A surface-coated modified cobalt tetroxide, its preparation method and application

Abstract

The present invention provides a surface-coated modified cobalt tetroxide, a preparation method thereof and an application. The preparation method includes: (1) performing surface hydroxylation treatment on cobalt carbonate to obtain cobalt hydroxide-coated cobalt carbonate; (2) mixing a metal salt and a complexing agent to carry out a complexation reaction to obtain a complexed metal salt; (3) mixing the cobalt hydroxide-coated cobalt carbonate, the complexed metal salt and a grafting initiator to carry out a grafting reaction to obtain metal ion-coated cobalt carbonate; (4) sintering the metal ion-coated cobalt carbonate to obtain the surface-coated modified cobalt tetroxide. The present invention performs surface hydroxylation treatment on cobalt carbonate and adds a complexed metal salt for a grafting reaction, so that the coating layer formed by the metal salt has the same texture as the cobalt hydroxide on the surface of cobalt carbonate, thereby forming a non-dense, flower-like structure metal oxide coating layer on the surface of cobalt tetroxide, improving the surface activity, being beneficial to the effective mixing with lithium salt, and thus improving the electrochemical performance of the lithium cobalt oxide battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for lithium-ion batteries, and relates to a surface-coated modified cobalt tetroxide, a preparation method thereof, and an application thereof. Background Art

[0002] In the past decade or so, due to its excellent electrochemical properties, cobalt metal has been widely used in secondary batteries, especially in the field of cathode materials for lithium-ion batteries. Currently, the mature cathode materials on the market mainly include lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, etc. Each cathode material has different properties and slightly different application fields.

[0003] Among the cathode materials for lithium-ion batteries, lithium cobaltate batteries have the advantages of stable structure, high specific capacity, and outstanding comprehensive performance, and are one of the most mature cathode materials at present. Lithium cobaltate is mainly sintered from cobalt tetroxide and lithium carbonate or lithium hydroxide. Among them, cobalt tetroxide is obtained by roasting cobalt carbonate. Therefore, the most important factor determining the quality of lithium cobaltate is cobalt carbonate, and its tap density, specific surface area, and electron microscopy morphology have a crucial impact on the final cathode material.

[0004] The patent document with the publication number CN108217753A discloses a preparation method of a gradient-doped cobalt tetroxide material. Under set conditions, a cobalt pre-precipitate is obtained, and then a doping element is added to obtain a doped precipitate through coprecipitation. Finally, the doped precipitate is moderately sintered to obtain a cobalt tetroxide material with a gradually increasing doping concentration from the inside to the outside along the radius direction of the particles. This preparation method is simple, the reaction process is controllable, and the prepared gradient-doped cobalt tetroxide material can improve the structural stability and electrical properties of the cathode material lithium cobaltate at high voltages.

[0005] The patent document with the publication number CN108609666A discloses a preparation method of cobalt tetroxide with gradient doping of metal elements, which provides a preparation method of cobalt tetroxide with gradient doping of metal elements with more doping elements distributed in the center and less in the outer layer. This method can ensure that the doping elements are more distributed in the cobalt tetroxide lattice rather than existing on the surface of cobalt tetroxide in the form of metal oxides.

[0006] The patent document with the publication number CN112723422A discloses an aluminum-doped cobalt tetroxide core-shell material and a preparation method thereof. The core of this material is aluminum-doped cobalt tetroxide, and the shell is cobalt tetroxide. The shell does not contain Al and is not prone to segregation, which can improve the cycle performance of the material.

[0007] In the prior art, various methods are used to dope cobalt tetroxide with elements to obtain cobalt tetroxide with different doped element distributions, so as to improve the electrochemical performance of lithium-ion batteries. However, the above preparation methods do not start from cobalt carbonate, and do not consider the influence of the element distribution after doping on the lithium matching during the sintering of cobalt tetroxide. The formed element coating layer is relatively dense, which affects the entry of lithium, and further affects the electrochemical performance of lithium-ion batteries. Summary of the Invention

[0008] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a surface-coated modified cobalt tetroxide, its preparation method and application. The present invention hydroxylates the surface of cobalt carbonate and adds a metal salt treated with a complexing agent to carry out a grafting reaction to achieve in-situ doping of metal elements, so that the coating layer formed by the metal salt has the same texture as the cobalt hydroxide formed on the surface of cobalt carbonate, thereby forming a non-dense, flower-like metal oxide coating layer on the surface of cobalt tetroxide, improving the surface activity of cobalt tetroxide, facilitating the effective mixing with lithium salt subsequently, and thus improving the electrochemical performance such as the battery capacity and storage performance of lithium cobalt oxide batteries.

[0009] To achieve the purpose of this invention, the following technical solutions are adopted by the present invention:

[0010] In the first aspect, the present invention provides a preparation method of surface-coated modified cobalt tetroxide, and the preparation method includes:

[0011] (1) Hydroxylate the surface of cobalt carbonate to obtain cobalt hydroxide-coated cobalt carbonate;

[0012] (2) Mix a metal salt and an acidic complexing agent to carry out a complexing reaction to obtain a complexed metal salt;

[0013] (3) Mix the cobalt hydroxide-coated cobalt carbonate obtained in step (1), the complexed metal salt obtained in step (2), and a grafting initiator to carry out a grafting reaction to obtain metal ion-coated cobalt carbonate;

[0014] (4) Sinter the metal ion-coated cobalt carbonate obtained in step (3) to obtain surface-coated modified cobalt tetroxide.

[0015] When modifying the surface of cobalt tetroxide by coating it with metal elements in the prior art, a dense coating layer will be formed on its surface. This dense coating layer will hinder the entry of lithium during the sintering process of cobalt tetroxide and lithium salt, thereby affecting the electrochemical performance of the generated lithium cobalt oxide.

