A polydopamine modified polyethylene oxide solid-state electrolyte, and a preparation method and application thereof

Abstract

The application provides a kind of polydopamine modified polyethylene oxide solid electrolyte and its preparation method and application, the solid electrolyte includes polyethylene oxide (PEO) polymer matrix, lithium salt and polydopamine (PDA), by PDA blend modification, surface coating modification or mixed modification three ways, utilize the strong adhesion of PDA to improve electrolyte and electrode interface peeling strength, with the aid of PDA oxidation resistance improves electrolyte oxidation stability.PEO molecular weight is 100000-5000000 g / mol in the application, EO:Li⁺=10:1-20:1, PDA blend addition amount is 0.1-10 wt%, coating thickness is 50-500 nm.Preparation method includes solution blending casting, surface in-situ polymerization, etc., simple process, low cost.The electrolyte can make the peeling strength up to 1.40 N / cm, the oxidative decomposition voltage is up to 5.2 V, the initial interface impedance is as low as 150 Ωcm², suitable for lithium metal negative electrode and high voltage positive electrode of all-solid-state lithium ion battery, significantly improve the energy density and safety of battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a polydopamine-modified polyethylene oxide solid electrolyte, its preparation method, and its application. Background Technology

[0002] Current mainstream lithium battery systems are primarily based on traditional liquid lithium-ion batteries. However, their energy density is approaching its theoretical limit, and organic electrolytes suffer from flammability and low thermal stability, posing serious safety hazards and failing to meet the dual requirements of high energy density and high safety for power batteries. Solid-state electrolytes, with their excellent thermal stability and mechanical strength, have become a key solution to these problems and represent the core direction for the future development of power batteries.

[0003] Among numerous solid-state electrolyte materials, polymer-based solid-state electrolyte polyethylene oxide (PEO) has become an important research object in the field of solid-state electrolytes due to its excellent flexibility, good electrode wettability, low interfacial contact resistance, and ease of continuous film formation. It has shown broad application prospects in the development of high-energy-density composite solid-state batteries. However, PEO-based solid-state electrolytes still face two major challenges: First, there is a problem of poor solid-solid interface contact between the solid electrolyte (SE) and the electrode (especially the lithium metal anode), resulting in high interfacial resistance and easy growth of lithium dendrites, which in turn leads to poor battery cycle stability. Insufficient interfacial peel strength (i.e., interfacial adhesion) is the core reason for interfacial failure (such as delamination). Second, traditional PEO-based solid-state electrolytes are prone to oxidative decomposition at higher voltages (>3.9V vs. Li⁺ / Li), which limits their compatibility with high-voltage cathodes (such as NCM, NCA, LCO) and seriously affects the energy density and cycle life of the battery.

[0004] To improve the performance of PEO-based solid electrolytes, existing technologies have proposed various methods such as blending, crosslinking, adding inorganic fillers, copolymerization, adding plasticizers, and introducing antioxidants. However, all of these methods have significant limitations: surface coatings and adhesives used to improve interfacial adhesion can easily introduce additional impedance or increase process complexity, and their effect on improving peel strength is not targeted enough; adding high-voltage stable lithium salts and antioxidants to improve oxidation resistance may sacrifice the electrolyte's ionic conductivity or cause compatibility problems, with limited effectiveness and poor stability; adding inorganic fillers can easily lead to agglomeration, increasing interfacial impedance and reducing electrolyte flexibility; and using plasticizers can cause a decrease in the electrolyte's mechanical strength and thermal stability.

