Modified negative electrode sheet and preparation method therefor, secondary battery and electric device

Abstract

A modified negative electrode sheet and a preparation method therefor, 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 the side of the negative electrode active material layer away from the negative electrode current collector, wherein 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 hydrazide substance, raw materials for preparing which comprise the unsaturated fatty acid; and 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 an SEI film on a negative electrode, thereby slowing down storage degradation and prolonging storage life.

Description

Modified negative electrode sheet, preparation method thereof, secondary battery and electric device

[0001] Related applications

[0002] The present application claims priority to the Chinese patent application No. 2024103617859, filed on March 27, 2024, and entitled "Modified negative electrode sheet, preparation method thereof, secondary battery and electric device", the content of which is hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, and in particular to a modified negative electrode sheet, a preparation method thereof, a secondary battery and an electric device. BACKGROUND

[0004] The statements herein are merely provided for background information related to the present application and do not necessarily constitute the prior art.

[0005] In recent years, with the increasingly wide range of applications of secondary batteries, secondary batteries are widely used in energy storage power supply systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their storage life.

[0006] SUMMARY

[0007] The present application provides a modified negative electrode sheet with a longer storage life, a preparation method thereof, a secondary battery and an electric device.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a modified negative electrode sheet, comprising:

[0009] a negative current collector;

[0010] a negative active material layer located on at least one side of the negative current collector; and

[0011] an artificial SEI film located on the side of the negative active material layer away from the negative current collector, the artificial SEI film comprising one or more of a first component and a second component, the first component comprising 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, and the second component comprising a lithium salt.

[0012] Thus, the present application forms a stable artificial SEI film comprising the first component and / or the second component on the surface of the negative active material layer, which can slow down the growth of the negative SEI film and thus slow down the storage decay and improve the storage life.

[0013] In some embodiments of the application, the first component comprises one or more of maleic acid, malehydrazide and maleic acid dihydrazide.

[0014] In some embodiments of the application, the second component comprises one or more of an organic lithium salt and an inorganic lithium salt; the organic lithium salt comprises lithium acetate; the inorganic lithium salt comprises one or more of lithium carbonate and lithium chloride.

[0015] In some embodiments of the application, the artificial SEI film comprises a first component and a second component, and the mass ratio of the first component to the second component is (0.5-4):1.

[0016] In some embodiments of the application, the mass ratio of the first component to the second component is (1-2):1.

[0017] In some embodiments of the application, the artificial SEI film comprises maleic acid and lithium carbonate.

[0018] In some embodiments of the application, the thickness of the artificial SEI film is 10 nm-120 nm.

[0019] In some embodiments of the application, the mass ratio of the artificial SEI film to the negative active material layer is (0.5-5):100.

[0020] In some embodiments of the application, the mass ratio of the artificial SEI film to the negative active material layer is (1-1.5):100.

[0021] In some embodiments of the application, the negative active material layer comprises a negative active material, and the negative active material comprises one or more of a carbon-based material and a silicon-based material.

[0022] In some embodiments of the application, the negative active material comprises graphite, and the graphite comprises one or more of artificial graphite and natural graphite.

[0023] In some embodiments of the application, the specific surface area of the graphite is 1 m 2 / g-2 m 2 / g, and the volume average particle size Dv50 is 12 μm-20 μm.

[0024] The second aspect of the application further provides a preparation method of the modified negative electrode sheet of the first aspect of the application, comprising the following steps:

[0025] Preparation of the negative active material layer on at least one side of the negative current collector;

[0026] The artificial SEI solution is applied on the surface of the negative electrode active material layer far 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 to prepare the modified negative electrode sheet.

[0027] The artificial SEI solution comprises one or more of the first component and the second component.

[0028] Thus, by applying the artificial SEI solution on the surface of the negative electrode active material layer by spraying or transfer coating, and forming an artificial SEI film after drying, the artificial SEI film is combined with the negative electrode active material layer on the surface layer, 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 the storage attenuation and improving the storage life.

[0029] In some embodiments of the present application, the solid content of the artificial SEI solution is 0.5wt%-3wt%; and / or

[0030] The artificial SEI solution further comprises a solvent, and the solvent comprises one or more of N-methyl pyrrolidone, tetrahydrofuran and ethanol.

[0031] The third aspect of the present application provides a secondary battery comprising the modified negative electrode sheet of the first aspect of the present application or the modified negative electrode sheet prepared by the preparation method of the second aspect of the present application.

[0032] The fourth aspect of the present application provides an electric device comprising the secondary battery of the third aspect of the present application.

[0033] The electric device of the present application comprises the secondary battery provided by the present application, and thus at least has the same advantages as the secondary battery.

