SECONDARY BATTERY

Abstract

A secondary battery includes a positive electrode (14), a negative electrode (12), an electrolyte layer (15), and a shutdown layer (16). The electrolyte layer is made of an electrolyte material with lithium ion conductivity. The shutdown layer contains a lithium ion conductive solid material with lithium ion conductivity. The electrolyte layer is interposed between the negative electrode and the shutdown layer. The electrolyte material is a solid electrolyte, an electrolyte solution, a polymer, or a mixture thereof. The shutdown layer is made of only a lithium ion conductive solid material or a mixture of the lithium ion conductive solid material and at least one of a solid electrolyte, an electrolyte solution, and a polymer.The lithium-ion conductive solid-state material is at least one of a pyrochlore solid-state electrolyte, a NASICON solid-state electrolyte, or a perovskite solid-state electrolyte. The lithium-ion conductive solid-state material exhibits a greater decrease in lithium-ion conductivity upon contact with lithium metal than the electrolyte material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2022-175676 filed on November 1, 2022, the disclosure of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to a secondary battery that suppresses a short circuit between the electrodes. STATE OF THE ART

[0003] A secondary battery is a lithium-ion battery in which charging and discharging occurs through the movement of lithium ions between a positive and a negative electrode. With lithium-ion batteries, there is a risk of a short circuit occurring between the electrodes during repeated charging and discharging, as dendrites of lithium metal can grow from the negative electrode and reach the positive electrode.

[0004] Patent Document 1 discloses a shutdown layer provided between an electrolyte layer and a positive electrode of a lithium-ion battery. The shutdown layer contains a lithium-ion conductive liquid that reacts with lithium metal to generate an electronic insulator. According to the secondary battery of Patent Document 1, when the dendrite grown from the negative electrode reaches the shutdown layer, an electronic insulator is generated, and dendrite growth is suppressed. LITERATURE ON THE STATE OF THE ART PATENT LITERATURE

[0005] Patent Document 1: JP 2020-53172 A SUMMARY OF THE INVENTION

[0006] In the secondary battery of Patent Document 1, although the lithium-ion conductive liquid of the shutdown layer is held by the porous membrane, it is difficult to completely retain the liquid. Due to the expansion and contraction stresses associated with the charging and discharging of the secondary battery, the lithium-ion conductive liquid may leak and contact the negative electrode. When the lithium-ion conductive liquid comes into contact with the negative electrode, an insulator is formed near the interface between the negative electrode and the electrolyte, resulting in a decrease in battery performance due to an increase in resistance.

[0007] In view of the above, an object of the present disclosure is to provide a secondary battery that can be used stably while suppressing a short circuit between the electrodes.

[0008] A secondary battery of the present disclosure includes a positive electrode, a negative electrode, an electrolyte layer, and a shutdown layer. The positive electrode contains a positive electrode active material. The negative electrode contains a negative electrode active material. The electrolyte layer is provided adjacent to the negative electrode and is made of an electrolyte material with lithium ion conductivity. The shutdown layer is provided adjacent to the positive electrode and contains a lithium ion conductive solid material with lithium ion conductivity. The electrolyte layer is interposed between the negative electrode and the shutdown layer.

[0009] In a first aspect of the present disclosure, the electrolyte material is a solid electrolyte, an electrolyte solution, a polymer, or a mixture thereof. The shutdown layer is made of only a lithium ion conductive solid material or a mixture of the lithium ion conductive solid material and at least one of a solid electrolyte, an electrolyte solution, and a polymer. The lithium ion conductive solid material is at least one of a pyrochlore solid electrolyte, a NASICON solid electrolyte, or a perovskite solid electrolyte. The lithium ion conductive solid material exhibits a greater decrease in lithium ion conductivity upon contact with lithium metal than the electrolyte material.

[0010] In a second aspect of the present disclosure, the solid-state lithium ion conductive material forms a non-conductor for lithium ions upon contact with lithium metal.

[0011] Accordingly, it is possible to provide a stable usable secondary battery while suppressing a short circuit between the electrodes. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing a configuration of a secondary battery according to a first embodiment. Fig. Figure 2 is a diagram showing a method for manufacturing a pyrochlore solid electrolyte. Fig. Figure 3 is a diagram showing the crystal structure of a pyrochlore solid electrolyte. Fig. Figure 4 is a graph showing a change in resistance with time when lithium metal is brought into contact with a lithium ion conductive solid material. Fig. Figure 5 is a graph showing a time change in the resistance value increase rate when lithium metal is brought into contact with a lithium ion conductive solid material. Fig. 6 is a cross-sectional view showing an initial state configuration of a secondary battery according to a sixth embodiment. Fig. 7 is a cross-sectional view showing a charge state of the secondary battery according to the sixth embodiment. Fig. 8 is a cross-sectional view showing an initial state configuration of a secondary battery according to a seventh embodiment. Fig. 9 is a cross-sectional view showing a configuration of a secondary battery according to an eighth embodiment. Fig. 10 is a table showing whether or not a short circuit occurred in the secondary batteries of Examples 1 to 4 and Comparative Example. DETAILED DESCRIPTION

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to those described in a previous embodiment may be designated by the same reference numerals, and overlapping explanations may be omitted. When only a part of the configuration is described in each embodiment, the previously described other embodiments may also be applied to other parts of the configuration. A combination of parts is possible when it is expressly stated in each embodiment that the combination is possible. A partial combination of the embodiments is possible even if it is not expressly stated that the partial combination is possible, unless there is a particular problem with the partial combination. (First embodiment)

[0013] A first embodiment in which the secondary battery of the present disclosure is applied to a lithium-ion battery will be described below with reference to the drawings. The secondary battery 10 of the present embodiment is a lithium-ion battery cell in which charging and discharging are performed by lithium ions moving between a negative electrode 12 and a positive electrode 14.

[0014] As in Fig. 1, the secondary battery 10 includes a negative electrode current collector 11, a negative electrode 12, a positive electrode current collector 13, a positive electrode 14, an electrolyte layer 15, and a shutdown layer 16. These layers of the negative electrode current collector 11, the negative electrode 12, the positive electrode current collector 13, the positive electrode 14, the electrolyte layer 15, and the shutdown layer 16 are arranged one above the other.

[0015] The electrolyte layer 15 and the shutdown layer 16 are provided between the negative electrode 12 and the positive electrode 14. The electrolyte layer 15 is provided adjacent to the negative electrode 12, and the negative electrode 12 and the electrolyte layer 15 are in contact with each other. The shutdown layer 16 is provided adjacent to the positive electrode 14, and the positive electrode 14 and the shutdown layer 16 are in contact with each other. The negative electrode 12 and the positive electrode 14 are connected to each other via the electrolyte layer 15 and the shutdown layer 16.

[0016] The negative electrode 12, the positive electrode 14, the electrolyte layer 15, and the shutdown layer 16 are provided between the negative electrode current collector 11 and the positive electrode current collector 13. The negative electrode current collector 11 and the negative electrode 12 are in contact with each other, and the positive electrode current collector 13 and the positive electrode 14 are in contact with each other. The negative electrode current collector 11 and the positive electrode current collector 13 are connected to each other via a stacked body including the negative electrode 12, the positive electrode 14, the electrolyte layer 15, and the shutdown layer 16.

