Positive electrode active material layer and all-solid-state battery

Abstract

To provide a positive electrode active material, a positive electrode active material layer, and an all-solid-state battery with excellent rate characteristics.SOLUTION: A positive electrode active material according to an embodiment includes active material particles, and a coating material that coats the active material particles, the coating material is different in composition or material from a solid electrolyte contained in a solid electrolyte layer, and the coating material is represented by the chemical formula LiαAβBγ, where A is one or more elements selected from an alkali metal, an alkaline earth metal, and a transition metal, B consists of halogen or halogen and a predetermined anion, α satisfies 1≤α≤3, β satisfies 0.5≤β≤1.5, and γ satisfies 4≤γ≤6.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention , positive The present invention relates to an electrode active material layer and an all-solid-state battery. [Background technology]

[0002] In recent years, electronics technology has made remarkable progress, leading to efforts to make portable electronic devices smaller, lighter, thinner, and more multifunctional. Accordingly, there is a strong demand for batteries that serve as the power source for electronic devices to be smaller, lighter, thinner, and more reliable, and all-solid-state batteries that use solid electrolytes have attracted attention.

[0003] An all-solid-state battery includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte sandwiched between them. It has been reported that coating the surface of the positive electrode active material with a compound can improve the performance of all-solid-state batteries (e.g., Patent Documents 1 to 3).

[0004] For example, Patent Document 1 describes coating the surface of lithium-cobalt composite oxide powder with alumina. Patent Document 2 describes coating the surface of a positive electrode active material with a mixed ionic conductor composed of Li3VO4 and Li3PO4. Patent Document 3 describes coating with a Li-containing compound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-276454 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-251256 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-26003 Summary of the Invention [Problem to be solved by the invention]

[0006] However, coating materials containing these oxides have poor conformability to the surface of active material particles during molding. As a result, when molding the positive electrode active material layer, voids or the like are formed between the active material particles, which can result in insufficient rate characteristics. The C rate indicates the speed of charge and discharge. In constant current charge / discharge measurements, the magnitude of the current that fully charges (or discharges) the theoretical capacity of a battery in one hour is defined as 1C. The higher the ratio of the capacity when the C rate is increased to the capacity when discharged at a specified C rate, the better the rate characteristics. A battery with excellent discharge rate characteristics is capable of rapid discharge.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a positive electrode active material, a positive electrode active material layer, and an all-solid-state battery that are excellent in rate characteristics. [Means for solving the problem]

[0008] In order to solve the above problems, the following means are provided.

[0009] (1) A positive electrode active material according to a first aspect is a positive electrode active material included in the positive electrode active material layer of an all-solid-state battery including a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer sandwiched between the positive electrode active material layer and the negative electrode active material layer, the positive electrode active material including active material particles and a coating material that coats the active material particles, the coating material having a composition or material different from that of the solid electrolyte included in the solid electrolyte layer, and the coating material including Li α A β B γ In the chemical formula, A is one or more elements selected from alkali metals, alkaline earth metals and transition metals, and B is a halogen or a combination of a halogen and O, OH, BO2, BO3, B4O7, CO3, NO3, AlO2, SiO3, SiO4, PO3, PO4, P2O7, or P3O 10 , SO3, SO4, S2O3, S2O4, S2O7, BF4, PF6, and BOB, and α satisfies 1≦α≦3, β satisfies 0.5≦β≦1.5, and γ satisfies 4≦γ≦6.

[0010] (2) In the positive electrode active material according to the above aspect, in the chemical formula, A may be one or more selected from Ti, Zr, Y, Hf, Sc, Mg, Ca, Sr, Ba, Na, K, Al, Ga, and In; B may be a halogen or a halogen and one or more groups selected from O, CO3, SO4, and PO4; and α may be 1.5≦α≦2.5.

[0011] (3) In the positive electrode active material according to the above aspect, the coating material may have a coverage of 85% or more of the active material particles.

[0012] (4) The positive electrode active material layer according to the second embodiment contains the positive electrode active material according to the above embodiment.

[0013] (5) The positive electrode active material layer according to the above embodiment may further contain the solid electrolyte.

[0014] (6) The all-solid-state battery according to the above aspect includes the positive electrode active material layer according to the above aspect, a negative electrode active material layer, and a solid electrolyte layer sandwiched between the positive electrode active material layer and the negative electrode active material layer. [Effects of the Invention]

[0015] The positive electrode active material, the positive electrode active material layer, and the all-solid-state battery according to the above aspects have excellent rate characteristics. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of an all-solid-state battery according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view of a positive electrode active material according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0017] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.

