Negative electrode plate, secondary battery and electrical device

Abstract

This application provides a negative electrode sheet, a secondary battery, and an electrical device. The negative electrode sheet includes a negative current collector and a negative active layer located on at least one surface of the negative current collector. The surface of the negative active layer away from the negative current collector contains an alkali metal salt polymer. Introducing the alkali metal polymer onto the surface of the negative active layer allows the polymer chains to provide channels for lithium ion transport, promoting lithium ion transport towards the interior of the negative active layer. This reduces concentration polarization in the thickness direction of the electrode sheet and improves the fast-charging performance of the battery.

Description

Technical Field

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

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

[0003] With the increasing popularity of rechargeable batteries, their fast-charging performance has received widespread attention. Improving fast-charging performance is crucial for further expanding the application range of batteries. Summary of the Invention

[0004] A first aspect of this application provides a negative electrode sheet, including a negative current collector and a negative active layer located on at least one surface of the negative current collector, wherein the surface of the negative active layer away from the negative current collector contains an alkali metal salt polymer.

[0005] In the aforementioned negative electrode sheet, alkali metal polymers are introduced on the surface of the negative electrode active layer. The polymer chains of the alkali metal polymers can provide channels for the transport of lithium ions, which can promote the transport of lithium ions toward the interior of the negative electrode active layer, thereby reducing concentration polarization in the thickness direction of the electrode sheet and improving the fast charging performance of the battery.

[0006] In some embodiments, the molecular chains of the alkali metal salt polymer include a linear structure. This linear structure can further enhance the transport rate of lithium ions in the negative electrode, thus improving the battery's fast-charging performance.

[0007] In some embodiments, the number-average molecular weight of the alkali metal salt polymer is 3,000 to 1,000,000. Optionally, the number-average molecular weight of the alkali metal salt polymer is 100,000 to 500,000.

[0008] In some embodiments, the alkali metal salt polymer contains 3% to 8.9% by mass of alkali metal. Optionally, the alkali metal salt polymer contains 5% to 7.5% by mass of alkali metal.

[0009] In some embodiments, the alkali metal salt polymer includes an alkali metal acrylate polymer. The negatively charged carboxylate groups in the alkali metal acrylate polymer can complex with small Lewis acid molecules in the electrolyte, increasing the electronegativity of the carboxylate groups. This allows more lithium ions to dissociate and enter the negative electrode active layer, further improving the battery's fast-charging performance. Optionally, the alkali metal acrylate polymer includes one or more of lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate.

[0010] In some embodiments, the alkali metal salt polymer is contained within a predetermined thickness of the negative electrode active layer along the direction close to the negative electrode current collector, the predetermined thickness being 10% to 90% of the thickness of the negative electrode active layer. This can further promote the transport of lithium ions towards the negative electrode active layer, further improving the fast-charging performance of the battery. Optionally, the predetermined thickness is 40% to 50% of the thickness of the negative electrode active layer.

[0011] In some embodiments, the mass percentage of the alkali metal salt polymer contained within the preset thickness of the negative electrode active layer is 0% to 1.5%. This can reduce the risk of bulging or peeling off in the preset thickness portion while promoting fast charging, thus maintaining a relatively stable structure of the negative electrode active layer. Optionally, the mass percentage of the alkali metal salt polymer contained within the preset thickness of the negative electrode active layer is 0.3% to 1%.

[0012] In some embodiments, the negative electrode active layer comprises a plurality of sub-active layers stacked sequentially, wherein the mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is less than the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector. This smaller mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector further promotes lithium-ion transport towards the interior of the active layer, thereby further improving the battery's fast-charging performance.

[0013] In some embodiments, the mass percentage of alkali metal salt polymers in the sub-active layer closest to the negative electrode current collector is less than or equal to the mass percentage of alkali metal salt polymers in the sub-active layer furthest from the negative electrode current collector multiplied by 0.5. This allows the mass percentage of alkali metal salt polymers in each sub-active layer to be maintained within a suitable range, which is beneficial for further improving the lithium-ion transport kinetics in the negative electrode and further improving the fast-charging performance of the battery.

[0014] In some embodiments, the mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is 0-1%. This can reduce the risk of bulging or detachment of the sub-active layer closest to the negative electrode current collector during negative electrode sheet processing, while promoting fast charging, thereby improving the processing performance of the negative electrode sheet. Optionally, the mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is 0.1%-0.7%.

[0015] In some embodiments, the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector is 0% to 1.5%. This can reduce the risk of bulging or detachment of the sub-active layer furthest from the negative electrode current collector during negative electrode sheet processing, while promoting fast charging, thereby improving the processing performance of the negative electrode sheet. Optionally, the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector is 0.3% to 1%.

[0016] In some embodiments, the mass percentage of the alkali metal salt polymer in each of the sub-active layers gradually increases in the direction away from the negative electrode current collector. This gradual increase in the mass percentage of the alkali metal salt polymer in each sub-active layer allows for better matching of lithium-ion transport kinetics between adjacent sub-active layers, further improving the lithium-ion transport kinetics in the negative electrode and thus enhancing the battery's fast-charging performance.

[0017] In some embodiments, the mass percentage of alkali metal salt polymers in adjacent sub-active layers increases by 0.1% to 0.5% in the direction away from the negative electrode current collector. This increase in the mass percentage of alkali metal salt polymers in adjacent sub-active layers allows for better matching of lithium-ion transport kinetics between adjacent sub-active layers, which is beneficial for further improving the lithium-ion transport kinetics in the negative electrode and further improving the fast-charging performance of the battery.

[0018] In some embodiments, in the direction away from the negative electrode current collector, the negative electrode active layer includes a first sub-active layer and a second sub-active layer stacked sequentially, wherein the mass percentages of the alkali metal salt polymer in the first sub-active layer and the second sub-active layer are w1 and w2, respectively, where w1 < w2. The cooperation between the first sub-active layer and the second sub-active layer is beneficial for improving the fast-charging performance of the battery.

