in the middle-side cell. As the thickness is thicker, the strain rate tends to be higher. Furthermore, the cathode current collector in the surface-side cell and the cathode current collector in the middle-side cell may contain the same material (such as Al), but their thicknesses are different. Similarly, the anode current collector in the surface-side cell and the anode current collector in the middle-side cell may contain the same material (such as Cu), but their thicknesses are different. The thickness difference is, for example, 5 µm or more. 2. Properties of the stack battery

[0037] Each of the plurality of cells included in the stacked battery of the present invention is numbered in order along the thickness direction of the stacked battery from a 1st cell to an Nth cell. N refers to the total number of cells included in the stacked battery; for example, N is 3 or more, may be 10 or more, 30 or more, and 50 or more. Meanwhile, N is, for example, 200 or less, may be 150 or less, and may be 100 or less.

[0038] The surface-side cell is preferably a cell belonging to a cell range including the 1st cell up to an (N / 3)th cell. Here, the (N / 3)th cell is a cell whose rank corresponds to a value obtained by dividing the total number of cells N by three. For example, if the total number of cells is 60, the (N / 3)th cell is a 20th cell. Incidentally, if (N / 3) is not an integer, then the (N / 3)th cell is determined by rounding down to the nearest integer. Also, the surface-side cell may, for example, be a cell belonging to a cell range including the 1st cell to the 20th cell, and may be a cell belonging to a cell range including the 1st cell up to a 10th cell.

[0039] Also, for example, the surface-side cell may be a cell belonging to a cell range including a 5th cell to (N / 3)th cell, and may be a cell belonging to a cell range including the 10th cell to (N / 3)th cell. As mentioned in Reference Examples 1 and 2 described later, due to the influence of an outer covering such as a laminate film, the short-circuit resistance of the 1st cell during nail penetration may sometimes be high. Therefore, the surface-side cell can be specified excluding the 1st cell and the adjacent cells.

[0040] Meanwhile, the center cell is a cell that, unlike the surface cell, is located on the center side. "Center side" refers to the middle side in the thickness direction of the stacked cells. The center cell is preferably a cell that belongs to a cell range that includes an ((N / 3) + 1)th cell to a (2N / 3)th cell. Here, the ((N / 3) + 1)th cell refers to a cell adjacent to the (N / 3)th cell when numbering from the 1st cell. Meanwhile, the (2N / 3)th cell is a cell whose rank corresponds to a value obtained by dividing twice the total number of cells N by three. For example, if the total number of cells is 60, the (2N / 3)th cell is a 40th cell. Incidentally, if (2N / 3) is not an integer, the (2N / 3)th cell is determined by rounding down to the nearest integer. The middle cell can also be, for example, a cell that belongs to a cell range that contains the 21st.Cell up to 40. Cell contains.

[0041] Also, a cell range that includes the 1st cell to (N / 3)th cell is considered as a cell range A, and a cell range that includes the ((N / 3) + 1)th cell to (2N / 3)th cell is considered as a cell range B. The average strain rate E AC of the cathode current collector in the cell region A is preferably less than the average strain rate E BC of the cathode current collector in cell region B.

[0042] The value of E BC / E AC is, for example, 1.1 or more, and can be 1.7 or more. Meanwhile, the value of E BC / E AC for example, 10 or less. Analogously, the average strain rate E AA of the anode current collector in the cell region A is preferably less than the average strain rate E BAof the anode current collector in the cell region B. The preferred region of E BA / E AA is similar to that of E BC / E AC .

[0043] Also, a cell region including the 1st cell to the 20th cell is regarded as a cell region C, and a cell region including the 21st cell to the 40th cell is regarded as a cell region D. The average strain rate Ecc of the cathode current collector in the cell region C is preferably less than the average strain rate E DC of the cathode current collector in the cell region D. The value of E DC / E CC is, for example, 1.1 or more, and can be 1.7 or more. Meanwhile, the value of E DC / E CC for example, 10 or less. Analogously, the average strain rate E CA of the anode current collector in the cell region C is preferably less than the average strain rate E DAof the anode current collector in the cell region D. The preferred region of E DA / E CA is similar to that of E DC / E CC .

