CN114883748A - Composite diaphragm for lithium ion battery and preparation method thereof - Google Patents
Composite diaphragm for lithium ion battery and preparation method thereof Download PDFInfo
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- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
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Abstract
The invention discloses a composite diaphragm for a lithium ion battery and a preparation method thereof, belongs to the technical field of lithium ion batteries, and is beneficial to improving the ion transmission rate in a lithiated molecular sieve coating composite diaphragm, improving the interface compatibility of the diaphragm and an electrolyte and improving the charge-discharge cycle stability and the capacity retention capacity of the lithium ion battery. The method comprises the steps of firstly treating a polyethylene diaphragm by adopting an aqueous solution of an organic monomer, obtaining lithiated molecular sieve particles by an ion replacement mode, then preparing a molecular sieve particle aqueous slurry, coating the slurry on the single surface or double surfaces of a polyethylene base film by scraping, drying to obtain the required composite diaphragm, and assembling the composite diaphragm into a lithium ion battery for performance test. The result shows that the introduction of the composite coating can reduce the impedance borne by the battery and the polarization inside the battery in the ion transmission process, and stabilize the electrode interface, thereby effectively improving the electrochemical performance of the lithium ion battery.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a composite diaphragm for a lithium ion battery and a preparation method thereof.
Background
With the large-scale popularization and application of new energy electric vehicles and power grid energy storage, people aim to the next generation of power batteries with higher power density and higher working voltage. The lithium ion battery has the remarkable advantages of no memory effect, environmental protection, high safety and the like, is expected to meet the future requirements on energy, and is widely concerned. The diaphragm mainly plays a role in physically separating a positive electrode from a negative electrode in the lithium ion battery to avoid short circuit of the battery, and in addition, the unique porous structure of the diaphragm can also provide a channel for efficient transmission of lithium ions, so that the electrochemical performance of the lithium ion battery is restricted. At present, due to mature production process and low manufacturing cost, the polyolefin diaphragm becomes the most widely applied lithium ion battery diaphragm. However, as the operating voltage and the charge/discharge current density are increased, a series of problems, such as uncontrolled growth of lithium dendrites, rapid consumption of electrolyte, excessive charge transfer resistance, etc., are induced in the battery. Higher demands are made on a separator, which is an important component in a lithium ion battery, so that efficient and stable operation of the lithium ion battery is facilitated.
Currently, surface coating of commercial polyolefin diaphragms is the most common and effective modification method, and the preparation process is simple, the investment cost is low, and the method is suitable for large-scale production; the functional coating constructed on the surface of the base film can stably exist and play a role. At present, the most widely popularized industrial ceramic particles (such as SiO) 2 、TiO 2 、Al 2 O 3 Etc.) and a binder (PVDF, PTFE, CMC, etc.) are uniformly mixed and coated on the surface of the polyolefin base film according to a certain thickness. The method can obviously improve the mechanical strength and puncture resistance of the diaphragm and inhibit the heat shrinkage phenomenon of the diaphragm; and the wettability of the diaphragm to electrolyte is improved, and the circulation stability in the battery is improved to a certain extent. However, the composite diaphragm prepared by the method has lower ionic conductivity, and the resistance suffered by lithium ions during diffusion is overlarge, so that the polarization phenomenon in the battery is aggravated, and the stable work of the lithium ion battery under the conditions of high current density and high working voltage is not facilitated. Therefore, designing a functional coating with high-efficiency ion transmission rate and uniform ion transmission channel is an important research direction of the current lithium ion battery diaphragm.
