A doped cobalt tetroxide and its preparation method

Abstract

The present disclosure relates to a doped cobalt tetroxide and a preparation method thereof, belonging to the technical field of lithium battery materials. The preparation method of the doped cobalt tetroxide described herein can effectively improve the "sticking to the furnace" phenomenon by adopting a pre-oxidation process in combination with specific processing aids. At the same time, the prepared product has high particle uniformity, no obvious cracking phenomenon, and the doped elements show a gradient distribution. The further prepared lithium cobalt oxide material has good electrochemical performance. This technical solution provides the possibility for the full-chain integrated production of doped cobalt tetroxide in the lithium battery field.

Description

Technical Field

[0001] This text relates to the technical field of lithium battery materials, and particularly to a doped cobalt tetroxide and a preparation method thereof. Background Art

[0002] Cobalt tetroxide is a precursor for the preparation of lithium cobaltate, a cathode active material widely used in the lithium battery field. The quality of cobalt tetroxide is directly related to the electrochemical performance of lithium cobaltate during use. Currently, in the lithium battery field, cobalt tetroxide is mainly obtained by high-temperature sintering of cobalt carbonate. However, due to the poor fluidity of cobalt carbonate itself, the phenomenon of "sticking to the furnace" is likely to occur during high-temperature sintering, resulting in obstacles to the addition and mixing of materials. Not only is the yield of the final product low, but also if there is too much adhering material, the cleaning difficulty of the sintering device is large, and even its normal operation will be affected. Therefore, a relatively high cleaning frequency needs to be set to ensure the normal operation of the equipment. On the other hand, in related technologies, people gradually replace pure cobalt tetroxide with higher-performance doped cobalt tetroxide, which is generally obtained by introducing doping materials for modification during the synthesis stage of cobalt carbonate and then sintering. However, due to the easy occurrence of particle cracking of cobalt carbonate during this process, the doping materials are also unevenly dispersed, and the expected effect cannot be achieved during application. Summary of the Invention

[0003] The purpose of this text is to overcome the deficiencies of the above-mentioned prior art and provide a preparation method of doped cobalt tetroxide. This method can effectively improve the "sticking to the furnace" phenomenon by adopting a pre-oxidation process in combination with specific processing aids. At the same time, the product prepared has high particle uniformity, no obvious cracking phenomenon, and the doped elements show a gradient distribution. The further prepared lithium cobaltate material has good electrochemical performance.

[0004] To achieve the above purpose, the technical solution adopted in this text is as follows:

[0005] A preparation method of doped cobalt tetroxide, comprising the following steps:

[0006] Oxidize cobalt carbonate at 200 - 400°C for 2 - 4 h in an air and / or oxygen atmosphere;

[0007] Mix the oxidized cobalt carbonate, oxidation aid, and doping aid, and then calcine at 700 - 750°C for 3 - 8 h in an air or oxygen atmosphere to obtain doped cobalt tetroxide; the oxidation aid is at least one of perchlorate, persulfate, and metal peroxide; the doping aid includes metal salt and doped oxide; the mass ratio of the oxidized cobalt carbonate, oxidation aid, and doping aid is 1:(0.0001 - 0.0003):(0.0001 - 0.01).

[0008] In one embodiment, the melting point of the metal salt ≤ 720°C.

[0009] In one embodiment, the mass ratio of the oxidized cobalt carbonate, the oxidation aid, and the doping aid is 1:(0.0001 - 0.0003):(0.0001 - 0.005).

[0010] In the preparation method of the doped cobalt tetroxide described herein, since the cobalt carbonate has been pre-oxidized and then mixed and calcined with the oxidation aid, the calcination process can be carried out at a relatively low temperature. During this process, the fluidity and stability between the mixture particles are relatively high, and the particles are not easily cracked, effectively alleviating the phenomenon of material adhesion to the inner wall of the sintering device that often occurs in the conventional process. On the other hand, since the cobalt carbonate particle material is pre-oxidized and has a high surface density, it is difficult to achieve penetration doping of doped elements by using a general solid-phase sintering method. However, in the preparation method described herein, metal salts and doped oxides are used as doping aids. Among them, the metal salts have a low melting point and can be melted at 700 - 750 °C. As a flux, the doped oxides gradually penetrate into the cobalt tetroxide particles and achieve liquid-phase sintering. Eventually, the metal doping elements show a gradient distribution from the inside to the outside in the product. When this product is further used to prepare lithium cobaltate materials, good electrochemical performance can be achieved.