[0019] In some implementations, 0 ≤ w1 ≤ 1%. This can reduce the risk of bulging and detachment of the first sub-active layer during the negative electrode processing, while promoting fast charging, thereby improving the processing performance of the negative electrode. Optionally, 0.1% ≤ w1 ≤ 0.7%.

[0020] In some implementations, 0 < w2 ≤ 1.5%. This can reduce the risk of bulging and detachment of the second sub-active layer during the negative electrode processing, while promoting fast charging, thereby improving the processing performance of the negative electrode. Optionally, 0.3% ≤ w2 ≤ 1%.

[0021] In some embodiments, the thickness ratio of the first sub-active layer to the second sub-active layer in the thickness direction of the negative electrode current collector is (0.1-2):(3-8). The second sub-active layer has a larger thickness, which can increase the overall amount of alkali metal salt polymer in the negative electrode active layer and further improve the fast charging performance of the battery.

[0022] In some embodiments, the first sub-active layer includes a first binder, wherein the mass percentage of the first binder in the first sub-active layer is w1', and 0 ≤ w1 / w1' ≤ 1. Introducing the first binder into the first sub-active layer can improve the bonding performance of the first sub-active layer, enhance the bonding performance between the first sub-active layer and the negative electrode current collector, further reduce the risk of bulging or detachment of the first sub-active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet.

[0023] In some embodiments, the first adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0024] In some embodiments, the second sub-active layer includes a second binder, wherein the mass percentage of the second binder in the second sub-active layer is w2', and 0.15 ≤ w2 / w2' ≤ 5. Introducing a second binder into the second sub-active layer can improve the adhesion performance of the second sub-active layer, enhance the adhesion between the second sub-active layer and the first sub-active layer, further reduce the risk of bulging or detachment of the second sub-active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet.

[0025] In some embodiments, the second adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0026] In some embodiments, the negative electrode active layer further includes a third sub-active layer, which is located on the surface of the second sub-active layer away from the first sub-active layer. The mass percentage of the alkali metal salt polymer in the third sub-active layer is w3, where w1 < w2 < w3. The combination of the first, second, and third sub-active layers is beneficial for improving the fast-charging performance of the battery.

[0027] In some embodiments, 0 ≤ w1 ≤ 1%; and / or, 0 < w2 ≤ 1.5%; and / or, 0 < w3 ≤ 1.5%. w1, w2, and w3 falling within these ranges allows for better matching of lithium-ion transport kinetics among the first, second, and third sub-active layers, which is beneficial for promoting an overall improvement in lithium-ion transport kinetics in the negative electrode. Optionally, 0.1% ≤ w1 ≤ 0.7%; and / or, 0.3% ≤ w2 ≤ 1%; and / or, 0.4% ≤ w3 ≤ 1.2%.

[0028] In some embodiments, the thickness ratio of the first sub-active layer, the second sub-active layer, and the third sub-active layer in the thickness direction of the negative electrode current collector is (0.1–2):(3–8):(2–5). This thickness ratio can increase the overall amount of alkali metal salt polymer in the negative electrode active layer, further improving the fast-charging performance of the battery.

[0029] In some embodiments, the third sub-active layer comprises a third binder, wherein the mass percentage of the third binder in the third sub-active layer is w3', and 0.25 ≤ w3 / w3' ≤ 6.67. Introducing a third binder into the third sub-active layer can improve its bonding performance, enhance the bonding performance between the third sub-active layer and the second sub-active layer, further reduce the risk of bulging or detachment of the third sub-active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet.

[0030] In some embodiments, the third adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0031] In some embodiments, the areal density of the negative electrode active layer is less than or equal to 0.16 mg / mm². 2 .

[0032] In some embodiments, the compaction density of the negative electrode active layer is 1.50 g / cm³. 3 ~1.75g / cm 3 .

[0033] In some embodiments, the active material of the negative electrode active layer includes artificial graphite. The addition of artificial graphite can further improve the fast-charging performance of the battery.

[0034] In some embodiments, the artificial graphite accounts for more than or equal to 40% of the mass percentage of the active material in the negative electrode active layer.

[0035] In some embodiments, the Dv50 of the artificial graphite is 8 μm to 15 μm.

[0036] A second aspect of this application provides a secondary battery. The secondary battery includes the negative electrode plate.

[0037] A third aspect of this application provides an electrical device. The electrical device includes at least one of the negative electrode and the secondary battery. Attached Figure Description

[0038] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0039] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0040] Figure 2 for Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0041] Figure 3 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.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0044] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0046] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, and they can be combined arbitrarily; 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 expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0047] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0050] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, and in some embodiments they are performed 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.

[0051] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members."

[0052] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0053] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0054] One embodiment of this application provides a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative active layer located on at least one surface of the negative current collector. The surface of the negative active layer away from the negative current collector contains an alkali metal salt polymer. Introducing the alkali metal polymer onto the surface of the negative active layer allows the polymer chains of the alkali metal polymer to provide channels for lithium ion transport, promoting lithium ion transport towards the interior of the negative active layer. This, in turn, reduces concentration polarization in the thickness direction of the electrode sheet and improves the fast-charging performance of the battery.

[0055] In some embodiments, the negative electrode active layer contains an alkali metal salt polymer within a predetermined thickness along the direction close to the negative electrode current collector, and the predetermined thickness is 10% to 90% of the thickness of the negative electrode active layer. This can further promote the transport of lithium ions towards the negative electrode active layer and further improve the fast charging performance of the battery. Optionally, the predetermined thickness is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the thickness of the negative electrode active layer, or any value within the range of any two of the above values. More optionally, the predetermined thickness is 40% to 50% of the thickness of the negative electrode active layer.

[0056] It is understandable that the preset thickness refers to the thickness of the negative electrode active layer from the surface away from the negative electrode current collector towards the negative electrode current collector. For example, the preset thickness refers to the thickness of the outer surface of the negative electrode active layer towards the negative electrode current collector, and the outer surface of the negative electrode active layer refers to the surface of the negative electrode active layer away from the negative electrode current collector.

