High-ionic-conductivity polymer electrolyte with high sodium metal compatibility and preparation method of high-ionic-conductivity polymer electrolyte

Abstract

The invention discloses a high-ionic-conductivity polymer electrolyte with strong sodium metal compatibility and a preparation method thereof, and the high-ionic-conductivity polymer electrolyte comprises a three-dimensional cross-linked polymer network formed by free radical polymerization cross-linking of an ether oxygen-containing cross-linking agent or an ether oxygen-containing polymerizable monomer; and, a deep eutectic solvent dispersed in the polymer network; wherein the deep eutectic solvent is formed by at least one sodium salt and at least one hydrogen bond donor and / or hydrogen bond acceptor according to a predetermined molar ratio, and the mass fraction of the deep eutectic solvent in the electrolyte is 50-80 wt%. And high room-temperature sodium ion conductivity is realized while the solid-state / quasi-solid-state safety is maintained. Compared with the traditional PEO-based solid sodium electrolyte, the total ionic conductivity greater than or equal to 2 mS / cm can be realized at room temperature, and is obviously superior to the typical 10 <-5 >-10 <-4 > S.cm <-1 > level; meanwhile, the mechanical strength and the shape retention which are obviously higher than those of a pure gel system are still kept, so that the conductivity and the safety are both considered.

Description

Technical Field

[0001] This invention belongs to the field of solid-state sodium battery technology, specifically relating to a high-ionic-conductivity polymer electrolyte with strong sodium metal compatibility and its preparation method. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, the requirements for energy density, safety, and cycle life of power batteries are constantly increasing. Traditional liquid organic electrolyte systems generally use a combination of carbonate solvents and lithium (sodium) salts, which suffer from high volatility, flammability, significant leakage risk, and the tendency to induce dendrite growth on the lithium / sodium anode, making them insufficient to meet the development demands for high-safety, high-energy-density batteries. Therefore, replacing liquid electrolytes with solid or quasi-solid polymer electrolytes has become a current research hotspot. Sodium-ion batteries, due to their similar electrochemical characteristics to lithium-ion batteries, are one of the most promising alternatives, and sodium resources are abundant and widely distributed, making them more suitable for large-scale energy storage. Therefore, using solid electrolytes to replace liquid electrolytes to improve battery safety performance and developing all-solid-state sodium-ion batteries is of great significance.

[0003] Deep eutectic solvents (DES) have been introduced into polymer electrolyte systems due to their advantages such as low volatility, non-flammability, and wide electrochemical window, balancing safety and ionic conductivity. Patent CN114006030B discloses a "deep eutectic solvent + siloxane polymer" electrolyte, where the deep eutectic solvent is composed of lithium salt and hydrogen bond donors such as succinic acid, N-methylacetamide, or urea. By introducing a siloxane crosslinking agent grafted with poly(ethylene glycol) monomethyl ether, the electrolyte exhibits good rate performance and cycle performance at both room and low temperatures, and is non-flammable. However, this electrolyte is also primarily targeted at lithium-ion batteries; the polymer backbone is based on siloxane, with limited ether oxygen content, resulting in insufficient ability to control the dissolution and coordination environment of lithium / sodium salts; simultaneously, it requires 70-95 wt% DES, resulting in relatively low solid content and low mechanical modulus, which is detrimental to suppressing interfacial deformation and dendrite growth in high-voltage cathode / sodium metal anode systems.

[0004] Taking advantage of the high room-temperature ionic conductivity and wide electrochemical window of succinonitrile (SN) plastic crystals, existing technologies combine them with polymer networks to construct solid-state electrolytes. Patent CN117457995A uses an organically coated LATP / PAN composite spun membrane as a framework, and then thermally polymerizes a precursor composed of PEGDA, SN, lithium salt, and an initiator in situ within the fiber membrane to obtain a composite solid-state lithium electrolyte that exhibits both high room-temperature conductivity and certain mechanical strength. Patent TW202320378A prepares an all-solid-state composite polymer electrolyte membrane by mixing PEGDMA or PEGDA, LiTFSI, and SN, coating and curing it on a substrate, and applying it to all-solid-state lithium batteries. Patent CN116315072A discloses a polymer solid-state electrolyte with a multilayer structure, where the first layer contains an aliphatic dinitrile compound (including succinonitrile), lithium salt, and a lithium-ion conducting polymer, and the second layer contains an ionic liquid, lithium salt, and polymer to broaden the electrochemical stability window. While the aforementioned technologies have demonstrated the feasibility of combining SN with polymers / lithium salts, most of them are based on lithium systems and focus on improving mechanical strength and high-pressure stability through multilayer structures or inorganic fillers. They do not systematically design the coupling relationship between the ether-oxygen / Na⁺ coordination ratio, deep eutectic content, and interface stability in sodium systems. At the same time, multilayer structures or multi-step electrospinning / impregnation processes are still quite complex in terms of large-scale manufacturing and cell integration.