[0011] In addition, during the calcination process, the addition amount of the oxidation aid cannot be too much or too little. If too little is added, the cobalt content in the mixture fluctuates, and effective regulation cannot be achieved. The doped elements cannot provide the necessary stable structure function either. If too much is added, it will lead to the enrichment of the doped elements, and instead, the uniformity of the product will become worse.

[0012] In one embodiment, the cobalt content of the cobalt carbonate is 72.0 - 73.0%, and the particle size D , ,

[0017] ,

[0012] , ,

[0016] , , 50 ,

[0015] , ,

[0014] , ,

[0013] , is 3 - 20 μm.

[0013] In one embodiment, the flow rate of the air and / or oxygen atmosphere during oxidation is 20 - 40 L / h / kg of cobalt carbonate.

[0014] During the pre-oxidation process of cobalt carbonate, the addition amount of oxygen needs to be sufficient so as to ensure that the complete conversion of cobalt carbonate to cobalt tetroxide can be achieved at a relatively low temperature during the subsequent sintering process.

[0015] In one embodiment, the temperature during oxidation is 300 - 400 °C.

[0016] The temperature during oxidation has a great influence on the morphology of the final product. If the temperature is too high, the particles in the product may crack. If the temperature is too low, the conversion of cobalt tetroxide and the doping of doped elements in the product may be incomplete, and at the same time, it will also affect the particle fluidity.

[0017] In one embodiment, the heating rate during oxidation is 2 - 3 °C / min.

[0018] In one embodiment, the metal salt in the doping assistant is at least one of MgCl2, NaNO3, Ba(NO)2, ZnCl2, FeCl2, and ZnSO4.

[0019] In one embodiment, the doped oxide is a metal or non-metal oxide, and the metal or non-metal oxide is at least one of MgO, Al2O3, TiO2, Nb2O5, B2O3, and V2O5.

[0020] These above-mentioned metal salts have a relatively low melting point, which can assist the metal oxide to effectively enter the interior of cobalt carbonate wrapped by the dense surface layer and improve the structural stability of the overall material.

[0021] In one embodiment, the heating rate during calcination is 2 - 5 °C / min.

[0022] Another object of the present invention is to provide doped cobalt tetroxide prepared by the preparation method of the doped cobalt tetroxide.

[0023] Another object of the present invention is to provide the application of the doped cobalt tetroxide in the preparation of lithium cobalt oxide materials.

[0024] The doped cobalt tetroxide obtained by the preparation method described herein has a uniform morphology, complete particles, a high cobalt content, and high crystal form stability. The lithium cobalt oxide material further synthesized from the doped cobalt tetroxide has ideal electrochemical properties. Since there is no need to consider the problem of "sticking to the furnace" during the preparation process, the product can be continuously produced for a long time.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The present invention provides a preparation method of doped cobalt tetroxide. By adopting a pre-oxidation process in combination with specific processing aids to prepare the product, the phenomenon of "sticking to the furnace" can be effectively improved. At the same time, the particles in the prepared product have high uniformity, no obvious cracking phenomenon, and the doped elements show a gradient distribution. The further prepared lithium cobalt oxide material has good electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an EDS point scan map and the elemental composition of the scanning points of the particles of the doped cobalt tetroxide described herein from the outer layer to the inner layer (from left to right).

