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

Abstract

To provide a positive electrode active material that improves output in a low SOC region while suppressing a decrease in discharge capacity.SOLUTION: A positive electrode active material includes first particles made of a first lithium transition metal composite oxide having a layered structure, in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.7 or more and less than 1, second particles made of a second lithium transition metal composite oxide having a layered structure, in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.33 or more and less than 1, and the ratio of the number of moles of cobalt to the total number of moles is 0.01 or more and 0.35 or less, and third particles made of a third lithium transition metal composite oxide having a layered structure, in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.4 or more and 0.6 or less, and the ratio of the number of moles of cobalt to the total number of moles is 0.35 or more and 0.55 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Lithium transition metal composite oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium nickel cobalt manganese oxide are used as the positive electrode active material for non-aqueous electrolyte secondary batteries. Various studies have been conducted to improve the characteristics of positive electrode active materials, and it is known that lithium nickel-based composite oxides, which have a higher nickel ratio instead of cobalt, a scarce resource, have a high charge / discharge capacity per unit weight. On the other hand, Patent Document 1 describes that the DC resistance value of nickel-containing lithium transition metal oxides increases as the nickel content increases. Patent Document 2 also describes that LiNi 0.4 Co 0.2 Mn 0.4 Lithium nickel cobalt manganese composite oxide represented by O2 is 0.4 Co 0.5 Mn 0.1 It is described that the resistance in the low SOC (State of Charge) region is reduced by mixing a lithium nickel cobalt manganese composite oxide represented by O2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 043190 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-228466 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one aspect of the present disclosure is to provide a positive electrode active material and a positive electrode for a non-aqueous electrolyte secondary battery that improve output in a low SOC region while suppressing a decrease in discharge capacity. [Means for solving the problem]

[0005] A first aspect is a positive electrode active material comprising: first particles made of a first lithium transition metal composite oxide having a layered structure and in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.7 or more and less than 1; second particles made of a second lithium transition metal composite oxide having a layered structure and having a volume average particle size smaller than the volume average particle size of the first particles; and third particles made of a third lithium transition metal composite oxide having a layered structure and in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.4 or more and 0.6 or less and the ratio of the number of moles of cobalt to the total number of moles is 0.35 or more and 0.55 or less, wherein the content of the first particles is 60 mass% or more and less than 100 mass% with respect to the total of the first particles, the second particles, and the third particles, and the content of the third particles is 10 mass% or less with respect to the total of the first particles, the second particles, and the third particles.

[0006] A second aspect is a positive electrode for a non-aqueous electrolyte secondary battery, which includes the positive electrode active material. [Effects of the Invention]

[0007] According to one aspect of the present disclosure, it is possible to provide a positive electrode active material and a positive electrode for a non-aqueous electrolyte secondary battery that improve output in a low SOC region while suppressing a decrease in discharge capacity. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram plotting the results of measuring DC internal resistance in a low SOC region in Examples and Comparative Examples. [Figure 2] FIG. 1 is a diagram plotting the measurement results of discharge capacity in Examples and Comparative Examples. [Figure 3A] 3 is an example of a scanning electron microscope (SEM) image of a first particle according to Example 1. [Figure 3B] 3 is an example of a scanning electron microscope (SEM) image of a second particle according to Example 1. [Figure 3C] 4 is an example of a scanning electron microscope (SEM) image of a third particle according to Example 1. [Figure 3D] 2 is an example of a scanning electron microscope (SEM) image of the positive electrode active material according to Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this specification, the content of each component in a composition refers to the total amount of the multiple substances present in the composition when multiple substances corresponding to each component are present in the composition, unless otherwise specified. Furthermore, the upper and lower limits of the numerical ranges described in this specification can be arbitrarily selected and combined from the numerical values ​​exemplified as numerical ranges. Below, embodiments of the present disclosure are described in detail. However, the embodiments described below are examples of positive electrode active materials for embodying the technical concept of the present disclosure, and the present disclosure is not limited to the positive electrode active materials shown below.

[0010] positive electrode active material The positive electrode active material includes: first particles made of a first lithium transition metal composite oxide having a layered structure, the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition being 0.7 or more and less than 1; second particles made of a second lithium transition metal composite oxide having a layered structure and a volume average particle size smaller than the volume average particle size of the first particles; and third particles made of a third lithium transition metal composite oxide having a layered structure, the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition being 0.4 or more and 0.6 or less and the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium in the composition being 0.35 or more and 0.55 or less. The content of the first particles is 60% by mass or more and less than 100% by mass of the total of the first, second, and third particles, and the content of the third particles is 10% by mass or less of the total of the first, second, and third particles.

[0011] When third particles are mixed into a positive electrode active material containing first particles to improve output power in the low SOC region, there is a concern that the addition of third particles may result in a decrease in charge / discharge capacity. On the other hand, if the amount of third particles mixed is reduced to counter this decrease in charge / discharge capacity, the proportion of first particles, which have a slow lithium ion intercalation rate in the low SOC region, increases. Therefore, despite the inclusion of third particles, it tends to be difficult to achieve an improvement in output power in the low SOC region. In this case, by further including second particles with a volume average particle size smaller than that of the first particles, the second particles, which are smaller than the first particles, are thought to play a role in assisting the migration of lithium ions between the first particles and the third particles in the low SOC region. When such a positive electrode active material is used in a positive electrode for a nonaqueous electrolyte secondary battery, it is possible to promote the diffusion of lithium ions throughout the positive electrode. This facilitates improving output power in the low SOC region while suppressing a decrease in charge / discharge capacity.

