Negative electrode sheet, secondary battery, and electrical apparatus

Abstract

A negative electrode sheet, a secondary battery, and an electrical apparatus. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer formed on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a middle region and an edge region, and the edge region being located around the middle region. The mass percent of an alkali metal salt polymer in the middle region is greater than the mass percent of the alkali metal salt polymer in the edge region. The alkali metal salt polymer can improve the quick charging performance of the battery. Furthermore, in the negative electrode active layer, the mass percentage of the alkali metal salt polymer in the middle region is greater than the mass percentage of the alkali metal salt polymer in the edge region, such that the reabsorption of electrolyte during cycling of the secondary battery can be promoted, and the negative electrode active layer can be more fully infiltrated by the electrolyte, thereby further improving the cycle performance of the secondary battery.

Description

Negative electrode sheet, secondary battery and electrical device

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2023116486748, filed on December 1, 2023, entitled “Negative Electrode Sheet, Secondary Battery and Electrical Device,” the entire text of which is hereby incorporated by reference. Technical Field

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

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

[0005] With the continuous deepening of research on secondary batteries, the performance of secondary batteries has been continuously improved. However, the fast charging performance and cycle performance of batteries still need to be further improved.

[0006] Summary of the Invention

[0007] A first aspect of the present application provides a negative electrode plate, comprising 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 negative electrode active layer comprises a middle region and an edge region, and the edge region is located outside the middle region; the mass percentage of the alkali metal salt polymer in the middle region is greater than the mass percentage of the alkali metal salt polymer in the edge region.

[0008] In the aforementioned negative electrode sheet, by designing the negative electrode active layer and introducing an alkali metal salt polymer into the negative electrode active layer, the polymer chains of the alkali metal salt polymer provide channels for the transport of lithium ions, promoting the internal transport of lithium ions toward the negative electrode active layer, thereby reducing concentration polarization across the thickness of the sheet and improving the battery's fast-charging performance. Furthermore, in the negative electrode active layer, the mass percentage of the alkali metal salt polymer in the central region is greater than that in the edge region. This promotes electrolyte resorption during the secondary battery cycle, allowing the negative electrode active layer to be more fully infiltrated with the electrolyte, thereby improving the secondary battery's cycling performance.

[0009] In some embodiments, the mass percentage of the alkali metal salt polymer in the middle region is 0.4% to 1.5%; and / or the mass percentage of the alkali metal salt polymer in the edge region is 0 to 0.8%. The alkali metal salt polymer in the middle region and the alkali metal salt polymer in the edge region, respectively, within the corresponding ranges, can promote fast charging and electrolyte resorption, reduce the risk of bulging and falling off of the negative electrode active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet. Optionally, the mass percentage of the alkali metal salt polymer in the middle region is 0.5% to 1%; and / or the mass percentage of the alkali metal salt polymer in the edge region is 0 to 0.5%.

[0010] In some embodiments, the molecular chain of the alkali metal salt polymer includes a linear structure. The linear structure can further promote the increase in the transmission speed of lithium ions in the negative electrode plate, which is beneficial to further improve the fast charging performance of the battery.

[0011] In some embodiments, the number average molecular weight of the alkali metal salt polymer is 3,000 to 1,000,000. Alternatively, the number average molecular weight of the alkali metal salt polymer is 100,000 to 500,000.

[0012] In some embodiments, the mass percentage of alkali metal in the alkali metal salt polymer is 3% to 8.9%. Alternatively, the mass percentage of alkali metal in the alkali metal salt polymer is 5% to 7.5%.

[0013] In some embodiments, the alkali metal salt polymer includes an alkali metal salt polymer of acrylic acid. The negatively charged carboxylate groups in the alkali metal salt polymer of acrylic acid can complex with Lewis acid small molecules in the electrolyte, thereby increasing the electronegativity of the carboxylate groups, thereby allowing more lithium ions to dissociate and enter the negative electrode active layer, further improving the fast charging performance of the battery. Optionally, the alkali metal salt polymer of acrylic acid includes one or more of lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate.

[0014] In some embodiments, the negative electrode current collector includes a tab region and an active region in contact with each other, and the negative electrode active layer is located in the active region. The negative electrode active layer includes a first active portion, a second active portion, and a third active portion sequentially distributed along the direction from the tab region to the active region. The mass percentages of the alkali metal salt polymer in the first active portion, the second active portion, and the third active portion are w1, w2, and w3, respectively, where w2>w1 and w2>w3. In the negative electrode active layer, the mass percentage of the alkali metal salt polymer in the second active portion is greater than the mass percentage of the alkali metal salt polymer in the first active portion, and the mass percentage of the alkali metal salt polymer in the second active portion is greater than the mass percentage of the alkali metal salt polymer in the third active portion. This can promote electrolyte resorption during the cycle of the secondary battery, allowing the negative electrode active layer to be more fully infiltrated by the electrolyte, thereby improving the cycle performance of the secondary battery.

