A positive electrode integrated metal-organic framework-based composite solid electrolyte and its preparation method

Abstract

The present invention discloses a preparation method of a cathode integrated metal-organic framework-based composite solid electrolyte, comprising the following steps: loading the treated lithium ion liquid on the activated MOFs to obtain Li-IL@MOFs; dropping a photocurable polymer monomer solution into Li-IL@MOFs, adding an organic dispersant, and ultrasonically stirring until a uniform slurry is formed; dropping or coating the slurry obtained in the second step on the cathode, standing and drying the organic dispersant, and irradiating with ultraviolet light in a glove box filled with inert gas, and curing to obtain an in-situ cathode integrated MOFs-based composite solid electrolyte. The present invention also discloses the metal-organic framework-based composite solid electrolyte obtained by the preparation method. The in-situ photocuring technology adopted by the present invention can enable the electrolyte to enter the pores of the cathode, solve the problem of interface contact between the solid electrolyte and the cathode, and the photocured solid electrolyte can play a role in inhibiting lithium dendrites.

Description

Technical Field

[0001] The present invention belongs to the field of solid-state batteries, and particularly relates to a cathode-integrated metal-organic framework-based composite solid electrolyte and a preparation method thereof. Background Art

[0002] With the widespread popularity of new energy vehicles and the booming development of intelligent electronic devices, developing energy storage devices with high safety and high energy density is an inevitable strategy to advance the trend of the times. Lithium metal batteries directly use metallic lithium as the battery anode and have an extremely high specific capacity. However, overcharging, overheating, and short circuits cause traditional highly active organic electrolytes to burn, inducing a large number of safety problems. Therefore, solid-state lithium batteries using solid electrolytes are considered the most promising alternatives to traditional lithium batteries. However, the solid-solid contact between the solid electrolyte and the cathode leads to a large interfacial impedance, which affects the practical application of solid electrolytes.

[0003] Since the in-situ curing technology can integrate the cathode and the solid electrolyte, it can optimize the interfacial impedance between solids. The existing mainstream in-situ curing technologies are divided into photo-curing and thermal curing. Thermal curing consumes a high amount of energy, has a low production efficiency, and is more complex in process. In photo-curing, initiators generate free radicals under the action of ultraviolet light and can initiate the polymerization and crosslinking of monofunctional or polyfunctional monomers of acrylate esters at room temperature. The polymer monomers and initiator solution can penetrate into the pores of the cathode material, and after in-situ curing, the solid electrolyte is tightly combined with the cathode material, solving the problem of excessive interfacial impedance. Summary of the Invention

[0004] Object of the Invention: In order to overcome the deficiencies in the prior art, the object of the present invention is to provide a preparation method of a cathode-integrated metal-organic framework-based composite solid electrolyte that improves the interface between the electrode and the solid electrolyte, is simple and convenient, and has low energy consumption. Another object of the present invention is to provide a cathode-integrated metal-organic framework-based composite solid electrolyte with good cycle stability.

[0005] Technical Solution: The preparation method of a cathode-integrated metal-organic framework-based composite solid electrolyte according to the present invention includes the following steps:

[0006] Step 1: Activated MOFs (metal-organic frameworks) are loaded with a lithium-ion liquid (Li-IL) according to a mass ratio of 1:1.5. After mixing evenly, Li-IL@MOFs is prepared.

[0007] Step 2: A photo-curing polymer monomer solution is dropped into Li-IL@MOFs, and an organic dispersant is added. Ultrasonic stirring is carried out until a uniform slurry is formed.

[0008] Step 3: Drop or coat the slurry obtained in Step 2 on the positive electrode, let it stand and dry, and irradiate it with ultraviolet light in an argon glove box. After curing, a positive electrode integrated metal-organic framework-based composite solid electrolyte is prepared.

[0009] Further, in Step 1, the MOFs are completely activated in a vacuum environment before use. The MOFs are ZIF-8, MIL101 or CuBTC, which have a large specific surface area, good thermal stability and many activation sites. The activation temperature is 120 - 160 °C, and the activation time is 2 - 24 h. The lithium ionic liquid is vacuum dried at 100 - 120 °C for 4 - 48 h before use to remove water molecules. The reaction temperature is 0 - 120 °C.

