Separator, method for manufacturing the same, battery, battery pack, and electric device

Abstract

The embodiment of the present application provides a diaphragm and a preparation method thereof, a battery, a battery pack and an electric device. The diaphragm provided by the embodiment of the present application comprises a diaphragm base and an inorganic coating layer arranged on at least part of the surface of the diaphragm base; the diaphragm base comprises a diaphragm substrate and a whisker material dispersed in the diaphragm substrate. The diaphragm of the embodiment of the present application has good elastic modulus and creep recovery rate, and can improve the cycle life and safety performance of the battery.

Description

Separator and its preparation method, battery, battery pack, electrical equipment Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a separator and its preparation method, a battery, a battery pack, and an electrical device. Background Technology

[0002] As one of the core components of lithium-ion batteries, the battery separator's main function is to physically isolate the positive and negative electrode active materials to prevent short circuits, while allowing active metal ions to pass through for charge transport. In applications such as power batteries, energy storage batteries, and consumer electronics batteries (e.g., mobile phones, laptops, electric vehicles), the performance of the separator directly affects the battery's cycle life and safety performance.

[0003] However, the commonly used membrane materials are polymer materials, which have simple structures and weak intermolecular interactions, resulting in poor elastic modulus and creep resistance. During battery cycling, membrane roll deformation is likely to occur, which deteriorates the cycle life and safety performance of the battery.

[0004] Therefore, it is urgent to improve the elastic modulus and creep recovery rate of the separator in order to enhance the cycle life and safety performance of the battery. Summary of the Invention

[0005] This invention provides a separator and its preparation method, a battery, a battery pack, and an electrical device. The separator has a high elastic modulus and creep recovery rate, which can improve the cycle life and safety performance of the battery.

[0006] This invention provides a diaphragm, including a diaphragm substrate and an inorganic coating disposed on at least a portion of the surface of the diaphragm substrate; the diaphragm substrate includes a diaphragm base material and whisker material dispersed in the diaphragm base material.

[0007] In some embodiments of the present invention, the diaphragm satisfies: 0.01h 0.5 ≤w≤18(1-e -0.05d );

[0008] Wherein, w is the mass percentage of the whisker material in the membrane matrix, expressed in %;

[0009] h represents the thickness of the inorganic coating, expressed in μm.

[0010] d represents the thickness of the membrane substrate, expressed in μm.

[0011] e is the base of the natural logarithm.

[0012] In some embodiments of the present invention, 0μm < h ≤ 3μm;

[0013] And / or, 8μm≤d≤25μm;

[0014] And / or, 0% < w ≤ 12%.

[0015] In some embodiments of the present invention, the whisker material is uniformly distributed in the membrane matrix;

[0016] Alternatively, the whisker material decreases in the direction from one surface of the membrane substrate to the other.

[0017] In some embodiments of the present invention, the aspect ratio of the whisker material is 5:1 to 100:1;

[0018] And / or, the whisker material has an average length of 20 nm to 300 nm and an average diameter of 0.003 μm to 0.04 μm;

[0019] And / or, the whisker material includes one or more of alumina whisker material, silicon nitride whisker material, zirconium oxide whisker material, silicon carbide whisker material, and cellulose oxide whisker material;

[0020] And / or, the inorganic coating includes at least one of inorganic particles and the whisker material;

[0021] And / or, the membrane substrate includes at least one of polyethylene, polypropylene, and polyimide.

[0022] In some embodiments of the present invention, the inorganic particles include one or more of ceramics, boehmite, alumina, and clay;

[0023] And / or, the inorganic particles include one or more of the following: flaky inorganic particles, spherical inorganic particles, and rod-shaped inorganic particles;

[0024] The sheet-like inorganic particles have a particle size of 0.1 μm to 2 μm and an average sheet diameter of 0.5 μm to 3 μm.

[0025] And / or, the average particle size of the spherical inorganic particles is 0.3 μm to 1.5 μm;

[0026] And / or, the average length of the rod-shaped inorganic particles is 50 μm to 100 μm, and the average diameter is 0.1 μm to 20 μm.

[0027] In some embodiments of the present invention, the whisker material includes a modifying group, wherein the modifying group includes at least one of amino and epoxy groups;

[0028] And / or, the whisker material includes a dopant, the dopant being yttrium oxide.

[0029] In some embodiments of the present invention, the membrane substrate includes N sub-membrane substrates stacked in the thickness direction, where N≥2, and at least one of the sub-membrane substrates contains the whisker material.

[0030] This invention also provides a method for preparing the diaphragm as described above, comprising the following steps:

[0031] A separator substrate is obtained by dispersing whisker material in a separator substrate, and then coating raw material is applied to at least a portion of the surface of the separator substrate to obtain the separator.

[0032] In some embodiments of the present invention, dispersing the whisker material in the membrane matrix includes the following steps:

[0033] The diaphragm matrix is ​​obtained by sequentially mixing the whisker material with the diaphragm matrix precursor and then extruding them.

[0034] Alternatively, the whisker material can be sprayed and melted with the membrane substrate precursor to obtain the membrane substrate.

[0035] In some embodiments of the present invention, before dispersing the whisker material in the membrane matrix, the method further includes: modifying the whisker material precursor with a modifier to obtain the whisker material, wherein the modifier includes a silane coupling agent;

[0036] And / or, the whisker material precursor is doped with a dopant to obtain the whisker material, wherein the dopant includes yttrium oxide.

[0037] In some embodiments of the present invention, the membrane matrix precursor includes N sub-membrane matrix precursors, where N≥2. The whisker material is dispersed in at least one sub-membrane matrix precursor, and then the N sub-membrane matrix precursors are extruded to obtain the membrane matrix.

[0038] This invention also provides a battery comprising the separator as described above, or the separator prepared by the method described above.

[0039] This invention also provides a battery pack comprising at least two batteries as described above.

[0040] This invention also provides an electrical device, including the battery or battery pack described above.

[0041] The present invention provides a separator and its preparation method, a battery, a battery pack, and an electrical device. By adding whisker materials to the separator substrate, the interfacial interaction between the separator substrate and the inorganic coating can be enhanced, the creep of the separator can be suppressed, and the elastic modulus of the separator can be increased, which is beneficial to improving the cycle life and safety performance of the battery. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] Currently, commonly used separators (such as PP separators and PE separators) have problems with poor elastic modulus and creep resistance. The main reason is that their intermolecular forces are weak. Under continuous stress, the molecular chains are prone to slippage. Therefore, after these separators are cut, they are very prone to creep, which leads to separator curling and deformation, affecting the cycle life and safety performance of the battery.

[0044] Existing technologies enhance the strength of diaphragms by stretching them to give the molecules a highly oriented structure. However, the breakage productivity of such diaphragms is low, and the creep recovery rate is still insufficient.

