Separator, battery cell, battery, and electric device

Abstract

The present application discloses a separator, a battery cell, a battery, and an electric device. The separator comprises a porous base material and a ferroelectric coating located on at least one surface of the porous base material. The ferroelectric coating comprises a ferroelectric material. The ferroelectric material comprises an inorganic ferroelectric and a ferroelectric polymer. The ferroelectric polymer comprises polyvinylidene fluoride and a copolymer thereof, the ferroelectric polymer comprises β-phase polyvinylidene fluoride, and the content of the β-phase polyvinylidene fluoride in the ferroelectric polymer is greater than or equal to 60%. The separator can slow the continuous growth of dendrites in a direction perpendicular to an electrode sheet, reduce internal short circuits of the battery and improve the reliability of the battery, and can further improve the coulombic efficiency and rate performance of the battery.

Description

Separator, battery cell, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311276950.2, filed on September 28, 2023, entitled “Separation membrane, battery cell, battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to an isolation film, a battery cell, a battery and an electrical device. Background Art

[0004] In recent years, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in consumer electronics, power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. With the application and promotion of batteries, their reliability has received more and more attention. During the battery charging and discharging process, the dendrite problem on the negative electrode is one of the important reasons affecting the reliability and service life of the battery. How to slow down the growth of dendrites without affecting the performance of the battery is a technical problem that needs to be solved urgently. The above statements are only used to provide background technical information related to this application and do not necessarily constitute prior art.

[0005] Summary of the Invention

[0006] The present application provides an isolation membrane, a battery cell, a battery and an electrical device. The isolation membrane can slow down the continuous growth of dendrites in the direction perpendicular to the pole piece, reduce internal short circuits in the battery, improve the reliability of the battery, and also improve the coulombic efficiency and rate performance of the battery.

[0007] In a first aspect, the present application provides an isolation membrane comprising a porous substrate and a ferroelectric coating disposed on at least one surface of the porous substrate. The ferroelectric coating comprises a ferroelectric material, wherein the ferroelectric material comprises an inorganic ferroelectric and a ferroelectric polymer, wherein the ferroelectric polymer comprises polyvinylidene fluoride and a copolymer thereof, wherein the ferroelectric polymer comprises β-phase polyvinylidene fluoride, and wherein the content of the β-phase polyvinylidene fluoride in the ferroelectric polymer is greater than or equal to 60%.

[0008] The ferroelectric polymer provided in the embodiment of the present application can not only act as a binder, but also have a high dielectric constant ε r , which can also slow down the continuous growth of dendrites in the direction perpendicular to the electrode and reduce the internal short circuit of the battery. When applied to batteries, it can improve the reliability, coulombic efficiency and rate performance of the battery.

[0009] In any embodiment, the content of β-phase polyvinylidene fluoride in the ferroelectric polymer is greater than or equal to 80%, and can be optionally greater than or equal to 90%.

[0010] This can further slow down the continuous growth of dendrites in the direction perpendicular to the electrode, reduce internal short circuits in the battery, and improve the coulombic efficiency and rate performance of the battery.

[0011] In any embodiment, the dielectric constant ε of the ferroelectric coating is r Greater than the dielectric constant ε of the inorganic ferroelectric r Optionally, the dielectric constant ε of the ferroelectric coating is r The dielectric constant ε of the inorganic ferroelectric r The ratio is greater than or equal to 1.6, and can be optionally greater than or equal to 2.0.

[0012] This can further slow down the continuous growth of dendrites in the direction perpendicular to the electrode, reduce internal short circuits in the battery, and improve the coulombic efficiency and rate performance of the battery.

[0013] In any embodiment, the dielectric constant ε of the inorganic ferroelectric r greater than the dielectric constant ε of the ferroelectric polymer r .

[0014] In any embodiment, the dielectric constant ε of the inorganic ferroelectric r It is 200-8000, and can be selected as 2000-6000.

[0015] In any embodiment, the dielectric constant ε of the ferroelectric polymer is r The range is 5-100, and the optional range is 8-70.

[0016] In any embodiment, at least a portion of the ferroelectric polymer is located on at least a portion of the surface of the inorganic ferroelectric.

[0017] When the ferroelectric polymer is located on at least part of the surface of the inorganic ferroelectric, it can further reduce the probability of the ferroelectric coating losing its ferroelectricity due to the ferroelectric-paraelectric transition of the inorganic ferroelectric during the preparation of the isolation film, thereby better slowing down the continuous growth of dendrites in the direction perpendicular to the electrode, and also helping to improve the coulombic efficiency of the battery. When the ferroelectric polymer is located on at least part of the surface of the inorganic ferroelectric, it can also help to reduce the dielectric constant ε of the ferroelectric coating. r The dielectric constant ε is greater than that of inorganic ferroelectrics r , which is larger than the dielectric constant ε of the ferroelectric polymer r .

[0018] In any embodiment, the weight content of the inorganic ferroelectric in the ferroelectric material is 80%-99%, optionally 85%-95%.

[0019] In any embodiment, the weight content of the ferroelectric polymer in the ferroelectric material is 1%-20%, optionally 5%-15%.

[0020] By adjusting the weight content of the inorganic ferroelectric and ferroelectric polymer in the ferroelectric material within the above range, the dielectric constant ε of the ferroelectric coating can be increased. r , so that the dielectric constant ε of the ferroelectric coating r The dielectric constant ε is greater than that of inorganic ferroelectrics r , which is larger than the dielectric constant ε of the ferroelectric polymer r , which can better slow down the continuous growth of dendrites in the direction perpendicular to the electrode, reduce internal short circuits in the battery, and improve battery reliability and Coulomb efficiency; in addition, it can also increase the adhesion between the ferroelectric coating and the porous structure.

[0021] In any embodiment, the Curie point temperature of the ferroelectric polymer is 150°C-250°C, optionally 160°C-200°C.

[0022] In any embodiment, the remanent polarization of the ferroelectric polymer is 10 mC / m 2 -1000mC / m 2 , optional 20mC / m 2 -800mC / m 2 .

[0023] In any embodiment, the weight average molecular weight of the ferroelectric polymer is 200,000-800,000, and can be optionally 400,000-650,000.

[0024] The weight average molecular weight of the ferroelectric polymer is within the above range, which can make the ferroelectric polymer have appropriate crystallinity, appropriate Curie point temperature, and higher dielectric constant ε r , and can also make the ferroelectric polymer have suitable viscosity.

[0025] In any embodiment, the melting temperature of the ferroelectric polymer is 140°C-220°C, optionally 143°C-200°C.

[0026] The melting point of the ferroelectric polymer is within the above range, which can make the ferroelectric polymer have appropriate crystallinity, appropriate Curie point temperature, and higher dielectric constant ε r , and can also make the ferroelectric polymer have suitable viscosity.

[0027] In any embodiment, the crystallinity of the ferroelectric polymer is greater than or equal to 45%, and can be optionally 45%-68%. When the crystallinity of the ferroelectric polymer is within the above range, the thermal shrinkage of the isolation membrane can be reduced and the mechanical strength of the isolation membrane can be improved.

[0028] In any embodiment, the Curie point temperature of the inorganic ferroelectric is 110°C-150°C, and can be optionally 120°C-140°C.

[0029] In any embodiment, the ferroelectric polymer includes one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride monomer and other monomers.

[0030] Optionally, the other monomers include one or more of trifluoroethylene, chlorotrifluoroethylene, fluorinated acetylene, and hexafluoropropylene.

[0031] Optionally, the copolymer of the vinylidene fluoride monomer and other monomers includes one or more of vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene-fluorinated acetylene copolymer, and vinylidene fluoride-hexafluoropropylene copolymer.

[0032] In any embodiment, the inorganic ferroelectric includes one or more of a perovskite type, a tungsten bronze type, a bismuth layered type, a pyrochlore type, a niobate type, and a lead barium lithium niobate.

[0033] In any embodiment, the volume distribution particle size Dv50 of the inorganic ferroelectric is 0.05 μm-5 μm, and can be optionally 0.1 μm-1 μm.

