Positive electrode active material for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery

Abstract

To provide a positive electrode active material capable of suppressing thermal runaway, and a nonaqueous electrolyte secondary battery using the same.SOLUTION: A positive electrode active material for a nonaqueous electrolyte secondary battery includes a composite oxide represented by Li1+xNi1-y-z-w-vCoyMnzTiwMvO2+α (where M is one or more elements other than Li, Ni, Co, Mn, and O, and -0.1≤x≤0.15, 0≤y≤0.4, 0<z≤0.4, 0.001≤w≤0.03, 0≤v≤0.1, -0.5≤α≤0.5). When a derivative thermogravimetric curve is separated into peaks, the positive electrode active material has a first peak that shows the greatest derivative thermogravimetric value in a predetermined temperature range, and a second peak that shows the greatest derivative thermogravimetric value among peaks whose peak tops occur at a temperature at least 20°C different from the temperature at which the peak top of the first peak occurs. A ratio of the derivative thermogravimetric value at the peak top of the first peak to the derivative thermogravimetric value at the peak top of the second peak is one or more and 9 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Lithium-ion secondary batteries have attracted attention as power sources for electronic devices such as AV equipment and personal computers, due to their small size, light weight, high energy density, high charge / discharge voltage, and large charge / discharge capacity.

[0003] Lithium-ion secondary batteries typically use flammable organic solvents as electrolytes, so they require high thermal stability. For example, in lithium-ion secondary batteries, when heat is applied during charging, oxygen is released from the positive electrode active material crystals. This oxygen reacts with the electrolyte, causing thermal runaway.

[0004] In particular, active materials containing Ni, Co, and Mn have been widely used as positive electrode active materials in recent years. In such positive electrode active materials, the higher the Ni content, the lower the temperature at which the phase transition reaction of the positive electrode active material occurs, resulting in rapid oxygen release, making the positive electrode active material more susceptible to thermal runaway. Meanwhile, there is a growing demand for materials with a high Ni content that provide large battery capacities, and as a result, the thermal stability inherent to materials with a high Ni content tends to decrease.

[0005] To suppress thermal runaway in such positive electrode active materials, for example, Patent Document 1 proposes a positive electrode active material containing 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 number of moles of metal elements excluding Li, where B and at least one element (M1) selected from Groups 4 to 6 are present at least on the particle surface of the lithium transition metal composite oxide, and the molar fraction of M1 relative to the total number of moles of metal elements excluding Li on the surface of particles smaller than 30% particle size is greater than the molar fraction of M1 relative to the total number of moles of metal elements excluding Li on the surface of particles with a volumetric particle size greater than 70% particle size. Patent Document 1 also describes that the use of such a composite oxide in lithium-ion secondary batteries suppresses the self-heating rate even at high temperatures. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-51979 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the positive electrode active material of Patent Document 1, by coating the particle surfaces of the positive electrode active material with a boron compound, it is expected that there will be a certain degree of suppression effect against thermal runaway caused by the reaction between oxygen released from the positive electrode active material and the electrolyte, but this alone is not sufficient to suppress thermal runaway, and there is still room for improvement.

[0008] Therefore, there is a need for a method of suppressing thermal runaway other than the above-mentioned method of coating the surface of the positive electrode active material with a compound.

[0009] The present disclosure has been made in view of the above circumstances, and has an object to provide a positive electrode active material that can suppress thermal runaway in a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery using the same.

Means for Solving the Problems

[0010] The inventors of the present invention have intensively studied to solve the above-described problems. As a result, a composite oxide represented by the general formula Li 1+x Ni 1-y-z-w-v Co y Mn z Ti w M v O 2+α (where M is one or more elements other than Li, Ni, Co, Mn, and O, -0.1 ≦ x ≦ 0.15, 0 ≦ y ≦ 0.4, 0 < z ≦ 0.4, 0.001 ≦ w ≦ 0.03, 0 ≦ v ≦ 0.1, -0.5 ≦ α ≦ 0.5). When the differential thermogravimetric curve obtained by heating the sample containing the composite oxide from 50°C to 600°C at 5°C / min with the counter electrode being lithium is separated into a plurality of peaks, in the temperature range of 150°C or higher and 350°C or lower, there are a first peak in which the value of the differential thermogravimetry at the peak top shows the maximum value, and among the peaks showing the peak top at a temperature more than 20°C away from the temperature showing the peak top of the first peak, there is a second peak in which the value of the differential thermogravimetry at the peak top shows the maximum value. When a positive electrode active material having a ratio of the value of the differential thermogravimetry at the peak top of the first peak to the value of the differential thermogravimetry at the peak top of the second peak of 1 or more and 9 or less is used in a non-aqueous electrolyte secondary battery, it has been found that the maximum oxygen release rate (hereinafter referred to as "oxygen release rate") from the positive electrode active material can be suppressed, and furthermore, thermal runaway can be suppressed. Specifically, the present disclosure provides the following.

[0011] (1) General formula Li 1+x Ni 1-y-z-w-v Co y Mn z Ti w M v O 2+α(where M is one or more elements other than Li, Ni, Co, Mn, and O, -0.1 ≦ x ≦ 0.15, 0 ≦ y ≦ 0.4, 0 < z ≦ 0.4, 0.001 ≦ w ≦ 0.03, 0 ≦ v ≦ 0.1, -0.5 ≦ α ≦ 0.5), and the composite oxide is obtained by separating the differential thermogravimetric curve obtained by raising the temperature of a sample charged to 4.30 V with lithium as the counter electrode from 50 °C to 600 °C at 5 °C / min into a plurality of peaks. When separated into a plurality of peaks, in the temperature range of 150 °C or higher and 350 °C or lower, there are a first peak in which the value of the differential thermogravimetry at the peak top shows the maximum value, and among the peaks showing the peak top at a temperature separated from the temperature showing the peak top of the first peak by 20 °C or more, there is a second peak in which the value of the differential thermogravimetry at the peak top shows the maximum value, and the ratio of the value of the differential thermogravimetry at the peak top of the first peak to the value of the differential thermogravimetry at the peak top of the second peak is 1 or more and 9 or less. A positive electrode active material for a non-aqueous electrolyte secondary battery.

[0012] (2) The positive electrode active material for a non-aqueous electrolyte secondary battery according to (1), wherein in the composite oxide, 0 < x ≦ 0.15.

[0013] (3) The positive electrode active material for a non-aqueous electrolyte secondary battery according to (1) or (2), wherein the value of the differential thermogravimetry at the peak top of the first peak is 3% / min or less.

[0014] (4) A non-aqueous electrolyte secondary battery including a positive electrode containing the positive electrode active material according to (1) or (2).

Advantages of the Invention

[0015] According to the present disclosure, it is possible to provide a positive electrode active material capable of suppressing thermal runaway when used in a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present disclosure will be described. However, the present disclosure is not limited by the description of the embodiments and can be implemented with appropriate modifications.

[0017] <Positive electrode active material for non-aqueous electrolyte secondary battery> The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure has a general formula Li 1+x Ni 1-y-z-w-v Co y Mn z Ti w M v O 2+α (where M is one or more elements other than Li, Ni, Co, Mn, and O, -0.1 ≦ x ≦ 0.15, 0 ≦ y ≦ 0.4, 0 < z ≦ 0.4, 0.001 ≦ w ≦ 0.03, 0 ≦ v ≦ 0.1, -0.5 ≦ α ≦ 0.5), and when the composite oxide is separated into a plurality of peaks for a sample charged to 4.30 V with the counter electrode being lithium, by increasing the temperature from 50 °C to 600 °C at 5 °C / min, in the temperature range of 150 °C or higher and 350 °C or lower, it has a first peak where the value of the differential thermogravimetry at the peak top shows the maximum value, and among the peaks showing the peak top at a temperature separated by 20 °C or more from the temperature showing the peak top of the first peak, it has a second peak where the value of the differential thermogravimetry at the peak top shows the maximum value, and the ratio of the value of the differential thermogravimetry at the peak top of the first peak to the value of the differential thermogravimetry at the peak top of the second peak is 1 or more and 9 or less.)

[0018] When oxygen release from the positive electrode active material occurs in a plurality of temperature zones that are separated from each other, compared with the case where oxygen release from the positive electrode active material occurs only in one narrow temperature zone, oxygen release is suppressed per temperature zone, and as a result, the reaction with the electrolyte is also suppressed, and the calorific value decreases. Therefore, by causing oxygen release from the positive electrode active material to occur in a plurality of temperature zones that are separated from each other, thermal runaway of the positive electrode active material can be suppressed.)

[0019] When the inventors of the present invention performed TG measurement on a composite oxide, it was confirmed by TG-MS that almost all of the weight loss at temperatures up to around 350°C was oxygen release. As a result, oxygen release from the positive electrode active material occurs in the temperature range of 150°C or higher and 350°C or lower, while in this temperature range, the positive electrode active material does not undergo other reactions. Therefore, when the differential thermogravimetric curve of the positive electrode active material (hereinafter sometimes referred to as the "DTG curve") is separated into a plurality of peaks, in the temperature range of 150°C or higher and 350°C or lower, it has the largest first peak and a second peak separated from each other by a temperature of 20°C or higher, and the size of the first peak is 9 times or less the size of the second peak, so that oxygen release from the positive electrode active material occurs in a plurality of temperature zones separated from each other.

[0020] On the other hand, in the DTG curve, when it cannot be separated into a plurality of peaks (consisting of a single peak), or when it can be separated into a plurality of peaks but the size of the first peak is much larger than the size of the second peak, oxygen release from the positive electrode active material occurs in one narrow temperature zone, so that thermal runaway is likely to occur.

[0021] The requirements for the positive electrode active material to exhibit such a DTG curve are related to many factors such as the elemental composition, crystal structure, crystallinity, and synthesis conditions of the positive electrode active material, and can also vary depending on the balance thereof. As a material having a tendency to exhibit such a DTG curve, a composite oxide represented by the general formula Li 1+x Ni 1-y-z-w-v Co y Mn z Ti w M v O 2+α (where M is one or more elements other than Li, Ni, Co, Mn, and O, -0.1 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.4, 0 < z ≤ 0.4, 0.001 ≤ w ≤ 0.03, 0 ≤ v ≤ 0.1, -0.5 ≤ α ≤ 0.5) can be mentioned, but even if it has such a composition, the two predetermined peaks of the DTG curve do not necessarily satisfy the above-mentioned requirements. In other words, the two predetermined peaks of the DTG curve do not depend only on the composition of the compound.

[0022] In the following, the mechanism by which a composite oxide releases oxygen in a charged state, when a large amount of lithium is released from the crystal structure and the crystal structure is generally unstable, is referred to as Li 1-x-δ NiO2 will be used as an example. Note that oxygen release also occurs in the composite oxides disclosed herein through a similar mechanism. When such a composite oxide is used as a positive electrode active material and heated in a charged state, 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 in the following formulas (1) and (2). The temperature of these phase transitions depends on the depth of charge, but they occur in a temperature range of approximately 190 to 310°C. Furthermore, as is clear from formulas (1) and (2), it is believed that the transitions proceed while generating oxygen gas.

[0023] Formula (1): Li 1-x-δ NiO2 (layered rock salt structure R-3m) →{(1-x-δ) / (1-δ)}Li 1-δ NiO2 (layered rock salt structure 1 R-3m) +{x / 3(1-δ)}Ni3O4 (spinel structure Fd-3m) +{x / 3(1-δ)}O2↑

[0024] Formula (2): ·{(1-x-δ) / (1-δ)}Li 1-δ NiO2 (layered rock salt structure 1 R-3m) →(1-x-δ)LiNiO2 (layered rock salt structure 2 R-3m) +{δ(1-x-δ) / (1-δ)}NiO(Halite structure 1 Fm3m) +{δ(1-x-δ) / 2(1-δ)}O2↑ {x / 3(1-δ)}Ni3O4 (spinel structure Fd-3m) →{x / 3(1-δ)}NiO (rock salt structure 2 Fm3m) +{x / 6(1-δ)}O2↑

[0025] Note that the "-" in R-3m is normally placed above the 3, but for convenience it will be written as above. Similarly, the "-" in Fd-3m is normally placed above the 3, but for convenience it will be written as above.

