Negative electrode sheet, method for manufacturing the same, secondary battery, and power using device

Abstract

The application relates to a negative electrode sheet, a preparation method thereof, a secondary battery and an electric device. The negative electrode sheet comprises a negative electrode current collector, a negative electrode material layer and a coating layer arranged on at least one surface of the negative electrode current collector in sequence. The negative electrode material layer comprises a graphite-based negative electrode active material. The coating layer contains at least one of tin, a tin compound and a tin-containing alloy as an additive. The mass of the additive is 0.2-10% of the mass of the graphite-based negative electrode active material in the negative electrode material layer. The application of the coating layer containing tin in the negative electrode sheet improves the low-temperature performance of the secondary battery.

Description

Technical Field

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

[0002] In recent years, secondary batteries, represented by lithium-ion batteries, have been continuously developed and have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] Among these challenges, the application of secondary batteries in low-temperature environments at high latitudes faces difficulties. At lower temperatures, especially below 0°C, the discharge capacity and discharge voltage of lithium-ion batteries drop sharply, failing to meet the increasing demands under low-temperature conditions. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode sheet and its preparation method, a secondary battery, and an electrical device, which improves the low-temperature performance of the secondary battery by applying a tin-containing coating layer to the negative electrode sheet.

[0005] Therefore, the first aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector, and a negative electrode material layer and a coating layer sequentially disposed on at least one surface of the negative electrode current collector;

[0006] The negative electrode material layer contains a graphite-based negative electrode active material;

[0007] The coating layer contains an additive; the additive contains at least one of elemental tin, tin compounds, and tin-containing alloys; the mass of the additive is 0.2% to 10% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0008] In electrochemical reactions, elemental tin alloys and dealloys with lithium ions, accelerating the desolvation process of lithium ions and promoting their insertion into graphite-based anode active materials, thereby improving the low-temperature charging capability of lithium-ion batteries. Furthermore, since the dealloying reaction of tin is superior to that of graphite materials at low temperatures, it helps improve the low-temperature discharge capability of the battery. When using tin-containing alloys, the elemental tin in the alloy can also improve the low-temperature performance of the battery through the above principles. When using tin compounds, the tin element in the tin compound can be reduced to elemental tin during electrochemical processes, thus improving the low-temperature performance of the battery through the above principles. In addition, synergies formed by elements other than tin also help improve the structural stability of the anode surface. For example, in electrochemical reactions, SnS can generate Li2S and a sulfur-containing protective layer, SnF2 can generate LiF, SnSe can generate Li2Se, and SnO2 can generate LiO2. These synergies provide a certain degree of protection for the anode. Furthermore, when the mass of the additive is 0.2% to 10% of the mass of the graphite-based anode active material in the anode material layer, it has a good ability to improve low-temperature performance.

[0009] In any embodiment, the mass of the additive is 0.2% to 4% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0010] Optimizing the amount of additives can help them function better during charging and discharging, and improve battery performance under low-temperature conditions.

[0011] In any embodiment, the additive is a particulate material formed from at least one of elemental tin, tin compounds, and tin-containing alloys.

[0012] A good low-temperature performance improvement effect can be achieved by directly using particulate materials formed from at least one of elemental tin, tin compounds, and tin-containing alloys as additives.

[0013] In any embodiment, the particle size Dv50 of the additive is 50 to 500 nm.

[0014] By giving the additive a smaller particle size (50-500 nm), it can have faster reaction kinetics, thereby accelerating the reaction rate and improving its performance at low temperatures.

[0015] In any embodiment, the additive accounts for 40% to 90% of the mass of the coating layer.

[0016] In the coating layer, the mass ratio of the additive is within the above range, which is conducive to faster dynamics in the entire coating layer, accelerates the rapid ion release during the discharge process, and improves the low-temperature discharge capability.

[0017] In any embodiment, the coating layer further includes a graphite-based negative electrode active material; the particle size Dv50 of the graphite-based negative electrode active material in the coating layer is 5 to 10 μm.

