Method for manufacturing all-solid-state battery, and all-solid-state battery laminate

Abstract

The present invention provides: a method for manufacturing an all-solid-state battery, with which it is possible to suppress flowing of current into a short-circuit battery cell from another battery cell even in cases where a short circuit has occurred, during manufacturing, in a battery cell that contains Li metal or a Li alloy in a negative electrode; and an all-solid-state battery laminate. The present invention includes: a step for pressing a laminate in which a negative electrode that contains lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly disposed and an insulating layer is interposed between the solid electrolyte layer and a positive electrode current collector so as to form an all-solid-state battery laminate in which a plurality of battery cells are pressure-bonded in a non-dischargeable state; a step for inspecting the presence or absence of an internal short circuit of a battery cell; a step for electrically connecting negative electrode current collectors included in the negative electrodes to each other, and electrically connecting positive electrode current collectors to each other so as to connect the battery cells in parallel; and a step for removing at least a part of the insulating layer when there is no internal short circuit, and bringing the battery cell into a dischargeable state.

Description

All-solid-state battery manufacturing method and all-solid-state battery stack

[0001] The present invention relates to a method for manufacturing an all-solid-state battery and an all-solid-state battery stack.

[0002] Patent Document 1 discloses an all-solid-state battery including a positive electrode in which a first current collector layer and a first active material layer are laminated, a negative electrode in which a second current collector layer containing at least copper and a second active material layer are laminated, and a solid electrolyte layer disposed between the first active material layer and the second active material layer.

[0003] Japanese Patent Application Laid-Open No. 2023-149424

[0004] In an all-solid-state battery that contains lithium (Li) metal or a Li alloy in the negative electrode during manufacturing, the battery cells are formed in a charged state. Because the battery cells are in a charged state from the beginning of manufacturing, for example, when connecting current collectors of the same polarity together to connect multiple battery cells in parallel after the battery cells are formed, if any of the battery cells contains an internally short-circuited battery cell (hereinafter also referred to as a short-circuited cell), current will flow into the short-circuited cell from the other battery cells connected in parallel, which is undesirable.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a method for manufacturing an all-solid-state battery and an all-solid-state battery stack that can suppress current from flowing into a short-circuited cell from other battery cells, even if a short circuit occurs in a battery cell containing Li metal or a Li alloy in the negative electrode during manufacturing.

[0006] A method for manufacturing an all-solid-state battery according to one aspect of the present invention includes the steps of pressing a laminate in which a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly arranged, with an insulating layer interposed between the solid electrolyte layer and a positive electrode current collector, to form an all-solid-state battery laminate in which a plurality of battery cells are pressure-bonded in a non-dischargeable state; inspecting the battery cells for the presence or absence of an internal short circuit; electrically connecting the negative electrode current collectors included in the negative electrode to each other and electrically connecting the positive electrode current collectors to each other to connect the battery cells in parallel; and, if no internal short circuit is present, removing at least a portion of the insulating layer to make the battery cells dischargeable.

[0007] According to one aspect of the present invention, even if a short circuit occurs in a battery cell containing Li metal or a Li alloy in the negative electrode during manufacturing, it is possible to prevent current from flowing through the short-circuited cell.

[0008] FIG. 1 is a cross-sectional view showing an example of the configuration of an all-solid-state battery manufactured by a manufacturing method according to the present embodiment. FIG. 2 is a flowchart showing a manufacturing method of an all-solid-state battery according to the present embodiment. FIG. 3 is a diagram for explaining a stacking and compression bonding step. FIG. 4 is a diagram for explaining an inspection step of FIG. 2. FIG. 5 is a diagram for explaining the inspection step of FIG. 2. FIG. 6 is a diagram showing an example of the configuration of a battery cell in a dischargeable state after an insulating layer has been removed. FIG. 7 is a diagram for explaining a removal step. FIG. 8 shows the results of an experiment conducted by the present inventor. FIG. 9 is a diagram showing a comparative example of the present invention. FIG. 10 is a diagram showing a first modified example of the manufacturing method according to the present embodiment. FIG. 11 is a diagram showing a third modified example of the manufacturing method according to the present embodiment.

[0009] An embodiment of the present invention (the present embodiment) will be described below. In the following drawings, identical or similar parts are designated by identical or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratios of each device and each component, and the like may differ from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. It goes without saying that the dimensional relationships and ratios of parts included in the drawings may differ from one another. The definitions of directions such as up and down in the following description are merely for the convenience of explanation and do not limit the technical concept of the present invention. For example, if an object is rotated 90 degrees and observed, up and down are read as being converted to left and right, and if it is rotated 180 degrees and observed, up and down are read as being reversed.

[0010] 1 is a cross-sectional view showing an example of the configuration of an all-solid-state battery 1 manufactured by the manufacturing method according to the present embodiment. As shown in Fig. 1, the all-solid-state battery 1 manufactured by the manufacturing method according to the present embodiment includes an anode 4 having an anode layer 2 and an anode current collector 3, a cathode 7 having a cathode layer 5 and a cathode current collector 6, a solid electrolyte layer 8 disposed between the anode 4 and the positive electrode 7, an anode tab lead 11 joined to the anode current collector 3, a cathode tab lead 12 joined to the cathode current collector 6, and an exterior body (not shown).

