Low-moisture composite diaphragm as well as preparation method and application thereof

Abstract

The embodiment of the invention relates to a low-moisture composite diaphragm as well as a preparation method and application thereof. The preparation method comprises the following steps: adding a coating material into a composite solvent containing ammonia gas, and carrying out wet grinding to obtain a nano-scale dispersion liquid; centrifuging and enriching the nanoscale dispersion liquid to obtain material particles, adding the material particles into a solvent containing a hydrophobic dispersant, uniformly dispersing the material particles, and centrifuging and enriching the material particles again to obtain nano powder particles coated with the hydrophobic dispersant; drying and crushing the nano powder particles under a gradient heating condition to obtain a nano powder material; the preparation method comprises the following steps: homogenizing a nano powder material and a coating auxiliary agent together to prepare coating slurry, filtering, coating a base membrane with the coating slurry, and drying to obtain the low-moisture composite diaphragm. New hydrogen bonds are formed by lone pair electrons of ammonia molecules and hydrogen atoms in water molecules, the number of hydrogen bonds directly formed between the water molecules is reduced, the density of the hydrogen bonds between the water molecules is reduced, moisture in a coating material is more volatile, and therefore the moisture content of the diaphragm is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, and in particular to a low-moisture composite separator, its preparation method, and its application. Background Technology

[0002] The coated separator is one of the key internal components in the structure of lithium batteries. Its function is to separate and recover the positive and negative electrodes of the battery to prevent short circuits. At the same time, ions in the electrolyte can form a pathway through the separator, making it a high-value-added industrial product.

[0003] The properties of the coated separator mainly include air permeability, thickness, heat shrinkage, peel strength, and water content. These properties will affect the charging and discharging performance and safety performance of the battery, and make a great contribution to the overall performance of the battery.

[0004] Currently, the coated membrane manufacturing industry widely uses alumina, boehmite, and emerging solid electrolyte materials as membrane coatings, with oxides being the primary solid electrolyte material. Oxide solid electrolyte coatings not only possess the high heat resistance of alumina and boehmite-based materials but also provide additional ion conduction channels, significantly improving battery cycle life and safety performance.

[0005] However, oxide solid electrolytes typically have high hydrophilicity and are more prone to water absorption compared to alumina and boehmite. Therefore, their use in coated separators may increase the moisture content of the separator, thus affecting battery safety and cycle performance. Controlling and reducing the moisture content and water absorption of oxide solid electrolyte separators is therefore a key condition for the widespread application of this technology. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-moisture composite separator, its preparation method, and its applications. By introducing ammonia to regulate the solvent environment, the direct hydrogen bonding between water molecules is reduced, lowering the density of hydrogen bonds and enhancing the volatility of water in the material, thus reducing the moisture content in the final separator. Adding a hydrophobic dispersant during centrifugation further reduces the separator's moisture content. A multi-step gradient temperature drying process avoids particle agglomeration caused by drying, and by controlling the temperature gradient, free and bound water in the nanoparticle material are removed stepwise. The preparation method of this invention effectively reduces separator moisture, improves the separator's moisture resistance and water evaporation performance, thereby enhancing the battery's cycle stability.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a low-moisture composite membrane, comprising:

[0008] The coating material is added to a composite solvent containing ammonia and wet-milled to obtain a nanoscale dispersion. The coating material includes an oxide solid electrolyte material. In the nanoscale dispersion, the lone pair electrons of ammonia molecules form new hydrogen bonds with hydrogen atoms in water molecules, thereby reducing the number of hydrogen bonds directly formed between water molecules and lowering the density of hydrogen bonds between water molecules. This makes the water in the coating material more volatile and reduces the water content.

[0009] The nanoscale dispersion was centrifuged and enriched to obtain material particles;

[0010] The enriched material particles were added to a solvent containing a hydrophobic dispersant and dispersed evenly. The particles were then centrifuged and enriched again to obtain nanoparticles coated with a hydrophobic dispersant.

[0011] The nanoparticles are dried under a gradient heating condition, and the dried material is pulverized to obtain nanoparticle material.

[0012] The nanoparticle material is homogenized with a coating aid to prepare a coating slurry. The coating slurry is filtered and then coated onto a base membrane. After drying, the low-moisture composite membrane is obtained.

[0013] Preferably, before adding the enriched material particles to a solvent containing a hydrophobic dispersant and dispersing them evenly, and then centrifuging and enriching them again to obtain nanoparticles coated with the hydrophobic dispersant, the method further includes:

[0014] The nanoscale dispersion is centrifuged and enriched, and the resulting material particles are evenly dispersed in a solvent containing or without the hydrophobic dispersant. The process is repeated once or multiple times.

[0015] Preferably, the oxide solid electrolyte material includes one or more of lithium titanium aluminum phosphate, lithium lanthanum titanate, lithium lanthanum zirconium oxide, or lithium lanthanum zirconium tantalum oxide.

[0016] The coating material further includes: alumina and / or boehmite;

[0017] The composite solvent includes at least one of acetone, alcohol, ethyl acetate, deionized water, isopropanol, isobutanol, and dimethyl sulfoxide; the ammonia content in the composite solvent is 0.5-35 wt%.

