Battery

Abstract

A battery 1000 according to the present disclosure comprises: a positive electrode 201; a negative electrode 203; and an electrolyte layer 202 disposed between the positive electrode 201 and the negative electrode 203. The positive electrode 201 contains a positive electrode active material 204. The positive electrode active material 204 contains an oxide formed from Li, Co, Mn, and O. The electrolyte layer 202 contains Li, Ti, M1, and F. M1 represents at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr.

Description

Technical Field

[0001] The present disclosure relates to a battery. Background Art

[0002] Patent Document 1 discloses an all-solid battery using a sulfide solid electrolyte. Patent Document 2 discloses LiBF4 as a fluoride solid electrolyte material. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2011-129312 Patent Document 2 Japanese Unexamined Patent Publication No. 2008-277170 Summary of the Invention Problem to be Solved by the Invention

[0004] The present disclosure provides a technique for improving the charge-discharge capacity of a battery. Means for Solving the Problem

[0005] The present disclosure provides: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode,[[''END'']] comprising: the positive electrode contains a positive electrode active material, the positive electrode active material contains an oxide composed of Li, Co, Mn, and O, the electrolyte layer contains Li, Ti, M1, and F, and M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr,[[''END'']] a battery. Effect of the Invention

[0006] According to the technology of the present disclosure, the charge and discharge capacity of a battery can be improved. [BRIEF DESCRIPTION OF DRAWINGS]

[0007] [Figure 1] FIG. 1 is a diagram showing a solid electrolyte according to Embodiment 1. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery according to Embodiment 2. [Figure 3] FIG. 3 is a cross-sectional view showing a schematic configuration of a battery according to Embodiment 3. [MODES FOR CARRYING OUT THE INVENTION]

[0008] (Findings forming the basis of the present disclosure) Lithium cobalt manganate is expected as a positive electrode active material that can achieve a high operating voltage. On the other hand, halide solid electrolytes are promising as battery electrolytes because they exhibit excellent lithium ion conductivity. It is considered that combining these materials can achieve a battery with high operating voltage and high output.

[0009] However, as a result of studies by the present inventors, it has been found that a halide solid electrolyte may decompose due to an oxidation reaction during charging of a battery, significantly increasing the internal resistance of the battery. Here, the oxidation reaction means a side reaction in which electrons are extracted from the halide solid electrolyte in contact with the positive electrode active material, in addition to the normal charging reaction in which lithium and electrons are extracted from the positive electrode active material. Along with this oxidation reaction, an oxidative decomposition layer with low lithium ion conductivity is formed between the positive electrode active material and the halide solid electrolyte, and this oxidative decomposition layer is considered to function as large interfacial resistance in the electrode reaction of the positive electrode. As a result, sufficient charge and discharge capacity cannot be obtained.

[0010] The problem of electrolyte decomposition becomes particularly apparent when lithium cobalt manganese oxide is used as a positive electrode active material. Therefore, in order to improve the charge-discharge capacity of a battery using lithium cobalt manganese oxide, it is necessary to suppress the formation of an oxidative decomposition layer caused by a halide solid electrolyte, thereby suppressing an increase in internal resistance.

[0011] Based on the above findings, the present inventors have arrived at the battery of the present disclosure described below.

[0012] (Summary of One Aspect According to the Present Disclosure) The battery according to the first aspect of the present disclosure a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, comprising: the positive electrode contains a positive electrode active material, the positive electrode active material contains an oxide composed of Li, Co, Mn, and O, the electrolyte layer contains Li, Ti, M1, and F, and M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr.

[0013] That is, since the electrolyte contained in the electrolyte layer contains F, it has high oxidation resistance. Since the electrolyte is less prone to oxidative decomposition, decomposition products of the electrolyte are less likely to be generated at the interface between the positive electrode and the electrolyte layer. This suppresses an increase in the internal resistance of the battery. As a result, the charge-discharge capacity of the battery is improved compared to the case where an electrolyte with poor oxidation resistance is used.

[0014] In the second aspect of the present disclosure, for example, in the battery according to the first aspect, the oxide is LiCo x Mn (2-x) O4, and x may satisfy 0<x<2. The oxide represented by this chemical formula is a material obtained by substituting part of Mn in LiMn2O4 having a spinel structure with Co, and is suitable for improving the operating voltage of the battery.

[0015] In a third aspect of this disclosure, for example, in a battery according to the first or second aspect, the positive electrode active material may have a spinel structure. The spinel-type crystal structure is less prone to damage during charging and has excellent stability.

[0016] In a fourth aspect of this disclosure, for example, in a battery according to any one of the first to third aspects, the oxide may have a composition represented by LiCoMnO4. This oxide is a material obtained by substituting some of the Mn in LiMn2O4 having a spinel structure with Co, and is suitable for improving the operating voltage of a battery.

