Separation film, method for manufacturing the same, secondary battery, and electric device

Abstract

The application relates to the technical field of secondary batteries, and particularly provides an isolation film, a preparation method thereof, a secondary battery and a power utilization device. The isolation film comprises a porous base film, the porous base film comprises a base phase and a filling phase dispersed in the base phase, the test curve of the differential scanning calorimeter of the porous base film simultaneously comprises a melting peak of the base phase and a melting peak of the filling phase, and the temperature of the melting peak of the base phase is higher than that of the melting peak of the filling phase. The isolation film provided by the application can provide the reliability of the secondary battery.

Description

Separating membrane and its preparation method, secondary battery and power device Technical Field

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

[0002] Rechargeable batteries are widely used in various consumer electronics and electric vehicles due to their outstanding advantages of being lightweight, pollution-free, and having no memory effect. With the continuous development of the new energy industry, users are placing higher demands on the reliability of rechargeable batteries. However, existing separators are insufficient to prevent abnormal temperature rises in rechargeable batteries. Summary of the Invention

[0003] In view of the technical problems existing in the background art, this application provides a separator and its preparation method, a secondary battery and an electrical device, aiming to solve the problem of secondary battery termination under abnormal temperature conditions.

[0004] To solve the above-mentioned technical problems, the first technical solution adopted in this application is: to provide a separation membrane, which includes a porous base membrane, the porous base membrane including a matrix phase and a filling phase dispersed in the matrix phase, the test curve of the differential scanning calorimeter of the porous base membrane includes the melting peak of the matrix phase and the melting peak of the filling phase, and the temperature of the melting peak of the matrix phase is higher than the temperature of the melting peak of the filling phase.

[0005] In the technical solution of this application embodiment, the melting peak temperature of the matrix phase is higher than that of the filling phase, that is, the matrix phase has better thermal stability than the filling phase. Therefore, when the internal temperature of the secondary battery is high, the filling phase melts first due to its poorer thermal stability, thereby sealing the pores of the separator membrane in time, terminating the electrochemical reaction, preventing the internal temperature of the secondary battery from continuing to rise, and improving the reliability of the secondary battery.

[0006] In any embodiment of this application, the ratio of the peak area of ​​the melting peak of the matrix phase to the peak area of ​​the melting peak of the filling phase is greater than 1, and can be selected as 1.2-2.0.

[0007] In the technical solution of this application embodiment, the ratio of the peak area of ​​the melting peak of the matrix phase to the peak area of ​​the melting peak of the filling phase is within the above range, which enables the formation of a sufficient amount of filling phase crystals in the separator, which is beneficial to the realization of closed-cell performance; and makes the finished separator have good pore-forming performance and high strength.

[0008] In any embodiment of this application, the porous base film has diffraction peaks in the X-ray diffraction pattern of the porous base film in the range of 15° < 2θ < 17°.

[0009] In the technical solution of this application embodiment, the porous base film has diffraction peaks in the range of 15° < 2θ < 17°. The diffraction peaks here are the diffraction peaks of the β crystal form in the porous base film. The higher the content of the β crystal form in the porous base film, the higher the overall strength of the porous base film.

[0010] In any embodiment of this application, the porous base film has diffraction peaks in the X-ray diffraction pattern of the porous base film in the range of 23° < 2θ < 25°.

[0011] In the technical solution of this application embodiment, the porous base film has diffraction peaks in the range of 23° < 2θ < 25°. Here, the diffraction peaks are the diffraction peaks of the α crystal form in the porous base film. The α crystal form in the porous base film is beneficial to the realization of the thermal pore-closing function.

[0012] In any embodiment of this application, in the X-ray diffraction pattern of the porous base film, the porous base film includes a first diffraction peak in the range of 15° < 2θ < 17°, and the porous base film includes a second diffraction peak in the range of 23° < 2θ < 25°, wherein the diffraction peak intensity of the first diffraction peak is greater than that of the second diffraction peak.

[0013] In the technical solution of this application embodiment, the porous base film includes a first diffraction peak in the range of 15° < 2θ < 17°, and a second diffraction peak in the range of 23° < 2θ < 25°. The intensity of the first diffraction peak is greater than that of the second diffraction peak. The greater intensity of the first diffraction peak indicates that the content of β crystal form is greater than that of α crystal form. Therefore, under the premise of high overall strength of the separator, the thermal pore-closing function of the separator can be realized, thereby improving the reliability of the separator.

[0014] In any embodiment of this application, the filling phase comprises α-crystalline grains; the base film phase comprises β-crystalline grains.

[0015] In the technical solution of this application embodiment, the filling phase of the separator includes α-crystalline grains and the matrix phase includes β-crystalline grains, so that the separator has high overall strength and can achieve the thermal pore-closing function, thereby improving the reliability of the separator.

[0016] In any embodiment of this application, the grain size of the filling phase is 0.1μm-2μm, and can be selected as 0.1μm-0.5μm.

[0017] In the technical solution of this application embodiment, the grain size of the filling phase is controlled within the above-mentioned range. When the internal temperature of the secondary battery is high, the filling phase melts first due to its low melting point, thereby sealing the pores of the separator in time, realizing rapid shutdown, terminating the electrochemical reaction, and preventing the internal temperature of the secondary battery from continuing to rise. At the same time, the separator has better strength and elongation at break, so as to improve the reliability of the secondary battery.

[0018] In any embodiment of this application, the mass percentage of the filler phase in the substrate is 10%-40%, optionally 15%-25%.

[0019] In the technical solution of this application embodiment, the mass ratio of the filling phase is controlled within the above range. When the internal temperature of the secondary battery is high, a sufficient amount of filling phase melts and seals the pores of the separator, achieving thermal shutdown. At the same time, the matrix phase and the filling phase can balance the physical strength of the separator, improving the reliability of the secondary battery.

[0020] In any embodiment of this application, the relative molecular mass of the filling phase material is less than or equal to 1.2 million, and can be selected as 400,000 to 600,000; the relative molecular mass of the matrix phase material is greater than or equal to 300,000, and can be selected as 300,000 to 2.5 million.

[0021] In the technical solution of this application embodiment, the relative molecular masses of the filling phase and the matrix phase are limited to the above range. The matrix phase and the filling phase can balance the physical strength of the separator and improve the reliability of the secondary battery.

[0022] In any embodiment of this application, the melting peak temperature of the matrix phase is 160℃-350℃, and can be selected as 160℃-180℃; the melting peak temperature of the filler phase is 60℃-180℃, and can be selected as 80℃-130℃.

[0023] In the technical solution of this application embodiment, the temperature of the melting peak of the matrix phase and the temperature of the melting peak of the filling phase are limited to the above range, which can balance the physical strength of the separator and seal the pores of the separator in time when the internal temperature of the secondary battery is high, thereby improving the reliability of the secondary battery.

[0024] In any embodiment of this application, the matrix phase is made of at least one of polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene terephthalate, polyetheretherketone, polyurethane, and polyester; the filler phase is made of at least one of polyethylene and polypropylene.

[0025] In the technical solution of this application embodiment, the materials of the matrix phase and the filling phase are limited to the above-mentioned range, which can meet the material requirements of the separator. When the internal temperature of the secondary battery is high, the filling phase can seal the pores of the separator in time, thereby improving the reliability of the secondary battery.

[0026] In any embodiment of this application, the pore size of the porous base membrane is less than or equal to 0.5 μm, and can be selected as 0.02 μm-0.1 μm.