[0045] The inventors attempted to improve the above problems by coating the surface of the separator with an inorganic coating. However, there are significant differences in the creep resistance and mechanical properties between the inorganic coating and the organic separator substrate, resulting in a serious interface effect. When the separator substrate creeps or is stretched by external forces, the inorganic coating cannot follow the deformation and generate microcracks, causing damage to the separator and deteriorating the cycle life and safety performance of the battery.

[0046] Therefore, the inventors attempted to improve the cycle life and safety performance of the battery by taking into account both the elastic modulus and creep recovery rate of the separator.

[0047] Based on this, embodiments of the present invention provide a diaphragm, including a diaphragm substrate and an inorganic coating disposed on at least a portion of the surface of the diaphragm substrate; the diaphragm substrate includes a diaphragm base material and whisker material dispersed in the diaphragm base material.

[0048] The separator in this invention has both high elastic modulus and creep recovery rate, which can improve the cycle life and safety performance of the battery.

[0049] The inventors analyzed that the reason why the separator of the present invention can improve the cycle life and safety performance of the battery is as follows: First, the separator of the present invention includes a separator substrate and an inorganic coating disposed on at least a portion of the surface of the separator substrate. The inorganic coating restricts the deformation ability of the separator substrate under stress, thereby enhancing the mechanical strength (such as mechanical properties such as elastic modulus) and dimensional stability of the separator during battery cycling. It is not easy to curl and deform during battery cycling, which is conducive to improving the cycle life and safety performance of the battery. At the same time, in order to overcome the interface problem between the separator substrate and the inorganic coating, the separator substrate of the present invention includes a separator base material and an inorganic coating dispersed in the separator substrate. The present invention utilizes whisker materials dispersed in the separator substrate. On one hand, the mechanical interlocking effect of the whisker materials allows them to cross the crystalline regions of the separator substrate, restricting molecular chain slippage and thus improving the creep recovery rate of the separator. On the other hand, the whisker materials can be partially embedded in the separator substrate and partially exposed on its surface. This cross-interface structure effectively transfers stress under load, preventing the inorganic coating from peeling off, thereby significantly improving interfacial bonding strength. Furthermore, the whisker materials possess high elastic modulus and a certain degree of flexibility, serving as a stress buffer phase to suppress the thermal expansion of the separator substrate, effectively enhancing both the elastic modulus and creep recovery rate of the separator. Therefore, the separator provided by the present invention, by leveraging the synergistic effect of the separator substrate and whisker materials, can effectively improve the elastic modulus and creep recovery rate of the separator, thereby contributing to improved battery cycle life and safety performance. In addition, the whisker materials can establish continuous conductive paths within the separator, which helps reduce battery internal resistance and improve rate performance.

[0050] In this embodiment of the invention, conventional testing methods and instruments can be used to test the whisker material in the separator substrate. For example, SEM or TEM can be used to test the whisker material in the separator substrate. In specific implementation, the battery can be completely discharged and disassembled to separate the separator. The inorganic coating on the surface of the separator can be washed away with a large amount of water to obtain the separator substrate. Then, the cross-section of the separator substrate can be obtained and tested using SEM or TEM. Based on the morphological characteristics of the whisker material (specifically, it can be a slender needle-like / rod-like structure), the whisker material in the separator substrate can be observed.

[0051] In some embodiments of the present invention, the diaphragm satisfies: 0.01h 0.5 ≤w≤18(1-e -0.05d ), where w is the mass percentage of whisker material in the membrane substrate, expressed as %; h is the thickness of the inorganic coating, expressed as μm; d is the thickness of the membrane substrate, expressed as μm; and e is the base of the natural logarithm.

[0052] When the diaphragm of the present invention meets the above conditions, it can further balance the elastic modulus and interface stability of the diaphragm, which is beneficial to further improve the cycle life and safety performance of the battery.

[0053] In detail, the embodiments of the present invention use 0.01h 0.5 ≤w≤18(1-e -0.05d When performing calculations, units are not substituted into the calculations. However, the thickness of the inorganic coating, the thickness of the membrane substrate, and the mass ratio of whisker material in the membrane substrate need to be converted according to the corresponding units. Then, the converted values ​​are substituted into the above conditions for calculation.

[0054] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the above-mentioned parameters. In specific implementation, the following method can be used for testing: After the battery is fully discharged, it is disassembled and the separator is separated. The inorganic coating on the surface of the separator is washed away with a large amount of water to obtain the separator substrate. Take 5mg~10mg of the cleaned and dried separator substrate (referred to as the initial sample mass) and place it in a crucible under an air or oxygen atmosphere. The temperature is increased from room temperature to 150°C at a rate of 20°C / min, and held for 20min. Then, the temperature is increased to 600°C~800°C at a rate of 10°C / min and held until the weight no longer decreases (referred to as the final plateau mass); w = final plateau mass / initial sample mass × 100%. The thickness h of the inorganic coating and the thickness d of the separator substrate can be tested by the following method: after the battery is fully discharged, it is disassembled, the separator is separated, the cross-section of the separator is obtained, and then the cross-section is tested by SEM. The separator substrate and the inorganic coating are distinguished under SEM. At least 5 fields of view are selected for each, and their average values ​​are calculated to obtain the thickness h of the inorganic coating and the thickness d of the separator substrate.

[0055] In some embodiments, 0 μm < h ≤ 3 μm can further improve the elastic modulus and conductivity of the separator, thereby contributing to improved cycle life and safety performance of the battery. For example, the value of h is, for instance, a range of 1 μm, 1.5 μm, 2 μm, 3 μm, or any combination thereof.

[0056] In some embodiments, 8μm ≤ d ≤ 25μm can further improve the elastic modulus and conductivity of the separator, thereby contributing to improved cycle life and safety performance of the battery. For example, the value of d is, for instance, a range of 8μm, 10μm, 15μm, 20μm, 25μm, or any combination thereof.

[0057] In some embodiments, when 0% < w ≤ 12%, the elastic modulus and creep recovery rate of the separator can be further improved, thereby contributing to further enhancement of the battery's cycle life and safety performance. For example, the value of w is, for instance, a range of 0.01%, 5%, 10%, 12%, or any combination thereof.

[0058] In some embodiments of the present invention, the whisker material is uniformly distributed in the separator substrate, which is beneficial to better enhance the interaction between the separator substrate and the inorganic coating, thereby further improving the elastic modulus and creep recovery rate of the separator, and thus further improving the cycle life and safety performance of the battery.

[0059] In some embodiments, the whisker material decreases in the direction from one surface of the separator substrate to the other, which can further improve the transport path of active metal ions in the separator and further enhance the mechanical properties of one side of the separator substrate, better blocking dendrite penetration, thereby contributing to further improvement in battery cycle life and safety performance. In some embodiments, the above-mentioned improvement effect is better when the surface containing the high concentration of whisker material faces the negative electrode of the battery. Specifically, the decreasing direction can be the thickness direction of the separator substrate, which is not particularly limited.