Disclosure of Invention
The invention provides a composite diaphragm for a lithium ion battery and a preparation method thereof, wherein the composite diaphragm is a lithiated molecular sieve coating composite diaphragm, lithiation treatment is carried out on molecular sieve particles, so that efficient and uniform lithium ions pass through the composite diaphragm, resistance borne by the composite diaphragm in an electrochemical conversion process is reduced, stability of a diaphragm-electrolyte-electrode interface is maintained, and the cycle stability and the capacity retention capability of the lithium ion battery are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
the composite diaphragm is characterized in that lithiated molecular sieve particles are coated on the surface of a base film, functional particles of the lithiated molecular sieve uniformly cover the surface of a polyethylene base film, the base film is the polyethylene base film, and the thickness of the lithiated molecular sieve composite diaphragm is 10-35 mu m.
A preparation method of a composite diaphragm for a lithium ion battery comprises the following steps:
(1) crushing molecular sieve particles into powder in a manual grinding and mechanical ball milling mode;
(2) adding the molecular sieve powder obtained in the step (1) into a LiCl aqueous solution, and uniformly stirring and mixing to form a suspension;
(3) heating the mixed solution obtained in the step (2) at 50 ℃ and stirring for 6-10 h;
(4) centrifuging the mixed solution treated in the step (3) for 5-8 min at the rotating speed of 8000-10000 r/min, and washing for 3 times by using deionized water;
(5) repeating the molecular sieve powder obtained in the step (4) for 3-5 times according to the experimental processes of the steps (2), (3) and (4), and drying to obtain lithiated molecular sieve powder;
(6) mixing the lithiated molecular sieve powder obtained in the step (5) with a binder, a surfactant and a solvent according to a certain mass ratio, and performing ball milling at a rotating speed of 250-350 r/min for 4 hours to obtain slurry of a lithiated molecular sieve coating;
(7) respectively preparing an aqueous solution of tannic acid and an aqueous solution of polyethyleneimine, sequentially placing the base film cleaned by ethanol in the aqueous solutions of tannic acid and polyethyleneimine for reacting for 1-3 h, taking out, cleaning with deionized water and drying;
(8) coating the slurry obtained in the step (6) on the single surface or double surfaces of the base film obtained in the step (7) in a blade mode;
(9) and (4) drying the uniformly coated composite membrane obtained in the step (8) at 70 ℃ for 24 h in vacuum to obtain the lithiated molecular sieve coating composite membrane.
In the above steps, the time of the manual grinding in the step (1) is 2-5 h, the time of the mechanical ball milling is 8-12 h, and the rotating speed is 300-500 r/min;
the mass of the molecular sieve powder in the step (2) is 2-5 g, the concentration of the LiCl aqueous solution is 1.0-2.0 mol/L, and the volume is 60-120 ml;
and (3) mixing the lithiated molecular sieve powder with a binder, a surfactant and a solvent according to the ratio of 8-10: 2-3: 0.1-0.2: 45-55, wherein the binder is polyvinylidene fluoride, lithium polyacrylate, styrene butadiene rubber or sodium carboxymethylcellulose, the surfactant is PVP or CTAB, and the solvent is DMF, water, absolute ethyl alcohol or NMP;
the concentration of the tannic acid aqueous solution in the step (7) is 1-3 mg/ml, and the concentration of the polyethyleneimine aqueous solution is 0.25-1 mg/ml.
The base film in the steps (7) and (8) is a polyethylene base film, and the thickness of the polyethylene base film is 5-25 μm.
Has the advantages that: the invention provides a composite diaphragm for a lithium ion battery and a preparation method thereof, wherein the composite diaphragm is a lithiated molecular sieve coating composite diaphragm, and a commercial polyolefin diaphragm has the problems of low puncture resistance, nonuniform pore size distribution, poor affinity with electrolyte, slow ion migration rate and the like. According to the invention, the ball-milled molecular sieve particles are subjected to ion replacement treatment, and the surface of the polar organic monomer modified polyethylene diaphragm is used for preparing the lithiated molecular sieve functional coating, the ordered and uniform pore structure of the functional coating improves the ion transmission rate in the lithiated molecular sieve coating composite diaphragm, promotes lithium ions to rapidly and uniformly pass through the composite diaphragm, effectively relieves the polarization phenomenon in the battery, improves the interface compatibility of the diaphragm and electrolyte, and improves the electrochemical stability and capacity retention capability of the lithium ion battery.
