A battery separator composed of chitosan aerogel microspheres and CNF and a preparation method thereof

Abstract

The application discloses a kind of battery separators of chitosan aerogel microspheres and CNF composite and preparation method thereof, belong to lithium ion battery technical field.The battery separator includes polyolefin porous base film and the coating layer of at least one side surface of the base film;The coating layer is formed by coating and drying by coating slurry including chitosan aerogel microspheres and CNF;The chitosan aerogel microspheres are porous particles formed after chitosan is crosslinked, freeze-dried and crushed.The application constructs light, multistage pore structure coating layer by chitosan aerogel microspheres and CNF composite, significantly improves the wettability of electrolyte, liquid absorption rate and liquid retention rate of separator under the premise of extremely low weight gain, and has good thermal stability, effectively solves the contradiction that traditional ceramic coating weight and wettability cannot be compatible.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator technology, specifically relating to a battery separator composed of chitosan aerogel microspheres and CNF and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems. The separator, as a core component, plays a crucial role in isolating the positive and negative electrodes, preventing short circuits, and conducting lithium ions. Currently, the mainstream separators are polyolefin microporous membranes such as polypropylene (PP) and polyethylene (PE), but their poor thermal stability and insufficient electrolyte wettability make them unsuitable for meeting the safety requirements of high-energy-density batteries.

[0003] Surface coating modification is currently the most promising optimization strategy for industrialization, but existing technologies have significant drawbacks. Traditional inorganic ceramic coatings, such as alumina and boehmite, can improve heat resistance, but their high particle density and coating thickness significantly increase the membrane's surface density, sacrificing battery energy density, making it difficult to balance safety and energy density. Meanwhile, polyolefin-based membranes are non-polar and have poor affinity for carbonate electrolytes, resulting in low liquid absorption and slow wetting speed, affecting electrolyte injection efficiency and battery performance.

[0004] Cellulose-based coatings represent a trend towards lightweighting, but the hydroxyl groups on the cellulose surface tend to aggregate and stack in water through hydrogen bonding, making it difficult to form a uniform porous structure. Existing chemical modification methods, such as chitosan grafting, are complex, costly, and may compromise the intrinsic properties of cellulose. Furthermore, existing cellulose-chitosan-based membrane solutions either involve multi-step chemical modification or the introduction of high-density inorganic nanoparticles, failing to simultaneously achieve lightweight coatings and high liquid absorption and retention properties. Therefore, how to achieve membranes with excellent electrolyte wettability, high liquid absorption and retention capacity, and good thermal stability while maintaining low weight gain remains a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of traditional battery separators in the prior art, such as high coating density leading to increased separator surface density, poor wettability, low ionic conductivity, and insufficient thermal stability, and to provide a battery separator composed of chitosan aerogel microspheres and CNF and its preparation method.

[0006] To address the aforementioned technical problems, this invention provides a battery separator composed of chitosan aerogel microspheres and CNF, and its preparation method.

[0007] In a first aspect, the present invention provides a battery separator composed of chitosan aerogel microspheres and CNF, comprising:

[0008] Polyolefin porous base membrane;

[0009] and a coating layer disposed on at least one side surface of the polyolefin porous base membrane;

[0010] The coating layer comprises chitosan aerogel microspheres and CNF;

[0011] The chitosan aerogel microspheres are porous particles formed by cross-linking, freeze-drying, and pulverizing chitosan.

[0012] As an optional embodiment of the present invention, the skeletal density of the chitosan aerogel microspheres is 0.04-0.12 g / cm³. 3 It has mesopores with a pore size of 5-50 nm inside.

[0013] As an optional embodiment of the present invention, the chitosan aerogel microspheres have a particle size D50 of 0.4-0.6 μm and a D90 of 1.4-1.8 μm; the single-sided thickness of the coating layer is 1.5-4 μm.

[0014] As an optional embodiment of the present invention, the polyolefin porous base membrane is a PP membrane or a PE membrane with a thickness of 5-12 μm.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned battery separator, comprising the following steps:

[0016] Step S1: Dissolve chitosan in an aqueous acetic acid solution, add a crosslinking agent, stir to form a gel, wash the gel and freeze-dry it to obtain chitosan aerogel, then pulverize the chitosan aerogel and sieve it to obtain chitosan aerogel microspheres.

[0017] Step S2: Disperse CNF in water, add an aqueous crosslinking agent, and stir to obtain an aqueous CNF solution;

[0018] Step S3: Disperse the chitosan aerogel microspheres obtained in step S1 in deionized water, add the CNF aqueous solution obtained in step S2, and add toughening agent, binder and wetting agent, mix evenly to obtain coating slurry;

[0019] Step S4: Apply the coating slurry obtained in step S3 to at least one surface of the polyolefin porous base membrane and dry it to obtain the battery separator.

