Method for producing lithium transition metal composite oxide

Abstract

A method for producing a lithium transition metal composite oxide according to the present invention comprises: a step for preparing a first mixture that contains a lithium-containing compound and a transition metal compound; a step for obtaining a compressed body by compressing the first mixture at least once; a step for obtaining a molded body by molding at least the compressed body; and a step for obtaining a fired body by firing the molded body.

Description

Technical Field

[0001] The present disclosure relates to a method for producing a lithium transition metal composite oxide.

Background Art

[0002] A secondary battery typified by a lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes, as a positive electrode active material, for example, a lithium-containing composite oxide. As the lithium-containing composite oxide, for example, lithium nickelate, which is advantageous for increasing the capacity, is used, and a part of nickel is replaced with a different metal for the purpose of further improving the battery performance.

[0003] Patent Document 1 discloses, as a method for producing a lithium nickel composite oxide, a method in which a mixed powder of a lithium compound and a compound mainly composed of a transition metal is molded, and the molded body is filled on a porous body of a reaction vessel provided on a support table of a firing furnace having an electric heater to form a molded body filling layer. An oxidizing gas such as air is forcibly passed through the filling layer at an empty tower velocity of a certain level or higher by an air pump, a flow regulator, and an air supply pipe connecting a preheating heater for compressing the air, and the gas passing through the filling layer is discharged from a ventilation port.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] When molding a mixed powder of a lithium compound and a transition metal compound as in Patent Document 1, if the strength of the molded body is low, a part of the molded body collapses, and the productivity of the positive electrode active material decreases. Therefore, it is required to obtain a molded body with sufficient pressure. However, if the pressure applied to the mixed powder is increased, cracks occur in the particles of the transition metal compound, and the productivity of the positive electrode active material decreases.

[0006] One aspect of the present disclosure relates to a method for producing a lithium transition metal composite oxide, including a step of preparing a first mixture containing a lithium-containing compound and a transition metal compound, a step of compressing the first mixture at least once to obtain a compressed body, a step of shaping at least the compressed body to obtain a shaped body, and a step of firing the shaped body to obtain a fired body.

[0007] According to the present disclosure, it is possible to obtain a shaped body having sufficient strength while suppressing cracking of particles of the transition metal compound, thereby improving the productivity of the positive electrode active material.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] The method for producing a lithium transition metal composite oxide according to an embodiment of the present disclosure includes a first step of obtaining a first mixture containing a lithium-containing compound and a transition metal compound, a second step of compressing the first mixture at least once to obtain a compressed body, a third step of shaping at least the compressed body to obtain a shaped body, and a fourth step of firing the shaped body to obtain a fired body (i.e., a lithium transition metal composite oxide).

[0010] By creating a shaped body from a mixture of a lithium-containing compound and a transition metal compound and firing the shaped body, the contact points between particles in the shaped body increase, the thermal conductivity of the shaped body improves, which is advantageous for the progress of firing. The higher the strength (e.g., crushing strength) of the shaped body, the more the contact points between particles increase, and the thermal conductivity of the shaped body also improves.

[0011] If the strength of the formed body is low, a part of the formed body may break during handling such as conveyance of the formed body, resulting in crushed materials, insufficient contact between particles, and a decrease in the thermal conductivity of the formed body. In addition, due to the moisture generated from the formed body during firing, a part of the formed body is likely to break, and the contact between particles is likely to be insufficient. Further, when the formed body breaks, a sparse part and a dense part are generated, and the degree of firing is likely to vary. To avoid such problems and improve the crystallinity of the lithium transition metal composite oxide, it is important to increase the strength of the formed body.

[0012] However, if an attempt is made to ensure sufficient strength of the formed body, cracks will occur in the particles of the transition metal compound due to the application of pressure during forming, and the productivity of the positive electrode active material will decrease.

[0013] Therefore, in this embodiment, by performing the first to third steps, pressure is applied to the first mixture containing the lithium-containing compound and the transition metal compound in at least two stages. As a result, by applying an appropriate pressure to the first mixture, the strength of the formed body can be sufficiently increased. Therefore, cracking of the particles of the transition metal compound can be suppressed.

[0014] Hereinafter, description will be made with reference to FIGS. 1 and 2.

