Waste lithium iron phosphate battery positive electrode material and direct regeneration method thereof, directly regenerated lithium iron phosphate positive electrode and preparation method thereof

Abstract

The invention relates to the field of waste lithium batteries, and mainly relates to a waste lithium iron phosphate battery positive electrode material, a direct regeneration method, a directly regenerated lithium iron phosphate positive electrode and a preparation method. The invention relates to a direct regeneration method of a waste lithium iron phosphate battery positive electrode material, which comprises the following steps: mixing waste lithium iron phosphate positive electrode powder, a structure repairing agent and tartaric acid, ball-milling and sintering to obtain the waste lithium iron phosphate battery positive electrode material, the structure repairing agent comprises one of lithium phosphate and phenyl lithium phosphate; the lithium supplementing amount is calculated according to ICP-MS data of the lithium iron phosphate positive electrode, and the mass of the structure repairing agent is calculated according to the atomic ratio of Li being 1.0-1.1; the mass fraction of the tartaric acid is 10-20wt% of the sum of m waste lithium iron phosphate positive electrode powder and m structure repairing agent. According to the method, lithium supplement and phosphorus supplement are rapidly and simultaneously realized through a one-step method, the crystal structure of the lithium iron phosphate can be better repaired, and high-capacity and high-stability regeneration of the lithium iron phosphate is realized.

Description

Technical Field

[0001] This application relates to the field of waste lithium batteries, and mainly to a cathode material for waste lithium iron phosphate batteries and a direct regeneration method, as well as a directly regenerated lithium iron phosphate cathode and its preparation method. Background Technology

[0002] With the widespread adoption of new energy vehicles and energy storage batteries, the shipment volume and total output value of lithium batteries continue to break new records. In the passenger vehicle and energy storage sectors, ternary lithium batteries and lithium iron phosphate batteries are the most widely used, classified by their cathode material. While lithium iron phosphate batteries have a lower specific capacity compared to ternary lithium batteries, their advantages such as low cost, long cycle life, and high safety have led to an increase in their market share in energy storage and power lithium batteries, giving them a dominant position. Since lithium batteries have a lifespan of 8-10 years, the next few years will see a surge in the retirement of lithium batteries, especially lithium iron phosphate batteries. Such a massive volume of retired lithium batteries will inevitably put significant pressure on the environment. How to harmlessly dispose of and recycle used lithium batteries is an urgent problem to be solved. Green recycling of used lithium batteries not only helps reduce environmental problems caused by improper disposal but also extends the lifespan of valuable materials such as cathode materials, improving the economic efficiency of lithium batteries.

[0003] However, current mainstream lithium battery recycling technologies both domestically and internationally, including hydrometallurgy and pyrometallurgy, all generate significant amounts of wastewater and exhaust emissions, leading to pollution problems. Furthermore, recycling is a high-energy-consuming process. With the continuous decline in international lithium prices, this energy-intensive production process is highly likely to result in losses, leading to a situation where the cost of recycled cathode materials exceeds the cost of manufacturing new cathode materials. Therefore, to address the upcoming wave of battery retirements and improve the economic viability of lithium batteries through the harmless treatment of waste batteries, the best strategy is to develop green and low-carbon direct recycling technologies for waste lithium iron phosphate cathode materials.

[0004] Current technologies involve calculating the lithium loss in spent lithium-ion battery cathode materials, replenishing lithium, and then sintering at high temperatures to regenerate the cathode material for reuse. However, focusing solely on lithium loss is insufficient to truly repair lithium iron phosphate (LFP) cathodes. After long-term use, LFP batteries not only lose lithium but also suffer structural damage, resulting in phosphorus loss and microstructural disruption. Therefore, simply replenishing lost lithium cannot fully restore the LFP structure. To improve the performance of directly regenerated LFP cathodes, both Li and P need to be replenished simultaneously to repair the structure. However, different lithium and phosphorus sources, due to their different crystal structures and reaction temperatures, cannot be simultaneously incorporated into the LFP structure.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide a cathode material for waste lithium iron phosphate batteries and a direct regeneration method, a directly regenerated lithium iron phosphate cathode and a preparation method, with the aim of realizing the recycling and regeneration of waste lithium iron phosphate batteries.