[0005] Polydopamine (PDA), a common biomimetic adhesive material for mussels, possesses unique molecular structure and performance advantages. The catechol / quinone groups in the PDA molecule can be linked by covalent bonds and coordination bonds (such as with Co...). 3+ / Ni 2 + Through bonding, hydrogen bonding, and π-π stacking interactions, PDA achieves universal and ultra-strong adhesion, with a peel strength of 50-100 N / m, far exceeding the 10-20 N / m of PEO. This makes it particularly suitable for bonding highly active electrode surfaces such as silicon anodes and lithium metal. Furthermore, the quinone / hydroquinone structure of PDA exhibits redox reversibility, enabling dynamic repair of interfacial microcracks caused by volume changes during battery charging and discharging. The nitrogen-containing groups (-NH-) in its molecule can promote Li... + Uniform diffusion at the interface reduces ion transport impedance. Simultaneously, PDA, rich in reducing groups such as phenolic hydroxyl and amino groups, effectively scavenges free radicals in the electrolyte system, enhancing the electrolyte's chemical stability and antioxidant capacity. In terms of processing, PDA can be formed in situ using room-temperature aqueous solutions, offering extremely low cost and simple processing, and enabling three-dimensional permeation and coating of materials with pore sizes >50 nm. PDA, as a single-component material, achieves a three-in-one function of "bonding-conduction-protection," providing an ideal solution to the interface problems of high-energy-density solid-state batteries. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a polydopamine-modified polyethylene oxide solid electrolyte, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a polydopamine PDA-modified polyethylene oxide (PEO)-based solid electrolyte, wherein the solid electrolyte comprises a polyethylene oxide (PEO) polymer matrix, a lithium salt, and polydopamine PDA as a functional additive; the polydopamine PDA is used to simultaneously improve the peel strength between the solid electrolyte and the electrode, as well as the oxidative stability of the solid electrolyte.

[0008] Preferably, the molecular weight of the polyethylene oxide (PEO) is 100,000 - 5,000,000 g / mol; the lithium salt is selected from at least one of LiTFSI, LiFSI, or LiClO4, and the EO unit in the PEO is related to the Li... + The molar ratio is 10:1-20:1.

[0009] Preferably, the polydopamine PDA is uniformly dispersed in the form of nanoparticles in the polyethylene oxide (PEO) polymer matrix, and the amount of polydopamine PDA added is 0.1wt%-10wt% of the weight of the polyethylene oxide (PEO), preferably 0.5wt%-5wt%.

[0010] A method for preparing a polydopamine (PDA) modified polyethylene oxide (PEO) based solid electrolyte membrane includes the following steps: S1: Polyethylene oxide (PEO) is dissolved in an anhydrous volatile solvent to form a polyethylene oxide (PEO) solution; the anhydrous volatile solvent is selected from acetonitrile or tetrahydrofuran; S2: Add lithium salt to the polyethylene oxide (PEO) solution and stir until completely dissolved to obtain a mixed solution of polyethylene oxide (PEO) and lithium salt. S3: Add the pre-prepared polydopamine PDA nanoparticle dispersion to the polyoxyethylene PEO / lithium salt mixed solution, or add dopamine hydrochloride and Tris-HCl buffer solution, pH=8.5 and stir to allow dopamine to polymerize in situ to generate polydopamine PDA, and obtain the polyoxyethylene PEO / lithium salt / polydopamine PDA mixed solution. S4: The polyethylene oxide (PEO) / lithium salt / polydopamine (PDA) mixed solution is cast onto a flat plate carrier; the flat plate carrier is selected from polytetrafluoroethylene plate or glass plate; S5: The cast plate is placed in a vacuum environment to dry and remove the solvent, thus obtaining the solid electrolyte membrane.

[0011] Application of polydopamine-modified polyethylene oxide solid electrolyte in all-solid-state lithium-ion batteries, wherein the all-solid-state lithium-ion battery comprises a lithium metal anode and, or a cathode with an operating voltage ≥ 4.0V; the cathode is selected from NCM cathode, NCA cathode or LCO cathode.

[0012] Preferably, the polydopamine-modified polyoxyethylene solid electrolyte in an all-solid-state lithium-ion battery has a peel strength to the electrode ≥0.45 N / cm, an oxidation decomposition voltage ≥4.6 V, and an initial interface impedance ≤600 Ωcm².

[0013] Furthermore, in addition to the above-mentioned polydopamine PDA blending modification method, the present invention can also prepare polydopamine PDA modified polyethylene oxide (PEO) based solid electrolyte membranes by polydopamine PDA surface coating modification and combination modification.

