A separator containing a functional coating of inverse perovskite halide and a method of preparation and use thereof

Abstract

The present application relates to the technical field of battery separator, and particularly relates to a separator containing a functional coating of anti-perovskite halide and a preparation method and application thereof. The functional coating is prepared by coating, drying and hot pressing of a slurry prepared from an anti-perovskite halide, a binder and a medium-polarity anhydrous solvent, and the surface of a polyolefin-based film is activated, and the solid content of the anti-perovskite halide in the slurry and the thickness of the coating are controlled, so that the ion conductivity, thermal stability and interface compatibility with the electrode of the separator are significantly improved, the thermal shrinkage of the separator is effectively inhibited, and the rate performance and fast charging capacity of the battery are improved. The method is simple in process and suitable for large-scale coating production, and can be widely applied to lithium ion batteries, solid-state batteries and electric equipment.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and in particular to a separator containing an anti-perovskite halide functional coating, its preparation method, and its application. Background Technology

[0002] Polyolefin separators in lithium-ion batteries primarily function to isolate the positive and negative electrodes, prevent direct electron conduction, and provide lithium-ion channels. They are key materials determining the battery's internal interface structure, internal resistance, capacity, cycle performance, and safety. Existing polyolefin separators are mostly made of polypropylene (PP) or polyethylene (PE), forming a porous structure through unidirectional or bidirectional stretching. However, due to internal stress during the stretching process, the separator is prone to thermal shrinkage or softening at high temperatures, causing the pore-closing temperature to approach the melting point. This leads to separator structural damage, resulting in short circuits between the positive and negative electrodes and severely impacting battery safety. Therefore, improving the high-temperature stability and mechanical properties of the separator is crucial for enhancing battery performance.

[0003] Currently, the common approach is to construct inorganic or ceramic coatings on the membrane surface, such as alumina, titanium dioxide, or siloxane particle coatings. While these coatings can suppress membrane shrinkage to some extent, they are prone to peeling or powdering under high temperatures or long-term cycling, making it difficult to simultaneously achieve optimal membrane mechanical and electrochemical properties.

[0004] Therefore, how to balance the mechanical and electrochemical properties of the membrane is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] In view of this, the present invention proposes a separator with an anti-perovskite halide functional coating, its preparation method, and its application. A functional coating based on an anti-perovskite halide solid electrolyte is constructed on the surface of a polyolefin separator. Utilizing the high lithium-ion conductivity and good thermal stability of anti-perovskite halides, as well as their good chemical stability in moderately and low-polarity anhydrous solvents, they synergistically form a uniform and stable coating structure with the binder system, thereby constructing continuous ion transport channels on the separator surface and improving interfacial stability. Through this structural design, the high-temperature safety and ion transport performance of the separator can be significantly improved without damaging the original pore structure of the separator, thus achieving a synergistic improvement in battery safety and electrochemical performance.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a diaphragm containing an anti-perovskite halide functional coating, the diaphragm comprising a base film and a functional coating coated on one side of the base film, wherein the slurry composition of the functional coating comprises an anti-perovskite halide and a binder.

[0007] Based on the above technical solutions, preferably, the anti-perovskite halide includes one or more of Li3OCl, Li3OBr, and Li2OHCl; the binder includes one or more of PEO (polyethylene oxide), PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), and PTFE (polytetrafluoroethylene); and the base membrane is a polyolefin membrane.

[0008] The polyolefin separator can be selected from polypropylene (PP), polyethylene (PE), or copolymers thereof, with a thickness of 10-50 μm and a porosity of 30-50%. It provides a good lithium-ion transport channel while ensuring the separator's flexibility and mechanical strength. The anti-perovskite halide material exhibits high lithium-ion conductivity (≥10). -4 With its good thermal stability (S / cm), it can form a continuous ion-conducting network on the membrane surface.

