All-solid-state batteries

Abstract

To provide an all-solid battery that can be prevented from shorting due to current concentration.SOLUTION: The all-solid battery is provided, comprising: a power-generating element in which a positive electrode and a negative electrode are laminated via a solid electrolyte layer; and a pressurizing mechanism that applies a constraining pressure to the power-generating element from the lamination direction. The negative electrode has a negative electrode current collecting foil. On a surface opposite to a surface in contact with the solid electrolyte layer, of the negative electrode current collecting foil, skeleton layers having skeletons with holes at least on the surface opposite to the negative electrode current collecting foil are laminated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery. [Background technology]

[0002] Patent Document 1 discloses an all-solid-state battery in which a negative electrode current collector having an elastic portion is used to improve the ability of the negative electrode current collector to follow variations in the thickness of the negative electrode layer, with the aim of ensuring high Coulomb efficiency even when the thickness of the negative electrode active material layer varies due to charge and discharge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-13752 Summary of the Invention [Problem to be solved by the invention]

[0004] In typical all-solid-state batteries, a confining jig is used to apply a confining pressure to the power generating element in the thickness direction to ensure good solid-state contact. However, in lithium deposition-type all-solid-state batteries, for example, the amount of lithium metal deposition increases in more reactive areas, resulting in an increase in thickness, resulting in an in-plane non-uniformity in the thickness of the anode layer. When the thickness of the anode layer becomes in-plane, even with the application of confining pressure, variations in the surface pressure at the solid-state contact areas result, leading to a decrease in battery utilization. Furthermore, the surface pressure increases in thicker areas, resulting in current concentration, further promoting lithium metal deposition, which may cause the deposited lithium metal to penetrate the solid electrolyte layer and cause a short circuit.

[0005] In this regard, even if a negative electrode current collector having an elastic portion is used as in the above-mentioned document, the surface pressure at the portion where the amount of lithium metal deposition is large remains high. In other words, the all-solid-state battery described in the above-mentioned document cannot prevent short circuits due to current concentration caused by the above-mentioned imbalance in surface pressure.

[0006] Therefore, an object of the present invention is to provide an all-solid-state battery that can prevent short circuits caused by current concentration. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided an all-solid-state battery including a power generating element in which a positive electrode and a negative electrode are stacked with a solid electrolyte layer interposed therebetween, and a pressure mechanism for applying a confining pressure to the power generating element in the stacking direction. The negative electrode has a negative electrode current collector foil, and a hole is provided on at least the surface of the negative electrode current collector foil opposite to the surface in contact with the solid electrolyte layer, the surface facing the negative electrode current collector foil. Made of metal A skeleton layer having a skeleton is laminated. [Effects of the Invention]

[0008] According to the above aspect, it is possible to provide an all-solid-state battery that can prevent a short circuit due to current concentration. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a power generating element of an all-solid-state battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another example of a power generating element of an all-solid-state battery according to an embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram of an all-solid-state battery 100 according to an embodiment of the present invention. [Figure 4] 4A to 4C are schematic cross-sectional views of a power generating element in each state of a conventionally known lithium deposition type all-solid-state battery. [Figure 5] FIG. 5 is a schematic cross-sectional view of the power generating element shown in FIG. 1 in a charged state. [Figure 6] FIG. 6 is an enlarged view of area A in FIG. [Figure 7] FIG. 7 is a diagram showing the steps of producing the power generating element. [Figure 8] FIG. 8 is a schematic cross-sectional view of a power generating element according to a modified example of the first embodiment. [Figure 9]FIG. 9 is a schematic cross-sectional view of a power generating element according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing an example of a process for producing a skeleton layer according to the second embodiment. [Figure 11] FIG. 11 is a diagram showing another example of the process of producing a skeleton layer according to the second embodiment. [Figure 12] FIG. 12 is a schematic cross-sectional view of a power generating element according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] [First embodiment] Fig. 1 is a schematic cross-sectional view showing an example of a power generating element 1 of an all-solid-state battery 100 according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing another example of a power generating element 1 of an all-solid-state battery 100 according to an embodiment of the present invention.

