JP7246199B2 - Active material, positive electrode mixture and solid battery using the same - Google Patents

Description

The present invention relates to active materials used in solid-state batteries.

Solid electrolytes used in solid batteries are required to have as high an ionic conductivity as possible and to be chemically and electrochemically stable. For example, lithium halides, lithium nitrides, lithium salts, derivatives thereof, and the like are known as candidate materials for solid electrolytes.

A sulfide solid electrolyte is being studied as one of the solid electrolytes used in solid batteries. However, a solid battery containing a sulfide solid electrolyte has a problem that when it is charged and discharged, the interface resistance between the electrode active material and the sulfide solid electrolyte increases, restricting the movement of lithium ions. It is believed that the reason for this is that the reaction between the electrode active material and the sulfide solid electrolyte forms a resistance layer at the interface between the two. 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.

JP 2018-125214 A

By the way, rapid charging is expected for solid-state batteries. For rapid charging, it is necessary to speed up the reaction of extracting lithium ions from the positive electrode active material and transferring them to the solid electrolyte. However, the current technology does not provide a satisfactory reaction rate.

In view of the above-mentioned problems, an active material with improved charging characteristics by improving the mobility (desorption) of lithium ions during charging and by suppressing the reaction between the positive electrode active material and the solid electrolyte. The main purpose is to provide

The present invention relates to an active material used in a solid-state battery,
The active material has at least one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by measurement of the X-ray absorption fine structure, and 0.280 nm or more and 0.310 nm or less. At least one peak is observed in the range of
The active material has a core particle and a coating layer disposed on the surface of the core particle, and a halogen element is present on or near the surface of the core particle. This solves the above problems.

The present invention also provides an active material used in a solid-state battery,
The active material has at least one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by measurement of the X-ray absorption fine structure, and 0.280 nm or more and 0.310 nm or less. At least one peak is observed in the range of
The active material has core particles and a coating layer disposed on the surface of the core particles,
The above problem is solved by providing an active material in which the Li1s binding energy measured by X-ray photoelectron spectroscopy (XPS) has a peak apex at 54.0 eV or more and 55.4 eV or less.

According to the present invention, an active material with improved charge characteristics is provided by improving the mobility (detachability) of lithium ions during charging and by suppressing the reaction between the positive electrode active material and the solid electrolyte. provided. Therefore, the use of the active material of the present invention enables rapid charging of solid-state batteries.

FIG. 1 is a radial distribution function obtained by measuring the X-ray absorption fine structure of the positive electrode active materials obtained in Examples 1 and 2. FIG. FIG. 2 shows a method for determining whether or not a peak exists in the radial distribution function obtained by measuring the X-ray absorption fine structure of the positive electrode active materials obtained in Examples 1 and 2. graph. FIG. 3 is a radial distribution function obtained by X-ray absorption fine structure measurements on LiNbO ₃ .

The present invention will be described below based on its preferred embodiments. The present invention relates to active materials used in solid-state batteries.

A. Active material1. Halogen The active material of the present invention preferably has core particles and a coating layer disposed on the surfaces of the core particles. A halogen element is preferably present on the surface of the core particles or in the vicinity thereof. Due to the presence of a halogen element on the surface of the core particles, the peak position of the radial distribution function obtained by the measurement of the X-ray absorption fine structure described later is observed in a specific range. The mobility (detachability) of lithium ions from is improved. In addition, it is possible to suppress the reaction between the oxygen contained in the core particles and the sulfur contained in the sulfide solid electrolyte, which may occur during charging of the battery. come to occur spontaneously. “The surface of the core particle or its vicinity” means the surface itself of the core particle or a region within 200 nm, particularly within 100 nm, particularly within 50 nm from the surface along the thickness direction. The existence of a halogen element within a predetermined range along the thickness direction from the surface of the core particles means, for example, the case where the halogen element exists in the coating layer, the case where the halogen element exists in the outermost surface of the coating layer, and the like. is assumed.

Further, the active material of the present invention has a core particle and a coating layer disposed on the surface of the core particle, and the binding energy of Li1s measured by X-ray photoelectron spectroscopy (XPS) is 54.0 eV. The observation of the peak apex at 55.4 eV or less, coupled with the fact that the peak position of the radial distribution function obtained by the measurement of the X-ray absorption fine structure described later, is observed in a specific range, indicates that the activity during charging The mobility (detachability) of lithium ions from substances is improved. In addition, it is possible to suppress the reaction between the oxygen contained in the core particles and the sulfur contained in the sulfide solid electrolyte, which may occur during charging of the battery. come to occur spontaneously.

A halogen element means at least one of fluorine (F) element, chlorine (Cl) element, bromine (Br) element and iodine (I) element. The number of halogen elements present on the surface of the core particles may be one or a combination of two or more. From the viewpoint of suppressing the formation of lithium halide that contributes to interfacial resistance, the halogen element is preferably chlorine (Cl) element or bromine (Br) element, from the viewpoint of further increasing the mobility (detachability) of lithium ions. is preferably a fluorine (F) element.

The halogen element existing on the surface of the core particles may be dissolved in the LiAO compound described later, or may exist in the form of a halogen compound separately from the LiAO compound.

The concentration of halogen present on the surface of the core particles is preferably 0.00075 or more in terms of halogen concentration measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS). If the halogen concentration is 0.00075 or more, it is possible to suppress the reaction between oxygen in the LiAO compound or core particles described later and sulfur in the sulfide solid electrolyte, which is preferable. On the other hand, there is no particular upper limit to the value of the concentration, but empirically, for example, if it is 0.155 or less, the surface of the core particles does not impair the conductivity of lithium ions, so it is preferable. From this point of view, the concentration of halogen measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS), that is, using TOF-SIMS, the secondary ion polarity is measured under negative conditions, core particles The ratio (X - /total) of the count number (X ^- ) of secondary ion species related to halogen ions to the sum (total) of all the count numbers ^of secondary ions collected from the surface of the surface is 0.00075 or more. is preferably 0.0015 or more, among them 0.0075 or more, among them 0.010 or more, among them 0.015 or more, further among them 0.020 or more, further among them 0.025 or more is preferred. Surface analysis by TOF-SIMS is performed, for example, by the following method.

<Surface analysis by TOF-SIMS>
Using TRIFT IV, a time-of-flight secondary ion mass spectrometer (TOF-SIMS) manufactured by ULVAC-Phi, the particle surface of the positive electrode active material is analyzed, and the concentration of halogen present on the surface is measured. do. Specifically, the number of counts of fluorine ions (F ⁻ ) with respect to the total number of counts of all secondary ions collected from the surface of the positive electrode active material, which is measured under the condition that the secondary ion polarity is negative. ratio (F ⁻ /total) is measured.

