High-tap-density cobalt oxide and preparation method and application thereof

Abstract

The invention discloses cobalt oxide with high tap density and a preparation method and application thereof, the preparation method comprises the following steps: 1) adding a first cobalt-containing salt solution into an ammonium bicarbonate solution, and carrying out a co-precipitation reaction under a stirring condition to obtain a reaction system containing cobalt carbonate with small particle size; (2) introducing a second cobalt-containing salt solution and a first precipitant solution, and reacting, so that the small-particle-size cobalt carbonate is quickly agglomerated to form large-particle seed crystals, thereby obtaining a reaction system containing the large-particle seed crystals; and 3) introducing a third cobalt-containing salt solution and a second precipitant solution, carrying out a co-precipitation reaction to make the particle size grow slowly, and then drying and calcining the product of the co-precipitation reaction to obtain the cobalt oxide with high tap density. According to the method disclosed by the invention, the reaction period is greatly shortened by rapidly preparing the large-particle seed crystal. Moreover, the internal densification of the material is ensured, and the distribution uniformity of doped elements can be ensured for the preparation of the doped cobalt carbonate, so that the doped elements in the high-tap-density cobalt oxide are uniformly distributed.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a high tap density cobalt oxide, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) are widely used in energy storage due to their long lifespan and high energy density. Lithium cobalt oxide (LCO), as the earliest commercially available cathode material, still holds an unshakeable position in the current consumer electronics market. The performance of lithium cobalt oxide is highly dependent on the physical properties of its precursor, cobalt tetroxide (Co3O4). Traditional Co3O4 precursors suffer from low tap density, resulting in loose material packing and numerous interparticle pores, which limits the improvement of electrode tap density and volumetric energy density.

[0003] To improve the tap density (TD) of Co3O4, existing technologies disclose several improvement methods, such as optimizing the precursor morphology, particle size distribution, and crystallinity, which can improve the compactness and structural stability of lithium cobalt oxide particles, thereby increasing the active material loading per unit volume of the electrode sheet, while reducing the structural stress during lithium ion insertion / extraction and extending its cycle life.

[0004] CN117509746A discloses a method for preparing high-tap, aluminum-doped large-particle cobalt tetroxide and its application. By improving the preparation process of aluminum-doped large-particle cobalt tetroxide, specifically limiting parameters such as pH, temperature, and stirring speed in seed preparation and co-precipitation reactions, the method enables the aluminum-doped cobalt carbonate to have higher density during the precipitation stage, while also allowing aluminum to enter the cobalt carbonate particles more uniformly. Furthermore, the method limits conditions such as the calcination temperature of the cobalt carbonate, resulting in large-particle cobalt tetroxide with higher tap density, better sphericity, and more uniform aluminum doping. This ultimately leads to lithium-ion batteries with better electrical performance and longer lifespan.

[0005] CN105271441A discloses a method for preparing battery-grade large-particle cobalt tetroxide, comprising the following steps: 1) dissolving cobalt salt or diluting cobalt liquid to prepare a cobalt solution; 2) preparing a hydroxide solution with a concentration of 2 mol / L to 5 mol / L, and adding a certain proportion of complexing agent to prepare a mixed precipitant solution; 3) preparing an additive solution with a molar concentration of 0.05 mol / L to 10 mol / L; 4) adding the above solutions to a reaction apparatus for a synthesis reaction, wherein the cobalt solution and the precipitant solution are added in a co-current manner, and the additive solution is added directly to the synthesis base solution or mixed with the precipitant solution and added in a co-current manner or added separately in a co-current manner. After the reaction yields a precursor, it is washed and filtered, and then calcined at 500℃ to 850℃ for 2h to 5h to obtain large-particle cobalt tetroxide. The battery-grade cobalt tetroxide powder prepared by this method can achieve a particle size of over 13 μm, with good uniformity, high sphericity, and high tap density, making it suitable for preparing cathode materials for high-voltage lithium cobalt oxide batteries.

[0006] However, current co-precipitation methods for high-tap-density materials exhibit slow growth rates and extended reaction cycles. Large particle sizes (15μm~20μm) require 150h~300h of reaction time, which is unfavorable for industrial production. Furthermore, doping with other elements further limits the improvement of tap density. In traditional co-precipitation preparation of highly doped (e.g., Al-doped) cobalt carbonate, the early precipitation reaction often generates porous structures in the core, reducing its tap density, and Al at the core segregates in the pores. On the other hand, the slow growth rate in the later stages of traditional co-precipitation necessitates separate reactors to reduce the amount of seed crystals. This results in ring-shaped growth layers with an abrupt change in growth rate before and after reactor separation, creating delamination after calcination that hinders ion transport in the cathode material.

[0007] Therefore, providing a method for preparing cobalt oxide with high tap density, reducing the reaction cycle, and avoiding the calcination stratification problem caused by separate reactors is a technical problem that urgently needs to be solved. Summary of the Invention

[0008] In view of the above-mentioned technical problems existing in the prior art, the purpose of this invention is to provide a high tap density cobalt oxide, its preparation method and application.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing high tap density cobalt oxide, the method comprising the following steps:

[0011] (1) Add a first cobalt salt solution to an ammonium bicarbonate solution and carry out a coprecipitation reaction under stirring to obtain a reaction system containing small-particle cobalt carbonate, wherein the particle size D50 of the small-particle cobalt carbonate is in the range of 800 nm to 1200 nm.

