A positive electrode sheet supporting a double-layer polymer electrolyte membrane and a method for manufacturing the same

Abstract

The application provides a composite electrode with a positive plate supporting a double-layer polymer electrolyte film and a preparation method thereof, the composite electrode comprising: a positive plate, a layer of polymer electrolyte film A located on one side surface of the positive plate, and another layer of polymer electrolyte film B located on the side surface of the polymer electrolyte film A away from the positive plate. The application composites a double-layer polymer electrolyte film on the surface of the positive plate in situ, on the one hand, different polymer materials bear corresponding functions in the electrolyte film: the positive side has good high-voltage stability, mechanical support and fast ion conduction channels, the negative side has excellent interface compatibility and lithium dendrite inhibition capacity, and meanwhile, the adverse interface reaction between different layers of materials is avoided; on the other hand, the double-layer polymer electrolyte film is directly composited on the positive plate in situ, the interface contact between the positive plate and the solid-state electrolyte film layer is effectively enhanced, the weak combination of the two is improved, and the interface impedance is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte membrane technology, and particularly relates to a composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane and its preparation method. Background Technology

[0002] In solid-state lithium-ion batteries, polymer solid electrolytes have attracted widespread attention due to their good flexibility and easy interface adaptation. Polyethylene oxide (PEO), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF) are three typical matrix materials, but each has significant limitations: PEO-based electrolytes are widely studied due to their good compatibility with lithium salts, ease of film formation, and low cost; however, the high crystallinity of PEO molecular chains at room temperature leads to relatively low ionic conductivity. PVDF-based electrolytes, on the other hand, possess excellent film-forming properties, high mechanical strength, and strong polarity (promoting lithium-ion exchange). + While polyacrylonitrile (PAN)-based membranes possess characteristics such as salt dissociation and a wide electrochemical stability window, their semi-crystalline nature hinders lithium-ion migration, leaving room for improvement in ionic conductivity. PAN-based membranes, with their high mechanical strength, good thermal stability, excellent solvent resistance, and controllable porous structure, are ideal composite electrolyte membrane materials. However, their own ionic conductivity is limited, and their interfacial impedance with the electrode is relatively high, making it difficult to achieve the high cycle life requirements of applications when used alone.

[0003] In existing technologies, a single polymer is often used as a functional layer to composite with a PAN-based film. However, this approach is difficult to adapt to the interface requirements of different types of electrode materials, and the composite structure is too simple to be flexibly adjusted according to battery performance requirements, thus limiting its industrial application. In addition, solid electrolyte membranes are usually prepared independently and then assembled with electrode sheets, resulting in a lack of tight bonding between the two, leading to poor interfacial contact and low ion transport efficiency.

[0004] Therefore, developing a composite electrode sheet that can integrate the electrode sheet and the double-layer electrolyte membrane in one piece while meeting the requirements of mechanical support and compatibility of the two-sided interface is of great practical significance. Summary of the Invention

[0005] To address the aforementioned technical issues, this invention provides a composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane and its preparation method. By in-situ compositing a double-layer polymer electrolyte membrane on the surface of the positive electrode sheet, on the one hand, different polymer materials in the double-layer polymer electrolyte membrane each assume corresponding functions within the electrolyte membrane: facing the positive electrode side, it exhibits good high voltage stability, mechanical support, and a fast ion conduction channel; facing the negative electrode side, it possesses excellent interfacial compatibility and lithium dendrite suppression capabilities, while simultaneously avoiding adverse interfacial reactions between different layers of materials. On the other hand, directly compositing the double-layer polymer electrolyte membrane in-situ onto the positive electrode sheet effectively enhances the interfacial contact between the positive electrode sheet and the solid electrolyte membrane layer, improving the weak bonding force between the two while significantly reducing interfacial impedance.

[0006] The present invention proposes a composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane, comprising: a positive electrode sheet, a polymer electrolyte membrane A located on one side surface of the positive electrode sheet, and another polymer electrolyte membrane B located on the side surface of polymer electrolyte membrane A away from the positive electrode sheet; The polymer electrolyte membrane A comprises polyacrylonitrile (PAN), lithium salt, and active inorganic filler; the polymer electrolyte membrane B comprises polyethylene oxide (PEO) and / or polyvinylidene fluoride (PVDF), lithium salt, and inert inorganic filler.

