Gel electrolyte and sodium metal secondary battery

Abstract

The application discloses a kind of gel electrolyte and sodium metal secondary battery, belong to sodium metal secondary battery technical field, including polymer skeleton and ether electrolyte, polymer skeleton is polymerized by small molecule monomer I, small molecule monomer II and crosslinking agent, wherein small molecule monomer I contains acrylate group and isocyanate group, and small molecule monomer II contains acrylate group;The application provides a kind of gel electrolyte, can inhibit electrolyte and sodium metal anode direct contact, and capture trace moisture in battery, alleviate the problem of serious sodium metal secondary battery side reaction.

Description

Technical Field

[0001] This application relates to a gel electrolyte and a sodium metal secondary battery, belonging to the technical field of sodium metal secondary batteries. Background Technology

[0002] Sodium metal secondary batteries have gained widespread application due to their abundant reserves, low raw material costs, high theoretical specific capacity, and excellent low-temperature performance. However, during the charge-discharge cycles and long-term storage of sodium metal secondary batteries, the continuous generation of gas from side reactions has become a core technological bottleneck restricting the commercialization of sodium metal batteries.

[0003] The gas generation in sodium metal batteries originates from irreversible side reactions involving multiple interfaces and pathways: 1. Sodium metal undergoes strong reducing decomposition with the electrolyte, generating combustible gases such as H2, CO2, CO, and alkanes / olefins; 2. The solid electrolyte interphase (SEI) membrane on the anode surface has poor mechanical properties and an unstable structure, repeatedly breaking and reconstructing during cycling, exposing fresh sodium surfaces and allowing them to continuously react with the electrolyte; 3. Trace amounts of moisture in the system react with hexafluorophosphate anions to generate HF acid, which corrodes the sodium metal surface and further exacerbates the side reactions in the electrolyte.

[0004] Due to the limitations of sodium metal anode characteristics, improving the intrinsic stability of the chemical system to reduce side reactions is extremely difficult. Therefore, there is an urgent need to develop a technology that can suppress the continuous reaction between the electrolyte and sodium metal to address issues such as gas generation, capacity decay, and safety risks. Currently, industry solutions to address the serious problem of battery side reactions mainly focus on electrolyte additive modification and the development of highly stable electrolytes. Chinese patent CN202411621060.5 discloses a fluorine-rich composite additive and electrolyte, and its application in suppressing gas generation in sodium-ion batteries. It utilizes the preferential oxidation and graded reduction characteristics of different components in the composite additive to synergistically construct the cathode electrolyte membrane (CEI) and the anode solid electrolyte membrane (SEI), suppressing gas generation in sodium-ion batteries. However, in sodium metal secondary batteries, the sodium metal deposited on the anode side has high reactivity and easily reduces the electrolyte additive, causing it to lose its function. Therefore, electrolyte additives are difficult to apply to sodium metal batteries. Summary of the Invention

[0005] In view of the above problems, the first objective of this application is to provide a gel electrolyte to absorb hydrogen gas generated during battery cycling and alleviate the problem of cell bulging.

[0006] The technical solution adopted in this application is as follows: A gel electrolyte includes a polymer backbone and an ether electrolyte. The polymer backbone is polymerized from small molecule monomer I, small molecule monomer II and a crosslinking agent, wherein small molecule monomer I contains acrylate groups and isocyanate groups, and small molecule monomer II contains acrylate groups.

[0007] Further settings are as follows: The polymer backbone is formed by in-situ polymerization of small molecule monomer I, small molecule monomer II and crosslinking agent under the catalysis of initiator, with a polymerization temperature of 60-90℃ and a polymerization time of 6-12h.

[0008] The small molecule monomer I has the following general structural formula: Formula I; In Formula I: R1 is a hydrogen atom or a methyl group, and X1 is a C1-C20 alkylene group, a C1-C20 alkoxy group, or a C1-C20 fluoroalkylene group.

[0009] Preferably, the small molecule monomer I is selected from any one of the following structural formulas: Ⅰ-1; Ⅰ-2; Ⅰ-3; Ⅰ-4; Ⅰ-5.

