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

Abstract

Provided are: a method for manufacturing an all-solid-state battery containing a Li metal or a Li alloy in a negative electrode, the all-solid-state battery being capable of suppressing occurrence of short-circuiting during manufacturing; and a laminate for manufacturing an all-solid-state battery. This method for manufacturing an all-solid-state battery comprises: a step for performing first pressing on a laminate in which a negative electrode containing a lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are disposed, thus forming an all-solid-state battery laminate in which a plurality of battery cells are crimped without reaching a state in which discharge is possible; and a step for performing second pressing on the all-solid-state battery laminate to bring the battery cells into the state in which discharge is possible. In the step for performing the first pressing, an intermediate layer having a slower lithium diffusion rate than the solid electrolyte layer is interposed between the negative electrode and the solid electrolyte layer.

Description

Manufacturing method of all-solid-state battery, laminate for manufacturing all-solid-state battery

[0001] The present invention relates to a method for producing an all-solid-state battery and a laminate for use in producing an all-solid-state battery.

[0002] Patent Document 1 discloses "an all-solid-state lithium secondary battery comprising, in this order, a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer that forms an alloy or compound with lithium, wherein the negative electrode active material layer contains Ag."

[0003] Japanese Patent Application Laid-Open No. 2020-191202

[0004] In all-solid-state batteries containing lithium (Li) metal or a Li alloy in the negative electrode, a technique for suppressing the occurrence of short circuits during manufacturing is desired.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing an all-solid-state battery that can suppress the occurrence of a short circuit during manufacturing an all-solid-state battery containing Li metal or a Li alloy in the negative electrode, and a laminate for use in manufacturing the all-solid-state battery.

[0006] A method for manufacturing an all-solid-state battery according to one aspect of the present invention includes a step of performing a first press on a laminate including a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode to form an all-solid-state battery laminate in which a plurality of battery cells are pressure-bonded without reaching a dischargeable state, and a step of performing a second press on the all-solid-state battery laminate to bring the battery cells into a dischargeable state. In the first press, an intermediate layer having a slower lithium diffusion rate than the solid electrolyte layer is interposed between the negative electrode and the solid electrolyte layer.

[0007] According to one aspect of the present invention, it is possible to provide a method for manufacturing an all-solid-state battery that can suppress the occurrence of a short circuit during manufacturing an all-solid-state battery containing Li metal or a Li alloy in the negative electrode, and a laminate for manufacturing the all-solid-state battery.

[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 method for manufacturing an all-solid-state battery according to the present embodiment. FIG. 3 is a schematic diagram for explaining in detail step ST1 of the flowchart shown in FIG. 2. FIG. 4 is a cross-sectional view showing example 1 of the configuration of a battery cell in a lamination and pressure bonding process according to the present embodiment. FIG. 5 is a cross-sectional view showing example 2 of the configuration of a battery cell in a lamination and pressure bonding process according to the present embodiment. FIG. 6 is a cross-sectional view showing example 3 of the configuration of a battery cell in a lamination and pressure bonding process according to the present embodiment. FIG. 7 is a cross-sectional view showing example 4 of the configuration of a battery cell in a lamination and pressure bonding process according to the present embodiment. FIG. 8 is a diagram illustrating an internal resistance inspection process according to the present embodiment. FIG. 9 is a plan view showing an example of the configuration of an all-solid-state battery laminate sealed with an insulating sheet in a sealing process according to the present embodiment. FIG. 10 is a cross-sectional view showing an example of the configuration of an all-solid-state battery laminate sealed with an insulating sheet in a sealing process according to the present embodiment. FIG. 11 is a diagram illustrating a pressurizing process according to the present embodiment. FIG. 12 is a diagram showing an example of an experiment conducted by the present inventor. Fig. 13 is a graph showing the relationship between the cell voltage and the pressurization time of the second press, which is an experimental result of the present invention. Fig. 14 is a graph showing the relationship between the pressurization time of the second press and the discharge curve of the cell, which is an experimental result of the present invention. Fig. 15 is a Bode plot of the cell (pressure 5 MPa) before and after suspension, which is an experimental result of the present invention. Fig. 16 is a Bode plot of the cell (pressure 10 MPa) before and after suspension, which is an experimental result of the present invention. Fig. 17 is a Bode plot of the cell (pressure 20 MPa) before and after suspension, which is an experimental result of the present invention.