[0028] Figure 2 It is a schematic diagram of the "sticking to the furnace" phenomenon that occurred in the rotary kiln used in the preparation process of the product in Comparative Example 5 ( Figure 2 left, where the marked area is the adhered material) and a schematic diagram of the rotary kiln used in the preparation process of the product in Example 1 ( Figure 2 right). Detailed implementation manners

[0029] To better illustrate the purpose, technical solutions, and advantages of this article, the following will further explain this article in combination with the accompanying drawings and specific embodiments.

[0030] Unless otherwise specified, the materials used in the examples and comparative examples can all be obtained through commercial channels.

[0031] The cobalt content of the cobalt carbonate used in each example and comparative example is 72.0 - 73.0%, and the particle size D 50 is 3 - 20 μm.

[0032] Example 1

[0033] An embodiment of the doped cobalt tetroxide and its preparation method described in this article. The preparation method of the doped cobalt tetroxide in this embodiment is as follows:

[0034] (1) Heat 20 kg of cobalt carbonate in an oven to 300 °C at a rate of 2 °C / min and oxidize for 4 h; during oxidation, introduce air with a flow rate of 20 L / h / kg of cobalt carbonate.

[0035] (2) First, mix 20 kg of the oxidized cobalt carbonate, 3 g of oxidation aid, and doping aid at a low speed of 500 rpm in a mixer for 2 min, then mix at 1500 rpm for 30 min, and finally mix at 500 rpm for 5 min. Then, calcine in a rotary kiln under an oxygen atmosphere at a rate of 2 °C / min to 740 °C for 4 h to obtain doped cobalt tetroxide; the oxidation aid is lithium perchlorate; the doping aid is 60 g of metal salt magnesium chloride and 4 g of metal oxide magnesium oxide.

[0036] Example 2

[0037] An embodiment of the doped cobalt tetroxide and its preparation method described in this article. The preparation method of the doped cobalt tetroxide in this embodiment is as follows:

[0038] (1) Heat 30 kg of cobalt carbonate in a rotary kiln to 400 °C at a rate of 4 °C / min and oxidize for 4 h; during oxidation, introduce air with a flow rate of 40 L / h / kg of cobalt carbonate.

[0039] (2) First, mix 30 kg of the oxidized cobalt carbonate, 6 g of oxidation aid, and doping aid at a low speed of 500 rpm in a mixer for 2 min, then mix at 1500 rpm for 30 min, and finally mix at 500 rpm for 5 min. Then, calcine in a rotary kiln under an oxygen atmosphere at a rate of 2 °C / min to 740 °C for 4 h to obtain doped cobalt tetroxide; the oxidation aid is vanadium peroxide; the doping aid is 4 g of metal salt sodium nitrate and 150 g of metal oxide vanadium pentoxide.

[0040] Example 3

[0041] An embodiment of the doped cobalt tetroxide and its preparation method described in this article. The preparation method of the doped cobalt tetroxide in this embodiment is as follows:

[0042] (1) Heat 40 kg of cobalt carbonate to 400 °C in a rotary kiln at a rate of 4 °C / min and oxidize for 4 h; during the oxidation, introduce air with a flow rate of 26 L / h / kg of cobalt carbonate.

[0043] (2) First, mix 40 kg of oxidized cobalt carbonate, 5 g of oxidation aid and doping aid at a low speed of 500 rpm in a mixer for 2 min, then mix at 1500 rpm for 30 min, and finally mix at 500 rpm for 5 min. Then, calcine in a rotary kiln under an oxygen atmosphere at a rate of 3 °C / min to 730 °C for 3.5 h to obtain doped cobalt tetroxide; the oxidation aid is ammonium persulfate; the doping aid includes 160 g of metal salt Ba(NO)2 and 16 g of non-metal oxide boron trioxide.

[0044] Example 4

[0045] An embodiment of the doped cobalt tetroxide and its preparation method described in this article. The preparation method of the doped cobalt tetroxide in this embodiment is as follows:

[0046] (1) Heat 40 kg of cobalt carbonate to 400 °C in a rotary kiln at a rate of 4 °C / min and oxidize for 4 h; during the oxidation, introduce air with a flow rate of 35 L / h / kg of cobalt carbonate.

