Flame-retardant double-salt polymer solid-state electrolyte, preparation method and application thereof

Abstract

The application provides a flame-retardant double-salt polymer solid electrolyte, a preparation method and application thereof, and the application selects specific polymer monomers TFEA and flame-retardant additives DEEP, ensures the interface stability between the electrolyte and a lithium metal anode through strong interaction between the polymer monomers and the flame-retardant additives, and combines other electrolyte formula components, so that the polymer solid electrolyte prepared based on the application has excellent ion conductivity and good flame-retardant safety performance. In addition, the preparation method of the flame-retardant double-salt polymer solid electrolyte is simple, production efficiency is high, manufacturing cost is low, and the application is suitable for winding batteries or columnar batteries, and shows potential in consumer electronics.

Description

Technical Field

[0001] This invention belongs to the field of polymer solid electrolyte technology, specifically relating to a flame-retardant dual-salt polymer solid electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries include lithium-ion batteries and lithium metal batteries, among which lithium metal batteries (LMBs) have attracted widespread attention due to their energy density greater than 500 kJ / L. However, the flammability of liquid electrolytes poses safety risks. A typical solution to improve the safety of liquid electrolytes is the use of flame-retardant additives. These additives include triphenyl phosphate, tributyl phosphate, triethyl phosphate, and trimethyl phosphate (TMP). These additives generally have advantages such as a wide temperature window, high dielectric constant, and the ability to dissolve lithium salts; therefore, they can be used to develop safety-enhanced lithium metal batteries. However, for lithium metal batteries, these additives are all phosphate esters, which are unstable at the lithium metal anode and can induce unstable SEI, thus affecting battery performance (G. Zhou, X. Lin, et al., Energy Storage Mater. 2021, 34, 629).

[0003] Some researchers (M. Zhou, W. Chen, H. Yang, Y. Hu, T. Lei, D. Chen, S. Wang, Y. Zhang, J. Xiong, Adv. Energy Mater. 2024, 2403082) have proposed that replacing liquid electrolytes with polymer solid electrolytes can significantly improve the safety of lithium metal batteries. The reasons why polymer solid electrolytes are safer than liquid electrolytes are twofold: First, they are less prone to leakage: Liquid electrolytes are fluid and easily leak when the battery is subjected to external impacts, casing damage, or poor sealing. Polymer solid electrolytes, existing in a solid form, are non-fluid and do not leak, thus avoiding the corrosion, short circuits, and other safety hazards that can result from electrolyte leakage. Second, they have higher mechanical strength: Polymer solid electrolytes possess a certain degree of mechanical strength, better resisting internal mechanical stress and preventing lithium dendrites from penetrating the separator and causing short circuits. In contrast, liquid electrolytes are more susceptible to damage to their separator and other structures when the battery is subjected to mechanical abuse, leading to lithium dendrite penetration and short circuits, which can potentially cause battery fires and explosions. However, polymer solid electrolytes have an inherent problem: low ionic conductivity. For example, literature reports that the ionic conductivity of PEO-based polymer electrolytes at room temperature is generally around 10. -7 -10 -8 On the order of S / cm.

[0004] Therefore, how to prepare a polymer solid electrolyte with excellent flame retardant properties and high ionic conductivity has become a research focus. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide a flame-retardant dual-salt polymer solid electrolyte, its preparation method, and its applications. The present invention selects specific polymer monomers and flame-retardant additives. Through the strong interaction between the polymer monomers and the flame-retardant additives, the interfacial stability between the electrolyte and the lithium metal anode is ensured, while simultaneously improving the ionic conductivity of the prepared polymer solid electrolyte.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A flame-retardant dual-salt polymer solid electrolyte comprises a polymer monomer, an initiator, a flame retardant, and a lithium salt;

[0008] The polymer monomer is 2,2,2-trifluoroethyl acrylate (TFEA);

[0009] The initiator is azobisisobutyronitrile (AIBN);

[0010] The flame retardant is diethyl ethylphosphonate (DEEP);

[0011] The lithium salts are lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalate)borate (LiDFOB).

