Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a separator and a negative electrode current collector, wherein the separator comprises a base film and a coating arranged on at least one side, which is close to the negative electrode current collector, of the base film, with the coating comprising one of or a blend of more of an ester polymer, a polysiloxane polymer, and an amide compound having a cyclic structure. The separator of the secondary battery has a high ionic conductivity and excellent electrolyte wettability, and can improve the cycling stability of the battery.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 2024103537572, filed on March 26, 2024, entitled “Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the widespread use of secondary batteries, higher requirements have been placed on their cycle performance and service life.

[0005] The battery separator is an important component of the secondary battery, which directly affects the battery's cycle performance. However, the separator in the existing technology has problems such as low ionic conductivity and poor electrolyte wettability, which can easily lead to the formation of lithium dendrites or sodium dendrites at the negative electrode, thereby deteriorating the battery's cycle stability.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery whose isolation membrane has high ionic conductivity and excellent electrolyte wettability, which can inhibit the formation of lithium dendrites or sodium dendrites and improve the cycle stability of the secondary battery.

[0008] The first aspect of the present application provides a secondary battery, which includes an isolation membrane and a negative electrode current collector, the isolation membrane includes a base membrane and a coating arranged on at least one side of the base membrane close to the negative electrode current collector, and the coating includes a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound with a cyclic structure.

[0009] Ester polymers, polysiloxane polymers and amide compounds with a cyclic structure have excellent ion conductivity. Coating them on the surface of the base membrane to form a coating is beneficial to improving the ionic conductivity of the isolation membrane and the migration number of active ions (such as lithium ions or sodium ions), reducing the precipitation of active ions on the surface of the negative electrode active material, and inhibiting the formation of dendrites such as lithium dendrites or sodium dendrites; and ester polymers, polysiloxane polymers, and amide compounds with a cyclic structure have good affinity and liquid absorption and retention capabilities for the electrolyte, so that the isolation membrane has excellent wettability to the electrolyte, which is beneficial to the uniform transmission of active ions and further improves the migration number of active ions, inhibits the formation of dendrites, and improves the cycle stability of the battery. At the same time, ester polymers and polysiloxane polymers have excellent resistance to reduction by metallic lithium or metallic sodium; the cyclic structure of cyclic amide compounds has a uniformly distributed electron cloud, which can improve the stability of amide compounds and make amide compounds have excellent resistance to reduction by metallic lithium or metallic sodium, so that the coating including the above materials is not easy to react with metallic lithium or metallic sodium that cannot be embedded in the negative electrode active material in time, avoiding the irreversible loss of active ions and improving the cycle stability of the battery.

[0010] When the isolation membrane of the present application is applied to a negative electrode-free battery, the excellent ionic conductivity and electrolyte wettability of the isolation membrane of the present application can enable metallic lithium or metallic sodium to be uniformly deposited on the negative electrode current collector, inhibit the formation of lithium dendrites or sodium dendrites, and improve the cycle stability of the negative electrode-free battery; and the coating including the above-mentioned material is not easy to react with the metallic lithium or metallic sodium deposited on the negative electrode current collector, which is beneficial to improving the cycle stability of the negative electrode-free battery.

[0011] In any embodiment, the ester polymer includes one or more of polymethyl methacrylate, polyvinyl acetate-methyl methacrylate, polyethylene oxide, and polymethyl methacrylate copolymer.

[0012] In any embodiment, the polysiloxane polymer includes one or more of polymethylsiloxane, polyvinylsiloxane, and dimethylpolysiloxane.

[0013] In any embodiment, the amide compound having a cyclic structure includes one or more of cyclopropylcarboxamide and N-cyclopropyl-N-(phenylmethyl)-carboxamide.

[0014] In any embodiment, the weight average molecular weight of the ester polymer is 100,000 to 400,000.

[0015] In any embodiment, the weight average molecular weight of the polysiloxane polymer is 10,000 to 100,000.

[0016] The ester polymers and polysiloxane polymers with molecular weights within the above range have excellent ion conductivity and electrolyte affinity, and at the same time have excellent resistance to reduction by metallic lithium or metallic sodium, so that the coating comprising the above materials is not easy to react with metallic lithium or metallic sodium, which is beneficial to improving the cycle stability of the battery.

[0017] In any embodiment, the coating is provided on both sides of the base film.

[0018] In any embodiment, the coating has a thickness of 1 μm to 5 μm.