[0016] The present invention performs surface hydroxylation treatment on cobalt carbonate to obtain flaky hydroxy cobalt-coated cobalt carbonate. The cobalt tetroxide generated by sintering the flaky hydroxy cobalt-coated cobalt carbonate has high surface activity and low battery gas production, which is conducive to uniform mixing and increasing the lithium matching effect. Meanwhile, the surface hydroxylated cobalt carbonate can be easily grafted. Under the initiation of a grafting initiator, the cobalt carbonate is grafted with a doping element (metal ion in a metal salt) treated with a complexing agent. The hydroxyl group and the complexing metal group are used as active sites. In-situ doping is performed according to the flaky morphology, and the doping element can be coated on the surface of the cobalt carbonate according to the pattern of the hydroxyl group, thereby avoiding The appearance of a dense structure results in metal ion-coated cobalt carbonate; after sintering, the cobalt carbonate generates cobalt tetroxide of the same morphology, and the metal ions generate a non-dense, flower-like metal oxide coating layer on the surface of the cobalt tetroxide, thereby preparing a surface-coated modified cobalt tetroxide with high surface activity and adjustable surface doping amount. The non-dense coating layer in the surface-coated modified cobalt tetroxide forms a lithium pathway, which improves the diffusion performance of lithium and can be effectively mixed with lithium salts in the subsequent preparation to obtain a lithium cobalt oxide material with excellent electrochemical properties, thereby improving the electrochemical properties of the lithium cobalt oxide battery, such as the capacity and storage performance.

[0017] In the present invention, taking metal chloride M(Cl) and acidic complexing agent RH as an example, the complexing reaction of step (2) is shown in formula (1):

[0018] RH+M(Cl)→RM (1)

[0019] It should be noted that the order of the operations of step (1) and step (2) is not specifically limited in the present invention. The purpose is only to obtain hydroxycobalt-coated cobalt carbonate and complex metal salt so as to facilitate the subsequent mixing of the two for grafting. Step (1) can be performed first, i.e., surface hydroxylation of cobalt carbonate, or step (2) can be performed first, i.e., the metal salt and the acidic complexing agent are mixed for complexing reaction, or the operations of step (1) and step (2) can be performed separately in two reaction kettles at the same time.

[0020] Preferably, the surface hydroxylation treatment in step (1) is to introduce oxygen-containing gas under weak alkaline conditions or to add hydrogen peroxide under weak alkaline conditions.

[0021] It should be noted that the type of oxygen-containing gas is not specifically limited in the present invention, as long as the gas component contains oxygen, for example, it can be air.

[0022] Preferably, the weakly alkaline condition is pH=7.2-8.0, for example, it can be 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9 or 8.0.

[0023] Preferably, the temperature of the hydroxylation treatment in step (1) is 60-70 °C, for example, it can be 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C or 70 °C, etc.

[0024] Preferably, the mass ratio of cobalt hydroxide to cobalt carbonate in the cobalt hydroxide-coated cobalt carbonate in step (1) is 1:(23-31), for example, it can be 1:23, 1:24, 1:25, 1:26, 1:27, 1:28, 1:29, 1:30 or 1:31, etc. Selecting an appropriate content of cobalt hydroxide can improve the uniformity of the surface coating. When the content of cobalt hydroxide is too high, the sintering uniformity will decrease; when the content of cobalt hydroxide is too low, the subsequent coating process will be affected.

[0025] As a preferred technical solution of the preparation method of the present invention, the cobalt carbonate in step (1) is prepared as follows:

[0026] Mix the cobalt doping solution and the precipitation solution to obtain cobalt carbonate.

[0027] Preferably, during the process of mixing the cobalt doping solution and the precipitation solution, the pH value of the mixed solution is 7.0-7.8, for example, it can be 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7 or 7.8, etc.

[0028] Preferably, the cobalt doping solution includes any one or a combination of at least two of cobalt chloride, cobalt sulfate, cobalt nitrate and cobalt acetate. For example, it can be a combination of cobalt chloride and cobalt sulfate, a combination of cobalt nitrate and cobalt acetate, a combination of cobalt sulfate and cobalt acetate, or a combination of cobalt chloride, cobalt sulfate, cobalt nitrate and cobalt acetate, etc.

[0029] Preferably, the cobalt doping solution also includes aluminum. Exemplarily, the cobalt doping solution includes a cobalt chloride-aluminum solution.

[0030] Preferably, the precipitation solution includes any one or a combination of at least two of ammonium bicarbonate, ammonium carbonate and sodium carbonate. For example, it can be a combination of ammonium bicarbonate and sodium carbonate, a combination of ammonium bicarbonate and ammonium carbonate, or a combination of ammonium bicarbonate, ammonium carbonate and sodium carbonate, etc.

[0031] The cobalt tetroxide obtained by sintering flaky cobalt carbonate has the advantages of high surface activity and low gas production in the battery. However, when it is doped with elements, it is easy to be uneven, resulting in poor electrical and storage properties. The tap density and specific surface area of massive cobalt carbonate are large, and the cobalt tetroxide prepared therefrom has excellent electrical properties. However, when cobalt carbonate is mixed and sintered with lithium carbonate or lithium hydroxide, its large surface activity is more conducive to uniform mixing and increasing the lithium coordination effect. Therefore, in the present invention, massive cobalt carbonate is prepared by a simple precipitation method, and then flaky cobalt hydroxide coated with cobalt carbonate is formed by hydroxylation. The surface-hydroxylated cobalt carbonate can be more easily subjected to a grafting reaction to graft the treated doping elements, and in-situ doping is carried out according to the flaky morphology, which can avoid the appearance of a dense structure and prevent the problem of uneven doping in the conventional flaky structure. The prepared material has the advantages of high surface activity, adjustable doping amount, and efficient and uniform mixing with lithium salts.

