Benzoxazine monomers, resins containing long ether oxygen segments, and methods of making and using the same

Abstract

The application belongs to the technical field of electrolyte, and particularly relates to a benzoxazine monomer containing long ether oxygen chain segments, a benzoxazine resin, and a preparation method and application thereof. The application takes a phenol source, an amine source and paraformaldehyde as raw materials, and synthesizes a benzoxazine monomer in a solvent under heating and condensation reflux conditions. The application introduces a structure easy to transport lithium ions on a benzoxazine chain segment, thereby obtaining a new type of benzoxazine which has both the performance of traditional benzoxazine and the ability to transport lithium ions. The application solidifies the benzoxazine monomer to obtain a benzoxazine resin, and absorbs an electrolyte to form a gel polymer electrolyte. Under the synergistic action of the special structure of the benzoxazine and the electrolyte, the gel polymer electrolyte has a room temperature ionic conductivity beyond that of the electrolyte.

Description

TECHNICAL FIELD

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

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

[0003] Gel polymer electrolytes composed of polymers and organic liquids have excellent ion conductivity and interface compatibility, and thus have 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

[0004] A first object of the application is to provide a benzoxazine monomer containing a long ether oxygen chain segment, which has the following structural formula:

[0005] ;

[0006] In the formula, n is the polymerization degree of the ether oxygen chain segment, and is 7, 35 and 86 respectively, and m is the polymerization degree of the benzoxazine monomer, and is about 2-3.

[0007] A second object of the application is to provide a preparation method of the benzoxazine monomer containing a long ether oxygen chain segment, which uses a phenol source, an amine source and paraformaldehyde as raw materials, and synthesizes benzoxazine under the conditions of heating and condensation reflux in a solvent.

[0008] The phenol source has the structure shown in formula (I):

[0009] Formula (I);

[0010] 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.

[0011] The amine source has the structure shown in formula (II):

[0012] Formula (II);

[0013] In formula (II), R is a long chain structure, which can contain one or more of -CH2CH2O-, -COO-, O-COO-, -Si-O.

[0014] A third object of the present application is to provide a benzoxazine resin, which has the following structural formula:

[0015] ;

[0016] In formula (II), R is a long chain structure, which can contain one or more of -CH2CH2O-, -COO-, O-COO-, -Si-O.

[0017] A fourth object of the present application is to provide a preparation method of the benzoxazine resin, which heats and solidifies the benzoxazine monomer; under the condition of stepwise heating, the oxazine ring in the benzoxazine monomer is opened to perform chain segment polymerization, so as to obtain the benzoxazine resin with a crosslinked network structure.

[0018] A fifth object of the present application is to provide an application of the benzoxazine resin in preparing a gel polymer electrolyte.

[0019] A sixth object of the present application is to provide an application of the benzoxazine resin in preparing a lithium battery.

[0020] A seventh object of the present application is to provide a preparation method of a lithium battery, which modifies the surface of lithium metal by using a surface treatment agent; prepares a gel polymer electrolyte by using the benzoxazine resin, and assembles the gel polymer electrolyte with the modified lithium metal, so as to obtain the lithium battery, which has super-long cycle stability.

[0021] Specifically, the surface treatment agent has a structure as shown in formula (III):

[0022] Formula (III);

[0023] In formula (III), Y is an organic functional group, including an amino group, an epoxy group, a vinyl group, an alkoxy group, and a methacryloyloxy group; X is a hydrolysable group, such as a methoxy group, an ethoxy group, and a chloro group; and n=0-3.

[0024] Specifically, the surface treatment agent has a structure as shown in formula (IV):

[0025] Formula (IV);

[0026] In formula (IV), R is an alkane chain segment, which can be a fluorine-containing alkane chain, a nitrogen-containing alkane chain, etc.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) The benzoxazine monomer for preparing the gel polymer matrix material is simple in synthesis, easy to implement, cheap in raw materials, low in cost and suitable for large-scale industrial production.

[0029] (2) The monomer prepared by the method has a simple curing process, and the curing temperature required is lower than that of traditional benzoxazine. The ring-opening of the oxazine ring can occur in a lower temperature range to form a crosslinked network structure, thereby improving the mechanical properties of the benzoxazine resin.

[0030] (3) According to the molecular structure design concept, the structure of the amine source in the synthesis of the benzoxazine monomer is regulated, and a long ether oxygen segment is introduced into the polymer main chain structure, so that the benzoxazine has a very low glass transition temperature, and is suitable for the electrolyte field.

[0031] (4) The cured benzoxazine resin has a long ether oxygen segment and a crosslinked structure. The former can promote the adsorption of the electrolyte, and the latter can 'lock' the adsorbed electrolyte, and can adsorb organic solvents much higher than its own mass.

