A preparation method of lithium ion battery safety coating material based on polyaniline

Abstract

The present invention relates to the technical field of lithium-ion batteries, and in particular to a method for preparing a lithium-ion battery safety coating material based on polyaniline. The present invention provides a non-toxic, harmless, recyclable material capable of effectively improving the thermal stability of a battery, namely polyaniline (PANI), as a battery thermal protection material replacing polythiophene (PTh). The safety coating based on polyaniline (PANI) can respond quickly when the battery temperature exceeds a set threshold, increase the internal resistance of the material, and quickly cut off the flow of current to prevent thermal runaway. In addition, polyaniline is a non-toxic raw material, meets the needs of green development, is recyclable, can be processed by micro-scraping and heat treatment, is suitable for large-scale production, and has no significant negative impact on energy density and cycle performance.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing a lithium ion battery safety coating material based on polyaniline. Background Art

[0002] With the widespread application of new energy batteries, lithium-ion batteries have become an important technology in the current energy storage field. Lithium-ion batteries are widely used in consumer electronics, transportation and energy storage systems due to their high energy density, long cycle life and stable performance. However, with the continuous improvement of the capacity of lithium-ion batteries, their safety issues have attracted widespread attention. When the battery encounters abnormal conditions such as internal short circuit, overcharge or overheating, thermal runaway is prone to occur, leading to explosion or fire accidents. Existing battery designs have integrated some external safety measures, such as pressure valves, fire suppressants and thermal insulation materials. However, these measures often respond slowly in the case of thermal runaway caused by internal short circuits and it is difficult to avoid serious consequences. In order to further improve the safety of the battery, researchers have developed a built-in thermal response layer based on polymer thermal response materials. The positive temperature coefficient (PTC) effect of the material is used to rapidly increase the material resistance when the temperature rises, thereby cutting off the current. Among them, polythiophene (PTh) is a commonly used PTC material. Polythiophene is in a highly conductive state (p-type doping) at room temperature. When the temperature exceeds the set value, a dedoping reaction occurs, resulting in a sharp drop in conductivity, forming a circuit-breaking mechanism. In addition, polythiophene can be used as a coating material to cover the surface of the electrode current collector or diaphragm to form a safety enhancement layer. The thermal response effect of polythiophene near 100°C is significant, which can effectively prevent the spread of thermal runaway. However, polythiophene has problems of toxicity and difficulty in recycling, which poses challenges to environmental protection and sustainable development. Some other studies have attempted to compound conductive polymer materials with carbon nanotubes, graphene, etc. to further optimize their thermal response and conductive properties. However, the complex preparation process and high cost limit its industrial application.

[0003] In order to ensure the safety performance of the battery and solve the problem of explosion caused by abnormal conditions such as internal short circuit, overcharging or overheating, researchers introduced polythiophene (PTh) and developed a built-in thermal response layer. When the temperature rises, the material resistance is rapidly increased to ensure safety. However, it is toxic, difficult to recycle, and polythiophene has poor solubility in common solvents, making it difficult to adapt to the large-scale production needs of modern industry. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a polyaniline-based lithium-ion battery safety coating material to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a lithium ion battery safety coating material based on polyaniline, comprising the following steps: Step 1: Mix aniline monomer with hydrochloric acid solution, adjust the pH value to the acidic range, dissolve the oxidant in distilled water, add aniline solution dropwise, control the reaction temperature, continue stirring for a certain period of time, let stand to form a dark green polyaniline precipitate, wash the precipitate with deionized water, dry it at a certain temperature until the filtrate is neutral, and obtain high-purity polyaniline powder.

[0006] Step 2: Weigh an appropriate amount of polyaniline powder and a conductive additive (such as carbon black) and mix them in a certain proportion, add a solvent (such as N-methylpyrrolidone), disperse and stir evenly by ultrasonication to prepare a coating solution.

[0007] Step 3: Use micro-scraping technology to evenly apply the coating solution in step 2 to the surface of the battery electrode current collector to form a coating of a certain thickness, and then perform heat curing at a certain temperature.

[0008] Preferably, the oxidant in step 1 is ammonium persulfate.

[0009] Preferably, in step 1, the reaction temperature is 0-10° C., the reaction time is 3-6 h, and the standing time is 1-5 h.

[0010] Preferably, the drying temperature of the sample in step 1 is 40-70° C., and the drying time is 3-5 h.

[0011] Preferably, in step 2, the mass fraction ratio of the polyaniline powder material, carbon black and N-methylpyrrolidone is 10:20:70.

[0012] Preferably, the ultrasonic dispersion time in step 2 is 0.5-1 h, and the standing time is 4 h.