[0027] In the technical solution of this application embodiment, the pore size of the porous base film is less than or equal to 0.5 μm, which enables the filling phase to effectively seal the pores after melting, achieve thermal shutdown, and improve the reliability of the secondary battery.

[0028] In any embodiment of this application, the separator membrane satisfies at least one of the following (1)-(9):

[0029] (1) The closure temperature of the separator is 120℃-170℃, and can be selected as 120℃-130℃;

[0030] (2) The closure time of the isolation membrane is less than or equal to 10s, and can be selected as 5s-10s;

[0031] (3) The transverse breaking elongation of the separator is ≥100%, and can be selected as 100%-120%;

[0032] (4) The longitudinal elongation at break of the separator is ≥60%, and can be selected as 60%-80%;

[0033] (5) The transverse tensile strength of the separator is ≥1500 kgf / cm 2 2000 kgf / cm² is optional. 2 -4000 kgf / cm 2 ;

[0034] (6) The longitudinal tensile strength of the separator is ≥2000 kgf / cm 2 2000gf / cm can be selected. 2 -4000 kgf / cm 2 ;

[0035] (7) The puncture strength of the isolation membrane is ≥60gf, and can be selected as 120gf-420gf;

[0036] (8) The porosity of the isolation membrane is 30%-90%, and can be selected as 30%-50%;

[0037] (9) The air permeability of the separator is less than or equal to 300sec / 100cc, and can be selected as 100sec / 100cc-300sec / 100cc.

[0038] In the technical solution of this application embodiment, the separator membrane satisfies at least one of the above conditions.

[0039] It can effectively improve the extensibility of the separator, enhance its puncture resistance, and enable rapid response to thermal anomalies to achieve thermal shutdown, thereby further improving the reliability of secondary batteries.

[0040] The second technical solution adopted in this application is: providing a method for preparing the isolation membrane as described above. The preparation method includes: mixing raw materials forming a matrix phase, raw materials forming a filler phase, and a nucleating agent to form a precursor, wherein the crystallization temperature of the raw materials forming the filler phase is lower than the crystallization temperature of the raw materials forming the matrix phase; extruding the precursor to form a first intermediate product; casting the first intermediate product to form a second intermediate product, wherein the casting process includes a first temperature stage and a second temperature stage, the casting temperature in the first temperature stage being higher than the casting temperature in the second temperature stage; and stretching the second intermediate product to obtain a porous base membrane. The porous base membrane includes a matrix phase and a filler phase dispersed in the matrix phase. The differential scanning calorimeter test curve of the porous base membrane simultaneously includes the melting peak of the matrix phase and the melting peak of the filler phase, and the temperature of the melting peak of the matrix phase is higher than the temperature of the melting peak of the filler phase.

[0041] In the technical solution of this application embodiment, the raw materials for forming the matrix phase, the raw materials for forming the filler phase, and the nucleating agent are mixed. The crystallization temperature of the filler phase raw materials is lower than that of the raw materials for forming the matrix phase. In the casting process, a casting process in which the casting temperature in the first temperature stage is higher than that in the second temperature stage is adopted, so that the raw materials of the matrix phase crystallize first and the raw materials of the filler phase crystallize later. The filler phase is dispersed in the matrix phase. After stretching, a porous separator is formed. The melting peak temperature of the matrix phase of the separator is higher than that of the filler phase. The matrix phase has better thermal stability than the filler phase. Therefore, when the internal temperature of the secondary battery is high, the filler phase melts first due to its poorer thermal stability, thereby sealing the pores of the separator in time, terminating the electrochemical reaction, preventing the internal temperature of the secondary battery from continuing to rise, and improving the reliability of the secondary battery.

[0042] In any embodiment of this application, the melt index of the filler phase material is greater than the melt index of the matrix phase material; optionally, the ratio of the melt index of the filler phase material to the melt index of the matrix phase material is equal to 1.1-10.1, and can be 1.1-2.1.

[0043] In the technical solution of this application embodiment, the melt index of the filler phase raw material is greater than that of the matrix phase raw material, and the ratio of the two is limited to the above range. The matrix phase has better thermal stability than the filler phase. When the internal temperature of the secondary battery is high, the filler phase melts first, thereby sealing the pores of the separator membrane in time, terminating the electrochemical reaction, preventing the internal temperature of the secondary battery from continuing to rise, and improving the reliability of the secondary battery.

[0044] In any embodiment of this application, the crystallization temperature of the filler phase raw material is 80℃-120℃, optionally 80℃-100℃; and / or, the crystallization temperature of the matrix phase raw material is 125℃-135℃, optionally 125℃-130℃.

[0045] In the technical solution of this application embodiment, the crystallization temperature of the filler phase raw material and the crystallization temperature of the matrix phase raw material are limited to the above range, so that the melting peak temperature of the matrix phase is higher than the melting peak temperature of the filler phase. When the internal temperature of the secondary battery is high, the filler phase melts first, thereby sealing the pores of the separator membrane in time, terminating the electrochemical reaction, preventing the internal temperature of the secondary battery from continuing to rise, and improving the reliability of the secondary battery.

[0046] In any embodiment of this application, the casting temperature in the first temperature stage is 125℃-135℃, optionally 125℃-130℃; and / or, the casting temperature in the second temperature stage is 105℃-125℃, optionally 105℃-110℃; and / or, the difference between the casting temperature in the first temperature stage and the casting temperature in the second temperature stage is 10℃-20℃.

[0047] In the technical solution of this application embodiment, limiting the casting temperature to the above range enables the separator to fully crystallize and form the filling phase and the matrix phase.

[0048] In any embodiment of this application, in the step of stretching the second intermediate product, the transverse stretching temperature is 110℃-120℃, optionally 110℃-115℃; and / or, the longitudinal stretching temperature is 85℃-120℃, optionally 110℃-120℃.

[0049] In the technical solution of this application embodiment, by limiting the transverse stretching temperature and the longitudinal stretching temperature within the above-mentioned range, the resulting separator membrane can have better physical and chemical properties.

[0050] The third technical solution adopted in this application is: providing a secondary battery, which includes a separator as described above or a separator prepared by the method described above. The secondary battery includes a positive electrode and a negative electrode, and the separator is disposed between the positive electrode and the negative electrode.

[0051] The fourth technical solution adopted in this application is: to provide an electrical device, including the secondary battery as described above.

[0052] In the technical solution of this application embodiment, the power-consuming device includes the above-mentioned secondary battery, and thus has the same advantage of good fast charging performance.

[0053] The above description is merely an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0054] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0055] Figure 1 is a SEM image of one embodiment of the separator provided in this application.

[0056] Figure 2 is a melting curve of the separator shown in Figure 1.

[0057] Figure 3 is a schematic diagram of one embodiment of the secondary battery provided in this application.

[0058] Figure 4 is an exploded view of Figure 3.

[0059] Figure 5 is a schematic diagram of one embodiment of the battery module provided in this application.

[0060] Figure 6 is a schematic diagram of one embodiment of the battery pack provided in this application.

[0061] Figure 7 is an exploded view of Figure 6.

[0062] Figure 8 is a schematic diagram of one embodiment of the device for using a secondary battery as a power source provided in this application. Detailed Implementation

[0063] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0064] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0065] In this description, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0066] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0067] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0068] [Rechargeable Battery]

[0069] A rechargeable battery is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a rechargeable battery consists of individual battery cells (positive electrode, negative electrode, and separator), electrolyte, and a casing. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, acting as a conductor of ions, lies between the positive and negative electrodes.

