Modified polyoxyethylene solid electrolyte as well as preparation method and application thereof

Abstract

The invention provides a modified polyoxyethylene solid electrolyte and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing polyoxyethylene, a reducing agent and a solvent to obtain a polyoxyethylene mixed solution; and (2) heating the polyoxyethylene mixed solution to a reaction temperature, and dropwise adding the initiator solution and the electronegative active monomer into the heated polyoxyethylene mixed solution to obtain the modified polyoxyethylene solid electrolyte. According to the invention, polyoxyethylene is modified, branched chain components are introduced, the intermolecular hydrogen-bond interaction of polyoxyethylene is destroyed, the crystallinity of polyoxyethylene can be reduced, and the ionic conductivity of polyoxyethylene is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery materials and relates to a modified polyethylene oxide solid electrolyte and a preparation method and application thereof. Background Art

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

[0003] In the temperature range below the glass transition temperature (Tg), the polymer is mainly in a crystalline state. The lower the glass transition temperature, the better the polymer chain flexibility. Therefore, in order to achieve high ionic conductivity of PEO at room temperature, measures such as reducing the crystallinity and glass transition temperature of the polymer are generally adopted to accelerate the movement of polymer chain segments, and its properties are changed by blending with other polymers, composite nanofillers, etc.

[0004] CN105355974A discloses a solid electrolyte and a preparation method thereof, belonging to the field of polymer materials. The method comprises: preparing a sulfonylurea polymer and a polyphenylene sulfone sulfonic acid polymer; subjecting the sulfonylurea polymer and the polyphenylene sulfone sulfonic acid polymer to a condensation reaction to obtain a polysulfoxide sulfonylurea; subjecting the polysulfoxide sulfonylurea to a condensation reaction with the polyethylene oxide, subjecting the product to a ring-opening polymerization reaction with an epoxy resin to obtain a polysulfoxide sulfonylurea / polyethylene oxide cross-linked complex; dissolving the polysulfoxide sulfonylurea / polyethylene oxide cross-linked complex with chloroform, subjecting the polysulfoxide sulfonylurea / polyethylene oxide cross-linked complex to a lithium ion exchange treatment with an acidic solution of lithium hydride; subjecting the polysulfoxide sulfonylurea / polyethylene oxide cross-linked complex to a lithium ion treatment with an ion exchange solution to obtain a solid electrolyte.

[0005] CN111952662A discloses a deep-frozen polyethylene oxide solid electrolyte and a preparation method and a lithium ion battery. The preparation method comprises: dissolving polyethylene oxide and lithium salt in a solvent to obtain a solid electrolyte solution; removing the solvent from the solid electrolyte solution by drying to obtain a polyethylene oxide solid electrolyte; sealing the polyethylene oxide solid electrolyte with a thermal conductive material to obtain a sealed polyethylene oxide solid electrolyte; heating the sealed polyethylene oxide solid electrolyte to melt the polyethylene oxide solid electrolyte, and then transferring it to an environment with a temperature not higher than 0°C to freeze it, and recovering it to room temperature to obtain a deep-frozen polyethylene oxide solid electrolyte.

[0006] The above scheme improves the ionic conductivity of polyethylene oxide by subjecting it to a condensation reaction or deforming it under extreme conditions. However, the polyethylene oxide obtained by the above scheme is easily affected by changes in the external environment, resulting in changes in the crystallization characteristics of polyethylene oxide and poor environmental adaptability. Summary of the invention

[0007] The purpose of the present invention is to provide a modified polyethylene oxide solid electrolyte and a preparation method and application thereof. The present invention modifies polyethylene oxide, introduces a branched component, destroys the hydrogen bonding effect between polyethylene oxide molecules, reduces the crystallinity of polyethylene oxide, and further improves the ionic conductivity of polyethylene oxide.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

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

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

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

[0012] In the process of dropwise addition into the heated polyethylene oxide mixed solution of the present invention, heating is still maintained, so that the temperature during the dropwise addition is maintained at a suitable reaction temperature.

[0013] The present invention introduces active units into polyethylene oxide by a liquid phase method under the action of an initiator through a grafted branching method, which can destroy the hydrogen bond crystal structure of polyethylene oxide, form an amorphous non-crystalline structure, reduce the crystallinity of polyethylene oxide, and improve the ionic conductivity of polyethylene oxide. The present invention introduces a branched structure into polyethylene oxide, which can not only improve the softness of the polyethylene oxide chain segment and improve the motion characteristics of the polyethylene oxide chain segment, but also the negatively charged active monomer structure can also improve the polymer's Li + The complexing properties of the metal improve the conductivity.

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

[0015] Preferably, the polar solvent comprises water and / or N-methylpyrrolidone (NMP), preferably water.

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

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

[0018] Preferably, the mass ratio of the polyethylene oxide to the 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., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] Preferably, the molecular weight of the polyethylene oxide is 1×10 5 ~1×10 6 , for example: 1×10 5 , 2×10 5 , 5×10 5 , 8×10 5 or 1×10 6 The present invention is not limited to the numerical values ​​listed, and other numerical values ​​not listed within the numerical range are also applicable.

