Nano cobalt carbonate as well as preparation method and application thereof

Abstract

The invention discloses nano cobalt carbonate as well as a preparation method and application thereof, and relates to the technical field of nano materials. The prepared nano cobalt carbonate is rice-grain-shaped, the particle size D50 of the nano cobalt carbonate is 300-500nm, the length-diameter ratio of the nano cobalt carbonate is 2-7, and the nano cobalt carbonate has the characteristic of adjustable length-diameter ratio; more compact accumulation is realized through long-axis arrangement, the compactness and conductivity of the material are improved, meanwhile, exposure of active crystal faces is increased, and the material is expected to be popularized and applied in the fields of energy and catalysis. According to the preparation method, through the synergistic effect of the morphology guiding agent and the reaction temperature, efficient preparation of the rice-grain-shaped nanometer cobalt carbonate is achieved, no complex equipment is needed in the preparation process, and industrialization is easy to achieve.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and more specifically, to a nano cobalt carbonate and its preparation method and application. Background Art

[0002] As an important functional material, nano cobalt carbonate shows broad application prospects in the fields of energy storage and conversion, catalytic reactions, etc. due to its high specific surface area and excellent chemical activity. In electrochemical energy storage devices such as lithium-ion batteries and supercapacitors, nano cobalt carbonate is often used as an electrode material or a catalyst support, and its performance is closely related to the morphological characteristics of the material.

[0003] Among the preparation methods of cobalt carbonate, the commonly used ones mainly include hydrothermal method, solvothermal method, co-precipitation method, etc. The cobalt carbonate particles obtained by these methods are mostly spherical or quasi-spherical in shape. However, spherical or quasi-spherical particles have limitations in terms of packing density, directional arrangement, etc. For example, in the application of electrode materials, spherical particles are prone to form pores during the coating process, resulting in a decrease in the tap density and affecting the conductivity and energy density of the electrode; while in catalytic reactions, the exposed crystal planes of spherical particles are limited, which may affect their catalytic activity.

[0004] The morphology control of nano cobalt carbonate mostly relies on complex processes or expensive additives. For example, Chinese Patent CN202210618689.9 obtains nano cobalt powder through a staged synthesis and pulverization process, but the cost is relatively high; Chinese Patent CN221831745U uses a secondary concentration device to optimize the slurry density, but does not involve morphology regulation. Therefore, there is an urgent need to provide a preparation method of nano cobalt carbonate, which has low cost, can be used to prepare nano cobalt carbonate on a large scale, and the obtained nano cobalt carbonate has improved packing density and directional arrangement.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a nano cobalt carbonate and its preparation method and application to solve the above technical problems.

[0007] The present invention is implemented as follows:

[0008] In the first aspect, an embodiment of the present invention provides a nano cobalt carbonate, which is rice grain-shaped, with a D50 particle size of 300 nm - 500 nm and an aspect ratio of 2 - 7.

[0009] In the second aspect, an embodiment of the present invention provides a preparation method of the nano cobalt carbonate as described above, including the following preparation steps:

[0010] A cobalt salt solution and a morphology-directing agent are added to a bicarbonate solution for reaction. The reaction temperature is 10°C - 20°C, and the pH of the reaction system is 7.2 - 7.5;

[0011] After reacting for 15 min - 25 min, the temperature of the reaction system is raised to 40°C - 60°C. After reacting for 2 h - 3 h, post-treatment is carried out to produce nano cobalt carbonate.

[0012] Thirdly, an embodiment of the present invention provides an application of the aforementioned nano cobalt carbonate or the nano cobalt carbonate prepared by the aforementioned preparation method in the preparation of a cathode material for a lithium-ion battery.

[0013] Fourthly, an embodiment of the present invention provides a cathode material for a lithium-ion battery, which comprises the aforementioned nano cobalt carbonate or the nano cobalt carbonate prepared by the aforementioned preparation method.

