A method for preparing a high-stability polymer used as an anode material for lithium-ion batteries

Abstract

The invention discloses a preparation method of a high-stability polymer used as a lithium ion battery anode material, which is divided into two steps: first, using dicyandiamide and 1,2-dicyanobenzene as raw materials, using ethylene glycol monomethyl ether as solvent, and reacting in an alkaline environment provided by potassium hydroxide to obtain 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene; then using 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene and phenyl ring-containing aldehydes as raw materials and using dimethyl sulfoxide as solvent, polymerization is performed to obtain a high-stability polymer used as a lithium ion battery anode material. The organic electrode material preparation method provided by the present invention is low in cost, has a high safety factor, and the resulting material itself has a longer chain conjugated structure, which greatly improves cyclic stability.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and in particular relates to a preparation method of an organic electrode material and application thereof. Background Art

[0002] Lithium-ion batteries have always been a research hotspot in the field of new energy, especially the research on electrode materials. Compared with the inevitable problems of low theoretical capacity and high price of inorganic electrode materials, organic electrode materials have gradually become the first choice for new environmentally friendly electrode materials due to their advantages such as adjustable structure and low cost.

[0003] At present, there are two methods for preparing 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene, one is microwave radiation method and the other is synthesis method. The microwave radiation method requires a special reaction instrument, specifically, a mixture of dicyandiamide, 1,2-dicyanobenzene, potassium hydroxide and DMSO is introduced into a heat-resistant flask and irradiated in an improved focused microwave reactor, and finally filtered and dried. The synthesis method is to heat dicyandiamide, 1,2-dicyanobenzene, potassium hydroxide and methylcellulose solution at a temperature of 130-140°C for 7h, and then filter and dry. The method for preparing 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene disclosed in the prior art has a high cost and a low safety factor. In addition, the current method for synthesizing meta- or para-polymers used as anode materials for lithium-ion batteries is to use 1,3-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene or 1,4-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene and benzene ring-containing aldehydes as raw materials and dimethyl sulfoxide as solvent for polymerization. The para- and meta-polymers synthesized by this method have poor cyclic stability. Summary of the Invention

[0004] Based on the above-mentioned shortcomings of the prior art, the present invention provides a method for preparing a highly stable polymer used as an anode material for lithium-ion batteries, aiming to save preparation costs, reduce the risk factor during preparation, and make the obtained ortho-polymer have higher stability.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for preparing a high-stability polymer used as an anode material for lithium-ion batteries. The method is characterized in that: first, dicyandiamide and 1,2-dicyanobenzene are used as raw materials, ethylene glycol monomethyl ether is used as solvent, and 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene is reacted in an alkaline environment provided by potassium hydroxide; then, 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene and a benzene ring-containing aldehyde are used as raw materials, and dimethyl sulfoxide is used as solvent. The method specifically comprises the following steps:

[0007] Step 1: adding dicyandiamide, 1,2-dicyanobenzene and potassium hydroxide to ethylene glycol monomethyl ether, and heating to reflux temperature for reaction; after the reaction is completed, the mixture is allowed to stand to obtain 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene monomer;

[0008] Step 2: adding 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene monomer and benzene ring-containing aldehyde monomer to dimethyl sulfoxide solvent, heating to reflux temperature for polymerization, and obtaining a crude reaction product;

[0009] Step 3: Recrystallize the obtained crude reaction product from toluene to obtain a purified product;

[0010] Step 4: vacuum-drying the purified product to obtain a highly stable polymer used as an anode material for lithium-ion batteries.

[0011] Furthermore, the molar ratio of dicyandiamide to 1,2-dicyanobenzene is 4.4-4.6:1; the amount of potassium hydroxide used is 33%-34% of the mass of dicyandiamide; and the amount ratio of dicyandiamide to ethylene glycol monomethyl ether is 1g:23-24mL.

[0012] Furthermore, the molar ratio of the 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene to the benzene ring-containing aldehyde is 1:2-4.

[0013] Furthermore, in step 1, the reaction temperature is 120-125° C. and the reaction time is 48 h.

[0014] Furthermore, in step 2, the polymerization reaction temperature is 160-180° C. and the reaction time is 72 h.

[0015] Furthermore, in step 4, the vacuum drying temperature is 80° C. and the time is 16 hours.

[0016] The high-stability polymer prepared according to the preparation method of the present invention can be used as a negative electrode material for lithium-ion batteries.

[0017] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0018] 1. The preparation method of the present invention is simple and easy to operate, low in cost, and has a high safety factor. Furthermore, the method of preparing 1,2-bis(2,4-diamino-1,3,5-triazin-6-yl)benzene monomer of the present invention is different from existing preparation methods. The improved method has a lower concentration of raw materials in the solvent, and a slow reaction is conducive to the production of a more stable monomer.