[0005] In recent years, polymerizable deep eutectic solvents have been used to construct quasi-solid-state Na / Li gel electrolytes. Patent CN119361815A discloses a deep eutectic gel electrolyte consisting of a polymerizable monomeric deep eutectic solvent and an initiator. The deep eutectic solvent is prepared by heating and mixing metal salts (including various Na / Li salts) as hydrogen bond acceptors, succinate, and amide monomers containing unsaturated double bonds as hydrogen bond donors. Polymerization is then initiated under light irradiation to obtain the deep eutectic gel electrolyte, suitable for quasi-solid-state sodium / lithium-ion batteries, with a conductivity exceeding 1 mS·cm at 25°C. -1 Furthermore, this system exhibits a wide electrochemical window. Its key characteristic lies in incorporating the polymerizable amide monomer itself as part of the deep eutectic component, resulting in a gel network dominated by the amide backbone through polymerization, thus maintaining the overall electrolyte as a continuous deep eutectic phase. However, in this approach, the polymer network is primarily composed of amide structures with fewer ether oxygen sites, which may negatively impact Na+. + The chelating effect is limited; at the same time, it has not been systematically optimized from the perspective of "polymer network ether oxygen / metal ion coordination ratio" and "polymer crosslinking density and deep eutectic phase content matching", making it difficult to obtain comprehensive performance with high mechanical modulus, high sodium ion transference number and long-term stability of sodium metal interface while maintaining high room temperature conductivity.

[0006] Based on the above existing technologies, significant progress has been made in the research of solid or quasi-solid electrolytes with deep eutectic and polymer components: on the one hand, increasing the content of deep eutectic solvent can significantly improve room temperature conductivity; on the other hand, introducing polymer networks such as siloxanes, PAN, and PEGDA can improve mechanical properties and interfacial contact to a certain extent. However, existing solutions still mainly focus on lithium systems. For sodium-ion batteries and even sodium metal batteries, there are still the following shortcomings: (1) There are insufficient ether oxygen sites in the polymer skeleton or the O / Na coordination ratio is not quantitatively controlled, making it difficult to suppress excessive solvation and interfacial side reactions while ensuring high salt solubility / high conductivity; (2) The mass fraction of deep eutectic solvent is generally high (e.g., 70-95 wt%), resulting in a low overall modulus of the electrolyte and limited mechanical suppression of sodium dendrites; (3) Most technologies use pre-made films or multilayer structures, making it difficult to fully wet the electrode channels and form an integrated structure with low interfacial impedance during actual battery assembly; (4) Research on the chemical stability of the interface between sodium systems, especially SN / nitrile deep eutectic and sodium metal, and the synergistic regulation of interface stability and cycle life by crosslinking agent molecular weight and deep eutectic content is still relatively lacking.

[0007] Therefore, it is still necessary to develop a solid-state or quasi-solid-state polymer electrolyte system for sodium-ion / sodium metal batteries. While maintaining the high ionic conductivity advantage of deep eutectic solvents, an ether-oxygen-rich three-dimensional cross-linked polymer network should be introduced. The molar ratio of ether oxygen to sodium ions (O / Na) in the polymer network, as well as the molecular weight of the cross-linking agent and the mixed cross-linking strategy, should be finely controlled within a wide range of deep eutectic content (e.g., 40-80 wt%). This will enable the achievement of high sodium-ion conductivity and migration number at room temperature, while significantly improving mechanical strength and interfacial stability, thus meeting the application requirements of high-safety and long-life sodium-ion batteries. Summary of the Invention

[0008] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments.

[0009] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0010] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a polymer electrolyte with high ionic conductivity and strong sodium metal compatibility.

[0011] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a polymer electrolyte with high ionic conductivity and strong sodium metal compatibility, comprising, A three-dimensional crosslinked polymer network formed by free radical polymerization of a crosslinking agent containing ether oxygen or a polymerizable monomer containing ether oxygen; and, Deep eutectic solvent dispersed in a polymer network; The deep eutectic solvent is formed by at least one sodium salt and at least one hydrogen bond donor and / or hydrogen bond acceptor in a predetermined molar ratio, and the mass fraction of the deep eutectic solvent in the electrolyte is 50-80 wt%. In the polymer network, the molar ratio of etheroxy groups to sodium ions is 6~20:1.

[0012] As a preferred embodiment of the high ionic conductivity polymer electrolyte of the present invention, wherein the total ionic conductivity of the electrolyte at 30°C is ≥2 mS·cm -1 Furthermore, the sodium ion transference number is ≥0.5; at 30°C, its anodic stability window for a metallic sodium / sodium ion electrode is ≥4.0 V.

[0013] As a preferred embodiment of the high ionic conductivity polymer electrolyte of the present invention, the sodium salt is one or more of sodium perchlorate, sodium di(fluorosulfonyl)imide (NaFSI), sodium di(trifluoromethanesulfonyl)imide (NaTFSI), sodium hexafluorophosphate (NaPF6), or sodium bis(oxaloyl)borate (NaBOB).

[0014] As a preferred embodiment of the high ionic conductivity polymer electrolyte of the present invention, wherein the ether-oxygen-containing crosslinking agent is selected from polyethylene glycol di(meth)acrylate or glycidyl ether. Wherein, the polyethylene glycol di(meth)acrylate is selected from at least one of polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), diethylene glycol diacrylate (DEGDA), and triethylene glycol dimethacrylate (TEGDMA); The glycidyl ether is selected from at least one of ethylene glycol diglycidyl ether (EGDGE), 1,4-butanediol diglycidyl ether (BDGE), ethylene glycol divinyl ether (EGDVE), and diethylene glycol divinyl ether (DEGDVE).

