Flame-retardant interfacial optimization agent with high lithium ion conductivity and preparation method thereof

Abstract

The application discloses a high lithium ion conductivity flame-retardant interface modifier and a preparation method thereof. The material is synthesized by one-pot one-step reaction of phosphorus oxychloride, diamine and alcohol ether compound, and is used in combination with lithium salt to form a flame-retardant interface modifier with high lithium ion conduction function. The molecular structure is rich in ether bonds, which can effectively coordinate with lithium ions, promote the efficient migration of lithium ions at the electrode interface, and significantly improve the cycle stability and rate performance of the solid-state battery. At the same time, the nitrogen and phosphorus elements introduced in the material endow it with excellent flame-retardant properties, which helps to improve the safety of the battery system. In addition, the modifier has good flowability and wettability, which can enhance the interface compatibility between the components in the solid-state battery. The preparation process of the application is simple, controllable, reproducible and low in cost, and is suitable for interface modification of solid-state lithium ion batteries, and has important prospects for promoting the development of high-safety, high-energy-density and low-cost solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of key technologies for solid-state batteries, and in particular to a flame-retardant interface optimizer with high lithium-ion conductivity and its preparation method. Background Technology

[0002] To improve solid-solid interface contact, existing technologies often introduce a small amount of liquid medium at the interface for wetting, with materials such as diethyl carbonate (DEC) and ethylene carbonate (EC) being common solvents of traditional alkyl carbonates. These substances generally have low flash points and high volatility, and their inherent flammability and explosiveness prevent them from fundamentally improving battery safety. On the other hand, while some studies have attempted to use flame-retardant solvents such as triethyl phosphate and trimethyl phosphate as alternatives, these materials often struggle to balance interfacial wettability, lithium-ion conductivity, flame-retardant efficiency, and cost, failing to meet the practical application requirements of high-performance solid-state batteries. Therefore, developing a flame-retardant interface optimizer with high lithium-ion conductivity for solid-state batteries is of significant practical importance.

[0003] A search revealed no publicly available reports on the synthesis of an all-solid-state battery interface optimizer that combines nitrogen and phosphorus elements and possesses both lithium-ion conduction and flame retardant functions through a one-step reaction using phosphorus oxychloride, diamine, and alcohol ethers as raw materials. Summary of the Invention

[0004] To address the technical bottleneck of existing solid-state battery interface modification materials, which struggle to simultaneously achieve high ionic conductivity, excellent flame retardancy, and good process compatibility, this invention aims to provide a flame-retardant interface optimizer with high lithium-ion conductivity and its preparation method. This interface optimizer aims to solve core problems in solid-state batteries such as poor electrode-electrolyte interface contact, high interfacial impedance, and insufficient safety. Furthermore, its preparation method is characterized by simple steps, good reproducibility, strong controllability, and low cost, making it suitable for large-scale applications.

[0005] To address the aforementioned technical bottlenecks, this invention utilizes phosphorus oxychloride, diamine, and alcohol ethers as raw materials, synthesized through a one-step reaction, simultaneously introducing nitrogen and phosphorus elements into the molecule and enriching it with ether bonds. The design mechanism lies in the following: the introduction of organophosphorus units increases the flash point of the material and generates a phosphate ester flame-retardant layer upon thermal decomposition, significantly suppressing the battery's combustion tendency under thermal or electrical abuse conditions; the introduction of nitrogen elements allows for a synergistic flame-retardant effect with phosphorus, further enhancing the material's flame-retardant properties. Simultaneously, the abundant ether bonds (-COC-) in the molecular structure effectively coordinate with lithium ions, promoting rapid lithium ion migration at the interface and significantly improving the interfacial compatibility between the electrode and the solid electrolyte, thereby enhancing the battery's cycle life and rate performance. Furthermore, the synthesized target product, the interface optimizer matrix PODE, has a suitable molecular weight (approximately 269.3 g / mol), giving it good fluidity and spreading ability, which is beneficial for achieving uniform coating and interface filling during actual battery manufacturing.

[0006] The specific technical solution of the present invention is as follows:

[0007] A flame-retardant interface optimizer with high lithium-ion conductivity is composed of an interface optimizer matrix and a lithium salt. The lithium salt accounts for 24-30% of the total mass of the flame-retardant interface optimizer. The structural formula of the interface optimizer matrix is ​​shown in formula (1), where m and n are arbitrary integers and both m and n are greater than 0.

[0008]

[0009] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide.

