JP7460437B2 - Positive electrode active material, positive electrode, lithium ion secondary battery, and method for producing positive electrode active material - Google Patents

Description

The present invention relates to a positive electrode active material, a positive electrode, a lithium ion secondary battery, and a method for producing a positive electrode active material.

Lithium-ion secondary batteries are already being put into practical use not only as small power supplies for mobile phones and notebook computers, but also as medium- and large-scale power supplies for automobiles and power storage applications. As a lithium ion secondary battery, a structure having a positive electrode having a positive electrode active material, a negative electrode, and an electrolyte in contact with the positive electrode and the negative electrode is known.

As electrolytes used in lithium ion secondary batteries, electrolytes containing organic solvents and solid electrolytes are known. In the following description, the electrolytic solution and the solid electrolyte may be collectively referred to as a "nonaqueous electrolyte."

At the interface between the positive electrode and the non-aqueous electrolyte, the positive electrode active material of the positive electrode is in contact with the non-aqueous electrolyte. In a lithium-ion secondary battery, lithium ions are inserted from the non-aqueous electrolyte into the positive electrode active material and desorbed from the positive electrode active material to the non-aqueous electrolyte in response to charging and discharging of the battery.

In the past, in the development of lithium-ion secondary batteries, studies have been conducted on improving the battery performance of lithium-ion secondary batteries by coating the particle surface of the positive electrode active material, which is closely related to the insertion and desorption of the above-mentioned ions, with a coating layer of lithium metal composite oxide (see, for example, Patent Documents 1 and 2).

Japanese Patent Application Publication No. 2010-170715 JP 2018-116903 Publication

As the application fields of lithium-ion secondary batteries advance, further improvements in the charge and discharge characteristics of the positive electrode active material of lithium-ion secondary batteries are required. For example, batteries for mobile devices such as electric cars and electric motorcycles are required to provide large output during high-voltage operation and to enable rapid charging. Lithium-ion secondary batteries used for such applications are required to have the characteristics that enable charging and discharging at high currents (high rates), known as "rate characteristics." "Good rate characteristics" means that they are easy to charge and discharge at large currents.

To further improve the rate characteristics of lithium-ion secondary batteries, there is room for further improvement in the positive electrode active materials described in Patent Documents 1 and 2.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a positive electrode active material exhibiting excellent rate characteristics. Another object of the present invention is to provide a positive electrode and a lithium ion secondary battery having such a positive electrode active material. Another object of the present invention is to provide a method for producing a positive electrode active material that enables efficient production of a positive electrode active material having excellent rate characteristics.

In order to solve the above problems, the present invention includes the following aspects:

[1] A core particle having a lithium metal composite oxide as a forming material and a coating layer covering at least a portion of the core particle, the lithium metal composite oxide having a layered crystal structure. , and contains at least lithium and a transition metal, and the coating layer satisfies the following (1) to (3).
(1) The coating layer is formed using an oxide containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr, and Ge.
(2) The average thickness of the coating layer is 1 nm or more and less than 100 nm.
(3) The Si element ratio α obtained from the XPS analysis results of the coating layer and the sum β of the element ratios of the transition metal and the coating element obtained from the XPS analysis results of the coating layer. α/(α+β) is 0.02 or more.

[2] In the XPS analysis of the coating layer, A/α obtained from the Si element ratio α and the total element ratio A of the coating elements is 1.0 or more and 10.0 or less [1] The positive electrode active material described.

[3] The coating layer is made of at least one oxide selected from the group consisting of Nb ₂ O ₅ , Ta ₂ O ₅ , TiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , WO ₃ , ZrO ₂ and GeO ₂ The positive electrode active material according to [1] or [2], wherein the main component is amorphous.

[4] The transition metal is at least selected from the group consisting of Ni, Co, Mn, Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V. The positive electrode active material according to any one of [1] to [3], which is one type.

[5] The positive electrode active material according to [4], wherein the lithium metal composite oxide is represented by the following formula (1):
Li[Li _x (Ni _(1-y-z-w) Co _y Mn _z M _w ) _1-x ] O ₂ ... (1)
(wherein M is at least one element selected from the group consisting of Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V, and satisfies -0.10≦x≦0.30, 0<y≦0.40, 0≦z≦0.40, and 0≦w≦0.10.)

[6] The positive electrode active material according to [5], which satisfies 1-yz-w≧0.50 and y≦0.30 in the above formula (1).

[7] A positive electrode having a positive electrode active material layer containing the positive electrode active material according to any one of [1] to [6].

[8] The positive electrode according to [7], further comprising a solid electrolyte.

[9] A lithium ion secondary battery comprising the positive electrode according to [7] or [8], a negative electrode, and a nonaqueous electrolyte sandwiched between the positive electrode and the negative electrode.

[10] The lithium ion secondary battery according to [9], wherein the non-aqueous electrolyte is a solid electrolyte.

[11] The lithium ion secondary battery according to [10], wherein the positive electrode contains the same material as the solid electrolyte that constitutes the nonaqueous electrolyte.

[12] The lithium ion secondary battery according to [11], wherein the positive electrode active material layer includes the positive electrode active material and the solid electrolyte.

[13] A lithium ion secondary battery according to any one of [10] to [12], in which the solid electrolyte constituting the non-aqueous electrolyte has an amorphous structure.

[14] The lithium ion secondary battery according to any one of [10] to [13], wherein the solid electrolyte constituting the nonaqueous electrolyte is an oxide solid electrolyte.

[15] A method for producing a positive electrode active material, comprising the steps of: reacting lithium metal composite oxide particles dispersed in a first dispersion liquid with a surface treatment agent to obtain a first reaction product; adding a compound containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr, and Ge to a second dispersion liquid in which the first reaction product is dispersed in a dispersion medium; dripping water or a basic aqueous solution into the second dispersion liquid to which the compound has been added to obtain a second reaction product; and drying the second reaction product, wherein the lithium metal composite oxide has a layered crystal structure and contains at least lithium and a transition metal, and the surface treatment agent is a silane coupling agent having a first functional group capable of coordinating with the coating element and a second functional group capable of bonding to the lithium metal composite oxide.

[16] The method for producing a positive electrode active material according to [15], wherein the basic aqueous solution is added dropwise in the step of obtaining the second reaction product.

[17] After the drying step, the method for producing a positive electrode active material according to [15] or [16], further comprising a step of heat-treating the dried product obtained in the drying step at 100° C. or higher and 800° C. or lower.

[18] The method for producing a positive electrode active material according to any one of [15] to [17], wherein the first functional group is an amino group.

[19] A method for producing a positive electrode active material according to any one of [15] to [18], wherein the second functional group is an alkoxy group.

[20] The method for producing a positive electrode active material according to any one of [15] to [19], wherein the compound is an alkoxide containing the coating element.

[21] Any one of [15] to [20], further comprising a step of adding a monodentate ligand to the second dispersion between the step of adding the compound and the step of obtaining the second reaction product. A method for producing a positive electrode active material according to item 1.

[22] The method for producing a positive electrode active material according to [21], wherein the monodentate ligand is acetonitrile.

According to the present invention, it is possible to provide a positive electrode active material that exhibits excellent rate characteristics. It is also possible to provide a positive electrode and a lithium ion secondary battery that have such a positive electrode active material. It is also possible to provide a method for producing a positive electrode active material that enables efficient production of a positive electrode active material that has excellent rate characteristics.

FIG. 1 is a line profile showing an example of the analysis result of STEM-EDX of the positive electrode active material of this embodiment. FIG. 2 is a line profile showing an example of the analysis result of STEM-EDX of the positive electrode active material of this embodiment. FIG. 3A is a schematic diagram showing an example of a lithium ion secondary battery. FIG. 3B is a schematic diagram showing an example of a lithium ion secondary battery. FIG. 4 is a schematic diagram showing a laminate included in an all-solid-state lithium ion secondary battery. FIG. 5 is a schematic diagram showing the overall configuration of an all-solid-state lithium ion secondary battery. FIG. 6 is a graph showing the evaluation results of rate characteristics.

<Cathode active material>
The positive electrode active material of this embodiment includes core particles made of a lithium metal composite oxide and a coating layer that covers at least a portion of the core particles.

Moreover, the positive electrode active material of this embodiment satisfies the following requirements (1) to (3).
(1) The coating layer is formed from an oxide containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr and Ge.
(2) The average thickness of the coating layer is 1 nm or more and less than 100 nm.
(3) The Si element ratio α obtained from the results of XPS analysis of the coating layer and the total element ratio β of the transition metal, Al, and B obtained from the results of XPS analysis of the coating layer, α/(α+β), is 0.1 or more.
The following explains each in order.

(Lithium metal composite oxide)
The lithium metal composite oxide contained in the positive electrode active material of this embodiment has a layered crystal structure and contains at least Li and a transition metal.

The lithium metal composite oxide contained in the positive electrode active material of this embodiment contains at least one transition metal selected from the group consisting of Ni, Co, Mn, Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V.

The lithium metal composite oxide contained in the positive electrode active material of this embodiment contains at least one transition metal selected from the group consisting of Ni, Co, Mn, Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V, and the resulting lithium metal composite oxide forms a stable crystal structure from which Li ions can be desorbed or inserted. Therefore, when the positive electrode active material of this embodiment is used in the positive electrode of a secondary battery, a high charge/discharge capacity can be obtained.

Further, the lithium metal composite oxide contained in the positive electrode active material of this embodiment is Ni, Co, Mn, Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti. , Nb, and V, the obtained lithium metal composite oxide has a strong crystal structure. Therefore, the positive electrode active material of this embodiment becomes a positive electrode active material whose crystal structure is difficult to break even when it is charged and discharged at a high rate.

More specifically, the lithium metal composite oxide is represented by the following composition formula (1).
Li[Li _x (Ni _(1-y-z-w) Co _y Mn _z M _w ) _1-x ] O ₂ ... (1)
(wherein M is one or more elements selected from the group consisting of Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V, and satisfies -0.1≦x≦0.30, 0≦y≦0.40, 0≦z≦0.40, and 0≦w≦0.10.)

(About x)
From the viewpoint of obtaining a lithium ion secondary battery having good cycle characteristics, x in the composition formula (1) is preferably more than 0, more preferably 0.01 or more, and even more preferably 0.02 or more. Moreover, from the viewpoint of obtaining a lithium ion secondary battery having a higher initial coulombic efficiency, x in the composition formula (1) is preferably 0.25 or less, and more preferably 0.10 or less.

In this specification, "good cycle characteristics" refers to characteristics in which the amount of decrease in battery capacity due to repeated charging and discharging is small, and the capacity ratio when remeasured to the initial capacity is unlikely to decrease.

In addition, in this specification, "initial coulombic efficiency" is a value calculated by "(initial discharge capacity)/(initial charge capacity) x 100 (%)". A secondary battery with a high initial coulombic efficiency has a small irreversible capacity during the first charge/discharge and tends to have a larger capacity per volume and weight.

The upper and lower limits of x can be combined in any combination. In the above composition formula (1), x may be -0.10 or more and 0.25 or less, or -0.10 or more and 0.10 or less.

x may be greater than 0 and less than or equal to 0.30, greater than 0 and less than or equal to 0.25, or greater than 0 and less than or equal to 0.10.

x may be 0.01 or more and 0.30 or less, 0.01 or more and 0.25 or less, or 0.01 or more and 0.10 or less.

x may be 0.02 or more and 0.3 or less, 0.02 or more and 0.25 or less, or 0.02 or more and 0.10 or less.

In this embodiment, it is preferable that 0<x≦0.30.

(Regarding y)
From the viewpoint of obtaining a lithium ion secondary battery having a low internal resistance, y in the composition formula (1) is preferably more than 0, more preferably 0.005 or more, even more preferably 0.01 or more, and particularly preferably 0.05 or more. From the viewpoint of obtaining a lithium ion secondary battery having high thermal stability, y in the composition formula (1) is more preferably 0.35 or less, even more preferably 0.33 or less, and even more preferably 0.30 or less.

The upper and lower limits of y can be arbitrarily combined. In the above compositional formula (1), y may be 0 or more and 0.35 or less, 0 or more and 0.33 or less, or 0 or more and 0.30 or less.

y may be greater than 0 and not greater than 0.40, greater than 0 and not greater than 0.35, greater than 0 and not greater than 0.33, or greater than 0 and not greater than 0.30.

y may be 0.005 or more and 0.40 or less, 0.005 or more and 0.35 or less, 0.005 or more and 0.33 or less, 0.005 or more and 0. It may be .30 or less.

y may be 0.01 or more and 0.40 or less, 0.01 or more and 0.35 or less, 0.01 or more and 0.33 or less, and 0.01 or more and 0. It may be .30 or less.

y may be 0.05 or more and 0.40 or less, 0.05 or more and 0.35 or less, 0.05 or more and 0.33 or less, or 0.05 or more and 0.30 or less.

In this embodiment, it is preferable that 0<y≦0.40.

In this embodiment, it is more preferable that in composition formula (1), 0<x≦0.10 and 0<y≦0.40.

(About z)
Further, from the viewpoint of obtaining a lithium ion secondary battery with high cycle characteristics, z in the compositional formula (1) is preferably 0.01 or more, more preferably 0.02 or more, and 0.1 or more. It is more preferable that Further, from the viewpoint of obtaining a lithium ion secondary battery with high storage stability at high temperatures (for example, in a 60°C environment), z in the composition formula (1) is preferably 0.39 or less, and 0.38 or less. It is more preferably 0.35 or less, and even more preferably 0.35 or less.

The upper and lower limits of z can be arbitrarily combined. In the above compositional formula (1), z may be 0 or more and 0.39 or less, 0 or more and 0.38 or less, or 0 or more and 0.35 or less.

z may be 0.01 or more and 0.40 or less, 0.01 or more and 0.39 or less, 0.01 or more and 0.38 or less, and 0.01 or more and 0. It may be .35 or less.

z may be 0.02 or more and 0.40 or less, 0.02 or more and 0.39 or less, 0.02 or more and 0.38 or less, and 0.02 or more and 0. It may be .35 or less.

z may be 0.10 or more and 0.40 or less, 0.10 or more and 0.39 or less, 0.10 or more and 0.38 or less, or 0.10 or more and 0.35 or less.

(About w)
Furthermore, from the viewpoint of obtaining a lithium ion secondary battery with low internal resistance, w in the compositional formula (1) is preferably greater than 0, more preferably 0.0005 or more, and more preferably 0.001 or more. It is even more preferable that there be. Further, from the viewpoint of obtaining a lithium ion secondary battery with a large discharge capacity at a high current rate, w in the composition formula (1) is preferably 0.09 or less, more preferably 0.08 or less, More preferably, it is 0.07 or less.

The upper and lower limits of w can be combined in any combination. In the above composition formula (1), w may be 0 or more and 0.09 or less, 0 or more and 0.08 or less, or 0 or more and 0.07 or less.

w may be more than 0 and less than or equal to 0.10, more than 0 and less than or equal to 0.09, more than 0 and less than or equal to 0.08, more than 0 and less than or equal to 0.07 There may be.

w may be from 0.0005 to 0.10, from 0.0005 to 0.09, from 0.0005 to 0.08, from 0.0005 to 0. It may be .07 or less.

w may be from 0.001 to 0.10, from 0.001 to 0.09, from 0.001 to 0.08, from 0.001 to 0. It may be .07 or less.

(Regarding y + z + w)
In addition, from the viewpoint of obtaining a lithium ion secondary battery with a large battery capacity, in this embodiment, y+z+w in the composition formula (1) is preferably 0.50 or less, more preferably 0.48 or less, and even more preferably 0.46 or less.

The lithium metal composite oxide contained in the positive electrode active material of this embodiment preferably satisfies 1-yz-w≧0.50 and y≦0.30 in compositional formula (1). That is, the lithium metal composite oxide contained in the positive electrode active material of the present embodiment has a Ni content molar ratio of 0.50 or more and a Co content molar ratio of 0.30 or less in composition formula (1). preferable.

(About M)
In the composition formula (1), M represents one or more elements selected from the group consisting of Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb and V.