[0034] The details of one or more embodiments of the present application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the application will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0035] For better describing and illustrating the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments or examples, and any one of the best modes of these applications presently understood. Moreover, the same reference numbers are used to represent the same components throughout the drawings. In the drawings:

[0036] FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0037] FIG. 2 is an exploded view of the battery cell shown in FIG. 1 according to an embodiment of the present application.

[0038] FIG. 3 is a schematic view of a battery module according to an embodiment of the present application.

[0039] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present application.

[0040] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4.

[0041] FIG. 6 is a schematic view of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0042] Explanation of Reference Numerals:

[0043] 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: case; 52: electrode assembly; 53: cover plate; 6: electric device. DETAILED DESCRIPTION

[0044] Hereinafter, some embodiments of the modified negative electrode sheet and the method of manufacturing the same, the secondary battery, and the electric device according to the present application are described in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known in the art, repetitive descriptions of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0045] "ranges" disclosed herein can be defined, for example, by the lower and upper values. Any lower limit can independently be combined with any upper limit to define a range of any value. For example, if a range of 60-120 and 80-110 is listed as exemplary, it is understood that a range of 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, the use of "or" means "and / or" unless specifically stated otherwise, e.g., "x employs A or B" means "x employs A or B or both." Unless otherwise noted, the use of the term "comprising" means "including but not limited to" and the use of the term "comprises" is interpreted as meaning "including but not limited to." It will be further noted that the

[0046] The use of the terms "a" and "an" and "the" and "at least one" in the context of the application is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by the context. For example, the phrase "at least one of" followed by a list using the term "comprises" or "includes" one or more items should be interpreted to mean that one or more of the listed items are present. In other words, "at least one of" indicates that one or more of the listed items are present, but not limited to, one of only those items specifically listed. In addition, it is to be understood that such phrasing as "one or more of the a or b or c" or "one or more of the a, b, or c" or "one or more of the a, b, and c" or "one or more of a, b, c" means one or more of the a only, or one or more of the b only, or one or more of the c only, or any combination thereof. For example, "one or more of the a, b, and c" means that a alone can be used, b alone can be used, c alone can be used, or any combination of a, b, and c can be used.

[0047] If not otherwise specified, all embodiments and optional embodiments in the present application can be combined with each other to form new technical solutions.

[0048] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the application. The appearance of the phrase in various places in the specification is not necessarily all referring to the same embodiment, nor is it necessarily referring to a separate or alternative embodiment to the other embodiments. It will be explicitly understood by one of ordinary skill in the art that the embodiments described herein can be combined with other embodiments. Reference herein to "an implementation" has a similar understanding.

[0049] Those skilled in the art can understand that the order of writing each step in the method of each embodiment or example does not mean a strict execution order and constitutes any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method comprises steps (a) and (b), which means that the method can comprise sequentially performed steps (a) and (b), or sequentially performed steps (b) and (a). For example, the method can also comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0050] In the present application, the open technical features or technical solutions described by the words "containing", "including", "comprising" and the like do not exclude additional members other than the listed members, and can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members or can not include additional members, and can be regarded as providing both the feature or solution that "A is composed of a1, a2 and a3" and the feature or solution that "A includes a1, a2 and a3, and also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0051] In the present application, "optionally", "optional" and "optional" mean that it can or can not be present, i.e. it can be selected from either of the two parallel solutions "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified, and there is no contradiction or mutual restriction, each "option" is independent.

[0052] At present, secondary batteries have made great progress, so higher requirements are put forward for their storage life. The storage life decay of secondary batteries is mainly in the negative electrode, and the loss of active material in the negative electrode and the continuous growth of SEI film are the main reasons for the storage life decay, among which the continuous growth of SEI film in the negative electrode is the main reason for the storage life decay.

[0053] In the related art, an artificial SEI material is 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 the growth of the SEI film. However, there is a problem of failure of the artificial SEI film. The present applicant found in the failure analysis thereof that, due to the addition of the artificial SEI material in the negative electrode slurry, the performance of the battery cell is unstable, some groups of battery cells have good performance, and some battery cells do not have improved performance, which may be due to the fact that the artificial SEI material is prone to fall off and peel off during kneading and stirring of the slurry, and finally causes the failure of the artificial SEI film.

[0054] Based on the above problems, the present application sprays an artificial SEI solution on the surface of the negative electrode active material layer, and forms an artificial SEI film after drying. The artificial SEI film is combined with the negative electrode active material layer at the surface layer, has better stability, and effectively slows down the growth of the negative electrode SEI film.

[0055] The first aspect of the present application provides a modified negative electrode sheet, which 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 the side of the negative electrode active material layer away from the negative electrode 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 a hydrazine substance prepared from a raw material including an unsaturated fatty acid. The second component includes a lithium salt.