[0047] (2) First, mix 40 kg of oxidized cobalt carbonate, 5 g of oxidation aid and doping aid at a low speed of 500 rpm in a mixer for 2 min, then mix at 1500 rpm for 30 min, and finally mix at 500 rpm for 5 min. Then, calcine in a rotary kiln under an oxygen atmosphere at a rate of 3 °C / min to 730 °C for 3.5 h to obtain doped cobalt tetroxide; the oxidation aid is ammonium persulfate; the doping aid includes 85 g of chloride salt zinc chloride and 6 g of metal oxide titanium dioxide.

[0048] Comparative Example 1

[0049] A doped cobalt tetroxide and its preparation method. The preparation method of the doped cobalt tetroxide is as follows:

[0050] (1) Heat 20 kg of cobalt carbonate to 300 °C in an oven at a rate of 2 °C / min and oxidize for 4 h; during the oxidation, introduce air with a flow rate of 20 L / h / kg of cobalt carbonate.

[0051] (2) First, mix 20 kg of oxidized cobalt carbonate, 8 g of oxidation aid and doping aid in a mixer at a low speed of 500 rpm for 2 min, then at 1500 rpm for 30 min, and finally at 500 rpm for 5 min. Subsequently, calcine in a rotary kiln under an oxygen atmosphere at a heating rate of 2 °C / min to 740 °C for 4 h to obtain doped cobalt tetroxide; the oxidation aid is lithium perchlorate; the doping aid is 120 g of metal salt magnesium chloride and 8 g of metal oxide magnesium oxide.

[0052] Comparative Example 2

[0053] A doped cobalt tetroxide and its preparation method, the preparation method of the doped cobalt tetroxide is as follows:

[0054] (1) Heat 20 kg of cobalt carbonate in an oven to 300 °C at a heating rate of 2 °C / min for 4 h; during oxidation, introduce air with a flow rate of 20 L / h / kg of cobalt carbonate.

[0055] (2) First, mix 20 kg of oxidized cobalt carbonate, 1 g of oxidation aid and doping aid in a mixer at a low speed of 500 rpm for 2 min, then at 1500 rpm for 30 min, and finally at 500 rpm for 5 min. Subsequently, calcine in a rotary kiln under an oxygen atmosphere at a heating rate of 2 °C / min to 740 °C for 4 h to obtain doped cobalt tetroxide; the oxidation aid is lithium perchlorate; the doping aid is 20 g of metal salt magnesium chloride and 2 g of metal oxide magnesium oxide.

[0056] Comparative Example 3

[0057] A doped cobalt tetroxide and its preparation method, the preparation method of the doped cobalt tetroxide is as follows:

[0058] Mix 30 kg of cobalt carbonate, 1 g of oxidation aid and doping aid in a mixer at a low speed of 500 rpm for 2 min, then at 1500 rpm for 30 min, and finally at 500 rpm for 5 min. Subsequently, calcine in a rotary kiln under an air atmosphere at a heating rate of 2 °C / min to 740 °C for 4 h to obtain doped cobalt tetroxide; the oxidation aid is vanadium peroxide; the doping aid is 4 g of metal salt NaNO3 and 150 g of metal oxide vanadium pentoxide.

[0059] Comparative Example 4

[0060] A doped cobalt tetroxide and its preparation method, the preparation method of the doped cobalt tetroxide is as follows:

[0061] (1) Heat 40 kg of cobalt carbonate in a rotary kiln to 550 °C at a heating rate of 4 °C / min for 3.5 h; during oxidation, introduce air with a flow rate of 33 L / h / kg of cobalt carbonate.

[0062] (2) First, mix 40 kg of oxidized cobalt carbonate, 5 g of oxidation aid and doping aid in a mixer at a low speed of 500 rpm for 2 min, then at 1500 rpm for 30 min, and finally at 500 rpm for 5 min. Subsequently, calcine in a rotary kiln under an oxygen atmosphere at a heating rate of 3 °C / min to 730 °C for 3.5 h to obtain doped cobalt tetroxide; the oxidation aid is ammonium persulfate; the doping aid includes 160 g of metal salt Ba(NO)₂ and 16 g of non-metal oxide boron trioxide.

