A method for preparing a composite solid electrolyte for a lithium metal battery

Abstract

The present application relates to a preparation method of a composite solid-state electrolyte for lithium metal batteries, belonging to the technical field of lithium metal batteries. The composite solid-state electrolyte is prepared by compounding samarium fluoride nanofibers as inorganic fillers with polyethylene oxide-based polymer electrolyte. The features include: 1) electrostatic solution blowing to prepare polytetrafluoroethylene and samarium acetate nascent nanofiber membranes; 2) high-temperature calcination to prepare samarium fluoride nanofibers; and 3) solution casting to prepare samarium fluoride nanofiber and polyethylene oxide-based composite solid-state electrolyte. The composite solid-state electrolyte prepared by the method has one-dimensional long-range ordered lithium ion transmission channels, in-situ formation of LiF can effectively inhibit lithium dendrites, and the electrolyte has high ionic conductivity and an electrochemical stability window, and can be widely used in lithium metal batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, and specifically relates to a method for preparing a composite solid electrolyte for lithium metal batteries. Background Technology

[0002] With the continuous improvement of industrialization, the massive consumption of energy has attracted great attention, and the development of efficient electrochemical energy storage has become an urgent problem to be solved in the field of energy technology. To achieve the ultimate goal of carbon peaking and carbon neutrality, the development of rechargeable batteries has become an inevitable trend. Lithium is lightweight, has the lowest electronegativity, and high energy density, making it an ideal high-efficiency energy storage device. Solid-state electrolytes can effectively solve the problems of flammability, explosiveness, and leakage associated with traditional liquid electrolytes, improving battery safety. Furthermore, the wide electrochemical stability window and excellent thermal stability of solid-state electrolytes broaden the operating voltage and temperature range of batteries, demonstrating good commercial prospects.

[0003] Solid electrolytes are mainly classified into polymer electrolytes, inorganic electrolytes, and organic-inorganic composite electrolytes. Solid polymer electrolyte matrices are primarily composed of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF) and its derivatives, polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). Among these, PEO-based solid electrolytes have attracted widespread attention due to their high dissociation properties for lithium salts, flexibility, and good film-forming properties. However, PEO-based solid electrolytes have high crystallinity, low room-temperature ionic conductivity, and poor oxidation resistance, making them unsuitable for high-voltage cathodes. Introducing inorganic materials to form organic-inorganic composite electrolytes to improve the mechanical strength of PEO-based solid electrolytes, reduce the crystallinity of PEO, and enhance the interfacial contact between PEO and the electrode has become a consensus. Not only does the particle size of the inorganic filler significantly affect lithium-ion transport, but the morphology of the inorganic filler also has a considerable impact on ion transport.

[0004] One-dimensional nanofibers can be continuously prepared using electrospinning, but the yield is low. Electrostatic melt-blowing technology introduces a high-speed airflow onto the fibers within an electrostatic field to achieve efficient nanofiber preparation. Further high-temperature calcination of the prepared precursor nanofibers yields high aspect ratio one-dimensional inorganic nanofibers, which are then mixed with PEO and lithium salt solutions and cast to produce a composite solid electrolyte. This increases the organic-inorganic interface, forming long-range ordered rapid lithium-ion transport channels. Lithium fluoride (LiF) has a low lithium-ion diffusion barrier and electronic insulation. The LiF-containing solid electrolyte interphase (SEI) passivation layer can effectively block electron transfer at the lithium anode and electrolyte interface, promoting rapid lithium-ion migration and uniform deposition. Therefore, preparing a composite solid electrolyte that can both increase the organic-inorganic interface to promote high-speed lithium-ion transport and form a LiF interface passivation layer to suppress lithium dendrites is key to realizing high-performance lithium metal batteries. Summary of the Invention

[0005] To address the problems existing in the background technology mentioned above, the purpose of this invention is to propose a method for preparing a composite solid electrolyte for lithium metal batteries. By introducing one-dimensional samarium fluoride nanofibers with a large specific surface area and high aspect ratio, the interfacial area between the inorganic filler and PEO is increased, enabling rapid lithium-ion transport at a continuous interface. In-situ formation of LiF can reduce the nucleation overpotential of lithium and induce uniform lithium-ion deposition to suppress lithium dendrites. Simultaneously, fluorides have a high formation potential, which can improve the oxidation stability of the solid electrolyte, thereby increasing the battery energy density. This invention, based on a composite solid electrolyte of samarium fluoride nanofibers and polyethylene oxide, possesses a one-dimensional long-range ordered lithium-ion transport channel, excellent lithium dendrite suppression ability, high ionic conductivity, and an electrochemical stability window. To achieve the above objectives, this invention provides a method for preparing a composite solid electrolyte for lithium metal batteries, characterized by the following steps:

[0006] (1) Preparation of polytetrafluoroethylene (PTFE) and samarium acetate nascent nanofiber membranes: Polyvinylpyrrolidone, water, samarium acetate hydrate and commercially available PTFE emulsion were mixed evenly in a certain proportion to prepare a precursor solution; the above solution was spun using electrostatic melt blowing technology to obtain PTFE and samarium acetate nascent nanofiber membranes.

