Cathode active materials for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries

Abstract

This invention provides a positive electrode active material for a nonaqueous electrolyte secondary battery comprises a composite oxide represented by Li1+xNi1-y-z-w-vCoyMnzTiwMvO2+α (where M is 1 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), wherein, when the 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 prescribed 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 top of the first peak occurs, and the derivative thermogravimetric value at the top of the first peak is 1 to 9 times the derivative thermogravimetric value at the top of the second peak.

Description

CATHODE ACTIVE MATERIALS FOR NON-AQUEOUS ELECTROLYTE SECONDARY BATTERIES AND NON-AQUEOUS ELECTROLYTE SECONDARY BATTERIES[Technical Field]

[0001] The present disclosure relates to a positive electrode active material for a nonaqueous electrolyte secondary battery as well as to a nonaqueous electrolyte secondary battery.[Background Art]

[0002] Lithium ion secondary batteries are small and lightweight as well as having a high energy density, a high charge / discharge voltage, and a substantial charge / discharge capacity, and have thus garnered attention as power sources for operating AV devices or personal computers and other such electronic devices.

[0003] Flammable organic solvents are ordinarily used primarily as the electrolyte in lithium ion secondary batteries, and high thermal stability is therefore a requirement. It is known, for example, that by applying heat to lithium ion secondary batteries in a charged state, oxygen is released from the positive electrode active material crystals, but that this oxygen reacts with the electrolyte, resulting in thermal runaway.

[0004] In particular, active materials containing Ni, Co, and Mn have been widely used recently as positive electrode active materials. As the Ni content in this sort of positive electrode active material increases, the phase transition reaction of the positive electrode active material occurs in lower temperature regions, and oxygen is released more rapidly, resulting in a greater likelihood of thermal runaway. On the other hand, there is growing demand for materials having a greater battery capacity and a high Ni content, which has led to a trend toward a loss of the inherent thermal stability of materials that have a high Ni content.

[0005] To control such thermal runaway in positive electrode active materials, Patent Document 1, for example, has proposed a positive electrode active material comprising a lithium-transition metal composite oxide that contains 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, wherein B and at least one element (M1) selected from Groups 4 to 6 are present on at least the surface of particles of the lithium- transition metal composite oxide, and the molar fraction of M1 relative to the total number of moles of metallic elements, excluding Li, on the surface of particles having a volume-based particle size smaller than 30% is greater than the molar fraction of M1 relative to the total number of moles of metallic elements, excluding Li, on the surface of particles having a particle size greater than 70%. Patent Document 1 states that the use of this kind of composite oxide inlithium ion secondary batteries allows the self-heating rate to be controlled even at elevated temperatures.[Prior Art Documents][Patent Documents]

[0006] [Patent Document 1] JP 2021-51979 A[Summary of the Invention][Problems to be Solved by the Invention]

[0007] In the positive electrode active material of Patent Document 1 , the surface of the positive electrode active material particles is coated with a boron compound, which can thus be anticipated to control, to some extent, thermal runaway resulting from the reaction between the electrolyte and the oxygen released from the positive electrode active material, but this alone is not enough to control thermal runaway, and there is still room for improvement.

[0008] There is thus still a need for a method, other than the method of coating the surface of the positive electrode active material with a compound as noted above, that would control thermal runaway.

[0009] In light of the circumstances noted above, the present disclosure is intended to provide a positive electrode active material capable of controlling thermal runaway in nonaqueous electrolyte secondary batteries, as well as a nonaqueous electrolyte secondary battery in which the positive electrode active material is employed.[Means for Solving the Problems]

[0010] The inventors engaged in extensive research to solve the problems noted above. As a result, it was discovered that the maximum rate of oxygen release from a positive electrode active material (referred to below as "maximum oxygen release rate") can be curbed and that thermal runaway can also be curbed when using a positive electrode active material for a nonaqueous electrolyte secondary battery, comprising a composite oxide represented by general formula Lii+xNii.y.z-w.vCoy nzTiw vO2+a (where M is 1 or more elements other than Li, Ni, Co, Mn, 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<a<0.5), wherein when a derivative thermogravimetric curve is obtained after a sample of the composite oxide, that has been charged to 4.30 V using lithium as the counter electrode, is heated from 50°C to 600°C at a rate of 5°C / min, and the resulting curve is separated into a plurality of peaks, within the temperature range of 150°C to 350°C, the top of the first peak shows the greatest derivative thermogravimetric value and the top of the second peak 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 top of the first peak occurs, and the ratio of the derivative thermogravimetric value at the top of the first peak to the derivative thermogravimetricvalue at the top of the second peak is 1 to 9. Specifically, the present disclosure provides the following.

[0011] (1) A positive electrode active material for a nonaqueous electrolyte secondary battery, comprising a composite oxide represented by general formula Lii+xNii-y-z-w-vCoyMnzTiwMvO2+a (where M is 1 or more elements other than Li, Ni, Co, Mn, 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<a<0.5), wherein when a derivative thermogravimetric curve is obtained after a sample of the composite oxide, that has been charged to 4.30 V using lithium as the counter electrode, is heated from 50°C to 600°C at a rate of 5°C / min, and the resulting curve is separated into a plurality of peaks, within the temperature range of 150°C to 350°C, the top of the first peak shows the greatest derivative thermogravimetric value and the top of the second peak 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 top of the first peak occurs, and the ratio of the derivative thermogravimetric value at the top of the first peak to the derivative thermogravimetric value at the top of the second peak is 1 to 9.

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

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

[0014] (4) A nonaqueous electrolyte secondary battery comprising a positive electrode that contains a positive electrode active material according to (1) or (2).[Effects of the Invention]

[0015] According to the present disclosure, it is possible to provide: a positive electrode active material that allows thermal runaway to be curbed when used in a nonaqueous electrolyte secondary battery; and a nonaqueous electrolyte secondary battery using the positive electrode active material.[Embodiments of the Invention]

[0016] Embodiments of the present disclosure are described below, but the present disclosure is not limited in any way by the description of the embodiments and can be carried out with additional modifications, as appropriate.

[0017] <Positive Electrode Active Material for Nonaqueous Electrolyte Secondary Battery>The positive electrode active material for a nonaqueous electrolyte secondary battery in embodiments of the present disclosure comprises a composite oxide represented by general formula Lii+xNii-y-z-w-vC0yMnzTiwMv02+a (where M is 1 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<a<0.5), and has a first peak and a second peak within a temperature range of 150°C to 350°C when a derivative thermogravimetric curve is obtained after a sample of the composite oxide, that has been charged to 4.30 V using lithium as the counter electrode, is heated from 50°C to 600°C at a rate of 5°C / min, and the resulting curve is separated into a plurality of peaks, wherein the top of the first peak shows the greatest derivative thermogravimetric value and the top of the second peak 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 top of the first peak occurs, and the derivative thermogravimetric value at the top of the first peak is 1 to 9 times the derivative thermogravimetric value at the top of the second peak.

[0018] When oxygen is released from a positive electrode active material over a plurality of mutually separate temperature zones, less oxygen is released per temperature zone than when oxygen is released from the positive active material in only one narrow temperature zone, resulting in less reaction with the electrolyte and less generation of heat. Thermal runaway of the positive electrode active material can therefore be curbed by ensuring that oxygen is released from the positive electrode active material over a plurality of mutually separate temperature zones.