[0018] [All-solid battery] 1 is a cross-sectional schematic diagram of an all-solid-state battery 10 according to this embodiment. The all-solid-state battery 10 has a laminate 4 and terminal electrodes 5 and 6. The terminal electrodes 5 and 6 are in contact with opposing surfaces of the laminate 4. The terminal electrodes 5 and 6 extend in a direction intersecting (orthogonal to) the laminate surface of the laminate 4.

[0019] The laminate 4 has a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3. The number of positive electrode 1 and negative electrode 2 layers is not important. The solid electrolyte layer 3 is located between the positive electrode 1 and the negative electrode 2. One end of the positive electrode 1 is connected to a terminal electrode 5. One end of the negative electrode 2 is connected to a terminal electrode 6. Between the positive electrode 1 and the terminal electrode 6 and between the negative electrode 2 and the terminal electrode 5, for example, the solid electrolyte layer 3 is located.

[0020] The all-solid-state battery 10 is charged or discharged by the exchange of ions between the positive electrode 1 and the negative electrode 2 via the solid electrolyte layer 3. Although a stacked-type battery is shown in FIG. 1, a wound-type battery may also be used. The all-solid-state battery 10 is used, for example, in laminated batteries, prismatic batteries, cylindrical batteries, coin-type batteries, button-type batteries, etc. The all-solid-state battery 10 may also be an injection-type battery in which the solid electrolyte layer 3 is dissolved or dispersed in a solvent.

[0021] "Positive electrode" As shown in FIG. 1, the positive electrode 1 includes, for example, a positive electrode current collector 1A and a positive electrode active material layer 1B containing a positive electrode active material.

[0022] (Positive electrode current collector) The positive electrode current collector 1A preferably has high electrical conductivity. For example, metals such as silver, palladium, gold, platinum, aluminum, copper, nickel, titanium, and stainless steel, alloys thereof, or conductive resins can be used. The positive electrode current collector 1A may be in the form of powder, foil, punched, or expanded.

[0023] (Cathode active material layer) The positive electrode active material layer 1B is formed on one or both surfaces of the positive electrode current collector 1A. The positive electrode active material layer 1B contains a positive electrode active material, and may also contain a conductive additive, a binder, and a solid electrolyte described below, as necessary.

[0024] (Cathode active material) 2 is a cross-sectional view of a positive electrode active material 20 included in the positive electrode active material layer 1B. In the positive electrode active material layer 1B, a plurality of positive electrode active materials 20 are in close contact with each other. The positive electrode active material 20 includes active material particles 21 and a coating material 22.

[0025] The active material particles 21 are, for example, lithium-containing transition metal oxides, transition metal fluorides, polyanions, transition metal sulfides, transition metal oxyfluorides, transition metal oxysulfides, or transition metal oxynitrides.

[0026] The active material particles 21 are not particularly limited as long as they are capable of reversibly absorbing and desorbing lithium ions and inserting and desorbing lithium ions. For example, any positive electrode active material used in known lithium ion secondary batteries can be used.

[0027] The active material particles 21 are, for example, composite metal oxides. The active material particles 21 are, for example, lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese spinel (LiMnO), and a compound represented by the general formula: LiNi x Co y Mn z M aComposite metal oxides represented by O2(x + y + z + a = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, where M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium vanadium compounds (LiV2O5, Li3V2(PO4)3, LiVOPO4), olivine-type LiMPO4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, V, Nb, Ti, Al, Zr), lithium titanate (Li4Ti5O 12 ), LiNi x Co y Al z O2(0.9 < x + y + z < 1.1), etc.

[0028] Also, as the active material particles 21, active material particles 21 that do not contain lithium can also be used. These active material particles 21 can be used by arranging a negative electrode active material previously doped with metallic lithium or lithium ions on the negative electrode and starting the battery from discharge. For example, lithium-free metal oxides (such as MnO2, V2O5, etc.), lithium-free metal sulfides (such as MoS2, etc.), lithium-free fluorides (such as FeF3, VF3, etc.) are examples of these positive electrode active materials.

[0029] The coating material 22 coats the surface of the active material particles 21. The coating material 22 does not have to coat the entire surface of the active material particles 21, and it is sufficient to coat a part of the surface of the active material particles 21. The coating rate of the coating material 22 with respect to the active material particles 21 is preferably 85% or more.

