Composite separator, method for preparing the same, and sodium-ion battery
By using a composite separator coated with sodium molecular sieves in sodium-ion batteries, the side reaction problem caused by trace moisture was solved, improving the battery's cycle and storage performance.
Patent Information
- Application Number
- CN202211624566.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-16
- Publication Date
- 2025-11-04
- Estimated Expiration
- 2042-12-16
AI Technical Summary
Side reactions caused by trace amounts of moisture in sodium-ion batteries lead to poor cycle performance and storage performance, and existing technologies are unable to effectively remove free moisture from the battery.
Sodium-treated molecular sieves are used as coating materials and are uniformly coated on the base membrane to form a composite membrane, which adsorbs trace amounts of free water in the electrolyte and reduces side reactions caused by water.
It improves the cycle performance and storage performance of sodium-ion batteries, reduces moisture and acidity inside the battery, and enhances the high-temperature cycle and storage performance of the battery.
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Figure CN116014357B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of sodium ion batteries, in particular to a composite diaphragm, a preparation method thereof and a sodium ion battery. BACKGROUND
[0002] The sodium ion battery is composed of a positive electrode, a negative electrode, an electrolyte, a diaphragm and an outer packaging material. The diaphragm is composed of a base film and a coating layer. The base film is generally porous polypropylene or polyethylene, and the coating layer is composed of several hundred nanometer or micrometer molecular sieve of aluminum oxide and a certain proportion of a binder. The purpose of the coating layer is to improve the thermal stability of the diaphragm.
[0003] The performance of the sodium ion battery is greatly affected by the moisture inside the battery. In order to minimize the moisture in the battery, the positive electrode sheet, the negative electrode sheet and the diaphragm need to be fully baked and dehydrated before assembling the battery, and the electrolyte also needs to maintain a low moisture content. The battery is assembled in a dry room. However, in practice, it is difficult to completely remove the moisture in the materials by baking. Considering the influence of cost and production progress, the moisture content of the electrode sheet is usually controlled within a few hundred ppm, and the moisture content of the electrolyte is within a few tens of ppm. The trace amount of moisture inside the battery can still cause side reactions inside the battery, accelerate the capacity decay of the battery during the cycle process and storage process, and also cause the increase of internal resistance. Therefore, there is an urgent need for a diaphragm to adsorb the trace amount of free moisture inside the battery, so that the moisture and acidity of the electrolyte are lower, the side reactions caused by the moisture are reduced, and the cycle performance and storage performance of the battery are improved. SUMMARY
[0004] In order to solve the problem of excessive moisture inside the existing sodium ion battery and the low cycle performance and storage performance of the battery, the present application provides a composite diaphragm, a preparation method thereof and a sodium ion battery. The diaphragm is different from the traditional coated diaphragm, and the coating material used is a molecular sieve. Through sodium treatment of the molecular sieve, the sodium-treated molecular sieve can better adsorb the trace amount of free moisture in the electrolyte, the moisture and acidity of the electrolyte are lower, the side reactions caused by the moisture are reduced, and the cycle performance and storage performance of the sodium ion battery are improved.
[0005] In order to solve the above problems, the present application provides a technical scheme.
[0006] In a first aspect, the present application provides a composite diaphragm, comprising a base film and a coating layer uniformly coated on one side of the base film; the coating layer comprises a sodium-treated molecular sieve and a binder; the slurry of the coating layer comprises the following components in mass percentage: 95% to 99% of the molecular sieve and 1% to 5% of the binder.
[0007] Preferably, the binder comprises at least one of polyvinylidene fluoride, polyacrylic acid or polyvinyl alcohol.
[0008] As preferred, the sodium-modified molecular sieve is a sodium-modified 3A molecular sieve, and the particle size is 0.2-5 microns.
[0009] As preferred, the base film is a porous polypropylene or polyethylene diaphragm, and the thickness is 7-20 microns.
[0010] As preferred, the thickness of the coating layer is 1-5 microns.
