Pre-carbonization process for improving the thermal stability of anode materials

Abstract

The present invention relates to the technical field of anode material preparation, specifically to a pre-carbonization process that can improve the thermal stability of anode materials. The process includes the following steps: After grinding the anode active material and transition metal oxide to form a granular material, they are mixed and melted to produce a conductive material; after drying the prefabricated conductive material, it is fully mixed with a doping agent, and after high-temperature sintering, it is ground to produce a powder; a conductive binder is uniformly mixed into the powder and dried and rolled to form an anode material with a certain shape, and an alumina coating is applied to the surface of the anode material; after drying the anode material, it is placed in a rotary kiln for heating to achieve pre-carbonization treatment. The pre-carbonization process provided by the present invention that can improve the thermal stability of anode materials can reduce the elongation rate of anode materials and improve the thermal stability of anode materials.

Description

Technical Field

[0001] The present invention relates to the technical field of anode material preparation, and specifically, to a pre-carbonization process that can improve the thermal stability of anode materials. Background Art

[0002] Anode materials generally constitute the anode of a lithium battery. Temperature affects the discharge state of the lithium battery. A decrease in temperature will cause the reaction rate of the electrode to decrease, resulting in a lower discharge current. Therefore, lithium batteries are generally used under relatively high temperature conditions. However, at high temperatures, there will be problems related to the thermal stability of the electrode, that is, the deformation problem of the electrode at high temperatures.

[0003] For example, in CN106532024A, a preparation method for an anode material of a lithium-ion battery involving graphene-supported nano-boron includes ball-milling NaCl and KCl and then heating and cooling to obtain a NaCl-KCl eutectic salt; then ball-milling and mixing it with glucose monohydrate, urea, and metaboric acid monohydrate; heating three times under a nitrogen atmosphere, washing away the salts with distilled water, and then vacuum drying to obtain graphene-supported nano-boron. In this preparation method, the nano-boron formed between the nitrogen-containing graphene layers stabilizes the electrode structure, so that the anode material has good thermal stability. However, in this preparation method, the carbonized material needs to be coated on the particles composed of the eutectic salt and boron oxide. Subsequently, heating is carried out to complete the carbonization of the material and melt the eutectic salt. In order to separate and remove the eutectic salt, a large amount of distilled water is consumed, and it is impossible to ensure the complete removal of the eutectic salt, resulting in impurities in the generated material, affecting the thermal stability of the prepared anode material.

[0004] In order to ensure that the prepared anode material has good thermal stability and avoid the melting of the anode material during the carbonization process, a pre-carbonization process that can improve the thermal stability of the anode material is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a pre-carbonization process that can improve the thermal stability of anode materials to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the present invention aims to provide a pre-carbonization process that can improve the thermal stability of anode materials, including the following steps:

[0007] S1. After grinding the anode active material and transition metal oxide to form a granular material, perform mixed melting to produce a conductive material;

[0008] S2. After drying the prefabricated conductive material, mix it fully with a doping agent, and then perform high-temperature sintering and then grinding to produce a powder;

[0009] S3. Uniformly mix a conductive binder into the powder and then perform drying and rolling to form an anode material with a certain shape, and coat an alumina coating on the surface of the anode material;

[0010] S4. After drying the negative electrode material, place it in a rotary kiln for heating to achieve pre-carbonization treatment.

[0011] As a further improvement of this technical solution, in S1, the negative electrode active material includes mesocarbon microbeads and spinel lithium titanate, wherein the weight ratio of the mesocarbon microbeads to the spinel lithium titanate is 1:1.

[0012] As a further improvement of this technical solution, in S1, the transition metal oxide is spinel lithium manganate.

[0013] As a further improvement of this technical solution, in S1, the material formed after grinding has a regular particle shape with a size of 10 - 25 μm.

[0014] As a further improvement of this technical solution, in S2, the dopant is a boride.

[0015] As a further improvement of this technical solution, in S2, the sintering temperature is 700 - 1000 °C.

[0016] As a further improvement of this technical solution, in S3, the conductive binder is a binder filled with pure silver powder.