[0007] (2) Preparation of samarium fluoride nanofibers: The nascent nanofiber membrane prepared in step (1) was calcined at high temperature in a muffle furnace through a certain heating program to prepare samarium fluoride nanofibers.

[0008] (3) Preparation of composite solid electrolyte: Samarium fluoride nanofibers are used as inorganic fillers and are mixed with polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonylimide) (LITFSI) and acetonitrile in a certain proportion to prepare an electrolyte solution; the electrolyte solution is cast and then vacuum dried to obtain composite solid electrolyte.

[0009] Preferably, the mass fraction of the PTFE emulsion in step (1) is 60%, and the mass ratio of PTFE to samarium acetate is 1:1 to 4:1.

[0010] Preferably, the electrostatic melt-blown spinning parameters in step (1) are: spinning solution flow rate 15-25 ml / h, voltage 35-45 kV, air pressure 0.05-0.1 MPa, and receiving distance 70-90 cm.

[0011] Preferably, the high-temperature calcination in step (2) is carried out in a sealed crucible, and the heating program is to raise the temperature to 600°C at a rate of 3°C per minute and hold it for 2 hours.

[0012] Preferably, the molar ratio of [EO] to [Li] in PEO and LITFSI in step (3) is 12:1.

[0013] Preferably, in step (3), the mass ratio of samarium fluoride nanofiber filler to PEO and LITFSI is 0% to 15%.

[0014] Due to the adoption of the above technical solutions, the composite solid electrolyte of the present invention has the following characteristics:

[0015] 1) The introduction of one-dimensional samarium fluoride nanofibers with large specific surface area and high aspect ratio greatly increases the interfacial area between inorganic filler and PEO, enabling rapid lithium-ion transport on a continuous interface.

[0016] 2) Lewis acids on the surface of the inorganic phase can capture anions, promote the dissociation of lithium salts, and increase the concentration of freely moving lithium ions.

[0017] 3) Fluorides have low electronic conductivity. The introduction of fluorine sources can promote the in-situ formation of LiF, reduce the nucleation overpotential of lithium, and induce uniform deposition of lithium ions to suppress lithium dendrites.

[0018] 4) Fluorides have a high formation potential, which can improve the oxidation stability of solid electrolytes and thus improve battery energy density.

[0019] The above four characteristics enable the prepared composite solid electrolyte to have superior electrochemical performance and broad application prospects in lithium metal batteries. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation process of the composite solid electrolyte for lithium metal batteries according to the present invention.

[0021] Figure 2 This is an electron microscope image of samarium fluoride nanofibers prepared using Example 1 of the present invention.

[0022] Figure 3 This is an electron microscope image of samarium fluoride nanofibers prepared using Example 2 of the present invention.

[0023] Figure 4 This is an electron microscope image of samarium fluoride nanofibers prepared using Example 3 of the present invention.

[0024] Figure 5 This is an electron microscope image of samarium fluoride nanofibers prepared using Example 4 of the present invention.

[0025] Figure 6 The X-ray diffraction patterns are of samarium fluoride nanofibers prepared using Examples 1-4 of this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments.

[0027] Example 1

[0028] (1) In this invention, the precursor spinning solution needs to be prepared first: take a certain amount of polyvinylpyrrolidone (PVP) powder and dissolve it in water, stir at room temperature for 2 hours to prepare a 15% PVP aqueous solution, add samarium acetate powder at a ratio of PVP: samarium acetate = 2:3, stir at room temperature for 1 hour, then add 60% PTFE emulsion at a ratio of samarium acetate: PTFE = 1:1, stir at room temperature for 1 hour, and let stand for half an hour to remove bubbles for later use.

[0029] (2) Preparation of electrostatic melt-blown PTFE and samarium acetate nascent nanofiber membranes: The spinning solution supply rate was set to 30 ml / h, voltage to 40 kV, air pressure to 0.1 MPa, and receiving distance to 80 cm. The above solution was then spun.

[0030] (3) Preparation of samarium fluoride nanofibers: The nascent nanofiber membrane prepared in step (2) was placed in a sealed crucible and heated to 600°C in a muffle furnace at a heating rate of 3°C / min and held for 2 hours to prepare samarium fluoride nanofibers.

