Biomass composite membrane with water removal and corrosion resistance functions, preparation method and lithium-ion battery

Abstract

This invention provides a biomass composite separator with dehydration and corrosion resistance functions, its preparation method, and a lithium-ion battery. Specifically, it relates to the field of lithium-ion battery materials. The biomass composite separator includes a base film and a functional coating, the latter containing biomass hydroxyl-rich materials and basic functional group materials. This invention utilizes the water-absorbing properties of biomass hydroxyl-rich materials and the neutralization effect of basic functional groups on hydrofluoric acid to efficiently remove moisture from the battery cell, neutralize hydrofluoric acid, and inhibit electrode corrosion and gas generation. Simultaneously, it is environmentally friendly, produces a stable film, and significantly improves the cycle life and safety of lithium-ion batteries, making it suitable for new energy vehicles, energy storage, and other fields.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, and in particular to a biomass composite separator with water removal and corrosion resistance functions, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the explosive growth of the new energy vehicle and energy storage industries, the energy density of lithium-ion batteries has been continuously improving, but their safety issues have become increasingly prominent.

[0003] Commercial lithium-ion batteries commonly use lithium hexafluorophosphate (LiPF6) as the electrolyte salt. However, this system has significant safety hazards: LiPF6 is extremely sensitive to moisture, and trace amounts of residual moisture in the cell can induce hydrolysis to produce highly corrosive hydrofluoric acid (HF). HF not only corrodes the positive electrode material, causing lattice collapse, but also damages the solid electrolyte interface film of the negative electrode and generates gas, which is a major cause of battery degradation and bulging at high temperatures. Summary of the Invention

[0004] In view of this, the present invention provides a biomass composite separator with water removal and corrosion resistance functions, a preparation method and a lithium-ion battery, which can solve the fundamental technical problem that acidic corrosion caused by electrolyte hydrolysis in lithium-ion batteries cannot be actively eliminated.

[0005] Some embodiments of this application provide a biomass composite membrane with water removal and corrosion resistance functions. The following describes this application from multiple aspects, and the embodiments and beneficial effects described below can be referenced interchangeably.

[0006] In a first aspect, the present invention provides a biomass composite membrane with water removal and corrosion resistance functions, comprising: a base membrane and a functional coating formed on at least one side surface of the base membrane, wherein the functional coating contains at least a biomass hydroxyl-rich material and an alkaline functional group material.

[0007] According to the embodiments of this application, the high-density hydroxyl groups in the biomass-rich hydroxyl material physically lock in trace amounts of moisture, blocking the source of LiPF6 hydrolysis. The amino groups in the basic functional group material chemically neutralize the highly toxic HF. The two work synergistically to significantly reduce the acidity of the electrolyte.

[0008] In one possible implementation of the first aspect mentioned above, the biomass hydroxyl-rich material is a porous sponge powder with a rigid framework.

[0009] According to the embodiments of this application, the sponge micro powder has a natural bio-silicon rigid skeleton, which has the property of not swelling in carbonate electrolytes, and retains the sponge's unique "spicule-channel" hierarchical porous structure to ensure rapid lithium ion transport.

[0010] In one possible implementation of the first aspect described above, the median particle size of the sponge powder is less than 2 μm.

[0011] According to the embodiments of this application, the median particle size of the sponge powder is limited to less than 2μm, which can increase the specific surface area of ​​the material, improve the adsorption and neutralization efficiency of moisture and hydrofluoric acid, and at the same time ensure that the functional coating is uniformly dispersed and densely structured, without clogging the membrane pores. While achieving water removal, corrosion resistance and gas generation suppression, it also ensures efficient lithium-ion transport and improves the cycle stability and safety of the battery.

[0012] In one possible implementation of the first aspect described above, the basic functional group material includes at least chitosan.

[0013] According to the embodiments of this application, chitosan is used as an alkaline functional group material. On the one hand, its alkaline groups can be used to efficiently neutralize hydrofluoric acid and reduce cell corrosion and gas generation. On the other hand, it can synergistically improve the water removal capacity of the separator. At the same time, chitosan is green and environmentally friendly, has good film-forming properties, and can improve coating stability, battery cycle life and safety.