[0070] [Isolation membrane]

[0071] As shown in Figures 1 and 2, Figure 1 is a SEM image of one embodiment of the separator, and Figure 2 is a melt curve of the separator shown in Figure 1. The separator provided in this application includes a porous base membrane, which comprises a matrix phase and a filling phase dispersed in the matrix phase. The differential scanning calorimeter test curve of the porous base membrane simultaneously includes the melting peaks of the matrix phase and the filling phase, and the temperature of the melting peak of the matrix phase is higher than the temperature of the melting peak of the filling phase.

[0072] Differential scanning calorimetry (DSC) can be used to determine the curing reaction temperature and thermal effects of polymer materials, the phase transition temperature and its thermal effects, the crystallization and melting temperatures and their thermal effects, and the glass transition temperature of polymer materials. The melting peak reflects the melting process of a substance, that is, the process by which a solid substance melts into a liquid substance when the temperature rises to a certain level, releasing a certain amount of heat. The temperature of the melting peak can be used to evaluate the thermal stability of a material. Thermal stability refers to the stability of a material at high temperatures. If the melting peak temperature of a material is high, it indicates that the material is not easily melted at high temperatures and has good thermal stability; if the melting peak temperature is low, it indicates that the material is easily melted at high temperatures and has poor thermal stability. In other words, the temperature of the melting peak can also be understood as the melting point, that is, the melting point of the matrix phase is higher than the melting point of the filler phase. In this embodiment, the melting peak temperature of the matrix phase is higher than that of the filling phase, meaning that the matrix phase has better thermal stability than the filling phase. Therefore, when the internal temperature of the secondary battery is high, the filling phase melts first due to its poorer thermal stability, thereby sealing the pores of the separator membrane in time, terminating the electrochemical reaction, preventing the internal temperature of the secondary battery from continuing to rise, and improving the reliability of the secondary battery.

[0073] In some embodiments, the ratio of the peak area of ​​the molten peak of the matrix phase to the peak area of ​​the molten peak of the filling phase is greater than 1, and can be selected as 1.2-2.0. For example, the ratio of the peak area of ​​the molten peak of the matrix phase to the peak area of ​​the molten peak of the filling phase can be 1, 1.1, 1.2, 1.3, 1.4, 1.6, 1.8, 2.0, 2.2, 2.5, 2.8, 3.2, 4, etc., or a range consisting of any two of the above values, such as 1-1.2, 1.1-1.4, 1.3-1.8, 1.6-2.2, 2.2-2.8, 2.8-4, etc. The molten peak area in the X-ray diffraction pattern represents the crystal content; the larger the area, the higher the crystal phase content. The peak area ratio indicates the proportion of different crystals in the separator. When the peak area ratio of the melting peak of the matrix phase to the melting peak of the filling phase is within the above range, it can enable the formation of a sufficient number of filling phase crystals in the separator, which is beneficial to the realization of closed-cell performance. It also results in good pore formation performance and high strength of the finished separator.

[0074] In some embodiments, the porous base film exhibits diffraction peaks in the X-ray diffraction pattern within the range of 15° < 2θ < 17°. Diffraction is the physical phenomenon of coherent scattering of X-rays onto a crystal. The diffraction angle refers to the angle by which the light path changes during diffraction. For example, in an X-ray diffractometer, 2θ is used as the diffraction angle, where 2θ is the angle at which the X-ray changes direction after diffraction. The diffraction peaks of the porous base film within the range of 15° < 2θ < 17° are β-crystal diffraction peaks, and β-crystal is the matrix phase crystallization. β-crystal refers to a crystal structure type of a substance in the solid state. β-crystal refers to the face-centered cubic crystal system, belonging to the hexagonal crystal system. The higher the β-crystal content, the higher the overall strength of the porous base film. The presence of diffraction peaks in the range of 15° < 2θ < 17° in the porous base film ensures sufficient strength for the separator.

[0075] In some embodiments, the porous base film exhibits diffraction peaks in the X-ray diffraction pattern within the range of 23° < 2θ < 25°. These diffraction peaks in the 23° < 2θ < 25° range represent α-crystal form, which is the filling phase crystallization. α-crystal form refers to another crystal structure type of a substance in the solid state. α-crystal form generally refers to the body-centered cubic crystal system, belonging to the monoclinic crystal system. A higher α-crystal form content makes the filling phase crystallization more conducive to achieving the thermally closed-pore function of the separator. The presence of diffraction peaks in the 23° < 2θ < 25° range of the porous base film is beneficial for achieving the thermally closed-pore function of the separator.

[0076] In some embodiments, in the X-ray diffraction pattern of the porous base film, the porous base film includes a first diffraction peak in the range of 15° < 2θ < 17°, and a second diffraction peak in the range of 23° < 2θ < 25°. The intensity of the first diffraction peak is greater than that of the second diffraction peak. The intensity of the diffraction peaks depends on properties such as the type, content, and relative position of atoms. The position and intensity of the diffraction peaks can reflect the characteristics of the crystal structure, thus serving as a basis for phase identification. The diffraction intensity of each phase increases with its phase content. As mentioned earlier, the diffraction peaks of the porous base film in the range of 15° < 2θ < 17° are β-type diffraction peaks. The higher the β-type content, the higher the overall intensity of the porous base film. The diffraction peaks of the porous base film in the range of 23° < 2θ < 25° are α-type diffraction peaks. The α-type is the filling phase crystallization, which makes the filling phase crystallization beneficial for achieving the thermal pore-closing function of the isolation membrane. The porous base film includes a first diffraction peak in the range of 15° < 2θ < 17°, and a second diffraction peak in the range of 23° < 2θ < 25°. The intensity of the first diffraction peak is greater than that of the second diffraction peak, indicating that the content of the β crystal form of the matrix phase is greater than that of the α crystal form of the filling phase. Therefore, under the premise of high overall strength of the separator, the thermal pore-closing function of the separator can be realized, thereby improving the reliability of the separator.

[0077] In some embodiments, the filler phase comprises α-crystalline grains, and the matrix phase comprises β-crystalline grains. As mentioned earlier, a higher α-crystalline content facilitates the thermal pore-closure function of the separator membrane through filler phase crystallization. A higher β-crystalline content results in higher overall strength of the porous matrix membrane. Therefore, having the filler phase comprise α-crystalline grains and the matrix phase comprise β-crystalline grains allows for the thermal pore-closure function of the separator membrane while maintaining high overall strength, thereby improving the reliability of the separator membrane.

[0078] In some embodiments, the grain size of the filler phase is 0.1 μm-2 μm, optionally 0.1 μm-0.5 μm. For example, the grain size can be 0.1 μm, 0.15 μm, 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.2 μm, 1.4 μm, 1.7 μm, 2 μm, etc., or a range consisting of any two of the above values, such as 0.1 μm-0.15 μm, 0.15 μm-0.3 μm, 0.25 μm-0.4 μm, 0.4 μm-0.5 μm, 0.5 μm-0.9 μm, 0.7 μm-1.4 μm, 1.4 μm-2 μm, etc. Generally speaking, the larger the grain size of the polymer crystals, the higher the melting point. Therefore, by controlling the grain size of the filler phase within the above range, the melting point of the filler phase can be controlled. When the internal temperature of the secondary battery is high, the filler phase melts first due to its low melting point, achieving rapid shutdown, terminating the electrochemical reaction, and preventing the internal temperature of the secondary battery from continuing to rise. At the same time, it enables the separator to have better strength and elongation at break, thereby improving the reliability of the secondary battery.

