Lithium metal battery composite solid electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of inorganic material preparation and new energy materials, and particularly discloses a lithium metal battery composite solid electrolyte as well as a preparation method and application thereof. Lithium niobate with high lithium ion conductivity and high dielectric constant is used as an inorganic filler, polyvinylidene fluoride-co-hexafluoropropylene is used as a polymer matrix, and the lithium metal battery composite solid electrolyte is prepared. The lithium metal battery solid electrolyte with a continuous lithium ion transport path is constructed through a freeze casting technology, the dielectric constant of the solid electrolyte is effectively improved by adding the dielectric inorganic filler lithium niobate, lithium salt dissociation is promoted, preparation of the modified electrolyte can be simply completed on a large scale, industrial expansion is facilitated, coulombic efficiency is improved, and the lithium metal battery solid electrolyte is suitable for industrial production. According to the present invention, the lithium metal battery electrolyte meets the industrial requirement on the high lithium utilization rate, the lithium negative electrode can be well protected, the cycle life of the lithium electrode can be improved, the battery electrolyte and the lithium electrode show the good interface compatibility and the good cycle stability, and the new feasible way is provided for the application of the lithium metal battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic material preparation and new energy material, and specifically relates to a lithium metal battery composite solid electrolyte and a preparation method and application thereof. Background Art

[0002] Since the effective utilization of renewable energy relies on the support of energy storage media, high-efficiency energy storage technologies and equipment have extremely broad application prospects. Since their commercialization 30 years ago, lithium-ion batteries have been the current winners in consumer electronics and new energy vehicle applications due to their high energy density, small size, light weight, and long cycle life.

[0003] However, the theoretical capacity of conventional graphite anode is only 372 mAh g -1 , which severely limits the improvement of lithium-ion battery energy density and can no longer meet the current market demand. Among the many negative electrode materials, lithium metal negative electrode has a high theoretical specific capacity (3860mAh g -1 ), low chemical potential (-3.04 V vs SHE) and low density (0.59 g cm -3 ) and is considered to be one of the ideal choices for the negative electrode materials of the new generation of rechargeable batteries.

[0004] At the same time, the liquid electrolytes used in lithium-ion batteries pose safety risks such as leakage, corrosion, and flammability. Compared to liquid electrolytes, solid-state electrolytes offer advantages such as improved safety, high energy density, excellent cycle performance, and a wide operating temperature range. Therefore, the development of high-performance, high-safety solid-state electrolytes, paired with high-voltage cathodes and lithium metal anodes, can achieve higher energy density and improved safety, which is essential for the practical application of lithium metal batteries.

[0005] However, the chemical properties of lithium metal itself are very active. The lithium dendrites and interfacial side reactions formed on the surface of lithium metal during the cycle seriously affect the service life of lithium metal batteries. In addition, the dissociation efficiency of lithium salts in traditional solid-state electrolytes is low, and the lithium ion solvation environment is not conducive to rapid conduction, resulting in insufficient ionic conductivity and low coulombic efficiency, which makes it difficult to meet the industrial demand for high lithium utilization. There is a large interfacial contact impedance between the solid-state electrolyte and the lithium electrode, resulting in poor interface compatibility and insufficient cycle stability, which restricts the overall performance of the battery. Summary of the Invention

[0006] The purpose of the present invention is to provide a lithium metal battery composite solid electrolyte and its preparation method and application, so as to solve the problems raised in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a composite solid electrolyte for a lithium metal battery comprises the following steps:

[0009] The following steps are involved:

[0010] S1. Lithium niobate (LiNbO3, LNO) nanoparticles and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) are dissolved in dimethyl sulfoxide (DMSO) in a weight ratio of 1:1 to form a mixed solution with a solid content of 20-22 wt%; the mixture is maintained at 60°C for 4 hours to form a homogeneous solution;

[0011] S2, coating the mixed solution on a substrate, placing it in a liquid nitrogen environment and freezing it to obtain a solid film;

[0012] S3, then transferring the solid membrane to ethanol below 0°C to extract the DMSO solvent, and then washing and drying to obtain the LNO / PVDF-HFP basement membrane;

[0013] S4. Add VEC-based electrolyte on the base film and form an integrated solid electrolyte through UV curing.