[0007] In this invention, to address the challenges of existing polymer solid electrolytes where a single polymer cannot simultaneously meet the performance requirements of both the positive and negative electrodes, and the interfacial degradation caused by direct contact between polyacrylonitrile electrolytes and lithium metal negative electrodes, a bilayer polymer electrolyte membrane is formed directly in situ on the positive electrode. The layer in direct contact with the positive electrode is polymer electrolyte membrane A, which is essentially a PAN-based electrolyte membrane, exhibiting excellent high voltage stability, mechanical support, and a fast ion conduction channel. The layer facing the negative electrode is polymer electrolyte membrane B, which is essentially a PEO and / or PVDF-based electrolyte membrane, possessing excellent interfacial compatibility and lithium dendrite suppression capabilities. Ultimately, a multilayer polymer solid electrolyte-electrode battery module with high ionic conductivity, a wide electrochemical window, good interfacial stability, and long cycle life is obtained.

[0008] Preferably, the polymer electrolyte membrane A comprises, by mass percentage: 50-80% polyacrylonitrile, 10-40% lithium salt, and 5-20% active inorganic filler; the polymer electrolyte membrane B comprises, by mass percentage: 40-70% polyethylene oxide and / or polyvinylidene fluoride, 10-40% lithium salt, and 5-25% inert inorganic filler.

[0009] In this invention, the active inorganic filler promotes lithium salt dissociation and possesses ion-conducting properties, while the inert inorganic filler achieves ion transport through a transition mechanism. Both components effectively utilize their respective advantages to construct an ion-conducting network structure with the polymer, enabling multi-channel fast Li-ion transport. + Transmission; This invention obtains a composite bilayer polymer solid electrolyte membrane that meets the requirements of mechanical support and dual-sided interface compatibility by combining PAN with active inorganic fillers to form a high-pressure stabilizing layer and PEO and / or PVDF with inert inorganic fillers to construct a negative electrode compatible layer.

[0010] Preferably, the lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalateborate)borate (LiBOB), or lithium perchlorate (LiClO4). The active inorganic filler is at least one of lithium titanium aluminum phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium germanium phosphorus sulfide (LGPS), lithium phosphorus sulfide chlorine (LPSC), lithium lanthanum zirconium oxide (LLZO), lithium zirconium oxychloride (LZOC), lithium aluminate (LiAlO2), or lithium lanthanum zirconium titanium oxide / tantalum niobium co-doped lithium lanthanum zirconium oxide (LLZTO). The inert inorganic filler is at least one of titanium dioxide (TiO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), zirconium dioxide (ZrO2), cerium dioxide (CeO2), silicon nitride (Si3N4), or titanium nitride (TiN).

[0011] Preferably, the particle size of the active inorganic filler is 1-3 μm, and the average particle size of the inert inorganic filler is 12-25 μm.

[0012] Preferably, the active inorganic filler is a polydopamine-coated active inorganic filler grafted with mercapto polyethylene glycol; specifically, after modifying the surface of the active inorganic filler with polydopamine, it is first subjected to amidation condensation with methacrylic anhydride, and then grafted with mercapto polyethylene glycol through a mercapto-olefin click chemical reaction.

[0013] The structural diagram of the polydopamine-coated active inorganic filler grafted with thiol polyethylene glycol is shown below.

[0014] In this invention, by coating active inorganic fillers with polydopamine (PDA) and grafted mercapto polyethylene glycol (HS-PEG-SH), and then combining them with PAN to form a film, the compatibility between the filler and the PAN matrix can be effectively improved, thereby significantly inhibiting filler agglomeration. On the other hand, while improving the flexibility of PAN, the amorphous region of PEO is increased, thus taking into account both the flexibility and chain segment mobility of the polymer. Furthermore, the microscopic interfacial impedance between the inorganic filler and the polymer can be reduced, ultimately achieving efficient lithium ion migration. Preferably, the inert inorganic filler is a silane coupling agent modified inert inorganic filler; specifically, it is obtained by modifying the surface of the inert inorganic filler with a silane coupling agent.

[0015] In this invention, by grafting silane coupling agents onto inert inorganic fillers and then combining them with PEO and / or PVDF to form a composite film, the compatibility between the fillers and the PEO and / or PVDF matrix can be effectively improved, thereby significantly inhibiting filler agglomeration. On the other hand, the mechanical properties of the solid electrolyte membrane are enhanced, thereby improving the interfacial contact between solid electrolyte membrane layers and reducing interfacial impedance.

