Positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Abstract

The present invention relates to a positive electrode active material as defined in the claims and the description, to the use thereof for suppressing thermal runaway in a non-aqueous electrolyte secondary battery, and to a non-aqueous electrolyte secondary battery employing the same.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, its use for controlling oxygen release from the positive electrode active material and / or suppressing or avoiding thermal runaway in a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery comprising the material. Background Art

[0002] Lithium ion secondary batteries have the advantages of being compact and lightweight and having high energy density, while also having high charge / discharge voltage and large charge / discharge capacity, and are therefore of interest as power sources for driving AV equipment and electronic devices such as personal computers.

[0003] Organic solvents, which are primarily flammable, are commonly used as electrolytes in lithium-ion secondary batteries, and therefore require high thermal stability. For example, due to the heat provided when the lithium-ion secondary battery is in a charging state, oxygen is released from the positive electrode active material crystals, but this oxygen reaction with the electrolyte is known to cause thermal runaway.

[0004] In particular, active materials containing Ni, Co, and Mn have been widely used as positive electrode active materials in recent years. When this type of positive electrode active material has a high Ni content, the phase transition reaction of the positive electrode active material occurs in a lower temperature region, causing a sudden release of oxygen, which therefore makes it possible for thermal runaway to occur in the positive electrode active material. At the same time, due to the large battery capacity, there is a demand for materials with a high Ni content, and this therefore leads to a trend of reduced thermal stability (which is a characteristic of materials with a high Ni content).

[0005] In order to suppress thermal runaway of this type of positive electrode active material, Patent Document 1, for example, proposes a positive electrode active material comprising a lithium-transition metal composite oxide containing 80 mol% or more of Ni and 0.1 mol% to 1.5 mol% of B relative to the total moles of metal elements excluding Li, wherein B and at least one element (M1) selected from Groups 4 to 6 are present on the surface of particles of the lithium-transition metal composite oxide, and the mole fraction of M1 relative to the total moles of metal elements excluding Li on the surface of particles having a particle size of less than 30% is greater than the mole fraction of M1 relative to the total moles of metal elements excluding Li on the surface of particles having a particle size of greater than 70% on a volume basis. Patent Document 1 then points out that the use of this type of composite oxide in lithium-ion secondary batteries limits the self-heating rate, even at high temperatures.

[0006] Prior art literature:

[0007] [Patent Document 1] JP 2021-51979A Summary of the Invention

[0008] [Problems to be Solved by the Invention]

[0009] However, although the positive electrode active material of Patent Document 1 can be expected to have a certain inhibitory effect on thermal runaway caused by the reaction between oxygen released from the positive electrode active material and the electrolyte because the particle surface of the positive electrode active material is covered with a boron compound, this alone does not have a sufficient effect of suppressing thermal runaway, and there is still room for improvement.

[0010] Therefore, there is a need for a method of suppressing thermal runaway other than the method in which the surface of the cathode active material is covered with a compound as described above.

[0011] The present disclosure has been devised in view of the above circumstances, and an object thereof is to provide a cathode active material capable of suppressing thermal runaway in a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery employing the cathode active material.

[0012] [Methods of solving the problem]

[0013] The inventors of the present invention have conducted careful research to solve the above problems. As a result of these studies, the inventors of the present invention have obtained a positive electrode active material, wherein when the volume-based particle size frequency distribution of the primary particles of the composite oxide containing at least lithium and transition metals is divided into multiple peaks, these peaks include the following specific peaks: a main peak showing a maximum peak area value, and at least one peak having an area of ​​0.1-1 in terms of an area ratio relative to the area of ​​the main peak, and the ratio of the primary particle size at the peak top of the adjacent specific peaks (large particle size / small particle size) is all 1.2-8, and it is found that when such a positive electrode active material is used in a non-aqueous electrolyte secondary battery, the maximum release rate of oxygen from the positive electrode active material (hereinafter referred to as "maximum oxygen release rate") can be limited, and thermal runaway can also be suppressed. Specifically, the present disclosure provides the following features.

[0014] (1) In a first aspect, the present invention relates to the use of a positive electrode active material for a non-aqueous electrolyte secondary battery for suppressing or avoiding thermal runaway in the non-aqueous electrolyte secondary battery, the positive electrode active material comprising a composite oxide containing at least lithium, a transition metal and oxygen, wherein, when the volume-based particle size frequency distribution of primary particles of the composite oxide is divided into a plurality of peaks, the peaks include specific peaks comprising: a main peak exhibiting a maximum peak area value, and at least one peak having an area of ​​0.1-1 in terms of an area ratio relative to the area of ​​the main peak, and the ratios of the primary particle sizes at the peak tops of adjacent specific peaks (large particle size / small particle size) are all 1.2-8.

[0015] (2) In a second aspect, the present invention relates to the use of a positive electrode active material for a non-aqueous electrolyte secondary battery for controlling the release of oxygen from the positive electrode active material, the positive electrode active material comprising a composite oxide containing at least lithium, a transition metal and oxygen, wherein, when the volume-based particle size frequency distribution of primary particles of the composite oxide is divided into a plurality of peaks, the peaks include specific peaks comprising: a main peak exhibiting a maximum peak area value, and at least one peak having an area of ​​0.1-1 in terms of an area ratio relative to the area of ​​the main peak, and the ratios of the primary particle sizes at the peak tops of adjacent specific peaks (large particle size / small particle size) are all 1.2-8.

[0016] (3) In a third aspect, the present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, the positive electrode active material comprising a composite oxide containing at least lithium, a transition metal and oxygen, wherein, when the volume-based particle size frequency distribution of primary particles of the composite oxide is divided into a plurality of peaks, the peaks include specific peaks comprising: a main peak exhibiting a maximum peak area value, and at least one peak having an area of ​​0.1-1 in terms of an area ratio relative to the area of ​​the main peak, and the ratios of the primary particle sizes at the peak tops of adjacent specific peaks (large particle size / small particle size) are all 1.2-8.

[0017] The composite oxide is preferably a lithium-nickel composite oxide. More preferably, the composite oxide is a lithium-nickel composite oxide having a layered rock salt structure and having the general formula Li a Ni 1-b-c Mn b M c O2 represents (in this formula, M is at least one element other than Li, Ni, Mn and O, 0.95≤a≤1.15, and 0≤b+c≤0.70).

[0018] In the positive electrode active material for a nonaqueous electrolyte secondary battery as disclosed in (1) or (2) or (3) above or in the preferred embodiments below, preferably, the primary particle diameters at the peak tops of the specific peaks are all 80 nm to 15 μm.

[0019] (4) In a fourth aspect, the present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material as disclosed in (3) or in its above or below preferred embodiments.

[0020] [Effects of the Invention]

[0021] According to the present disclosure, the particle size of primary particles present in a cathode active material is controlled, thereby making it possible to provide a cathode active material capable of suppressing thermal runaway, and a nonaqueous electrolyte secondary battery using the cathode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] [ Figure 1A ] is an example of a scanning electron microscope photograph of a complex oxide.

[0023] [ Figure 1B ] is one of them Figure 1A The primary particles are enclosed by dotted lines in a scanning electron micrograph of a composite oxide.

[0024] [ Figure 2 ] is a volume-based particle size frequency distribution curve of primary particles in the positive electrode active material sample according to Example 1.

[0025] [ Figure 3 ] is a DTG (differential thermogravimetry) curve of the positive electrode active material sample according to Example 1.

[0026] [ Figure 4 ] is a volume-based particle size frequency distribution curve of the primary particles in the positive electrode active material sample according to Example 2.

[0027] [ Figure 5 ] is the DTG curve of the positive electrode active material sample according to Example 2.

[0028] [ Figure 6 ] is a volume-based particle size frequency distribution curve of primary particles in the positive electrode active material sample according to Example 3.

[0029] [ Figure 7 ] is the DTG curve of the positive electrode active material sample according to Example 3.

[0030] [ Figure 8 ] is a volume-based particle size frequency distribution curve of the primary particles in the positive electrode active material sample according to Example 4.

