High-concentration localized flame-retardant gel polymer electrolyte, battery and its preparation method

Abstract

This invention relates to a locally high-concentration flame-retardant gel polymer electrolyte, a battery, and its preparation method, belonging to the field of lithium metal battery technology. The locally high-concentration flame-retardant gel polymer electrolyte is prepared by in-situ polymerization of an initiator and a precursor solution; the precursor solution includes a locally high-concentration electrolyte, pentaerythritol tetraacrylate, and pentafluorophenol acrylate. This invention's flame-retardant, high-voltage, and high-temperature resistant lithium metal battery electrolyte fundamentally solves the safety hazards of flammability inherent in traditional electrolytes, overcomes the low room-temperature ionic conductivity of conventional polymer electrolytes, and effectively solves the problem of low ionic conductivity in polymer electrolytes. + Despite the drawback of low migration number, the lithium metal battery prepared by the polymer electrolyte of this invention exhibits high thermal stability and high voltage resistance.

Description

Technical Field

[0001] This invention relates to a locally high-concentration base flame-retardant gel polymer electrolyte, a battery, and a method for preparing the same, belonging to the field of lithium metal battery technology. Background Technology

[0002] Lithium metal batteries, with their extremely high energy density, have shown great potential in electric vehicles and large-scale energy storage. However, their commercialization has always been limited by serious safety issues. Currently widely used carbonate-based liquid electrolytes, characterized by low flash points, high volatility, and extreme flammability, are the primary source of thermal runaway risk in batteries. Under extreme conditions such as thermal abuse, mechanical abuse, or electrical abuse, the electrolyte can burn violently, even causing fires and explosions, severely restricting the practical application of lithium metal batteries. Therefore, developing novel electrolyte systems that combine high safety with excellent electrochemical performance has become a key issue driving the development of lithium metal batteries.

[0003] To improve battery safety, gel polymer electrolytes (GPEs) have attracted widespread attention due to their unique semi-solid structure, good mechanical flexibility, and high ionic conductivity. However, existing systems still face the dilemma of "difficulty in balancing safety and performance." On the one hand, a common industry strategy is to physically blend organophosphorus (such as triphenyl phosphate TPP) or halogenated flame retardants into the polymer matrix to achieve flame retardancy through gas-phase free radical capture mechanisms. However, these small-molecule flame retardants are prone to reduction reactions at the lithium metal anode interface, which can damage the stability of the solid electrolyte interphase (SEI) film, leading to a decrease in coulombic efficiency and deterioration in cycle performance. Furthermore, high addition levels (usually >10 wt%) can significantly degrade the ion transport performance of the electrolyte. On the other hand, using intrinsically non-flammable ionic liquids as plasticizers to prepare GPEs can improve thermal stability and flame retardancy. However, the inherent high viscosity of ionic liquids reduces ionic conductivity, and their poor interfacial compatibility with the lithium metal anode makes it difficult to form a stable SEI film.

[0004] In recent years, in-situ polymerization technology has provided a new approach for GPE preparation—by initiating monomer polymerization inside the battery, a gel electrolyte layer with tight contact with the electrode and excellent interfacial stability can be formed. However, existing research mainly focuses on improving the mechanical properties and ionic conductivity of the electrolyte, while neglecting the improvement of its intrinsic safety; most polymerizable monomers are still flammable organic compounds, which cannot fundamentally solve the combustion risk of the electrolyte. Although some studies have attempted to introduce flame retardants into the polymerization system through blending, the inherent defects of physical blending still make it difficult to avoid the negative impact of small molecule flame retardants on interfacial stability.

[0005] Therefore, current GPE flame retardant technology faces two core challenges: firstly, it is difficult to maintain high ionic conductivity (>1 mS cm⁻¹). -¹) While achieving good interfacial stability, the inherent flame-retardant properties of the electrolyte are realized; secondly, physical blending methods cannot overcome the bottleneck of synergistic optimization of "interfacial compatibility-ion transport-intrinsic safety".