[0017] As a further improvement of this technical solution, in S3, the coating thickness of the alumina coating is 5 - 25 μm.

[0018] As a further improvement of this technical solution, in S4, the heating temperature is 850 - 1050 °C.

[0019] In the present invention, the thermal stability of the negative electrode material is improved through bulk doping and surface treatment. Bulk doping means infiltrating a boride into a conductive material composed of mesocarbon microbeads, spinel lithium titanate, and spinel lithium manganate. After high-temperature sintering, the boride decomposes to produce boron oxide, which is evenly distributed in the conductive material. Boron oxide forms composite structures such as carbon-boron bonds and carbon-boron-oxygen bonds with the carbon atom structure in the conductive material, ensuring the structural stability of the conductive material, thereby generating a bulk-doped powder with a higher charge-discharge plateau and lower charging-state activity. Surface treatment means that after polymerizing the powder through a conductive binder to produce a negative electrode material with a conductive network, an alumina coating is applied to the surface of the negative electrode material, which can reduce the change amplitude of the volume of the negative electrode material during lithium-ion insertion and extraction during charge and discharge, thereby reducing the pulverization degree of the negative electrode material and improving the structural stability of the negative electrode material. Finally, through pre-carbonization treatment of the negative electrode material, the thermal stability of the negative electrode material can be further improved, thereby avoiding the melting of the negative electrode material during carbonization.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] In the pre-carbonization process that can improve the thermal stability of the negative electrode material, through high-temperature sintering, boride decomposes to generate boron oxide, which forms composite structures such as carbon-boron bonds and carbon-boron-oxygen bonds with the carbon atom structure in the conductive material, ensuring the structural stability of the conductive material. After using a conductive binder to polymerize the powder to produce a negative electrode material with a conductive network, an alumina coating is applied on the surface of the negative electrode material, which can reduce the change amplitude of the volume of the negative electrode material during charge and discharge due to the insertion and extraction of lithium ions, improve the structural stability of the negative electrode material. Finally, by performing pre-carbonization treatment on the negative electrode material, the thermal stability of the negative electrode material can be further improved, thereby avoiding the melting of the negative electrode material during carbonization. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flowchart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Please refer to Figure 1 As shown, the object of the present invention is to provide a pre-carbonization process that can improve the thermal stability of the negative electrode material, including the following steps:

[0025] S1. After grinding the negative electrode active material and the transition metal oxide to form a regular granular material with a size of 10 - 25 μm, they are mixed and melted to produce a conductive material. Among them, the negative electrode active material includes mesocarbon microbeads and spinel lithium titanate. The weight ratio of mesocarbon microbeads to the spinel lithium titanate is 1:1. The advantage of mesocarbon microbeads as a carbon material is that it has a relatively low specific surface area. Since its charge-discharge plateau is higher than that of flake graphite, the charging-state activity of mesocarbon microbeads is smaller than that of flake graphite, and it has better thermal stability. Spinel lithium titanate has better structural stability than flake graphite, and its charge-discharge plateau is higher than that of flake graphite, with higher safety and better thermal stability. In addition, the transition metal oxide is spinel lithium manganate. The advantage of spinel lithium manganate is its good overcharge resistance and excellent safety performance. When used as the negative electrode of a lithium battery, spinel lithium manganate mainly exists in the form of -MnO2 in the charged state and has good thermal stability. Electrodes composed of the same materials and the same specifications will have quite large differences in polarization, stress accumulation, and capacity decay due to the different sizes and geometric shapes of their constituent particles;

[0026] S2. After drying the prefabricated conductive material, it is fully mixed with the dopant. After high-temperature sintering at 700 - 1000 °C and then grinding, a powder is produced. Among them, the dopant is a boride. By mixing a boride into the prefabricated conductive material, the boride decomposes at high temperature to produce boron oxide. Boron oxide combines with carbon atoms in the conductive material at high temperature to form composite structures such as carbon-boron bonds and carbon-boron-oxygen bonds, which can improve the structural stability of the negative electrode material. The impurity doping is mainly completed by the diffusion method at high temperature, and the temperature determines the diffusion distribution of the boride in the prefabricated conductive material;