[0019] When the thickness of the coating is within the above range, the separator has excellent ionic conductivity and electrolyte wettability, which improves the cycle stability of the secondary battery while the secondary battery has excellent energy density.

[0020] In any embodiment, the coating is a non-porous coating.

[0021] Traditional separators often have a high porosity. Lithium dendrites or sodium dendrites generated at the negative electrode can easily pass through the pores of the separator, connecting the positive and negative electrodes and causing an internal short circuit, which deteriorates the battery's cycle stability and safety performance. The present application provides a dense, non-porous coating composed of a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound with a cyclic structure on the base membrane. The separator has excellent electrolyte wettability and ionic conductivity. While inhibiting the formation of lithium dendrites or sodium dendrites, it can further prevent the formed dendrites from passing through the separator to connect the positive and negative electrodes, reducing the probability of internal short circuits in the battery and improving the battery's cycle stability and safety performance.

[0022] In any embodiment, the base film includes one or more of a polyethylene film, a polypropylene film, and a polyimide film.

[0023] In any embodiment, the base film has a thickness of 3 μm to 30 μm.

[0024] In any embodiment, the secondary battery comprises a negative electrode-less battery.

[0025] A second aspect of the present application further provides an electrical device comprising the secondary battery of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a scanning electron microscope schematic diagram of a separator of a secondary battery according to Example 1 of the present application;

[0027] FIG2 is a scanning electron microscope diagram of the separator of the secondary battery of Comparative Example 3 of the present application;

[0028] 3 is a scanning electron microscope diagram of a cross section of a negative electrode sheet of a secondary battery in a fully charged state according to Example 1 of the present application;

[0029] FIG4 is a scanning electron microscope diagram of a cross section of a negative electrode sheet of a secondary battery in a fully charged state according to Comparative Example 3 of the present application;

[0030] FIG5 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0031] FIG6 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG5 ;

[0032] FIG7 is a schematic diagram of a battery module according to an embodiment of the present application;

[0033] FIG8 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0034] FIG9 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG8 ;

[0035] FIG. 10 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0036] Description of reference numerals:

[0037] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0038] Below, the embodiments of the secondary battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0039] " 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.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0041] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0042] 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.

[0043] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0044] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] The separator is a material located between the positive and negative electrodes of a battery. It is used to prevent internal short circuits caused by contact between the positive and negative electrodes. It also provides a channel for the transmission of active ions (such as lithium ions or sodium ions) between the positive and negative electrodes. Therefore, the separator has a very important impact on the cycle performance of the battery. Existing separators (such as polyethylene separators, polypropylene separators, etc.) have the disadvantages of poor electrolyte wettability and low ionic conductivity. These can easily lead to the precipitation of active ions on the surface of the negative electrode active material or uneven deposition of active ions on the surface of the negative electrode current collector of a battery without a negative electrode. This can then cause the formation of lithium dendrites or sodium dendrites, resulting in irreversible loss of active lithium or active sodium, and worsening the cycle stability of the battery.

[0046] [Secondary battery]

[0047] Based on this, the present application proposes a secondary battery, which includes an isolation membrane and a negative electrode current collector, the isolation membrane includes a base membrane and a coating arranged on at least one side of the base membrane close to the negative electrode current collector, and the coating includes a blend of one or more ester polymers, polysiloxane polymers, and amide compounds with a cyclic structure.

[0048] In this article, the term "separator" refers to a material placed between the positive electrode and the negative electrode of the battery to separate the positive electrode and the negative electrode, prevent the positive electrode and the negative electrode from contacting and short-circuiting, and allow electrolyte ions to pass through.

[0049] In this context, the term "polymer" includes, on the one hand, a collection of chemically uniform macromolecules prepared by polymerization reactions, but differing in degree of polymerization, molar mass and chain length; on the other hand, it also includes derivatives of such a collection of macromolecules formed by polymerization reactions, i.e. polymers that can be obtained by reactions of functional groups in the above-mentioned macromolecules, such as addition or substitution, and which can be chemically uniform or chemically heterogeneous.

[0050] As used herein, the term "ester polymer" refers to a type of polymer containing an ester group in its structural unit.

[0051] As used herein, the term "ester group" refers to a group having the structure -COO-.

[0052] In some embodiments, the ester polymer includes one or more of polymethyl methacrylate, polyvinyl acetate-methyl methacrylate, polyethylene oxide, and polymethyl methacrylate copolymer.

[0053] In this article, the term "polysiloxane polymer" is a general term for a class of polymers whose backbone is composed of alternately linked silicon atoms and oxygen atoms, and different organic groups are further linked to the silicon atoms.