[0012] The all-solid-state battery 100 of this embodiment is a lithium deposition type, and Fig. 1 shows the battery in a fully discharged state.

[0013] The power generating element 1 has a configuration in which a positive electrode 2 and a negative electrode 3 are stacked with a solid electrolyte layer 4 interposed therebetween. The positive electrode 2 has at least a positive electrode foil 2A as a positive electrode current collector and a positive electrode active material layer 2B. The negative electrode 3 has at least a negative electrode foil 3A as a negative electrode current collector, and upon charging, lithium metal is deposited between the negative electrode foil 3A and the solid electrolyte layer 4, forming a lithium metal layer 3B described below.

[0014] In addition, a skeleton layer 5 having a skeleton 5A is laminated on the surface of the power generating element 1 opposite to the surface of the negative electrode foil 3A that is in contact with the solid electrolyte layer 4.

[0015] The skeleton layer 5 shown in FIG. 1 is composed of a frame-shaped skeleton 5A that follows the outer periphery of the negative electrode foil 3A, and one void 5B surrounded by the skeleton 5A.

[0016] 2 is composed of a plate-like skeleton 5A having a plurality of through-holes 5C. The through-holes 5C preferably have an opening diameter of at least 40 to 150 μm on the solid electrolyte layer 4 side, and are arranged at equal intervals along the surface of the skeleton 5A. The ratio of the total area of ​​the openings of the through-holes 5C to the area of ​​the skeleton 5A (hereinafter also referred to as the opening ratio) is preferably within the range of 5 to 50%.

[0017] The material used for the positive electrode foil 2A is not particularly limited as long as it is a known material that can be used as a positive electrode current collector for this type of battery, such as aluminum.

[0018] As the positive electrode active material, known compounds that have been conventionally used in this type of battery, such as NMC-based positive electrode active materials, can be used.

[0019] In addition to the above, the positive electrode active material layer 2B may also contain a sulfide solid electrolyte, an auxiliary agent, and a binder. In this case, the ratios (wt%) of the positive electrode active material, solid electrolyte, auxiliary agent, and binder are 83 wt%, 11 wt%, 3 wt%, and 3 wt%, respectively. Examples of sulfide solid electrolytes that can be used include Li2S-P2S5-based electrolytes, Li2S, and lithium halides (e.g., Li2S-P2S5-based LiCl, LiBr, and LiI). Examples of auxiliary agents that can be used include carbon black, such as acetylene black, and other carbon materials (graphite, carbon nanotubes, etc.). Examples of binders that can be used include fluorine-based binders, such as polyvinylidene fluoride (PVDF), and styrene-butadiene rubber (SBR).

[0020] The solid electrolyte layer 4 is made of a sulfide solid electrolyte and a binder. The sulfide solid electrolyte and the binder are the same as those of the solid electrolyte of the positive electrode 2 described above.

[0021] Copper foil is used for the negative electrode foil 3A.

[0022] A perforated current collecting foil is used for the skeleton 5A. In this embodiment, a perforated current collecting foil with fine holes formed by laser processing is used, but for example, a commercially available punched sheet or the like may also be used as the perforated current collecting foil.

[0023] FIG. 3 is a schematic diagram of an all-solid-state battery 100 according to an embodiment of the present invention. The all-solid-state battery 100 includes a stack 6 in which multiple power-generating elements 1 are stacked, and a pressure mechanism 20 that applies a confining pressure to the stack 6 in the stacking direction. The pressure mechanism 20 includes an upper end plate 10 that contacts the power-generating element 1 at the upper end of the stack 6, a lower end plate 11 that contacts the power-generating element 1 at the lower end of the stack 6, multiple shafts 12 that connect the upper end plate 10 and the lower end plate 11, and an adjustment mechanism 13 that adjusts the amount of pressure. The adjustment mechanism 13 includes, for example, a thread groove on the shaft 12 and a nut that engages with the thread groove, and adjusts the confining pressure by the tightening of the nut. The confining pressure can be set arbitrarily depending on the power-generating element 1 used, and is set to a magnitude that maintains good contact between the layers of the power-generating element 1.

