Secondary batteries

Abstract

The device comprises a positive electrode layer (14), a negative electrode layer (12), and an electrolyte layer (15) that conducts lithium ions between the positive and negative electrode layers. The positive electrode layer is provided with a positive electrode active material (14a) containing Mn in its composition and an oxide-based ion conductor (14b) having lithium ion conductivity. The electrolyte layer contains a fluorine-containing lithium salt containing fluorine atoms and a solvent capable of dissolving the fluorine-containing lithium salt. The ion conductor is a dielectric that can promote the dissociation of lithium ions from the fluorine-containing lithium salt.

Description

Cross-reference to related applications

[0001] This application is based on Japanese Patent Application No. 2024-192060 filed on October 31, 2024, the contents of which are incorporated herein by reference.

Technical Field

[0002] This disclosure relates to secondary batteries.

Background Art

[0003] In recent years, in lithium-ion batteries, in order to increase the energy density, reduce the cost, and enhance the safety, a mixed material in which a silicon-based negative electrode material is mixed with a graphite negative electrode material, and a mixed material in which a lithium manganese iron phosphate (LMFP) positive electrode material is mixed with a ternary positive electrode material have been used. In these mixed materials, there is a possibility of containing a large amount of moisture such as adsorbed water adsorbed on the surface of the material and crystal water incorporated into the crystal of the material.

[0004] When such a mixed material containing a large amount of moisture is used in the manufacture of a battery, if the moisture cannot be sufficiently removed in the battery manufacturing process, a trace amount of moisture remains inside the battery. When lithium hexafluorophosphate (LiPF6), which is a fluorine-containing lithium salt, is used as an electrolyte in such a battery, PF5 generated from LiPF6 reacts with the moisture, and hydrogen fluoride (HF) is likely to be generated. The generation of hydrogen fluoride causes deterioration such as the destruction of the SEI (Solid Electrolyte Interface) film, which is an inert film containing metal at the negative electrode, and the elution of metal from the positive electrode active material, and the durability of the secondary battery decreases.

[0005] In Patent Document 1, it is proposed to suppress the generation of hydrogen fluoride by adding an additive to the electrolytic solution to trap PF5 generated from LiPF6.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, in the configuration described in Patent Document 1, an additive is added to the electrolyte, which increases the resistance of the electrolyte and reduces the output of the secondary battery.

[0008] In view of the above points, this disclosure aims to suppress degradation caused by hydrogen fluoride generation from fluorine-containing lithium salts while suppressing a decrease in output in a secondary battery using fluorine-containing lithium salts.

[0009] To achieve the above objectives, this disclosure First, second In one embodiment, the device comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer that conducts lithium ions between the positive and negative electrode layers. The positive electrode layer is provided with a positive electrode active material containing Mn in its composition and an oxide-based ion conductor having lithium ion conductivity. The electrolyte layer contains a fluorine-containing lithium salt containing fluorine atoms and a solvent capable of dissolving the fluorine-containing lithium salt. The oxide-based ion conductor is a dielectric that can promote the dissociation of lithium ions from the fluorine-containing lithium salt. The oxide-based ion conductor contains an oxyfluoride. In a first aspect of this disclosure, the oxyfluoride has a pyrochlore-type crystalline structure and a defect structure. In a second aspect of this disclosure, the dielectric constant of the oxide-based ionic conductor is 90 or higher.

[0010] This allows the dielectric effect of the oxide-based ion conductor to prioritize the dissociation of lithium ions from the fluorine-containing lithium salt, thereby suppressing the generation of hydrogen fluoride from the fluorine-containing lithium salt. The oxide-based ion conductor possesses lithium ion conductivity, which suppresses the decrease in the resistance of the secondary battery while also suppressing the degradation of the secondary battery caused by the generation of hydrogen fluoride from the fluorine-containing lithium salt. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of the present disclosure. [Figure 2] This is a perspective view showing the components of a secondary battery separated. [Figure 3] This is a conceptual diagram showing the composition of the positive electrode active material and the oxide-based ion conductor. [Figure 4] This is a conceptual diagram showing the composition of the positive electrode active material and the oxide-based ion conductor. [Figure 5] This is a conceptual diagram showing the composition of the positive electrode active material and the oxide-based ion conductor. [Figure 6] This figure shows the crystal structure of a pyrochlore-type oxide. [Figure 7] This diagram shows the manufacturing process for pyrochlore-type oxides. [Figure 8] This chart shows the initial resistance and durability of secondary batteries in the examples and comparative examples. [Modes for carrying out the invention]

[0012] Embodiments of this disclosure will be described below with reference to the drawings. Unless otherwise specified, the particle diameter in these embodiments is the particle median diameter D50. The particle median diameter D50 refers to the volume-based particle diameter when the volume is integrated from the smallest particle in the particle diameter distribution and reaches 50% of the total particle volume. In other words, the particle median diameter D50 refers to the particle diameter corresponding to the median of the particle diameter distribution.

[0013] The secondary battery 10 of this embodiment is a lithium-ion battery in which lithium ions are conducted as conductive ions.

[0014] As shown in Figure 1, the secondary battery 10 comprises a negative electrode current collector 11, a negative electrode layer 12, a positive electrode current collector 13, a positive electrode layer 14, and an electrolyte layer 15 as its components. The negative electrode current collector 11, the negative electrode layer 12, the positive electrode current collector 13, the positive electrode layer 14, and the electrolyte layer 15 are stacked along a predetermined stacking direction. In Figure 1, the left-right direction is the stacking direction of the secondary battery 10.

[0015] The electrolyte layer 15 comprises an electrolyte 15a and an insulating layer 15b. The electrolyte 15a is present from the negative electrode layer 12 to the positive electrode layer 14 and penetrates into the interior of both the negative electrode layer 12 and the positive electrode layer 14. The electrolyte layer 15 may consist of a liquid, or it may contain a solid electrolyte in addition to the liquid. Furthermore, the secondary battery 10 may contain a small amount of water (H2O) in the electrolyte 15a. It is preferable that the amount of water be small relative to the total amount of electrolyte 15a.

[0016] An electrolyte layer 15 is sandwiched between a pair of electrodes 12 and 14, which consist of a negative electrode layer 12 and a positive electrode layer 14. The negative electrode layer 12 and the electrolyte layer 15 are in contact. The positive electrode layer 14 and the electrolyte layer 15 are in contact. The negative electrode layer 12 and the positive electrode layer 14 are bonded together via the electrolyte layer 15. The secondary battery 10 is charged and discharged by lithium ions moving between the negative electrode layer 12 and the positive electrode layer 14 via the electrolyte layer 15.

[0017] The secondary battery 10 of this embodiment is configured as a high-output battery in which the reaction area of ​​electrodes 12 and 14 is large relative to the battery capacity. In a high-output battery, the area A (mm²) of the opposing surfaces where the negative electrode layer 12 and the positive electrode layer 14 face each other is large relative to the battery capacity B (mAh) of the secondary battery 10. 2 The ratio of ) is increasing.

[0018] The negative electrode layer 12 has a surface facing the positive electrode layer 14 via the electrolyte layer 15. The positive electrode layer 14 also has a surface facing the negative electrode layer 12 via the electrolyte layer. Hereinafter, the surfaces facing the negative electrode layer 12 and the positive electrode layer 14 will also be referred to as electrode facing surfaces, and the area of ​​the surfaces facing the negative electrode layer 12 and the positive electrode layer 14 will also be referred to as the electrode facing area.

[0019] As described later, in this embodiment, an oxide-based ion conductor 14b is provided in the positive electrode layer 14 to suppress the generation of hydrogen fluoride and thereby suppress the degradation of the secondary battery 10.

[0020] The secondary battery 10 has an electrode facing area A (mm²) relative to its battery capacity B (mAh). 2The larger the ratio A / B, the greater the degradation of the secondary battery 10 when hydrogen fluoride is generated. However, the presence of an oxide-based ion conductor 14b in the positive electrode layer 14 enhances the degradation suppression effect of the secondary battery 10. The degradation suppression effect of the oxide-based ion conductor 14b on the secondary battery 10 is greater when A / B is 10 (mm 2 It becomes higher when the mAh is greater than or equal to 30 (mm²), and A / B ratio is 30 (mm²). 2 If the value is above ( / mAh), it will be higher, and A / B will be 40 (mm 2 If the value is above ( / mAh), it will be even higher.

