A method for microwave treatment of negative electrode material of lithium battery

Abstract

The invention discloses a method for microwave treatment of negative electrode materials of lithium batteries, and belongs to the field of production and manufacture of negative electrode materials of lithium batteries and microwave technology. The negative electrode materials of lithium batteries are pre-carbonized in a microwave device. The efficiency of microwave heating is 4 to 13 times that of traditional heating methods. Therefore, microwave heating can theoretically most effectively make up for the problem that the internal temperature of traditional carbonized negative electrode materials of lithium batteries lags far behind, and achieve uniform heating of negative electrode materials of lithium batteries in a short time, ultimately improving product quality, reducing roasting costs, and reducing energy consumption by 30% to 50%.

Description

Technical Field

[0001] The invention belongs to the field of production and manufacturing of lithium battery negative electrode materials and microwave technology, and in particular relates to a method for microwave processing of lithium battery negative electrode materials. Background Art

[0002] As the energy shortage problem becomes more serious, the development of renewable energy and the research of related energy storage equipment have received widespread attention. As the concept of low-carbon economy and life has become popular, electric vehicles have ushered in a good opportunity for further development. The investment in the research and development of electric vehicle-related products has doubled in this field, among which high-performance lithium-ion batteries occupy an important position. In addition, power lithium-ion batteries are also the first choice of energy storage batteries that match environmentally friendly energy such as wind power generation and solar power generation. Lithium-ion batteries have huge development prospects and market value in the near future and for a long time to come.

[0003] Lithium-ion batteries are mainly composed of positive electrodes, negative electrodes, electrolytes and separators. The choice of negative electrode materials is directly related to the energy density of the battery. Negative electrode materials mainly affect the initial efficiency and cycle performance of lithium batteries, accounting for about 5-15% of the total cost of lithium batteries.

[0004] At present, graphite-based carbon materials have become the main carbon material negative electrode for commercial lithium battery negative electrode materials due to their low cost, environmental friendliness, low charge and discharge voltage, and good stability. The preparation of high-performance artificial graphite negative electrode materials for lithium batteries mainly involves the crushing of raw materials, surface modification of powder particles, pre-carbonization, graphitization, screening, demagnetization and packaging. The above processes are further divided into several small processes, and the processes are basically the same. Among them, needle coke, as a new type of carbon material, is widely used as a raw material for graphite negative electrodes because of its good graphite microcrystalline structure and texture orientation. Different needle coke raw materials contain 10%-15% volatile matter, and the scale and output of needle coke are gradually expanding. However, in the graphitization production process, the production cost has exceeded the raw material cost. How to reduce the graphitization cost has become an urgent problem that all companies need to solve.

[0005] Traditional graphite negative electrode material carbonization process equipment uses tunnel kilns, roller kilns, etc. These kiln technologies are outdated, and heat is mainly generated by thermal radiation and heat conduction. The carbonization material production cycle is long, the loading and unloading operations are cumbersome, the degree of automation is not high, the carbonization roasting time is long, the energy consumption is high, and the flue gas is difficult to handle. The small square saggers used to hold negative electrode materials are easily damaged at high temperatures and have limited loading and unloading capacity, resulting in a short service life, which affects output and increases production costs. Summary of the invention

[0006] The purpose of the present invention is to provide a method for microwave processing of lithium battery negative electrode materials to solve the problems existing in the above-mentioned prior art.

[0007] The present invention performs microwave pre-carbonization treatment on the carbon negative electrode material of lithium batteries. Since the carbon negative electrode material of lithium batteries is a polar material, it generates heat after absorbing microwaves, thereby causing the carbon negative electrode material to generate heat and the temperature to rise. Since microwave heating is not a traditional thermal radiation heating method, it causes the vibration of the polar molecules of the carbon material to generate heat, so the heating efficiency is high, the heating rate is fast, and the temperature control is precise, thereby achieving the improvement of thermal efficiency and thermal utilization, and can achieve energy saving and improve the performance indicators of the carbonized negative electrode material, increase the loading capacity of the graphitization furnace, reduce the power consumption of the graphitization of the negative electrode material, and thus reduce the production cost. In summary, since the microwave carbonization roasting technology can quickly heat the carbon negative electrode material of lithium batteries in a short time, the carbonization roasting cost of the negative electrode material is reduced, and the purpose of reducing energy consumption and increasing production capacity is achieved.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] A method for microwave processing of lithium battery negative electrode materials, wherein the lithium battery negative electrode materials are pre-carbonized in a microwave device; the pre-carbonization process is carried out in a gradient heating manner; the lithium battery negative electrode materials are lithium battery carbon negative electrode materials.

