Secondary battery and method for preventing melting of lithium

Abstract

This secondary battery comprises: a battery element structured to have a positive electrode layer, a solid electrolyte layer, and a negative electrode layer stacked in the stated order; and an exterior body that accommodates the battery element. The negative electrode layer contains metallic lithium. A carbon dioxide generation layer containing a carbon dioxide generation substance that generates carbon dioxide when heated is provided in the exterior body.

Description

Method for preventing melting of secondary batteries and lithium

[0001] The present invention relates to a secondary battery and a method for preventing lithium leakage from a secondary battery.

[0002] Some rechargeable batteries contain metallic lithium in the negative electrode layer. In rechargeable batteries using metallic lithium, there is a possibility that the metallic lithium may melt if it overheats excessively. Therefore, some kind of countermeasure is necessary.

[0003] As a related technology, a solid-state battery described in Patent Document 1 (Japanese Patent Application Publication No. 2023-69252) can be cited. This solid-state battery is a solid-state battery in which a power generation element having a negative electrode containing metallic lithium (Li) is housed in a laminated casing, wherein the casing has a sealing portion formed by overlapping and bonding laminated sheets, the sealing portion has a Li leakage prevention member positioned in contact with at least the end face of the laminated sheet, and the Li leakage prevention member contains a metal that alloys with the metallic Li to form an alloy with a higher melting point than the metallic Li.

[0004] According to the invention described in Patent Document 1, leakage of metallic lithium to the outside of the outer casing is prevented.

[0005] On the other hand, if the metallic lithium contained in the negative electrode melts, the molten metallic lithium inside the casing may reach the positive electrode. In this case, the secondary battery will short-circuit. Short circuits can cause overheating and should be avoided.

[0006] Therefore, the object of the present invention is to provide a technology that can prevent short circuits caused by the melting of metallic lithium.

[0007] In one embodiment, the secondary battery according to the present invention comprises a battery element having a configuration in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are stacked in that order, and an outer casing that houses the battery element. The negative electrode layer contains metallic lithium. The outer casing is provided with a carbon dioxide generating layer containing a carbon dioxide generating substance that generates carbon dioxide when heated.

[0008] In one embodiment, the lithium melting prevention method according to the present invention comprises the steps of providing a secondary battery, the secondary battery comprising a battery element having a configuration in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are stacked in that order, and an outer casing housing the battery element, wherein the negative electrode layer contains metallic lithium, and generating carbon dioxide inside the outer casing when the secondary battery generates abnormal heat.

[0009] Figure 1 is a schematic cross-sectional view showing a secondary battery according to the first embodiment. Figure 2A is a diagram showing the configuration during abnormal heat generation in a secondary battery according to a reference example. Figure 2B is a diagram showing the configuration during abnormal heat generation in a secondary battery according to the first embodiment. Figure 3 is a schematic diagram showing an example of the form of a carbon dioxide generating substance. Figure 4 is a schematic cross-sectional view showing a secondary battery according to the second embodiment. Figure 5 is a schematic cross-sectional view showing a secondary battery 1 according to the third embodiment. Figure 6 is a schematic cross-sectional view showing a secondary battery 1 according to the fourth embodiment.

[0010] Embodiments of the present invention will be described below with reference to the drawings.

[0011] (1) Figure 1 of the first embodiment is a schematic cross-sectional view showing the secondary battery 1 according to this embodiment.

[0012] In general terms, the secondary battery 1 according to this embodiment comprises a battery element 2 and an outer casing 3. The battery element 2 is housed within the outer casing 3. The battery element 2 has a configuration in which a positive electrode layer 5, a solid electrolyte layer 6, and a negative electrode layer 7 are stacked in this order. The negative electrode layer 7 contains metallic lithium. Specifically, the negative electrode layer 7 is configured to deposit metallic lithium during charging. Furthermore, a carbon dioxide generating layer 4 is provided within the outer casing 3. The carbon dioxide generating layer 4 contains a carbon dioxide generating substance that generates carbon dioxide when heated.

