Benzoxazine monomer containing long ether oxygen chain segment, resin and preparation method and application thereof

Abstract

The invention belongs to the technical field of electrolyte, and particularly relates to a benzoxazine monomer containing a long ether oxygen chain segment, resin and a preparation method and application of the benzoxazine monomer. A phenol source, an amine source and paraformaldehyde are used as raw materials; adding the mixture into a solvent, and synthesizing a benzoxazine monomer under the conditions of heating and reflux condensation; a structure capable of easily transmitting lithium ions is introduced to a benzoxazine chain segment, so that the novel benzoxazine which not only has the performance of traditional benzoxazine, but also has the capability of transmitting the lithium ions is obtained. The benzoxazine monomer is cured to obtain the benzoxazine resin, the benzoxazine resin adsorbs the electrolyte to prepare the gel polymer electrolyte, and under the synergistic effect of the special structure of benzoxazine and the electrolyte, the gel polymer electrolyte has room-temperature ionic conductivity superior to that of the electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and particularly relates to a benzoxazine monomer containing a long ether oxygen chain segment, a resin thereof, and a preparation method and application thereof. Background Art

[0002] In recent years, with the large-scale application of liquid electrolyte-based commercial lithium batteries, the defects of easy leakage, flammability, and explosiveness of liquid organic electrolytes make them unable to cope with some occasions with high safety performance requirements. Solid electrolytes have become the best choice to replace liquid organic electrolytes due to their advantages of high safety, high energy density, low self-discharge, and high temperature resistance. However, the low ionic conductivity and poor interfacial compatibility of solid electrolytes at room temperature have hindered their further development.

[0003] The gel polymer electrolyte composed of polymers and organic liquids has excellent ionic conductivity and interfacial compatibility, thus having extremely high application potential. Therefore, it is urgent to develop a gel polymer electrolyte that can replace or even outperform traditional commercial liquid organic electrolytes. Summary of the Invention

[0004] The first object of the present invention is to provide a benzoxazine monomer containing a long ether oxygen chain segment, and its structural formula is as follows: ; Wherein, n is the degree of polymerization of the ether oxygen chain segment, which are 7, 35, and 86 respectively, and m is the degree of polymerization of the benzoxazine monomer, which is about 2 - 3.

[0005] The second object of the present invention is to provide a preparation method of a benzoxazine monomer containing a long ether oxygen chain segment, using a phenol source, an amine source, and paraformaldehyde as raw materials; putting them into a solvent, and synthesizing benzoxazine under heating and reflux conditions. The phenol source has the structure shown in formula (Ⅰ): Formula (Ⅰ); In formula (I), R1, R2, R3, and R4 are each independently selected from a hydrogen atom, a hydroxyl group, a carboxyl group, a nitro group, a halogen, a substituted or unsubstituted alkyl group, an olefin group, an ester group, an alkoxy group, a phenyl group, and a naphthyl group; The amine source has the structure shown in formula (Ⅱ): Formula (Ⅱ); In formula (Ⅱ), R is a long-chain structure, which may contain one or more of -CH 2 CH 2 O-, -COO-, O-COO-, -Si-O.

[0006] The third object of the present invention is to provide a benzoxazine resin, and its structural formula is as follows: ; Among them, n is the degree of polymerization of the ether oxygen chain segment, and m is the degree of polymerization of the benzoxazine monomer.

[0007] The fourth object of the present invention is to provide a preparation method of a benzoxazine resin, heating and curing the benzoxazine monomer; under the condition of stepwise heating, the oxazine ring in the benzoxazine monomer will open, so as to carry out chain polymerization to obtain a benzoxazine resin with a cross-linked network structure.

[0008] The fifth object of the present invention is to provide the application of the benzoxazine resin in the preparation of a gel polymer electrolyte.

[0009] The sixth object of the present invention is the application of the benzoxazine resin in the preparation of a lithium battery.

[0010] The seventh object of the present invention is to provide a preparation method of a lithium battery, using a surface treatment agent to modify the surface of lithium metal; using the benzoxazine resin to prepare a gel polymer electrolyte, and assembling the gel polymer electrolyte with the modified lithium metal to obtain a lithium battery, promoting the lithium battery to have ultra-long cycle stability.

