Copolymer electrolyte based on N-vinyl pyrrolidone and preparation method thereof

Abstract

The invention provides a copolymer electrolyte based on N-vinyl pyrrolidone and a preparation method thereof, and belongs to the technical field of lithium ion batteries. The preparation method comprises the following steps: firstly, mixing N-vinyl pyrrolidone, lithium salt, bis (vinyl sulfuryl) methane and a plasticizer to obtain an intermediate mixture; and adding an initiator into the intermediate mixture to carry out polymerization reaction to obtain the copolymer based on N-vinyl pyrrolidone. According to the invention, the bis (vinyl sulfuryl) methane is introduced into an N-vinyl pyrrolidone reaction system, and the prepared copolymer electrolyte based on N-vinyl pyrrolidone has higher ionic conductivity.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a copolymer electrolyte based on N-vinyl pyrrolidone and a preparation method thereof. Background Art

[0002] N-vinylpyrrolidone (NVP) contains active unsaturated vinyl groups (CH2=CH-), which are easy to copolymerize with other vinyl monomers. The strong polar group lactam bond is conducive to ion conduction, and its five-membered ring structure makes it thermally stable. Polyvinylpyrrolidone has good hygroscopicity and thermal stability, and can be used in gel polymer electrolytes or modified by blending with other polymer electrolytes.

[0003] Nallamuthu et al. prepared a PEO / PVP blended polymer solid electrolyte containing LiBr. After doping with 4wt% LiBr, the room temperature ionic conductivity of the polymer solid electrolyte 30% PEO / 70% PVP can reach 1.59×10 -6 S / cm, see Sundaramahalingam K, Vanitha D, Nallamuthu N, et al. Electrical properties of lithium bromide poly ethylene oxide / poly vinyl pyrrolidone polymer blend electrolyte [J]. Physica B: Condensed Matter, 2019, 553: 120-126. Wang Cui et al. prepared an N-vinyl pyrrolidone-sodium styrene sulfonate copolymer gel electrolyte, using N-vinyl pyrrolidone and sodium styrene sulfonate as raw materials, N, N-methylenebisacrylamide as a crosslinker, and azobisisobutyronitrile as an initiator, and prepared a copolymer P (NVP-co-SSS) gel electrolyte by free radical aqueous solution polymerization, see "Synthesis and Performance Study of N-vinyl pyrrolidone-sodium styrene sulfonate copolymer gel electrolyte". However, the research on copolymer electrolytes based on N-vinyl pyrrolidone is relatively small. The present invention studies a copolymer electrolyte based on N-vinyl pyrrolidone and a preparation method thereof, which is of great significance to improve the ionic conductivity of the copolymer electrolyte. Summary of the invention

[0004] The object of the present invention is to provide a copolymer electrolyte based on N-vinyl pyrrolidone and a preparation method thereof, so as to solve the problem of low ionic conductivity of the polymer electrolyte based on N-vinyl pyrrolidone in the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a copolymer electrolyte based on N-vinyl pyrrolidone, comprising the following steps:

[0007] (1) mixing N-vinyl pyrrolidone, lithium salt, bis(vinyl sulfone)methane and a plasticizer to obtain an intermediate mixture;

[0008] (2) Adding an initiator to the intermediate mixture to carry out a polymerization reaction to obtain a copolymer based on N-vinyl pyrrolidone.

[0009] Preferably, in step (1), the mass ratio of N-vinyl pyrrolidone, lithium salt and bis(vinyl sulfone)methane is 40-60:15-25:3-8.

[0010] Preferably, in step (1), the mass of the plasticizer accounts for 1 to 3% of the mass of N-vinyl pyrrolidone.

[0011] Preferably, in step (1), the lithium salt comprises lithium difluorooxalatoborate, lithium bis(difluorosulfonyl)imide or lithium tetrafluoroborate.

[0012] Preferably, the plasticizer comprises ethylene carbonate, dimethyl carbonate, ethyl acetate or triethyl glycerol.

[0013] Preferably, the mass of the initiator accounts for 0.5-2% of the mass of N-vinyl pyrrolidone; the initiator comprises one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

[0014] Preferably, in step (2), the polymerization reaction temperature is 70 to 90° C., and the polymerization reaction time is 4 to 8 hours.

[0015] The present invention also provides a copolymer electrolyte based on N-vinyl pyrrolidone prepared by the above-mentioned method for preparing the copolymer electrolyte based on N-vinyl pyrrolidone.

