An ether group functionalized urotropinium dicyanamide salt, a preparation method and application thereof

Abstract

The application discloses ether group functionalized urotropinium dicyanamide salt and a preparation method and application thereof, belongs to the technical field of electrolyte additives, and has a general structure of [RUr]DCA, wherein a cation part is ether group functionalized urotropinium ion [RUr] + , Ur represents a urotropine parent nucleus, R represents an ether group functionalized side chain, and an anion part is dicyanamide ion DCA ‑ . When the ether group functionalized urotropinium dicyanamide salt is prepared, quaternary ammonium reaction is performed on urotropine and bromo ether hydrocarbon in an organic solvent to generate an ether group functionalized urotropinium bromide intermediate; anion exchange reaction is performed on the obtained intermediate and dicyanamide salt to obtain a target product. By adding the ether group functionalized urotropinium dicyanamide salt into an electrolyte, the ether group functionalized urotropinium dicyanamide salt is beneficial to promote the formation of a stable SEI film as a nitrogen-rich electrolyte additive, so that the performance and cycle stability of a lithium battery are improved.

Description

Technical Field

[0001] This invention relates to the field of electrolyte additives, and in particular to an ether-functionalized hexamethylene dicyandiamide salt, its preparation method, and its application. Background Technology

[0002] In the field of lithium-ion battery technology, the design and development of electrolyte additives play a crucial role in improving the overall performance of batteries. Among them, nitrogen-rich additives have received widespread attention in recent years due to their unique chemical properties. These compounds can participate in interfacial chemical reactions on the electrode surface, promoting the formation of a stable, dense, and highly ionicly conductive solid electrolyte interphase (SEI) film. A superior SEI film can effectively inhibit the continuous decomposition of the electrolyte, prevent electrode structure damage, and promote the rapid migration of lithium ions, thereby significantly improving the battery's initial coulombic efficiency, cycle life, and rate performance.

[0003] Traditional SEI film-forming additives, such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), while improving battery performance to some extent, still suffer from problems such as uneven film formation, insufficient stability, or easy decomposition under high voltage. In contrast, nitrogen-rich compounds, due to the presence of multi-electron nitrogen atoms in their molecular structure, possess strong coordination ability and reduction stability, enabling them to preferentially undergo reduction reactions on the negative electrode surface to form a nitrogen-containing interface layer. This type of interface layer typically exhibits high mechanical strength and good lithium-ion conductivity, helping to reduce lithium dendrite formation, improve interface stability, and thus extend battery cycle life.

[0004] However, most nitrogen-enriched additives still face problems in practical applications, such as poor solubility, poor compatibility with electrolytes, or complex synthesis processes, which limit their large-scale application. Therefore, developing a nitrogen-enriched additive with novel structure, simple synthesis, and superior electrochemical performance has become an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide an ether-functionalized hexamethylene dicyandiamide salt, its preparation method, and its application, in order to solve the above-mentioned problems.

[0006] This invention provides an ether-functionalized hexamethylene dicyandiamide salt with the general structural formula [RUr]DCA, wherein the cationic moiety is an ether-functionalized hexamethylene ion [RUr]. + Ur is the hexamethylenetetramine core, R is an ether-functionalized side chain, and the anionic moiety is a dicyandiamide ion (DCA). - Its structural formula is as follows:

[0007] ,

[0008] The ether-functionalized side chain R is one of -C2H4OCH3, -C2H4OC2H5, -(C2H4O)2CH3 or -(C2H4O)2C2H5.

[0009] A method for preparing the ether-functionalized hexamethylene dicyandiamide salt as described above is provided, comprising the following steps:

[0010] (a) Hexamethylenetetramine is quaternized with a brominated ether in an organic solvent to generate an ether-functionalized hexamethylenetetramine bromide intermediate;

[0011] (b) The intermediate obtained in step (a) is subjected to anion exchange reaction with a dicyandiamide salt to obtain ether-functionalized hexamethylene dicyandiamide salt.

[0012] Preferably, the reaction formula of this method is as follows:

[0013] .

