Method for eliminating flocculent carbon in lithium iron phosphate

Abstract

The invention discloses a method for eliminating flocculent carbon in lithium iron phosphate, which comprises the following steps: putting a lithium iron phosphate raw material into microwave heating equipment, setting the power of microwaves to be 700-900W and the frequency to be 2.45 GHz, simultaneously introducing carbon dioxide gas with the flow of 1L / min, and then heating for 30-60 minutes; the specific heating effect on flocculent carbon is achieved through specific microwaves, the flocculent carbon is more effectively eliminated, the flocculent carbon in the lithium iron phosphate finished product is eliminated in combination with selective oxidation of carbon dioxide, the electrochemical performance of lithium iron phosphate is improved, meanwhile, the method is environmentally friendly and can be completed within a relatively short time, and the method is suitable for industrial production. The production efficiency is improved, adverse effects on the structure and performance of the lithium iron phosphate are avoided, no additional substance is added, and the production cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate preparation, and more specifically, to a method for eliminating flocculent carbon in lithium iron phosphate. Background Art

[0002] Lithium iron phosphate cathode materials are widely used in the new energy vehicle market and energy storage field due to their safety, environmental protection, low raw material prices, and stable discharge platform. However, due to their low electronic conductivity and small lithium ion diffusion coefficient, their performance in high-power applications is limited, and the prepared lithium iron phosphate battery has a short cycle life and is prone to capacity decay. Therefore, in order to improve its performance, a common method is to use carbon coating to improve the conductivity and rate performance of lithium iron phosphate cathode materials and the life of lithium iron phosphate batteries. However, during the carbon coating process, due to local temperature unevenness or improper atmosphere control during the carbonization process, fine flocculent carbon is sometimes produced on the surface of the material, and these generated flocculent carbons will have some adverse effects on the material, such as rough and uneven surface, gaps between the substrate and the coating layer, resulting in voids or protrusions, etc., thereby affecting the conductivity, specific capacity and other properties of the material.

[0003] Existing technologies mainly reduce the formation of flocculent carbon by changing sintering conditions, such as temperature, time, and atmosphere, or by adding specific additives to change the morphology of flocculent carbon to reduce its impact on material properties. However, existing technologies still have some problems in practical applications. First, changing sintering conditions may affect other properties of lithium iron phosphate, such as capacity and rate performance; second, adding specific additives may increase production costs and may have an impact on the environment; finally, while eliminating flocculent carbon, existing technologies may affect the carbon coating on the surface of lithium iron phosphate crystals, which has an adverse effect on the structure and performance of lithium iron phosphate.

[0004] Therefore, how to effectively eliminate flocculent carbon without affecting other properties of lithium iron phosphate is an important challenge facing current technology. Summary of the invention

[0005] In view of the above, the present invention provides a method for eliminating flocculent carbon in lithium iron phosphate, which effectively eliminates the flocculent carbon in lithium iron phosphate without affecting other properties of lithium iron phosphate, has no additional additives, has low production cost, and is environmentally friendly.

[0006] The present invention provides a method for eliminating flocculent carbon in lithium iron phosphate, which comprises placing lithium iron phosphate raw materials into a microwave heating device, setting the microwave power to 700-900W, setting the frequency to 2.45GHz, introducing carbon dioxide gas at the same time, and then heating for 30-60min, wherein the flow rate of the carbon dioxide gas is controlled at 1L / min.

[0007] Different material components absorb microwaves differently. The present invention utilizes the penetrating and selective heating characteristics of microwaves to carry out targeted heating of the flocculent carbon in the lithium iron phosphate through a specific microwave frequency, causing it to react at a relatively low temperature. At the same time, carbon dioxide gas is introduced and its selective oxidation characteristics are utilized to oxidize the flocculent carbon into carbon monoxide, thereby effectively eliminating the flocculent carbon. At the same time, while eliminating the flocculent carbon, damage to the coated carbon of the lithium iron phosphate is avoided, and adverse effects on the structure and performance of the lithium iron phosphate are avoided, thereby improving the electrochemical properties of the lithium iron phosphate.

[0008] The beneficial effects of the present invention are: (1) The present invention adopts a method for eliminating flocculent carbon in lithium iron phosphate with the assistance of microwaves. The flocculent carbon can be heated in a targeted manner by specific microwaves, thereby eliminating the flocculent carbon more effectively. (2) The present invention combines the selective oxidation of carbon dioxide to achieve the elimination of flocculent carbon in the finished lithium iron phosphate product. This method is not only environmentally friendly, but can also be completed in a relatively short time, thereby improving production efficiency; (3) The present invention does not change the sintering conditions of lithium iron phosphate, thus avoiding adverse effects on the structure and performance of lithium iron phosphate, and does not add any additional substances, thus having low production costs; (4) At the same time, the method of the present invention effectively eliminates flocculent carbon and improves the electrochemical performance of lithium iron phosphate; (5) Collect and treat the waste gas generated during microwave-assisted heating and selective oxidation of carbon dioxide to reduce the impact on the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is the SEM image of lithium iron phosphate raw material.

[0010] Figure 2 This is a SEM image of lithium iron phosphate after the sintering temperature is increased to eliminate the flocculent carbon.