[0017] A specific material suitable for use as a current collector for a lithium-ion battery is used for the negative electrode current collector 11 and the positive electrode current collector 13. In the present embodiment, Cu is used as the negative electrode current collector 11, and Al is used as the positive electrode current collector 13.

[0018] The negative electrode current collector 11 and the positive electrode current collector 13 may have a predetermined shape, such as a foil shape or a plate shape. In the present embodiment, the foil-shaped current collector 11, 13 is used. The current collector 11, 13 may have a three-dimensional structure, such as a structure provided with protrusions or a mesh structure.

[0019] The negative electrode 12 contains a negative electrode active material. A specific material that can be used as a negative electrode active material for a lithium-ion battery, such as lithium metal, graphite, Si, or a mixture thereof, is used as the negative electrode active material. In the present embodiment, lithium metal is used as the negative electrode active material.

[0020] The positive electrode 14 contains a positive electrode active material. The positive electrode active material used is a specific material that can be used as a positive electrode active material for a lithium-ion battery.

[0021] A layered active material, a spinel active material, or an olivine active material can be used as the positive electrode active material. A ternary positive electrode material such as LiCoO2 (LCO), LiNiO2 (LNO), LiNi 0,8 C00,15 Al 0,05 O2 (NCA) or LiNi 0,8 Co 0,1 Mn 0,1 O2 (NCM811) can be used. As spinel-type active material, for example, LiMn2O4 or LiNi 0,5 Mn 1,5 O4 can be used. For example, LiMn 0,8 Fe 0,2 PO4 (LMFP) or LiFePO4 (LFP) can be used.

[0022] Among the positive electrode active materials described above, the olivine-type active material generally has the lowest ionic conductivity. Therefore, when the olivine-type active material is used as the positive electrode active material of the secondary battery 10, dendritic structures are likely to form on the negative electrode 12 during charging.

[0023] The positive electrode 14 may contain, in addition to the positive electrode active material, at least one of an electrolyte solution and a polymer. For example, ethylene carbonate or the like may be used as the electrolyte solution. The electrolyte solution may be an ionic liquid. For example, polyethylene oxide may be used as the polymer.

[0024] The electrolyte layer 15 is provided in direct contact with the negative electrode 12. The electrolyte layer 15 is made of an electrolyte material with lithium ion conductivity. The electrolyte layer 15 serves to conduct lithium ions between the negative electrode 12 and the positive electrode 14 and to ensure insulation between the negative electrode 12 and the positive electrode 14.

[0025] In principle, the lithium ion conductivity of the electrolyte material used for the electrolyte layer 15 does not decrease even when it comes into contact with lithium metal. However, this does not preclude the possibility that when the electrolyte material comes into contact with lithium metal, the lithium ion conductivity of the electrolyte material may be slightly altered due to factors such as the presence of surface impurities and the nature of the interface. Even when the electrolyte material comes into contact with the lithium metal and the lithium ion conductivity is at its lowest, the lithium ion conductivity before coming into contact with the lithium metal is only reduced by a factor of several, and the resistance is only increased by a factor of several or less.

[0026] A solid electrolyte, an electrolyte solution, a polymer, or a mixture thereof can be used as the electrolyte material of the electrolyte layer 15. Among these electrolyte materials, the electrolyte solution generally has the highest lithium ion conductivity, while the polymer and solid electrolyte, in that order, have lower lithium ion conductivity. Generally, the usable temperature range is highest for the solid electrolyte, and the usable temperature range becomes lower for the polymer and electrolyte, in that order.

[0027] Generally, the safety in the event of a short circuit in the secondary battery 10 is highest in the solid electrolyte, and decreases in the order of the polymer and the electrolyte solution. Since a short circuit in the secondary battery 10 occurs due to an uneven reaction caused by an uneven current density, the poorer the contact between the negative electrode active material and the electrolyte material, the more likely a short circuit is to occur. Therefore, in general, a short circuit is most likely to occur in the solid electrolyte, and less likely to occur in the polymer and the electrolyte solution, in that order.

[0028] In the present embodiment, a solid electrolyte is used as the electrolyte material for the electrolyte layer 15. For example, an oxide solid electrolyte or a sulfide solid electrolyte can be used as the solid electrolyte. In the present embodiment, LLZO (Li7La3Zr2O 12 ), which is an oxide-based solid electrolyte, is used as the solid electrolyte layer 15. The solid electrolyte layer 15 may contain, in addition to the solid electrolyte, at least one of an electrolyte solution and a polymer. For example, ethylene carbonate or the like may be used as the electrolyte solution. The electrolyte solution may be an ionic liquid. For example, polyethylene oxide may be used as the polymer.

[0029] The shutdown layer 16 and the negative electrode 12 are provided so that they are not in direct contact with each other, and the electrolyte layer 15 is interposed between the shutdown layer 16 and the negative electrode 12. The shutdown layer 16 contains a lithium ion conductive solid material that comes into contact with lithium metal to reduce lithium ion conductivity. The lithium ion conductive solid material is an ion conductor with lithium ion conductivity. The lithium ion conductive solid material of the shutdown layer 16 can be provided by applying it to the surface of the positive electrode 14 or the solid electrolyte layer 15 formed in a sheet form, or it can be provided by applying it to the surface of a particulate positive electrode active material.

[0030] The lithium ion conductive solid material exhibits a greater decrease in lithium ion conductivity when in contact with lithium metal than the electrolyte material used for the electrolyte layer 15. As described above, even when the electrolyte material of the electrolyte layer 15 comes into contact with lithium metal, the lithium ion conductivity hardly decreases. In contrast, when the lithium ion conductive solid material comes into contact with lithium metal, the lithium ion conductivity decreases to at least 1 / 100 or less, and the resistance increases to 100 times or more compared to before contact with lithium metal.

[0031] That is, when the lithium-ion conductive solid material comes into contact with the lithium metal, the ionic conductivity decreases by two or more orders of magnitude and the resistance increases by two or more orders of magnitude. As described above, when the lithium-ion conductive solid material comes into contact with the lithium metal, the lithium-ion conductivity decreases by two or more orders of magnitude and the resistance increases by two or more orders of magnitude. The current value that can be supplied becomes 1 / 100 or less, and it becomes difficult to function as a battery. Note that the electrolyte layer 15 is interposed between the shutdown layer 16 and the negative electrode 12. In the normal state, the lithium metal does not come into contact with the shutdown layer 16, and the lithium-ion conductivity of the lithium-ion conductive solid material does not decrease.

[0032] In addition to the lithium-ion conductive solid-state material, the shutdown layer 16 may contain at least one of an electrolyte solution or a polymer. For example, ethylene carbonate or the like may be used as the electrolyte solution. The electrolyte solution may be an ionic liquid. For example, polyethylene oxide may be used as the polymer.

[0033] The thickness of the shutdown layer 16 is preferably as thin as possible from the viewpoint of reducing cell resistance. In the present embodiment, the thickness of the shutdown layer 16 is 10 μm or less. If the thickness of the shutdown layer 16 is too thin, it is difficult to form the shutdown layer 16 uniformly, and there is a possibility of forming a region where the shutdown layer 16 is absent. Therefore, the thickness of the shutdown layer 16 is preferably in a range of 2 to 3 μm or more.