[0010] Further, in Step 2, the photocurable polymer monomer solution includes a photoinitiator and a functional monomer. The photoinitiator is α-hydroxyisobutyrophenone (HMPP), and the functional monomer is ethoxylated trimethylolpropane triacrylate (ETPTA). The mass ratio of the photoinitiator to the functional monomer is 1:100 - 150. The organic dispersant is any one or more of dichloromethane, acetonitrile, and acetone.

[0011] Further, in Step 3, the time of ultraviolet light irradiation is 30 s - 2 h.

[0012] The positive electrode integrated metal-organic framework-based composite solid electrolyte obtained by the preparation method of the above positive electrode integrated metal-organic framework-based composite solid electrolyte includes 80 - 95 wt% of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 50 μm - 150 μm.

[0013] Preparation principle: Through an in-situ process, the electrolyte precursor slurry enters the pores of the positive electrode. After photocuring, the electrolyte is in close contact with the positive electrode, and a large number of MOFs loaded with lithium ionic liquid construct an ordered lithium ion transport channel inside the electrolyte. The unsaturated sites of the metal-organic framework bind to anions, enabling a large number of free lithium ions to migrate. The metal-organic framework shows good prospects as an inorganic filler applied in solid electrolytes. It has a large number of unsaturated metal sites that can bind anions in ionic liquids, promoting the dissociation of lithium salts. The porous structure of MOFs materials provides a path for the ordered migration of lithium ions, promotes the uniform deposition of lithium metal, and inhibits the growth of lithium dendrites.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0015] 1. The solid-state lithium metal battery assembled by the in-situ photocuring technology enables the electrolyte to enter the pores of the positive electrode, solves the problem of interface contact with the positive electrode, and the photocured solid electrolyte can play a role in inhibiting lithium dendrites;

[0016] 2. The lithium-ion liquid coated on the surface of the metal-organic framework has a nano-wetting effect, enabling a rigid-flexible interface contact on the lithium metal anode;

[0017] 3. Compared with traditional electrolytes, lithium-ion liquids have high thermal and chemical stability, can be recycled, and are environmentally friendly, and are regarded as "green" chemical solvents;

[0018] 4. Ethoxylated trimethylolpropane triacrylate is easier to cure and crosslink than other acrylate monomers, and the mechanical properties of the cured product are better. In addition, the loaded Li-IL@MOFs is also beneficial to enhancing the mechanical properties of the solid electrolyte and inhibiting dendrites. Description of the Drawings

[0019] Figure 1 It is the scanning electron microscope image of ZIF-8 after loading lithium-ion liquid in Example 5 of the present invention;

[0020] Figure 2 It is the scanning electron microscope image of the cross-section after brittle fracture of the product obtained in Example 5 of the present invention;

[0021] Figure 3 It is the ionic conductivity diagram of the stainless-steel symmetric battery of the electrolyte device prepared in Examples 4, 5, 5 and Comparative Example 1 at different temperatures;

[0022] Figure 4 It is the cycle performance diagram of the lithium symmetric battery of the electrolyte device prepared in Example 5, Example 6 and Comparative Example 1;

[0023] Figure 5 It is the cycle performance diagram of the lithium metal battery of the device in Example 5 and Comparative Example 2. Detailed Embodiments

[0024] In the following examples, the preparation method of the lithium-ion liquid is: Weigh 1 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a glove box filled with inert gas, and add dropwise 5.46 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) ionic liquid, stir and ultrasonically remove bubbles to obtain the lithium-ion liquid.

