Functional material, diaphragm and lithium battery

Abstract

The invention provides a functional material, a diaphragm and a lithium battery. The functional material comprises porous hollow microspheres, holes are distributed in the surfaces of the porous hollow microspheres, the holes are mesopores, hydrogen fluoride double decomposition type lithium salt is packaged in the porous hollow microspheres, when the functional material is used for the diaphragm, a layer of functional material is coated on a commercial polymer base membrane, the porous hollow microspheres are used as a shell, and the porous hollow microspheres are used as the shell. Lithium salts such as lithium phosphate, lithium oxalate and the like which are encapsulated in the microspheres in an internal confinement manner are taken as cores, hydrogen fluoride in an electrolyte can be efficiently and continuously captured through a synergistic effect of physical adsorption enrichment, chemical conversion immobilization and space confinement locking, and reaction byproducts can be limited in nano pore channels, so that the hydrogen fluoride in the electrolyte can be efficiently and continuously captured. Therefore, the problem of HF corrosion is fundamentally solved, secondary pollution is avoided, and finally, the cycle life and the capacity retention ratio of the battery under severe conditions such as high voltage and high temperature are remarkably improved. The invention also provides a diaphragm and a lithium battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a functional material, a separator, and a lithium battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density and long cycle life, have been widely used in consumer electronics, new energy vehicles, and other fields, becoming a core component of current energy storage systems. In the composition of lithium-ion batteries, the electrolyte, as a key medium for ion transport, directly affects the overall stability and lifespan of the battery. Currently, the most commonly used lithium salt in commercial lithium-ion battery electrolytes is lithium hexafluorophosphate (LiPF6). This lithium salt has the characteristics of high ionic conductivity and moderate electrochemical stability, which can meet the battery usage requirements under normal operating conditions, thus maintaining its mainstream application position for a long time.

[0003] However, lithium hexafluorophosphate (LiPF6) suffers from poor thermal and chemical stability, an inherent defect that poses a serious threat to battery performance. During battery production, storage, and use, trace amounts of moisture inevitably remain in the electrolyte. LiPF6 readily reacts with this moisture to generate highly corrosive hydrogen fluoride (HF). HF, a highly corrosive substance, causes multifaceted damage to critical internal battery components: firstly, it corrodes the positive electrode active material and aluminum current collector, leading to structural collapse of the active material and damage to the current collector, directly impacting the battery's charge and discharge efficiency; secondly, HF damages the solid electrolyte interphase (SEI) film formed on the graphite negative electrode surface. The SEI film is a crucial barrier ensuring negative electrode stability and preventing continuous electrolyte decomposition; its damage accelerates electrolyte decomposition and catalyzes the dissolution of transition metal ions. These chain reactions ultimately lead to irreversible and rapid capacity decay, a significant increase in internal resistance, and severely shortened battery cycle life, especially under harsh application scenarios such as high temperature and high voltage.

[0004] To address the negative impacts of HF, various solutions have been proposed in existing technologies, primarily including strictly controlling the dryness of the production environment, adding HF scavengers to the electrolyte, and applying protective coatings to the positive electrode surface. Among these, the method of directly adding HF scavengers (such as alkaline inorganic salts and organic bases) to the electrolyte or coating them onto the separator is widely used. However, this method has significant drawbacks: First, the scavenging efficiency is low; the contact area between the powdered scavenger and HF is limited, and the reaction kinetics are slow, making it difficult to quickly and thoroughly remove HF. Second, there is a risk of secondary pollution; the products generated from the reaction between the scavenger and HF (such as LiF and organic acid salts) are easily soluble in the electrolyte and can migrate to the electrode surface, triggering new side reactions and further damaging the electrode interface stability. Third, it affects battery performance; some scavengers may reduce the ionic conductivity of the electrolyte or interfere with the interfacial reaction between the electrode and the electrolyte, leading to a decline in overall battery performance. Therefore, developing a technology that efficiently removes HF without secondary pollution and without affecting the original battery performance has become a critical technical problem urgently needing to be solved in the current lithium-ion battery field. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a functional material that, when used in lithium battery separators, can efficiently and synergistically remove HF, purify the internal environment of the battery, and possesses structural stability and compatibility, ensuring the core electrical performance of the battery.