[0016] Preferably, the polymer electrolyte membrane B further includes 0.5-5% additives; The additive is at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0017] The present invention also proposes a method for preparing the above-mentioned composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane, comprising the following steps: S1. Polyacrylonitrile, lithium salt and active inorganic filler are dissolved in organic solvent A to obtain a spinning solution; using a positive electrode as a receiving substrate, the spinning solution is used to directly form a polymer electrolyte film A on the surface of the positive electrode using an electrospinning process. S2. Dissolve polyethylene oxide and / or polyvinylidene fluoride, lithium salt and inert inorganic filler in organic solvent B, and disperse by ultrasonication to obtain a uniform and stable coating solution; apply the coating solution to the substrate to form a wet polymer electrolyte membrane B, and cover the surface of the wet polymer electrolyte membrane B with polymer electrolyte membrane A to form a double wet film. S3. After drying the double-layer wet film, peel off the substrate to obtain the composite electrode based on the positive electrode sheet-supported double-layer polymer electrolyte membrane.

[0018] In this invention, a double-layer polymer solid electrolyte membrane is formed into a stable multilayer electrolyte membrane through electrospinning and coating processes.

[0019] Preferably, in step S1, the organic solvent A is a mixed solvent of N,N-dimethylformamide and ethanol; the electrospinning voltage is 10-20 kV, the receiving distance is 15-20 cm, and the spinning time is 0.5-1 h. Preferably, in step S2, the organic solvent B is a mixed solvent of acetonitrile and ethanol; the ultrasonic dispersion power is 200-400 W, and the time is 0.5-1 h; Preferably, in step S3, the drying includes forced air drying and vacuum drying, with the temperature of forced air drying being 40-60℃ and the temperature of vacuum drying being 50-55℃.

[0020] The polymer electrolyte membrane A has a thickness of 20-50 μm, and the polymer electrolyte membrane B has a thickness of 50-70 μm.

[0021] The present invention also proposes a lithium-ion battery comprising the above-described composite electrode or the composite electrode prepared by the above-described preparation method.

[0022] Compared with the prior art, the present invention has the following technical effects: (1) The present invention uses a double-layer asymmetric polymer electrolyte membrane. The interface layer on the negative electrode side is made of polyethylene oxide and / or polyvinylidene fluoride and compounded with oxide filler, which can effectively reduce the crystallinity of the matrix, improve the ion conduction performance, and inhibit the generation and growth of lithium dendrites. The interface layer on the positive electrode side is made of nitrile polymer matrix and compounded with solid electrolyte filler, which can further improve the ionic conductivity, enhance the mechanical strength of the system and broaden the electrochemical stability window.

[0023] (2) The present invention does not require the separate preparation of the positive electrode and the solid electrolyte membrane. It can be assembled into a positive electrode supported all-solid-state lithium-ion battery by simply combining the solid electrolyte membrane supported by the positive electrode with the lithium metal negative electrode, which simplifies the production process of all-solid-state lithium-ion batteries.

[0024] (3) The present invention prepares an integrated double-layer composite electrode-electrolyte membrane by electrospinning and solution coating composite process. The resulting membrane has a dense structure, tight interlayer interface, good controllability of membrane thickness, and significantly reduced interfacial impedance. Attached Figure Description

[0025] Figure 1 The graph shows the room temperature cycling performance of the composite electrodes described in Examples 1-3 of this invention under 1C conditions. Figure 2 The linear sweep voltammetry curves of the composite electrodes described in Examples 1-3 of this invention are shown. Figure 3 The following are the rate performance diagrams of the composite electrode described in Embodiment 3 of the present invention: (a) is the long cycle performance diagram at 25°C and 1C, and (b) is the rate performance diagram. Figure 4 The infrared spectrum of LATP-coated polydopamine grafted with thiol as described in Example 6 of this invention. Detailed Implementation

