A method for preparing a single-ion conducting gel polymer electrolyte membrane

Abstract

This invention provides a method for preparing a single-ion conductive gel polymer electrolyte membrane, comprising the following steps: S1: Adding P(VDF-co-MAF) and a certain mass of boric acid to a dehydrated N,N-dimethylformamide solution, under N2 protection, and magnetically stirring for 4 hours, then adding lithium carbonate and oxalic acid, and continuing stirring for another 4 hours to form a homogeneous solution; adding P(VDF-co-HFP) to the above solution, and continuing stirring to form a homogeneous solution; S2: Using a wet membrane forming device, uniformly coating the homogeneous slurry obtained in step S2 onto a clean glass plate, immediately immersing it in deionized water for 24 hours, and then drying it in an oven at 40°C. This invention uses P(VDF-co-MAF) as the matrix and forms a single-ion conductive gel polymer electrolyte through oxalization. By crosslinking boron and oxalic acid, a boron-centered oxalized single-ion conductive polymer network is formed, which increases the lithium-ion transference number, reduces concentration polarization, promotes uniform deposition of lithium ions at the interface, inhibits the generation of lithium dendrites during cycling, and improves cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte membrane technology and relates to a method for preparing a single-ion conductive gel polymer electrolyte membrane. Background Technology

[0002] With the continuous development of industrial technology and the increasing scarcity of non-renewable resources, lithium batteries with rechargeable and re-discharge capabilities have gained widespread attention. Lithium batteries are widely used in mobile phones, electric vehicles, and other fields due to their small size, high energy density, lack of memory effect, ability to be charged and discharged at any time, and environmental friendliness.

[0003] The core technology of polymer lithium batteries lies in the preparation of high-performance polymer electrolyte membranes. Polymer electrolytes are mainly divided into pure solid polymer electrolytes and gel polymer electrolytes. The former has too low conductivity at room temperature, which cannot meet the requirements of actual production. Gel polymer electrolytes are a type of polymer electrolyte that is between solid and liquid, similar to gel properties. They have high room temperature ionic conductivity, which can basically meet the needs of actual production. However, their mechanical strength is low, making it difficult to suppress dendrite growth, which affects subsequent performance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a single-ion conductive gel polymer electrolyte membrane to solve the problems mentioned in the background art.

[0005] The objective of this invention can be achieved through the following technical solution: A method for preparing a single-ion conductive gel polymer electrolyte membrane, comprising the following steps:

[0006] S1: Add P(VDF-co-MAF) and a certain mass of boric acid to the dehydrated N,N-dimethylformamide solution, protect with N2, stir magnetically for 4 hours, then add lithium carbonate and oxalic acid, continue stirring for 4 hours to form a homogeneous solution; add P(VDF-co-HFP) to the above solution, continue stirring to form a homogeneous solution;

[0007] S2: Using a wet film forming machine, the uniform slurry obtained in step S2 is evenly coated onto a clean glass plate, immediately immersed in deionized water for 24 hours, and then dried in an oven at 40°C to obtain a polymer electrolyte membrane.

[0008] S3: Immerse the prepared polymer electrolyte membrane in the electrolyte to obtain a gel-state polymer electrolyte membrane, with different ratios of M0, M10, M20, M30, M40, and M45 respectively;

[0009] S4: Immerse the prepared polymer electrolyte membrane in the electrolyte to obtain a gel-state polymer electrolyte membrane;

[0010] Electrolyte preparation: 1M lithium difluorooxalate borate / EC:DMC, wherein the volume ratio of EC:DMC is 1:1.

[0011] In the above-mentioned method for preparing a single-ion conductive gel polymer electrolyte membrane, in step S3, the numbers M0, M10, M20, M30, M40, and M45 represent the mass ratio of P(VDF-co-MAF) in P(VDF-co-MAF) and P(VDF-co-HFP).

[0012] Compared with existing technologies, the advantages of the single-ion conductive gel polymer electrolyte membrane preparation method of this invention are as follows: The single-ion conductive gel polymer electrolyte, formed by oxalization of P(VDF-co-MAF) as the matrix, forms a boron-centered oxalicized single-ion conductive polymer network through crosslinking of boron and oxalic acid. This significantly increases the lithium-ion transference number, reduces concentration polarization, promotes uniform lithium-ion deposition at the interface, suppresses lithium dendrite formation during cycling, and improves cycle stability. Furthermore, by blending P(VDF-co-HFP), the mechanical strength of the electrolyte membrane can be significantly improved without changing the ionic conductivity. Compared with previous single-ion conductive gel polymer electrolytes based on P(VDF-co-MAF), the conductivity of this polymer is increased by an order of magnitude, and the strain is also significantly increased, better meeting the needs of actual production. Attached Figure Description

[0013] Figure 1 This is a synthesis diagram of the LiP(VDF-co-MAF)B oxalate-modified single-ion conductive gel polymer electrolyte membrane of the present invention.

[0014] Figure 2 This is an infrared image of the electrolyte membranes oxalated with different proportions of LiP(VDF-co-MAF)B according to the present invention.