[0009] An embodiment of the present invention (the present embodiment) will be described below. In the following description of the drawings, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each device and each component, etc., differ from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, it goes without saying that the drawings also include parts with different dimensional relationships and ratios.

[0010] The definitions of directions such as up and down in the following explanation are merely for the convenience of explanation and do not limit the technical idea of ​​the present invention. For example, if an object is rotated 90 degrees and observed, up and down are converted to left and right and read as such, and if it is rotated 180 degrees and observed, up and down are obviously read as reversed.

[0011] 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, and a cathode tab lead 12 joined to the cathode current collector 6. The all-solid-state battery 1 also includes a lithiated intermediate layer 21A disposed between the anode 4 and the solid electrolyte layer 8.

[0012] 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.

[0013] 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, 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. The positive electrode layer 5 can be made of, for example, manganese dioxide, sulfide, or fluoride, but are not limited to these.

[0014] 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.

[0015] The negative electrodes 4 and positive electrodes 7 are alternately stacked with lithiated intermediate layers 21A and solid electrolyte layers 8 interposed therebetween to form an all-solid-state battery stack 10. The lithiated intermediate layer 21A and solid electrolyte layer 8 are 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. 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 lithiated intermediate layer 21A and the solid electrolyte layer 8.

[0016] (Manufacturing Method) Next, a method for manufacturing the all-solid-state battery 1 according to this embodiment will be described. FIG. 2 is a flowchart showing a method for manufacturing the all-solid-state battery 1 according to this embodiment. Note that other steps may be included between the steps in the flowchart of FIG. 2. FIG. 3 is a schematic diagram for explaining in detail step ST1 of the flowchart shown in FIG. 2. Note that the all-solid-state battery 1 is manufactured using various devices, such as a device for stacking the negative electrode 4, the positive electrode 7, the solid electrolyte layer 8, and the pre-lithiation intermediate layer 21 (hereinafter simply referred to as the intermediate layer), a press device for pressing the all-solid-state battery stack 10, a device for performing a discharge treatment on the all-solid-state battery stack 10, and a welding device for welding the current collector and the tab lead. Hereinafter, these devices will be collectively referred to as manufacturing devices.

[0017] In step ST1 of FIG. 2 , the manufacturing equipment performs a stacking and compression bonding process. For example, as shown in the left diagram of FIG. 3 , the manufacturing equipment repeatedly arranges a negative electrode 4 containing Li metal or a lithium alloy, an intermediate layer 21, a solid electrolyte layer 8, and a positive electrode 7 in one direction (hereinafter also referred to as the stacking direction) to form an unpressurized laminate 10′. At this point, a negative electrode layer 2 composed of Li metal or a Li alloy has already been provided on both sides of the negative electrode current collector 3. Similarly, a positive electrode layer 5 has already been provided on both sides of the positive electrode current collector 6. In addition, an intermediate layer 21 has been provided on the surface of the solid electrolyte layer 8 facing the negative electrode 4.

[0018] In the left-hand drawing, the negative electrode 4 and the intermediate layer 21, and the solid electrolyte layer 8 and the positive electrode 7 are shown separated from each other; however, in the laminate 10′, the negative electrode 4 and the intermediate layer 21, and the solid electrolyte layer 8 and the positive electrode 7 may be in contact with each other in an unpressed state.

[0019] In addition, in the left-hand drawing, the solid electrolyte layer 8 is shown separated from the positive electrode 7, but the solid electrolyte layer 8 may be attached to the positive electrode 7 in advance. That is, the positive electrode 7 may be a positive electrode with a solid electrolyte layer, in which the solid electrolyte layer 8 is pre-laminated on the positive electrode layer 5. For example, the positive electrode 7 and the solid electrolyte layer 8 are overlapped and pressed so that the positive electrode layer 5 and the solid electrolyte layer 8 are in contact with each other, and after pressing, the substrate of the solid electrolyte layer 8 is removed, thereby transferring the solid electrolyte layer 8 to the positive electrode 7. A positive electrode with a solid electrolyte layer may be obtained in this manner. Furthermore, an intermediate layer 21 may be disposed on the surface of the solid electrolyte layer 8 after it has been transferred to the positive electrode 7.

[0020] Next, as shown in the right diagram of FIG. 3 , the manufacturing apparatus performs a first press on the laminate 10′ in the stacking direction with a first press pressure P1. For example, the first press pressure P1 is greater than the second press pressure P2 performed in step ST5 described below. Furthermore, the press time with the first press pressure P1 (hereinafter referred to as the first press time) is shorter than the press time with the second press pressure (hereinafter referred to as the second press time). For example, the first press pressure is 40 MPa, and the press time with the first press pressure is 1 second (sec).