[0015] As a preferred embodiment of the high ionic conductivity polymer electrolyte of the present invention, wherein the ether-oxygen-containing polymerizable monomer is selected from side-chain oligoethylene glycol (meth)acrylates, including methyl polyethylene glycol methacrylate (OEGMA) and polyethylene glycol methyl ether methacrylate (PEGMA).

[0016] In a preferred embodiment of the high ionic conductivity polymer electrolyte of the present invention, the number-average molecular weight Mn of the multifunctional crosslinking agent is 600~1200 g·mol⁻¹. -1 .

[0017] As a preferred embodiment of the high ionic conductivity polymer electrolyte of the present invention, the molar ratio of the sodium salt to the hydrogen bond donor is 1:(7~9), and the hydrogen bond donor includes 1,2-dimethylimidazolium, butyrolactam, N-methylacetamide, 2,2'-dithiopyridine, and succinate.

[0018] Another object of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a polymer electrolyte with high ionic conductivity, comprising, A deep eutectic solvent was prepared by mixing sodium salt and hydrogen bond donor at a salt:donor molar ratio of 1:(7–9). A deep eutectic solvent is mixed with a polymerizable monomer containing ether oxygen, a multifunctional crosslinking agent and a free radical initiator to obtain an electrolyte precursor liquid. The precursor liquid is subjected to free radical polymerization and crosslinking by ultraviolet light irradiation and / or thermal curing to form an electrolyte structure; The free radical initiator is selected from bis(2,4,6-trimethylbenzoyl)phosphonates (TPO) or azobisisobutyronitrile (AIBN), and its mass fraction in the precursor is 0.2~1 wt%.

[0019] Another object of the present invention is to overcome the shortcomings of the prior art and provide a sodium-ion battery, comprising a positive electrode, a negative electrode, and a polymer electrolyte as described in any one of claims 1 to 7 disposed therebetween; wherein, The negative electrode is hard carbon or metallic sodium; The positive electrode is selected from Prussian blue compounds, Na3V2(PO4)3, or layered transition metal oxides.

[0020] As a preferred embodiment of the battery described in this invention, the capacity retention rate is ≥80% after ≥1000 cycles at 30°C and 1C rate, and the capacity retention rate is ≥0.5 mA·cm⁻¹. -2 Current density, 0.5 mAh·cm -2 Sodium stripping stabilization time in Na‖Na symmetric cells under area capacity conditions is ≥1000 h.

[0021] Beneficial effects of this invention: (1) Achieving high room-temperature sodium ion conductivity while maintaining solid / quasi-solid-state safety. This invention introduces 20-80 wt% of a deep eutectic phase into the electrolyte by combining an ether-oxygen-rich three-dimensional cross-linked polymer network with a deep eutectic solvent composed of sodium salts and hydrogen bond donors / acceptors, and controls the molar ratio of ether-oxygen groups to sodium ions in the polymer network within the range of 6-20. Compared with traditional PEO-based solid sodium electrolytes, this invention achieves a total ion conductivity of ≥2 mS / cm at room temperature, significantly superior to typical 10 mS / cm electrolytes. -5 -10-4 S·cm -1 It achieves a high level of performance while maintaining significantly higher mechanical strength and shape retention than pure gel systems, thus balancing conductivity and safety.

[0022] (2) Achieving synergy between high migration number and interfacial stability through the O / Na design window. This invention, for the first time, uses the molar ratio of ether oxygen groups to sodium ions (O / Na) in the polymer network as a key design parameter, limiting it to a window of approximately 6-20. The inventors found that when O / Na is too low, excessively high salt concentration leads to local overcoordination, increased glass transition, and intensified interfacial side reactions; when O / Na is too high, insufficient current carriers significantly reduce conductivity. By optimizing O / Na within the above window, this invention achieves synergy between high salt solubility and high sodium ion migration number (tNa). + Achieving a balance between ≥0.5 and lower interfacial polarization is beneficial for reducing concentration polarization and suppressing dendrite formation at the sodium metal interface.

[0023] (3) The three-dimensional network constructed by multi-molecular-weight and multi-type ether-oxygen-rich crosslinking agents takes into account both conductive channels and mechanical support. In this invention, multifunctional monomers containing polyethylene glycol segments such as PEGDA, PEGDMA, DEGDA, TEGDMA, EGDGE, BDGE, EGDVE, and DEGDVE are selected as crosslinking agents. If necessary, ether-oxygen-rich copolymer monomers such as OEGMA and PEGMA are introduced to construct a three-dimensional crosslinking network. By controlling the molecular weight Mn of the crosslinking agent to 600-1200 g / mol, preferably 600-900 g / mol, and using at least two crosslinking agents with different Mn values ​​in combination, the resulting polymer network provides continuous and flexible ether-oxygen coordination sites, which facilitates sodium ion migration, and also has sufficient crosslinking density and modulus to resist electrode volume changes and local stress concentration at dendrite tips. This is significantly better than systems that use only a single molecular weight crosslinking agent or a polymer with low ether-oxygen density.