Drawings
FIG. 1 is an XRD (a) and XPS (b, c) plot of molecular sieve (Zeolite) nanoparticles and lithiated molecular sieve (Zeolite) nanoparticles in an example of the present invention;
FIG. 2 is an SEM photograph of a PE separator (a), a PE separator (b) after polarization treatment, a Zeolite @ TA/PEI-PE composite separator (c) and a Li-Zeolite @ TA/PEI-PE composite separator (d) in an example of the present invention;
FIG. 3 is LiCoO assembled from different separators in an embodiment of the invention 2 Li button typeAn electrochemical impedance plot of the cell;
FIG. 4 LiCoO assembled with different separators according to an embodiment of the invention 2 Cycling performance (a) and rate performance (b) of a/Li button cell;
fig. 5 is a galvanostatic cycling test of Li/Li symmetric cells of different separator assemblies in an example of the invention.
Detailed Description
The invention is described in detail below with reference to the following figures and specific examples:
example 1
A preparation method of a composite diaphragm for a lithium ion battery comprises the following steps:
(1) manually grinding commercial 3A molecular sieve particles for 2 h, then mechanically ball-milling the particles for 6 h at the rotating speed of 400 r/h, and crushing the particles into powder;
(2) adding 3 g of 3A molecular sieve powder obtained in the step (1) into 100 ml of LiCl aqueous solution with the concentration of 1.2 mol/L, and uniformly stirring and mixing to form suspension;
(3) heating the mixed solution obtained in the step (2) at 50 ℃ and stirring for 8 hours;
(4) centrifuging the mixed solution treated in the step (3) for 5 min at the rotating speed of 8000 r/min, and washing for 3 times by using deionized water;
(5) repeating the molecular sieve powder obtained in the step (4) for 3 times according to the experimental processes of the steps (2), (3) and (4), and drying to obtain lithiated molecular sieve powder;
(6) mixing the lithiated molecular sieve powder obtained in the step (5) with a binder lithium polyacrylate, a surfactant CTAB and solvent water according to the weight ratio of 16: 5: 0.2: 100, and then ball-milling for 4 hours at the rotating speed of 300 r/min to obtain slurry of the lithiated molecular sieve coating;
(7) respectively preparing 500 ml of tannin aqueous solution with the mass fraction of 2 mg/L and 500 ml of polyethyleneimine aqueous solution with the mass fraction of 0.5 mg/ml, sequentially placing the base membrane cleaned by ethanol in the tannin and polyethyleneimine aqueous solution for reacting for 2 hours, taking out, cleaning by using deionized water and drying;
(8) coating the slurry obtained in the step (6) on the single surface or double surfaces of the base film obtained in the step (7) in a scraping mode, wherein the thickness of the base film is 16 microns;
(9) and (4) drying the uniformly coated composite membrane obtained in the step (8) at 70 ℃ for 24 h in vacuum to obtain a lithiated molecular sieve coating composite membrane, wherein the thickness of the composite membrane is 19 microns.
XRD and XPS test results of the molecular sieve particles before and after lithiation prepared in the above experiment are shown in fig. 1(a) and (b), respectively, and crystal diffraction peaks of the molecular sieve particles before and after lithiation are consistent with their corresponding standard PDF cards; na of lithiated molecular sieve particles 1s And Si 2p The signal peak intensity is reduced and Li appears 1s The signal peak of (1) proves the successful implementation of the lithiation process, and fig. 2 shows that the molecular sieve particles after lithiation can be more uniformly coated on the surface of the PE diaphragm, and the PE diaphragm, the molecular sieve coating composite diaphragm and the molecular sieve coating composite diaphragm after lithiation which are subjected to the polarization treatment.