[0044] Also, in the stacked battery, after a nail penetration test, the short-circuit resistance of the cell with the lowest short-circuit resistance is determined as R Min considered, and the short-circuit resistance of the cell with the highest short-circuit resistance is called R Max For example, if a metal active material (especially Si or a Si alloy) is used as the anode active material, the value of R Max / R Min preferably 100 or less, and more preferably 5.0 or less. Incidentally, the nail penetration test is conducted under the conditions mentioned in Reference Examples 1 and 2 described later. 3rd cell

[0045] The cell in the present invention includes a cathode current collector, a cathode active material layer, a solid electrolyte layer, an anode active material layer, and an anode current collector, in this order. The cell is typically a cell that utilizes lithium-ion conductivity (a lithium-ion cell). Also, the cell is preferably a cell that can be charged and discharged (a secondary battery). (1) Anode active material layer

[0046] The anode active material layer includes at least one anode active material and may include a solid electrolyte material, a conductive material and / or a binder as required.

[0047] The anode active material is not particularly limited, and examples thereof may include a metal active material, a carbon active material, and an oxide active material. Examples of the metal active material may include a simple metal substance and a metal alloy. Examples of the metal element included in the metal active material may include Si, Sn, In, and Al. The metal alloy is preferably an alloy including the above-described metal element as the main component. Examples of the Si alloy may include a Si-Al-based alloy, a Si-Sn-based alloy, a Si-In-based alloy, a Si-Ag-based alloy, a Si-Pb-based alloy, a Si-Sb-based alloy, a Si-Bi-based alloy, a Si-Mg-based alloy, a Si-Ca-based alloy, a Si-Ge-based alloy, and a Si-Pb-based alloy.Incidentally, for example, a Si-Al-based alloy refers to an alloy containing at least Si and Al, may be an alloy containing only Si and Al, and may be an alloy further containing an additional metal element. The same applies to alloys other than a Si-Al-based alloy. The metal alloy may be a two-component alloy or a multi-component alloy containing three or more components.

[0048] Meanwhile, examples of the carbon active material may include a mesocarbon microbead (MCMB), a highly oriented pyrolitic graphite (HOPG), a hard carbon, and a soft carbon. Examples of the oxide active material may also include a lithium titanate such as Li4Ti5O. 12 include.

[0049] Examples of the form of the anode active material may include a granular form. The average particle size (D 50 ) of the anode active material is, for example, within a range of 10 nm to 50 µm, and may be within a range of 100 nm to 20 µm. The proportion of the anode active material in the anode active material layer is, for example, 50 wt% or more, and may be within a range of 60 wt% to 99 wt%.

[0050] The solid electrolyte material is not particularly limited, and examples thereof may include an inorganic solid electrolyte material such as a sulfide solid electrolyte material and an oxide solid electrolyte material. Examples of the sulfide solid electrolyte material may include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiI-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (where m and n are each a positive number; Z is one of Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are each a positive number; M is one of P, Si, Ge, B, Al, Ga, and In). Incidentally, the "Li2S-P2S5" described above refers to a sulfide solid electrolyte material using a raw material composition including Li2S and P2S5, and is largely the same for other descriptions.

[0051] In particular, the sulfide solid electrolyte material is preferably provided with an ion conductor including Li, A (A is at least one of P, Si, Ge, Al and B) and S. Furthermore, the ion conductor preferably includes an anion structure (PS4 3- -structure, SiS4 4- -structure, GeS4 4- -structure, AlS3 3- -Structure, BS3 3- Structure) of an ortho compound as the main anion component. This is to obtain a sulfide solid electrolyte material with high chemical stability. The proportion of the anion structure of the ortho compound to the total anion structures in the ion conductor is preferably 70 mol% or more, and more preferably 90 mol% or more. The proportion of the anion structure of the ortho compound can be determined using, for example, Raman spectroscopy, NMR, and XPS.