[0012] The content of the first particles in the positive electrode active material is 60% by mass or more and less than 100% by mass, preferably 65% ​​by mass or more and 95% by mass or less, more preferably 70% by mass or more and 90% by mass or less, and even more preferably 75% by mass or more and 85% by mass or less, based on the total of the first particles, second particles, and third particles. When the proportion of the first particles is within the above range, the charge / discharge capacity becomes good, and output in the low SOC region tends to be improved.

[0013] The content of the second particles in the positive electrode active material may be 1% by mass or more and less than 30% by mass, preferably 2% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 20% by mass or less, and even more preferably 8% by mass or more and 20% by mass or less, or 12% by mass or more and 19% by mass or less, based on the total of the first particles, second particles, and third particles. When the proportion of the second particles is within the above range, output in a low SOC region can be improved more efficiently while suppressing a decrease in charge / discharge capacity.

[0014] The content of the third particles in the positive electrode active material is 10% by mass or less, preferably greater than 0% by mass and less than 10% by mass, more preferably 1% by mass or more and 8% by mass or less, and even more preferably 2% by mass or more and 6% by mass or less, relative to the total of the first particles, second particles, and third particles. As in the present disclosure, when the ratio of the moles of nickel to the total moles of metals other than lithium in the composition of the first particles is 0.7 or more and less than 1, by keeping the proportion of the third particles within the above range, it is possible to more efficiently improve output in the low SOC region while suppressing a decrease in charge / discharge capacity.

[0015] The content of the second particles is preferably 1 to 25 times, more preferably 1.2 to 15 times, even more preferably 1.5 to 10 times, and particularly preferably 2 to 9 times, the mass ratio of the content of the third particles. When the content of the second particles relative to the third particles is within the above range, output in a low SOC region tends to be more easily improved.

[0016] The content of the first particles is preferably 5 to 80 times, more preferably 6 to 50 times, and even more preferably 10 to 36 times, the mass ratio of the third particles. When the content of the first particles relative to the third particles is within the above range, the charge / discharge capacity tends to be better.

[0017] Furthermore, the content of the first particles is preferably 2 to 15 times, more preferably 2.5 to 12 times, even more preferably 3.6 to 12 times, and particularly preferably 4 to 6 times, the content of the second particles in terms of mass ratio. When the content of the first particles relative to the content of the second particles is within the above range, output in a low SOC region tends to be more easily improved.

[0018] 1st particle The first particles are composed of a first lithium transition metal composite oxide having a layered structure, and may be secondary particles formed by aggregating a plurality of primary particles containing the first lithium transition metal composite oxide.

[0019] The ratio of the moles of nickel to the total moles of metals other than lithium in the first lithium transition metal composite oxide constituting the first particles is 0.7 or more and less than 1, preferably 0.7 or more and 0.95 or less, and more preferably 0.8 or more and 0.95 or less. Positive electrode active material particles containing a first lithium transition metal composite oxide having a mole ratio of nickel within the above range tend to have a higher charge / discharge capacity. Furthermore, when the mole ratio of nickel is within the above range, the output improvement effect in the low SOC region of the present disclosure tends to be easily achieved even when the mixed amount of the third particles is 10 mass% or less. Furthermore, when the mole ratio of nickel is within the above range, the decrease in charge / discharge capacity during output improvement in the low SOC region of the present disclosure is further suppressed. The composition of the lithium transition metal composite oxide can be measured, for example, using an inductively coupled plasma optical emission spectrometer.

[0020] The first lithium transition metal composite oxide constituting the first particles may contain cobalt in its composition. When the first lithium transition metal composite oxide constituting the first particles contains cobalt in its composition, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is, for example, greater than 0 and less than 0.3, preferably 0.02 or more and less than 0.2, and more preferably 0.02 or more and less than 0.1. The first lithium transition metal composite oxide constituting the first particles may contain at least one of manganese and aluminum. When the first lithium transition metal composite oxide contains at least one of manganese and aluminum, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals other than lithium is, for example, greater than 0, preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more. Furthermore, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium is, for example, 0.3 or less, preferably 0.25 or less, more preferably 0.2 or less, and even more preferably 0.15 or less. When the ratio of the total number of moles of manganese and aluminum is within the above range, there is a tendency for safety to be improved while maintaining good charge / discharge capacity.

[0021] In the first lithium transition metal composite oxide constituting the first particles, the ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 0.95 or more, preferably 1.0 or more, more preferably 1.03 or more, and even more preferably 1.05 or more. The ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 1.5 or less, preferably 1.3 or less, more preferably 1.25 or less, and even more preferably 1.2 or less. When the ratio of the number of moles of lithium is 0.95 or more, the output of a nonaqueous electrolyte secondary battery using a positive electrode active material containing the first lithium transition metal composite oxide tends to be improved. On the other hand, when the ratio of the number of moles of lithium is 1.5 or less, the initial discharge capacity tends to be improved when the positive electrode active material is used in a positive electrode.

[0022] The first lithium transition metal composite oxide has a composition containing at least one element M selected from the group consisting of magnesium (Mg), calcium (Ca), titanium (Ti), zirconium (Zr), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), iron (Fe), copper (Cu), silicon (Si), tin (Sn), bismuth (Bi), gallium (Ga), yttrium (Y), samarium (Sm), erbium (Er), cerium (Ce), neodymium (Nd), lanthanum (La), cadmium (Cd), and lutetium (Lu). 2 and preferably contains at least one element M selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo and W. 2 may include:

[0023] The ratio of the element M to the total number of moles of metals other than lithium in the first lithium transition metal composite oxide 2 The ratio of the number of moles of may be, for example, 0 or more and 0.02 or less, and preferably 0.015 or less.

