Lithium supplementing diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a lithium supplementing diaphragm as well as a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The preparation method of the lithium supplement diaphragm comprises the following steps: S1, preparing a lithium supplement agent: dispersing a lithium supplement material in a first solvent, adding a silane coupling agent for modification, washing with the first solvent, and drying to obtain powder; mixing the powder, a polymer monomer and a second solvent, adding an initiator for polymerization reaction, filtering, washing and drying to obtain a polymer coated lithium supplement agent; s2, preparing lithium supplementing slurry: uniformly mixing a polymer coated lithium supplementing agent, inorganic ceramic, a dispersing agent, a binding agent, a thickening agent, a wetting agent and a third solvent to obtain the lithium supplementing slurry; and S3, coating: coating at least one surface of a diaphragm base material with the lithium supplementing slurry, drying, rolling and slitting. The lithium supplementing diaphragm provided by the invention not only solves the problem of poor environmental stability of a lithium supplementing material, but also improves the bonding force between the diaphragm and the pole piece, and the positive pole piece, the negative pole piece and the diaphragm do not need to be additionally glued when a battery is assembled.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a lithium-supplementing separator and a preparation method and application thereof. Background Art

[0002] During the first charge and discharge process of the battery, the electrolyte will undergo a reduction decomposition reaction on the surface of the negative electrode and form a solid electrolyte interface film (SEI film). The formation of the SEI film will consume a large amount of active lithium, resulting in a decrease in the actual energy density of the battery compared to the theoretical calculated value. In order to improve the first efficiency of lithium-ion batteries, the lithium-supplementing technology has emerged, that is, by means of lithium supplementation, this part of the irreversible capacity loss is eliminated, and the battery energy density and other electrical properties are improved. Currently known lithium-supplementing methods include positive electrode lithium supplementation, negative electrode lithium supplementation, separator lithium supplementation, and electrolyte lithium supplementation.

[0003] Chinese Patent CN 117438581 A coats rare metal elements on the surface of the Li 5 FeO 4 material to improve the electronic conductivity of the material. Compared with other metals (such as manganese, cobalt, aluminum, vanadium, etc.), it has the advantages of strong activity and high electronic conductivity, and can significantly improve the first efficiency of the Li 5 FeO 4 material and reduce the impedance of the material; then an organic polymer material is coated on the outermost layer to isolate air, moisture from contacting the inner core Li 5 FeO 4 contact, prevent the formation of lithium carbonate, reduce the pH value and improve the specific capacity performance of the material. However, after the lithium-supplementing agent is injected, the organic polymer is dissolved, and then the rare metal oxide composite directly contacts the electrolyte. The polymer dissolved in the electrolyte may cause unknown side reactions.

[0004] Chinese Patent CN111613759A discloses a separator slurry, a preparation method thereof, a separator and a lithium-ion battery. The separator slurry includes a dispersant, a main material of the glue layer, a thickener, a binder, and a lithiated material. In the separator slurry provided by this solution, there is a synergistic effect between the main material of the glue layer and the lithiated material. The lithiated material occupies the position of the main material of the glue layer. During the electrochemical reaction process, the lithiated material will react, migrate lithium ions in the electrolyte, and release some occupied sites, achieving the purpose of pore formation and improving the problem of the coating layer clogging the pores of the base film. At the same time, the released lithiated material will supplement lithium to the electrode during pore formation, increase the first-week reversible capacity of the battery, increase the battery energy density, and reduce the electrode polarization phenomenon. However, this solution is only applicable to oil-based glue layer coating, which is not environmentally friendly and costly. In addition, the too strong adhesive force of the electrode will affect the electrolyte infiltration performance, and there is a risk of failure of the lithium-supplementing material in direct contact with air. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a lithium supplementing separator capable of improving the battery cycle performance; another purpose of the present invention is to provide a preparation method of a lithium supplementing separator capable of improving the battery cycle performance; another purpose of the present invention is to provide an application of a lithium supplementing separator capable of improving the battery cycle performance.