[0018] The solid content in the nanoscale dispersion is 1-60 wt%.

[0019] The particle size D50 of the nanoscale dispersion is 10-1000 nm, and the particle size distribution span is between 1 and 5.

[0020] The solvent containing the hydrophobic dispersant contains 0.1-10 wt% of the hydrophobic dispersant.

[0021] The hydrophobic dispersant includes at least one of the following: ammonium polyacrylate, sodium polyacrylate, styrene-acrylic acid copolymer, polyoxyethylene fatty acid ester, polyoxyethylene-polyoxypropylene polymer, lignin sulfonate, hydrophobic eutectic solvent HDESs, and polyacetonitrile.

[0022] Preferably, the centrifugation speed is 1000-20000 r / min, and the centrifugation time is 0.1-5 hours;

[0023] The particle size distribution of the material has a span between 0.5 and 1.

[0024] The particle size distribution of the nanopowder particles spans between 0.1 and 0.5.

[0025] Preferably, the drying under gradient temperature conditions specifically includes:

[0026] First, dry at 80-130℃ for 1-48 hours, then raise the temperature and dry at 131-180℃ for 1-48 hours, then continue to raise the temperature and dry at 181-300℃ for 1-36 hours.

[0027] Preferably, the coating aid includes: a thickener, a wetting and dispersing agent, and a binder; or, the coating aid includes a wetting and dispersing agent and a binder.

[0028] The thickener includes one or more of the following: carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide wax, polyoxyethylene, and hydroxypropyl cellulose methyl ether; the mass ratio of the thickener to the coating material is 0:100 to 5:95.

[0029] The dispersant comprises one or more of the following: sodium metasilicate, trisodium nitrate, sodium pyrophosphate, sodium dodecyl sulfate, sodium hexametaphosphate, polyacrylic acid, sodium polyacrylate, polybutyl acrylate-styrene-acrylic acid, polyethylene glycol, polyvinylpyrrolidone, maleic anhydride-styrene copolymer, sodium lauryl sulfate, sodium lauryl polyoxyethylene ether sulfate, sodium dioctyl succinate sulfonate, sodium glycol monobutyl ether phosphate, sodium dodecylbenzene sulfonate, and octylphenol polyoxyethylene ether; the mass ratio of the dispersant to the coating material is 0.5:99.5 to 10:90.

[0030] The adhesive comprises one or more of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, polymethyl methacrylate, polymethyl methacrylate-butyl acrylate, styrene-butadiene rubber, and polyvinyl acetate; the mass ratio of the adhesive to the coating material is 1:99 to 30:70.

[0031] Preferably, the step of filtering the coating slurry, coating it onto the base membrane, and drying it to obtain the low-moisture composite membrane specifically includes:

[0032] The coating slurry is filtered through a 100-2000 mesh and then coated onto the base membrane by roller coating. The coating thickness is 0.1-4 μm. The coating is then dried at 40-85℃ for 5-60 min to obtain the low-moisture composite membrane.

[0033] Preferably, the base film includes: a polyethylene film prepared by wet process, a polyethylene film prepared by dry process, a polypropylene film, or a cellulose film;

[0034] The thickness of the base film is 3-50 μm; the porosity is 30%-50%.

[0035] Secondly, embodiments of the present invention provide a low-moisture composite membrane prepared by the preparation method described in the first aspect above.

[0036] Thirdly, embodiments of the present invention provide an application of the low-moisture composite separator prepared by the preparation method described in the first aspect above, wherein the low-moisture composite separator is used in liquid lithium-ion batteries or semi-solid lithium-ion batteries.

[0037] The method for preparing a low-moisture composite separator provided in this invention involves firstly using a composite solvent containing ammonia during wet milling. This allows the lone pairs of electrons in the ammonia molecules to form new hydrogen bonds with the hydrogen atoms in the water molecules, reducing the direct hydrogen bond connections between water molecules and lowering the density of hydrogen bonds, thereby significantly enhancing the volatility of moisture. Combined with hydrophobic dispersant coating during centrifugation enrichment, this further helps reduce the moisture content of the separator. A gradient-heating drying step effectively avoids powder agglomeration and further reduces free and bound water in the nanoparticles, ultimately producing a separator with low moisture content and high moisture resistance. The low-moisture composite separator prepared by this invention has a moisture content of less than 2000 ppm. When applied to lithium batteries, it can effectively improve the cycle stability and safety performance of the battery. Attached Figure Description

[0038] Figure 1 A flowchart illustrating the preparation method of the low-moisture composite membrane provided in this embodiment of the invention;

[0039] Figure 2This is a comparison chart showing the cycle capacity retention of soft-pack batteries assembled with separators in the embodiments of the present invention and in the comparative examples. Detailed Implementation

[0040] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] This invention provides a low-moisture composite membrane, its preparation method, and its application. Figure 1 The following is a flowchart of the preparation method for low-moisture composite membranes, combined with... Figure 1 First, the preparation method will be explained.