[0054] In some embodiments, the polysiloxane polymer includes one or more of polymethylsiloxane, polyvinylsiloxane, and dimethylpolysiloxane.

[0055] In this article, the term "amide compound" refers to a compound formed by replacing the hydrogen atom on the nitrogen atom in an ammonia (NH3) or amine (RNH2, R2NH) molecule with an acyl group. It can also be regarded as a compound formed by replacing the hydroxyl group in a carboxylic acid molecule with an amino group (-NH2) or a hydrocarbon amino group (-NHR or -NR2).

[0056] Herein, the term "amide compound having a cyclic structure" refers to an amide compound including a cyclic structure, wherein the cyclic structure includes at least one of a cycloalkyl group, an aromatic group, and a heterocycle.

[0057] As used herein, the term "cycloalkyl" refers to a hydrocarbon compound in which the carbon chain in the molecule is a ring structure.

[0058] In this article, the term "aromatic" refers to a six-membered ring structure with alternating single and double bonds between carbon atoms. The simplest compound is benzene. Aromatic hydrocarbons can be categorized as monocyclic, bicyclic, and condensed-ring aromatics, depending on the number of benzene rings and their structural relationships.

[0059] In this article, the term "heterocycle" refers to a ring structure that contains other heteroatoms in addition to carbon atoms. Common heteroatoms include oxygen, sulfur, nitrogen, etc.

[0060] In some embodiments, the amide compound having a cyclic structure includes one or more of cyclopropylcarboxamide and N-cyclopropyl-N-(phenylmethyl)-carboxamide.

[0061] In some embodiments, the coating is disposed on both sides of the base film.

[0062] In some embodiments, the coating layers disposed on both sides of the base film each independently include a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound having a cyclic structure.

[0063] Ester polymers, polysiloxane polymers and amide compounds with a cyclic structure have excellent ion conductivity. Coating them on the surface of the base membrane to form a coating is beneficial to improving the ionic conductivity of the isolation membrane and the migration number of active ions (such as lithium ions or sodium ions), reducing the precipitation of active ions on the surface of the negative electrode active material, and inhibiting the formation of dendrites such as lithium dendrites or sodium dendrites; and ester polymers, polysiloxane polymers, and amide compounds with a cyclic structure have good affinity and liquid absorption and retention capabilities for the electrolyte, so that the isolation membrane has excellent wettability to the electrolyte, which is beneficial to the uniform transmission of active ions and further improves the migration number of active ions, inhibits the formation of dendrites, and improves the cycle stability of the battery. At the same time, ester polymers and polysiloxane polymers have excellent resistance to reduction by metallic lithium or metallic sodium; the cyclic structure of cyclic amide compounds has a uniformly distributed electron cloud, which can improve the stability of amide compounds and make amide compounds have excellent resistance to reduction by metallic lithium or metallic sodium, so that the coating including the above materials is not easy to react with metallic lithium or metallic sodium that cannot be embedded in the negative electrode active material in time, avoiding the irreversible loss of active ions and improving the cycle stability of the battery.

[0064] In some embodiments, the secondary battery comprises a negative electrode-free battery.

[0065] In this article, the term "negative electrode-free battery" refers to a battery that does not actively provide a negative electrode active material layer on the negative electrode side during the battery manufacturing process. For example, during the battery manufacturing process, a lithium / sodium metal or carbonaceous active material layer is not provided on the negative electrode through a coating or deposition process to form a negative electrode active material layer. During the first charge, lithium ions or sodium ions gain electrons at the anode side, and metallic lithium or metallic sodium is deposited on the current collector surface to form a lithium metal phase or a sodium metal phase. During discharge, the metallic lithium or metallic sodium can be converted into lithium ions or sodium ions and returned to the positive electrode, achieving cyclic charge and discharge.

[0066] When the isolation membrane of the present application is applied to a negative electrode-free battery, the excellent ionic conductivity and electrolyte wettability of the isolation membrane of the present application can enable metallic lithium or metallic sodium to be uniformly deposited on the negative electrode current collector, inhibit the formation of lithium dendrites or sodium dendrites, and improve the cycle stability of the negative electrode-free battery; and the coating including the above-mentioned material is not easy to react with the metallic lithium or metallic sodium deposited on the negative electrode current collector, which is beneficial to improving the cycle stability of the negative electrode-free battery.

[0067] In some embodiments, the weight average molecular weight of the ester polymer is 100,000 to 400,000.