[0024] (4) Optimized deep eutectic solvent combination and content for sodium system to achieve a balance between wide electrochemical window and high modulus. This invention selects sodium salts such as NaClO4, NaFSI, NaTFSI, or NaBOB, and forms deep eutectic solvents with hydrogen bond donors such as 1,2-dimethylimidazole, butyrolactam, N-methylacetamide, 2,2'-dithiopyridine, and succinate at a molar ratio of 1:(2-6), and controls its mass fraction at 20-80 wt%. Compared with existing systems that require 55-95 wt% DES, this invention significantly increases polymer content and overall mechanical modulus while maintaining high ionic conductivity, which is beneficial for suppressing electrolyte flow and deformation; in addition, the synergistic effect of imidazole, amide, dithiopyridine, and nitrile components with sodium salt can form a stable interfacial film on the surface of metallic sodium and the cathode, making the electrolyte more responsive to Na / Na + Its anode stable potential reaches or exceeds 4.0 V, making it more suitable for matching with Prussian blue, Na3V2(PO4)3 and layered high-voltage cathode materials.

[0025] (5) In-situ curing process constructs an integrated electrode-electrolyte structure with low interfacial impedance and long-term stability. This invention employs a "low-viscosity precursor injection – in-situ photo / thermal curing" process, directly injecting a precursor containing DES, crosslinking agent, polymer monomer, and initiator into the assembled positive / negative electrode and membrane channels, and then performing in-situ crosslinking at 60–90℃ or under ultraviolet light to form an integrated structure that is highly compatible with the electrode. Compared with traditional external film lamination or multilayer composite structures, this invention significantly reduces the initial interfacial impedance and exhibits slower interfacial impedance growth during long-term cycling, making it suitable for high-load positive electrodes and metallic sodium negative electrodes.

[0026] (6) The full cell exhibits excellent long cycle life and symmetrical cell peeling stability. Thanks to the above structural and formulation design, the electrolyte of this invention, when applied to sodium-ion batteries with hard carbon or metallic sodium as the negative electrode and Prussian blue, Na3V2(PO4)3, or layered oxides as the positive electrode, can achieve a capacity retention of ≥80% after ≥1000 cycles at 30℃ and 1C rate; at 0.5 mA / cm²... 2 Current density, 0.5 mAh / cm 2 In the Na‖Na symmetric cell under the areal capacity condition, the sodium ion stripping stability time can reach ≥1000 h, which is significantly better than the existing deep eutectic gel or polymer electrolyte system without O / Na optimization and high ether oxygen crosslinking network, demonstrating excellent comprehensive electrochemical performance and safety. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a comparison chart of room temperature conductivity data of Examples 1 and 2 and Comparative Examples A and C under different DES mass ratios.

[0028] Figure 2 This is a comparison chart of the conductivity at 30°C of Examples 1 and 2 and Comparative Example A.

[0029] Figure 3 This is a comparison chart of migration numbers at 30°C between Examples 1 and 2 and Comparative Example A.

[0030] Figure 4 This is a comparison diagram of the electrochemical windows of Examples 1 and 2 and Comparative Example A.

[0031] Figure 5 This is a comparison diagram of Na‖Na symmetric cells in Examples 1 and 2 and Comparative Example A.

[0032] Figure 6 This is a comparison chart of the full-cell cycle capacity retention rates of Examples 1 and 2 and Comparative Example A.

[0033] Figure 7 The images show a comparison of physical photos and SEM images of sodium metal after cycling in Examples 1 and 2 and Comparative Example A using Na‖Na symmetric cells.

[0034] Figure 8 This is a comparison diagram of Na‖Cu half-cells in Examples 1 and 2 and Comparative Example A.

[0035] Figure 9 This is the ion transport number diagram of Example 3.

[0036] Figure 10 This is a graph showing the long-cycle performance of the full battery in Example 3.

[0037] Figure 11 This is a cycling diagram of Na||Na symmetric cells in both cross-linked and non-cross-linked conditions for Example 4 and Comparative Example B.

[0038] Figure 12 This is a comparison chart of Comparative Example C before and after curing, where a is before curing and b is after curing. Detailed Implementation

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0040] Unless otherwise specified, the following general preparation and testing conditions were used in all the following embodiments: (A) Explanation of raw materials and terminology: PEGDA represents polyethylene glycol diacrylate; the listed Mn is the number average molecular weight.

[0041] SN represents succinonitrile, which is one of the components of the deep eutectic solvent.

[0042] NaTFSI represents sodium bis(trifluoromethanesulfonyl)imide; NaClO4 represents sodium perchlorate.

[0043] AIBN (or TPO) is used as an initiator.

[0044] (B) Formulation representation method: "DES content (wt%)" refers to the mass fraction of deep eutectic solvent (SN+ salt) relative to the total mass of the precursor.

[0045] SN: Salt is a molar ratio, expressed as SN: NaTFSI (or NaClO4).

[0046] (C) General preparation steps: In an inert atmosphere (N2) glove box, weigh PEGDA, SN and sodium salt according to the formula; add initiator AIBN or TPO to the precursor mixture (the mass fraction of initiator relative to the precursor is 0.5 wt%, which can be adjusted in the range of 0.2–1.5 wt%); stir thoroughly to make the system homogeneous and clear (if necessary, heat briefly at 50–60 ℃ until dissolved).

[0047] Inject the well-mixed precursor liquid into the prepared battery assembly (such as between electrodes / separators) or into a mold, ensuring complete saturation.