[0052] In addition to the ionic conductor, the sulfide solid electrolyte material may contain a lithium halide. Examples of the lithium halide include LiF, LiCl, LiBr, and LiI, and of these, LiCl, LiBr, and LiI are preferred. The proportion of LiX (X = I, Cl, Br) in the sulfide solid electrolyte material is, for example, within a range of 5 mol% to 30 mol%, and may be within a range of 15 mol% to 25 mol%.

[0053] The solid electrolyte material can be a crystalline material or an amorphous material. The solid electrolyte material can also be a glass or a crystallized glass (a glass-ceramic). Examples of the form of the solid electrolyte material can include a granular form.

[0054] Examples of the conductive material may include carbon materials such as acetylene black (AB), Ketjen Black (KB), carbon fiber, carbon nanotubes (CNT), and carbon nanofiber (CNF). Furthermore, examples of the binder may include rubber-based binders such as butylene rubber (BR), styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF).

[0055] For example, the thickness of the anode active material layer is within a range of 0.1 µm to 300 µm, and may be within a range of 0.1 µm to 100 µm. (2) Cathode active material layer

[0056] The cathode active material layer includes at least one cathode active material and may include a solid electrolyte material, a conductive material and / or a binder as required.

[0057] The cathode active material is not particularly limited, and examples may include an oxide active material. Examples of the oxide active material may include a rock salt bed type active material such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2; a spinel-type active material such as LiMn2O4, Li4Ti5O 12 and Li(Ni 0,5 Mn 1,5 )O4; and an olivine-type active material such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. Also, as the oxide active material, for example, a LiMn spinel active material represented by Li 1+x Mn2- x-y M y O4 (M is at least one of Al, Mg, Co, Fe, Ni and Zn, and 0 < x + y < 2), and a lithium titanate can be used.

[0058] A coating layer including a lithium-ion conductive oxide may also be formed on the surface of the cathode active material. This is to prevent the reaction between the cathode active material and the solid electrolyte material. Examples of lithium-ion conductive oxide include LiNbO3, Li4Ti5O. 12 and Li3PO4. The thickness of the coating layer is, for example, within a range of 0.1 nm to 100 nm, and may be within a range of 1 nm to 20 nm. The coverage of the cathode active material surface with the coating layer is, for example, 50% or more, and may be 80% or more.

[0059] The solid electrolyte material, the conductive material, and the binder used for the cathode active material layer are each present in the same proportions as those described in "(1) Anode Active Material Layer" above; thus, their description is omitted here. Also, the thickness of the cathode active material layer is, for example, within a range of 0.1 μm to 300 μm, and may be within a range of 0.1 μm to 100 μm. (3) Solid electrolyte layer

[0060] The solid electrolyte layer is a layer formed between the cathode active material layer and the anode current collector. Furthermore, the solid electrolyte layer includes at least one solid electrolyte material and may further include a binder if necessary. The solid electrolyte material and the binder used for the solid electrolyte layer are each present in the same proportions as those described in "(1) Anode Active Material Layer" above; therefore, their description is omitted here.

[0061] The proportion of the solid electrolyte material in the solid electrolyte layer is, for example, within a range of 10 wt% to 100 wt%, and may be within a range of 50 wt% to 100 wt%. Furthermore, the thickness of the solid electrolyte layer is, for example, within a range of 0.1 µm to 300 µm, and may be within a range of 0.1 µm to 100 µm. (4) Cathode current collector and anode current collector

[0062] The cathode current collector collects currents from the cathode active material layer described above, and the anode current collector collects currents from the anode active material layer described above. The metal element included in the cathode current collector is not particularly limited, and examples include Al, Fe, Ti, Ni, Zn, Cr, Au, and Pt. The cathode current collector can be a simple metal element substance or an alloy containing the metal element as the main component. Stainless steel (SUS) is an example of the Fe alloy, and SUS304 is preferred.

