An MXene hybrid polymer electrolyte and its preparation method

Abstract

The present invention discloses an MXene hybrid polymer electrolyte and a preparation method thereof. The electrolyte includes an MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer and a lithium salt, and the electrolyte has good ionic conductivity at room temperature. The electrolyte is obtained by compounding the MXene grafted 3-(trimethoxysilyl)propyl acrylate with polyethylene glycol methyl ether methacrylate after a free radical polymerization reaction and a lithium salt. The preparation method has the advantages of simple steps and mild conditions.

Description

Technical Field

[0001] The present invention relates to a solid polymer electrolyte and a preparation method thereof, and specifically relates to an MXene hybrid polymer electrolyte and a preparation method thereof, belonging to the technical field of solid electrolytes. Background Art

[0002] As an important energy storage technology, lithium-ion batteries have been applied in various portable electronic devices and electric vehicle fields. Compared with nickel-cadmium batteries, they have better battery capacity, relatively high working voltage. At the same time, lithium batteries also have good cycle life and safety, are small in size and light in weight, and can be applied to various wearable devices, showing good development prospects. However, traditional lithium-ion batteries are composed of lithium salts and liquid organic solvents. The high price of lithium salts leads to high costs of lithium-ion batteries. And during use, there is also a risk of leakage of organic solvents, resulting in the lithium secondary battery being prone to catching fire or explosion during overcharge, over-discharge, short circuit, overheating and severe impact, causing great potential safety hazards.

[0003] In order to overcome these problems, solid electrolytes have been developed to replace liquid electrolytes, thus effectively ensuring the safety of the battery. Compared with liquid electrolytes, solid electrolytes have the advantages of non-volatility, high temperature resistance, non-corrosion, non-explosion, etc., and the reactivity with metallic lithium is greatly reduced. In addition, solid electrolytes can inhibit the growth of lithium dendrites, and their safety performance is much higher than that of liquid electrolytes, promoting the safe commercialization of lithium batteries. Replacing the electrolyte and separator in traditional lithium batteries with solid electrolytes to achieve safe and high-energy-density lithium batteries has become a popular research topic for researchers.

[0004] However, such polymer electrolytes also have characteristics such as low conductivity and poor interfacial stability. Summary of the Invention

[0005] Aiming at the problem of low conductivity of polymer electrolytes in the prior art, the first object of the present invention is to provide a solid polymer electrolyte material with high ionic conductivity and interfacial stability at room temperature.

[0006] The second object of the present invention is to provide a preparation method of an MXene hybrid polymer electrolyte, which has the advantages of simple steps, mild conditions, etc.

[0007] To achieve the above technical objects, the present invention provides an MXene hybrid polymer electrolyte, including an MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer and a lithium salt.

[0008] The main reason why the MXene hybrid polymer electrolyte of the present invention has a high ionic conductivity is that there is MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer in the electrolyte. On the one hand, due to the large number of ether oxygen atoms on the molecular chain of this copolymer, the ether oxygen atoms can coordinate with the lithium ions provided by the lithium salt in the electrolyte. Through the continuous breaking / formation process of the lithium-oxygen bond, the lithium ions in the electrolyte are transported through intra-chain or inter-chain loops; on the other hand, the MXene existing in the molecular chain of this copolymer has a relatively stable lamellar structure, which can provide channels for the transport of lithium ions, thereby increasing the lithium ion transference number; at the same time, due to the introduction of MXene, the crystallinity of the copolymer is reduced, thereby further improving the transport rate of lithium ions.

[0009] As a preferred embodiment, the MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer has the structural formula of Formula 1:

[0010]

[0011] Wherein, x is 15-25, and the ratio of m / n is (10-50):1.

[0012] As a preferred embodiment, the molar ratio of the MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer to the lithium salt is (15-20):1.

[0013] As a preferred embodiment, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0014] The present invention also provides a preparation method of the MXene hybrid polymer electrolyte. This method is to carry out a free radical polymerization reaction on MXene grafted 3-(trimethoxysilyl)propyl acrylate (γ-TPA-g-MXene) and polyethylene glycol methyl ether methacrylate (PEGMEM) to obtain MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer (PEGMEM-grafted MXene), and mix the MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer with the lithium salt to obtain the product.