Example 2
A preparation method of a novel composite diaphragm for a lithium ion battery comprises the following steps:
(1) manually grinding commercial 3A molecular sieve particles for 3 h, then mechanically ball-milling for 6 h at the rotating speed of 300 r/h, and crushing into powder;
(2) adding 4 g of 3A molecular sieve powder obtained in the step (1) into 120 ml of LiCl aqueous solution with the concentration of 2 mol/L, and uniformly stirring and mixing to form suspension;
(3) heating the mixed solution obtained in the step (2) at 60 ℃ and stirring for 12 hours;
(4) centrifuging the mixed solution treated in the step (3) for 5 min at the rotating speed of 8000 r/min, and washing for 3 times by using deionized water;
(5) repeating the molecular sieve powder obtained in the step (4) for 3 times according to the experimental processes of the steps (2), (3) and (4), and drying to obtain lithiated molecular sieve powder;
(6) and (3) mixing the lithiated molecular sieve powder obtained in the step (5) with a binder sodium carboxymethyl cellulose, a surfactant PVP and a solvent water according to a ratio of 17: 5: 0.15: 90, and then ball-milling for 5 hours at the rotating speed of 350 r/min to obtain slurry of the lithiated molecular sieve coating;
(7) respectively preparing 500 ml of tannic acid aqueous solution with the mass fraction of 3 mg/L and 500 ml of polyethyleneimine aqueous solution with the mass fraction of 1 mg/ml, sequentially placing the base membrane cleaned by ethanol in the tannic acid and polyethyleneimine aqueous solution for reaction for 4 hours, taking out, cleaning by using deionized water and drying;
(8) coating the slurry obtained in the step (6) on the single surface or double surfaces of the base film obtained in the step (7) in a scraping mode, wherein the thickness of the base film is 16 microns;
(9) and (4) drying the uniformly coated composite membrane obtained in the step (8) at 70 ℃ for 24 h in vacuum to obtain a lithiated molecular sieve coating composite membrane, wherein the thickness of the composite membrane is 19 microns.
Example 3
A preparation method of a novel composite diaphragm for a lithium ion battery comprises the following steps:
(1) manually grinding commercial 3A molecular sieve particles for 4 h, then mechanically ball-milling for 4 h at the rotating speed of 350 r/h, and crushing into powder;
(2) adding 5 g of 3A molecular sieve powder obtained in the step (1) into 120 ml of LiCl aqueous solution with the concentration of 2 mol/L, and uniformly stirring and mixing to form suspension;
(3) heating the mixed solution obtained in the step (2) at 80 ℃ and stirring for 4 h;
(4) centrifuging the mixed solution treated in the step (3) for 5 min at the rotating speed of 8000 r/min, and washing for 3 times by using deionized water;
(5) repeating the molecular sieve powder obtained in the step (4) for 3 times according to the experimental processes of the steps (2), (3) and (4), and drying to obtain lithiated molecular sieve powder;
(6) mixing the lithiated molecular sieve powder obtained in the step (5) with a binder polyvinylidene fluoride, a surfactant PVP and a solvent DMF according to a ratio of 20: 6: 0.4: uniformly mixing the components in a mass ratio of 100, and then ball-milling the mixture for 3 hours at a rotating speed of 400 r/min to obtain slurry of the lithiated molecular sieve coating;
(7) respectively preparing 500 ml of tannin aqueous solution with the mass fraction of 2.5 mg/L and 500 ml of polyethyleneimine aqueous solution with the mass fraction of 1.0 mg/ml, sequentially placing the base membrane cleaned by ethanol in the tannin and polyethyleneimine aqueous solution for reaction for 5 hours, taking out, cleaning by using deionized water and drying;
(8) coating the slurry obtained in the step (6) on the single surface or double surfaces of the base film obtained in the step (7) in a scraping mode, wherein the thickness of the base film is 16 microns;
(9) and (4) drying the uniformly coated composite membrane obtained in the step (8) at 70 ℃ for 24 h in vacuum to obtain a lithiated molecular sieve coating composite membrane, wherein the thickness of the composite membrane is 19 microns.