[0014] Preferably, the specific process of step (a) is as follows:

[0015] 0.10 mol of hexamethylenetetramine and an equimolar amount of a brominated ether hydrocarbon were added to a 250 mL round-bottom flask containing 100 mL of chloroform, and the mixture was reacted at reflux for 24 hours. After the reaction was complete, the mixture was cooled to room temperature, and a solid precipitated. 100 mL of anhydrous diethyl ether or 50 mL of anhydrous diethyl ether and 50 mL of n-hexane were added, and the mixture was allowed to stand for another 10 hours to allow the crystals to grow and precipitate completely. The mixture was filtered through a Buchner funnel and washed with 3 × 50 mL of anhydrous diethyl ether. It was then dried under vacuum at 60 °C for 5 hours and weighed to obtain a white powdery solid, which is the ether-functionalized hexamethylenetetramine bromide intermediate.

[0016] Preferably, the specific process of step (b) is as follows:

[0017] Dissolve 0.06 mol sodium dicyandiamide in 50 mL of deionized water, then add dropwise 50 mL of an aqueous solution containing 0.06 mol silver nitrate, and continue stirring for 0.5 hours; after standing for 2 hours, filter using a Buchner funnel, wash with 5 × 50 mL of anhydrous diethyl ether, and obtain a white solid;

[0018] The white solid was added to 100 mL of an aqueous solution containing 0.05 mol of ether-functionalized hexamethylene dicyandiamide bromide intermediate and stirred for 2 hours. After standing for 2 hours, the mixture was filtered through a Buchner funnel, washed with 3 × 50 mL of anhydrous diethyl ether, and the filtrate was collected. The filtrate was concentrated under vacuum at 60 °C to obtain a pale yellow solid, namely ether-functionalized hexamethylene dicyandiamide salt.

[0019] Preferably, the bromoether hydrocarbon is one of 2-bromoethylmethyl ether, 2-bromoethylethyl ether, 2-(2-methoxyethoxy)ethyl bromide, and 2-(2-ethoxyethoxy)ethyl bromide.

[0020] An application of the ether-functionalized hexamethylene dicyandiamide salt as described above is provided, which is used as an electrolyte additive in lithium-ion batteries.

[0021] Preferably, the electrolyte additive has a mass fraction of 1%-5% in the electrolyte, which is used to promote the formation of a stable solid electrolyte interface film and improve the battery's initial discharge capacity and cycle stability.

[0022] Therefore, this invention employs the aforementioned ether-functionalized hexamethylene dicyandiamide salt, its preparation method, and its application, achieving the following beneficial effects: Based on the hexamethylene dicyandiamide parent structure, an ether-functionalized side chain is innovatively introduced, and a series of ether-functionalized hexamethylene dicyandiamide salts are designed and synthesized. These compounds possess both the inherent nitrogen-rich characteristics of hexamethylene dicyandiamide and the flexible adjustment capability of the ether chain, exhibiting excellent comprehensive performance: the introduction of the ether chain significantly improves the solubility and dispersion stability of the onium salt in organic electrolytes; the ether chain can weakly interact with lithium ions through coordination, not only increasing the degree of dissociation of the lithium salt but also increasing the lithium ion transference number, thereby improving the conductivity of the electrolyte; the introduction of the ether chain can effectively weaken the Coulombic force between cations and anions, inhibiting their ordered stacking, providing more space for ion migration, and further optimizing ion transport behavior; these additives also have good electrode wettability, contributing to the formation of a uniform and stable SEI film. Furthermore, the provided ether-functionalized hexamethylene dicyandiamide salt not only boasts a simple synthetic route, high yield, and excellent purity, with its structure verified by 1H NMR spectroscopy and purity exceeding 98%, but also exhibits remarkable performance enhancement in lithium-ion battery applications. Experimental results show that the addition of this series of compounds significantly enhances cycle stability while maintaining high capacity, resulting in a denser and more stable SEI film formation, effectively suppressing capacity decay, and demonstrating promising application prospects and industrialization potential. This invention addresses the shortcomings of current nitrogen-rich additives in terms of solubility, film-forming properties, and synthesis processes, providing a novel, high-performance, and easily prepared ether-functionalized hexamethylene dicyandiamide salt additive, offering a new solution for the design and development of high-performance lithium-ion battery electrolytes.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 The proton NMR spectrum of [MOEUr]DCA in Example 1;

[0025] Figure 2The proton NMR spectrum of [EOEUr]DCA in Example 2;

[0026] Figure 3 The proton NMR spectrum of [MOEOEUr]DCA in Example 3;

[0027] Figure 4 The proton NMR spectrum of [EOEOEUr]DCA in Example 4;

[0028] Figure 5 The first charge-discharge curve of the commercial electrolyte battery in Example 5;

[0029] Figure 6 The first charge-discharge curves of the battery containing 5% [MOEUr]DCA electrolyte additive in Example 6 and their comparison with commercial electrolytes are shown below.