[0010] The small molecule monomer II has the following general structural formula: Formula II; In Formula II: R2 is a hydrogen atom or a methyl group, and X2 is a C1-C20 alkyl, C1-C20 alkoxy, or C1-C20 fluoroalkyl group.

[0011] Preferably, the small molecule monomer II is selected from any one of the following structural formulas: II-1; II-2; II-3; II-4; II-5.

[0012] The crosslinking agent has the following general structural formula: Formula III; In Formula III: R3, R5, and R6 can each be a hydrogen atom or a methyl group, and the value of n ranges from 5 to 30.

[0013] The crosslinking agent can preferably have the structural formula shown in Table 1 below: Table 1 .

[0014] In particular, in order to make the activities of small molecule monomer I, small molecule monomer II, and crosslinking agent similar, so as to obtain an ideal polymer molecular network, R1, R2, R3, and R6 are all hydrogen atoms or all methyl atoms.

[0015] The molar ratio of small molecule monomer I, small molecule monomer II, and crosslinking agent is 1-3:10-30:1-3. Preferably, the molar ratio of small molecule monomer I, small molecule monomer II, and crosslinking agent is 3:30:2. This ratio is beneficial for obtaining copolymers with suitable three-dimensional network structures, reducing the solid content of the gel electrolyte (i.e., the proportion of the polymer backbone to the total mass of the gel electrolyte), and thus improving the kinetics of maintaining the sodium metal secondary battery.

[0016] The initiator is azobisisobutyronitrile (AIBN), and its mass is generally 0.1%-10% of the total mass of small molecule monomer I, small molecule monomer II and crosslinking agent.

[0017] The polymer backbone accounts for 1-5% of the total mass (i.e., solid content) of the gel electrolyte, preferably 2%.

[0018] The ether electrolyte includes sodium salts and ether solvents.

[0019] The sodium salt includes at least sodium hexafluorophosphate, with a concentration of 0.8-5 mol / L, preferably 1 mol / L. In some embodiments, some auxiliary salts may be added to optimize battery performance, including one or more of sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium bis(oxalate)borate, sodium difluorooxalateborate, sodium difluorobis(oxalate)phosphate, sodium tetrafluorooxalate phosphate, sodium bis(trifluoromethanesulfonate)imide, sodium di(fluorosulfonyl)imide, and sodium perchlorate, with a concentration of 0.1-0.5 mol / L.

[0020] The ether solvent is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol dibutyl ether, preferably ethylene glycol dimethyl ether.

[0021] The second objective of this application is to provide a sodium metal secondary battery comprising the aforementioned gel electrolyte.

[0022] The sodium metal secondary battery includes an anode electrode, a cathode electrode, a separator, and the aforementioned gel electrolyte. The anode electrode, cathode electrode, and separator are stacked or wound to form an electrode assembly.

[0023] The anode electrode is at least one selected from copper foil, aluminum foil, carbon-coated copper foil, carbon-coated aluminum foil, porous copper foil, and porous aluminum foil. In some embodiments, the anode electrode may also include a sodium-supplementing material selected from one or more selected from sodium foil, sodium strip, sodium powder, and pre-sodiumization reagent.

[0024] The cathode electrode comprises an active material, conductive carbon, a binder, and a current collector.

[0025] The active substance is selected from one or more of sodium ferric pyrophosphate, sodium ferric sulfate, sodium vanadium phosphate, sodium vanadium fluorophosphate, layered oxides, Prussian blue, Prussian white and their analogues.

[0026] The conductive carbon is selected from one or more of Superp, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, and graphene.

[0027] The adhesive is selected from one or more of styrene-butadiene rubber, acrylonitrile, acrylate, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, and carboxymethyl cellulose.

[0028] The current collector is one or more of aluminum foil, carbon-coated aluminum foil, and porous aluminum foil.

[0029] The diaphragm is selected from one or more of polypropylene diaphragms, polyethylene diaphragms, inorganic ceramic coated diaphragms, and polypropylene or polyethylene composite ceramic diaphragms.