[0020] As an optional embodiment of the present invention, in step S1: the chitosan is 2.4-5.7 parts by mass, the acetic acid aqueous solution is 64.2-84.7 parts by mass, and the mass fraction of the acetic acid aqueous solution is 0.8-1.9%; the crosslinking agent is selected from at least one of glutaraldehyde, genipin or sodium tripolyphosphate, and the crosslinking agent is 0.24-1.14 parts by mass.

[0021] As an optional embodiment of the present invention, in step S2: by mass parts, the CNF is 4.6-5.4 parts, and the water is 46-54 parts; the aqueous crosslinking agent is selected from at least one of citric acid, epichlorohydrin, glyoxal, or polyamide epichlorohydrin resin, and by mass parts, the aqueous crosslinking agent is 0.05-0.12 parts; the stirring time is 690-750 min, and the rotation speed is 1150-1250 r / min.

[0022] As an optional embodiment of the present invention, in step S3: by mass parts, the chitosan aerogel microspheres are 3.2-4.2 parts, the deionized water is 14.5-16.5 parts, the CNF aqueous solution is 5.4-6.6 parts, the toughening agent is 0.5-2 parts, the adhesive is 1.3-1.8 parts, and the wetting agent is 0.08-0.16 parts; the toughening agent is one or more of polyethylene oxide (PEO), ethylene-vinyl acetate copolymer (EVA), or acrylate elastomer (ACR); the adhesive is one or more of polyacrylic acid (PAA) or polyvinyl alcohol (PVA); and the wetting agent is a nonionic modified polyether.

[0023] As an optional embodiment of the present invention, in step S3: the mixing is carried out using a dual planetary mixer. First, chitosan aerogel microspheres and deionized water are mixed at a revolution speed of 45-55 r / min and a rotation speed of 2400-2600 r / min for 25-35 min. Then, CNF aqueous solution, toughening agent, binder and wetting agent are added and mixed at a revolution speed of 27-33 r / min and a rotation speed of 1450-1550 r / min for 55-65 min.

[0024] As an optional embodiment of the present invention, in step S4: the coating method is roller coating, the coating speed is 10-15 m / min, the drying temperature is 75-95℃, and the drying time is 3-6 min; the coating layer is a single-sided coating or a double-sided coating.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The core of this invention's battery separator lies in the unique structure and formation process of the coating layer. This coating layer is composed of chitosan aerogel microspheres and cellulose nanofibers (CNF). The chitosan aerogel microspheres are porous particles formed by cross-linking, freeze-drying, and pulverizing chitosan, containing mesopores of 5-50 nm and a framework density of only 0.04-0.12 g / cm³. 3CNF acts as a network builder, adhering to the surface of the microspheres and interweaving between them during the mixing process. When the coating slurry is applied to the polyolefin porous film and dried, the moisture evaporates, and the CNF network fixes the aerogel microspheres within the coating layer, while simultaneously forming micron-sized interstitial channels between the microspheres. These interstitial channels are interconnected with the nanopores inside the aerogel microspheres.

[0027] During the battery electrolyte filling process, the electrolyte first contacts the coating surface. Due to the abundance of polar functional groups such as hydroxyl and carboxyl groups on the CNF surface, the coating surface exhibits excellent hydrophilicity, allowing the electrolyte to spread rapidly. Subsequently, micron-sized interstitial channels serve as rapid liquid conduction pathways, guiding the electrolyte to quickly penetrate within the coating layer. Simultaneously, the nanopores inside the aerogel microspheres actively absorb the electrolyte through capillary action, storing the liquid within the microsphere's internal pores, thus significantly improving both the absorption rate and the absorption volume.

[0028] During battery charge-discharge cycles, electrolyte is prone to evaporation or loss. At this time, the nanopores of aerogel microspheres utilize capillary coagulation effect to firmly lock the electrolyte within the pores, slowing down its evaporation and leakage. At the same time, the CNF network acts like a skeleton to wrap around and support the microspheres, preventing the coating structure from collapsing, thereby maintaining the electrolyte storage capacity for a long time.

[0029] Furthermore, since the majority of the volume of the aerogel microspheres is occupied by air, their apparent density is extremely low. Even with a certain coating thickness, the actual weight gain of the coating is only about 50% of that of traditional ceramic coatings, which has almost no impact on the battery's energy density. When the battery operates in a high-temperature environment, the heat-resistant framework formed by the chitosan aerogel microspheres and CNF can effectively resist the thermal shrinkage of the polyolefin-based film, thereby ensuring the battery's high-temperature safety. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] To illustrate the technical solution of the present invention, specific embodiments are described below.

