JP2020135949A - Active material, and positive electrode mixture and solid battery using the same - Google Patents

Abstract

To provide an active material having an increased operating voltage at the initial stage of discharge.SOLUTION: An active material according to the present invention is used for a solid-state battery. In a radial distribution function obtained by the measurement of an X-ray absorption fine structure of the active material, at least one peak is observed in the range of 0.115 nm or more and 0.144 nm or less, and at least one peak is observed in the range of 0.310 nm to 0.340 nm or less. The active material includes core material particles and a coating layer arranged on the surfaces of the core material particles. A halogen element exists on the surface of the core material particles or in the vicinity thereof.SELECTED DRAWING: Figure 1

Description

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

The solid electrolyte used in the solid-state battery is required to have as high an ionic conductivity as possible and to be chemically and electrochemically stable. For example, lithium halide, lithium nitride, lithium salt, or derivatives thereof are known as material candidates for solid electrolytes.

A sulfide solid electrolyte is being studied as one of the solid electrolytes used in a solid battery. However, a solid-state battery containing a sulfide solid electrolyte has a problem that when charging / discharging is performed on the solid battery, the interfacial resistance between the electrode active material and the sulfide solid electrolyte increases, and the movement of lithium ions is restricted. It is considered that the reason for this is that a resistance layer is formed at the interface between the electrode active material and the sulfide solid electrolyte by reacting with each other. To solve this problem, for example, in Patent Document 1, it is attempted to suppress an increase in interfacial resistance by coating the surface of the positive electrode active material with a specific compound.

JP-A-2018-125214

By the way, as the charged battery is discharged, the voltage of the battery gradually decreases. In particular, the voltage drop at the initial stage of discharge affects the performance of the battery. It is considered that the voltage drop at the initial stage of discharge is partly due to the generation of the above-mentioned substance that increases the interfacial resistance when the battery is charged. However, the technique described in Patent Document 1 sufficiently suppresses the increase in the interfacial resistance. Can't.

In view of the above problems, the present invention mainly provides an active material capable of reducing the interfacial resistance with the solid electrolyte, suppressing the voltage drop at the initial stage of discharge, and maintaining a high operating voltage at the initial stage of discharge. The purpose.

The present invention is an active material used in a solid-state battery.
In the radial distribution function obtained by measuring the X-ray absorption fine structure, at least one peak is observed in the range of 0.115 nm or more and 0.144 nm or less, and the active material is more than 0.310 nm and 0.340 nm or less. At least one peak is observed in the range of
The active material provides an active material having a core material particle and a coating layer arranged on the surface of the core material particle, and a halogen element is present on or near the surface of the core material particle. By doing so, the above-mentioned problems are solved.

The present invention is an active material used in a solid-state battery.
In the radial distribution function obtained by measuring the X-ray absorption fine structure, at least one peak is observed in the range of 0.115 nm or more and 0.145 nm or less, and the active material is more than 0.310 nm and 0.340 nm or less. At least one peak is observed in the range of
The active material has core material particles and a coating layer arranged on the surface of the core material particles.
The above-mentioned problems are solved by providing an active material in which a peak peak is observed when the binding energy of Li1s measured by X-ray photoelectron spectroscopy (XPS) is 54.0 eV or more and 55.4 eV or less.

According to the present invention, an active material having a high operating voltage at the initial stage of discharge is provided.

FIG. 1 is a radial distribution function obtained by measuring the X-ray absorption fine structure measured for oxides containing lithium and niobium. FIG. 2 is a graph showing a method for determining whether or not there is a peak in the radial distribution function obtained by measuring the X-ray absorption fine structure measured for the positive electrode active material obtained in Example 1. is there. FIG. 3 is a radial distribution function obtained by measuring the X-ray absorption fine structure measured for Li ₃ NbO ₄ .

Hereinafter, the present invention will be described based on its preferred embodiment. The present invention relates to an active material used in a solid-state battery.

A. Active material 1. Halogen The active material of the present invention preferably has core material particles and a coating layer arranged on the surface of the core material particles. It is preferable that a halogen element is present on or near the surface of the core material particles. The presence of halogen elements on the surface of the core material particles increases the interfacial resistance, 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. It is suppressed that the obtained substance is generated during charging, thereby suppressing the voltage drop of the battery at the initial stage of discharging. In addition, the reaction between oxygen contained in the core material particles and sulfur contained in the sulfide solid electrolyte, which may occur when the battery is charged, can be suppressed, thereby suppressing the voltage drop of the battery at the initial stage of discharge. To. The "surface of the core material particles or the vicinity thereof" is a region within 200 nm, particularly within 100 nm, particularly within 50 nm along the thickness direction from the surface itself or the surface of the core material particles. The presence of a halogen element within a predetermined range along the thickness direction from the surface of the core material particles means that, for example, the halogen element is present in the coating layer, or the halogen element is present on the outermost surface of the coating layer. Is assumed. Further, the "initial discharge" is, for example, a state from the start of discharge to the discharge of 0.5 mAh / g.

Further, the active material of the present invention has core material particles and a coating layer arranged on the surface of the core material particles, and the binding energy of Li1s measured by X-ray photoelectron spectroscopy (XPS) is 54.0 eV. By observing the peak peak below 55.4 eV, 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, and the activity during charging is observed. The mobility (desorption) of lithium ions from the substance is improved. In addition, it is possible to suppress the reaction between oxygen contained in the core material particles and sulfur contained in the sulfide solid electrolyte, which may occur when charging the battery, which also gives priority to the movement (desorption) of lithium ions. Will occur.