[0006] The present invention discloses a preparation method of a lithium supplementing separator, comprising the following steps:

[0007] S1 Preparation of lithium supplementing agent: Dispersing the lithium supplementing material in a first solvent, adding a silane coupling agent for modification, then washing with a first organic solvent, and drying to obtain a powder; Mixing the powder, polymer monomer and a second solvent, adding an initiator for polymerization reaction, filtering, washing, and drying to obtain the lithium supplementing agent;

[0008] S2 Preparation of lithium supplementing slurry: Mixing the lithium supplementing agent, inorganic ceramic, dispersant, binder, thickener, wetting agent and a third solvent uniformly to obtain the lithium supplementing slurry;

[0009] S3 Coating: Coating the lithium supplementing slurry on at least one side of the separator substrate, drying, winding, and slitting to obtain the lithium supplementing separator.

[0010] Further, in the step S1, the lithium supplementing material includes one or at least two of lithium powder, lithium ferrite, lithium nickelate, lithium oxide, and lithium sulfide.

[0011] Further, the surface of the lithium supplementing material is coated with a carbon layer.

[0012] After the lithium supplementing material is coated with a carbon layer, its de-lithiation decomposition potential can be reduced, enabling it to play a lithium supplementing role at a lower voltage.

[0013] Further, in the step S1, the first solvent includes one or at least two of methanol, ethanol, and propylene glycol.

[0014] Further, in the step S1, the silane coupling agent includes one or at least two of vinyl silane, amino silane, methacryloxy silane, and ureido silane.

[0015] The second solvent includes toluene and / or xylene. The initiator includes one or at least two of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, and persulfate.

[0016] The particle size of the lithium supplementing material is 2 - 10 μm.

[0017] Further, in the step S1, the mass ratio of the added polymer monomer to the added lithium supplement material is 5-20:100; the polymer monomer includes olefin monomers and acrylate monomers, and the mass ratio of olefin monomers to acrylate monomers is 2:8-8:2.

[0018] Acrylate monomers can provide adhesion to the electrode sheet, and olefin monomers can reduce the swelling degree of the entire polymer and reduce the risk of coating diaphragm pore blockage.

[0019] The olefin monomers include one or more of ethylene, propylene, butadiene, styrene, and acrylonitrile.

[0020] The acrylate monomers include one or more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, and butyl acrylate.

[0021] The third solvent includes one or more of methanol, ethanol, propylene glycol, acetone, N,N-dimethylacetamide, N-methylpyrrolidone, and water.

[0022] The polymer monomer undergoes a polymerization reaction under the action of an initiator, and the generated polymer coats the outer surface of the lithium supplement material particles to form a lithium supplement agent with a core-shell structure. The lithium supplement material particles are the core, and the polymer coating layer is the shell layer. The shell layer thickness is 0.3-5 μm, and the D50 of the lithium supplement agent particles is 0.5-7 μm. The glass transition temperature of the polymer coating layer is 30-70 °C.

[0023] Controlling the glass transition temperature of the polymer coating layer within this range can obtain good electrode sheet adhesion at a lower hot pressing temperature.

[0024] Further, in the step S2, according to mass parts, the composition of the solid substances in the lithium supplement slurry:

[0025] Lithium supplement agent 1.5-10 parts;

[0026] Inorganic ceramic 15-45 parts;

[0027] Dispersant 0-4 parts;

[0028] Binder 0.1-7 parts;

[0029] Thickener 1-8 parts;

[0030] Wetting agent 0.05-0.3 parts.

[0031] The inorganic ceramic includes at least one of alumina, boehmite, silica, magnesia, titanium dioxide, zirconium dioxide, barium sulfate, and oxide solid electrolyte; the dispersant is selected from one or more of polyacrylic acid, ammonium polyacrylate, sodium polyacrylate, potassium polyacrylate, polyacrylamide, and sodium lauryl ether sulfate; the thickener is selected from one or more of hydroxymethyl cellulose, sodium carboxymethyl cellulose, water-soluble biopolysaccharide, and polyamide wax; the binder is selected from one or more of polyacrylic acid, butyl acrylate, polyacrylamide, polymethyl methacrylate-butyl acrylate, polyvinylidene fluoride, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoropropylene copolymer, and the wetting agent is selected from one or more of polyoxyethylene alkylphenol ether, alkylphenol polyoxyethylene ether, sodium dodecyl sulfate, sodium alkylbenzene sulfonate, and polyoxyethylene alkylamine.