[0031] [ Figure 9 ] is the DTG curve of the positive electrode active material sample according to Example 4.

[0032] [ Figure 10 ] is a volume-based particle size frequency distribution curve graph of primary particles in the positive electrode active material sample according to Comparative Example 1.

[0033] [ Figure 11 ] is the DTG curve of the positive electrode active material sample according to Comparative Example 1. DETAILED DESCRIPTION

[0034] [Examples of the invention]

[0035] Embodiments of the present disclosure will be described below, but the present disclosure is by no means limited to the description of the embodiments and the present disclosure can be implemented with appropriate modifications added thereto.

[0036] Unless otherwise specified, the comments on the preferred embodiments apply both to the use of the present invention and the positive electrode active material of the present invention and to the secondary battery of the present invention.

[0037] <Positive electrode active material for non-aqueous electrolyte secondary battery and its use>

[0038] According to an embodiment of the present disclosure, the positive electrode active material for a non-aqueous electrolyte secondary battery includes a composite oxide containing at least lithium, a transition metal and oxygen, wherein, when the volume-based particle size frequency distribution of the primary particles of the composite oxide is divided into multiple peaks, these peaks include specific peaks comprising: a main peak exhibiting a maximum peak area value, and at least one peak having an area of ​​0.1-1 in terms of an area ratio relative to the area of ​​the main peak, and the ratios of the primary particle sizes at the peak tops of adjacent specific peaks (large particle size / small particle size) are all 1.2-8.

[0039] The present inventors have discovered that the temperature at which a composite oxide releases oxygen is related to the particle size distribution of the primary particles of the composite oxide. Specifically, the relationship is such that the larger the particle size of the primary particles of the composite oxide, the higher the oxygen release temperature. When performing DTG measurements of the composite oxide, TG-MS (thermogravimetric mass spectrometry) confirmed that almost all weight loss at temperatures up to approximately 310°C was due to oxygen release. The present inventors further discovered that there is a corresponding relationship between the temperature at each peak top obtained when the DTG curve is divided into multiple oxygen release peaks and the particle size at each peak top obtained when the particle size frequency distribution is divided into multiple peaks.

[0040] Furthermore, it is also understood that the release amount of oxygen released from the composite oxide particles depends on the area of ​​each peak obtained when the particle size frequency distribution of the primary particles of the composite oxide is divided into a plurality of peaks.

[0041] Assume a case where the particle sizes of the primary particles of the composite oxide are arranged so that only one sharp peak exists in the particle size frequency distribution and division into multiple peaks is impossible (see Figure 10 ), or in the case where even if separation into multiple peaks is possible, these peaks are close together, oxygen is released from the primary particles within a specific narrow temperature range in the DTG curve (see Figure 11 ), and this oxygen reacts with the electrolyte, and thus there is sudden heat generation, causing thermal runaway.

[0042] In contrast, in the positive electrode active material according to the embodiment of the present disclosure, this means that the volume-based particle size frequency distribution of the primary particles of the composite oxide can be divided into a plurality of peaks (specific peaks) having a fixed area or larger area relative to the main peak (see Figure 2In this type of composite oxide, the oxygen release peak in the DTG curve can then be split into multiple peaks (see Figure 3 ). In addition, the presence of a peak having a fixed area or larger in the particle size frequency distribution of primary particles means that a fixed amount or larger amount of oxygen is released. This further means that by providing a plurality of such specific peaks, the temperature at which a fixed amount or larger amount of oxygen is released can be divided into a plurality of temperatures.

[0043] Furthermore, by setting a fixed ratio for the particle sizes of primary particles corresponding to the peak tops of adjacent specific peaks, multiple primary particles with fixed differences in the corresponding peak tops are coexisting in the particle size frequency distribution. This results in a large difference in the temperature at which a fixed amount or greater of oxygen is released, and by distributing the oxygen release amount and temperature, it is possible to suppress sudden heat generation in the electrolyte.

[0044] It should be noted that while the phrase "a plurality of primary particles... exist together" is mentioned above, this does not necessarily require mixing of the plurality of primary particles. There are also composite oxides that have multiple specific peaks in their as-synthesized state without further processing, and such composite oxides can be used without any mixing. Furthermore, composite oxides having multiple specific peaks can be mixed, provided that the respective specific peaks after mixing have the relationship described above.

[0045] Next we will use Li 1-x-δ The example of NiO2 (x+δ indicates the amount of Li extracted / released from LiNiO2 due to charging) describes the mechanism of oxygen release when the composite oxide is in a charged state, which is a state in which lithium is released from the crystal structure in large quantities and the crystal structure is generally in an unstable state. When this type of composite oxide is used as a positive electrode active material and the charged state is heated, the crystalline state undergoes a phase transition from a layered rock salt structure (R-3m) to a spinel structure (Fd-3m) or a rock salt structure (Fm3m) within a specific temperature range, as shown by the following formulas (1) and (2). The temperature of these phase transitions depends on the depth of charge, but the phase transition occurs in a temperature range of about 190°C-310°C. In addition, as is clear from formulas (1) and (2), it is believed that the phase transition occurs while generating oxygen.

[0046] Formula (1):

[0047] Li 1-x-δ NiO2 (layered rock salt structure R-3m)

[0048] →{(1-x-δ) / (1-δ)}Li 1-δ NiO2 (layered rock salt structure 1R-3m)

[0049] +{x / 3(1-δ)}Ni3O4(spinel structure Fd-3m)

[0050] +{x / 3(1-δ)}O2↑

[0051] Formula (2):

[0052] ·{(1-x-δ) / (1-δ)}Li 1-δ NiO2 (layered rock salt structure 1R-3m)

[0053] →(1-x-δ)LiNiO2 (layered rock salt structure 2R-3m)

[0054] +{δ(1-x-δ) / (1-δ)}NiO(rock salt structure 1Fm3m)

[0055] +{δ(1-x-δ) / 2(1-δ)}O2↑

[0056] ·{x / 3(1-δ)}Ni3O4(spinel structure Fd-3m)

[0057] →{x / 3(1-δ)}NiO (rock salt structure 2Fm3m)

[0058] +{x / 6(1-δ)}O2↑

[0059] It should be noted that the symbol "-" is usually added after the 3 in R-3m, but this is for convenience as indicated above. The symbol "-" is also added after the 3 in Fd-3m, but this is for convenience as indicated above.

[0060] The inventors of the present invention have considered that the sudden formation of oxygen gas has a considerable influence on the thermal stability of a charged non-aqueous electrolyte secondary battery.

[0061] When the non-aqueous electrolyte secondary battery in a charged state overheats and the temperature rises, the organic electrolyte in the non-aqueous electrolyte secondary battery is mainly oxidized (including combustion) due to the oxygen generated in the reaction of formula (1) or formula (2). This reaction is an exothermic reaction, so the temperature of the non-aqueous electrolyte secondary battery rises. The rise in temperature further causes the oxidation of the electrolyte and generates heat, and therefore when the temperature rise enters an uncontrollable state, this leads to thermal runaway.

[0062] The temperature rise is proportional to the difference between the amount of heat generated per unit time in the non-aqueous electrolyte secondary battery and the amount of heat dissipated per unit time from the non-aqueous electrolyte secondary battery. Therefore, by ensuring that the amount of heat generated and the heat flow rate generated by equations (1) and (2) are not concentrated in a short period of time, safety can be improved by suppressing the temperature rise and preventing uncontrollable thermal runaway.

[0063] In view of the above, the inventors of the present invention believe that restricting the release rate of oxygen from the positive electrode active material is the most important factor in suppressing uncontrollable thermal runaway. Thus, it can be said that controlling the particle size of the primary particles of the composite oxide as in the present disclosure is effective for achieving this.

[0064] [Chemical structure]

[0065] There is no particular limitation on the chemical structure of the composite oxide, provided that the composite oxide contains at least lithium, a transition element, and oxygen.

[0066] There is no particular limitation on the transition element, provided that it is an element belonging to Groups 3-11 of the periodic table, but nickel is at least preferably used. The battery capacity can be increased by using nickel as the transition metal.

