A coated separator for lithium batteries and its preparation method

Abstract

This invention relates to the field of lithium battery technology and discloses a coated separator for lithium batteries and its preparation method. The coated separator provided by this invention forms an integrated membrane layer by combining an LATP solid electrolyte interface layer and a binder layer comprising nitrile rubber, polyurethane, and maleic anhydride. This improves the hydrophilicity and heat resistance of the coated separator, overcoming the low electrochemical performance of traditional polyolefin separators, and enabling the coated separator to exhibit excellent electrochemical performance and long-lasting electrochemical cycling performance. In this invention, the LATP solid electrolyte, as the interface layer material, helps reduce the solvents and additives in traditional liquid electrolytes, increasing the energy density of the battery, thereby enhancing the energy transfer efficiency and power output. Furthermore, the presence of the binder layer combines the polyolefin base membrane with the LATP solid electrolyte, jointly improving the thermal stability of the separator. Under high-temperature conditions, the separator can maintain morphological stability, preventing thermal runaway and short-circuit risks.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a coated separator for lithium batteries and its preparation method. Background Technology

[0002] Lithium-ion battery technology is developing rapidly, and with its advantages such as high capacity, long lifespan, and no memory effect, it has become one of the most widely used energy devices in electronic products. It is even expected to become the main power source for other high-power devices such as pure electric vehicles (EVs) and hybrid electric vehicles (HEVs). As a crucial component of lithium-ion batteries, the performance of the separator directly affects the battery's rate performance, cycle life, and basic electrical performance, which has always been a bottleneck limiting further breakthroughs in lithium-ion batteries.

[0003] One of the bottlenecks is the degradation of the electrolyte-membrane interface, which affects the integrity and lifespan of the battery, further complicating the reliable application of lithium metal batteries.

[0004] Polyolefin (PO) separators have long dominated the lithium-ion battery separator market due to their advantages such as good electrochemical stability, excellent mechanical properties, and low cost. However, the hydrophobic structure and low porosity of PO materials lead to poor electrochemical performance in lithium-ion batteries. The low porosity results in low ionic conductivity, severely limiting the high-rate performance of the battery and making it difficult to meet the requirements of high-current rapid charging and discharging. Furthermore, the stretching and orientation process of PO material separators leads to uneven shrinkage due to molecular chain deorientation at high temperatures. Combined with the material's inherent poor heat resistance, this affects the high-temperature safety performance of lithium-ion batteries. Therefore, PO material separators currently suffer from a serious problem of electrolyte-separator interface degradation.

[0005] To address these issues, researchers primarily employ modification treatments for polyolefin membranes, including surface coatings and chemical grafting. Chemical grafting improves polymer surface properties, compatibility, mechanical properties, and chemical stability, thereby enhancing its performance as a membrane. However, chemical grafting methods often involve complex manufacturing processes, high costs, and are difficult to mass-produce. Surface coating methods improve membrane performance by covering the membrane surface with a thin film or adding specific materials, offering advantages such as low cost and easy availability. However, inorganic material surface coatings often reduce membrane porosity and cannot guarantee structural integrity. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a coated separator for lithium batteries and its preparation method. The coated separator provided by this invention forms an integrated membrane layer by combining an LATP solid electrolyte interface layer and an adhesive layer comprising nitrile rubber, polyurethane, and maleic anhydride. This improves the hydrophilicity and heat resistance of the coated separator, overcoming the shortcomings of low electrochemical performance in traditional polyolefin separators, and enabling the coated separator to exhibit excellent electrochemical performance and long-lasting electrochemical cycling performance.

[0007] The specific technical solution of this invention is as follows:

[0008] In a first aspect, the present invention provides a coated separator for lithium batteries, comprising a base film and an interface layer disposed on the base film, wherein the base film and the interface layer are connected by an adhesive layer, and the interface layer and the adhesive layer form an integral film layer; wherein:

[0009] The base membrane is a polyolefin;

[0010] The interface layer includes LATP solid electrolyte;

[0011] The adhesive layer comprises nitrile rubber, polyurethane, and maleic anhydride.

[0012] The coated membrane provided by this invention forms an integrated membrane layer by combining an LATP solid electrolyte interface layer and an adhesive layer containing nitrile rubber, polyurethane, and maleic anhydride. This improves the hydrophilicity and heat resistance of the coated membrane, solves the defect of low electrochemical performance of traditional polyolefin membranes, and enables the coated membrane to exhibit excellent electrochemical performance and long-term electrochemical cycling performance.