[0042] like Figure 1 As shown, the preparation method of the low-moisture composite membrane proposed in this invention mainly includes the following steps:

[0043] Step 110: The coating material is added to a composite solvent containing ammonia and wet-milled to obtain a nanoscale dispersion.

[0044] The coating material includes oxide solid electrolyte materials; the oxide solid electrolyte materials preferably include one or more of lithium titanium aluminum phosphate, lithium lanthanum titanate, lithium lanthanum zirconium oxide, or lithium lanthanum zirconium tantalum oxide.

[0045] In addition, the coating material may optionally include, in addition to oxide solid electrolyte materials, alumina and / or boehmite.

[0046] The composite solvent of this invention is selected from volatile solvents, including at least one of acetone, alcohol, ethyl acetate, deionized water, isopropanol, isobutanol, and dimethyl sulfoxide, and more preferably includes at least two of them.

[0047] The ammonia content in the composite solvent is 0.5-35 wt%.

[0048] The particle size D50 of the nanoscale dispersion is 10-1000 nm, and the particle size distribution span is between 1 and 5.

[0049] In the nanoscale dispersion obtained in this step, the introduction of ammonia gas allows the lone pair electrons of ammonia molecules to form new hydrogen bonds with hydrogen atoms in water molecules, thereby reducing the number of hydrogen bonds directly formed between water molecules and lowering the density of hydrogen bonds between water molecules. This makes the moisture in the coating material more volatile, thus effectively reducing the moisture content of the final membrane.

[0050] The present invention achieves the above-mentioned effect by introducing ammonia gas because:

[0051] Ammonia (NH3) molecules possess a lone pair of electrons, enabling them to form hydrogen bonds with hydrogen atoms in water molecules. Specifically, the nitrogen atom in the ammonia molecule carries a high negative charge density, making it easier for its lone pair of electrons to form strong hydrogen bonds with hydrogen atoms in water molecules. Normally, hydrogen bonds between water molecules are formed primarily through oxygen atoms in the water and hydrogen atoms in adjacent water molecules. When ammonia molecules are introduced, the nitrogen atom also participates in this interaction, weakening the hydrogen bonds that would otherwise form between oxygen atoms and hydrogen atoms in adjacent water molecules. This reduced density of hydrogen bonds between water molecules lowers the boiling point of water, making it more volatile.

[0052] Furthermore, using two or more solvents in a composite solvent can further enhance the water volatility of the material. For example, combining alcohol with other organic compounds can interfere with the intermolecular forces of water, reduce the surface tension of water, and make water more volatile. Similarly, combining alcohol and water can reduce the external hydrogen bonds of ethanol molecules by adding water, thereby reducing the degree of association between ethanol molecules and making them more volatile. An ethanol molecule consists of a hydrophobic group (-C₂H₅) and a hydrophilic group (-OH), which allows hydrogen bonds to form between ethanol molecules. In the presence of water, the oxygen atoms of water molecules can form hydrogen bonds with the hydrogen atoms of ethanol molecules, thus reducing both the hydrogen bonds between ethanol molecules and between water molecules, thereby enhancing volatility.

[0053] Step 120: Centrifuge and enrich the nanoscale dispersion to obtain material particles;

[0054] Specifically, the centrifugation speed is 1000-20000 r / min, and the centrifugation time is 0.1-5 hours. Subsequent centrifugations will use the same speed and time range.

[0055] After the first centrifugation and enrichment, the particle size distribution of the material particles spans between 0.5 and 1.

[0056] Step 130: The enriched material particles are added to a solvent containing a hydrophobic dispersant and dispersed evenly, and then centrifuged and enriched again to obtain nanoparticles coated with a hydrophobic dispersant.

[0057] Specifically, after the second centrifugation enrichment, the particle size distribution of the obtained nanoparticles spans between 0.1 and 0.5.

[0058] Preferably, the centrifugation and enrichment process can be performed multiple times. Therefore, before this step, the material particles obtained by centrifuging and enriching the nanoscale dispersion can be evenly dispersed in a solvent containing or without a hydrophobic dispersant, and then centrifuged and enriched again, repeating this process once or multiple times. If more centrifugation and enrichment are used, a smaller particle size distribution span of the material may be obtained.

[0059] This invention removes small-diameter particles through at least two dispersion and centrifugation processes followed by enrichment. After this step, large particles in the slurry are enriched and separated, leaving the remaining material almost free of small particles, thereby ensuring the uniformity of the resulting nanoparticle material.

[0060] Hydrophobic dispersants may or may not be added to the solvent used in the repeated dispersion processes described above. However, hydrophobic dispersants need to be added in the last dispersion process performed in step 130 to ensure that the nanoparticles are coated with hydrophobic dispersants.

[0061] The amount of hydrophobic dispersant added is 0.1-10 wt% in the solvent containing the hydrophobic dispersant.

[0062] Hydrophobic dispersants may specifically include at least one of the following: ammonium polyacrylate, sodium polyacrylate, styrene-acrylic acid copolymer, polyoxyethylene fatty acid ester, polyoxyethylene-polyoxypropylene polymer, lignin sulfonate, hydrophobic eutectic solvent (HDESs), and polyacetonitrile.