[0032] The separator substrate includes polyethylene (PE) and / or polypropylene (PP).

[0033] Further, in the step S3, the coating amount of the lithium supplement slurry is 1-8 g / m 2 .

[0034] The present invention also discloses a lithium supplement separator obtained by the preparation method described above.

[0035] The present invention also discloses an application of the lithium supplement separator. As described above, the lithium supplement separator is applied to the preparation of a lithium-ion battery. The positive electrode sheet, the separator, and the negative electrode sheet are stacked and hot-pressed to obtain a lithium battery cell.

[0036] A lithium supplement separator provided by the present invention coats a lithium supplement agent with a core-shell structure on a separator substrate to prepare a lithium supplement separator. The separator and the electrode sheet are hot-pressed through a hot-pressing process. Under the action of pressure, the polymer shell layer breaks to release the lithium supplement material, and the lithium supplement material can participate in the electrochemical reaction to play a lithium supplement role. At the same time, the polymer shell layer softens and bonds with the electrode sheet under the action of temperature, which not only solves the problem of poor environmental stability of the lithium supplement material, but also improves the adhesion between the separator and the electrode sheet. When assembling the battery, the positive electrode sheet and the negative electrode sheet do not require additional glue coating with the separator. Detailed Embodiments

[0037] To make the technical solution of the present invention clearer, the following further describes the present invention in detail with specific embodiments.

[0038] Example 1

[0039] S1 Preparation of lithium supplement agent: Lithium ferrite is dispersed in ethanol, and methacryloxypropyltrimethoxysilane is added dropwise (the mass ratio of methacryloxypropyltrimethoxysilane to lithium ferrite is 5:100). The reaction is carried out at 80 °C for 24 h, washed with ethanol and dried at 65 °C for 12 h. The lithium ferrite modified with silane coupling agent is dispersed in toluene, and styrene monomer and methyl methacrylate monomer with a mass ratio of 6:4 are added, and the total monomer mass accounts for 8 wt% of the lithium ferrite mass. The temperature is raised to 80 °C. An azodiisobutyronitrile initiator with a mass ratio of 5 wt% of the total polymer monomer mass is added, and the reaction time is 12 h, and the drying temperature is 80 °C. The prepared composite lithium supplement material has a core diameter of 4 μm, a polymer shell layer thickness of 0.8 μm, a glass transition temperature of 55 °C, and a lithium supplement agent particle size D50: 5 μm.

[0040] S2 Preparation of lithium supplement slurry: 3 parts of lithium supplement agent, 27 parts of alumina, 0.5 part of sodium polyacrylate, 3 parts of sodium carboxymethylcellulose, 5 parts of butyl acrylate, and 0.1 part of sodium dodecyl sulfate are added to 62 parts of acetone according to mass parts and mixed evenly to obtain the lithium supplement slurry.

[0041] S3 Coating: The lithium supplement slurry is coated on one side of a 9um PE base film, and the coating areal density is 5 g / m 2 .

[0042] The dried separator is assembled with the positive and negative electrode plates into an electric core, and hot pressing is carried out before injection. The temperature is 50 °C and the hot pressing time is 90 s, and then normal injection, pre-charging formation, and cycling are carried out.

