Solid electrolyte and all-solid-state battery

Abstract

This solid electrolyte is formed from a compound represented by general formula (1) below.　(1) … LixM2(PO4)z (in general formula (1), M represents at least one element having a valence of 1-4, x represents a number that satisfies 1.003 ≤ x ≤ 1.900, and z represents a number that satisfies 3.001 ≤ z ≤ 3.200.)

Description

Technical Field

[0001] The present invention relates to a solid electrolyte and an all-solid-state battery. This application claims priority based on Japanese Patent Application No. 2019-227465 filed in Japan on December 17, 2019, the content of which is incorporated herein by reference.

Background Art

[0002] In recent years, the development of electronics technology has been remarkable, and mobile electronic devices have been made smaller, lighter, thinner, and more multifunctional. Along with this, there is a strong demand for batteries that power electronic devices to be smaller, lighter, thinner, and more reliable, and all-solid-state batteries using solid electrolytes as electrolytes have attracted attention.

[0003] In order to improve the characteristics such as the cycle characteristics of all-solid-state batteries, it is effective to improve the ionic conductivity of solid electrolytes. Therefore, as a material for solid electrolytes, phosphate compounds having a NASICON-type crystal structure are widely used (Patent Documents 1 to 4). Phosphate compounds having a NASICON-type crystal structure are generally represented by LiM 2 (PO 4 ) 3 . Here, M is a tetravalent metal.

[0004] Also, in order to further improve the ionic conductivity, substitution of part of M with a monovalent to trivalent metal has been studied. For example, Patent Document 4 describes a solid electrolyte material represented by the chemical formula Li 1+X M y (PO 4 ) 3 (a part of P may be substituted with at least one selected from the group consisting of Si, B, and V, M contains at least one of elements that become monovalent to tetravalent cations, -0.200 ≦ x ≦ 0.900, 2.001 ≦ y ≦ 2.200). According to this Patent Document 4, when M contains at least one of elements that become monovalent to tetravalent cations and 2.001 ≦ y ≦ 2.200, it is said that the ionic conductivity of the solid electrolyte can be improved. This is generally LiM2 (PO 4 ) 3 In comparison with the phosphoric acid compound having a Nasicon-type crystal structure represented by PO 4 The composition ratio of is small. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-258165 A [Patent Document 2] JP 2001-143754 A [Patent Document 3] JP 2015-065021 A [Patent Document 4] International Publication No. 2017 / 183255 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to improve cycle characteristics, a solid electrolyte with high ionic conductivity is desirable. The present invention aims to provide a novel solid electrolyte with improved ionic conductivity and an all-solid-state battery using the same that exhibits excellent cycle characteristics. [Means for solving the problem]

[0007] Therefore, the present inventors have developed a compound having the general formula Li x M 2 (PO 4 ) z In the solid electrolyte having a Nasicon-type crystal structure represented by 4 As a result of careful consideration of the composition ratio of PO 4 They found that the ionic conductivity of the solid electrolyte can be improved by setting the composition ratio of PO in the range of 3.001≦z≦3.200. 4 The present invention was completed based on the finding that an all-solid-state battery using a solid electrolyte having a composition ratio of more than 3 exhibits excellent cycle characteristics. That is, in order to solve the above problems, the present invention provides the following means.

[0008] [1] The solid electrolyte according to the first aspect is composed of a compound represented by the following general formula (1). Li x M 2 (PO 4 ) z ···(1) (In the general formula (1), M represents at least one element having a valence of 1 to 4, x represents a number satisfying 1.003 ≦ x ≦ 1.900, and z represents a number satisfying 3.001 ≦ z ≦ 3.200.)

[0009] [2] In the general formula (1), M may be a configuration containing at least one element selected from the group consisting of Na, K, Ag, Au, Ba, Cr, Mn, Fe, Co, Ni, Pd, Pt, Sc, Y, V, Nb, Ta, Ru, Rh, Ir, Al, Ga, In, Mo, W, Tc, Re, Os, Ti, Zr, Hf, Ge, Si, Sn.

[0010] [3] In the general formula (1), M may be a configuration containing at least one element having a valence of 4.

[0011] [4] In the solid electrolyte according to the above aspect, the general formula (1) may be a configuration represented by the following general formula (2). Li x M’ y M” 2-y (PO 4 ) z ···(2) (In general formula (2), M' represents at least one element selected from the group consisting of Na, K, Ag, Au, Ba, Cr, Mn, Fe, Co, Ni, Pd, Pt, Sc, Y, V, Nb, Ta, Ru, Rh, Ir, Al, Ga, In, Mo, W, Tc, Re, and Os; M'' represents at least one element having a tetravalent valence; x represents a number satisfying 1.003 ≦ x ≦ 1.900; y represents a number satisfying 0.001 ≦ y ≦ 1.999; and z represents a number satisfying 3.001 ≦ z ≦ 3.200.)

[0012] [5]In the solid electrolyte according to the above aspect, M'' in the general formula (2) may be configured to represent at least one element selected from the group consisting of Ti, Zr, Hf, Ge, Si, and Sn.

[0013] [6]The all-solid-state battery according to the second aspect includes a solid electrolyte layer containing the solid electrolyte according to the above aspect, a positive electrode joined to one surface of the solid electrolyte layer, and a negative electrode joined to the other surface of the solid electrolyte.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a novel solid electrolyte with improved ionic conductivity and an all-solid-state battery exhibiting excellent cycle characteristics using the same.

Brief Description of the Drawings

[0015]

Figure 1

Modes for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show, for the sake of clarity, the characteristic parts enlarged for the convenience of understanding the features of the present invention, and the dimensional ratios of the respective components may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and it can be implemented with appropriate changes without changing the gist thereof.