[0012] (2) Continue to pass the second cobalt salt solution and the first precipitant solution into the reaction system obtained in step (1) to react, so that the small-diameter cobalt carbonate aggregates to form large-particle seed crystals, and obtain a reaction system containing large-particle seed crystals.

[0013] (3) Continue to pass a third cobalt salt solution and a second precipitant solution into the reaction system obtained in step (2) for coprecipitation reaction. Then, dry and calcine the product of the coprecipitation reaction to obtain the high tap density cobalt oxide.

[0014] This invention first prepares dense, small-particle cobalt carbonate with a particle size D50 in the range of 800 nm to 1200 nm using a nanonucleation process. Then, through a reaction, the small-particle cobalt carbonate rapidly agglomerates to form dense, large-particle seed crystals without voids, increasing the tap density of the material while shortening the reaction cycle. Finally, cobalt carbonate is slowly grown on these large-particle seed crystals to complete the preparation of cobalt carbonate. After calcination, high-tap-density cobalt oxide is obtained. The method of this invention significantly shortens the reaction cycle by rapidly preparing large-particle seed crystals. The preparation of large-particle cobalt carbonate with a particle size D50 of 15 μm to 21 μm requires only a co-precipitation reaction time of 40 h to 145 h, more preferably 40 h to 80 h. Moreover, the cobalt carbonate prepared by the method of this invention has a uniform morphology with a diameter-to-gap ratio in the range of 0.29 to 1.29, preferably in the range of 0.29 to 0.34. Meanwhile, the method of this invention ensures the densification of the material's interior by rapidly agglomerating small-particle seeds to prepare large-particle seed crystals, and also ensures the uniformity of dopant element distribution in the preparation of doped cobalt carbonate, thereby resulting in a uniform distribution of dopant elements in high-tap-density cobalt oxide. The tap density of the high-tap-density cobalt oxide is 2.52 g / m³. 3 ~3.2 g / m 3 Within the range, preferably 2.89 g / m 3 ~3.2 g / m 3 Within the range.

[0015] The method of this invention can prepare cobalt carbonate in a single reaction, and high-tap-density cobalt oxide can be obtained by simple calcination. It eliminates the need for frequent adjustments to the feed rate and separate reactors to reduce the seed crystal amount based on the growth rate.

[0016] In this invention, the cobalt carbonate prepared by the coprecipitation reaction can be undoped cobalt carbonate or element-doped cobalt carbonate (e.g., Al). The method of this invention not only ensures the high tap density of the doped cobalt carbonate but also guarantees the uniformity of the dopant element distribution. In one embodiment, when preparing the doped cobalt carbonate, the dopant element is added to a first cobalt-containing solution, a second cobalt-containing solution, and a third cobalt-containing solution.

[0017] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0018] Preferably, the cobalt salt in the first cobalt-containing salt solution, the second cobalt-containing salt solution, and the third cobalt-containing salt solution independently includes at least one of cobalt chloride, cobalt sulfate, and cobalt nitrate.

[0019] Preferably, the concentrations of the first cobalt salt solution, the second cobalt salt solution, and the third cobalt salt solution are independently 80 g / L to 150 g / L, for example, they can be 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, 130 g / L, 135 g / L, 140 g / L, 145 g / L, or 150 g / L, etc.

[0020] Preferably, the first cobalt-containing salt solution, the second cobalt-containing salt solution, and the third cobalt-containing salt solution further independently include salts of doping elements, wherein the doping elements include at least one selected from Al, Ni, Mg, Y, W, Nb, La, Zr, and Ti.

[0021] Preferably, the mass of the doping element accounts for 0.1% to 2% of the total mass of high tap density cobalt oxide, for example, it can be 0.1%, 0.3%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.6%, 1.8% or 2%, etc.

[0022] Preferably, the first precipitant solution and the second precipitant solution are ammonium bicarbonate solutions.

[0023] Preferably, the concentrations of the first precipitant solution and the second precipitant solution are independently 100 g / L to 200 g / L, for example, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L or 200 g / L, etc.

[0024] As a preferred embodiment of the preparation method described in this invention, the stirring speed is greater than 400 r / min and less than or equal to 600 r / min, for example, it can be 405 r / min, 410 r / min, 420 r / min, 450 r / min, 460 r / min, 480 r / min, 500 r / min, 525 r / min, or 550 r / min. Within this range, the compactness of small-diameter cobalt oxide particles can be guaranteed, avoiding the formation of porous structures in the core. More preferably, the reaction is carried out under high temperature and high rotation speed conditions to improve the compactness of small-diameter cobalt oxide particles. Further increasing the stirring speed does not further improve the particle properties and increases energy consumption; therefore, the above-mentioned preferred range is preferred.

[0025] Preferably, the temperature for the coprecipitation reaction in step (1) is 40℃~50℃, for example, it can be 40℃, 42℃, 43℃, 44℃, 45℃, 46℃, 48℃ or 50℃, etc. Higher temperature and rotation speed conditions are more conducive to the formation of dense cobalt carbonate.