[0068] In the present application, the weight average molecular weight of the polymer can be tested by methods known in the art, such as using an ultra-high performance polymer chromatograph: ACQUITY APC; detector: ACQUITY differential refractive index detector. The test steps are as follows: (1) Preheating: Install the chromatographic column and pipelines, turn on the console in turn, test the power supply, etc., and open the test software Empower; (2) Parameter setting, injection volume: 0μL to 50μL (depending on the sample concentration); pump flow rate: 0.2mL / min; mobile phase: 30mol / LLiBr in N-methylpyrrolidone (NMP) solution; sealing cleaning liquid: isopropanol; pre-column: PLgel10umMiniMIX-BGuard (size: 50mm×4.6mm×2); analytical phase: PLgel10umMiniMIX-B (size: 250mm×4.6mm); standard: polystyrene; running time: 30min; detector: ACQUITY differential refractive index (RI) detector; column oven temperature: 90℃; detector temperature: 55℃. (3) Sample testing: a. Standard sample and test sample preparation: Weigh 0.002g to 0.004g of standard sample / test sample respectively and add 2mL of mobile phase liquid to prepare a 0.1% to 0.5% mixed standard, and store in the refrigerator for >8h; b. Standard solution / sample testing: Edit the sample group to be tested, select the established sample group method, and after the baseline is stable, click the run queue to start testing the sample; (4) Data processing: Based on the relationship between retention time and molecular weight, use the chemical workstation to establish a calibration curve, integrate and quantify the sample spectrum, and the chemical workstation automatically generates the molecular weight and molecular weight distribution results.

[0069] In some embodiments, the weight average molecular weight of the ester polymer is 100,000, 130,000, 160,000, 190,000, 220,000, 250,000, 280,000, 310,000, 340,000, 370,000, 400,000, or any value therebetween.

[0070] In some embodiments, the weight average molecular weight of the polysiloxane polymer is 10,000 to 100,000.

[0071] In some embodiments, the weight average molecular weight of the polysiloxane polymer is 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, or any value therebetween.

[0072] The ester polymers and polysiloxane polymers with molecular weights within the above range have excellent ion conductivity and electrolyte affinity, and at the same time have excellent resistance to reduction by metallic lithium or metallic sodium, so that the coating comprising the above materials is not easy to react with metallic lithium or metallic sodium, which is beneficial to improving the cycle stability of the battery.

[0073] In some embodiments, the coating includes an amide compound having a cyclic structure.

[0074] In some embodiments, the ionic conductivity of the separator is 1.5×10 -1 mS / cm-2.5×10 -1 mS / cm.

[0075] In this application, the term "ionic conductivity" is a physical quantity that describes the ability of ions to migrate in an electrolyte solution.

[0076] In this application, the ionic conductivity of the isolation membrane can be tested using methods known in the art. For example, the isolation membrane is cut into a disc of a certain area, dried, and placed between two stainless steel electrodes. The model of the stainless steel electrode is DDG-01. The distance between the stainless steel electrodes is 3mm to 5mm, and an electrolyte is provided between the electrodes. The electrolyte is a mixture of diethylene glycol dimethyl ether and tetrahydrofuran in a mass ratio of 1:3. Sodium hexafluorophosphate (NaPF6) is added and stirred to obtain an electrolyte with a NaPF6 concentration of 1.0 mol / L. After absorbing a sufficient amount of electrolyte, the button cell is sealed to form a button cell. The button cell is subjected to an AC impedance spectroscopy experiment using an electrochemical workstation to obtain the ionic conductivity of the isolation membrane. The electrochemical workstation can be a Shanghai Chenhua CHI 660C electrochemical workstation. The AC signal frequency range is 0.01Hz to 1MHz, and the sine wave potential amplitude is 5mV. For accuracy, the average value of 5 parallel samples is taken as the test result.

[0077] In some embodiments, the ionic conductivity of the separator is 1.5×10 -1 mS / cm, 1.6×10 -1 mS / cm, 1.7×10 -1 mS / cm, 1.8×10 -1 mS / cm, 1.9×10 -1 mS / cm, 2.0×10 -1 mS / cm, 2.2×10 -1 mS / cm, 2.3×10 -1 mS / cm, 2.4×10 -1 mS / cm, 2.5×10 -1 mS / cm or any value therebetween.

[0078] The ionic conductivity of the isolation membrane is within the above range, which is beneficial to increasing the migration number of active ions, inhibiting the formation of dendrites, and improving the cycle stability of the battery.