[0063] Examples of the shape of the cathode current collector include a foil shape and a grid shape. The thickness of the cathode current collector is, for example, 0.1 µm or more, and may be 1 µm or more. If the cathode current collector is too thin, the current collection function may be impaired. Meanwhile, the thickness of the cathode current collector is, for example, 1 mm or less, and may be 100 µm or less. If the cathode current collector is too thick, the energy density of a battery may be impaired.

[0064] The metal element included in the anode current collector is not particularly limited, and examples include Cu, Fe, Ti, Ni, Zn, and Co. The anode current collector can be a simple metal element substance or an alloy containing the metal element as the main component. Stainless steel (SUS) is an example of the Fe alloy, and SUS304 is preferred.

[0065] Examples of the shape of the anode current collector include a foil shape and a grid shape. The thickness of the anode current collector is, for example, 0.1 µm or more, and may be 1 µm or more. If the anode current collector is too thin, the current collection function may be impaired. Meanwhile, the thickness of the anode current collector is, for example, 1 mm or less, and may be 100 µm or less. If the anode current collector is too thick, the energy density of a battery may be impaired.

[0066] Incidentally, the present invention is not limited to the embodiments. Examples

[0067] The present invention will now be described in more detail. First, in Reference Examples 1 and 2, it was confirmed that the short-circuit resistance disparity between a plurality of cells in a conventional stacked battery was large. [Reference Example 1]Manufacture of a cathode

[0068] Using a drum fluidized bed granulation coating machine (manufactured by Powrex Corp.), the cathode active material (Li 1,15 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 W 0,005 O2) in the atmospheric environment coated with LiNbO3.

[0069] Subsequently, a coating layer including LiNbO3 was formed on the surface of the cathode active material by combustion in the atmosphere. This resulted in a cathode active material having the coating layer on its surface.

[0070] Next, butyl butyrate, a 5 wt% butyl butyrate solution of a PVDF-based binder (manufactured by Kureha Corp.), the obtained cathode active material, a sulfide solid electrolyte material (glass-ceramic based on Li2S-P2S5 including LiI and LiBr, average particle size D 50= 0.8 µm) and a conductive material (vapor-drawn carbon fiber, VGCF, manufactured by Showa Denko KK) were placed in a propylene (PP) container at a weight ratio of cathode active material: sulfide solid electrolyte material: conductive material: binder = 85:13:1:1. Next, the PP container was stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT Corp.). Next, the PP container was shaken for 3 minutes using a vibrating mixer (TTM-1, manufactured by Sibata Scientific Technology LTD.) and further stirred for 30 seconds using the ultrasonic disperser to obtain a coating solution.

[0071] Next, an Al foil (manufactured by Nippon Foil Mfg. Co. Ltd., a cathode current collector) was prepared. The resulting coating solution was applied to the Al foil using a doctor blade method and an applicator. The coated electrode was naturally dried and then baked on a hot plate at 100°C for 30 minutes to form a cathode active material layer on one surface of the cathode current collector. Next, the resulting product was cut according to the size of the battery to obtain a cathode. Manufacturing an anode

[0072] Butyl butyrate, a 5 wt.% butyl butyrate solution of a PVDF-based binder (manufactured by Kureha Corp.), an anode active material (silicon, manufactured by Kojundo Chemical Lab. Co., Ltd., average particle size D 50= 5 µm), a sulfide solid electrolyte material (glass-ceramic based on Li2S-P2S5 including LiI and LiBr, average particle size D 50 = 0.8 µm) and a conductive material (vapor-drawn carbon fiber, VGCF, manufactured by Showa Denko KK) were placed in a PP container at a weight ratio of anode active material: sulfide solid electrolyte material: conductive material: binder = 55:42:2:1. Next, the PP container was stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT Corp.). Next, the PP container was shaken for 30 minutes using a vibrating mixer (TTM-1, manufactured by Sibata Scientific Technology LTD.) and further stirred for 30 seconds using the ultrasonic disperser to obtain a coating solution.