[0017] In a fifth aspect of this disclosure, for example, in a battery according to any one of the first to fourth aspects, M1 may be Al. Al is inexpensive and suitable as an element that improves the ionic conductivity of the electrolyte contained in the electrolyte layer.

[0018] In a sixth aspect of this disclosure, for example, in a battery according to any one of the first to fifth aspects, the positive electrode may further include a positive electrode electrolyte, which may include Li, Ti, M2, and F, wherein M2 may be at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. When the positive electrode electrolyte contains Li, Ti, M2, and F, the same effects obtained in the electrolyte contained in the electrolyte layer are obtained in the positive electrode electrolyte.

[0019] In a seventh aspect of this disclosure, for example, in the battery according to the sixth aspect, the positive electrode electrolyte may have the same composition as the electrolyte contained in the electrolyte layer. With such a configuration, the effects described for the electrolyte contained in the electrolyte layer can be obtained for the positive electrode as a whole.

[0020] In the eighth aspect of this disclosure, for example, in a battery according to any one of the first to seventh aspects, the electrolyte layer may include a first electrolyte layer and a second electrolyte layer, and the second electrolyte layer may be located between the first electrolyte layer and the negative electrode. With such a configuration, an electrolyte with high oxidation resistance can be used as the material for the first electrolyte layer, and an electrolyte with high reduction resistance can be used as the material for the second electrolyte layer.

[0021] In a ninth aspect of this disclosure, for example, in a battery according to the eighth aspect, the first electrolyte layer may contain Li, Ti, M1, and F, and the second electrolyte layer may contain a sulfide solid electrolyte. Electrolytes containing Li, Ti, M1, and F are suitable as materials for the first electrolyte layer because they have excellent oxidation resistance. Sulfide solid electrolytes are suitable as materials for the second electrolyte layer because they have excellent reduction resistance.

[0022] Embodiments of the present disclosure will be described below with reference to the drawings. First, a solid electrolyte usable in the battery of the present disclosure will be described, and then the battery of the present disclosure will be described.

[0023] (Embodiment 1) Figure 1 shows the solid electrolyte 102 in Embodiment 1. The solid electrolyte 102 comprises Li, Ti, M1, and F. M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. Hereinafter, the solid electrolyte 102 will also be referred to as the "first solid electrolyte" in this specification.

[0024] Solid electrolyte 102 has high oxidation resistance because it contains F. This is because F has a high redox potential. On the other hand, F has high electronegativity, so the bond between F and Li is relatively strong. Therefore, the lithium ion conductivity of solid electrolytes containing Li and F tends to be low. For example, LiBF4 disclosed in Patent Document 2 has a conductivity of 6.67 × 10⁻⁶. -9It has a low ionic conductivity of S / cm. In contrast, the solid electrolyte 102 in this embodiment contains Ti and M1 in addition to Li and F. As a result, for example, 1 × 10 -8 Ionic conductivity of S / cm or higher can be achieved.

[0025] M1 is typically Al. Al is inexpensive and suitable as an element to improve the ionic conductivity of the solid electrolyte 102.

[0026] It is desirable that the solid electrolyte 102 does not contain sulfur. A sulfur-free solid electrolyte does not generate hydrogen sulfide when exposed to the atmosphere, and therefore offers superior safety. The sulfide solid electrolyte disclosed in Patent Document 1 may generate hydrogen sulfide when exposed to the atmosphere.

[0027] To increase ionic conductivity, the solid electrolyte 102 may contain anions other than F. The anions other than F are at least one selected from the group consisting of Cl, Br, I, O, and Se.

[0028] The solid electrolyte 102 may consist substantially of Li, Ti, M1, and F. Here, "the solid electrolyte 102 consists substantially of Li, Ti, M1, and F" means that the molar ratio (i.e., mole fraction) of the total amount of substance of Li, Ti, M1, and F to the total amount of substance of all elements constituting the solid electrolyte 102 is 90% or more. For example, this molar ratio may be 95% or more. The solid electrolyte 102 may consist only of Li, Ti, M1, and F.

[0029] However, the solid electrolyte 102 may contain elements that are inevitably mixed in. Examples of such elements include hydrogen, oxygen, and nitrogen. Such elements may be present in the raw material powder of the solid electrolyte 102 or in the atmosphere used for manufacturing and storing the solid electrolyte 102.

[0030] In order to further increase the ionic conductivity of the solid electrolyte 102, the ratio of the amount of Li substance to the total amount of Ti and M1 substances may be not less than 1.7 and not more than 4.2.

[0031] The solid electrolyte 102 may have a composition represented by the following formula (1). Formula (1) satisfies 0<x<1 and 0<b≦1.5.

[0032] Li 6-(4-x)b (Ti 1-x M1 x ) b F6 ··· Formula (1)

[0033] In order to increase the ionic conductivity of the solid electrolyte 102, formula (1) may satisfy 0.1≦x≦0.9.