[0034] If the lithium metal is unevenly deposited on the negative electrode 12, dendrites are likely to grow from the negative electrode 12. When the dendrite reaches the shutdown layer 16 from the negative electrode 12 through the electrolyte layer 15, the lithium ion conductivity of the solid-state lithium ion conductive material in a portion of the shutdown layer 16 that comes into contact with the lithium metal decreases, and the resistance increases to be isolated. That is, when the solid-state lithium ion conductive material comes into contact with the lithium metal, the ionic conductivity is greatly reduced to form a lithium ion non-conductor. "Lithium ion non-conductor" means a state in which the solid-state lithium ion conductive material is in contact with the lithium metal, and the ionic conductivity is reduced to 1 / 100 or less.

[0035] In the shutdown layer 16, the lithium precipitation reaction near the contact portion with the lithium metal is interrupted, and dendrite growth is stopped. That is, the shutdown layer 16 has the shutdown function of limiting the movement of lithium ions between the negative electrode 12 and the positive electrode 14 to stop the operation of the secondary battery 10 and suppressing a short circuit between the negative electrode 12 and the positive electrode 14.

[0036] As a lithium-ion conductive solid material in which lithium-ion conductivity is reduced upon contact with lithium metal, at least one of a pyrochlore-type oxide-based solid electrolyte, a NASICON-type oxide-based solid electrolyte, or a perovskite-type oxide-based solid electrolyte can be used. For example, Li can be used as a pyrochlore-type oxide-based solid electrolyte. 1,25 La0,58 Nb2O6F can be used. As an oxide-based solid electrolyte of the NASICON type, for example, Li 1,4 Al 0,4 Ti 1,6 (PO4)3 (LATP) can be used. As an oxide-based solid-state electrolyte of the perovskite type, for example, La 0,57 Li 0,29 TiO3 (LLTO) can be used.

[0037] Fig. Figure 4 shows the change in resistance (Ω) over time when lithium metal is treated with Li 1,25 La 0,58 Nb2O6F, Li 1,4 Al 0,4 Ti 1,6 (PO4)3 and La 0,57 Li 0,29 TiO3 is brought into contact.

[0038] As in Fig. 4, the resistance value before contact with lithium metal is about 80 to 200 Ω, Li 1,25 La 0,58 Nb2O6F is the lowest, La 0,57 Li 0,29 TiO3 is the second lowest and Li 1,4 Al 0,4 Ti 1,6 (PO4)3 is the highest.

[0039] When the lithium metal is then brought into contact, the resistance values ​​of Li 1,25 La 0,58 Nb2O6F, Li 1,4 Al 0,4 Ti 1,6 (PO4)3 and La 0,57 Li 0,29 TiO3 gradually increases and becomes constant after reaching about 100,000 Ω. The resistance value after contacting the lithium metal with Li 1,25 La 0,58 Nb2O6F, Li 1,4 Al 0,4 Ti 1,6 (PO4)3 and La 0,57 Li 0,29 TiO3 increases to about 500 times or more of the resistance value before contact with the lithium metal. The resistance increase rate is fastest for Li 1,25 La 0,8 Nb2O6F, second fastest at Li 1,4 Al 0,4 Ti 1,6 (PO4)3 and slowest at La 0,57 Li 0,29 TiO3.

[0040] Fig. Figure 5 shows the time change of the resistance value increase rate when lithium metal is in contact with Li 1,25 La 0,58 Nb2O6F, Li1,4 Al 0,4 Ti 1,6 (PO4)3 and La 0,57 Li 0,29 TiO3 is brought.

[0041] As in Fig. 5, the resistance value increase rate when contacting lithium metal is greatest for Li 1,25 La 0,58 Nb2O6F, second largest for Li 1,4 Al 0,4 Ti 1,6 (PO4)3 and smallest for La 0,57 Li 0,29 TiO3.

[0042] That is, among the lithium-ion conductive solid materials described above, the pyrochlore solid electrolyte has the fastest resistance rise rate and the largest resistance rise rate when in contact with lithium metal. Therefore, when the pyrochlore solid electrolyte is used as the lithium-ion conductive solid material included in the shutdown layer 16, the shutdown time is the shortest, and safety is improved.

[0043] The pyrochlore solid electrolyte has the lowest resistance value before contact with the lithium metal (i.e., in the normal state). Therefore, among the lithium ion conductive solid materials described above, the pyrochlore solid electrolyte has the highest ion conductivity in the normal state, and the input / output characteristics of the secondary battery 10 are excellent.

[0044] The pyrochlore solid-state electrolyte is very safe and has higher ionic conductivity than other oxide-based solid-state electrolytes. Furthermore, the pyrochlore solid-state electrolyte is characterized by the fact that, when it contains a certain type of cation, it increases the resistance upon contact with lithium metal and decreases the ionic conductivity.

[0045] The lithium ion conductive solid material of the present embodiment is an oxide-based solid electrolyte having a pyrochlore structure represented by the composition formula “Aa 2-α Away (1+α) / 3 B2O 7-β X β ". In the above composition formula, O is an oxygen atom, and Aa, Ab, B, and X represent elements or groups. Aa, Ab, and B are different types of cations, and O and X are different types of anions. In the above composition formula, 0.6<α<2.0 and 0<β≤1 are satisfied. When α changes, the composition ratio of Aa and Ab changes. When β changes, the composition ratio of O and X also changes.

[0046] Aa is an alkali metal. Any of the metals Li, Na, and K can be used as the alkali metal represented by Aa. In the present embodiment, Li is used as Aa. The composition ratio (2-α) of Aa is in the range of 0<(2-α)<1.4.

[0047] Ab contains at least one lanthanide. At least one of La, Ce, Nd, and Sm can be used as the lanthanide represented by Ab. In the present embodiment, La is used as Ab. The composition ratio (1+α) / 3 of Ab is in the range of 0.53<(1+α) / 3<1.

[0048] A basic structure of Ab consists of lanthanide, and a part of the lanthanide constituting Ab can be replaced with an alkaline earth metal (such as Ca, Mg, Sr, or the like). In the shutdown layer 16 of the present embodiment, it is assumed that ionic conductivity is improved when defects are created in the crystal structure because the lanthanide is contained in the pyrochlore structure where 0.6<α<2.0 and 0<β≤1 are satisfied.

[0049] In the pyrochlore solid electrolyte of the present embodiment, the A cation in the general pyrochlore composition formula "A2B2O7" is a cation composed of lithium metal and lanthanide. This is believed to contribute to improving the ionic conductivity of the pyrochlore solid electrolyte.

[0050] B is a cationic metal, different from Aa and Ab, and is a metal selected from a Group 4 element, a Group 5 element, or a Group 15 element. B forms an octahedron surrounded by six O atoms in a crystal. As a Group 4 element, Group 5 element, or Group 15 element represented by B, at least one of Nb, V, Sb, Bi, Ta, Zr, Ti, and Hf can be used. In the pyrochlore solid electrolyte using at least one of Nb, V, Sb, Bi, Ta, Zr, Ti, and Hf as the B cation, lithium ion conductivity decreases upon contact with metallic lithium. This point will be described in detail later.

