Negative electrode active material and solid battery including the negative electrode active material

Abstract

The present invention provides a solid-state battery that has a sufficiently high capacity retention rate at a heightened charging rate, and sufficiently little interfacial resistance between a negative electrode active material and a solid electrolyte that has a garnet crystal structure. The present invention pertains to a negative electrode active material that has a β-LVO crystal structure, some of the vanadium of the β-LVO crystal structure being substituted with one or more elements capable of forming a four-coordinate structure.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material and a solid battery including the negative electrode active material.

Background Art

[0002] In recent years, the demand for batteries has significantly increased as a power source for portable electronic devices such as mobile phones and portable personal computers. For batteries used in such applications, electrolytes (electrolyte solutions) such as organic solvents have conventionally been used as a medium for moving ions.

[0003] However, in a battery having the above configuration, there is a risk of electrolyte leakage, and moreover, there is a problem that organic solvents and the like used in the electrolyte are flammable substances. For this reason, it has been proposed to use a solid electrolyte instead of the electrolyte solution. In addition, the development of a solid secondary battery (so-called "solid battery") using a solid electrolyte as the electrolyte and having other components also made of solids is underway.

[0004] As a negative electrode active material for a solid battery, a negative electrode active material having an unsubstituted β II -Li3VO4 (LVO) type crystal structure or a γ-Li3VO4 (LVO) type crystal structure composed of only Li, V, and O is known (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The inventor of the present invention noticed that there are problems to be overcome in the conventional technology as described above and found the necessity to take countermeasures therefor. Specifically, the inventor of the present invention found that there are the following new problems.

[0007] In a solid battery using an unsubstituted β II -Li3VO4 (LVO) type crystal structure as the negative electrode active material, although the initial reversible capacity is high, in a solid battery using a solid electrolyte having a garnet type crystal structure, the interface resistance between the negative electrode active material and the solid electrolyte is relatively high. On the other hand, in a solid battery using a γ-Li3VO4 (LVO) type crystal structure as the negative electrode active material, although the initial reversible capacity is high, the capacity retention rate when the charging rate is increased is relatively low.

[0008] The present invention has been made in view of such problems. That is, an object of the present invention is to provide a solid battery having a sufficiently high capacity retention rate when the charging rate is increased and a sufficiently small interface resistance between the negative electrode active material and a solid electrolyte having a garnet type crystal structure.

Means for Solving the Problems

[0009] The present invention relates to a negative electrode active material having a β-LVO type crystal structure and in which a part of the V element of the β-LVO type crystal structure is substituted by one or more elements capable of taking a four-coordinate structure.

[0010] The present invention also relates to a solid battery including a negative electrode layer, a positive electrode layer, and a solid electrolyte layer disposed between the negative electrode layer and the positive electrode layer, wherein the negative electrode layer contains the negative electrode active material.

Effects of the Invention

[0011] The solid battery containing the negative electrode active material of the present invention has a sufficiently high capacity retention rate when the charging rate is increased and a sufficiently small interface resistance between the negative electrode active material and a solid electrolyte having a garnet type crystal structure.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0013] [Solid Battery] The present invention provides a solid battery. As used herein, the "solid battery" broadly refers to a battery in which the electrolyte layer as its component is solid, and narrowly refers to an "all-solid battery" in which all its components are solid. The "solid battery" as used herein includes a so-called "secondary battery" capable of repeated charging and discharging, and a "primary battery" capable of discharging only. The "solid battery" is preferably a "secondary battery". The "secondary battery" is not to be overly restricted by its name, and may include, for example, a "power storage device".

[0014] The solid battery of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, and usually has a laminated structure in which the solid electrolyte layer is laminated between the positive electrode layer and the negative electrode layer. The positive electrode layer and the negative electrode layer may each be laminated in two or more layers as long as the solid electrolyte layer is provided between them. The solid electrolyte layer is in contact with the positive electrode layer and the negative electrode layer and is sandwiched between them. The positive electrode layer and the solid electrolyte layer may be integrally fired, and / or the negative electrode layer and the solid electrolyte layer may be integrally fired. Being integrally fired means that two or more adjacent or contacting members (especially layers) are fired together. The two or more members (especially layers) may all be fired bodies, and it is preferable that they are integrally fired. The solid battery of the present invention can be referred to as a "fired solid battery" or a "co-fired solid battery" in the sense that the positive electrode layer and the solid electrolyte layer are integrally fired, and / or the negative electrode layer and the solid electrolyte layer are integrally fired.

[0015] (Negative electrode layer) The negative electrode layer contains a negative electrode active material and may further contain a solid electrolyte. In the negative electrode layer, both the negative electrode active material and the solid electrolyte may be in the form of fired bodies. For example, when the negative electrode layer contains a negative electrode active material and a solid electrolyte, while the solid electrolyte binds between the negative electrode active material particles, the space between the negative electrode active material particles and between the negative electrode active material particles and the solid electrolyte may have a form of a fired body that is mutually joined by firing.

[0016] The negative electrode active material has a β-LVO type structure, but a part of the V element in the β-LVO type crystal structure is replaced by one or more elements that can form a four-coordinate structure. For the negative electrode active material to have a β-LVO type structure means that the negative electrode active material (especially its particles) has a β-LVO type crystal structure. By including a negative electrode active material having a β-LVO type structure in the negative electrode layer, the capacity retention rate when the charging rate is increased is improved. Furthermore, when at least one of the negative electrode layer or the solid electrolyte layer contains a solid electrolyte having a garnet type crystal structure, if the negative electrode layer does not contain a negative electrode active material having a β-LVO type structure (for example, when the negative electrode layer contains only a negative electrode active material having a γ-Li3VO4 (LVO) type crystal structure), the capacity retention rate when the charging rate is increased decreases.

[0017] The capacity retention rate characteristic is a characteristic related to the capacity retention rate when the charging rate is increased, and is the maintenance rate ((C1 / C 0.1 ) × 100 (%)) of the charging capacity (C1) when charging is performed at 1C with respect to the charging capacity (C 0.1 ) when charging is performed at 0.1C. The higher the capacity retention rate characteristic, the more preferable. When charging is performed at a high rate, the charging capacity at the same voltage decreases compared to when charging is performed at a low rate.

[0018] The interfacial resistance characteristic is a characteristic related to the interfacial resistance between the negative electrode active material and the solid electrolyte, and the smaller the interfacial resistance characteristic, the more preferable.

[0019] Specific examples of the β-LVO type crystal structure of the negative electrode active material include, for example, β II -Li3VO4 type crystal structure and the like. Among these, from the viewpoint of further improving the capacity retention rate characteristic and the interfacial resistance characteristic, it is preferable for the negative electrode active material to have a β II -Li3VO4 type structure. Note that it is sufficient if at least the main component contained in the negative electrode active material has a β-LVO type crystal structure.

[0020] For the negative electrode active material to have a β II -Li3VO4 type structure means that the negative electrode active material (especially its particles) has a βII -It means having a crystal structure of the Li3VO4 type, and in a broad sense, β is defined by those skilled in the art in the field of solid-state batteries II -It means having a crystal structure that can be recognized as a crystal structure of the Li3VO4 type. In a narrow sense, the negative electrode active material is β II -When the negative electrode active material has a β-Li3VO4 type structure, it means that the negative electrode active material (especially its particles) shows one or more main peaks corresponding to the Miller indices specific to the β II -Li3VO4 type crystal structure at a predetermined incident angle. As an example of a negative electrode active material having a β II -Li3VO4 type structure, for example, ICDD Card No. 01-073-6058 can be mentioned.

