Composite solid-state electrolyte with polymer protective layer based on mofs and preparation method and application thereof

Abstract

The application belongs to the technical field of electrolytes, and specifically discloses a MOFs-based polymer protective layer composite solid-state electrolyte and a preparation method and application thereof.The composite solid-state electrolyte comprises an inorganic solid-state electrolyte and an interface protective layer, and the interface protective layer is arranged on both sides of the inorganic solid-state electrolyte; the interface protective layer contains a metal organic framework material, polyethylene oxide and lithium bis(trifluoromethylsulfonyl) imide.The application changes the traditional interface design idea of a full solid-state battery, uses an organic interface protective layer with MOFs as an additive, adds the interface protective layer between the solid-state electrolyte and the negative electrode, in the battery cycle process, the MOFs in the interface effectively improve the overall conductivity of the electrolyte due to the Lewis sites, and effectively limit the anions through the pore size effect, and meanwhile, a uniform lithium ion passage is formed, so that the lithium dendrite phenomenon on the surface of the negative electrode is inhibited, and the comprehensive performance of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, and particularly relates to a composite solid electrolyte with a MOFs-based polymer protective layer, its preparation method and application. Background Technology

[0002] Improving the energy density of lithium-ion batteries is crucial for the development of clean energy. Currently, the energy density of lithium-ion batteries mainly used in pure electric vehicles is capped at approximately 300 Eh / kg. However, improvements in existing battery systems and processes have limited effectiveness in further increasing energy density. Meanwhile, liquid lithium-ion batteries are criticized by consumers due to the flammability of their electrolyte. Therefore, developing power batteries with higher energy density and greater safety and stability is essential for promoting electric vehicles. Rechargeable lithium metal batteries, with their high theoretical specific capacity (3860 mAh / g) and ultra-low electrode potential of -3.04V, are currently the most promising anode material, far exceeding the energy density of commercially available rechargeable batteries and ten times that of commercial graphite anodes. Furthermore, the high operating voltage of solid-state lithium batteries can meet the needs of various application scenarios, and their potential advantages such as safety, stability, and environmental friendliness have attracted widespread attention.

[0003] Lithium is abundant in nature, non-toxic, and an environmentally friendly raw material. Although lithium metal batteries have high energy density, using them as the negative electrode presents several problems, primarily due to the dendrite effect unique to lithium metal batteries. During charging and discharging, dendrites can easily puncture the separator, causing short circuits and potentially leading to hazards. However, introducing a high-mechanical-strength solid-state electrolyte instead of a traditional liquid electrolyte can effectively alleviate the lithium metal dendrite problem. Solid-state electrolytes possess high chemical and thermodynamic stability, ensuring greater battery safety during operation. Furthermore, the wide voltage range of solid-state electrolytes effectively improves the overall energy density of the battery. However, the high mechanical strength of solid-state electrolytes leads to poor contact between the electrolyte and electrode, resulting in the formation of a space charge layer and dendrite growth, which reduces the battery's coulombic efficiency and safety performance to some extent. Therefore, solving the interface problem between the electrolyte and electrode is a hot topic in the research field of solid-state lithium metal batteries.

[0004] Currently, most efforts to address these issues involve surface modification of lithium metal to achieve compatibility with solid-state electrolytes. Inorganic materials are used to form interfaces, bridging the physical contact between the solid-state electrolyte and the lithium metal anode, facilitating battery potential transition, and protecting the lithium metal anode. However, this approach typically has overly stringent technical requirements, and more effective modification methods such as vapor deposition have not yet been widely adopted in industry, hindering large-scale adoption and increasing the cost of lithium metal batteries, thus slowing their commercialization. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a composite solid electrolyte with a MOF-based polymer protective layer, its preparation method and application, wherein the composite solid electrolyte can effectively suppress lithium dendrite nucleation and improve the cycle performance and service life of lithium metal batteries.

