Tricobalt tetraoxide, preparation method thereof, positive electrode material, lithium ion battery and electrical equipment

Abstract

The application provides a kind of tricobalt tetroxide and its preparation method, positive electrode material, lithium ion battery and electrical equipment, the tricobalt tetroxide includes the secondary particle consisting of multiple primary particles, the secondary particle is spherical or spheroidal, the tricobalt tetroxide is obtained by XRD in (311) crystal face Grain size is the tricobalt tetroxide provided in the application includes spherical or spheroidal secondary particle consisting of multiple primary particles, by controlling the grain size in (311) crystal face in a suitable range, so that the prepared positive electrode material has good structural stability, so that the cycle performance is improved, and also has better first discharge capacity.

Description

Technical Field

[0001] This application relates to the field of cathode material technology, and in particular to a cobalt tetroxide and its preparation method, cathode material, lithium-ion battery and related electrical equipment. Background Technology

[0002] With the increasingly frequent updates and replacements of 3C products (computers, communications, and consumer electronics), the trend towards "thinner and lighter, more durable" products is growing, which places higher demands on battery life and cycle retention. Correspondingly, the energy density and structural stability of battery cathode materials have become the main areas for improvement, and the quality of battery cathode materials largely depends on the performance of the precursor.

[0003] Cobalt tetroxide, as a precursor material for preparing lithium cobalt oxide cathode materials, has been widely used in the market. However, current cobalt tetroxide still suffers from insufficient energy density and structural strength, and there is still room for improvement in the range and capacity retention of batteries made from it. Summary of the Invention

[0004] This application aims to at least improve one of the technical problems existing in the prior art. To this end, this application provides cobalt tetroxide and its preparation method, a cathode material, a lithium-ion battery, and an electrical device.

[0005] This application provides a cobalt tetroxide, which includes secondary particles composed of multiple primary particles. The secondary particles are spherical or near-spherical. The cobalt tetroxide has a grain size of 620-765 Å on the (311) crystal plane obtained by XRD.

[0006] The grain size of cobalt tetroxide on the (311) crystal plane obtained by XRD can be, for example, any value between 620Å, 625Å, 630Å, 635Å, 640Å, 645Å, 650Å, 655Å, 660Å, 665Å, 670Å, 675Å, 680Å, 685Å, 690Å, 695Å, 700Å, 705Å, 710Å, 715Å, 720Å, 725Å, 730Å, 735Å, 740Å, 745Å, 750Å, 755Å, 760Å, 765Å, or 620-765Å.

[0007] In some embodiments of this application, the crystallinity of the secondary particles is ≥70%; and / or the half-width of the characteristic peak corresponding to the (311) crystal plane of the secondary particles is 0.115°-0.145°.

[0008] The crystallinity of the secondary particles can be, for example, any value of 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88% or ≥70%; the half-width of the characteristic peak corresponding to the (311) crystal plane of the secondary particles can be, for example, any value between 0.115°, 0.118°, 0.120°, 0.122°, 0.125°, 0.128°, 0.130°, 0.132°, 0.135°, 0.138°, 0.140°, 0.142°, 0.145° or 0.115°-0.145°.

[0009] In some embodiments of this application, the secondary particle comprises an inner layer and an outer layer from the inside out, wherein the porosity of the outer layer is 15%-25%; and / or the porosity of the inner layer is ≤5%; and / or the area of ​​the inner layer on the cross-section of the secondary particle is 10%-65%; and / or the outer layer has gaps extending radially along the secondary particle, the length of which is 1.5-6 μm. The length of the gaps in this application is obtained by measuring the length of the radially continuous pores on the cross-section of the secondary particle.

[0010] The porosity of the outer layer can be any value between 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or 15%-25%; the porosity of the inner layer can be any value between 5%, 4.8%, 4.5%, 4.2%, 4%, 3.8%, 3.5%, 3.2%, 3%, 2.8%, 2.5%, 2.2%, 2%, 1.8%, 1.5%, 1.2%, 1%, or ≤5%; the area ratio of the inner layer on the cross-section of the secondary particles can be, for example, 10%, 12%. The percentages are 10%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, or any value between 10% and 65%; the outer layer has gaps extending radially along the secondary particles, the length of which can be, for example, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, or any value between 1.5 and 6μm.

[0011] In some embodiments of this application, cobalt tetroxide satisfies at least one of the following conditions: a. The average particle size D50 of the secondary particles is 15-20 μm; wherein, the average particle size D50 of the secondary particles can be, for example, any value between 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm or 15-20 μm.

[0012] b. The change rate of D00 of secondary particles under 35MPa pressure is ≤3%; wherein, the change rate of D00 of secondary particles under 35MPa pressure can be any value of 3%, 2.8%, 2.5%, 2.2%, 2%, 1.8%, 1.5%, 1.2%, 1%, 0.8%, 0.5%, 0.2%, 0.1%, 0.09%, 0.08% or ≤3%.

[0013] c. The average pore size inside the secondary particles is 60-90 nm; wherein, the average pore size inside the secondary particles can be, for example, any value between 60 nm, 62 nm, 65 nm, 68 nm, 70 nm, 72 nm, 75 nm, 78 nm, 80 nm, 82 nm, 85 nm, 88 nm, 90 nm or 60-90 nm.

[0014] d. The specific surface area of ​​secondary particles is 1.8-3.5 m². 2 / g; where the specific surface area of ​​the secondary particles can be, for example, 1.8m². 2 / g、2m 2 / g, 2.2m 2 / g, 2.4m 2 / g, 2.6m 2 / g, 2.8m 2 / g、3m 2 / g, 3.2m 2 / g, 3.4m 2 / g, 3.5m 2 / g or 1.8-3.5m 2 Any value between / g.

[0015] e. The tap density of secondary particles is 2.6-3.0 g / cm³. 3 The tap density of the secondary particles can be, for example, 2.6 g / cm³. 3 2.65g / cm 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 2.85g / cm 3 2.9g / cm 3 2.95g / cm 3 3.0g / cm3 Or 2.6-3.0 g / cm³ 3 Any value between.

[0016] Another embodiment of this application provides a method for preparing cobalt tetroxide, comprising the following steps: A reaction base solution containing a precipitant is prepared, and a precipitant solution and a cobalt-containing solution are simultaneously added to the reaction base solution to carry out a first reaction to obtain a first reaction product; A precipitant solution and a cobalt-containing solution are added to the first reaction product to carry out a second reaction, yielding a second reaction product. The second reaction product was post-treated and sintered to obtain cobalt tetroxide.