[0009] Based on the above technical solutions, a further preferred embodiment is that the anti-perovskite halide is Li3OCl; the binder is PVDF, and the binder is used to improve the adhesion between the coating and the polyolefin membrane.

[0010] Based on the above technical solutions, preferably, the amount of the anti-perovskite halide is 30~60wt% of the total mass of the slurry; the mass ratio of the anti-perovskite halide to the binder is 2.4~4.8:1.

[0011] Controlling the amount of anti-perovskite halide in the slurry ensures good flowability and dispersion stability, while also enabling the formation of a continuous and dense functional coating after application. This is because when the solid electrolyte content is too low, the slurry viscosity is too low, which can easily lead to material sedimentation and is detrimental to subsequent coating processes; conversely, when the content is too high, the slurry viscosity increases significantly, easily causing particle agglomeration or uneven coating.

[0012] Based on the above technical solution, a further preferred embodiment is that the amount of the anti-perovskite halide is 50 wt% of the total mass of the slurry; and the mass ratio of the anti-perovskite halide to the binder is 4:1.

[0013] Based on the above technical solutions, preferably, the thickness of the functional coating is 1~10μm.

[0014] Ensuring the thickness of the functional coating is within an appropriate range is crucial for balancing the overall performance of the separator, including its mechanical, electrical, and safety properties. The functional coating can suppress the shrinkage of the base film at high temperatures, and a coating of a certain thickness is fundamental to maintaining its structural integrity, good adhesion to the base film, and preventing it from falling off during cycling. However, when the coating thickness increases to a certain extent, it can increase the resistance to lithium-ion migration, leading to higher internal resistance of the battery and affecting its electrochemical performance.

[0015] Based on the above technical solutions, a further preferred embodiment is that the thickness of the functional coating is 4 μm.

[0016] Secondly, a method for preparing a membrane with an anti-perovskite halide functional coating as described above is provided, comprising the following steps: S1, dissolve the anti-perovskite halide and binder in a solvent to form a homogeneous slurry; S2, perform surface activation treatment on the base film, and uniformly coat the slurry obtained in step S1 onto one side of the activated base film to obtain a diaphragm with a wet coating. S3, the membrane with the wet coating is dried to obtain a functional membrane.

[0017] Based on the above technical solutions, preferably, in step S1, the solvent includes any one of diethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), ethyl acetate, and dimethoxyethane.

[0018] In this invention, a medium- to low-polarity solvent system, as described above, is preferred. This system promotes uniform dispersion of particles in the slurry and ensures tight bonding with the PP and PE membranes. A solvent with suitable polarity effectively reduces interfacial tension between particles, preventing significant agglomeration of the solid electrolyte powder in the slurry. It also facilitates uniform distribution of the binder within the system, ensuring the continuity and uniformity of subsequent coatings. Furthermore, anti-perovskite halide solid electrolytes are highly sensitive to moisture; therefore, the water content in the solvent system should be kept as low as possible. Anhydrous or low-aqueous solvents are preferred to reduce surface hydrolysis, side reactions, or localized structural changes caused by moisture. The stability of the slurry is maintained by the following reasons: firstly, a solvent with suitable polarity forms a relatively stable solvation layer on the surface of the anti-perovskite halide particles, preventing decomposition of the halide electrolyte in the solvent; secondly, low-aqueous or anhydrous conditions reduce the likelihood of side reactions between the halide particles and moisture, thus preventing changes in particle surface composition or structural instability.

[0019] Based on the above technical solution, in a further preferred embodiment, in step S1, the solvent is tetrahydrofuran.

[0020] Based on the above technical solutions, preferably, in step S2, the surface activation treatment of the base film includes methods such as plasma treatment, ultraviolet ozone treatment, or mechanical roughening treatment. This forms a certain micro-rough structure on the surface of the diaphragm or introduces polar functional groups, thereby improving the interfacial bonding between the coating and the base film and enhancing the adhesion between them.

[0021] Based on the above technical solutions, preferably, in step S2, the thickness of the wet coating is 30~40μm.