[0011] Specifically, the surface treatment agent has the structure shown in formula (Ⅲ): Formula (Ⅲ); In formula (Ⅲ), Y is an organic functional group, including amino group, epoxy group, vinyl group, mercapto group, methacryloxy group; X is a hydrolyzable group, such as methoxy group, ethoxy group and chloro group; n = 0 - 3.

[0012] Specifically, the surface treatment agent has the structure shown in formula (Ⅳ): Formula (Ⅳ); In formula (Ⅳ), R is an alkane chain segment, which can be a fluorinated alkane chain, a nitrogen-containing alkane chain, etc.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The benzoxazine monomer used in the present invention for preparing the gel polymer matrix material is simple to synthesize, easy to implement, the raw materials are cheap, the cost is low, and it is suitable for large-scale industrial production.

[0014] (2) The monomer curing process prepared by the present invention is simple, and the required curing temperature is different from that of traditional benzoxazines. The oxazine ring can open at a lower temperature range to form a cross-linked network structure, which can improve the mechanical properties of the benzoxazine resin.

[0015] (3) In the present invention, based on the molecular structure design concept, by regulating the structure of the amine source in the synthesis of benzoxazine monomers, a long ether oxygen chain segment is introduced into the polymer main chain structure, thereby enabling benzoxazine to have an extremely low glass transition temperature and making it suitable for the electrolyte field.

[0016] (4) In the present invention, the cured benzoxazine resin has a long ether oxygen chain segment and a cross-linked structure. The former can promote the adsorption of the electrolyte, and the latter can "lock" the adsorbed electrolyte, and it can adsorb organic solvents far higher than its own mass.

[0017] (5) In the present invention, due to the synergistic effect between the long ether oxygen chain segment and the electrolyte in the process of transporting lithium ions in the benzoxazine gel polymer electrolyte after adsorbing the electrolyte, the gel polymer electrolyte in the present invention has an ionic conductivity higher than that of the electrolyte itself.

[0018] (5) In the present invention, the lithium sheet is modified by a surface treatment agent, including treating the surface of lithium metal with surface treatment agents such as silane coupling agent and heptafluorobutyric acid. It can not only remove the "destructive molecules" on the surface of lithium metal, but also form an "artificial solid interface layer" that promotes the uniform deposition of lithium ions, so that the lithium sheet and the novel benzoxazine-based gel polymer electrolyte described above have excellent interfacial compatibility, and thus the modified lithium sheet and the benzoxazine-based gel polymer electrolyte prepared in the present invention are assembled into a battery with excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 It is a physical diagram of the benzoxazine monomer synthesized in Example 1 of the present invention.

[0021] Figure 2 It is a Fourier transform infrared spectrum diagram of the benzoxazine monomer synthesized in Example 1 of the present invention.

[0022] Figure 3 It is a nuclear magnetic resonance hydrogen spectrum of the benzoxazine monomer synthesized in Example 1 of the present invention.

[0023] Figure 4 It is a physical diagram of the benzoxazine resin after the monomer is heated and cured in Example 2 of the present invention.

[0024] Figure 5 It is a Fourier transform infrared spectrum diagram of the benzoxazine resin in Example 2 of the present invention.

[0025] Figure 6 It is the thermal analysis curve of the benzoxazine resin in Example 2 of the present invention.

[0026] Figure 7 It is a physical picture of the benzoxazine-based gel polymer electrolyte in Example 3 of the present invention

[0027] Figure 8 It is the ionic conductivity of the benzoxazine-based gel polymer electrolyte in Example 3 of the present invention at different temperatures.

[0028] Figure 9 It is a schematic diagram of treating the lithium metal surface with a silane coupling agent in Example 4 of the present invention.

[0029] Figure 10 It is the Fourier infrared spectrum of the lithium metal surface before and after modification in Example 4 of the present invention.

[0030] Figure 11 It is the infrared spectrum of the lithium metal surface before and after treatment with heptafluorobutyric acid in Example 5 of the present invention.

[0031] Figure 12 It is the long cycle data of the lithium symmetric based on the benzoxazine-based gel polymer electrolyte in Example 6 of the present invention.