[0030] The coverage is determined as follows. First, a cross section of the positive electrode active material layer 1B is cut out and measured using a scanning electron microscope (SEM). Multiple positive electrode active materials 20 are visible in the cross-sectional SEM image. Some of the multiple positive electrode active materials 20 are in close contact with each other, making the interfaces difficult to see. Therefore, 30 positive electrode active materials 20 whose grain boundaries are clearly visible are randomly selected from the cross-sectional SEM image. Next, the perimeter of the cross section of each positive electrode active material 20 is determined. Furthermore, within the perimeter of each positive electrode active material 20, the length of the portion of the active material particle 21 coated with the coating material 22 is measured. Whether the surface of the active material particle 21 is coated with the coating material 22 can be determined from the contrast of the image. The coverage of each positive electrode active material 20 is then determined by dividing the "length of the portion of the active material particle 21 coated with the coating material 22" by the "perimeter of the positive electrode active material 20." Finally, the coverage of the coating material 22 with respect to the active material particles 21 is determined by finding the average of the coverage of each positive electrode active material 20 .

[0031] The coating material 22 is Li α A β B γ The coating material 22 is a compound represented by the following chemical formula: The coating material 22 has a different composition or material from the solid electrolyte that constitutes the solid electrolyte layer 3, which will be described later.

[0032] In the chemical formula, A is one or more elements selected from alkali metals, alkaline earth metals, and transition metals, such as Ti, Zr, Y, Hf, Sc, Mg, Ca, Sr, Ba, Na, K, Al, Ga, and In, and preferably Zr or Y.

[0033] In the chemical formula, B includes halogens such as F, Cl, Br, and I. B may consist of only halogens, or may consist of halogens and polyvalent polyanions. Examples of polyanions include O, OH, BO2, BO3, BO7, CO3, NO3, AlO2, SiO3, SiO4, PO3, PO4, PO7, and PO. 10, SO3, SO4, S2O3, S2O4, S2O7, BF4, PF6, and BOB. It is particularly preferred that B is only halogen, or has halogen and one or more groups selected from O, CO3, SO4, and PO4.

[0034] In the chemical formula, α satisfies 1≦α≦3, β satisfies 0.5≦β≦1.5, and γ satisfies 4≦γ≦6. In addition, α preferably satisfies 1.5≦x≦2.5.

[0035] Examples of the coating material 22 include Li2ZrCl6, Li3YCl6, Li2ZrSO4Cl4, and Li2Zr(PO4). 1 / 3 Cl5, Li2Zr(CO3) 1 / 2 Cl5 etc.

[0036] (Conductive additive) The conductive additive is not particularly limited as long as it improves the electronic conductivity in the positive electrode active material layer 1B, and known conductive additives can be used. Examples of the conductive additive include carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes; metals such as gold, platinum, silver, palladium, aluminum, copper, nickel, stainless steel, and iron; conductive oxides such as ITO; and mixtures thereof. The conductive additive may be in the form of powder or fiber.

[0037] (binding material) The binder bonds the positive electrode current collector 1A and the positive electrode active material layer 1B, the positive electrode active material layer 1B and the solid electrolyte layer 3, and the various materials constituting the positive electrode active material layer 1B.

[0038] The binder can be used within a range that does not impair the function of the positive electrode active material layer 1B. If the binder is not necessary, it may not be contained. The content of the binder in the positive electrode active material layer 1B is, for example, 0.5 to 30% by volume of the positive electrode active material layer. If the content of the binder is within this range, the resistance of the positive electrode active material layer 1B will be sufficiently low.

[0039] The binder may be any material capable of forming the above-described bond, such as fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Other binders may also be used, such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, and polyamide-imide resin. Alternatively, a conductive polymer with electronic conductivity or an ionic conductive polymer with ionic conductivity may be used. An example of an electrically conductive polymer with electronic conductivity is polyacetylene. In this case, the binder also functions as a conductive additive particle, so no conductive additive is required. Examples of ionic conductive polymers with ionic conductivity include those that conduct lithium ions, such as polymers (polyether-based polymers such as polyethylene oxide and polypropylene oxide, polyphosphazene, etc.) that are composited with a monomer of a polymer compound and a lithium salt or lithium-based alkali metal salt such as LiClO4, LiBF4, or LiPF6. The polymerization initiator used for the composite is, for example, a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-mentioned monomers. The properties required for the binder include oxidation / reduction resistance and good adhesiveness.

[0040] (solid electrolyte) The solid electrolyte contained in the positive electrode active material layer 1B improves ion conduction within the positive electrode active material layer 1B. The solid electrolyte is different from the above-mentioned coating material 22. Details of the solid electrolyte will be described later.