[0013] According to the above configuration, since a carbon dioxide generating layer 4 is provided, melting of metallic lithium during abnormal heat generation is prevented. This point will be explained with reference to a reference example. Figure 2A is a diagram showing the configuration of a secondary battery 1 according to a reference example during abnormal heat generation, and is a diagram showing the configuration of the battery element 2. In this reference example, a carbon dioxide generating layer 4 is not provided. Suppose that in the reference example, some abnormality occurs and the temperature of the secondary battery 1 rises abnormally. If metallic lithium is present in the negative electrode layer 7, when the temperature of the negative electrode layer 7 reaches the melting point of metallic lithium (180°C), the metallic lithium melts. The molten metallic lithium flows. As a result, the molten metallic lithium may come into contact with the positive electrode layer 5, etc. This can cause a short circuit in the battery element 2. Short circuits can cause heat generation, so they should be avoided.

[0014] On the other hand, Figure 2B is a diagram showing the configuration of the secondary battery 1 according to this embodiment when abnormal heat generation occurs. According to this embodiment, when heat is generated, the carbon dioxide generation layer 4 generates carbon dioxide. As a result, the metallic lithium contained in the negative electrode layer 7 reacts with the generated carbon dioxide. When metallic lithium reacts with carbon dioxide, it produces lithium carbonate (Li) according to the following formula. ２ CO ３ ) changes to.

[0015] (Formula 1) 4Li+3CO ２ →2Li ２ CO ３ +C

[0016] The melting point of lithium carbonate is 723°C, which is significantly higher than the melting point of metallic lithium (180°C). Therefore, even if the temperature of secondary battery 1 reaches the melting point of metallic lithium, the metallic lithium will not melt or flow. This prevents a short circuit, unlike the reference example shown in Figure 2A.

[0017] The above is an overview of this embodiment. Next, this embodiment will be described in detail.

[0018] (Secondary Battery) First, let's explain the overall configuration of secondary battery 1. Please refer to Figure 1 again.

[0019] As previously described, the secondary battery 1 comprises a battery element 2, an outer casing 3, and a carbon dioxide generating layer 4. Furthermore, as shown in Figure 1, the secondary battery 1 is provided with current collector foils (positive electrode current collector foil 8 and negative electrode current collector foil 9) and tabs (positive electrode tab 10 and negative electrode tab 11).

[0020] Battery element 2 is the part that realizes the charging and discharging function. Battery element 2 is sandwiched in the stacking direction by the positive electrode current collector foil 8 and the negative electrode current collector foil 9. Battery element 2 is positioned between the positive electrode current collector foil 8 and the negative electrode current collector foil 9 such that the positive electrode layer 5 is connected to the positive electrode current collector foil 8 and the negative electrode layer 7 is connected to the negative electrode current collector foil 9.

[0021] In Figure 1, multiple battery elements 2 are provided. The multiple battery elements 2 are stacked in the stacking direction via each current collector foil (positive electrode current collector foil 8 or negative electrode current collector foil 9). However, the battery element 2 may be a single unit.

[0022] The positive electrode current collector foil 8 and the negative electrode current collector foil 9 each extend laterally from the connection portion with the battery element 2. Each current collector foil (positive electrode current collector foil 8 and negative electrode current collector foil 9) is connected to a tab (positive electrode tab 10 and negative electrode tab 11) at the end opposite to the connection portion with the battery element 2.

[0023] The positive electrode tab 10 and the negative electrode tab 11 are provided to electrically connect the battery element 2 to an external device. One end of each tab (positive electrode tab 10 and negative electrode tab 11) is located inside the casing 3, and the other end is located outside the casing 3.

[0024] (Battery Element) Next, the configuration of battery element 2 will be explained in detail. As previously described, battery element 2 has a positive electrode layer 5, a solid electrolyte layer 6, and a negative electrode layer 7. Battery element 2 is configured to perform charging and discharging by the conduction of lithium ions. Specifically, during charging, lithium contained in the positive electrode layer 5 moves as ions to the negative electrode layer 7 via the solid electrolyte layer 6. The moved ions then precipitate as metallic lithium in the negative electrode layer 7. On the other hand, during discharging, metallic lithium contained in the negative electrode layer 7 moves as ions to the positive electrode layer 5 and is absorbed into the positive electrode layer 5.

[0025] In the discharged state, there may be almost no metallic lithium present in the negative electrode layer 7. However, even in such a secondary battery, metallic lithium will be present in the negative electrode layer 7, at least in the charged state, so it can be said that it falls under the secondary battery according to this embodiment, that is, a secondary battery in which "the negative electrode layer contains metallic lithium".