[0017] In some embodiments of this application, the preparation method satisfies at least one of the following conditions (1)-(5): (1) The precipitant includes at least one of sodium bicarbonate, sodium carbonate, and ammonium bicarbonate; (2) The concentration of the precipitant in the reaction substrate is 20-120 g / L; wherein, the concentration of the precipitant in the reaction substrate can be, for example, any value between 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L or 20-120 g / L.

[0018] (3) The volume of the reaction base liquid is 20-60% of the usable volume of the reaction vessel; wherein, the volume of the reaction base liquid can be any value between 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60% or 20-60% of the usable volume of the reaction vessel.

[0019] (4) The concentration of the precipitant in the precipitant solution is 200-230 g / L; wherein, the concentration of the precipitant in the precipitant solution can be, for example, any value between 200 g / L, 202 g / L, 205 g / L, 208 g / L, 210 g / L, 212 g / L, 215 g / L, 218 g / L, 220 g / L, 222 g / L, 225 g / L, 228 g / L, 230 g / L or 200-230 g / L.

[0020] (5) The cobalt-containing solution includes cobalt and a doped metal, wherein the doped metal is selected from at least one of Al, Ni, Mn, Zr, Ti, La, Mg and Y elements; optionally, the cobalt concentration of the cobalt-containing solution is 100-130 g / L, and the mass ratio of the doped metal to the cobalt is 0.0036-0.0273:1. The cobalt concentration of the cobalt-containing solution can be, for example, any value between 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, 130 g / L, or 100-130 g / L; the mass ratio of the doped metal to the cobalt can be, for example, any value between 0.0036:1, 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.027:1, 0.0273:1, or 0.0036-0.0273:1.

[0021] In some embodiments of this application, the preparation method satisfies at least one of the following conditions ①-⑨: ① The particle size D50 of the first reaction product is 11-13 μm; wherein, the particle size D50 of the first reaction product can be, for example, any value between 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm or 11-13 μm.

[0022] ② In the first reaction process, the flow rate of the cobalt-containing solution is 5-8% / h of the available volume of the reaction vessel; wherein, the flow rate of the cobalt-containing solution can be any value between 5% / h, 5.5% / h, 6% / h, 6.5% / h, 7% / h, 7.5% / h, 8% / h or 5-8% / h of the available volume of the reaction vessel.

[0023] ③ The pH value of the first reaction is 7.2-7.5; wherein, the pH value of the first reaction can be, for example, any value between 7.2, 7.25, 7.3, 7.35, 7.4, 7.45, 7.5 or 7.2-7.5.

[0024] ④ The reaction temperature of the first reaction is 38-40℃; wherein, the reaction temperature of the first reaction can be any value between 38℃, 38.5℃, 39℃, 39.5℃, 40℃ or 38-40℃.

[0025] ⑤ The particle size D50 of the second reaction product is 19-21 μm; wherein, the particle size D50 of the second reaction product can be, for example, any value between 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm or 19-21 μm.

[0026] ⑥ In the second reaction process, the flow rate of the cobalt-containing solution is 3-5% / h of the available volume of the reaction vessel; wherein, the flow rate of the cobalt-containing solution can be, for example, any value between 3% / h, 3.2% / h, 3.5% / h, 3.8% / h, 4% / h, 4.2% / h, 4.5% / h, 4.8% / h, 5% / h or 3-5% / h of the available volume of the reaction vessel.

[0027] ⑦ The pH value of the second reaction is 7.0-7.2; wherein, the pH value of the second reaction can be, for example, 7.0, 7.02, 7.05, 7.08, 7.1, 7.12, 7.15, 7.18, 7.2 or any value between 7.0 and 7.2.

[0028] ⑧ The reaction temperature of the second reaction is 40-42℃; wherein, the reaction temperature of the second reaction can be, for example, any value between 40℃, 40.5℃, 41℃, 41.5℃, 42℃ or 40-42℃.

[0029] ⑨ The sintering includes pre-sintering and high-temperature sintering, wherein the pre-sintering temperature is 200-300℃ and the high-temperature sintering temperature is 700-750℃; optionally, the total sintering time is 1-3h, the ratio of the pre-sintering time to the high-temperature sintering time is 1:(2-4), and the time required for the pre-sintering temperature to rise to the high-temperature sintering temperature is ≤1h. The pre-sintering temperature can be, for example, any value between 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, or 200-300℃; the high-temperature sintering temperature can be, for example, any value between 700℃, 705℃, 710℃, 715℃, 720℃, 725℃, 730℃, 735℃, 740℃, 745℃, 750℃, or 700-750℃; the total sintering time can be, for example, 1 hour or 1.2 hours. The time required for the pre-sintering temperature to rise to the high-temperature sintering temperature can be any value between 1.5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h, 3h, or 1-3h; the ratio of the pre-sintering time to the high-temperature sintering time can be, for example, any value between 1:2, 1:2.5, 1:3, 1:3.5, 1:4, or 1:(2-4); the time required for the pre-sintering temperature to rise to the high-temperature sintering temperature can be, for example, any value between 1h, 0.9h, 0.8h, 0.7h, 0.6h, 0.5h, 0.4h, 0.3h, 0.2h, 0.1h, or ≤1h.

[0030] Another embodiment of this application provides a cathode material prepared from the cobalt tetroxide described above.

[0031] Another embodiment of this application provides a lithium-ion battery, including the positive electrode material described in the above embodiments.

[0032] Another embodiment of this application provides an electrical device, including the lithium-ion battery described in the above embodiments.

[0033] The cobalt tetroxide provided in this application includes spherical or near-spherical secondary particles composed of multiple primary particles. By controlling the grain size of the (311) crystal plane within a suitable range, the crystal structure develops well. When the grain size is too large, it is not conducive to the diffusion of lithium ions and the compressibility of the particles, thus reducing the electrochemical performance of the material; when the grain size is too small, the crystallinity of the material is low, which affects the cycle performance of the material. By controlling the grain size of the (311) crystal plane within a suitable range, this application enables the prepared cathode material to have good structural stability, thereby improving the cycle performance and also possessing a good first-cycle discharge capacity.

[0034] The method for preparing cobalt tetroxide provided in this application obtains cobalt tetroxide with a (311) crystal plane grain size within a suitable range by controlling the reaction steps, reactant flow rate, reaction temperature, etc., so that the prepared cathode material has good structural stability, thereby improving the cycle performance and also having a good first-cycle discharge capacity.