[0014] The preferred method for preparing polydopamine PDA-modified polyethylene oxide (PEO)-based solid electrolyte membranes by surface coating modification of polydopamine PDA is as follows: T1: Prepare a polyoxyethylene PEO / lithium salt solid electrolyte base film according to the S1-S2 and S4-S5 methods in the polydopamine PDA blending modification. T2: Immerse the polyoxyethylene PEO / lithium salt base film in a Tris-HCl buffer solution (pH=8.5) containing dopamine monomer for 6-24 h to allow dopamine to oxidize and polymerize on the base film surface to form a polydopamine PDA coating. T3: Remove the base membrane, wash it with deionized water and then vacuum dry it to obtain a solid electrolyte membrane with a polydopamine (PDA) coating on its surface.

[0015] The preferred method for preparing polydopamine PDA-modified polyethylene oxide (PEO)-based solid electrolyte membranes is as follows: U1: A polyoxyethylene PEO / lithium salt composite electrolyte membrane containing polydopamine PDA nanoparticles was prepared by following the method of polydopamine PDA blending modification. U2: Following the methods in T2-T3 of polydopamine PDA surface coating modification, a polydopamine PDA coating was applied to the surface of the polyethylene oxide (PEO) / lithium salt composite electrolyte membrane to obtain a hybrid modified solid electrolyte membrane.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention significantly improves the peel strength between the polyoxyethylene PEO-based solid electrolyte and the electrode by utilizing the strong adhesion properties of polydopamine PDA, improves interface compatibility, effectively suppresses interface delamination, and at the same time reduces interface impedance and improves battery ion transport efficiency.

[0017] Secondly, the reducing groups such as phenolic hydroxyl and amino groups in polydopamine PDA can effectively remove free radicals and improve the oxidative stability of the electrolyte, making it well matched with high-voltage positive electrodes (such as NCM, NCA, LCO) with working voltage ≥4.0V. At the same time, it can stabilize the lithium metal negative electrode, promote uniform Li⁺ deposition, inhibit lithium dendrite growth, and significantly improve battery cycle performance and safety.

[0018] Furthermore, polydopamine (PDA) can be prepared by in-situ polymerization in aqueous solution at room temperature. The modification process (blending, coating) does not require complex equipment, is easy to operate, and can achieve three-dimensional permeation and coating of electrolyte pores, making it easy to carry out large-scale industrial production and reduce production costs.

[0019] Finally, this invention achieves the integration of "bonding-conduction-protection" functions through a single polydopamine PDA component, avoiding compatibility issues that may be caused by adding multiple components. It also achieves synergistic optimization of electrolyte interface performance, chemical stability, and ion transport performance, providing key technical support for the development of high-energy-density, high-safety all-solid-state lithium-ion batteries. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the polymerization process of dopamine on the surface of an electrolyte membrane. Figure 2 TEM image of PDA particles; Figure 3 The curves show the changes in PDA deposition amount at different times. Detailed Implementation

[0021] To provide a further understanding of the purpose, structure, features, and functions of the present invention, detailed descriptions are provided below with reference to specific embodiments.

[0022] Please refer to the reference. Figure 1 Figure 2 as well as Figure 3 This invention provides a polydopamine-modified polyethylene oxide solid electrolyte, its preparation method, and its applications. (See figure.) Figure 1 The core process of surface coating modification of polydopamine (PDA) was demonstrated, including immersing a polyethylene oxide (PEO) base film in a Tris buffer solution at pH 8.5, where PDA undergoes an oxidative polymerization reaction on the film surface to ultimately form a PDA@PEO modified film. The key steps and reaction environment of surface coating modification were clearly presented.

[0023] Figure 2 The image shows a transmission electron microscope (TEM) image of polydopamine PDA particles obtained by the method of this invention, with the scale bar marked at 1 μm. The image reveals that the polydopamine PDA particles exhibit nanoscale morphology, good dispersibility, and no obvious agglomeration, verifying the quality of the prepared polydopamine PDA particles and providing microstructural support for their uniform dispersion and functional performance in the polyethylene oxide (PEO) matrix.