[0006] To address the aforementioned technical problems, a first aspect of the present invention provides a composite solid electrolyte comprising an inorganic solid electrolyte and an interface protective layer, wherein the interface protective layer is disposed on both sides of the inorganic solid electrolyte; the interface protective layer contains metal-organic framework materials (MOFs), polyethylene oxide (PEO), and lithium bis(trifluoromethanesulfonate)imide (LiTFSI).

[0007] As a further improvement to the above scheme, the synthesis method of the metal-organic framework material is as follows: first, 2-sulfoterephthalic acid monosodium, 1,2,4,5-benzenetetracarboxylic acid and HfCl4 are dissolved in a solvent and heated; then, the resulting solid powder is washed, soaked and vacuum activated with methanol in sequence to obtain the material, hereinafter referred to as NUS-6. In the synthesis process of NUS-6, after 2-sulfoterephthalic acid monosodium dissolves in the solvent, it forms 2-sulfoterephthalic acid through proton exchange. The carboxyl group of 2-sulfoterephthalic acid bonds with hafnium ions to construct a metal-organic framework structure.

[0008] Specifically, the interface protective layer of the present invention uses NUS-6, PEO, and LiTFSI as the main raw materials to form an NUS-6 / PEO@LiTFSI film. Among them: NUS-6 has a stable and ordered pore structure with a pore diameter of 0.5-1.4 nm; the polymer contains lithium salt LiTFSI anions TFSI - With a diameter of 0.8 nm, the pore size of MOFs can effectively confine TFSI. - Shuttle. According to the principles of reaction kinetics, Li + The increased migration number of lithium ions, coupled with the formation of a uniform lithium-ion flow as they pass through the channels during migration, results in NUS-6 exhibiting a pore size sieving effect. This effect creates a pore size sieving interface on the lithium anode surface, controlling the uniform movement of lithium ions to the anode surface and thus suppressing dendrite nucleation, thereby improving the cycle performance of lithium metal batteries. Simultaneously, NUS-6 utilizes its unique ferroelectric effect to create a micro-internal electric field on the lithium anode surface. Under the influence of this internal electric field, lithium ions migrate uniformly through the MOF channels to the anode surface, completing lithium-ion deposition. Therefore, NUS-6 effectively suppresses lithium dendrite growth in the lithium metal anode during the charge and discharge process of solid-state lithium metal batteries, thereby improving the coulombic efficiency and cycle performance of solid-state lithium metal batteries.

[0009] Furthermore, NUS-6 is a MOF with a small particle size, which allows it to be uniformly distributed within the NUS-6 / PEO@LiTFSI film, ensuring the stability of lithium ion sieving. During battery cycling, the polarized NUS-6 can generate a self-generating field, controlling the uniform transport of lithium ions and effectively suppressing the nucleation and growth of lithium dendrites. Moreover, the soft polymer interface protective layer ensures good contact between the electrode and the electrolyte, suppressing excessive interfacial impedance and the formation of a space charge layer, and playing a good transition role between the inorganic solid electrolyte and the lithium metal anode potential.

[0010] Preferably, the molar ratio of 2-sulfoterephthalic acid monosodium, 1,2,4,5-benzenetetracarboxylic acid and HfCl4 is (0.2-5):(0.2-5):1.

[0011] Preferably, the molar concentration of the sodium 2-sulfoterephthalate in the solvent is 0.025-0.3 mol / L.

[0012] Preferably, the solvent is a mixed solution of water and acetic acid, wherein the volume ratio of water to acetic acid is (2-4):2.

[0013] Preferably, the heating is performed by oil bath heating and reflux at 80-110°C for 20-28 hours;

[0014] Preferably, the vacuum activation is performed by vacuum drying at 120-180°C for 20-28 hours.

[0015] A further preferred embodiment of the metal-organic framework material preparation method is as follows: First, 2-10 mmol of monosodium 2-sulfoterephthalate, 2-10 mmol of 1,2,4,5-benzenetetracarboxylic acid, and 2-10 mmol of HfCl4 are dissolved in a mixed solvent of water and acetic acid in 30-80 mL, and the solution is heated under reflux in an oil bath at 80-110 °C for 20-28 hours; then, the resulting solid powder is washed with anhydrous methanol at least three times, and soaked in anhydrous methanol at room temperature for at least 72 hours, with fresh anhydrous methanol replaced every 20-28 hours; then, the anhydrous methanol is removed by centrifugation; finally, the solution is vacuum dried at 120-180 °C for 20-28 hours to obtain the final product.

