Modified negative electrode sheet, method for manufacturing the same, secondary battery, and electric device

Abstract

The application relates to a modified negative electrode sheet, a preparation method thereof, a secondary battery and an electric device. The modified negative electrode sheet comprises a negative electrode current collector, a negative electrode active material layer located on at least one side of the negative electrode current collector, and an artificial SEI film located on a side of the negative electrode active material layer away from the negative electrode current collector. The artificial SEI film comprises one or more of a first component and a second component. The first component comprises one or more of an unsaturated fatty acid containing a carbon-carbon double bond and a hydrazine compound prepared from a raw material comprising the unsaturated fatty acid. The second component comprises a lithium salt. By forming a stable artificial SEI film containing the first component and / or the second component on the surface of the negative electrode active material layer, the artificial SEI film can slow down the growth of the negative electrode SEI film, thereby slowing down the storage attenuation and improving the storage life.

Description

Technical Field

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

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] In recent years, with the increasingly wide application of rechargeable batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of rechargeable batteries, higher requirements have been placed on their storage lifespan. Summary of the Invention

[0004] This application provides a modified negative electrode sheet with a long storage life, a method for preparing the same, a secondary battery, and an electrical device.

[0005] To achieve the above objectives, a first aspect of this application provides a modified negative electrode sheet, comprising:

[0006] Negative electrode current collector;

[0007] A negative electrode active material layer is located on at least one side of the negative electrode current collector; and

[0008] An artificial SEI membrane is located on the side of the negative electrode active material layer away from the negative electrode current collector. The artificial SEI membrane comprises one or more of a first component and a second component. The first component comprises one or more of an unsaturated fatty acid containing a carbon-carbon double bond and an acylhydrazine substance whose raw material includes the unsaturated fatty acid. The second component comprises a lithium salt.

[0009] Therefore, this application forms a stable artificial SEI film containing a first component and / or a second component on the surface of the negative electrode active material layer. The artificial SEI film can slow down the growth of the negative electrode SEI film, thereby slowing down storage degradation and improving storage life.

[0010] In some embodiments of this application, the first component includes one or more of maleic acid, maleic hydrazide, and maleic dihydrazide.

[0011] In some embodiments of this application, the second component includes one or more of an organic lithium salt and an inorganic lithium salt; the organic lithium salt includes lithium acetate; and the inorganic lithium salt includes one or more of lithium carbonate and lithium chloride.

[0012] In some embodiments of this application, the artificial SEI membrane comprises a first component and a second component, wherein the mass ratio of the first component to the second component is (0.5-4):1.

[0013] In some embodiments of this application, the mass ratio of the first component to the second component is (1-2):1.

[0014] In some embodiments of this application, the artificial SEI membrane comprises maleic acid and lithium carbonate.

[0015] In some embodiments of this application, the thickness of the artificial SEI film is 10nm-120nm.

[0016] In some embodiments of this application, the mass ratio of the artificial SEI membrane to the negative electrode active material layer is (0.5-5):100.

[0017] In some embodiments of this application, the mass ratio of the artificial SEI membrane to the negative electrode active material layer is (1-1.5):100.

[0018] In some embodiments of this application, the negative electrode active material layer includes a negative electrode active material, which includes one or more of carbon-based materials and silicon-based materials.

[0019] In some embodiments of this application, the negative electrode active material includes graphite, which includes one or more of artificial graphite and natural graphite.

[0020] In some embodiments of this application, the specific surface area of ​​the graphite is 1 m². 2 / g -2 m 2 / g, with a volume average particle size Dv50 of 12μm-20μm.

[0021] The second aspect of this application also provides a method for preparing the modified negative electrode sheet of the first aspect of this application, comprising the following steps:

[0022] The negative electrode active material layer is prepared on at least one side of the negative electrode current collector;

[0023] An artificial SEI solution is applied to the surface of the negative electrode active material layer away from the negative electrode current collector by spraying or transfer coating to form an artificial SEI film on the surface of the negative electrode active material layer, thereby preparing the modified negative electrode sheet.

[0024] The artificial SEI solution comprises one or more of the first component and the second component.