[0012] The present invention also provides a method for preparing the above-mentioned flame-retardant dual-salt polymer solid electrolyte, comprising the following steps:

[0013] Step 1. Mix the polymer monomer, flame retardant, lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalate)borate, and stir until homogeneous to obtain solution A;

[0014] Step 2. Add an initiator to solution A to obtain a polymer precursor solution;

[0015] Step 3. Coat the polymer precursor solution onto the substrate, heat the substrate for a period of time, and after the reaction is complete, the desired flame-retardant dual-salt polymer solid electrolyte can be obtained.

[0016] Furthermore, the volume ratio of polymer monomer to flame retardant is (3-7):(7:3).

[0017] Furthermore, the volume ratio of polymer monomer to flame retardant is preferably 7:3, 6:4, 4:6 or 3:7.

[0018] Furthermore, the mass ratio of the initiator to the polymer monomer is 1–1.5 wt%.

[0019] Furthermore, in the polymer precursor solution, excessively high lithium salt concentrations are detrimental to ion transport. The concentration of LiTFSI is 0.2 mol / L to 1 mol / L, and the concentration of lithium difluoro(oxalate)borate is 0.5 to 1 mol / L.

[0020] Furthermore, in step 3, the heating temperature is 60–70°C, and the heating time is 12–16 hours.

[0021] The present invention also provides the application of the above-mentioned flame-retardant dual-salt polymer solid electrolyte in lithium metal batteries.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] 1. Strong interactions exist between DEEP and TFEA monomers. Through the polar interactions between -P=O and -CH2CF3, DEEP is firmly anchored to the PTFEA matrix. This reduces free DEEP molecules, significantly mitigating interfacial reactions and ensuring interfacial stability with the lithium metal anode. Simultaneously, DEEP can modulate fast ion channels as a high-dielectric molecule, thereby improving ion conductivity. Furthermore, when DEEP is subjected to combustion, the phosphoric acid produced through thermal decomposition can form phosphate esters with the hydroxyl groups in the polymer material. These phosphate esters can lower the surface temperature of the material, forming a protective layer on the material surface that reduces oxygen and heat transfer, thus inhibiting the combustion reaction.

[0024] 2. The TFEA monomers selected in this invention contain three CF groups in each monomer. This increases the polarity of the polymer chain, which helps to effectively capture DEEP molecules through intermolecular interactions, thereby limiting DEEP migration and weakening lateral interactions. An anion-dominated lithium-ion dissolution structure is thus constructed. On the one hand, anions may attract lithium ions more strongly through electrostatic interactions, altering the charge distribution and chemical environment around the lithium ions, thereby affecting their migration rate and transport path. On the other hand, the specific arrangement of anions may provide specific channels or spaces for lithium ions, guiding their directional movement and improving their transport efficiency in the electrolyte, thereby forming an anion-derived solid electrolyte interface / cathode electrolyte interface (SEI / CEI) protective layer and rapid lithium-ion structural transport.

[0025] 3. This invention employs a LiTFSI-LiDFOB dual lithium salt. Due to the high dissociation capability of LiTFSI and the excellent film-forming properties of LiDFOB, the electrode-electrolyte interface is further strengthened. The in-situ crosslinking polymerization strategy containing TFEA precursors ensures good wettability of the electrolyte on the electrode surface, thereby significantly reducing interfacial resistance caused by poor interfacial contact. Through these electrochemical optimization strategies, rapid lithium-ion transport kinetics, high conductivity, and higher lithium-ion transfer numbers can be achieved on the lithium anode, making it an ideal choice for quasi-solid-state lithium metal batteries with broad application potential.

[0026] 4. The method for preparing the flame-retardant dual-salt polymer solid electrolyte of the present invention is simple, has high production efficiency and low manufacturing cost, and is suitable for practical wound batteries or cylindrical batteries, showing potential in consumer electronics products. Attached Figure Description

[0027] Figure 1 This is a physical image of the flame-retardant dual-salt polymer solid electrolyte prepared in Example 1 of the present invention.

[0028] Figure 2 This is a comparison chart of the ionic conductivity of Examples 1-3 and Comparative Examples 1-2.

[0029] Figure 3 The graph shows a performance comparison of lithium iron phosphate full batteries in Examples 1-3 and Comparative Examples 1-2.