[0016] Preferably, the mass ratio of the metal-organic framework material, polyethylene oxide and lithium bis(trifluoromethanesulfonate) is (1-5):1:(0.1-3).

[0017] Preferably, the inorganic solid electrolyte is lithium aluminum titanium phosphate (LATP).

[0018] Preferably, the thickness of the interface protective layer is 0.5-1% of the total thickness of the composite solid electrolyte.

[0019] A second aspect of the present invention provides a method for preparing a composite solid electrolyte, comprising the following steps:

[0020] (1) A slurry was prepared by grinding metal-organic framework material, polyethylene oxide and lithium bis(trifluoromethanesulfonate) lithium in a solvent;

[0021] (2) The slurry is poured onto both sides of the inorganic solid electrolyte and dried under vacuum to obtain the composite solid electrolyte.

[0022] As a further improvement to the above scheme, the inorganic solid electrolyte is further subjected to a step of polishing its surface with sandpaper before pouring the slurry.

[0023] Preferably, in step (1), the solvent is acetonitrile.

[0024] Preferably, in step (1), the mass-to-volume ratio of the metal-organic framework material to the solvent is 10-50 g: 1 L.

[0025] Preferably, in step (2), the temperature of the vacuum drying is 50-60°C.

[0026] Preferably, in step (2), the vacuum drying time is 20-28 hours.

[0027] More preferably, the preparation method of the composite solid electrolyte includes the following steps:

[0028] (1) A liquid mixture of metal-organic framework material, polyethylene oxide, lithium bis(trifluoromethanesulfonate) and acetonitrile is ball-milled for 1-2 hours to ensure uniform mixing of the raw materials and to obtain a slurry.

[0029] (2) After sanding the LATP surface with sandpaper, the slurry is poured onto both sides of the inorganic solid electrolyte, and after being smoothed with a scraper, it is vacuum dried at 50-60℃ for 20-28 hours to remove acetonitrile and obtain the composite solid electrolyte.

[0030] A third aspect of the present invention provides a solid-state lithium metal battery, comprising a positive electrode, a lithium metal negative electrode, and an electrolyte, wherein the electrolyte is the aforementioned composite solid electrolyte, and the interface protective layer is located between the lithium metal negative electrode and the inorganic solid electrolyte.

[0031] Preferably, the active material of the positive electrode is lithium iron phosphate.

[0032] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0033] (1) This invention uses an NUS-6 / PEO@LiTFSI membrane as the interface protective layer of the composite solid electrolyte. Utilizing the pore size sieving effect of NUS-6, a pore size sieving interface is formed on the surface of the lithium anode. Under the action of pore size sieving, the lithium ion flow is controlled to move uniformly to the anode surface, thereby suppressing dendrite nucleation and improving the cycle performance of the lithium metal battery. Simultaneously, NUS-6 is a MOF material with a small particle shape, which can be uniformly dispersed in the NUS-6 / PEO@LiTFSI membrane, ensuring the stability of sieved lithium ions. Furthermore, through its unique ferroelectric effect, NUS-6 can effectively suppress lithium dendrite growth on the lithium metal anode during the charging and discharging process of the solid lithium metal battery, thereby improving the coulombic efficiency and cycle performance of the solid lithium metal.

[0034] (2) The byproducts obtained by the NUS-6 / PEO@LiTFSI membrane interface protective layer of the present invention after reacting with lithium metal are Li2CO3, LiF, Li2O, Li2S, etc., which can effectively suppress the formation of lithium metal anode dendrites, thereby improving the cycle performance of the battery and protecting the battery to avoid safety problems caused by short circuit.