[0035] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of this application or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a cross-sectional view of cobalt tetroxide prepared in Example 1 of this application; Figure 2 SEM image of cobalt tetroxide prepared in Example 1 of this application (left), and SEM image of cobalt tetroxide after compaction at 35 MPa (right). Figure 3 This is a cross-sectional view of cobalt tetroxide prepared in Example 2 of this application; Figure 4 SEM image of cobalt tetroxide prepared in Example 2 of this application (left), and SEM image of cobalt tetroxide after compaction at 35 MPa (right). Figure 5This is a cross-sectional view of cobalt tetroxide prepared in Example 3 of this application; Figure 6 SEM image of cobalt tetroxide prepared in Example 3 of this application (left), and SEM image of cobalt tetroxide after compaction at 35 MPa (right). Figure 7 SEM image of cobalt tetroxide prepared in Comparative Example 1 of this application (left), and SEM image of cobalt tetroxide after compaction at 35 MPa (right). Figure 8 This is a cross-sectional view of cobalt tetroxide prepared in Comparative Example 2 of this application. Figure 9 SEM image of cobalt tetroxide prepared in Comparative Example 2 of this application (left), and SEM image of cobalt tetroxide after compaction at 35 MPa (right). Figure 10 The CP cross-section of cobalt tetroxide prepared in Comparative Example 3 of this application is shown. Figure 11 The image shows a SEM image (left) of cobalt tetroxide prepared in Comparative Example 3 of this application, and a SEM image (right) after compaction at 35 MPa. Detailed Implementation

[0038] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0040] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0041] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0042] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0043] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0044] This application provides a cobalt tetroxide, comprising secondary particles composed of multiple primary particles, the secondary particles being spherical or near-spherical. The cobalt tetroxide grain size on the (311) crystal plane, obtained by XRD (X-ray diffraction), is 620-765 Å. The cobalt tetroxide provided in this application achieves better crystal development by controlling the grain size of the (311) crystal plane within a suitable range. When the grain size is too large, the prepared cathode material is not conducive to lithium-ion diffusion, reducing the electrochemical performance of the material; when the grain size is too small, the material has low crystallinity, affecting the cycle performance of the material. This application, by controlling the grain size of the (311) crystal plane within a suitable range, enables the prepared cathode material to have good structural stability, thereby improving the cycle performance of the corresponding battery and also possessing a better first-cycle discharge capacity. The cobalt tetroxide in this application also includes doped cobalt tetroxide.

[0045] Grain size is calculated using the following formula: D = K·γ / (B·cosθ); where D is the average thickness of the grain perpendicular to the crystal plane, i.e., the grain size; K is the Scherrer constant; B is the measured half-peak width or integral width of the diffraction peak of the sample; θ is the Bragg angle; γ is the X-ray wavelength (1.54056 Å).

[0046] In some embodiments, the crystallinity of the secondary particles is ≥70%. A higher crystallinity range indicates better crystallinity in the material, resulting in batteries with excellent cycle performance. The crystallinity is calculated as the percentage contribution of the crystalline region to the total area of ​​intensity peaks in the X-ray diffraction pattern of the partially crystalline polymer. The formula for calculating crystallinity is: K = (I / S) / (2B·cosθ) ;where K is the crystallinity; I is the peak area of ​​the diffraction peak; S is the sample weight; B is the width of the diffraction peak; and θ is the wavelength of the diffraction peak.

[0047] In some embodiments, the full width at half maximum (FWHM) of the characteristic peak corresponding to the (311) crystal plane of the secondary particles is 0.115°-0.145°. The narrower FWHM of the (311) crystal plane of the secondary particles indicates higher crystallinity and fewer impurities in the corresponding material, which is beneficial to improving the cycle performance of the corresponding battery.

[0048] To evaluate the characteristics of porosity, this application uses image analysis software (avizo) to directly calculate the pore area and cross-sectional area of ​​each region. The porosity of different regions is calculated by (porosity = pore area of ​​each region / cross-sectional area of ​​each region × 100%). The porosity of this application is characterized by this method.

[0049] In some embodiments, the secondary particles comprise an inner layer and an outer layer from the inside out, wherein the porosity of the outer layer is 15%-25%; and / or, the porosity of the inner layer is ≤5%. Within the aforementioned suitable porosity ranges of the inner and outer layers, it is advantageous to further balance the reactivity and cycling performance of the material.

[0050] In some embodiments, the area of ​​the inner layer on the cross-section of the secondary particle is 10%-65%. In this application, the area ratio of the inner layer refers to the ratio of the area of ​​the inner layer to the total area of ​​the cross-section on any cross-section of the secondary particle.

[0051] Because the inner layer is dense while the outer layer is porous, this embodiment balances the material's reactivity and cycle performance by controlling the area ratio of the inner layer within a suitable range. Specifically, if the inner layer ratio is too high, it hinders the penetration of molten lithium carbonate into the particles during cathode material preparation, affecting the material's reactivity. Furthermore, it reduces the buffer space for the particles under pressure, making them prone to breakage. Conversely, if the inner layer ratio is too low, the overall pressure-bearing capacity of the particles is too small, also making them prone to breakage under pressure, thus affecting the battery's cycle performance.

[0052] In some embodiments, the outer layer has gaps extending radially along the secondary particles, with a gap length of 1.5-6 μm. The cobalt tetroxide outer layer provided in this application embodiment has radially extending and radially distributed gaps, with a large gap width and a length on the micrometer scale. When cobalt tetroxide is sintered with lithium sources such as lithium carbonate to prepare cathode materials, molten lithium carbonate can more easily penetrate into the particle interior through the gaps in the outer layer, resulting in higher lithium carbonate permeability and permeation efficiency during the sintering process. This is beneficial for improving reaction activity and enhancing the charge and discharge efficiency of the corresponding battery.

[0053] Because the outer layer of the particles has gaps, these gaps provide a buffer space for the particles to deform when compressed, effectively releasing pressure and preventing them from easily breaking, thus improving the structural strength of the particles. Furthermore, the radially uniform distribution of these gaps on the outer layer allows for more even absorption of external compressive forces, further enhancing the particle's structural strength. Moreover, these gaps reduce the impact on lithium-ion conductivity, resulting in superior battery cycle performance when used in lithium-ion battery manufacturing.

[0054] In some embodiments, the average particle size D50 of the secondary particles is 15-20 μm. The average particle size D50 of the cathode material can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. The D50 of the cathode materials in each embodiment and comparative example is shown in Table 1.

[0055] D50 refers to the particle size at which the cumulative volume distribution percentage of secondary particles reaches 50% or more.

[0056] D00 refers to the particle size corresponding to the cumulative volume distribution percentage of secondary particles reaching 0% or more, that is, the particle size corresponding to the smallest secondary particle.