[0067] Specific examples of the composite oxide that can be used include: lithium cobalt oxide (LiCoO2); lithium nickel oxide (LiNiO2); lithium manganese oxide (LiMnO2); lithium manganese spinel (LiMn2O4); a composite oxide having a layered rock salt structure, which has the general formula Li a Ni 1-b-c Mn b M c O2 (in this formula, M is at least one element other than Li, Ni, Mn, and O, 0.95 ≤ a ≤ 1.15, and 0 ≤ b + c ≤ 0.70), in which a part of Ni in the lithium nickel oxide has been replaced by another element; lithium vanadium compound (LiV2O5); olivine LiMPO4 (where M is at least one element selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr; or VO); lithium titanium oxide (Li4Ti5O 12 ); and LiNi a Co b Al c O2 (0.9 < a + b + c < 1.1), etc.

[0068] Among the above-mentioned composite oxides, a lithium-nickel composite oxide is preferably used, and more preferably one having a layered rock salt structure and having the general formula Li a Ni 1-b-c Mn b M cA lithium-nickel composite oxide represented by O2 (in this formula, M is at least one element other than Li, Ni, Mn, and O, 0.95 ≤ a ≤ 1.15, and 0 ≤ b + c ≤ 0.70). Specific examples of the element M other than Li, Ni, and O that can be used include: Co, Al, Mn, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, and B, etc. More specific examples are Co, Al, Mn, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, and B. Using such a lithium-nickel composite oxide as a positive electrode active material for a non-aqueous electrolyte secondary battery enables an increase in battery capacity and also has the characteristic of causing oxygen to be released from the crystal structure, which may lead to thermal runaway. In order to utilize the high battery capacity of the above-mentioned lithium-nickel composite oxide, thermal runaway caused by oxygen release is suppressed by using a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0069] Although there is no particular limitation on M, in a specific embodiment, M is Co or Al or represents both Co and Al (that is, both Co and Al are present in the composite). More specifically, M is Co or both Co and Al. Even more specifically, M is both Co and Al.

[0070] In addition, there is no particular limitation on b + c, provided that it is within the range of 0 ≤ b + c ≤ 0.70, and it can be, for example, 0.65 or less, 0.60 or less, 0.55 or less, 0.50 or less, 0.45 or less, 0.40 or less, 0.35 or less, 0.30 or less, 0.25 or less, or 0.20 or less. If b + c is small, this means there is a high nickel content. When there is a high nickel content, this increases the amount of oxygen released and thus tends to make thermal runaway more likely to occur. At the same time, with the positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure, even when using a compound with a high nickel content, thermal runaway can be suppressed.

[0071] In a specific embodiment, 0 < b + c ≤ 0.70, that is, at least one of Mn and M is present in the composite. Preferably, 0 < b + c ≤ 0.60, more preferably 0.05 ≤ b + c ≤ 0.50, particularly 0.05 ≤ b + c ≤ 0.40, more particularly 0.05 ≤ b + c ≤ 0.30, specifically 0.10 ≤ b + c ≤ 0.25 or 0.15 ≤ b + c ≤ 0.20.

[0072] Preferably, 0.98 ≤ a ≤ 1.10, more preferably 1.00 ≤ a ≤ 1.10.

[0073] In a specific embodiment, the composite oxide is a composite oxide having the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2 O2, where 0.95 ≤ a ≤ 1.15, 0.75 ≤ [1 - b - c1 - c2] ≤ 0.90; 0.01 ≤ b ≤ 0.10; 0.05 ≤ c1 ≤ 0.20 and 0 ≤ c2 ≤ 0.05.

[0074] In another specific embodiment, the composite oxide is a composite oxide having the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2 O2, where 0.98 ≤ a ≤ 1.10, 0.80 ≤ [1 - b - c1 - c2] ≤ 0.85; 0.02 ≤ b ≤ 0.08; 0.10 ≤ c1 ≤ 0.15 and 0 ≤ c2 ≤ 0.03.

[0075] In a specific embodiment, the composite oxide is a composite oxide having the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2 O2, where 1.04 ≤ a ≤ 1.05, 0.82 ≤ [1 - b - c1 - c2] ≤ 0.84; 0.04 ≤ b ≤ 0.06; 0.11 ≤ c1 ≤ 0.13 and 0 ≤ c2 ≤ 0.02.

[0076] In another specific embodiment, the composite oxide is a composite oxide having the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2 O2, where 1.04 ≤ a ≤ 1.05, 0.82 ≤ [1 - b - c1 - c2] ≤ 0.84; 0.04 ≤ b ≤ 0.06; 0.11 ≤ c1 ≤ 0.13 and 0 ≤ c2 < 0.02.

[0077] In a very specific embodiment, the composite oxide is a composite oxide having the formula Li a Ni 1-b-c1-c2 Mn b Co<00​​​​

[0078] However, controlled oxygen release and thus reduced suppressed thermal runaway is also achieved with compositions other than those of the above specific and particular embodiments if the claimed volume-based primary particle size frequency distribution characteristics are met.

[0079] [Primary particles]

[0080] The primary particle of the complex oxide refers to the smallest unit of fine-particle material in which no grain boundary exists when powder of the complex oxide is observed under a field emission scanning electron microscope.

[0081] Figure 1A is an example of a scanning electron microscope photograph of a complex oxide. Figure 1B It is among them Figure 1A The primary particles are enclosed by dotted lines in the scanning electron micrograph of the composite oxide. Figure 1A and 1B As shown in , particulate material in which no grain boundaries are present is considered to be a primary particle.

[0082] The primary particles may be aggregated to form secondary particles, or may simply exist as primary particles, or the secondary particles and primary particles may be mixed. If the primary particles have the same particle size distribution, the temperature at which oxygen is released from the composite metal oxide does not change significantly regardless of the state in which the primary particles exist.

[0083] Furthermore, when primary particles agglomerate to form secondary particles, primary particles exhibiting a plurality of specific peaks may be mixed within one secondary particle, or a plurality of types of secondary particles including agglomerates of primary particles exhibiting only the same specific peak may exist together.

[0084] (Specific Peak)

[0085] When the volume-based particle size frequency distribution of primary particles is divided into a plurality of peaks, the specific peaks include a main peak exhibiting a maximum peak area value, and at least one peak having an area of ​​0.1-1 in area ratio relative to the area of ​​the main peak.

[0086] Particle size frequency distribution is obtained by the following method. Electron micrographs are observed using a field emission scanning electron microscope (such as JSM-7100F: produced by JEOL Co., Ltd.) with an accelerating voltage of 10kV and a magnification of 3000-20,000 times. Specifically, a field of view in which at least 100 primary particles in which the particle outline can be confirmed are randomly selected, and while changing the magnification in the above-mentioned range as needed, electron micrographs are obtained for all particles in which the outline can be confirmed from the particles included in the field of view. For example, if there is a large difference in particle size and the outline of the particle cannot be confirmed at one magnification in one field of view, the electron micrograph can be divided into multiple photos as needed. Sphere equivalent diameter is calculated using image processing software (such as ImageJ, etc.), and the sphere equivalent diameter serves as the particle size of the primary particle. In this case, the scale shown in the electron micrograph is used as a reference scale.

[0087] The data calculation of the particle size of the primary particles obtained adopts standard normal distribution as the kernel density distribution of kernel function (based on quantity). Afterwards, the primary particles are approximated by sphere, and the particle size frequency distribution based on volume is obtained from the distribution based on quantity. It should be noted that in the particle size frequency distribution based on volume, the logarithm of particle size is used as horizontal axis. In addition, the reliability (see equation (1) below) of the bandwidth parameter h related to distribution is determined with reference to Silverman (Silverman's) bandwidth (Silverman, BW:Density Estimation for Statistics and Data Analysis [density estimation for statistics and data analysis]. Chapman & Hall [Chapman and Hall Publishing Company], London-New York [London-New York] 1986, 175).