[0014] Preferably, the VEC-based electrolyte is prepared by: polyethylene glycol diacrylate, vinyl ethylene carbonate, lithium bis(fluorosulfonyl)imide (LiFSI), fluoroethylene carbonate and photoinitiator 2-hydroxy-2-methylpropiophenone, with a weight ratio of 1:10:3:1:0.11, and fully stirring to obtain a VEC-based electrolyte.

[0015] Preferably, the freezing in S2 is achieved by a copper cooler, which is immersed in liquid nitrogen to completely solidify the solution within 10 seconds.

[0016] Preferably, the LNO nanoparticles in S1 are prepared by a hydrothermal method: niobium pentoxide and lithium hydroxide are mixed in a molar ratio of 1:2, an ethylenediamine aqueous solution is added, and the mixture is reacted at 220° C. for 96 hours, followed by washing and drying.

[0017] Preferably, the UV curing conditions in S4 are: wavelength 365nm, intensity 20mW / cm 2 , time: 3 to 5 minutes.

[0018] Composite solid-state electrolyte is used to inhibit lithium dendrite growth and improve battery cycle life, allowing lithium iron phosphate / lithium metal batteries to stably cycle ≥850 times at a 1C rate.

[0019] A lithium metal battery, characterized by comprising a positive electrode, a lithium metal negative electrode and a solid electrolyte layer.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention provides a method for preparing a composite solid electrolyte for lithium metal batteries. By introducing lithium niobate as an inorganic filler, the modified electrolyte can be prepared simply and on a large scale, which is conducive to industrial expansion.

[0022] (2) The addition of lithium niobate, a dielectric inorganic filler, effectively improves the dielectric constant of the solid electrolyte and promotes the dissociation of lithium salts. At the same time, lithium niobate changes the lithium ion solvation environment of the electrolyte in the channel structure. The increased aggregated ion pairs effectively improve the reaction kinetics of lithium ions, increase the coulombic efficiency, and meet the industrial requirements for high lithium utilization.

[0023] (3) Lithium niobate nanoparticles are uniformly embedded in the wall of the polymer matrix to form a gradient pore structure. The dense lower layer serves as the lithium metal contact end, which can well protect the lithium negative electrode and improve the cycle life of the lithium electrode.

[0024] (4) The lithium metal battery composite solid electrolyte prepared by the present invention exhibits good interfacial compatibility with the lithium electrode, cycle stability, and safety and reliability, providing a new and feasible approach for the application of lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a comparison chart of the LFP full cell efficiency of Example 1 of the present invention and Comparative Example 1;

[0026] Figure 2 This is a comparison chart of the LFP full battery cycles of Example 1 of the present invention and Comparative Example 1;

[0027] Figure 3 1 is a comparison chart of the charge and discharge curves of the LFP full battery of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Example 1:

[0030] refer to Figures 1 to 3 , a preparation method of a lithium metal battery composite solid electrolyte, the method steps are as follows:

[0031] 1 g of LNO and 1 g of PVDF-HFP were dissolved in 7 g of dimethyl sulfoxide (DMSO) solution (the weight ratio of LNO and PVDF-HFP was 1:1, and the solid content was about 20-22 wt%), and maintained at 60 °C for 4 h to form a homogeneous solution.

[0032] The solution was evenly coated onto a glass plate (10 x 10 cm) using a 200 μm doctor blade. The glass plate was then placed on a copper cooler immersed in liquid nitrogen. The solution coated on the glass plate was rapidly frozen into an opaque solid film.