The conditions, etc. used for the measurement are as follows.
Primary ion: Au ⁺
Accelerating voltage: 30 kV
Measurement area area: 10000 μm ² (100 μm×100 μm)
Measurement time unit: 10 minutes Measurement ion species: Positive/Negative
Electronic neutralization: Yes

In the active material of the present invention, it is preferable that the Li1s binding energy measured by X-ray photoelectron spectroscopy (XPS) has a peak apex at 54.0 eV or more and 55.4 eV or less. More preferably, the peak apex is observed at 54.0 eV or more and 55.3 eV or less, further 54.0 eV or more and 55.2 eV or less, further 54.0 eV or more and 55.1 eV or less, and further 54.0 eV or more and 55.0 eV or less. preferable. It can also be inferred that the reason why the XPS binding energy of Li1s is within the above range is that part of the O in the LiAO compound described later is replaced with F. A portion of O in the LiAO compound is substituted with F, which is preferable because the reaction between oxygen contained in the LiAO compound and the core material particles and sulfur contained in the sulfide solid electrolyte can be suppressed. Halogen present on the surface of the core particles may be dissolved in the LiAO compound described later, or may exist in the form of a halogen compound separate from the LiAO compound.

2. LiAO compound The coating layer in the active material of the present invention contains Li, A (A is one or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W and Al) and O. It is preferable to contain a compound (also referred to as a “LiAO compound”). By coating the surface of the core particles with the LiAO compound, the lithium ion conductivity is improved, the mobility of lithium ions between the positive electrode active material and the solid electrolyte can be improved, and the charge characteristics are enhanced. be able to. Moreover, the interfacial resistance between the positive electrode active material and the solid electrolyte can be reduced. The A element is a group of metal elements called valve metals, which have similar properties.

The state in which "the surface of the core material particles is coated with the LiAO compound" means that the LiAO compound exists as particles on the surface of the core particles, and exists as aggregated particles formed by aggregation of the particles. It includes an aspect in which a layer is formed and an aspect in which a layer is formed. "Present by forming a layer" means a state in which the LiAO compound is present with a thickness.

When the LiAO compound forms a layer, the thickness is preferably 0.5 nm to 200 nm, more preferably 0.7 nm or more or 100 nm or less, more preferably 1 nm or more or 50 nm or less, more preferably 25 nm or less. is preferably By setting the content in such a range, the mobility of lithium ions can be improved, and the interfacial resistance can be reduced. Therefore, it can function as a good lithium ion conductive layer. The layer thickness can be measured, for example, by scanning transmission electron microscopy (STEM). Moreover, energy dispersive X-ray spectroscopy (EDS) can be used in combination for observation and measurement, if necessary.

There may be a part or a part of the surface of the core particles where the LiAO compound does not exist. Among them, the LiAO compound preferably covers 30% or more of the entire surface area of the core particles, more preferably 40% or more, and more preferably 50% or more. The coating of the surface of the core material particles with the LiAO compound can be confirmed, for example, by combining scanning transmission electron microscopy (STEM) and, if necessary, energy dispersive X-ray analysis (EDS) as described above. It can be confirmed by observing the surface of the material particles or by Auger electron spectroscopy. Also, the thickness of the LiAO compound covering the surfaces of the core particles does not have to be uniform.

3. XAFS
In the active material of the present invention, at least one peak is observed in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by measurement of the X-ray absorption fine structure (hereinafter also referred to as "XAFS"). At least one peak is observed in the range of 0.280 nm to 0.310 nm.

Specifically, as shown in FIG. 1, the active material of the present invention has at least one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by XAFS measurement. A peak position is identified by the position of the peak apex. The definition of peak will be described later. The peak position observed in the present invention may be, for example, 0.120 nm or more, 0.125 nm or more, or 0.130 nm or more. On the other hand, the peak position may be 0.140 nm or less, for example. The number of peaks observed in the above range may be at least one, for example, only one, or two or more. Along with this, the active material of the present invention has at least one peak in the range of 0.280 nm or more and 0.310 nm or less. The peak position observed in the present invention may be, for example, 0.285 nm or more. On the other hand, the peak position may be, for example, 0.305 nm or less, or 0.300 nm or less.

Various LiAO compounds have been known in the art, and it is preferable to use a compound having a specific chemical structure in the present invention. The LiAO compound used in the present invention is characterized by the observation of peaks at specific interatomic distances in the radial distribution function obtained by XAFS measurement. For example, when the LiAO compound is a compound containing Li, Nb, and O (hereinafter, this compound is also referred to as a “LiNbO compound”), an example of the radial distribution function of the LiNbO compound is as shown in FIG. becomes. The horizontal axis of the radial distribution function shown in FIG. 1 indicates the interatomic distance based on the position of the niobium atom. The vertical axis indicates the existence probability of atoms located around the niobium atom. The peak observed in the range of 0.115 nm or more and 0.144 nm or less corresponds to the distance between the niobium atom and the oxygen atom, and the peak observed in the range of 0.280 nm or more and 0.310 nm or less is the niobium atom. It corresponds to the distance between them. In the radial distribution function obtained from XAFS, by including the LiNbO compound in which the peak is observed in the predetermined range described above in the coating layer, the active material of the present invention has improved lithium ion mobility, and as a result It is possible to improve charging characteristics. Moreover, the interfacial resistance between the active material and the solid electrolyte can be reduced.

The observation of a peak in the radial distribution function means that the radial distribution function may include an upwardly convex portion or a shoulder portion. It has a peak when the second derivative obtained by differentiating twice the function y = f(x), where the horizontal axis of the radial distribution function is x and the vertical axis is y, has a minimum value. Then define In the present invention, the presence or absence of a peak was determined by differentiating the radial distribution function twice using Origin 9.1 (manufactured by Light Stone). In addition, for example, in Examples 1 and 2 described later, as shown in FIG. 2, the minimum value have. From this, it can be said that in Examples 1 and 2, a peak is observed in the range of 0.115 nm or more and 0.144 nm or less.

As described above, the LiAO compound preferably used in the present invention has a peak at a predetermined position with a specific interatomic distance in the radial distribution function obtained from XAFS. In contrast, conventionally known Li—A—O-based compounds do not have a peak at the predetermined position defined in the present invention in the radial distribution function obtained from XAFS. For example, as shown in FIG. 3, LiNbO ₃ , which is one of the conventionally known Li--A--O compounds, has a peak in the range of 0.115 nm or more and 0.144 nm or less. No peak is observed in the range from 280 nm to 0.310 nm.