[0032] As a preferred technical solution of the preparation method described in the present invention, the mass ratio of the metal salt to the complexing agent in step (2) is (5-10):1, for example, it can be 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc.

[0033] In the present invention, a suitable ratio of the metal salt and the complexing agent is selected for the complexation reaction, which can ensure sufficient complexation. When the content of the complexing agent is too high, it will cause waste of the complexing agent and reduce the pH of the solution. When the content of the complexing agent is too low, it will affect the grafting reaction rate in the next step.

[0034] Preferably, the metal salt in step (2) includes any one or a combination of at least two of salts of Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, Ce and B. For example, it can be a combination of Al and Mg, a combination of Ti and Sr, a combination of Ce and B, or a combination of W, Y, Mo and Sb, etc.

[0035] Preferably, the metal salt is a chloride salt, and the chloride salt has a relatively high solubility, which is beneficial to the progress of the reaction.

[0036] Preferably, the complexing agent in step (2) includes an acidic complexing agent, and the acidic complexing agent includes any one or a combination of at least two of citric acid, malonic acid, glycine, p-toluenesulfonic acid, malic acid and ascorbic acid. For example, it can be a combination of citric acid and malonic acid, a combination of malic acid and ascorbic acid, a combination of malonic acid, glycine and p-toluenesulfonic acid, or a combination of citric acid, malonic acid, glycine, p-toluenesulfonic acid, malic acid and ascorbic acid, etc.

[0037] The acidic complexing agent preferably adopted in the present invention is more conducive to the complexation of metal ions and can prevent problems such as metal ion precipitation caused by basic complexing agents.

[0038] As a preferred technical solution of the preparation method of the present invention, the grafting rate of the grafting reaction in step (3) is 60% to 80%, for example, it can be 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78% or 80%, etc. Within this range, it is beneficial to the uniform distribution of the coated metal elements; when the grafting rate is too high, a dense structure is formed on the surface, affecting the uniformity of lithium mixing, and when the grafting rate is too low, some active sites are not coated with metal elements.

[0039] It should be noted that the grafting rate in the present invention is a well-known term in the art, also known as the grafting efficiency, which refers to the ratio of the mass of the grafted monomer to the total mass of the initially introduced monomer to be grafted.

[0040] Preferably, the temperature of the grafting reaction in step (3) is 70 to 80 °C, for example, it can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C or 80 °C, etc.

[0041] Preferably, the time of the grafting reaction in step (3) is 3 to 10 h, for example, it can be 5 h.

[0042] In the present invention, by controlling the temperature and time of the grafting reaction, the progress of the grafting reaction can be regulated, the grafting rate can be adjusted, and the coated modified cobalt tetroxide with better coating layer performance can be obtained, further improving the surface activity and electrochemical performance of the material.

[0043] Preferably, the stirring rate of the grafting reaction in step (3) is 40 to 45 Hz, for example, it can be 40 Hz, 41 Hz, 42 Hz, 43 Hz, 44 Hz or 45 Hz, etc.

[0044] It should be noted that the unit Hz of the stirring rate in the present invention is one of the rate units. In actual operation, 40 Hz is approximately 80 rpm / min; in a specific embodiment, the stirring rate of the grafting reaction is adjusted by a frequency converter, and the rate in the frequency converter is in units of Hz.

[0045] Preferably, the mass ratio of the cobalt hydroxide-coated cobalt carbonate, the complex metal salt and the grafting initiator in step (3) is (300 - 400):(20 - 30):1, where the selection range of the cobalt hydroxide-coated cobalt carbonate (300 - 400) can be, for example, 300, 320, 350, 380 or 400, etc., and the selection range of the complex metal salt (20 - 30) can be, for example, 20, 22, 25, 28 or 30, etc.

[0046] Preferably, the grafting initiator described in step (3) includes any one or a combination of at least two of toluene diisocyanate, stannous octoate, toluene, and benzoyl chloride. For example, it can be a combination of toluene diisocyanate and stannous octoate, a combination of toluene and benzoyl chloride, or a combination of toluene diisocyanate, stannous octoate, toluene, and benzoyl chloride, etc.

[0047] The preferred grafting initiator in the present invention has a certain selective initiation effect. It uses hydroxyl groups and complex metal active groups as active sites for grafting reactions, which is conducive to making the metal ions on the surface of cobalt carbonate coated with metal ions and the hydroxyl cobalt on the surface of cobalt carbonate coated with hydroxyl cobalt have the same texture, facilitating the formation of a non-dense coating layer on the surface of cobalt tetroxide and improving the diffusion performance of lithium.

[0048] Preferably, the grafting reaction is carried out in an organic solvent. Most grafting initiators are soluble in organic solvents and insoluble in water. Conducting the grafting reaction in an organic solvent is conducive to dissolving the grafting initiator and facilitating the progress of the grafting reaction.

[0049] As a preferred technical solution of the preparation method described in the present invention, after the grafting reaction in step (3) and before the sintering in step (4), steps of washing and drying are also carried out.

[0050] Preferably, the washing liquid for the washing includes an ammonium bicarbonate solution. The ammonium bicarbonate solution is an ammonium hydrogen carbonate solution. As a washing liquid, it has weak alkalinity, can prevent metal ions, especially neutral metal ions, from undergoing hydrolysis reactions, easily washes away impurity ions, and improves the purity of the product.

[0051] Preferably, the concentration of the ammonium bicarbonate solution is 10 - 200 g / L. For example, it can be 10 g / L, 15 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 80 g / L, 100 g / L, 150 g / L, or 200 g / L, etc. Preferably, it is 15 - 40 g / L.

