Positive electrode active material

Abstract

To reduce the initial resistance of a positive electrode active material.SOLUTION: A positive electrode active material includes a secondary particle. The secondary particle includes crystallites of 3-20. Each of the crystallites has a maximum Feret's diameter of 1 μm or more. An open pore is formed in at least one of the crystallite and the secondary particle. The open pore has an opening diameter of 10 to 500 nm. A relationship of 0.50≤L / D is satisfied. The L represents a path length of the opening pore. The D represents a maximum Feret's diameter of the secondary particle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material. [Background technology]

[0002] WO 2022 / 137360 discloses a lithium composite oxide sintered plate having a specific range of porosity, average pore diameter, and interface length. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 137360 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, a positive electrode active material is synthesized, for example, as follows: A precursor (such as a metal hydroxide) is synthesized; A mixture of the precursor and a lithium (Li) compound is heat-treated; This heat treatment is also called "calcination." By calcination, Li penetrates into the precursor, and a positive electrode active material can be synthesized.

[0005] The precursor is a secondary particle. The secondary particle contains multiple crystallites (primary particles). During firing, the crystallites also grow. This growth causes the secondary particles to become densely packed. This can hinder the movement of Li ions and reduce the reaction area. The small reaction area can increase the initial resistance.

[0006] The objective of the present disclosure is to reduce the initial resistance. [Means for solving the problem]

[0007] 1. The positive electrode active material contains secondary particles. The secondary particles contain 3 to 20 crystallites. Each of the crystallites has a maximum Feret diameter of 1 μm or more. Open pores are formed in at least one of the crystallites and the secondary particles. The open pores have an opening diameter of 10 to 500 nm. The relationship "0.50≦L / D" is satisfied. "L" represents the path length of the open pores. "D" represents the maximum Feret diameter of the secondary particles.

[0008] The open pores can serve as entrances and exits for Li ions into the secondary particles. In the present disclosure, long micropores are formed in the secondary particles. That is, the opening diameter of the open pores is 10 to 500 nm. Furthermore, the ratio (L / D) of the path length of the open pores to the maximum Feret diameter of the secondary particles is 0.5 or more. This is expected to promote the reaction between the crystallites and Li ions inside the secondary particles. That is, an increase in the reaction area is expected to reduce the initial resistance.

[0009] 2. The positive electrode active material described in the above item "1" may include, for example, the following configuration: The relationship "0.50≦L / D≦1.3" is satisfied.

[0010] The upper limit of the ratio (L / D) is arbitrary, and may be, for example, 1.3.

[0011] 3. The positive electrode active material described in the above item "1" or "2" may include, for example, the following configuration: The open pores are open between the crystallites.

[0012] In the secondary particles, the open pores may be, for example, gaps between crystallites (primary particles). For example, as in "4" below, open pores may be formed in the crystallites themselves. The open pores may include both paths that pass through the gaps between the crystallites and paths that pass through the crystallites.

[0013] 4. The positive electrode active material according to any one of the above items "1" to "3" may have, for example, the following configuration: The open pores are open to the surface of the crystallite.

[0014] 5. The positive electrode active material according to any one of the above items "1" to "4" may have, for example, the following configuration: The cross section of the secondary particle includes a central region. The central region has a shape similar to the outline of the secondary particle. The central region shares a geometric center with the outline of the secondary particle. The maximum Feret diameter of the central region is 0.5D. At least a portion of the open pores pass through the central region.

[0015] The open pores passing through the central region of the secondary particles are expected to reduce the initial resistance.