[0014] The present invention has the following beneficial effects:

[0015] The nano cobalt carbonate provided by the embodiment of the present invention is rice-grain-shaped, which has a high aspect ratio. It can achieve closer packing through the arrangement of the long axis, improving the denseness and conductivity of the material, and at the same time increasing the exposure of the active crystal plane, and is expected to be widely applied in the fields of energy and catalysis. The preparation method realizes the efficient preparation of rice-grain-shaped nano cobalt carbonate through the synergistic effect of the morphology-directing agent and the reaction temperature. The preparation process does not require complex equipment and is easy to industrialize. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0017] Figure 1 SEM image of the rice-grain-shaped nano cobalt carbonate prepared in Example 1;

[0018] Figure 2 XRD pattern of the rice-grain-shaped nano cobalt carbonate prepared in Example 1;

[0019] Figure 3 SEM image of the rice-grain-shaped nano cobalt carbonate prepared in Example 3. Detailed Embodiments

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not indicated with the manufacturer are all conventional products that can be obtained through commercial purchase.

[0021] In a first aspect, an embodiment of the present invention provides a nano cobalt carbonate, which is in the shape of rice grains, with a particle size D50 of 300 nm - 500 nm and an aspect ratio of 2 - 7.

[0022] It should be noted that the nano cobalt carbonate provided by the embodiment of the present invention has a rice grain-like structure, and the nano material of rice grain-like particles has the following characteristics: it has a certain aspect ratio, and the slender shape is more likely to form a close arrangement during stacking, reducing the porosity, especially suitable for scenarios that require high-density filling; and the edges and corners of the rice grains can reduce the contact area and lower the risk of caking; it is easy to form a stronger physical bond with the matrix, improving the mechanical properties of the product. The above can effectively avoid the limitations of spherical or similar-shaped particles in terms of packing density, orientation arrangement, etc., resulting in high porosity and low true density of the product.

[0023] When the rice grain-like nano material is applied in a battery, such as in the cathode material of a lithium-ion battery, it has unique advantages. Its irregular surface and edges and corners provide a larger specific surface area compared to spherical particles, increasing the contact area between the electrode and the electrolyte, thereby improving the transmission efficiency of lithium ions (or other carriers); it is beneficial to accelerating the charge and discharge rate, exposing more electrochemically active sites, and enhancing the specific capacity. The non-uniform pore network formed during the stacking of rice grain-like particles forms continuous channels, which are easy to provide an optimized path for ion transport, facilitating the rapid penetration of the electrolyte, reducing the ion diffusion resistance, and alleviating the stress concentration during the charge and discharge process.

[0024] In addition, the asymmetric shape of the rice grains can effectively reduce the surface contact and lower the risk of agglomeration during sintering or cycling; in a lithium-ion battery, the porous or fibrous structure formed by the stacking of rice grain-like particles can better accommodate the volume expansion during charge and discharge, delaying the pulverization of the electrode.

[0025] In a second aspect, an embodiment of the present invention provides a preparation method of the nano cobalt carbonate as described above, including the following preparation steps:

[0026] Add a cobalt salt solution and a morphology-directing agent to a bicarbonate solution for reaction, with a reaction temperature of 10°C - 20°C and a pH of 7.2 - 7.5 for the reaction system;

[0027] After reacting for 15 min - 25 min, raise the temperature of the reaction system to 40°C - 60°C, and after reacting for 2 h - 3 h, perform post-treatment to generate nano cobalt carbonate.

[0028] In an optional embodiment of the present invention, the molar ratio of the bicarbonate solution to the cobalt salt solution is 3.4-4.4.

[0029] It should be noted that in the process of preparing cobalt carbonate, the molar ratio of bicarbonate ions (HCO3-) to cobalt ions (Co2+) is a key parameter for controlling product morphology, purity, crystallinity and reaction efficiency. To ensure that Co2+ is completely precipitated as CoCO3, an appropriate excess of HCO3- can compensate for the loss of carbonate caused by CO2 escape. The relevant reaction equation is as follows:

[0030]

[0031] In addition, a moderate excess of HCO3- can maintain a relatively stable pH value in the solution and inhibit the precipitation of Co(OH)2; excess HCO3- acts as a buffer to stabilize the CO3 2 - concentration to avoid sudden changes in local pH.

[0032] If there are insufficient bicarbonate ions, that is, the molar ratio is low, the precipitation of cobalt ions will be incomplete, and Co2+ will remain in the solution, reducing the yield; basic cobalt carbonate (such as Co(OH)(CO3)) may be generated, affecting the purity of the product cobalt carbonate (CoCO3); in addition, it will also lead to a slow reaction rate and a tendency to produce large particles and high crystallinity CoCO3 (such as spheres or blocks).