[0043] Example 2

[0044] The difference between this example and Example 1 is that the styrene monomer is replaced with acrylonitrile. The prepared composite lithium supplement material has a core diameter of 4 μm, a shell layer thickness of 0.8 μm, a particle size D50: 5 μm, and a glass transition temperature of 65 °C, and this composite lithium supplement material is configured into a slurry and coated on a polyolefin substrate

[0045] Example 3

[0046] The difference between this example and Example 1 is that the proportion of the total polymer monomer mass is reduced to 5% of the lithium ferrite mass. The prepared composite lithium supplement material has a core diameter of 2 μm, a shell layer thickness of 0.4 μm, a particle size D50: 3 μm, and a glass transition temperature of 55 °C, and this composite lithium supplement material is configured into a slurry and coated on a polyolefin substrate

[0047] Example 4

[0048] The difference between this example and Example 1 is that the ratio of styrene to acrylate in the polymer monomer is adjusted to 3:7, the total mass ratio of the polymer monomer is increased to 15% of the mass of lithium ferrite, the core diameter of the prepared composite lithium supplement material is 2 μm, the shell thickness is 2 μm, the particle size D50 is 5 μm, the glass transition temperature is 45 °C, and this composite lithium supplement material is configured into a slurry and coated on a polyolefin substrate.

[0049] Example 5

[0050] The difference between this example and Example 1 is that lithium ferrite is replaced with carbon-coated lithium ferrite. The core diameter of the prepared composite lithium supplement material is 4 μm, the shell thickness is 0.8 μm, the particle size D50 is 5 μm, the glass transition temperature is 55 °C, and this composite lithium supplement material is configured into a slurry and coated on a polyolefin substrate.

[0051] Example 6

[0052] The difference between this example and Example 1 is that acetone in Step S2 is replaced with pure water. The core diameter of the prepared composite lithium supplement material is 4 μm, the polymer shell thickness is 0.8 μm, the glass transition temperature is 55 °C, the particle size of the lithium supplement agent D50 is 5 μm, the glass transition temperature is 55 °C, and this composite lithium supplement material is configured into a slurry and coated on a polyolefin substrate.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is that "lithium ferrite" is not added, and only the polymer is used for coating.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that lithium ferrite is directly mixed into the diaphragm coating slurry for coating.

[0057] Performance test:

[0058] The pole piece adhesion, delithiation decomposition potential, initial efficiency and normal temperature cycle tests were carried out on the batteries assembled with Examples 1-6 and Comparative Examples 1-2, and the test results are shown in Table 1 below.

[0059] Table 1 Performance test result table

[0060] Sample Pole piece adhesion force (N / m) <![CDATA[De-lithiation decomposition potential (V vs Li ＋ / Li)]]> Initial efficiency (%) Capacity retention rate after 500 cycles at room temperature (%) Example 1 5.4 4.25 97.0 95.2 Example 2 2.7 4.2 96.6 95.7 Example 3 2.2 4.22 94.3 93.5 Example 4 7.3 4.19 90.9 91.0 Example 5 5.8 3.89 97.3 95.4 Example 6 4.3 4.21 96.7 94.5 Comparative Example 1 5.6 \ 90.7 90.2 Comparative Example 2 0 4.25 90.8 90.4

[0061] Comparing the test data of the coated diaphragms of each example and comparative example, the electrode adhesion of Example 4 > Example 5 ≈ Comparative Example 1 ≈ Example 1 > Example 6 > Example 2 ≈ Example 3 > Comparative Example 2. The electrode adhesion is related to the thickness of the polymer shell layer. After the polymer shell layer in Example 4, the electrode adhesion is strong. The electrode adhesion is also related to the glass transition temperature of the polymer. In Example 2, acrylonitrile was used, and the obtained polymer-coated lithium supplement agent had a relatively high glass transition temperature. Under the same hot pressing conditions, the polymer was not completely softened, and the adhesion was weaker than that of Example 1. The electrode adhesion of Example 3 was also weak because the particle size of the lithium supplement agent used was small, and the finally obtained polymer-coated lithium supplement agent had a small particle size and was embedded in the inorganic ceramic particles during the mixing and coating process with the inorganic ceramic, resulting in a small electrode adhesion. Example 6 adopted an aqueous coating process, and the adhesion decreased slightly compared with Example 1, but it could still meet the production requirements of the battery cell.

[0062] Comparing the delithiation decomposition potential, it can be seen that the delithiation decomposition potential of Example 5 decreased significantly. This is because the use of carbon-coated lithium supplement material improved the conductivity, enabling it to play the role of lithium supplementation at a lower voltage.