[0017] [All-solid-state battery] FIG. 1 is an enlarged cross-sectional schematic view of a main part of an all-solid-state battery according to the first embodiment. As shown in FIG. 1, the all-solid-state battery 10 has a laminate 4. The laminate 4 has a plurality of positive electrode layers 1, a plurality of negative electrode layers 2, and a solid electrolyte layer 3 located between the positive electrode layer 1 and the negative electrode layer 2. The positive electrode layer 1 is an example of a first electrode layer, and the negative electrode layer 2 is an example of a second electrode layer. Either the first electrode layer or the second electrode layer functions as a positive electrode, and the other functions as a negative electrode. The positive and negative of the electrode layer change depending on which polarity is connected to the external terminal.

[0018] Each positive electrode layer 1 is connected to a positive electrode external terminal 5, and each negative electrode layer 2 is connected to a negative electrode external terminal 6. The all-solid-state battery 10 is of a parallel type in which a plurality of positive electrode layers 1 connected to the positive electrode external terminal 5 and a plurality of negative electrode layers 2 connected to the negative electrode external terminal 6 are connected in parallel.

[0019] [Laminate] The laminate 4 has a plurality of positive electrode layers 1, a plurality of negative electrode layers 2, a plurality of solid electrolyte layers 3, and a plurality of side margin layers 7. A solid electrolyte layer 3 is located between each positive electrode layer 1 and negative electrode layer 2. Also, at one end of the positive electrode layer 1 not connected to the positive electrode external terminal 5, a side margin layer 7 having substantially the same thickness as the positive electrode layer 1 is formed. Similarly, at one end of the negative electrode layer 2 not connected to the negative electrode external terminal 6, a side margin layer 7 having substantially the same thickness as the negative electrode layer 2 is formed. Charging and discharging of the all-solid-state battery 10 are performed by the transfer of lithium ions through the solid electrolyte layer 3 between the positive electrode layer 1 and the negative electrode layer 2.

[0020] (Solid electrolyte layer) The solid electrolyte layer 3 contains a solid electrolyte. The solid electrolyte is composed of a compound represented by the following general formula (1).

[0021] Li x M 2 (PO 4 ) z ···(1) In the general formula (1), x represents a number satisfying 1.003 ≤ x ≤ 1.900. Preferably, x is a number satisfying 1.004 ≤ x ≤ 1.604, and more preferably, x is a number satisfying 1.103 ≤ x ≤ 1.503. z represents a number satisfying 3.001 ≤ z ≤ 3.200. Preferably, z is a number satisfying 3.001 ≤ z ≤ 3.050. Note that the x and the z are calculated with the composition ratio of M being 2.

[0022] In the general formula (1), M represents at least one element having a valence of 1 to 4. M preferably contains at least one element selected from the group consisting of Na (sodium), K (potassium), Ag (silver), Au (gold), Ba (barium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Pd (palladium), Pt (platinum), Sc (scandium), Y (yttrium), V (vanadium), Nb (niobium), Ta (tantalum), Ru (ruthenium), Rh (rhodium), Ir (iridium), Al (aluminum), Ga (gallium), In (indium), Mo (molybdenum), W (tungsten), Tc (technetium), Re (rhenium), Os (osmium), Ti (titanium), Zr (zirconium), Hf (hafnium), Ge (germanium), Si (silicon), and Sn (tin). More preferably, M contains only an element having a valence of 4 or contains an element having a valence of 1 to 3 and an element having a valence of 4.

[0023] As the element having a tetravalent valence, Ti, Zr, Hf, Ge, Si, Sn can be used. These elements may be used alone or in combination of two. When M contains only the element having a tetravalent valence, M is preferably Ti alone or contains at least one of Zr, Hf, Ge, Si and Ti.

[0024] When M contains an element having a valence of 1 to 3 and an element having a tetravalent valence, it is preferably a compound represented by the following general formula (2).

[0025] Li x M’ y M” 2-y (PO 4 ) z ···(2) In the general formula (2), x and z are the same as in the case of the general formula (1). y is a number satisfying 0.001 ≦ y ≦ 1.999, and preferably a number satisfying 0.100 ≦ y ≦ 0.300. Note that the x and the z are calculated with the sum of the composition ratios of M' and M'' being 2.

[0026] In the general formula (2), M’ represents at least one element selected from the group consisting of Na, K, Ag, Au, Ba, Cr, Mn, Fe, Co, Ni, Pd, Pt, Sc, Y, V, Nb, Ta, Ru, Rh, Ir, Al, Ga, In, Mo, W, Tc, Re, Os. Among these elements, it is preferably at least one element selected from the group consisting of Ag, Au, Ba, Cr, Mn, Fe, Co, Ni, Pd, Pt, Sc, Y, V, Nb, Ta, Ru, Rh, Ir, Al, Ga, In, Mo, W, Tc, Re, Os.

[0027] In the general formula (2), M” represents at least one element having a tetravalent valence. M” is preferably at least one element selected from the group consisting of Ti, Zr, Hf, Ge, Si, Sn.

[0028] The solid electrolyte preferably has a NASICON-type crystal structure. A phosphate compound having a NASICON-type crystal structure is generally represented by LiM 2 (PO 4 ) 3 . In contrast, as is clear from the general formula (1) above, the solid electrolyte of the present invention has a composition ratio of PO 4 greater than 3 times the stoichiometric composition. The reason for the improvement in the ionic conductivity of the solid electrolyte is not necessarily clear, but it is considered that the composition ratio of the anion PO 4 being greater than the stoichiometric composition causes distortion in the crystal structure, and this distortion makes it easier for cations (especially Li ions) to move within the crystal. Note that in the solid electrolyte, a part of the P in the PO 4 site may be substituted with an element that forms a tetrahedral structure together with oxygen such as Si (silicon), B (boron), Mo (molybdenum), S (sulfur), W (tungsten), V (vanadium).

[0029] The shape of the solid electrolyte is not particularly limited. The shape of the solid electrolyte is, for example, spherical, ellipsoidal, needle-like, plate-like, flaky, tubular, wire-like, rod-like, or amorphous. The average particle diameter (D50) of the solid electrolyte is, for example, 0.1 μm or more and 10 μm or less, and may also be 0.3 μm or more and 9 μm or less. D50 is the diameter of the particle at which the integrated value in the distribution curve obtained by particle size distribution measurement is 50%. The particle size distribution of the particles is measured, for example, by a particle size distribution measuring device using the laser diffraction / scattering method (Microtrac method).