[0034] In order to increase the ionic conductivity of the solid electrolyte 102, formula (1) may satisfy 0.8≦b≦1.2.

[0035] When having the specific composition represented by formula (1), the solid electrolyte 102 exhibits, for example, the following ionic conductivity. For example, when M1 is Zr, the solid electrolyte 102 exhibits an ionic conductivity of about 2.1 µS / cm. When M1 is Mg, the solid electrolyte 102 exhibits an ionic conductivity of about 2.1 µS / cm. When M1 is Ca, the solid electrolyte 102 exhibits an ionic conductivity of about 0.02 µS / cm. When M1 is Al, the solid electrolyte 102 exhibits an ionic conductivity of about 5.4 µS / cm. On the other hand, the oxidation resistance of the solid electrolyte 102 is mainly attributed to F. Considering these facts, even if M1 is replaced from one specific element to another, the charge and discharge capacity of the battery is still improved.

[0036] The solid electrolyte 102 may be crystalline or amorphous.

[0037] The shape of the solid electrolyte 102 is not limited. The solid electrolyte 102 may have a particulate shape. Examples of the particulate shape include acicular shape, spherical shape, and ellipsoidal spherical shape. The solid electrolyte 102 may have a pellet shape or a plate shape.

[0038] When the shape of the solid electrolyte 102 is, for example, particulate, the particles of the solid electrolyte 102 may have a median diameter of 0.1 µm or more and 100 µm or less. The median diameter means a particle diameter at which the cumulative particle volume in a volume-based particle size distribution is 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measuring apparatus or an image analysis apparatus.

[0039] The particles of the solid electrolyte 102 may have a median diameter of 0.5 µm or more and 10 µm or less. Thereby, the solid electrolyte 102 has higher ionic conductivity. Furthermore, when the solid electrolyte 102 is mixed with another material such as an active material, a good dispersion state between the solid electrolyte 102 and the other material can be obtained.

[0040] The solid electrolyte 102 is produced, for example, by the following method.

[0041] Raw material powders are prepared and mixed so as to obtain a target composition. The raw material powders are, for example, halides.

[0042] As an example, when the target composition is Li 2.7 Ti 0.3 Al 0.7 F₆, LiF, TiF₄, and AlF₃ are mixed at a molar ratio of approximately 2.7:0.3:0.7. The raw material powders may be mixed at a molar ratio adjusted in advance so as to offset compositional changes that may occur in the synthesis process.

[0043] The raw material powders are reacted mechanochemically with each other in a mixing device such as a planetary ball mill, i.e., by a mechanochemical milling method, a reaction product is obtained. The reaction product may be calcined in a vacuum or an inert atmosphere. Alternatively, the mixture of raw material powders may be calcined in a vacuum or an inert atmosphere to obtain the reaction product. Calcination is carried out, for example, at a temperature of 100°C or higher and 300°C or lower for 1 hour or more. To suppress compositional changes during calcination, the raw material powders may be calcined in a sealed container such as a quartz tube.

[0044] Solid electrolyte 102 is obtained by the method described above.

[0045] (Embodiment 2) Figure 2 is a cross-sectional view showing the schematic configuration of the battery 1000 in Embodiment 2. The battery 1000 comprises a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The positive electrode 201 and the electrolyte layer 202 are positioned between the positive electrode 201 and the negative electrode 203.

[0046] (Electrolyte layer 202) The electrolyte layer 202 is in contact with the positive electrode 201 and the negative electrode 203. The electrolyte layer 202 contains the solid electrolyte 102 described in Embodiment 1. Therefore, the advantageous effects described in Embodiment 1 can be obtained in the electrolyte layer 202. That is, because the solid electrolyte 102 contains F, it has high oxidation resistance. Since the solid electrolyte 102 is not easily oxidized and decomposed, decomposition products of the solid electrolyte 102 are less likely to be generated at the interface between the positive electrode 201 and the electrolyte layer 202. This suppresses an increase in the internal resistance of the battery 1000. As a result, the charge and discharge capacity of the battery 1000 is improved compared to when a solid electrolyte with poor oxidation resistance is used. This effect is maximized when the positive electrode 201 contains lithium cobalt manganese oxide.

[0047] The electrolyte layer 202 may consist substantially of the solid electrolyte 102, or it may contain another solid electrolyte having a different composition from that of the solid electrolyte 102. The solid electrolyte 102 may also be the main component of the electrolyte layer 202. "The electrolyte layer 202 consists substantially of the solid electrolyte 102" means that, apart from unavoidable impurities, no materials other than the solid electrolyte 102 have been intentionally added.

[0048] In this specification, "principal component" refers to the component that is present in the highest amount by mass.