[0006] This invention also provides a method for preparing functional materials.

[0007] The present invention also provides a functional diaphragm.

[0008] The present invention also provides a lithium battery.

[0009] A first aspect of the present invention provides a functional material comprising porous hollow microspheres, wherein the surface of the porous hollow microspheres is provided with pores, the pores being mesopores, and the porous hollow microspheres are encapsulated with a hydrogen fluoride metathesis lithium salt, wherein the hydrogen fluoride metathesis lithium salt comprises at least one of lithium phosphate, lithium oxalate, and lithium acetate.

[0010] The functional material of the present invention has at least the following beneficial effects: It can efficiently and synergistically remove HF and purify the internal environment of the battery. The pores on the surface of the porous hollow microspheres can rapidly enrich HF in the electrolyte through physical adsorption, greatly increasing the contact probability between lithium salts and HF. Lithium phosphate, lithium oxalate, and lithium acetate, as hydrogen fluoride metathesis lithium salts, can undergo irreversible metathesis reactions with HF (LiX + HF = LiF + HX), converting the highly corrosive HF into stable products. This achieves a synergistic effect of physical adsorption and chemical conversion, with an HF adsorption capacity of up to 38.1 mg / g, far superior to existing common capture agents (comparative ratio only 2.5~8.5 mg / g), completely solving the problems of slow reaction kinetics and low capture efficiency in traditional HF removal technologies.

[0011] This technology efficiently and synergistically removes HF, purifying the internal environment of the battery. Hydrogen fluoride metathesis-type lithium salt is encapsulated within porous hollow microspheres, with the lithium salt particle size larger than the pore size of the microspheres, forming a robust confined structure. This design effectively traps byproducts such as LiF generated during the metathesis reaction within the porous hollow microspheres, preventing their dissolution into the electrolyte and avoiding the migration of byproducts to the electrode surface that could trigger new side reactions. Test data shows that after cycling, the fluoride ion concentration in the electrolyte of batteries using this functional material only increased from a maximum of 2.1 ppm to 3.0 ppm, while the fluoride ion concentration in batteries without this material reached as high as 7.2 ppm, significantly reducing the destructive impact of secondary pollution on battery performance.

[0012] It features a stable and compatible structure, ensuring the core electrical performance of the battery. The porous hollow microspheres are stable and do not affect ion transport; lithium phosphate, lithium oxalate, and lithium acetate are all lithium salts compatible with lithium-ion battery systems, and will not damage the electrode interface stability or reduce the electrolyte ionic conductivity. Simultaneously, the structural design of this functional material prevents lithium salt loss, ensuring its continuous HF removal function during battery cycling. This allows the battery to achieve a capacity retention rate of up to 96% after 500 cycles at 25℃, and up to 84% at 60℃, far exceeding traditional solutions (63%~65%). Furthermore, it exhibits low cell expansion, significantly improving the battery's cycle stability and lifespan.

[0013] The selection is flexible and adaptable, meeting the needs of large-scale production. Hydrogen fluoride metathesis lithium salts include a variety of options such as lithium phosphate, lithium oxalate, and lithium acetate, which can be flexibly combined or replaced according to actual application scenarios; the composite of porous hollow microspheres and lithium salts can be achieved through various processes, and this functional material is compatible with existing battery separator coating processes, making it easy to prepare functional coatings for application on commercial base films without requiring significant modifications to existing production equipment, thus demonstrating the feasibility of large-scale application.

[0014] refer to Figure 1 The working principle of the functional materials of this invention is easily understood as shown.

[0015] Hydrogen fluoride metathesis lithium salts refer to lithium salts that can chemically react with hydrogen fluoride (HF).

[0016] According to some embodiments of the present invention, the particle size of the porous hollow microspheres is ≤5μm.