[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., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0022] The present invention uses lithium perchlorate as an initiator. Lithium perchlorate and a reducing agent form a redox initiation system. Perchlorate is 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, further improving the polymer's solubility and conductivity properties for lithium salts.

[0023] Preferably, the negatively charged active monomer in step (2) comprises any one of methoxy polyethylene glycol acrylate monomer, vinyl pyrrolidone monomer or vinyl pyridine monomer, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of methoxy polyethylene glycol acrylate monomer and vinyl pyrrolidone monomer, a combination of vinyl pyrrolidone monomer and vinyl pyridine monomer, or a combination of methoxy polyethylene glycol acrylate monomer and vinyl pyrrolidone monomer, etc.

[0024] Preferably, the mass ratio of the polyethylene oxide in the polyethylene oxide mixed solution to 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 dropping process in step (2) is carried out under a protective atmosphere;

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

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

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

[0029] Preferably, after the dropwise addition in step (2), the reaction is kept warm and then dried in vacuum.

[0030] Preferably, the insulation reaction time is 2h to 3h, for example: 2h, 2.2h, 2.5h, 2.8h or 3h, etc. 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 the present invention retains the characteristics of high flexibility, low cost, low interface resistance, good compatibility with lithium salts and small interface impedance between electrode materials, and has the characteristics of low crystallinity and high ion conductivity, and has high mechanical strength, a wider range of applications, lower cost and greater practical value.

[0032] In a third aspect, the present invention provides a solid-state battery, comprising the 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 to destroy the hydrogen bonding between its molecules, thereby reducing the crystallinity of polyethylene oxide and improving the ionic conductivity of polyethylene oxide.

[0035] (2) The method for modifying polyethylene oxide described in the present invention is mild, simple in conditions, and does not need to be carried out under extreme conditions. The obtained 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 costs, and greater practical value.

[0036] (3) The conductivity of the modified polyethylene oxide solid electrolyte of the present invention can reach 1.18×10 -5 S / cm or more. By adjusting the preparation conditions and the selection of raw materials, the conductivity of the modified polyethylene oxide solid electrolyte can reach 6.43×10 -5 S / cm or more. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0038] The methoxy polyethylene glycol acrylate described in the embodiment 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, and the modified polyethylene oxide solid electrolyte is prepared by the following method:

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

[0042] (2) heating the polyethylene oxide mixed solution to 35° C. in a nitrogen environment, and respectively adding a lithium perchlorate aqueous solution and a vinyl pyrrolidone monomer to the polyethylene oxide mixed solution, the addition time is 8 hours, and the temperature is kept for 3 hours after the addition is completed. After the reaction is completed, vacuum drying is performed to obtain the modified polyethylene oxide solid electrolyte;

[0043] The mass ratio of polyethylene oxide and vinyl pyrrolidone in the polyethylene oxide mixed solution to lithium perchlorate in the lithium perchlorate aqueous solution is 1:0.2:0.005.

[0044] Example 2

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

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

[0047] (2) The polyethylene oxide mixed solution was heated to 45° C. in an argon environment, and lithium perchlorate NMP solution and MEPG350A were added dropwise to the polyethylene oxide mixed solution for 5 hours. After the addition was completed, the mixture was kept warm for 2 hours. After the reaction was completed, the mixture was dried in a vacuum oven to obtain the modified polyethylene oxide solid electrolyte.

[0048] The mass ratio of the monomers of polyethylene oxide and MEPG350A in the polyethylene oxide mixed solution to the 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, and the modified polyethylene oxide solid electrolyte is prepared by the following method:

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

[0052] (2) heating the polyethylene oxide mixed solution to 60° C. in a nitrogen environment, and respectively adding a lithium perchlorate aqueous solution and a vinyl pyridine monomer to the polyethylene oxide mixed solution for 3 hours, and then keeping the temperature for 2 hours. After the reaction is completed, vacuum drying is performed to obtain the modified polyethylene oxide solid electrolyte;

[0053] The mass ratio of polyethylene oxide, vinyl pyridine monomer and lithium perchlorate in the 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, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0056] Example 5

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

[0058] Example 6

[0059] The only difference between this embodiment and embodiment 1 is that the mass ratio of polyethylene oxide to vinyl pyrrolidone is 1:0.5, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0060] Example 7

[0061] The only difference between this embodiment and embodiment 1 is that the mass ratio of polyethylene oxide to vinyl pyrrolidone is 1:0.15, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0062] Example 8

[0063] The only difference between this embodiment and embodiment 1 is that lithium perchlorate is replaced with tert-butyl hydroperoxide, and other conditions and parameters are exactly the same as those in embodiment 1.

[0064] Comparative Example 1

[0065] The only difference between this comparative example and Example 1 is that vinyl pyrrolidone is not added, and other conditions and parameters are exactly the same as those 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, and other conditions and parameters are exactly the same as those in Example 1.