[0079] In some embodiments, the contact angle between the side of the separator coated with the coating and the electrolyte is less than or equal to 30°.

[0080] In this application, the contact angle between the coated side of the isolation membrane and the electrolyte can be tested using methods known in the art. For example, the electrolyte is dripped onto the surface of the isolation membrane, and the contact angle is measured using a contact angle meter according to the GB / T 14210 method. The wettability of the electrolyte is determined based on the contact angle between the electrolyte and the isolation membrane. The electrolyte is a mixture of diethylene glycol dimethyl ether and tetrahydrofuran in a mass ratio of 1:3, and sodium hexafluorophosphate (NaPF6) is added and stirred to obtain an electrolyte with a NaPF6 concentration of 1.0 mol / L. A contact angle close to 0 degrees indicates that the electrolyte is well wetted on the isolation membrane surface, while a contact angle close to 90 degrees indicates that the electrolyte has poor wettability on the isolation membrane surface.

[0081] In some embodiments, the contact angle of the coated side of the separator with the electrolyte is 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, or any value therebetween.

[0082] The contact angle between the coated side of the isolation membrane and the electrolyte is within the above range. The isolation membrane has excellent wettability to the electrolyte, which is beneficial to improving the migration number and transmission uniformity of active ions, inhibiting the formation of dendrites, and improving the cycle stability of the battery.

[0083] In some embodiments, the coating has a thickness of 1 μm to 5 μm.

[0084] In this application, coating thickness can be measured using methods known in the art. For example, prepare a battery separator sample to be tested and ensure it is in a safe condition. Place the probe of a thickness gauge on the surface of the battery separator and record the measurement results. Repeat these steps to measure the separator thickness at multiple locations to obtain more accurate data. Analyze the measurement results of the uncoated and coated separators to calculate the average coating thickness.

[0085] In some embodiments, the coating has a thickness of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value therebetween.

[0086] When the thickness of the coating is within the above range, the separator has excellent ionic conductivity and electrolyte wettability, which improves the cycle stability of the secondary battery while the secondary battery has excellent energy density.

[0087] In some embodiments, the coating is a non-porous coating.

[0088] In this application, the term "non-porous coating" refers to a coating having no pores or almost no pores, with a porosity of zero.

[0089] In the present application, the porosity of the coating can be tested by methods known in the art, for example, referring to GB / T21650.2-2008, the porosity of the coating can be measured by nitrogen adsorption method.

[0090] The morphology of the coating in this application can be tested using methods known in the art, such as using a scanning electron microscope (SEM) to observe the microscopic morphology of the isolation membrane. Figure 1 is a schematic SEM image of an isolation membrane according to one embodiment of the present application. As shown in Figure 1, the surface of the isolation membrane is dense and non-porous.

[0091] Traditional separators often have a high porosity. Lithium dendrites or sodium dendrites generated at the negative electrode can easily pass through the pores of the separator, connecting the positive and negative electrodes and causing an internal short circuit, which deteriorates the battery's cycle stability and safety performance. The present application provides a dense, non-porous coating composed of a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound with a cyclic structure on the base membrane. The separator has excellent electrolyte wettability and ionic conductivity. While inhibiting the formation of lithium dendrites or sodium dendrites, it can further prevent the formed dendrites from passing through the separator to connect the positive and negative electrodes, reducing the probability of internal short circuits in the battery and improving the battery's cycle stability and safety performance.

[0092] In some embodiments, the base film includes one or more of a polyethylene film, a polypropylene film, and a polyimide film.

[0093] In some embodiments, the base film has a thickness of 3 μm to 30 μm.

[0094] In some embodiments, the base film has a thickness of 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, 21 μm, 24 μm, 27 μm, 30 μm, or any value therebetween.

[0095] In some embodiments, the base membrane has a pore size of 5 nm to 80 nm.

[0096] In some embodiments, the pore size of the basement membrane is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, or any value therebetween.

[0097] In some embodiments, the secondary battery is any one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0098] [Negative electrode]

[0099] In some embodiments, the secondary battery is a negative electrode-less battery.

[0100] In some embodiments, the negative electrode sheet includes a negative electrode current collector.

[0101] In some embodiments, to improve battery performance, the negative electrode side of a negative electrode-free battery may be provided with some conventional negative electrode active materials, such as carbonaceous materials, metal oxides, alloys, etc. Although these materials have a certain capacity, due to the small amount of these materials, they are not used as the main negative electrode active material in the battery and are therefore not considered to form a negative electrode active material layer that plays a role in lithium or sodium intercalation. The secondary battery thus constructed can still be considered a negative electrode-free battery.

