Gel-state battery separator and preparation method thereof, lithium-sulfur battery

Abstract

The application discloses a gel-state battery diaphragm and a preparation method thereof and a lithium-sulfur battery, wherein the gel-state battery diaphragm comprises a base film and a gel layer, the gel layer is coated on the base film, and the material of the gel layer is a polyethylene oxide-urea gel. The method for preparing the gel-state battery diaphragm comprises the following steps: mixing and stirring a polyethylene oxide solution and a urea solution, carrying out a bonding reaction, preparing a polyethylene oxide-urea solution, coating the polyethylene oxide-urea solution on a base film, drying, and forming a gel layer; and preparing the gel-state battery diaphragm. According to the application, the hydroxyl groups in the polyethylene oxide and the amino groups in the urea are bonded to each other in the gel layer to form a hydrogen bond complex, the hydrogen bond makes the structure of the gel layer more stable, thereby inhibiting the "shuttle effect" of polysulfides in the lithium-sulfur battery, the cycle stability of the battery is improved, and the complex is swollen in the electrolyte to form a gel-state battery diaphragm, thereby improving the liquid absorption rate and the liquid retention rate of the battery diaphragm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium-sulfur batteries, in particular to a gel-state battery separator, a preparation method thereof and a lithium-sulfur battery. BACKGROUND

[0002] Due to the low price, wide source and environmental friendliness of the positive active material (elemental sulfur) of the lithium-sulfur battery, the lithium-sulfur battery has become one of the most promising energy storage systems after the lithium-ion battery. The main structure of the lithium-sulfur battery includes a positive electrode using elemental sulfur, a negative electrode using metal lithium, an electrolyte and a separator. The positive electrode mainly includes active material sulfur, conductive additive, binder and current collector, and the active material sulfur, conductive additive and binder are uniformly coated on the current collector. However, as the positive active material of the lithium-sulfur battery, sulfur has very low conductivity, with a conductivity of 5*10-30 S / cm at 25℃, which reduces the utilization rate of the active material sulfur, and makes the lithium-sulfur battery have low cycle performance, poor electrochemical reversibility and fast capacity decay.

[0003] Chinese patent CN103840199A discloses a preparation method of a PEO-based gel polymer electrolyte film. The method uses PEO (polyethylene oxide), an organic solvent and a pore-forming agent as raw materials to prepare the PEO-based gel polymer electrolyte film. However, the stability of this film is poor, and it is only suitable for use in lithium batteries. Due to the "shuttle effect" in lithium-sulfur batteries, the unstable gel structure can easily cause polysulfides to pass from the positive electrode to the negative electrode through the gel material, thereby causing rapid capacity decay. In addition, referring to Figure 1 , Figure 1 The picture shows that part of the polyethylene oxide film is swelled and then dissolved. The pure PEO film is soaked in the electrolyte of the lithium-sulfur battery, and the phenomenon of swelling and then dissolving occurs, which leads to low liquid absorption rate of the lithium-sulfur battery. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a gel-state battery separator, a preparation method thereof and a lithium-sulfur battery.

[0005] The gel-state battery separator disclosed by the present application comprises a base film and a gel layer, the gel layer is coated on the base film, and the material of the gel layer is polyethylene oxide-urea gel.

[0006] A method for preparing the gel-state battery separator described above comprises the following steps:

[0007] The polyethylene oxide solution and the urea solution are mixed and stirred to perform a bonding reaction, and a polyethylene oxide-urea solution is prepared. The bonding reaction is shown in the following formula (I):

[0008]

[0009] coating the polyethylene oxide-urea solution on the base film, drying to form a gel layer;

[0010] The gel-state battery separator is prepared.

[0011] According to an embodiment of the present application, the mass ratio of polyethylene oxide to urea in the polyethylene oxide-urea solution is 1:(0.2-1.75).

[0012] According to an embodiment of the present application, before the step of mixing and stirring the polyethylene oxide solution and the urea solution, the method further comprises the following steps:

[0013] The polyethylene oxide solution is prepared.