[0079] In some embodiments, the mass percentage of the filler phase in the substrate is 10%-40%, optionally 15%-25%. For example, the mass percentage of the filler phase in the substrate can be 10%, 12%, 15%, 18%, 20%, 22%, 24%, 25%, 28%, 30%, 35%, 38%, 40%, etc., or a range consisting of any two of the above values, such as 10%-15%, 12%-18%, 15%-22%, 18%-25%, 25%-30%, 35%-38%, 38%-40%, etc. When the mass percentage of the filler phase is too low, when the internal temperature of the secondary battery is high, the amount of melted filler phase is insufficient to seal the pores of the separator. When the mass percentage of the filler phase is too high, the physical strength of the separator cannot be maintained. Therefore, by controlling the mass ratio of the filling phase within the above range, when the internal temperature of the secondary battery is high, a sufficient amount of filling phase melts and seals the pores of the separator, achieving thermal shutdown. At the same time, the matrix phase and the filling phase can balance the physical strength of the separator, thereby improving the reliability of the secondary battery.

[0080] In some embodiments, the relative molecular mass of the filling phase material is less than or equal to 1.2 million, and can be selected from 400,000 to 600,000; the relative molecular mass of the matrix phase material is greater than or equal to 300,000, and can be selected from 300,000 to 2.5 million. The relative molecular mass of the filling phase material can be 200,000, 300,000, 400,000, 450,000, 480,000, 500,000, 550,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, etc., or a range consisting of any two of the above values, such as 200,000-300,000, 300,000-450,000, 450,000-500,000, 500,000-600,000, 600,000-800,000, 800,000-1,000,000, 1,000,000-1,200,000, etc. The relative molecular mass of the matrix phase material can be 300,000, 500,000, 600,000, 750,000, 860,000, 1,000,000, 1,200,000, 1,400,000, 1,650,000, 1,900,000, 2,200,000, 2,500,000, 3,000,000, 4,000,000, or a range of any two of the above values, such as 300,000-600,000, 500,000-750,000, 600,000-1,000,000, 860,000-1,400,000, 1,200,000-1,900,000, 1,650,000-2,200,000, 1,900,000-2,500,000, 2,500,000-4,0 ...

[0081] The relative molecular mass of the separator has a meaning known in the art and can be tested using equipment and methods known in the art. For example, it can be tested using a high-temperature GPC test (differential refractive index detector).

[0082] Smaller molecular weight filler phases have stronger crystallinity and are more easily and stably dispersed within larger molecular weight matrix phases. This reduces the filler phase's sensitivity to high temperatures; that is, after the filler phase is heated, it requires a certain amount of time to conduct heat to the matrix phase. The matrix phase, with its larger molecular weight and greater temperature resistance, transfers heat more slowly and requires a higher temperature (i.e., the pore-closing temperature) to melt and close the pores. The pore-closing temperature refers to the temperature at which the separator pores close. Smaller molecular weight filler phases can achieve higher pore-closing temperatures for the separator. In other words, when the secondary battery temperature abnormally rises to a certain level, the smaller molecular weight filler phase melts, thus sealing the separator pores. By limiting the relative molecular weights of the filler and matrix phases within the aforementioned range, the physical strength of the separator can be balanced, improving the reliability of the secondary battery.

[0083] In some embodiments, the melting peak temperature of the matrix phase is 160℃-350℃, optionally 160℃-180℃; the melting peak temperature of the filler phase is 60℃-180℃, optionally 80℃-130℃. The melting peak temperature of the matrix phase can be 160℃, 165℃, 170℃, 175℃, 180℃, 200℃, 250℃, 300℃, 350℃, etc., or a range consisting of any two of the above values, such as 160℃-170℃, 170℃-175℃, 175℃-200℃, 200℃-300℃, 250℃-350℃, etc. The melting peak temperature of the filler phase can be 60℃, 65℃, 70℃, 75℃, 80℃, 100℃, 110℃, 120℃, 140℃, 160℃, 180℃, or any range of two of the above values, such as 60℃-70℃, 70℃-80℃, 75℃-110℃, 100℃-140℃, 120℃-160℃, 140℃-180℃, etc. Limiting the melting peak temperatures of the matrix phase and the filler phase to these ranges balances the physical strength of the separator while promptly sealing the separator pores when the internal temperature of the secondary battery is high, thereby improving the reliability of the secondary battery.

[0084] In some embodiments, the matrix phase is made of at least one of polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene terephthalate, polyetheretherketone, polyurethane, and polyester; the filler phase is made of at least one of polyethylene and polypropylene. For example, in some embodiments, the matrix phase is made of polytetrafluoroethylene, and the filler phase is made of polyethylene. The porous membrane includes a first diffraction peak and a second diffraction peak in the range of 15° < 2θ < 17°, where the first diffraction peak corresponds to polytetrafluoroethylene and the second diffraction peak corresponds to polyethylene. The intensity of the first diffraction peak is greater than the intensity of the second diffraction peak. For example, in some embodiments, the matrix phase is made of polypropylene, and the filler phase is made of polyethylene. The porous membrane includes a first diffraction peak in the range of 15° < 2θ < 17°, and a second diffraction peak in the range of 23° < 2θ < 25°, where the first diffraction peak corresponds to polypropylene and the second diffraction peak corresponds to polyethylene. The intensity of the first diffraction peak is greater than the intensity of the second diffraction peak. By limiting the materials of the matrix phase and the filler phase to the above range, the material requirements of the separator can be met. When the internal temperature of the secondary battery is high, the filler phase can seal the pores of the separator in time, thereby improving the reliability of the secondary battery.

[0085] In some embodiments, the pore size of the porous base membrane is less than or equal to 0.5 μm, and can be selected as 0.02 μm-0.1 μm. For example, the pore size of the porous base membrane can be 0.01 μm, 0.02 μm, 0.04 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.5 μm, etc., or a range consisting of any two of the above values, such as 0.01 μm-0.04 μm, 0.02 μm-0.06 μm, 0.04 μm-0.1 μm, 0.08 μm-0.3 μm, 0.1 μm-0.35 μm, 0.3 μm-0.5 μm, etc. When the pore size of the porous base membrane is too large, the passage of active material particles can easily cause pore blockage. The porous base membrane has a pore size of less than or equal to 0.5 μm, which can effectively seal the pores after the filling phase melts, achieve thermal shutdown, and improve the reliability of the secondary battery.

[0086] In some embodiments, the separator membrane satisfies at least one of the following (1)-(9):

[0087] (1) The closure temperature of the separator is 120℃-170℃, and can be selected as 120℃-130℃;

[0088] (2) The closure time of the isolation membrane is less than or equal to 10s, and can be selected as 5s-10s;

[0089] (3) The transverse breaking elongation of the separator is ≥100%, and can be selected as 100%-120%;

[0090] (4) The longitudinal elongation at break of the separator is ≥60%, and can be selected as 60%-80%;

[0091] (5) The transverse tensile strength of the separator is ≥1500 kgf / cm 2 2000 kgf / cm² is optional. 2 -4000 kgf / cm 2 ;

[0092] (6) The longitudinal tensile strength of the separator is ≥2000 kgf / cm 2 2000gf / cm can be selected. 2 -4000 kgf / cm 2 ;

[0093] (7) The puncture strength of the isolation membrane is ≥60gf, and can be selected as 120gf-420gf;

[0094] (8) The porosity of the isolation membrane is 30%-90%, and can be selected as 30%-50%;

[0095] (9) The air permeability of the separator is less than or equal to 300sec / 100cc, and can be selected as 100sec / 100cc-300sec / 100cc.