[0021] The negative electrode active material contains one or more elements that can take a four-coordinate structure. The element that can take a four-coordinate structure is an element that can be substituted for the V element having a four-coordinate structure in the β-LVO type crystal structure. Therefore, in the present invention, although the negative electrode active material has a β-LVO type crystal structure, a part of the V element of the β-LVO type crystal structure is substituted by one or more elements that can take a four-coordinate structure. By the negative electrode active material containing one or more elements that can take a four-coordinate structure, the capacity retention rate characteristics are improved. Furthermore, when at least one of the negative electrode layer or the solid electrolyte layer contains a solid electrolyte having a garnet-type crystal structure, the interfacial resistance characteristics between the solid electrolyte and the negative electrode active material are improved. Even if the negative electrode layer contains a negative electrode active material having a β-LVO type structure, if the negative electrode active material does not contain an element that can take a four-coordinate structure, the interfacial resistance characteristics between the solid electrolyte and the negative electrode active material deteriorate.

[0022] Examples of the element that can take a four-coordinate structure include Zn, Al, Ga, Si, Ge, P, Ti, S, and Cr, etc. The negative electrode active material usually contains one or more elements selected from the group consisting of the above elements as the element that can take a four-coordinate structure. From the viewpoint of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, it is preferable that the negative electrode active material contains, as the element that can take a four-coordinate structure, one element selected from the group consisting of the above elements alone.

[0023] From the perspective of further improving the capacity retention characteristics and interfacial resistance characteristics, the negative electrode active material contains, as an element capable of forming a four-coordinate structure, at least one element preferably selected from the group consisting of Si, Ge, P, and Ti, more preferably contains only one element selected from the group, and still more preferably contains only one element selected from the group consisting of Si, Ge, and Ti.

[0024] In the present invention, the negative electrode active material has the β-LVO type crystal structure as described above, but a part of the V element of the β-LVO type crystal structure is substituted by at least one element capable of forming a four-coordinate structure. From the perspective of further improving the capacity retention characteristics and interfacial resistance characteristics, when at least one element capable of forming a four-coordinate structure is defined as Z, and r = the amount of substance of Z / (the amount of substance of V element + the amount of substance of Z), it is preferable to satisfy 0 < r ≤ 0.20. In particular, it is preferable to satisfy the relationship of 0.005 ≤ r ≤ 0.200. When Z contains two or more elements, r is a number based on the total number thereof. The amount of substance of the V element and the amount of substance of Z can be calculated by obtaining the following general formula (1) as the average chemical composition of the negative electrode active material. Note that r obtained from the amounts of substance of V and Z contained in the negative electrode active material, and y in the general formula (1) representing the average chemical composition of the negative electrode active material detailed below correspond to each other, and the value of r may be used as y in the general formula (1).

[0025] From the perspective of further improving the capacity retention characteristics and interfacial resistance characteristics, the negative electrode active material has the general formula (1):

Chemical formula

[0026] In formula (1), A is one or more elements selected from the group consisting of Na (sodium), K (potassium), Mg (magnesium), Ca (calcium), Al (aluminum), Ga (gallium), Zn (zinc), Fe (iron), Cr (chromium), and Co (cobalt). From the perspective of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, A is one or more elements selected from the group consisting of Mg, Al, Ga, and Zn. Z is one or more elements that can take the above-mentioned four-coordinate structure. From the perspective of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, Z is preferably one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, P, Ti, S, and Cr, and more preferably one or more elements selected from the group consisting of Si, Ge, P, and Ti. From the perspective of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, it is even more preferable that Z is a single element selected from each of the above-mentioned groups. x satisfies the relationship of 0 ≦ x ≦ 1.00. From the perspective of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, x preferably satisfies the relationship of 0 ≦ x ≦ 0.20, and more preferably is 0. When A contains two or more elements, x is a number based on the total number of them. y is defined as y = amount of substance of Z / (amount of substance of V + amount of substance of Z) when the element that can take the above-mentioned four-coordinate structure with V is Z. It satisfies the relationship of 0 < y ≦ 0.200, and particularly satisfies the relationship of 0.005 ≦ y ≦ 0.200. When Z contains two or more elements, y is a number based on the total number of y for each of these elements. For example, the value corresponding to y for the element Z1 that can take the four-coordinate structure is represented as y Z1 and so on. Also, for example, the value corresponding to y for the element Z2 that can take the four-coordinate structure is represented as y Z2 and so on. For example, when Z contains only Z1 and Z2, the sum of y Z1 and y Z2 only needs to satisfy the above y range. Specifically, y Z1 = amount of substance of Z1 / {amount of substance of V + (amount of substance of Z1 + amount of substance of Z2)} and y Z2 = amount of substance of Z2 / {amount of substance of V + (amount of substance of Z1 + amount of substance of Z2)}, and the calculated yZ1 and y Z2 The sum of and y only needs to satisfy the range of the above y. y corresponds to r derived based on the amounts of substances V and Z contained in the negative electrode active material as defined above. Specifically, y in the general formula (1) may be used as the value of r obtained based on the amounts of substances V and Z contained in the negative electrode active material. δ represents the amount of oxygen deficiency and may be 0. δ usually only needs to satisfy 0 ≦ δ ≦ 0.5. Since the amount of oxygen deficiency δ cannot be quantitatively analyzed even using the latest device, it may be considered to be 0. a is the average valence of A. The average valence of A is, for example, when as A, n1 elements X with valence a +, n2 elements Y with valence b +, and n3 elements Z with valence c + are recognized, the value represented by (n1×a + n2×b + n3×c) / (n1 + n2 + n3). b is the average valence of Z. The average valence of Z is, for example, when as Z, n1 elements X with valence a +, n2 elements Y with valence b +, and n3 elements Z with valence c + are recognized, the same value as the above-mentioned average valence of A.

[0027] In formula (1), particularly, the preferred value of y may be determined depending on Z. By y satisfying the following range, a β-LVO structure is likely to be obtained, which is preferable. However, it is not necessarily limited to the following composition range, and the effects of the present invention can be obtained by Z being contained in the β-LVO structure. For example, when Z contains Si (particularly when Z is Si alone), y satisfies the relationship of 0 < y ≦ 0.050. From the viewpoint of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, preferably 0.005 ≦ y ≦ 0.050, more preferably 0.005 ≦ y ≦ 0.045, still more preferably 0.015 ≦ y ≦ 0.045, and particularly preferably 0.025 ≦ y ≦ 0.045. From the viewpoint of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, the range of the above y when Z contains Si is the value corresponding to y for Si. si can be set as.

[0028] For example, when Z contains Ge (especially when Z is Ge alone), y satisfies the relationship of 0 < y ≤ 0.100, and from the viewpoint of further improving the capacity retention characteristic and the interface resistance characteristic, preferably 0.005 ≤ y ≤ 0.100, more preferably 0.015 ≤ y ≤ 0.100, still more preferably 0.030 ≤ y ≤ 0.100, and particularly preferably 0.060 ≤ y ≤ 0.100. From the viewpoint of further improving the capacity retention characteristic and the interface resistance characteristic, the range of y in the case where Z contains Ge is the value of y corresponding to y with respect to Ge Ge can be set as.

[0029] For example, when Z contains Ti (especially when Z is Ti alone), y satisfies the relationship of 0 < y ≤ 0.150, and from the viewpoint of further improving the capacity retention characteristic and the interface resistance characteristic, preferably 0.005 ≤ y ≤ 0.130, more preferably 0.010 ≤ y ≤ 0.120, still more preferably 0.030 ≤ y ≤ 0.110, and particularly preferably 0.060 ≤ y ≤ 0.110. From the viewpoint of further improving the capacity retention characteristic and the interface resistance characteristic, the range of y in the case where Z contains Ti is the value of y corresponding to y with respect to Ti Ti can be set as.

