JP7822187B2 - Battery cell - Google Patents

Description

The present invention relates to a battery cell.

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 relative to the layer thickness direction, and this inclined outer surface is covered with a solid electrolyte layer.

JP 2013-182842 A

In all-solid-state secondary batteries such as those 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 way, stress concentrates at the corners of the solid electrolyte layer that face the edges of the positive electrode layer, potentially causing cracks to form in the solid electrolyte layer. Such cracks could impair the reliability of the secondary battery.

The present invention was developed in consideration of these technical challenges, and aims to suppress stress concentration in the solid electrolyte layer during charge and discharge, thereby preventing the occurrence of cracks.

In one embodiment of the present invention, a battery cell is formed by stacking a positive electrode current collector, a solid electrolyte layer, and a negative electrode current collector. The battery cell also includes: a positive electrode layer disposed between the positive electrode current collector and the flat solid electrolyte layer, the positive electrode layer having an inclined surface that slopes outward toward the positive electrode current collector at the outer edge of the flat surface facing the solid electrolyte layer; and an ion conductor layer disposed between the positive electrode current collector and the solid electrolyte layer so as to surround the outer periphery of the positive electrode layer and be in contact with the inclined surface, the ion conductor layer having a Young's modulus lower than that of the solid electrolyte layer.

This aspect reduces stress concentration in the solid electrolyte layer during charge and discharge, preventing cracks from occurring.

FIG. 1 is a cross-sectional view of a battery cell according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a battery cell according to an embodiment of the present invention when expanded. FIG. 3 is a cross-sectional view of a battery cell according to a comparative example. FIG. 4 is a cross-sectional view of a battery cell according to a comparative example when it is expanded. FIG. 5 is a cross-sectional view of the structure of a battery cell according to a modified example. FIG. 6 is a cross-sectional view of the structure of a battery cell according to a modified example.

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.

An all-solid-state battery is a secondary battery that can be charged and discharged multiple times. An all-solid-state battery is composed of multiple stacked battery cells 1 (not shown).

The battery cell 1 is formed, for example, into a substantially rectangular shape in plan view. As shown in Figures 1 and 2, the battery cell 1 is composed of a positive electrode current collector 2, a positive electrode layer 3, a solid electrolyte layer 4, and a negative electrode current collector 5 stacked together.

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.

The positive electrode layer 3 is provided between the positive electrode collector 2 and the solid electrolyte layer 4, contacting both main surfaces of the positive electrode collector 2 (only one surface is shown in Figures 1 and 2). The positive electrode layer 3 contains, as a positive electrode active material, a substance that utilizes an oxidation-reduction reaction to release lithium ions during charging and absorb lithium ions during discharging. Examples of materials for the positive electrode active material include lithium-transition metal composite oxides such as LiMn2O4, LiCoO2, LiNiO2, and Li(Ni-Mn-Co)O2, as well as those in which part of the transition metal is replaced with another element, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds.

As shown in Figures 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 circumference of the positive electrode layer 3. The inclined surface 3b is formed so that the angle θ (see Figure 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° to 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 form between the positive electrode layer 3 and the ion conductor layer 6 (described later) during battery cell 1 manufacturing. For this reason, the angle θ (see Figure 1) is set to be in the range of 10° to 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.

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 that can be used include LPS-based materials (e.g., argyrodite (Li ₆ PS ₅ Cl)) and LGPS-based materials (e.g., Li ₁₀ GeP ₂ S ₁₂ ).

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, surrounding the outer periphery of the positive electrode layer 3 and contacting 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 (as shown in Figure 1). This allows the solid electrolyte layer 4 to be formed in a flat plate shape.

The ion conductor layer 6 is formed from 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.

The ion conductor layer 6 is also formed so that its Young's modulus is smaller than that of the solid electrolyte layer 4. The ion conductivity of the ion conductor layer 6 is preferably formed so that it is 1/30 or less of the ion conductivity of the solid electrolyte layer 4.

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

As shown in Figures 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 ion conductor layer 6 in the battery cell 1 of this embodiment are provided.

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. The amount of change in the thickness direction associated with the expansion and contraction of the flat portion 3A and the inclined portion 3B of the positive electrode layer 3 varies depending on their 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 due to 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.