[0021] As a result, the layers of the laminate 10′ (for example, between the anode layer 2 and the intermediate layer 21, between the intermediate layer 21 and the solid electrolyte layer 8, and between the solid electrolyte layer 8 and the cathode layer 5) are respectively pressure-bonded, and an all-solid-state battery laminate 10 in which a plurality of battery cells 9 are stacked is formed.

[0022] By this molding, the anode layer 2 made of Li metal or Li alloy is pressure-bonded to the solid electrolyte layer 8 via the intermediate layer 21. Because the anode layer 2 is made of Li metal or Li alloy, each battery cell 9 included in the all-solid-state battery stack 10 is formed in a charged state.

[0023] Here, the intermediate layer 21 interposed between the anode layer 2 and the solid electrolyte layer has a slower Li diffusion rate than the solid electrolyte layer 8. The intermediate layer 21, which has a slower Li diffusion rate, functions as an insulating layer in the stacking and pressing process of step ST1. Therefore, each battery cell 9 cannot discharge even though it is in a charged state. Note that the intermediate layer 21 is a layer that does not allow Li ions to pass through until Li ions are absorbed (for example, before the start of step ST5, which will be described later). After Li ions are absorbed (i.e., after lithiation, i.e., after step ST5 in FIG. 2 is completed), the intermediate layer 21 remains as a layer that allows Li ions to pass through.

[0024] In the lamination and compression bonding step, the first pressing is performed under conditions that take into account the presence of the intermediate layer 21 and that do not destroy the intermediate layer 21 or lithiate the intermediate layer 21 so that it allows Li ions to pass through. These conditions can be set by adjusting the first pressing pressure and the first pressing time. As a result, the battery cells 9 are compressed without reaching a dischargeable state, and the all-solid-state battery stack 10 is formed.

[0025] Before describing step ST2 in FIG. 2 , configuration examples of the battery cell 9 in the stacking and pressure bonding process will be described. FIGS. 4 to 7 are cross-sectional views showing configuration examples 1 to 4 of the battery cell 9 in the stacking and pressure bonding process according to this embodiment. As shown in FIG. 4 , the battery cell 9 in the stacking and pressure bonding process has a laminated structure in which, from the negative electrode current collector 3 toward the positive electrode current collector 6, an anode layer 2 composed of Li metal or a Li alloy, a non-lithiated intermediate layer 21, a solid electrolyte layer 8, and a positive electrode current collector 6 are arranged in this order. The non-lithiated intermediate layer 21 is composed of, for example, carbon. The non-lithiated intermediate layer 21 may also contain carbon (C) and a metal species that can be alloyed with lithium. The metal species that can be alloyed with lithium is not particularly limited, but examples include silver (Ag), magnesium (Mg), silicon (Si), aluminum (Al), zinc (Zn), tin (Sn), and bismuth (Bi).

[0026] As shown in FIG. 5 , the battery cell 9 in the lamination and compression bonding process may have, as the intermediate layer 21, a first intermediate layer 21L and a second intermediate layer 21H having a faster Li diffusion rate than the first intermediate layer 21L. The second intermediate layer 21H may be located between the first intermediate layer 21L and the solid electrolyte layer 8. The first intermediate layer 21L having a slower lithium diffusion rate can improve insulation performance compared to the second intermediate layer 21H having a faster lithium diffusion rate. Furthermore, the second intermediate layer 21H having a faster lithium diffusion rate can accelerate lithiation during the second press compared to the first intermediate layer 21L having a slower lithium diffusion rate. In this way, the first intermediate layer 21L has the advantage of improving insulation in the first press process, and the second intermediate layer 21H has the advantage of accelerating lithiation in the second press process.

[0027] 6 , the first intermediate layer 21L and the second intermediate layer 21H may each contain carbon and a metal species (e.g., Ag) that alloys with lithium. The first intermediate layer 21L may have a lower metal species content than the second intermediate layer 21H. The low metal species content of the intermediate layer 21 can suppress lithium diffusion, while the high metal species content can promote lithium diffusion.