[0049] Other solid electrolytes include Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li3(Al,Ga,In)X6, and LiI. X is at least one selected from the group consisting of F, Cl, Br, and I. One or more of these selected solid electrolytes or mixtures thereof may be used as the other solid electrolyte. In this specification, the other solid electrolyte may be referred to as the "second solid electrolyte".

[0050] In this specification, when elements in a chemical formula are represented as "(Al,Ga,In)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(Al,Ga,In)" is synonymous with "at least one element selected from the group consisting of Al, Ga, and In". The same applies to other elements.

[0051] When the electrolyte layer 202 contains not only the first solid electrolyte, which is the solid electrolyte 102, but also the second solid electrolyte, the first and second solid electrolytes may be uniformly dispersed in the electrolyte layer 202. As will be described later, the layer made of the first solid electrolyte and the layer made of the second solid electrolyte may be stacked along the stacking direction of the battery 1000.

[0052] To increase the energy density and output of the battery 1000, the electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less.

[0053] (Positive electrode 201) The positive electrode 201 comprises a positive electrode active material 204 and a positive electrode electrolyte 100.

[0054] The positive electrode active material 204 comprises a material capable of occluding and releasing metal ions such as lithium ions. In the present embodiment, the positive electrode active material 204 comprises an oxide composed of Li, Co, Mn, and O. In other words, the positive electrode active material 204 comprises lithium cobalt manganate. Lithium cobalt manganate is a material suitable for increasing the operating voltage of the battery 1000.

[0055] The oxide composed of Li, Co, Mn, and O is, for example, LiCo x Mn (2-x) has a composition represented by O4. x satisfies 0<x<2. x may satisfy 0<x<0.6. The oxide typically has a composition represented by LiCoMnO4. The oxides represented by these chemical formulas are materials obtained by substituting a part of Mn in LiMn2O4 having a spinel structure with Co, and are suitable for increasing the operating voltage of the battery 1000. The oxide composed of Li, Co, Mn, and O may also have a spinel structure. The expression "oxide composed of Li, Co, Mn, and O" means that no elements other than Li, Co, Mn, and O are intentionally added, excluding unavoidable impurities. The spinel-type crystal structure is less likely to be broken even during charging and is excellent in stability.

[0056] The positive electrode active material 204 may contain known positive electrode active materials other than lithium cobalt manganate. Lithium cobalt manganate may be a main component of the positive electrode active material 204.

[0057] The positive electrode electrolyte 100 comprises Li, Ti, M2, and F. M2 is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. The positive electrode electrolyte 100 may be a solid electrolyte. When the positive electrode electrolyte 100 contains Li, Ti, M2, and F, the same effect as that obtained in the solid electrolyte 102 can be obtained in the positive electrode electrolyte 100.

[0058] The positive electrode electrolyte 100 may have the same composition as the electrolyte contained in the electrolyte layer 202. In other words, the positive electrode electrolyte 100 may have the same composition as the solid electrolyte 102. In this case, the effects described for the solid electrolyte 102 are obtained for the entire positive electrode 201. Of course, the positive electrode electrolyte 100 may have a different composition from the solid electrolyte 102.

[0059] The positive electrode 201 may contain only the positive electrode electrolyte 100, or it may contain another electrolyte having a different composition from the positive electrode electrolyte 100. The positive electrode electrolyte 100 may be the main component of the electrolyte contained in the positive electrode 201.

[0060] The positive electrode active material 204 has, for example, a particle shape. The positive electrode electrolyte 100 has, for example, a particle shape.

[0061] The particles of the positive electrode active material 204 may have a median diameter of 0.1 μm or more and 100 μm or less. When the particles of the positive electrode active material 204 have a median diameter of 0.1 μm or more, the dispersion state of the particles of the positive electrode active material 204 and the particles of the positive electrode electrolyte 100 in the positive electrode 201 becomes good. This improves the charge and discharge characteristics of the battery 1000. When the particles of the positive electrode active material 204 have a median diameter of 100 μm or less, the lithium diffusion rate within the particles of the positive electrode active material 204 improves. This allows the battery 1000 to operate at high power.

[0062] The particles of the positive electrode active material 204 may have a larger median diameter than the particles of the positive electrode electrolyte 100. This results in a better dispersion state of the particles of the positive electrode active material 204 and the particles of the positive electrode electrolyte 100 in the positive electrode 201.

[0063] In order to increase the energy density and output of the battery 1000, the ratio of the volume of the positive electrode active material 204 to the sum of the volume of the positive electrode active material 204 and the volume of the positive electrode electrolyte 100 in the positive electrode 201 may be 0.30 or more and 0.95 or less.