[0026] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0027] Example 1 A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane is prepared by the following method: (1) Preparation of electrospinning solution: 70wt% of PAN (molecular weight 150,000), 21wt% of LiTFSI and 9wt% of LATP (average particle size 2 μm) were added to a mixed solvent of N,N-dimethylformamide (DMF) and ethanol in a volume ratio of 1:1 by mass percentage. The mixture was magnetically stirred at room temperature until it was completely dissolved and dispersed to obtain a uniform electrospinning solution with a solid content of 40wt%. (2) Electrospinning to form a PAN-based electrolyte membrane in situ on the surface of the positive electrode: Using the positive electrode as the receiving substrate, under the conditions of a spinning voltage of 20 kV and a receiving distance of 15 cm, the obtained electrospinning solution is directly electrospinned on the surface of the positive electrode. After spinning for 0.5 h, a PAN-based electrolyte membrane is formed. The obtained PAN-based electrolyte membrane is combined with the positive electrode to form a positive electrode / PAN-based electrolyte membrane composite. No peeling is required. The thickness of the PAN-based electrolyte membrane is 25 μm. (3) Preparation of PEO-based coating solution: PEO (molecular weight 600,000) 61wt%, LiTFSI2 2wt%, TiO2 (average particle size 12 μm) 12wt% and EC 5wt% were added to a mixed solvent of acetonitrile and ethanol in a volume ratio of 1:1 by mass percentage. The mixture was magnetically stirred at room temperature for 6 h until completely dissolved and dispersed. The bubbles were removed by ultrasonication at 200 W for 0.5 h using a small ultrasonic machine to obtain a uniform PEO-based coating solution with a solid content of 10wt%. (4) Coating and Composite: The obtained PEO-based coating solution is uniformly coated onto a clean glass plate with a thickness of 1000 μm to form a wet PEO-based electrolyte membrane. The obtained positive electrode / PAN-based electrolyte membrane composite is then quickly and lightly covered onto the surface of the wet PEO-based electrolyte membrane with the PAN-based electrolyte membrane facing down to ensure tight adhesion between the layers and form a double wet membrane of positive electrode / PAN / PEO. (5) Stepwise drying: The obtained double-layer wet film of positive electrode / PAN / PEO is first placed in a 50 ℃ forced air drying oven for 4 h, and then transferred to a 50 ℃ vacuum drying oven for 12 h. The vacuum degree is ≤-0.08 MPa to fully remove the solvent. After drying, it is peeled off from the glass plate to obtain the integrated composite structure of positive electrode / PAN / PEO. The total thickness of the electrolyte layer after drying is 80 μm, which is the composite electrode.

[0028] A solid-state lithium-ion battery is prepared by the following method: Lithium iron phosphate (LFP), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry. The obtained positive electrode slurry is coated on the surface of aluminum foil, and then dried and rolled to obtain a positive electrode sheet. The obtained positive electrode sheet is used in step (2) of the aforementioned composite electrode preparation method to obtain a positive electrode sheet / PAN / PEO integrated composite structure, which is the composite electrode, and is cut into an electrode sheet with a diameter of 14 mm. A solid-state lithium-ion battery is obtained by directly assembling a lithium metal sheet as the negative electrode and the aforementioned electrode sheet as the positive electrode in an argon-protected glove box, without the need for an additional electrolyte membrane.