[0057] In this embodiment, the compressive strength of the particles is evaluated by measuring the change rate of particle size D00 under a pressure of 35 MPa. The measured change rate of particle size D00 is ≤3%, where the change rate of D00 = (particle size D00 before compression - particle size D00 after compression) / particle size D00 before compression. The particles in this embodiment are less prone to cracking and breakage, which is beneficial to improving the cycle performance of the battery.

[0058] The average pore size inside the secondary particles was tested using a fully automated specific surface area analyzer. In some embodiments, the average pore size inside the secondary particles was 60-90 nm, which is beneficial for further balancing the material's reactivity and cycling performance.

[0059] To obtain materials with better performance, the specific surface area and tap density should be controlled within appropriate ranges. In some embodiments, the specific surface area of ​​the secondary particles is 1.8-3.5 m². 2 By controlling the specific surface area within a suitable range, the secondary particles are less likely to undergo side reactions with the electrolyte. In some embodiments, the tap density of the secondary particles is 2.6-3.0 g / cm³. 3 Controlling the tap density within a suitable range is beneficial to improving the energy density of the corresponding battery.

[0060] Another embodiment of this application provides a method for preparing cobalt tetroxide, comprising the following steps: A reaction base solution containing a precipitant was prepared, and a precipitant solution and a cobalt-containing solution were simultaneously added to the reaction base solution to carry out the first reaction to obtain the first reaction product. A precipitant solution and a cobalt-containing solution are added to the first reaction product to carry out a second reaction, yielding the second reaction product. The second reaction product was post-treated and sintered to obtain cobalt tetroxide.

[0061] According to the preparation method provided in the embodiments of this application, cobalt tetroxide comprising spherical or near-spherical secondary particles composed of multiple primary particles is prepared by the above specific steps and conditions. The cobalt tetroxide has a grain size of 620-765 Å on the (311) crystal plane, which makes the prepared cathode material have good structural stability, thereby improving the cycle performance of the corresponding battery and also having a good first-cycle discharge capacity.

[0062] In some embodiments, the cobalt-containing solution comprises cobalt and a dopant metal selected from at least one element chosen from Al, Ni, Mn, Zr, Ti, La, Mg, and Y. In some embodiments, the cobalt concentration of the cobalt-containing solution is 100-130 g / L, and the mass ratio of the dopant metal to cobalt is 0.0036-0.0273:1. In some embodiments, the anions in the cobalt-containing solution may be sulfate, nitrate, chloride, etc.

[0063] In some embodiments, the precipitant includes a carbonate, preferably at least one of sodium bicarbonate, sodium carbonate, and ammonium bicarbonate. The carbonate can react with cobalt ions in a cobalt-containing solution to form cobalt carbonate precipitate, which can then be decomposed by sintering to obtain the desired cobalt tetroxide.

[0064] In some embodiments, the concentration of the precipitant in the reaction substrate is 20-120 g / L; the volume of the reaction substrate is 20-60% of the usable volume of the reaction vessel; and the concentration of the precipitant in the precipitant solution is 200-230 g / L. By controlling the concentrations of the precipitant in the reaction substrate and the precipitant solution separately, it is beneficial for the precipitant to react fully with the cobalt ions in the cobalt-containing solution, so as to obtain the corresponding cobalt carbonate precipitate.

[0065] In some embodiments, the particle size D50 of the first reaction product is 11-13 μm, and the particle size D50 of the second reaction product is 19-21 μm. By controlling the preparation conditions of cobalt tetroxide in stages, it is beneficial to achieve the layered growth of cobalt tetroxide, thereby forming cobalt tetroxide with specific inner and outer layer structures.

[0066] In some embodiments, during the first reaction, the flow rate of the cobalt-containing solution is 5-8% / h of the available volume of the reaction vessel, the pH value of the first reaction is 7.2-7.5, and the reaction temperature of the first reaction is 38-40°C; during the second reaction, the flow rate of the cobalt-containing solution is 3-5% / h of the available volume of the reaction vessel, the pH value of the second reaction is 7.0-7.2, and the reaction temperature of the second reaction is 40-42°C. By controlling the reaction conditions of the first and second reactions within the aforementioned larger flow rate and lower temperature range, it is beneficial to obtain cobalt carbonate precipitate with lower crystallinity and density, thereby preparing cobalt tetroxide with larger grain size using cobalt carbonate.

[0067] In some embodiments, sintering includes pre-sintering and high-temperature sintering, wherein the pre-sintering temperature is 200-300℃ and the high-temperature sintering temperature is 700-750℃. In some embodiments, the total sintering time is 1-3 hours, wherein the ratio of the pre-sintering time to the high-temperature sintering time is 1:(2-4), and the time required to rise from the pre-sintering temperature to the high-temperature sintering temperature is ≤1 hour. Pre-sintering the cobalt carbonate precipitate obtained during the reaction for a short time at a low temperature during the sintering process can remove the moisture entrained in the cobalt carbonate precipitate. Then, rapidly heating to the temperature required for high-temperature sintering at a high heating rate and performing high-temperature sintering for a longer time is beneficial for decomposing the cobalt carbonate to obtain cobalt tetroxide with larger grain sizes.

[0068] According to another embodiment of this application, a cathode material is provided, which is prepared using the aforementioned cobalt tetroxide. Due to the use of cobalt tetroxide, the resulting cathode material has advantages such as structural stability and high energy density.

[0069] According to another embodiment of this application, a lithium-ion battery is provided, comprising the positive electrode material of the above embodiment.

[0070] According to another embodiment of this application, an electrical device is provided, including the lithium-ion battery of the above embodiment.

[0071] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all reagents and raw materials used in the embodiments are commercially available or synthesized by conventional methods, and the instruments used in the embodiments are also commercially available.

[0072] Example 1 This embodiment provides a method for preparing cobalt tetroxide, including the following steps: (1) Raw material preparation: Cobalt-containing solution: Prepare a cobalt sulfate solution containing cobalt and a doped metal. The cobalt content in the cobalt-containing solution is 115 g / L, the doped metal is Al, and the mass ratio of the doped metal to cobalt is 0.0090.

[0073] Precipitating agent solution: Prepare an ammonium bicarbonate solution with a concentration of 220 g / L.

[0074] (2) First reaction: An ammonium bicarbonate solution diluted to 80 g / L was added to the reactor as the reaction base liquid, with a volume of 40% of the reactor's usable volume. A cobalt-containing solution and a precipitant solution were then simultaneously pumped into the reactor for the first reaction, and the supernatant was continuously removed using a thickener or similar device. During the first reaction, the flow rate of the cobalt-containing solution was 6% / h of the reactor's usable volume. The pH of the first reaction was controlled to 7.3 by adjusting the flow rate of the precipitant solution, and the reaction temperature was controlled at 39°C until a first reaction product with a particle size D50 of 12 μm was obtained.