[0010] Furthermore, the pre-carbonization heating process adopts a four-stage gradient heating method; the heating rate is 100℃ / h~800℃ / h, and the heating power density is 3kw / cm 3 ~10kw / cm 3 .

[0011] Furthermore, the pre-carbonization heating process is: 30°C as the starting temperature, heating to 200-400°C at a heating rate of 100°C / h; then 200-400°C as the starting temperature, heating to 400-700°C at a heating rate of 200-300°C / h; then 400-700°C as the starting temperature, heating to 600-1000°C at a heating rate of 300-500°C / h; finally, 600-1000°C as the starting temperature, heating to the highest treatment temperature at a heating rate of 400-800°C / h.

[0012] Furthermore, the maximum treatment temperature of the pre-carbonization is 800-1300° C., and the treatment time is 1-10 h.

[0013] Furthermore, the carbonization process is carried out entirely in an inert gas atmosphere.

[0014] Furthermore, the inert gas is one of nitrogen, helium and argon.

[0015] Furthermore, during the carbonization process, the negative electrode material of the lithium battery is placed in a crucible and then placed in a microwave device.

[0016] Furthermore, the holding time after pre-carbonization is 0.5-3h, and the microwave power density during the holding process is 3kw / cm 3 -5kw / cm 3 .

[0017] The lithium battery negative electrode material prepared by the above method provided by the present invention has a volatile matter of ≤1.5% and a tap density of ≥0.896 g / cm 3 Specific surface area: 0.825~2.0m 2 / g.

[0018] The present invention discloses the following technical effects: pre-carbonizing the carbon negative electrode material of a lithium battery by using a microwave high-temperature device, and the process is carried out under an inert gas atmosphere. After reaching the highest temperature by controlling the heating rate and heating time, the temperature is kept constant for a period of time to achieve the carbonization effect on the carbon negative electrode material of the lithium battery.

[0019] As a highly efficient and energy-saving technology, microwave heating technology generates "internal friction" through the high-frequency reciprocating motion of the dipole molecules inside the heated body to increase the temperature of the heated material. Without any heat conduction process, the material can be heated both inside and outside at the same time, and the heating speed is fast and uniform. Traditional heating technology is based on the principles of heat conduction, convection and radiation to transfer heat from the outside to the inside of the material. Heat is always transferred from the outside to the inside to heat the material. There is inevitably a temperature gradient in the material, so the heated material is uneven, causing local overheating of the material. In comparison, microwaves process various materials and products with faster heating speeds and lower processing costs, and in most cases the products have better performance.

[0020] The efficiency of microwave heating is 4 to 13 times that of traditional heating methods. Therefore, microwave heating can theoretically most effectively compensate for the problem of the far lagging internal temperature of traditional carbonized lithium battery negative electrode materials, and achieve uniform heating of lithium battery negative electrode materials in a short time, ultimately improving product quality, reducing roasting costs, and reducing energy consumption by 30% to 50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 This is an electron microscope image of the carbon negative electrode material for lithium battery treated by microwave carbonization obtained in Example 1;

[0023] Figure 2 This is an electron microscope image of the carbon negative electrode material for lithium battery treated by microwave carbonization obtained in Example 2;

[0024] Figure 3 This is an electron microscope image of the carbon negative electrode material for lithium battery treated by microwave carbonization obtained in Example 3;

[0025] Figure 4 This is an electron microscope image of the lithium battery carbon negative electrode material treated by microwave carbonization obtained in Example 4. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] The raw materials in the present invention are all provided by Inner Mongolia Xinyuan Graphene Technology Co., Ltd., among which the model of the carbon negative electrode material for lithium battery is CY-1.

[0032] The carbon negative electrode material of lithium battery is placed in a crucible made of special materials, and the crucible is placed in a microwave device. After power is turned on, microwave carbonization is performed on the carbon negative electrode material of lithium battery. The whole carbonization process is kept in an inert atmosphere. The heating power density of the microwave device is selected according to the characteristics of the carbon negative electrode material of lithium battery. After reaching the required temperature, the material is kept warm and cooled out of the furnace.