[0029] Example 2 A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane is prepared by the following method: (1) Preparation of electrospinning solution: 65wt% of PAN (molecular weight 150,000), 25wt% of LiFSI and 10wt% of LLZO (average particle size 2 μm) were added to a mixed solvent of N,N-dimethylformamide (DMF) and ethanol in a volume ratio of 1:1 by mass percentage. The mixture was magnetically stirred at room temperature until it was completely dissolved and dispersed to obtain a uniform electrospinning solution with a solid content of 40wt%. (2) Electrospinning to form a PAN-based electrolyte membrane in situ on the surface of the positive electrode: Using the positive electrode as the receiving substrate, under the conditions of a spinning voltage of 10 kV and a receiving distance of 20 cm, the obtained electrospinning solution is directly electrospinned on the surface of the positive electrode. After spinning for 1 h, a PAN-based electrolyte membrane is formed. The obtained PAN-based electrolyte membrane is combined with the positive electrode to form a positive electrode / PAN-based electrolyte membrane composite. No peeling is required. The thickness of the PAN-based electrolyte membrane is 40 μm. (3) Preparation of PVDF-based coating solution: 58wt% of PVDF (molecular weight 600,000), 25wt% of LiFSI, 15wt% of Al2O3 (average particle size 15 μm) and 2wt% of FEC were added to a mixed solvent of acetonitrile and ethanol in a volume ratio of 1:1 by mass percentage. The mixture was magnetically stirred at room temperature for 6 h until it was completely dissolved and dispersed. The bubbles were removed by ultrasonication at 400 W for 1 h using a small ultrasonic machine to obtain a uniform PVDF-based coating solution with a solid content of 10wt%. (4) Coating and Composite: The obtained PVDF-based coating liquid is uniformly coated onto a clean glass plate with a thickness of 1000 μm to form a wet PVDF-based electrolyte membrane. The obtained positive electrode / PAN-based electrolyte membrane composite is then quickly and lightly covered onto the surface of the wet PVDF-based electrolyte membrane with the PAN-based electrolyte membrane facing down to ensure tight adhesion between the layers and form a double wet membrane of positive electrode / PAN / PVDF. (5) Stepwise drying: The obtained double-layer wet film of positive electrode / PAN / PVDF is first placed in a 50 ℃ forced air drying oven for 4 h, and then transferred to a 50 ℃ vacuum drying oven for 12 h. The vacuum degree is ≤-0.08 MPa to fully remove the solvent. After drying, it is peeled off from the glass plate to obtain the integrated composite structure of positive electrode / PAN / PVDF. The total thickness of the electrolyte layer after drying is 105 μm, which is the composite electrode.

[0030] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this example.

[0031] Example 3 A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane is prepared by the following method: (1) Preparation of electrospinning solution: 70wt% of PAN (molecular weight 150,000), 21wt% of LiTFSI and 9wt% of LATP (average particle size 2 μm) were added to a mixed solvent of N,N-dimethylformamide (DMF) and ethanol in a volume ratio of 1:1 by mass percentage. The mixture was magnetically stirred at room temperature until it was completely dissolved and dispersed to obtain a uniform electrospinning solution with a solid content of 40wt%. (2) Electrospinning to form a PAN-based electrolyte membrane in situ on the surface of the positive electrode: Using the positive electrode as the receiving substrate, under the conditions of a spinning voltage of 20 kV and a receiving distance of 15 cm, the obtained electrospinning solution is directly electrospinned on the surface of the positive electrode. After spinning for 1 h, a PAN-based electrolyte membrane is formed. The obtained PAN-based electrolyte membrane is combined with the positive electrode to form a positive electrode / PAN-based electrolyte membrane composite. No peeling is required. The thickness of the PAN-based electrolyte membrane is 35 μm. (3) Preparation of PEO-PVDF-based coating solution: PEO (molecular weight 600,000) 31wt%, PVDF (molecular weight 600,000) 30wt%, LiTFSI 22wt%, TiO2 (average particle size 12 μm) 12wt% and EC 5wt% were added to a mixed solvent of acetonitrile and ethanol in a volume ratio of 1:1 by mass percentage. The mixture was magnetically stirred at room temperature for 6 h until completely dissolved and dispersed. The mixture was then ultrasonicated at 200 W for 0.5 h to remove air bubbles, resulting in a uniform PEO-PVDF-based coating solution with a solid content of 10wt%. (4) Coating and Composite: The obtained PEO-PVDF-based coating liquid is uniformly coated onto a clean glass plate with a thickness of 1000 μm to form a wet PEO-PVDF-based electrolyte membrane. The obtained positive electrode / PAN-based electrolyte membrane composite is then quickly and lightly covered onto the surface of the wet PEO-PVDF-based electrolyte membrane with the PAN-based electrolyte membrane facing down to ensure tight adhesion between the layers and form a double wet membrane of positive electrode / PAN / PEO-PVDF. (5) Stepwise drying: The obtained double-layer wet film of positive electrode / PAN / PEO-PVDF is first placed in a 50 ℃ forced air drying oven for 4 h, and then transferred to a 50 ℃ vacuum drying oven for 12 h. The vacuum degree is ≤-0.08 MPa to fully remove the solvent. After drying, it is peeled off from the glass plate to obtain the integrated composite structure of positive electrode / PAN / PEO-PVDF. The total thickness of the electrolyte layer after drying is 90 μm, which is the composite electrode.

[0032] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this example.

