Flame-retardant double-salt polymer solid electrolyte as well as preparation method and application thereof

Abstract

According to the flame-retardant double-salt polymer solid electrolyte, the preparation method and the application of the flame-retardant double-salt polymer solid electrolyte, the specific polymer monomer TFEA and the flame-retardant additive DEEP are selected, and the interface stability between the electrolyte and a lithium metal anode is ensured through the strong interaction between the polymer monomer and the flame-retardant additive; meanwhile, other electrolyte formula components are combined, so that the polymer solid electrolyte prepared on the basis of the preparation method has excellent ionic conductivity and good flame-retardant safety performance. In addition, the flame-retardant double-salt polymer solid electrolyte is simple in preparation method, high in production efficiency, low in manufacturing cost and suitable for winding batteries or columnar batteries, and shows potential in consumer electronics.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer solid electrolytes, and particularly relates to a flame-retardant double-salt polymer solid electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium batteries include lithium-ion batteries and lithium metal batteries. Among them, lithium metal batteries (LMBs) have received extensive attention due to their energy density greater than 500. However, the flammability of liquid electrolytes poses a safety risk. For liquid electrolytes, a typical solution to improve safety is to use flame-retardant additives. These additives include triphenyl phosphate, tributyl phosphate, triethyl phosphate, trimethyl phosphate (TMP), etc. These additives generally have advantages such as a wide temperature window, a 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 ester additives, which are not stable to lithium metal anodes and will induce an unstable SEI, thus affecting the performance of the battery (G. Zhou, X. Lin, et al., Energy Storage Mater. 2021, 34, 629.).

[0003] It has been proposed (M. Zhou, W. Chen, H. Yang, Y. Hu, T. Lei, D. Chen, S. Wang, Y. Zhang, J. Xiong, Adv. Energy Mater. 2024, 2403082) to replace liquid electrolytes with polymer solid electrolytes, which can greatly improve the safety of lithium metal batteries. The reasons why polymer solid electrolytes are safer than liquid electrolytes are as follows: First, they are not easily leaked: Liquid electrolytes have fluidity and are likely to leak when the battery is subjected to external impact, the outer shell is damaged, or the seal is poor. In contrast, polymer solid electrolytes exist in a solid state and have no fluidity, so there will be no leakage problem, thus avoiding potential safety hazards such as corrosion and short circuit caused by electrolyte leakage. Second, they have high mechanical strength: Polymer solid electrolytes have a certain mechanical strength and can better resist the mechanical stress inside the battery, preventing lithium dendrites from penetrating the separator and causing short circuit. In contrast, when the battery is mechanically abused, the structures such as the separator of liquid electrolytes are more likely to be damaged, resulting in lithium dendrites penetrating and causing short circuit, which may further lead to dangerous situations such as battery fire and explosion. However, polymer solid electrolytes have an inherent problem, that is, their ionic conductivity is relatively low. For example, as reported in the literature, the ionic conductivity of PEO-based polymer electrolytes at room temperature is generally on the order of 10 -7 -10 -8 S / cm.

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

[0005] Aiming at the problems existing in the background technology, the purpose of the present invention is to provide a flame-retardant double-salt polymer solid electrolyte, a preparation method thereof and an application thereof. The present invention selects specific polymer monomers and flame-retardant additives, and 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, and at the same time, the ionic conductivity of the prepared polymer solid electrolyte is improved.

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

[0007] A flame-retardant double-salt polymer solid electrolyte, comprising 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 salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB).

[0012] The present invention also provides a preparation method of the above flame-retardant double-salt polymer solid electrolyte, comprising the following steps:

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

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

[0015] Step 3. Coat the polymer precursor solution on a substrate, heat the substrate for a period of time, and the required flame-retardant double-salt polymer solid electrolyte can be obtained after the reaction ends.

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

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

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

[0019] Furthermore, in the polymer precursor solution, too high a concentration of lithium salt is not conducive to ion transport. The concentration of LiTFSI is 0.2 mol / L to 1 mol / L, and the concentration of lithium difluoro(oxalato)borate is 0.5 to 1 mol / L.

[0020] Furthermore, in Step 3, the heating temperature is 60 to 70 °C, and the heating time is 12 to 16 h.

[0021] The present invention also provides the application of the above flame-retardant double-salt polymer solid electrolyte in a lithium metal battery.