[0041] "Negative electrode" As shown in FIG. 1, the negative electrode 2 includes, for example, a negative electrode current collector 2A and a negative electrode active material layer 2B containing a negative electrode active material.

[0042] (Negative electrode current collector) The negative electrode current collector 2A preferably has a high conductivity. For example, it is preferable to use metals such as silver, palladium, gold, platinum, aluminum, copper, nickel, stainless steel, iron, and their alloys, or conductive resins. The negative electrode current collector 2A may be in the form of powder, foil, punching, or expansion.

[0043] (Negative electrode active material layer) The negative electrode active material layer 2B is formed on one or both sides of the negative electrode current collector 2A. The negative electrode active material layer 2B contains a negative electrode active material and a predetermined compound, and may contain a conductive assistant, a binder, and the above-mentioned solid electrolyte as required.

[0044] (Negative electrode active material) The negative electrode active material contained in the negative electrode active material layer 2B is a compound capable of occluding and releasing mobile ions. As the negative electrode active material, a negative electrode active material used in a known lithium ion secondary battery can be used. Examples of the negative electrode active material include simple alkali metals, alkali metal alloys, graphite (natural graphite, artificial graphite), carbon nanotubes, non-graphitizable carbon, graphitizable carbon, carbon materials such as low-temperature fired carbon, metals such as aluminum, silicon, tin, germanium and their alloys, which can combine with metals such as alkali metals, SiO x (0 < x < 2), oxides such as iron oxide, titanium oxide, tin dioxide, lithium titanate (Li4Ti5O 12 ) and other lithium metal oxides.

[0045] (Conductive assistant) The conductive assistant improves the electron conductivity of the negative electrode active material layer 2B. The same materials as those used in the positive electrode active material layer 1B can be used as the conductive assistant.

[0046] (Binder) The binder joins the negative electrode current collector 2A and the negative electrode active material layer 2B, the negative electrode active material layer 2B and the solid electrolyte layer 3, and various materials constituting the negative electrode active material layer 2B. The same materials as those used in the positive electrode active material layer 1B can be used as the binder. The content ratio of the binder can also be the same as that of the positive electrode active material layer 1B. If the binder is not necessary, it may not be contained.

[0047] "Solid electrolyte layer" The solid electrolyte layer 3 includes a solid electrolyte that can move ions by an externally applied electric field, etc. For example, the solid electrolyte conducts lithium ions and inhibits the movement of electrons.

[0048] The solid electrolyte contains, for example, lithium. The solid electrolyte may be, for example, an oxide-based material, a sulfide-based material, or a halide-based material.

[0049] Examples of oxide-based solid electrolytes include perovskite-type compounds, lysicone-type compounds, garnet-type compounds, Nasicon-type compounds, glass compounds, and phosphate compounds.

[0050] La 0.5 Li 0.5 TiO3 is an example of a perovskite compound. 14 Zn(GeO4)4 is an example of a lysicone-type compound. i7 La3Zr2O 12 is an example of a garnet-type compound. LiZr2(PO4)3, Li 1.3 Al 0.3 Ti 1.7 (PO4) 3、 Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 1.55 Al 0.2 Zr 1.7 Si 0.25 P 9.75 O 12 , Li 1.4 Na 0.1 Zr 1.5 Al 0.5 (PO4)3, Li 1.4 Ca 0.25 Er 0.3 Zr 1.7 (PO4) 3.2 , Li 1.4 Ca 0.25 Yb 0.3 Zr 1.7 (PO4) 3.2 is an example of a Nasicon-type compound. Li2O-V2O5-SiO2 is an example of a glass compound. Li3PO4, Li3.5 Si 0.5 P 0.5 O4, Li 2.9 PO 3.3 N 0.46 is an example of a phosphate compound.

[0051] The solid electrolyte of sulfide-based materials is, for example, Li 3.25 Ge 0.25 P 0.75 S4 (crystal), Li 10 GeP2S 12 (crystal, LGPS), Li6PS5Cl (crystal, argyrodite type), Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (crystal), Li 3.25 P 0.95 S4 (glass ceramics), Li7P3S 11 (glass ceramics), 70Li2S·30P2S5 (glass), 30Li2S·26B2S3·44LiI (glass), 50Li2S·17P2S5·33LiBH4 (glass), 63Li2S·36SiS2·Li3PO4 (glass), 57Li2S·38SiS2·5Li4SiO4 (glass).