[0017] Porous hollow microspheres with a particle size ≤5μm, when used in separators, significantly improve the dispersion uniformity and coating density of the microspheres in functional coatings, avoiding coating defects caused by particle agglomeration, and ensuring tight bonding between the separator and the base film and unobstructed ion transport channels. Simultaneously, they increase the specific surface area per unit mass of material, and combined with high porosity, enhance the physical adsorption and enrichment effect of HF, improving the reaction contact efficiency with hydrogen fluoride metathesis lithium salts within the pores, achieving efficient HF removal. Furthermore, the denser pore distribution on the surface of the small-particle-size porous hollow microspheres further enhances the spatial confinement effect, firmly locking in reaction byproducts such as LiF, preventing their dissolution and secondary pollution (the electrolyte fluoride ion concentration only slightly increases after cycling). They are also compatible with existing separator coating processes, significantly improving battery cycle stability and reducing cell expansion rate without affecting battery electrical performance, making them particularly suitable for harsh applications such as high temperature and high voltage.

[0018] According to some embodiments of the present invention, the particle size of the porous hollow microspheres is 10 nm to 5 μm.

[0019] According to some embodiments of the present invention, the aperture of the hole is 2~50 nm.

[0020] According to some embodiments of the present invention, the aperture of the hole is 20~40 nm.

[0021] According to some embodiments of the present invention, the aperture of the hole is 25~35nm.

[0022] According to some embodiments of the present invention, the porosity of the porous hollow microspheres is 50% to 99.9%.

[0023] The porous hollow microspheres have a porosity of 50% to 99.9%. This provides a sufficient number of pores, which on the one hand efficiently accommodates and securely confines hydrogen fluoride metathesis-type lithium salts such as lithium phosphate, lithium oxalate, and lithium acetate, ensuring stable encapsulation of the lithium salts within the microspheres without leakage; on the other hand, it maximizes the physical adsorption area, rapidly enriching HF in the electrolyte and significantly increasing the contact probability between HF and the lithium salts within the microspheres. This, combined with the metathesis reaction, achieves efficient HF removal. Simultaneously, the high porosity structure does not hinder ion transport, ensuring that the battery's ionic conductivity remains unaffected. Ultimately, this results in a battery with a capacity retention rate of up to 96% after 500 cycles at 25°C, low cell expansion, and excellent cycle stability even at high temperatures. Furthermore, it is compatible with existing separator coating processes, facilitating large-scale production.

[0024] According to some embodiments of the present invention, the porous hollow microspheres include at least one of porous alumina microspheres or porous carbon microspheres.

[0025] Porous hollow microspheres include at least one of porous alumina microspheres or porous carbon microspheres. The pores on the surface of the microspheres and their excellent physicochemical properties can bring multiple key benefits to functional materials: On the one hand, both have high specific surface area and good physical adsorption performance, which can efficiently enrich HF in the electrolyte, providing sufficient reaction targets for hydrogen fluoride metathesis lithium salts inside the microspheres, realizing the rapid capture and conversion of HF, and the chemical properties are stable, without side reactions with the battery system, ensuring that the core electrical performance of the battery is not affected; on the other hand, the pore structure on the surface of porous hollow microspheres is regular and controllable, which can firmly confine and encapsulate lithium salts such as lithium phosphate and lithium oxalate, while locking reaction by-products (such as LiF) inside the microspheres by means of spatial confinement effect, avoiding their dissolution and secondary pollution; in addition, both have good dispersibility and process adaptability, and can be mixed with binders to prepare a uniform and dense functional coating, which can be tightly bonded when coated on the surface of commercial base films without destroying ion transport channels, and the preparation process is compatible with existing battery separator coating technology, which is conducive to large-scale production.

[0026] According to some embodiments of the present invention, the hydrogen fluoride metathesis lithium salt is in particulate form, and the particle size of the hydrogen fluoride metathesis lithium salt is larger than the size of the pores on the surface of the porous hollow microspheres, so that the hydrogen fluoride metathesis lithium salt can be confined inside the microspheres.

[0027] The hydrogen fluoride metathesis lithium salt is particulate with a particle size larger than the pore size of the porous hollow microspheres. This allows for robust encapsulation of the lithium salt within the microspheres, effectively preventing its loss from the pores during battery cycling. This ensures continuous metathesis reactions with the HF enriched in the porous hollow microspheres, guaranteeing the long-term effectiveness of HF removal. Simultaneously, this design utilizes spatial confinement to firmly lock the generated byproducts, such as LiF, inside the porous hollow microspheres, completely preventing them from dissolving into the electrolyte, migrating to the electrode surface, and triggering new side reactions. This avoids secondary pollution and does not damage the battery's ion transport channels.

