Active material, electrode mixture containing said active material, and battery

Abstract

This active material contains: a compound A that contains Li element, M element (which represents one or more elements selected from among Ni element, Co element and Mn element) and O element; and a compound B that contains Li element, Nb element and O element. With respect to the Raman spectrum as obtained by means of Raman spectroscopy, if SPA is the area of a peak associated with the compound A, said peak being observed within the range of from 540 cm-1 to 650 cm-1, and SPB is the area of a peak associated with the compound B, the value of SPB / SPA, which is the ratio of the SPB to SPA, satisfies the relational expression 0 < SPB / SPA ≤ 1.2.

Description

[Technical Field]

[0001] The present invention relates to an active material for a battery, and also to an electrode mixture and a battery containing the active material. [Background technology]

[0002] Lithium-ion secondary batteries have a high energy density and can be easily made smaller and lighter, and are therefore widely used as power sources for portable electronic devices such as notebook computers and mobile phones. Recently, development has been progressing on high-output, high-capacity lithium-ion secondary batteries that can be installed in electric vehicles, hybrid electric vehicles, and the like.

[0003] Currently, many lithium-ion secondary batteries use electrolytes containing flammable organic solvents. This poses a risk of the electrolyte catching fire if the battery becomes too hot due to a short circuit or other cause. In contrast, solid-state batteries, which use a solid electrolyte instead of an electrolyte and do not contain flammable organic solvents, are expected to be put to practical use as batteries that combine safety and high energy density, as they have a reduced risk of fire.

[0004] Sulfide solid electrolytes have been investigated as one type of solid electrolyte for use in solid-state batteries. However, solid-state batteries containing sulfide solid electrolytes have a problem in that, when they are charged and discharged, the interfacial resistance between the electrode active material and the sulfide solid electrolyte increases, restricting the movement of lithium ions. This is thought to be due to the formation of a resistive layer at the interface between the electrode active material and the sulfide solid electrolyte as a result of a reaction between the electrode active material and the sulfide solid electrolyte. To address this problem, for example, Patent Document 1 attempts to suppress the increase in interfacial resistance by coating the surface of the positive electrode active material with a specific compound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US2018 / 219229A1 Summary of the Invention

[0006] While various active material technologies have been proposed, the current demand for further improvements in battery performance has created a need for active materials that can reduce the interfacial resistance with solid electrolytes, such as sulfide solid electrolytes.

[0007] In view of the above problems, the main object of the present invention is to provide an active material that can reduce the interfacial resistance with the solid electrolyte and improve the battery performance.

[0008] The present invention relates to a compound A containing lithium (Li), M (wherein M represents one or more elements selected from nickel (Ni), cobalt (Co), and manganese (Mn)), and oxygen (O); and a compound B containing lithium (Li), niobium (Nb), and oxygen (O), In the Raman spectrum measured by Raman spectroscopy, -1 More than 650cm -1 The area of ​​the peaks derived from the compound A observed in the following range is S PA The area of ​​the peak derived from compound B is S PB When I said that, S PA and S PB The ratio of S PB / S PA The value of is 0 PB / S PA ≦1.2.

[0009] The present invention also provides an electrode mixture containing the above active material and a solid electrolyte.

[0010] The present invention further provides a battery including a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer containing a solid electrolyte, wherein the positive electrode active material is the active material described above. [Brief explanation of the drawings]

[0011] ​ [Figure 1] FIG. 1 is a graph showing the Raman spectrum of the active material obtained in Example 4 and the results of peak separation. [Figure 2] 2(a) to 2(c) are scanning transmission electron microscope images of the active materials obtained in Examples 2 to 4, respectively. [Figure 3] FIG. 3 is a graph showing the Raman spectra of the active materials obtained in Examples 1 to 5 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below based on preferred embodiments thereof. The present invention relates to an active material used in a battery, an electrode mixture containing the active material, and a battery. Each of these will be described below.

[0013] A. Active material The active material of the present invention is configured to contain two specific compounds, Compound A and Compound B. The active material of the present invention is only required to contain Compound A and Compound B, and may also contain other compounds as necessary. Each compound will be explained below.

[0014] A-1. Compound A Compound A contains lithium (Li), M (where M represents one or more elements selected from nickel (Ni), cobalt (Co), and manganese (Mn)), and oxygen (O). In other words, compound A is composed of a lithium transition metal composite oxide. Examples of the lithium transition metal composite oxide used as compound A include a lithium-containing composite oxide having a layered rock-salt structure represented by LiMO2 (where M is as defined above) and a lithium-containing composite oxide having a spinel structure represented by LiMO4 (where M is as defined above), or a combination of both. However, the lithium transition metal composite oxide is not limited to these.