[0035] (3) The preparation process of the composite solid electrolyte of the present invention is simple and easy to operate, with a short production cycle, and is suitable for large-scale industrial production. Attached Figure Description

[0036] Figure 1 The X-ray diffraction (XRD) patterns of the composite solid electrolyte and LATP prepared in Example 1 are shown.

[0037] Figure 2 The image shows a scanning electron microscope (SEM) image of the composite solid electrolyte and LATP prepared in Example 1.

[0038] Figure 3 A graph showing the comparison of the cycle performance of solid metal batteries assembled in Example 1 and Comparative Example 1.

[0039] Figure 4 The graph shows the cycle performance of the solid lithium metal battery assembled in Example 1 at different resolutions. Detailed Implementation

[0040] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0041] Example 1

[0042] A composite solid electrolyte includes an inorganic solid electrolyte LATP and an interface protective layer. The interface protective layer is disposed on both sides of the inorganic solid electrolyte, and the thickness of the interface protective layer is 1% of the total thickness of the composite solid electrolyte.

[0043] A method for preparing a composite solid electrolyte includes the following steps:

[0044] (1) Synthesis of MOF material NUS-6:

[0045] 5 mmol of monosodium 2-sulfoterephthalate, 5 mmol of 1,2,4,5-benzenetetracarboxylic acid and 5.2 mmol of HfCl4 were dissolved in 50 mL of a mixed solvent (water and acetic acid in a volume ratio of 3:2) and heated under reflux in an oil bath at 100 °C for 24 hours to obtain a colorless powder.

[0046] The obtained colorless powder was washed three times with anhydrous methanol and then soaked in anhydrous methanol for 72 hours, with fresh anhydrous methanol being replaced every 24 hours. The anhydrous methanol was then removed by centrifugation and the powder was dried under vacuum at 150°C for 24 hours to obtain the activated product NUS-6.

[0047] (2) Preparation of NUS-6 / PEO@LiTFSI slurry

[0048] The NUS-6 synthesized in step (1) and PEO and LiTFSI were added to acetonitrile (the mass-volume ratio of NUS-6 to acetonitrile was 30g:1L) at a mass ratio of 3:3:2. The mixture was ball-milled for 2 hours to ensure that the raw materials were mixed evenly and to obtain NUS-6 / PEO@LiTFSI slurry.

[0049] (3) Preparation of composite solid electrolyte

[0050] The surface of LATP was sanded with sandpaper, and then the NUS-6 / PEO@LiTFSI slurry obtained in step (2) was poured onto both sides of LATP and smoothed with a scraper. Vacuum drying was carried out at 55°C for 24 hours to remove acetonitrile and obtain the NUS-6 / PEO / LiTFSI-LATP composite solid electrolyte of this embodiment.

[0051] Figure 1 The X-ray diffraction pattern of the composite solid electrolyte prepared in Example 1 is shown below. Figure 1 In the diagram, the horizontal axis 2Theta represents the diffraction angle, and the vertical axis Intensity represents the intensity of the diffraction peak. Figure 1 It can be seen that the XRD pattern of the sintered LATP pellets (LATPPellet) matches well with that of the standard NASICON electrolyte; the XRD pattern of the synthesized NUS-6 (Simulated NUS-6) also matches the simulation results highly. This indicates that stable NUS-6 crystals and LATP electrolyte exist in the synthesized NUS-6 / PEO@LiTFSI-LATP electrolyte.

[0052] Figure 2 The images shown are scanning electron microscope (SEM) images of the composite solid electrolyte and LATP prepared in Example 1, wherein: Figure 2 -A and Figure 2 -B is the SEM image of LATP. Figure 2 -C and Figure 2 -D is the SEM image of the composite solid electrolyte. (From...) Figure 2 As can be seen, sintered LATP is composed of nanoparticles with an uneven surface. The contact between the electrolyte and the rough electrode surface easily leads to significant interfacial resistance. Furthermore, the gaps formed between the electrode and electrolyte during point-to-point contact result in the formation of a space charge layer, all of which severely hinder battery cycle performance. In contrast, the NUS-6 / PEO@LiTFSI-LATP composite solid electrolyte exhibits high flexibility and adhesion. Its ultra-thin interfacial layer tightly connects the electrolyte and electrode, alleviating the interfacial contact problem. Simultaneously, the NUS-6 in the interfacial layer effectively filters lithium ions, helping them to deposit uniformly on the negative electrode surface and inhibiting lithium dendrite growth, thereby achieving more stable battery cycle performance.