Furthermore, from the viewpoint of obtaining a lithium ion secondary battery with high cycle characteristics, M in compositional formula (1) may be one or more elements selected from the group consisting of Mg, Al, W, B, and Zr. Preferably, it is more preferably one or more elements selected from the group consisting of Al and Zr. Further, from the viewpoint of obtaining a lithium ion secondary battery with high thermal stability, it is preferable that the element is one or more elements selected from the group consisting of Al, W, B, and Zr.

An example of a preferable combination of x, y, z, and w described above is that x is 0.02 or more and 0.3 or less, y is 0.05 or more and 0.30 or less, and z is 0.02 or more and 0.30 or less. 35 or less, and w is 0 or more and 0.07 or less.

Examples of lithium metal oxides having preferable combinations of x, y, z, and w include lithium metal composite oxides in which x=0.05, y=0.20, z=0.30, and w=0; Lithium metal composite oxide where x = 0.05, y = 0.08, z = 0.04, w = 0, x = 0.25, y = 0.07, z = 0.02, w = Examples include lithium metal composite oxides having a

In this embodiment, the composition analysis of the lithium metal composite oxide can be performed by dissolving the lithium metal composite oxide in hydrochloric acid and then using an inductively coupled plasma emission spectrometer (e.g., SPS3000, manufactured by SII NanoTechnology Inc.).

(Crystal structure)
In this embodiment, the lithium metal composite oxide has a layered crystal structure, and more preferably has a hexagonal crystal structure or a monoclinic crystal structure.

The hexagonal crystal structure is P3, P3 ₁ , P3 ₂ , R3, P-3, R-3, P312, P321, P3 ₁ 12, P3 ₁ 21, P3 _{2 12, P3 2 21} , R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P6 ₁ , P6 ₅ , P6 ₂ , P6 ₄ , P6 ₃ , P-6, P6/m, P6 ₃ /m, P622, P6 ₁ 22, P6 ₅ 22, P6 ₂ 22, P6 ₄ 22, P6 ₃ 22, P6mm, P6cc, P6 ₃ It is assigned to any one space group selected from the group consisting of P6/cm, P6 ₃ mc, P-6m2, P-6c2, P-62m, P-62c, P6/mmm, P6/mcc, P6 ₃ /mcm and P6 ₃ /mmc.

In addition, the monoclinic crystal structure belongs to any one space group selected from the group consisting of P2, _P21 , C2, Pm, Pc, Cm, Cc, P2/m, _P21 /m, C2/m, P2/c, _P21 /c and C2/c.

Of these, in order to obtain a lithium ion secondary battery with a high discharge capacity, it is particularly preferable that the crystal structure is a hexagonal crystal structure belonging to the space group R-3m, or a monoclinic crystal structure belonging to the space group C2/m.

(Coating layer: Requirement (1))
The coating layer of the positive electrode of this embodiment is formed using an oxide containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr, and Ge.

The presence of the above-mentioned coating elements in the coating layer was confirmed by analysis using a scanning transmission electron microscope (STEM)-Energy Dispersive X-ray Spectroscopy (EDX). Can be confirmed.

Specifically, a sample is prepared by forming particles of lithium metal composite oxide into a thin film using a commonly known method such as focused ion beam (FIB). Next, the obtained sample is placed on a Cu mesh, irradiated with an electron beam with an accelerating voltage of 200 kV, and STEM observation (photographing of a bright field image and a dark field image) is performed.

Next, EDX analysis is performed in the same field of view as the STEM observation range. Characteristic X-rays are generated for each particle in the field of view by electron beam excitation, and an X-ray spectrum containing characteristic X-rays of multiple elements contained in the measurement position is obtained. The number of characteristic X-rays (count number, intensity) of each element contained in the measured spectrum corresponds to the concentration of each element.

Next, for any particle included in the field of view, the coating elements (Nb, Ta, Ti, Al, B, W, Zr, and Ge) contained in the coating layer are measured along an imaginary line set from the outside of the particle to the center of the particle. Obtain a line profile of concentration. At the same time, a line profile of the concentration of transition metals contained in the core particles is obtained.

The line profile is created by plotting the X-ray spectrum intensity for each distance from the outside of the particle, with the horizontal axis being the distance from the outside of the particle along a virtual line set from the outside of the particle to the center (unit: nm) and the vertical axis being the characteristic X-ray spectrum intensity (unit: X-ray count number, arbitrary unit: a.u.) of each element in the range where the outer edge and coating layer of the particle can be confirmed.

At this time, the line profile of the coating element is compared with the line profile of the elements contained in the core particle, and if the line profile of the coating element is obtained as a continuous shape with a peak outside the core particle, it can be determined that a coating layer containing the detected coating element is present on the surface of the core particle.
The method of defining the "surface of a core particle" using a line profile will be described later.
The term "outside the core particle" means the positive electrode active material particle surface side relative to the surface of the core particle defined by the method described below.

The material for forming such a coating layer is at least one selected from the group consisting of Nb ₂ O ₅ , Ta ₂ O ₅ , TiO ₂ , Al ₂ O ₃ , WO ₃ , B ₂ O ₃ , ZrO ₃ and GeO _{2 .} Preferably, the main component is an oxide of a species. These oxides (main components of the coating layer) are preferably amorphous. The fact that these oxides are amorphous is demonstrated by the fact that in the coating layer identified by the method described above, when the coating layer was magnified 10 million times by STEM observation, a regular atomic arrangement derived from the crystal structure was observed. This can be determined from the fact that it is not.

Regarding the material forming the covering layer, "containing the above-mentioned oxide as a main component" means that the content of the above-mentioned oxide is the highest among the materials forming the covering layer. The content of the oxide in the entire coating layer is preferably 50 mol% or more, more preferably 60 mol% or more. Moreover, the content rate of the said oxide with respect to the whole coating layer is preferably 90 mol% or less.

The remainder of the material for forming the coating layer, excluding the above-mentioned oxide, is a reaction residue generated during the formation of the coating layer. Specifically, it includes reaction residues produced by the production method described below.

(Coating layer: requirement (2))
The average thickness of the coating layer included in the positive electrode active material of this embodiment is 1 nm or more and less than 100 nm. The average thickness of the coating layer is preferably 1.5 nm or more, more preferably 2.0 nm or more. Further, the average thickness of the coating layer is preferably 50 nm or less, more preferably 30 nm or less.

The upper and lower limits of the average thickness of the coating layer can be arbitrarily combined. In the positive electrode active material of this embodiment, the average thickness of the coating layer may be 1.5 nm or more and 100 nm or less, or 2.0 nm or more and 100 nm or less. Moreover, the average thickness of the coating layer may be 1 nm or more and 50 nm or less, 1.5 nm or more and 50 nm or less, or 2.0 nm or more and 50 nm or less. Furthermore, the average thickness of the coating layer may be 1 nm or more and 30 nm or less, 1.5 nm or more and 30 nm or less, or 2.0 nm or more and 30 nm or less.

In this embodiment, the average thickness of the coating layer is determined based on the analysis results using a scanning transmission electron microscope (STEM)-energy dispersive X-ray spectroscopy (EDX). demand.

Figures 1 and 2 are line profiles showing an example of the results of STEM-EDX analysis of the positive electrode active material of this embodiment. The horizontal axis indicates the measurement position (unit: nm) from the outside of the particle toward the center of the particle. The origin side of the horizontal axis is the outside of the particle, and the + side of the horizontal axis is the center of the particle. The vertical axis indicates the detected amount of each element (unit: X-ray count number, arbitrary unit a.u.).

FIG. 1 shows the case where a positive electrode active material having a core particle of a lithium metal composite oxide containing Ni as a transition metal and a coating layer containing Nb as a coating element on the surface of the core particle is analyzed. FIG. 1 shows the case where Nb exists only in the coating layer.

(Identification of the surface of the core particle)
First, the position of the surface of the core particle is specified.
Perform STEM-EDX analysis of the cross section of the positive electrode active material to identify the element that is detected with the highest sensitivity, that is, the element that is contained in the highest concentration among the transition metals that are not contained in the coating layer but are contained only in the core particles. . In the description of this specification, it is assumed that the element detected with the highest sensitivity is Ni.

Next, a line profile for Ni is created from the outside of the particle toward the center of the particle based on the STEM-EDX analysis results. Concerning the Ni line profile, a range in which positive values are continuously detected for 30 nm or more from the outside of the particle toward the center of the particle is confirmed, and a starting point A outside the particle in this range is determined.

Next, when the detected amount of Ni at position B, which is 20 nm from the starting point A toward the center of the particle, is defined as X, the position C, which is the position where the detected amount of Ni is X/2 and is closest to the starting point A, is the core particle. The surface of

(Identification of the surface of the coating layer)
Next, the location of the surface of the coating layer is identified.
A line profile based on the analysis results of STEM-EDX is created for coating elements that overlap with position C and are continuously detected as positive values from the outside of the particle toward the center of the particle. In the description of this specification, the line profile of Nb is created.

Next, when the maximum value of the Nb line profile is located outside the particle from position C, it is defined that a coating layer exists. In FIG. 1, since the peak position D of the Nb line profile is located outside the particle from the position C, it can be determined that a coating layer exists.

Next, when the detected amount of Nb at position D is Y, position E, which is a position where the detected amount of Nb is Y/2 outside the particle from position D and is closest to position D, is defined as the surface of the coating layer. stipulate.

Then, the distance L between position E and position C is the thickness of the coating layer.

The above measurement is carried out three times, and the arithmetic average of the thicknesses of each coating layer is the desired thickness of the coating layer. When calculating the average, if no coating layer is present, it is treated as 0 nm.

Figure 2 shows the analysis of a positive electrode active material in which the core particles are lithium metal composite oxides containing Ni and Nb as transition metals, and the surface of the core particles has a coating layer containing Nb as a coating element.

As shown in the figure, when the lithium metal composite oxide and the coating layer contain the common element Nb, it is thought that the line profile of Nb continues uninterrupted from the outside of the particle toward the center of the particle. Therefore, if the focus is only on Nb, the surface of the core particle cannot be detected, and the thickness of the coating layer cannot be measured.

On the other hand, according to the above method, the surface of the core particle is first determined from the line profile of the transition metal contained only in the core particle, and then the surface of the coating layer is determined, so that the surface of the core particle and the coating layer are common to each other. The thickness of the coating layer can also be determined when it contains elements.

(Covering layer: requirement (3))
In the coating layer of the positive electrode active material of this embodiment, Si element is detected in the XPS analysis of the coating layer.

As will be described in detail later, the coating layer of the positive electrode active material of this embodiment is manufactured by a method using a silane coupling agent. Therefore, when the positive electrode active material having the coating layer is subjected to XPS analysis, photoelectrons corresponding to the bond energy of the Si element are detected as a trace of the use of the silane coupling agent. In the positive electrode active material of this embodiment, if the coating layer is manufactured using an amount of the silane coupling agent that satisfies the requirement (3), it is determined that the coating layer covers the surface of the core particle in the desired state.

In this embodiment, the Si contained in the coating layer is determined by the results of analysis using XPS.

Specifically, the surface composition of the positive electrode active material is analyzed under the following conditions to obtain a narrow scan spectrum of elements on the surface of the positive electrode active material.
Measurement method: X-ray photoelectron spectroscopy (XPS)
X-ray source: AlKα radiation (1486.6 eV)
X-ray spot diameter: 100 μm
Neutralization conditions: neutralization electron gun (accelerating voltage 0.3 V, current 100 μA)

The detection depth of XPS under the above conditions is within a range of approximately 3 nm from the surface of the positive electrode active material. In the positive electrode active material, in areas where the coating layer is thin or there is no coating layer, not only the coating layer but also the surface of the core particle is analyzed.

The integral value of the Si2p waveform is used as the photoelectron intensity of Si.

In addition, in the same XPS analysis, the transition metals contained in the lithium metal composite oxide existing inside the coating layer, Nb, Ta, Ti, Al, B, W, Zr, and Ge contained in the coating layer were also analyzed for each element. A photoelectron corresponding to the binding energy of is detected.

The peaks corresponding to each element can be identified using existing databases.
For example, the integral value of the waveform of Ni2p3/2 is used as the photoelectron intensity of Ni.

As the photoelectron intensity of Co, the integral value of the waveform of Co2p3/2 is used.

As the photoelectron intensity of Mn, the integral value of the waveform of Mn2p1/2 is used.

As the photoelectron intensity of Nb, the integral value of the waveform of Nb3d is used.

The integral value of the Ti2p waveform is used as the Ti photoelectron intensity.

The integral value of the waveform of Ta4f is used as the photoelectron intensity of Ta.

The integral value of the Al2p waveform is used as the photoelectron intensity of Al.

As the photoelectron intensity of B, the integral value of the waveform of B1s is used.

As the photoelectron intensity of W, the integral value of the waveform of W4f is used. However, when measuring at the same time as Ge, the background integral value of W4d is used.

As the photoelectron intensity of Zr, the integral value of the waveform of Zr3d is used.

As the photoelectron intensity of Ge, the integral value of the waveform of Ge2p is used.

The ratio of photoelectron intensities of each element in the obtained spectrum corresponds to the element ratio of the positive electrode active material determined by XPS measurement.

The positive electrode active material of the present embodiment is characterized in that the Si It contains silicon atoms to such an extent that the element ratio α' (α/(α+β)) is 0.02 or more.

Note that in the positive electrode active material to be measured, the coating layer and the lithium metal composite oxide may each contain a common element. In this case, the element ratio in the result of the XPS analysis is handled without distinguishing whether the element is contained in the coating layer or the lithium metal composite oxide.

For example, when Ti is contained in both the coating layer and the lithium metal composite oxide, the elemental ratio of Ti determined as a result of XPS analysis is the Ti contained in the lithium metal composite oxide and the Ti contained in the coating layer. Treated as the total elemental ratio with Ti.

It is preferable that α/(α+β) is 0.05 or more. It is also preferable that α/(α+β) is 0.5 or less, more preferably 0.3 or less, and even more preferably 0.2 or less.

The upper limit and lower limit of α/(α+β) can be arbitrarily combined. As a combination example, α/(α+β) is preferably 0.02 or more and 0.3 or less, and more preferably 0.05 or more and 0.2 or less.

(Covering layer: other provisions)
In addition, the positive electrode active material of this embodiment preferably has a ratio (A/α) of 1.0 to 10.0 of "total element ratio A of coating elements" to "Si element ratio α" obtained by XPS analysis of the coating layer measured by the above-mentioned method. More specifically, the total element ratio A of coating elements is "the total of Nb element ratio, Ta element ratio, Ti element ratio, Al element ratio, B element ratio, W element ratio, Zr element ratio, and Ge element ratio."

A/α is preferably 1.2 or more, more preferably 1.5 or more. Further, A/α is preferably 8.0 or less, more preferably 5.0 or less.

The upper and lower limit values of A/α can be combined in any way. As an example of a combination, A/α is preferably 1.2 or more and 8.0 or less, and more preferably 1.5 or more and 5.0 or less.

In the positive electrode active material configured as described above, the surface of the lithium metal composite oxide particle (core particle) is coated with the oxide of the coating element. Therefore, when the positive electrode active material is used as a positive electrode, direct contact between the lithium metal composite oxide and the electrolyte can be suppressed, and side reactions such as deterioration of the lithium metal composite oxide and decomposition of the electrolyte can be suppressed.

The material forming the coating layer described above is a chemically stable oxide and is resistant to oxidation reactions. Therefore, in the positive electrode active material having the above-mentioned coating layer, the coating layer effectively protects the core particles made of lithium metal composite oxide, and significantly suppresses the deterioration of the core particles. As a result, when the positive electrode active material of this embodiment is used as a material for the positive electrode of a battery and a high voltage is applied, the performance degradation caused by the deterioration of the positive electrode active material can be suppressed.

