Composite particles, a positive electrode, a all-solid-state battery, and a method for producing the composite particles

Abstract

To provide a coating film having low resistance.SOLUTION: A composite particle includes a positive electrode active material particle and a coating film that covers at least a part of the surface of the positive electrode active material particle. The coating film includes at least one of a first element (glass network forming element) and a second element (transition element). In a Raman spectrum of a cross section of the coating film, a peak having a peak top exists within the range of 600 to 200 cm-1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to composite particles, a positive electrode, an all-solid-state battery, and a method for manufacturing the composite particles.

Background Art

[0002] In Patent No. 4982866 (Patent Document 1), in an all-solid-state lithium battery (sulfide-based all-solid-state battery) using a lithium-ion conductive solid electrolyte (sulfide solid electrolyte), the surface of the positive electrode active material is coated with a lithium-ion conductive oxide, and the lithium-ion conductive oxide is interposed between the positive electrode active material and the sulfide solid electrolyte, thereby suppressing the formation of a high-resistance layer at the contact interface between the sulfide solid electrolyte and the positive electrode active material at a high potential. A technique is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a sulfide-based all-solid-state battery (hereinafter may be abbreviated as "all-solid-state battery"), when the sulfide solid electrolyte comes into direct contact with the positive electrode active material particles or the like, the sulfide solid electrolyte may deteriorate. Due to the deterioration of the sulfide solid electrolyte (ion conduction path), the battery resistance may increase. Therefore, it has been proposed to form a coating film on the surface of the positive electrode active material particles. By inhibiting the direct contact between the coating film and the sulfide solid electrolyte, the deterioration of the sulfide solid electrolyte can be reduced.

[0005] Conventionally, as materials for the coating film, LiNbO 3 and Li 3 PO 4 are known. LiNbO 3 is Li 3 PO 4may have a lower resistance compared thereto. Therefore, the popularity of LiNbO 3 is progressing. However, according to the new findings of the present inventors, regarding the durability under high voltage, phosphorus compounds such as Li 3 PO 4 etc. are superior to LiNbO 3 . Therefore, the development of a phosphorus-based coating film having a low resistance is desired.

[0006] An object of the present disclosure is to provide a coating film having a low resistance.

Means for Solving the Problems

[0007] [1] A composite particle comprising a positive electrode active material particle and a coating film covering at least a part of the surface of the positive electrode active material particle, the coating film contains at least one of a first element which is a glass network forming element and a second element which is a transition element, in the Raman spectrum of the cross section of the coating film, there is a peak having a peak top within the range of 600 to 200 cm -1 .

[0008] According to the composite particle of the above [1], a coating film having a low resistance (particularly, a phosphorus-based coating film excellent in durability under high voltage) can be provided.

[0009] As a result of examining the Raman spectra of various coating films, the present inventors have found that for a coating film containing at least one of a first element (glass network forming element) and a second element (transition element), when there is at least one peak having a peak top within the range of (Raman shift value) 600 to 200 cm -1 in the Raman spectrum of its cross section, the coating film has a low resistance.

[0010] [2] The composite particles according to [1], wherein the first element is at least one selected from the group consisting of boron, silicon, nitrogen, sulfur, germanium, and hydrogen.

[0011] [3] The composite particles according to [1] or [2], wherein the second element is at least one selected from the group consisting of second transition elements and third transition elements.

[0012] [4] In the Raman spectroscopy spectrum of the cross-section of the coating film, further, in the range of 1250 to 1050 cm -1 and 800 to 630 cm -1 there is a peak having a peak top, and the composite particles according to any one of [1] to [3].

[0013] As a result of examining the Raman spectroscopy spectra of various coating films, the inventors have found that for a coating film containing at least one of a first element (glass network-forming element) and a second element (transition element), in the Raman spectroscopy spectrum of its cross-section, further, (Raman shift value) in the range of 1250 to 1050 cm -1 and 800 to 630 cm -1 when there is a peak having a peak top, it is expected that the coating film has low resistance and excellent durability under high voltage.

[0014] [5] The coating film contains a phosphorus compound, the phosphorus compound contains at least one of the first element and the second element and phosphorus, The composite particles according to claim 1, wherein in the coating film, the following relationship of formula (1) is satisfied. C Li / (C P +C E1 +C E2 ) ≤ 2.5 …(1) (In the above formula (1), C Li , C P , C E1 , CE2 represents the elemental concentration measured by X-ray photoelectron spectroscopy, C Li represents the elemental concentration of lithium, C P represents the elemental concentration of phosphorus, C E1 represents the elemental concentration of the first element, C E2 represents the elemental concentration of the second element.)

[0015] In the conventional phosphorus-based coating film (Li 3 PO 4 ), the composition ratio of Li is "3.0". In Li 3 PO 4 , Li + is considered to be a carrier. Therefore, the more carriers there are, the more improvement in ionic conductivity is expected. In other words, the larger the composition ratio of Li in the phosphorus compound, the more reduction in battery resistance is expected.

[0016] However, according to the new findings of the present disclosure, when the composition ratio of Li in the phosphorus compound is small and a specific element is added to the phosphorus compound, ionic conductivity equal to or higher than that of LiNbO 3 can be exhibited. That is, the composite particles satisfy the relationship of the above formula (1), and the phosphorus compound contains at least one selected from the group consisting of the first element and the second element.