[0033] Example 4 A composite electrode with a positive electrode supporting a double-layer polymer electrolyte membrane is prepared by the preparation method described in Example 1. The difference is that in step (1), 50wt% of PAN (molecular weight 150,000), 40wt% of LiTFSI and 10wt% of LATP (average particle size 2 μm) are added to a mixed solvent of N,N-dimethylformamide (DMF) and ethanol in a volume ratio of 1:1 by mass percentage.

[0034] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this example.

[0035] Example 5 A composite electrode with a positive electrode supporting a double-layer polymer electrolyte membrane is prepared by the preparation method described in Example 1. The difference is that in step (3), 70wt% PEO (molecular weight 600,000), 10wt% LiTFSI, 15wt% TiO2 (average particle size 12 μm) and 5wt% EC are added to a mixed solvent of acetonitrile and ethanol in a volume ratio of 1:1 by mass percentage.

[0036] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this example.

[0037] Example 6 A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane is prepared by the preparation method described in Example 1, the difference being that in step (1), LATP is LATP coated with polydopamine and then grafted with thiol polyethylene glycol. The specific preparation method is as follows: LATP was added to methanol and dispersed evenly. Then, tris(hydroxymethyl)aminomethane and sodium hydroxide were added to adjust the pH of the solution to 8.5. Next, dopamine hydrochloride was added. The mass ratio of LATP to dopamine hydrochloride was 1:0.1. After stirring and reacting for 12 h, the mixture was filtered, washed, and dried to obtain PDA@LATP. PDA@LATP was dissolved in concentrated ammonia (28 wt%), and a tetrahydrofuran solution containing 2-methacrylic anhydride was added. The mass ratio of PDA@LATP to 2-methacrylic anhydride was 1:0.02. After stirring at room temperature for 6 h, the mixture was filtered, washed, and dried to obtain methacrylamide-modified PDA@LATP. Methacrylamide-modified PDA@LATP, α,ω-dimercaptopolyethylene glycol (molecular weight 1000), and benzoin dimethyl ether were added to N,N-dimethylacetamide. The mass ratio of methacrylamide-modified PDA@LATP, α,ω-dimercaptopolyethylene glycol, and benzoin dimethyl ether was 1:0.05:0.01. After ultrasonic dispersion, the mixture was irradiated under a UV lamp (365nm) for 10 min. After filtration, washing, and drying, the polydopamine-coated LATP grafted with thiol polyethylene glycol was obtained.

[0038] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this example.

[0039] Example 7 A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane is prepared by the preparation method described in Example 1, the difference being that in step (3), TiO2 is silane coupling agent modified TiO2, and its preparation method is as follows: TiO2 was added to ethanol and ultrasonically dispersed evenly. Under stirring, an aqueous solution containing silane coupling agent KH-550 was added. The mass ratio of TiO2 to silane coupling agent KH-550 was 1:0.02. The mixture was stirred at 70 °C for 3 h, centrifuged, washed, and dried to obtain the silane coupling agent modified TiO2.

[0040] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this example.

[0041] Comparative Example 1 A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane is prepared by the preparation method described in Example 1, the difference being that in step (1), LATP is polydopamine-coated LATP (PDA@LATP), and its preparation method is as follows: LATP was added to methanol and dispersed evenly. Then, tris(hydroxymethyl)aminomethane and sodium hydroxide were added to adjust the pH of the solution to 8.5. Next, dopamine hydrochloride was added, with a mass ratio of LATP to dopamine hydrochloride of 1:0.1. After stirring and reacting for 12 h, the mixture was filtered, washed, and dried to obtain the PDA@LATP.

[0042] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this comparative example.

[0043] Comparative Example 2 A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane is prepared by the preparation method described in Example 1, the difference being that in step (1), LATP is LATP coated with polydopamine and then grafted with amino polyethylene glycol. The specific preparation method is as follows: LATP was added to methanol and dispersed evenly. Then, tris(hydroxymethyl)aminomethane and sodium hydroxide were added to adjust the pH of the solution to 8.5. Next, dopamine hydrochloride was added. The mass ratio of LATP to dopamine hydrochloride was 1:0.1. After stirring and reacting for 12 h, the mixture was filtered, washed, and dried to obtain PDA@LATP. PDA@LATP was added to methanol and dispersed evenly. Sodium hydroxide was added to adjust the pH to 8.5, and then terminal diamine polyethylene glycol (molecular weight 2000) was added. The mass ratio of PDA@LATP to terminal diamine polyethylene glycol was 1:0.05. The mixture was stirred at room temperature for 12 h, then filtered, washed, and dried to obtain the polydopamine-coated LATP grafted amino polyethylene glycol.