[0024] Next, the reason for providing the skeleton layer 5 and the effect of providing the skeleton layer 5 will be described with reference to FIGS.

[0025] FIG. 4 is a schematic cross-sectional view of a power generating element 1 of a conventionally known lithium deposition type all-solid-state battery (hereinafter also referred to as a conventional all-solid-state battery), where (A) shows a fully discharged state, (B) shows an ideal charged state, and (C) shows an actual charged state. The same components as in FIG. 1 are assigned the same numbers as in FIG. 1. FIG. 5 is a schematic cross-sectional view of the power generating element 1 shown in FIG. 1 in a charged state. FIG. 6 is an enlarged view of region A in FIG. 5.

[0026] In a conventional all-solid-state battery, when fully discharged, the solid electrolyte layer 4 and the anode foil 3A are in contact, as shown in (A). On the other hand, upon charging, lithium metal deposits on the surface of the anode foil 3A facing the solid electrolyte layer 4, forming a lithium metal layer 3B, as shown in (B). However, (B) shows an ideal deposition state; in reality, lithium metal deposits unevenly, as shown in (C). This is because lithium metal deposits uniformly at the beginning of charging, but eventually the amount of deposition increases in the more reactive areas, causing variations in the height of the lithium metal layer. Lower areas are no longer able to contact the solid electrolyte layer 4, further increasing the variations. Such uneven deposition of lithium metal reduces the contact area between the solid electrolyte layer 4 and the lithium metal layer 3B, thereby reducing battery utilization. Furthermore, current concentration occurs at the contact points, causing concentrated lithium deposition in those areas, potentially resulting in a short circuit, in which the deposited lithium penetrates the solid electrolyte layer and reaches the cathode 2.

[0027] In contrast, in the power generating element 1 according to this embodiment, as shown in FIG. 5, the height of the deposited lithium metal is almost uniform. This is for the following reasons. First, the anode foil 3A is more susceptible to deformation due to the heat of reaction during charging, and the greater the amount of deposited lithium metal, the greater the amount of lithium metal sinks into the pores 5B, absorbing the variation in the height of the lithium metal. This ensures that the confining pressure is applied evenly, and a uniform reaction occurs throughout the electrode portion (the contact surface between the solid electrolyte layer 4 and the anode foil 3A). Furthermore, the uniform reaction suppresses current concentration, making the aforementioned short circuit less likely to occur.

[0028] The above-described short-circuit prevention effect is obtained not only during charging, when the thickness of the lithium metal layer 3B increases, but also during discharging, when the thickness decreases. This is because the elastic force of the negative electrode foil 3A as it tries to return to its original state from a sunken state and the repulsive force of the framework 5A, which is pressed by the negative electrode foil 3A while its outer periphery is pressed down by the binding pressure, can follow the change in the thickness of the lithium metal layer 3B.

[0029] As described above, in this embodiment, based on the idea of ​​utilizing the deformation of the negative electrode foil 3A to absorb variations in the amount of lithium metal deposition, the framework layer 5 is provided to provide space to accommodate the deformation of the negative electrode foil 3A. Considering the strength of the foil materials used for the positive electrode foil 2A and the negative electrode foil 3A and the strength of lithium metal, it is difficult to imagine that the negative electrode foil 3A would deform due to lithium metal deposition. However, while observing the behavior of the negative electrode 3 during charging and operation at high temperatures, the applicant confirmed that the deposited lithium metal pushed the foil material into the small gap in the jig. In other words, the idea of ​​utilizing the deformation of the negative electrode foil 3A to absorb variations in the amount of lithium metal deposition is based on a new finding discovered by the applicant.