[0017] The first element is a glass network-forming element. The first element can form an oxide glass having a network structure by bonding with oxygen (O). The coating film (for example, a phosphorus compound) is considered to be an oxide. By adding the first element to the coating film, in the coating film, for example, "PO x a- ", "BO y b- ", "SiO z c-Multiple types of anions such as "」" can be generated. The coexistence of multiple types of anions can exhibit a mixed anion effect. The mixed anion effect can promote the movement of carriers (cations). Furthermore, it is considered that the small amount of carriers further promotes the movement of carriers.

[0018] The second element is a transition element. The transition element has an ionic radius larger than that of P. When the coating film contains phosphorus (phosphorus compound), the addition of the second element can inhibit the crystallization of the phosphorus compound. That is, partial structural defects (disorder of order) can be introduced into the phosphorus compound. The introduction of structural defects can promote the movement of carriers. Furthermore, it is considered that the small amount of carriers further promotes the movement of carriers.

[0019] By the synergistic effect of the above actions, the phosphorus-based coating film of the present disclosure can have a low resistance equal to or higher than that of LiNbO 3 When the phosphorus-based coating film has a low resistance, both durability under high voltage and high output are expected.

[0020] [6] A positive electrode comprising the composite particles according to any one of [1] to [5] and a sulfide solid electrolyte.

[0021] [7] An all-solid-state battery comprising the positive electrode according to [6].

[0022] [8] (a) Preparing a mixture by mixing a coating liquid and positive electrode active material particles, and (b) Manufacturing composite particles by drying the mixture, comprising, The coating liquid contains a solute and a solvent, The solute contains at least one of a first element which is a glass network forming element and a second element which is a transition element, A method for manufacturing composite particles.

[0023] When the coating liquid adhering to the surface of the positive electrode active material particles dries, a coating film can be formed on the surface of the positive electrode active material particles. That is, the coating film described in the above [1] can be formed.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0025] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "the present embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure.

[0026] In this specification, elements expressed in the singular form include the plural form as well, unless otherwise specified. For example, "particle" can mean not only "one particle" but also "an aggregate of particles (powder, powder, particle group)".

[0027] When a compound is expressed by a stoichiometric composition formula (for example, "LiCoO 2 " etc.), the stoichiometric composition formula is only a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobaltate is expressed as "LiCoO 2 ", unless otherwise specified, lithium cobaltate is not limited to the composition ratio of "Li / Co / O = 1 / 1 / 2", and may contain Li, Co, and O in any composition ratio. Furthermore, doping, substitution, etc. with trace elements may also be allowed.

[0028] <Composite particle> Referring to FIG. 2, the composite particle 5 includes a positive electrode active material particle 1 and a coating film 2. The composite particle 5 may be referred to as, for example, "coated positive electrode active material" or the like.

[0029] The composite particles 5 may, for example, form aggregates. That is, one composite particle 5 may contain two or more positive electrode active material particles 1. The composite particles 5 may have a D50 of, for example, 1 to 50 μm, or may have a D50 of 1 to 20 μm, or may have a D50 of 5 to 15 μm.

[0030] In this specification, "D50" indicates the particle diameter at which the cumulative frequency from the smaller particle diameter side reaches 50% in the particle diameter distribution based on volume. D50 can be measured by the laser diffraction method.

[0031] 《Coating film》 The coating film 2 covers at least a part of the surface of the positive electrode active material particle 1. The coating film 2 is the shell of the composite particle 5.

[0032] The coating film 2 contains at least one of a first element (E1) and a second element (E2). E1 and E2 will be described later.

[0033] In the Raman spectrum of the cross-section of the coating film 2 (the part of the coating film 2 in the cross-section of the composite particle 5), there is a peak having a peak top (maximum position) within the range of a Raman shift value of 600 to 200 cm -1 .

[0034] In the Raman spectrum of the cross-section of the coating film 2, further, it is preferable that there are peaks having peak tops within the ranges of a Raman shift value of 1250 to 1050 cm -1 and 800 to 630 cm -1 ..

[0035] The Raman spectrum of the cross-section of the coating film 2 can be obtained by various known methods using a Raman spectrometer. The above-mentioned peak is, for example, a peak detected when the S / N ratio is set to 30 or more. The cross-section sample is prepared according to the same procedure as (film thickness measurement) described later.

[0036] (Phosphorus compound) The coating film 2 may further contain phosphorus (P). The coating film 2 may contain, for example, a phosphorus compound.

[0037] The phosphorus compound contains at least one of the first element (E1) and the second element (E2) and P. In this specification, the first element may be abbreviated as "E1" and the second element may be abbreviated as "E2".

[0038] The first element (E1) is an element having glass-forming ability (glass network-forming element), that is, an element that can form an oxide glass having a network structure by bonding with O. The expression of the mixed anion effect is expected by the addition of E1.

[0039] E1 is, for example, at least one selected from the group consisting of boron (B), silicon (Si), nitrogen (N), sulfur (S), germanium (Ge), and hydrogen (H). E1 is, for example, at least one selected from the group consisting of B and Si. E1 may form an oxide glass alone. E1 may form a composite oxide glass together with P.

[0040] The second element (E2) is a transition element. The "transition element" is an element in Groups 3 to 11 of the periodic table.