[0088] [Equation 1]

[0089] h = 0.9σn -1 / 5 … (1)

[0090] Standard deviation, IQR (interquartile range): value obtained by subtracting the 25th percentile (first quartile, Q1) from the 75th percentile (third quartile, Q3), n: number of particles measured

[0091] The volume-based particle size frequency distribution obtained in this manner is then fitted using a lognormal distribution function and divided into multiple peaks, thereby calculating the particle size at the peak top of each peak (central particle size of primary particles) and the peak area of ​​the corresponding peak.

[0092] Note that if peaks not meeting specific peaks (peaks with an area ratio of less than 0.1 relative to the area of ​​the main peak) are evident when separating the peaks, these peaks are considered not to be peaks and are ignored, and then the peaks are separated again.

[0093] There are no particular restrictions on the peaks corresponding to specific peaks, provided that they have an area ratio of 0.1 to 1 relative to the area of ​​the main peak, and they may have an area ratio of 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, 0.19 or more, 0.2 or more, 0.22 or more, 0.25 or more, 0.27 or more, 0.3 or more, 0.32 or more, 0.35 or more, 0.37 or more, 0.4 or more, 0.45 or more, or 0.5 or more. The effect of suppressing thermal runaway can be further enhanced by setting the area ratio to be at or above a desired value.

[0094] When there are a plurality of peaks exhibiting the maximum peak area value, the peak having the smallest primary particle size at its peak top is regarded as the main peak, and the other peaks exhibiting the maximum peak area value are included in the specific peak.

[0095] It is important that the peaks are dispersed for the primary particle diameter at the top of the specific peak, and although not particularly limited, the primary particle diameters are preferably all 80 nm or more, 100 nm or more, 120 nm or more, 150 nm or more, 170 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, or 450 nm or more. The oxygen release temperature can be raised by setting the primary particle diameter at the top of the specific peak to be at or above a desired value. At the same time, the primary particle size at the peak top of the specific peak is preferably 15 μm or less, 14.5 μm or less, 14 μm or less, 13.5 μm or less, 13 μm or less, 12.5 μm or less, 12 μm or less, 11.5 μm or less, 11 μm or less, 10.5 μm or less, 10 μm or less, 9.5 μm or less, 9 μm or less, 8.5 μm or less, 8 μm or less, 7.5 μm or less, 7 μm or less, 6.5 μm or less, 6 μm or less, 5.5 μm or less, 5 μm or less, or 4.5 μm or less. The energy density can be increased, and the particle damage and rate characteristic reduction accompanying the cycle can be suppressed by setting the particle size at the peak top of the specific peak to be at or below the desired value.

[0096] There are no particular restrictions on the ratio of the primary particle sizes at the peak tops of adjacent specific peaks (large particle size / small particle size), provided that the ratios are all 1.2-8, and they are all preferably 1.22 or greater, 1.25 or greater, 1.27 or greater, 1.3 or greater, 1.32 or greater, 1.35 or greater, 1.37 or greater, 1.4 or greater, 1.45 or greater, 1.5 or greater, 1.55 or greater, 1.6 or greater, 1.65 or greater, 1.7 or greater, 1.75 or greater, 1.8 or greater, 1.85 or greater, 1.9 or greater, 1.95 or greater, 2 or greater, 2.1 or greater, 2.2 or greater, 2.3 or greater, 2.4 or greater, 2.5 or greater, 2.6 or greater, 2.7 or greater, 2.8 or greater, 2.9 or greater, or 3 or greater. A plurality of temperatures at which oxygen is released from the composite oxide can be suitably separated, and the effect of suppressing thermal runaway can be further enhanced by setting the ratio of the primary particle diameter at the peak of adjacent specific peaks to be at or above a desired value. Meanwhile, the ratio of the primary particle diameter at the peak of adjacent specific peaks is preferably 7.7 or less, 7.5 or less, 7.2 or less, 7 or less, 6.7 or less, 6.5 or less, 6.2 or less, 6 or less, 5.7 or less, 5.5 or less, 5.2 or less, 5 or less, 4.7 or less, 4.5 or less, 4.2 or less, or 4 or less. The characteristic change of the primary particles exhibiting the corresponding specific peak can be limited by setting the primary particle diameter ratio at the peak of adjacent specific peaks to be at or below a desired value.

[0097] Specifically, when there are four specific peak tops and the primary particle sizes of the corresponding peaks are A, B, C and D (where the primary particle sizes increase in this order), the ratios of the primary particle sizes at the peak tops of adjacent specific peaks are A / B, B / C and C / D, and all ratios are preferably within the ranges mentioned above.

[0098] [Maximum oxygen release rate]

[0099] There is no particular limitation on the maximum oxygen release rate of the composite oxide, but it is preferably, for example, 1.92% or less, 1.9% or less, 1.85% or less, 1.8% or less, 1.75% or less, 1.7% or less, 1.65% or less, 1.6% or less, 1.55% or less, 1.5% or less, 1.45% or less, 1.4% or less, 1.35% or less, 1.3% or less, 1.25% or less, or 1.2% or less.

[0100] It should be noted that the maximum oxygen release rate is obtained by the following method using a thermogravimetric differential thermal analysis (TG-DTA) apparatus (for example, DTG-60H manufactured by Shimadzu Corp.).

[0101] (Sample Preparation)

[0102] A 2032-type button cell using lithium as a counter electrode was prepared according to the following method, and after constant current charging to 4.30V at 0.3C under an environment of 25°C, constant voltage charging was performed until a current value of 0.05C was reached. Thereafter, a 20-minute pause was performed after the charging was completed, and a constant current discharge was performed at 0.3C to 2.50V, followed by a constant current discharge at 0.1C, and then a 20-minute pause. This charge and discharge was repeated twice. After constant current charging to 4.30V at 0.3C, a constant voltage charge was then performed until a current value of 0.05C was reached, and a 20-minute pause was performed after the charging was completed.

[0103] The button cells in the charged state were disassembled in a glove box (dew point: -70 ° C or lower) so that short circuits did not occur, and the positive electrodes were collected. The collected positive electrodes were washed in DMC for 10 minutes and dried under vacuum in the side box. Thereafter, the positive electrode compound material was scraped off from the Al foil using a spatula in the same glove box. The TG measurement container made of Al was filled with 15 mg of the obtained positive electrode compound material powder, and then the lid was covered and hermetically sealed using a crimping machine.

[0104] The Al measurement container obtained in this manner was removed from the glove box and left to stand on the measurement-side balance of the TG-DTA apparatus.

[0105] (TG-DTA measurement)

[0106] Reference: Pt container filled with 15-20 mg Al2O3

[0107] Maximum temperature: 600℃

[0108] Heating rate:

[0109] (1) 25℃ (room temperature) to 50℃: 1℃ / min

[0110] (2) 50℃ to 600℃: 5℃ / min

[0111] Measurement environment: N2 gas atmosphere (200mL / min)

[0112] Immediately before measurement, a small hole is formed in the lid of the hermetically sealed Al measurement container within the TG-DTA apparatus under an N2 gas atmosphere, after which the temperature is increased. This method allows the positive electrode compound material powder used for measurement to be measured without being exposed to the atmosphere.

[0113] Based on the obtained results, a DTG curve was generated in which the horizontal axis is temperature and the vertical axis is the time differential value of the weight change (TG) (this value is dTG, meaning the weight reduction rate, which corresponds to the oxygen release rate of the composite oxide), and the maximum weight reduction rate between the peaks obvious in the region of 150°C to 350°C was regarded as the maximum oxygen release rate (% / min).

[0114] <Method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery>

[0115] The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure can be produced by, for example, performing the following steps in the order described. It should be noted that the following description gives an example of a method for producing a composite oxide containing 30 mol% or more of Ni in elements other than Li, and that the method for producing the composite oxide is otherwise based on a conventional method.

[0116] Step 1: Synthesize a precursor complex compound containing at least a transition metal, and mix the precursor complex compound with a lithium compound to prepare a mixture.

[0117] Step 2: Firing the mixture prepared in step 1.