[0030] Figure 7 The first charge-discharge curves of the battery containing 5% [EOEUr]DCA electrolyte additive in Example 7 and their comparison with commercial electrolytes are shown below.

[0031] Figure 8 The first charge-discharge curves of the battery containing 5% [MOEOEUr]DCA electrolyte additive in Example 8 and their comparison with commercial electrolytes are shown below.

[0032] Figure 9 The first charge-discharge curves of the battery containing 5% [EOEOEUr]DCA electrolyte additive in Example 9 are shown, and their comparison with commercial electrolytes are also shown. Detailed Implementation

[0033] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0035] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0036] This invention provides an ether-functionalized hexamethylene dicyandiamide salt with the general structural formula [RUr]DCA, wherein the cationic moiety is an ether-functionalized hexamethylene ion [RUr]. + Ur is the hexamethylenetetramine core, R is an ether-functionalized side chain, and the anionic moiety is a dicyandiamide ion (DCA). - Its structural formula is as follows:

[0037] ,

[0038] The ether-functionalized side chain R is one of -C2H4OCH3, -C2H4OC2H5, -(C2H4O)2CH3 or -(C2H4O)2C2H5.

[0039] Specifically, the ether-functionalized side chain R effectively weakens the coulombic interaction between cations and anions and inhibits their ordered stacking, thus providing more space for ion transport and facilitating efficient ion migration in the electrolyte, thereby improving the electrolyte's conductivity. Furthermore, the ether chain significantly enhances the wettability of the electrolyte on various material surfaces. Its coordination with lithium ions also helps improve the solubility of lithium salts and the lithium ion transference number.

[0040] A method for preparing the ether-functionalized hexamethylene dicyandiamide salt as described above is provided, comprising the following steps:

[0041] (a) Hexamethylenetetramine is quaternized with a brominated ether in an organic solvent to generate an ether-functionalized hexamethylenetetramine bromide intermediate;

[0042] (b) The intermediate obtained in step (a) is subjected to anion exchange reaction with a dicyandiamide salt to obtain ether-functionalized hexamethylene dicyandiamide salt.

[0043] To further optimize the above technical solution, the reaction formula of this method is as follows:

[0044] .

[0045] To further optimize the above technical solution, the specific process of step (a) is as follows:

[0046] 0.10 mol of hexamethylenetetramine and an equimolar amount of a brominated ether hydrocarbon were added to a 250 mL round-bottom flask containing 100 mL of chloroform, and the mixture was reacted at reflux for 24 hours. After the reaction was complete, the mixture was cooled to room temperature, and a solid precipitated. 100 mL of anhydrous diethyl ether or 50 mL of anhydrous diethyl ether and 50 mL of n-hexane were added, and the mixture was allowed to stand for another 10 hours to allow the crystals to grow and precipitate completely. The mixture was filtered through a Buchner funnel and washed with 3 × 50 mL of anhydrous diethyl ether. It was then dried under vacuum at 60 °C for 5 hours and weighed to obtain a white powdery solid, which is the ether-functionalized hexamethylenetetramine bromide intermediate.

[0047] To further optimize the above technical solution, the specific process of step (b) is as follows:

[0048] Dissolve 0.06 mol sodium dicyandiamide in 50 mL of deionized water, then add dropwise 50 mL of an aqueous solution containing 0.06 mol silver nitrate, and continue stirring for 0.5 hours; after standing for 2 hours, filter using a Buchner funnel, wash with 5 × 50 mL of anhydrous diethyl ether, and obtain a white solid;

[0049] The white solid was added to 100 mL of an aqueous solution containing 0.05 mol of ether-functionalized hexamethylene dicyandiamide bromide intermediate and stirred for 2 hours. After standing for 2 hours, the mixture was filtered through a Buchner funnel, washed with 3 × 50 mL of anhydrous diethyl ether, and the filtrate was collected. The filtrate was concentrated under vacuum at 60 °C to obtain a pale yellow solid, namely ether-functionalized hexamethylene dicyandiamide salt.