[0056] It should be noted that in the present application, "first component", "second component" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second" and the like only serve the purpose of non-exhaustive enumeration description and should be understood as not constituting a closed limitation on the quantity.

[0057] When the artificial SEI film contains the unsaturated fatty acid containing a carbon-carbon double bond, the cation conductivity of the artificial SEI film is higher, which is more conducive to the passage of lithium ions, thereby benefiting the stability of the artificial SEI film. The higher the stability of the artificial SEI film, the more conducive it is to protect the negative electrode material, and thus improve the storage life of the battery cell.

[0058] When the artificial SEI film contains the hydrazine substance prepared from a raw material including an unsaturated fatty acid, the artificial SEI film is less likely to have a side reaction with the electrolyte, thereby making the artificial SEI film more stable and more conducive to protecting the negative electrode material from corrosion and consumption by the electrolyte, and thus conducive to improving the life of the battery cell.

[0059] When the artificial SEI film contains the lithium salt, the lithium salt can offset the irreversible lithium consumption during the formation process of the battery, thereby reducing the irreversible lithium consumption and thus being conducive to improving the storage life of the battery cell.

[0060] Thus, the present application forms a stable artificial SEI film containing the first component and / or the second component on the surface of the negative electrode active material layer, and the artificial SEI film can slow down the growth of the negative electrode SEI film, thereby slowing down storage decay and improving storage life.

[0061] In some embodiments, the first component includes one or more of maleic acid, malehydrazide, and maleic acid dihydrazide.

[0062] In some alternative embodiments, the first component includes maleic acid.

[0063] In some embodiments, the second component includes one or more of an organic lithium salt and an inorganic lithium salt.

[0064] As one possible embodiment, the organic lithium salt includes lithium acetate.

[0065] In some exemplary embodiments, the inorganic lithium salt includes one or more of lithium carbonate and lithium chloride.

[0066] In some of these embodiments, the inorganic lithium salt includes lithium carbonate.

[0067] In some embodiments, the artificial SEI film contains the first component and the second component, and 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 a range between any two of the above ratios, etc. When the mass ratio of the first component to the second component is in the above range, the artificial SEI film can further benefit from the function thereof.

[0068] In some alternative embodiments, the artificial SEI film contains the first component and the second component, and the mass ratio of the first component to the second component is (1-2): 1.

[0069] In some embodiments, the artificial SEI film contains 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 further improving the storage life.

[0070] In some embodiments, the thickness of the artificial SEI film is 10 nm-120 nm; for example, it can be but is not limited to 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, or a range between any two of the above thicknesses, etc. When the thickness of the artificial SEI film is in the above range, the artificial SEI film can benefit from the function thereof.

[0071] In some embodiments, the mass ratio of the artificial SEI film and the negative 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 a range between any two of the above ratios, etc. When the mass ratio of the artificial SEI film and the negative active material layer is in the above range, the artificial SEI film can further play a role.

[0072] In some alternative embodiments, the mass ratio of the artificial SEI film and the negative active material layer is (1-1.5): 100.

[0073] In some embodiments, the negative active material layer comprises a negative active material, and the negative active material comprises one or more of a carbon-based material and a silicon-based material.

[0074] In some alternative embodiments, the negative active material comprises graphite, and the graphite comprises one or more of artificial graphite and natural graphite.

[0075] In some exemplary embodiments, the specific surface area of the graphite is 1 m 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, 1.8 m 2 / g, 1.9 m 2 / g, 2 m 2 / g, or a range between any two of the above specific surface areas, etc. When the specific surface area of the graphite is in the above range, the artificial SEI film can further play a role.

[0076] In some alternative embodiments, the specific surface area of the graphite is 1.2 m 2 / g-1.5 m 2 / g.

[0077] As an example, the specific surface area of the graphite mentioned above can be measured by the following method:

[0078] A small amount of pure water is first dripped on the negative electrode sheet, and then the wet negative electrode is gently scraped off from the current collector. After drying, the sample to be tested is obtained by sieving through a 375 mesh sieve after heat treatment at 400°C in an air atmosphere for 2h. A special sample tube is used to take an appropriate amount of sample, which is heated and vacuum degassed for 2h. After cooling to room temperature, the total weight is measured, and the sample mass is obtained by subtracting the sample tube mass. The sample tube is loaded into the workstation, and the adsorption amount of gas on the solid surface under different adsorption pressures is measured at a constant low temperature. Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample is obtained, and the specific surface area of the unit mass of solid sample is calculated. Adsorption gas: nitrogen; adsorption pressure points: 0.05 / 0.10 / 0.15 / 0.20 / 0.25 / 0.30; test atmosphere: high-purity liquid nitrogen atmosphere.