[0019] Upon TG analysis of composite oxides, the inventors confirmed via TG-MS that nearly all weight loss at temperatures up to around 350°C was caused by the release of oxygen. As a result, even though oxygen is released from the positive electrode active material at temperatures ranging from 150°C to 350°C, the positive electrode active material does not undergo any other reactions within that temperature range. Accordingly, oxygen is released from a positive electrode active material over a plurality of mutual temperature zones when a derivative thermogravimetric curve (referred to below as "DTG curve") of a positive electrode active material is separated into a plurality of peaks, and has a first peak, which is the greatest, and second peaks, that are separated from each other by a temperature of at least 20°C, within a temperature range of 150°C to 350°C, where the size of the first peak is no more than 9 times the size of the second peaks.

[0020] On the other hand, when a DTG curve cannot be separated into a plurality of peaks (consists of a single peak), or can be separated into a plurality of peaks but the first peak is much larger than the second peaks, oxygen is released from the positive electrode active material in a single narrow temperature zone, resulting in a greater likelihood of thermal runaway.

[0021] The requirements for ensuring that a positive electrode active material will show this sort of DTG curve involve many factors, such as the composition, crystal structure, crystallinity, and conditions of synthesis of the positive electrode active material, and can also vary depending onthe balance of these factors. Examples of materials that tend to exhibit such a DTG curve include composite oxides represented by general formula Lii+xNii.y.z-w-vC0yMnzTiw02+a (where M is 1 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<a<0.5), but even if a material has such a composition, the two prescribed peaks of the DTG curve may not necessarily satisfy the above-mentioned requirements. In other words, the two prescribed peaks of the DTG curve do not depend only on the composition of the compound.

[0022] Lii-x-6NiO2 is used as an example in the following discussion of the mechanism involved in the release of oxygen from a composite oxide while in a charged state, during which a large amount of lithium is desorbed from the crystal structure, and the crystal structure is generally unstable. Note that oxygen release also occurs by a similar mechanism in the composite oxide of the present disclosure. When such a composite oxide is used as the positive electrode active material and is heated in a charged state, the crystalline state undergoes phase transition from a layered rock-salt structure (R-3m) to a spinel structure (Fd-3m) or a rock-salt structure (Fm3m) within a prescribed temperature range, as shown by the following formulas (1) and (2). The temperature of the phase transition is within a temperature range of about 190 to 310°C but will depend on the depth of charge. As shown by formulas (1) and (2), the transition is also thought to progress as oxygen gas is generated.

[0023] Formula (1):Lii-x-6NiO2 (layered rock-salt structure R-3m)— (1-x-b) / (1-b)}Lii.5NiO2 (layered rock-salt structure 1 R-3m)+{x / 3(1-b)}Ni3O4 (spinel structure Fd-3m)+{x / 3(1-b)}O2T

[0024] Formula (2):• {(1 -x-6) / (1 -5)}Li I-5N iC>2 (layered rock-salt structure 1 R-3m)— >(1-x-b)LiNiO2 (layered rock-salt structure 2 R-3m)+{5(1-x-b) / (1-b)}NiO (rock-salt structure 1 Fm3m)+{6(1 -X-6) / 2(1-6)}O2T• {x / 3(1-5)}Ni3O4 (spinel structure Fd-3m)-^{x / 3(1-6)}NiO (rock-salt structure 2 Fm3m)+{X / 6(1-6)}O2T

[0025] The symbol in R-3m originally appears above the 3, but is written here as shown above for the sake of convenience. Similarly, the symbol in Fd-3m also originally appears above the 3, but is written here as shown above for the sake of convenience.

[0026] The inventors believed that this rapid generation of oxygen gas significantly affects the thermal stability of charged nonaqueous electrolyte secondary batteries.

[0027] When a charged nonaqueous electrolyte secondary battery overheats and the battery temperature rises, it is primarily the organic electrolyte in the nonaqueous electrolyte secondary battery that is oxidized (including combustion) by the oxygen gas generated via the reactions shown in formulas (1) and (2). As the reactions are exothermic, the temperature of the nonaqueous electrolyte secondary battery rises. As the rise in temperature results in further oxidation of the electrolyte, generating heat, the rise in temperature becomes uncontrollable, leading to thermal runaway.

[0028] The rise in temperature is proportional to the difference between the amount of heat that is generated per unit time in the nonaqueous electrolyte secondary battery and the amount of heat that is dissipated per unit time from the nonaqueous electrolyte secondary battery. Preventing the rapid concentration of the amount of heat and thermal flow that are brought about as shown in formulas (1) and (2) could curb the rise in temperature and prevent uncontrollable thermal runaway, resulting in better safety.

[0029] In view of the above, the inventors concluded that controlling the rate of oxygen release from the positive electrode active material is most important in order to curb uncontrollable thermal runaway. It can therefore be said, as noted in the present disclosure, that adjusting the release of oxygen from the composite oxide so that the oxygen is released over a plurality of temperature zones is an effective way to avoid rapid oxygen release in a narrow temperature zone.

[0030] [Chemical Structure]The composite oxide is not particularly limited, as long as the composite oxide is represented by Lii+xNii.y-z-w-vCoyl\ / lnzTiwMvO2+c. (where M is 1 or more elements other than Li, Ni, Co, Mn, O; and -0.1<x<0.15, 0<y<0.4, 0<z<0.4, and 0.001<w<0.03, 0<v<0.1 , -0.5<a<0.5).

[0031] The reason why the composite oxide serving as the positive electrode active material in the present disclosure exhibits multiple peaks on the derivative thermogravimetric curve is not necessarily known and is not bound to any particular theory, but the following has been considered by the inventors. In such a composite oxide, when Ti is further included in the composite oxide, two Ni2 +and one vacancy is formed per one Ti4+. Among these, Ti4+and Ni2+are arranged at 3b sites (metal sites), and Ni2+and vacancies are arranged at 3a sites (Li sites). At the 3a site, Ni undergoes cation mixing, and vacancies are also generated, thereby ejecting the two Li from the site. In this manner, the Li supplied to the 3b site reacts with Mn to form Li2nC>3.

[0032] This Li2MnO3 further aggregates to form a Li2MnO3 domain. In this domain, the Li of the 3a site is filled even in a charged state of 4.3 V, and thus the Li is considered to function as a pillar to strengthen the structure. Thermal decomposition is unlikely in the vicinity of this domain, even in a charged state, and thus it is possible to shift a portion of the decomposition peak to a high temperature side. In the present disclosure, as described above, from the one Ti, two Li can be ejected from the 3a site to the 3b site, and thus the amount of Ti can efficiently form a large amount of Li2MnO3. As a result, it is considered to be possible to increase the shifted high temperature-side peak, thereby making it possible to decrease the normal low temperature-side peak.

[0033] In the general formula, the value of x is not particularly limited, provided that it is within the range of -0.10<x<0.15, but is, for example, preferably -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, 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, or 0.15 or more. On the other hand, the value of x is preferably 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, 0.025 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, 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, -0.008 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. Ensuring that the value of x is within the prescribed range means that the Li content will be within the prescribed range.Ensuring that the value of x is at least the prescribed minimum value can increase the Li content, reduce Li vacancies, curb first-order reduction of Ni occurring between about 200 and 250°C, and increase second-order reduction occurring between about 260°C and 320°C. As a result, the peak top on the low temperature side of the derivative thermogravimetric curve will tend to decrease, whereas the peak top on the high temperature side will tend to increase. Ensuring that the value of x is no greater than the prescribed maximum value can keep Li vacancies at a constant level and can curb loss of charging capacity.

[0034] In the general formula, the value of 1-y-z-w-v is not particularly limited, provided that it is a combination within the applicable range for y, z, w, and v, but is, for example, preferably 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, 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-y-z-w-v 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. Ensuring that the value of 1-y-z-w-v is within the prescribed range means that the Ni content will be within the prescribed range. Ensuring that the value of 1-y-z-w-v is at least the prescribed minimum value can ensure greater Ni migration in the composite oxide. On the other hand, ensuring that the value of 1-y-z-w-v is no greater than the prescribed maximum value will make it possible to leave room to include functional elements that can inhibit some Ni migration, although it will depend on the balance with other elements, etc.

