ACTIVE MATERIAL AND FULLY SOLID SECONDARY BATTERY

Abstract

Active material characterized by a chemical formula Li 3+a V 2-x M x (PO4)3 (0.1≤a≤0.2; 0.1≤x≤1.4), where M is an element present as a divalent or tetravalent cation in a crystal structure, and where an element represented as M in the chemical formula is one or more elements selected from the group consisting of Mg, Ca, Ti, and Zr.

Description

[Technical Area]

[0001] The present disclosure relates to an active material and a fully solid secondary battery. Priority is claimed to Japanese Patent Application No. 2018-033252, filed on February 27, 2018, the contents of which are incorporated herein by reference. [Technical background]

[0002] Lithium-ion secondary batteries are widely used to power small portable devices, such as mobile phones, laptops, and PDAs. Lithium-ion secondary batteries used in such small portable devices must be as small, thin, and reliable as possible.

[0003] Regarding lithium-ion secondary batteries, there are two types of lithium-ion batteries: those that use an organic electrolyte solution as the electrolyte and those that use a solid electrolyte. Compared with a lithium-ion secondary battery that uses an organic electrolyte solution, a lithium-ion secondary battery that uses a solid electrolyte as the electrolyte (fully solid secondary battery) has the advantages of greater freedom in battery shape design, easy availability of a small and thin battery, and high reliability without electrolyte solution leakage.

[0004] On the other hand, fully solid secondary batteries generally have lower lithium-ion conductivity than lithium-ion secondary batteries using an organic electrolyte solution. Furthermore, it is difficult to add a conductivity aid to an active material part, and the electron conductivity is low. Therefore, fully solid secondary batteries have problems such as higher internal resistance and lower output current than lithium-ion secondary batteries using an organic electrolyte solution. Therefore, for fully solid secondary batteries, it is necessary to reduce the internal resistance by increasing the ionic conductivity of lithium ions and the electron conductivity of the active material.

[0005] For example, in Patent Literature 1, some PO4 anions of an active material for a Li3V2(PO4)3-based lithium secondary battery are replaced with BO3 anions, ensuring excellent storage performance and, in particular, maintaining high-temperature performance. In this design, it is important that carbon is bonded to the surface of the active material by coating, thus improving electronic conductivity during use. Other similar compositions containing Li, V, and PO4 anions can also be found in other patent literature. [List of cited literature][Patent literature]

[0006] [Patent Literature 1] WO 2011 / 052632 A1 [Further patent literature] US 2012 0 295 163 A1 US 5 871 866 A US 2015 0 333 330 A1 [Brief description of the invention][Technical problem]

[0007] However, to improve the volume energy density of a fully solid secondary battery, the active material ratio between the positive electrode active material layer and the negative electrode active material layer is preferably high, and it is preferable to use active materials without admixing a conductivity aid such as carbon. Therefore, it is necessary to improve the electronic conductivity of the active material itself. By improving the electronic conductivity of the positive electrode active material and the negative electrode active material, the internal resistance of the fully solid secondary battery can be further reduced.

[0008] The present disclosure has been made in view of the above circumstances and provides an active material having high electron conductivity and an all-solid secondary battery including the active material. [Solution to the problem]

[0009] To address the above-mentioned problems, the inventors conducted extensive studies. As a result, they found that when a portion of V (vanadium) in a conventional active material Li3V2(PO4)3 (hereinafter abbreviated as LVP) is replaced with an element containing a divalent or tetravalent cation, high electronic conductivity is achieved.

[0010] To solve the above problems, the following aspects are provided.

[0011] (1) An active material according to a first aspect is represented by the chemical formula Li 3+a V 2-x M x (PO4)3 (0.1≤a≤0.2, 0.1≤x≤1.4), where M is an element present as a divalent or tetravalent cation in a crystal structure.

[0012] In the active material according to the above aspect, an element represented as M in the chemical formula is one or more elements selected from the group consisting of Mg, Ca, Ti and Zr.

[0013] (2) In the active material according to the above aspect, x can satisfy the relationship 0.2≤x≤1.1.

[0014] (3) M can be Ti.

[0015] (4) A fully solid secondary battery according to a second aspect comprises the active material according to any one of the first aspects.

[0016] (5) The all-solid secondary battery according to the above aspect may comprise an oxide-based solid electrolyte layer containing an element represented as M in this chemical formula.

[0017] (6) The all-solid secondary battery according to the above aspect may comprise a positive electrode current collector layer and a negative electrode current collector layer, wherein the positive electrode current collector layer may contain a positive electrode active material and the negative electrode current collector layer may contain a negative electrode active material, a ratio between the content of the positive electrode current collector and the active material contained in the positive electrode current collector layer may be in a range of 90 / 10 to 70 / 30, and a ratio between the content of the negative electrode current collector and the active material contained in the negative electrode current collector layer may be in a range of 90 / 10 to 70 / 30. [Beneficial effects of inventions]

[0018] The scope of the invention is defined by the claims. Examples within the scope of the invention are marked "according to the invention."

[0019] The active material according to the above aspect has a high electron conductivity. [Brief description of the drawings] Fig. 1 is a schematic diagram showing an example of a cross section of a completely solid secondary battery according to a first embodiment. [Description of the embodiments]

[0020] Preferred examples of the present disclosure will be described appropriately and in detail below with reference to the drawings. In the drawings used in the following description, in order to facilitate understanding of the features of the present disclosure, in some cases, parts of the features are enlarged for clarity. Therefore, the relationships between sizes and the like of the components illustrated in the drawings may differ from those of the actual components. Materials, sizes, and the like exemplified in the following description are examples; the present disclosure is not limited thereto, and they can be appropriately changed within a range where the corresponding effects are achieved.The present disclosure is not limited to the following embodiments, and these may be appropriately modified within a range where the corresponding effects are achieved. For example, numbers, numerical values, amounts, ratios, characteristics, and the like may be omitted, added, and changed without departing from the spirit and scope of the present disclosure. [Fully solid secondary battery]

[0021] Fig. 1 is a schematic diagram showing an example of a cross section of a completely solid secondary battery 10 according to the present embodiment.