[0026] The present inventors believe that this sudden generation of oxygen gas has a significant effect on the thermal stability of a charged non-aqueous electrolyte secondary battery.

[0027] When a charged non-aqueous electrolyte secondary battery overheats and its temperature rises, the oxygen gas generated by the reactions of formulas (1) and (2) primarily oxidizes (including combustion) the organic electrolyte solution inside the non-aqueous electrolyte secondary battery. Because this reaction is exothermic, the temperature of the non-aqueous electrolyte secondary battery rises. This temperature rise further oxidizes the electrolyte solution, generating heat, leading to an uncontrollable temperature rise and thermal runaway.

[0028] 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 preventing the amount of heat generated and the heat flow from concentrating in a short period of time according to formulas (1) and (2), the temperature rise can be suppressed, and uncontrollable thermal runaway can be prevented, thereby improving safety.

[0029] From the above, the inventors have concluded that the most important thing to do to prevent uncontrollable thermal runaway is to suppress the rate of oxygen release from the positive electrode active material. To achieve this, it is effective to adjust the oxygen release from the composite oxide so that it occurs in multiple temperature ranges, as described in the present disclosure, and to control the oxygen release so that it does not occur suddenly in a narrow temperature range.

[0030] [Chemical structure] As for composite oxides, Li 1+x Ni 1-y-z-w-v Co y Mn z Ti w M v O 2+α(In the formula, M is one or more elements other than Li, Ni, Co, Mn, and O; -0.1 ≦ x ≦ 0.15, 0 ≦ y ≦ 0.4, 0 < z ≦ 0.4, 0.001 ≦ w ≦ 0.03, 0 ≦ v ≦ 0.1, -0.5 ≦ α ≦ 0.5), and it is not particularly limited as long as it is represented by this formula.)

[0031] Regarding the reason why the composite oxide as the positive electrode active material according to the present disclosure shows multiple peaks in its differential thermogravimetric curve, it is not necessarily clear, and it is not limited to a specific theory. However, the inventors consider it as follows. In such a composite oxide, here, when Ti is further contained in the composite oxide, Ti 4+ For each one, Ni 2+ Two and one vacancy are formed. Among these, Ti 4+ and Ni 2+ are located at the 3b site (metal site), and Ni 2+ and the vacancy are arranged at the 3a site (Li site). At the 3a site, Ni undergoes cation mixing, and two Li are ejected from this site due to the generation of a vacancy. The Li thus supplied to the 3b site reacts with Mn to form Li2MnO3.

[0032] This Li2MnO3 further aggregates to form a Li2MnO3 domain. Within this domain, since the Li at the 3a site is filled even at a charged state of 4.3V, it is considered to play the role of a pillar and strengthen the structure. Since it is difficult to thermally decompose in the vicinity of this domain even in the charged state, a part of the decomposition peak can be shifted to the high-temperature side. In the present disclosure, as described above, two Li can be ejected from the 3a site to the 3b site from one Ti. Therefore, a large amount of Li2MnO3 can be efficiently formed by the amount of Ti. As a result, it is considered that the peak on the high-temperature side that has been shifted can be made larger, thereby making the peak on the low-temperature side that usually appears smaller.

[0033] In the general formula, the value of x is not particularly limited as long as it is within the range of -0.10≦x≦0.15, and may be, for example, -0.095 or more, -0.09 or more, -0.085 or more, -0.08 or more, -0.075 or more, -0.07 or more, -0.065 or more, -0.06 or more, -0.055 or more, -0.05 or more, -0.045 or more, -0.04 or more, -0.035 or more, -0.03 or more, -0.025 or more, -0.02 or more, -0.015 or more, -0.01 or more, -0.0095 or more, -0.009 or more, -0.0085 or more, -0.008 or more, -0.0075 or more, -0.007 or more, -0.0065 or more, -0.006 or more, -0.0055 or more, -0.005 or more, -0.0045 or more, -0.004 or more, -0.0035 or more, -0.003 or more, -0.0025 or more, -0.002 or more, -0.0015 or more, -0.001 or more, 0 or more, greater than 0, 0.001 or more, 0.0015 or more, 0.002 or more, 0.0025 or more, 0.003 or more ,0.0035 or more,0.004 or more,0.0045 or more,0.005 or more,0.0055 or more,0.006 or more,0.0065 or more,0.007 or more,0.0075 or more,0.008 or more,0.0085 or more,0.009 or more,0.0095 or more,0.01 or more,0.015 or more,0.02 or more,0.025 or more,0.03 or more,0.035 or more,0.04 or more,0.045 or more,0.05 or more,0.055 or more,0.06 or more,0.065 or more,0.07 or more, It is preferably 0.075 or more, 0.08 or more, 0.085 or more, 0.09 or more, 0.095 or more, 0.1 or more, 0.102 or more, 0.105 or more, 0.107 or more, 0.11 or more, 0.112 or more, 0.115 or more, 0.117 or more, 0.12 or more, 0.122 or more, 0.125 or more, 0.127 or more, 0.13 or more, 0.132 or more, 0.135 or more, 0.137 or more, 0.14 or more, 0.142 or more, 0.145 or more, 0.147 or more, or 0.15 or more.On the other hand, the values of x are 0.147 or less, 0.145 or less, 0.142 or less, 0.14 or less, 0.137 or less, 0.135 or less, 0.132 or less, 0.13 or less, 0.127 or less, 0.125 or less, 0.122 or less, 0.12 or less, 0.117 or less, 0.115 or less, 0.112 or less, 0.11 or less, 0.107 or less, 0.105 or less, 0.102 or less, 0.1 or less, 0.095 or less, 0.09 or less, 0.085 or less, 0. 075 or less, 0.07 or less, 0.065 or less, 0.06 or less, 0.055 or less, 0.05 or less, 0.045 or less, 0.04 or less, 0.035 or less, 0.03 or less, 0.025 or less, 0.02 or less, 0.015 or less, 0.0 1 or less, 0.0095 or less, 0.009 or less, 0.0085 or less, 0.008 or less, 0.0075 or less, 0.007 or less, 0.0065 or less, 0.006 or less, 0.0055 or less, 0.005 or less, 0.0045 or less, 0 .004 or less, 0.0035 or less, 0.003 or less, 0.0025 or less, 0.002 or less, 0.0015 or less, 0.001 or less, 0 or less, -0.001 or less, -0.0015 or less, -0.002 or less, -0.0025 or less , -0.003 or less, -0.0035 or less, -0.004 or less, -0.0045 or less, -0.005 or less, -0.0055 or less, -0.006 or less, -0.0065 or less, -0.007 or less, -0.0075 or less, -0. Preferably, x is 0.008 or less, -0.0085 or less, -0.009 or less, -0.0095 or less, -0.01 or less, -0.015 or less, -0.02 or less, -0.025 or less, -0.03 or less, -0.035 or less, -0.04 or less, -0.045 or less, -0.05 or less, -0.055 or less, -0.06 or less, -0.065 or less, -0.07 or less, -0.075 or less, -0.08 or less, -0.085 or less, -0.09 or less, or -0.095 or less. The value of x being within the required range means that the Li content is within the required range. By setting the value of x to a required value or more, the Li content can be increased, Li vacancies can be reduced, and the first reduction of Ni that occurs between about 200 and 250°C can be suppressed, while the proportion of the second reduction that occurs between about 260 and 320°C can be increased. This tends to decrease the peak top on the low-temperature side of the differential thermogravimetric curve and increase the peak top on the high-temperature side.By setting the value of x to a required value or less, a certain amount of Li vacancies can be ensured, and a decrease in charge capacity can be suppressed.

[0034] In the general formula, the value of 1-yzwv is not particularly limited as long as it is a combination of the ranges that y, z, w and v can take, and examples thereof include 0.6 or more, 0.605 or more, 0.61 or more, 0.615 or more, 0.62 or more, 0.625 or more, 0.63 or more, 0.635 or more, 0.64 or more, 0.645 or more, 0.65 or more, 0.655 or more, 0.66 or more, 0.665 or more, 0.67 or more, 0.675 or more, 0.68 or more, It is preferably 0.685 or more, 0.69 or more, 0.695 or more, 0.70 or more, 0.705 or more, 0.71 or more, 0.715 or more, 0.72 or more, 0.725 or more, 0.73 or more, 0.735 or more, 0.74 or more, 0.745 or more, 0.75 or more, 0.755 or more, 0.76 or more, 0.765 or more, 0.77 or more, 0.775 or more, 0.78 or more, 0.785 or more, 0.79 or more, or 0.795 or more. On the other hand, the value of 1-yzwv may be 1 or less, 0.995 or less, 0.99 or less, 0.985 or less, 0.98 or less, 0.975 or less, 0.97 or less, 0.965 or less, 0.96 or less, 0.955 or less, 0.95 or less, 0.945 or less, 0.94 or less, 0.935 or less, 0.93 or less, 0.925 or less, 0.92 or less, 0.915 or less, 0.91 or less, 0.905 or less, 0.90 or less, 0.895 or less, 0.89 or less, 0.885 or less, 0.88 or less, 0.875 or less, 0.87 or less, 0.865 or less, 0.86 or less, 0.855 or less, 0.85 or less, 0.845 or less, or 0.84 or less. The value of 1-yzwv being within the required range means that the Ni content is within the required range. By setting the value of 1-yzwv to a required value or higher, it is possible to increase the amount of Ni that moves within the composite oxide. On the other hand, by setting the value of 1-yzwv to a certain value or less, it is possible to include elements that have functionality that can inhibit the movement of some of the Ni, although this depends on the balance with other elements, etc.