[0060] In some embodiments of the present invention, when the aspect ratio of the whisker material is 5:1 to 100:1, it is beneficial to further improve the elastic modulus and creep recovery rate of the separator, thereby further improving the cycle life and safety performance of the battery. For example, the aspect ratio of the whisker material is, for example, 5:1, 10:1, 20:1, 40:1, 60:1, 80:1, 100:1, or any combination thereof.

[0061] In some embodiments, the average length of the whisker material is 20 nm to 300 nm, and the average diameter is 0.003 μm to 0.04 μm, which is beneficial for further improving the elastic modulus and creep recovery rate of the separator, thereby further improving the cycle life and safety performance of the battery. For example, the average length of the whisker material is, for example, a range of 20 nm, 100 nm, 200 nm, 300 nm, or any combination thereof; the average diameter of the whisker material is, for example, a range of 0.003 μm, 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, or any combination thereof.

[0062] The embodiments of this invention can employ conventional testing methods and instruments in the art to test the aspect ratio, average length, and average diameter of whisker materials. For example, SEM can be used for testing. Specifically, after the battery is fully discharged, it can be disassembled, the separator separated, and a cross-section of the separator obtained. Then, SEM testing is performed on the cross-section, selecting at least 100 whisker materials, and their lengths and diameters are statistically analyzed to obtain the aspect ratio, average length, and average diameter of the whisker materials. The aspect ratio of the whisker material is its average length divided by its average diameter.

[0063] In some embodiments, the whisker material includes one or more of alumina whisker material, silicon nitride whisker material, zirconium oxide whisker material, silicon carbide whisker material, and cellulose oxide whisker material, which can further improve the elastic modulus and creep recovery rate of the separator, thereby helping to further improve the cycle life and safety performance of the battery.

[0064] In some embodiments, the inorganic coating includes at least one of inorganic particles and whisker materials, which is beneficial for further improving the elastic modulus of the diaphragm. In some embodiments, carbon materials can be used to modify the inorganic particles, and the carbon materials may include graphene. For example, the inorganic particles may include graphene-modified alumina (graphene-modified Al2O3).

[0065] The embodiments of this invention can test the types of whisker materials and inorganic particles using conventional testing methods and instruments in the art, such as EDS testing. In specific implementation, the battery can be fully discharged and disassembled to separate the separator, obtain its cross-section, and then perform EDS testing on the cross-section. The types of whisker materials and inorganic particles can be analyzed based on the elemental analysis results of the EDS. Alternatively, SEM or TEM can be used to determine the presence of whisker materials in the inorganic coating based on the morphological differences between the whisker materials and inorganic particles.

[0066] In the embodiments of the present invention, the mass ratio of whisker material in the inorganic coating is not specifically limited and can be selected according to the actual situation.

[0067] In some embodiments, the separator substrate includes at least one of polyethylene (PE), polypropylene (PP), and polyimide (PI), which is beneficial to further improve the elastic modulus of the separator and thus better improve the cycle performance of the battery.

[0068] In some embodiments of the present invention, the inorganic particles include one or more of ceramics, boehmite, alumina, and clay, which is beneficial to further improve the elastic modulus of the separator and thus better improve the cycle performance of the battery.

[0069] In some embodiments of the present invention, the inorganic particles include one or more of flaky inorganic particles, spherical inorganic particles, and rod-shaped inorganic particles, which is beneficial to further improve the elastic modulus of the separator and thus better improve the cycle performance of the battery.

[0070] In some embodiments, the average thickness of the sheet-like inorganic particles is 0.1 μm to 2 μm, and the average sheet diameter is 0.5 μm to 3 μm. This is beneficial for further improving the conductivity and elastic modulus of the separator, thereby better enhancing the cycle performance of the battery. For example, the average thickness of the sheet-like inorganic particles is, for example, a range of 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, or any combination thereof; the average sheet diameter of the sheet-like inorganic particles is, for example, a range of 0.5 μm, 1 μm, 1.5 μm, 2 μm, or any combination thereof.

[0071] In some embodiments, the average particle size of the spherical inorganic particles is 0.3 μm to 1.5 μm, which is beneficial for further improving the conductivity and elastic modulus of the separator, thereby better improving the cycle performance of the battery. For example, the average particle size of the spherical inorganic particles is, for example, a range of 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, or any combination thereof.

[0072] In some embodiments, the average length of the rod-shaped inorganic particles is 50 μm to 100 μm, and the average diameter is 0.1 μm to 20 μm. This is beneficial for further improving the conductivity and elastic modulus of the separator, thereby better enhancing the cycle performance of the battery. For example, the average length of the rod-shaped inorganic particles is, for example, a range of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any combination thereof; the average diameter of the rod-shaped inorganic particles is, for example, a range of 0.1 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, or any combination thereof.

[0073] The dimensions of inorganic particles can be tested using conventional testing methods and instruments in the art, such as SEM. Specifically, the battery can be fully discharged and disassembled to separate the separator, obtain its cross-section, and then perform SEM testing on the cross-section. At least 100 inorganic particles are selected, and their average size is calculated to obtain the aforementioned size data of the inorganic particles. In this embodiment of the invention, the alumina (Al2O3) inorganic particles can be spherical or rod-shaped.

[0074] In some embodiments of the present invention, the whisker material includes a modifying group, which includes at least one of amino and epoxy groups, which can enable the whisker material to better bond with the separator substrate, and further enhance the interaction between the separator substrate and the inorganic coating, thereby better improving the elastic modulus and creep recovery rate of the separator, and better improving the cycle performance of the battery.

[0075] In some embodiments, the whisker material includes a dopant, such as yttrium oxide, which can further stabilize the structure of the whisker material and improve the cycle performance of the battery.

[0076] In some embodiments, when the whisker material includes zirconium oxide whisker material and the dopant includes yttrium oxide, the stability, mechanical properties, and conductivity of the separator can be further enhanced, thereby improving the cycle performance of the battery.

[0077] The embodiments of the present invention can test the modified groups or dopants in whisker materials using conventional testing methods and instruments in the art, such as XPS. In specific implementation, the battery can be completely discharged and disassembled to separate the separator. The inorganic coating on the surface of the separator can be washed away with a large amount of water to obtain the separator substrate, and then the surface of the separator substrate can be tested with XPS.

[0078] In some embodiments of the present invention, the separator substrate includes N sub-separator substrates stacked in the thickness direction, where N≥2, which can further improve the elastic modulus of the separator and thus better improve the cycle performance of the battery. When at least one sub-separator substrate contains dispersed whisker material, the elastic modulus of the separator can be further improved, thereby better improving the cycle performance of the battery.