[0011] In a second aspect, the present application provides a method for preparing the composite diaphragm of the first aspect, comprising the following steps:
[0012] S1: ball milling or sand milling the 3A molecular sieve to obtain a molecular sieve with a particle size of 0.2-5 microns;
[0013] S2: soaking the molecular sieve obtained in step S1 in a solution of NaClO4 with ethanol as the solvent;
[0014] S3: taking the molecular sieve out of the solution in step S2, heating under reduced pressure at a temperature of 78-82℃, and then transferring to a temperature of 180-220℃ for reduced pressure calcination, and repeating the operation of this step for 4-6 times;
[0015] S4: transferring the molecular sieve obtained in step S3 to a temperature of 340-360℃ for baking to obtain a treated molecular sieve; S5: uniformly mixing the treated molecular sieve in step S4, a binder, and a solvent to obtain a mixture of the molecular sieve and the binder, uniformly coating the mixture on the surface of the base film, and forming a coating layer of 1-5 microns after drying to obtain a molecular sieve-coated composite diaphragm.
[0016] As preferred, the soaking time in step S2 is 70-74 hours.
[0017] As preferred, the time for heating under reduced pressure in step S3 is 1.5-2.5 hours, and the time for reduced pressure calcination is 2.5-3.5 hours.
[0018] As preferred, the baking time in step S4 is 4.5-5.5 hours.
[0019] In a third aspect, the present application provides a sodium-ion battery comprising a layered oxide or polyanion positive electrode, a hard carbon negative electrode, a composite diaphragm, an electrolyte with NaPF6 as the salt, and an aluminum plastic film, wherein the composite diaphragm is the composite diaphragm according to the first aspect.
[0020] Beneficial effects: The coating material adopted by the present application is molecular sieve. Through sodium treatment of the molecular sieve, the sodium-treated molecular sieve can better adsorb free trace water in the electrolyte, reduce the side reactions caused by water, and after the sodium-treated molecular sieve, the binder and the solvent are uniformly mixed, the composite diaphragm is obtained by coating on the base film, and is applied to the sodium ion battery. Reduce the moisture in the battery, improve the cycle performance and storage performance of the sodium ion battery. BRIEF DESCRIPTION OF DRAWINGS
[0021] Figure 1 is a structure diagram of the composite diaphragm of the present application.
[0022] Figure 2 is a flow chart of the preparation method of the composite diaphragm of the present application.
[0023] Figure legend: 1-sodium-treated molecular sieve, 2-base film, 3-binder. DETAILED DESCRIPTION
[0024] In order for those skilled in the art to better understand the technical solutions of the present application, the specific embodiments thereof will be described in detail below with reference to the accompanying drawings.
[0025] English abbreviations appearing in the embodiments of the present application are annotated as follows:
[0026] PVDF: polyvinylidene fluoride; PE: polyethylene;
[0027] NMP: full name N-methyl pyrrolidone, is a polar aprotic solvent.
[0028] A kind of molecular sieve coated composite diaphragm and its sodium ion battery, positive and negative electrode, electrolyte packaging material and other materials are the same as ordinary commercial sodium ion battery, diaphragm is different from traditional coated diaphragm, the coating material adopted is molecular sieve;This kind of molecular sieve can adsorb free trace water in electrolyte, reduce the side reactions caused by water. In addition, since the molecular sieve contains more monovalent, divalent cations such as K+, Na+ and Ca2+, Ba2+, Na+ in sodium ion battery will occur ion exchange, and the water in it will have side reactions with electrolyte, direct application in sodium ion battery will cause performance deterioration. Therefore, the molecular sieve must be sodiumized and water removed before use.
[0029] In the first aspect, see Figure 1 The present application provides a kind of composite diaphragm, including base film and the coating of uniform coating on one side of base film;Coating includes sodium-treated molecular sieve and binder;The slurry of coating includes the following components according to mass percentage: molecular sieve 95%~99%, binder 1%~5%.