[0030] Next, test results regarding the difference in discharge capacity between the all-solid-state battery 100 according to this embodiment and a conventional all-solid-state battery will be described.

[0031] The all-solid-state battery 100 used in this embodiment has a skeleton 5A with each opening having a diameter of 43 μm and an opening ratio of 14%. The conventional all-solid-state battery is the same as the all-solid-state battery 100 of this embodiment except that it does not have a skeleton layer 5.

[0032] The test method is as follows. (1) The power generating element 1 is placed in the center of a jig that serves as the lower end plate 11 so that the electrode portion of 20 mm×20 mm is positioned therein. (2) A jig that serves as the upper end plate 10 is placed on top of it, and the confining pressure is adjusted to 3 MPa by fastening the upper and lower jigs with bolts. (3) The test battery prepared as described above is left standing in a thermostatic chamber at 60°C for 5 hours to raise the battery temperature to 60°C. (4)Current density 0.22mA / cm 2 Charging begins at a constant current (equivalent to 0.05C). (5) When the voltage reaches 4.2V, switch charging to constant voltage mode. (6) Current value is 0.04mA / cm 2 When it reaches 0.01C (equivalent), pause for 0.5 hours. (7) After the pause, the current density was 0.22 mA / cm 2 Discharge begins at a constant current (equivalent to 0.05C). (8) Discharge ends when the voltage reaches 2.5V. (9) After discharge is complete, calculate the discharge charge amount divided by the mass of the positive electrode active material [mAh / g].

[0033] In the conventional all-solid-state battery, the capacity increased despite the voltage fluctuations during charging (4) and (5) above, but no discharge capacity was obtained. This is presumably due to the occurrence of the short circuit described above.

[0034] In contrast, the all-solid-state battery 100 of this embodiment had a discharge capacity of approximately 130 mAh / g, which means that no short circuit occurred.

[0035] Next, a method for producing the power generating element 1 will be described with reference to Fig. 7. Fig. 7 is a diagram showing the steps for producing the power generating element 1.

[0036] In an actual all-solid-state battery 100, the power generating element 1 shown in FIGS. 1 and 2 is used as a single unit, and a plurality of these are stacked to form a laminate. The orientation of the power generating elements 1 in the laminate may all be the orientation shown in FIGS. 1 and 2, but is not limited to this. In this embodiment, the power generating element 1 is fabricated by the process shown in FIG. 7. The fabrication process will be specifically described below.

[0037] In step (A), a positive electrode active material layer 2B is formed on both sides of a positive electrode foil 2A by a method such as coating.

[0038] In the configuration (B), the solid electrolyte layer 4 is formed on the outer surface of each positive electrode active material layer 2B by a method such as coating or transfer.

[0039] In step (C), a negative electrode foil 3A is placed on the outer surface of each solid electrolyte layer 4.

[0040] In step (D), a framework layer 5 is placed on the outer surface of each negative electrode foil 3A.

[0041] In step (E), the product obtained in step (D) is packaged in a laminate and vacuum sealed, completing the power generating element 1.

[0042] That is, in this embodiment, two power generating elements 1 facing each other and sharing one positive electrode foil 2A constitute one unit of the laminate 6. This allows the power generating elements 1 to be produced efficiently. Furthermore, by sharing one positive electrode foil 2A between two power generating elements 1, space efficiency is improved and the energy density of the all-solid-state battery 100 can be improved.

[0043] [Variations] Here, a modification of this embodiment will be described, which also falls within the scope of the present invention, just like this embodiment.

[0044] Fig. 8 is a schematic cross-sectional view of a power generating element 1 according to this modification, which is one unit constituting the laminate 6. In the above embodiment, two power generating elements 1 facing each other and sharing one positive electrode foil 2A constitute one unit, but in this modification, as shown in Fig. 8, the two power generating elements 1 are oriented so that their negative electrodes 3 face each other, and one framework layer 5 is disposed between them.