[0079] This invention also provides a method for preparing the above-mentioned diaphragm, comprising the following steps:

[0080] A separator substrate is obtained by dispersing whisker material in a separator substrate, and then coating raw materials are applied to at least a portion of the surface of the separator substrate to obtain a separator.

[0081] The separator prepared by the above-described method in this invention exhibits good elastic modulus and creep recovery rate, which is beneficial for improving the cycle performance of the battery. The separator obtained by the above-described method comprises a separator substrate and an inorganic coating disposed on at least a portion of the surface of the separator substrate; the separator substrate comprises a separator base material and whisker material dispersed in the separator base material.

[0082] The embodiments of the present invention do not impose special limitations on the method of dispersing whisker materials in the membrane substrate, and can be selected according to the actual situation.

[0083] The embodiments of the present invention do not impose special limitations on the coating method. For example, coating raw materials such as inorganic particles and binders used to form the coating can be dissolved in a solvent (such as deionized water) to obtain a coating slurry, and then the coating slurry can be coated onto at least a portion of the surface of the membrane substrate. Alternatively, a vapor deposition method can be used to directly coat the coating raw material (such as alumina) onto at least a portion of the surface of the membrane substrate.

[0084] In some embodiments of the present invention, after coating the coating slurry onto at least a portion of the surface of the diaphragm substrate, the coated product is further subjected to a drying process. The present invention does not specifically limit the drying temperature, for example, the drying temperature can be 100°C to 150°C.

[0085] The coating material in this embodiment of the invention includes inorganic particles. The selection of inorganic particles is as described above and will not be repeated here.

[0086] In some embodiments of the present invention, dispersing the whisker material in the separator substrate includes the following steps: sequentially mixing the whisker material with a separator substrate precursor and extruding to obtain the separator substrate. Through the above method, the whisker material can be uniformly distributed in the separator substrate, which is beneficial for improving the elastic properties of the separator and thus improving the cycle performance of the battery.

[0087] In one specific embodiment, whisker material can be dissolved in a solvent (e.g., NMP solvent) and then mixed with a membrane matrix precursor (specifically, a membrane raw material used to form a membrane substrate, such as PP material, PE material, etc.) to form a mixed slurry. The mixed slurry is then extruded to prepare the membrane matrix.

[0088] In this embodiment of the invention, after the above extrusion process, the product after the extrusion process is further subjected to a stretching and film-forming process. This embodiment of the invention does not impose special limitations on the transverse stretching ratio and the longitudinal stretching ratio for the stretching and film-forming process, and they can be selected according to the actual situation.

[0089] In some embodiments of the present invention, the drying process further includes heat setting of the dried product (diaphragm precursor). Heat setting can be performed using hot pressing. The embodiments of the present invention do not impose special limitations on the temperature and time of the hot pressing process, which can be selected according to actual conditions. For example, the temperature of the hot pressing process can be 75℃~135℃, and the time can be 5s~60s.

[0090] In some embodiments, dispersing whisker material in a separator substrate includes the following steps: sputtering the whisker material and a separator substrate precursor together to obtain a separator substrate. Through the above method, the whisker material can decrease in thickness from one surface to the other of the separator substrate, better blocking dendrite penetration and thus further improving the cycle life and safety performance of the battery. Specifically, the whisker material can be laid on one surface of the separator substrate precursor and then sputtered. The decreasing direction can be the thickness direction of the separator substrate, and is not specifically limited thereto. The temperature and time of the sputtering process are not specifically limited in this embodiment and can be selected according to actual conditions. For example, the sputtering temperature can be 60℃~120℃, and the sputtering time can be 10s~100s.

[0091] In some embodiments of the present invention, before dispersing the whisker material in the separator substrate, the method further includes: modifying the whisker material precursor with a modifier to obtain the whisker material, wherein the modifier includes a silane coupling agent. Specifically, KH550 can impart amino groups to the surface of the whisker material, and KH560 can impart epoxy groups to the surface of the whisker material. Through the above methods, the embodiments of the present invention enable the whisker material to better bond with the separator substrate, thereby improving the elastic modulus of the separator and enhancing the cycle life and safety performance of the battery. The embodiments of the present invention do not specifically limit the specific method of modification treatment. For example, it can be surface chemical modification. In specific implementation, taking KH550 as an example, firstly, the whisker material precursor is acid-washed or ultrasonically dispersed to remove surface impurities and ensure good dispersion. Then, KH550 is mixed with ethanol / water mixed solvent to adjust the pH value to acidic. The whisker material precursor is added to the KH550 solution and stirred at a constant temperature to allow it to react fully. Finally, the reaction solution is filtered, washed, and dried to obtain modified whiskers (i.e., whisker material). The surface of the whisker material has amino groups.

[0092] In some embodiments of the present invention, before dispersing the whisker material in the separator matrix, the method further includes: doping the whisker material precursor with a dopant to obtain the whisker material, wherein the dopant includes yttrium oxide. The embodiments of the present invention, through the above method, can make the structure of the whisker material more stable, thereby improving the cycle life and safety performance of the battery. The embodiments of the present invention do not specifically limit the doping treatment method; for example, hydrothermal synthesis, precursor conversion, or molten salt method can be used for the above doping treatment. Taking hydrothermal synthesis as an example, the whisker material precursor (e.g., zirconium oxychloride) and the dopant (e.g., yttrium oxide, Y₂O₃) can be mixed (e.g., the mass percentage of zirconium oxychloride in the mixed system (mixed solution) can be 75wt%~80wt%, and the mass percentage of yttrium oxide in the mixed solution can be 10wt%), and then a precipitant (e.g., ammonia) is added, reacting to generate a precipitate. The precipitate is then washed, dried, and calcined to obtain yttrium oxide-stabilized zirconium oxide powder (whisker material).

[0093] In some embodiments of the present invention, the membrane substrate precursor includes N sub-membrane substrate precursors, where N≥2. Whisker material is dispersed in at least one sub-membrane substrate precursor, and then the N sub-membrane substrate precursors are extruded to obtain the membrane substrate. In the embodiments of the present invention, the membrane obtained by the above preparation method includes N sub-membrane substrates, where N≥2, stacked in the thickness direction, and whisker material is dispersed in at least one sub-membrane substrate.

[0094] In some embodiments of the present invention, an adhesive layer can be provided on at least a portion of the surface of the inorganic coating away from the separator substrate. Specifically, the adhesive can be applied to at least a portion of the surface of the separator substrate by spraying or dot coating, which can further improve the stability of the inorganic coating and thus better improve the cycle life and safety performance of the battery.

[0095] This invention also provides a battery including the above-described positive electrode sheet. The battery of this invention has advantages corresponding to the above-described separator, which will not be elaborated here.

[0096] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0097] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0098] Specifically, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector. Specifically, the positive active material layer can be provided on one side surface in the thickness direction of the positive current collector, or positive active material layers can be provided on both opposite sides surface in the thickness direction of the positive current collector.