[0015] In some embodiments, 0 ≤ w1 ≤ 0.8%; and / or, 0.4% ≤ w2 ≤ 1.5%; and / or, 0 ≤ w3 ≤ 0.8%. w1, w2, and w3, respectively, within corresponding ranges, can promote fast charging and electrolyte resorption, reduce the risk of swelling and detachment of the first active portion during negative electrode sheet processing, and improve the processing performance of the negative electrode sheet. Optionally, 0 ≤ w1 ≤ 0.5%; and / or, 0.5% ≤ w2 ≤ 1%; and / or, 0 ≤ w3 ≤ 0.5%.

[0016] In some embodiments, along the direction from the tab region to the active region, the widths of the first active portion, the second active portion, and the third active portion are D1, D2, and D3, respectively; and 0.6≤D2 / (D1+D2+D3)≤0.9. Compared to the first and third active portions, the second active portion has a larger width, which can increase the overall amount of the alkali metal salt polymer in the negative electrode active layer, further improving the fast-charging and cycling performance of the battery.

[0017] In some embodiments, 0.05≤D1 / (D1+D2+D3)≤0.2; and / or, 0.05≤D3 / (D1+D2+D3)≤0.2. The widths of the first active portion and the third active portion are within corresponding ranges. This facilitates electrolyte resorption during cycling while maintaining a larger width for the second active portion having a higher mass percentage of the alkali metal salt polymer. This further increases the overall amount of the alkali metal salt polymer in the negative electrode active layer, thereby improving the fast-charging and cycling performance of the battery.

[0018] In some embodiments, the first active portion further contains a first binder, and the mass percentage of the first binder in the first active portion is w1', where 0≤w1 / w1'≤1. Introducing the first binder into the first active portion can improve the bonding properties of the first active portion, enhancing the bonding properties between the first active portion and the negative electrode current collector, further reducing the risk of bulging or falling off of the first active portion during processing of the negative electrode sheet, and improving the processing performance of the negative electrode sheet. Optionally, the first binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0019] In some embodiments, the second active portion further contains a second binder, where the mass percentage of the second binder in the second active portion is w2', where 0.25 ≤ w2 / w2' ≤ 1. Introducing the second binder into the second active portion can improve the bonding properties of the second active portion, enhancing the bonding between the second active portion and the negative electrode current collector, further reducing the risk of bulging or detachment of the second active portion during negative electrode sheet processing, and improving the processing performance of the negative electrode sheet. Optionally, the second binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0020] In some embodiments, the third active portion further contains a third binder, where the mass percentage of the third binder in the third active portion is w3', where 0 ≤ w3 / w3' ≤ 1. Introducing the third binder into the third active portion can improve the bonding properties of the third active portion, enhancing the bonding between the third active portion and the negative electrode current collector, further reducing the risk of bulging or detachment of the third active portion during negative electrode sheet processing, and improving the processing performance of the negative electrode sheet. The third binder includes one or more of styrene-butadiene rubber and modified compounds thereof, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0021] In some embodiments, the surface density of the negative electrode active layer is less than or equal to 0.14 mg / mm 2 ; and / or, the compaction density of the negative electrode active layer is 1.50g / cm 3 ~1.75g / cm 3 .

[0022] A second aspect of the present application provides a secondary battery comprising the negative electrode plate.

[0023] A third aspect of the present application provides an electrical device comprising at least one of the negative electrode plate and the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0025] FIG1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0026] FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .

[0027] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0028] FIG4 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present application.

[0029] Explanation of the accompanying symbols: 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Power-consuming device; 3. Negative electrode sheet; 31. Tab area; 32. Negative electrode active layer; 321. First active portion; 322. Second active portion; 323. Third active portion. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0033] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0035] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0036] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, and in some embodiments 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0037] In this application, open technical features or technical solutions described with words such as "contain," "include," and "includes" do not exclude additional members beyond the listed members unless otherwise specified, and can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may or may not include other members unless otherwise specified. This can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members."

[0038] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0039] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0040] One embodiment of the present application provides a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector. The negative electrode active layer includes a central region and an edge region, wherein the edge region is located peripheral to the central region. The mass percentage of the alkali metal salt polymer in the central region is greater than the mass percentage of the alkali metal salt polymer in the edge region.

[0041] In the negative electrode plate of this embodiment, an alkali metal salt polymer is introduced into the negative electrode active layer through design. The polymer chains of the alkali metal salt polymer provide channels for the transport of lithium ions, promoting the internal transport of lithium ions toward the negative electrode active layer, thereby reducing concentration polarization across the thickness of the plate and improving the battery's fast-charging performance. Furthermore, in the negative electrode active layer, the mass percentage of the alkali metal salt polymer in the central region is greater than that in the edge regions. This promotes electrolyte resorption during the secondary battery cycle, allowing the negative electrode active layer to be more fully infiltrated with electrolyte, thereby improving the secondary battery's cycling performance.

[0042] Furthermore, alkali metal salt polymers have certain bonding properties. Introducing alkali metal salt polymers into the negative electrode active layer can also adjust the bonding properties between the negative electrode active layer and the negative electrode current collector, which is beneficial to improving the structural stability of the negative electrode sheet.

[0043] It can be understood that the edge area may surround the entire middle area or may surround part of the middle area.