[0006] Patent CN117423898A proposes a solid polymer electrolyte with a locally high concentration structure, but it does not involve the design of flame-retardant monomers. CN117747935A uses fluorinated monomers (such as dodecafluorooctyl acrylate) and a flame-retardant framework, but it is based on a traditional electrolyte system and lacks a locally high concentration structure. CN119050465A uses succinic anhydride as a flame-retardant solvent, but the electrolyte is not a locally high-concentration electrolyte (LHCE) structure, resulting in insufficient interfacial stability. CN120432630A discloses the use of halogenated polymerizable monomers such as pentafluorophenol acrylate to prepare flame-retardant gel electrolytes. However, this technology is mainly based on a traditional electrolyte system, which has a loose solvation structure, many free solvent molecules, and high intrinsic flammability. Even with the introduction of flame-retardant monomers, its flame-retardant efficiency still needs to withstand a large amount of flammable solvents, and this document does not solve the synergistic problem between the flame-retardant monomer polymerization network and the electrolyte bulk phase ion transport and electrode interface stability. CN119297391A combines phosphate ester flame retardants with LHCE. While this approach combines the LHCE concept with flame-retardant solvents, it has significant shortcomings: First, the monomers themselves do not possess strong flame-retardant properties, and the flame retardancy of the system mainly depends on the physically blended phosphate ester solvent, posing a risk of interfacial side reactions. Second, and more importantly, introducing a polymerization reaction into the LHCE system, which is highly sensitive to solvation structure, can easily damage the carefully constructed localized high-concentration solvation sheath if the monomer selection or polymerization process is inappropriate, leading to a decrease in ionic conductivity and changes in interfacial properties, thus losing the core advantages of LHCE.

[0007] These existing technologies suffer from the following drawbacks: It is difficult to balance flame retardancy and electrochemical performance; physically blended flame retardants are prone to deteriorating the interface and ion transport; localized high-concentration structures are easily destroyed by polymerization; monomer addition may damage the solvation sheath, affecting ionic conductivity; and they have poor high-pressure / high-temperature adaptability: traditional GPEs undergo severe oxidative decomposition at >4.3 V or high temperatures. The field urgently needs a novel design strategy that not only breaks the traditional trade-off between "flame retardancy" and "electrochemical performance," but also solves the key technical challenge of successfully integrating polymeric flame retardant functionality into the sensitive LHCE system without compromising its core solvation structure and interfacial advantages. Summary of the Invention

[0008] The first objective of this invention is to provide a method for preparing a locally high-concentration base flame-retardant gel polymer electrolyte.

[0009] To achieve the first objective of this invention, the locally high-concentration base flame-retardant gel polymer electrolyte is prepared by in-situ polymerization of an initiator and a precursor solution;

[0010] The precursor solution includes a locally high-concentration electrolyte, pentaerythritol tetraacrylate, and pentafluorophenol acrylate.

[0011] The mass content of pentafluorophenol acrylate in the precursor solution is 1% to 10%.

[0012] The local high-concentration electrolyte is prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in a specific mixed solvent. The specific mixed solvent is prepared by uniformly mixing triethyl phosphate (TEP), bis(2,2,2-trifluoroethyl) ether (BTFE), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a molar ratio of 0.8–1.2:0.8–1.2:1.8–2.2, and the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) in the local high-concentration electrolyte is controlled within the range of 1.0–2.0 mol / L.

[0013] In one specific embodiment, the mass of the initiator is 0.05% to 0.5% of the mass of the precursor solution.

[0014] In one specific embodiment, the mass content of the pentafluorophenol acrylate in the precursor solution is 1.5% to 3.0%.

[0015] In one specific embodiment, the molar ratio of pentafluorophenol acrylate to pentaerythritol tetraacrylate is 1 to 3:1.

[0016] In one specific embodiment, the in-situ polymerization is carried out at 60–80 °C for more than 3 hours.

[0017] In one specific embodiment, the in-situ polymerization is carried out at 65–75 °C.

[0018] A second objective of this invention is to provide a locally high-concentration base flame-retardant gel polymer electrolyte.

[0019] To achieve the second objective of this invention, the locally high-concentration flame-retardant gel polymer electrolyte is prepared by the above-described method, possesses self-extinguishing capability, and has a lithium-ion transference number of not less than 0.49; the polymer electrolyte exhibits an ionic conductivity of 0.94 mS / cm at 25 °C. -1 above.

[0020] In one specific embodiment, the lithium-ion transference number of the locally high-concentration flame-retardant gel polymer electrolyte is not less than 0.52; the ionic conductivity of the polymer electrolyte at 25 °C is 1.14 mS / cm. -1 above.

[0021] A third objective of this invention is to provide a lithium metal battery.

[0022] To achieve a third objective of the present invention, the lithium metal battery comprises the aforementioned locally high-concentration base flame-retardant gel polymer electrolyte.

[0023] In one specific embodiment, the positive electrode material of the battery is NCM811.

[0024] Beneficial effects:

[0025] 1. The local high-concentration flame-retardant gel polymer electrolyte of this invention utilizes the synergistic effect of polymerizable fluorinated flame-retardant monomer (PFPA) and local high-concentration electrolyte (LHCE) to form a three-dimensional network structure through in-situ polymerization, achieving a molecular-level flame-retardant functional distribution. This fundamentally solves the safety hazard of flammability of traditional electrolytes. Combustion tests show that the electrolyte does not burn when exposed to a fire source.

[0026] 2. The limiting oxygen index of the locally high-concentration flame-retardant gel polymer electrolyte of this invention is as high as 49.1%, which significantly enhances the flame-retardant performance and safety stability of the battery, and effectively improves the defects of traditional electrolytes that have poor flame retardancy and are prone to safety hazards.