[0016] Hereinafter, one embodiment of the present disclosure (hereinafter may be abbreviated as "this embodiment") and one example of the present disclosure (hereinafter may be abbreviated as "this example") will be described. However, this embodiment and this example do not limit the technical scope of the present disclosure. This embodiment and this example are illustrative in all respects. This embodiment and this example are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configurations may be extracted from this embodiment and arbitrarily combined. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a conceptual diagram showing a positive electrode active material according to the present embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing a central region and a peripheral region in the present embodiment. [Figure 3] 1 is a schematic flowchart of a method for producing a positive electrode active material according to the present embodiment. [Figure 4] 10 is a table showing experimental results. DETAILED DESCRIPTION OF THE INVENTION

[0018] -Terms and phrases- Geometric terms should not be interpreted in their strict sense. Examples of geometric terms include "parallel," "perpendicular," and the like. For example, "parallel" may deviate slightly from the strict meaning of "parallel." For example, directions, angles, distances, etc. may be relatively displaced as long as substantially the same function is obtained. Geometric terms may include, for example, tolerances, errors, etc. in design, work, manufacturing, etc. The dimensional relationships in each figure may not match the actual dimensional relationships. The dimensional relationships in each figure may be changed to aid the reader's understanding. For example, length, width, thickness, etc. may be changed. Some components may be omitted.

[0019] Numerical ranges such as "m to n%" include the upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% but less than n%." "Equal to or more" and "equal to or less" are expressed by inequality symbols with equality signs "≦, ≧." "More than" and "less than" are expressed by inequality symbols without equality signs "<, >."

[0020] All numerical values ​​are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximate values ​​that may vary depending on the application of the subject technology. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be average values ​​of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, such as those associated with the detection limits of the measuring device.

[0021] For example, the phrase "at least one of A and B" includes "A or B" as well as "A and B." "At least one of A and B" can also be written as "A and / or B."

[0022] "Crystallite" refers to the smallest unit of a particle, a solid particle with boundaries between particles that cannot be further subdivided. "Secondary particle" refers to an aggregate of two or more crystallites. The crystallites that form a secondary particle may also be referred to as primary particles.

[0023] FIG. 1 is a conceptual diagram illustrating a positive electrode active material according to this embodiment. The "maximum Feret diameter (D1) of crystallite 1," "maximum Feret diameter (D) of secondary particle 2," "opening diameter (d) of open pore 3," and "path length (L) of open pore 3" are all measured in a cross-sectional SEM (Scanning Electron Microscope) image of the secondary particle 2. The observation magnification can be adjusted depending on the particle size. The observation magnification may be, for example, approximately 1000x. A cross-sectional sample of the particle can be prepared by a conventionally known method. For example, a cross-sectional sample may be prepared using a cross-section polisher (CP) or a focused ion beam (FIB). Various dimensions in the image are measured using image analysis software. For example, "ImageJ Fiji" or the like may be used. Note that "ImageJ Fiji" is merely an example. Any image analysis software having equivalent functions to "ImageJ Fiji" may be used. For example, image analysis software included with various SEM devices may be used.

[0024] The "maximum Feret diameter" indicates the distance between the two most distant points on the outline of a particle in an SEM image.

[0025] In the cross-sectional SEM image of the secondary particle 2, the surface of the secondary particle 2 is observed. The pores that are in communication with the outside air are "open pores 3." The diameter of the opening of the open pore 3 is the "opening diameter (d)." "Communicating pores" refer to open pores 3 that have multiple openings. In the case of communicating pores, the arithmetic mean value of the multiple opening diameters is considered to be the "opening diameter (d)."

[0026] When multiple open pores 3 are formed within a secondary particle 2, the longest path length is considered to be the "path length (L)." When the open pores branch or merge, the sum of all path lengths is considered to be the "path length (L)."

[0027] The stoichiometric composition formula indicates a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to a compound having a substance ratio (molar ratio) of "Al / O=2 / 3." Unless otherwise specified, "Al2O3" indicates a compound containing Al and O in any molar ratio. For example, the compound may be doped with a trace element. A portion of the Al and O may be substituted with another element.

[0028] -Cathode active material- Hereinafter, the positive electrode active material in this embodiment may be abbreviated as "the positive electrode active material." The positive electrode active material is for use in a secondary battery. That is, the present disclosure also provides a "positive electrode including the positive electrode active material" and a "secondary battery including the positive electrode active material." The secondary battery may be, for example, a liquid battery, a polymer battery, or an all-solid-state battery. The secondary battery may be, for example, a monopolar battery or a bipolar battery.