[0021] As shown in Figure 2, the negative electrode layer 12 and the positive electrode layer 14 are plate-shaped and face each other via the insulating layer 15b of the electrolyte layer 15. That is, the opposing surface of the negative electrode layer 12 faces the insulating layer 15b of the electrolyte layer 15, and the opposing surface of the positive electrode layer 14 faces the insulating layer 15b of the electrolyte layer. When viewed from the stacking direction of the negative electrode layer 12 and the positive electrode layer 14, they overlap; in other words, there is a portion where the projected surface of the negative electrode layer 12 in the stacking direction and the projected surface of the positive electrode layer 14 in the stacking direction overlap. The electrode facing area is the area of ​​the overlapping portion of the negative electrode layer 12 and the positive electrode layer 14. In Figure 2, the area of ​​the portion indicated by the upward-sloping diagonal line is the electrode facing area.

[0022] If the area of ​​the negative electrode layer 12 and the area of ​​the positive electrode layer 14 are different, the electrode facing area is defined as the area of ​​the overlapping portion of the negative electrode layer 12 and the positive electrode layer 14.

[0023] The electrolyte 15a is lithium ion conductive and conducts conductive ions between the negative electrode layer 12 and the positive electrode layer 14. The electrolyte 15a contains an electrolyte made of a lithium salt and a solvent capable of dissolving the lithium salt.

[0024] In this embodiment, a fluorine-containing lithium salt containing fluorine atoms is used as the lithium salt of the electrolyte 15a. Examples of fluorine-containing lithium salts that can be used include LiPF6, LiFSI (lithium bis(fluorosulfonyl)imide), and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide). These fluorine-containing lithium salts may be used individually or in combination. In this embodiment, LiPF6 is used as the fluorine-containing lithium salt.

[0025] Fluorine-containing lithium salts readily dissociate into LiF and fluorine compounds through thermal decomposition, etc. Fluorine compounds dissociated from fluorine-containing lithium salts are substances capable of reacting with H2O to generate hydrogen fluoride (HF). Therefore, if fluorine compounds dissociate from fluorine-containing lithium salts, they may react with moisture contained in the secondary battery 10 to generate hydrogen fluoride (HF). The generation of hydrogen fluoride leads to the deterioration of the secondary battery 10.

[0026] In this embodiment, LiPF6, used as a fluorine-containing lithium salt, is prone to thermal decomposition, leading to the dissociation reaction of PF5 ("LiPF6 → LiF + PF5") and the reaction of PF5 with water to produce hydrogen fluoride ("PF5 + H2O → 2HF + POF3"). In particular, in high-power batteries with a large reaction area, such as the secondary battery 10 of this embodiment, the impact of hydrogen fluoride generation tends to be significant.

[0027] As the solvent for electrolyte 15a, organic electrolytes, ionic liquids, gel polymers, etc., can be used. As organic electrolytes, ethylene carbonate, diethyl carbonate, propylene carbonate, etc., can be used. These solvents may be used individually or in combination.

[0028] The insulating layer 15b is positioned between the negative electrode layer 12 and the positive electrode layer 14, preventing the opposing surface of the negative electrode layer 12 from making direct physical contact with the opposing surface of the positive electrode layer 14. The insulating layer 15b is an insulating ion-permeable film that prevents physical contact between the negative electrode layer 12 and the positive electrode layer 14, thereby suppressing electrical short circuits, while also allowing ions to pass through.

[0029] In this embodiment, a porous separator is used as the insulating layer 15b. As the separator, a porous material such as polypropylene, polyethylene, or nonwoven fabric can be used. A solid electrolyte may be coated on the surface of the separator. A polymer sheet or a solid electrolyte sheet may also be used as the insulating layer 15b. The solid electrolyte sheet is a self-supporting membrane.

[0030] The negative electrode current collector 11 and the positive electrode current collector 13 can be made of any material suitable for use as a current collector in a lithium-ion battery. In this embodiment, Cu is used as the negative electrode current collector 11 and Al is used as the positive electrode current collector 13.

[0031] The negative electrode material constituting the negative electrode layer 12 can be any material usable as a negative electrode active material for lithium-ion batteries, such as carbon-based negative electrode materials, oxide-based negative electrode materials, or metal-based negative electrode materials. These negative electrode materials may be used individually or in combination.

[0032] As carbon-based anode materials, for example, natural graphite, artificial graphite, and hard carbon can be used. As oxide-based anode materials, for example, Li4Ti5O 12 TiO2(B) and TiNb2O7 can be used. As for metallic anode materials, for example, silicon-based anode materials and lithium metal can be used.

[0033] In this embodiment, graphite and a silicon-based anode material are used as the anode active material. The silicon-based anode material is an anode material containing Si. Graphite can be used alone as the anode active material, or a mixed material of graphite and the silicon-based anode material can be used as the anode active material.

[0034] Silicon-based anode materials containing Si have a high moisture adsorption capacity and retain a large amount of moisture. Therefore, when silicon-based anode materials are included in the anode active material, when PF5 dissociates from LiPF6, a fluorine-containing lithium salt, PF5 readily reacts with moisture to generate hydrogen fluoride.

[0035] Silicon-based anode materials include Si, SiO, and Si / C composite materials. In this embodiment, Si compounds containing Si, such as SiO and Si / C, are used as silicon-based anode materials. The smaller the particle size of the Si compound, the greater the amount of moisture it can carry. When the particle size of the Si compound is 5 μm or less, the amount of moisture carried is particularly large, making it easier to generate hydrogen fluoride from fluorine-containing lithium salts.

[0036] The particle size of Si compounds is the particle median diameter D50. The particle median diameter D50 represents the volume-based particle size when the volume is integrated from the smallest particle size in the particle size distribution and reaches 50% of the total particle volume. In other words, the particle median diameter D50 represents the particle size corresponding to the median of the particle size distribution.

[0037] Furthermore, an SEI film is formed at the interface with the electrolyte 15a in the negative electrode layer 12. The SEI film plays a role in inserting and removing lithium ions, but if hydrogen fluoride is generated from the fluorine-containing lithium salt, it may destroy the SEI film and cause the secondary battery 10 to deteriorate.

[0038] The negative electrode layer 12 may contain a conductive additive, a binder, and a polymer. The conductive additive can be, for example, a carbon material such as carbon black. As the binder, an aqueous binder such as a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose) can be used. Furthermore, polyacrylic binders using polyacrylic acid are hygroscopic, which increases the amount of moisture carried in, making it easier to generate hydrogen fluoride from fluorine-containing lithium salts.

[0039] Furthermore, the negative electrode layer 12 may contain a solid electrolyte. If the negative electrode layer 12 contains a solid electrolyte, the solid electrolyte may be mixed with the negative electrode material, or the surface of the negative electrode material may be coated with the solid electrolyte.

[0040] The positive electrode layer 14 releases lithium ions when the secondary battery 10 is charged and accepts lithium ions when the secondary battery 10 is discharged. The positive electrode layer 14 contains a positive electrode active material 14a as a positive electrode material and an oxide-based ion conductor 14b having ion conductivity. The oxide-based ion conductor 14b is an oxide-based solid electrolyte having lithium ion conductivity and can suppress the generation of hydrogen fluoride from fluorine-containing lithium salts.

[0041] The positive electrode layer 14 may contain a conductive additive, a binder, and a polymer. The conductive additive can be, for example, a carbon material such as carbon black. As the binder, for example, polyvinylidene fluoride (PVdF) can be used. Furthermore, the positive electrode layer 14 may contain a solid electrolyte. If the positive electrode layer 14 contains a solid electrolyte, the solid electrolyte may be mixed with the positive electrode active material 14a, or the surface of the positive electrode active material 14a may be coated with the solid electrolyte.