[0099] The positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. In the positive electrode active material layer, the mass percentage of the positive electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass fraction of the positive electrode conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof. The mass fraction of the positive electrode binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0100] In some embodiments, the battery is a lithium-ion battery, and the positive electrode active material includes, but is not limited to, LiCoO2, LiNiO2, and LiCo. x Ni 1-x O2 (0≤x≤1), LiCo x Ni 1-x-y Al y O2 (0≤x≤1, 0≤y≤1), LiMn2O4, LiFe x Mn y M z O4 (M is one or more of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn or Mo, 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), Li 1＋ x L 1－y－z M y N z O2 (L, M, N are one or more of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S, B, -0.1≤x≤0.2, 0≤y≤1, 0≤z≤1, 0≤y+z≤1), LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, Li2CuO2, Li5FeO4, and metal sulfides and oxides (such as TiS2, V2S3, FeS, FeS2, LiMS) x(M is at least one of the transition metal elements such as Ti, Fe, Ni, Cu, Mo, etc., 1≤x≤2.5), TiO2, Cr3O8, V2O5, MnO2, etc.

[0101] In some embodiments, the battery is a sodium-ion battery, and the positive electrode active material includes, but is not limited to, one or a combination of transition metal oxides, polyanionic compounds, organic compounds, and Prussian blue materials. The transition metal oxides may be, but are not limited to, NaMO2 (M may be Fe, Co, Ni, Mn, etc.); the polyanionic compounds may be, but are not limited to, Na3V2(PO4)3, NaFePO4, Na2FePO4F, etc.; the Prussian blue materials may be, but are not limited to, Na2Fe(CN)6, etc.; and the organic compounds may be, but are not limited to, sodium terephthalic acid salts, etc.

[0102] In some embodiments, the battery is a potassium-ion battery, and the positive electrode active material includes, but is not limited to, one or more of the following: Prussian blue analogues, layered transition metal oxides, polyanionic compounds (such as KFeSO4F, KVPO4F), organic compounds (such as potassium terephthalate), sulfides (such as K2FeS2), phosphates (such as K3V2(PO4)3), potassium manganese oxides (such as KMnO4 derivatives), potassium cobalt oxides (such as KCoO2), and potassium nickel oxides (such as KNiO2).

[0103] In this embodiment of the invention, the positive electrode conductive agent in the positive electrode active material layer can be a conventional conductive material in the art. For example, the positive electrode conductive agent in the positive electrode active material layer may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0104] In this embodiment of the invention, the positive electrode binder in the positive electrode active material layer can be a conventional binder in the art. For example, the positive electrode binder in the positive electrode active material layer may include one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0105] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0106] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the positive electrode active material layer, such as the positive electrode conductive agent and the positive electrode binder, can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0107] In practice, a slurry containing positive electrode active material can be prepared at a temperature of 20~45℃; conventional coating equipment in the field, such as continuous coating equipment, can be used to coat the slurry containing positive electrode active material onto the surface of the positive electrode current collector.

[0108] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector. Specifically, the negative electrode active material layer can be provided on one side surface of the negative electrode current collector, or negative electrode active material layers can be provided on both opposite sides of the negative electrode current collector in the thickness direction.

[0109] Specifically, the negative electrode active material layer may include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, all of which can be conventional materials in the art. For example, the negative electrode active material may include graphite, and the negative electrode conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the negative electrode binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0110] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0111] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active material layer, negative electrode conductive agent, negative electrode binder, etc., can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0112] In practice, a slurry containing negative electrode active material can be prepared at a temperature of 20℃~45℃; conventional coating equipment in the field, such as continuous coating equipment, can be used to coat the slurry containing negative electrode active material onto the surface of the negative electrode current collector.

[0113] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from coming into contact and short-circuiting.

[0114] The electrolyte in this embodiment of the invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Electrolyte salts may include lithium salts (if it is a lithium-ion battery), such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0115] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection (i.e., injection of electrolyte) and encapsulation, the battery is obtained.

[0116] This invention also provides a battery pack comprising at least two of the above-described batteries, which has advantages corresponding to the above-described separator, and will not be described in detail hereafter.

[0117] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0118] This invention also provides an electrical device including the battery described above, which has advantages corresponding to the diaphragm described above, and will not be described in detail here.

[0119] The electrical equipment used in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0120] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0121] Example 1

[0122] The diaphragm in this embodiment is prepared by the following method:

[0123] 1) Whisker dispersion: Alumina whisker material (specifically α-alumina whiskers) is added to NMP solvent, ultrasonically dispersed for 30 min, and then added to PE base film slurry (diaphragm matrix precursor) for mixing treatment to obtain mixed slurry.

[0124] 2) Casting film: The above mixed slurry is extruded through a twin-screw extruder and stretched into a film (longitudinal stretching ratio 4:1, transverse stretching ratio 3:1) to obtain the diaphragm matrix.

[0125] 3) Coating process: Boehmite slurry (coating slurry) is applied to both sides of the membrane substrate using a micro-gravure coating at a speed of 10 m / min, and then dried at 120℃ to form an inorganic coating, thus obtaining the membrane precursor. The boehmite slurry has a solid content of 30%, uses deionized water as the solvent, and comprises 95% boehmite particles (AlOOH, i.e., inorganic particles) and 5% binder (PVDF-HFP) by total solid mass.

[0126] 4) Heat setting: The dried diaphragm precursor is hot-pressed at 155°C for 5 minutes to obtain the diaphragm.

[0127] In this embodiment, the whisker material is uniformly dispersed in the membrane matrix.

[0128] Example 2

[0129] 1) β-Si3N4 whiskers (whisker material) are modified with silane coupling agent (KH550) to give the surface of the whisker material modified groups (amino groups). Specifically, the whisker material precursor is first acid-washed or ultrasonically dispersed to remove surface impurities and ensure good dispersion. Then, KH550 is mixed with an ethanol / water mixed solvent (ethanol:water = 1:1 (mass ratio), KH550 mass percentage is 20wt%) to adjust the pH value to acidic. The above-washed whisker material precursor is added to the KH550 solution and stirred at a constant temperature to allow it to react fully. Finally, the reaction solution is filtered, washed and dried to obtain modified whiskers (whisker material).

[0130] 2) The modified whisker material and PP material are subjected to a melt-spraying process (processing temperature is 90℃, processing time is 90s) to obtain a membrane substrate. The whisker material decreases in length from one side surface of the membrane substrate (the surface where the whisker material contacts the PP material) to the other side surface.

[0131] 3) Alumina (coating material) is coated onto the surface of the diaphragm substrate using vapor deposition to obtain the diaphragm precursor.

[0132] 4) Heat setting: The above-mentioned diaphragm precursor is hot-pressed at 155°C for 5 minutes to obtain the diaphragm.