[0032] To address the aforementioned technical problems, this invention provides a battery separator composed of chitosan aerogel microspheres and CNF, and its preparation method.

[0033] In a first aspect, the present invention provides a battery separator composed of chitosan aerogel microspheres and CNF, comprising: a polyolefin porous base membrane; and a coating layer disposed on at least one side surface of the polyolefin porous base membrane; the coating layer is formed by coating and drying a coating slurry comprising chitosan aerogel microspheres and CNF; the chitosan aerogel microspheres are porous particles formed by cross-linking, freeze-drying and pulverizing chitosan.

[0034] Chitosan aerogel microspheres possess numerous nanoscale pores and extremely low density. The surface of CNF (cellulose nanofibers) is rich in hydroxyl and carboxyl groups, exhibiting high hydrophilicity and a high aspect ratio. During the coating and drying process, CNF acts as a network builder, uniformly dispersing and fixing the aerogel microspheres within the coating layer, while micron-sized gaps naturally form between the microspheres. When the electrolyte comes into contact with the coating layer, the polar groups of CNF rapidly wet the surface, allowing the electrolyte to quickly penetrate along the micron-sized gaps and be actively absorbed and stored through the capillary effect of the mesopores within the microspheres.

[0035] In the membrane preparation stage, chitosan aerogel microspheres and CNF are mixed in an aqueous phase to form a slurry, which is then coated onto the surface of a polyolefin-based membrane by roller coating. After drying, a composite coating layer is formed. In the use stage, this coating layer is in direct contact with the electrolyte, and the electrolyte is absorbed and retained through physical adsorption and capillary action.

[0036] This allows the diaphragm to achieve high electrolyte wettability, liquid absorption rate, and liquid retention rate with extremely low weight gain. At the same time, the CNF network enhances the structural stability of the coating layer and avoids the problem of peeling off traditional ceramic coatings.

[0037] As an optional embodiment of the present invention, the skeletal density of the chitosan aerogel microspheres is 0.04-0.12 g / cm³. 3 The internal structure of chitosan aerogel microspheres contains mesopores with a pore size of 5-50 nm. In other words, the low skeletal density of chitosan aerogel microspheres stems from their highly porous internal structure; the solid skeleton accounts for only about 5-10% of the total volume, with the remainder being air-filled nanopores of approximately 5-50 nm. These mesopores are within the critical range for capillary condensation of electrolyte molecules, generating significant capillary pressure that drives the electrolyte to spontaneously enter and be trapped within the pores. During slurry mixing and coating, the aerogel microspheres maintain their porous structure. When the diaphragm injects the electrolyte, the mesopore openings on the microsphere surface directly contact the electrolyte, drawing the liquid into the internal pores of the microspheres through capillary action. Due to the uniform size and interconnectedness of the mesopores, the liquid absorption process is continuous and rapid.

[0038] As an optional embodiment of the present invention, the chitosan aerogel microspheres have a particle size D50 of 0.4-0.6 μm and a D90 of 1.4-1.8 μm; the single-sided thickness of the coating layer is 1.5-4 μm. Specifically, the submicron-sized aerogel microspheres, with a D50 ≈ 0.5 μm, when stacked in the coating layer, have a gap size between the microspheres that is on the same order of magnitude as the microsphere particle size, approximately 0.1-1 μm, forming a micron-sized pore network. Controlling the coating layer thickness to 1.5-4 μm ensures that the multi-layer stacking of microspheres forms continuous pore channels without increasing ion transport resistance or causing coating cracking due to excessive thickness. During the coating drying process, the microspheres in the slurry randomly stack, and CNF fills the gaps between the microspheres, acting as a bond and support. Controlling the coating thickness within the range of 1.5-4 μm ensures complete coverage of the base membrane surface while maintaining the overall air permeability and flexibility of the membrane.

[0039] As an optional embodiment of the present invention, the polyolefin porous base membrane is a PP or PE membrane with a thickness of 5-12 μm. PP (polypropylene) and PE (polyethylene) porous membranes have a natural microporous structure with a pore size of approximately 0.03-0.1 μm, enabling lithium-ion conduction. In the battery, the micropores of the base membrane itself are responsible for the transmembrane transport of lithium ions, while the coating layer functions as an electrolyte reservoir and a thermally stable framework. The present invention uses a thin base membrane of 5-12 μm, which has a low areal density of approximately 5-6 g / m³. 2 This provides a good foundation for the lightweight coating of the present invention.