[0015] Figure 3 This is a conductivity diagram of the present invention at different proportions and temperatures.

[0016] Figure 4 These are stress-strain curves of different proportions in this invention. Detailed Implementation

[0017] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0018] like Figure 1 , Figure 2 , Figure 3 and Figure 4As shown, the present invention discloses a method for preparing a single-ion conductive gel polymer electrolyte membrane, comprising the following steps:

[0019] S1: Add P(VDF-co-MAF) and a certain mass of boric acid to the dehydrated N,N-dimethylformamide solution, protect with N2, stir magnetically for 4 hours, then add lithium carbonate and oxalic acid, continue stirring for 4 hours to form a homogeneous solution; add P(VDF-co-HFP) to the above solution, continue stirring to form a homogeneous solution;

[0020] S2: Using a wet film forming machine, the uniform slurry obtained in step S2 is evenly coated onto a clean glass plate, immediately immersed in deionized water for 24 hours, and then dried in an oven at 40°C to obtain a polymer electrolyte membrane.

[0021] S3: Immerse the prepared polymer electrolyte membrane in the electrolyte to obtain a gel-state polymer electrolyte membrane, with different ratios of M0, M10, M20, M30, M40, and M45 respectively;

[0022] S4: Immerse the prepared polymer electrolyte membrane in the electrolyte to obtain a gel-state polymer electrolyte membrane;

[0023] Wherein: Electrolyte preparation: 1M lithium difluorooxalate borate / EC:DMC, wherein the volume ratio of EC:DMC is 1:1; In step S3, the numbers M0, M10, M20, M30, M40, and M45 represent the mass ratio of P(VDF-co-MAF) in P(VDF-co-MAF) and P(VDF-co-HFP).

[0024] like Figure 2 As shown, from Figure 2 As can be seen, the absorption peaks at 1406 cm⁻¹ and 1174 cm⁻¹ correspond to the stretching vibrations of -CH₂ and -CF₂ in P(VDF-co-HFP). The absorption peak at 1720 cm⁻¹ corresponds to the stretching vibration of the C=O bond in the ester group, the peak at 1658 cm⁻¹ to the antisymmetric stretching vibration of the C=OO bond in the ester group, the anti-stretching vibration of the BO bond at 1336 cm⁻¹, and the stretching vibration of the BOC bond at 1079 cm⁻¹. All of these indicate that a single-ion conductive polymer gel electrolyte centered on B was successfully prepared.

[0025] like Figure 3 As shown, from Figure 3 As can be seen, the conductivity increases continuously with increasing temperature. At room temperature, compared to M0, the conductivity of M40 is increased by two orders of magnitude, reaching 1.74*10-3 S / cm3, which can well meet the conductivity requirements of gel electrolytes at room temperature.

[0026] like Figure 4 As shown, from Figure 4 As can be seen, by introducing the oxalic acid-crosslinked polymer LiP(VDF-co-MAF)B, the strain of the membrane is improved while the flexibility is well maintained. As a result, after the battery is assembled, it has good compatibility with the electrode and can effectively prevent lithium dendrite penetration, thereby improving cycle stability and extending battery life.

[0027] This invention relates to a single-ion conductive gel polymer electrolyte formed by oxalization of P(VDF-co-MAF) as a matrix. Through crosslinking of boron and oxalic acid, a boron-centered oxalicized single-ion conductive polymer network is formed, which significantly increases the lithium-ion transference number, reduces concentration polarization, promotes uniform lithium-ion deposition at the interface, suppresses lithium dendrite formation during cycling, and improves cycle stability. Furthermore, by blending P(VDF-co-HFP), the mechanical strength of the electrolyte membrane can be significantly improved without altering the ionic conductivity. Compared to previous single-ion conductive gel polymer electrolytes based on P(VDF-co-MAF), the conductivity of this polymer is increased by an order of magnitude, and the strain is also significantly increased, better meeting the needs of practical production.

[0028] Contents not described in detail herein are existing technologies known to those skilled in the art. The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a single-ion conducting gel polymer electrolyte film, characterized by, Comprising the following steps: S1: adding P(VDF-co-MAF) and a certain mass of boric acid to the dehydrated N,N-dimethylformamide solution, N2 protection, magnetic stirring for 4 hours, then adding lithium carbonate and oxalic acid, continuing to stir for 4 hours to form a uniform solution; adding P(VDF-co-HFP) to the above solution and continuing to stir to form a uniform solution; S2: using a wet film maker to uniformly scrape the uniform slurry obtained in step S1 on a clean glass plate, immediately immersing in deionized water for 24 hours, and then drying in an oven at 40℃ to obtain a polymer electrolyte film; S3: immersing the prepared polymer electrolyte film in an electrolyte to obtain a gel polymer electrolyte film, corresponding to different proportions, respectively M10, M20, M30, M40, M45; The electrolyte is prepared: 1M lithium difluoro(oxalato)borate / EC:DMC, wherein the volume ratio of EC:DMC is =1:1; In the step S3, the numbers M10, M20, M30, M40, M45 are the mass ratios of P(VDF-co-MAF) in P(VDF-co-MAF) and P(VDF-co-HFP).

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