[0118] Step 3: The composite oxide obtained by the firing in Step 2 is subjected to water washing treatment as necessary.

[0119] Step 4: The composite oxide obtained in step 2 or 3 is subjected to surface treatment as necessary.

[0120] Step 5: A plurality of types of composite oxides having different primary particle sizes and particle size frequency distributions are mixed by changing the conditions of Steps 1 to 3 as needed.

[0121] [Step 1]

[0122] First, a precursor composite compound serving as an aggregate containing a large number of primary particles containing at least a transition metal is synthesized. There are no particular restrictions on the method for synthesizing the precursor composite compound, and for example, an alkaline aqueous solution such as an aqueous sodium hydroxide solution or an ammonia solution is used as a mother liquor. Depending on the desired composition of the composite oxide, various aqueous solutions including an aqueous transition metal solution and a compound containing another element are added dropwise to a reaction tank under stirring. While sodium hydroxide or the like is also added dropwise, the pH is monitored and controlled to a suitable range. The precursor composite compound is obtained by coprecipitation through a wet reaction. A method for obtaining the precursor composite compound using, for example, a hydroxide, an oxide obtained by calcining a hydroxide, or a carbonate can be used.

[0123] It should be noted that once the alkaline aqueous solution used as the mother liquid for the reaction related to the synthesis is prepared, it is preferable to set the nitrogen atmosphere in the reaction tank using an inert gas or industrially preferred nitrogen gas so that the oxygen concentration in the reaction tank system and in the solution is as low as possible. If the oxygen concentration is too high, there is a risk of excessive oxidation of the coprecipitated hydroxide due to residual oxygen at or above a predetermined amount, and there is a risk of hindering the formation of agglomerates due to crystallization.

[0124] There is no particular limitation on the transition metal aqueous solution, but it is preferable to use, for example, an acidic aqueous solution, and more preferably a sulfuric acid aqueous solution such as a nickel sulfate aqueous solution. In addition, one or more types of transition metal aqueous solutions may be used.

[0125] The titanium compound is not particularly limited, but for example, one or more selected from titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium can be used.

[0126] The iron compound is not particularly limited, but for example, one or more selected from iron sulfate, iron oxide, iron hydroxide, iron nitrate, iron carbonate, iron chloride, iron iodide, metallic iron, and the like can be used.

[0127] The manganese compound is not particularly limited, but for example, one or more selected from manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and metallic manganese can be used.

[0128] The cobalt compound is not particularly limited, but for example, one or more selected from the group consisting of cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt can be used.

[0129] The nickel compound is not particularly limited, but for example, one or more selected from nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel can be used.

[0130] The niobium compound is not particularly limited, but for example, one or more selected from niobium oxide, niobium chloride, lithium niobate, and niobium iodide can be used.

[0131] The tungsten compound is not particularly limited, but for example, one or more selected from tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, tungsten sulfide, and the like can be used.

[0132] The magnesium compound is not particularly limited, but for example, one or more selected from magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium can be used.

[0133] The aluminum compound is not particularly limited, but for example, one or more selected from aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum can be used.

[0134] The zinc compound is not particularly limited, but for example, one or more selected from zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and metallic zinc can be used.

[0135] Likewise, as for other elements, one or more selected from sulfates, oxides, hydroxides, nitrates, carbonates, chlorides, iodides, metals, and the like can be used.

[0136] The ratio in which the corresponding compounds are blended should be appropriately adjusted in consideration of the intended composition of the composite oxide so that the amounts of the corresponding elements reach a desired ratio.

[0137] There is no particular limitation on the appropriate pH range when synthesizing the precursor composite compound, and the range can be determined so as to achieve desired secondary particle size and coarseness / fineness, and the pH should generally be in the range of about 10-13.

[0138] The precursor composite compound obtained by the wet reaction is preferably subjected to a washing treatment and then to a drying treatment after dehydration.

[0139] By subjecting the precursor composite compound to a washing treatment, impurities such as sulfate and carbonate, and sodium moieties, which are carried into the agglomerated particles or adhered to the surface layer during the reaction, can be rinsed away. Washing treatments that can be used include the Nutsche washing method using a Buchner funnel, provided that there are only a small amount of impurities, and a method in which the reacted suspension is fed to a filter press, washed with water, and dehydrated. It should be noted that washing treatments can employ pure water, aqueous sodium hydroxide solution, or aqueous sodium carbonate solution, but pure water is preferably used from an industrial point of view. However, when there is a large amount of residual sulfate, a pH-controlled aqueous sodium hydroxide solution can also be used according to the residual amount.

[0140] The precursor composite compound and the lithium compound synthesized in this manner are then mixed at a predetermined ratio to prepare a mixture. This mixing may be a solvent-based mixing in which the precursor composite compound and the lithium compound are each in the form of a solution, such as an aqueous solution, and these solutions are mixed at a predetermined ratio, or it may be a non-solvent-based mixing in which a powder of the precursor composite compound and a powder of the lithium compound are weighed out at a predetermined ratio and mixed by a dry method.

[0141] There are no particular limitations on the lithium compound, and various types of lithium salts can be used. Specific examples of usable lithium compounds include one or more selected from the following: anhydrous lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, and lithium oxide. Among these, one or more selected from anhydrous lithium hydroxide and lithium hydroxide hydrate are preferably used.

[0142] There is no particular limitation on the ratio in which the lithium compound and the precursor composite compound are blended, but the ratio should be appropriately adjusted in consideration of the intended composition of the composite oxide so that the amount of lithium and the total amount of the corresponding elements reach a desired ratio.

[0143] [Step 2]

[0144] When producing a composite oxide containing at least a transition metal as described above, a lithiation reaction and crystal growth are achieved during firing, and during this process, a fixed oxygen partial pressure is required for the lithiation reaction. A composite oxide containing lithium is obtained through the lithiation reaction. Thereafter, crystal growth is promoted by increasing the temperature to a predetermined temperature.

[0145] The maximum temperature of the mixture during firing is preferably 650°C to 1100°C, 670°C to 1000°C, or 700°C to 980°C. Furthermore, the firing time at the maximum temperature is preferably 1 to 24 hours, 1 to 20 hours, 1 to 15 hours, 1 to 10 hours, 2 to 9 hours, or 3 to 8 hours. The desired composite compound can be obtained by setting the maximum temperature and time so that the firing temperature is equal to or greater than the melting point of the lithium compound in the mixture and the desired crystal growth and particle growth of the lithium-containing composite oxide are achieved.

[0146] Firing is usually carried out in the following manner: the lithium compound, the precursor composite compound, and the compound M are weighed as needed, and these compounds are mixed in a mixer to obtain a mixed powder, and then the mixed powder is filled in a container such as a crucible or a sagger. However, in particular, in the lithiation reaction, it becomes difficult to discharge the generated gas to the outside and diffuse oxygen at a desired concentration, especially near the lower part of the container filled with the mixed powder. As a result, it is difficult to achieve a uniform reaction and difficult to control the primary particle size.

[0147] Therefore, when producing the composite oxide according to the embodiment of the present disclosure, it is preferable to use the following method in which preliminary firing is first performed under the following predetermined conditions and then main firing is performed under predetermined conditions in step 2. However, preliminary firing is not an essential step.

[0148] During the preliminary firing in step 2, a firing method that particularly promotes the lithiation reaction is preferably employed. Specifically, the mixture is placed in a state where heat is more readily applied, gases generated by the lithiation reaction are easily discharged, and gases with a high oxygen partial pressure are able to diffuse within the mixture (intra-particles). For example, desired characteristics can be achieved by subjecting a relatively small amount of the mixture to preliminary firing.

[0149] When the mixture is subjected to primary firing in step 2, the mixture is loaded in a sagger or a crucible, and firing can also be performed in a stationary furnace, a roller hearth kiln, or a pusher furnace, but a rotary kiln for firing the mixture while it is fluidized can be used.