[0053] A solid-state lithium metal battery includes a positive electrode, a lithium metal negative electrode, and an electrolyte, wherein: the active material of the positive electrode is lithium iron phosphate, and the mass ratio of the active material, polyvinylidene fluoride (PVDF), and conductive carbon is 8:1:1; the electrolyte is the NUS-6 / PEO / LiTFSI-LATP composite solid electrolyte prepared in this embodiment, and the interface protective layer is located between the lithium metal negative electrode and the inorganic solid electrolyte, and the battery is assembled into a CR2025 type button cell.

[0054] Comparative Example 1

[0055] A solid-state lithium metal battery includes a positive electrode, a lithium metal negative electrode, and an electrolyte, wherein: the active material of the positive electrode is lithium iron phosphate, and the mass ratio of the active material, polyvinylidene fluoride (PVDF), and conductive carbon is 8:1:1; the electrolyte is LATP, and it is assembled into a CR2025 type button cell using the same method as in Example 1.

[0056] Comparative Example 2

[0057] A composite solid electrolyte includes an inorganic solid electrolyte LATP and an interface protective layer. The interface protective layer is disposed on both sides of the inorganic solid electrolyte, and the thickness of the interface protective layer is 1% of the total thickness of the composite solid electrolyte.

[0058] A method for preparing a composite solid electrolyte includes the following steps:

[0059] (1) Preparation of PEO@LiTFSI slurry

[0060] The PEO and LiTFSI synthesized in step (1) were added to acetonitrile (the mass-volume ratio of PEO to acetonitrile was 30g:1L) at a mass ratio of 3:2, and ball milled for 2 hours to make the raw materials evenly mixed, thus obtaining PEO@LiTFSI slurry.

[0061] (2) Preparation of composite solid electrolyte

[0062] The surface of LATP was sanded with sandpaper, and then the PEO@LiTFSI slurry obtained in step (1) was poured onto both sides of LATP and smoothed with a scraper. It was then vacuum dried at 55°C for 24 hours to remove acetonitrile and obtain the PEO / LiTFSI-LATP composite solid electrolyte of this comparative example.

[0063] A solid-state lithium metal battery includes a positive electrode, a lithium metal negative electrode, and an electrolyte, wherein: the active material of the positive electrode is lithium iron phosphate, and the mass ratio of the active material, polyvinylidene fluoride (PVDF), and conductive carbon is 8:1:1; the electrolyte is a PEO / LiTFSI-LATP composite solid electrolyte prepared in this comparative example, and the interface protective layer is located between the lithium metal negative electrode and the inorganic solid electrolyte, and the battery is assembled into a CR2025 type button cell.

[0064] Performance testing

[0065] The cycle performance of the solid-state lithium metal batteries assembled in Example 1 and Comparative Example 1 was tested under constant current charge-discharge conditions at 60°C and 0.1C. The results are as follows: Figure 3 As shown. By Figure 3It can be seen that the solid-state lithium metal battery assembled in Example 1 achieved an initial discharge specific capacity of 165 mAh / g, and after 100 charge-discharge cycles, it still maintained 161 mAh / g, with a capacity retention of 97.6%, while also exhibiting a coulombic efficiency close to 100%. In contrast, the solid-state lithium metal battery assembled in Comparative Example 1 had an initial charge-discharge specific capacity of 168 mAh / g, and after 20 cycles, the specific capacity remained at 2.6 mAh / g, demonstrating extremely poor battery performance. This indicates that the NUS-6 / PEO@LiTFSI-LATP electrolyte plays an effective role in repeated charge-discharge cycles, maintaining good ionic conductivity, excellent stability, and uniform Li₂ concentration over long battery cycles. + Flux to the protective negative electrode.