[0024] Figure 3 The curves show the deposition amount of polydopamine PDA on the surface of polyethylene oxide (PEO) based film as a function of immersion time (6 h, 12 h, 18 h, 24 h). The vertical axis represents the deposition amount (unit: mg), and the horizontal axis represents the immersion time (unit: h).

[0025] The curves show that as the soaking time increases, the amount of polydopamine (PDA) deposited gradually increases. After 12-18 hours, the growth of the deposit tends to level off. This provides experimental basis for determining the optimal soaking time (such as 12 hours in the implementation case), and can avoid the problem of insufficient soaking time leading to an excessively thin coating or excessive soaking time leading to resource waste.

[0026] Example 1: Preparation of blended modified PEO / PDA / Li salt electrolyte membrane.

[0027] Preparation of PDA nanoparticles: Dopamine hydrochloride was dissolved in Tris-HCl buffer (pH=8.5) (concentration 2 mg / ml), oxidized and self-polymerized at room temperature for 12 h, and the solvent was dried to obtain PDA nanoparticles.

[0028] Preparation of mixed solution: PDA nanoparticles were used as a functional additive (5 wt% of PEO weight) and uniformly mixed with PEO (molecular weight 3,000,000 g / mol), lithium salt (LiFSI) and solvent (acetonitrile). The molar ratio of EO units to Li⁺ was controlled at 15:1 and the solution concentration was 10 wt% to form a PEO / LiFSI / PDA mixed solution.

[0029] Film formation and drying: The mixed solution was uniformly cast onto a polytetrafluoroethylene plate and dried in a vacuum environment at 40-60℃ for 12 h to remove the solvent, resulting in a blended modified PEO / PDA / Li salt solid electrolyte membrane with a thickness of 25 μm.

[0030] Example 2: Preparation of Coated Modified PEO / Li Salt Electrolyte Membrane Preparation of PEO / LiFSI based film: PEO and LiFSI were dissolved in acetonitrile (EO:Li⁺=15:1) according to conventional solution casting method, and then vacuum dried after casting to obtain PEO / LiFSI based film.

[0031] Surface PDA coating preparation: The PEO / LiFSI base film was immersed in a dopamine Tris buffer solution at pH=8.5 for 12 h to allow dopamine to polymerize on the base film surface to form a PDA coating with a thickness of 100 nm.

[0032] Cleaning and drying: Remove the base film, clean the surface of unreacted monomers and loose PDA with deionized water, and then vacuum dry to obtain a coating-modified PEO / Li salt solid electrolyte membrane with a thickness of 25 μm.

[0033] Example 3: Preparation of a hybrid modified PEO / PDA / Li salt electrolyte membrane First, prepare a PEO / LiFSI composite electrolyte membrane containing 5 wt% PDA particles according to the method in Implementation Case 1.

[0034] Following the method in Implementation Case 2, the above-mentioned composite electrolyte membrane was immersed in a dopamine Tris buffer solution for 12 hours to form a 100 nm thick surface PDA coating.

[0035] After cleaning and vacuum drying, a mixed modified PEO / PDA / Li salt solid electrolyte membrane with a thickness of 25 μm was obtained.

[0036] In summary, the modified electrolyte membranes prepared in the above three implementation cases, as well as the unmodified PEO / LiFSI electrolyte membrane, were tested for electrochemical stability (LSV), peel strength (180° peel test), and initial interfacial impedance. The test methods are as follows: Electrochemical stability (LSV): The electrolyte membrane was assembled with lithium wafers and steel sheets into a coin cell, and the oxidation decomposition voltage of the electrolyte was tested using linear sweep voltammetry.

[0037] Peel strength: A 90° peel test (electrolyte membrane vs. positive electrode) was performed using a universal testing machine at a peel rate of 10 mm / min, and the peel strength (unit: N / cm) was recorded.