[0034] When the volume distribution particle size Dv50 of the inorganic ferroelectric is within the above range, the ferroelectric coating slurry can have a suitable viscosity, which is convenient for coating and can improve the uniformity and consistency of the ferroelectric coating; it can also increase the adhesion between the ferroelectric coating and the porous body and reduce the "powder falling" phenomenon; in addition, it can also reduce the pore blocking problem and improve the air permeability and ion transmission properties of the isolation membrane.

[0035] In any embodiment, the volume distribution particle size Dv50 of the ferroelectric polymer is 10 nm-150 nm, and can be optionally 15 nm-50 nm.

[0036] In any embodiment, the thickness of the ferroelectric coating is 1 μm-3.5 μm, and optionally 1.5 μm-3 μm, thereby enabling the battery to have high reliability, high coulombic efficiency, and good rate performance.

[0037] In any embodiment, the surface density of the ferroelectric coating is 2.5 g / m 2 -15g / m 2 , 3g / m2 is optional 2 -12g / m 2 This allows the battery to have high reliability, high coulombic efficiency and good rate performance.

[0038] In any embodiment, the ferroelectric coating further comprises a dispersant and / or a thickener,

[0039] In any embodiment, the dispersant includes one or more of hydrolyzed polymaleic anhydride, polyacrylic acid, acrylic acid block copolymers, polyester block copolymers, polyethylene glycol-type polyols, polyethyleneimine, and derivatives thereof.

[0040] In any embodiment, the ratio of the total weight of the ferroelectric material to the weight of the dispersant is 1:(0.01-0.02), and can be optionally 1:(0.010-0.015).

[0041] An appropriate amount of dispersant can make the ferroelectric coating slurry dispersed evenly, facilitate coating, and also help to increase the film weight of the ferroelectric coating.

[0042] In any embodiment, the thickener includes one or more of sodium hydroxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxypropyl methylcellulose, polyacrylate, polyurethane, and polyether.

[0043] In any embodiment, the ratio of the total weight of the ferroelectric material to the weight of the thickener is 1:(0.01-0.02), and can be optionally 1:(0.010-0.015).

[0044] An appropriate amount of thickener can improve the stability of the ferroelectric coating slurry, facilitate coating, and also help increase the film weight of the ferroelectric coating.

[0045] In any embodiment, the ferroelectric coating is located on one surface of the porous substrate, and a ceramic coating is provided on the other surface of the porous substrate. When used in a battery, the ferroelectric coating faces the negative electrode, and the ceramic coating faces the positive electrode.

[0046] In any embodiment, the thickness of the porous substrate is 4 μm-15 μm, optionally 5 μm-10 μm.

[0047] In any embodiment, the porous substrate comprises one or more of polyolefins, halogenated polyolefins, polyamides, polyesters, and derivatives thereof.

[0048] A second aspect of the present application provides a battery cell, which includes the isolation membrane of the first aspect of the present application.

[0049] A third aspect of the present application provides a battery, which includes the battery cell of the third aspect of the present application.

[0050] A fourth aspect of the present application provides an electrical device comprising the battery according to the third aspect of the present application.

[0051] The electric device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0053] FIG1 is a schematic diagram of a battery cell provided by some embodiments of the present application.

[0054] FIG2 shows an exploded schematic diagram of a battery cell provided in some embodiments of the present application.

[0055] FIG3 shows a schematic diagram of a battery module provided in some embodiments of the present application.

[0056] FIG4 shows a schematic diagram of a battery pack provided in some embodiments of the present application.

[0057] FIG5 is an exploded schematic diagram of the battery pack shown in FIG4 .

[0058] FIG6 is a schematic diagram of an isolation membrane provided in some embodiments of the present application.

[0059] FIG7 shows schematic diagrams of isolation membranes provided in other embodiments of the present application.

[0060] FIG8 shows a schematic diagram of an isolation membrane provided in some other embodiments of the present application.

[0061] FIG9 shows a schematic diagram of an electrical device provided in some embodiments of the present application.

[0062] FIG. 10 shows a scanning electron microscope (SEM) image of the isolation film prepared in Example 1. FIG.

[0063] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 battery cell, 51 housing, 52 electrode assembly, 53 cover plate, 10 separator, 101 porous substrate, 102 ferroelectric coating, 103 second coating. DETAILED DESCRIPTION

[0064] Below, the embodiments of the separator, battery cell, battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0065] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0066] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0067] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0068] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0069] In this application, the terms "plurality" and "multiple" refer to two or more.

[0070] In the description of the embodiments of the present application, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0071] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0072] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0073] The Dv50 of a material is generally known in the art and can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer (such as the Malvern Mastersizer 3000) in accordance with GB / T 19077-2016. The physical definition of Dv50 is the particle size at which the cumulative volume distribution percentage of a material reaches 50%.

[0074] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0075] A battery cell is the smallest unit of a battery, independently capable of charging and discharging. A battery cell can be cylindrical, rectangular, or have other shapes, though this is not a limitation in the present invention. Figure 1 shows a battery cell 5 with a rectangular structure as an example.

[0076] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed series via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam.

[0077] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0078] A battery cell generally includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a laminated structure, which is not limited in the present embodiment.

[0079] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The soft package can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0080] In some embodiments, as shown in Figure 2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, which together form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening, thereby sealing the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and can be adjusted according to needs.

[0081] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 3 is a schematic diagram of a battery module 4 as an example. As shown in Figure 3, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can further be fixed by fasteners.

[0082] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0083] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0084] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing comprises an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the housing.

[0085] The battery cells provided in the embodiments of the present application may include lithium battery cells and sodium battery cells, for example, lithium ion battery cells, lithium metal battery cells, negative electrode-free lithium metal battery cells, sodium ion battery cells, sodium metal battery cells, negative electrode-free sodium metal battery cells, etc.

[0086] A negative electrode-free battery cell generally refers to a battery cell constructed without the active negative electrode layer being applied during the manufacturing process. For example, a negative electrode active material layer is not applied to the negative electrode through coating or deposition, or a carbonaceous active material layer is used to form the negative electrode active material layer. During initial charging, ions on the negative electrode side gain electrons and deposit on the surface of the negative electrode current collector to form metal. During discharge, the metal can be converted back to ions and returned to the positive electrode, enabling cyclic charge and discharge. Compared to other battery cells, negative electrode-free battery cells can achieve higher energy density due to the lack of a negative electrode active material layer. In some embodiments, to improve battery cell performance, the negative electrode side of the negative electrode-free battery cell may also be provided with some conventional negative electrode active materials, such as carbon materials. Although these materials have a certain capacity, their content is relatively low and they are not used as the primary negative electrode active material in the battery cell. Therefore, the battery cell constructed in this manner can still be considered a negative electrode-free battery cell. The CB (Cell Balance) value of a battery cell without a negative electrode is typically very small. For example, in some embodiments, the CB value of a battery cell without a negative electrode can be less than or equal to 0.1. The CB value is the unit area capacity of the negative electrode in the battery cell divided by the unit area capacity of the positive electrode. Because a battery cell without a negative electrode contains no or only a small amount of negative electrode active material, the unit area capacity of the negative electrode is relatively small, and thus the CB value is very small, for example, typically less than or equal to 0.1.

[0087] As an important component of a battery cell, the performance of the separator is crucial to the performance of the battery. The separator is located between the positive and negative electrodes and mainly serves to prevent short circuits. The separators currently used in commercial batteries are usually porous membranes made of polyolefins (such as polyethylene, polypropylene, etc.). However, these separators have poor electrolyte wettability and thermal stability. In addition, as the number of charge and discharge cycles of the battery increases, dendrites will form at the negative electrode interface. The continued growth of dendrites will pierce the separator, causing internal short circuits, and in severe cases, even fires, explosions and other safety accidents.

[0088] In addition, a ceramic coating is usually provided on the conventional isolation membrane, but the ceramic coating usually acts as a physical barrier. As the number of charge and discharge times of the battery increases, there is still the possibility that dendrites will grow along the pores of the ceramic coating and pierce the isolation membrane, and thus the dendrite growth problem cannot be effectively alleviated.

