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

Abstract

The application provides a modified polyethylene oxide solid electrolyte and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing polyethylene oxide, a reducing agent and a solvent to obtain a polyethylene oxide mixed solution; (2) after the polyethylene oxide mixed solution is heated to a reaction temperature, an initiator solution and a negative electrically active monomer are respectively added dropwise into the heated polyethylene oxide mixed solution to obtain the modified polyethylene oxide solid electrolyte. The polyethylene oxide is modified in the application, a branched component is introduced, and the intermolecular hydrogen bond effect is destroyed, so that the crystallinity of the polyethylene oxide can be reduced, and the ionic conductivity of the polyethylene oxide is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a modified polyethylene oxide solid electrolyte, its preparation method, and its application. Background Technology

[0002] Polyethylene oxide (PEO) has become the most studied solid electrolyte matrix due to its strong dissociation ability of lithium salts, excellent electrochemical stability, low glass transition temperature, and good flexibility. PEO-based electrolytes exist in various morphologies at room temperature, including crystalline and amorphous regions. In PEO-based solid electrolytes, the molecular motion in the amorphous region is faster than in the crystalline region. In the amorphous region, Li... + Ionic conductivity is mainly transmitted through the movement of polymer chain segments. The ionic conductivity depends primarily on the mobility of the chain segments in the amorphous region, and ion conduction mainly relies on the amorphous region.

[0003] Below the glass transition temperature (Tg), polymers are predominantly crystalline, and the lower the glass transition temperature, the better the polymer chain flexibility. Therefore, to achieve high ionic conductivity of PEO at room temperature, measures such as reducing the crystallinity and glass transition temperature are generally used to accelerate polymer chain segment movement, and methods such as blending with other polymers and composite nanofillers are employed to modify its properties.

[0004] CN105355974A discloses a solid electrolyte and its preparation method, belonging to the field of polymer materials. The method includes: preparing a sulfonamide polymer and a polyphenylene sulfonate sulfonic acid polymer; performing a condensation reaction between the sulfonamide polymer and the polyphenylene sulfonate sulfonic acid polymer to obtain polysulfonyl sulfonamide; performing a condensation reaction between the polysulfonyl sulfonamide and polyethylene oxide, and performing a ring-opening polymerization reaction between the product and an epoxy resin to obtain a polysulfonyl sulfonamide / polyethylene oxide crosslinked composite; dissolving the polysulfonyl sulfonamide / polyethylene oxide crosslinked composite in chloroform; subjecting the polysulfonyl sulfonamide / polyethylene oxide crosslinked composite to lithium-ion exchange treatment with an acidic lithium hydride solution; and treating the polysulfonyl sulfonamide / polyethylene oxide crosslinked composite with an ion exchange solution to obtain a solid electrolyte.

[0005] CN111952662A discloses a deep-frozen vinyl oxide solid electrolyte, its preparation method, and a lithium-ion battery. The preparation method includes: dissolving vinyl oxide and a lithium salt in a solvent to obtain a solid electrolyte solution; removing the solvent from the solid electrolyte solution by drying to obtain a vinyl oxide solid electrolyte; sealing the vinyl oxide solid electrolyte using a thermally conductive material to obtain a sealed vinyl oxide solid electrolyte; heating the sealed vinyl oxide solid electrolyte to melt it, then transferring it to an environment with a temperature not exceeding 0°C for freezing, and restoring it to room temperature to obtain a deep-frozen vinyl oxide solid electrolyte.

[0006] The above methods improve the ionic conductivity of polyethylene oxide by condensing it or deforming it under extreme conditions. However, the polyethylene oxide obtained by these methods is easily affected by changes in the external environment, leading to changes in the crystallization characteristics of polyethylene oxide and poor environmental adaptability. Summary of the Invention

[0007] The purpose of this invention is to provide a modified polyethylene oxide solid electrolyte, its preparation method, and its application. This invention modifies polyethylene oxide by introducing branched components, thereby disrupting the intermolecular hydrogen bonding of polyethylene oxide, reducing the crystallinity of polyethylene oxide, and thus improving the ionic conductivity of polyethylene oxide.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a modified polyethylene oxide solid electrolyte, the method comprising the following steps:

[0010] (1) Mix polyethylene oxide, reducing agent and solvent to obtain polyethylene oxide mixed solution;

[0011] (2) After heating the polyethylene oxide mixed solution to the reaction temperature, the initiator solution and the negatively charged active monomer are added dropwise to the heated polyethylene oxide mixed solution to obtain the modified polyethylene oxide solid electrolyte.