[0032] (5) The benzoxazine gel polymer electrolyte after adsorbing the electrolyte has a synergistic effect between the long ether oxygen segment and the electrolyte in the process of transporting lithium ions, so that the gel polymer electrolyte has a higher ionic conductivity than the electrolyte itself.

[0033] (5) The lithium sheet is modified by a surface treatment agent in the application, including using a silane coupling agent and a heptafluorobutyric acid surface treatment agent to treat the surface of the lithium metal. The 'destructive molecules' on the surface of the lithium metal can be removed, and an 'artificial solid interface layer' that promotes uniform deposition of lithium ions can be formed, so that the lithium sheet has excellent interface compatibility with the new benzoxazine-based gel polymer electrolyte described above, and the modified lithium sheet and the benzoxazine-based gel polymer electrolyte prepared in the application have excellent cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0035] Figure 1 is the actual picture of the benzoxazine monomer synthesized in embodiment 1 of the present application.

[0036] Figure 2 is the Fourier infrared spectrum of the benzoxazine monomer synthesized in embodiment 1 of the present application.

[0037] Figure 3 is the nuclear magnetic resonance hydrogen spectrum of the synthesized benzoxazine monomer in Example 1 of the present application.

[0038] Figure 4 is the physical picture of the benzoxazine resin after the monomer is cured by heating in Example 2 of the present application.

[0039] Figure 5 is the Fourier infrared spectrum of the benzoxazine resin in Example 2 of the present application.

[0040] Figure 6 is the thermal analysis curve of the benzoxazine resin in Example 2 of the present application.

[0041] Figure 7 is the physical picture of the benzoxazine-based gel polymer electrolyte in Example 3 of the present application

[0042] Figure 8 is the ionic conductivity of the benzoxazine-based gel polymer electrolyte at different temperatures in Example 3 of the present application.

[0043] Figure 9 is a schematic diagram of treating the surface of lithium metal with a silane coupling agent in Example 4 of the present application.

[0044] Figure 10 is the Fourier infrared spectrum of the surface of lithium metal before and after modification in Example 4 of the present application.

[0045] Figure 11 is the infrared spectrum before and after treating the surface of lithium metal with heptafluorobutyric acid in Example 5 of the present application.

[0046] Figure 12 is the lithium symmetric long cycle data based on the benzoxazine-based gel polymer electrolyte in Example 6 of the present application.

[0047] Figure 13 is the long cycle data of the lithium battery based on the benzoxazine-based gel polymer electrolyte in Example 6 of the present application. DETAILED DESCRIPTION

[0048] In view of the defects of the prior art, the present inventors have long studied and practiced to come up with the technical solution of the present application, which will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0049] The design principle of the present application is that the polymer electrolyte mainly transmits lithium ions through the movement of chain segments, and the movement ability of the chain segments affects the size of the electrolyte ion conductivity. Introducing a structure with excellent lithium ion transmission ability into the polymer chain segment through molecular structure design is an important means to improve the electrochemical performance of the polymer electrolyte. The ether oxygen chain segment which is easy to combine with lithium ions is introduced into the chain segment by using the designability of the structure of benzoxazine, so that the benzoxazine resin with excellent performance itself has lithium ion transmission ability. At the same time, due to the presence of the ether oxygen chain segment and the crosslinked structure of the benzoxazine curing, it has excellent advantages in adsorbing and fixing electrolyte.

[0050] At the same time, since the lithium metal inevitably contacts with the air, lithium hydroxide, lithium carbonate and lithium oxide exist on the surface of the lithium metal, which not only hinders the transmission of lithium ions, but also inevitably causes side reactions with the electrolyte, thereby causing the performance of the battery to rapidly decrease. By reacting the surface treatment agent with lithium hydroxide, lithium carbonate and lithium oxide, not only can these 'destructive molecules' be removed, but also some special structures can be introduced on the surface of the lithium metal through the structure of the surface treatment agent, thereby improving the overall performance of the lithium battery.

[0051] Specifically, as one aspect of the technical scheme of the present application, the preparation method of the benzoxazine monomer includes: using a phenol source, an amine source and an aldehyde source as raw materials, synthesizing a benzoxazine monomer through a Mannich reaction, and then obtaining a benzoxazine resin through heating curing.

[0052] In some preferred embodiments, the phenol source has a structure as shown in formula (I):

[0053] Formula (I);

[0054] 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.

[0055] In some preferred embodiments, the amine source has a structure as shown in formula (II):

[0056] Formula (II);

[0057] In formula (II), R is a long chain structure which can contain one or more of -CH2CH2O-, -COO-, O-COO-, -Si-O.

[0058] Another aspect of the technical solution of the present application is the modification of the surface of lithium sheet: the lithium sheet metal is soaked in a mixed solution of surface treatment agent and tetrahydrofuran, or the mixed solution of surface treatment agent and tetrahydrofuran is dropped on the surface of the lithium sheet, and the surface treatment agent and the surface of the lithium sheet are thus modified to obtain the modified lithium sheet.