[0057] In some embodiments, the mass percentage of alkali metal salt polymer contained within the preset thickness of the negative electrode active layer is 0% to 1.5%. This can reduce the risk of bulging or detachment in the preset thickness portion while promoting fast charging, thus maintaining a relatively stable structure of the negative electrode active layer. Optionally, the mass percentage of alkali metal salt polymer contained within the preset thickness of the negative electrode active layer can be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value within the range of any two of the above values. Optionally, the mass percentage of alkali metal salt polymer contained within the preset thickness of the negative electrode active layer is greater than 0. Further optionally, the mass percentage of alkali metal salt polymer contained within the preset thickness of the negative electrode active layer is 0.3% to 1%.

[0058] In some embodiments, the negative electrode active layer includes multiple sub-active layers stacked sequentially. The mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is less than the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector. This smaller mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector can further promote lithium-ion transport towards the interior of the active layer, further improving the battery's fast-charging performance. It is understood that the sub-active layer closest to the negative electrode current collector may contain alkali metal salt polymers. The sub-active layer furthest from the negative electrode current collector may represent the surface of the negative electrode active layer furthest from the negative electrode current collector; furthermore, the sub-active layer furthest from the negative electrode current collector may also represent a predetermined thickness of the negative electrode active layer.

[0059] Furthermore, alkali metal salt polymers possess certain adhesive properties. Introducing alkali metal salt polymers into the negative electrode active layer can adjust the adhesive properties of the active layer, thereby improving the structural stability of the negative electrode sheet.

[0060] In some embodiments, the mass percentage of alkali metal salt polymers in the sub-active layer closest to the negative electrode current collector is less than or equal to the mass percentage of alkali metal salt polymers in the sub-active layer furthest from the negative electrode current collector multiplied by 0.5. This allows the mass percentage of alkali metal salt polymers in each sub-active layer to be maintained within a suitable range, which is beneficial for further improving the lithium-ion transport kinetics in the negative electrode and further improving the battery's fast-charging performance.

[0061] In some embodiments, the mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is 0-1%. This can reduce the risk of bulging or detachment of the sub-active layer closest to the negative electrode current collector during negative electrode sheet processing, while promoting fast charging, thereby improving the processing performance of the negative electrode sheet. Optionally, the mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector can be 0, 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any value within the range of any two of the above values. It is understood that a mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector of 0 indicates that the sub-active layer closest to the negative electrode current collector does not contain alkali metal salt polymer. Further optionally, the mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is 0.1% to 0.7%. When the mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is large, the sub-active layer closest to the negative electrode current collector may bulge or detach.

[0062] In some embodiments, the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector is 0% to 1.5%. This can reduce the risk of bulging and detachment of the sub-active layer furthest from the negative electrode current collector during negative electrode sheet processing, while promoting fast charging, thereby improving the processing performance of the negative electrode sheet. Optionally, the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector can be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value within the range of any two of the above values. Optionally, the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector is greater than 0. Further optionally, the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector is 0.3% to 1%.

[0063] It is understandable that the direction away from the negative electrode current collector can be represented as the direction from the inside to the outside. In this case, the sub-active layer closest to the negative electrode current collector is the innermost sub-active layer, and the sub-active layer farthest from the negative electrode current collector is the outermost sub-active layer.

[0064] In some embodiments, the alkali metal salt polymer includes at least one of lithium, sodium, and potassium.

[0065] In some embodiments, the alkali metal salt polymer includes an alkali metal acrylate polymer. The negatively charged carboxylate groups in the alkali metal acrylate polymer can complex with small Lewis acid molecules in the electrolyte, increasing the electronegativity of the carboxylate groups. This allows more lithium ions to dissociate and enter the negative electrode active layer, further improving the battery's fast-charging performance. Optionally, the alkali metal acrylate polymer includes at least one of lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate. Lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate have similar effects in promoting the speed of lithium ion transport in the negative electrode.

[0066] In this application, the alkali metal salt polymer in the negative electrode sheet can be determined by testing as follows: Take the negative electrode sheet and dry it thoroughly with DMC. Scrape off the material of the negative electrode active layer to obtain powder. Mark the infrared characteristic peaks of the powder. Typical characteristic peaks of alkali metal salt polymers: at 1702 cm⁻¹. -1 This occurs at [location], corresponding to tensile vibration at C=O. [Location] is 1167 cm. -1 1405cm -1 1447cm -1 The characteristic peak at 2739 cm⁻¹ corresponds to the -CH₂ tensile vibration. -1 and 3372cm -1 The characteristic peaks correspond to the stretching vibration and absorption of the OH group from the carboxyl group, respectively, and are located at 2952 cm⁻¹. -1 The characteristic peak corresponds to the absorption of the CH stretching peak.

[0067] In this application, the mass percentage of alkali metal salt polymers in the negative electrode sheet can be determined by testing as follows: Take the negative electrode sheet and dry it using DMC cleaning agent. Scrape off the material of the corresponding active part in the negative electrode active layer to obtain powder. Soak the powder in deionized water, and stir and sonicate until the binder on the powder is fully dissolved in the deionized water. Filter off the powder and wash it repeatedly at least three times. Then add calcium chloride solution to the filtrate, stir until the precipitate is completely formed, filter, and calculate the mass percentage of alkali metal salt polymers by weighing the filter residue.

[0068] In some embodiments, the preparation method of the alkali metal salt polymer of acrylate includes: preparing a homogeneous solution of MOH with a mass fraction of 10% by weight; then adding a 30% by weight polyacrylic acid solution to the MOH solution and mixing at high speed until homogeneous; and drying and ball milling the homogeneous solution. Optionally, M includes an alkali metal element. Further optionally, MOH includes at least one selected from lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0069] In some embodiments, the molecular chains of the alkali metal salt polymer include a linear structure. This linear structure can further enhance the transport rate of lithium ions in the negative electrode, thus improving the battery's fast-charging performance.