[0040] Secondly, the present invention provides a method for preparing the above-mentioned battery separator, comprising the following steps:

[0041] Step S1: Dissolve chitosan in an aqueous acetic acid solution, add a crosslinking agent, stir to form a gel, wash the gel and freeze dry to obtain chitosan aerogel, then pulverize the chitosan aerogel and sieve it to obtain chitosan aerogel microspheres.

[0042] Step S2: Disperse CNF in water, add an aqueous crosslinking agent, and stir to obtain an aqueous CNF solution;

[0043] Step S3: Disperse the chitosan aerogel microspheres obtained in step S1 in deionized water, add the CNF aqueous solution obtained in step S2, and add toughening agent, binder and wetting agent, mix evenly to obtain coating slurry;

[0044] Step S4: Apply the coating slurry obtained in step S3 to at least one surface of the polyolefin porous base membrane and dry it to obtain the battery separator.

[0045] In an optional embodiment of the present invention, in step S1: by mass parts, chitosan comprises 2.4-5.7 parts, and acetic acid aqueous solution comprises 64.2-84.7 parts, with the acetic acid aqueous solution having a mass fraction of 0.8-1.9%; the crosslinking agent is selected from at least one of glutaraldehyde, genipin, or sodium tripolyphosphate, and by mass parts, the crosslinking agent comprises 0.24-1.14 parts. Furthermore, the freeze-drying temperature is below -20°C, the vacuum degree is not higher than 0.8 kPa, and the drying time is not less than 24 hours; the pulverization is performed using ball milling or air jet milling.

[0046] After chitosan dissolves in dilute acetic acid, the amino groups are protonated to form cationic polyelectrolytes. Crosslinking agents such as glutaraldehyde react with the amino groups on the chitosan molecular chains via a Schiff base reaction, forming a three-dimensional network structure. Controlling the amount of crosslinking agent to approximately 10-20% of the chitosan mass ensures a suitable crosslinking density in the gel, guaranteeing a stable mesoporous structure after freeze-drying while avoiding excessive crosslinking that could increase brittleness.

[0047] Under stirring conditions, the crosslinking agent diffuses uniformly and reacts with chitosan, gradually increasing the solution viscosity until a non-flowing gel that can be inverted is formed. After washing to remove unreacted small molecules and byproducts, freeze-drying causes ice crystals to sublimate, leaving mesopores, resulting in an aerogel. Since the chitosan has already undergone some pre-treatment before being purchased from the manufacturer, this invention only requires a final step of processing the chitosan in step S1. Therefore, a short stirring time is sufficient to form a gel, which is existing technology and will not be elaborated further.

[0048] As an optional embodiment of the present invention, in step S2: CNF is 4.6-5.4 parts by mass, and water is 46-54 parts; the aqueous crosslinking agent is selected from at least one of citric acid, epichlorohydrin, glyoxal, or polyamide epichlorohydrin resin, and the aqueous crosslinking agent is 0.05-0.12 parts by mass; the stirring time is 690-750 min, and the rotation speed is 1150-1250 r / min.

[0049] CNF forms a highly entangled network in water through hydrogen bonds; direct use at excessively high concentrations can lead to uneven dispersion. Adding an appropriate amount of aqueous crosslinking agent, such as citric acid, can induce esterification with the hydroxyl groups on the CNF surface, forming a mild crosslink between the fibers. This maintains the dispersibility of CNF while enhancing its mechanical strength after film formation. Prolonged high-speed stirring for approximately 12 hours allows for complete dissociation and uniform dispersion of the CNF, with the crosslinking agent reacting gradually during stirring. The final result is a uniform, transparent or semi-transparent CNF aqueous solution with moderate viscosity, suitable for mixing with aerogel microspheres.

[0050] As an optional embodiment of the present invention, in step S3: by mass parts, chitosan aerogel microspheres are 3.2-4.2 parts, deionized water is 14.5-16.5 parts, CNF aqueous solution is 5.4-6.6 parts, toughening agent is 0.5-2 parts, adhesive is 1.3-1.8 parts, and wetting agent is 0.08-0.16 parts; the toughening agent is one or more of polyethylene oxide (PEO), ethylene-vinyl acetate copolymer (EVA), or acrylate elastomer (ACR); the adhesive is one or more of polyacrylic acid (PAA) or polyvinyl alcohol (PVA); and the wetting agent is a nonionic modified polyether.