[0035] In the general formula, the value of y is not particularly limited as long as it is within the range of 0≦y≦0.4, and examples thereof include greater than 0, 0.001 or more, 0.0015 or more, 0.002 or more, 0.0025 or more, 0.003 or more, 0.0035 or more, 0.004 or more, 0.0045 or more, 0.005 or more, 0.0055 or more, 0.006 or more, 0.0065 or more, 0.007 or more, 0.0075 or more, 0.008 or more, 0.0085 or more, 0.009 or more, 0.0095 or more, 0.01 or more, 0.015 or more, 0.02 or more, 0.025 or more, 0.03 or more, 0.035 or more, 0.04 or more, 0.045 or more, 0.05 or more, 0.055 or more, 0.06 or more, 0.065 or more, 0.07 or more, 0.075 or more, 0.08 or more, 0.085 or more, 0.09 or more, 0.095 or more, 0.1 or more, 0.102 or more, 0.105 or more, 0.107 or more, 0.11 or more, 0.112 or more, 0.115 or more, 0.117 or more, 0.12 or more, 0.122 or more, 0.125 or more, 0.127 or more, 0.13 or more, 0.132 or more, 0.135 or more, 0.137 or more, 0.14 or more, 0.142 or more, 0.145 or more, 0.147 or more, 0.15 or more, 0.152 or more, 0.155 or more, 0.157 or more, 0.16 or more, 0.162 or more, 0.165 or more, 0.167 or more, 0.17 or more, 0.172 or more, 0.175 or more, 0.177 or more, 0.18 or more, 0.182 or more, 0.185 or more, 0.187 or more, 0.19 or more, 0.192 or more, 0.195 or more, 0.197 or more, 0.2 or more, 0.202 or more, 0.205 or more, 0.207 or more, 0.21 or more, 0.212 or more, 0.215 or more, 0.217 or more, 0.22 or more, 0.222 or more, 0.225 or more, 0.227 or more, 0.23 or more, 0.232 or more , 0.235 or more, 0.237 or more, 0.24 or more, 0.242 or more, 0.245 or more, 0.247 or more, 0.25 or more, 0.252 or more, 0.255 or more, 0.257 or more, 0.26 or more, 0.262 or more, 0.265 or more, 0.267 or more, 0.27 or more, 0.272 or more, 0.275 or more, 0.277 or more, 0.282 or more, 0.285 or more, 0.287 or more, 0.29 or more, 0.292 or more, 0.295 or more, 0.297 or more, 0.3 or more, 0.302 or more, 0.305 or more, 0.307 or more, 0.31 or more, 0.312 or more, 0.315 or more, 0.317 or more, 0.32 or more, 0.322 or more, 0.325 or more, 0.327 or more, 0.33 or more, 0.332 or more, 0.335 or more, 0.337 or more, 0.34 or more, 0.342 or more, 0.345 or more, 0.347 or more, 0.35 or more, 0.352 or more, 0.355 or more, 0.357 or more, 0.362 or more, 0.365 or more, 0.367 or more, 0.37 or more, 0.372 or more, 0.375 or more, 0.377 or more, 0.382 or more, 0.385 or more, 0.387 or more, 0.39 or more, 0.392 or more, 0.395 or more, 0.397 or more is preferred. On the other hand, the values of y are 0.397 or less, 0.395 or less, 0.392 or less, 0.39 or less, 0.387 or less, 0.385 or less, 0.382 or less, 0.38 or less, 0.377 or less, 0.375 or less, 0 .372 or less, 0.367 or less, 0.365 or less, 0.362 or less, 0.36 or less, 0.357 or less, 0.355 or less, 0.352 or less, 0.35 or less, 0.347 or less, 0.345 or less, 0.342 or less Below, 0.34 or less, 0.337 or less, 0.335 or less, 0.332 or less, 0.33 or less, 0.327 or less, 0.325 or less, 0.322 or less, 0.32 or less, 0.317 or less, 0.315 or less, 0.3 12 or less, 0.31 or less, 0.307 or less, 0.305 or less, 0.302 or less, 0.3 or less, 0.297 or less, 0.295 or less, 0.292 or less, 0.29 or less, 0.287 or less, 0.285 or less, 0. 282 or less, 0.28 or less, 0.277 or less, 0.275 or less, 0.272 or less, 0.27 or less, 0.267 or less, 0.265 or less, 0.26 or less, 0.257 or less, 0.255 or less, 0.252 or less , 0.25 or less, 0.247 or less, 0.245 or less, 0.242 or less, 0.24 or less, 0.237 or less, 0.235 or less, 0.232 or less, 0.23 or less, 0.227 or less, 0.225 or less, 0.222 0.22 or less, 0.217 or less, 0.215 or less, 0.212 or less, 0.21 or less, 0.207 or less, 0.205 or less, 0.202 or less, 0.2 or less, 0.197 or less, 0.195 or less, 0.19 2 or less, 0.19 or less, 0.187 or less, 0.185 or less, 0.182 or less, 0.18 or less, 0.177 or less, 0.175 or less, 0.172 or less, 0.17 or less, 0.167 or less, 0.165 or less, 0.162 or less, 0.16 or less, 0.155 or less, 0.152 or less, 0.15 or less, 0.147 or less, 0.145 or less, 0.142 or less, 0.14 or less, 0.137 or less, 0.135 or less, 0.132 or less, 0.13 or less, 0.127 or less, 0.125 or less, 0.122 or less, 0.12 or less, 0.117 or less, 0.115 or less, 0.112 or less, 0.11 or less, 0.107 or less, 0.105 or less, 0.102 or less, 0.1 or less, 0.095 or less, 0.09 or less, 0.085 or less, 0.08 or less, 0.075 or less, 0.07 or less, 0.065 or less, 0 Preferably, y is 0.06 or less, 0.055 or less, 0.05 or less, 0.045 or less, 0.04 or less, 0.035 or less, 0.03 or less, 0.025 or less, 0.02 or less, 0.015 or less, 0.01 or less, 0.0095 or less, 0.009 or less, 0.0085 or less, 0.008 or less, 0.0075 or less, 0.007 or less, 0.0065 or less, 0.0055 or less, 0.005 or less, 0.0045 or less, 0.004 or less, 0.0035 or less, 0.003 or less, 0.0025 or less, 0.0015 or less, or 0.001 or less. The value of y being within the required range means that the Co content is within the required range. By setting the value of y to a value greater than the required value, Co is increased, which leads to Ni. 4+ On the other hand, even if the value of y is set to a certain value or more, the increase in the amount of the second reduction may reach a plateau, so it is set to a required value or less.

[0036] In the general formula, the value of z is not particularly limited as long as it is within the range of 0 < z ≤ 0.4. For example, it can be 0.001 or more, 0.0015 or more, 0.002 or more, 0.0025 or more, 0.003 or more, 0.0035 or more, 0.004 or more, 0.0045 or more, 0.005 or more, 0.0055 or more, 0.006 or more, 0.0065 or more, 0.007 or more, 0.0075 or more, 0.008 or more, 0.0085 or more, 0.009 or more, 0.0095 or more, 0.01 or more, 0.015 or more, 0.02 or more, 0.025 or more, 0.03 or more, 0.035 or more, 0.04 or more, 0.045 or more, 0.05 or more, 0.055 or more, 0.06 or more, 0.065 or more, 0.07 or more, 0.075 or more, 0.08 or more, 0.085 or more, 0.09 or more, 0.095 or more, 0.1 or more, 0.102 or more, 0.105 or more, 0.107 or more, 0.11 or more, 0.112 or more, 0.115 or more, 0.117 or more, 0.12 or more, 0.122 or more, 0.125 or more, 0.127 or more, 0.13 or more, 0.132 or more, 0.135 or more, 0.137 or more, 0.14 or more, 0.142 or more, 0.145 or more, 0.147 or more, 0.15 or more, 0.152 or more, 0.155 or more, 0.157 or more, 0.16 or more, 0.162 or more, 0.165 or more, 0.167 or more, 0.17 or more, 0.172 or more, 0.175 or more, 0.177 or more, 0.18 or more, 0.182 or more, 0.185 or more, 0.187 or more, 0.19 or more, 0.192 or more, 0.195 or more, 0.197 or more, 0.2 or more, 0.202 or more, 0.205 or more, 0.207 or more, 0.21 or more, 0.212 or more, 0.215 or more, 0.217 or more, 0.22 or more, 0.222 or more, 0.225 or more, 0.227 or more, 0.23 or more, 0.232 or more, 0.235 or more, 0.237 or more, 0.24 or more, 0.242 or more, 0.245 or more, 0.247 or more, 0.25 or more, 0.252 or more, 0.255 or more, 0.257 or more, 0.26 or more, 0.262 or more, 0.265 or more, 0.267 or more, 0.27 or more, 0.272 or more, 0.275 or more, 0.277 or more, 0.28 or more, 0.282 or more, 0.285 or more, 0.287 or more, 0.29 or more, 0.292 or more, 0.295 or more, 0.297 or more, 0.3 or more, 0.302 or more, 0.305 or more, 0.307 or more, 0.31 or more, 0.312 or more, 0.315 or more, 0.317 or more, 0.32 or more, 0.322 or more, 0.325 or more, 0.327 or more, 0.33 or more, 0.332 or more, 0.335 or more, 0.337 or more, 0.34 or more, 0.342 or more, 0.345 or more, 0.347 or more, 0.35 or more, 0.352 or more, 0.355 or more, 0.357 or more, 0.362 or more, 0.365 or more, 0.367 or more, 0.37 or more, 0.372 or more, 0.375 or more, 0.377 or more, 0.382 or more, 0.385 or more, 0.387 or more, 0.39 or more, 0.392 or more, 0.395 or more, 0.397 or more is preferred. On the other hand, the values of z are 0.397 or less, 0.395 or less, 0.392 or less, 0.39 or less, 0.387 or less, 0.385 or less, 0.382 or less, 0.38 or less, 0.377 or less, 0.375 or less, 0 .372 or less, 0.367 or less, 0.365 or less, 0.362 or less, 0.36 or less, 0.357 or less, 0.355 or less, 0.352 or less, 0.35 or less, 0.347 or less, 0.345 or less, 0.342 or less Below, 0.34 or less, 0.337 or less, 0.335 or less, 0.332 or less, 0.33 or less, 0.327 or less, 0.325 or less, 0.322 or less, 0.32 or less, 0.317 or less, 0.315 or less, 0.3 12 or less, 0.31 or less, 0.307 or less, 0.305 or less, 0.302 or less, 0.3 or less, 0.297 or less, 0.295 or less, 0.292 or less, 0.29 or less, 0.287 or less, 0.285 or less, 0. 282 or less, 0.28 or less, 0.277 or less, 0.275 or less, 0.272 or less, 0.27 or less, 0.267 or less, 0.265 or less, 0.26 or less, 0.257 or less, 0.255 or less, 0.252 or less , 0.25 or less, 0.247 or less, 0.245 or less, 0.242 or less, 0.24 or less, 0.237 or less, 0.235 or less, 0.232 or less, 0.23 or less, 0.227 or less, 0.225 or less, 0.222 0.22 or less, 0.217 or less, 0.215 or less, 0.212 or less, 0.21 or less, 0.207 or less, 0.205 or less, 0.202 or less, 0.2 or less, 0.197 or less, 0.195 or less, 0.19 2 or less, 0.19 or less, 0.187 or less, 0.185 or less, 0.182 or less, 0.18 or less, 0.177 or less, 0.175 or less, 0.172 or less, 0.17 or less, 0.167 or less, 0.165 or less, 0.162 or less, 0.16 or less, 0.155 or less, 0.152 or less, 0.15 or less, 0.147 or less, 0.145 or less, 0.142 or less, 0.14 or less, 0.137 or less, 0.135 or less, 0.132 or less, 0.13 or less, 0.127 or less, 0.125 or less, 0.122 or less, 0.12 or less, 0.117 or less, 0.115 or less, 0.112 or less, 0.11 or less, 0.107 or less, 0.105 or less, 0.102 or less, 0.1 or less, 0.095 or less, 0.09 or less, 0.085 or less, 0.08 or less, 0.075 or less, 0.07 or less, 0.065 or less, 0 Preferably, z is 0.06 or less, 0.055 or less, 0.05 or less, 0.045 or less, 0.04 or less, 0.035 or less, 0.03 or less, 0.025 or less, 0.02 or less, 0.015 or less, 0.01 or less, 0.0095 or less, 0.009 or less, 0.0085 or less, 0.008 or less, 0.0075 or less, 0.007 or less, 0.0065 or less, 0.0055 or less, 0.005 or less, 0.0045 or less, 0.004 or less, 0.0035 or less, 0.003 or less, 0.0025 or less, 0.0015 or less, or 0.001 or less. A value of z within the required range means that the Mn content is within the required range. Setting the value of z above the required value makes it easier to form Li2MnO3 and promotes the migration of Ni and Co to the Li layer. Setting the value of z below the required value increases the formation of Li2MnO3, which can suppress the decrease in charge capacity due to an excessive increase in Li vacancies.