[0027] 3. The locally high-concentration flame-retardant gel polymer electrolyte of this invention exhibits an ionic conductivity of up to 1.29 mS / cm at 25 °C. -1 This overcomes the drawback of low room temperature ionic conductivity in conventional polymer electrolytes;

[0028] 4. The locally high-concentration base-based flame-retardant gel polymer electrolyte of this invention has a lithium-ion transference number as high as 0.66, effectively solving the problem of Li in polymer electrolytes. + The drawback of low migration count;

[0029] 5. This invention utilizes a synergistic design of a "locally high-concentration electrolyte substrate" and a "fluorine-containing functional monomer." The former regulates the bulk solvation structure to guide interfacial reactions, while the latter polymerizes in situ to construct an interfacial protective layer. The two work synergistically to build a solid electrolyte interface (SEI) primarily composed of stable inorganic materials such as LiF, possessing both high ionic conductivity and high mechanical strength. This synergistically achieves effective suppression of lithium dendrites and a significant improvement in battery cycle life.

[0030] 6. This invention, through the synergistic design of a locally high-concentration substrate and a fluorine-containing monomer, not only prepares materials with high electrical conductivity and Li... + The polymer electrolyte exhibits high migration number, and the lithium metal battery prepared with this polymer electrolyte has high thermal stability and high voltage resistance. After cycling at 4.5 V and 60 °C, the capacity retention rate exceeds 80%, which is far superior to that of traditional electrolytes. Attached Figure Description

[0031] Figure 1 The images are photographs of the reaction solution provided in Example 1 before and after thermal polymerization; where a is a photograph of the reaction solution before thermal polymerization and b is a photograph of the polymer electrolyte after thermal polymerization.

[0032] Figure 2 Fourier transform infrared spectra of polymer electrolyte, PFPA, PETEA and precursor solution in Example 1;

[0033] Figure 3 The images show the combustion experiment, limiting oxygen (LOI) and thermogravimetric analysis (TGA) results of the high-concentration base flame-retardant gel polymer electrolyte in Example 1; where a is a photograph of the combustion experiment, b is a bar chart of limiting oxygen (LOI), and c is a curve of thermogravimetric analysis (TGA).

[0034] Figure 4 The image shows the Raman spectrum of the locally high-concentration flame-retardant gel polymer electrolyte in Example 1; where a represents the Raman spectrum of the conventional carbonate electrolyte and b represents the Raman spectrum of the locally high-concentration flame-retardant gel polymer electrolyte.

[0035] Figure 5 This is a bar chart showing the ionic conductivity of a locally high-concentration flame-retardant gel polymer electrolyte and a traditional carbonate electrolyte in Example 1.

[0036] Figure 6 The figures show the chronoamperometry curves and AC impedance spectra before and after polarization of the locally high-concentration flame-retardant gel polymer electrolyte and the conventional carbonate electrolyte as electrolytes for the Li||Li symmetric battery in Example 1; where a is the chronoamperometry curve and AC impedance spectra before and after polarization of the conventional carbonate electrolyte (inset), and b is the chronoamperometry curve and AC impedance spectra before and after polarization of the locally high-concentration flame-retardant gel polymer electrolyte in Example 1 (inset).

[0037] Figure 7 The image shows an in-situ optical microscope comparison of lithium deposition behavior at the same current density between the locally high-concentration flame-retardant gel polymer electrolyte based on Example 1 and the conventional carbonate electrolyte.

[0038] Figure 8 The image shows a comparison of the lithium metal anode after the same number of cycles in a Li||Li symmetric battery assembled with the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 and a conventional carbonate electrolyte.

[0039] Figure 9The image shows a comparison of the X-ray photoelectron spectroscopy (XPS) of the lithium metal anode surface after 50 cycles of a Li||NCM811 battery assembled with the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 and a conventional carbonate electrolyte.

[0040] Figure 10 The graph shows the cycling performance of the Li||NCM811 battery assembled using the locally high-concentration base flame-retardant gel polymer electrolyte and conventional carbonate electrolyte from Example 1 at 4.3 V and 0.5 C.

[0041] Figure 11 The graph shows the cycling performance of the Li||NCM811 battery assembled using the locally high-concentration base flame-retardant gel polymer electrolyte and conventional carbonate electrolyte from Example 1 at 4.5 V and 0.5 C.

[0042] Figure 12 The graph shows the cycling performance of the Li||NCM811 battery assembled using the locally high-concentration base flame-retardant gel polymer electrolyte and conventional carbonate electrolyte from Example 1 at 4.3 V and 60 °C. Detailed Implementation

[0043] To achieve the first objective of this invention, the locally high-concentration base flame-retardant gel polymer electrolyte is prepared by in-situ polymerization of an initiator and a precursor solution;

[0044] The precursor solution includes a locally high-concentration electrolyte, pentaerythritol tetraacrylate, and pentafluorophenol acrylate.

