Battery cell

Abstract

To prevent cracking by suppressing stress concentration in a solid electrolyte layer during charging and discharging.SOLUTION: A battery cell 1 is composed of a cathode current collector 2, a solid electrolyte layer 4, and an anode current collector 5, stacked on top of each other. Furthermore, the battery cell 1 includes a cathode layer 3 provided between the cathode current collector 2 and the solid electrolyte layer 4, the outer edge of the surface facing the solid electrolyte layer 4 having an inclined surface 3b that slopes toward the cathode current collector 2 as it moves outward and an ion conductor layer 6 that covers the inclined surface 3b of the cathode layer 3 and has a lower Young's modulus than the solid electrolyte layer 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery cell. [Background technology]

[0002] Patent Document 1 discloses an all-solid-state secondary battery in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer, and current collectors are disposed on the outer surfaces of these electrode layers. In the all-solid-state secondary battery described in Patent Document 1, the outer surface of the positive electrode layer is inclined with respect to the layer thickness direction, and this inclined outer surface is covered with a solid electrolyte layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-182842 Summary of the Invention [Problem to be solved by the invention]

[0004] In an all-solid-state secondary battery such as that described in Patent Document 1, the positive electrode layer expands and contracts during charging and discharging. This expansion and contraction of the positive electrode layer causes the solid electrolyte layer to deform. When the solid electrolyte layer deforms in this manner, stress is concentrated at the corners of the solid electrolyte layer that face the edges of the positive electrode layer, which can lead to cracks in the solid electrolyte layer. Such cracks can impair the reliability of the secondary battery.

[0005] The present invention has been made in view of these technical problems, and has an object to suppress stress concentration in the solid electrolyte layer during charge and discharge, thereby preventing the occurrence of cracks. [Means for solving the problem]

[0006] In one embodiment of the present invention, the battery cell is configured by stacking a positive electrode current collector, a solid electrolyte layer, and a negative electrode current collector. FlatA layer is provided between the solid electrolyte layer and faces the solid electrolyte layer. flat outer edge of face In a positive electrode layer having an inclined surface that inclines toward the positive electrode current collector as it extends outward; Surrounding the periphery, slope and a conductive layer is provided between the positive electrode current collector and the solid electrolyte layer so as to be in contact with the and an ion conductor layer having a Young's modulus lower than that of the solid electrolyte layer. [Effects of the Invention]

[0007] According to this aspect, stress concentration in the solid electrolyte layer during charge and discharge can be suppressed, and cracks can be prevented from occurring. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a battery cell according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of the battery cell according to the embodiment of the present invention when expanded. [Figure 3] FIG. 3 is a cross-sectional view of a battery cell according to a comparative example. [Figure 4] FIG. 4 is a cross-sectional view of a battery cell according to a comparative example when it is expanded. [Figure 5] FIG. 5 is a cross-sectional view of the structure of a battery cell according to a modified example. [Figure 6] FIG. 6 is a cross-sectional view of the structure of a battery cell according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] A battery cell 1 used in an all-solid-state battery according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Figures 1 and 2 are cross-sectional views of the battery cell 1.

[0010] An all-solid-state battery is a secondary battery that can be charged and discharged multiple times. The all-solid-state battery is configured by stacking multiple battery cells 1 (not shown).

[0011] The battery cell 1 is formed, for example, in a substantially rectangular shape in a plan view. As shown in Figures 1 and 2, the battery cell 1 is configured by laminating a positive electrode current collector 2, a positive electrode layer 3, a solid electrolyte layer 4, and a negative electrode current collector 5.

[0012] The positive electrode current collector 2 and the negative electrode current collector 5 are formed in the shape of a rectangular thin plate from a metal material such as aluminum, nickel, iron, stainless steel, titanium, or copper. The positive electrode current collector 2 and the negative electrode current collector 5 each have an extraction electrode (not shown) extending from one side that forms the outer edge.

[0013] The positive electrode layer 3 is provided between the positive electrode current collector 2 and the solid electrolyte layer 4 so as to contact both main surfaces of the positive electrode current collector 2 (only one surface is shown in FIGS. 1 and 2). The positive electrode layer 3 contains, as a positive electrode active material, a substance that can release lithium ions during charging and absorb lithium ions during discharging using an oxidation-reduction reaction. Examples of materials for the positive electrode active material include lithium-transition metal composite oxides such as LiMnO, LiCoO, LiNiO, and Li(Ni-Mn-Co)O, and oxides in which part of the transition metal in these oxides is substituted with other elements, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds.