[0102] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0103] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer can be disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0104] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil or aluminum foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0106] In some embodiments, the negative electrode film layer may further optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0107] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0109] In some embodiments, the negative electrode plate can be prepared by the following method: dispersing the components for preparing the negative electrode plate described above, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0110] [Positive electrode plate]

[0111] The positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0112] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0113] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following materials: Prussian blue analogs, sodium-containing phosphates, sodium-containing transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, the Prussian blue analog is Na x P[R(CN)6] δ ·zH2O, where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10; the sodium-containing phosphate is Na b Me c (PO4) dO2X, wherein A is one or more of H, Li, Na, K and NH4, Me is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, X is one or more of F, Cl and Br, 0 < b ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3; the sodium-containing transition metal oxide is Na a M b N c Fe d Mn e O2, M, N include at least one of Sc, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 0.05≤b≤0.2, 0.2≤c≤0.3, 0.2≤d≤0.3, 0.3≤e≤0.4, 0.75≤a / (b+c+d+e)≤1.

[0114] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0115] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0116] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0117] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0118] [Electrolytes]

[0119] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0120] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0121] In some embodiments, the electrolyte includes an electrolyte salt selected from at least one of NaPF6, NaBF4, NaN(SO2F)2(NaFSI), NaClO4, NaAsF6, NaB(C2O4)2(NaBOB), NaBF2(C2O4)(NaDFOB), NaN(SO2RF)2, and NaN(SO2F)(SO2RF), wherein RF is represented by C b F 2b+1 , b is an integer between 1 and 10, and can be optionally an integer between 1 and 3.

[0122] In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2, and NaBF2(C2O4). In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2RF)2, and NaBF2(C2O4). In some embodiments, RF is -CF3, -C2F5, or -CF2CF2CF3.

[0123] In some embodiments, the electrolyte includes a solvent, and the solvent includes at least one of a chain carbonate, a chain carboxylate, a cyclic carbonic acid, an ether solvent, a sulfone solvent, and a nitrile solvent. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). In some embodiments, the chain carboxylate includes at least one of methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the linear carboxylic acid ester includes at least one of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the ether solvent includes at least one of dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), tetrahydropyran (THP), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DG), 1,2-diethoxyethane, and 1,2-dibutoxyethane.

[0124] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0125] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0126] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0127] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] In this application, the shape of the secondary battery includes but is not limited to cylindrical, square or any other shape. For example, FIG5 is a secondary battery 5 with a square structure as an example.

[0129] In some embodiments, referring to FIG6 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0130] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0131] Figure 7 shows an example battery module 5. Referring to Figure 7 , within a battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0132] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0133] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0134] Figures 8 and 9 illustrate an example battery pack 1. Referring to Figures 8 and 9 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0135] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0136] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0137] Figure 10 shows an example of an 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 the secondary battery, a battery pack or battery module can be used.

[0138] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0139] Example

[0140] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0141] 1. Preparation method

[0142] Example 1:

[0143] 1) Preparation of isolation membrane

[0144] A polyethylene film was used as a base film. A solution of polyvinyl acetate-methyl methacrylate (PVA) with a weight-average molecular weight of 200,000 was sprayed on both sides of the film. The solution was dried at 80°C to form a non-porous coating. The base film had a thickness of 7 μm, a pore size of 35 nm, and a porosity of 40%. The coating had a thickness of 2 μm on one side. The PVA-methyl methacrylate was purchased from Sigma-Aldrich.

[0145] 2) Preparation of negative electrode sheet

[0146] Weigh 5g of sodium carboxymethylcellulose (CMC-Na) and dissolve it in 1000mL of water with stirring. Then, add 5g of single-walled carbon nanotubes and disperse them ultrasonically to prepare a slurry. This slurry is coated on the surface of the negative electrode current collector copper foil. After drying, slitting, and cutting, the negative electrode sheet is obtained.

[0147] 3) Preparation of positive electrode sheet

[0148] A positive electrode slurry was prepared by fully dissolving 10 wt% of polyvinylidene fluoride binder in N-methylpyrrolidone, adding 10 wt% of carbon black conductive agent and 80 wt% of positive electrode active material Na4Fe3(PO4)2(P2P7) and dispersing them evenly. This slurry was evenly coated on the surface of the positive electrode current collector aluminum foil. After drying, cold pressing, slitting, and cutting, the positive electrode sheets were obtained.