[0041] E2 has an ionic radius larger than that of P. E2 can inhibit the crystallization of the phosphorus compound. E2 is at least one selected from the group consisting of, for example, a first transition element (3d transition element), a second transition element (4d transition element), a third transition element (5d, 4f transition element), and a fourth transition element. E2 is at least one selected from the group consisting of, for example, a second transition element and a third transition element. The third transition element includes lanthanoids. That is, E2 may contain, for example, lanthanoids.

[0042] E2 is at least one selected from the group consisting of, for example, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), copper (Cu), Y, zirconium (Zr), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au). E2 is at least one selected from the group consisting of, for example, La, Ce, Zr, and Y. E2 is at least one selected from the group consisting of, for example, La, Ce, and Y.

[0043] The ratio of P contained in the phosphorus compound (or composite particles) is, for example, 1 to 10% by mass based on the total amount of the composite particles 5.

[0044] The phosphorus compound may further contain, for example, Li, O, carbon (C), etc.

[0045] The phosphorus compound may contain, for example, a phosphate backbone. That is, the phosphorus compound may be a phosphate compound. When the phosphorus compound contains a phosphate backbone, for example, when analyzing the composite particle 5 by TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), PO 2 - and PO 3 - and other fragments can be detected.

[0046] In the coating film (or phosphorus compound), the composition ratio of Li, “C Li / (C P +C E1 +C E2 )” is 2.5 or less (see the above formula (1)). When the composition ratio of Li is 2.5 or less and at least one of E1 and E2 is present, the battery resistance can be significantly reduced.

[0047] The above composition ratio of Li may be, for example, 2.38 or less, 2.26 or less, 2.18 or less, 2.03 or less, 1.89 or less, 1.73 or less, 1.42 or less, or 1.1 or less. The composition ratio of Li may be, for example, 0.1 or more, 0.5 or more, or 1.05 or more. The composition ratio of Li may be, for example, 1.05 to 2.38. Note that the composition ratio of Li may be zero. That is, Li may not be present on the surface of the coating film (composite particle), and the coating film (or phosphorus compound) may not contain any Li at all.

[0048] (XPS measurement of the composition ratio of Li) The composition ratio of Li on the surface of the composite particle, “C Li / (C P +C E1 +C E2) can be measured by XPS according to the following procedure. An XPS apparatus is prepared. For example, an XPS apparatus "product name PHI X-tool" manufactured by ULVAC-PHI, Inc. (or an equivalent product) may be used. A sample powder composed of composite particles is set in the XPS apparatus. Narrow scan analysis is performed with a pass energy of 224 eV. The measurement data is processed by analysis software. For example, analysis software "product name MulTiPak" manufactured by ULVAC-PHI, Inc. (or an equivalent product) may be used. The peak area (integrated value) of the Li1s spectrum is converted into the elemental concentration (C Li ) of Li. The peak area of the P2p spectrum is converted into the elemental concentration (C P ) of P. For E1 and E2, appropriate spectra are selected according to their types. For example, in the case of B, the peak area of the B1s spectrum is converted into the elemental concentration (C E1 ) of B. For example, in the case of La, the peak area of the La3d5 spectrum is converted into the elemental concentration (C E2 ) of La. C P , C E1 and C E2 are excluded from the total of 、 C Li to obtain the composition ratio of Li on the particle surface.

[0049] For example, when the coating film contains multiple types of E1, C E1 represents the total elemental concentration of multiple types of E1. The same applies to E2 and C E2 .

[0050] The composition ratio "C Li / (C P +C E1 +C E2 )" by XPS reflects the composition ratio of Li in the coating film (phosphorus compound), but is not equivalent to the composition ratio of Li in the coating film. This is because in XPS, the composition of the substrate (positive electrode active material particles) can also be reflected. For example, if Li in the substrate is detected in XPS, the composition ratio of Li by XPS may be larger than the composition ratio of Li in the actual coating film.

[0051] The chemical composition of the phosphorus compound may be represented by, for example, the following formula (2). Li w E 1 x E 2 y PO z …(2) In the above formula (2), E 1 represents E1. E 2 represents E2. w, x, y, and z are arbitrary numbers. w, x, y, and z can be specified, for example, by analyzing the portion of the coating film 2 on the cross-section of the composite particle 5 by STEM-EDX (Scanning Transmission Electron Microscope - Energy Dispersive X-ray Spectroscopy) or the like. The cross-section sample is prepared according to the same procedure as (film thickness measurement) described later.

[0052] Specific phosphorus compounds include, for example, Li 3 PO 4 (LPO), BPO 4 (BPO) and POx (P 4 O 6、 P 2 O 5 etc.) and at least one selected from the group consisting of them.

[0053] In the composite particle 5, the coverage rate of the surface of the positive electrode active material particle 1 by the coating film 2 may be, for example, 70% or more. By having a coverage rate of 70% or more, a reduction in battery resistance is expected. The coverage rate may be, for example, 85% or more, 88% or more, 89% or more, 90% or more, 94% or more, 95% or more, 97% or more. The coverage rate may be, for example, 100% or 99% or less. The coverage rate may be, for example, 85 to 97% or 90 to 97%.

[0054] (XPS measurement of the coverage rate) The coverage rate is also measured by XPS. Measurement data obtained in the same manner as the above (XPS measurement of the composition ratio of Li), except that the pass energy is set to 120 eV, is analyzed. From the peak areas (intensity values) of C1s, O1s, P1s, M2p3, etc., the ratio (element concentration) of each element is determined. The coverage rate is determined by the following formula (3). θ=(P + E1 + E2) / (P + E1 + E2 + M)×100 …(3) In the above formula (3), θ represents the coverage rate (%). P, E1, E2, and M represent the ratios of the respective elements.