[0014] As shown in FIGS. 1 and 2 , the outer edge of the flat surface 3a of the positive electrode layer 3 facing the solid electrolyte layer 4 is provided with an inclined surface 3b that slopes outward toward the positive electrode current collector 2. The inclined surface 3b is provided around the entire periphery of the positive electrode layer 3. The inclined surface 3b is formed so that the angle θ (see FIG. 1 ) between the inclined surface 3b and the main surface of the positive electrode layer 3 that contacts the positive electrode current collector 2 is in the range of 10° or more and less than 90°. If the angle θ is less than 10°, the area of ​​the inclined surface 3b becomes large, resulting in reduced battery performance. On the other hand, if the angle θ is 90°, a gap may be generated between the positive electrode layer 3 and the ion conductor layer 6 (described later) during the manufacture of the battery cell 1. For this reason, the angle θ (see FIG. 1 ) is set to be in the range of 10° or more and less than 90°. Hereinafter, the portion of the positive electrode layer 3 that constitutes the flat surface 3a is referred to as the flat portion 3A, and the portion of the positive electrode layer 3 that constitutes the inclined surface 3b is referred to as the inclined portion 3B.

[0015] The solid electrolyte layer 4 contains a solid electrolyte as a main component and is a layer interposed between the positive electrode layer 3 and the negative electrode current collector 5. Examples of the solid electrolyte material include sulfide solid electrolytes and oxide solid electrolytes, with sulfide solid electrolytes being preferred. Examples of sulfide solid electrolytes include LPS-based (e.g., argyrodite (Li6PS5Cl)), LGPS-based (e.g., Li 10 GeP2S 12 ) materials are used.

[0016] The battery cell 1 further includes an ion conductor layer 6 formed to cover the inclined surface 3b. The ion conductor layer 6 is provided between the positive electrode current collector 2 and the solid electrolyte layer 4 so as to surround the outer periphery of the positive electrode layer 3 and to be in contact with the inclined surface 3b. The ion conductor layer 6 is formed so that, during manufacturing (fully discharged), the surface facing the solid electrolyte layer 4 is flush with the flat surface 3a of the positive electrode layer 3 (the state shown in FIG. 1). This allows the solid electrolyte layer 4 to be formed in a flat plate shape.

[0017] The ion conductor layer 6 is formed of a mixture of an insulating polymer such as PVDF (polyvinylidene fluoride) or PET (polyethylene terephthalate) and the solid electrolyte used in the solid electrolyte layer 4. This allows the ion conductor layer 6 to allow the movement of lithium ions.

[0018] The ion conductor layer 6 is formed so as to have a smaller Young's modulus than the solid electrolyte layer 4. The ion conductor layer 6 is preferably formed so as to have an ionic conductivity that is 1 / 30 or less of the ionic conductivity of the solid electrolyte layer 4.

[0019] The effects of the battery cell 1 configured in this manner will be described. First, a comparative example will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a cross-sectional view of a battery cell 10 according to the comparative example (when fully discharged). Fig. 4 is a cross-sectional view of the battery cell 10 according to the comparative example when expanded.

[0020] As shown in FIGS. 3 and 4, the battery cell 10 in the comparative example differs from the battery cell 1 in that a solid electrolyte layer 14 is provided in the region where the solid electrolyte layer 4 and the ion conductor layer 6 in the battery cell 1 of the present embodiment are provided.

[0021] In the battery cell 10, the positive electrode layer 3 expands and contracts in the thickness direction (the vertical direction in the drawing) as the battery cell 10 is charged and discharged. At this time, the amount of change in the thickness direction accompanying the expansion and contraction of the flat portion 3A and the inclined portion 3B of the positive electrode layer 3 varies depending on the thickness. Specifically, as shown in FIG. 4, the thickness of the inclined portion 3B of the positive electrode layer 3 becomes thinner toward the tip, and therefore the amount of deformation decreases toward the tip. Therefore, the stress acting on the solid electrolyte layer 4 caused by the expansion and contraction of the positive electrode layer 3 decreases toward the tip of the inclined portion 3B of the positive electrode layer 3.

[0022] In addition, in the battery cell 10, the solid electrolyte layer 14 is formed so as to continuously cover the flat surface 3a and the inclined surface 3b of the positive electrode layer 3, and therefore a corner 14a exists at a position in the solid electrolyte layer 14 opposite the portion where the flat surface 3a and the inclined surface 3b of the positive electrode layer 3 intersect (hereinafter referred to as the "corner 3c").