[0037] In the general formula, the value of w is not particularly limited as long as it is within the range of 0.001≦w≦0.03, and examples thereof include 0.001 or more, 0.0012 or more, 0.0015 or more, 0.0017 or more, 0.002 or more, 0.0022 or more, 0.0025 or more, 0.0027 or more, 0.003 or more, 0.0032 or more, 0.0035 or more, 0.0037 or more, 0.004 or more, 0.0042 or more, 0.0045 or more, 0.0047 or more, 0.005 or more, 0.0052 or more, 0.0055 or more, 0.0057 or more, 0.006 or more, 0.0062 or more, 0.0065 or more, 0.0067 or more, 0.007 or more, It is preferably 0.0072 or more, 0.0075 or more, 0.0077 or more, 0.008 or more, 0.0082 or more, 0.0085 or more, 0.0087 or more, 0.009 or more, 0.0092 or more, 0.0095 or more, 0.0097 or more, 0.01 or more, 0.011 or more, 0.012 or more, 0.013 or more, 0.014 or more, 0.015 or more, 0.016 or more, 0.017 or more, 0.018 or more, 0.019 or more, 0.021 or more, 0.022 or more, 0.023 or more, 0.024 or more, 0.025 or more, 0.026 or more, 0.027 or more, 0.028 or more, or 0.029 or more.On the other hand, the value of w is 0.029 or less, 0.028 or less, 0.027 or less, 0.026 or less, 0.025 or less, 0.024 or less, 0.023 or less, 0.022 or less, 0.021 or less, 0.02 or less, 0.019 or less, 0.018 or less, 0.017 or less, 0.016 or less, 0.015 or less, 0.014 or less, 0.013 or less, 0.012 or less, 0.011 or less, 0.01 or less, 0.0097 or less, 0.0095 or less, 0.0092 or less, 0.009 or less, 0.0087 or less, 0.0085 or less, 0.0082 or less, 0.008 or less, 0.00 Preferably, the w value is 0.77 or less, 0.0075 or less, 0.0072 or less, 0.007 or less, 0.0067 or less, 0.0065 or less, 0.0062 or less, 0.006 or less, 0.0057 or less, 0.0055 or less, 0.0052 or less, 0.005 or less, 0.0047 or less, 0.0045 or less, 0.0042 or less, 0.004 or less, 0.0037 or less, 0.0035 or less, 0.0032 or less, 0.003 or less, 0.0027 or less, 0.0025 or less, 0.0022 or less, 0.002 or less, 0.0017 or less, 0.0015 or less, 0.0012 or less. 2+ By appropriately mixing the cations, the crystal structure of the 3a site is stabilized, and the Li that is expelled from the 3a site is mixed with Ni. 2+ The vacancies in the 3b sites created by cation mixing can be arranged, and a large amount of Li2MnO3 domains can be efficiently formed. By setting the w value below the required value, excess Ni 2+ This can suppress the deterioration of battery characteristics due to cation mixing.

[0038] In the general formula, the value of v is not particularly limited as long as it is within the range of 0≦w≦0.1, and may be, for example, 0.001 or more, 0.0012 or more, 0.0015 or more, 0.0017 or more, 0.002 or more, 0.0022 or more, 0.0025 or more, 0.0027 or more, 0.003 or more, 0.0032 or more, 0.0035 or more, 0.0037 or more, 0.004 or more, 0.0042 or more. Above, 0.0045 or more, 0.0047 or more, 0.005 or more, 0.0052 or more, 0.0055 or more, 0.0057 or more, 0.006 or more, 0.0062 or more, 0.0065 or more, 0.0067 or more, 0.007 or more, 0.0072 or more, 0.0075 or more, 0.0077 or more, 0.008 or more, 0.0082 or more, 0.0085 or more, 0.0087 or more, 0 0.009 or more, 0.0092 or more, 0.0095 or more, 0.0097 or more, 0.01 or more, 0.012 or more, 0.015 or more, 0.017 or more, 0.02 or more, 0.022 or more, 0.025 or more, 0.027 or more, 0.03 or more, 0.032 or more, 0.035 or more, 0.037 or more, 0.04 or more, 0.042 or more, 0.045 or more, 0.047 or more, 0.0 It is preferable that the molecular weight is 5 or more, 0.052 or more, 0.055 or more, 0.057 or more, 0.06 or more, 0.062 or more, 0.065 or more, 0.067 or more, 0.07 or more, 0.072 or more, 0.075 or more, 0.077 or more, 0.082 or more, 0.085 or more, 0.087 or more, 0.09 or more, 0.092 or more, 0.095 or more, or 0.097 or more.On the other hand, the values of v are 0.097 or less, 0.095 or less, 0.092 or less, 0.09 or less, 0.087 or less, 0.085 or less, 0.082 or less, 0.08 or less, 0.077 or less, 0.075 or less, 0.072 or less, 0.07 or less, 0.067 or less, 0.065 or less, 0.062 or less, 0.06 or less, 0.057 or less, 0.055 or less, 0. 052 or less, 0.05 or less, 0.047 or less, 0.045 or less, 0.042 or less, 0.04 or less, 0.037 or less, 0.035 or less, 0.032 or less, 0.03 or less, 0. 027 or less, 0.025 or less, 0.022 or less, 0.02 or less, 0.017 or less, 0.015 or less, 0.012 or less, 0.01 or less, 0.0097 or less, 0.0095 or less , 0.0092 or less, 0.009 or less, 0.0087 or less, 0.0085 or less, 0.0082 or less, 0.008 or less, 0.0077 or less, 0.0075 or less, 0.0072 less than or equal to 0.007, less than or equal to 0.0067, less than or equal to 0.0065, less than or equal to 0.0062, less than or equal to 0.006, less than or equal to 0.0057, less than or equal to 0.0055, less than or equal to 0.0052, 0.00 Preferably, v is 5 or less, 0.0047 or less, 0.0045 or less, 0.0042 or less, 0.004 or less, 0.0037 or less, 0.0035 or less, 0.0032 or less, 0.003 or less, 0.0027 or less, 0.0025 or less, 0.0022 or less, 0.002 or less, 0.0017 or less, 0.0015 or less, 0.0012 or less, or 0.001 or less. The value of v being within the required range means that the content of element M is within the required range. By setting the value of v to a required value or more, the effect of adding element M can be exerted. By setting the value of v to a required value or less, the contents of Ni, Co, and Mn can be ensured, and battery performance such as a high charge capacity due to these elements can be maintained.

[0039] In the formula, the element M is not particularly limited as long as it is one or more elements other than Li, Ni, Co, Mn, and O, and examples that can be used include Al, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, and B. The type of element M may be selected depending on the purpose of addition. When multiple elements are contained as element M, the value of v represents the total amount of the multiple elements.

[0040] In the general formula, the value of α is not particularly limited as long as it is within the range of −0.5≦α≦0.5, and may be, for example, −0.5 or more, −0.45 or more, −0.4 or more, −0.35 or more, −0.30 or more, −0.25 or more, −0.2 or more, −0.15 or more, −0.1 or more, −0.075 or more, −0.05 or more, −0.025 or more, 0.001 or more, 0.0015 or more, 0.002 or more, 0.0025 or more, 0.003 or more, 0.0035 or more, 0.004 or more, 0.0045 or more, 0.005 or more, 0.0055 or more, 0.006 or more, 0.0065 or more, 0.007 or more, 0.0085 or more, 0.009 ... 0.0075 or more, 0.008 or more, 0.0085 or more, 0.009 or more, 0.0095 or more, 0.01 or more, 0.015 or more, 0.02 or more, 0.025 or more, 0.03 or more, 0.035 or more, 0.04 or more, 0.045 or more, 0.05 or more, 0.055 or more, 0.06 or more, 0.065 or more, 0.07 or more, 0.075 or more, 0.08 or more, 0.085 or more, 0.09 or more, 0.095 or more, 0.1 or more, 0.102 or more, 0.105 or more, 0.107 or more, 0.11 or more, 0.112 or more, 0.115 or more, 0.117 or more, 0.12 or more, 0.122 or more, 0.125 or more, 0.127 or more, 0.13 or more, 0.132 or more, 0.135 or more, 0.137 or more, 0.14 or more, 0.142 or more, 0.145 or more, 0.147 or more, 0.15 or more, 0.152 or more, 0.155 or more, 0.157 or more, 0.16 or more, 0.162 or more, 0.165 or more, 0.167 or more, 0.17 or more, 0.172 or more, 0.175 or more, 0.177 or more, 0.18 or more, 0.182 or more, 0.185 or more, 0.187 or more, 0.19 or more, 0.192 or more, 0.195 or more, 0.197 or more, 0.2 or more, 0.202 or more, 0.205 or more, 0.207 or more, 0.21 or more, 0.212 or more, 0.215 or more, 0.217 or more, 0.22 or more, 0.222 or more, 0.225 or more, 0.227 or more, 0.23 or more, 0.232 or more, 0.235 or more, 0.237 or more, 0.24 or more, 0.242 or more, 0.245 or more, 0.247 or more, 0.25 or more, 0.252 or more, 0.255 or more, 0.257 or more, 0.262 or more, 0.265 or more, 0.267 or more, 0.27 or more, 0.272 or more, 0.275 or more, 0.277 or more, 0.28 or more, 0.285 or more, 0.287 or more, 0.29 or more, 0.292 or more, 0.295 or more, 0.297 or more, 0.3 or more, 0.302 or more, 0.305 or more, 0.307 or more, 0.31 or more, 0.312 or more, 0.315 or more, 0.317 or more, 0.32 or more, 0.322 or more, 0.325 or more, 0.327 or more, 0.33 or more, 0.332 or more, 0.335 or more, 0.337 or more, 0.34 or more, 0.342 or more, 0.345 or more, 0.347 or more, 0.35 or more, 0.352 or more, 0.355 or more, 0.357 or more, 0.36 or more, 0.362 or more, 0.365 or more , 0.367 or more, 0.37 or more, 0.372 or more, 0.375 or more, 0.377 or more, 0.38 or more, 0.382 or more, 0.385 or more, 0.387 or more, 0.39 or more, 0.392 or more Above, 0.395 or more, 0.397 or more, 0.4 or more, 0.402 or more, 0.405 or more, 0.407 or more, 0.41 or more, 0.412 or more, 0.415 or more, 0.417 or more, 0.42 or more, 0.422 or more, 0.425 or more, 0.427 or more, 0.43 or more, 0.432 or more, 0.435 or more, 0.437 or more, 0.44 or more, 0.442 or more, 0.445 or more, 0.44 It is preferable that the molecular weight is 7 or more, 0.45 or more, 0.452 or more, 0.455 or more, 0.457 or more, 0.46 or more, 0.462 or more, 0.465 or more, 0.467 or more, 0.47 or more, 0.472 or more, 0.475 or more, 0.477 or more, 0.482 or more, 0.485 or more, 0.487 or more, 0.49 or more, 0.492 or more, 0.495 or more, or 0.497 or more. On the other hand, the values of α are 0.497 or less, 0.495 or less, 0.492 or less, 0.49 or less, 0.487 or less, 0.485 or less, 0.482 or less, 0.48 or less, 0.477 or less, 0.475 or less, 0.472 or less, 0.467 or less, 0.465 or less, 0.462 or less, 0.46 or less, 0.457 or less, 0.455 or less, 0.452 or less, 0.45 or less, 0. 447 or less, 0.445 or less, 0.442 or less, 0.44 or less, 0.437 or less, 0.435 or less, 0.432 or less, 0.43 or less, 0.427 or less, 0.425 or less, 0.422 0.42 or less, 0.417 or less, 0.415 or less, 0.412 or less, 0.41 or less, 0.407 or less, 0.405 or less, 0.402 or less, 0.4 or less, 0.397 or less, 0.395 or less, 0.392 or less, 0.39 or less, 0.387 or less, 0.385 or less, 0.382 or less, 0.38 or less, 0.377 or less, 0.375 or less, 0.372 or less, 0.367 or less, 0.365 or less, 0.362 or less, 0.36 or less, 0.357 or less, 0.355 or less, 0.352 or less, 0.35 or less, 0.347 or less, 0.345 or less, 0.342 or less, 0.34 or less, 0.337 or less, 0.335 or less, 0.332 or less, 0.33 or less, 0.327 or less, 0.325 or less, 0.322 or less, 0.32 or less, 0.317 or less, 0.315 or less, 0.3 12 or less, 0.31 or less, 0.307 or less, 0.305 or less, 0.302 or less, 0.3 or less, 0.297 or less, 0.295 or less, 0.292 or less, 0.29 or less, 0.287 or less, 0.285 or less, 0.282 or less, 0.28 or less, 0.277 or less, 0.275 or less, 0.272 or less, 0.27 or less, 0.267 or less, 0.265 or less, 0.26 or less, 0.257 or less, 0.255 or less, 0.252 or less, 0.25 or less, 0.247 or less, 0.245 or less, 0.242 or less, 0.24 or less, 0.237 or less, 0.235 or less, 0.232 or less, 0.23 or less , 0.227 or less, 0.225 or less, 0.222 or less, 0.22 or less, 0.217 or less, 0.215 or less, 0.212 or less, 0.21 or less, 0.207 or less, 0.205 or less, 0.202 or less, 0.2 or less, 0.197 or less, 0.195 or less, 0.192 or less, 0.19 or less, 0.187 or less, 0.185 or less, 0.182 or less, 0.18 or less, 0.177 or less, 0.175 or less, 0.172 or less, 0.17 or less, 0.167 or less, 0.165 or less, 0.162 or less, 0.16 or less, 0.155 or less, 0.152 or less, 0.15 or less, 0.147 or less, 0. 145 or less, 0.142 or less, 0.14 or less, 0.137 or less, 0.135 or less, 0.132 or less, 0.13 or less, 0.127 or less, 0.125 or less, 0.122 or less, 0.12 or less, 0.117 or less, 0.115 or less, 0.112 or less, 0.11 or less, 0.107 or less, 0.105 or less, 0.102 or less, 0.1 or less, 0.095 or less, 0.09 or less, 0.085 or less, 0.08 or less, 0.075 or less, 0.07 or less, 0.065 or less, 0.06 or less, 0.055 or less, 0.05 or less, 0.045 or less, 0.04 or less, 0.035 or less, 0.03 or less, 0.Preferably, the molecular weight is 0.025 or less, 0.02 or less, 0.015 or less, 0.01 or less, 0.0095 or less, 0.009 or less, 0.0085 or less, 0.008 or less, 0.0075 or less, 0.007 or less, 0.0065 or less, 0.006 or less, 0.0055 or less, 0.005 or less, 0.0045 or less, 0.004 or less, 0.0035 or less, 0.003 or less, 0.0025 or less, 0.002 or less, 0.0015 or less, or 0.001 or less.