[0045] The mass content of pentafluorophenol acrylate in the precursor solution is 1% to 10%.

[0046] The local high-concentration electrolyte is prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in a specific mixed solvent. The specific mixed solvent is prepared by uniformly mixing triethyl phosphate (TEP), bis(2,2,2-trifluoroethyl) ether (BTFE), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a molar ratio of 0.8–1.2:0.8–1.2:1.8–2.2, and the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) in the local high-concentration electrolyte is controlled within the range of 1.0–2.0 mol / L.

[0047] The final molar concentration of LiFSI in the electrolyte was controlled within the range of 1.0–2.0 mol / L.

[0048] In one specific embodiment, the initiator is azobisisobutyronitrile (AIBN).

[0049] Azobisisobutyronitrile (AIBN) was used as a polymerization initiator to initiate the polymerization of pentaerythritol tetraacrylate with pentafluorophenol acrylate. The endpoint of the polymerization reaction was complete polymerization or the polymer electrolyte obtained from the polymerization reaction had a weight loss of less than 16 wt% at 400 °C.

[0050] In one specific embodiment, the mass of the initiator is 0.05% to 0.5% of the mass of the precursor solution.

[0051] In one specific embodiment, the mass content of the pentafluorophenol acrylate in the precursor solution is 1.5% to 3.0%.

[0052] In one specific embodiment, the molar ratio of pentafluorophenol acrylate to pentaerythritol tetraacrylate is 1 to 3:1.

[0053] In one specific embodiment, the in-situ polymerization is carried out at 60–80 °C for more than 3 hours.

[0054] In one specific embodiment, the in-situ polymerization is carried out at 65–75 °C.

[0055] To achieve the second objective of this invention, the locally high-concentration flame-retardant gel polymer electrolyte is prepared by the above-described method, possesses self-extinguishing capability, and has a lithium-ion transference number of not less than 0.49; the polymer electrolyte exhibits an ionic conductivity of 0.94 mS / cm at 25 °C. -1 above.

[0056] In one specific embodiment, the lithium-ion transference number of the locally high-concentration flame-retardant gel polymer electrolyte is not less than 0.52; the ionic conductivity of the polymer electrolyte at 25 °C is 1.14 mS / cm. -1 above.

[0057] To achieve a third objective of the present invention, the lithium metal battery comprises the aforementioned locally high-concentration base flame-retardant gel polymer electrolyte.

[0058] In one specific embodiment, the positive electrode material of the battery is NCM811.

[0059] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0060] In the following examples, pentafluorophenol acrylate (hereinafter referred to as PFPA) has a purity of 98%.

[0061] Pentaerythritol tetraacrylate (hereinafter referred to as PETEA) is used as a polymerization crosslinking agent with a purity of 80%.

[0062] Azobisisobutyronitrile (AIBN) is used as a thermal polymerization initiator with a purity of 98%.

[0063] Lithium bis(fluorosulfonyl)imide (LiFSI), 98% purity.

[0064] Triethyl phosphate (TEP), purity 99.8%.

[0065] Bis(2,2,2-trifluoroethyl) ether (BTFE), purity 99.5%.

[0066] 1,1,2,2-Tetrafluoroethyl 2,2,3,3-Tetrafluoropropyl ether (TTE) with a purity of 99.5%.

[0067] Example 1

[0068] This embodiment provides a method for preparing a flame-retardant, high-voltage, high-temperature resistant polymer electrolyte for lithium metal batteries, including the following steps:

[0069] Step 1: 47.6 mg (1.6 wt%) of PFPA monomer (98% purity) and 70.5 mg (2.4 wt%) of PETEA (80% purity) were added to 2.83 g of local high-concentration electrolyte and stirred until homogeneous to obtain a precursor solution. The local high-concentration electrolyte was prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in a specific mixed solvent. The mixed solvent was prepared by uniformly mixing triethyl phosphate, bis(2,2,2-trifluoroethyl) ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a molar ratio of 1:1:2, and the molar concentration of LiFSI was 1.2 M.

[0070] Step 2: Add 0.1 wt% AIBN to the precursor solution and stir until homogeneous to obtain the reaction solution;

[0071] Step 3: The reaction solution is heated at 70 °C for 3 h to polymerize and obtain a locally high concentration of flame-retardant gel polymer electrolyte.