[0051] Toughening agents, such as PEO, improve the flexibility of the coating and prevent drying cracking; adhesives, such as PAA, enhance the adhesion between the coating and the base film; wetting agents reduce the surface tension of the slurry, ensuring uniform spreading on the hydrophobic polyolefin base film. Specifically, the microspheres are first initially mixed with deionized water to fully wet and disperse them; then, CNF aqueous solution, toughening agent, adhesive, and wetting agent are added, and stirring continues. The components work synergistically: CNF provides the network framework, the toughening agent regulates mechanical properties, the adhesive enhances adhesion, and the wetting agent improves coating uniformity.

[0052] As an optional embodiment of the present invention, in step S3: a dual planetary mixer is used for mixing. First, chitosan aerogel microspheres and deionized water are mixed at a revolution speed of 45-55 r / min and a rotation speed of 2400-2600 r / min for 25-35 min. Then, CNF aqueous solution, toughening agent, binder and wetting agent are added and mixed at a revolution speed of 27-33 r / min and a rotation speed of 1450-1550 r / min for 55-65 min.

[0053] In other words, the revolution of the dual planetary mixer circulates the material as a whole, while the rotating dispersion disc provides high shear force. The first stage, with a high rotation speed of 2400-2600 r / min, is used to quickly disperse and uniformly distribute the chitosan aerogel microspheres in water, preventing microsphere aggregation. The second stage, with a lower rotation speed of 1450-1550 r / min, is used to gently mix CNF and other additives, avoiding damage to the long fiber structure of CNF by high shear.

[0054] As an optional embodiment of the present invention, in step S4: the coating method is roller coating, the coating speed is 10-15 m / min, the drying temperature is 75-95℃, and the drying time is 3-6 min; the coating layer is a single-sided coating or a double-sided coating. Specifically, roller coating uses the gap between the metering roller and the coating roller to control the wet film thickness, which is suitable for continuous production. The drying temperature is controlled at 75-95℃, which can quickly evaporate moisture without causing thermal shrinkage of the polyolefin-based film (PE melting point is about 130℃). Single-sided coating is suitable for scenarios with extremely high energy density requirements, while double-sided coating can further improve thermal stability and electrolyte retention.

[0055] The present invention is further illustrated below with specific embodiments and comparative examples, but these are not intended to limit the scope of protection of the present invention. Unless otherwise specified, all reagents and materials used are commercially available.

[0056] Example 1

[0057] (1) Preparation of chitosan aerogel microspheres:

[0058] 2.6 parts by mass of chitosan were dissolved in 65.8 parts by mass of an aqueous acetic acid solution (acetic acid aqueous solution mass fraction 0.86%). The solution was mixed for 31 min using a high-speed disperser at a dispersion speed of 806 r / min to obtain solution A. 0.36 parts by mass of the crosslinking agent glutaraldehyde were added to solution A, and the mixture was slowly stirred for 5 min. The mixture was then allowed to stand and age until a gel was formed. The gel was washed with deionized water and then freeze-dried at -31℃ and a vacuum of 0.9 kPa to obtain chitosan aerogel. The chitosan aerogel was ball-milled and sieved to obtain chitosan aerogel microspheres with a particle size D50 of 0.452 μm and a D90 of 1.526 μm.

[0059] (2) Preparation of CNF aqueous solution:

[0060] Take 4.8 parts by weight of CNF, add it to 48.9 parts by weight of water, and add 0.068 parts by weight of water-based crosslinking agent citric acid. Mix and stir for 722 min at a stirring speed of 1186 r / min to obtain CNF aqueous solution.

[0061] (3) Preparation of coating slurry:

[0062] Take 3.36 parts by weight of the chitosan aerogel microspheres obtained in step (1) and add them to 14.6 parts by weight of deionized water. Mix them for 29 min using a double planetary mixer at a revolution speed of 48 r / min and a rotation speed of 2486 r / min to obtain mixed solution C. Add 5.6 parts by weight of the CNF aqueous solution obtained in step (2) to mixed solution C, and simultaneously add 0.76 parts by weight of toughening agent PEO, 1.46 parts by weight of binder PAA and 0.09 parts by weight of wetting agent polyether modified polysiloxane. Mix them again using a double planetary mixer at a revolution speed of 31 r / min and a rotation speed of 1510 r / min for 61 min to obtain coating slurry.

[0063] (4) Coating and drying:

[0064] The above-mentioned coating slurry was applied to one side of a 9 μm thick PE porous base membrane by roller coating at a speed of 10.8 m / min. The membrane was then dried at 86.3℃ for 4 min to obtain the battery separator. The coating thickness on one side was 2.1 μm.

[0065] Example 2

[0066] (1) The preparation of chitosan aerogel microspheres is the same as in Example 1.