[0028] 7 , the first intermediate layer 21L may contain carbon but may not contain a metal species that alloys with lithium. The second intermediate layer 21H may contain carbon and a metal species. The absence of a metal species in the intermediate layer 21 can suppress lithium diffusion, while the inclusion of a metal species can promote lithium diffusion.

[0029] Next, step ST2 in FIG. 2 will be described. In step ST2 in FIG. 2 , the manufacturing apparatus performs an internal resistance inspection step. For example, the manufacturing apparatus inspects the internal resistance of each of the plurality of battery cells 9 included in the all-solid-state battery laminate 10. FIG. 8 is a diagram illustrating the internal resistance inspection step according to this embodiment. As shown in FIG. 8 , for each battery cell 9, a resistance measuring device 23 is connected to the negative electrode current collector 3 and the positive electrode current collector 6, a DC voltage is applied between the negative electrode current collector 3 and the positive electrode current collector 6, and the current value is measured. This detects the internal resistance of each battery cell 9. In the battery cell 9, the non-lithiated intermediate layer 21 accounts for a large portion of the resistance component, and therefore, by detecting the internal resistance, the resistance of the intermediate layer 21 can be indirectly detected (measured).

[0030] In this internal resistance inspection step, for example, if the detected internal resistance is equal to or greater than a preset value, the manufacturing device (inspection device) determines that there is no abnormality because the anode current collector 3 and the cathode current collector 6 are insulated by the intermediate layer 21. On the other hand, if the detected internal resistance is lower than the preset value, the insulating function of the intermediate layer 21 is not being exerted, and there is a possibility of a short circuit between the anode current collector 3 and the cathode current collector 6, so it is determined that there is an abnormality. In step ST2, the manufacturing process of the all-solid-state battery stack 10 including the battery cell 9 determined to have an abnormality ends.

[0031] 2 , the manufacturing equipment joins the negative electrode current collector 3 to the negative electrode tab lead 11 (see FIG. 1 ) for the all-solid-state battery stack 10 determined to be normal in step ST2. Also, before, after, or in parallel with this, the manufacturing equipment joins a plurality of positive electrode current collectors 6 to the positive electrode tab lead 12 (see FIG. 1 ). The welding method is not particularly limited, but examples include welding using an ultrasonic welding machine and laser welding.

[0032] Next, in step ST4 of FIG. 2 , the manufacturing equipment performs a sealing process. FIGS. 9 and 10 are plan and cross-sectional views showing a configuration example of the all-solid-state battery stack 10 sealed with an insulating sheet 25 in the sealing process according to this embodiment. FIG. 10 shows a cross section taken along line X1-X1′ in FIG. 9 . As shown in FIGS. 9 and 10 , the manufacturing equipment seals the all-solid-state battery stack 10 with the insulating sheet 25, except for the negative electrode tab lead 11 and the positive electrode tab lead 12. The joint between the negative electrode tab lead 11 and the negative electrode current collector 3 and the joint between the positive electrode tab lead 12 and the positive electrode current collector 6 are also sealed with the insulating sheet 25. For example, the insulating sheet 25 is a laminate film. The manufacturing equipment laminates and seals the all-solid-state battery stack 10 and the above-mentioned joints.

[0033] Next, in step ST5 of FIG. 2 , the manufacturing apparatus performs a pressurizing step. FIG. 11 is a diagram illustrating the pressurizing step according to this embodiment. As shown in FIG. 11 , the manufacturing apparatus stacks, for example, a plurality of all-solid-state battery stacks 10 sealed with insulating sheets 25 in one direction, and performs a second press in one direction (i.e., the stacking direction) with a second press pressure P2. A pressing unit 26 of the manufacturing apparatus presses the plurality of all-solid-state battery stacks 10 together in the stacking direction. As a result, in each of the plurality of all-solid-state battery stacks 10, lithium diffuses from the anode layer 2 (e.g., see FIG. 4 ) to the intermediate layer 21 (e.g., see FIG. 4 ), causing the intermediate layer 21 to become lithiated, thereby enabling the battery cell 9 (e.g., see FIG. 4 ) to be discharged.

[0034] Next, in step ST6 of FIG. 2, the manufacturing equipment performs a discharge operation process. For example, in an environment above room temperature and in an inert atmosphere (for example, N ２ All of the battery cells 9 included in the all-solid-state battery stack 10 are discharged via the negative electrode tab lead 11 and the positive electrode tab lead 12 shown in FIG. 1 under a low-temperature atmosphere or vacuum. This allows all of the battery cells 9 included in the all-solid-state battery stack 10 to be efficiently discharged.