[0070] In some embodiments, the number average molecular weight of the alkali metal salt polymer is 3,000 to 1,000,000. Optionally, the number average molecular weight of the alkali metal salt polymer can be 3,000 to 3,500, 5,000 to 5,500, 10,000 to 11,000, 20,000 to 21,000, 30,000 to 31,000, 40,000 to 41,000, 50,000 to 51,000, 60,000 to 61,000, 70,000 to 71,000, 80,000 to 81,000, 90,000 to 91,000, or 100,000. The number average molecular weight of the alkali metal salt polymer is 100,000 to 110,000, 200,000 to 210,000, 300,000 to 310,000, 400,000 to 410,000, 500,000 to 510,000, 600,000 to 610,000, 700,000 to 710,000, 800,000 to 810,000, 900,000 to 910,000, 990,000 to 1,000,000, and any range of the above values. Further optionally, the number average molecular weight of the alkali metal salt polymer is 100,000 to 500,000.

[0071] As is understandable, the symbol for number-average molecular weight is Mn, which measures molecular weight based on a number fraction. Number-average molecular weight equals the molecular weight of each component multiplied by the mole fraction of each component.

[0072] Number-average molecular weight determination methods: This parameter is typically determined using methods such as gel permeation chromatography, static light scattering, mass spectrometry, membrane osmotic pressure, end-group analysis, gas phase permeation, boiling point elevation method, and freezing point depression method. Optionally, the number-average molecular weight can be determined using gel permeation chromatography, referring to the national standard GB / T21863-2008 "Gel permeation chromatography (GPC) using tetrahydrofuran as eluent".

[0073] In some embodiments, the mass percentage of alkali metal in the alkali metal salt polymer is 3% to 8.9%. Optionally, the mass percentage of alkali metal in the alkali metal salt polymer can be 3%, 4%, 5%, 6%, 7%, 8%, 8.9%, or any value within the range of any two of the above values. More optionally, the mass percentage of alkali metal in the alkali metal salt polymer is 5% to 7.5%.

[0074] In this application, the mass percentage of alkali metals in alkali metal salt polymers can be tested in the following way: Take an alkali metal salt polymer sample with mass m0, and use inductively coupled plasma atomic emission spectrometry (ICP) to test the mass m1 of the alkali metals. Then, the average mass percentage of alkali metals in the alkali metal salt polymer = m1 / m0 × 100%. Specifically, weigh 0.2g of alkali metal salt polymer sample into a beaker, add 10mL of concentrated HNO3 solution, place it on a 180℃ heating plate for digestion for 30min. After the sample digestion is completed for 30min, cool it to room temperature, and transfer the digestion solution to a 50mL volumetric flask through a funnel and make up to volume. The tests were conducted according to USEPA-6010D-2018. Standard test solutions were prepared, specifically the multi-element ICP analytical standard solution from the National Nonferrous Metals Testing Center. The curve concentration points were 0, 0.2 mg / L, 0.5 mg / L, 1.0 mg / L, and 2.0 mg / L. The instrument was first used to create a calibration curve for the standard solutions. The sample mass and volume were input, and then the digested solutions were tested. Solutions exceeding the curve range needed to be diluted before testing. Finally, the presence of elements was identified through atomic emission spectra (qualitative analysis), and the element content was determined based on the intensity of the spectral lines (quantitative analysis).

[0075] In some embodiments, the mass percentage of alkali metal salt polymers in each sub-active layer gradually increases in the direction away from the negative electrode current collector. This gradual increase in the mass percentage of alkali metal salt polymers in each sub-active layer allows for better matching of lithium-ion transport kinetics between adjacent sub-active layers, further improving lithium-ion transport kinetics in the negative electrode and thus enhancing the battery's fast-charging performance.

[0076] It is understood that in this application, the direction away from the negative electrode current collector refers to the direction away from the negative electrode current collector in the thickness direction of the negative electrode current collector.

[0077] In some embodiments, the mass percentage of alkali metal salt polymers in adjacent sub-active layers increases by 0.1% to 0.5% in the direction away from the negative electrode current collector. This range of increase in the mass percentage of alkali metal salt polymers in adjacent sub-active layers allows for better matching of lithium-ion transport kinetics between adjacent sub-active layers, which is beneficial for further improving the lithium-ion transport kinetics in the negative electrode and further improving the fast-charging performance of the battery. Optionally, the mass percentage increase in the mass percentage of alkali metal salt polymers in adjacent sub-active layers can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value within the range of any two of the above values.

[0078] In some embodiments, in the direction away from the negative electrode current collector, the negative electrode active layer includes a first sub-active layer and a second sub-active layer stacked sequentially, wherein the mass percentages of the alkali metal salt polymer in the first and second sub-active layers are w1 and w2, respectively, where w1 < w2. The cooperation between the first and second sub-active layers is beneficial for improving the fast-charging performance of the battery.

[0079] In some implementations, 0 ≤ w1 ≤ 1%. This can reduce the risk of bulging and detachment of the first sub-active layer during the negative electrode processing while promoting fast charging, thereby improving the processing performance of the negative electrode. Optionally, w1 can be 0, 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any value within the range of any two of the above values. Further optionally, 0.1% ≤ w1 ≤ 0.7%. It is understood that w1 being 0 indicates that the first sub-active layer does not contain alkali metal salt polymers.

[0080] In some implementations, 0 < w2 ≤ 1.5%. This can reduce the risk of bulging and detachment of the second sub-active layer during the negative electrode processing, while promoting fast charging, thereby improving the processing performance of the negative electrode. Optionally, w2 can be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value within the range of any two of the above values. Further optionally, 0.3% ≤ w2 ≤ 1%.

[0081] In some embodiments, the thickness ratio of the first sub-active layer to the second sub-active layer in the thickness direction of the negative electrode current collector is (0.1-2):(3-8). The second sub-active layer has a larger thickness, which can increase the overall amount of alkali metal salt polymer in the negative electrode active layer, further improving the fast-charging performance of the battery. Optionally, the thickness ratio of the first sub-active layer to the second sub-active layer is 0.1:3, 0.1:4, 0.1:5, 0.1:6, 0.1:7, 0.1:8, 0.5:3, 0.5:4, 0.5:5, 0.5:6, 0.5:7, 0.5:8, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 2:3, 2:4, 2:5, 2:7, and any value within the range of any two of the above values.