[0033] If there are too many bicarbonate ions, that is, when the molar ratio is too high, soluble cobalt complexes (such as [Co(CO3)2]2-) may be formed, which is not conducive to precipitation. At the same time, excessive use will increase cost investment; when the molar ratio is high, small particles, high specific surface area, rice-shaped or amorphous CoCO3 are formed due to rapid nucleation, which is suitable for battery electrode materials and other needs.

[0034] After extensive experimental research, the inventors found that the molar ratio of bicarbonate ions to cobalt ions is set to 3.4-4.4. It can be selected from any one of 3.4, 3.6, 3.9, 4.0, 4.3 and 4.4 according to actual needs, or other values within the range of 3.4-4.4.

[0035] In an optional embodiment of the present invention, the bicarbonate is selected from at least one of ammonium bicarbonate, sodium bicarbonate and potassium bicarbonate.

[0036] It should be noted that bicarbonate is used as a precipitant in the preparation of cobalt carbonate, and its functions mainly include providing carbonate ions and adjusting reaction conditions. Specifically, bicarbonate can react with metal cobalt ions to form cobalt carbonate precipitate; it can also optimize the preparation efficiency and purity of cobalt carbonate and affect the preparation process of cobalt carbonate by controlling parameters such as the concentration, temperature, and pH value of the reactants.

[0037] Furthermore, ammonium bicarbonate is used in the embodiments of the present invention. In other embodiments of the present invention, other types of bicarbonates can be selected according to actual situations.

[0038] In an alternative embodiment of the present invention, the concentration of bicarbonate is 90 g / L - 150 g / L, and it can be selected from any one of 90 g / L, 100 g / L, 120 g / L, 130 g / L, and 150 g / L according to actual needs, or other values within the range of 90 g / L - 150 g / L.

[0039] In an alternative embodiment of the present invention, the cobalt salt is selected from at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate.

[0040] It should be noted that the cobalt salt is used to provide cobalt ions and is easily soluble itself.

[0041] Furthermore, cobalt chloride is used in the embodiments of the present invention. In other embodiments of the present invention, other types of cobalt sulfate can be selected according to actual situations.

[0042] In an alternative embodiment of the present invention, in the cobalt salt solution, the concentration of cobalt ions is 110 g / L - 140 g / L, and it can be selected from any one of 110 g / L, 115 g / L, 120 g / L, 125 g / L, 130 g / L, and 140 g / L according to actual needs, or other values within the range of 110 g / L - 140 g / L.

[0043] In an alternative embodiment of the present invention, the morphology-directing agent is selected from at least one of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), 7-theophylline acetic acid, and sodium 2-pyrrolidone-5-carboxylate.

[0044] A morphology-directing agent refers to a chemical substance used to control the morphology of nanomaterials during synthesis. They interact with the growth process of the target material and affect the shape, size, and structure of the material.

[0045] Polyvinylpyrrolidone (PVP) is commonly used in the synthesis of various nanomaterials, such as nanoparticles, nanowires, etc. PVP forms coordination bonds with metal ions and affects the growth direction of crystals, thereby controlling the morphology of the material.

[0046] Sodium dodecyl sulfate (SDS) is an anionic surfactant. Due to its specific molecular structure and chemical properties, it can play a controlling role during the crystal growth process, thereby generating nanomaterials with different crystal forms and special morphologies.

[0047] Polyethylene glycol (PEG) affects the crystallization process by interacting with substances, thereby obtaining nanomaterials with specific morphologies.

[0048] 7-Theophylline acetic acid serves as a structure-directing agent during the synthesis of nanomaterials. By changing its concentration and the feeding ratio of metal precursors, the formation mechanism and morphology of nanomaterials can be regulated.

[0049] Sodium 2-pyrrolidone-5-carboxylate serves as a regulating molecule during the synthesis of nanomaterials. By influencing the crystal growth process, nanomaterials with specific morphologies are obtained.

[0050] Furthermore, the morphology-directing agent includes polyvinylpyrrolidone (PVP).

[0051] It should be noted that in the embodiments of the present invention, PVP is selected as the surfactant mainly because PVP can selectively adsorb on the (001) crystal plane of cobalt carbonate, inhibit the growth in this direction, and force the crystal to preferentially grow along the axial direction, thereby increasing the aspect ratio. If PVP is not used or the dosage of PVP is reduced, short rod-shaped or nanoscale cobalt carbonate with inconsistent morphologies will be obtained, which is not conducive to the dispersion of nanoparticles. PVP has the advantages of environmental friendliness and being cheap and easily available compared with other morphology-directing agents, and the experimental effect is remarkable.