[0022] The Fig.The all-solid secondary battery 10 shown in FIG. 1 includes at least one first electrode layer 1, at least one second electrode layer 2, and a solid electrolyte 3 disposed between the first electrode layer 1 and the second electrode layer 2. A laminate 4 has a configuration in which the first electrode layer 1, the solid electrolyte 3, and the second electrode layer 2 are laminated in this order. Each of the first electrode layers 1 is connected to a terminal electrode 5 disposed on one end face. Each of the second electrode layers 2 is connected to a terminal electrode 6 disposed on the other end face.

[0023] Here, in the present embodiment, the vertical direction will be defined, and then the positional relationships between the respective configurations will be described. In the following, the upward direction will be Fig. 1 as the upward direction and the downward in Fig. 1 is referred to as the downward direction. The orientation of the configuration of the fully solid secondary battery according to the present embodiment is not limited here, and the configuration may be reversed.

[0024] One of the first electrode layer 1 and the second electrode layer 2 functions as a positive electrode layer, and the other as a negative electrode layer. Hereinafter, for convenience of understanding, in the present embodiment, a case where the first electrode layer 1 is the positive electrode layer 1 and the second electrode layer 2 is the negative electrode layer 2 is exemplified. However, the present embodiment is not limited to a configuration in which the first electrode layer 1 is a positive electrode layer and the second electrode layer 2 is a negative electrode layer, and may be a configuration in which the first electrode layer 1 is a negative electrode layer and the second electrode layer is a positive electrode layer. Hereinafter, in this specification, reference numeral 1 denotes the positive electrode layer, and reference numeral 2 denotes the negative electrode layer.

[0025] As in Fig. As shown in Figure 1, the positive electrode layer 1 and the negative electrode layer 2 are alternately laminated with the solid electrolyte 3 therebetween. The all-solid secondary battery is charged when lithium ions are transferred between the positive electrode layer 1 and the negative electrode layer 2 with the solid electrolyte 3 therebetween. < Positive electrode layer and negative electrode layer>

[0026] The positive electrode layer 1 includes a positive electrode current collector layer 1A and a positive electrode active material layer 1B containing a positive electrode active material. The negative electrode layer 2 includes a negative electrode current collector layer 2A and a negative electrode active material layer 2B containing a negative electrode active material.

[0027] The positive electrode current collector layer 1A and the negative electrode current collector layer 2A preferably have high conductivity. Therefore, it is preferable to use, for example, silver, palladium, gold, platinum, aluminum, copper, nickel, or the like for the positive electrode current collector layer 1A and the negative electrode current collector layer 2A. Among these materials, copper is unlikely to react with a positive electrode active material, a negative electrode active material, or a solid electrolyte. Therefore, 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 secondary battery 10 can be reduced. In this case, the materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may be the same as or different from each other.

[0028] The positive electrode active material layer 1B is formed on one or both surfaces of the positive electrode current collector layer 1A. For example, when the positive electrode layer 1 is formed as the uppermost layer of the laminate 4 in the lamination direction between the positive electrode layer 1 and the negative electrode layer 2, there is no negative electrode layer 2 opposing the positive electrode layer 1 located in the uppermost layer. That is, in the positive electrode layer 1 positioned in the uppermost layer, the positive electrode active material layer 1B can be provided only on a surface on the lower side in the lamination direction.

[0029] As in the positive electrode active material layer 1B, the negative electrode active material layer 2B is also formed on one or both surfaces of the negative electrode current collector layer 2A. When the negative electrode layer 2 is formed as the lowest layer of the laminate 4 in the lamination direction between the positive electrode layer 1 and the negative electrode layer 2, the negative electrode active material layer 2B in the negative electrode layer 2, which is located in the lowest layer, can be provided only on one surface on the upper side in the lamination direction.

[0030] The positive electrode active material layer 1B contains a positive electrode active material that transfers electrons. Furthermore, the negative electrode active material layer 2B contains a negative electrode active material that transfers electrons. Furthermore, the positive electrode active material layer 1B and the negative electrode active material layer 2B may contain a conductivity aid, a binder, and the like. Preferably, the positive electrode active material and the negative electrode active material can effectively intercalate and release lithium ions.

[0031] Regarding the negative electrode active material and the positive electrode active material, an active material is used in which a part of V in Li3V2(PO4)3 is replaced by another element M, and a composition amount of Li is additionally adjusted. Specifically, the negative electrode active material and the positive electrode active material are active materials represented by a chemical formula Li. 3+a V 2-x M x (PO4)3 (0.1≤a≤0.2, 0.1≤x≤1.4). Here, an active material is used in which M is an element that can occur as a divalent or tetravalent cation in the crystal structure. When the composition amount of Li is adjusted within the above range, high electronic conductivity can be achieved.