[0007] The technical solution of this application is as follows: A method for direct regeneration of spent lithium iron phosphate battery cathode material includes the following steps: Waste lithium iron phosphate cathode powder, structural repair agent, and tartaric acid are mixed, ball-milled, and sintered to obtain the waste lithium iron phosphate battery cathode material. The structural repair agent includes one of lithium phosphate and phenyl (2,4,6-trimethylbenzoyl) lithium phosphate; The amount of lithium replenishment was calculated based on the ICP-MS data of the lithium iron phosphate cathode, and the mass of the structural repair agent was calculated according to the atomic ratio of Li being between 1.0 and 1.1. The mass fraction of tartaric acid is m. 废旧磷酸铁锂正极粉末 +m 结构修复剂 10-20wt% of the sum.

[0008] Tartaric acid can promote the fusion of lithium phosphate and spent lithium iron phosphate, accelerate the entry of Li ions, and open channels for lithium ions.

[0009] Lithium phenyl (2,4,6-trimethylbenzoyl)phosphate has a similar melting point to tartaric acid and can melt it at a lower temperature. Therefore, it can provide a melting environment at a lower temperature, which can better coat carbon materials and build a fast Li ion channel, thereby achieving the repair of cathode materials at a lower temperature and in a shorter time.

[0010] This application achieves simultaneous lithium and phosphorus replenishment in a one-step process, which can better repair the crystal structure of lithium iron phosphate and realize its high-capacity and high-stability regeneration.

[0011] Furthermore, the sintering is carried out at a temperature of 500-900℃ for 6-12 hours.

[0012] Furthermore, the sintering atmosphere is Ar gas or a mixture of H2 / Ar gas.

[0013] Furthermore, the ball milling time for the waste lithium iron phosphate cathode powder, the structural repair agent, and the tartaric acid is 2-10 hours, and the ball-to-material ratio is 1:50-1:5.

[0014] Furthermore, the preparation method of the waste lithium iron phosphate cathode powder includes the following steps: Discharge treatment is performed on the recycled waste lithium iron phosphate batteries; The waste lithium iron phosphate batteries are disassembled to obtain the positive electrode and current collector; the positive electrode and current collector are subjected to high-temperature treatment; the positive electrode material is collected, i.e., recycled material. The recycled material is ball-milled for 1-2 hours at a ball-to-material ratio of 1:50-1:5 to obtain the waste lithium iron phosphate cathode powder.

[0015] The high-temperature treatment serves two purposes: first, to allow the electrolyte to evaporate, and second, to remove the binder, thus separating the positive electrode material from the current collector.

[0016] Furthermore, the conditions for the high-temperature treatment are 400-600℃ for 1-4 hours.

[0017] Furthermore, the high-temperature treatment involves placing the positive electrode and current collector in a muffle furnace or tube furnace and sintering them at 400-600°C for 1-4 hours.

[0018] This application also provides a cathode material for waste lithium iron phosphate batteries.

[0019] This application also provides a directly recycled lithium iron phosphate cathode, comprising the following raw materials: waste lithium iron phosphate battery cathode material, binder, conductive carbon black, and solvent; The mass ratio of the waste lithium iron phosphate battery cathode material, the binder, and the conductive carbon black is 8:1:1.

[0020] The solvent mass ratio (total mass of the waste lithium iron phosphate battery cathode material, the binder, and the conductive carbon black) is 30:1-50:1.

[0021] This application also provides a method for preparing a directly regenerated lithium iron phosphate cathode, comprising the following steps: mixing the waste lithium iron phosphate battery cathode material, the binder, the conductive carbon black, and the solvent, coating the mixture on the surface of a current collector, and drying it to obtain a directly regenerated lithium iron phosphate cathode.

[0022] Furthermore, the thickness of the scraped film is 20-200 μm.

[0023] Compared with the prior art, this application has the following beneficial effects: (1) By using solid-state sintering and structural repair agent to simultaneously supplement Li / P elements and better repair the structure.

[0024] (2) The addition of P element plays a role in repairing the microstructure of waste lithium iron phosphate cathode and enhances the stability of the regenerated cathode material, which enables the repaired battery to have better stability and high rate performance.