[0052] Preferably, the temperature of the sintering in step (4) is 500 - 900 °C. For example, it can be 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, or 900 °C, etc.

[0053] Preferably, the time of the sintering in step (4) is 3 - 10 h. For example, it can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0054] As a preferred technical solution of the preparation method described in the present invention, the preparation method includes:

[0055] (1) Mix the cobalt-doped solution and the precipitation solution, control the pH value of the mixed solution to be 7.0 - 7.8 to obtain cobalt carbonate, and subject the cobalt carbonate to surface hydroxylation treatment at 60 - 70 °C to obtain cobalt hydroxide-coated cobalt carbonate;

[0056] Among them, the surface hydroxylation treatment is to introduce an oxygen-containing gas under weakly alkaline conditions with pH = 7.2 - 8.0 or add hydrogen peroxide under weakly alkaline conditions with pH = 7.2 - 8.0. The mass ratio of cobalt hydroxide to cobalt carbonate in the cobalt hydroxide-coated cobalt carbonate is 1:(23 - 31);

[0057] (2) Mix a metal salt and an acidic complexing agent with a mass ratio of (5 - 10):1 for a complexation reaction to obtain a complexed metal salt;

[0058] Among them, the metal salt includes any combination of at least two of the chlorides of Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, Ce, and B, and the acidic complexing agent includes any one or at least two combinations of citric acid, malonic acid, glycine, p-toluenesulfonic acid, malic acid, and ascorbic acid;

[0059] (3) Mix the cobalt hydroxide-coated cobalt carbonate in step (1), the complexed metal salt in step (2), and a grafting initiator with a mass ratio of (300 - 400):(20 - 30):1, carry out a grafting reaction at 70 - 80 °C for 3 - 10 h, with a stirring rate of 40 - 45 Hz and a grafting rate of 60% - 80% to obtain metal ion-coated cobalt carbonate;

[0060] (4) Wash the metal ion-coated cobalt carbonate in step (3) with an ammonium carbonate solution with a concentration of 10 - 200 g / L, dry it, and sinter it at 500 - 900 °C for 3 - 10 h to obtain surface-coated and modified cobalt tetroxide.

[0061] In the second aspect, the present invention provides a surface-coated and modified cobalt tetroxide. The surface-coated and modified cobalt tetroxide is prepared by using the preparation method according to the first aspect. The surface-coated and modified cobalt tetroxide includes cobalt tetroxide and a coating layer coated on the surface of the cobalt tetroxide, and the coating layer includes metal oxides.

[0062] In the present invention, the surface of the surface-coated and modified cobalt tetroxide contains a non-dense, loose, flower-like structure metal oxide coating layer. The structure of the coating layer is beneficial to the diffusion of lithium into the mixture of cobalt tetroxide and lithium salt during sintering, which is beneficial to improving the surface activity of the material and the electrochemical performance of the prepared lithium cobaltate.

[0063] Preferably, the mass ratio of the cobalt oxide to the coating layer is (15-20):1, for example, it can be 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, etc.; by coating the surface of the cobalt oxide with a suitable coating layer, while lithium is fully diffused into it, the metal ions further enhance the effect of inhibiting lithium dissolution, improving the material cycle performance, and increasing the capacity.

[0064] Preferably, the metal oxide includes any one of the oxides of Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, Ce and B, or a combination of at least two thereof, such as a combination of Al oxide and Mg oxide, a combination of Ti oxide and Sr oxide, a combination of Ce oxide and B oxide, or a combination of W oxide, Y oxide, Mo oxide and Sb oxide, etc.

[0065] Preferably, the cobalt tetroxide is also doped with aluminum.

[0066] In a third aspect, the present invention provides a lithium ion battery, wherein the positive electrode of the lithium ion battery comprises lithium cobalt oxide, and the lithium cobalt oxide is prepared by using the surface-coated modified cobalt tetroxide according to the second aspect.

[0067] The lithium cobalt oxide of the present invention has uniform lithium distribution and sufficient lithium content. The lithium cobalt oxide is used as a positive electrode material for lithium ion batteries, and the prepared lithium ion batteries have excellent electrochemical properties such as high capacity and strong storage stability.

[0068] It should be noted that the present invention does not specifically limit the preparation method of lithium cobalt oxide. For example, the surface-coated modified cobalt oxide and lithium salt can be mixed and then sintered to obtain lithium cobalt oxide.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] The present invention performs surface hydroxylation treatment on cobalt carbonate. The cobalt carbonate with hydroxylation on the surface is relatively easy to undergo a grafting reaction. Under the initiation of a grafting initiator, the cobalt carbonate is grafted with a doping element (metal salt) treated with a complexing agent. The hydroxyl group and the complexing metal group are used as active sites. In-situ doping is performed according to a sheet-like morphology. The doping element is coated on the surface of the cobalt carbonate according to the pattern of the hydroxyl group to avoid the appearance of a dense structure, so as to obtain the metal ion-coated cobalt carbonate. After sintering, the metal ions generate a non-dense, flower-structured metal oxide coating layer on the surface of the cobalt oxide. The non-dense coating layer forms a lithium path, improves the diffusion performance of lithium, and can be effectively mixed with the lithium salt in the subsequent step, thereby improving the electrochemical performance of the cobalt oxide lithium battery, such as the charging capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 This is a cross-sectional SEM image of the surface-coated modified cobaltous oxide prepared in Example 1 of the present invention.

[0072] Figure 2 This is a 10,000-fold SEM image of the surface-coated modified cobaltous oxide prepared in Example 1 of the present invention.

[0073] Figure 3 1 is the XRD diagram of the surface-coated modified cobaltous oxide prepared in Example 2, Example 3 and Comparative Example 1 of the present invention.