[0089] Therefore, developing an isolation membrane with good thermal stability, excellent electrolyte wettability and the ability to alleviate dendrite growth is a technical problem that needs to be urgently solved in this field.

[0090] Figure 6 shows a schematic diagram of an isolation membrane provided by some embodiments of the present application. Figure 7 shows a schematic diagram of an isolation membrane provided by other embodiments of the present application. Figure 8 shows a schematic diagram of an isolation membrane provided by still other embodiments of the present application.

[0091] As shown in Figures 6 to 8, isolation film 10 includes a porous substrate 101 and a ferroelectric coating 102 disposed on at least one surface of porous substrate 101. Ferroelectric coating 102 includes a ferroelectric material, which includes an inorganic ferroelectric and a ferroelectric polymer. The ferroelectric polymer includes polyvinylidene fluoride and its copolymers. The ferroelectric polymer includes β-phase polyvinylidene fluoride, and the β-phase polyvinylidene fluoride content in the ferroelectric polymer is greater than or equal to 60%.

[0092] The porous substrate is highly hydrophobic, while the electrolyte usually uses a polar solvent, which results in poor electrolyte wettability of the porous substrate and high ion transfer impedance. The ferroelectric coating introduced in the isolation membrane provided in the embodiment of the present application includes an inorganic ferroelectric and a ferroelectric polymer, which can improve the compatibility of the isolation membrane with the electrolyte, improve the isolation membrane's wetting properties for the electrolyte, and reduce the isolation membrane's ion transfer impedance, thereby helping the battery to have good cycle performance and rate performance. In addition, the ferroelectric coating introduced in the isolation membrane provided in the embodiment of the present application can also improve the heat resistance and mechanical strength of the isolation membrane.

[0093] During the reduction and deposition of ions at the negative electrode, stress accumulates due to local volume expansion. Inorganic ferroelectrics have high dielectric constants and spontaneous polarization. Under stress, inorganic ferroelectrics undergo spontaneous polarization under the influence of the electric field. As a result, the positive charge center of the inorganic ferroelectric moves toward the electron accumulation area of ​​the negative electrode, thereby enveloping the electron accumulation area. At the same time, because the positive charge center of the inorganic ferroelectric is positively charged, it repel the positively charged ions on the dendrite surface, thereby changing the direction of dendrite growth, slowing the continuous growth of dendrites in the direction perpendicular to the electrode, and reducing internal short circuits in the battery. However, the Curie point temperature of inorganic ferroelectrics is generally low. During the preparation of the isolation membrane, a ferroelectric-paraelectric transition may occur, causing the ferroelectric coating to lose its ferroelectricity and cause failure. In addition, inorganic ferroelectrics often have problems such as uneven distribution and low content in the isolation membrane coating.

[0094] Typical examples of polyvinylidene fluoride are α-phase polyvinylidene fluoride and β-phase polyvinylidene fluoride. α-phase polyvinylidene fluoride is a monoclinic crystal with a TGTG arrangement and a zero net dipole moment, indicating no apparent polarity. β-phase polyvinylidene fluoride is an orthorhombic crystal with an all-trans TTTT arrangement and exhibits a large spontaneous polarization strength. It is easily polarized under an external electric field, resulting in excellent dielectric properties. Currently, the binder used in isolation film coatings is mostly α-phase polyvinylidene fluoride, which is not ferroelectric.

[0095] The ferroelectric polymer in the ferroelectric coating of the isolation film provided in the embodiment of the present application includes β-phase polyvinylidene fluoride, and the content of β-phase polyvinylidene fluoride in the ferroelectric polymer is greater than or equal to 60%. Therefore, the ferroelectric polymer provided in the embodiment of the present application can not only act as a binder, but also have a higher dielectric constant ε r , which can also slow down the continuous growth of dendrites in the direction perpendicular to the pole piece and reduce the internal short circuit of the battery.

[0096] Placing the ferroelectric polymer together with the inorganic ferroelectric in the ferroelectric coating can also reduce the probability of the ferroelectric coating losing its ferroelectricity due to the ferroelectric-paraelectric transition of the inorganic ferroelectric during the preparation of the isolation membrane, thereby playing a long-term role in slowing down the continuous growth of dendrites in the direction perpendicular to the pole piece. In addition, "dead lithium" and "dead sodium" may also be generated during the growth of dendrites, thereby significantly reducing the capacity and coulombic efficiency of the battery. Therefore, the isolation membrane provided in the embodiment of the present application can also play a role in improving the coulombic efficiency of the battery, especially improving the coulombic efficiency of the battery at high rates.

[0097] Therefore, the isolation membrane provided in the embodiment of the present application can slow down the growth of dendrites, and can also have good electrolyte wettability, low ion transfer impedance, low thermal shrinkage and high mechanical strength. When used in batteries, it can improve the reliability, coulombic efficiency and rate performance of the battery.

[0098] In some embodiments, the content of β-phase polyvinylidene fluoride in the ferroelectric polymer can be greater than or equal to 80%, and optionally greater than or equal to 90%. This can further slow down the continuous growth of dendrites in the direction perpendicular to the electrode, reduce internal short circuits in the battery, and improve the coulombic efficiency and rate performance of the battery.

[0099] In some embodiments, the ferroelectric polymer may further contain a small amount of α-phase polyvinylidene fluoride and / or γ-phase polyvinylidene fluoride.

[0100] Optionally, the content of α-phase polyvinylidene fluoride in the ferroelectric polymer may be less than or equal to 20%.

[0101] Optionally, the content of γ-phase polyvinylidene fluoride in the ferroelectric polymer may be less than or equal to 10%.

[0102] The contents of β-phase polyvinylidene fluoride, α-phase polyvinylidene fluoride and γ-phase polyvinylidene fluoride in the ferroelectric polymer can be calculated by FTIR infrared absorption spectrum. F α =100%-F (β，γ)

[0103] F α It represents the content of α phase in ferroelectric polymer.

[0104] F β It represents the content of β phase in ferroelectric polymer.

[0105] F γ It represents the content of γ phase in ferroelectric polymer.

[0106] A m Indicates the peak intensity of the absorption peak at different wavelengths m. The peak intensity of each absorption peak can be expressed as the integrated area of ​​each absorption peak.

[0107] K m Represents the absorption coefficient of the absorption peak at different wavelengths m.

[0108] In some embodiments, the dielectric constant ε of the ferroelectric coating is r Greater than the dielectric constant ε of inorganic ferroelectrics r .

[0109] Optionally, the dielectric constant ε of the ferroelectric coating r and the dielectric constant ε of inorganic ferroelectrics r The ratio can be greater than or equal to 1.6, and can be more preferably greater than or equal to 2.0.

[0110] The dielectric constant ε of the ferroelectric coating of the isolation film provided in the embodiment of the present application is r Greater than the dielectric constant ε of inorganic ferroelectrics r This can further slow down the continuous growth of dendrites in the direction perpendicular to the electrode, reduce internal short circuits in the battery, improve battery reliability, and also improve the coulombic efficiency and rate performance of the battery.

[0111] In some embodiments, the dielectric constant ε of the inorganic ferroelectric r Greater than the dielectric constant ε of ferroelectric polymers r .

[0112] In some embodiments, the dielectric constant ε of the inorganic ferroelectric r It can be 200-8000, optionally 2000-6000.

[0113] In some embodiments, the dielectric constant ε of the ferroelectric polymer is rIt can be 5-100, optionally 8-70.

[0114] The dielectric constant ε of the above ferroelectric coating is r , the dielectric constant ε of inorganic ferroelectrics r , the dielectric constant ε of ferroelectric polymers r The test can be performed as follows: at 25°C, take an appropriate amount of sample powder, cover both sides with aluminum foil, place it in a mold, and use a powder tablet press to press it into a disc at a pressure of 2 MPa and a holding time of 2 minutes; after the pressing is completed, remove the sample disc and use a precision digital bridge instrument to measure the dielectric constant ε in the frequency range of 20 Hz-2 MHz. r test.

[0115] The dielectric constant mentioned in this application is the relative dielectric constant ε r .