[0025] (3) Simultaneous supplementation of Li / P elements avoids the difficulty of simultaneously supplementing different lithium and phosphorus sources into the lithium iron phosphate structure due to different crystal structures and reaction temperatures; (4) The combination of lithium phosphate and tartaric acid lowers the repair temperature and can better construct lithium ion transport channels to achieve rapid lithium replenishment. Attached Figure Description

[0026] Figure 1 XRD images of the waste lithium iron phosphate battery cathode material of Example 1 of this application, the sintered waste lithium iron phosphate cathode powder of Comparative Example 1, the sintered waste lithium iron phosphate cathode powder of Comparative Example 2, and standard lithium iron phosphate. Figure 1 In the middle, from top to bottom, there are sintered waste lithium iron phosphate cathode powder of Comparative Example 1, waste lithium iron phosphate battery cathode material of Example 1, sintered waste lithium iron phosphate cathode powder of Comparative Example 2, and standard lithium iron phosphate.

[0027] Figure 2 Scanning electron microscope image of the cathode material of waste lithium iron phosphate batteries in Example 1, which is a recycled material.

[0028] Figure 3 This is a battery cycle performance diagram. From top to bottom, it corresponds to Comparative Example 1, Example 1, Comparative Example 2, and Comparative Example 3. Gray-black circle - charge / discharge efficiency (%), red diamond - discharge specific capacity (mAh / g).

[0029] Figure 4 The diagram shows the rate performance of LFP batteries. (a)-(d) correspond to Comparative Example 1, Example 1, Comparative Example 2, and Comparative Example 3, respectively. Detailed Implementation

[0030] This application provides a cathode material from spent lithium iron phosphate batteries and a direct regeneration method, as well as a directly regenerated lithium iron phosphate cathode and its preparation method. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] This application provides a method for the direct regeneration of spent lithium iron phosphate battery cathode materials, including the following steps: Step 1: Discharge the recycled waste lithium iron phosphate batteries by connecting an external electrical appliance to physically discharge them until the voltage drops below 2.0V.

[0032] Step 2: Disassemble the waste lithium iron phosphate batteries, collect the positive electrode, and place the positive electrode in a muffle furnace or tube furnace for sintering at 400-600℃ for 1-4 hours.

[0033] Collect the cathode material and define the collected cathode material as recycled material.

[0034] After discharge, the used batteries are manually disassembled to separate the positive electrode (positive electrode material loaded on the current collector), negative electrode, separator, etc. The separated positive electrode (positive electrode material loaded on the current collector) is then placed in a high-temperature, oxygen-free environment for pyrolysis to remove residual electrolyte and binder. After sintering, due to the removal of the binder, the positive electrode material separates from the current collector, and the positive electrode material (recycled material) is collected.

[0035] Step 3: Perform high-energy ball milling on the recycled material for 1-2 hours, with a ball-to-material ratio of 1:50-1:5.

[0036] Waste lithium iron phosphate cathode powder was obtained.

[0037] Step 4: The structural repair agent includes one of lithium phosphate or lithium phenyl phosphate.

[0038] The amount of lithium replenishment was calculated based on the ICP-MS data of the lithium iron phosphate cathode, and the mass of the structural repair agent was calculated based on the atomic ratio of Li between 1.0 and 1.1.

[0039] The mass fraction of tartaric acid is m 废旧磷酸铁锂正极粉末 +m 结构修复剂 10-20wt% of the sum.

[0040] Step 5: Mix the structural repair agent, tartaric acid, and waste lithium iron phosphate cathode powder, and then perform high-energy ball milling for 2-10 hours with a ball-to-material ratio of 1:50-1:5.

[0041] Step 6: Sinter the material after ball milling in Step 5.

[0042] The sintering atmosphere can be either Ar or a H2 / Ar mixture, the sintering time is 6-12 hours, and the sintering temperature is 500-900℃.

[0043] The cathode material from waste lithium iron phosphate batteries was obtained.

[0044] This application also provides a directly regenerated lithium iron phosphate cathode, comprising waste lithium iron phosphate battery cathode material, binder, conductive carbon black, and solvent.

[0045] The mass ratio of waste lithium iron phosphate battery cathode material, binder, and conductive carbon black is 8:1:1.