[0010] A method for preparing a flame-retardant interface optimizer with high lithium-ion conductivity includes the following steps: dissolving phosphorus oxychloride, diamine, triethylamine and alcohol ether in tetrahydrofuran solvent, reacting them in a one-pot one-step process at -20°C to obtain an interface optimizer matrix, and then adding lithium salt to synthesize the flame-retardant interface optimizer.

[0011] The interface optimizer matrix is ​​composited with lithium salt to construct an efficient lithium-ion conduction channel; its synthesis route is shown in equation (2) below:

[0012]

[0013] The preparation method of a flame-retardant interface optimizer with high lithium-ion conductivity specifically includes the following steps:

[0014] S1. In an inert atmosphere glove box, phosphorus oxychloride and tetrahydrofuran solvent were added to a dry three-necked flask, sealed, and transferred to the reaction apparatus. Under nitrogen protection, at -20°C and with mechanical stirring at 300-500 rpm, a mixed solution containing tetrahydrofuran, triethylamine, diamine, and alcohol ether was slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition was complete, the reaction system was continued to react for 1 hour under nitrogen protection and at -20°C to obtain a crude product containing the target product.

[0015] S2. After the reaction, the crude product was filtered to remove triethylamine hydrochloride precipitate; the filtrate was concentrated by rotary evaporation at 45°C and -0.1 MPa to remove excess raw materials, by-products, and most of the tetrahydrofuran solvent; the concentrate was transferred to a separatory funnel and extracted with a 1:1 volume ratio of deionized water and dichloromethane, repeated three times. During extraction, water-soluble impurities entered the aqueous phase, and the lower organic phase was collected; the combined organic phases were rotary evaporated at 45°C and -0.1 MPa to remove dichloromethane, and then dried for 4 hours at the same temperature of 45°C and a vacuum of -0.1 MPa to completely remove residual water, obtaining a purified interface optimizer matrix; lithium salt was added to the purified interface optimizer matrix and magnetically stirred at room temperature until the lithium salt was completely dissolved and mixed evenly to obtain a flame-retardant interface optimizer with high lithium-ion conductivity.

[0016] Preferably, the diamine is diethylamine, dipropylamine, or dibutylamine.

[0017] Preferably, the alcohol ether is ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, or triethylene glycol monomethyl ether.

[0018] Preferably, the molar ratio of phosphorus oxychloride to diamine is 1:(1~1.1), and the molar ratio of phosphorus oxychloride to alcohol ether is 1:(2~2.2).

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. Excellent flame retardant safety:

[0021] The interface optimizer described in this invention is a phosphorus-nitrogen synergistic flame retardant system. The nitrogen and phosphorus elements it contains jointly endow the interface optimizer with PODE flame retardant properties. Its flame retardant mechanism manifests in the dual effects of the gas phase and condensed phase: under high temperature or thermal abuse conditions, the phosphorus-containing units in the molecular structure decompose, releasing phosphorus-oxygen free radicals, which can effectively capture active free radicals such as H· and HO· in the combustion chain reaction, thereby interrupting the gas phase combustion process; simultaneously, the strongly dehydrating substances such as metaphosphoric acid and polymetaphosphoric acid generated by thermal decomposition can promote rapid dehydration and carbonization of the material surface, forming a dense and stable carbonized protective layer, effectively isolating oxygen and heat from the material's interior. The introduction of nitrogen further enhances the synergistic flame retardant effect, not only promoting char formation at lower temperatures but also significantly increasing the residual amount and density of the carbon layer. This phosphorus-nitrogen synergistic mechanism enables the interface optimizer of this invention to possess excellent intrinsic flame retardant properties without relying on external flame retardants, fundamentally improving the thermal safety of solid-state batteries.

[0022] 2. Good ionic conductivity and interfacial compatibility:

[0023] The interface optimizer of this invention is used to optimize the interface of solid-state lithium-ion batteries. The ether bonds (-COC-) in its molecular structure can coordinate with lithium ions, promoting lithium ion transport between the positive and negative electrodes, thereby improving the cycle performance and rate performance of the solid-state battery. It has strong coordination and solvation capabilities for lithium ions, enabling the construction of efficient lithium-ion transport channels. The ionic conductivity of the interface optimizer is in the range of 3 × 10⁻⁶. -4 S / cm up to 5×10 -4 The S / cm ratio significantly promotes the rapid migration of lithium ions at the electrode / electrolyte solid-solid interface. This characteristic helps to substantially reduce interfacial impedance and improve the transport kinetics of lithium ions at the interface, thereby significantly improving the cycle stability and rate performance of the battery. Simultaneously, this optimizer possesses a suitable molecular weight, good flowability, and excellent interfacial wetting ability, which can fully fill the microscopic voids between the electrode active material layer and the solid electrolyte membrane, effectively eliminating poor interfacial contact, improving the interfacial affinity and contact integrity between various components of the solid-state battery, and thus suppressing interfacial polarization and side reactions.