Furthermore, when the positive electrode active material is used as a positive electrode and a voltage is applied, it is believed that in the positive electrode active material, lithium ions diffuse from the lithium metal composite oxide constituting the core particle to the coating layer. Also, in the positive electrode active material having a coating layer with the above-mentioned average thickness, it is believed that lithium ions diffuse favorably throughout the entire coating layer. Therefore, in the positive electrode active material having a coating layer with the above-mentioned average thickness, it is believed that lithium ion conductivity is expressed even if the lithium ion conductivity of the oxide constituting the coating layer is low.

In this case, in the coating layer made of an oxide containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr, and Ge, lithium ions diffuse throughout the layer, resulting in high lithium ion conductivity.

As a result, the positive electrode active material having the above-mentioned configuration exhibits excellent rate characteristics and can improve battery performance when used in a positive electrode.

<Method for producing positive electrode active material>
Next, a method for manufacturing the positive electrode active material of this embodiment will be explained. The positive electrode active material of this embodiment is manufactured by first manufacturing a particulate lithium metal composite oxide and then forming a coating layer on the particle surface.

(Method for producing lithium metal composite oxide 1)
In manufacturing the lithium metal composite oxide contained in the positive electrode active material of this embodiment, first metals other than lithium, such as Ni, Co, Mn, Fe, Cu, Mg, Al, W, B, Mo, Zn , Sn, Zr, Ga, La, Ti, Nb, and V. A metal composite compound containing one or more arbitrary metals is prepared, and the metal composite compound is sintered with an appropriate lithium salt and an inert melting agent. It is preferable to do so. As the metal composite compound, a metal composite hydroxide or a metal composite oxide is preferable.

Below, an example of a method for producing lithium metal composite oxide is explained, divided into the process for producing the metal composite compound and the process for producing the lithium metal composite oxide.

(Metal composite compound manufacturing process)
The metal complex compound can be produced by a commonly known batch coprecipitation method or continuous coprecipitation method. Hereinafter, a method for producing the metal complex hydroxide containing nickel, cobalt, and manganese as metals will be described in detail.

First, a nickel salt solution, a cobalt salt solution, a manganese salt solution, and a complexing agent are reacted by a coprecipitation method, especially a continuous method described in JP-A No. 2002-201028, to form Ni _a Co _b Mn _c (OH). A metal composite hydroxide represented by ₂ (wherein a+b+c=1) is produced.

The nickel salt that is the solute of the nickel salt solution is not particularly limited, but may be, for example, one or more of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate.

The cobalt salt that is the solute of the cobalt salt solution may be, for example, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate.

As the manganese salt which is the solute of the manganese salt solution, for example, one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate can be used.

The above metal salts are used in a ratio corresponding to the composition ratio of the above Ni _a Co _b Mn _c (OH) _2. In addition, water is used as a solvent.

Complexing agents are compounds capable of forming complexes with nickel, cobalt, and manganese ions in aqueous solution. Examples include ammonium ion donors (ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine. A complexing agent may not be included, and if a complexing agent is included, the amount of the complexing agent contained in a mixed solution containing a nickel salt solution, a cobalt salt solution, an arbitrary metal M salt solution, and a complexing agent is For example, the molar ratio of the metal salt to the total number of moles is greater than 0 and less than 2.0.

During precipitation, in order to adjust the pH value of the aqueous solution, an alkali metal hydroxide (eg, sodium hydroxide, potassium hydroxide) is added if necessary.

In addition to the above nickel salt solution, cobalt salt solution, and manganese salt solution, when a complexing agent is continuously supplied to the reaction tank, nickel, cobalt, and manganese react, and Ni _a Co _b Mn _c (OH) ₂ is manufactured.

During the reaction, the temperature of the reaction tank is controlled within a range of, for example, 20°C or higher and 80°C or lower, preferably 30 to 70°C.

The pH value in the reaction tank is controlled within the range of, for example, pH 9 or more and pH 13 or less, preferably pH 11 or more and pH 13 or less.
In this specification, the pH value is defined as the value measured when the temperature of the aqueous solution is 40°C.

The substances in the reaction tank are appropriately stirred and mixed. The reaction vessel is of the type that allows the formed reaction precipitate to overflow for separation.

By appropriately controlling the concentration of metal salt supplied to the reaction tank, stirring speed, reaction temperature, reaction pH, and firing conditions described below, the secondary particle size of the lithium metal composite oxide finally obtained in the following process can be adjusted. , various physical properties such as pore radius can be controlled.

In addition to controlling the above conditions, various gases such as inert gases such as nitrogen, argon, and carbon dioxide, oxidizing gases such as air and oxygen, or mixed gases thereof are supplied into the reaction tank to obtain The oxidation state of the reaction product may also be controlled.

Compounds that can be used to oxidize the resulting reaction product include peroxides such as hydrogen peroxide, peroxide salts such as permanganates, perchlorates, hypochlorites, nitric acid, halogens, ozone, etc.

As a compound for reducing the resulting reaction product, organic acids such as oxalic acid and formic acid, sulfites, hydrazine, etc. can be used.

After the above reaction, the resulting reaction precipitate is washed with water and then dried to obtain a metal composite compound. In this embodiment, nickel cobalt manganese hydroxide as a nickel cobalt manganese composite compound is obtained as the metal composite compound. Further, if necessary, the reaction precipitate may be washed with weak acid water or an alkaline solution containing sodium hydroxide or potassium hydroxide.

In this embodiment, the metal composite compound obtained by drying is crushed by applying an appropriate external force and adjusting the dispersion state of the particles, thereby obtaining a metal composite hydroxide in which the requirements (2) and (3) can be easily controlled within the range of this embodiment.

The term "appropriate external force" refers to an external force that disperses the aggregated state without destroying the crystallites of the metal composite compound. In this embodiment, it is preferable to use a grinder as the grinding machine during the above-mentioned grinding, and a stone mill type grinder is particularly preferable. When a stone mill type grinder is used, it is preferable to adjust the clearance between the upper mill and the lower mill according to the aggregated state of the metal composite hydroxide.
The clearance between the upper mill and the lower mill is preferably in the range of, for example, 10 μm or more and 200 μm or less.

In the above example, nickel-cobalt-manganese composite hydroxide is produced, but nickel-cobalt-manganese composite oxide may also be prepared.

For example, a nickel cobalt manganese composite oxide can be prepared by firing a nickel cobalt manganese composite hydroxide. As for the firing time, it is preferable that the total time from the start of temperature increase to the end of temperature maintenance is 1 hour or more and 30 hours or less. The temperature increase rate in the heating step to reach the maximum holding temperature is preferably 180°C/hr or more, more preferably 200°C/hr or more, and particularly preferably 250°C/hr or more.

In this specification, the maximum holding temperature refers to the maximum temperature held in the atmosphere inside the firing furnace during the firing process, and means the firing temperature during the firing process. In the case of a main firing process that has multiple heating steps, the maximum holding temperature means the maximum temperature during each heating step.

In this specification, the temperature increase rate refers to the time from the start of temperature increase until reaching the maximum holding temperature in the firing apparatus, and the time from the temperature at the start of temperature increase in the firing furnace of the firing apparatus to the maximum holding temperature. It is calculated from the temperature difference.

(Production process of lithium metal composite oxide)
The lithium metal composite oxide can be produced by mixing a metal composite oxide or metal composite hydroxide with a lithium salt, and then calcining the resulting mixture.

First, the metal composite oxide or metal composite hydroxide is dried and then mixed with a lithium salt. Moreover, in this embodiment, it is preferable to further mix an inert melting agent into the mixture of the metal composite oxide or metal composite hydroxide and the lithium salt.

By firing a mixture containing a metal composite oxide or metal hydroxide, a lithium salt, and an inert melting agent, the mixture of the metal composite oxide or metal composite hydroxide and the lithium salt can be made into an inert mixture. It will be fired in the presence of an active melting agent. By firing in the presence of an inert melting agent, it is possible to suppress the primary particles of the lithium metal composite oxide produced in the firing from sintering with each other and the generation of secondary particles. Moreover, the primary particles of the lithium metal composite oxide tend to grow independently from the secondary particles.

In this embodiment, a primary particle that does not aggregate and exists independently from other particles is referred to as a "single particle."
In addition, aggregated particles produced by aggregation of primary particles produced in a reaction are referred to as "secondary particles."
That is, the particles generated by the reaction consist of single particles and secondary particles.

In this embodiment, drying conditions are not particularly limited.
For example, conditions under which metal composite oxides or metal composite hydroxides are not oxidized or reduced (oxides are maintained as oxides, hydroxides are maintained as hydroxides), metal composite hydroxides are Any of the conditions for oxidation (a hydroxide is oxidized to an oxide) and the condition for a reduction of a metal composite oxide (an oxide is reduced to a hydroxide) may be used.

To prevent the metal composite oxide or metal composite hydroxide from being oxidized or reduced, it is advisable to dry it in an environment using an inert gas such as nitrogen, helium, or argon.

To oxidize the metal complex hydroxide, it is recommended to dry it in an environment using oxygen or air.

Further, in order to reduce the metal composite oxide, it is preferable to dry it in an environment using a reducing agent such as hydrazine or sodium sulfite in an inert gas atmosphere.

As the lithium salt, any one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, and lithium oxide, or a mixture of two or more of them, can be used.

After drying the metal composite oxide or metal composite hydroxide, classification may be performed as appropriate.

The lithium salt and the metal composite hydroxide are used in consideration of the composition ratio of the final product. For example, when a nickel-cobalt-manganese composite hydroxide is used, the lithium salt and the metal composite hydroxide are used in a ratio corresponding to the composition ratio of LiNi _a Co _b Mn _c O ₂ (wherein a + b + c = 1). In addition, when the lithium metal composite oxide, which is the final product, contains an excess of lithium (the molar ratio of the lithium contained in the lithium salt exceeds 1), the lithium and the metal element contained in the metal composite hydroxide are mixed in a ratio that exceeds 1.

A lithium-nickel cobalt manganese composite oxide is obtained by firing a mixture of a nickel cobalt manganese metal composite hydroxide and a lithium salt. Note that dry air, an oxygen atmosphere, an inert atmosphere, etc. are used for the firing depending on the desired composition, and a plurality of heating steps are performed if necessary.

In this embodiment, the mixture may be fired in the presence of an inert melting agent. Calcining in the presence of an inert melting agent can accelerate the reaction of the mixture. The inert melting agent may remain in the lithium metal composite oxide after firing, or may be removed by washing with water or alcohol after firing. In this embodiment, the lithium metal composite oxide after firing is preferably washed using water or alcohol.

By adjusting the holding temperature during firing, the particle diameter of the single particles of the obtained lithium metal composite oxide can be controlled within the preferred range of this embodiment.

Generally, the higher the holding temperature is, the larger the particle size of a single particle of the lithium metal composite oxide tends to be, and the BET specific surface area tends to be smaller. The holding temperature during firing may be adjusted as appropriate depending on the type of transition metal used, the type and amount of the precipitant and inert melting agent.

In this embodiment, the holding temperature is set by taking into consideration the melting point of the inactive melting agent described below, and is preferably set in the range of 100°C below the melting point of the inactive melting agent and 100°C above the melting point of the inactive melting agent.

Specifically, the holding temperature can be in the range of 200°C or more and 1150°C or less, preferably 300°C or more and 1050°C or less, and more preferably 500°C or more and 1000°C or less.

Further, the time for holding at the holding temperature is 0.1 hour or more and 20 hours or less, preferably 0.5 hour or more and 10 hours or less. The temperature increase rate to the holding temperature is usually 50° C./hour or more and 400° C./hour or less, and the temperature decreasing rate from the holding temperature to room temperature is usually 10° C./hour or more and 400° C./hour or less. Further, as the firing atmosphere, air, oxygen, nitrogen, argon, or a mixed gas thereof can be used.

The lithium metal composite oxide obtained by firing is crushed and appropriately classified to become a positive electrode active material that can be used in lithium ion secondary batteries.

In this embodiment, the lithium metal composite oxide obtained by calcination is pulverized by applying an appropriate external force, and the dispersion state of the particles is adjusted to obtain a lithium metal composite oxide in which the requirements (2) and (3) are controlled within the range of this embodiment.

In this embodiment, the lithium metal composite oxide obtained by firing is pulverized by applying an appropriate external force, and the dispersion state of the particles is adjusted to meet the requirements (2) and (3) within the scope of this embodiment. A lithium metal composite oxide with a controlled temperature can be obtained.

"Appropriate external force" refers to an external force that is sufficient to disperse the agglomerated state without destroying the crystallites of the lithium metal composite oxide. In this embodiment, it is preferable to use a grinder as the grinder during the above-mentioned grinding, and a stone mill-type grinder is particularly preferable. When using a stone mill type grinder, the clearance between the upper mill and the lower mill is preferably adjusted depending on the state of aggregation of the lithium metal composite oxide. The clearance between the upper mill and the lower mill is preferably in the range of 10 μm or more and 200 μm or less, for example.

The inert melting agent that can be used in this embodiment is not particularly limited as long as it does not easily react with the mixture during firing. In this embodiment, a fluoride of one or more elements (hereinafter referred to as "A") selected from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr, and Ba, a chloride of A, , A carbonate, A sulfate, A nitrate, A phosphate, A hydroxide, A molybdate, and A tungstate. .

Examples of fluorides of A include NaF (melting point: 993°C), KF (melting point: 858°C), RbF (melting point: 795°C), CsF (melting point: 682°C), _CaF2 (melting point: 1402°C), _MgF2 (melting point: 1263°C), _SrF2 (melting point: 1473°C) and _BaF2 (melting point: 1355°C).

Chlorides of A include NaCl (melting point: 801°C), KCl (melting point: 770°C), RbCl (melting point: 718°C), CsCl (melting point: 645°C), _CaCl2 (melting point: 782°C), _MgCl2 (melting point: 714°C), SrCl ₂ (melting point: 857°C) and BaCl ₂ (melting point: 963°C).

Examples of _{carbonates of A include Na2CO3 (} melting point: 854°C), _K2CO3 (melting _{point: 899°C), Rb2CO3 (melting point: 837°C), Cs2CO3 ( melting point} : 793°C), _CaCO3 (melting point: 825°C), _MgCO3 (melting point: 990°C), _SrCO3 (melting point: 1497°C) and _BaCO3 (melting point: 1380° _C ).

Sulfates of A include Na ₂ SO ₄ (melting point: 884°C), K ₂ SO ₄ (melting point: 1069°C), Rb ₂ SO ₄ (melting point: 1066°C), Cs ₂ SO ₄ (melting point: 1005°C). , CaSO ₄ (melting point: 1460°C), MgSO ₄ (melting point: 1137°C), SrSO ₄ (melting point: 1605°C) and BaSO ₄ (melting point: 1580°C).

Nitrates of A include _NaNO3 (melting point: 310°C), _KNO3 (melting point: 337°C), _RbNO3 (melting point: 316°C), _CsNO3 (melting point: 417°C), Ca( _NO3 ) ₂ (melting point: 561°C), Mg( _NO3 ) ₂ , Sr( _NO3 ) ₂ (melting point: 645°C) and Ba( _NO3 ) ₂ (melting point: 596°C).

Phosphates of A include Na ₃ PO ₄ , K ₃ PO ₄ (melting point: 1340°C), Rb ₃ PO ₄ , Cs ₃ PO ₄ , Ca ₃ (PO ₄ ) ₂ , Mg ₃ (PO ₄ ) ₂ ( (melting point: 1184°C), Sr ₃ (PO ₄ ) ₂ (melting point: 1727°C) and Ba ₃ (PO ₄ ) ₂ (melting point: 1767°C).

The hydroxides of A include NaOH (melting point: 318°C), KOH (melting point: 360°C), RbOH (melting point: 301°C), CsOH (melting point: 272°C), Ca(OH) ₂ (melting point: 408°C). ), Mg(OH) ₂ (melting point: 350°C), Sr(OH) ₂ (melting point: 375°C) and Ba(OH) ₂ (melting point: 853°C).

Examples of the molybdate of A include Na ₂ MoO ₄ (melting point: 698°C), K ₂ MoO ₄ (melting point: 919°C), Rb ₂ MoO ₄ (melting point: 958°C), Cs ₂ MoO ₄ (melting point: 956°C). ), CaMoO ₄ (melting point: 1520°C), MgMoO ₄ (melting point: 1060°C), SrMoO ₄ (melting point: 1040°C) and BaMoO ₄ (melting point: 1460°C).