[0031] (4) Preparation of composite electrolyte solution: Add samarium fluoride nanofiber filler (accounting for 10% of the mass ratio of PEO and LITFSI) to acetonitrile and disperse evenly. Then add PEO and LiTFSI (the molar ratio of [EO] and [Li] in PEO and LiTFSI is 12:1) and stir continuously for 24 hours until a uniform solution is obtained.

[0032] (5) Preparation of composite solid electrolyte: The electrolyte solution was poured onto a polytetrafluoroethylene plate, dried at room temperature for 12 hours, and then dried in a vacuum drying oven at 60°C for 12 hours to obtain the composite solid electrolyte.

[0033] Example 2

[0034] (1) In this invention, the precursor spinning solution needs to be prepared first: take a certain amount of polyvinylpyrrolidone (PVP) powder and dissolve it in water, stir at room temperature for 2 hours to prepare a 15% PVP aqueous solution, add samarium acetate powder at a ratio of PVP: samarium acetate = 2:3, stir at room temperature for 1 hour, then add 60% PTFE emulsion at a ratio of samarium acetate: PTFE = 1:2, stir at room temperature for 1 hour, and let stand for half an hour to remove bubbles for later use.

[0035] (2) Same as Example 1.

[0036] (3) Same as Example 1.

[0037] (4) Same as Example 1.

[0038] (5) Same as Example 1.

[0039] Example 3

[0040] (1) In this invention, the precursor spinning solution needs to be prepared first: take a certain amount of polyvinylpyrrolidone (PVP) powder and dissolve it in water, stir at room temperature for 2 hours to prepare a 15% PVP aqueous solution, add samarium acetate powder at a ratio of PVP: samarium acetate = 2:3, stir at room temperature for 1 hour, then add 60% PTFE emulsion at a ratio of samarium acetate: PTFE = 1:3, stir at room temperature for 1 hour, and let stand for half an hour to remove bubbles for later use.

[0041] (2) Same as Example 1.

[0042] (3) Same as Example 1.

[0043] (4) Same as Example 1.

[0044] (5) Same as Example 1.

[0045] Example 4

[0046] (1) In this invention, the precursor spinning solution needs to be prepared first: take a certain amount of polyvinylpyrrolidone (PVP) powder and dissolve it in water, stir at room temperature for 2 hours to prepare a 15% PVP aqueous solution, add samarium acetate powder at a ratio of PVP: samarium acetate = 2:3, stir at room temperature for 1 hour, and then add 60% PTFE emulsion at a ratio of samarium acetate: PTFE = 1:4, stir at room temperature for 1 hour, and let stand for half an hour to remove bubbles for later use.

[0047] (2) Same as Example 1.

[0048] (3) Same as Example 1.

[0049] (4) Same as Example 1.

[0050] (5) Same as Example 1.

[0051] Comparative Example 1

[0052] (1) Same as Example 1.

[0053] (2) Same as Example 1.

[0054] (3) Same as Example 1.

[0055] (4) Preparation of electrolyte solution: PEO and LiTFSI (the molar ratio of [EO] and [Li] in PEO and LiTFSI is 12:1) are added to acetonitrile and dispersed evenly. Stir continuously for 24 hours until a homogeneous solution is obtained.

[0056] (5) Same as Example 1.

[0057] Comparative Example 2

[0058] (1) Same as Example 1.

[0059] (2) Same as Example 1.

[0060] (3) Same as Example 1.

[0061] (4) Preparation of composite electrolyte solution: Add samarium fluoride nanofiber filler (5% of the mass ratio of PEO and LITFSI) to acetonitrile and disperse evenly. Then add PEO and LiTFSI (the molar ratio of [EO] and [Li] in PEO and LiTFSI is 12:1) and stir continuously for 24 hours until a uniform solution is obtained.

[0062] (5) Same as Example 1.

[0063] Comparative Example 3

[0064] (1) Same as Example 1.

[0065] (2) Same as Example 1.

[0066] (3) Same as Example 1.

[0067] (4) Preparation of composite electrolyte solution: Add samarium fluoride nanofiber filler (accounting for 15% of the mass ratio of PEO and LITFSI) to acetonitrile and disperse evenly. Then add PEO and LiTFSI (the molar ratio of [EO] and [Li] in PEO and LiTFSI is 12:1) and stir continuously for 24 hours until a uniform solution is obtained.

[0068] (5) Same as Example 1.

[0069] Performance testing:

[0070] This application discloses a composite solid-state electrolyte for lithium metal batteries, characterized by controlling the ratio of samarium acetate and PTFE and combining it with a high-temperature calcination process to prepare samarium fluoride nanofibers with large specific surface area, high aspect ratio, and good crystallinity. Using samarium fluoride nanofibers as the inorganic filler and PEO as the polymer matrix, the composite solid-state electrolyte is prepared. This electrolyte possesses one-dimensional long-range ordered lithium-ion transport channels, excellent lithium dendrite suppression ability, high ionic conductivity, and a long electrochemical stability window. Lithium metal batteries assembled using this composite solid-state electrolyte and lithium iron phosphate and lithium wafers exhibit excellent electrochemical performance and cycle life.