[0074] Figure 4 It is a cross-sectional SEM image of cobalt tetroxide prepared in Comparative Example 1 of the present invention.

[0075] Figure 5 The charge and discharge curves of Example 1 and Comparative Example 1 of the present invention are shown in FIG. DETAILED DESCRIPTION

[0076] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0077] Example 1

[0078] This embodiment provides a method for preparing surface-coated modified cobalt tetroxide, the preparation method comprising:

[0079] (1) Within 10m 3 Add 3m 3 120g / L ammonium carbonate solution was used as the base, and then 240g / L ammonium carbonate solution and 120g / L cobalt chloride aluminum solution (aluminum 1.2g / L) were introduced into the reactor at 600L / h and 800L / h respectively, with the reaction temperature of 42°C, stirring frequency of 40Hz, pH controlled at 7.0-7.5, reaction particle size of 15μm, to obtain cobalt carbonate solution; then air was introduced at a flow rate of 10m 3 / h, and continue to pass the solid cobalt carbonate for 1h after it turns completely black to obtain a hydroxycobalt-coated cobalt carbonate solution, wherein the mass ratio of hydroxycobalt to cobalt carbonate in the hydroxycobalt-coated cobalt carbonate is 1:27;

[0080] (2) adding 2.6 kg of citric acid to 1000 L of water, and then adding 13.7 kg of aluminum chloride, and stirring evenly to obtain an aluminum salt solution after complex reaction;

[0081] (3) Add 5 ml of acetone solution into reactor 2. 3, then concentrate the cobalt hydroxycarbonate-coated cobalt carbonate solution in step (1) into a slurry with a solid content of 700 g / L, transfer it to reactor 2, add the aluminum salt solution after the complexation reaction in step (2) and 15 g of stannous octoate, and carry out a grafting reaction at 80 °C for 5 h with a stirring rate of 40 Hz and a grafting rate of 72% to obtain metal ion-coated cobalt carbonate;

[0082] Among them, the mass ratio of cobalt hydroxycarbonate-coated cobalt carbonate, the aluminum salt in the aluminum salt solution after the complexation reaction, and stannous octoate is 320:25:1;

[0083] (4) Wash the metal ion-coated cobalt carbonate described in step (3) with an ammonium carbonate solution with a concentration of 30 g / L, dry it, and sinter it at 780 °C for 5 h to obtain surface-coated modified cobalt tetroxide.

[0084] The surface-coated modified cobalt tetroxide prepared in this example includes cobalt tetroxide and aluminum oxide coated on the surface of cobalt tetroxide, and the mass ratio of cobalt tetroxide to aluminum oxide is 20:1. Al is also doped in cobalt tetroxide, and the content of Al accounts for 0.7 wt% of the content of cobalt tetroxide. Figure 1 is the cross-sectional view of the surface-coated modified cobalt tetroxide prepared in this example, Figure 2 is the electron microscope image magnified 10,000 times; from Figure 1 it can be seen that the aluminum oxide coating layer on the surface of cobalt tetroxide has a flower-like structure and is a non-dense coating. This structure is beneficial to the diffusion of lithium, realizes the effective mixing of surface-coated modified cobalt tetroxide and lithium salt, and improves the performance of lithium cobalt oxide batteries.

[0085] Example 2

[0086] This example provides a preparation method of surface-coated modified cobalt tetroxide, and the preparation method includes:

[0087] (1) Add 3 m 3 of 120 g / L ammonium carbonate solution for priming to reactor 1 with a volume of 10 m 3 , then introduce 240 g / L ammonium carbonate solution and 120 g / L cobalt aluminum chloride solution (aluminum 1.2 g / L) into the reactor at a flow rate of 600 L / h and 800 L / h respectively. The reaction temperature is 42 °C, the stirring frequency is 40 Hz, the pH is controlled at 7.0 - 7.5, and the reaction particle size is 15 μm to obtain a cobalt carbonate solution; then add hydrogen peroxide at a flow rate of 200 L / h, and continue to introduce it for 1 h after all the solid cobalt carbonate turns black to obtain a cobalt hydroxycarbonate-coated cobalt carbonate solution, and the mass ratio of cobalt hydroxy to cobalt carbonate in the cobalt hydroxycarbonate-coated cobalt carbonate is 1:27;

[0088] (2) Add 2.8 kg of glycine to 1000 L of water, and then add 15 kg of magnesium chloride, and stir evenly to obtain a magnesium salt solution after the complexation reaction;

[0089] (3) Add 5 ml of tetrahydrofuran solution into reactor 2 3 Then, the hydroxycobalt-coated cobalt carbonate solution in step (1) is concentrated into a slurry with a solid content of 600 g / L and transferred into reactor 2, and the magnesium salt solution after the complex reaction in step (2) and 20 g of toluene diisocyanate are added, and the grafting reaction is carried out at 80° C. for 7 h, the stirring rate is 40 Hz, and the grafting rate is 76%, thereby obtaining metal ion-coated cobalt carbonate;

[0090] The mass ratio of the cobalt carbonate coated with hydroxycobalt, the magnesium salt in the magnesium salt solution after the complex reaction, and toluene diisocyanate is 330:26:1;

[0091] (4) The metal ion-coated cobalt carbonate in step (3) is washed with a 40 g / L ammonium carbonate solution, dried, and sintered at 750° C. for 4 h to obtain surface-coated modified cobalt tetroxide.

[0092] The surface-coated modified cobalt oxide prepared in this embodiment includes cobalt oxide and magnesium oxide coated on the surface of cobalt oxide, and the mass ratio of cobalt oxide to magnesium oxide is 18: 1. Cobalt oxide is also doped with Al, and the content of Al accounts for 0.7wt% of the cobalt oxide content. Figure 3 Curve C in the middle is the XRD curve of the surface-coated modified cobalt tetroxide prepared in this example. From curve C, it can be seen that cobalt tetroxide is successfully prepared in this example.