[0024] 3. The preparation process is simple and inexpensive:

[0025] This invention employs a one-pot, one-step synthesis strategy, directly condensing phosphorus oxychloride, diamine, and alcohol ether compounds to prepare the target product. The entire preparation process is simple and efficient, with mild reaction conditions (low temperature and ambient pressure), eliminating the need for stringent anhydrous and oxygen-free operations and complex purification equipment, thus exhibiting excellent reproducibility and process controllability. The raw materials used, such as phosphorus oxychloride, diamine, and alcohol ethers, are all readily available and inexpensive chemical products. This technological advantage effectively reduces the production cost of interface optimizers, laying a solid foundation for their large-scale preparation and industrial application in the field of solid-state lithium batteries. Attached Figure Description

[0026] The accompanying drawings are provided to further illustrate and explain the technical solutions and embodiments of the present invention, and do not constitute a limitation thereof. In the drawings:

[0027] Figure 1 The hydrogen NMR spectrum of Example 1;

[0028] Figure 2 This is the high-performance liquid chromatogram of Example 1;

[0029] Figure 3 The impedance test diagrams and ionic conductivity calculation results for Example 1 and Comparative Example 1 are shown.

[0030] Figure 4 These are flame retardant test diagrams for Example 1 and Comparative Example 1;

[0031] Figure 5 The weight loss test process for Example 4 is as follows: (A. Drop test for 4 min; B. Mass m0 before heating; C. Heating at 120℃ and -0.1 MPa; D. Mass m1 after heating). Detailed Implementation

[0032] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the embodiments described. Unless otherwise specified, the reagents, methods and equipment used in the present invention are all conventionally selected in the art. Example 1

[0033] 1. In an argon atmosphere glove box, add 1.86 mL (0.02 mol) of phosphorus oxychloride (POCl3) and 50 mL of anhydrous tetrahydrofuran with a moisture content of <40 ppm to a dry three-necked flask, seal it, remove it, and place it in a low-temperature reactor. Stir and mix it evenly with a polytetrafluoroethylene stirrer at -20°C.

[0034] 2. In an argon-filled glove box, 2.07 mL (0.02 mol) of diethylamine (DEA), 3.16 mL (0.04 mol) of ethylene glycol monomethyl ether (EGME), and 9.2 mL (0.066 mol) of triethylamine (TEA) were dissolved in 80 mL of anhydrous tetrahydrofuran with a water content <40 ppm. The solution was transferred to a constant-pressure dropping funnel and sealed. The dropping funnel was then attached to the reaction apparatus from step 1. Under nitrogen protection, at -20°C, and with mechanical stirring at 350 rpm, the mixture was added dropwise to a three-necked flask at a constant rate over approximately 3 hours. After the addition was complete, the reaction was continued for 0.5 hours to obtain the crude product.

[0035] 3. The crude product was vacuum filtered and then concentrated by rotary evaporation. The concentrate was then transferred to a separatory funnel and extracted with 50 mL of deionized water and 50 mL of dichloromethane, retaining the lower organic phase. This process was repeated three times. After removing the dichloromethane by rotary evaporation, the organic phase was vacuum dried at 45 °C and -0.1 MPa for 4 hours to completely remove residual water, yielding the purified interface optimizer matrix.

[0036] 4. Add lithium bis(trifluoromethanesulfonylimide) (LiTFSI) to the above interface modifier matrix at an amount of 23.2% of the mass of the interface modifier matrix, and stir magnetically at room temperature until completely dissolved to obtain the interface modifier PODE.

[0037] 5. Lithium iron phosphate active material (LFP), conductive agent (Super P), and binder (PVDF) are added to N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is then coated onto carbon-coated aluminum foil using a blade coater and vacuum dried at 60℃ and -0.1 MPa for 6 hours. The dried electrode sheet is then compacted by roller pressing and cut into circular electrode sheets with a diameter of 12mm to obtain the lithium iron phosphate positive electrode sheet.