The halogen element means at least one element of fluorine (F) element, chlorine (Cl) element, bromine (Br) element and iodine (I) element. The halogen element present on the surface of the core material particles may be one kind or a combination of two or more kinds. From the viewpoint of suppressing the formation of lithium halide, which contributes to the interfacial resistance, the halogen elements are preferably chlorine (Cl) element and bromine (Br) element, and the viewpoint of further enhancing the mobility (desorption) of lithium ions. Therefore, the fluorine (F) element is preferable.

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

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

<Surface analysis by TOF-SIMS>
Using TRIFT IV, a time-of-flight secondary ion mass spectrometry (TOF-SIMS) device 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. To do. Specifically, the count number of fluorine ions (F ⁻ ) with respect to the total count number (total) of all the secondary ions collected from the surface of the positive electrode active material whose secondary ion polarity is measured under negative conditions. The ratio (F ⁻ / total) of is measured.

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

In the active material of the present invention, it is preferable that the peak peak is observed when the binding energy of Li1s measured by X-ray photoelectron spectroscopy (XPS) is 54.0 eV or more and 55.4 eV or less. More preferably, peak vertices are 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. The fact that the binding energy of XPS of Li1s is in the above range can be inferred that a part of O of the LiAO compound described later is replaced with F. It is preferable that a part of O of the LiAO compound is replaced with F 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. The halogen present on the surface of the core material particles may be dissolved in the LiAO compound described later, or may be present in the state of a halogen compound separately from the LiAO compound.

2. 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 containing the compound (also referred to as "LiAO compound"). By coating the surface of the core material 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 charging characteristics are enhanced. be able to. In addition, the interfacial resistance between the positive electrode active material and the solid electrolyte can be reduced. The element A is a group of metal elements having similar properties called valve metal.

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 material particles, and exists as agglomerated particles formed by aggregating the particles. Includes aspects that are present and aspects that are present in layers. "Existing in layers" means a state in which the LiAO compound exists with a thickness.

When the LiAO compound forms a layer, its thickness is preferably 0.5 nm to 200 nm, particularly preferably 0.7 nm or more or 100 nm or less, particularly preferably 1 nm or more or 50 nm or less, and further preferably 25 nm or less. Is preferable. Within 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 a scanning transmission electron microscope (STEM). In addition, energy dispersive X-ray analysis (EDS) can be combined for observation and measurement as needed.

There may be a part or a part of the surface of the core material 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 material particles, particularly 40% or more, and particularly preferably 50% or more. The fact that the surface of the core material particles is coated with the LiAO compound means that, for example, as described above, a scanning transmission electron microscope (STEM) and, if necessary, energy dispersive X-ray analysis (EDS) are combined to form a core. It can be confirmed by observing the surface of the material particles or by Auger electron spectroscopy. Further, the thickness of the LiAO compound covering the surface of the core material particles does not have to be uniform.

3. 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 measuring the X-ray absorption fine structure (hereinafter, also referred to as “XAFS”). At the same time, at least one peak is observed in the range of more than 0.310 nm and 0.340 nm or less.

Specifically, as shown in FIG. 1, 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 the measurement of XAFS. The peak position is specified by the position of the peak apex. The definition of the 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. The number of peaks observed in the above range may be at least one, for example, only one or two or more. At the same time, in the active material of the present invention, at least one peak is observed in the range of more than 0.310 nm and 0.340 nm or less. The peak position observed in the present invention may be, for example, 0.315 nm or more. On the other hand, the peak position may be, for example, 0.335 nm or less, or 0.330 nm or less.

As for the above-mentioned LiAO compound, various compounds have been known in the art, and in the present invention, it is preferable to use a compound having a specific chemical structure. The LiAO compound used in the present invention is characterized by the observation of a peak at a specific interatomic distance in the radial distribution function obtained by measuring XAFS. For example, when the LiAO compound is a compound containing Li, Nb and O (hereinafter, this compound is also referred to as “LiNbO compound”), an example of the radial distribution function of the LiNbO compound is as shown in FIG. It becomes. The horizontal axis of the radial distribution function shown in FIG. 1 indicates the interatomic distance with respect to the position of the niobium atom. The vertical axis shows 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 more than 0.310 nm and 0.340 nm or less is the niobium atom. It is equivalent to the distance between each other. In the radial distribution function obtained from XAFS, by incorporating the LiNbO compound whose peak is observed in the above-mentioned predetermined range in the coating layer, the active material of the present invention improves the mobility of lithium ions, and as a result, It is possible to suppress the voltage drop at the initial stage of discharge and maintain a high operating voltage at the initial stage of discharge. In addition, the interfacial resistance between the active material and the solid electrolyte can be reduced.

The fact that a peak is observed in the radial distribution function means that the radial distribution function may include an upwardly convex portion or a shoulder portion. The peak is the case where the quadratic derivative has a minimum value obtained by differentiating the function y = f (x) whose horizontal axis is x and its vertical axis is y twice. Defined to have. 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). For example, in Example 1 described later, as shown in FIG. 2, the radial distribution function for peaks observed in the range of 0.115 nm or more and 0.144 nm or less and the range of more than 0.310 nm and 0.340 nm or less. Has a minimum value by differentiating twice. From this, it can be said that in Example 1, peaks are observed in the range of 0.115 nm or more and 0.144 nm or less and in the range of more than 0.310 nm and 0.340 nm or less.