Examples _of tungstates of A include _Na2WO4 (melting point: 687°C), _{K2WO4 , Rb2WO4 , Cs2WO4} , _{CaWO4 , MgWO4} , _SrWO4 , and _BaWO4 .

In this embodiment, two or more of these inert melting agents can also be used. When two or more types are used, the melting point may be lowered. Among these inert melting agents, carbonates and sulfates of A, chlorides of A, or a combination thereof are used as inert melting agents for obtaining a lithium metal composite oxide with higher crystallinity. It is preferable that Furthermore, A is preferably one or both of sodium (Na) and potassium (K). That is, among the above, particularly preferred inert melting agents are one or more selected from the group consisting of NaCl, KCl, Na ₂ CO ₃ , K ₂ CO _3, Na ₂ SO _4, and K ₂ SO ₄ .
By using these inert melting agents, the average crushing strength of the obtained lithium metal composite oxide can be controlled within the preferred range of this embodiment.

In this embodiment, when either one or both of K ₂ SO ₄ and Na ₂ SO ₄ is used as the inert melting agent, the average crushing strength of the obtained lithium metal composite oxide is Can be controlled within a range.

In this embodiment, the amount of the inert melting agent present during firing may be appropriately selected. In order to keep the average crushing strength of the obtained lithium metal composite oxide within the range of this embodiment, the amount of inert melting agent present during firing is 0.1 parts by mass or more per 100 parts by mass of the lithium compound. The amount is preferably 1 part by mass or more, and more preferably 1 part by mass or more. Furthermore, if necessary, inert melting agents other than those listed above may be used in combination. Examples of the melting agent include ammonium salts such as NH ₄ Cl and NH ₄ F.

(Method for producing lithium metal composite oxide 2)
When the positive electrode active material of the present embodiment includes single particles and secondary particles, the lithium metal composite oxide may be manufactured by making the following changes from the lithium metal composite oxide manufacturing method 1 described above. .

(Manufacturing process of metal composite compound)
In method 2 for producing a lithium metal composite oxide, a metal composite compound that will ultimately form single particles and a metal composite compound that will form secondary particles are each manufactured in the metal composite compound manufacturing process. In the following, a metal composite compound that ultimately forms a single particle may be referred to as a "single particle precursor." Further, a metal composite compound that ultimately forms secondary particles may be referred to as a "secondary particle precursor."

In manufacturing method 2 of lithium metal composite oxide, when manufacturing a metal composite compound by the above-mentioned coprecipitation method, a first coprecipitation tank is used to manufacture a single particle precursor, and a first coprecipitation tank is used to form a secondary particle precursor. 2 coprecipitation tanks are used.

By appropriately controlling the concentration of the metal salt supplied to the first coprecipitation tank, the stirring speed, the reaction temperature, the reaction pH, and the firing conditions described below, a single particle precursor can be produced.

Specifically, the temperature of the reaction tank is, for example, preferably 30°C or more and 80°C or less, more preferably controlled within a range of 40 to 70°C, and within a range of ±20°C with respect to the second reaction tank described below. It is more preferable that In addition, the pH value in the reaction tank is preferably controlled within a range of, for example, pH 10 or more and pH 13 or less, more preferably within a range of pH 11 or more and pH 12.5 or less, and within a range of ±pH 2 relative to the second reaction tank described below. It is more preferable that the pH is higher than that of the second reaction tank, and it is particularly preferable that the pH is higher than that of the second reaction tank.

The reaction product thus obtained is washed with water and then dried to isolate the single particle precursor of nickel cobalt manganese hydroxide. After drying, the single particle precursor may be appropriately classified.

Further, the secondary particle precursor can be produced by appropriately controlling the concentration of the metal salt supplied to the second coprecipitator, the stirring speed, the reaction temperature, the reaction pH, and the firing conditions described below.

Specifically, the temperature of the reaction tank is preferably, for example, 20°C or higher and 80°C or lower, more preferably controlled within the range of 30 to 70°C, and even more preferably within a range of ±20°C relative to the second reaction tank described below. The pH value in the reaction tank is preferably, for example, pH 10 or higher and pH 13 or lower, more preferably controlled within a range of pH 11 or higher and pH 12.5 or lower, and even more preferably within a range of ±2 relative to the second reaction tank described below, and is particularly preferably a lower pH than the second reaction tank.

The reaction product thus obtained is washed with water and then dried to isolate the secondary particle precursor of nickel cobalt manganese hydroxide. After drying, the secondary particle precursor may be appropriately classified.

In the above example, nickel-cobalt-manganese composite hydroxide is produced as the single particle precursor and the secondary particle precursor, but nickel-cobalt-manganese composite oxide may also be prepared.

(Manufacturing process of lithium metal composite oxide)
In the manufacturing process of the lithium metal composite oxide, the single particle precursor obtained in the above process, the secondary particle precursor, and the lithium salt are mixed.

By mixing the single particle precursor and the secondary particle precursor at a predetermined mass ratio during mixing, the abundance ratio of the single particles and secondary particles of the obtained lithium metal composite oxide can be approximately controlled.

In addition, in the process after mixing, secondary particle precursors produced by agglomeration of single particle precursors and single particle precursors produced by separation of secondary particle precursors may also exist. However, by adjusting the mixing ratio of the single particle precursor and the secondary particle precursor and the conditions of the steps after mixing, the abundance ratio of the single particles and secondary particles in the final lithium metal composite oxide can be adjusted. Can be controlled.

By adjusting the holding temperature during sintering, the average particle size of the single particles and the average particle size of the secondary particles of the resulting lithium metal composite oxide can be controlled within the preferred range of this embodiment.

(Method for producing lithium metal composite oxide 3)
Further, when the positive electrode active material of this embodiment includes single particles and secondary particles, the lithium metal composite oxide contained in the positive electrode active material includes a single particle of the lithium metal composite oxide and a double particle of the lithium metal composite oxide. It can be manufactured by separately manufacturing secondary particles and mixing the obtained single particles and secondary particles. The single particles of lithium metal composite oxide (first lithium metal composite oxide) and the secondary particles of lithium metal composite oxide (second lithium metal composite oxide) are the lithium metal composite oxide described above. It can be manufactured by manufacturing method 1.

In the lithium metal composite oxide manufacturing method 3, in the lithium metal composite oxide manufacturing process, the holding temperature when firing the first lithium metal composite oxide is the same as that of the second lithium metal composite oxide. It is recommended to set the temperature higher than the actual holding temperature. Specifically, when producing the first lithium metal composite oxide, the holding temperature is preferably 30°C or more higher than the holding temperature of the second lithium metal composite oxide, more preferably 50°C or more higher, and 80°C or more. It is even more preferable that it is higher than that.

By mixing the obtained first lithium metal composite oxide and second lithium metal composite oxide at a predetermined ratio, a lithium metal composite oxide containing single particles and secondary particles can be obtained.

By employing any one of the above-mentioned lithium metal composite oxide manufacturing methods 1 to 3, a lithium metal composite oxide having a layered crystal structure and containing at least Li and a transition metal can be manufactured.

(Coating layer formation process)
Next, a coating layer is formed on the surface of the lithium metal composite oxide particles (core particles) produced as described above. In this embodiment, a coating layer is formed on the surface of the lithium metal composite oxide particles by performing the following (1) to (3).
(1) Step of reacting the alkali metal composite oxide particles dispersed in the first dispersion liquid with a surface treatment agent to obtain a first reaction product (2) Dispersing the first reaction product in a dispersion medium (3) Adding a compound containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr, and Ge to the second dispersion liquid. A step of dropping water or a basic aqueous solution to the added second dispersion to obtain a second reaction product (4) Drying the second reaction product

(Step (1))
As the dispersion medium, alcohols such as methanol, ethanol, and propanol, N-methylpyrrolidone (NMP), toluene, and acetone can be used.

The particles of the lithium metal composite oxide produced by the above method are dispersed in a dispersion medium to prepare a first dispersion, and a surface treatment agent is added dropwise to the obtained first dispersion and mixed. Thereby, the lithium metal composite oxide and the surface treatment agent react, and a first reaction product is obtained.

The surface treatment agent used is the first one capable of coordinating with at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr, and Ge, which is characteristically contained in the above-mentioned coating layer. This is a silane coupling agent having a functional group and a second functional group capable of bonding to the lithium metal composite oxide used.

Coordinating atoms possessed by the first functional group include nitrogen, oxygen, sulfur, and phosphorus. The first functional group may have one or more of these coordinating atoms. Since one functional group can coordinate to a plurality of coating elements, it is preferable that the first functional group has a plurality of coordination atoms.

The coordinating atom is preferably nitrogen. The first functional group may be a functional group having a group obtained by removing one hydrogen atom bonded to a terminal nitrogen atom from a compound represented by the composition formula NH ₂ (CH ₂ CH ₂ NH) _n H (n is an integer of 0 or more), such as ammonia, ethylenediamine, or diethylenetriamine. The "group obtained by removing one hydrogen atom bonded to a terminal nitrogen atom from a compound represented by the composition formula NH ₂ (CH ₂ CH ₂ NH) _n H (n is an integer of 0 or more)" corresponds to the "amino group" in the present invention.

When the silane coupling agent has multiple first functional groups, the multiple first functional groups may be the same or different.

The second functional group may be a hydroxyl group or an alkoxy group that is directly bonded to the silicon atom of the silane coupling agent. Examples of the alkoxy group include a methoxy group, an ethoxy group, and a propoxy group.

When the silane coupling agent has multiple second functional groups, the multiple second functional groups may be the same or different.

As such a silane coupling agent, for example, N-(3-trimethoxysilylpropyl)diethylenetriamine represented by the following formula (A) can be suitably used.

The silane coupling agent is added to the dispersion of lithium metal composite oxide, and the mixture is stirred until the reaction between the second functional group of the silane coupling agent and the lithium metal composite oxide has progressed sufficiently. After stirring, the remaining liquid is subjected to suction filtration or centrifugation to recover the solid, and the filtered solid is dried.

Drying can be performed by heating, reducing pressure, blowing air, or a combination of these. For example, drying can be performed under multiple drying conditions, such as vacuum drying at room temperature followed by vacuum drying at 100°C.

The obtained solid may be pulverized using a mortar or a pulverizer, as appropriate.

In step (1), the silane coupling agent reacts with the surface of the lithium metal composite oxide particles at the ethoxysilyl group, which is the second functional group, to obtain a reaction product in which a layer of the silane coupling agent is formed on the surface of the lithium metal composite oxide particles. For example, when a compound represented by the above formula (1) is used as the silane coupling agent, step (1) obtains a reaction product in which amino groups are introduced on the surface of the lithium metal composite oxide particles.

(Step (2))
Next, the first reaction product obtained in step (1) is dispersed in a dispersion medium to prepare a second dispersion liquid. Examples of the dispersion medium used to prepare the second dispersion liquid include the same dispersion medium as the dispersion medium usable to prepare the first dispersion liquid described above.

Next, a compound containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr, and Ge is added to the second dispersion. In the following description, the "second dispersion to which the compound containing the coating element has been added" may be referred to as the "third dispersion."

Examples of the "compound containing a coating element" used in this step include salts of Nb, Ta, Ti, Al, B, W, Zr, or Ge. Examples of such salts include hydroxides, alkoxides, and acetates of Nb, Ta, Ti, Al, B, W, Zr, or Ge.
In the third dispersion liquid, the compound containing the coating element is uniformly dispersed in the liquid.

(Step (3))
The water used in this step causes hydrolysis of the salt of Nb, Ta, Ti, Al, B, W, Zr, or Ge, and a dehydration condensation reaction of the hydroxide produced by the hydrolysis.

In this step, a catalyst having a function of increasing the pH of the third dispersion may be used. As the catalyst, a compound whose aqueous solution obtained by dissolving in water shows basicity can be used. Examples of the catalyst include ammonia, alkali metal hydroxides (sodium hydroxide, potassium hydroxide), and alkali metal carbonates (sodium carbonate, potassium carbonate).

When water and a catalyst are used simultaneously in this process, it is advisable to use the catalyst as an aqueous solution in which it is dissolved in water. Such an aqueous solution is a basic aqueous solution.

When a salt other than a hydroxide, such as an alkoxide or an acetate, is used as the compound containing the coating element, when the basic aqueous solution is added to the third dispersion, the salt is hydrolyzed by water. This produces a hydroxide containing the coating element.

The generated hydroxide is electrostatically attracted to the amino group introduced into the surface of the lithium metal composite oxide and electrostatically adheres to the surface of the lithium metal composite oxide.

In addition, the hydroxide containing the coating element undergoes a dehydration condensation reaction due to the water present in the system, and becomes an oxide of the coating element on the surface of the lithium metal composite oxide particles.

Here, the above-mentioned hydrolysis reaction proceeds more easily when the reaction system is basic than when it is neutral. Therefore, in this step, it is more preferable to drop a basic aqueous solution than to drop only water.

Furthermore, the amino group that electrostatically adsorbs the hydroxide containing the coating element acts as a base catalyst, promoting the dehydration condensation reaction of the hydroxide containing the coating element.
Note that the dehydration condensation reaction of the compound containing the coating element tends to proceed even when the reaction system is acidic. However, in an acidic environment, hydrolysis of the hydroxide containing the coating element tends to proceed, and the hydroxide containing the coating element is hydrolyzed in the dispersion before it adheres to the surface of the lithium metal composite oxide. Reactions are likely to occur. Therefore, in step (3), it is preferable to control the reaction system to be alkaline by adding a catalyst.

The above reaction allows the production of oxides of the coating elements to be limited to the surface of the lithium metal composite oxide particles, suppressing side reactions that produce the above oxides outside the particle surface.

Note that it is preferable to include a step of adding a monodentate ligand to the second dispersion between step (2) and step (3). By adding a monodentate ligand to the second dispersion liquid, side reactions in the entire liquid are suppressed when a catalyst is added, and the condensation reaction of the salt can be more limited to the surface of the lithium metal composite oxide particles. can. This improves the coverage of the lithium metal composite oxide particles.

An example of a monodentate ligand is acetonitrile.

(Step (4))
In this step, the reaction product obtained in step (3) is filtered from the dispersion, and the reaction product is dried. As a result, on the particle surface of the lithium metal composite oxide, the compound (hydroxide) condensed on the particle surface in step (3) is oxidized, and the compound consisting of Nb, Ta, Ti, Al, B, W, Zr, or Ge is oxidized. An oxide film containing at least one coating element selected from the group is produced.

Drying may be performed in an oxidizing atmosphere or a non-oxidizing atmosphere. An oxidizing atmosphere includes an air atmosphere. When performing the heat treatment described below, the drying in this step may be performed in a non-oxidizing atmosphere.

Drying can be performed by heating, reducing pressure, blowing air, or a combination of these. For example, it can be heated to 120°C and vacuum dried for 1 hour.

The obtained solid may be pulverized using a mortar or a pulverizer, as appropriate.

After step (4), the method may further include a step of heat-treating the dried product obtained in step (4) at a temperature of 100° C. or more and 800° C. or less. The heat treatment temperature is preferably 200°C or higher. Further, the heat treatment temperature is preferably 700°C or lower.

The upper and lower limits of the heat treatment temperature described above can be combined in any way. That is, the heat treatment temperature in the heat treatment step described above may be 100°C or higher and 700°C or lower, 200°C or higher and 800°C or lower, or 200°C or higher and 700°C or lower.

The above-mentioned heat treatment is preferably carried out in an oxidizing atmosphere, since it is easy to oxidize the compounds condensed on the surface of the lithium metal composite oxide particles and generate oxides.

The average thickness, α/(α+β), and A/α of the coating layer of the obtained positive electrode active material can be varied by adjusting the amount of the silane coupling agent used in step (1), the amount of the compound containing the coating element used in step (2), the amount of water or the basic aqueous solution used in step (3), and the amount of the catalyst used in step (3).
It is advisable to carry out a preliminary experiment in advance to confirm the tendency of the corresponding relationship between the amount of each reagent used and the average thickness of the coating layer of the positive electrode active material, α/(α+β) or A/α.