[0116] In testing the dielectric constant ε of the ferroelectric coating r When preparing the isolation film, sampling and analysis can be performed, or a suitable amount of ferroelectric coating powder can be obtained from the dried finished isolation film, for example, by scraping powder and sampling to obtain a suitable amount of ferroelectric coating powder.

[0117] By adjusting the distribution morphology, weight content, particle size and β-phase content of the inorganic ferroelectric and ferroelectric polymer in the ferroelectric coating, the inorganic ferroelectric and ferroelectric polymer can play a synergistic role and the dielectric constant ε of the ferroelectric coating can be increased. r The dielectric constant ε is greater than that of inorganic ferroelectrics r , which is larger than the dielectric constant ε of the ferroelectric polymer r .

[0118] In some embodiments, at least a portion of the ferroelectric polymer in the ferroelectric coating is located on at least a portion of the surface of the inorganic ferroelectric. When the ferroelectric polymer is located on at least a portion of the surface of the inorganic ferroelectric, the probability of the ferroelectric coating losing its ferroelectricity due to the ferroelectric-paraelectric transition of the inorganic ferroelectric during the preparation of the isolation film can be further reduced, thereby better slowing down the continuous growth of dendrites in the direction perpendicular to the pole piece. In addition, it also helps to improve the coulombic efficiency of the battery. When the ferroelectric polymer is located on at least a portion of the surface of the inorganic ferroelectric, it also helps to reduce the dielectric constant ε of the ferroelectric coating. r The dielectric constant ε is greater than that of inorganic ferroelectrics r , which is larger than the dielectric constant ε of the ferroelectric polymer r .

[0119] In some embodiments, the weight content of the inorganic ferroelectric in the ferroelectric material may be 80%-99%, optionally 85%-95%.

[0120] In some embodiments, the weight content of the ferroelectric polymer in the ferroelectric material may be 1%-20%, optionally 5%-15%.

[0121] By adjusting the weight content of the inorganic ferroelectric and ferroelectric polymer in the ferroelectric material within the above range, the dielectric constant ε of the ferroelectric coating can be increased. r , so that the dielectric constant ε of the ferroelectric coating r The dielectric constant ε is greater than that of inorganic ferroelectrics r , which is larger than the dielectric constant ε of the ferroelectric polymer r , which can better slow down the continuous growth of dendrites in the direction perpendicular to the electrode, reduce internal short circuits in the battery, and improve battery reliability and Coulomb efficiency; in addition, it can also increase the adhesion between the ferroelectric coating and the porous structure.

[0122] In some embodiments, the Curie point temperature of the ferroelectric polymer may be 150°C-250°C, optionally 160°C-200°C.

[0123] In some embodiments, the remanent polarization of the ferroelectric polymer may be 10 mC / m 2 -1000mC / m 2 , optional 20mC / m 2 -800mC / m 2 .

[0124] In some embodiments, the weight average molecular weight of the ferroelectric polymer may be 200,000-800,000, optionally 400,000-650,000.

[0125] The weight average molecular weight of the ferroelectric polymer is within the above range, which can make the ferroelectric polymer have appropriate crystallinity, appropriate Curie point temperature, and higher dielectric constant ε r , and can also make the ferroelectric polymer have suitable viscosity.

[0126] The weight average molecular weight of the ferroelectric polymer has a well-known meaning in the art and can be measured using methods known in the art, for example, by gel permeation chromatography (GPC).

[0127] In some embodiments, the melting temperature of the ferroelectric polymer may be 140°C-220°C, optionally 143°C-200°C.

[0128] The melting point of the ferroelectric polymer is within the above range, which can make the ferroelectric polymer have appropriate crystallinity, appropriate Curie point temperature, and higher dielectric constant ε r , and can also make the ferroelectric polymer have suitable viscosity.

[0129] The melting temperature of the ferroelectric polymer can be tested using a differential scanning calorimeter (DSC). The test temperature range can be 25° C. to 400° C., and the heating rate can be 10° C. / min.

[0130] In some embodiments, the crystallinity of the ferroelectric polymer can be greater than or equal to 45%, and can be optionally 45%-68%. When the crystallinity of the ferroelectric polymer is within the above range, the thermal shrinkage of the isolation film can be reduced and the mechanical strength of the isolation film can be improved.

[0131] In some embodiments, the ferroelectric polymer may include one or more of polyvinylidene fluoride (ie, homopolymer of vinylidene fluoride VDF monomer, abbreviated as PVDF), and copolymers of vinylidene fluoride monomer and other monomers.

[0132] By introducing other monomers into the VDF crystal region, the large-sized ferroelectric domains can be divided into nano-sized ones. The nano-ferroelectric domains are easy to respond to changes in the external electric field, thus showing a unique relaxor ferroelectric behavior, which can further increase the dielectric constant ε of the ferroelectric polymer. r Further improvement and further reduction of dielectric loss.

[0133] Alternatively, other monomers may include, but are not limited to, one or more of trifluoroethylene, chlorotrifluoroethylene, fluorinated acetylene, and hexafluoropropylene.

[0134] Optionally, the copolymer of vinylidene fluoride monomer and other monomers may include but is not limited to one or more of vinylidene fluoride-trifluoroethylene copolymer (abbreviated as P(VDF-TrFE)), vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene copolymer (abbreviated as P(VDF-TrFE-CFE)), vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene-fluorinated acetylene copolymer (abbreviated as P(VDF-TrFE-CFE-FA)), and vinylidene fluoride-hexafluoropropylene copolymer (abbreviated as P(VDF-HFP)).

[0135] In some embodiments, the volume distribution particle size Dv50 of the ferroelectric polymer may be 10 nm-150 nm, optionally 15 nm-50 nm.

[0136] In some embodiments, the volume distribution particle size Dv50 of the inorganic ferroelectric can be 0.05 μm-5 μm, optionally 0.1 μm-1 μm. A volume distribution particle size Dv50 of the inorganic ferroelectric within the above range can provide the ferroelectric coating slurry with a suitable viscosity, facilitate coating, and improve the uniformity and consistency of the ferroelectric coating. It can also increase the adhesion between the ferroelectric coating and the porous structure, reducing "powder shedding" and reducing pore blockage, thereby improving the permeability and ion transport properties of the isolation membrane.

[0137] In some embodiments, the Curie point temperature of the inorganic ferroelectric can be 110°C - 150°C, and optionally 120°C - 140°C.

[0138] In some embodiments, the inorganic ferroelectric can include, but is not limited to, one or more of perovskite type, tungsten bronze type, bismuth layer type, pyrochlore type, niobate type, and lead barium lithium niobate. Optionally, the inorganic ferroelectric can include the perovskite type.

[0139] Optionally, the perovskite type can have the molecular formula Ba 1-x A x Ti 1-y B y O3. A can include, but is not limited to, a combination of one or more of Bi, Pb, Sr, Ca, K, Na, and Cd, and B can include, but is not limited to, a combination of one or more of Fe, Sn, Hf, Zr, Ce, Nb, and Th, where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1.

[0140] Optionally, the perovskite type can include, but is not limited to, barium titanate (BaTiO3), Ba 1-x1 Sr x1 TiO3 (0 ≤ x1 ≤ 1), SrTiO3, PbTiO3, BiFeO3, PbZr y1 Ti 1-y1 O3 (0 ≤ y1 ≤ 1), BaZr y2 Ti 1-y2 O3 (0 < y2 < 1), or one or more of them.

[0141] Optionally, the tungsten bronze type can have the molecular formula M z WO3. M can include, but is not limited to, one or more of Na, K, Rb, and Cs, where 0 < z < 1.

[0142] Optionally, the tungsten bronze type can include, but is not limited to, Na z1 WO3 (0 < z1 < 1), K z2 WO3 (0 < z2 < 1), or one or more of them.

[0143] Optionally, the bismuth layer type can have the molecular formula (Bi2O2)(C n-1 D n O 3n+1 ). C can include, but is not limited to, one or more of Na, K, Ba, Sr, Pb, Ca, Ln, and Bi, and D can include, but is not limited to, one or more of Zr, Cr, Nb, Ta, Mo, W, Fe, Ti, and V, where 2 ≤ n ≤ 5.