[0079] As a possible implementation, the volume average particle size Dv50 of the graphite is 12-20 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 a range between any two of the above particle sizes. When the volume average particle size Dv50 of the graphite is in the above range, the artificial SEI film can further play a role.

[0080] In some embodiments thereof, the volume average particle size Dv50 of the graphite is 13-15 μm.

[0081] As an example, the volume average particle size Dv50 of the graphite mentioned above can be measured by the following method:

[0082] A small amount of pure water is first dripped on the negative electrode sheet, and then the wet negative electrode is gently scraped off from the current collector. After drying, the sample to be tested is obtained by sieving through a 375 mesh sieve after heat treatment at 400°C in an air atmosphere for 2h. A clean beaker is taken, and an appropriate amount of sample is added. After adding a surfactant, a dispersant is added, and the sample is ultrasonically dispersed at 120W for 5min to ensure that the sample is completely dispersed in the dispersant. The sample is poured into a sample tower and circulated to the test light path system with the solution. 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 the volume average particle size Dv50 of the graphite is calculated, wherein the light shading degree is 8%-12%.

[0083] In some embodiments, the silicon-based material can include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0084] As a non-limiting example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative active material layer is disposed on either one or both of the two opposite surfaces of the negative current collector.

[0085] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base layer. Non-limiting examples of the metal material in the negative current collector can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like. Non-limiting examples of the polymer material base layer in the negative current collector can include one or more of a polypropylene (PP) base layer, a polyethylene terephthalate (PET) base layer, a polybutylene terephthalate (PBT) base layer, a polystyrene (PS) base layer, a polyethylene (PE) base layer, and the like.

[0086] In some embodiments, the negative active material can also employ a negative active material for a battery known in the art. As a non-limiting example, the negative active material can also include one or more of soft carbon, hard carbon, a tin-based material, lithium titanate, and the like. The tin-based material can include one or more of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination with two or more.

[0087] In some embodiments, the negative active material layer can also optionally include a binder. The binder can 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).

[0088] In some embodiments, the negative active material layer can also optionally include a conductive agent. The conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments, the negative active material layer can also optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0090] The second aspect of the present application provides a method for preparing the modified negative electrode sheet of the first aspect of the present application, including the following steps:

[0091] Preparation of the negative active material layer on at least one side of the negative current collector;

[0092] The artificial SEI solution is applied on the surface of the negative active material layer away from the negative current collector by spraying or transfer coating to form an artificial SEI film on the surface of the negative active material layer, thereby preparing a modified negative electrode sheet.

[0093] The artificial SEI solution comprises one or more of the first component and the second component.

[0094] Understandably, by applying the artificial SEI solution on the surface of the negative active material layer by spraying or transfer coating, the artificial SEI film is formed after drying, the artificial SEI film is combined with the negative active material layer on the surface layer, the artificial SEI film is more stable, and the stable artificial SEI film can slow down the growth of the negative SEI film, thereby reducing storage decay and improving storage life.

[0095] It should be noted that by spraying or transfer coating, the artificial SEI film is more easily combined with the negative active material layer on the surface layer.

[0096] In some embodiments, when preparing the artificial SEI solution, the maleic acid and lithium carbonate can be first prepared into a lithium maleate solution with a solid content of 40wt%-65wt%, and then the lithium maleate solution is prepared into the artificial SEI solution.

[0097] 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 a range between any two of the above solid contents, etc. When the solid content of the artificial SEI solution is in the above range, the artificial SEI film composition can be further dispersed in the solvent.

[0098] In some embodiments, the artificial SEI solution further comprises a solvent, and the solvent comprises one or more of N-methylpyrrolidone, tetrahydrofuran, and ethanol.

[0099] In some embodiments, the modified negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the modified negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector, and after drying, cold pressing and the like, the negative electrode sheet is obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be on a single surface of the negative electrode current collector, or on 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 2000mPa·s-10000mPa·s. When coating the negative electrode slurry, the coating unit area density (excluding the solvent) can be 75g / m 2 -220 g / m 2 . The compaction density of the negative electrode sheet can be 1.0g / cm 3 -1.8g / cm 3 . Then, the 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.

[0100] It should be noted that the artificial SEI solution can be sprayed or transfer coated on the surface of the sheet after cold pressing or without cold pressing. After spraying or transfer coating, drying can be performed at 80℃.

[0101] The third aspect of the present application provides a secondary battery comprising the modified negative electrode sheet of the first aspect of the present application or the modified negative electrode sheet prepared by the preparation method of the second aspect of the present application.

[0102] The secondary battery of the present application comprises the modified negative electrode sheet of the present application, and the storage life is significantly improved.