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

[0023] 1. There is a strong interaction between DEEP and TFEA monomers. Through the polar interaction between -P=O and -CH2CF3, DEEP is firmly anchored on the PTFEA matrix, which reduces the free DEEP molecules, significantly alleviates the interfacial reaction, and thus ensures the interfacial stability with the lithium metal anode. At the same time, DEEP can also regulate the fast ion channels in the form of a high-dielectric molecule, thereby improving the ionic conductivity. In addition, when DEEP is burned by a fire source, the phosphoric acid generated by thermal decomposition can form phosphate esters with the hydroxyl groups in the polymer material. These phosphate esters can reduce the surface temperature of the material, form a protective layer on the material surface to reduce the transfer of oxygen and heat, and thus inhibit the progress of the combustion reaction.

[0024] 2. The TFEA monomer selected in the present invention contains three C-F groups in each TFEA monomer, which increases the polarity of the polymer chain and helps to effectively capture DEEP molecules through intermolecular interactions, thereby restricting the migration of DEEP and weakening the lateral interaction. An anion-dominated lithium ion dissolution structure is constructed. On the one hand, the anion may more strongly attract lithium ions through electrostatic interaction with lithium ions, change the charge distribution and chemical environment around lithium ions, and thus affect their migration rate and transport path. On the other hand, the special arrangement of anions may provide specific channels or spaces for lithium ions, guide the directional movement of lithium ions, and improve their transport efficiency in the electrolyte, thereby forming an anion-derived solid electrolyte interface / cathode electrolyte interface (SEI / CEI) protective layer and a fast lithium ion structure transport.

[0025] 3. The present invention uses LiTFSI-LiDFOB double lithium salts. Due to the high dissociation ability of LiTFSI and the excellent film-forming performance of LiDFOB, the electrode-electrolyte interface is further strengthened. The in-situ cross-linking polymerization strategy containing TFEA precursor enables the electrolyte to have good wettability on the electrode surface, thus greatly reducing the interfacial resistance caused by poor interface contact. Through these electrochemical optimization strategies, fast lithium-ion transport kinetics, high conductivity, and higher lithium-ion transfer numbers can be achieved on the lithium anode. Therefore, it is an ideal choice for quasi-solid-state lithium-metal batteries and has broad application potential.

[0026] 4. The preparation method of the flame-retardant double-salt polymer solid electrolyte of the present invention is simple, has high production efficiency, and low manufacturing cost. It is suitable for practical winding batteries or columnar batteries and shows potential in consumer electronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a physical diagram of the flame-retardant double-salt polymer solid electrolyte prepared in Example 1 of the present invention.

[0028] Figure 2 It is a comparison diagram of ionic conductivities of Examples 1-3 and Comparative Examples 1-2.

[0029] Figure 3 It is a comparison diagram of the performance of lithium iron phosphate full batteries of Examples 1-3 and Comparative Examples 1-2.

[0030] Figure 4 It is a safety experiment diagram before and after cutting a winding battery;

[0031] Among them, (a) the assembled winding battery cell; (b) the voltage display diagram of the battery before cutting; (c) the actual appearance diagram of the battery at the moment of cutting; (d) the long-term static diagram after cutting the battery.

[0032] Figure 5 It is a safety experiment diagram before and after igniting a winding battery;

[0033] Among them, (a) the voltage display diagram of the winding battery during static; (b) the actual appearance diagram of the cell leaking out after cutting the battery; (c) the actual appearance diagram of burning the cell with a lighter; (d) the actual appearance diagram of the battery and the cell after burning. DETAILED DESCRIPTION OF THE EMBODIMENTS

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

[0035] A flame-retardant double-salt polymer solid electrolyte includes polymer monomers, initiators, flame retardants, and lithium salts;

[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(oxalato)borate (LiDFOB).

[0040] The TFEA-containing precursor and the initiator undergo in-situ crosslinking polymerization, enabling the polymer electrolyte to directly form a tight coating or network structure on the electrode surface. This direct contact and interaction enhance the interfacial binding force between the electrolyte and the electrode, allowing the electrolyte to better adhere to the electrode surface, thereby improving wettability. In-situ crosslinking polymerization can in-situ cure the liquid precursor inside the battery to form a superconformal interface, greatly solving the solid / solid interface contact problem, enabling better fitting and wetting between the electrolyte and the electrode; meanwhile, through the polar interaction between -P=O and -CH2CF3, DEEP is anchored on the PTFEA matrix, and the migration of DEEP is inhibited by the polarity of the polymer chain, avoiding side reactions that would occur when DEEP migrates to the interface.