[0048] Curing and crosslinking: Thermal curing is used: the battery is heat-treated at 70 ℃ for 12 h (or thermally cured at 60-90 ℃ for 6-8 h) to complete crosslinking and promote system homogenization. After curing, it is recommended to keep the battery at 40-60 ℃ for 2 h for post-treatment; or photopolymerization can be initiated by irradiation with ultraviolet light (365 nm, 30 min, light intensity depends on the equipment).

[0049] Take out the sample and perform electrochemical characterization according to the test methods described below.

[0050] (D) Overview of Test Methods: AC impedance measurement (EIS): The measurement is performed at a certain temperature (e.g., 25 ℃) with an impedance frequency range of 1 MHz-0.1 Hz and a perturbation amplitude of 10 mV. The sample is a metal / electrolyte / metal pair or an inactive blocking electrode (e.g., stainless steel SS) fixture. The AC impedance spectrum is obtained by measuring with a conventional electrochemical workstation. The conductivity is calculated from the high-frequency cutoff resistance value (σ = L / (R·A), where L is the electrolyte thickness and A is the electrode area).

[0051] Sodium ion transport number (t) + The Bruce-Vincent DC polarization method was used for measurement. The DC polarization potential was 10 mV. The initial impedance and steady-state impedance were recorded, and t was calculated according to the Bruce-Vincent formula. + .

[0052] Na‖Na symmetric cell peeling test: Assemble a Na‖sample‖Na symmetric cell (commonly a 2032 coin cell or a custom symmetric cell fixture, electrode area 1.13 cm²) in an Ar glove box. 2 (i.e., a 12 mm diameter disc), at 30 ℃ with a current density of 0.5 mA·cm⁻¹ -2 0.5 mAh·cm³ per half cycle -2 The capacity was subjected to cyclic stripping (constant current-constant capacity cycle), and the voltage change over time was recorded to evaluate the stripping settling time.

[0053] Na‖Cu cell peeling test: Assemble a Na‖Cu symmetrical cell (commonly a 2032 coin cell or a custom symmetrical cell fixture, electrode area 1.13 cm²) in an Ar glove box. 2 (i.e., a 12 mm diameter disc), at 30 °C with a current density of 0.5 mA·cm⁻¹ -2 0.5 mAh·cm³ per half cycle -2 The capacity was subjected to cyclic stripping (constant current-constant capacity cycle), and the voltage change over time was recorded to evaluate the stripping settling time.

[0054] Linear scan voltammetry (LSV): The anodic steady potential (relative to Na / Na⁺) is determined by scanning from the open circuit potential in the positive direction at a scan rate of 1 mV·s⁻¹.

[0055] Full cell (e.g., Na / cathode) cycle test: Cycle at ≥ 1C rate at 30 °C and record capacity retention. If used to evaluate battery life, record capacity retention after ≥ 1000 cycles (if applicable).

[0056] Example 1 (Medium Mn content with O / Na ratio of 12) (1) Electrolyte composition formula (expressed as mass fraction): Deep eutectic solvent DES (SN + NaTFSI), accounting for 60~80 wt% of the total electrolyte (where the molar ratio of SN to NaTFSI is 8:1); Polymer monomers and crosslinking components (mainly PEGDA, Mn = 600) account for 20-40 wt% of the total electrolyte; thermal initiator (AIBN): 0.5 wt% (relative to the total mass of the precursor).

[0057] Taking 60 wt% DES + 40 wt% polymer monomer (PEGDA, Mn = 600) as an example, the detailed preparation method is as follows: S1: Weigh 0.31 g NaTFSI and dissolve it in 0.64 g succinate, stir at 60°C until a room-temperature stable solution is formed, and use this as the deep eutectic solvent A; S2: Then add 0.6 g of PEGDA (Mn = 600) to A, stir at room temperature for 0.5 h, and use the clear, non-layered mixture as solvent B; S3: Then add 0.008 g of thermal initiator AIBN to B, mix and stir until AIBN is completely dissolved, at which point the polymer electrolyte precursor is obtained.

[0058] (2) Preparation steps: The method described in general preparation steps (C) is used.

[0059] The prepared precursor was injected between the positive electrode / separator / negative electrode and thermosetting in situ polymerization was carried out. It was then heat-treated at 70℃ for 12 hours and finally held at 50℃ for 2 hours as a post-treatment.

[0060] (3) Test conditions: Conductivity was measured at 25 ℃ (EIS, 1 MHz–0.1 Hz, 10 mV), t⁺ (Bruce–Vincent method, DC bias 10 mV), peeling lifetime test of Na‖Na symmetric cell (0.5 mA·cm⁻², 0.5 mAh·cm⁻²), and anode stability window was measured by LSV (1 mV·s⁻¹).

[0061] (4) Results overview: The conductivity of the sample in this embodiment at 30 °C is in the range of 2–6 mS·cm⁻¹, and the Na⁺ transport number t⁺ ≈ 0.5–0.6 (which can be adjusted according to conditions).

[0062] Example 2 (High Mn vs. O / Na ratio of 20) (1) Composition formula: DES (SN + NaTFSI) 60 wt% (SN:NaTFSI molar ratio = 8:1); PEGDA (Mn = 1000) 40 wt%; AIBN: 0.5 wt%.

[0063] (2) Preparation and curing: Same as in Example 1.

[0064] (3) Test conditions: Same as in Example 1.