[0066] Figure 4 The graphs show the cycle performance of the solid-state lithium metal battery assembled in Example 1 at different resolutions. Figure 4 It can be seen that, at different rates (0.05C, 0.1C, 0.2C, 0.3C, 0.4C, and 0.5C), the solid-state metal battery assembled in Example 1 exhibits discharge specific capacities of 160 mAh / g, 157 mAh / g, 149 mAh / g, 140 mAh / g, 129 mAh / g, and 120 mAh / g, respectively. This demonstrates that the NUS-6 / PEO@LiTFSI-LATP electrolyte maintains a highly stable buffering effect even at high rates.

[0067] The cycle performance of the solid lithium metal batteries assembled in Example 1 and Comparative Example 2 was tested under constant current charge-discharge conditions at 60°C and 0.2C. The results are shown in Table 1.

[0068] Table 1:

[0069]

[0070] As shown in Table 1, the solid lithium metal battery assembled with NUS-6 / PEO@LiTFSI-LATP composite solid electrolyte (Example 1) has significantly improved specific capacity and cycle performance compared with the solid lithium metal battery assembled without NUS-6 electrolyte (Comparative Example 2).

[0071] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A composite solid electrolyte, characterized in that, The composite solid electrolyte comprises an inorganic solid electrolyte and an interface protective layer, wherein the interface protective layer is disposed on both sides of the inorganic solid electrolyte; the interface protective layer contains a metal-organic framework material, polyethylene oxide, and lithium bis(trifluoromethanesulfonate)imide. The method for synthesizing the metal-organic framework material is as follows: first, 2-sulfoterephthalic acid monosodium, 1,2,4,5-benzenetetracarboxylic acid and HfCl4 are dissolved in a solvent and heated; then, the resulting solid powder is washed, soaked and vacuum activated in methanol in sequence to obtain the final product.

2. The composite solid electrolyte according to claim 1, characterized in that, The molar ratio of sodium 2-sulfoterephthalate, 1,2,4,5-benzenetetracarboxylic acid, and HfCl4 is (0.2-5):(0.2-5):1; And / or, the molar concentration of the sodium 2-sulfoterephthalate in the solvent is 0.025-0.3 mol / L; And / or, the heating is performed by oil bath heating and reflux at 80-110°C for 20-28 hours; And / or, the vacuum activation is to perform vacuum drying at 120-180°C for 20-28 hours.

3. The composite solid electrolyte according to claim 1, characterized in that, The mass ratio of the metal-organic framework material, polyethylene oxide and lithium bis(trifluoromethanesulfonate) is (1-5):1:(0.1-3).

4. The composite solid electrolyte according to claim 1, characterized in that, The inorganic solid electrolyte is lithium aluminum titanium phosphate.

5. The composite solid electrolyte according to any one of claims 1-4, characterized in that, The thickness of the interface protective layer is 0.5-1% of the total thickness of the composite solid electrolyte.

6. A method for preparing a composite solid electrolyte as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) A slurry was prepared by grinding metal-organic framework material, polyethylene oxide and lithium bis(trifluoromethanesulfonate) in a solvent; (2) The slurry is poured onto both sides of the inorganic solid electrolyte and dried under vacuum to obtain the composite solid electrolyte.

7. The method for preparing the composite solid electrolyte according to claim 6, characterized in that, In step (1), the mass-to-volume ratio of the metal-organic framework material to the solvent is 10-50 g: 1 L.

8. The method for preparing the composite solid electrolyte according to claim 6, characterized in that, In step (2), the temperature of the vacuum drying is 50-60°C; and / or the time of the vacuum drying is 20-28 hours.

9. A solid-state lithium metal battery, characterized in that, It includes a positive electrode, a lithium metal negative electrode, and an electrolyte, wherein the electrolyte is a composite solid electrolyte as described in any one of claims 1 to 5, and the interface protective layer is located between the lithium metal negative electrode and the inorganic solid electrolyte.

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