[0035] In the general formula, the value of y is not particularly limited, provided that it is within the range of 0<y<0.4, but is, for example, preferably more 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, 0.202or 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, 0.36 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, 0.395 or more, or 0.397 or more. Meanwhile, the value of y is preferably 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, 0.312 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, 0.025 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. Ensuring that the value of y is within the prescribed range means that the Co content will be within the prescribed range. Ensuring that the value of y is at least the prescribed minimum value can increase the Co, which can increase the level of second-order reduction of Ni4+. On the other hand, even if the value of y is at least the prescribed minimum value, the value should be no greater than the prescribed maximum value in order to cap the increase in second-order reduction.

[0036] In the general formula, the value of z is not particularly limited, provided that it is within the range of 0<z<0.4, but it is, for example, preferably 0.001 or more, 0.0015 or more, 0.002 ormore, 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, 0.36 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, 0.395 or more, or 0.397 or more. Meanwhile, the value of z is preferably 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, 0.312 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, 0.025 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. Ensuring that the value of z is within the prescribed range means that the Mn content will be within the prescribed range. Ensuring that the value of z is at least the prescribed minimum value can facilitate the formation of Li2MnO3, and promote the migration of Ni and Co into the Li layer. Ensuring that the value of z is no greater than the prescribed maximum value will allow more Li2MnC>3 to be formed, thereby curbing loss of charging capacity caused by an excessive increase in Li vacancies.

[0037] In the general formula, the value of w is not particularly limited, provided that it is within the range of 0.001 <w<0.03, but it is, for example, preferably 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, 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, 0.02 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, or0.029 or more. Meanwhile, the value of w is preferably 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, 0.0077 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, or 0.0012 or less. Ensuring that the value of w is within the prescribed range allows Ni2+to undergo appropriate cation mixing and stabilization of the crystal structure of the 3a site, while arranging the Li ejected from the 3a site in the vacancy in the 3b site generated by Ni2+cation mixing, and to efficiently form a large amount of Li2MnC>3 domains. Ensuring that the w value is no greater than the prescribed range makes it possible to curb a reduction in battery characteristics caused by excessive Ni2+cation mixing.

[0038] In the general formula, the value of v is not particularly limited, provided that it is within the range of 0<w<0.1 , but is, for example, preferably 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, 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, 0.012 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, 0.05 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, 0.08 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 value of v is preferably 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 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, or 0.001 or less. Ensuring that the value of v is within the prescribed range means that the content of the element M will be within the prescribed range. Ensuring that the value of v is at least the prescribed minimum value will ensure that the addition of the element M produces the intended effect. Ensuring that the value of v is no greater than the maximum value will ensure the prescribed content of Ni, Co, and Mn, thus preserving the battery performance, including a high charging capacity, that is afforded by those elements.

[0039] In the formula, the element M is not particularly limited, provided that it is one or more elements other than Li, Ni, Co, Mn and O, where 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, etc. The type of element M should be selected depending on the purpose for which it is being added. When a plurality of elements are used as the element M, the value of v represents the total amount of the plurality of elements.

[0040] In the general formula, the value of a is not particularly limited, provided that it is within the range of -0.5<a<0.5, but is, for example, preferably -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, 0.0075 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 ormore, 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, 0.36 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, 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, 0.447 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, 0.48 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 value of a is preferably 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 or less, 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, 0.312 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 orless, 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, 0.025 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 configuration of the composite oxide is not particularly limited, and may be, for example, in the form of particles. When a composite oxide in the form of particles is used, the particles may be in the form of secondary particles formed by the aggregation of primary particles, or may be in the form of primary particles as such, or may be in the form of a mixture of secondary particles and primary particles. If the primary particles have the same particle size distribution, the temperature at which oxygen is released from the composite oxide will not change substantially, no matter what the state may be.

[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. Ensuring that the average particle size of the composite oxide is at least the minimum prescribed value will make it possible to increase the temperature at which oxygen is released. On the other hand, the average particle size of the primary particles is preferably 15 pm or less, 14.5 pm or less, 14 pm or less, 13.5 pm or less, 13 pm or less, 12.5 pm or less, 12 pm or less, 11.5 pm or less, 11 pm or less, 10.5 pm or less, 10 pm or less, 9.5 pm or less, 9 pm or less, 8.5 pm or less, 8 pm or less, 7.5 pm or less, 7 pm or less, 6.5 pm or less, 6 pm or less, 5.5 pm or less, 5 pm or less, or 4.5 pm or less. Ensuring that the average particle size of the primary particles is no greater than the prescribed maximum value will make it possible to increase the energy density and to control cycle-associated particle destruction or loss of rate characteristics. The average particle size of the primary particles of the composite oxide is calculated via observation of electron micrographs taken using a field emission scanning electron microscope (JSM-7100F: manufactured by JEOL Ltd.) at an acceleration voltage of 10 kV and at 3000 to 20000 x magnification. Specifically, a field of view in which 100 or more primary particles (confirmed particle outline) are visible is randomly selected, and electron micrographs of all particles (confirmed particle outline) among the particles in the field of view are obtained, with the magnification changed as needed within the range noted above. The electron micrographs are then used to calculate the equivalent spherical diameter via image processing software (such as Imaged) to determine the particle size of the primary particles.

[0043] The average particle size (D50) of the primary particles of the composite oxide is also not particularly limited, but is preferably, for example, 80 nm or more, 100 nm or more, 120 nm ormore, 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. Ensuring that the D50 is at least the prescribed minimum value will make it possible to increase the temperature at which oxygen is released and to also increase the electrode density. Meanwhile, the D50 is preferably 25 pm or less, 24.5 pm or less, 24 pm or less, 23.5 pm or less, 23 pm or less, 22.5 pm or less, 22 pm or less, 21.5 pm or less, 21 pm or less, 20.5 pm or less, 20 pm or less, 19.5 pm or less, 19 pm or less, 18.5 pm or less, 18 pm or less, 17.5 pm or less, 17 pm or less, 16.5 pm or less, 16 pm or less, 15.5 pm or less, 15 pm or less, 14.5 pm or less, 14 pm or less, 13.5 pm or less, 13 pm or less, 12.5 pm or less, 12 pm or less, 11.5 pm or less, 11 pm or less, 10.5 pm or less, 10 pm or less, 9.5 pm or less, 9 pm or less, 8.5 pm or less, 8 pm or less, 7.5 pm or less, 7 pm or less, 6.5 pm or less, 6 pm or less, 5.5 pm or less, 5 pm or less, or 4.5 pm or less. Ensuring that the D50 is no greater than the prescribed maximum value will make it possible to increase the energy density of nonaqueous electrolyte secondary batteries in which the composite oxide is used, and also to control cycle-associated particle destruction or loss of rate characteristics. The D50 is determined on a volume basis by a wet laser method using a laser type particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0044] [DTG Curve]The DTG curve of the composite oxide in the present disclosure is obtained when a sample of the composite oxide, that has been charged by the charging method shown below, is heated from 50°C to 600°C at a rate of 5°C / min.

[0045] The derivative thermogravimetric curve obtained in this manner is fitted using a log-normal distribution function to separate the peaks and to thereby calculate the peak top temperature and thermogravimetric derivative (oxygen release rate) of each peak.