XAFS is a method of analyzing an absorption spectrum obtained by irradiating a substance with X-rays. In the absorption spectrum obtained by irradiating a substance with X-rays, a sharp rise, that is, an absorption edge, peculiar to the element contained in the substance is observed. A fine structure appearing in the vicinity of the absorption edge of about ±50 eV is called XANES (X-ray Absorption Near Edge Structure). A vibrational structure appearing at about 1000 eV on the high energy side from the absorption edge is called EXAFS (Extended X-ray Absorption Fine Structure). The combined region of XANES and EXAFS is called XAFS. According to XAFS, it is possible to evaluate the local structure (interatomic distance, coordination number) and the chemical state (valence, coordination structure) around the element of interest in the sample. In addition, since XAFS is a non-destructive measurement method and a measurement method that can obtain information on the outermost surface of a substance, the active material itself of the present invention can be used as a measurement target, and information on the coating layer in the active material can be obtained. can be obtained.

In the present invention, in order to measure the XAFS of the active material, the procedure described below is performed.
Sample preparation After grinding the sample in an agate mortar, it is mixed with boron nitride powder and made into tablets with a diameter of 10 mm and a thickness of about 1 mm. Depending on the concentration of element A contained in the sample to be measured and the absorption coefficients of the LiAO compound and the compound composing the core particles, the amounts of the sample and boron nitride are appropriately optimized.

The conditions for measuring XAFS at the Nb-K end are as follows.
・Experimental facility: SPring-8
・Experiment station: BL14b2
・Spectrometer: Monochromator Si (311)
・High-order light removal: Rh-coated mirror 2.4 mrad x 2 pieces ・Incident X-ray size: Vertical 1 mm x Horizontal 5 mm (slit size in front of sample)
・Measurement method: transmission method ・Detector: ion chamber ・Measurement absorption edge: Nb-K absorption edge (18986 eV)
At each incident X-ray energy (E, x-axis), I0 and It were measured, the X-ray absorbance (y-axis) was determined by the following formula, and plotted on the x-y axis to obtain an XAFS spectrum. .
X-ray absorbance μt = -ln (It/I0)

In order to obtain the radial distribution function and determine the interatomic distance based on the data obtained as described above, the following procedure is performed.
A radial distribution function obtained by Fourier transforming the EXAFS spectrum will be described.
"Athena" (Demeter Ver. 0.9.25) is used as analysis software.
First, after reading the XAFS spectrum with the same software, the background absorption Pre-edge region (about -150 to -45 eV from the absorption edge) and Post-edge region (about 150 to 1300 eV from the absorption edge area) is fitted to normalize the XAFS spectrum. Next, spline curve fitting is performed to extract the EXAFS spectrum (χ(k)). The parameters used for spline curve fitting in the analysis with the same software are the following values.
・Rbkg=1
・Spline range in k: 1 to 15
・Spline clamps low: None, high: None
・k-weight=3
・Plotting k-weights: 3
Finally, the EXAFS spectrum (x(k)) is Fourier transformed to obtain a spectrum representing the radial distribution function. The following values were used for the parameters of the Fourier transform in the same software.
・k-range: 3.5 to 11.5
・dk: 1
・window: Hanning
・arbitrary k-weight: 1
・phase correction: unused

The composition of each element in the LiAO compound can be represented by, for example, Li _x AO _y when the A element is at least one of Ta and Nb. x and y in the formula can take arbitrary values within the range corresponding to the valence of the element. Among them, it is particularly preferable to have a composition (x>1) in which Li is contained in excess of 1 mol with respect to 1 mol of the A element. By doing so, the formation of a compound of A and O can be suppressed, and the mobility of lithium ions can be improved. Moreover, the interfacial resistance between the active material and the solid electrolyte can be reduced.

When the LiAO compound is represented by Li _x AO _y , as a method of satisfying x>1, the blending amount of the lithium raw material with respect to the A element raw material is adjusted to the composition expected to be produced, for example, the stoichiometric composition of LiAO ₃ A method of using an excess rather than a ratio can be mentioned. At this time, if Li is simply added in excess, lithium carbonate is generated on the surface of the present positive electrode active material due to the excess Li, and this becomes resistance, which may rather deteriorate the charging characteristics. . Therefore, considering the formation of lithium carbonate, which is an undesirable compound, it is preferable to adjust the blending amount of element A raw material and the blending amount of lithium raw material so that Li _x AO _y has a predetermined composition.

From this point of view, the molar ratio (Li/A) of the amount of Li to the amount of the A element present on the surface of the core particles, which is obtained by X-ray photoelectron spectroscopy (XPS), is 1.0 or more and 33.3. is preferred. Among them, 1.1 to 33.3, further 1.3 to 33.3, further 1.5 to 33.3, further 2.0 to 15, further 3.0 to 15, further 3.0 12 or less, 4.0 or more and 12 or less, more preferably 5.0 or more and 12 or less. Li in the mol ratio (Li/A) is a value including that resulting from lithium carbonate (if present) and that resulting from the core material particles themselves.

In order to control the ratio of Li and A element present on the surface of the core particles to the above range, the mol ratio ( It is preferable to adjust the blending amount of the A element raw material and the blending amount of the lithium raw material so that Li/A) falls within the above range. By doing so, the charging characteristics can be improved. However, it is not limited to this method.

In the present invention, the active material is completely dissolved, and the amount of A element (% by mass) measured by inductively coupled plasma (ICP) emission spectrometry is measured by ion chromatography after thermally decomposing the active material. The mass ratio (X/A) of the halogen (X) amount (ppm) is preferably 0.5×10 ⁻⁴ or more. If the mass ratio (X/A) of the amount of halogen to the amount of A element is 0.5 × 10 ^-4 or more, the reaction between the oxygen contained in the LiAO compound and the core material particles and the sulfur contained in the sulfide solid electrolyte It is preferable because it can be further suppressed. Although there is no particular upper limit to the mass ratio, empirically, for example, if it is 3000×10 ⁻⁴ or less, further 2000×10 ⁻⁴ or less, further 1000×10 ⁻⁴ or less, further 500×10 ⁻⁴ or less, It is preferable because the surfaces of the core particles do not impair the conductivity of lithium ions. From this point of view, the mass ratio (X/A) of the amount of halogen to the amount of A element is preferably 0.5 × 10 ^-4 or more, especially 1.5 × 10 ^-4 or more, especially 1.54 × 10 ⁻⁴ or more, further 3.3×10 ⁻⁴ or more, further 5.0×10 ⁻⁴ or more, among them 25×10 ⁻⁴ or more, further 50×10 ⁻⁴ or more, further 70.0×10 ^{− 4} or more, more preferably 100×10 ⁻⁴ or more, more preferably 150.0×10 ⁻⁴ or more.

