Flame-retardant cyclic phosphamide eutectic electrolyte and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery electrolyte, and particularly relates to flame-retardant cyclic phosphamide eutectic electrolyte as well as a preparation method and application thereof. According to the invention, through reasonable molecular design, the flame-retardant cyclic phosphamide eutectic electrolyte is obtained. Through the design of the annular structure, a film is formed on the positive and negative electrode interface of the electrode in the battery operation process, so that the stability of the battery is improved. Phosphamide groups are introduced into the cyclic structure, hydroxyl radicals generated in the battery operation process are captured through phosphorus-oxygen bonds, and the chain reaction of combustion is blocked. Meanwhile, different designs of amino groups on phosphamide can achieve a self-cleaning effect, hydrofluoric acid and water generated in a battery circulation process are removed, and the battery is protected from electrode structure collapse caused by the hydrofluoric acid and the water in an operation process. The safety performance of the lithium battery in the cycle process is obviously improved, and the development of the lithium battery with high safety and stable operation is effectively promoted. The preparation process is simple, safe to operate, high in purity and suitable for industrialization.

Description

Technical Field

[0001] This invention belongs to the field of battery electrolyte technology, specifically relating to a flame-retardant cyclic phosphoramide eutectic electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) have become the mainstream power source for portable electronic devices and electric vehicles due to their high energy / power density. Although new battery systems (such as lithium-sulfur / lithium-air batteries) and solid-state electrolytes have been extensively studied, the former is hampered by polysulfide shuttling and lithium dendrite corrosion, while the latter faces bottlenecks such as high interfacial impedance and low ionic conductivity. Therefore, LIBs will remain the market leader for a considerable period of time.

[0003] However, the safety concerns surrounding LIBs have not been completely resolved. Frequent combustion / explosion accidents in recent years have highlighted the high flammability (flash point <40℃) of traditional organic electrolytes. Existing safety improvement strategies (such as electrode modification and additives) cannot eliminate the risk—as long as the electrolyte is flammable, the threat of thermal runaway will persist. Therefore, developing inherently flame-retardant electrolytes is crucial to breaking this deadlock.

[0004] Against this backdrop, cyclic phosphate ester systems exhibit irreplaceable advantages. They inherently possess high flame retardancy, with the cyclic structure contributing to a high phosphorus content (>10wt%). Through a gas-phase free radical quenching mechanism, they achieve UL94 V-0 non-flammability (self-extinguishing time <3s). High-voltage compatibility is also a key advantage: the cyclic molecular chains exhibit strong stability, withstanding voltages >4.8V, significantly inhibiting the dissolution of transition metals from high-nickel cathodes (dissolution after cycling <50ppm). Furthermore, interfacial stability is crucial, as the P=O groups promote the formation of Li3PO4 / Li-rich surfaces. x PO y F z The SEI / CEI film effectively buffers the volume expansion of the silicon anode.

[0005] However, how to rationally design cyclic phosphate esters to prepare a flame-retardant lithium battery electrolyte system, and match it with high-voltage cathode materials, thereby improving the energy density and safety performance of lithium metal batteries, is the technical problem that this invention needs to solve. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides a flame-retardant cyclic phosphoramide eutectic electrolyte, its preparation method, and its applications. Through rational molecular design, this invention yields a flame-retardant cyclic phosphoramide eutectic electrolyte. Furthermore, it can be matched with high-voltage cathode materials, thereby improving the energy density and safety performance of lithium metal batteries.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of the present invention provides a flame-retardant cyclic phosphoramide eutectic electrolyte, wherein the raw materials for preparing the flame-retardant cyclic phosphoramide eutectic electrolyte include lithium salt and cyclic phosphoramide;

[0009] The cyclic phosphoramide has the following structure:

[0010]

[0011] Furthermore, the group -NR1R2 is any one of the following structures:

[0012]

[0013] Furthermore, the groups R3, R4, R5, R6, R7, and R8 are any one of the following structures:

[0014]

[0015] Further, the lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium difluorooxalateborate, lithium tetrafluoroborate, lithium dioxalateborate, lithium perchlorate, and lithium hexafluoroarsenate.