[0015] In particular, compound A is preferably the lithium-containing composite oxide having the spinel structure described above. Hereinafter, the lithium-containing composite oxide having the spinel structure may be simply referred to as a "spinel composite oxide." When the active material of the present invention containing such compound A is used as a positive electrode active material, it has an operating potential of 4.5 V or higher relative to metallic Li. The phrase "having an operating potential of 4.5 V or higher relative to metallic Li" does not necessarily mean that the active material has only an operating potential of 4.5 V or higher in the plateau region, but also encompasses cases where the active material has a partial operating potential of 4.5 V or higher. Therefore, the present invention is not limited to a positive electrode active material consisting solely of a 5 V-class positive electrode active material having an operating potential of 4.5 V or higher in the plateau region. For example, the active material of the present invention may also contain a positive electrode active material having an operating potential of less than 4.5 V in the plateau region.

[0016] When compound A is a spinel-type composite oxide, compound A preferably contains at least Mn, and more preferably contains Li, Mn, and O, as well as one or more other elements. Here, the "one or more other elements" is preferably a metal element M1 selected from the group consisting of Ni and Co.

[0017] When compound A is a spinel-type composite oxide, compound A also preferably contains Li, Mn, and O, as well as two or more other elements. At least one of the "two or more other elements" is preferably a metal element M1 selected from the group consisting of Ni and Co, and the other element is preferably a metal element M2 consisting of one or a combination of two or more selected from the group consisting of Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce.

[0018] A particularly preferred example of compound A is LiMnO 4-δ Examples of such a spinel-type lithium-manganese-containing composite oxide include those having a crystal structure in which some of the Mn sites in the formula (I) are substituted with Li, a metal element M1, and another metal element M2.

[0019] The metal element M1 is a substitution element that mainly contributes to realizing an operating potential of 4.5 V or more relative to metallic Li, and preferably contains at least one element of Ni and Co as described above. On the other hand, the metal element M2 is a substitution element that mainly contributes to stabilizing the crystal structure and improving characteristics. Examples of substitution elements that contribute to improving the capacity retention rate include Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. Among these, Na, Mg, Al, P, K, Ca, Ti, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, Ta, and W are preferred. The metal element M2 may be one or a combination of two or more of the above-mentioned elements. The metal element M2 preferably contains at least one of the above-mentioned elements, and may also contain metal elements other than the above-mentioned elements. The metal element M2 contained in the structure is a different element species from the metal element M1.

[0020] An example of the composition of compound A is a compound represented by the formula (1): Li x (M1 y M2 z Mn 3-x-y-z )O 4-δ Examples include a spinel-type lithium-manganese-containing composite oxide represented by the following formula (1): The metal element M1 and the metal element M2 in formula (1) are as described above.

[0021] In the formula (1), "x" is preferably 1.00 or more and 1.20 or less, particularly 1.01 or more and 1.10 or less, and even more preferably 1.02 or more and 1.08 or less. "y", which indicates the content of metal element M1, is preferably 0.20 or more and 1.20 or less, particularly 0.30 or more and 1.10 or less, and even more preferably 0.35 or more and 1.05 or less. "z", which indicates the content of metal element M2, is preferably 0.001 or more and 0.400 or less, particularly 0.002 or more and 0.400 or less, and even more preferably 0.005 or more and 0.30 or less, and even more preferably 0.10 or more. In particular, by making it 0.10 or more, the cycle characteristics can be more effectively improved.

[0022] Another example of the composition of compound A is a compound represented by the formula (2): x (Ni y M3 z Mn 3-x-y-z )O 4-δ In formula (2), "x" is preferably 1.00 or more and 1.20 or less, more preferably 1.01 or more and 1.10 or less, and even more preferably 1.02 or more and 1.08 or less. In formula (2), "y" is preferably 0.20 or more and 0.70 or less, more preferably 0.30 or more and 0.60 or less, and even more preferably 0.35 or more and 0.55 or less.

[0023] In the formula (2), examples of the metal element M3 include Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. Of these, Na, Mg, Al, P, K, Ca, Ti, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, Ta, and W are preferred. The metal element M3 may be one or a combination of two or more of the above elements. The "z" (molar ratio) of the metal element M3 is preferably greater than 0 and less than or equal to 0.5, more preferably greater than 0.01 or less than 0.45, even more preferably greater than 0.05 or less than 0.40, and even more preferably greater than 0.10 or less than 0.35. A molar ratio of 0.10 or greater can more effectively improve cycle performance.

[0024] In the formulas (1) and (2), "4-δ" indicates that oxygen vacancies may be present. Furthermore, some of the oxygen atoms may be substituted with fluorine or other elements. In this case, δ is preferably 0 or more or 0.2 or less, more preferably 0.1 or less, and even more preferably 0.05 or less.