[0018] Using graphite-based anode active materials with smaller particle sizes (5-10 μm) in the coating layer is beneficial to improving the reaction kinetics in the coating layer and is more suitable for applications under low temperature conditions.

[0019] In any embodiment, the additive is a particulate material with a core-shell structure; the core is a graphite-based negative electrode active material, and the shell contains at least one of elemental tin, tin compounds, and tin-containing alloys; the mass of the shell is 0.2% to 4% of the mass of the core.

[0020] In coatings, tin can be applied in several ways. Besides directly using particulate materials formed from at least one of elemental tin, tin compounds, or tin-containing alloys, tin-containing materials can also be coated onto the surface of graphite-based negative electrode active materials to form core-shell structured particulate materials. These core-shell structured particulate materials are then used in the coating layer. Optimizing the amount of tin-containing material in the core-shell structure improves its performance during charging and discharging, and enhances battery performance at low temperatures.

[0021] In any embodiment, the thickness of the coating layer is 10 to 100 nm.

[0022] Keeping the coating thickness within the above range is beneficial for further improving the low-temperature performance of the battery.

[0023] In any embodiment, the additive includes at least one of the following: elemental tin, SnO2, SnO, SnS, SnSe, SnTe, SnF4, SnF2, SnCl4, SnCl2, SnBr4, SnBr2, SnI4, SnI2, Sn-P alloy, Sn-S alloy, Sn-Li alloy, Na-Sn alloy, Sn-K alloy, etc.

[0024] In any embodiment, the negative electrode material layer comprises at least two stacked layers, and the mass percentage of graphite-based negative electrode active material in each negative electrode material layer increases from the direction closest to the negative electrode current collector to the direction furthest from the negative electrode current collector.

[0025] With the above structure, during the charging process: it helps to improve the low-temperature desolvation rate on the side away from the current collector, thereby accelerating the insertion of lithium ions into the side away from the current collector and preventing the deposition of metallic lithium on the side away from the current collector, thus improving the low-temperature charging capability. During the discharging process: the dealloying process of the additive, with its three-dimensional transport channels, is faster than the two-dimensional transport channels of graphite-based anode active materials. Therefore, when the mass proportion of graphite-based anode active material near the coating layer is higher, the current response is faster, more lithium ions are extracted, and thus the low-temperature discharge capability is improved.

[0026] In any embodiment, the particle size Dv50 of the graphite-based anode active material in the anode material layer is 10-18 μm.

[0027] Using graphite-based anode active materials with the above-mentioned particle size range in the anode material layer is beneficial to improving reaction kinetics and is more suitable for applications under low-temperature conditions.

[0028] A second aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; wherein the negative electrode is the negative electrode provided in the first aspect of this application.

[0029] In any embodiment, the secondary battery is a lithium-ion secondary battery.

[0030] A third aspect of this application provides an electrical device comprising the secondary battery described in the second aspect of this application.

[0031] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this application more obvious and understandable, the specific implementation methods of this application are listed below. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. 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 secondary battery according to one embodiment of this application;

[0034] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an 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 yes 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 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0041] Exemplary embodiments of this disclosure will now be described in more detail. It should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0042] The "range" disclosed in this application is defined by 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 and can be arbitrarily combined; that is, 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 also 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 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 "a–b" 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 "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

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

[0045] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may 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.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Rechargeable batteries, represented by lithium-ion batteries, have achieved widespread application. However, their application in low-temperature conditions (such as high-latitude regions and winter seasons) faces challenges. Current technologies show that at lower temperatures, especially below 0°C, the discharge capacity and discharge voltage of lithium-ion batteries drop sharply, making it difficult to meet the practical application requirements under low-temperature conditions.

[0048] This application mainly improves the performance of secondary batteries under low-temperature conditions by applying a tin-containing coating layer to the graphite-based negative electrode sheet.

[0049] The solutions described in the embodiments of this application are applicable to negative electrode sheets, secondary batteries containing the negative electrode sheets, battery modules using the secondary batteries, battery packs using the secondary batteries or battery modules, and electrical devices using at least one of secondary batteries, battery modules, and battery packs.