[0013] In the coated separator of this invention, LATP solid electrolyte serves as the interface layer material, which helps reduce the solvents and additives in traditional liquid electrolytes, thereby increasing the energy density of the battery and enhancing its energy transfer efficiency and power output. Simultaneously, LATP solid electrolyte exhibits excellent ion conductivity, significantly improving the migration rate of lithium ions, resulting in high ionic conductivity of the separator. The presence of the adhesive layer combines the polyolefin-based membrane with the LATP solid electrolyte, jointly enhancing the thermal stability of the separator. Under high-temperature conditions, the separator maintains morphological stability, preventing thermal runaway and short-circuit risks.

[0014] Preferably, the mass ratio of nitrile rubber, polyurethane, and maleic anhydride is 2:3~4:1~2.

[0015] The nitrile rubber, polyurethane, and maleic anhydride in the adhesive layer material work together to improve the electrochemical performance of the coated separator, ensuring good connection and stable transmission between the coated separator and other parts of the battery, thereby improving the overall performance of the battery. Therefore, in the adhesive layer of this invention, the amounts of nitrile rubber, polyurethane, and maleic anhydride need to be controlled within a certain range to maximize the electrochemical performance of the lithium battery, and their mass ratio is preferably 2:3~4:1~2.

[0016] Specifically, the binder layer, composed of nitrile rubber, polyurethane, and maleic anhydride, plays a crucial role in connecting the base membrane and the interface layer in the coated separator, ensuring the overall stability and durability of the coated separator. Using nitrile rubber as a binder, its elasticity helps alleviate stress caused by volume changes during battery use, maintaining the integrity of the coated separator and reducing performance degradation due to stress concentration. Nitrile rubber's excellent bonding properties ensure a strong bond between the interface layer (LATP solid electrolyte) and the base membrane (polyolefin). This strong bond helps reduce interfacial resistance, improves lithium-ion transport efficiency, and thus enhances the battery's electrochemical performance. In the binder layer, polyurethane, during curing, develops a porous structure. These pores facilitate electrolyte penetration and lithium-ion transport, thereby increasing the battery's energy density and power output. The excellent bonding properties of nitrile rubber are essential to ensure a strong bond, allowing the polyurethane material to function effectively and resulting in a low aging rate of the binder layer under high temperatures or harsh environments. This maintains the long-term electrochemical performance of the coated separator and ensures stable performance over a wide temperature range. Maleic anhydride can undergo cross-linking reactions with other components in the binder layer, forming a denser network structure. This network structure helps improve the overall strength and stability of the binder layer, reducing performance degradation caused by stress or solvent erosion during use. At the same time, the introduction of maleic anhydride may improve the hydrophilicity of the binder layer, promote lithium-ion transport and reaction, and improve the battery's charge-discharge efficiency and cycle stability.

[0017] Preferably, the thickness of the adhesive layer is 1~10μm.

[0018] Preferably, the thickness of the interface layer is 1~10μm.

[0019] Secondly, the present invention provides a method for preparing a coated separator for lithium batteries, comprising the following steps:

[0020] Step S1: At 50~65℃, nitrile rubber, polyurethane, glycerol and maleic anhydride are mixed evenly to obtain adhesive slurry;

[0021] Step S2: Add LATP solid electrolyte powder to the bonding slurry and disperse it evenly to obtain the coating slurry;

[0022] Step S3: Apply the coating slurry to the polyolefin base film at 50~65℃. Immediately after coating, transfer the base film to a low temperature environment of 0~20℃ and let it stand for a period of time. Then, perform vacuum drying to obtain the coated diaphragm.

[0023] The present invention prepares a coated separator for lithium batteries through the above steps S1 to S3, which has excellent electrochemical performance and long-term electrochemical cycling performance.