[0026] Preferably, the coprecipitation reaction time in step (1) is 3h to 5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h.

[0027] Preferably, the concentration of the ammonium bicarbonate solution in step (1) is 50 g / L to 100 g / L, for example, it can be 50 g / L, 60 g / L, 65 g / L, 70 g / L, 80 g / L, 85 g / L, 90 g / L, or 100 g / L. In this invention, ammonium bicarbonate is used as the base liquid. If the concentration of ammonium bicarbonate is less than 50 g / L, the concentration of the precipitant will be too low after the cobalt salt solution is added, and it will not be able to form nuclei quickly and uniformly. The number of crystal nuclei will be small and the particle size will be large and irregular, with a wide diameter distribution. This will result in uneven particle size when the growth is completed in the later stage, a loose and porous material structure, and a low tap density (TD). If the concentration of ammonium bicarbonate is too high, the cobalt carbonate will precipitate in a flocculent manner and will not be able to form nuclei. It will form a hollow structure when entering the growth stage, resulting in a decrease in TD.

[0028] Preferably, the volume ratio of the first cobalt-containing salt solution to the ammonium bicarbonate solution in step (1) is 1:(3~5), for example, it can be 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.7, 1:4.8 or 1:5, etc. If the amount of ammonium bicarbonate solution is too small, the first cobalt-containing salt solution will not react completely, and the reaction will be rapid when the material is re-fed in step (2), resulting in an insufficiently dense internal structure. If the amount of ammonium bicarbonate solution is too large, the residual ammonium bicarbonate will continue to react with the cobalt in step (2) to form small particles of cobalt oxide, which cannot quickly agglomerate into seed crystals, resulting in a longer reaction cycle.

[0029] As a preferred technical solution of the preparation method of the present invention, in step (2), the reaction temperature is 30℃~35℃, for example, it can be 30℃, 31℃, 32℃, 33℃, 34℃ or 35℃, etc.

[0030] Preferably, in step (2), the reaction is carried out at a speed of 300 r / min to 400 r / min. For example, the speed can be 300 r / min, 320 r / min, 340 r / min, 350 r / min, 365 r / min, 380 r / min or 400 r / min, etc.

[0031] Preferably, in step (2), during the reaction process, the feed rate of the second cobalt salt solution is 60 L / h to 80 L / h, for example, it can be 60 L / h, 63 L / h, 66 L / h, 68 L / h, 70 L / h, 72 L / h, 75 L / h, 77 L / h, or 80 L / h, etc.; the particle size growth rate is controlled to be 0.4 μm / h to 0.6 μm / h, for example, it can be 0.4 μm / h, 0.42 μm / h, 0.44 μm / h, 0.46 μm / h, 0.48 μm / h, 0.5 μm / h, 0.52 μm / h, 0.55 μm / h, 0.56 μm / h, 0.58 μm / h, or 0.6 μm / h, etc. Here, the particle size growth rate refers to the increase in D50 per hour.

[0032] If the feed rate of the second cobalt salt solution is too slow, the small crystal nuclei will have difficulty agglomerating quickly and will begin to grow slowly. Too many crystal nuclei in the system will make later growth difficult and the preparation cycle will be long. If the feed rate of the second cobalt salt solution is too fast, the agglomeration of crystal nuclei will be uncontrolled, resulting in a large number of uneven agglomerations with abnormal morphology, large irregular spheres, poor sphericity and wide particle size distribution when the reactor is shut down in the later stage.

[0033] Preferably, in step (2), during the reaction process, the ratio of the feed rate of the second cobalt salt solution to the feed rate of the first precipitant solution is (1~1.5):1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.4:1 or 1.5:1, etc.

[0034] Preferably, the reaction time in step (2) is 8h to 12h, for example, it can be 8h, 9h, 10h, 11h or 12h.

[0035] Preferably, the particle size D50 of the aggregated lithium cobalt oxide obtained in step (2) is in the range of 10 μm to 12 μm. For example, the particle size can be 10 μm, 10.5 μm, 11 μm, 11.5 μm or 12 μm, etc.

[0036] As a preferred technical solution of the preparation method of the present invention, in the coprecipitation reaction in step (3), the pH value is controlled in the range of 6.5 to 8.5. For example, the pH value can be 6.5, 7, 7.5, 7.7, 7.8, 8, 8.2, 8.3 or 8.5, etc.

[0037] Preferably, during the coprecipitation reaction in step (3), the stirring is performed at a speed of 100 r / min to 200 r / min. For example, the speed can be 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min or 200 r / min, etc.

[0038] Preferably, in the co-precipitation reaction described in step (3), the feed volume ratio of the third cobalt salt solution and the second precipitant solution is 1:(1.5~2), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc.; the particle size growth rate is controlled at 0.1μm / h~0.2μm / h, for example, it can be 0.1μm / h, 0.11μm / h, 0.12μm / h, 0.13μm / h, 0.14μm / h, 0.15μm / h or 0.2μm / h, etc. Here, the particle size growth rate refers to the increase in D50 per hour.

