Solid electrolyte membrane for lithium metal battery with wide temperature range, battery and preparation method thereof

Abstract

The application relates to a solid electrolyte film for a wide-temperature-range lithium metal battery, a battery and a preparation method thereof, and belongs to the technical field of lithium metal batteries. The method comprises the following steps: mixing dioxolane, polyvinylidene fluoride-hexafluoropropylene polymer and lithium difluoro(oxalato)borate to obtain a PH solution; mixing the PH solution and ceramic filler LLZO to obtain a PHZO solution; mixing the PHZO solution and a functional monomer to obtain a precursor solution; coating the precursor solution on a substrate and performing heat treatment to obtain a solid electrolyte film for a wide-temperature-range lithium metal battery. The conductivity of the solid electrolyte at 25 DEG C can reach 1.3 mS / cm or above; the Li||NCM811 battery based on the solid electrolyte can maintain high capacity retention at-20 DEG C and 45 DEG C, and the application bottleneck of the battery under extreme environments is solved.

Description

Technical Field

[0001] This invention relates to a solid electrolyte membrane, a battery, and a method for preparing the same for a wide-temperature-range lithium metal battery, belonging to the field of lithium metal battery technology. Background Technology

[0002] The development of high-performance lithium metal batteries with a wide temperature range is crucial for improving the reliability of applications in extreme environments. Constructing a solid-state electrolyte that combines high ionic conductivity (>1.0 mS / cm), excellent mechanical stability, and thermal stability is a core challenge. However, traditional polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) based composite solid-state electrolytes have significant drawbacks: at low temperatures (<0 °C), the polymer chain mobility decreases and the increased interfacial impedance leads to a sharp drop in ionic conductivity; at high temperatures (>40 °C), the electrolyte's mechanical properties are affected, making lithium dendrites prone to puncturing the separator, and the inorganic filler (lithium lanthanum zirconium oxide LLZO) doped in the composite electrolyte is prone to agglomeration, resulting in uneven distribution and preventing the formation of continuous and efficient lithium-ion transport channels; furthermore, the poor solid-solid interface compatibility between the filler and the electrolyte further increases the interfacial transport impedance, limiting the battery's electrochemical stability over a wide temperature range.

[0003] Currently, although composite all-solid electrolytes have shown some potential, they still have obvious shortcomings: First, it is difficult to achieve long-range ordered distribution of fillers in polymer substrates by external physical fields or external field-induced alignment methods, which limits the overall improvement of their performance; Second, there is a lack of precise chemical control of the filler-matrix interface, which makes it impossible to solve the problems of interfacial impedance and stability at the same time.

[0004] Existing technologies such as CN113067030A modify PVDF-HFP through sulfonation, but their room temperature ionic conductivity is low (approximately 0.057 mS / cm), and the problem of wide temperature range adaptability has not been solved. CN120289843A improves high-temperature fast-charging performance by introducing specific monomers and crosslinking agents, but its ionic conductivity (0.35 mS / cm) and mechanical properties still have room for improvement, and it does not address the optimization of low-temperature performance.

[0005] Therefore, it is crucial to develop a solid electrolyte that combines high ionic conductivity, excellent mechanical strength, and wide-temperature electrochemical stability. Summary of the Invention

[0006] The first objective of this invention is to provide a method for preparing a solid electrolyte membrane for a wide-temperature-range lithium metal battery.

[0007] To achieve the first objective of this invention, the method includes the following steps:

[0008] A. Mix dioxolane, polyvinylidene fluoride-hexafluoropropylene polymer and lithium difluorooxalate borate to obtain a pH solution;

[0009] B. Mix the pH solution obtained in step A with the ceramic filler LLZO to obtain a pHZO solution, wherein LLZO accounts for 9 wt% to 10 wt% of the pHZO solution;

[0010] C. The PHZO solution obtained in step B is mixed with the functional monomer to obtain a precursor solution; the functional monomer is 2-hydroxy-2-methyl-N-[4-cyano-3-(trifluoromethyl)phenyl]-3-[4-(fluorophenyl)thio]propionamide, and the functional monomer accounts for 9 wt% to 10 wt% of the precursor solution;

[0011] D. The precursor solution obtained in step C is coated onto a substrate and subjected to heat treatment to obtain a solid electrolyte membrane for wide-temperature-range lithium metal batteries.

[0012] The substrate can be glass, PVC board, etc.

[0013] Outside the scope of the present invention, all-solid electrolytes have low conductivity or poor mechanical properties, or all-solid electrolyte membranes cannot be obtained.