[0026] Furthermore, the negative electrode layer 7 may have a negative electrode protective layer. The negative electrode protective layer is a layer provided for purposes such as protecting the solid electrolyte layer 6. In a secondary battery 1 having a negative electrode protective layer, metallic lithium is deposited between the negative electrode protective layer and the negative electrode current collector foil 9. Since metallic lithium is highly reactive, if the metallic lithium deposited during charging comes into contact with the solid electrolyte layer 6, the solid electrolyte layer 6 may be damaged. By providing a negative electrode protective layer, direct contact between metallic lithium and the solid electrolyte layer can be avoided, and the solid electrolyte layer 6 can be protected.

[0027] (Carbon dioxide generating layer) The carbon dioxide generating layer 4 is located inside the outer casing 3. The location of the carbon dioxide generating layer 4 is not particularly limited. For example, the carbon dioxide generating layer 4 may be supported on the inner surface of the outer casing 3 (see carbon dioxide generating layer 4-1 in Figure 1).

[0028] However, preferably, the carbon dioxide generating layer 4 is arranged to be in contact with either the positive electrode current collector foil 8, the negative electrode current collector foil 9, the positive electrode tab 10, or the negative electrode tab 11 (see carbon dioxide generating layers 4-2 and 4-3 in Figure 1). The current collector foils and tabs are usually made of metal and have high thermal conductivity. Also, abnormal heat generation in the secondary battery 1 is likely to occur in the electrode layers (positive electrode layer 5 and negative electrode layer 7). If the carbon dioxide generating layer 4 is arranged to be in contact with the current collector foil or tab, when the electrode layers abnormally heat up, the generated heat is easily transferred to the carbon dioxide generating layer 4 via the current collector foil or tab. Therefore, when abnormal heat generation occurs, the temperature of the carbon dioxide generating layer 4 rises rapidly, and carbon dioxide is rapidly generated. This makes it possible to more reliably prevent the melting of metallic lithium.

[0029] The carbon dioxide generating substance contained in the carbon dioxide generating layer 4 is a substance that does not generate carbon dioxide at normal temperature (25°C), but generates carbon dioxide when heated. Preferably, the carbon dioxide generating substance is a substance that generates carbon dioxide at a temperature lower than the melting point of metallic lithium (180°C). The temperature at which the carbon dioxide generating substance generates carbon dioxide is, for example, 50 to 180°C, preferably 100 to 160°C. Also, the carbon dioxide generating substance is preferably a substance that does not melt even during abnormal heat generation.

[0030] Particularly preferred carbon dioxide generating substances include zinc carbonate (ZnCO ３ ). Zinc carbonate decomposes at 140°C to generate carbon dioxide. That is, it generates carbon dioxide at a preferable temperature. Also, at 140°C, zinc carbonate thermally decomposes into carbon dioxide and zinc oxide according to the following reaction formula. (Formula 2) ZnCO ３ →ZnO + CO ２

[0031] The melting point of zinc oxide generated after the thermal decomposition of zinc carbonate is 1975°C, which is extremely high. Therefore, the zinc oxide generated after thermal decomposition is difficult to melt even during abnormal heat generation. From the point of generating carbon dioxide at a preferable temperature and the point that it itself has a low possibility of melting, zinc carbonate is suitable as a carbon dioxide generating substance.

[0032] The form of the carbon dioxide generating substance is not particularly limited, but is preferably particulate. FIG. 3 is a schematic diagram showing an example of the form of the carbon dioxide generating substance. FIG. 3(a) is a schematic diagram showing particulate carbon dioxide generating substance. On the other hand, FIG. 3(b) is a schematic diagram showing carbon dioxide generating substance formed into a sheet shape. As shown in FIG. 3(a), when the carbon dioxide generating substance is particulate, the surface area of the carbon dioxide generating substance is larger than when it is sheet-shaped. As a result, during abnormal heat generation, the carbon dioxide generating substance generates carbon dioxide more promptly. The melting of metallic lithium is more surely prevented, and a short circuit is more surely prevented.

[0033] Incidentally, the particulate carbon dioxide generating substance can be formed into a predetermined shape by, for example, pressing or the like. Therefore, as the carbon dioxide generation layer 4, a molded product of such a particulate carbon dioxide generating substance can be used.