[0050] Negative electrode sheet

[0051] In some embodiments, a negative electrode sheet is provided, which includes a negative electrode current collector, and a negative electrode material layer and a coating layer sequentially disposed on at least one surface of the negative electrode current collector;

[0052] The negative electrode material layer contains a graphite-based negative electrode active material;

[0053] The coating layer contains an additive; the additive contains at least one of elemental tin, tin compounds, and tin-containing alloys; the mass of the additive is 0.2% to 10% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0054] In electrochemical reactions, elemental tin alloys and dealloys with lithium ions, accelerating the desolvation process of lithium ions and promoting their insertion into graphite-based anode active materials, thereby improving the low-temperature charging capability of lithium-ion batteries. Furthermore, since the dealloying reaction of tin is superior to that of graphite materials at low temperatures, it helps improve the low-temperature discharge capability of the battery. When using tin-containing alloys, the elemental tin in the alloy can also improve the low-temperature performance of the battery through the above principles. When using tin compounds, the tin element in the tin compound can be reduced to elemental tin during electrochemical processes, thus improving the low-temperature performance of the battery through the above principles. In addition, synergies formed by elements other than tin also help improve the structural stability of the anode surface. For example, in electrochemical reactions, SnS can generate Li2S and a sulfur-containing protective layer, SnF2 can generate LiF, SnSe can generate Li2Se, and SnO2 can generate LiO2. These synergies provide a certain degree of protection for the anode.

[0055] Furthermore, when the mass of the additive is 0.2% to 10% of the graphite-based anode active material in the anode material layer, it exhibits excellent low-temperature performance improvement capabilities. Using this dosage effectively reduces the anode surface activation energy without causing a decrease in cell energy due to excessive content.

[0056] The morphology of the additive is not limited; for example, it can be granular, fibrous, or flake-like, all of which can improve low-temperature performance. In some embodiments, granular additives are used because, on the one hand, since graphite-based anode active materials are usually close to spherical, using granular additives facilitates slurry processing; on the other hand, granular materials have a larger specific surface area, more reaction sites, and greater ion flux, which is more conducive to improving low-temperature performance.

[0057] In some embodiments, the negative electrode material layer comprises a negative electrode active material; the negative electrode active material includes a graphite-based negative electrode active material.

[0058] In some embodiments, the negative electrode material layer comprises a negative electrode active material; the negative electrode active material is a graphite-based negative electrode active material.

[0059] Graphite-based anode active materials refer to anode active materials containing a graphite structure. The graphite structure refers to a crystalline structure of stacked carbon hexagonal meshes, the spacing between which is not particularly limited. As examples, graphite-based anode active materials may include, for example, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, and graphitized pitch-based carbon fibers. The particle shape of graphite-based anode active materials is not particularly limited; it can be spherical, flake-like, blocky, etc.; in some embodiments, it is spherical or nearly spherical.

[0060] In some embodiments, the coating layer is disposed on at least a portion of the surface of the negative electrode material layer, for example, at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 100% of the surface area of ​​the negative electrode material layer.

[0061] In some embodiments, the coating layer is distributed continuously or discontinuously on the surface of the negative electrode material layer.

[0062] In some embodiments, the mass of the additive is 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0063] In some embodiments, the mass of the additive is 0.2% to 4% of the mass of the graphite-based anode active material in the anode material layer.

[0064] Optimizing the amount of additives can help them function better during charging and discharging, and improve battery performance under low-temperature conditions.

[0065] In some embodiments, the additive is a particulate material formed from at least one of elemental tin, tin compounds, and tin-containing alloys.

[0066] A good low-temperature performance improvement effect can be achieved by directly using particulate materials formed from at least one of elemental tin, tin compounds, and tin-containing alloys.

[0067] In some embodiments, the particle size Dv50 of the additive is 50 to 500 nm; for example, it can be about 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc.