[0039] The growth rate can be adjusted within a small range by regulating the feed rate of the third cobalt salt solution and the second precipitant solution during the coprecipitation reaction process described in step (3).

[0040] Preferably, the temperature of the coprecipitation reaction in step (3) is 35℃~45℃, for example, it can be 35℃, 36℃, 37℃, 38℃, 40℃, 42℃, 43℃ or 45℃, etc.

[0041] Preferably, in step (3), the coprecipitation reaction is stopped when the particle size D50 of the product is 15μm~21μm. For example, the particle size D50 can be 15μm, 15.5μm, 16μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 20.5μm or 21μm, etc.

[0042] As a preferred technical solution of the preparation method of the present invention, the drying temperature in step (3) is 80℃~130℃, for example, it can be 80℃, 90℃, 100℃, 110℃, 120℃ or 130℃.

[0043] Preferably, the calcination temperature in step (3) is 600℃~800℃, for example, it can be 600℃, 625℃, 650℃, 660℃, 680℃, 700℃, 720℃, 750℃, 770℃, 780℃ or 800℃, etc.

[0044] Preferably, the calcination time in step (3) is 0.5h to 2h, for example, it can be 0.5h, 1h, 1.2h, 1.5h, 1.8h or 2h.

[0045] Preferably, the calcination atmosphere in step (3) is an air atmosphere.

[0046] Secondly, the present invention provides a high-tap-density cobalt oxide, which is prepared by the method described in the first aspect. The high-tap-density cobalt oxide is undoped cobalt tetroxide or M-doped cobalt tetroxide, and the tap density of the high-tap-density cobalt oxide is 2.8 g / m³. 3 ~3.1g / m 3 For example, it could be 2.8g / m 3 2.82g / m 3 2.84g / m 3 2.86g / m 3 2.88g / m 3 2.9g / m 3 2.92g / m 3 2.95g / m 3 2.96g / m 3 2.98g / m 3 3.00g / m 3 3.02g / m 3 3.05g / m 3 3.07g / m 3 3.08g / m 3 Or 3.1g / m 3 wait.

[0047] Thirdly, the present invention provides a lithium cobalt oxide, which is prepared by using the high tap density cobalt oxide described in the second aspect.

[0048] Fourthly, the present invention provides a lithium-ion battery comprising the lithium cobalt oxide described in the third aspect.

[0049] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0050] Compared with existing technologies, the present invention has the following beneficial effects:

[0051] (1) In this invention, dense small-particle cobalt carbonate with a particle size D50 in the range of 800 nm to 1200 nm is first prepared by nanonucleation process. Then, the small-particle cobalt carbonate is rapidly agglomerated through reaction to form dense large-particle seed crystals without voids, thereby increasing the tap density of the material and shortening the reaction cycle. Finally, cobalt carbonate is slowly grown on the large-particle seed crystals to complete the preparation of cobalt carbonate. After calcination, high-tap-density cobalt oxide is obtained. The method of this invention greatly shortens the reaction cycle by rapidly preparing large-particle seed crystals. The preparation of large-particle cobalt carbonate with a particle size D50 of 15 μm to 21 μm only requires a co-precipitation reaction time of 40 h to 145 h, more preferably 40 h to 80 h. Moreover, the cobalt carbonate prepared by the method of this invention has a uniform morphology with a diameter-to-size distance in the range of 0.29 to 1.29, preferably in the range of 0.29 to 0.34. Meanwhile, the method of this invention ensures the densification of the material's interior by rapidly agglomerating small-particle seeds to prepare large-particle seed crystals, and also ensures the uniformity of dopant element distribution in the preparation of doped cobalt carbonate, thereby resulting in a uniform distribution of dopant elements in high-tap-density cobalt oxide. The tap density of the high-tap-density cobalt oxide is 2.52 g / m³. 3 ~3.2 g / m 3 Within the range, preferably 2.89 g / m 3 ~3.2g / m 3 Within the range.

[0052] (2) The method of the present invention can prepare cobalt oxide in one reaction, and high tap density cobalt oxide can be obtained by simple calcination. It does not require frequent adjustment of the feed rate and reduction of seed crystal amount according to the growth rate. Attached Figure Description

[0053] Figure 1 This is a cross-sectional SEM image of the aluminum-doped cobalt carbonate prepared in Example 1.

[0054] Figure 2 This is a surface SEM image of aluminum-doped cobalt carbonate prepared in Example 1.

[0055] Figure 3 This is a SEM image of the cobalt carbonate prepared in Example 4.

[0056] Figure 4 This is a cross-sectional SEM image of cobalt carbonate prepared in Example 5.