[0028] According to some embodiments of the present invention, the particle size of the hydrogen fluoride metathesis lithium salt is 0.01~0.15 μm.

[0029] According to some embodiments of the present invention, the particle size of the hydrogen fluoride metathesis lithium salt is 0.03~0.1μm.

[0030] According to some embodiments of the present invention, the particle size of the hydrogen fluoride metathesis lithium salt is 0.03~0.08 μm.

[0031] According to some embodiments of the present invention, the particle size of the hydrogen fluoride metathesis lithium salt is 0.05~0.08 μm.

[0032] The second aspect of the present invention provides a method for preparing the functional material of the first aspect of the present invention, including a melt impregnation method, a solution impregnation-evaporation method, or an in-situ synthesis method.

[0033] The method for preparing functional materials according to the present invention has at least the following beneficial effects: With strong adaptability, these methods can meet the composite needs of different lithium salts and porous materials. The melt-wetting method is suitable for high-temperature resistant lithium salts, where high-temperature melting allows the lithium salt to penetrate into the porous hollow microspheres through capillary action, making it suitable for poorly soluble lithium salts such as lithium phosphate. The solution-wetting-evaporation method is for soluble lithium salts, using solution wetting and solvent evaporation to achieve crystallization and encapsulation of the lithium salt within the microspheres; this method is simple and controllable. The in-situ synthesis method can directly generate the target lithium salt within the porous hollow microspheres, precisely controlling the particle size and distribution of the lithium salt to ensure that the lithium salt particle size is larger than the pores on the surface of the porous hollow microspheres, achieving robust confinement. These three methods cover raw material combinations with different properties, providing diverse options for the preparation of functional materials.

[0034] The preparation results are excellent, ensuring the core performance of the functional materials. Regardless of the method used, uniform encapsulation of lithium salt within porous hollow microspheres can be achieved, ensuring that the high porosity (50%~99.9%) and physical adsorption capacity of the porous hollow microspheres are not compromised. Simultaneously, the metathesis reaction efficiency between lithium salt and HF is guaranteed, resulting in high HF adsorption capacity in the functional materials, far exceeding that of traditional scavenging agents. Furthermore, the lithium salt is firmly encapsulated during the preparation process, preventing loss during subsequent use and ensuring the stable operation of the synergistic mechanism of physical adsorption, chemical conversion, and spatial confinement.

[0035] The process is controllable and compatible with large-scale production. The three methods have clear operating procedures and easily adjustable parameters, effectively controlling batch stability. The preparation process is compatible with existing battery material processing technologies, requiring no special equipment, and can be seamlessly integrated with subsequent processes such as functional coating preparation and separator coating, providing a reliable guarantee for the large-scale production of functional materials and facilitating the industrialization and promotion of the technology.

[0036] According to some embodiments of the present invention, the melt impregnation method includes mixing the porous material with the hydrogen fluoride metathesis lithium salt, heating it in an inert atmosphere to above the melting point of the hydrogen fluoride metathesis lithium salt and holding it at that temperature, so that the molten hydrogen fluoride metathesis lithium salt, under capillary action, penetrates from the pores on the surface of the porous hollow microspheres into the interior of the microspheres, and then solidifies after cooling.

[0037] According to some embodiments of the present invention, the solution wetting-evaporation method includes preparing a solution of soluble hydrogen fluoride metathesis lithium salt, immersing it in porous hollow microspheres, and then evaporating to remove the solvent, so that the soluble hydrogen fluoride metathesis lithium salt crystallizes and precipitates within the porous hollow microspheres.

[0038] According to some embodiments of the present invention, the in-situ synthesis method includes directly generating the hydrogen fluoride metathesis lithium salt through a chemical reaction inside the porous hollow microspheres.

[0039] A third aspect of the present invention provides a functionalized membrane, comprising a base membrane and a functionalized material layer disposed on at least one surface of the base membrane, the functionalized material layer being prepared from the functional material of the first aspect of the present invention or the functional material obtained by the method of the second aspect of the present invention.