[0064] At least a portion of the surface of the positive electrode active material 204 may be covered with a coating layer. The coating layer may be formed on the surface of the positive electrode active material 204, for example, before mixing the positive electrode active material 204 with a conductive additive and a binder. Examples of coating materials included in the coating layer include sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. If the positive electrode electrolyte 100 contains a sulfide solid electrolyte, the coating material may contain the first solid electrolyte described in Embodiment 1 in order to suppress the oxidative decomposition of the sulfide solid electrolyte. If the positive electrode electrolyte 100 contains the first solid electrolyte described in Embodiment 1, the coating material may contain an oxide solid electrolyte in order to suppress the oxidative decomposition of the first solid electrolyte. As the oxide solid electrolyte, lithium niobate, which has excellent stability at high potentials, may be used. By suppressing the oxidative decomposition of the solid electrolyte, the rise in overvoltage of the battery can be suppressed.

[0065] To increase the energy density and output of battery 1000, the positive electrode 201 may have a thickness of 10 μm or more and 500 μm or less.

[0066] (Negative electrode 203) The negative electrode 203 includes a negative electrode active material 205 and a negative electrode electrolyte 101.

[0067] The negative electrode active material 205 includes a material capable of intercalating and releasing metal ions such as lithium ions. Examples of negative electrode active material 205 include metallic materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. The metallic material may be a pure metal or an alloy. Examples of metallic materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, carbon in the process of graphitization, carbon fibers, spheroidal carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, preferred examples of negative electrode active materials are silicon (i.e., Si), tin (i.e., Sn), silicon compounds, and tin compounds. One or more of these materials can be used as the negative electrode active material 205.

[0068] Examples of negative electrode electrolytes 101 include sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes.

[0069] The negative electrode electrolyte 101 may have the same composition as the electrolyte contained in the electrolyte layer 202. In other words, the negative electrode electrolyte 101 may have the same composition as the solid electrolyte 102. Of course, the negative electrode electrolyte 101 may have a different composition from the solid electrolyte 102.

[0070] The negative electrode 203 may contain only the negative electrode electrolyte 101 as its electrolyte, or it may contain another electrolyte having a different composition from the negative electrode electrolyte 101. The negative electrode electrolyte 101 may be the main component of the electrolyte contained in the negative electrode 203.

[0071] The negative electrode active material 205 may be selected considering the reduction resistance of the negative electrode electrolyte 101. For example, if the negative electrode 203 contains the first solid electrolyte described in Embodiment 1, the negative electrode active material 205 may be a material capable of intercalating and releasing lithium ions at a voltage of 0.27 V or higher relative to lithium. Examples of such negative electrode active materials include titanium oxide, indium metal, and lithium alloy. An example of titanium oxide is Li4Ti5O 12 Examples include LiTi2O4 and TiO2. By using these negative electrode active materials 205, the reductive decomposition of the first solid electrolyte contained in the negative electrode 203 can be suppressed. As a result, the charge and discharge capacity of the battery 1000 is improved.

[0072] The negative electrode active material 205 has, for example, a particle shape. The negative electrode electrolyte 101 has, for example, a particle shape.

[0073] The particles of the negative electrode active material 205 may have a median diameter of 0.1 μm or more and 100 μm or less. When the particles of the negative electrode active material 205 have a median diameter of 0.1 μm or more, the dispersion state of the particles of the negative electrode active material 205 and the particles of the negative electrode electrolyte 101 in the negative electrode 203 becomes good. This improves the charge and discharge characteristics of the battery 1000. When the particles of the negative electrode active material 205 have a median diameter of 100 μm or less, the lithium diffusion rate within the particles of the negative electrode active material 205 improves. This allows the battery 1000 to operate at high power.

[0074] The particles of the negative electrode active material 205 may have a larger median diameter than the particles of the negative electrode electrolyte 101. This results in a better dispersion state of the particles of the negative electrode active material 205 and the particles of the negative electrode electrolyte 101 in the negative electrode 203.

[0075] In order to increase the energy density and output of the battery 1000, the ratio of the volume of the negative electrode active material 205 to the sum of the volume of the negative electrode active material 205 and the volume of the negative electrode electrolyte 101 in the negative electrode 203 may be 0.30 or more and 0.95 or less.

[0076] To increase the energy density and output of battery 1000, the negative electrode 203 may have a thickness of 10 μm or more and 500 μm or less.

[0077] (Other configurations) At least one selected from the group consisting of a positive electrode 201, an electrolyte layer 202, and a negative electrode 203 may contain a second solid electrolyte for the purpose of enhancing ionic conductivity, chemical stability, and electrochemical stability.

[0078] The second solid electrolyte may be a sulfide solid electrolyte.

[0079] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12These are some examples.

[0080] The negative electrode electrolyte 101 may contain a sulfide solid electrolyte. By covering the negative electrode active material 205 with an electrochemically stable sulfide solid electrolyte, it is possible to prevent the solid electrolyte 102 contained in the electrolyte layer 202 from coming into contact with the negative electrode active material 205. This suppresses the reductive decomposition of the solid electrolyte 102 contained in the electrolyte layer 202. As a result, the increase in the internal resistance of the battery 1000 is suppressed.