[0030] In this embodiment, the binder comprises at least one of polyvinylidene fluoride, polyacrylic acid or polyvinyl alcohol.
[0031] In this embodiment, the sodiumized molecular sieve is a sodiumized 3A type molecular sieve, and the particle size is 0.2-5 microns.
[0032] In this embodiment, the base film is a porous polypropylene or polyethylene diaphragm, and the thickness is 7-20 microns.
[0033] In this embodiment, the thickness of the coating layer is 1-5 microns.
[0034] The second aspect, see Figure 2 The present application provides a method for preparing the composite diaphragm of the first aspect, comprising the following steps:
[0035] S1: ball milling or sand milling the 3A type molecular sieve to prepare a molecular sieve with a particle size of 0.2-5 microns;
[0036] S2: soaking the molecular sieve obtained in step S1 in a NaClO4 solution with ethanol as the solvent;
[0037] S3: taking the molecular sieve from the solution in step S2, heating under reduced pressure at a temperature of 78-82℃, and then transferring to a temperature of 180-220℃ for reduced pressure calcination, and repeating this step operation 4-6 times;
[0038] S4: transferring the molecular sieve obtained in step S3 to a temperature of 340-360℃ for baking for 4.5-5.5 hours to obtain a treated molecular sieve;
[0039] S5: uniformly mixing the molecular sieve obtained in step S4, the binder and the solvent to obtain a mixture of the molecular sieve and the binder, uniformly coating the mixture on the surface of the base film, and forming a coating layer of 1-5 microns after drying to obtain a molecular sieve coated composite diaphragm.
[0040] In this embodiment, the solvent in step S5 is water or NMP.
[0041] In this embodiment, the soaking time in step S2 is 70-74 hours.
[0042] In this embodiment, the time for heating under reduced pressure in step S3 is 1.5-2.5 hours, and the time for reduced pressure calcination is 2.5-3.5 hours.
[0043] The third aspect, the present application provides a sodium ion battery, comprising a layered oxide or polyanion positive electrode, a hard carbon negative electrode, a composite diaphragm, an electrolyte with NaPF6 as a salt and an aluminum plastic film, and the composite diaphragm is a composite diaphragm according to the first aspect.
[0044] Example 1
[0045] The present example provides a composite separator, including a polyethylene base film with a thickness of 7 microns and a coating layer with a thickness of 1 micron uniformly coated on one side of the polyethylene base film; the coating layer includes sodiumized molecular sieve and binder; the slurry of the coating layer includes the following components in mass percentage: 95% of molecular sieve, 5% of binder.
[0046] The present example provides a method for preparing a composite separator, including the following steps:
[0047] The 3A type molecular sieve with a particle size of 1.7-2.5 mm is dispersed in water, ground in a sand mill, and filtered to obtain molecular sieve with a particle size of 0.2 microns. The molecular sieve is soaked in a sodiumized solution of NaClO4 with ethanol as solvent for 70 hours, taken out, heated at 78°C under reduced pressure for 1.5 hours, and then baked at 180°C under reduced pressure for 2.5 hours. This process is repeated 4 times, and finally baked at 350°C for 4.5 hours. 5g of polyvinyl alcohol is dissolved in 1000ml of water, 95g of molecular sieve is mixed on a stirrer for 2 hours, and the molecular sieve slurry is uniformly coated on a 7 micron thick polyethylene base film using a coating machine. The single layer coating after drying has a thickness of 1 micron. The separator is used to assemble a soft package sodium ion battery with a capacity of 50 Ah, using a nickel iron manganese sodium positive electrode sheet, a hard carbon negative electrode sheet, and NaPF6 electrolyte.
[0048] Example 2
[0049] The present example provides a composite separator, including a polyethylene base film with a thickness of 13 microns and a coating layer with a thickness of 3 microns uniformly coated on one side of the polyethylene base film; the coating layer includes sodiumized molecular sieve and binder; the slurry of the coating layer includes the following components in mass percentage: 97% of molecular sieve, 3% of binder.