[0075] (3) Second reaction: A cobalt-containing solution and a precipitant solution are simultaneously pumped into a reactor containing the first reaction product to carry out a second reaction, and the supernatant is continuously removed using a thickener or similar device. During the second reaction, the flow rate of the cobalt-containing solution is 4% / h of the available volume of the reactor. The pH value of the second reaction is controlled to 7.1 by adjusting the flow rate of the precipitant solution, and the reaction temperature is controlled at 41℃ until a second reaction product with a particle size D50 of 20 μm is obtained.

[0076] (4) Post-processing: The resulting second reaction product was pumped into a centrifuge, and after centrifugation, washing, and dehydration, a post-processed product was obtained.

[0077] (5) Sintering: The post-processed product was sintered in a rotary kiln. The pre-sintering temperature was 250℃, the pre-sintering time was 0.5h, the heating time was 20min, the high-temperature sintering temperature was 725℃, and the high-temperature sintering time was 1.5h. Cobalt tetroxide was obtained after sintering.

[0078] In this embodiment, cobalt tetroxide was obtained after the above treatment, with a particle size D50 of 15.4 μm and a specific surface area of ​​1.88 m². 2 / g, tap density = 2.90g / cm³ 3 .

[0079] Example 2 This embodiment provides a method for preparing cobalt tetroxide, including the following steps: (1) Raw material preparation: Cobalt-containing solution: Prepare a cobalt sulfate solution containing cobalt and doped metals. The cobalt content in the cobalt-containing solution is 130 g / L, and the doped metals are Al, Ni, Mn, and Mg, with a mass ratio of doped metal to cobalt of 0.0214.

[0080] Precipitating agent solution: Prepare an ammonium bicarbonate solution with a concentration of 230 g / L.

[0081] (2) First reaction: An ammonium bicarbonate solution diluted to a concentration of 120 g / L was added to the reactor as the reaction base liquid, with the volume of the base liquid being 60% of the reactor's usable volume. A cobalt-containing solution and a precipitant solution were then simultaneously pumped into the reactor for the first reaction, and the supernatant was continuously removed using a thickener or similar device. During the first reaction, the flow rate of the cobalt-containing solution was 5% / h of the reactor's usable volume. The pH value of the first reaction was controlled to 7.2 by adjusting the flow rate of the precipitant solution, and the reaction temperature was controlled at 40℃ until a first reaction product with a particle size D50 of 13 μm was obtained.

[0082] (3) Second reaction: A cobalt-containing solution and a precipitant solution were simultaneously pumped into a reactor containing the first reaction product to carry out a second reaction, and the supernatant was continuously removed using a thickener or similar device. During the second reaction, the flow rate of the cobalt-containing solution was 3% / h of the available volume of the reactor, the pH value of the second reaction was controlled to 7.0 by adjusting the flow rate of the precipitant solution, and the reaction temperature was controlled at 42℃ until a second reaction product with a particle size D50 of 21 μm was obtained.

[0083] (4) Post-processing: The resulting second reaction product was pumped into a centrifuge, and after centrifugation, washing, and dehydration, a post-processed product was obtained.

[0084] (5) Sintering: The post-processed product was sintered in a rotary kiln. The pre-sintering temperature was 300℃, the pre-sintering time was 0.6 h, the heating time was 30 min, the high-temperature sintering temperature was 750℃, and the high-temperature sintering time was 2.4 h. Cobalt tetroxide was obtained after sintering.

[0085] In this embodiment, cobalt tetroxide was obtained after the above treatment, with a particle size D50 of 16.9 μm and a specific surface area of ​​2.01 m². 2 / g, tap density = 2.82g / cm³ 3 .

[0086] Example 3 This embodiment provides a method for preparing cobalt tetroxide, including the following steps: (1) Raw material preparation: Cobalt-containing solution: Prepare a cobalt-containing solution containing cobalt and doped metals. The cobalt content in the cobalt-containing solution is 100 g / L, and the doped metals are Al, Zr, Ti, La, and Y, with a mass ratio of doped metal to cobalt of 0.0273.

[0087] Precipitating agent solution: Prepare an ammonium bicarbonate solution with a concentration of 200 g / L.

[0088] (2) First reaction: An ammonium bicarbonate solution diluted to a concentration of 20 g / L was added to the reactor as the reaction base liquid, with the volume of the base liquid being 20% ​​of the reactor's usable volume. A cobalt-containing solution and a precipitant solution were then simultaneously pumped into the reactor for the first reaction, and the supernatant was continuously removed using a thickener or similar device. During the first reaction, the flow rate of the cobalt-containing solution was 8% / h of the reactor's usable volume. The pH value of the first reaction was controlled to 7.5 by adjusting the flow rate of the precipitant solution, and the reaction temperature was controlled at 38℃ until a first reaction product with a particle size D50 of 11 μm was obtained.

[0089] (3) Second reaction: A cobalt-containing solution and a precipitant solution are simultaneously pumped into a reactor containing the first reaction product to initiate a second reaction. The supernatant is continuously removed using a thickener or similar device. During the second reaction, the flow rate of the cobalt-containing solution is 5% / h of the available reactor volume. The pH value of the second reaction is controlled to 7.2 by adjusting the flow rate of the precipitant solution. The reaction temperature of the second reaction is controlled at 40℃ until a second reaction product with a particle size D50 of 19 μm is obtained.

[0090] (4) Post-processing: The resulting second reaction product was pumped into a centrifuge, and after centrifugation, washing, and dehydration, a post-processed product was obtained.

[0091] (5) Sintering: The post-processed product was sintered in a rotary kiln for a total sintering time of 1.5 h. The pre-sintering temperature was 250 °C, the pre-sintering time was 0.4 h, the heating time was 15 min, the high-temperature sintering temperature was 740 °C, and the high-temperature sintering time was 1.1 h. Cobalt tetroxide was obtained after sintering.

[0092] In this embodiment, cobalt tetroxide was obtained after the above treatment, with a particle size D50 of 16.8 μm and a specific surface area of ​​2.53 m². 2 / g, tap density = 2.78g / cm³ 3 .

[0093] Comparative Example 1 This comparative example provides a method for preparing cobalt tetroxide, comprising the following steps: (1) Raw material preparation: Cobalt-containing solution: Prepare a cobalt-containing solution containing cobalt and doped metals. The cobalt content in the cobalt-containing solution is 100 g / L, and the doped metals are Al, Ni, and Mn. The mass ratio of cobalt to doped metals is Co:Al:Ni:Mn=1:0.0139:0.0035:0.0055.