[0081] The second solid electrolyte may be an oxide solid electrolyte.

[0082] Examples of oxide solid electrolytes include the following materials. (i) NASICON-type solid electrolytes such as LiTi2(PO4)3 or its elemental substitutions, (ii) Perovskite-type solid electrolytes such as (LaLi)TiO3, (iii) Li 14 ZnGe4O 16 , LiSICON-type solid electrolytes such as Li4SiO4, LiGeO4, or elementally substituted versions thereof, (iv)Li7La3Zr2O 12 or garnet-type solid electrolytes such as those with elemental substitutions, (v) Li3PO4 or its N-substituted derivative

[0083] As explained earlier, the second solid electrolyte may be a halide solid electrolyte.

[0084] Other examples of halide solid electrolytes include Li a Me b Y cThis is a compound represented by X6, where a+mb+3c=6 and c>0 are satisfied. Me is at least one selected from the group consisting of metallic elements other than Li and Y and metalloid elements. m represents the valence of Me. "Metalloid elements" are B, Si, Ge, As, Sb, and Te. "Metallic elements" are all elements in groups 1 through 12 of the periodic table (except hydrogen), and all elements in groups 13 through 16 of the periodic table (except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0085] To increase the ionic conductivity of the halide solid electrolyte, Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. The halide solid electrolyte may be Li3YCl6 or Li3YBr6.

[0086] The second solid electrolyte may be a polymer solid electrolyte. The polymer solid electrolyte may be a compound of a polymer compound and a lithium salt. The polymer compound may have an ethylene oxide structure. Polymer compounds having an ethylene oxide structure can contain a large amount of lithium salt. Therefore, the ionic conductivity can be further increased. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One type of lithium salt may be used alone, or two or more types may be used in combination.

[0087] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a non-aqueous electrolyte, a gel electrolyte, or an ionic liquid for the purpose of facilitating the transfer of lithium ions and improving the output characteristics of the battery.

[0088] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0089] Examples of non-aqueous solvents include cyclic carbonate ester solvents, linear carbonate ester solvents, cyclic ether solvents, linear ether solvents, cyclic ester solvents, linear ester solvents, and fluorine solvents. Examples of cyclic carbonate ester solvents include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of linear carbonate ester solvents include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic ether solvents include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of linear ether solvents include 1,2-dimethoxyethane and 1,2-diethoxyethane. Examples of cyclic ester solvents include γ-butyrolactone. Examples of linear ester solvents include methyl acetate. Examples of fluorine solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone. Alternatively, a combination of two or more non-aqueous solvents selected from these may be used.

[0090] Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L or more and 2 mol / L or less.

[0091] As the gel electrolyte, a polymer material impregnated with a non-aqueous electrolyte can be used. Examples of polymer materials include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polymers having ethylene oxide bonds.

[0092] Examples of cations contained in ionic liquids include (i) aliphatic chain quaternary salts such as tetraalkylammonium and tetraalkylphosphonium, (ii) aliphatic cyclic ammonium compounds such as pyrrolidinium, morpholinium, imidazolinium, tetrahydropyrimidinium, piperadinium, and piperidinium, and (iii) nitrogen-containing heterocyclic aromatic cations such as pyridinium and imidazolium.

[0093] An anion contained in ionic liquids is PF6. - BF4 - SbF6 - AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , C(SO2CF3)3 - These are some examples.

[0094] The ionic liquid may contain lithium salts.

[0095] At least one selected from the group consisting of a positive electrode 201, an electrolyte layer 202, and a negative electrode 203 may contain a binder for the purpose of improving the adhesion between particles.

[0096] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamide-imide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethylcellulose. Copolymers can also be used as binders. Such binders may be copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. A mixture of two or more materials selected from these materials may also be used as a binder.

[0097] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive to reduce electronic resistance.

[0098] Examples of conductive additives include (i) graphites such as natural graphite and artificial graphite, (ii) carbon blacks such as acetylene black and Ketjenblack, (iii) conductive fibers such as carbon fibers and metal fibers, (iv) carbon fluoride, (v) metal powders such as aluminum, (vi) conductive whiskers such as zinc oxide and potassium titanate, (vii) conductive metal oxides such as titanium oxide, and (viii) conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. To reduce costs, conductive additives of (i) or (ii) above may be used.

[0099] Battery 1000 may be an all-solid-state battery, or a battery that uses a liquid electrolyte or gel electrolyte in part. Battery 1000 may be a primary battery or a secondary battery.

[0100] Battery 1000 can have the following shapes: coin-shaped, cylindrical, prismatic, sheet-shaped, button-shaped, flat, or stacked.