[0038] 6. The lithium-ion battery is assembled in a glove box. The assembly sequence is as follows: positive electrode battery case, lithium iron phosphate positive electrode sheet, GF / D glass fiber separator, interface optimizer PODE, lithium sheet, negative electrode battery case, and then packaged to obtain the lithium-ion battery. Example 2

[0039] The difference between this embodiment and Example 1 lies in the selection of raw materials. Specifically, the diamine is dihexylamine, and the alcohol ether is diethylene glycol monomethyl ether. The remaining raw material ratios, synthesis steps, and post-processing are consistent with those of Example 1. Example 3

[0040] The difference between this embodiment and Example 1 lies in the adjustment of the molar ratio of the raw materials. Specifically, the molar ratio of phosphorus oxychloride to diamine is 1:1, and the molar ratio of phosphorus oxychloride to alcohol ether is 1:2.2. The remaining raw material types, synthesis steps, and post-processing techniques are consistent with those of Example 1.

[0041] Comparative Example 1

[0042] 1. Prepare a ternary electrolyte, wherein the ternary electrolyte is composed of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:1:1, wherein the mass fraction of the solute lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is 20.2%.

[0043] 2. The lithium-ion battery is assembled in a glove box. The assembly sequence is as follows: positive electrode battery case, lithium iron phosphate positive electrode sheet, GF / D glass fiber separator, ternary electrolyte, lithium sheet, negative electrode battery case, and then packaged to obtain the lithium-ion battery.

[0044] Example 4: Assembly of Solid-State Full Cells

[0045] Assemble the lithium-ion pouch cell for weight loss testing according to the following steps:

[0046] 1. Prepare lithium iron phosphate cathode slurry according to the method described in step 5 of Example 1, and uniformly coat it onto the surface of carbon-coated aluminum foil. After vacuum drying at 80°C for 6 hours, compact it by roller pressing and cut it into rectangular cathode sheets of 50 mm × 40 mm.

[0047] 2. Modified lotus root starch (MLR), boric acid (H3BO3), and lithium carbonate (Li2CO3) were added in a mass percentage ratio of 73.3:4.7:12.0 and reacted in an aqueous solution at 65℃ for 6 hours. Then, 10.0wt% LiTFSI was added and the reaction was continued for another hour. After stopping the reaction, the mixture was directly spray-dried. The dried polymer electrolyte powder was mixed with 0.2-0.1wt% PTFE to prepare a solid electrolyte membrane, which was then cut into 60 mm × 50 mm pieces for later use.

[0048] 3. Graphite anode active material, conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are placed in deionized water at a mass ratio of 92:2:2:4 and stirred until homogeneous to prepare a negative electrode slurry. The slurry is then evenly coated onto the surface of copper foil. After vacuum drying at 80℃ for 6 hours, it is compacted by roller pressing and cut into rectangular negative electrode sheets of 52 mm × 42 mm.

[0049] 4. The interface optimizer PODE synthesized in step 4 of Example 1 was uniformly injected into the surface of the positive electrode and between the solid electrolyte membrane using a micropipette, with the amount added being 20 wt% of the solid electrolyte membrane.

[0050] 5. Stack the electrodes in the order of "positive electrode sheet - solid electrolyte membrane - negative electrode sheet" to ensure uniform distribution of the interface modifier. Place the stacked cells in an aluminum-plastic film packaging bag and heat-seal them under a vacuum of -0.1 MPa to obtain a soft-pack battery. Let the packaged battery stand at room temperature for 12 hours.

[0051] Test Example 1: Weight Loss Rate Test of Solid-State Full Cells

[0052] To further verify the applicability of the interface optimizer PODE prepared in this invention in solid-state battery systems, a weight loss rate test was conducted on the interface optimizer obtained in Example 1. The specific test steps are as follows:

[0053] 1. Pretreatment: Solid-state full cells were assembled using Example 4, and after encapsulation, they were left to stand at 25°C for 2 hours.

[0054] 2. Observe the opening: Make an opening in the battery in a dry environment, invert it and let it stand for 5 minutes, and observe whether any liquid flows out.

[0055] 3. Weight Loss Rate Test: Place the battery with no obvious liquid leakage in a constant temperature drying oven at 120℃ and a vacuum of -0.1 MPa, and heat continuously for 6 hours. Record the mass m0 before heating and the mass m1 after heating, and calculate the weight loss rate using the following formula:

[0056]

[0057] Table 1. Elemental analysis results of Example 1

[0058]

[0059] Based on the results of 1H NMR, HPLC and elemental analysis, the PODE product obtained in Example 1 is not a single structure, but a mixture of three compounds.