[0057] Figure 5 This is a SEM image of the cobalt oxide prepared in Example 9. Detailed Implementation

[0058] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0060] The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0061] Example 1

[0062] This embodiment provides a method for preparing high tap density cobalt oxide, including the following steps:

[0063] (1) The first cobalt salt solution (the first cobalt salt solution is a mixed solution of cobalt chloride and aluminum chloride, the mass of aluminum element accounts for 0.1% of the total mass of high tap density cobalt oxide, and the concentration of the first cobalt salt solution is 80 g / L) is rapidly added to the ammonium bicarbonate solution (concentration is 50 g / L), and the co-precipitation reaction is carried out at 40℃ and 450 r / min for 4 h to obtain a reaction system containing small-particle cobalt carbonate, wherein the particle size D50 of the small-particle cobalt carbonate is 1000 nm;

[0064] The volume ratio of the first cobalt-containing salt solution to the ammonium bicarbonate solution in step (1) is 1:4;

[0065] (2) Continue to pass a second cobalt salt solution (the second cobalt salt solution is a mixed solution of cobalt chloride and aluminum chloride, the mass of aluminum element accounts for 0.1% of the total mass of high tap density cobalt oxide, and the concentration of the second cobalt salt solution is 80 g / L) and a first precipitant solution (ammonium bicarbonate solution with a concentration of 100 g / L) into the reaction system obtained in step (1). Co-precipitate reaction is carried out at 30℃ and 300 r / min for 18 h, so that small-diameter cobalt carbonate particles can quickly agglomerate to form large-particle seed crystals (particle size D50 is 10 μm), and a reaction system containing large-particle seed crystals is obtained.

[0066] In step (2), the feed rate of the second cobalt salt solution is 60 L / h, the feed volume ratio of the second cobalt salt solution to the first precipitant solution is 1:1, and the particle size growth rate in step (2) is 0.5 μm / h.

[0067] (3) Continue to pass a third cobalt salt solution (the third cobalt salt solution is a mixed solution of cobalt chloride and aluminum chloride, the mass of aluminum element accounts for 0.1% of the total mass of high tap density cobalt oxide, and the concentration of the third cobalt salt solution is 80 g / L) and a second precipitant solution (ammonium bicarbonate solution with a concentration of 140 g / L) into the reaction system obtained in step (2). The co-precipitation reaction is carried out under the conditions of pH 7.0 and stirring speed of 100 r / min. The reaction is stopped when the particle size reaches 15 μm. Then the product of the co-precipitation reaction (aluminum-doped cobalt carbonate) is dried in an oven at 80 °C and then calcined at 600 °C for 0.5 h under air conditions to obtain the high tap density cobalt oxide.

[0068] The ratio of the feed rates of the third cobalt salt solution and the second precipitant solution in step (3) is 1:2, and the particle size growth rate in step (3) is 0.12 μm / h.

[0069] Figure 1 The image shows a cross-sectional SEM image of the aluminum-doped cobalt carbonate prepared in Example 1. As can be seen from the image, the sample particles have good sphericity and the overall cross-section is dense. No large pores were found in the cross-section at different depths. This structure ensures the high TD and stability of the sample.

[0070] Figure 2 The image shows a surface SEM image of the aluminum-doped cobalt oxide prepared in Example 1. As can be seen from the image, the sample did not crack after calcination, and the surface was uniform. The small grains and micropores provided abundant lithium-ion channels for the subsequent preparation of lithium cobalt oxide cathodes. By improving the compactness and structural stability of lithium cobalt oxide particles, the active material loading per unit volume of the electrode sheet was increased, while the structural stress during the lithium-ion insertion / extraction process was reduced, thus extending its cycle life.

[0071] Example 2

[0072] This embodiment provides a method for preparing high tap density cobalt oxide, including the following steps:

[0073] (1) The first cobalt salt solution (the first cobalt salt solution is a mixed solution of cobalt sulfate and nickel sulfate, the mass of nickel element accounts for 0.3% of the total mass of high tap density cobalt oxide, and the concentration of the first cobalt salt solution is 120 g / L) is rapidly added to the ammonium bicarbonate solution (concentration is 60 g / L), and the co-precipitation reaction is carried out at 50℃ and a stirring speed of 600 r / min for 3 h to obtain a reaction system containing small-diameter cobalt carbonate, wherein the particle size D50 of the small-diameter cobalt carbonate is 800 nm;

[0074] The volume ratio of the first cobalt-containing salt solution to the ammonium bicarbonate solution in step (1) is 1:3;

[0075] (2) Continue to pass a second cobalt salt solution (the second cobalt salt solution is a mixed solution of cobalt sulfate and nickel sulfate, the mass of nickel element accounts for 1% of the total mass of high tap density cobalt oxide, and the concentration of the second cobalt salt solution is 90 g / L) and a first precipitant solution (ammonium bicarbonate solution with a concentration of 200 g / L) into the reaction system obtained in step (1). Co-precipitate reaction is carried out at 32℃ and 350 r / min for 20 h, so that small-diameter cobalt carbonate particles can quickly agglomerate to form large-particle seed crystals (particle size D50 is 11.6 μm), and a reaction system containing large-particle seed crystals is obtained.

[0076] In step (2), the feed rate of the second cobalt salt solution is 80 L / h, the feed volume ratio of the second cobalt salt solution to the first precipitant solution is 1:1.2, and the particle size growth rate in step (2) is 0.55 μm / h.