[0030] For example, when Z contains P (especially when Z contains only P and Si), y satisfies the relationship of 0 < y ≤ 0.080, and from the viewpoint of further improving the capacity retention characteristic and the interface resistance characteristic, preferably 0.010 ≤ y ≤ 0.060, more preferably 0.020 ≤ y ≤ 0.050, still more preferably 0.030 ≤ y ≤ 0.050, and particularly preferably 0.035 ≤ y ≤ 0.045. In particular, when Z contains only P and elements other than P (especially Si), the above y is the y corresponding to y with respect to P P (that is, y based only on P) and the number based on the sum of y corresponding to y with respect to elements Z3 other than P Z3 is. y p satisfies the relationship of 0 < y p ≤ 0.100, and from the viewpoint of further improving the capacity retention characteristic and the interface resistance characteristic, preferably 0.005 ≤ y p≦0.070, more preferably 0.005 ≦ y p ≦0.050, even more preferably 0.010 ≦ y p satisfies the relationship of ≦0.040. Specifically, y P = the amount of substance of P / {the amount of substance of V + (the amount of substance of P + the amount of substance of element Z3 other than P)} calculated y P is the above y P only needs to satisfy the range. y Z3 is 0 < y Z3 satisfies the relationship of ≦0.100. From the perspective of further improving the capacity retention rate characteristics and interfacial resistance characteristics, preferably 0.005 ≦ y Z3 ≦0.070, more preferably 0.005 ≦ y Z3 ≦0.050, even more preferably 0.010 ≦ y Z3 satisfies the relationship of ≦0.040. Specifically, y Z3 = the amount of substance of element Z3 other than P / {the amount of substance of V + (the amount of substance of P + the amount of substance of element Z3 other than P)} calculated y Z3 is the above y Z3 only needs to satisfy the range.

[0031] Specific examples of the negative electrode active material include, for example, Li 3.01 (V 0.99 Si 0.01 )O4, Li 3.02 (V 0.98 Si 0.02 )O4, Li 3.04 (V 0.96 Si 0.04 )O4, Li 3.01 (V 0.98 Ge 0.02 )O4, Li 3.02 (V 0.95 Ge 0.05 )O4, Li 3.04 (V 0.91 Ge 0.09 )O4, Li 3.01 (V 0.98 Ti 0.02 )O4, Li 3.02 (V 0.96 Ti 0.04 )O4, Li 3.10 (V 0.90 Ti 0.10 )O4, Li 3.02 (V0.96 Si 0.02 P 0.02 )O4), etc. can be mentioned.

[0032] The chemical composition of the negative electrode active material may be an average chemical composition. The average chemical composition of the negative electrode active material means the average value of the chemical composition of the negative electrode active material in the thickness direction of the negative electrode layer. The average chemical composition of the negative electrode active material can be analyzed and measured by breaking the solid battery and performing composition analysis by EDX or WDX in a field of view that includes the entire thickness direction of the negative electrode layer using SEM-EDX (energy dispersive X-ray spectroscopy) or WDX (wavelength dispersive X-ray analysis). In the negative electrode layer, the average chemical composition of the negative electrode active material and the average chemical composition of the solid electrolyte described later can be automatically distinguished and measured according to their compositions in the above composition analysis.

[0033] The negative electrode active material can be produced, for example, by the following method. First, a raw material compound containing a predetermined metal atom is weighed so that the chemical composition becomes a predetermined chemical composition, water is added and mixed to obtain a slurry. The slurry is dried, calcined at 700 °C or higher and 1000 °C or lower for 4 hours or longer and 6 hours or shorter, and pulverized to obtain a negative electrode active material.

[0034] The average particle size of the negative electrode active material is not particularly limited, and may be, for example, 0.01 μm or more and 20 μm or less, preferably 0.1 μm or more and 5 μm or less.

[0035] The average particle size of the negative electrode active material can be obtained, for example, by randomly selecting 10 or more and 100 or less particles from the SEM image and simply averaging their particle sizes to obtain the average particle size (arithmetic mean). The particle size is defined as the diameter of a spherical particle assuming that the particle is a perfect sphere. Such a particle size can be obtained, for example, by cutting out a cross-section of the solid battery, taking a cross-sectional SEM image using SEM, calculating the cross-sectional area S of the particles using image analysis software (for example, "A Image-kun" (manufactured by Asahi Kasei Engineering Co., Ltd.)), and then obtaining the particle diameter R using the following formula.

[0036]

Number

[0037] Note that the average particle diameter of the negative electrode active material in the negative electrode layer can be automatically measured by specifying the negative electrode active material according to the composition when measuring the above-mentioned average chemical composition. Since the particle diameter of the negative electrode active material can be easily discriminated by performing a thermal etching treatment after polishing, a thermal etching treatment may be performed before measuring the average particle diameter. Specifically, the average particle diameter of the negative electrode active material may be the average particle diameter after heat treatment at 700 °C for 1 hour after polishing.

[0038] The volume ratio of the negative electrode active material in the negative electrode layer is not particularly limited, and from the viewpoint of further improving the capacity retention rate characteristics and the interfacial resistance characteristics, it is preferably 20% or more and 80% or less, more preferably 30% or more and 75% or less, and even more preferably 30% or more and 60% or less.

[0039] The volume ratio of the negative electrode active material in the negative electrode layer can be measured from the SEM image after FIB cross-section processing. Specifically, the cross-section of the negative electrode layer is observed using SEM-EDX and / or WDX. The site where V is detected from EDX and / or WDX is determined to be the negative electrode active material, and by calculating the area ratio of the above site, it is possible to measure the volume ratio of the negative electrode active material.

[0040] The particle shape of the negative electrode active material in the negative electrode layer is not particularly limited, and may be, for example, any of a spherical shape, a flat shape, and an irregular shape.

[0041] The negative electrode layer may further contain a solid electrolyte in addition to the negative electrode active material. The solid electrolyte contained in the negative electrode layer is not particularly limited, and examples thereof include a solid electrolyte having a garnet-type crystal structure, a solid electrolyte having a LISICON-type crystal structure, a solid electrolyte having a perovskite-type crystal structure, a solid electrolyte having an amorphous structure, and an oxide glass ceramic-based lithium ion conductor (for example, a phosphate compound (LATP) containing lithium, aluminum, and titanium as constituent elements, a phosphate compound (LAGP) containing lithium, aluminum, and germanium as constituent elements), and the like. It is preferable that at least one of the negative electrode layer or the solid electrolyte layer described later (particularly at least the negative electrode layer, preferably both the negative electrode layer and the solid electrolyte layer) contains a solid electrolyte having a garnet-type crystal structure. By including a solid electrolyte having a garnet-type crystal structure in at least one of the negative electrode layer or the solid electrolyte layer (particularly at least the negative electrode layer, preferably both the negative electrode layer and the solid electrolyte layer), not only excellent capacity retention characteristics can be obtained, but also excellent interfacial resistance characteristics between the above-described negative electrode active material and the solid electrolyte having the garnet-type crystal structure can be obtained. That at least one of the negative electrode layer or the solid electrolyte layer contains a solid electrolyte having a garnet-type crystal structure means that one of the negative electrode layer or the solid electrolyte layer may contain a solid electrolyte having a garnet-type crystal structure, or both of them may contain a solid electrolyte having a garnet-type crystal structure. When both the negative electrode layer and the solid electrolyte layer contain a solid electrolyte having a garnet-type crystal structure, the solid electrolyte having a garnet-type crystal structure contained in the negative electrode layer and the solid electrolyte having a garnet-type crystal structure contained in the solid electrolyte layer may have the same chemical composition or may have different chemical compositions from each other. From the viewpoint of further improving the capacity retention characteristics and the interfacial resistance characteristics, it is preferable that both the negative electrode layer and the solid electrolyte layer contain a solid electrolyte having a garnet-type crystal structure.