As described above, the LiAO compound preferably used in the present invention has a peak at a predetermined position of a specific interatomic distance in the radial distribution function obtained from XAFS. In contrast, the Li-AO-based compounds known so far do not have a peak at a predetermined position specified in the present invention in the radial distribution function obtained from XAFS. For example, as shown in FIG. 3, Li ₃ NbO _4, 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, but is 0. No peak is observed in the range of more than 310 nm and less than 0.340 nm.

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

In the present invention, in order to measure the XAFS of the active material, an operation is performed according to the procedure described below.
Sample preparation After crushing the sample in an agate mortar, it is mixed with boron nitride powder to make tablets with a diameter of 10 mm and a thickness of about 1 mm. The amount of the sample and boron nitride is appropriately optimized according to the concentration of element A contained in the sample to be measured and the absorption coefficient of the LiAO compound and the compound constituting the core material particles.

The conditions for measuring XAFS at the Nb-K end are as follows.
・ Experimental facility: SPring-8
・ Experimental station: BL14b2
・ Spectrometer: Monochromator Si (311)
・ Higher-order light removal: Rh coat mirror 2.4 mrad x 2 ・ Incident X-ray size: length 1 mm x width 5 mm (slit size in front of sample)
-Measurement method: Permeation method-Detector: Ion chamber-Measurement absorption end: Nb-K absorption end (18986eV)
At each incident X-ray energy (E, x-axis), I0 and It were measured, the X-ray absorbance (y-axis) was obtained by the following equation, and the X-ray spectrum was obtained by plotting on the x-axis-y-axis. ..
X-ray absorbance μt = -ln (It / I0)

To obtain the radial distribution function based on the data obtained as described above and determine the interatomic distance, the procedure described below is performed.
The radial distribution function obtained by Fourier transforming the EXAFS spectrum will be described.
"Athena" (Demeter Ver. 0.9.25) is used as the analysis software.
First, after reading the XAFS spectrum with the same software, the background absorption Pre-edge region (a region of about -150 to -45 eV from the absorption end) and the Post-edge region (about 150 to 1300 eV from the absorption end). XAFS spectrum is standardized by fitting with. Next, in order to extract the EXAFS spectrum (χ (k)), fitting is performed with a spline curve. The parameters used to fit the spline curve in the analysis with the software are as follows.
・ 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 (χ (k)) is Fourier transformed to obtain a spectrum showing a radial distribution function. The following values were used as the parameters of the Fourier transform in the software.
・ K-range: 3.5 ~ 11.5
・ Dk: 1
・ Window: Hanning
・ Arbitrary k-weight: 1
・ Phase correction: unused

The composition of each element in the LiAO compound can be indicated by, for example, Li _x AO _y when the element A is at least one element of Ta and Nb. X and y in the formula can take arbitrary values within a range corresponding to the valence of the element. Above all, it is particularly preferable that the composition (x ≧ 1) contains Li in an equimolar amount or more with respect to 1 mol of the A element. By doing so, it is possible to suppress the formation of a compound of A and O and improve the mobility of lithium ions. In addition, 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 element A raw material is set to the composition expected to be produced, for example, the stoichiometric composition of LiAO _3. There are ways to make it more than a ratio. At this time, if Li is simply added in excess, lithium carbonate is generated on the surface of the positive electrode active material due to the excess Li, which acts as a resistance and rather lowers the operating voltage during discharge. In some cases. Therefore, in consideration of the formation of lithium carbonate, which is an undesired compound, it is preferable to adjust the amount of the A element raw material and the amount of the lithium raw material blended so that Li _x AO _y has a predetermined composition.

From this point of view, the mol ratio (Li / A) of the amount of Li to the amount of the element A present on the surface of the core material particles obtained by X-ray photoelectron spectroscopy (XPS) is 1.0 or more and 33.3 or less. Is preferable. Among them, it is preferably larger than 1.0 and 33.3 or less. Among them, 1.1 or more and 33.3 or less, 1.1 or more and 15.0 or less, 1.1 or more and 10.0 or less, 1.2 or more and 10.0 or less, 1.2 or more and 6.0 or less, Further, it is more preferably 1.3 or more and 6.0 or less, further more than 1.3 or 6.0 or less. Li in the mol ratio (Li / A) is a value including those caused by lithium carbonate (if present) and those caused by the core material particles themselves.

In order to control the ratio of Li existing on the surface of the core material particles to the element A within the above range, the mol ratio (the mol ratio (the Li content) caused by lithium carbonate generated on the surface of the core material particles is taken into consideration. It is preferable to adjust the amount of the A element raw material and the amount of the lithium raw material blended so that Li / A) is within the above range. By doing so, the voltage drop at the initial stage of discharge can be suppressed, and the operating voltage at the initial stage of discharge can be maintained high. However, the method is not limited to this method.