[0024] When representing the first lithium transition metal composite oxide constituting the first particle as a composition, for example, a lithium transition metal composite oxide represented by the following formula (1) can be mentioned. The first lithium transition metal composite oxide may have a layered structure and may have a hexagonal crystal structure. Li p1 Ni x1 Co y1 M 1 z1 M 2 w1 O α1 (1)

[0025] Here, p1, x1, y1, z1, w1, and α1 satisfy 0.95 ≤ p1 ≤ 1.5, 0.7 ≤ x1 < 1, 0 < y1 ≤ 0.3, 0 < z1 ≤ 0.3, 0 ≤ w1 ≤ 0.02, x1 + y1 + z1 + w1 = 1, 1.5 ≤ α1 ≤ 2.5. x1, y1, z1, and w1 may satisfy 0.7 ≤ x1 ≤ 0.95, 0.02 ≤ y1 ≤ 0.2, 0.01 ≤ z1 ≤ 0.25, 0 ≤ w1 ≤ 0.015, may satisfy 0.8 ≤ x1 ≤ 0.95, 0.02 ≤ y1 ≤ 0.2, 0.05 ≤ z1 ≤ 0.2, 0 ≤ w1 ≤ 0.015, may satisfy 0.8 ≤ x1 ≤ 0.95, 0.02 ≤ y1 ≤ 0.1, 0.07 ≤ z1 ≤ 0.15, 0 ≤ w1 ≤ 0.015. Also, p1 may satisfy 1.0 ≤ p1, 1.03 ≤ p1, or 1.05 ≤ p1, may satisfy p1 ≤ 1.3, p1 ≤ 1.25, or p1 ≤ 1.2, and α1 may satisfy 1.8 ≤ α1 ≤ 2.8.

[0026] M 1 may contain at least one of Mn and Al. M 2 may contain at least one selected from the group consisting of Mg, Ca, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu, and may contain at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0027] The volume average particle diameter of the first particles is, for example, 6 μm or more and 30 μm or less, preferably 7 μm or more, more preferably 8 μm or more, and preferably 25 μm or less, more preferably 20 μm or less. When the volume average particle diameter of the first particles is within the above range, the packing property when mixed with other particles may be improved, and the battery characteristics may be further improved. Here, the volume average particle diameter is the 50% particle diameter D corresponding to the cumulative 50% from the small diameter side in the cumulative particle size distribution based on volume. 50 is.

[0028] The first particles preferably have a narrow particle size distribution with a single peak. The particle size distribution of the first particles is defined as a 90% particle size D , which corresponds to the cumulative 90% from the smallest diameter side in the cumulative particle size distribution based on volume. 90 10% particle diameter D corresponding to the cumulative 10% from the small diameter side 10 Ratio to (D 90 / D 10 ) may be, for example, 3 or less, preferably 2.5 or less, 2 or less, 1.8 or less, 1.6 or less, or 1.5 or less. 90 / D 10 ) may be, for example, 1 or more, or 1.1 or more.

[0029] The first particles may contain compounds other than the first lithium transition metal composite oxide, such as a compound containing sodium or a compound containing boron. The content of the compounds other than the first lithium transition metal composite oxide may be 0 ppm or more and 12,000 ppm or less, 0 ppm or more and 10,000 ppm or less, 0 ppm or more and 8,000 ppm or less, or 0 ppm or more and 6,000 ppm or less, relative to the first lithium transition metal composite oxide.

[0030] The first particles may have a boron-containing compound attached to their surfaces. When the first particles having the boron-containing compound attached thereto are used in a non-aqueous electrolyte secondary battery, the charge / discharge characteristics and cycle characteristics tend to be improved.

[0031] Examples of boron-containing compounds include lithium metaborate (LiBO2). The boron-containing compound may form a composite with the first lithium transition metal composite oxide. The content of the boron-containing compound in the first particles may be 0 ppm to 2000 ppm, or 0 ppm to 1500 ppm, in terms of elemental boron relative to the first lithium transition metal composite oxide. The content of the boron-containing compound in the first particles may be, for example, 0.1 mol% to 2 mol%, preferably 0.1 mol% to 1.5 mol%, expressed as the ratio of the number of moles of elemental boron to the total number of moles of metals other than lithium in the first lithium transition metal composite oxide constituting the first particles. The boron content in the positive electrode active material can be measured, for example, by an inductively coupled plasma optical emission spectrometer.

[0032] The first particles may have a sodium-containing compound on the particle surface. Examples of the sodium-containing compound include sodium sulfate (Na2SO4). When the sodium compound is present on the surface of the first particles, the effect of the attached substance, such as a boron-containing compound, tends to be enhanced. For example, when the boron-containing compound is present as the attached substance, better cycle characteristics can be achieved when the battery is applied to a non-aqueous electrolyte secondary battery. Furthermore, when the first particles are secondary particles formed by aggregating a plurality of primary particles containing a first lithium transition metal composite oxide, the presence of sodium at the grain boundaries of the secondary particles containing the first lithium transition metal composite oxide that constitute the first particles allows boron to be uniformly distributed throughout the grain boundaries of the first particles, which is believed to result in better cycle characteristics.

[0033] 2nd particle The second particles are made of a second lithium transition metal composite oxide having a layered structure and have a volume average particle size smaller than that of the first particles. The second particles may be secondary particles formed by aggregating a plurality of primary particles containing the second lithium transition metal composite oxide.

[0034] The second lithium transition metal composite oxide constituting the second particles may have a ratio of the number of moles of nickel to the total number of moles of metals other than lithium in its composition of 0.33 or more and less than 1, preferably 0.7 or more and less than 1, more preferably 0.7 or more and 0.95 or less, and even more preferably 0.8 or more and 0.95 or less. Positive electrode active material particles containing a second lithium transition metal composite oxide having a ratio of the number of moles of nickel within the above range tend to have a larger charge / discharge capacity.