[0014] In one possible implementation of the first aspect above, the hydroxyl value of the functional coating is greater than 50 mg KOH / g; and / or, the thickness of one side of the functional coating is 1~5 μm; and / or, the thickness of the base film is 5~12 μm.

[0015] According to the embodiments of this application, by limiting the hydroxyl value of the functional coating to greater than 50 mg KOH / g, sufficient active sites can be ensured in the separator, thereby improving its ability to remove water and neutralize hydrofluoric acid. Controlling the single-sided thickness of the functional coating to 1–5 μm and the base film thickness to 5–12 μm can reduce ion transport impedance while ensuring the separator's mechanical strength, structural stability, and water removal and corrosion resistance, thus ensuring efficient lithium-ion conduction and enabling the battery to possess excellent safety, cycle stability, and electrochemical performance.

[0016] In one possible implementation of the first aspect described above, the functional coating further includes a binder, wherein, based on the total mass of the functional coating, the biomass hydroxyl-rich material accounts for 70% to 95% by mass, the basic functional group material accounts for 1% to 20% by mass, and the binder accounts for 1% to 10% by mass.

[0017] According to the embodiments of this application, by introducing a binder into the functional coating and controlling the biomass hydroxyl-rich material, alkaline functional group material, and binder within the above-mentioned mass percentage range, it is possible to ensure that the separator has excellent water removal, hydrofluoric acid neutralization, corrosion resistance, and gas generation suppression capabilities, while also improving the adhesion and structural stability of the functional coating, and ensuring efficient lithium-ion transport, so that the battery achieves the optimal balance in terms of safety, cycle stability, and electrochemical performance.

[0018] In one possible implementation of the first aspect above, the binder is one or more of polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, or polyvinylidene fluoride;

[0019] And / or, the base film is one or more of polyethylene, polypropylene, polypropylene / polyethylene / polypropylene, or polyimide.

[0020] According to embodiments of this application, by selecting one or more of polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, or polyvinylidene fluoride as a binder, the adhesion and structural stability of the functional coating can be improved. By selecting one or more of polyethylene, polypropylene, polypropylene / polyethylene / polypropylene, or polyimide as the base membrane, the excellent mechanical properties, chemical stability, and ion transport performance of the composite separator can be ensured, achieving an optimal balance between water removal, corrosion resistance, structural strength, and electrochemical performance, thereby improving the overall safety and cycle life of the battery.

[0021] Secondly, this application provides a method for preparing a biomass composite membrane with water removal and corrosion resistance functions, comprising:

[0022] Biomass hydroxyl-rich materials and basic functional group materials are dispersed in an aqueous solution and mixed evenly to obtain a functional slurry;

[0023] A functional slurry is applied to at least one side of the base membrane, and the base membrane after applying the functional slurry is dried to obtain a biomass composite membrane.

[0024] In one possible implementation of the second aspect, the aqueous solution also contains a binder;

[0025] A functional slurry is obtained by dispersing hydroxyl-rich biomass materials and basic functional group materials in an aqueous solution and mixing them evenly, including:

[0026] Alkaline functional group materials are dissolved in an acid solution to form a glue solution. Then, biomass hydroxyl-rich materials and binders are added to the glue solution and stirred evenly to obtain a functional glue solution.

[0027] The functional adhesive is added to the aqueous solution and stirred until homogeneous to obtain the functional slurry.

[0028] Thirdly, this application provides a lithium-ion battery, including a biomass composite separator with water removal and corrosion resistance functions, or a biomass composite separator prepared by a method for preparing a biomass composite separator with water removal and corrosion resistance functions. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the battery cell structure according to an embodiment of this application;

[0030] Figure 2This is a schematic diagram of the structure of the biomass composite membrane according to an embodiment of this application;

[0031] Figure 3 This is a flowchart illustrating the preparation method of the biomass composite membrane according to an embodiment of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Positive electrode; 2. Base membrane; 3. Functional coating; 4. Biomass composite membrane; 5. Negative electrode. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application, and preferred embodiments are given. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application. This application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application; therefore, this application is not limited to the specific embodiments disclosed below.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0036] To facilitate understanding of the technical solution of this application, the technical problem to be solved by this application will now be described in detail.