In the present invention, the molar ratio (X/A) of the amount of halogen (X) to the amount of element A present on the surface of the active material (particle) obtained by X-ray photoelectron spectroscopy (XPS) is 0.011 or more. is preferably If the molar ratio (X/A) of the amount of halogen to the amount of A element present on the surface of the active material (particle) is 0.011 or more, oxygen and sulfide contained in the LiAO compound and the core material particles are contained in the solid electrolyte. It is preferable from the point of being able to further suppress the reaction with sulfur. There is no particular upper limit to the value of X/A, but empirically, for example, if the mol ratio (X/A) is 1.95 or less, the surface of the core particles does not impair the conductivity of lithium ions, so it is preferable. . From this point of view, the molar ratio (X/A) of the amount of halogen to the amount of A element present on the surface of the active material (particle) obtained by X-ray photoelectron spectroscopy (XPS) is 0.011 or more and 1.95 or less. , further 0.011 to 1.50, further 0.011 to 1.00, further 0.011 to 0.50, further 0.015 to 0.50, further 0.020 to 0.50 , 0.025 or more and 0.50 or less, more preferably 0.030 or more and 0.50 or less. Above all, the lower limit of (X/A) is preferably 0.033 or more, more preferably 0.055 or more, and more preferably 0.11 or more.

From the viewpoint of reducing the interfacial resistance between the active material and the solid electrolyte, it is advantageous that the moisture content of the active material of the present invention is adjusted within a certain range. Specifically, if the moisture content of the active material is too high, the interfacial resistance between the active material and the sulfide solid electrolyte may increase.

When the core particles in the active material contain a layered compound, the active material may have a moisture content B (mass ppm) up to 110° C. measured by the Karl Fischer method of, for example, 50 ppm or more, or 140 ppm or more. or 200 ppm or more. On the other hand, the moisture content B may be, for example, 8000 ppm or less, 7000 ppm or less, 3500 ppm or less, or 3000 ppm or less.

When the core particles in the active material contain a spinel compound, the active material has a moisture content B (mass ppm) up to 110° C. measured by the Karl Fischer method, for example, may be 1 ppm or more, and may be 50 ppm. or more, 100 ppm or more, or 200 ppm or more. On the other hand, the moisture content B may be, for example, 8000 ppm or less, 5000 ppm or less, 3500 ppm or less, 2000 ppm or less, or 1000 ppm or less.

The active material of the present invention may have a BET specific surface area A (m ² /g) of 0.2 m ² /g or more, 0.3 m ² /g or more, or 0.4 m ² /g or more, or 0.5 m ² /g or more. It may be 5.0 m ² /g or less, 3.0 m ² /g or less, 2.5 m ² /g or less, or 2.0 m ² /g or less good.

Furthermore, in the active material of the present invention, the value of B/A, which is the ratio of the moisture content B (mass ppm) up to 110 ° C. measured by the Karl Fischer method to the BET specific surface area A (m ² /g), is, for example, It may be 1 or more, 20 or more, 40 or more, 50 or more, 100 or more, or 200 or more. On the other hand, the B/A value may be, for example, 8000 or less, 5000 or less, 3500 or less, 2000 or less, or 1500 ppm or less. , 1000 or less, or less than 1000. For the value of B/A, selecting an appropriate range according to the type of material constituting the active material further suppresses the reaction between the active material and the sulfide solid electrolyte, thereby reducing the interfacial resistance. is advantageous from

Specifically, when the core particles are composed of a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel-cobalt manganate (Li(Ni, Co, Mn) O ₂ ), B/A may be, for example, 50 or more, 100 or more, or 200 or more. On the other hand, the B/A value may be, for example, 8000 or less, 5000 or less, or 2000 or less.
Further, when the core particles are composed of a spinel compound such as lithium nickel manganate (LiNi _0.5 Mn _1.5 O ₄ ), the value of B/A is, for example, 5 or more. may be 20 or more, 50 or more, 100 or more, 150 or more, or 200 or more. On the other hand, the B/A value may be 8000 or less, 5000 or less, 2000 or less, or 1500 or less.

In the technical field, it has been generally believed that the lower the moisture content of the active material, the better. The reason for this is that the sulfide solid electrolyte was thought to react with water and deteriorate. However, as a result of detailed studies by the present inventors, it was found that the interfacial resistance between the active material and the sulfide solid electrolyte tends to increase even when the moisture content of the active material is excessively low. The reason for this is that the presence of a small amount of water in the active material enhances the adhesion between the active material and the sulfide solid electrolyte, forming a good interface, which reduces the interfacial resistance. The inventor believes that Note that the water to be measured for the moisture content of the active material includes both adhering water and water of crystallization contained in the active material.

Regarding the moisture content of the active material, the reason for dividing the moisture content B measured by the Karl Fischer method by the BET specific surface area A is to normalize the moisture content of the active material. The procedure for measuring the moisture content by the Karl Fischer method is as follows. That is, using a Karl Fischer moisture meter, a measurement sample is heated to 110° C. or 250° C., and the amount of water released (ppm) is measured. Measurement is performed in an argon atmosphere, and for example, 899 Coulometer (manufactured by Metrohm) and 860 KF Thermoprep (manufactured by Metrohm) are used as measuring devices.

On the other hand, the BET specific surface area is determined by the BET one-point method using, for example, a fully automatic specific surface area measuring apparatus Macsorb (manufactured by Mountec Co., Ltd.) as a measuring apparatus. Specifically, the sample is weighed in a glass cell (standard cell), and after the inside of the glass cell is replaced with nitrogen gas, the sample is heat-treated at 250° C. for 15 minutes in the nitrogen gas atmosphere. After that, cooling is performed for 4 minutes while flowing a nitrogen/helium mixed gas. After cooling, the sample (powder) is measured by the BET single-point method. A mixed gas of 30 vol % nitrogen and 70 vol % helium is used as the adsorbed gas during cooling and measurement.

The B/A value of the active material can be adjusted, for example, by heat-treating the active material after manufacturing it by the method described later, or by drying it by heating in a vacuum.

If the ratio of the LiAO compound contained in the active material is expressed as the ratio of the mass of the A element to the mass of the active material for convenience, it may be, for example, 0.01% by mass or more, or 0.1% by mass or more. may be 0.5% by mass or more, or 1% by mass or more. On the other hand, the ratio may be, for example, 10% by mass or less, 5% by mass or less, or 3% by mass or less. The ratio can be obtained by ICP emission spectroscopic analysis for the solution in which the active material is dissolved. Moreover, the ratio can be controlled by adjusting the amount of the A element source compound used in the method for producing an active material, which will be described later.