[0150] There are no particular restrictions on the maximum temperature of the mixture subjected to preliminary firing, and the maximum temperature is preferably adjusted according to the type of lithium compound used to prepare the mixture. By this means, a reliable reaction occurs between the precursor composite compound and the lithium compound in the mixture, the lithiation reaction proceeds uniformly and reliably, it is possible to ensure that no different phases are formed, and the desired composite oxide can be obtained.

[0151] There is no particular limitation on the atmosphere during the preliminary firing, and it may be an oxidizing atmosphere in which the lithiation reaction proceeds reliably and uniformly. For example, a decarbonated oxidizing gas atmosphere having a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere having an oxygen concentration of 80 vol% to 90 vol% is preferably used.

[0152] The time for the preliminary firing is not particularly limited, and should be a time that allows the lithiation reaction to proceed reliably and uniformly. For example, a time of 1 to 10 hours or 2 to 8 hours is preferred.

[0153] In order to promote crystal growth and particle growth at even higher temperatures, the mixture that has undergone preliminary firing is subjected to main firing. In this case, it is necessary to allow crystal growth to proceed reliably and uniformly and to obtain a composite oxide having a desired crystal structure.

[0154] The atmosphere used for the main firing is not particularly limited, and may be an atmosphere in which reliable and uniform crystal growth is achieved (the atmosphere has an oxygen partial pressure such that the transition metal contained in the fired mixture is not reduced), preferably an atmosphere having a low moisture content and a low carbon dioxide concentration. For example, a decarbonated oxidizing gas atmosphere having a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere preferably having an oxygen concentration of 80 vol% to 90 vol% is preferably used.

[0155] There is no particular restriction on the temperature in the main firing, provided that it is a higher temperature than that in the preliminary firing, and it can be adjusted according to the composition of the composite oxide to be obtained, etc. For example, the maximum temperature is preferably adjusted to 700°C-1100°C, 710°C-1000°C, or 720°C-980°C. By setting the maximum temperature within the desired range, a composite oxide having a desired crystal structure can be obtained with fewer unreacted components, and in addition, a decrease in the battery characteristics of a non-aqueous electrolyte secondary battery that employs the resulting composite oxide in its positive electrode can be prevented. In addition, for example, when a composite oxide having a Ni content of 20 mol%-80 mol% in elements other than Li is obtained, firing is preferably performed with the maximum temperature of the mixture not exceeding 1100°C.

[0156] The time for the main firing is not particularly limited and may be a time sufficient to form a composite oxide having a desired crystal structure. For example, a time of 1 to 15 hours, 2 to 12 hours, or 2 to 10 hours is preferred.

[0157] [Step 3]

[0158] Unreacted lithium compounds and lithium compounds that have emerged from the crystal structure in the particle surface layer during the firing step may sometimes be present as impurities in the composite oxide obtained in step 2. For this reason, water washing and heat treatment may be performed, for example, to remove and reduce these impurities. It should be noted that step 3 is not an essential component.

[0159] [Step 4]

[0160] A predetermined element compound may be blended with the composite oxide obtained in step 2 or 3, and heat treatment may be performed to surface-treat the surfaces of the primary particles and / or secondary particles of the composite oxide with a compound of lithium and the added element, thereby achieving effects such as reducing the amount of lithium compounds remaining on the surface layer of the particles, improving lithium ion conductivity, and reducing reaction resistance. It should be noted that step 4 is not an essential component.

[0161] The element compound added for the surface treatment can be selected from aluminum compounds, boron compounds, tungsten compounds, manganese compounds, cobalt compounds, phosphorus compounds, niobium compounds, strontium compounds, antimony compounds, zirconium compounds, and titanium compounds, and one or more of these compounds can be used, for example.

[0162] [Step 5]

[0163] When the composite oxide obtained in any one of steps 2 to 4 does not have a plurality of the above-mentioned specific peaks or does not have a specific primary particle size ratio, or when it is desired to further increase the effect of suppressing thermal runaway even if specific requirements regarding the specific peaks and primary particle size ratios are met, a plurality of types of composite oxides in which the primary particle size and particle size frequency distribution are varied by changing the conditions in the production of the composite oxide (conditions of steps 1 to 4) are mixed. It should be noted that when the composite oxide obtained in any one of steps 2 to 4 satisfies the specific requirements regarding the specific peaks and primary particle size ratios, step 5 is not an essential component.

[0164] Furthermore, the order of steps 3-5 may be varied.

[0165] <Non-aqueous electrolyte secondary battery>

[0166] The nonaqueous electrolyte secondary battery according to the present disclosure includes a positive electrode containing the above-mentioned composite oxide as a positive electrode active material, and the nonaqueous electrolyte secondary battery includes the positive electrode, the negative electrode, and an electrolytic solution containing an electrolyte.

[0167] When producing the positive electrode, a conductive agent and a binder are mixed with the composite oxide according to an embodiment of the present disclosure by a conventional method. For example, acetylene black, carbon black, and graphite are preferably used as the conductive agent. For example, polytetrafluoroethylene and polyvinylidene fluoride are preferably used as the binder.

[0168] There is no particular limitation on the negative electrode, but not only negative electrode active materials such as lithium metal, graphite, and low-crystallinity carbon materials can be used, but also at least one non-metallic or metallic element selected from Si, Al, Sn, Pb, Zn, Bi and Cd, or alloys containing them, or sulfide compounds containing them, etc. can be used.

[0169] There is no particular limitation on the solvent of the electrolyte, but examples of solvents that can be used include organic solvents including at least one selected from carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, and ethers such as dimethoxyethane.

[0170] In addition to lithium hexafluorophosphate (LiPF 6 ) in particular, at least one selected from lithium salts such as, for example, lithium perchlorate or lithium tetrafluoroborate may be dissolved in a solvent to be used as an electrolyte.

[0171] [Example]

[0172] The present disclosure will be described in further detail below through examples, but the present disclosure is not limited to these examples.

[0173] <Preparation of Composite Oxide>

[0174] Composite Oxide 1-3 was prepared by the method described below.

[0175] (Preparation of Composite Oxide 1)

[0176] The Ni 0.83 Co 0.12 Mn 0.05 The volume-based D of the substantially spherical agglomerated particles obtained in this manner is 50 It is 11.2μm.

[0177] The obtained nickel-cobalt-manganese composite hydroxide, lithium hydroxide and aluminum hydroxide were weighed and mixed so that Li / (Ni+Co+Mn)=1.04 and Al / (Ni+Co+Mn)=0.5mol%. Thereafter, the mixture was heat-treated at 570°C in an oxygen atmosphere for 6 hours and then further fired at 775°C in an oxygen atmosphere (oxygen concentration: 97vol%) for 6 hours. The obtained fired material was ground to obtain a lithium-nickel composite oxide.

[0178] The slurry prepared by mixing the obtained lithium-nickel composite oxide powder with pure water adjusted to 25° C. at a ratio of 1500 g / L was stirred for 10 minutes and then dehydrated to obtain a cake-like compound. The cake-like compound was dried in a vacuum dryer at 75° C. for 2 hours and at 120° C. for 10 hours.

[0179] 1000 ppm of boron as a boron compound is blended with the obtained lithium-nickel composite oxide, and the mixture is heat-treated at 325°C for 2 hours under an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a composite oxide 1 having a particle size (center particle size) at the peak top of the particle size frequency distribution of primary particles of 0.5 μm (L1).

[0180] (Preparation of Composite Oxide 2)

[0181] The Ni 0.83 Co 0.12 Mn 0.05 The volume-based D of the substantially spherical agglomerated particles obtained in this manner is 50 It is 4.1μm.

[0182] The obtained nickel-cobalt-manganese composite hydroxide and lithium hydroxide powder were weighed and mixed so that Li / (Ni+Co+Mn)=1.05. Thereafter, the mixture was fired at 860°C in an oxygen atmosphere (oxygen concentration: 97 vol%) for 12 hours. The fired material was ground, and the supply pressure and grinding pressure were adjusted using a jet mill so that the primary particles were not ground. Thereafter, 0.6 mol% alumina powder Al2O3 was added and heat treated at 600°C in an air atmosphere for 7 hours to obtain a lithium-metal composite oxide.