[0045] According to the above configuration, the framework layer 5, which is an additional element to the conventional all-solid-state battery, is shared by the two power-generating elements 1, so that the energy density of the all-solid-state battery 100 can be improved.

[0046] Although not shown, a skeleton layer 5 is also placed on both ends of the laminate 6. This allows the skeleton layer 5 to absorb displacement at the end plate positions that are most likely to bend when a confining pressure is applied to the laminate 6, making it possible to equalize the confining pressure.

[0047] As described above, this embodiment provides an all-solid-state battery 100 including a power generating element 1 in which a positive electrode 2 and a negative electrode 3 are stacked with a solid electrolyte layer 4 interposed therebetween, and a pressure mechanism 20 that applies a confining pressure to the power generating element 1 in the stacking direction. The negative electrode 3 has a negative electrode foil (negative electrode current collector foil) 3A, and a skeleton layer 5 including a skeleton 5A with holes formed on at least the surface facing the negative electrode foil 3A is stacked on the surface opposite to the surface of the negative electrode foil 3A that contacts the solid electrolyte layer 4. This allows the negative electrode foil 3A in areas where deposits (lithium metal) are likely to deposit to sink into the holes, thereby absorbing variations in the height of the deposits. As a result, a uniform reaction occurs, current concentration is suppressed, and short circuits are less likely to occur.

[0048] In this embodiment, the holes in the skeleton 5A are through-holes, which can absorb larger variations in the height of the precipitates.

[0049] In this embodiment, a plurality of power generating elements 1 are stacked such that the positive electrodes 2 and the negative electrodes 3 face each other, and a skeletal body layer 5 is disposed between the two opposing negative electrodes 3. This allows the skeletal body layer 5 to be shared by the two power generating elements 1, thereby improving the energy density of the all-solid-state battery 100.

[0050] In this embodiment, end plates 10, 11 are arranged at both ends of the stack 6 of the power generating element 1 in the stacking direction, and the skeleton layer 5 is arranged between the stack 6 and the end plates 10, 11. This allows the skeleton layer 5 to absorb displacement at the end plate positions that are most likely to bend when a confining pressure is applied to the stack 6, making it possible to equalize the confining pressure.

[0051] [Second embodiment] FIG. 9 is a schematic cross-sectional view of the power generating element 1 according to this embodiment.

[0052] The difference from the first embodiment is that elastic bodies 21 are disposed in the holes 5B of the skeleton layer 5.

[0053] The elastic body 21 preferably has a modulus of longitudinal elasticity in the range of 0.3 to 100 MPa. In this embodiment, a lambda gel sheet (COH-1016LVC) manufactured by Taica Corporation is used as the elastic body 21. In this case, the method for producing the skeleton layer 5 is as shown in FIG. 10. First, the sheet-like elastic body 21 is cut out to have the same area as the holes 5B. Then, the cut-out piece is fitted into the holes 5B of the skeleton 5A.

[0054] The elastic body 21 is not limited to the above. For example, in the case of a skeleton 5A in which a plurality of pores 5B are arranged, a gel-like elastic body 21 is used. In this case, the method for producing the skeleton layer 5 is as shown in FIG. 11. First, a mass of the elastic body 21 is placed at the end of the skeleton 5A, and the side where the elastic body 21 is placed is passed between a pair of rollers of a press 22. This produces a skeleton layer 5 in which the elastic body 21 is kneaded into the pores 5B.

[0055] By disposing elastic body 21 in pores 5B as described above, the ability to follow the volumetric fluctuation of lithium metal layer 3B during charge and discharge is improved, making it possible to prevent short circuits.

[0056] When a discharge capacity test similar to that of the first embodiment was carried out using a skeleton layer 5 having pores 5B with a diameter of 155 μm and an opening ratio of 12%, the result was approximately 160 mAh / g, which means that short circuits during charge and discharge could be prevented similarly to the first embodiment.

[0057] [Variations] Here, a modification of this embodiment will be described, which also falls within the scope of the present invention, just like this embodiment.