[0144] Alternatively, the bismuth layered type may include but is not limited to SrBi2Nb2O9, SrBi2Ta2O9, SrBi2Nb2O9, Bi4Ti3O 12 One or more of .

[0145] Optionally, the pyrochlore type may include but is not limited to one or more of lead metaniobate (PbNb2O6) and Cd2Nb2O7.

[0146] Alternatively, the niobate type may include but is not limited to one or more of LiNbO 3 , KNbO 3 , and NaNbO 3 .

[0147] In some embodiments, the thickness of the ferroelectric coating may be 1 μm-3.5 μm, and optionally 1.5 μm-3 μm, thereby enabling the battery to have high reliability, high coulombic efficiency, and good rate performance.

[0148] In some embodiments, the areal density of the ferroelectric coating may be 2.5 g / m 2 -15g / m 2 , 3g / m2 is optional 2 -12g / m 2 This allows the battery to have high reliability, high coulombic efficiency and good rate performance.

[0149] In some embodiments, the ferroelectric coating may further include a dispersant.

[0150] Alternatively, the dispersant may include, but is not limited to, one or more of hydrolyzed polymaleic anhydride, polyacrylic acid, acrylic acid block copolymers, polyester block copolymers, polyethylene glycol-type polyols, polyethyleneimine, and their respective derivatives. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups.

[0151] Optionally, the ratio of the total weight of the ferroelectric material to the weight of the dispersant may be 1:(0.01-0.02), or optionally 1:(0.010-0.015).

[0152] An appropriate amount of dispersant can make the ferroelectric coating slurry dispersed evenly, facilitate coating, and also help to increase the film weight of the ferroelectric coating.

[0153] In some embodiments, the ferroelectric coating may further include a thickener.

[0154] Optionally, the thickener may include, but is not limited to, one or more of sodium hydroxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxypropyl methylcellulose, polyacrylate, polyurethane, and polyether.

[0155] Optionally, the ratio of the total weight of the ferroelectric material to the weight of the thickener may be 1:(0.01-0.02), or optionally 1:(0.010-0.015).

[0156] An appropriate amount of thickener can improve the stability of the ferroelectric coating slurry, facilitate coating, and also help increase the film weight of the ferroelectric coating.

[0157] The ferroelectric coating 102 is located on at least one surface of the porous substrate 101. In some embodiments, as shown in FIG6 , the ferroelectric coating 102 may be located on one surface of the porous substrate 101; in some embodiments, as shown in FIG7 , the ferroelectric coating 102 may be located on both surfaces of the porous substrate 101.

[0158] In some embodiments, as shown in FIG8 , the ferroelectric coating 102 is located on one surface of the porous substrate 101 , and a ceramic coating 103 may be provided on the other surface of the porous substrate 101 . When used in a battery, the ferroelectric coating 102 may face the negative electrode, and the ceramic coating 103 may face the positive electrode.

[0159] In some embodiments, the thickness of the porous substrate may be 4 μm to 15 μm, optionally 5 μm to 10 μm.

[0160] In some embodiments, the porous substrate may include, but is not limited to, one or more of polyolefins (e.g., polyethylene, polypropylene, etc.), halogenated polyolefins (e.g., polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, etc.), polyamides, polyesters (e.g., polyethylene terephthalate, etc.), and their respective derivatives. Derivatives generally refer to products derived from the substitution of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups.

[0161] [Method for preparing isolation film]

[0162] An embodiment of the present application also provides a method for preparing an isolation film.

[0163] The preparation method includes the following steps: providing a porous substrate; providing a ferroelectric coating slurry: dispersing the ferroelectric material in a solvent to obtain the ferroelectric coating slurry; coating: coating the ferroelectric coating slurry on at least one surface of the porous substrate, and obtaining an isolation film after drying.

[0164] In some embodiments, the drying temperature of the ferroelectric coating slurry may be 60° C.-80° C., and the drying time may be 5 min-30 min.

[0165] In some embodiments, the coating method of the ferroelectric coating slurry may include but is not limited to gravure transfer coating, spin spray coating, dip coating, blade coating, etc.

[0166] In some embodiments, the solvent in the ferroelectric coating slurry may include but is not limited to one or more of deionized water, N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), and tetrahydrofuran (THF).

[0167] In some embodiments, the solid content of the ferroelectric coating slurry may be 25%-45%, and optionally 30%-40%, which is beneficial for coating.

[0168] In some embodiments, the ferroelectric coating slurry may further include one or more of a dispersant and a thickener.

[0169] In some embodiments, the step of providing a ferroelectric coating slurry may include the following steps: dispersing the ferroelectric material, dispersant and solvent once to obtain a primary dispersion solution; adding a thickener to the obtained primary dispersion solution for secondary dispersion to obtain a ferroelectric coating slurry.

[0170] Optionally, the primary dispersion process may be ultrasonic dispersion, and stirring may be performed during the ultrasonic dispersion process. Optionally, the stirring speed during the ultrasonic dispersion process may be 700 rpm-1200 rpm, and the ultrasonic dispersion time may be 30 min-60 min.

[0171] Optionally, the secondary dispersion process may be ultrasonic dispersion, and stirring may be performed during the ultrasonic dispersion process. Optionally, the stirring speed during the ultrasonic dispersion process may be 1000 rpm-1600 rpm, and the ultrasonic dispersion time may be 30 min-90 min.

[0172] In some embodiments, the method for preparing the isolation film may further include the following steps: providing a ferroelectric material; stirring and dispersing the ferroelectric polymer and the first solvent evenly to obtain a clear solution; adding an inorganic ferroelectric to the obtained clear solution and stirring and dispersing the solution evenly to obtain a slurry; and subjecting the obtained slurry to a drying process to obtain a ferroelectric material.

[0173] Alternatively, the first solvent may include anhydrous ethanol, N-methylpyrrolidone (NMP), or the like.

[0174] Optionally, after the ferroelectric polymer and the first solvent are uniformly stirred, ultrasonic dispersion can be performed, and the ultrasonic dispersion time can be 20 minutes to 60 minutes.

[0175] Optionally, after adding the inorganic ferroelectric to the obtained clear solution and stirring evenly, ultrasonic dispersion can be performed. The ultrasonic dispersion time can be 30 minutes to 60 minutes.

[0176] Optionally, the slurry can be dried in a drying oven at a drying temperature of 75°C-95°C.

[0177] Optionally, the method for preparing the isolation film may further include the step of grinding the obtained ferroelectric material.

[0178] In some embodiments, the method for preparing the isolation film may further include the steps of: preparing a ceramic coating slurry, and coating the ceramic coating slurry on the surface of the porous substrate where the ferroelectric coating is not provided.

[0179] Some parameters such as raw materials and their contents used in the preparation method of the isolation membrane provided in the embodiments of the present application can refer to the isolation membrane provided in the embodiments of the present application, and will not be repeated here.

[0180] Unless otherwise specified, all raw materials used in the preparation method of the separator can be obtained commercially.

[0181] [Positive electrode]

[0182] The structure and composition of the positive electrode plate can be selected according to the type of battery cell, and the embodiments of the present application are not limited thereto.

[0183] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0184] When the battery is a lithium battery, the positive electrode active material includes a material capable of extracting and inserting lithium. As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, metal chalcogenides, 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 oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium titanium oxide, and their respective modified compounds. Lithium transition metal oxides may include, but are not limited to, layered structures and spinel structures. Examples of lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0185] In some embodiments, in order to further improve the energy density of the battery, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e D fOne or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include but is not limited to one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and D may include but is not limited to one or more of N, F, S and Cl.

[0186] In some embodiments, the positive electrode active material may include both a lithium transition metal oxide and a lithium-containing phosphate, thereby facilitating the production of a battery with both high capacity and high reliability.

[0187] As an example, the positive electrode active material may include but is not limited to LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 2 Mn 1 / 2 O2、LiMn2O4、Li 4 / 3 Ti 5 / 3 O4、LiNi 1 / 2 Mn 1 / 2 O2、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 One or more of S2.

[0188] When the battery is a sodium battery, the positive electrode active material includes a material capable of extracting and inserting sodium. As an example, the positive electrode active material may be, but is not limited to, one or more of layered transition metal oxides (including but not limited to P2 type, O3 type, etc.), polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian materials.