[0019] 2. The present method for preparing ortho-polymers increases the amount of aldehyde used, facilitating a complete reaction and producing a more stable polymer with improved cyclic stability compared to para- and meta-polymers. Furthermore, the ortho-polymer structure is connected by triazine and benzene rings, forming a polyamine polymer with a network structure, which significantly reduces its solubility in the electrolyte. The highly conjugated structure in the polymer shortens the lithium ion transmission path and increases the transmission speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the reaction of dicyandiamide and 1,2-dicyanobenzene according to the present invention;

[0021] Figure 2 This is the NMR spectrum of the 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene monomer obtained in Example 1 of the present invention;

[0022] Figure 3 Schematic diagram of the reaction of the polymers in Examples 1, 2, and 3 of the present invention;

[0023] Figure 4 IR spectra of the polymers obtained in Examples 1, 2, and 3 of the present invention;

[0024] Figure 5 This is a transmission electron micrograph of the polymer obtained in Example 1 of the present invention;

[0025] Figure 6 The polymer in Example 1 of the present invention is 1Ag -1 Cycling performance diagram under current density;

[0026] Figure 7 The polymer in Example 1 of the present invention is 1Ag -1 Rate performance diagram under current density;

[0027] Figure 8 The polymers in Examples 1, 2 and 3 of the present invention are -1 Comparison of cycling performance under different current densities; DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described in detail below through specific embodiments. The following embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] Weigh dicyandiamide and 1,2-dicyanobenzene in a molar ratio of 4.5:1, and weigh potassium hydroxide at 33% of the mass of dicyandiamide. Add dicyandiamide, 1,2-dicyanobenzene, and potassium hydroxide to a three-necked flask containing ethylene glycol monomethyl ether (the ratio of ethylene glycol monomethyl ether to dicyandiamide is 23-24 mL:1 g). React at 125°C under an inert gas atmosphere for 48 hours. Allow to stand for 24 hours to obtain a crude reaction product. Filter the crude reaction product and vacuum dry it at 80°C for 16 hours to obtain 1,2-bis(2,4-diamino-1,3,5-triazin-6-yl)benzene monomer.

[0031] Figure 1 Schematic diagram of the reaction of dicyandiamide and 1,2-dicyanobenzene. Under alkaline conditions, 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene monomer is generated. Figure 2 This is the NMR spectrum of 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene monomer. The spectrum contains three types of hydrogen in a ratio of 4:1:1, which is consistent with the expected structure, proving that the monomer was successfully prepared. Its structural formula is as follows Figure 1 As shown in .

[0032] 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene and terephthalaldehyde were weighed in a molar ratio of 1:2, and the two were added to a three-necked flask containing dimethyl sulfoxide (the ratio of dimethyl sulfoxide to 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene was 45-46 mL:1 g), and the mixture was refluxed at 180°C under an inert gas atmosphere for 72 h to obtain a crude reaction product.

[0033] The crude reaction product was filtered and dried, and then placed in a flask filled with toluene for recrystallization to obtain a purified product.

[0034] The purified product was transferred to a watch glass and dried under vacuum at 80°C for 16 h to obtain a polymer.

[0035] The polymer obtained in this example was mixed with superconducting carbon Ketjen black and polyvinylidene fluoride in a mass ratio of 6:2:2. An appropriate amount of N-methylpyrrolidone was added to form a slurry. The slurry was evenly applied to copper foil using a 250μm scraper. After vacuum drying at 70°C for 16 hours, a polymer electrode was obtained.

[0036] The fabricated polymer electrode was punched into a 12mm diameter disc. A lithium metal sheet served as the positive electrode, and a 16mm diameter Celgard 2400 disc served as the separator. The electrolyte, lithium hexafluorophosphate, was dissolved in a 1:1 volume ratio of dimethyl carbonate and ethylene carbonate to create a 1 mol / L electrolyte. These materials were assembled into a button cell in an argon-filled glove box. Electrochemical performance was tested using a NEWARE-CT-4008T battery test system and a CHI660E electrochemical workstation over a charge-discharge voltage range of 0.01 to 3V.

[0037] Example 2

[0038] 1,3-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene and terephthalaldehyde were weighed in a molar ratio of 1:2, and the two were added to a three-necked flask containing dimethyl sulfoxide (the ratio of dimethyl sulfoxide to 1,3-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene was 100 mL:1 g), and the mixture was refluxed at 180°C under an inert gas atmosphere for 72 h to obtain a crude reaction product.

[0039] The crude reaction product was filtered and dried, and then placed in a flask filled with toluene for recrystallization to obtain a purified product.

[0040] The purified product was transferred to a watch glass and dried under vacuum at 80°C for 16 h to obtain a polymer.