[0030] The solid electrolyte can be produced, for example, by a method including a step of weighing a Li source, an M source, and a PO 4 source so as to have a target composition and mixing them to obtain a mixed powder, and a step of calcining and firing the obtained mixed powder. The obtained fired product (solid electrolyte) may be pulverized into a powder form.

[0031] The Li source, the M source, and the PO 4There is no particular limitation on the materials used as the source. As the Li source and the M source, carbonates, nitrates, oxides, hydroxides, chlorides, phosphates, etc. can be used. The phosphate also acts as a PO 4 source. As the PO 4 source, phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, etc. can be used.

[0032] The mixing of the Li source, the M source and the PO 4 source may be carried out dry or wet. Also, the mixing is preferably carried out while grinding the Li source, the M source and the PO 4 source using a mixing device having a grinding function.

[0033] The temperature for calcining the mixed powder is not particularly limited as long as it is 600 °C or higher, but it is preferably calcined at a temperature below the sintering temperature. The atmosphere during calcination is not particularly limited either, but it can be an air atmosphere, a nitrogen atmosphere, an argon atmosphere, or an oxygen atmosphere. Also, when calcining, the mixed powder is formed into a square or circular shape by a mold press and can be calcined under a pressure of 0.1 to 300 MPa by uniaxial pressure sintering (hot press) or hot isostatic pressing (HIP). By calcining under pressure, a solid electrolyte of a phosphate compound having a NASICON-type crystal structure can be obtained while maintaining a large composition ratio of phosphoric acid. The calcined mixed powder maintains the NASICON-type crystal structure while maintaining a large composition ratio of phosphoric acid even when fired later.

[0034] The firing temperature can be in the range of 600 to 1500 °C. The atmosphere during firing is not particularly limited and can be carried out in the same atmosphere as the calcination. When firing, a solid electrolyte having a NASICON-type crystal structure with a large composition ratio of phosphoric acid can be obtained without using uniaxial pressure sintering or hot isostatic pressing, but firing can also be carried out by uniaxial pressure sintering or hot isostatic pressing as in the case of calcination.

[0035] (Positive electrode layer and negative electrode layer) The positive electrode layer 1 and the negative electrode layer 2 are, for example, plural in the laminate 4. The positive electrode layer 1 is joined to one main surface of the solid electrolyte layer 3, and the negative electrode layer 2 is joined to the other main surface of the solid electrolyte layer 3.

[0036] The positive electrode layer 1 has a positive electrode current collector layer 1A and a positive electrode active material layer 1B. The negative electrode layer 2 has a negative electrode current collector layer 2A and a negative electrode active material layer 2B.

[0037] The positive electrode current collector layer 1A and the negative electrode current collector layer 2A contain a conductive material. The positive electrode current collector layer 1A and the negative electrode current collector layer 2A preferably contain 50% or more of the conductive material. Examples of the conductive material include, for example, silver, palladium, gold, platinum, aluminum, copper, nickel, carbon, etc. In particular, copper hardly reacts with the positive electrode active material, the negative electrode active material, and the solid electrolyte. For example, when copper is used for the positive electrode current collector layer 1A and the negative electrode current collector layer 2A, the internal resistance of the all-solid-state battery 10 can be reduced. Note that the conductive material is not limited to this as long as it does not decompose within the operating voltage range of the battery. Furthermore, the materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may be the same or different.

[0038] The positive electrode current collector layer 1A may contain a positive electrode active material described later. The negative electrode current collector layer 2A may contain a negative electrode active material described later. The content ratio of the active material contained in each current collector layer is not particularly limited as long as it functions as a current collector. The volume ratio of the conductive material and the positive electrode active material in the positive electrode current collector layer 1A is, for example, in the range of 90:10 to 70:30. Similarly, the volume ratio of the conductive material and the negative electrode active material in the negative electrode current collector layer 2A is, for example, in the range of 90:10 to 70:30. When the positive electrode current collector layer 1A and the negative electrode current collector layer 2A contain the positive electrode active material and the negative electrode active material, respectively, the adhesion between the positive electrode current collector layer 1A and the positive electrode active material layer 1B and the adhesion between the negative electrode current collector layer 2A and the negative electrode active material layer 2B are improved.

[0039] The positive electrode active material layer 1B is formed on one or both sides of the positive electrode current collector layer 1A. The positive electrode active material layer 1B may not be provided on the surface of the positive electrode current collector layer 1A on the side where the opposing negative electrode layer 2 does not exist. Further, the negative electrode active material layer 2B is formed on one or both sides of the negative electrode current collector layer 2A. The negative electrode active material layer 2B may not be provided on the surface of the negative electrode current collector layer 2A on the side where the opposing positive electrode layer 1 does not exist. For example, the positive electrode layer 1 or the negative electrode layer 2 located in the uppermost layer or the lowermost layer of the laminate 4 may not have the positive electrode active material layer 1B or the negative electrode active material layer 2B on one side.

[0040] The positive electrode active material layer 1B and the negative electrode active material layer 2B contain, as the positive electrode active material and the negative electrode active material, at least a compound capable of occluding and releasing lithium ions. The positive electrode active material layer 1B and the negative electrode active material layer 2B may contain, in addition to the active material, a conductive assistant, an ion conductive assistant, a binder, and the like. It is preferable that the positive electrode active material and the negative electrode active material can efficiently insert and desorb lithium ions.