[0030] This application also provides a method for preparing the above-mentioned sodium metal secondary battery, comprising the following steps: Small molecule monomer I, small molecule monomer II, crosslinking agent, sodium salt and ether solvent are mixed to obtain a cured solution; The electrode assembly is placed in the outer packaging to obtain a dry battery cell; After injecting the curing liquid into the dry cell, the outer packaging is sealed and placed at 60-90℃ for 6-12 hours to obtain the secondary battery.

[0031] The beneficial effects of this application are as follows: This application provides a gel electrolyte comprising a polymer backbone and an ether-based electrolyte, which can inhibit direct contact between the electrolyte and the sodium metal anode and capture trace amounts of moisture within the battery cell, alleviating the severe side reactions problem in sodium metal secondary batteries. The polymer backbone anchors the solvent, preventing it from flowing to the anode and reacting with the sodium metal to cause side reactions, thereby suppressing gas generation. Simultaneously, through the design of the small molecule monomers, crosslinking agent structure, and addition ratio, the polymer network structure is rationally designed with a large pore structure, allowing complete swelling of the entire electrolyte at a low solid content. Therefore, the gel electrolyte of this invention has almost no deterioration on battery kinetics. The polymer backbone contains an appropriate amount of isocyanate groups, which can undergo nucleophilic addition reactions with the unavoidable trace amounts of moisture in the electrode and electrolyte, inhibiting the hydrolysis of moisture with hexafluorophosphate anions to produce HF, thereby reducing side reactions and electrode corrosion. Attached Figure Description

[0032] Figure 1 This is a product morphology diagram of the curing liquid prepared in Example 1.

[0033] Figure 2This is a product morphology diagram of the gel electrolyte prepared in Example 1. Detailed Implementation

[0034] The present application will be further described below with reference to specific embodiments. Unless otherwise specified, the raw materials and reagents described in the embodiments are all existing technologies in the field or commercially available products.

[0035] Example 1

[0036] A gel electrolyte, prepared by the following method: (1) Preparation of ether electrolyte In an argon atmosphere glove box, the water and oxygen contents are both less than 0.1 ppm. Ethylene glycol dimethyl ether is used as a solvent, and sodium hexafluorophosphate is dissolved in the solvent to obtain a uniform, colorless, and transparent electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L.

[0037] (2) Preparation of curing liquid In an argon-atmospheric glove box, small molecule monomer I-1, small molecule monomer II-1, and crosslinking agent III-1 are added to an ether electrolyte in the following ratio: the molar ratio of small molecule monomer I-1: small molecule monomer II-1: crosslinking agent III-1 is 3:30:2. 1% AIBN (based on the total mass of small molecule monomer I-1, small molecule monomer II-1, and crosslinking agent III-1) is added to adjust the solid content to 2%. The mixture is stirred until homogeneous to obtain a cured solution.

[0038] Prepared curing solution, such as Figure 1 As shown, the electrolyte is in a liquid state at this time.

[0039] (3) Preparation of gel electrolyte The above curing solution was left to stand at 70°C for 10 hours to obtain the gel electrolyte.

[0040] Figure 2 This is a diagram showing the product morphology of the prepared gel electrolyte. (Example:) Figure 2 As shown, in step (2), the curing liquid undergoes monomer polymerization under high-temperature catalysis, thereby transforming... Figure 1 The liquid electrolyte shown transforms into Figure 2 The solid gel electrolyte is shown.

[0041] To investigate the effects of the types of small molecule monomer I, small molecule monomer II, and crosslinking agent on the performance of the gel electrolyte, the experiments shown in Examples 2 to 5 were conducted.

[0042] Examples 2 to 5 The preparation method is the same as in Example 1, except that the types of small molecule monomer I, small molecule monomer II and crosslinking agent shown in Table 2 for Examples 2 to 5 are used.

[0043] To investigate the effect of the ratio of small molecule monomer I, small molecule monomer II and crosslinking agent on the performance of gel electrolyte, the experiments shown in Examples 6 to 9 were conducted.

[0044] Examples 6 to 9 The preparation method is the same as in Example 1, except that the ratio of small molecule monomer I, small molecule monomer II and crosslinking agent shown in Table 2 for Examples 6 to 9 is used.