[0029] The positive electrode active material is a powder. The D50 of the positive electrode active material may be, for example, 0.1 μm or more, 1 μm or more, 5 μm or more, or 10 μm or more. The D50 may be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. The D50 can be measured, for example, by laser diffraction or the like.

[0030] -Secondary particles- As shown in FIG. 1 , the present positive electrode active material includes secondary particles 2. The secondary particles 2 include 3 to 20 crystallites 1. If the number of crystallites 1 in the secondary particles 2 is less than 3, the desired initial resistance may not be obtained. This is thought to be because the reaction area is small. If the number of crystallites 1 in the secondary particles 2 exceeds 20, durability may be reduced, for example. The number of crystallites 1 included in the secondary particles 2 may be, for example, 15 or less, 10 or less, or 5 or less. The number of crystallites 1 included in the secondary particles 2 may be, for example, 5 or more, 10 or more, or 15 or more.

[0031] The maximum Feret diameter (D) of the secondary particles 2 may be, for example, 2 to 30 μm. The maximum Feret diameter (D) of the secondary particles 2 may be, for example, 3 μm or more, 6 μm or more, 9 μm or more, 12 μm or more, 15 μm or more, 18 μm or more, 21 μm or more, 24 μm or more, or 27 μm or more. The maximum Feret diameter (D) of the secondary particles 2 may be, for example, 27 μm or less, 24 μm or less, 21 μm or less, 18 μm or less, 15 μm or less, 12 μm or less, 9 μm or less, or 6 μm or less.

[0032] -Crystallite- The crystallite 1 has a maximum Feret diameter (D1) of 1 μm or more. The maximum Feret diameter (D1) of the crystallite 1 may be, for example, 1.5 μm or more, 2 μm or more, or 2.5 μm or more. The maximum Feret diameter (D1) of the crystallite 1 may be, for example, 3 μm or less, 2.5 μm or less, 2 μm or less, or 1.5 μm or less.

[0033] The crystallite 1 may have an aspect ratio of, for example, 1 to 2. The aspect ratio may be, for example, 1.8 or less, 1.6 or less, 1.4 or less, or 1.2 or less. The aspect ratio may be, for example, 1.2 or more, 1.4 or more, 1.6 or more, or 1.8 or more. The "aspect ratio" is the ratio of the major axis diameter to the minor axis diameter. The major axis diameter indicates the maximum Feret diameter. The minor axis diameter indicates the minimum Feret diameter.

[0034] -Open pores- Open pores 3 are formed in at least one of the crystallites 1 and the secondary particles 2. There may be a single open pore 3 or multiple open pores 3. One open pore 3 may branch. Multiple open pores 3 may merge. The number of open pores 3 contained in one secondary particle 2 may be, for example, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. The number of open pores 3 may be, for example, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, or 4 or less.

[0035] The open pores 3 may be open to the surface of the crystallite 1, for example. The open pores 3 may penetrate the crystallite 1, for example. The open pores 3 may terminate within the crystallite 1, for example. The open pores 3 may open between the crystallites 1, for example. The open pores 3 may penetrate the secondary particle 2, for example. The open pores 3 may terminate within the secondary particle 2, for example. The open pores 3 may be interconnected holes, for example. The interconnected holes have multiple openings within the secondary particle 2 (or the crystallite 1). Within the secondary particle 2, the open pores 3 do not have to pass through the crystallite 1. For example, the open pores 3 may be gaps between the crystallites 1. When multiple open pores 3 are formed within one secondary particle 2, both open pores 3 that pass through the crystallite 1 and open pores 3 that are gaps between the crystallites 1 may be formed. One open pore 3 may include both a path that passes through the crystallites 1 and a path that passes through the gaps between the crystallites 1 .