[0035] During this discharge operation, in each battery cell 9, Li ions migrate from the negative electrode 4 through the lithiated intermediate layer 21A and the solid electrolyte layer 8 to the positive electrode 7 and are absorbed in the positive electrode layer 5. As described above, each battery cell 9 included in the all-solid-state battery stack 10 is in a charged state at the time of stacking and pressing in step ST1 of FIG. 2 . When a discharge operation is performed on a charged battery cell 9, 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 gone. By performing a discharge operation via the negative electrode tab lead 11 and the positive electrode tab lead 12, the SOC of all battery cells 9 included in the all-solid-state battery stack 10 can be set to 0% or almost 0%.

[0036] The manufacturing apparatus may also perform a charging operation on the all-solid-state battery stack 10 that has undergone the discharging operation. This charging operation is performed, for example, 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 migrate to the negative electrode current collector 3 via the solid electrolyte layer 8 and the lithiated intermediate layer 21A, and Li metal or Li alloy precipitates as the negative electrode layer 2. As described above, the lithiated intermediate layer 21A remains as a layer that transmits Li ions. Through the above steps, the all-solid-state battery 1 shown in FIG. 1 is completed.

[0037] (Experiment and Results) The present inventors conducted an experiment to investigate the relationship between the time for which the pressurized state is maintained (hereinafter referred to as the pressurization time) and the lithiation of the intermediate layer in the pressurization step performed in step ST5 of FIG. 2 . FIG. 12 illustrates the experiment conducted by the present inventors. As shown in the left diagram of FIG. 12 , a cell 30 was prepared as an experimental sample. The cell 30 includes a stainless steel (SUS) plate 31, a lithium (Li) metal layer 32 provided on the upper surface of the stainless steel (SUS) plate 31, a SUS plate 33, a Li metal layer 34 provided on the lower surface of the SUS plate 33, an intermediate layer 35 provided between the Li metal layers 32 and 34, and a solid electrolyte layer 36. The cell 30 has a structure in which the Li metal layer 32, the intermediate layer 35, the solid electrolyte layer 36, and the Li metal layer 34 are stacked in this order from the SUS plate 31 located on one side to the SUS plate 33 located on the other side. The intermediate layer 35 is composed of carbon and a binder, with the carbon acting as a positive electrode.

[0038] In this experiment, the cell 30 was subjected to a first press in the stacking direction at a first press pressure P1 to compress the layers of the cell 30. The first press pressure P1 was 40 MPa, and the pressurization time was 1 second (sec). Next, as shown in the right diagram of FIG. 12 , the cell 30 was subjected to a second press in the stacking direction at a second press pressure P2 to diffuse Li from the Li metal layer 32 into the intermediate layer 35. As a result, the intermediate layer 35 was lithiated to form a lithiated intermediate layer 35A. The press pressure (second press pressure) P2 of the second press was 20 MPa. The pressurization time using the second press pressure P2 was set to three times: 0 hours (h), 1 hour, and 5 hours. The pressurization time of 0 hours was a comparative example. In Examples 1 and 2, the product of the second press pressure and the second press time was greater than the product of the first press pressure and the first press time.

[0039] FIG. 13 is a graph showing the relationship between the voltage of the cell 30 and the pressure time of the second press, which is an experimental result of the present invention. The vertical axis of FIG. 13 represents the voltage of the cell 30, and the horizontal axis represents the pressure time of the second press. The voltage of the cell 30 is the voltage between the Li metal layers 32 and 34 (i.e., between the positive electrode and the negative electrode). In this experiment, the voltage of the cell 30 was measured while performing the second press (20 MPa). As shown in FIG. 13 , it was confirmed that the longer the pressure time of the second press, the lower the voltage of the cell 30. This result confirmed that the longer the pressure time of the second press, the more lithiation of the intermediate layer 35 progresses.

[0040] FIG. 14 is a graph showing the experimental results of the present invention, illustrating the relationship between the pressure time of the second press and the discharge curve of the cell 30. The vertical axis of FIG. 14 represents the voltage of the cell 30, and the horizontal axis represents the discharge capacity. In this experiment, three types of cells 30 were prepared after the second press, with the pressure time of the second press P2 being 0 hours (Comparative Example), 1 hour (Example 1), and 5 hours (Example 2). A pressure of 20 MPa was then applied to these three types of cells 30 in the stacking direction in an environment of 25°C. While maintaining this room-temperature pressurized state, a current of 0.2 mA / cm was applied until the voltage of the cell 30 reached 2V. ２ The battery was discharged at a constant current of .