[0042] In the positive electrode layer 14, the positive electrode active material 14a and the oxide-based ion conductor 14b can be provided in any configuration. In the positive electrode layer 14, it is sufficient that the oxide-based ion conductor 14b is in direct contact with the electrolyte 15a. In the examples shown in Figures 3 to 5, the configurations of the positive electrode active material 14a and the oxide-based ion conductor 14b in the positive electrode layer 14 are different.

[0043] Figure 3 shows an example in which the positive electrode layer 14 has a random structure in which particulate positive electrode active material 14a and particulate oxide-based ion conductor 14b are randomly mixed. Figure 4 shows an example in which the positive electrode layer 14 has a layered structure in which the outer surface of the particulate positive electrode active material 14a is coated with oxide-based ion conductor 14b.

[0044] FIG. 5 shows an example in which the oxide-based ion conductor 14b is provided between the separator forming the insulating layer 15b and the positive electrode active material 14a. In the example shown in FIG. 5, the oxide-based ion conductor 14b can be coated on the positive electrode side surface of the separator or the separator side surface of the positive electrode active material 14a.

[0045] The positive electrode active material 14a used in the present embodiment contains Mn in its composition. When hydrogen fluoride is generated from the fluorine-containing lithium salt as described above, a metal element may elute from the crystal structure of the positive electrode active material 14a, and the positive electrode active material 14a may deteriorate. Among the metal elements constituting the positive electrode active material 14a, Mn is particularly likely to elute due to hydrogen fluoride, and the positive electrode active material 14a is likely to deteriorate.

[0046] As the positive electrode active material 14a containing Mn, for example, a layered rock salt type active material, an olivine type active material, a spinel type active material, or an acid halide type active material can be used.

[0047] As the layered rock salt type active material containing Mn, for example, ternary system positive electrode materials such as LiNi x Co y Mn<000,009>O2 (NCM) can be used. As the olivine type active material containing Mn, for example, LiMn 1-x Fe x PO4 (LMFP), LiMnPO4 (LMP) can be used. As the spinel type active material containing Mn, for example, LiMn2O4 (LMO), LiNi 0.5 Mn 1.5 O4 (LNMO) can be used. LNMO has a high operating potential of about 4.7V, and it is possible to operate the secondary battery 10 at a high potential. On the other hand, when a positive electrode active material 14a having a high operating potential such as LNMO is used, the deterioration of the positive electrode active material 14a is promoted by the generation of hydrogen fluoride. As the acid halide type active material containing Mn, for example, Li2MnO 3-x F x can be used.

[0048] In this embodiment, layered rock salt type active material NCM and olivine type active material LMFP are used as the positive electrode active material 14a. NCM can be used alone as the positive electrode active material 14a, or a mixed material of NCM and LMFP can be used as the positive electrode active material 14a. In this embodiment, NCM with a particle size of 5 μm and LMFP with a particle size of 1 μm are used. The particle size of the positive electrode active material 14a is the particle median diameter D50.

[0049] In LMFP, a higher Mn content enhances the effect of suppressing Mn elution by inhibiting hydrogen fluoride generation through the oxide-based ion conductor 14b. In this embodiment, the composition formula of LMFP is LiMn 1-x Fe x The x value of PO4 is set to 0.5 or less. In other words, LMFP with a higher Mn content than Fe is used.

[0050] The oxide-based ion conductor 14b is a dielectric material that can promote the dissociation of lithium ions from the fluorine-containing lithium salt contained in the electrolyte 15a. The oxide-based ion conductor 14b has a higher dielectric constant than oxides such as Al2O3, and an electrostatic attraction acts on the lithium ions contained in the fluorine-containing lithium salt, promoting the dissociation of lithium ions from the fluorine-containing lithium salt.

[0051] The higher the dielectric constant of the oxide-based ion conductor 14b, the greater the effect of promoting the dissociation of lithium ions from fluorine-containing lithium salts. For this reason, it is desirable that the relative permittivity of the oxide-based ion conductor 14b be 90 or higher, and it is even more desirable that the relative permittivity of the oxide-based ion conductor 14b be 200 or higher.

[0052] The oxide-based ion conductor 14b promotes the dissociation of lithium ions from fluorine-containing lithium salts. Therefore, when the fluorine-containing lithium salt is LiPF6, Li ions are released from LiPF6. + The reaction in which LiPF6 dissociates is "LiPF6 → Li + +PF6 -" occurs preferentially over the reaction "LiPF6 → LiF + PF5" in which PF5 dissociates from LiPF6, promoting the decrease of LiPF6. As a result, the reaction "LiPF6 → LiF + PF5" in which PF5 dissociates from LiPF6 becomes less likely to occur, and the reaction of PF5 with moisture to generate hydrogen fluoride can be suppressed.

[0053] As the oxide-based ion conductor 14b which is a high dielectric, for example, pyrochlore-type oxides, NASICON-type oxides, etc. can be used. As the pyrochlore-type oxide, for example, Li 2-x La (1+x) / 3 Nb2O6F (LLNOF), Li 2-x La (1+x) / 3 Ta2O6F (LLTOF) can be used. These pyrochlore-type oxides have a defect structure, are oxyfluorides, and are Lewis acidic. As the NASICON-type oxide, for example, Li 1+x Al x Ti 2-x (PO4)3 (LATP) can be used. The dielectric constant of LLNOF is higher than that of LATP.

[0054] In this embodiment, a pyrochlore-type oxide is used as the oxide-based ion conductor 14b. The pyrochlore-type oxide has high ionic conductivity and can improve the ionic conductivity of the secondary battery 10. Further, the pyrochlore-type oxide is a material with a high dielectric constant and has a high effect of promoting the dissociation of lithium ions from the fluorine-containing lithium salt. The pyrochlore-type oxide will be described in detail later.

[0055] The addition ratio of the oxide-based ion conductor 14b to the positive electrode active material 14a is not particularly limited. From the viewpoint of achieving both a greater resistance reduction and durability improvement effect and the energy density of the battery, the addition ratio x of the oxide-based ion conductor 14b to the positive electrode active material 14a is preferably, for example, 0 wt% < x ≤ 10 wt%.

[0056] In this embodiment, the oxide-based ionic conductor 14b exhibits electronic conductivity through the insertion of lithium ions, which are conduction ions, into its crystal structure. When the electrode potential of the oxide-based ionic conductor 14b is reduced, the lithium ion insertion and deinsertion reaction of the oxide-based ionic conductor 14b is accelerated. For pyrochlore-type oxides, the electrode potential at which the lithium ion insertion and deinsertion reaction occurs changes depending on the type of cation B. In pyrochlore-type oxides, the effect of exhibiting electronic conductivity can be enhanced when Nb is used as the cation metal represented by B in the composition formula.

[0057] The smaller the particle size of the oxide-based ion conductor 14b, the larger the specific surface area of ​​the oxide-based ion conductor 14b, and the higher the dielectric effect of the oxide-based ion conductor 14b. This increases the effect of the oxide-based ion conductor 14b in promoting the dissociation of lithium ions from the fluorine-containing lithium salt. For this reason, in this embodiment, the particle size of the oxide-based ion conductor 14b is made smaller than the particle size of the positive electrode active material 14a. In this embodiment, the particle size of the positive electrode active material 14a is 1 to 5 μm, and the particle size of the oxide-based ion conductor 14b is 0.1 to 0.5 μm. The particle size of the positive electrode active material 14a and the oxide-based ion conductor 14b is the particle median diameter D50.

[0058] Here, we will describe the pyrochlore-type oxide used as the oxide-based ion conductor 14b of the positive electrode layer 14.

[0059] The pyrochlore-type oxide used in this embodiment has the compositional formula "Aa 2-α Ab (1+α) / 3 B2O 7-β X γIt has a pyrochlore structure represented by the above compositional formula. In the above compositional formula, O is an oxygen atom, and Aa, Ab, B, and X represent any element or group. Aa, Ab, and B are each different types of cations, and O and X are each different types of anions. Aa is an alkali metal cation. Pyrochlore-type oxides contain multiple cations in their composition, consisting of the alkali metal cation Aa and multiple cations Ab and B other than the alkali metal cation Aa. In other words, pyrochlore-type oxides contain multiple cations in their composition, including the alkali metal cation Aa.