[0011] The negative electrode layer 2 is provided on both surfaces in the thickness direction of the negative electrode current collector 3 (top and bottom surfaces in FIG. 1 ). For example, the negative electrode 4 can be obtained by pressure-bonding lithium (Li) metal or a Li alloy to both surfaces of the negative electrode current collector 3 as the negative electrode layer 2. For the negative electrode current collector 3 and the negative electrode tab lead 11, for example, a metal foil such as copper (Cu), a Cu alloy, nickel, or a nickel alloy can be used, but is not limited to these. The negative electrode layer 2 is made of Li metal or a Li alloy. More specifically, examples of Li alloys include, but are not limited to, a Li-Mg alloy, a Li-Si alloy, a Li-Al alloy, a Li-Zn alloy, a Li-Sn alloy, and a Li-Bi alloy.

[0012] The positive electrode layer 5 is provided on both surfaces in the thickness direction of the positive electrode current collector 6 (top and bottom surfaces in FIG. 1 ). For example, a positive electrode 7 can be obtained by preparing a slurry by weighing and mixing predetermined amounts of a positive electrode active material, a sulfide solid electrolyte, an oxide solid electrolyte, a conductive additive, a binder, and an organic solvent, applying the slurry to both surfaces of the positive electrode current collector 6, and then drying the slurry. The positive electrode current collector 6 and the positive electrode tab lead 12 can be made of, for example, aluminum (Al) foil, but are not limited to these. Examples of the positive electrode layer 5 include, but are not limited to, manganese dioxide, sulfides, fluorides, and oxides.

[0013] The solid electrolyte layer 8 may be made of any material as long as it functions as an electrolyte layer in a secondary battery. For example, the solid electrolyte layer 8 may include a sulfide solid electrolyte. Examples of sulfide solid electrolytes include materials containing Li, phosphorus (P), sulfur (S), and a halide. For example, the solid electrolyte layer 8 can be obtained by weighing and mixing predetermined amounts of the sulfide solid electrolyte, a binder, and an organic solvent to prepare a slurry, which is then applied to a substrate and dried.

[0014] The negative electrodes 4 and positive electrodes 7 are alternately stacked with solid electrolyte layers 8 interposed therebetween to form an all-solid-state battery stack 10. The solid electrolyte layer 8 is interposed between the negative electrode 4 and the positive electrode 7 to form one battery cell 9. The all-solid-state battery stack 10 includes a plurality of battery cells 9 stacked and compressed in one direction (the vertical direction in FIG. 1 ; hereinafter, also referred to as the stacking direction). In each battery cell 9, charging and discharging are performed by exchange of alkali metal ions (e.g., Li ions) between the negative electrode 4 and the positive electrode 7 via the solid electrolyte layer 8.

[0015] The all-solid-state battery laminate 10, a welded portion 14 between the negative electrode tab lead 11 and the negative electrode current collector 3, and a welded portion 15 between the positive electrode tab lead 12 and the positive electrode current collector 6 are covered and sealed by an exterior body. The negative electrode tab lead 11 and the positive electrode tab lead 12 extend from the inside to the outside of the exterior body.

[0016] As shown in Fig. 3 and other figures, in the process of manufacturing the all-solid-state battery 1, an insulating layer 51 is interposed between the solid electrolyte layer 8 and the positive electrode current collector 6 in step ST1 (lamination and pressure bonding step) in Fig. 2 which will be described later. The insulating layer 51 is removed in step ST4 (removal step) in Fig. 2 which will be described later. Therefore, in the all-solid-state battery 1 manufactured through the removal step, the insulating layer 51 is not present between the solid electrolyte layer 8 and the positive electrode current collector 6.

[0017] (Manufacturing Method) Next, a manufacturing method of the all-solid-state battery 1 according to the present embodiment will be described. FIG. 2 is a flowchart showing a manufacturing method of the all-solid-state battery 1 according to the present embodiment. Note that other processes may be included between the flowchart of FIG. 2. FIG. 3 is a diagram for explaining step ST1 (lamination and pressure bonding process) in FIG. 2. FIGS. 4 and 5 are diagrams for explaining step ST2 (inspection process) in FIG. 2. FIG. 4 shows a battery cell 9 determined to have no internal short circuit (OK) in the inspection process, and FIG. 5 shows a battery cell (i.e., a short-circuited cell) 9S determined to have an internal short circuit (NG). FIG. 6 is a diagram showing an example of the configuration of a battery cell in a dischargeable state after the insulating layer 51 has been removed. FIG. 7 is a diagram for explaining step ST4 (removal process) in FIG. 2. The all-solid-state battery 1 is manufactured using various types of equipment, such as an equipment for stacking the negative electrode 4, the positive electrode 7, and the solid electrolyte layer 8, a press equipment for pressing the all-solid-state battery laminate 10, an equipment for inspecting the battery cells 9 included in the all-solid-state battery laminate 10 for short circuits, an equipment for heating the all-solid-state battery laminate 10, and a welding equipment for welding current collectors and tab leads. Hereinafter, these equipment will be collectively referred to as manufacturing equipment.