[0036] The open pores 3 have an opening diameter (d). The opening diameter (d) is 10 to 500 nm. If the opening diameter (d) is less than 10 nm, the desired initial resistance may not be obtained. If the opening diameter (d) exceeds 500 nm, for example, cracks may occur in the secondary particles 2, originating from the open pores 3. The opening diameter (d) may be, for example, 25 nm or more, 50 nm or more, 75 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, or 450 nm or more. The opening diameter (d) may be, for example, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, 150 nm or less, 100 nm or less, 75 nm or less, 50 nm or less, or 25 nm or less.

[0037] The open pores 3 have a path length (L). The ratio (L / D) of the path length (L) to the maximum Feret diameter (D) of the secondary particles 2 is 0.50 or more. When the ratio (L / D) is 0.50 or more, a reduction in initial resistance is expected. The ratio (L / D) may be, for example, 0.72 or more, 1.1 or more, or 1.3 or more. The ratio (L / D) may be, for example, 5 or less, 4 or less, 3 or less, 2 or less, 1.5 or less, 1.3 or less, 1.1 or less, or 0.72 or less.

[0038] FIG. 2 is a conceptual diagram showing the central region and peripheral region in this embodiment. The cross section of the secondary particle 2 includes a central region 2c and a peripheral region 2p. The central region 2c has a shape similar to the outline of the secondary particle 2. The central region 2c shares a geometric center with the outline of the secondary particle 2. The maximum Feret diameter of the central region 2c is 0.5D. The remaining portion of the cross section of the secondary particle 2 excluding the central region 2c is the peripheral region 2p. The peripheral region 2p surrounds the central region 2c.

[0039] For example, the open pores 3 may extend toward the central region 2c. For example, the open pores 3 may extend toward the geometric center of the secondary particle 2. For example, at least a portion of the open pores 3 may pass through the central region 2c. For example, the open pores 3 may pass through the central region 2c. The open pores 3 passing through the central region 2c of the secondary particle 2 may reduce the initial resistance. The open pores 3 may terminate within the peripheral region 2p. The open pores 3 may terminate within the peripheral region 2p after passing through the central region 2c. The maximum Feret diameter of the central region 2c may be, for example, 0.4D, 0.3D, 0.2D, or 0.1D. The smaller the maximum Feret diameter of the central region 2c is set, the more the central region 2c may be limited to the particle center. The closer the open pores 3 pass to the particle center, the more the initial resistance may be reduced.

[0040] The open pores 3 may, for example, extend linearly. The open pores 3 may, for example, extend curvedly. The curved shape of the open pores 3 may reduce the initial resistance. The open pores 3 may, for example, have a linearity of more than 1.5. The linearity may, for example, be 1.6 or more, 1.8 or more, 2 or more, 2.2 or more, or 2.4 or more. The linearity may, for example, be 5 or less, 4 or less, 3 or less, or 2 or less.

[0041] The "linearity" of the open pores 3 is calculated by the following formula. The closer the linearity is to 1, the more linear the open pores 3 are considered to be. In other words, the farther the linearity is from 1, the more curved the open pores 3 are considered to be. S=L0 / L1 S:Straightness L0: Path length of open pore 3 in cross-sectional SEM image L1: Linear distance between the openings of the open pores 3 in the cross-sectional SEM image (linear distance between the inlet and outlet)

[0042] -Chemical composition- Crystallite 1 may contain, for example, a lithium metal composite oxide. Crystallite 1 may be made of, for example, a lithium metal composite oxide. The lithium metal composite oxide may have, for example, a layered rock salt structure. The layered rock salt structure is also referred to as an "α-NaFeO2 structure." The space group of the layered rock salt structure is "R-3m." The crystal structure can be identified by powder XRD (X-ray diffraction).

[0043] The lithium metal composite oxide may have any chemical composition, for example, a composition represented by the following general formula: Li 1-a MO2 In the formula, the relationship "-0.5≦a≦0.5" is satisfied. "M" includes at least one selected from the group consisting of Ni, Co, Mn, and Al.