[0068] Particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the additive material. In this paper, Dv50 can be measured by the following method: particle size distribution measurement using laser scattering method, which measures the particle size at a cumulative particle size distribution percentage of 50%.

[0069] By giving the additive a smaller particle size (50-500 nm), it can have faster reaction kinetics, thereby accelerating the reaction rate and improving its performance at low temperatures.

[0070] In some embodiments, the additive accounts for 40% to 90% of the mass of the coating layer; for example, it can be about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0071] In the coating layer, the mass ratio of the additive is within the above range, which is conducive to faster dynamics in the entire coating layer, accelerates the rapid ion release during the discharge process, and improves the low-temperature discharge capability.

[0072] In some embodiments, the coating layer may optionally include a negative electrode active material, such as a graphite-based negative electrode active material. In some embodiments, the mass percentage of the negative electrode active material in the coating layer may be, for example, about 30%, or, for example, 20% to 40%.

[0073] In some embodiments, the coating layer further includes a graphite-based negative electrode active material; the particle size Dv50 of the graphite-based negative electrode active material in the coating layer is 5 to 10 μm; for example, it can be about 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0074] Using graphite-based anode active materials with smaller particle sizes (5-10 μm) in the coating layer is beneficial to improving the reaction kinetics in the coating layer and is more suitable for applications under low temperature conditions.

[0075] In some embodiments, the coating layer may also include an optional conductive agent, for example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In some embodiments, the coating layer may also include an adhesive, for example, the adhesive may include one or more combinations selected from the group consisting of sodium carboxymethyl cellulose (CMC-Na), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0077] In some embodiments, the coating layer may also include other additives. For example, other additives may be dispersants (such as styrene-butadiene rubber (SBR)).

[0078] In some embodiments, the additive is a particulate material with a core-shell structure; the core is a graphite-based negative electrode active material, and the shell contains at least one of elemental tin, tin compounds, and tin-containing alloys; the mass of the shell is 0.2% to 4% of the mass of the core; for example, it can be about 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0079] In coatings, tin can be applied in several ways. Besides directly using particulate materials formed from at least one of elemental tin, tin compounds, or tin-containing alloys, tin-containing materials can be coated onto the surface of graphite-based negative electrode active materials to form core-shell structured particulate materials. These core-shell structured particulate materials are then used in the coating layer. Optimizing the amount of tin-containing material in the core-shell structure material allows it to function better during charging and discharging, improving battery performance at low temperatures.

[0080] In some embodiments, the thickness of the coating layer is 10 to 100 nm; for example, it can be about 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0081] Keeping the thickness of the coating layer within the above range is beneficial for further improving the low-temperature performance of the battery.

[0082] In some embodiments, the additive includes at least one of the following: elemental tin; tin compounds, such as tin oxide (SnO2), stannous oxide (SnO), tin sulfide (SnS), tin selenide (SnSe), tin telluride (SnTe), stannous fluoride (SnF4), stannous fluoride (SnF2), tin chloride (SnCl4), stannous chloride (SnCl2), tin bromide (SnBr4), stannous bromide (SnBr2), tin iodide (SnI4), stannous iodide (SnI2), etc.; tin-containing alloys, such as Sn-P alloys (e.g., Sn4P3, SnP). 0.94 Sn-P3, Sn-S alloys (such as Sn2S3), Sn-Li alloys, Na-Sn alloys, Sn-K alloys, etc.

[0083] In some embodiments, the negative electrode material layer comprises at least two stacked layers, and the mass percentage of graphite-based negative electrode active material in each negative electrode material layer increases from the direction closest to the negative electrode current collector to the direction furthest from the negative electrode current collector.

[0084] With the above structure, during the charging process: it helps to improve the low-temperature desolvation rate away from the current collector side, thereby accelerating the insertion of lithium ions into the side away from the current collector and preventing the deposition of metallic lithium on the side away from the current collector, thus improving the low-temperature charging capability. During the discharging process: the dealloying process of the additive, with its three-dimensional transport channels, is faster than the two-dimensional transport channels of graphite-based anode active materials. Therefore, when the graphite-based anode active material closer to the coating layer is higher, the current response is faster, and more lithium ions are extracted, thus improving the low-temperature discharge capability.