[0024] Step S1 involves preparing the adhesive slurry. Glycerol is added to nitrile rubber, polyurethane, and maleic anhydride at a suitable temperature of 50-65°C and mixed thoroughly, providing a good adhesion and performance foundation for the subsequent coating. This step, conducted at a relatively high temperature of 50-65°C, helps reduce viscosity and facilitates uniform mixing. As mentioned earlier, the nitrile rubber, polyurethane, and maleic anhydride in the adhesive layer material work together to improve the electrochemical performance of the coated membrane, ensuring good connection and stable transmission between the coated membrane and other parts of the battery, thereby improving the overall performance of the battery. The addition of glycerol during the preparation of the adhesive slurry utilizes the significant viscosity change of glycerol under high and low temperature variations, resulting in a more porous structure in the polyurethane agent and adhesive layer. Step S2 involves adding LATP solid electrolyte powder as the interface layer material, which forms the basis for the subsequent preparation of an integrated membrane layer of the interface layer and adhesive layer. Step S3 is the coating and drying step. After coating, the coated diaphragm is placed in a low temperature environment of 0~20℃ for a period of time. The instantaneous change in temperature from 50~65℃ to 0~20℃ causes a significant change in the viscosity of glycerol in the adhesive slurry, resulting in a more porous structure in the polyurethane agent and adhesive layer. Then, vacuum drying is performed to completely remove the solvent and moisture from the coating and cure it. This process of coating the coating slurry onto the polyolefin base film not only improves the mechanical strength and thermal stability of the diaphragm, but also optimizes its electrochemical performance.

[0025] Preferably, in step S1, the mass ratio of nitrile rubber, polyurethane, glycerol, and maleic anhydride is 2:3~4:1~2:1~2.

[0026] Preferably, in step S2, the mass ratio of LATP solid electrolyte to nitrile rubber is 0.5~3:1.

[0027] Preferably, in step S3, the polyolefin-based film is polypropylene (PP) or / and polyethylene (PE).

[0028] Preferably, in step S3, the settling time is 40s to 120s.

[0029] Thirdly, the present invention provides a lithium battery, comprising a positive electrode, a negative electrode and a separator, wherein the separator is a coated separator prepared by the above-described preparation method.

[0030] Compared with the prior art, the present invention has the following technical effects:

[0031] (1) This invention provides a coated separator, which forms an integrated membrane layer by combining an LATP solid electrolyte interface layer and an adhesive layer containing nitrile rubber, polyurethane, and maleic anhydride. This improves the hydrophilicity and heat resistance of the coated separator, solving the problem of low electrochemical performance of traditional polyolefin separators, and enabling the coated separator to exhibit excellent electrochemical performance and long-term electrochemical cycling performance. In the coated separator of this invention, the LATP solid electrolyte serves as the interface layer material, which helps to reduce the solvents and additives in traditional liquid electrolytes, improve the energy density of the battery, and thus enhance the energy transfer efficiency and power output of the battery. At the same time, the LATP solid electrolyte has excellent ion conductivity, which can significantly improve the migration rate of lithium ions, resulting in a high ionic conductivity of this separator. Due to the presence of the adhesive layer, the combination of the polyolefin base membrane and the LATP solid electrolyte enhances the thermal stability of the separator. Under high temperature conditions, the separator can maintain morphological stability, preventing thermal runaway and short-circuit risks.

[0032] (2) This invention also provides a method for preparing a coated separator. First, at a suitable temperature of 50-65°C, glycerol is added to nitrile rubber, polyurethane, and maleic anhydride, and mixed evenly to obtain a bonding slurry. The nitrile rubber, polyurethane, and maleic anhydride in the bonding slurry work together to improve the electrochemical performance of the coated separator, ensuring good connection and stable transmission between the coated separator and other parts of the battery, thereby improving the overall performance of the battery. During the preparation of the bonding slurry, glycerol is added. Taking advantage of the significant viscosity change of glycerol during high and low temperature changes, this results in the formation of a more porous structure in the polyurethane agent and the bonding layer. Step S2 is the step of adding LATP solid electrolyte powder as the interface layer material, which forms the basis for the subsequent preparation of an integrated membrane layer of the interface layer and the bonding layer. Step S3 is the coating and drying step. After coating, the coated diaphragm is placed in a low temperature environment of 0~20℃ for a period of time. The instantaneous change in temperature from 50~65℃ to 0~20℃ causes a significant change in the viscosity of glycerol in the adhesive slurry, resulting in a more porous structure in the polyurethane agent and adhesive layer. Then, vacuum drying is performed to completely remove the solvent and moisture from the coating and cure it. This process of coating the coating slurry onto the polyolefin base film not only improves the mechanical strength and thermal stability of the diaphragm, but also optimizes its electrochemical performance.