[0025] Therefore, by applying an artificial SEI solution to the surface of the negative electrode active material layer through spraying or transfer coating, and drying it to form an artificial SEI film, the artificial SEI film is bonded to the negative electrode active material layer on the surface. The artificial SEI film is more stable, and the stable artificial SEI film can slow down the growth of the negative electrode SEI film, thereby slowing down storage degradation and improving storage life.

[0026] In some embodiments of this application, the solid content of the artificial SEI solution is 0.5wt%-3wt%; and / or

[0027] The artificial SEI solution further includes a solvent, which includes one or more of N-methylpyrrolidone, tetrahydrofuran, and ethanol.

[0028] A third aspect of this application provides a secondary battery, including a modified negative electrode sheet according to the first aspect of this application or a modified negative electrode sheet prepared using the preparation method of the second aspect of this application.

[0029] The fourth aspect of this application provides an electrical device, including the secondary battery of the third aspect of this application.

[0030] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0031] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0032] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0033] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0034] Figure 2 for Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0035] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0036] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0037] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0038] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0041] The modified negative electrode sheet, its preparation method, secondary battery, and some embodiments of the electrical device of this application are described in detail below with appropriate reference to the accompanying drawings. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0043] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0046] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0048] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0049] Currently, rechargeable batteries have made great strides, thus placing higher demands on their storage life. The degradation of rechargeable battery storage life mainly occurs at the negative electrode. The loss of active materials in the negative electrode and the continuous growth of the SEI film are the main reasons for the degradation, with the continuous growth of the SEI film on the negative electrode being the primary cause.

[0050] In related technologies, artificial SEI materials are added to the negative electrode slurry to form a stable artificial SEI film on the surface of the negative electrode active material, thereby protecting the negative electrode active material and slowing down SEI film growth. However, the artificial SEI film fails. During failure analysis, the technicians of this application found that the addition of artificial SEI materials to the negative electrode slurry caused instability in cell performance. Some cell groups showed good performance, while others did not see any improvement. This may be because the artificial SEI material easily detaches and peels off during slurry kneading and stirring, ultimately leading to the failure of the artificial SEI film.

[0051] Based on the above problems, this application sprays an artificial SEI solution onto the surface of the negative electrode active material layer, and after drying, forms an artificial SEI film. The artificial SEI film and the negative electrode active material layer are bonded to the surface, resulting in better stability and effectively slowing down the growth of the negative electrode SEI film.

[0052] The first aspect of this application provides a modified negative electrode sheet, including a negative current collector, a negative active material layer located on at least one side of the negative current collector, and an artificial SEI film located on the side of the negative active material layer away from the negative current collector. The artificial SEI film contains one or more of a first component and a second component. The first component includes one or more of an unsaturated fatty acid containing a carbon-carbon double bond and an acylhydrazine substance whose preparation raw material includes unsaturated fatty acid. The second component includes a lithium salt.

[0053] It should be noted that in this invention, terms such as "first component" and "second component" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first" and "second" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0054] When an artificial SEI film contains unsaturated fatty acids with carbon-carbon double bonds, the artificial SEI film has a higher cationic conductivity, which is more conducive to the passage of lithium ions, thus facilitating the stability of the artificial SEI film. The higher the stability of the artificial SEI film, the better it is for protecting the negative electrode material, thereby improving the battery cell's storage life.

[0055] When the artificial SEI membrane contains hydrazide-like substances, including unsaturated fatty acids, as raw materials, the artificial SEI membrane is less likely to undergo side reactions with the electrolyte. As a result, the artificial SEI membrane is more stable and better protects the negative electrode material from electrolyte erosion and consumption, thereby improving the cell life.

[0056] When artificial SEI films contain lithium salts, the lithium salts can offset irreversible lithium consumption during the battery formation process, thereby reducing irreversible lithium consumption and thus improving the cell's storage life.

[0057] Therefore, this application forms a stable artificial SEI film containing a first component and / or a second component on the surface of the negative electrode active material layer. The artificial SEI film can slow down the growth of the negative electrode SEI film, thereby slowing down storage degradation and improving storage life.