[0025] Example 1

[0026] A preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte, comprising the following steps:

[0027] (a) Weigh 0.5 g of ZIF-8 and activate it in vacuum at 120 °C for 24 h; the lithium-ion liquid is dried in vacuum at 100 °C for 48 h to remove water molecules;

[0028] (b) adding 0.75 g of lithium ion liquid to the activated MOFs, grinding and mixing, and reacting at 0°C until a slight amount of wetting appears on the surface of Li-IL@MOFs and Li-IL@MOFs is in a solid-like state;

[0029] (c) weighing 4 g of ethoxylated trimethylolpropane triacrylate monomer, adding dropwise 0.04 g of photoinitiator α-hydroxyisobutyrophenone, stirring and mixing to obtain a photocurable polymer monomer solution;

[0030] (d) 0.05 g of photocurable polymer monomer solution was added dropwise to 0.8 g of Li-IL@MOFs, and 7 ml of dichloromethane was added, followed by ultrasonic stirring to prepare a uniform milky white slurry;

[0031] (e) dripping or coating the slurry obtained in step (d) on the positive electrode, standing at room temperature to evaporate the solvent, then placing it in a vacuum drying oven and drying it in a stepwise manner to remove the remaining solvent, irradiating the electrolyte surface with 365nm ultraviolet light for 30s in a glove box filled with argon, and obtaining a positive electrode integrated MOFs-based composite solid electrolyte after curing.

[0032] The positive electrode integrated metal organic framework-based composite solid electrolyte obtained in this embodiment includes 80% by mass of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 50 μm.

[0033] Example 2

[0034] A method for preparing a positive electrode integrated metal organic framework-based composite solid electrolyte comprises the following steps:

[0035] (a) 0.5 g of MIL101 was weighed and vacuum activated at 160 °C for 2 h; the lithium ion liquid was vacuum dried at 120 °C for 4 h to remove water molecules;

[0036] (b) 0.75 g of lithium ion liquid was added dropwise to the activated MOFs, the mixture was ground and mixed evenly, and the mixture was reacted at 120 °C until a slight amount of wetting appeared on the surface of the Li-IL@MOFs and the Li-IL@MOFs was in a solid-like state;

[0037] (c) weighing 6 g of monomer ethoxylated trimethylolpropane triacrylate, adding dropwise 0.04 g of photoinitiator α-hydroxyisobutyrophenone, stirring and mixing to obtain a photocurable polymer monomer solution;

[0038] (d) 0.2 g of photocurable polymer monomer solution was added dropwise to 0.95 g of Li-IL@MOFs, and 7 ml of acetonitrile was added, followed by ultrasonic stirring to prepare a uniform milky white slurry;

[0039] (e) Drop or coat the slurry obtained in step (d) on the positive electrode, let it stand at room temperature to volatilize the solvent, and then put it into a vacuum drying oven to dry by stepwise heating to remove the remaining solvent. Irradiate the surface of the electrolyte with 365 nm ultraviolet light for 2 h in a glove box filled with argon, and a positive electrode integrated MOF-based composite solid electrolyte is prepared after curing.

[0040] The positive electrode integrated metal-organic framework-based composite solid electrolyte obtained in this example includes 95% by mass of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 150 μm.

[0041] As Figure 1 , the ZIF-8 loaded with ionic liquid obtained in this example has a complete crystal shape after being modified by the ionic liquid.

[0042] As Figure 2 , it can be seen from the cross-sectional view of the positive electrode integrated metal-organic framework-based composite solid electrolyte prepared in this example after being brittle fractured by liquid nitrogen: there is close contact between the positive electrode and the composite solid electrolyte without extra pores. The thickness of the positive electrode is about 12 μm, and the thickness of the electrolyte is about 50 μm. The inset is the surface structure of the positive electrode before coating the electrolyte precursor, and it can be seen that there are many pores on the surface of the positive electrode.