[0015] In the first step (S1) of preparing the first mixture, a lithium-containing compound and a transition metal compound, which are raw materials of the lithium transition metal composite oxide, are prepared and mixed. The method of mixing the lithium-containing compound and the transition metal compound is not particularly limited. For example, by dry-mixing the lithium-containing compound and the transition metal compound, a first mixture in an advantageous state for use in subsequent steps can be obtained. In the dry mixing of the lithium-containing compound and the transition metal compound, the lithium-containing compound and the transition metal compound are mixed without using a dispersion medium such as water.

[0016] In the second step (S2) of obtaining a compressed body by compressing the first mixture at least once, a pressure for aggregating the lithium-containing compound and the transition metal compound in the first mixture is applied. The compressed body obtained in the second step may be a massive material in which a plurality (for example, 1000 or more) of particles of the transition metal compound are aggregated. Note that the compressed body includes not only the compressed body obtained by compressing the first mixture only once, but also the compressed body obtained by compressing the first mixture two or more times. The compressed body includes crushed materials of the compressed body. In addition, the subordinate concept of the compressed body obtained by compressing the first mixture two or more times includes a molded body, and also includes crushed materials of the molded body.

[0017] In the second step, the method of compressing the first mixture is not particularly limited. Compression of the first mixture can be performed using, for example, a briquetting machine, a pelletizing machine, a granulating machine, a tableting machine, or the like. That is, the compressed body itself may be a molded body (hereinafter, also referred to as a preliminary molded body) compressed with an appropriate pressure. However, the pressure when forming the preliminary molded body is preferably limited to a pressure at which cracking of the particles constituting the first mixture is suppressed.

[0018] Compression of the first mixture may be performed using, for example, nip rolls. By passing the first mixture through the nip between a pair of rolls, for example, a flaky compressed body can be obtained.

[0019] Compression or compression molding of the first mixture is preferably performed dry. In dry compression, the mixture is compressed without using a dispersion medium such as water.

[0020] The shape or property of the compressed body is not particularly limited, and may be, for example, a granular shape, a flaky shape, a spherical shape, an ellipsoidal shape (prolate spheroid), a cylindrical shape, an elliptical cylindrical shape, a prismatic shape, a disc shape, an almond shape, or the like.

[0021] The size of the compressed body is not particularly limited, but in order to facilitate molding in the third step, it is desirable that the maximum diameter be 5 mm or less. When the compressed body is an amorphous massive material, it may be sized to coarse particles that pass through, for example, a 5 mm mesh.

[0022] The density (d1) of the compressed body is, for example, 1 g / cm 3 or more and 1.8 g / cm 3 or less, or 1.4 g / cm 3 or more and 1.7 g / cm 3 or less. When the density of the compressed body is 1 g / cm 3 or more, a compressed body that is difficult to crush can be obtained. When the density of the compressed body is 1.8 g / cm 3 or less, cracks in the particles of the transition metal compound are less likely to occur when obtaining the compressed body.

[0023] The third step (S3) of obtaining the molded body may be any step of obtaining the molded body from the compressed body by applying further pressure to at least the compressed body. Since the compressed body has higher fluidity than the first mixture which is a powder mixture, when molding the compressed body in the third step, the pressure is applied more uniformly by the compressed body. Therefore, even with a lower pressure, the contact points between the particles can be efficiently increased, and a molded body with high strength can be obtained.

[0024] It is preferable that the molding of the compressed body in the third step is also performed dry, and it can be performed using, for example, a briquetting machine, a pelletizing machine, a granulating machine, a tableting machine, etc.

[0025] The density (d2) of the molded body is, for example, 1.5 g / cm 3 or more and 2.2 g / cm 3 or less, or 1.6 g / cm 3 or more and 1.9 g / cm 3 or less. When the density of the molded body is 1.5 g / cm 3 or more, the particles constituting the molded body can be sufficiently brought into contact (adhered) with each other, and the reaction between the particles easily proceeds. When the density of the molded body is 2.2 g / cm 3 or less, voids are appropriately formed inside the molded body, and oxidizing gases such as oxygen can be easily supplied inside the molded body, and it is easy to suppress variations in the firing degree of the molded body.

[0026] The density (d2) of the formed body is preferably greater than the density (d1) of the compressed body (d2 > d1). The ratio of the density (d2) of the formed body to the density (d1) of the compressed body: d2 / d1 is preferably, for example, 1.1 to 1.5 times, and may also be 1.1 to 1.3 times.