[0055] "M2p3" and M in the above formula (3) are constituent elements of the positive electrode active material particles and represent elements other than Li and O. That is, the positive electrode active material particles may be represented by the following formula (4). LiMO 2 …(4) M may consist of one element or may consist of a plurality of elements. M may be, for example, at least one selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). When M contains a plurality of elements, the sum of the composition ratios of the respective elements may be 1.

[0056] For example, when the positive electrode active material particles are "LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ", the above formula (3) can be transformed into the following formula (3'). θ=(P + E1 + E2) / (P + E1 + E2 + Ni + Co + Mn)×100 …(3’) Ni in the above formula (3') represents the element ratio of nickel determined from the peak area of Ni2p3. Co represents the element ratio of cobalt determined from the peak area of Co2p3. Mn represents the element ratio of manganese determined from the peak area of Mn2p3.

[0057] The coating film 2 may have a thickness of, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm.

[0058] (Film thickness measurement) The film thickness (thickness of the coating film) can be measured by the following procedure. A sample is prepared by embedding the composite particles in a resin material. The sample is subjected to cross-section machining using an ion milling apparatus. For example, an ion milling apparatus "product name Arblade (registered trademark) 5000" (or an equivalent product) manufactured by Hitachi High-Technologies Corporation may be used. The cross-section of the sample is observed by SEM (Scanning Electron Microscope). For example, an SEM apparatus "product name SU8030" (or an equivalent product) manufactured by Hitachi High-Technologies Corporation may be used. For 10 composite particles, the film thickness is measured in 20 fields of view for each. The arithmetic mean of the film thicknesses at a total of 200 locations is regarded as the film thickness.

[0059] In the positive electrode and the battery, by using the composite particles containing the above-mentioned phosphorus compound and having a phosphorus-based coating film with low resistance, it is expected to achieve both durability under high voltage and high output.

[0060] 《Positive electrode active material particles》 The positive electrode active material particles 1 are the core of the composite particles 5. The positive electrode active material particles 1 may be secondary particles (aggregates of primary particles). The positive electrode active material particles 1 (secondary particles) may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm. The primary particles may have a maximum Feret diameter of, for example, 0.1 to 3 μm.

[0061] The positive electrode active material particles 1 may contain any components. The positive electrode active material particles 1 are, for example, LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4, Li(NiCoMn)O 2 , Li(NiCoAl)O 2 , and LiFePO 4 may contain at least one selected from the group consisting of. For example, in "Li(NiCoMn)O 2 ", "(NiCoMn)" indicates that the total of the composition ratios within the parentheses is 1. As long as the total is 1, the individual component amounts are arbitrary. Li(NiCoMn)O 2 may be, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O 2 , Li(Ni 0.5 Co 0.2 Mn 0.3 )O 2 , Li(Ni 0.8 Co 0.1 Mn 0.1 )O 2 etc. may be included.

[0062] <All-solid-state battery> Figure 3 is a conceptual diagram showing the all-solid-state battery in this embodiment. The all-solid-state battery 100 may include, for example, an exterior body (not shown). The exterior body may be, for example, a pouch made of a metal foil laminate film or the like. The exterior body may house the power generation element 50. The power generation element 50 includes a positive electrode 10, a separator layer 30, and a negative electrode 20. That is, the all-solid-state battery 100 includes a positive electrode 10, a separator layer 30, and a negative electrode 20.

[0063] 《Positive electrode》 The positive electrode 10 is layered. The positive electrode 10 may include, for example, a positive electrode active material layer and a positive electrode current collector. For example, the positive electrode active material layer may be formed by coating a positive electrode composite material on the surface of the positive electrode current collector. The positive electrode current collector may include, for example, Al foil or the like. The positive electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0064] The positive electrode active material layer may have a thickness of, for example, 10 to 200 μm. The positive electrode active material layer is in close contact with the separator layer 30. The positive electrode active material layer contains a positive electrode composite material. The positive electrode composite material contains composite particles (coated positive electrode active material) and a sulfide solid electrolyte. That is, the positive electrode 10 contains composite particles and a sulfide solid electrolyte. The details of the composite particles are as described above.

[0065] The sulfide solid electrolyte can form an ion conduction path in the positive electrode active material layer. The blending amount of the sulfide solid electrolyte may be, for example, 1 to 200 parts by volume, 50 to 150 parts by volume, or 50 to 100 parts by volume with respect to 100 parts by volume of the composite particles (positive electrode active material). The sulfide solid electrolyte contains S. The sulfide solid electrolyte may contain, for example, Li, P, and S. The sulfide solid electrolyte may further contain, for example, O, Si, etc. The sulfide solid electrolyte may further contain, for example, halogen, etc. The sulfide solid electrolyte may further contain, for example, iodine (I), bromine (Br), etc. The sulfide solid electrolyte may be, for example, of the glass-ceramics type or the argyrodite type. The sulfide solid electrolyte is, for example, LiI-LiBr-Li 3 PS 4 、Li 2 S-SiS 2 、LiI-Li 2 S-SiS 2 、LiI-Li 2 S-P 2 S 5 、LiI-Li 2 O-Li 2 S-P 2 S 5 、LiI-Li 2 S-P 2 O 5 、LiI-Li 3 PO 4 -P 2 S 5 、Li 2 S-P 2 S 5 、and Li 3 PS 4 and may contain at least one selected from the group consisting of.