[0015] The chemical reaction structural formula of γ-TPA-g-MXene and PEGMEM is shown as Formula 2 below:

[0016]

[0017] As a preferred embodiment, the mass ratio of the MXene grafted with 3-(trimethoxysilyl)propyl acrylate to methoxypolyethylene glycol methacrylate is (1-5):100. The amount of 3-(trimethoxysilyl)propyl acrylate chemically modified MXene added in the present invention directly affects the conductivity of the prepared solid electrolyte.

[0018] As a preferred embodiment, the conditions for the radical polymerization reaction are: under a protective atmosphere, through an initiator polymerization reaction, at 60-80 °C, the polymerization reaction is carried out for 6-8 h. The protective atmosphere used in the present invention is argon, and the initiator used is azobisisobutyronitrile (AIBN).

[0019] As a preferred embodiment, the MXene grafted with 3-(trimethoxysilyl)propyl acrylate is obtained by the hydrolysis and condensation reaction of 3-(trimethoxysilyl)propyl acrylate with MXene under acidic conditions.

[0020] In the technical solution of the present invention, the chemical modification of MXene is a key step. After the siloxymethyl group in 3-(trimethoxysilyl)propyl acrylate is hydrolyzed under acidic conditions, it can quickly undergo a condensation reaction with the hydroxyl groups on the surface of MXene. The specific process is shown in Equation 3. By introducing a carbon-carbon double bond onto MXene, MXene that can reduce the crystallinity of the polymer matrix and increase the ion transference number can be further introduced into the copolymer through radical polymerization with PEGMEM.

[0021]

[0022] As a preferred embodiment, the mass ratio of 3-(trimethoxysilyl)propyl acrylate to MXene is 1:(1-5).

[0023] As a preferred embodiment, the conditions for the hydrolysis and condensation reaction are: the temperature is 70-80 °C, and the time is 5-7 h.

[0024] As a preferred embodiment, the acidic condition refers to a pH of 3-4. Within this pH range, it is more conducive to the hydrolysis of 3-(trimethoxysilyl)propyl acrylate. The reagent used to adjust the pH in the present invention is formic acid.

[0025] The preparation method of the MXene hybrid polymer electrolyte provided by the present invention comprises the following specific steps:

[0026] 1. Synthesis of γ-TPA-g-MXene:

[0027] Under the protection of argon gas environment, 3-(trimethoxysilyl)propyl acrylate (TPA) and MXene with a monomer mass ratio of 1:(1-5) were added, and uniformly mixed in a three-necked flask with deionized water and alcohol as solvents. The pH value of the mixed solution was adjusted to 3-4 with formic acid, and then reacted in a water bath at 70-80 °C for 5-7 h with magnetic stirring. After the reaction, the precipitate was collected by centrifugation, and then the sample was washed with deionized water to remove unreacted monomers, and then placed in a vacuum oven at 40-60 °C for drying for 12-36 h to obtain γ-TPA-g-MXene.

[0028] 2. Synthesis of MXene-grafted NHPE:

[0029] (1) Under the protection of argon gas environment, first dissolve polyethylene glycol methyl ether methacrylate (PEGMEM) in ethyl acetate, add modified γ-TPA-g-MXene and mix well in a three-necked flask (the mass ratio of γ-TPA-g-MXene to PEGMEM is (1-5):100), and then react in a water bath at 60-80 °C for 6-8 h with magnetic stirring. After the simple free radical polymerization reaction is complete, a viscous mixture PEGMEM-grafted MXene is obtained.

[0030] (2) Dissolve the PEGMEM-grafted MXene mixture prepared in step (1) in ethyl acetate and then precipitate with petroleum ether. After washing three times like this, a white viscous polymer is obtained, and then placed in a vacuum oven at 50-80 °C for drying for 12-36 h.

[0031] (3) Dissolve the PEGMEM-grafted MXene and lithium bis(trifluoromethanesulfonyl)imide prepared in step (2) in a tetrahydrofuran solution, stir and mix at room temperature, and then pour into a polytetrafluoroethylene mold to obtain the hybrid polymer electrolyte MXene-grafted NHPE by vacuum drying.

