Modified polypropylene diaphragm as well as preparation method and application thereof
By corona treatment on the polypropylene separator and multiple immersions in a specific solution, the CMC-Na/CS layer is formed, which solves the problem that the polyolefin separator is difficult to be wet and filled by the electrolyte, improves the electrolyte liquid absorbance, thermal stability and electrochemical properties of the separator, and enhances the cycling performance and safety of the battery.
Patent Information
- Application Number
- CN202411840215.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-13
- Publication Date
- 2025-03-21
AI Technical Summary
The polyolefin separator has a poor ability to absorb and retain the electrolyte due to the lack of polar groups in the main chain of the molecular, high crystallinity and low surface energy, making it difficult to be wet and filled by the electrolyte with high polarity, resulting in poor ability to absorb and retain the electrolyte, reducing the ability to ion migration. At the same time, the thermal stability is poor, which will cause the separator to shrink severely after the battery operating temperature rises, posing a safety hazard.
The polypropylene separator was treated by corona and soaked and washed multiple times in chitosan and sodium carboxymethylcellulose solution to form a CMC-Na/CS layer, enhancing the surface hydrophilicity and hierarchy of the separator, thereby improving the wetting and thermal stability of the electrolyte.
The electrolyte absorbance, thermal stability and electrochemical properties of the diaphragm are improved, the circulation performance and safety of the battery are enhanced, and the risk of severe shrinkage of the diaphragm at high temperatures is avoided.
Smart Images
Figure CN119674435A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of diaphragms, and in particular to a modified polypropylene diaphragm and a preparation method and application thereof. Background Art
[0002] Polyolefin separators have become the most widely used separator material in the field of lithium-ion batteries due to their low cost, good mechanical strength, electrochemical stability and other excellent properties. However, due to the lack of polar groups in the main chain of the molecule, high crystallinity and low surface energy, polyolefin separators are difficult to be wetted and filled with highly polar electrolytes, resulting in poor ability of the separator to absorb and retain electrolytes, and reduced ion migration capacity. In addition, the poor thermal stability of polyolefin separators will cause the separator to shrink severely after the battery operating temperature rises, posing a safety hazard. Summary of the invention
[0003] The purpose of the present invention is to address the above-mentioned deficiencies of the prior art and to provide a modified polypropylene diaphragm and its preparation method and application, thereby improving the electrolyte absorption rate, thermal stability, and electrochemical properties of the diaphragm.
[0004] A method for preparing a modified polypropylene diaphragm of the present invention comprises the following steps:
[0005] S1, corona treated polypropylene diaphragm;
[0006] S2, soaking the corona-treated polypropylene diaphragm in a chitosan solution and then washing it, and then soaking it in a sodium carboxymethylcellulose solution and then washing it;
[0007] S3, repeating the operation of step S2 5-20 times and then drying to obtain a modified polypropylene diaphragm.
[0008] Furthermore, the concentration of the chitosan solution is 0.1-0.5 wt %.
[0009] Furthermore, the concentration of the sodium carboxymethylcellulose solution is 1-5wt%.
[0010] Furthermore, the power of the corona treatment is 10-60W, the distance from the polypropylene diaphragm is 5mm, and the duration is 1-10min.
[0011] Further, the corona-treated polypropylene separator was cleaned with anhydrous ethanol and then dried.
[0012] Furthermore, the corona-treated polypropylene membrane is immersed in a 0.1-0.5 wt % chitosan solution for 1-10 min.
[0013] Furthermore, in step S2, the substrate is washed with deionized water for 1-10 minutes.
[0014] Further, soaking in a 1-5wt% sodium carboxymethyl cellulose solution for 1-5 minutes.
[0015] A modified polypropylene diaphragm prepared by the above preparation method.
[0016] An application of the modified polypropylene separator as described above is used as a lithium ion battery separator.
[0017] The invention provides a modified polypropylene diaphragm with excellent performance. The introduction of CMC-Na / CS on the surface of the diaphragm enables the modified diaphragm to exhibit better electrolyte wettability and thermal stability.
[0018] The modified polypropylene separator prepared by the present invention exhibits higher capacity retention rate and higher ion conductivity during the entire cycle process of assembling the battery.
[0019] The modified polypropylene diaphragm prepared by the present invention has only organic components. The advantage of having only organic components is that the polyelectrolytes can be more closely combined together, there will be no compatibility problem of inorganic / organic phases, the preparation process is simpler, and fewer factors need to be controlled. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1a is the wettability of the modified polypropylene separator of Example 1 to the electrolyte;
[0021] Figure 1b is the wettability of the unmodified polypropylene separator to the electrolyte;
[0022] Figure 2a is a SEM image of the modified polypropylene separator of implementation case 1;
[0023] Figure 2b is the SEM image of the unmodified polypropylene diaphragm;
[0024] Figure 3a This is a heat shrinkage picture of the modified polypropylene diaphragm of implementation case 2;
[0025] Figure 3b It is a heat shrink picture of unmodified polypropylene diaphragm;
[0026] Figure 4 The electrochemical cycle performance of the modified polypropylene diaphragm of implementation case 3, the polypropylene diaphragm only subjected to corona treatment, and the unmodified polypropylene diaphragm are compared;
[0027] Figure 5 This is a comparison of the AC impedance spectra of the modified polypropylene diaphragm of implementation case 3, the polypropylene diaphragm that has only been corona treated, and the unmodified polypropylene diaphragm. DETAILED DESCRIPTION
[0028] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.