[0041] The positive electrode active material and the negative electrode active material are, for example, transition metal oxides and transition metal composite oxides. Specifically, the positive electrode active material and the negative electrode active material are, for example, lithium manganese composite oxide Li 2 Mn a Ma 1-a O 3 (0.8 ≦ a ≦ 1, Ma = Co, Ni), lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganese spinel (LiMn 2 O 4 ), general formula: LiNi x Co y Mn z O 2 (x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) composite metal oxide represented by, lithium vanadium compound (LiV 2 O 5 ), olivine type LiMbPO 4(However, Mb is one or more elements selected from Co (cobalt), Ni (nickel), Mn (manganese), Fe (iron), Mg (magnesium), Nb (niobium), Ti (titanium), Al (aluminum), Zr (zirconium)), lithium vanadium phosphate (Li 3 V 2 (PO 4 ) 3 or LiVOPO 4 ), Li 2 MnO 3 -LiMcO 2 (Mc = Mn, Co, Ni) represents a Li-excess solid solution cathode, lithium titanate (Li 4 Ti 5 O 12 ), titanium oxide (TiO 2 ), Li s Ni t Co u Al v O 2 (0.9 < s < 1.3, 0.9 < t + u + v < 1.1) is a composite metal oxide or the like.

[0042] As the cathode active material and the anode active material of this embodiment, it is preferable to contain a phosphate compound as a main component. For example, lithium vanadium phosphate (LiVOPO 4 , Li 3 V 2 (PO 4 ) 3 , Li 4 (VO)(PO 4 ) 2 ), lithium vanadium pyrophosphate (Li 2 VOP 2 O 7 , Li 2 VP 2 O 7 ), and Li 9 V 3 (P 2 O 7 ) 3 (PO 4 ) 2 is preferably any one or more of them. In particular, LiVOPO 4 and Li 3 V 2 (PO4 ) 3 It is preferably one or both of them.

[0043] The main component in this embodiment refers to the case where, when the total amount of the positive electrode active material and the negative electrode active material in the positive electrode active material layer and the negative electrode active material layer is 100 parts by mass, the proportion occupied by the phosphate compound is greater than 50 parts by mass. The proportion occupied by the phosphate compound is preferably 80 parts by weight or more.

[0044] In addition, these positive electrode active materials and negative electrode active materials may have a part of each element substituted with a different element or may vary from the stoichiometric composition. LiVOPO 4 and Li 3 V 2 (PO 4 ) 3 preferably has a lithium deficiency, and Li x VOPO 4 (0.94 ≦ x ≦ 0.98) or Li x V 2 (PO 4 ) 3 (2.8 ≦ x ≦ 2.95) is more preferable.

[0045] In addition, as the negative electrode active material, for example, Li metal, Li - Al alloy, Li - In alloy, carbon, silicon (Si), silicon oxide (SiO x )), lithium titanate (Li 4 Ti 5 O 12 ), titanium oxide (TiO 2 ) can be used.

[0046] Here, there is no clear distinction between the active materials constituting the positive electrode active material layer 1B or the negative electrode active material layer 2B. By comparing the potentials of the two types of compounds, namely the compound in the positive electrode active material layer and the compound in the negative electrode active material layer, the compound showing a nobler potential can be used as the positive electrode active material, and the compound showing a lower potential can be used as the negative electrode active material. Also, if it is a compound having both a lithium ion release function and a lithium ion occlusion function, the active materials constituting the positive electrode active material layer 1B and the negative electrode active material layer 2B may use the same material. By using the same material for the active materials constituting the positive electrode active material layer 1B and the negative electrode active material layer 2B, a non-polar all-solid-state battery is formed. Therefore, when attaching to a circuit board, it is not necessary to specify the direction, and the mountability can be facilitated.

[0047] Examples of the conductive assistant include carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotubes, graphite, graphene, activated carbon, and metal materials such as gold, silver, palladium, platinum, copper, and tin.

[0048] As the ion-conducting assistant, for example, a solid electrolyte can be used. Specifically, the solid electrolyte can use the same material as the solid electrolyte contained in the solid electrolyte layer 3.

[0049] As the binder, for example, an organic binder or an inorganic binder can be used. Examples of the organic binder include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylate (PAA), polyimide (PI), polyamideimide (PAI), and the like. Examples of the inorganic binder include lithium halide, silicate-based compounds, phosphate-based compounds, low melting point glass, and the like.

[0050] <External terminal> For the positive electrode external terminal 5 and the negative electrode external terminal 6, for example, a material with excellent conductivity is used. The positive electrode external terminal 5 and the negative electrode external terminal 6 preferably contain any one of silver, gold, platinum, aluminum, copper, tin, and nickel. The positive electrode external terminal 5 and the negative electrode external terminal 6 may be a single layer or multiple layers.

[0051] <Protective layer> The all-solid-state battery 10 may have a protective layer on its outer periphery that electrically, physically, and chemically protects the laminate 4 and the terminals. The protective layer is preferably made of a material that is excellent in, for example, insulation, durability, and moisture resistance and is environmentally safe. The protective layer is, for example, glass, ceramics, a thermosetting resin, or a photocurable resin. The material of the protective layer may be only one type or a plurality of types may be used in combination. The protective layer may be a single layer or a plurality of layers. The protective layer is preferably an organic-inorganic hybrid in which a thermosetting resin and ceramic powder are mixed.

[0052] Next, a method for manufacturing the all-solid-state battery according to the present embodiment will be described. The all-solid-state battery 10 may be manufactured by a simultaneous firing method or a sequential firing method. The simultaneous firing method is a method in which the materials for forming each layer are laminated and then fired all at once. The sequential firing method is a method in which firing is performed each time a layer is laminated. The simultaneous firing method has a simpler working process than the sequential firing method. Also, the laminate 4 manufactured by the simultaneous firing method is denser than the laminate 4 manufactured by the sequential firing method. Hereinafter, the case of using the simultaneous firing method will be described as an example.

[0053] First, pastes for each layer constituting the laminate 4 are prepared. The materials for the positive electrode current collector layer 1A, the positive electrode active material layer 1B, the solid electrolyte layer 3, the negative electrode active material layer 2B, the negative electrode current collector layer 2A, and the side margin layer 7 are each made into a paste. The method of making the paste is not particularly limited. For example, a paste can be obtained by mixing the powder of each material in a vehicle. A vehicle is a general term for a medium in a liquid phase. The vehicle contains a solvent and a binder.