[0103] It should be noted that the secondary battery provided by the present application can be a lithium ion battery or a sodium ion battery.

[0104] In addition, the secondary battery and the electric device of the present application are described below with appropriate reference to the accompanying drawings.

[0105] Generally, the secondary battery comprises a positive electrode sheet, a negative electrode sheet (i.e. the negative electrode sheet of the first aspect of the present application or the negative electrode sheet prepared by the preparation method of the second aspect of the present application), an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0106] Positive electrode tab

[0107] The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material.

[0108] As a non-limiting example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0109] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base material. Non-limiting examples of the metal material in the positive electrode current collector can include one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. Non-limiting examples of the polymer material base material in the positive electrode current collector can include one or more of a polypropylene (PP) base material, a polyethylene terephthalate (PET) base material, a polybutylene terephthalate (PBT) base material, a polystyrene (PS) base material, a polyethylene (PE) base material, and the like.

[0110] In some embodiments, the positive electrode active material can further include one or more of a ternary material and a lithium manganese iron phosphate material; wherein the ternary material includes Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y (x is 0.2-1.2, 0≤a≤1, 0≤b≤1, 0≤c≤1, a+b+c=1, 0≤d≤1, 0≤y≤2, M includes at least one element selected from Mg, Zr, Al, B (boron), Ta, Mo, W, Nb, Ti, Sr, Cr, Ce, V, Sb, and La, and A includes one or more elements selected from F, N, P, S) and / or Li x A e (Ni a Co b Mn c ) 1-d M d O 2-y D y(x + e is 0.2-1.2, 0≤a≤1, 0≤b≤1, 0≤c≤1, a+b+c=1, 0≤d≤1, 0≤y≤2, A includes other cations, M includes at least one element selected from Mg, Zr, Al, B (boron), Ta, Mo, W, Nb, Ti, Sr, Cr, Ce, V, Sb and La, D includes one or several elements selected from F, N, P, S); the lithium manganese iron phosphate material includes Li a Mn 1-y B y P 1-z C z O 4-n D n (a is 0-1.1, y is 0-0.6, z is 0-0.1, n is 0-0.1, B includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Sr, Cr, Ce, La, Ni, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B (boron), S, Si and N, D includes one or more elements selected from S, F, Cl and Br) 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, x is 0.9-1.1, y is 0-0.6, z is 0-0.1, n is 0-0.1, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Sr, Cr, Ce, La, Ni, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B (boron), S, Si and N, D includes one or more elements selected from S, F, Cl and Br).

[0111] It should be noted that the above limitation of x includes the molar content of Li in different charge and discharge states of the battery (typically the battery voltage is between 2V and 5V).

[0112] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during charging and discharging, and the content of Li in the positive plate is different when the battery is discharged to different states. In the enumeration of the positive electrode material in this application, the content of Li is the initial state of the material unless otherwise stated. The positive electrode material is applied to the positive plate in the battery system, and after charging and discharging cycle, the content of Li in the positive material contained in the plate will usually change. Among them, the content of Li can be quantified by molar content, but not limited to this. As for "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is put into the positive slurry. It is understood that the new material obtained by properly modifying the listed positive electrode material is also within the scope of the positive electrode material, and the foregoing proper modification refers to acceptable modification of the positive electrode material, and non-limiting examples include coating modification.

[0113] In the enumeration of the positive electrode material in this application, the content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will appear to be floating. Among them, the content of O can be quantified by molar content, but not limited to this.

[0114] In some embodiments, the positive active material can use the positive active material for battery known in the art. As a non-limiting example, the positive active material can include one or more of the following materials: lithium-containing phosphate with olivine structure, lithium transition metal oxide 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 active materials can also be used. These positive active materials can be used alone or in combination with two or more. Among them, examples of lithium transition metal oxides can include but are not limited to one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their modified compounds, etc. Non-limiting examples of lithium-containing phosphate with olivine structure can include but are not limited to one or more of lithium iron phosphate, lithium iron phosphate and carbon composite, lithium manganese phosphate, lithium manganese phosphate and carbon composite, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composite. Non-limiting examples of lithium cobalt oxide can include LiCoO2; non-limiting examples of lithium nickel oxide can include LiNiO2; non-limiting examples of lithium manganese oxide can include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide can include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523 LiNi0.5Mn1.5O4, 0.5 LiNi0.5Mn1.5O4, 0.25 LiNi0.5Mn1.5O4, 0.25 LiNi0.5Mn1.5O4, 211 LiNi0.5Mn1.5O4, 0.6 LiNi0.5Mn1.5O4, 0.2 LiNi0.5Mn1.5O4, 0.2 LiNi0.5Mn1.5O4, 622 LiNi0.5Mn1.5O4, 0.8 LiNi0.5Mn1.5O4, 0.1 LiNi0.5Mn1.5O4, 0.1 LiNi0.5Mn1.5O4, 811 LiNi0.5Mn1.5O4, 0.80 LiNi0.5Mn1.5O4, 0.15 LiNi0.5Mn1.5O4, 0.05 LiNi0.5Mn1.5O4.