[0067] (2) Preparation of CNF aqueous solution:

[0068] Take 5.1 parts by weight of CNF, add it to 52.3 parts by weight of water, and add 0.086 parts by weight of waterborne crosslinking agent epichlorohydrin. Mix and stir for 718 min at a stirring speed of 1206 r / min to obtain CNF aqueous solution.

[0069] (3) Preparation of coating slurry:

[0070] Take 4.1 parts by weight of chitosan aerogel microspheres and add them to 15.9 parts by weight of deionized water. Mix them for 31 min using a dual planetary mixer at a revolution speed of 52 r / min and a rotation speed of 2503 r / min. Then add 6.4 parts by weight of CNF aqueous solution, along with 1.7 parts by weight of toughening agent EVA, 1.48 parts by weight of binder PVA, and 0.147 parts by weight of wetting agent. Mix them for 58 min at a revolution speed of 30 r / min and a rotation speed of 1486 r / min to obtain the coating slurry.

[0071] (4) Coating and drying:

[0072] The coating speed was 13.1 m / min, the drying temperature was 89.7℃, the drying time was 5 min, the coating thickness was 2.4 μm, the base film was a 9 μm PE film, and the rest was the same as in Example 1.

[0073] Example 3

[0074] (1) Preparation of chitosan aerogel microspheres:

[0075] 5.3 parts by mass of chitosan were dissolved in 79.4 parts by mass of an aqueous acetic acid solution (acetic acid aqueous solution mass fraction 1.7%). The solution was mixed for 31 min using a high-speed disperser at a dispersion speed of 798 r / min to obtain solution A. 1.03 parts by mass of the crosslinking agent genipin were added to solution A, and the mixture was slowly stirred for 5 min. The mixture was then allowed to stand and age until a gel was formed. The gel was washed with deionized water and then freeze-dried at -27℃ and a vacuum of 0.9 kPa to obtain chitosan aerogel. The chitosan aerogel was ball-milled and sieved to obtain chitosan aerogel microspheres with a particle size D50 of 0.447 μm and a D90 of 1.633 μm.

[0076] (2) The preparation of CNF aqueous solution is the same as in Example 1.

[0077] (3) Preparation of coating slurry:

[0078] Take 3.90 parts by weight of chitosan aerogel microspheres and add them to 15.7 parts by weight of deionized water. Mix them for 29 min using a dual planetary mixer at a revolution speed of 48 r / min and a rotation speed of 2507 r / min. Then add 6.0 parts by weight of CNF aqueous solution, along with 1.2 parts by weight of toughening agent ACR, 1.69 parts by weight of binder PAA, and 0.112 parts by weight of wetting agent. Mix them for 62 min at a revolution speed of 32 r / min and a rotation speed of 1524 r / min to obtain the coating slurry.

[0079] (4) Coating and drying:

[0080] The coating speed was 11.4 m / min, the drying temperature was 90.7℃, the drying time was 4 min, the coating thickness was 1.8 μm, and the base film was a 9 μm PE film, thus obtaining the battery separator.

[0081] Comparative Example 1

[0082] Preparation of lithium battery separator slurry: Take 18.6 parts by weight of nano-alumina powder, add 41.6 parts by weight of ultrapure water, then add 0.58 parts by weight of dispersant, and stir and disperse for 60 min; under ultrasonic mixing conditions, add 1.9 parts by weight of binder, and continue ultrasonic mixing for 15 min; add 0.09 parts by weight of wetting agent and 3.5 parts by weight of pore-forming agent, and mix and stir for 30 min to obtain the slurry. Roll coat the slurry onto a 9 μm PE base film, with a coating thickness of 2.1 μm, and dry at 75℃ for 3 min to obtain the battery separator.

[0083] Comparative Example 2

[0084] Preparation of lithium battery separator slurry: Take 13.5 parts by weight of nano-boehmite powder, add 32.4 parts by weight of ultrapure water, then add 0.29 parts by weight of dispersant, and stir and disperse for 60 min; under ultrasonic mixing conditions, add 1.46 parts by weight of binder, and continue ultrasonic mixing for 15 min; add 0.07 parts by weight of wetting agent and 2.9 parts by weight of pore-forming agent, mix and stir for 30 min to obtain the slurry. Roll coat it onto a 9 μm PE base film, with a coating thickness of 2.2 μm, and dry at 75℃ for 3 min.

[0085] Comparative Example 3

[0086] Preparation of lithium battery separator slurry: Take 19.2 parts by weight of nano-alumina powder, add 42.8 parts by weight of ultrapure water, then add 0.6 parts by weight of dispersant, and stir and disperse for 60 min; under ultrasonic mixing conditions, add 1.9 parts by weight of binder, and continue ultrasonic mixing for 15 min; add 0.102 parts by weight of wetting agent again, and mix and stir for 30 min to obtain the slurry. Roll coat it onto a 9 μm PE base film, with a coating thickness of 2.3 μm, and dry at 75℃ for 3 min.