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

[0047] (Sample Preparation)A 2032 type coin cell having a lithium counter electrode is produced in accordance with the method described below, and is charged at a constant current of 0.3 C to 4.30 V at a temperature of 25°C and then charged at a constant voltage to a current value of 0.05 C. After a 20-minute break following the completion of charging, the coin cell is discharged at a constant current of 0.3 C to 2.50 V, and is then discharged at a constant current of 0.1 C, followed by a 20-minute break. The charging and discharging are repeated twice. The coin cell is then charged at a constant current of 0.3 C to 4.30 V, and then charged at a constant voltage to a current value of 0.05 C, followed by a 20-minute break after the completion of charging.

[0048] The charged coin cell is disassembled in a glove box (dew point: -70°C or lower) to prevent short circuits, and the positive electrode is retrieved. The retrieved positive electrode is washed for 10 minutes in dimethyl carbonate (DMC) and is dried in vacuo in a side box. The positive electrode active mix is then scraped off the Al foil using a spatula in the same glove box. A thermogravimetric container made of aluminum is then filled with 15 mg of powder of the positive electrode active mix that has been obtained, and is capped and sealed using a crimper.

[0049] The aluminum analysis container obtained in this manner is taken out of the glove box and placed on a balance on the measuring side of a TG-DTA analyzer.

[0050] (TG-DTA Analysis)Reference: Platinum vessel filled with 15 to 20 mg of AI2O3Maximum temperature: 600°CHeating rate:(1) 25°C (room temperature) to 50°C: 1°C / min(2) 50°C to 600°C: 5°C / minAnalytical environment: N2 gas atmosphere (200 mL / min)

[0051] Just before the start of the analysis, a small hole is made in the lid of the sealed aluminum analysis container, which has been placed in the TG-DTA analyzer in an N2gas atmosphere, and heating is initiated. The use of this method will allow the analyzed positive electrode active mix powder to be analyzed without being exposed to the atmosphere.

[0052] DTG curves were prepared on the basis of the results that were obtained, where the horizontal axis shows the temperature, and the vertical axis shows the change in weight (TG) over time (derivative thermogravimetry (DTG), meaning the rate of weight loss, which corresponds to the rate of oxygen release from the composite oxide within the range of 150 to 350°C).

[0053] The first peak is defined as the peak showing the greatest derivative thermogravimetric value at the top of the peak among all peaks having a peak top between 150 and 350°C. The derivative thermogravimetric value at the top of the peak is defined as the oxygen release rate (% / min). The second peak is defined as the peak showing the greatest derivative thermogravimetric value at the top of the peak among peaks whose peak tops occur at a temperature at least 20°C different from the temperature at which the top of the first peak occurs.

[0054] The derivative thermogravimetric value at the top of the first peak versus the derivative thermogravimetric value at the top of the second peak is then calculated.

[0055] [First Peak]The first peak is the peak showing the greatest derivative thermogravimetric value at the top of the peak within the temperature range of 150°C to 350°C when the DTG curve obtained in the manner noted above is separated into a plurality of peaks.

[0056] The derivative thermogravimetric value at the 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 showing the greatest derivative thermogravimetric value at the top of the peak among peaks whose peak tops occur at a temperature at least 20°C different from the temperature at which the top of the first peak occurs.

[0058] The temperature at which the top of the second peak occurs should be at least 20°C different from the temperature at which the top of the first peak occurs, with no limitations on the height thereof. Specifically, the temperature at which the top of the second peak occurs may be at least 20°C higher, or at least 20°C lower, than the temperature at which the top of the first peak occurs.

[0059] The temperature at which the top of the second peak occurs is preferably, for example, at least 21 °C, at least 22°C, at least 23°C, at least 24°C, at least 25°C, at least 26°C, at least 27°C, at least 28°C, at least 29°C, at least 30°C, at least 31 °C, at least 32°C, at least 33°C, at least 34°C, at least 35°C, at least 36°C, at least 37°C, at least 38°C, at least 39°C, or at least 40°C different from the temperature at which the top of the first peak occurs. The temperature at which the top of the second peak occurs is preferably, for example, no more than 160°C, no more than 155°C, no more than 150°C, no more than 145°C, no more than 140°C, no more than 135°C, no more than 130°C, no more than 125°C, no more than 120°C, no more than 115°C, no more than 110°C, no more than 105°C, no more than 100°C, no more than 95°C, no more than 90°C, no more than 85°C, no more than 80°C, no more than 75°C, or no more than 60°C different from the temperature at which the top of the first peak occurs.

[0060] [Derivative Thermogravimetric Value Ratio]In the positive electrode active material of the present disclosure, the ratio of the derivative thermogravimetric value of the first peak to the derivative thermogravimetric value of the second peak (derivative thermogravimetric of the first peak / derivative thermogravimetric of the second peak) is not particularly limited, provided that it is 1 to 9, and is preferably, 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, 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, or 1.6 or less. On the other hand, the ratio of the derivative thermogravimetric value of the first peak to the derivative thermogravimetric 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 for Producing Positive Electrode Active Material for Nonaqueous Electrolyte Secondary Battery>The positive electrode active material for a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure can be produced, for example, by carrying out the following steps, in that order. A method for producing the composite oxide containing 30 mol% or more of Ni among elements other than Li is also given as an example below; other methods for producing composite oxides conform to common practice.

[0062] Precursor preparing step: a precursor composite compound containing at least a transition metal is adjusted.Raw material mixing step: the precursor composite compound prepared in the precursor preparing step and a lithium compound are mixed to prepare a mixture.Pre-firing step: the precursor prepared in the mixing step is pre-fired as necessary. Titanium compound adding step: a titanium compound is added to the pre-fired product obtained in the pre-firing step.Primary firing step: the fired product prepared in the mixing step, the pre-firing step, or the titanium compound adding step is subjected to main firing.Washing step: the composite oxide obtained by firing in the main firing step is subjected to a washing treatment as necessary.Surface treatment step: the composite oxide obtained in the primary firing step or the washing step is subjected to a surface treatment as necessary.Composite oxide mixing step: the conditions in any one of the precursor preparing step, mixing step, pre-firing step, and primary firing step are changed as necessary to thereby mix a plurality of types of composite oxides in which the primary particle size or average particle size, for example, has been modified.

[0063] [Precursor Preparing Step]A precursor composite compound, in the form of an aggregate comprising clusters of primary particles that contain at least a transition metal, is first synthesized. The method for synthesizing the precursor composite compound is not particularly limited, and the following method can be used, for example: an aqueous solution comprising an aqueous solution of a transition metal aswell as a variety of aqueous solutions of compounds including other elements, depending on the composition of the intended composite oxide, is added drop-wise into a reaction tank in which an aqueous alkali solution, such as a sodium hydroxide solution or ammonia solution, is stirred as the mother liquor, for example; the pH is monitored and controlled to within a suitable range as sodium hydroxide, for example, is added drop-wise; and co-precipitation is brought about by means of a wet reaction to obtain a product in the form of, for example, a hydroxide, an oxide obtained by firing the hydroxide, or a carbonate.

[0064] In synthesis-related reactions, after the alkaline aqueous solution serving as the mother liquor has been prepared, the interior of the reactor is purged with an inert gas or preferably nitrogen gas, for industrial purposes, to create a nitrogen atmosphere in order to keep the oxygen concentration within the reaction tank system or in the solution as low as possible. If the oxygen concentration is excessively high, there is a risk that the co-precipitated hydroxide will be overoxidized by any oxygen remaining over the prescribed amount, and a risk that the formation of agglomerates due to crystallization will be compromised.

[0065] The transition metal aqueous solution is not particularly limited, although the use of an acidic aqueous solution, for example, is preferred, and the use of a sulfuric acid aqueous solution such as a nickel sulfate aqueous solution is even more preferred in the case of nickel compounds. One or more transition metal aqueous solutions can also be used.