[0018] In step ST1 of Fig. 2, the manufacturing equipment performs a lamination and compression bonding process. For example, step ST1 of Fig. 2 includes steps ST11 and ST12 shown in Fig. 3. In step ST11 of Fig. 3, the manufacturing equipment places a positive electrode 7 with an insulating layer 51. The positive electrode 7 with an insulating layer 51 can be obtained, for example, by forming sulfur (S) as the insulating layer 51 on both sides of the positive electrode current collector 6 in the thickness direction (e.g., the vertical direction in Fig. 3), and then forming the positive electrode layer 5 thereon. The electronic conductivity of sulfur is approximately 1 × 10 －１４ [S / m] and has high insulating properties.

[0019] The method for forming sulfur is not particularly limited, but may be, for example, solution growth. ２ S is thoroughly dissolved in distilled water while stirring, and the substrate is placed in this solution and reacted at a temperature of 300 K for 48 hours. This allows sulfur to be deposited on the surface of the substrate. The sulfur deposited on the surface of the substrate is placed on both sides of the positive electrode current collector 6 and pressurized. After pressing, the substrate is removed, and the sulfur is transferred to both sides of the positive electrode current collector 6.

[0020] Alternatively, sulfur may be provided directly on both surfaces of the positive electrode current collector 6 without using a substrate. For example, the positive electrode current collector 6 may be placed in the solution in the reaction tank and reacted at a temperature of 300 K for 48 hours to deposit sulfur on both surfaces of the positive electrode current collector 6. By this manufacturing method, sulfur can be provided on the positive electrode current collector 6. Thereafter, positive electrode layers 5 are provided on both surfaces of the positive electrode current collector 6 via sulfur, thereby completing a positive electrode 7 with an insulating layer 51.

[0021] Furthermore, in the manufacturing method according to this embodiment, solid electrolyte layers 8 may be further laminated on both sides of the cathode 7 with the insulating layer 51 to obtain a cathode 7 with the insulating layer 51 and the solid electrolyte layer 8. In this manufacturing method, for example, the cathode 7 and the solid electrolyte layer 8 are overlapped and pressed so that the cathode layer 51 and the solid electrolyte layer 8 are in contact with each other, and after pressing, the base material of the solid electrolyte layer 8 is removed, thereby transferring the solid electrolyte layer 8 to the cathode 7. With this manufacturing method, a cathode 7 with the insulating layer 51 and the solid electrolyte layer 8 can be obtained.

[0022] In the manufacturing method according to this embodiment, the solid electrolyte layer 8 may be provided on the negative electrode 4 instead of the positive electrode 7. As in the case of the positive electrode 7, the solid electrolyte layer 8 can be transferred to the negative electrode 4 to obtain the negative electrode 4 with the solid electrolyte layer 8. Alternatively, the solid electrolyte layer 8 may be prepared separately from the positive electrode 7 and the negative electrode 4.

[0023] Next, the manufacturing equipment places the anode 4 in a position facing the cathode 7 with the solid electrolyte layer 8 interposed therebetween in the stacking direction. The process of placing the cathode 7 and the anode 4 facing each other with the solid electrolyte layer 8 interposed therebetween is the stacking process of one battery cell. This stacking process is repeated a preset number of times (i.e., a predetermined number of times). As a result, as shown in step ST11 of FIG. 3 , an unbonded laminate 10′ is formed in which the anode 4 containing Li metal or Li alloy as the anode layer 2, the solid electrolyte layer 8, and the cathode 7 are repeatedly arranged in the stacking direction, and an insulating layer 51 (e.g., sulfur) is interposed between the positive electrode current collector and the positive electrode layer.

[0024] Next, in step ST12 of Fig. 3, the manufacturing equipment presses the unbonded laminate 10'. For example, as shown in Fig. 3, the manufacturing equipment presses the laminate 10' with a press pressure P at least in the stacking direction. The press pressure P is equal to or greater than the yield stress of Li metal, for example, 5 MPa or greater. The yield stress of Li metal is the stress at which Li metal begins to become plastic. This pressing causes the anode layer 2 and the solid electrolyte layer 8, and the solid electrolyte layer 8 and the cathode layer 5, to be bonded together with high pressure, thereby forming the all-solid-state battery laminate 10.

[0025] By this molding, the anode layer 2 composed of Li metal or Li alloy is pressure-bonded to the solid electrolyte layer 8. Therefore, each battery cell 9 included in the all-solid-state battery laminate 10 is formed in a charged state. For example, each battery cell 9 included in the all-solid-state battery laminate 10 is formed in a state of 100% SOC (State of Charge) or a high SOC (e.g., 95%, 90%, or 85%). However, an insulating layer 51 is interposed between the solid electrolyte layer 8 and the positive electrode current collector 6 (e.g., between the positive electrode layer 5 and the positive electrode current collector 6). Therefore, the battery cell 9 is formed in a charged state but in a non-dischargeable state. Each battery cell 9 maintains a non-dischargeable state until the insulating layer 51 is removed in step ST4 (removal process) described below.

[0026] 2 , the manufacturing apparatus performs an inspection step of inspecting the battery cells 9 for the presence or absence of an internal short circuit. For example, the manufacturing apparatus inspects each of the plurality of battery cells 9 included in the all-solid-state battery stack 10 for the presence or absence of a short circuit between the negative electrode 4 and the positive electrode 7 (i.e., an internal short circuit). The presence or absence of an internal short circuit can be inspected by measuring the thickness of the battery cell 9 and comparing it with a preset (i.e., predetermined) value.