The positive electrode active material of this embodiment can be obtained by the above manufacturing method.

According to the manufacturing method of the positive electrode active material configured as described above, a coating layer can be easily and uniformly formed on the surface of the lithium metal composite oxide particles. Therefore, according to the manufacturing method of the positive electrode active material configured as described above, it is possible to efficiently manufacture a positive electrode active material having excellent rate characteristics.

<Lithium ion secondary battery>
Next, while explaining the configuration of a lithium ion secondary battery, a positive electrode using a positive electrode active material according to one embodiment of the present invention and a lithium ion secondary battery having this positive electrode will be described.

The positive electrode active material of this embodiment can be suitably used for a positive electrode of a lithium ion secondary battery. Further, such a positive electrode can be suitably used in both a lithium ion secondary battery using an electrolyte as an electrolyte and an all-solid lithium ion secondary battery using a solid electrolyte as an electrolyte. In the following description, a "lithium ion secondary battery using an electrolyte" will be referred to as a "liquid-based lithium ion secondary battery" to distinguish it from an all-solid lithium ion secondary battery.

The configurations of a liquid-based lithium ion secondary battery and an all-solid lithium ion secondary battery will be described below.

<Lithium-ion secondary battery>
An example of a lithium ion secondary battery suitable for use with the positive electrode active material of this embodiment includes a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

An example of a lithium ion secondary battery includes a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode.

3A and 3B are schematic diagrams showing an example of a lithium ion secondary battery. The cylindrical lithium ion secondary battery 10 of this embodiment is manufactured as follows.

First, as shown in FIG. 3A, a pair of band-shaped separators 1, a band-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a band-shaped negative electrode 3 having a negative electrode lead 31 at one end are connected to each other. 1 and negative electrode 3 are laminated in this order and wound to form an electrode group 4.

Next, as shown in FIG. 3B, the electrode group 4 and an insulator (not shown) are placed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with an electrolyte solution 6, and the electrolyte is disposed between the positive electrode 2 and the negative electrode 3. Furthermore, the top of the battery can 5 is sealed with a top insulator 7 and a sealing body 8, thereby producing a lithium-ion secondary battery 10.

Examples of the shape of the electrode group 4 include a cylindrical shape such that the cross-sectional shape when the electrode group 4 is cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

The shape of a lithium ion secondary battery having such an electrode group 4 can be any shape specified by IEC 60086, a battery standard established by the International Electrotechnical Commission (IEC), or JIS C 8500. Examples include cylindrical and rectangular shapes.

Furthermore, the lithium ion secondary battery is not limited to the above-mentioned wound type configuration, but may be a laminated type configuration in which a laminated structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of laminated lithium ion secondary batteries include so-called coin type batteries, button type batteries, and paper type (or sheet type) batteries.

Each component will be described in order below.
(Positive electrode)
The positive electrode can be produced by first preparing a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder, and then supporting the positive electrode mixture on a positive electrode current collector.

(conductive material)
A carbon material can be used as the conductive material included in the positive electrode. Examples of carbon materials include graphite powder, carbon black (eg, acetylene black), and fibrous carbon materials. Carbon black is fine particles and has a large surface area, so adding a small amount to the positive electrode mixture can increase the conductivity inside the positive electrode and improve charge/discharge efficiency and output characteristics, but if too much is added, the binder The binding force between the positive electrode mixture and the positive electrode current collector and the binding force inside the positive electrode mixture are both reduced, causing an increase in internal resistance.

The proportion of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less based on 100 parts by mass of the positive electrode active material. When using a fibrous carbon material such as graphitized carbon fiber or carbon nanotube as the conductive material, it is possible to lower this ratio.

(binder)
A thermoplastic resin can be used as the binder included in the positive electrode. Examples of this thermoplastic resin include polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. Fluororesins such as copolymers, propylene hexafluoride/vinylidene fluoride copolymers, and ethylene tetrafluoride/perfluorovinylether copolymers; polyolefin resins such as polyethylene and polypropylene;

These thermoplastic resins may be used in combination of two or more. By using a fluororesin and a polyolefin resin as a binder, and setting the proportion of the fluororesin to the entire positive electrode mixture to be 1% by mass or more and 10% by mass or less, and the proportion of the polyolefin resin to be 0.1% by mass or more and 2% by mass or less, the positive electrode It is possible to obtain a positive electrode mixture that has both high adhesion to the current collector and high bonding force within the positive electrode mixture.

(Positive electrode current collector)
The positive electrode current collector of the positive electrode can be a strip-shaped member made of a metal material such as Al, Ni, stainless steel, etc. Among them, a thin film made of Al is preferred because it is easy to process and inexpensive.

One method for supporting the positive electrode mixture on the positive electrode current collector is to pressure mold the positive electrode mixture on the positive electrode current collector. Alternatively, the positive electrode mixture may be made into a paste using an organic solvent, and the resulting paste of the positive electrode mixture may be applied to at least one side of the positive electrode current collector, dried, and pressed to adhere the positive electrode mixture to the positive electrode current collector.

When forming the positive electrode mixture into a paste, examples of organic solvents that can be used include amine-based solvents such as N,N-dimethylaminopropylamine and diethylenetriamine; ether-based solvents such as tetrahydrofuran; ketone-based solvents such as methyl ethyl ketone; ester-based solvents such as methyl acetate; and amide-based solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

Examples of methods for applying the positive electrode mixture paste to the positive electrode current collector include slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.
The positive electrode can be produced by the method mentioned above.

(Negative electrode)
The negative electrode of a lithium ion secondary battery may be an electrode in which a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector, as long as it is capable of doping and dedoping lithium ions at a potential lower than that of the positive electrode. and an electrode consisting of only a negative electrode active material.

(Negative electrode active material)
Examples of the negative electrode active material included in the negative electrode include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, and alloys, which can be doped and dedoped with lithium ions at a lower potential than the positive electrode. It will be done.

Carbon materials that can be used as the negative electrode active material include graphite such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fiber, and fired organic polymer compounds.

Oxides _{that can be used as negative electrode active materials include silicon oxides represented by the formula SiO x (where x is a positive real number) such as SiO 2 and SiO ;} , x is a positive real number); Vanadium oxide represented by the formula VO _x (where x is a positive real number) such as V ₂ O ₅ , VO ₂ ; Fe ₃ O ₄ , Fe ₂ O ₃ , FeO, etc. Iron oxides represented by the formula FeO _x (where x is a positive real number); SnO ₂ , SnO, etc., represented by the formula SnO _x (where x is a positive real number) Tungsten oxides represented by the general formula WO _x (where x is a positive real number) such as WO ₃ and WO ₂ ; Lithium and titanium such as Li ₄ Ti ₅ O ₁₂ and LiVO ₂ or a composite metal oxide containing vanadium.

Sulfides that can be used as the negative electrode active material include titanium sulfides represented by the formula TiS _x (where x is a positive real number), such as Ti ₂ S ₃ , TiS ₂ , and TiS; vanadium sulfides represented by the formula VS _x (where x is a positive real number), such as V ₃ S ₄ , VS _{2 ,} and VS; iron sulfides represented by the formula FeS _x (where x is a positive real number), such as Fe ₃ S ₄ , FeS ₂ , and FeS; molybdenum sulfides represented by the formula MoS _x (where x is a positive real number), such as Mo ₂ S ₃ and MoS ₂ ; tin sulfides represented by the formula SnS _x (where x is a positive real number), such as SnS _{2 and} SnS; and sulfides represented by the formula WS _x , such as WS ₂ . (wherein x is a positive real number); antimony sulfides such as _Sb2S3 , represented by _{the formula SbSx (wherein x is a positive real number); and selenium sulfides such as Se5S3, SeS2 , and SeS} , represented by the formula _SeSx (wherein x is a positive real number).

Nitrides that can be used as negative electrode active materials include Li ₃ N, Li _3-x A _x N (where A is either or both of Ni and Co, and 0<x<3). Examples include lithium-containing nitrides such as.

These carbon materials, oxides, sulfides, and nitrides may be used alone or in combination of two or more. Furthermore, these carbon materials, oxides, sulfides, and nitrides may be either crystalline or amorphous.

Further, examples of metals that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

Examples of alloys that can be used as the negative electrode active material include lithium alloys such as Li-Al, Li-Ni, Li-Si, Li-Sn, and Li-Sn-Ni; silicon alloys such as Si-Zn; tin alloys such as Sn-Mn, Sn-Co, Sn-Ni, Sn-Cu, and Sn-La; and alloys such as Cu ₂ Sb and La ₃ Ni ₂ Sn ₇ .

These metals and alloys are mainly used alone as electrodes after being processed into a foil shape, for example.

Among the above negative electrode active materials, the potential of the negative electrode hardly changes from the uncharged state to the fully charged state during charging (good potential flatness), the average discharge potential is low, and the capacity retention rate when repeatedly charged and discharged is low. Carbon materials containing graphite as a main component, such as natural graphite and artificial graphite, are preferably used because of their high performance (good cycle characteristics). The shape of the carbon material may be, for example, flaky like natural graphite, spherical like mesocarbon microbeads, fibrous like graphitized carbon fiber, or aggregates of fine powder.

The negative electrode mixture may contain a binder as necessary. Examples of binders include thermoplastic resins, specifically PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.

(Negative electrode current collector)
Examples of the negative electrode current collector included in the negative electrode include a band-shaped member made of a metal material such as Cu, Ni, or stainless steel. Among these, it is preferable to use Cu as a forming material and process it into a thin film because it is difficult to form an alloy with lithium and is easy to process.

Methods for supporting the negative electrode mixture on such a negative electrode current collector include, as in the case of the positive electrode, a pressure molding method, a method in which a paste is made using a solvent or the like, which is then applied to the negative electrode current collector, dried, and then pressed to bond it together.

(Separator)
The separator of the lithium ion secondary battery may be, for example, a material having a form of a porous film, a nonwoven fabric, a woven fabric, etc., made of a material such as a polyolefin resin such as polyethylene or polypropylene, a fluororesin, a nitrogen-containing aromatic polymer, etc. The separator may be formed by using two or more of these materials, or the separator may be formed by laminating these materials.

In this embodiment, the separator has an air permeability resistance of 50 seconds/100cc or more and 300 seconds/100cc according to the Gurley method defined in JIS P 8117 in order to allow the electrolyte to pass through the separator well during battery use (charging and discharging). It is preferably below, and more preferably 50 seconds/100cc or more and 200 seconds/100cc or less.

The porosity of the separator is preferably 30% by volume or more and 80% by volume or less, more preferably 40% by volume or more and 70% by volume or less. The separator may be a laminate of separators with different porosities.

(electrolyte)
The electrolytic solution that a lithium ion secondary battery has contains an electrolyte and an organic solvent.

The electrolytes contained in the electrolytic solution are _LiClO4 , _LiPF6 , _LiAsF6 , _LiSbF6 , _LiBF4 , _{LiCF3SO3 , LiN} ( _SO2CF3 ) ₂ , _{LiN ( SO2C2F5} ) ₂ , _LiN ( _SO2CF3 )( _COCF3 ), _{Li ( C4F9SO3} ), LiC _{( SO2CF3} ) _{3 , Li2B10Cl10 .} , LiBOB (here, BOB stands for bis(oxalato)borate), LiFSI (here, FSI stands for bis(fluorosulfonyl)imide), lithium salts of lower aliphatic carboxylic acids, _LiAlCl4 , and the like. A mixture of two or more of these may also be used.
Among them, _{it is} preferable to use an electrolyte containing at least one selected from _the group consisting of fluorine-containing _LiPF6 , _LiAsF6 , _LiSbF6 , _LiBF4 , _LiCF3SO3 , LiN( _SO2CF3 ) ₂ and LiC( _SO2CF3 ) ₃ .

Examples of organic solvents contained in the electrolytic solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-dioxolan-2-one. Carbonates such as (methoxycarbonyloxy)ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2- Ethers such as methyltetrahydrofuran; Esters such as methyl formate, methyl acetate, and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; Amides such as N,N-dimethylformamide and N,N-dimethylacetamide; 3-methyl Carbamates such as -2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propanesultone; or organic solvents with a fluoro group (one of the hydrogen atoms in the organic solvent); (substituted with fluorine atoms) can be used.

As the organic solvent, it is preferable to use a mixture of two or more of these. Among these, mixed solvents containing carbonates are preferred, and mixed solvents of cyclic carbonates and acyclic carbonates and mixed solvents of cyclic carbonates and ethers are more preferred. The mixed solvent of cyclic carbonate and acyclic carbonate is preferably a mixed solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Electrolytes using such mixed solvents have a wide operating temperature range, are resistant to deterioration even when charged and discharged at high current rates, and are resistant to deterioration even after long periods of use. It has many features such as being difficult to decompose even when graphite materials such as artificial graphite are used.

Further, as the electrolytic solution, it is preferable to use an electrolytic solution containing a lithium salt containing fluorine such as LiPF ₆ and an organic solvent having a fluorine substituent, in order to increase the safety of the obtained lithium ion secondary battery. A mixed solvent containing dimethyl carbonate and an ether having a fluorine substituent such as pentafluoropropyl methyl ether or 2,2,3,3-tetrafluoropropyl difluoromethyl ether has a low capacity even when charged and discharged at a high current rate. It is more preferred because of its high retention rate.

In this embodiment, the battery performance of the positive electrode and lithium ion secondary battery configured as described above can be confirmed by the following method.

<Production of Liquid Lithium-Ion Secondary Battery>
(Preparation of positive electrode for lithium ion secondary battery)
A positive electrode active material obtained by the manufacturing method described later, a conductive material (acetylene black), and a binder (PVdF) are added in a ratio of positive electrode active material:conductive material:binder=92:5:3 (mass ratio) and kneaded to prepare a paste-like positive electrode mixture. N-methyl-2-pyrrolidone is used as an organic solvent when preparing the positive electrode mixture.

The obtained positive electrode mixture is applied to a 40 μm thick Al foil serving as a current collector and vacuum dried at 150° C. for 8 hours to obtain a positive electrode for a lithium ion secondary battery. The electrode area of this positive electrode for a lithium ion secondary battery is 1.65 cm ² .

(Preparation of lithium ion secondary battery (coin type half cell))
Perform the following operations in a glove box with an argon atmosphere.

Place the positive electrode for a lithium ion secondary battery prepared in (Preparation of a positive electrode for a lithium ion secondary battery) on the bottom cover of a coin-type battery R2032 part (manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down. , and place a separator (porous polyethylene film) on top of it.

Inject 300 μl of electrolyte here. The electrolytic solution used is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (30:35:35 (volume ratio)) in which LiPF ₆ is dissolved at a concentration of 1.0 mol/l.

Next, using metal lithium as the negative electrode, place the negative electrode on the upper side of the laminated film separator, cover the top with a gasket, and swage it with a crimping machine to lithium ion secondary battery (coin type half cell R2032). (hereinafter sometimes referred to as a "half cell").

<Charge/discharge test>
Using the half cell produced by the above method, a charge/discharge test is conducted under the conditions shown below to evaluate the initial charge/discharge capacity and rate characteristics.

(Charge/discharge conditions: initial charge/discharge capacity)
Test temperature: 25°C
Maximum charging voltage 4.5V, charging current density 0.2C, cutoff current density 0.05C, constant current-constant voltage charging Minimum discharging voltage 2.5V, discharge current density 0.2C, constant current discharging

(Charge/discharge conditions: rate characteristics)
Test temperature 25℃
Maximum charging voltage 4.5V, charging current density 1C, cut-off current density 0.05C, constant current-constant voltage charging, minimum discharge voltage 2.5V, discharge current density 0.2C, 0.5C, 1C, 2C, 3C, 5C, 10C

Regarding the charge/discharge test results, a graph is created in which the horizontal axis is the current density (unit: mA/cm ² ) and the vertical axis is the discharge capacity (unit: mAh/g). From the graph, the rate characteristics are evaluated by evaluating how the discharge capacity decreases when the operating voltage is changed to a high voltage.