[0038] Initial interfacial impedance (EIS): The initial interfacial impedance (unit: Ωcm²) is measured by electrochemical impedance spectroscopy after assembling two lithium wafers with an electrolyte membrane into a coin cell.

[0039] The test results show that the present invention significantly improves the electrochemical stability (oxidative decomposition voltage increased to a maximum of 5.2 V) and interfacial peel strength (up to a maximum of 1.40 N / cm) of PEO-based solid electrolytes through PDA modification, and greatly reduces the initial interfacial impedance (down to a minimum of 150 Ωcm²). The mixed modification method has the best effect, which fully verifies the effectiveness of the technical solution of the present invention.

[0040] The present invention has been described in the above-described embodiments; however, these embodiments are merely examples for implementing the present invention. It must be noted that the disclosed embodiments do not limit the scope of the present invention. Conversely, any modifications and refinements made without departing from the spirit and scope of the present invention are within the scope of patent protection of the present invention.

Claims

1. A polydopamine PDA-modified polyethylene oxide (PEO)-based solid electrolyte, characterized in that: The solid electrolyte comprises a polyethylene oxide (PEO) polymer matrix, a lithium salt, and polydopamine (PDA) as a functional additive; the PDA is used to simultaneously improve the peel strength between the solid electrolyte and the electrode, as well as the oxidative stability of the solid electrolyte.

2. The polydopamine PDA-modified polyoxyethylene PEO-based solid electrolyte as described in claim 1, characterized in that: The molecular weight of the polyethylene oxide (PEO) is 100,000 - 5,000,000 g / mol; the lithium salt is selected from at least one of LiTFSI, LiFSI, or LiClO4, and the EO unit in the PEO is related to the Li... + The molar ratio is 10:1-20:

1.

3. The polydopamine PDA-modified polyoxyethylene PEO-based solid electrolyte as described in claim 1, characterized in that: The polydopamine (PDA) is uniformly dispersed in the form of nanoparticles in the polyethylene oxide (PEO) polymer matrix, and the amount of PDA added is 0.1wt%-10wt% of the weight of the PEO, preferably 0.5wt%-5wt%.

4. A method for preparing the polydopamine PDA-modified polyethylene oxide (PEO)-based solid electrolyte membrane as described in claim 3, characterized in that: Includes the following steps: S1: Polyethylene oxide (PEO) is dissolved in an anhydrous volatile solvent to form a polyethylene oxide (PEO) solution; the anhydrous volatile solvent is selected from acetonitrile or tetrahydrofuran; S2: Add lithium salt to the polyethylene oxide (PEO) solution and stir until completely dissolved to obtain a mixed solution of polyethylene oxide (PEO) and lithium salt. S3: Add the pre-prepared polydopamine PDA nanoparticle dispersion to the polyoxyethylene PEO / lithium salt mixed solution, or add dopamine hydrochloride and Tris-HCl buffer solution, pH=8.5 and stir to allow dopamine to polymerize in situ to generate polydopamine PDA, and obtain the polyoxyethylene PEO / lithium salt / polydopamine PDA mixed solution. S4: The polyethylene oxide (PEO) / lithium salt / polydopamine (PDA) mixed solution is cast onto a flat plate carrier; the flat plate carrier is selected from polytetrafluoroethylene plate or glass plate; S5: The cast plate is placed in a vacuum environment to dry and remove the solvent, thus obtaining the solid electrolyte membrane.

5. The application of the polydopamine-modified polyoxyethylene solid electrolyte according to any one of claims 1-3 in an all-solid-state lithium-ion battery, characterized in that: The all-solid-state lithium-ion battery includes a lithium metal negative electrode and, or a positive electrode with an operating voltage ≥ 4.0V; the positive electrode is selected from NMC positive electrode, NCA positive electrode or LCO positive electrode.

6. The application according to claim 5, characterized in that: The polydopamine-modified polyoxyethylene solid electrolyte exhibits a peel strength to the electrode ≥0.45 N / cm, an oxidation decomposition voltage ≥4.6 V, and an initial interface impedance ≤600 Ωcm² in all-solid-state lithium-ion batteries.

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