[0033] Traditional carbonization process equipment for lithium battery carbon negative electrode materials uses tunnel kilns, roller kilns, etc. These kiln technologies are outdated, and heat is mainly generated by thermal radiation and heat conduction. The pre-carbonization material production cycle is long (96-240h), and the maximum temperature used in the pre-carbonization process is 750-880°C. The energy consumption is much higher than that of the present invention, and it takes longer than the present invention. The smoke generated is difficult to handle, and the present invention does not generate smoke.

[0034] The embodiment of the present invention provides a method for microwave processing of lithium battery negative electrode materials, wherein the lithium battery negative electrode materials are pre-carbonized in a microwave device; the pre-carbonization process is carried out in a gradient heating manner; the lithium battery negative electrode material is a lithium battery carbon negative electrode material.

[0035] Pre-carbonization of carbon negative electrode materials for lithium batteries can significantly increase the tap density, thereby increasing the furnace load, reducing the total energy consumption and reducing processing costs.

[0036] Furthermore, the pre-carbonization heating process adopts a four-stage gradient heating method; the heating rate is 100℃ / h~1200℃ / h, and the heating power density is 3kw / cm 3 ~10kw / cm 3 .

[0037] Furthermore, the pre-carbonization heating process is: 30°C as the starting temperature, heating to 200-400°C at a heating rate of 100°C / h; then 200-400°C as the starting temperature, heating to 400-700°C at a heating rate of 200-300°C / h; then 400-700°C as the starting temperature, heating to 600-1000°C at a heating rate of 300-500°C / h; finally, 600-1000°C as the starting temperature, heating to the highest treatment temperature at a heating rate of 400-800°C / h.

[0038] Furthermore, the maximum treatment temperature of the pre-carbonization is 800-1300° C., and the treatment time is 1-10 h.

[0039] Furthermore, the carbonization process is carried out entirely in an inert gas atmosphere.

[0040] Furthermore, the inert gas is one of nitrogen, helium and argon.

[0041] Furthermore, during the carbonization process, the negative electrode material of the lithium battery is placed in a crucible and then placed in a microwave device.

[0042] The crucible used in the embodiment of the present invention is an alumina crucible. Microwaves can penetrate the alumina crucible and will not be absorbed. The microwaves can all act on the carbon negative electrode material of the lithium battery, and the temperature difference and temperature distribution are uniform. The structure and performance of the obtained microwave-treated lithium battery carbon negative electrode material are stable. In contrast, the common graphite crucible can absorb microwaves, so that the microwaves cannot penetrate into the negative electrode material and cannot heat the negative electrode material.

[0043] Furthermore, the holding time after pre-carbonization is 0.5-3h, and the microwave power density during the holding process is 3kw / cm 3 -5kw / cm 3 .

[0044] The lithium battery negative electrode material prepared by the above method provided by the present invention has a volatile matter of ≤1.5% and a tap density of ≥0.896 g / cm 3 ; Specific surface area 0.825~2.0m 2 / g.

[0045] Example 1

[0046] Weigh 5000g of lithium battery carbon negative electrode material and place it in an alumina crucible, then place the alumina crucible in a microwave device to pre-carbonize the lithium battery carbon negative electrode material. The entire test is in a nitrogen atmosphere. The temperature rise curve of the pre-carbonization process is shown in Table 1. Then, the temperature is kept at 1200℃ for 3h, and the microwave power density is 4kw / cm 3 The negative electrode material calcined by microwave is naturally cooled to below 450°C and taken out of the furnace to obtain the lithium battery carbon negative electrode material treated by microwave carbonization. Figure 1 , compared with the lithium battery carbon negative electrode material (sample 1) that has not been microwave treated, see Table 5 for details.

[0047] Table 1

[0048]

[0049] Example 2

[0050] The same as Example 1, except that the heating curve is shown in Table 2. After that, the negative electrode material calcined by microwave is cooled to below 450°C and taken out of the furnace to obtain a lithium battery carbon negative electrode material treated by microwave carbonization. The electron microscope image is shown in Figure 2 , compared with the lithium battery carbon negative electrode material (sample 2) that has not been microwave treated, see Table 5 for details.