[0115] In some embodiments, the positive active material comprises a sodium-ion active material.

[0116] As an example, the sodium-ion active material can comprise one or more of: one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue analogs. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive active materials for sodium-ion batteries can also be used.

[0117] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can comprise one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Non-limiting examples of sodium transition metal oxides can be Na x MO2, where M can comprise one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1.

[0118] As an optional technical solution of the present application, the polyanionic compound can be a type of compound having sodium ions, transition metal ions, and tetrahedral (YO4) n- anion units. The transition metal can comprise one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si; and n represents the valence of (YO4) n- .

[0119] The polyanionic compound can also be a type of compound having sodium ions, transition metal ions, tetrahedral (YO4) n-Anionic units and halogen anions. The transition metal can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si, n represents the valence of (YO4) n- ; and the halogen can be one or more of F, Cl, and Br.

[0120] The polyanionic compound can also be a compound having sodium ions, tetrahedral (YO4) n- anionic units, polyhedral (ZO y ) m+ ; and optional halogen anions. Y can be one or more of P, S, and Si, n represents the valence of (YO4) n- ; Z represents a transition metal, which can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents the valence of (ZO y ) m+ ; and the halogen can be one or more of F, Cl, and Br.

[0121] The polyanionic compound can include one or more of NaFeP04, Na3V2(P04)3 (sodium vanadate phosphate, abbreviated as NVP), Na4Fe3(P04)2(P207), NaM’P04F, and Na3(VO y )2(P04)2F 3-2y (0≤y≤1). In NaM’P04F, M’ can include one or more of V, Fe, Mn, and Ni.

[0122] Prussian blue compounds can be a compound having sodium ions, transition metal ions, and cyanide ions (CN - ). The transition metal can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Non-limiting examples of Prussian blue compounds can be Na a Me b Me’ c (CN)6, where Me and Me’ can each independently be one or more of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a < 2, 0 < b < 1, and 0 < c < 1.

[0123] In some embodiments, the positive electrode active material layer can optionally further include a binder. As non-limiting examples, the binder can include one or more 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.

[0124] In some embodiments, the positive electrode active material layer can optionally further include a conductive agent. As non-limiting examples, the conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0125] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and then drying, cold-pressing, or the like to obtain the positive electrode tab. The type of the solvent can be selected from, but is not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector to which the positive electrode slurry is coated can be a single surface of the positive electrode current collector, or both surfaces of the positive electrode current collector. The surface of the positive electrode current collector to which the positive electrode slurry is coated can be a single surface of the positive electrode current collector, or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating unit area density, in terms of dry weight (excluding the solvent), can be 15 mg / cm 2 - 35 mg / cm 2 . The compaction density of the positive electrode tab can be 3.0 g / cm 3 - 3.6 g / cm 3 , optionally 3.3 g / cm 3 - 3.5 g / cm 3 .

[0126] Electrolyte

[0127] The electrolyte has the function of conducting ions between the positive electrode tab and the modified negative electrode tab. The type of the electrolyte is not particularly limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0128] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0129] In some embodiments, the electrolyte salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium difluoro-bis-oxalato-phosphate (LiDFOP), and lithium tetrafluoro-oxalato-phosphate (LiTFOP).

[0130] In some embodiments, the solvent can include one or more of 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 , 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, methyl ethyl sulfone, and diethyl sulfone.

[0131] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0132] In some embodiments, the additive in the electrolyte solution can include, but is not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0133] Separator film

[0134] In some embodiments, the secondary battery further includes a separator film. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0135] In some embodiments, the material of the separator film can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0136] In some embodiments, the thickness of the separator film is 6-40 μm, optionally 12-20 μm.

[0137] In some of the embodiments, the positive electrode sheet, the modified negative electrode sheet and the separator film can be made into an electrode assembly through a winding process or a stacking process.

[0138] In some of the embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte as described above.

[0139] In some of the embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, polybutylene succinate, etc.

[0140] The secondary battery includes at least one battery cell. The secondary battery can include one or more battery cells.

[0141] In the present application, unless otherwise specified, a "battery cell" refers to a basic unit capable of converting chemical energy and electrical energy to each other, and further, generally includes at least a positive electrode sheet, a modified negative electrode sheet and an electrolyte. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the modified negative electrode sheet. The electrolyte plays a role of conducting the active ions between the positive electrode sheet and the modified negative electrode sheet.