[0065] Objective and Explanation: This study aims to verify the effect of increasing the number-average molecular weight of the crosslinking agent (increased Mn) on the Na⁺ transport number and the stability of metallic sodium. Generally, it is observed that with increasing Mn, the t⁺ value increases (reaching a maximum of 0.67 in the example), but the conductivity may decrease slightly; the lifetime and interfacial stability of Na‖Na are further improved. The peeling stability time of the Na‖Na symmetric cell can reach approximately 1000 h (fluctuating depending on the sample and preparation precision). This embodiment, as one of the preferred embodiments of the present invention, supports the key technical features in the claims.

[0066] (2) Preparation and curing: Same as in Example 1.

[0067] (3) Test conditions: Same as in Example 1.

[0068] Objective and Explanation: This study aims to compare the effects of different sodium salts (NaTFSI and NaPF6) on conductivity, t⁺, and the stability of the sodium metal interface. Experiments show that the ionic dissociation of different salts and their interactions with SN₂ can cause differences in electrochemical performance. However, within the framework of this invention, good conductivity and a certain degree of metal compatibility can still be achieved, thus ensuring the stable operation of the full cell.

[0069] Example 3 (Salt comparison: NaClO4) (1) Composition formula: DES (SN + NaClO4) 60 wt% (SN: NaClO4 = 9:1); PEGDA Mn = 1000 accounting for 40 wt%; AIBN: 0.5 wt%. Table 1 shows the changes in the component ratios of different samples in Example 3.

[0070] (2) Preparation and curing: Same as in Example 1.

[0071] (3) Test conditions: Same as in Example 1.

[0072] Objective and Explanation: This study aims to compare the effects of different sodium salts (NaTFSI and NaClO4) on conductivity, t⁺, and the stability of the sodium metal interface. Experiments show that the ionic dissociation of different salts and their interactions with SN₂ can cause differences in electrochemical performance. However, within the framework of this invention, good conductivity and a certain degree of metal compatibility can still be obtained, thus ensuring the stable operation of the full cell.

[0073] Example 4 (medium Mn, O / Na ratio of 12, containing branched PEGDMA) (1) Composition formulation: DES (SN + NaTFSI) 80 wt% (SN:NaTFSI = 8:1); polymer monomer (PEGDA, Mn = 600) and PEGDMA each account for 10 wt% of the polymer precursor; AIBN: 0.5 wt%.

[0074] (2) Preparation and curing: Same as in Example 1.

[0075] (3) Test conditions: Same as in Example 1.

[0076] Objective and Explanation: This invention is used to verify the effect of crosslinking agent and monomer combination on the stability of metallic sodium. The lifetime and interfacial stability of Na‖Na are further improved, and the peeling stability of Na‖Na symmetric cells is enhanced. This demonstrates the reasonable scope of the claims. Different formulations within the scope of the claims can achieve beneficial effects.

[0077] Table 1 Actual Amounts of Components Used in Each Example in the Embodiments

[0078] Comparative Example A (low Mn compared to O / Na ratio of 3) (1) Composition formula: DES (SN + NaTFSI) 60 wt% (SN:NaTFSI = 8:1); PEGDA (Mn = 200) 40 wt%; AIBN: 0.5 wt%.

[0079] (2) Preparation and curing: Same as in Example 1.

[0080] (3) Test conditions: Same as in Example 1.

[0081] Objective and Explanation: To verify the impact of excessively high network flexibility due to low Mn content on sodium metal compatibility. Such samples typically exhibit high room temperature conductivity but significantly shortened Na‖Na symmetric cell peel-off lifetime, thus illustrating the necessity of PEGDA Mn in the range of 400–2000 (preferably 600–1200).

[0082] Comparative Example B (uncrosslinked network O / Na ratio of 12, but not cured) Composition and formulation: Similar to the formulation in Example 1: DES accounts for 80 wt% of the polymer precursor, and the polymer monomer (PEGDA, Mn = 600) and PEGDMA each account for 10 wt% of the polymer precursor. The formulation of DES is (SN:NaTFSI = 8:1), but without the addition of AIBN initiator.

[0083] (2) Preparation and curing: No photo / thermal curing crosslinking is performed; that is, the uncrosslinked polymer monomers are mixed evenly with DES and filled into the battery.

[0084] (3) Test conditions: Same as in Example 1.

[0085] Expected / actual observations: Despite potentially high initial conductivity (due to free solvent flow), insufficient mechanical strength makes Na‖Na symmetric cells highly susceptible to dendrite short circuits, resulting in a significant decrease in plating lifetime (far less than 1000 h, e.g., <100 h). This demonstrates that the cross-linked network is a key element for suppressing dendrites and achieving long-term stability.

[0086] Comparative Example C (O / Na ratio significantly deviates from the O / Na ratio of 30) Formulation: Based on Example 1, the ether-oxygen / sodium (O / Na) molar ratio was adjusted to 30, and other formulation parameters were the same as in Example 1. (60 wt% DES + 40 wt% polymer monomer (PEGDA, Mn = 2000)) Preparation and curing: Same as in Example 1.

[0087] Test conditions: Same as in Example 1.

[0088] Expected / actual observations: When O / Na is significantly lower or higher than the range of the claims, the conductivity and interface stability decrease significantly, indicating that the limitation of O / Na = 6–20 in the claims is technically necessary and reasonable.