[0027] The densities d1 and d2 can be measured, for example, by the Archimedes method or a method using X-ray CT.

[0028] In the third step of obtaining the formed body, an uncompressed material may be formed together with the compressed body. Here, the crushed material of the preform (the crushed material of the compressed body) is not distinguished from the preform (compressed body).

[0029] For example, the third step (S3) may include a step (S31) of obtaining a second mixture including the compressed body and the first mixture, and a step (S32) of compressing the second mixture to obtain a formed body (see Figure 2). When mixing the compressed body and the first mixture, it is possible to appropriately control the fluidity of the second mixture, and it becomes easier to arbitrarily control the density (d2) of the formed body.

[0030] Also, when mixing the crushed material of the formed body as part of the compressed body, the material can be reused and productivity is improved.

[0031] The amount of the compressed body contained in the second mixture may be, for example, 10% by mass or more of the second mixture. When forming a mixture of 10% by mass or more of the compressed body and 90% by mass or less of the first mixture with a total of 100% by mass, even at the same pressure, the strength of the formed body is greatly improved and cracking of the particles is also significantly suppressed compared to the case of forming only the first mixture. The amount of the compressed body contained in the second mixture may be 10% to 60% by mass of the second mixture.

[0032] The maximum length L of the molded body may be, for example, 25 mm or more, or may be 28 mm or more. By using such large-grained molded bodies, the convection of gas in the gaps between the molded bodies is promoted. On the other hand, from the viewpoint of more rapidly advancing the firing of the central portion of the molded body, the maximum length L of the molded body may be, for example, 60 mm or less, or may be 40 mm or less. Further, the aspect ratio h / L of the minimum length h to the maximum length L may be, for example, 0.4 or more. The larger the aspect ratio, the more the convection of gas in the gaps between the molded bodies is promoted.

[0033] The maximum length L and the minimum length h of the molded body are obtained from the smallest rectangular parallelepiped circumscribing the molded body. Among all the sides of the six quadrilaterals constituting the smallest rectangular parallelepiped, the length of the longest side is the maximum length L. On the other hand, among all the sides, the length of the shortest side is the minimum length h. The maximum length L and the minimum length h of the molded body may be, for example, the average values of the 10 maximum lengths L and the 10 minimum lengths h respectively obtained for any 10 molded bodies. The aspect ratio may also be the average value of the 10 aspect ratios obtained for any 10 molded bodies.

[0034] In the fourth step (S4) of obtaining the fired body, the molded body is fired, for example, at 600 °C or higher and 850 °C or lower, and a fired body (lithium transition metal composite oxide) is obtained. The firing time may be, for example, 2 hours or more and 30 hours or less. The firing is usually carried out in an oxidizing atmosphere containing oxygen or the like. The oxidizing atmosphere may be air, or may be an atmosphere having a higher oxygen partial pressure than air. The oxygen concentration in the oxidizing atmosphere is, for example, 20% or more.

[0035] Firing is performed, for example, by filling a plurality of green compacts into a predetermined container and supplying an oxidizing gas into the container. Considering the durability against high temperatures, the material of the container is preferably a metal such as ceramics or stainless steel. The container usually has an open top shape and has a bottom surface and side surfaces rising from the periphery of the bottom surface. The depth of the container (the height of the space capable of accommodating the green compacts inside the container) may be, for example, 20 mm or more and 300 mm or less, or may be 100 mm or more and 200 mm or less. From the viewpoint of facilitating the handling of the green compacts in the firing process of the green compacts, the container may have a shape of, for example, 100 mm or more and 500 mm or less in length and 100 mm or more and 500 mm or less in width.

[0036] The firing furnace may be vertical or horizontal. For example, a tunnel-shaped horizontal firing furnace can be used.

[0037] Next, the raw materials of the first mixture will be described.

[0038] As the lithium-containing compound, lithium hydroxide, lithium oxide, lithium carbonate, etc. can be used. Among them, lithium hydroxide has high reactivity with the nickel-containing compound and is advantageous for improving the crystallinity of the lithium nickel composite oxide.

[0039] Lithium hydroxide is usually in powder form, and the average particle size of lithium hydroxide (D50: the particle size at a cumulative volume of 50% measured by a laser diffraction particle size distribution measuring device) is, for example, 10 μm or more and 500 μm or less.