[0052] Furthermore, the concentration of the morphology-directing agent is 0.01 mol / L - 0.05 mol / L. It can be selected from any one of 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L according to actual needs, or other values within the range of 0.01 mol / L - 0.05 mol / L.

[0053] It should be noted that for the nanoscale cobalt carbonate prepared in the present invention, its aspect ratio is jointly controlled by the dosage of PVP and temperature. The higher the PVP concentration and the lower the temperature, the more conducive it is to obtaining a high aspect ratio. The higher the aspect ratio, the better the dispersibility, but the lower the tap density. Therefore, conditions need to be controlled to control the aspect ratio at an appropriate value.

[0054] In an alternative embodiment of the present invention, after the cobalt salt solution and the morphology-directing agent are mixed, they are added to the bicarbonate solution at a feeding rate of 10 L / min - 20 L / min for reaction.

[0055] It should be noted that too fast feeding will rapidly generate a large number of small-sized seeds in a short time, which is not conducive to particle dispersion; too slow feeding will result in too large initial particle size of the seeds.

[0056] In an alternative embodiment of the present invention, the post-treatment includes centrifugation, washing, and drying of the reaction system after the reaction ends.

[0057] Among them, centrifuging the reaction system after the reaction ends is conducive to the rapid sedimentation of the product.

[0058] The washing treatment is mainly to wash away the unreacted ions to avoid their adsorption on the surface of the product, which affects its purity and subsequent applications. The type of water used in the washing process can be deionized water, high-purity water, distilled water, purified water, etc. according to the actual situation.

[0059] In an embodiment of the present invention, the drying treatment uses the flash drying method, which has the following characteristics: it is applicable to various forms of materials, such as powdery, granular, and paste-like materials, etc., and can meet the requirements of different production processes; it can effectively control the final moisture content and fineness, ensuring the uniform consistency of the wet content and fineness of the product; it can effectively prevent the material from sticking to the wall; in addition, it can enable the material to rapidly evaporate water in a short time, thereby achieving an efficient and rapid drying effect, greatly improving the production efficiency, shortening the production cycle, and reducing energy consumption. In other embodiments of the present invention, other drying means can be selected according to the actual situation to dry the product.

[0060] In summary, the specific implementation steps of the present invention for preparing rice-grain-shaped nano cobalt carbonate are as follows:

[0061] Prepare a cobalt salt solution with a cobalt ion concentration of 110 g / L - 140 g / L, and add a morphology-directing agent with a concentration of 0.01 mol / L - 0.05 mol / L to the cobalt salt solution to obtain a first mixed solution for standby.

[0062] Prepare a bicarbonate solution with a concentration of 90 g / L - 150 g / L for standby.

[0063] Add 16 L - 22 L of ammonium bicarbonate solution as the bottom water to the reaction vessel, and then add the first mixed solution for reaction, so that the molar ratio of bicarbonate ions to cobalt ions in the reaction system is 3.4 - 4.4; among them, the feeding rate of the first mixed solution is 10 L / min - 20 L / min, the reaction temperature is 10 °C - 20 °C, the rotation speed is 400 r / min - 500 r / min, and the pH of the reaction system is 7.2 - 7.5.

[0064] It should be noted that the generation of nano seeds is the main process in this process.

[0065] After reacting for 15 min - 25 min, raise the temperature of the reaction system to 40°C - 60°C. After reacting for 2 h - 3 h, perform centrifugation, washing, and drying to produce nano cobalt carbonate.

[0066] It should be noted that through the synergistic effect of PVP and temperature, during this process, it is beneficial to promote the growth of seeds along specific crystal planes. Finally, the obtained cobalt carbonate is rice-grain-shaped nanoparticles with a particle size D50 of 300 nm - 500 nm and an aspect ratio of 2 - 7.

[0067] In a third aspect, an embodiment of the present invention provides an application of the aforementioned nano cobalt carbonate or nano cobalt carbonate prepared by the aforementioned preparation method in the preparation of a cathode material for a lithium-ion battery.