[0022] Based on the above technical solutions, preferably, in step S3, after the drying process, hot pressing is also included.

[0023] Drying allows the solvent to fully evaporate and form a stable functional coating. During the drying process, the solvent is controlled to evaporate gradually at an appropriate rate, promoting the formation of a continuous and dense particle network structure of anti-perovskite halide particles on the membrane surface. Simultaneously, the binder forms stable connections between the particles, resulting in a structurally stable functional coating. Furthermore, to further improve the coating's density and interfacial adhesion, the resulting membrane can be subjected to a slight hot-pressing process in a roller press. After hot pressing, the coating bonds more tightly to the polyolefin membrane, exhibiting better surface continuity, further enhancing the coating's density, mechanical stability, and interfacial adhesion to the membrane substrate, thereby improving the membrane's stability under high-temperature and cycling conditions.

[0024] Based on the above technical solutions, preferably, the drying treatment temperature is 50~70℃ and the time is 5~7h; the hot pressing treatment temperature is 70~90℃, the pressure is 2~8 MPa, and the time is 5~15min.

[0025] Based on the above technical solutions, a further preferred embodiment is that the drying treatment temperature is 60℃ and the time is 6h; the hot pressing treatment temperature is 80℃, the pressure is 5 MPa, and the time is 10 min.

[0026] Thirdly, the application of the separator with the anti-perovskite halide functional coating as described above in the preparation of batteries and electrical devices is provided.

[0027] The membrane with an anti-perovskite halide functional coating of the present invention has the following advantages over the prior art: 1. By constructing a functional coating based on an anti-perovskite halide solid electrolyte on the surface of a polyolefin separator, a synergistic improvement in the separator's structural stability and ion conductivity under high-temperature and cycling conditions was achieved. Firstly, due to the high lithium-ion conductivity of the coating material itself, it provides a continuous ion transport channel while maintaining the separator's thermal stability, effectively solving the problem of traditional ceramic coatings hindering lithium-ion conduction. Secondly, this functional coating forms a stable interfacial bond with the polyolefin base membrane. By rationally controlling the coating thickness, the coating can maintain its structural integrity under high-temperature or long-term cycling conditions, preventing detachment or pulverization, thereby enhancing the separator's mechanical stability and long-term cycling reliability. Simultaneously, because the anti-perovskite material possesses certain mechanical strength and ion-selective conductivity, it can regulate the distribution of lithium ions at the separator interface during battery charging and discharging, helping to homogenize lithium-ion flux and, to some extent, suppressing lithium dendrite formation, thus improving battery operation safety.

[0028] 2. Anti-perovskite halide solid electrolytes have good thermal and electrochemical stability, which means that the functional layer formed on the membrane surface can not only improve the heat resistance of the membrane, but also build a stable interfacial environment between the electrolyte and the electrode, thereby reducing interfacial side reactions and improving the interfacial stability of the battery under high voltage or long-term cycling conditions.

[0029] 3. Due to the high cost of active inorganic solid electrolyte particles (oxides, sulfides), and the requirement of rare earth elements for traditional halide solid electrolytes, the synthesis of anti-perovskite solid electrolytes is simple and the raw material cost is low. The anti-perovskite halide solid electrolyte functional coating membrane provided by this invention is superior to existing technologies in terms of economy, safety, cycle stability, interface stability and ion transport performance. It not only effectively solves the problems of easy softening, easy coating peeling and limited ion transport of existing polyolefin membranes under high temperature conditions, but also achieves synergistic improvement of membrane thermal stability, interface stability and electrochemical performance, thereby significantly improving the safety and overall performance of lithium-ion batteries. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] The PEO involved in this invention was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a molecular weight of 1,000,000; PVDF was purchased from Solvay, Inc., USA, with a molecular weight of 900,000 to 1,100,000; PVDF-HFP was purchased from ARKEMA, France, with a molecular weight of 400,000; PTFE was purchased from Shenzhen Kejing Zhida Technology Co., Ltd., with a molecular weight of 7,700,000; and the remaining materials and reagents were all commercially available products.