[0041] As shown in Figure 14, discharge was not possible after 0 hours (Comparative Example). In contrast, discharge was possible after 1 hour (Example 1) and 5 hours (Example 2). Furthermore, the cell voltage during discharge was lower and the discharge capacity was greater after 5 hours (Example 2) than after 1 hour (Example 1). This indicates that the longer the pressure application time of the second press (i.e., the more lithiation of the intermediate layer 35 progresses), the lower the internal resistance of the cell 30 tends to be.

[0042] 15 to 17 are Bode plots of the cell 30 before and after the pause, showing the experimental results of the present invention. Specifically, FIGS. 15 to 17 show Bode plots of the cell 30 after two hours of pressing at a predetermined pressure (before the pause) and the cell 30 after the two-hour pressing was further pressed at the predetermined pressure for five hours (h) (after the pause). In each of FIGS. 15 to 17, the upper diagram is the Bode plot before the pause, and the lower diagram is the Bode plot after the pause. FIG. 15 is a Bode plot when the predetermined pressure is 5 MPa, FIG. 16 is a Bode plot when the predetermined pressure is 10 MPa, and FIG. 17 is a Bode plot when the predetermined pressure is 20 MPa. In each diagram, the vertical axis represents the phase difference, and the horizontal axis represents the frequency of the AC voltage (10 mV).

[0043] 15 to 17, the frequencies enclosed by the dotted lines are 10 Hz to 10 ５ Focusing on the frequency range of 10 Hz, a frequency-dependent phase difference was confirmed in the data before the pause, regardless of whether the predetermined pressure was 5 MPa, 10 MPa, or 20 MPa. This phase difference is thought to be due to insufficient lithiation, and is manifested as a phase difference due to frequency-dependent impedance variations. In contrast, in the data after the pause, a frequency range of 10 Hz to 10 ５ In the Hz range, the frequency-dependent phase difference was reduced. This is thought to indicate that after the pause, lithiation was sufficient and the frequency-dependent impedance variation was reduced. Furthermore, the absolute value of the phase difference data after the pause was lower than the data before the pause. These results demonstrate that, regardless of whether the predetermined pressure was 5 MPa, 10 MPa, or 20 MPa, increasing the pressing time (pressure application time) promotes lithiation of the intermediate layer 35 and reduces resistance.

[0044] 15 to 17, the lower figures are overlapped. ５ In the range of Hz, the lines in each figure overlap. This shows that, at least as long as the predetermined pressure is in the range of 5 MPa to 20 MPa, lithiation is promoted in the same way regardless of the pressure used for pressing, and battery cells in the same state can be manufactured.

[0045] Effect of the embodiment As described above, the method for manufacturing an all-solid-state battery according to the present embodiment includes a step of performing a first press on a stack 10′ in which a negative electrode 4 containing Li metal or a Li alloy, a solid electrolyte layer 8, and a positive electrode 7 are repeatedly arranged in one direction (stacking direction) to form an all-solid-state battery stack 10 in which a plurality of battery cells 9 are pressure-bonded without reaching a dischargeable state, and a step of performing a second press on the all-solid-state battery stack 10 in at least the stacking direction to bring the battery cells 9 into a dischargeable state. In the first pressing step, an intermediate layer 21 having a slower Li diffusion rate than the solid electrolyte layer 8 is interposed between the negative electrode 4 and the solid electrolyte layer 8.

[0046] According to this, in the lamination and compression bonding step of forming the all-solid-state battery laminate 10 by compressing the laminate 10′ using the first press, the intermediate layer 21 functions as an insulating layer, and therefore, it is possible to prevent a short circuit between the negative electrode 4 and the positive electrode 7. It is possible to suppress the occurrence of a short circuit during manufacturing, and to prevent heat generation due to the occurrence of a short circuit.

[0047] In the above manufacturing method, the second pressing causes Li to diffuse from the negative electrode 4 into the intermediate layer 21, causing the intermediate layer 21 to become lithiated. As a result, the intermediate layer 21 is a layer that does not allow Li ions to pass through until it is lithiated, and can function as an insulating layer. After it is lithiated, the intermediate layer 21 can remain as a layer that allows Li ions to pass through.