[0033] The membrane was then transferred to ethanol below 0°C to extract the DMSO solvent. The solidified polymer membrane was then washed with deionized water and ethanol, transferred to a vacuum drying oven, and vacuum dried at 60°C for 12 hours to obtain the LNO / PVDF-HFP substrate membrane.

[0034] PVDF-HFP was dissolved in a DMSO solution (15 wt %) dispersed therein, and a pure PVDF-HFP basement membrane was prepared according to the above steps. The basement membrane obtained above was cut into discs with a diameter of 18 mm for use in the next step.

[0035] A VEC-based electrolyte was dropped into the prepared base film, and the base film was irradiated with ultraviolet light with a wavelength of 365 nm and an intensity of 20 mW cm-2 for 3-5 minutes to obtain an integrated solid lithium metal solid electrolyte.

[0036] The lithium niobate particles are prepared by weighing niobium pentoxide and lithium hydroxide in a molar ratio of 1:2 and mixing them evenly. The mixture is then placed in a 50ml polytetrafluoroethylene jar, and 5ml of ethylenediamine solution and 30ml of deionized water are added, bringing the volume up to 70% of the total volume. The mixture is heated at 220°C for 96 hours without shaking or stirring, and then cooled naturally to room temperature. The white precipitate is collected and repeatedly washed with ethanol to remove any residual ethylenediamine. Finally, the mixture is dried at 60°C for 5 hours to obtain the lithium niobate particles.

[0037] The VEC-based electrolyte was prepared by stirring 0.2 g of polyethylene glycol diacrylate, 2 g of vinyl ethylene carbonate, 0.6 g of lithium bis(fluorosulfonyl)imide, and 0.2 g of vinyl fluorocarbon until uniformly mixed to obtain a 2M VEC-based electrolyte (weight ratio of 1:10:3:1). Furthermore, 0.022 g of a photoinitiator, 2-hydroxy-2-methylpropiophenone, was added and stirred uniformly.

[0038] Preparation method of the positive electrode sheet:

[0039] The LFP positive electrode sheet is prepared with lithium iron phosphate, lithium niobate, conductive carbon black, and polyvinylidene fluoride in a ratio of 7.5:0.5:1:1. Lithium iron phosphate (LiFePO4, LFP), LNO, and conductive carbon black are weighed and ground in a mortar for 30 minutes to thoroughly mix the solid powders. Polyvinylidene fluoride is then added. The materials are mixed and degassed using a degassing machine to obtain a slurry. This is then evenly coated on a carbon-coated aluminum foil current collector using a coater and dried in a vacuum oven at 60°C for 24 hours. Finally, a tablet press is used to cut it into circular positive electrode sheets with a diameter of 18 mm.

[0040] In summary, the present invention utilizes lithium niobate (LiNbO3, LNO) as an inorganic filler and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as a polymer matrix, using freeze-casting technology to construct a solid-state electrolyte for lithium metal batteries with a continuous lithium ion transport path. On the one hand, lithium niobate nanoparticles are uniformly embedded in the walls of the polymer matrix, forming a gradient pore structure. The dense lower layer serves as the lithium metal contact end, effectively protecting the lithium negative electrode. On the other hand, the addition of lithium niobate, a dielectric inorganic filler, effectively increases the dielectric constant of the solid-state electrolyte, promoting the dissociation of lithium salts. Simultaneously, lithium niobate alters the lithium ion solvation environment of the electrolyte within the channel structure, and the increased aggregated ion pairs effectively improve the reaction kinetics of lithium ions. The resulting lithium metal battery exhibits improved cycling performance.

[0041] Comparative Example:

[0042] Assemble a CR2025 button cell in the order of positive electrode shell / positive electrode sheet / composite solid electrolyte / lithium metal / gasket / spring sheet / negative electrode shell to evaluate the battery's cycling performance. All of the above materials are commercially available.

[0043] A solid electrolyte prepared using LNO / PVDF-HFP was prepared according to the operation of Example 1, and assembled with an LFP positive electrode sheet and a lithium metal negative electrode into a full battery to test the performance.