[0072] The properties of the locally high-concentration base flame-retardant gel polymer electrolyte obtained in Example 1 were characterized:

[0073] 1. Properties before and after thermal polymerization

[0074] The reaction solution of Example 1 was photographed before and after thermal polymerization, and the results are shown in the attached figure. Figure 1 The images shown are before and after thermal polymerization; where a is a photo of the reaction solution before thermal polymerization, and b is a photo of a local high-concentration base flame-retardant gel polymer electrolyte after thermal polymerization.

[0075] Depend on Figure 1It can be seen that the local high-concentration base flame-retardant gel polymer electrolyte is made by adding PFPA and PETEA to a local high-concentration electrolyte, stirring evenly, and then adding AIBN and polymerizing at 70 °C.

[0076] 2. Verification by Fourier transform infrared spectroscopy

[0077] Fourier transform infrared spectroscopy was performed on the locally high-concentration flame-retardant gel polymer electrolyte, PFPA, PETEA and their precursor solutions from Example 1. The results are as follows: Figure 2 As shown.

[0078] Depend on Figure 2 It can be seen that at 1600-1650 cm -1 Within the range, C=C bending and tensile vibrations of acrylic groups in PFPA and PETEA monomers were observed respectively. No characteristic C=C peaks were observed in the locally high-concentration radical flame retardant gel polymer electrolyte after polymerization, indicating that the locally high-concentration radical flame retardant gel polymer electrolyte was successfully crosslinked and cured.

[0079] 3. Combustion and thermogravimetric analysis

[0080] The locally high-concentration flame-retardant gel polymer electrolyte from Example 1 was subjected to combustion experiments, limiting oxygen (LOI), and thermogravimetric analysis (TGA). The test results are as follows: Figure 3 As shown; where a is a photograph of the combustion experiment, b is a bar chart of limiting oxygen (LOI), and c is a thermogravimetric analysis (TGA) curve.

[0081] Depend on Figure 3 As can be seen from the combustion experiment (a), the traditional carbonate electrolyte continues to burn once ignited; while the locally high-concentration flame-retardant gel polymer electrolyte did not burn under continuous ignition source exposure, demonstrating excellent flame-retardant performance. The limiting oxygen index (LOI) test results (b) show that the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 has a limiting oxygen index as high as 49.1%, significantly higher than the non-flammable threshold of 28%, indicating that this material is inherently non-flammable. In contrast, the limiting oxygen index of the traditional carbonate electrolyte is only 15.9%, classifying it as a highly flammable material. The above quantitative comparison fully demonstrates that the locally high-concentration flame-retardant gel polymer electrolyte achieves a qualitative improvement in flame-retardant performance compared to the traditional electrolyte, exhibiting superior safety characteristics. Thermogravimetric analysis (c) shows that during the pyrolysis of the locally high-concentration flame-retardant gel polymer electrolyte and the conventional carbonate electrolyte, the total weight loss rates from room temperature to 200 °C were 53.96% and 13.78%, respectively. This indicates that the locally high-concentration flame-retardant gel polymer electrolyte has good thermal stability.

[0082] 4. Raman spectroscopy test

[0083] The locally high-concentration flame-retardant gel polymer electrolyte of Example 1 and the conventional carbonate electrolyte were subjected to Raman spectroscopy at room temperature. The test results are as follows: Figure 4 As shown; where a represents the Raman spectrum of a conventional carbonate electrolyte, and b represents the Raman spectrum of a locally high-concentration flame-retardant gel polymer electrolyte from Example 1.

[0084] Depend on Figure 4 Raman spectroscopy was used to analyze the solvation structure of LiFSI in the locally high-concentration LiFSI-based flame-retardant gel polymer electrolyte of Example 1 and the conventional carbonate electrolyte. Quantitative analysis showed that the locally high-concentration LiFSI-based flame-retardant gel polymer electrolyte of Example 1 exhibited a significantly higher aggregate (AGG) ratio (59.9%), far exceeding that of the control group (7.6%). This highly aggregated solvation structure is a typical characteristic of locally high-concentration electrolytes, effectively reducing the number of flammable free solvent molecules in the system and fundamentally reducing the flammability of the electrolyte, providing key evidence for its excellent intrinsic flame retardancy. Simultaneously, this structure is more conducive to inducing the formation of a stable and inorganic LiF-rich SEI layer at the electrode interface, thereby simultaneously improving interfacial stability and the cycle performance of lithium metal batteries, achieving a synergistic enhancement of safety and electrochemical performance.

[0085] 5. Ionic conductivity

[0086] Based on electrochemical impedance spectroscopy, the ionic conductivity of the locally high-concentration flame-retardant gel polymer electrolyte from Example 1 and the conventional carbonate electrolyte at 25 °C was measured, and the results are as follows: Figure 5 As shown.

[0087] Depend on Figure 5 As can be seen, at 25 °C, the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 achieved a flux of 1.29 mS / cm. -1 Its high ionic conductivity is close to that of traditional carbonate electrolytes (1.49 mS / cm). -1 This indicates that the locally high-concentration base-based flame-retardant gel polymer electrolyte of Example 1 has excellent ionic conductivity.