[0052] Halide-based solid electrolytes include, for example, Li2ZrCl6, Li3YCl6, Li2ZrSO4Cl4, and Li2Zr(PO4). 1 / 3 Cl5, Li2Zr(CO3) 1 / 2 Cl5, Li3ZrOCl5. In addition, Cl in these may be replaced with F, Br, or I.

[0053] The solid electrolyte layer 3 may contain a substance other than the solid electrolyte material. For example, the solid electrolyte layer 3 may contain an oxide or halide of an alkali metal element, an oxide or halide of a transition metal element, or the like. The solid electrolyte layer 3 may also contain a binder. The binder may be the same as that described above.

[0054] At least one of the positive electrode active material layer 1B, the negative electrode active material layer 2B, and the solid electrolyte layer 3 may contain a nonaqueous electrolyte solution, an ionic liquid, or a gel electrolyte. When any of the above contains such a substance, the rate characteristic, which is one of the battery characteristics, is improved.

[0055] [Manufacturing method for all-solid-state batteries] All-solid-state batteries can be fabricated, for example, using a powder molding method. First, a resin holder with a through hole in the center, a lower punch, and an upper punch are prepared. The diameter of the through hole in the resin holder is, for example, 10 mm, and the diameters of the lower punch and upper punch are, for example, 9.99 mm. The lower punch is inserted from below the through hole in the resin holder, and powdered solid electrolyte is poured from the opening side of the resin holder. Next, the upper punch is inserted on top of the poured powdered solid electrolyte, and the resin holder is placed in a press and pressed. The pressing pressure is, for example, 373 MPa. The powdered solid electrolyte is pressed between the upper punch and lower punch within the resin holder to form the solid electrolyte layer 3.

[0056] The material for the powdered positive electrode active material layer contains active material particles and a coating material. The active material particles are obtained by mixing and reacting raw material powders in a predetermined molar ratio to achieve the desired composition. The reaction method is not limited, and mechanochemical milling, sintering, melting, liquid-phase, solid-phase, and other methods can be used. The active material particles and the coating material are then mixed in a predetermined molar ratio and treated using mechanochemical milling. The mechanochemical treatment causes the coating material to adhere to the surfaces of the active material particles, coating the surfaces of the active material particles with the coating material.

[0057] Next, the upper punch is temporarily removed, and the material for the positive electrode active material layer is placed on the upper punch side of the solid electrolyte layer 3. Thereafter, the upper punch is reinserted and pressed. The pressing pressure is, for example, 373 MPa. The material for the positive electrode active material layer becomes the positive electrode active material layer 1B by pressing.

[0058] Next, the lower punch is temporarily removed, and the material for the negative electrode active material layer is placed on the lower punch side of the solid electrolyte layer 3. For example, the sample is turned upside down, and the material for the negative electrode active material layer is placed on the solid electrolyte layer 3.

[0059] Next, the lower punch is inserted again and pressed. The pressing pressure is, for example, 373 MPa. The material of the negative electrode active material layer becomes the negative electrode active material layer 2B by pressing. Through the above procedure, the all-solid-state battery 10 of this embodiment is obtained.

[0060] If necessary, the all-solid-state battery 10 may be mounted on a stainless steel disk and a Teflon (registered trademark) disk having four screw holes in the following order: stainless steel disk / Teflon (registered trademark) disk / all-solid-state battery 10 / Teflon (registered trademark) disk / stainless steel disk, and the four screws may be fastened. The all-solid-state battery 10 may also have a similar mechanism having a shape-retaining function.

[0061] If necessary, the battery may be inserted into an exterior body (aluminum laminate bag) to which an externally drawn positive electrode terminal and an externally drawn negative electrode terminal are attached, and lead wires may be connected between the screw on the side of the upper punch and the externally drawn positive electrode terminal inside the exterior body, and between the screw on the side of the lower punch and the externally drawn negative electrode terminal inside the exterior body, and finally the opening of the exterior body may be heat-sealed. The exterior body improves weather resistance.

[0062] Although the above-mentioned method for manufacturing the all-solid-state battery 10 has been described using a powder molding method as an example, the battery may also be manufactured using a resin-containing sheet molding method.

[0063] For example, first, a solid electrolyte paste containing a powdered solid electrolyte is prepared. The prepared solid electrolyte paste is applied to a PET film, a fluorine-based resin film, or the like, dried, and peeled off to prepare a solid electrolyte layer 3. A positive electrode active material paste containing a positive electrode active material is applied to a positive electrode current collector 1A and dried to form a positive electrode active material layer 1B, thereby preparing a positive electrode 1. A negative electrode 2 is prepared by applying a paste containing a negative electrode active material and a compound to a negative electrode current collector 2A and drying to form a negative electrode active material layer 2B.