[0051] X is an anion that can be replaced by an O atom, forming the pyrochlore structure. X differs from an O atom in electronegativity and polarizability. At least one of F, S, Cl, and OH can be used as the anion represented by X. The composition ratio β of X is in the range of 0<β≤1, and at least a portion of the O atoms forming the pyrochlore structure is replaced by X. In the present embodiment, F is used as X.

[0052] The pyrochlore solid electrolyte of the present embodiment has a defect structure in which lattice defects are included in the crystal by replacing some of the O atoms constituting the pyrochlore structure with anions whose electronegativity and polarizability differ from those of the O atoms. It is believed that the pyrochlore solid electrolyte of the present embodiment has improved ionic conductivity because the pyrochlore structure includes the defect structure.

[0053] In the pyrochlore solid electrolyte of the present embodiment, Aa and Ab are partially deficient as a defect structure. The structural formula of the general pyrochlore structure is "A2B2O7", and the composition ratio of the A cation is 2. In contrast, in the pyrochlore solid electrolyte of the present embodiment, the composition ratios of Aa and Ab are "2-α" and "(1+α) / 3", respectively, and 0.6<α<2.0 are satisfied, so that the overall composition ratio of Aa and Ab is less than 2. That is, in the crystal structure of the pyrochlore solid electrolyte of the present embodiment, at least one of Aa and Ab is partially deficient. The composition ratio corresponding to the deficient portion of Aa and Ab is (2α-1) / 3.

[0054] In addition to the deviation of the composition ratio, the defect structure can also be formed by the sum of the valences of the cations consisting of Aa, Ab and B and the anions consisting of O and X in the above composition formula becoming negative.

[0055] Furthermore, the pyrochlore solid electrolyte of the present embodiment is a composite anionic compound in which multiple anions such as O and X are contained in the pyrochlore structure. The anion represented by X is contained in the BO6 coordination octahedron structure. Therefore, the alkali metal of Aa can be positioned in the central portion of the space with the BO6 coordination octahedron without being displaced toward the BO6 coordination octahedron. Thus, the pyrochlore solid electrolyte of the present embodiment is expected to exhibit high ionic conductivity when used by applying an electric field, such as in a battery.

[0056] Furthermore, since α and β in the above composition formula affect lattice defects and ionic conductivity, it is desirable to adjust α and β within an appropriate range. When the values ​​of α and β are large, the defect concentration in the crystal lattice increases, but when the values ​​exceed a certain amount, the concentration of the alkali metal represented by Aa decreases and the ionic conductivity decreases. Therefore, it is desirable to control α within a range of 0.6<α<2.0 and β within a range of 0<β≤1.

[0057] Here, a decrease in lithium ion conductivity of the pyrochlore solid electrolyte of the present embodiment is described. As described above, the pyrochlore solid electrolyte in which at least one of Nb, V, Sb, Bi, Ta, Zr, Ti, and Hf is used as the B cation has the property that the lithium ion conductivity is reduced by contact with metallic lithium.

[0058] In pyrochlore solid electrolytes using Nb as the B cation, Nb is chemically reduced when it comes into contact with lithium metal, resulting in an increase in resistance and a decrease in ionic conductivity. When the pyrochlore solid electrolyte, in which Nb is the B cation, comes into contact with lithium metal for several tens of minutes, the volume conductivity drops from 3.3×10 -3 S / cm to 6.3×10 -4 S / cm, and the grain boundary conductivity decreases from 2.0×10 -3 S / cm to 6.4×10 -5 S / cm.

[0059] In addition, it was confirmed that even in the pyrochlore solid electrolyte with Ta or Zr as B cation, when the pyrochlore solid electrolyte is brought into contact with lithium metal, Ta or Zr is chemically reduced, so that the resistance increases and the ionic conductivity decreases.

[0060] The band gap Eg of the pyrochlore solid electrolyte can be used as an index of the difficulty of chemical reduction of B cations upon contact with lithium metal, in other words, the difficulty of reducing ionic conductivity. The smaller the band gap Eg, the more likely the B cation is to be reduced, and the more likely the ionic conductivity is to decrease. It is assumed that the B cation contained in the pyrochlore solid electrolyte, whose band gap is smaller than that of the pyrochlore solid electrolyte containing at least Nb, Ta, and Zr, will be reduced when the B cation comes into contact with lithium metal. That is, it is assumed that the ionic conductivity of the pyrochlore solid electrolyte, whose band gap is smaller than that of the pyrochlore solid electrolyte containing Nb, Ta, and Zr as B cations, will be reduced upon contact with lithium metal.

[0061] The band gap Eg of the pyrochlore solid electrolyte, calculated according to the first principle calculation, is 3.293 eV for Li2Nb2O6F, 4.163 eV for Li2Ta2O6F, 3.401 eV for Li2Zr2O6F, 3.429 eV for Li2Ti2O6F, 4.082 eV for Li2Hf2O6F, 1.415 eV for Li2V2O6F, 1.469 eV for Li2Sb2O6F and 0.789 eV for Li2Bi2O6F.

[0062] Li2Nb2O6F, Li2Ta2O6F, and Li2Zr2O6F are pyrochlore solid electrolytes containing Nb, Ta, and Zr as B cations, respectively. Li2Ti2O6F, Li2Hf2O6F, Li2V2O6F, Li2Sb2O6F, and Li2Bi2O6F are pyrochlore solid electrolytes that exhibit a narrower band gap than pyrochlore solid electrolytes containing Nb, Ta, and Zr as B cations. This means that in pyrochlore solid electrolytes containing at least one of Nb, V, Sb, Bi, Ta, Zr, Ti, and Hf as B cations, lithium ion conductivity decreases when the pyrochlore solid electrolyte is in contact with metallic lithium.

[0063] Hereinafter, the pyrochlore solid electrolyte of the present embodiment will be described with reference to Fig. 2. In the method for producing the pyrochlore solid electrolyte, a first mixing process S10, a first firing process S20, a second mixing process S30, a molding process S40, and a second firing process S50 are carried out successively. (First mixing process)

[0064] First, a lanthanum source, a lithium source, and a niobium source are prepared as raw materials, and a first mixing process S10 is performed to mix these materials. A metal oxide, a metal carbonate, or the like can be used as the lanthanum source, lithium source, and niobium source. In the present embodiment, L2O3 is used as the lanthanum source, Li2CO3 as the lithium source, and Nb2O5 as the niobium source. In the first mixing process, La2O3, Li2CO3, and Nb2O5 are mixed in a specific ratio. (First firing process)

[0065] Subsequently, the first firing process S20 is carried out to fire the mixture of La2O3, Li2CO3, and Nb2O5. In the first firing process S20, two firing stages are carried out. In the first stage, a provisional firing is carried out by heating the mixture in air at 500°C for 6 hours. The provisional firing removes moisture and the like from the mixture and can increase the reactivity. Following the provisional firing, a main firing is carried out in which the mixture is heated in air at 1200°C for 4 hours. Accordingly, Li 0,5 La 0,5 Nb2O6 is obtained, which is a precursor to a target product. (Second mixing process)

[0066] Next, a fluorine source is prepared as a raw material, and the fluorine source is reacted with Li 0,5 La 0,5Nb2O6, the precursor, in the second mixing process S30. A metal fluoride can be used as the fluorine source. In the present embodiment, LiF and LaF3 are used as fluorine sources. LiF is a fluorine source and a lithium source, and LaF3 is a fluorine source and a lanthanum source. In the second mixing process S30, LiF and LaF3 are mixed with Li 0,5 La 0,5 Nb2O6 mixed in a specific ratio to obtain a mixed powder. (molding process)

[0067] The S40 forming process is then carried out, in which the mixed powder of Li 0,5 La 0,5 Nb2O6, LiF and LaF3 are pelletized and pressurized to 100 MPa. Accordingly, the mixture of Li 0,3 La 0,3 Nb2O6, LiF and LaF3 were pelletized. (Second firing process)

[0068] Subsequently, the second firing process S50 is used to fire the mixture of Li 0,5 La0,5 Nb2O6, LiF and LaF3. In the second firing process S50, the mixture of Li 0,5 La 0,5 Nb2O6, LiF and LaF3 were fired at 1000°C for 6 hours in a nitrogen atmosphere.