[0041] The polymer obtained in this example was assembled into button batteries using the same method as in Example 1.

[0042] Example 3

[0043] 1,4-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene and terephthalaldehyde were weighed in a molar ratio of 1:4, and the two were added to a three-necked flask containing dimethyl sulfoxide (the ratio of dimethyl sulfoxide to 1,4-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene was 100 mL:1 g), and the mixture was refluxed at 180°C under an inert gas atmosphere for 72 h to obtain a crude reaction product.

[0044] The crude reaction product was filtered and dried, and then placed in a flask filled with toluene for recrystallization to obtain a purified product.

[0045] The purified product was transferred to a watch glass and dried under vacuum at 80°C for 16 h to obtain a polymer.

[0046] The polymer obtained in this example was assembled into button batteries using the same method as in Example 1.

[0047] Figure 3 Schematic diagram of the reaction between monomers with different substitution positions and terephthalaldehyde, which are connected through aldehyde-ammonia condensation.

[0048] Figure 4 The infrared spectra of the polymers obtained in Examples 1, 2 and 3 are shown at 1600 cm -1 ~1300cm -1 The nearby peaks are characteristic signals of triazine ring and benzene ring structures, proving the successful preparation of the polymers in Examples 1, 2 and 3.

[0049] Figure 5 This is a transmission electron microscope image of the polymer obtained in Example 1. In the image, it can be seen that the polymer is a porous structure formed by aggregation of particles.

[0050] Figure 6 This is the cycling performance diagram of the button cell in Example 1 at a current density of 1 A / g. It can be observed that its cycling capacity has been in a relatively stable state. Even after 1000 cycles, there is no capacity decay. In addition, except for the low coulombic efficiency (25%) in the first cycle, the coulombic efficiency is stable at 99% thereafter, showing excellent cycling stability.

[0051] Figure 7 This is the rate performance diagram of the button battery in Example 1. After rate performance tests at different current densities of 0.1A / g, 0.3A / g, 0.5A / g, 1A / g, 3A / g, and 5A / g, its capacity can still be restored to about 750mAh / g, indicating that the material has excellent rate performance.

[0052] Figure 8 For the button cells in Examples 1, 2, and 3 at 1Ag -1 The comparison of cycling performance under current density shows that among the three polymers, the ortho-polymer obtained in Example 1 has the best stability, and its coulombic efficiency has been stable at around 99%. Its capacity remains basically stable during the cycle, showing good cycling stability, and after 500 cycles, the capacity gradually increases. However, Example 2 (the stability deteriorates after 400 cycles, and its capacity fluctuates between 150 and 170 mAh / g) and Example 3 have poor cycling stability. In particular, Example 3 has a capacity that fluctuates between 100 and 130 mAh / g during the cycle, and its coulombic efficiency, while partially stable at around 99%, also has many cases below 98% and above 100%, indicating poor cycling stability.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-stability polymer used as an anode material for lithium-ion batteries, characterized in that: First, dicyandiamide and 1,2-dicyanobenzene are used as raw materials, ethylene glycol monomethyl ether is used as solvent, and 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene is reacted in an alkaline environment provided by potassium hydroxide; then, 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene and aldehydes containing benzene rings are used as raw materials, and dimethyl sulfoxide is used as solvent, and polymerization is performed to obtain a high-stability polymer used as an anode material for lithium-ion batteries; the specific steps include: Step 1, adding dicyandiamide, 1,2-dicyanobenzene and potassium hydroxide to ethylene glycol monomethyl ether, heating to a reflux temperature of 120-125° C. and reacting for 48 hours; after the reaction is completed, standing to obtain 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene monomer; the molar ratio of dicyandiamide to 1,2-dicyanobenzene is 4.4-4.6:1; the amount of potassium hydroxide used is 33%-34% of the mass of dicyandiamide; the amount ratio of dicyandiamide to ethylene glycol monomethyl ether is 1 g: 23-24 mL; Step 2: adding 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene monomer and benzene ring-containing aldehyde monomer to dimethyl sulfoxide solvent, heating to a reflux temperature of 160-180° C. for polymerization for 72 hours to obtain a crude reaction product; the molar ratio of the 1,2-bis(2,4-diamino-1,3,5-triazine-6-yl)benzene to the benzene ring-containing aldehyde is 1:2-4; Step 3: Recrystallize the obtained crude reaction product from toluene to obtain a purified product; Step 4: vacuum-drying the purified product to obtain a highly stable polymer used as an anode material for lithium-ion batteries.

2. The preparation method according to claim 1, wherein: In step 4, the vacuum drying temperature is 80° C. and the time is 16 h.

3. A highly stable polymer obtained by the preparation method according to any one of claims 1 to 2.

4. Use of the high-stability polymer according to claim 3 in anode materials for lithium-ion batteries.

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