[0063] Comparative Example 5

[0064] A cobalt tetroxide and its preparation method, the preparation method of the cobalt tetroxide is as follows:

[0065] Calcine 40 kg of cobalt carbonate in a rotary kiln under an air atmosphere at a heating rate of 4 °C / min to 750 °C for 3.5 h to obtain unmodified cobalt tetroxide.

[0066] Comparative Example 6

[0067] A doped cobalt tetroxide and its preparation method, which is only different from Example 1 in that the metal salt magnesium chloride is replaced by magnesium oxide, and the added mass of magnesium atoms finally added is kept unchanged:

[0068] (1) Oxidize 20 kg of cobalt carbonate in an oven at a heating rate of 2 °C / min to 300 °C for 4 h; during oxidation, pass in air with a flow rate of 20 L / h / kg of cobalt carbonate.

[0069] (2) First, mix 20 kg of oxidized cobalt carbonate, 3 g of oxidation aid and doping aid in a mixer at a low speed of 500 rpm for 2 min, then at 1500 rpm for 30 min, and finally at 500 rpm for 5 min. Subsequently, calcine in a rotary kiln under an oxygen atmosphere at a heating rate of 2 °C / min to 740 °C for 4 h to obtain doped cobalt tetroxide; the oxidation aid is lithium perchlorate; the doping aid is 29.3 g of metal oxide magnesium oxide.

[0070] Effect Example 1

[0071] In order to explore the effects of the doped cobalt tetroxide prepared by the preparation method of the present invention, the cobalt content in the products of each example and comparative example was tested by elemental analysis method. At the same time, electron microscopy observation and XRD test were used to confirm whether there was cracking in the particles of the products and whether there were fluctuations in the grain size; on the other hand, observe whether there is a "sticking furnace" phenomenon in the rotary kiln where the products of each example and comparative example are calcined; finally, sinter at 1000 °C after mixing lithium carbonate and cobalt tetroxide in the doped cobalt tetroxide at a molar ratio of 1.03:1 to obtain the finished lithium cobaltate. The lithium cobaltate prepared under the same conditions was made into a button battery and the first charge-discharge Coulomb efficiency was tested at a charge-discharge voltage of 2.5 - 4.3 V and 0.1 C.

[0072] The results are shown in Table 1.

[0073] Table 1

[0074] Product Cobalt content % Whether it adheres to the furnace Whether the particles crack 311 Grain size Initial efficiency of button cell % Example 1 72.0 No No 678 94 Example 2 72.3 No No 684 93.2 Example 3 72.6 No No 673 93.4 Example 4 72.4 No No 682 93.7 Comparative example 1 71.6 No No 684 91.8 Comparative example 2 72.6 No No 681 91.4 Comparative example 3 72.3 Yes Yes 652 92.4 Comparative example 4 72.4 No Yes 690 91.7 Comparative example 5 73.0 Yes Yes 684 91.5 Comparative example 6 72.0 No No 670 91.8

[0075] As can be seen from Table 1, the cobalt content of the product described in the present invention is not much different from that of the pure cobalt tetroxide prepared in Comparative Example 5, indicating that the doping does not cause the loss of cobalt element, and there is no obvious cracking phenomenon in the product particles, and the fluctuation of the grain size of 311 is small. Further, the product of Example 1 was observed by EDS point scanning, and the results are as Figure 1 shown. It can be found that the doped elements are dispersedly distributed on the surface of the product particles in a gradient manner. During the production process, compared with the product of Comparative Example 5, the "furnace sticking phenomenon" of the products of each example is significantly improved, and there is no adhesion of the materials in the rotary kiln as described in the product of Comparative Example 5, as Figure 1 shown.