[0085] In some embodiments, the negative electrode material layer is configured as a two-layer, three-layer, or four-layer stack.

[0086] In some embodiments, the negative electrode material layer is a two-layer stack, with the layer closer to the negative electrode current collector being the first negative electrode material layer and the layer farther from the negative electrode current collector being the second negative electrode material layer; the mass percentage of graphite-based negative electrode active material in the second negative electrode material layer is higher than that in the first negative electrode material layer. For example, in some embodiments, the mass percentage of graphite-based negative electrode active material in the first negative electrode material layer is 96%, and the mass percentage of graphite-based negative electrode active material in the second negative electrode material layer is 95%.

[0087] In some embodiments, the particle size Dv50 of the graphite-based negative electrode active material in the negative electrode material layer is 10-18 μm; for example, it can be about 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc.

[0088] Using graphite-based anode active materials with the above-mentioned particle size range in the anode material layer is beneficial to improving reaction kinetics and is more suitable for applications under low-temperature conditions.

[0089] In some embodiments, the negative electrode material layer may also include an optional conductive agent, for example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the negative electrode material layer may also include an adhesive, for example, the adhesive may include one or more combinations selected from the group consisting of sodium carboxymethyl cellulose (CMC-Na), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0091] In some embodiments, the negative electrode material layer may also include other additives. For example, other additives may be dispersants (such as styrene-butadiene rubber (SBR)).

[0092] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0093] Preparation method of negative electrode sheet

[0094] In some embodiments, the negative electrode sheet can be prepared by dispersing the components provided in the embodiments of this application for preparing the negative electrode material layer, such as negative electrode active material (e.g., graphite-based negative electrode active material), conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode material slurry; coating the negative electrode material slurry onto the negative electrode current collector, and after drying and other processes, a negative electrode material layer can be formed on the negative electrode current collector;

[0095] Then, the coating slurry containing the additives is coated onto the negative electrode material layer, and after drying and other processes, the negative electrode sheet is obtained.

[0096] In some methods, the coating layer uses particulate material formed from at least one of elemental tin, tin compounds, and tin-containing alloys as an additive, and the coating layer slurry is prepared as follows:

[0097] The components used to prepare the coating, including the additives, optional graphite-based negative electrode active materials, conductive agents, binders, and any other components, are dispersed in a solvent (e.g., deionized water) to form a coating slurry.

[0098] In some embodiments, the additive in the coating layer is a particulate material with a core-shell structure; the core is a graphite-based negative electrode active material, and the shell contains at least one of elemental tin, tin compounds, and tin-containing alloys; the particulate material with the core-shell structure is prepared in the following manner:

[0099] A tin-containing material (at least one of elemental tin, tin compounds, or tin alloys) is mixed with a graphite-based anode active material, wherein the mass of the tin-containing material is 0.2% to 4% of the mass of the graphite-based anode active material. Then, the mixture is heated under an inert atmosphere until the tin-containing material is in a molten state and held at that temperature for a certain time. After cooling, a coating layer is formed on the surface of the graphite-based anode active material, thus obtaining the particulate material with a core-shell structure.

[0100] The components used to prepare the coating, including the core-shell structured particulate material, optional conductive agent, binder and any other components, are dispersed in a solvent (e.g., deionized water) to form a coating slurry.

[0101] In some embodiments, the heating temperature is 300–2000°C. A suitable temperature can be selected based on the specific composition of the additive, as long as the heating temperature ensures that the tin-containing material is in a molten state. In some embodiments, the holding time is 12–24 hours; for example, it can be selected from approximately 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc.

[0102] Secondary batteries

[0103] In some embodiments of this application, a secondary battery is provided, which includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; the negative electrode is the negative electrode provided in any embodiment of this application.