[0012] The present invention maintains heating during the dropwise addition to the heated polyethylene oxide mixed solution to keep the temperature at a suitable reaction temperature.

[0013] This invention utilizes a liquid-phase method, under the action of an initiator, to introduce active units into polyethylene oxide (PEO) through grafting of branched chains. This disrupts the hydrogen-bonded crystalline structure of PEO, forming an amorphous structure, reducing the crystallinity of PEO, and increasing its ionic conductivity. The introduction of branched structures into PEO not only enhances the flexibility and mobility of PEO chain segments, but also, the negatively charged active monomer structure improves the polymer's affinity for Li. + Its complexing properties improve conductivity.

[0014] Preferably, the solvent in step (1) includes a polar solvent.

[0015] Preferably, the polar solvent includes water and / or N-methylpyrrolidone (NMP), with water being the most preferred.

[0016] Preferably, the reducing agent in step (1) includes ascorbic acid and / or amine reducing agents.

[0017] Preferably, the amine reducing agent includes any one or a combination of at least two of N,N-dimethyltoluidine, N,N-dimethyl-p-toluidine, or diethylenetriamine.

[0018] Preferably, the mass ratio of polyethylene oxide to reducing agent in step (1) is 1:(0.005~0.01), for example: 1:0.005, 1:0.006, 1:0.007, 1:0.008, 1:0.009 or 1:0.01, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the molecular weight of the polyethylene oxide is 1×10⁻⁶. 5 ~1×10 6 For example: 1×10 5 2×10 5 5×10 5 8×10 5 Or 1×10 6 The term "etc." is not limited to the listed values; it also applies to other unlisted values ​​within the range.

[0020] Preferably, the mass concentration of polyethylene oxide in the polyethylene oxide mixed solution in step (1) is 10% to 30%, for example: 10%, 15%, 20%, 25% or 30%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the initiator in step (2) includes lithium perchlorate.

[0022] This invention uses lithium perchlorate as an initiator. Lithium perchlorate and a reducing agent form a redox initiation system. Perchlorate ions are reduced to generate chlorate active free radicals. These chlorate active free radicals can initiate or terminate chain growth groups, thereby introducing chlorate groups into the polymer and further improving the polymer's solubility and conductivity of lithium salts.

[0023] Preferably, the negatively charged active monomer in step (2) includes any one or a combination of at least two of methoxy polyethylene glycol acrylate monomers, vinylpyrrolidone monomers, or vinylpyridine monomers. Typical but non-limiting combinations include combinations of methoxy polyethylene glycol acrylate monomers and vinylpyridine monomers, combinations of vinylpyrrolidone monomers and vinylpyridine monomers, or combinations of methoxy polyethylene glycol acrylate monomers and vinylpyrrolidone monomers.

[0024] Preferably, the mass ratio of polyethylene oxide in the polyethylene oxide mixed solution to that of the active monomer and the initiator in the initiator solution in step (2) is 1:(0.2-0.4):(0.005-0.02), for example: 1:0.2:0.005, 1:0.25:0.008, 1:0.3:0.01, 1:0.3:0.02 or 1:0.4:0.02, etc.

[0025] Preferably, the heating and dripping process in step (2) is carried out under a protective atmosphere;

[0026] Preferably, the protective atmosphere includes any one or a combination of at least two of nitrogen, argon, or helium. Typical but non-limiting combinations include combinations of nitrogen and argon, nitrogen and helium, or helium and argon.

[0027] Preferably, the reaction temperature in step (2) is 35℃~60℃, for example: 35℃, 38℃, 40℃, 45℃, 50℃, 55℃ or 60℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] Preferably, the dripping time in step (2) is 3h to 8h, for example: 3h, 4h, 5h, 6h, 7h or 8h.