[0060] As shown in Figure 6, pyrochlore-type oxides have a crystalline structure in which a three-dimensional octahedral network of BO6 atoms is formed. In BO6 atoms, cation B is at the center, with oxygen atoms at the vertices, and these vertices are shared with adjacent BO6 atoms. Within the three-dimensional network of BO6 atoms, hexagonal tunnel structures are formed in which cation A and anion X are arranged.

[0061] In the above compositional formula, 0.6 < α < 2.0, 0 < β ≤ 1, and 0 < γ ≤ 1. A change in α alters the compositional ratio of Aa and Ab, and a change in β and γ alters the compositional ratio of O and X.

[0062] Cation Aa is an alkali metal cation. Any of Li, Na, K, Rb, or Cs can be used as the alkali metal represented by Aa. Alternatively, Mg or H, which are not alkali metals, may be used as cation Aa. In other words, cation Aa contains at least one selected from Li, Na, K, Rb, Cs, Mg, and H. In this embodiment, Li is used as Aa. The composition ratio (2-α) of Aa is in the range of 0 < (2-α) < 1.4.

[0063] The cation Ab contains at least one lanthanide. At least one of La, Ce, Nd, or Sm can be used as the lanthanide represented by Ab. In this embodiment, La is used as Ab. The composition ratio of Ab (1+α) / 3 is in the range of 0.53 < (1+α) / 3 < 1.

[0064] The basic structure of the cation Ab consists of lanthanides, and some of the lanthanides constituting Ab may be substituted with alkaline earth metals (such as Ca, Mg, and Sr). In this embodiment, the pyrochlore-type oxide has a pyrochlore structure where 0.6 < α < 2.0 and 0 < β ≤ 1. It is thought that the inclusion of lanthanides in this pyrochlore structure creates defects in the crystal structure, thereby improving ionic conductivity. In this embodiment, La is used as Ab.

[0065] In this embodiment, the pyrochlore-type oxide has a composite cation in which cation A in the typical pyrochlore structure's composition formula "A2B2O7" is composed of lithium metal and a lanthanide. This is thought to contribute to the improved ionic conductivity of the pyrochlore-type oxide.

[0066] Cation B is a metallic cation distinct from Aa and Ab, and is a transition metal or a metal selected from group 13 to 15 elements. In a crystal, B forms an octahedron surrounded by six oxygen atoms. As the transition metal represented by B, group 4 or group 5 transition metals can be used, and more specifically, at least one of Nb, Ta, Ti, Zr, Hf, or V can be used. As group 13 elements represented by B, Al, Ga, and In can be used; as group 14 elements, Ge and Sn can be used; and as group 15 elements, Sb and Bi can be used.

[0067] Anion X is a substituteable anion for the oxygen (O) atoms that make up the pyrochlore structure. X has different electronegativity and polarizability from the oxygen atom. At least one of O, F, Cl, Br, I, S, OH, or P can be used as the anion represented by X. The composition ratio γ of X is in the range of 0 < γ ≤ 1, and at least some of the oxygen atoms that make up the pyrochlore structure are substituted with X.

[0068] The pyrochlore-type oxide of this embodiment has a defect structure in which lattice defects are included in the crystal, as some of the oxygen atoms constituting the pyrochlore structure are replaced by anions with different electronegativity and polarizability from the oxygen atoms. It is believed that the ionic conductivity of the pyrochlore-type oxide of this embodiment is improved because the pyrochlore structure contains defect structures.

[0069] Pyrochlore-type oxides are preferably halogen-containing oxides in which a halogen element is used as anion X. Pyrochlore-type oxides containing halogen elements are more likely to exhibit electron conductivity because defects are easily formed in the crystal structure, facilitating the insertion and removal of Li. Among halogen elements, it is particularly desirable to use F as anion X. In other words, pyrochlore-type oxides are preferably acid fluorides in which some of the O is substituted with F.

[0070] In the pyrochlore-type oxide of this embodiment, a portion of Aa and Ab is missing as a defect structure. The composition formula of a typical pyrochlore structure is "A2B2O7", and the composition ratio of cation A is 2. In contrast, in the pyrochlore-type oxide of this embodiment, the composition ratios of Aa and Ab are "2-α" and "(1+α) / 3", respectively, and since 0.6 < α < 2.0, the sum of the composition ratios of Aa and Ab is less than 2. In other words, in the crystal structure of the pyrochlore-type oxide of this embodiment, a portion of at least one of Aa and Ab is missing. The composition ratio corresponding to the missing portions of Aa and Ab is (2α-1) / 3.

[0071] In addition to deviations in compositional ratios, defect structures can also be formed by making the sum of the valencies of the cations consisting of Aa, Ab, and B and the anions consisting of O and X in the above compositional formula negative.

[0072] Furthermore, the pyrochlore-type oxide of this embodiment is a complex anionic compound in which multiple anions such as O and X are contained in the pyrochlore structure. Since there is an anion represented by X in the BO6 octahedron structure, the alkali metal Aa can be located in the center of the space between the BO6 octahedron and the BO6 octahedron without being pushed towards it. For this reason, it is thought that the pyrochlore-type oxide of this embodiment exhibits high ionic conductivity when used with an electric field such as in a battery.

[0073] Furthermore, since α, β, and γ in the above compositional formula affect lattice defects and ionic conductivity, it is desirable to use them within an appropriate range. Larger values ​​of α, β, and γ increase the defect concentration in the crystal lattice, but beyond a certain amount, the concentration of alkali metal represented by Aa decreases, and the ionic conductivity declines. For this reason, it is desirable to control α within the range of 0.6 < α < 2.0, β within the range of 0 < β ≤ 1, and γ within the range of 0 < γ ≤ 1.

[0074] As a pyrochlore-type oxide, "Li 1.25 La 0.58 An example of a pyrochlore-type oxide represented as "Nb2O6F(LLNOF)" is used. In LLNOF, Li is used as cation Aa, La as cation Ab, Nb as cation B, and F as anion X, with α=0.75, β=1, and γ=1.

[0075] The pyrochlore-type oxide of this embodiment is 1 × 10 -3 Ionic conductivity of S / cm or higher has been achieved. The pyrochlore-type oxide of this embodiment exhibits significantly higher ionic conductivity than other oxide-based solid electrolytes such as garnet-type oxides.

[0076] Figure 7 shows the method for producing pyrochlore-type oxide according to this embodiment. In the method for producing pyrochlore-type oxide, the first mixing step S10, the first calcination step S11, the second mixing step S12, and the second calcination step S13 are carried out in order.

[0077] First, a lanthanum source, a lithium source, and a niobium source are prepared as raw materials for the pyrochlore-type oxide, and a first mixing step S10 is performed to mix them. Metal oxides and metal carbon oxides can be used as the lanthanum source, lithium source, and niobium source. In this embodiment, La2O3 is used as the lanthanum source, Li2CO3 as the lithium source, and Nb2O5 as the niobium source. In the first mixing step, La2O3, Li2CO3, and Nb2O5 are mixed in predetermined ratios.

[0078] Next, the first calcination step S11 is performed to calcine the mixture prepared in the first mixing step. The first calcination step S11 consists of two stages. In the first stage, the mixture is calcined in air at 500°C for 6 hours. Calcination removes moisture and other substances from the mixture, thereby increasing its reactivity. Following the calcination, the mixture is calcined in air at 1200°C for 4 hours. This process yields Li, a precursor of the target product. 0.5 La 0.5 Nb2O6 is obtained.

[0079] Next, a second mixing step S12 is performed in which a fluorine source is prepared as a raw material and mixed with the precursor. Metal fluorides can be used as the fluorine source. In this embodiment, LiF and LaF3 are used as the fluorine source. LiF is both a fluorine source and a lithium source, and LaF3 is both a fluorine source and a lanthanum source. In the second mixing step, LiF and LaF3 are mixed with the precursor in a predetermined ratio.