[0051] Table 2

[0052]

[0053]

[0054] The microwave carbonized lithium battery carbon negative electrode materials obtained in Examples 1 and 2 were analyzed and tested, and compared with the lithium battery carbon negative electrode materials (Sample 1 and Sample 2) that were not microwave carbonized. The results are as follows:

[0055] The lithium battery negative electrode materials treated by microwave carbonization in Example 1 and Example 2 have agglomeration after being taken out of the furnace, and the color is gray-black, but very loose and easy to break up. Compared with the raw materials that have not been carbonized, the volatile matter is reduced and the tap density is increased, which is the same as the indicators of the traditional carbonization process. The specific indicators are shown in Table 5.

[0056] Example 3

[0057] Weigh 5000g of lithium battery carbon negative electrode material and place it in an alumina crucible. Place the alumina crucible in a microwave device to pre-carbonize the lithium battery carbon negative electrode material. The entire test is in a helium atmosphere. The pre-carbonization process is shown in Table 3. Then, keep warm at 800℃ for 4h. The microwave power density is 3kw / cm 3 The microwave-battery carbon negative electrode material is naturally cooled to below 450°C and taken out of the furnace to obtain the microwave-carbonized lithium battery negative electrode material. The electron microscope image is shown in Figure 3 .

[0058] Table 3

[0059]

[0060]

[0061] Example 4

[0062] Weigh 5000g of lithium battery carbon negative electrode material and place it in an alumina crucible. Place the alumina crucible in a microwave device to pre-carbonize the lithium battery carbon negative electrode material. The entire test is in an argon atmosphere. The temperature rise process of the pre-carbonization process is shown in Table 4. Then, keep the temperature at 1000℃ for 4h. The microwave power density is 4kw / cm 3 The microwave-battery carbon negative electrode material is naturally cooled to below 450°C and taken out of the furnace to obtain the microwave-carbonized lithium battery carbon negative electrode material. Figure 4 .

[0063] Table 4

[0064]

[0065] Comparative Example 1

[0066] 5000g of lithium battery carbon negative electrode material was weighed and placed in an alumina crucible, and the alumina crucible was placed in a microwave device to pre-carbonize the lithium battery carbon negative electrode material. The whole test was in a nitrogen atmosphere, and the temperature was not increased step by step, but at the same rate of 400℃ / h, with a microwave power density of 8kw / cm 3 , heating to 1200℃, keeping the microwave power density at 4kw / cm 3 , then keep warm at 1200℃ for 3h.

[0067] In order to investigate the effects of different gradient temperature increase methods on lithium-ion negative electrode materials, the present invention provides comparative examples 2-5.

[0068] Comparative Example 2

[0069] The only difference from Example 1 is that the pre-carbonization heating method is a three-stage gradient heating method, specifically:

[0070] 30~300℃, heating rate 100℃ / h;

[0071] 300~1000℃, heating rate 200℃ / h;

[0072] 1000~1200℃, heating rate 500℃ / h;

[0073] 1200~1200℃, holding time 180 minutes.

[0074] The negative electrode material baked by microwave is taken out of the furnace when it cools naturally to below 450°C.

[0075] Comparative Example 3

[0076] The only difference from Example 1 is that the pre-carbonization heating method is a three-stage gradient heating method, which is as follows:

[0077] 30~600℃, heating rate 200℃ / h;

[0078] 600~1000℃, heating rate 400℃ / h;

[0079] 1000~1200℃, heating rate 500℃ / h;

[0080] 1200~1200℃, holding time 180 minutes.

[0081] The negative electrode material baked by microwave is taken out of the furnace when it cools naturally to below 450°C.

[0082] Comparative Example 4

[0083] The only difference from Example 1 is that the pre-carbonization heating method is a five-stage gradient heating method, and the specific method is as follows:

[0084] 30~300℃, heating rate 100℃ / h;

[0085] 300~500℃, heating rate 200℃ / h;

[0086] 500~800℃, heating rate 300℃ / h;

[0087] 800~1000℃, heating rate 400℃ / h;

[0088] 1000~1200℃, heating rate 500℃ / h;

[0089] 1200~1200℃, holding time 180 minutes.

[0090] The negative electrode material baked by microwave is taken out of the furnace when it cools naturally to below 450°C.