[0069] Through the above-mentioned processes, a crystal with a pyrochlore structure represented by the composition formula “Li 1,25 La 0,58 Nb2O6F" can be obtained. This time, the crystal obtained in the second firing process S50 is in the form of a pellet. The relative density of the solid electrolyte sintered body in the form of a pellet is 78%.

[0070] A crystal with a pyrochlore structure, represented by the composition formula “Li 2-a La (1+α) / 3 Nb2O 7-β F β “, can be obtained by changing the mixing ratio of La2O3, Li3CO3 and Nb3O3 and the mixing ratio of LiF and LaF3 during the manufacturing process.

[0071] In the composition formula, α can be adjusted by changing the mixing ratio of La2O3, Li2CO3, and Nb2O5, and β can be adjusted by changing the mixing ratio of LiF and LaF3. During firing, some of the materials will sublimate. Therefore, α and β can also be adjusted by changing the firing conditions, the furnace atmosphere, and the size of the furnace in the first and second firing processes.

[0072] The crystal structure of the pyrochlore solid electrolyte is shown below with reference to Fig. 3 described. Fig. Figure 3 shows a crystal structure obtained by analyzing a pyrochlore solid electrolyte with radiant light. In radiant light analysis, the crystal structure was obtained by performing a Rietveld analysis using X-ray diffraction (XRD) data.

[0073] As in Fig. As shown in Figure 3, the pyrochlore solid electrolyte exhibits a crystal structure in which a three-dimensional octahedral network composed of NbO6 is formed. In NbO6, O is arranged at each vertex with Nb as the center, and each vertex is shared with the neighboring NbO6. In the three-dimensional network composed of NbO6, a hexagonal tunnel structure is formed in which cations composed of La / Li and anions composed of F are arranged.

[0074] The secondary battery 10 of the present embodiment includes the shutdown layer 16 containing a solid-state lithium ion conductive material whose lithium ion conductivity is reduced upon contact with lithium metal. As a result, the lithium ion conductivity in the shutdown layer 16 decreases even when dendrites grow from the negative electrode 12. The resistance increases to be insulated, and a barrier to lithium ions is formed. As a result, the growth of dendrites in the shutdown layer 16 can be stopped, and a short circuit between the negative electrode 12 and the positive electrode 14 can be suppressed.

[0075] The lithium-ion conductive solid material is a solid and is stably held inside the secondary battery 10. For example, even if the secondary battery 10 expands and contracts during charging and discharging, the lithium-ion conductive solid material of the shutdown layer 16 does not come into direct contact with the negative electrode 12. Therefore, the lithium-ion conductivity of the lithium-ion conductive solid material does not decrease, and the secondary battery 10 can be used stably as long as dendrites do not grow from the negative electrode 12 and reach the shutdown layer 16.

[0076] Furthermore, by using the pyrochlore solid electrolyte as a lithium-ion conductive solid material, the secondary battery 10 can be shut down in a short time by contact with lithium metal. Therefore, the safety of the secondary battery 10 can be improved.

[0077] The pyrochlore solid electrolyte of the present embodiment is a material with higher ionic conductivity than an oxide-based solid electrolyte commonly known as a solid electrolyte for a secondary battery. Therefore, in the configuration in which the shutdown layer 16 is provided in the secondary battery 10, it is possible to prevent a decrease in ionic conductivity while suppressing a short circuit of the secondary battery 10.

[0078] When lithium metal is used as the negative electrode active material of the negative electrode 12, a short circuit may occur in the secondary battery 10. In the secondary battery 10 using lithium metal as the negative electrode active material, the short circuit of the secondary battery 10 can be effectively suppressed by providing the shutdown layer 16.

[0079] When an olivine-type active material is used as the positive electrode active material of the positive electrode 14, a short circuit of the secondary battery 10 may occur. In the secondary battery 10 using the olivine-type positive electrode active material as the positive electrode active material, the short circuit of the secondary battery 10 can be effectively suppressed by providing the shutdown layer 16.

[0080] In the present embodiment, a solid electrolyte is used for the electrolyte layer 15. A solid electrolyte is an electrolyte material that has high safety but is more likely to cause a short circuit. In the secondary battery 10 using such a solid electrolyte, the short circuit of the secondary battery 10 can be effectively suppressed by providing the shutdown layer 16. (Second embodiment)

[0081] A second embodiment of the present disclosure will be described below. Only portions different from the first embodiment will be described below.

[0082] The positive electrode 14 of the second embodiment contains, in addition to the positive electrode active material, the same lithium ion conductive solid material as the lithium ion conductive solid material used in the shutdown layer 16. The secondary battery 10 of the second embodiment having such a configuration can also achieve the same effects as in the first embodiment. In addition, by providing a lithium ion conductive solid material for the positive electrode 14, the ionic conductivity of the positive electrode 14 can be improved. (Third embodiment)

[0083] A third embodiment of the present disclosure will be described below. Only portions different from the above embodiments will be described below.

[0084] The shutdown layer 16 of the third embodiment contains, in addition to the lithium-ion conductive solid material, the same solid electrolyte (e.g., LLZO) as the solid electrolyte used in the electrolyte layer 15. Even in the secondary battery 10 of the third embodiment having such a configuration, the same effects as in the first embodiment can be achieved. (Fourth embodiment)

[0085] Next, a fourth embodiment of the present disclosure will be described. Only portions different from the above embodiments will be described below.

[0086] The positive electrode 14 of the fourth embodiment contains, in addition to the positive electrode active material, the same lithium ion conductive solid material as the lithium ion conductive solid material used in the shutdown layer 16. The shutdown layer 16 of the fourth embodiment contains, in addition to the lithium ion conductive solid material, the same solid electrolyte (e.g., LLZO) as the solid electrolyte used in the electrolyte layer 15. Even in the secondary battery 10 of the fourth embodiment having such a configuration, the same effects as in the first embodiment can be achieved. (Fifth embodiment)

[0087] Next, a fifth embodiment of the present disclosure will be described. Only portions different from the above embodiments will be described below.