[0063] This invention modifies the surface properties of nanoparticles by adding a solvent containing a hydrophobic dispersant, thereby increasing the hydrophobicity of the material by forming a hydrophobic coating layer on the particle surface. Simultaneously, by enhancing the hydrophobicity of the nanoparticles, it helps prevent particle agglomeration or aggregation in subsequent steps, thus improving the performance of the nanoparticle material.

[0064] Step 140: Dry the nanoparticles under gradient heating conditions, and then pulverize the dried material to obtain nanoparticle material.

[0065] First, dry at 80-130℃ for 1-48 hours, then raise the temperature and dry at 131-180℃ for 1-48 hours, then continue to raise the temperature and dry at 181-300℃ for 1-36 hours.

[0066] In practice, the specific parameters for gradient heating can be set beyond those described above. Those skilled in the art can set appropriate gradient heating parameters according to the actual product requirements.

[0067] By gradually increasing the temperature during the drying process and baking at different temperatures, the free water and bound water in the nanoparticles can be removed in stages, thus preventing the nanoparticles from agglomerating during rapid heating.

[0068] Drying under gradient heating conditions can produce dry nanoparticles with good particle dispersion, which is more conducive to the air jet milling process.

[0069] Air jet milling is used to further reduce particle size and ensure the uniformity of the coating slurry. This can be implemented using an air jet mill. In this embodiment, the milling frequency is 55-95Hz, but the parameters for implementing air jet milling are not limited to these. Those skilled in the art can set appropriate parameters to implement the technical solution based on the specific equipment used in the process and the requirements for the powder.

[0070] Step 150: The nanoparticle material and coating agent are homogenized together to prepare a coating slurry. The coating slurry is filtered and then coated onto the base membrane. After drying, a low-moisture composite membrane is obtained.

[0071] Specifically, coating aids include wetting and dispersing agents and binders, and may or may not include thickeners.

[0072] The dispersant includes one or more of the following: sodium metasilicate, trisodium nitrate, sodium pyrophosphate, sodium dodecyl sulfate, sodium hexametaphosphate, polyacrylic acid, sodium polyacrylate, polybutyl acrylate-styrene-acrylic acid, polyethylene glycol, polyvinylpyrrolidone, maleic anhydride-styrene copolymer, sodium lauryl sulfate, sodium lauryl polyoxyethylene ether sulfate, sodium dioctyl succinate sulfonate, sodium glycol monobutyl ether phosphate, sodium dodecylbenzene sulfonate, and octylphenol polyoxyethylene ether; the mass ratio of the dispersant to the coating material is 0.5:99.5 to 10:90.

[0073] The adhesive includes one or more of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, polymethyl methacrylate, polymethyl methacrylate-butyl acrylate, styrene-butadiene rubber, and polyvinyl acetate; the mass ratio of the adhesive to the coating material is 1:99 to 30:70.

[0074] The thickener includes one or more of the following: carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide wax, polyoxyethylene, and hydroxypropyl cellulose methyl ether; the mass ratio of the thickener to the coating material is 0:100 to 5:95.

[0075] According to the above proportions, the nanopowder material and coating additive are homogenized together to prepare a coating slurry. Then, the coating slurry is filtered through a 100-2000 mesh and coated onto the base film by roller coating. The coating thickness is 0.1-4 μm, and the coating is dried at 40-85℃ for 5-60 min.

[0076] The addition of coating additives can further improve the fluidity and uniformity of the slurry, and filtration can remove impurities, ensuring the purity of the slurry.

[0077] The base membrane can be selected from: wet-processed polyethylene membrane, dry-processed polyethylene membrane, polypropylene membrane, or cellulose membrane, etc. The thickness of the base membrane is preferably 3-50 μm, and the porosity is preferably 30%-50%, but is not limited to the above parameters.

[0078] The method for preparing a low-moisture composite membrane provided in this invention first involves using a composite solvent containing ammonia during wet milling. This allows the lone pairs of electrons in the ammonia molecules to form new hydrogen bonds with the hydrogen atoms in the water molecules, reducing the direct hydrogen bond connections between water molecules and lowering the density of hydrogen bonds between water molecules, thereby significantly enhancing the volatility of moisture. Combined with the coating of a hydrophobic dispersant during the centrifugal enrichment process, this helps to reduce the moisture content of the membrane. A gradient-heating drying step effectively avoids powder agglomeration and further reduces free and bound water in the nanoparticle material, ultimately producing a membrane with low moisture content and high moisture resistance.

[0079] The low-moisture composite separator prepared by the above-mentioned preparation method of the present invention has a moisture content of less than 2000 ppm, and can be used in liquid lithium-ion batteries or semi-solid lithium-ion batteries, which can effectively improve the cycle stability and safety performance of the battery.

[0080] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0081] Example 1

[0082] This embodiment provides a method for preparing a low-moisture composite membrane.

[0083] Step 1: Pass 400g of ammonia gas into a mixed solvent of 4kg of deionized water and 4kg of alcohol to prepare the desired composite solvent.