[0027] As shown in Fig. 4, in a battery cell 9 without an internal short circuit (OK), a solid electrolyte layer 8 is interposed between the Li metal or Li alloy that constitutes the anode layer 2 and the positive electrode layer 5, and the Li metal or Li alloy is not in contact with the Li metal or Li alloy. In contrast, as shown in Fig. 5, in a short-circuited cell 9S with an internal short circuit (NG), a portion of the Li metal or Li alloy that constitutes the anode layer 2 extends toward the positive electrode layer 5 and contacts the positive electrode layer 5. In the short-circuited cell 9S, an ion path IP is formed in the following order: Li metal or Li alloy → positive electrode layer 5 → solid electrolyte layer 8 → Li metal or Li alloy. Because electrons and Li ions move through the ion path IP, the thickness of the Li metal or Li alloy is reduced in the short-circuited cell 9S.

[0028] The thickness of the battery cell 9 is indicated, for example, by the distance between the negative electrode current collector 3 and the positive electrode current collector 6. As shown in FIGS. 4 and 5 , if the thickness of a battery cell 9 without a short circuit is T and the thickness of a short-circuited cell 9S is Ts, the thickness of the Li metal or Li alloy in the short-circuited cell 9S is reduced, so that T>Ts. Therefore, the presence or absence of an internal short circuit in the battery cell 9 can be detected by investigating in advance the thickness of the battery cell that serves as a criterion for determining whether or not an internal short circuit exists, and comparing this thickness (i.e., a predetermined value) with the thickness T of the battery cell 9 to be inspected. If the thickness T of the battery cell 9 is equal to or greater than the predetermined value, it is determined that there is no internal short circuit (OK). If it is less than the predetermined value (e.g., Ts), it is determined that there is an internal short circuit (NG). An all-solid-state battery stack 10 including a battery cell 9 that is determined to be OK is treated as a non-defective product and proceeds to the next process (step ST3). An all-solid-state battery stack including a battery cell 9S determined to be NG (i.e., a short-circuited cell) is treated as a defective product, and the manufacturing process is terminated.

[0029] Next, in step ST3 of FIG. 2 , the manufacturing equipment performs a connection process in which current collectors of the same electrode are connected to each other to connect multiple battery cells 9 in parallel. That is, the connection process is performed by electrically connecting the negative electrode current collectors 3 to each other and electrically connecting the positive electrode current collectors 6 to each other to connect multiple battery cells 9 in parallel. In the connection process, for example, for an all-solid-state battery stack 10 determined to be free of short circuits (OK), the negative electrode current collector 3 is joined to the negative electrode tab lead 11, and the positive electrode current collector 6 is joined to the positive electrode tab lead 12. The joining method is not particularly limited, and examples include ultrasonic welding and laser welding that utilize heat generated by friction between metals. The welding temperature is set according to the melting temperature of the metal material constituting the current collectors and the welding temperature of the metal material constituting the tab leads. The welding temperature is, for example, 300°C or higher and 500°C or lower.

[0030] 2, the manufacturing equipment performs a removal process to remove the insulating layer 51 from the all-solid-state battery laminate 10. By removing the insulating layer 51 in the removal process, the positive electrode current collector 6 and the positive electrode layer 5 are brought into contact with each other, as shown in Fig. 6. This allows each battery cell 9 included in the all-solid-state battery laminate 10 to be dischargeable.

[0031] In the step of removing the insulating layer 51, for example, the all-solid-state battery stack 10 is heated to sublimate and remove the insulating layer 51. For example, as shown in FIG. 7 , the all-solid-state battery stack 10 is placed in a treatment chamber 53 where a heating treatment is performed, and the insulating layer 51 is heated and sublimated in this treatment chamber 53, thereby removing the insulating layer 51 from the all-solid-state battery stack 10. As an example, the insulating layer 51 may be heated from the positive electrode current collector 6. A jig (e.g., a clamp, etc.) serving as a heating source is attached to the positive electrode tab lead 12 or the positive electrode current collector 6, and the insulating layer 51 is heated from this jig via the positive electrode current collector 6. In this way, since the positive electrode current collector 6 and the insulating layer 51 are adjacent to each other, it is possible to selectively heat and sublimate the insulating layer 51 while suppressing a temperature rise in each of the positive electrode layer 5, the solid electrolyte layer 8, and the negative electrode layer 2.

[0032] The positive electrode layer 5 is located in a position that is less susceptible to heating than the insulating layer 51, because an insulating layer 51 is interposed between the positive electrode layer 5 and the positive electrode current collector 6, which serves as a heat source. However, the positive electrode layer 5 is also heated through the insulating layer 51. After the insulating layer 51 is removed, the positive electrode layer 5 comes into contact with the positive electrode current collector 6. For this reason, the positive electrode layer 5 is preferably made of a material that has a higher boiling point (i.e., is less likely to sublime) than the insulating layer 51. In other words, the insulating layer 51 preferably has a lower boiling point than the positive electrode layer 5. For example, if the insulating layer 51 is made of sulfur (S), the positive electrode layer 5 adjacent to the insulating layer 51 may be made of a sulfide as long as it has a boiling point higher than that of sulfur, but it is more preferable that the positive electrode layer 5 be made of an oxide with a boiling point even higher than that of sulfide. This more reliably prevents the positive electrode layer 5 from sublimating.