[0101] The battery 1000 can be manufactured, for example, by preparing a material for forming a positive electrode, a material for forming an electrolyte layer, and a material for forming a negative electrode, and then fabricating a laminate in which the positive electrode, electrolyte layer, and negative electrode are arranged in this order using a known method.

[0102] (Embodiment 3) Figure 3 is a cross-sectional view showing the schematic configuration of the battery 2000 in Embodiment 3. Except that the electrolyte layer 202 is composed of multiple layers, the battery 2000 has the same configuration as the battery 1000 in Embodiment 2.

[0103] The electrolyte layer 202 includes a first electrolyte layer 212 and a second electrolyte layer 222. The first electrolyte layer 212 is located between the positive electrode 201 and the second electrolyte layer 222. The second electrolyte layer 222 is located between the first electrolyte layer 212 and the negative electrode 203. With this configuration, an electrolyte with high oxidation resistance can be used as the material for the first electrolyte layer 212, and an electrolyte with high reduction resistance can be used as the material for the second electrolyte layer 222. The second electrolyte layer 222 is separated from the positive electrode 201 by the first electrolyte layer 212. Therefore, oxidative decomposition of the electrolyte contained in the second electrolyte layer 222 can be suppressed. The first electrolyte layer 212 is separated from the negative electrode 203 by the second electrolyte layer 222. Therefore, reductive decomposition of the electrolyte contained in the first electrolyte layer 212 can be suppressed.

[0104] The first electrolyte layer 212 is in contact with the positive electrode 201. The second electrolyte layer 222 is in contact with the negative electrode 203. The first electrolyte layer 212 is in contact with the second electrolyte layer 222. The electrolyte layer 202 may have another layer disposed between the first electrolyte layer 212 and the second electrolyte layer 222.

[0105] The solid electrolyte contained in the second electrolyte layer 222 may have a lower reduction potential than the solid electrolyte contained in the first electrolyte layer 212. This prevents the solid electrolyte contained in the first electrolyte layer 212 from being reduced. As a result, the charge and discharge efficiency of the battery 2000 is improved.

[0106] For example, if the first electrolyte layer 212 contains the first solid electrolyte described in Embodiment 1, the second electrolyte layer 222 may contain a sulfide solid electrolyte to suppress the reductive decomposition of the first solid electrolyte. In other words, the first electrolyte layer 212 contains Li, Ti, M1, and F. The first solid electrolyte is suitable as a material for the first electrolyte layer 212 because it has excellent oxidation resistance. The sulfide solid electrolyte is suitable as a material for the second electrolyte layer 222 because it has excellent reduction resistance. By using materials suitable for the first electrolyte layer 212 and the second electrolyte layer 222, the decomposition of the electrolyte in the electrolyte layer 202 can be effectively suppressed. As a result, the charge and discharge efficiency of the battery 2000 is improved. [Examples]

[0107] The present disclosure will be described in more detail below with reference to examples and comparative examples.

[0108] <Example 1> (Preparation of the first solid electrolyte) In an argon atmosphere, LiF, TiF4, and AlF3 were weighed as raw material powders in a molar ratio of LiF:TiF4:AlF3 = 2.7:0.3:0.7. These raw material powders were then milled using a planetary ball mill (Fritsch, P-7 type) at 500 rpm for 12 hours to produce Li as the first solid electrolyte. 2.7 Ti 0.3 Al0.7 We obtained powder F6.

[0109] [Fabrication of positive electrode active material] A mixture was obtained by mixing 0.40 g of lithium carbonate, 1.24 g of manganese carbonate, and 1.42 g of cobalt carbonate hydrate in a mortar. The mixture was then calcined at 800°C for 48 hours to obtain a positive electrode active material represented by LiCoMnO4.

[0110] [Fabrication of cathode materials] LiCoMnO4, Li 2.7 Ti 0.3 Al 0.7 F6 and VGCF (manufactured by Showa Denko Corporation) as a conductive additive were weighed in a mass ratio of 27.8:64.7:7.5. These materials were then mixed in a mortar. This prepared the positive electrode material for Example 1. "VGCF" is a registered trademark of Showa Denko Corporation.

[0111] <Reference example 1> [Fabrication of cathode materials] The cathode material for Reference Example 1 was prepared in the same manner as in Example 1, except that Li3YBr2Cl4 was used as the first solid electrolyte.

[0112] [Battery construction] A battery using the positive electrode material of Example 1 and Reference Example 1 was fabricated by the following process.

[0113] First, 80 mg of Li6PS5Cl powder was placed inside an insulating outer casing and molded under pressure of 2 MPa. Next, 20 mg of the first solid electrolyte powder was added and molded under pressure of 2 MPa. Furthermore, 25.2 mg of the positive electrode material was added and molded under pressure of 720 MPa. This resulted in a laminate consisting of a positive electrode and an electrolyte layer.