[0133] Example 3

[0134] 1) Zirconia whiskers are doped with yttrium oxide to obtain whisker materials. The specific doping steps are as follows: First, a mixed solution of zirconium oxychloride and yttrium oxide (the mass percentage of zirconium oxychloride in the mixed solution is 80 wt%, and the mass percentage of yttrium oxide in the mixed solution is 10 wt%) is reacted with a precipitant (ammonia) to generate a precipitate. The precipitate is washed, dried, and calcined to obtain yttrium oxide-stabilized zirconium oxide powder (whisker material, i.e., Y2O3 doped ZrO2 whiskers).

[0135] 2) The membrane substrate precursor of this embodiment includes three sub-membrane substrate precursors. The first sub-membrane substrate precursor is made of PP material, the second sub-membrane substrate precursor is made of PE material, and the third sub-membrane substrate precursor is made of PP material. The whisker material is dispersed in the second sub-membrane substrate precursor. Then, the first sub-membrane substrate precursor, the second sub-membrane substrate precursor, and the third sub-membrane substrate precursor are extruded to obtain the membrane substrate. The membrane substrate has a PP / PE / PP layered structure, and the PE layer contains whisker material.

[0136] 3) The boehmite slurry (coating slurry) is coated onto the surface of the diaphragm substrate using a microgravure coating at a speed of 10 m / min, and then dried at 120°C to form an inorganic coating, thus obtaining the diaphragm precursor. The boehmite slurry has a solid content of 30%, uses deionized water as the solvent, and comprises 95% boehmite particles (AlOOH, i.e., inorganic particles) and 5% binder (PVDF) by total solid mass.

[0137] 4) Heat setting: The dried diaphragm precursor is hot-pressed at 155°C for 5 minutes to obtain the diaphragm.

[0138] Example 4

[0139] This embodiment is basically the same as Embodiment 1, except that the whisker material in this embodiment includes alumina whisker material and silicon carbide whisker material, and the inorganic particles in this embodiment are graphene-modified alumina.

[0140] Example 5

[0141] This embodiment is basically the same as Embodiment 1, except that the whisker material in this embodiment is oxidized cellulose whisker material, the inorganic particles in this embodiment are clay, and the binder of the coating slurry is chitosan.

[0142] Example 6

[0143] This embodiment is basically the same as Embodiment 1, except that the inorganic particles in this embodiment are alumina, forming an alumina inorganic coating. In this embodiment, PVDF is also sprayed onto the surface of the alumina inorganic coating away from the membrane substrate to form an adhesive layer.

[0144] Example 7

[0145] This embodiment is basically the same as Embodiment 1, except that the inorganic particles in this embodiment are alumina, and an alumina inorganic coating is formed on both sides of the membrane substrate. In this embodiment, PVDF is also dotted on the surface of the alumina inorganic coating away from the membrane substrate to form an adhesive layer.

[0146] The difference between Examples 8-17 and Example 1 lies in the different parameters such as h value, d value, w value, average length of whisker material, average diameter of whisker material, aspect ratio of whisker material, type of inorganic particles, and size of inorganic particles, as detailed in Tables 1 and 2.

[0147] Example 18

[0148] The difference between this embodiment and Embodiment 1 is that the inorganic coating in this embodiment also includes α-alumina whisker material, and the mass ratio of the whisker material to the inorganic particles is 1:1.

[0149] Comparative Example 1

[0150] The difference in this comparative example is that the membrane substrate in this comparative example does not contain whisker material, while the inorganic particles in this embodiment are alumina, forming an alumina inorganic coating.

[0151] Comparative Example 2

[0152] The difference between this comparative example and Example 1 is that the mass percentage of the membrane matrix in this comparative example is different from that in Example 1, as shown in Table 1.

[0153] The h value, d value, w value, whisker material type, average length of whisker material, average diameter of whisker material, aspect ratio of whisker material, inorganic particle type, and inorganic particle size of the diaphragms prepared in the above embodiments and comparative examples are detailed in Tables 1 and 2.

[0154]

[0155]

[0156] In Table 2, "-" indicates that the substance is not present.

[0157] Battery assembly

[0158] The separators from Examples 1-18 and Comparative Examples 1-2 were assembled into batteries. Specifically, the process included the following steps:

[0159] 1) Preparation of positive electrode slurry

[0160] Raw material ratio: NCM811 active material (positive electrode active material): conductive agent (SP): binder (PVDF) = 96:2:2 (mass ratio), solvent is NMP (N-methylpyrrolidone). Specific preparation steps are as follows: Dissolve PVDF in NMP and stir until completely dissolved (40℃ water bath, 2h); add conductive agent SP and disperse under high-speed shear (2000rpm, 30min); add NCM811 powder in batches and stir under vacuum (500rpm, 4h) until the slurry viscosity reaches 5000Pa·s.

[0161] 2) Preparation of negative electrode slurry

[0162] Raw material ratio: Artificial graphite: conductive agent (SP): binder (SBR / CMC) = 96:1:3 (mass ratio), solvent is deionized water. Specific preparation steps are as follows: Dissolve CMC in water and stir until a transparent colloid is formed (room temperature, 1 h); add graphite and SP, and planetarily stir (50 rpm, 2 h); add SBR emulsion and stir at low speed (100 rpm, 1 h) until the slurry viscosity reaches 1500 mPa·s.

[0163] 3) Electrode preparation

[0164] Coating process: The above-mentioned positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil (12μm thick), with an areal density designed to be 20mg / cm³. 2 (Single-sided) The above-mentioned negative electrode slurry is coated on both sides of the negative electrode current collector copper foil (8μm thick), with an areal density designed to be 10mg / cm³. 2 (Single-sided) During coating, the coating speed is 0.5 m / min. After coating, dry in an oven at temperatures of 80℃ / 100℃ / 120℃ in stages (the positive electrode requires an NMP recovery system).

[0165] Rolling and slitting: Positive electrode rolling involves compacting the dried positive electrode sheet to 3.2 g / cm³ using a hot press (80°C). 3 The thickness is controlled at 140μm. The negative electrode is then cold-pressed to 1.6g / cm² after drying. 3 The thickness is controlled at 160μm. The cutting dimensions are 120mm for the positive electrode and 124mm for the negative electrode (with a 4mm edge allowance).

[0166] 4) Cell assembly

[0167] The Z-type stacking process is adopted, and the positive electrode (NCM811) → the separator of the above embodiment and comparative example → the negative electrode (graphite) is stacked in a Z-type manner.

[0168] Electrode tab welding: The positive electrode is welded with aluminum tabs using ultrasonic welding, and the negative electrode is welded with nickel tabs using laser welding.

[0169] Packaging: Flexible packaging was performed using an aluminum-plastic film (113μm thick). The heat sealing parameters were: temperature 180℃, pressure 0.5MPa, and time 5s.