[0027] S3. A conductive binder is uniformly mixed into the powder and dried and rolled to form a negative electrode material with a certain shape. An alumina coating with a thickness of 5 - 25 μm is coated on the surface of the negative electrode material. Among them, the conductive binder is a binder filled with pure silver powder. The binder filled with pure silver powder has good and stable electrical conductivity and can polymerize the powder to form a highly conductive negative electrode material. By firmly combining with the surface of the negative electrode material through the coated alumina coating, it can reduce the change range of the volume of the negative electrode material during the insertion and extraction of lithium ions and can improve the high-temperature resistance of the negative electrode material;

[0028] S4. After drying the negative electrode material, it is placed in a rotary kiln and heated at 850 - 1050 °C to achieve pre-carbonization treatment. By performing pre-carbonization treatment on the negative electrode material, the thermal stability of the accessory and the material can be improved, thereby avoiding the melting of the negative electrode material during carbonization.

[0029] In the present invention, the thermal stability of the anode material is improved through bulk doping and surface treatment. Bulk doping means infiltrating boride into the conductive material composed of mesocarbon microbeads, spinel lithium titanate, and spinel-structured lithium manganate. Through high-temperature sintering, the boride decomposes to produce boron oxide, which is uniformly distributed in the conductive material. Boron oxide forms composite structures such as carbon-boron bonds and carbon-boron-oxygen bonds with the carbon atom structure in the conductive material, ensuring the structural stability of the conductive material, thereby generating bulk-doped powder materials with a relatively high charge-discharge plateau and low charging-state activity. Surface treatment means that after polymerizing the powder through a conductive adhesive to produce an anode material with a conductive network, an alumina coating is applied to the surface of the anode material, which can reduce the change amplitude of the anode material volume during lithium-ion insertion and extraction during charge and discharge, thereby reducing the pulverization degree of the anode material and improving the structural stability of the anode material. Finally, through pre-carbonization treatment of the anode material, the thermal stability of the anode material can be further improved, thereby avoiding the melting of the anode material during carbonization.

[0030] According to the differences in process parameters during the process, the following specific examples are used to further illustrate the pre-carbonization process provided by the present invention that can improve the thermal stability of the anode material.

[0031] Example 1

[0032] S1. After grinding the anode active material and the transition metal oxide to form a material with a regular particle shape of 10 μm in size, they are mixed and melted to produce a conductive material. Among them, the anode active material includes mesocarbon microbeads and spinel lithium titanate, and the weight ratio of mesocarbon microbeads to the spinel lithium titanate is 1:1. In addition, the transition metal oxide is spinel-structured lithium manganate;

[0033] S2. After drying the prefabricated conductive material, it is fully mixed with the dopant, and after high-temperature sintering at 700 °C and then grinding, powder is produced. Among them, the dopant is boride;

[0034] S3. A conductive adhesive is uniformly mixed into the powder and dried and rolled to form an anode material with a certain shape. An alumina coating with a thickness of 5 μm is applied to the surface of the anode material. Among them, the conductive adhesive is an adhesive filled with pure silver powder;

[0035] S4. After drying the anode material, it is placed in a rotary kiln and heated at 850 °C to achieve pre-carbonization treatment.

[0036] Example 2

[0037] S1. After grinding the negative electrode active material and transition metal oxide to form a regular granular material with a size of 18 μm, they are mixed and melted to produce a conductive material. Among them, the negative electrode active material includes mesophase carbon microspheres and spinel lithium titanate, and the weight ratio of mesophase carbon microspheres to the spinel lithium titanate is 1:1. In addition, the transition metal oxide is spinel-structured lithium manganate;

[0038] S2. After drying the prefabricated conductive material, it is fully mixed with a dopant, and after high-temperature sintering at 850 °C and then grinding, a powder is produced. Among them, the dopant is a boride;

[0039] S3. A conductive binder is uniformly mixed into the powder and dried and rolled to form a negative electrode material with a certain shape. An alumina coating with a thickness of 14 μm is coated on the surface of the negative electrode material. Among them, the conductive binder is a binder filled with pure silver powder;

[0040] S4. After drying the negative electrode material, it is placed in a rotary kiln and heated at 960 °C to achieve pre-carbonization treatment.