[0045] To investigate the effect of the solid content of the polymer backbone in the gel electrolyte on the performance of the gel electrolyte, the experiments shown in Examples 10 and 11 were conducted.

[0046] Examples 10 to 11 The preparation method is the same as in Example 1, except that the polymer backbone of Examples 10 to 11 shown in Table 2 is used in the gel electrolyte with the same solid content.

[0047] To investigate the effect of ether electrolytes on the performance of gel electrolytes, the experiments shown in Examples 12 to 14 were conducted.

[0048] Examples 12 to 14 The preparation method is the same as in Example 1, except that the ether electrolytes of Examples 12 to 14 shown in Table 2 are used.

[0049] Comparative Example 1 Based on Example 1, the gel electrolyte uses only ether electrolytes and does not contain a polymer backbone formed by the polymerization of small molecule monomers and crosslinking agents.

[0050] Application Example 1 To investigate the electrochemical performance of gel electrolytes in sodium metal secondary batteries, the following examples were conducted.

[0051] The curing solutions obtained in Examples 1 to 14 and the ether electrolyte of Comparative Example 1 were applied to sodium metal secondary batteries, and their electrochemical performance was tested.

[0052] Sodium metal secondary batteries are prepared using the following method: Separator: Select a 12-micron thick polyethylene porous membrane and cut it into rectangles of 60 mm × 47 mm for later use.

[0053] Cathode electrode: Active material sodium iron pyrophosphate, conductive agent Super P, and binder PVDF are mixed at a mass ratio of 98:1:1. N-methylpyrrolidone solvent is added and stirred until homogeneous, resulting in a cathode slurry with a viscosity of 40,000 mPas and a solid content of 65%. The cathode slurry is then coated using a coating machine with a single-sided coating thickness of 18 mg / cm². 2The loading capacity is coated on both sides of the aluminum foil, dried thoroughly until the moisture content is below 150 ppm, and then cut into rectangles of 56 mm × 43 mm as cathode plates.

[0054] Anode electrode: Select carbon-coated aluminum foil with a thickness of 13 micrometers and cut it into rectangles with a size of 58 mm × 45 mm for later use.

[0055] Battery assembly: The cut cathode plates, separator, and anode plates are stacked in sequence, with 10 layers of cathode plates and 11 layers of anode plates to obtain a bare cell. The bare cell is then welded with tabs and placed in an aluminum-plastic film outer packaging bag to obtain a dry cell. The curing solution is injected into the dry cell and vacuum hot-pressed for sealing. After standing at room temperature for 1 hour, it is placed in a 70°C environment for 10 hours. Finally, hot and cold pressing, formation, shaping, and capacity testing are performed in sequence to obtain a sodium metal secondary battery with a rated capacity of 800mAh.

[0056] Performance testing Cycle performance test: The ambient temperature was set to 25℃. The prepared battery was left to stand for 1 hour, then charged at a constant current of 0.5C to 3.35V, followed by constant voltage charging at 3.35V until the current dropped to 0.05C. After standing for 1 hour, it was discharged at a constant current of 1C to 2V to obtain the discharge capacity. The above steps were repeated for the same battery, and the number of cycles when the discharge capacity decayed to 80% was recorded. The number of cycles completed at this point is taken as the battery cycle life.

[0057] Rate performance test: The ambient temperature was set to 25℃. The prepared battery was left to stand for 1 hour, then charged at a constant current of 0.5C to 3.35V, followed by constant voltage charging at 3.35V until the current dropped to 0.05C. After standing for 1 hour, it was discharged at a constant current of 1C to 2V to obtain the 1C discharge capacity. Freshly prepared batteries were left to stand for 1 hour, then charged at a constant current of 0.5C to 3.35V, followed by constant voltage charging at 3.35V until the current dropped to 0.05C. After standing for 1 hour, it was discharged at a constant current of 10C to 2V to obtain the 10C discharge capacity. The 10C discharge capacity divided by the 1C discharge capacity is the 10C discharge capacity retention rate.

[0058] The test results are shown in Table 2: Table 2 .