[0029] Preferably, after the dropwise addition in step (2), a heat preservation reaction and vacuum drying treatment are performed.

[0030] Preferably, the heat preservation reaction time is 2h to 3h, for example: 2h, 2.2h, 2.5h, 2.8h, or 3h. In a second aspect, the present invention provides a modified polyethylene oxide solid electrolyte, which is prepared by the preparation method described in the first aspect.

[0031] The modified polyethylene oxide solid electrolyte of this invention retains the characteristics of high flexibility, low cost, low interfacial resistance, good compatibility with lithium salts, and low interfacial impedance between electrode materials. At the same time, it has the characteristics of low crystallinity, high ionic conductivity, and high mechanical strength, making it more widely used, lower in cost, and more practical.

[0032] Thirdly, the present invention provides a solid-state battery comprising a modified polyethylene oxide solid electrolyte as described in the second aspect.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention modifies polyethylene oxide by introducing branched components and destroying its intermolecular hydrogen bonding, which can reduce the crystallinity of polyethylene oxide and thus improve the ionic conductivity of polyethylene oxide.

[0035] (2) The method for modifying polyethylene oxide described in this invention is mild and simple, and does not need to be carried out under extreme conditions. The resulting modified polyethylene oxide solid electrolyte has strong environmental adaptability and can maintain the characteristics of high ionic conductivity and low crystallinity under most conditions. It has a wider range of applications, lower cost, and greater practical value.

[0036] (3) The conductivity of the modified polyethylene oxide solid electrolyte of the present invention can reach 1.18 × 10⁻⁶. -5 With a conductivity exceeding S / cm, the modified polyethylene oxide solid electrolyte can achieve a conductivity of 6.43 × 10⁻⁶. -5 S / cm or higher. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0038] The methoxy polyethylene glycol acrylate described in the embodiments of the present invention has a polyethylene glycol molecular weight of 350 (MEPG350A), 500 (MPEG500A), or 750 (MEPG750A).

[0039] Example 1

[0040] This embodiment provides a modified polyethylene oxide solid electrolyte, which is prepared by the following method:

[0041] (1) The molecular weight is 1×10 5 ~3×10 5Polyethylene oxide and ascorbic acid were mixed with water at a mass ratio of 1:0.008 to obtain a polyethylene oxide mixed solution with a mass concentration of 10%.

[0042] (2) The polyethylene oxide mixed solution was heated to 35°C in a nitrogen atmosphere. Lithium perchlorate aqueous solution and vinylpyrrolidone monomer were then added dropwise to the polyethylene oxide mixed solution for 8 hours each. After the addition was complete, the solution was kept at the same temperature for another 3 hours. After the reaction was complete, the solution was dried under vacuum to obtain the modified polyethylene oxide solid electrolyte.

[0043] The mass ratio of polyethylene oxide, vinylpyrrolidone, and lithium perchlorate in the polyethylene oxide mixed solution is 1:0.2:0.005.

[0044] Example 2

[0045] This embodiment provides a modified polyethylene oxide solid electrolyte, which is prepared by the following method:

[0046] (1) The molecular weight is 3×10 5 ~8×10 5 Polyethylene oxide, ascorbic acid and NMP were mixed at a mass ratio of 1:0.01 to obtain a polyethylene oxide mixed solution with a mass concentration of 30%.

[0047] (2) The polyethylene oxide mixed solution was heated to 45°C in an argon atmosphere. Lithium perchlorate NMP solution and MEPG350A were then added dropwise to the polyethylene oxide mixed solution over a period of 5 hours. After the addition was completed, the solution was kept at the same temperature for another 2 hours. After the reaction was completed, the solution was dried under vacuum to obtain the modified polyethylene oxide solid electrolyte.

[0048] The mass ratio of polyethylene oxide and MEPG350A monomers in the polyethylene oxide mixed solution to lithium perchlorate in the lithium perchlorate NMP solution is 1:0.4:0.02.

[0049] Example 3

[0050] This embodiment provides a modified polyethylene oxide solid electrolyte, which is prepared by the following method:

[0051] (1) The molecular weight is 1×10 5 ~1×10 6 Polyethylene oxide and N,N-dimethylamine were mixed with water at a mass ratio of 1:0.005 to obtain a polyethylene oxide mixed solution with a mass concentration of 20%.