[0089] The polymer electrolytes prepared in the examples and comparative examples were used as test electrolytes. Commercially available positive electrode materials were used: positive electrode active material, conductive agent Super P, and binder PVDF-900 were mixed at a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone was added. The mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto carbon-coated aluminum foil, and after drying, rolling, and slitting, positive electrode sheets were obtained. Using sodium metal sheets as the negative electrode, CR2032 coin cells were assembled in an argon-filled glove box. The following are the material characterization and performance tests of specific examples.

[0090] Figure 1The table shows the room temperature conductivity of Examples 1, 2, Comparative Examples A and C under different DES mass ratios. It can be seen that, under different O / Na ratios, even with changes in the mass ratio of the polymer electrolyte DES and the polymer monomers, the conductivity changes are higher when the O / Na ratio is between 6 and 20, while outside this range, the conductivity shows significant differences.

[0091] Figure 2 The electrochemical impedance spectroscopy (EIS) spectra of Examples 1, 2, and Comparative Example A at 30°C are shown. The thicknesses of the three electrolytes are consistent. Their conductivity can be calculated from the impedance magnitudes, revealing that the conductivity of the three electrolytes is 6.1 mS / cm. -1 (Example 1: PEGDA with moderate Mn 600P), 4.0 mS cm -1 (Example 2: PEGDA high Mn 1000P), 2.8 mS cm -1 (Comparative Example A: PEGDA low Mn 200P) This indicates that the conductivity of all three electrolytes is ≥2 mS / cm. -1 However, as the polymer monomer Mn gradually increases, the conductivity gradually increases.

[0092] Figure 3 The comparison of ion transport numbers and effective conductivity at 30°C between Examples 1, 2, and Comparative Example A demonstrates that gradually increasing the Mn content of PEGDA has an effect on increasing the ion transport numbers of the electrolyte, which can effectively increase the effective conductivity of the electrolyte. The effective conductivity of Examples 1 and 2 can also be ≥2 mS / cm. -1， While meeting current practical application requirements, Comparative Example A exhibits an ion transference number of only 0.25 and an effective conductivity of only 0.68, which falls short of actual production applications. This indicates that the polymer Mn is crucial, and maintaining a suitable O / Na ratio in the electrolyte is beneficial for achieving its advantageous properties.

[0093] Figure 4 The electrochemical windows for Examples 1, 2, and Comparative Example A are shown. The decomposition voltages for Examples 1, 2, and Comparative Example A are 5.41V, 5.51V, and 5.28V, respectively, illustrating the importance of a suitable Mn content in the polymer monomer. Maintaining a suitable O / Na ratio in the polymer electrolyte is beneficial for improving the electrochemical stability and resistance to electrochemical oxidation of the polymer electrolyte.

[0094] Figure 5 The Na||Na symmetric cells of Examples 1, 2, and Comparative Example A were tested at 30°C and 0.5 mA cm⁻¹. -2 - 1 mAhcm -2The comparison chart under the conditions shows that Example 1 can be stably cycled for about 300 hours, Example 2 can be stably cycled for 1000 hours, and Comparative Example A can only be stably cycled for 200 hours. This indicates that the improvement of the stability of sodium metal by polymer electrolyte can be achieved by constructing a suitable O / Na design.

[0095] Figure 6 This section compares the long-cycle performance of batteries from Examples 1, 2, and Comparative Example A at 30°C and 2C rate. It shows that the battery using the electrolyte of Comparative Example A can cycle for at most 400 hours, while the batteries using the electrolytes of Examples 1 and 2 achieve a long-cycle performance exceeding 4000 hours. Example 2, in particular, reaches 8000 hours, twice that of the comparative example, indicating that a suitable O / Na ratio in the electrolyte is beneficial for improving battery stability.

[0096] Figure 7 The images show physical photos and SEM images of the Na||Na symmetric batteries of Examples 1, 2, and Comparative Example A after 20 cycles. It can be seen that the sodium metal image of Comparative Example A shows obvious black dendrites, while the physical photos of sodium metal in Examples 1 and 2 do not show obvious black dendrites. Further comparison of the SEM images of the three batteries shows that as the O / Na ratio of the polymer electrolyte gradually increases, the sodium metal deposition on the surface becomes denser and more uniform. This indicates that an electrolyte with a suitable O / Na ratio is beneficial for sodium metal deposition and stripping, which is advantageous for the practical application of the batteries.

[0097] Figure 8 The diagram shows the coulombic efficiency of Na-Cu half-cells for Examples 1, 2, and Comparative Example A. It can be seen that the average coulombic efficiency of Comparative Example A is 77.42%, while the average coulombic efficiencies of Examples 1 and 2 are 85.32% and 97.36%, respectively.

[0098] Figure 9 The ion transport number plot for Example 3 shows that, with different sodium salt substitutions and under the same polymer monomer Mn conditions, the electrolyte transport numbers all exceed 0.5. This indicates that the effective conductivity of the electrolyte can be ensured by designing and applying a suitable O / Na ratio.

[0099] Figure 10 The diagram shows the long-cycle performance of the full battery in Example 3. It reveals that the battery can stably cycle 1000 times at 3C while maintaining 77% capacity. This demonstrates that under suitable O / Na ratio conditions, the application of different sodium salts can produce beneficial effects, further illustrating the innovativeness of this invention.