[0066] Examples of nickel compounds that can be used include, but are not particularly limited to, one or more selected from nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel.

[0067] Examples of cobalt compounds that can be used include, but are not particularly limited to, one or more selected from cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt.

[0068] Examples of manganese compounds that can be used include, but are not particularly limited to, one or more selected from manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and metallic manganese.

[0069] Examples of titanium compounds that can be used include, but are not particularly limited to, one or more selected from titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium. Note that the titanium compound does not necessarily need to be added in the precursor preparing step. Details will be described in the titanium compound adding step, which is described later.

[0070] Examples of aluminum compounds that can be used include, but are not particularly limited to, aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum.

[0071] Examples of iron compounds that can be used include, but are not particularly limited to, one or more selected from iron sulfate, iron oxide, iron hydroxide, iron nitrate, iron carbonate, iron chloride, iron iodide, and metallic iron.

[0072] Examples of niobium compounds that can be used include, but are not particularly limited to, one or more selected from niobium oxide, niobium chloride, lithium niobate, and niobium iodide.

[0073] Examples of tungsten compounds that can be used include, but are not particularly limited to, one or more selected from tungsten oxide, sodium tungstate, ammonium para-tungstate, tungsten hexacarbonyl, and tungsten sulfide.

[0074] Examples of magnesium compounds that can be used include, but are not particularly limited to, one or more selected from magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium.

[0075] Examples of zirconium compounds that can be used include, but are not particularly limited to, one or more selected from zirconium sulfate, zirconium oxide, zirconium nitrate, zirconium ammonium carbonate, zirconium chloride, zirconium iodide, and metallic zirconium.

[0076] Examples of other elements that can be used include one or more selected from sulfates, oxides, hydroxides, nitrates, carbonates, chlorides, iodides, and metals.

[0077] The proportions in which the various compounds are blended should be adjusted to ensure the desired proportions of the amounts of the various elements in the composition of the intended composite oxide.

[0078] The appropriate pH range for when the precursor composite compound is synthesized is not particularly limited, and can be determined so as to achieve the desired secondary particle size and density, but the pH is generally in the range of around 10 to 13.

[0079] The precursor composite compound obtained by means of a wet reaction is preferably subjected to a washing treatment, and then a drying treatment after being de-watered.

[0080] Subjecting the precursor composite compound to a washing treatment will make it possible to wash out impurities such as sulfate radicals or carbonate radicals and sodium fractions that have been incorporated into agglomerated particles or that have become stuck on the surface layer during the reaction. Washing treatments that can be used for small amounts of impurities include a procedure in which Nutsche washing using a Buchner funnel is performed, or a procedure in which the reacted suspension is pumped through a press filter, washed with water, and de-watered. Moreover, pure water, a sodium hydroxide aqueous solution, or a sodium carbonate aqueous solution, for example, can be used in the washing treatment, but the use of pure water is preferred for industrial purposes. For sizable residual sulfate radicals, however, a sodium hydroxide aqueous solution in which the pH is controlled according to amount that remains may be used.

[0081] [Mixing step]The precursor composite compound synthesized in this way and a lithium compound are then mixed in a predetermined ratio to prepare a mixture. The materials may be mixed with the use of a solvent, where the precursor composite compound and the lithium compound are each in the form of a solution, such as an aqueous solution, and the solutions are mixed in a predetermined ratio, or they may be mixed without a solvent, where a powder of the precursor composite compound and a powder of the lithium compound are weighed out in predetermined proportions and mixed by a dry method.

[0082] The lithium compound is not particularly limited, and a variety of lithium salts may be used. Specific examples of lithium compounds that can be used include one or more 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. Of these, the use of one or more selected from anhydrous lithium hydroxides and lithium hydroxide hydrates is preferred.

[0083] The proportions in which the lithium compound and the precursor composite compound are blended are not particularly limited, but should be adjusted, as appropriate, to ensure the desired proportions of the total amounts of the lithium and various other elements in the composition of the intended composite oxide.

[0084] [Preliminary firing step]The primary firing, which will be described later, is commonly carried out by weighing out the lithium compound, the precursor composite compound, and a compound of another element, if needed, mixing the contents in a mixer, and loading the resulting powder mixture into a container such as a crucible or sagger, but it will become more and more difficult for the gas that is produced to be externally discharged and for the required oxygen concentration diffusion to be achieved as one gets closer and closer to the bottom of the container loaded with the powder mixture, in particular, during the lithiation reaction, in particular. As a result, it becomes difficult to control the reaction homogeneity and the primary particle size.

[0085] A method in which primary firing is first preceded by preliminary firing under the following method is therefore preferably used when producing the composite oxide according to the embodiment of the present disclosure. The preliminary firing is not an essential step, however.

[0086] Incorporating a firing method that promotes the lithiation reaction, in particular, is preferred for this preliminary firing step. A specific example that may be cited is a method that allows the mixture to be more easily heated, allows the gas that is generated from the lithium compound to be easily discharged, and allows gas having a high oxygen partial pressure to be diffused into the mixture (into the particles). The desired properties can be achieved by, for example, prefiring less of the mixture.

[0087] In the preliminary firing step, the mixture can be loaded into a sagger or crucible and fired in a static furnace, roller hearth kiln, or pusher furnace, but it is preferable to fire the mixture while causing the mixture to flow, and, in such case, a rotary kiln can be used as the device.

[0088] The preliminary firing temperature is not particularly limited, but is preferably 500°C-650°C, 510°C-640°C, or 520°C-630°C, for example. Furthermore, the preliminary firing time is not particularly limited, provided that it is a time ensuring the reliable and homogeneous progress of the lithiation reaction, and is preferably, for example, 1 to 10 hours or 2 to 8 hours. Note that the preliminary firing temperature in the present disclosure is the highest temperature when the object to be heated is heated. Highest temperature refers to the part where the temperature is highest of the object to be heated. The term highest temperature is also used with the same definition hereinafter. Furthermore, preliminary firing time refers to, after the preliminary firing temperature has reached a prescribed range, the time for maintaining said range.

[0089] The pre-firing atmosphere is not particularly limited, and should be an oxidizing atmosphere that ensures reliable and homogeneous lithiation reaction progress. For example, the use of an oxidative decarboxylation gas atmosphere having a carbon dioxide gas concentration of 30 ppm or less or an oxygen atmosphere having an oxygen concentration of 80 vol% to 90 vol% is preferred.

[0090] Primary firing of the pre-fired mixture is carried out in order to bring about crystal growth or particle growth at a higher temperature. Reliable and homogeneous crystal growth progress is required at this time to obtain a composite oxide having a desired crystal structure.

[0091] [Titanium compound adding step]In the present disclosure, a titanium compound is added to the pre-fired product obtained in the pre-firing step. The titanium compound to be added, the added amount thereof, and the adding method are the same as described in the precursor preparing step. Furthermore, the titanium compound may be added in only the raw material mixing step, only the titanium compound adding step, or both the raw material mixing step and the titanium compound adding step. In other words, the titanium compound adding step is not a necessary step.

[0092] [Primary firing step]When a composite oxide containing at least a transition metal is produced as noted above, a lithiation reaction and crystal growth will occur during the firing process, but the lithiation reaction will require a certain oxygen partial pressure. The lithiation reaction will produce a composite oxide that contains lithium. The temperature is then increased to a prescribed temperature to promote crystal growth.