[0104] In some embodiments, the secondary battery is a lithium-ion secondary battery. As an example, the lithium-ion battery is any one of the following: lithium iron phosphate / graphite series, lithium cobalt oxide / graphite series, lithium manganese oxide / graphite series, or ternary material / graphite series batteries.

[0105] [Positive electrode plate]

[0106] The positive electrode sheet includes a positive current collector and a positive electrode material disposed on at least one surface of the positive current collector, wherein the positive electrode material includes a positive active material.

[0107] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present invention is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode 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, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 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 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0109] In some embodiments, the positive electrode material may optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting of: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0110] In some embodiments, the cathode material may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned positive electrode material, such as positive electrode active material, conductive agent, binder and any other components in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0112] [Negative electrode plate]

[0113] The negative electrode sheet provided in any embodiment of this application is used.

[0114] [Isolation membrane]

[0115] As for the separator, this application does not have any particular limitations, and any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, the separator can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0116] [Electrolytes]

[0117] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0118] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0119] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0120] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, 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.

[0121] 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.

[0122] [Preparation of Secondary Batteries]

[0123] A secondary battery can be prepared by using a winding process or a stacking process to form an electrode assembly consisting of a positive electrode, a negative electrode, and a separator. After being packaged and encapsulated, an electrolyte is injected.

[0124] The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. It can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0125] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0126] In some implementations, refer 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. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0127] Battery modules, battery packs

[0128] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0129] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 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 secondary batteries 5 can be fixed in place using fasteners.

[0130] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0131] In some implementations, the secondary batteries can also be assembled into a battery pack.

[0132] In some embodiments, the battery module 4 can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0133] 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.

[0134] Electrical appliances

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

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

[0137] Figure 6This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0138] 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.

[0139] Example 1

[0140] This embodiment provides a lithium-ion secondary battery, the preparation method of which is as follows:

[0141] (1) Positive electrode plate

[0142] 93g of LiNi was used as the positive electrode active material. 0.9 Co 0.05 Mn 0.05 O2, 5g of super carbon black as a conductive agent, and 1g of PVDF as a binder are mixed together. An appropriate amount of N-methylpyrrolidone (NMP) is added, and the mixture is thoroughly mixed. Then, it is wetted, kneaded, and dispersed to obtain a positive electrode slurry, with the viscosity adjusted to approximately 10,000 mPa·s. The prepared positive electrode is coated onto a current collector aluminum foil and dried at 100°C to obtain the positive electrode sheet.

[0143] (2) Negative electrode plate

[0144] Preparation of the first negative electrode slurry: Artificial graphite (Dv50 10μm) and natural graphite (Dv50 14μm) in a mass ratio of 6:4 are used as negative electrode active materials. Weigh 50g of this negative electrode active material. Mix 50g of negative electrode active material, sodium carboxymethyl cellulose as a binder, SP-Li as a conductive agent, and styrene-polybutadiene rubber as a dispersant in a mass ratio of 95:1:2:2. Add an appropriate amount of deionized water to control the solid content to about 55%, and the first negative electrode slurry is prepared.

[0145] Preparation of the second negative electrode slurry: Weigh 50g of artificial graphite (Dv50 10μm) as the negative electrode active material; mix 50g of the negative electrode active material, sodium carboxymethyl cellulose as a binder, SP-Li as a conductive agent, and styrene-polybutadiene rubber as a dispersant in a mass ratio of 96:1:2:1, add an appropriate amount of deionized water to control the solid content to about 55%, and the second negative electrode slurry is thus prepared.

[0146] Preparation of coating slurry: Weigh 2g of SnS (particle size Dv50 is 0.2μm) as an additive; mix 2g of additive, artificial graphite (Dv50 5μm) as the negative electrode active material, Super P as the conductive agent, sodium carboxymethyl cellulose as the binder, and styrene-polybutadiene rubber as the dispersant in a mass ratio of 70:20:3:3:4, add an appropriate amount of deionized water to control the solid content to about 55%, and the coating slurry is prepared.