[0041] Example 3

[0042] S1. After grinding the negative electrode active material and transition metal oxide to form a regular granular material with a size of 25 μm, they are mixed and melted to produce a conductive material. Among them, the negative electrode active material includes mesophase carbon microspheres and spinel lithium titanate, and the weight ratio of mesophase carbon microspheres to the spinel lithium titanate is 1:1. In addition, the transition metal oxide is spinel-structured lithium manganate;

[0043] S2. After drying the prefabricated conductive material, it is fully mixed with a dopant, and after high-temperature sintering at 1000 °C and then grinding, a powder is produced. Among them, the dopant is a boride;

[0044] S3. A conductive binder is uniformly mixed into the powder and dried and rolled to form a negative electrode material with a certain shape. An alumina coating with a thickness of 25 μm is coated on the surface of the negative electrode material. Among them, the conductive binder is a binder filled with pure silver powder;

[0045] S4. After drying the negative electrode material, it is placed in a rotary kiln and heated at 1050 °C to achieve pre-carbonization treatment.

[0046] Example 4

[0047] S1. After grinding the negative electrode active material and transition metal oxide to form a regular granular material with a size of 12 μm, they are mixed and melted to produce a conductive material. Among them, the negative electrode active material includes mesophase carbon microspheres and spinel lithium titanate, and the weight ratio of mesophase carbon microspheres to the spinel lithium titanate is 1:1. In addition, the transition metal oxide is spinel-structured lithium manganate;

[0048] S2. After drying the prefabricated conductive material, it is fully mixed with the dopant, and then ground after high-temperature sintering at 950 °C to produce powder. The dopant is boride;

[0049] S3. A conductive binder is uniformly mixed into the powder and dried and rolled to form a negative electrode material with a certain shape. An alumina coating with a thickness of 10 μm is coated on the surface of the negative electrode material. The conductive binder is a binder filled with pure silver powder;

[0050] S4. After drying the negative electrode material, it is placed in a rotary kiln and heated at 1000 °C to achieve pre-carbonization treatment.

[0051] Table 1 Comparison of process parameters in Examples 1-4

[0052]

[0053]

[0054] Comparative Example 1

[0055] This comparative example adopts the processing technology of Example 1, sets the particle size after grinding to 8 μm, and the rest remains unchanged. The specific steps are similar to those of Example 1 and will not be elaborated here.

[0056] Comparative Example 2

[0057] This comparative example adopts the processing technology of Example 2, sets the particle size after grinding to 30 μm, and the rest remains unchanged. The specific steps are similar to those of Example 2 and will not be elaborated here.

[0058] Table 2 Comparison of process parameters in Comparative Examples 1-2

[0059] Particle size / μm Sintering temperature / °C Coating thickness / μm Heating temperature / °C Comparative example 1 8 700 5 850 Comparative example 2 30 850 14 960

[0060] Comparative Example 3

[0061] This comparative example adopts the processing technology of Example 3, sets the sintering temperature to 650 °C, and the rest remains unchanged. The specific steps are similar to those of Example 3 and will not be elaborated here.

[0062] Comparative Example 4

[0063] This comparative example adopts the processing technology of Example 4, sets the sintering temperature to 1200 °C, and the rest remains unchanged. The specific steps are similar to those of Example 4 and will not be elaborated here.

[0064] Table 3 Comparison of process parameters in Comparative Examples 3-4

[0065] Particle size / μm Sintering temperature / °C Coating thickness / μm Heating temperature / °C Comparative example 3 25 650 25 1050 Comparative example 4 12 1200 10 1000

[0066] Comparative Example 5

[0067] This comparative example adopts the processing technology of Example 1, sets the thickness of the alumina coating to 3 μm, and keeps the rest unchanged. The specific steps are similar to those of Example 1 and will not be elaborated here.