[0093] The primary firing temperature is not particularly limited, provided that it is higher than the prefiring temperature, but can be adjusted depending on the composition, for example, of the composite oxide that is going to be obtained. The maximum temperature is preferably adjusted to between 700°C and 1100°C, between 710°C and 1000°C, or between 720°C and 980°C, for example. A maximum temperature within the prescribed range will make it possible to obtain a composite oxide that has the desired crystal structure, with fewer unreacted components, and to prevent the loss of the battery characteristics of the nonaqueous electrolyte secondary batteries in which the resulting composite oxide is used as the positive electrode. To obtain, for example, a composite oxide having an Ni content of 20 mol% to 80 mol% among elements other than Li, the mixture is preferably fired at a maximum temperature not to exceed 1100°C. Furthermore, the primary firing time is not particularly limited, and it should be sufficient time to form a composite oxide having the desired crystal structure. For example, a time of 1 to 15 hours, 2 to 12 hours, or 2 to 10 hours is preferred. Note that the primary firing temperature in the present disclosure is the highest temperature when the object to be heated is heated. Highest temperature refers to the part where the temperature is highest of the object to be heated. The term highest temperature is also used with the same definition hereinafter. Furthermore, primary firing time refers to, after the preliminary firing temperature has reached a prescribed range, the time for maintaining said range.

[0094] The primary firing atmosphere is not particularly limited, and should be an atmosphere that has an oxygen partial pressure, and preferably a low moisture content or carbon dioxide gasconcentration, that will ensure reliable and homogeneous crystal growth, without reducing the transition metal contained in the mixture that is being fired. For example, an oxidative decarboxylation gas atmosphere having a carbon dioxide gas concentration of 30 ppm or less, or an oxygen atmosphere having an oxygen concentration preferably of 80 vol% or more, or 90 vol% or more, is preferably used.

[0095] [Washing step]The composite oxide obtained in the primary firing step may contain unreacted lithium compounds or lithium compounds that have moved from the crystal structure to the particle surface layer over the course of the firing step. A water washing and heat treatment can therefore be performed, for example, in order to remove or minimize such impurities. It should be noted that the washing step is not mandatory.

[0096] [Surface treatment step]A prescribed elemental compound is added to, and mixed with, the composite oxide obtained in the primary firing step or the washing step, and a heat treatment is carried out to allow the surface of the primary particles and / or secondary particles of the composite oxide to be surface treated with a compound of lithium and the added elements, making it possible to leave fewer lithium compounds on the particle surface layer, to improve lithium ion conductivity, and to lower reaction resistance, for example. Note that Step 4 is not mandatory.

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

[0098] [Composite oxide mixing step]When, for example, the composite oxide obtained in any of the primary firing step through the surface treatment step does not exhibit the plurality of peaks satisfying the requirements of the first peak and the second peak, or exhibits the plurality of peaks satisfying the requirements of the first peak and the second peak but more effective control of thermal runaway is desired, the conditions for producing the composite oxide (the conditions of the precursor preparing step through the main firing step) are modified to mix multiple types of composite oxides in which the primary particle size or average particle size has been modified. The composite oxide mixing step is not mandatory if the composite oxide obtained in any of the precursor preparing step through the main firing step does by itself satisfy the requirements of the present disclosure for peaks of the derivative thermogravimetric curve.

[0099] <Nonaqueous electrolyte secondary battery>A nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure comprises a positive electrode that contains the above positive electrode active material, wherein the nonaqueous electrolyte secondary battery comprises the positive electrode, a negative electrode, and an electrolytic solution comprising an electrolyte.

[0100] When the positive electrode is produced, a conductive agent and a binder are admixed by a normal process with the composite oxide according to the embodiment of the present disclosure. Acetylene black, carbon black or graphite, etc., is preferably used as the conductive agent, for example. Polytetrafluoroethylene or polyvinylidene fluoride, etc., is preferably used as the binder, for example.

[0101] The negative electrode is not particularly limited, but it is possible to use not only a negative electrode active material such as lithium metal, graphite, or a low-crystallinity carbon material, for example, but also one or more non-metal or metal elements selected from Si, Al, Sn, Pb, Zn, Bi and Cd, or alloys comprising same, or chalcogen compounds comprising same, etc.

[0102] The solvent of the electrolytic solution is not particularly limited, but it is possible to use an organic solvent comprising one or more selected from carbonates, such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, or ethers such as dimethoxyethane, for example.

[0103] In addition to, in particular, lithium hexafluorophosphate (LiPFe), one or more selected from lithium salts such as lithium perchlorate or lithium tetrafluoroborate may be used, while dissolved in a solvent, as the electrolyte, for example.[Examples]

[0104] The present disclosure is illustrated in greater detail below using examples but is not limited to these examples.

[0105] Preparation of Composite Oxide Samples>The composite oxide materials of Examples 1 through 17 and Comparative Example 1 were prepared by the following methods.

[0106] [Preparation of Precursor Composite Hydroxide][Preparation of Precursor Composite Hydroxide 1]A nickel sulfate aqueous solution as well as cobalt sulfate and manganese sulfate aqueous solution were mixed to an Ni and Co and Mn ratio (molar ratio) of Ni:Co:Mn=83:5:12, giving an aqueous solution mixture. 10 L of pure water to which 300 g of a sodium hydroxide aqueoussolution and 500 g of aqueous ammonia had been added were prepared in advance as the mother liquor in a reactor, the interior of the reactor was purged with nitrogen gas at a flow rate of 0.7 L / min to create a nitrogen atmosphere, and the reaction was also carried out under a nitrogen atmosphere.

[0107] After this, the mixed aqueous solution, sodium hydroxide aqueous solution and ammonia water were simultaneously dripped using a metering pump while a stirring blade was rotated at 1000 rpm, the dripping amount of alkaline solution was adjusted to achieve a pH of 11.4, and a crystallization reaction was performed. In the crystallization reaction, a reaction slurry was sampled as appropriate from an overflow pipe installed on the upper part of a reaction tank, the particle size of the reaction slurry was confirmed to be stable at 13.5 pm, and the slurry was recovered.

[0108] The slurry was then separated into liquid and solids, which were washed with pure water to lower residual impurities, and the co-precipitate in the form of cake was then dried for 10 hours at 100°C in the atmosphere to obtain a nickel-cobalt-manganese composite hydroxide represented by the compositional formula Nio.83Coo.o5Mno.i2(OH)2. The D50 of the resulting composite hydroxide precursor was 13.4 pm.

[0109] [Preparation of Precursor Composite Hydroxide 2]A nickel sulfate aqueous solution as well as cobalt sulfate and manganese sulfate aqueous solution were mixed to an Ni and Co and Mn ratio (molar ratio) of Ni:Co:Mn=83:5:12, giving an aqueous solution mixture. 10 L of pure water to which 310 g of a sodium hydroxide aqueous solution and 500 g of aqueous ammonia had been added were prepared in advance as the mother liquor in a reactor, the interior of the reactor was purged with nitrogen gas at a flow rate of 0.7 Umin to create a nitrogen atmosphere, and the reaction was also carried out under a nitrogen atmosphere.

[0110] After this, the mixed aqueous solution, sodium hydroxide aqueous solution and ammonia water were simultaneously dripped using a metering pump while a stirring blade was rotated at 1000 rpm, the dripping amount of alkaline solution was adjusted to achieve a pH of 11.4, and the crystallization reaction was continued. The dripping of the raw material was then ended and the reaction slurry was recovered.

[0111] The slurry inside the reactor was then separated into liquid and solids, which were washed with pure water to lower residual impurities, the co-precipitate in the form of cake was then dried for 10 hours at 100°C in the atmosphere, and a nickel-cobalt-manganese composite hydroxide represented by the compositional formula Nio.83Coo.o5Mno.i2(OH)2was obtained via coprecipitation. The D50 of the resulting composite hydroxide precursor was 17.1 pm.