[0088] 6. Timing Ampere and AC Impedance Testing

[0089] A battery was prepared using the locally high-concentration flame-retardant gel polymer electrolyte from Example 1 and a traditional carbonate electrolyte as electrolytes for a Li||Li symmetric cell. The chronoampere and AC impedance of the battery were tested at a polarization voltage of 10 mV. The test results are as follows: Figure 6As shown; where a is the chronoamperometry curve of the conventional carbonate electrolyte and the AC impedance spectrum before and after polarization (inset), and b is the chronoamperometry curve of the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 and the AC impedance spectrum before and after polarization (inset).

[0090] Depend on Figure 6 As can be seen, in Example 1, a localized high-concentration base flame-retardant gel polymer electrolyte Li + Number of migrations t Li + =0.66 compared to the Li in traditional carbonate electrolytes + Number of migrations t Li + =0.45 high. This significant enhancement can be attributed to the localized high concentration of anion-rich solvation structure in the flame-retardant gel polymer electrolyte, which modulates rapid Li... + Conduction, multiple Li + The presence of ligands accelerates the Li + The migration.

[0091] 7. In-situ optical microscope

[0092] The locally high-concentration flame-retardant gel polymer electrolyte prepared in Example 1 was mixed with a conventional carbonate electrolyte at 0.5 mA cm⁻¹ - In-situ optical microscopy comparative tests were performed at a current density of ², and the results are as follows: Figure 7 As shown.

[0093] Depend on Figure 7 It is evident that the lithium deposition behavior of the two systems differs significantly: the locally high-concentration flame-retardant gel polymer electrolyte system of Example 1 consistently guides the formation of a uniform and dense lithium metal coating throughout the entire test, with no obvious dendrites observed. In stark contrast, the conventional carbonate electrolyte system rapidly generates irregular dendrites in the initial stage of the test, and develops into an uneven, moss-like lithium deposition within 10 minutes over time. This result directly confirms that the electrolyte system of Example 1 possesses excellent interface control capabilities and can effectively suppress the growth of lithium dendrites.

[0094] 8. Scanning Electron Microscope (SEM)

[0095] The Li||Li symmetric batteries assembled using the locally high-concentration base-based flame-retardant gel polymer electrolyte prepared in Example 1 and a conventional carbonate electrolyte were subjected to scanning electron microscopy (SEM) observation of their lithium metal anodes after 100 cycles. The results are as follows: Figure 8 As shown in the figure. In the figure, a represents a scanning electron microscope image of a conventional carbonate electrolyte, and b represents a scanning electron microscope image of a locally high-concentration flame-retardant gel polymer electrolyte from Example 1.

[0096] Depend on Figure 8 It is evident that the two electrolytes exert distinctly different effects on the lithium deposition morphology: the electrode surface based on the traditional carbonate electrolyte is covered with a porous and highly uneven moss-like structure formed by the aggregation and stacking of numerous loose dendrites; in stark contrast, the electrode surface based on the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 exhibits a uniform, dense, and smooth metal deposition layer morphology. This direct comparison of microstructures confirms that the locally high-concentration flame-retardant gel polymer electrolyte system, by constructing a stable interface layer, can effectively guide the uniform deposition of lithium, thereby maintaining the integrity and flatness of the electrode structure even after long-term cycling.

[0097] 9. X-ray photoelectron spectroscopy (XPS)

[0098] Li||NCM811 full cells assembled using the locally high-concentration flame-retardant gel polymer electrolyte prepared in Example 1 and a conventional carbonate electrolyte were subjected to X-ray photoelectron spectroscopy (XPS) analysis of their lithium metal anodes after 50 cycles. The results are as follows: Figure 9 As shown.

[0099] Depend on Figure 9 It is evident that the two types of solid electrolyte interfaces (SEIs) exhibit fundamental differences in chemical composition: the SEI based on the locally high-concentration base-based flame-retardant gel polymer electrolyte of Example 1 shows a dominant LiF characteristic peak at ~685 eV in its F 1s spectrum, indicating the formation of a LiF-rich inorganic interface layer; while the SEI based on the conventional carbonate electrolyte shows a significant CF bond signal near ~688 eV in its F 1s spectrum, indicating that its fluorine-containing components mainly originate from the decomposition products of the organic solvent. This stark contrast in chemical composition confirms that the locally high-concentration base-based flame-retardant gel polymer electrolyte system successfully guided the preferential decomposition of the anion (LiFSI), constructing an SEI dominated by stable inorganic LiF. This provides direct surface chemical evidence to explain its excellent interfacial stability and ability to inhibit dendrite growth.