[0044] A solid electrolyte prepared using pure PVDF-HFP was assembled with an LFP positive electrode sheet and a lithium metal negative electrode to test the performance of a full battery.

[0045] It can be seen from the performance comparison chart of Example 1 and Comparative Example 1 that:

[0046] The integrated lithium metal solid electrolyte produced by in-situ technology using LNO as the inorganic filler and PVDF-HFP as the polymer matrix showed significant performance improvement when matched with the LFP positive electrode.

[0047] Among them, the discharge capacity of the lithium metal solid-state battery prepared without pure PVDF-HFP membrane began to decay from 80 cycles and could not work normally after 150 cycles. After adding LNO, it could stably cycle for 850 cycles and had better rate performance.

[0048] Practice has proved that the composite solid electrolyte prepared by freeze casting technology with LNO as inorganic filler and PVDF-HFP as polymer matrix can significantly improve the cycle stability and service life of the lithium negative electrode, and has high practical value.

[0049] It will be appreciated that in the development of any actual embodiment, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will, for those of ordinary skill having the benefit of this disclosure, be a routine undertaking of design, fabrication, and production without undue experimentation.

[0050] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a composite solid electrolyte for a lithium metal battery, characterized in that: The following steps are involved: S1. Lithium niobate (LiNbO3, LNO) nanoparticles and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) are dissolved in dimethyl sulfoxide (DMSO) in a weight ratio of 1:1 to form a mixed solution with a solid content of 20-22 wt%; the mixture is maintained at 60°C for 4 hours to form a homogeneous solution; S2, coating the mixed solution on a substrate, placing it in a liquid nitrogen environment and freezing it to obtain a solid film; S3, then transferring the solid membrane to ethanol below 0°C to extract the DMSO solvent, and then washing and drying to obtain the LNO / PVDF-HFP basement membrane; S4. Add VEC-based electrolyte on the base film and form an integrated solid electrolyte through UV curing.

2. The method for preparing a composite solid electrolyte for lithium metal batteries according to claim 1, wherein: The VEC-based electrolyte is prepared by: polyethylene glycol diacrylate, vinyl ethylene carbonate, lithium bis(fluorosulfonyl)imide (LiFSI), fluoroethylene carbonate, and a photoinitiator, 2-hydroxy-2-methylpropiophenone, in a weight ratio of 1:10:3:1:0.11, and fully stirring to obtain a VEC-based electrolyte.

3. The method for preparing a composite solid electrolyte for lithium metal batteries according to claim 1, wherein: The freezing in S2 is achieved by a copper cooler, which is immersed in liquid nitrogen to completely solidify the solution within 10 seconds.

4. The method for preparing a composite solid electrolyte for lithium metal batteries according to claim 1, wherein: The LNO nanoparticles in S1 are prepared by a hydrothermal method: niobium pentoxide and lithium hydroxide are mixed in a molar ratio of 1:2, an ethylenediamine aqueous solution is added, and the mixture is reacted at 220° C. for 96 hours, followed by washing and drying.

5. The method for preparing a composite solid electrolyte for lithium metal batteries according to claim 1, characterized in that: The UV curing conditions in S4 are: wavelength 365nm, intensity 20mW / cm 2 , time: 3 to 5 minutes.

6. A composite solid electrolyte for lithium metal batteries, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5.

7. The lithium metal battery composite solid electrolyte prepared according to the method for preparing a lithium metal battery composite solid electrolyte according to any one of claims 1 to 5 is used in lithium metal batteries.

8. The use of the composite solid electrolyte according to claim 7, characterized in that: Used to inhibit lithium dendrite growth and improve battery cycle life, allowing lithium iron phosphate / lithium metal batteries to stably cycle ≥850 times at a 1C rate.

9. A lithium metal battery, characterized in that: It includes a positive electrode, a lithium metal negative electrode and a solid electrolyte layer.

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