Comparative example 1
The cell was assembled using a polyethylene-based film as the separator for testing. The assembled battery type is CR-2032 button cell battery with LiCoO 2 As positive electrode material (when assembling Li/Li symmetrical battery, the positive electrode material is also lithium sheet), lithium sheet is used as negative electrode material, and a certain quantity of LiPF is added 6 The battery was assembled in a vacuum glove box filled with argon.
Comparative example 2
The polarization treatment method of the separator was the same as that in the step (7) of example 1, and the battery was assembled by using the polyethylene separator after the polarization treatment as the separator. The assembled battery type is CR-2032 button cell battery with LiCoO 2 As positive electrode material (when assembling Li/Li symmetrical battery, the positive electrode material is also lithium sheet), lithium sheet is used as negative electrode material, and a certain quantity of LiPF is added 6 The battery was assembled in a vacuum glove box filled with argon.
Comparative example 3
The preparation method of the molecular sieve coated composite separator was the same as in example 1, step (1), step (6), step (7), step (8) and step (9), except that the unlithiated molecular sieve was used and the unlithiated molecular sieve coated composite separator was used as a separator to assemble a battery for testing. The assembled battery type is CR-2032 button cell type, and LiCoO 2 As positive electrode material (when assembling Li/Li symmetrical battery, the positive electrode material is also lithium sheet), lithium sheet is used as negative electrode material, and a certain quantity of LiPF is added 6 The battery was assembled in a vacuum glove box filled with argon.
Four different membranes were assembled into LiCoO 2 The electrochemical performance of the/Li button cell is tested. Figure 3 reflects the results of impedance testing, with cells assembled using lithiated molecular sieve coated composite separator membranes having minimal interfacial impedance and experiencing significantly reduced resistance to ion diffusion. Fig. 4 illustrates that the long cycle stability and capacity retention of the cell assembled with the lithiated molecular sieve coated composite separator are significantly improved, and the cell has a discharge capacity decay rate of only 0.12% after 100 cycles, which is much lower than 0.26% of that of the PE separator and 0.27% of that of the untreated molecular sieve coated composite separator; even under the high current density of 5C, the battery using the lithiated molecular sieve coating composite diaphragm can still maintain 0.70 mAh/cm 2 The capacity retention rate of the discharge capacity is obviously improved.
FIG. 5 shows the results of constant current tests performed on Li/Li symmetric batteries assembled by the PE separator and the lithiated composite separator with the molecular sieve coating. It can be seen from the figure that after the lithiated molecular sieve coating is introduced, the polarization voltage of the symmetrical cell is obviously reduced, and the stable cycle can exceed 500 h.
The foregoing is only a preferred embodiment of this invention and it should be noted that modifications can be made by those skilled in the art without departing from the principle of the invention and these modifications should also be considered as the protection scope of the invention.
Claims (10)
1. The composite diaphragm for the lithium ion battery is characterized in that the composite diaphragm is formed by coating lithiated molecular sieve particles on the surface of a base film, and the lithiated molecular sieve functional particles uniformly cover the surface of a polyethylene base film.
2. The composite separator for a lithium ion battery according to claim 1, wherein the thickness of the lithiated molecular sieve composite separator is 10 to 35 μm.
3. The composite separator for a lithium ion battery according to claim 1 or 2, wherein the base film is an organic monomer-modified polyethylene film.