[0034] (2) Second Embodiment Next, the second embodiment will be described. Note that detailed description will be omitted for the points where the same configuration as that of the first embodiment can be adopted. In the present embodiment, the arrangement location of the carbon dioxide generation layer 4 is devised.

[0035] FIG. 4 is a schematic cross-sectional view showing the secondary battery 1 according to the present embodiment. FIG. 4 shows the configuration of the battery element 2.

[0036] In the present embodiment, the carbon dioxide generation layer 4 is arranged around the negative electrode layer 7 in a direction perpendicular to the stacking direction. Further, the carbon dioxide generation layer 4 is in contact with the negative electrode current collector foil 9. The carbon dioxide generation layer 4 is supported by the negative electrode current collector foil 9.

[0037] Specifically, the outer peripheral end of the negative electrode current collector foil 9 is located outside the outer peripheral end of the negative electrode layer 7 when viewed along the stacking direction. That is, the negative electrode current collector foil 9 is wider than the negative electrode layer 7. As a result, an excess portion where the negative electrode layer 7 is not arranged is formed in the outer peripheral portion of the negative electrode current collector foil 9. The carbon dioxide generation layer 4 is arranged in this excess portion. Note that the carbon dioxide generation layer 4 preferably surrounds the entire circumference of the negative electrode layer 7, but may be provided in a portion corresponding to a part of the outer circumference of the negative electrode layer 7.

[0038] The above is the configuration of the present embodiment. According to the present embodiment, the carbon dioxide generation layer 4 is arranged near the negative electrode layer 7. Therefore, at the time of abnormal heat generation, carbon dioxide reaches the negative electrode layer 7 promptly. As a result, melting of metallic lithium can be more reliably prevented.

[0039] Furthermore, as shown in Figure 4, it is preferable that the carbon dioxide generating layer 4 and the negative electrode layer 7 are not in contact. In other words, it is preferable that a gap exists between the carbon dioxide generating layer 4 and the negative electrode layer 7. If the carbon dioxide generating layer 4 is in contact with the negative electrode layer 7, there is a possibility that the metallic lithium and the carbon dioxide generating material may react unintentionally. If the carbon dioxide generating layer 4 is separated from the negative electrode layer 7, the reaction between the metallic lithium and the carbon dioxide generating material can be prevented.

[0040] In the example shown in Figure 4, the solid electrolyte layer 6 covers the side surface of the positive electrode layer 5 at its edges. That is, the edges of the solid electrolyte layer 6 are bent to follow the side surface of the positive electrode layer 5. The carbon dioxide generation layer 4 is in contact with the side surface of the solid electrolyte layer 6. However, the shape of the solid electrolyte layer 6 does not necessarily have to be as described above. As shown in Figures 1 and 2B in the first embodiment, the solid electrolyte layer 6 is flat and does not have to cover the side surface of the positive electrode layer 5.

[0041] (3) Third Embodiment Next, a third embodiment will be described. Detailed explanations will be omitted for aspects where the same configuration as the previously described embodiments can be adopted.

[0042] Figure 5 is a schematic cross-sectional view showing a secondary battery 1 according to a third embodiment. Figure 5 shows the configuration of the battery element 2.

[0043] In this embodiment as well, the carbon dioxide generation layer 4 is positioned around the negative electrode layer 7 when viewed along the stacking direction, similar to the second embodiment. That is, when viewed along the stacking direction, the outer edge of the negative electrode current collector foil 9 is located further out than the outer edge of the negative electrode layer 7. The carbon dioxide generation layer 4 is positioned to surround the negative electrode layer 7 and is supported by the negative electrode current collector foil 9. Similar to the second embodiment, the carbon dioxide generation layer 4 is separated from the negative electrode layer 7.

[0044] In addition, in this embodiment, the outer edge of the solid electrolyte layer 6 is located outside the outer edge of the negative electrode layer 7 when viewed along the lamination direction. The carbon dioxide generation layer 4 is positioned between the negative electrode current collector foil 9 and the solid electrolyte layer 6 in the lamination direction.