[0032] Example 1 Preparation of a diaphragm containing an anti-perovskite halide functional coating.

[0033] 1) Preparation of halide slurry: In a dry atmosphere or glove box, mix 10.0 g Li3OCl powder with 2.5 g PVDF powder, at which point the mass ratio of Li3OCl to binder is 4:1. Slowly add 7.5 g anhydrous THF while stirring to obtain a homogeneous slurry.

[0034] 2) Base membrane surface treatment: The PP membrane is placed in a plasma treatment device, using oxygen plasma with a power of 100 W and a treatment time of 2 min, to generate a micro-rough structure and polar functional groups on the surface.

[0035] 3) Coating and drying: The treated PP diaphragm is flattened and fixed on the doctor blade coating machine. The doctor blade gap is adjusted to 30μm. The uniform slurry from step 1) is coated on one side of the diaphragm. After coating, the wet film is placed in a 60 ℃ vacuum oven and dried for 6 h to allow THF to evaporate completely.

[0036] 4) Post-hot pressing treatment: The dried diaphragm is placed in a roller press and hot-pressed at 80 ℃ and 5 MPa for 10 min. After natural cooling to room temperature, a composite diaphragm with a Li3OCl functional coating on one side is obtained. After drying, the coating thickness is about 4 μm, the coating surface is continuous and dense, and it is well bonded to the base film.

[0037] Example 2 Preparation of a diaphragm containing an anti-perovskite halide functional coating.

[0038] 1) Preparation of halide slurry: In a dry atmosphere or glove box, mix 6.0 g Li3OBr powder with 2.5 g PEO powder, so that the mass ratio of Li3OBr to binder is 2.4:1. Slowly add 11.5 g anhydrous 2-MeTHF while stirring to obtain a homogeneous slurry.

[0039] 2) Base film surface treatment: The PE membrane is placed in a plasma treatment device, using oxygen plasma with a power of 100 W and a treatment time of 2 min, to generate a micro-rough structure and polar functional groups on the surface.

[0040] 3) Coating and drying: The treated PP diaphragm is flattened and fixed on the doctor blade coating machine. The doctor blade gap is adjusted to 30μm. The uniform slurry from step 1) is coated on one side of the diaphragm. After coating, the wet film is placed in a vacuum oven at 50 ℃ and dried for 7 h to allow 2-MeTHF to completely evaporate.

[0041] 4) Post-hot pressing treatment: The dried diaphragm is placed in a roller press and hot-pressed at 70 ℃ and 2 MPa for 15 min. After that, it is naturally cooled to room temperature to obtain a composite diaphragm with a single-sided Li3OBr functional coating. The coating thickness is about 1 μm, the coating surface is continuous and dense, and it is well bonded to the base film.

[0042] Example 3 Preparation of a diaphragm containing an anti-perovskite halide functional coating.

[0043] 1) Preparation of halide slurry: In a dry atmosphere or glove box, mix 12 g of Li2OHCl powder with 2.5 g of PTFE powder. At this point, the mass ratio of Li2OHCl to adhesive is 4.8:1. Slowly add 5.5 g of anhydrous diethyl ether while stirring to obtain a homogeneous slurry.

[0044] 2) Base membrane surface treatment: The PP membrane is placed in a plasma treatment device, using oxygen plasma with a power of 100 W and a treatment time of 2 min, to generate a micro-rough structure and polar functional groups on the surface.

[0045] 3) Coating and drying: The treated PP diaphragm is flattened and fixed on the doctor blade coating machine. The doctor blade gap is adjusted to 30μm. The uniform slurry from step 1) is coated on one side of the diaphragm. After coating, the wet film is placed in a vacuum oven at 70 ℃ and dried for 5 h to allow the diethyl ether to evaporate completely.