[0025] Compound A can be confirmed to have a spinel structure, for example, when fitted to a cubic crystal structure model of space group Fd-3m (Origin Choice 2), by finding that the ranges of Rwp and S, which indicate the degree of agreement between observed intensity and calculated intensity, are Rwp<10 or S<2.5.

[0026] A-2.Compound B The compound B constituting the active material of the present invention contains lithium (Li), niobium (Nb) and oxygen (O). The composition of each element in the compound B is, for example, Li x NbO yIt can be shown by the formula. x and y in the formula can take arbitrary values within a range corresponding to the valence of the element. Among these, a composition (x > 1) in which Li is contained in an amount exceeding 1 mol with respect to 1 mol of Nb is particularly preferred. By doing so, the formation of a compound of Nb and O can be suppressed, and the interfacial resistance with the solid electrolyte can be effectively reduced. Specifically, the values of x and y are preferably 1 < x ≦ 2 with respect to x, and preferably 3 ≦ y ≦ 8 with respect to y.

[0027] Compound B is Li x NbO y When represented by, as a method for satisfying x > 1, a method of making the blending amount of the lithium raw material with respect to the niobium raw material exceed the assumed composition, for example, the stoichiometric composition ratio of LiNbO3, can be mentioned. At this time, simply adding lithium in excess will cause lithium carbonate to be generated on the surface of the active material due to the excess lithium, which becomes a resistance and rather tends to deteriorate the rate characteristics and cycle characteristics. Therefore, considering the generation of lithium carbonate, which is an undesirable compound, it is preferable to adjust the blending amount of the niobium raw material and the blending amount of the lithium raw material so that Li x NbO y has a predetermined composition.

[0028] The ratio of compound B in the active material is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 15% by mass or less, and still more preferably 0.5% by mass or more and 10% by mass or less, in terms of the niobium (Nb) element contained in compound B. By containing the niobium (Nb) element in this range in the active material, as will be described later, the generation of a high-resistance region between the active material and the solid electrolyte can be effectively suppressed, and the interfacial resistance between the active material and the solid electrolyte is reduced. The amount of the niobium (Nb) element contained in the active material can be measured by ICP emission spectrometry for a solution in which the active material is dissolved.

[0029] A-3. Raman Spectrum When the active material of the present invention containing the above-mentioned compound A and compound B is measured by Raman spectroscopy, a peak in the Raman spectrum derived from compound A and a peak in the Raman spectrum derived from compound B are observed. In detail, in the Raman spectrum obtained by measuring by Raman spectroscopy, for compound A, depending on its composition, the Raman shift is 540 cm -1 More than 650cm -1 One or more peaks derived from compound A are observed in the following wavenumber range. Peaks in this wavenumber range are observed regardless of whether compound A has a layered rock-salt structure or a spinel structure. Furthermore, peaks in this wavenumber range include both those derived from one-to-one vibrations between the transition element and oxygen element constituting compound A (e.g., those derived from MnO, CoO, NiO), and those derived from the overall vibration of the transition element and all oxygen elements located around the transition element (e.g., those derived from MnO6). On the other hand, for compound B, depending on its composition, for example, 850 cm -1 More than 950cm -1 One or more peaks derived from Compound B are observed in the following ranges. For example, "JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 25 (2013) 205901 (8pp) 'Identification of LiNbO3, LiNb3O8, and Li3NbO4 phases in thin films synthesized with different deposition techniques by means of XRD and Raman spectroscopy'" discloses Raman spectra of Li3NbO4, LiNbO3, and LiNb3O8, but none of them exhibit the peak positions and peak area ratios specified in the present invention. Therefore, it can be said that Compound B has a novel structure from the Raman spectrum specified in the present invention.

[0030] The above mentioned 540cm -1More than 650cm -1 The area of ​​the peaks in the Raman spectrum derived from compound A observed in the following range is S PA The area of ​​the peak derived from compound B is S PB In this case, in the active material of the present invention, S PA and S PB The ratio of S PB / S PA The value of is preferably 0 PB / S PA ≦1.2. Since the Raman spectrum is obtained by measuring the Raman scattered light of incident light, the Raman spectrum obtained by measuring the active material of the present invention reflects the surface state of the active material (not the outermost surface, but the surface layer). Whether or not compound B is present in the surface layer can be confirmed by a scanning transmission electron microscope (hereinafter also referred to as "STEM") or the like. PB / S PA The fact that the value of (hereinafter, this value is also referred to as the "Raman spectral ratio") is within a specific range means that the abundance ratio of compound A to compound B in the surface layer of the active material is within a specific range. The inventors have found that, with the active material of the present invention in which compound A and compound B are present in the surface layer at a specific Raman spectral ratio, when the active material is in contact with a solid electrolyte, such as a sulfide solid electrolyte, the formation of a high-resistance region with respect to lithium ion migration at the interface between the two is suppressed. As a result, the interfacial resistance between the active material and the solid electrolyte is reduced, lithium ion migration is facilitated, and battery capacity is improved. This advantage is even more pronounced when compound A constituting the active material has a 5V-class spinel structure.