[0142] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square or any other shape. For example, FIG. 1 is a battery cell 5 of a square structure as an example.

[0143] In some of the embodiments, referring to FIG. 2, the outer package can include a shell 51 and a cover plate 53. The shell 51 can 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 communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the modified negative electrode sheet and the separator film can be made into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assembly 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.

[0144] The secondary battery can be a battery module 4 or a battery pack 1.

[0145] The battery module includes at least one battery cell. The number of battery cells included in the battery module can be one or more, and a person skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0146] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0147] Optionally, the battery module 4 can also include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0148] In some embodiments, the above-described battery module can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and a person skilled in the art can select a suitable number according to the application and capacity of the battery pack.

[0149] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0150] In addition, the application also provides a power utilization device including the secondary battery provided by the application. The secondary battery can be used as a power source of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0151] As the power utilization device, the secondary battery can be selected according to the use requirements thereof.

[0152] FIG. 6 is a power utilization device 6 as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0153] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinness, and a secondary battery can be used as a power source.

[0154] Examples

[0155] Hereinafter, the examples of the present application will be described. The examples described below are exemplary and are for the purpose of explanation of the present application and cannot be understood as a limitation of the present application. In the examples, the technology or conditions not noted are performed in accordance with the technology or conditions described in the literature in the field or in accordance with the product manual. The reagents or instruments not noted for the manufacturer are all conventional products that can be obtained on the market.

[0156] Preparation of primary and secondary batteries

[0157] Example 1

[0158] 1. Preparation of modified negative electrode sheet

[0159] The negative electrode active material graphite, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, and a solvent deionized water was added. The system was stirred to be uniform by a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of the negative electrode current collector copper foil. After air drying at room temperature, the negative electrode slurry was transferred to an oven for further drying. Then, the negative electrode sheet was obtained by cold pressing and slitting. After the preparation of the negative electrode sheet, an artificial SEI solution with a solid content of 1wt% was sprayed on the cold-pressed or un-pressed electrode sheet. After drying at 80°C, a modified negative electrode sheet was prepared. The artificial SEI solution contains maleic acid (as the first component) and lithium carbonate (as the second component) in a mass ratio of 1.6:1. The mass ratio of the artificial SEI film to the negative electrode active material layer in the finally formed modified negative electrode sheet is 1:100.

[0160] 2. Preparation of positive electrode sheet

[0161] The positive electrode active material lithium iron phosphate, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, and a solvent N-methyl pyrrolidone (NMP) was added. The system was stirred to be uniform by a vacuum stirrer to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil. After air drying at room temperature, the positive electrode slurry was transferred to an oven for further drying. Then, the positive electrode sheet was obtained by cold pressing and slitting.

[0162] 3. Preparation of electrolyte

[0163] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, the dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1mol / L.

[0164] 4. Separation film

[0165] A polyethylene film is used as the separator film.

[0166] 5. Preparation of the secondary battery

[0167] The above positive electrode sheet, separator film, and modified negative electrode sheet are stacked in order with the separator film between the positive and negative electrode sheets to play a role of separation, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, electrolyte is injected after drying, and the secondary battery is obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0168] Examples 2-19

[0169] Examples 2-19 and Example 1 differ as shown in Table 1.

[0170] Comparative Example 1

[0171] Comparative Example 1 and Example 1 differ in that only an unmodified negative electrode sheet is prepared, and no artificial SEI film is prepared on the surface of the negative active material layer.

[0172] Comparative Example 2

[0173] Comparative Example 2 and Example 1 differ in that the composition of the artificial SEI solution is different. Specifically, polyacrylonitrile is used instead of maleic acid and lithium carbonate in the artificial SEI solution.

[0174] Comparative Example 3

[0175] Comparative Example 3 and Example 1 differ in that the artificial SEI solution is added to the negative slurry during preparation of the negative electrode sheet. Specifically as follows:

[0176] The negative active material graphite, conductive agent acetylene black, thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber are mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water is added, and the system is stirred to be uniform under the action of a vacuum stirrer to obtain a negative slurry; then the artificial SEI solution is mixed with the negative slurry at a dry weight ratio of 1:100, and then uniformly coated on both sides of the negative current collector copper foil, dried at room temperature, then transferred to an oven for further drying, and then cold-pressed and cut to obtain a negative electrode sheet. The artificial SEI solution contains maleic acid (as the first component) and lithium carbonate (as the second component) in a mass ratio of 1.6:1.

[0177] Comparative Example 4

[0178] Trimethylaluminum and water are used as precursors to coat aluminum oxide on the surface of graphite in a PECVD furnace at 220°C, and the mass ratio of aluminum oxide to graphite is 1:100 to obtain coated modified graphite. Then the coated modified graphite is used to prepare a modified negative electrode sheet according to the method in Example 1.