[0037] In commercial lithium-ion batteries, the electrolyte salt is a key component for maintaining the battery's ionic conductivity, and lithium hexafluorophosphate (LiPF6) is commonly used. A battery cell is encapsulated with core materials such as a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte salt (LiPF6) is the core substance constituting the electrolyte inside the cell. However, because LiPF6 is extremely sensitive to moisture, trace amounts of residual moisture within the cell can induce hydrolysis, producing highly corrosive hydrofluoric acid (HF). HF not only corrodes the positive electrode material, causing lattice collapse, but also damages the solid electrolyte interface film at the negative electrode. Once the interface film is damaged, fresh negative electrode material is exposed, continuing to react with the electrolyte and generating gas, leading to high-temperature cycle degradation and bulging of the battery.

[0038] In some embodiments, the aforementioned problems are attempted to be addressed by coating the separator of the battery cell with inorganic ceramic particles (such as alumina), adding electrolyte additives, or preparing hydrophilic coatings using common biomass (such as starch and cellulose). However, inorganic ceramic coatings only provide a physical barrier and cannot actively remove moisture and HF, making it difficult to block the acidic corrosion caused by LiPF6 hydrolysis. Electrolyte additives, as consumables, face a trade-off between long-term protection and performance degradation. Common biomass hydrophilic coatings, lacking a rigid framework, are prone to swelling, blockage, or detachment in organic electrolytes. Furthermore, most biomass modifications rely solely on physical water absorption and lack the specific ability to capture HF, failing to form a closed-loop chemical protection system from moisture removal to acid neutralization.

[0039] In view of the shortcomings of the prior art, this application provides a biomass composite separator with water removal and corrosion resistance functions. The separator includes a base membrane and a functional coating disposed on at least one side of the base membrane, and the functional coating contains at least a biomass hydroxyl-rich material and a basic functional group material. The high-density hydroxyl groups and strong hydrogen bonds of the biomass hydroxyl-rich material capture residual moisture, blocking the source of LiPF6 hydrolysis. Simultaneously, a basic amino group acts as a Lewis base to actively neutralize HF, converting it into a harmless solid salt, which is then fixed onto the separator. This solution eliminates electrolyte acidification and interfacial side reaction accumulation at the source, providing key technical support for high-safety, long-life, and high-energy-density lithium-ion batteries.

[0040] To better understand the biomass composite membrane with water removal and corrosion resistance functions in the embodiments of this application, the following detailed description of the corresponding scheme of the biomass composite membrane in the embodiments of this application is provided in conjunction with the accompanying drawings.

[0041] refer to Figure 1 and Figure 2 , Figure 1 A schematic diagram of the cell structure according to an embodiment of the present invention is shown. Figure 2 A schematic diagram of the structure of the biomass composite membrane according to an embodiment of the present invention is shown.

[0042] like Figure 1 As shown, in this embodiment of the invention, the battery cell includes a positive electrode 1 and a negative electrode 5, and a biomass composite membrane 4 disposed between the positive electrode 1 and the negative electrode 5, wherein the biomass composite membrane 4 includes a base film 2 and a functional coating 3.

[0043] The functional coating 3 is formed on at least one side of the base film 2, and the functional coating 3 contains at least a biomass-rich hydroxyl material and an alkaline functional group material.

[0044] It should be noted that the aforementioned biomass hydroxyl-rich materials may include sponge powder and diatom powder, as well as other biomass hydroxyl-rich materials. The aforementioned basic functional group materials may include chitosan, arginine-derived materials, and polybenzimidazole, as well as other basic functional group materials.

[0045] like Figure 2 As shown, functional coating 3 utilizes the high-density hydroxyl groups in the biomass-rich hydroxyl material to lock moisture in the coating network through strong hydrogen bonds (i.e., OH in the diagram), thus blocking the source of hydrolysis. The amino group (i.e., NH2 in the diagram) in the basic functional group material acts as a Lewis base, actively reacting with the generated hydrogen fluoride in an acid-base neutralization reaction (i.e., R-NH2 + HF = R-NH3). + F - This process transforms highly toxic liquid acid into harmless solid salts that are fixed onto the separator. This mechanism breaks through the traditional passive water removal mode of separators, fundamentally solving the problems of electrolyte acidification and the accumulation of interfacial side reactions, and providing key technical support for the design and development of high-energy-density, high-safety, and long-life lithium-ion batteries.