The positive electrode having the above-mentioned configuration has the positive electrode active material having the above-mentioned configuration, and therefore can improve the rate characteristics of the lithium-ion secondary battery.

Furthermore, since the lithium ion secondary battery configured as described above has the above-described positive electrode, it becomes a secondary battery with high rate characteristics.

<All-solid-state lithium-ion secondary battery>
4 and 5 are schematic diagrams showing an example of the all-solid-state lithium-ion secondary battery 1000 of this embodiment. Fig. 4 is a schematic diagram showing a laminate included in the all-solid-state lithium-ion secondary battery 1000 of this embodiment. Fig. 5 is a schematic diagram showing the overall configuration of the all-solid-state lithium-ion secondary battery 1000 of this embodiment.

In the following description, the all-solid-state lithium-ion secondary battery 1000 will simply be referred to as the "all-solid-state secondary battery 1000."

The all-solid-state secondary battery 1000 includes a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an exterior body 200 that houses the laminate 100.
The materials constituting each member will be described later.

The laminate 100 may have an external terminal 113 connected to the positive electrode current collector 112 and an external terminal 123 connected to the negative electrode current collector 122. In addition, the all-solid-state secondary battery 1000 may have a separator between the positive electrode 110 and the negative electrode 120, as used in conventional liquid lithium-ion secondary batteries.

The all-solid-state secondary battery 1000 includes an insulator (not shown) that insulates the stacked body 100 and the exterior body 200 and a sealing body (not shown) that seals the opening 200a of the exterior body 200.

The exterior body 200 may be a container molded from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel. It may also be a container made of a laminate film processed into a bag shape with corrosion resistance applied to at least one side.

Examples of the shape of the all-solid-state secondary battery 1000 include a coin shape, a button shape, a paper shape (or sheet shape), a cylindrical shape, and a square shape.

Although the all-solid-state secondary battery 1000 is illustrated as having one laminate 100, this is not limited thereto. The all-solid-state secondary battery 1000 may have a configuration in which the laminate 100 is a unit cell and multiple unit cells (laminated bodies 100) are sealed inside the exterior body 200.

Each component will be explained in turn below.

(Positive electrode)
The positive electrode 110 of this embodiment has a positive electrode active material layer 111 and a positive electrode current collector 112 .

The positive electrode active material layer 111 contains the positive electrode active material that is one embodiment of the present invention described above. Further, the positive electrode active material layer 111 may include a solid electrolyte (second solid electrolyte), a conductive material, and a binder.

(Solid electrolyte)
As the solid electrolyte that may be included in the positive electrode active material layer 111 of this embodiment, a solid electrolyte having lithium ion conductivity and used in a known all-solid-state battery can be adopted. Examples of such a solid electrolyte include inorganic electrolytes and organic electrolytes. Examples of the inorganic electrolyte include oxide-based solid electrolytes, sulfide-based solid electrolytes, and hydride-based solid electrolytes. Examples of the organic electrolyte include polymer-based solid electrolytes.

(Oxide-based solid electrolyte)
Examples of oxide-based solid electrolytes include perovskite-type oxides, NASICON-type oxides, LISICON-type oxides, and garnet-type oxides.

Examples of perovskite oxides include Li-La-Ti oxides such as Li _a La _1-a TiO ₃ (0<a<1), Li-La-Ta oxides such as Li _b La _1-b TaO ₃ (0<b<1), and Li-La-Nb oxides such as Li _c La _1-c NbO ₃ (0<c<1).

Examples of the NASICON type oxide include Li _1+d Al _d Ti _2-d (PO ₄ ) ₃ (0≦d≦1). The NASICON type oxide is formed by Li _m M ¹ _n M ² _o P _p O _q (where M ¹ is selected from the group consisting of B, Al, Ga, In, C, Si, Ge, Sn, Sb and Se). ^M2 is one or more elements selected from the group consisting of Ti, Zr, Ge, In, Ga, Sn, and Al. m, n, o, p, and q are any positive It is an oxide represented by the number ).

Examples of LISICON type oxides include oxides represented by Li ₄ M ³ O ₄ --Li ₃ M ⁴ O ₄ (M ³ is one or more elements selected from the group consisting of Si, Ge, and Ti; M ⁴ is one or more elements selected from the group consisting of P, As, and V).

The garnet type oxide may be Li-La-Zr oxide such as Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ).

The oxide solid electrolyte may be a crystalline material or an amorphous material. Examples of the amorphous solid electrolyte include Li-BO compounds such as Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , and LiBO ₂ . The oxide solid electrolyte preferably contains an amorphous material.

(Sulfide-based solid electrolyte)
The sulfide-based solid electrolyte may be at least one selected from the group consisting of Li ₂ S-P ₂ S ₅ based compounds, Li ₂ S-SiS ₂ based compounds, Li ₂ S-GeS ₂ based compounds, Li ₂ S-B ₂ S ₃ based compounds, Li ₂ S-P ₂ S ₃ based compounds, LiI-Si ₂ S-P ₂ S ₅ , LiI-Li ₂ S-P ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , and Li ₁₀ GeP ₂ S ₁₂ .

In this specification, the expression "sulfide-based compound" referring to a sulfide-based solid electrolyte is used as a general term for solid electrolytes mainly containing raw materials such as "Li ₂ S" and "P ₂ S ₅ " described before "sulfide-based compound". For example, Li ₂ S-P ₂ S ₅ -based compounds include solid electrolytes that contain Li ₂ S and P ₂ S ₅ and further contain other raw materials. In addition, Li ₂ S-P ₂ S ₅ -based compounds also include solid electrolytes with different mixing ratios of Li ₂ S and P ₂ S ₅ .

The Li ₂ S-P ₂ S ₅ based compound may be at least one selected from the group consisting of Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiI, Li ₂ S-P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S ₅ -LiBr, Li ₂ S-P ₂ S ₅ -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI and Li ₂ S-P ₂ S ₅ -Z _m S _n (m and n are positive numbers; Z is Ge, Zn or Ga).

Examples of Li ₂ S-SiS ₂ -based compounds include Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, and Li ₂ S-SiS. ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li ₂ SO ₄ and Li ₂ S -SiS ₂ -Li _x MO _y (x, y are positive numbers; M is P, Si, Ge, B, Al, Ga, or In).

Examples of Li ₂ S—GeS ₂ based compounds include Li ₂ S—GeS ₂ , Li ₂ S—GeS ₂ —P ₂ S ₅ and the like.

The sulfide-based solid electrolyte may be a crystalline material or a non-crystalline (amorphous) material. It is preferable that the sulfide-based solid electrolyte contains an amorphous material.

(Hydride solid electrolyte)
Examples of hydride solid electrolyte materials include LiBH ₄ , LiBH ₄ -3KI, LiBH ₄ -PI ₂ , LiBH ₄ -P ₂ S ₅ , LiBH ₄ -LiNH ₂ , 3LiBH ₄ -LiI, LiNH ₂ , Li ₂ AlH ₆ , Li( _NH2 ) _2I , _Li2NH , LiGd( _BH4 ) _3Cl , _Li2 ( _BH4 )( _NH2 ), _Li3 ( _NH2 )I and _Li4 ( _BH4 )( _NH2 ) ₃ At least one selected from the group consisting of:

Examples of polymer-based solid electrolytes include organic polymer electrolytes such as polyethylene oxide-based polymer compounds, polymer compounds containing at least one selected from the group consisting of polyorganosiloxane chains and polyoxyalkylene chains. In addition, so-called gel-type electrolytes in which a non-aqueous electrolyte is held in a polymer compound can also be used.

Two or more solid electrolytes can be used in combination as long as the effects of the invention are not impaired.

(conductive material)
As the conductive material that the positive electrode active material layer 111 of this embodiment may have, a carbon material or a metal compound can be used. Examples of carbon materials include graphite powder, carbon black (eg, acetylene black), and fibrous carbon materials. Since carbon black is fine particles and has a large surface area, by adding an appropriate amount to the positive electrode active material layer 111, it is possible to increase the internal conductivity of the positive electrode 110 and improve the charge/discharge efficiency and output characteristics. On the other hand, if the amount of carbon black added is too large, the binding strength between the positive electrode active material layer 111 and the positive electrode current collector 112 and the binding strength inside the positive electrode active material layer 111 will both decrease, and the internal resistance will increase instead. Cause. Examples of the metal compound include metals, metal alloys, and metal oxides that have electrical conductivity.

In the case of a carbon material, the proportion of the conductive material in the positive electrode active material layer 111 is preferably 5 parts by mass or more and 20 parts by mass or less based on 100 parts by mass of the positive electrode active material. When using a fibrous carbon material such as graphitized carbon fiber or carbon nanotube as the conductive material, it is possible to lower this ratio.

(binder)
When the positive electrode active material layer 111 has a binder, the binder may be a thermoplastic resin. As the thermoplastic resin, any of the materials listed above as binders used in the liquid lithium ion secondary battery may be used.

These thermoplastic resins may be used in a mixture of two or more kinds. By using a fluororesin and a polyolefin resin as a binder and setting the ratio of the fluororesin to the entire positive electrode active material layer 111 to be 1% by mass or more and 10% by mass or less, and the ratio of the polyolefin resin to be 0.1% by mass or more and 2% by mass or less, the positive electrode active material layer 111 has high adhesion between the positive electrode active material layer 111 and the positive electrode current collector 112, and high bonding strength inside the positive electrode active material layer 111.

The positive electrode active material layer 111 may be processed in advance into a sheet-like molded body containing a positive electrode active material and used as an "electrode" in the present invention. Furthermore, in the following description, such a sheet-like molded body may be referred to as a "positive electrode active material sheet." A laminate in which a current collector is laminated on a positive electrode active material sheet may be used as an electrode.

The positive electrode active material sheet may include any one or more selected from the group consisting of the above-mentioned solid electrolyte, conductive material, and binder.

The positive electrode active material sheet can be prepared by, for example, preparing a slurry by mixing a positive electrode active material, a sintering aid, the above-mentioned conductive material, the above-mentioned binder, a plasticizer, and a solvent, and then using the obtained slurry. It is obtained by coating on a carrier film and drying it.

As the sintering aid, for example, Li ₃ BO ₃ or Al ₂ O ₃ can be used.

As the plasticizer, for example, dioctyl phthalate can be used.

As the solvent, for example, at least one selected from the group consisting of acetone, ethanol, and N-methyl-2-pyrrolidone can be used.

When preparing the slurry, a ball mill can be used for mixing. The resulting mixture often contains air bubbles that were mixed in during mixing, so it is a good idea to degas it by reducing the pressure. When degassing, some of the solvent evaporates and becomes concentrated, increasing the viscosity of the slurry.

The slurry can be applied using a known doctor blade.

A PET film can be used as the carrier film.

The positive electrode active material sheet obtained after drying is peeled off from the carrier film and processed into the required shape by appropriate punching processing for use. The positive electrode active material sheet may also be uniaxially pressed in the thickness direction as appropriate.

(Positive electrode current collector)
As the positive electrode current collector 112 included in the positive electrode 110 of this embodiment, a sheet-like member made of a metal material such as Al, Ni, stainless steel, or Au can be used. Among these, it is preferable to use Al as a forming material and process it into a thin film because it is easy to process and inexpensive.

One method for supporting the positive electrode active material layer 111 on the positive electrode current collector 112 is to pressure mold the positive electrode active material layer 111 on the positive electrode current collector 112. Cold pressing or hot pressing can be used for pressure molding.

Further, a mixture of a positive electrode active material, a solid electrolyte, a conductive material, and a binder is made into a paste using an organic solvent to form a positive electrode mixture, and the resulting positive electrode mixture is applied to at least one side of the positive electrode current collector 112 and dried. The positive electrode active material layer 111 may be supported on the positive electrode current collector 112 by pressing and fixing.

Alternatively, a mixture of the positive electrode active material, solid electrolyte, and conductive material may be made into a paste using an organic solvent to form a positive electrode mixture, and the resulting positive electrode mixture may be applied to at least one side of the positive electrode current collector 112, dried, and sintered to support the positive electrode active material layer 111 on the positive electrode current collector 112.

Organic solvents that can be used in the positive electrode mixture include amine solvents such as N,N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; and ester solvents such as methyl acetate. and amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

Examples of the method for applying the positive electrode mixture to the positive electrode current collector 112 include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method.

The positive electrode 110 can be manufactured using the methods described above.

(Negative electrode)
The negative electrode 120 includes a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 includes a negative electrode active material. Further, the negative electrode active material layer 121 may include a solid electrolyte and a conductive material. As the solid electrolyte, conductive material, and binder, those mentioned above can be used.

(Negative electrode active material)
The negative electrode active material included in the negative electrode active material layer 121 is a carbon material, a chalcogen compound (oxide, sulfide, etc.), nitride, metal, or alloy, and can be doped and dedoped with lithium ions at a lower potential than the positive electrode 110. Possible materials include:

As the carbon materials, oxides, sulfides, nitrides, metals, and alloys that can be used as the negative electrode active material, the materials listed above as the negative electrode active materials used in the liquid lithium ion secondary batteries can be used.

Among the negative electrode active materials mentioned above, the potential of the negative electrode 120 hardly changes from an uncharged state to a fully charged state during charging (good potential flatness), a low average discharge potential, and a capacity retention rate when repeatedly charged and discharged. Carbon materials containing graphite as a main component, such as natural graphite and artificial graphite, are preferably used because of their high cycle characteristics (good cycle characteristics). The shape of the carbon material may be, for example, flaky like natural graphite, spherical like mesocarbon microbeads, fibrous like graphitized carbon fiber, or aggregates of fine powder.

Among the above negative electrode active materials, oxides are preferably used because they have high thermal stability and are less likely to form dendrites due to Li metal. The oxides are preferably in the form of fibers or fine powder aggregates.

(Negative electrode current collector)
Examples of the negative electrode current collector 122 included in the negative electrode 120 include a band-shaped member made of a metal material such as Cu, Ni, or stainless steel. Among these, it is preferable to use Cu as a forming material and process it into a thin film because it is difficult to form an alloy with lithium and is easy to process.

As a method for supporting the negative electrode active material layer 121 on the negative electrode current collector 122, as in the case of the positive electrode 110, a method of pressure molding, a method of applying a paste-like negative electrode mixture containing a negative electrode active material onto the negative electrode current collector 122, Examples include a method in which a paste-like negative electrode mixture containing a negative electrode active material is applied on the negative electrode current collector 122, dried, and then sintered.

(Solid electrolyte layer)
The solid electrolyte layer 130 has the above-mentioned solid electrolyte (first solid electrolyte). When the positive electrode active material layer 111 contains a solid electrolyte, the solid electrolyte (first solid electrolyte) constituting the solid electrolyte layer 130 and the solid electrolyte (second solid electrolyte) contained in the positive electrode active material layer 111 may be the same material. The solid electrolyte layer 130 functions as a medium for transmitting lithium ions and also functions as a separator for separating the positive electrode 110 and the negative electrode 120.

The solid electrolyte layer 130 can be formed by depositing an inorganic solid electrolyte on the surface of the positive electrode active material layer 111 included in the above-described positive electrode 110 by a sputtering method.

The solid electrolyte layer 130 can be formed by applying a paste-like mixture containing a solid electrolyte to the surface of the positive electrode active material layer 111 of the positive electrode 110 described above and drying it. After drying, the mixture may be press-molded and further pressed by cold isostatic pressing (CIP) to form the solid electrolyte layer 130.

The solid electrolyte layer 130 can be formed by forming the solid electrolyte into pellets in advance, stacking the pellets of the solid electrolyte and the above-mentioned positive electrode active material sheet, and uniaxially pressing them in the stacking direction. The positive electrode active material sheet becomes the positive electrode active material layer 111.

In the obtained laminate of the positive electrode active material layer 111 and the solid electrolyte layer 130, a positive electrode current collector 112 is further placed on the positive electrode active material layer 111. The solid electrolyte layer 130 and the positive electrode 110 can be formed by uniaxial pressing in the stacking direction and further sintering.