[0071] Figure 1 This is a flowchart illustrating the preparation process of a composite solid-state electrolyte for lithium metal batteries. The composite solid-state electrolyte for lithium metal batteries in this application is mainly prepared using an electrostatic melt-blowing spinning method combined with high-temperature calcination and a solution casting method. Electrostatic melt-blowing has high efficiency, and the samarium fluoride nanofibers prepared after high-temperature calcination possess a large specific surface area, high aspect ratio, and good crystallinity. The composite solid-state electrolyte prepared using this method exhibits one-dimensional long-range ordered lithium-ion transport channels, excellent lithium dendrite suppression ability, high ionic conductivity, and an electrochemical stability window, making it widely applicable in lithium metal batteries.

[0072] Figure 2-5 The images show the surface morphology of samarium fluoride nanofibers after calcination at 600℃ with samarium acetate to PTFE ratios of 1:1, 1:2, 1:3, and 1:4, respectively. It can be seen that when the samarium acetate to PTFE ratios are 1:1, 1:2, and 1:3, the samarium fluoride nanofibers all exhibit a large aspect ratio and good fiber morphology. However, when the PTFE content increases to 1:4, the fiber morphology disappears, leaving only randomly distributed particles.

[0073] Figure 6 The XRD patterns are of samarium fluoride nanofibers calcined at 600℃ with samarium acetate to PTFE ratios of 1:1, 1:2, 1:3, and 1:4. It can be seen that the resulting samarium fluoride exhibits a coexistence of two crystal systems at these ratios. PDF#12-0792 and PDF#32-0981 correspond to hexagonal and orthorhombic samarium fluoride, respectively.

[0074] Based on SEM and XRD characterization, Example 1 represents the optimal ratio of samarium acetate to PTFE in this application. In summary, the composite solid electrolyte for lithium metal batteries of this application, due to its one-dimensional long-range ordered lithium-ion transport channels and the current density homogenization effect of the in-situ formed LiF passivation layer, possesses high ionic conductivity and excellent lithium dendrite suppression effect, and can be widely used in lithium metal batteries.

Claims

1. A method for preparing a composite solid electrolyte for lithium metal batteries, characterized in that, Includes the following steps: (1) Preparation of polytetrafluoroethylene (PTFE) and samarium acetate nascent nanofiber membranes: Polyvinylpyrrolidone, water, samarium acetate hydrate and commercially available polytetrafluoroethylene (PTFE) emulsion were mixed evenly in a certain proportion to prepare a precursor solution; the above solution was spun using electrostatic melt blowing technology to obtain polytetrafluoroethylene (PTFE) and samarium acetate nascent nanofiber membranes; (2) Preparation of samarium fluoride nanofibers: The nascent nanofiber membrane prepared in step (1) was calcined at high temperature in a muffle furnace through a certain heating program to prepare samarium fluoride nanofibers. (3) Preparation of composite solid electrolyte: Samarium fluoride nanofibers were used as inorganic fillers and mixed with polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonylimide) (LITFSI) and acetonitrile in a certain proportion to prepare an electrolyte solution; the electrolyte solution was cast and then vacuum dried to obtain the composite solid electrolyte. In step (1), the mass fraction of the polytetrafluoroethylene (PTFE) emulsion is 60%, and the mass ratio of polytetrafluoroethylene (PTFE) to samarium acetate is 1:1 to 3:

1.

2. The method for preparing the composite solid electrolyte for lithium metal batteries as described in claim 1, characterized in that, The electrostatic melt-blown spinning parameters are: spinning solution flow rate 15-25 ml / h, voltage 35-45 kV, air pressure 0.05-0.1 MPa, and receiving distance 70-90 cm.

3. The method for preparing the composite solid electrolyte for lithium metal batteries as described in claim 1, characterized in that, In step (2), the high-temperature calcination is carried out in a sealed crucible, and the heating program is to raise the temperature to 600°C at a rate of 3°C per minute and hold it for 2 hours.

4. The method for preparing a composite solid electrolyte for lithium metal batteries as described in claim 1, characterized in that, In step (3), the molar ratio of [EO] to [Li] in the polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonylimide) lithium (LITFSI) is 12:1; the mass ratio of samarium fluoride nanofiber filler to PEO and LITFSI is 0% to 15%, wherein the mass ratio of samarium fluoride nanofiber filler to PEO and LITFSI is not 0%.

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