[0096] In some embodiments, the pore-closing temperature of the separator is 120℃-170℃, optionally 120℃-130℃; the pore-closing time of the separator is less than or equal to 10s, optionally 5s-10s. For example, the pore-closing temperature of the separator can be 120℃, 124℃, 130℃, 132℃, 140℃, 146℃, 150℃, 158℃, 163℃, 170℃, etc., or a range consisting of any two of the above values, such as 120℃-130℃, 124℃-140℃, 140℃-150℃, 146℃-158℃, 150℃-170℃, etc. The pore-closing time of the separator can be 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s, etc., or a range consisting of any two of the above values, such as 3s-5s, 4s-7s, 5s-8s, 7s-10s, etc. If the pore-closing temperature of the separator is too high and the pore-closing time is too long, it indicates that the filling phase in the separator needs to reach a certain temperature and time before it can seal the pores in time. If the pore-closing temperature of the separator is too low and the pore-closing time is too short, the filling phase in the separator will close the pores at a lower temperature. When the pore-closing temperature and pore-closing time of the separator are within the above range, it can quickly respond to thermal anomalies and achieve thermal shutdown, thus improving the reliability of the secondary battery.

[0097] The transverse tensile strength (MD), longitudinal tensile strength (TD), transverse elongation at break, and longitudinal elongation at break of the separator all have meanings known in the art and can be measured using methods known in the art. For example, they can all be tested according to the standard GB / T 36363-2018.

[0098] The puncture strength of the separator has a well-known meaning in the art and can be tested using equipment and methods known in the art. For example, puncture strength can be tested according to the standard GB / T 10004-2008. Specifically, the sample to be tested can be cut into strips, with a width of 100 mm. The 100 mm wide sample is mounted on the sample membrane fixing ring, and then a steel needle with a diameter of 1.0 mm and a tip radius of 0.5 mm is used to puncture the sample at a speed of (50±5) mm / min. The maximum load of the steel needle penetrating the sample is read. Usually, five parallel test samples can be taken simultaneously, with three points measured for each sample, and the arithmetic mean is taken as the final puncture strength.

[0099] According to some embodiments, porosity has a well-known meaning in the art and can be tested using known equipment and methods. For example, it can be tested with reference to GB / T 24586-2009. The test method is as follows: the separator or substrate is punched into small circular samples with a diameter of 14 mm, the thickness is measured, and the apparent volume V1 of the separator or substrate is calculated according to the formula for cylindrical volume; referring to GB / T 24586-2009, using an inert gas such as helium or nitrogen as a medium, the true volume V2 of the separator or substrate is measured using a true density meter with the gas displacement method. Then the porosity of the separator or substrate = (V1-V2) / V1×100%. The testing instrument can be the AccuPyc II 1340 fully automatic true density meter from Micromeritics, USA.

[0100] According to some embodiments, the air permeability of the separator can be tested using equipment and methods known in the art. For example, the air permeability of the separator can be determined using the ASTM (Standard Test Method for Resistance of Nonporous Paper to Passage of Air) method. Porosity can be tested using equipment and methods known in the art.

[0101] If the separator meets at least one of (1)-(7) above, it can effectively improve the extensibility of the separator and improve the puncture performance of the separator, thereby further improving the reliability of the secondary battery.

[0102] The second technical solution adopted in this application is: providing a method for preparing the separator membrane as described above. The preparation method includes the following steps:

[0103] S100: The raw materials for forming the matrix phase, the raw materials for forming the filler phase, and the nucleating agent are mixed to form a precursor, wherein the crystallization temperature of the raw materials for forming the filler phase is lower than the crystallization temperature of the raw materials for forming the matrix phase.

[0104] The raw materials forming the matrix phase include at least one selected from polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene terephthalate, polyetheretherketone, polyurethane, and polyester; the raw materials forming the filler phase include at least one selected from polyethylene and polypropylene. For example, in some embodiments, the matrix phase is made of polypropylene, and the filler phase is made of polyethylene.

[0105] Nucleating agents may include α-crystalline nucleating agents. There are no particular limitations on α-crystalline nucleating agents; various existing and known α-crystalline nucleating agents can be used, and one or more α-crystalline nucleating agents may be used in combination.

[0106] Alpha nucleating agents include inorganic alpha nucleating agents and organic alpha nucleating agents.

[0107] Inorganic α-crystalline nucleating agents mainly include talc, calcium oxide, carbon black, calcium carbonate, mica, inorganic pigments, kaolin, and catalyst residues.

[0108] Organic α-crystalline nucleating agents may include at least one of aromatic acid metal soap α-nucleating agents, sorbitol α-nucleating agents, rosin α-nucleating agents, and organophosphate α-nucleating agents.

[0109] Aromatic acid metal soap α-nucleating agents may include at least one of the following: sodium benzoate, aluminum benzoate, and aluminum p-tert-butylbenzoate, all metal salts of aromatic carboxylic acids. Sorbitol α-nucleating agents may include at least one of the following: dibenzylpyridinium sorbitol, substituted dibenzylpyridinium sorbitol, 1,3:2,4-di-p-methylbenzylpyridinium sorbitol, and di-(3,4-dimethyldibenzylpyridinium)sorbitol. Rosin α-nucleating agents may include at least one of the following: dehydroabsicoic acid, abirate rosinate, a mixture of abietic acid and its salts, and abiamide. Organophosphate α-nucleating agents may include at least one of the following: organophosphate esters, basic metal salts of organophosphates, and their complexes.

[0110] Nucleating agents may include β-crystalline nucleating agents. There are no particular limitations on β-crystalline nucleating agents; various existing and known β-crystalline nucleating agents can be used, and one or more β-crystalline nucleating agents may be used in combination.

[0111] β-crystal nucleating agents include inorganic oxide β-nucleating agents, inorganic salt β-nucleating agents, polycyclic aromatic hydrocarbon β-nucleating agents, organic carboxylic acids and their salts β-nucleating agents, aromatic amide β-nucleating agents, and rare earth β-nucleating agents, etc.

[0112] Inorganic oxide β-nucleating agents may include at least one of oxides of Group IIA metals in the periodic table and aluminum oxide. Inorganic salt β-nucleating agents may include at least one of calcium silicate, calcium carbonate, and calcium sulfate. Polycyclic aromatic hydrocarbon β-nucleating agents may include at least one of quinacridone quinone, triphenyldiazepine, and diazo yellow. Organic carboxylic acid β-nucleating agents may include at least one of dibenzoylhydrazine adipate and octanoic acid. Organic carboxylic acid salt β-nucleating agents may include at least one of calcium tetrahydrophthalate, calcium octanoate, calcium pimecrolate, calcium polycarboxylate, and zinc polycarboxylate. Aromatic amide β-nucleating agents may include at least one of cyclohexylamide 2,6-phthalic acid, cyclohexylamide 2,6-naphthalenedicarboxylate, and aryldicarboxamide. Rare earth β-nucleating agents may include at least one of rare earth lanthanide mononuclear metal compounds, rare earth multi-component complexes, and binuclear complexes formed by rare earth elements and Group IIA metals.

[0113] Nucleating agents are used to form crystals in the matrix phase. Higher crystallization temperatures result in faster crystallization. If the crystallization temperature of the filler phase is lower than that of the matrix phase, the filler phase crystallizes preferentially over the matrix phase.