[0063] Comparing the first efficiency and normal temperature cycle data, it can be seen that the polymer-coated lithium supplement agent and ceramic mixed-coated diaphragm can improve the first efficiency and normal temperature cycle capacity retention rate. In Comparative Example 1, an uncoated lithium supplement agent was used, and the lithium supplement material became ineffective due to long-term exposure to air, resulting in no improvement in the first efficiency and normal temperature cycle capacity retention rate of the battery. In Example 4, due to the large thickness of the polymer shell layer, the polymer shell layer could not be destroyed under pressure to expose the lithium supplement material, so it could not play its lithium supplementation role either. The first efficiency and normal temperature cycle of Example 6 also increased significantly, indicating that the air and moisture stability of the lithium supplement material after polymer coating was significantly improved. The polymer-coated lithium supplement material can adopt an aqueous coating process, which is more environmentally friendly.

[0064] In summary, the polymer-coated lithium supplement agent and ceramic mixed-coated diaphragm can achieve excellent electrode adhesion and at the same time exhibit excellent lithium supplementation effect.

[0065] The above-described examples only represent several embodiments of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A method for preparing a lithium supplementing diaphragm, characterized in that: The following steps are involved: S1: preparing a lithium supplement agent: dispersing a lithium supplement material in a first solvent, adding a silane coupling agent for modification, washing with the first solvent, and drying to obtain a powder; mixing the powder, a polymer monomer, and a second solvent, adding an initiator for polymerization, filtering, washing, and drying to obtain a polymer-coated lithium supplement agent; S2 preparing lithium replenishing slurry: uniformly mixing the polymer-coated lithium replenishing agent, inorganic ceramics, dispersant, binder, thickener, wetting agent and third solvent to obtain lithium replenishing slurry; S3 coating: coating the lithium supplement slurry on at least one side of the separator substrate, drying, rolling up, and slitting to obtain a lithium supplement separator.

2. The method for preparing a lithium supplementing diaphragm according to claim 1, characterized in that: In the step S1, the lithium supplement material includes one or at least two of lithium powder, lithium ferrite, lithium nickelate, lithium oxide, and lithium sulfide.

3. The method for preparing a lithium supplementing diaphragm according to claim 2, characterized in that: The surface of the lithium supplement material is coated with a carbon layer.

4. The method for preparing a lithium supplementing diaphragm according to claim 1, characterized in that: In the step S1, the first solvent includes one or at least two of methanol, ethanol, and propylene glycol.

5. The method for preparing a lithium supplementing diaphragm according to claim 1, characterized in that: In the step S1, the silane coupling agent includes one or at least two of vinyl silane, amino silane, methacryloxy silane, and urea silane.

6. The method for preparing a lithium supplementing diaphragm according to claim 1, characterized in that: In the step S1, the mass ratio of the added polymer monomer to the added lithium supplement material is 5-20:100; the polymer monomer includes olefin monomers and acrylates, wherein the mass ratio of olefin monomers to acrylate monomers is 2:8-8:

2.

7. The method for preparing a lithium supplementing diaphragm according to claim 1, characterized in that: In the step S2, the composition of the solid matter in the lithium supplement slurry is as follows according to the mass fraction: 1.5-10 parts of lithium supplement; 15-45 parts of inorganic ceramics; Dispersant 0-4 parts; Binder 0.1-7 parts; Thickener 1-8 parts; Wetting agent 0.05-0.3 parts.

8. The method for preparing a lithium supplementing diaphragm according to claim 1, characterized in that: In step S3, the coating amount of lithium supplement slurry is 1-8 g / m 2 .

9. A lithium supplementing diaphragm, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. An application of a lithium supplementing diaphragm, characterized in that: The lithium-supplementing diaphragm as claimed in claim 9 is used in the preparation of lithium-ion batteries, and the positive electrode sheet, the diaphragm, and the negative electrode sheet are stacked and hot-pressed to obtain a lithium battery cell.