[0093] Example 3

[0094] This embodiment provides a method for preparing surface-coated modified cobalt tetroxide, the preparation method comprising:

[0095] (1) Within 10m 3 Add 3m 3 120g / L ammonium carbonate solution is used as the base, and then 240g / L ammonium carbonate solution and 120g / L aluminum cobalt chloride solution (aluminum 1.2g / L) are introduced into the reactor at 600L / h and 800L / h respectively, the reaction temperature is 42°C, the stirring frequency is 40Hz, the pH is controlled at 7.0-7.5, and the reaction particle size is 15μm to obtain a cobalt carbonate solution; then hydrogen peroxide is added at a flow rate of 200L / h, and after the solid cobalt carbonate turns completely black, it is continuously introduced for 1h to obtain a hydroxycobalt-coated cobalt carbonate solution, and the mass ratio of hydroxycobalt to cobalt carbonate in the hydroxycobalt-coated cobalt carbonate is 1:29;

[0096] (2) adding 3 kg of p-toluenesulfonic acid to 1000 L of water, and then adding 20 kg of yttrium chloride, and stirring evenly to obtain an yttrium salt solution after complex reaction;

[0097] (3) Add 5 ml of toluene solution into the reactor 2. 3, then concentrate the cobalt hydroxycarbonate solution in step (1) into a slurry with a solid content of 800 g / L, transfer it to reactor 2, add the yttrium salt solution after the complexation reaction in step (2) and 24 g of benzoyl chloride, carry out a grafting reaction at 80 °C for 6 h, with a stirring rate of 40 Hz and a grafting rate of 74%, to obtain metal ion-coated cobalt carbonate;

[0098] Among them, the mass ratio of cobalt hydroxycarbonate, the yttrium salt in the yttrium salt solution after the complexation reaction, and toluene diisocyanate is 340:28:1;

[0099] (4) Wash the metal ion-coated cobalt carbonate described in step (3) with an ammonium carbonate solution with a concentration of 25 g / L, dry it, and sinter it at 750 °C for 5 h to obtain surface-coated modified cobalt tetroxide.

[0100] The surface-coated modified cobalt tetroxide prepared in this example includes cobalt tetroxide and yttrium oxide coated on the surface of cobalt tetroxide, and the mass ratio of cobalt tetroxide to yttrium oxide is 19:1. Al is also doped in cobalt tetroxide, and the content of Al accounts for 0.7 wt% of the content of cobalt tetroxide. Figure 3 Curve D in is the XRD curve of the surface-coated modified cobalt tetroxide prepared in this example. It can be seen from curve D that cobalt tetroxide is successfully prepared in this example.

[0101] Example 4

[0102] Except that the air flow rate in step (1) is replaced with 8 m 3 / h to make the mass ratio of cobalt hydroxy to cobalt carbonate in cobalt hydroxycarbonate 1:22, the rest are the same as in Example 1. 3 / h, so that the mass ratio of cobalt hydroxy to cobalt carbonate in cobalt hydroxycarbonate is 1:22, and the rest are the same as in Example 1.

[0103] Example 5

[0104] Except that the air flow rate in step (1) is replaced with 12 m 3 / h to make the mass ratio of cobalt hydroxy to cobalt carbonate in cobalt hydroxycarbonate 1:32, the rest are the same as in Example 1.

[0105] Example 6

[0106] Except that the mass ratio of citric acid to aluminum chloride in step (2) is 0.09, the rest are the same as in Example 1.

[0107] Example 7

[0108] Except that the mass ratio of citric acid to aluminum chloride in step (2) is 0.5, the rest are the same as in Example 1.

[0109] Example 8

[0110] Except that 80 °C in step (3) is replaced with 60 °C, so that the grafting rate is 55%, the rest is the same as in Example 1.

[0111] Example 9

[0112] Except that the reaction time of 2 h in step (3) is replaced with 4 h, so that the grafting rate is 85%, the rest is the same as in Example 1.

[0113] Example 10

[0114] Except that citric acid in step (2) is replaced with ammonia water, the rest is the same as in Example 1.

[0115] Comparative Example 1

[0116] Except that air is not introduced in step (1), the rest is the same as in Example 1.

[0117] Figure 3 Curves A and B in it are the XRD curves of cobalt tetroxide prepared in this example. A and B are the results of two tests on the materials of this comparative example respectively. It can be seen from the two curves that cobalt tetroxide is successfully prepared in this comparative example.

[0118] Figure 4 is the cross-sectional SEM image of cobalt tetroxide prepared in this comparative example. From Figure 4 it can be seen that the outer layer of cobalt tetroxide is extremely dense and there are no voids, and this structure is not conducive to the diffusion of lithium.

[0119] Comparative Example 2

[0120] Except that citric acid is not added in step (2), the rest is the same as in Example 1.

[0121] Comparative Example 3

[0122] Except that stannous octoate is not added in step (3), the rest is the same as in Example 1.

[0123] I. Preparation of lithium cobaltate and assembly of lithium-ion battery

[0124] (1) Preparation of lithium cobaltate

[0125] Mix the surface-coated and modified cobalt tetroxide prepared in Examples 1-10 and Comparative Examples 1-4 of the present invention with lithium carbonate in a molar ratio of 1:1.04, and sinter at 950 °C for 10 h to obtain lithium cobaltate.

[0126] (2) Assembly of lithium-ion battery

[0127] The prepared lithium cobaltate is used as the positive electrode active material. The positive electrode sheet is prepared by mixing the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent SP according to a mass ratio of 97.8:1.2:2. For the negative electrode sheet, the mass ratio of graphite G49: conductive agent: binder is 96:2:2. The electrolyte is lithium hexafluorophosphate. The battery is assembled by stacking and injecting electrolyte to obtain a lithium-ion battery.