[0046] In some embodiments, the above-mentioned biomass hydroxyl-rich material is a porous sponge powder with a rigid skeleton.

[0047] It is understandable that the sponge micropowder, through its triple structural advantages of a rigid framework, hierarchical channels, and surface hydroxyl groups, overcomes the bottlenecks of swelling, clogging, and structural collapse in organic electrolytes faced by traditional biomass materials. This allows it to maintain the integrity of the membrane's microporous structure at the physical level, ensuring rapid lithium-ion transport. At the chemical level, the high-density hydroxyl groups actively lock in water, preventing electrolyte acidification at its source. At the interface level, the rigid spicules stabilize the electrode or membrane interface, suppressing the accumulation of side reactions.

[0048] In some embodiments, the median particle size (i.e., D50) of the sponge powder is less than 2 μm.

[0049] Understandably, controlling the median particle size D50 of the sponge powder to less than 2μm can make the powder more uniformly dispersed and the coating surface smoother and denser. This can improve the dimensional stability and anti-swelling performance of the membrane, increase the effective contact area and the number of active sites, enhance the removal effect of moisture and HF, and at the same time reduce interfacial impedance and optimize ion transport.

[0050] In some embodiments, the above-mentioned basic functional group material includes at least chitosan. The amino groups in components such as chitosan act as Lewis bases, actively reacting with the generated HF in an acid-base neutralization reaction (R-NH2 + HF → R-NH3). + F - This process converts highly toxic liquid acid into harmless solid salts that are fixed on the membrane, which not only neutralizes HF but also effectively prevents the generation of gas.

[0051] In addition, chitosan's molecular chains are rich in hydroxyl groups, which can synergistically enhance the water removal capacity of the separator. Moreover, it has good film-forming properties, electrochemical stability, and is green and biodegradable. It is compatible with aqueous coating processes and overcomes the defects of traditional alkaline materials, such as easy agglomeration, difficulty in film formation, excessive alkalinity, or poor environmental performance, thus significantly improving the cycle life and safety of the battery.

[0052] In some embodiments, the hydroxyl value of the functional coating is greater than 50 mg KOH / g; and / or, the thickness of one side of the functional coating is 1~5 μm; and / or, the thickness of the base film is 5~12 μm.

[0053] Understandably, by controlling the hydroxyl value of the functional coating to be greater than 50 mg KOH / g, limiting the thickness of a single side to 1~5 μm, and setting the thickness of the base film to 5~12 μm, the coating can have both sufficient active sites and suitable structural size, ensuring the efficiency of water adsorption, HF neutralization and ion transport, while avoiding the risk of increased impedance and swelling caused by excessive coating thickness.

[0054] In some embodiments, the functional coating further includes a binder, wherein, based on the total mass of the functional coating, the biomass hydroxyl-rich material accounts for 70% to 95% of the mass, the basic functional group material accounts for 1% to 20% of the mass, and the binder accounts for 1% to 10% of the mass.

[0055] Understandably, by limiting the proportions of 70%–95% biomass-rich hydroxyl-rich materials, 1%–20% basic functional group materials, and 1%–10% binder, the membrane thickness expansion rate can be effectively reduced and swelling deformation suppressed. The basic functional groups enable efficient removal of moisture and HF, inhibiting side reactions and electrode corrosion. Combined with the binder to optimize interfacial adhesion and coating integrity, the long-term cycle stability and safety of the battery are significantly improved under harsh high-temperature and high-moisture conditions.

[0056] In some embodiments, the adhesive is one or more of polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, or polyvinylidene fluoride;

[0057] And / or, the base film is one or more of polyethylene, polypropylene, polypropylene / polyethylene / polypropylene, or polyimide.

[0058] It should be noted that polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, and polyvinylidene fluoride are all common adhesive materials. Polyethylene, polypropylene, polypropylene / polyethylene / polypropylene, or polyimide are all common base film materials.

[0059] It is understood that the aforementioned polypropylene / polyethylene / polypropylene is a three-layer composite membrane material composed of polypropylene and polyethylene, with the outermost layer being polypropylene and the middle layer being polyethylene.

[0060] The following is for reference. Figure 3 , Figure 3 A flowchart illustrating the preparation method of the biomass composite membrane in an embodiment of the present invention is shown.