[0058] In some embodiments, the first component includes one or more of maleic acid, maleic hydrazide, and maleic dihydrazide.

[0059] In some alternative implementations, the first component includes maleic acid.

[0060] In some embodiments, the second component includes one or more of organic lithium salts and inorganic lithium salts.

[0061] As one possible implementation, organic lithium salts include lithium acetate.

[0062] In some exemplary embodiments, the inorganic lithium salt includes one or more of lithium carbonate and lithium chloride.

[0063] In some of these embodiments, the inorganic lithium salt includes lithium carbonate.

[0064] In some embodiments, the artificial SEI membrane comprises a first component and a second component, wherein the mass ratio of the first component to the second component is (0.5-4):1; for example, it can be, but is not limited to, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or any range between two of the above ratios. When the mass ratio of the first component to the second component is within the above range, it can further facilitate the function of the artificial SEI membrane.

[0065] In some alternative embodiments, the artificial SEI membrane comprises a first component and a second component, wherein the mass ratio of the first component to the second component is (1-2):1.

[0066] In some embodiments, the artificial SEI film comprises maleic acid and lithium carbonate. When maleic acid and lithium carbonate are used to form the artificial SEI film, the artificial SEI film is more stable, thereby contributing to a further improvement in storage life.

[0067] In some embodiments, the thickness of the artificial SEI film is 10nm-120nm; for example, it can be, but is not limited to, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, or any range between two of the above thicknesses. A thickness within the above range is more conducive to the effective functioning of the artificial SEI film.

[0068] In some embodiments, the mass ratio of the artificial SEI film to the negative electrode active material layer is (0.5-5):100; for example, it can be, but is not limited to, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, or any range between two of the above ratios. When the mass ratio of the artificial SEI film to the negative electrode active material layer is within the above range, it can further facilitate the functioning of the artificial SEI film.

[0069] In some alternative embodiments, the mass ratio of the artificial SEI film to the negative electrode active material layer is (1-1.5):100.

[0070] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes one or more of carbon-based and silicon-based materials.

[0071] In some alternative embodiments, the negative electrode active material includes graphite, which includes one or more of synthetic graphite and natural graphite.

[0072] In some exemplary embodiments, the specific surface area of ​​graphite is 1 m². 2 / g -2 m 2 / g; for example, it can be, but is not limited to, 1 m. 2 / g、1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4 m 2 / g, 1.5 m 2 / g, 1.6 m 2 / g, 1.7 m 2 / g, 1.8m 2 / g, 1.9 m 2 / g、2 m 2 / g or any of the two specific surface areas mentioned above. When the specific surface area of ​​graphite is within the above range, it can further facilitate the function of artificial SEI films.

[0073] In some alternative implementations, the specific surface area of ​​graphite is 1.2 m². 2 / g -1.5 m 2 / g.

[0074] As an example, the specific surface area of ​​the graphite mentioned above can be determined using the following method:

[0075] First, drop a small amount of pure water onto the negative electrode plate, then gently scrape the moistened negative electrode off the current collector. After drying, heat-treat it at 400℃ in air for 2 hours, and finally sieve it through a 375-mesh sieve to obtain the sample to be tested. Use a special sample tube to collect an appropriate amount of sample, heat and degas under vacuum for 2 hours, and weigh it after cooling to room temperature. Subtract the mass of the sample tube to obtain the sample mass. Place the sample tube into the workstation and, under constant low temperature, determine the amount of gas adsorbed on the solid surface at different adsorption pressures. Based on the BET multilayer adsorption theory and its formula, calculate the monolayer adsorption amount of the sample, and thus calculate the specific surface area per unit mass of the solid sample. Adsorbed gas: nitrogen; Adsorption pressure points: 0.05 / 0.10 / 0.15 / 0.20 / 0.25 / 0.30; Test atmosphere: high-purity liquid nitrogen atmosphere.

[0076] As one possible implementation, the volume average particle size Dv50 of graphite is 12 μm-20 μm; for example, it can be, but is not limited to, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, or any two of the above particle sizes. When the volume average particle size Dv50 of graphite is within the above range, it can further facilitate the function of the artificial SEI film.