[0033] (3) The present invention provides a diaphragm and its preparation method. The coating process is simple and efficient, which helps to improve production efficiency and reduce production costs, thereby meeting the needs of large-scale production. Detailed Implementation

[0034] This invention provides a coated separator for lithium batteries, comprising a base film and an interface layer disposed on the base film, wherein the base film and the interface layer are connected by an adhesive layer, and the interface layer and the adhesive layer form an integrated film layer; wherein:

[0035] The base membrane is a polyolefin;

[0036] The interface layer includes LATP solid electrolyte;

[0037] The adhesive layer comprises nitrile rubber, polyurethane, and maleic anhydride.

[0038] The above-mentioned coated membrane, by combining the LATP solid electrolyte interface layer and the adhesive layer containing nitrile rubber, polyurethane and maleic anhydride, forms an integrated membrane layer, thereby improving the hydrophilicity and heat resistance of the coated membrane, solving the defect of low electrochemical performance of traditional polyolefin membranes, and enabling the coated membrane to exhibit excellent electrochemical performance and long-term electrochemical cycling performance.

[0039] In the aforementioned coated separator, the LATP solid electrolyte serves as the interface layer material, helping to reduce the solvents and additives found in traditional liquid electrolytes, thereby increasing the battery's energy density and enhancing its energy transfer efficiency and power output. Simultaneously, the LATP solid electrolyte exhibits excellent ion conductivity, significantly improving the migration rate of lithium ions, resulting in a high ionic conductivity for this separator. The presence of the adhesive layer, combining the polyolefin-based membrane with the LATP solid electrolyte, further enhances the separator's thermal stability. Under high-temperature conditions, the separator maintains morphological stability, preventing thermal runaway and short-circuit risks.

[0040] Preferably, the mass ratio of nitrile rubber, polyurethane, and maleic anhydride is 2:3~4:1~2.

[0041] The nitrile rubber, polyurethane, and maleic anhydride in the adhesive layer material work together to improve the electrochemical performance of the coated separator, ensuring good connection and stable transport between the coated separator and other parts of the battery, thereby enhancing the overall performance of the battery. Therefore, the amounts of nitrile rubber, polyurethane, and maleic anhydride in the adhesive layer need to be controlled within a certain range to maximize the electrochemical performance of the lithium battery; their preferred mass ratio is 2:3~4:1~2.

[0042] Specifically, the binder layer, composed of nitrile rubber, polyurethane, and maleic anhydride, plays a crucial role in connecting the base membrane and the interface layer in the coated separator, ensuring the overall stability and durability of the coated separator. Using nitrile rubber as a binder, its elasticity helps alleviate stress caused by volume changes during battery use, maintaining the integrity of the coated separator and reducing performance degradation due to stress concentration. Nitrile rubber's excellent bonding properties ensure a strong bond between the interface layer (LATP solid electrolyte) and the base membrane (polyolefin). This strong bond helps reduce interfacial resistance, improves lithium-ion transport efficiency, and thus enhances the battery's electrochemical performance. In the binder layer, polyurethane, during curing, develops a porous structure. These pores facilitate electrolyte penetration and lithium-ion transport, thereby increasing the battery's energy density and power output. The excellent bonding properties of nitrile rubber are essential to ensure a strong bond, allowing the polyurethane material to function effectively and resulting in a low aging rate of the binder layer under high temperatures or harsh environments. This maintains the long-term electrochemical performance of the coated separator and ensures stable performance over a wide temperature range. Maleic anhydride can undergo cross-linking reactions with other components in the binder layer, forming a denser network structure. This network structure helps improve the overall strength and stability of the binder layer, reducing performance degradation caused by stress or solvent erosion during use. At the same time, the introduction of maleic anhydride may improve the hydrophilicity of the binder layer, promote lithium-ion transport and reaction, and improve the battery's charge-discharge efficiency and cycle stability.

[0043] Preferably, the thickness of the adhesive layer is 1~10μm.

[0044] Preferably, the thickness of the interface layer is 1~10μm.

[0045] The present invention also provides a method for preparing a coated separator for lithium batteries, comprising the following steps:

[0046] Step S1: At 50~65℃, nitrile rubber, polyurethane, glycerol and maleic anhydride are mixed evenly to obtain adhesive slurry;

[0047] Step S2: Add LATP solid electrolyte powder to the bonding slurry and disperse it evenly to obtain the coating slurry;

[0048] Step S3: Apply the coating slurry to the polyolefin base film at 50~65℃. Immediately after coating, transfer the base film to a low temperature environment of 0~20℃ and let it stand for a period of time. Then, perform vacuum drying to obtain the coated diaphragm.