[0032] According to such an active material in which a part of V in Li3V2(PO4)3 is replaced by another element M, higher electronic conductivity is obtained than in an active material Li3V2(PO4)3 in which no element is replaced. When replaced with an element that can become a divalent cation, oxygen deficiency in the crystal lattice is more likely to occur, and free electrons are generated due to the occurrence of oxygen deficiency. In addition, when an element is replaced with an element that can become a tetravalent cation, holes are more likely to appear in the crystal lattice and generate holes. Accordingly, when a part of V is replaced with an element that becomes divalent or tetravalent in the crystal lattice, the electronic conductivity of the active material can be improved and the internal resistance of the all-solid-state secondary battery can be reduced. That is, the output current can be increased.

[0033] For simplicity, an active material used in a completely solid secondary battery is described, but the active material can be used not only in completely solid secondary batteries but also in completely solid batteries.

[0034] In the chemical formula Li 3+a V 2-x M x In (PO4)3, an element represented as M can be an element that is a divalent or tetravalent cation in the crystal structure. In the chemical formula Li 3+a V 2-x M x (PO4)3 is an element represented as M, preferably one or more elements selected from the group consisting of Mg, Ca, Ti and Zr. In the chemical formula Li 3+a V 2-x M x (PO4)3 is an element represented as M, most preferably Ti.

[0035] For example, Ti has an ionic radius close to that of a (hexacoordinate) trivalent V cation. It is assumed that an element with an ionic radius close to that of a (hexacoordinate) trivalent V cation will readily replace V. For an element with an ionic radius larger than that of a (hexacoordinate) trivalent V cation, the bond between the element and O in the Li 3+a In a V2(PO4)3 crystal, replacing V with this element leads to a weakening of the bond between the element and O. Therefore, oxygen is easily released during heat treatment under a reducing atmosphere.

[0036] The ionic radius of the (hexacoordinate) trivalent cation V in the active material Li 3+aV2(PO4)3 is 0.64 Å. On the other hand, the (hexacoordinate) divalent Ti cation has an ionic radius of 0.86 Å, the (hexacoordinate) trivalent Ti cation has an ionic radius of 0.67 Å, ​​and the (hexacoordinate) tetravalent Ti cation has an ionic radius of 0.61 Å. The (hexacoordinate) divalent Mg cation has an ionic radius of 0.72 Å. The (hexacoordinate) divalent Ca cation has an ionic radius of 1.00 Å. The (hexacoordinate) tetravalent Zr cation has an ionic radius of 0.72 Å.

[0037] In the above chemical formula Li 3+a V 2-x M x In (PO4)3, the replacement amount x of element M is preferably 0.2≤x≤1.1. The replacement amount x of element M is preferably 0.4≤x≤0.9.

[0038] If the replacement amount x of element M is greater than 1.1, the V content in the final active material becomes smaller, and the capacity of the active material may decrease. This is because the presence of V, whose valence varies, is converted into Li during a Li release reaction. 3+a V2(PO4)3, which is used in the positive electrode active material layer 1B and the negative electrode active material layer 2B, is considered essential.

[0039] When the replacement amount x of element M is less than 0.2, the M content in the final active material becomes smaller, and oxygen deficiency and / or holes are unlikely to occur, so the improvement in electronic conductivity is small. When the replacement amount of element M is 0.4≤x≤0.9, the capacity of the active material can be improved and the electronic conductivity can be improved more appropriately.

[0040] A preferable range of the replacement amount x of the element M may be wider depending on an element used as the element M. For example, when the element M is Ti, the capacity of the active material can be kept high in a range of 0.05≤x≤1.3, with 0.2≤x≤1.1 being preferable and 0.2≤x≤0.75 being even more preferable. When the element is Mg, the capacity of the active material can be kept high in a range of 0.05≤x≤1.1, with 0.1≤x≤0.75 being preferable and 0.1≤x≤0.5 being even more preferable. When the element M is Ca, the capacity of the active material can be kept high in a range of 0.1≤x≤1.1, with 0.1≤x≤0.75 being preferable and 0.1≤x≤0.5 being even more preferable. When the element M is Zr, the capacity of the active material can be kept high in a range of 0.05≤x≤1.3, with 0.1≤x≤1.1 being preferable and 0.1≤x≤0.75 being even more preferable.

[0041] There is no clear distinction between the active materials that make up the positive electrode active material layer 1B and the negative electrode active material layer 2B. Comparing the potentials of two compounds, a compound with a higher potential can be used for the positive electrode active material, and a compound with a lower potential can be used for the negative electrode active material.

[0042] Furthermore, the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may contain a positive electrode active material and a negative electrode active material, respectively. The content ratios of the active materials contained in the electrode current collector layers are not particularly limited as long as the active materials function as current collectors. For example, the volume ratio of the positive electrode current collector / positive electrode active material or the negative electrode current collector / negative electrode active material is preferably in a range of 90 / 10 to 70 / 30, and more preferably in a range of 85 / 15 to 75 / 25.

[0043] When the positive electrode current collector layer 1A contains a positive electrode active material, the adhesion between the positive electrode current collector layer 1A and the positive electrode active material layer 1B is improved. When the negative electrode current collector layer 2A contains a negative electrode active material, the adhesion between the negative electrode current collector layer 2A and the negative electrode active material layer 2B is improved. “Solid electrolyte”

[0044] The solid electrolyte 3 is preferably a phosphate-based solid electrolyte. A material with low electron conductivity and high lithium ion conductivity is preferably used for the solid electrolyte 3. Specifically, it is desirable, for example, to select at least one compound from the group consisting of perovskite-type compounds such as La 0,5 Li 0,5 TiO3, lisicon compounds such as Li 14Zn(GeO4)4, garnet-type compounds such as Li7La3Zr2O 12 , Nasicon-type compounds such as Li 1.3 Al 0,3 Ti 1.7 (PO4)3 and Li 1.5 A1 0,5 Ge 1.5 (PO4)3, thio-lisicon compounds such as Li 3.25 Ge 0,25 P 0,75 S4 and Li3PS4, glass compounds such as Li2S-P2S5 and Li2O-V2O5-SiO2, and phosphoric acid compounds such as Li3PO4, Li 3.5 Si 0,5 P 0,5 O4 and Li 2.9 PO 3.3 N 0,46 consists.