[0046] Solvent mass: (total mass of waste lithium iron phosphate battery cathode material, binder, and conductive carbon black) = 30:1-50:1.

[0047] A method for preparing a directly regenerated lithium iron phosphate cathode includes the following steps: Step A: Weigh the waste lithium iron phosphate battery cathode material, binder, and conductive carbon black in a mass ratio of 8:1:1, add NMP as a solvent, and mix evenly using magnetic stirring for 12 hours to obtain a slurry.

[0048] Step B: Pour the prepared slurry onto the current collector, set the thickness of the doctor blade, and coat the film, controlling the film thickness to be between 20-200 μm. Then dry it in a vacuum drying oven at 80℃ for 12 hours.

[0049] Step C: Use a punching machine to cut the material obtained in step B to obtain directly regenerated lithium iron phosphate cathode.

[0050] The directly regenerated lithium iron phosphate cathode will then be placed in a glove box for coin cell assembly.

[0051] The present application will be further described below through specific embodiments.

[0052] Example 1 An external resistor is used to discharge the recycled waste lithium iron phosphate batteries. Once the voltage of the waste lithium iron phosphate batteries to be recycled drops below 2.0V, the discharge process stops.

[0053] The recycled waste lithium iron phosphate batteries are disassembled to obtain the positive electrode, which is then placed in a tube furnace and sintered at 500°C for 2 hours. The positive electrode material is collected and defined as recycled material.

[0054] The recycled material was subjected to high-energy ball milling for 1-2 hours with a ball-to-material ratio of 1:50-1:5 to obtain waste lithium iron phosphate cathode powder.

[0055] Lithium supplementation was performed according to a Li:Fe atomic ratio of 1.05:1, with lithium phosphate selected as the structural repair agent. Waste lithium iron phosphate cathode powder, lithium phosphate, and tartaric acid were weighed and mixed according to calculations, then ball-milled for 2 hours at a ball-to-material ratio of 15:1. The amount of tartaric acid added = (m...) 废旧磷酸铁锂正极粉末 +m 磷酸锂 )*15%.

[0056] After mixing, the mixture was heat-treated in an Ar atmosphere at a temperature of 550°C for 7 hours to obtain waste lithium iron phosphate battery cathode material.

[0057] After sintering, the waste lithium iron phosphate battery cathode material, PVDF (binder), and conductive carbon black were weighed according to a mass ratio of 8:1:1. A certain mass of NMP (solvent) was added and the mixture was magnetically stirred for 12 hours to obtain a slurry.

[0058] Solvent mass ratio: (total mass of waste lithium iron phosphate battery cathode material, PVDF, and conductive carbon black) = 40:1.

[0059] The prepared slurry is poured onto the current collector, and the thickness of the doctor blade is set for coating. The slurry is controlled to achieve a coating thickness of 50 micrometers. The slurry is then placed in a vacuum drying oven and dried for 12 hours. The slurry is then cut using a punching machine to obtain the directly regenerated lithium iron phosphate cathode.

[0060] The batteries were assembled using directly regenerated lithium iron phosphate cathodes in a glove box. Finally, the lithium battery performance was tested.

[0061] Comparative Example 1 An external resistor is used to discharge the recycled waste lithium iron phosphate batteries. Once the voltage of the waste lithium iron phosphate batteries to be recycled drops below 2.0V, the discharge process stops.

[0062] The recycled waste lithium iron phosphate batteries are disassembled to obtain the positive electrode, which is then placed in a tube furnace and sintered at 500°C for 2 hours. The positive electrode material is collected and defined as recycled material.

[0063] The recycled material was subjected to high-energy ball milling for 1-2 hours at a ball-to-material ratio of 15:1 to obtain waste lithium iron phosphate cathode powder.

[0064] Weigh out the waste lithium iron phosphate cathode powder.

[0065] Waste lithium iron phosphate cathode powder was ground and then heat-treated in an Ar atmosphere at a temperature of 750°C for 10 hours to obtain sintered waste lithium iron phosphate cathode powder (active material).

[0066] After sintering, the active material, PVDF, and conductive carbon black were weighed according to a mass ratio of 8:1:1. A certain mass of NMP (solvent) was added and the mixture was magnetically stirred for 12 hours to obtain a slurry.