[0014] According to an embodiment of the present application, the preparation of the polyethylene oxide solution comprises the following sub-steps:

[0015] 2g of polyethylene oxide is weighed, and 98mL of deionized water is measured;

[0016] The polyethylene oxide is mixed with the deionized water and stirred until completely dissolved;

[0017] The polyethylene oxide solution is obtained.

[0018] According to an embodiment of the present application, before the step of mixing and stirring the polyethylene oxide solution and the urea solution, the method further comprises the following steps:

[0019] The urea solution is prepared.

[0020] According to an embodiment of the present application, the preparation of the polyethylene oxide solution comprises the following sub-steps:

[0021] 2g of urea is weighed, and 8mL of deionized water is measured;

[0022] The urea is mixed with the deionized water;

[0023] The urea solution is obtained.

[0024] According to an embodiment of the present application, in the step of coating the polyethylene oxide-urea solution on the base film, drying, the drying time is 2-4h, and the drying temperature is 50-70℃.

[0025] According to an embodiment of the present application, in the step of preparing the gel-state battery separator, the thickness of the gel-state battery separator is 23-28μm.

[0026] A lithium-sulfur battery comprises a positive electrode, a negative electrode, an electrolyte, and the gel-state battery separator described above.

[0027] The application has the beneficial effects that the hydroxyl in the polyethylene oxide and the amino in the urea in the gel layer are bonded to each other to form a hydrogen bond complex, the hydrogen bond makes the structure of the gel layer more stable, thereby inhibiting the "shuttle effect" of the polysulfide in the lithium-sulfur battery, improving the cycle stability of the battery, and the complex swells in the electrolyte to form a gel-state battery separator, thereby improving the liquid absorption rate and liquid retention rate of the battery separator to store more lithium ions, improving the battery capacity, and the gel-state battery separator has good polysulfide adsorption, which can also effectively inhibit the shuttle of the polysulfide. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings described herein are used to provide further understanding of the application, and form a part of the application. The illustrative embodiments of the application and their descriptions serve to explain the application, and do not constitute an improper limitation on the application. In the drawings:

[0029] Figure 1 Picture of the polyethylene oxide film after swelling and partial dissolution;

[0030] Figure 2 Structure diagram of the gel-state battery separator in the embodiment;

[0031] Figure 3 Flowchart of the preparation method of the gel-state battery separator in the embodiment;

[0032] Figure 4 Capacity cycle diagram of the lithium-sulfur battery prepared by the gel-state battery separators A2, A4 and A6;

[0033] Figure 5 Capacity cycle diagram of the lithium-sulfur battery prepared by the gel-state battery separator A4 and the battery separator D1. DETAILED DESCRIPTION

[0034] The following will disclose multiple embodiments of the application by means of drawings. Many practical details will be described in the following description for the purpose of clear illustration. However, it should be understood that these practical details should not be used to limit the application. That is, in some embodiments of the application, these practical details are unnecessary. In addition, for the purpose of simplifying the drawings, some conventional structures and components will be shown in a simple schematic manner in the drawings.

[0035] It should be noted that all directional indications such as up, down, left, right, front, back, etc. in the embodiments of the application are used only to explain the relative positional relationship, movement condition, etc. between the components in a certain specific posture such as shown in the drawings, and if the specific posture changes, the directional indications will also change accordingly.

[0036] In addition, the descriptions such as "first", "second" and the like in the present application are only for the purpose of description, and are not intended to particularly indicate the order or sequence, nor to limit the present application, which are merely for distinguishing the components or operations described by the same technical terms, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, and when the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist, nor within the protection scope required by the present application.

[0037] Embodiment one

[0038] Referring to Figure 2 , Figure 2 The structure diagram of the gel-state battery separator in the embodiment. The gel-state battery separator in the embodiment includes a base film 1 and a gel layer 2, the gel layer 2 is coated on the base film 1, and the material of the gel layer 2 is polyethylene oxide-urea gel. In the embodiment, the material of the base film 1 is polypropylene, the thickness of the base film 1 is 17-23 μm, and the thickness of the gel-state battery separator is 23-28 μm.