[0149] 4) Preparation of electrolyte

[0150] In an argon-filled glove box with a water content of <1 ppm, diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a mass ratio of 1:3, sodium hexafluorophosphate (NaPF6) was added, and after stirring evenly, an electrolyte with a NaPF6 concentration of 1.0 mol / L was obtained.

[0151] 5) Battery Preparation

[0152] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to isolate the positive and negative electrode sheets. The bare battery cell is wound, the tabs are welded, and the bare battery cell is placed in an outer package. The electrolyte prepared above is injected into the dried battery cell, and then the secondary battery product of Example 1 is obtained after packaging, standing, formation, shaping, capacity testing and other processes.

[0153] Examples 2-4

[0154] The secondary battery preparation methods of Examples 2-4 are basically the same as the preparation method of Example 1, except that the materials coated on the base film are different. Example 2 is polyvinyl siloxane with a weight-average molecular weight of 50,000, Example 3 is N-cyclopropyl-N-(phenylmethyl)-formamide, and Example 4 is a blend polymer of polyvinyl acetate-methyl methacrylate with a weight-average molecular weight of 200,000 and polyvinyl siloxane with a weight-average molecular weight of 50,000 with a molar ratio of 1:1. Polyvinyl siloxane and N-cyclopropyl-N-(phenylmethyl)-formamide were both purchased from Sigma-Aldrich.

[0155] Example 5

[0156] The preparation method of the secondary battery of Example 5 is basically the same as that of Example 1, except that the preparation method of the negative electrode sheet is:

[0157] The negative electrode active material hard carbon, the conductive agent carbon black, and the binder sodium carboxymethyl cellulose are fully stirred and mixed in a deionized water solvent system in a mass ratio of 90:5:5 to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain a negative electrode sheet.

[0158] Comparative Example 1

[0159] The preparation method of the secondary battery of Comparative Example 1 is substantially the same as that of Example 1, except that the base film is coated with a polyhexamethylene adipamide polymer having a weight average molecular weight of 20,000, which is purchased from Sigma-Aldrich.

[0160] Comparative Example 2

[0161] The preparation method of the secondary battery of Comparative Example 2 is substantially the same as that of Example 5, except that the base film of the isolation membrane is coated with octamethylsiloxane purchased from Sigma-Aldrich.

[0162] Comparative Example 3

[0163] The preparation method of the secondary battery of Comparative Example 3 is substantially the same as that of Example 1, except that the base film does not have a coating layer.

[0164] Comparative Example 4

[0165] The preparation method of the secondary battery of Comparative Example 4 is substantially the same as that of Example 5, except that the base film does not have a coating layer.

[0166] 2. Battery performance test

[0167] 1. Deposition uniformity of metallic sodium

[0168] The battery was charged at a constant current rate of 0.33C at 25°C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current less than 0.05C, which was considered to be fully charged. The fully charged battery without a negative electrode was disassembled to obtain a negative electrode sheet with sodium metal deposited. Using argon ion polishing technology, also known as CP cross-sectional polishing technology, the cross-section of the negative electrode sheet sample was bombarded to obtain a flat polished section. At the same time, a scanning electron microscope (SEM) was used to observe and analyze the microscopic characteristics of the internal structure of the negative electrode sheet sample and observe the uniformity of the sodium metal deposition on the negative electrode sheet.

[0169] 2. Material resistance to sodium metal reduction

[0170] The film of the material forming the base film coating was dried in a 70°C oven for 24 hours and cut into coin-sized pieces. The film, sodium sheet, electrolyte prepared in Example 1, a rubber-tipped dropper, a marker, tweezers, and a centrifuge tube were transferred to a glove box. The film was placed in the centrifuge tube. The protective film on the surface of the sodium sheet was removed with tweezers and added to the centrifuge tube (the rough surface of the composite sodium sheet was the pure sodium metal layer, and the bright surface was the other metal lining). The electrolyte was added to 1 / 2 to 2 / 3 of the centrifuge tube. The centrifuge tube and other items were transferred out of the glove box and cleaned thoroughly. The centrifuge tube was placed in a 60°C oven and observed for bubbles, surface phenomena of the sodium sheet (rough surface), electrolyte color changes, and other special phenomena. The changes in the film state were observed. If, after 24 hours, the film did not produce bubbles and the electrolyte did not change color, the material had strong resistance to sodium metal reduction. If, after 24 hours, the film produced bubbles and the electrolyte changed color, the material had weak resistance to sodium metal reduction.