[0059] In some preferred embodiments, the surface treatment agent has a structure as shown in Formula (III) or Formula (IV):

[0060] Formula (III);

[0061] In Formula (III), Y is an organic functional group, including amino, epoxy, vinyl, mercapto, and methacryloxy; and X is a hydrolysable group, such as methoxy, ethoxy, and chloro.

[0062] Formula (IV);

[0063] In Formula (IV), R is an alkane segment, which can be a fluorine-containing alkane chain, a nitrogen-containing alkane chain, etc.

[0064] The technical solution of the present application will be further described in detail below in combination with several preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. It should be noted that the following described embodiments are intended to facilitate the understanding of the present application, and do not have any limiting effect on the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application. The experimental methods not specified in the following embodiments are usually carried out according to the conventional conditions, or according to the conditions suggested by the equipment or raw material manufacturers.

[0065] Embodiment 1

[0066] (1) Synthesis: first, 0.02 mol of 3,4-dihydrocoumarin and 0.04 mol of polyetheramine 400 are added to a mixed solvent of 100 mL of ethyl acetate, 50 mL of ethanol, and 50 mL of acetonitrile, and the mixture is subjected to condensation reflux reaction at 80°C for 24 h; then 0.1 mol of polyformaldehyde powder is added to the mixture, and the reaction is continued for 24 h; the obtained mixture is subjected to vacuum solvent removal at 80°C, and then a crude product of benzoxazine monomer containing long ether oxygen chain segments is obtained;

[0067] ;

[0068] The amine source type is polyetheramine 400, polyetheramine 2000, or polyetheramine 5000.

[0069] (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;

[0070] (3) Drying: the organic solvent obtained in step (2) was dried with anhydrous sodium sulfate and anhydrous calcium sulfate in turn, and the drying time was 24 h; then the organic layer was obtained by filtration, and the organic solvent was removed by vacuum distillation at a temperature of 50°C, to obtain the benzoxazine monomer.

[0071] According to the different types of amine sources, three kinds of benzoxazine monomers were obtained, which were respectively denoted as benzoxazine 400, benzoxazine 2000 and benzoxazine 5000. Figure 1 The three kinds of benzoxazine monomers prepared in Example 1 were characterized and analyzed. Figure 2 The Fourier infrared spectrum of the three kinds of benzoxazine monomers is shown in Figure 2, Figure 3 The nuclear magnetic hydrogen spectrum of the three kinds of benzoxazine monomers is shown in Figure 3 (-CH3 1.23-1.09 ppm, -CH- 3.10-3.07 ppm, -CH2- 3.61-3.39 ppm, -NH- 4.08-4.10 ppm, -CH2- 2.83, 2.54-2.37 ppm, -OCH2N- 4.91-4.94 ppm, -PhCH2N- 4.02-4.04 ppm, Aromatic ring 6.90-7.74 ppm).

[0072] Example 2

[0073] The synthesized benzoxazine monomer was heated and cured. Under the condition 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 was opened, thereby performing chain segment polymerization to obtain a benzoxazine resin with a crosslinked network structure. Due to the presence of long ether oxygen chain segments, the benzoxazine has a very low glass transition temperature.

[0074] ;

[0075] Figure 4 The benzoxazine resin film after curing of the benzoxazine monomer is shown in Figure 4. The cured benzoxazine resin film was characterized and analyzed. Figure 5 The Fourier infrared spectrum of the benzoxazine resin film is shown in Figure 5. Among them, the characteristic absorption peak of the oxazine ring at 923 cm -1 disappeared, indicating that the oxazine ring has undergone ring-opening reaction and formed a chemical crosslinked structure. Figure 6DSC curves of benzoxazine resin film, it can be seen that the glass transition temperature of benzoxazine monomer with ether oxygen chain segment molecular weight of 400, 2000 and 5000 is -2.69℃, -36.53℃ and -41.41℃ respectively, which shows that the longer the ether oxygen chain segment, the lower the glass transition temperature of benzoxazine monomer.

[0076] Example 3

[0077] The cured benzoxazine resin film is immersed in electrolyte until adsorption and swelling equilibrium is reached, and then it is taken out and left to volatilize for 12 h to prepare a gel polymer electrolyte, and then the ionic conductivity of the gel polymer electrolyte is tested. Figure 7 It is a physical diagram of the gel polymer electrolyte. Figure 8 It is the ionic conductivity of the gel polymer electrolyte at different temperatures. Among them, the ionic conductivity of the polybenzoxazine gel electrolyte with ether oxygen chain segment of 2000 is 9.62 mS·cm -1 , higher than that of the commercial electrolyte of 8.05 mS·cm -1 . While the ionic conductivity of the polybenzoxazine gel electrolyte with ether chain segment of 400 and 5000 is 0.0698 mS·cm -1 and 2.57 mS·cm -1 .