[0054] The laminate is preferably prepared by preparing a positive electrode active material layer unit and a negative electrode active material layer unit described below and manufacturing the laminate using the positive electrode active material layer unit and the negative electrode active material layer unit.

[0055] The positive electrode active material layer unit can be manufactured by the following procedure. First, a paste for the solid electrolyte layer is formed into a sheet shape on a PET film by the doctor blade method and dried to form a solid electrolyte green sheet. Next, a paste for the positive electrode active material layer is screen-printed on a part of the obtained solid electrolyte green sheet and dried to form a positive electrode active material layer.

[0056] Next, a paste for the positive electrode current collector layer is screen-printed on the obtained positive electrode active material layer and dried to form a positive electrode current collector layer. Then, a paste for the positive electrode active material layer is screen-printed again on the obtained positive electrode current collector layer and dried to form a positive electrode active material layer. In this way, a positive electrode layer is formed on a part of the solid electrolyte layer. Next, a paste for the side margin layer is screen-printed on the solid electrolyte layer where the positive electrode layer is not formed and dried to form a side margin layer. Then, the PET film is peeled off to produce a positive electrode unit. The positive electrode unit has a positive electrode layer 1 (positive electrode active material layer 1B / positive electrode current collector layer 1A / positive electrode active material layer 1B) and a side margin layer 7 formed on the solid electrolyte layer 3.

[0057] Note that the side margin layer 7 eliminates the step between the solid electrolyte layer 3 and the positive electrode layer 1 and the step between the solid electrolyte layer 3 and the negative electrode layer 2 at the end faces where the positive electrode layer 1 and the negative electrode layer 2 do not extend. As the side margin layer 7, it is necessary to use a material with low electronic conductivity. For example, a solid electrolyte is used. The side margin layer 7 may be formed separately as described above. Also, without forming it separately, what is caused by the deformation of the solid electrolyte layer 3 during lamination may be provided together with the positive electrode layer 1 and the negative electrode layer 2 as the side margin layer 7.

[0058] A negative electrode unit is produced by the same procedure. The negative electrode unit has a negative electrode layer 2 (negative electrode active material layer 2B / negative electrode current collector layer 2A / negative electrode active material layer 2B) and a side margin layer 7 formed on the solid electrolyte layer 3.

[0059] Next, the positive electrode unit and the negative electrode unit are laminated. An offset is made so that one end of each of the positive electrode layer and the negative electrode layer does not face each other, and the positive electrode layer and the negative electrode layer are laminated so as to be comb-shaped via the solid electrolyte layer. Thereby, a laminated substrate including a plurality of positive electrode layers 1, a plurality of negative electrode layers 2, and a solid electrolyte layer 3 positioned between the positive electrode layer 1 and the negative electrode layer 2 is produced. Note that, if necessary, outer layers can be provided on both main surfaces of the uppermost layer and the lowermost layer of the laminated substrate. The outer layer can use the same material as the solid electrolyte and can be formed by laminating solid electrolyte green sheets.

[0060] The above method for laminating the positive electrode unit and the negative electrode unit is useful when manufacturing a parallel-type all-solid-state battery 10 in which a plurality of positive electrode layers 1 connected to the positive electrode external terminal 5 and a plurality of negative electrode layers 2 connected to the negative electrode external terminal 6 are connected in parallel. When manufacturing a series-type all-solid-state battery in which the positive electrode layer and the negative electrode layer are connected in series, lamination may be performed without offset so that one end of each of the positive electrode layer and the negative electrode layer faces each other.

[0061] Next, the produced laminated substrate is pressure-bonded all at once. The pressure-bonding is performed while heating at a low temperature. The heating temperature is, for example, 40 to 95°C.

[0062] The produced laminate is cut into chips using a dicing device, and then, after performing a debinding process if necessary, firing is performed to manufacture a laminate of the all-solid-state battery.

[0063] The obtained unfired laminate chip is sintered to obtain the laminate 4 of the all-solid-state battery of the present embodiment. The sintering is performed, for example, by heating in a nitrogen atmosphere in a temperature range of 600°C or higher and 1500°C or lower. The firing time is, for example, 0.1 to 3 hours.

[0064] As described above, before the firing process, a debinding process may be performed as a process separate from the firing process. By thermally decomposing the binder component contained in the laminate 5 before firing, rapid decomposition of the binder component in the firing process can be suppressed. The debinding process is performed, for example, at a temperature in the range of 300°C to 800°C for 0.1 to 10 hours in a nitrogen atmosphere. If it is a reducing atmosphere, firing may be performed, for example, in an argon atmosphere or a nitrogen-hydrogen mixed atmosphere instead of the nitrogen atmosphere.

[0065] The laminate 4 may be placed in a cylindrical container together with an abrasive such as alumina and barrel-polished. The corners of the laminate 4 are chamfered by polishing. The polishing may be performed by sandblasting or the like.

[0066] Finally, the positive electrode external terminal 5 and the negative electrode external terminal 6 are attached to the laminate 4. The positive electrode external terminal 5 and the negative electrode external terminal 6 are each formed so as to be in electrical contact with the positive electrode current collector layer 1A or the negative electrode current collector layer 2A. For example, the positive electrode external terminal 5 is connected to the positive electrode current collector layer 1A exposed from the side surface of the laminate 4, and the negative electrode external terminal 6 is connected to the negative electrode current collector layer 2A exposed from the side surface of the laminate 4. The positive electrode external terminal 5 and the negative electrode external terminal 6 can be manufactured by, for example, a sputtering method, a dipping method, a spray coating method, or the like.

[0067] The solid electrolyte contained in the solid electrolyte layer 3 of the all-solid-state battery 10 according to the present embodiment is composed of the compound represented by the above general formula (1), and the proportion of the PO 4 sites is large, so the ionic conductivity is improved. Since the all-solid-state battery 10 according to the present embodiment has improved ionic conductivity of the solid electrolyte layer 3, it has excellent electrical characteristics such as cycle characteristics.