[0064] Next, the solid electrolyte layer 3 is sandwiched between the positive electrode 1 and the negative electrode 2, and the whole is pressed and bonded together. Through the above steps, the all-solid-state battery 10 of this embodiment is obtained.

[0065] In the all-solid-state battery 10 according to this embodiment, the surfaces of the active material particles 21 are coated with a predetermined coating material 22. Oxide-based coating materials are hard materials and have poor conformability to the surfaces of the active material particles 21, but the above-described coating material 22 has high conformability to the surfaces of the active material particles 21. As a result, irregularities due to the coating material 22 are less likely to form on the surface of the positive electrode active material 20, and gaps are less likely to form between other positive electrode active materials 20. In other words, the positive electrode active material layer 1B has a high density. The rate characteristics tend to improve when ion conduction paths between the positive electrode active materials 20 are secured. In the all-solid-state battery 10 according to this embodiment, the positive electrode active material layer 1B has a high density and is excellent in rate characteristics.

[0066] The above describes the embodiments of the present invention in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope that does not deviate from the spirit of the present invention. [Example]

[0067] "Example 1" (Preparation of positive electrode mixture) First, LCO (LiCoO) was prepared as the active material particles 21. LiCl and ZrCl were weighed as the raw materials for the coating material 22 in a molar ratio of 2:1. These were placed in a ZrO container together with 5 mm diameter ZrO balls in a glove box. These were then subjected to mechanochemical milling using a planetary ball mill. The mechanochemical milling was performed at a rotation speed of 500 rpm for 24 hours to obtain the coating material 22. Next, the active material particles 21 and the coating material 22 were placed in a ZrO container together with 5 mm diameter ZrO balls in a glove box. These were then subjected to mechanochemical milling using a planetary ball mill. The mechanochemical milling was performed at a rotation speed of 150 rpm for 3 hours. The resulting powder was then sieved through a 100 μm mesh sieve. These were then weighed out so that the ratio of the positive electrode active material, conductive additive, and solid electrolyte was 65 parts by weight, 3 parts by weight, and 32 parts by weight, and mixed in an agate mortar to prepare a positive electrode mixture. The conductive additive was carbon black, and the solid electrolyte was Li6PS5Cl.

[0068] (Preparation of negative electrode mixture) The negative electrode active material, conductive additive, and solid electrolyte were weighed out to a ratio of 60 parts by weight, 2 parts by weight, and 38 parts by weight, and mixed in an agate mortar to prepare a negative electrode mixture. The conductive additive was carbon black, and the solid electrolyte was Li6PS5Cl.

[0069] (Preparation of solid electrolyte) The solid electrolyte was Li6PS5Cl. The solid electrolyte was made by weighing out Li2S, P2S5, and LiCl in a molar ratio of 2.5:0.5:1. Inside a glove box, the mixture was placed in a ZrO2 container along with 5 mm diameter ZrO2 balls. Then, the mixture was subjected to mechanochemical milling using a planetary ball mill. The mixture was mixed at a rotation speed of 600 rpm for 10 hours. The resulting powder was then sieved through a 100 μm mesh sieve.

[0070] (Fabrication of Battery Elements) A resin holder, a lower punch (also serving as a negative electrode current collector), and an upper punch (also serving as a positive electrode current collector) were prepared. A lower punch was inserted from below the resin holder, and 110 mg of solid electrolyte was added from above the resin holder. An upper punch was then inserted on top of the solid electrolyte. This first unit was placed in a press, and a solid electrolyte layer was formed at a pressure of 186 MPa. The first unit was then removed from the press, and the upper punch was removed.

[0071] Next, 12 mg of a positive electrode mixture was placed on top of the solid electrolyte layer (upper punch side) in the resin holder, and the upper punch was inserted on top of it. The second unit was then placed in a press and compacted at a pressure of 186 MPa. The second unit was then removed, turned upside down, and the lower punch was removed. 8 mg of a negative electrode mixture was placed on top of the solid electrolyte layer (lower punch side), and the lower punch was inserted on top of it. The third unit was then placed in a press and compacted at a pressure of 373 MPa. In this way, a battery element consisting of a positive electrode current collector / positive electrode / solid electrolyte layer / negative electrode / negative electrode current collector was produced.