[0094] Precipitating agent solution: Prepare an ammonium bicarbonate solution with a concentration of 190 g / L.

[0095] (2) Reaction steps: A diluted ammonium bicarbonate solution with a concentration of 10 g / L was added to the reactor as the reaction base liquid. Then, a cobalt-containing solution and a precipitant solution were simultaneously pumped into the reactor to carry out the reaction. During the reaction, the flow rate of the cobalt-containing solution was controlled to be 3% / h of the available volume of the reactor. The stirring speed was gradually adjusted from 300 r / min to 250 r / min until a reaction product with a particle size D50 of 7 μm was obtained.

[0096] Next, half of the reaction product in the reactor was discharged, and the remaining half was reacted for another 2 hours according to the above process. Then, the flow rate of the cobalt-containing solution was increased to 4% / h of the available volume of the reactor, and the stirring speed was gradually adjusted from 250 r / min to 200 r / min until a reaction product with a particle size D50 of 10 μm was obtained.

[0097] Next, half of the reaction product in the reactor was discharged, and the remaining half was reacted for another 2 hours according to the above process. Then, the flow rate of the cobalt-containing solution was increased to 5% / h of the usable volume of the reactor, and the stirring speed was gradually adjusted from 200 r / min to 150 r / min until a reaction product with a particle size D50 of 14 μm was obtained.

[0098] Next, half of the reaction product in the reactor was discharged, and the remaining half was reacted for another 2 hours according to the above process. Then, the flow rate of the cobalt-containing solution was controlled to be 5% / h of the usable volume of the reactor, and the stirring speed was gradually adjusted from 150 r / min to 100 r / min until a reaction product with a particle size D50 of 19 μm was obtained.

[0099] (3) Post-processing: The final reaction product obtained in step (2) is pumped into a centrifuge, and after centrifugation, washing, and dehydration, the post-processed product is obtained.

[0100] (5) Sintering: The post-processed product was sintered in a rotary kiln. The pre-sintering time was 1 hour at 450℃ with a heating time of 80 minutes, and the high-temperature sintering time was 2 hours at 700℃. Cobalt tetroxide was obtained after sintering.

[0101] In this comparative example, cobalt tetroxide was obtained after the above treatment, with a particle size D50 of 16.5 μm and a specific surface area of ​​6.75 m². 2 / g, tap density = 2.35g / cm³ 3 .

[0102] Comparative Example 2 This comparative example provides a method for preparing cobalt tetroxide, comprising the following steps: (1) Raw material preparation: Cobalt-containing solution: Prepare a cobalt-containing solution containing cobalt and doped metals. The cobalt content in the cobalt-containing solution is 95 g / L, and the doped metals are Al and Mg. The mass ratio of cobalt to doped metals is Co:Al:Mg=1:0.0083:0.0056.

[0103] Precipitating agent solution: Prepare an ammonium bicarbonate solution with a concentration of 190 g / L.

[0104] (2) Reaction steps: A diluted ammonium bicarbonate solution with a concentration of 10 g / L was added to the reactor as the reaction base liquid. Then, a cobalt-containing solution and a precipitant solution were simultaneously pumped into the reactor to carry out the reaction. During the reaction, the flow rate of the cobalt-containing solution was controlled to be 3% / h of the available volume of the reactor. The stirring speed was gradually adjusted from 300 r / min to 250 r / min until a reaction product with a particle size D50 of 9.5 μm was obtained.

[0105] Next, half of the reaction product in the reactor was discharged, and the remaining half was reacted for another 2 hours according to the above process. Then, the flow rate of the cobalt-containing solution was increased to 4% / h of the usable volume of the reactor, and the stirring speed was gradually adjusted from 250 r / min to 200 r / min until a reaction product with a particle size D50 of 13 μm was obtained.

[0106] Next, half of the reaction product in the reactor was discharged, and the remaining half was reacted for another 2 hours according to the above process. Then, the flow rate of the cobalt-containing solution was increased to 5% / h of the usable volume of the reactor, and the stirring speed was gradually adjusted from 200 r / min to 150 r / min until a reaction product with a particle size D50 of 17 μm was obtained.

[0107] Next, half of the reaction product in the reactor was discharged, and the remaining half was reacted for another 2 hours according to the above process. Then, the flow rate of the cobalt-containing solution was controlled to be 5% / h of the usable volume of the reactor, and the stirring speed was gradually adjusted from 150 r / min to 100 r / min until a reaction product with a particle size D50 of 21 μm was obtained.

[0108] (3) Post-processing: The final reaction product obtained in step (2) is pumped into a centrifuge, and after centrifugation, washing, and dehydration, the post-processed product is obtained.

[0109] (5) Sintering: The post-processed product was sintered in a rotary kiln for a total sintering time of 3 hours, including a pre-sintering time of 1.5 hours at 250°C and a high-temperature sintering time of 1.5 hours at 730°C. Cobalt tetroxide was obtained after sintering.

[0110] In this comparative example, cobalt tetroxide was obtained after the above treatment, with a particle size D50 of 17.3 μm and a specific surface area of ​​3.17 m². 2 / g, tap density = 2.65g / cm³ 3 .

[0111] Comparative Example 3 This comparative example provides a method for preparing cobalt tetroxide, comprising the following steps: (1) Raw material preparation: Cobalt-containing solution: Prepare a cobalt-containing solution containing cobalt and a doped metal. The cobalt content in the cobalt-containing solution is 100 g / L, the doped metal is Al, and the mass ratio of the doped metal to cobalt is 0.0273.

[0112] Precipitating agent solution: Prepare an ammonium bicarbonate solution with a concentration of 200 g / L.

[0113] (2) First reaction: An ammonium bicarbonate solution diluted to a concentration of 120 g / L was added to the reactor as the reaction base liquid, with the volume of the base liquid being 20% ​​of the reactor's usable volume. A cobalt-containing solution and a precipitant solution were then simultaneously pumped into the reactor for the first reaction, and the supernatant was continuously removed using a thickener or similar device. During the first reaction, the flow rate of the cobalt-containing solution was 6% / h of the reactor's usable volume. The pH value of the first reaction was controlled to 7.5 by adjusting the flow rate of the precipitant solution, and the reaction temperature was controlled at 36℃ until a first reaction product with a particle size D50 of 11 μm was obtained.

[0114] (3) Second reaction: A cobalt-containing solution and a precipitant solution are simultaneously pumped into a reactor containing the first reaction product to carry out a second reaction, and the supernatant is continuously removed using a thickener or similar device. During the second reaction, the flow rate of the cobalt-containing solution is 6% / h of the available volume of the reactor, the pH value of the second reaction is controlled to 7.3 by adjusting the flow rate of the precipitant solution, and the reaction temperature is controlled at 38℃ until a second reaction product with a particle size D50 of 20 μm is obtained.