[0044] In some embodiments, the mass percentage of the alkali metal salt polymer in the middle region is 0.4% to 1.5%. The mass percentage of the alkali metal salt polymer in the edge region is 0 to 0.8%. The alkali metal salt polymer in the middle region and the alkali metal salt polymer in the edge region can promote fast charging and electrolyte resorption, reduce the risk of bulging and falling off of the negative electrode active layer during the processing of the negative electrode sheet, and improve the processing performance of the negative electrode sheet. Optionally, the mass percentage of the alkali metal salt polymer in the middle region can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% and any value within the range consisting of any two of the above values. Optionally, the mass percentage of the alkali metal salt polymer in the edge region is 0, 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or any value within a range consisting of any two of the above values. It is understood that when the mass percentage of the alkali metal salt polymer in the edge region is 0, it means that the edge region does not contain any alkali metal salt polymer. Further optionally, the mass percentage of the alkali metal salt polymer in the middle region is 0.5% to 1%. The mass percentage of the alkali metal salt polymer in the edge region is 0 to 0.5%.

[0045] In some embodiments, in the alkali metal salt polymer, the alkali metal includes at least one of lithium, sodium, and potassium.

[0046] In some embodiments, the alkali metal salt polymer includes an alkali metal salt polymer of acrylic acid. The negatively charged carboxylate groups in the alkali metal salt polymer of acrylic acid can be complexed with the Lewis acid small molecules in the electrolyte, thereby increasing the electronegativity of the carboxylate group, thereby allowing more lithium ions to dissociate, allowing more lithium ions to enter the negative electrode active layer, and further improving the fast charging performance of the battery. Optionally, the alkali metal salt polymer of acrylic acid includes at least one of lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate. In terms of promoting the increase in the transmission speed of lithium ions in the negative electrode plate, lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate have similar effects.

[0047] In this application, the alkali metal salt polymer of acrylic acid in the negative electrode plate can be determined by testing as follows: Take the negative electrode plate and dry it with DMC. Scrape off the material of the negative electrode active layer to obtain a powder. Mark the infrared characteristic peak of the powder. Typical characteristic peaks of alkali metal salt polymer of acrylic acid: at 1702cm -1 It appears at 1167cm, corresponding to the stretching vibration of C=O. -1 、1405cm -1 、1447cm -1 The characteristic peak at 2739 cm corresponds to the -CH2 stretching vibration. -1 and 3372cm -1 The characteristic peaks correspond to the stretching vibration and absorption of OH groups from carboxyl groups, located at 2952 cm -1 The characteristic peak corresponds to the absorption of the CH stretching peak.

[0048] In some embodiments, a method for preparing an alkali metal salt of acrylic acid polymer includes: preparing MOH into a uniform solution having a mass fraction of 10% M. Then, adding a 30% mass fraction of polyacrylic acid solution to the MOH solution and mixing at high speed until uniform. The uniformly mixed solution is dried and ball-milled. Optionally, M comprises an alkali metal element. Further, optionally, MOH comprises at least one of lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0049] In the present application, the mass percentage of the alkali metal salt polymer in the negative electrode plate can be determined by testing in the following manner: take the negative electrode plate and dry it clearly using DMC. Scrape off the material of the corresponding active part in the negative electrode active layer to obtain a powder. Soak the powder in deionized water, stir, and sonicate. After the binder on the powder is fully dissolved in the deionized water, filter out the powder and wash the powder repeatedly for more than 3 times. Then add calcium chloride solution to the filtrate, stir until the precipitate is completely precipitated, and filter it. The mass percentage of the alkali metal salt polymer is converted by weighing the filter residue.

[0050] In some embodiments, the molecular chain of the alkali metal salt polymer includes a linear structure. The linear structure can further promote the increase in the transmission speed of lithium ions in the negative electrode plate, which is beneficial to further improve the fast charging performance of the battery.

[0051] In some embodiments, the number average molecular weight of the alkali metal salt polymer is 3000-3500, 5000-5500, 10000-11000, 20000-21000, 30000-31000, 40000-41000, 50000-51000, 60000-61000, 70000-71000, 80000-81000, 90000-91000, 1 00000-110000, 200000-210000, 300000-310000, 400000-410000, 500000-510000, 600000-610000, 700000-710000, 800000-810000, 900000-910000, 990000-1000000, and ranges consisting of any of the above values. Further optionally, the number average molecular weight of the alkali metal salt polymer is 100000-500000.

[0052] It is understood that the symbol for number-average molecular weight is Mn, which measures molecular weight based on the number fraction. The number-average molecular weight is equal to the molecular weight of each component multiplied by the mole fraction of each component.

[0053] Number Average Molecular Weight Test Method: This parameter is typically determined using methods such as gel permeation chromatography, static light scattering, mass spectrometry, membrane osmotic pressure, end group analysis, vapor permeation, boiling point elevation, and freezing point depression. Alternatively, the number average molecular weight can be determined using gel permeation chromatography in accordance with the national standard GB / T 21863-2008, "Gel Permeation Chromatography (GPC) Using Tetrahydrofuran as the Eluent."