[0040] When using lithium hydroxide, it is preferable to preheat and dry the lithium hydroxide. When performing the heating and drying of lithium hydroxide, the release of water during the firing of the green compacts is suppressed, and a lithium nickel composite oxide with high crystallinity is easily obtained.

[0041] The heating temperature of lithium hydroxide is preferably 100 °C or higher and lower than the melting point. When it is 100 °C or higher, the moisture contained in lithium hydroxide can be efficiently removed. Further, when the heating temperature is lower than the melting point, the particle shape of lithium hydroxide is maintained, workability is improved, and a homogeneous mixture of a lithium-containing compound and a nickel-containing compound is easily obtained. The heating time of lithium hydroxide is, for example, 1 hour or longer and 10 hours or shorter. The heating of lithium hydroxide may be carried out in the air, but it is preferably carried out in a non-oxidizing atmosphere containing nitrogen, argon, or the like.

[0042] Examples of the transition metal compound include transition metal hydroxides, transition metal oxides, transition metal sulfates, transition metal nitrates, transition metal carbonates, and transition metal oxalates.

[0043] Examples of the metal contained in the transition metal compound include Ni, Co, Al, Mn, Nb, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Si, Ti, Fe, Cr, etc. The transition metal compound may be used alone or in combination of two or more. Further, a composite transition metal compound containing two or more metals may be used. Among them, in order to obtain a high-capacity positive electrode active material, it is preferable to use at least Ni. Therefore, it is preferable to use a nickel-containing compound as the transition metal compound.

[0044] Examples of the nickel-containing compound include nickel hydroxide, nickel oxide, nickel sulfate, nickel nitrate, nickel carbonate, and nickel oxalate. The nickel-containing compound may contain a metal M1 other than lithium and nickel. For example, a composite hydroxide containing nickel and metal M1 (hereinafter also referred to as composite hydroxide A), and a composite oxide containing nickel and metal M1 (hereinafter also referred to as composite oxide B) can be used.

[0045] Composite oxide B can be obtained, for example, by heating composite hydroxide A at 300°C or higher and 800°C or lower. By using composite oxide B obtained by heat-treating composite hydroxide A as a material for the molded body, the generation of water from the molded body during firing is suppressed. Therefore, a decrease in the degree of contact between the lithium-containing compound and composite oxide B and a decrease in the thermal conductivity of the molded body are suppressed, and the crystallinity of the fired body (lithium nickel composite oxide) is likely to be improved. Among them, it is preferable to use a mixture of lithium hydroxide and composite oxide B (first mixture) for the production of the molded body.

[0046] Composite oxide B includes a state in which part of the Ni sites in the crystal lattice of nickel oxide is substituted with metal M1 or a state in which metal M1 is dissolved in nickel oxide. When the heating temperature of composite hydroxide A is within the above range, composite oxide B can be efficiently obtained. The heating time of composite hydroxide A is, for example, 30 minutes or longer and 10 hours or shorter. The heating of composite hydroxide A may be performed in a non-oxidizing atmosphere containing nitrogen or the like, or may be performed in an oxidizing atmosphere containing oxygen or the like. The oxidizing atmosphere may be air or an atmosphere having a higher oxygen partial pressure than air. The oxygen concentration of the oxidizing atmosphere is, for example, 20% or higher.

[0047] Composite hydroxide A can be produced using a known method such as the coprecipitation method. In the coprecipitation method, an alkali is added to an aqueous solution containing a nickel salt and a salt of metal M1 to coprecipitate composite hydroxide A. As the nickel salt, nickel sulfate or the like can be used. When metal M1 contains cobalt and aluminum, as the salt of metal M1, cobalt sulfate, aluminum sulfate or the like can be used. As the alkali, sodium hydroxide or the like can be used. However, the salts and alkalis are not limited to the above.

[0048] Nickel is advantageous for increasing the capacity and reducing the cost. Metal M1 may contain cobalt or may contain a metal M2 other than cobalt. Cobalt is advantageous for extending the battery life. Metal M2 preferably contains at least aluminum. Aluminum is advantageous for improving thermal stability. By using a lithium-containing composite oxide containing nickel and aluminum or a lithium-containing composite oxide containing nickel, cobalt, and aluminum as a positive electrode active material, it is possible to increase the capacity and extend the life of the secondary battery.