[0041] The form of the composite oxide is not particularly limited, and may be, for example, particulate. When particulates are used, the particles may be aggregated as primary particles to form secondary particles, or may exist as primary particles, or may be a mixture of secondary particles and primary particles. As long as the primary particles have the same particle size distribution, the temperature at which oxygen is released from the composite oxide does not change significantly regardless of the state in which they exist.

[0042] The average particle size of the primary particles of the composite oxide is not particularly limited, but is preferably, for example, 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. By making the average particle size of the composite oxide a required value or more, the oxygen release temperature can be increased. On the other hand, the average particle size of the primary particles 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. By having the average particle size of the primary particles be equal to or less than the required value, the energy density can be increased and particle breakage and deterioration of rate characteristics due to cycling can be suppressed. The average particle size of the primary particles of the composite oxide is calculated by observing electron micrographs at 3,000 to 20,000 magnifications using a field-emission scanning electron microscope (JSM-7100F, manufactured by JEOL Ltd.) at an acceleration voltage of 10 kV. Specifically, a field of view in which 100 or more primary particles with visible outlines are visible is randomly selected, and electron micrographs are taken of all particles with visible outlines within the above-mentioned range, with the magnification varied as necessary. Next, the equivalent sphere diameter of the electron micrograph is calculated using image processing software (e.g., ImageJ, etc.) to determine the particle size of the primary particles.

[0043] The average particle diameter (D50) of the composite oxide is not particularly limited, but is preferably, for example, 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. By having a D50 equal to or greater than the required value, the oxygen release temperature can be increased, and in addition, the electrode density can be improved. On the other hand, D50 is 25μm or less, 24.5μm or less, 24μm or less, 23.5μm or less, 23μm or less, 22.5μm or less, 22μm or less, 21.5μm or less, 21μm or less, 20.5μm or less, 20μm or less, 19.5μm or less, 19μm or less, 18.5μm or less, 18μm or less, 17.5μm or less, 17μm or less, 16.5μm or less, 16μm or less, 15.5μm or less, 15 Preferably, the D50 of the composite oxide is 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. By ensuring that the D50 of the composite oxide is below the required value, the energy density of a nonaqueous electrolyte secondary battery using this composite oxide can be increased and particle breakage and deterioration of rate characteristics due to cycling can be suppressed. Note that D50 is measured on a volume basis by a wet laser method using a laser particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0044] [DTG curve] The DTG curve of the composite oxide of the present disclosure is obtained when the sample of the composite oxide is charged by the charging method described below and the temperature is increased from 50°C to 600°C at a rate of 5°C / min.

[0045] The differential thermogravimetric curve thus obtained is fitted using a log-normal distribution function to separate the peaks, and the temperature and thermogravimetric derivative (oxygen release rate) at the peak top of each peak are calculated.

[0046] Specifically, a thermogravimetric weight curve is obtained using a thermogravimetric differential thermal analyzer (TG-DTA) (DTG-60H, manufactured by Shimadzu Corporation) according to the method described below, and then the first and second peaks are analyzed.

[0047] (Sample preparation) Following the method described below, a 2032-type coin cell with a lithium counter electrode was prepared. It was charged at a constant current of 0.3C to 4.30V in a 25°C environment, followed by a constant voltage charge until the current reached 0.05C. After charging, a 20-minute pause was allowed, followed by a constant current discharge at 0.3C to 2.50V, followed by a constant current discharge at 0.1C and a 20-minute pause. This charge / discharge cycle was repeated twice. Next, a constant current charge at 0.3C to 4.30V was followed by a constant voltage charge until the current reached 0.05C. After charging, a 20-minute pause was allowed.

[0048] The charged coin cell is disassembled in a glove box (dew point: -70°C or below) while taking care not to short-circuit, and the positive electrode is separated. The separated positive electrode is washed with dimethyl carbonate (DMC) for 10 minutes and dried under vacuum in a side box. Then, in the same glove box, the positive electrode mixture is scraped off from the Al foil using a spatula. 15 mg of the obtained positive electrode mixture powder is filled into an Al TG measurement container, and the lid is sealed using a crimping machine.

[0049] The Al measurement vessel thus obtained is taken out of the glove box and placed on the measurement side balance of the TG-DTA apparatus.

[0050] (TG-DTA measurement) Reference: Pt container filled with 15-20 mg of Al2O3 Maximum temperature: 600℃ Heating rate: (1) 25°C (room temperature) to 50°C: 1°C / min (2) 50°C to 600°C: 5°C / min Measurement environment: N2 gas atmosphere (200 ml / min)

[0051] Just before measurement, a small hole is opened in the lid of the sealed Al measurement container in the TG-DTA device, which is in an N2 gas atmosphere, and then the temperature is raised. By using this method, the cathode composite powder, which is the measurement target, can be measured without being exposed to the air atmosphere.

[0052] Based on the obtained results, a DTG curve is created with the horizontal axis representing temperature and the vertical axis representing the value obtained by differentiating the weight change (TG) with time (differential thermogravimetric DTG, which means the weight loss rate and corresponds to the oxygen release rate of the complex oxide in the range of 150 to 350°C).

[0053] Among the peaks in this DTG curve that have peak tops between 150 and 350°C, the peak with the maximum value of the differential thermogravimetry is defined as the first peak. The value of the differential thermogravimetry at the peak top is defined as the oxygen release rate (% / min). Furthermore, among the peaks that have peak tops at temperatures 20°C or more away from the temperature at which the first peak tops, the peak with the maximum value of the differential thermogravimetry is defined as the second peak.

[0054] Next, the value of the derivative thermogravimetry at the peak top of the first peak relative to the value of the derivative thermogravimetry at the peak top of the second peak is calculated.

[0055] [First peak] The first peak is the peak at which the differential thermogravimetry value at the peak top is the maximum value in the temperature range of 150°C or higher and 350°C or lower when the DTG curve obtained as described above is separated into multiple peaks.

[0056] The value of the differential thermogravimetry at the peak top of the first peak is not particularly limited, but is preferably, for example, 3% or less, 2.9% or less, 2.8% or less, 2.7% or less, 2.6% or less, 2.5% or less, 2.4% or less, 2.3% or less, 2.2% or less, 2.1% or less, or 2% or less.

[0057] [Second Peak] The second peak is the peak whose differential thermogravimetry value at the peak top is the maximum value among the peaks whose peak top is at a temperature 20°C or more away from the temperature at which the first peak shows its peak top.

[0058] The temperature at which the second peak shows its top may be at least 20°C higher than the temperature at which the first peak shows its top, and there are no limitations on this. That is, the temperature at which the second peak shows its top may be at least 20°C higher or lower than the temperature at which the first peak shows its top.

[0059] The temperature at which the second peak shows its peak top is preferably at least 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, or 40°C away from the temperature at which the first peak shows its peak top. On the other hand, the temperature at which the second peak shows its peak top may be, for example, 160°C or less, 155°C or less, 150°C or less, 145°C or less, 140°C or less, 135°C or less, 130°C or less, 125°C or less, 120°C or less, 115°C or less, 110°C or less, 105°C or less, 100°C or less, 95°C or less, 90°C or less, 85°C or less, 80°C or less, 75°C or less, or 60°C or less away from the temperature at which the first peak shows its peak top.

[0060] [Ratio of differential thermogravimetry values] In the positive electrode active material of the present disclosure, the ratio of the value of the differential thermogravimetry of the first peak to the value of the differential thermogravimetry of the second peak (differential thermogravimetry of the first peak / differential thermogravimetry of the second peak) is not particularly limited as long as it is 1 or more and 9 or less, and may be, for example, 8.9 or less, 8.8 or less, 8.7 or less, 8.6 or less, 8.5 or less, 8.4 or less, 8.3 or less, 8.2 or less, 8.1 or less, 8 or less, 7.9 or less, 7.8 or less, 7.7 or less, 7.6 or less, 7.5 or less, 7.4 or less, 7.3 or less, 7.2 or less, 7.1 or less, 7 or less, 6.9 or less, 6.8 or less, 6.7 or less, 6.6 or less, 6.5 or less, 6.4 or less, 6.3 or less, 6.2 or less, 6.1 or less, It is preferable that the range is 6 or less, 5.9 or less, 5.8 or less, 5.7 or less, 5.6 or less, 5.5 or less, 5.4 or less, 5.3 or less, 5.2 or less, 5.1 or less, 5 or less, 4.9 or less, 4.8 or less, 4.7 or less, 4.6 or less, 4.5 or less, 4.4 or less, 4.3 or less, 4.2 or less, 4.1 or less, 4 or less, 3.9 or less, 3.8 or less, 3.7 or less, 3.6 or less, 3.5 or less, 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.2 or less, 2.1 or less, 2 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less. On the other hand, the ratio of the differential thermogravimetry value of the first peak to the differential thermogravimetry value of the second peak may be 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, 1.6 or more, 1.7 or more, 1.8 or more, or 1.9 or more.

[0061] <Method of manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery> The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure can be produced, for example, by performing the following steps in this order: Note that the following describes an example of a method for producing a composite oxide containing 30 mol % or more of Ni among elements other than Li, and other composite oxides can be produced according to conventional methods.