[0045] With the configuration described above, since the carbon dioxide generation layer 4 is provided between the negative electrode current collector foil 9 and the solid electrolyte layer 6, the carbon dioxide generated from the carbon dioxide generation layer 4 is more easily guided to the negative electrode layer 7. In other words, the carbon dioxide released inward from the carbon dioxide generation layer 4 is more easily guided to the negative electrode layer 7 without diffusing outward. Therefore, in the event of abnormal heat generation, the melting of metallic lithium can be prevented more reliably.

[0046] (4) Fourth Embodiment Next, a fourth embodiment will be described. This embodiment can be said to be a modified version of the third embodiment. Detailed explanations will be omitted regarding the fact that the same configuration as the third embodiment can be adopted.

[0047] Figure 6 is a schematic cross-sectional view showing a secondary battery 1 according to the fourth embodiment. Figure 6 shows the configuration of the battery element 2. Figure 6(a) shows the configuration in the charged state, and Figure 6(b) shows the configuration in the discharged state.

[0048] In this embodiment, the thickness of the carbon dioxide generation layer 4 has been modified. Specifically, the thickness of the carbon dioxide generation layer 4 (a) is smaller than the thickness of the negative electrode layer 7 (b).

[0049] A secondary battery 1 using a solid electrolyte layer 6 is usually pressurized in the stacking direction to obtain good charge-discharge characteristics. In addition, a pressing process may be performed during manufacturing to stack multiple layers. In this case, if the thickness of the carbon dioxide generating layer 4 is greater than or equal to the thickness of the negative electrode layer 7, pressure may be concentrated on the carbon dioxide generating layer 4, which could destroy the secondary battery 1.

[0050] In contrast, according to this embodiment, since the thickness (a) of the carbon dioxide generation layer 4 is smaller than the thickness (b) of the negative electrode layer 7, pressure does not concentrate on the carbon dioxide generation layer 4. This prevents the secondary battery 1 from being destroyed.

[0051] In the example shown in FIG. 6, the thickness of the negative electrode layer 7 differs between the charged state and the discharged state. Specifically, the negative electrode layer 7 has a negative electrode protective layer 7-1 and a metallic lithium layer 7-2 in the charged state. The thickness of the negative electrode layer 7 in the charged state is the total thickness of the negative electrode protective layer 7-1 and the metallic lithium layer 7-2. On the other hand, during discharge, lithium moves from the negative electrode layer 7 side to the positive electrode layer 5 side, so the metallic lithium layer 7-2 disappears. Therefore, the thickness of the negative electrode layer 7 in the discharged state is approximately equal to the thickness of the negative electrode protective layer 7-1. That is, the thickness of the negative electrode layer 7 differs by the thickness of the metallic lithium layer 7-2 between the charged state and the discharged state. In such a case, the thickness (a) of the carbon dioxide generation layer 4 is preferably smaller than the thickness of the negative electrode layer 7 in the discharged state (the thickness of the negative electrode protective layer 7-1 in FIG. 6). Thereby, regardless of the charge / discharge state, concentration of pressure in the carbon dioxide generation layer 4 can be prevented, and destruction of the secondary battery 1 can be prevented.

[0052] (5) Others As described above, the embodiments of the present invention have been described using the first to fourth embodiments. Subsequently, materials and the like of each part included in the secondary battery 1 described in the above-described embodiments will be described.

[0053] (Solid electrolyte layer) The solid electrolyte layer 6 is a layer containing a solid electrolyte and may be any layer that functions as an electrolyte layer in a secondary battery. The solid electrolyte layer 6 includes, for example, a resin binder and a solid electrolyte dispersed in the resin binder. The solid electrolyte preferably includes a sulfide solid electrolyte. The thickness of the solid electrolyte layer 6 is, for example, 5 to 100 μm.

[0054] (Positive electrode layer) The positive electrode layer 5 may be formed of a material that can release lithium ions during charging and occlude lithium ions during discharging. The positive electrode layer 5 is formed, for example, of a material including a resin binder and a positive electrode active material dispersed in the resin binder. The positive electrode layer 5 may also contain a solid electrolyte, a conductive auxiliary agent, and the like. As the positive electrode active material, for example, a lithium metal composite oxide or the like can be used. As the lithium metal composite oxide, for example, LiCoO ２ 、LiMnO ２ 、LiNiO２ LiVO ２ , and Li(Ni-Mn-Co)O ２ Layered rock salt compounds such as LiMn ２ O ４ , and LiNi ０．５ Mn １．５ O ４ Spinel-type compounds such as LiFePO ４ , and LiMnPO ４ Olivine-type compounds such as, or Li ２ FeSiO ４ , and Li ２ MnSiO ４ Examples include Si-containing compounds such as Li ４ Ti ５ O １２ Other materials can also be used. The thickness of the positive electrode layer is, for example, 10 to 500 μm, preferably 50 to 200 μm.