[0045] The solid electrolyte 3 is preferably an oxide-based solid electrolyte containing an element represented by the above chemical formula Li 3+a V 2-x M x(PO4)3 is represented as M. That is, an element that can exist as a divalent or tetravalent cation in the crystal structure should be used. For example, one or more elements selected from the group consisting of Mg, Ca, Ti, Zr, Sr, Ba, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, and W can be used. Furthermore, the solid electrolyte 3 is preferably one or more elements selected from the group consisting of Mg, Ca, Ti, and Zr, and more preferably Ti. Such a solid electrolyte 3 can be used, for example, for an all-solid secondary battery.

[0046] When the solid electrolyte 3 contains the element M, the concentration change of the element M at the bonding interface between the positive electrode active material layer 1B containing the solid electrolyte 3 and the element M and / or the negative electrode active material layer 2B is gentle. Therefore, the activation energy at the bonding interface between the positive electrode active material layer 1B and the solid electrolyte 3 and the activation energy of Li ions at the bonding interface between the negative electrode active material layer 2B and the solid electrolyte 3 become small. Here, the activation energy at the bonding interface between the positive electrode active material layer 1B and the solid electrolyte 3 is an energy required for Li ions to pass through the bonding interface between the positive electrode active material layer 1B and the solid electrolyte 3.Furthermore, the activation energy of the bonding interface between the negative electrode active material layer 2B and the solid electrolyte 3 is the energy required to pass through the bonding interface between the negative electrode active material layer 2B and the solid electrolyte 3. Therefore, Li ions move easily at the bonding interface between the positive electrode active material layer 1B and the solid electrolyte 3 and at the bonding interface between the negative electrode active material layer 2B and the solid electrolyte 3, and the Li ion conductivity at the bonding interface is improved. This reduces the internal resistance of the all-solid secondary battery. (connection electrode)

[0047] As in Fig.As shown in Figure 1, the terminal electrodes 5 and 6 are shaped to contact the side surfaces (exposed end surfaces of the positive electrode layer 1 and the negative electrode layer 2) of the laminate 4. The terminal electrodes 5 and 6 are connected to external terminals and are responsible for transferring electrons into the laminate 4.

[0048] A material with high conductivity is preferably used for the connecting electrodes 5 and 6. Examples of materials that can be used include silver, gold, platinum, aluminum, copper, tin, nickel, gallium, indium, and their alloys. "Method for producing a fully solid secondary battery." (Formation of the laminate)

[0049] For a method of forming the laminate 4, for example, a simultaneous firing method or a sequential firing method may be used.

[0050] The simultaneous firing method is a method in which layer-forming materials are laminated and then fired together to produce a laminate. The sequential firing method is a method for sequentially producing layers and is a method in which firing is performed every time a layer is formed. Compared with the sequential firing method, the simultaneous firing method makes it possible to form the laminate 4 with fewer working processes than with the sequential firing method. Moreover, the laminate 4 becomes denser with the simultaneous firing method compared with the sequential firing method. Regarding a method for forming the laminate 4 according to the present embodiment, a known sequential firing method or the like can be used, but a case in which the laminate 4 is produced by the simultaneous firing method will be exemplified below.

[0051] The simultaneous firing method includes a process of preparing a paste of materials constituting the laminate 4, a process of applying and drying the paste to produce a green sheet, and a process of laminating the green sheets to form a laminated sheet and simultaneously firing these sheets.

[0052] First, the materials of the positive electrode current collector layer 1A, the positive electrode active material layer 1B, the solid electrolyte 3, the negative electrode active material layer 2B, and the negative electrode current collector layer 2A, which form the laminate 4, are processed into pastes.

[0053] There are no particular limitations to the method for processing materials into pastes. For example, a paste can be obtained by mixing material powders in a carrier. Here, the carrier is a general term for a liquid-phase medium. The carrier contains a solvent, a binder, and the like.

[0054] According to such a method, a paste for the positive electrode current collecting layer 1A, a paste for the positive electrode active material layer 1B, a paste for the solid electrolyte 3, a paste for the negative electrode active material layer 2B, and a paste for the negative electrode current collecting layer 2A are prepared.

[0055] Next, a green film is produced. The green film is obtained by applying the prepared paste to a substrate such as polyethylene terephthalate (PET) film, drying it if necessary, and then peeling it off the substrate. The method for applying the paste is not particularly limited. For example, known methods such as screen printing, coating, transfer, and a doctor blade method can be used.

[0056] Next, the prepared green sheets are laminated into a laminated sheet in the desired order and number of laminates. Once the green sheets are laminated, alignment, cutting, and the like are performed as needed. For example, when manufacturing a parallel-type or series-parallel-type battery, alignment is preferably performed so that one end face of the positive electrode current collector layer and one end face of the negative electrode current collector layer are not aligned, and the green sheets are laminated.

[0057] The laminated film can be prepared using a known method. For example, the laminated film can be produced by a method in which a positive electrode active material layer unit and a negative electrode active material layer unit, which are described below, are prepared and laminated.