[0066] For example, "LiI-LiBr-Li 3 PS 4 " indicates a sulfide solid electrolyte formed by mixing LiI, LiBr, and Li 3 PS 4 in any molar ratio. For example, the sulfide solid electrolyte may be formed by a mechanochemical method. "Li 2 S-P 2 S 5 " contains Li 3 PS 4 . Li 3 PS 4 can be formed, for example, by mixing Li 2 S and P 2 S 5 in a ratio of "Li 2 S / P 2 S 5 = 75 / 25 (molar ratio)".

[0067] The positive electrode active material layer may further contain, for example, a conductive material. The conductive material can form an electron conduction path within the positive electrode active material layer. The blending amount of the conductive material may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the composite particles (positive electrode active material). The conductive material may contain any component. The conductive material may contain, for example, at least one selected from the group consisting of carbon black, vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake.

[0068] The positive electrode active material layer may further contain, for example, a binder. The blending amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the composite particles (positive electrode active material). The binder may contain any component. The binder may contain, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride - hexafluoropropylene copolymer (PVdF - HFP), styrene butadiene rubber (SBR), and polytetrafluoroethylene (PTFE).

[0069] 《Negative Electrode》 The negative electrode 20 is layered. The negative electrode 20 may include, for example, a negative electrode active material layer and a negative electrode current collector. For example, a negative electrode active material layer may be formed by coating a negative electrode composite material on the surface of the negative electrode current collector. The negative electrode current collector may include, for example, a Cu foil, a Ni foil, or the like. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0070] The negative electrode active material layer may have a thickness of, for example, 10 to 200 μm. The negative electrode active material layer is in close contact with the separator layer 30. The negative electrode active material layer contains a negative electrode composite material. The negative electrode composite material contains negative electrode active material particles and a sulfide solid electrolyte. The negative electrode composite material may further contain a conductive material and a binder. The sulfide solid electrolyte may be of the same type or different types between the negative electrode composite material and the positive electrode composite material. The negative electrode active material particles may contain any component. The negative electrode active material particles may contain, for example, graphite, Si, SiO x (0 < x < 2), and Li 4 Ti 5 O 12 and may contain at least one selected from the group consisting of.

[0071] 《Separator Layer》 The separator layer 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator layer 30 separates the positive electrode 10 from the negative electrode 20. The separator layer 30 contains a sulfide solid electrolyte. The separator layer 30 may further contain a binder. The sulfide solid electrolyte may be of the same type or different types between the separator layer 30 and the positive electrode composite material. The sulfide solid electrolyte may be of the same type or different types between the separator layer 30 and the negative electrode composite material.

[0072] <Method for Manufacturing Composite Particles> FIG. 4 is a schematic flowchart of the method for manufacturing composite particles in the present embodiment. Hereinafter, the "method for manufacturing composite particles in the present embodiment" may be abbreviated as "the present manufacturing method". The present manufacturing method includes "(a) preparation of a mixture" and "(b) manufacturing of composite particles". The present manufacturing method may further include, for example, "(c) heat treatment" or the like.

[0073] 《(a) Preparation of the Mixture》 This manufacturing method includes preparing a mixture by mixing a coating solution and cathode active material particles (adhering the coating solution to the surface of the cathode active material particles). The details of the cathode active material particles are as described above.

[0074] The mixture may be, for example, a suspension or wet powder. In the mixture, it is sufficient that the coating solution adheres to the surface of the cathode active material particles. For example, a suspension may be formed by dispersing cathode active material particles (powder) in the coating solution. For example, wet powder may be formed by spraying the coating solution onto the powder containing the cathode active material particles. In this manufacturing method, any mixing device, granulating device, etc. may be used.

[0075] The coating solution includes a solute (including the solute and the dispersoid) and a solvent (the solvent and the dispersion medium or the solvent). The solute includes at least one of a first element (E1) and a second element (E2) as a raw material for the coating film. The solute may further contain phosphorus (P). The coating solution may further include, for example, a suspension (insoluble component), a precipitate, etc.

[0076] The total amount of the solute may be, for example, 0.1 to 20 parts by mass, 1 to 15 parts by mass, or 5 to 10 parts by mass with respect to 100 parts by mass of the solvent.

[0077] The solvent may contain any component as long as the solute can dissolve. The solvent may include, for example, water, alcohol, etc. The solvent may include, for example, ion-exchanged water, etc.

[0078] The details of E1 and E2 are as described above. The solute may contain at least one selected from the group consisting of, for example, oxo acids of E1 and oxides of E1. The solute may contain at least one selected from the group consisting of, for example, boric acid, silicic acid, nitric acid, sulfuric acid, and germanic acid. The solute may contain, for example, orthoboric acid, metaboric acid, etc. The solute may contain, for example, an oxide of E2. The solute may contain at least one selected from the group consisting of, for example, lanthanum oxide, cerium oxide, and yttrium oxide.

[0079] The solute may contain, for example, a phosphate compound. Thereby, the solute may contain P. The phosphate compound may be, for example, at least one selected from the group consisting of phosphoric anhydride (P 2 O 5 ), orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid [(HPO 3 ) n , and polyphosphoric acid. The phosphate compound may be, for example, at least one selected from the group consisting of metaphosphoric acid and polyphosphoric acid. Metaphosphoric acid and polyphosphoric acid may have a longer molecular chain than other phosphate compounds. When the phosphate compound has a long molecular chain, it is considered that a continuous coating film is likely to be formed. When the coating film has continuity, for example, an improvement in the coverage rate is expected.