When carbonate ions are present on the surface of the active material, the amount of carbonate ions is preferably within a predetermined range. This is because it is possible to effectively suppress the reaction between the active material and the sulfide solid electrolyte. The amount of carbonate ions present on the surface of the active material is preferably less than 2.0% by mass, particularly less than 1.5% by mass, particularly less than 1.0% by mass, and more particularly less than 1.0% by mass. It is preferably less than 0.5% by weight, more preferably less than 0.35% by weight, more preferably less than 0.30% by weight, more preferably less than 0.20% by weight. As a method for reducing the amount of carbonate ions present on the surface of the active material, for example, there is a method of firing in an atmosphere that does not contain carbon dioxide, such as a nitrogen atmosphere or an oxygen atmosphere.

When the core particles contain a layered compound, the amount of carbonate ions present on the surface of the active material is preferably less than 0.35% by mass, especially less than 0.30% by mass, especially less than 0.30% by mass. More preferably, it is less than 0.20% by mass.
On the other hand, when the core particles contain a spinel compound, the amount of carbonate ions present on the surface of the active material is preferably less than 2.0% by mass, more preferably less than 1.5% by mass, relative to the active material. , among these, less than 1.0% by mass, among these, less than 0.5% by mass, among these, less than 0.3% by mass, and among these, preferably less than 0.2% by mass.

Examples of methods for measuring the amount of carbonate ions include the following methods. That is, 0.48 g of the active material is added to 48 mL of pure water, stirred for 5 minutes, and then filtered. The amount of carbonate ions can be obtained by subjecting the liquid from which carbonate ions have been extracted in this manner to ion chromatography measurement and quantifying CO ₃ ²⁻ . DIONEX ICS-2000 manufactured by Thermo Fisher Scientific Co., Ltd. is used as the measurement apparatus, DIONEX IonPac AS17-C is used as the column, and an aqueous potassium hydroxide solution is used as the carrier liquid (eluent), and the measurement is performed under the conditions of 35°C. be able to.

The active material has a volume cumulative particle diameter _D50 at a cumulative volume of 50% by volume measured by a laser diffraction scattering particle size distribution measurement method, for example, 20 μm or less, especially less than 15 μm, more than 1 μm and less than 10 μm, more than 2 μm and less than 8 μm. It is even more preferable to have When _D50 is 20 μm or less, for example, when the active material is used in the positive electrode mixture, good contact with the sulfide solid electrolyte in the positive electrode mixture can be ensured, and the lithium ion utilization rate in the active material can be improved. can be enhanced. In addition, when _D50 is larger than 1 μm, it is possible to prevent particles from aggregating and increasing slurry viscosity. In order to adjust the _D50 of the active material within the above range, the operating conditions of the spray dry granulation method or the tumbling fluidized bed granulation method may be adjusted, or the pulverization conditions may be adjusted. is not limited to

4. Core Particle The core particle is not particularly limited as long as it functions as an active material. The core particles may contain, for example, a lithium metal composite oxide. A known lithium metal composite oxide can be used as the lithium metal composite oxide. For example, a lithium-containing composite oxide having a layered rock salt structure represented by the general formula LiMO ₂ (M is a metal element), a lithium-containing composite oxide having a spinel structure represented by the general formula LiM ₂ O ₄ , and a lithium-containing composite oxide represented by the general formula LiMPO ₄ (M is a metal element). element) or a lithium-containing composite oxide having an olivine structure represented by LiMSiO ₄ (M is a metal element), or a combination of two or more thereof. However, it is not limited to these.

As the metal element M in the lithium metal composite oxide, for example, both transition elements and typical elements can be used, and transition elements are preferably used. Examples of lithium metal composite oxides include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium nickel cobalt manganate (Li(Ni, Co, Mn) O ₂ ), lithium manganate (LiMn _{2 )} , O ₄ ), and lithium transition metal oxides such as lithium nickel manganate (LiNi _0.5 Mn _1.5 O _{4 )} . The structure of these oxides is not particularly limited, and may be, for example, a layered rock salt type compound or a spinel type compound.

The core particles of the spinel-type compound are preferably particles containing Li, Mn, O and one or more elements other than these. Further, as additive elements, Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re and It is possible to add a combination of one or more elements selected from the group consisting of Ce. Among these, it is preferably selected from the group consisting of Na, Mg, Al, P, K, Ca, Ti, Fe, Co, Ni, Zr, Nb, Mo and W.

Furthermore, as described below, by selecting the additive element species and the additive element amount, it is possible to express an operating potential of 4.5 V or more mainly at the metal Li reference potential. The core material particles of the spinel compound are particles containing Li, Mn and O and one or more elements other than these, and at least one element is Ni, Co , and Fe, it is possible to express an operating potential of 4.5 V or more mainly at the metal Li reference potential. The amount of the M1 element contained in the core particles is preferably, for example, 7% by mass or more, preferably 9% by mass or more, and among these, 11% by mass, based on the total elements in the core particles. It is preferable that it is above. On the other hand, the amount of the M1 element contained in the core particles is, for example, preferably 35% by mass or less, preferably 30% by mass or less, and preferably 25% by mass with respect to all elements in the core particles. When these elements are contained, an operating potential of 4.5 V or higher is developed mainly at the metal Li reference potential. In addition to the M1 element, the M2 element may be included, and the M2 element includes Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Ga, Y, Zr. , Nb, Mo, In, Ta, W, Re and Ce. Among the M2 elements, it is preferably selected from the group consisting of Na, Mg, Al, P, K, Ca, Ti, Fe, Co, Ni, Zr, Nb, Mo and W.

When the core particles contain a lithium metal composite oxide, the content of the lithium metal composite oxide in the core particles may be, for example, 80% by mass or more, 90% by mass or more, or 95% by mass. % or more. Moreover, the core material particles may consist of only the lithium metal composite oxide. Only one type of lithium metal composite oxide may be used, or two or more types may be used in combination.

5. Method for Producing Active Material Next, a preferred method for producing the active material of the present invention will be described. For the active material of the present invention, for example, a water-soluble salt of element A containing halogen and lithium hydroxide are dissolved in water to prepare a surface treatment liquid, and core particles are added to the surface treatment liquid and kneaded. It can be suitably produced by making it into a slurry and drying it. However, the manufacturing method of the active material is not limited to such a method. For example, rolling fluid coating method (sol-gel method), mechanofusion method, CVD method, PVD method, etc. can be used by adjusting the conditions.

Examples of water-soluble element A salts include element A chloride, potassium element A fluoride, ammonium element A oxalate, ammonium peroxo element A, and the like. Among them, ammonium peroxo-A element is preferable from the viewpoint of suppressing residual carbon-based impurities.

In the above manufacturing method, the LiAO compound is produced by adding the core material particles to the surface treatment liquid to form a slurry and heating the slurry at 90° C. or higher. Along with this, the halogen and the LiAO compound can be fixed to the surfaces of the core particles. Since the LiAO compound has the property of being easily adsorbed on the surface of the core particles, by drying the slurry, it is possible to form a coating layer containing the LiAO compound and halogen on the surface of the core particles. Instead of this method, a surface treatment liquid heated to 90° C. or higher may be used and sprayed onto the core particles. Thereafter, pulverization and heat treatment are performed as necessary.