[0042] The solid electrolyte having a garnet-type crystal structure shall mean not only a solid electrolyte having simply a "garnet-type crystal structure", but also a solid electrolyte having a "garnet-type similar crystal structure". Specifically, in X-ray diffraction, the solid electrolyte has a crystal structure that can be recognized as a garnet-type or garnet-type similar crystal structure by those skilled in the art in the field of solid-state batteries. More specifically, in X-ray diffraction, the solid electrolyte may show one or more main peaks corresponding to the Miller indices specific to a so-called garnet-type crystal structure (diffraction pattern: ICDD Card No. 01-080-6142) at a predetermined incident angle, or as a garnet-type similar crystal structure, one or more main peaks corresponding to the Miller indices specific to a so-called garnet-type crystal structure may show one or more main peaks whose incident angle (i.e., peak position or diffraction angle) and intensity ratio (i.e., peak intensity or diffraction intensity ratio) are different due to the difference in composition. Representative diffraction patterns of garnet-type similar crystal structures include, for example, ICDD Card No. 00-045-0109, etc.

[0043] The solid electrolyte having a garnet-type crystal structure is, for example, of the general formula (2): [Chemical formula] preferably has an average chemical composition represented by. By including a solid electrolyte having the above average chemical composition in the negative electrode layer, further improvement in the capacity retention characteristic and the interfacial resistance characteristic can be achieved.

[0044] In formula (2), A is one or more elements selected from the group consisting of Ga (gallium), Al (aluminum), Mg (magnesium), Zn (zinc), and Sc (scandium). Z is one or more elements selected from the group consisting of Nb (niobium), Ta (tantalum), W (tungsten), Te (tellurium), Mo (molybdenum), and Bi (bismuth). x has a relationship of 0 ≦ x ≦ 0.5. y has a relationship of 0 ≦ y ≦ 2.0. a is the average valence of A, which is the same as the average valence of A in formula (1). b is the average valence of Z, which is the same as the average valence of Z in formula (1).

[0045] In formula (2), from the viewpoint of further improving the capacity retention characteristics and the interfacial resistance characteristics, in a preferred embodiment, it is as follows: A is one or more elements selected from the group consisting of Ga and Al. Z is one or more elements selected from the group consisting of Nb, Ta, W, Mo, and Bi. x has a relationship of 0.1 ≦ x ≦ 0.3. When A contains two or more elements, x is a number based on the total number of x for each of these elements. y has a relationship of 0 ≦ y ≦ 1.0, preferably 0 ≦ y ≦ 0.7. When Z contains two or more elements, y is a number based on the total number of y for each of these elements. a is the average valence of A. b is the average valence of Z.

[0046] As specific examples of the solid electrolyte represented by general formula (2), for example, (Li 6.4 Ga 0.05 Al 0.15 )La3Zr2O 12 , (Li 6.4 Ga 0.2 )La3Zr2O 12 , Li 6.4 La3(Zr 1.6 Ta 0.4 )O 12 , (Li 6.4 Al 0.2 )La3Zr2O 12 , Li 6.5 La3(Zr 1.5 Mo 0.25 )O 12 may be mentioned.

[0047] The average chemical composition of the solid electrolyte (especially the solid electrolyte having a garnet-type crystal structure) in the negative electrode layer means the average value of the chemical composition of the solid electrolyte in the thickness direction of the negative electrode layer. The average chemical composition of the solid electrolyte can be analyzed and measured by breaking the solid battery and performing composition analysis by EDX in a field of view that encompasses the entire thickness direction of the negative electrode layer using SEM-EDX (energy-dispersive X-ray spectroscopy). In the negative electrode layer, the average chemical composition of the negative electrode active material and the average chemical composition of the solid electrolyte can be automatically distinguished and measured according to their compositions in the above composition analysis.

[0048] The solid electrolyte in the negative electrode layer can be obtained by the same method as the negative electrode active material except by using a raw material compound containing a predetermined metal atom, or can also be obtained as a commercially available product.

[0049] The volume ratio of the solid electrolyte (especially the solid electrolyte having a garnet-type crystal structure) in the negative electrode layer is not particularly limited, and from the viewpoint of further improving the capacity retention characteristics and the interfacial resistance characteristics, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0050] The volume ratio of the solid electrolyte in the negative electrode layer can be measured by the same method as the volume ratio of the negative electrode active material. The fact that it is a garnet-type solid electrolyte is based on the site where Zr and / or La are detected by EDX and / or WDX.

[0051] In addition to the negative electrode active material and the solid electrolyte, the negative electrode layer may further contain, for example, a sintering aid and a conductive material.

[0052] As the sintering aid, a sintering aid known in the field of solid-state batteries can be used. From the viewpoint of further improving the capacity retention characteristics and the interfacial resistance characteristics, as a result of investigations by the inventors, it has been found that the composition of the sintering aid contains at least Li (lithium), B (boron), and O (oxygen), and it is preferable that the molar ratio of Li to B (Li / B) is 2.0 or more. These sintering aids have low melting points, and densification of the negative electrode layer is possible at a lower temperature by promoting liquid-phase sintering. Examples of the sintering aid include Li3BO3, (Li 2.7 Al 0.3 )BO3, Li 2.8 (B 0.8 C 0.2 )O3, etc. Among these, it is particularly preferable to use (Li 2.7 Al 0.3 )BO3, which has particularly high ionic conductivity.

[0053] The volume ratio of the sintering aid in the negative electrode layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 0.1% or more and 10% or less, and more preferably 1% or more and 7% or less. Note that the battery characteristics mean the characteristics of the battery required in the fields where battery use or power storage is assumed, and include, for example, capacity retention characteristics, interfacial resistance characteristics, etc.

[0054] The volume ratio of the sintering aid in the negative electrode layer can be measured by the same method as the volume ratio of the negative electrode active material. As the detection element in EDX and / or WDX for determining the region of the sintering aid, attention can be paid to B.

[0055] In the negative electrode layer, as the conductive material, a conductive material known in the field of solid-state batteries can be used. From the viewpoint of improving the performance of battery characteristics, preferably used conductive materials include, for example, metal materials such as Ag (silver), Au (gold), Pd (palladium), Pt (platinum), Cu (copper), Sn (tin), Ni (nickel); and carbon materials such as carbon nanotubes such as acetylene black, ketjen black, Super P (registered trademark), VGCF (registered trademark), etc. Regarding the shape of the carbon material, it is not particularly limited, and any shape such as spherical, plate-like, fibrous, etc. may be used. From the viewpoint of improving the performance of battery characteristics, it is preferable to use a metal material (especially Ag) as the conductive material.

[0056] The volume ratio of the conductive material in the negative electrode layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0057] The volume ratio of the conductive material in the negative electrode layer can be measured by the same method as the volume ratio of the negative electrode active material. From SEM-EDX and WDX analysis, the site where only the signal of the used metal element is observed can be regarded as the conductive material.

[0058] In the negative electrode layer, the porosity is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0059] The porosity of the negative electrode layer uses the value measured from the SEM image after FIB cross-section processing.

[0060] The negative electrode layer is a layer that can be called a "negative electrode active material layer". The negative electrode layer may have a so-called negative electrode current collector or negative electrode current collecting layer.

[0061] (Positive electrode layer) In the present invention, the positive electrode layer is not particularly limited. For example, the positive electrode layer contains a positive electrode active material. The positive electrode layer preferably has a form of a fired body containing positive electrode active material particles.