[0040] The functionalized diaphragm of the present invention has at least the following beneficial effects: It can efficiently remove HF, suppressing battery performance degradation at its source. The core-shell structure of the functional material has confinement and conversion functions. With porous hollow microspheres as the shell and lithium salts such as lithium phosphate (hydrofluoride metathesis type) as the core, it can rapidly enrich and irreversibly remove HF from the electrolyte through a synergistic mechanism of physical adsorption and chemical conversion. The HF adsorption capacity reaches 38.1 mg / g, far exceeding traditional methods (2.5~8.5 mg / g). It effectively avoids HF corrosion of the positive electrode active material, aluminum current collector, and damage to the negative electrode SEI film, solving the problem of battery capacity degradation and increased internal resistance caused by HF at its source.

[0041] By spatially confining the electrolyte to prevent the leaching of byproducts, secondary pollution is eliminated. The lithium salt particles in the functional material layer are larger than the pores on the surface of the porous hollow microspheres, thus effectively trapping byproducts such as LiF generated from the reaction of HF and lithium salt within the microspheres, preventing them from dissolving into the electrolyte and triggering new side reactions. Tests show that after cycling, the electrolyte fluoride ion concentration in batteries using this separator only slightly increased from 2.1 ppm to 3.0 ppm, while that in batteries without the functional material layer reached as high as 7.2 ppm, significantly ensuring the stability of the battery's internal environment.

[0042] Structural compatibility ensures electrical performance, making it suitable for harsh application scenarios. The base membrane uses commercially available materials such as polyethylene (PE) and polypropylene (PP). The functional material layer is tightly bonded to the base membrane, and the chemical properties of the functional materials are stable and do not disrupt ion transport channels, ensuring that the battery's ionic conductivity remains unaffected. Batteries using this separator maintain a capacity retention rate of up to 96% after 500 cycles at 25°C, with low cell expansion. At a high temperature of 60°C, the capacity retention rate reaches up to 84%, far exceeding comparative studies, demonstrating stable adaptability to harsh operating conditions such as high temperature and high voltage.

[0043] It is easy to scale up and has industrialization advantages. Functional materials can be prepared through mature processes such as melt impregnation and solution impregnation-evaporation. The coating process of functional material layer and base film is compatible with the existing battery separator production process, without the need for major modification of existing equipment. Moreover, the selection of base film and functional materials is flexible and the cost is controllable, which is conducive to achieving large-scale production and industrialization promotion, and provides a highly feasible solution for upgrading lithium battery performance.

[0044] The separator of this invention is a functional separator with active HF removal function. It is a commercial polymer base membrane coated with a special core-shell structure composite material coating. The coating has a porous hollow microsphere as the shell and lithium salts such as lithium phosphate and lithium oxalate encapsulated inside the microsphere as the core. Through the synergistic mechanism of physical adsorption enrichment, chemical conversion fixation and spatial confinement locking, it can efficiently and permanently capture hydrogen fluoride in the electrolyte and confine reaction byproducts inside the microsphere. This fundamentally solves the problem of HF corrosion and avoids secondary pollution, ultimately significantly improving the cycle life and capacity retention of the battery under harsh conditions such as high voltage and high temperature.

[0045] According to some embodiments of the present invention, the base film is polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), or a composite thereof.

[0046] A fourth aspect of the present invention provides a lithium battery comprising a positive electrode, a negative electrode, an electrolyte, and a functionalized separator according to a third aspect of the present invention.