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

In the present invention, the mol ratio (X / A) of the amount of halogen (X) to the amount of the element A present on the surface of the active material (particle) obtained by X-ray photoelectron spectroscopy (XPS) is 0.011 or more. Is preferable. If the mol ratio (X / A) x of the amount of halogen to the amount of element A existing on the surface of the active material (particle) is 0.011 or more, the oxygen and sulfide solid electrolyte contained in the LiAO compound and the core material particles can be used. It is preferable because the reaction with the contained sulfur can be further suppressed. 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 material particles does not impair the conductivity of lithium ions, which is preferable. .. From this point of view, the mol ratio (X / A) of the amount of halogen to the amount of element A present on the surface of the active material (particles) obtained by X-ray photoelectron spectroscopy (XPS) is 0.011 or more and 1.95 or less. Further 0.011 or more and 1.50 or less, further 0.011 or more and 1.00 or less, further 0.011 or more and 0.50 or less, further 0.015 or more and 0.50 or less, and further 0.020 or more and 0.500 or less. Further, it is preferably 0.025 or more and 0.500 or less, and further preferably 0.030 or more and 0.500 or less. Above all, the lower limit of (X / A) is preferably 0.033 or more, more preferably 0.055 or more, and further preferably 0.11 or more.

From the viewpoint of reducing the interfacial resistance between the active material and the sulfide solid electrolyte, it is advantageous that the water content of the active material of the present invention is adjusted within a certain range.

When the core material 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 Fisher method, for example, 50 ppm or more, or 140 ppm or more. It may be 200 ppm or more. On the other hand, the water 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 material particles in the active material contain a spinel-type compound, the active material may have a moisture content B (mass ppm) up to 110 ° C. measured by the Karl Fisher method, for example, 1 ppm or more, or 50 ppm. It may be more than 100 ppm, it may be 100 ppm or more, and it may be 200 ppm or more. On the other hand, the water 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 has 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 It may be / g or more, and may be 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.

Further, in the active material of the present invention, the value of B / A, which is the ratio of the water content B (mass ppm) up to 110 ° C. measured by the Carl Fisher 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 value of B / A 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. From the viewpoint that selecting an appropriate range for the B / A value according to the type of substance constituting the active material further suppresses the reaction between the active material and the sulfide solid electrolyte and reduces the interfacial resistance. It is advantageous from.

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

In the technical field, it has been generally considered that the lower the water content of the active material, the more preferable it is. The reason for this is that it was thought that the sulfide solid electrolyte would react with water and deteriorate. However, as a result of detailed examination by the present inventor, it has been found that the interfacial resistance between the active material and the sulfide solid electrolyte tends to increase even when the water 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, forms a good interface, and thereby reduces the interface resistance. The present inventor thinks that. The water to be measured for the water content of the active material includes both adhering water and water of crystallization contained in the active material.

Regarding the water content of the active material, the reason why the water content B measured by the Karl Fisher method is divided by the BET specific surface area A is to standardize the water content of the active material. The procedure for measuring the water content by the Karl Fisher method is as follows. That is, the measurement sample is heated to 110 ° C. or 250 ° C. using a Karl Fischer titer, and the amount of water released (ppm) is measured. The measurement is carried out 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 1-point method using, for example, a fully automatic specific surface area measuring device Macsorb (manufactured by Mountech Co., Ltd.) as a measuring device. Specifically, the sample is weighed in a glass cell (standard cell), the inside of the glass cell is replaced with nitrogen gas, and then heat treatment is performed at 250 ° C. for 15 minutes in the nitrogen gas atmosphere. Then, cooling is performed for 4 minutes while flowing a mixed gas of nitrogen and helium. After cooling, the sample (powder) is measured by the BET 1-point method. As the adsorbed gas during cooling and measurement, a mixed gas of nitrogen 30 vol%: helium 70 vol% is used.

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

When the ratio of the LiAO compound contained in the active material is expressed as the ratio of the mass of the element A 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. It may be 0.5% by mass or more, and may be 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 determined by ICP emission spectroscopy for a solution in which the active material is dissolved. Further, the ratio can be controlled by adjusting the amount of the element A source compound used in the method for producing an active material 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 the reaction between the active material and the sulfide solid electrolyte can be effectively suppressed. 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 even more. It is preferably less than 0.5% by mass, more preferably less than 0.35% by mass, further less than 0.30% by mass, and more preferably less than 0.20% by mass. Examples of the method for reducing the amount of carbonate ions present on the surface of the active material include a method of firing in a carbon dioxide-free atmosphere such as a nitrogen atmosphere or an oxygen atmosphere.

When the core material 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 with respect to the active material, particularly less than 0.30% by mass, among which. It is more preferably less than 0.20% by mass.
On the other hand, when the core material particles contain a spinel type compound, 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 with respect to the active material. Among them, it is preferably less than 1.0% by mass, more preferably less than 0.5% by mass, further preferably less than 0.3% by mass, and further preferably less than 0.2% by mass.

Examples of the method for measuring the amount of carbonate ions include the following methods. That is, 0.48 g of the active material is put into 48 ml of pure water, stirred for 5 minutes, and then filtered. In this way, by ion chromatography measurement as an object a solution obtained by extracting the carbonate ion, CO ₃ ^2-a to quantify, it is possible to determine the amount of carbonate ion. As a measuring device, DIONEX ICS-2000 manufactured by Thermo Fisher Scientific Co., Ltd. is used, DIONEX IonPac AS17-C is used as a column, and an aqueous potassium hydroxide solution is used as a carrier solution (eluent), and measurement is performed under the condition of 35 ° C. be able to.

The active material has a volume cumulative particle size D _{50 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, particularly less than 15 μm, particularly more than 1 μm and less than 10 μm, and more than 2 μm and 8 μm or less. It is even more preferable to have. When D ₅₀ is 20 μm or less, for example, when an 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 increased. Can be enhanced. Further, when D ₅₀ is larger than 1 μm, it is possible to prevent the particles from agglomerating and increasing the slurry viscosity. In order to adjust the D ₅₀ of the active material within the above range, the operating conditions of the spray-dry granulation method and the rolling fluidized bed granulation method may be adjusted, or the crushing conditions may be adjusted. It is not limited to.