[0033] Furthermore, layers other than the insulating layer 51 and the positive electrode layer 5 (for example, the solid electrolyte layer 8) are also indirectly heated from the positive electrode current collector 6 via the insulating layer 51, etc. The other layers are located further away from the positive electrode current collector 6 than the positive electrode layer 5 and are less likely to be heated than the positive electrode layer 5, but a certain degree of temperature rise is expected. For this reason, the other layers are also preferably made of a material with a higher boiling point than the insulating layer 51.

[0034] In this removal step, the all-solid-state battery stack 10 may be placed in the treatment chamber 53 and heated while the treatment chamber 53 is depressurized (or in a depressurized state) to sublimate the insulating layer 51. That is, the insulating layer 51 may be heated and sublimated while the all-solid-state battery stack 10 is placed in a depressurized environment. This lowers the temperature required for sublimation of the insulating layer 51. For example, if the insulating layer 51 is made of sulfur (S) and the anode layer is made of lithium (Li) metal, the boiling point of sulfur is higher than the melting point of Li metal in a normal pressure environment. However, in a depressurized environment, the boiling point of sulfur can be lowered below the melting point of Li metal. Therefore, by performing the removal step of the insulating layer 51 in a depressurized environment, it is possible to efficiently remove the insulating layer 51 while sufficiently suppressing the melting of Li metal. By performing the removal step in a depressurized environment, it is possible to suppress the heating temperature and improve the efficiency of removing the insulating layer 51. Note that a depressurized environment refers to an environment with a pressure lower than 1 atmosphere (atm), for example. The reduced pressure environment can be achieved, for example, by evacuating the processing chamber with a pump. The normal pressure environment means, for example, an environment of 1 atmosphere (atm).

[0035] FIG. 8 shows the results of an experiment conducted by the present inventors, and is a graph showing the relationship between the heating temperature and the mass reduction rate of sulfur when sulfur (S) is used as the insulating layer 51. The vertical axis of FIG. 8 represents the mass of sulfur before heating as 100%. The experimental results show that the mass of sulfur begins to decrease when the heating temperature exceeds 200°C, and the mass of sulfur becomes less than 5% (i.e., the mass reduction rate is 95% or more) at around 240°C. These results confirm that when the insulating layer 51 is made of sulfur in the removal process of step ST4 in FIG. 2 , the insulating layer 51 can be sublimated by heating the insulating layer 51 at, for example, 240°C.

[0036] Through the above steps, the all-solid-state battery 1 shown in FIG. 1 is completed. In the manufacturing method according to this embodiment, a sealing step, a discharging step, and a charging step may be performed following step ST4 in FIG. 2 . In the sealing step, the manufacturing apparatus seals the all-solid-state battery stack 10 with an exterior body, excluding the negative electrode tab lead 11 and the positive electrode tab lead 12. In the discharging step, the manufacturing apparatus performs a discharging operation on the all-solid-state battery stack 10 formed in a charged state. For example, a discharging operation is performed on all battery cells 9 included in the all-solid-state battery stack 10 via the negative electrode tab lead 11 and the positive electrode tab lead 12 shown in FIG. 1 . During this discharging operation, in each battery cell 9, Li ions migrate from the negative electrode 4 through the solid electrolyte layer 8 to the positive electrode 7 and are occluded in the positive electrode layer 5. During the discharging operation, the Li metal or Li alloy in the negative electrode layer 2 decreases as the discharge progresses. When the discharge progresses to an SOC of 0%, the Li metal or Li alloy in the negative electrode layer 2 is almost completely depleted. In the charging step, the manufacturing equipment charges the discharged all-solid-state battery stack 10. This charging operation is performed via the negative electrode tab lead 11 and the positive electrode tab lead 12. During this charging operation, in each battery cell 9, Li ions occluded in the positive electrode layer 5 move to the negative electrode current collector 3 via the solid electrolyte layer 8, and Li metal or a Li alloy is deposited as the negative electrode layer 2.

[0037] Effect of the embodiment As described above, the manufacturing method of the all-solid-state battery 1 according to the present embodiment includes: a lamination-compression step of pressing a laminate 10′ in which the anode 4 containing Li metal or Li alloy, the solid electrolyte layer 8, and the cathode 7 are repeatedly arranged, with the insulating layer 51 interposed between the solid electrolyte layer 8 and the cathode current collector 6 of the cathode 7, to form an all-solid-state battery laminate 10 in which a plurality of battery cells 9 are compressed in a non-dischargeable state; an inspection step of inspecting the battery cells 9 for the presence or absence of an internal short circuit during or after the lamination-compression step; a connection step of electrically connecting the anode current collectors 3 included in the anode 4 to each other and electrically connecting the cathode current collectors 6 to each other, to connect the battery cells 9 in parallel, after the lamination-compression step; and a step of removing at least a portion of the insulating layer 51 from the all-solid-state battery laminate 10 to make the battery cells 9 dischargeable, if it is determined in the inspection step that no internal short circuit is present.