[0082] In some embodiments, the first sub-active layer includes a first binder, and the mass percentage of the first binder in the first sub-active layer is w1', where 0 ≤ w1 / w1' ≤ 1. Introducing the first binder into the first sub-active layer can improve the bonding performance of the first sub-active layer, enhance the bonding performance between the first sub-active layer and the negative electrode current collector, further reduce the risk of bulging or detachment of the first sub-active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet. Optionally, w1 / w1' can be 0, 0.01, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value within the range of any two of the above values.

[0083] In some embodiments, 1% ≤ w1 + w1' ≤ 4%. Within this range, w1 + w1' allows for good adhesion between the first sub-active layer and the negative electrode current collector, thereby increasing the proportion of the negative electrode active material and improving the battery's energy density. Optionally, w1 + w1' can be 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, or any value within the range of any two of the above values.

[0084] Optionally, 1% ≤ w1' ≤ 3%. Further optionally, w1' can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any value within the range of any two of the above values.

[0085] In some embodiments, the first adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0086] In some embodiments, the second sub-active layer includes a second binder, and the mass percentage of the second binder in the second sub-active layer is w2', where 0.15 ≤ w2 / w2' ≤ 5. Introducing a second binder into the second sub-active layer can improve the adhesion performance of the second sub-active layer, enhance the adhesion between the second sub-active layer and the first sub-active layer, further reduce the risk of bulging or detachment of the second sub-active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet. Optionally, w2 / w2' can be any value within the range of 0.15, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.5, 4, 4.5, 5, or any two of the above values. Further optionally, 0.1 ≤ w2 / w2' ≤ 1.

[0087] In some embodiments, 0.3% ≤ w2 + w2' ≤ 3.5%. Within this range, w2 + w2' allows for good adhesion between the second and first sub-active layers, resulting in a higher proportion of negative electrode active material, which is beneficial for improving the battery's energy density. Optionally, w2 + w2' can be any value within the range of 0.3%, 0.6%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, or any two of the above values. Further optionally, 1.2% ≤ w2 + w2' ≤ 2.3%.

[0088] Optionally, 0.3% ≤ w2' ≤ 2%. Further optionally, w2' can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0089] In some embodiments, the second adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0090] In some embodiments, the negative electrode active layer further includes a third sub-active layer, which is located on the surface of the second sub-active layer away from the first sub-active layer. The mass percentage of the alkali metal salt polymer in the third sub-active layer is w3, where w1 < w2 < w3. The combination of the first, second, and third sub-active layers is beneficial to improving the fast-charging performance of the battery.

[0091] In some implementations, 0 ≤ w1 ≤ 1%, 0 < w2 ≤ 1.5%, and 0 < w3 ≤ 1.5%. The ranges of w1, w2, and w3 allow for better matching of the lithium-ion transport kinetics between the first, second, and third sub-active layers, which is beneficial for promoting the overall improvement of lithium-ion transport kinetics in the negative electrode. Optionally, w1 can be 0, 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any value within the range of any two of the above values. w2 can be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value within the range of any two of the above values. w3 can be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value within the range of any two of the above values. Further optionally, 0.1% ≤ w1 ≤ 0.7%, 0.3% ≤ w2 ≤ 1%, and 0.4% ≤ w3 ≤ 1.2%.

[0092] In some embodiments, the thickness ratio of the first sub-active layer, the second sub-active layer, and the third sub-active layer in the thickness direction of the negative electrode current collector is (0.1–2):(3–8):(2–5). This thickness ratio can increase the overall amount of alkali metal salt polymer in the negative electrode active layer, further improving the fast-charging performance of the battery. Optionally, the thickness ratio of the first sub-active layer, the second sub-active layer, and the third sub-active layer is 0.1:3:2, 0.5:3:2, 1:3:2, 1.5:3:2, 2:3:2, 1:4:2, 1:5:2, 1:6:2, 1:7:2, 1:8:2, 1:3:3, 1:3:4, 1:3:5, or any value within the range of any two of the above values.

[0093] It is understood that, in the thickness direction of the negative electrode current collector, the thicknesses of the first sub-active layer, the second sub-active layer, and the third sub-active layer are D1, D2, and D3, respectively, where 0.01≤D1 / (D1+D2+D3)≤0.2, 0.3≤D2 / (D1+D2+D3)≤0.8, and 0.2≤D3 / (D1+D2+D3)≤0.5. Optionally, D1 / (D1+D2+D3) can be 0.01, 0.05, 0.1, 0.12, 0.15, 0.18, 0.2, or any value within the range of any two of the above values. D2 / (D1+D2+D3) can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any value within the range of any two of the above values. D3 / (D1+D2+D3) can be 0.2, 0.3, 0.4, 0.5, or any value within the range of any two of the above values.

[0094] In some embodiments, the third sub-active layer comprises a third binder, and the mass percentage of the third binder in the third sub-active layer is w3', where 0.25 ≤ w3 / w3' ≤ 6.67. Introducing a third binder into the third sub-active layer can improve the bonding performance of the third sub-active layer, enhance the bonding performance between the third sub-active layer and the second sub-active layer, further reduce the risk of bulging or detachment of the third sub-active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet. Optionally, w3 / w3' can be any value within the range of 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 4, 5, 6, 6.67, or any two of the above values.

[0095] In some embodiments, 0.3% ≤ w3 + w3' ≤ 3.5%. Within this range, w3 + w3' allows for good adhesion between the third and second sub-active layers, resulting in a higher proportion of negative electrode active material, which is beneficial for improving the battery's energy density. Optionally, w3 + w3' can be 0.3%, 0.8%, 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.5%, 3%, 3.5%, or any value within the range of any two of the above values.