[0073] Next, as in Fig.As shown in Figure 6A, a Cu foil (anode current collector 5) was prepared. The resulting coating solution was applied to the Cu foil by a doctor blade method using an applicator. The coated electrode was dried naturally and then dried on a hot plate at 100°C for 30 minutes. As shown in Fig. 6B, an anode active material layer 2 was formed on one surface of the Cu foil (anode current collector 5). Then, using the same treatment, an anode active material layer 2 was formed on another surface of the Cu foil (anode current collector 5), as shown in Fig. 6C. Next, the resulting product was cut according to the size of the battery to obtain an anode. Production of a solid electrolyte layer

[0074] Heptane, a 5 wt% heptane solution of a butylene rubber-based binder (manufactured by JSR Corp.) and a sulfide solid electrolyte material (Li2S-P2S5-based glass-ceramic including LiI and LiBr, average particle size D 50 = 2.5 µm) were added to a PP container. Next, the PP container was stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT Corp.). Next, the PP container was shaken for 30 minutes using a vibrating mixer (TTM-1, manufactured by Sibata Scientific Technology LTD.) and further stirred for 30 seconds using the ultrasonic disperser to obtain a coating solution.

[0075] Next, an Al foil (manufactured by Nippon Foil Mfg. Co. Ltd.) was prepared. The resulting coating solution was applied to the Al foil using a doctor blade method and an applicator. The coated electrode was dried naturally and then dried on a hot plate at 100°C for 30 minutes. Next, the resulting product was cut according to the size of the battery to obtain a transfer element including the Al foil and the solid electrolyte layer. Production of an evaluation battery

[0076] Each of the two obtained transfer elements was placed on the anode active material layers formed on both sides of the anode current collector, and the product was subjected to a pressure of 4 t / cm 2using a cold isostatic pressing (CIP) process. The aluminum foils of the transfer elements were then removed. This resulted in, as shown in Fig. 6D, solid electrolyte layers 3 were formed on anode active material layers 2. Next, each of the two cathodes obtained above was placed on the solid electrolyte layers formed on the two sides of the anode current collector, and the product was molded under the pressure of 4 t / cm 2 using the cold isostatic pressing (CIP) process. This resulted in, as described in Fig. As shown in Figure 6E, the cathode active material layers 1 and the cathode current collectors 4 were formed on the solid electrolyte layers 3. As described above, a two-stack cell was obtained. Further, 30 of the obtained two-stack cells were stacked, and the resulting product was sealed with an aluminum laminate film to obtain an evaluation battery. [Reference Example 2]Preparation of an anode

[0077] Butyl butyrate, a 5 wt% butyl butyrate solution of a PVDF-based binder (manufactured by Kureha Corp.), an anode active material (natural graphite, manufactured by Nippon Carbon Co., Ltd., average particle size D 50 = 10 µm) and a sulfide solid electrolyte material (glass ceramic based on Li2S-P2S5 including LiI and LiBr, average particle size D 50= 0.8 µm) were placed in a PP container in a weight ratio of anode active material: sulfide solid electrolyte material: binder = 59:40:1. Next, the PP container was stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT Corp.). Next, the PP container was shaken for 30 minutes using a vibrating mixer (TTM-1, manufactured by Sibata Scientific Technology LTD.) and further stirred for 30 seconds using the ultrasonic disperser to obtain a coating solution. Production of an evaluation battery or test battery

[0078] A two-stack cell was obtained in the same manner as in Reference Example 1, except that the obtained coating solution was used. Furthermore, an evaluation battery was obtained in the same manner as in Reference Example 1, except that 40 of the obtained two-stack cells were stacked. [Evaluation]

[0079] For each evaluation battery obtained in Reference Examples 1 and 2, a nail penetration test was conducted under the following conditions. Charging status: uncharged Resistance meter: RM3542, manufactured by Hioki EE Corp. Nail: SK (carbon tool steel) material (ϕ: 8 mm, point angle: 60°) Nail speed: 25 mm / s