[0038] With this, even if an internal short circuit occurs in a battery cell 9 during the lamination and compression bonding process, the other battery cells 9 other than the short-circuited cell are unable to discharge due to the presence of the insulating layer 51. Therefore, even if current collectors of the same polarity come into contact with each other before the process of removing the insulating layer 51, it is possible to prevent current from flowing from the other battery cells 9 into the short-circuited cell. This effect will be explained in more detail using a comparative example.

[0039] FIG. 9 is a comparative example of the present invention, and is a diagram schematically illustrating the flow of current I when current collectors come into contact with each other when an internal short circuit occurs in a battery cell 109. During the lamination and compression process in which a negative electrode containing Li metal or a Li alloy, a solid electrolyte layer, and a positive electrode are stacked and pressed, an internal short circuit may occur in the battery cell 109. FIG. 8 illustrates a case in which a short circuit occurs between the negative electrode 4 and the positive electrode 7 in one battery cell (short-circuited cell) 109S among the multiple battery cells 109 included in the all-solid-state battery stack 110. In this state, when the negative electrode current collectors 3 come into contact with each other and the positive electrode current collectors 6 come into contact with each other, an external parallel circuit is formed. In this external parallel circuit, current I flows from all of the non-shorted battery cells 109 to the short-circuited cell 109S, resulting in a large current. A large current flowing through the short-circuited cell 109S may cause the short-circuited cell 109S to generate a large amount of heat, which is undesirable.

[0040] In contrast, in the manufacturing method according to this embodiment, an insulating layer 51 is interposed between the solid electrolyte layer 8 and the positive electrode current collector 6 in the lamination and compression bonding step, and the multiple battery cells 9 are compressed in a state where they cannot discharge. Even if a short circuit occurs in some of the multiple battery cells 9 and current collectors of the same polarity come into contact with each other, the non-shorted battery cells 9 are in a state where they cannot discharge due to the presence of the insulating layer 51, so no current flows into the shorted cells from the other non-shorted battery cells 9. Because a large current does not flow in the shorted cells and only a current equivalent to the charge capacity of the shorted cells flows, heat generation in the shorted cells can be suppressed.

[0041] In the all-solid-state battery stack 10 according to this embodiment, a negative electrode 4 containing Li metal or a Li alloy, a solid electrolyte layer 8, and a positive electrode 7 are repeatedly arranged, and an insulating layer 51 is interposed between the solid electrolyte layer 8 and a positive electrode current collector 6 of the positive electrode 7, and a plurality of battery cells 9 are pressure-bonded in a non-dischargeable state, and the insulating layer 51 is made of sulfur (or polycarbonate, as shown in Modification 5 described later). This makes it possible to prevent current from flowing into the shorted cell from other battery cells 9, even if a shorted cell occurs in the stacking and pressure-bonding process. After it is determined in the inspection process that no internal short circuit exists, at least a portion of the insulating layer 51 can be removed to make each battery cell 9 included in the all-solid-state battery stack 10 dischargeable.

[0042] In this embodiment, the sulfur used for the insulating layer 51 may be either rhombic sulfur or monoclinic sulfur, but rhombic sulfur is preferable because it has a lower sublimation (vaporization) temperature than monoclinic sulfur.

[0043] (Modifications) The present embodiment may be modified as follows. (1) Modification 1 In the manufacturing method of the present invention, an inspection step of inspecting the battery cells 9 for internal short circuits may be performed during step ST1 (lamination and compression bonding step) of FIG. 2 . In the inspection step performed during the lamination and compression bonding step, the presence or absence of a short circuit may be determined by measuring the insulation resistance of an arbitrary battery cell 9 while pressing the laminate 10′ (see FIG. 3 ). FIG. 10 is a diagram showing Modification 1 of the manufacturing method according to the present embodiment. As shown in FIG. 10 , a resistance measuring device 23 is attached to the negative electrode current collector 3 and the positive electrode current collector 6 of an arbitrary battery cell 9, and the resistance between the negative electrode current collector 3 and the positive electrode current collector 6 (i.e., the insulation resistance of the battery cell 9) is measured while pressing the laminate 10′ (see FIG. 3 ). If the measured insulation resistance is equal to or less than a predetermined value, it is determined that an internal short circuit has occurred in the battery cell 9, and pressing is stopped. This allows the manufacturing process of the all-solid-state battery laminate including the short-circuited cell to be stopped early, even if a short circuit occurs, thereby contributing to reducing manufacturing costs.

[0044] If the inspection step is performed during the lamination and compression bonding step as described above, an additional inspection step may be performed after the lamination and compression bonding step. In the inspection step performed after the lamination and compression bonding step, the thickness T of the battery cells 9 is measured to determine whether or not an internal short circuit exists, as described with reference to Figures 4 and 5, for example. During the lamination and compression bonding step, the presence or absence of an internal short circuit is determined based on the insulation resistance of the battery cells 9, and after the lamination and compression bonding step, the presence or absence of an internal short circuit is determined based on the thickness of the battery cells 9. By performing two inspections using different methods, the presence or absence of an internal short circuit can be detected with higher accuracy.