[0183] The slurry prepared by mixing the obtained lithium-nickel composite oxide powder with pure water adjusted to 25° C. at a ratio of 1500 g / L was stirred for 10 minutes and then dehydrated to obtain a cake-like compound. Thereafter, the cake-like compound was dried in a vacuum dryer at 75° C. for 2 hours and at 120° C. for 10 hours.

[0184] 500 ppm of boron was blended as a boron compound with the obtained lithium-nickel composite oxide, and the mixture was heat-treated at 300°C in an atmosphere for 7 hours to obtain a composite oxide 2 having two peaks when the particle size frequency distribution of the primary particles was divided into multiple peaks, and the particle size (center particle size) at the top of each peak was 1.4 μm (P1) and 2.7 μm (P2).

[0185] (Preparation of Composite Oxide 3)

[0186] The Ni 0.83 Co 0.12 Mn 0.05 The volume-based D of the substantially spherical agglomerated particles obtained in this manner is 50 It is 4μm.

[0187] The obtained nickel-cobalt-manganese composite hydroxide and lithium hydroxide powder were weighed and mixed so that Li / (Ni+Co+Mn)=1.05. Thereafter, the mixture was fired at 850°C in an oxygen atmosphere (oxygen concentration: 97 vol%) for 12 hours. Thereafter, 0.6 mol% of Al2O3 as aluminum oxide was added, and heat treatment was performed at 600°C in an atmosphere for 7 hours to obtain a lithium-metal composite oxide.

[0188] The slurry prepared by mixing the obtained lithium-nickel composite oxide powder with pure water adjusted to 25° C. at a ratio of 1500 g / L was stirred for 10 minutes and then dehydrated to obtain a cake-like compound. Thereafter, the cake-like compound was dried in a vacuum dryer at 75° C. for 2 hours and at 120° C. for 10 hours.

[0189] 500 ppm of boron was blended as a boron compound with the obtained lithium-nickel composite oxide, and the mixture was heat-treated at 300°C in an air atmosphere for 7 hours to obtain a composite oxide 3 having three peaks when the particle size frequency distribution of the primary particles was divided into multiple peaks, and the particle size (center particle size) at the top of each peak was 1.5 μm (M1), 2.2 μm (M2), and 3.0 μm (M3).

[0190] [Example 1]

[0191] Composite oxide 1 and composite oxide 2 were mixed so that the peak area ratio was 50:50, and used as a positive electrode active material sample. Figure 2 : is a volume-based particle size frequency distribution curve of the primary particles of the positive electrode active material sample of Example 1. In addition, Figure 3 is the DTG curve of the positive electrode active material sample of Example 1.

[0192] [Example 2]

[0193] Composite oxide 1 and composite oxide 2 were mixed so that the peak area ratio was 81:19, and used as a positive electrode active material sample. Figure 4 : is a volume-based particle size frequency distribution curve of the primary particles of the positive electrode active material sample of Example 2. In addition, Figure 5 is the DTG curve of the positive electrode active material sample of Example 2.

[0194] [Example 3]

[0195] Composite Oxide 2 alone was used as a positive electrode active material sample. Figure 6 : is a volume-based particle size frequency distribution curve of the primary particles of the positive electrode active material sample of Example 3. In addition, Figure 7 is the DTG curve of the positive electrode active material sample of Example 3.

[0196] [Example 4]

[0197] Composite Oxide 3 alone was used as a positive electrode active material sample. Figure 8 4 is a volume-based particle size frequency distribution curve of the primary particles of the positive electrode active material sample of Example 4. In addition, Figure 9 is the DTG curve of the positive electrode active material sample of Example 4.

[0198] [Comparative Example 1]

[0199] Composite Oxide 1 alone was used as a positive electrode active material sample. Figure 10 : is a volume-based particle size frequency distribution curve of the primary particles of the positive electrode active material sample of Comparative Example 1. In addition, Figure 11 is the DTG curve of the positive electrode active material sample of Comparative Example 1.

[0200] <Evaluation>

[0201] The obtained samples were evaluated by the methods described below.

[0202] [Composition Analysis of Precursor Compounds and Composite Oxides]

[0203] The composition of the precursor composite compound and the positive electrode active material particles was determined by the following method. A 0.2 g sample of the positive electrode active material was heated and dissolved in 25 mL of a 20% hydrochloric acid solution, and the material was cooled and then transferred to a 100 mL volumetric flask, and pure water was introduced to prepare a conditioned liquid. The elements in the resulting conditioned liquid were quantitatively determined using ICP-AES (Optima 8300, manufactured by PerkinElmer, Inc.).

[0204] [Average agglomerated particle size of the precursor compound (D 50 )]

[0205] This is measured on a volume basis by a wet laser method using a laser-type particle size distribution measuring device (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0206] [Scanning electron microscopy observation and generation of particle size frequency distribution]

[0207] Electron micrographs of the obtained positive electrode active material samples were observed using a field emission scanning electron microscope (JSM-7100F: manufactured by JEOL Co., Ltd.) at an accelerating voltage of 10 kV and a magnification of 3000-20,000 times. Specifically, a field of view in which at least 100 primary particles in which the particle outlines can be confirmed is randomly selected, and while changing the magnification within the range mentioned above as needed, an electron micrograph is obtained for all particles in which the outlines can be confirmed from the particles included in the field of view. The sphere equivalent diameter is calculated from the electron micrograph using image processing software (e.g., ImageJ, etc.), and the sphere equivalent diameter serves as the particle size of the primary particles.

[0208] The data of the particle diameter of the primary particles obtained are calculated using standard normal distribution as the kernel density distribution of kernel function (based on quantity). After this, primary particles are approximated by sphere, and the particle diameter frequency distribution based on volume is obtained from the distribution based on quantity. It should be noted that in the particle diameter frequency distribution based on volume, the logarithm of particle diameter is used as horizontal axis. In addition, the reliability (Silverman, BW:Density Estimation for Statistics and Data Analysis [density estimation for statistics and data analysis] .Chapman & Hall [Chapman and Hall Publishing Company], London-New York [London-New York] 1986, 175) of the bandwidth parameter h related to distribution is determined with reference to Silverman (Silverman's) bandwidth. The particle diameter frequency distribution based on volume obtained in this way is then fitted using lognormal distribution function and divided into multiple peaks, so as to calculate the particle diameter (central particle diameter of primary particles) at the peak of each peak and the peak area of ​​corresponding peak.

[0209] It should be noted that if peaks that do not meet the specified peak (peaks with an area ratio of less than 0.1 relative to the area of ​​the main peak) are obvious when separating the peaks, these peaks are considered not to be peaks and are ignored, and then the peaks are separated again. For example, P1 in Example 2 was ignored because it was a peak that did not meet the specified peak.

[0210] [Thermogravimetric Differential Thermal Analysis]

[0211] In order to confirm the oxygen release behavior of the positive electrode active material sample, thermogravimetric differential thermal analysis (TG-DTA) was performed by using a thermogravimetric differential thermal analyzer (DTG-60H, manufactured by Shimadzu Corporation).

[0212] (Sample Preparation)

[0213] A 2032-type button cell using lithium as a counter electrode was prepared according to the following method, and after constant current charging to 4.30V at 0.3C under an environment of 25°C, constant voltage charging was performed until a current value of 0.05C was reached. Thereafter, a 20-minute pause was performed after the charging was completed, and a constant current discharge was performed at 0.3C to 2.50V, followed by a constant current discharge at 0.1C, and then a 20-minute pause. This charge and discharge was repeated twice. After constant current charging to 4.30V at 0.3C, a constant voltage charge was then performed until a current value of 0.05C was reached, and a 20-minute pause was performed after the charging was completed.

[0214] The button cells in the charged state were disassembled in a glove box (dew point: -70 ° C or lower) so that short circuits did not occur, and the positive electrodes were collected. The collected positive electrodes were washed in DMC for 10 minutes and dried under vacuum in the side box. Thereafter, the positive electrode compound material was scraped off from the Al foil using a spatula in the same glove box. The TG measurement container made of Al was filled with 15 mg of the obtained positive electrode compound material powder, and then the lid was covered and hermetically sealed using a crimping machine.