[0035] The second lithium transition metal composite oxide constituting the second particles may contain cobalt in its composition. When the second lithium transition metal composite oxide constituting the second particles contains cobalt in its composition, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is, for example, greater than 0 and less than 0.6, preferably 0.01 to 0.35, more preferably 0.02 to 0.2, and even more preferably 0.02 to 0.1. The second lithium transition metal composite oxide constituting the first particles may contain at least one of manganese and aluminum. When the second lithium transition metal composite oxide contains at least one of manganese and aluminum, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals other than lithium is, for example, greater than 0, preferably greater than 0, more preferably 0.01 or greater, even more preferably 0.05 or greater, and particularly preferably 0.07 or greater. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium is, for example, 0.6 or less, preferably 0.3 or less, more preferably 0.25 or less, even more preferably 0.2 or less, and particularly preferably 0.15 or less. When the ratio of the total number of moles of manganese and aluminum is within the above-mentioned range, there is a tendency for safety to be improved while maintaining good charge / discharge capacity.

[0036] In the second lithium transition metal composite oxide constituting the second particles, the ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 0.95 or more, preferably 1.0 or more, more preferably 1.03 or more, and even more preferably 1.05 or more. The ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 1.5 or less, preferably 1.3 or less, more preferably 1.25 or less, and even more preferably 1.2 or less. When the ratio of the number of moles of lithium is 0.95 or more, the output of a nonaqueous electrolyte secondary battery using a positive electrode active material containing the second lithium transition metal composite oxide tends to be improved. On the other hand, when the ratio of the number of moles of lithium is 1.5 or less, the initial discharge capacity tends to be improved when the positive electrode active material is used in a positive electrode.

[0037] The second lithium transition metal composite oxide contains, in its composition, an element M containing at least one element selected from the group consisting of Mg, Ca, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu. 2 and preferably contains at least one element M selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo and W. 2 may include:

[0038] The ratio of element M to the total number of moles of metals other than lithium in the second lithium transition metal composite oxide 2 The ratio of the number of moles of may be, for example, 0 or more and 0.02 or less, and preferably 0.015 or less.

[0039] The second lithium transition metal composite oxide constituting the second particles may have a composition represented by the following formula (2): The second lithium transition metal composite oxide may have a layered structure or a hexagonal crystal structure. Li p2 Ni x2 Co y2 M 1 z2 M 2 w2 Oα2 (2)

[0040] Here, p2, x2, y2, z2, w2, and α2 satisfy 0.95 ≤ p2 ≤ 1.5, 0.33 ≤ x2 < 1, 0 < y2 ≤ 0.6, 0 ≤ z2 ≤ 0.6, 0 ≤ w2 ≤ 0.02, x2 + y2 + z2 + w2 = 1, and 1.5 ≤ α2 ≤ 2.5. x2, y2, z2, and w2 may satisfy 0.33 ≤ x2 < 1, 0.01 ≤ y2 ≤ 0.35, 0 ≤ z2 ≤ 0.6, 0 ≤ w2 ≤ 0.02, may satisfy 0.7 ≤ x2 < 1, 0.02 ≤ y2 ≤ 0.2, 0.01 ≤ z2 ≤ 0.25, 0 ≤ w2 ≤ 0.015, may satisfy 0.7 ≤ x2 ≤ 0.95, 0.02 ≤ y2 ≤ 0.2, 0.01 ≤ z2 ≤ 0.25, 0 ≤ w2 ≤ 0.015, may satisfy 0.8 ≤ x2 ≤ 0.95, 0.02 ≤ y2 ≤ 0.2, 0.05 ≤ z2 ≤ 0.2, 0 ≤ w2 ≤ 0.015, may satisfy 0.8 ≤ x2 ≤ 0.95, 0.02 ≤ y2 ≤ 0.1, 0.07 ≤ z2 ≤ 0.15, 0 ≤ w2 ≤ 0.015. Also, p2 may satisfy 1.0 ≤ p2, 1.03 ≤ p2, or 1.05 ≤ p2, may satisfy p2 ≤ 1.3, p2 ≤ 1.25, or p2 ≤ 1.2, and α2 may satisfy 1.8 ≤ α2 ≤ 2.8.

[0041] M 1 may contain at least one of Mn and Al. M 2 may contain at least one selected from the group consisting of Mg, Ca, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu, and may contain at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0042] The volume average particle diameter of the second particle is, for example, 1 μm or more and 10 μm or less, preferably 1.5 μm or more, more preferably 2 μm or more, still more preferably 3 μm or more, and also preferably 9 μm or less, more preferably less than 8 μm, still more preferably 7.5 μm or less. When the volume average particle diameter of the second particle is within the above range, the filling property may be improved and the battery characteristics may be further improved when mixed with other particles.

[0043] The ratio of the volume average particle size of the first particles to the volume average particle size of the second particles (first particles / second particles) may be, for example, 1.3 or more and 10 or less, preferably 1.5 or more or 1.6 or more, and preferably 6.7 or less or 2.6 or less. When the volume average particle size ratio is within the above range, the movement of lithium ions between the first particles, the second particles, and the third particles tends to be more promoted.

[0044] The second particles preferably have a narrow particle size distribution with a single peak. 90 10% particle size D 10 Ratio to (D 90 / D 10 ) may be, for example, 3.2 or less, preferably 3 or less, 2.6 or less, 2.4 or less, 2.2 or less, or 2.0 or less. 90 / D 10 The lower limit of the 90% particle diameter D of the second particles may be, for example, 1 or more, 1.4 or more, or 1.6 or more. 90 is the 10% particle diameter D of the first particle 10 Smaller is preferable.