[0080] In the above coating solution, for example, the relationship of the following formula (5) may be satisfied. 0.040 < (n E1 + n E2 ) / n P ≦ 1.51 …(5) In the above formula (5), n P represents the molar concentration of P in the coating solution. n E1 represents the molar concentration of the first element in the coating solution. n E2 represents the molar concentration of the second element in the coating solution.

[0081] “(n E1 + n E2 ) / n P ” represents the total molar ratio (amount-of-substance ratio) of the first element (E1) and the second element (E2) to P in the coating liquid. When the molar ratio is more than 0.040 and 1.51 or less, a reduction in battery resistance is expected.

[0082] The above molar ratio may be, for example, 1.03 or less, 0.67 or less, 0.48 or less, 0.098 or less, or 0.051 or less. The molar ratio may be, for example, 0.048 or more, or 0.10 or more. The molar ratio may be, for example, 0.048 to 1.03.

[0083] (ICP measurement) The above molar ratio “(n E1 + n E2 ) / n P ” in the coating liquid is measured by the following procedure. 0.01 g of the coating liquid is diluted with pure water to prepare 100 mL of a sample solution. Aqueous solutions (1000 ppm, 10000 ppm) of P, E1, and E2 are prepared. 0.01 g of the aqueous solution is diluted with pure water to prepare a standard solution. An ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) apparatus is prepared. The emission intensity of the standard solution is measured by the ICP-AES apparatus. A calibration curve is created from the emission intensity of the standard solution. The emission intensity of the sample solution (diluted coating liquid) is measured by the ICP-AES apparatus. From the emission intensity of the sample solution and the calibration curve, the mass concentrations of P, E1, and E2 in the coating liquid are obtained. Further, the mass concentrations of P, E1, and E2 are converted to molar concentrations. The sum of the molar concentration of E1 (n E1 ) and the molar concentration of E2 (n E2 ) is divided by the molar concentration of P (n P ) to obtain the molar ratio.

[0084] The solute may further contain Li, for example, it may further contain a lithium compound. The lithium compound may be, for example, lithium hydroxide, lithium carbonate, lithium nitrate, etc.

[0085] The molar ratio of Li to the total of P, E1, and E2, "n Li / (n P +n E1 +n E2 )" may be, for example, less than 1.1, or 1.0 or less, or 0.45 or less, or 0.1 or less, or 0.05 or less. Note that the molar ratio "n Li / (n P +n E1 +n E2 )" may be, for example, zero. That is, the solute may not contain Li. n Li may be less than the detection limit in ICP measurement. The smaller the molar ratio "n Li / (n P +n E1 +n E2 )", the more expected it is to reduce the composition ratio of Li on the particle surface.

[0086] 《(b) Fabrication of Composite Particles》 This manufacturing method includes manufacturing composite particles by drying the above mixture. When the coating liquid adhering to the surface of the positive electrode active material particles dries, a coating film is formed and composite particles are manufactured. In this manufacturing method, any drying method can be used.

[0087] When the mixture is a suspension containing positive electrode active material particles and a coating liquid, for example, composite particles may be formed by the spray drying method. That is, a suspension containing positive electrode active material particles and a coating liquid is sprayed from a nozzle, and the sprayed droplets are dried, for example, by hot air, whereby composite particles can be formed. By using the spray drying method, for example, an improvement in the coating rate is expected.

[0088] The solid content fraction of the suspension for spray drying may be, for example, 1 to 50% or 10 to 30% in terms of volume fraction. The nozzle diameter may be, for example, 0.1 to 10 mm or 0.1 to 1 mm. The hot air temperature may be, for example, 100 to 200 °C.

[0089] For example, composite particles may be produced by a tumbling fluidized bed coating apparatus. In the tumbling fluidized bed coating apparatus, "(a) Preparation of the mixture" (adhesion of the coating liquid to the surface of the positive electrode active material particles) and "(b) Production of the composite particles" can be carried out simultaneously.

[0090] 《(c) Heat treatment》 This production method may include subjecting the composite particles to heat treatment. The coating film can be fixed by heat treatment. Heat treatment may also be referred to as "firing". In this production method, any heat treatment apparatus can be used. The heat treatment temperature may be, for example, 150 to 300 °C. The heat treatment time may be, for example, 1 to 10 hours. For example, heat treatment may be carried out in air or under an inert atmosphere.

Examples

[0091] <Comparative Example 1> 〔Preparation of composite particles〕 870.4 parts by mass of hydrogen peroxide solution (mass concentration 30%) was put into a container. Next, 987.4 parts by mass of ion-exchanged water and 44.2 parts by mass of phosphoric acid [P 2 O 5 ·3H 2 O] were put into the container. Next, 87.9 parts by mass of aqueous ammonia (mass concentration 28%) was put into the container. By sufficiently stirring the contents of the container, a solution was prepared. The solution is considered to contain a peroxo complex of P. Further, 0.1 part by mass of lithium hydroxide monohydrate (LiOH·H 2 O) was dissolved in the solution to prepare a coating liquid.