[0014] In one specific embodiment, the mass ratio of dioxolane, polyvinylidene fluoride-hexafluoropropylene polymer and lithium difluorooxalate borate in step A is 4.0–5.2:0.8–0.9:0.08–0.13.

[0015] In one specific embodiment, the mixing in step A further includes heating and stirring to obtain a pH solution, wherein the heating temperature is 60–80 °C.

[0016] In one specific embodiment, the mass ratio of the ceramic filler LLZO to the functional monomer is 0.8:1 to 1:1.

[0017] In one specific embodiment, the heat treatment temperature in step D is above 70 °C, and the heat treatment time is above 12 hours.

[0018] In one specific embodiment, the temperature of the heat treatment in step D is 70 ℃ to 120 ℃.

[0019] A second objective of this invention is to provide a solid electrolyte membrane for wide-temperature-range lithium metal batteries.

[0020] To achieve the second objective of this invention, the solid electrolyte membrane for wide-temperature-range lithium metal batteries is prepared by the method described above, and the solid electrolyte membrane has an ionic conductivity of 1.3 mS / cm or higher at 25 °C.

[0021] In one specific embodiment, the solid electrolyte membrane has a tensile strength of 11.6–14.6 MPa and an elongation at break of 1028–1065%.

[0022] A third objective of this invention is to provide a lithium metal battery.

[0023] To achieve the third objective of the present invention, the lithium metal battery comprises the solid electrolyte membrane described above.

[0024] In one specific embodiment, the positive electrode material of the battery is lithium nickel cobalt manganese oxide NCM811.

[0025] Beneficial effects:

[0026] 1. The wide-temperature-range PVDF-HFP-based all-solid-state electrolyte of the present invention delays the volatilization of the electrolyte and achieves high thermal stability of the polymer electrolyte by introducing the thermally stable comonomer 2-hydroxy-2-methyl-N-[4-cyano-3-(trifluoromethyl)phenyl]-3-[4-(fluorophenyl)thio]propionamide;

[0027] 2. The wide-temperature-range PVDF-HFP based all-solid-state electrolyte of the present invention can achieve a conductivity of more than 1.3 mS / cm at 25 ℃, which solves the defect of low ionic conductivity of polymer electrolytes at 25 ℃;

[0028] 3. The wide-temperature-range PVDF-HFP based all-solid-state electrolyte of the present invention has higher tensile strength, with a tensile strength of up to 14.6 MPa and a pull-out ratio of up to 1065%, which solves the defect of low tensile modulus of polymer electrolytes;

[0029] 4. Excellent wide temperature range stability: The Li||NCM811 battery based on this electrolyte can maintain a high capacity retention rate at -20 ℃ and 45 ℃, which solves the bottleneck of battery application in extreme environments. Attached Figure Description

[0030] Figure 1 Photographs comparing the state of the precursor solution prepared in Example 1 before and after polymerization. A is the image before polymerization; B is the image after polymerization.

[0031] Figure 2 XRD comparison diagram of the electrolyte membrane (C-PHZO) prepared in Example 1 and the electrolyte membranes (PH, PHZO) of Comparative Examples 1 and 2.

[0032] Figure 3 : FTIR spectrum of the electrolyte membrane prepared in Example 1.

[0033] Figure 4 : The ¹H NMR spectrum of the electrolyte membrane prepared in Example 1.

[0034] Figure 5 Thermogravimetric analysis (TGA) curves of the electrolyte membrane prepared in Example 1 and Comparative Examples 1 and 2.

[0035] Figure 6 Stress-strain curves of the electrolyte membrane prepared in Example 1 compared with those of Comparative Examples 1 and 2.

[0036] Figure 7 Long-cycle performance of Li||NCM811 batteries using electrolyte membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 at 45°C.

[0037] Figure 8 Long-cycle performance of Li||NCM811 batteries using electrolyte membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 at -20°C.

[0038] Figure 9 Electrochemical impedance spectroscopy of Comparative Example 3.

[0039] Figure 10 Electrochemical impedance spectroscopy of Comparative Example 4.

[0040] Figure 11 Electrochemical impedance spectroscopy of Comparative Example 5.