[0050] The present example provides a method for preparing a composite separator, including the following steps:
[0051] The 3A type molecular sieve with a particle size of 1.7-2.5 mm is dispersed in water, ground in a sand mill, and filtered to obtain molecular sieve with a particle size of 0.2 microns. The molecular sieve is soaked in a sodiumized solution of NaClO4 with ethanol as solvent for 70 hours, taken out, heated at 78°C under reduced pressure for 1.5 hours, and then baked at 180°C under reduced pressure for 2.5 hours. This process is repeated 4 times, and finally baked at 350°C for 4.5 hours. 5g of polyvinyl alcohol is dissolved in 1000ml of water, 95g of molecular sieve is mixed on a stirrer for 2 hours, and the molecular sieve slurry is uniformly coated on a 7 micron thick polyethylene base film using a coating machine. The single layer coating after drying has a thickness of 1 micron. The separator is used to assemble a soft package sodium ion battery with a capacity of 50 Ah, using a nickel iron manganese sodium positive electrode sheet, a hard carbon negative electrode sheet, and NaPF6 electrolyte.
[0052] Example 3
[0053] The present example provides a composite separator, which comprises a polyethylene base film with a thickness of 20 microns and a coating layer with a thickness of 5 microns uniformly coated on one side of the polyethylene base film; the coating layer comprises sodiumized molecular sieve and a binder; the slurry of the coating layer comprises the following components in terms of mass percentage: 99% of molecular sieve and 1% of binder.
[0054] The present example provides a method for preparing a composite separator, which comprises the following steps:
[0055] 1.7-2.5 mm 3A type molecular sieve is dispersed in water, ground in a sand mill, and filtered to obtain molecular sieve with a particle size of 5 microns. The molecular sieve is soaked in a sodiumized NaClO4 solution with ethanol as the solvent for 74 hours, taken out, heated at 82°C under reduced pressure for 2.5 hours, and then calcined at 180°C under reduced pressure for 3.5 hours; this process is repeated 6 times, and finally baked at 350°C for 5.5 hours. 1 g of polyvinyl alcohol is dissolved in 1000 ml of water, 99 g of molecular sieve is added and mixed on a stirrer for 2 hours, and the molecular sieve slurry is uniformly coated on a 20 micron thick polyethylene base film using a coating machine. The single-layer coating thickness after drying is 5 microns. The separator is used to assemble a soft package sodium ion battery with a capacity of 50 Ah, using a nickel-iron sodium manganese acid positive electrode sheet, a hard carbon negative electrode sheet, and a NaPF6 electrolyte.
[0056] Example 4
[0057] The present example provides a composite separator, which comprises a polyethylene base film with a thickness of 9 microns and a coating layer with a thickness of 3 microns uniformly coated on one side of the polyethylene base film; the coating layer comprises sodiumized molecular sieve and a binder; the slurry of the coating layer comprises the following components in terms of mass percentage: 95% of molecular sieve and 5% of binder.
[0058] The present example provides a method for preparing a composite separator, which comprises the following steps:
[0059] The 3A type molecular sieve of 1.7-2.5 mm is dispersed in water, ground in a sand mill for 12 hours, and filtered to obtain a molecular sieve with a particle size of 1 micron. The molecular sieve is immersed in a sodium solution of NaClO4 with ethanol as a solvent for 72 hours, the molecular sieve is taken out, heated at 80°C under reduced pressure for 2 hours, and then calcined at 200°C under reduced pressure for 3 hours. This is repeated 5 times, and finally baked at 350°C for 5 hours. 5 g of polyvinyl alcohol is dissolved in 1000 ml of water, 95 g of the molecular sieve is mixed on a stirrer for 2 hours, and the molecular sieve slurry is uniformly coated on a 9 micron thick polypropylene base film by a coating machine. The single layer coating thickness after coating and drying is 3 microns. The sodium ion battery with a capacity of 50 Ah is assembled by using the separator, a nickel-iron-manganese sodium positive electrode sheet, a hard carbon negative electrode sheet and a NaPF6 electrolyte. After the battery formation is completed, the high temperature cycle and high temperature storage performance of the battery are tested. After 1000 cycles, the capacity retention rate of the battery is 90%; after high temperature storage for one month, the capacity retention rate is 96%; the water content in the electrolyte extracted from the battery is 10 ppm, and the acidity is 50 ppm. The high temperature cycle performance of the battery is tested by performing 1000 cycles of charge and discharge on the battery, and the high temperature storage performance of the battery is tested by performing high temperature storage on the battery for one month.