[0058] First, a paste for the solid electrolyte 3 is applied to a substrate such as a PET film by a doctor blade method and dried to form a sheet solid electrolyte 3. Next, a paste for the positive electrode active material layer 1B is screen-printed on the solid electrolyte 3 and dried to form the positive electrode active material layer 1B. Next, a paste for the positive electrode current collector layer 1A is screen-printed on the positive electrode active material layer 1B and dried to form the positive electrode current collector layer 1A. In addition, a paste for the positive electrode active material layer 1B is screen-printed on the positive electrode current collector layer 1A and dried to form the positive electrode active material layer 1B.

[0059] Then, the PET film is peeled off to obtain a positive electrode active material layer assembly. The positive electrode active material layer assembly is a laminated film in which the solid electrolyte 3 / the positive electrode active material layer 1B / the positive electrode current collector layer 1A / the positive electrode active material layer 1B are laminated in this order.

[0060] A negative electrode active material layer assembly is manufactured using the same process. The negative electrode active material layer assembly is a laminated film in which the solid electrolyte 3 / the negative electrode active material layer 2B / the negative electrode current collector layer 2A / the negative electrode active material layer 2B are laminated in this order.

[0061] Next, a positive electrode active material layer unit and a negative electrode active material layer unit are laminated. In this case, the solid electrolyte 3 of the positive electrode active material layer unit, the negative electrode active material layer 2B of the negative electrode active material layer unit, or the positive electrode active material layer 1B of the positive electrode active material layer unit, and the solid electrolyte 3 of the negative electrode active material layer unit are laminated in contact with each other.In this way, a laminated film is obtained in which the positive electrode active material layer 1B / the positive electrode current collector layer 1A / the positive electrode active material layer 1B / the solid electrolyte 3 / the negative electrode active material layer 2B / the negative electrode current collector layer 2A / the negative electrode active material layer 2B / the solid electrolyte 3 are laminated in this order. Next, debinding and firing are performed to produce a complete all-solid-state battery laminate.

[0062] Here, when the positive electrode active material layer unit and the negative electrode active material layer unit are laminated, the units are shifted and laminated such that the electrode current collector layer 1A of the positive electrode active material layer unit extends only to one end surface and the electrode current collector layer 2A of the negative electrode active material layer unit extends only to the other surface. Then, on the surface of the laminate in which the units are laminated and on whose surface the solid electrolyte 3 is not present, a film for the solid electrolyte 3 is additionally laminated with a predetermined thickness to obtain a laminated film. Debinding and firing can be performed, for example, by firing in a nitrogen atmosphere at a temperature of 600°C to 1000°C. The maintenance time for debinding and firing is, for example, 0.1 to 6 hours.

[0063] Next, the resulting laminated films are pressed together. Compression is preferably achieved with heating. The heating temperature during compression can be, for example, 40 to 95°C, but is preferably 50 to 80°C.

[0064] Next, the pressed laminated films are fired simultaneously to form the laminate 4 from a single sintered component. The laminated film is fired, for example, by heating under a nitrogen atmosphere at 600°C to 1,000°C. A firing time is, for example, 0.1 to 3 hours.

[0065] The resulting sintered component (the laminate 4) can be placed in a cylindrical container together with an abrasive material such as aluminum oxide and subjected to tumbling. This makes it possible to chamfer the corners of the laminate 4. As another method, the laminate 4 can be polished by sandblasting. This method is preferable because only a specified section can be polished. The laminate 4 is manufactured using the above-mentioned processes.

[0066] By forming terminal electrodes 5 and 6 at the ends of the fabricated laminate 4, a fully solid lithium-ion secondary battery can be manufactured. Terminal electrodes 5 and 6 can be manufactured using a known method, such as a sputtering method.

[0067] As described above, the active material according to the present embodiment has high electron conductivity.

[0068] If Li3+a V 2-x M x (PO4)3 (0.1≤a≤0.2, and 0.1 <x≤1,4), das eine höhere Elektronenleitfähigkeit als das Aktivmaterial Li3V2(PO4)3 hat, als Aktivmaterial der positiven Elektrode oder als Aktivmaterial der negativen Elektrode der vollkommen festen Sekundärbatterie verwendet wird, kann die Elektronenleitfähigkeit der Aktivmaterialschicht der positiven Elektrode oder der Aktivmaterialschicht der negativen Elektrode in der vollkommen festen Sekundärbatterie verbessert werden. Das heißt, der Innenwiderstand der vollkommen festen Sekundärbatterie kann reduziert werden.

[0069] While the preferred embodiments of the present disclosure have been described in detail above with reference to the drawings, it goes without saying that configurations and combinations thereof in the embodiments are merely examples, and the present disclosure is not limited to such examples. Additions, omissions, substitutions, and various other modifications to the configuration of the embodiments may be made without departing from the scope of the present disclosure. [Examples](Examples 1 to 10 and Comparative Examples 1 and 2)

[0070] The laminate 4, in which the solid electrolyte 3 / the positive electrode active material layer 1B / the positive electrode current collector layer 1A / the positive electrode active material layer 1B / the solid electrolyte 3 / the negative electrode active material layer 2B / the negative electrode current collector layer 2A / the negative electrode active material layer 2B / the solid electrolyte 3 were laminated in this order, was manufactured by a simultaneous firing process. The layer structure was as follows.