[0084] Step 2: Add 1 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.5 A l 0.5 Ti 1.5 (PO4)3 material and 4 kg of the composite solvent prepared in step 1 were ground in a sand mill to D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0085] Step 3: Centrifuge the above dispersion, discard the supernatant, then add 4 kg of the composite solvent prepared in Step 1 and 20 g of polyacetonitrile. Disperse the mixture evenly with the centrifuged solid particles in a disperser, then centrifuge again and discard the supernatant. In this step, the centrifuge speed is 5000 r / min for 1 hour for both centrifugation processes. The disperser speed is 2000 r / min for 0.5 hours.

[0086] Step 4: Dry the solids obtained from centrifugation in an oven. First, keep the temperature at 80°C for 8 hours, then raise the temperature to 150°C at a rate of 2°C / min and keep it at 150°C for 4 hours, then raise the temperature to 250°C at a rate of 2°C / min and keep it at 250°C for 1 hour.

[0087] Step 5: The dried powder is pulverized using an air jet mill. The mill's process parameters are: classification frequency 90Hz, feeding frequency 20Hz, fan frequency 50Hz, and air pressure 0.5MPa. Lithium aluminum titanium phosphate nanoparticles are obtained after pulverization.

[0088] Step 6: Mix 1 kg of lithium aluminum titanium phosphate nanopowder obtained in the previous step with 4 kg of deionized water, 10 g of carboxymethyl cellulose, 10 g of sodium polyacrylate, 10 g of sodium dodecylbenzene sulfonate and 40 g of polyacrylate to prepare a coating slurry.

[0089] Step 7: After filtering the coating slurry through a 200-mesh stainless steel screen, apply it to a 9µm wet-process polyethylene (PE) base membrane with a coating thickness of 2µm and a base membrane porosity of 40%. After drying at 80℃ for 10 minutes, the desired low-moisture composite membrane is obtained.

[0090] Example 2

[0091] This embodiment provides a method for preparing a low-moisture composite membrane.

[0092] Step 1 is the same as in Example 1.

[0093] Step 2, add 0.5 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.3 A l 0.3 Ti 1.7 (PO4)3 material, 0.5 kg alumina material, and 4 kg of the composite solvent prepared in step 1 are ground in a sand mill to D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion is 20%.

[0094] Steps 3-7 are the same as in Example 1.

[0095] Example 3

[0096] This embodiment provides a method for preparing a low-moisture composite membrane.

[0097] Step 1 is the same as in Example 1.

[0098] Step 2, add 0.5 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.3 A l 0.3 Ti 1.7 (PO4)3 material, 0.5 kg oxide solid electrolyte lithium lanthanum titanium oxide Li 0.33 La 0.557 TiO3 material and 4 kg of the composite solvent prepared in step 1 were ground in a sand mill to D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0099] Steps 3-7 are the same as in Example 1.

[0100] Example 4

[0101] This embodiment provides a method for preparing a low-moisture composite membrane.

[0102] Step 1 is the same as in Example 1.

[0103] Step 2, add 1 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.5 A l 0.5 Ti 1.5 (PO4)3 material and 4 kg of the composite solvent prepared in step 1 were ground in a sand mill to D50 = 700 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0104] Steps 3-7 are the same as in Example 1.

[0105] Example 5

[0106] This embodiment provides a method for preparing a low-moisture composite membrane.

[0107] Step 1 is the same as in Example 1.

[0108] Step 2, add 1 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.5 A l 0.5 Ti 1.5 (PO4)3 material and 4 kg of the composite solvent prepared in step 1 were ground in a sand mill to D50 = 300 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0109] Steps 3-7 are the same as in Example 1.

[0110] Example 6

[0111] This embodiment provides a method for preparing a low-moisture composite membrane.

[0112] Step 1 is the same as in Example 1.

[0113] Step 2: Add 1 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.5 A l 0.5 Ti 1.5 (PO4)3 material and 1.5 kg of the composite solvent prepared in step 1 were ground in a sand mill to D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 40%.

[0114] Step 3: Centrifuge the above dispersion, discard the supernatant, then add 4 kg of the composite solvent prepared in Step 1 and 20 g of polyacetonitrile. Disperse the mixture evenly with the centrifuged solid particles in a disperser, then centrifuge again and discard the supernatant. In this step, the centrifuge speed is 10000 r / min for 1 hour for both centrifugation processes. The disperser speed is 2000 r / min for 0.5 hours.

[0115] Steps 4-7 are the same as in Example 1.

[0116] Example 7

[0117] This embodiment provides a method for preparing a low-moisture composite membrane.

[0118] Step 1 is the same as in Example 1.

[0119] Step 2: Add 1 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.5 A l 0.5 Ti 1.5 (PO4)3 material and 1.5 kg of the composite solvent prepared in step 1 were ground in a sand mill to D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 40%.

[0120] Step 3: Centrifuge the above dispersion, discard the supernatant, then add 4 kg of the composite solvent prepared in Step 1 and 20 g of polyacetonitrile. Disperse the mixture evenly with the centrifuged solid particles in a disperser, then centrifuge again and discard the supernatant. In this step, the centrifuge speed is 3500 r / min for 1 hour for both centrifugation processes. The disperser speed is 2000 r / min for 0.5 hours.