[0049] From the viewpoint of stabilizing the crystal structure and the like, metal M2 may further contain at least one selected from the group consisting of manganese, tungsten, niobium, magnesium, zirconium, and zinc.

[0050] Composite hydroxide A preferably contains a composite hydroxide containing nickel, cobalt, and metal M2. When using such a composite hydroxide, it is easy to uniformly disperse nickel, cobalt, and metal M2 in the molded body.

[0051] When the atomic ratio of nickel, cobalt, and metal M2 contained in composite hydroxide A is Ni:Co:M2 = (1 - x - y):x:y, x preferably satisfies 0 ≤ x < 0.15, more preferably 0.01 < x < 0.15, and y preferably satisfies 0.001 < y < 0.1. In this case, the effects of using nickel, cobalt, and metal M2 (or nickel and metal M2) can be obtained in a well-balanced manner.

[0052] The composite hydroxide obtained by the coprecipitation method can form secondary particles in which primary particles are aggregated. The average particle diameter (D50: the particle diameter at 50% cumulative volume measured by a laser diffraction particle size distribution analyzer) of the secondary particles of the composite hydroxide is, for example, 2 μm or more and 20 μm or less.

[0053] When a molded body obtained from a first mixture containing lithium hydroxide and composite oxide B is fired at 600 °C or higher and 850 °C or lower to obtain a lithium nickel composite oxide (fired body), a layered rock salt type lithium nickel composite oxide in which a part of nickel in lithium nickel oxide (LiNiO2) is substituted with metal M1 can be obtained. By substituting a part of nickel with metal M1, further improvement in battery performance becomes possible.

[0054] The lithium nickel composite oxide preferably has a composition represented by the formula: Li a Ni 1-x-y Co x M2 y O2. In the formula, a satisfies 0.9 < a < 1.1, x satisfies 0 ≦ x < 0.15, further 0.01 < x < 0.15, and y satisfies 0.001 < y < 0.1. By using the lithium nickel composite oxide having the above composition as a positive electrode active material, a high-capacity and long-life secondary battery can be obtained.

[0055] When producing the lithium nickel composite oxide having the above composition, Ni 1-x-y Co x M2 y (OH)2 may be used as the composite hydroxide A. Further, in the first mixture used for the production of the compressed body and the molded body, lithium hydroxide and composite oxide B may be mixed so that the atomic ratio of lithium to the total of nickel and metal M1 in composite oxide B: Li / (Ni + M1) exceeds 0.9 and is less than 1.1, for example.

[0056] The obtained fired body may be crushed into a powder. Further, the powder may be classified so as to have a desired particle size distribution. For the crushing of the fired body, a ball mill, a mortar, etc. are used. For classification, a sieve, etc. are used.

[0057] The lithium transition metal composite oxide can form secondary particles in which primary particles are aggregated. The average particle diameter (D50: the particle diameter at a cumulative volume of 50% measured by a laser diffraction particle size distribution measuring device) of the secondary particles of the lithium transition metal composite oxide is, for example, 2 μm or more and 20 μm or less.

[0058] The lithium transition metal composite oxide obtained by the above manufacturing method is suitably used as a cathode active material for a secondary battery. The secondary battery includes a cathode containing a cathode active material capable of electrochemically occluding and releasing lithium ions, an anode containing an anode active material capable of electrochemically occluding and releasing lithium ions, and an electrolyte.

[0059] The cathode includes, for example, a cathode current collector and a cathode mixture layer formed on the surface of the cathode current collector. The cathode mixture contains a cathode active material as an essential component and may contain, as optional components, a binder, a conductive agent, and the like.

[0060] The anode includes, for example, an anode current collector and an anode mixture layer formed on the surface of the anode current collector. The anode mixture contains an anode active material as an essential component and may contain, as optional components, a binder, a thickener, and the like.

[0061] Examples of the anode active material include carbon materials, silicon, silicon compounds, metallic lithium, and lithium alloys. Examples of the carbon material include graphite (natural graphite, artificial graphite, etc.) and amorphous carbon.

[0062] The electrolyte may be a liquid electrolyte in which a solute such as a lithium salt is dissolved in a solvent. As the solvent, a non-aqueous solvent can be used, or water can also be used. Further, the electrolyte may be a solid electrolyte.