[0048] In the manufacturing method of this embodiment, Li metal or Li alloy is already present in the negative electrode 4 in the lamination and compression step, which is an early stage of the manufacturing process. Therefore, a battery cell 9 in a charged state is formed when the negative electrode 4 and the positive electrode 7 are compressed to the solid electrolyte layer 8 by the first press. However, in the lamination and compression step, the non-lithiated intermediate layer 21 is interposed as an insulating layer between the negative electrode and the solid electrolyte layer 8, so that a short circuit between the positive electrode 7 and the negative electrode 4 can be avoided. Therefore, this contributes to reducing the difficulty of manufacturing an all-solid-state battery 1 in which Li metal or Li alloy is present in the negative electrode 4 in the early stage of the manufacturing process.

[0049] In the laminate for producing an all-solid-state battery according to this embodiment (for example, the laminate 10′ or the all-solid-state battery laminate 10), an anode 4 containing Li metal or a Li alloy, a solid electrolyte layer 8, and a cathode 7 are repeatedly arranged in one direction (stacking direction), and an intermediate layer 21 having a slower Li diffusion rate than the solid electrolyte layer 8 is interposed between the anode 4 and the solid electrolyte layer 8. For example, when pressure is applied between the anode 4 and the cathode 7 by the second press, Li diffuses from the anode 4 to the intermediate layer 21, and the intermediate layer 21 is lithiated. This allows the laminate for producing an all-solid-state battery to be suitably used in the production method according to this embodiment, and makes it possible to suppress the occurrence of a short circuit during production.

[0050] (Modifications of the Embodiment) (1) In step ST1 (lamination and compression bonding process) of FIG. 2 , a first press may be applied to at least the laminate 10′ while measuring the resistance of the intermediate layer 21. For example, the first press may be applied to the laminate 10′ while measuring the resistance of the intermediate layer 21, and if the measured resistance value falls outside a predetermined range (control value), i.e., if an abnormality is detected, the pressure may be released. The resistance may be measured using, for example, a resistance measuring device 23 shown in FIG. 8 . This makes it possible to confirm that the insulating function of the intermediate layer 21 is ON in the lamination and compression bonding process, and to take action if the insulating function is defective. (2) In step ST5 (pressure application process) of FIG. 2 , the resistance of the intermediate layer 21 may be measured while applying pressure to the all-solid-state battery laminate 10. For example, a second press may be applied to the all-solid-state battery laminate 10 while measuring the resistance of the intermediate layer 21, and if the measured resistance value falls outside the control value, i.e., if an abnormality is detected, the pressure may be released. The resistance may be measured using, for example, a resistance measuring device 23 shown in FIG. 8 . This makes it possible to confirm that the insulating function of the intermediate layer 21 is turned off, and the function as a battery can be ensured. (3) In step ST5 (pressure application step) of FIG. 2, the impedance of the intermediate layer 21 is measured at a frequency of 10 Hz to 10 Hz while applying pressure to the all-solid-state battery stack 10. ５Hz or less. For example, the second press may be performed on the all-solid-state battery stack 10 while measuring the impedance of the intermediate layer 21 in the above frequency range, and if the measured impedance value falls outside the control value, i.e., if an abnormality is detected, the pressure may be released. This makes it possible to confirm that the insulating function of the intermediate layer 21 is turned off, thereby ensuring the battery's functionality. (4) In step ST5 (pressurizing step) of FIG. 2 , pressure may be applied to the all-solid-state battery stack 10 while heating it. This can promote the diffusion of Li and shorten the time required for lithiation of the intermediate layer 21.

[0051] <Other Embodiments> As described above, the present invention has been described using embodiments, examples, 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 this embodiment, step ST2 (internal resistance inspection process) in the flowchart shown in FIG. 2 may be omitted. As such, the present technology naturally includes various embodiments not described herein. Various omissions, substitutions, and / or modifications of components may be made without departing from the spirit of the above-described embodiments. Furthermore, the effects described in this specification are merely exemplary and are not limiting, and other effects may also be present.