[0061] like Figure 3 As shown in the embodiments of this application, a method for preparing a biomass composite membrane with water removal and corrosion resistance functions includes steps S100-S200.

[0062] In S100, 70-95 parts by mass of biomass hydroxyl-rich material and 1-20 parts by mass of alkaline functional group material are dispersed in an aqueous solution and mixed evenly to obtain a functional slurry.

[0063] It should be noted that the aqueous solution containing biomass-rich hydroxyl materials and basic functional group materials can be mixed evenly by high-speed shearing or ball milling.

[0064] S200 involves applying a functional slurry to at least one side of a base membrane and drying the base membrane after applying the functional slurry at a temperature of 70°C to 90°C to obtain a biomass composite membrane.

[0065] Understandably, using an aqueous system to prepare the slurry is environmentally friendly, safe, and non-toxic, with a simple process and low cost, making it suitable for industrial production. High-speed shearing or ball milling ensures uniform material dispersion, guaranteeing consistent composition and structure of the functional coating, thus improving the performance consistency of the biomass composite membrane. The coating adheres firmly to the base membrane, stably performing its water removal and corrosion resistance functions, inhibiting hydrofluoric acid formation and cell corrosion at the source, and significantly improving battery safety and cycle life.

[0066] In some embodiments, the aqueous solution further contains 1 to 10 parts by weight of a binder. Therefore, dispersing biomass hydroxyl-rich materials and basic functional group materials in an aqueous solution and mixing them uniformly to obtain a functional slurry can specifically include:

[0067] Dissolve 1-20 parts by weight of alkaline functional group material in an acid solution to form a glue solution, then add 70-95 parts by weight of biomass hydroxyl-rich material and 1-10 parts by weight of binder to the glue solution, stir evenly to obtain a functional glue solution.

[0068] The functional adhesive is added to the aqueous solution and stirred until homogeneous to obtain the functional slurry.

[0069] It should be noted that the acid solution mentioned above can be acetic acid, and the aqueous solution mentioned above can be deionized water.

[0070] Understandably, the alkaline functional group material fully dissolves to form a colloid, increasing the viscosity of the system, effectively preventing the sedimentation of biomass hydroxyl-rich materials, improving the dispersion stability of the slurry, and making the coating uniform and dense, which helps to ensure the stable and reliable performance of the diaphragm.

[0071] In this application embodiment, a lithium-ion battery is also provided, including a biomass composite separator with water removal and anti-corrosion functions, or a biomass composite separator prepared by a method for preparing a biomass composite separator with water removal and anti-corrosion functions.

[0072] The specific functions and technical effects of the lithium-ion battery in this application embodiment can be found in the above-mentioned section on biocomposite separators, and will not be repeated here.

[0073] The preparation process of the lithium-ion battery in this application is described in detail below with reference to specific embodiments.

[0074] Examples 1-4: Detailed explanation of the preparation process of the above-mentioned lithium-ion batteries.

[0075] Example 1: 20 parts by weight of chitosan were dissolved in acetic acid to form a gel solution. Then, 70 parts by weight of sponge micro powder and 10 parts by weight of styrene-butadiene rubber were added to the gel solution and stirred evenly to obtain a functional gel solution. This functional gel solution was added to 100 parts by weight of deionized water and stirred at high speed for 4 hours to obtain a functional slurry.

[0076] The aforementioned functional slurry was coated onto a 12 μm thick polyethylene base membrane. The base membrane coated with the functional slurry was then placed in an oven and dried at 70°C for 12 hours to remove moisture, thus obtaining a biomass composite membrane. The functional slurry can be coated onto the base membrane multiple times, followed by drying, to achieve a functional coating thickness of 2 μm on the base membrane.

[0077] The biomass composite separator was applied to a lithium-ion battery using conventional techniques to obtain lithium-ion battery S1.

[0078] Example 2: 10 parts by weight of chitosan were dissolved in acetic acid to form a gel solution. Then, 85 parts by weight of sponge micro powder and 5 parts by weight of polyvinyl alcohol were added to the gel solution and stirred evenly to obtain a functional gel solution. This functional gel solution was added to 100 parts by weight of deionized water and stirred at high speed for 2 hours to obtain a functional slurry.