[0072] (Measurement of coverage) A cross-section of the produced battery element was photographed with an SEM to determine the coverage of the active material particles 21 with the coating material 22. The coverage of the positive electrode active material of Example 1 was 90%.

[0073] (Battery evaluation: discharge rate maintenance characteristics) The discharge rate characteristics of the fabricated lithium-ion batteries were evaluated. The discharge rate characteristics were calculated as the ratio (%) of the discharge capacity at a discharge rate of 1 C (the current value at which discharge ends in 1 hour when constant current discharge is performed at 25°C) to the discharge capacity at a discharge rate of 0.1 C (the current value at which discharge ends in 10 hours when constant current discharge is performed at 25°C) taken as 100%, and the discharge rate characteristics were calculated as the ratio (%) of the discharge capacity at a discharge rate of 1 C (the current value at which discharge ends in 1 hour when constant current discharge is performed at 25°C) to the discharge capacity at a discharge rate of 0.1 C (the current value at which discharge ends in 10 hours when constant current discharge is performed at 25°C) taken as 100%.

[0074] The discharge rate retention characteristics were evaluated under the conditions of 0.05 mA / cm 2 The actual capacity of the fabricated cell was measured by performing an initial charge / discharge cycle at a current density of 0.1C. Based on the actual capacity obtained, the current densities for discharge rates of 0.1C and 1C were determined.

[0075] After the initial charge / discharge, the battery was charged at a constant current of 0.1 C to 4.1 V, and then charged at a constant voltage of 0.02 C until the current density reached 0.02 C. After a 5-minute rest period, the battery was discharged at a constant current of 0.1 C to 2.5 V, and the discharge capacity at 0.1 C was measured. After the measurement, a 5-minute rest period was taken.

[0076] Thereafter, the battery was charged at a constant current of 0.1 C up to 4.1 V, and then charged at a constant voltage until the current density reached 0.02 C. After a 5-minute rest period, the battery was discharged at a constant current of 1 C down to 2.5 V, and the discharge capacity at 1 C was measured.

[0077] The discharge rate characteristic was determined by dividing the measured discharge capacity at 1 C by the discharge capacity at 0.1 C. The discharge rate retention characteristic of the all-solid-state battery of Example 1 was 86%.

[0078] "Examples 2 to 9" Examples 2 to 9 differ from Example 1 in that the covering material 22 is changed. In Example 2, Li2ZrSO4Cl4 was used as the coating material 22. In Example 2, Li2SO4 and ZrCl4 were used as the raw materials for the coating material 22. In Example 3, Li3YCl6 was used as the coating material 22. In Example 3, LiCl and YCl3 were used as the raw materials for the coating material 22. In Example 4, Li3InCl6 was used as the coating material 22. In Example 4, LiCl and InCl3 were used as the raw materials for the coating material 22. In Example 5, the coating material 22 is Li2Zr(PO4) 1 / 3 In Example 5, LiCl, ZrCl4, and Li3PO4 were used as the raw materials for the coating material 22. In Example 6, the coating material 22 is Li 2.3 Zr 0.9 Na 0.1 In Example 6, LiCl, ZrCl4, and NaCl were used as the raw materials for the coating material 22. In Example 7, the coating material 22 is Li 2.1 Zr 0.9 Al 0.1In Example 7, LiCl, ZrCl4, and AlCl3 were used as the raw materials for the coating material 22. In Example 8, the coating material 22 is Li 2.8 Zr 0.6 Ba 0.4 In Example 8, LiCl, ZrCl4, and BaCl2 were used as the raw materials for the coating material 22. In Example 9, the coating material 22 was Li2Zr(CO3) 1 / 2 In Example 9, LiCl, ZrCl4, and Li2CO3 were used as the raw materials for the coating material 22.

[0079] Then, similarly to Example 1, the coverage and discharge rate retention of the covering material 22 were determined. The coverage was 90% in both Examples 2 and 3. The discharge rate retention of Example 2 was 87%, and the discharge rate retention of Example 3 was 70%. The coverage was 89% in Example 4, 88% in Example 5, 91% in Example 6, 87% in Example 7, 89% in Example 8, and 90% in Example 9. The discharge rate retention of Example 4 was 71%, 79% in Example 5, 85% in Example 6, 82% in Example 7, 69% in Example 8, and 86% in Example 9.

[0080] "Examples 10 to 14" Examples 10 to 14 differ from Example 1 in that the coverage of the coating material 22 was changed. The coverage of the coating material 22 can be changed by changing the mixing ratio of the active material particles and the raw material of the coating material in the mechanochemical milling process when producing the positive electrode active material.