[0077] (3) Continue to pass a third cobalt salt solution (the third cobalt salt solution is a mixed solution of cobalt sulfate and nickel sulfate, the mass of nickel element accounts for 1.5% of the total mass of high tap density cobalt oxide, and the concentration of the third cobalt salt solution is 115 g / L) and a second precipitant solution (ammonium bicarbonate solution with a concentration of 180 g / L) into the reaction system obtained in step (2). The co-precipitation reaction is carried out under the conditions of pH 7 and stirring speed of 150 r / min. The reaction is stopped when the particle size reaches 18 μm. Then the product of the co-precipitation reaction (nickel-doped cobalt carbonate) is dried in an oven at 80 °C and then calcined at 700 °C for 1 h under air conditions to obtain the high tap density cobalt oxide.

[0078] The ratio of the feed rates of the third cobalt salt solution and the second precipitant solution in step (3) is 1:1.8, and the particle size growth rate in step (3) is 0.1 μm / h.

[0079] Example 3

[0080] This embodiment provides a method for preparing high tap density cobalt oxide, including the following steps:

[0081] (1) The first cobalt salt solution (the first cobalt salt solution is a mixed solution of cobalt nitrate and magnesium nitrate, the mass of magnesium element accounts for 1.3% of the total mass of high tap density cobalt oxide, and the concentration of the first cobalt salt solution is 150 g / L) is rapidly added to the ammonium bicarbonate solution (concentration is 100 g / L), and the co-precipitation reaction is carried out at 45℃ and a stirring speed of 500 r / min for 5 h to obtain a reaction system containing small-diameter cobalt carbonate, wherein the particle size D50 of the small-diameter cobalt carbonate is 1200 nm;

[0082] The volume ratio of the first cobalt-containing salt solution to the ammonium bicarbonate solution in step (1) is 1:4.5;

[0083] (2) Continue to pass a second cobalt salt solution (the first cobalt salt solution is a mixed solution of cobalt nitrate and magnesium nitrate, the mass of magnesium element accounts for 0.8% of the total mass of high tap density cobalt oxide, and the concentration of the second cobalt salt solution is 105 g / L) and a first precipitant solution (ammonium bicarbonate solution with a concentration of 150 g / L) into the reaction system obtained in step (1). Co-precipitate reaction is carried out at 35℃ and 400 r / min for 24 h, so that small-diameter cobalt carbonate particles can quickly agglomerate to form large-particle seed crystals (particle size D50 is 10.8 μm), and a reaction system containing large-particle seed crystals is obtained.

[0084] In step (2), the feed rate of the second cobalt salt solution is 70 L / h, the feed volume ratio of the second cobalt salt solution to the first precipitant solution is 1:1.5, and the particle size growth rate in step (2) is 0.4 μm / h.

[0085] (3) Continue to pass a third cobalt salt solution (the third cobalt salt solution is a mixed solution of cobalt nitrate and magnesium nitrate, the mass of magnesium element accounts for 0.5% of the total mass of high tap density cobalt oxide, and the concentration of the third cobalt salt solution is 80 g / L) and a second precipitant solution (ammonium bicarbonate solution with a concentration of 200 g / L) into the reaction system obtained in step (2). The co-precipitation reaction is carried out under the conditions of pH value of 8.0 and stirring speed of 200 r / min. The reaction is stopped when the particle size reaches 21 μm. Then the product of the co-precipitation reaction (magnesium-doped cobalt carbonate) is dried in an oven at 80 °C and then calcined at 800 °C for 0.5 h under air conditions to obtain the high tap density cobalt oxide.

[0086] The ratio of the feed rates of the third cobalt salt solution and the second precipitant solution in step (3) is 1:1.9, and the particle size growth rate in step (3) is 0.2 μm / h.

[0087] Example 4

[0088] The difference between this embodiment and Embodiment 1 is that the concentration of ammonium bicarbonate in step (1) is 30 g / L, and the particle size D50 of the small-particle cobalt carbonate is 7000 nm.

[0089] Figure 3 The image shows the SEM image of cobalt carbonate prepared in Example 4. As can be seen from the image, due to the low concentration of ammonium bicarbonate in the base solution, the particle size D50 of the small-diameter cobalt carbonate obtained in step (1) is too large and the diameter distribution is wide, resulting in uneven particle size when the growth is completed in the later stage.

[0090] Example 5

[0091] The difference between this embodiment and Embodiment 1 is that the concentration of ammonium bicarbonate in step (1) is 120 g / L.

[0092] Figure 4 This is a cross-sectional SEM image of cobalt carbonate prepared in Example 5. As can be seen from the figure, if the concentration of ammonium bicarbonate as the substrate is too high, the cobalt carbonate will precipitate in a flocculent manner and will not be able to nucleate. When it enters the growth stage, it will form a hollow structure, which will lead to a decrease in TD.

[0093] Example 6

[0094] The difference between this embodiment and embodiment 1 is that in step (1), the volume ratio of the first cobalt salt solution to the ammonium bicarbonate solution is 1:6.

[0095] Example 7

[0096] The difference between this embodiment and embodiment 1 is that in step (1), the volume ratio of the first cobalt salt solution to the ammonium bicarbonate solution is 1:2.

[0097] Example 8

[0098] The difference between this embodiment and embodiment 1 is that in step (2), the feed rate of the second cobalt salt solution is 40 L / h.

[0099] Example 9

[0100] The difference between this embodiment and embodiment 1 is that in step (2), the feed rate of the second cobalt salt solution is 100 L / h.