[0062] The positive electrode active material is not particularly limited, and positive electrode active materials known in the field of solid-state batteries can be used. Examples of the positive electrode active material include, for example, lithium-containing phosphate compound particles having a NASICON-type structure, lithium-containing phosphate compound particles having an olivine-type structure, lithium-containing layered oxide particles, lithium-containing oxide particles having a spinel-type structure, and the like. Specific examples of the preferably used lithium-containing phosphate compound having a NASICON-type structure include Li3V2(PO4)3 and the like. Specific examples of the preferably used lithium-containing phosphate compound having an olivine-type structure include Li3Fe2(PO4)3, LiMnPO4, and the like. Specific examples of the preferably used lithium-containing layered oxide particles include LiCoO2, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2 and the like. Specific examples of the preferably used lithium-containing oxide having a spinel-type structure include LiMn2O4, LiNi 0.5 Mn 1.5 O4, Li4Ti5O 12 and the like. From the viewpoint of reactivity during co-firing with the LISICON-type solid electrolyte used in the present invention, as the positive electrode active material, lithium-containing layered oxides such as LiCoO2, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2 are more preferably used. Note that only one type of these positive electrode active material particles may be used, or a plurality of types may be mixed and used.

[0063] When the positive electrode active material has a NASICON-type structure in the positive electrode layer, it means that the positive electrode active material (especially its particles) has a NASICON-type crystal structure. In a broad sense, it means having a crystal structure that can be recognized as a NASICON-type crystal structure by those skilled in the art of solid-state batteries. In a narrow sense, when the positive electrode active material has a NASICON-type structure in the positive electrode layer, it means that the positive electrode active material (especially its particles) shows one or more main peaks corresponding to the Miller indices specific to the so-called NASICON-type crystal structure at a predetermined incident angle in X-ray diffraction. Preferred positive electrode active materials having a NASICON-type structure include the compounds exemplified above.

[0064] When the positive electrode active material has an olivine-type structure in the positive electrode layer, it means that the positive electrode active material (especially its particles) has an olivine-type crystal structure. In a broad sense, it means having a crystal structure that can be recognized as an olivine-type crystal structure by those skilled in the art of solid-state batteries. In a narrow sense, when the positive electrode active material has an olivine-type structure in the positive electrode layer, it means that the positive electrode active material (especially its particles) shows one or more main peaks corresponding to the Miller indices specific to the so-called olivine-type crystal structure at a predetermined incident angle in X-ray diffraction. Preferred positive electrode active materials having an olivine-type structure include the compounds exemplified above.

[0065] When the positive electrode active material has a spinel-type structure in the positive electrode layer, it means that the positive electrode active material (especially its particles) has a spinel-type crystal structure. In a broad sense, it means having a crystal structure that can be recognized as a spinel-type crystal structure by those skilled in the art of solid-state batteries. In a narrow sense, when the positive electrode active material has a spinel-type structure in the positive electrode layer, it means that the positive electrode active material (especially its particles) shows one or more main peaks corresponding to the Miller indices specific to the so-called spinel-type crystal structure at a predetermined incident angle in X-ray diffraction. Preferred positive electrode active materials having a spinel-type structure include the compounds exemplified above.

[0066] The chemical composition of the positive electrode active material may be an average chemical composition. The average chemical composition of the positive electrode active material means the average value of the chemical composition of the positive electrode active material in the thickness direction of the positive electrode layer. The average chemical composition of the positive electrode active material can be analyzed and measured by breaking the solid battery and performing composition analysis by EDX in a field of view that includes the entire thickness direction of the positive electrode layer using SEM-EDX (energy dispersive X-ray spectroscopy).

[0067] The positive electrode active material can be obtained by the same method as the negative electrode active material except by using a raw material compound containing a predetermined metal atom, or can also be obtained as a commercially available product.

[0068] The average particle size of the positive electrode active material is not particularly limited, and may be, for example, 0.01 μm or more and 10 μm or less, preferably 0.05 μm or more and 4 μm or less.

[0069] The average particle size of the positive electrode active material can be determined by the same method as the average particle size of the negative electrode active material in the negative electrode layer.

[0070] The volume ratio of the positive electrode active material in the positive electrode layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 30% or more and 90% or less, and more preferably 40% or more and 70% or less.

[0071] In addition to the positive electrode active material, the positive electrode layer may further contain, for example, a solid electrolyte, a sintering aid, and a conductive material.

[0072] The type of solid electrolyte contained in the positive electrode layer is not particularly limited. As the solid electrolyte contained in the positive electrode layer, for example, a solid electrolyte having a garnet-type crystal structure (for example, a solid electrolyte represented by the general formula (2), particularly (Li 6.4 Ga 0.2 )La3Zr2O 12 , Li 6.4 La3(Zr 1. 6Ta 0.4 )O 12 , (Li 6.4 Al 0.2 )La3Zr2O 12 , Li6.5 La3(Zr 1.5 Mo 0.25 )O 12 ) and solid electrolytes having a LISICON-type structure (for example, Li 3+x (V 1-x Si x )O4), solid electrolytes having a perovskite-type crystal structure (for example, La 2 / 3-x Li 3x TiO3), solid electrolytes having an amorphous structure (for example, Li3BO3-Li4SiO4), etc. can be mentioned. Among these, from the viewpoint of improving the performance of battery characteristics, it is particularly preferable to use a solid electrolyte having a garnet-type crystal structure.

[0073] The solid electrolyte of the positive electrode layer can be obtained by the same method as the negative electrode active material except for using a raw material compound containing a predetermined metal atom, or can also be obtained as a commercially available product.

[0074] The volume ratio of the solid electrolyte in the positive electrode layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 20% or more and 60% or less, and more preferably 30% or more and 45% or less.

[0075] As the sintering aid in the positive electrode layer, the same compounds as those in the negative electrode layer can be used.

[0076] The volume ratio of the sintering aid in the positive electrode layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 0.1% or more and 20% or less, and more preferably 1% or more and 10% or less.

[0077] As the conductive material in the positive electrode layer, the same compounds as those in the negative electrode layer can be used.

[0078] The volume ratio of the conductive material in the positive electrode layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0079] In the positive electrode layer, the porosity is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 20% or less, more preferably 15% or less, and still more preferably 10% or less.

[0080] The porosity of the positive electrode layer uses the value measured by the same method as the porosity of the negative electrode layer.

[0081] The positive electrode layer is a layer that can be called a "positive electrode active material layer". The positive electrode layer may have a so-called positive electrode current collector or positive electrode current collecting layer.

[0082] (Solid electrolyte layer) The solid electrolyte layer contains a solid electrolyte. The solid electrolyte contained in the solid electrolyte layer is not particularly limited. For example, a solid electrolyte having a garnet-type crystal structure, a solid electrolyte having a LISICON-type structure (for example, Li 3+x (V 1-x Si x )O4), a solid electrolyte having a perovskite-type structure (for example, La 2 / 3-x Li 3x TiO3), a solid electrolyte having an amorphous structure (for example, Li3BO3-Li4SiO4), etc. can be mentioned. Among these, from the viewpoint of improving the performance of battery characteristics, it is particularly preferable to use a solid electrolyte having a garnet-type crystal structure.

[0083] The garnet-type solid electrolyte contained in the solid electrolyte layer is the same as the solid electrolyte having a garnet-type crystal structure contained in the negative electrode layer, and may be selected from the same range as the solid electrolyte having a garnet-type crystal structure described in the description of the negative electrode layer. When both the solid electrolyte layer and the negative electrode layer contain a solid electrolyte having a garnet-type structure, the solid electrolyte having a garnet-type crystal structure contained in the solid electrolyte layer and the solid electrolyte having a garnet-type crystal structure contained in the negative electrode layer may have the same chemical composition or may have mutually different chemical compositions.

[0084] The garnet-type solid electrolyte contained in the solid electrolyte layer is not particularly limited as long as it has a garnet-type crystal structure. For example, similar to the garnet-type solid electrolyte contained in the negative electrode layer, it preferably has a chemical composition within the range of the chemical composition represented by the above general formula (2). By including a solid electrolyte having such a chemical composition in the solid electrolyte layer, it is possible to achieve an improvement in the interfacial resistance characteristics between the solid electrolyte and the negative electrode active material.