[0054] In some embodiments, the mass percentage of alkali metal in the alkali metal salt polymer is 3% to 8.9%. Alternatively, 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 a range consisting of any two of the foregoing values. Further alternatively, the mass percentage of alkali metal in the alkali metal salt polymer is 5% to 7.5%.

[0055] In the present application, the mass percentage of alkali metal in an alkali metal salt polymer can be tested by the following method: taking an alkali metal salt polymer sample with a mass of m0 and measuring the mass of alkali metal m1 by inductively coupled plasma emission spectroscopy (ICP), then, the average mass percentage of alkali metal in the alkali metal salt polymer = m1 / m0 × 100%. Specifically, 0.2 grams (g) of the alkali metal salt polymer sample is weighed in a beaker, 10 milliliters (mL) of concentrated HNO3 solution is added, and the sample is placed on a hot plate at 180 degrees Celsius (°C) and digested for 30 minutes (min). After the sample is digested for 30 minutes, it is cooled to room temperature and the digested solution is transferred to a 50 mL volumetric flask via a funnel and made up to volume. The test was conducted according to the industry standard USEPA-6010D-2018. A standard test solution was prepared. The standard test solution was a multi-element standard solution for ICP analysis 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 used to calibrate the standard solution curve, input the sample mass and volume, and then test the digested solution. Solutions outside the curve range needed to be diluted before testing. Finally, the presence of elements was identified through the characteristic spectrum of atomic emission, i.e., qualitative analysis. The content of elements was determined based on the intensity of the spectral lines, i.e., quantitative analysis.

[0056] In some embodiments, the negative electrode current collector includes a tab region and an active region in contact with each other, and the negative electrode active layer is located in the active region. In the direction from the tab region to the active region, the negative electrode active layer includes a first active portion, a second active portion, and a third active portion distributed in sequence. The mass percentages of the alkali metal salt polymer in the first active portion, the second active portion, and the third active portion are w1, w2, and w3, respectively, where w2>w1 and w2>w3. In the negative electrode active layer, the mass percentage of the alkali metal salt polymer in the second active portion is greater than the mass percentage of the alkali metal salt polymer in the first active portion, and the mass percentage of the alkali metal salt polymer in the second active portion is greater than the mass percentage of the alkali metal salt polymer in the third active portion. This can promote the reabsorption of the electrolyte during the cycle of the secondary battery, allowing the negative electrode active layer to be more fully infiltrated by the electrolyte, thereby improving the cycle performance of the secondary battery.

[0057] For better understanding, please refer to Figure 4. It shows the structure of the negative electrode plate in one embodiment of the present application. Here, X is the direction from the tab area to the active area. The negative electrode plate 3 includes a negative electrode current collector and a negative electrode active layer 32 located on at least one surface of the negative electrode current collector. The negative electrode current collector includes a tab area 31 and an active area in contact with each other, and the negative electrode active layer 32 is located in the active area. In the direction from the tab area to the active area, the negative electrode active layer 32 includes a first active portion 321, a second active portion 322, and a third active portion 323 distributed in sequence.

[0058] It is understandable that the tab region can be used directly as a tab, or additional tabs can be extended from the tab region.

[0059] As some optional examples of the mass percentage w1 of the alkali metal salt polymer in the first active portion, 0≤w1≤0.8%. The mass percentage w1 of the alkali metal salt polymer in the first active portion within this range can reduce the risk of bulging and falling off of the first active portion during the processing of the negative electrode sheet on the basis of promoting fast charging and promoting electrolyte resorption, thereby improving the processing performance of the negative electrode sheet. Optionally, the mass percentage w1 of the alkali metal salt polymer in the first active portion 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% and any value within the range consisting of any two of the above values. It is understandable that when w1 is 0, it means that the first active portion does not contain an alkali metal salt polymer. Further optionally, 0≤w1≤0.5%.

[0060] As some optional examples of the mass percentage w2 of the alkali metal salt polymer in the second active portion, 0.4% ≤ w2 ≤ 1.5%. The mass percentage w2 of the alkali metal salt polymer in the second active portion within this range can reduce the risk of bulging and falling off of the second active portion during the processing of the negative electrode sheet on the basis of promoting fast charging and promoting electrolyte resorption, thereby improving the processing performance of the negative electrode sheet. Optionally, the mass percentage w2 of the alkali metal salt polymer in the second active portion can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% and any value within the range consisting of any two of the above values. Further optionally, 0.5% ≤ w2 ≤ 1%.

[0061] As some optional examples of the mass percentage w3 of the alkali metal salt polymer in the third active part, 0≤w3≤0.8%. The mass percentage w3 of the alkali metal salt polymer in the third active part can reduce the risk of bulging and falling off of the third active part during the processing of the negative electrode sheet on the basis of promoting fast charging and promoting electrolyte resorption, thereby improving the processing performance of the negative electrode sheet. Optionally, the mass percentage w3 of the alkali metal salt polymer in the third active part 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% and any value within the range consisting of any two of the above values. It is understandable that when w3 is 0, it means that the third active part does not contain an alkali metal salt polymer. Further optionally, 0≤w3≤0.5%.

[0062] In some embodiments, the mass percentage w1 of the alkali metal salt polymer in the first active portion is equal to the mass percentage w3 of the alkali metal salt polymer in the third active portion.