[0016] Furthermore, the cyclic phosphoramide is one or a combination of two of the following molecular structures in any proportion:

[0017]

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned flame-retardant cyclic phosphoramide eutectic electrolyte, the method comprising the following steps:

[0019] (1) Using fluoro alcohol as raw material, tetrahydrofuran solvent, and triethylamine as acid-absorbing agent, fluoro alcohol and phosphorus oxychloride react under ice bath conditions to generate a six-membered ring of phosphate ester, and then the reaction is restored to room temperature; amine is added dropwise to the six-membered ring of phosphate ester under ice bath conditions, and the reaction is restored to room temperature after the addition is completed; after the reaction is completed, the product is obtained by direct distillation, which is cyclic phosphoramide.

[0020] (2) Dissolve lithium salt in a mixture of one or two cyclic phosphoramides to obtain the product.

[0021] Further, in step (1), the fluoroalcohol is any one of 1,3-propanediol, 2,2-difluoro-1,3-propanediol, 1,2-difluoro-1,3-propanediol, 1,2,3-trifluoro-1,3-propanediol, 1,2,2,3-tetrafluoro-1,3-propanediol, 1,3-difluoro-1,3-propanediol, and 1-fluoro-1,3-propanediol.

[0022] Further, in step (1), the amine is any one of 1-methylamine, 1-ethylamine, 1-propylamine, N-methylmethylamine, ethylethylamine, methylethylamine, ethylpropylamine, and methylpropylamine.

[0023] Furthermore, in step (2), the molar ratio of the lithium salt and the cyclic phosphoramide is 1:4.

[0024] Furthermore, in step (2), the lithium salt is dissolved in the cyclic phosphoramide by heating and stirring overnight.

[0025] A third aspect of this invention provides the application of the above-mentioned flame-retardant cyclic phosphoramide eutectic electrolyte in a lithium battery. The lithium battery comprises a positive electrode, a negative electrode, a separator, and the above-mentioned flame-retardant cyclic phosphoramide eutectic electrolyte, forming a sealed, flame-retardant, high-safety lithium battery.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] (1) This invention, through rational molecular design, yields a flame-retardant cyclic phosphoramide eutectic electrolyte. The cyclic structure allows it to form a film at the positive and negative electrode interfaces during battery operation, thereby improving battery stability. Introducing phosphoramide groups into the cyclic structure captures hydroxyl radicals generated during battery operation via phosphorus-oxygen bonds, blocking the chain reaction of combustion. Simultaneously, the different designs of the amine groups on the phosphoramide achieve a self-cleaning effect, removing hydrofluoric acid and water generated during battery cycling, thus protecting the battery from electrode structure damage caused by hydrofluoric acid and water during operation. This significantly improves the safety performance of lithium batteries during cycling, resulting in a flame-retardant protective electrolyte system, effectively promoting the development of highly safe and stable lithium batteries.

[0028] (2) The preparation method of the present invention is simple, safe to operate, and has high purity, making it suitable for industrialization. Attached Figure Description

[0029] Figure 1 The 1H NMR spectrum of compound 51 in Example 1;

[0030] Figure 2 The carbon NMR spectrum of compound 51 in Example 1;

[0031] Figure 3 The phosphorus NMR spectrum of compound 51 in Example 1;

[0032] Figure 4 3.5mg cm -2 Performance graph of NMC811||Li battery (2.8-4.3V) assembled with LiFSI in DFPHPO (1:4n:n) electrolyte.

[0033] Figure 5 3.5mg cm -2 Performance graph of NMC811||Li battery (2.8-4.5V) assembled with LiFSI in DFPHPO (1:4n:n) electrolyte.

[0034] Figure 6 3.5mg cm -2 Performance graph of NMC811||Li battery (2.8-4.3V) assembled with LiTFSI in DFPHPO (1:4n:n) electrolyte.

[0035] Figure 7 3.5mg cm -2 Performance graph of NMC811||Li battery (2.8-4.5V) assembled with LiTFSI in DFPHPO (1:4n:n) electrolyte.

[0036] Figure 8 3.5mg cm -2 Performance graph of NMC811||Li battery (2.8-4.3V) assembled with LiDFOB in DFPHPO (1:4n:n) electrolyte.