[0079] The aforementioned functional slurry was coated onto a 9 μm thick polyethylene base membrane. The base membrane coated with the functional slurry was then placed in an oven and vacuum-dried at 80°C for 12 hours to remove moisture, resulting in a biomass composite membrane. The functional slurry can be coated onto the base membrane multiple times, followed by drying, to achieve a functional coating thickness of 2 μm on the base membrane.

[0080] The biomass composite separator was applied to a lithium-ion battery using conventional techniques to obtain lithium-ion battery S2.

[0081] Example 3: 5 parts by weight of chitosan were dissolved in acetic acid to form a gel solution. Then, 90 parts by weight of sponge micropowder and 5 parts by weight of polyvinyl alcohol were added to the gel solution and stirred evenly to obtain a functional gel solution. This functional gel solution was added to 100 parts by weight of deionized water and stirred at high speed for 2 hours to obtain a functional slurry.

[0082] The aforementioned functional slurry was coated onto a 9 μm thick polyethylene base membrane. The base membrane coated with the functional slurry was then placed in an oven and vacuum-dried at 80°C for 12 hours to remove moisture, resulting in a biomass composite membrane. The functional slurry can be coated onto the base membrane multiple times, followed by drying, to achieve a functional coating thickness of 2 μm on the base membrane.

[0083] The biomass composite separator was applied to a lithium-ion battery using conventional techniques to obtain lithium-ion battery S3.

[0084] Example 4: 3 parts by weight of chitosan were dissolved in acetic acid to form a gel solution. Then, 95 parts by weight of sponge micropowder and 2 parts by weight of polyvinyl alcohol were added to the gel solution and stirred evenly to obtain a functional gel solution. This functional gel solution was added to 100 parts by weight of deionized water and stirred at high speed for 2 hours to obtain a functional slurry.

[0085] The aforementioned functional slurry was coated onto a 9 μm thick polyethylene base membrane. The base membrane coated with the functional slurry was then placed in an oven and vacuum-dried at 80°C for 12 hours to remove moisture, resulting in a biomass composite membrane. The functional slurry can be coated onto the base membrane multiple times, followed by drying, to achieve a functional coating thickness of 2 μm on the base membrane.

[0086] The biomass composite separator was applied to a lithium-ion battery using conventional techniques to obtain lithium-ion battery S4.

[0087] Comparative Examples 1-6 prepared different biomass composite separators by adjusting the content of biomass hydroxyl-rich materials, basic functional group materials, and binders, or by replacing the biomass hydroxyl materials with other materials, following the same preparation steps as Examples 1-4. These biomass composite separators were then applied to lithium-ion batteries using conventional techniques to obtain lithium-ion batteries S5-S10. Steps not described in the comparative examples can be found in existing technologies and will not be detailed here. Specific components can be found in Table 1.

[0088] Table 1 Comparison of component content between experimental group and control group

[0089]

[0090] As shown in Table 1, Examples 1-4 are specific implementations of the technical solution of the present invention. Their core feature is the use of biomass hydroxyl-rich materials as the main body, combined with alkaline functional group materials and binders, without the addition of other materials. Specifically, the content of the biomass hydroxyl-rich materials ranges from 70% to 95%, the content of the alkaline functional group materials ranges from 1% to 20%, and the content of the binder ranges from 1% to 10%.

[0091] Comparative Examples 1-6 are comparative examples used to contrast with Examples 1-4, highlighting the superiority of the technical solution of the present invention. Comparative Example 1 compares the substrate performance by reducing the content of hydroxyl-rich biomass materials and increasing the binder content. Comparative Example 2 significantly reduces the content of basic functional group materials to verify their key role. Comparative Example 3 uses a blank control without substrate coating. Comparative Example 4 replaces the substrate with ordinary ceramic materials to compare material compatibility. Comparative Example 5 eliminates basic functional group materials to verify their necessity. Comparative Example 6 replaces the hydroxyl-rich biomass materials with general biomass materials to compare substrate specificity; the general biomass materials can be cellulose, etc.