[0100] Cyclic performance testing at 10, 4.3 V and 0.5 C

[0101] The Li||NCM811 battery assembled using the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 and a conventional carbonate electrolyte was subjected to cycle performance testing under the test conditions of a cutoff voltage of 4.3 V (2.8-4.3 V), 0.5 C, and 25 °C; the test results are as follows. Figure 7 As shown.

[0102] Depend on Figure 7As can be seen, after long-term cycling tests at a cutoff voltage of 4.3 V and a room temperature of 25 °C, the Li||NCM811 battery with locally high concentration of flame-retardant gel polymer electrolyte can stably cycle for more than 330 cycles with a capacity retention rate of 79.6%. In contrast, the cycling performance of the conventional carbonate electrolyte Li||NCM811 battery decays rapidly, with a capacity retention rate of only 73.1% after 162 cycles.

[0103] Cyclic performance testing at 11, 4.5 V and 0.5 C

[0104] The Li||NCM811 battery assembled using the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 and a conventional carbonate electrolyte was subjected to cycle performance testing under the test conditions of a cutoff voltage of 4.5 V (2.8-4.5 V), 0.5 C, and 25 °C; the test results are as follows. Figure 8 As shown.

[0105] Depend on Figure 8 As can be seen, after long-cycle testing at a high cutoff voltage of 4.5 V and a room temperature of 25 °C, the Li||NCM811 battery with locally high concentration of flame-retardant gel polymer electrolyte can stably cycle for more than 200 cycles with a capacity retention rate of 82.7%. In contrast, the cycling performance of the traditional carbonate electrolyte-based Li||NCM811 battery decays rapidly, with a capacity retention rate of only 79.6% after 94 cycles.

[0106] Cyclic performance testing at 12, 4.3 V and 60 °C

[0107] The Li||NCM811 battery assembled using the locally high-concentration flame-retardant gel polymer electrolyte of Example 1 and a conventional carbonate electrolyte was subjected to cycle performance testing under the test conditions of a cutoff voltage of 4.3 V (2.8-4.3 V), 0.5 C, and 60 °C; the test results are as follows. Figure 9 As shown.

[0108] Depend on Figure 9 As can be seen, long-cycle tests were conducted on both batteries at a cutoff voltage of 4.3 V and a high temperature of 60 °C. The Li||NCM811 battery with a locally high-concentration flame-retardant gel polymer electrolyte showed stable cycling for over 180 cycles with a capacity retention of 80%. Conversely, the cycling performance of the traditional carbonate electrolyte-based Li||NCM811 battery rapidly declined, with a capacity retention of only 61.6% after 67 cycles. This indicates that the improved polymer electrolyte structure of this invention enhances high-voltage stability and thermal stability.

[0109] Example 2

[0110] This embodiment prepares a locally high-concentration base flame-retardant gel polymer electrolyte according to the steps of Example 1, except that: in step 1, "2.83 g of locally high-concentration electrolyte" is adjusted to "2.7 g of locally high-concentration electrolyte"; other steps remain unchanged.

[0111] Example 3

[0112] This embodiment prepares a locally high-concentration base flame-retardant gel polymer electrolyte according to the steps of Example 1, except that: in step 1, "2.83 g of locally high-concentration electrolyte" is adjusted to "3 g of locally high-concentration electrolyte"; other steps remain unchanged.

[0113] Example 4

[0114] This embodiment prepares a locally high-concentration base flame-retardant gel polymer electrolyte according to the steps of Example 1, except that: in step 3, "heating and reacting at 70 ℃ for 3 h" is changed to "heating and reacting at 65 ℃ for 3 h"; the other steps remain unchanged.

[0115] Example 5

[0116] This embodiment prepares a locally high-concentration base flame-retardant gel polymer electrolyte according to the steps of Example 1, the difference being that: in step 3, "heating and reacting at 70 ℃ for 3 h" is changed to "heating and reacting at 75 ℃ for 3 h"; the other steps remain unchanged.

[0117] Comparative Example 1

[0118] This embodiment follows the steps of Example 1 to prepare a locally high-concentration base flame-retardant gel polymer electrolyte, the difference being that: the locally high-concentration electrolyte is prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in a specific mixed solvent; the mixed solvent is prepared by uniformly mixing triethyl phosphate and bis(2,2,2-trifluoroethyl) ether in a molar ratio of 1:3, and the molar concentration of LiFSI is 1.2 M.

[0119] Comparative Example 2

[0120] This embodiment prepares a locally high-concentration flame-retardant gel polymer electrolyte according to the steps of Example 1, with the difference being that: the locally high-concentration electrolyte is prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in a specific mixed solvent; the mixed solvent is prepared by uniformly mixing triethyl phosphate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a molar ratio of 1:3, and the molar concentration of LiFSI is 1.2 M.