[0092] As the positive electrode active material particles, Li(Ni 1 / 3 Co1 / 3 Mn 1 / 3 )O 2 was prepared. A suspension was prepared by dispersing 50 parts by mass of the powder of the positive electrode active material particles in 53.7 parts by mass of the coating solution. The powder of the composite particles was prepared by spray-drying the suspension.

[0093] The obtained composite particles were heat-treated in an air atmosphere. The heat treatment temperature was 200 °C and the heat treatment time was 5 hours. Thereby, the composite particles (coated positive electrode active material) of Example 1 having a coating film with a thickness of 20 nm were obtained. In the composite particles of Example 1, the coating film is considered to contain Li 3 PO 4 (LPO).

[0094] 〔Fabrication of all-solid-state battery〕 (Fabrication of positive electrode) The following materials were prepared. Sulfide solid electrolyte: Li containing LiI 2 S-P 2 S 5 -based glass ceramics (D50: 0.8 μm) Conductive material: VGCF (vapor-grown carbon fiber) Binder: SBR (butadiene rubber) Dispersion medium: heptane Positive electrode current collector: Al foil

[0095] A positive electrode slurry was prepared by mixing the composite particles, the sulfide solid electrolyte, the conductive material, the binder, and the dispersion medium. The mixing ratio of the composite particles to the sulfide solid electrolyte was "composite particles / sulfide solid electrolyte = 7 / 3 (volume ratio)". The compounding amount of the conductive material was 3 parts by mass with respect to 100 parts by mass of the composite particles. The compounding amount of the binder was 0.7 parts by mass with respect to 100 parts by mass of the composite particles. The positive electrode slurry was sufficiently stirred by an ultrasonic homogenizer (manufactured by SMT: UH-50). A coating film was formed by coating the positive electrode slurry on the surface of the positive electrode current collector. The coating film was dried at 100 °C for 30 minutes using a hot plate. Thereby, a positive electrode green sheet was manufactured. A disk-shaped positive electrode was cut out from the positive electrode green sheet. The area of the positive electrode was 1 cm2 It was.

[0096] (Fabrication of the negative electrode) Into the kneading vessel of a film mixer (Primix 30-L type), a sulfide solid electrolyte (Li containing LiI 2 S-P 2 S 5 -based glass ceramics, D50: 0.8 μm), 1 mass% of a conductive assistant (VGCF), 2 mass% of a binder (SBR), and heptane were charged and stirred at 20,000 rpm for 30 minutes. Next, a negative electrode active material (Li 4 Ti 5 O 12 particles, D50: 1 μm) and the solid electrolyte were charged into the kneading vessel so that the volume ratio became 6:4, and the mixture was stirred at 15,000 rpm for 60 minutes using a film mixer to prepare a negative electrode mixture. The prepared negative electrode mixture was coated on a copper foil and dried at 100 °C for 30 minutes. Thereby, a negative electrode precursor was manufactured. A disk-shaped negative electrode was cut out from the negative electrode precursor. The area of the negative electrode was 1 cm 2 It was.

[0097] (Fabrication of the separator layer) Into a cylindrical ceramic having an inner diameter cross-sectional area of 1 cm 2 64.8 mg of a sulfide solid electrolyte (Li containing LiI 2 S-P 2 S 5 -based glass ceramics, D50: 2.5 μm) were put, smoothed, and then pressed at 1 ton / cm 2 to fabricate a separator layer (solid electrolyte layer).

[0098] (Fabrication of the battery) The positive electrode fabricated on one surface of the solid electrolyte layer was stacked, and the negative electrode fabricated on the other surface of the solid electrolyte layer was stacked, and pressed at 6 ton / cm 2 for 1 minute. Next, with terminals (stainless steel rods) inserted into the positive electrode and the negative electrode, a full solid-state battery (full solid-state lithium-ion battery) was fabricated by restraining with 1 ton.

[0099] <Example 1> In Example 1, a solution was prepared by dissolving 10.8 parts by mass of orthophosphoric acid (85%, manufactured by Kishida Chemical Co., Ltd.) in 166 parts by mass of ion-exchanged water. Further, lithium hydroxide monohydrate was dissolved in the solution so that the molar ratio “n Li / (n P +n E1 +n E2 )” became 0.45, thereby preparing a coating solution. Except for this point, the composite particles and the battery of Example 1 were produced in the same manner as in Comparative Example 1. In the composite particles of Example 1, the coating film is considered to contain, for example, Li 0.5 PO 3 such as Li x PO y (x and y are arbitrary numbers).

[0100] <Example 2> In Example 2, a coating solution was prepared by dissolving 6.7 parts by mass of boric acid (manufactured by Nacalai Tesque, Inc.) in 166 parts by mass of ion-exchanged water. Except for this point, the composite particles and the battery of Example 2 were produced in the same manner as in Comparative Example 1. In the composite particles of Example 2, the coating film is considered to contain, for example, BO such as BO x (x is an arbitrary number).

[0101] <Example 3> In Example 3, a solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) in 166 parts by mass of ion-exchanged water. Further, boric acid (manufactured by Nacalai Tesque, Inc.) was dissolved in the solution so that the molar ratio “(n E1 +n E2 ) / n P ” became 1.0, thereby preparing a coating solution. Except for this point, the composite particles and the battery of Example 3 were produced in the same manner as in Comparative Example 1. In the composite particles of Example 3, the coating film is considered to contain, for example, BPO X such as B x PO y (x and y are arbitrary numbers).