[0085] In the solid electrolyte layer, the chemical composition of the solid electrolyte may be the average chemical composition. The average chemical composition of the solid electrolyte (particularly the solid electrolyte having a garnet-type crystal structure) in the solid electrolyte layer means the average value of the chemical composition of the solid electrolyte in the thickness direction of the solid electrolyte layer. The average chemical composition of the solid electrolyte can be analyzed and measured by breaking the solid battery and performing composition analysis by EDX in a field of view that includes the entire thickness direction of the solid electrolyte layer using SEM-EDX (energy dispersive X-ray spectroscopy).

[0086] The chemical composition and crystal structure of the solid electrolyte in the solid electrolyte layer usually hardly change even by firing. It is preferable that the solid electrolyte has the above-described chemical composition and crystal structure in the solid battery after firing the solid electrolyte layer together with the negative electrode layer and the positive electrode layer.

[0087] The volume ratio of the solid electrolyte in the solid electrolyte layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 10% or more and 100% or less, more preferably 20% or more and 100% or less, and even more preferably 30% or more and 100% or less.

[0088] The volume ratio of the solid electrolyte in the solid electrolyte layer can be measured by the same method as the volume ratio of the solid electrolyte in the negative electrode layer.

[0089] The solid electrolyte layer may further contain, in addition to the solid electrolyte, for example, a sintering aid or the like. From the viewpoint of improving the performance of battery characteristics, at least one of the negative electrode layer and the solid electrolyte layer, preferably both, more preferably contain a sintering aid. The fact that at least one of the negative electrode layer and the solid electrolyte layer further contains a sintering aid means that either one of the negative electrode layer and the solid electrolyte layer may further contain a sintering aid, or both of them may further contain a sintering aid.

[0090] As the sintering aid in the solid electrolyte layer, the same compounds as those in the negative electrode layer can be used.

[0091] The volume ratio of the sintering aid in the solid electrolyte layer is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 0.1% or more and 20% or less, more preferably 1% or more and 10% or less.

[0092] The thickness of the solid electrolyte layer is usually 0.1 μm or more and 30 μm or less, and from the viewpoint of thinning the solid electrolyte layer, it is preferably 1 μm or more and 20 μm or less.

[0093] The thickness of the solid electrolyte layer uses the average value of the thicknesses measured at any 10 locations in the SEM image.

[0094] In the solid electrolyte layer, the porosity is not particularly limited, and from the viewpoint of improving the performance of battery characteristics, it is preferably 20% or less, more preferably 15% or less, still more preferably 10% or less.

[0095] The porosity of the solid electrolyte layer uses the value measured by the same method as the porosity of the negative electrode layer.

[0096] The solid battery of the present invention may further include all members that a conventional solid battery may have, such as a positive electrode current collector layer, a negative electrode current collector layer, a protective layer, and an end face electrode.

[0097] [Method for manufacturing a solid battery] The solid-state battery can be manufactured, for example, by the so-called green sheet method, printing method, or a method combining these methods.

[0098] The green sheet method will be described. First, a paste is prepared by appropriately mixing a positive electrode active material or a raw material to be a positive electrode active material, a solvent, a resin, etc. The paste is applied onto a sheet and dried to form a first green sheet for forming a positive electrode layer. The first green sheet may contain a solid electrolyte, a conductive material, and / or a sintering aid, etc.

[0099] A paste is prepared by appropriately mixing a negative electrode active material or a raw material to be a negative electrode active material, a solvent, a resin, etc. The paste is applied onto a sheet and dried to form a second green sheet for forming a negative electrode. The second green sheet may contain a solid electrolyte, a conductive material, and / or a sintering aid, etc.

[0100] A paste is prepared by appropriately mixing a solid electrolyte or a raw material to be a solid electrolyte, a solvent, a resin, etc. The paste is applied and dried to produce a third green sheet for forming a solid electrolyte layer. The third green sheet may contain a sintering aid, etc.

[0101] Next, a laminate is produced by appropriately laminating the first to third green sheets. The produced laminate may be pressed. Preferred pressing methods include the hydrostatic pressure pressing method, etc. Thereafter, the laminate can be fired at, for example, 600 to 800 °C to obtain a solid-state battery.

[0102] The printing method will be described. The printing method is the same as the green sheet method except for the following matters. · Prepare the paste for each layer so that the blending amounts of the solvent and resin suitable for manufacturing by the printing method are obtained. ·Print and laminate using the paste of each layer to produce a laminate.

[0103] Hereinafter, the present invention will be described in more detail based on specific examples. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

Example

[0104] [Manufacture of Materials] In the following (1) to (3), solid electrolyte powder, negative electrode active material, and sintering aid were manufactured. Table 1 described later shows the average chemical composition of each material of each layer after firing both the negative electrode layer and the solid electrolyte layer, etc. for half-cell manufacturing in each of the examples / comparative examples. However, in each of the examples / comparative examples, the average chemical composition did not change before and after the firing. Therefore, in the table, the average chemical composition described in these examples and comparative examples also means the average chemical composition of each material used.

[0105] (1) Manufacture of solid electrolyte LLZ powder having a garnet-type crystal structure (solid electrolyte powder for the negative electrode layer and solid electrolyte powder for the solid electrolyte layer) The solid electrolyte powder LLZ having a garnet-type crystal structure used in the examples and comparative examples was manufactured as follows. Lithium hydroxide monohydrate LiOH·H2O, lanthanum hydroxide La(OH)3, zirconium oxide ZrO2, and tantalum oxide Ta2O5 were used as raw materials. Each raw material was weighed so that the chemical composition was Li 6.4 La3Zr 1.6 Ta 0.4 O 12 and water was added, and it was sealed in a 100 ml polyethylene polypot and rotated at 150 rpm for 16 hours on the pot rack to mix the raw materials. Also, lithium hydroxide monohydrate LiOH·H2O, which is the Li source, was charged 3 wt% in excess with respect to the target composition in consideration of Li deficiency during firing. After evaporating and drying the obtained slurry, the target phase was obtained by calcining at 900°C for 5 hours. A mixed solvent of toluene - acetone was added to the obtained calcined powder, and it was pulverized in a planetary ball mill for 6 hours. This pulverized powder was dried to obtain a solid electrolyte powder. The composition of the above powder was confirmed to be Li 6.4 La3Zr 1.6 Ta 0.4 O 12 without deviation by ICP measurement.

[0106] (2) Production of negative electrode active material powder (Examples 1 - 3) Raw materials containing lithium hydroxide monohydrate (LiOH·H2O), vanadium pentoxide (V2O5), and silicon oxide (SiO2) were weighed so as to have the chemical compositions of Examples 1 - 3, and thoroughly mixed in a mortar. Next, ethanol was added, and it was sealed in a 100 - ml polyethylene polypot and rotated at 150 rpm on a pot rack for 16 hours to mix the raw materials. After drying the obtained slurry, it was calcined at 900 °C in the air for 5 hours. Then, a mixed solvent of toluene - acetone was added to the obtained calcined product, pulverized in a planetary ball mill for 6 hours, and then dried to obtain the negative electrode active material powder shown in Table 1.

[0107] (Examples 4 - 6) Negative electrode active material powder was prepared in the same manner as in Examples 1 - 3, except that lithium hydroxide monohydrate (LiOH·H2O), vanadium pentoxide (V2O5), and germanium oxide (GeO2) were used as raw materials and weighed so as to have the chemical compositions of the negative electrode active materials shown in Examples 4 - 6.