[0059] As shown in Table 2: As can be seen from Comparative Examples 1-5 and Comparative Example 1, the different types of small molecule monomers I, II and crosslinking agents provided in this application can all achieve polymer network construction, suppress the free flow of electrolyte, reduce side reactions, improve battery cycle life, and do not deteriorate kinetic performance.

[0060] Comparing Examples 1 and 6-7, it can be seen that the ratio of small molecule monomer I and small molecule monomer II provided in this application should not be too large or too small. If it is too large, there will be too many isocyanate groups, and the gel anode interface will be prone to reaction; if it is too small, there will be too few isocyanate groups, and the trace moisture in the system cannot be effectively removed.

[0061] Comparing Examples 1 and 8-9, it can be seen that the ratio of small molecule monomer II and crosslinking agent provided in this application should not be too large or too small. If the ratio is too large, the polymer skeleton will have a smaller binding effect on the electrolyte and will not be able to fully suppress the side reaction between the electrolyte and sodium metal; if the ratio is too small, there will be too many polymer crosslinking sites, which will affect the battery dynamic performance.

[0062] Comparing Examples 1 and 10-11, it can be seen that the solid content of the gel electrolyte provided in this application should not be too high or too low. If it is too high, the polymer skeleton will have too much binding effect on the electrolyte, which will hinder the migration of sodium ions and deteriorate the kinetics; if it is too low, the binding effect on the electrolyte will be too small.

[0063] As can be seen from the comparison of Examples 1 and 12-14, the ether electrolyte provided in this application has excellent compatibility with the polymer skeleton, which enables the sodium metal battery to have a long cycle life.

[0064] The above description is merely a preferred embodiment of this application and is not intended to limit the invention. Various modifications and variations can be made to this invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A gel electrolyte, characterized in that: It includes a polymer backbone and an ether electrolyte. The polymer backbone is polymerized from small molecule monomer I, small molecule monomer II and a crosslinking agent. Small molecule monomer I contains acrylate groups and isocyanate groups, and small molecule monomer II contains acrylate groups.

2. The gel electrolyte according to claim 1, characterized in that: The polymer backbone is formed by in-situ polymerization of small molecule monomer I, small molecule monomer II and crosslinking agent under the catalysis of initiator, with a polymerization temperature of 60-90℃ and a polymerization time of 6-12h.

3. The gel electrolyte according to claim 1, characterized in that: The small molecule monomer I has the following general structural formula: Formula I; In Formula I: R1 is a hydrogen atom or a methyl group, and X1 is a C1-C20 alkylene group, a C1-C20 alkoxy group, or a C1-C20 fluoroalkylene group.

4. The gel electrolyte according to claim 1, characterized in that: The small molecule monomer I is selected from any of the following structural formulas: Ⅰ-1； Ⅰ-2； Ⅰ-3； Ⅰ-4； Ⅰ-5 。 5. A gel electrolyte according to claim 1, characterized in that: The small molecule monomer II has the following general structural formula: Formula II; In Formula II: R2 is a hydrogen atom or a methyl group, and X2 is a C1-C20 alkyl, C1-C20 alkoxy, or C1-C20 fluoroalkyl group.

6. The gel electrolyte according to claim 1, characterized in that: Small molecule monomer II is selected from any of the following structural formulas: Ⅱ-1； Ⅱ-2； Ⅱ-3； Ⅱ-4； Ⅱ-5。 7. The gel electrolyte according to claim 1, characterized in that: The crosslinking agent has the following general structural formula: Formula III; In Formula III: R3, R5, and R6 can each be a hydrogen atom or a methyl group, and the value of n ranges from 5 to 30.

8. The gel electrolyte according to claim 1, characterized in that: The molar ratio of small molecule monomer I, small molecule monomer II, and crosslinking agent is 1-3:10-30:1-3.

9. A gel electrolyte according to claim 1, characterized in that: The ether electrolyte comprises a sodium salt and an ether solvent, wherein the sodium salt comprises at least sodium hexafluorophosphate with a concentration of 0.8-5 mol / L; and the ether solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol dibutyl ether.

10. The application of the gel electrolyte of claim 1 in a sodium metal secondary battery.

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