[0121] Steps 4-7 are the same as in Example 1.

[0122] Example 8

[0123] This embodiment provides a method for preparing a low-moisture composite membrane.

[0124] Steps 1-3 are the same as in Example 1.

[0125] Step 4: Dry the solids obtained from centrifugation in an oven. First, keep the temperature at 100°C for 8 hours, then raise the temperature to 180°C at a rate of 2°C / min and keep it at that temperature for 3 hours, then raise the temperature to 280°C at a rate of 2°C / min and keep it at that temperature for 1 hour.

[0126] Steps 5-7 are the same as in Example 1.

[0127] Comparative Example 1

[0128] This comparative example provides a method for preparing a composite diaphragm.

[0129] Step 1: Add 1 kg of lithium titanium aluminum phosphate (LiFePO4) oxide solid electrolyte to the electrolyte. 1.5 A l 0.5 Ti 1.5 (PO4)3 material, 2 kg of deionized water and 2 kg of alcohol were ground in a sand mill until D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0130] Step 2: Homogenize 5 kg of the above dispersion with 10 g of carboxymethyl cellulose, 10 g of sodium polyacrylate, 10 g of sodium dodecylbenzenesulfonate and 40 g of polyacrylate to prepare a coating slurry.

[0131] Step 3: After filtering the coating slurry through a 200-mesh stainless steel screen, apply it to a 9µm wet-process PE base membrane with a coating thickness of 2µm and a base membrane porosity of 40%. After drying at 80℃ for 10 minutes, the desired composite membrane is obtained.

[0132] Comparative Example 2

[0133] This comparative example provides a method for preparing a composite diaphragm.

[0134] Step 1: Add 0.5 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.3 A l 0.3 Ti 1.7 (PO4)3 material, 0.5 kg alumina material, 2 kg deionized water and 2 kg alcohol were ground in a sand mill to D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0135] Steps 2-3 are the same as in Comparative Example 1.

[0136] Comparative Example 3

[0137] This comparative example provides a method for preparing a composite diaphragm.

[0138] This comparative example provides a method for preparing a composite diaphragm.

[0139] Step 1: Add 0.5 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.3 A l 0.3 Ti 1.7 (PO4)3 material, 0.5 kg oxide solid electrolyte lithium lanthanum titanium oxide Li 0.33 La 0.557 TiO3 material, 2 kg of deionized water and 2 kg of alcohol were ground in a sand mill until D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0140] Steps 2-3 are the same as in Comparative Example 1.

[0141] Comparative Example 4

[0142] This comparative example provides a method for preparing a composite diaphragm.

[0143] Step 1: Add 1 kg of the oxide solid electrolyte lithium titanium aluminum phosphate Li 1.5 A l 0.5 Ti 1.5 (PO4)3 material, 2 kg of deionized water and 2 kg of alcohol were ground in a sand mill to D50 = 700 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0144] Steps 2-3 are the same as in Comparative Example 1.

[0145] Comparative Example 5

[0146] This comparative example provides a method for preparing a composite diaphragm.

[0147] Step 1: Add 1 kg of lithium titanium aluminum phosphate (LiFePO4) oxide solid electrolyte to the electrolyte. 1.5 A l 0.5 Ti 1.5 (PO4)3 material, 2 kg of deionized water and 2 kg of alcohol were ground in a sand mill until D50 = 300 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 20%.

[0148] Steps 2-3 are the same as in Comparative Example 1.

[0149] Comparative Example 6

[0150] This comparative example provides a method for preparing a composite diaphragm.

[0151] Step 1: Add 1 kg of lithium titanium aluminum phosphate (LiFePO4) oxide solid electrolyte to the electrolyte. 1.5 A l 0.5 Ti 1.5(PO4)3 material, 0.75 kg of deionized water and 0.75 kg of alcohol were ground in a sand mill until D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 40%.

[0152] Steps 2-3 are the same as in Comparative Example 1.

[0153] Comparative Example 7

[0154] This comparative example provides a method for preparing a composite diaphragm.

[0155] Step 1: Add 1 kg of lithium titanium aluminum phosphate (LiFePO4) oxide solid electrolyte to the electrolyte. 1.5 A l 0.5 Ti 1.5 (PO4)3 material, 0.5 kg of deionized water and 1 kg of alcohol were ground in a sand mill until D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion was 40%.

[0156] Steps 2-3 are the same as in Comparative Example 1.

[0157] Comparative Example 8

[0158] This comparative example provides a method for preparing a composite diaphragm.

[0159] Step 1: Grind 1 kg of alumina material, 2 kg of deionized water and 2 kg of alcohol in a sand mill until D50 = 500 nm to obtain a nanoscale dispersion, wherein the solid content of the dispersion is 20%.

[0160] Steps 2-3 are the same as in Comparative Example 1.

[0161] The materials obtained from the above embodiments and comparative examples were tested. The moisture content test method was as follows: the moisture content of the diaphragm was tested using a Calfishu moisture meter at a test temperature of 150°C, with a deviation value of <10. The diaphragm dehydration test method was as follows: the diaphragm was placed in a dry room with a dew point of -60°C and left to stand before the moisture content was tested. The specific test results are shown in Table 1 below.