[0023] When the solid electrolyte layer 14 is deformed due to the expansion and contraction of the positive electrode layer 3, stress is concentrated at the corners 14a, which may cause cracks to occur in the area A enclosed by the line in the solid electrolyte layer 14. If a crack occurs in the solid electrolyte layer 14, for example, lithium ion dendrites may form in the cracked area. If the crack expands with repeated charge and discharge, the dendrites may grow, potentially causing a short circuit between the positive electrode layer 3 and the negative electrode current collector 5.

[0024] Therefore, in the battery cell 1 of this embodiment, in order to suppress the occurrence of cracks in the solid electrolyte layer 4, the inclined surface 3b of the positive electrode layer 3 is covered with the ion conductor layer 6 instead of being covered with the solid electrolyte layer 4. With this configuration, the solid electrolyte layer 4 is formed in a flat plate shape, as shown in FIG. 1 , in other words, corners at which stress is likely to concentrate in the solid electrolyte layer 4 can be eliminated. As a result, even if the positive electrode layer 3 expands and contracts as the battery cell 1 is charged and discharged, as shown in FIG. 2 , stress concentration in the solid electrolyte layer 4 can be suppressed, and therefore cracks can be suppressed from occurring in the solid electrolyte layer 4. As a result, the reliability of the battery cell 1 can be improved.

[0025] Furthermore, as described above, by making the Young's modulus of the ion conductor layer 6 lower than that of the solid electrolyte layer 4, the stress acting on the solid electrolyte layer 4 from the inclined portion 3B when the positive electrode layer 3 expands and contracts can be absorbed.

[0026] Furthermore, in the battery cell 1 of this embodiment, as described above, the ionic conductivity of the ion conductor layer 6 is smaller than that of the solid electrolyte layer 4. The inclined portion 3B of the positive electrode layer 3 is thinner than the flat portion 3A, and therefore absorbs and releases fewer lithium ions. Therefore, by making the ionic conductivity of the ion conductor layer 6 smaller than that of the solid electrolyte layer 4, the migration of lithium ions in the thinner inclined portion 3B is suppressed by the ion conductor layer 6. More specifically, by making the ion conductor layer 6 thicker as the thickness of the positive electrode layer 3 decreases, the migration of lithium ions decreases as the thickness of the positive electrode layer 3 decreases. This allows the amount of lithium ions exchanged in the inclined portion 3B of the positive electrode layer 3 to be uniform. As a result, deterioration of the positive electrode layer 3 due to charge and discharge can be suppressed.

[0027] Here, modified examples of the battery cell 1 of this embodiment will be described with reference to Figures 5 and 6. First, the modified example shown in Figure 5 will be described.

[0028] 5, the battery cell 1 further includes a frame 7 that is provided on the outside of the inclined surface 3b of the positive electrode layer 3 and covers the outer periphery of the positive electrode layer 3. The frame 7 is a rectangular frame, and is made of, for example, an insulating polymer with low ionic conductivity such as PVDF (polyvinylidene fluoride) or PET (polyethylene terephthalate), or a mixture of such a polymer with insulating particles.

[0029] According to this modification, the frame 7 made of a material with low ion conductivity is provided in the region where the positive electrode layer 3 is not present, thereby preventing the lithium ions from moving in regions unrelated to the flow of electricity, thereby suppressing the deterioration of battery performance.

[0030] Next, a modified example shown in FIG. 6 will be described.

[0031] 6, the frame 7 is configured to further cover the outer periphery of the solid electrolyte layer 4. As shown in FIG. 6, in this modification, the frame 7 is configured to be in contact with the positive electrode current collector 2 and the negative electrode current collector 5.

[0032] 1, 5, etc., the volume of the solid electrolyte layer 4 located outside the positive electrode layer 3 can be reduced. This allows the cost of the battery cell 1 to be reduced by the amount of the reduced volume of the solid electrolyte layer 4.

[0033] Although the above embodiment and modified examples have been described with reference to an example in which the battery cell 1 does not include a negative electrode layer, the present invention can also be applied to a battery cell that includes a negative electrode layer. In this case, the negative electrode layer is disposed on both main surfaces of the negative electrode current collector 5. The negative electrode layer is configured to include, for example, at least lithium metal or a substance that forms an alloy with lithium as the negative electrode active material.

[0034] A battery cell including such a negative electrode layer can also achieve the same effects as the battery cell 1.

[0035] The configuration, operation, and effects of the embodiment of the present invention configured as above will be described below.