[0081] Then, the coverage and discharge rate retention of the covering material 22 were determined in the same manner as in Example 1. The coverage of Example 10 was 85%, the coverage of Example 11 was 84%, the coverage of Example 12 was 95%, the coverage of Example 13 was 98%, and the coverage of Example 14 was 70%. The discharge rate retention of Example 10 was 81%, the discharge rate retention of Example 11 was 50%, the discharge rate retention of Example 12 was 93%, the discharge rate retention of Example 13 was 95%, and the discharge rate retention of Example 14 was 45%.

[0082] "Example 15" In Example 15, the solid electrolyte was Li7La3Zr2O 12 This is different from Example 1. The solid electrolyte was produced by treating raw material powders by a solid-phase reaction method.

[0083] The coverage and discharge rate retention of the covering material 22 were determined in the same manner as in Example 1. The coverage of Example 15 was 90%, and the discharge rate retention of Example 15 was 47%.

[0084] "Comparative Example 1" Comparative Example 1 differs from Example 1 in that no coating material 22 was formed. That is, the active material particles 21 were used as they were as the positive electrode active material.

[0085] The coverage rate and discharge rate retention of the covering material 22 were determined in the same manner as in Example 1. In Comparative Example 1, the covering rate was 0% because no covering material 22 was formed. The discharge rate retention of Comparative Example 1 was 8%.

[0086] "Comparative Example 2 and Comparative Example 3" Comparative Example 2 differs from Example 1 in that the coating material 22 is LiNbO3. Comparative Example 3 differs from Example 15 in that the coating material 22 is LiNbO3.

[0087] The coverage and discharge rate retention of the covering material 22 were determined in the same manner as in Example 1. The coverage was 90% in both Comparative Examples 2 and 3. The discharge rate retention of Comparative Example 2 was 12%, and the discharge rate retention of Comparative Example 3 was 3%.

[0088] The results of Examples 1 to 9 and Comparative Examples 1 to 3 are summarized in Table 1.

[0089] [Table 1]

[0090] As shown in Table 1, it was confirmed that the discharge rate retention characteristics improved when the positive electrode active material was coated with a specified coating material. It was also confirmed that the discharge rate retention improved significantly when the coating rate exceeded 85%. [Explanation of symbols]

[0091] 1...Positive electrode, 1A...Positive electrode current collector, 1B...Positive electrode active material layer, 2...Negative electrode, 2A...Negative electrode current collector, 2B...Negative electrode active material layer, 3...Solid electrolyte layer, 4...Laminated body, 5,6...Terminal electrode, 10...All solid state battery, 20...Positive electrode active material, 21...Active material particles, 22...Coating material

Claims

1. a positive electrode active material and a solid electrolyte, the positive electrode active material includes active material particles and a coating material that coats the active material particles, the coating material has a different composition or material from the solid electrolyte, The coating material is Li α A β B γ It is represented by the chemical formula In the above chemical formula: A is one or more elements selected from alkali metals, alkaline earth metals, and transition metals; B is a halogen, or a halogen and O, OH, or BO ２ , B.O. ３ , B ４ O ７ , CO ３ , NO ３ , AlO ２ , SiO ３ , SiO ４ , P.O. ３ , P.O. ４ , P ２ O ７ , P ３ O １０ , S.O. ３ , S.O. ４ , S ２ O ３ , S ２ O ４ , S ２ O ７ , B.F. ４ , P.F. ６ and at least one group selected from the group consisting of BOB, α satisfies 1≦α≦3, β satisfies 0.5≦β≦1.5, and γ satisfies 4≦γ≦6, The positive electrode active material layer, wherein the solid electrolyte is a solid electrolyte containing a halogen, and the halogen is any one of F, Br, and Cl.

2. In the above chemical formula: A is one or more selected from Ti, Zr, Y, Hf, Sc, Mg, Ca, Sr, Ba, Na, K, Al, Ga, and In; B is a halogen, or a halogen and O, CO ３ , S.O. ４ , P.O. ４ is one or more groups selected from The positive electrode active material layer according to claim 1 , wherein α satisfies the condition 1.5≦α≦2.

5.

3. 3. The positive electrode active material layer according to claim 1, wherein the coating material has a coverage of 85% or more of the active material particles.

4. 4. An all-solid-state battery comprising: the positive electrode active material layer according to claim 1; a negative electrode active material layer; and a solid electrolyte layer sandwiched between the positive electrode active material layer and the negative electrode active material layer.

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