[0044] The lithium metal composite oxide may be, for example, a lithium nickel composite oxide. The composition of the lithium nickel composite oxide may be represented by, for example, the following general formula. The compound represented by the following general formula may also be referred to as "NCM". Li 1-a Ni x Co y Mn z O2 In the formula, the relationships of "-0.5 ≦ a ≦ 0.5", "0 < x < 1", "0 < y < 1", "0 < z < 1", and "x + y + z = 1" are satisfied. For example, relationships such as "0.5 ≦ x < 1", "0 < y ≦ 0.25", and "0 < z ≦ 0.25" may be satisfied.

[0045] The composition of the lithium nickel composite oxide may be represented by, for example, the following general formula. The compound represented by the following general formula may also be referred to as "NCA". Li 1-a Ni x Co y Al z O2 In the formula, the relationships of "-0.5 ≦ a ≦ 0.5", "0 < x < 1", "0 < y < 1", "0 < z < 1", and "x + y + z = 1" are satisfied. For example, relationships such as "0.5 ≦ x < 1", "0 < y ≦ 0.25", and "0 < z ≦ 0.25" may be satisfied.

[0046] A dopant may be added to the lithium metal composite oxide. The dopant may be diffused throughout the particle or distributed locally. For example, the dopant may be unevenly distributed on the particle surface. The dopant may be a substitutional solid solution atom or an interstitial solid solution atom. The amount of dopant added (substance amount fraction relative to the entire positive electrode active material) may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. One or more dopants may be added. Two or more dopants may form a composite. The dopant may include at least one selected from the group consisting of, for example, B, C, N, halogen, Si, Na, Mg, Al, Mn, Co, Cr, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Pb, Bi, Sb, Sn, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and actinides.

[0047] -Method of manufacturing positive electrode active material- 3 is a schematic flowchart of a method for producing a positive electrode active material according to this embodiment. Hereinafter, the method for producing a positive electrode active material according to this embodiment may be abbreviated as "this method." This method includes "(a) preparation of a precursor," "(b) first heat treatment," "(c) crushing," "(d) granulation," and "(e) second heat treatment."

[0048] -(a) Preparation of precursor- The present manufacturing method includes preparing a precursor. The precursor may include, for example, a metal hydroxide. The metal hydroxide may be synthesized, for example, by a coprecipitation method. For example, a sulfate may be prepared. The sulfate may include, for example, at least one selected from the group consisting of NiSO4, CoSO4, MnSO4, and Al2(SO4)3. A raw material solution is prepared by dissolving the sulfate in water. The concentration of the raw material solution may be, for example, 10 to 50% by mass fraction. A metal hydroxide precipitate may be generated by dropping the raw material solution into an alkaline aqueous solution. For example, the precipitate (metal hydroxide) may be collected by filtration. After collection, the metal hydroxide may be washed with water. After washing with water, the metal hydroxide may be dried.

[0049] The precursor is mixed with a Li compound. For example, grinding and mixing may be performed in a mortar or the like. The Li compound refers to a compound containing Li. The Li compound may include, for example, at least one selected from the group consisting of LiOH and Li2CO3. The Li compound is a Li source for the lithium metal composite oxide. The ratio of the substance amount of Li to the substance amount of the metal hydroxide may be, for example, 0.5 or more, 0.75 or more, 1 or more, 1.1 or more, or 1.25 or more. The ratio may be, for example, 1.5 or less, 1.25 or less, 1.1 or less, 1 or less, or 0.75 or less.

[0050] -(b) First heat treatment- This manufacturing method includes subjecting a mixture of a precursor and a Li compound to a first heat treatment. In this manufacturing method, any heat treatment device or firing furnace may be used. For example, a muffle furnace, an electric furnace, or the like may be used. The first heat treatment may be carried out, for example, in an oxygen atmosphere. The same applies to the second heat treatment described below.