[0045] The second particles may contain compounds other than the second lithium transition metal composite oxide, such as a compound containing sodium or a compound containing boron. The content of the compounds other than the second lithium transition metal composite oxide may be 0 ppm or more and 12,000 ppm or less, 0 ppm or more and 10,000 ppm or less, 0 ppm or more and 8,000 ppm or less, or 0 ppm or more and 6,000 ppm or less, relative to the second lithium transition metal composite oxide.

[0046] The second particles may have a boron-containing compound attached to their surfaces. When the second particles having the boron-containing compound attached thereto are used in a non-aqueous electrolyte secondary battery, the charge / discharge characteristics and cycle characteristics tend to be improved.

[0047] Examples of boron-containing compounds include lithium metaborate (LiBO2). The boron-containing compound may form a composite with the second lithium transition metal composite oxide. The content of the boron-containing compound in the second particles may be 0 ppm to 2000 ppm, or 0 ppm to 1500 ppm, in terms of elemental boron relative to the second lithium transition metal composite oxide. The content of the boron-containing compound in the second particles may be, for example, 0.1 mol% to 2 mol%, preferably 0.1 mol% to 1.5 mol%, expressed as the ratio of the number of moles of elemental boron to the total number of moles of metals other than lithium in the second lithium transition metal composite oxide constituting the second particles.

[0048] The second particles may have a sodium-containing compound on the particle surface. Examples of sodium-containing compounds include sodium sulfate (Na2SO4). When the sodium compound is present on the surface of the second particles, the effect of the attached substance, such as a boron-containing compound, tends to be enhanced. For example, when the boron-containing compound is present as the attached substance, better cycle characteristics can be achieved when the second particles are applied to non-aqueous electrolyte secondary batteries. Furthermore, when the second particles are secondary particles formed by aggregating a plurality of primary particles containing a second lithium transition metal composite oxide, the presence of sodium at the grain boundaries of the secondary particles containing the second lithium transition metal composite oxide that constitute the second particles allows boron to be uniformly distributed throughout the grain boundaries of the second particles, which is believed to result in better cycle characteristics.

[0049] 3rd particle The third particles are composed of a third lithium transition metal composite oxide having a layered structure, and may be secondary particles formed by aggregating a plurality of primary particles containing the third lithium transition metal composite oxide.

[0050] The third lithium transition metal composite oxide constituting the third particles has a ratio of the number of moles of nickel to the total number of moles of metals other than lithium in its composition of 0.4 or more and 0.6 or less, preferably 0.4 or more and less than 0.55, more preferably 0.4 or more and 0.5 or less, and even more preferably 0.4 or more and less than 0.5. Positive electrode active material particles containing a third lithium transition metal composite oxide with a large ratio of the number of moles of nickel tend to have a larger charge / discharge capacity.

[0051] The third lithium transition metal composite oxide constituting the third particles contains cobalt in its composition. In the composition of the third particles, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is, for example, 0.35 or more and 0.55 or less, preferably greater than 0.35 and 0.5 or less, and more preferably 0.4 or more and 0.5 or less. When the ratio of the number of moles of cobalt is within the above range, the effect of improving output in the low SOC range when mixed with the first particles tends to be improved. The third lithium transition metal composite oxide constituting the third particles may contain at least one of manganese and aluminum. When the third lithium transition metal composite oxide contains at least one of manganese and aluminum, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals other than lithium is, for example, greater than 0, preferably 0.01 or more, more preferably 0.05 or more. Furthermore, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium is, for example, 0.25 or less, preferably 0.2 or less, and more preferably 0.15 or less. When the ratio of the total number of moles of manganese and aluminum is within the above range, it is possible to achieve both good charge / discharge capacity and safety.

[0052] In the third lithium transition metal composite oxide constituting the third particles, the ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 0.95 or more, preferably 1.0 or more, more preferably 1.03 or more, and even more preferably 1.05 or more. The ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 1.5 or less, preferably 1.3 or less, more preferably 1.25 or less, and even more preferably 1.2 or less. When the ratio of the number of moles of lithium is 0.95 or more, the output of a nonaqueous electrolyte secondary battery using a positive electrode active material containing the third lithium transition metal composite oxide tends to be improved. On the other hand, when the ratio of the number of moles of lithium is 1.5 or less, the initial discharge capacity tends to be improved when the positive electrode active material is used in a positive electrode.

[0053] The third lithium transition metal composite oxide contains, in its composition, an element M containing at least one element selected from the group consisting of Mg, Ca, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu. 2 and preferably contains at least one element M selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo and W. 2 may include:

[0054] The moles of element M relative to the total number of moles of metals other than lithium in the third lithium transition metal composite oxide 2 The ratio of the number of moles of may be, for example, 0 or more and 0.02 or less, and preferably 0.015 or less.