[0047] The lithium battery of the present invention has significant performance advantages by employing a functionalized separator that includes a core-shell structure for confinement and conversion of functional materials. Specifically, the porous shell of the functionalized separator can efficiently adsorb and enrich HF generated by the reaction of lithium hexafluorophosphate and water in the electrolyte. The lithium salts such as lithium phosphate and lithium oxalate (with particle sizes larger than the pores on the surface of the porous hollow microspheres) encapsulated in the porous hollow microspheres undergo irreversible decomposition reactions with HF. At the same time, the spatial confinement effect locks in byproducts such as LiF to avoid secondary pollution (the concentration of fluoride ions in the electrolyte only increases slightly after cycling). This effectively prevents HF from corroding the positive electrode active material, aluminum current collector, and damaging the negative electrode SEI film. With a suitable positive electrode, negative electrode (graphite, silicon carbon materials, etc.) and electrolyte system, the battery can achieve a capacity retention rate of up to 96% and low cell expansion rate after 500 cycles at 25°C, and a capacity retention rate of up to 84% at a high temperature of 60°C, which is significantly better than traditional lithium batteries. It can still maintain excellent cycle stability and long service life under harsh conditions such as high temperature and high voltage. Moreover, the manufacturing process is compatible with existing lithium battery production, which is conducive to large-scale application.

[0048] According to some embodiments of the present invention, the cathode material includes LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiMnPO4, LiFePO4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.85 Co 0.15 Al 0.05 One or more of O2.

[0049] According to some embodiments of the present invention, the negative electrode material includes one or more composites of graphite and silicon-carbon materials.

[0050] According to some embodiments of the present invention, the electrolyte includes an electrolyte salt and an organic solvent, wherein the specific types and compositions of the electrolyte salt and the organic solvent are not specifically limited, and include positive electrode film-forming additives, negative electrode film-forming additives, and additives for improving cycle performance and low temperature. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the synergistic HF removal process of the functional material in this invention, involving physical adsorption and chemical conversion. Detailed Implementation

[0052] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0053] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0054] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0055] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0056] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0057] The porous hollow microspheres were prepared by conventional methods. After preparation, microspheres with porosity that met the experimental design were selected for the experiment.

[0058] In performance testing: The porosity of porous hollow microspheres made of shell material is tested directly using the mercury intrusion porosimetry method to confirm the porosity.

[0059] The specific surface area of ​​the porous hollow microspheres of the shell material was determined by nitrogen adsorption-desorption method and calculated based on BET theory.

[0060] The particle size of hydrogen fluoride metathesis lithium salt refers to the Dv50 particle size filled into porous hollow microspheres of the shell material. The test is carried out by measuring the core size of a large number of particles (>100) on high-resolution images using transmission electron microscopy, and the Dv50 particle size and distribution are obtained by statistical analysis using software (such as ImageJ).

[0061] The particle size of the porous hollow microspheres in the shell material refers to the Dv50 particle size of the microspheres, which is directly measured and confirmed using a laser particle size analyzer.

[0062] The pore size on the surface of porous hollow microspheres was determined by nitrogen adsorption-desorption and calculated based on the BJH model theory.

[0063] The porosity of the porous hollow microspheres was tested using the nitrogen adsorption-desorption method and calculated based on BET theory.

[0064] The method for testing the specific surface area reduction rate is to use the nitrogen adsorption-desorption method to test the metathesis lithium salt before and after filling the shell material, and then calculate it using BET theory.

[0065] The HF adsorption capacity was measured by adding the prepared core-shell material to a fixed volume of electrolyte, sealing and standing at 60°C for 12 hours, and then testing the content using a hydrogen fluoride tester. The HF adsorption capacity was determined by comparing it with the blank electrolyte group without the added material.

[0066] The method for determining the cell expansion rate is based on the cell expansion rate formula: Cell expansion rate = [(Cell thickness at 100% SOC after 500 weeks - Cell thickness at 100% SOC in the first week) / Cell thickness at 100% SOC in the first week] × 100%.

[0067] The cycle retention rate test involves charging the battery at 1C to the cutoff voltage and calculating the percentage of capacity remaining after 500 cycles relative to the initial capacity.

[0068] The fluoride ion concentration was tested by removing the battery cell before and after 500 cycles at room temperature, extracting the electrolyte, diluting it, and performing ion chromatography to analyze the fluoride ion signal.

[0069] Example 1 A functional material comprising porous alumina microspheres, wherein the surface of the porous alumina microspheres is distributed with pores that are mesoporous, and the interior of the porous alumina microspheres is encapsulated with a hydrogen fluoride metathesis type lithium salt Li3PO4.