[0045] Alternatively, when the inspection step is performed during the lamination and pressure bonding step as described above, the inspection step performed after the lamination and pressure bonding step may be omitted. This makes it possible to reduce the inspection cost compared to when two inspections are performed.

[0046] (2) Modification 2 In the inspection process performed after the lamination and pressure bonding process, the presence or absence of an internal short circuit may be determined based on the insulation resistance of the battery cells 9, rather than the thickness T of the battery cells 9. For example, after the lamination and pressure bonding process, the insulation resistance of the battery cells 9 may be measured using the resistance measuring device 23 shown in FIG. 10 , and the presence or absence of an internal short circuit may be determined based on the measured insulation resistance.

[0047] (3) Modification 3 Fig. 11 is a diagram showing Modification 3 of the manufacturing method according to this embodiment. As shown in Fig. 11 , in the lamination and compression step, the insulating layer 51 may be interposed between the positive electrode layer 5 and the solid electrolyte layer 8, rather than between the positive electrode layer 5 and the positive electrode current collector 6. Even in this embodiment, the battery cells 9 are compressed in a state in which discharge is disabled due to the presence of the insulating layer 51. Therefore, as in the above embodiment, even if current collectors of the same polarity come into contact with each other before the step of removing the insulating layer 51, it is possible to prevent current from flowing from other battery cells 9 into the short-circuited cell.

[0048] 11 , an insulating layer 51 is interposed between the positive electrode layer 5 and the solid electrolyte layer 8, and the positive electrode layer 5 and the solid electrolyte layer 8 are not in contact with each other. Therefore, even if a short circuit occurs, an ion path IP as shown in FIG. 5 is not formed, and the thickness of the short-circuited cell may not decrease. In that case, for example, as described in the above-mentioned Modifications 1 and 2, the presence or absence of an internal short circuit may be determined based on the insulation resistance of the battery cell 9, rather than the thickness T of the battery cell 9.

[0049] (4) Modification 4 The step of removing the insulating layer 51 (removal step) may be performed in parallel with the connection step of connecting current collectors of the same electrode. For example, step ST3 and step ST4 in FIG. 2 may be performed simultaneously. When the positive electrode current collector 6 and the positive electrode tab lead 12 are joined by welding, the welding heat is transferred from the positive electrode current collector 6 to the insulating layer 51. Therefore, it may be possible to remove the insulating layer 51 by using the welding heat to heat and sublimate the insulating layer 51. This method eliminates the need for a dedicated heating step for removing the insulating layer 51, thereby shortening the manufacturing process and reducing manufacturing costs.

[0050] (5) Modification 5 In the embodiment of the present invention, the insulating layer 51 is not limited to sulfur (S). The insulating layer 51 may be made of a material (e.g., polycarbonate) that has high insulating properties and a low boiling point similar to sulfur and can be removed by heating and sublimating. For example, polycarbonate can be formed into a thin film by casting a polycarbonate solution in chloroform or the like, thereby providing the insulating layer 51 on both surfaces of the positive electrode current collector 6.

[0051] (Other Embodiments) As described above, the present invention has been described with reference to embodiments and modifications. However, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments and modifications will be apparent to those skilled in the art from this disclosure. For example, in the lamination and compression process, the insulating layer 51 may be interposed both between the positive electrode layer 5 and the positive electrode current collector 6 and between the positive electrode layer 5 and the solid electrolyte layer 8.

[0052] Furthermore, in the step of removing the insulating layer 51 (removal step), instead of removing all of the insulating layer 51 in each of the plurality of battery cells 9, a portion of the insulating layer 51 may remain. Even if a portion of the insulating layer 51 remains in each battery cell 9, by removing most of the insulating layer 51 and creating a state in which the positive electrode current collector 6 and the positive electrode layer 5 are in contact with each other and the positive electrode layer 5 and the solid electrolyte layer 8 are in contact with each other, each battery cell 9 can be made dischargeable. As described above, it goes without saying that the present technology includes various embodiments not described here. At least one of various omissions, substitutions, and modifications of components can be made within the scope of the above-described embodiments. Furthermore, the effects described in this specification are merely examples and are not limited thereto, and other effects may also be provided.