[0013] Preferably, the thickness of the slurry coating in step 3 is 0.6 μm.

[0014] Preferably, the drying temperature in step 3 is 80-120° C. and the drying time is 1-4 hours.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The safety coating based on polyaniline (PANI) can respond quickly when the battery temperature exceeds the set threshold, showing good rapid responsiveness, which can significantly improve battery safety, increase the internal resistance of the material to quickly cut off the current flow to prevent thermal runaway, and significantly reduce the risk of thermal runaway of lithium-ion batteries.

[0016] In terms of environmental protection and recyclability, polyaniline is non-toxic and recyclable, which solves the environmental defects of polythiophene (PTh) materials, takes into account high safety and environmental protection and recyclability, and meets the future needs of green energy development.

[0017] Polyaniline supports roll coating process, is suitable for large-scale production, and has good industrial prospects; it has strong compatibility and has little effect on the energy density and cycle performance of lithium-ion batteries. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] The present invention provides a technical solution: a method for preparing a polyaniline-based lithium-ion battery safety coating material, comprising the following steps: Step 1, mixing an appropriate amount of aniline monomer with a hydrochloric acid solution, adjusting the pH value to an acidic range, dissolving ammonium persulfate in distilled water, adding the aniline solution dropwise, controlling the reaction temperature, continuously stirring for a certain period of time, standing to form a dark green polyaniline precipitate, washing the precipitate with deionized water, drying at a certain temperature until the filtrate is neutral, and obtaining a high-purity polyaniline powder.

[0020] Specifically, the volume ratio of aniline monomer and 1 mol / L hydrochloric acid is 1:5, the molar ratio of aniline monomer to ammonium persulfate is 1 mmol: (1.5-2) mol; the liquid volume ratio of ammonium persulfate to water is 1:10; the reaction temperature is 0-10°C, preferably 0-5°C, the reaction time is 3-6h, preferably 4-5h, the standing time is 1-5h, preferably 2-3h, the drying temperature of the sample is 40-70°C, preferably 50°C, and the drying time is 3-5h, preferably 4h; Step 2, weighing an appropriate amount of polyaniline powder and a conductive additive (such as carbon black) and mixing them in a certain proportion, adding a solvent (such as N-methylpyrrolidone), and preparing a coating solution by ultrasonic dispersion and stirring.

[0021] Specifically, the mass fraction ratio of polyaniline powder material, carbon black and NMP is (5-20): (10-25): (60-80), preferably 10:20:70; the ultrasonic dispersion time is 0.5~1h, and the standing time is 4h.

[0022] Step 3, using micro-scraping technology, uniformly apply the coating solution in step 2 to the surface of the battery electrode current collector to form a coating of a certain thickness, and then perform heat curing treatment at a certain temperature.

[0023] Specifically, the thickness of the slurry coating in the above step 3 is 0.6 μm; the drying temperature is 80-120° C., preferably 90-100° C.; and the drying time is 1-4 h, preferably 1-2 h. Example

[0024] Weigh a certain molar mass of aniline monomer and mix it with 1 mol / L hydrochloric acid solution at a volume ratio of 1:5, adjust the pH value to the acidic range of 1-3, dissolve ammonium persulfate in distilled water at a volume ratio of 1:10, add the ammonium persulfate solution dropwise to the aniline solution, stir continuously for 4 hours at 0-5°C, form a dark green polyaniline precipitate, and let it stand for 2 hours. Take out the product and wash the precipitate with deionized water until the filtrate is neutral and the pH is about 6-7, dry the product at 50°C for 4 hours, and take out the product after cooling to obtain high-purity polyaniline powder.

[0025] Then, an appropriate amount of polyaniline powder and carbon black were weighed and mixed in a certain proportion, and solvent N-methylpyrrolidone was added. The mass fraction ratio of polyaniline powder material, carbon black and N-methylpyrrolidone was 10:20:70. After ultrasonic dispersion for 1 hour and stirring evenly, a coating solution was prepared. A certain amount of coating solution was evenly coated on the surface of the battery electrode current collector to form a coating with a thickness of 0.6 μm, and then heat-cured at 90-100°C for 2 hours to finally obtain a polyaniline-based lithium-ion battery safety coating material.

[0026] Comparative Example 1 Weigh a certain molar mass of polythiophene and dissolve it in 100 mL of 80% chloroform, stirring until completely dissolved. Add carbon black powder (15% by weight of the solution) and disperse it by ultrasonic for 30 minutes to form a uniformly dispersed coating solution.

[0027] A certain amount of coating solution was uniformly coated on the surface of the battery electrode current collector by roller coating to form a coating with a thickness of 0.5 μm. The solvent was naturally evaporated at room temperature, and then thermally cured at 80°C for 2 hours to obtain a lithium-ion battery safety coating material based on polythiophene.