[0043] Example 3

[0044] A preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte includes the following steps:

[0045] (a) Weigh 0.5 g of CuBTC and activate it in vacuum at 140 °C for 13 h; the ionic liquid is vacuum dried at 110 °C for 26 h to remove water molecules;

[0046] (b) Drop 0.75 g of the ionic liquid onto the activated MOFs, grind and mix evenly, and react at 60 °C until there is a trace of wetting on the surface of Li-IL@MOFs and Li-IL@MOFs is in a quasi-solid state;

[0047] (c) Weigh 5 g of monomer ethoxylated trimethylolpropane triacrylate, drop 0.04 g of photoinitiator α-hydroxyisobutyrophenone, and stir and mix evenly to obtain a photocurable polymer monomer solution;

[0048] (d) Drop 0.14 g of the photocurable polymer monomer solution into 0.87 g of Li-IL@MOFs, add 7 ml of acetone, and ultrasonically stir to make a uniform milky white slurry;

[0049] (e) Drop or apply the slurry obtained in step (d) onto the positive electrode, let it stand at room temperature to volatilize the solvent, then place it in a vacuum drying oven and dry it by stepwise heating to remove the remaining solvent. Irradiate the surface of the electrolyte with 365 nm ultraviolet light for 1 h in a glove box filled with argon, and a positive electrode integrated MOFs-based composite solid electrolyte is obtained after curing.

[0050] The positive electrode integrated MOFs-based composite solid electrolyte obtained in this example includes 87 wt% of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 100 μm.

[0051] Example 4

[0052] A preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte includes the following steps:

[0053] (a) Weigh 0.5 g of ZIF-8 and activate it in vacuum at 160 °C for 12 h; weigh the lithium ion liquid and dry it in vacuum at 120 °C for 12 h to remove water molecules.

[0054] (b) Drop 0.75 g of the lithium ion liquid onto the activated MOFs, grind and mix evenly, and react at 80 °C until there is slight wetting on the surface of Li-IL@MOFs and Li-IL@MOFs is in a quasi-solid state.

[0055] (c) Weigh 6 g of monomer ethoxylated trimethylolpropane triacrylate, drop 0.04 g of photoinitiator α-hydroxyisobutyrophenone, and stir and mix evenly to obtain a photocurable polymer monomer solution.

[0056] (d) Drop 0.2 g of the photocurable polymer monomer solution into 0.8 g of Li-IL@MOFs, add 7 ml of dichloromethane, and ultrasonically stir to make a uniform milky white slurry.

[0057] (e) Drop or apply the slurry obtained in step (d) onto the positive electrode, let it stand at room temperature to volatilize the solvent, then place it in a vacuum drying oven and dry it by stepwise heating to remove the remaining solvent. Irradiate the surface of the electrolyte with 365 nm ultraviolet light for 30 s in a glove box filled with argon, and a positive electrode integrated MOFs-based composite solid electrolyte is obtained after curing.

[0058] The positive electrode integrated MOFs-based composite solid electrolyte obtained in this example includes 85 wt% of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 50 μm.

[0059] Example 5

[0060] A preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte includes the following steps:

[0061] (a) Weigh 0.5 g of ZIF-8 and activate it under vacuum at 160 °C for 12 h; the lithium ionic liquid is dried under vacuum at 120 °C for 12 h to remove water molecules;

[0062] (b) Add 0.75 g of the lithium ionic liquid dropwise to the activated MOFs, grind and mix evenly, and react at 120 °C until slight wetting appears on the surface of Li-IL@MOFs and Li-IL@MOFs is in a quasi-solid state;

[0063] (c) Weigh 6 g of the monomer ethoxylated trimethylolpropane triacrylate, add 0.04 g of the photoinitiator α-hydroxyisobutyrophenone dropwise, and stir and mix evenly to obtain a photocurable polymer monomer solution;

[0064] (d) Add 0.1 g of the photocurable polymer monomer solution dropwise to 0.9 g of Li-IL@MOFs, add 7 ml of dichloromethane, and ultrasonically stir to make a uniform milky white slurry;

[0065] (e) Drop or coat the slurry obtained in step (d) on the positive electrode, let it stand at room temperature to volatilize the solvent, then put it into a vacuum drying oven and dry it by stepwise heating to remove the remaining solvent, and irradiate the surface of the electrolyte with 365 nm ultraviolet light for 30 s in a glove box filled with argon, and a positive electrode integrated MOF-based composite solid electrolyte is obtained after curing.

[0066] The positive electrode integrated MOF-based composite solid electrolyte obtained in this example includes 90% by mass of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 55 μm.