[0031] From the viewpoint of further suppressing the generation of the above-mentioned high resistance region and further improving the battery capacity, the Raman spectral ratio is more preferably 0.01 or more and 0.50 or less, and even more preferably 0.02 or more and 0.30 or less.

[0032] The peak area S for calculating the Raman spectral ratio PA As mentioned above, 540cm -1 ​More than 650cm -1 It is calculated from the peaks in the Raman spectrum of compound A observed in the following wavenumber range. Multiple peaks may be observed in this wavenumber range. In such cases, a mathematical operation is performed to separate the overlapping peaks into individual peaks, and the sum of the areas of each separated peak is used to calculate the peak area S. PA In this case, the peak area is determined for the separated peaks whose peak tops fall within the above wavenumber range. On the other hand, the area of ​​the peak due to compound B, S PB Generally, only one peak is observed in the wavenumber range in which the area of ​​the peak S is to be calculated. However, if two or more peaks are observed overlapping each other, the area of ​​the peak S PA As in the case of , the peak separation operation is performed, and the peak area S is calculated by adding up the areas of each separated peak. PB Let's say.

[0033] In the active material of the present invention, the state in which compound A and compound B are present is not particularly limited as long as the Raman spectral ratio satisfies the above-mentioned range. In the active material, for example, particles of compound A and particles of compound B may be in a mixed state. Alternatively, particles of compound B may be present on the surface of particles of compound A. In particular, it is preferable that the active material has a structure in which compound B is present on at least a part of the surface of a core material containing compound A, since this makes it possible to easily set the Raman spectral ratio within the above-mentioned range.

[0034] When the active material has a structure in which compound B is present on at least a portion of the surface of a core material containing compound A, compound B may coat the surface of the core material evenly, or may coat the surface of the core material partially so that a portion of the surface of the core material is exposed. That is, compound B preferably coats the surface of the core material containing compound A to an extent that the effects of the present invention can be obtained. When compound B is present on the surface of the core material containing compound A so that a portion of the surface is exposed, compound B may be present so that "island regions" made of compound B are scattered across a "sea region" made up of the surface of the core material containing compound A.

[0035] The shape and size of the core material are not particularly limited as long as they can be used as an active material and are applicable to batteries. The core material is preferably particulate, for example. The thickness of the coating can be adjusted appropriately depending on the material of the coating, and is preferably set to a level that achieves the effects of the present invention. The thickness of the coating can be, for example, 1 nm or more and 1 μm or less. The thickness of the coating can be measured, for example, from an image observed using a high-angle annular dark-field scanning transmission microscope (HAADF-STEM) and determined from the average value (n≧10). The proportion of the coating on the core material surface, i.e., the coverage, can be adjusted appropriately depending on the material of the coating, and is preferably set to a level that achieves the effects of the present invention. The coverage is preferably, for example, 30% or more, more preferably 50% or more, particularly preferably 80% or more, and even more preferably 90% or more. The coverage can be determined, for example, by X-ray photoelectron spectroscopy (XPS).

[0036] When the active material of the present invention has a core material and a coating portion, the core material preferably contains compound A, and the coating portion preferably contains compound B. Of all compounds A contained in the active material, the proportion of compound A contained in the core material may be, for example, 70% by mass or more, 80% by mass or more, or 90% by mass or more. On the other hand, of all compounds B contained in the active material, the proportion of compound B contained in the coating portion may be, for example, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0037] In the present invention, the core material preferably contains, as a main component, Compound A. "Containing as a main component" means that the content is, for example, 50% by mass or more, particularly 70% by mass or more, and particularly 90% by mass or more.

[0038] The content of compound B in the coating portion is determined by measuring the active material by Raman spectroscopy, and the Raman spectrum obtained is -1 More than 650cm -1The area of ​​the peaks derived from the compound A observed in the following range is S PA The area of ​​the peak derived from compound B is S PB As mentioned above, S PA and S PB The ratio of S PB / S PA The value of is 0 PB / S PA It is preferable that the ratio satisfies the range of ≦1.2.

[0039] Whether or not compound B is present on the surface of a core material containing compound A can be confirmed by the Raman spectrum described above, as well as by elemental mapping, X-ray photoelectron spectroscopy (XPS), STEM, a combination of STEM and energy dispersive X-ray analysis (EDS), Auger electron spectroscopy, etc.