[0170] 5) Liquid injection and formation

[0171] Electrolyte formulation: Dissolve 1M LiPF6 in a solvent, which contains EC:DMC:DEC in a volume ratio of 3:4:3, and also contains 5wt% FEC.

[0172] Electrolyte injection: The injection volume is calculated based on the positive electrode capacity, with a volume coefficient of 1.2 (3.5 g / Ah). Electrolyte injection is carried out in a dry room with a dew point ≤ -40℃.

[0173] Formation process: Stepped charging is adopted, specifically charging the above-mentioned electrolyte-filled battery with a constant current of 0.02C to 3.0V, letting it stand for 2 hours, and then using 0.05C to 3.8V.

[0174] High-temperature aging: The battery after the above formation was left to stand at 45°C for 48 hours to promote the formation of SEI film.

[0175] 6) Post-processing

[0176] Second sealing and shaping: After evacuating to -95kPa, heat seal and then maintain pressure at 0.5T for 2 hours for pressure shaping.

[0177] 7) Capacity testing

[0178] The capacity grading system is 0.2C charge / discharge (2.5-4.2V).

[0179] Capacity screening: Remove cells with a capacity deviation >3%.

[0180] Assembly environment: glove box (O2<1ppm, H2O<1ppm), vacuum sealing, to obtain the battery.

[0181] Test case

[0182] (a) Diaphragm performance testing

[0183] Whisker material mass ratio test: After the battery is fully discharged, it is disassembled and the separator is separated. The inorganic coating on the surface of the separator is washed away with a large amount of water to obtain the separator substrate. Take 5mg of the cleaned and dried separator substrate (recorded as the initial sample mass) and put it into a crucible under air or oxygen atmosphere protection. The temperature is increased from room temperature to 150℃ at a rate of 20℃ / min and held for 20min. Then, the temperature is increased to 700℃ at a rate of 10℃ / min and held until the weight no longer decreases (recorded as the final plateau mass); w = final plateau mass / initial sample mass × 100%.

[0184] Testing of the inorganic coating thickness h and the separator substrate thickness d: After the battery was fully discharged, it was disassembled, the separator was separated, and its cross-section was obtained. SEM analysis was then performed on the cross-section to differentiate the separator substrate and the inorganic coating. Five fields of view were selected for each, and their average values ​​were calculated to obtain the thickness h of the inorganic coating and the thickness d of the separator substrate. Based on these values, 0.01h can be calculated. 0.5 and 1-e -0.05d The value.

[0185] Aspect ratio, average length, and direct diameter testing of whisker materials: After the battery is fully discharged, it is disassembled, the separator is separated, and the cross-section of the separator is obtained. Then, SEM testing is performed on the cross-section. 100 whisker materials are selected, and their length and diameter are counted to obtain the aspect ratio, average length, and average diameter of the whisker materials. Among them, the aspect ratio of the whisker material is the ratio of the average length to the average diameter of the whisker material.

[0186] Size testing of inorganic particles: After the battery is fully discharged, it is disassembled, the separator is separated, the cross-section of the separator is obtained, and then the cross-section is tested by SEM. At least 100 inorganic particles are selected and their sizes are counted.

[0187] Elastic modulus testing: The diaphragms of Examples 1-18 and Comparative Examples 1-2 were tested using a universal testing machine (Instron 5967) according to the standard ASTM D882 / GB / T1040.3. The sample size of the diaphragms in the above examples and comparative examples was set to 15mm × 100mm (5 lines each in the MD and TD directions), the tensile rate was 10mm / min, the preload was 0.1N, and the modulus calculation range was 0.05%-0.25% of strain. Data processing: The slope of the linear segment of the stress-strain curve was taken as the elastic modulus of the diaphragm, and the values ​​were recorded separately in the MD and TD directions.

[0188] Creep recovery rate test: The diaphragms of Examples 1-18 and Comparative Examples 1-2 were tested using a high-temperature creep tester (equipped with a constant pressure loading module). The sample size was a Φ20mm circular disc (three layers of the diaphragms from the above examples and comparative examples stacked together). The test procedure included:

[0189] 1) Preloading: Preload at 0.1MPa for 5 minutes at 25℃ to eliminate gaps;

[0190] 2) Creep stage: Apply 0.5 MPa pressure at 150℃ and maintain for 1 hour;

[0191] 3) Recovery phase: After depressurization, allow to stand at the same temperature for 30 minutes;

[0192] 4) Measurement: A laser displacement sensor records thickness changes (accuracy 0.1μm);

[0193] 5) Creep recovery rate = The test results are shown in Table 3.

[0194] Thermal conductivity test: The thermal conductivity of the diaphragms in Example 4 and Comparative Example 1 was tested. Specifically, 15 layers of diaphragms were stacked and compressed to form a sufficiently thick sample. Gold was sputtered onto the sample surface, and the front surface of the sample was uniformly irradiated with a short-pulse laser. The temperature change of the rear surface of the sample was monitored using a high-speed infrared detector, and the thermal diffusivity α of the diaphragm was measured. The final thermal conductivity was calculated as α × specific heat capacity × density. The thermal conductivity of the diaphragm in Example 4 was 0.58 W / m·K, while the thermal conductivity of the diaphragm in Comparative Example 1 was 0.2 W / m·K. Compared to Comparative Example 1, the diaphragm in Example 4 of this invention exhibits improved thermal conductivity.

[0195] (II) Battery Electrochemical Performance Testing

[0196] Battery internal resistance test: The separators obtained in Example 3 and Comparative Example 1 were assembled into batteries according to the above method, and the battery internal resistance was tested. The battery internal resistance was characterized by a combination of DC-IR and AC-IR methods. First, after being fully charged (4.2 V) for 2 hours using an electrochemical workstation (such as Gamry 3000), a sinusoidal signal with a frequency of 1 kHz and an amplitude of 5 mV was applied. The ohmic impedance in the high-frequency region was measured by AC impedance method and used as the AC-IR of the battery, reflecting the ion conduction characteristics of the electrolyte, separator, and electrode interface. Subsequently, the DC-IR test was performed according to the national standard method. A discharge pulse of 1C current was applied and lasted for 10 seconds under the same fully charged and resting state. The instantaneous voltage change ΔV before and after the pulse was recorded, and combined with the current change ΔI, the DC internal resistance was calculated according to the formula DC-IR = ΔV / ΔI. According to the above test, the battery internal resistance in Example 3 was 22.3 mΩ, and the battery internal resistance in Comparative Example 1 was 25.3 mΩ. Compared to Comparative Example 1, the separator of Embodiment 3 of the present invention can effectively reduce the internal resistance of the battery.