[0067] Example 6

[0068] A preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte includes the following steps:

[0069] (a) Weigh 0.5 g of ZIF-8 and activate it under vacuum at 160 °C for 12 h; the lithium ionic liquid is dried under vacuum at 120 °C for 12 h to remove water molecules;

[0070] (b) Add 0.75 g of the lithium ionic liquid dropwise to the activated MOFs, grind and mix evenly, and react at 110 °C until slight wetting appears on the surface of Li-IL@MOFs and Li-IL@MOFs is in a quasi-solid state;

[0071] (c) Weigh 6 g of the monomer ethoxylated trimethylolpropane triacrylate, add 0.04 g of the photoinitiator α-hydroxyisobutyrophenone dropwise, and stir and mix evenly to obtain a photocurable polymer monomer solution;

[0072] (d) 0.05 g of a photocurable polymer monomer solution was added dropwise to 0.95 g of Li-IL@MOFs, and 7 ml of dichloromethane was added. The mixture was sonicated and stirred to form a homogeneous milky white slurry.

[0073] (e) The slurry obtained in step (d) was dropped or coated on the positive electrode. The solvent was allowed to evaporate at room temperature, and then it was placed in a vacuum drying oven and dried by stepwise heating to remove the remaining solvent. The surface of the electrolyte was irradiated with 365 nm ultraviolet light for 30 s in a glove box filled with argon. After curing, an integrated positive electrode MOFs-based composite solid electrolyte was prepared.

[0074] The integrated positive electrode MOFs-based composite solid electrolyte obtained in this example includes 95% by mass of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 80 μm.

[0075] In the above examples, considering the electrochemical and physical properties of the composite solid electrolyte comprehensively, Example 5 is the most preferred example.

[0076] Example 7

[0077] To explore the optimal mixing ratio of different mass ratios of lithium ion liquid (Li-IL) and ZIF-8, five groups of parallel experiments were designed: 1 g of ZIF-8 was respectively loaded with 0 g, 0.5 g, 1.0 g, 1.5 g, and 2.0 g of Li-IL. Among them, 2 g of Li-IL added was in excess and remained in a wet gel state, while 1.5 g of Li-IL could be completely absorbed by ZIF-8 to form a quasi-solid state. Therefore, when the mass ratio of Li-IL to ZIF-8 is 1.5:1, the mixing effect is the best. When the ratio of 0 - 1 g of Li-IL is mixed, the ionic conductivity is too low, so it is not adopted.

[0078] Comparative Example 1

[0079] In this comparative example, the Li-IL@ZIF-8 prepared in Example 5 was pressed into an electrolyte disc with a thickness of 1 cm in diameter under a pressure of 5 MPa to obtain a metal-organic framework-based solid electrolyte.

[0080] Comparative Example 2

[0081] The remaining steps of this comparative example are the same as those in Example 5, except that: the milky white slurry was poured on a polytetrafluoroethylene mold, the solvent was removed by stepwise heating, and then it was placed in a glove box filled with inert gas and irradiated with ultraviolet light for 30 s. The obtained flexible and smooth solid electrolyte membrane could be easily demolded, and then cut into several electrolyte discs with a diameter of 1 cm with a cutter. After being assembled with the electrode, a non-in-situ metal-organic framework-based solid-state lithium metal battery could be obtained.

[0082] As Figure 3, the composite solid electrolyte obtained in Example 5 and Comparative Example 1 was assembled into a stainless steel symmetric battery, and their ionic conductivities at different temperatures were tested. From Figure 3 It can be seen that as the proportion of Li-IL@ZIF-8 increases, the ionic conductivity becomes higher.

[0083] As Figure 4 , the cycling performances of the lithium symmetric batteries assembled with the composite solid electrolytes obtained in Example 5, Example 6 and Comparative Example 1 with relatively high ionic conductivities were tested at a current density of 0.1 mA cm -2 at room temperature. From Figure 4 It can be seen that Example 5 can be stably cycled for 900 hours. Although Comparative Example 1 has a higher ionic conductivity, its mechanical strength is poor, and the battery assembled based on Comparative Example 1 has a lower cycle life.