[0040] Regardless of the state of existence of compound A and compound B, the active material has a volume cumulative particle size D at 50% by volume of cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method. 50 However, for example, it is preferably 20 μm or less, more preferably less than 15 μm, even more preferably more than 1 μm and less than 10 μm, and even more preferably more than 2 μm and 8 μm or less. 50 By making the diameter of the active material 20 μm or less, for example, when the active material is used in a positive electrode mixture, good contact with the solid electrolyte in the positive electrode mixture can be ensured, and the utilization rate of lithium ions in the active material can be increased. 50 By making the D50 larger than 1 μm, it is possible to prevent the particles from agglomerating and increasing the viscosity of the slurry. The D50 of the active material can be adjusted to fall within the above range by adjusting the operating conditions of the spray dry granulation method or the tumbling fluidized bed granulation method, or by adjusting the crushing conditions, but is not limited to these adjustment methods.

[0041] A-4. Production of active materials Next, a preferred method for producing the active material of the present invention will be described. ​First, a method for producing a core material containing compound A will be described. Compound A can be obtained by weighing and mixing raw materials such as a lithium source compound and a manganese source compound, and, if necessary, a nickel source compound, a cobalt source compound, and a titanium source compound, pulverizing the mixture using a wet pulverizer or the like, followed by granulation, calcining, heat treating if necessary, crushing the mixture under preferred conditions, and further classifying the mixture if necessary. Instead of this method, a core material containing compound A can also be obtained by adding a basic substance such as sodium hydroxide to an aqueous solution containing a manganese source compound, and, if necessary, a nickel source compound, a cobalt source compound, and a titanium source compound to precipitate a metal composite hydroxide, and then mixing the metal composite hydroxide with a lithium source compound and calcining the mixture. The detailed method for producing the core material containing compound A can be the same as that described in, for example, International Publication No. 2019 / 044733, and therefore will not be described here. The contents of this publication are incorporated herein by reference.

[0042] Next, the production of compound B will be described. Compound B is preferably formed on the surface of a core material containing compound A obtained as described above. To form compound B on the surface of a core material containing compound A, compound A may be contacted with a treatment solution containing a lithium source compound and a niobium source compound. Examples of lithium source compounds that can be used include lithium hydroxide, lithium sulfate, and lithium chloride. Examples of niobium source compounds that can be used include ammonium peroxoniobate. These compounds are dissolved in water, and the treatment solution is mixed with compound A to form a slurry. The slurry is heated to 90°C or higher, whereby the lithium source compound and ammonium peroxoniobate react in the solution to form compound B. Compound B has the property of being easily adsorbed to the surface of a core material containing compound A. Therefore, compound B can be formed on the surface of the core material by drying the slurry. A treatment liquid containing a lithium source compound and ammonium peroxoniobate and heated to 90°C or higher may be sprayed onto the core material containing compound A, or compound B may be generated from the treatment liquid heated to 90°C or higher and applied to the surface of the core material containing compound A. Thereafter, crushing and heat treatment are carried out as necessary.

[0043] The amount of the treatment solution used is preferably such that the proportion of niobium in the active material is, for example, 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more. On the other hand, the proportion is preferably such that the proportion of niobium in the active material is, for example, 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. The concentration of the treatment solution is not particularly limited.

[0044] By drying the slurry, compound B can be arranged on the surface of the core material containing compound A. To dry the slurry, for example, spray-drying granulation or tumbling fluidized bed granulation can be used. Heat treatment can then be performed as needed. Heat treatment may also be performed in an air atmosphere. The drying and heat treatment temperature can be set to a relatively low temperature, preferably between 25°C and 700°C, more preferably between 40°C and 500°C, and even more preferably between 60°C and 200°C. The heat treatment time is preferably between 1 hour and 20 hours, more preferably between 1 hour and 15 hours, and even more preferably between 1 hour and 10 hours. This allows for the successful production of an active material whose Raman spectral ratio satisfies the above-mentioned range. If the heat treatment is performed at an excessively high temperature, it becomes difficult for the resulting active material to satisfy the above-mentioned Raman spectral ratio.

[0045] A-5. Uses of active materials The active material of the present invention can be suitably used as a positive electrode active material for a battery.

[0046] B. Electrode mixture The electrode mixture of the present invention is a mixture containing at least the active material described above, and may contain at least one of an electrolyte, a conductive material, and a binder as necessary. When the active material is used as a positive electrode active material, the electrode mixture becomes a positive electrode mixture that constitutes a positive electrode layer. Note that the active material contained in the electrode mixture can be the same as that described in the above section "A. Active material," and therefore will not be described here.