[0046] 4) Post-hot pressing treatment: The dried diaphragm is placed in a roller press and hot-pressed at 90 ℃ and 8 MPa for 5 min. After that, it is naturally cooled to room temperature to obtain a composite diaphragm with a single-sided Li2OHCl functional coating. The coating thickness is about 10 μm. The coating surface is continuous and dense and has good adhesion to the base film.

[0047] Example 4 The preparation method of this embodiment is basically the same as that of Example 1, except that in step 1), the amount of Li3OCl powder used is 6 g, and the mass ratio of Li3OCl to binder is 2.4:1.

[0048] Example 5 The preparation method of this embodiment is basically the same as that of Example 1, except that in step 1), the amount of Li3OCl powder used is 12 g, and the mass ratio of Li3OCl to binder is 4.8:1.

[0049] Comparative Example 1 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 1), the amount of Li3OCl powder used is 5 g, and the mass ratio of Li3OCl to binder is 2:1.

[0050] Comparative Example 2 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 1), the amount of Li3OCl powder used is 14 g, and the mass ratio of Li3OCl to binder is 5.6:1.

[0051] Example 6 The preparation method of this embodiment is basically the same as that of Example 1, except that in step 3), the gap between the scrapers is adjusted to 15 μm, and a membrane with a coating thickness of about 1 μm is finally prepared.

[0052] Comparative Example 3 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 3), the gap between the scrapers is adjusted to 14 μm, and a membrane with a coating thickness of about 0.8 μm is finally prepared.

[0053] Example 7 The preparation method of this embodiment is basically the same as that of Example 1, except that in step 3), the gap between the scrapers is adjusted to 60 μm to obtain a membrane with a coating thickness of about 10 μm.

[0054] Comparative Example 4 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 3), the gap between the scrapers is adjusted to 85 μm to obtain a membrane with a coating thickness of about 15 μm.

[0055] Comparative Example 5 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 1), Li3OCl powder is replaced with an equal amount of traditional binary halide lithium chloride (LiCl).

[0056] Comparative Example 6 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 1), Li3OCl powder is replaced with an equal amount of active non-perovskite halide electrolyte Li3InCl6 (LIC).

[0057] Comparative Example 7 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 1), anhydrous THF is replaced with an equal amount of 95% ethanol.

[0058] Comparative Example 8 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 1), anhydrous THF is replaced with an equal amount of N-methylpyrrolidone (NMP).

[0059] Performance testing: The separators prepared in the above examples and comparative examples were assembled into batteries, and various performance tests were conducted using conventional methods. The results are shown in Table 1.

[0060] Table 1

[0061] As shown in Table 1, by using a low-polarity aprotic solvent, the anti-perovskite halide electrolyte can be successfully combined with the traditional PP separator to form a uniform and dense functional coating. The coulombic efficiency is higher during cycling, the battery cycle life is significantly extended, and the problem of easy decomposition of traditional active halide electrolytes in polar solvents is avoided. A 4μm beneficial coating with lithium-ion conductivity is formed on the surface of the PP separator, forming a uniform lithium-ion flux and inhibiting the growth of lithium dendrites. The capacity remaining after 100 cycles at 1C rate using commercial electrolyte can reach up to 97%.

[0062] In Comparative Examples 1 and 2, the amount of anti-perovskite halide electrolyte Li3OCl was too low or too high, and the coating was prone to powdering and falling off if there was too little binder, while too much binder would hinder ion migration, both of which led to a reduction in battery cycle life. In Comparative Examples 3 and 4, the thickness of the separator was too thin or too thick. If the separator was too thin, the structural integrity would be insufficient, and if it was too thick, the resistance to lithium ion migration would increase, resulting in an increase in the battery's internal resistance and affecting its electrochemical performance.