[0030] Figure 4 The diagram shows a safety test before and after the wound battery was cut.

[0031] Among them, (a) is the assembled wound battery cell; (b) is the voltage display of the battery before it is cut; (c) is the actual appearance of the battery at the moment it is cut; and (d) is the battery left to stand for a long time after it is cut.

[0032] Figure 5 The diagram shows a safety test before and after ignition of a wound battery.

[0033] Among them, (a) is a voltage display diagram of the wound battery when it is stationary; (b) is an actual image of the battery cell exposed after the battery is cut open; (c) is an actual image of the battery cell burned with an igniter; and (d) is an actual image of the battery and battery cell after burning. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0035] A flame-retardant dual-salt polymer solid electrolyte comprises a polymer monomer, an initiator, a flame retardant, and a lithium salt;

[0036] The polymer monomer is 2,2,2-trifluoroethyl acrylate (TFEA);

[0037] The initiator is azobisisobutyronitrile (AIBN);

[0038] The flame retardant is diethyl ethylphosphonate (DEEP);

[0039] The lithium salts are lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalate)borate (LiDFOB).

[0040] By in-situ crosslinking polymerization of TFEA-containing precursors and initiators, the polymer electrolyte can directly form a tight coating or network structure on the electrode surface. This direct contact and interaction enhances the interfacial bonding between the electrolyte and the electrode, allowing the electrolyte to adhere better to the electrode surface and thus improving wettability. In-situ crosslinking polymerization can solidify the liquid precursor in situ inside the battery, forming a hyperconformal interface, which greatly solves the solid / solid interface contact problem, enabling better adhesion and wetting between the electrolyte and the electrode. At the same time, through the polar interaction between -P=O and -CH2CF3, DEEP is anchored to the PTFEA matrix, and the polarity of the polymer chain inhibits the migration of DEEP, avoiding side reactions that would occur when DEEP migrates to the interface.

[0041] Example 1

[0042] A method for preparing a flame-retardant dual-salt polymer solid electrolyte includes the following steps:

[0043] Step 1. Pour 7 ml of DEEP into a brown glass bottle, then add 3 ml of TFEA and mix well. Then add 1.435 g of LiTFSI and stir at room temperature for 2 h. The concentration of LiTFSI is 0.5 mol / L. Then add 0.715 g of LiDFOB and stir at room temperature for 2 h to obtain solution A, where the concentration of LiDFOB is 0.5 mol / L.

[0044] Step 2. Add 0.12 g of AIBN to solution A and stir at room temperature for 30 min to obtain a polymer precursor solution;

[0045] Step 3. Coat the polymer precursor solution onto a glass substrate, place the substrate in a 60°C oven for 12 hours, and the desired flame-retardant dual-salt polymer solid electrolyte will be obtained after the reaction is complete.

[0046] A physical image of the flame-retardant dual-salt polymer solid electrolyte prepared in this embodiment is shown below. Figure 1 As shown.

[0047] Example 2

[0048] The polymer solid electrolyte was prepared according to the steps of Example 1, except that the volume ratio of DEEP and TFEA in step 1 was adjusted to 6:4 and 3:7, while the other steps remained unchanged.

[0049] Example 3

[0050] The polymer solid electrolyte was prepared according to the steps of Example 1, except that the amount of LiTFSI added in step 2 was adjusted to 0.574 g or 2.87 g, corresponding to a concentration of 0.2 mol / L or 1 mol / L, while the other steps remained unchanged.

[0051] Comparative Example 1

[0052] LiTFSI and LiDFOB were added to 10 ml of DEEP solution to obtain a liquid electrolyte, with the concentration of both lithium salts in the solution being 0.5 mol / L.

[0053] Comparative Example 2

[0054] The polymer electrolyte was prepared according to the steps of Example 1, with 0.5 mol / L of Li TFSI and LiDFOB precursor solution added to 10 ml of TFEA solution, and 0.2 g of AIBN added.

[0055] Figure 1 This is a photograph of the flame-retardant dual-salt polymer solid electrolyte prepared in Example 1 of the present invention. As can be seen from the figure, the electrolyte prepared in this example is indeed solid.