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, so that 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").

When the solid electrolyte layer 14 deforms due to the expansion and contraction of the positive electrode layer 3, stress concentrates at the corners 14a, which can cause cracks to form 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. As the charge and discharge cycles are repeated, the cracks expand, and the dendrites grow, potentially causing a short circuit between the positive electrode layer 3 and the negative electrode current collector 5.

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 an ion conductor layer 6 instead of being covered with the solid electrolyte layer 4. With this configuration, the solid electrolyte layer 4 is formed into a flat plate, as shown in FIG. 1; in other words, corners at which stress is likely to concentrate in the solid electrolyte layer 4 are 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, thereby suppressing the occurrence of cracks in the solid electrolyte layer 4. As a result, the reliability of the battery cell 1 can be improved.

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, it is possible to absorb the stress acting on the solid electrolyte layer 4 from the inclined portion 3B when the positive electrode layer 3 expands and contracts.

Furthermore, in the battery cell 1 of this embodiment, as described above, the ionic conductivity of the ion conductor layer 6 is lower 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, resulting in a smaller amount of lithium ions being absorbed and released. Therefore, by making the ionic conductivity of the ion conductor layer 6 lower than that of the solid electrolyte layer 4, the movement 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 becomes thinner, the amount of lithium ion movement decreases as the thickness of the positive electrode layer 3 becomes thinner. This makes it possible to uniformize the amount of lithium ions exchanged in the inclined portion 3B of the positive electrode layer 3. As a result, deterioration of the positive electrode layer 3 due to charging and discharging can be suppressed.

Now, with reference to Figures 5 and 6, we will explain modified examples of the battery cell 1 of this embodiment. First, we will explain the modified example shown in Figure 5.

In the modified example shown in Figure 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, for example, of 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.

In this modified example, a frame 7 made of a material with low ionic conductivity is provided in the area where the positive electrode layer 3 is not present, preventing lithium ions from moving in areas unrelated to the flow of electricity. This helps prevent a decrease in battery performance.

Next, we will explain the modified example shown in Figure 6.

In the modified example shown in Figure 6, the frame 7 is configured to further cover the outer periphery of the solid electrolyte layer 4. As shown in Figure 6, in this modified example, the frame 7 is configured to contact the positive electrode current collector 2 and the negative electrode current collector 5.

In this modified example, the volume of the solid electrolyte layer 4 located outside the positive electrode layer 3 can be reduced compared to the battery cell 1 shown in Figures 1 and 5. This allows for a reduction in the cost of the battery cell 1 by the amount of the reduced volume of the solid electrolyte layer 4.

In the above embodiment and modified example, the battery cell 1 does not include a negative electrode layer. However, 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.

A battery cell equipped with such a negative electrode layer can achieve the same effects as battery cell 1.

The configuration, operation, and effects of the embodiment of the present invention configured as described above will now be explained.

The battery cell 1 is constructed 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 disposed 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 lower Young's modulus than the solid electrolyte layer 4.

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.

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 the ionic conductivity of the solid electrolyte layer 4.

In this configuration, the ionic 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, 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, with this configuration, the amount of lithium ion exchange in the inclined portion 3B of the positive electrode layer 3 can be made uniform. This prevents the positive electrode layer 3 from deteriorating due to charging and discharging.

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

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

This configuration prevents lithium ions from migrating in areas where the positive electrode layer 3 is not present.

In the battery cell 1, the frame 7 further covers the outer periphery of the solid electrolyte layer 4.

In this configuration, the volume of the solid electrolyte layer 4 can be reduced by the amount of the frame 7 provided. This reduces the cost associated with the battery cell 1.

The above describes embodiments of the present invention, but these embodiments merely illustrate some of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. Furthermore, the above embodiments can be combined as appropriate.

DESCRIPTION OF SYMBOLS 1... Battery cell, 2... Positive electrode current collector, 3... Positive electrode layer, 3a... Plane, 3A... Flat part, 3b... Inclined surface, 3B... Inclined part, 4... Solid electrolyte layer, 6... Ion conductor layer, 7... Frame.

Claims (6)

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