[0076] In contrast, since the product of Comparative Example 3 prepared by conventional means did not undergo a pre-oxidation step, obvious material adhesion occurred in the fired rotary kiln. It was precisely due to the occurrence of the "furnace sticking" phenomenon that the material could not effectively release stress during the reaction process, resulting in cracking of the particles during the rapid heating and calcination process. In the product of Comparative Example 1, the addition amount of the oxidation aid was too much, and the doped elements also increased correspondingly, resulting in an enrichment phenomenon during the product preparation process. Therefore, the cobalt element content was low and the product consistency was poor. Although the product of Comparative Example 4 also adopted a pre-oxidation process during the preparation process, the treatment temperature of this step was too high, and the product still showed particle cracking.

[0077] In the battery application of the product, since the properties of the doped cobalt tetroxide directly affect the performance of the final cathode material lithium cobaltate, the initial efficiency of the coin cell can also be regarded as the electrochemical performance results of the products of each example and comparative example. Compared with the product of Comparative Example 5, the initial efficiency of the coin cells of each example is relatively high, reaching more than 93%; in contrast, the initial efficiency of the products of each comparative example is relatively poor. Among them, in the product of Comparative Example 2, due to the too small addition amount of the oxidation aid during the preparation process, the final structure of the product is not stable, so the initial efficiency during lithium deintercalation is only 91.4%. In the product of Comparative Example 6, the doping aid does not contain low-melting metal salts, and the doped elements cannot achieve a good gradient distribution, and the electrochemical performance is also not ideal.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article rather than to limit the protection scope of this article. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of this article can be modified or equivalently replaced, but do not deviate from the essence and scope of the technical solutions of this article.

Claims

1. A preparation method of doped cobalt tetroxide, characterized in that, Comprising the following steps: Oxidize cobalt carbonate at 200 - 400 °C for 2 - 4 h in an air and / or oxygen atmosphere; Mix the oxidized cobalt carbonate, oxidation aid, and doping aid, and then calcine at 700 - 750 °C for 3 - 8 h in an air or oxygen atmosphere to obtain doped cobalt tetroxide; the oxidation aid is at least one of perchlorate, persulfate, and metal peroxide; the doping aid includes metal salts and doping oxides; the mass ratio of the oxidized cobalt carbonate, oxidation aid, and doping aid is 1:(0.0001 - 0.0003):(0.0001 - 0.01); The melting point of the metal salt is ≤720 °C.

2. The preparation method of doped cobalt tetroxide according to claim 1, characterized in that, The mass ratio of the oxidized cobalt carbonate, oxidation aid, and doping aid is 1:(0.0001 - 0.0003):(0.0001 - 0.005).

3. The preparation method of cobalt tetroxide doped as described in claim 1, wherein, The temperature during oxidation is 300 - 400 °C.

4. The preparation method of cobalt ferrite doped as described in claim 3, characterized in that, The flow rate of the air and / or oxygen atmosphere during oxidation is 20 - 40 L / h / kg of cobalt carbonate.

5. The preparation method of cobalt tetroxide doped as described in claim 1, characterized in that, The metal salt in the doping aid is at least one of MgCl2, NaNO3, Ba(NO)2, ZnCl2, FeCl2, ZnSO4.

6. The preparation method of doped cobalt tetroxide according to claim 1, characterized in that, The doping oxide is a metal or non-metal oxide, and the metal or non-metal oxide is at least one of MgO, Al2O3, TiO2, Nb2O5, B2O3, V2O5.

7. The preparation method of doped cobalt tetroxide according to claim 1, characterized in that, The cobalt content of the cobalt carbonate is 72.0 - 73.0%, and the particle size D 50 is 3 - 20 μm.

8. The preparation method of doped cobalt tetroxide according to claim 1, characterized in that, The heating rate during oxidation is 1 - 3 °C / min, and the heating rate during calcination is 2 - 5 °C / min.

9. Doped cobalt tetroxide prepared by the method for preparing doped cobalt tetroxide according to any one of claims 1 - 8.

10. Use of the doped cobalt tetroxide prepared by the preparation method according to any one of claims 1 - 8 or the doped cobalt tetroxide according to claim 9 in the preparation of lithium cobaltate materials.

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