[0044] A solid-state lithium-ion battery is prepared according to the method described in Example 1, except that the composite electrode is prepared by the method described above in this comparative example.

[0045] Figure 1 The graph shows the cycling performance of the composite electrodes described in Examples 1-3 at room temperature (25°C) under 1C conditions. Figure 2 The linear sweep voltammetry curves are for the composite electrodes described in Examples 1-3. (Refer to...) Figure 1 , 2 As can be seen, the solid-state lithium-ion battery assembled with the composite electrode of the present invention exhibits excellent cycle performance and decomposition voltage (cycle performance curves are shown in the figure). Figure 1 Decomposition voltage see Figure 2 ( ); Among them, after 100 cycles, the capacity retention rate of Example 1 was 92.3% and the decomposition voltage was 4.32V; after 100 cycles, the capacity retention rate of Example 2 was 96.3% and the decomposition voltage was 4.45V; after 100 cycles, the capacity retention rate of Example 3 was 95.5% and the decomposition voltage was 4.71V.

[0046] Figure 3 This is a rate performance diagram of the composite electrode described in Example 3. (Refer to...) Figure 3 It can be seen that after 300 cycles, Example 3 still has a capacity retention rate of 94.57% and can support charge and discharge tests at a 5C rate. It is evident that the solid-state lithium-ion battery assembled with the electrolyte membrane of the present invention has excellent charge and discharge performance, can stably complete the charge and discharge process at a high rate of 5C, and exhibits good high current transmission capability.

[0047] Figure 4 The infrared spectrum of LATP-coated polydopamine grafted with amino polyethylene glycol as described in Example 6; refer to Figure 4 It can be seen that at 3450 cm -1 The peak at 1650 cm⁻¹ represents the stretching vibration of -OH / -NH. -1 The stretching vibration peak of -C=O, 1100 cm⁻¹ -1 The stretching vibration peak of COC, 650 cm⁻¹ -1 The peak at -CS indicates that mercapto polyethylene glycol was successfully grafted onto the LATP surface via methacrylamide-modified polydopamine.

[0048] The performance of the composite electrodes obtained in the examples and comparative examples was tested, and the results are shown in Table 1 below: Ionic conductivity: The integrated composite electrode was cut into 16 mm diameter discs to serve as the working electrode of the battery, and a stainless steel sheet was used as the counter electrode. A coin cell was assembled in an argon-protected glove box. Electrochemical impedance spectroscopy (EIS) was used for testing, with a frequency range of 1 Hz to 100 kHz, an AC amplitude of 5 mV, and a testing temperature of room temperature (25 ℃). The ionic conductivity was calculated using the following formula: Where σ is the ionic conductivity (S / cm), L is the thickness of the electrolyte membrane (cm), R is the bulk resistance read from the AC impedance spectrum (Ω), and S is the effective contact area between the integrated electrode and the steel sheet (cm²). 2 ); Decomposition voltage: The electrochemical stability window was tested using linear sweep voltammetry (LSV). An integrated composite electrode was cut into 16 mm diameter discs to serve as the negative electrode and solid electrolyte, with a stainless steel sheet as the positive electrode. A coin cell was assembled in an argon-protected glove box. Tests were conducted at room temperature (25 °C) with a scan rate of 0.5 mV / s, covering a voltage range from open circuit voltage to 6.5 V (vs. Li). + / Li); where the potential at which the current begins to increase significantly is defined as the decomposition voltage.

[0049] Table 1. Performance test results of composite electrodes and batteries in the examples and comparative examples.

[0050] Based on Table 1, the composite electrode obtained in this invention exhibits high ionic conductivity and decomposition voltage, indicating that the electrolyte membrane possesses excellent ionic conductivity and high-voltage withstand performance. The results of Examples 1 and 6 show that coating the active inorganic filler with polydopamine (PDA) and grafting with mercapto polyethylene glycol (HS-PEG-SH) can further improve ionic conductivity and high-voltage withstand performance. However, the results of Examples 1 and Comparative Example 2 show that while coating the active inorganic filler with polydopamine (PDA) and grafting with diamine polyethylene glycol (NH2-PEG-NH2) improves ionic conductivity to some extent, it does not significantly improve high-voltage withstand performance. This may be because diamine polyethylene glycol cannot undergo a chemical grafting reaction, resulting in low grafting efficiency.