[0147] The first negative electrode slurry is coated onto the current collector aluminum foil and dried at 100°C to form the first negative electrode material layer on the current collector. Then, the second negative electrode slurry is coated onto the first negative electrode material layer and dried at 100°C to form the second negative electrode material layer. Then, the coating layer slurry is coated onto the second negative electrode material layer and dried at 100°C to prepare a negative electrode sheet with an additive content of 70% in the coating layer.

[0148] (3) Electrolyte

[0149] The basic electrolyte is prepared by mixing the organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a ratio of 3:6:1. Then, lithium hexafluorophosphate (LiPF6) with a final concentration of 0.7-1.0M and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a mass fraction of 3% are added.

[0150] (4) Separating membrane

[0151] A film with a multilayer composite structure of polyethylene, polypropylene, and polyethylene is used.

[0152] (5) Preparation of secondary batteries

[0153] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, the electrode assembly is wound to obtain an electrode assembly. Tabs are welded onto the electrode assembly, and the electrode assembly is installed in an aluminum shell. It is then baked at 80°C to remove moisture, followed by the injection of the electrolyte and sealing. Finally, after processes such as settling, hot and cold pressing, formation (voltage 3.7–4.5V), and shaping, a lithium-ion secondary battery is obtained.

[0154] test:

[0155] Low-temperature capacity retention tests were conducted on the prepared negative electrode sheet and lithium-ion secondary battery.

[0156] The battery cells were placed on the electrochemical test channel and charged to 4.25V at 0.33C at room temperature. They were then left to stand at -10℃ for 4 hours and discharged at 0.33C at -10℃. The capacity released when the cells were discharged to 2.5V was recorded as C in Ah. The results are shown in Table 1.

[0157] Examples 2-5, Comparative Examples 1-3

[0158] Except for the following conditions, the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 1:

[0159] Example 2: The amount of additive used is 0.5g, that is, the mass of the additive is 0.5% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0160] Example 3: The amount of additive used is 1g, that is, the mass of the additive is 1% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0161] Example 4: The amount of additive used is 5g, that is, the mass of the additive is 5% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0162] Example 5: The amount of additive used is 10g, that is, the mass of the additive is 10% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0163] Comparative Example 1: The coating does not contain any additives.

[0164] Comparative Example 2: The amount of additive used was 15g, that is, the mass of the additive was 15% of the mass of the graphite-based anode active material in the anode material layer.

[0165] Comparative Example 3: The amount of additive used was 0.1g, that is, the mass of the additive was 0.1% of the mass of the graphite-based negative electrode active material in the negative electrode material layer.

[0166] Table 1

[0167]

[0168] Examples 6-9

[0169] Except for the following conditions, the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 2:

[0170] Example 6: In the coating slurry, the mass ratio of additives, negative electrode active material, conductive agent, binder and dispersant is 60:30:3:3:4.

[0171] Example 7: In the coating slurry, the mass ratio of additives, negative electrode active material, conductive agent, binder and dispersant is 80:10:3:3:4.

[0172] Example 8: In the coating slurry, the mass ratio of additives, negative electrode active material, conductive agent, binder and dispersant is 90:5:1.5:1.5:2.

[0173] Example 9: In the coating slurry, the mass ratio of additives, negative electrode active material, conductive agent, binder and dispersant is 40:50:3:3:4.

[0174] Table 2

[0175]

[0176] Examples 10-11

[0177] Except for the following differences, the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 3:

[0178] Example 10: The second negative electrode slurry is used instead of the first negative electrode slurry, that is, the two negative electrode materials are the same and are both prepared using the second negative electrode slurry.

[0179] Example 11: First, a second negative electrode slurry is placed on the current collector to form a second negative electrode material layer, and then a first negative electrode slurry is placed on the surface of the second negative electrode material layer to form a first negative electrode material layer.