[0070] The preparation process of functional materials is as follows: Weigh 1g of porous alumina microspheres (surface pore size approximately 50nm, specific surface area approximately 250m²). 2 (g) and 0.8g of Li3PO4 powder are thoroughly ground and mixed.

[0071] The mixture was placed in a tube furnace and heated to 1000°C at a rate of 5°C / min under an argon atmosphere, and held at this temperature for 3 hours.

[0072] Subsequently, the material was cooled to room temperature at a rate of 2°C / min to obtain a white functional material.

[0073] Nitrogen adsorption tests showed that its specific surface area and pore volume were significantly lower than those of pure mesoporous alumina, proving that Li3PO4 successfully filled the pores.

[0074] Furthermore, functionalized membranes were prepared. The specific process is as follows: The functional materials and polyvinylidene fluoride (PVDF) binder were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 90:10 and stirred until a uniform slurry was formed.

[0075] The slurry was coated onto one side of a 9μm thick polyethylene (PE) membrane using a doctor blade coater, dried at 60°C for 12 hours, and then rolled to obtain a functionalized membrane.

[0076] Assembly and testing of lithium-ion batteries: Using lithium cobalt oxide (LiCoO2) as the positive electrode, graphite as the negative electrode, a functionalized separator, and injecting conventional carbonate electrolyte (containing 1M LiPF6), a soft-pack battery was assembled as an example.

[0077] The batteries in the remaining embodiments and comparative examples were prepared using a method similar to that in Example 1, as detailed in Table 1. Table 1 shows the separator design parameters and specific surface area test results for all embodiments and comparative examples.

[0078] Table 1

[0079] In Table 1, the specific surface area of ​​the functional materials refers to the specific surface area of ​​the porous hollow microspheres after being filled with lithium salt. The specific surface area before filling is 250 m². 2 / g.

[0080] As can be seen from Table 1: The construction of the core-shell structure significantly reduced the specific surface area of ​​the porous hollow microspheres, demonstrating the successful encapsulation of lithium salts within the porous hollow microspheres. Specifically: All embodiments constructed a core-shell structure consisting of a porous material shell and a lithium salt core, with the functional material having a specific surface area of ​​70~88.8 m². 2 / g) compared to Comparative Example 2 (with only porous hollow microspheres and a specific surface area of ​​250m²) without a lithium salt core. 2 The significant decrease in the number of lithium salts (lithium phosphate, lithium oxalate, lithium acetate) indicates that lithium salts have been successfully filled into the porous hollow microspheres, occupying the original space and verifying the effectiveness of the confined packaging design.

[0081] Comparative Example 3 used ordinary alumina (non-hollow microspheres, with a porosity of only 20%) as the shell material. Even with the addition of a lithium salt core, its specific surface area decreased by only 2%, far lower than that of the Example. This indicates that the low porosity and non-hollow microsphere structure of ordinary alumina makes it difficult to achieve effective encapsulation of lithium salts, further highlighting that the porous hollow microspheres in the Example are key to ensuring the formation of the core-shell structure.

[0082] Furthermore, Table 1 also shows that the type and porosity of porous hollow microspheres affect the specific surface area and lithium salt encapsulation effect. Specifically: Comparison of embodiments using different porous material shells: Example 2, using porous carbon microspheres (porosity 95%) as the shell, shows that the specific surface area of ​​the functional material produced is 75m². 2 The / g) is higher than that of the embodiment with porous alumina microspheres as the shell. This difference is due to the higher porosity of the porous carbon microspheres. Even after filling with lithium salt, more open channels are still retained. This shows that the porosity of porous materials directly affects the final specific surface area of ​​the coating, and high porosity is more conducive to retaining a certain adsorption space after encapsulating lithium salt.

[0083] Based on the specific surface area data, it can be seen that porous hollow microspheres with high porosity can provide sufficient encapsulation space for lithium salts, while ordinary materials with low porosity cannot meet the requirements for core-shell structure construction.