[0087] Performance testing

[0088] The battery separators obtained in Examples 1-3 and Comparative Examples 1-3 were tested for thickness, areal density, breakdown voltage, air permeability, needle penetration strength, heat shrinkage rate (150℃ / 1h), tensile strength, tensile elongation, liquid absorption, liquid retention and electrolyte contact angle.

[0089] Thickness was measured according to GB / T 6672-2001, using an electronic thickness gauge to measure at 10 evenly selected points on the diaphragm and taking the average value. Areal density was measured according to GB / T 36363-2018, with the diaphragm cut into 100mm × 100mm samples, weighed, and the mass per unit area calculated. Tensile strength and elongation were also tested according to GB / T 36363-2018 using an electronic tensile testing machine at a tensile speed of 50mm / min. Needle penetration strength was measured according to GB / T 36363-2018, using a 1.0mm diameter needle to vertically puncture the diaphragm at a speed of 100mm / min, and the maximum puncture force was recorded. Air permeability was measured according to the Gurley method in GB / T 36363-2018, determining the time required for 100mL of air to permeate a fixed area of ​​the diaphragm under a pressure of 1.21kPa. The heat shrinkage rate was determined by placing the diaphragm in a 150℃ oven for 1 hour and measuring the dimensional changes in the longitudinal (MD) and transverse (TD) directions of the sample. The breakdown voltage was determined according to GB / T 1408.1 using a dielectric strength tester with a continuous and uniform voltage increase method.

[0090] Liquid absorption, liquid retention, and electrolyte contact angle were tested as follows. For the liquid absorption rate test, the diaphragm was cut into 50mm × 50mm samples. The dry mass M0 was weighed and immersed in a 1 mol / L LiPF6 electrolyte solution (a 1:1 volume ratio of ethylene carbonate and dimethyl carbonate), and allowed to stand at 25°C for 60 minutes. After removal, excess electrolyte was absorbed with filter paper, and the wet mass M1 was weighed. The liquid absorption rate was calculated using the formula (M1 - M0) / M0 × 100%. For the liquid retention rate test, the saturated sample was placed in a centrifuge and centrifuged at 2000 r / min for 10 minutes. The remaining mass M2 was weighed, and the liquid retention rate was calculated using the formula (M2 - M0) / (M1 - M0) × 100%. The electrolyte contact angle was measured using a contact angle meter. At room temperature, 2 μL of the electrolyte was dropped onto the diaphragm surface using the seated drop method. After standing, the angle between the droplet and the surface was measured. Five different locations were tested for each sample, and the average value was taken.

[0091] The test results are shown in Table 1.

[0092] Table 1 Performance test results of the examples and comparative examples

[0093] Appearance - White film White film White film White film White film White film thickness μm 11.1 11.4 10.8 11.1 11.2 11.3 areal density <![CDATA[g / m 2 ]]> 6.18 6.47 5.9 7.86 7.58 7.92 Single-micron surface density <![CDATA[g / (m 2 ·μm)]]> 0.8 0.82 0.78 1.6 1.4 1.62 Breakdown voltage kV 1.98 2.04 1.89 1.86 1.79 1.84 Breathability Sec / 100ml 174 182 176 186 174 194 Needle intensity N 5.1 5.2 5.1 5.1 5.0 5.0 Shrinkage rate 150℃ / 1h (MD) % 1.8 1.6 2.3 3.2 3.6 3.1 Shrinkage rate 150℃ / 1h (TD) % 1.2 1.1 1.4 2.4 2.7 2.2 Tensile strength (MD) <![CDATA[Kgf / cm 2 ]]> 1456 1503 1438 1453 1468 1484 Tensile strength (TD) <![CDATA[Kgf / cm 2 ]]> 1325 1376 1298 1289 1268 1245 Tensile elongation (MD) % 101 102 102 101 101 100 Tensile elongation (TD) % 98 99 98 98 98 99 absorbency % 246 238 236 102 98 96 Liquid retention % 156 164 154 89 88 81 Electrolyte contact angle ° 3.6 3.2 3.8 8.9 9.1 9.4

[0094] As shown in Table 1, compared with the traditional ceramic-coated separators (Comparative Examples 1-3), the battery separators of Examples 1-3 of the present invention exhibit a reduction of more than 50% in the single-micron surface density of the coating layer (Examples 1-3: 0.78-0.82, Comparative Examples 1.4-1.62), an increase of approximately 140% in liquid absorption rate (Examples 2: 36-246%, Comparative Examples 96-102%), an increase of approximately 75% in liquid retention rate (Examples 1: 154-164%, Comparative Examples 81-89%), and a reduction of approximately 60% in electrolyte contact angle (Examples 1: 3.2-3.8°, Comparative Examples 8.9-9.4°). Furthermore, the thermal shrinkage rate at 150°C is significantly better than that of ceramic separators (MD ≥ 3.1%, TD ≥ 2.2%), demonstrating that the present invention has achieved remarkable technological advancements in terms of lightweighting, electrolyte wettability, liquid absorption and retention capacity, and high-temperature dimensional stability.