[0068] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, each configuration and their combinations in each embodiment are examples, and additions, omissions, substitutions, and other changes of the configuration are possible without departing from the spirit of the present invention.

Examples

[0069] [Example 1] (Fabrication of Solid Electrolyte) As starting materials, Li 2 CO 3 (lithium carbonate), TiO 2 (titanium oxide), Al 2 O 3 (aluminum oxide) and NH 4 H 2 PO 4 (ammonium dihydrogen phosphate) were prepared. The prepared Li 2 CO 3 , TiO 2 , Al 2 O 3 and NH 4 H 2 PO 4 were weighed so that the composition ratio of Li, Al, Ti, PO 4 was 1.303:0.3000:1.700:3.001 (=Li:Al:Ti:PO 4 ). Next, the weighed Li 2 CO 3 , TiO 2 , Al 2 O 3 and NH 4 H 2 PO 4 were put into a zirconia pot mill and mixed for 16 hours to obtain a mixed powder. Then, 0.2 g of the obtained mixed powder was put into a circular mold with a diameter of 12 mm and press-molded at a pressure of 2.0 t / cm 2 to produce a circular molded body. A plurality of these molded bodies were prepared and calcined in a nitrogen atmosphere at a temperature of 700 °C for 1 hour while applying a pressure of 10 MPa with a hot press device. A part of the calcined molded body was crushed to obtain a calcined powder of the solid electrolyte. Also, the rest of the calcined molded body was fired at 850 °C for 2 hours in a nitrogen atmosphere to obtain a sintered body of the solid electrolyte.

[0070] [Examples 2 to 7, Comparative Examples 1 and 2] Li 2 CO 3 , TiO 2 , Al 2 O 3 and NH 4 H2 PO 4 was mixed with Li, Al, Ti, and PO 4 in the same manner as in Example 1 except that the ratios were mixed so as to have the composition ratios shown in Table 1 below, and solid electrolyte sintered compacts according to Examples 2 to 7 and Comparative Example 2 were obtained. Note that Comparative Example 1 was obtained in the same manner as in Example 1 except that pressure was not applied using a hot press apparatus during the calcination of the molded body, and a calcined powder and a sintered body of the solid electrolyte were obtained.

[0071]

Table 1

[0072] [Evaluation] (Composition) A part of the solid electrolyte sintered compact was pulverized, dissolved using nitric acid, and the concentrations of Li, Al, Ti, and P in the obtained solution were measured by ICP emission spectrometry. Then, from the concentrations of the respective elements obtained, the composition ratios of Li, Al, Ti, and PO 4 of the solid electrolyte were calculated. In the calculation of the composition ratio, in the general formula (2) Li x M’ y M” 2-y (PO 4 ) z , the x and z were calculated by converting with the sum of the composition ratios of M' and M'' being 2. The results are shown in Table 2 below.

[0073] (X-ray Diffraction Pattern) Regarding the crystal structure of the solid electrolyte sintered compact, an X-ray diffraction pattern was measured using CuKα rays. As a result of analyzing the obtained X-ray diffraction pattern, since it showed the same X-ray diffraction pattern as LiTi 2 (PO 4 ) 3 (lithium titanium phosphate) of ICDD card 35-0754, it was confirmed that it has a NASICON-type crystal structure. The results are shown in Table 2 below.

[0074] (Ionic Conductivity) Gold electrodes were formed by performing gold sputtering on both sides of the solid electrolyte sintered body. When performing gold sputtering, masking was performed on the side surface of the sintered body with tape so that the gold electrodes on both sides would not conduct.

[0075] Thereafter, the solid electrolyte sintered body was set in a jig for measuring ionic conductivity, and the ionic conductivity of each solid electrolyte sintered body was measured using a potentiostat equipped with a frequency response analyzer by the electrochemical impedance measurement method. The measurement was performed under the conditions of a frequency range of 7 MHz to 0.1 Hz, an amplitude of 10 mV, and a temperature of 25°C. The results are shown in Table 2 below.

[0076] (Charge and Discharge Cycle Characteristics of All-Solid-State Battery) The all-solid-state battery was fabricated by the following procedure. Pastes containing each material were prepared to form a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, a negative electrode current collector layer, and a side margin layer. Next, a solid electrolyte green sheet was prepared, and an electrode layer and a side margin layer were formed on this solid electrolyte green sheet to fabricate an electrode unit. Then, the all-solid-state battery of this embodiment was fabricated by alternately laminating the electrode units. Hereinafter, taking Example 1 as a representative, the manufacturing method will be described in more detail step by step.

[0077] (Fabrication of Positive Electrode Active Material and Negative Electrode Active Material) As the positive electrode active material and the negative electrode active material, Li 3 V 2 (PO 4 ) 3 was used. As the manufacturing method, Li 2 CO 3 and V 2 O 5 and NH 4 H 2 PO 4Using [materials] as starting materials, wet mixing was carried out for 16 hours with a ball mill. After dehydration and drying, the obtained powder was calcined at 700 °C for 2 hours in a nitrogen-hydrogen mixed gas. After the calcined product was wet milled with a ball mill, dehydration and drying were carried out to obtain calcined powders of the positive electrode active material and the negative electrode active material. As a result of measuring the X-ray diffraction pattern of the prepared calcined powder by X-ray diffraction method and measuring the composition by ICP emission spectroscopic analysis, Li having a NASICON-type crystal structure 3 V 2 (PO 4 ) 3 was confirmed.

[0078] (Preparation of Paste for Positive Electrode Active Material Layer and Paste for Negative Electrode Active Material Layer) For both the paste for the positive electrode active material layer and the paste for the negative electrode active material layer, 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent were added to 100 parts of the calcined powder of Li 3 V 2 (PO 4 ) 3 . Mixing and dispersion were carried out to prepare a paste for the positive electrode active material layer and a paste for the negative electrode active material layer.