4. Core material particles The core material particles are not particularly limited as long as they function as active materials. The core material particles may contain, for example, a lithium metal composite oxide. As the lithium metal composite oxide, a known lithium metal composite oxide can be used. 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 general formula LiMPO ₄ (M is a metal). It may be any one or a combination of two or more of the lithium-containing composite oxides having an olivine structure represented by (element) or LiMSiO ₄ (M is a metal element). However, it is not limited to these.

As the metal element M in the lithium metal composite oxide, for example, both a transition element and a typical element can be used, and a transition element is preferably used. Examples of the lithium metal composite oxide include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium nickel cobalt manganate (Li (Ni, Co, Mn) O ₂ ), and lithium manganate (LiMn _2). O _4), and lithium nickel manganese oxide _{(LiNi 0.5 Mn} 1.5 _{O 4)} include lithium transition metal oxides such as. 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 material particles of the spinel-type compound are preferably particles containing Li, Mn, O and one or more other elements other than these. In addition, 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 can be added in combination of one or more elements selected from the group consisting of Ce. Among these, it is preferable to select from the group consisting of Na, Mg, Al, P, K, Ca, Ti, Fe, Co, Ni, Zr, Nb, Mo and W.

Further, by selecting the additive element type and the additive element amount as described below, it is possible to develop an operating voltage of 4.5 V or more mainly at the metal Li reference potential. The core material particles of the spinel-type compound are particles containing Li, Mn, O and one or more kinds of elements other than these, and at least one element among the above-mentioned "one or more kinds of elements other than these" is Ni, Co. By using the element M1 selected from the group consisting of, and Fe, it is possible to develop an operating potential of 4.5 V or more mainly at the metal Li reference potential. The amount of M1 element contained in the core material particles is preferably, for example, 7% by mass or more, particularly preferably 9% by mass or more, and 11% by mass among all the elements in the core material particles. The above is preferable. On the other hand, the amount of M1 element contained in the core material particles is, for example, preferably 35% by mass or less, preferably 30% by mass or less, and preferably 25% by mass, based on all the elements in the core material particles. When these elements are contained, an operating voltage of 4.5 V or more is developed mainly at the metal Li reference potential. M2 element may be contained in addition to M1 element, 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 from a combination of one or more elements selected from the group. Among the above M2 elements, it is preferable to select from the group consisting of Na, Mg, Al, P, K, Ca, Ti, Fe, Co, Ni, Zr, Nb, Mo and W.

When the core material particles contain a lithium metal composite oxide, the content of the lithium metal composite oxide in the core material particles may be, for example, 80% by mass or more, 90% by mass or more, or 95% by mass. It may be% or more. Further, the core material particles may be composed of only a 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 suitable 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 element A salt containing halogen and lithium hydroxide are dissolved in water to prepare a surface treatment liquid, and core material particles are put into the surface treatment liquid and kneaded. It can be suitably produced by forming a slurry and drying it. However, the method for producing the active material is not limited to such a method. For example, the rolling flow coating method (sol-gel method), the mechanofusion method, the CVD method, the PVD method, and the like can also be manufactured by adjusting the conditions.

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

In the above-mentioned production method, core material particles are put into a surface treatment liquid to form a slurry, and the slurry is heated at 90 ° C. or higher to produce a LiAO compound. At the same time, the halogen and the LiAO compound can be fixed to the surface of the core material particles. Since the LiAO compound has a property of being easily adsorbed on the surface of the core material particles, a coating layer composed of the LiAO compound and halogen can be formed on the surface of the core material particles by drying the slurry. Instead of this method, a surface treatment liquid heated to 90 ° C. or higher may be used and sprayed onto the core material particles. Then, if necessary, crushing and heat treatment are performed.

By drying the slurry, a coating layer containing a LiAO compound having a specific structure and a halogen can be obtained. To dry the slurry, for example, a spray-dry granulation method or a rolling fluidized bed granulation method can be used. After that, heat treatment may be performed if necessary. Specifically, it is preferable to perform heat treatment in an oxygen, nitrogen, or argon atmosphere that does not contain carbon dioxide gas as much as possible. The drying and heat treatment temperatures are preferably 105 ° C. or higher and 600 ° C. or lower, more preferably 200 ° C. or higher and 600 ° C. or lower, still more preferably 200 ° C. or higher and 500 ° C. or lower, still more preferably 300 ° C. or higher and 500 ° C. or lower, and particularly even more preferably. Can be 350 ° C. or higher and 500 ° 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 further preferably 1 hour or more and 10 hours or less. This makes it possible to successfully generate a LiAO compound having a peak at a specific interatomic distance position in the radial distribution function obtained from XAFS. When heat-treated at an excessively high temperature, for example, when element A is a niobium (Nb) element, Li ₃ NbO ₄ (this compound peaks at a specific interatomic distance position in the radial distribution function obtained from XAFS. The present inventor has confirmed that (not possessed) is generated.

The core material particles used in the present invention are prepared by weighing and mixing raw materials such as a lithium salt compound, a manganese salt compound, a nickel salt compound and a cobalt salt compound, pulverizing them with a wet pulverizer or the like, granulating them, and firing them. , If necessary, heat-treat, pulverize under preferable conditions, and further classify 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 combined with the metal composite hydroxide. Core material particles can also be obtained by mixing with a lithium salt compound and firing.