[0189] In some embodiments, as examples, the positive electrode active material may include but is not limited to NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, Na0.67 MO2 (M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, Mo), NaMO2 (M includes at least two of Fe, Co, Ni, V, Ti, Mo), NaFePO4, NaMnPO4, NaCoPO4, Na4Fe3(PO4)2O7, Na3V2(PO4)2F3, Na3V2(PO4)3, Prussian blue, Prussian white, and one or more of their respective modified compounds.

[0190] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0191] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0192] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylic resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and one or more of carboxymethyl chitosan (CMCS).

[0193] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include but is not limited to one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0194] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional positive electrode conductive agent, optional positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0195] [Negative electrode]

[0196] The battery cell includes a negative electrode plate. The structure and composition of the negative electrode plate can be selected according to the type of battery cell, and the embodiments of the present application are not limited thereto.

[0197] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector may have two opposing surfaces in its thickness direction, and the negative electrode film layer may be disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0198] The negative electrode active material may be a material known in the art. As an example, the negative electrode active material may include, but is not limited to, one or more of carbon-based materials, silicon-based materials, tin-based materials, and lithium titanate. Carbon-based materials may include, but are not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, pyrolytic carbon, coke, glassy carbon, a sintered product of an organic polymer compound, and mesophase carbon microbeads. Silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. Tin-based materials may include, but are not limited to, one or more of elemental tin, tin oxide, and tin alloy materials.

[0199] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. As examples, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0200] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. As examples, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0201] In some embodiments, the negative electrode film layer may further include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0202] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0203] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer; in some embodiments, the negative electrode plate may further include a protective layer covering the surface of the negative electrode film layer.

[0204] In some embodiments, the negative electrode plate may include a negative electrode current collector and a metal layer disposed on at least one surface of the negative electrode current collector. The metal material in the metal layer may include but is not limited to one or more of lithium, lithium alloy, sodium, and sodium alloy.

[0205] Lithium alloys may be alloys of metallic lithium with other metallic elements or non-metallic elements. For example, the other metallic elements in the lithium alloy may include, but are not limited to, one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum. The non-metallic elements in the lithium alloy may include one or more of boron, carbon, and silicon.

[0206] Sodium alloys may be alloys of metallic sodium with other metallic elements or non-metallic elements. For example, the other metallic elements in the sodium alloy may include, but are not limited to, one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, and the non-metallic elements in the sodium alloy may include one or more of boron, carbon, and silicon.

[0207] In some embodiments, the negative electrode sheet may be a lithium sheet (foil), a lithium alloy sheet (foil), a sodium sheet (foil), or a sodium alloy sheet (foil).

[0208] In some embodiments, the negative electrode sheet may include a negative electrode current collector to be assembled into a negative electrode-free battery cell.

[0209] In some embodiments, the negative electrode current collector may include, but is not limited to, one or more of a metal foil, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector.

[0210] Examples of metal foil materials include copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil. Examples of metal foam current collectors include copper foam, nickel foam, and aluminum foam. Examples of metal mesh current collectors include copper mesh, nickel mesh, and aluminum mesh.

[0211] The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, aluminum, aluminum alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0212] [Electrolytes]

[0213] The battery cell includes an electrolyte. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected according to needs. For example, the electrolyte can include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolytes).

[0214] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and an organic solvent.

[0215] The electrolyte salt may include phosphates, perchlorates, organic boron salts, fluorine-containing organic salts, imide salts, and the like.

[0216] When the battery is a lithium battery, as an example, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0217] When the battery is a sodium battery, as an example, the electrolyte salt may include, but is not limited to, sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP), and sodium tetrafluorooxalatophosphate.

[0218] In some embodiments, the concentration of the electrolyte salt may be 0.3 mol / L or more, and may be 0.7 mol / L or more. The concentration of the electrolyte salt may be 4 mol / L or less, and may be 2.5 mol / L or less, or 1.7 mol / L or less.

[0219] Organic solvent can include but not limited to one or more in esters, ethers, sulfones, nitriles etc. Esters can include but not limited to one or more in carbonate, phosphate, carboxylate, sulfate, sulfonate etc. Carbonate can comprise cyclic carbonate and / or chain carbonate. Chain carbonate can comprise low-viscosity polar chain carbonate, aliphatic branched-chain carbonate etc.

[0220] As an example, the organic solvent may include, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), tetraethylene glycol dimethyl ether (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), trimethyl phosphate, 3-methoxypropionitrile, H(CF2)2OCH3, C4F9O CH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2O(CF2)2H, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethylhexafluoropropyl ethyl ether, 2-trifluoromethylhexafluoropropyl propyl ether, 3-trifluoromethyloctafluorobutyl methyl ether, 3-trifluoromethyloctafluorobutyl ethyl ether, 3-trifluoromethyloctafluorobutyl propyl ether, 4-trifluoromethyl One or more of trifluoromethyl decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecafluorohexyl methyl ether, 5-trifluoromethyl dodecafluorohexyl ethyl ether, 5-trifluoromethyl dodecafluorohexyl propyl ether, 6-trifluoromethyl tetradecafluoroheptyl methyl ether, 6-trifluoromethyl tetradecafluoroheptyl ethyl ether, 6-trifluoromethyl tetradecafluoroheptyl propyl ether, 7-trifluoromethyl hexafluorooctyl methyl ether, 7-trifluoromethyl hexafluorooctyl ethyl ether, and 7-trifluoromethyl hexafluorooctyl propyl ether.

[0221] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0222] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with the above-mentioned electrolyte, and then vacuum packaged, allowed to stand, formed and other processes to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0223] The present application also provides an electrical device, which includes a battery provided in the present application. The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0224] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0225] Figure 9 is a schematic diagram of an exemplary electric device. This device is 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 this device, a battery pack or battery module may be used.

[0226] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0227] Example

[0228] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0229] Example 1

[0230] Weigh barium titanate (BaTiO3) powder and ferroelectric polymer powder in a weight ratio of 90:10. The barium titanate powder is a tetragonal phase with a volume distribution particle size Dv50 of 0.3 μm and a dielectric constant ε r 5460. Ferroelectric polymer PVDF, wherein the β phase content is 90%, the crystallinity is 65%, and the dielectric constant ε r The molecular weight is 9.6, the melting temperature is 150°C, and the weight average molecular weight is 540,000.

[0231] Ferroelectric polymer powder is mixed with anhydrous ethanol and stirred until uniformly mixed. The mixture is then ultrasonically dispersed in an ultrasonic machine for 35-45 minutes to obtain a clear solution. Barium titanate powder is added to the clear solution and shaken until uniformly mixed. The mixture is then ultrasonically dispersed in an ultrasonic machine for 45-50 minutes to obtain a slurry. The slurry is dried in a drying oven at 90°C. The dried powder is then ground in a mortar to obtain a ferroelectric material powder.

[0232] The resulting ferroelectric material powder was evenly dispersed in NMP, and ultrasonic dispersion was performed by adding hydrolyzed polymaleic anhydride. After ultrasonic dispersion for 2 hours, sodium hydroxymethyl cellulose was added for secondary dispersion to obtain a ferroelectric coating slurry with a solid content of approximately 35%. The weight ratio of the ferroelectric material, hydrolyzed polymaleic anhydride, and sodium hydroxymethyl cellulose in the ferroelectric coating slurry was 1:0.01:0.01.

[0233] The obtained ferroelectric coating slurry was coated on one surface of a PE porous substrate with a porosity of 50% and a thickness of 9 μm by gravure transfer coating, and then vacuum dried at 60°C to obtain an isolation film. The thickness of the ferroelectric coating was 3 μm and the surface density was 6 g / m 2 .

[0234] Examples 2 to 5

[0235] The preparation method of the isolation film is similar to that of Example 1, except that the β-phase content of the ferroelectric polymer used is different. Specific parameters are shown in Table 1.