[0047] Examples of the electrolyte used in the present invention include solid electrolytes. Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and organic polymer electrolytes such as polymer electrolytes. From the viewpoint of making the effects of the present invention more pronounced, the electrolyte used in the present invention is preferably a sulfide solid electrolyte. The sulfide solid electrolyte may be the same as the sulfide solid electrolyte used in general solid-state batteries. The sulfide solid electrolyte may contain, for example, Li and S and have lithium ion conductivity. The sulfide solid electrolyte may be any of a crystalline material, glass ceramics, and glass. The sulfide solid electrolyte may have an argyrodite-type crystal structure. Examples of such sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (where "X" represents one or more halogen elements), Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, and Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, Li7P3S 11 , Li 3.25 P 0.95 S4, Li a PS b X c (X is at least one halogen element; a is a number of 3.0 or more and 6.0 or less; b is a number of 3.5 or more and 4.8 or less; c is a number of 0.1 or more and 3.0 or less). Other examples include sulfide solid electrolytes described in WO 2013 / 099834 and WO 2015 / 001818.

[0048] The active material contained in the electrode mixture may be the active material of the present invention alone, or may be used in combination with other active materials. Examples of other active materials include active materials containing known lithium transition metal composite oxides. The proportion of the active material of the present invention in the electrode mixture may be, for example, 20% by mass or more, 30% by mass or more, or 40% by mass or more. On the other hand, the proportion may be, for example, 70% by mass or less, or 60% by mass or less.

[0049] C.Battery The battery of the present invention includes a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer containing a solid electrolyte, and the positive electrode active material is preferably the active material described above. The battery can be fabricated, for example, by stacking the three layers of the positive electrode layer, solid electrolyte layer, and negative electrode layer fabricated as described above and pressure molding them.

[0050] In order to achieve the desired effect more significantly, the battery of the present invention preferably has an interface where the positive electrode active material and the solid electrolyte are in contact. Here, "the positive electrode active material and the solid electrolyte are in contact" includes both contact between the positive electrode active material contained in the positive electrode layer and the solid electrolyte, and contact between the positive electrode active material contained in the positive electrode layer and the solid electrolyte contained in the solid electrolyte layer.

[0051] The battery of the present invention can be used as a solid-state battery, particularly a lithium solid-state battery. The lithium solid-state battery may be a primary battery or a secondary battery, but is preferably used as a lithium secondary battery. The term "solid-state battery" includes not only a solid-state battery that does not contain any liquid or gel-like substance as an electrolyte, but also an embodiment that contains, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0052] The negative electrode active material used in the negative electrode layer can be the same as the negative electrode active material used in general lithium batteries. Specific negative electrode active materials include known materials that absorb and release lithium ions, such as carbon materials, silicon oxide compounds such as silicon and Si-O, tin compounds, and lithium titanate. Examples of the carbon material include sintered organic polymer compounds such as polyacrylonitrile, phenolic resin, phenolic novolac resin, and cellulose, as well as artificial graphite and natural graphite. The negative electrode layer can be fabricated in the same manner as the positive electrode layer, except that such negative electrode active materials are used. [Example]

[0053] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0054] Example 1 A lithium-manganese-containing composite oxide was obtained using the same method as that described in Example 1 of International Publication No. 2019 / 044733, except that no Al raw material was used. This lithium-manganese-containing composite oxide was confirmed to be a spinel-type lithium-manganese-containing composite oxide by XRD measurement. Furthermore, chemical analysis of this spinel-type lithium-manganese-containing composite oxide, i.e., Compound A, revealed the following: Li: 4.2%, Mn: 41.6%, Ni: 13.5%, Ti: 5.1%. The same applies to the following Examples and Comparative Examples.

[0055] Compound B was formed on the surface of the core material containing compound A obtained in this manner. Compound B was formed by the following procedure. A mixed aqueous solution was prepared by dissolving 6.4 g of ammonium peroxoniobate in 450 mL of a lithium hydroxide aqueous solution with a lithium ion concentration adjusted to 11.4 g / L. 100 g of the core material obtained above was added to this mixed aqueous solution to prepare a slurry. The slurry was heated to 90°C or higher and held for 10 minutes. By heating at 90°C or higher, Li-Nb-O-based compounds, which tend to be easily adsorbed to the surface of the core material, were formed on the surface of the core material. After decanting the liquid, the core material was washed twice with 900 mL of a 0.14 mol / L lithium sulfate solution. After drying at 120°C, the active material was heat-treated at 200°C for 2 hours in an air atmosphere to obtain the desired active material. The volume-cumulative particle size D of the obtained active material was 50 was 3.8 μm. The percentage of niobium in the active material measured by ICP atomic emission spectroscopy is shown in Table 1 below.

[0056] Example 2 In Example 1, the amount of ammonium peroxoniobate used to produce Compound B was 8.5 g. Except for this, an active material was obtained in the same manner as in Example 1. The volume-cumulative particle diameter D of the obtained active material 50 was 3.8 μm. The percentage of niobium in the active material measured by ICP atomic emission spectroscopy is shown in Table 1 below.