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

[0113] The resulting lithium-nickel composite oxide powder was mixed with pure water (adjusted to a liquid temperature of 25°C) to a water ratio of 1500 g / L, and the resulting slurry was stirred for 10 minutes and then de-watered to obtain a compound in the form of cake. The compound in the form of cake was dried for 2 hours at 75°C and 10 hours at 120°C in a vacuum dryer.

[0114] As the boron compound, boric acid was added (1000 ppm) to, and mixed with, the dried lithium- nickel composite oxide, and the mixture was heat treated for 2 hours at 325°C in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain the composite oxide sample of Example 1. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.051.

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

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

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

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

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

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

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

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

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

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

[0125] [Example 12]The precursor composite hydroxide 2, lithium hydroxide, titanyl sulfate added as the titanium raw material, and titanium oxide were adjusted such that the total was 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 the titanium oxide was 15:85.

[0126] Firstly, the precursor composite hydroxide 2, lithium hydroxide, and titanyl sulfate added as the titanium raw material were weighed out and mixed. The mixture was then heat treated for 6 hours at 570°C in an oxygen atmosphere (oxygen concentration: 97 vol%), to obtain preliminary firing powder.

[0127] The obtained preliminary firing powder was then crushed, and the titanium oxide that was first adjusted as the remaining titanium raw material was added and mixed. The mixture was then fired for 6 hours at 815°C in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting fired product was milled to obtain a lithium-nickel composite oxide powder. After this, the same operation as in Example 1 was performed to obtain a composite oxide sample. The Li / (N i+Co+M n+Ti) ratio of the resulting composite oxide sample was 1 .054.

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

[0129] Firstly, the precursor composite hydroxide 1 and lithium hydroxide were weighed out and mixed. The mixture was then heat treated for 6 hours at 570°C in an oxygen atmosphere (oxygen concentration: 97 vol%), to obtain preliminary firing powder.

[0130] The obtained preliminary firing powder was then crushed, and the titanyl sulfate that was first adjusted as the titanium raw material and the titanium oxide were added and mixed. The mixture was then fired for 6 hours at 815°C in an oxygen atmosphere (oxygen concentration: 97vol%). The resulting fired product was milled to obtain a lithium-nickel composite oxide powder. After this, the same operation as in Example 1 was performed 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 precursor composite hydroxide 2, lithium hydroxide, and titanyl sulfate added as the titanium raw material were adjusted such that the total was Li / (Ni+Co+Mn)=1 .050 and Ti / (Ni+Co+Mn+Ti)=1.8 mol%.

[0132] Firstly, the precursor composite hydroxide 1 and lithium hydroxide were weighed out and mixed. The mixture was then heat treated for 6 hours at 570°C in an oxygen atmosphere (oxygen concentration: 97 vol%), to obtain preliminary firing powder.

[0133] The obtained preliminary firing powder was then crushed, and the titanium oxide that was first adjusted as the titanium raw material was added and mixed. The mixture was then fired for 6 hours at 815°C in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting fired product was milled to obtain a lithium-nickel composite oxide powder. After this, the same operation as in Example 1 was performed to obtain a composite oxide sample. The Li / (N i+Co+M n+Ti) ratio of the resulting composite oxide sample was 1 .049.

[0134] [Example 15]The precursor composite hydroxide 2, lithium hydroxide, titanyl sulfate added as the titanium raw material, and titanium oxide were adjusted such that the total was Li / (Ni+Co+Mn)=1 .050 and Ti / (Ni+Co+Mn+Ti)=2.0 mol%. At this time, the Ti molar ratio of the added titanyl sulfate to the titanium oxide was 13:87.

[0135] Firstly, the precursor composite hydroxide 2, lithium hydroxide, and titanyl sulfate added as the titanium raw material were weighed out and mixed. The mixture was then heat treated for 6 hours at 570°C in an oxygen atmosphere (oxygen concentration: 97 vol%), to obtain preliminary firing powder.

[0136] The obtained preliminary firing powder was then crushed, and the titanium oxide that was first adjusted as the remaining titanium raw material was added and mixed. The mixture was then fired for 6 hours at 815°C in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting fired product was milled to obtain a lithium-nickel composite oxide powder. After this, the same operation as in Example 1 was performed to obtain a composite oxide sample. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1 .050.

[0137] [Example 16]The precursor composite hydroxide 2, lithium hydroxide, titanyl sulfate added as the titanium raw material, and titanium oxide were adjusted such that the total was 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 the titanium oxide was 13:87.

[0138] Firstly, the precursor composite hydroxide 1 and lithium hydroxide were weighed out and mixed. The mixture was then heat treated for 6 hours at 570°C in an oxygen atmosphere (oxygen concentration: 97 vol%), to obtain preliminary firing powder.

[0139] The obtained preliminary firing powder was then crushed, and the titanyl sulfate that was first adjusted as the titanium raw material and the titanium oxide were added and mixed. The mixture was then fired for 6 hours at 815°C in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting fired product was milled to obtain a lithium-nickel composite oxide powder. After this, the same operation as in Example 1 was performed to obtain a composite oxide sample. The Li / (Ni+Co+Mn+Ti) ratio of the resulting composite oxide sample was 1.056.

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

[0141] Firstly, the precursor composite hydroxide 1 and lithium hydroxide were weighed out and mixed. The mixture was then heat treated for 6 hours at 570°C in an oxygen atmosphere (oxygen concentration: 97 vol%), to obtain preliminary firing powder.

[0142] The obtained preliminary firing powder was then crushed, and the titanium oxide that was first adjusted as the titanium raw material was added and mixed. The mixture was then fired for 6 hours at 815°C in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting fired product was milled to obtain a lithium-nickel composite oxide powder. After this, the same operation as in Example 1 was performed to obtain a composite oxide sample. 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 out such that the total was Li / (Ni+Co+Mn+AI)=1.030 and AI / (Ni+Co+Mn+AI)=1.0 mol%, and were mixed. The mixture was then fired for 12 hours at820°C in an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting fired product was milled to obtain a lithium-nickel composite oxide powder.

[0144] The resulting lithium-nickel composite oxide powder was mixed with pure water (adjusted to a liquid temperature of 25°C) to a water ratio of 1500 g / L, and the resulting slurry was stirred for 10 minutes and then de-watered to obtain a compound in the form of cake. The compound in the form of cake was dried for 2 hours at 75°C and 10 hours at 120°C in a vacuum dryer.

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

[0146] <Assessment>The samples were assessed in the following manner.

[0147] [Compositional Analysis of Precursor Compounds and Composite Oxides]The compositions of the precursor composite compounds and positive electrode active material particles were determined by the following method. Composite oxide samples (0.2 g) were heated and dissolved in 25 ml_ of 20% hydrochloric acid solution, the sample solutions were cooled and then transferred to 100 mL measuring flasks, and pure water was introduced to adjust the solutions. An ICP-AES (Optima 8300, by PerkinElmer) was used for elemental quantification of the adjusted solutions.

[0148] [Average Particle Size (D50) of Precursor Compound]This was determined on a volume basis by a wet laser method using a laser type particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

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

[0150] (Sample Preparation)2032 type coin cells having a lithium counter electrode were produced in accordance with the method described below, and were charged at a constant current of 0.3 C to 4.30 V at a temperature of 25°C and then charged at a constant voltage to a current value of 0.05 C. After a20-minute break following the completion of charging, the coin cells were discharged at a constant current of 0.3 C to 2.50 V, and were then discharged at a constant current of 0.1 C, followed by a 20-minute break. The charging and discharging were repeated twice. The coin cells were then charged at a constant current of 0.3 C to 4.30 V, and then charged at a constant voltage to a current value of 0.05 C, followed by a 20-minute break after the completion of charging.