[0029] A method for preparing a modified polypropylene diaphragm of the present invention is as follows:
[0030] The surface of the polyolefin diaphragm is treated by corona oxidation to enhance its surface hydrophilicity, facilitating further modification through layer-by-layer self-assembly.
[0031] The power of the corona machine is 10-60W, the distance between the sample and the corona machine is 5mm, and the treatment time of the PP separator is 1-10min.
[0032] The corona-treated diaphragm was cleaned and dried with anhydrous ethanol, and placed in a vacuum drying oven at 60°C for 24 h.
[0033] The corona treated polypropylene diaphragm is immersed in a 0.1-0.5wt% CS solution for 1-10 minutes, then rinsed in deionized water for 3 minutes. Then, it is immersed in a 1-5wt% CMC-Na solution for 3 minutes, and rinsed with deionized water for 1-10 minutes. The above process is one cycle.
[0034] The modified polypropylene diaphragm is prepared through 5-20 cycles and placed in a vacuum drying oven for thorough drying to obtain a modified polypropylene diaphragm with improved properties.
[0035] Table 1 shows the process parameters for preparing modified polypropylene diaphragms using the above method in various embodiments.
[0036] Table 1
[0037]
[0038]
[0039] Table 2
[0040]
[0041] Table 2 shows the performance test results of the modified polypropylene diaphragms prepared in Examples 1-6 and the unmodified polypropylene diaphragms. From the above data, it can be seen that the modified polypropylene diaphragms prepared in the present invention have better wettability, smaller heat shrinkage rate and smaller contact angle.
[0042] Figure 1a is the wettability of the modified polypropylene separator of Example 1 to the electrolyte; Figure 1b is the wettability of the unmodified polypropylene separator to the electrolyte; Figure 1a and 1b It can be seen that the modified polypropylene separator of Example 1 has better wettability to the electrolyte.
[0043] Figure 2a is a SEM image of the modified polypropylene separator of implementation case 1; Figure 2b is the SEM image of the unmodified polypropylene diaphragm; Figure 2a and 2b It can be seen that the surface of the modified polypropylene separator is covered with a rough and uniform self-assembled layer, thereby increasing the contact area between the separator and the electrolyte.
[0044] Figure 3a This is a heat shrinkage picture of the modified polypropylene diaphragm of implementation case 2; Figure 3b This is a heat shrink image of unmodified polypropylene diaphragm; Figure 3a and 3b It can be seen that the thermal shrinkage rate of the modified polypropylene diaphragm of Implementation Example 2 is smaller.
[0045] Figure 4 The electrochemical cycle performance of the modified polypropylene diaphragm of implementation case 3, the polypropylene diaphragm with only corona treatment, and the unmodified polypropylene diaphragm is compared. Figure 4 It can be seen that the modified polypropylene diaphragm of implementation case 3 has better electrochemical cycle performance.
[0046] Figure 5 This is a comparison of the AC impedance spectra of the modified polypropylene diaphragm of implementation case 3, the polypropylene diaphragm that has only been corona treated, and the unmodified polypropylene diaphragm. It can be seen from the figure that the ohmic resistance and charge transfer resistance of the diaphragm after layer-by-layer self-assembly modification are significantly reduced.
[0047] For matters not mentioned above, the prior art applies.
[0048] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for preparing a modified polypropylene diaphragm, characterized in that: The steps include: S1, corona treated polypropylene diaphragm; S2, soaking the corona-treated polypropylene diaphragm in a chitosan solution and then washing it, and then soaking it in a sodium carboxymethylcellulose solution and then washing it; S3, repeating the operation of step S2 5-20 times and then drying to obtain a modified polypropylene diaphragm.
2. The preparation method according to claim 1, characterized in that: The concentration of the chitosan solution is 0.1-0.5 wt%.
3. The preparation method according to claim 1, characterized in that: The concentration of the sodium carboxymethylcellulose solution is 1-5 wt %.
4. The preparation method according to claim 1, characterized in that: The power of corona treatment is 10-60W, the distance from the polypropylene diaphragm is 5mm, and the duration is 1-10min.
5. The preparation method according to claim 1, characterized in that: The corona-treated polypropylene diaphragm was cleaned with anhydrous ethanol and then dried.
6. The preparation method according to claim 1, characterized in that: The corona-treated polypropylene diaphragm is immersed in a 0.1-0.5 wt % chitosan solution for 1-10 min.
7. The preparation method according to claim 1, characterized in that: In step S2, the sample is washed in deionized water for 1-10 minutes.
8. The preparation method according to claim 1, characterized in that: Soak in 1-5wt% sodium carboxymethyl cellulose solution for 1-5 minutes.
9. A modified polypropylene diaphragm prepared by the preparation method according to any one of claims 1 to 8.
10. An application of the modified polypropylene diaphragm according to claim 9, characterized in that: Used as lithium-ion battery separator.