[0088] In the solid electrolyte layer 15 of the fifth embodiment, not a solid electrolyte but an electrolytic solution and a separator are provided. The separator has a porous structure and functions to separate the negative electrode 12 and the positive electrode 14 and to allow ions to pass through. For example, a porous body can be used as the separator. For example, ethylene carbonate or the like can be used as the electrolytic solution. The lithium ion conductive solid material of the shutdown layer 16 can be provided by applying it to the surface of the positive electrode 14 or the separator in the form of a sheet, or it can be provided by applying it to the surface of a particulate positive electrode active material.

[0089] Even in the secondary battery 10 of the fifth embodiment having such a configuration, the same effects as in the first embodiment can be achieved. Furthermore, by using an electrolytic solution for the solid electrolyte layer 15, the occurrence of a short circuit can be suppressed compared to a case where a solid electrolyte is used. (Sixth Embodiment)

[0090] Next, a sixth embodiment of the present disclosure will be described. Only portions different from the above embodiments will be described below.

[0091] As in Fig. As shown in Figure 6, the secondary battery 10 of the sixth embodiment includes, in the initial state, a negative electrode current collector 11, an electrolyte layer 15, a cutoff layer 16, a positive electrode 14, and a positive electrode current collector 13. That is, the secondary battery 10 of the sixth embodiment is configured as an anode-less battery in which the negative electrode 12 is not formed between the negative electrode current collector 11 and the electrolyte layer 15 in the initial state. The initial state is a state in which the components of the secondary battery 10 are assembled and is a state in which the secondary battery 10 is not charged.

[0092] In the secondary battery 10 of the sixth embodiment, a solid electrolyte (e.g., LLZO) is used as the solid electrolyte layer 15. In the initial state, the negative electrode current collector 11 and the electrolyte layer 15 are arranged adjacent to each other.

[0093] As in Fig. As shown in Figure 7, the negative electrode 12 in the secondary battery 10 is formed by charging. When the secondary battery 10 is charged, lithium ions migrate from the positive electrode 14 to the negative electrode current collector 11. Lithium metal is deposited on the negative electrode current collector 11 through a dissolution and deposition reaction, and the negative electrode 12 is formed by the lithium metal. The lithium metal formed on the negative electrode current collector 11 serves as the negative electrode active material.

[0094] The negative electrode 12 is formed between the negative electrode current collector 11 and the shutdown layer 16. In the sixth embodiment, the negative electrode 12 is formed between the negative electrode current collector 11 and the electrolyte layer 15 and is formed at the interface between the negative electrode current collector 11 and the electrolyte layer 15. The negative electrode 12 is formed so that it is in contact with the negative electrode current collector 11 and can exchange electrons with the negative electrode current collector 11. The lithium metal forming the negative electrode 12 becomes lithium ions during discharge and migrates to the positive electrode 14.

[0095] Also, in the secondary battery 10 of the sixth embodiment having the configuration described above, the same effects as in the first embodiment can be achieved.

[0096] In the secondary battery 10 of the sixth embodiment, a coating layer that promotes the dissolution and deposition reaction of lithium metal can be provided on the surface of the negative electrode current collector 11 adjacent to the electrolyte layer 15. This coating layer can make the dissolution and deposition reaction of lithium metal uniform and promote the deposition of lithium metal. An alloy material or a carbon material can be used as such a coating layer. (Seventh Embodiment)

[0097] Next, a seventh embodiment of the present disclosure will be described. Only portions different from the above embodiments will be described below.

[0098] The secondary battery 10 of the seventh embodiment is configured as an anode-less battery, similar to the sixth embodiment. In the secondary battery 10 of the seventh embodiment, a solid electrolyte (e.g., LLZO) is used as the solid electrolyte layer 15.

[0099] As in Fig. As shown in Figure 8, the electrolyte layer 15 in the secondary battery 10 of the seventh embodiment includes a dense layer 15a and a porous layer 15b. The dense layer 15a is provided adjacent to the positive electrode current collector 13 and is in contact with the shutdown layer 16. The porous layer 15b is provided adjacent to the negative electrode current collector 11 and is in contact with the negative electrode current collector 11.

[0100] The dense layer 15a and the porous layer 15b are made of the same solid electrolyte and have different densities. The dense layer 15a has a dense structure in which no holes are formed. The dense layer 15a can ensure insulation between the negative electrode 12 and the positive electrode 14. The porous layer 15b has a porous structure in which a large number of pores are formed and has a lower density than the dense layer 15a.

[0101] The porous layer 15b has a specific shape, for example, a porous structure in which a large number of pores are regularly formed, or a porous structure in which a large number of pores are irregularly formed. The porous layer 15b with a regular porous structure can be produced, for example, using a 3D printer. The porous layer 15b with an irregular porous structure can be produced, for example, by heating and removing a pore-forming agent mixed with a solid electrolyte.

[0102] When the secondary battery 10 is charged, lithium ions migrate from the positive electrode 14 to the negative electrode current collector 11, and lithium metal is deposited on the negative electrode current collector 11 through a dissolution and deposition reaction, thereby forming the negative electrode 12.

[0103] The negative electrode 12 is formed between the negative electrode current collector 11 and the shutdown layer 16. In the seventh embodiment, the negative electrode 12 is formed inside the hole of the porous layer 15b in a state in contact with the negative electrode current collector 11. Therefore, the negative electrode 12 is formed between the negative electrode current collector 11 and the dense layer 15a of the electrolyte layer 15. The negative electrode 12 formed in the porous layer 15b is in contact with the negative electrode current collector 11, and electrons can be exchanged with the negative electrode current collector 11.

[0104] Also in the secondary battery 10 of the seventh embodiment having the above configuration, the same effects as in the first embodiment can be achieved.

[0105] When the negative electrode 12 is formed at the interface between the negative electrode current collector 11 and the electrolyte layer 15, the thickness of the secondary battery 10 is increased by the increase in the thickness of the negative electrode 12 during charging, and the thickness of the secondary battery 10 is reduced by the decrease in the thickness of the negative electrode 12 during discharging. In contrast, in the secondary battery 10 of the seventh embodiment, the lithium metal is deposited within the pores of the porous layer 15b of the electrolyte layer 15 to form the negative electrode 12. Therefore, the distance between the negative electrode current collector 11 and the electrolyte layer 15 does not increase during charging, and the distance between the negative electrode current collector 11 and the electrolyte layer 15 does not decrease during discharging.In this way, the thickness of the secondary battery 10 can be prevented from changing during charging and discharging.

[0106] In the secondary battery 10 of the seventh embodiment, a coating layer that promotes the dissolution and deposition reaction of lithium metal can be provided on the surface of the pores of the porous layer 15b. This coating layer can make the dissolution and deposition reaction of the lithium metal uniform. An alloy material or a carbon material can be used as such a coating layer. (Eighth Embodiment)

[0107] Next, an eighth embodiment of the present disclosure will be described. Only portions different from the above embodiments will be described below.

[0108] As in Fig. As shown in Figure 9, the secondary battery 10 of the eighth embodiment has a bipolar structure. The secondary battery 10 of the eighth embodiment has a plurality of battery cells 100 and 101. The battery cells 100 and 101 are stacked and connected in series. The number of battery cells 100, 101 constituting the secondary battery 10 can be arbitrarily determined, and Fig. 9 shows an example in which two battery cells 100, 101 are provided in stacked form.