[0114] S200: The precursor is extruded to form the first intermediate product.

[0115] S300: The first intermediate product is cast into a sheet to form the second intermediate product.

[0116] The casting process includes a first temperature stage and a second temperature stage, where the casting temperature in the first temperature stage is higher than that in the second temperature stage.

[0117] S400: Stretch treatment of the second intermediate product.

[0118] In the technical solution of this application embodiment, the raw materials for forming the matrix phase, the raw materials for forming the filler phase, and the nucleating agent are mixed. The crystallization temperature of the filler phase raw material is lower than that of the matrix phase raw material. In conventional casting processing, using only one temperature will result in homogeneous crystals, exhibiting only one melting peak. However, in the casting processing provided in this application embodiment, a casting process is adopted where the casting temperature in the first temperature stage is higher than that in the second temperature stage. This allows the matrix phase raw material to crystallize first, followed by the filler phase raw material, with the filler phase dispersed within the matrix phase, thus exhibiting two melting peaks. After stretching, a porous separator is formed. The melting peak temperature of the matrix phase in the separator is higher than that of the filler phase, indicating better thermal stability of the matrix phase. Therefore, when the internal temperature of the secondary battery is high, the filler phase, due to its poorer thermal stability, melts first, promptly sealing the pores of the separator, terminating the electrochemical reaction, preventing further increases in the internal temperature of the secondary battery, and improving the reliability of the secondary battery.

[0119] In some embodiments, the melt index of the filler phase material is greater than the melt index of the matrix phase material, and the ratio between the two is 1.1-10.1, optionally 1.1-2.1. For example, the ratio of the melt index of the filler phase material to the melt index of the matrix phase material is 1.1, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, etc., or a range consisting of any two of the above values, such as 1.1-1.5, 1.4-1.6, 1.5-1.8, 1.7-2.0, 1.9-2.1, etc. Melt flow index (MFI) is a numerical value indicating the flowability of plastic materials during processing. It was developed by the American Society for Measurement Standards (ASTM) based on a method commonly used by DuPont to assess plastic properties. The test method involves melting plastic granules into a fluid, then passing the fluid through a 2.1mm diameter tube for a specified time (10 minutes) at specific temperatures and pressures (which vary depending on the material standard). The higher the MFI, the better the flowability of the plastic material, and vice versa. When the filler phase has a higher MFI than the matrix phase, and the ratio is kept within the specified range, the matrix phase exhibits better thermal stability. When the internal temperature of the secondary battery is high, the filler phase melts first, effectively sealing the pores of the separator membrane, terminating the electrochemical reaction, and preventing the internal temperature of the secondary battery from rising further, thus improving the reliability of the secondary battery.

[0120] In some embodiments, the crystallization temperature of the filler phase material is 80℃-120℃, optionally 80℃-100℃; the crystallization temperature of the matrix phase material is 125℃-135℃, optionally 125℃-130℃. By limiting the crystallization temperatures of the filler phase material and the matrix phase material to the above ranges, the melting peak temperature of the matrix phase is higher than that of the filler phase. When the internal temperature of the secondary battery is high, the filler phase melts first, thereby promptly sealing the pores of the separator membrane, terminating the electrochemical reaction, preventing the internal temperature of the secondary battery from continuing to rise, and improving the reliability of the secondary battery.

[0121] In some embodiments, the casting temperature in the first temperature stage is 125℃-135℃, optionally 125℃-130℃; the casting temperature in the second temperature stage is 105℃-125℃, optionally 105℃-110℃; optionally, the difference between the casting temperature in the first temperature stage and the casting temperature in the second temperature stage is 10℃-20℃. For example, in some embodiments, the casting temperature in the first temperature stage can be 125℃, 126℃, 128℃, 130℃, 131℃, 133℃, 135℃, etc., or a range of any of the above values, such as 125℃-126℃, 126℃-130℃, 130℃-133℃, 133℃-135℃, etc. In some embodiments, the casting temperature of the second temperature stage can be 105°C, 108°C, 110°C, 115°C, 118°C, 120°C, 122°C, 125°C, etc., or a range of any of the above values, such as 105°C-110°C, 108°C-115°C, 115°C-120°C, 120°C-125°C, etc. In some embodiments, the difference between the casting temperature of the first temperature stage and the casting temperature of the second temperature stage is 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, or a range of any of the above values, such as 10°C-12°C, 12°C-16°C, 16°C-20°C, etc. The filler phase has a higher crystallization temperature. In the first temperature stage, it preferentially crystallizes and separates from the matrix phase, while in the second temperature stage, the matrix phase has the highest crystallization rate and is fully crystallized. Limiting the casting temperature within the above range allows the separator film to fully crystallize and form both the filler phase and the matrix phase.

[0122] In some embodiments, during the stretching process of the second intermediate product, the transverse stretching temperature is 110℃-120℃, optionally 110℃-115℃; the longitudinal stretching temperature is 85℃-120℃, optionally 110℃-120℃. For example, in some embodiments, the transverse stretching temperature can be 110℃, 112℃, 114℃, 115℃, 116℃, 118℃, 120℃, etc., or any range of the above values, such as 110℃-114℃, 112℃-115℃, 115℃-118℃, 116℃-120℃, etc. In some embodiments, the longitudinal stretching temperature can be 85°C, 90°C, 95°C, 100°C, 104°C, 110°C, 115°C, 120°C, or any range of the above values, such as 85°C-90°C, 90°C-104°C, 100°C-115°C, 115°C-120°C, etc. By limiting the transverse and longitudinal stretching temperatures within the above ranges during the stretching process of the second intermediate product, the resulting separator film can have better performance.

[0123] [Positive electrode plate]

[0124] In a secondary battery, the positive electrode typically includes a positive current collector and a positive electrode film layer disposed on the positive current collector, the positive electrode film layer including a positive active material.

[0125] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal material on a polymer substrate). As an example, the positive electrode current collector can be aluminum foil.

[0126] The specific type of positive electrode active material is not limited. Any active material known in the art that can be used as the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0127] As examples, positive electrode active materials may include, but are not limited to, one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. All of these materials are commercially available.

[0128] The modified compounds for the above materials can be used to modify the materials by doping and / or by surface coating.

[0129] The positive electrode film layer typically includes binders, conductive agents, and other optional additives.

[0130] As an example, the conductive agent can be one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P, SP), graphene, and carbon nanofibers.

[0131] As an example, the adhesive may be one or more of the following: polymerized styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0132] [Negative electrode plate]

[0133] In a secondary battery, the negative electrode typically includes a negative current collector and a negative electrode film layer disposed on the negative current collector, the negative electrode film layer including a negative electrode active material.

[0134] The negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a composite current collector can be formed by setting a metal material on a polymer substrate). As an example, the negative electrode current collector can be a copper foil.

[0135] The specific type of negative electrode active material is not limited; any active material known in the art that can be used as the negative electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials, and tin-based materials. Silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds (e.g., silicon suboxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. All of these materials are commercially available.

[0136] In some implementations, the negative electrode active material may include a silicon-based material in order to further improve the energy density of the battery.

[0137] The negative electrode film layer typically includes binders, conductive agents, and other optional additives.

[0138] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0139] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0140] As an example, other optional additives could be thickeners and dispersants (such as sodium carboxymethyl cellulose).

[0141] Carboxymethylcellulose Sodium (CMC-Na) and PTC thermistor materials.

[0142] Electrolyte

[0143] A secondary battery may include an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte may include an electrolyte salt and a solvent.