[0084] Furthermore, Table 1 shows that the type of base film material and lithium salt has no significant negative impact on the formation of the core-shell structure, allowing for design flexibility. Specifically: The base film materials used in the embodiments include polyethylene (PE) and polypropylene (PP), and the lithium salt types include lithium phosphate, lithium oxalate, and lithium acetate, but their specific surface area reduction rate is relatively stable. This indicates that within the range of base film (PE, PP) and lithium salt selection defined by this invention, different combinations of raw materials can achieve effective encapsulation of lithium salts within porous hollow microspheres, and the formation of the core-shell structure is not significantly affected by the above factors. This proves that the technical solution has strong raw material adaptability and flexible design, providing diversified space for raw material selection in subsequent large-scale production.

[0085] For Comparative Example 1, which did not include porous hollow microspheres and lithium salt cores, there was no relevant specific surface area data.

[0086] Comparative Example 2 contained only porous alumina microspheres and no lithium salt core, and its specific surface area did not decrease (decrease rate 0). These two comparative examples stand in stark contrast to the embodiments, demonstrating that only by simultaneously possessing porous hollow microspheres and a lithium salt core can a core-shell structure be formed, leading to a significant decrease in specific surface area. This further confirms the uniqueness of the core-shell structure design for confining and converting functional materials in this invention, distinguishing it from traditional membranes without a core-shell structure.

[0087] Furthermore, the batteries were placed in constant temperature chambers at 25°C and 60°C respectively, and charge-discharge cycle tests were conducted at a 1C rate. After 500 cycles, the battery capacity retention rate and cell expansion rate were recorded, as shown in Table 2.

[0088] Table 2

[0089] The electrolyte was extracted from the cells before and after 500 cycles at room temperature, diluted, and subjected to ion chromatography to analyze the fluoride ion signal, as shown in Table 3.

[0090] New Table 3

[0091] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A functional material, characterized in that, The functional material comprises porous hollow microspheres, the surface of which is distributed with pores, which are mesopores, and the interior of which is encapsulated a hydrogen fluoride metathesis lithium salt, which includes at least one of lithium phosphate, lithium oxalate, and lithium acetate.

2. The functional material according to claim 1, characterized in that, The porous hollow microspheres include at least one of porous alumina microspheres or porous carbon microspheres; and / or, the particle size of the porous hollow microspheres is ≤5μm; and / or, the pore size is 2~50nm; and / or, the porosity of the porous hollow microspheres is 50%~99.9%.

3. The functional material according to claim 1, characterized in that, The particle size of the hydrogen fluoride metathesis lithium salt is 0.01~0.15μm.

4. The functional material according to any one of claims 1 to 3, characterized in that, The hydrogen fluoride metathesis lithium salt is in particulate form, and the particle size of the hydrogen fluoride metathesis lithium salt is larger than the pore size of the porous hollow microspheres.

5. A method for preparing a functional material as described in any one of claims 1 to 4, characterized in that, These include melt impregnation, solution impregnation-evaporation, or in-situ synthesis.

6. The method according to claim 5, characterized in that, The melt impregnation method includes mixing the porous hollow microspheres with the hydrogen fluoride metathesis lithium salt, heating the mixture under an inert atmosphere to above the melting point of the hydrogen fluoride metathesis lithium salt and holding it at that temperature, so that the molten hydrogen fluoride metathesis lithium salt can penetrate into the porous hollow microspheres through the pores under capillary action, and then solidifying it after cooling.

7. The method according to claim 5, characterized in that, The solution immersion-evaporation method involves preparing a solution of soluble hydrogen fluoride metathesis lithium salt, immersing it in the porous hollow microspheres, and then evaporating to remove the solvent, thereby causing the soluble hydrogen fluoride metathesis lithium salt to crystallize and precipitate within the porous hollow microspheres.

8. The method according to claim 5, characterized in that, The in-situ synthesis method involves directly generating the hydrogen fluoride metathesis lithium salt through a chemical reaction inside the porous hollow microspheres.

9. A functionalized diaphragm, characterized in that, It includes a base film and a functionalized material layer disposed on at least one surface of the base film, the functionalized material layer being prepared from the functional material of any one of claims 1 to 4 or the functional material prepared by the method of any one of claims 5 to 8.

10. A lithium battery, characterized in that, The lithium battery includes a positive electrode, a negative electrode, an electrolyte, and the functionalized separator as described in claim 9.

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