[0055] The third lithium transition metal composite oxide constituting the third particles may be expressed as a composition, for example, by the lithium transition metal composite oxide represented by the following formula (3): The third lithium transition metal composite oxide may have a layered structure or a hexagonal crystal structure. Li p3 Ni x3 Co y3 M 1 z3 M 2 w3 Oα3 (3)

[0056] Here, p3, x3, y3, z3, w3, and α3 satisfy 0.95 ≤ p3 ≤ 1.5, 0.4 ≤ x3 ≤ 0.6, 0.35 ≤ y3 ≤ 0.55, 0 ≤ z3 ≤ 0.25, 0 ≤ w3 ≤ 0.02, x3 + y3 + z3 + w3 = 1, and 1.5 ≤ α3 ≤ 2.5. x3, y3, z3, and w3 may satisfy 0.4 ≤ x3 ≤ 0.55, 0.35 < y3 ≤ 0.5, 0.01 ≤ z3 ≤ 0.20, and 0 ≤ w3 ≤ 0.015, may satisfy 0.4 ≤ x3 < 0.55, 0.35 < y3 ≤ 0.5, 0.01 ≤ z3 ≤ 0.20, and 0 ≤ w3 ≤ 0.015, may satisfy 0.4 ≤ x3 ≤ 0.5, 0.4 ≤ y3 ≤ 0.5, 0.05 ≤ z3 ≤ 0.15, and 0 ≤ w3 ≤ 0.015, may satisfy 0.4 ≤ x3 < 0.5, 0.4 ≤ y3 ≤ 0.5, 0.05 ≤ z3 ≤ 0.15, and 0 ≤ w3 ≤ 0.015. Also, p3 may satisfy 1.0 ≤ p3, 1.03 ≤ p3, or 1.05 ≤ p3, may satisfy p3 ≤ 1.3, p3 ≤ 1.25, or p3 ≤ 1.2, and α3 may satisfy 1.8 ≤ α3 ≤ 2.8.

[0057] M 1 may contain at least one of Mn and Al. M 2 may contain at least one selected from the group consisting of Mg, Ca, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu, and may contain at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0058] The volume average particle diameter of the third particles is, for example, 1 μm or more and 10 μm or less, preferably 1.5 μm or more, more preferably 2 μm or more, still more preferably 3 μm or more, and also preferably 9 μm or less, more preferably less than 8 μm, still more preferably 7.5 μm or less. Also, it is preferable that the volume average particle diameter of the third particles is smaller than the volume average particle diameter of the first particles. When the volume average particle diameter of the third particles is within the above range, the packing property may be improved and the battery characteristics may be further improved when mixed with other particles.

[0059] The ratio of the volume average particle size of the first particles to the volume average particle size of the third particles (first particles / third particles) may be, for example, 1.3 to 20, preferably 1.5 to 1.6, and preferably 6.7 to 3.6. The ratio of the volume average particle size of the second particles to the volume average particle size of the third particles (second particles / third particles) may be, for example, 0.5 to 5.0, preferably 0.7 to 1.0, and preferably 3.5 to 2.0. When the volume average particle size ratio is within the above range, the movement of lithium ions between the first particles, second particles, and third particles tends to be more promoted.

[0060] The third particles preferably have a single-peak particle size distribution. 90 10% particle size D 10 Ratio to (D 90 / D 10 ) may be, for example, 4.2 or less, preferably 4 or less, or 3.7 or less. 90 / D 10 ) may be, for example, 1 or more, 2 or more, 2.8 or more, or 3 or more.

[0061] The third particles may contain compounds other than the third lithium transition metal composite oxide, such as a compound containing sodium or a compound containing boron. The content of the compounds other than the third lithium transition metal composite oxide may be 0 ppm or more and 12,000 ppm or less, 0 ppm or more and 10,000 ppm or less, 0 ppm or more and 8,000 ppm or less, or 0 ppm or more and 6,000 ppm or less, relative to the third lithium transition metal composite oxide.

[0062] Positive electrode for non-aqueous electrolyte secondary batteries A positive electrode for a non-aqueous electrolyte secondary battery (hereinafter simply referred to as a positive electrode) includes a current collector and a positive electrode active material layer disposed on the current collector and containing the above-described positive electrode active material. A non-aqueous electrolyte secondary battery including such a positive electrode can have improved charge / discharge capacity and output characteristics in a low SOC region.

[0063] Examples of materials for the current collector include aluminum, nickel, and stainless steel. The positive electrode active material layer can be formed by applying a positive electrode composition obtained by mixing the above-mentioned positive electrode active material, conductive additive, binder, and the like with a solvent onto the current collector, followed by drying and pressure treatment. Examples of conductive additives include carbon materials such as natural graphite, artificial graphite, acetylene black, ketjen black (KB), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, butylene rubber, styrene butadiene rubber, and polyamide acrylic resin. Examples of solvents include N-methyl-2-pyrrolidone (NMP). The positive electrode may further contain a thickener in the positive electrode active material layer. While examples of each component are given above, the positive electrode for a nonaqueous electrolyte secondary battery of the present disclosure is not particularly limited in other components as long as it contains the above-mentioned positive electrode active material.

[0064] Nonaqueous electrolyte secondary battery The nonaqueous electrolyte secondary battery includes the above-described positive electrode for a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery may be configured with a negative electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte, a separator, and the like in addition to the positive electrode for a nonaqueous electrolyte secondary battery. The negative electrode, nonaqueous electrolyte, separator, and the like for the nonaqueous electrolyte secondary battery may be appropriately selected from those for nonaqueous electrolyte secondary batteries described in, for example, JP 2002-075367 A, JP 2011-146390 A, and JP 2006-12433 A (the entire disclosures of which are incorporated herein by reference). The nonaqueous electrolyte secondary battery of the present disclosure is not limited to those using a liquid electrolyte, but also includes all-solid-state lithium batteries using a solid electrolyte. The components of the all-solid-state lithium battery may be appropriately selected from those for all-solid-state lithium batteries described in, for example, JP 2017-016794 A. The nonaqueous electrolyte secondary battery of the present disclosure is not particularly limited in other configurations as long as it contains the above-described positive electrode active material. [Example]

[0065] [Example 1] Preparation of positive electrode active material Li with a compound containing 1000 ppm of boron on the surface as the first particle 1.05 Ni 0.81 Co 0.05 Mn 0.12 Al 0.02 O2 (volume average particle size: 9.8 μm) and Li with a compound containing 1100 ppm of boron on the surface as the second particle. 1.05 Ni 0.81 Co 0.05 Mn 0.12 Al 0.02 O2 (volume average particle size: 4.4 μm) and Li as the third particle. 1.07 Ni 0.45 Co 0.45 Mn 0.10 Third particles A of O2 (volume average particle size: 3.9 μm) were prepared. The first particles, second particles, and third particles were mixed in a mass ratio of 80:17.5:2.5 to prepare a positive electrode active material.