[0079] (Preparation of Paste for Solid Electrolyte Layer) To 100 parts of the calcined powder of the solid electrolyte prepared in Example 1, 100 parts of ethanol and 200 parts of toluene were added as solvents, and wet mixing was carried out with a ball mill. Then, 16 parts of a polyvinyl butyral-based binder and 4.8 parts of benzyl butyl phthalate were further added and mixed to prepare a paste for the solid electrolyte layer.

[0080] (Preparation of Sheet for Solid Electrolyte Layer) The paste for the solid electrolyte layer was formed into a sheet on a PET film by the doctor blade method to obtain a sheet for the solid electrolyte layer with a thickness of 15 μm.

[0081] (Preparation of Paste for Positive Electrode Current Collector Layer and Paste for Negative Electrode Current Collector Layer) As the positive electrode current collector and the negative electrode current collector, Cu powder and Li 3 V 2 (PO 4) 3 After mixing the calcined powder and the like so that the volume ratio is 80 / 20, 10 parts of ethyl cellulose as a binder and 50 parts of dihydroterpineol as a solvent were added and mixed and dispersed to prepare a paste for the positive electrode current collector layer and a paste for the negative electrode current collector layer.

[0082] (Preparation of Paste for Side Margin Layer) To 100 parts of the calcined powder of the solid electrolyte prepared in Example 1, 100 parts of ethanol and 100 parts of toluene were added as solvents and wet-mixed with a ball mill. Then, 16 parts of a polyvinyl butyral-based binder and 4.8 parts of benzyl butyl phthalate were further added and mixed to prepare a paste for the side margin layer.

[0083] (Preparation of Paste for External Terminal) Silver powder, an epoxy resin, and a solvent were mixed and dispersed to prepare a thermosetting paste for the external terminal.

[0084] (Preparation of Positive Electrode Unit) On the above-mentioned solid electrolyte green sheet, the paste for the positive electrode active material layer was screen-printed to form a positive electrode active material layer with a thickness of 5 μm and dried at 80°C for 10 minutes. Next, on the positive electrode active material layer, the paste for the positive electrode current collector layer was screen-printed to form a positive electrode current collector layer with a thickness of 5 μm and dried at 80°C for 10 minutes. Further, on the positive electrode current collector layer, the paste for the positive electrode active material layer was screen-printed to re-form a positive electrode active material layer with a thickness of 5 μm and dried at 80°C for 10 minutes to prepare a positive electrode layer on the solid electrolyte green sheet. Then, in the region of the solid electrolyte green sheet where the positive electrode layer was not formed, the paste for the side margin layer was screen-printed to form a side margin layer having a height substantially the same as that of the positive electrode layer, and dried at 80°C for 10 minutes to prepare a positive electrode unit.

[0085] (Preparation of Negative Electrode Unit) For the negative electrode unit, the negative electrode unit was prepared in the same manner as the positive electrode unit.

[0086] (Preparation of Laminate) The positive electrode unit and the negative electrode unit were peeled off from the PET film, offset and laminated so that one end of the positive electrode layer and one end of the negative electrode layer did not coincide, and the solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer was taken as one layer, and laminated so that the solid electrolyte layer became 50 layers, thereby producing a laminated substrate. Next, a plurality of solid electrolyte green sheets were laminated as outer layers on both main surfaces of the uppermost layer and the lowermost layer of the laminated substrate to provide an outer layer of 500 μm. After this was thermocompression bonded by a mold press, it was cut to produce a laminate of an unfired all-solid-state battery. Next, the laminate was debinded and fired to obtain a laminate of an all-solid-state battery. The firing was carried out by raising the temperature at a rate of 200 °C / hour to a firing temperature of 850 °C in a nitrogen atmosphere, holding at that temperature for 2 hours, and taking it out after natural cooling.

[0087] (Fabrication of external terminals) An external terminal paste was applied to the end face of the fired laminate of the all-solid-state battery, and heat curing was carried out at 150 °C for 30 minutes to form a pair of external terminals.

[0088] (Charge and discharge cycle test) The all-solid-state batteries fabricated in this example and the comparative example were evaluated for charge and discharge cycle characteristics under the following charge and discharge conditions. The charge and discharge current is hereinafter expressed in C (C) rate notation. The C rate is expressed as nC (or current value [A]) (n is a numerical value), and means a current that can charge and discharge the nominal capacity (μAh) in 1 / n (h). For example, 1C is a charge and discharge current that can charge the nominal capacity in 1 h, and 2C means a charge and discharge current that can charge the nominal capacity in 0.5 h. For example, in the case of an all-solid-state battery with a nominal capacity of 100 μAh, the current of 0.1C is 10 μA (calculation formula 100 μA × 0.1 = 10 μA). Similarly, the current of 0.2C is 20 μA, and the current of 1C is 100 μA.

[0089] The charge-discharge cycle test conditions were as follows: in an environment of 25°C, constant current charging (CC charging) was performed at a constant current rate of 0.2C until the battery voltage reached 1.6V, and then discharging was carried out at a constant current rate of 0.2C until the battery voltage reached 0V (CC discharging). The above charging and discharging were regarded as one cycle, and after repeating this up to 500 cycles, the discharge capacity retention rate was evaluated as the charge-discharge cycle characteristics. Note that the charge-discharge cycle characteristics in this embodiment were calculated by the following formula. Discharge capacity retention rate after 500 cycles (%) = (Discharge capacity after 500 cycles ÷ Discharge capacity after 1 cycle) × 100

[0090]

Table 2

[0091] From the results in Table 2, for the solid electrolyte sintered bodies of Examples 1 to 7 where the composition ratio of Al + Ti was 2 and the amount of PO 4 exceeded 3, the ionic conductivity was higher than that of Comparative Example 1 where the amount of PO 4 was 3. In particular, it can be seen that the solid electrolyte sintered bodies with the amount of PO 4 in the range of 3.001 or more and 3.050 or less had particularly high ionic conductivity. Also, it can be seen that the all-solid-state battery using this as the solid electrolyte had improved cycle characteristics. Although the detailed reason for this is unknown, it is considered that the solid electrolytes obtained in Examples 1 to 7 had improved ionic conductivity due to the distortion in the crystal structure caused by the excessive presence of PO 4 . On the other hand, for the solid electrolyte sintered body of Comparative Example 2 where the amount of PO 4 exceeded 3.200, the ionic conductivity began to decrease, and in the all-solid-state battery using this solid electrolyte, the cycle characteristics tended to decrease slightly.