[0071] The positive electrode current collector layer 1A and the negative electrode current collector layer 2A: Cu+Li3V2(PO4)3

[0072] The active material layer 1B of the positive electrode and the active material layer 2B of the negative electrode: Li 3+a V 2-x Ti x (PO4)3 (where a=0, 0≤x≤1.5)

[0073] The solid electrolyte 3: Li 1,3 Al 0,3 Ti 1,7 (PO4)3

[0074] The number of layers was 25. They were prepared such that the respective thicknesses of the positive electrode current collector layer 1A, the negative electrode current collector layer 2A, the positive electrode active material layer 1B, and the negative electrode active material layer 2B after firing were 3 µm, and the thickness of the solid electrolyte layer between the positive electrode active material layer 1B and the negative electrode active material layer 2B after firing was 20 µm.

[0075] The temperature during simultaneous firing was 800°C, and the firing time was 1 hour.

[0076] In the following, Li 3+a V 2-x Ti x (PO4)3 with a=0 in some cases as Li3V 2-x Ti x (PO4)3.

[0077] The electronic conductivity [S / cm] of the active material used for the positive electrode active material layer 1B and the negative electrode active material layer 2B was measured. In addition, the internal resistance [Ω] of the laminate 4 prepared with the active material was measured.

[0078] The electronic conductivity [S / cm] of the active material used for the positive electrode active material layer 1B and the negative electrode active material layer 2B was measured as follows.

[0079] An active material powder was formed into a disc (10 mm in diameter and approximately 2 mm thick) and fired at 850 to 1000°C under a nitrogen atmosphere to obtain a disc-shaped sintered component with a relative density of 92% or more. The surface of the resulting disc-shaped sintered component was polished, the dimensions (diameter R, thickness t) were measured, and then Pt sputtering was performed using a magnetron sputtering device. A Pt electrode was formed on both surfaces of the disc-shaped sintered component, thus producing a sample for measuring electronic conductivity. The sample was applied with 1 V to measure electronic conductivity using an impedance analyzer (1260 commercially available from Solartron), and the electronic conductivity was calculated from the current value I' after 15 minutes. σ e =I'×t / (π(R / 2) 2) was used as the calculation formula.

[0080] The internal resistance [Ω] of laminate 4 was measured as follows.

[0081] A resin-Ag paste was applied to the terminal electrodes 5 and 6 of the laminate 4 to form electrodes, and then a CC 20 µA charge was performed up to 1.6 V. After 10 minutes of rest (the voltage immediately before the start of the discharge was V in this case), the internal resistance was calculated from the voltage value V' 1 second immediately after the start of the CC 20 µA discharge. The calculation formula used was internal resistance = (V - V') / 20 µ. [Table 1] Li3V 2-x Of x (PO4)3 Electronic conductivity InnerResistance x S / cm Ω Example 1 0,03 2,0×10 -7 4k Example 2 0,05 2,7×10 -7 500 Example 3 0,1 3,0×10 -7 300 Example 4 0,2 9,3×10 -7 200 Example 5 0,5 8,7×10 -7 190 Example 6 0,75 7,4×10 -7 190 Example 7 1,0 6,6×10 -7 200 Example 8 1,1 4,7×10 -7 240 Example 9 1,3 3,5× 10-7 600 Example 10 1,4 2,3×10 -7 5k Comparison example 1 0 7,4×10 -8 20k Comparison example 2 1,5 9,6×10 -8 21k

[0082] As can be seen from Table 1, the active material in which part of V in Li3V2(PO4)3 was replaced by Ti showed an increase in electronic conductivity, and the laminate 4 containing the active material showed a decrease in internal resistance. In particular, when the replacement amount x of Ti in the chemical formula Li3V 2-x Ti x (PO4)3 was 0.2 to 1.1 (Examples 4 to 8), the electronic conductivity was 4.7×10 -7 S / cm or more and the internal resistance 240 Ω or less.

[0083] Although not bound by theory, it is suspected that such an increase in electronic conductivity and decrease in internal resistance was caused by the valence achieved upon ionization of Ti in the active material's crystal lattice and the ionic radius of the Ti ions. When Ti became a divalent cation in the active material's crystal lattice, oxygen deficiency in the crystal lattice was more likely to occur, and free electrons were generated. When Ti became a tetravalent cation in the active material's crystal lattice, holes were more likely to appear in the crystal lattice, and holes were generated.The ionic radius of Ti (divalent and hexacoordinate cation, 0.86 Å), which was larger than the ionic radius of V (trivalent and hexacoordinate cation, 0.64 Å), weakened the Ti-O bonding force in the crystal lattice of the active material, thus promoting the release of oxygen during heat treatment and creating oxygen deficiency. This was assumed to be the reason for the increase in the electronic conductivity of the active material.

[0084] On the other hand, when V was not replaced by Ti (Comparative Example 1), the electronic conductivity was 7.4×10 -8 S / cm, which was about an order of magnitude lower than in Examples 4 to 8. Furthermore, almost no improvement in electronic conductivity was observed when a large amount of Ti was replaced (Comparative Example 2). Furthermore, the internal resistance increased when a large amount of Ti was replaced. (Examples 11 to 20 and comparative example 3)

[0085] The conditions of Examples 11 to 20 were the same as in Examples 1 to 10, except that the positive electrode active material layer 1B and the negative electrode active material layer 2B, Li 3+a V 2-x Ti x (PO4)3 (where a=0, 0≤x≤1.5) in Examples 1 to 10, in Li 3+a V 2-x Mg x (PO4)3 (where a=0, 0≤x≤1.5). That is, the electronic conductivity [S / cm] and internal resistance [Ω] were measured under the same conditions as in Examples 1 to 10. [Table 2] Li3V 2-x Mg x (PO4)3 Electronic conductivity InnerResistance x S / cm Ω Example 11 0,03 9,0×10 -8 6k Example 12 0,05 1,4×10 -7 600 Example 13 0,1 3,2×10 -7 340 Example 14 0,2 3,1×10 -7 300 Example 15 0,5 2,9×10 -7 400 Example 16 0,75 2,4×10 -7 470 Example 17 1,0 1,9×10 -7 530 Example 18 1,1 1,7×10 -7 580 Example 19 1,3 1,3×10 -7 1k Example 20 1,4 9,9×10 -8 12k Comparison example 1 0 7,4×10 -8 20k Comparison example 3 1,5 7,0×10 -8 25k