[0128] II. Electrochemical Performance Test

[0129] Capacity Test: The prepared lithium-ion battery is charged and discharged at a rate of 0.1C in the voltage range of 2 - 4.48V, and the first charge capacity and the first discharge capacity of the battery are recorded. The first discharge efficiency is obtained by dividing the first discharge capacity by the first charge capacity. The test results of the first discharge capacity and the first discharge efficiency are shown in Table 1.

[0130] Storage Performance Test: The prepared lithium-ion battery is left standing at room temperature of 25°C for 7 days. The voltage on the first day and the voltage on the seventh day of the battery are measured. The storage performance for 7 days is obtained by dividing the voltage on the seventh day by the voltage on the first day. The test results are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] In summary, in the present invention, by hydroxylating the surface of cobalt carbonate and carrying out grafting reaction with the metal salt treated by the complexing agent, in-situ doping of metal elements is realized, so that the coating layer formed by the metal salt and the cobalt hydroxide formed on the surface of cobalt carbonate have the same texture, thereby forming a non-dense, flower-like structure metal oxide coating layer on the surface of cobalt tetroxide, improving the surface activity of cobalt tetroxide, being beneficial to the subsequent effective mixing with lithium salt, and thus improving the electrochemical performance of the lithium cobaltate battery.

[0135] It can be seen from the comparison between Example 1 and Examples 4 - 5 that by adjusting the ratio of cobalt hydroxide and cobalt carbonate in the present invention, the more uniform distribution of surface cobalt hydroxide can be achieved, thereby improving the interfacial stability performance. In Example 4, the content of cobalt hydroxide is too low, resulting in some parts not being coated; in Example 5, the content of cobalt hydroxide is too high, resulting in a high coating content of cobalt hydroxide on the surface of cobalt carbonate, making it difficult to accurately control the lithium doping amount. Therefore, compared with Examples 4 - 5, the comprehensive electrochemical performance of the surface-coated and modified cobalt tetroxide prepared in Example 1 is the best.

[0136] From the comparison between Example 1 and Examples 6 - 7, it can be seen that in the present invention, there is an optimal proportion range for the complexing agent and the metal salt. Within this range, the number of active sites can be increased, and the surface can be uniformly covered. In Example 6, the content of citric acid is too low, which will affect the uniformity of coverage; in Example 7, the content of citric acid is too high, which will affect the pH and cause loss of metal ions in the synthesis reaction. Therefore, the performance of the complexing agent proportion in Example 1 is the best.

[0137] From the comparison between Example 1 and Examples 8 - 9, it can be seen that the grafting rate will affect the content of the coating layer on the surface of cobalt tetroxide, affect the structure and compactness of the coating layer, affect the diffusion of lithium, and thus affect the electrochemical performance of the lithium-ion battery. In Example 8, the grafting rate is too low, which will cause some areas to be unable to be coated with metal ions; in Example 9, the grafting rate is too high, which will cause a high surface density and a large lithium-ion migration impedance; therefore, compared with Examples 8 - 9, the stability of the material prepared within the appropriate grafting rate range in Example 1 is the best.

[0138] From the comparison between Example 1 and Example 10, it can be seen that using an acidic complexing agent in the present invention has a better effect and is more conducive to the complexing agent to play its role; in Example 10, a basic complexing agent is used, which easily causes precipitation of metal ions and affects the complexation of metal ions. Therefore, the capacity and storage performance of the surface-coated modified cobalt tetroxide finally prepared in Example 10 are slightly worse than those in Example 1.

[0139] From the comparison between Example 1 and Comparative Examples 1 - 3, it can be seen that the hydroxylation of cobalt carbonate, the complexation reaction of the metal salt, and the grafting reaction in the present invention are all indispensable. In Comparative Example 1, cobalt carbonate was not hydroxylated, and the grafted hydroxyl groups could not be obtained. The metal salt after complexation treatment could not be effectively grafted onto the surface of cobalt carbonate, resulting in a dense structure of the coating layer on the surface of the cobalt tetroxide prepared subsequently, which affected the diffusion of lithium; Figure 5 are the charge-discharge curves of the materials in Example 1 and Comparative Example 1. From Figure 5 it can also be seen that the electrochemical performance of Comparative Example 1 is worse than that of Example 1; in Comparative Example 2, no complexing agent was added, and the metal salt did not undergo a complexation reaction, which would cause the combination of the metal salt and the active sites to be blocked and the combination of groups could not occur; in Comparative Example 3, no grafting initiator was added, which would cause low grafting efficiency; therefore, the electrochemical performance of Comparative Examples 1 - 3 is significantly worse than that of Example 1.

[0140] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of surface-coated modified cobalt tetroxide, characterized in that, The preparation method includes: (1) Subjecting cobalt carbonate to surface hydroxylation treatment to obtain cobalt hydroxide-coated cobalt carbonate; (2) Mixing a metal salt and a complexing agent to carry out a complexation reaction to obtain a complex metal salt; (3) Mixing the cobalt hydroxide-coated cobalt carbonate obtained in step (1), the complex metal salt obtained in step (2), and a grafting initiator, and carrying out a grafting reaction to obtain metal ion-coated cobalt carbonate; (4) Sintering the metal ion-coated cobalt carbonate obtained in step (3) to obtain surface-coated and modified cobalt tetroxide; In the cobalt hydroxide-coated cobalt carbonate obtained in step (1), the mass ratio of cobalt hydroxide to cobalt carbonate is 1:(23 - 31); In step (2), the mass ratio of the metal salt to the complexing agent is (5 - 10):1; The complexing agent in step (2) includes an acidic complexing agent, and the acidic complexing agent includes any one or a combination of at least two of citric acid, malonic acid, glycine, p-toluenesulfonic acid, malic acid, and ascorbic acid; The grafting rate of the grafting reaction in step (3) is 60% - 80%.