[0055] (Negative electrode layer) The negative electrode layer can be any layer containing metallic lithium, as described above. The negative electrode layer 7 includes, for example, a negative electrode protective layer 7-1.

[0056] The negative electrode protective layer 7-1 can be realized by a layer containing, for example, metal particles such as silver, carbon particles, and a binder resin.

[0057] (Positive electrode current collector foil and negative electrode current collector foil) The positive electrode current collector foil 8 and the negative electrode current collector foil 9 are not particularly limited. For example, aluminum foil can be used as the positive electrode current collector foil 8. For example, a thin film of copper, copper alloy, nickel, and nickel alloy can be used as the negative electrode current collector foil 9.

[0058] (Outer casing) The outer casing 3 is not particularly limited and can be anything that houses the battery element 2. For example, the outer casing 3 can be a film (laminate film) having a metal foil and a resin layer provided on both sides of the metal foil.

[0059] [Note] The main embodiments and their effects included in the present invention are summarized below as a note.

[0060] (Note 1) A secondary battery comprising a battery element 2 having a configuration in which a positive electrode layer 5, a solid electrolyte layer 6, and a negative electrode layer 7 are stacked in this order, and an outer casing 3 that houses the battery element 2, wherein the negative electrode layer 7 contains metallic lithium, and a carbon dioxide generating layer 4 containing a carbon dioxide generating substance that generates carbon dioxide when heated is provided inside the outer casing 3.

[0061] With this configuration, in the event of abnormal heat generation, the carbon dioxide generation layer generates carbon dioxide. As a result, metallic lithium reacts with carbon dioxide and changes into lithium carbonate, which has a high melting point. Therefore, the melting of metallic lithium is prevented, and short circuits are prevented.

[0062] (Note 2) A secondary battery as described in Note 1, wherein the carbon dioxide generating substance is zinc carbonate.

[0063] Zinc carbonate decomposes at a temperature lower than the melting point of metallic lithium, releasing carbon dioxide. Therefore, using zinc carbonate can more reliably prevent the melting of metallic lithium. Furthermore, the melting point of zinc oxide, which is produced after the thermal decomposition of zinc carbonate, is very high. Consequently, the possibility of the zinc oxide melting after thermal decomposition is low. In other words, the possibility of problems arising from the melting of carbon dioxide-producing substances is also low.

[0064] (Note 3) A secondary battery as described in Note 1 or 2, further comprising a positive electrode current collector foil 8 connected to a positive electrode layer 5, a negative electrode current collector foil 9 connected to a negative electrode layer 7, a positive electrode tab 10 connected to the positive electrode current collector foil 8, and a negative electrode tab 11 connected to the negative electrode current collector foil 9, wherein the carbon dioxide generating layer 4 is arranged to be in contact with any of the positive electrode current collector foil, negative electrode current collector foil, positive electrode tab, and negative electrode tab.

[0065] With this configuration, when abnormal heat generation occurs, heat is quickly transferred to the carbon dioxide generation layer, resulting in rapid carbon dioxide generation. Therefore, the melting of metallic lithium can be prevented more reliably.

[0066] (Note 4) A secondary battery according to any of Notes 1 to 3, further comprising a negative electrode current collector foil 9 connected to a negative electrode layer 7, wherein, when viewed along the stacking direction, the outer edge of the negative electrode current collector foil 9 is located further out than the outer edge of the negative electrode layer 7, and the carbon dioxide generating layer 4 is arranged around the negative electrode layer 7 in a direction perpendicular to the stacking direction and is supported by the negative electrode current collector foil 9.

[0067] With this configuration, the carbon dioxide generated from the carbon dioxide generation layer 4 quickly reaches the negative electrode layer 7. Therefore, in the event of abnormal heat generation, the melting of metallic lithium can be prevented more reliably.