[0162]

[0163] Table 1

[0164] As can be seen from the comparison of physical properties of the diaphragms in Table 1 between the examples and the comparative examples:

[0165] The winding moisture content of Example 2 and Comparative Example 8 was lower than that of Example 1 and 3, while the moisture content of Example 2 and Comparative Example 8 after standing for 3 days was close to that of Example 1 and 3. This indicates that the initial moisture content of alumina was slightly lower than that of the oxide solid electrolyte. This is due to the hydrophilicity of the material itself. The moisture content after standing was close, indicating that the moisture in the oxide solid electrolyte has no strongly bound water and is easy to remove.

[0166] Moisture content during winding: Example 4 < Example 1 < Example 5, indicating that the particle size (i.e., specific surface area) of the powder has a significant impact on moisture content. Larger particle sizes result in smaller specific surface areas, weakening the ability to absorb moisture. Therefore, the moisture content during winding is relatively lower compared to materials with smaller particle sizes.

[0167] Moisture content during winding and moisture content after standing: The data for Example 6 are all greater than those for Example 1, while the data for Example 7 are all less than those for Example 1. This indicates that the degree of centrifugation affects the moisture content. The more thorough the centrifugation, the fewer small particles are removed, the higher the specific surface area, and the less the moisture content is reduced.

[0168] The moisture content of Example 8 was lower than that of Example 1, indicating that the higher the drying temperature, the more thoroughly the moisture in the powder is removed, which can further reduce the moisture content of the subsequent diaphragm.

[0169] The moisture content of Comparative Examples 1-7 was significantly higher than that of Examples 1-7.

[0170] In summary, the low-moisture composite membrane prepared by the method of this invention has a significant advantage in moisture control compared with the comparative composite membrane. The preparation method proposed in this invention can play an important role in the application of oxide solid electrolyte membranes, and the low-moisture composite membrane prepared by this invention can have superior performance.

[0171] Battery assembly tests were conducted using the materials obtained from the above embodiments and comparative examples to further verify the advantages of the low-moisture composite separator.

[0172] The positive electrode, separator (in each embodiment and comparative example), and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound and placed in a casing, infused with electrolyte, and encapsulated to obtain a lithium-ion soft-pack battery. Specifically, according to the mass ratio, 94 parts of active material lithium cobalt oxide, 3 parts of conductive carbon, and 3 parts of binder polyvinylidene fluoride are mixed evenly in an N-methylpyrrolidone solvent system, coated onto aluminum foil, dried, cold-pressed, and slit to form the positive electrode. 97.5 parts of active material artificial graphite, 1.5 parts of binder styrene-butadiene rubber, and 1 part of thickener sodium carboxymethyl cellulose are mixed evenly in deionized water, coated onto copper foil, dried, cold-pressed, and slit to form the negative electrode. A 1 mol / L LiPF6 solution of ethylene carbonate (EC) / dimethyl carbonate (DEC) (volume ratio 1:1) is used as the electrolyte.

[0173] 25℃ Cycling Performance (Capacity Retention) Test: Three separators from Examples 1-8 and Comparative Examples 1-8 were used to prepare three test lithium-ion pouch cells for each example and comparative example. The cells were charged at a constant current rate of 1C to 4.4V at 25℃, and then charged at a constant voltage of 4.4V to 0.05C to obtain the initial capacity of the cell. The cycling process was as follows: discharged at a discharge current of 1C to 2.0V, then charged at a constant current rate of 1C to 4.4V, and then charged at a constant voltage of 4.4V to 0.05C. This process was repeated. The average remaining capacity of the three lithium-ion pouch cells from each example and comparative example was taken as the final capacity. The capacity retention rate was calculated as the ratio of the final capacity to the initial capacity for each example and comparative example. Specific data are as follows: Figure 2 As shown.

[0174] Figure 2 Comparing the soft-pack batteries assembled with the separators of the examples and the comparative examples, the capacity retention data of Examples 1-8 are significantly better than those of Comparative Examples 1-7, indicating that low moisture content is beneficial to battery cycling. The capacity retention of Examples 1-8 is comparable to that of Comparative Example 8 at 200 cycles, but the capacity retention at 500 cycles is significantly better than that of Comparative Example 8, indicating that the ion transport channels provided by the oxide solid electrolyte coating material have an advantage over alumina, which has no ion conduction capacity, in long-term cycling. In summary, the low-moisture composite separator of the present invention can effectively improve the cycle life of the battery.