[0115] (4) Post-processing: The resulting second reaction product was pumped into a centrifuge, and after centrifugation, washing, and dehydration, a post-processed product was obtained.

[0116] (5) Sintering: The post-processed product was sintered in a rotary kiln for 1.5 hours, followed by a pre-sintering time of 0.8 hours at 300°C and a high-temperature sintering time of 2.2 hours at 800°C. Cobalt tetroxide was obtained after sintering.

[0117] In this comparative example, cobalt tetroxide was obtained after the above treatment, with a particle size D50 of 16.5 μm and a specific surface area of ​​2.38 m². 2 / g, tap density = 2.81g / cm³ 3 .

[0118] Comparative Example 4 This comparative example provides a method for preparing cobalt tetroxide, comprising the following steps: (1) Raw material preparation: Cobalt-containing solution: Prepare a cobalt-containing solution containing cobalt and a doped metal. The cobalt content in the cobalt-containing solution is 100 g / L, the doped metal is Al, and the mass ratio of the doped metal to cobalt is 0.0273.

[0119] Precipitating agent solution: Prepare an ammonium bicarbonate solution with a concentration of 200 g / L.

[0120] (2) First reaction: An ammonium bicarbonate solution diluted to a concentration of 120 g / L was added to the reactor as the reaction base liquid, with the volume of the base liquid being 20% ​​of the reactor's usable volume. A cobalt-containing solution and a precipitant solution were then simultaneously pumped into the reactor for the first reaction, and the supernatant was continuously removed using a thickener or similar device. During the first reaction, the flow rate of the cobalt-containing solution was 6% / h of the reactor's usable volume. The pH value of the first reaction was controlled to 7.5 by adjusting the flow rate of the precipitant solution, and the reaction temperature was controlled at 36℃ until a first reaction product with a particle size D50 of 11 μm was obtained.

[0121] (3) Second reaction: A cobalt-containing solution and a precipitant solution were simultaneously pumped into a reactor containing the first reaction product to carry out a second reaction, and the supernatant was continuously removed using a thickener or similar device. During the second reaction, the flow rate of the cobalt-containing solution was 6% / h of the available volume of the reactor, the pH value of the second reaction was controlled to 7.3 by adjusting the flow rate of the precipitant solution, and the reaction temperature was controlled at 38℃ until a second reaction product with a particle size D50 of 20.2 μm was obtained.

[0122] (4) Post-processing: The resulting second reaction product was pumped into a centrifuge, and after centrifugation, washing, and dehydration, a post-processed product was obtained.

[0123] (5) Sintering: The post-processed product was sintered in a rotary kiln for 1.5 hours, followed by a pre-sintering time of 0.8 hours at 400°C and a high-temperature sintering time of 2.2 hours at 900°C. Cobalt tetroxide was obtained after sintering.

[0124] In this comparative example, cobalt tetroxide was obtained after the above treatment, with a particle size D50 of 16.2 μm and a specific surface area of ​​0.97 m². 2 / g, tap density = 2.98g / cm³ 3 .

[0125] Table 1 Performance indicators of cobalt tetroxide obtained in the examples and comparative examples In Table 1, the grain size of the (311) crystal plane is calculated using the formula D = K·γ / (B·cosθ).

[0126] For Example 1, B is the half-maximum width at half maximum (FWHM) of the (311) crystal plane (0.115°), the Scherrer constant K is 0.89, γ is the X-ray wavelength (1.54056 Å), and cosθ is 0.9488. Therefore, the grain size of the (311) crystal plane in Example 1 is calculated using the formula: = 0.89 * 1.54046 / [(0.115 / 180 * 3.14) * 0.9488)] = 719 Å. The calculation methods for other examples and comparative examples are the same as for Example 1, and the calculation results are shown in Table 1 above.

[0127] Test methods (a) Preparation of cathode materials: Lithium carbonate was selected as the lithium source, and the molar ratio of lithium in the lithium source to the sum of cobalt and other doped metals in cobalt tetroxide was 1.05:1. The selected lithium source was sintered with cobalt tetroxide prepared in each example and comparative example to obtain the corresponding cathode materials, which were lithium cobalt oxide cathode materials.

[0128] (II) Battery fabrication: Using the positive electrode materials prepared in the above examples and comparative examples, conductive carbon black and polyvinylidene fluoride were dissolved in NMP solvent under vacuum at a mass ratio of 85:10:5 to prepare positive electrode slurries with a solid content of 80% by weight. These slurries were then coated, dried, and stamped to obtain positive electrode discs. Lithium-ion batteries were then prepared in the following order: positive electrode shell - positive electrode sheet - separator - negative electrode sheet - stainless steel sheet - spring sheet - negative electrode shell. The electrolyte was a 1 mol / L LiPF6 / EC:DMC solution (volume ratio 1:1) with 10% (volume fraction) fluoroethylene carbonate (FEC). The separator was a polypropylene microporous membrane. Lithium-ion batteries of Examples 1 to 3 and Comparative Examples 1 to 4 were prepared. At room temperature, charge-discharge tests at 0.1C and 50 cycles at 0.2C (1C = 190 mAh g⁻¹) were conducted at 3.0-4.6V. The battery performance of each example and comparative example is shown in Table 2.

[0129] Table 2. Electrochemical performance of batteries prepared from cobalt tetroxide according to the various examples and comparative examples. According to Table 1-2, the cobalt tetroxide prepared in Examples 1-3 has a grain size in the (311) crystal plane of 620-765 Å, and the prepared cathode material has good structural stability, thereby improving the cycle performance of the corresponding battery and also having a good first-cycle discharge capacity. However, the cobalt tetroxide prepared in Comparative Examples 1-4 has a grain size in the (311) crystal plane of not being in the 620-765 Å range, and its cycle performance is much lower than that of Examples 1-3, and its first-cycle discharge capacity is also lower.