[0067] Solvent mass ratio (total mass of active material, PVDF, and conductive carbon black) = 40:1.

[0068] The prepared slurry is poured onto the current collector, and the thickness of the scraper is set for coating. The coating thickness of the slurry is controlled at 50 micrometers. It is then placed in a vacuum drying oven and dried for 12 hours. The positive electrode sheet is then cut using a punching machine.

[0069] The batteries are assembled in the glove box. Finally, the lithium battery performance is tested.

[0070] Comparative Example 2 An external resistor is used to discharge the recycled waste lithium iron phosphate batteries. Once the voltage of the waste lithium iron phosphate batteries to be recycled drops below 2.0V, the discharge process stops.

[0071] The recycled waste lithium iron phosphate batteries are disassembled to obtain the positive electrode, which is then placed in a tube furnace and sintered at 500°C for 2 hours. The positive electrode material is collected and defined as recycled material.

[0072] The recycled material was subjected to high-energy ball milling for 1-2 hours at a ball-to-material ratio of 15:1 to obtain waste lithium iron phosphate cathode powder.

[0073] Lithium replenishment was performed with a Li:Fe atomic ratio of 1.05:1, and lithium phosphate was selected as the structural repair agent. Waste lithium iron phosphate cathode powder and lithium phosphate were weighed according to calculations, mixed, and ball-milled for 2 hours at a ball-to-material ratio of 15:1.

[0074] After mixing, the mixture is heat-treated in an Ar atmosphere at a temperature of 750°C for 7 hours to obtain sintered waste lithium iron phosphate cathode powder (active material).

[0075] After sintering, the active material, PVDF, and conductive carbon black were weighed according to a mass ratio of 8:1:1, and a certain mass of NMP (solvent) was added and the mixture was magnetically stirred for 12 hours.

[0076] Solvent mass ratio (total mass of active material, PVDF, and conductive carbon black) = 40:1.

[0077] The prepared slurry is poured onto the current collector, and the thickness of the scraper is set for coating. The coating thickness of the slurry is controlled at 50 micrometers. It is then placed in a vacuum drying oven and dried for 12 hours. The positive electrode sheet is then cut using a punching machine.

[0078] The batteries are assembled in the glove box. Finally, the lithium battery performance is tested.

[0079] Comparative Example 3 An external resistor is used to discharge the recycled waste lithium iron phosphate batteries. Once the voltage of the waste lithium iron phosphate batteries to be recycled drops below 2.0V, the discharge process stops.

[0080] The recycled waste lithium iron phosphate batteries are disassembled to obtain the positive electrode, which is then placed in a tube furnace and sintered at 500°C for 2 hours. The positive electrode material is collected and defined as recycled material.

[0081] The recycled material was subjected to high-energy ball milling for 1-2 hours at a ball-to-material ratio of 15:1 to obtain waste lithium iron phosphate cathode powder.

[0082] Weigh out waste lithium iron phosphate cathode powder and tartaric acid and mix them.

[0083] The amount of tartaric acid used is 15% of the total mass of waste lithium iron phosphate cathode powder and structural repair agent.

[0084] Since no structural repair agent was used in this comparative example, the mass of the structural repair agent is 0.

[0085] After mixing, the mixture is heat-treated in an Ar atmosphere at a temperature of 750°C for 7 hours to obtain sintered waste lithium iron phosphate cathode powder (active material).

[0086] After sintering, the active material, PVDF, and conductive carbon black were weighed according to a mass ratio of 8:1:1, and a certain mass of NMP was added and the mixture was magnetically stirred for 12 hours.

[0087] Solvent mass ratio (total mass of active material, PVDF, and conductive carbon black) = 40:1.

[0088] The coating thickness of the slurry was controlled at 50 micrometers, and it was dried in a vacuum drying oven for 12 hours; the positive electrode sheet was then cut using a punching machine.

[0089] The batteries are assembled in the glove box. Finally, the lithium battery performance is tested.

[0090] The test results for lithium battery capacity and cycle data are shown in Table 1.

[0091] Table 1

[0092] XRD images of sintered waste lithium iron phosphate cathode powder of Comparative Example 1, waste lithium iron phosphate battery cathode material of Example 1, sintered waste lithium iron phosphate cathode powder of Comparative Example 2, and standard lithium iron phosphate are shown below. Figure 1 .