[0057] Example 3 In Example 1, the amount of ammonium peroxoniobate used to produce Compound B was 17.0 g. Except for this, an active material was obtained in the same manner as in Example 1. The volume-cumulative particle diameter D of the obtained active material 50 was 3.8 μm. The percentage of niobium in the active material measured by ICP atomic emission spectroscopy is shown in Table 1 below.

[0058] Example 4 In Example 1, the amount of ammonium peroxoniobate used to produce Compound B was 25.5 g. Except for this, an active material was obtained in the same manner as in Example 1. The volume-cumulative particle diameter D of the obtained active material 50 was 3.8 μm. The percentage of niobium in the active material measured by ICP atomic emission spectroscopy is shown in Table 1 below.

[0059] Example 5 In Example 1, the amount of ammonium peroxoniobate used to produce Compound B was 42.5 g. Except for this, an active material was obtained in the same manner as in Example 1. The volume-cumulative particle diameter D of the obtained active material 50 was 3.6 μm. The percentage of niobium in the active material measured by ICP atomic emission spectroscopy is shown in Table 1 below.

[0060] Comparative Example 1 In Example 1, compound B was not formed on the surface of the particles of compound A. Except for this, the active material was obtained in the same manner as in Example 1. Volume cumulative particle diameter D of the active material 50 was 4.6 μm.

[0061] [Rating 1] The active materials obtained in the examples and comparative examples were measured for Raman spectrum by the procedure described below, and the area S of the peak derived from compound A was calculated. PA , and the area S of the peak attributed to compound B PB The results are shown in Table 1 below. The Raman spectrum measured for the active material of Example 4 and the results of its peak separation are shown in Figure 1. STEM images were also taken for the active materials obtained in Examples 2 to 4. The results are shown in Figures 2(a) to 2(c). Furthermore, the Raman spectra measured for the active materials of each of the Examples including Example 4 and the Comparative Examples are shown in FIG.

[0062] <Raman spectrum measurement> (Sample preparation) When measuring the Raman spectrum of a powder sample, the less unevenness there is on the sample surface and the higher the particle density, the more particles there are in the space where the excitation light and Raman scattered light are focused, and the higher the Raman light intensity can be obtained with a lower laser excitation power. Therefore, using a Specac mini hydraulic press and a Φ7mm pellet molding die, the active materials obtained in the examples and comparative examples were each pressed at 1 ton to form pellets.

[0063] (Measurement conditions) Equipment: LabRAM HR Evolution (Horiba, Ltd.) Excitation wavelength: 325nm Pump power: 0.6mW Detector: Syncerity OE Attenuation filter: 10% Grating: 1200gr / mm Confocal hole: 100μm Exposure time: 40 seconds Objective lens: ×40 / VIS Mapping area: 30μm x 9μm ·Measurement interval: 2μm Accumulation count: 1

[0064] Wavenumber calibration was performed by measuring the standard sample Si, with the main peak at 520.0 cm -1 I made it so that it would be like this. Mapping measurements were performed under the above conditions, and then all spectra in the mapping area were averaged to obtain the final spectrum. Note that if the S / N ratio of the spectrum is poor and it is difficult to determine whether a peak is due to the sample or noise, it is possible to increase the measurement points and average the spectrum. Also, peaks due to cosmic rays may be included in the spectrum. It is possible to determine whether a peak is due to cosmic rays, and if no peak appears at a certain wavenumber when measurements are repeated reproducibly, the peak can be determined to be cosmic rays. The laser excitation wavelength was 325 nm. The reason for this is that, in general, the shorter the excitation wavelength, the shallower the penetration depth of light into a substance, making it easier to observe a peak derived from compound B coated on the surface of compound A. In fact, the present inventors measured the sample of Example 1 using an excitation wavelength of 532 nm and confirmed that no peak derived from compound B was observed.

[0065] =Peak Analysis= Peak fitting of the Raman spectra was performed using the fitting program "Peak Analyzer" in the graph creation software "OriginPro 2019" by OriginLab Corporation. Peak fitting yielded the parameters of the peak wavenumber, full width at half maximum, and area. Prior to fitting, the baseline was subtracted from the spectrum to perform baseline correction. The baseline was 350 cm -1 From 1500cm -1 In the range of 180cm -1 , 300cm -1 , 1125cm -1 , 1425cm -1 The 5th-order polynomial was created and determined by passing through the four points at 540 cm. The baseline was then subtracted from the measured spectrum. The function used for fitting was -1 From 650cm -1 The peaks were treated as Vogit functions, and the other peaks were treated as Gaussian functions. <Peak area S PA and S PB Calculation of> 540cm -1 More than 650cm -1 The area of ​​the peak derived from compound A having a peak top in the following wavenumber range is S PA , the area of ​​the peak attributed to compound B is S PB The above S PA and S PB The area ratio of the peaks is S PA / S PB It was decided.