[0180] Table 3

[0181]

[0182] Example 12

[0183] Except for the following differences, the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 4:

[0184] Preparation of coating slurry:

[0185] First, a core-shell structured particulate material is prepared: 2g of SnS (particle size Dv50 0.2μm) and 100g of graphite (particle size Dv50 11μm) are mixed evenly and placed in a muffle furnace under an inert atmosphere. The temperature is increased to 650℃ at 5℃ / min and maintained for 24h. The mixture is then cooled to room temperature, so that the additive is coated on the graphite surface, thus obtaining a core-shell structured particulate material.

[0186] Then, take 2g of the core-shell structured particulate material as an additive, and mix the 2g additive, Super P as a conductive agent, sodium carboxymethyl cellulose as a binder, and styrene-polybutadiene rubber as a dispersant in a mass ratio of 95:1:2:2. Add an appropriate amount of deionized water to control the solid content to about 55%, and the coating slurry is prepared.

[0187] Table 4

[0188] Example 1 88.37 Example 12 87.85

[0189] Examples 13-18

[0190] Except for the following differences, the preparation and testing were carried out in the same manner as in Example 1: the thickness of the coating was controlled as shown in Table 5, and relevant tests were performed.

[0191] Table 5

[0192]

[0193] Examples 19-23

[0194] Refer to Table 6. Except for the particle size Dv50 of the additives, the preparation and testing were carried out in the same manner as in Example 1.

[0195] Table 6

[0196]

[0197] Examples 24-28

[0198] Refer to Table 7. Except for the different additive materials used, the preparation and testing were carried out in the same manner as in Example 1.

[0199] Table 7

[0200]

[0201] Examples 29-31

[0202] Referring to Table 8, except for the particle size Dv50 of the negative electrode active material used, the preparation and testing were carried out in the same manner as in Example 1.

[0203] Table 8

[0204]

[0205]

[0206] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector, and a negative electrode material layer and a coating layer sequentially disposed on at least one surface of the negative electrode current collector; The negative electrode material layer contains a graphite-based negative electrode active material; The coating layer comprises an additive; the additive comprises at least one of elemental tin, tin compounds, and tin-containing alloys; the mass of the additive is 0.2-10% of the mass of the graphite-based negative electrode active material in the negative electrode material layer; The additive is a particulate material with a core-shell structure; the core is a graphite-based negative electrode active material, and the shell contains at least one of elemental tin, tin compounds, and tin-containing alloys; the mass of the shell is 0.2% to 4% of the mass of the core.

2. The negative electrode sheet as described in claim 1, characterized in that, The particle size Dv50 of the additive is 50~500 nm.

3. The negative electrode sheet as described in claim 1, characterized in that, In the coating layer, the additive accounts for 40-90% by mass.

4. The negative electrode sheet as described in any one of claims 1 to 3, characterized in that, The coating layer also includes a graphite-based negative electrode active material; the particle size Dv50 of the graphite-based negative electrode active material in the coating layer is 5~10μm.

5. The negative electrode sheet as described in any one of claims 1 to 3, characterized in that, The thickness of the coating layer is 10~100 nm.

6. The negative electrode sheet as described in any one of claims 1 to 3, characterized in that, The additives include at least one selected from the group consisting of elemental tin, SnO2, SnO, SnS, SnSe, SnTe, SnF4, SnF2, SnCl4, SnCl2, SnBr4, SnBr2, SnI4, SnI2, Sn-P alloy, Sn-S alloy, Sn-Li alloy, Na-Sn alloy, and Sn-K alloy.

7. The negative electrode sheet as described in any one of claims 1 to 3, characterized in that, The negative electrode material layer comprises at least two stacked layers, and the mass percentage of graphite-based negative electrode active material in each negative electrode material layer increases from the direction closest to the negative electrode current collector to the direction furthest from the negative electrode current collector.

8. The negative electrode sheet as described in any one of claims 1 to 3, characterized in that, The particle size Dv50 of the graphite-based anode active material in the anode material layer is 10-18 μm.

9. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; the negative electrode is the negative electrode as described in any one of claims 1 to 8.

10. An electrical device, characterized in that, Includes the secondary battery as described in claim 9.

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