[0068] In a fourth aspect, an embodiment of the present invention provides a cathode material for a lithium-ion battery, which includes the aforementioned nano cobalt carbonate or nano cobalt carbonate prepared by the aforementioned preparation method.

[0069] The features and properties of the present invention will be further described in detail below in conjunction with examples.

[0070] Example 1

[0071] This example provides a nano cobalt carbonate, and its preparation steps are as follows:

[0072] (1) Solution preparation

[0073] Prepare a cobalt salt solution with a cobalt ion concentration of 130 g / L, and add a morphology-directing agent PVP with a concentration of 0.02 mol / L to the cobalt salt solution to obtain a first mixed solution for standby.

[0074] Prepare a ammonium bicarbonate solution with a concentration of 100 g / L for standby.

[0075] (2) Synthesis reaction

[0076] ① Seed generation stage

[0077] Add 20 L of ammonium bicarbonate solution as the bottom water to a 50-L reaction kettle, and then add 2.6 L of the first mixed solution for reaction, so that the molar ratio of bicarbonate ions to cobalt ions in the reaction system is 4.4;

[0078] Among them, the feeding rate is 15 L / min, the pH of the reaction system is 7.3, the rotation speed is 500 r / min, the temperature is (15 ± 2)°C, and the reaction time is 20 min.

[0079] ② Rice-grain-shaped cobalt carbonate generation stage

[0080] After the reaction in step ① is completed, raise the temperature of the reaction system to 50°C and react for 3 h.

[0081] (3) Post-treatment

[0082] The system after the reaction in step (2) is subjected to post-treatment, specifically centrifugation, washing, and flash drying, and finally nano cobalt carbonate is produced.

[0083] Example 2

[0084] This example provides a nano cobalt carbonate, and the difference in its preparation steps from those of Example 1 is only that:

[0085] (1) In the solution preparation, the concentration of the morphology-directing agent PVP is 0.05 mol / L.

[0086] (2) In the stage of generating rice-grain-shaped cobalt carbonate in the synthesis reaction ②, the temperature of the reaction system is raised to 40 °C.

[0087] Example 3

[0088] This example provides a nano cobalt carbonate, and the difference in its preparation steps from those of Example 1 is only that:

[0089] (1) In the solution preparation, the concentration of the morphology-directing agent PVP is 0.01 mol / L.

[0090] (2) In the stage of generating rice-grain-shaped cobalt carbonate in the synthesis reaction ②, the temperature of the reaction system is raised to 60 °C.

[0091] Example 4

[0092] This example provides a nano cobalt carbonate, and the difference in its preparation steps from those of Example 1 is only that:

[0093] (2) In the stage of generating rice-grain-shaped cobalt carbonate in the synthesis reaction ②, the temperature of the reaction system is raised to 40 °C.

[0094] Example 5

[0095] This example provides a nano cobalt carbonate, and the difference in its preparation steps from those of Example 1 is only that:

[0096] (2) In the stage of generating rice-grain-shaped cobalt carbonate in the synthesis reaction ②, the temperature of the reaction system is raised to 60 °C.

[0097] Example 6

[0098] This example provides a nano cobalt carbonate, and the difference in its preparation steps from those of Example 1 is only that:

[0099] (1) In the solution preparation, the morphology-directing agent used is polyethylene glycol with a concentration of 0.02 mol / L.

[0100] Example 7

[0101] This embodiment provides a nano cobalt carbonate, and the difference in its preparation steps from those of Embodiment 1 is only that:

[0102] (2) In the seed crystal formation stage of the synthesis reaction ①, the molar ratio of bicarbonate ions to cobalt ions in the reaction system is 3.4.

[0103] Comparative Example 1

[0104] This comparative example provides a nano cobalt carbonate, and the difference in its specific implementation steps from those of Embodiment 1 is only that it adopts a conventional preparation process:

[0105] No morphology guiding agent is used.

[0106] Test Example 1

[0107] This test example tests the properties of the nano cobalt carbonate prepared in Embodiments 1-7 and Comparative Example 1: particle size D50, aspect ratio, and tapped density. The specific instruments used for the relevant property tests are as follows:

[0108] Particle size D50 test: Malvern 3000 laser particle size analyzer; aspect ratio test: particle image analyzer; tapped density test: BT-1006 tapped density meter; the relevant test results are shown in Table 1.