[0066] [Rating 2] Using the active materials obtained in the examples and comparative examples as the positive electrode active materials, solid state batteries were fabricated according to the following procedure. The discharge capacity of the fabricated solid state batteries was measured according to the following procedure. The results are shown in Table 1 below.

[0067] <Fabrication of solid-state batteries and measurement of discharge capacity> The positive electrode active material was prepared in the examples and comparative examples, the negative electrode active material was graphite (Gr) powder, and the solid electrolyte powder was a sulfide solid electrolyte having an argyrodite-type crystal structure. The positive electrode mixture powder was prepared by mixing the positive electrode active materials, solid electrolyte powder, and conductive material (carbon-based material) powder produced in the examples and comparative examples in a mortar at a ratio of 60%:30%:10%. The negative electrode mixture powder was prepared by mixing graphite (Gr) powder and solid electrolyte powder in a mortar at a ratio of 50%:50%.

[0068] 50 mg of solid electrolyte powder was filled into an insulating cylinder (φ10.5 mm) of a sealed cell and uniaxially molded at 184 MPa. Next, 13 mg of positive electrode mixture powder was filled into the insulating cylinder, and 10 mg of negative electrode mixture powder was filled into the opposite side. After uniaxial molding at 551 MPa, the cells were fastened with pressure screws to obtain a solid battery (solid-state lithium secondary battery) equipped with a positive electrode layer, a negative electrode layer, and a solid electrolyte layer.

[0069] The resulting solid-state battery was subjected to constant current charging at 0.1 C up to a charge cut-off voltage of 5.0 V in the first cycle. Thereafter, constant voltage charging was performed at a charge voltage of 5.0 V until the current value reached 0.01 C. Next, constant current discharging was performed at 0.1 C up to a discharge cut-off voltage of 3.0 V. The capacity obtained by constant current discharging until 3.0 V was reached was taken as the discharge capacity.

[0070] [Table 1]

[0071] As is clear from the results shown in Table 1, the solid state batteries using the active materials obtained in the examples as the positive electrode active materials have a larger discharge capacity than the solid state batteries using the active materials of the comparative examples.

[0072] 1, a peak attributable to Compound A and a peak attributable to Compound B were observed in the Raman spectrum of the active material of Example 4. The peak attributable to Compound A at a wavenumber of 540 cm -1 More than 650cm -1 The peaks in the following range were observed in a state where multiple peaks were superimposed. The results of peak separation of the multiple superimposed peaks are also shown in the same figure. Of the two peaks separated, the peak on the low wavenumber side is due to one-to-one vibration between the transition element and oxygen element that constitutes compound A. The peak on the high wavenumber side is due to the overall vibration between the transition element and all oxygen elements located around the transition element. The area S of the peak on the low wavenumber side PA1 and the area of ​​the peak on the high wavenumber side S PA2 S is the sum of PA1 +S PA2 is the area S of the peak derived from compound A PA is.

[0073] As shown in FIGS. 2(a) to (c), it was confirmed that in the active materials of Examples 2 to 4, a coating portion containing compound B was present on the surface of the core material containing compound A. [Industrial Applicability]

[0074] According to the present invention, an active material is provided that can reduce the interfacial resistance with the solid electrolyte and improve the capacity of the battery.

Claims

1. a compound A containing lithium (Li), M (wherein M represents one or more elements selected from nickel (Ni), cobalt (Co), and manganese (Mn)), and oxygen (O); and a compound B containing lithium (Li), niobium (Nb), and oxygen (O), The composition of each element in the compound B is Li ｘ NbO ｙ (1<x≦2, 3≦y≦8), In the Raman spectrum measured by Raman spectroscopy, －１ More than 650cm －１ The area of ​​the peak derived from the compound A observed in the following range is S ＰＡ The area of ​​the peak derived from the compound B is S ＰＢ When I said that, S ＰＡ and S ＰＢ The ratio of S ＰＢ / S ＰＡ The value of 0<S ＰＢ / S ＰＡ ≦1.2 and 540 cm －１ More than 650cm －１ The peaks observed in the following range include a peak on the low wavenumber side resulting from one-to-one vibration between the transition element and oxygen elements constituting compound A, and a peak on the high wavenumber side resulting from the overall vibration between the transition element and all oxygen elements located around the transition element, in an active material:

2. 2. The active material according to claim 1, wherein the compound A is a spinel-type composite oxide or a layered rock salt-type composite oxide.

3. The active material according to claim 1 or 2, containing niobium (Nb) element in an amount of 0.1 mass % to 20 mass %.

4. The active material according to claim 1 , wherein the compound B is present on at least a portion of the surface of a core material containing the compound A.

5. An electrode mixture comprising the active material according to claim 1 and a solid electrolyte.

6. A battery comprising a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer containing a solid electrolyte, A battery in which the positive electrode active material is the active material according to claim 1 .

Images