Examples of the lithium salt compound as a raw material include lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), LiOH / H ₂ O, lithium oxide (Li ₂ O), and lithium fatty acid. And lithium hydroxide and the like. Of these, lithium hydroxide, carbonate and nitrate are preferable.

Examples of the manganese salt compound include manganese carbonate, manganese nitrate, manganese chloride and manganese dioxide. Of these, manganese carbonate and manganese dioxide are preferable, and electrolytic manganese dioxide obtained by an electrolytic method is particularly preferable.
Examples of the nickel salt compound include nickel carbonate, nickel nitrate, nickel chloride, nickel oxyhydroxide, nickel hydroxide and nickel oxide, and nickel carbonate, nickel hydroxide and nickel oxide are preferable.
Examples of the cobalt salt compound include basic cobalt carbonate, cobalt nitrate, cobalt chloride, cobalt oxyhydroxide, cobalt hydroxide and cobalt oxide, and among them, basic cobalt carbonate, cobalt hydroxide, cobalt oxide and oxywater. Cobalt oxide is preferred.

For mixing the above-mentioned raw materials, it is preferable to add a liquid medium such as water or a dispersant and wet-mix to form a slurry. Then, when the spray-drying method described later is adopted, it is preferable to pulverize the obtained slurry with a wet pulverizer, but dry pulverization may be used.

The above-mentioned granulation method may be wet or dry as long as the various raw materials crushed in the previous step are dispersed in the granulated particles without being separated. For example, an extrusion granulation method, a rolling granulation method, a flow granulation method, a mixed granulation method, a spray drying granulation method, a pressure molding granulation method, a flake granulation method using a roll or the like can be mentioned.

In the case of wet granulation, it is necessary to sufficiently dry it 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, or a freeze drying method may be used, and the spray heat drying method is particularly preferable. The spray heat drying method is preferably performed using a heat spray dryer (spray dryer).

The firing is performed in a firing furnace in an air atmosphere, an oxygen gas atmosphere, an atmosphere in which the oxygen partial pressure is adjusted, a carbon dioxide gas atmosphere, or another atmosphere, for example, at a temperature higher than 700 ° C and 1000 ° C or lower. It is preferably held at a temperature of 750 ° C. or higher and lower than 1000 ° C., more preferably 800 ° C. or higher and 950 ° C. or lower for 0.5 hours or longer and 30 hours or lower. At this time, it is preferable to select a firing condition in which the transition metal is solid-solved at the atomic level to form 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 another firing furnace.

The heat treatment after calcination is preferably performed when it is necessary to adjust the crystal structure, and the heat treatment is performed under the conditions of an oxidizing atmosphere such as an air atmosphere, an oxygen gas atmosphere, or an atmosphere in which the oxygen partial pressure is adjusted.

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

6. Use of active material The active material of the present invention can usually be used as a positive electrode active material. Further, the active material of the present invention is used for a solid-state battery. In particular, it is advantageous that the active material of the present invention is used in a solid battery containing a sulfide solid electrolyte as a solid electrolyte. In the solid-state battery, the effect of the present invention can be enjoyed by the presence of the contact portion between the active material of the present invention and the sulfide solid electrolyte. Here, "there is a contact portion between the active material and the sulfide solid electrolyte" means that (a) the sulfide solid electrolyte is contained in the positive electrode mixture (in this case, the solid electrolyte layer may be non-sulfide. Yes), (a) Do not contain the sulfide solid electrolyte in the positive electrode mixture, but contain the sulfide solid electrolyte in the solid electrolyte layer, and (c) contain the sulfide solid electrolyte in the positive electrode mixture. And, it means 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. The active material contained in the positive electrode mixture can be the same as that described in the above section "A. Active material", and thus the description thereof is omitted here.

The solid electrolyte used in the present invention can be the same as the solid electrolyte used in a general solid-state battery. For example, a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, a halide solid electrolyte and the like can be mentioned, and among them, a sulfide solid electrolyte containing a sulfur (S) element is preferable. 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 a crystalline material, glass ceramics, and glass. The sulfide solid electrolyte may have a crystal phase having an algyrodite type structure. Such sulfide solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 5 -LiX ( "X" indicates one or more halogen element.), _Li 2 S -P ₂ S ₅ -P ₂ O ₅ , Li ₂ S-Li ₃ PO ₄ -P ₂ S ₅ , Li ₃ PS ₄ , Li ₄ P ₂ S ₆ , Li ₁₀ GeP ₂ S ₁₂ , Li _3.25 Ge _{0 .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 types The halogen element of the above is shown, and examples thereof include 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 only the active material of the present invention, or may be used in combination with other active materials. Examples of other active materials include particles made of the above-mentioned known lithium transition metal composite oxide, and the particles may or may not have a coating layer. When used in combination, it is preferable that the active material of the present invention is contained in an amount of 50 mol% or more, more preferably 70% or more, based on the entire 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. Further, the positive electrode mixture may contain other materials such as a conductive auxiliary agent and a binder, if necessary. Further, the positive electrode layer can be prepared by mixing the positive electrode mixture and the solvent to prepare a paste, applying the paste onto a current collector such as an aluminum foil, and drying the paste.

C. Solid-state battery The solid-state 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 above-mentioned positive electrode mixture.