[0175] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a low-moisture composite membrane, characterized in that, The preparation method includes: The coating material is added to a composite solvent containing ammonia and wet-milled to obtain a nanoscale dispersion. The coating material includes an oxide solid electrolyte material. In the nanoscale dispersion, the lone pair electrons of ammonia molecules form new hydrogen bonds with hydrogen atoms in water molecules, thereby reducing the number of hydrogen bonds directly formed between water molecules and lowering the density of hydrogen bonds between water molecules. This makes the water in the coating material more volatile and reduces the water content. The nanoscale dispersion was centrifuged and enriched to obtain material particles; The enriched material particles were added to a solvent containing a hydrophobic dispersant and dispersed evenly. The particles were then centrifuged and enriched again to obtain nanoparticles coated with a hydrophobic dispersant. The nanoparticles are dried under a gradient heating condition, and the dried material is pulverized to obtain nanoparticle material. The nanoparticle material is homogenized with a coating aid to prepare a coating slurry. The coating slurry is filtered and then coated onto a base membrane. After drying, the low-moisture composite membrane is obtained.

2. The preparation method according to claim 1, characterized in that, Before adding the enriched material particles to a solvent containing a hydrophobic dispersant and dispersing them evenly, and then centrifuging and enriching them again to obtain nanoparticles coated with a hydrophobic dispersant, the method further includes: The material particles obtained by centrifuging and enriching the nanoscale dispersion are evenly dispersed in a solvent containing or without the hydrophobic dispersant, and then centrifuged and enriched again, repeating this process once or multiple times.

3. The preparation method according to claim 1, characterized in that, The oxide solid electrolyte material includes one or more of lithium titanium aluminum phosphate, lithium lanthanum titanate, lithium lanthanum zirconium oxide, or lithium lanthanum zirconium tantalum oxide. The coating material further includes: alumina and / or boehmite; The composite solvent includes at least one of acetone, alcohol, ethyl acetate, deionized water, isopropanol, isobutanol, and dimethyl sulfoxide; the ammonia content in the composite solvent is 0.5-35 wt%. The solid content in the nanoscale dispersion is 1-60 wt%. The particle size D50 of the nanoscale dispersion is 10-1000 nm, and the particle size distribution span is between 1 and 5. The solvent containing the hydrophobic dispersant contains 0.1-10 wt% of the hydrophobic dispersant. The hydrophobic dispersant includes at least one of the following: ammonium polyacrylate, sodium polyacrylate, styrene-acrylic acid copolymer, polyoxyethylene fatty acid ester, polyoxyethylene-polyoxypropylene polymer, lignin sulfonate, hydrophobic eutectic solvent HDESs, and polyacetonitrile.

4. The preparation method according to claim 1, characterized in that, The centrifugation speed is 1000-20000 r / min, and the centrifugation time is 0.1-5 hours; The particle size distribution of the material has a span between 0.5 and 1. The particle size distribution of the nanopowder particles spans between 0.1 and 0.

5.

5. The preparation method according to claim 1, characterized in that, The drying under gradient heating conditions specifically includes: First, dry at 80-130℃ for 1-48 hours, then raise the temperature and dry at 131-180℃ for 1-48 hours, then continue to raise the temperature and dry at 181-300℃ for 1-36 hours.

6. The preparation method according to claim 1, characterized in that, The coating aid includes: a thickener, a wetting and dispersing agent, and a binder; or, the coating aid includes a wetting and dispersing agent and a binder. The thickener includes one or more of the following: carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide wax, polyoxyethylene, and hydroxypropyl cellulose methyl ether; the mass ratio of the thickener to the coating material is 0:100 to 5:

95. The dispersant comprises one or more of the following: sodium metasilicate, trisodium nitrate, sodium pyrophosphate, sodium dodecyl sulfate, sodium hexametaphosphate, polyacrylic acid, sodium polyacrylate, polybutyl acrylate-styrene-acrylic acid, polyethylene glycol, polyvinylpyrrolidone, maleic anhydride-styrene copolymer, sodium lauryl sulfate, sodium lauryl polyoxyethylene ether sulfate, sodium dioctyl succinate sulfonate, sodium glycol monobutyl ether phosphate, sodium dodecylbenzene sulfonate, and octylphenol polyoxyethylene ether; the mass ratio of the dispersant to the coating material is 0.5:99.5 to 10:

90. The adhesive comprises one or more of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, polymethyl methacrylate, polymethyl methacrylate-butyl acrylate, styrene-butadiene rubber, and polyvinyl acetate; the mass ratio of the adhesive to the coating material is 1:99 to 30:

70.

7. The preparation method according to claim 1, characterized in that, The process of filtering the coating slurry, coating it onto the base membrane, and drying it to obtain the low-moisture composite membrane specifically includes: The coating slurry is filtered through a 100-2000 mesh and then coated onto the base membrane by roller coating. The coating thickness is 0.1-4 μm. The coating is then dried at 40-85℃ for 5-60 min to obtain the low-moisture composite membrane.

8. The preparation method according to claim 1, characterized in that, The base membrane includes: a polyethylene membrane prepared by wet process, a polyethylene membrane prepared by dry process, a polypropylene membrane, or a cellulose membrane; The thickness of the base film is 3-50 μm; the porosity is 30%-50%.

9. A low-moisture composite membrane prepared by any one of the preparation methods described in claims 1-8.

10. An application of a low-moisture composite membrane prepared by the method according to any one of claims 1-8, characterized in that, The low-moisture composite separator is used in liquid lithium-ion batteries or semi-solid lithium-ion batteries.

Images