[0032] Compared with the prior art, the beneficial technical effects brought by the technical solution of the present invention:

[0033] 1. The MXene hybrid polymer electrolyte of the present invention has good ionic conductivity at room temperature, solves the problems such as side reactions and anion concentration polarization existing in the liquid electrolyte of traditional lithium-ion batteries, and improves the Coulomb efficiency and cycle life of the battery.

[0034] 2. The preparation method of the MXene hybrid polymer electrolyte of the present invention is relatively simple, and the raw material cost is low, which is conducive to large-scale production.

[0035] 3. In the MXene hybrid polymer electrolyte of the present invention, there are a large number of ether oxygen atoms that can coordinate with lithium ions provided by lithium salts in the electrolyte. Through the continuous breaking / formation process of lithium-oxygen bonds, the lithium ions in the electrolyte are transported through intra-chain or inter-chain loops. At the same time, by uniformly introducing the modified MXene into the polymer matrix, the crystallinity of the polymer matrix is reduced, the lithium ion transport rate is increased, and the stable lamellar structure of MXene can provide a channel for the transport of lithium ions, improving the lithium ion transference number.

[0036] 4. The MXene hybrid polymer electrolyte of the present invention introduces MXene by means of covalent bonds. Compared with the way of introducing MXene by physical blending, it can be introduced more uniformly, and the ionic conductivity of the prepared hybrid polymer electrolyte is increased by an order of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 are the infrared spectra of monomer PEGMEM and γ-TPA-g-MXene, and the PEGMEM-grafted MXene copolymer prepared in Example 3. In the spectra, the vibration absorption peak of C=C in the two monomers of PEGMEM and γ-TPA-g-MXene is at 1670~1620 cm -1 . After polymerization, the characteristic absorption peak of C=C disappears, indicating that the two monomers have polymerized.

[0038] Figure 2 is a comparison chart of the conductivities of the solid electrolytes of Examples 1-5 at different temperatures. It can be seen that as the temperature increases, the conductivity of the composite electrolyte membrane MXene-grafted NHPE has been increasing. When the mass ratio of PEGMEM:γ-TPA-g-MXene is 100:3, the conductivity of the electrolyte membrane is the highest, which is 3.44×10 -4 S / cm at 30℃.

[0039] Figure 3 is a comparison chart of the conductivities of the solid electrolyte of Example 3 and the solid electrolytes of Comparative Example 1 and Comparative Example 2 at different temperatures. It can be seen that the conductivities of the three increase with the increase of temperature. The conductivity of the electrolyte membrane grafted with MXene by chemical grafting is the highest, which is 3.44×10 -4 S / cm at 30℃. DETAILED DESCRIPTION OF THE INVENTION

[0040] For the convenience of understanding the present invention, the following will describe the present invention in a more comprehensive and detailed manner in combination with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0041] Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present invention.

[0042] Unless otherwise specified, various reagents and raw materials used in the present invention are commercially available products or products that can be prepared by well-known methods.

[0043] The sources of each reagent used in the examples and comparative examples of the present invention are as follows: polyethylene glycol methyl ether methacrylate (PEGMEM) (M = 950 g mol -1 , purchased from Aladdin, and the number of ether oxygen bonds is 19), 3-(trimethoxysilyl)propyl acrylate (TPA) (M = 234.32 g mol-1, purchased from Aladdin); MXene was purchased from jilin 11Technology Co., Ltd.

[0044] Example 1

[0045] Prepare the MXene hybrid polymer electrolyte according to the following steps.

[0046] Step (1): Dissolve 0.3 g of 3-(trimethoxysilyl)propyl acrylate and 0.3 g of MXene in a mixed solution of 90 ml of deionized water and 10 ml of alcohol, and obtain a mixed solution after ultrasonic dispersion for 5 min. Adjust the pH value of the mixed solution to 3.5 with formic acid, and then stir and react at 75 °C for 5 h under the protection of argon gas.