The solid-state battery of the present invention can be produced, for example, by stacking three layers of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer produced as described above and press-molding them. The "solid-state battery" includes, for example, 50% by mass or less, 30% by mass or less, 10% by mass or less of a liquid substance or a gel-like substance as an electrolyte, in addition to a solid-state battery containing no liquid substance or a gel-like substance as an electrolyte. Also includes aspects.

The negative electrode active material used for the negative electrode layer can be the same as the negative electrode active material used for a general solid-state battery. As a specific negative electrode active material, a material that absorbs and releases lithium ions, for example, a carbon material, a known material such as a silicon oxide compound such as silicon and Si—O, a tin compound, or lithium titanate can be used. .. Examples of the carbon material include those obtained by sintering an organic polymer compound such as polyacrylonitrile, phenol resin, phenol novolac resin, and cellulose, and 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 words]
When expressed as "X to Y" (X, Y are arbitrary numbers) in the present specification, unless otherwise specified, it means "X or more and Y or less" and "preferably larger than X" or "preferably better than Y". It also includes the meaning of "small". Further, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it means "preferably larger than X" or "preferably less than Y". Including intention.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "mass%".

[Example 1]
(1) Production of core material 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 prepared by the 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 and calcined in the air at 720 ° C. for 5 hours using a static electric furnace, and then fired in the air at 905 ° C. for 22 hours. Got This lithium metal composite oxide was crushed in a mortar and then classified by a sieve having a mesh size of 53 μm, and core material particles composed of lithium metal composite oxide powder under the sieve were recovered. The core material particles are layered rock salt type compounds, and the molar ratio of nickel, cobalt and manganese is Ni: Co: Mn = 0.33: 0.33: 0.33, as in the case of the metal composite hydroxide. It was.

(2) Production of positive electrode active material Nb was used as the element A. The amounts of lithium ethoxydo and pentaethoxyniobium are adjusted so that the mol ratio (Li / Nb) of the amount of Li to the amount of Nb is 1.0, and these are added to ethanol to dissolve them in a coating solgel solution (lithium). Amount of 3 mmol, niobium amount of 3 mmol) was prepared. 5 g of the lithium metal composite oxide powder was added to the sol-gel solution for coating. Further, after dropping water containing fluorine, the mixture was hydrolyzed by heating at 60 ° C. for 30 minutes using a rotary evaporator and irradiating with ultrasonic waves. Then, the solvent was removed by reducing the pressure over 30 minutes while maintaining 60 ° C., and then the mixture was allowed to stand at room temperature for 24 hours to dry. Next, using NHK-170, which is a small tabletop electric furnace manufactured by Nikko Kagaku Co., Ltd., firing was performed in an air atmosphere at 350 ° C. for 5 hours to obtain a positive electrode active material containing fluorine on the surface. The D ₅₀ of the obtained positive electrode active material was as shown in Table 1 below. As shown in FIG. 1, this sample has one peak in the range of 0.115 nm or more and 0.144 nm or less in the radial distribution function obtained by the measurement of XAFS, and 1 in the range of more than 0.310 nm and 0.340 nm or less. It had this peak.

[Comparative Example 1]
(2) was not performed in Example 1. 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 water content B (mass ppm) up to 110 ° C. measured by the Carl Fisher method to the BET specific surface area A (m ² / g) by the above method. the value of which is B / a is, the particle diameter _D 50, BET specific surface area and moisture content (110 ° C. and 250 ° C.), as well as to measure the concentration of residual carbonate ions. In addition, various physical property values of the positive electrode active material 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 spectroscopy.

<Analysis of fluorine content>
The positive electrode active material was decomposed by heating with oxygen and a steam stream, and fluorine in the positive electrode active material was collected in a hydrogen peroxide solution to prepare a sample solution. Next, ion chromatography measurement of the sample solution was performed, and the amount of fluorine was measured by quantifying fluoride ions. As a measuring device, ICS-2100 manufactured by Thermo Fisher Scientific Co., Ltd. was used, Ion Pac AS19 was used as a column, and an aqueous potassium hydroxide solution was used as a carrier solution (eluent), and measurement was performed at 35 ° C. In this way, the ratio (ppm) of the amount of fluorine to the positive electrode active material was determined, and the amount of fluorine (ppm) determined by ion chromatography with respect to the content (% by mass) of the niobium (Nb) element determined by ICP. "F / Nb" was calculated as the mass ratio. The above measurement conditions can be applied to halogens other than fluorine.

<Surface analysis by XPS>
The particle surface of the positive electrode active material was analyzed using QUANTUM2000, which is an XPS device manufactured by ULVAC-PHI. The conditions used for the measurement are as follows.
Excited X-ray: Monomer Al-Kα ray (1486.6 eV)
Output: 100W
Acceleration voltage: 20kV
X-ray irradiation diameter: 100 μmφ
Measurement area: 100 μm x 1 mm
Take of Angle: 45 °
Path energy: 23.5 eV
Energy step: 0.1 eV

XPS data was analyzed using data analysis software ("Multipack Ver9.0" manufactured by ULVAC-PHI, Inc.). The background mode used was Alterated Shirley. Considering the interference between the LMM peak of Ni and the LMM peak of Mn, the orbits used for the calculation were 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, the surface of the positive electrode active material is analyzed using XPS for the positive electrode active material, the peak area is obtained from the obtained X-ray photoelectron spectroscopic spectrum, and the atomic composition percentage for all the above-mentioned elements. Was calculated. Hereinafter, the value obtained from this calculation will be quantified. The ratio of the quantification of F to the quantification of Nb (F / Nb) and the ratio of the quantification of Li to the quantification of Nb (Li / Nb) were determined.