[0066] The first particles, second particles, third particles, and positive electrode active material in Example 1 were observed using a scanning electron microscope (Hitachi High-Technologies SU8230) at an accelerating voltage of 1.5 kV to obtain scanning electron microscope (SEM) images. The results are shown in Figures 3A to 3D. Figure 3A is an SEM image of the first particles, Figure 3B is an SEM image of the second particles, Figure 3C is an SEM image of the third particles, and Figure 3D is an SEM image of the positive electrode active material. As shown in Figure 3D, the positive electrode active material contains a mixture of first particles 10, second particles 20, and third particles 30.

[0067] [Example 2] A positive electrode active material was prepared in the same manner as in Example 1, except that the first particles, second particles, and third particles were mixed in a mass ratio of 80:16.5:3.5.

[0068] [Example 3] A positive electrode active material was prepared in the same manner as in Example 1, except that the first particles, the second particles, and the third particles were mixed in a mass ratio of 80:15:5.

[0069] [Example 4] A positive electrode active material was prepared in the same manner as in Example 1, except that the first particles, second particles, and third particles were mixed in a mass ratio of 80:10:10.

[0070] [Example 5] Li as the third particle 1.07 Ni 0.55 Co 0.35 Mn 0.10 A positive electrode active material was prepared in the same manner as in Example 1, except that third particles B of O2 (volume average particle size: 4.4 μm) were prepared.

[0071] [Comparative Example 1] A positive electrode active material was prepared in the same manner as in Example 1, except that only the first particles and the second particles were mixed in a mass ratio of first particles:second particles=80:20.

[0072] Comparative Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that only the first particles and the third particles were mixed at a mass ratio of 80:20.

[0073] Comparative Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that only the first particles and the third particles were mixed at a mass ratio of 95:5.

[0074] The particle size distribution of the first, second, and third particles used above was measured. The results are shown in Table 1.

[0075] [Table 1]

[0076] (DC internal resistance measurement in the low SOC region) The output characteristics of the positive electrode active materials of each Example and Comparative Example were evaluated by measuring DC-IR (direct current internal resistance). The measurement was performed as follows.

[0077] Preparation of the positive electrode 92 parts by mass of the above positive electrode active material, 3 parts by mass of acetylene black, and 5 parts by mass of PVDF (polyvinylidene fluoride) were dispersed and dissolved in NMP (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry. The obtained positive electrode slurry was applied to an aluminum foil current collector, dried, and then pressed with a roll press until the density of the positive electrode active material layer became 3.3 g / cm. 3 Compression molded to a size of 15cm 2 The positive electrode was obtained by cutting the sheet into pieces.

[0078] Preparation of the negative electrode A negative electrode slurry was prepared by dispersing 97.5 parts by mass of artificial graphite, 1.5 parts by mass of CMC (carboxymethyl cellulose), and 1.0 part by mass of SBR (styrene butadiene rubber) in water. The resulting negative electrode slurry was applied to a copper foil, dried, and then compression-molded to obtain a negative electrode.

[0079] Preparation of non-aqueous electrolyte A mixed solvent was prepared by mixing EC (ethylene carbonate) and EMC (ethyl methyl carbonate) at a volume ratio of 3:7. Lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent to a concentration of 1 mol / L, thereby preparing a non-aqueous electrolyte solution.

[0080] Preparation of evaluation battery Lead electrodes were attached to the positive and negative electrode current collectors, and the resulting materials were vacuum dried at 120°C. A separator was then placed between the positive and negative electrodes, and the resulting materials were housed in a bag-shaped laminate pack. This was then vacuum dried at 60°C to remove moisture adsorbed to each component. A nonaqueous electrolyte was then poured into the laminate pack under an argon atmosphere, and the pack was sealed to prepare a battery for evaluation.

[0081] aging The evaluation battery was subjected to constant-voltage / constant-current charging (cutoff current 0.005C) with a charging voltage of 4.2V and a charging current of 0.1C (1C is a current at which discharging is completed in 1 hour), and constant-current discharging with a discharge end voltage of 2.5V and a discharge current of 0.1C, allowing the nonaqueous electrolyte to become familiar with the positive and negative electrodes.

[0082] DC internal resistance measurement The aged test battery was placed in a 25°C environment and the DC internal resistance (DC-IR) was measured. After constant current charging to 95% SOC at a full charge voltage of 4.2V, the open-circuit potential at 95% SOC was measured. Pulse discharge at a specific current i was then performed for 10 seconds, and the voltage V after 10 seconds was measured. The DC internal resistance was calculated from the difference between the open-circuit potential and the voltage V after 10 seconds. The current i was set to 0.08A. The battery was then discharged at a constant current to 80%, 50%, 20%, 10%, and 5% SOC, and the DC internal resistance was measured repeatedly at each SOC.

[0083] (Measurement of discharge capacity) The discharge capacity of the positive electrode active materials of the Examples and Comparative Examples was evaluated as follows.