[0049] Through steps S1 to S3 described above, a coated separator for lithium batteries is prepared, exhibiting excellent electrochemical performance and long-lasting electrochemical cycling characteristics. Step S1 involves preparing the binder slurry. Glycerol is added to nitrile rubber, polyurethane, and maleic anhydride at a suitable temperature of 50-65°C and mixed thoroughly, providing a good adhesion and performance foundation for the subsequent coating. This step, conducted at a relatively high temperature of 50-65°C, helps reduce viscosity and facilitates uniform mixing. As mentioned earlier, the nitrile rubber, polyurethane, and maleic anhydride in the binder material work together to improve the electrochemical performance of the coated separator, ensuring good connection and stable transport between the coated separator and other parts of the battery, thereby enhancing the overall battery performance. The addition of glycerol during the binder slurry preparation utilizes the significant viscosity changes of glycerol under high and low temperature variations, resulting in a more porous structure in the polyurethane agent and binder layer. Step S2 involves adding LATP solid electrolyte powder as the interface layer material, which forms the basis for the subsequent preparation of an integrated membrane layer combining the interface layer and the binder layer. Step S3 is the coating and drying step. After coating, the coated diaphragm is placed in a low temperature environment of 0~20℃ for a period of time. The instantaneous change in temperature from 50~65℃ to 0~20℃ causes a significant change in the viscosity of glycerol in the adhesive slurry, resulting in a more porous structure in the polyurethane agent and adhesive layer. Then, vacuum drying is performed to completely remove the solvent and moisture from the coating and cure it. This process of coating the coating slurry onto the polyolefin base film not only improves the mechanical strength and thermal stability of the diaphragm, but also optimizes its electrochemical performance.

[0050] Preferably, in step S1, the mass ratio of nitrile rubber, polyurethane, glycerol, and maleic anhydride is 2:3~4:1~2:1~2.

[0051] Preferably, in step S2, the mass ratio of LATP solid electrolyte to nitrile rubber is 0.5~3:1.

[0052] Preferably, in step S3, the polyolefin-based film is polypropylene (PP) or / and polyethylene (PE).

[0053] Preferably, in step S3, the settling time is 40s to 120s.

[0054] The present invention will be further described below with reference to embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0055] Example 1

[0056] A coated separator for lithium batteries is provided, the preparation method of which includes the following steps:

[0057] Step S1: At 60°C, nitrile rubber, polyurethane, glycerol, and maleic anhydride are mixed, and an appropriate amount of solvent N-methylpyrrolidone is added. The mixture is then thoroughly mixed to obtain an adhesive slurry.

[0058] Step S2: At 60°C, LATP solid electrolyte powder is added to the adhesive slurry and dispersed evenly to obtain the coating slurry. The mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:3:1:2:5.

[0059] Step S3: Apply the coating slurry to the polypropylene base film at 60℃. Immediately after coating, transfer the base film to a 0℃ environment and let it stand for 60 seconds. Then, perform vacuum drying to obtain the coated diaphragm with a coating thickness of 5μm.

[0060] Example 2

[0061] A coated separator for lithium batteries is provided, the preparation method of which includes the following steps:

[0062] Step S1: At 60°C, nitrile rubber, polyurethane, glycerol, and maleic anhydride are mixed, and an appropriate amount of solvent N-methylpyrrolidone is added. The mixture is then thoroughly mixed to obtain an adhesive slurry.

[0063] Step S2: At 60°C, LATP solid electrolyte powder is added to the adhesive slurry and dispersed evenly to obtain the coating slurry. The mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:3:1:2:5.

[0064] Step S3: Apply the coating slurry to the polypropylene base film at 60℃. Immediately after coating, transfer the base film to a 0℃ environment and let it stand for 60 seconds. Then, perform vacuum drying to obtain the coated diaphragm with a coating thickness of 4μm.

[0065] Example 3

[0066] A coated separator for lithium batteries is provided, the preparation method of which includes the following steps:

[0067] Step S1: At 60°C, nitrile rubber, polyurethane, glycerol, and maleic anhydride are mixed, and an appropriate amount of solvent N-methylpyrrolidone is added. The mixture is then thoroughly mixed to obtain an adhesive slurry.