[0039] The hydroxyl in the polyethylene oxide and the amino in the urea in the gel layer 2 are bonded with each other to form a hydrogen bond complex, the hydrogen bond makes the structure of the gel layer more stable, thereby inhibiting the "shuttle effect" of the polysulfide in the lithium-sulfur battery, to improve the cycle stability of the battery, and the complex will swell in the electrolyte to form a gel-state battery separator, thereby improving the liquid absorption rate and liquid retention rate of the battery separator, to store more lithium ions, improve the battery capacity, and the gel-state battery separator has good polysulfide adsorption, which can also effectively inhibit the shuttle of polysulfide.

[0040] Embodiment two

[0041] Referring to Figure 3 , Figure 3 The flow chart of the preparation method of the gel-state battery separator in the embodiment. The embodiment provides a preparation method of a gel-state battery separator, which is used for preparing the gel-state battery separator in embodiment one, and includes the following steps:

[0042] S1: preparing a polyethylene oxide solution.

[0043] S2: preparing a urea solution.

[0044] S3: mixing and stirring the polyethylene oxide solution and the urea solution to perform a bonding reaction, to prepare a polyethylene oxide-urea solution, and the bonding reaction is shown in the following formula (I):

[0045]

[0046] S4: The polyethylene oxide-urea solution is coated on the base film 1, dried, and a gel layer 2 is formed.

[0047] S5: A gel-state battery separator is prepared.

[0048] Specifically, step S1 further comprises the following sub-steps:

[0049] S11: 2g of polyethylene oxide is weighed, and 98mL of deionized water is measured.

[0050] S12: The polyethylene oxide is mixed with the deionized water and stirred until completely dissolved.

[0051] S13: A polyethylene oxide solution is obtained.

[0052] Preferably, in step S12, the stirring time is 2.5-3.5h, and the stirring temperature is room temperature. In step S13, the concentration of the polyethylene oxide solution is 20mg / mL.

[0053] Specifically, step S2 further comprises the following sub-steps:

[0054] S21: 2g of urea is weighed, and 8mL of deionized water is measured.

[0055] S22: The urea is mixed with the deionized water.

[0056] S23: A urea solution is obtained.

[0057] In step S23, the concentration of the urea solution is 200mg / mL.

[0058] Preferably, in step S3, the mass ratio of polyethylene oxide to urea in the polyethylene oxide-urea solution is 1:(0.2-1.75), and the stirring time is 1.5-2.5h. The hydroxyl groups in the polyethylene oxide and the amino groups in the urea bond with each other to form a hydrogen bond complex. The bonded substance forms a PEOUIC substance of a specific crystal system, which can inhibit the shuttle of polysulfides and improve the cycle stability of lithium-sulfur batteries. At the same time, the hydrogen bond makes the gel layer structure more stable, thereby inhibiting the "shuttle effect" of polysulfides in lithium-sulfur batteries to improve the cycle stability of the battery. Moreover, the complex swells in the electrolyte to form a gel-state battery separator, thereby improving the liquid absorption rate and liquid retention rate of the battery separator to store more lithium ions, improve the battery capacity, and the gel-state battery separator has good polysulfide adsorption, which can also effectively inhibit the shuttle of polysulfides.

[0059] Specifically, step S4 comprises the following sub-steps:

[0060] S41: The base film 1 is laid flat on a glass plate.

[0061] S42: The polyethylene oxide-urea solution is coated on the base film 1.

[0062] S43: Drying, forming a gel layer.

[0063] Preferably, in S41, the base film 1 is made of polypropylene, and has a thickness of 17-23 μm. In S42, the polyethylene oxide-urea solution is uniformly coated on the base film 1 using a 75 μm doctor blade. In S43, the glass plate and the base film coated with the polyethylene oxide-urea solution are transferred to a hot stage for drying, and the drying time is 2-4 h, and the drying temperature is 50-70 °C.