[0093] Figure 2 In the image, (a) on the left is a scanning electron microscope (SEM) image of the recycled material; (b) on the right is a SEM image of the waste lithium iron phosphate battery cathode material from Example 1.

[0094] Reference Figure 2 It can be seen that the technical solution of lithium phosphate + tartaric acid in Example 1 can effectively repair the lithium iron phosphate cathode.

[0095] Figure 3 This is a battery cycle performance diagram. From top to bottom, it corresponds to Comparative Example 1, Example 1, Comparative Example 2, and Comparative Example 3.

[0096] Figure 4 The diagram shows the rate performance of LFP batteries. (a)-(d) correspond to Comparative Example 1, Example 1, Comparative Example 2, and Comparative Example 3, respectively.

[0097] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for direct regeneration of spent lithium iron phosphate battery cathode material, characterized in that, The method comprises the following steps: mixing, ball-milling, and sintering waste lithium iron phosphate positive electrode powder, a structure repairing agent, and tartaric acid to obtain the waste lithium iron phosphate battery positive electrode material; the structure repairing agent comprises one of lithium phosphate and lithium phenylphosphate; the amount of lithium supplement is calculated according to ICP-MS data of the lithium iron phosphate positive electrode, and the mass of the structure repairing agent is calculated according to the atomic ratio of Li being between 1.0 and 1.1; The mass fraction of tartaric acid is m 废旧磷酸铁锂正极粉末 + m 结构修复剂 10-20 wt%.

2. The method for direct regeneration of spent lithium iron phosphate battery cathode material according to claim 1, characterized in that, the sintering is performed at a temperature of 500-900 ℃ for 6-12 h.

3. The method for direct regeneration of spent lithium iron phosphate battery cathode material according to claim 1, characterized in that, the sintering atmosphere is Ar gas or H2 / Ar mixed gas.

4. The method for direct regeneration of spent lithium iron phosphate battery cathode material according to claim 1, characterized in that, the ball-milling time of the waste lithium iron phosphate positive electrode powder, the structure repairing agent, and the tartaric acid is 2-10 h, and the ball-to-material ratio is 1:50-1:

5.

5. The method for direct regeneration of spent lithium iron phosphate battery cathode material according to claim 1, characterized in that, The preparation method of the waste lithium iron phosphate positive electrode powder comprises the following steps: discharging the recycled waste lithium iron phosphate battery; disassembling the waste lithium iron phosphate battery to collect the positive electrode and the current collector, high-temperature treating the positive electrode and the current collector, and collecting the positive electrode material, i.e., the recycled material; ball-milling the recycled material for 1-2 h at a ball-to-material ratio of 1:50-1:5 to obtain the waste lithium iron phosphate positive electrode powder.

6. The method for direct regeneration of spent lithium iron phosphate battery cathode material according to claim 5, characterized in that, The high-temperature treatment is performed at a temperature of 400-600 ℃ for 1-4 h.

7. A waste lithium iron phosphate battery positive electrode material obtained by a direct regeneration method based on the waste lithium iron phosphate battery positive electrode material according to any one of claims 1-6.

8. A directly regenerated lithium iron phosphate cathode characterized by, The method comprises the following raw materials: the waste lithium iron phosphate battery positive electrode material according to claim 7, a binder, conductive carbon black, and a solvent; the mass ratio of the waste lithium iron phosphate battery positive electrode material, the binder, and the conductive carbon black is 8:1:1; the mass of the solvent: (the total mass of the waste lithium iron phosphate battery positive electrode material, the binder, and the conductive carbon black) = 30:1-50:

1.

9. A method for producing a directly regenerated lithium iron phosphate cathode according to claim 8, characterized by, The method comprises the following steps: mixing the waste lithium iron phosphate battery positive electrode material, the binder, the conductive carbon black, and the solvent, coating a film on the surface of the current collector, and drying to obtain the directly regenerated lithium iron phosphate positive electrode.

10. The method of claim 9, wherein the direct regenerated lithium iron phosphate cathode is prepared by the steps of: The thickness of the film is 20-200 μm. ​

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