[0236] Comparative Example 1

[0237] Alumina powder and polyacrylic acid were evenly dispersed in NMP at a weight ratio of 90:10 to produce a ceramic coating slurry. The resulting ceramic coating slurry was applied to one surface of a 9μm thick PE porous substrate with a porosity of 50% by gravure transfer coating. The separator was then vacuum-dried at 60°C to produce a 3μm thick ceramic coating.

[0238] Comparative Example 2

[0239] The preparation method of the isolation film is similar to that of Example 1, except that ferroelectric polymer is not used, but α-phase polyvinylidene fluoride is used, and the α-phase content is above 75%.

[0240] Comparative Example 3

[0241] The preparation method of the isolation film is similar to that of Example 1, except that the β-phase content of the ferroelectric polymer used is 30%. Specific parameters are shown in Table 1.

[0242] Example 6

[0243] The preparation method of the isolation film is similar to that of Example 1, except that the weight ratio of the barium titanate powder to the ferroelectric polymer powder is 99.5:0.5.

[0244] Example 7

[0245] The preparation method of the isolation film is similar to that of Example 1, except that the weight ratio of the barium titanate powder to the ferroelectric polymer powder is 99:1.

[0246] Example 8

[0247] The preparation method of the isolation film is similar to that of Example 1, except that the weight ratio of the barium titanate powder to the ferroelectric polymer powder is 95:5.

[0248] Example 9

[0249] The preparation method of the isolation film is similar to that of Example 1, except that the weight ratio of the barium titanate powder to the ferroelectric polymer powder is 85:15.

[0250] Example 10

[0251] The preparation method of the isolation film is similar to that of Example 1, except that the weight ratio of the barium titanate powder to the ferroelectric polymer powder is 80:20.

[0252] Example 11

[0253] The preparation method of the isolation film is similar to that of Example 1, except that the weight ratio of the barium titanate powder to the ferroelectric polymer powder is 75:25.

[0254] Example 12

[0255] The preparation method of the isolation film is similar to that of Example 1, except that the volume distribution particle size Dv50 of the barium titanate powder is 5 μm.

[0256] Example 13

[0257] The preparation method of the isolation film is similar to that of Example 1, except that the volume distribution particle size Dv50 of the barium titanate powder is 3 μm.

[0258] Example 14

[0259] The preparation method of the isolation film is similar to that of Example 1, except that the volume distribution particle size Dv50 of the barium titanate powder is 1 μm.

[0260] Example 15

[0261] The preparation method of the isolation film is similar to that of Example 1, except that the volume distribution particle size Dv50 of the barium titanate powder is 0.5 μm.

[0262] Example 16

[0263] The preparation method of the isolation film is similar to that of Example 1, except that the volume distribution particle size Dv50 of the barium titanate powder is 0.1 μm.

[0264] Example 17

[0265] The preparation method of the isolation film is similar to that of Example 1, except that the volume distribution particle size Dv50 of the barium titanate powder is 0.05 μm.

[0266] Example 18

[0267] The preparation method of the isolation film is similar to that of Example 1, except that the thickness of the ferroelectric coating is 1 μm.

[0268] Example 19

[0269] The preparation method of the isolation film is similar to that of Example 1, except that the thickness of the ferroelectric coating is 1.5 μm.

[0270] Example 20

[0271] The preparation method of the isolation film is similar to that of Example 1, except that the thickness of the ferroelectric coating is 3.5 μm.

[0272] Examples 21 to 26

[0273] The preparation method of the isolation film is similar to that of Example 1, except that the types of inorganic ferroelectrics or ferroelectric polymers in the ferroelectric coating are different. Specific parameters are shown in Table 2.

[0274] The inorganic ferroelectric and ferroelectric polymer materials used in the above embodiments and comparative examples are all commercially available.

[0275] Performance Testing

[0276] (1) Puncture strength test of isolation film

[0277] The puncture strength of the isolation film is tested according to GB / T36363-2018.

[0278] Cut the barrier film into samples with a width of 10 mm and a length of 150 mm, then flatten and clamp them in a fixture. A steel needle is then used for puncture testing at a rate of 100 mm / min. After completion, remove the sample and perform a thickness test at four points around the needle hole in accordance with GB / T6672-2001. The average value is used to calculate the puncture strength. The steel needle can have a diameter of 1 mm and a spherical tip radius of 0.5 mm. The surface of the steel needle must be smooth and free of rust, oxide layers, and oil stains. Six or more barrier film samples can be tested, and the test results are averaged.

[0279] (2) Tensile strength test of isolation film

[0280] The tensile strength of the separator in the transverse (TD) and longitudinal (MD) directions was tested according to GB / T36363-2018.

[0281] Cut the separator film into samples with a width of 10 mm and a length of 150 mm (with the length direction parallel to the transverse direction of the separator film) for testing to determine the tensile strength in the transverse direction (TD) of the separator film. The testing instrument can be a universal tensile testing machine with a tensile rate of 50 mm / min. Six or more separator film samples can be tested, and the test results are averaged.

[0282] Cut the separator film into samples with a width of 10 mm and a length of 150 mm (with the longitudinal direction parallel to the longitudinal direction of the separator film) for testing to determine the tensile strength in the longitudinal direction (TD) of the separator film. The testing instrument can be a universal tensile testing machine with a tensile rate of 50 mm / min. Six or more separator film samples can be tested, and the test results are averaged.

[0283] (3) Thermal shrinkage test of isolation film

[0284] The thermal shrinkage of the isolation film in the transverse (TD) and longitudinal (MD) directions is tested according to GB / T36363-2018.

[0285] The separator sample was 50 mm wide and 100 mm long. The oven temperature was 105°C and the heat treatment time was 60 minutes. The length and width of the separator were measured and labeled a and b, respectively.

[0286] The heat shrinkage in the longitudinal direction (MD) = [(100-a) / 100] × 100%, and the heat shrinkage in the transverse direction (TD) = [(50-b) / 50] × 100%. During the test, the number of separator samples can be more than 6, and the test results are averaged.

[0287] (4) Air permeability test of isolation membrane

[0288] The air permeability of the isolation membrane is tested according to GB / T36363-2018.

[0289] The time required for 100 mL of air to pass through the separator is used as the air permeability of the separator. The greater the air permeability, the worse the separator's air permeability. Six or more separator samples can be tested, and the average result is taken. The test instrument can be a Kumagai KRK Wangyan air permeability tester.

[0290] (5) Dielectric constant ε of ferroelectric material powder r test

[0291] At 25°C, take an appropriate amount of ferroelectric material powder, cover both sides with aluminum foil, place it in a mold, and use a powder tablet press to press it into a disc with a pressure of 2 MPa and a holding time of 2 minutes. After the pressing is completed, remove the sample disc and use a precision digital bridge instrument to measure the dielectric constant ε in the frequency range of 20 Hz-2 MHz. r Test. When testing, the number of samples can be more than 6, and the test results are averaged.

[0292] Next, the above-mentioned isolation membrane was assembled into a button-type battery, and the rate performance was tested.

[0293] The button cell can be prepared as follows.

[0294] Lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed uniformly in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 8:1:1 to form a positive electrode slurry. The slurry was then coated onto aluminum foil, the positive electrode current collector, and dried to form a positive electrode sheet. In an argon-protected glove box, the positive electrode sheet, separator, and lithium sheet were assembled into a CR2430 button cell. The electrolyte salt was LiFSI at a concentration of 1 mol / L, and the solvent was ethylene glycol dimethyl ether.

[0295] The ferroelectric coating layers of the separators of Examples 1 to 26 and Comparative Examples 1 to 3 all faced the lithium sheet.

[0296] At 25°C, charge the button cell at a constant current of 0.1C to 3.65V, then charge it at a constant voltage of 3.65V to 0.05C. After allowing the button cell to rest for 10 minutes, discharge it at a constant current of 0.1C to 2.5V. After cycling the button cell twice using the above method, perform the following cycling performance test.

[0297] A button cell was charged at constant current rates of 0.5C, 1C, and 2C to 3.65V, followed by constant voltage charge at 3.65V to 0.05C. After standing for 10 minutes, the cell was discharged at a constant current of 0.2C to 2.5V. The cell was cycled 100 times using this method to determine the charge capacity and discharge capacity at the 100th cycle. The coulombic efficiency of the cell after 100 cycles is calculated as: discharge capacity at the 100th cycle / charge capacity at the 100th cycle.