[0068] Step S2: At 60°C, LATP solid electrolyte powder is added to the adhesive slurry and dispersed evenly to obtain the coating slurry. The mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:3:1:2:5.

[0069] Step S3: Apply the coating slurry to the polypropylene base film at 60℃. Immediately after coating, transfer the base film to a 0℃ environment and let it stand for 60 seconds. Then, perform vacuum drying to obtain the coated diaphragm with a coating thickness of 7μm.

[0070] Example 4

[0071] A coated separator for lithium batteries is provided, the preparation method of which includes the following steps:

[0072] Step S1: At 60°C, nitrile rubber, polyurethane, glycerol, and maleic anhydride are mixed, and an appropriate amount of solvent N-methylpyrrolidone is added. The mixture is then thoroughly mixed to obtain an adhesive slurry.

[0073] Step S2: At 60°C, LATP solid electrolyte powder is added to the adhesive slurry and dispersed evenly to obtain the coating slurry. The mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:3:1:2:5.

[0074] Step S3: Apply the coating slurry to the polypropylene base film at 60℃. Immediately after coating, transfer the base film to a 0℃ environment and let it stand for 60 seconds. Then, perform vacuum drying to obtain the coated diaphragm with a coating thickness of 1μm.

[0075] Example 5

[0076] A coated separator for lithium batteries is provided, the preparation method of which includes the following steps:

[0077] Step S1: At 60°C, nitrile rubber, polyurethane, glycerol, and maleic anhydride are mixed, and an appropriate amount of solvent N-methylpyrrolidone is added. The mixture is then thoroughly mixed to obtain an adhesive slurry.

[0078] Step S2: At 60°C, LATP solid electrolyte powder is added to the adhesive slurry and dispersed evenly to obtain the coating slurry. The mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:3:1:2:5.

[0079] Step S3: Apply the coating slurry to the polypropylene base film at 60℃. Immediately after coating, transfer the base film to a 0℃ environment and let it stand for 60 seconds. Then, perform vacuum drying to obtain the coated diaphragm with a coating thickness of 10μm.

[0080] Example 6

[0081] A coated separator for lithium batteries is provided, the preparation method of which includes the following steps:

[0082] Step S1: At 50°C, mix nitrile rubber, polyurethane, glycerol, and maleic anhydride, and add an appropriate amount of solvent N-methylpyrrolidone. Mix evenly to obtain an adhesive slurry.

[0083] Step S2: At 50°C, LATP solid electrolyte powder is added to the adhesive slurry and dispersed evenly to obtain the coating slurry. The mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:4:2:1:5.

[0084] Step S3: Apply the coating slurry to the polypropylene base film at 50°C. Immediately after coating, transfer the base film to a 0°C environment and let it stand for 40 seconds. Then, perform vacuum drying to obtain the coated diaphragm with a coating thickness of 5 μm.

[0085] Example 7

[0086] A coated separator for lithium batteries is provided, the preparation method of which includes the following steps:

[0087] Step S1: At 65°C, nitrile rubber, polyurethane, glycerol, and maleic anhydride are mixed, and an appropriate amount of solvent N-methylpyrrolidone is added. The mixture is then thoroughly mixed to obtain an adhesive slurry.

[0088] Step S2: At 65°C, LATP solid electrolyte powder is added to the adhesive slurry and dispersed evenly to obtain the coating slurry. The mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:4:2:2:5.

[0089] Step S3: Apply the coating slurry to the polypropylene base film at 65°C. Immediately after coating, transfer the base film to a 5°C environment and let it stand for 120 seconds. Then, perform vacuum drying to obtain the coated diaphragm with a coating thickness of 5 μm.

[0090] Comparative Example 1

[0091] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that the coating thickness is 0.5 μm. Other steps are the same as in Example 1.

[0092] Comparative Example 2

[0093] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that the coating thickness is 11 μm. Other steps are the same as in Example 1.

[0094] Comparative Example 3

[0095] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that polyurethane is not added. Other steps are the same as in Example 1.

[0096] Comparative Example 4

[0097] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that the mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:1:1:2:5. Other steps are the same as in Example 1.

[0098] Comparative Example 5

[0099] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that the mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:5:1:2:5. Other steps are the same as in Example 1.

[0100] Comparative Example 6

[0101] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that maleic anhydride is not added. Other steps are the same as in Example 1.