[0063] In some embodiments, in the direction from the tab region to the active region, the widths of the first active portion, the second active portion, and the third active portion are D1, D2, and D3, respectively; 0.6≤D2 / (D1+D2+D3)≤0.9. Compared with the first active portion and the third active portion, the second active portion has a larger width, which can increase the overall amount of the alkali metal salt polymer in the negative electrode active layer, further improving the fast charging performance and cycle performance of the battery. Optionally, D2 / (D1+D2+D3) can be 0.6, 0.7, 0.8, 0.9, or any value within the range consisting of any two of the above values.

[0064] In some embodiments, 0.05≤D1 / (D1+D2+D3)≤0.2. The width of the first active portion is within this range. On the basis of promoting electrolyte resorption during the cycle, the second active portion having a higher mass percentage of alkali metal salt polymer can maintain a larger width, which is beneficial to further increase the overall amount of alkali metal salt polymer in the negative electrode active layer and further improve the fast charging performance and cycle performance of the battery. Optionally, D1 / (D1+D2+D3) can be 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, and any value within the range consisting of any two of the above values.

[0065] In some embodiments, 0.05≤D3 / (D1+D2+D3)≤0.2. The width of the third active portion is within this range. On the basis of promoting electrolyte resorption during the cycle, the second active portion with a higher mass percentage of alkali metal salt polymer can maintain a larger width, which is beneficial to further increase the overall amount of alkali metal salt polymer in the negative electrode active layer and further improve the fast charging performance and cycle performance of the battery. Optionally, D3 / (D1+D2+D3) can be 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, and any value within the range consisting of any two of the above values.

[0066] In some embodiments, the first active portion further contains a first binder, and the mass percentage of the first binder in the first active portion is w1', where 0≤w1 / w1'≤1. Introducing the first binder into the first active portion can improve the bonding properties of the first active portion, enhance the bonding properties between the first active portion and the negative electrode current collector, further reduce the risk of bulging or falling off of the first active portion during negative electrode sheet processing, and enhance the processing performance of the negative electrode sheet. Alternatively, w1 / w1' can be 0.01, 0.05, 0.08, 0.1, 0.12, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or any value within a range consisting of any two of the above values. Alternatively, the first binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0067] In some embodiments, 1.2% ≤ w1 + w1' ≤ 3.3%. Within this range, w1 + w1' can achieve good bonding between the first active portion and the negative electrode current collector, thereby increasing the proportion of negative electrode active material, thereby improving the energy density of the battery. Alternatively, w1 + w1' can be 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, or any value within a range consisting of any two of the foregoing values.

[0068] In some embodiments, 0.8%≤w1'≤2.5%. Alternatively, w1' may be 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within a range consisting of any two of the above values.

[0069] In some embodiments, the second active portion further contains a second binder, and the mass percentage of the second binder in the second active portion is w2', 0.25≤w2 / w2'≤1. By introducing the second binder into the second active portion, the bonding properties of the second active portion can be improved, the bonding properties between the second active portion and the negative electrode current collector can be improved, the risk of bulging or falling off of the second active portion during the processing of the negative electrode sheet can be further reduced, and the processing performance of the negative electrode sheet can be improved. Optionally, w2 / w2' can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and any value within the range consisting of any two of the above values. Optionally, the second binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0070] In some embodiments, 1.3% ≤ w2 + w2' ≤ 4%. Within this range, w2 + w2' can achieve good bonding between the second active portion and the negative electrode current collector, thereby increasing the proportion of negative electrode active material, thereby improving the energy density of the battery. Alternatively, w2 + w2' can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, or any value within a range consisting of any two of the above values.

[0071] In some embodiments, 0.8%≤w2'≤2.5%. Alternatively, w2' may be 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within a range consisting of any two of the above values.

[0072] In some embodiments, the third active portion further contains a third binder, with the mass percentage of the third binder in the third active portion being w3', where 0 ≤ w3 / w3' ≤ 1. Introducing the third binder into the third active portion can improve the bonding properties of the third active portion, enhancing the bonding properties between the third active portion and the negative electrode current collector, further reducing the risk of bulging or detachment of the third active portion during negative electrode sheet processing, and improving the processing performance of the negative electrode sheet. Alternatively, w3 / w3' can be 0.01, 0.05, 0.08, 0.1, 0.12, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or any value within a range consisting of any two of the aforementioned values. Alternatively, the third binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0073] Optionally, 1.2% ≤ w3 + w3' ≤ 2.3%. Within this range, w3 + w3' can ensure good bonding between the third active portion and the negative electrode current collector, thereby increasing the proportion of negative electrode active material, thereby improving the energy density of the battery. Optionally, w3 + w3' can be 1.2%, 1.5%, 1.8%, 2%, 2.3%, or any value within a range consisting of any two of the foregoing values.

[0074] In some embodiments, 0.8%≤w3'≤2.5%. Alternatively, w3' may be 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within a range consisting of any two of the above values.

[0075] It is understood that the mass percentage of the negative electrode active material in the negative electrode active layer is 94% to 99%. Alternatively, 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 a range consisting of any two of the foregoing 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.