[0101] Figure 5 The image shows an SEM image of the cobalt oxide prepared in Example 9. As can be seen from the image, the prepared cobalt carbonate has poor sphericity, with a large number of spheres, and the particles grow together and adhere to each other.

[0102] Example 10

[0103] The difference between this comparative example and Example 1 is that the stirring speed in step (1) is 300 r / min.

[0104] The stirring speed in this embodiment is too slow, causing small particles to clump together and not disperse evenly, resulting in a D50 that is too large, with a D50 of 4000 nm.

[0105] Example 11

[0106] The difference between this comparative example and Example 1 is that the stirring speed in step (1) is 650 r / min.

[0107] The stirring speed in this embodiment is faster than that in Example 1, which wastes energy and has little effect on improving the sample indicators.

[0108] Comparative Example 1

[0109] The difference between this comparative example and Example 1 is that steps (1) and (2) are omitted, and cobalt carbonate is prepared using only step (3) by conventional methods.

[0110] The method in this embodiment generates too many seed crystals, which makes it impossible to guarantee the growth rate in the later stages, resulting in a very slow growth rate.

[0111] The total time for the coprecipitation reaction in steps (1), (2), and (3) of each embodiment and comparative example is recorded in Table 1.

[0112] The particle size of cobalt carbonate was tested for each example and comparative example when the reaction was stopped in step (3), and the results are shown in Table 1.

[0113] The diameter of cobalt carbonate was tested in each example and comparative example when the reaction was stopped in step (3). The formula was Span=(D90-D10) / D50. The smaller the diameter, the more uniform the particle size. The better the uniformity of particle size. The results are shown in Table 1.

[0114] The tap density of cobalt oxide prepared in each example and comparative example was tested, and the results are shown in Table 1.

[0115]

[0116] In summary, the method of this invention significantly shortens the reaction cycle by rapidly preparing large-particle seed crystals. The preparation of large-particle cobalt oxide with a particle size D50 of 15 μm to 21 μm requires only 40 h to 145 h of reaction time, more preferably 40 h to 80 h of co-precipitation reaction time. Furthermore, the cobalt carbonate prepared by the method of this invention has a uniform morphology with a particle size distribution in the range of 0.29 to 1.29, preferably in the range of 0.29 to 0.34. Simultaneously, the method of this invention ensures the densification of the material interior by rapidly agglomerating small-particle seed crystals, and for the preparation of doped cobalt carbonate, it ensures the uniformity of dopant element distribution, thereby resulting in a uniform distribution of dopant elements in high-tap-density cobalt oxide. The tap density of the high-tap-density cobalt oxide is 2.52 g / m³. 3 ~3.2 g / m 3 Within the range, preferably 2.89 g / m 3 ~3.2 g / m 3 Within the range. Conventional methods (Comparative Example 1) require up to 203 hours to prepare cobalt oxide with the same particle size D50.

[0117] Comparing Example 1 and Example 4, since the concentration of ammonium bicarbonate used in step (1) of Example 4 was too low, the particle size D50 of the small-diameter cobalt oxide obtained in step (1) was too large and the diameter distribution was wide, resulting in uneven particle size when the growth was completed in the later stage. The diameter of cobalt carbonate prepared in Example 4 was larger than that in Example 1.

[0118] Comparing Example 1 and Example 5, since the concentration of ammonium bicarbonate used in step (1) of Example 5 is too high, it will cause cobalt oxide to precipitate in a flocculent manner and not nucleate. When it enters the growth stage, it will form a hollow structure, resulting in a decrease in the tap density (TD) of cobalt oxide compared with Example 1.

[0119] Comparing Example 1 and Example 6, since the amount of ammonium bicarbonate solution used in Example 6 is too large, the residual ammonium bicarbonate will continue to react with the cobalt in step (2) to generate small particles of cobalt oxide, which cannot quickly agglomerate into seed crystals, resulting in a longer reaction cycle and a significantly longer total co-precipitation time compared to Example 1.

[0120] Comparing Example 1 and Example 7, in Example 7, the amount of ammonium bicarbonate was too small, which caused the first cobalt salt solution to react incompletely. When the material was re-fed in step (2), the reaction was rapid and the resulting internal structure was not dense enough. The tap density of the prepared cobalt oxide was lower than that of Example 1.

[0121] Comparing Example 1 and Example 8, the feeding rate of the second cobalt salt solution in Example 8 was too slow, which made it difficult for small crystal nuclei to quickly agglomerate and instead caused them to grow slowly. As a result, there were too many crystal nuclei in the system, which made the later growth difficult and the preparation cycle was longer than that in Example 1.

[0122] Comparing Example 1 and Example 9, since the feed rate of the second cobalt salt solution in Example 9 was too fast, the crystal nuclei agglomerated uncontrollably, resulting in a large amount of uneven agglomeration with abnormal morphology, including large irregular spheres. When the reactor was shut down later, the sphericity was poor and the particle size distribution was wide. The diameter of Example 9 was larger than that of Example 1.

[0123] Comparing Example 1 and Example 10, due to the slow stirring speed, the small particles agglomerate and cannot be evenly dispersed, resulting in a larger D50. This leads to an increase in the radial distance of the prepared cobalt carbonate compared to Example 1, while the tap density of cobalt oxide is lower than that of Example 1.