[0084] As Figure 5 , between 2.8 and 4 V, at a current density of 0.3 C, the coin cells of the solid electrolytes of Example 5 and Comparative Example 2 were respectively subjected to a constant current cycling test. The discharge specific capacity of the coin cell obtained in Example 5 after in-situ photocuring for 200 cycles was 134 mAh g -1 , which has a higher specific capacity and battery life compared with the data of Comparative Example 2.

[0085] Comparative Example 3

[0086] All the other steps of this comparative example are the same as those of Example 5, except that the lithium salt in the lithium ion liquid is changed from LiTFSI to LiPF6.

[0087] The composite solid electrolytes of Example 5 and Comparative Example 2 were assembled into a lithium stainless steel battery, and their electrochemical window performances were tested. It was found that: the electrochemical window decreased to 3.8 V, which is not suitable for the practical application of lithium metal batteries.

[0088] Comparative Example 4

[0089] All the other steps of this comparative example are the same as those of Example 5, except that the activation temperature is replaced by 110 °C.

[0090] The composite solid electrolytes of Example 5 and Comparative Example 3 were assembled into a stainless steel symmetric battery, and the ionic conductivity was tested. It was found that: due to the decrease of the activation temperature, the pores of the MOF were not fully utilized, and the loaded amount of Li-IL was too low, resulting in the ionic conductivity decreasing from 6.53×10 -4 S cm -1 to 2.36×10 -5 S cm -1 .

[0091] Comparative Example 5

[0092] All other steps of this comparative example are the same as those of Example 5, except that: the treatment temperature of the lithium-ion liquid is 170 °C, and the lithium-ion liquid will decompose at 170 °C. The prepared composite solid electrolyte does not have the ability to conduct electricity.

Claims

1. A preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte, characterized in that: It includes the following steps: Step 1: Load the treated lithium ion liquid onto the activated MOFs, and after mixing evenly, obtain Li-IL@MOFs; Step 2: Dropwise add a photocurable polymer monomer, a photoinitiator, and an organic dispersant into the Li-IL@MOFs, and stir ultrasonically until a uniform slurry is formed; Step 3: Dropwise add or coat the slurry obtained in Step 2 onto the positive electrode, let it stand and dry, and irradiate with ultraviolet light in a glove box filled with inert gas. After curing, obtain a positive electrode integrated MOF-based composite solid electrolyte; In Step 1, the MOFs are completely activated in a vacuum environment before use. The MOFs are ZIF-8, MIL101, or CuBTC; the activation temperature is 120~160°C, and the activation time is 2~24 h; In Step 2, the photoinitiator is α-hydroxyisobutyrophenone, and the photocurable polymer monomer is ethoxylated trimethylolpropane triacrylate; The mass ratio of the photoinitiator to the photocurable polymer monomer is 1:100~150; The preparation method of the lithium ion liquid is as follows: Weigh 1 g of lithium bis(trifluoromethanesulfonyl)imide in a glove box filled with inert gas, dropwise add 5.46 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid, and stir and ultrasonically remove the bubbles.

2. The preparation method of a cathode integrated metal-organic framework-based composite solid electrolyte according to claim 1, wherein: In Step 1, the lithium ion liquid is vacuum dried at 100~120°C for 4~48 h before use.

3. The preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte according to claim 1, characterized in that: In Step 1, the reaction temperature is 0~120°C.

4. The preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte according to claim 1, characterized in that: In Step 2, the organic dispersant is any one or more of dichloromethane, acetonitrile, and acetone.

5. The preparation method of a cathode integrated metal-organic framework-based composite solid electrolyte according to claim 1, wherein: In Step 3, the time of ultraviolet light irradiation is 30 s~2 h.

6. The metal-organic framework-based composite solid electrolyte obtained by the preparation method of a positive electrode integrated metal-organic framework-based composite solid electrolyte according to any one of claims 1 to 5, characterized in that: It includes 80~95% by mass of Li-IL@MOFs, and the thickness of the composite solid electrolyte is 50 μm~150 μm.

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