The laminate 100 can be manufactured by laminating the negative electrode 120 on the solid electrolyte layer 130 provided on the positive electrode 110 as described above, by contacting the negative electrode active material layer 121 with the surface of the solid electrolyte layer 130 using a known method.

In this embodiment, the battery performance of the positive electrode and lithium ion secondary battery configured as described above can be confirmed by the following method.

<Manufacture of sulfide-based all-solid-state lithium ion secondary battery>
Perform the following operations in a glove box with an argon atmosphere.

(Preparation of Positive Electrode Composite)
0.222 g of the positive electrode active material obtained by the above method, 0.01 g of a conductive material (acetylene _black ), and 0.120 g of a solid electrolyte ( _{75Li2S.25P2S5 ,} manufactured by MSE) are weighed out. The positive electrode active material, the conductive material, and the solid electrolyte are mixed in a mortar for 15 minutes to prepare a positive electrode mixture.

(Preparation of pellets with solid electrolyte and positive electrode composite layer)
Next, 0.3 g of solid electrolyte (75Li ₂ S·25P ₂ S ₅ , manufactured by MSE) is placed in a φ15 mm pellet molding die (manufactured by LabNect), and upper and lower punches are pressed into the die, followed by applying a pressure of 5 MPa with a uniaxial press.

Next, the upper punch is pulled out, and 0.250 g of the above-mentioned positive electrode mixture is placed on top of the solid electrolyte formed in the mold. Insert the upper punch again and apply pressure to 5 MPa using a uniaxial press.

Once the press pressure is released (press pressure is 0 MPa), the pressure is further increased to 120 MPa using a uniaxial press, and the pressurized state is maintained for 5 minutes.

After the pressure is released, a molded pellet in which the solid electrolyte layer and the positive electrode composite layer are integrated is removed from inside the mold. The pellet produced has a diameter of, for example, about 15 mm and a thickness of 2.0 mm.

(Battery Construction)
A battery cell for an all-solid-state battery (manufactured by Hosen Co., Ltd., for electrode size φ15 mm) is used.
The above-mentioned molded pellet is placed inside a cylindrical insulator so that the positive electrode composite layer faces downward. Furthermore, a lithium metal (thickness: 300 μm) punched to a diameter of φ13.5 mm is inserted as a negative electrode on top of the upper solid electrolyte layer.

Furthermore, after inserting a SUS foil with a diameter of 15 mm and a thickness of 50 μm over the negative electrode, a battery cell punch is inserted and the case screws are tightened to produce a sulfide-based all-solid-state lithium ion secondary battery.

<Charge/discharge test>
Using the all-solid-state battery produced by the above method, a charge/discharge test is conducted under the conditions shown below.

(Charge/discharge conditions)
Test temperature: 60℃
(1st charge/discharge (first time))
Maximum charging voltage 4.5V, charging current density 0.01C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.01C, constant current discharge (second charge/discharge )
Maximum charging voltage 4.5V, charging current density 0.10C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.10C, constant current discharge

The ratio of the second discharge capacity (0.10C discharge capacity) to the initial discharge capacity (0.01C discharge capacity) is evaluated as the rate characteristic.

<Manufacture of oxide-based all-solid-state lithium ion secondary battery>
(Manufacture of positive electrode active material sheet)
The positive electrode active material obtained by the above-described manufacturing method and Li ₃ BO ₃ are mixed in a composition of positive electrode active material:Li ₃ BO ₃ =80:20 (molar ratio) to obtain a mixed powder. A resin binder (polypropylene carbonate) and a solvent (1,4-dioxane) were added to the obtained mixed powder in a ratio of mixed powder: resin binder: solvent = 100:20:80 (mass ratio), and a planetary type Mix using a stirring/defoaming device.

The resulting slurry is defoamed using a planetary stirring/defoaming device to obtain a positive electrode mixture slurry.

Using a doctor blade, the resulting positive electrode mixture slurry is applied onto a PET film, and the coating is dried to form a positive electrode film with a thickness of 50 μm.

The positive electrode film is peeled from the PET film, punched into a circular shape with a diameter of 14.5 mm, and further uniaxially pressed in the thickness direction of the positive electrode film at 20 MPa for 1 minute to obtain a positive electrode active material sheet with a thickness of 40 μm. . Li ₃ BO ₃ contained in the positive electrode active material sheet functions as a solid electrolyte in contact with the positive electrode active material within the positive electrode active material sheet. Moreover, Li ₃ BO ₃ functions as a binder that binds the positive electrode active material together within the positive electrode active material sheet.

(Manufacturing of all-solid-state lithium-ion secondary batteries)
The positive electrode active material sheet and solid electrolyte _pellets of _{Li6.75La3Zr1.75Nb0.25O12} (manufactured by Toshima Manufacturing Co., Ltd.) are laminated and uniaxially pressed parallel to the lamination direction to obtain a laminate. The solid electrolyte pellets used have _a diameter of _14.5 mm and a _thickness of 0.5 mm.

A positive electrode current collector (gold foil, thickness 500 μm) is further layered on the positive electrode active material sheet of the obtained laminate, and heated at 300° C. for 1 hour under pressure of 110 gf to burn off organic components. The temperature is further increased to 800°C at a rate of 5°C/min, and then sintered at 800°C for 1 hour to obtain a laminate of a solid electrolyte layer and a positive electrode.

Next, the following operations are performed in a glove box with an argon atmosphere.

A negative electrode (Li foil, 300 μm thick), a negative electrode current collector (stainless steel plate, 50 μm thick), and a wave washer (made of stainless steel) are further stacked on the solid electrolyte layer of the laminate of the solid electrolyte layer and the positive electrode.

For the stacked stack from the positive electrode to the wave washer, place the positive electrode on the bottom cover of parts for coin-type battery R2032 (manufactured by Hosen Co., Ltd.), stack it on the wave washer, cover the top cover, and swage it with a swaging machine. , fabricate an oxide-based all-solid-state lithium ion secondary battery.

<Charge/discharge test>
Using the all-solid-state battery produced by the above method, a charge-discharge test is carried out under the following conditions.

(Charge/discharge conditions)
Test temperature: 60℃
(1st charge/discharge (first time))
Maximum charging voltage 4.5V, charging current density 0.01C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.01C, constant current discharge (second charge/discharge )
Maximum charging voltage 4.5V, charging current density 0.10C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.10C, constant current discharge

The ratio of the second discharge capacity (0.10C discharge capacity) to the initial discharge capacity (0.01C discharge capacity) is evaluated as the rate characteristic.

The electrode configured as described above has the above-mentioned positive electrode active material, which improves the rate characteristics and enhances the battery performance of the lithium-ion secondary battery.

The lithium-ion secondary battery configured as described above exhibits excellent battery performance due to the presence of the above-mentioned positive electrode active material.

Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. The various shapes and combinations of the constituent members shown in the above example are merely examples, and can be variously changed based on design requirements and the like without departing from the gist of the present invention.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

<Composition analysis of lithium metal composite oxide>
The composition analysis of the lithium metal composite oxide produced by the method described below was carried out by dissolving the obtained lithium metal composite oxide particles in hydrochloric acid and then using an inductively coupled plasma optical emission spectrometer (SPS3000, manufactured by SII NanoTechnology Inc.).

<Confirmation of coating elements contained in the coating layer>
The coating elements contained in the coating layer were confirmed by STEM-EDX.
Specifically, a sample was prepared by forming particles of the positive electrode active material into a thin film. Next, the obtained sample was placed on a Cu mesh and irradiated with an electron beam at an accelerating voltage of 200 kV to perform STEM-EDM analysis. The Cu mesh used in the measurements does not affect the measurement results. Therefore, any Cu mesh that is normally used in STEM-EDX can be used.

The measurement equipment and measurement conditions used for STEM observation are as follows.
Analytical electron microscope: ARM200F (manufactured by JEOL Ltd.)
EDX detector: JED-2300T (manufactured by JEOL Ltd.)
Acceleration voltage: 200kV

Next, EDX analysis was performed in the same field of view as the STEM observation range. Characteristic X-rays were generated for each particle in the field of view by electron beam excitation, and an X-ray spectrum was obtained containing characteristic X-rays of multiple elements contained in the measurement position. The number of characteristic X-rays (count number, intensity) of each element contained in the measured spectrum corresponds to the concentration of each element.

Next, for any particle included in the field of view, the coating elements (Nb, Ta, Ti, Al, B, W, Zr, and Ge) contained in the coating layer are measured along an imaginary line set from the outside of the particle to the center of the particle. A line profile of concentration was obtained. At the same time, a line profile of the concentration of transition metals contained in the core particles was obtained.

The line profile was created by plotting the X-ray spectrum intensity for each distance from the outside of the particle, with the horizontal axis representing the distance from the outside of the particle along a virtual line set from the outside of the particle to the center (unit: nm) and the vertical axis representing the characteristic X-ray spectrum intensity of each element (unit: X-ray count number, arbitrary unit: a.u.) in the range where the outer edge and coating layer of the particle can be confirmed.

At this time, the line profile of the coating element is compared with the line profile of the element contained in the core particle, and if the line profile of the coating element has a continuous shape with a peak outside the core particle, it has been detected. It was determined that a coating layer containing a coating element was present on the surface of the core particle.

<Measurement of Coating Layer Thickness>
The thickness of the coating layer was determined by STEM-EDX.
EDX analysis was performed under the above conditions, and a line profile was created from the outside of the particles to the center of the particles for the element that was most sensitively detected in the EDX analysis results among the transition metals that were not included in the coating layer but were only included in the core particles. For the obtained line profile, a range in which positive values were detected continuously for 30 nm or more from the outside of the particles to the center of the particles was confirmed, and the start point of the outside of the particles in that range was determined. In the positive electrode active material prepared in the examples described below, the "element that was most sensitively detected in the EDX analysis results" was Ni.

Next, when the detected amount of Ni at a position 20 nm from the starting point toward the center of the particle is defined as X, the position where the detected amount of Ni is X/2 and the position closest to the starting point is determined as the surface of the core particle. Ta.

Next, a line profile was created for the coating elements that overlapped with the surface of the core particle and continuously detected positive values from the outside of the particle toward the center of the particle. Regarding the obtained line profile of the coating element, when the maximum value was located outside the core particle surface, it was defined that the coating layer was present.

Next, when the detected amount of the coating element at the position where the line profile of the coating element shows the maximum value (peak position) is Y, the detected amount of the coating element is at a position outside the particle that is Y/2 from the peak position. The position closest to the peak position was determined as the surface of the coating layer.

Then, the distance between the surface of the coating layer and the surface of the core particle was taken as the thickness of the coating layer. The above measurement was performed three times, and the arithmetic average of the thicknesses of each coating layer was taken as the desired thickness of the coating layer.

<Measurement of the ratio of the Si element ratio to the total of the Si element ratio and the transition metal element ratio on the surface of the coating layer>
The surface of the positive electrode active material was subjected to XPS analysis under the following conditions to obtain a narrow scan spectrum of elements on the surface of the positive electrode active material.
Measurement method: X-ray photoelectron spectroscopy (XPS)
X-ray source: AlKα radiation (1486.6 eV)
X-ray spot diameter: 400 μm
Neutralization conditions: neutralization electron gun (accelerating voltage 0.2 V, current 100 μA)

The integral value of the Si2p waveform was used as the photoelectron intensity of Si.

As the photoelectron intensity of Ni, the integral value of the waveform of Ni2p3/2 was used.

The integral value of the Co2p3/2 waveform was used as the photoelectron intensity of Co.

As the photoelectron intensity of Mn, the integral value of the waveform of Mn2p1/2 was used.

As the photoelectron intensity of Nb, the integral value of the waveform of Nb3d was used.

The integral value of the waveform of Ti2p was used as the photoelectron intensity of Ti.

The integral value of the Ta4f waveform was used as the photoelectron intensity of Ta.

When the "element ratio of transition metals" is β, the ratio of "Si element ratio α" to "the sum of Si element ratio α and transition metal element ratio β" (α/(α+β)) is determined based on the measurement results. was calculated.

<Measurement of the ratio between the total element ratio of coating elements on the surface of the coating layer and the Si element ratio>
Based on the XPS measurement results under the above-mentioned measurement conditions, the ratio (A/α) of "total element ratio A of coating elements" to "Si element ratio α" was calculated.

<Example 1>
(Production of lithium metal composite oxide)
After putting water into a reaction tank equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A mixed raw material liquid is prepared by mixing a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution at an atomic ratio of 0.50:0.20:0.30 of nickel atoms, cobalt atoms, and manganese atoms. did.

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent to the reaction vessel under stirring, and nitrogen gas was continuously passed through the reaction vessel. An aqueous solution of sodium hydroxide was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 11.1, and nickel-cobalt-manganese composite hydroxide particles were obtained. After washing, the particles were dehydrated in a centrifuge, washed, dehydrated, isolated, and dried at 120°C to obtain nickel-cobalt-manganese composite hydroxide 1.

Nickel cobalt manganese composite hydroxide particles 1 and lithium hydroxide powder were weighed and mixed at a ratio of Li/(Ni+Co+Mn)=1.05, and then baked at 970°C for 4 hours in an air atmosphere to form layered crystals. A lithium metal composite oxide 1 having a structure was obtained. The particles of lithium metal composite oxide 1 correspond to "core particles" in the present invention.

When the composition of lithium metal composite oxide 1 was analyzed and made to correspond to compositional formula (1), it was found that x=1.05, y=0.20, z=0.30, and w=0.

(Production of First Reaction Product)
Next, 1600 ml of ethanol was placed in a reaction vessel equipped with a stirrer, and then 20 g of lithium metal composite oxide 1 and 200 μl of a silane coupling agent represented by the following formula (A) were added to the ethanol and stirred for 18 hours. The resulting dispersion corresponds to the "first dispersion" in the present invention.

After stirring, the resulting dispersion was filtered under suction. The filtered solid was vacuum dried at room temperature for 1 hour, and then vacuum dried at 100°C for 1 hour.

The obtained dried product was crushed in a mortar to obtain a reaction product 1 in which the surface of the lithium metal composite oxide 1 was coated with a silane coupling agent. Reaction product 1 corresponds to the "first reaction product" in the present invention.

(Production of Positive Electrode Active Material)
Next, 36 ml of ethanol was placed in a reaction vessel equipped with a stirrer, and then 5 g of reaction product 1 and 1 g of Nb(OC ₂ H ₅ ) ₅ were added to the ethanol, followed by stirring at a stirring speed of 400 rpm for 15 minutes.
Nb(OC ₂ H ₅ ) ₅ corresponds to the "compound containing a coating element" in the present invention. The obtained dispersion corresponds to the "second dispersion" in the present invention.

Next, 40 ml of acetonitrile, which is a monodentate ligand, was added to the obtained dispersion while stirring it.

Next, while stirring the dispersion, a liquid catalyst prepared separately was added to the dispersion at an addition rate of 55.6 μl/min. The catalyst used was prepared by mixing 80 ml of ethanol, 50 μl of 28% aqueous ammonia solution, and 175 μl of water.

After adding the catalyst, the dispersion was stirred at a stirring speed of 400 rpm for 19 hours.

After stirring, the resulting dispersion was filtered under suction. The filtered solid was dried in vacuum at 120°C for 1 hour. This formed a coating layer on the particle surfaces of the core particles.

The obtained dried material was crushed in a mortar to obtain positive electrode active material 1.

<Example 2>
In the above (manufacture of positive electrode active material), the amount of all the materials used was increased by 1.4 times, and after vacuum drying the filtered solid at 120°C for 1 hour, A positive electrode active material 2 of Example 2 was obtained in the same manner as in Example 1, except that the material was heat-treated at 500° C. for 2 hours.

<Example 3>
Positive electrode active material 3 of Example 3 was obtained in the same manner as in Example 1 except that 1 g of Ti(OC ₂ H ₅ ) ₄ was used instead of Nb(OC ₂ H ₅ ) ₅ .