[0060] Example 5
[0061] The present embodiment provides a composite separator, which comprises a polyethylene base film with a thickness of 7 microns and a coating layer with a thickness of 3 microns uniformly coated on one side of the polyethylene base film; the coating layer comprises sodiumized molecular sieve and a binder; the slurry of the coating layer comprises the following components in mass percentage: 95% of molecular sieve and 5% of binder.
[0062] The 3A type molecular sieve of 1.7-2.5 mm is dispersed in water, ground in a sand mill for 12 hours, and filtered to obtain a molecular sieve with a particle size of 1 micron. The molecular sieve is immersed in a sodium solution of NaClO4 with ethanol as a solvent for 72 hours, the molecular sieve is taken out, heated at 80°C under reduced pressure for 2 hours, and then calcined at 200°C under reduced pressure for 3 hours. This is repeated 5 times, and finally baked at 350°C for 5 hours. 5 g of PVDF is dissolved in 100 ml of NMP, 95 g of the molecular sieve is mixed on a stirrer for 2 hours, and the molecular sieve slurry is uniformly coated on a 7 micron thick polyethylene base film by a coating machine. The single layer coating thickness after coating and drying is 3 microns. The sodium ion battery with a capacity of 50 Ah is assembled by using the separator, a sodium vanadium phosphate positive electrode sheet, a hard carbon negative electrode sheet and a NaPF6 electrolyte.
[0063] Inventive effect comparison 1 of the present application:
[0064] As a comparative example, the separator in Example 4 is replaced by a conventional coated separator with 7 microns PE + 3 microns alumina coating to make a 50 Ah sodium ion battery. After the end of battery formation, the high-temperature cycle and high-temperature storage performance of the two batteries are tested respectively, as well as the moisture and acidity in the electrolyte after 1000 high-temperature cycles.
[0065] Effect comparison 2 of the present application:
[0066] As a comparative example, the separator in Example 4 is replaced by a conventional 16 micron PP separator to make a 50 Ah sodium ion battery. After the end of battery formation, the high-temperature cycle and high-temperature storage performance of the battery are tested, as well as the moisture and acidity in the electrolyte.
[0067] Effect comparison 3 of the present application:
[0068] As a comparative example, the molecular sieve in Example 4 is not subjected to sodium treatment and is directly coated on a 9 micron thick polyethylene separator. The single-layer coating after drying has a thickness of 3 microns. Using this separator and a nickel-iron-manganese sodium positive electrode sheet, a hard carbon negative electrode sheet, and a NaPF6 electrolyte, a 50 Ah soft-pack sodium ion battery is assembled. After the end of battery formation, the high-temperature cycle and high-temperature storage performance of the battery are tested, as well as the moisture and acidity in the electrolyte. The test results are as follows:
[0069]
[0070] The results show that after 1000 cycles, the capacity retention rate of the separator coated with the molecular sieve of the present application is significantly higher than that of the conventional separator, and after 1 month of high-temperature storage, the capacity retention rate is significantly higher. The electrolyte in the battery is extracted and tested for moisture and acidity content. The results show that compared with the conventional separator, the moisture and acidity of the electrolyte in the battery of the present application separator are lower.