[0109] The first battery cell 100 and the second battery cell 101 each include a negative electrode 12, an electrolyte layer 15, a shutdown layer 16, and a positive electrode 14. A common current collector 17 is provided between the first battery cell 100 and the second battery cell 101, which are adjacent to each other. The first battery cell 100 and the second battery cell 101 share the common current collector 17.

[0110] The common current collector 17 is arranged between the positive electrode 14 of the first battery cell 100 and the negative electrode 12 of the second battery cell 101. The first battery cell 100 and the second battery cell are connected in series via the common current collector 17. Therefore, the positive electrode 14 of the first battery cell 100, the common current collector 17, and the negative electrode 12 of the second battery cell 101 form a bipolar structure.

[0111] In the bipolar secondary battery 10 of the eighth embodiment, current irregularities are structurally likely to occur, and lithium metal dendrites are likely to form. In the bipolar secondary battery 10, the short circuit of the secondary battery 10 can be effectively suppressed by providing the shutdown layer 16. EXAMPLES

[0112] Examples of the present disclosure are described below. At least one of the lithium ion conductive solid material of the shutdown layer 16 and the positive electrode active material of the positive electrode 14 differs between Examples 1 to 4. Furthermore, a secondary battery 10 in which the shutdown layer 16 is not provided is used as a comparative example. In Examples 1 to 4 and the comparative example, the configuration of the secondary battery 10 of the second embodiment is used.

[0113] In the secondary batteries 10 of Examples 1 to 4 and the comparative example, the thickness of the negative electrode 12 is 25 µm, the thickness of the electrolyte layer 15 is 100 µm, and the thickness of the positive electrode 14 is 50 µm. In the secondary battery 10 of Examples 1 to 4, the thickness of the shutdown layer 16 is 10 µm.

[0114] In the secondary batteries 10 of Examples 1 to 4 and the Comparative Example, the positive electrode 14 contains 50% of the positive electrode active material and 50% of the lithium ion conductive solid material. In Examples 1 to 3 and the Comparative Example, LiNi 0,8 CoMn 0,1 O2 (NCM811), in which a layered active material is used as the positive electrode active material. In Example 4, LiMn 0,8 Fe 0,2 PO4 (LMFP), which uses an olivine-type active material as the positive electrode active material.

[0115] In the secondary batteries 10 of Examples 1 to 4 and Comparative Example, lithium metal is used as the negative electrode active material of the negative electrode 12 and Li7La3Zr2O 12 (LLZO) is used as the electrolyte material of the electrolyte layer 15.

[0116] In Examples 1 and 4, 16 Li is used as the lithium ion conductive solid material of the shutdown layer.1,25 La 0,58 Nb2O6F is used, which is a pyrochlore solid electrolyte. In Example 2, Li 1,4 Al 0,4 Ti 1,6 (PO4)3 (LATP), which is a NASICON-type oxide solid electrolyte, is used as the lithium ion conductive solid material for the shutdown layer 16. In Example 3, La is used as the lithium ion conductive solid material of the shutdown layer 16. 0,57 Li 0,29 TiO3 (LLTO), a perovskite-type oxide solid-state electrolyte, is used. In the comparative example, the shutdown layer 16 is not provided.

[0117] Fig. 10 shows the results of a cycle test in which the secondary battery 10 is repeatedly charged and discharged. In the cycle test, the presence or absence of a short circuit, the time from the rapid increase in the resistance of the secondary battery 10 to shutdown, the DC resistance before the rapid increase in the DC resistance, and the number of cycles until the rapid increase in the resistance of the secondary battery 10 are measured. During the cycle test, the battery temperature is 10°C, the voltage is 4.3V to 2.7V, and the C-rate is 0.2C. The resistance of the secondary battery 10 is evaluated by measuring the resistance at an SOC of 50% using an AC impedance method. The rapid increase in the resistance of the secondary battery 10 occurs when dendrites grow from the negative electrode 12 and the lithium ion conductive solid material contained in the shutdown layer 16 is reduced by contact with lithium metal.

[0118] As in Fig. 10, in the comparative example in which the shutdown layer 16 was not provided, a short circuit occurred in the secondary battery 10 and the voltage became 0 V. In contrast, in Examples 1 to 4 in which the shutdown layer 16 was provided, the resistance of the secondary battery 10 increases before the voltage became 0 V, and the charging and discharging of the secondary battery 10 is stopped while maintaining the voltage.

[0119] The number of cycles until the resistance of the secondary battery 10 rapidly increases is 113 in Example 1, 108 in Example 2, 98 in Example 3, 70 in Example 4, and 110 in Comparative Example. Among Examples 1 to 3 using the layered active material as the positive electrode active material, Example 1 has the largest number of cycles until the resistance of the secondary battery 10 rapidly increases. Therefore, when the pyrochlore solid electrolyte is used as the lithium ion conductive solid material, the number of charge and discharge cycles of the secondary battery 10 can be further increased.

[0120] Furthermore, when comparing Examples 1 and 4, using the pyrochlore solid electrolyte in Example 4 with the olivine-type active material as the positive electrode active material, the number of cycles until the resistance of the secondary battery 10 rapidly increases is significantly lower than in Example 1 with the layered active material as the positive electrode active material layer. That is, when an olivine-type active material is used as the positive electrode active material of the secondary battery 10, the formation of dendrites is likely.

[0121] The time from the rapid increase in the resistance of the secondary battery 10 to shutdown is 65 hours in Example 1, 90 hours in Example 2, 120 hours in Example 3, and 62 hours in Example 4. The secondary battery 10 of the comparative example was not shut down. Of Examples 1 to 4, Examples 1 and 4 using the pyrochlore solid electrolyte have the shortest time between the rapid increase in the resistance of the secondary battery 10 and shutdown. Therefore, when the pyrochlore solid electrolyte is used as a lithium ion conductive solid material, the secondary battery 10 can be shut down in a short time, and the safety of the secondary battery 10 can be further improved.

[0122] Furthermore, comparing Examples 1 and 4 using the pyrochlore solid electrolyte, the shutdown time in Example 4 using the olivine-type active material as the positive electrode active material is shorter than in Example 1 using the layered active material as the positive electrode active material. That is, in the secondary battery 10 using the olivine-type active material, in which dendrites are easily formed, the occurrence of a short circuit can be effectively suppressed by providing the shutdown layer 16.

[0123] The DC resistance of the secondary battery 10 before the rapid increase in DC resistance (i.e., in the normal state) is 80 Ω in Example 1, 207 Ω in Example 2, 147 Ω in Example 3, 74 Ω in Example 4, and 220 Ω in the comparative example. The DC resistance of the secondary battery 10 in the normal state was the highest in Example 1. This means that Example 1, using the pyrochlore solid electrolyte, has the best input / output characteristics of the secondary battery 10.

[0124] The present disclosure is not limited to the embodiments described above, and various changes may be made without departing from the spirit of the present disclosure. The means disclosed in each embodiment may be combined as appropriate, as long as the combination is feasible.

[0125] Although the present disclosure has been described with reference to embodiments, the disclosure is not limited to these embodiments and constructions. The present disclosure is intended to cover various modifications and equivalent arrangements. Moreover, although various combinations and modes are shown in the present disclosure, other combinations and modes including only one element, more than that, or fewer than that are also within the scope and spirit of the present disclosure.