[0041] Figure 12 Electrochemical impedance spectroscopy of Comparative Example 6. Detailed Implementation

[0042] To achieve the first objective of this invention, the method includes the following steps:

[0043] A. Mix dioxolane, polyvinylidene fluoride-hexafluoropropylene polymer and lithium difluorooxalate borate to obtain a pH solution;

[0044] B. Mix the pH solution obtained in step A with the ceramic filler LLZO to obtain a pHZO solution, wherein LLZO accounts for 9 wt% to 10 wt% of the pHZO solution;

[0045] C. The PHZO solution obtained in step B is mixed with the functional monomer to obtain a precursor solution; the functional monomer is 2-hydroxy-2-methyl-N-[4-cyano-3-(trifluoromethyl)phenyl]-3-[4-(fluorophenyl)thio]propionamide, and the functional monomer accounts for 9 wt% to 10 wt% of the precursor solution;

[0046] D. The precursor solution obtained in step C is coated onto a substrate and subjected to heat treatment to obtain a solid electrolyte membrane for wide-temperature-range lithium metal batteries.

[0047] The substrate can be glass, PVC board, etc.

[0048] Outside the scope of the present invention, all-solid electrolytes have low conductivity or poor mechanical properties, or all-solid electrolyte membranes cannot be obtained.

[0049] In one specific embodiment, the mass ratio of dioxolane, polyvinylidene fluoride-hexafluoropropylene polymer and lithium difluorooxalate borate in step A is 4.0–5.2:0.8–0.9:0.08–0.13.

[0050] In one specific embodiment, the mixing in step A further includes heating and stirring to obtain a pH solution, wherein the heating temperature is 60–80 °C.

[0051] In one specific embodiment, the mass ratio of the ceramic filler LLZO to the functional monomer is 0.8:1 to 1:1.

[0052] In one specific embodiment, the heat treatment temperature in step D is above 70 °C, and the heat treatment time is above 12 hours.

[0053] In one specific embodiment, the temperature of the heat treatment in step D is 70 ℃ to 120 ℃.

[0054] To achieve the second objective of this invention, the solid electrolyte membrane for wide-temperature-range lithium metal batteries is prepared by the method described above, and the solid electrolyte membrane has an ionic conductivity of 1.3 mS / cm or higher at 25 °C.

[0055] In one specific embodiment, the solid electrolyte membrane has a tensile strength of 11.6–14.6 MPa and an elongation at break of 1028–1065%.

[0056] To achieve the third objective of the present invention, the lithium metal battery comprises the solid electrolyte membrane described above.

[0057] In one specific embodiment, the positive electrode material of the battery is lithium nickel cobalt manganese oxide NCM811. The following description, in conjunction with examples, further illustrates specific embodiments of the present invention, but does not limit the invention to the scope of these embodiments.

[0058] Example 1

[0059] Dioxolane DOL; Polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP; Lithium difluorooxalate borate LIDFOB; Lithium lanthanum zirconium oxide LLZO; 2-hydroxy-2-methyl-N-[4-cyano-3-(trifluoromethyl)phenyl]-3-[4-(fluorophenyl)thio]propionamide CTMOA.

[0060] Step 1: Mix 5 mL of DOL, 0.89 g of PVDF-HFP, and 0.13 g of LIDFOB evenly and heat and stir at 70 °C for 20 minutes to obtain a pH solution.

[0061] Step 2: Mix 5 mL of pH solution and 10 wt% (0.622 g) of LLZO evenly, heat and stir at 70 ℃ for 20 min to obtain pHZO solution.

[0062] Step 3: Mix 5 mL of PHZO solution and 10 wt% (0.68 g) of CTMOA monomer evenly, heat and stir at 70 °C for 20 min to obtain C-PHZO solution.

[0063] Step 4: Apply the solution to a glass plate using a doctor blade, and then heat the reaction solution at 70 °C for 12 h to obtain a wide-temperature-range PVDF-HFP based all-solid-state electrolyte membrane. In this experiment, the conductivity of the C-PHZO solid electrolyte membrane at 25 °C was 1.389 mS / cm.

[0064] Comparative Example 1

[0065] Take the pH solution from Example 1, apply the solution to a glass plate using a spatula, and then heat the reaction solution at 70 °C for 12 h to obtain a pH electrolyte membrane.

[0066] Comparative Example 2

[0067] Take the PHZO solution from Example 1, apply the solution to a glass plate using a spatula, and then heat the reaction solution at 70 °C for 12 h to obtain a PHZO electrolyte membrane.

[0068] The modified PVDF-HFP membrane prepared in Example 1 was characterized below:

[0069] Figure 1 These are photographs of C-PHZO before and after thermal polymerization in Example 1; where a is a photograph of the solution before the thermal polymerization reaction, and b is a photograph of the polymer electrolyte after the thermal polymerization reaction. Figure 1 It is evident that the C-PHZO solution changed from a liquid to a solid before and after the polymerization reaction.