[0028] Comparative Example 2 A certain molar mass of alumina powder was weighed and mixed with PVDF at a mass ratio of 1:2.5, and solvent N-methylpyrrolidone was added, stirred evenly, and ultrasonically treated for 1 hour to ensure the formation of a uniform ceramic slurry.

[0029] A certain amount of coating solution is evenly coated on the surface of the battery electrode current collector. The coating thickness is about 1 μm. The coating is thermally cured at 150°C for 3 hours to completely cure the ceramic coating. Finally, a safe coating material based on ceramic material is obtained. The diaphragm materials described in Example 1, Comparative Example 1 and Comparative Example 2 were respectively assembled into lithium batteries and subjected to cycle testing, the steps being as follows: The current collector with polyaniline coating material is roll-formed together with lithium iron phosphate positive electrode active material slurry to prepare positive electrode sheets with uniform thickness, which are assembled into button batteries in sequence with negative electrode sheets made of graphite negative electrode and electrolyte in a glove box with argon atmosphere. The assembled batteries are then placed on a battery testing system for charge and discharge tests. The test voltage range is 1.5-3.0 V, and the cycle test rate is 0.33C (0.1C for the first two cycles).

[0030] Sample name First discharge capacity (mAh / g) Capacity retention rate (%, 0.33C, 100cls) Internal resistance at 100℃ (Ω) Example 1 150 98.5 500 Comparative Example 1 140 90.0 700 Comparative Example 2 100 95.0 1000 Table 1 Electrochemical performance results of batteries assembled with polyaniline, polythiophene and ceramic materials in Example 1, Comparative Example 1 and Comparative Example 2 It can be seen from Table 1 that after 100 charge and discharge cycles, the capacity retention rate of the polyaniline battery of Example 1 is 98.5%, the capacity retention rate of Comparative Example 1 is 90.0%, and the capacity retention rate of Comparative Example 2 is 95.0%.

[0031] It can be seen that the lithium-ion battery assembled with the lithium-ion battery safety coating material of polyaniline in Example 1 has a higher discharge capacity retention rate and better cycle performance.

[0032] It is obvious to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive in all respects, and the scope of the invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims be included in the invention.

[0033] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a lithium ion battery safety coating material based on polyaniline, characterized in that: The following steps are involved: Step 1: Mix aniline monomer with hydrochloric acid solution, adjust the pH value to the acidic range, dissolve the oxidant in distilled water, add aniline solution dropwise, control the reaction temperature, continue stirring for a certain period of time, let stand to form a dark green polyaniline precipitate, wash the precipitate with deionized water, dry it at a certain temperature until the filtrate is neutral, and obtain high-purity polyaniline powder.

2. Step 2: Weigh an appropriate amount of polyaniline powder and a conductive additive and mix them in a certain proportion, add a solvent, disperse them by ultrasonic and stir them evenly to prepare a coating solution.

3. Step 3: Use micro-scraping technology to evenly apply the coating solution in step 2 to the surface of the battery electrode current collector to form a coating of a certain thickness, and then perform heat curing treatment at a certain temperature.

4. The method for preparing a polyaniline-based lithium-ion battery safety coating material according to claim 1, characterized in that: The oxidant in step 1 is ammonium persulfate.

5. The method for preparing a polyaniline-based lithium-ion battery safety coating material according to claim 1, characterized in that: In step 1, the reaction temperature is 0-10°C, the reaction time is 3-6h, and the standing time is 1-5h.

6. The method for preparing a polyaniline-based lithium-ion battery safety coating material according to claim 1, characterized in that: In step 1, the drying temperature of the sample is 40~70℃, and the drying time is 3~5h.

7. The method for preparing a polyaniline-based lithium-ion battery safety coating material according to claim 1, characterized in that: In step 2, the conductive additive is carbon black, the solvent is N-methylpyrrolidone, and the mass fraction ratio of the polyaniline powder material, carbon black and N-methylpyrrolidone is 10:20:

70.

8. The method for preparing a polyaniline-based lithium-ion battery safety coating material according to claim 1, characterized in that: The ultrasonic dispersion time in step 2 is 0.5-1 h, and the standing time is 4 h.

9. The method for preparing a polyaniline-based lithium-ion battery safety coating material according to claim 1, characterized in that: The thickness of the slurry coating in step 3 is 0.6 μm.

10. The method for preparing a polyaniline-based lithium-ion battery safety coating material according to claim 1, characterized in that: The drying temperature in step 3 is 80-120° C. and the drying time is 1-4 hours.