[0096] Optionally, 0.3% ≤ w3' ≤ 2%. Further optionally, w2' can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0097] In some embodiments, the third adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0098] In some embodiments, in the direction away from the negative electrode current collector, the negative electrode active layer includes a first sub-active layer, a second sub-active layer, and a third sub-active layer stacked sequentially. The mass percentages of the alkali metal salt polymer in the first, second, and third sub-active layers are w1, w2, and w3, respectively. The first, second, and third sub-active layers each contain a first binder, a second binder, and a third binder, respectively. The mass percentage of the first binder in the first sub-active layer is w1', the mass percentage of the second binder in the second sub-active layer is w2', and the mass percentage of the third binder in the third sub-active layer is w3'. Wherein, 0 ≤ w1 ≤ 1%, 1% ≤ w1' ≤ 3%, 0 < w2 ≤ 1.5%, 0.3% ≤ w2' ≤ 2%, 0 < w3 ≤ 1.5%, and 0.3% ≤ w3' ≤ 2%. 0 ≤ w1 / w1' ≤ 1. 0.15 ≤ w2 / w2' ≤ 5. 0.25 ≤ w3 / w3' ≤ 6.67. 1% ≤ w1 + w1' ≤ 4%. 0.3% ≤ w2 + w2' ≤ 3.5%. 0.3% ≤ w3 + w3' ≤ 3.5%. It is understood that w1, w2, w3, w1', w2', and w3' can be independently selected from the contents described in this application.

[0099] In some embodiments, the areal density (CW) of the negative electrode active layer is less than or equal to 0.16 mg / mm². 2 Optionally, the areal density (CW) of the negative electrode active layer is 0.078 mg / mm². 2 ~0.136mg / mm 2 Further optionally, the areal density (CW) of the negative electrode active layer can be 0.05 mg / mm². 2 0.08 mg / mm 2 0.1 mg / mm 2 0.11 mg / mm 2 0.12 mg / mm 2 0.13 mg / mm 2 And any value within the range consisting of any two of the above values.

[0100] In some embodiments, the compaction density (PD) of the negative electrode active layer is 1.50 g / cm³. 3 ~1.75g / cm 3 Optionally, the compaction density (PD) of the negative electrode active layer is 1.50 g / cm³. 3 1.55g / cm 3 1.60g / cm3 1.65g / cm 3 1.70g / cm 3 And any value within the range consisting of any two of the above values.

[0101] It is understood that the mass percentage of the negative electrode active material in the negative electrode active layer is 94% to 99%. Optionally, the mass percentage of the negative electrode active material in the negative electrode active layer can be 94%, 95%, 96%, 97%, 98%, 99%, or any value within the range of any two of the above values. Further optionally, the negative electrode active material in the negative electrode active layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Further optionally, the negative electrode active material in the negative electrode active layer includes artificial graphite. The mass percentage of artificial graphite in the negative electrode active material is greater than or equal to 40%. The Dv50 of the artificial graphite is 8 μm to 15 μm. The graphitization degree of the artificial graphite is 94% to 95%. The specific capacity of the artificial graphite is 350 mAh / g to 358 mAh / g. The addition of artificial graphite can further improve the fast-charging performance of the battery.

[0102] It is understood that in this application, Dv50 refers to the particle size corresponding to the cumulative particle size distribution number reaching 50% in the volume cumulative distribution curve. Physically, it means that 50% of the particles are smaller (or larger) than Dv50. As an example, Dv50 can be obtained by referring to the test method in GB / T 19077-2016 and using the particle size distribution curve obtained by a Mastersizer3000 laser diffraction particle size distribution measuring instrument.

[0103] Optionally, the mass percentage of artificial graphite in the negative electrode active material can be ≥45%, ≥50%, ≥60%, or ≥70%, etc. The Dv50 of the artificial graphite can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any value within the range of any two of the above values.

[0104] It is also understood that, in the negative electrode active layer, the sum of the mass percentages of the alkali metal salt polymer, the first binder, the second binder, and the third binder, based on the mass percentage of the negative electrode active layer, is 1% to 4%, optionally 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, and any value within the range of any two of the above values.

[0105] Another embodiment of this application provides a secondary battery. The secondary battery includes the aforementioned negative electrode plate.

[0106] Another embodiment of this application provides an electrical device. This electrical device includes at least one of the above-described negative electrode and the above-described secondary battery.

[0107] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0108] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0109] Positive electrode sheet

[0110] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0111] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0112] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0113] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries 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, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0114] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0115] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 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 areal density per unit area, based on dry weight (excluding solvent), can be 15 mg / cm³. 2 ~35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 .

[0117] Negative electrode sheet

[0118] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0119] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0120] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0121] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0122] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0123] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0125] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s.

[0126] electrolytes

[0127] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely 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 may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0130] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butene 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, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0131] 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.

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

[0133] Separating membrane

[0134] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0135] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0136] In some embodiments, the thickness of the isolation membrane is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0137] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0138] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

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

[0140] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0141] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0142] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 1.

[0143] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0144] Secondary batteries can be battery modules or battery packs.

[0145] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0146] In a battery module, multiple battery cells can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these battery cells can be secured using fasteners.

[0147] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0148] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0149] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0150] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0151] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0152] Figure 3 Here is an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0153] 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.

[0154] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0155] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0156] Example 1

[0157] (1) Preparation of positive electrode sheet.

[0158] The positive electrode active material LiFePO4, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a mass ratio of 97:1:2 to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly coated onto the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. The areal density of the positive electrode sheet was 400 mg / 1540.25 mm². 2 The compacted density is 2.55 g / cm³. 3 .

[0159] (2) Preparation of negative electrode sheet.

[0160] First slurry: The negative electrode active material graphite, alkali metal salt polymer of acrylic acid, first binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose, and conductive agent carbon black (Super P) are stirred evenly in deionized water to obtain the first slurry.

[0161] Second slurry: The negative electrode active material graphite, alkali metal salt polymer of acrylic acid, second binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose, and conductive agent carbon black (Super P) are stirred evenly in deionized water to obtain the second slurry.

[0162] The third slurry is prepared by mixing graphite (anode active material), alkali metal salt polymer of acrylic acid, styrene-butadiene rubber (third binder), sodium carboxymethyl cellulose (dispersant), and carbon black (Super P) (conductive agent) in deionized water.

[0163] The first, second, and third slurries are sequentially and uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained. The areal density (CW) of the negative electrode sheet is 0.1 mg / mm². 2 The compaction density (PD) is 1.6 g / cm³. 3 The first slurry forms the first sub-active layer, the second slurry forms the second sub-active layer, and the third slurry forms the third sub-active layer.