[0114] Next, a layer of metallic lithium foil was laminated onto the laminate so that the electrolyte layer was positioned between the metallic lithium foil, which served as the negative electrode, and the positive electrode. The thickness of the metallic lithium foil was 200 μm. The laminate was then pressurized at a pressure of 2 MPa to produce a laminate consisting of a positive electrode, an electrolyte layer, and a negative electrode.

[0115] Next, stainless steel current collectors were placed above and below the laminate. Current collector leads were attached to the current collectors.

[0116] Finally, the insulating outer casing was sealed with an insulating ferrule so that the inside of the insulating outer casing was isolated from the outside atmosphere. Through these steps, the batteries of Example 1 and Reference Example 1 were obtained.

[0117] [Charge / Discharge Test] The charge and discharge tests of the batteries in Example 1 and Reference Example 1 were conducted under the following conditions.

[0118] First, the battery was placed in a constant temperature bath at 85°C.

[0119] Next, with a current value of 42μA, which corresponds to a 0.05C rate (20-hour rate) relative to the battery's theoretical capacity, the voltage is 5.3V (vs. Li / Li + Constant current charging was performed until the battery was fully charged. The charging capacity during this charging process was measured as the initial charging capacity.

[0120] Next, at a current value of 42μA, which corresponds to a 0.05C rate (20-hour rate), the voltage is 3.0V (vs.Li / Li). + A constant current discharge was performed until the discharge rate was reached. The discharge capacity during this discharge process was measured as the initial discharge capacity.

[0121] The results are shown in Table 1. The characteristics of the solid electrolyte and battery in Example 1 and Reference Example 1 are shown in Table 1.

[0122] [Table 1]

[0123] In Reference Example 1, where Li3YBr2Cl4 was used as the solid electrolyte, the voltage was 5.3V (vs.Li / Li + During the charging process up to ), Li3YBr2Cl4 was oxidatively decomposed. Therefore, the battery in Reference Example 1 could hardly be discharged. On the other hand, if Li3YBr2Cl4 is used instead, 2.7 Ti 0.3 Al0.7 In Example 1, where F6 was used as the solid electrolyte, an initial discharge capacity of 101 mAh / g was obtained. + In the case of ), in order to suppress the decomposition of the solid electrolyte and improve the charge / discharge capacity, Li should be used as the solid electrolyte. 2.7 Ti 0.3 Al 0.7 It becomes clear that using F6 is important.

[0124] The reason why the initial charge capacity of Reference Example 1 is so large is thought to be as follows: In Reference Example 1, oxidative decomposition of Li3YBr2Cl4 is likely to occur during the charging process, and the oxidation current caused by the oxidative decomposition of Li3YBr2Cl4 flows for a long time. As a result, the battery voltage does not rise easily, it takes a long time to reach the charging completion voltage, and the charge capacity also increases. [Industrial applicability]

[0125] The technology disclosed herein is useful, for example, in all-solid-state lithium-ion secondary batteries.

Claims

1. Positive electrode and, The negative electrode and, An electrolyte layer disposed between the positive electrode and the negative electrode, Equipped with, The positive electrode includes a positive electrode active material. The positive electrode active material comprises an oxide composed of Li, Co, Mn, and O. The electrolyte layer comprises a solid electrolyte containing Li, Ti, M1, and F. The aforementioned M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. The positive electrode further comprises a positive electrode electrolyte, The positive electrode electrolyte comprises Li, Ti, M2, and F. The aforementioned M2 is at least one selected from the group consisting of Ca, Mg, Al, and Zr. The solid electrolyte contained in the electrolyte layer has a composition represented by the following formula (1): Li 6-(4-x)b (Ti 1-x M1 x ) b F 6 ...Formula (1) The above equation (1) satisfies 0 < x < 1 and 0 < b ≤ 1.5, The positive electrode electrolyte has the same composition as the solid electrolyte contained in the electrolyte layer. battery.

2. The oxide is LiCo x Mn (2-x) O 4 Having a composition represented by, x satisfies 0 < x < 2. The battery according to claim 1.

3. The positive electrode active material has a spinel structure. The battery according to claim 1.

4. The oxide is LiCoMnO 4 Having a composition represented by, The battery according to claim 1.

5. The above M1 is Al. The battery according to claim 1.

6. The formula (1) satisfies 0.1 ≤ x ≤ 0.9 and 0.8 ≤ b ≤ 1.2, The battery according to claim 1.

7. The electrolyte layer includes a first electrolyte layer and a second electrolyte layer. The second electrolyte layer is located between the first electrolyte layer and the negative electrode. The battery according to claim 1.

8. The first electrolyte layer comprises the solid electrolyte, The second electrolyte layer contains a sulfide solid electrolyte. The battery according to claim 7.

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