[0076] It can also be 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, calculated as a percentage by mass 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 consisting of any two of the above values.

[0077] In some embodiments, the surface density CW of the negative electrode active layer is less than or equal to 0.14 mg / mm2 (mg / mm 2 ). Optionally, the surface density CW of the negative electrode active layer is 0.08 mg / mm 2 ~0.12mg / mm 2 Optionally, the surface density CW of the negative electrode active layer is 0.05 mg / mm 2 , 0.08mg / mm 2 , 0.1mg / mm 2 , 0.11mg / mm 2 , 0.12mg / mm 2 , 0.13mg / mm 2 , 0.14mg / mm 2 wait.

[0078] In some embodiments, the compacted density PD of the negative electrode active layer is 1.50 g / cm3 (g / cm 3 )~1.75g / cm 3 Optionally, the compaction density PD of the negative electrode active layer is 1.50 g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 wait.

[0079] Another embodiment of the present application provides a secondary battery comprising the above-mentioned negative electrode plate.

[0080] Another embodiment of the present application provides an electrical device, which includes at least one of the above-mentioned negative electrode sheet and the above-mentioned secondary battery.

[0081] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0082] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0083] Positive electrode

[0084] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0085] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0086] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0087] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. 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 referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0088] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0089] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, 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.

[0090] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from, but is not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40% by weight (wt%) to 80% by weight. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascals·seconds (mPa·s) to 25000 mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm2 (mg / cm 2 )~35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0091] Negative electrode

[0092] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0093] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0094] 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 polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0095] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. 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, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0096] In some embodiments, the negative electrode active material layer may further 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).

[0097] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0099] In some embodiments, the negative electrode sheet can be prepared by dispersing the components for preparing 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 the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet can be obtained. The negative electrode current collector surface 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 2000mPa·s to 10000mPa·s.

[0100] electrolytes

[0101] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0102] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0103] 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 bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0104] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of 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.

[0105] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0106] 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), trifluoromethylethylene carbonate (TFPC), and the like.

[0107] Isolation film

[0108] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0109] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven 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.

[0110] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0111] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0112] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0113] In some embodiments, the outer packaging of the secondary battery can be a hard 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 shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0114] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0115] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0116] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 1 with a square structure as an example.

[0117] In some embodiments, referring to Figure 2, the outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to actual needs.

[0118] The secondary battery may be a battery module or a battery pack.

[0119] A battery module includes at least one battery cell. The number of battery cells contained 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.

[0120] In a battery module, multiple battery cells can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Further, the multiple battery cells can be fixed by fasteners.

[0121] Optionally, the battery module may further include a housing having an accommodation space, wherein the plurality of battery cells are accommodated in the accommodation space.

[0122] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0123] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0124] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can 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 these.

[0125] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0126] Figure 3 shows an example of an electric device 2. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0127] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0128] In order 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 the embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0129] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0130] Example 1

[0131] (1) Preparation of positive electrode sheet.

[0132] The positive electrode active material LiFePO4, the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent NMP at a mass ratio of 97:1:2 to form a uniform positive electrode slurry. The positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet. The surface density of the positive electrode sheet is 400 mg / 1540.25 mm2 (mg / 1540.25 mm 2 ), compacted density is 2.55g / cm 3 .

[0133] (2) Preparation of negative electrode sheets.

[0134] First slurry: The negative electrode active material graphite, acrylic acid alkali metal salt polymer, the first binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose, and the conductive agent carbon black (Super P) are stirred uniformly in deionized water to obtain the first slurry.

[0135] Second slurry: The negative electrode active material graphite, acrylic acid alkali metal salt polymer, the second binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose, and the conductive agent carbon black (Super P) are stirred uniformly in deionized water to obtain the second slurry.

[0136] Third slurry: The negative electrode active material graphite, acrylic acid alkali metal salt polymer, the third binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose, and the conductive agent carbon black (Super P) are stirred uniformly in deionized water to obtain the third slurry.

[0137] The first slurry, the second slurry and the third slurry are evenly coated on different areas of the surface of the negative electrode current collector copper foil, and after drying and cold pressing, the negative electrode sheet is obtained. The surface density CW of the negative electrode sheet is 0.095 mg / mm 2 , compacted density PD is 1.6g / cm 3 The first slurry forms the first active portion, the second slurry forms the second active portion, and the third slurry forms the third active portion.

[0138] In the first active portion, the mass percentage of the active material graphite is 95.8%, the mass percentage of the acrylic acid alkali metal salt polymer is w1, the mass percentage of the first binder styrene-butadiene rubber is w1', and the width of the first active portion is D1. D1 / (D1+D2+D3)=0.1.

[0139] In the second active portion, the mass percentage of graphite active material is 96.3%, the mass percentage of acrylic acid alkali metal salt polymer is w2, the mass percentage of styrene-butadiene rubber second binder is w2', and the width of the first active portion is D2. D2 / (D1+D2+D3)=0.8.