[0064] Specifically, in step S5, the gel-state battery separator has a thickness of 23-28 μm, and is stored in a 45 °C vacuum oven.

[0065] Example Three

[0066] The lithium-sulfur battery of the present embodiment comprises the gel-state battery separator of Example One, and further comprises a positive electrode, a negative electrode, and an electrolyte.

[0067] In the preparation of the lithium-sulfur battery, the gel-state battery separator is first cut into 19 mm round pieces using a slicer, the weight of each piece is measured, and the pieces are labeled, packed in a self-sealing bag, and placed in a desiccator for standby use. Before assembling the battery, the gel-state battery separator is dried on a 100 °C hot stage for 2 h to remove residual moisture, and then assembled together with the positive electrode, the negative electrode, and the electrolyte to form the lithium-sulfur battery.

[0068] In order to further understand the inventive content, characteristics and effects of the present application, the following examples are provided, and are described in detail as follows in conjunction with the accompanying drawings:

[0069] Example One

[0070] 2 g of polyethylene oxide is weighed, and 98 mL of deionized water is measured, and the polyethylene oxide and the deionized water are mixed in a beaker, and stirred at room temperature for 3 h to obtain a polyethylene oxide solution with a concentration of 20 mg / mL.

[0071] 2 g of urea is weighed, and 8 mL of deionized water is measured, and the urea and the deionized water are mixed in a beaker to obtain a urea solution with a concentration of 200 mg / mL.

[0072] The 20 mL of polyethylene oxide solution and the 0.4 mL of urea solution are mixed and stirred for 2 h to perform a bonding reaction, and a polyethylene oxide-urea solution with a mass ratio of polyethylene oxide to urea of 1:0.2 is prepared, and the bonding reaction is shown in the following formula (I):

[0073]

[0074] The polyethylene oxide-urea solution was uniformly coated on the base film 1 using a 75 μm doctor blade, and then the glass plate and the base film coated with the polyethylene oxide-urea solution were transferred to a hot stage to dry for 3 h at 60°C to form a gel layer 2.

[0075] After drying, the gel-state battery separator Al was prepared.

[0076] Example 2

[0077] In this example, 20 mL of a polyethylene oxide solution was mixed with 1 mL of a urea solution and stirred for 2 h to perform a bonding reaction, thereby preparing a polyethylene oxide-urea solution having a mass ratio of polyethylene oxide to urea of 1:0.5. The remaining conditions were the same as in Example 1, and a gel-state battery separator A2 was prepared.

[0078] Example 3

[0079] In this example, 20 mL of a polyethylene oxide solution was mixed with 1.5 mL of a urea solution and stirred for 2 h to perform a bonding reaction, thereby preparing a polyethylene oxide-urea solution having a mass ratio of polyethylene oxide to urea of 1:0.75. The remaining conditions were the same as in Example 1, and a gel-state battery separator A3 was prepared.

[0080] Example 4

[0081] In this example, 20 mL of a polyethylene oxide solution was mixed with 2 mL of a urea solution and stirred for 2 h to perform a bonding reaction, thereby preparing a polyethylene oxide-urea solution having a mass ratio of polyethylene oxide to urea of 1:1. The remaining conditions were the same as in Example 1, and a gel-state battery separator A4 was prepared.

[0082] Example 5

[0083] In this example, 20 mL of a polyethylene oxide solution was mixed with 2.5 mL of a urea solution and stirred for 2 h to perform a bonding reaction, thereby preparing a polyethylene oxide-urea solution having a mass ratio of polyethylene oxide to urea of 1:1.25. The remaining conditions were the same as in Example 1, and a gel-state battery separator A25 was prepared.

[0084] Example 6

[0085] In this example, 20 mL of a polyethylene oxide solution was mixed with 3 mL of a urea solution and stirred for 2 h to perform a bonding reaction, thereby preparing a polyethylene oxide-urea solution having a mass ratio of polyethylene oxide to urea of 1:1.5. The remaining conditions were the same as in Example 1, and a gel-state battery separator A6 was prepared.