[0197] High-temperature cycle life test: The batteries of Examples 1-18 and Comparative Examples 1-2 were tested according to the national standard GB / T 31486-2015. Specifically, a constant temperature chamber and a charge / discharge test system (Neware BTS-4000) were used together, and the ambient temperature was set to 60℃. During the test, the batteries were first charged to 4.2V at a constant current / constant voltage (CC / CV) of 0.5C, with a cutoff current of 0.05C; then left to stand for 5 minutes, and then discharged to 2.8V at a constant current of 1C, completing one cycle. The above cycle was repeated for 1000 cycles. The capacity retention rate was the ratio of the capacity after 1000 cycles to the capacity before the cycle.

[0198] Rate performance testing: The rate performance of the battery assembled with the separator in Example 1 and the battery assembled with the separator in Comparative Example 1 was evaluated through a stepped discharge test. Specifically, the batteries were charged and discharged sequentially at discharge rates of 0.2C, 0.5C, 1C, 2C, 3C, and 5C under standard conditions, with three consecutive cycles at each rate. Charging was performed at 0.5C constant current / constant voltage (CC / CV) to 4.2V (cutoff current of 0.05C), and the discharge cutoff voltage was 2.8V. The average discharge capacity at 0.2C was used as the baseline capacity, and the capacity retention rate at each higher rate was calculated as: Capacity retention rate = (current rate discharge capacity) / (0.2C discharge capacity) × 100%, used to evaluate the battery's rate performance. The capacity retention rate of the battery in Example 1 was 91%, and the capacity retention rate of the battery in Comparative Example 1 was 82%. Compared to Comparative Example 1, the separator in Example 1 of this invention can improve the rate performance of the battery.

[0199] (III) Battery safety testing

[0200] Hot Box Test: The batteries of Examples 1-18 and Comparative Examples 1-2 were tested according to the national standard GB / T31485-2015. The specific procedure was as follows: the battery cells at 100% state of charge (SOC) were placed in a constant temperature chamber and heated to 150°C at a heating rate of 5°C / min, and maintained at this temperature for 1 hour. During this period, the cells were continuously observed for fire or explosion to evaluate their thermal stability and safety performance under high-temperature abuse conditions. The test results are shown in Table 3.

[0201] Nail Penetration Test: Nail penetration tests were performed on the batteries of Examples 1-18 and Comparative Examples 1-2. The tests were conducted at an ambient temperature of 25°C. A 3mm diameter steel needle was used in a nail penetration testing machine to vertically pierce the geometric center of the battery cell at a speed of 80mm / s. The cell's condition and surface temperature were monitored in real time during the test. The passing criteria were no fire, no explosion, and a maximum surface temperature below 150°C, to evaluate the battery's safety performance under extreme internal short-circuit conditions. The test results are shown in Table 3.

[0202]

[0203] In Table 3, " / " indicates that the sample quality is too poor to test this performance.

[0204] As shown in Table 3, compared with the comparative example, the embodiments of the present invention effectively improve the elastic modulus and creep recovery rate of the separator by dispersing whisker materials in the separator matrix, which is beneficial to improving the cycle life and safety performance of the battery.

[0205] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A diaphragm, characterized in that, The membrane includes a membrane substrate and an inorganic coating disposed on at least a portion of the surface of the membrane substrate; the membrane substrate includes a membrane base material and whisker material dispersed in the membrane base material; the whisker material is uniformly distributed in the membrane substrate; or, the whisker material decreases in size from one surface of the membrane substrate to the other surface; the membrane satisfies: 0.01h 0.5 ≤w≤18(1-e -0.05d ); where w is the mass percentage of the whisker material in the membrane substrate, expressed as % (0% < w ≤ 12%); h is the thickness of the inorganic coating, expressed as μm (0 μm < h ≤ 3 μm); d is the thickness of the membrane substrate, expressed as μm (8 μm ≤ d ≤ 25 μm); and e is the base of the natural logarithm.

2. The diaphragm according to claim 1, characterized in that, The aspect ratio of the whisker material is 5:1 to 100:1; and / or, the average length of the whisker material is 20 nm to 300 nm, and the average diameter is 0.003 μm to 0.04 μm; and / or, the whisker material includes one or more of alumina whisker material, silicon nitride whisker material, zirconium oxide whisker material, silicon carbide whisker material, and cellulose oxide whisker material; and / or, the inorganic coating includes at least one of inorganic particles and the whisker material; and / or, the membrane substrate includes at least one of polyethylene, polypropylene, and polyimide.

3. The diaphragm according to claim 2, characterized in that, The inorganic particles include one or more of ceramics, boehmite, alumina, and clay; and / or, the inorganic particles include one or more of flake-shaped inorganic particles, spherical inorganic particles, and rod-shaped inorganic particles; wherein the average thickness of the flake-shaped inorganic particles is 0.1 μm to 2 μm, and the average flake diameter is 0.5 μm to 3 μm; and / or, the average particle size of the spherical inorganic particles is 0.3 μm to 1.5 μm; and / or, the average length of the rod-shaped inorganic particles is 50 μm to 100 μm, and the average diameter is 0.1 μm to 20 μm.

4. The diaphragm according to any one of claims 1-3, characterized in that, The whisker material includes a modifying group, which includes at least one of amino and epoxy groups; and / or, the whisker material includes a dopant, which includes yttrium oxide.

5. The diaphragm according to any one of claims 1-3, characterized in that, The membrane substrate includes N sub-membrane substrates stacked in the thickness direction, where N≥2, and at least one of the sub-membrane substrates contains the whisker material.

6. A method for preparing a diaphragm according to any one of claims 1-5, characterized in that, The process includes the following steps: dispersing whisker material in a membrane substrate to obtain a membrane matrix, and then coating at least a portion of the surface of the membrane matrix with a coating material to obtain the membrane.

7. The method for preparing the diaphragm according to claim 6, characterized in that, The method of dispersing the whisker material in the membrane matrix includes the following steps: sequentially mixing the whisker material and the membrane matrix precursor, and extruding them to obtain the membrane matrix; or, performing a melt spraying process on the whisker material and the membrane matrix precursor to obtain the membrane matrix.

8. The method for preparing the diaphragm according to claim 7, characterized in that, Before dispersing the whisker material in the membrane matrix, the method further includes: modifying the whisker material precursor with a modifier, wherein the modifier includes a silane coupling agent; and / or doping the whisker material precursor with a dopant, wherein the dopant includes yttrium oxide.

9. The method for preparing the diaphragm according to claim 8, characterized in that, The membrane matrix precursor includes N sub-membrane matrix precursors, where N≥2. The whisker material is dispersed in at least one sub-membrane matrix precursor, and then the N sub-membrane matrix precursors are extruded to obtain the membrane matrix.

10. A battery, characterized in that, This includes the diaphragm as described in any one of claims 1-5, or the diaphragm prepared by the method described in any one of claims 6-9.

11. A battery pack, characterized in that, It includes at least two batteries as described in claim 10.

12. An electrical appliance, characterized in that, Includes the battery of claim 10 or the battery pack of claim 11.

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