[0080] The short-circuit resistance of a cell was obtained from a voltage profile during nail penetration. An example of the voltage profile is shown in Fig. 7. As shown in Fig.As shown in Figure 7, the cell voltage decreases due to nail penetration. Here, the initial voltage is denoted as V0, and the minimum voltage at nail penetration is denoted as V. Also, the internal resistance of the cell was measured in advance, and the internal resistance of the cell is denoted as r. Furthermore, the short-circuit resistance of the cell is denoted as R. Assuming that the total current generated due to the voltage drop at nail penetration is the short-circuit current, the relationship V / R = (V0 - V) / r is established. The short-circuit resistance R of the cell can be calculated from this relationship. By plotting the voltage profile of each cell, a variation in the short-circuit resistance in the thickness direction was confirmed. The results are shown in Table 1 and Table 2. Incidentally, the short-circuit resistance values ​​in Table 1 and Table 2 are relative values ​​when the short-circuit resistance of the 1st cell is 1.Also, the cell near the nail penetration surface was numbered as the 1st cell. [Table 1] <si> Nth cell Short-circuit resistance 1 1 10 0,005 20 28859 30 38255 40 671141 50 18121 60 0,026 [Table 2] <c> Nth cell Short-circuit resistance 1 1 10 0,159 40 0,968 60 3,683 80 0,698

[0081] As shown in Table 1 and Table 2, the short-circuit resistance of the 1st cell in both Reference Examples 1 and 2 was higher than the short-circuit resistance of the 10th.

[0082] Cell. The reason for this is believed to be that the insulating part of the laminate film was pulled inward during nail penetration. Also, in Reference Example 1, the short-circuit resistance of the 40th cell was higher compared to the short-circuit resistance of the 1st cell or the 10th cell, and in Reference Example 2, the short-circuit resistance of the 60th cell was higher compared to the short-circuit resistance of the 1st cell or the 10th cell. As described above, the short-circuit resistance was lower in the surface-side cell and higher in the middle-side cell. In particular, in Reference Example 1, in which Si was used as the anode active material, the unevenness of the short-circuit resistance was extremely large compared to Reference Example 2, in which C was used as the anode active material. [Experimental Example 1]

[0083] A two-stack cell was prepared in the same manner as in Reference Example 1, except that an Al foil (thickness 15 µm, 1N30, manufactured by UACJ Corp.) was used as a cathode current collector and a Cu foil (thickness 14 µm, electrolytically grown Cu foil with roughened surface, manufactured by Furukawa Electric Co., Ltd.) was used as an anode current collector. [Experimental Example 2]

[0084] A two-stack cell was constructed in the same manner as in Reference Example 1, except that an Al foil (thickness 6 µm, manufactured by Toyo Aluminum KK) was used as a cathode current collector. [Experimental Example 3]

[0085] A two-stack cell was prepared in the same manner as in Reference Example 1, except that a SUS film (SUS304, thickness 15 µm, manufactured by Toyo Seihaku Co., Ltd.) was used as a cathode current collector. [Evaluation]

[0086] The nail penetration test was conducted for each two-stack cell obtained in Experimental Examples 1 to 3 by placing it on a 3 mm thick Al plate under the following conditions. Charging status: uncharged Resistance meter: RM3542, manufactured by Hioki EE Corp. Nail: SK material (ϕ: 8 mm, point angle: 60°) Nail speed: 0.5mm / s

[0087] The short-circuit resistance of each cell was obtained from a voltage profile during nail penetration. The results are shown in Table 3. Incidentally, the short-circuit resistance values ​​in Table 3 are relative values ​​when the short-circuit resistance in Experimental Example 1 is 100. [Table 3] Cathode current collector Anode current collector Short-circuit resistance Type Strain rate (%) Type Strain rate (%) Experimental example 1 Al (15 µm) 4,5 Cu (14 µm) 5,8 100 Experimental example 2 Al (6 µm) 2,3 Cu (14 µm) 5,8 346 Experimental example 3 SUS (15 µm) 1,6 Cu (14 µm) 5,8 425