[0144] As an example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0145] As an example, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl ethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), diisopropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (n-Propyl Acetate (PA), methyl propionate (MP), and ethyl propionate (Ethyl... One or more of the following: Propanoate (EP), n-PropylPropionate (PP), Methyl Butyrate (MB), Ethyl Butyrate (EB), 1,4-Butyrolactone (GBL), Tetramethylene Sulfone (SF), Methyl Sulfone (MSM), Methyl Ethyl Sulfone (EMS), and Diethyl Sulfone (ESE).

[0146] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0147] In some embodiments, the secondary battery can be a lithium-ion secondary battery. When the porous coating 13 is located between the first porous base film 11 and the first porous base film 12, the adhesive 14 not only serves to bond the first porous base film 11 and the first porous base film 12, but also at least a portion of the filler particles 15 are embedded in the first porous base film 11 and / or the second porous base film 12 to a depth greater than or equal to 1 μm, which increases the bonding force between the porous coating 13 and the first porous base film 11 and the first porous base film 12, thereby improving the reliability of the secondary battery.

[0148] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 4 shows a square-structured secondary battery 5 as an example.

[0149] In some embodiments, the secondary battery may include an outer packaging. This outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0150] In some embodiments, the outer packaging of the secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic, including one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0151] In some embodiments, referring to FIG5, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is capable of covering the opening to close the receiving cavity.

[0152] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator 10, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator 10, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0153] Figure 6 shows a battery module 4 as an example. Referring to Figure 6, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0154] The battery module 4 may also include a housing with a receiving space in which multiple secondary batteries 5 are received.

[0155] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0156] Figures 7 and 8 show a battery pack 1 as an example. Referring to Figures 7 and 8, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0157] [Device]

[0158] This application also provides an electrical device, which includes the secondary battery of this application. A single battery cell, battery module, or battery pack can serve as a power source for the device, or as an energy storage unit. The device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, and energy storage systems.

[0159] The device can be configured to use individual battery cells, battery modules, or battery packs depending on its application requirements.

[0160] Figure 7 shows an example of an electrical device 6. This electrical device 6 can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this electrical device 6, a battery pack or battery module can be used.

[0161] As another example, the power device 6 could be a mobile phone, tablet, or laptop. This power device typically requires a slim and lightweight design and can use a single battery cell as its power source.

[0162] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0163] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0164] I. Preparation of the separating membrane

[0165] Example 1

[0166] The raw materials provided are polyethylene with a crystallization temperature of 127℃ and polypropylene with a crystallization temperature of 114℃. The nucleating agent is calcium carbonate. They are mixed to form a precursor. After the precursor is extruded and molded, it is subjected to casting treatment. The temperature of the first temperature stage is 135℃, the temperature of the second temperature stage is 120℃, and stretching treatment is performed.

[0167] The preparation processes of Examples 2-16 and Comparative Examples 1-2 are similar, except that the raw material composition, nucleating agent, and casting were adjusted. Please refer to Table 1.

[0168] II. For the performance test of the separator membrane, please refer to Table 2.

[0169] (1) Closed-cell temperature

[0170] 1. Sample preparation: Cut the separator membrane samples into 50mm*100mm shapes, with at least 20 pieces per group.

[0171] 2. Testing: Place the sample in an oven and heat it from room temperature to 110°C. Then take it out and test its air permeability. Test the air permeability every 1°C increase in temperature and record the air permeability change curve with temperature. Record the temperature point where the air permeability changes abruptly as the closure temperature.

[0172] (2) Closure time

[0173] 1. Sample preparation: Cut the separator membrane samples into 50mm*100mm shapes, with at least 20 pieces per group.

[0174] 2. Testing: Place the sample in an oven and heat it from room temperature to the closed-cell temperature. Then, take it out at regular intervals to test its air permeability. Record the change curve of air permeability over time. The time point when the air permeability changes abruptly is recorded as the closed-cell time.

[0175]

[0176]

[0177]

[0178] As shown in Table 1, compared with Comparative Examples 1-2, Examples 1-16 satisfy the requirement that the porous base membrane includes a matrix phase and a filling phase dispersed in the matrix phase. The differential scanning calorimeter test curve of the porous base membrane simultaneously includes the melting peak of the matrix phase and the melting peak of the filling phase, and the temperature of the melting peak of the matrix phase is higher than that of the melting peak of the filling phase. Therefore, the performance data of Examples 1-16 are better than those of Comparative Examples 1-2.

[0179] Compared with Examples 3-9, Examples 1-2 show that when the ratio of the peak area of ​​the melting peak of the matrix phase to the peak area of ​​the melting peak of the filling phase is greater than 1, the performance data of Examples 3-9 need to be better than those of Examples 1-2.

[0180] Compared with Examples 5-8, Examples 1-4 and 9 show that when the ratio of the peak area of ​​the melting peak of the matrix phase to the peak area of ​​the melting peak of the filling phase is 1.2-2.0, the performance data of Examples 1-4 and 9 are better than those of Examples 5-8.

[0181] Compared with Examples 10 and 11, Examples 6, 7, and 12 show that when the porous base film has diffraction peaks in the range of 15° < 2θ < 17°, the performance data of Examples 6, 7, and 12 are better than those of Examples 10 and 11.

[0182] Compared with Example 11, Examples 6, 7, 10, and 12 show that when the porous base film has diffraction peaks in the range of 23° < 2θ < 25°, the performance data of Examples 6, 7, 10, and 12 are better than those of Example 11.

[0183] Compared with Examples 10-12, Examples 6 and 7 show that the porous base film includes a first diffraction peak in the range of 15° < 2θ < 17° and a second diffraction peak in the range of 23° < 2θ < 25°. When the diffraction peak intensity of the first diffraction peak is greater than that of the second diffraction peak, the performance data of Examples 6 and 7 are better than those of Examples 10-12.

[0184] In summary, the separator provided in this application includes a porous base membrane, which comprises a matrix phase and a filling phase dispersed within the matrix phase. The differential scanning calorimeter (DSC) test curve of the porous base membrane simultaneously includes melting peaks of both the matrix phase and the filling phase, with the temperature of the matrix phase melting peak being higher than that of the filling phase. The higher temperature of the matrix phase melting peak indicates that the matrix phase has better thermal stability than the filling phase. Therefore, when the internal temperature of the secondary battery is high, the filling phase, due to its lower thermal stability, melts first, thus promptly sealing the pores of the separator membrane, terminating the electrochemical reaction, preventing the internal temperature of the secondary battery from continuing to rise, and improving the reliability of the secondary battery.

[0185] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A separating membrane comprising a porous base membrane, the porous base membrane comprising a matrix phase and a filling phase dispersed in the matrix phase, wherein the differential scanning calorimeter test curve of the porous base membrane simultaneously includes a melting peak of the matrix phase and a melting peak of the filling phase, and the temperature of the melting peak of the matrix phase is higher than the temperature of the melting peak of the filling phase.

2. The separator membrane as described in claim 1, characterized in that, The ratio of the peak area of ​​the melting peak of the matrix phase to the peak area of ​​the melting peak of the filling phase is greater than 1.

3. The separator membrane as described in claim 1, characterized in that, The ratio of the peak area of ​​the melting peak of the matrix phase to the peak area of ​​the melting peak of the filling phase is 1.2-2.

0.

4. The separator membrane as described in claim 1, characterized in that, In the X-ray diffraction pattern of the porous base film, the porous base film has diffraction peaks in the range of 15° < 2θ < 17°.