[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane, characterized in that, include: Positive electrode, a polymer electrolyte membrane A located on one side surface of the positive electrode, and another polymer electrolyte membrane B located on the side surface of polymer electrolyte membrane A away from the positive electrode; The polymer electrolyte membrane A comprises polyacrylonitrile, lithium salt, and active inorganic filler; the polymer electrolyte membrane B comprises polyethylene oxide and / or polyvinylidene fluoride, lithium salt, and inert inorganic filler. The active inorganic filler is a polydopamine-coated active inorganic filler grafted with mercapto polyethylene glycol; specifically, after modifying the surface of the active inorganic filler with polydopamine, it is first subjected to amidation condensation with methacrylic anhydride, and then grafted with mercapto polyethylene glycol through a mercapto-olefin click chemical reaction.

2. The composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane according to claim 1, characterized in that, The polymer electrolyte membrane A comprises, by mass percentage: 50-80% polyacrylonitrile, 10-40% lithium salt, and 5-20% active inorganic filler; the polymer electrolyte membrane B comprises, by mass percentage: 40-70% polyethylene oxide and / or polyvinylidene fluoride, 10-40% lithium salt, and 5-25% inert inorganic filler.

3. The composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane according to claim 1 or 2, characterized in that, The lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalateborate) or lithium perchlorate. The active inorganic filler is at least one of lithium titanium aluminum phosphate, lithium aluminum germanium phosphate, lithium germanium phosphorus sulfur, lithium phosphorus sulfur chlorine, lithium lanthanum zirconium oxide, lithium zirconium oxychlorine, lithium aluminate, or lithium lanthanum zirconium titanium oxide / tantalum niobium co-doped lithium lanthanum zirconium oxide. The inert inorganic filler is at least one of titanium dioxide, aluminum oxide, silicon dioxide, zirconium dioxide, cerium dioxide, silicon nitride, or titanium nitride.

4. The composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane according to claim 1 or 2, characterized in that, The inert inorganic filler is a silane coupling agent modified inert inorganic filler; specifically, it is obtained by modifying the surface of the inert inorganic filler with a silane coupling agent.

5. The composite electrode with a positive electrode sheet supporting a double-layer polymer electrolyte membrane according to claim 1 or 2, characterized in that, The polymer electrolyte membrane B also includes 0.5-5% additives; The additive is at least one of ethylene carbonate, fluoroethylene carbonate, or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

6. A method for preparing a composite electrode with a positive electrode sheet supported by a double-layer polymer electrolyte membrane as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Polyacrylonitrile, lithium salt and active inorganic filler are dissolved in organic solvent A to obtain a spinning solution; using a positive electrode as a receiving substrate, the spinning solution is used to directly form a polymer electrolyte film A on the surface of the positive electrode using an electrospinning process. S2. Dissolve polyethylene oxide and / or polyvinylidene fluoride, lithium salt and inert inorganic filler in organic solvent B, and disperse by ultrasonication to obtain a uniform and stable coating solution; apply the coating solution to the substrate to form a wet polymer electrolyte membrane B, and cover the surface of the wet polymer electrolyte membrane B with polymer electrolyte membrane A to form a double wet film. S3. After drying the double-layer wet film, peel off the substrate to obtain the composite electrode with the positive electrode sheet supporting the double-layer polymer electrolyte membrane.

7. The method for preparing the composite electrode with a positive electrode sheet supported by a double-layer polymer electrolyte membrane according to claim 6, characterized in that, In step S1, organic solvent A is a mixed solvent of N,N-dimethylformamide and ethanol; the electrospinning voltage is 10-20 kV, the receiving distance is 15-20 cm, and the spinning time is 0.5-1 h.

8. The method for preparing the composite electrode with a positive electrode sheet supported by a double-layer polymer electrolyte membrane according to claim 6, characterized in that, In step S2, organic solvent B is a mixed solvent of acetonitrile and ethanol; the ultrasonic dispersion power is 200-400W, and the time is 0.5-1 h.

9. A lithium-ion battery, characterized in that, This includes the composite electrode according to any one of claims 1-5 or the composite electrode prepared by the preparation method according to any one of claims 6-8.

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