[0051] The temperature of the first heat treatment may be, for example, 1000 to 1300°C. The temperature of the first heat treatment may be, for example, 1100°C or higher, or 1200°C or higher. The temperature of the first heat treatment may be, for example, 1200°C or lower, or 1100°C or lower. The time of the first heat treatment may be, for example, 2 to 8 hours. The time of the first heat treatment may be, for example, 3 hours or higher, 4 hours or higher, or 5 hours or higher. The time of the first heat treatment may be, for example, 7 hours or lower, 6 hours or lower, or 5 hours or lower.

[0052] -(c) Crushing- The method includes crushing the material after the first heat treatment. For example, crushing may be performed using a crusher. Any crusher (e.g., a jet mill, etc.) may be used.

[0053] -(d) Granulation- This manufacturing method includes granulating the crushed material to form secondary particles 2. Through the crushing and granulation processes, long open pores 3 can be formed in the secondary particles 2. The open pores 3 may also be formed in a curved shape. For example, granulation may be performed using a spray dryer. That is, the secondary particles 2 may be formed by spray-drying the slurry. For example, the ratio (L / D) may be adjusted based on the solid content of the slurry. The solid content of the slurry may be, for example, 5% or more, 10% or more, 20% or more, or 30% or more, in mass fraction. The solid content of the slurry may be, for example, less than 40%, 35% or less, 30% or less, 20% or less, or 10% or less. The dispersion medium of the slurry may contain, for example, isopropyl alcohol (IPA).

[0054] -(e) Second heat treatment- The present production method includes subjecting the granulated secondary particles 2 to a second heat treatment. The second heat treatment can be carried out at a temperature lower than that of the first heat treatment. The temperature difference between the second heat treatment and the first heat treatment may be, for example, 600°C or higher, 700°C or higher, 800°C or higher, or 900°C or higher. The temperature difference between the second heat treatment and the first heat treatment may be, for example, 900°C or lower, 800°C or lower, 700°C or lower, or 600°C or lower.

[0055] The temperature of the second heat treatment may be, for example, 200°C or more, 300°C or more, or 400°C or more. The temperature of the second heat treatment may be, for example, 600°C or less, 500°C or less, or 400°C or less. The time of the second heat treatment may be, for example, 2 to 8 hours. The time of the second heat treatment may be, for example, 3 hours or more, 4 hours or more, or 5 hours or more. The time of the second heat treatment may be, for example, 7 hours or less, 6 hours or less, or 5 hours or less. The total time of the second heat treatment and the first heat treatment may be, for example, 8 hours or more, 9 hours or more, or 10 hours or more. The total time of the second heat treatment and the first heat treatment may be, for example, 12 hours or less, 11 hours or less, or 10 hours or less.

[0056] -others- In this manner, secondary particles 2 having open pores 3 can be synthesized. In another embodiment, the open pores 3 may be formed, for example, by pressing a needle-shaped tool into the secondary particles 2. This method can also form open pores 3 that open to the surface of the crystallite 1. This method can also form open pores 3 that extend linearly. [Example]

[0057] -Production of positive electrode active material- No.1 FIG. 4 is a table showing the experimental results. In No. 1, a positive electrode active material was produced by the first synthesis method. NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to form a raw material solution. In the raw material solution, the molar ratio of Ni, Co, and Mn was "Ni / Co / Mn=8 / 1 / 1." The concentration of the raw material solution was 30% by mass fraction.

[0058] Ammonia water was placed in a reaction vessel. While stirring the ammonia water with a stirrer, the atmosphere in the reaction vessel was replaced with nitrogen. NaOH was then added to the reaction vessel to form a reaction liquid.

[0059] The raw material solution and ammonia water were added dropwise to the reaction solution so that the pH of the reaction solution remained within a certain range, thereby forming a precipitate (metal hydroxide). The reaction solution was filtered, and the metal hydroxide was collected. The metal hydroxide was dispersed in ion-exchanged water, forming a dispersion. The dispersion was thoroughly stirred with a spatula; that is, the metal hydroxide was washed with water. After washing with water, the dispersion was filtered, and the metal hydroxide was collected. The metal hydroxide was dried at 120°C for 16 hours, forming a precursor.