[0063] Usually, a separator is interposed between the cathode and the anode. The separator has high ion permeability and appropriate mechanical strength and insulation. As the separator, a microporous thin film, a woven fabric, a non-woven fabric, or the like can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0064] FIG. 3 is a schematic perspective view of a part of a rectangular secondary battery cut away. The battery includes a bottomed rectangular battery case 4, an electrode group 1 housed in the battery case 4, and an electrolytic solution (not shown). The electrode group 1 is of a wound type having a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed therebetween.

[0065] One end of a negative electrode lead 3 is attached to the negative electrode current collector of the negative electrode, and the other end is connected to a negative electrode terminal 6 provided on the sealing plate 5. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. One end of a positive electrode lead 2 is attached to the positive electrode current collector of the positive electrode, and the other end is connected to the back surface of the sealing plate 5. The opening of the battery case 4 is sealed by laser welding the periphery of the sealing plate 5 to the opening end. The injection hole for the electrolytic solution provided in the sealing plate 5 is closed by a seal 8.

[0066] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0067] <<Example 1>> <<First Step>> Lithium hydroxide monohydrate (average particle diameter (D50) 50 μm) was heated and dried at 150° C. for 1 hour to prepare lithium hydroxide. Using the coprecipitation method, Ni 0.85 Co 0.12 Al 0.03 (OH)2 (average particle diameter (D50) of secondary particles: about 15 μm) was obtained. Ni 0.85 Co 0.12 Al 0.03 (OH)2 was heated in air at 700° C. for 2 hours to obtain Ni 0.85 Co 0.12 Al 0.03 O. Lithium hydroxide and Ni 0.85 Co 0.12 Al 0.03 O were dry-mixed so that the atomic ratio of Li to the total of Ni, Co, and Al: Li / (Ni + Co + Al) was 1.05 / 1 to obtain a first mixture.

[0068] <<Second Step>> The first mixture was passed dry through the nip of the nip roll to obtain a flaky compact. The pressure (linear pressure) applied to the first mixture by the nip roll was adjusted to 0.75 ton / cm so that the density d1 of the compact was 1.5 g / cm 3 The flaky compact was sized to coarse particles passing through a 5 mm mesh.

[0069] <Step 3> The coarse particles of the compact were compression-molded dry using a briquetting machine to obtain an almond-shaped molded body A1 (maximum length L = 28 mm, minimum length h = 13.7 mm, aspect ratio: h / L = 0.49). The pressure (linear pressure) applied to the coarse particles of the compact by the briquetting machine was adjusted to 1.0 ton / cm so that the density d2 of the molded body A1 was 1.75 g / cm 3 (d2 / d1 = 1.17).

[0070] <Step 4> The molded body A1 was filled into a rectangular parallelepiped container made of ceramics with a length of 330 mm, a width of 330 mm, and a depth of 220 mm, and fired at 750 °C for 5 hours in an oxidizing atmosphere (oxygen concentration 99%) to obtain a fired body (lithium nickel composite oxide) A1.

[0071] The composition of the obtained lithium nickel composite oxide was Li 1.05 Ni 0.85 Co 0.12 Al 0.03 O2. The composition of the lithium nickel composite oxide was confirmed by ICP emission spectroscopic analysis.

[0072] 《Example 2》 In Step 3, a molded body A2 was prepared by changing the pressure (linear pressure) applied to the coarse particles of the compact by the briquetting machine to 1.25 ton / cm, and a lithium nickel composite oxide A2 was obtained in the same manner as in Example 1 except that the molded body A2 was fired. The density d2 of the molded body A2 was 1.8 g / cm 3 (d2 / d1 = 1.2).

[0073] 《Example 3》 In the third step, first, 10 parts by mass of coarse particles of the compressed body and 90 parts by mass of the first mixture prepared in the first step were mixed to obtain a second mixture. Next, in the same manner as in Example 2, the second mixture was dry-compression molded using a briquette molding machine with the pressure (linear pressure) adjusted to 1.25 ton / cm to obtain an almond-shaped molded body A3. Except as described above, a lithium nickel composite oxide A3 was obtained in the same manner as in Example 1. The density d2 of the molded body A3 was 1.8 g / cm 3 It was.

[0074] <<Comparative Example 1>> A lithium nickel composite oxide B1 was obtained in the same manner as in Example 1, except that the first mixture was not compressed by a nip roll and was directly molded using a briquette molding machine with the pressure (linear pressure) adjusted to 1.25 ton / cm to form a molded body B1, and the molded body B1 was fired. The density of the molded body B1 was 1.7 g / cm 3 It was.