[0071] As can be seen, the sodium ion battery using the composite separator of the molecular sieve of the present application significantly improves the high-temperature cycle performance and high-temperature storage performance of the sodium ion battery.
Claims
1. A composite diaphragm, characterized in that, The composite membrane includes a base membrane and a coating uniformly coated on one side of the base membrane; The coating comprises sodium-modified molecular sieves and a binder; The coating slurry comprises the following components by mass percentage: 95%-99% molecular sieve and 1%-5% binder; The method for preparing the composite membrane includes the following steps: S1: Ball milling or sand milling of type 3A molecular sieve to produce molecular sieves with a particle size of 0.2 micrometers to 5 micrometers; S2: Soak the molecular sieve obtained in step S1 in a solution of NaClO4 with ethanol as the solvent. S3: Remove the molecular sieve from the solution described in step S2, heat it under reduced pressure at a temperature of 78℃-82℃, and then transfer it to a temperature of 180℃-220℃ for reduced pressure calcination. Repeat this step 4-6 times. S4: Transfer the molecular sieve obtained in step S3 to a temperature of 340℃-360℃ for baking to obtain the processed molecular sieve. S5: The molecular sieve and binder processed in step S4 are uniformly mixed with the solvent to obtain a mixture of molecular sieve and binder. The mixture is uniformly coated on the surface of the base membrane and dried to form a 1-5 micrometer coating, thus obtaining a composite membrane coated with molecular sieve.
2. The composite diaphragm according to claim 1, characterized in that, The adhesive includes at least one of polyvinylidene fluoride, polyacrylic acid, or polyvinyl alcohol.
3. A composite diaphragm according to claim 1 or 2, characterized in that, The sodium-modified molecular sieve is a sodium-modified type 3A molecular sieve with a particle size of 0.2 micrometers to 5 micrometers.
4. The composite diaphragm according to claim 1, characterized in that, The base membrane is a porous polypropylene or polyethylene membrane with a thickness of 7-20 micrometers.
5. A composite diaphragm according to claim 1, characterized in that, The thickness of the coating is 1 micrometer to 5 micrometers.
6. A preparation method, characterized in that, The method for preparing the composite separator according to any one of claims 1-5 comprises the following steps: S1: Ball milling or sand milling of type 3A molecular sieve to produce molecular sieves with a particle size of 0.2 micrometers to 5 micrometers; S2: Soak the molecular sieve obtained in step S1 in a solution of NaClO4 with ethanol as the solvent. S3: Remove the molecular sieve from the solution described in step S2, heat it under reduced pressure at a temperature of 78℃-82℃, and then transfer it to a temperature of 180℃-220℃ for reduced pressure calcination. Repeat this step 4-6 times. S4: Transfer the molecular sieve obtained in step S3 to a temperature of 340℃-360℃ for baking to obtain the processed molecular sieve. S5: The molecular sieve and binder processed in step S4 are uniformly mixed with the solvent to obtain a mixture of molecular sieve and binder. The mixture is uniformly coated on the surface of the base membrane and dried to form a 1-5 micrometer coating, thus obtaining a composite membrane coated with molecular sieve.
7. The method according to claim 6, characterized in that, The soaking time in step S2 is 70-74 hours.
8. The method according to claim 7, characterized in that, The time for depressurized heating in step S3 is 1.5-2.5 hours, and the time for depressurized roasting is 2.5-3.5 hours.
9. The method according to any one of claims 6-8, characterized in that, The baking time in step S4 is 4.5-5.5 hours.
10. A sodium-ion battery, characterized in that, It includes a layered oxide or polyanion positive electrode, a hard carbon negative electrode, a composite membrane, an electrolyte with NaPF6 as salt, and an aluminum-plastic membrane, wherein the composite membrane is the composite membrane according to any one of claims 1-5.
Citation Information
Patent Citations
Novel lithium ion battery diaphragm with inorganic coating and preparation method thereof
CN103107301A