[0109] In Embodiments 1-3, as the amount of PVP increases and the temperature decreases, D50 increases significantly. This is mainly because the dispersibility becomes worse, resulting in serious particle agglomeration. At the same time, the aspect ratio increases and the tapped density becomes worse.

[0110] Table 1 Performance data of nano cobalt carbonate

[0111]

[0112]

[0113] Combined with the data in Table 1, it can be seen that the aspect ratio is controlled by the amount of PVP and temperature in a coordinated manner. The higher the PVP concentration and the lower the temperature, the more conducive it is to obtaining a high aspect ratio. The higher the aspect ratio, the better the dispersibility, but the lower the compacted density.

[0114] Test Example 2

[0115] This test example conducts SEM tests on the rice grain-shaped nano cobalt carbonate prepared in Embodiment 1 and Embodiment 3. The specific results are shown in Figure 1 (Embodiment 1), Figure 3 (Embodiment 3).

[0116] Combined with Figure 1 and Figure 3 SEM pictures, it can be seen that Figure 1The medium-sized nano cobalt carbonate has a large aspect ratio and the particles are evenly dispersed; Figure 3 The cobalt carbonate obtained has a low aspect ratio and smaller particles, but poor dispersion leads to serious agglomeration.

[0117] Test Example 3

[0118] In this test example, XRD testing was performed on the rice-grain-shaped nano cobalt carbonate prepared in Example 1. The specific results are shown in Figure 2 .

[0119] From Figure 2 it can be seen that the cobalt carbonate obtained by this method has high purity and no impurity phase.

[0120] In summary, through the synergistic effect of the morphology guiding agent and the reaction temperature, the implementation mode of the present invention realizes the efficient preparation of rice-grain-shaped nano cobalt carbonate. The preparation process does not require complex equipment and is easy to industrialize. The prepared nano cobalt carbonate has the characteristic of adjustable aspect ratio. It achieves closer packing through the arrangement of the long axis, improves the density and conductivity of the material, and at the same time increases the exposure of the active crystal plane, and is expected to be widely used in the fields of energy and catalysis.

[0121] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A nano cobalt carbonate, characterized in that, The nano cobalt carbonate is in the shape of rice grains, with a particle size D50 of 300 nm - 500 nm and an aspect ratio of 2 - 7.

2. A method for preparing nano cobalt carbonate as described in claim 1, characterized in that, It includes the following preparation steps: Add a cobalt salt solution and a morphology-directing agent to a bicarbonate solution for reaction, with the reaction temperature being 10°C - 20°C and the pH of the reaction system being 7.2 - 7.5; After reacting for 15 min - 25 min, raise the temperature of the reaction system to 40°C - 60°C, react for 2 h - 3 h, and then perform post-treatment to produce nano cobalt carbonate.

3. The preparation method according to claim 2, wherein, The molar ratio of bicarbonate ions to cobalt ions is 3.4 - 4.

4.

4. The preparation method according to claim 2, characterized in that, The bicarbonate is selected from at least one of ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate; Preferably, the concentration of the bicarbonate is 90 g / L - 150 g / L.

5. The preparation method according to claim 2, characterized in that, The cobalt salt is selected from at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate; Preferably, in the cobalt salt solution, the concentration of cobalt ions is 110 g / L - 140 g / L.

6. The preparation method according to claim 2, characterized in that, The morphology-directing agent is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, 7-theophylline acetic acid, and sodium 2-pyrrolidone-5-carboxylate; Preferably, the morphology-directing agent includes polyvinylpyrrolidone; Preferably, the concentration of the morphology-directing agent is 0.01 mol / L - 0.05 mol / L.

7. The preparation method according to claim 2, characterized in that, After mixing the cobalt salt solution and the morphology-directing agent, add them to the bicarbonate solution at a feeding rate of 10 L / min - 20 L / min for reaction.

8. The preparation method according to claim 2, wherein The post-treatment includes centrifuging, washing, and drying the system after the reaction ends.

9. Use of the nano cobalt carbonate as described in claim 1 or the nano cobalt carbonate prepared by the preparation method as described in any one of claims 2 - 8 in the preparation of a cathode material for a lithium-ion battery.

10. A cathode material for a lithium-ion battery, characterized in that, It includes the nano cobalt carbonate as described in claim 1 or the nano cobalt carbonate prepared by the preparation method as described in any one of claims 2 - 8.

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