Example 4
A positive electrode active material 4 of Example 4 was obtained in the same manner as in Example 2, except that 1.4 g of Ta(OC ₂ H ₅ ) ₅ was used instead of Nb(OC ₂ H ₅ ) ₅ .

<Comparative example 1>
Lithium metal composite oxide 1 was used as positive electrode active material C1 in Comparative Example 1.

<Comparative Example 2>
A positive electrode active material C2 of Comparative Example 2 was obtained in the same manner as in Example 2, except that, instead of the reaction product 1, the lithium metal composite oxide 1 was reacted with Nb(OC ₂ H ₅ ) ₅ , i.e., the lithium metal composite oxide 1 was reacted directly with Nb(OC ₂ H ₅ ) ₅ without reacting it with a silane coupling agent.

<Manufacture of liquid-based lithium ion secondary batteries>
(Preparation of positive electrode for lithium ion secondary battery)
A positive electrode active material obtained by the manufacturing method described below, a conductive material (acetylene black), and a binder (PVdF) are added and kneaded in a ratio of positive electrode active material: conductive material: binder = 92:5:3 (mass ratio). In this way, a paste-like positive electrode mixture was prepared. When preparing the positive electrode mixture, N-methyl-2-pyrrolidone was used as an organic solvent.

The obtained positive electrode mixture was applied to a 40 μm thick Al foil serving as a current collector and vacuum dried at 150° C. for 8 hours to obtain a positive electrode for a lithium ion secondary battery. The electrode area of this positive electrode for a lithium ion secondary battery was 1.65 cm ² .

(Fabrication of lithium-ion secondary battery (coin-type half cell))
The following operations were carried out in a glove box under an argon atmosphere.

The positive electrode for lithium ion secondary batteries prepared in (Preparation of positive electrode for lithium ion secondary batteries) was placed on the bottom cover of a part for coin type battery R2032 (manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down, and a separator (porous polyethylene film) was placed on top of it.

300 μl of an electrolyte was poured into the battery. The electrolyte was prepared by dissolving LiPF ₆ in a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate to a concentration of 1.0 mol/l.

Next, using metal lithium as the negative electrode, place the negative electrode on the upper side of the laminated film separator, cover the top with a gasket, and swage it with a crimping machine to lithium ion secondary battery lithium ion secondary battery (coin type half cell R2032). (hereinafter sometimes referred to as "half cell") was produced.

<Charge/discharge test>
Using the half cell produced by the above method, a charge/discharge test was conducted under the conditions shown below, and the initial charge/discharge capacity and rate characteristics were evaluated.

(Charge/discharge conditions: initial charge/discharge capacity)
Test temperature 25℃
Maximum charging voltage 4.5V, charging current density 0.2C, cut-off current density 0.05C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.2C, constant current discharge

(Charge/discharge conditions: rate characteristics)
Test temperature 25℃
Maximum charging voltage 4.5V, charging current density 1C, cut-off current density 0.05C, constant current-constant voltage charging, minimum discharge voltage 2.5V, discharge current density 0.2C, 0.5C, 1C, 2C, 3C, 5C, 10C

The evaluation results are shown in Tables 1 and 2 below. Table 1 shows the measurement results for the coating layer. Table 2 shows the battery characteristics of half cells using each of the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 and 2.

6 is a graph showing the results of the evaluation of rate characteristics. The horizontal axis of Fig. 6 shows current density (unit: mA/ ^cm2 ), and the vertical axis shows discharge capacity (unit: mAh/g). In the figure, Examples 1 and 2 and Comparative Examples 1 and 2 are shown as representative samples.

As a result of the evaluation, it was found that the positive electrode active materials of Examples 1 and 2 were less likely to decrease in discharge capacity even during high-voltage operation and had excellent rate characteristics.

<Manufacture of sulfide-based all-solid-state lithium ion secondary battery>
The following operations were performed in a glove box with an argon atmosphere.

(Preparation of Positive Electrode Composite)
0.222 g of the positive electrode active material obtained by the above method, 0.01 g of a conductive material (acetylene _black ), and 0.120 g of a solid electrolyte ( _{75Li2S.25P2S5 ,} manufactured by MSE) were weighed out. The positive electrode active material, the conductive material, and the solid electrolyte were mixed in a mortar for 15 minutes to prepare a positive electrode mixture.

(Preparation of pellets with solid electrolyte and positive electrode composite layer)
Next, 0.3 g of a solid electrolyte (75Li ₂ S·25P ₂ S ₅ , manufactured by MSE) was placed in a φ15 mm pellet molding die (manufactured by LabNect), and upper and lower punches were pressed into the die, followed by applying a pressure of 5 MPa with a uniaxial press.

Next, the upper punch was removed, and 0.250 g of the above-mentioned positive electrode composite was placed on top of the solid electrolyte formed in the mold. The upper punch was reinserted, and the mixture was pressurized to 5 MPa using a uniaxial press.

After the press pressure was once released (press pressure 0 MPa), the pressure was further increased to 120 MPa using a uniaxial press, and the pressurized state was maintained for 5 minutes.

After the pressure was released, a molded pellet in which the solid electrolyte layer and the positive electrode composite layer were integrated was removed from inside the mold. The pellet had a diameter of 15 mm and a thickness of about 2.0 mm.

(Battery Construction)
A battery cell for an all-solid-state battery (manufactured by Hosen Co., Ltd., for electrode size φ15 mm) was used.
The above-mentioned molded pellet was placed inside a cylindrical insulator so that the positive electrode composite layer was facing down. Furthermore, a lithium metal (thickness: 300 μm) punched to a diameter of φ13.5 mm was inserted as a negative electrode on the upper solid electrolyte layer.

Furthermore, after inserting a SUS foil with a diameter of 15 mm and a thickness of 50 μm over the negative electrode, a battery cell punch was inserted and the case screws were tightened to produce a sulfide-based all-solid-state lithium ion secondary battery.

<Charge/discharge test>
A charge/discharge test was conducted under the conditions shown below using the all-solid-state battery produced by the above method.

(Charge/discharge conditions)
Test temperature: 60℃
(1st charge/discharge (first time))
Maximum charging voltage 4.5V, charging current density 0.01C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.01C, constant current discharge (second charge/discharge )
Maximum charging voltage 4.5V, charging current density 0.10C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.10C, constant current discharge

The ratio of the second discharge capacity (0.10C discharge capacity) to the first discharge capacity (0.01C discharge capacity) was evaluated as the rate characteristic.

The evaluation results are shown in Table 3 below. The battery characteristics using each of the positive electrode active materials of Example 2 and Comparative Example 1 are shown. The "rate characteristics" shown in Table 3 indicate the "ratio of 0.10C discharge capacity to 0.01C discharge capacity" expressed as a percentage (%).

As a result of the evaluation, the rate characteristics of the all-solid lithium ion secondary battery using the positive electrode active material of Example 2 were significantly higher than those of the all-solid lithium ion secondary battery using the positive electrode active material of Comparative Example 1. It turned out to be excellent.

<Production of oxide-based all-solid-state lithium-ion secondary battery>
(Production of Positive Electrode Active Material Sheet)
The positive electrode active material obtained by the above-mentioned manufacturing method and Li ₃ BO ₃ were mixed in a composition of positive electrode active material:Li ₃ BO ₃ = 80:20 (molar ratio) to obtain a mixed powder. A resin binder (polypropylene carbonate) and a solvent (1,4-dioxane) were added to the obtained mixed powder in a ratio of mixed powder:resin binder:solvent = 100:20:80 (mass ratio), and mixed using a planetary stirring and degassing device.

The resulting slurry was defoamed using a planetary mixing and defoaming device to obtain a positive electrode mixture slurry.

The resulting positive electrode mixture slurry was applied to a PET film using a doctor blade, and the coating was dried to form a positive electrode film with a thickness of 50 μm.

The positive electrode film was peeled off from the PET film, punched into a circle with a diameter of 14.5 mm, and then uniaxially pressed in the thickness direction of the positive electrode film at 20 MPa for 1 minute to obtain a positive electrode active material sheet with a thickness of 40 μm. The Li ₃ BO ₃ contained in the positive electrode active material sheet functions as a solid electrolyte that contacts the positive electrode active material in the positive electrode active material sheet. In addition, the Li ₃ BO ₃ functions as a binder that binds the positive electrode active material in the positive electrode active material sheet.

(Manufacture of all-solid-state lithium ion secondary battery)
A positive electrode active material sheet and solid electrolyte pellets of Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ (manufactured by Toyoshima Seisakusho Co., Ltd.) were laminated and uniaxially pressed in parallel to the lamination direction to form a laminate. Obtained. The solid electrolyte pellets used had a diameter of 14.5 mm and a thickness of 0.5 mm.

A positive electrode current collector (gold foil, 500 μm thick) was further placed on the positive electrode active material sheet of the obtained laminate, and heated at 300°C for 1 hour while being pressed at 110 gf to burn off the organic matter. The temperature was then increased to 800°C at a rate of 5°C/min, and the laminate was sintered at 800°C for 1 hour to obtain a laminate of a solid electrolyte layer and a positive electrode.

Next, the following operations were performed in a glove box with an argon atmosphere.

A negative electrode (Li foil, 300 μm thick), a negative electrode current collector (stainless steel plate, 50 μm thick), and a wave washer (made of stainless steel) were further stacked on the solid electrolyte layer of the laminate of the solid electrolyte layer and the positive electrode.

For the stacked stack from the positive electrode to the wave washer, place the positive electrode on the bottom cover of parts for coin-type battery R2032 (manufactured by Hosen Co., Ltd.), stack it on the wave washer, cover the top cover, and swage it with a swaging machine. , we fabricated an oxide-based all-solid-state lithium-ion secondary battery.

<Charge/discharge test>
Using the all-solid-state battery prepared by the above method, a charge/discharge test was carried out under the following conditions.

(Charge/discharge conditions)
Test temperature: 60℃
(1st charge/discharge (first time))
Maximum charging voltage 4.5V, charging current density 0.01C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.01C, constant current discharge (second charge/discharge )
Maximum charging voltage 4.5V, charging current density 0.10C, cut-off current density 0.002C, constant current-constant voltage charging Minimum discharge voltage 2.5V, discharge current density 0.10C, constant current discharge

The ratio of the second discharge capacity (0.10C discharge capacity) to the first discharge capacity (0.01C discharge capacity) was evaluated as the rate characteristic.

The evaluation results are shown in Table 4 below. The battery characteristics using each positive electrode active material of Example 2 and Comparative Example 1 are shown. The "rate characteristic" shown in Table 4 indicates a value expressed as a percentage (%) of "ratio of 0.10C discharge capacity to 0.01C discharge capacity".

As a result of the evaluation, it was found that the all-solid-state lithium-ion secondary battery using the positive electrode active material of Example 2 had significantly higher rate characteristics than the all-solid-state lithium-ion secondary battery using the positive electrode active material of Comparative Example 1, and was therefore superior in rate characteristics.

DESCRIPTION OF SYMBOLS 1... Separator, 2... Positive electrode, 3... Negative electrode, 4... Electrode group, 5... Battery can, 6... Electrolyte, 7... Top insulator, 8... Sealing body, 10... Lithium ion secondary battery, 21... Positive electrode lead, 31... Negative electrode lead, 100... Laminate, 110... Positive electrode, 111... Positive electrode active material layer, 112... Positive electrode current collector, 113... External terminal, 120... Negative electrode, 121... Negative electrode active material layer, 122... Negative electrode current collector , 123... External terminal, 130... Solid electrolyte layer, 200... Exterior body, 200a... Opening, 1000... All solid state secondary battery

Claims (22)

A core particle made of a lithium metal composite oxide;
a coating layer that coats at least a portion of the core particle;
The lithium metal composite oxide has a layered crystal structure and contains at least lithium and a transition metal,
The coating layer is a positive electrode active material that satisfies the following (1) to (3).
(1) The coating layer is made of an oxide containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr and Ge.
(2) The coating layer has an average thickness of 1 nm or more and less than 100 nm.
(3) The Si element ratio α obtained from the results of XPS analysis of the coating layer and the sum β of the element ratios of the transition metal and the coating element obtained from the results of XPS analysis of the coating layer are used to determine α/(α+β), which is 0.02 or more. The positive electrode active material according to claim 1, wherein in an XPS analysis of the coating layer, A/α, obtained from the Si element ratio α and the total element ratio A of the coating elements, is 1.0 or more and 10.0 or less. The coating layer mainly contains at least one oxide selected from the group consisting of Nb ₂ O ₅ , Ta ₂ O ₅ , TiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , WO ₃ , ZrO ₂ and GeO _{2 .} As an ingredient,
The positive electrode active material according to claim 1 or 2, wherein the main component is amorphous. The positive electrode active material according to any one of claims 1 to 3, wherein the transition metal is at least one selected from the group consisting of Ni, Co, Mn, Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V. The positive electrode active material according to claim 4 , wherein the lithium metal composite oxide is represented by the following formula (1):
Li[Li _x (Ni _(1-y-z-w) Co _y Mn _z M _w ) _1-x ] O ₂ ... (1)
(wherein M is at least one element selected from the group consisting of Fe, Cu, Mg, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V, and satisfies -0.10≦x≦0.30, 0<y≦0.40, 0≦z≦0.40, and 0≦w≦0.10.) The positive electrode active material according to claim 5, wherein in the above formula (1), 1-y-z-w≧0.50 and y≦0.30 are satisfied. A positive electrode having a positive electrode active material layer containing the positive electrode active material according to any one of claims 1 to 6. The positive electrode according to claim 7, further comprising a solid electrolyte. A lithium ion secondary battery comprising the positive electrode according to claim 7 or 8, a negative electrode, and a non-aqueous electrolyte sandwiched between the positive electrode and the negative electrode. The lithium ion secondary battery according to claim 9, wherein the non-aqueous electrolyte is a solid electrolyte. The lithium ion secondary battery according to claim 10, wherein the positive electrode contains the same material as the solid electrolyte that constitutes the nonaqueous electrolyte. The lithium ion secondary battery according to claim 11, wherein the positive electrode active material layer includes the positive electrode active material and the solid electrolyte. The lithium ion secondary battery according to any one of claims 10 to 12, wherein the solid electrolyte constituting the nonaqueous electrolyte has an amorphous structure. The lithium ion secondary battery according to any one of claims 10 to 13, wherein the solid electrolyte constituting the nonaqueous electrolyte is an oxide solid electrolyte. a step of reacting the lithium metal composite oxide particles dispersed in the first dispersion with a surface treatment agent to obtain a first reaction product;
A step of adding a compound containing at least one coating element selected from the group consisting of Nb, Ta, Ti, Al, B, W, Zr and Ge to a second dispersion in which the first reaction product is dispersed in a dispersion medium;
adding water or a basic aqueous solution dropwise to the second dispersion containing the compound to obtain a second reaction product;
and drying the second reaction product,
The lithium metal composite oxide has a layered crystal structure and contains at least lithium and a transition metal,
The method for producing a positive electrode active material, wherein the surface treatment agent is a silane coupling agent having a first functional group capable of coordinating with the coating element and a second functional group capable of bonding to the lithium metal composite oxide. The method for producing a positive electrode active material according to claim 15, wherein the basic aqueous solution is dripped in the step of obtaining the second reaction product. The method for producing a positive electrode active material according to claim 15 or 16, further comprising a step of heat-treating the dried product obtained in the drying step at 100° C. or higher and 800° C. or lower after the drying step. The method for producing a positive electrode active material according to any one of claims 15 to 17, wherein the first functional group is an amino group. The method for producing a positive electrode active material according to any one of claims 15 to 18, wherein the second functional group is an alkoxy group. The method for producing a positive electrode active material according to any one of claims 15 to 19, wherein the compound is an alkoxide containing the coating element. 21. The method according to claim 15, further comprising a step of adding a monodentate ligand to the second dispersion between the step of adding the compound and the step of obtaining the second reaction product. A method for producing a positive electrode active material. 22. The method for producing a positive electrode active material according to claim 21, wherein the monodentate ligand is acetonitrile.

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