[0077] In some of these embodiments, the volume average particle size Dv50 of graphite is 13 μm-15 μm.

[0078] As an example, the volume average particle size Dv50 of the graphite mentioned above can be determined using the following method:

[0079] First, drop a small amount of pure water onto the negative electrode plate, then gently scrape the moistened negative electrode off the current collector. After drying, heat-treat it at 400℃ in air for 2 hours, and finally sieve it through a 375-mesh sieve to obtain the sample to be tested. Take a clean beaker, add an appropriate amount of sample, add a surfactant, and then add a dispersant. Sonicate at 120W / 5min to ensure that the sample is completely dispersed in the dispersant. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics of the particles are obtained by receiving and measuring the energy distribution of the scattered light, and then the volume average particle size Dv50 of graphite is calculated, with the occlusion degree being 8%-12%.

[0080] In some embodiments, the silicon-based material may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0081] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0082] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0083] In some embodiments, the negative electrode active material may also be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may also include one or more of the following materials: soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0084] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more 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).

[0085] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0087] The second aspect of this application provides a method for preparing the modified negative electrode sheet of the first aspect of this application, comprising the following steps:

[0088] A negative electrode active material layer is prepared on at least one side of the negative electrode current collector;

[0089] An artificial SEI solution is applied to the surface of the negative electrode active material layer away from the negative electrode current collector by spraying or transfer coating to form an artificial SEI film on the surface of the negative electrode active material layer, thereby preparing a modified negative electrode sheet.

[0090] The artificial SEI solution contains one or more of the first component and the second component.

[0091] Understandably, by applying an artificial SEI solution to the surface of the negative electrode active material layer through spraying or transfer coating, and then drying it to form an artificial SEI film, the artificial SEI film is bonded to the negative electrode active material layer on the surface. The artificial SEI film is more stable, and the stable artificial SEI film can slow down the growth of the negative electrode SEI film, thereby slowing down storage degradation and improving storage life.

[0092] It should be noted that using spraying or transfer coating methods makes it easier for the artificial SEI film to bond with the negative electrode active material layer on the surface.

[0093] In some embodiments, when preparing an artificial SEI solution, maleic acid and lithium carbonate can first be formulated into a lithium maleate solution with a solid content of 40wt%-65wt%, and then the lithium maleate solution can be used to prepare an artificial SEI solution.

[0094] In some embodiments, the solid content of the artificial SEI solution is 0.5wt%-3wt%; for example, it can be, but is not limited to, 0.5wt%, 0.7wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.3wt%, 2.5wt%, 2.8wt%, 3wt%, or any range between two of the above solid contents. When the solid content of the artificial SEI solution is within the above range, it can further facilitate the dispersion of the artificial SEI membrane components in the solvent.

[0095] In some embodiments, the artificial SEI solution further includes a solvent, which includes one or more of N-methylpyrrolidone, tetrahydrofuran, and ethanol.

[0096] In some embodiments, the modified negative electrode sheet can be prepared by dispersing the components used to prepare the modified negative electrode sheet, such as negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt%~60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s - 10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, deducting solvent) can be 75 g / m². 2 -220 g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 -1.8 g / cm 3 Then, an artificial SEI solution is applied to the surface of the negative electrode active material layer away from the negative electrode current collector by spraying or transfer coating to form an artificial SEI film on the surface of the negative electrode active material layer, thus preparing a modified negative electrode sheet.

[0097] It should be noted that artificial SEI solution can be sprayed or transferred onto the surface of the electrode, whether it is cold-pressed or not. After spraying or transferring, it can be dried at 80°C.

[0098] A third aspect of this application provides a secondary battery, including a modified negative electrode sheet according to the first aspect of this application or a modified negative electrode sheet prepared using the preparation method of the second aspect of this application.

[0099] The secondary battery of this application includes the modified negative electrode sheet of this application, which significantly improves its storage life.

[0100] It should be noted that the secondary battery provided in this application can be a lithium-ion battery or a sodium-ion battery.