[0108] (Examples 7 - 9) Negative electrode active material powder was prepared in the same manner as in Examples 1 - 3, except that lithium hydroxide monohydrate (LiOH·H2O), vanadium pentoxide (V2O5), and titanium oxide (TiO2) were used as raw materials and weighed so as to have the chemical compositions of the negative electrode active materials shown in Examples 7 - 9.

[0109] (Example 10) As raw materials, lithium hydroxide monohydrate LiOH·H₂O, vanadium pentoxide V₂O₅, silicon dioxide SiO₂, and lithium phosphate Li₃PO₄ were used. A negative electrode active material powder was produced in the same manner as in Examples 1 to 3, except that the materials were weighed so as to obtain the chemical compositions of the negative electrode active materials shown in Examples 7 to 9.

[0110] (Comparative Example 1) A negative electrode active material powder was produced in the same manner as in Examples 1 to 3, except that lithium hydroxide monohydrate LiOH·H₂O and vanadium pentoxide V₂O₅ were used as raw materials.

[0111] (Comparative Example 2) A negative electrode active material powder was produced in the same manner as in Examples 1 to 3, except that the raw materials were weighed so as to obtain the chemical composition of Comparative Example 2.

[0112] (3) Production of Sintering Aid Powder The sintering aid powders used in the examples and comparative examples were produced as follows. Lithium hydroxide monohydrate LiOH·H₂O, boron oxide B₂O₃, and lithium carbonate Li₂CO₃ were used as raw materials. Each raw material was appropriately weighed so that the chemical composition would be the predetermined chemical composition Li₃BO₃, and after thoroughly mixing in a mortar, it was calcined at 650 °C for 5 hours. Thereafter, the calcined powder was pulverized and mixed well again in a mortar, and then sintered at 680 °C for 40 hours. A mixed solvent of toluene - acetone was added to the obtained sintered powder, and it was pulverized in a planetary ball mill for 6 hours and dried to obtain a sintering aid powder. It was confirmed by ICP measurement that there was no compositional deviation in the above powder.

[0113] (Manufacture of Half Cell) Half cells were manufactured as follows.

[0114] Powder of a solid electrolyte having a garnet-type crystal structure, butyral resin, and alcohol were mixed at a mass ratio of 200:15:140, and then the alcohol was removed on a hot plate at 80 °C to obtain solid electrolyte powder coated with the butyral resin serving as a binder. Next, the solid electrolyte powder coated with the butyral resin was pressed at 90 MPa using a tablet molding machine to be molded into a tablet shape. The obtained tablets of the solid electrolyte were sufficiently covered with mother powder and fired at a temperature of 500 °C in an oxygen atmosphere to remove the butyral resin, and then fired at about 1200 °C for 3 hours in an oxygen atmosphere. Thereafter, a sintered body of the solid electrolyte was obtained by lowering the temperature. By polishing the surface of the obtained sintered body, a garnet-type solid electrolyte substrate (solid electrolyte layer) was obtained.

[0115] Solid electrolyte powder LLZ having a garnet-type crystal structure, negative electrode active material powder having the chemical composition described in Table 1, sintering aid powder, and conductive material powder (Ag particles) were weighed so as to have a volume ratio of 35:30:5:30, and kneaded with alcohol and a binder to prepare a negative electrode layer paste. Next, the negative electrode layer paste was applied onto a solid electrolyte layer (i.e., a solid electrolyte substrate) and dried to obtain a laminate. After removing the binder by heating the laminate to 400 °C, a laminate of the solid electrolyte layer and the negative electrode layer was prepared by heat treatment firing at 800 °C for 2 hours in an air atmosphere. Thereafter, metallic lithium was attached as a counter electrode and a reference electrode onto the surface of the solid electrolyte layer of the laminate opposite to the surface on the negative electrode layer side, and warm isostatic pressing was performed at 60 °C under a pressure of 200 MPa to form a Li / solid electrolyte interface. A half cell was manufactured by sealing this with a 2032-type coin cell. Also, in order to evaluate the interfacial resistance value between Li and the solid electrolyte, a Li / LLZ / Li cell was also prepared in which Li was attached to both surfaces of the solid electrolyte substrate and warm isostatic pressing was performed at 60 °C under a pressure of 200 MPa.

[0116] [Measurement] (Average Chemical Composition) The chemical formulas in Table 1 indicate the average chemical composition of the negative electrode active material. The average chemical composition was measured by the following method. The average chemical composition was obtained by breaking the half cell, polishing the cross section by ion milling, and then performing quantitative analysis on 10 points of the negative electrode active material sites in the negative electrode layer using SEM-WDX (energy dispersive X-ray spectroscopy) by point analysis of WDX and averaging them. By performing quantitative analysis (composition analysis) by WDX in a field of view that encompasses the entire thickness direction of each layer, the average chemical composition of the negative electrode active material and the solid electrolyte in the negative electrode layer, and the average chemical composition of the garnet-type solid electrolyte LLZ in the solid electrolyte layer were obtained. In the present invention, composition analysis using JXA-8530F manufactured by JEOL Ltd. was used. Since it is difficult to quantify Li and O in the negative electrode active material, the chemical formula (Li [3-ax+(5-b)y] A x )(V 1-y Z y )O 4-δ was calculated using the above chemical formula with the oxygen deficiency amount δ = 0 based on the information of A and Z charged before firing and the information of x and y obtained by the composition analysis of WDX. Also for the solid electrolyte layer, it was obtained by performing quantitative analysis on 10 points of the solid electrolyte sites in the negative electrode layer and the solid electrolyte layer by point analysis of WDX and averaging them. Similar to the negative electrode active material, since it is difficult to quantify Li and oxygen, the chemical formula (Li [7-ax-(b-4)y] A x )La3Zr 2-y Z y O 12 was calculated using the above chemical formula based on the information of A and Z charged before firing and the information of x and y obtained by the composition analysis of WDX. In Examples 1 to 10 and Comparative Examples 1 to 2, it was confirmed that the average chemical compositions of the negative electrode active material and the solid electrolyte in the negative electrode layer and the solid electrolyte in the solid electrolyte layer after firing for manufacturing the half cell were equivalent to their respective compositions before the firing (charging).

[0117] (Garnet-type crystal structure) The garnet-type crystal structure was confirmed by obtaining an X-ray diffraction pattern attributable to a garnet-type similar crystal structure from X-ray diffraction (XRD measurement) (ICDD Card No. 00-045-0109). Also, regarding the negative electrode active material in the negative electrode layer, the crystal structure was confirmed by performing XRD measurement on the negative electrode layer of the half cell. For Comparative Example 1 and Examples 1 to 10, it was confirmed by obtaining an X-ray diffraction pattern attributable to the β-LVO structure, and for Comparative Example 2, it was confirmed by obtaining an X-ray diffraction pattern attributable to the γ-LVO structure.

[0118] (Evaluation of Solid State Batteries) The half cells of each example / comparative example were evaluated for the following items.

[0119] [Evaluation Method 1: Evaluation of Capacity Retention Characteristics] The solid state batteries fabricated in each comparative example and each example were evaluated at 25°C with the following details. Charge and discharge were performed using constant current charge-discharge measurement, and the lower limit potential at the end of charge was 0.2 V (vs. Li / Li + ) and the upper limit potential at the end of discharge was 3.0 V (vs. Li / Li + ). The constant current value of the charge and discharge current was 0.1 C. The theoretical value of the charge-discharge capacity was defined as the amount of electricity when a two-electron reaction proceeded with respect to V in the negative electrode active material, and the current value for charging and discharging this amount of electricity in 10 hours was 0.1 C, and the current value for charging and discharging in 1 hour was 1.0 C. Note that charging in the present invention corresponds to a reduction reaction in which lithium ions are inserted into the negative electrode active material, and discharging corresponds to an oxidation reaction in which lithium ions are desorbed from the negative electrode active material. In any of the cells used in the present invention, it was confirmed that a reversible capacity of 80% or more of the above-mentioned theoretical value of the charge-discharge capacity was obtained. Also, the initial charge capacity at 0.1 C and the initial charge capacity at 1.0 C of the fabricated solid state battery were measured. This "(Capacity at 1.0 C charge / Capacity at 0.1 C charge) × 100" was defined as the 1 C capacity retention rate. ◎; 67% < 1.0 C capacity retention rate ≤ 100% (best); ○; 50% < 1.0 C capacity retention rate ≤ 67% (good); ×; 1 C capacity retention rate ≤ 50% (problematic in practical use).