[0179] The part parameter settings of the above examples and comparative examples are shown in Table 1.

[0180] Table 1

[0181] In Table 1, the ratio refers to the mass ratio of the first component and the second component. The spraying ratio in Examples 1-19 and Comparative Examples 1-2 refers to the mass ratio of the artificial SEI film and the negative active material layer in the modified negative electrode sheet.

[0182] Secondary battery performance test

[0183] 1. Storage life test

[0184] At 25°C, the secondary battery was charged at 0.33C rate to 3.65V and discharged at 0.33C rate to 2V, and the discharge capacity was recorded as C0. The constant volume battery was placed in a 60°C oven for 90 days, and then taken out to test the capacity at 25°C. The battery was charged at 0.33C rate to 3.65V and discharged at 0.33C rate to 2V, and the discharge capacity was recorded as C1. The ratio of C1 to C0 was the capacity retention rate of 90 days storage at 60°C. The results are shown in Table 2.

[0185] 2. Initial efficiency test

[0186] After the prepared secondary battery was left for 12 hours, it was charged at a current of 0.02C for 10 hours, left for 10 minutes, charged at a current of 0.33C to 3.65V, left for 10 minutes, and charged at a voltage of 3.65V to 0.05C, and the charge capacity was recorded. Then, it was discharged at a current of 0.33C to 2V, left for 10 minutes, and discharged at a current of 0.05C to 2V, and the discharge capacity was recorded. The ratio of the discharge capacity to the mass of the graphite was the gram capacity of the graphite; the ratio of the discharge capacity to the charge capacity was the initial efficiency of the graphite. The test results are shown in Table 2.

[0187] Table 2

[0188] As can be seen from the results in Table 2, compared with Comparative Example 1-4, the artificial SEI film with a specific component formed on the surface of the negative active material layer in Examples 1-19 can effectively improve the storage capacity retention rate of the modified secondary battery; it shows that the artificial SEI film provided by the application has high stability on the surface layer of the modified negative electrode sheet, can slow down the growth of the negative SEI film, thereby slowing down the storage decay and improving the storage life.

[0189] The above description of each example tends to emphasize the differences between each example, and the same or similar parts can be referred to each other. For the sake of brevity, the same or similar parts will not be described again.

[0190] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. In addition, other modes constructed by combining part of the configurations of the embodiments in a manner that a person skilled in the art can think of within the scope of the present application are also included in the scope of the present application.

Claims

1. A modified negative electrode sheet, comprising: 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 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.

2. The modified negative electrode sheet as described in claim 1, wherein, The first component includes one or more of maleic acid, maleic hydrazide, and maleic dihydrazide.

3. The modified negative electrode sheet according to any one of claims 1 to 2, wherein, 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 modified negative electrode sheet according to any one of claims 1 to 3, wherein, 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.

5. The modified negative electrode sheet as described in claim 4, wherein, The mass ratio of the first component to the second component is (1-2):

1.

6. The modified negative electrode sheet according to any one of claims 1 to 5, wherein, The artificial SEI membrane contains maleic acid and lithium carbonate.

7. The modified negative electrode sheet according to any one of claims 1 to 6, wherein, The thickness of the artificial SEI film is 10nm-120nm.

8. The modified negative electrode sheet according to any one of claims 1 to 7, wherein, The mass ratio of the artificial SEI membrane to the negative electrode active material layer is (0.5-5):

100.

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

100.

10. The modified negative electrode sheet according to any one of claims 1 to 9, wherein, 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 modified negative electrode sheet as described in claim 10, wherein, The negative electrode active material includes graphite, which includes one or more of artificial graphite and natural graphite.

12. The modified negative electrode sheet as described in claim 11, wherein, The specific surface area of ​​the graphite is 1m². 2 / g-2m 2 / g, with a volume average particle size Dv50 of 12μm-20μm.

13. A method for preparing a modified negative electrode sheet as described in any one of claims 1 to 12, comprising 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. in, The artificial SEI solution comprises one or more of the first component and the second component.

14. The method for preparing the modified negative electrode sheet as described in claim 13, wherein, The solid content of the artificial SEI solution is 0.5wt%-3wt%.

15. The method for preparing the modified negative electrode sheet according to any one of claims 13 to 14, wherein, The artificial SEI solution further includes a solvent, which includes one or more of N-methylpyrrolidone, tetrahydrofuran, and ethanol.

16. A secondary battery, comprising a modified negative electrode sheet as described in any one of claims 1 to 12 or a modified negative electrode sheet prepared by the preparation method described in any one of claims 13 to 15.

17. An electrical device comprising the secondary battery as described in claim 16.

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