[0140] In the third active portion, the mass percentage of the active material graphite is 95.8%, the mass percentage of the acrylic acid alkali metal salt polymer is w3, the mass percentage of the first binder styrene-butadiene rubber is w3', and the width of the first active portion is D3. D3 / (D1+D2+D3)=0.1.

[0141] (3) Preparation of electrolyte.

[0142] In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0143] (4) Preparation of isolation membrane.

[0144] A polyethylene (PE) film coated with nano-aluminum oxide was used as the separator.

[0145] (5) Preparation of secondary batteries.

[0146] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to form a wound electrode assembly. The electrode assembly is placed in a square aluminum casing, dried, and then filled with electrolyte. After packaging, standing, formation, aging, secondary packaging, and capacity measurement, a secondary battery is obtained.

[0147] Example 2 to Example 11

[0148] Compared to Example 1, Examples 2 to 11 differ in the material selection of the alkali metal salt of acrylic acid polymer, and the mass percentages of the alkali metal salt of acrylic acid polymer, the first binder, the second binder, and the third binder in the first active portion, the second active portion, and the third active portion, as shown in Table 1.

[0149] Comparative Examples 1 to 3

[0150] Compared with Example 1, the differences between Comparative Examples 1 to Comparative Examples 3 are that the mass percentages of lithium polyacrylate in the first active portion, the second active portion, and the third active portion are different, as shown in Table 1.

[0151] Test Case

[0152] (1) The battery cells in the embodiment and comparative example were subjected to a pole piece processing performance test. The test method was as follows: the battery cells were disassembled and the fully charged negative pole pieces were observed to see whether there were obvious problems of bulging or shedding of the active layer.

[0153] (2) The batteries in the examples and comparative examples were subjected to a cycle performance test. The test method was as follows: at 25°C, the secondary battery was charged to 3.8 volts (V) at a constant current of 1 coulomb (C), allowed to stand for 30 minutes, and then discharged to 2.0 V at a constant current of 1C. This was one cycle of charge and discharge. The discharge capacity at this time was recorded, which was the initial capacity of the secondary battery. The secondary battery was subjected to a cycle charge and discharge test according to the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decayed to 80% of the initial capacity of the secondary battery. The number of cycles was recorded.

[0154] (3) The fast charging performance of the batteries in the examples and comparative examples was tested. The test method was: a laminated three-electrode test method. The positive and negative electrodes of the hard shell battery were taken out and soaked in DMC solvent for more than 72 hours (h). After the electrolyte solvent, lithium salt, and additives were completely leached, the electrodes were dried in a vacuum oven. The positive and negative electrodes were then assembled into a laminated three-electrode battery cell, in which copper wire was used as a reference electrode. The laminated three-electrode battery cell was then tested for lithium deposition charging rate at each SOC of the laminated battery cell at 25°C. The maximum charging rate was cut off when the reference electrode potential dropped to 0 millivolts (mV), and the maximum charging rate at this SOC was recorded. According to this method, with 5% SOC as a point, the maximum charging rate at each 5% SOC was tested, such as 5% SOC, 10% SOC, 15% SOC to 100% SOC. The continuous charging time at 10% to 80% SOC was calculated according to the maximum charging rate at 10% to 80% SOC obtained from this test, which is the fast charging time. The results are shown in Table 1. The unit of fast charging time is minute (min).

[0155] Table 1

[0156] It is understood that the "number average molecular weight" in Table 1 represents the number average molecular weight of the alkali metal salt polymer of acrylic acid, in units of ten thousand. The number average molecular weight of the alkali metal salt polymer of acrylic acid in the embodiments and comparative examples is approximately the value given in this column. "Mass percentage" represents the mass percentage of alkali metal in the alkali metal salt polymer of acrylic acid. w1 represents the mass percentage of the alkali metal salt polymer of acrylic acid in the first active portion. w2 represents the mass percentage of the alkali metal salt polymer of acrylic acid in the second active portion. w3 represents the mass percentage of the alkali metal salt polymer of acrylic acid in the third active portion. w1' represents the mass percentage of the first binder in the first active portion. w2' represents the mass percentage of the second binder in the second active portion. w3' represents the mass percentage of the third binder in the third active portion. "Qualified" represents whether the processing performance of the electrode is qualified, where "yes" means qualified and "no" means unqualified. The unqualified standard is that the active layer falls off. In Table 1, the active layer at the edge of the electrode in Comparative Example 1 falls off. It is also understandable that when the processing performance of the electrode is unqualified, the fast charging time test and cycle number test will not be performed.

[0157] As can be seen from Table 1, in terms of fast charging time, the fast charging time of the battery in the embodiment is shorter than that of the battery in the comparative example. In terms of cycling performance, the number of cycles of the battery in the embodiment is greater than that of the battery in the comparative example. This indicates that the fast charging performance and cycling performance of the battery in the embodiment are superior to those of the battery in the comparative example.

[0158] It can be seen from Example 1 and Example 2 that when w1 and w3 are not 0, the battery exhibits better fast charging performance and cycle performance.

[0159] It can be seen from Examples 2 to 4 that when the content of the acrylic acid alkali metal salt polymer in the negative electrode sheet increases, the fast charging performance and cycle performance of the battery are improved.