[0086] Example 7

[0087] In this embodiment, 20 mL of polyethylene oxide solution and 3.5 mL of urea solution were mixed and stirred for 2 hours to carry out a bonding reaction, thereby obtaining a polyethylene oxide-urea solution with a mass ratio of polyethylene oxide to urea of ​​1:1.75. All other conditions were the same as in Example 1, resulting in a gel-state battery separator A7.

[0088] The liquid absorption rate of gel battery separator A1-7 was tested, and the test results are shown in Table 1. Table 1 shows the liquid absorption rate of the gel battery separator after soaking for 1 hour.

[0089] Table 1. Liquid absorption rate of gel battery separator after soaking for 1 hour

[0090] Gel state battery separator A1 A2 A3 A4 A5 A6 A7 Wicking rate 33.4％ 100.2％ 144.9％ 162.8％ 152.6％ 140.7％ 128.7％

[0091] As shown in Table 1, when the mass of polyethylene oxide in the separator is greater than the mass of urea, the liquid absorption rate of the separator increases with the increase of the mass ratio of urea in the separator until the mass ratio of polyethylene oxide to urea is 1:1. The liquid absorption rate of the gel battery separator is the best, at 162.8%. However, when the mass of polyethylene oxide in the separator is less than the mass of urea, the liquid absorption rate of the separator decreases with the increase of the mass ratio of urea in the separator. This indicates that the liquid absorption rate is best when the mass ratio of polyethylene oxide to urea in the separator is 1:1.

[0092] Meanwhile, when the mass of polyethylene oxide in the separator is greater than the mass of urea, the liquid absorption rate of the separator increases with the increase of the mass ratio of urea in the separator. This indicates that at this time, the polyethylene oxide in the gel layer has not completely bonded with urea, resulting in the dissolution of some free polyethylene oxide during the soaking process. That is, the gel battery separator A1-3 exhibits the phenomenon of swelling first and then dissolving.

[0093] Lithium-sulfur batteries were fabricated using the gel-state battery separators A2, A4, and A6 described above. The cycle stability of the lithium-sulfur batteries at a 1C rate was tested, and the results are as follows: Figure 4 As shown, Figure 4 Capacity cycling diagrams of lithium-sulfur batteries prepared using gel-state battery separators A2, A4, and A6.

[0094] Depend on Figure 4 It can be seen that when the mass ratio of polyethylene oxide to urea in the separator is 1:1, that is, the lithium-sulfur battery prepared using gel-state battery separator A2 has the best cycle stability.

[0095] Comparative Example D1

[0096] A polypropylene-based membrane was used as a comparative example, which is the battery separator D1.

[0097] The liquid absorption rate and liquid retention rate of gel-state battery separators A4 and D1 were tested, and the test results are shown in Tables 2 and 3.

[0098] Table 2 Liquid absorption rate of diaphragms D1 and A4 after soaking for 1 hour.

[0099] Separator As received mass (mg) After 1 h of wicking Wicking rate D1 4.0 6.7 69％ A4 8.0 21.02 162.8％

[0100] Table 3. Liquid holdup of diaphragms D1 and A4 after soaking for 1 hour and then placing them at 25°C for different times.

[0101] 1h 2h 4h 8h 24h 48h D1 5％ 5％ 2.5％ 2.5％ 2.5％ 2.5％ A4 150.3％ 142.4％ 120.5％ 93.4％ 77.2％ 77.6％

[0102] Table 2 shows the liquid absorption rates of separators D1 and A4 after soaking for 1 hour. As can be seen from Table 2, the liquid absorption rate of gel-state battery separator A4 is greater than that of battery separator D1. That is, the liquid absorption rate of polyoxyethylene-urea gel-state battery separator is greater than that of pure polypropylene battery separator, indicating that coating with a gel layer improves the liquid absorption rate of gel-state battery separator.