[0092] To objectively evaluate the comprehensive performance of the lithium-ion batteries prepared in Examples 1-4 and Comparative Examples 1-6 of this invention, tests were conducted on lithium-ion batteries S1-S10 from four core dimensions: anti-swelling dimensional stability, in-situ water removal performance, anti-HF elimination performance, and battery cycle performance. The specific test methods are as follows:

[0093] (a) Dimensional stability test against swelling

[0094] Sample preparation: The biomass composite membranes in Examples 1-4 and Comparative Examples 1-6 were cut into square samples with a size of 5cm×5cm. The sample surface was ensured to be free of damage and wrinkles, and the initial thickness of the sample was accurately recorded.

[0095] Immersion treatment: The sample was completely immersed in a carbonate electrolyte [the electrolyte composition was ethylene carbonate (EC): dimethyl carbonate (DMC) = 1:1] and placed in a constant temperature environment of 60℃ for 48 hours in a sealed container.

[0096] Test calculation: After removing the sample, use dust-free filter paper to quickly absorb the residual electrolyte on the surface. Use a high-precision thickness gauge to measure the thickness of the sample after immersion. Calculate the thickness expansion rate (%) according to the following formula: Thickness expansion rate = [(Thickness after immersion - Initial thickness) / Initial thickness] × 100%.

[0097] (ii) In-situ water removal performance test

[0098] Electrolyte preparation: Prepare a carbonate-based electrolyte, precisely controlling its initial moisture content to 500 ppm.

[0099] Immersion experiment: Take equal amounts of the above-mentioned aqueous electrolyte and add them to the biomass composite membrane samples of each group with equal area. Seal and immerse for 48 hours at room temperature.

[0100] Content determination: After soaking, the supernatant of the electrolyte was taken and the residual water content was determined by a Karl Fischer moisture analyzer. The residual water content was used to characterize the in-situ water removal performance of the diaphragm.

[0101] (III) HF Elimination Performance Test

[0102] Simulated electrolyte preparation: Prepare a carbonate-based electrolyte, add HF reagent and precisely control it so that the initial HF concentration in the electrolyte is 200 ppm, to simulate the HF impurity environment generated by the hydrolysis of LiPF6.

[0103] Immersion test: Each group of biomass composite membrane samples with equal area was added to the above simulated electrolyte, sealed and left to soak for 48 hours.

[0104] Concentration determination: After soaking, the remaining HF concentration in the electrolyte was determined by acid-base titration. The remaining HF concentration value was used to characterize the diaphragm's resistance to HF elimination.

[0105] (iv) Battery cycle performance test

[0106] Cyclic testing: Lithium-ion batteries S1-S10 were placed in a 60℃ high-temperature environment, and their cyclic performance was tested using a battery testing system. The cyclic performance test involved charging and discharging at a rate of 1C (C-rate) / 1C (C-rate), with a voltage window set between 3.0V and 4.3V, for a total of 100 charge-discharge cycles.

[0107] Results Record: Record the capacity retention rate (%) of each group of batteries after the 100th cycle. The calculation formula is: Capacity retention rate = (Discharge capacity of the 100th cycle / Discharge capacity of the 1st cycle) × 100%.

[0108] Table 2. Test Data for Examples and Comparative Examples

[0109]

[0110] As shown in Table 2, compared with Examples 1-4, Comparative Examples 1-6 either deviate from the core ratio, lack key components, or are replaced with ordinary materials, resulting in significant differences in performance.

[0111] Regarding dimensional stability against swelling, the thickness expansion rate of the biomass composite membranes in Examples 1-4 was 0.50%–0.85%. In Comparative Examples 1 and 2, due to imbalanced proportions, the expansion rate increased to 1.20%–1.62%. Comparative Example 6, using a mixture of general biomass materials, alkaline functional group materials, and binders, exhibited an even higher expansion rate of 16.50%. Regarding in-situ water removal performance, the residual moisture concentration in Examples 1-4 was only 8–15 ppm. In Comparative Examples 3 and 4, without functional coatings or using ceramic coatings, the residual moisture reached 485–492 ppm. In Comparative Example 5, due to the lack of alkaline functional group materials, the residual moisture rose to 28 ppm. Although Comparative Example 2 had a lower residual moisture, its HF resistance was significantly deteriorated. Regarding HF elimination performance, the residual HF concentration in Examples 1-4 was 4–10 ppm. In Comparative Examples 2 and 5, due to insufficient or absent alkaline functional group materials, the residual HF concentration soared to 17–158 ppm. The residual HF concentration in Comparative Examples 3 and 4 was close to the initial level, indicating almost no elimination ability. In terms of battery cycle performance, the capacity retention rate of Examples 1 to 4 after 100 cycles was 88% to 92.1%, while the capacity retention rates of Comparative Examples 3 and 4 were only 12.4% and 25.6%, respectively, and the remaining comparative examples were all below 71%.