[0102] Comparative Example 7

[0103] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that the mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:3:1:0.5:5. Other steps are the same as in Example 1.

[0104] Comparative Example 8

[0105] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that the mass ratio of nitrile rubber, polyurethane, glycerol, maleic anhydride, and LATP solid electrolyte is 2:3:1:3:5. Other steps are the same as in Example 1.

[0106] Comparative Example 9

[0107] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that glycerol is not added. Other steps are the same as in Example 1.

[0108] Comparative Example 10

[0109] A coated separator for lithium batteries is provided, the main difference between its preparation method and that of Example 1 is that the 60-second standing period at 0°C is not performed, and vacuum drying is carried out directly after coating. Other steps are the same as in Example 1.

[0110] Performance Characterization

[0111] The ionic conductivity of the coated separators obtained in Examples 1-7 and Comparative Examples 1-10 was tested at room temperature using an electrochemical workstation via AC impedance spectroscopy. Their thermal stability and electrochemical cycling performance were also tested, and the results are shown in Table 1. Thermal stability was characterized by thermal shrinkage rate. The test method involved cutting the coated separator for lithium batteries into 4cm × 5cm pieces and measuring the area change after 1 hour in an oven at 180℃. Electrochemical cycling performance was characterized by capacity retention rate. The test method involved preparing lithium batteries using the coated separator, charging the lithium-ion secondary battery at 25℃ with a constant current of 1C to 4.3V, then charging at a constant voltage of 4.3V until the current was less than 0.05C, allowing it to stand for 12 minutes, and then discharging at a constant current of 1C to 2.5V. The discharge capacity of the lithium battery at this point was measured, which was the discharge capacity of the first cycle. The battery was then subjected to multiple cycles under the same conditions, and the capacity retention rate after 500 cycles was calculated.

[0112] Table 1

[0113] Group Ionic conductivity (mS / cm) Heat shrinkage rate (%) Capacity retention rate (%) Example 1 1.63 3.12 94.1 Example 2 1.64 3.17 93.7 Example 3 1.63 3.42 93.9 Example 4 1.66 9.03 87.1 Example 5 1.54 9.11 89.0 Example 6 1.64 3.14 93.7 Example 7 1.65 3.22 93.2 Comparative Example 1 1.26 11.20 86.1 Comparative Example 2 1.29 10.38 86.4 Comparative Example 3 1.27 10.71 85.6 Comparative Example 4 1.24 10.65 84.7 Comparative Example 5 1.28 10.40 85.2 Comparative Example 6 1.31 10.11 85.4 Comparative Example 7 1.36 11.23 82.4 Comparative Example 8 1.40 13.23 81.7 Comparative Example 9 1.42 5.70 80.4 Comparative Example 10 1.39 6.14 80.1

[0114] The characterization data in Table 1 show that:

[0115] (1) The coating membrane provided by the present invention forms an integrated membrane layer by combining the LATP solid electrolyte interface layer and the adhesive layer containing nitrile rubber, polyurethane and maleic anhydride. This can improve the hydrophilicity and heat resistance of the coating membrane, thereby solving the defects of low hydrophilicity and poor heat resistance of traditional polyolefin membranes. The coating membrane provided by the present invention exhibits excellent electrochemical performance and long-term electrochemical cycling performance.

[0116] (2) As can be seen from the comparative analysis of Comparative Examples 1-2 and Example 1, the coating thickness of the present invention has a significant impact on the performance of the diaphragm, and its thickness should be controlled within a certain range. As can be seen from Examples 1-3, the thickness of the integrated film layer formed by the adhesive layer and the interface layer of the present invention is preferably 1-10 μm.

[0117] (3) Comparative analysis of Comparative Examples 3-8 and Example 1 shows that the content ratio of nitrile rubber, polyurethane, and maleic anhydride in the adhesive layer material should be controlled within a certain range; otherwise, the performance of the separator will be reduced to varying degrees. The reason for this is that in the adhesive layer, nitrile rubber, polyurethane, and maleic anhydride work together to improve the electrochemical performance of the coated separator, thereby ensuring good connection and stable transmission between the coated separator and other parts of the battery, thus improving the overall performance of the battery. Therefore, in the adhesive layer of this invention, the amount of nitrile rubber, polyurethane, and maleic anhydride needs to be controlled within a certain range to maximize the electrochemical performance of the lithium battery, and the preferred mass ratio is 2:3~4:1~2.