[0068] (Note 5) A secondary battery as described in Note 4, wherein, when viewed along the stacking direction, the outer edge of the solid electrolyte layer 6 is located further out than the outer edge of the negative electrode layer 7, the carbon dioxide generating layer 4 is positioned between the negative electrode current collector foil 9 and the solid electrolyte layer 6 in the stacking direction, and the carbon dioxide generating layer 4 is positioned away from the negative electrode layer 7.

[0069] With this configuration, carbon dioxide generated from the carbon dioxide generation layer 4 is quickly guided to the negative electrode layer 7. Furthermore, because the carbon dioxide generation layer 4 is separated from the negative electrode layer 7, it is possible to prevent the carbon dioxide generating material from reacting with metallic lithium under normal conditions.

[0070] (Note 6) A secondary battery as described in Note 5, wherein the thickness of the carbon dioxide generating layer 4 is less than the thickness of the negative electrode layer 7.

[0071] With this configuration, since the thickness of the carbon dioxide generation layer 4 is smaller than the thickness of the negative electrode layer 7, pressure concentration on the carbon dioxide generation layer is prevented. This prevents damage to the secondary battery 1 due to pressure concentration.

[0072] (Note 7) A secondary battery as described in any of Notes 1 to 6, wherein the carbon dioxide generating substance is in particulate form.

[0073] Particulate carbon dioxide-generating materials have a large surface area. Therefore, they rapidly generate carbon dioxide when abnormal heat is generated. This makes it possible to more reliably prevent the melting of metallic lithium.

[0074] (Note 8) A method for preventing lithium melting, comprising the steps of providing a secondary battery, wherein the secondary battery 1 comprises a battery element 2 having a configuration in which a positive electrode layer 5, a solid electrolyte layer 6, and a negative electrode layer 7 are stacked in that order, and an outer casing 3 housing the battery element 2, the negative electrode layer 7 containing metallic lithium, and generating carbon dioxide inside the outer casing 3 when the secondary battery 1 generates abnormal heat.

[0075] According to this method, when abnormal heat generation occurs, carbon dioxide reacts with metallic lithium, transforming it into lithium carbonate, which has a high melting point. Therefore, the melting of metallic lithium can be prevented, and a short circuit in the secondary battery can be prevented.

Claims

1. A secondary battery comprising: a battery element having a configuration in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are stacked in this order; and an outer casing housing the battery element, wherein the negative electrode layer contains metallic lithium, and the outer casing is provided with a carbon dioxide generating layer containing a carbon dioxide generating substance that generates carbon dioxide when heated.

2. A secondary battery according to claim 1, wherein the carbon dioxide generating substance is zinc carbonate.

3. A secondary battery according to claim 1 or 2, further comprising: a positive electrode current collector foil connected to the positive electrode layer; a negative electrode current collector foil connected to the negative electrode layer; a positive electrode tab connected to the positive electrode current collector foil; and a negative electrode tab connected to the negative electrode current collector foil, wherein the carbon dioxide generating layer is arranged to be in contact with any of the positive electrode current collector foil, the negative electrode current collector foil, the positive electrode tab, and the negative electrode tab.

4. A secondary battery according to claim 1 or 2, further comprising a negative electrode current collector foil connected to the negative electrode layer, wherein, when viewed along the stacking direction, the outer edge of the negative electrode current collector foil is located further outward than the outer edge of the negative electrode layer, and the carbon dioxide generating layer is arranged around the negative electrode layer in a direction perpendicular to the stacking direction and is supported by the negative electrode current collector foil.

5. A secondary battery according to claim 4, wherein, when viewed along the stacking direction, the outer edge of the solid electrolyte layer is located further out than the outer edge of the negative electrode layer, the carbon dioxide generating layer is disposed between the negative electrode current collector foil and the solid electrolyte layer in the stacking direction, and the carbon dioxide generating layer is located away from the negative electrode layer.

6. A secondary battery according to claim 5, wherein the thickness of the carbon dioxide generating layer is less than the thickness of the negative electrode layer.

7. A secondary battery according to claim 1 or 2, wherein the carbon dioxide generating substance is in particulate form.

8. A method for preventing lithium melting, comprising the steps of: providing a secondary battery, the secondary battery comprising a battery element having a configuration in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are stacked in that order, and an outer casing housing the battery element, wherein the negative electrode layer contains metallic lithium; and generating carbon dioxide inside the outer casing when the secondary battery generates abnormal heat.

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