[0100] Figure 11The cycling diagrams of Na||Na symmetric batteries in Example 4 and Comparative Example B under crosslinked and non-crosslinked conditions show that without in-situ solidification of the polymer electrolyte, even with a suitable O / Na ratio, no beneficial effect can be achieved on the stability of the sodium metal interface. This demonstrates that in polymer electrolytes, only when a polymer network is formed and a suitable O / Na ratio is the key to improving battery performance, highlighting the uniqueness of this invention.

[0101] Figure 12 The comparison diagram of Comparative Example C before and after curing shows that when the O / Na ratio is very high, combined with the required DES range, a small amount of polymer monomers is difficult to cure into an effective polymer electrolyte, similar to the uncured effect of Comparative Example B. This also demonstrates the unique beneficial effect of setting an O / Na ratio of 6-20.

[0102] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A polymer electrolyte with high ionic conductivity and strong sodium metal compatibility, characterized in that: include, A three-dimensional crosslinked polymer network formed by free radical polymerization of a crosslinking agent containing ether oxygen or a polymerizable monomer containing ether oxygen; and, Deep eutectic solvent dispersed in a polymer network; The deep eutectic solvent is formed by at least one sodium salt and at least one hydrogen bond donor and / or hydrogen bond acceptor in a predetermined molar ratio, and the mass fraction of the deep eutectic solvent in the electrolyte is 40-80 wt%. In the polymer network, the molar ratio of etheroxy groups to sodium ions is 6~20:

1.

2. The high ionic conductivity polymer electrolyte as described in claim 1, characterized in that: The total ionic conductivity of the electrolyte at 30°C is ≥2 mS·cm -1 Furthermore, the sodium ion transference number is ≥0.5; at 30°C, its anodic stability window for a metallic sodium / sodium ion electrode is ≥4.0 V.

3. The high ionic conductivity polymer electrolyte as described in claim 1 or 2, characterized in that: The sodium salt is one or more of sodium perchlorate, sodium di(fluorosulfonyl)imide (NaFSI), sodium di(trifluoromethanesulfonyl)imide (NaTFSI), sodium hexafluorophosphate (NaPF6), or sodium perchlorate (NaClO4).

4. The high ionic conductivity polymer electrolyte as described in claim 1, characterized in that: The crosslinking agent containing ether oxygen is selected from polyethylene glycol di(meth)acrylate or glycidyl ether; Wherein, the polyethylene glycol di(meth)acrylate is selected from at least one of polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), diethylene glycol diacrylate (DEGDA), and triethylene glycol dimethacrylate (TEGDMA); The glycidyl ether is selected from at least one of ethylene glycol diglycidyl ether (EGDGE), 1,4-butanediol diglycidyl ether (BDGE), ethylene glycol divinyl ether (EGDVE), and diethylene glycol divinyl ether (DEGDVE).

5. The high ionic conductivity polymer electrolyte as described in claim 1 or 4, characterized in that: The ether-containing polymerizable monomer is selected from side-chain oligoethylene glycol (meth)acrylates, including methyl polyethylene glycol methacrylate (OEGMA) and polyethylene glycol methyl ether methacrylate (PEGMA).

6. The high ionic conductivity polymer electrolyte as described in claim 5, characterized in that: The number-average molecular weight Mn of the multifunctional crosslinking agent is 600~1200 g·mol⁻¹ -1 .

7. The high ionic conductivity polymer electrolyte as described in claim 1 or 6, characterized in that: The molar ratio of the sodium salt to the hydrogen bond donor is 1:(7~9), and the hydrogen bond donor includes 1,2-dimethylimidazolium, butyrolactam, N-methylacetamide, 2,2'-dithiopyridine, and succinate.

8. The method for preparing the high ionic conductivity polymer electrolyte according to any one of claims 1 to 7, characterized in that: include, A deep eutectic solvent was prepared by mixing sodium salt and hydrogen bond donor at a salt:donator molar ratio of 1:(7~9). A deep eutectic solvent is mixed with a polymerizable monomer containing ether oxygen, a multifunctional crosslinking agent and a free radical initiator to obtain an electrolyte precursor liquid. The precursor liquid is subjected to free radical polymerization and crosslinking by ultraviolet light irradiation and / or thermal curing to form an electrolyte structure; The free radical initiator is selected from bis(2,4,6-trimethylbenzoyl)phosphonates (TPO) or azobisisobutyronitrile (AIBN), and its mass fraction in the precursor is 0.2~1 wt%.

9. A sodium-ion battery, characterized in that: Includes a positive electrode, a negative electrode, and a polymer electrolyte as described in any one of claims 1 to 7 disposed therebetween; wherein The negative electrode is hard carbon or metallic sodium; The positive electrode is selected from Prussian blue compounds, Na3V2(PO4)3, or layered transition metal oxides.

10. The sodium-ion battery as described in claim 9, characterized in that: Capacity retention is ≥80% after ≥1000 cycles at 30℃ and a C rate of ≥1C, and remains constant at 0.5 mA·cm⁻¹. -2 Current density, 0.5 mAh·cm -2 Sodium stripping stabilization time in Na‖Na symmetric cells under area capacity conditions is ≥1000 h.

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