<Manufacturing and evaluation of solid-state lithium secondary batteries>
A solid lithium secondary battery was prepared using a positive electrode active material (sample) and a solid electrolyte, and the battery characteristics were evaluated (charging characteristics).

(material)
Using the positive electrode active material prepared in Examples and Comparative Examples, graphite (Gr) powder was used as the negative electrode active material, and the powder represented by the composition formula: Li _5.8 PS _4.8 Cl _1.2 was used as the solid electrolyte powder. Using. The positive electrode mixture powder was prepared by mixing a positive electrode active material, a solid electrolyte powder, and acetylene black powder, which is a conductive material, in a mortar at a mass ratio of 60:37: 3.

(Manufacturing of solid-state lithium secondary battery)
A positive electrode mixture powder pellet was prepared by filling 14.5 mg of the positive electrode mixture powder in an insulating cylinder (φ9 mm) of a closed cell and uniaxially molding at 500 MPa. The obtained positive electrode pellets were transferred into an insulating cylinder (φ10.5 mm) of a closed cell, and 100 mg of solid electrolyte powder was filled on the positive electrode pellets. Next, after uniaxial molding at 184 MPa together with the positive electrode mixture pellets, 18 mg of graphite (Gr) powder was filled on the solid electrolyte, and uniaxial molding was performed at 551 MPa. Further, it was tightened with a pressure screw to prepare a solid lithium secondary battery.

(Battery characteristic evaluation)
The solid-state lithium secondary batteries of Examples and Comparative Examples were charged at a constant current of 0.3 C up to a final charge voltage of 4.5 V in one cycle. Then, constant voltage charging was performed at 4.5 V until the current value became 0.01 C. At the time of discharge, constant current discharge was performed up to 2.5 V at 0.3 C. The operating voltage at 0.5 mAh / g discharge from the start of discharge was defined as the initial discharge voltage, and the voltage dropped was obtained by subtracting the initial discharge voltage from 4.5 V. The value obtained by subtracting the voltage drop of Comparative Example 1 from the voltage drop of Example 1 is divided by the voltage drop of Comparative Example 1 and multiplied by 100, and the obtained value is used as the discharge initial voltage drop improvement rate and is shown in the table. did.

As is clear from the results shown in Table 1, the solid-state battery using the positive electrode active material obtained in Example 1 has a smaller voltage drop at the initial stage of discharge than the comparative example, and can maintain a high operating voltage at the initial stage of discharge. You can see that.

Claims (13)

An active material used in solid-state batteries
In the radial distribution function obtained by measuring the X-ray absorption fine structure, at least one peak is observed in the range of 0.115 nm or more and 0.144 nm or less, and the active material is more than 0.310 nm and 0.340 nm or less. At least one peak is observed in the range of
The active material is an active material having core material particles and a coating layer arranged on the surface of the core material particles, and a halogen element is present on or near the surface of the core material particles. An active material used in solid-state batteries
In the radial distribution function obtained by measuring the X-ray absorption fine structure, at least one peak is observed in the range of 0.115 nm or more and 0.145 nm or less, and the active material is more than 0.310 nm and 0.340 nm or less. At least one peak is observed in the range of
The active material has core material particles and a coating layer arranged on the surface of the core material particles.
An active material in which a peak peak is observed when the binding energy of Li1s measured by X-ray photoelectron spectroscopy (XPS) is 54.0 eV or more and 55.4 eV or less. The coating layer comprises a lithium (Li) element, an element A (A is one or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W and Al) and oxygen (O). The active material according to claim 1 or 2, which comprises a compound containing an element. The amount of halogen (X) element (ppm) measured by ion chromatography after thermal decomposition of the active material with respect to the amount of element A (mass%) measured by inductively coupled plasma emission spectroscopy by completely dissolving the active material. The active material according to claim 3, wherein the mass ratio (X / A) of) is 0.5 × 10 ^-4 or more. According to claim 3 or 4, the mol ratio (X / A) of the amount of halogen (X) element to the amount of element A present on the surface of the core material particles measured by X-ray photoelectron spectroscopy is 0.011 or more. The active material described. Claimed that the mol ratio (Li / A) of the amount of lithium (Li) element to the amount of element A existing on the surface of the core material particles measured by X-ray photoelectron spectroscopy is 0.5 or more and 33.3 or less. Item 2. The active material according to any one of Items 3 to 5. The active material according to any one of claims 1 to 6, wherein the halogen (X) element is a 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. Claims 1 to 8 in which the value of B / A, which is the ratio of the water content B (mass ppm) up to 110 ° C. measured by the Carl Fisher 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 the above. A positive electrode mixture containing the active material according to any one of claims 1 to 9 and a solid electrolyte. The positive electrode mixture according to claim 10, wherein the solid electrolyte contains a lithium (Li) element, a phosphorus (P) element, and a sulfur (S) element, and has lithium ion conductivity. The positive electrode mixture according to claim 11, wherein the solid electrolyte has a crystal phase having an algyrodite type structure. In a solid-state battery provided with a positive electrode layer, a negative electrode layer, and a solid electrolyte layer,
A solid-state battery in which the positive electrode layer contains the active material according to any one of claims 1 to 9.