[0060] The impedance test diagrams and ionic conductivity calculation results of Example 1 and Comparative Example 1 are as follows: Figure 3 As shown, based on the above test results, the ionic conductivity of the interface optimizer prepared in Example 1 is 4.05 × 10⁻⁶. -3 S cm -1 Although this value is lower than that of commercial carbonate-based mixed solvent electrolyte systems (20.37 × 10⁻⁶). -3 S cm -1 However, it still has the potential to be applied to solid-state battery systems, and it also has comprehensive advantages such as flame retardancy and interface compatibility.

[0061] according to Figure 4The flame retardant test results shown show that Comparative Example 1 continued to burn after direct ignition and remained burning even after the flame source was removed; while Example 1, which uses PODE, an interface optimizer with both lithium-ion conduction and flame retardant functions prepared in this invention, did not burn after 10 seconds of contact with the same flame and only produced a small amount of white smoke after the flame source was removed, indicating that PODE has good flame retardant properties.

[0062] Table 2. Weightlessness test results of Example 2

[0063]

[0064] Test results show that:

[0065] The pouch cell assembled using the PODE flame-retardant interface optimizer of this invention showed no significant liquid leakage after rupture, and its weight loss was only 0.3% after heating at 120°C and -0.1 MPa for 6 hours, meeting the judgment threshold (≤0.5%) specified in the draft national standard. This confirms that the PODE interface optimizer prepared in this invention can achieve good compatibility and synergy with the solid electrolyte system, and the battery assembled with it meets the core characteristic requirements of solid-state batteries, improving interfacial ion transport capabilities while ensuring battery safety.

Claims

1. A flame-retardant interface modifier with high lithium-ion conductivity, characterized in that... It is composed of an interface optimizer matrix and a lithium salt, wherein the mass of the lithium salt is 24-30% of the total mass of the flame retardant interface optimizer. The structural formula of the interface optimizer matrix is ​​shown in formula (1), where m and n are arbitrary integers and both m and n are greater than 0. 。 2. The flame-retardant interface optimizer with high lithium-ion conductivity according to claim 1, characterized in that... The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

3. A method for preparing a flame-retardant interface optimizer with high lithium-ion conductivity as described in claim 1, characterized in that... The process includes the following steps: dissolving phosphorus oxychloride, diamine, triethylamine, and alcohol ether in tetrahydrofuran solvent, reacting them in a one-pot, one-step process at -20°C to obtain an interface optimizer matrix, and then adding lithium salt to synthesize a flame-retardant interface optimizer.

4. The method for preparing the flame-retardant interface optimizer with high lithium-ion conductivity according to claim 3, characterized in that... Includes the following steps: S1. In an inert atmosphere glove box, phosphorus oxychloride and tetrahydrofuran solvent were added to a dry three-necked flask, sealed, and transferred to the reaction apparatus. Under nitrogen protection, at -20°C and with mechanical stirring at 300-500 rpm, a mixed solution containing tetrahydrofuran, triethylamine, diamine, and alcohol ether was slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition was complete, the reaction system was continued to react for 1 hour under nitrogen protection and at -20°C to obtain a crude product containing the target product. S2. After the reaction, the crude product was filtered to remove triethylamine hydrochloride precipitate; the filtrate was concentrated by rotary evaporation at 45°C and -0.1 MPa to remove excess raw materials, by-products, and most of the tetrahydrofuran solvent; the obtained concentrate was transferred to a separatory funnel and extracted with a 1:1 volume ratio of deionized water and dichloromethane, repeated 3 times. During the extraction, water-soluble impurities entered the aqueous phase, and the lower organic phase was collected; the combined organic phases were rotary evaporated at 45°C and -0.1 MPa to remove dichloromethane, and then dried for 4 hours at the same temperature of 45°C and a vacuum of -0.1 MPa to completely remove residual water, obtaining the purified interface optimizer matrix; lithium salt was added to the purified interface optimizer matrix and magnetically stirred at room temperature until the lithium salt was completely dissolved and mixed evenly to obtain a flame-retardant interface optimizer with high lithium-ion conductivity.

5. The method for preparing the flame-retardant interface optimizer with high lithium-ion conductivity according to claim 3, characterized in that, The diamine is diethylamine, dipropylamine, or dibutylamine.

6. The method for preparing the flame-retardant interface optimizer with high lithium-ion conductivity according to claim 3, characterized in that, The alcohol ether is ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, or triethylene glycol monomethyl ether.

7. The method for preparing the flame-retardant interface optimizer with high lithium-ion conductivity according to claim 3, characterized in that, The molar ratio of phosphorus oxychloride to diamine is 1:(1~1.1), and the molar ratio of phosphorus oxychloride to alcohol ether is 1:(2~2.2).

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