[0086] As can be seen from Table 2, the active material in which a portion of V in Li3V2(PO4)3 was replaced by Mg showed an increase in electronic conductivity compared to the active material in which no portion of V was replaced by Mg. Laminate 4 containing the active material showed a decrease in internal resistance. In particular, when the replacement amount x of Mg in the chemical formula Li3V 2-x Mg x (PO4)3 was 0.1 to 1.1 (Examples 13 to 18), an increase in electronic conductivity and a decrease in internal resistance were observed.

[0087] Although not bound by theory, it was assumed that such an increase in electronic conductivity and a decrease in internal resistance were caused by the valence that could be achieved upon ionization of Mg in the crystal lattice of the active material and the ionic radius of the Mg ions. When Mg became a divalent cation in the crystal lattice of the active material, oxygen deficiency in the crystal lattice was more likely to occur and free electrons were generated. The ionic radius (divalent and hexacoordinate cation, 0.72 Å) of Mg, which was larger than the ionic radius (trivalent and hexacoordinate cation, 0.64 Å) of V, weakened the bonding force between Mg and O in the crystal lattice of the active material, thus promoting the release of oxygen during heat treatment and generating oxygen deficiency. This was assumed to be the cause of the increase in the electronic conductivity of the active material.

[0088] On the other hand, when a large amount of Mg was replaced (Comparative Example 3), no improvement in electronic conductivity was observed. Furthermore, the internal resistance increased when a large amount of Mg was replaced. (Examples 21 to 30 and Comparative Example 4)

[0089] The conditions of Examples 21 to 30 were the same as in Examples 1 to 10, except that the positive electrode active material layer 1B and the negative electrode active material layer 2B, Li3V 2-x Ti x (PO4)3 (where 0≤x≤1.5) in Examples 1 to 10, in Li3V 2-x Ca x (PO4)3 (where 0≤x≤1.5). The electronic conductivity [S / cm] and internal resistance [Ω] were measured under the same conditions as in Examples 1 to 10. [Table 3] Li3V 2-x Ca x (PO4)3 Electronic conductivity InnerResistance x S / cm Ω Example 21 0,03 7,0×10 -8 7k Example 22 0,05 6,6×10 -8 2k Example 23 0,1 9,4×10 -7 270 Example 24 0,2 8,7×10 -7 220 Example 25 0,5 7,3×10 -7 230 Example 26 0,75 5,9×10 -7 250 Example 27 1,0 3,8×10 -7 250 Example 28 1,1 3,8×10 -7 590 Example 29 1,3 2,0×10 -7 2k Example 30 1,4 1,1×10 -7 14k Comparison example 1 0 7,4×10 -8 20k Comparison example 4 1,5 4,8×10 -8 41k

[0090] As can be seen from Table 3, the active material in which part of V in Li3V2(PO4)3 was replaced by Ca showed an increase in electronic conductivity, and the laminate 4 containing the active material showed a decrease in internal resistance. In particular, when the replacement amount x of Ca in the chemical formula Li3V 2-x Ca x (PO4)3 was 0.1 to 1.1 (Examples 23 to 28), a significant increase in electronic conductivity and a decrease in internal resistance were observed.

[0091] Although not bound by theory, it is suggested that such an increase in electronic conductivity and decrease in internal resistance was caused by the valence achieved upon ionization of Ca in the active material's crystal lattice and the ionic radius of the Ca ions. When Ca became a divalent cation in the active material's crystal lattice, oxygen deficiency was more likely to occur in the crystal lattice and free electrons were generated. The ionic radius (divalent and hexacoordinate cation, 1.00 Å) of Ca, which was larger than the ionic radius (trivalent and hexacoordinate cation, 0.64 Å) of V, weakened the Ca-O bonding force in the active material's crystal lattice, thus promoting the release of oxygen during heat treatment and generating oxygen deficiency. This was hypothesized to be the cause of the increase in the active material's electronic conductivity.

[0092] On the other hand, no improvement in electronic conductivity was observed when replacing the Ca ions with a large amount (Comparative Example 4). Furthermore, the internal resistance increased when a large amount of Ca was replaced. (Examples 31 to 40 and Comparative Example 5)

[0093] The conditions of Examples 31 to 40 were the same as in Examples 1 to 10, except that the positive electrode active material layer 1B and the negative electrode active material layer 2B, Li3V 2-x Ti x (PO4)3 (where 0≤x≤1.5) in Examples 1 to 10, in Li3V 2-x Zr x (PO4)3 (where 0≤x≤1.5). The electronic conductivity [S / cm] and internal resistance [Ω] were measured under the same conditions as in Examples 1 to 10. [Table 4] Li3V 2-x Zr x (PO4)3 Electronic conductivity InnerResistance x S / cm Ω Example 31 0,03 9,8×10 -8 7k Example 32 0,05 1,2×10 -7 800 Example 33 0,1 3,2×10 -7 500 Example 34 0,2 3,1×10 -7 400 Example 35 0,5 2,9×10 -7 380 Example 36 0,75 2,4×10 -7 350 Example 37 1,0 1,9×10 -7 380 Example 38 1,1 1,7×10 -7 400 Example 39 1,3 1,2×10 -7 670 Example 40 1,4 9,9×10 -8 11k Comparison example 1 0 7,4×10 -8 20k Comparison example 5 1,5 6,8×10 -8 30k

[0094] As can be seen from Table 4, the active material in which part of V in Li3V2(PO4)3 was replaced by Zr showed an increase in electronic conductivity, and the laminate 4 containing the active material showed a decrease in internal resistance. In particular, when the replacement amount x of Zr in the chemical formula Li3V 2-x Zr x (PO4)3 was 0.1 to 1.1 (Examples 33 to 38), an increase in electronic conductivity and a decrease in internal resistance were observed.