[0052] DESCRIPTION OF SYMBOLS 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, 36... solid electrolyte layer, 9... battery cell, 10'... laminate, 10... all-solid-state battery laminate, 11... negative electrode tab lead, 12... positive electrode tab lead, 21, 35... intermediate layer, 21A, 35A... (lithiated) intermediate layer, 21H... second intermediate layer, 21L... first intermediate layer, 23... resistance measuring device, 25... insulating sheet, 26... pressing part, 30... cell, 31, 33... SUS plate, 32, 34... Li metal layer, P1... first pressing pressure, P2... second pressing pressure

Claims

1. A method for manufacturing an all-solid-state battery, comprising: a step of performing a first press in at least one direction on a stack in which a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly arranged in the same direction, to form an all-solid-state battery stack in which a plurality of battery cells are pressed together without reaching a dischargeable state; and a step of performing a second press on the all-solid-state battery stack in at least the same direction to bring the battery cells into a dischargeable state, wherein in the first press step, an intermediate layer in which lithium diffusion speed is slower than that of the solid electrolyte layer is interposed between the negative electrode and the solid electrolyte layer.

2. The method for producing an all-solid-state battery according to claim 1, wherein the second pressing causes lithium to diffuse from the negative electrode into the intermediate layer, thereby lithiating the intermediate layer.

3. The method for producing an all-solid-state battery according to claim 1 or 2, wherein the intermediate layer comprises: a first intermediate layer; and a second intermediate layer located between the first intermediate layer and the solid electrolyte layer, the second intermediate layer having a faster lithium diffusion rate than the first intermediate layer.

4. The method for producing an all-solid-state battery according to claim 3, wherein the first intermediate layer and the second intermediate layer each contain carbon and a metal species that alloys with lithium, and the first intermediate layer has a lower content of the metal species than the second intermediate layer.

5. The method for producing an all-solid-state battery according to claim 3, wherein the first intermediate layer contains carbon and does not contain a metal species that alloys with lithium, and the second intermediate layer contains carbon and the metal species.

6. The method for manufacturing an all-solid-state battery according to claim 1 or 2, further comprising a step of inspecting the internal resistance of the battery cell between the step of performing the first press and the step of performing the second press.

7. The method for manufacturing an all-solid-state battery according to claim 6, wherein the step of inspecting the battery cell for an internal short circuit comprises measuring the resistance of the intermediate layer.

8. The method for manufacturing an all-solid-state battery according to claim 1 or 2, wherein in the step of applying the first press, the first press is applied to the laminate while measuring the resistance of the intermediate layer, and the pressure is released if the measured value is outside a predetermined range.

9. The method for producing an all-solid-state battery according to claim 1 or 2, further comprising a step of discharging the battery cell after the second pressing.

10. The method for manufacturing an all-solid-state battery according to claim 6, wherein in the step of performing the second pressing, the resistance of the intermediate layer is measured while pressure is being applied to the all-solid-state battery laminate.

11. In the second pressing step, the impedance of the intermediate layer is measured at a frequency of 10 Hz to 10 Hz while pressure is being applied to the all-solid-state battery stack. ５ The method for producing an all-solid-state battery according to claim 1 or 2, wherein the method is carried out at a frequency in the range of 100 Hz or less.

12. The method for manufacturing an all-solid-state battery according to claim 1 or 2, wherein in the step of performing the second pressing, pressure is applied to the all-solid-state battery laminate while heating it.

13. The method for manufacturing an all-solid-state battery according to claim 6, further comprising, between the step of inspecting for an internal short circuit and the step of performing the second pressing, a step of connecting a negative electrode current collector included in the negative electrode to a negative electrode tab lead and connecting a positive electrode current collector included in the positive electrode to a positive electrode tab lead, and a step of sealing the all-solid-state battery stack with an insulating sheet except for the negative electrode tab lead and the positive electrode tab lead, wherein in the step of performing the second pressing, the second pressing is performed on the all-solid-state battery stack sealed with the insulating sheet.

14. The method for manufacturing an all-solid-state battery according to claim 1 or 2, wherein, when the pressure of the first press is defined as a first press pressure, the time during which the first press pressure is applied is defined as a first press time, the pressure of the second press is defined as a second press pressure, and the time during which the second press pressure is applied is defined as a second press time, the product of the second press pressure and the second press time is greater than the product of the first press pressure and the first press time.

15. A laminate for producing an all-solid-state battery, in which a negative electrode containing lithium metal or a lithium alloy, a solid electrolyte layer, and a positive electrode are repeatedly arranged in one direction, an intermediate layer having a slower lithium diffusion rate than the solid electrolyte layer is interposed between the negative electrode and the solid electrolyte layer, and when pressure is applied between the negative electrode and the positive electrode under preset conditions, lithium diffuses from the negative electrode to the intermediate layer, and the intermediate layer is lithiated.

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