[0070] Depend on Figure 2 The XRD diffraction pattern shows that, compared with the pH and PHZO electrolytes, the diffraction peaks of the LLZO ceramic particles in the prepared wide-temperature-range PVDF-HFP-based electrolyte are stronger, indicating that its crystallinity is greater and proving that there is a certain directional arrangement structure.

[0071] Depend on Figure 3 As shown, the polymerization of the precursor solution was verified by Fourier transform infrared spectroscopy (FTIR) in the range of 750-1300 cm⁻¹.−1 Within the range, 886 cm⁻¹ was observed in DOL and CTMOA, respectively. -1 -(CH2)- oscillation and vibration, and 1149cm -1 The vibrational characteristic peaks at -COC- indicate successful polymerization of surface DOL. Furthermore, at 2941 cm⁻¹... -1 The OH groups at the point of contraction demonstrate the presence of NH···O hydrogen bonds. These bonds serve as anchor points for LLZO particles.

[0072] Depend on Figure 4 As shown, the polymerization of the solution was further verified by proton nuclear magnetic resonance spectroscopy. Figure 4 Figure a shows the proton NMR spectra of PHZO and C-PHZO. 1 The presence of a chemical shift of H in the 1H NMR spectrum indicates that DOL has undergone ring-opening polymerization. Meanwhile, in figure b, CTMOA... 1 The ¹H NMR spectrum showed a characteristic peak at 2.6–3.0 ppm, while the corresponding position was not observed in C-PHZO, indicating that CTMOA and DOL successfully polymerized simultaneously during the ring-opening of DOL. In this invention, CTMOA is an abbreviation for 2-hydroxy-2-methyl-N-[4-cyano-3-(trifluoromethyl)phenyl]-3-[4-(fluorophenyl)thio]propionamide.

[0073] Depend on Figure 5 As shown in the figure, thermogravimetric analysis reveals that during the thermal decomposition of the pH electrolyte membrane, PHZO electrolyte membrane, and wide-temperature-range PVDF-HFP electrolyte membrane, the mass loss is only 6% when the temperature reaches 500 ℃. This indicates that the CTMOA monomer introduced in this experimental design significantly delays the volatilization of the electrolyte membrane.

[0074] Depend on Figure 6 As shown, the tensile strength indicates that among the three prepared electrolyte membranes, the wide-temperature-range PVDF-HFP based electrolyte membrane has a higher tensile strength, reaching 1065% and 14.6 MPa, which is far superior to the PHZO and PH electrolyte membranes.

[0075] Depend on Figure 7As shown, the wide-temperature-range PVDF-HFP-based all-solid-state electrolyte membrane prepared in Example 1 was used as the separator (electrolyte) for a lithium metal battery. It was matched with NCM811 and Li anodes to assemble a Li||NCM811 battery. Li||NCM811 batteries with PH and PHZO membranes were used as comparisons. Long-term cycle tests were conducted on all three batteries under 0.5 C charge-discharge conditions at 45 °C. It can be seen that the Li||NCM811 battery with the wide-temperature-range PVDF-HFP-based all-solid-state electrolyte could stably cycle for more than 150 cycles with a capacity retention of 88.29%. Conversely, the cycle performance of the PHZO and PH electrolyte membrane-based Li||NCM811 batteries rapidly declined, with capacity retention of only 67.76% and 69.27% ​​after 140 and 50 cycles, respectively. These results demonstrate that the wide-temperature-range PVDF-HFP-based all-solid-state electrolyte significantly improves thermal safety and electrochemical performance in practical lithium metal batteries.

[0076] Depend on Figure 8 As shown, the wide-temperature-range PVDF-HFP-based all-solid-state electrolyte membrane prepared in Example 1 was used as the separator (electrolyte) for a lithium metal battery. It was matched with NCM811 and Li anodes to assemble a Li||NCM811 battery. Li||NCM811 batteries with PH and PHZO membranes were used as comparisons. The three batteries underwent long-term cycling tests at 0.5 C charge / discharge and -20 °C. It can be seen that the Li||NCM811 battery with the wide-temperature-range PVDF-HFP-based all-solid-state electrolyte could stably cycle for over 300 cycles with a capacity retention of 84.4%. Conversely, the cycling performance of the PHZO and PH electrolyte membrane-based Li||NCM811 batteries rapidly declined, with capacity retention of only 78.1% and 75% after 207 and 186 cycles, respectively. These results demonstrate that the wide-temperature-range PVDF-HFP-based all-solid-state electrolyte exhibits significant reliability and electrochemical performance under extreme environmental conditions in practical lithium metal batteries.