[0080] Next, a second calcination step S13 is performed in which the precursor, LiF, and LaF3 mixture is calcined. In the second calcination step S13, the precursor, LiF, and LaF3 mixture is heated at 1000°C for 6 hours under a nitrogen atmosphere. In the second calcination step S13, in order to suppress compositional shifts due to the volatilization of Li and F elements, calcination may be performed in a sealed state or in a state covered with mother powder.

[0081] By cooling the product from the second calcination process, the composition formula "Li 1.25 La 0.58 A pyrochlore-type oxide represented as "Nb2O6F(LLNOF)" is obtained. The resulting pyrochlore-type oxide is particulate.

[0082] By changing the mixing ratio of La2O3, Li2CO3, Nb2O5, LiF, and LaF3 in the above manufacturing process, "Li 2-α La (1+α) / 3 Nb2O 7-β F γ A pyrochlore-type solid electrolyte represented by can be obtained. By changing the mixing ratio of La2O3, Li2CO3, Nb2O5, LiF, and LaF3, α, β, and γ in the composition formula can be adjusted. In addition, a portion of the material sublimes during firing. Therefore, α, β, and γ can also be adjusted by changing the firing conditions, firing furnace atmosphere, and firing furnace size in the first and second firing processes.

[0083] Next, the initial resistance and durability of the secondary battery 10 will be described using examples and comparative examples. Figure 8 shows the initial resistance and durability of the secondary battery 10 when the type of positive electrode active material 14a, the type or presence of positive electrode additives, the type of negative electrode active material, and the ratio of electrode facing area A to battery capacity B (A / B) are different.

[0084] The secondary batteries 10 of Examples 1 to 11 and Comparative Examples 1 to 6 shown in Figure 8 have the following common configuration: The negative electrode layer 12 uses a conductive additive and a binder consisting of CMC and SBR. The positive electrode layer 14 uses a conductive additive and a binder consisting of PVdF. The electrolyte layer 15 uses an electrolyte solution 15a in which a fluorine-containing lithium salt consisting of LiPF6 is dissolved in a solvent which is a mixture of ethylene carbonate and diethyl carbonate in a 1:1 ratio. The concentration of LiPF6 in electrolyte solution 15a is 1M.

[0085] In Examples 1, 3-11, and Comparative Examples 1, 3-6, NCM811 (LiNi) was used as the positive electrode active material 14a. 0.8 Co 0.1 Mn 0.1 O2) is used. In Example 2 and Comparative Example 2, NCM811 and LMFP (LiMn) are used as the positive electrode active material. 0.6 Fe 0.4 A mixed material was used, consisting of PO4) in a 50% ratio. The particle size of NCM811 used in Examples 1-11 and Comparative Examples 1-6 was 5 μm. The particle size of LMFP used in Example 2 and Comparative Example 2 was 1 μm.

[0086] In this embodiment, the particle size was measured as follows. The target powder was dispersed in ethanol, and the volume-averaged particle size distribution was obtained using a Partica LA-960 laser diffraction / scattering particle size distribution analyzer manufactured by Horiba, Ltd. The particle size is the particle median diameter D50, which is the volume-based particle size when the volume is integrated from the smallest particle in the particle size distribution until it reaches 50% of the total particle volume.

[0087] In Examples 1-8, 10, and 11, LLNOF(Li), a pyrochlore-type oxide which is an example of an oxide-based ion conductor 14b, was used as a positive electrode additive. 1.25 La 0.58 Nb2O6F) is used. In Example 9, LATP(Li), which is a NASICON-type oxide, is used. 1.4 Al 0.4 Ti 1.6(PO4)3) is used. The positive electrode can be manufactured as follows: The positive electrode active material, conductive additive, binder, and oxide ion conductor were mixed and NMP (N-methylpyrrolidone) was added to prepare a paste. This paste was applied to an Al foil current collector and dried. Then, it was pressed to a predetermined thickness and cut to a predetermined electrode size to produce the positive electrode.

[0088] Comparative Examples 1-4 do not have an oxide-based ion conductor 14b in the positive electrode layer 14. In Comparative Example 5, the oxide-based ion conductor 14b in the positive electrode layer 14 is LLZ(Li7La3Zr2O 12 In Comparative Example 6, Al2O3 is provided as a positive electrode additive in the positive electrode layer 14.

[0089] In Examples 1-9 and 11, the addition ratio of oxide-based ion conductor 14b to positive electrode active material 14a was 3 wt%. In Example 10, the addition ratio of oxide-based ion conductor 14b to positive electrode active material 14a was 6 wt%.

[0090] The particle size of the oxide-based ion conductor 14b used in Examples 1-10 and Comparative Examples 5 and 6 is 0.1 μm. The particle size of the oxide-based ion conductor 14b used in Example 11 is 0.5 μm. In Examples 1-11 and Comparative Examples 5 and 6, the particle size of the oxide-based ion conductor 14b is smaller than the particle size of the positive electrode active material 14a.

[0091] The relative permittivity of the oxide-based ion conductor 14b in Examples 1-11 and Comparative Examples 5 and 6 was calculated by dividing the measured dielectric constant ε' of the oxide-based ion conductor 14b by the dielectric constant ε0 of vacuum. The dielectric constant ε0 of vacuum is 8.85 × 10⁻⁶. -12 The value was given as (F / m). The dielectric constant ε' of the oxide-based ionic conductor 14b was measured as follows.

[0092] The oxide-based ion conductor 14b powder to be measured was pressure-molded to produce pellets. The oxide-based ion conductor 14b pellets were sintered at a high temperature. The sintering conditions differed depending on the type of oxide-based ion conductor 14b. For example, LLNOF was wrapped in Pt foil to prevent fluorine volatilization, sealed in an alumina crucible, and heated at 1000°C for 6 hours. The sintered oxide-based ion conductor 14b pellets were removed, and electrodes were formed by sputtering Ag to a thickness of 300 nm on both sides of the pellets to prepare samples for dielectric constant measurement.

[0093] The sample for measurement was placed in a 25°C constant temperature bath and connected to a high-frequency impedance measuring device, and the dielectric constant was measured in voltage mode (PEIS). Impedance measurements were performed with a voltage amplitude of 10mV and a frequency range of 100MHz to 20Hz.

[0094] The dielectric constant ε' of the measurement sample was calculated using the impedance measurement value according to the following formula (1).

[0095]

number

[0096] However, z' = the real part of the impedance, z'' = the imaginary part of the impedance, ω = 2πf, and f = the frequency at which the impedance was measured, which is specifically 11 MHz. C0 is the capacitance when there is no measurement sample, and was calculated using the following formula (2).

[0097]

number

[0098] Here, ε0 = permittivity of vacuum, S = area of ​​the electrode, and d = distance between electrodes.

[0099] Furthermore, the measured dielectric constant may have an error of up to ±10%. This error can be caused by variations in the sintering density of the pellet sample during firing, variations in the contact properties of the Ag electrode in the sample, and other factors. In addition, pyrochlore-type oxides such as LLNOF tend to have larger errors when measuring the dielectric constant because halogens and lithium are desorbed during sintering, causing variations in the content of these elements.

[0100] The relative permittivity of LLNOF used in Examples 1-8, 10, and 11 is 215. The relative permittivity of LATP used in Example 9 is 93. In other words, Examples 1-11 are provided with an oxide-based ion conductor 14b having a high dielectric constant of 90 or more in the positive electrode layer 14. In particular, Examples 1-8, 10, and 11 are provided with an oxide-based ion conductor 14b having an even higher dielectric constant of 200 or more in the positive electrode layer 14.

[0101] The relative permittivity of LLZ used in Comparative Example 5 is 35. The relative permittivity of Al2O3 used in Comparative Example 6 is 3. In other words, in Comparative Example 5, an oxide-based ion conductor 14b having a low dielectric constant of 35 is used in the positive electrode layer 14, while in Comparative Example 6, a positive electrode additive having a low dielectric constant of less than 10 is provided in the positive electrode layer 14.

[0102] In Examples 1, 2, 4-11 and Comparative Examples 1, 2, 4-6, graphite is used as the negative electrode active material for the negative electrode layer 12. In Example 3 and Comparative Example 3, a mixed material of graphite and Si / C composite material is used as the negative electrode active material for the negative electrode layer 12.