[0032] Figure 13 It is the long cycle data of the lithium battery based on the benzoxazine-based gel polymer electrolyte in Example 6 of the present invention. Detailed implementation manners

[0033] In view of the defects of the prior art, through long-term research and a large number of practices by the inventors of this case, the technical solution of the present invention has been proposed. The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0034] The design principle of the present invention lies in that: polymer electrolytes mainly conduct lithium ions through the movement of chain segments, and the movement ability of chain segments affects the ionic conductivity of the electrolyte. Introducing a structure with excellent lithium ion transport ability into the polymer chain segment through molecular structure design is an important means to improve the electrochemical performance of polymer electrolytes. Utilizing the structural designability of benzoxazine, an ether oxygen chain segment that is easy to combine with lithium ions is introduced into its chain segment, so that the benzoxazine resin with excellent properties itself has the ability to transport lithium ions. At the same time, due to the presence of the ether oxygen chain segment and the cross-linked structure formed by the curing of benzoxazine, it has excellent advantages in adsorbing and fixing electrolytes.

[0035] Meanwhile, since lithium metal inevitably comes into contact with air, lithium hydroxide, lithium carbonate, and lithium oxide will exist on the surface of lithium metal. These substances will not only hinder the transmission of lithium ions but also inevitably react with the electrolyte as a side reaction, resulting in a rapid decline in battery performance. By reacting the surface treatment agent with lithium hydroxide, lithium carbonate, and lithium oxide, not only can these 'troublemakers' be removed, but also some special structures can be introduced on the surface of lithium metal through the structure of the surface treatment agent, thereby improving the overall performance of the lithium battery.

[0036] Specifically, as an aspect of the technical solution of the present invention, the preparation method of the benzoxazine monomer involved includes: using a phenol source, an amine source, and an aldehyde source as raw materials, synthesizing the benzoxazine monomer through a Mannich reaction, and then obtaining the benzoxazine resin through heat curing.

[0037] In some preferred embodiments, the phenol source has the structure shown in formula (Ⅰ): Formula (Ⅰ); In formula (I), R1, R2, R3, and R4 are each independently selected from a hydrogen atom, a hydroxyl group, a carboxyl group, a nitro group, a halogen, a substituted or unsubstituted alkyl group, an alkenyl group, an ester group, an alkoxy group, a phenyl group, and a naphthyl group.

[0038] In some preferred embodiments, the amine source has the structure shown in formula (Ⅱ): Formula (Ⅱ); In formula (Ⅱ), R is a long-chain structure, which may include -CH 2 CH 2 O-, -COO-, O-COO-, -Si-O, or one or more of them.

[0039] Another aspect of the technical solution of the present invention is the surface modification of the lithium sheet: soaking the lithium sheet metal in a mixed solution of the surface treatment agent and tetrahydrofuran, or dropping the mixed solution of the surface treatment agent and tetrahydrofuran on the surface of the lithium sheet, so as to obtain a modified lithium sheet on the surface of the surface treatment agent and the lithium sheet.

[0040] In some preferred embodiments, the surface treatment agent has the structures shown in formula (Ⅲ) and formula (Ⅳ): Formula (Ⅲ); In formula (Ⅲ), Y is an organic functional group, including an amino group, an epoxy group, a vinyl group, a mercapto group, and a methacryloyloxy group; X is a hydrolyzable group, such as a methoxy group, an ethoxy group, and a chloro group.

[0041] Formula (Ⅳ); In formula (IV), R is an alkane chain segment, which can be a fluorinated alkane chain, a nitrogen-containing alkane chain, etc.

[0042] The technical solutions of the present invention will be further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not limit it in any way. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the equipment or raw material manufacturers. Example 1

[0043] (1) Synthesis: First, 0.02 mol of 3,4-dihydrocoumarin and 0.04 mol of polyetheramine 400 were added to a mixed solvent of 100 mL of ethyl acetate, 50 mL of ethanol, and 50 mL of acetonitrile, and the reaction was refluxed under condensation at 80 °C for 24 h; then 0.1 mol of paraformaldehyde powder was added to the mixed solution and the reaction was continued for 24 h; the obtained mixed solution was subjected to vacuum solvent removal at 80 °C, and then a crude product of benzoxazine monomer containing a long ether oxygen chain segment was obtained. ; Among them, the amine source types are polyetheramine 400, polyetheramine 2000, and polyetheramine 5000.

[0044] (2) Purification: The crude product obtained in step (1) was dissolved in dichloromethane solvent, and the organic solvent containing benzoxazine monomer was washed with 2 mol / L sodium hydroxide solution three times, and then washed with deionized water three times. (3) Drying: The organic solvent obtained in step (2) was dried with anhydrous sodium sulfate and anhydrous calcium sulfate in turn for 24 h; then the organic layer was filtered, and the organic solvent was removed by vacuum distillation at 50 °C to obtain benzoxazine monomer.