[0151] The charged coin cells were disassembled in a glove box (dew point: -70°C or lower) to prevent short circuits, and the positive electrodes were retrieved. The retrieved positive electrodes were washed for 10 minutes in DMC and were dried in vacuo in a side box. The positive electrode active mix was then scraped off the Al foil using a spatula in the same glove box.Thermogravimetric containers made of aluminum were then filled with 15 mg of the positive electrode active mix that had been obtained, and were capped and sealed using a crimper.

[0152] The aluminum analysis containers obtained in this manner were taken out of the glove box and placed on a balance on the measuring side of a TG-DTA analyzer.

[0153] (TG-DTA Analysis)Reference: Platinum vessel filled with 15 to 20 mg of AI2O3Maximum temperature: 600°CHeating rate:(1) 25°C (room temperature) to 50°C: 1°C / min(2) 50°C to 600°C: 5°C / minAnalytical environment: N2 gas atmosphere (200 mL / min)

[0154] Just before the start of the analysis, a small hole was made in the lids of the sealed aluminum analysis containers, which had been placed in the TG-DTA analyzer in an N2gas atmosphere, and heating was initiated.

[0155] DTG curves were prepared on the basis of the results that were obtained, where the horizontal axis shows the temperature, and the vertical axis shows the change in weight (TG) over time (derivative thermogravimetry (DTG), meaning the rate of weight loss, which corresponds to the rate of oxygen release from the composite oxide within the range of 150 to 350°C).

[0156] The first peak was defined as the peak showing the greatest derivative thermogravimetric value at the top of the peak among all peaks having a peak top between 150 and 350°C. The derivative thermogravimetric value at the top of the peak was defined as the oxygen release rate (% / min). The second peak was defined as the peak showing the greatest derivative thermogravimetric value at the top of the peak among peaks whose peak tops occurred at atemperature at least 20°C different from the temperature at which the top of the first peak occurred. Figs. 1 through 13 are DTG curves of samples of the composite oxide materials of Examples 1 through 13. Fig. 14 is a DTG curve of a sample of the composite oxide material of Comparative Example 1.

[0157] [Analysis of Crystal Structures by Rietveld Analysis]XRD diffraction data of the positive electrode active material was obtained under the following X-ray diffraction conditions using an X-ray diffraction apparatus [SmartLab, produced by Rigaku Corp ], after which a Rietveld analysis was performed using this XRD diffraction data, with reference to “R. A. Young, ed., “The Rietveld Method”, Oxford University Press (1992)”. Specifically, the proportion of lithium contained at the 3a site and the 3b site, as well as the unit cell volume were calculated.(X-ray diffraction conditions)X-ray source: Cu-KaAcceleration voltage and current: 45 kV and 200 mASampling width: 0.02 deg.Scan width: 15 deg. to 122 deg.Scan speed: 1 .0 steps / secDivergence slit: 2 / 3 deg.Receiving slit width: 0.15 mmScattering slit: 2 / 3 deg.

[0158] [Assessment of Coin Cell Charge Capacity Using Positive Electrode Active Material Samples] In the present specification, 2032 type coin cells using positive electrode active material particles were produced using positive electrodes, negative electrodes, and electrolytic solutions prepared by the following methods.

[0159] (Positive electrode)The positive electrode active material, conductor (acetylene black:graphite weight ratio of 1:1), and binder (polyvinylidene fluoride) were blended in a positive electrode active materiahconductor: binder weight ratio of 90:6:4, and a mixture of these materials with N- methylpyrrolidone was applied onto aluminum foil. The foil was dried at 110°C to prepare a sheet, which was punched to a diameter of 15 mm and then rolled at 3 t / cm2to produce a positive electrode.

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

[0161] (Electrolytic solution)A solvent mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) prepared to an EC:DMC volume ratio of 1 :2 was mixed with 1 mol / L of LiPF6electrolyte for use as the electrolytic solution.

[0162] (Separator)A 0.5 mm thick separator (Celgard #2400, manufactured by Celgard) that had been punched to a size of 20 mm was used.

[0163] (Measurement of Total Charge Capacity)The coin cells produced by the method above were charged at a constant current of 0.3 C to 4.30 at a temperature of 25°C and then charged at a constant voltage to a current value of 0.05 C. After a 20-minute break following the completion of charging, the coin cells were discharged at a constant current of 0.3 C to 2.50 V, and were then discharged at a constant current of 0.1 C, followed by a 20-minute break. The charging and discharging were repeated twice. The coin cells were then charged at a constant current of 0.3 C to 4.30 V, and then charged at a constant voltage to a current value of 0.05 C. The total charging capacity (mAh / g) was calculated as follows.First charge / discharge: 4.3 V at 0.3 C (constant voltage charging to 0.05 C) 20-Minute breakDischarge at current of 0.3 C to 2.5 V and then at a current of 0.1 C to 2.5 V 20-Minute breakSecond charge / discharge: 4.3 V at 0.3 C (constant voltage charging to 0.05 C) 20-Minute breakDischarge at current of 0.3 C to 2.5 V and then at a current of 0.1 C to 2.5 VThird charge / discharge: 4.3 V at 0.3 C (constant voltage charging to 0.05 C)Total charge capacity= first charge capacity + (second charge capacity - first discharge capacity at 0.3 C - first discharge capacity at 0.1 C) + (third charge capacity - second discharge capacity at 0.3 C - second discharge capacity at 0.1 C)

[0164] Table 1 shows, with respect to Examples 1-17 and Comparative Example 1 , the composition of the composite oxide constituting the sample, the Ti source added amount (molar ratio Ti / (Ni+Co+Mn+Ti)) before and after preliminary firing, the Li ratio present on the 3a site and 3b site and unit cell volume by XRD diffraction, the peak top temperature of the first peak of the DTG curve, the derivative thermogravimetry (oxygen release rate), and the rate of decrease in the derivative thermogravimetry relative to Comparative Example 1, the peak top temperature of the second peak and the derivative thermogravimetry (oxygen release rate), 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 thermogravimetric derivative at the peak top of the first peak to the thermogravimetric derivative at the peak top of the second peak (derivative thermogravimetry at the peak top of the first peak / derivative thermogravimetry at thepeak top of the second peak), the total charge capacity, and the rate of decrease in the peak oxygen release rate on the low temperature side relative to Comparative Example 1 .

[0165] [Table 1]

Claims

CLAIMS

1. A positive electrode active material for a nonaqueous electrolyte secondary battery, comprising a composite oxide represented by general formula Lii+xNii.y-z-w-vCoyMnzTiwMvO2+ci (where M is 1 or more elements other than Li, Ni, Co, Mn, 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<a<0.5), wherein when a derivative thermogravimetric curve is obtained after a sample of the composite oxide, that has been charged to 4.30 V using lithium as the counter electrode, is heated from 50°C to 600°C at a rate of 5°C / min, and the resulting curve is separated into a plurality of peaks, within the temperature range of 150°C to 350°C, the top of the first peak shows the greatest derivative thermogravimetric value and the top of the second peak 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 top of the first peak occurs, and the ratio of the derivative thermogravimetric value at the top of the first peak to the derivative thermogravimetric value at the top of the second peak is 1 to 9.

2. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein in the composite oxide, 0<x<0.15.

3. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the derivative thermogravimetric value at the top of the first peak is 3% / min or less.

4. A nonaqueous electrolyte secondary battery, comprising a positive electrode containing the positive electrode active material according to claim 1 or 2.

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