[0103] The negative electrode can be manufactured as follows: The negative electrode active material, conductive additive, and binder were mixed with deionized water to form a paste. This paste was applied to a Cu foil current collector and dried. After that, it was pressed to a predetermined thickness and cut to a predetermined electrode size to produce the negative electrode.

[0104] Then, the positive and negative electrodes obtained as described above were stacked with a separator in between to create an electrode body. The fabricated electrode body was placed in a laminate film case, a non-aqueous electrolyte was poured in, and the case was sealed and welded to create a battery.

[0105] In Examples 1, 9, and 11, the electrode facing area A was 810,000 mm². 2 In this example, the battery capacity B is set to 18800mAh, and A / B is set to 43. In Example 2, the electrode facing area A is 810000mm². 2 In this example, the battery capacity B is set to 17,000 mAh, and A / B is set to 48. In Example 3, the electrode facing area A is 810,000 mm². 2 The battery capacity B is set to 19800mAh, and A / B is set to 41.

[0106] In Example 4, the electrode facing area A was 810,000 mm² 2 In this example, the battery capacity B is set to 23,000 mAh, and A / B is set to 35. In Example 5, the electrode facing area A is 810,000 mm². 2 In this example, the battery capacity B is set to 27,000 mAh, and A / B is set to 30. In Example 8, the electrode facing area A is 810,000 mm². 2 The battery capacity B is set to 81000mAh, and A / B is set to 10. In Examples 4, 5, and 8, the A / B value is lower than in Example 1.

[0107] In Example 6, the electrode facing area A was 559,000 mm² 2 In this example, the battery capacity B is set to 13000mAh, and A / B is set to 43. In Example 7, the electrode facing area A is 43000mm². 2 In this example, the battery capacity B is set to 1000mAh, and A / B is set to 43. In Examples 6 and 7, the battery size is different from that of Example 1, but the A / B value is the same as that of Example 1.

[0108] In Example 10, the electrode facing area A was 810,000 mm² 2 The battery capacity B is set to 18240mAh, and A / B is set to 44.

[0109] In Examples 1-11, the ratio of electrode-facing area A to battery capacity B (A / B) is 10-48. In Examples 1-7 and 9-11, A / B is 30 or higher, indicating a larger reaction area. In Examples 1-3, 6, 7, and 9-11, A / B is 40 or higher, indicating an even larger reaction area.

[0110] In Comparative Example 1, the electrode facing area A was 810,000 mm². 2 In this example, the battery capacity B is set to 19370mAh, and A / B is set to 42. In comparative example 2, the electrode facing area A is 810000mm². 2 In this example, the battery capacity B is set to 17510mAh, and A / B is set to 46. In comparative example 3, the electrode facing area A is 810000mm². 2 In this example, the battery capacity B is set to 20400mAh, and A / B is set to 40. In Comparative Example 4, the electrode facing area A is 810000mm². 2 In this example, the battery capacity B is set to 81,000 mAh, and the ratio A / B is set to 10. In comparative examples 1 to 4, the ratio of the electrode facing area A to the battery capacity B, A / B, is 10 or greater.

[0111] In comparative examples 5 and 6, the electrode facing area A was 810,000 mm². 2 In this example, the battery capacity B is set to 18800mAh, and the A / B ratio is set to 43. Comparative Examples 5 and 6 have the same battery size as Example 1, and the ratio of the electrode facing area A to the battery capacity B, A / B, is 30 or more.

[0112] Next, the initial resistance of the secondary batteries 10 in Examples 1 to 11 and Comparative Examples 1 to 6 will be described. The initial resistance is the internal resistance of the secondary battery 10 in its initial state, and the initial resistance shown in Figure 8 is a relative value with the resistance value of Comparative Example 1 set to 100%.

[0113] The resistance of the secondary battery 10 was measured by placing the battery in a constant temperature bath at 25°C and charging it until its state of charge (SOC) reached 50%, after which AC impedance measurement was performed. The AC impedance measurement was performed with an AC amplitude of 10mV and a frequency range of 1MHz to 0.1Hz. A curve was obtained by fitting the waveform of the arc portion of the Nyquist plot obtained from the AC impedance measurement. The value of the x-axis intercept on the low-frequency side of the obtained curve was defined as the internal resistance.

[0114] As shown in Figure 8, in Comparative Examples 1 to 3, where the oxide-based ion conductor 14b is not provided in the positive electrode layer 14 and A / B is 40 to 46, the initial resistance of the secondary battery 10 is 98% to 105%, while in Comparative Example 4, where the oxide-based ion conductor 14b is not provided in the positive electrode layer 14 and A / B is 10, the initial resistance of the secondary battery 10 is 120%. Using these Comparative Examples 1 to 4 as a reference, the initial resistance of the secondary battery 10 can be evaluated by comparing it with that of Comparative Examples 1 to 4. That is, provided that the initial resistance of the secondary battery 10 shown in the example is lower than the initial resistance of the secondary battery 10 shown in the corresponding comparative example, the resistance of the secondary battery 10 shown in the example can be evaluated as being suppressed, that is, the decrease in output of the secondary battery 10 is suppressed.

[0115] In Examples 1-7 and 9-11, where A / B is 30-46, the initial resistance of the secondary battery 10 is 78-98%, while in Example 8, where A / B is 10, the initial resistance of the secondary battery 10 is 105%. Comparing the examples with similar A / B ratios to the comparative examples, Examples 1-7 and 9-11 have lower initial resistances than Comparative Examples 1-3, and Example 8 has a lower initial resistance than Comparative Example 4. In particular, Examples 1-8, 10, and 11, which use LLNOF as the oxide-based ion conductor 14b, show significantly lower initial resistances than Comparative Examples 1-4.

[0116] In Comparative Example 5, where LLZ with a relative permittivity of 35 was used as the oxide-based ion conductor 14b, the initial resistance of the secondary battery 10 was a high value of 150%. In Comparative Example 6, where Al2O3 with a relative permittivity of 3 was used as the positive electrode additive, the initial resistance of the secondary battery 10 was a high value of 288%.

[0117] Next, the durability of the secondary batteries 10 in Examples 1 to 11 and Comparative Examples 1 to 6 will be described. The durability shown in Figure 8 is the battery capacity retention rate of the secondary battery 10 after 100 cycle charge-discharge tests. The durability shown in Figure 8 is a relative value with the durability of Comparative Example 1 set to 100%.

[0118] In the cycle charge / discharge test, the battery was placed in a constant temperature bath at 60°C, and the charge / discharge cycle was repeated 100 times.

[0119] Battery charging was performed using a constant current at a 0.5C rate until the State of Charge (SOC) reached 100%, followed by constant voltage charging, which was terminated when the charging current reached the equivalent of 0.02C. Battery discharging was performed using a constant current at a 0.5C rate until the SOC reached 0%.

[0120] As shown in Figure 8, in Comparative Examples 1 to 3, where the oxide-based ion conductor 14b is not provided in the positive electrode layer 14 and the A / B ratio is 40 to 46, the durability of the secondary battery 10 is 88% to 90.4%. In Comparative Example 4, where the oxide-based ion conductor 14b is not provided in the positive electrode layer 14 and the A / B ratio is 10, the durability of the secondary battery 10 is 88%. By using these Comparative Examples 1 to 4 as a baseline and comparing the durability of the secondary battery 10 with those of Comparative Examples 1 to 4, the durability can be evaluated.

[0121] In Comparative Examples 5 and 6, although the ratio of electrode facing area A to battery capacity B (A / B) is 30 or more, the dielectric constant of the oxide-based ion conductor 14b is less than 100, resulting in a lower durability of the secondary battery 10 (88.8-90%) compared to Comparative Examples 1-3.

[0122] In Examples 1-7 and 9-11, where A / B is 30-46, the durability of the secondary battery 10 is 91.6-97%, while in Example 8, where A / B is 10, the durability of the secondary battery 10 is 90%. Comparing the examples with similar A / B ratios to the comparative example, Examples 1-7 and 9-11 have higher durability than Comparative Example 1, and Example 8 has higher durability than Comparative Example 4. In particular, in Examples 1-7, 10, and 11, where LLNOF is used as the oxide-based ion conductor 14b and A / B is 30 or higher, a high durability of 92.5-97% for the secondary battery 10 was obtained.