[0068] Comparative Example 6

[0069] This comparative example adopts the processing technology of Example 2, sets the thickness of the alumina coating to 30 μm, and keeps the rest unchanged. The specific steps are similar to those of Example 2 and will not be elaborated here.

[0070] Table 4 Comparison of process parameters in Comparative Examples 5 - 6

[0071] Particle size / μm Sintering temperature / °C Coating thickness / μm Heating temperature / °C Comparative example 5 10 700 3 850 Comparative example 6 18 850 30 960

[0072] Comparative Example 7

[0073] This comparative example adopts the processing technology of Example 3, sets the heating temperature of the pre - carbonization treatment to 700 °C, and keeps the rest unchanged. The specific steps are similar to those of Example 3 and will not be elaborated here.

[0074] Comparative Example 8

[0075] This comparative example adopts the processing technology of Example 4, sets the heating temperature of the pre - carbonization treatment to 1100 °C, and keeps the rest unchanged. The specific steps are similar to those of Example 4 and will not be elaborated here.

[0076] Table 5 Comparison of process parameters in Comparative Examples 7 - 8

[0077] Particle size / μm Sintering temperature / °C Coating thickness / μm Heating temperature / °C Comparative example 3 25 1000 25 700 Comparative example 4 12 950 10 1100

[0078] Test Example

[0079] Multiple batches of anode materials are processed respectively according to the pre - carbonization processes provided in Examples 1 - 4 and Comparative Examples 1 - 8 to improve the thermal stability of the anode materials. The anode materials are placed at 200 °C for 1 h, and the elongation rate of the anode materials is tested by YBT 5289 - 2017 "Test Method for Elongation Rate of Electrode Paste" (the elongation rate is the percentage of the relative length of the sample heated and extended, and the lower the elongation rate, the better the thermal stability), and the elongation rate is filled in Table 6.

[0080] Table 6 Comparison of elongation rates of anode materials processed in Examples and Comparative Examples

[0081]

[0082]

[0083] As can be seen from Table 6, when comparing the pre-carbonization process provided in Examples 1-4, which can improve the thermal stability of the anode material, with the pre-carbonization process provided in Comparative Examples 1-8, which can also improve the thermal stability of the anode material, the elongation rate of the anode material processed by the process of the Examples is lower than that of the anode material processed by the process of the Comparative Examples. Moreover, the elongation rate of the anode material processed by the process of the Examples is all lower than 1.82%, while the elongation rate of the anode material processed by the process of the Comparative Examples with different process parameters has increased. Therefore, the pre-carbonization process provided by the present invention, which can improve the thermal stability of the anode material, can process an anode material with good thermal stability and a low elongation rate.

[0084] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A pre-carbonization process for improving the thermal stability of the anode material, characterized in that, it includes the following steps: S1. After grinding the anode active material and the transition metal oxide to form a granular material, mix and melt them to produce a conductive material; S2. After drying the prefabricated conductive material, fully mix it with the doping agent, and after high-temperature sintering, grind it to produce a powder; S3. Uniformly mix a conductive binder into the powder and form an anode material with a certain shape through drying and rolling, and coat an alumina coating on the surface of the anode material; S4. After drying the anode material, place it in a rotary kiln for heating to achieve pre-carbonization treatment; wherein, in the said S1, the anode active material includes mesophase carbon microspheres and spinel lithium titanate; in the said S1, the transition metal oxide is spinel lithium manganate; in the said S1, the ground material forms regular granular materials with a size of 10-25 μm; in the said S2, the doping agent is a boride; in the said S2, the sintering temperature is 700-1000 °C; in the said S3, the coating thickness of the alumina coating is 5-25 μm; in the said S4, the heating temperature is 850-1050 °C.

2. The pre-carbonization process for improving the thermal stability of the anode material according to claim 1, characterized in that: the weight ratio of the mesophase carbon microspheres to the spinel lithium titanate is 1:

1.

3. The pre-carbonization process for improving the thermal stability of the anode material according to claim 1, characterized in that: in the said S3, the conductive binder is a binder filled with pure silver powder.

Images