[0058] FIG. 12 is a schematic cross-sectional view of the power generating element 1 according to this modification.

[0059] In addition to the above-mentioned short circuit caused by the precipitated lithium metal penetrating the solid electrolyte layer 4, the short circuit that can be a problem in the all-solid-state battery 100 can also occur when the precipitated lithium metal wraps around the end of the solid electrolyte layer 4 and reaches the positive electrode 2.

[0060] Therefore, in this modification, the elastic body 21 is arranged at least along the outer edge of the portion of the positive electrode 2 that contacts the solid electrolyte layer 4 when viewed from the stacking direction of the power generating element. In other words, the elastic body 21 is arranged so that the left and right ends of the elastic body 21 in FIG. 12 coincide with the left and right ends of the positive electrode active material layer 2B (indicated by the dashed lines in the figure). The same applies to a cross section perpendicular to the cross section shown in FIG. 12.

[0061] 12 shows a skeleton layer 5 in which one void 5B is surrounded by a skeleton 5A, but a plurality of voids 5B may be evenly arranged. In this case, a plurality of small voids 5B are evenly arranged inside the frame-shaped void 5B along the outer edge of the above-described positive electrode active material layer 2B.

[0062] With the above-described configuration, when lithium metal precipitated near the end of the solid electrolyte layer 4 attempts to grow, the negative electrode foil 3A sinks, causing the growth to occur in the direction of the framework layer 5. This slows down the growth in the direction around the solid electrolyte layer 4, thereby suppressing the occurrence of short circuits.

[0063] As described above, in this embodiment, the holes in the skeleton 5A are filled with the elastic body 21. This improves the ability to follow the volumetric fluctuations of the lithium metal layer 3B during charge and discharge, thereby preventing short circuits.

[0064] In this embodiment, the elastic body 21 is disposed at least along the outer edge of the portion of the positive electrode 2 that contacts the solid electrolyte layer 4 when the power generating element 1 is viewed from the stacking direction. This makes it possible to prevent a short circuit from occurring, in which a precipitate travels around the solid electrolyte layer 4 and reaches the positive electrode 2.

[0065] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical concept described in the claims. For example, when multiple holes are arranged in the skeleton 5A, some holes are filled with the elastic body 21 and some are not. Furthermore, one hole may be filled with two or more components of the elastic body 21, or each component of the two or more components of the elastic body 21 may be filled in a different hole. [Explanation of symbols]

[0066] 1 power generating element, 2 positive electrode, 3 negative electrode, 4 solid electrolyte layer, 5 framework layer, 6 laminate, 20 pressure mechanism, 100 all-solid-state battery

Claims

1. a power generating element in which a positive electrode and a negative electrode are stacked with a solid electrolyte layer interposed therebetween; a pressure mechanism that applies a confining pressure to the power generating element in the stacking direction; In an all-solid-state battery comprising: the negative electrode has a negative electrode current collector foil, an all-solid-state battery, wherein a skeleton layer is laminated on a surface of the negative electrode current collector foil opposite to a surface in contact with the solid electrolyte layer, the skeleton layer having a metal skeleton with holes provided at least on a surface facing the negative electrode current collector foil.

2. The all-solid-state battery according to claim 1, The holes of the skeleton are filled with an elastic material.

3. The all-solid-state battery according to claim 2, the elastic body is disposed at least along an outer edge of a portion of the positive electrode that is in contact with the solid electrolyte layer when the power generating element is viewed from the stacking direction.

4. The all-solid-state battery according to claim 1, The hole portion of the skeleton body is a through-hole.

5. The all-solid-state battery according to claim 1, A plurality of the power generating elements are stacked in a direction such that the positive electrodes face each other and the negative electrodes face each other, The all-solid-state battery, wherein the framework layer is disposed between two of the negative electrodes facing each other.

6. The all-solid-state battery according to claim 5, end plates are disposed on both ends of the power-generating element stack in the stacking direction, the framework layer is disposed between the laminate and the end plate.

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