[0126] The secondary battery described in this specification has the following characteristics. (Point 1)

[0127] A secondary battery that contains: a positive electrode (14) containing a positive electrode active material; a negative electrode (12) containing a negative electrode active material; an electrolyte layer (15) provided adjacent to the negative electrode and made of an electrolyte material having lithium ion conductivity; and a shutdown layer (16) provided adjacent to the positive electrode and containing a lithium ion conductive solid material having lithium ion conductivity, wherein the electrolyte layer is inserted between the negative electrode and the shutdown layer, the electrolyte material is a solid electrolyte, an electrolyte solution, a polymer or a mixture thereof, the shutdown layer is made only of the lithium-ion conductive solid material or a mixture of the lithium-ion conductive solid material and at least one of a solid electrolyte, an electrolyte solution and a polymer, the lithium ion conductive solid material is at least one of a pyrochlore solid electrolyte, a NASICON solid electrolyte and a perovskite solid electrolyte and the lithium ion conductive solid material exhibits a greater decrease in lithium ion conductivity upon contact with lithium metal than the electrolyte material. (Point 2)

[0128] A secondary battery that contains: a positive electrode (14) containing a positive electrode active material; a negative electrode (12) containing a negative electrode active material; an electrolyte layer (15) provided adjacent to the negative electrode and containing an electrolyte material having lithium ion conductivity; and a shutdown layer (16) provided adjacent to the positive electrode and containing a lithium ion conductive solid material having lithium ion conductivity, wherein the electrolyte layer is inserted between the negative electrode and the shutdown layer, and the lithium ion conductive solid material forms a non-conductor for lithium ions when in contact with lithium metal. (Point 3)

[0129] The secondary battery according to item 2, wherein the lithium ion conductive solid material is at least one of a pyrochlore solid electrolyte, a NASICON solid electrolyte, and a perovskite solid electrolyte. (Point 4)

[0130] The secondary battery according to one of the items 1 to 3, where the lithium ion conductive solid material is an oxide-based solid electrolyte having a pyrochlore structure represented by a composition formula Aa2–α Away (1+α) / 3 B2O7- β X β (Aa: alkali metal, Ab: lanthanide, B: cationic metal, X: anion substitutable by O), in the composition formula, α is in a range of 0.6<α<2.0, β is in a range of 0<β≤1, where a sum of the valences of the cations composed of Aa, Ab and B and the anions composed of O and X is negative, and a defective structure is included, and B is at least one of a Group 4 element, a Group 5 element or a Group 15 element. (Point 5)

[0131] The secondary battery according to item 2 or 3, wherein the B is at least one of Nb, V, Sb, Bi, Ta, Zr, Ti and Hf. (Point 6)

[0132] The secondary battery according to any one of items 1 to 5, wherein the positive electrode active material includes an olivine type active material. (Point 7)

[0133] The secondary battery according to any one of items 1 to 6, wherein the negative electrode active material includes lithium metal. (Point 8)

[0134] The secondary battery according to any one of items 1 to 7, wherein the electrolyte material includes a solid electrolyte. (Point 9)

[0135] The secondary battery according to any one of items 1 to 8, comprising a negative electrode current collector (11), wherein the negative electrode is not provided in an initial state in which no charging occurs, and the negative electrode is formed so that it comes into contact with the negative electrode current collector upon charging. (Point 10)

[0136] The secondary battery according to one of the items 1 to 9, where a plurality of battery cells (100, 101) are provided, each of which includes the positive electrode, the negative electrode, the electrolyte layer and the shutdown layer, a common current collector (17) is inserted between a positive electrode of one of the adjacent battery cells and a negative electrode of the other of the battery cells, and one of the battery cells and the other of the battery cells are connected in series via the common current collector. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2022

[0001] JP 175676

[0001] JP 2020-53172 A

[0005]

Claims

[1] Secondary battery which has: a positive electrode (14) containing a positive electrode active material; a negative electrode (12) containing a negative electrode active material; an electrolyte layer (15) provided adjacent to the negative electrode and made of an electrolyte material having lithium ion conductivity; and a shutdown layer (16) provided adjacent to the positive electrode and containing a lithium ion conductive solid material having lithium ion conductivity, wherein the electrolyte layer is inserted between the negative electrode and the shutdown layer, the electrolyte material is a solid electrolyte, an electrolyte solution, a polymer or a mixture thereof, the shutdown layer is made only of the lithium-ion conductive solid material or a mixture of the lithium-ion conductive solid material and at least one of a solid electrolyte, an electrolyte solution and a polymer, the lithium ion conductive solid material is at least one of a pyrochlore solid electrolyte, a NASICON solid electrolyte and a perovskite solid electrolyte and the lithium ion conductive solid material exhibits a greater decrease in lithium ion conductivity upon contact with lithium metal than the electrolyte material. [2] Secondary battery which has: a positive electrode (14) containing a positive electrode active material; a negative electrode (12) containing a negative electrode active material; an electrolyte layer (15) provided adjacent to the negative electrode and containing an electrolyte material having lithium ion conductivity; and a shutdown layer (16) provided adjacent to the positive electrode and containing a lithium ion conductive solid material having lithium ion conductivity, wherein the electrolyte layer is inserted between the negative electrode and the shutdown layer, and the lithium ion conductive solid material forms a non-conductor for lithium ions when in contact with lithium metal. [3] The secondary battery according to claim 2, wherein the lithium ion conductive solid material is at least one of a pyrochlore solid electrolyte, a NASICON solid electrolyte, and a perovskite solid electrolyte. [4] Secondary battery according to one of claims 1 to 3, wherein the lithium ion conductive solid material is an oxide-based solid electrolyte having a pyrochlore structure represented by a composition formula Aa 2-α Away (1+α) / 3 B2O 7-β X β (Aa: alkali metal, Ab: lanthanide, B: cationic metal, X: anion substitutable by O), in the composition formula, α is in a range of 0.6 <α<2,0, β liegt in einem bereich von 0<β≤1, wobei eine summe der valenzen kationen, die sich aus dem aa, ab und b zusammensetzen, anionen, o x negativ ist, defekte struktur beinhaltet undB is at least one of a Group 4 element, a Group 5 element or a Group 15 element. [5] A secondary battery according to claim 4, wherein the B is at least one of Nb, V, Sb, Bi, Ta, Zr, Ti and Hf. [6] The secondary battery according to claim 1, wherein the positive electrode active material includes an olivine type active material. [7] The secondary battery according to claim 1, wherein the negative electrode active material includes lithium metal. [8] The secondary battery according to claim 1, wherein the electrolyte material includes a solid electrolyte. [9] A secondary battery according to claim 1, comprising a negative electrode current collector (11), wherein the negative electrode is not provided in an initial state in which no charging occurs, and the negative electrode is formed so that it comes into contact with the negative electrode current collector upon charging. [10] A secondary battery according to claim 1, wherein a plurality of battery cells (100, 101) are provided, each of which includes the positive electrode, the negative electrode, the electrolyte layer and the shutdown layer, a common current collector (17) is inserted between a positive electrode of one of the adjacent battery cells and a negative electrode of the other of the battery cells, and one of the battery cells and the other of the battery cells are connected in series via the common current collector.

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