[0041] Example 1

[0042] A preparation method of a flame-retardant double-salt polymer solid electrolyte, comprising the following steps:

[0043] Step 1. Inject 7 ml of DEEP into a brown glass bottle, then add 3 ml of TFEA and mix well by stirring, then add 1.435 g of LiTFSI, stir at room temperature for 2 h, where the concentration of LiTFSI is 0.5 mol / L; then add 0.715 g of LiDFOB, 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 on a glass substrate, place the substrate in an oven at 60 °C for 12 h, and the required flame-retardant double-salt polymer solid electrolyte can be obtained after the reaction ends.

[0046] The physical diagram of the flame-retardant double-salt polymer solid electrolyte prepared in this example is as Figure 1 shown.

[0047] Example 2

[0048] Prepare the polymer solid electrolyte according to the steps of Example 1, only adjust the volume ratio of DEEP and TFEA in Step 1 to 6:4 and 3:7, and keep other steps unchanged.

[0049] Example 3

[0050] Prepare the polymer solid electrolyte according to the steps of Example 1, only adjust the addition amount of LiTFSI in Step 2 to 0.574 g or 2.87 g, and the corresponding concentrations are 0.2 mol / L or 1 mol / L, and keep other steps unchanged.

[0051] Comparative Example 1

[0052] Add LiTFSI and LiDFOB to 10 ml of DEEP solution to obtain a liquid electrolyte, so that the concentrations of the two lithium salts in the solution are both 0.5 mol / L.

[0053] Comparative Example 2

[0054] Prepare the polymer electrolyte according to the steps of Example 1, only add the precursor solution obtained by adding 0.5 mol / L of LiTFSI and LiDFOB to 10 ml of TFEA solution, and add 0.2 g of AIBN.

[0055] Figure 1 This is a physical picture of the flame-retardant double-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 This is a comparison chart of the ionic conductivities of Examples 1-3 and Comparative Examples 1-2. As can be seen from the figure, the conductivity of the polymer solid electrolyte prepared by the present invention is significantly better than that of the electrolyte prepared by the comparative examples.

[0057] Using LiFePO4 (LFP) as the battery positive electrode and lithium metal as the battery negative electrode, winding batteries were assembled using the electrolytes prepared in Examples 1-3 and Comparative Examples 1-2 above, and the discharge capacity of the winding batteries at a current density of 0.5C at room temperature was tested. The test results are as Figure 3 shown. The winding battery prepared based on the polymer solid electrolyte of the present invention has excellent electrical properties.

[0058] For the winding battery assembled with the flame-retardant double-salt polymer solid electrolyte prepared in Example 1, the safety experiment of cutting the battery is as Figure 4 shown. Figure 4 In the figure: (a) is the winding battery cell assembled; (b) is the voltage display diagram of the battery before cutting; (c) is the actual appearance diagram of the battery at the moment of cutting; (d) is the diagram of the battery after being cut and left standing for a long time. As Figure 4As shown in the actual appearance diagram of a, the 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 double-salt polymer solid electrolyte. As Figure 4 As shown in b-d, even under extreme conditions, the cutting process will not cause combustion. The cutting process will cause an internal short circuit between the lithium metal anode and the cathode. Nevertheless, the flame-retardant double-salt polymer solid electrolyte can still eliminate the ignition hazard and ensure the safety of the battery in practical applications.

[0059] Figure 5 In the middle: (a) is the voltage display diagram of the wound battery at rest; (b) is the actual appearance diagram of the cell leaking out after the battery is cut open; (c) is the actual appearance diagram of the cell being burned with a lighter; (d) is the actual appearance diagram of the battery and the cell after being burned. It can be seen from the figure that the wound battery prepared based on the polymer solid electrolyte of the present invention is not easily ignited and has excellent flame-retardant performance.

[0060] As described above, only the specific embodiments of the present invention are provided. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the features disclosed, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A flame-retardant double-salt polymer solid electrolyte, characterized in that, It includes 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 salts are lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate.

2. A preparation method of a flame-retardant double-salt polymer solid electrolyte, characterized in that, It includes the following steps: Step 1. Mix the polymer monomer, flame retardant, lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate, and then stir evenly to obtain Solution A; Step 2. Add the initiator to Solution A to obtain a polymer precursor solution; Step 3. Coat the polymer precursor solution on a substrate, heat the substrate for a period of time, and the desired flame-retardant double-salt polymer solid electrolyte can be obtained after the reaction ends.

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

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

7.

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

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

7. The preparation method of the flame-retardant double-salt polymer solid electrolyte according to claim 2, characterized in that, In Step 3, the heating temperature is 60-70 °C, and the heating time is 12-16 h.

8. Application of the flame-retardant double-salt polymer solid electrolyte obtained by the method according to any one of claims 2-7 in a lithium metal battery.

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