[0091] Comparative Example 5

[0092] The only difference from Example 1 is that the pre-carbonization heating method is a four-stage gradient heating method with different heating rates. The specific method is as follows:

[0093] 30~300℃, heating rate 500℃ / h;

[0094] 300~600℃, heating rate 400℃ / h;

[0095] 600~1000℃, heating rate 200℃ / h;

[0096] 1000~1200℃, heating rate 100℃ / h;

[0097] 1200~1200℃, holding time 180 minutes.

[0098] The negative electrode material baked by microwave is taken out of the furnace when it cools naturally to below 450°C.

[0099] The properties of the lithium battery negative electrode materials prepared in the above embodiments and comparative examples are shown in Table 5.

[0100] Table 5

[0101]

[0102]

[0103] It can be seen from Table 5 that the tap density of the negative electrode material obtained by the method for microwave treatment of lithium battery negative electrode material disclosed in the present invention is significantly improved compared with the untreated negative electrode material, so that the furnace loading capacity is increased, thereby increasing the output and reducing the cost.

[0104] Compared with uniform heating, the gradient heating method disclosed in the present invention has the following characteristics. First, the negative electrode material with gradient heating has low volatile matter, high weight loss (more volatile matter overflow), small specific surface area, and high tap density, while the negative electrode material with uniform heating has high volatile matter, low weight loss, large specific surface area, and low tap density; Second, the negative electrode material with uniform heating reduces the amount of negative electrode material loaded in the subsequent graphitization process, thereby reducing output, increasing the power consumption of the negative electrode material, and also increasing the production cost of the enterprise. Third, because the volatile matter of uniform heating is high, there will be a risk of furnace spraying. It is necessary to fully consider the safety risks of the graphitization process when formulating the power transmission curve of the graphitization process, thereby extending the power transmission time and reducing production capacity. Fourth, the negative electrode material will produce asphalt fume during the microwave carbonization process, and the removal of asphalt fume requires a specific temperature. The gradient heating method provided by the present invention realizes the change of the heating rate, which can quickly transform the macromolecular structure in the asphalt fume into a small molecular structure under the action of microwaves, and finally form harmless gases such as methane or hydrogen, so as to achieve the removal of asphalt fume at a specific temperature. In summary, the technical process of gradient heating is better than uniform heating, and it is recommended to use the gradient heating method for industrialization.

[0105] From the comparison between Comparative Examples 2-4 and Example 1, it can be seen that the three-stage and five-stage heating methods are not conducive to the removal of volatiles, and at the same time, the specific surface area is high and the tap density is low.

[0106] From the comparison between comparative example 5 and embodiment 1, it can be seen that when the heating rate of comparative example 5 is adopted, the specific surface area of ​​the carbon negative electrode material of the lithium battery is relatively high and the tap density is also relatively low.

[0107] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for microwave treatment of lithium battery negative electrode materials, characterized in that: Pre-carbonizing the negative electrode material of a lithium battery in a microwave device; the pre-carbonization process is carried out in a gradient heating manner; the negative electrode material of the lithium battery is a carbon negative electrode material of a lithium battery; The pre-carbonization heating process is as follows: starting at 30°C, heating to 200-400°C at a heating rate of 100°C / h; starting at 200-400°C, heating to 400-700°C at a heating rate of 200-300°C / h; starting at 400-700°C, heating to 600-1000°C at a heating rate of 300-500°C / h; and finally starting at 600-1000°C, heating to a maximum treatment temperature at a heating rate of 400-800°C / h.

2. The method according to claim 1, characterized in that The maximum treatment temperature of the pre-carbonization is 800-1300° C., and the treatment time is 1-10 hours.

3. The method according to claim 1, characterized in that The pre-carbonization process is carried out in an inert gas atmosphere throughout.

4. The method according to claim 3, characterized in that: The inert gas is one of nitrogen, helium and argon.

5. The method according to claim 1, characterized in that In the pre-carbonization process, the negative electrode material of the lithium battery is placed in a crucible and then placed in a microwave device.

6. The method according to claim 1, characterized in that The holding time after pre-carbonization is 0.5-3h, and the microwave power density during the holding process is 3kw / cm 3 -5kw / cm 3 .

7. A negative electrode material for a lithium battery prepared by the method according to any one of claims 1 to 6, characterized in that: Its volatile matter is ≤1.5%, and its tap density is ≥0.896g / cm 3 Specific surface area: 0.825~2.0m 2 / g.

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