[0047] Step (2): After the reaction, collect the precipitate by centrifugation, wash the obtained solid with deionized water three times, and then dry it in a vacuum oven at 50 °C for 24 h. The sample is denoted as γ-TPA-g-MXene.

[0048] Step (3): Under the protection of argon gas, add 2 g of PEGMEM, 0.02 g of γ-TPA-g-Mxene and 0.017 g of AIBN to a three-necked flask containing 20 mL of ethyl acetate, react in a water bath at 70 °C for 8 h, and stir with a magnetic stirrer. After the simple radical polymerization reaction is complete, a viscous mixture PEGMEM-grafted MXene is obtained; the mass ratio of PEGMEM to γ-TPA-g-MXene is 100:1.

[0049] Step (4): Dissolve the mixed product obtained in step (3) in ethyl acetate and then precipitate it with petroleum ether. After washing three times in this way, a white transparent polymer is obtained, and then it is dried in a vacuum oven at 60 °C for 24 h.

[0050] Step (5): Dissolve 1 g of PEGMEM-grafted MXene and 0.287 of lithium bis(trifluoromethanesulfonyl)imide in 4 ml of tetrahydrofuran solution, stir at room temperature for 12 h, then pour into a polytetrafluoroethylene mold, and obtain the hybrid polymer electrolyte MXene-grafted NHPE through vacuum drying. At room temperature, the ionic conductivity is 1.42×10 -4 S / cm.

[0051] Example 2

[0052] The difference between this example and Example 1 is only that the mass of γ-TPA-g-MXene is changed to 0.04 g, and the mass ratio of PEGMEM to γ-TPA-g-MXene is 100:2, and the other conditions are the same.

[0053] At room temperature, the ionic conductivity is 2.04×10 -4 S / cm.

[0054] Example 3

[0055] The difference between this example and Example 1 is only that the mass of γ-TPA-g-MXene is changed to 0.06 g, and the mass ratio of PEGMEM to γ-TPA-g-MXene is 100:3, and the other conditions are the same.

[0056] At room temperature, the ionic conductivity is 3.44×10 -4 S / cm.

[0057] Example 4

[0058] The difference between this example and Example 1 is only that the mass of γ-TPA-g-MXene is changed to 0.08 g, and the mass ratio of PEGMEM to γ-TPA-g-MXene is 100:4, and the other conditions are the same.

[0059] At room temperature, the ionic conductivity is 1.89×10 -4 S / cm.

[0060] Example 5

[0061] The difference between this example and Example 1 is only that the mass of γ-TPA-g-MXene is changed to 0.18 g, and the mass ratio of PEGMEM to γ-TPA-g-MXene is 100:5, and the other conditions are the same.

[0062] At room temperature, the ionic conductivity is 1.43×10 -4 S / cm.

[0063] Comparative Example 1

[0064] This comparative example is a polymer electrolyte formed by a pure PEGMEM matrix through a simple radical polymerization reaction. The pure polymer electrolyte is prepared according to the following steps.

[0065] Step (1): Under the protection of argon gas environment, 2 g of PEGMEM and 0.013 g of AIBN were added to a three-necked flask containing 20 mL of ethyl acetate, and the reaction was carried out in a water bath at 70 °C for 8 h with magnetic stirring. After the simple radical polymerization reaction was complete, a viscous mixture was obtained. It was dissolved in ethyl acetate and then precipitated with petroleum ether. After washing three times in this way, a white transparent polymer was obtained, and then it was placed in a vacuum oven at 60 °C and dried for 24 h.

[0066] Step (2): 1 g of the PEGMEM polymer and 0.287 of lithium bis(trifluoromethanesulfonyl)imide were dissolved in 4 ml of tetrahydrofuran solution, stirred at room temperature for 12 h, and then poured into a polytetrafluoroethylene mold. After vacuum drying, a pure PEGMEM polymer electrolyte was obtained. At room temperature, the ionic conductivity was 4.56×10 -5 S / cm.

[0067] Comparative Example 2

[0068] Comparative Example 2 forms a polymer electrolyte by physically adding MXene on the basis of Comparative Example 1. A composite polymer electrolyte is prepared according to the following steps.