[0037] Figure 9 3.5mg cm -2 Performance graph of NMC811||Li battery (2.8-4.5V) assembled with LiDFOB in DFPHPO (1:4n:n) electrolyte. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0040] Preparation Example

[0041] LiNi ternary cathode material 0.8 Co 0.1 Mn 0.1Preparation of O2 (NCM811) electrodes: NCM811, acetylene black, and PVDF binder were mixed in a ratio of 80:12:8 and dispersed in N-methylpyrrolidone (NMP) solution to prepare a slurry. This slurry was then uniformly coated onto aluminum foil using a 120 μm doctor blade and subsequently vacuum-dried at 120 °C for 12 h. The resulting electrode was then sliced ​​using a slicing machine to obtain a diameter of 12 mm and an active material loading of approximately 3.5 mg / cm². -2 The electrode discs were placed in the glove box for later use;

[0042] Fabrication of NCM811||Li batteries: In a glove box, the prepared electrode sheet was used as the positive electrode, lithium metal as the negative electrode, and Celgard 2500 was used as the separator to assemble the battery. NCM811||Li batteries were assembled using different electrolytes prepared in the following examples, and their electrochemical performance was tested at 55°C.

[0043] Example 1: Preparation and testing of a flame-retardant cyclic phosphoramide eutectic electrolyte (LiFSI in DFPHPO (1:4n:n))

[0044] (1) Synthesis of Compound 51: 10 g of 2,2-difluoro-1,3-propanediol was slowly injected into 20 ml of anhydrous tetrahydrofuran (THF) and 2.0 eq of triethylamine (TEA). Under ice bath conditions, 1.1 eq of phosphorus oxychloride (POCl3) was slowly added dropwise, and the reaction system was allowed to react at room temperature for 5 h. After the reaction was complete, 1.1 eq of 1-propylamine was slowly added dropwise, and the reaction system was allowed to react at room temperature for 5 h. After the reaction was complete, the filtrate was filtered, and the liquid was rotary evaporated until no liquid was discharged from the system. The solution was washed three times with saturated NaCl solution, retaining the organic phase after each wash. The solution was then dried over anhydrous sodium sulfate solid for 4 h, filtered, and distilled to obtain 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphazenecyclohexane (compound 51). The synthetic route is as follows:

[0045]

[0046] The prepared compound 51 was placed in a glove box at 25°C with a water content and oxygen content of less than 0.01 ppm for later use.

[0047] Figure 1 The 1H NMR spectrum of compound 51 in Example 1; Figure 2 The carbon NMR spectrum of compound 51 in Example 1; Figure 3 The phosphorus NMR spectrum of compound 51 in Example 1; by Figure 1 , Figure 2 and Figure 3 It can be seen that compound 51 was successfully prepared.

[0048] (2) In a glove box at 25°C with water and oxygen content below 0.01 ppm, 0.093 mg of lithium bisfluorosulfonylimide (LiFSI) was weighed and dissolved in 0.432 mg of 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphazenecyclohexane (compound 51). The mixture was heated and stirred overnight to ensure complete dissolution and uniform mixing, thus obtaining a molar ratio of lithium bisfluorosulfonylimide / 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphazenecyclohexane (compound 51) (denoted as LiFSI in DFPHPO(1:4n:n)).

[0049] Figure 4 The figure shows the performance of NCM811||Li batteries (2.8-4.3V) assembled with LiFSI in DFPHPO (1:4n:n) electrolyte. As can be seen from the figure, at 0.1C, the battery using LiFSI in DFPHPO (1:4n:n) electrolyte retains 95% of its capacity after 30 cycles at 55°C.

[0050] Figure 5 The graph shows the performance of NCM811||Li batteries (2.8-4.5V) assembled using LiFSI in DFPHPO (1:4n:n) electrolyte. As can be seen from the graph, at 0.1C, the battery using LiFSI in DFPHPO (1:4n:n) electrolyte retains 95% of its capacity after 30 cycles at 55°C.