4. A preparation method of a composite diaphragm for a lithium ion battery is characterized by comprising the following steps:
(1) pulverizing molecular sieve particles into powder;
(2) adding the molecular sieve powder obtained in the step (1) into a LiCl aqueous solution, and uniformly stirring and mixing to form a suspension;
(3) heating the mixed solution obtained in the step (2) at 50 ℃ and stirring for 6-10 h;
(4) centrifuging the mixed solution treated in the step (3) for 5-8 min at the rotating speed of 8000-10000 r/min, and washing for 3 times by using deionized water;
(5) repeating the molecular sieve powder obtained in the step (4) for 3-5 times according to the experimental processes of the steps (2), (3) and (4), and drying to obtain lithiated molecular sieve powder;
(6) mixing the lithiated molecular sieve powder obtained in the step (5) with a binder, a surfactant and a solvent according to a certain mass ratio, and performing ball milling at a rotating speed of 250-350 r/min for 4 hours to obtain slurry of a lithiated molecular sieve coating;
(7) respectively preparing an aqueous solution of tannic acid and an aqueous solution of polyethyleneimine, sequentially placing the base film cleaned by ethanol in the aqueous solutions of tannic acid and polyethyleneimine for reacting for 1-3 h, taking out, cleaning with deionized water and drying;
(8) coating the slurry obtained in the step (6) on the single surface or double surfaces of the base film obtained in the step (7) in a blade mode;
(9) and (4) drying the uniformly coated composite membrane obtained in the step (8) at 70 ℃ for 24 h in vacuum to obtain the lithiated molecular sieve coating composite membrane.
5. The preparation method of the composite diaphragm for the lithium ion battery according to claim 4, wherein the molecular sieve is pulverized into powder in step (1) through manual grinding and mechanical ball milling in sequence, the time of the manual grinding is 2-5 h, the time of the mechanical ball milling is 8-12 h, and the rotating speed is 300-500 r/min.
6. The method for preparing a composite separator for a lithium ion battery according to claim 4, wherein the mass of the molecular sieve powder in the step (2) is 2-5 g, the concentration of the LiCl aqueous solution is 1.0-2.0 mol/L, and the volume is 60-120 ml.
7. The preparation method of the composite separator for the lithium ion battery according to claim 4, wherein the ratio of the lithiated molecular sieve powder to the binder, the surfactant and the solvent in the step (6) is in the range of 8-10: 2-3: 0.1-0.2: 45-55 mass ratio.
8. The method according to claim 4 or 7, wherein the binder is polyvinylidene fluoride, lithium polyacrylate, styrene butadiene rubber or sodium carboxymethylcellulose, the surfactant is PVP or CTAB, and the solvent is DMF, water, absolute ethanol or NMP.
9. The method for preparing a composite separator for a lithium ion battery according to claim 4, wherein the concentration of the aqueous solution of tannic acid in the step (7) is 1 to 3 mg/ml, and the concentration of the aqueous solution of polyethyleneimine is 0.25 to 1 mg/ml.
10. The method of preparing a composite separator for a lithium ion battery according to claim 4 or 9, wherein the base film in steps (7) and (8) is a polyvinyl base film having a thickness of 5 to 25 μm.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115842214A (en) * | 2022-10-18 | 2023-03-24 | 福州大学 | High-voltage-resistant low-self-discharge diaphragm with screening effect, preparation method and application |
| CN116845483A (en) * | 2023-08-31 | 2023-10-03 | 天津市捷威动力工业有限公司 | Composite diaphragm, preparation method thereof and secondary battery |
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| CN115842214A (en) * | 2022-10-18 | 2023-03-24 | 福州大学 | High-voltage-resistant low-self-discharge diaphragm with screening effect, preparation method and application |
| CN115842214B (en) * | 2022-10-18 | 2024-07-09 | 福州大学 | High-pressure-resistant low-self-discharge diaphragm with screening effect, preparation method and application |
| CN116845483A (en) * | 2023-08-31 | 2023-10-03 | 天津市捷威动力工业有限公司 | Composite diaphragm, preparation method thereof and secondary battery |
| CN116845483B (en) * | 2023-08-31 | 2023-11-28 | 天津市捷威动力工业有限公司 | Composite diaphragm, preparation method thereof and secondary battery |
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| CN114883748B (en) | 2023-07-11 |
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