[0060] In a mortar, the precursor and a Li compound (Li2CO3) were mixed to form a mixture.

[0061] The mixture was subjected to heat treatment in a muffle furnace to obtain a fired product. The heat treatment conditions were as follows: Atmosphere: Oxygen atmosphere Temperature: 800 to 1100°C Duration: 10 hours

[0062] The fired product was pulverized using a jet mill. In this manner, a positive electrode active material (secondary particles) was produced.

[0063] No.2 In No. 2 to No. 6, positive electrode active materials were produced by the second synthesis method. Precursors were prepared in the same manner as in No. 1. The precursors were mixed with a Li compound (Li2CO3) to form mixtures.

[0064] The mixture was subjected to a first heat treatment in a muffle furnace to obtain a fired product. The conditions for the first heat treatment were as follows: Atmosphere: Oxygen atmosphere Temperature: 1000 to 1300°C Duration: 5 hours

[0065] The fired material was crushed using a jet mill to obtain a crushed material. The crushed material was dispersed in a dispersion medium to form a slurry. The solid content of the slurry was 40%. The slurry was spray-dried using a spray dryer to obtain secondary particles. The operating conditions of the spray dryer were as follows: Spray dryer: "MDL-050B", manufactured by GF Drying temperature: (inlet) 200℃, (exhaust) 100℃ Nozzle pressure: 0.5MPa Flow rate: 40L / min

[0066] The secondary particles were subjected to a second heat treatment in a muffle furnace to produce a positive electrode active material. The conditions for the second heat treatment were as follows: Atmosphere: Oxygen atmosphere Temperature: 400℃ Duration: 5 hours

[0067] No.3 to No.6 As shown in FIG. 4, each positive electrode active material was produced in the same manner as No. 2, except that the solid content of the slurry was changed.

[0068] -evaluation- A cylindrical lithium-ion secondary battery (evaluation cell) was manufactured. The initial resistance of the evaluation cell was measured. The evaluation cell had the following configuration:

[0069] Power generating element: Wound type Positive electrode: Positive electrode active material / AB / PVDF=88 / 10 / 2 (mass ratio) Negative electrode: Negative electrode active material (natural graphite), CMC, SBR Electrolyte: LiPF6 (1 mol / L), EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0070] The positive and negative electrodes were manufactured by coating the surface of the substrate (metal foil) with the slurry. An Allgood film applicator (with film thickness adjustment function) was used as the coating device. After coating the slurry, the coating was dried at 80°C for 5 minutes.

[0071] -result- The initial resistance in Figure 4 is a relative value when the initial resistance of No. 1 is considered to be 100%. When the ratio (L / D) is 0.50 or more, there is a tendency for the initial resistance to decrease. The larger the ratio (L / D), the more the initial resistance tends to decrease. [Explanation of symbols]

[0072] 1 crystallite, 2 secondary particle, 2c central region, 2p peripheral region, 3 open pore.

Claims

1. Contains secondary particles, the secondary particles contain 3 to 20 crystallites; Each of the crystallites has a maximum Feret diameter of 1 μm or more, open pores are formed in at least one of the crystallites and the secondary particles, the open pores have an opening diameter of 10 to 500 nm, 0.50≦L / D The relationship is satisfied, L represents the path length of the open pore, and The D indicates the maximum Feret diameter of the secondary particles, Cathode active material.

2. 0.50≦L / D≦1.3 The relationship is satisfied, The positive electrode active material according to claim 1 .

3. The open pores are open between the crystallites. The positive electrode active material according to claim 1 .

4. The open pores are open to the surface of the crystallite. The positive electrode active material according to claim 1 .

5. a cross section of the secondary particle includes a central region; the central region has a shape similar to the outline of the secondary particle, the central region shares a geometric center with the outline of the secondary particle, The maximum Feret diameter of the central region is 0.5D, and At least some of the open pores pass through the central region. The positive electrode active material according to claim 1 .

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