[0062] Precursor preparation step: A precursor complex compound containing at least a transition metal is prepared. Raw material mixing step: A mixture is prepared by mixing the precursor composite compound prepared in the precursor preparation step with a lithium compound. Pre-firing step: If necessary, the precursor prepared in the mixing step is pre-firing. Titanium compound addition step: If necessary, a titanium compound is added to the pre-fired product obtained in the pre-fired step. Firing step: The material to be fired prepared in the mixing step, pre-firing step or titanium compound addition step is subjected to firing. Water washing step: If necessary, the composite oxide obtained by firing in the main firing step is subjected to a water washing treatment. Surface treatment step: If necessary, the composite oxide obtained in the firing step or the water washing step is subjected to a surface treatment. Complex oxide mixing step: If necessary, multiple types of complex oxides with different primary particle sizes, average particle sizes, etc. are mixed by changing the conditions of any of the precursor preparation step, mixing step, pre-calcination step, and main calcination step.

[0063] [Precursor preparation step] First, a precursor composite compound is synthesized as an aggregate of primary particles containing at least a transition metal. The method for synthesizing the precursor composite compound is not particularly limited, and for example, a method can be used in which an aqueous solution containing a transition metal and various aqueous solutions of compounds containing other elements corresponding to the composition of the target composite oxide is dropped into a reaction vessel in which an alkaline aqueous solution such as a sodium hydroxide aqueous solution or an ammonia solution is stirred as a mother liquid, and while also dropping sodium hydroxide or the like, the pH is monitored and controlled to be within an appropriate range, and co-precipitation is carried out by a wet reaction to obtain, for example, a hydroxide, an oxide obtained by calcining the hydroxide, a carbonate, or the like.

[0064] In the synthesis reaction, after preparing the aqueous alkaline solution to serve as the mother liquid, it is preferable to create a nitrogen atmosphere in the reaction tank using an inert gas, or industrially preferably nitrogen gas, to reduce the oxygen concentration in the reaction tank system and in the solution as much as possible. If the oxygen concentration is too high, there is a risk that the coprecipitated hydroxide may be excessively oxidized by a predetermined amount or more of remaining oxygen, or that the formation of aggregates by crystallization may be hindered.

[0065] The aqueous solution of the transition metal is not particularly limited, but for example, an acidic aqueous solution is preferably used, and in the case of a nickel compound, it is more preferable to use an aqueous sulfuric acid solution such as an aqueous nickel sulfate solution. In addition, one or more kinds of aqueous solutions of the transition metal can be used.

[0066] 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, metallic nickel, and the like can be used.

[0067] The cobalt compound is not particularly limited, but for example, one or more compounds selected from cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt can be used.

[0068] The manganese compound is not particularly limited, but for example, one or more compounds selected from manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and manganese metal can be used.

[0069] The titanium compound is not particularly limited, and may be one or more selected from the group consisting of titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium. The titanium compound does not necessarily need to be added in the precursor preparation step. Details will be described later in the titanium compound addition step.

[0070] The aluminum compound is not particularly limited, but examples thereof include aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum.

[0071] 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.

[0072] The niobium compound is not particularly limited, but for example, one or more compounds selected from niobium oxide, niobium chloride, lithium niobate, niobium iodide, and the like can be used.

[0073] The tungsten compound is not particularly limited, but for example, one or more compounds selected from tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, tungsten sulfide, and the like can be used.

[0074] The magnesium compound is not particularly limited, but for example, one or more compounds selected from magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium can be used.

[0075] The zirconium compound is not particularly limited, but for example, one or more compounds selected from zirconium sulfate, zirconium oxide, zirconium nitrate, ammonium zirconium carbonate, zirconium chloride, zirconium iodide, and metallic zirconium can be used.

[0076] As for other elements, one or more selected from sulfates, oxides, hydroxides, nitrates, carbonates, chlorides, iodides, metals, and the like can be used.

[0077] The blending ratio of each compound may be adjusted so that the amount of each element is in the desired ratio, taking into consideration the composition of the target composite oxide.

[0078] The appropriate pH range for synthesizing the precursor complex compound is not particularly limited and can be determined so as to obtain the desired secondary particle size and shape, such as the degree of coarseness and density, and is generally in the range of about 10 to 13.

[0079] The precursor composite compound obtained by the wet reaction is preferably subjected to a washing treatment, dehydrated, and then dried.

[0080] By subjecting the precursor composite compound to a washing treatment, impurities such as sulfate groups, carbonate groups, and sodium that have been incorporated into the aggregated particles or attached to the surface during the reaction can be washed away. For small amounts of the washing, a Nutsche washing method using a Buchner funnel can be used, or a method in which the suspension after the reaction is sent to a press filter for washing and dehydration can be used. For example, pure water, an aqueous sodium hydroxide solution, an aqueous sodium carbonate solution, etc. can be used in the washing treatment, but pure water is preferred for industrial use. However, if a large amount of residual sulfate groups remains, an aqueous sodium hydroxide solution with its pH adjusted according to the amount of residual sulfate groups can also be used.

[0081] [Mixing process] Next, the precursor composite compound thus synthesized and a lithium compound are mixed in a predetermined ratio to prepare a mixture. The mixing may be a solvent-based mixing in which the precursor composite compound and the lithium compound are each made into solutions such as aqueous solutions and these solutions are mixed in a predetermined ratio, or a non-solvent-based mixing in which a powder of the precursor composite compound and a powder of the lithium compound are weighed out to give a predetermined ratio and then mixed together in a dry state.

[0082] The lithium compound is not particularly limited, and various lithium salts can be used. Specific examples of the lithium compound that can be used include one or more compounds selected from 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, it is preferable to use one or more compounds selected from anhydrous lithium hydroxide and lithium hydroxide hydrate.

[0083] The compounding ratio of the lithium compound and the precursor composite compound is not particularly limited, but may be adjusted appropriately so that the amount of lithium and the total amount of each element are in the desired ratio, taking into consideration the composition of the target composite oxide.

[0084] [Pre-firing process] The firing process, which will be described later, is generally carried out by weighing out a lithium compound, a precursor composite compound, and, if necessary, compounds of other elements, mixing them in a mixer, and then filling the resulting mixed powder into a container such as a crucible or a sagger. However, particularly in the lithiation reaction, it becomes difficult to vent the generated gas to the outside and to diffuse the required oxygen concentration, especially toward the bottom of the container where the mixed powder is filled. As a result, it becomes difficult to control the uniformity of the reaction and the primary particle size.

[0085] Therefore, when producing the composite oxide according to the embodiment of the present disclosure, it is preferable to use a method in which pre-calcination is performed by the method described below, followed by main calcination, although the pre-calcination step is not an essential step.

[0086] In this pre-firing step, it is preferable to adopt a firing method that particularly promotes the lithiation reaction. Specifically, a method can be used that makes the mixture more susceptible to heat, easily expelling gas generated from the lithium compound, and diffusing gas with a high oxygen partial pressure into the mixture (particles). For example, by pre-firing a smaller amount of the mixture, it is possible to achieve the desired properties.

[0087] In the pre-firing step, the mixture can be pre-fired by filling the mixture into a sagger or a crucible and firing it in a stationary furnace, a roller hearth kiln, or a pusher furnace. However, it is preferable to fire the mixture while flowing it, and in that case, a rotary kiln can be used as the firing apparatus.

[0088] The pre-baking temperature is not particularly limited, but is preferably, for example, 500°C to 650°C, 510°C to 640°C, or 520°C to 630°C. The pre-baking time is also not particularly limited as long as it is a time that allows the lithiation reaction to proceed reliably and uniformly, but is preferably, for example, 1 hour to 10 hours, or 2 hours to 8 hours. The pre-baking temperature in the present disclosure is the maximum temperature when the object to be heated is heated. The maximum temperature refers to the temperature of the hottest part of the object to be heated. The same definition is used below for the term maximum temperature. The pre-baking time refers to the time during which the pre-baking temperature is maintained within a predetermined range after reaching that range.

[0089] The atmosphere for the pre-baking is not particularly limited as long as it is an oxidizing atmosphere in which the lithiation reaction proceeds reliably and uniformly. For example, it is preferable to use a decarbonated oxidizing gas atmosphere with a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of 80 vol% or more, or 90 vol% or more.

[0090] The pre-calcined mixture is then subjected to main calcination at a higher temperature to promote crystal growth and particle growth. During this calcination, it is necessary to ensure that crystal growth proceeds uniformly and reliably to obtain a composite oxide with the desired crystal structure.

[0091] [Titanium compound addition step] In the present disclosure, a titanium compound is added to the pre-calcined product obtained in the pre-calcination step. The titanium compound to be added, its amount, and the method of addition are the same as those described in the precursor preparation step. Furthermore, the titanium compound may be added only in the raw material mixing step, only in the titanium compound addition step, or in both the raw material mixing step and the titanium compound addition step. In other words, the titanium compound addition step is not an essential step.

[0092] [Firing process] As described above, when producing a composite oxide containing at least a transition metal, a lithiation reaction and crystal growth occur during firing, and the lithiation reaction requires a certain oxygen partial pressure. The lithiation reaction produces a composite oxide containing lithium. Thereafter, the temperature is raised to a predetermined temperature to promote crystal growth.

[0093] The firing temperature is not particularly limited as long as it is higher than the pre-firing temperature and can be adjusted depending on the composition of the composite oxide to be obtained. For example, it is preferable to adjust the maximum temperature to 700°C to 1100°C, 710°C to 1000°C, or 720°C to 980°C. By keeping the maximum temperature within the required range, a composite oxide with a desired crystalline structure and reduced unreacted components can be obtained, and a deterioration in the battery characteristics of a nonaqueous electrolyte secondary battery using the resulting composite oxide as a positive electrode can be prevented. Furthermore, when obtaining a composite oxide with a Ni content of 20 mol% to 80 mol% of the elements other than Li, for example, it is preferable to fire the mixture at a maximum temperature not exceeding 1100°C. The firing time is not particularly limited, and may be long enough to form a composite oxide with the desired crystalline structure. For example, it is preferable to fire the mixture for 1 hour to 15 hours, 2 hours to 12 hours, or 2 hours to 10 hours. The firing temperature in this disclosure refers to the maximum temperature to which the object to be heated is heated. The maximum temperature refers to the temperature of the hottest part of the object to be heated. The same definition applies hereinafter. The firing time refers to the time during which the pre-firing temperature is maintained within a predetermined range after reaching that range.

[0094] The atmosphere for the main firing is not particularly limited, as long as it ensures reliable and uniform crystal growth, has an oxygen partial pressure that does not reduce the transition metals contained in the mixture to be fired, and preferably has a low water content and carbon dioxide concentration. For example, it is preferable to use a decarbonated oxidizing gas atmosphere with a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of preferably 80 vol% or more, or 90 vol% or more.

[0095] [Water washing process] The composite oxide obtained in this firing step may contain impurities such as unreacted lithium compounds and lithium compounds that appear on the particle surface due to the crystalline structure during the firing step. Therefore, in order to remove or reduce these impurities, the composite oxide may be subjected to, for example, water washing and heat treatment. Note that the water washing step is not an essential step.

[0096] [Surface treatment process] By adding and mixing a predetermined element compound to the composite oxide obtained in the main firing step or the water washing step and subjecting it to heat treatment, the surfaces of the primary particles and / or secondary particles of the composite oxide can be surface treated with a compound of lithium and the added element, thereby achieving effects such as reducing the amount of lithium compounds remaining on the particle surface, improving lithium ion conductivity, and reducing reaction resistance. Note that step 4 is not an essential step.