[0160] It can be seen from Examples 5 to 10 that when the mass percentage of the alkali metal in the acrylic acid alkali metal salt polymer is at an appropriate value, the battery has better fast charging performance and better cycle performance.

[0161] It can be seen from Example 1 and Example 11 that when the number average molecular weight of the alkali metal salt of acrylic acid polymer is within an appropriate range, the battery has better fast charging performance and better cycle performance.

[0162] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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.

[0163] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A negative electrode sheet, comprising 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 negative electrode active layer comprises a middle region and an edge region, wherein the edge region is located at the periphery of the middle region; and the mass percentage of the alkali metal salt polymer in the middle region is greater than the mass percentage of the alkali metal salt polymer in the edge region.

2. The negative electrode sheet according to claim 1, wherein: The mass percentage of the alkali metal salt polymer in the middle region is 0.4% to 1.5%.

3. The negative electrode sheet according to claim 2, wherein: The mass percentage of the alkali metal salt polymer in the middle region is 0.5% to 1%.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The mass percentage of the alkali metal salt polymer in the edge region is 0-0.8%.

5. The negative electrode sheet according to claim 4, wherein: The mass percentage of the alkali metal salt polymer in the edge region is 0-0.5%.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The molecular chain of the alkali metal salt polymer includes a linear structure.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The number average molecular weight of the alkali metal salt polymer is 3,000 to 1,000,000.

8. The negative electrode sheet according to claim 7, wherein: The number average molecular weight of the alkali metal salt polymer is 100,000 to 500,000.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein: The mass percentage of alkali metal in the alkali metal salt polymer is 3% to 8.9%.

10. The negative electrode sheet according to claim 9, wherein: The mass percentage of alkali metal in the alkali metal salt polymer is 5% to 7.5%.

11. The negative electrode sheet according to any one of claims 1 to 10, wherein: The alkali metal salt polymer includes an alkali metal salt polymer of acrylic acid.

12. The negative electrode sheet according to claim 11, wherein: The acrylic acid alkali metal salt polymer includes one or more of lithium polyacrylate, sodium polyacrylate and potassium polyacrylate.

13. The negative electrode sheet according to any one of claims 1 to 12, wherein: The negative electrode current collector includes a contacting tab region and an active region, and the negative electrode active layer is located in the active region; in the direction from the tab region to the active region, the negative electrode active layer includes a first active portion, a second active portion and a third active portion distributed in sequence; the mass percentages of alkali metal salt polymers in the first active portion, the second active portion and the third active portion are w1, w2 and w3 respectively, wherein w2>w1, w2>w3.

14. The negative electrode sheet according to claim 13, wherein: 0≤w1≤0.8％。 15. The negative electrode sheet according to claim 14, wherein: 0≤w1≤0.5％。 16. The negative electrode sheet according to any one of claims 13 to 15, wherein: 0.4％≤w2≤1.5％。 17. The negative electrode sheet according to claim 16, wherein: 0.5％≤w2≤1％。 18. The negative electrode sheet according to any one of claims 13 to 17, wherein: 0≤w3≤0.8％。 19. The negative electrode sheet according to claim 18, wherein: 0≤w3≤0.5％。 20. The negative electrode sheet according to any one of claims 13 to 19, wherein: In the direction from the tab region to the active region, the widths of the first active portion, the second active portion and the third active portion are D1, D2 and D3 respectively; 0.6≤D2 / (D1+D2+D3)≤0.

9.

21. The negative electrode sheet according to claim 20, wherein: 0.05≤D1 / (D1+D2+D3)≤0.

2.

22. The negative electrode sheet according to claim 20 or 21, wherein: 0.05≤D3 / (D1+D2+D3)≤0.

2.

23. The negative electrode sheet according to any one of claims 13 to 22, wherein: The first active portion further contains a first binder, and the mass percentage of the first binder in the first active portion is w1', 0≤w1 / w1'≤1.

24. The negative electrode sheet according to claim 23, wherein: The first binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride and polytetrafluoroethylene.

25. The negative electrode sheet according to any one of claims 13 to 24, wherein: The second active portion further contains a second binder, and the mass percentage of the second binder in the second active portion is w2', and 0.25≤w2 / w2'≤1.

26. The negative electrode sheet according to claim 25, wherein: The second binder includes one or more of styrene-butadiene rubber and modified compounds thereof, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride and polytetrafluoroethylene.

27. The negative electrode sheet according to any one of claims 13 to 26, wherein: The third active portion further contains a third binder, and the mass percentage of the third binder in the third active portion is w3', 0≤w3 / w3'≤1.

28. The negative electrode sheet according to claim 27, wherein: The third binder includes one or more of styrene-butadiene rubber and modified compounds thereof, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, polyvinylidene fluoride and polytetrafluoroethylene.

29. The negative electrode sheet according to any one of claims 1 to 28, wherein: The surface density of the negative electrode active layer is less than or equal to 0.14 mg / mm 2 .

30. The negative electrode sheet according to any one of claims 1 to 29, wherein: The compaction density of the negative electrode active layer is 1.50 g / cm 3 ~1.75g / cm 3 .

31. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 30.

32. An electrical device comprising 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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