[0045] According to different amine source types, three kinds of benzoxazine monomers were obtained, which were respectively denoted as benzoxazine 400, benzoxazine 2000, and benzoxazine 5000. Figure 1 It is a physical picture of the synthesized monomer. The three kinds of benzoxazine monomers prepared in this Example 1 were characterized and analyzed. Figure 2 It is the Fourier infrared spectrum of the three kinds of benzoxazine monomers. Figure 3 It is the nuclear magnetic resonance hydrogen spectrum of the three kinds of benzoxazine monomers (-CH 3 1.23 - 1.09 ppm, -CH- 3.10 - 3.07 ppm, -CH2 - 3.61 - 3.39 ppm, -NH- 4.08 - 4.10 ppm, -CH 2 - 2.83, 2.54 - 2.37 ppm, -OCH 2 N- 4.91 - 4.94 ppm, -PhCH 2 N- 4.02 - 4.04 ppm, Aromatic ring 6.90 - 7.74 ppm). Example 2

[0046] The synthesized benzoxazine monomer was heated and cured. Under the conditions of stepwise heating (80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h), the oxazine ring in the benzoxazine monomer would open, and thus segmental polymerization would occur to obtain a benzoxazine resin with a crosslinked network structure. Due to the presence of long ether oxygen chain segments, benzoxazine has an extremely low glass transition temperature.

[0047] ; Figure 4 This is the benzoxazine resin film after the curing of the benzoxazine monomer. The cured benzoxazine resin film was characterized and analyzed. Figure 5 This is the Fourier transform infrared spectrum of the benzoxazine resin film. Among them, the characteristic absorption peak of the oxazine ring at 923 cm -1 disappeared, indicating that the oxazine ring had undergone a ring-opening reaction and formed a chemically crosslinked structure. Figure 6 This is the DSC curve of the benzoxazine resin film. It can be seen that when the molecular weights of the ether oxygen chain segments are 400, 2000, and 5000, the glass transition temperatures of the benzoxazine monomers are -2.69 °C, -36.53 °C, and -41.41 °C respectively, indicating that the longer the ether oxygen chain segment, the lower the glass transition temperature of the benzoxazine monomer. Example 3

[0048] The cured benzoxazine resin film was immersed in the electrolyte until the adsorption swelling equilibrium was reached, and then taken out and left to stand for 12 h to volatilize, to prepare a gel polymer electrolyte. Subsequently, the ionic conductivity of the gel polymer electrolyte was tested. Figure 7 This is a physical picture of the gel polymer electrolyte. Figure 8 This is the ionic conductivity of the gel polymer electrolyte at different temperatures. Among them, the ionic conductivity of the polybenzoxazine gel electrolyte with an ether oxygen chain segment of 2000 is 9.62 mS·cm -1 , which is higher than that of the commercial electrolyte of 8.05 mS·cm -1。The ionic conductivities of polybenzoxazine gel electrolytes with ether chain segments of 400 and 5000 are 0.0698 mS·cm -1 and 2.57 mS·cm -1 。 Example 4

[0049] The silane coupling agent was uniformly blended with tetrahydrofuran in a certain volume ratio. Subsequently, the lithium sheet was immersed in the mixed solution for a period of time, and then the residual mixed solution on the surface of the lithium sheet was removed by heating at a certain temperature to obtain a modified lithium sheet. Among them, the volume ratios of the silane coupling agent to tetrahydrofuran were 9:1, 14:1, 19:1, 24:1, and 29:1, the immersion time was 12 h, the heating temperature was 100 °C, and the heating time was 2 h. Figure 9 It is a modification schematic diagram. Figure 10 It is the Fourier infrared spectrogram of the lithium metal surface before and after modification. It can be seen that after modification with the silane coupling agent, characteristic absorption peaks of Si-O-Si appear at 1192.3 cm -1 and 1084.8 cm -1 , indicating that the silane coupling agent successfully modified the surface of the lithium metal. Example 5