[0092] [Examples 8 to 14] Li 2 CO 3 , TiO 2 , Al 2 O 3 and NH 4 H 2 PO 4with Li, Al, Ti, PO 4 A solid electrolyte sintered body was obtained in the same manner as in Example 1, except that they were mixed so that the ratios of 4 were the composition ratios shown in Table 3 below. For the obtained solid electrolyte sintered body, the composition, X-ray diffraction pattern, ionic conductivity, and cycle characteristics of the all-solid-state battery were evaluated in the same manner as in Example 1.

[0093]

Table 3

[0094]

Table 4

[0095] From the results in Table 4, it can be seen that the solid electrolyte sintered body with the Li content in the range of 1.203 or more and 1.403 or less in the composition ratio has particularly high ionic conductivity, and the all-solid-state battery using this solid electrolyte sintered body has particularly improved cycle characteristics.

[0096] [Examples 15 to 18, Comparative Examples 3 to 6] Al 2 O 3 Instead of 2 and 3 , Na 2 CO 3 (sodium carbonate), CoO (cobalt(II) oxide), Y 2 O 3 (yttrium oxide) or ZrO 2 (zirconium oxide) were used, and a solid electrolyte sintered body was obtained in the same manner as in Example 1, except that these compounds were mixed so that the amounts of Na, Co, Y, or Zr were the composition ratios shown in Table 5 below. For the obtained solid electrolyte sintered body, the composition, X-ray diffraction pattern, and ionic conductivity were evaluated in the same manner as in Example 1. The results are shown in Table 6 below.

[0097]

Table 5

[0098]

Table 6

[0099] From the results in Table 6, even when Na (monovalent element), Co (divalent element), Y (trivalent element), and Zr (tetravalent element) are substituted for Al (trivalent element), PO 4 In the solid electrolyte sintered body with a P amount exceeding 3, it can be seen that the ionic conductivity is improved.

[0100] [Examples 19 to 22] TiO 2 Instead of, ZrO 2 (zirconium oxide), HfO 2 (hafnium oxide), GeO 2 (germanium oxide) or SnO 2 (tin(IV) oxide) were used, and these compounds were mixed so as to have the composition ratios shown in Table 7 below as the amounts of Zr, Hf, Ge, or Sn. Otherwise, in the same manner as in Example 3, a solid electrolyte powder and a solid electrolyte sintered body were obtained. For the obtained solid electrolyte sintered body, the composition, X-ray diffraction pattern, and ionic conductivity were evaluated in the same manner as in Example 1. In the analysis of the X-ray diffraction pattern, the solid electrolyte of Example 19 was LiZr of ICDD card 072-7742 2 (PO 4 ) 3 (lithium zirconium phosphate), the solid electrolyte of Example 20 was LiHf of ICDD card 004-0755 2 (PO 4 ) 3 (lithium hafnium phosphate), the solid electrolyte of Example 21 was LiGe of ICDD card 080-1992 2 (PO 4 ) 3 (lithium germanium phosphate), the solid electrolyte of Example 22 was LiSn of ICDD card 087-2078 2 (PO 4 ) 3 (lithium tin phosphate), and since they showed the same X-ray diffraction pattern, it was confirmed that they each had a NASICON-type crystal structure. The results are shown in Table 8 below together with the results of Example 3.

[0101]

Table 7

[0102]

Table 8

[0103] From the results of Table 8, it can be seen that for the case where Zr, Hf, Ge, or Sn is included instead of Ti, the ion conductivity also improves in the solid electrolyte sintered body with a PO 4 amount exceeding 3.

Explanation of Signs

[0104] 1... positive electrode layer, 1A... positive electrode current collector layer, 1B... positive electrode active material layer, 2... negative electrode layer, 2A... negative electrode current collector layer, 2B... negative electrode active material layer, 3... solid electrolyte layer, 4... laminate, 5... positive electrode external terminal, 6... negative electrode external terminal, 7... side margin layer, 10... all-solid-state battery

Claims

1. A solid electrolyte comprising a NASICON-type compound represented by the following general formula (2). LixM'yM"2-y(PO4)z...(2) (In the general formula (2), M' represents at least one element selected from the group consisting of Na, K, Ag, Au, Ba, Cr, Mn, Fe, Co, Ni, Pd, Pt, Sc, Y, V, Nb, Ta, Ru, Rh, Ir, Al, Ga, In, Mo, W, Tc, Re, Os; M" represents at least one element having a tetravalent valence; x represents a number satisfying 1.003 ≤ x ≤ 1.900; y represents a number satisfying 0.001 ≤ y ≤ 1.999; z represents a number satisfying 3.001 ≤ z ≤ 3.200.)

2. The solid electrolyte according to Claim 1, wherein in the general formula (2), M" represents at least one element selected from the group consisting of Ti, Zr, Hf, Ge, Si, Sn.

3. A solid electrolyte comprising a compound represented by the following general formula (2). Li ｘ M’ ｙ M” ２－ｙ (PO ４ ) ｚ ...(2) (In the general formula (2), x represents a number satisfying 1.003 ≤ x ≤ 1.900; y represents a number satisfying 0.001 ≤ y ≤ 1.999; z represents a number satisfying 3.001 ≤ z ≤ 3.200, (M', M") is any of the following combinations (Al, Ti), (Na, Ti), (Co, Ti), (Y, Ti), (Zr, Ti), (Al, Zr), (Al, Hf), (Al, Ge), (Al, Sn), the solid electrolyte according to Claim 1.

4. An all-solid-state battery comprising a solid electrolyte layer containing the solid electrolyte according to any one of Claims 1 to 3, a positive electrode joined to one surface of the solid electrolyte layer, and a negative electrode joined to the other surface of the solid electrolyte.

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