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A battery separator composed of chitosan aerogel microspheres and CNF, characterized in that, include: Polyolefin porous base membrane; as well as A coating layer disposed on at least one surface of the polyolefin porous base membrane; The coating layer comprises chitosan aerogel microspheres and CNF; The chitosan aerogel microspheres are porous particles formed by cross-linking, freeze-drying, and pulverizing chitosan.

2. The battery separator according to claim 1, characterized in that, The skeletal density of the chitosan aerogel microspheres is 0.04-0.12 g / cm³. 3 It has mesopores with a pore size of 5-50 nm inside.

3. The battery separator according to claim 1, characterized in that, The chitosan aerogel microspheres have a particle size D50 of 0.4-0.6 μm and a D90 of 1.4-1.8 μm. The coating layer has a single-sided thickness of 1.5-4 μm.

4. The battery separator according to claim 1, characterized in that, The polyolefin porous base membrane is a PP membrane or a PE membrane with a thickness of 5-12 μm.

5. A method for preparing the battery separator according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step S1: Dissolve chitosan in an aqueous acetic acid solution, add a crosslinking agent, stir to form a gel, wash the gel and freeze-dry it to obtain chitosan aerogel, then pulverize the chitosan aerogel and sieve it to obtain chitosan aerogel microspheres. Step S2: Disperse CNF in water, add an aqueous crosslinking agent, and stir to obtain an aqueous CNF solution; Step S3: Disperse the chitosan aerogel microspheres obtained in step S1 in deionized water, add the CNF aqueous solution obtained in step S2, and add toughening agent, binder and wetting agent, mix evenly to obtain coating slurry; Step S4: Apply the coating slurry obtained in step S3 to at least one surface of the polyolefin porous base membrane and dry it to obtain the battery separator.

6. The preparation method according to claim 5, characterized in that, In step S1: by mass parts, the chitosan is 2.4-5.7 parts, the acetic acid aqueous solution is 64.2-84.7 parts, and the mass fraction of the acetic acid aqueous solution is 0.8-1.9%; the crosslinking agent is selected from at least one of glutaraldehyde, genipin or sodium tripolyphosphate, and by mass parts, the crosslinking agent is 0.24-1.14 parts.

7. The preparation method according to claim 5, characterized in that, In step S2: by mass parts, the CNF is 4.6-5.4 parts, and the water is 46-54 parts; the aqueous crosslinking agent is selected from at least one of citric acid, epichlorohydrin, glyoxal, or polyamide epichlorohydrin resin, and by mass parts, the aqueous crosslinking agent is 0.05-0.12 parts; the stirring time is 690-750 min, and the rotation speed is 1150-1250 r / min.

8. The preparation method according to claim 5, characterized in that, In step S3: by mass parts, the chitosan aerogel microspheres are 3.2-4.2 parts, the deionized water is 14.5-16.5 parts, the CNF aqueous solution is 5.4-6.6 parts, the toughening agent is 0.5-2 parts, the binder is 1.3-1.8 parts, and the wetting agent is 0.08-0.16 parts; The toughening agent is one or more of polyethylene oxide, ethylene-vinyl acetate copolymer, or acrylate elastomer; The adhesive is one or more of polyacrylic acid or polyvinyl alcohol; the wetting agent is a nonionic modified polyether.

9. The preparation method according to claim 5, characterized in that, In step S3: The mixing is carried out using a dual planetary mixer. First, chitosan aerogel microspheres and deionized water are mixed at a revolution speed of 45-55 r / min and a rotation speed of 2400-2600 r / min for 25-35 min. Then, CNF aqueous solution, toughening agent, binder and wetting agent are added and mixed at a revolution speed of 27-33 r / min and a rotation speed of 1450-1550 r / min for 55-65 min.

10. The preparation method according to claim 5, characterized in that, In step S4: the coating method is roller coating, the coating speed is 10-15 m / min, the drying temperature is 75-95℃, and the drying time is 3-6 min; the coating layer is a single-sided coating layer or a double-sided coating layer.