[0123] Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, and Example 8 and Comparative Example 4 have similar battery configurations, except for the presence or absence of oxide-based ion conductor 14b (LLNOF) in the positive electrode layer 14. Also, Example 9 and Comparative Example 1 have similar battery configurations, except for the presence or absence of oxide-based ion conductor 14b (LATP) in the positive electrode layer 14.

[0124] In Comparative Example 1, the initial resistance of the secondary battery 10 was 100%, whereas in Example 1, the initial resistance of the secondary battery 10 was reduced to 81%. Furthermore, while the durability of the secondary battery 10 in Comparative Example 1 was 90.4%, the durability of the secondary battery 10 in Example 1 was improved to 94%.

[0125] In Comparative Example 2, the initial resistance of the secondary battery 10 was 105%, while in Example 2, the initial resistance of the secondary battery 10 was reduced to 84%. In Comparative Example 2, the durability of the secondary battery 10 was 93%, while in Example 2, the durability of the secondary battery 10 was improved to 97%.

[0126] In Comparative Example 3, the initial resistance of the secondary battery 10 was 98%, whereas in Example 3, the initial resistance of the secondary battery 10 was reduced to 78%. In Comparative Example 3, the durability of the secondary battery 10 was 88%, while in Example 3, the durability of the secondary battery 10 was improved to 92.5%.

[0127] In Comparative Example 4, the initial resistance of the secondary battery 10 was 120%, whereas in Example 8, the initial resistance of the secondary battery 10 was reduced to 105%. In Comparative Example 4, the durability of the secondary battery 10 was 88%, while in Example 4, the durability of the secondary battery 10 was improved to 90%.

[0128] In Comparative Example 1, the initial resistance of the secondary battery 10 was 100%, whereas in Example 9, the initial resistance of the secondary battery 10 was reduced to 98%. Furthermore, while the durability of the secondary battery 10 in Comparative Example 1 was 90.4%, the durability of the secondary battery 10 in Example 9 was improved to 91.6%.

[0129] From Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, Example 8 and Comparative Example 4, and Example 9 and Comparative Example 1, it can be seen that by providing a highly dielectric oxide-based ion conductor 14b in the positive electrode layer 14, the initial resistance of the secondary battery 10 can be reduced and its durability can be improved. In Example 9, LATP with a relative permittivity of 93 was used as the oxide-based ion conductor 14b, and it was confirmed that if the relative permittivity of the oxide-based ion conductor 14b is 93 or higher, the effect of suppressing the degradation of the secondary battery 10 while suppressing the decrease in output of the secondary battery 10 has been confirmed. Considering the measurement error of the relative permittivity, it is thought that by using an oxide-based ion conductor 14b with a relative permittivity of 90 or higher, the effect of suppressing the degradation of the secondary battery 10 and improving its durability can be obtained.

[0130] In Example 8, the ratio of electrode-facing area A to battery capacity B (A / B) is 10, and the durability of the secondary battery 10 is improved compared to Comparative Example 4, where A / B is 10. In Examples 4 and 5, the ratio of electrode-facing area A to battery capacity B (A / B) is 30 to 35, and the durability of the secondary battery 10 is improved compared to Comparative Example 1, where A / B is 42. In other words, if the ratio of electrode-facing area A to battery capacity B (A / B) is 10 or higher, an effect of improving the durability of the secondary battery 10 is reliably obtained, and if A / B is 30 or higher, an even greater effect of improving the durability of the secondary battery 10 is obtained.

[0131] Examples 6 and 7 differ from Example 1 in terms of electrode facing area A and battery capacity B, but the ratio of electrode facing area A to battery capacity B (A / B) is the same as in Example 1. In Examples 6 and 7, the durability of the secondary battery 10 is the same as in Example 1, at 94%. In other words, by providing a highly dielectric oxide-based ion conductor 14b in the positive electrode layer 14, the durability of the secondary battery 10 can be improved regardless of the battery size.

[0132] According to the embodiment described above, in a secondary battery 10 containing a fluorine-containing lithium salt, LiPF6, in the electrolyte 15a, a positive electrode layer 14 is provided with a positive electrode active material 14a and an oxide-based ion conductor 14b. The oxide-based ion conductor 14b is a dielectric material that has lithium ion conductivity and can promote the dissociation of lithium ions from the fluorine-containing lithium salt. Due to the dielectric effect of the oxide-based ion conductor 14b, the reaction in which lithium ions dissociate from LiPF6 occurs preferentially, and the amount of LiPF6 can be reduced. As a result, the reaction in which PF5 dissociates from LiPF6 becomes less likely to occur, and the generation of hydrogen fluoride can be suppressed. As a result, the deterioration of the secondary battery 10 caused by the generation of hydrogen fluoride from the fluorine-containing lithium salt can be suppressed while suppressing a decrease in the resistance of the secondary battery 10.

[0133] Furthermore, in this embodiment, by using an oxide-based ion conductor 14b (LLNOF, LATP) with a relative permittivity of 90 or higher, the effect of suppressing the generation of hydrogen fluoride and thereby suppressing the degradation of the secondary battery 10 can be enhanced. Moreover, by using an oxide-based ion conductor 14b (LLNOF) with a relative permittivity of 200 or higher, the effect of suppressing the generation of hydrogen fluoride and thereby suppressing the degradation of the secondary battery 10 can be further enhanced.

[0134] Furthermore, in high-power batteries, the larger the reaction area, the greater the impact of hydrogen fluoride on the degradation of the secondary battery 10. Therefore, providing an oxide-based ion conductor 14b enhances the effect of suppressing the degradation of the secondary battery 10 and improving its durability. For this reason, the electrode facing area A (mm²) relative to the battery capacity B (mAh) is important. 2 The ratio A / B is 10 (mm 2In a high-output secondary battery 10 with a power output of 1 / mAh or more, the durability of the secondary battery 10 can be effectively improved by providing a highly dielectric oxide-based ion conductor 14b in the positive electrode layer 14. Furthermore, A / B is 30 (mm) 2 By providing an oxide-based ion conductor 14b in the positive electrode layer 14 of a secondary battery 10 with a capacity of 40 (mm² / mAh or more), the durability of the secondary battery 10 can be more effectively improved, and A / B is 40 (mm² / mAh). 2 By providing an oxide-based ion conductor 14b in the positive electrode layer 14 of a secondary battery 10 with a capacity of 1 / mAh or more, the durability of the secondary battery 10 can be improved even more effectively.

[0135] Furthermore, in this embodiment, a pyrochlore-type oxide, which is an acid fluoride having a defect structure such as LLNOF, is used as the oxide-based ion conductor 14b. Such pyrochlore-type oxides have high ionic conductivity. By using an oxide with high ionic conductivity in the positive electrode layer 14, the resistance of the positive electrode can be reduced, and the output of the secondary battery 10 can be improved.

[0136] Furthermore, in this embodiment, LiPF6 is used as the electrolyte in the electrolyte solution 15a. Since LiPF6 readily generates hydrogen fluoride, providing a highly dielectric oxide-based ion conductor 14b in the positive electrode layer 14 enhances the effect of suppressing the generation of hydrogen fluoride.

[0137] Furthermore, in this embodiment, a positive electrode active material 14a containing Mn is used. Since the Mn contained in the positive electrode active material 14a is easily dissolved by hydrogen fluoride, when a highly dielectric oxide-based ion conductor 14b is provided in the positive electrode layer 14 of a secondary battery 10 using a positive electrode active material 14a containing Mn, the effect of suppressing the degradation of the secondary battery 10 is enhanced.

[0138] Furthermore, in this embodiment, LMFP with a higher Mn content than Fe is used as the positive electrode active material 14a. Therefore, when an oxide-based ion conductor 14b, which is a high dielectric material, is provided in the positive electrode layer 14, the effect of suppressing the degradation of the secondary battery 10 is further enhanced.