[0063] Comparative Example 5 uses LiCl, which lacks an anti-perovskite structure. LiCl itself has weak lithium-ion conductivity, hindering rapid ion transport in the battery, resulting in a significant decrease in fast-charging performance. Furthermore, it fails to form a uniform ion pathway, making it easier for lithium dendrites to form during lithium deposition stripping, thus piercing the separator. Additionally, the presence of LiCl exacerbates corrosion of the aluminum and copper current collectors during battery charging and discharging, negatively impacting long-term battery life. Comparative Example 6 uses a conventional halide electrolyte (non-perovskite type) LIC, which can conduct ions. During dispersion in THF, LIC degrades, turning the original white suspension into a light pink turbidity. LIC decomposes into LiOH, LiCl, InCl3, and numerous other byproducts. The final functional coating exhibits extremely poor performance; in fact, various byproducts dissolve in the electrolyte, further causing adverse chemical reactions that hinder lithium-ion transport and shorten battery life.

[0064] In Comparative Examples 7 and 8, the solvents were replaced with aqueous alcohols (95% ethanol) and highly polar solvents (NPM), respectively. As a result, the anti-perovskite halide electrolyte Li3OCl directly decomposed in the ethanol solution, forming LiOH and LiCl, which have extremely poor ionic conductivity. This severely hindered ion conduction and aggravated the corrosion of the current collector and battery casing. The side reactions were severely aggravated, leading to a sharp drop in cycle life and coulombic efficiency. In Comparative Example 8, Li3OCl underwent a similar decomposition as in Comparative Example 7, and it also complexed with NMP to form harmful complexes, which seriously damaged battery performance, aggravated internal corrosion of the cell, and reduced battery performance.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A diaphragm containing an anti-perovskite halide functional coating, characterized in that: The diaphragm includes a base membrane and a functional coating coated on one side of the base membrane. The slurry composition of the functional coating includes an anti-perovskite halide and a binder.

2. The diaphragm with an anti-perovskite halide functional coating as described in claim 1, characterized in that: The anti-perovskite halide includes one or more of Li3OCl, Li3OBr, and Li2OHCl; the binder includes one or more of PEO, PVDF, PVDF-HFP, and PTFE; and the base membrane is a polyolefin membrane.

3. The diaphragm with an anti-perovskite halide functional coating as described in claim 2, characterized in that: The amount of the anti-perovskite halide is 30-60 wt% of the total mass of the slurry; the mass ratio of the anti-perovskite halide to the binder is 2.4-4.8:

1.

4. The diaphragm with an anti-perovskite halide functional coating as described in claim 2, characterized in that: The thickness of the functional coating is 1~10μm.

5. A method for preparing a membrane with an anti-perovskite halide functional coating as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1, dissolve the anti-perovskite halide and binder in a solvent to form a homogeneous slurry; S2, perform surface activation treatment on the base film, and uniformly coat the slurry obtained in step S1 onto one side of the activated base film to obtain a diaphragm with a wet coating. S3, the membrane with the wet coating is dried to obtain a functional membrane.

6. The method for preparing the diaphragm with an anti-perovskite halide functional coating as described in claim 5, characterized in that: In step S1, the solvent includes any one of diethyl ether, tetrahydrofuran, dimethyltetrahydrofuran, ethyl acetate, and dimethoxyethane.

7. The method for preparing the diaphragm with an anti-perovskite halide functional coating as described in claim 5, characterized in that: In step S2, the thickness of the wet coating is 30~40μm.

8. The method for preparing the membrane with an anti-perovskite halide functional coating as described in claim 5, characterized in that: In step S3, after the drying process, a hot pressing process is also included.

9. The method for preparing the diaphragm with an anti-perovskite halide functional coating as described in claim 8, characterized in that: The drying process is carried out at a temperature of 50-70°C for 5-7 hours; the hot pressing process is carried out at a temperature of 70-90°C for 2-8 MPa for 5-15 minutes.

10. The application of the separator with an anti-perovskite halide functional coating as described in any one of claims 1 to 4 in the preparation of batteries and electrical devices.

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