[0164] In the first sub-active layer, the active material graphite accounts for 95.8% of the mass. The alkali metal salt polymer of acrylic acid accounts for w1 of the mass, the first binder styrene-butadiene rubber accounts for w1' of the mass, and the thickness of the first sub-active layer is D1. D1 / (D1+D2+D3)=0.1.

[0165] In the second sub-active layer, the active material graphite accounts for 96% by mass. The alkali metal salt polymer of acrylic acid accounts for w2 by mass, the second binder styrene-butadiene rubber accounts for w2' by mass, and the thickness of the second sub-active layer is D2. D2 / (D1+D2+D3) is shown in Table 1.

[0166] In the third sub-active layer, the active material graphite accounts for 96.3% by mass. The alkali metal salt polymer of acrylic acid accounts for w3 by mass, the third binder styrene-butadiene rubber accounts for w3' by mass, and the thickness of the third sub-active layer is D3. D3 / (D1+D2+D3) is shown in Table 1.

[0167] (3) Preparation of electrolyte.

[0168] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1mol / L.

[0169] (4) Preparation of the isolation membrane.

[0170] A polyethylene (PE) film coated with a nano-alumina layer is used as the isolation membrane.

[0171] (5) Preparation of secondary batteries.

[0172] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain a wound electrode assembly. The electrode assembly is then placed in an outer square aluminum shell, dried, and injected with electrolyte. After processes such as encapsulation, settling, formation, aging, secondary encapsulation, and capacity testing, a secondary battery is obtained.

[0173] Examples 2 to 9

[0174] Compared with Example 1, Examples 2 to 9 differ in the selection of the alkali metal salt polymer of acrylic acid, and the mass percentages of the alkali metal salt polymer of acrylic acid, the first binder, the second binder, and the third binder in the first sub-active layer, the second sub-active layer, and the third sub-active layer. In Examples 7 and 8, the third slurry is not applied, resulting in a double-layer structure for the negative electrode active layer, comprising a first sub-active layer and a second sub-active layer. Details are shown in Table 1.

[0175] Comparative Examples 1 to 2

[0176] Compared with Example 2, Comparative Examples 1 and 2 differ in that the mass percentage of alkali metal in the alkali metal salt polymer of acrylate differs in the first, second, and third sub-active layers. See Table 1 for details.

[0177] Test case

[0178] The negative electrode and battery in the examples and comparative examples were tested respectively.

[0179] (1) Fast charging performance tests were conducted on the batteries in the examples and comparative examples. The test method was a stacked three-electrode test method. The positive and negative electrode sheets of the hard-shell cell were removed and soaked in DMC solvent for more than 72 hours to ensure that the electrolyte solvent, lithium salt, and additives were completely leached out. The electrode sheets were then dried in a vacuum oven, and the anode and cathode electrode sheets were assembled into a stacked three-electrode cell, with copper wire serving as the reference electrode. The lithium plating charging rate of the stacked three-electrode cell was then tested at 25°C for each SOC. The maximum charging rate was recorded when the reference electrode potential dropped to 0mV. Following this method, the maximum charging rate was tested at each 5% SOC, such as 5% SOC, 10% SOC, 15% SOC to 100% SOC. The continuous charging time from 10% SOC to 80% SOC obtained from this test was calculated as the fast charging time. The results are shown in Table 1. Fast charging time is measured in minutes.

[0180] (2) Cyclic performance tests were conducted on the batteries in the examples and comparative examples. The test method was as follows: at 25°C, the secondary battery was charged to 3.8V at a constant current of 1C, left to stand for 30 minutes, and then discharged to 2.0V at a constant current of 1C. This constituted one cycle of charge and discharge. The discharge capacity at this point was recorded, which was the initial capacity of the secondary battery. The secondary battery was then subjected to cyclic charge and discharge tests according to the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decreased to 80% of the initial capacity of the secondary battery. The number of cycles was recorded. The results are shown in Table 1.

[0181] Table 1

[0182]

[0183]

[0184] It is understood that "Number Average Molecular Weight" in Table 1 represents the number average molecular weight of the alkali metal acrylate polymers, in ten thousand units. The number average molecular weight of the alkali metal acrylate polymers in the examples and comparative examples is approximately the value given in this column. "Mass Percentage" represents the mass percentage of the alkali metal in the alkali metal acrylate polymer. w1 represents the mass percentage of the alkali metal acrylate polymer in the first sub-active layer. w2 represents the mass percentage of the alkali metal acrylate polymer in the second sub-active layer. w3 represents the mass percentage of the alkali metal acrylate polymer in the third sub-active layer. w1' represents the mass percentage of the first binder in the first sub-active layer. w2' represents the mass percentage of the second binder in the second sub-active layer. w3' represents the mass percentage of the third binder in the third sub-active layer. D2 percentage represents D2 / (D1+D2+D3). D3 percentage represents D3 / (D1+D2+D3).

[0185] As shown in Table 1, the fast charging time of the battery in the embodiment is shorter than that of the battery in the comparative example. This indicates that the fast charging performance of the battery in the embodiment is superior to that of the battery in the comparative example.

[0186] As can be seen from Examples 1 to 3, when w1 is not 0, the battery exhibits better fast-charging and cycle performance. Furthermore, increasing the content of alkali metal acrylate polymer in the negative electrode plate improves the battery's fast-charging and cycle performance.

[0187] As can be seen from Examples 1 and 4 to 6, when the alkali metal in the alkali metal salt polymer of acrylic acid has a suitable mass percentage, the battery has good fast charging performance and cycle performance.

[0188] As can be seen from Examples 7 and 8, when the negative electrode active layer is a double-layer structure, that is, when the negative electrode active layer includes a first sub-active layer and a second sub-active layer, and when w1 and w2 have appropriate values, the battery has good fast charging performance and cycle performance.

[0189] As can be seen from Examples 1 and 9, batteries with a number-average molecular weight of alkali metal salt polymers in a suitable range have good fast-charging performance and good cycle performance.