[0052] (2) The polyethylene oxide mixed solution was heated to 60°C in a nitrogen atmosphere. Lithium perchlorate aqueous solution and vinylpyridine monomer were then added dropwise to the polyethylene oxide mixed solution over a period of 3 hours. After the addition was complete, the solution was kept at the same temperature for another 2 hours. After the reaction was complete, the solution was dried under vacuum to obtain the modified polyethylene oxide solid electrolyte.

[0053] The mass ratio of lithium perchlorate in polyethylene oxide, vinylpyridine monomer and lithium perchlorate aqueous solution is 1:0.3:0.01.

[0054] Example 4

[0055] The only difference between this embodiment and Embodiment 1 is that the mass ratio of polyethylene oxide to lithium perchlorate is 1:0.02; all other conditions and parameters are exactly the same as in Embodiment 1.

[0056] Example 5

[0057] The only difference between this embodiment and Example 1 is that the mass ratio of polyethylene oxide to lithium perchlorate is 1:0.003; all other conditions and parameters are exactly the same as in Example 1.

[0058] Example 6

[0059] The only difference between this embodiment and Example 1 is that the mass ratio of polyethylene oxide to vinylpyrrolidone is 1:0.5; all other conditions and parameters are exactly the same as in Example 1.

[0060] Example 7

[0061] The only difference between this embodiment and Example 1 is that the mass ratio of polyethylene oxide to vinylpyrrolidone is 1:0.15; all other conditions and parameters are exactly the same as in Example 1.

[0062] Example 8

[0063] The only difference between this embodiment and Embodiment 1 is that lithium perchlorate is replaced with tert-butyl hydrogen peroxide; all other conditions and parameters are exactly the same as in Embodiment 1.

[0064] Comparative Example 1

[0065] The only difference between this comparative example and Example 1 is that vinylpyrrolidone is not added; all other conditions and parameters are exactly the same as in Example 1.

[0066] Comparative Example 2

[0067] The only difference between this comparative example and Example 1 is that ascorbic acid is not added; all other conditions and parameters are exactly the same as in Example 1.

[0068] Performance testing:

[0069] The above-mentioned polymerization end product was dissolved in dichloromethane, and then mixed with a dichloromethane solution containing 10% lithium perchlorate (LiClO4). The mixture was ultrasonically and mechanically stirred for 2 hours. Finally, the mixture was cast into a polytetrafluoroethylene mold, and the solvent was evaporated under vacuum at room temperature for 12 hours to form a solid electrolyte membrane. The conductivity test results at room temperature are shown in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] As shown in Table 1, and based on Examples 1-8, the conductivity of the modified polyethylene oxide solid electrolyte of this invention can reach 1.18 × 10⁻⁶. -5 With a conductivity exceeding S / cm, the modified polyethylene oxide solid electrolyte can achieve a conductivity of 6.43 × 10⁻⁶. -5 S / cm or higher.

[0074] A comparison of Examples 1 and 4-5 shows that the amount of initiator added during the preparation of the modified polyethylene oxide solid electrolyte of the present invention affects its performance. Controlling the mass ratio of polyethylene oxide to initiator at 1:(0.005-0.02) yields a modified polyethylene oxide solid electrolyte with better performance. If the amount of initiator added is too low, the monomer grafting is insufficient, resulting in low utilization and hindering the improvement of polyethylene oxide crystallization. If the amount of initiator added is too high, the molecular weight of the grafted side chains is small, and the flexible segments are not conducive to complexation and migration with lithium ions.

[0075] A comparison of Examples 1 and 6-7 shows that the amount of negatively charged active monomer added during the preparation of the modified polyethylene oxide solid electrolyte of the present invention affects its performance. Controlling the mass ratio of polyethylene oxide to negatively charged active monomer at 1:(0.2-0.4) yields a modified polyethylene oxide solid electrolyte with better performance. If the amount of negatively charged active monomer added is too low, the polyethylene oxide will not be sufficiently branched, affecting the glass transition temperature and crystallization behavior. If the amount of negatively charged active monomer added is too high, it will damage the polyethylene oxide structure and cause changes in ionic conductivity.