By drying the slurry, a coating layer containing a LiAO compound having a specific structure and halogen can be obtained. To dry the slurry, for example, a spray dry granulation method or a tumbling fluidized bed granulation method can be used. After that, heat treatment may be performed as necessary. Specifically, the heat treatment is preferably performed in an oxygen, nitrogen, or argon atmosphere containing as little carbon dioxide as possible. The drying and heat treatment temperature is preferably 105° C. or higher and 700° C. or lower, more preferably 150° C. or higher and 700° C. or lower, still more preferably 200° C. or higher and 700° C. or lower, still more preferably 255° C. or higher and 700° C. or lower, still more preferably 305° C. °C or higher and 700 °C or lower, more preferably 355 °C or higher and 700 °C or lower, even more preferably 405 °C or higher and 700 °C or lower. The heat treatment time is preferably 1 hour or more and 20 hours or less, more preferably 1 hour or more and 15 hours or less, and still more preferably 1 hour or more and 10 hours or less. This can successfully produce LiAO compounds having peaks at specific interatomic distances in the radial distribution function obtained from XAFS.

The core particles used in the present invention are obtained by weighing and mixing raw materials such as lithium salt compounds, manganese salt compounds, nickel salt compounds and cobalt salt compounds, pulverizing them with a wet pulverizer or the like, granulating them, and firing them. , Heat treatment if necessary, pulverization under preferable conditions, and classification if necessary. Instead of this method, a basic substance such as sodium hydroxide is added to an aqueous solution containing a manganese salt compound, a nickel salt compound and a cobalt salt compound to precipitate a metal composite hydroxide, and then the metal composite hydroxide is Core particles can also be obtained by mixing with a lithium salt compound and firing.

Lithium salt compounds as raw materials include, for example, lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), LiOH·H ₂ O, lithium oxide (Li ₂ O), fatty acid lithium. and lithium halides. Among them, lithium hydroxide, carbonate and nitrate are preferable.

Manganese salt compounds include, for example, manganese carbonate, manganese nitrate, manganese chloride and manganese dioxide. Among them, manganese carbonate and manganese dioxide are preferred, and electrolytic manganese dioxide obtained by electrolysis is particularly preferred.
Nickel salt compounds include, for example, nickel carbonate, nickel nitrate, nickel chloride, nickel oxyhydroxide, nickel hydroxide and nickel oxide, among which nickel carbonate, nickel hydroxide and nickel oxide are preferred.
Examples of cobalt salt compounds include basic cobalt carbonate, cobalt nitrate, cobalt chloride, cobalt oxyhydroxide, cobalt hydroxide and cobalt oxide, among which basic cobalt carbonate, cobalt hydroxide, cobalt oxide and oxywater. Cobalt oxide is preferred.

The raw materials described above are preferably mixed by adding a liquid medium such as water or a dispersant and wet-mixing to form a slurry. When the spray drying method described later is employed, the obtained slurry is preferably pulverized with a wet pulverizer, but dry pulverization may also be used.

The granulation method described above may be either a wet method or a dry method as long as the various raw materials pulverized in the previous step are not separated and are dispersed within the granulated particles. Examples thereof include extrusion granulation, tumbling granulation, fluidized granulation, mixing granulation, spray drying granulation, pressure molding granulation, and flake granulation using rolls.

In the case of wet granulation, it is necessary to dry sufficiently before firing. As a drying method, a known drying method such as a spray heat drying method, a hot air drying method, a vacuum drying method, a freeze drying method, or the like may be used, and the spray heat drying method is particularly preferable. The spray heat drying method is preferably carried out using a thermal spray dryer (spray dryer).

Firing is carried out in a firing furnace at a temperature of, for example, 700° C. or higher and 1000° C. or lower in an atmospheric atmosphere, an oxygen gas atmosphere, an atmosphere with an adjusted oxygen partial pressure, a carbon dioxide gas atmosphere, or other atmospheres. Preferably, the temperature is 750° C. or more and less than 1000° C., more preferably 800° C. or more and 950° C. or less, and the temperature is maintained for 0.5 hours or more and 30 hours or less. At this time, it is preferable to select firing conditions under which the transition metal is solid-dissolved at the atomic level and becomes a single phase. The type of firing furnace is not particularly limited, and firing can be performed using, for example, a rotary kiln, a stationary furnace, or other firing furnaces.

The heat treatment after firing is preferably performed when the crystal structure needs to be adjusted. For example, the heat treatment is performed under the conditions of an oxidizing atmosphere such as an air atmosphere, an oxygen gas atmosphere, or an atmosphere with an adjusted oxygen partial pressure.

In order to further lower the moisture content of the active material thus obtained, for example, the active material may be subjected to heat treatment again, or the active material may be subjected to vacuum heat drying.

6. Use of Active Material The active material of the present invention can usually be used as a positive electrode active material. Moreover, the active material of the present invention is used in a solid battery. In particular, the active material of the present invention is advantageously used in a solid battery containing a sulfide solid electrolyte as the solid electrolyte. In the solid battery, the presence of the contact portion between the active material of the present invention and the sulfide solid electrolyte makes it possible to enjoy the effects of the present invention. Here, "there is a contact portion between the active material and the sulfide solid electrolyte" means (a) containing the sulfide solid electrolyte in the positive electrode mixture (in this case, the solid electrolyte layer may be non-sulfide ), (a) do not contain a sulfide solid electrolyte in the positive electrode mixture and contain a sulfide solid electrolyte in the solid electrolyte layer, and (c) contain a sulfide solid electrolyte in the positive electrode mixture. and that the solid electrolyte layer contains a sulfide solid electrolyte.

B. Positive Electrode Mixture The positive electrode mixture of the present invention contains an active material and a solid electrolyte. Note that the active material contained in the positive electrode mixture can be the same as described in the above section "A. Active material", so description thereof will be omitted here.

The solid electrolyte used in the present invention can be the same as solid electrolytes used in general solid batteries. Examples include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc. Among them, sulfide solid electrolytes containing sulfur (S) are preferred. The sulfide solid electrolyte in the present invention may contain, for example, Li and S and have lithium ion conductivity. The sulfide solid electrolyte may be any of crystalline material, glass ceramics, and glass. The sulfide solid electrolyte may have a crystal phase with an aldirodite structure. Examples of such sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX ("X" represents one or more halogen elements), Li ₂ S _{-P2S5 - P2O5 , Li2S - Li3PO4 - P2S5 , Li3PS4 , Li4P2S6 , Li10GeP2S12 , Li3.25Ge0 _ _ .25} P _0.75 S ₄ , Li ₇ P ₃ S ₁₁ , Li _3.25 P _0.95 S ₄ , Li _7-x PS _6-x X _x (Argyrodite type solid electrolyte, "X" is one or more and 0.2<x<2.0 or 0.2<x<1.8).