[0102] <Example 4> In Example 4, the heat treatment temperature of the composite particles was changed to 400 °C. Except for this point, the composite particles and batteries of Example 4 were produced in the same manner as in Example 3. In the composite particles of Example 4, the coating film is, for example, BPO X such as B x PO y (x and y are arbitrary numbers.) is considered to be included.

[0103] <Evaluation> [Measurement of Raman Spectrum of Composite Particles (Coating Film)] For each of the composite particles of the above Examples and Comparative Examples, a Raman spectrum was measured for the cross-section of the coating film. Figure 1 shows the Raman spectra of the composite particles (coating films) of the Examples and Comparative Examples. Table 1 shows the Raman shift values at the peak tops of the respective peaks of the Raman spectra. The measurement conditions of the Raman spectrum are as follows.

[0104] (Raman Spectroscopy Measurement Conditions) Raman spectrometer: "DXR3xi Imaging Micro Raman" (Thermo Fisher Scientific K.K.) Laser energy: 1.5 mW Exposure time: 50 - 100 Hz Number of scans: 100

[0105] [Reaction Resistance of Battery] For each of the above batteries (all-solid-state batteries) of the Examples and Comparative Examples, the output characteristics (reaction resistance) were evaluated by the following method.

[0106] (Confirmation of Initial Capacity) For each battery, constant current-constant voltage (CC-CV) charging and constant current (CC) discharging were repeated 3 cycles at a rate of 1 / 3C. The discharge capacity of the third cycle was confirmed as the initial capacity. Note that "C" is the unit of the current rate. "1C" indicates the current rate at which the state of charge (SOC) reaches from 0% to 100% by charging for 1 hour.

[0107] (Measurement of reaction resistance) The battery with the confirmed initial capacity was charged to a state where the SOC (state of charge) was 50% at a rate of 1 / 3C. Then, the AC impedance of the battery was measured under the conditions of 10 mV and 0.1 to 10 6 Hz. An arc was fitted to the Cole-Cole plot created based on the measurement results of the AC impedance, and the distance between two points of the intersection of the fitted arc and the real axis was measured as the reaction resistance (discharge resistance).

[0108] Table 1 shows the measurement results of the discharge resistance (ratio when the discharge resistance of Comparative Example 1 is set to 1.00). Note that the smaller the discharge resistance, the higher the output characteristics (discharge rate) of the battery.

[0109]

Table 1

[0110] From the results shown in Table 1, it can be seen that the batteries (composite particles) of Examples 1 to 4 having peaks with peak tops within the range of 600 to 200 cm -1 in the Raman spectrum of the cross-section of the coating film have a significantly lower reaction resistance than the battery (composite particles) of Comparative Example 1 in which such peaks do not exist in the Raman spectrum of the cross-section of the coating film. Note that in Examples 3 and 4, there are three peaks having peak tops within the range of 600 to 200 cm -1

[0111] ​In Examples 1, 3, and 4, in the Raman spectroscopy spectrum of the cross-section of the coating film, furthermore, in the range of 1250 to 1050 cm -1 and 800 to 630 cm -1 there is also at least one peak having a peak top. In this case, it is expected that the coating film has low resistance and excellent durability under high voltage.

[0112] This embodiment and these examples are illustrative in all respects. This embodiment and these examples are not restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, any configurations are extracted from this embodiment and these examples, and their arbitrary combinations are also initially planned.

Description of Reference Numerals

[0113] 1 Positive electrode active material particles, 2 Coating film, 5 Composite particles, 10 Positive electrode, 20 Negative electrode, 30 Separator layer, 50 Power generation element, 100 All-solid-state battery.

Claims

1. A composite particle comprising a positive electrode active material particle and a coating film covering at least a part of the surface of the positive electrode active material particle, wherein the coating film contains a phosphorus compound, the phosphorus compound contains at least one of a first element which is a glass network forming element and a second element which is a transition element, and phosphorus, the first element is at least one selected from the group consisting of boron, silicon, and germanium, In the Raman spectroscopy spectrum of the cross-section of the coating film, a peak having a peak top within the range of 600 to 200 cm －１ exists, and in the coating film, a composite particle satisfying the following formula (1). C Li / (C P + C E1 + C E2 ) ≤ 2.5 …(1) (In the above formula (1), C Li 、 C P 、 C E1 、 C E2 indicates the elemental concentration measured by X-ray photoelectron spectroscopy, C Li indicates the elemental concentration of lithium, C P represents the elemental concentration of phosphorus and C E1 indicates the element concentration of the first element, C E2 indicates the element concentration of the second element.)

2. The composite particle according to claim 1, wherein the second element is at least one selected from the group consisting of a second transition element and a third transition element.

3. In the Raman spectroscopic spectrum of the cross-section of the coating film, further, in the range of 1250 to 1050 cm －１ and 800 to 630 cm －１ There is a peak having a peak top within the range of, The composite particle according to claim 1.

4. A positive electrode comprising the composite particle according to claim 1 and a sulfide solid electrolyte.

5. An all-solid-state battery comprising the positive electrode according to claim 4.

6. A manufacturing method for manufacturing the composite particle according to claim 1, comprising: (a) preparing a mixture by mixing a coating solution and positive electrode active material particles; and (b) manufacturing the composite particle by drying the mixture, wherein the coating solution contains a solute and a solvent, and the solute contains at least one of the first element and the second element, and phosphorus. A manufacturing method for composite particles. ​

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