[0076] A comparison of Examples 1 and 8 shows that in the preparation process of the modified polyethylene oxide solid electrolyte of the present invention, lithium perchlorate is used as an initiator. Lithium perchlorate and a reducing agent form a redox initiation system. Perchlorate ions are reduced to generate chlorate active free radicals. The chlorate active free radicals can initiate or terminate chain growth groups, thereby introducing chlorate groups into the polymer and further improving the polymer's solubility and conductivity of lithium salts.

[0077] Comparing Example 1 and Comparative Example 1, it can be seen that the present invention, through a liquid-phase method and under the action of an initiator, introduces active units into PEO via grafting branching. This disrupts the hydrogen-bonded crystalline structure of PEO, forming an amorphous structure, reducing crystallinity, increasing ionic conductivity, and introducing branching structures to enhance chain segment flexibility and improve chain segment movement characteristics. Simultaneously, the negatively charged monomer structure enhances the polymer's affinity for Li. + Its complexing properties improve conductivity.

[0078] As can be seen from the comparison between Example 1 and Comparative Example 2, the present invention can significantly improve grafting efficiency by introducing a reducing agent, thus ensuring effective copolymerization of monomer and polyethylene oxide.

[0079] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a modified polyethylene oxide solid electrolyte, characterized in that, The preparation method includes the following steps: (1) Mix polyethylene oxide, reducing agent and solvent to obtain polyethylene oxide mixed solution; (2) After heating the polyethylene oxide mixed solution to the reaction temperature, the initiator solution and the negatively charged active monomer are added dropwise to the heated polyethylene oxide mixed solution to obtain the modified polyethylene oxide solid electrolyte. The reducing agent in step (1) includes ascorbic acid and / or amine reducing agents; The negatively charged active monomer in step (2) includes any one or a combination of at least two of methoxy polyethylene glycol acrylate monomers, vinylpyrrolidone monomers, or vinylpyridine monomers.

2. The preparation method according to claim 1, characterized in that, The solvent in step (1) includes polar solvents.

3. The preparation method according to claim 2, characterized in that, The polar solvent includes water and / or NMP.

4. The preparation method according to claim 3, characterized in that, The polar solvent is water.

5. The preparation method according to claim 1, characterized in that, The amine reducing agent includes any one or a combination of at least two of N,N-dimethyltoluidine, N,N-dimethyl-p-toluidine, or diethylenetriamine.

6. The preparation method according to claim 1, characterized in that, The mass ratio of polyethylene oxide to reducing agent in step (1) is 1:(0.005~0.01).

7. The preparation method according to claim 1, characterized in that, The molecular weight of the polyethylene oxide is 1×10⁻⁶. 5 ~1×10 6 .

8. The preparation method according to claim 1, characterized in that, The mass concentration of polyethylene oxide in the polyethylene oxide mixed solution in step (1) is 10%~30%.

9. The preparation method according to claim 1, characterized in that, The initiator in step (2) includes lithium perchlorate.

10. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of polyethylene oxide in the polyethylene oxide mixed solution to that of the active monomer and the initiator in the initiator solution is 1:(0.2~0.4):(0.005~0.02).

11. The preparation method according to claim 1, characterized in that, The heating and dripping process described in step (2) is carried out under a protective atmosphere.

12. The preparation method according to claim 11, characterized in that, The protective atmosphere includes any one or a combination of at least two of nitrogen, argon, or helium.

13. The preparation method according to claim 1, characterized in that, The reaction temperature in step (2) is 35℃~60℃.

14. The preparation method according to claim 1, characterized in that, The dripping time in step (2) is 3h~8h.

15. The preparation method according to claim 1, characterized in that, After the addition in step (2), the reaction is kept at a constant temperature and then dried under vacuum.

16. The preparation method according to claim 15, characterized in that, The heat preservation reaction time is 2h~3h.

17. A modified polyethylene oxide solid electrolyte, characterized in that, The modified polyethylene oxide solid electrolyte is prepared by the preparation method according to any one of claims 1-16.

18. A solid-state battery, characterized in that, The solid-state battery comprises the modified polyethylene oxide solid electrolyte as described in claim 17.

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