[0124] Comparing Example 1 and Example 11, Example 11 increased the stirring speed compared to Example 1, which wasted energy and had virtually no improvement on the sample indicators.

[0125] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing high tap density cobalt oxide, characterized in that, The preparation method includes the following steps: (1) Add a first cobalt salt solution to an ammonium bicarbonate solution and carry out a coprecipitation reaction under stirring to obtain a reaction system containing small-particle cobalt carbonate, wherein the particle size D50 of the small-particle cobalt carbonate is in the range of 800 nm to 1200 nm. (2) Continue to pass the second cobalt salt solution and the first precipitant solution into the reaction system obtained in step (1) to react, so that the small-diameter cobalt carbonate aggregates to form large-particle seed crystals, and obtain a reaction system containing large-particle seed crystals. (3) Continue to pass a third cobalt salt solution and a second precipitant solution into the reaction system obtained in step (2) for coprecipitation reaction. Then, dry and calcine the product of the coprecipitation reaction to obtain the high tap density cobalt oxide.

2. The preparation method according to claim 1, characterized in that, The cobalt salt in the first cobalt-containing solution, the second cobalt-containing solution, and the third cobalt-containing solution independently includes at least one of cobalt chloride, cobalt sulfate, and cobalt nitrate; Preferably, the concentrations of the first cobalt-containing salt solution, the second cobalt-containing salt solution, and the third cobalt-containing salt solution are independently 80 g / L to 150 g / L; Preferably, the first cobalt-containing salt solution, the second cobalt-containing salt solution, and the third cobalt-containing salt solution further independently include M salt, wherein M is a doping element, and M includes at least one of Al, Ni, Mg, Y, W, Nb, La, Zr, and Ti; Preferably, the mass of the dopant element in the first cobalt salt solution, the second cobalt salt solution, and the third cobalt salt solution independently accounts for 0.1% to 2% of the total mass of high tap density cobalt oxide.

3. The preparation method according to claim 1 or 2, characterized in that, The first precipitant solution and the second precipitant solution are ammonium bicarbonate solutions; Preferably, the concentrations of the first precipitant solution and the second precipitant solution are independently 100 g / L to 200 g / L.

4. The preparation method according to any one of claims 1-3, characterized in that, The stirring speed in step (1) is greater than 400 r / min and less than or equal to 600 r / min; Preferably, the temperature for the coprecipitation reaction in step (1) is 40℃~50℃; Preferably, the coprecipitation reaction in step (1) takes 3 to 5 hours; Preferably, the concentration of the ammonium bicarbonate solution in step (1) is 50 g / L to 100 g / L; Preferably, in step (1), the volume ratio of the first cobalt salt solution to the ammonium bicarbonate solution is 1:(3~5).

5. The preparation method according to any one of claims 1-4, characterized in that, In step (2), the reaction temperature is 30℃~35℃; Preferably, in step (2), the reaction is stirred at a speed of 300 r / min to 400 r / min. Preferably, in step (2), during the reaction process, the feed rate of the second cobalt salt solution is 60 L / h to 80 L / h, and the particle size growth rate is controlled to be 0.4 μm / h to 0.6 μm / h; Preferably, in step (2), during the reaction process, the feed volume ratio of the second cobalt salt solution and the first precipitant solution is (1~1.5):1; Preferably, the reaction time in step (2) is 8h~24h; Preferably, the particle size D50 of the aggregated lithium cobalt oxide obtained in step (2) is in the range of 10 μm to 12 μm.

6. The preparation method according to any one of claims 1-5, characterized in that, During the coprecipitation reaction described in step (3), the pH value is controlled within the range of 6.5 to 8.5; Preferably, during the coprecipitation reaction in step (3), the stirring is carried out at a speed of 100 r / min to 200 r / min; Preferably, in the co-precipitation reaction described in step (3), the feed volume ratio of the third cobalt salt solution and the second precipitant solution is 1:(1.5~2), and the particle size growth rate is controlled at 0.1μm / h~0.2μm / h; Preferably, the temperature of the coprecipitation reaction in step (3) is 35℃~45℃; Preferably, in step (3), the co-precipitation reaction is stopped when the particle size D50 of the product is 15μm~21μm.

7. The preparation method according to any one of claims 1-6, characterized in that, The drying temperature in step (3) is 80℃~130℃; Preferably, the calcination temperature in step (3) is 600℃~800℃; Preferably, the calcination time in step (3) is 0.5h to 2h; Preferably, the calcination atmosphere in step (3) is an air atmosphere.

8. A high tap density cobalt oxide, characterized in that, The high-tap-density cobalt oxide is prepared by the method according to any one of claims 1-7, wherein the high-tap-density cobalt oxide is undoped cobalt tetroxide or M-doped cobalt tetroxide, and the tap density of the high-tap-density cobalt oxide is 2.8 g / m³. 3 ~3.1g / m 3 .

9. A lithium cobalt oxide, characterized in that, The lithium cobalt oxide is prepared by using the high tap density cobalt oxide as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium cobalt oxide as described in claim 9.

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