The active material contained in the positive electrode mixture of the present invention may be the active material of the present invention alone, or may be used in combination with other active materials. Other active materials include particles made of the above-described known lithium-transition metal composite oxide, and the particles may or may not have a coating layer. When used in combination, the content of the active material of the present invention is preferably 50 mol % or more, more preferably 70 mol % or more, based on the total active material.

The proportion of the sulfide solid electrolyte in the positive electrode mixture of the present invention is typically 5% by mass or more and 50% by mass or less. Moreover, the positive electrode mixture may contain other materials such as a conductive aid and a binder as necessary. Alternatively, the positive electrode layer can be produced by mixing the positive electrode material mixture and a solvent to prepare a paste, applying the paste on a current collector such as an aluminum foil, and drying the paste.

C. Solid Battery The solid battery of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, and the positive electrode layer contains the positive electrode mixture described above.

The solid battery of the present invention can be produced, for example, by stacking three layers of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer produced as described above, and molding them under pressure. "Solid battery" means a solid battery that does not contain any liquid or gel material as an electrolyte, or a solid battery that contains, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of liquid or gel material as an electrolyte. Aspects are also included.

The negative electrode active material used for the negative electrode layer can be the same as the negative electrode active material used for general solid batteries. Specific negative electrode active materials that can be used include materials that occlude and release lithium ions, such as carbon materials, silicon oxide-based compounds such as silicon and Si—O, tin-based compounds, and known materials such as lithium titanate. . Examples of the carbon material include sintered organic polymer compounds such as polyacrylonitrile, phenolic resin, phenolic novolak resin, cellulose, artificial graphite, and natural graphite. The negative electrode layer can be produced in the same manner as the positive electrode layer, except that such a negative electrode active material is used.

[explanation of other terms]
In this specification, when the expression “X to Y” (X and Y are arbitrary numbers) is used, unless otherwise specified, it means “X or more and Y or less” and “preferably larger than X” or “preferably larger than Y”. It also includes the meaning of "small". In addition, when expressing "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), "preferably larger than X" or "preferably less than Y" It also includes intent.

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

[Example 1]
(1) Production of Core Particles Sodium hydroxide was supplied to an aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved, and a metal composite hydroxide was produced by a coprecipitation method. The molar ratio of nickel, cobalt and manganese in this metal composite hydroxide was Ni:Co:Mn=0.33:0.33:0.33. This metal composite hydroxide is mixed with lithium carbonate, calcined in the atmosphere at 720° C. for 5 hours using a stationary electric furnace, and then fired in the atmosphere at 905° C. for 22 hours to obtain a lithium metal composite oxide. got This lithium metal composite oxide was pulverized in a mortar and then classified with a sieve having an opening of 53 μm to collect core particles of the lithium metal composite oxide powder under the sieve. The core material particles are layered rock salt type compounds, and the molar ratio of nickel, cobalt and manganese was Ni:Co:Mn=0.33:0.33:0.33 as in the metal composite hydroxide. rice field.

(2) Production of Positive Electrode Active Material Nb was used as the A element. A surface treatment liquid was prepared by dissolving 5 g of fluorine-containing ammonium peroxoniobate and 0.70 g of lithium hydroxide in 100 mL of ion-exchanged water. This surface treatment liquid is called treatment liquid A.
20 g of the core particles obtained in the above (1) were put into 33 mL of treatment liquid A and heated at 90° C. or higher. By heating at 90° C. or higher, the lithium raw material and ammonium peroxoniobate react in the solution. As a result, a Li—Nb—O-based compound having a property of being easily adsorbed on the surfaces of the core particles is produced on the surfaces of the core particles. After that, it was dried at 120° C. using a hot air oven and heat-treated at 500° C. for 5 hours to obtain a positive electrode active material. The _D50 of the obtained positive electrode active material was as shown in Table 1 below. This sample had one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by XAFS measurement, and also had one peak in the range of 0.280 nm or more and 0.310 nm or less. .

[Example 2]
In (1), the composition of the core particles was set to Ni:Co:Mn=0.6:0.2:0.2. In (2), the positive electrode active material was obtained by drying at 140° C. by a spray dry granulation method and then heat-treating at 700° C. for 5 hours. A positive electrode active material was obtained in the same manner as in Example 1 except for these. This sample had one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by XAFS measurement, and also had one peak in the range of 0.280 nm or more and 0.310 nm or less. .

[Comparative Example 1]
(2) in Example 1 was not performed. A positive electrode active material was obtained in the same manner as in Example 1 except for these.

〔evaluation〕
For the positive electrode active materials obtained in Examples and Comparative Examples, the ratio of the moisture content B (mass ppm) up to 110 ° C. measured by the Karl Fischer method to the BET specific surface area A (m ² /g) by the method described above. B/A value, particle size D ₅₀ , BET specific surface area and moisture content (110° C. and 250° C.), and concentration of residual carbonate ions were measured. Various physical property values of the positive electrode active materials obtained in Examples and Comparative Examples were measured as follows. The results are shown in Table 1 below.

<Chemical analysis>
The content of each element contained in the positive electrode active material was measured by inductively coupled plasma (ICP) emission spectrometry.

<Analysis of fluorine content>
A positive electrode active material was thermally decomposed in a stream of oxygen and water vapor, and fluorine in the positive electrode active material was captured in a hydrogen peroxide solution to prepare a sample solution. Then, the sample solution was subjected to ion chromatography measurement, and the amount of fluorine was measured by quantifying fluoride ions. ICS-2100 manufactured by Thermo Fisher Scientific was used as a measurement apparatus, Ion Pac AS19 was used as a column, and an aqueous potassium hydroxide solution was used as a carrier liquid (eluent), and the measurement was performed at 35°C. In this way, the mass ratio (ppm) of the amount of fluorine to the positive electrode active material is obtained, and the amount of fluorine (ppm) obtained by ion chromatography with respect to the content (% by mass) of the niobium (Nb) element obtained by ICP. "F/Nb" was calculated as a mass ratio. The above measurement conditions can also be applied to halogen other than fluorine.