[0190] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0191] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, wherein the surface of the negative electrode active layer away from the negative electrode current collector contains an alkali metal salt polymer; the alkali metal salt polymer includes an alkali metal salt polymer of acrylate. The negative electrode active layer includes multiple sub-active layers stacked sequentially. The mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is less than the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector. In the direction away from the negative electrode current collector, the mass percentage of alkali metal salt polymer in the adjacent sub-active layer increases by 0.1% to 0.5%.

2. The negative electrode sheet according to claim 1, characterized in that, The molecular chains of the alkali metal salt polymers include linear structures; and / or, The number average molecular weight of the alkali metal salt polymer is 3,000 to 1,000,000.

3. The negative electrode sheet according to claim 1, characterized in that, The number average molecular weight of the alkali metal salt polymer is 100,000 to 500,000.

4. The negative electrode sheet according to claim 1, characterized in that, The alkali metal salt polymer contains 3% to 8.9% by mass of alkali metal.

5. The negative electrode sheet according to claim 4, characterized in that, The alkali metal salt polymer contains 5% to 7.5% by mass of alkali metal.

6. The negative electrode sheet according to claim 1, characterized in that, The alkali metal salt polymer of acrylate includes one or more of lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate.

7. The negative electrode sheet according to claim 1, characterized in that, Along the direction close to the negative electrode current collector, the negative electrode active layer contains the alkali metal salt polymer within a predetermined thickness, and the predetermined thickness is 10% to 90% of the thickness of the negative electrode active layer.

8. The negative electrode sheet according to claim 7, characterized in that, The preset thickness is 40% to 50% of the thickness of the negative electrode active layer.

9. The negative electrode sheet according to claim 7, characterized in that, The mass percentage of the alkali metal salt polymer contained within the preset thickness of the negative electrode active layer is greater than 0 and less than or equal to 1.5%.

10. The negative electrode sheet according to claim 7, characterized in that, The mass percentage of the alkali metal salt polymer contained in the preset thickness of the negative electrode active layer is 0.3% to 1%.

11. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is less than or equal to the mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector multiplied by 0.

5.

12. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is 0-1%; and / or, The mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector is greater than 0 and less than or equal to 1.5%.

13. The negative electrode sheet according to claim 12, characterized in that, The mass percentage of alkali metal salt polymer in the sub-active layer closest to the negative electrode current collector is 0.1% to 0.7%; and / or, The mass percentage of alkali metal salt polymer in the sub-active layer furthest from the negative electrode current collector is 0.3% to 1%.

14. The negative electrode sheet according to claim 1, characterized in that, In the direction away from the negative electrode current collector, the negative electrode active layer includes a first sub-active layer and a second sub-active layer stacked sequentially, wherein the mass percentages of alkali metal salt polymers in the first sub-active layer and the second sub-active layer are w1 and w2, respectively, where w1 < w2.

15. The negative electrode sheet according to claim 14, characterized in that, 0 ≤ w1 ≤ 1%; and / or, 0 < w2 ≤ 1.5%.

16. The negative electrode sheet according to claim 15, characterized in that, 0.1%≤w1≤0.7%; and / or, 0.3%≤w2≤1%.

17. The negative electrode sheet according to claim 14, characterized in that, In the thickness direction of the negative electrode current collector, the thickness ratio of the first sub-active layer to the second sub-active layer is (0.1~2):(3~8).

18. The negative electrode sheet according to claim 14, characterized in that, The first sub-active layer contains a first adhesive, and the mass percentage of the first adhesive in the first sub-active layer is w1', where 0 ≤ w1 / w1' ≤ 1.

19. The negative electrode sheet according to claim 18, characterized in that, The first adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

20. The negative electrode sheet according to claim 14, characterized in that, The second sub-active layer contains a second adhesive, and the mass percentage of the second adhesive in the second sub-active layer is w2', where 0.15≤w2 / w2'≤5.

21. The negative electrode sheet according to claim 20, characterized in that, The second adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

22. The negative electrode sheet according to claim 14, characterized in that, The negative electrode active layer further includes a third sub-active layer, which is located on the surface of the second sub-active layer away from the first sub-active layer. The mass percentage of the alkali metal salt polymer in the third sub-active layer is w3, where w1 < w2 < w3.

23. The negative electrode sheet according to claim 22, characterized in that, 0 ≤ w1 ≤ 1%; and / or, 0 < w2 ≤ 1.5%; and / or, 0 < w3 ≤ 1.5%.

24. The negative electrode sheet according to claim 23, characterized in that, 0.1%≤w1≤0.7%; and / or, 0.3%≤w2≤1%; and / or, 0.4%≤w3≤1.2%.

25. The negative electrode sheet according to claim 22, characterized in that, In the thickness direction of the negative electrode current collector, the thickness ratio of the first sub-active layer, the second sub-active layer and the third sub-active layer is (0.1~2):(3~8):(2~5).

26. The negative electrode sheet according to claim 22, characterized in that, The third sub-active layer contains a third adhesive, and the mass percentage of the third adhesive in the third sub-active layer is w3', where 0.25 ≤ w3 / w3' ≤ 6.

67.

27. The negative electrode sheet according to claim 26, characterized in that, The third adhesive includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

28. The negative electrode sheet according to claim 1, characterized in that, The areal density of the negative electrode active layer is less than or equal to 0.16 mg / mm². 2 ; and / or, The compaction density of the negative electrode active layer is 1.50 g / cm³. 3 ~1.75g / cm 3 .

29. The negative electrode sheet according to claim 1, characterized in that, The active material of the negative electrode active layer includes artificial graphite.

30. The negative electrode sheet according to claim 29, characterized in that, The artificial graphite accounts for a mass percentage of 40% or more of the active material in the negative electrode active layer; and / or, the Dv50 of the artificial graphite is 8μm to 15μm.

31. A secondary battery, characterized in that, Includes the negative electrode sheet according to any one of claims 1 to 30.

32. An electrical appliance, characterized in that, It includes at least one of the negative electrode sheet according to any one of claims 1 to 30 and the secondary battery according to claim 31.

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