[0139] Furthermore, in this embodiment, the particle size of the oxide-based ion conductor 14b is made smaller than the particle size of the positive electrode active material 14a. This increases the specific surface area of ​​the oxide-based ion conductor 14b, thereby enhancing the dielectric effect and increasing the effect of promoting the dissociation of lithium ions from the fluorine-containing lithium salt by the oxide-based ion conductor 14b.

[0140] Furthermore, in this embodiment, the negative electrode active material includes a silicon-based negative electrode material. Silicon-based negative electrode materials have a large water adsorption capacity and readily generate hydrogen fluoride from fluorine-containing lithium salts. Therefore, in a secondary battery 10 in which a silicon-based negative electrode material is included as the negative electrode active material, the generation of hydrogen fluoride from fluorine-containing lithium salts can be effectively suppressed by providing a highly dielectric oxide-based ion conductor 14b in the positive electrode layer 14.

[0141] This disclosure is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of this disclosure. Furthermore, the means disclosed in the embodiments may be combined as appropriate to the extent that they are feasible.

[0142] For example, the shape of the secondary battery 10 is not limited to the form described in the above embodiment, and can be used in various forms such as cylindrical, rectangular, or pouch-type (laminated).

[0143] Furthermore, the secondary battery 10 described in the above embodiment may be configured as a bipolar battery. Bipolar batteries have a structure in which multiple battery cells are stacked and connected in series, and adjacent battery cells share a current collector. In other words, the current collector that contacts the positive electrode of one adjacent battery cell also contacts the negative electrode of the other adjacent battery cell. When bipolar batteries are high-power batteries, they are greatly affected by degradation due to hydrogen fluoride generation. Therefore, in a secondary battery 10 configured as a bipolar battery, degradation due to hydrogen fluoride generation can be effectively suppressed by providing a highly dielectric oxide-based ion conductor 14b in the positive electrode layer 14.

[0144] Furthermore, the secondary battery 10 described in the above embodiment may be configured as an anode-free battery. In an anode-free battery, the negative electrode layer 12 is not formed on the negative electrode current collector 11 in the initial state, and lithium metal is deposited on the negative electrode current collector 11 by lithium ions that move from the positive electrode layer 14 during charging, thereby forming the negative electrode layer 12. The lithium metal constituting the negative electrode layer 12 then moves to the positive electrode layer 14 as lithium ions during discharge. When using an anode-free battery, since the negative electrode layer 12 is not formed in the initial state, the area of ​​the opposing surfaces of the electrodes depends on the area of ​​the positive electrode layer 14.

[0145] The characteristics of the secondary battery disclosed herein are as follows: (Item 1) It comprises a positive electrode layer (14), a negative electrode layer (12), and an electrolyte layer (15) that conducts lithium ions between the positive electrode layer and the negative electrode layer. The positive electrode layer is provided with a positive electrode active material (14a) containing Mn in its composition and an oxide-based ion conductor (14b) having lithium ion conductivity. The electrolyte layer contains a fluorine-containing lithium salt containing fluorine atoms and a solvent capable of dissolving the fluorine-containing lithium salt. The oxide-based ion conductor is a dielectric material that can promote the dissociation of lithium ions from the fluorine-containing lithium salt in a secondary battery. (Item 2) The secondary battery according to item 1, wherein the relative permittivity of the oxide-based ion conductor is 90 or higher. (Item 3) The secondary battery according to item 1 or 2, wherein the oxide-based ion conductor contains an oxyfluoride. (Item 4) The aforementioned oxyfluoride has a pyrochlore-type crystal structure and a defect structure, as described in item 3, for the secondary battery. (Item 5) The area A (mm²) of the opposing surfaces of the positive electrode layer and the negative electrode layer relative to the battery capacity B (mAh) 2 The ratio A / B is 30 (mm2 The secondary battery according to any one of Items 1 to 4, having a capacity of 100 mAh or more. (Item 6) The positive electrode active material contains LiMn 1-x Fe x PO4 (where 0 < x < 1). The secondary battery according to any one of Items 1 to 5. 。 ( Item 7) In the LiMn 1-x Fe x PO4, x is 0.5 or less. The secondary battery according to Item 6. of Secondary battery. (Item 8) The particle diameter of the oxide-based ion conductor is smaller than that of the positive electrode active material. The secondary battery according to any one of Items 1 to 7. (Item 9) The negative electrode layer includes a negative electrode active material. The negative electrode active material includes a silicon-based negative electrode material containing Si. The secondary battery according to any one of Items 1 to 8. (Item 10) In the positive electrode layer, the particulate positive electrode active material and the particulate oxide-based ion conductor are randomly mixed. The secondary battery according to any one of Items 1 to 9. (Item 11) In the positive electrode layer, the outer surface of the particulate positive electrode active material is coated with the oxide-based ion conductor. The secondary battery according to any one of Items 1 to 9. (Item 12) The addition ratio x of the oxide-based ion conductor to the positive electrode active material is 0 wt% < x ≤ 10 wt%. The secondary battery according to any one of Items 1 to 11. [[ID=​​​​​​This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, while various combinations and forms are shown in this disclosure, other combinations and forms that include one, more, or fewer of those elements also fall within the scope and concept of this disclosure.

Claims

1. It comprises a positive electrode layer (14), a negative electrode layer (12), and an electrolyte layer (15) that conducts lithium ions between the positive electrode layer and the negative electrode layer. The positive electrode layer is provided with a positive electrode active material (14a) containing Mn in its composition and an oxide-based ion conductor (14b) having lithium ion conductivity. The electrolyte layer contains a fluorine-containing lithium salt containing fluorine atoms and a solvent capable of dissolving the fluorine-containing lithium salt. The oxide-based ion conductor is a dielectric material that can promote the dissociation of lithium ions from the fluorine-containing lithium salt. The aforementioned oxide-based ion conductor contains an acid fluoride, The aforementioned oxyfluoride has a pyrochlore-type crystal structure and a defect structure in the secondary battery.

2. It comprises a positive electrode layer (14), a negative electrode layer (12), and an electrolyte layer (15) that conducts lithium ions between the positive electrode layer and the negative electrode layer. The positive electrode layer is provided with a positive electrode active material (14a) containing Mn in its composition and an oxide-based ion conductor (14b) having lithium ion conductivity. The electrolyte layer contains a fluorine-containing lithium salt containing fluorine atoms and a solvent capable of dissolving the fluorine-containing lithium salt. The oxide-based ion conductor is a dielectric material that can promote the dissociation of lithium ions from the fluorine-containing lithium salt. The aforementioned oxide-based ion conductor contains an acid fluoride, A secondary battery in which the relative permittivity of the oxide-based ion conductor is 90 or higher.

3. The area A (mm²) of the opposing surfaces of the positive electrode layer and the negative electrode layer relative to the battery capacity B (mAh) ２ The ratio A / B is 30 (mm ２ A secondary battery according to claim 1 or 2, wherein the battery is 1 / mAh or greater.

4. The positive electrode active material includes LiMn １－ｘ Fe ｘ PO ４ The secondary battery according to claim 1 or 2 (provided that 0 < x < 1).

5. The LiMn １－ｘ Fe ｘ PO ４ The secondary battery according to claim 4, wherein x in is 0.5 or less.

6. The secondary battery according to claim 1 or 2, wherein the particle size of the oxide-based ion conductor is smaller than the particle size of the positive electrode active material.

7. The aforementioned negative electrode layer is equipped with a negative electrode active material, The secondary battery according to claim 1 or 2, wherein the negative electrode active material includes a silicon-based negative electrode material containing Si.

8. The secondary battery according to claim 1 or 2, wherein the positive electrode layer is a random mixture of particulate positive electrode active material and particulate oxide-based ion conductor.

9. The secondary battery according to claim 1 or 2, wherein the positive electrode layer has an outer surface of particulate positive electrode active material covered with an oxide-based ion conductor.

10. The secondary battery according to claim 1 or 2, wherein the addition ratio x of the oxide-based ion conductor to the positive electrode active material is 0 wt% < x ≤ 10 wt%.

11. The electrolyte layer has an electrolytic solution (15a) in which a fluorine-containing lithium salt containing LiPF ６ is dissolved, according to claim 1 or 2, the secondary battery.

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