[0051] Example 2: Preparation and testing of a flame-retardant cyclic phosphoramide eutectic electrolyte (LiTFSI in DFPHPO (1:4n:n))

[0052] (1) Synthesis of Compound 51: 10 g of 2,2-difluoro-1,3-propanediol was slowly injected into 20 mL of anhydrous tetrahydrofuran (THF) and 2.0 eq of triethylamine (TEA). Under ice bath conditions, 1.1 eq of phosphorus oxychloride (POCl3) was slowly added dropwise, and the reaction system was allowed to react at room temperature for 5 h. After the reaction was complete, 1.1 eq of 1-propylamine was slowly added dropwise, and the reaction system was allowed to react at room temperature for 5 h. After the reaction was complete, the filtrate was filtered and rotary evaporated until no liquid was evaporated from the system. The filtrate was washed three times with saturated NaCl solution, and the organic phase was retained after each wash. Subsequently, the filtrate was dried with anhydrous sodium sulfate solid for 4 h, filtered, and distilled to obtain 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphacyclohexane (compound 51).

[0053] (2) In a glove box at 25°C with water and oxygen content below 0.01 ppm, 0.1435 mg of lithium bis(trifluorosulfonyl)imide (LiTFSI) was weighed and dissolved in 0.432 mg of 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphanecyclohexane (compound 51). The mixture was heated and stirred overnight to ensure complete dissolution and uniform mixing, thus obtaining a molar ratio of lithium bis(trifluorosulfonyl)imide / 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphanecyclohexane (compound 51) (denoted as LiTFSI inDFPHPO(1:4n:n)).

[0054] Figure 6 3.5mg cm -2 Performance graph of NMC811||Li battery assembled using LiTFSI in DFPHPO (1:4n:n) electrolyte at 2.8-4.3V. As shown in the graph, at 0.1C, the battery using LiTFSI in DFPHPO (1:4n:n) electrolyte retains 95% of its capacity after 30 cycles at 55°C.

[0055] Figure 7 3.5mg cm -2 The performance graph of the NMC811||Li battery assembled using LiTFSI in DFPHPO (1:4n:n) electrolyte at 2.8-4.5V. As shown in the graph, at 0.1C, the battery using LiTFSI in DFPHPO (1:4n:n) electrolyte retains 95% of its capacity after 30 cycles at 55°C.

[0056] Example 3: Preparation and testing of a flame-retardant cyclic phosphoramide eutectic electrolyte (LiDFOB in DFPHPO (1:4n:n))

[0057] (1) Synthesis of Compound 51: 10 g of 2,2-difluoro-1,3-propanediol was slowly injected into 20 mL of anhydrous tetrahydrofuran (THF) and 2.0 eq of triethylamine (TEA). Under ice bath conditions, 1.1 eq of phosphorus oxychloride (POCl3) was slowly added dropwise, and the reaction system was allowed to react at room temperature for 5 h. After the reaction was complete, 1.1 eq of 1-propylamine was slowly added dropwise, and the reaction system was allowed to react at room temperature for 5 h. After the reaction was complete, the filtrate was filtered and rotary evaporated until no liquid was evaporated from the system. The filtrate was washed three times with saturated NaCl solution, and the organic phase was retained after each wash. Subsequently, the filtrate was dried with anhydrous sodium sulfate solid for 4 h, filtered, and distilled to obtain 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphacyclohexane (compound 51).

[0058] (2) In a glove box at 25°C with water and oxygen content below 0.01 ppm, 0.07188 mg of lithium difluorooxalate borate (LiDFOB) was weighed and dissolved in 0.432 mg of 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphanecyclohexane (compound 51). The mixture was heated and stirred overnight to ensure complete dissolution and uniform mixing, thus obtaining a molar ratio of lithium difluorosulfonylimide / 5,5-difluoro-2-(propylamino)-2-oxo-1,3,2-dioxophosphanecyclohexane (compound 51) (denoted as LiDFOB inDFPHPO(1:4n:n)).

[0059] Figure 8 3.5mg cm -2 The performance graph of the NMC811||Li battery assembled using LiDFOB in DFPHPO (1:4n:n) electrolyte at 2.8-4.3V. As shown in the graph, at 0.1C, the battery using LiDFOB in DEAPO (1:4n:n) electrolyte retains 95% of its capacity after 30 cycles at 55°C.