[0215] The Al measurement container obtained in this manner was removed from the glove box and left to stand on the measurement-side balance of the TG-DTA apparatus.

[0216] (TG-DTA measurement)

[0217] Reference: Pt container filled with 15-20 mg Al2O3

[0218] Maximum temperature: 600℃

[0219] Heating rate:

[0220] (1) 25℃ (room temperature) to 50℃: 1℃ / min

[0221] (2) 50℃ to 600℃: 5℃ / min

[0222] Measurement environment: N2 gas atmosphere (200mL / min)

[0223] Immediately before measurement, a small hole was formed in the lid of the hermetically sealed Al measurement container within the TG-DTA apparatus under an N 2 gas atmosphere, after which the temperature increase was started.

[0224] Based on the obtained results, a DTG curve was generated in which the horizontal axis is temperature and the vertical axis is the time differential value of the weight change (TG) (this value is dTG, meaning the weight reduction rate, which corresponds to the oxygen release rate of the composite oxide), and the maximum weight reduction rate between the peaks obvious in the region of 150°C to 350°C was regarded as the maximum oxygen release rate (% / min).

[0225] [Evaluation of the Charging Capacity of Coin Cells Using Positive Electrode Active Material Samples]

[0226] In this specification, a 2032-type button cell using positive electrode active material particles is produced by using a positive electrode, a negative electrode, and an electrolyte produced by the following respective methods.

[0227] (positive electrode)

[0228] Acetylene black and graphite were used as conductive agents (acetylene black: graphite weight ratio = 1:1), and polyvinylidene fluoride was used as a binder. The positive electrode active material, conductive agent, and binder were blended to achieve a positive electrode active material: conductive agent: binder weight ratio = 90:6:4, and the mixture of these materials and N-methylpyrrolidone was coated on aluminum foil. The coated aluminum foil was dried at 110 ° C to prepare a sheet, which was punched to a diameter of 15 mm and then 3 t / cm 2 Roll pressing to form a positive electrode.

[0229] (negative electrode)

[0230] A lithium foil having a thickness of 500 μm punched out to a diameter of 16 mm was used as the negative electrode.

[0231] (Electrolyte)

[0232] A mixed solvent of EC and DMC was prepared at a volume ratio of EC:DMC=1:2, and a solution obtained by mixing 1 mol / L LiPF6 electrolyte with the mixed solvent was used as an electrolyte.

[0233] (diaphragm)

[0234] A septum punched to a diameter of 20 mm (Celgard #2400: manufactured by Celgard) was used.

[0235] (Measurement of total charge capacity)

[0236] Using the button cells produced by the above method, after constant current charging to 4.30V at 0.3C at 25°C, constant voltage charging was performed until a current value of 0.05C was reached. Thereafter, a 20-minute pause was performed after charging was completed, and constant current discharge was performed at 0.3C to 2.50V, followed by constant current discharge at 0.1C, and then a 20-minute pause. This charge and discharge was repeated twice. After constant current charging to 4.30V at 0.3C, constant voltage charging was then performed until a current value of 0.05C was reached. In this operation, the total charge capacity (mAh / g) was calculated as follows.

[0237] First charge / discharge:

[0238] 4.3V at 0.3C (constant voltage charge until reaching 0.05C)

[0239] 20-minute pause

[0240] Discharged to 2.5V at 0.3C, then further discharged to 2.5V at 0.1C

[0241] 20-minute pause

[0242] Second charge / discharge:

[0243] 4.3V at 0.3C (constant voltage charge until reaching 0.05C)

[0244] 20-minute pause

[0245] Discharged to 2.5V at 0.3C, then further discharged to 2.5V at 0.1C

[0246] Third charging:

[0247] 4.3V at 0.3C (constant voltage charge until reaching 0.05C)

[0248] Total charging capacity

[0249] =first charge capacity + (second charge capacity - first discharge capacity at 0.3C - first discharge capacity at 0.1C) + (third charge capacity - second discharge capacity at 0.3C - second discharge capacity at 0.1C)

[0250] Table 1 shows the peak area ratio of the composite oxides constituting the samples of Examples 1-4 and Comparative Example 1, the area ratio of other specific peaks to the main peak, the center particle diameter ratio of adjacent specific peaks, the total charge / discharge capacity, the DTG peak top temperature, the maximum oxygen release rate, and the reduction rate of the maximum oxygen release rate compared with Comparative Example 1.

[0251]

[0252] From the results in Table 1, it can be seen that when multiple specific peaks are present and the center particle diameter ratios of these specific peaks are all within a predetermined range, the maximum oxygen release rate can be reduced relative to Comparative Example 1 having only one specific peak.

Claims

1. Use of a positive electrode active material comprising a composite oxide for suppressing or avoiding thermal runaway in a non-aqueous electrolyte secondary battery, the composite oxide comprising at least lithium, a transition metal and oxygen, wherein: When the volume-based particle size frequency distribution of the primary particles of the composite oxide is divided into a plurality of peaks, the peaks include specific peaks comprising: a main peak exhibiting a maximum peak area value, and at least one peak having an area of ​​0.1 to 1 in terms of an area ratio relative to the area of ​​the main peak, and The ratio of primary particle diameters at the peak tops of adjacent specific peaks (large particle diameter / small particle diameter) was 1.2-8 in all cases. 2 . The use of the positive electrode active material according to claim 1 , which is used to control the release of oxygen from the positive electrode active material.

3. The use according to any one of the preceding claims, wherein The composite oxide is a lithium-nickel composite oxide.

4. The use according to claim 3, wherein The lithium-nickel composite oxide has a layered rock salt structure and is composed of the general formula Li a Ni 1-b-c Mn b M c O2 represents, wherein M is one or more elements other than Li, Ni, Mn and O, 0.95≤a≤1.15, and 0≤b+c≤0.

70.

5. The use according to claim 4, wherein M is selected from one or more of Co, Al, Mn, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr and B.

6. The use according to claim 5, wherein M is Co or Co and Al.

7. The use according to claim 6, wherein M is both Co and Al.

8. The method according to claim 4 , wherein the compound has the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2 O2, where 0.95≤a≤1.15, 0.75≤[1-b-c1-c2]≤0.90; 0.01≤b≤0.10; 0.05≤c1≤0.20 and 0≤c2≤0.

05.

9. The use according to any one of the preceding claims, wherein The primary particle sizes at the peak tops of these specific peaks are all between 80 nm and 15 μm.

10. A positive electrode active material for a non-aqueous electrolyte secondary battery, the positive electrode active material comprising a composite oxide containing at least lithium, a transition metal, and oxygen, wherein: When the volume-based particle size frequency distribution of the primary particles of the composite oxide is divided into a plurality of peaks, the peaks include specific peaks comprising: a main peak exhibiting a maximum peak area value, and at least one peak having an area of ​​0.1 to 1 in terms of an area ratio relative to the area of ​​the main peak, and The ratio of primary particle diameters at the peak tops of adjacent specific peaks (large particle diameter / small particle diameter) was 1.2-8 in all cases.

11. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, wherein The composite oxide is a lithium-nickel composite oxide having a layered rock salt structure and having the general formula Li a Ni 1-b-c Mn b M c O2 represents (in this formula, M is at least one element other than Li, Ni, Mn and O, 0.95≤a≤1.15, and 0≤b+c≤0.70).

12. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 11, wherein M is selected from one or more of Co, Al, Mn, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr and B.

13. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 12, wherein M is Co or Co and Al.

14. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 13, wherein M is both Co and Al.

15. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 14, having a formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2 O2, where 0.95≤a≤1.15, 0.75≤[1-b-c1-c2]≤0.90; 0.01≤b≤0.10; 0.05≤c1≤0.20 and 0≤c2≤0.

05.

16. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 15, wherein The primary particle sizes at the peak tops of these specific peaks are all between 80 nm and 15 μm. 17 . A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material according to claim 10 .

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