2. The preparation method according to claim 1, characterized in that, The surface hydroxylation treatment in step (1) is to introduce an oxygen-containing gas under weakly alkaline conditions or add hydrogen peroxide under weakly alkaline conditions.

3. The preparation method according to claim 2, characterized in that, The weakly alkaline condition is pH = 7.2 - 8.

0.

4. The preparation method according to claim 1, wherein The temperature of the hydroxylation treatment in step (1) is 60 - 70 °C.

5. The preparation method according to claim 1, wherein The cobalt carbonate in step (1) is prepared in the following manner: Mixing a cobalt doping solution and a precipitation solution to obtain cobalt carbonate.

6. The preparation method according to claim 5, wherein The cobalt doping solution includes any one or a combination of at least two of cobalt chloride, cobalt sulfate, cobalt nitrate, and cobalt acetate.

7. The preparation method according to claim 5, characterized in that The precipitation solution includes any one or a combination of at least two of ammonium bicarbonate, ammonium carbonate, and sodium carbonate.

8. The preparation method according to claim 5, characterized in that, During the process of mixing the cobalt doping solution and the precipitation solution, the pH value of the mixed solution is 7.0 - 7.

8.

9. The preparation method according to claim 1, wherein The metal salt in step (2) includes any one or a combination of at least two of salts of Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, and Ce.

10. The preparation method according to claim 1, wherein The metal salt is a chloride.

11. According to the preparation method described in claim 1, characterized in that, The temperature of the grafting reaction in step (3) is 70 - 80 °C.

12. The preparation method according to claim 1, wherein The time of the grafting reaction in step (3) is 3 - 10 h.

13. The preparation method according to claim 1, characterized in that, The stirring rate of the grafting reaction in step (3) is 40 - 45 Hz.

14. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the cobalt hydroxide-coated cobalt carbonate, the complex metal salt, and the grafting initiator is (300 - 400):(20 - 30):

1.

15. The preparation method according to claim 1, characterized in that, The grafting initiator in step (3) includes any one or a combination of at least two of toluene diisocyanate, stannous octoate, toluene, and benzoyl chloride.

16. The preparation method according to claim 1, wherein After the grafting reaction in step (3) and before the sintering in step (4), steps of washing and drying are also carried out.

17. The preparation method according to claim 16, wherein, The washing solution for the washing includes an ammonium carbonate solution.

18. The preparation method according to claim 17, wherein The concentration of the ammonium carbonate solution is 10 - 200 g / L.

19. The preparation method according to claim 18, characterized in that, The concentration of the ammonium carbonate solution is 15 - 40 g / L.

20. The preparation method according to claim 1, characterized in that, The temperature of the sintering in step (4) is 500 - 900 °C.

21. The preparation method according to claim 1, characterized in that, The time of the sintering in step (4) is 3 - 10 h.

22. The preparation method according to claim 1, wherein, The preparation method includes: (1) Mix the cobalt-doped solution and the precipitation solution, control the pH value of the mixed solution to be 7.0 - 7.8 to obtain cobalt carbonate, and subject the cobalt carbonate to surface hydroxylation treatment at 60 - 70 °C to obtain cobalt hydroxide-coated cobalt carbonate; Among them, the surface hydroxylation treatment is to introduce an oxygen-containing gas under a weakly alkaline condition with pH = 7.2 - 8.0 or add hydrogen peroxide under a weakly alkaline condition with pH = 7.2 - 8.

0. The mass ratio of cobalt hydroxide to cobalt carbonate in the cobalt hydroxide-coated cobalt carbonate is 1:(23 - 31); (2) Mix a metal salt and an acidic complexing agent with a mass ratio of (5 - 10):1 for a complexation reaction to obtain a complexed metal salt; Among them, the metal salt includes any one or a combination of at least two of the chlorides of Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, and Ce, and the acidic complexing agent includes any one or a combination of at least two of citric acid, malonic acid, glycine, p-toluenesulfonic acid, malic acid, and ascorbic acid; (3) Mix the cobalt hydroxide-coated cobalt carbonate in step (1), the complexed metal salt in step (2), and a grafting initiator in a mass ratio of (300 - 400):(20 - 30):1, carry out a grafting reaction at 70 - 80 °C for 3 - 10 h, with a stirring rate of 40 - 45 Hz and a grafting rate of 60% - 80% to obtain metal ion-coated cobalt carbonate; (4) Wash the metal ion-coated cobalt carbonate in step (3) with an ammonium carbonate solution with a concentration of 10 - 200 g / L, dry it, and sinter it at 500 - 900 °C for 3 - 10 h to obtain surface-coated modified cobalt tetroxide.

23. A surface-coated modified cobalt tetroxide, characterized in that, The surface-coated modified cobalt tetroxide is prepared by the preparation method according to any one of claims 1 - 22. The surface-coated modified cobalt tetroxide includes cobalt tetroxide and a coating layer coated on the surface of the cobalt tetroxide, and the coating layer includes metal oxides.

24. The surface-coated modified cobalt tetroxide according to claim 23, wherein The mass ratio of the cobalt tetroxide to the coating layer is (15 - 20):

1.

25. The surface-coated modified cobalt tetroxide according to claim 23, wherein The metal oxides include any one or a combination of at least two of the oxides of Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, and Ce.

26. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes lithium cobaltate, and the lithium cobaltate is prepared by using the surface-coated modified cobalt tetroxide according to any one of claims 23 - 25.

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