[0088] As shown in Table 3, the short-circuit resistance increases in the order of Experimental Example 1, Experimental Example 2, and Experimental Example 3. The reason for this is believed to be that the higher the strain rate of the current collector, the greater the amount of deformation during nail penetration, so that the cathode current collector and the anode current collector are easily in contact with each other. These results suggest that by setting the strain rate of the current collector relatively low in the surface-side cell and the strain rate of the current collector relatively high in the middle-side cell, the inequality in short-circuit resistance among a plurality of cells can be suppressed. List of reference symbols 1 cathode active material layer 2 Anode active material layer 3 Solid electrolyte layer 4 Cathode current collector 5 Anode current collector 10 cells 100 stackable batteries 110 nails< / c> < / si>

Claims

[1] Stack battery (100), comprising: a plurality of cells (10) in a thickness direction, wherein the plurality of cells (10) are electrically connected in parallel; each of the plurality of cells (10) includes a cathode current collector (4), a cathode active material layer (1), a solid electrolyte layer (3), an anode active material layer (2) and an anode current collector (5) in this order; the stacked battery (100) includes a surface-side cell located on a surface side of the stacked battery (100) and a center-side cell located on a center side other than the surface-side cell; and the surface cell and the middle cell satisfy at least one of: Condition i), according to which a strain rate of the cathode current collector (4) in the surface-side cell is lower than a strain rate of the cathode current collector (4) in the middle-side cell; and Condition ii), according to which a strain rate of the anode current collector (5) in the surface-side cell is lower than a strain rate of the anode current collector (5) in the middle-side cell, characterized by that condition i) further satisfies at least one of: Condition i-1) the material for the cathode current collector (4) in the surface-side cell is a material having a lower strain rate than that of the material for the cathode current collector (4) in the center-side cell; and Condition i-2) the thickness of the cathode current collector (4) in the surface-side cell is less than the thickness of the cathode current collector (4) in the center-side cell; and condition ii) further satisfies at least one of: Condition ii-1) the material for the anode current collector (5) in the surface-side cell is a material having a lower strain rate than that of the material for the anode current collector (5) in a center-side cell; and Condition ii-2) the thickness of the anode current collector (5) in the surface-side cell is less than the thickness of the anode current collector (5) in the center-side cell. [2] Stack battery (100) according to claim 1, characterized by that when each of the plurality of cells (10) is numbered in an order along the thickness direction of the stack battery (100) as a 1st cell to an Nth cell, the surface-side cell is a cell (10) belonging to a cell area A including the 1st cell to an (N / 3)th cell. [3] Stack battery (100) according to claim 2, characterized bythat the center cell is a cell (10) belonging to a cell range B that includes a ((N / 3) + 1)th cell up to a (2N / 3)th cell. [4] Stack battery (100) according to claim 3, characterized by that an average strain rate of the cathode current collector (4) in the cell region A is lower than an average strain rate of the cathode current collector (4) in the cell region B. [5] Stack battery (100) according to claim 3 or 4, characterized by that an average strain rate of the anode current collector (5) in the cell region A is lower than an average strain rate of the anode current collector (5) in the cell region B. [6] Stack battery (100) according to claim 1, characterized bythat when numbering each of the plurality of cells (10) in an order along the thickness direction of the stack battery (100) as a 1st cell up to an Nth cell, where N ≥ 60, the surface-side cell is a cell (10) belonging to a cell region C including the 1st cell up to a 20th cell. [7] Stack battery (100) according to claim 6, characterized by that the middle cell is a cell (10) belonging to a cell range D which includes a 21st cell up to a 40th cell. [8] Stack battery (100) according to claim 7, characterized by that an average strain rate of the cathode current collector (4) in the cell region C is lower than an average strain rate of the cathode current collector (4) in the cell region D. [9] Stack battery (100) according to claim 7 or 8, characterized bythat an average strain rate of the anode current collector (5) in the cell region C is lower than an average strain rate of the anode current collector (5) in the cell region D. [10] Stack battery (100) according to one of claims 1 to 9, characterized by that the anode active material layer (2) contains Si or a Si alloy as an anode active material.

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