[0121] In Example 2, combustion occurred under the influence of an ignition source, but it possessed self-extinguishing capability, with a self-extinguishing time of 12 seconds. Its ionic conductivity was 1.01 mS·cm. -¹, The lithium-ion transference number is 0.52.

[0122] In Example 3, the self-extinguishing time in the combustion test was 16 seconds, and the ionic conductivity was 0.94 mS·cm. - ¹, The lithium-ion transference number is 0.49.

[0123] The self-extinguishing time of Example 4 was 9 seconds, and the ionic conductivity was 1.14 mS·cm. - ¹, The lithium-ion transference number is 0.52.

[0124] The self-extinguishing time of Example 5 was 10 seconds, and the ionic conductivity was 1.09 mS·cm. - ¹, The lithium-ion transference number is 0.58.

[0125] Comparative Example 1 can be ignited by a direct flame source, but it possesses self-extinguishing capability with a self-extinguishing time of 9 seconds. The Li||NCM811 battery assembled using this electrolyte exhibits poor cycling stability at room temperature when tested within a voltage window of 2.8-4.3 V and a rate of 0.5 C. After 100 cycles, its capacity retention rate decreases to 78.9%. At a high temperature of 60℃, the battery degradation accelerates, with the capacity retention rate dropping to 78.2% after only 50 cycles.

[0126] Comparative Example 2 can be ignited by a direct flame source, but it possesses self-extinguishing capability with a self-extinguishing time of 9 seconds. The Li||NCM811 battery assembled using this electrolyte exhibited poor cycling stability at room temperature when tested within a voltage window of 2.8–4.3 V and a rate of 0.5 C. After 140 cycles, its capacity retention decreased to 80.3%. At a high temperature of 60°C, the battery degradation accelerated, with the capacity retention dropping to 79.4% after only 70 cycles.

[0127] A comprehensive comparison of the above results shows that Example 1 exhibits the best performance in all four aspects: flame retardancy (non-flammability), ion conduction efficiency, lithium-ion migration ability, and battery cycle performance.

Claims

1. A method for preparing locally high-concentration flame-retardant gel polymer electrolyte, characterized in that, The locally high-concentration flame-retardant gel polymer electrolyte is prepared by in-situ polymerization of an initiator and a precursor solution. The precursor solution includes a locally high-concentration electrolyte, pentaerythritol tetraacrylate, and pentafluorophenol acrylate. The mass content of pentafluorophenol acrylate in the precursor solution is 1% to 10%. The local high-concentration electrolyte is prepared by dissolving lithium difluorosulfonylimide in a specific mixed solvent; wherein, the specific mixed solvent is prepared by uniformly mixing triethyl phosphate, bis(2,2,2-trifluoroethyl) ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a molar ratio of 0.8-1.2:0.8-1.2:1.8-2.2, and the molar concentration of lithium difluorosulfonylimide in the local high-concentration electrolyte is controlled within the range of 1.0-2.0 mol / L.

2. The method for preparing the locally high-concentration flame-retardant gel polymer electrolyte according to claim 1, characterized in that, The mass of the initiator is 0.05% to 0.5% of the mass of the precursor solution.

3. The method for preparing the locally high-concentration flame-retardant gel polymer electrolyte according to claim 1, characterized in that, The mass content of the pentafluorophenol acrylate in the precursor solution is 1.5% to 3.0%.

4. The method for preparing the locally high-concentration flame-retardant gel polymer electrolyte according to claim 1, characterized in that, The molar ratio of pentafluorophenol acrylate to pentaerythritol tetraacrylate is 1 to 3:

1.

5. The method for preparing the locally high-concentration flame-retardant gel polymer electrolyte according to claim 1, characterized in that, The in-situ polymerization is carried out at 60–80 °C for more than 3 hours.

6. The method for preparing the locally high-concentration flame-retardant gel polymer electrolyte according to claim 5, characterized in that, The in-situ polymerization is carried out at 65–75 °C.

7. A locally high-concentration flame-retardant gel polymer electrolyte, characterized in that, Prepared by the method according to any one of claims 1 to 6, the polymer electrolyte possesses self-extinguishing capability and a lithium-ion transference number of not less than 0.49; the polymer electrolyte has an ionic conductivity of 0.94 mS / cm at 25 °C. -1 above.

8. The locally high-concentration flame-retardant gel polymer electrolyte according to claim 7, characterized in that, The lithium-ion transference number of the locally high-concentration flame-retardant gel polymer electrolyte is not less than 0.52; the ionic conductivity of the polymer electrolyte at 25 °C is 1.14 mS / cm. -1 above.

9. A lithium metal battery, characterized in that, The lithium metal battery comprises the locally high-concentration base flame-retardant gel polymer electrolyte as described in claim 7 or 8.

10. The lithium metal battery according to claim 9, characterized in that: The positive electrode material of the battery is NCM811.

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