[0050] To further optimize the above technical solution, the bromoether hydrocarbon is one of 2-bromoethylmethyl ether, 2-bromoethylethyl ether, 2-(2-methoxyethoxy)ethyl bromide, and 2-(2-ethoxyethoxy)ethyl bromide.

[0051] An application of the ether-functionalized hexamethylene dicyandiamide salt as described above is provided, which is used as an electrolyte additive in lithium-ion batteries.

[0052] Specifically, adding ether-functionalized hexamethylene dicyandiamide salt to the electrolyte as a nitrogen-rich electrolyte additive helps promote the formation of a stable SEI film, thereby improving the performance and cycle stability of lithium batteries.

[0053] To further optimize the above technical solution, the electrolyte additive has a mass fraction of 1%-5% in the electrolyte, which is used to promote the formation of a stable solid electrolyte interface film and improve the battery's initial discharge capacity and cycle stability.

[0054] To provide a clearer and more detailed description of the ether-functionalized hexamethylene dicyandiamide salt, its preparation method, and its applications provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0055] Example 1

[0056] Preparation and structural characterization of N-(2-methoxyethane)hexamethylene dicyandiamide salt [MOEUr]DCA:

[0057] First, 0.10 mol of hexamethylenetetramine and an equimolar amount of 2-bromoethylmethyl ether were added to a 250 mL round-bottom flask containing 100 mL of chloroform, and the mixture was reacted at reflux for 24 hours. After the reaction was completed, the mixture was cooled to room temperature, and a solid precipitated. 100 mL of anhydrous diethyl ether was added, and the mixture was allowed to stand for another 10 hours to allow the crystals to grow and precipitate completely. The mixture was filtered through a Buchner funnel and washed with 3 × 50 mL of anhydrous diethyl ether. The solution was dried under vacuum at 60 °C for 5 hours and weighed to obtain 16.5 g of a white powdery solid, N-(2-methoxyethane)hexamethylenetetramine bromide [MOEUr]Br, with a yield of 59%.

[0058] Next, 0.06 mol sodium dicyandiamide was dissolved in 50 mL of deionized water, and then 50 mL of an aqueous solution containing 0.06 mol silver nitrate was added dropwise. The mixture was stirred for 0.5 hours. After standing for 2 hours, the solution was filtered through a Buchner funnel and washed with 5 × 50 mL of anhydrous diethyl ether to obtain a white solid. This white solid was added to 100 mL of an aqueous solution containing 0.05 mol [MOEUr]Br and stirred for 2 hours. After standing for 2 hours, the solution was filtered through a Buchner funnel and washed with 3 × 50 mL of anhydrous diethyl ether. The filtrate was collected. The filtrate was concentrated under vacuum at 60 °C to obtain a pale yellow solid, [MOEUr]DCA, with a yield of 89%.

[0059] 1H NMR spectrum ( 1 ¹H-NMR (ppm, D₂O) analysis confirmed the structure of [MOEUr]DCA. Figure 1 As shown, all signals in the spectrum can be identified and correspond one-to-one with the theoretical chemical shifts, splitting patterns, and integral areas, indicating that the structure of the synthesized product is completely consistent with the design target.

[0060] Example 2

[0061] Preparation and structural characterization of N-(2-ethoxyethane)hexamethylene dicyandiamide salt [EOEUr]DCA:

[0062] The preparation process in this embodiment is the same as in Example 1, except that the reactant 2-bromoethylmethyl ether is replaced with 2-bromoethylethyl ether. The intermediate product in this embodiment is N-(2-ethoxyethane)hexamethylene bromide ([EOEUr]Br), and the yields of the two-step reactions are 65% and 90%, respectively.

[0063] like Figure 2 As shown, [EOEUr]DCA's 1All signals in the H-NMR spectrum (ppm, D2O) can be identified one-to-one with the theoretical chemical shift, splitting pattern and integral area, indicating that the structure of the synthesized product is completely consistent with the design target.