[0118] Specifically, nitrile rubber (NBR) is used as a binder. NBR possesses a certain degree of elasticity, which can alleviate stress caused by volume changes during battery use, maintain the integrity of the coating membrane, and reduce performance degradation due to stress concentration. NBR also exhibits excellent bonding properties, ensuring a strong bond between the interface layer (LATP solid electrolyte) and the base film (polyolefin). This strong bond helps reduce interfacial resistance, improves lithium-ion transport efficiency, and thus enhances the battery's electrochemical performance. In the binder layer, polyurethane, during curing, develops a certain porous structure. These pores facilitate electrolyte penetration and lithium-ion transport, thereby increasing the battery's energy density and power output. During this process, the excellent bonding properties of NBR are crucial to ensure a strong bond, allowing the polyurethane material to function effectively and resulting in a low aging rate of the binder layer under high temperatures or harsh environments. This maintains the long-term electrochemical performance of the coating membrane and ensures stable performance over a wide temperature range. Maleic anhydride can undergo cross-linking reactions with other components in the binder layer, forming a denser network structure. This network structure helps improve the overall strength and stability of the binder layer, reducing performance degradation caused by stress or solvent erosion during use. At the same time, the introduction of maleic anhydride may improve the hydrophilicity of the binder layer, promote lithium-ion transport and reaction, and improve the battery's charge-discharge efficiency and cycle stability.

[0119] (4) As can be seen from the comparative analysis of Comparative Examples 9-10 and Example 1, the addition of glycerol and the quenching step are important steps in the successful preparation of the coating membrane with excellent electrochemical performance of the present invention.

[0120] The hydrophilic polyurethane raw material used in this invention was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd. Unless otherwise specified, all raw materials and equipment used in this invention are commonly used in the field; and all methods used in this invention are conventional methods in the field unless otherwise specified.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A coated separator for lithium batteries, characterized in that: Includes a base film and an interface layer disposed on the base film, wherein the base film and The interface layer is connected by an adhesive layer, and the interface layer and the adhesive layer form an integrated film layer; wherein: The base membrane is a polyolefin; The interface layer includes LATP solid electrolyte; The adhesive layer comprises nitrile rubber, polyurethane, and maleic anhydride; the mass ratio of nitrile rubber, polyurethane, and maleic anhydride is 2:3~4:1~2; the thickness of the adhesive layer is 1~10μm; the thickness of the interface layer is 1~10μm. The method for preparing the coated separator for lithium batteries includes the following steps: Step S1: At 50~65℃, nitrile rubber, polyurethane, glycerol and maleic anhydride are mixed evenly to obtain adhesive slurry; Step S2: Add LATP solid electrolyte powder to the bonding slurry and disperse it evenly to obtain the coating slurry; Step S3: Apply the coating slurry to the polyolefin base film at 50~65℃. Immediately after coating, transfer the base film to a low temperature environment of 0~20℃ and let it stand for a period of time. Then, perform vacuum drying to obtain the coated diaphragm.

2. A method for preparing a coated separator for lithium batteries as described in claim 1, characterized in that: Includes the following steps: Step S1: At 50~65℃, nitrile rubber, polyurethane, glycerol and maleic anhydride are mixed evenly to obtain adhesive slurry; Step S2: Add LATP solid electrolyte powder to the bonding slurry and disperse it evenly to obtain the coating slurry; Step S3: Apply the coating slurry to the polyolefin base film at 50~65℃. Immediately after coating, transfer the base film to a low temperature environment of 0~20℃ and let it stand for a period of time. Then, perform vacuum drying to obtain the coated diaphragm.

3. The preparation method according to claim 2, characterized in that: In step S1, the mass ratio of nitrile rubber, polyurethane, glycerol, and maleic anhydride is 2:3~4:1~2:1~2.

4. The preparation method according to claim 2, characterized in that: In step S2, the mass ratio of LATP solid electrolyte to nitrile rubber is 0.5~3:

1.

5. The preparation method according to claim 2, characterized in that: In step S3, the polyolefin-based film is polypropylene and / or polyethylene.

6. The preparation method according to claim 2, characterized in that: In step S3, the settling time is 40s to 120s.

7. A lithium battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that: The diaphragm is the coated diaphragm as described in claim 1 or the coated diaphragm prepared by the preparation method as described in any one of claims 2 to 6.