<Surface analysis by XPS>
The particle surface of the positive electrode active material was analyzed using QUANTUM 2000, which is an XPS device manufactured by ULVAC-Phi. The conditions, etc. used for the measurement are as follows.
Excitation X-ray: Monomer Al-Kα ray (1486.6 eV)
Output: 100W
Accelerating voltage: 20 kV
X-ray irradiation diameter: 100 μmφ
Measurement area: 100 μm × 1 mm
Take of Angle: 45°
Pass energy: 23.5 eV
Energy step: 0.1 eV

The XPS data was analyzed using data analysis software ("Multipack Ver9.0" manufactured by ULVAC-PHI). Background mode used Iterated Shirley. Considering the interference of the LMM peak of Ni and the LMM peak of Mn, the trajectory used for calculation was determined for each element as shown below.
Li: 1s
Ni: 2p1
Nb: 3d
Mn: 2p1
Ti: 2p3
C: 1s
O: 1s
F: 1s
N: 1s

More specifically, using XPS for the positive electrode active material, the surface of the positive electrode active material is analyzed under the above conditions, the peak area is obtained from the obtained X-ray photoelectron spectroscopy spectrum, and the atomic composition percentage for all the elements listed above was calculated. Henceforth, the value obtained from this calculation is defined as a quantitative value. The ratio of F to Nb (F/Nb) and the ratio of Li to Nb (Li/Nb) were determined.

<Production and Evaluation of Solid Lithium Secondary Battery>
Using the positive electrode active material (sample) and the solid electrolyte, a solid lithium secondary battery was produced, and the battery characteristics (charging characteristics) were evaluated.

(material)
Using the positive electrode active materials produced in Examples and Comparative Examples, using graphite (Gr) powder as the negative electrode active material, and using the composition formula: Li _5.4 PS _4.8 Cl _0.8 Br _0.8 as the solid electrolyte powder The indicated powder was used. The positive electrode mixture powder was prepared by mixing the positive electrode active material, solid electrolyte powder, and VGCF (registered trademark) powder as a conductive material in a mass ratio of 80:17:3 in a mortar. The negative electrode mixture powder was prepared by mixing a negative electrode active material (graphite) and a solid electrolyte in a mass ratio of 64:36 in a mortar.

(Production of solid lithium secondary battery)
A positive electrode mixture powder pellet of 14.5 mg was filled in an insulating cylinder (φ9 mm) of a closed cell and uniaxially molded at 500 MPa to prepare a positive electrode mixture powder pellet. The obtained positive electrode pellet was transferred into an insulating cylinder (φ10.5 mm) of a closed cell, and 50 mg of solid electrolyte powder was filled on the positive electrode pellet. Next, after uniaxially molding at 184 MPa together with the positive electrode mixture pellet, 24.7 mg of graphite powder was filled on the solid electrolyte and uniaxially molded at 551 MPa. Furthermore, they were tightened with pressure screws to produce a solid lithium secondary battery.

(Battery characteristic evaluation)
The solid lithium secondary batteries of Examples and Comparative Examples were charged at a constant current of 0.3 C to a final charge voltage of 4.5 V in one cycle. After that, constant voltage charging was performed until the current value reached 0.01C at 4.5V. The capacity obtained by constant current charging until reaching 4.5 V is taken as the CC capacity. A value obtained by dividing the CC capacity by the total charge capacity in the first cycle and multiplying the value by 100 was taken as the charging characteristic. The value obtained by subtracting the charging characteristics of Comparative Example 1 from the charging characteristics of Examples 1 and 2 is divided by the charging characteristics of Comparative Example 1 and multiplied by 100. described in The charging characteristic improvement rate indicates the improvement rate of lithium ion mobility (detachability) during charging, and rapid charging can be evaluated based on the charging characteristic improvement rate.

As is clear from the results shown in Table 1, the solid-state batteries using the positive electrode active materials obtained in each example have better charging characteristics than the comparative examples, and are suitable for rapid charging.

Claims (13)

An active material used in a solid-state battery,
The active material has at least one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by measurement of the X-ray absorption fine structure, and 0.280 nm or more and 0.310 nm or less. At least one peak is observed in the range of
The active material has a core particle and a coating layer disposed on the surface of the core particle, and a halogen element is present on or near the surface of the core particle,
The coating layer includes a lithium (Li) element, an A element (A is one or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W and Al) and oxygen (O) consisting of a compound containing an element,
The active material, wherein the compound contains a lithium (Li) element in excess of 1 mol with respect to 1 mol of the A element . An active material used in a solid-state battery,
The active material has at least one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by measurement of the X-ray absorption fine structure, and 0.280 nm or more and 0.310 nm or less. At least one peak is observed in the range of
The active material has core particles and a coating layer disposed on the surface of the core particles,
A peak apex is observed at a binding energy of Li1s measured by X-ray photoelectron spectroscopy (XPS) of 54.0 eV or more and 55.4 eV or less ,
The coating layer includes a lithium (Li) element, an A element (A is one or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W and Al) and oxygen (O) consisting of a compound containing an element,
The compound is an active material having a composition in which the lithium (Li) element is contained in excess of 1 mol with respect to 1 mol of the A element. 3. The active material according to claim 1, wherein the coating layer has a thickness of 0.5 nm or more and 200 nm or less. Halogen (X) element amount (ppm) measured by ion chromatography after thermally decomposing the active material with respect to the amount of A element (% by mass) measured by inductively coupled plasma atomic emission spectrometry after dissolving the active material completely ) has a mass ratio (X/A) of 0.5×10 ⁻⁴ or more . 5. The molar ratio (X/A) of the amount of halogen (X) element to the amount of A element present on the surface of the core particles measured by X-ray photoelectron spectroscopy is 0.011 or more. The active material according to any one of the items . The molar ratio (Li/A) of the amount of lithium (Li) element to the amount of A element present on the surface of the core particles measured by X-ray photoelectron spectroscopy is 1.0 or more and 33.3 or less. Item 6. The active material according to any one of Items 1 to 5. 7. The active material according to any one of claims 1 to 6, wherein the halogen (X) element is fluorine (F) element. The core material particles are a lithium metal composite oxide having a layered rock salt structure represented by the general formula LiMO ₂ (M is a metal element) or a lithium metal composite oxide having a spinel structure represented by LiM ₂ O ₄ (M is a metal element). The active material according to any one of claims 1 to 7, comprising: Claims 1 to 8, wherein the value of B/A, which is the ratio of the moisture content B (mass ppm) up to 110°C measured by the Karl Fischer method to the BET specific surface area A (m ² /g), is 1 or more and 8000 or less. The active material according to any one of . A positive electrode mixture comprising the active material according to claim 1 and a solid electrolyte. 11. The positive electrode mixture according to claim 10, wherein the solid electrolyte contains lithium (Li) element, phosphorus (P) element and sulfur (S) element, and has lithium ion conductivity. 12. The positive electrode mixture according to claim 11, wherein the solid electrolyte has a crystal phase with an aldirodite structure. In a solid battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer,
A solid state battery, wherein the positive electrode layer comprises the active material according to any one of claims 1 to 9.

Images