[0298] During the test, the number of button battery samples can be more than 6, and the test results are averaged.

[0299] The test results are shown in Table 3.

[0300] Table 1

[0301] Table 2

[0302] Table 3

[0303] The test results of Examples 1 to 26 and Comparative Examples 1 to 3 demonstrate that by ensuring that the ferroelectric coating of the isolation membrane includes an inorganic ferroelectric and a ferroelectric polymer, and that the ferroelectric polymer contains β-phase polyvinylidene fluoride (PVDF) at least 60%, the coulombic efficiency and rate performance of the battery can be improved without affecting the permeability, thermal shrinkage, and mechanical strength of the isolation membrane. Figure 10 shows a scanning electron microscope (SEM) image of the isolation membrane prepared in Example 1. As can be seen from Figure 10, a portion of the ferroelectric polymer is dispersed on the surface of the inorganic ferroelectric.

[0304] It can also be seen from the test results of Examples 1 to 5 that the dielectric constant ε of the ferroelectric material can be further improved by further adjusting the content of β-phase polyvinylidene fluoride in the ferroelectric polymer. r , which can further improve the air permeability, thermal shrinkage and mechanical strength of the isolation membrane, and can also further improve the coulombic efficiency and rate performance of the battery.

[0305] The test results of Examples 6 to 11 also show that the dielectric constant ε of the ferroelectric material can be further improved by further adjusting the weight ratio of the inorganic ferroelectric and the ferroelectric polymer. r, which can further improve the air permeability, thermal shrinkage and mechanical strength of the isolation membrane, and can also further improve the coulombic efficiency and rate performance of the battery.

[0306] The test results of Examples 12 to 17 also show that the dielectric constant ε of the ferroelectric material can be further improved by further adjusting the particle size of the inorganic ferroelectric. r , which can further improve the air permeability, thermal shrinkage and mechanical strength of the isolation membrane, and can also further improve the coulombic efficiency and rate performance of the battery.

[0307] It can also be seen from the test results of Examples 21 to 26 that the dielectric constant ε of the ferroelectric material varies depending on the type of inorganic ferroelectric and / or ferroelectric polymer. r There will be differences, and the improvement effects on battery coulombic efficiency and rate performance will also be different.

[0308] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An isolation film comprising a porous substrate and a ferroelectric coating located on at least one surface of the porous substrate, wherein: The ferroelectric coating comprises a ferroelectric material, wherein the ferroelectric material comprises an inorganic ferroelectric and a ferroelectric polymer. The ferroelectric polymer includes polyvinylidene fluoride and copolymers thereof. The ferroelectric polymer includes β-phase polyvinylidene fluoride, and the content of β-phase polyvinylidene fluoride in the ferroelectric polymer is greater than or equal to 60%.

2. The isolation film according to claim 1, wherein: The content of β-phase polyvinylidene fluoride in the ferroelectric polymer is greater than or equal to 80%, and can be optionally greater than or equal to 90%.

3. The isolation film according to any one of claims 1 to 2, wherein: The dielectric constant ε of the ferroelectric coating r Greater than the dielectric constant ε of the inorganic ferroelectric r Optionally, the dielectric constant ε of the ferroelectric coating is r The dielectric constant ε of the inorganic ferroelectric r The ratio is greater than or equal to 1.6, and can be greater than or equal to 2.0; The dielectric constant ε of the inorganic ferroelectric r Greater than the dielectric constant ε of the ferroelectric polymer r .

4. The isolation film according to any one of claims 1 to 3, wherein: The dielectric constant ε of the inorganic ferroelectric r 200-8000, optionally 2000-6000; and / or, The dielectric constant ε of the ferroelectric polymer r 5-100, optional 8-70.

5. The isolation film according to any one of claims 1 to 4, wherein: At least a portion of the ferroelectric polymer is located on at least a portion of the surface of the inorganic ferroelectric.

6. The isolation film according to any one of claims 1 to 5, wherein: The weight content of the inorganic ferroelectric in the ferroelectric material is 80%-99%, optionally 85%-95%; and / or, The weight content of the ferroelectric polymer in the ferroelectric material is 1%-20%, and optionally 5%-15%.

7. The isolation film according to any one of claims 1 to 6, wherein: The ferroelectric polymer satisfies at least one of the following conditions (1) to (5): (1) The Curie point temperature of the ferroelectric polymer is 150°C-250°C, and can be optionally 160°C-200°C; (2) The residual polarization intensity of the ferroelectric polymer is 10 mC / m 2 -1000mC / m 2 , optional 20mC / m 2 -800mC / m 2 ; (3) The weight average molecular weight of the ferroelectric polymer is 200,000-800,000, and can be 400,000-650,000; (4) The melting temperature of the ferroelectric polymer is 140°C-220°C, and can be optionally 143°C-200°C; (5) The crystallinity of the ferroelectric polymer is greater than or equal to 45%, and can be optionally 45%-68%.

8. The isolation film according to any one of claims 1 to 7, wherein: The Curie point temperature of the inorganic ferroelectric is 110°C-150°C, and can be optionally 120°C-140°C.

9. The isolation film according to any one of claims 1 to 8, wherein: The ferroelectric polymer includes one or more of polyvinylidene fluoride, a copolymer of a vinylidene fluoride monomer and other monomers; Optionally, the other monomers include one or more of trifluoroethylene, chlorotrifluoroethylene, fluorinated acetylene, and hexafluoropropylene. Optionally, the copolymer of the vinylidene fluoride monomer and other monomers includes a vinylidene fluoride-trifluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene-fluorinated acetylene copolymer, One or more of vinylidene fluoride-hexafluoropropylene copolymers.

10. The isolation film according to any one of claims 1 to 9, wherein: The inorganic ferroelectric includes one or more of perovskite type, tungsten bronze type, bismuth layered type, pyrochlore type, niobate type and lead barium lithium niobate.

11. The isolation film according to any one of claims 1 to 10, wherein: The volume distribution particle size Dv50 of the inorganic ferroelectric is 0.05 μm-5 μm, and can be optionally 0.1 μm-1 μm; and / or, The volume distribution particle size Dv50 of the ferroelectric polymer is 10nm-150nm, and can be optionally 15nm-50nm.

12. The isolation film according to any one of claims 1 to 11, wherein: The thickness of the ferroelectric coating is 1 μm-3.5 μm, and can be 1.5 μm-3 μm; and / or, The surface density of the ferroelectric coating is 2.5 g / m 2 -15g / m 2 , optional 3g / m 2 -12g / m 2 .

13. The isolation film according to any one of claims 1 to 12, wherein: The ferroelectric coating further comprises a dispersant and / or a thickener, Optionally, the dispersant includes one or more of hydrolyzed polymaleic anhydride, polyacrylic acid, acrylic acid block copolymer, polyester block copolymer, polyethylene glycol type polyol, polyethylene imine, and their respective derivatives; Optionally, the ratio of the total weight of the ferroelectric material to the weight of the dispersant is 1:(0.01-0.02), optionally 1:(0.010-0.015); Optionally, the thickener includes one or more of sodium hydroxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxypropyl methylcellulose, polyacrylate, polyurethane, and polyether; Optionally, the ratio of the total weight of the ferroelectric material to the weight of the thickener is 1:(0.01-0.02), and optionally 1:(0.010-0.015).

14. The isolation film according to any one of claims 1 to 13, wherein: The ferroelectric coating is located on one surface of the porous substrate, and a ceramic coating is arranged on the other surface of the porous substrate. When used in a battery, the ferroelectric coating faces the negative electrode, and the ceramic coating faces the positive electrode.

15. The isolation film according to any one of claims 1 to 14, wherein: The thickness of the porous substrate is 4 μm-15 μm, and can be 5 μm-10 μm; and / or, The porous substrate includes one or more of polyolefins, halogenated polyolefins, polyamides, polyesters, and their respective derivatives.

16. A battery cell comprising the separator according to any one of claims 1 to 15.

17. A battery comprising the battery cell according to claim 16.

18. An electrical device comprising the battery according to claim 17.

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