[0036] The battery cell 1 is configured by stacking a positive electrode current collector 2, a solid electrolyte layer 4, and a negative electrode current collector 5. The battery cell 1 further includes a positive electrode layer 3 provided between the positive electrode current collector 2 and the solid electrolyte layer 4, the positive electrode layer 3 having an inclined surface 3b whose outer edge facing the solid electrolyte layer 4 slopes outward toward the positive electrode current collector 2, and an ion conductor layer 6 covering the inclined surface 3b of the positive electrode layer 3 and having a Young's modulus lower than that of the solid electrolyte layer 4.

[0037] In this configuration, the inclined surface 3b of the positive electrode layer 3 is covered with the ion conductor layer 6, eliminating corners where stress is likely to concentrate in the solid electrolyte layer 4. Furthermore, because the Young's modulus of the ion conductor layer 6 is lower than that of the solid electrolyte layer 4, the stress acting on the solid electrolyte layer 4 from the inclined surface 3b when the positive electrode layer 3 expands and contracts can be absorbed. This prevents stress concentration in the solid electrolyte layer 4 even when the positive electrode layer 3 expands and contracts as the battery cell 1 is charged and discharged, thereby preventing cracks from occurring in the solid electrolyte layer 4. As a result, the reliability of the battery cell 1 can be improved.

[0038] In the battery cell 1, the ionic conductivity of the ion conductor layer 6 is lower than that of the solid electrolyte layer 4. Furthermore, in the battery cell 1, the ionic conductivity of the ion conductor layer 6 is preferably 1 / 30 or less of that of the solid electrolyte layer 4.

[0039] In this configuration, the ion conductivity of the ion conductor layer 6 is lower than that of the solid electrolyte layer 4, thereby suppressing the movement of lithium ions in the ion conductor layer 6. In the battery cell 1, the ion conductor layer 6 becomes thicker toward the tip of the inclined portion 3B, thereby reducing the amount of lithium ion movement. In other words, the thinner the positive electrode layer 3, the smaller the amount of lithium ion movement. Therefore, this configuration makes it possible to uniformize the amount of lithium ions exchanged in the inclined portion 3B of the positive electrode layer 3. This makes it possible to suppress deterioration of the positive electrode layer 3 due to charge and discharge.

[0040] In the battery cell 1, the ion conductor layer 6 is made of a resin material that contains at least the same components as the solid electrolyte layer 4.

[0041] The battery cell 1 further includes a frame 7 that is provided on the outside of the inclined surface 3b of the positive electrode layer 3 and covers the outer periphery of the positive electrode layer 3.

[0042] In this configuration, the movement of lithium ions in the region where the positive electrode layer 3 is not present can be prevented.

[0043] In the battery cell 1, the frame 7 also covers the outer periphery of the solid electrolyte layer 4.

[0044] In this configuration, the volume of the solid electrolyte layer 4 can be reduced by the amount of the frame 7 provided, thereby reducing the cost of the battery cell 1.

[0045] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and the technical scope of the present invention is not intended to be limited to the specific configurations of the above embodiments. Furthermore, the above embodiments can be combined as appropriate. [Explanation of symbols]

[0046] 1. Battery cell, 2. Positive current collector, 3. Positive electrode layer, 3a. Plane, 3A. Plane portion, 3b. Inclined surface, 3B. Inclined portion, 4. Solid electrolyte layer, 6. Inductor layer, 7. Frame

Claims

1. A battery cell in which a positive electrode current collector, a solid electrolyte layer, and a negative electrode current collector are stacked, a positive electrode layer provided between the positive electrode current collector and the flat solid electrolyte layer, the positive electrode layer having an inclined surface that inclines toward the positive electrode current collector as it extends outward at an outer edge of a plane facing the solid electrolyte layer; an ion conductor layer that surrounds the outer periphery of the positive electrode layer and is provided between the positive electrode current collector and the solid electrolyte layer so as to be in contact with the inclined surface, the ion conductor layer having a lower Young's modulus than the solid electrolyte layer.

2. 2. The battery cell according to claim 1, A battery cell in which the ion conductivity of the ion conductor layer is lower than the ion conductivity of the solid electrolyte layer.

3. 3. The battery cell according to claim 2, A battery cell, wherein the ionic conductivity of the ion conductor layer is 1 / 30 or less of the ionic conductivity of the solid electrolyte layer.

4. 4. The battery cell according to claim 1, The ion conductor layer is made of a resin material containing at least the same components as the solid electrolyte layer.

5. 5. The battery cell according to claim 1, The battery cell further includes a frame provided outside the inclined surface of the positive electrode layer and covering the outer periphery of the positive electrode layer.

6. 6. The battery cell according to claim 5, The frame further covers the outer periphery of the solid electrolyte layer.

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