[0064] Example 3

[0065] Preparation and structural characterization of N-[2-(2-methoxyethoxy)ethyl]hexamethylene dicyandiamide salt [MOEOEUr]DCA:

[0066] First, 0.10 mol of hexamethylenetetramine and an equimolar amount of 2-(2-methoxyethoxy)ethyl bromide were added to a 250 mL round-bottom flask containing 100 mL of chloroform, and the mixture was reacted at reflux for 24 hours. After the reaction was completed, the mixture was cooled to room temperature, and a solid precipitated. 50 mL of anhydrous diethyl ether and 50 mL of n-hexane were added, and the mixture was allowed to stand for another 10 hours to allow the crystals to grow and precipitate completely. The mixture was filtered through a Buchner funnel and washed with a mixture of anhydrous diethyl ether and n-hexane (V / V = 1:1, 3 × 50 mL). The solution was dried under vacuum at 60 °C for 5 hours to obtain 17.8 g of a white powdery solid N-[2-(2-methoxyethoxy)ethyl]hexamethylenetetramine bromide [MOEOEUr]Br, with a yield of 55%.

[0067] Next, 0.06 mol sodium dicyandiamide was dissolved in 50 mL of deionized water, and then 50 mL of an aqueous solution containing 0.06 mol silver nitrate was added dropwise. The mixture was stirred for 0.5 hours. After standing for 2 hours, the solution was filtered through a Buchner funnel and washed with 5 × 50 mL of water to obtain a white solid. This white solid was added to 100 mL of an aqueous solution containing 0.05 mol [MOEOEUr]Br and stirred for 2 hours. After standing for 2 hours, the solution was filtered through a Buchner funnel and washed with 3 × 50 mL of water. The filtrate was collected. The filtrate was concentrated under vacuum at 60 °C to obtain a pale yellow solid, [MOEOEUr]DCA, with a yield of 89%.

[0068] like Figure 3 As shown, [MOEOEUr]DCA's 1 All signals in the H-NMR spectrum (ppm, D2O) can be identified one-to-one with the theoretical chemical shift, splitting pattern and integral area, indicating that the structure of the synthesized product is completely consistent with the design target.

[0069] Example 4

[0070] Preparation and structural characterization of N-[2-(2-ethoxyethoxy)ethyl]hexamethylene dicyandiamide salt [EOEOEUr]DCA:

[0071] The preparation process in this embodiment is the same as in Example 3, except that the reactant 2-(2-methoxyethoxy)ethyl bromide is replaced with 2-(2-ethoxyethoxy)ethyl bromide. The intermediate product in this embodiment is N-[2-(2-methoxyethoxy)ethyl]hexamethylene bromide [EOEOEUr]DCA, and the yields of the two-step reactions are 56% and 90%, respectively.

[0072] like Figure 4 As shown, [EOEOEUr]DCA's 1 All signals in the H-NMR spectrum (ppm, D2O) can be identified one-to-one with the theoretical chemical shift, splitting pattern and integral area, indicating that the structure of the synthesized product is completely consistent with the design target.

[0073] Example 5

[0074] Preparation and testing of lithium iron phosphate batteries:

[0075] The cathode is composed of LFP (lithium iron phosphate), PVDF (polyvinylidene fluoride), and Super-P (super conductive carbon black) in a weight ratio of 80:10:10. This anode composite material was dispersed in an NMP (N-methylpyrrolidone) solution to form a homogeneous slurry, which was then uniformly coated onto carbon-coated aluminum foil. The treated aluminum foil was vacuum-dried overnight at 110 °C, and after natural cooling, it was rolled into a sheet. The rolled electrode sheet was then stamped into a 13 mm diameter disc with an LFP mass loading of approximately 5 mg·cm³. -2 A commercial electrolyte (1.0 M LiPF6 in EC:DEC:EMC = 1:1:1 vol%) was used as a blank control group, and it could be modified by adding hexamethylenetetramine salt prepared in this invention. Using the newly prepared LFP positive electrode, lithium foil negative electrode, 80 μL of commercial electrolyte (or modified electrolyte), and 3501 separator, 2032 button cells were assembled in an argon atmosphere glove box with oxygen and moisture contents both below 0.1 ppm. Constant current charge-discharge (GCD) tests were performed using a Xinwei battery testing system (CT-4008Tn-5V50mA), with the voltage set between 2.5-4.0 V (relative to Li / Li). + The newly assembled Li / LFP battery was first activated by five cycles at a low rate of 0.05 C, and then its cycle performance was tested at 0.5 C for 200 cycles, and the cycle stability of the battery was recorded.

[0076] The initial 0.5C charge-discharge curves of commercial electrolyte batteries are as follows: Figure 5 As shown, the battery's discharge capacity is 147 mAhg. -1 After 200 cycles, the battery capacity decreased to 136 mAh g. -1 .