[0016] Beneficial effects of the present invention:

[0017] The present invention introduces bis(vinylsulfone)methane into the N-vinylpyrrolidone reaction system to prepare a copolymer electrolyte based on N-vinylpyrrolidone with higher ion conductivity. DETAILED DESCRIPTION

[0018] The present invention provides a method for preparing a copolymer electrolyte based on N-vinyl pyrrolidone, comprising the following steps:

[0019] (1) mixing N-vinyl pyrrolidone, lithium salt, bis(vinyl sulfone)methane and a plasticizer to obtain an intermediate mixture;

[0020] (2) Adding an initiator to the intermediate mixture to carry out a polymerization reaction to obtain a copolymer based on N-vinyl pyrrolidone.

[0021] In the present invention, in the step (1), the mass ratio of N-vinyl pyrrolidone, lithium salt and bis(vinyl sulfone)methane is 40-60:15-25:3-8, preferably 45-55:16-22:5-7, and more preferably 50:18-20:6.

[0022] In the present invention, in the step (1), the mass of the plasticizer accounts for 1 to 3% of the mass of N-vinyl pyrrolidone, preferably 1.5 to 2.5%, and more preferably 2%.

[0023] In the present invention, in step (1), the lithium salt comprises lithium difluorooxalatoborate, lithium bis(difluorosulfonyl)imide or lithium tetrafluoroborate, preferably lithium difluorooxalatoborate.

[0024] In the present invention, the plasticizer comprises ethylene carbonate, dimethyl carbonate, ethyl acetate or triethyl glycerol.

[0025] In the present invention, the mass of the initiator accounts for 0.5-2% of the mass of N-vinyl pyrrolidone, preferably 0.8-1.6%, and more preferably 1.0-1.4%; the initiator comprises one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate, preferably azobisisobutyronitrile.

[0026] In the present invention, in the step (2), the polymerization reaction temperature is 70 to 90° C., preferably 75 to 85° C., and more preferably 80° C.; the polymerization reaction time is 4 to 8 hours, preferably 5 to 7 hours, and more preferably 6 hours.

[0027] The present invention also provides a copolymer electrolyte based on N-vinyl pyrrolidone prepared by the above-mentioned method for preparing the copolymer electrolyte based on N-vinyl pyrrolidone.

[0028] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0029] Example 1

[0030] 0.5 g of N-vinyl pyrrolidone, 0.01 g of dimethyl carbonate and 0.05 g of bis(vinylsulfone)methane were weighed and placed in a flask, heated to 40° C. and stirred to dissolve, and then 0.2 g of lithium difluorooxalatoborate was added and stirred to obtain an intermediate mixture.

[0031] Under nitrogen protection, the intermediate mixture was heated to 80°C, 0.005 g of azobisisobutyronitrile was added, and polymerization was carried out at 80°C for 6 hours. After the reaction, the reaction product was placed in a vacuum drying oven and dried at 50°C for 20 hours to obtain a copolymer electrolyte based on N-vinyl pyrrolidone.

[0032] Example 2

[0033] 0.6 g of N-vinyl pyrrolidone, 0.018 g of glycerol triethyl ester and 0.08 g of bis(vinyl sulfone)methane were weighed and placed in a flask, heated to 40° C. and stirred to dissolve, and then 0.25 g of lithium difluorooxalatoborate was added and stirred to obtain an intermediate mixture.

[0034] Under nitrogen protection, the intermediate mixture was heated to 70°C, 0.018 g of azobisisoheptanonitrile was added, and polymerization was carried out at 70°C for 4 hours. After the reaction, the reaction product was placed in a vacuum drying oven and dried at 50°C for 20 hours to obtain a copolymer electrolyte based on N-vinyl pyrrolidone.

[0035] Example 3

[0036] 0.4 g of N-vinyl pyrrolidone, 0.004 g of ethyl acetate and 0.03 g of bis(vinylsulfone)methane were weighed and placed in a flask, heated to 40° C. and stirred to dissolve, and then 0.15 g of lithium tetrafluoroborate was added and stirred to obtain an intermediate mixture.

[0037] Under nitrogen protection, the intermediate mixture was heated to 90°C, 0.004 g of azobisisobutyronitrile was added, and polymerization was carried out at 90°C for 8 hours. After the reaction, the reaction product was placed in a vacuum drying oven and dried at 50°C for 20 hours to obtain a copolymer electrolyte based on N-vinyl pyrrolidone.

[0038] Comparative Example 1

[0039] The difference from Example 1 is that bis(vinyl sulfone)methane is not added, and other conditions are the same.

[0040] Comparative Example 2

[0041] The difference from Example 2 is that the added amount of bis(vinylsulfone)methane is 0.1 g, and other conditions are the same.

[0042] Comparative Example 3

[0043] The difference from Example 3 is that the added amount of bis(vinylsulfone)methane is 0.01 g, and other conditions are the same.

[0044] Comparative Example 4

[0045] The difference from Example 1 is that the polymerization reaction temperature is 100° C., and other conditions are the same.