[0112] Therefore, it can be seen that, through the synergistic regulation of high-proportion biomass hydroxyl-rich materials, alkaline functional group materials, and binders, the thickness expansion rate of the biomass composite separator in the electrolyte is strictly controlled within an extremely low range of 0.50% to 0.85%, effectively avoiding the risk of battery short circuits caused by swelling and deformation, and ensuring structural safety. Furthermore, based on the alkaline functional groups, dual efficient removal of moisture and HF is achieved, controlling residual moisture below 15 ppm and residual HF below 10 ppm, fundamentally inhibiting electrolyte decomposition and electrode corrosion. Ultimately, with the synergistic effect of dimensional stability and impurity removal, the battery retains a capacity of over 88%, reaching a maximum of 92.1%, after 100 cycles under harsh high-temperature and high-moisture conditions, significantly improving electrochemical stability and cycle life, and possessing outstanding industrial application value.

[0113] It should be noted that in the examples and description of this patent, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0114] Although this application has been illustrated and described with reference to certain preferred embodiments thereof, those skilled in the art should understand that various changes in form and detail may be made thereto without departing from the spirit and scope of this application.

Claims

1. A biomass composite membrane with water removal and corrosion resistance functions, characterized in that, The biomass composite membrane includes a base membrane and a functional coating formed on at least one side surface of the base membrane, wherein the functional coating contains at least a biomass hydroxyl-rich material and a basic functional group material.

2. The biomass composite membrane according to claim 1, characterized in that, The biomass hydroxyl-rich material is a porous sponge powder with a rigid framework.

3. The biomass composite membrane according to claim 2, characterized in that, The median particle size of the sponge powder is less than 2 μm.

4. The biomass composite membrane according to claim 1, characterized in that, The basic functional group material includes at least chitosan.

5. The biomass composite membrane according to any one of claims 1-4, characterized in that, The hydroxyl value of the functional coating is greater than 50 mg KOH / g; And / or, the single-sided thickness of the functional coating is 1~5μm; And / or, the thickness of the base film is 5~12μm.

6. The biomass composite membrane according to any one of claims 1-4, characterized in that, The functional coating further includes a binder, wherein, based on the total mass of the functional coating, the biomass hydroxyl-rich material accounts for 70% to 95% of the mass, the alkaline functional group material accounts for 1% to 20% of the mass, and the binder accounts for 1% to 10% of the mass.

7. The biomass composite membrane according to claim 6, characterized in that, The adhesive is one or more of polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, or polyvinylidene fluoride; And / or, the base film is one or more of polyethylene, polypropylene, polypropylene / polyethylene / polypropylene, or polyimide.

8. A method for preparing a biomass composite membrane with water removal and corrosion resistance functions as described in any one of claims 1-7, characterized in that, include: Biomass hydroxyl-rich materials and basic functional group materials are dispersed in an aqueous solution and mixed evenly to obtain a functional slurry; The functional slurry is applied to at least one side surface of the base membrane, and the base membrane after applying the functional slurry is dried to obtain a biomass composite membrane.

9. The method according to claim 8, characterized in that, The aqueous solution also contains a binder; The process of dispersing biomass hydroxyl-rich materials and basic functional group materials in an aqueous solution and mixing them evenly to obtain a functional slurry includes: The alkaline functional group material is dissolved in an acid solution to form a glue solution. Then, the biomass hydroxyl-rich material and the binder are added to the glue solution and stirred evenly to obtain a functional glue solution. The functional adhesive is added to an aqueous solution and stirred until homogeneous to obtain the functional slurry.

10. A lithium-ion battery, characterized in that, Includes the biomass composite membrane with water removal and corrosion resistance functions as described in any one of claims 1-7, or the biomass composite membrane prepared by the method described in claim 8 or 9.

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