[0053] The present invention can also employ the following configurations: (1) A method for manufacturing an all-solid-state battery, comprising: a lamination and compression step of pressing a laminate in which a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly arranged, with an insulating layer interposed between the solid electrolyte layer and a positive electrode current collector of the positive electrode, to form an all-solid-state battery laminate in which a plurality of battery cells are compressed in a non-dischargeable state; an inspection step of inspecting the battery cells for the presence or absence of an internal short circuit during or after the lamination and compression step; a connection step of electrically connecting the negative electrode current collectors included in the negative electrode and electrically connecting the positive electrode current collectors to connect the battery cells in parallel after the lamination and compression step; and a step of removing at least a portion of the insulating layer from the all-solid-state battery laminate to make the battery cells dischargeable when it is determined in the inspection step that no internal short circuit is present. (2) A method for manufacturing an all-solid-state battery according to (1), in which the insulating layer is sulfur or polycarbonate. (3) The method for producing an all-solid-state battery according to (1) or (2), wherein in the lamination and compression bonding step, the insulating layer is interposed between a positive electrode layer included in the positive electrode and the positive electrode current collector. (4) The method for producing an all-solid-state battery according to any one of (1) to (3), wherein in the insulating layer removing step, the insulating layer is heated to sublimate. (5) The method for producing an all-solid-state battery according to (4), wherein in the insulating layer removing step, the insulating layer is heated to sublimate in a state in which the all-solid-state battery laminate is placed in a reduced pressure environment. (6) The method for producing an all-solid-state battery according to (4) or (5), wherein in the insulating layer removing step, the insulating layer is heated from the positive electrode current collector. (7) The method for producing an all-solid-state battery according to (6), wherein the insulating layer has a lower boiling point than the positive electrode layer included in the positive electrode. (8) The method for producing an all-solid-state battery according to any one of (1) to (7), wherein the insulating layer removing step is performed in parallel with or after the connecting step. (9) The method for manufacturing an all-solid-state battery according to any one of (1) to (8), wherein the inspection step is performed during the lamination and compression bonding step, and in the inspection step, an insulation resistance of the battery cell is measured while the pressing is being performed, and if the measured insulation resistance is equal to or less than a preset value, it is determined that the internal short circuit has occurred.(10) The method for manufacturing an all-solid-state battery according to (9), wherein in the lamination and compression bonding step, the insulating layer is interposed between a positive electrode layer included in the positive electrode and the positive electrode current collector, and the inspection step is performed after the lamination and compression bonding step, and in the inspection step, a thickness of the battery cell is measured, and if the measured thickness is equal to or less than a predetermined value, it is determined that the internal short circuit has occurred. (11) An all-solid-state battery stack in which a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly arranged, an insulating layer is interposed between the solid electrolyte layer and the positive electrode current collector of the positive electrode, and a plurality of battery cells are compressed together in a non-dischargeable state, and the insulating layer is made of sulfur or polycarbonate.

[0054] 1... all-solid-state battery, 2... negative electrode layer, 3... negative electrode current collector, 4... negative electrode, 5... positive electrode layer, 6... positive electrode current collector, 7... positive electrode, 8... solid electrolyte layer, 9... battery cell 9S, 109S... short-circuit cell, 10... laminate, 10, 110... all-solid-state battery laminate, 11... negative electrode tab lead, 12... positive electrode tab lead, 14, 15... welded portion, 23... resistance measuring device, 51... insulating layer, 53... treatment chamber, IP... ion path

Claims

1. A method for manufacturing an all-solid-state battery, comprising: a lamination and compression step of pressing a laminate in which a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly arranged, with an insulating layer interposed between the solid electrolyte layer and a positive electrode current collector of the positive electrode, to form an all-solid-state battery laminate in which a plurality of battery cells are pressed together in a non-dischargeable state; an inspection step of inspecting the battery cells for the presence or absence of an internal short circuit during or after the lamination and compression step; a connection step of electrically connecting the negative electrode current collectors included in the negative electrodes and electrically connecting the positive electrode current collectors to connect the battery cells in parallel, after the lamination and compression step; and a step of removing at least a portion of the insulating layer from the all-solid-state battery laminate to make the battery cells dischargeable, when it is determined in the inspection step that no internal short circuit is present.

2. The method for producing an all-solid-state battery according to claim 1, wherein the insulating layer is made of sulfur or polycarbonate.

3. The method for producing an all-solid-state battery according to claim 1 or 2, wherein in the lamination and pressure bonding step, the insulating layer is interposed between the positive electrode layer included in the positive electrode and the positive electrode current collector.

4. The method for producing an all-solid-state battery according to claim 1 or 2, wherein the insulating layer is heated and sublimated in the step of removing the insulating layer.

5. The method for manufacturing an all-solid-state battery according to claim 4, wherein in the step of removing the insulating layer, the insulating layer is heated and sublimated in a state where the all-solid-state battery stack is placed in a reduced pressure environment.

6. The method for producing an all-solid-state battery according to claim 4, wherein the step of removing the insulating layer comprises heating the insulating layer from the positive electrode current collector.

7. The method for producing an all-solid-state battery according to claim 6, wherein the insulating layer has a boiling point lower than that of the positive electrode layer contained in the positive electrode.

8. The method for producing an all-solid-state battery according to claim 1 or 2, wherein the step of removing the insulating layer is carried out in parallel with or after the step of connecting.

9. The method for manufacturing an all-solid-state battery according to claim 1 or 2, wherein the inspection step is performed during the lamination and compression step, and in the inspection step, the insulation resistance of the battery cell is measured while the pressing is being performed, and if the measured insulation resistance is equal to or less than a preset value, it is determined that the internal short circuit has occurred.

10. The method for manufacturing an all-solid-state battery according to claim 9, wherein in the lamination and pressure bonding step, the insulating layer is interposed between the positive electrode layer included in the positive electrode and the positive electrode current collector, and the inspection step is carried out after the lamination and pressure bonding step, and in the inspection step, a thickness of the battery cell is measured, and if the measured thickness is equal to or less than a preset value, it is determined that the internal short circuit has occurred.

11. An all-solid-state battery stack in which a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly arranged, an insulating layer is interposed between the solid electrolyte layer and a positive electrode current collector of the positive electrode, and multiple battery cells are pressed together in a non-dischargeable state, and the insulating layer is made of sulfur or polycarbonate.

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