[0084] The same test batteries as those used for measuring the DC internal resistance were fabricated and aged in the same manner. After aging, the test batteries were charged at a constant voltage and constant current (cutoff current: 0.005 C) with a charge voltage of 4.2 V and a charge current of 0.1 C, followed by constant current discharge at a discharge cutoff voltage of 2.5 V and a discharge current of 0.1 C, and the discharge capacity was measured.

[0085] Table 2 shows the relative resistance and relative discharge capacity at SOC 5% in each example and comparative example when the resistance and discharge capacity of Comparative Example 1 at SOC 5% are set to 1 and 1, respectively.

[0086] [Table 2]

[0087] Based on Table 2, the relative resistance in the low SOC region of Examples 1 to 4 and Comparative Examples 1 and 2 is plotted against the content of the third particles in FIG. 1, and the relative discharge capacity is plotted in FIG. 2.

[0088] The results in Table 2 and Figure 1 show that Example 3, compared to Comparative Example 3, further improves output in the low SOC region while suppressing the decline in discharge capacity. This is thought to be due to the presence of second particles, which have a smaller volume average particle size than the first particles. It can be seen that the Examples containing first, second, and third particles improve output in the low SOC region while suppressing the decline in discharge capacity. Furthermore, in the Examples, the discharge capacity tends to decrease almost linearly with increasing third particle content. Meanwhile, for resistance in the low SOC region, the degree of improvement relative to the third particle content is large when the third particle content is low, but the degree of improvement relative to the third particle content tends to decrease as the third particle content increases. This shows that by including first, second, and third particles and limiting the amount of third particles to a certain level or less, the effect of improving output in the low SOC region and the effect of suppressing the decline in discharge capacity can be further achieved.

[0089] The disclosure of Japanese Patent Application No. 2020-141364 (filing date: August 25, 2020) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. first particles made of a first lithium transition metal composite oxide having a layered structure, in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.7 or more and less than 1; second particles made of a second lithium transition metal composite oxide having a layered structure, in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.33 or more and less than 1, and the ratio of the number of moles of cobalt to the total number of moles is 0.01 or more and 0.35 or less, and the ratio of the volume average particle size of the first particles to the volume average particle size of the second particles (first particles / second particles) is 1.3 or more and 10 or less; and third particles made of a third lithium transition metal composite oxide having a layered structure, in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is 0.4 or more and 0.6 or less, and the ratio of the number of moles of cobalt to the total number of moles is 0.35 or more and 0.55 or less, a content of the first particles is 60% by mass or more and less than 100% by mass with respect to the total of the first particles, the second particles, and the third particles, A positive electrode active material in which the content of the third particles is 10 mass % or less with respect to the total of the first particles, the second particles, and the third particles.

2. The positive electrode active material according to claim 1 , wherein the content of the third particles is 8 mass % or less with respect to the total of the first particles, the second particles, and the third particles.

3. 3. The positive electrode active material according to claim 1, wherein the content of the first particles is 70% by mass or more and 90% by mass or less, and the content of the second particles is 1% by mass or more and less than 30% by mass, relative to the total of the first particles, the second particles, and the third particles.

4. The positive electrode active material according to claim 1 , wherein the third particles have a volume average particle size smaller than the volume average particle size of the first particles.

5. 5. The cathode active material according to claim 1, wherein the first particles have a volume average particle size of 6 μm or more and 30 μm or less, the second particles have a volume average particle size of 1 μm or more and 10 μm or less, and the third particles have a volume average particle size of 1 μm or more and 10 μm or less.

6. 6. The positive electrode active material according to claim 1, wherein the first particles have a volume average particle size of 8 μm or more and 20 μm or less, the second particles have a volume average particle size of 2 μm or more and less than 8 μm, and the third particles have a volume average particle size of 2 μm or more and less than 8 μm.

7. The positive electrode active material according to claim 1 , wherein the first lithium transition metal composite oxide has a composition represented by the following formula (1): Li ｐ１ Ni ｘ１ Co ｙ１ M １ ｚ１ M ２ ｗ１ O α１ (1) Here, p1, x1, y1, z1, w1, and α1 satisfy 0.95≦p1≦1.5, 0.7≦x1<1, 0<y1≦0.3, 0<z1≦0.3, 0≦w1≦0.02, x1+y1+z1+w1=1, and 1.5≦α1≦2.

5. M １ represents at least one of Mn and Al. ２ represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu.

8. The positive electrode active material according to claim 1 , wherein the second lithium transition metal composite oxide has a composition represented by the following formula (2): Li ｐ２ Ni ｘ２ Co ｙ２ M １ ｚ２ M ２ ｗ２ O α２ (2) Here, p2, x2, y2, z2, w2, and α2 satisfy 0.95≦p2≦1.5, 0.33≦x2<1, 0.01≦y2≦0.35, 0≦z2≦0.6, 0≦w2≦0.02, x2+y2+z2+w2=1, and 1.5≦α2≦2.

5. M １ represents at least one of Mn and Al. ２ represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu.

9. The positive electrode active material according to claim 1 , wherein the third lithium transition metal composite oxide has a composition represented by the following formula (3): Li ｐ３ Ni ｘ３ Co ｙ３ M １ ｚ３ M ２ ｗ３ O α３ (3) Here, p3, x3, y3, z3, w3, and α3 satisfy 0.95≦p3≦1.5, 0.4≦x3≦0.6, 0.35≦y3≦0.55, 0≦z3≦0.25, 0≦w3≦0.02, x3+y3+z3+w3=1, and 1.5≦α3≦2.

5. M １ represents at least one of Mn and Al. ２ represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu.

10. A positive electrode for a non-aqueous electrolyte secondary battery, comprising the positive electrode active material according to claim 1 .

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