[0077] Example 6

[0078] [MOEUr]DCA electrolyte additive improves the performance of lithium iron phosphate batteries:

[0079] The specific implementation process of this embodiment is the same as that of Embodiment 5, the difference being that 5% (wt) [MOEUr]DCA is added to the commercial electrolyte in this embodiment. Tests showed that, compared with the commercial electrolyte, the addition of 5% [MOEUr]DCA significantly improved battery performance. Figure 6 As shown, the battery containing 5% [MOEUr]DCA achieves an initial 0.5C discharge capacity of 156 mAh g. -1 After 200 cycles, the battery discharge capacity still reaches 152 mAh g. -1 This is higher than the 147 and 136 mAh g of commercial electrolyte batteries. -1 .

[0080] Example 7

[0081] [EOEUr]DCA electrolyte additive improves the performance of lithium iron phosphate batteries:

[0082] The specific implementation process of this embodiment is the same as that of Embodiment 5, the difference being that 5% (wt) [EOEUr]DCA is added to the commercial electrolyte in this embodiment. Tests showed that, compared with the commercial electrolyte, the addition of 5% [EOEUr]DCA significantly improved battery performance. Figure 7 As shown, the battery containing 5% [EOEUr]DCA achieves an initial 0.5C discharge capacity of 163 mAh g. -1 After 200 cycles, the battery discharge capacity still reaches 155 mAh g. -1 This is higher than the 147 and 136 mAh g of commercial electrolyte batteries. -1 .

[0083] Example 8

[0084] [MOEOEUr]DCA electrolyte additive improves the performance of lithium iron phosphate batteries:

[0085] The specific implementation process of this embodiment is the same as that of Embodiment 5, the difference being that 5% (wt) [MOEOEUr]DCA is added to the commercial electrolyte in this embodiment. Tests showed that, compared with the commercial electrolyte, the addition of 5% [MOEOEUr]DCA significantly improved battery performance. Figure 8 As shown, the battery containing 5% [MOEOEUr]DCA achieves an initial 0.5C discharge capacity of 167mAh g. -1After 200 cycles, the battery discharge capacity still reaches 156 mAh g. -1 This is higher than the 147 and 136 mAh g of commercial electrolyte batteries. -1 .

[0086] Example 9

[0087] [EOEOEUr]DCA electrolyte additive improves the performance of lithium iron phosphate batteries:

[0088] The specific implementation process of this embodiment is the same as that of Embodiment 5, the difference being that 5% (wt) [EOEOEUr]DCA is added to the commercial electrolyte in this embodiment. Tests showed that, compared with the commercial electrolyte, the addition of 5% [EOEOEUr]DCA significantly improved battery performance. Figure 9 As shown, the battery containing 5% [EOEOEUr]DCA achieves an initial 0.5C discharge capacity of 169 mAh g. -1 After 200 cycles, the battery discharge capacity still reaches 160 mAh g. -1 This is higher than the 147 and 136 mAh g of commercial electrolyte batteries. -1 .

[0089] Therefore, this invention utilizes the aforementioned ether-functionalized hexamethylene dicyandiamide salt, its preparation method, and its application. Based on the hexamethylene dicyandiamide parent structure, an ether-functionalized side chain is innovatively introduced to design and synthesize a series of ether-functionalized hexamethylene dicyandiamide salts. These compounds combine the inherent nitrogen-rich properties of hexamethylene dicyandiamide with the flexible adjustment capability of the ether chain, exhibiting excellent comprehensive performance: the introduction of the ether chain significantly improves the solubility and dispersion stability of the onium salt in organic electrolytes; the ether chain can weakly interact with lithium ions through coordination, not only increasing the degree of dissociation of the lithium salt but also increasing the lithium ion transference number, thereby improving the conductivity of the electrolyte; the introduction of the ether chain can effectively weaken the Coulombic forces between cations and anions, inhibiting their ordered stacking and providing more space for ion migration, further optimizing ion transport behavior; these additives also have good electrode wettability, contributing to the formation of a uniform and stable SEI film. Furthermore, the provided ether-functionalized hexamethylene dicyandiamide salt not only boasts a simple synthetic route, high yield, and excellent purity, with its structure verified by 1H NMR spectroscopy and purity exceeding 98%, but also exhibits remarkable performance enhancement in lithium-ion battery applications. Experimental results show that the addition of this series of compounds significantly enhances cycle stability while maintaining high capacity, resulting in a denser and more stable SEI film formation, effectively suppressing capacity decay, and demonstrating promising application prospects and industrialization potential. This invention addresses the shortcomings of current nitrogen-rich additives in terms of solubility, film-forming properties, and synthesis processes, providing a novel, high-performance, and easily prepared ether-functionalized hexamethylene dicyandiamide salt additive, offering a new solution for the design and development of high-performance lithium-ion battery electrolytes.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An ether-functionalized hexamethylene dicyandiamide salt, characterized in that, Its general structural formula is [RUr]DCA, wherein the cationic moiety is an ether-functionalized hexamethylenetetramine ion [RUr]. + Ur is the hexamethylenetetramine core, R is an ether-functionalized side chain, and the anionic moiety is a dicyandiamide ion (DCA). - Its structural formula is as follows: ， The ether-functionalized side chain R is one of -C2H4OCH3, -C2H4OC2H5, -(C2H4O)2CH3 or -(C2H4O)2C2H5.