[0050] Heptafluorobutyric acid and tetrahydrofuran were stirred and blended in a certain mass ratio. A certain volume of the blended solution was selected with a pipette and dropped on the surface of the lithium sheet, and volatilized for a period of time to obtain a modified lithium sheet. Among them, the mass ratio of heptafluorobutyric acid to tetrahydrofuran was 9:1, the volume of the selected blended solution was 100 µL, and the volatilization time was 12 h. Figure 11 is the infrared spectrogram of the lithium sheet before and after modification. It can be seen that a new absorption peak appears at 1730 cm -1 on the surface of the modified lithium metal, indicating that heptafluorobutyric acid successfully modified the lithium metal. Example 6

[0051] The gel polymer electrolyte, modified lithium metal, and lithium iron phosphate cathode were assembled into a lithium battery, and then its long-term cycling performance was tested. Figure 12 It is the long-term cycling data of the lithium symmetric battery. It can be seen that after cycling for 1480 hours, the overpotential of the polybenzoxazine gel electrolyte with an ether chain segment molecular weight of 2000 is only 45 mV. As the cycling progresses, the overpotential gradually increases, but it still does not exceed 300 mV, and the operating time is close to 3000 h. Figure 13 It is the long-term cycling performance of the lithium iron phosphate lithium battery LFP|PBz-EO-GPE2000|KH560-Li. At room temperature, after cycling 1800 times at a rate of 2C, the charge-discharge capacity of the full battery decreased from 138.06 mAh·g -1 to 97.38 mAh·g -1, the capacity retention rate is 70.5%.

[0052] All aspects, embodiments, features and examples of the present invention should be considered illustrative in all respects and are not intended to limit the present invention, the scope of which is defined only by the claims. Without departing from the spirit and scope of the claimed invention, those skilled in the art will appreciate other embodiments, modifications and uses.

[0053] Although the present invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions and / or additions can be made without departing from the spirit and scope of the present invention and elements of the embodiments can be replaced with substantial equivalents. Additionally, many modifications can be made to adapt a particular situation or material to the teachings of the present invention without departing from the scope of the present invention. Accordingly, it is not intended that the present invention be limited to the particular embodiments disclosed for carrying out the present invention, but rather that the present invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A benzoxazine monomer containing a long ether oxygen chain segment, characterized in that the structural formula as follows: ； Wherein, n is the degree of polymerization of the ether oxygen segment, and m is the degree of polymerization of the benzoxazine monomer.

2. A method for preparing the benzoxazine monomer according to claim 1, characterized in that: A phenol source, an amine source and polyformaldehyde are used as raw materials; the raw materials are put into a solvent and a benzoxazine monomer is synthesized under heating and condensation reflux conditions; The phenol source has a structure as shown in formula (I): Formula (I); In formula (I), R1, R2, R3 and R4 are independently selected from hydrogen atom, hydroxyl group, carboxyl group, nitro group, halogen group, substituted or unsubstituted alkyl group, olefin group, ester group, alkoxy group, phenyl group and naphthyl group; The amine source has a structure as shown in formula (II): Formula (II); In formula (II), R is a long chain structure, which includes one or more of -CH2CH2O-, -COO-, O-COO-, and -Si-O.

3. A benzoxazine resin, characterized in that the structural formula as follows: ； Wherein, n is the degree of polymerization of the ether oxygen segment, and m is the degree of polymerization of the benzoxazine monomer.

4. A method for preparing the benzoxazine resin according to claim 3, characterized in that: The benzoxazine monomer of claim 1 is heated and cured; under the condition of step-wise heating, the oxazine ring in the benzoxazine monomer is opened, thereby performing segmental polymerization to obtain a benzoxazine resin having a cross-linked network structure.

5. Use of the benzoxazine resin according to claim 3 in preparing a gel polymer electrolyte.

6. Use of the benzoxazine resin according to claim 3 in the preparation of lithium batteries.

7. A method for preparing a lithium battery, characterized in that: The surface of lithium metal is modified by using a surface treatment agent; a gel polymer electrolyte is prepared by using a benzoxazine resin, and the gel polymer electrolyte is assembled with the modified lithium metal to obtain a lithium battery.

8. The preparation method according to claim 7, characterized in that: The surface treatment agent has a structure as shown in formula (III): Formula (III); In formula (III), Y is an organic functional group, including any one or more of amino, epoxy, vinyl, mercapto, and methacryloyloxy; X is a hydrolyzable group; and n=0-3.

9. The preparation method according to claim 7, characterized in that: The surface treatment agent has a structure as shown in formula (IV): Formula (IV); In formula (IV), R is an alkane chain segment.

Images