5. The separator membrane as described in claim 1, characterized in that, In the X-ray diffraction pattern of the porous base film, the porous base film has diffraction peaks in the range of 23° < 2θ < 25°.

6. The separator membrane as described in claim 1, characterized in that, In the X-ray diffraction pattern of the porous base film, the porous base film includes a first diffraction peak in the range of 15° < 2θ < 17°, and the porous base film includes a second diffraction peak in the range of 23° < 2θ < 25°, wherein the intensity of the first diffraction peak is greater than the intensity of the second diffraction peak.

7. The separator membrane as described in claim 1, characterized in that, The filling phase comprises α-type grains; and / or, the matrix phase comprises β-type grains.

8. The separator membrane according to any one of claims 1-7, characterized in that, The grain size of the filling phase is 0.1µm-2µm.

9. The separator membrane according to any one of claims 1-7, characterized in that, The grain size of the filling phase is 0.1µm-0.5µm.

10. The separator membrane according to any one of claims 1-7, characterized in that, The filler phase accounts for 10%-40% of the mass of the substrate.

11. The separator membrane according to any one of claims 1-7, characterized in that, The filler phase accounts for 15%-25% of the mass of the substrate.

12. The separator membrane according to any one of claims 1-7, characterized in that, The relative molecular mass of the filling phase is less than or equal to 1.2 million; and / or the relative molecular mass of the matrix phase is greater than or equal to 300,000.

13. The separator membrane according to any one of claims 1-7, characterized in that, The relative molecular mass of the filling phase is 400,000 to 600,000; and / or the relative molecular mass of the matrix phase is 300,000 to 2,500,000.

14. The separator membrane according to any one of claims 1-7, characterized in that, The melting peak temperature of the matrix phase is 160℃-350℃; and / or, the melting peak temperature of the filler phase is 60℃-180℃.

15. The separator membrane according to any one of claims 1-7, characterized in that, The melting peak temperature of the matrix phase is 160℃-180℃; and / or, the melting peak temperature of the filling phase is 80℃-130℃.

16. The separator membrane according to any one of claims 1-7, characterized in that, The matrix phase is made of at least one of polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene terephthalate, polyetheretherketone, polyurethane, and polyester; and / or the filler phase is made of at least one of polyethylene and polypropylene.

17. The separator membrane according to any one of claims 1-7, characterized in that, The porous base membrane has a pore size of less than or equal to 0.5 µm.

18. The separator membrane according to any one of claims 1-7, characterized in that, The porous base membrane has a pore size of 0.02µm-0.1µm.

19. The separator membrane according to any one of claims 1-7, characterized in that, The separator membrane satisfies at least one of the following (1)-(9): (1) the closure temperature of the separator membrane is 120℃-170℃; (2) the closure time of the separator membrane is less than or equal to 10 s; (3) the transverse elongation at break of the separator membrane is ≥100%; (4) the longitudinal elongation at break of the separator membrane is ≥60%; (5) the transverse tensile strength of the separator membrane is ≥1500 kgf / cm 2 (6) The longitudinal tensile strength of the separator is ≥2000 kgf / cm. 2 (7) The puncture strength of the isolation membrane is ≥60gf; (8) The porosity of the isolation membrane is 30%-90%; (9) The air permeability of the isolation membrane is less than or equal to 300sec / 100cc.

20. The separator membrane according to any one of claims 1-7, characterized in that, The separator membrane satisfies at least one of the following (1)-(9): (1) the closure temperature of the separator membrane is 120℃-130℃; (2) the closure time of the separator membrane is 5 s-10 s; (3) the transverse elongation at break of the separator membrane is 100%-120%; (4) the longitudinal elongation at break of the separator membrane is 60%-80%; (5) the transverse tensile strength of the separator membrane is 2000 kgf / cm. 2 -4000 kgf / cm 2 (6) The longitudinal tensile strength of the separator is 2000 gf / cm. 2 -4000 kgf / cm 2 (7) The puncture strength of the isolation membrane is 120gf-420gf; (8) The porosity of the isolation membrane is 30%-50%; (9) The air permeability of the isolation membrane is 100sec / 100cc-300sec / 100cc.

21. A method for preparing a separator membrane according to any one of claims 1-20, characterized in that, include: A precursor is formed by mixing raw materials for forming the matrix phase, raw materials for forming the filler phase, and a nucleating agent, wherein the crystallization temperature of the raw materials forming the filler phase is lower than the crystallization temperature of the raw materials forming the matrix phase; the precursor is extruded to form a first intermediate product; the first intermediate product is cast to form a second intermediate product, wherein the casting process includes a first temperature stage and a second temperature stage, the casting temperature of the first temperature stage being higher than the casting temperature of the second temperature stage; and the second intermediate product is stretched to obtain a porous base film; wherein the porous base film includes a matrix phase and a filler phase dispersed in the matrix phase, and the differential scanning calorimeter test curve of the porous base film simultaneously includes the melting peak of the matrix phase and the melting peak of the filler phase, and the temperature of the melting peak of the matrix phase is higher than the temperature of the melting peak of the filler phase.

22. The method for preparing the separator membrane according to claim 21, characterized in that, The melt index of the filler phase raw material is greater than that of the matrix phase raw material.

23. The method for preparing the separator membrane according to claim 21, characterized in that, The ratio of the melt index of the filler phase raw material to the melt index of the matrix phase raw material is equal to 1.1-10.

1.

24. The method for preparing the separator membrane according to claim 21, characterized in that, The ratio of the melt index of the filler phase raw material to the melt index of the matrix phase raw material is 1.1-2.

1.

25. The method for preparing the separator membrane according to any one of claims 21-24, characterized in that, The crystallization temperature of the filler phase raw material is 80℃-120℃; and / or, the crystallization temperature of the matrix phase raw material is 125℃-135℃.

26. The method for preparing the separator membrane according to any one of claims 21-24, characterized in that, The crystallization temperature of the filler phase raw material is 80℃-100℃; and / or, the crystallization temperature of the matrix phase raw material is 125℃-130℃.

27. The method for preparing the separator membrane according to any one of claims 21-24, characterized in that, The casting temperature in the first temperature stage is 125℃-135℃; and / or, the casting temperature in the second temperature stage is 105℃-125℃; and / or, the difference between the casting temperature in the first temperature stage and the casting temperature in the second temperature stage is 10℃-20℃.

28. The method for preparing the separator membrane according to any one of claims 21-24, characterized in that, The casting temperature in the first temperature stage is 125℃-130℃; and / or, the casting temperature in the second temperature stage is 105℃-110℃; and / or, the difference between the casting temperature in the first temperature stage and the casting temperature in the second temperature stage is 10℃-20℃.

29. The method for preparing the separator membrane according to any one of claims 21-24, characterized in that, In the step of stretching the second intermediate product, the transverse stretching temperature is 110°C-120°C; and / or the longitudinal stretching temperature is 85°C-120°C.

30. The method for preparing the separator membrane according to any one of claims 21-24, characterized in that, In the step of stretching the second intermediate product, the transverse stretching temperature is 110℃-115℃; and / or, the longitudinal stretching temperature is 110℃-120℃.

31. A secondary battery, comprising a separator as described in any one of claims 1-20 or a separator prepared by a method for preparing a separator as described in any one of claims 21-30, wherein the secondary battery comprises a positive electrode and a negative electrode, and the separator is disposed between the positive electrode and the negative electrode.

32. An electrical device comprising the secondary battery as described in claim 31.

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