2. A method for preparing the ether-functionalized hexamethylene dicyandiamide salt as described in claim 1, characterized in that, Includes the following steps: (a) Hexamethylenetetramine is quaternized with a brominated ether in an organic solvent to generate an ether-functionalized hexamethylenetetramine bromide intermediate; (b) The intermediate obtained in step (a) is subjected to anion exchange reaction with a dicyandiamide salt to obtain ether-functionalized hexamethylene dicyandiamide salt.

3. The method for preparing ether-functionalized hexamethylene dicyandiamide salt according to claim 2, characterized in that, The reaction formula for this method is as follows: 。 4. The method for preparing ether-functionalized hexamethylene dicyandiamide salt according to claim 2, characterized in that, The specific process of step (a) is as follows: 0.10 mol of hexamethylenetetramine and an equimolar amount of brominated ether hydrocarbon were added to a 250 mL round-bottom flask containing 100 mL of chloroform. The mixture was reacted at reflux for 24 hours. After the reaction was completed, the mixture was cooled to room temperature, and a solid precipitated. 100 mL of anhydrous diethyl ether or 50 mL of anhydrous diethyl ether and 50 mL of n-hexane were added, and the mixture was allowed to stand for another 10 hours until the crystals grew and precipitated completely. The crystals were filtered through a Buchner funnel and washed with 3 × 50 mL of anhydrous diethyl ether. The mixture was then dried under vacuum at 60 °C for 5 hours and weighed to obtain a white powdery solid, which is the intermediate of ether-functionalized hexamethylenetetramine bromide.

5. The method for preparing ether-functionalized hexamethylene dicyandiamide salt according to claim 2, characterized in that, The specific process of step (b) is as follows: Dissolve 0.06 mol sodium dicyandiamide in 50 mL of deionized water, then add dropwise 50 mL of an aqueous solution containing 0.06 mol silver nitrate, and continue stirring for 0.5 hours; after standing for 2 hours, filter using a Buchner funnel, wash with 5 × 50 mL of anhydrous diethyl ether, and obtain a white solid; The white solid was added to 100 mL of an aqueous solution containing 0.05 mol of ether-functionalized hexamethylene dicyandiamide bromide intermediate and stirred for 2 hours. After standing for 2 hours, the mixture was filtered through a Buchner funnel, washed with 3 × 50 mL of anhydrous diethyl ether, and the filtrate was collected. The filtrate was concentrated under vacuum at 60 °C to obtain a pale yellow solid, namely ether-functionalized hexamethylene dicyandiamide salt.

6. The method for preparing ether-functionalized hexamethylene dicyandiamide salt according to claim 2, characterized in that, The bromoether hydrocarbon is one of 2-bromoethylmethyl ether, 2-bromoethylethyl ether, 2-(2-methoxyethoxy)ethyl bromide, and 2-(2-ethoxyethoxy)ethyl bromide.

7. The application of the ether-functionalized hexamethylene dicyandiamide salt as described in claim 1, characterized in that, It is used as an electrolyte additive in lithium-ion batteries.

8. The application of the ether-functionalized hexamethylene dicyandiamide salt according to claim 7, characterized in that, The electrolyte additive has a mass fraction of 1%-5% in the electrolyte and is used to promote the formation of a stable solid electrolyte interface film, thereby improving the battery's initial discharge capacity and cycle stability.

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