[0078] Example 4

[0079] The silane coupling agent is uniformly blended with tetrahydrofuran in a certain volume ratio, then the lithium sheet is soaked in the mixed solution for a period of time, and then heated at a certain temperature to remove the residual mixed solution on the surface of the lithium sheet to obtain a modified lithium sheet. Among them, the volume ratio of silane coupling agent to tetrahydrofuran is 9:1, 14:1, 19:1, 24:1 and 29:1, the soaking time is 12 h, and the heating temperature is 100℃, and the heating time is 2 h. Figure 9 It is a modification diagram. Figure 10 It is the Fourier infrared spectrum of the surface of lithium metal before and after modification. It can be seen that after modification by silane coupling agent, the lithium metal sheet appears characteristic absorption peaks of Si-O-Si at 1192.3 cm -1 and 1084.8 cm -1 , which shows that the surface of lithium metal is successfully modified by silane coupling agent.

[0080] Example 5

[0081] The heptafluorobutyric acid and tetrahydrofuran are stirred and blended in a certain mass ratio, a certain volume of the blended liquid is selected by using a pipette and dropped on the surface of lithium sheet, and then volatilized for a period of time to obtain modified lithium sheet. The mass ratio of heptafluorobutyric acid to tetrahydrofuran is 9:1, the volume of the blended liquid is 100 µL, and the volatilization time is 12 h. FIG. 11 is the infrared spectrum 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, which is considered that the heptafluorobutyric acid successfully modifies the lithium metal.

[0082] Example 6

[0083] The gel polymer electrolyte and the modified lithium metal are assembled into a lithium battery with a lithium iron phosphate positive electrode, and then the long cycle performance test is carried out. Figure 12 The long cycle data of the lithium symmetric battery. It can be seen that the polybenzoxazine gel electrolyte with an ether chain segment molecular weight of 2000 has an overpotential of only 45 mV after 1480 hours of cycling. As the cycle progresses, the overpotential gradually increases, but still does not exceed 300 mV, and the running time is close to 3000 h. Figure 13 The long cycle performance of the lithium iron phosphate lithium battery LFP|PBz-EO-GPE2000|KH560-Li. After 1800 cycles at a rate of 2C at room temperature, the charge and discharge capacity of the full battery decreases from 138.06 mAh·g -1 to 97.38 mAh·g -1 , and the capacity retention rate is 70.5%.

[0084] Aspects, embodiments, features, and examples of the present application should be considered illustrative in all aspects and are not intended to limit the application, the scope of which is defined only by the claims. Those skilled in the art will understand other embodiments, modifications and uses as well as substitutions and equivalents without departing from the spirit and scope of the claimed application.

[0085] Although the present application 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 and elements of the described embodiments can be substituted with substantial equivalents without departing from the spirit and scope of the present application. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the present application without departing from the scope thereof. Therefore, the present application is not intended to be limited to the disclosed embodiments for carrying out the present application, but rather is intended to encompass all embodiments falling within the scope of the claims appended hereto.

Claims

1. A benzoxazine monomer containing a long ether oxygen segment, characterized by the following structural formula: As follows: ； Wherein, n is the polymerization degree of ether oxygen segment, respectively 7, 35 and 86; m is the polymerization degree of benzoxazine monomer, 2-3.

2. A process for the preparation of the benzoxazine monomer of claim 1, characterized by, The phenol source, amine source and paraformaldehyde are used as raw materials, and the benzoxazine monomer is synthesized by being put into a solvent 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 all hydrogen atoms; The amine source has a structure as shown in formula (II): Formula (II); In formula (II), R is .

3. A benzoxazine resin characterized by, The benzoxazine monomer of claim 1 is heated and cured.

4. A process for the preparation of the benzoxazine resin of claim 3, characterized by, The benzoxazine monomer of claim 1 is heated and cured; under the condition of stepwise heating, the oxazine ring in the benzoxazine monomer is opened to perform chain segment polymerization, so that the benzoxazine resin with crosslinked network structure is obtained.

5. Use of the benzoxazine resin of claim 3 in the preparation of a gel polymer electrolyte.

6. Use of the benzoxazine resin of claim 3 in the preparation of a lithium battery.

7. A method of producing a lithium battery, characterized by, The surface of lithium metal is modified by using a surface treatment agent; the gel polymer electrolyte is prepared by using the benzoxazine resin of claim 3, and the modified lithium metal is assembled with the gel polymer electrolyte, so that the lithium battery is obtained.

8. The production method according to claim 7, characterized by, 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 hydrolysable group; 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 a fluorine-containing alkane chain.

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