[0011] Figure 3 This is a SEM picture of lithium iron phosphate after eliminating flocculent carbon by the method of the present invention in Example 3. DETAILED DESCRIPTION

[0012] The embodiments of the present application will be described in more detail below. The application can be implemented in various forms, and should not be construed as being limited to the embodiments set forth herein, but rather these embodiments are provided to provide a more thorough and complete understanding of the present application. It should be understood that the embodiments of the present application are only for exemplary purposes and are not intended to limit the scope of protection of the present application.

[0013] The process of the present invention is shown in the attached Figure 1As shown, the embodiment is implemented according to the following technical solution, specifically: The lithium iron phosphate raw material is placed in a microwave heating device, the microwave power is set to 700-900W, the frequency is set to 2.45GHz, and carbon dioxide gas is introduced at the same time, wherein the flow rate of the carbon dioxide gas is controlled at 1L / min, and then heated for 30-60 minutes.

[0014] Comparative Example 1: lithium iron phosphate without eliminating flocculent carbon, i.e., the lithium iron phosphate raw material of the present invention.

[0015] Comparative Example 2: Increasing the sintering temperature to eliminate flocculent carbon: The preparation process of lithium iron phosphate raw materials includes batching, mixing, drying, and sintering. In Comparative Example 2, the sintering temperature in the box furnace is increased by 10°C, and other process steps remain unchanged.

[0016] Attached Figure 1 This is the SEM image of lithium iron phosphate raw material, attached Figure 2 This is the SEM image of lithium iron phosphate after increasing the sintering temperature to eliminate the flocculent carbon. Figure 3 is a SEM image of lithium iron phosphate after removing flocculent carbon by the method of the present invention in Example 3. Figures 1 to 3 It can be clearly seen that the lithium iron phosphate raw material has a lot of flocculent carbon. Although the lithium iron phosphate material that eliminates the flocculent carbon by increasing the sintering temperature has a significant reduction in flocculent carbon, it is still not thorough enough. The lithium iron phosphate material after the flocculent carbon is eliminated by the method of the present invention has a significantly reduced and more thorough flocculent carbon.

[0017] Table 1: Specific process conditions of the embodiments of the present invention and comparative examples and performance test results of the obtained lithium iron phosphate.

[0018] Table 1 shows the specific process conditions of the embodiments of the present invention and the comparative examples and the performance test results of lithium iron phosphate. It can be seen from Table 1 that in embodiments 1 to 6, the electrochemical properties of the lithium iron phosphate after the flocculent carbon is eliminated by the method of the present invention are significantly improved compared with the electrochemical properties of the lithium iron phosphate raw material without eliminating the flocculent carbon, including charge and discharge performance and conductivity. The smaller the resistivity, the better the conductivity. Figure 1 and attached Figure 2, indicating that the method of the present invention not only effectively eliminates the flocculent carbon, but also improves the electrochemical properties of lithium iron phosphate; wherein with the increase of microwave power, the electrochemical properties of the prepared lithium iron phosphate material show a trend of first increasing and then decreasing, indicating that the size of microwave power has an important influence on the performance of lithium iron phosphate. Too low power has a poor heating effect on the flocculent carbon, resulting in a poor reaction effect with carbon dioxide. Too high power may damage the carbon in the coating layer, resulting in a decrease in the electrochemical properties of lithium iron phosphate. At the same time, a short heating time cannot eliminate the flocculent carbon well, and a long heating time may not only cause the carbon in the coating layer to be damaged by the reaction, but also increase energy consumption. Therefore, at a power of 700 to 900 W and a heating time of 30 to 60 minutes, the elimination of flocculent carbon can be achieved better and the electrochemical properties of lithium iron phosphate can be improved.

[0019] The electrochemical performance of lithium iron phosphate that eliminates flocculent carbon by increasing the sintering temperature is lower than that of the lithium iron phosphate raw material that does not eliminate flocculent carbon. This is because the excessively high sintering temperature will destroy the generated amorphous carbon coating layer, and the grains will agglomerate and grow, increasing the transmission path of Li+. At the same time, the sintering temperature is too high to easily produce Fe2P impurities, which may block the one-dimensional diffusion channel of Li+ and reduce the diffusion coefficient, thereby reducing the electrochemical performance of the material.

[0020] In summary, the conventionally prepared lithium iron phosphate raw material without eliminating the flocculent carbon has a large amount of surface flocculent carbon and poor electrochemical performance. Eliminating the flocculent carbon by increasing the sintering temperature is actually not conducive to the electrochemical performance of lithium iron phosphate. The method of the present invention can heat the flocculent carbon in a targeted manner through microwave-assisted heating, more effectively make the flocculent carbon and carbon dioxide react, and more thoroughly eliminate the flocculent carbon without damaging the structure of lithium iron phosphate and the surface-coated carbon, thereby improving the electrochemical performance of the lithium iron phosphate material.

[0021] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. For example, any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in this application, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for eliminating flocculent carbon in lithium iron phosphate, characterized in that: The lithium iron phosphate raw material is placed in a microwave heating device for microwave heating, and carbon dioxide gas is introduced at the same time, wherein the microwave power of the microwave heating is set to 700-900W, the microwave frequency is set to 2.45GHz, and the heating time is 30-60min.

2. The method for eliminating flocculent carbon in lithium iron phosphate according to claim 1, characterized in that: The carbon dioxide gas flow rate is controlled at 1 L / min.

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