[0171] 3. Battery cycle number

[0172] Batteries from each of the aforementioned examples and comparative examples were tested in parallel. Each battery cell was charged at 0.33C to a voltage of 3.65V at 25°C, then discharged at 0.33C to a voltage of 1.5V. The reversible capacity (C0) was measured. This charge and discharge cycle was repeated until the discharge capacity (Cn / C0) at a given cycle was ≤80%. The total number of cycles was recorded as X-Cycle. Cn is the reversible capacity at the nth cycle.

[0173] 3. Analysis of test results of various embodiments and comparative examples

[0174] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0175] The secondary batteries of Examples 1-5 include an isolation membrane and a negative electrode current collector, the isolation membrane includes a base membrane and a coating arranged on at least one side of the base membrane close to the negative electrode current collector, and the coating includes a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound with a cyclic structure.

[0176] Figure 1 is a schematic SEM image of the separator of the secondary battery of Example 1; Figure 2 is a schematic SEM image of the separator of the secondary battery of Comparative Example 3; Figure 3 is a SEM image of a cross section of the negative electrode sheet of the secondary battery of Example 1 under full charge; Figure 4 is a SEM image of a cross section of the negative electrode sheet of the secondary battery of Comparative Example 3 under full charge. As shown in Figures 1 and 2, the coated separator of Example 1 is dense and non-porous, while the uncoated separator of Comparative Example 3 has pores. As shown in Figures 3 and 4, the sodium metal in Example 1 is uniformly deposited on the negative electrode current collector, while the sodium metal in Comparative Example 3 is unevenly deposited on the negative electrode current collector.

[0177] From the comparison of Examples 1-5 and Comparative Examples 1-4, it can be seen that when the isolation membrane includes a base membrane and a coating arranged on at least one side of the base membrane close to the negative electrode current collector, and the coating includes a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound with a cyclic structure, the cycle stability of the battery can be improved.

[0178] From the comparison between Examples 1-5 and Comparative Examples 3-4, it can be seen that the polymer coating is provided on the base film of the separator, which can reduce the contact angle between the separator and the electrolyte, improve the ionic conductivity of the separator, and improve the cycle stability and safety performance of the battery.

[0179] Comparison of Examples 1-5 and Comparative Examples 1-2 shows that when the coating comprises a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound with a cyclic structure, materials with strong resistance to sodium metal reduction can further enhance the battery's cycling stability. However, when the coating comprises amides or siloxanes without cyclic structures, even if the resulting separator exhibits considerable ionic conductivity and electrolyte wettability, the lack of sodium metal reduction resistance of these amides and siloxanes leads to poor battery cycling stability, making them unsuitable for use in the coating of the separator of the present application.

[0180] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a separator and a negative electrode current collector, characterized in that: The separator includes a base film and a coating layer provided on at least one side of the base film close to the negative electrode current collector, wherein the coating layer includes a blend of one or more of an ester polymer, a polysiloxane polymer, and an amide compound having a cyclic structure.

2. The secondary battery according to claim 1, wherein The ester polymer includes one or more of polymethyl methacrylate, polyvinyl acetate-methyl methacrylate, polyethylene oxide and polymethyl methacrylate copolymer; and / or, The polysiloxane polymer includes one or more of polymethylsiloxane, polyvinylsiloxane, and dimethylpolysiloxane; and / or, The amide compound having a cyclic structure includes one or more of cyclopropylformamide and N-cyclopropyl-N-(phenylmethyl)-formamide.

3. The secondary battery according to claim 1 or 2, characterized in that The weight average molecular weight of the ester polymer is 100,000-400,000; and / or, The weight average molecular weight of the polysiloxane polymer is 10,000-100,000.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The coating layer is disposed on both sides of the base film.

5. The secondary battery according to any one of claims 1 to 4, characterized in that The coating has a thickness of 1 μm to 5 μm.

6. The secondary battery according to any one of claims 1 to 5, characterized in that The coating is a non-porous coating.

7. The secondary battery according to any one of claims 1 to 6, characterized in that The base film includes one or more of a polyethylene film, a polypropylene film, and a polyimide film.

8. The secondary battery according to any one of claims 1 to 7, characterized in that The base film has a thickness of 3 μm to 30 μm.

9. The secondary battery according to any one of claims 1 to 8, characterized in that The secondary battery includes a negative electrode-less battery.

10. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

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