[0097] The element compound added for the above-mentioned surface treatment can be selected from, for example, aluminum compounds, boron compounds, tungsten compounds, manganese compounds, cobalt compounds, phosphorus compounds, niobium compounds, strontium compounds, antimony compounds, zirconium compounds, titanium compounds, etc., and one or more of these compounds can be used.

[0098] [Composite oxide mixing process] When the composite oxide obtained in any of the steps from the calcination step to the surface treatment step does not exhibit multiple peaks that satisfy the requirements for the first and second peaks by itself, or when it is desired to further enhance the effect of suppressing thermal runaway even if the composite oxide exhibits multiple peaks that satisfy the requirements for the first and second peaks, the conditions for producing the composite oxide (conditions from the precursor preparation step to the calcination step) are changed to mix multiple types of composite oxides with different primary particle sizes and average particle sizes. Note that when the composite oxide obtained in any of the steps from the precursor preparation step to the calcination step by itself satisfies the requirements of the present disclosure for peaks in the differential thermogravimetry curve, this composite oxide mixing step is not an essential configuration.

[0099] <Nonaqueous electrolyte secondary battery> The nonaqueous electrolyte secondary battery according to the embodiment of the present disclosure includes a positive electrode containing the above-described positive electrode active material, and is composed of a positive electrode, a negative electrode, and an electrolytic solution containing an electrolyte.

[0100] When manufacturing a positive electrode, a conductive agent and a binder are added to the composite oxide according to the embodiment of the present disclosure and mixed according to a conventional method. As the conductive agent, for example, acetylene black, carbon black, graphite, etc. are preferably used. As the binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, etc. are preferably used.

[0101] The negative electrode is not particularly limited, and examples thereof include negative electrode active materials such as lithium metal, graphite, and low-crystalline carbon materials, as well as one or more nonmetallic or metallic elements selected from Si, Al, Sn, Pb, Zn, Bi, and Cd, alloys containing them, or chalcogen compounds containing them.

[0102] The solvent for the electrolytic solution is not particularly limited, but may be, for example, an organic solvent containing one or more selected from carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, and ethers such as dimethoxyethane.

[0103] As the electrolyte, in addition to lithium hexafluorophosphate (LiPF6), one or more selected from lithium salts such as lithium perchlorate and lithium tetrafluoroborate can be dissolved in a solvent and used. [Example]

[0104] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0105] <Preparation of complex oxide samples> The composite oxide samples of Examples 1 to 17 and Comparative Example 1 were prepared by the methods described below.

[0106] [Preparation of precursor composite hydroxide] (Preparation of precursor composite hydroxide 1) A mixed aqueous solution was obtained by mixing an aqueous nickel sulfate solution, a cobalt sulfate solution, and an aqueous manganese sulfate solution so that the molar ratio of Ni to Co to Mn was Ni:Co:Mn = 83:5:12. 10 L of pure water containing 300 g of sodium hydroxide solution and 500 g of ammonia water was prepared in advance in the reaction vessel as a mother liquid. The reaction vessel was filled with nitrogen gas at a flow rate of 0.7 L / min to create a nitrogen atmosphere, and the reaction was also carried out in a nitrogen atmosphere.

[0107] Thereafter, while rotating the stirring blade at 1000 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously added dropwise using a metering pump, and the amount of the alkaline solution added was adjusted so that the pH was 11.4, thereby carrying out a crystallization reaction. During the crystallization reaction, the reaction slurry was suitably sampled from the overflow pipe installed at the top of the reaction vessel, and after confirming that the particle size of the reaction slurry was stable at 13.5 μm, the slurry was recovered.

[0108] The slurry was then subjected to solid-liquid separation and washed with pure water to reduce residual impurities. The coprecipitate cake was then dried at 100°C for 10 hours in an air environment to obtain the product with the formula Ni 0.83 Co 0.05 Mn 0.12A nickel-cobalt-manganese composite hydroxide represented by (OH)2 was obtained. The D50 of the obtained composite hydroxide precursor was 13.4 μm.

[0109] (Preparation of precursor composite oxide 2) A mixed aqueous solution was obtained by mixing an aqueous nickel sulfate solution, a cobalt sulfate solution, and an aqueous manganese sulfate solution so that the molar ratio of Ni to Co to Mn was Ni:Co:Mn = 83:5:12. 10 L of pure water containing 310 g of sodium hydroxide solution and 500 g of ammonia water was prepared in advance in the reaction vessel as a mother liquid. The reaction vessel was filled with nitrogen gas at a flow rate of 0.7 L / min to create a nitrogen atmosphere, and the reaction was also carried out in a nitrogen atmosphere.

[0110] Then, while rotating the stirring blade at 1000 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously added dropwise using a metering pump, and the amount of the alkaline solution added was adjusted so that the pH was 11.4, and the crystallization reaction was continued. Then, the addition of the raw materials was stopped, and the reaction slurry was recovered.

[0111] After that, the slurry in the reactor was separated into solid and liquid, and then washed with pure water to reduce the remaining impurities. The coprecipitate cake was then dried at 100°C for 10 hours in an air environment to obtain the product with the formula Ni 0.83 Co 0.05 Mn 0.12 The nickel-cobalt-manganese composite hydroxide represented by (OH)2 was obtained by coprecipitation. The D50 of the obtained composite hydroxide precursor was 17.1 μm.

[0112] Example 1 Precursor composite hydroxide 1, lithium hydroxide, and titanium oxide were weighed and mixed so that Li / (Ni+Co+Mn) = 1.050 and Ti / (Ni+Co+Mn+Ti) = 2.0 mol%. The mixture was then heat-treated at 570°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%), and then calcined at 805°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting calcined product was pulverized to obtain a lithium-nickel composite oxide powder.

[0113] The obtained lithium nickel composite oxide powder was mixed with pure water adjusted to a liquid temperature of 25°C at a ratio of 1500 g / L to prepare a slurry, which 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 then at 120°C for 10 hours.

[0114] To the dried lithium nickel composite oxide, 1000 ppm of boric acid was added as a boron compound and mixed, followed by heat treatment at 325°C for 2 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a composite oxide sample of Example 1. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.051.

[0115] Example 2 A composite oxide sample of Example 2 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 1, lithium hydroxide, and titanium oxide were weighed out so that Li / (Ni+Co+Mn) = 1.070 and Ti / (Ni+Co+Mn+Ti) = 2.0 mol%. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.072.

[0116] Example 3 A composite oxide sample of Example 3 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 1, lithium hydroxide, and titanium oxide were weighed out so that Li / (Ni+Co+Mn) = 1.090 and Ti / (Ni+Co+Mn+Ti) = 2.0 mol%. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.090.

[0117] Example 4 A composite oxide sample of Example 4 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 1, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.050, Ti / (Ni+Co+Mn+Ti) = 2.0 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 8:2. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.058.

[0118] Example 5 A composite oxide sample of Example 5 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 1, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.070, Ti / (Ni+Co+Mn+Ti) = 2.0 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 8:2. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.078.

[0119] Example 6 A composite oxide sample of Example 6 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 2, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.030, Ti / (Ni+Co+Mn+Ti) = 1.2 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 8:2. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.024.

[0120] Example 7 A composite oxide sample of Example 7 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 2, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.050, Ti / (Ni+Co+Mn+Ti) = 1.2 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 8:2. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.049.

[0121] Example 8 A composite oxide sample of Example 8 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 2, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.030, Ti / (Ni+Co+Mn+Ti) = 1.7 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 85:15. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.030.

[0122] Example 9 A composite oxide sample of Example 9 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 2, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.050, Ti / (Ni+Co+Mn+Ti) = 1.7 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 85:15. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.052.

[0123] Example 10 A composite oxide sample of Example 9 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 2, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.030, Ti / (Ni+Co+Mn+Ti) = 2.5 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 90:10. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.047.

[0124] Example 11 A composite oxide sample of Example 9 was obtained in the same manner as in Example 1, except that precursor composite hydroxide 2, lithium hydroxide, titanium oxide, and titanyl sulfate were weighed out so that Li / (Ni+Co+Mn) = 1.050, Ti / (Ni+Co+Mn+Ti) = 2.5 mol%, and the Ti molar ratio of titanium oxide to titanyl sulfate was 90:10. The Li / (Ni+Co+Mn+Ti) of the obtained composite oxide sample was 1.056.

[0125] Example 12 The total of precursor composite hydroxide 2, lithium hydroxide, titanyl sulfate added as titanium raw materials, and titanium oxide was adjusted to Li / (Ni+Co+Mn) = 1.050 and Ti / (Ni+Co+Mn+Ti) = 1.8 mol%. At this time, the Ti molar ratio of the added titanyl sulfate to titanium oxide was 15:85.

[0126] First, precursor composite hydroxide 2, lithium hydroxide, and titanyl sulfate as a titanium raw material were weighed and mixed. Then, heat treatment was carried out at 570°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain pre-fired powder.

[0127] The resulting pre-calcined powder was then crushed, and the remaining titanium raw material, titanium oxide, which had been previously prepared, was added and mixed. The mixture was then further calcined at 815°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting calcined product was pulverized to obtain a lithium nickel composite oxide powder. A composite oxide sample was then obtained by the same procedure as in Example 1. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.054.

[0128] Example 13 The total of precursor composite hydroxide 2, lithium hydroxide, titanyl sulfate added as titanium raw materials, and titanium oxide was adjusted to Li / (Ni+Co+Mn) = 1.050 and Ti / (Ni+Co+Mn+Ti) = 1.8 mol%. At this time, the Ti molar ratio of the added titanyl sulfate to titanium oxide was 15:85.

[0129] First, precursor composite hydroxide 1 and lithium hydroxide were weighed and mixed, followed by heat treatment at 570°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a pre-fired powder.

[0130] The pre-calcined powder was then crushed, and titanyl sulfate and titanium oxide, which had been prepared as titanium raw materials, were added and mixed. The mixture was then further calcined at 815°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The calcined product was pulverized to obtain a lithium-nickel composite oxide powder. The same procedure as in Example 1 was then repeated to obtain a composite oxide sample of Example 1. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.057.

[0131] Example 14 The total of the precursor composite hydroxide 2, lithium hydroxide, and titanyl sulfate added as a titanium raw material was adjusted to Li / (Ni+Co+Mn) = 1.050 and Ti / (Ni+Co+Mn+Ti) = 1.8 mol%.

[0132] First, precursor composite hydroxide 1 and lithium hydroxide were weighed and mixed, followed by heat treatment at 570°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a pre-fired powder.

[0133] The pre-calcined powder was then crushed, and titanium oxide, which had been prepared as a titanium raw material, was added and mixed. The mixture was then further calcined at 815°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The calcined product was pulverized to obtain a lithium-nickel composite oxide powder. A composite oxide sample was then obtained by the same procedure as in Example 1. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.049.

[0134] Example 15 The total of precursor composite hydroxide 2, lithium hydroxide, titanyl sulfate added as titanium raw materials, and titanium oxide was adjusted to Li / (Ni+Co+Mn) = 1.050 and Ti / (Ni+Co+Mn+Ti) = 2.0 mol%, and the Ti molar ratio of the titanyl sulfate and titanium oxide added was 13:87.

[0135] First, precursor composite hydroxide 2, lithium hydroxide, and titanyl sulfate as a titanium raw material were weighed and mixed. Then, heat treatment was carried out at 570°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain pre-fired powder.

[0136] The resulting pre-calcined powder was then crushed, and the remaining titanium raw material, titanium oxide, which had been prepared previously, was added and mixed. The mixture was then further calcined at 815°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting calcined product was pulverized to obtain a lithium nickel composite oxide powder. A composite oxide sample was then obtained by the same procedure as in Example 1. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.050.