[0095] Although not bound by theory, it is suggested that such an increase in electronic conductivity and decrease in internal resistance was caused by the valence achieved upon ionization of Zr in the active material's crystal lattice and the ionic radius of the Zr ions. When Zr became a tetravalent cation in the active material's crystal lattice, holes were more likely to appear in the crystal lattice and were generated. The ionic radius (tetravalent and hexacoordinate cation, 0.72 Å) of Zr, which was larger than the ionic radius (trivalent and hexacoordinate cation, 0.64 Å) of V, weakened the Zr-O bonding force in the active material's crystal lattice, thus promoting the release of oxygen during heat treatment and creating oxygen deficiency. This was assumed to be the cause of the increase in the active material's electronic conductivity.

[0096] On the other hand, no improvement in electronic conductivity was observed when replacing the ferrite with a large amount of Zr (Comparative Example 5). Furthermore, the internal resistance increased when a large amount of Zr was replaced. (Examples 41 to 50 and Comparative Examples 11 and 12)

[0097] The conditions of Examples 41 to 50 were the same as in Examples 1 to 10, except that the positive electrode active material layer 1B and the negative electrode active material layer 2B, Li 3+a V 2-x Ti x (PO4)3 (where a=0, 0≤x≤1.5) in Examples 1 to 10, in Li3V 2-x Ti x Ca x (PO4)3 (where -0.3≤a≤0.7, x=1). The electronic conductivity [S / cm] and internal resistance [Ω] were measured under the same conditions as in Examples 1 to 10. [Table 5] Li 3+a V 2-x You x (PO4)3 Electronic conductivity Inner resistance a x S / cm Ω Example 41 -0,3 1,0 1,9×10 -7 700 Example 42 -0,2 1,0 2,5×10 -7 430 Example 43 0 1,0 6,6×10 -7 200 Inventive Example 44 0,1 1,0 8,2×10 -7 190 Inventive Example 45 0,2 1,0 8,7×10 -7 180 Example 46 0,3 1,0 5,8×10 -7 220 Example 47 0,4 1,0 4,0×10 7 290 Example 48 0,5 1,0 3,3×10 -7 360 Example 49 0,6 1,0 2,9×10 -7 400 Example 50 0,7 1,0 2,2×10 -7 670 Comparison example11 -0,4 1,0 7,8×10 -8 17k Comparison example12 0,8 1,0 9,5×10 -8 13k

[0098] As can be seen from Table 5, the active material in which the composition amount of Li in Li 3+a V 2-x Ti x (PO4)3 was adjusted to a range of -0.3≤a≤0.7, an increase in the electronic conductivity and a decrease in the internal resistance of the active material were observed. In particular, when the range was adjusted to -0.2≤a≤0.6 (Example 42 to Example 49), a significant increase in the electronic conductivity and a decrease in the internal resistance were observed.

[0099] Such an increase in electronic conductivity and decrease in internal resistance is not bound by theory. It was assumed that the cause described above led to an increase in the electronic conductivity of the active material and a decrease in internal resistance.

[0100] On the other hand, when a≤-0.4 and 0.8≤a were satisfied, no improvement in electronic conductivity was observed. Furthermore, the internal resistance increased. [Reference symbol list] 1 first electrode layer and positive electrode layer 1A positive electrode current collector layer 1B Active material layer of the positive electrode 2 second electrode layer and negative electrode layer 2A negative electrode current collector layer 2B Active material layer of the negative electrode 3 Solid electrolyte 4 Laminat 5, 6 connection electrodes 10 fully solid secondary battery

Claims

[1] Active material characterized by a chemical formula Li 3+a V 2-x M x (PO4)3 (0.1≤a≤0.2; 0.1≤x≤1.4), where M is an element present as a divalent or tetravalent cation in a crystal structure, and where an element represented as M in the chemical formula is one or more elements selected from the group consisting of Mg, Ca, Ti and Zr. [2] The active material according to claim 1, wherein 0.2≤x≤1.1 is satisfied. [3] The active material according to any one of claims 1 to 2, wherein the element represented as M is Ti. [4] A fully solid secondary battery comprising the active material according to any one of claims 1 to 3. [5] A fully solid secondary battery according to claim 4, comprising an oxide-based solid electrolyte layer containing an element represented as M in this chemical formula. [6] A fully solid secondary battery according to claim 4 or 5, comprising a positive electrode current collector layer and a negative electrode current collector layer, wherein the positive electrode current collecting layer contains a positive electrode active material, wherein the negative electrode current collecting layer contains a negative electrode active material, wherein a ratio between the content of the positive electrode current collector and the positive electrode active material contained in the positive electrode current collector layer is in a range of 90 / 10 to 70 / 30, and wherein a ratio between the content of the negative electrode current collector and the negative electrode active material contained in the negative electrode current collector layer is in a range of 90 / 10 to 70 / 30.

Images