[0075] <<Comparative Example 2>> A lithium nickel composite oxide B2 was obtained in the same manner as in Example 1, except that the first mixture was not compressed by a nip roll and was directly molded using a briquette molding machine with the pressure (linear pressure) adjusted to 1.5 ton / cm to form a molded body B2, and the molded body B2 was fired. The density of the molded body B2 was 1.82 g / cm 3 It was.

[0076] [Evaluation] <Crushing test> The molded bodies A1 to A3, B1, and B2 obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were placed on an autograph manufactured by Shimadzu Corporation, and compressed at a compression speed of 10 mm / min to measure the crushing strength at the time of fracture.

[0077] <Particle cracking rate> Each fired body (lithium nickel composite oxide) A1 to A3, B1 and B2 was sized to an average particle size (D50) of 10 μm in a mortar. In the volume-based particle size distribution obtained when calculating the average particle size, particles with a particle size of 1 μm or less are considered to be fine powder generated by particle cracking. Therefore, the volume ratio (%) of particles with a particle size of 1 μm or less in the sample used for measurement was calculated and used as the particle cracking rate.

[0078]

Table 1

[0079] All of the lithium nickel composite oxides A1 to A3 obtained in Examples 1 to 3 have a significantly lower particle cracking rate than those in Comparative Examples 1 and 2. Further, when comparing Examples 2 and 3 with Comparative Example 1, the pressure when obtaining the compact in the third step is the same at 1.25 ton / cm in all cases, but the crushing strength of the compacts A2 and A3 in Examples 2 and 3 is about twice that of the compact B1 in Comparative Example 1. And the particle cracking rate of Examples 2 and 3 is significantly smaller than that of Comparative Example 1.

[0080] Further, from the results of Example 3, it can be understood that when obtaining a compact, even if a second mixture containing only about 10% of the compressed body is used, a compact with a very high crushing strength can be obtained, and the particle cracking rate can be maintained sufficiently low.

[0081] Further, from the results of Comparative Examples 1 and 2, it can be understood that when directly molding the first mixture which is a powder mixture, the crushing strength of the obtained compact is low, but the particle cracking rate is high.

Industrial Applicability

[0082] The lithium transition metal composite oxide obtained by the manufacturing method according to the present disclosure is suitably used, for example, as a positive electrode active material of a secondary battery that requires high capacity and high reliability.

Explanation of Symbols

[0083] 1 Electrode group 2 Positive electrode lead 3 Negative electrode lead 4 Battery case 5 Sealing plate 6 Negative electrode terminal 7 Gasket 8 Seal

Claims

1. A step of preparing a first mixture containing lithium hydroxide and at least one transition metal compound selected from the group consisting of transition metal hydroxides, transition metal oxides, transition metal sulfates, transition metal nitrates, transition metal carbonates, and transition metal oxalates, and not containing a binder; A step of compressing the first mixture at least once to obtain a compressed body with a density d1; A step of shaping the compressed body to obtain a plurality of shaped bodies with a density d2; A step of filling the plurality of shaped bodies into a container and firing them in the container to obtain a plurality of fired bodies (however, excluding the case where a step of firing the compressed body at 600°C or higher and 850°C or lower is included between the step of obtaining the compressed body and the step of obtaining the shaped body); In the step of obtaining the plurality of shaped bodies, one of the shaped bodies is obtained by shaping a plurality of the compressed bodies; The density d1 is 1 g / cm3 or more and 1.8 g / cm3 or less; The density d2 is 1.5 g / cm3 or more and 2.2 g / cm3 or less. A method for producing a lithium transition metal composite oxide.

2. The step of obtaining the shaped body includes: A step of obtaining a second mixture containing the compressed body and the first mixture; A step of compressing the second mixture to obtain the shaped body. The method for producing a lithium transition metal composite oxide according to Claim 1.

3. The amount of the compressed body contained in the second mixture is 10% by mass or more of the second mixture. The method for producing a lithium transition metal composite oxide according to Claim 2.

4. At least a part of the compressed body is a crushed product of the shaped body. The method for producing a lithium transition metal composite oxide according to any one of Claims 1 to 3.

5. The transition metal compound is a nickel-containing oxide. The method for producing a lithium transition metal composite oxide according to any one of Claims 1 to 4.

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