[0137] Example 16 The total of precursor composite hydroxide 2, lithium hydroxide, titanyl sulfate added as titanium raw materials, and titanium oxide was adjusted to Li / (Ni+Co+Mn) = 1.060 and Ti / (Ni+Co+Mn+Ti) = 2.0 mol%. At this time, the Ti molar ratio of the added titanyl sulfate to titanium oxide was 13:87.

[0138] First, precursor composite hydroxide 1 and lithium hydroxide were weighed and mixed, followed by heat treatment at 570°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a pre-fired powder.

[0139] The pre-calcined powder was then crushed, and titanyl sulfate and titanium oxide, which had been prepared as titanium raw materials, were added and mixed. The mixture was then further calcined at 815°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The calcined product was pulverized to obtain a lithium-nickel composite oxide powder. A composite oxide sample was then obtained by the same procedure as in Example 1. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.056.

[0140] Example 17 The total of the precursor composite hydroxide 2, lithium hydroxide, and titanyl sulfate added as a titanium raw material was adjusted to Li / (Ni+Co+Mn)=1.050 and Ti / (Ni+Co+Mn+Ti)=2.1 mol%.

[0141] First, precursor composite hydroxide 1 and lithium hydroxide were weighed and mixed, followed by heat treatment at 570°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a pre-fired powder.

[0142] The pre-calcined powder was then crushed, and titanium oxide, which had been prepared as a titanium raw material, was added and mixed. The mixture was then further calcined at 815°C for 6 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The calcined product was pulverized to obtain a lithium-nickel composite oxide powder. A composite oxide sample was then obtained by the same procedure as in Example 1. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.049.

[0143] Comparative Example 1 The precursor composite hydroxide 1, lithium hydroxide, and aluminum hydroxide added as an aluminum raw material were weighed and mixed so that the total was Li / (Ni + Co + Mn + Al) = 1.030 and Al / (Ni + Co + Mn + Al) = 1.0 mol%. The mixture was then fired at 820°C for 12 hours in an oxygen atmosphere (oxygen concentration: 97 vol%). The fired product was pulverized to obtain a lithium-nickel composite oxide powder.

[0144] The obtained lithium nickel composite oxide powder was mixed with pure water adjusted to a liquid temperature of 25°C at a ratio of 1500 g / L to prepare a slurry, which 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 then at 120°C for 10 hours.

[0145] 1000 ppm of boric acid as a boron compound was added to and mixed with the dried lithium nickel composite oxide, and the mixture was heat-treated at 325°C for 2 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a composite oxide sample of Comparative Example 1. The Li / (Ni+Co+Mn+Al) of the obtained composite oxide sample was 0.992.

[0146] <Evaluation> The obtained samples were evaluated by the following methods.

[0147] [Composition analysis of precursor compounds and composite oxides] The compositions of the precursor composite compound and the positive electrode active material particles were determined as follows: 0.2 g of a positive electrode active material sample was heated and dissolved in 25 ml of 20% hydrochloric acid solution, cooled, and then transferred to a 100 ml measuring flask. Pure water was added to prepare a solution. The elements in the resulting solution were quantified using ICP-AES (Optima 8300, manufactured by PerkinElmer Japan Co., Ltd.).

[0148] [Average particle size of precursor compound (D50)] The particle size distribution was measured on a volume basis by a wet laser method using a laser particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0149] [Thermogravimetric differential thermal analysis] To confirm the oxygen release behavior of the positive electrode active material sample, a thermogravimetric differential thermal analysis (TG-DTA) was performed using a thermogravimetric differential thermal analysis (TG-DTA) device (DTG-60H, manufactured by Shimadzu Corporation).

[0150] (Sample preparation) Following the method described below, a 2032-type coin cell with a lithium counter electrode was fabricated. It was charged at a constant current of 0.3 C to 4.30 V at 25°C, followed by a constant voltage charge until the current reached 0.05 C. After a 20-minute pause, the cell was discharged at a constant current of 0.3 C to 2.50 V, followed by a constant current discharge at 0.1 C and a 20-minute pause. This charge-discharge cycle was repeated twice. The cell was then charged at a constant current of 0.3 C to 4.30 V, followed by a constant voltage charge until the current reached 0.05 C. After a 20-minute pause, the cell was discharged at a constant current of 0.1 C and a 20-minute pause. This cycle was repeated twice.

[0151] The charged coin cell was disassembled in a glove box (dew point: -70°C or less) while taking care not to short-circuit, and the positive electrode was separated. The separated positive electrode was washed with DMC for 10 minutes and dried under vacuum in a side box. Then, in the same glove box, the positive electrode composite was scraped off from the Al foil using a spatula. 15 mg of the obtained positive electrode composite powder was filled into an Al TG measurement container, and the lid was sealed using a crimping machine.

[0152] The Al measurement vessel thus obtained was taken out of the glove box and placed on the measurement side balance of the TG-DTA apparatus.

[0153] (TG-DTA measurement) Reference: Pt container filled with 15-20 mg of Al2O3 Maximum temperature: 600℃ Heating rate: (1) 25°C (room temperature) to 50°C: 1°C / min (2) 50°C to 600°C: 5°C / min Measurement environment: N2 gas atmosphere (200 ml / min)

[0154] Just before the measurement, a small hole was opened in the lid of the sealed Al measurement vessel in the TG-DTA apparatus in a N2 gas atmosphere, and then the temperature was raised.

[0155] Based on the obtained results, a DTG curve is created with the horizontal axis representing temperature and the vertical axis representing the value obtained by differentiating the weight change (TG) with time (differential thermogravimetric DTG, which means the weight loss rate and corresponds to the oxygen release rate of the complex oxide in the range of 150 to 350°C).

[0156] Among the peaks in this DTG curve that have peak tops between 150 and 350°C, the peak with the maximum value of the differential thermogravimetry peak top was designated as the first peak. The value of the differential thermogravimetry at the peak top was designated as the oxygen release rate (% / min). Furthermore, among the peaks that have peak tops at temperatures 20°C or more away from the temperature at which the first peak tops, the peak with the maximum value of the differential thermogravimetry peak top was designated as the second peak. Figures 1 to 13 are DTG curves for the composite oxide samples of Examples 1 to 13, respectively. Figure 14 is a DTG curve for the composite oxide sample of Comparative Example 1.

[0157] [Crystal structure analysis by Rietveld analysis] Using an X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation), XRD diffraction data for the positive electrode active material was obtained under the following X-ray diffraction conditions. Rietveld analysis was then performed using the XRD diffraction data, with reference to R.A. Young, ed., "The Rietveld Method," Oxford University Press (1992). Specifically, the proportions of lithium in the 3a and 3b sites and the unit cell volume were calculated. (X-ray diffraction conditions) Source: Cu-Kα Acceleration voltage and current: 45 kV and 200 mA Sampling width: 0.02 deg. Scanning width: 15°~122° Scan speed: 1.0 step / sec Divergence slit: 2 / 3 deg. Receiving slit width: 0.15 mm Scattering slit: 2 / 3 deg.

[0158] [Evaluation of charge capacity of coin cells using positive electrode active material samples] In this specification, the 2032 type coin cell using the positive electrode active material particles was manufactured using a positive electrode, a negative electrode, and an electrolyte solution prepared by the following methods.

[0159] (positive electrode) Acetylene black and graphite were used as conductive agents in a weight ratio of 1:1, and polyvinylidene fluoride was used as a binder. The positive electrode active material, conductive agent, and binder were blended in a weight ratio of 90:6:4, and these were mixed with N-methylpyrrolidone. The mixture was applied to aluminum foil. This was dried at 110°C to produce a sheet, which was then punched into a 15 mm diameter sheet and then coated with a 3 t / cm 2 The resultant was rolled to form a positive electrode.

[0160] (Negative electrode) A lithium foil with a thickness of 500 μm and punched to 16 mm diameter was used as the negative electrode.

[0161] (electrolyte) A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was prepared so that the volume ratio of EC:DMC was 1:2, and the electrolyte was mixed with 1 mol / L of LiPF6 to prepare an electrolyte solution.

[0162] (separator) A separator (Celgard #2400, manufactured by Celgard) with a thickness of 0.5 mm and punched to 20 mm diameter was used.

[0163] (Total charge capacity measurement) Using the coin cell manufactured by the above method, a constant current charge of 0.3 C to 4.30 V was performed at 25°C, followed by a constant voltage charge until the current reached 0.05 C. After charging, a 20-minute pause was allowed, followed by a constant current discharge of 0.3 C to 2.50 V, followed by a constant current discharge of 0.1 C, followed by a 20-minute pause. This charge / discharge cycle was repeated twice. Next, a constant current charge of 0.3 C to 4.30 V was performed, followed by a constant voltage charge until the current reached 0.05 C. The total charge capacity (mAh / g) was calculated as follows: First charge / discharge: 4.3V at 0.3C (constant voltage charge until 0.05C) 20 minute break Discharge to 2.5V at 0.3C, then discharge to 2.5V at 0.1C 20 minute break Second charge / discharge: 4.3V at 0.3C (constant voltage charge until 0.05C) 20 minute break Discharge to 2.5V at 0.3C, then discharge to 2.5V at 0.1C 3rd charge: 4.3V at 0.3C (constant voltage charge until 0.05C) Total charging capacity = 1st charge capacity + (2nd charge capacity - 1st discharge capacity at 0.3C - 1st discharge capacity at 0.1C) + (3rd charge capacity - 2nd discharge capacity at 0.3C - 2nd discharge capacity at 0.1C)

[0164] Table 1 shows the composition of the composite oxides constituting the samples of Examples 1 to 17 and Comparative Example 1, the amount of Ti source added before and after pre-baking (molar ratio Ti / (Ni+Co+Mn+Ti)), the proportion of Li present at the 3a site and the 3b site and the unit cell volume determined by XRD diffraction, the peak-top temperature and differential thermogravimetry (oxygen release rate) of the first peak in the DTG curve, the reduction rate of the differential thermogravimetry compared to Comparative Example 1, the peak-top temperature and differential thermogravimetry (oxygen release rate) of the second peak, the difference (absolute value) between the peak-top temperature of the first peak and the peak-top temperature of the second peak, and the ratio of the thermogravimetry derivative at the first peak to the thermogravimetry derivative at the second peak (differential thermogravimetry at the peak top of the first peak / differential thermogravimetry at the peak top of the second peak), the total charge capacity, and the reduction rate of the peak oxygen release rate on the low-temperature side compared to Comparative Example 1.

[0165] [Table 1]

Claims

1. General formula Li １＋ｘ Ni １－ｙ－ｚ－ｗ－ｖ Co ｙ Mn ｚ Ti ｗ M ｖ O ２＋α (wherein M is one or more elements other than Li, Ni, Co, Mn, and O, and −0.1≦x≦0.15, 0≦y≦0.4, 0<z≦0.4, 0.001≦w≦0.03, 0≦v≦0.1, and −0.5≦α≦0.5), When a sample of the composite oxide was charged to 4.30 V using lithium as a counter electrode and heated from 50° C. to 600° C. at a rate of 5° C. / min, a differential thermogravimetric curve was obtained, and the resultant curve was separated into multiple peaks. a first peak having a maximum value of the derivative thermogravimetry at its peak top in a temperature range of 150°C or higher and 350°C or lower; and a second peak having a maximum value of the derivative thermogravimetry at its peak top, the second peak having a peak top at a temperature 20°C or higher away from the temperature at which the first peak has its peak top; the ratio of the differential thermogravimetry value at the peak top of the first peak to the differential thermogravimetry value at the peak top of the second peak is 1 or more and 9 or less; Positive electrode active material for non-aqueous electrolyte secondary batteries.

2. In the composite oxide, 0<x≦0.15 The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 .

3. The differential thermogravimetry value at the peak top of the first peak is 3% / min or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2.

4. A cathode containing the cathode active material according to claim 1 or 2 is provided. Nonaqueous electrolyte secondary battery.

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