[0056] Figure 2 The graph shows a comparison of the ionic conductivity of Examples 1-3 and Comparative Examples 1-2. As can be seen from the graph, the conductivity of the polymer solid electrolyte prepared in this invention is significantly better than that of the electrolyte prepared in the comparative examples.

[0057] Using LiFePO4 (LFP) as the positive electrode and lithium foil as the negative electrode, wound batteries were assembled using the electrolytes prepared in Examples 1-3 and Comparative Examples 1-2, respectively. The discharge capacity of the wound batteries at a current density of 0.5C at room temperature was tested, and the test results are as follows: Figure 3 As shown. The wound battery prepared based on the polymer solid electrolyte of this invention exhibits excellent electrical performance.

[0058] The flame-retardant dual-salt polymer solid electrolyte prepared in Example 1 was used in a shear safety test of the assembled wound battery as follows: Figure 4 As shown. Figure 4 In the image: (a) shows the assembled wound battery cell; (b) shows the battery voltage display before it is cut; (c) shows the battery's actual appearance at the moment it is cut; (d) shows the battery after it has been left to stand for a long time following the cut. Figure 4As shown in the actual image, a precursor solution is infiltrated into the battery cell, and in-situ polymerization is induced before the battery is sealed to prepare a wound battery based on a flame-retardant dual-salt polymer solid electrolyte. Figure 4 As shown in bd, even under extreme conditions, the cutting process does not cause combustion. The cutting process creates an internal short circuit between the lithium metal anode and cathode. Nevertheless, the flame-retardant dual-salt polymer solid electrolyte eliminates the ignition hazard, ensuring battery safety in practical applications.

[0059] Figure 5 In the figures: (a) shows the voltage display of the wound battery when it is stationary; (b) shows the actual appearance of the battery cell after it has been cut open; (c) shows the actual appearance of the battery cell after it has been burned with an igniter; (d) shows the actual appearance of the battery and battery cell after burning. As can be seen from the figures, the wound battery prepared based on the polymer solid electrolyte of this invention is not easily ignited and has excellent flame-retardant properties.

[0060] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A flame-retardant double-salt polymer solid-state electrolyte, characterized by, Including polymer monomers, initiators, flame retardants, and lithium salts; The polymer monomer is 2,2,2-trifluoroethyl acrylate; The initiator is azobisisobutyronitrile; The flame retardant is diethyl ethylphosphonate; The lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalate)borate.

2. The preparation method of the flame-retardant double-salt polymer solid-state electrolyte according to claim 1, characterized in that, Includes the following steps: Step 1. Mix the polymer monomer, flame retardant, lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalate)borate, and stir until homogeneous to obtain solution A; Step 2. Add an initiator to solution A to obtain a polymer precursor solution; Step 3. Coat the polymer precursor solution onto the substrate, heat the substrate for a period of time, and after the reaction is complete, the desired flame-retardant dual-salt polymer solid electrolyte can be obtained.

3. The preparation method of the flame-retardant double-salt polymer solid-state electrolyte according to claim 2, characterized in that, The volume ratio of polymer monomer to flame retardant is (3-7):(7:3).

4. The preparation method of the flame-retardant double-salt polymer solid-state electrolyte according to claim 3, characterized in that, The volume ratio of polymer monomer to flame retardant is 7:3, 6:4, 4:6 or 3:

7.

5. The preparation method of the flame-retardant double-salt polymer solid-state electrolyte according to claim 2, characterized in that, The mass ratio of initiator to polymer monomer is 1~1.5 wt%.

6. The preparation method of the flame-retardant double-salt polymer solid-state electrolyte according to claim 2, characterized in that, In the polymer precursor solution, the concentration of LiTFSI is 0.2 mol / L to 1 mol / L, and the concentration of lithium difluoro(oxalate)borate is 0.5 to 1 mol / L.

7. The method for preparing the flame-retardant dual-salt polymer solid electrolyte as described in claim 2, characterized in that, In step 3, the heating temperature is 60~70℃ and the heating time is 12~16h.

8. The application of the flame-retardant dual-salt polymer solid electrolyte obtained by the method of any one of claims 2-7 in lithium metal batteries.

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