[0046] Comparative Example 5

[0047] The difference from Example 1 is that the polymerization reaction temperature is 60° C., and other conditions are the same.

[0048] Performance Verification

[0049] The electrochemical performance of the N-vinyl pyrrolidone-based copolymer electrolytes prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was verified:

[0050] 120 mg of the copolymer electrolyte was weighed and mixed with 1000 μL of anhydrous tetrahydrofuran, stirred evenly by magnetic force, then cast on a polytetrafluoroethylene plate, and placed in a glove box to dry naturally to obtain a polymer electrolyte membrane with a thickness of 0.2 mm.

[0051] The polymer electrolyte membrane was placed in a glove box and dried at 70°C for 8 hours to completely remove the solvent, and then the battery was assembled in the order of negative electrode shell, stainless steel sheet negative electrode, polymer electrolyte membrane, gasket, stainless steel sheet positive electrode, spring, and positive electrode shell, and sealed using a packaging machine, and the ionic conductivity of the electrolyte membrane was tested. The test results are shown in Table 1:

[0052] Table 1 Measurement results of ionic conductivity of electrolyte membrane

[0053] serial number Ionic conductivity (mS / cm) Example 1 0.568 Example 2 0.515 Example 3 0.486 Comparative Example 1 0.089 Comparative Example 2 0.324 Comparative Example 3 0.212 Comparative Example 4 0.413 Comparative Example 5 0.398

[0054] As can be seen from Table 1, the present invention uses bis(vinylsulfone)methane as one of the monomers and adds it to the N-vinylpyrrolidone reaction system. The prepared copolymer electrolyte based on N-vinylpyrrolidone has higher ionic conductivity, and the addition amount of bis(vinylsulfone)methane needs to be controlled within a suitable range. In addition, the temperature of the polymerization reaction also affects the ionic conductivity of the polymer electrolyte. The ionic conductivity of the copolymer electrolyte based on N-vinylpyrrolidone can reach 0.568mS / cm.

[0055] As can be seen from the above embodiments, the present invention provides a copolymer electrolyte based on N-vinyl pyrrolidone and a preparation method thereof, which belongs to the technical field of lithium ion batteries. The present invention first mixes N-vinyl pyrrolidone, lithium salt, bis(vinyl sulfone) methane and a plasticizer to obtain an intermediate mixture; then an initiator is added to the intermediate mixture for polymerization reaction to obtain a copolymer based on N-vinyl pyrrolidone. The present invention introduces bis(vinyl sulfone) methane into the N-vinyl pyrrolidone reaction system, and the prepared N-vinyl pyrrolidone-based copolymer electrolyte has higher ionic conductivity.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a copolymer electrolyte based on N-vinyl pyrrolidone, characterized in that: The steps include: (1) mixing N-vinyl pyrrolidone, lithium salt, bis(vinyl sulfone)methane and a plasticizer to obtain an intermediate mixture; (2) Adding an initiator to the intermediate mixture to carry out a polymerization reaction to obtain a copolymer based on N-vinyl pyrrolidone.

2. The method for preparing the copolymer electrolyte based on N-vinyl pyrrolidone according to claim 1, characterized in that: In the step (1), the mass ratio of N-vinyl pyrrolidone, lithium salt and bis(vinyl sulfone)methane is 40-60:15-25:3-8.

3. The method for preparing the copolymer electrolyte based on N-vinyl pyrrolidone according to claim 2, characterized in that: In the step (1), the mass of the plasticizer accounts for 1 to 3% of the mass of N-vinyl pyrrolidone.

4. The method for preparing a copolymer electrolyte based on N-vinyl pyrrolidone according to any one of claims 1 to 3, characterized in that: In the step (1), the lithium salt comprises lithium difluorooxalatoborate, lithium bis(difluorosulfonyl)imide or lithium tetrafluoroborate.

5. The method for preparing the copolymer electrolyte based on N-vinyl pyrrolidone according to claim 4, characterized in that: The plasticizer comprises ethylene carbonate, dimethyl carbonate, ethyl acetate or triethyl glycerol.

6. The method for preparing a copolymer electrolyte based on N-vinyl pyrrolidone according to claim 2, 3 or 5, characterized in that: The mass of the initiator accounts for 0.5-2% of the mass of N-vinyl pyrrolidone; the initiator comprises one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

7. The method for preparing the copolymer electrolyte based on N-vinyl pyrrolidone according to claim 6, characterized in that: In the step (2), the polymerization reaction temperature is 70 to 90° C., and the polymerization reaction time is 4 to 8 hours. 8 . The N-vinyl pyrrolidone-based copolymer electrolyte prepared by the method for preparing the N-vinyl pyrrolidone-based copolymer electrolyte according to any one of claims 1 to 7 .