[0103] Table 3 shows the liquid retention rates of separators D1 and A4 after soaking for 1 hour and placing them at 25°C for different times. As can be seen from Table 3, under different soaking times, the liquid retention rate of gel-state battery separator A4 is greater than that of battery separator D1. That is, the liquid absorption rate of polyethylene oxide-urea gel-state battery separator is greater than that of pure polypropylene battery separator, indicating that coating with a gel layer improves the liquid retention rate of gel-state battery separator.

[0104] The above-mentioned gel-state battery separator A4 and battery separator D1 were used to prepare lithium-sulfur batteries. The cycle stability of the lithium-sulfur batteries at 1C rate was tested, and the test results are as follows: Figure 5 As shown, Figure 5 Capacity cycling diagrams of lithium-sulfur batteries fabricated using gel-state battery separator A4 and battery separator D1.

[0105] Depend on Figure 5 It can be seen that the lithium-sulfur battery prepared with gel-state battery separator A4 has better battery cycle performance than the lithium-sulfur battery prepared with battery separator D1. This is because coating with a gel layer increases the liquid absorption rate of the gel-state battery separator, allowing it to store more lithium ions, thereby increasing battery capacity and improving battery cycle stability.

[0106] In summary, the hydroxyl groups in the polyethylene oxide and the amino groups in the urea in the gel layer of this application are bonded to each other to form a hydrogen-bonded complex. The hydrogen bonds make the gel layer structure more stable, thereby suppressing the "shuttle effect" of polysulfides in lithium-sulfur batteries and improving the cycle stability of the battery. Furthermore, the complex will swell in the electrolyte to form a gel-like battery separator, thereby increasing the liquid absorption and liquid retention rate of the battery separator to store more lithium ions and increase the battery capacity. In addition, the gel-like battery separator has good polysulfide adsorption properties, which can also effectively suppress polysulfide shuttle.

[0107] The above merely illustrates the embodiments of the present application, and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

1. A method for preparing a gel-state lithium-sulfur battery separator, characterized in that, Includes the following steps: A polyethylene oxide solution and a urea solution were mixed and stirred to carry out a bonding reaction, thereby obtaining a polyethylene oxide-urea solution. The bonding reaction is shown in formula (I). （Ⅰ）； A polyethylene oxide-urea solution is coated onto the base film and dried to form a gel layer; A gel-state battery separator is prepared, the gel-state battery separator comprising a base membrane and a gel layer, the gel layer being coated on the base membrane, and the gel layer being made of polyethylene oxide-urea gel; In the polyethylene oxide-urea solution, the mass ratio of polyethylene oxide to urea is 1:(0.5-1.75).

2. The method for producing a gel-state lithium-sulfur battery separator according to claim 1, characterized in that, Before mixing and stirring the polyethylene oxide solution with the urea solution, the following steps are also included: Prepare the polyethylene oxide solution.

3. The method for producing a gel-state lithium-sulfur battery separator according to claim 2, characterized in that, The preparation of the polyethylene oxide solution includes the following sub-steps: Weigh out 2g of polyethylene oxide and measure out 98mL of deionized water; The ethylene oxide is mixed with the deionized water and stirred until completely dissolved. The polyethylene oxide solution is obtained.

4. The method for producing a gel-state lithium-sulfur battery separator according to claim 1, characterized in that, Before mixing and stirring the polyethylene oxide solution with the urea solution, the following steps are also included: Prepare the urea solution.

5. The method for producing a gel-state lithium-sulfur battery separator according to claim 4, characterized in that, The preparation of the urea solution includes the following sub-steps: Weigh out 2g of urea and measure out 8mL of deionized water; Mix the urea with the deionized water; The urea solution was obtained.

6. The method for producing a gel-state lithium-sulfur battery separator according to claim 1, characterized in that, The step involves coating the base film with the polyethylene oxide-urea solution and drying it for 2-4 hours at a temperature of 50-70°C.

7. The method for producing a gel-state lithium-sulfur battery separator according to claim 1, characterized in that, In the process of preparing the gel-state battery separator, the thickness of the gel-state battery separator is 23-28 μm.

8. A lithium-sulfur battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and the gel-state battery separator as described in claim 1.

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