[0060] Figure 9 3.5mg cm -2 The performance graph of the NMC811||Li battery assembled using LiDFOB in DFPHPO (1:4n:n) electrolyte at 2.8-4.5V. As shown in the graph, at 0.1C, the battery using the LiDFOB in DFPHPO (1:4n:n) electrolyte retains 95% of its capacity after 30 cycles at 55°C.

[0061] The results of the above embodiments demonstrate that the electrolyte containing the cyclic phosphoramide of the present invention exhibits excellent high-temperature stability and can form a denser and more stable electrode interface film (SEI) under high-temperature environments. This allows the lithium battery to maintain high cycle reversibility and long-term stable operation even under high-temperature conditions. In harsh high-temperature environments, the electrolyte containing the cyclic phosphoramide of the present invention can still maintain a high ion transport rate and good reaction kinetics, exhibiting excellent resistance to high-temperature decomposition. It is expected to be applied in high-temperature application scenarios such as equipment used in desert areas, vehicle power supplies for high-temperature environments, and power supply equipment that needs to cope with temperature fluctuations.

[0062] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A flame-retardant cyclic phosphoramide eutectic electrolyte, characterized in that, The raw materials for preparing the flame-retardant cyclic phosphoramide eutectic electrolyte include lithium salt and cyclic phosphoramide; The cyclic phosphoramide has the following general formula:

2. The flame-retardant cyclic phosphoramide eutectic electrolyte according to claim 1, characterized in that, (1) The group -NR1R2 is any one of the following structures: (2) The groups R3, R4, R5, R6, R7, and R8 are any one of the following structures:

3. The flame-retardant cyclic phosphoramide eutectic electrolyte according to claim 1, characterized in that, The lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium difluorooxalateborate, lithium tetrafluoroborate, lithium dioxalateborate, lithium perchlorate, and lithium hexafluoroarsenate.

4. The flame-retardant cyclic phosphoramide eutectic electrolyte according to claim 2, characterized in that, The cyclic phosphoramide is one or a combination of two of the following molecular structures in any proportion:

5. A method for preparing a flame-retardant cyclic phosphoramide eutectic electrolyte as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) Using fluoro alcohol as raw material, tetrahydrofuran solvent, and triethylamine as acid-absorbing agent, fluoro alcohol and phosphorus oxychloride react under ice bath conditions to generate a six-membered ring of phosphate ester, and then the reaction is restored to room temperature; amine is added dropwise to the six-membered ring of phosphate ester under ice bath conditions, and the reaction is restored to room temperature after the addition is completed; after the reaction is completed, the product is obtained by direct distillation, which is cyclic phosphoramide. (2) Dissolve lithium salt in a mixture of one or two cyclic phosphoramides to obtain the product.

6. The method for preparing a flame-retardant cyclic phosphoramide eutectic electrolyte according to claim 5, characterized in that, In step (1), the fluoroalcohol is any one of 1,3-propanediol, 2,2-difluoro-1,3-propanediol, 1,2-difluoro-1,3-propanediol, 1,2,3-trifluoro-1,3-propanediol, 1,2,2,3-tetrafluoro-1,3-propanediol, 1,3-difluoro-1,3-propanediol, and 1-fluoro-1,3-propanediol.

7. The method for preparing a flame-retardant cyclic phosphoramide eutectic electrolyte according to claim 5, characterized in that, In step (1), the amine is any one of 1-methylamine, 1-ethylamine, 1-propylamine, N-methylmethylamine, ethylethylamine, methylethylamine, ethylpropylamine, and methylpropylamine.

8. The method for preparing a flame-retardant cyclic phosphoramide eutectic electrolyte according to claim 5, characterized in that, In step (2), the molar ratio of the lithium salt and the cyclic phosphoramide is 1:

4.

9. The method for preparing a flame-retardant cyclic phosphoramide eutectic electrolyte according to claim 5, characterized in that, In step (2), the lithium salt is dissolved in the cyclic phosphoramide by heating and stirring overnight.

10. The application of the flame-retardant cyclic phosphoramide eutectic electrolyte as described in any one of claims 1-4 in lithium batteries.

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