[0069] Step (1): Under the protection of argon gas environment, 2 g of PEGMEM, 0.06 g of MXene and 0.013 g of AIBN were added to a three-necked flask containing 20 mL of ethyl acetate, and the reaction was carried out in a water bath at 70 °C for 8 h with magnetic stirring. After the simple radical polymerization reaction was complete, a viscous mixture PEGMEN / MXene was obtained; the mass ratio of PEGMEM to MXene was 100:3. The polymerization reaction was the self-polymerization reaction of PEGMEM, and the added MXene was different from the addition method in the examples. MXene was not introduced by covalent bond, but by a simple physical blending method to introduce MXene into the polymer matrix.

[0070] Step (2): The mixed product obtained in Step (1) was dissolved in ethyl acetate and then precipitated with petroleum ether. After washing three times in this way, a white transparent polymer was obtained, and then it was placed in a vacuum oven at 60 °C and dried for 24 h.

[0071] Step (3): 1 g of PEGMEN / MXene and 0.287 of lithium bis(trifluoromethanesulfonyl)imide were dissolved in 4 ml of tetrahydrofuran solution, stirred at room temperature for 12 h, and then poured into a polytetrafluoroethylene mold. After vacuum drying, a nano-composite polymer electrolyte MXene-blended NHPE was obtained. At room temperature, the ionic conductivity was 3.8×10-5 S / cm.

Claims

1. A MXene hybrid polymer electrolyte, characterized in that: It includes MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer and lithium salt; The MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer has the structural formula of Formula 1: ； Formula 1; wherein, x is 15-25, and the ratio of m / n is (10-50):1; The MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer is obtained by free radical polymerization of MXene grafted 3-(trimethoxysilyl)propyl acrylate and polyethylene glycol methyl ether methacrylate; the MXene grafted 3-(trimethoxysilyl)propyl acrylate is obtained by hydrolysis and condensation reaction of 3-(trimethoxysilyl)propyl acrylate and MXene under acidic conditions; the mass ratio of 3-(trimethoxysilyl)propyl acrylate to MXene is 1:(1-5).

2. The MXene hybrid polymer electrolyte according to claim 1, wherein: The molar ratio of the MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer to the lithium salt is (15-20):

1.

3. A MXene hybrid polymer electrolyte according to claim 1 or 2, characterized in that: The lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

4. The preparation method of an MXene hybrid polymer electrolyte according to claim 1, 2 or 3, characterized in that: MXene grafted 3-(trimethoxysilyl)propyl acrylate and polyethylene glycol methyl ether methacrylate are subjected to free radical polymerization to obtain the MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer, and the MXene grafted 3-(trimethoxysilyl)propyl acrylate-polyethylene glycol methyl ether methacrylate random copolymer is mixed with the lithium salt to obtain the product.

5. The preparation method of an MXene hybrid polymer electrolyte according to claim 4, characterized in that: The mass ratio of the MXene grafted 3-(trimethoxysilyl)propyl acrylate to the polyethylene glycol methyl ether methacrylate is (1-5):

100.

6. The preparation method of an MXene hybrid polymer electrolyte according to claim 4, characterized in that: The conditions of the free radical polymerization reaction are: under a protective atmosphere, the polymerization reaction is initiated by an initiator, and the polymerization reaction is carried out at 60-80°C for 6-8 h.

7. The preparation method of an MXene hybrid polymer electrolyte according to claim 5 or 6, characterized in that: The MXene grafted 3-(trimethoxysilyl)propyl acrylate is obtained by hydrolysis and condensation reaction of 3-(trimethoxysilyl)propyl acrylate and MXene under acidic conditions.

8. The preparation method of an MXene hybrid polymer electrolyte according to claim 7, characterized in that: The mass ratio of 3-(trimethoxysilyl)propyl acrylate to MXene is 1:(1-5).

9. The preparation method of an MXene hybrid polymer electrolyte according to claim 7, wherein: The conditions of the hydrolysis and condensation reaction are: the temperature is 70-80°C, and the time is 5-7 h.

10. The preparation method of an MXene hybrid polymer electrolyte according to claim 7, characterized in that: The acidic condition means that the pH is 3-4.

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