[0077] Comparative Example 3

[0078] In step 1, "0.89 g of PVDF-HFP" was changed to "0.95 g of PVDF-HFP", and the rest remained the same as in Example 1, to prepare a wide-temperature-range PVDF-HFP-based all-solid-state electrolyte membrane. Figure 9 The electrolyte membrane has a conductivity of 0.87 mS / cm at 25 °C.

[0079] Comparative Example 4

[0080] In step 2, the "0.622 g of LLZO" was changed to "0.75 g of LLZO", and the rest remained the same as in Example 1, to prepare a wide-temperature-range PVDF-HFP-based all-solid-state electrolyte membrane. Figure 10 The electrolyte membrane has a conductivity of 0.66 mS / cm at 25 °C.

[0081] Comparative Example 5

[0082] In step 3, "0.68 g of CTMOA" was changed to "0.55 g of CTMOA", and the rest remained the same as in Example 1, to prepare a wide-temperature-range PVDF-HFP-based all-solid-state electrolyte membrane. Figure 11 The electrolyte membrane has a conductivity of 0.63 mS / cm at 25 °C.

[0083] Comparative Example 6

[0084] In step 4, the step of "heating the reaction solution at 70 °C for 12 h" was changed to "heating the reaction solution at 60 °C for 12 h," while the rest remained the same as in Example 1, to prepare a wide-temperature-range PVDF-HFP-based all-solid-state electrolyte membrane. Figure 12 The electrolyte membrane has a conductivity of 0.71 mS / cm at 25 °C.

Claims

1. A method for preparing a solid electrolyte membrane for wide-temperature-range lithium metal batteries, characterized in that, Includes the following steps: A. Mix dioxolane, polyvinylidene fluoride-hexafluoropropylene polymer and lithium difluorooxalate borate to obtain a pH solution; B. Mix the pH solution obtained in step A with the ceramic filler LLZO to obtain a pHZO solution, wherein LLZO accounts for 9 wt% to 10 wt% of the pHZO solution; C. The PHZO solution obtained in step B is mixed with the functional monomer to obtain a precursor solution; the functional monomer is 2-hydroxy-2-methyl-N-[4-cyano-3-(trifluoromethyl)phenyl]-3-[4-(fluorophenyl)thio]propionamide, and the functional monomer accounts for 9 wt% to 10 wt% of the precursor solution; D. The precursor solution obtained in step C is coated onto a substrate and subjected to heat treatment to obtain a solid electrolyte membrane for wide-temperature-range lithium metal batteries.

2. The method for preparing a solid electrolyte membrane for a wide-temperature-range lithium metal battery according to claim 1, characterized in that, The mass ratio of dioxolane, polyvinylidene fluoride-hexafluoropropylene polymer and lithium difluorooxalate borate in step A is 4.0–5.2:0.8–0.9:0.08–0.

13.

3. The method for preparing a solid electrolyte membrane for a wide-temperature-range lithium metal battery according to claim 1 or 2, characterized in that, The mixing in step A also includes heating and stirring to obtain a pH solution, wherein the heating temperature is 60–80 °C.

4. The method for preparing a solid electrolyte membrane for a wide-temperature-range lithium metal battery according to claim 1 or 2, characterized in that, The mass ratio of the ceramic filler LLZO to the functional monomer is 0.8:1 to 1:

1.

5. The method for preparing a solid electrolyte membrane for a wide-temperature-range lithium metal battery according to claim 1 or 2, characterized in that, The heat treatment in step D is carried out at a temperature of 70 ℃ or higher and for a time of 12 hours or higher.

6. The method for preparing a solid electrolyte membrane for a wide-temperature-range lithium metal battery according to claim 1 or 2, characterized in that, The heat treatment temperature in step D is 70 ℃~120 ℃.

7. A solid electrolyte membrane for wide-temperature-range lithium metal batteries, characterized in that, The solid electrolyte membrane prepared by the method according to any one of claims 1 to 6 has an ionic conductivity of 1.3 mS / cm or higher at 25 °C.

8. The solid electrolyte membrane for wide-temperature-range lithium metal batteries according to claim 7, characterized in that, The solid electrolyte membrane has a tensile strength of 11.6–14.6 MPa and an elongation at break of 1028–1065%.

9. A lithium metal battery, characterized in that, The lithium metal battery comprises a solid electrolyte membrane 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 lithium nickel cobalt manganese oxide NCM811.

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