[0101] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0102] Typically, a secondary battery includes a positive electrode, a negative electrode (i.e., the negative electrode of the first aspect of this application or the negative electrode prepared using the method of the second aspect of this application), an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0103] Positive electrode sheet

[0104] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0105] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0106] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on a polymeric material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0107] In some embodiments, the positive electrode active material may further include one or more of ternary materials and lithium manganese iron phosphate materials; wherein, the ternary material includes Li x (Ni a Co b Mn c )1-dM d O2-yA y (x is 0.2-1.2) and / or Li x A a (Nia Co b Mn c )1-dM d O2-yA y (x+a is 0.2-1.2); Lithium manganese iron phosphate materials include Li a Mn 1-y B y P 1-z C z O 4-n D n (a is 0-1.1) and / or Li a A x Mn 1-y B y P 1-z C z O 4-n D n (a+x is 0-1.1).

[0108] It should be noted that the above limitation on x includes the molar content of Li under different charge and discharge states of the battery (typically the battery voltage is between 2V and 5V).

[0109] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. Unless otherwise specified, the Li content in the examples of positive electrode materials listed in this application refers to the initial state of the material. When a positive electrode material is applied to a positive electrode in a battery system, the Li content in the positive electrode material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0110] In the examples of cathode materials listed in this application, the oxygen (O) content is only a theoretical state value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this. In some embodiments, the cathode active material can be a cathode active material known in the art for use in batteries. As a non-limiting example, the cathode active material may include one or more of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as cathode active materials for batteries may also be used. These cathode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.80 Co 0.15 Al 0.05 O2.

[0111] In some embodiments, the positive electrode active material includes a sodium ion active material.

[0112] As an example, sodium-ion active materials may include one or more of the following: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0113] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of a sodium transition metal oxide is Na. x MO2, where M can include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0114] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si; n represents (YO4). n- The price state.

[0115] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds consisting of anionic units and halide anions. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si, and n represents (YO4). n- The valence state; halogens can be one or more of F, Cl and Br.

[0116] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be one or more of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents (ZO). y ) m+ The valence state; halogens can be one or more of F, Cl and Br.

[0117] Polyanionic compounds can include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F and Na3(VO y )2(PO4)2F 3-2y One or more of (0≤y≤1). Among them, M' in NaM'PO4F can include one or more of V, Fe, Mn and Ni.

[0118] Prussian blue compounds can contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds containing Prussian blue. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of Prussian blue compounds is Na. a Me b Me' c (CN)6, wherein Me and Me' can each independently be one or more of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0119] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0120] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt%~80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s-25000 mPa·s. When coating the positive electrode slurry, the coating areal density per unit area (dry weight, minus solvent) can be 15 mg / cm³. 2 -35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 -3.6 g / cm 3 The option is 3.3 g / cm³. 3 -3.5 g / cm 3 .

[0122] electrolytes

[0123] The electrolyte serves to conduct ions between the positive electrode and the modified negative electrode. This application does not impose any particular limitation on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0124] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0125] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0126] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate ( One or more of the following: fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0127] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0128] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0129] Separating membrane

[0130] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0131] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0132] In some embodiments, the thickness of the isolation membrane is 6μm-40μm, and optionally 12μm-20μm.

[0133] In some embodiments, the positive electrode, the modified negative electrode, and the separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0134] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0135] In some embodiments, the outer packaging of the secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0136] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0137] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a modified negative electrode, and an electrolyte. During the charging and discharging process, active ions repeatedly insert and extract between the positive and modified negative electrodes. The electrolyte acts as a conductor for the active ions between the positive and modified negative electrodes.

[0138] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0139] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, modified negative electrode sheet, and separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to actual needs.

[0140] The secondary battery can be either battery module 4 or battery pack 1.