[0130] according to Figure 1 , Figure 3 and Figure 5 It can be seen that the cobalt tetroxide in Examples 1-3 comprises an inner layer and an outer layer from the inside out. The inner layer is dense, while the outer layer is porous. The outer layer contains numerous gaps with relatively large widths and lengths on the micrometer scale. These gaps extend radially along the secondary particles and are distributed in a radial pattern. Figure 8 and Figure 10 The cobalt tetroxide shown has dispersed pores in the outer layer, with the gaps not arranged radially and being relatively short. For example, Figure 1 The lengths of the three gaps that were selected are 2.04 μm, 1.61 μm, and 3.18 μm, respectively. Figure 3 The lengths of the three gaps that were selected are 1.84μm, 2.88μm, and 4.76μm, respectively. Figure 5 The two gaps selected in the bidding are 2.35 μm and 3.88 μm in length, respectively. Because the outer layer has gaps arranged radially and reaching micrometer-scale lengths, molten lithium carbonate can more easily penetrate into the cobalt tetroxide during the sintering of cobalt tetroxide with lithium sources such as lithium carbonate to prepare the cathode material, which is beneficial for improving reaction activity. Furthermore, by controlling the proportion and porosity of the inner layer within a suitable range, the compressive strength of the particles can be further improved, resulting in a cathode material with good structural stability, thereby improving cycle performance and exhibiting good first-cycle discharge capacity. In addition, cobalt tetroxide with the above structure has high reactivity and can achieve the reaction requirements at a relatively low temperature, thus reducing the required sintering temperature and helping to reduce costs.

[0131] Fifty secondary particles of positive electrode material from Examples 1-3 and Comparative Examples 1-4 were randomly selected and subjected to compressive mechanical strength tests at 35 MPa. The D00 before and after compression was measured, and the particle size D00 change rate of Examples 1-3 was found to be less than 3%. Figure 2 , 4 Images 6 and 7 are SEM images of the secondary particles in Examples 1-3 before and after pressing, respectively. Figure 7 , 9Figures 1 and 11 show the SEM images of the secondary particles from Comparative Examples 1-3 before and after compression, respectively. Observation of the SEM images before and after compression reveals that the cobalt tetroxide particles from Comparative Examples 1-3 all exhibit varying degrees of cracking after compression, with Comparative Example 1 showing the most significant breakage. In contrast, the cobalt tetroxide particles from Examples 1-3 remain largely intact after compression. This demonstrates that the cobalt tetroxide with its specific inner and outer layer structure prepared according to the embodiments of this application exhibits higher structural strength. Correspondingly, referring to Table 2, the batteries prepared based on cobalt tetroxide from Comparative Examples 1-4 all show poor 50-cycle cycle retention rates, while the batteries corresponding to Examples 1-3 achieve a 50-cycle cycle retention rate of over 92.1%. This indicates that the batteries prepared according to the embodiments of this application have better cycle stability and higher capacity.

[0132] The technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification, provided that such combination does not contain contradictions.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A cobalt tetroxide, characterized in that, The secondary particles consist of multiple primary particles, which are spherical or near-spherical. The cobalt tetroxide has a grain size of 620-765 Å on the (311) crystal plane obtained by XRD. The secondary particles consist of an inner layer and an outer layer from the inside out. The porosity of the outer layer is 15%-25%, and the porosity of the inner layer is ≤5%.

2. The cobalt tetroxide according to claim 1, characterized in that, The secondary particles have a crystallinity ≥70%; and / or The half-width of the characteristic peak corresponding to the (311) crystal plane of the secondary particles is 0.115°-0.145°.

3. The cobalt tetroxide according to claim 1, characterized in that, On the cross-section of the secondary particles, the area of ​​the inner layer accounts for 10%-65%; and / or The outer layer has gaps extending radially along the secondary particles, the length of which is 1.5-6 μm.

4. The cobalt tetroxide according to any one of claims 1-3, characterized in that, The cobalt tetroxide satisfies at least one of the following ae conditions: a. The average particle size D50 of the secondary particles is 15-20 μm; b. The D00 change rate of the secondary particles under a pressure of 35 MPa is ≤3%; c. The average pore size inside the secondary particles is 60-90 nm; d. The specific surface area of ​​the secondary particles is 1.8-3.5 m². 2 / g; e. The tap density of the secondary particles is 2.6-3.0 g / cm³. 3 .

5. A method for preparing cobalt tetroxide according to any one of claims 1-4, characterized in that, Includes the following steps: A reaction base solution containing a precipitant is prepared, and a precipitant solution and a cobalt-containing solution are simultaneously added to the reaction base solution to carry out a first reaction to obtain a first reaction product. The particle size D50 of the first reaction product is 11-13 μm. During the first reaction, the flow rate of the cobalt-containing solution is 5-8% / h of the available volume of the reaction vessel. A precipitant solution and a cobalt-containing solution are added to the first reaction product to carry out a second reaction, thereby obtaining a second reaction product. During the second reaction, the flow rate of the cobalt-containing solution is 3-5% / h of the available volume of the reaction vessel. The second reaction product is post-processed and sintered to obtain cobalt tetroxide, wherein the sintering includes pre-sintering and high-temperature sintering, the pre-sintering temperature is 200-300℃, and the high-temperature sintering temperature is 700-750℃.

6. The method for preparing cobalt tetroxide according to claim 5, characterized in that, The preparation method satisfies at least one of the following conditions (1)-(5): (1) The precipitant includes at least one of sodium bicarbonate, sodium carbonate, and ammonium bicarbonate; (2) The concentration of the precipitant in the reaction substrate is 20-120 g / L; (3) The volume of the reaction substrate is 20-60% of the usable volume of the reaction vessel; (4) The concentration of the precipitant in the precipitant solution is 200-230 g / L; (5) The cobalt-containing solution includes cobalt and a doped metal, wherein the doped metal is selected from at least one of the elements Al, Ni, Mn, Zr, Ti, La, Mg and Y.

7. The method for preparing cobalt tetroxide according to claim 6, characterized in that, The cobalt concentration of the cobalt-containing solution is 100-130 g / L, and the mass ratio of the doped metal to the cobalt is 0.0036-0.0273:

1.

8. The method for preparing cobalt tetroxide according to any one of claims 5-7, characterized in that, The preparation method satisfies at least one of the following conditions: ② The pH value of the first reaction is 7.2-7.5; ③ The reaction temperature of the first reaction is 38-40℃; ④ The particle size D50 of the second reaction product is 19-21 μm; ⑥ The pH value of the second reaction is 7.0-7.2; ⑦ The reaction temperature of the second reaction is 40-42℃; ⑧ The total sintering time is 1-3 hours, wherein the ratio of the pre-sintering time to the high-temperature sintering time is 1:(2-4), and the time required for the pre-sintering temperature to rise to the high-temperature sintering temperature is ≤1 hour.

9. A positive electrode material, characterized in that, Cobalt tetroxide is prepared by the preparation methods of cobalt tetroxide according to any one of claims 1-4 and cobalt tetroxide according to any one of claims 5-8.

10. A lithium-ion battery, characterized in that, Includes the cathode material as described in claim 9.

11. An electrical-related device, characterized in that, Including the lithium-ion battery of claim 10.

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