[0068] Performance Test:

[0069] The above-mentioned final polymerization product was dissolved in dichloromethane, and then mixed with a dichloromethane solution containing 10% lithium perchlorate LiClO4. Ultrasonic and mechanical stirring were performed for 2 hours, and finally the mixed solution was cast in a polytetrafluoroethylene mold. After the solvent was evaporated under vacuum and room temperature for 12 hours, a solid electrolyte membrane was formed. The conductivity test results at room temperature are shown in Table 1:

[0070] Table 1

[0071]

[0072]

[0073] As can be seen from Table 1, from Examples 1-8, the conductivity of the modified polyethylene oxide solid electrolyte of the present invention can reach 1.18×10 -5 S / cm or more. By adjusting the preparation conditions and the selection of raw materials, the conductivity of the modified polyethylene oxide solid electrolyte can reach 6.43×10 -5 S / cm or more.

[0074] By comparing Example 1 with Examples 4-5, it can be seen that in the preparation process of the modified polyethylene oxide solid electrolyte of the present invention, the amount of initiator added will affect its performance. The mass ratio of polyethylene oxide to the initiator is controlled at 1: (0.005-0.02), and the performance of the modified polyethylene oxide solid electrolyte is better. If the amount of initiator added is too low, the monomer grafting is insufficient and the utilization rate is low, which is not conducive to improving the crystallization performance of polyethylene oxide. If the amount of initiator added is too high, the molecular weight of the grafted side chain is small, and the flexible segment is not conducive to the complexation and migration with lithium ions.

[0075] By comparing Example 1 with Examples 6-7, it can be seen that in the preparation process of the modified polyethylene oxide solid electrolyte of the present invention, the addition amount of the negatively charged active monomer will affect its performance. The mass ratio of polyethylene oxide to the negatively charged active monomer is controlled at 1:(0.2-0.4), and the performance of the modified polyethylene oxide solid electrolyte is better. If the addition amount of the negatively charged active monomer is too low, the polyethylene oxide is not branched enough, which affects the glass transition temperature and crystallization performance. If the addition amount of the negatively charged active monomer is too high, the polyethylene oxide structure is destroyed, causing changes in ionic conductivity.

[0076] By comparison between Example 1 and Example 8, it can be seen 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, and perchlorate is 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, further improving the polymer's solubility and conductivity properties for lithium salts.

[0077] By comparing Example 1 with Comparative Example 1, it can be seen that the present invention introduces active units into PEO by a liquid phase method under the action of an initiator through a grafting branching method, which can destroy the hydrogen bond crystalline structure of PEO, form an amorphous non-crystalline structure, reduce crystallinity, and improve ionic conductivity. The branched structure is introduced to enhance the softness of the chain segment and improve the motion characteristics of the chain segment. At the same time, the negatively charged monomer structure improves the polymer's Li + The complexing properties of the metal improve the conductivity.

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

[0079] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope 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 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 the reaction temperature, the initiator solution and the negatively charged active monomer are respectively added dropwise to the heated polyethylene oxide mixed solution to obtain the modified polyethylene oxide solid electrolyte.

2. The preparation method according to claim 1, characterized in that The solvent in step (1) comprises a polar solvent; Preferably, the polar solvent comprises water and / or NMP, preferably water.

3. The preparation method according to claim 1 or 2, characterized in that: The reducing agent in step (1) includes ascorbic acid and / or an amine reducing agent; Preferably, the amine reducing agent includes any one of N,N-dimethylbenzene idine, N,N-dimethyl-p-toluidine or diethylenetriamine, or a combination of at least two thereof.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The mass ratio of the polyethylene oxide to the reducing agent in step (1) is 1:(0.005-0.01); Preferably, the molecular weight of the polyethylene oxide is 1×10 5 ~1×10 6 ; Preferably, the mass concentration of polyethylene oxide in the polyethylene oxide mixed solution in step (1) is 10% to 30%.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The initiator in step (2) includes lithium perchlorate.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The negatively charged active monomer in step (2) includes any one of methoxy polyethylene glycol acrylate monomer, vinyl pyrrolidone monomer or vinyl pyridine monomer, or a combination of at least two thereof.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The mass ratio of the polyethylene oxide in the polyethylene oxide mixed solution to the active monomer and the initiator in the initiator solution in step (2) is 1:(0.2-0.4):(0.005-0.02).

8. The preparation method according to any one of claims 1 to 7, characterized in that: The heating and dropping process in step (2) is carried out under a protective atmosphere; Preferably, the protective atmosphere comprises any one of nitrogen, argon or helium, or a combination of at least two thereof; Preferably, the reaction temperature in step (2) is 35°C to 60°C; Preferably, the dripping time in step (2) is 3h to 8h; Preferably, after the dropwise addition in step (2), a heat preservation reaction and a vacuum drying treatment are performed; Preferably, the insulation reaction time is 2h to 3h.

9. 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 to 8.

10. A solid-state battery, characterized in that: The solid-state battery comprises the modified polyethylene oxide solid electrolyte as claimed in claim 9.

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