[0141] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0142] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0143] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0144] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0145] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0146] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0147] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0148] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0149] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0150] Example

[0151] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0152] Preparation of primary and secondary batteries

[0153] Example 1

[0154] 1. Preparation of modified negative electrode sheet

[0155] A mixture of graphite (negative electrode active material), acetylene black (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (binder) was prepared at a mass ratio of 96.4:1:1.2:1.4. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous, yielding a negative electrode slurry. This slurry was then uniformly coated onto both sides of a copper foil current collector. After air-drying at room temperature, the foil was transferred to an oven for further drying. Following cold pressing and slitting, the negative electrode sheet was obtained. After the negative electrode sheet was prepared, a 1 wt% artificial SEI solution was sprayed onto the cold-pressed or un-cold-pressed electrode sheet. The sheet was then dried at 80°C to obtain a modified negative electrode sheet. The artificial SEI solution contained maleic acid (as the first component) and lithium carbonate (as the second component) at a mass ratio of 1.6:1. The final modified negative electrode sheet had a mass ratio of 1:100 between the artificial SEI film and the negative electrode active material layer.

[0156] 2. Preparation of the positive electrode sheet

[0157] The positive electrode active material lithium iron phosphate, the conductive agent acetylene black, and the binder polyvinylidene fluoride PVDF were mixed at a mass ratio of 96:2:2. The solvent NMP was added, and the mixture was stirred under vacuum until the system was homogeneous to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the positive electrode sheet was obtained.

[0158] 3. Preparation of electrolyte

[0159] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0160] 4. Separating membrane

[0161] Polyethylene film is used as the separation membrane.

[0162] 5. Preparation of secondary batteries

[0163] The positive electrode, separator, and modified negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0164] Example 2-19

[0165] The differences between Examples 2-19 and Example 1 are detailed in Table 1.

[0166] Comparative Example 1

[0167] The difference between Comparative Example 1 and Example 1 is that only an unmodified negative electrode sheet was prepared, and no artificial SEI film was prepared on the surface of the negative electrode active material layer.

[0168] Comparative Example 2

[0169] The difference between Comparative Example 2 and Example 1 lies in the composition of the artificial SEI solution. Specifically, polyacrylonitrile is used instead of maleic acid and lithium carbonate in the artificial SEI solution.

[0170] Comparative Example 3

[0171] The difference between Comparative Example 3 and Example 1 is that an artificial SEI solution was added to the negative electrode slurry during the preparation of the negative electrode sheet. Specifically:

[0172] The negative electrode active material graphite, conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber were mixed in a mass ratio of 96.4:1:1.2:1.4. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. Then, an artificial SEI solution was mixed with the negative electrode slurry at a dry weight ratio of 1:100, and the mixture was uniformly coated onto both sides of the copper foil of the negative electrode current collector. After air-drying at room temperature, the mixture was transferred to an oven for further drying. Finally, the negative electrode sheets were obtained through cold pressing and slitting. The artificial SEI solution contained maleic acid (as the first component) and lithium carbonate (as the second component) in a mass ratio of 1.6:1.

[0173] Comparative Example 4

[0174] Using trimethylaluminum and water as precursors, alumina was coated onto the surface of graphite in a PECVD furnace at 220°C, with a mass ratio of alumina to graphite of 1:100, to obtain coated and modified graphite. The coated and modified graphite was then used to prepare modified negative electrode sheets according to the method described in Example 1.

[0175] The parameter settings for the above embodiments and comparative examples are shown in Table 1.

[0176] Table 1

[0177]

[0178] In Table 1, the ratio refers to the mass ratio of the first component and the second component. In Examples 1-19 and Comparative Examples 1-2, the spraying ratio refers to the mass ratio of the artificial SEI film and the negative electrode active material layer in the modified negative electrode sheet.

[0179] II. Secondary Battery Performance Testing

[0180] 1. Storage lifespan test

[0181] At 25℃, the capacity was determined by charging the secondary battery at a rate of 0.33C to 3.65V and discharging it at a rate of 0.33C to 2V, recording the discharge capacity as C0. The determined-capacity battery was then stored in a 60℃ oven for 90 days. Afterward, its capacity was tested at 25℃ by charging it at a rate of 0.33C to 3.65V and discharging it at a rate of 0.33C to 2V, recording the discharge capacity as C1. The ratio of C1 to C0 represents the remaining capacity after 90 days of storage at 60℃. The results are shown in Table 2.