[0120] From the comparison between Examples 1 to 10, Comparative Example 1, and Comparative Example 2, it can be seen that for the sample having the γ-Li3VO4 (LVO) crystal structure of Comparative Example 2, the 1C capacity retention rate of 49% is not sufficient. On the other hand, for the substituted β II -Li3VO4 (LVO) crystal structure of Examples 1 to 10 and the unsubstituted β II -Li3VO4 (LVO) crystal structure of Comparative Example 1, the 1C capacity retention rate is improved. It is considered that the charge-discharge reaction mechanisms are different between the β II -Li3VO4 (LVO) crystal structure and the γ-Li3VO4 (LVO) crystal structure. In the γ-Li3VO4 (LVO) crystal structure, the resistance after a charge depth of 60% is very high, and it is considered that the large diffusion resistance of Li in the negative electrode active material in this region is the cause of the low capacity retention rate (Figure 2). From the above, it was found that the sample having the β-Li3VO4 structure shows a high capacity retention rate even under high-rate charging, that is, high-speed charging is possible, which is more preferable.

[0121] [Evaluation Method 2: Interface Resistance Characteristics Evaluation] A "Li / LLZ / negative electrode active material - LLZ-Ag negative electrode" half-cell was constructed, and the impedance was measured under the conditions of a charge depth of 50% at the first charge, 25 °C, 7 MHz to 0.1 Hz, and an applied voltage of 10 mV. The relationship between the real component (Za) and the imaginary component (Zb) of the impedance is shown in Figure 1. In Figure 1, the first arc R SE is the solid electrolyte. The second arc R int is attributed to the interface resistance between the negative electrode active material and the garnet-type crystal structure solid electrolyte LLZ. The resistance was read from the intersection of this arc with the real axis. Also, the product of the area of the negative electrode layer after firing and this resistance value was calculated as the interface resistance value. It should be noted that it was confirmed that the interface resistance between Li / LLZ is sufficiently small (<5 Ωcm 2 ). ◎◎; Interface resistance ≦ 67 Ωcm 2 (Best); ◎; 67 Ωcm 2 < Interface resistance ≦ 82 Ωcm 2 (Excellent) ○; 82 Ωcm 2 <Interface resistance ≤ 150 Ωcm 2 (Good); ×; Interface resistance > 150 Ωcm 2 (Not acceptable) (There is a problem in practical use).

[0122] From the comparison with Examples 1 to 10, Comparative Example 1's unsubstituted β II -Li3VO4 (LVO)-type crystal structure-containing solid battery with a negative electrode active material shows a larger interface resistance with LLZ. On the other hand, in a solid battery containing a substituted β II -Li3VO4 (LVO)-type crystal structure and a γ-Li3VO4 (LVO)-type crystal structure-containing negative electrode active material, the value of the interface resistance with LLZ is significantly reduced, and it can be seen that the interface resistance characteristics are improved. Thus, by having a low interface resistance with LLZ, the overvoltage during charge and discharge can be reduced. Thereby, the energy loss during charging can be reduced, which is preferable.

[0123] From Table 1, in the solid batteries containing the substituted β II -Li3VO4 (LVO)-type crystal structure-containing negative electrode active material of Examples 1 to 10, it can be seen that sufficiently excellent results are obtained in both the capacity retention rate characteristics and the interface resistance characteristics.

[0124]

Table 1

Industrial Applicability

[0125] The solid-state battery according to an embodiment of the present invention can be used in various fields where battery use or power storage is assumed. Although merely illustrative, the solid-state battery according to an embodiment of the present invention can be used in the field of electronics mounting. The solid-state battery according to an embodiment of the present invention can also be used in the electrical, information, and communication fields (for example, mobile devices such as mobile phones, smartphones, smartwatches, notebook computers, digital cameras, activity meters, arm computers, electronic paper, wearable devices, RFID tags, card-type electronic money, small electronics such as smartwatches, etc., or the mobile device field), home and small industrial applications (for example, the fields of power tools, golf carts, home, care, and industrial robots), large industrial applications (for example, the fields of forklifts, elevators, and port cranes), transportation system fields (for example, the fields of hybrid vehicles, electric vehicles, buses, trains, electric assist bicycles, electric motorcycles, etc.), power system applications (for example, the fields of various power generations, load conditioners, smart grids, general household installation-type power storage systems, etc.), medical applications (the field of medical devices such as earphone hearing aids), pharmaceutical applications (the field of medication management systems, etc.), as well as the IoT field, space and deep-sea applications (for example, the fields of space exploration machines, submersible research vessels, etc.).

Claims

A solid battery including a negative electrode layer, a positive electrode layer, and a solid electrolyte layer disposed between the negative electrode layer and the positive electrode layer, wherein at least one of the negative electrode layer or the solid electrolyte layer includes a solid electrolyte having a garnet-type crystal structure, the negative electrode active material included in the negative electrode layer has a β-LVO type crystal structure, and a part of the V element of the β-LVO type crystal structure is substituted by one or more elements capable of taking a four-coordinate structure, the one or more elements capable of taking the four-coordinate structure are one or more elements selected from the group consisting of Si, Ge, and P, defining the one or more elements capable of taking the four-coordinate structure as Z, a solid battery satisfying 0 < r ≦ 0.10 when r = the amount of substance of Z / (the amount of substance of V element + the amount of substance of Z).

2. The negative electrode active material has the general formula (1): 【Chemical 1】 (In formula (1), A is at least one element selected from the group consisting of Na (sodium), K (potassium), Mg (magnesium), Ca (calcium), Al (aluminum), Ga (gallium), Zn (zinc), Fe (iron), Cr (chromium), and Co (cobalt); Z is one or more elements capable of taking the four-coordinate structure; x satisfies 0 ≦ x ≦ 1.0; y satisfies 0 < y ≦ 0.20; δ satisfies 0 ≦ δ ≦ 0.5; a is the average valence of A; b is the average valence of Z.) The solid battery according to claim 1, having an average chemical composition represented by

3. In the general formula (1), Z includes Si, and the solid battery according to claim 2, wherein y satisfies the relationship 0 < y ≦ 0.

05.

4. In the general formula (1), Z includes Si, and the solid battery according to claim 2, wherein y satisfies the relationship 0.025 ≦ y ≦ 0.

045.

5. In the general formula (1), Z includes Ge, and the solid battery according to claim 2, wherein y satisfies the relationship 0 < y ≦ 0.

10.

6. In the general formula (1), Z includes Ge, and the solid battery according to claim 2, wherein y satisfies the relationship 0.060 ≦ y ≦ 0.

100.

7. In the general formula (1), Z includes P, and the solid battery according to claim 2, wherein y satisfies the relationship 0 < y ≦ 0.

080.

8. In the general formula (1), the solid battery according to claim 2, wherein x has the relationship 0 ≦ x ≦ 0.

20.

9. The β-LVO type crystal structure is β ＩＩ -Li ３ VO ４ type crystal structure, the solid battery according to claim 1.

10. The solid battery according to claim 1, which is a co-fired molded solid battery.

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