[0182] 2. First-time effectiveness test

[0183] The prepared secondary battery was left to stand for 12 hours, then charged at a constant current of 0.02C for 10 hours, left to stand for 10 minutes, and then charged at a constant current of 0.33C to 3.65V. After standing for 10 minutes, it was charged at a constant voltage of 3.65V to 0.05C, and the charging capacity was recorded. Then, it was discharged at a constant current of 0.33C to 2V, left to stand for 10 minutes, and then discharged at a constant current of 0.05C to 2V, and the discharge capacity was recorded. The ratio of discharge capacity to graphite mass is the specific capacity of the graphite; the ratio of discharge capacity to charge capacity is the first-time efficiency of the graphite. The test results are shown in Table 2.

[0184] Table 2

[0185]

[0186] As shown in Table 2, compared with Comparative Examples 1-4, the artificial SEI film with specific components formed on the surface of the negative electrode active material layer in Examples 1-19 can effectively improve the storage capacity retention rate of the modified secondary battery; indicating that the artificial SEI film on the surface of the modified negative electrode sheet provided in this application has high stability and can slow down the growth of the negative electrode SEI film, thereby slowing down storage decay and improving storage life.

[0187] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0188] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, Includes a modified negative electrode sheet, wherein the modified negative electrode sheet comprises: Negative electrode current collector; A negative electrode active material layer is located on at least one side of the negative electrode current collector; and An artificial SEI membrane is located on the side of the negative electrode active material layer away from the negative electrode current collector. The artificial SEI membrane comprises a first component and a second component. The first component comprises one or more of an unsaturated fatty acid containing a carbon-carbon double bond and an acylhydrazine substance whose raw material includes the unsaturated fatty acid. The second component comprises a lithium salt. The mass ratio of the first component to the second component is (0.5-4):

1. The thickness of the artificial SEI membrane is 10nm-120nm.

2. The secondary battery as described in claim 1, characterized in that, The first component includes one or more of maleic acid, maleic hydrazide, and maleic dihydrazide.

3. The secondary battery as described in claim 1, characterized in that, The second component includes one or more of organic lithium salts and inorganic lithium salts; the organic lithium salt includes lithium acetate; the inorganic lithium salt includes one or more of lithium carbonate and lithium chloride.

4. The secondary battery as described in claim 1, characterized in that, The mass ratio of the first component to the second component is (1-4):

1.

5. The secondary battery as described in claim 4, characterized in that, The mass ratio of the first component to the second component is (1-2):

1.

6. The secondary battery as described in claim 1, characterized in that, The artificial SEI membrane contains maleic acid and lithium carbonate.

7. The secondary battery as described in claim 1, characterized in that, The thickness of the artificial SEI film is 20nm-120nm.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The mass ratio of the artificial SEI membrane to the negative electrode active material layer is (0.5-5):

100.

9. The secondary battery as described in claim 8, characterized in that, The mass ratio of the artificial SEI membrane to the negative electrode active material layer is (1-1.5):

100.

10. The secondary battery according to any one of claims 1 to 7 and 9, characterized in that, The negative electrode active material layer includes a negative electrode active material, which includes one or more of carbon-based and silicon-based materials.

11. The secondary battery as described in claim 10, characterized in that, The negative electrode active material includes graphite, which includes one or more of artificial graphite and natural graphite.

12. The secondary battery as described in claim 11, characterized in that, The specific surface area of ​​the graphite is 1 m². 2 / g -2 m 2 / g, with a volume average particle size Dv50 of 12μm-20μm.

13. A method for preparing a secondary battery as described in any one of claims 1 to 12, characterized in that, The preparation steps include those for a modified negative electrode sheet, which include the following steps: The negative electrode active material layer is prepared on at least one side of the negative electrode current collector; An artificial SEI solution is applied to the surface of the negative electrode active material layer away from the negative electrode current collector by spraying or transfer coating to form an artificial SEI film on the surface of the negative electrode active material layer, thereby preparing the modified negative electrode sheet. The artificial SEI solution comprises the first component and the second component.

14. The method for preparing a secondary battery as described in claim 13, characterized in that, The solid content of the artificial SEI solution is 0.5wt%-3wt%; and / or The artificial SEI solution further includes a solvent, which includes one or more of N-methylpyrrolidone, tetrahydrofuran, and ethanol.

15. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 12.

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